Depressant Effect of Trimyristin and Its Inhibition by Some Antidepressants in Mice

The depressant activity of trimyristin and its interaction with antidepressants like amitryptiline, imipramine, mianserin, and fluoxetine has been studied. In forced swim tests and tail suspension tests male albino mice were treated intraperitoneally with 10 mg/kg each of amitryptiline, imipramine, mianserin, and fluoxetine 30 min before vehicle or trimyristin (10 or 30 mg/kg i.p.). Some groups received trimyristin (10 or 30 mg/kg i.p.). In reserpine-induced hypothermia, the effect of trimyristin was observed on hypothermia induced by reserpine. In forced swim tests and tail suspension test, trimyristin increased the duration of immobility and pretreatment with antidepressants inhibited the effect of trimyristin. Trimyristin significantly lowered the rectal temperature and potentiated the reserpine-induced hypothermia. In the forced swim tests, the depressant effect of trimyristin was inhibited by prior administration of serotonin 5-HT2A receptor antagonist, saprogrelate suggesting involvement of serotonergic and noradrenergic mechanisms in the depressant action of trimyristin. INTRODUCTION Myristica fragrans Houtt (Myristicaceae), commonly known as nutmeg, is now cultivated in many tropical countries. A ligroin extract of M. fragrans caused significant increase in duration of sleep in chickens (Sherry et al., 1982). The hexane extract of nutmeg significantly inhibited drug metabolizing enzyme activity and showed prolongation of hexobarbital-induced sleep (Shin et al., 1988). Truitt et al. (1988) reported hallucinogenic activity of nutmeg. The ethanolic extract of M. fragrans demonstrated significant hypolipidemic effects and lowered the high-density lipoprotein and low-density lipoprotein ratio in rabbits. It also lowered the level of total cholesterol in the heart and liver (Sharma et al., 1995; Ram et al., 1966). The volatile oil of nutmeg was found to be effective as antioxidant (Kumarvelu et al., 1996). In addition to these properties, nutmeg is reported to be possess stimulant, narcotic, carminative, astringent, aphrodisiac (Nadkarni, 1998), anti-thrombotic and anti-platelet aggregation (Olajide et al., 1999), antibacterial, antifungal (Orabi et al., 1991), anti-dysenteric (Gills, 1994), antiinflammatory and analgesic activities (Ozaki et al., 1989; Olajide et al., 1999). Previous studies from our laboratory have shown sedative, analgesic, anticonvulsant, and anxiogenic actions of nutmeg. Trimyristin has been shown to be responsible for the anxiogenic activity (Sonavane et al., 2001, 2002 a,b). Since anxiety is often associated with depression (Nutt, 1999) and nutmeg increases hexobarbital-induced sleep, we studied the effect of trimyristin on reserpine-induced hypothermia in rats and behavioral despair induced by forced swimming and tail suspension in mice to study the possibility of developing depression with trimyristin. Several antidepressants, having different modes of action, were used in the present study to elucidate the probable mode of action. Since the serotonin 5-HT2 receptor blocker has been tried in the care of depressed patients with anxiety symptoms (Fuller, 1991; Nutt, 1999), we have also studied the effect of selective 5-HT2 antagonist, saprogrelate on trimyristin induced depression. Proc. WOCMAP III, Vol. 1: Bioprospecting & Ethnopharmacology Eds. J. Bernáth, É. Németh, L.E. Craker and Z.E.Gardner Acta Hort 675, ISHS 2005 148 MATERIALS AND METHODS Animals Albino mice (Swiss, 20-25g of either sex) were housed in groups of 6-8 per cage at the ambient temperature of 25±1°C and relative humidity of 50±5%. A 12:12h light: dark cycle was followed during the experiments. The animals had free access to animal chow (Lipton, India) and water however, food was withheld overnight before the experiments. The experiments were performed between 10:00 and 15:00h. The Institutional Animal Ethical Committee approved the protocol. Drugs Imipramine, amitryptiline, and mianserin were gifts from Torrent Pharmaceuticals (Ahmedabad). Cadila Laboratories (Ahmedabad), supplied the fluoxetine. Saprogrelate was a gift of Dr. R.K. Goyal, L.M. College of Pharmacy (Ahmedabad). The solvents used in the study were purchased from Modern Scientific Co. (Nashik). Trimyristin (TM) was isolated from the petroleum ether extract of Myristica fragrans seeds as described earlier by Sonavane et al. (2001). Trimyristin was dissolved in polyethylene glycol 400 for administration. The volume of injection was 0.1 ml per animal. Effect on Reserpine-induced Hypothermia Rats were divided into four groups of five each. Reserpine (3 mg/kg i.p.) was administered 30 min after vehicle or trimyristin (10 mg/kg i.p. each). In another set of experiments, one group received trimyristin alone and in the other group amitryptiline (10 mg/kg i.p.) was administered 30 min before trimyristin. The rectal temperature was measured using a telethermometer as described earlier by Turner (1972). The rectal temperature was recorded at 0, 30, 60, 90, 120, 150 and 180 min after reserpine or trimyristin. Forced Swim Test Mice were placed in a glass cylinder (40 x 18 cm) containing 10 cm water, maintained at 25°C. After 10 min the mice were removed and dried. The next day, the mice were treated intraperitoneally with imipramine, amitryptiline, fluoxetine and mianserin (10 mg/kg each) or saprogrelate (2 mg/kg) 30 min before TM (10 and 30 mg/kg) or vehicle. Thirty min after administration of TM administration animals were gently put in water and the total duration of immobility was measured during 5 min test period, after discarding first 2 min since animals exhibited vigorous attempts to escape (Porsolt et al., 1977). Tail Suspension Test The tail suspension test was carried out as described earlier by Steru et al. (1985). The drugs were administered as described in the forced swimming test. The duration of immobility was measured during the test period of 8 min. Statistical Analysis All data were presented as mean ± SEM. The Kruskal Wallis test was used for reserpine-induced hypothermia. The data obtained from other tests was analyzed by one way ANOVA followed by Dunnett’s test. P < 0.05 was considered significant.