Behavioural Studies on BR-16A (Mentat), A Herbal Psychotropic Formulation

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1 [Indian Journal of Experimental Biology (1994): (32), 1, 37] Behavioural Studies on BR-16A (Mentat), A Herbal Psychotropic Formulation Bhattacharya, S.K. Department of Pharmacology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India ABSTRACT The anxiolytic, antidepressant and anti-aggression activities of Mentat were investigated in rats and mice, using standard behavioural paradigms. Single acute administration of Mentat, up to a dose of 200 mg/kg, ip, induced insignificant behavioural effects on the test parameters. However, when Mentat was administered subchronically for 7 days at two dose levels (50 and 100 mg/kg, intragastrically), the drug induced dose-related behavioural effects. Thus, it exhibited anxiolytic effect, as assessed by paradigms like the open-field test and elevated plus-maze tests in mice, and the social interaction test and Vogel s drink conflict test in rats. Furthermore, Mentat attenuated the increase in rat brain tribulin, a putative endocoid marker of anxiety, levels induced by pentylenetetrazole (20 mg/kg sc), a known anxiogenic agent. Mentat attenuated footshock-induced aggressive behaviour in paired rats but failed to affect clonidine-induced automutilative behaviour. The observed aggression-attenuating effect of Mentat may be related to its anxiolytic activity. Mentat exhibited significant antidepressant effect as indicated by its ability to reduce swim stress induced immobility in Porsolt s behavioural despair test, reduction in escape failures concomitant with an increase in avoidance response in the learned helplessness test, and attenuation of muricidal behaviour, in rats. The observed behavioural effects are consonant with the reported clinical utility of Mentat as an adjuvant in the treatment of anxiety and depression. In Ayurveda, compound formulations are generally used in therapy, based on the concept that such combinations provide synergistic therapeutic effect and also include ingredients, which help to minimize likely adverse effects of the major drugs. BR-16A (Mentat) is such a herbal formulation consisting of the following Indian medicinal plants: Brahmi (Hydrocotyl asiatica), Shatavari (Asparagus racemosus), Bach (Acorus calamus), Ashwagandha (Withania somnifera), Giloi (Tinospora cordifolia), Shankhpuspi (Evolvulus alsinoide), Kuth (Saussurea lappa), Amla (Embelica officinalis) and Triphala 1. Preliminary toxicity studies have indicated that this compound formulation is safe even on chronic use 1. Clinical studies have indicated that Mentat is effective in anxiety-neurosis, depression, cognitive deficits, behavioural disturbances in mentally retarded children, hyperkinetic states, nocturnal enuresis and aggressive behaviour 2-4. Experimental studies have shown that Mentat can prevent development of tolerance and dependence to morphine in mice and attenuates alcohol withdrawal induced anxiety and convulsions 5. The present study was designed to investigate the anxiolytic, antidepressant and anti-aggressive effects of Mentat, using well accepted and

2 validated experimental paradigms of anxiety, depression and aggression, so as to provide supportive evidence for the reported clinical observations with the drug. MATERIALS AND METHODS Animals Male Charles Foster rats ( g) and Wistar mice (20-25 g) were used. The animals were group housed in colony cages, unless otherwise mentioned at an ambient temperature of 25 C±1 C and 45-55% relative humidity, with a 12 hr/12 hr light-dark cycle. The animals had free access to standard (Lever) pellet chow and tap water given through drinking bottles. Experiments were conducted between 0900 and 1400 hrs. Drugs Drugs used were BR-16A (Mentat) (The Himalaya Drug Co., India), buspirone (Zoldec Pharmaceuticals, India), haloperidol (Biddle Sawyer, India) and imipramine (SG Pharma, India). Mentat was suspended in distilled water and administered orally through an orogastric tube in a volume of 1 ml/100 g, once daily for 7 days at two dose levels (50 and 100 mg/kg), the last dose being given on day 7 one hour to experimentation. Control animals received equivalent volume of distilled water through the same route for the same time period. The standard drugs, used for qualitative comparison, were dissolved or suspended in distilled water and administered ip, 1 hr before experimentation, in doses mentioned in the tables. Anxiolytic activity The following methods were used to assess anti-anxiety effect of Mentat: Open-field test in mice: The apparatus consisted of a dimly lit green area, 96 x 96 cm, divided in to 16 squares. Naïve drug or vehicle treated mice were placed individually at one corner of the apparatus and observed for a period of 3 min for the number of squares crossed, periods of immobility, number of rearings and fecal pellets 6. Elevated plus-maze test in mice: The plus-maze consisted of two opposite arms, 25 x 5 cm crossed with two closed arms of the same dimensions with 30 cm high walls. The arms were connected with a central square 7.5 x 7.5 cm to give the apparatus in the shape of a plus sign. The whole apparatus was elevated 25 cm above the floor in a dimly illuminated room. Naïve mice, pretreated with drug or vehicle were placed individually in the centre of the maze facing a closed arm, and thereafter the number of entries and time spent on the closed and open arms were recorded during the next 5 min. An arm entry was defined as all four feet in the respective arm 7. Vogel s thirsty rat conflict test: Rats were water deprived for 48 hr. Two hours before testing each rat was placed in a polypropylene cage (25x25x20 cm) and allowed to locate the metallic drinking spout of the water bottle, the whole exercise taking usually less than 2 min. For testing, vehicle or drug treated rats were placed back individually, for a period of 3 min. Electric shock (0.5 ma, 1 sec) was given through the spout on each contact of the snout of

3 the rat with the metallic spout. The total number of such drink contacts was recorded during the 3 min observation period 8. Social interaction test in rats: Rats were housed individually for 5 days prior to experimentation. The social interaction arena was a wooden box (60x60x35 cm) with a solid floor and testing was done under dim illumination. Rats were paired on basis of weight and received two 7.5-min familiarization sessions in the test arena 24 hr before experimentation. During testing, the rat pairs were placed in the test arena for a period of 7.5 min and the total time spent by the pair in active social interaction (sniffing, following, grooming, kicking, boxing, biting, wrestling, crawling under or over partner and mounting) was scored by a neutral observer 9. Rat brain tribulin activity: Pentylenetetrazol (PTZ Sigma, UK) was administered (20 mg/kg. sc) to drug or vehicle treated rats. 30 min later the animals were killed by decapitation and the whole brain was removed for tribulin level estimation in terms of monoamine oxidase (MAO) inhibiting activity 10. Anti-aggression activity The following methods were used to assess the aggression attenuating effect of Mentat: Footshock-induced aggressive behaviour in paired rats: Aggressive behaviour was induced in rat pairs by administering a train of impulses through an electronic stimulator (Techno) to a grid floor for 0.25 sec/sec for 100 sec (100 V, 0.5 msec pulse width 200 pulses/sec). A pair of weight matched rats were placed on the grid floor and allowed one min period of adaptation after covering them with an inverted glass bell jar (300 x 140 mm). Thereafter, the train of impulses as indicated earlier, was administered. Aggressive behaviour was scored by using three paradigms: latency to fight, total period of physical contact and cumulative aggression scores (jumps + rearing x 2 + fighting bouts x 3) 11. Clonidine-induced automutilative behaviour in mice: Mice were food, but not water, deprived for 24 hr before experimentation. Clonidine (Unichem, India) was administered (100 mg/kg i.p.) and mice were observed in pairs in small round wire mesh cage for 15 min. for signs of overt aggressive behaviour characterised by fighting and biting. The mice which proved aggressive were then removed, placed on a smooth surface table and covered individually with a glass beaker of 15 cm diameter. The animals were then observed for the next 30 min for self-mutilative behaviour characterised by self-biting of the digits of the fore-limbs, preceded and interspersed by stereotyped behaviour, including abnormal grooming preeening and persistent licking or biting of the glass surface of the beaker. The percentage of mice exhibiting at least one episode of self-biting, with evidence of bleeding, during the 30 min observation period was determined 12. Antidepressant activity The following methods were used to evaluate the anti-depressant activity of Mentat.

4 Swim stress induced behaviour despair in rats. Rats were made to swim individually in a polypropylene vessel (45x40x30 cm) with a water level of 20 cm at 30 ±2 C. This ensured that the rat s feet did not touch the floor of the vessel and that id did not escape from the vessel. The rat was initially allowed to swim for 10 min and, thereafter, the total periods of immobility characterized by complete cessation of swimming with the head just floating above water level, was determined during the subsequent 5 minute period. This immobility period, after initial frenzied attempts to escape is postulated to represent behavioural despair, where it is assumed that the animal has given up hope of escaping from the confines of the vessel 13. Learned helplessness test in rats: Rats were subjected to footshock (60 scrambled shocks, 15 sec duration 0.8 ma, every min) in a two compartment jumping box (Techno) with the escape door to the unelectrified chamber closed. Control vehicle treated animals were kept in the chamber but received no shock. The exercise was continued for 1 hr. 48 hr later, on day 3 after this inescapable shock treatment, the rats were subjected to avoidance training, using the same apparatus but keeping the escape route to the unelectrified chamber open. During this avoidance training, the rat was placed in the electrified chamber and allowed to acclimatise for 5 minutes before being subjected to 30 avoidance trials, with an inter-trial interval of 30 secs. During the first 3 sec of the trial a buzzer stimulus (conditional stimulus) was presented, followed by electric shock (conditioned stimulus) through the grid floor (0.8mA) for the next 3 sec. The avoidance response characterised by escape to adjoining safe chamber, following the buzzer, within sec during the test session was noted, and the failure to escape was assessed as escape failure. Escape failure in rats exposed to inescapable shock is postulated to represent depressive behaviour 14. Muricidal behaviour: Muricadal, or mouse killing behaviour, is characterised by compulsive killing by rats of mice introduced in the former s cage within 30 sec, irrespective of the satiety status of the killer rat. Rats are prescreened for muricidal activity by introducing a mouse in the rat cage. Approximately 25 to 30% Charles Foster rats exhibit compulsive mouse killing behaviour, the muricidal interval being reduced following repeated exposure to mice. The percentage of prescreened rats exhibiting muricidal behaviour with 30 sec of introduction of a mouse into a rat cage following vehicle or drug administration was noted 15. Statistical analysis For quantitative data statistical analysis was initially performed by using a one way analysis of variance (ANOVA), followed by a two-tailed Student s t-test for comparison between vehicle and drug treated groups. The chi-square test was used for quantal data. A 0.05 level of probability was accepted as statistically significant. The type of statistical analysis used has been mentioned in the respective tables. RESULTS Acute single administration (200 mg/kg i.p.) of Mentat did not induce any discernible effect on any of the test paradigms used when investigations were carried out 1 hr after drug

5 administration (data not shown). Preliminary studies indicated that, following oral administration, the behavioural effects of Mentat could be affected by 7 days at dose levels of 50 and 100 mg/kg. Anxiolytic activity Open-field test in mice: Mentat induced significant dose-related anxiolytic effect in this paradigm, which was qualitatively similar to that induced by single acute administration of buspirone (2.5 mg/kg, ip). Thus, both drugs induced an increase in the number of squares crossed, reduced the period of immobility, increased rearing episodes and reduced the number of fecal pellets (Table 1). Table 1: Effects of Mentat and buspirone on open-field paradigms in mice (Values are mean ± SE) Treatment (mg/kg) n Squares crossed (number) Immobility (sec) Rearing (number) Fecal pellets Vehicle ± ± ± ± 1.8 Mentat (50) ± ± 5.2 a 36.8 ± ± 1.6 a Mentat (100) ± 12.6 a 16.9 ± 6.8 b 59.2 ± 7.4 b 4.4 ± 0.9 b Buspirone (2.5) ± 10.6 b 16.2 ± 3.8 c 53.8 ± 8.2 b 2.9 ± 0.4 c p values: a <0.05; b <0.01; c <0.001; in comparison to vehicle-treated control group. Values without superscripts are statistically non-significant. Elevated plus-maze test in mice: Mentat, administered for 7 days, induced dose-related anxiolytic activity in this paradigm which was comparable qualitatively to that induced by acute single administration of buspirone (2.5 mg/kg ip). Thus, both the drugs induced significant increase in the number of entries and time spent in the open arms of the maze with concomitant decrease in the number of entries and time spent in the open arms of the maze with concomitant decrease in the number of entries and time spent by the mice in the closed arms (Table 2). Table 2: Effects of Mentat and buspirone on the elevated plus-maze test in mice (Values are mean ± SE) Treatment (mg/kg) n Number of entries Time spent (sec) Open arms Closed arms Open arms Closed arms Vehicle ± ± ± ± 15.9 Mentat (50) ± 1.5 b 9.4 ± 0.8 b 63.9 ± 8.2 a ± 14.0 a Mentat (100) ± 1.3 c 5.9 ± 0.8 c 83.7 ± 13.8 b ± 13.2 b Buspirone (2.5) ± 1.0 c 7.8 ± 0.9 c 78.4 ±9.8 b ± 10.4 b p values: a <0.05; b <0.01; c <0.001; in comparison to vehicle-treated control group. Vogel s drink-conflict test: Mentat (100 mg/kg) and buspirone (2.5 mg/kg, ip), the former being administered orally for 7 days, exhibited statistically significant anti-conflict behaviour, as evidenced by the increase in the number of drink contacts during the 3 min observation period. The effect of the lower dose of Mentat was, however, statistically insignificant (Table 3).

6 Social interaction test: Mentat (50 and 100 mg/kg, po), administered for 7 days, and buspirone (2.5 mg/kg ip), significantly increased the time spent in social interaction during the 7.5 min period of observation in 5-day isolated and then paired rats (Table 4). Table 3: Effects of Mentat and buspirone on Vogel s drink-conflict test in water deprived rats (Values are mean ± SE) Treatment (mg/kg) n Drink contacts (number) Vehicle ± 1.2 Mentat (50) ± 1.6 NS Mentat (100) ± 1.9 <0.01 Buspirone (2.5) ± 0.8 <0.001 p Table 4: Effects of Mentat and buspirone on social interaction test in paired rats (Values are mean ± SE) Treatment (mg/kg) n Time spent in social interaction (sec) Vehicle ± 7.6 Mentat (50) ± 7.6 <0.05 Mentat (100) ±7.8 <0.001 Buspirone (2.5) ± 8.2 <0.01 p Rat brain tribulin activity: Mentat (50 and 100 mg/kg po) administered for 7 days, and buspirone (2.5 mg/kg ip) had insignificant per se effects on rat brain tribulin activity and this increase was significantly attenuated dose-dependently by Mentat (50 and 100 mg/kg po) administered for 7 days and by buspirone (2.5 mg/kg ip), the drug effects being qualitatively similar (Table 5). Table 5: Effects of Mentat and buspirone on pentylenetetrazole (20 mg/kg, sc) (PTZ) induced increase in rat brain tribulin activity (Values are mean ± SE) Treatment (mg/kg) n Brain weight (g) MAO inhibition (%) Vehicle ± ± 1.6 Mentat (50) ± ± 1.2 Mentat (100) ± ± 1.8 Buspirone (2.5) ± ± 0.9 PTZ ± ± 1.9* Mentat (50) + PTZ ± ± 1.8 a Mentat (100) + PTZ ± ± 1.6 c Buspirone (2.5) ± ± 1.2c p values: * <0.001 in comparison to vehicle-treated control group; a <0.05; c <0.001 in comparison to PTZ group. Anti-aggression activity Footshock induced aggressive behaviour: Mentat (50 and 100 mg/kg po) administered for 7 days and haloperidol (0.5 mg/kg ip) induced qualitatively similar aggression-attenuating effects, characterised by an increase in latency to fight with concomitant decreases in total contact period and cumulative scores in comparison to vehicle treated controls, in foot shocked paired rats (Table 6).

7 Clonidine-induced automutilative behaviour: Both the doses of Mentat used had insignificant effects on clonidine-induced automutilation, though haloperidol (0.5 mg/kg ip) significantly reduced the incidence of automutilation (Table 7). Table 6: Effects of Mentat and haloperidol on footshock induced aggression in paired rats [(+) and ( ) signs indicate percent increase or decrease, respectively, of values from vehicle-treated control data ± SE] Treatment (mg/kg) n Latency Total contact period Cumulative score Mentat (50) 10 (+) 38.2 ± 2.6 a ( ) 44.8 ± 2.9 a ( ) 41.6 ± 3.0 a Mentat (100) 10 (+) 64.1 ± 4.2 b ( ) 76.4 ± 6.2 b ( ) 61.2 ± 4.8 b Haloperidol (0.5) 8 (+) 82.8 ± 3.6 c ( ) 89.4 ± 2.8 c ( ) 87.6 ± 3.9 c p values: a <0.05; b <0.01; c <0.001; in comparison to vehicle-treated group. Table 7: Effects of Mentat and haloperidol on clonidine-induced automutilation in mice Treatment (mg/kg) n Incidence of automutilation (%) p (x 2 test) Vehicle Mentat (50) NS Mentat (100) NS Haloperidol (0.5) <0.05 Antidepressant activity Swim-stress induced behavioural despair: Mentat (50 and 100 mg/kg po) administered for 7 days, induced a dose-related decrease in the total period of immobility in this paradigm, which was qualitatively comparable to that induced by imipramine (10 mg/kg ip) administered 60 min prior to experimentation (Table 8). Table 8: Effects of Mentat and imipramine on swim-stress induced immobility in rats (Values are mean ± SE) Treatment (mg/kg) n Duration of immobility (sec) p Vehicle ± 7.6 Mentat (50) ± 6.0 <0.05 Mentat (100) ± 4.1 <0.001 Imipramine (10) ± 3.6 <0.001 Learned helplessness test: Mentat (50 and 100 mg/kg po) administered for 7 days, and imipramine (10 mg/kg po) produced qualitatively similar effects in this paradigm namely reduction in the number of escape failures concomitant with an increase in avoidance responses, indicative of antidepressant activity (Table 9).

8 Table 9: Effects of Mentat and imipramine on the learned helplessness test in rats (Values are mean ± SE) Treatment (mg/kg) n Escape failures (number) Avoidance response (number) Escapable shocks Vehicle ± ± 1.2 Vehicle ± 1.8* 0.8 ± 0.2* Inescapable shocks Mentat (50) ± 1.6 a 2.4 ± 0.6 b Mentat (100) ± 1.2 c 4.8 ± 1.2 c Imipramine (10) ± 1.6 c 4.4 ± 1.6 c p values: *<0.001 in comparison to escapable shock vehicle treated group; while a <0.05; c <0.01 in comparison to inescapable shock vehicle treated group. Muricidal behaviour: Mentat (100 mg/kg, po), but not the dose of 50 mg/kg, administered for 7 days, and imipramine (10 mg/kg, ip), significantly reduced the incidence of muricide in killer rats (Table 10). Table 10: Effects of Mentat and imipramine on muricidal behaviour in killer rats Treatment (mg/kg) n Muricide (%) p (x 2 test) Vehicle Mentat (50) NS Mentat (100) 8 25 <0.01 Imipramine (10) 8 50 <0.05 DISCUSSION The use of animal models of human mental disorders, despite their obvious limitations have proved to be of value in the pre-clinical behavioural analysis of putative psychotropic agents or for experimental validification of such psychopharmacological agents already in clinical use. The validity of these animal models of clinical psychiatric illness has often been questioned and the problem has been further confounded by the rigid set of criteria proposed by McKinney and Bunney 16 which states that the animal model should correspond to the psychiatric disorder in terms of aetiology, biochemistry, symptomatology and treatment. However, these criteria for validating animal models have been shown to be impractical and often unsuitable since the aetiology and neurochemical basis of mental disease remain subjects of intense speculation and research, with equivocal results 17. Though there is little question that animal models of psychiatric disorders suffer from a lack of understanding of the basic disease process being modelled, they should be of predictive validity wherein the model should be able to correctly identify a particular class of psychotropic agents without making errors of omission or commissions 17. The animal models used in this investigation have been shown to meet this criteria, following extensive use in experimental psychopharmacology. Mentat, a herbal formulation has been shown to be clinically effective in a variety of neuropsychiatric disorders including anxiety-neurosis, depression and aggressive behaviour 2-4. Single acute administration of the drug, even in a fairly large dose, failed to induce any significant behavioural effect. This observation is consonant with earlier reports

9 emanating from this laboratory and elsewhere 6,18,19 that herbal psychotropic agents are behaviourally effective after subacute but not acute administration. Clinical reports with Mentat also indicate that the drug is effective only after sub-chronic administration 2-4. Mentat induced significant anxiolytic activity, comparable to that of the non-benzodiazepine anti-anxiety agent buspirone 20, in all the animal models of anxiety used in this study. The open-field test is considered as an indicator of the emotional state of the test animal 6. Animals removed form their acclimatized home cage and placed in a novel environment express their anxiety and fear by showing decreases in ambulation and exploration, immobilization or freezing reduction in normal rearing and grooming behaviour and increased micturtion and defecation due to augmented autonomic activity. These paradigms are attenuated by classical anxiolytics and potentiated by anxiogenic agents 6,21. Likewise, the elevated plus maze test is based on the principle that exposure to an elevated and open arm maze leads to an approach conflict that is considerably stronger than that evoked by exposure to an enclosed maze arm. Thus, the total entries and time spent on the open arms, as a percentage of total entries and time spent in both open and closed arms, provides a measure of anxiety or fear induced inhibition of normal exploratory activity. This value is increased by anxiolytics and reduced by anxiogenic agents 7. This model has been effectively used to evaluate both anxiogenic and anxiolytic agents under identical experimental situations 18,21. The inhibition of water intake by mild electric shock in water-deprived rats is regarded as a paradigm to assess conflict behaviour 8. The anti-conflict effect of anxiolytics has been proposed to be due to specific inhibition of fear motivation 8 though other factors, including a facilitatory effect on water intake or reduced sensitivity to pain cannot be entirely ruled out 22. However, anxiogenic agents have been shown to potentiate the conflict behaviour 23 thus proving the predictive validity of the method. Similarly, the social interaction test has been extensively validated as an animal model of anxiety 9. The time spent in social interaction in previously isolated rat pairs is increased by anxiolytics 9,18 and decreased by anxiogenic agents The test can distinguish between sedatives and anxiolytics, and is not sensitive to the action of other cases of psychotropic agents 9. Tribulin, an endogenous MAO inhibitor has been proposed to function as an edocoid marker of anxiety based on extensive experimental and clinical evidence 24. Rat brain tribulin levels have been shown to be increased by axiogenic agents including PTZ and this increase can be attenuated by anxiolytics 18,23,25. Clinical studies have also shown that the increase in urinary tribulin levels in anxiety situations can be attenuated by anxiolytic agents 26. The reduction in rat brain tribulin levels following augmentation by PTZ, by Mentat provides confirmatory neurochemical evidence for its observed anxiolytic activity following sub-acute administration. The qualitatively comparable effects induced by buspirone in all the test paradigms not only validate the experimental methods used but also confirms the anxiolytic activity of Mentat.

10 Subchronic administration of Mentat was effective in reducing aggressive behaviour induced by footshock but proved ineffective in the more severe form of aggression, namely selfmutilation induced by clonidine in mice. However, haloperidol the neuroleptic agent extensively used in different types of aggression and frequently used, as a standard antiaggression agent in experimental situations 27, proved effective in both the parameters of aggression used in the study. It is likely that the observed effect of Mentat is due to its anxiolytic activity, since though benzodiasepines reduce footshock induced fighting behaviour at doses which do not induce significant motor deficits 27, they do not affect selfinjurious behaviour induced by clonidine or other agents 12. It is now evident that different types of aggressive behaviour exist, namely offensive and defensive behaviour. Defensive behaviour is essential for coping with a wide variety of challenging situations, whereas intensive and inappropriate offensive aggression may require therapy 28. Unfortunately, the available anti-aggression agents, including haloperidol, suppress both forms of aggressive behaviour 27. A new class of psychotropic agents, the serenics have been found to suppress offensive behaviour. A new class of psychotropic agents, the serenics have been found to suppress offensive behaviour selectively without significantly affecting defensive aggression. The differential beneficial of Mentat against the two different forms of experimental aggression used in this study necessitates further evaluation as a putative serenic agent 28. Until recently, there were relatively few behavioural models for investigating putative antidepressant activity, most of the tests being used involving pharmacological interactions between existing antidepressants and other drugs, which were of little psychological relevance 29. The recognition that endogenous depression may have environmental precipitants, led to the postulate that stress may be a factor in genesis of depression 29. Swimstress induced behavioural despair and learned helplessness following exposure to uncontrollable stress are paradigms, which have been evolved from this concept. Both the tests have been subjected to extensive investigations and shown to have excellent predictive validity while screening putative antidepressants of a wide variety of chemical classes 29. Mentat was found to have significant antidepressant effect following subchronic administration, which was qualitatively comparable to that induced by the standard tricyclic antidepressant imipramine. Unlike these two paradigms, the third method used, namely muricidal behaviour, has been less extensively used or pilocarpine-induced muricide has been utilised instead of spontaneous mouse-killing behaviour 29. However, this model also exhibits good predictive validity and a large number of classical antidepressants were shown to attenuated muricide at does much lower than that inducing motor deficits 29. The efficacy of Mentat in reducing mouse-killing behaviour confirms its putative antidepressant activity. The present study, thus, corroborates some of the clinical reports indicating that Mentat may be effective in therapy of anxiety, depression and aggression, particularly as an adjunct with main therapeutic measures. It would be premature to hazard a cogent explanation, in terms of neurochemical effects for the observed behavioural effects of Mentat given the wide variety of neurotransmitters said to be involved in anxiety, depression and aggressive behaviour 17,27,29.

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