STUDY OF THE EFFECT OF MELATONIN ON RETENTION OF CONDITIONED AVOIDANCE RESPONSE AND ON ENHANCEMENT OF SEROTONIN MEDIATED BEHAVIOURAL RESPONSES AFTER ELECTROCONVULSIVE SHOCK (ECS) ADMINISTRATION IN RATS

Objectives: To obtain the data regarding the effects of melatonin on retention of conditioned avoidance response (CAR) and on enhancement of serotonin mediated behavioural responses after electroconvulsive shock (ECS) administration in rats. Methods: Forty rats after training for conditioned avoidance response by using Cook’s pole climbing apparatus were divided in four groups with ten rats in each group and treatment duration was kept for ten days in all the groups. 1) Control group- distilled water (2ml daily) 2) ECS pretreated group- single ECS daily (150 V, 50 Hz sinusoidal with intensity of 210 mA for 0.5 s through crocodile clip ear electrodes)  3) Melatonin group- melatonin suspension (10 mg/kg/day, p.o.) daily 4) Test group- Single ECS daily + melatonin suspension one hour after ECS (10mg/kg/day, p.o.).Then percentage of retention of conditioned avoidance response and number of lithium induced head twitches were calculated in each group on day 11. Data was analysed by chi square and student unpaired t test. Results: Findings show that administration of single ECS daily for consecutive 10 days results in enhancement of 5-HT-mediated behaviour (lithium-induced head twitches) and also led to disruption of the retention of CAR. Melatonin administration significantly increased the retention of conditioned avoidance response compared to control & ECS group. Also melatonin significantly prevented ECS induced attenuation of the retention of conditioned avoidance response. On the other hand, melatonin significantly retarded the ECS-induced enhancement of 5-HT-mediated behaviour. Conclusion: Melatonin by attenuation of enhancement of 5-HT mediated activity may be responsible for attenuation of disruptive effect on retention of conditioned avoidance behaviour by ECS.