ANTIANXIETY PROPERTY OF BASELLA ALBA LINN LEAVES EXTRACT IN EXPERIMENTAL ANIMALS - REVIEW OF LITERATURE

 

3. REVIEW OF LITERATURE

 

             WHO defines herbal medicine as finished, labeled medicinal products that contain as active ingredients, the aerial or underground parts of plants or other plant material, or combinations thereof, whether in the crude state or as plant preparations. Plant materials include juice, gums, fatty oils, and any other substances of this nature.

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, folk lore 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 Classification⁵⁰:

Ø  Kingdom: Plantae

Ø  Order: Caryophyllales

Ø  Family : Basellaceae

Ø  Genus: Basella

Ø  Species: Basella alba

Ø  Binomial name: Basella alba L.

Vernacular Names⁵⁰:

Ø  English: Malabar-, Malabar climbing-, Ceylon-, Indian-, East-Indian-, spinach

Ø  Gujarati: Poi ni bhaji

Ø  Kannada: Basale soppu

Ø  Marathi: Mayalu

Ø  Bengali: Pui shak             

            Basella alba is a wildly cultivated, cool season vegetable with climbing growth habit. It is a succulent, branched, smooth, twining herbaceous vine, several meters in length. Stems are purplish or green. Leaves are fleshy, ovate or heart-shaped, 5 to 12 cms long, stalked, tapering to a pointed tip with a cordate base. Spikes are axillary, solitary, 5-29 cm long. Fruit is fleshy, stalkless, ovoid or spherical, 5-6 mm long, and purple when mature. Mainly leaves and stems are used for the medicinal purpose. ⁵⁰

 

 

Ethanobotany

            Basella alba has been used for many of its useful product from ancient times. Nowadays its properties have been utilized for the extraction of some useful material so that it can be used for the beneficial human activities. Some of the uses of this plant parts in the cure of certain problems occurred to humans has been explained here:

Ø  The paste of root of red Basella alba along with rice washed water is taken in the morning in empty stomach for one month to cure irregular periods by the rural people of Orissa, India ^34,35.

Ø  Leaves of Basella alba is used for the treatment of hypertension by Nigerians in Lagos³⁶

Ø  .Basella alba is used as antimalarial  in  cameroonian  folk  medicine³⁷.

Ø  The daily consumption of Indian spinach has a positive effect on vitamin A stores in populations at high risk of vitamin A deficiency³⁸.

Ø  The cooked roots and leaves have been reported to be used in the treatment of diarrhoea and as laxative, respectively³⁸

Ø  The flowers are used as an antidote for poisons³⁸.

Ø  It is also a safe aperient for pregnant women and its decoction has been used to alleviate labour³⁸.Basella alba traditionally claimed to increase libido³⁹

Ø  Aqueous extract of Basella alba leaves increases red blood cell count in albino rats³⁸.

Ø  Basella alba leaves extract possess anti inflammatory activity⁴⁰.

Ø  Betacyanin present in Basella alba fruit gives antioxidant activity³¹.

Ø  Basella alba extracts significantly enhances testosterone production in bull and rat Leydig cells in a concentration-dependent manner⁴¹.

Ø  Extract of aerial parts of Basella alba shows CNS depressant activity³⁰.

Ø  Basella alba leaves extract possess gastro protective action⁴².

 Pharmacognosy and Phytochemistry

            The relevant work has not been carried out on B. alba till date, and hence research focusing on pharmacognostic profile is undertaken in near future. The chemical composition of the leaf extract include: proteins, fat, vitamin A, vitamin C, vitamin E, vitamin K, vitamin B9 (folic acid), riboflavin, niacin, thiamine and minerals such as calcium, magnesium and iron. Kaempherol is the flavonoid present in Basella alba at a concentration of 1.4mg/100g. ⁵¹Basella mucilage is viscous with low swelling capacity. Its pH is good for skin (5.3-5.4). Partial purification of Basella mucilage proved to be composed of polysaccharide with D-galactose as a major compound. The cell toxicity to Chang liver cell shows tendency of mild toxicity. The gel preparation of Basella mucilage provide good stability that serve for further development as cosmetic and medicine for skin diseases. Basella alba contains basellasaponins ⁵², amino acid such as arginine, leucine, isoleucine, lysine, threonine and tryptophan ⁵³, peptide, phenolic compounds in various extracts. ⁵⁴Basella fruit contains gomphrenin derivative which is betalain pigment. ⁵⁵ The mucilage of B. alba consists of mixture of polysaccharides ⁵⁶, and starch-type glucan which can be separated by starch iodine complex. ⁵⁷ Plant mucilage is composed of water soluble polysaccharide, which functions as water retention, germination, food reservoir and secondary metabolite storage²⁴. Basella mucilage was also proposed for the applications of medicine and cosmetics. The antityrosinase which was accorded to traditional used for anti freckle is tested. Antioxidant activity related to the inflammation mechanisms caused by free radicals is assayed. Then formulation of gel from Basella mucilage was prepared which can be used for further development of cosmetic and anti-inflammatory purposes as topical usage. Anthocyanins are a natural pigment which is responsible for the blue, purple, violet and red colours in fruits, flowers, stem and leaves. ⁵⁵ Antioxidant activities, total phenolic, flavonoid and ascorbic acid contents of B. alba commonly consumed in Nigeria are determined. A high and significant correlation existed between antioxidant activity and total phenolic content indicating that total phenolic content is the major contributor to the antioxidant activity of the plant. Ascorbic acid fairly correlated with antioxidant and phenolic content. ⁵⁹ B. alba contains β carotene. ⁶⁰ The phytochemical contents of the leafy vegetables serve as supplements for food and also have the potential to improve the health status of its users as a result of the presence of various compounds vital for good health. Their fiber content provides bulk in the diet and this helps to reduce the intake of starchy foods, enhances gastrointestinal function, prevents constipation and may thus reduce the incidence of metabolic diseases like maturity onset, diabetes mellitus and hypercholesterolemia. They are also potent antibiotics, antihypertensives and blood building agents and improve fertility in females when eaten in soups. Total oxalate, soluble oxalate and nitrate were determined for leaves of Basella alba L. grown on soils of medium and high fertility. Higher soil fertility resulted in increased total oxalate in Basella. Leaves grown on high-fertility soil had more nitrate than those from medium fertility. ⁶¹

Pharmacology

         In vitro pharmacology⁶²

            Mucilaginous substances from Basella alba was studied for in vitro glucose entrapment and compared to glucomannan powder. The mucilage solution showed gel-forming characteristics and concentration response on glucose entrapment activity. Anthocyanin pigments are reported to have many therapeutic benefits including vasoprotective and anti-inflammatory properties, anti cancer, chemo protective and anti-neoplastic properties, reversing age related deficits and useful in controlling oxidative stress during pregnancies complicated by intrauterine growth retardation.

            It has also been suggested that anthocyanins has got the ability to stabilize DNA triple helical complexes  and can also protect the chloroplast against high light intensities.  In the present scenario, there is a rising demand for natural sources of food colorants with nutraceutical benefits with anthocyanins. Antioxidant assays were done by enzymatic assay methods like Super oxide dismutase, Catalase and Peroxidase, Basella alba showed higher activity.  Crude aqueous extract possess mild antioxidant, and no tyrosinase inhibitory activity. Basella alba is used traditionally in Thailand for anti-inflammatory, cytotoxicity and antioxidant activities of anti-inflammatory remedies. This allowed the selection of lead extracts for various ethnopharmacological researches by Nisarat et al.  The methanolic extracts exhibited marked antimicrobial activity against gram positive and gram negative bacteria and fungi. Basella alba showed good inhibitory activity against Aspergillus niger.  The leaf extracts (methanolic extract and aqueous extract) of Basella alba Linn.var. alba were investigated for in-vitro anti-inflammatory activity by human red blood cell membrane stabilization method (HRBC). Aqueous extract showed significant in vitro anti-inflammatory activity compared to methanolic extract. The in-vitro anti inflammatory activity of the extracts were concentration dependent, with the increasing concentration, the activity is also increased. Basella alba L. leaf extracts exhibited membrane stabilization effect by inhibiting hypotonicity induced lysis of erythrocyte membrane. The erythrocyte membrane is analogous to the lysosomal membrane and its stabilization implies that the extract may as well stabilize lysosomal membranes. Stabilization of lysosomal membrane is important in limiting the inflammatory response by preventing the release of lysosomal constituents of activated neutrophil such as bactericidal enzymes and proteases, which cause further tissue inflammation and damage upon extracellular release.  Antioxidant and antimutagenic activities of plant extracts act as functional foods for cancer prevention. Antioxidant activity was expressed as the ability of each extract to scavenge the free radicals 1, 1-diphenyl-2-picrylhydrazyl (DPPH). Antimutagenic activity was evaluated with the Ames test using Salmonella typhimurium strains TA 98 and TA 100. Basella alba Linn. extract had the strongest antimutagenicity with both strains of S. typhimurium with high percentage of inhibition value. Flavonoids and phenolic compounds from the herbal extracts are proposed to be antioxidant and antimutagenic agents, respectively. The apparent antioxidant and antimutagenic activities of the plant further suggests their potential usefulness in cancer prevention. The possible mechanisms may be classified as: Firstly, B. alba extracts might include the blocking of the mutagen transfer into the cytosol by phenolic binding or insertion into the transporters of the outer membrane of the cell. Secondly, B. alba extracts modified the permeability for mutagens across bacterial membranes.

In-vivo pharmacology⁶²

            The effects of the aqueous leaf extract of Basella alba on haematological and biochemical parameters were studied in Wistar strain albino rats. The results showed that B. alba significantly increased red blood cell count, white blood cell count, packed cell volume, haemoglobin concentration and platelet count. However, the extract significantly reduced the activity of the liver enzymes such as ALP, ALT and AST. Totally, adding B. alba leaves as part of daily diet may reduce anemia and maintain good health. Basella alba is a plant used in traditional medicine in the West Cameroon region to treat sexual asthenia and infertility in man. Its methanol extracts stimulated testosterone production in testicular fractions and Leydig cell cultures, and in normal adult albino male rats. In Leydig cells, testosterone is partly metabolized into estradiol by aromatase. The stimulatory effect on estradiol level may result from its effect on aromatase gene transcription and translation into a biologically active enzyme.CNS depressant activity of the aerial parts of B. alba was determined by Anandarajagopal et al.  Petroleum ether, methanol and aqueous extracts were prepared from dried aerial parts of Basella alba by cold maceration method and CNS (Central Nervous System) depressant activity was evaluated by pentobarbitone induced sleeping time test, open field test and hole cross test in mice. Methanol extract showed highly significant CNS depressant activity than other extracts tested. An attempt was made to screen the anti-inflammatory activity of Basella alba leaf in experimentally induced inflammations in rats. The aim was met by two methods, one is carrageenan induced paw edema and another is cotton pellet granuloma. Basella alba extract showed a significant activity at a dose of 500 mg/kg. Basella alba possesses a good anti-inflammatory activity and shows a dose depending activity. Basella alba has been used from a long time back for the treatment of many diseases like dysentery, diarrhea, anemia, cancer etc. It has also been utilized for different kinds of healing activities. Various kinds of extract like aqueous extract, methanolic extract, petroleum extract, chloroform extract has been prepared from different parts of the plant has been utilized in the treatment of many diseases since time immortal all over the world. India and China are the two major countries harbouring this plant and utilizing it for the benefit of human being. It also consists of compounds that can be used for the preparation of medicine by pharmacological industry. The chemical composition of the leaf extract has been found to be: proteins, fat, vitamin A, vitamin C, vitamin E, vitamin K, vitamin B9 (folic acid), riboflavin, niacin, thiamine and minerals such as calcium, magnesium and iron. Some unique constituents of the plant are basellasaponins, kaempherol and betalain. The pharmacological activities of Basella alba has been tested by both in-vitro as well as in-vivo methods. Antioxidant activity, antimutagenic activity has been carried out by the scientist to explore the dynamics of the plant for the advancement in the treatment of the diseases. CNS depressant activity, anti inflammatory activity has also been observed for this plant. Knowing that plants have a large number of chemical substances, which have several pharmacological actions, we should exploit more natural products, which in the future could show the cure for many illnesses. It is hoped that compilation of this review will serve as a guide to all those involved in this particular field of research.  

 

3.1.2        The other plants having Anxiolytic activities :

There have been several reports of natural drugs which possessing anxiolytic activities . 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 brain ³².

Following research work of plant extracts reveals that their constituents posses anxiolytic activity and this has lead us to investigate anxiolytic activity of Basella alba leaves extracts.

1. Methanol and ethyl acetate extract of Eriobotrya japonica leaf extracts contains flavinoids, at dose 300 mg/kg markedly increased the average time spent in the open arm of EPM hence show anxiolytic effect⁶⁴
2. Ethanolic extract of Pisonia grandis R. Br leaves contains flavinoids, posses anxiolytic activity at doses 150 mg/kg and 300 mg/kg in mice⁶⁵.
3. Anxiolytic effect of hydroalcoholic extract of teprosia purpuria (L) pers on EPM, EZM, Y-Maze and hole / board at doses 200 mg/kg and 400 mg/kg in swiss alwino mice⁶⁶.
4. Anxiolytic effect of Equisetum arvense Linn. Extract could be related at least in part to flavinoids or specifically to apigenin, which recognise and bind with high affinity BZD site of GABA receptor and exerting anxiolytic and slightly sedative effect⁶⁷.
5. Anxiolytic effect of acute administration of ursolic acid, active principle of Ocimum Sanctum on EPM, and L/D tests at doses 0.1 and 0.2 mg/kg in rats⁶⁸.
6. Hydroalcoholic extract of Boerhaavia diffusa leaves contains flavinods, exhibited anxiolytic activity in rats at a dose 100 mg/kg on EPM⁶⁹.
7. Evaluation of anxiolytic activity of ethanolic extract from the leaves of Trichosanthes cucumerina L. in mice at doses 200 and 400 mg/kg⁷⁰.
8. Effect of the active constituent of Crocus sativus L., crocins, in light/dark animal model of anxiety in mice shows significant results at 50mg/kg dose ⁷¹.
9. Anxiolytic effect of saponins from Panax quinquefolium on EPM, L/D, HB, in mice shows significant results at 25 – 100mg/kg dose ⁷².
10. Evaluation of anxiolytic properties of Gotukola- (Centella asiatica) extracts and asiaticoside- is active triterpenes found in this plant in rat behavioral models ⁷³.
11. Anxiolytic effect of Stachys lavandulifolia Vahl on the elevated plus maze model at 100mg/kg dose on mice ⁷⁴.
12. Lemon grass (Cymbopogon citratus) A placebo-controlled, double-blind RCT of Lemon grass extract included 18 patients suffering from trait anxiety. The extract was administered as a single dose of abafado (Brazilian lemon grass tea), and its effects were quantified 30 min later under the stress of a cognitive test. The results revealed no significant inter-group differences to suggest an anxiolytic effect ⁷⁵.
13. Passion flowers (Passiflora incarnata) in a double-blind RCT, 32 patients with generalized anxiety disorder were randomized to receive 45 drops of a passionflower tincture or 30 mg oxazepam per day. After 4 days of treatment, no significant differences in terms of anxiety levels were noted. Patients treated with passionflower reported fewer adverse effects than those receiving the synthetic anxiolytic ⁷⁶.
14. Aqueous extract of dried Ginkgo leaves have been reported to inhibit MAO-A and MAO-B.Ginkgo biloba (Ginkgoaceae) leaves contain active constituent flavonol glycosides and it shows effect on behavior, learning and memory. It also shows anxiolytic effect at 0.01-10 mg/kg dose range ⁷⁷.
15. Anxiolytic effects of the aqueous extract of Uncaria rhynchophylla⁷⁸.
16. Evidence that total extract of Hypericum perforatum affects Exploratory behavior and exerts anxiolytic effects in Rats⁷⁹.
17. Coriandrum sativum: evaluation of its anxiolytic effect in the elevated plus maze⁸⁰.
18. The anxiolytic-like effects of Aloysia polystachya (Griseb.) Moldenke (Verbenaceae) in mice⁸¹.
19. Kaempferol from the leaves of Apocynum venetum possesses anxiolytic activities in the elevated plus maze test in mice⁸².
20. Flavonoids from Tilia Americana with anxiolytic activity in plus-maze test⁸³.
21. Anxiolytic-like effect of Sonchus oleraceus L. in mice⁸⁴.
22. Barakol: A potential anxiolytic extracted from Cassia siamea⁸⁵.
23. Comparative studies on anxiolytic activities and flavonoid compositions of Passiflora edulis ‘edulis’ and Passiflora edulis ‘flavicarpa⁸⁶.
24. An anxiolytic effect of Dolichandrone Falcata leaves extract in experimental animals⁸⁷.
25. Anxiolytic Activity of Seed Extract of Caesalpinia Bonducella (Roxb) In Laboratory Animals⁸⁸.
26. Studies on the anxiolytic effect of Sponndias Mombin L (Anacardiaceae) extracts⁸⁹.
27. Anxiolytic effects of Elaeocarpus sphaericus fruits on the elevated plus-maze model of anxiety in mice may be related to their content of flavinoids⁹⁰.
28. Anxiolytic effect of hydroethanolic extract of Drymaria cordata L. Willd⁹¹.
29. Bioactivity-directed separation of an anxiolytic fraction from Aethusa cynapium Linn, flavinoids constituents present in the plant may responsible for its anxiolytic activity⁹².
30. Methanolic extract of Sapindus Mukorossi Gaertn. contains flavinoids, may be responsible for anxiolytic activity in mice⁹³.
31. Anxiolytic and sedative effects of Byrsocapus coccineus Schum. and Thonn. (Connaraceae) extract⁹⁴.
32. Evaluation of anti-anxiety activity of Actaea spicata Linn⁹⁵.

 

 

PART-II

3.2. ANXIETY:

3.2.1 Introduction:

Anxiety disorders are conditions in which extreme, often disabling, anxiety or fear is the shared primary symptom. Normal anxiety may be defined as “a diffuse, unpleasant, vague sense of apprehension, often accompanied by autonomic symptoms-such as headaches, palpitations, tightness in the chest, restlessness, mild stomach discomfort that can be an appropriate response to a threatening situation or stimulus” ⁹⁶. 

Whereas fear is considered specific and targeted, anxiety is considered more diffuse and unfocused. Pathological anxiety and fear, as compared to normal symptoms, are diagnosable conditions when the anxiety, fear, or both cause significant distress, interfere with functioning, or are marked by time consumption ⁹⁷.

3.2.2 Epidemiology:

Several large, methodologically rigorous epidemiological studies have indicated that anxiety disorders are one of the most prevalent categories of childhood and adolescent psychopathology ⁹⁸. 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) ⁹⁹.

            Although comorbidity rates vary depending upon the primary diagnosis, there exists a strong comorbidity among anxiety disorders in youth ¹⁰⁰. 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%) ¹⁰¹. The most common comorbid diagnoses include other anxiety disorders and depressive disorders ¹⁰². Additionally, children with anxiety disorders frequently experience other psychiatric conditions, including attention deficit/hyperactivity disorder and the disruptive disorders ¹⁰³.

3.2.3 Etiology:

            The etiology of child and adolescent anxiety may be of a biological and/or learned nature. Indeed, researchers posit that anxiety arises from a complex interaction of specific characteristics related to the child (e.g., biological, psychological, and genetic factors) and his or her environment (e.g., conditioning, observational learning, family relations, traumatic events ¹⁰⁴. There are an abundance of theoretical models that would define child and adolescent anxiety, some are as follows.

Biological Model:

Within a biological model of etiology, researchers have investigated genetic influences as well as neurobiological structures and circuits. A recent meta-analysis of the genetic epidemiology of anxiety disorders demonstrated that PD, phobias, OCD, and GAD aggregate in families and concluded that genetic factors have a moderate influence on the development of anxiety disorders ¹⁰⁵. Researchers have suggested that, although clearly not the only contributing influences, genetic factors may help us understand why certain individuals exposed to similar experiences have different responses and outcomes concerning the development of pathological anxiety ¹⁰⁶.

Research aimed at identifying specific brain areas and circuits underlying anxiety disorders has provided support for neurobiological influences in anxiety. The most support for neuroanatomical influences has come from research investigating the amygdala's role in fear conditioning. Research in this area has implicated the amygdala in the pathophysiology of anxiety disorders ¹⁰⁷. Neurochemical factors have also been implicated in the development of anxiety symptoms. Abnormal functions of serotonin, norepinephrine, dopamine, and γ-aminobutyric acid systems as well as abnormal chemoreceptor reactivity have all been implicated in anxiety ¹⁰⁸.

Cognitive–Behavioral Model:

Within a cognitive–behavioural model, abnormal thoughts, feelings, and behaviours are described as reactions that have been learned as a result of conditioning and observation ¹⁰⁹. A behavioural theorist highlighted behavioural conditioning as an important etiological factor in the development and maintenance of anxiety and posited that an individual associates a threatening stimulus with a non threatening stimulus so that the latter by itself triggers anxiety. Once the fearful or anxious reaction has been learned through classical conditioning, the fear or anxiety is maintained through the operant mechanism of negative reinforcement.  Negative reinforcement is manifested by avoidance learning, escape learning, or both. Escape learning involves terminating an aversive situation, whereas avoidance learning involves avoiding fear- or anxiety-provoking situations. Consequently, without opportunities for new learning provided by exposure, the fear or anxiety does not extinguish. This process of acquisition and maintenance of fears is known as Mowrer’s two factor theory ¹¹⁰.

In addition to the two-factor theory, observational learning influences the development of anxiety. Children learn about anxiety-provoking situations by observing others experience such situations or by acquiring information through activities like reading or watching the news on television ¹¹¹. Furthermore, they are capable of retaining and reproducing event memories acquired via observational learning ¹¹².

Ecological Models:

Ecological models focus on the impact of the family system and other environmental influences on the development of anxiety disorders and particularly highlight the bidirectional relationships among child, family, and other environmental contributions to anxiety. For example, research has revealed relationships among levels of child temperamental characteristics (i.e., behavioural inhibition), insecure parent–child attachment, and anxious and controlling parenting styles ¹¹³. Parental modelling of fearful and anxious expressions and behaviours has also been found to contribute to the development of anxiety in children ¹¹⁴.

3.2.4 Types of Anxiety Disorders:

            The core symptoms for six anxiety disorders are listed in the Diagnostic and Statistical   Manual of Mental Disorders,   Fourth Edition, Text Revision (DSM-IV-TR) ⁹⁷, are described below.

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 diagnosis ¹¹⁵.

            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 behaviour 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 behaviour to avoid school or separation ¹¹⁶.

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 dying ⁹⁷.

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 youth ¹¹⁵.

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 presentation ¹¹⁷. PD is less common in childhood than in adolescence, and the clinical presentation of PD varies across the developmental span ¹¹⁸. 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 event ¹¹⁷.

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 manner ⁹⁷. 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 behaviours ¹¹⁹.

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 participate ¹²⁰.

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) ⁹⁷.

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 behaviours (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 collecting ¹²¹.

Youth with OCD may present to health professionals with a number of physical or behavioural 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 cleaning ¹²².

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 rituals ¹²³.

Posttraumatic Stress Disorder (PTSD):

            PTSD is characterized by recurrent symptoms of anxiety related to past trauma, such as physical abuse or natural disasters ⁹⁷. 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 mortality ¹²⁴. This disorder always involves significant distress and can result in marked interference with functioning ⁹⁷.

            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 experience ¹²⁰.

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 information ¹²⁵.

Avoidant behaviour 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 fatigue ¹²⁵. Symptoms must interfere with some aspect of daily functioning to meet the diagnostic criteria of GAD ⁹⁷. 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 situations ¹²⁰.

3.2.5 Symptoms of anxiety:

According to Lang's multiple-systems theory of emotion, symptoms are of a cognitive (e.g., worry thoughts), physiological (e.g., racing heart rate), or behavioural (e.g., avoidance) nature. The cognitive component of anxiety is related to the anxious thoughts that develop in response to cognitive distortions in the attention, interpretation, and memory components of information processing ¹²⁷.

            The physiological component of anxiety disorders consists of the associated autonomic or somatic sensations. Although individuals experience physiological arousal symptoms in response to feared situations, individuals with anxiety disorders experience physiological symptoms that are excessive in duration or intensity for the particular situation or stimulus ¹²⁸.

Sleep-related problems are more prevalent among clinically anxious youth and are associated with increased anxiety severity and interference in family functioning. In a recent study of sleep-related problems in children with generalized anxiety disorder (GAD), separation anxiety disorder (SAD), and/or social phobia. Alfano reported that the most common sleep-related problems were insomnia, nightmares, and refusal/reluctance to sleep alone ¹²⁹.

 

The followings are the complete list of the most common physiological symptoms associated with anxiety disorders ⁹⁷.

Systems		Symptoms
Cardiac	-	Accelerated heart rate, Heart palpitations, Chest pain Shortness of breath, Heart pounding.
Gastrointestinal	-	Difficulty swallowing, Nausea, Diarrhea, Gastrointestinal discomfort, Frequent urination.
Respiratory	-	Shortness of breath, Smothering sensation, Choking sensation, Dry mouth.
Neurological	-	Numbness, Tingling,Trembling/Shaking
Temperature regulation	-	Sweating, Hot flashes,Chills, Cold, clammy hands
Vestibular system	-	Dizziness, Lightheadedness, Faintness, Feeling unsteady
Sleep related problem	-	Insomnia, Reluctance/Refusal to sleep alone, Nightmares, Talks/Walks in sleep, Excessive tiredness
Other	-	Exaggerated startle response,  Muscle tension

 

The behavioural component of anxiety refers to the action that individuals take to prevent exposure to feared stimuli or to reduce anxiety associated with exposure to the feared stimuli. Among the most common behavioural symptoms associated with the anxiety disorders is avoidance, in which individuals avoid specific stimuli (e.g., bridges) or situations (e.g., public speaking) to prevent anticipated harm. Avoidance often leads to impairment in maintaining normal routines or in family, academic and/or social domains of functioning.Another behavioural symptom associated primarily with obsessive–compulsive disorder (OCD) is the engagement of rituals (e.g., hand washing) that serve to reduce anxiety. These rituals are either excessive or unrealistic strategies for preventing the feared situation from occurring ¹³⁰.

3.2.6 Treatment ¹³¹: 

Antianxiety drugs include the benzodiazepines and the nonbenzodiazepines.  Benzodiazepines:  

1. Alprazolam.
2. Chlordiazepoxide.
3. Clorazepate.
4. Diazepam.
5.  Lorazepam.
6. Oxazepam
7. Flurazepam

 All benzodiazepines are classified as Schedule IV in the Controlled Substances

Act by the Drug Enforcement Agency (DEA) regulations.

Nonbenzodiazepines:

1. Zolpidem
2. Zolpiclone
3. Zoleplon

Atypical Anxiolytics:

1. Buspirone
2. Ipsapirone
3. Gepirone

Mechanism of Action:

            Benzodiazepines (once thought to be acting as 'non-specific depressants') act selectively on GABA_A 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 glutamate ⁴.

Uses:

Antianxiety drugs are used in the management of anxiety disorders and short-term treatment of the symptoms of anxiety. Long-term use of these drugs is usually not recommended because prolonged therapy can result in drug dependence and serious withdrawal symptoms. Some of these drugs may have additional uses as sedatives, muscle relaxants, anticonvulsants, and in the treatment of alcohol withdrawal. For example, clorazepate and diazepam are used as anticonvulsants⁴.

 

Adverse reactions:

Transient, mild drowsiness is commonly seen during the first few days of treatment with antianxiety drugs. Discontinuation of therapy because of the undesirable effects of the antianxiety agent is rare. Depending on The severity of anxiety or other circumstances, it may be desirable to allow some degree of sedation to occur during early therapy. Other adverse reactions include lethargy, apathy, fatigue, disorientation, anger, restlessness, constipation, diarrhoea, dry mouth, nausea, visual disturbances, and incontinence. Some adverse Reactions may be seen only when higher dosages are used⁴.

Dependence:

Long-term use of antianxiety drugs may result in physical drug dependence (addiction) and tolerance (increasingly larger dosages required to obtain the desired effect). Withdrawal syndrome has occurred after as little as 4 to 6 weeks of therapy with a benzodiazepine. Withdrawal syndrome is more likely to occur when the benzodiazepine is taken for 3 months or more and is abruptly discontinued. The antianxiety drugs must never be discontinued abruptly because withdrawal symptoms, which can be extremely severe, may occur. The onset of withdrawal symptoms is usually within 1 to 10 days after discontinuing the drug, with the duration of withdrawal symptoms from 5 days to 1 month⁴.

Symptoms of Withdrawal⁴:

Increased anxiety                                            Fatigue

Hypersomnia                                                   Metallic taste

Concentration difficulties                               Fatigue

Headache                                                        Tremors

Numbness in the extremities                           Nausea

Sweating                                                         Muscle tension and cramps

Psychoses                                                        Hallucinations

Memory impairment                                       Convulsions (possible)

Contraindications⁴:

The antianxiety drugs are contraindicated in patients with known hypersensitivity, psychoses, acute narrow-angle glaucoma, and shock. These drugs are also contraindicated in patients in a coma or with acute alcoholic intoxication with depression of vital signs. The benzodiazepines are Pregnancy Category D drugs, and the drug metabolite freely crosses the placenta. Use of these drugs during pregnancy is contraindicated because of the risk of birth defects or neonatal withdrawal syndrome manifested by irritability tremors and respiratory problems. The benzodiazepines are contraindicated during labor because of reports of floppy infant syndrome manifested by sucking difficulties, lethargy, and hypotonia. Lactating women should also avoid the benzodiazepines because of the effect on the infant, who becomes lethargic and loses weight.

Precautions⁴:

Antianxiety drugs are used cautiously in patients with impaired liver or kidney function and in elderly and debilitated patients. The metabolism of the benzodiazepines is slowed in the liver, increasing the risk of benzodiazepine toxicity. Lorazepam and oxazepam are the only benzodiazepines whose elimination is not significantly affected by liver metabolism. Two nonbenzodiazepines are Pregnancy Category B drugs (buspirone and zolpidem); hydroxyzine is a Pregnancy Category C drug. No adequate studies have been performed in pregnant women. These drugs should be used during pregnancy only when clearly needed and when the potential good would outweigh any harm to the fetus.

Interactions⁴

Central nervous system (CNS) depressants such as alcohol, narcotic analgesics, tricyclic antidepressants, and the antipsychotic drugs, increase the sedative effects of the antianxiety drugs. Combination of any of these drugs with the antianxiety drugs is dangerous and can cause serious respiratory depression and profound sedation. Ingestion of alcohol with the antianxiety drugs can cause convulsions and coma. Buspirone causes fewer additives CNS depression than do the other antianxiety drugs. However, it is recommended that concurrent use with a CNS depressant be avoided. Buspirone may increase serum digoxin levels, which increases the risk of digitalis toxicity.

 

PART - III

3.3 The use of animal behavioural models to assess 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 Mc.Kinney, 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 state ¹³².

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 patients.

For in vivo studies, most investigators use a battery of anticonvulsive tests, anti-aggressive tests and evaluation of conditioned behaviour. Most of the actions of benzodiazepines are thought to be mediated by potentiation of g-amino-butyric acid (GABA). Two subtypes of GABA receptors (GABA_A and GABA_B) 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 GABA_A receptors. This implies that the GABA_A receptor is involved in anxiety and that its direct activation would have an anxiolytic effect. Based in these findings various in vitro tests have been developed ¹³³.

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 poor¹³⁴.

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 efficacy¹³⁵. This was the time when unconditioned conflict tests such as the elevated plus maze were developed¹³⁶.

            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, Lister described them as animal 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 behavioural 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 Griebel¹³⁷, 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 behaviour in rodents (e.g., elevated plus maze and the light-dark test), models based on social behaviour 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^{136, 138}. 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 schedules¹³⁹. 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 method¹⁴⁰. 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 avoidance¹⁴¹.

            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 recorded¹⁴².

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 factors¹⁴³.

3. Social interaction test:-

            The social interaction test that was originally introduced by File¹⁴⁴, and that quantifies the level of social behavior between animals, is a valuable behavioral paradigm for testing anxiolytic drugs. Experimental animals unfamiliar to each other are 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^{145, 146}.

5. Defense tests:-

            Defensive behaviors in mammals are thought to constitute a significant parameter that can be studied to understand human emotional disorders, including anxiety¹⁴⁷. These behaviours 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^148,149. Specific situational and behavioural 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 behaviours. 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 behavioural 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^150,151. 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 anxiety¹⁵¹.

            Further examples of models for pathological anxiety are mice that were gene targeted for the corticotrophin-releasing factor (CFR) ¹⁵² or for the γ₂ subunit of the GABA_A receptor. This receptor subunit is known to be essential in mediating the anxiolytic actions of benzodiazepines¹⁵³. An “anxious” phenotype was also observed in mutant mice lacking the gene for the neuroactive peptide NPY¹⁵⁴. 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 factors¹⁵⁵.

          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 system¹⁵⁵. Also in rats, several strains of trait anxiety have been described, e.g., the Maudsley rat¹⁵⁶, the Wistar-Kyoto¹⁵⁷, the Roman¹⁵⁸, or the Sardinian alcohol-preferring line¹⁵⁹. Recently, two breeding lines were generated from the same strain of Wister rats showing a maximum difference in other behaviours as well as in physiological parameters not directly related to anxiety. These two rat lines are now called high anxiety-related behaviour (HAB) and low anxiety-related behaviour (LAB) ¹⁶⁰. Their overall performance in various behaviour tests suggests that selective breeding has resulted in lines not only differing markedly in their innate anxiety-related behaviour 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.