Proactive and retroactive effects of repeated electroconvulsive shock on passive avoidance retention in rats.

In spite of technical modifications, the therapeutic administration of electroconvulsive shock (ECS) to humans is still associated with significant memory impairment. Studies aimed at elucidating the neurobiologic basis of this impairment and developing appropriate treatment approaches have been limited by the absence of an appropriate animal model. We report here that ECS administered daily for 1-7 days to male albino rats (ECS X 1-ECS X 7) cumulatively impaired retention of passive avoidance when animals were trained 24 hours after the last ECS and tested 24 hours after training. Retention was directly proportional to the interval between training and testing; animals trained 24 hours after ECS X 7 and tested 1 hour later showed no deficit while animals tested after 24 hours showed maximal impairment. Retention was significantly improved by 10 days following the last of ECS X 7 and intact by 21 days. These findings parallel the effects of ECS on memory function in humans. The retrograde effects of ECS also paralleled those demonstrated in humans; while retention of a passive avoidance task learned 24 hours before ECS X 7 was grossly impaired, retention was intact if learning took place 7 days before the ECS course. The application of these findings as an animal model of ECS-induced memory impairment in humans, is discussed.