HIPPOCAMPAL CGMP AND CAMP ARE DIFFERENTIALLY INVOLVED IN MEMORY PROCESSING OF INHIBITORY AVOIDANCE-LEARNING

CYCLIC GMP (cGMP) and cyclic AMP (cAMP) have been proposed to particip ate in the early and late stages of long-term potentiation (LTP), resp ectively. Here we report on the effect of post-training intrahippocamp al infusion of membrane-permeable analogues of these cyclic nucleotide s on the consolidation of inhibitory avoidance learning in rats and on the effect of this task on hippocampal cGMP and cAMP levels. Bilatera l intrahippocampal microinjection of 8 Br-cGMP (1.25 mu g per side) en hanced retention test performance when given immediately (0 min), but not when given 180 min, after training. In marked contrast, intrahippo campal infusion of the same dose of 8 Br-cAMP facilitated memory conso lidation when given 180 min, but not 0 min, after training. Rats submi tted to an inhibitory avoidance task showed a significant increase in the amount of cGMP in the hippocampus at 0 and 30 min after training, and in the amount of cAMP 30 and 180 min after training. Taken togethe r, these results indicate that cGMP-regulated processes in the hippoca mpus play an important role in the early stages of memory consolidatio n and that cAMP signalling pathways are involved in the late post-trai ning memory processing of inhibitory avoidance learning.