Impairment of an electroconvulsive stimulus on reconsolidation of memories established by conditioning.

The deduced memory consolidation and reconsolidation phases are sensitive to similar amnesic and memory-enhancing treatment. Electroconvulsive stimulus has been well known to impair memory consolidation. Therefore, we hypothesized that electroconvulsive stimulus might disrupt reconsolidation for conditioning-established memories. Delivery of a 200-msec electroconvulsive stimulus (500 V, 25 mA) between mouse pinnas immediately after recall of the cocaine-induced conditioned place preference (CPP) impaired the reconsolidation and subsequent expression of this memory. In contrast, the electroconvulsive stimulus (500 V, 25 mA, lasting for 200 ms) did not affect subsequent cocaine-induced CPP performance when the recall procedure was omitted. Systemic pentobarbital injection immediately after the CPP test did not affect subsequent cocaine-induced CPP. Interestingly, several regimens of electroconvulsive stimulus given immediately after the recall of cocaine-induced CPP did not affect subsequent CPP performance when mice were anesthetized by pentobarbital throughout the ECS regimens. Finally, delivery of the ECS (500 V, 25 mA, lasting for 200 ms) immediately after the reactivation of passive avoidance (PA) and food-induced CPP impaired subsequent performance of these memories in the retest. Taken together, we conclude that a short-lasting electroconvulsive stimulus can deteriorate the reconsolidation of various forms of memory established by conditioning.