REVIEW OF LITERATURE - AXIOLYTIC PROPERTY OF CAESALPINIA PULCHERRIMA LEAVES EXTRACTS IN EXPERIMENTAL ANIMALS

 

REVIEW OF LITERATURE

             Review of literature was made from various sources, including e-sources, to access various pharmacological and chemical natures of herbs. For the sake of convenience, it is divided into three parts.

 

            In part I, preliminary details of herbs viz., taxonomical data, vernacular names, geographical distribution, chemical nature, constituents, traditional uses, folklore uses and reported pharmacological activities of plant.

 

            In part II contains detail information of anxiety disorders from various journals and web sources (abstract data bases) etc., relevant for current study have been reviewed.

 

            In part III, animal models for screening and evaluating anxiolytic potential of plant with including rodent models of anxiety.

PART – I

3.1.1 ABOUT PLANT:

Botanical classification:¹⁶

Kingdom                 :           Plantae

Division                   :           Magnoliophyta

Class                        :           Magnoliopsida

Order                       :           Fabales

Family                     :           Fabaceae

Subfamily                :           Caesalpinioideae

Genus                      :           Caesalpinia

Species                    :           C. pulcherrima

Botanical name      :           Caesalpinia pulcherrima L.

Synonyms               :           Poinciana pulcherrima, Poinciana bijuga

Common names     :           Peacock flower

 

Vernacular Name¹⁷ :

            English                        :           Pride of Barbados, dwarf Poinciana,

                                                            red bird of paradise,

            Hindi                           :           Guletura

            Kannada                      :           Kenjige

            Telugu                         :           Ratnagandhi

            Marathi                        :           Sankasur

            Tamil                           :           Mayirkonrai, Nazhal

            Bengali                        :           Krishnachura or Radhachura

            Sanskrit                       :           Sidhakya

DISTRIBUTION:

            Caesalpinia pulchirrima (Fabaceae) is native to tropics and subtropics area of the Americas.¹⁸ This plant is widely distributed in Bangladesh and India.¹⁹ It is a common medicinal plant in India, Taiwan and South East Asian conutries.²⁰

 

            Caesalpinia pulchirrima is a striking ornamental plant, widely grown in domestic and public gardens and has a beautiful inflorescence in yellow, red and orange.¹⁸

                                          

DESCRIPTION:

            Caesalpinia pulchirrima species is a shrub growing to 3 m tall. The leaves are bipinnate, 20-40 cm long, bearing 3-10 pairs of pinnae, each with 6-10 pairs of leaflets 15-25 mm long and 10-15 mm broad. The flowers are borne in racemes up to 20 cm long, each flower with five yellow, orange or red petals. The fruit is a pod 6-12 cm long¹⁸. Flowers are red or yellow, fragrant²⁰. Flowering season of this plant start from September to November and fruits from March to april.²¹

                                                               

            Traditionally leaves of Caesalpinia pulchirrima are used as purgative, tonic, antipyretic, emmenagogue, where as roots have folkforic use in convulsion, intermittent fever, lungs and skin diseases.²² Flavonoids are polyphenolic compounds, widely distributed in the plant kingdom. They are reported to exhibit various pharmacological activities such as CNS, cardiotonic, lipid lowering, anti-oxidant, hepatoprotective and hypoglycemic activities.²³

CHEMICAL CONSTITUENTS:

            The Caesalpinia pulchirrima possesses various bioactive compounds such as steroid, reducing sugar, triterpenoids, sugar, alkaloids, phenolic compounds, flavonoids, catechins, saponins, tannins, anthraquinons and amino acid.²⁵ The stem contains peltogynoids bhonducellin, 6-methoxypulcherrimin and homomisoflavonoids.²⁶

 

            The leaf oils of caesalpinia pulcherrima contains pinene,  camphene, benzalaldehyde, sabinene,  1-octen-3-ol, beta-pinene, myrcene, alpha-phellandrene, alpha-terpinene, P-cymene limonene, benzyl alcohol, 1,8 – cineole, cis-ocimene, transocimene, 2,6-dimethyl -5-heptanal, terpinene isoartemisia Ketone,  terpinolene, linalool, allo-ocimene, citronellal, borneol, terpinen -4 –ol, terpinol, citronellol,  nerol,  ascaridole, neral, citral, linalylacetate, geranial, borneol acetate, alpha-tepinenyl acetate, neryl acetate,  alpha-copaene, geranyl acetate, cyperene,  alpha-gurjunene, beta-caryophyllene,  alpha-bergamotene, aromadendrene, alpa-selinene, ethyl cinnamate, humulene, germacreneD, beta-selinene, valencene, germacreneB, murolene alpha-bisabolene,  beta-bisabolene, trans-beta-farnesene, viridiflorol, alpha-bisabolol, aristolone.²⁷

 

MEDICINAL USES:

1)      Used to induce abortion in the first trimester of pregnancy.¹⁸

2)      Used in pyrexia.²⁸

3)      Used in menoxenia.²⁸

4)      Used in wheezing.²⁸

5)      Used in bronchitis.²⁸

6)      Used in malarial infection.²⁸

Folkloric uses:²⁹

1. In La Union, decoction or infusion of leaves, flowers, roots, and bark used as purgative and emmenagogue.
2. In Angola, decoction of roots used for intermittent fevers.
3. In Nicaragua astringent infusion used as wash for the teeth and gums. Infusion of leaves, roots, and bark used for colds, fevers, skin ailments and purging; also used as emmenagogue.
4. Reported to be abortifacient.
5. In Mexico, a decoction of leaves used for liver affections and as mouth wash and gargle for mouth and throat ulcers.
6. In the West Indies, decoction of leaves used for fevers.
7. Flowers reputed to be purgative, febrifuge and emmenagogue. Decoction of flowers used for erysipelas and inflammation of the eyes.
8. Powdered flowers used as insecticide; also used as tonic.
9. Seeds also used as abortifacient.
10. Fruit is astringent and used for diarrhea and dysentery.
11. In the Amazon, leaf juice used for fevers; the flower juice for sores.
12. Seeds used for cough, chest pains, breathing difficulty.
13. Roots used to induce first trimester abortion.
14. Leaves are purgative; used for renal stones, malaria, bronchitis.
15. In Ayurvedic medicine, used for fever, jaundice, colic, flatulence, malignant tumors.
16. In Nicaragua, astringent infusion of the bark is used as a wash for teeth and gums.
17. In the West Indies, decoction used for fevers.
18. In the Antilles, the leaves are used as emmenagogue and abortifacient. A sweetened infusion is used as purgative.
19. In Jamaica, decoction of leaves used as a purgative.
20. In the East Indies, pods and leaves used as substitute for senna.
21. In India, infusion of flowers used as pectoral and febrifuge; also used in bronchitis, asthma and malarial fevers. Leaves used as antipyretic and antimicrobial.

 

REPORTS FROM MODERN LITERATURE:

1)      The ethanolic and aqueous extracts of Caesalpinia pulchirrima flower have been reported for antimicrobial activity.³⁰

2)      The methanolic and aqueous extracts of the wood of Caesalpinia pulchirrima Linn has been reported for antioxidant and cytotoxic activities.³¹

3)      The various extracts of pods of Caesalpinia pulchirrima showed anti-inflammatory and antinociceptiveproperties.³²

4)      The methanolic extract of Caesalpinia pulchirrima flower has been reported for analgesic and anti-inflammatory activities.³³

5)      The ethanolic extract of Caesalpinia pulchirrima leaves possess anticomvualsant properties²¹.

6)      The methanolic extracts of Caesalpinia pulchirrima, cassia fistula, and senna alata leaf reported to possess weight lowering properties.³⁴

7)      The ethanolic extract of the dry fruits of Caesalpinia pulchirrima, arial parts of euphorbia hirta and flowers of Asystasiagangeticum has been reported for antimicrobial activity.³⁵

8)      The aqueous extract of Caesalpinia pulchirrima leaf showed some effects on the liver function enzyme and blood glucose concentration in normal rabbits.³⁶

9)      Antibacterial activity of methanolic extract of roots of Caesalpinia pulcherrima.³⁷

10)  Phytochemical investigation and anticonvulsant activity of seeds of Caesalpinia bonduc.³⁸

11)  Effect of Caesalpinia pulcherrima L. on streptozotocin-induced diabetes and its associated neuropathy and cardiac complications in rats.³⁹

12)  Antifertility potential of the ethanolic extract of Caesalpinia pulcherrima Linn. leaves.⁴⁰

 

            Review of literature, till date, regarding Caesalpinia pulchirrima was carried out by chemical abstract, biological abstract, medicinal abstract and other national and international scientific journals. The Caesalpinia pulchirrima possesses various bioactive compounds such as steroid, reducing sugar, triterpenoids, sugar, alkaloids, phenolic compounds, flavonoids, catechins, saponins, tannins, anthraquinons and amino acid.²⁵ The leaves of the plant Caesalpinia pulchirrima are reported to contain hydrocyanic acid, tannins and benzoic acid.⁴¹ The plant contains various phytoactive consituents such as glycosides, rotenids, isoflavones, flavonone, chalcones, flavanols, flavones and sterols ,diterpenoids.²⁰ Root of Caesalpinia pulchirrima showed the presence of diterpenoids, isovouacapenol C and pulcherrimin A.⁴² The stem contains peltogynoids bhonducellin, 6-methoxypulcherrimin and homomisoflavonoids.²⁶

 

            The flavonoids are polyphenolic compounds and reported to exhibit various pharmacological activities such as CNS activity, cardiotonic activity, lipid lowering activity, antioxidant activity, hepatoprotective activity, hypoglycemic activity²³ etc. These active constituents and the above mention activities in turn appear to correlate with some other biological activities.⁴³ Our literature survey revealed that the different parts of Caesalpinia pulchirrima have been screened for various pharmacological activities but anxiolytic activity was not investigated in Caesalpinia pulchirrima leaves so far.

 

            Therefore, the present study is planned to investigate the possible anxiolytic potential of Caesalpinia pulchirrima leaves. Hence this study is essential and justifiable.

 

3.1.2 The other plants having Anxiolytic activity

             There have been several reports of natural drugs which possessing anxiolytic activities⁴⁴. Plant extracts, teas and food provide an ever increasing number of constituents and ingredients which seem to interact functionally with different organ systems of body including brain¹⁶.

 

              Following research work of plant extracts reveals that their constituent posses’ anxiolytic activity and this has leaded us to investigate anxiolytic activity of Agave Americanaleaf extracts.

1.      Anxiolytic activity of aerial and underground parts of Passiflora incarnate ⁴⁵.

2.      Anxiolytic effects of the aqueous extract of Uncaria rhynchophylla ⁴⁶.

3.      Evidence That Total Extract of Hypericum perforatum Affects Exploratory Behavior and Exerts Anxiolytic Effects in Rats ⁴⁷.

4.      Coriandrum sativum: evaluation of its anxiolytic effect in the elevated plus maze ⁴⁸.

5.      The anxiolytic-like effects of Aloysia polystachya (Griseb.) Moldenke (Verbenaceae) in mice ⁴⁹.

6.      Kaempferol from the leaves of Apocynum venetum possesses anxiolytic activities in the elevated plus maze test in mice ⁵⁰.

7.      Flavonoids from Tilia Americana with anxiolytic activity in plus-maze test ⁵¹.

8.      Anxiolytic-like effect of Sonchus oleraceus L. in mice ⁵².

9.      Barakol: APotential Anxiolytic Extracted from Cassia siamea ⁵³.

10.  Comparative studies on anxiolytic activities and flavonoid compositions of Passiflora edulis ‘edulis’ and Passiflora edulis ‘flavicarpa ⁵⁴.

11.  An anxiolytic effect of Dolichandrone Falcata leaves extract in experimental animals¹³.

12.  Evaluation of anxiolytic activity of hydro alcoholic activity of Tephrosia   purpuria (L) pers on Swiss albino mice ⁵⁵.

13.  Anxiolytic Activity of Seed Extract of Caesalpinia Bonducella (Roxb) In Laboratory Animals ⁵⁶.

14.  Anxiolytic effects of Equisetum arvense Linn. Extracts in mice.⁵⁷

15.  Evaluation of anxiolytic effect of Erythrina mysorensis Gamb. in mice.⁵⁸

16.  Anxiolytic activity of methanol leaf extract of Achyranthes aspera Linn. in mice using experimental models of anxiety.⁵⁹

17.  Anti-anxiety activity of successive extracts of Angelica archangelica Linn. on the elevated T- maze and forced swimming test in rats.⁶⁰

18.  Flavonoids from Tilia Americana with anxiolytic activity in plus-maze test.⁶¹

19.  Anti-anxiety activity studies of various extracts of Turnera aphrodisiaca Ward.⁶²

20.  Evaluation of anxiolytic activity of methanolic extract of Sapindus mukorossi geartn in mice.⁶³

21.  Anti-anxiety activity studies of various extracts of Pulsatilla nigricans stoerck.⁶⁴

22.  Anxiolytic anxiety of Nymphaea alba Linn. In mice as experimental models of anxiety.⁶⁵

23.  Anxiolytic activity of Glycyrrhiza glabra Linn.⁶⁶

24.  Anti-anxiety activity of Gelremium sempervirens.⁶⁷

25.  Anti-anxiety activity of Coriandrum sativum assessed using different experimental anxiety models.⁶⁸

PART-II

3.2. ANXIETY:

3.2.1 Introduction:

            It’s normal to feel anxious when facing a challenging situation, such as a job interview, a tough exam, or a blind date. But if your worries and fears seem overwhelming and interfere with your daily life, you may be suffering from an anxiety disorder. There are many different types of anxiety disorders and many effective treatments and self-help strategies. Once you understand your anxiety disorder, there are steps you can take to reduce your symptoms and regain control of your life.¹

 

            Anxiety is a normal reaction to stress and can actually be beneficial in some situations. For some people, however, anxiety can become excessive. While the person suffering may realize their anxiety is too much, they may also have difficulty controlling it and it may negatively affect their day-to-day living.²

 

3.2.2. Anatomy:

            The brain circuits and regions associated with anxiety disorders are beginning to be understood with the development of functional and structural imaging. The brain amygdala appears key in modulating fear and anxiety. Patients with anxiety disorders often show heightened amygdala response to anxiety cues. The amygdala and other limbic system structures are connected to prefrontal cortex regions. Hyperresponsiveness of the amygdala may relate to reduced activation thresholds when responding to perceived social threat. Prefrontal-limbic activation abnormalities have been shown to reverse with clinical response to psychologic or pharmacologic interventions.³

3.2.3. Epidemiology:

            Several large, methodologically rigorous epidemiological studies have indicated that anxiety disorders are one of the most prevalent categories of childhood and adolescent psychopathology⁶⁹. The most recent prevalence estimates from a paediatric primary care sample including more than 700 families suggest that approximately 20% of children (ages 8–17 years) were above the clinical cut off on a brief anxiety screen measure by Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) ⁷⁰.

 

            Although comorbidity rates vary depending upon the primary diagnosis, there exists a strong comorbidity among anxiety disorders in youth⁷¹. For example, an epidemiological study of paediatric OCD revealed that 84% of youth diagnosed with OCD had comorbid disorders, including major depression (62%), social phobia (38%), alcohol dependence (24%), and dysthymia (22%) ⁷². The most common comorbid diagnoses include other anxiety disorders and depressive disorders⁷³. Additionally, children with anxiety disorders frequently experience other psychiatric conditions, including attention deficit/hyperactivity disorder and the disruptive disorders⁷⁴.

 

3.2.4. Etiology:

            The first consideration is the possibility that anxiety is due to a known or unrecognized medical condition. Substance-induced anxiety disorder (over-the-counter medications, herbal medications, substances of abuse) is a diagnosis that often is missed.³

 

            Genetic factors significantly influence risk for many anxiety disorders. Environmental factors such as early childhood trauma can also contribute to risk for later anxiety disorders. The debate whether gene or environment is primary in anxiety disorders has evolved to a better understanding of the important role of the interaction between genes and environment. Some individuals appear resilient to stress, while others are vulnerable to stress, which precipitates an anxiety disorder.³

 

3.2.5. Pathophysiology:

            In the central nervous system (CNS), the major mediators of the symptoms of anxiety disorders appear to be norepinephrine, serotonin, dopamine, and gamma-aminobutyric acid (GABA). Other neurotransmitters and peptides, such as corticotropin-releasing factor, may be involved. Peripherally, the autonomic nervous system, especially the sympathetic nervous system, mediates many of the symptoms.³

Positron emission tomography (PET) scanning has demonstrated increased flow in the right parahippocampal region and reduced serotonin type 1A receptor binding in the anterior and posterior cingulate and raphe of patients with panic disorder. MRI has demonstrated smaller temporal lobe volume despite normal hippocampal volume in these patients. The CSF in studies in humans shows elevated levels of orexin, also known as hypocretin, which is thought to play an important role in the pathogenesis of panic in rat models.³

 

            Research and treatment trials suggest that abnormalities in serotonin neurotransmission in the brain are meaningfully involved in obsessive-compulsive disorder (OCD). This is strongly supported by the efficacy of serotonin reuptake inhibitors in the treatment of OCD.³

            Evidence also suggests abnormalities in dopaminergic transmission in at least some cases of OCD. In some cohorts, Tourette disorder (also known as Tourette syndrome) and multiple chronic tics genetically co-vary with OCD in an autosomal dominant pattern. OCD symptoms in this group of patients show a preferential response to a combination of selective serotonin reuptake inhibitors (SSRIs) and antipsychotics. ³

 

            Functional imaging studies in OCD have demonstrated some reproducible patterns of abnormality. Specifically, magnetic resonance imaging (MRI) and PET scanning have shown increases in blood flow and metabolic activity in the orbitofrontal cortex, limbic structures, caudate, and thalamus, with a trend toward right-sided predominance. In some studies, these areas of overactivity have been shown to normalize following successful treatment with either SSRIs or cognitive-behavioral therapy (CBT).³

 

3.2.6. Symptoms of anxiety:

            Unlike the relatively mild, brief anxiety caused by a stressful event (such as speaking in public or a first date), anxiety disorders last at least 6 months and can get worse if they are not treated. Each anxiety disorder has different symptoms, but all the symptoms cluster around excessive, irrational fear and dread.²

 

            Despite their different forms, all anxiety disorders share one major symptom: persistent or severe fear or worry in situations where most people wouldn’t feel threatened.⁴

 

Emotional symptoms of anxiety:

            In addition to the primary symptoms of irrational and excessive fear and worry, other common emotional symptoms of anxiety include:⁴

• Feelings of apprehension or dread
• Trouble concentrating
• Feeling tense and jumpy
• Anticipating the worst
• Irritability
• Restlessness
• Watching for signs of danger
• Feeling like your mind’s gone blank

 

Physical symptoms of anxiety:

            Anxiety is more than just a feeling. As a product of the body’s fight-or-flight response, anxiety involves a wide range of physical symptoms. Because of the numerous physical symptoms, anxiety sufferers often mistake their disorder for a medical illness. They may visit many doctors and make numerous trips to the hospital before their anxiety disorder is discovered.⁴

 

Common physical symptoms of anxiety include:

• Pounding heart
• Sweating
• Stomach upset or dizziness
• Frequent urination or diarrhea
• Shortness of breath
• Tremors and twitches
• Muscle tension
• Headaches
• Fatigue
• Insomnia        

 

3.2.7. Types of Anxiety Disorders:

Separation Anxiety Disorder (SAD):

            SAD is characterized by excessive worry about separation from another person who represents safety for the affected child, typically a parent. In new, unfamiliar, or feared situations, youth with SAD are often dependent on their safety figure. Common features of the disorder include excessive demonstration of distress upon real or threatened separation (e.g., tantrums, crying, somatic complaints), fear of harm or permanent separation from caretaker, and fear of getting lost, kidnapped, or dying. School refusal is a common symptom of SAD, occurring in approximately 75% of children with the diagnosis⁷⁵.

 

            Within the clinical setting, children with SAD may present with sleep problems, such as nightmares. Furthermore, these children may experience a number of somatic complaints (e.g., stomach-ache) related to the distress associated with SAD. The presence of clingy and whiny behavior within the clinical setting may also be an indicator of SAD. The clinical presentation of SAD may vary with age, with younger children exhibiting excessive crying and temper tantrums upon separation from the attachment figure and older children displaying social withdrawal and manipulative behavior to avoid school or separation⁷⁶.

Panic Disorder (PD):

            PD is characterized by both the actual occurrence of panic attacks and persistent worry and vigilance about prospective symptoms of another panic attack. Panic attacks involve an overwhelming fear of being in danger for no apparent reason as well as physiological symptoms such as pounding heart or chest pain, sweating, trembling or shaking, shortness of breath or choking sensation, nausea, dizziness, feelings of unreality or depersonalization, and fear of going crazy or dying⁷⁷.

 

            The most common symptoms reported are palpitations, shortness of breath, sweating, faintness, and weakness. In adolescence, chest pain, flushes, trembling, headache, and vertigo are also commonly reported symptoms. In youth, cognitive symptoms are less common, with the most frequent cognitive symptoms being a fear of losing control. As with adults, there is a strong association between PD and agoraphobia in youth⁷⁵.

 

            The presenting problem for youth with PD will pertain to one or more of the many physiological symptoms of panic attacks. Parents of youth with PD may also report agoraphobic symptoms related to their child's panic attacks. Unlike in adulthood, catastrophic interpretations of physiological symptoms may not be part of the clinical presentation⁷⁸. PD is less common in childhood than in adolescence, and the clinical presentation of PD varies across the developmental span⁷⁹. Specifically, younger children's panic attacks are often related to particular triggering events whereas adolescent's panic attacks are more often reported as unexpected and not linked to a particular antecedent event⁷⁸.

 

Social Phobia:

            Social phobia, or the fear of embarrassment or negative evaluation in social or performance situations, is manifested by the avoidance of situations in which the child fears acting in a humiliating or embarrassing manner⁷⁷. Three main factors in the development and maintenance of social phobia are highlighted: (a) cognitive biases (e.g., beliefs that individuals will predictably interact with others in a manner that will elicit rejection and/or negative evaluation from others), (b) deficits in social skills, and (c) operant conditioning (e.g., negative reinforcement for avoidance behaviors⁸⁰.

 

            Within the clinical setting, youth with social phobia may present as shy and socially withdrawn and may exhibit noticeable anxious–somatic symptoms, including blushing, sweating, and shaking, when interacting with unfamiliar people. Limited eye contact is also quite common. In extreme presentations, youth may have difficulty with articulation or may become mute. Interpersonal deficits may be evident when interacting with socially phobic youth, who often report having few close friendships with their peers. Whereas younger children with social phobia tend to hide behind adults or attempt to physically escape from a social situation, elder children tend to remain in the social situation but with few efforts to engage or participate⁸¹.

 

Obsessive–Compulsive Disorder (OCD):

            OCD is characterized by recurring intrusive thoughts or excessive worries (obsessions) and/or activities or habits the person feels driven to perform to reduce anxiety (compulsions). The obsessions and/or compulsions are distressing, time consuming (more than one hour per day), or debilitating (interfere with normal functioning) ⁷⁷.

            The most common obsessive themes in the paediatric population include fears of contamination (e.g., dirt, germs, toxins); preoccupations about harm to self or others; the need for symmetry, exactness, and order; concerns with religious or moral conduct (e.g., being concerned with committing a sin); lucky or unlucky numbers; and preoccupations concerning forbidden sexual or aggressive thoughts. The most common compulsive themes include cleaning or decontamination rituals (e.g., excessive washing, bathing, or grooming); checking, counting, repeating, straightening, and routinized behaviors (e.g., doors, locks, homework, appliances); confessing, praying, and reassurance seeking; touching, tapping, and rubbing; measures to prevent harm to self or others; and hoarding and collecting⁸².

 

            Youth with OCD may present to health professionals with a number of physical or behavioral complaints that are consequences of obsessive–compulsive symptoms. For example, dermatological problems may arise secondary to compulsive hand washing or skin picking. Weight loss may occur due to refusal to eat certain foods that are perceived as contaminated. Compulsive avoidance of bathrooms due to contamination fears may lead to the development of secondary encopresis or enuresis. Additionally, youth may present to their dentists with bleeding gums as a result of excessive teeth cleaning⁸³.

 

            Research has supported a distinction between early- and late-onset OCD, such that early-onset (i.e., prepubertal) OCD is more likely to occur in males, to be characterized by symptom presentations characteristic of compulsions without obsessions and more primitive compulsions (i.e., touching, tapping, rubbing), to have comorbid tic symptomatology, and to involve family members in their rituals⁸⁴.

Posttraumatic Stress Disorder (PTSD):

            PTSD is characterized by recurrent symptoms of anxiety related to past trauma, such as physical abuse or natural disasters⁷⁷. Cognitive, autonomic, and behavioural symptoms of anxiety are typically involved. The main manifestations of traumatic reactions include repetitive and intrusive thoughts about the trauma, flashbacks or nightmares in which the child reexperiences the trauma, heightened arousal, avoidance of stimuli associated with the trauma, sleep disturbances, and separation difficulties Cognitive changes, such as difficulties in concentration and memory problems, are also common. Additionally, a child may report a sense of foreshortened future or a premature awareness of his or her own mortality⁸⁵. This disorder always involves significant distress and can result in marked interference with functioning⁷⁷.

 

            Primary complaints of youth with PTSD in the clinical setting may involve physiological arousal symptoms such as difficulty sleeping or exaggerated startle response. Parents of youth with PTSD may report a temporal association between a particular traumatic event and the onset of atypical behaviour such as sexual acting out or aggression. It is common for youth with PTSD to be reluctant about discussing the traumatic event, and their descriptions of the traumatic event often lack a discussion of their associated emotional experience⁸¹.

 

Generalized Anxiety Disorder (GAD):

            GAD involves diffuse excessive worry over a wide variety of routine daily activities such as school performance, social concerns, or family interaction. It is characterized by 6 months or more of chronic, exaggerated worry and tension that are unfounded or much more severe than the anxiety that most people experience. The excessively anxious thoughts generally involve thoughts related to negative, uncontrollable, or catastrophic outcomes. Studies of youth with GAD have demonstrated that youth selectively attend to negative and the threat-related information⁸⁶.

 

            Avoidant behavior is common for situations that provoke anxiety. GAD may be accompanied by physiological or somatic symptoms, including trembling, twitching, muscle tension, irritability, hot flashes, nausea, frequent urination and fatigue⁸⁷. Symptoms must interfere with some aspect of daily functioning to meet the diagnostic criteria of GAD⁷⁷. Within the clinical setting, nurses may observe children with GAD engage in excessive attempts to seek approval from their parents or other adults. Whereas younger children report anxiety pertaining to specific situations, older children increasingly report “generalized” anxiety about a number of different situations⁸¹.

 

3.2.8. Related Illnesses: ⁸⁸

·         Bipolar Disorder

·         Eating Disorders

·         Headaches

·         Irritable Bowel Syndrome (IBS)

·         Sleep Disorders

·         Substance Abuse

 

Bipolar Disorder

            Bipolar disorder, also known as manic-depressive illness, is a brain disorder that causes unusual shifts in a person's mood, energy, and ability to function.⁸⁸

 

            The mood episodes associated with the disorder persist from days to weeks or longer, and can be dramatic, with periods of being overly high and/or irritable to periods of persistent sadness and hopelessness.⁸⁸

 

            Severe changes in behavior go along with the mood changes. These periods of highs and lows, called episodes of mania and depression, can be distinct episodes often recurring over time, or they may occur together in a so-called mixed state. Often people with bipolar disorder experience periods of normal mood in between mood episodes.⁸⁸

 

Eating Disorders

            Eating disorders commonly co-occur with anxiety disorders. For those who have an anxiety disorder, a co-occurring eating disorder may make their symptoms worse and recovery more difficult. It’s essential to be treated for both disorders.⁸⁸

 

            An eating disorder is present when a person experiences severe disturbances in eating behavior, such as extreme reduction of food intake or extreme overeating, or feelings of extreme distress or concern about body weight or shape. A person with an eating disorder may diet, exercise, or eats excessively, which can have life-threatening or even fatal consequences.⁸⁸

 

Anorexia Nervosa

            People with the eating disorder called anorexia nervosa see themselves as overweight even though they are dangerously thin.⁸⁸

 

Bulimia Nervosa

            Bulimia nervosa is characterized by recurrent and frequent episodes of eating unusually large amounts of food and feeling a lack of control over the eating. This binge-eating is followed by purging (vomiting, excessive use of laxatives or diuretics), fasting, or excessive exercise.⁸⁸

 

Headaches

            For some people with anxiety disorders, headache pain, sometimes severe, may be all too familiar.⁸⁸

 

            Headaches can be a common symptom and sometimes a good indicator of an anxiety disorder, particularly generalized anxiety disorder, or GAD. And chronic co-occurring headaches can make functioning even more difficult for someone with an anxiety disorder.⁸⁸

 

            But you can manage anxiety disorders and such pain to lead a full and productive life.⁸⁸

 

Irritable Bowel Syndrome (IBS)

            Irritable bowel syndrome also called IBS, this disorder is characterized by abdominal pain, cramping, bloating, gas, constipation, and diarrhea. Women are more likely to experience symptoms, which usually begin in late adolescence or early adulthood.⁸⁸

 

            People with IBS frequently suffer from anxiety and depression, which can worsen symptoms. That’s because the colon is in part controlled by the nervous system, which responds to stress. Evidence also suggests that the immune system, also responding to stress, plays a role. IBS can also make you feel more anxious and depressed.⁸⁸

 

Sleep Disorders

            Stress and anxiety may cause sleeping problems or make existing problems worse. And having an anxiety disorder exacerbates the problem.⁸⁸

 

            Sleep disorders are characterized by abnormal sleep patterns that interfere with physical, mental, and emotional functioning. Stress or anxiety can cause a serious night without sleep, as do a variety of other problems.⁸⁸

 

            Insomnia is the clinical term for people who have trouble falling asleep, difficulty staying asleep, waking too early in the morning, or waking up feeling unrefreshed.⁸⁸

 

Substance Abuse

            Moderate alcohol consumption a glass of wine with dinner or a few drinks at a party is no cause for concern for many people.⁸⁸

 

            However those with anxiety disorders may find that alcohol or other substances can make their anxiety symptoms worse. And they are two to three times more likely to have an alcohol or other substance abuse disorder at some point in their lives than the general population.⁸⁸

            The symptoms of one disorder can make the symptoms another worse; an anxiety disorder may lead to using alcohol or other substances to self-medicate or alleviate anxiety symptoms.⁸⁸

 

3.2.9. Treatment:

            In general, anxiety disorders are treated with medication, specific types of psychotherapy, or both. Treatment choices depend on the problem and the person’s preference.²

 

Medication

Antidepressants

            Antidepressants were developed to treat depression but are also effective for anxiety disorders. Although these medications begin to alter brain chemistry after the very first dose, their full effect requires a series of changes to occur; it is usually about 4 to 6 weeks before symptoms start to fade. It is important to continue taking these medications long enough to let them work.²

 

SSRIs

            Some of the newest antidepressants are called selective serotonin reuptake inhibitors, or SSRIs. SSRIs alter the levels of the neurotransmitter serotonin in the brain, which, like other neurotransmitters, helps brain cells communicate with one another.²

 

            Fluoxetine (Prozac®), sertraline (Zoloft®), escitalopram (Lexapro®), paroxetine (Paxil®), and citalopram (Celexa®) are some of the SSRIs commonly prescribed for panic disorder, OCD, PTSD, and social phobia. SSRIs are also used to treat panic disorder when it occurs in combination with OCD, social phobia, or depression. Venlafaxine (Effexor®), a drug closely related to the SSRIs, is used to treat GAD. These medications are started at low doses and gradually increased until they have a beneficial effect.²

 

            SSRIs have fewer side effects than older antidepressants, but they sometimes produce slight nausea or jitters when people first start to take them. These symptoms fade with time. Some people also experience sexual dysfunction with SSRIs, which may be helped by adjusting the dosage or switching to another SSRI.²

 

Tricyclics                               

            Tricyclics are older than SSRIs and work as well as SSRIs for anxiety disorders other than OCD. They are also started at low doses that are gradually increased. They sometimes cause dizziness, drowsiness, dry mouth, and weight gain, which can usually be corrected by changing the dosage or switching to another tricyclic medication.²

 

            Tricyclics include imipramine (Tofranil®), which is prescribed for panic disorder and GAD, and clomipramine (Anafranil®), which is the only tricyclic antidepressant useful for treating OCD.²

 

MAOIs

            Monoamine oxidase inhibitors (MAOIs) are the oldest class of antidepressant medications. The MAOIs most commonly prescribed for anxiety disorders are phenelzine (Nardil®), followed by tranylcypromine (Parnate®), and isocarboxazid (Marplan®), which are useful in treating panic disorder and social phobia. People who take MAOIs cannot eat a variety of foods and beverages (including cheese and red wine) that contain tyramine or take certain medications, including some types of birth control pills, pain relievers (such as Advil®, Motrin®, or Tylenol®), cold and allergy medications, and herbal supplements; these substances can interact with MAOIs to cause dangerous increases in blood pressure. The development of a new MAOI skin patch may help lessen these risks. MAOIs can also react with SSRIs to produce a serious condition called “serotonin syndrome,” which can cause confusion, hallucinations, increased sweating, muscle stiffness, seizures, changes in blood pressure or heart rhythm, and other potentially life-threatening conditions.²

Anti-Anxiety Drugs

            High-potency benzodiazepines combat anxiety and have few side effects other than drowsiness. Because people can get used to them and may need higher and higher doses to get the same effect, benzodiazepines are generally prescribed for short periods of time, especially for people who have abused drugs or alcohol and who become dependent on medication easily. One exception to this rule is people with panic disorder, who can take benzodiazepines for up to a year without harm.²

 

            Clonazepam (Klonopin®) is used for social phobia and GAD, lorazepam (Ativan®) is helpful for panic disorder, and alprazolam (Xanax®) is useful for both panic disorder and GAD.²

 

            Some people experience withdrawal symptoms if they stop taking benzodiazepines abruptly instead of tapering off, and anxiety can return once the medication is stopped. These potential problems have led some physicians to shy away from using these drugs or to use them in inadequate doses.²

 

            Buspirone (Buspar®), an azapirone, is a newer anti-anxiety medication used to treat GAD. Possible side effects include dizziness, headaches, and nausea. Unlike benzodiazepines, buspirone must be taken consistently for at least 2 weeks to achieve an anti-anxiety effect.²

 

Beta-Blockers

            Beta-blockers, such as propranolol (Inderal®), which is used to treat heart conditions, can prevent the physical symptoms that accompany certain anxiety disorders, particularly social phobia. When a feared situation can be predicted (such as giving a speech), a doctor may prescribe a beta-blocker to keep physical symptoms of anxiety under control.²

Mechanism of Action:

            Benzodiazepines (once thought to be acting as 'non-specific depressants') act selectively on GABAA receptors, which mediate fast inhibitory synaptic transmission throughout the central nervous system (CNS). Benzodiazepines enhance the response to GABA by facilitating the opening of GABA-activated chloride channels. They bind specifically to a regulatory site of the receptor, distinct from the GABA-binding site, and act allosterically to increase the affinity of GABA for the receptor. Single-channel recordings show an increase in the frequency of channel opening by a given concentration of GABA, but no change in the conductance or mean open time, consistent with an effect on GABA binding rather than the channel-gating mechanism. Benzodiazepines do not affect receptors for other amino acids, such as glycine or glutamate⁸⁹.

3.2.10. Adverse reactions:

            Antianxiety drugs, like other drugs used in psychiatry, can cause a wide range of adverse effects. Many physiological systems may be affected, but, as the main action of antianxiety drugs is on the central nervous system, this system is particularly vulnerable. All antianxiety drugs have the potential to produce untoward effects on higher cerebral functions, although the effect seen is also influenced by psychological and social factors. The most common effects is oversedation, which is a particular problem for the very young and the very old. It is also a serious problem for those who drive motor vehicles and may be a hazard when working in dangerous situations. Subjects are especially vulnerable when (a) antianxiety drugs are first introduced; (b) the dose is increased; and (c) these agents are taken in combination with alcohol and other drugs. Dependence on antianxiety drugs is well known, but only recently has it been recognised that dependence on benzodiazepines is a larger problem than previously realized.⁷

 

3.2.11. Advantages of drugs fom plant:

            Natural drug from the plants are gaining popularity because of several advantages such as often fewer side effect, better patient tolerance, relatively less expensive and acceptance due to a long history of use, especially herbal medicines provide rational means for the treatment of many diseases that are obstinate and incurable in other system of medicine.⁸

 

                The first point to make is that roughly half of today’s prescription and over-the-counter medicines are derived from plants. New drugs don’t just get created in the lab. Scientists trawl through jungles, rivers, wetlands and any other natural habitat they can find, looking for a new compound to test against all the sample viruses and bacteria they keep for this purpose.⁹

                In other words, natural medicine really is the basis for modern medical practice, just a few steps back along the line of development. The difference is that you are taking a 100% natural product, rather than one that has been processed in a lab and lost much of its goodness along the way.⁹

           

            Secondly, herbal medicine has gone through the most rigorous clinical trial imaginable! After thousands of years of regular use by a cross-section of the population, it’s safe to say that any side effects or interactions have been well documented and explored.⁹

 

            Compare this to a typical 10 week clinical trial, commissioned by a pharmaceutical company desperate to bring its new drug to market, that will often take no heed of longer term effects.⁹

 

            Lastly, remember that natural supplements often bring other benefits beyond what you strictly expect. For example, you might take feverfew to give relief from a migraine, then find that your stomach upset has also disappeared. These dual effects are what makes herbology so interesting.⁹

            Additionally, many herbs contain a variety of vitamins and minerals that your body desperately needs. Needless to say, it’s far better to get your Recommended Daily Amount from a natural plant or herb than from a manufactured supplement.⁹

 

            The increasing awareness of herbal medicine is acknowledged by WHO⁷.  WHO estimate about three quarters of the world population currently used herbs and other forms of traditional  medicine  to  treat  there diseases⁷.  WHO has recently defined traditional medicine (including herbal drugs) as comprising therapeutic practices that have been in existence, almost for several hundred years⁷. The traditional preparation comprises medicinal plants, minerals, organic matter, etc⁷. Herbal drugs constitute only those traditional medicines which are primarily use medicinal plant preparation for therapy⁷.

 

            There are several plants very effective in treating stress / anxiety; such plants include Passiflora incarnata (Passion flower) due to presence of bioactive phytomoiety (benzoflavone)¹⁰  and flavonoids in Dolichandrone falcata leaves.¹¹  One such plant Caesalpinia pulcherrima contains isoflavones, flavones,chalcones, flavanols, flavones, sterols and diterpenoids.¹² Recent study on anxiety claims that the flavonoids, alkaloids and terpenoids are responsible for anxiolytic (anti anxiety) and sedative activity.^13,14,15

 

                The literature reveals that the plant Caesalpinia pulcherrima possesses various bioactive compounds along with flavonoids (flavones) and there is no scientific data on anxiolytic activity of Caesalpinia pulcherrima leaves. In view of this, the primary aim of the present study is to investigate the possible anxiolytic activity of Caesalpinia pulcherrima leaves extract in laboratory animal.

PART – III

 

3.3. Experimental Animal Models for Simulation of Anxiety:

3.3.1 Introduction:

            Animal models of psychiatric diseases attempt to capture various feature of the human condition, from behavioral and physiological changes that are indicative of the emotional state to the disease and the effects of therapeutic intervention. According to McKinney, animal models are “experimental preparation developed in one species for the purpose of studying phenomena occurring in another species. In the case of animal models in human psychopathology one seeks to develop syndromes in animals which resemble those of human in certain ways in order to study selected aspects of human psychopathology”. Currently, the third criteria is regarded as having heuristic value because the central nervous processes that lead to anxiety still have to be elucidated; therefore this criterion is regarded as desirable, but not essential. Thus, in an ideal and perfect model one would like to have causative conditions, symptom profiles and treatment response identical to those seen in the human disease state⁹⁰.

 

            The anti-anxiety and antipsychotic indicate a qualitative distinction in the clinical use and mode of action of the drug. Pathological anxiety in man has been defined by its interference with normal functions, by manifestations of somatic disorders, emotional discomfort, interference with productivity at work, etc. This complex characterization of anxiety in man already indicates the difficulties to find appropriate pharmacological models. Therefore, several tests have to be performed to find a spectrum of activities which can be considered to be predictive for therapeutic efficacy in patients⁹¹.

            For in vivo studies, most investigators use a battery of anticonvulsive tests, anti aggressive tests and evaluation of conditioned behavior. Most of the actions of benzodiazepines are thought to be mediated by potentiation of g-amino-butyric acid (GABA). Two subtypes of GABA receptors (GABAA and GABAB) have been described. Moreover, specific binding sites for benzodiazepines have been discovered near these GABA receptors in various areas of the brain. These sites occur in a macromolecular complex that includes GABA-receptors, benzodiazepine receptors and receptors for other drugs, and a chloride channel. The benzodiazepines potentiate the neurophysiological actions of GABA at the chloride ion channel by increasing the binding of GABA to GABAA receptors. This implies that the GABAA receptor is involved in anxiety and that its direct activation would have an anxiolytic effect. Based in these findings various invitro tests have been developed⁹¹.

 

3.3.2 Animal models of anxiety:

            Anxiety enables the individual to recognize danger and to deal with an unknown or vague internal or external threat. Fear is a similar alerting signal, but differs from anxiety in that it is regarded as response to a known, definite, nonconflictual threat. Clinicians assessing anxiety distinguish between “normal” and “pathological” anxiety. Normal anxiety is an advantageous response to a threatening situation that accompanies many aspects of daily life. By contrast, pathological anxiety is an inappropriate response to an external or internal stimulus. In light of the high complexity of anxiety disorders and the comorbidity with major depressive disorder, the chance of succeeding in developing comprehensive animal models that accurately reflect the relative influences of contributing factors in human is probably quite poor⁹².

3.3.3 Validity criteria for animal models of anxiety disorders:

            Numerous procedures with experimental animals have been developed to facilitate preclinical research on the behavioral pharmacology of anxiety. The discovery of benzodiazepines (BZs) about 50 years ago, and their therapeutic and commercial success in the treatment of anxiety, has stimulated the development of a number of experimental test procedures. Because BZs were the only effective anxiolytic drugs at that time, the predictive validity of the animal models has been mainly based on their ability to detect the pharmacological action of BZs and related compound. Later, clinicians discovered that patients can become addicted to BZs, and consequently paid more attention to non-benzodiazepine anxiolytics. However, it turned out that these new drugs were a challenge to the validity of the existing screening models. The best known example is Buspirone, a clinically effective serotonin (5-HT) _1A receptor partial agonist whose anxiolytic potential was missed by conventional screening procedures in animals, in particular conflict tests in rats, and was only recognized during clinical assessment for possible anti psychotic efficacy⁹³. This was the time when unconditioned conflict tests such as the elevated plus maze were developed⁹⁴.

 

            A further complication appeared when it became evident that anxiety is not a unitary phenomenon, but could be divided into various forms including normal or state anxiety, on the one hand and pathological or trait anxiety on the other hand. According to today’s terminology, pathological anxiety should not be considered just as an excess of normal anxiety, but it rather appears that the pathological forms have a different neurobiological basis. Furthermore, the various forms of human disorders have been shown to be differentially sensitive to pharmacological treatment.

            Most of the experimental paradigms involve exposure of animals to external stimuli (e.g., cues paired with foot shock, bright light for rodents or exposure to a predator) or internal stimuli (e.g., drugs) that are assumed to induce anxiety. Because none of these models involves pathological anxiety, that is an anxiety-like state independent of an obvious (external) stimulus, Listerdescribed them asanimal models of state anxiety. In these experimental set ups, subjects experience normal anxiety at a particular moment in time and their emotional state is just potentiated by an external anxiogenic stimulus.

 

            Despite these problems in the use of animals to study anxiety, these models have been, and are still, indispensable for neurobiological/ neuropharmacological research. Much of our understanding of the neural substrates of anxiety has emerged from studies employing animal models that emulate aspects of the presumed etiology, physiology, and behavioral expression of fear and anxiety. A survey of current literature reveals a confusing diversity of experimental procedures with more than 30 behavioral paradigms claiming face, construct, and/or predictive validity as animal models of anxiety disorders.

 

I.    Models for normal anxiety:

            An overview of the existing models for normal anxiety is schematically represented (scheme 1). As proposed by Griebel⁹⁵ these models are distinguished according to the following categories: (i. Models based on unconditioned responses; and ii. Models based on conditioned responses). The first category is further divided into four subgroups: models based on exploratory behavior in rodents (e.g., elevated plus maze and the light-dark test), models based on social behavior in rodents (social interaction test) or in non-human primates (human threat), and models based on somatic stress reactions (e.g., stress-induced hyperthermia). In the fourth group, other paradigms are summarized which do not fit easily into the other sub groups such as the anxiety/fear test battery.

 

1.         Elevated plus maze (EPM):

         Today, the majority of studies using animal models of normal or state anxiety employ unconditioned-based procedures that rely on the natural behavior of the animals. Among these, the elevated plus maze has become one of the most popular behavioral tests^{94, 96}. Its popularity is mainly due to practical reasons, because the elevated plus maze permits a quick screening of potential anxiety-modulating drugs or of genetically modified laboratory rodents without training the animals or involvement of complex schedules⁹⁷. The elevated maze consists of two opposite open and two closed alleys. When the animal is taken straight from its home cage it explores the different alleys and the total number of entries is counted. Anxiolytics help to overcome the fear induced inhibition of open-alley exploration, while anxiogenic agents suppress open-alley exploration. Unfortunately, the plus maze behavior patterns may be influenced by variations in the parameters that are not always obvious, e.g., the species or strain investigated, housing conditions, day time of the testing, intensity of the light, and scoring method⁹⁸. As a result, a vast number of studies employing the elevated plus maze have yielded inconsistent findings. To overcome these problems, Rodgers and Johnson have developed an “ethological” version of the mouse plus maze that incorporates species specific behavioral postures (e.g., risk assessment, head dipping) together with the conventional spatiotemporal measures of open arm avoidance⁹⁹.

 

         The elevated zero maze is a recent modification of the plus maze designed for investigations in mice. It is an elevated annular platform with two opposite open and two closed quadrants. Animals are placed in one of the closed quadrants designated as the starting quadrant and anxiety related behaviors are recorded¹⁰⁰.

 

2.         Open field test:

            Rodents are night-active animals that prefer darkness and avoid bright areas. This has to be taken in to account when using the open field test, a very common observation method. For the open field test, the animal is taken from its home cage and placed in a novel and relatively lit arena that is large enough for the animal to move around in. The area is divided in to peripheral and central units, and locomotion and rearing can be recorded in these units. Because of its photophobicity, the animal avoids the brightly lit open spaces and prefers to stay close to the walls. Exploratory or locomotor behavior is therefore measured while determining the distance from the wall, and autonomic activity such as urination and defecation is evaluated. By using infrared beam array system, locomotion, rearing and time spent in certain predefined areas of the open field are measured automatically. One also has to consider that the behavior displayed in the open field- similar to that in the elevated plus maze is remarkably sensitive to a variety of internal and external factors¹⁰¹.

 

3. Social interaction test:

            The social interaction test that was originally introduced by File¹⁰², and that quantifies the level of social behavior between animals, is a valuable behavioral paradigm for testing anxiolytic drugs. Experimental animals unfamiliar to each otherare placed in pairs in to an open arena. When the arena is brightly illuminated the situation is aversion for the animals, so that they reduce their social interactions. Anxiolytic usually increase the time spent in social interaction.

4. Fear-potentiated startle test:

            David and colleagues have utilized the fear-potentiated startle test to study the fear circuitry in the brain. This test includes a classical fear conditioning in that a stimulus (e.g., light) is paired with a mild electric foot shock. During the fear-conditioning phase a light stimulus signals the occurrence of a shock. The startle response is elicited by a loud noise, and its amplitude is augmented when the light and the noise are presented together. BZs have anxiolytic effects in this paradigm in that they inhibit the enhancement of the startle response but do not block the startle response per se.  Briefly, the paradigm involves placing the animal in a cage equipped to measure the amplitude of the presence or absence of a light previously paired with an electric shock. Animals that have already been exposed to the shock-paired light show a greater startle response to the noise in the presence of light than in its absence. Using this kind of potentiated startle response as an operational measure, it was found that the central nucleus of the amygdale and a variety of hypothalamic and brain stem areas are involved in physiological (e.g., activation of the sympathetic and the parasympathetic system, release of “stress hormones”) and behavioral responses (e.g., changes in locomotors activity, freezing) that reflect fear and anxiety^{103, 104}.

 

5. Defense tests:

            Defensive behaviors in mammals are thought to constitute a significant parameter that can be studied to understand human emotional disorders, including anxiety¹⁰⁵.These behaviors occur in response to a number of threatening stimuli including predators, attacks by nonspecific, or presence of dangerous objects. The Mouse Defense Test Battery (MDTB) consists of an oval runway that allows the extensive investigation of state anxiety following drug treatment^{106, 107}.Specific situational and behavioral components of the anxiety defense test battery, including reactivity to stimuli associated with potential threat such as presentation of an anesthetized predator (a rat), are incorporated into the MDTB. Drug experiments have demonstrated that anxiolytic compounds generally tend to decrease defensive behaviors. These tests may thus represent a considerable methodological improvement because a major concern with traditional animal models of state anxiety that are based on single measures is that they are often unable to discriminate between effects of different classes of anxiolytics.EPM and the MDTB provide new tools to differentiate anxiolytic drugs of various classes that induce specific behavioral profiles.

 

II. Animal models for pathological anxiety:

            Pathological anxiety in humans is often an enduring feature of the individual, at least in part due to a genetic predisposition. To model genetically based anxiety, mice with target mutation in distinct genes were created that exhibit phenotypic changes indicative of increased anxiety. In addition, rat or mouse lines were bred to select for high or low emotional reactivity.

 

            The neurotransmitter 5-HT is centrally involved in the neuropathology of many neuropsychiatric disorders. More than a dozen pharmacologically distinct serotonin receptor sub types regulate a wide range of functions in different brain areas and in the periphery of the body. There is pharmacological and neuroanatomical evidence that at least one 5-HT receptor; 5-HT_1A is involved in the regulation of anxiety like behaviors^{108, 109}. Results of recent studies employing mutant mice with targeted deletions of the 5-HT_1A receptor gene further support a role of this receptor in anxiety¹⁰⁹.

 

            Further examples of models for pathological anxiety are mice that were gene targeted for the corticotrophin-releasing factor (CFR) ¹¹⁰ or for the γ₂ subunit of the GABA_A receptor. This receptor subunit is known to be essential in mediating the anxiolytic actions of benzodiazepines¹¹¹. An “anxious” phenotype was also observed in mutant mice lacking the gene for the neuroactive peptide NPY¹¹². At first glance, these lines of mutant mice seem to provide a unique opportunity to model pathological or trait anxiety. Moreover, compared with the state anxiety, here anxiety is increased artificially by exposure to external (aversive) stimuli, the new models seem be advantageous in that they may represent a kind of “general anxiety” due to a certain genetic modification. This sounds reasonable since genetic studies in humans have indicated that there are genetic components contributing to the development of anxiety disorders. However, one has to consider that in humans, the modulation of anxiety processes involves multiple genes. In the future, the use of mice strains that display elevated emotionality due to a distinct “genetic back ground” or mice selected for their high levels of anxiety using gene targeting experiments may lead to greater progress in our understanding of the neurobiological substrate of anxiety. Such animals would exhibit increased anxiety not because of a defect in a single gene, but because of a complex set of genes that result in an enduring feature of the strain/individual, thus determining its phenotype in combination with environment factors¹¹³.

 

            Inbred strains which show constantly high levels of anxiety/fearfulness have already been created. In mice, the BALB/c strain has been considered to be a realistic model of trait anxiety, which is probably not related to only one particular target gene but to abnormalities in various neurotransmitter circuits such as the GABAergic, dopaminergic and the opioid system¹¹³. Also in rats, several strains of trait anxiety have been described, e.g., the Maudsley rat¹¹⁴, the Wistar-Kyoto¹¹⁵, the Roman¹¹⁶, or the Sardinian alcohol-preferring line¹¹⁷. Recently, two breeding lines were generated from the same strain of Wister rats showing a maximum difference in other behaviors as well as in physiological parameters not directly related to anxiety. These two rat lines are now called high anxiety-related behavior (HAB) and low anxiety-related behavior (LAB) ¹¹⁸. Their overall performance in various behavior tests suggests that selective breeding has resulted in lines not only differing markedly in their innate anxiety-related behavior but also in stress-related behavioral performance, suggesting a close link between the emotional evaluation of a novel and stressful situation and a subject’s capability to cope with such situations.

           

          In conclusion, animal models are indispensable tools for research on the neurobiological mechanisms underlying anxiety disorders and for the development of new anxiolytic drugs. It appears that the use of several models, either successively or in parallel, provides the greatest chance to elucidate the neurobiological processes of psychiatric diseases and to identify new, effective anxiolytic compounds.