ACUTE ADMINISTRATION OF A PERMEANT ANALOG OF CAMP AND A PHOSPHODIESTERASE INHIBITOR IMPROVE LONG-TERM HABITUATION IN THE CRAB CHASMAGNATHUS

A shadow passing overhead acts as a danger stimulus and elicits an esc ape response in the crab Chasmagnathus that habituates promptly and fo r a long period. Robust retention is shown at 24 h after 15 trials of shadow presentation or at 120 h after 30 trials, but no significant re tention is disclosed at 24 h after 5 trials or at 72 h after 15. A coc ktail of the cAMP membrane permeable analog 8-(4-chlorophenylthio)-cAM P (CPT-cAMP), plus the phosphodiesterase inhibitor isobutyl methylxant hine (IBMX), was given by systemic administration. Pretraining injecti on of the cocktail (25 or 50 mu M, 15 min before a 5-trial session) fa iled to affect short-term habituation, but induced significant retenti on when tested at 24 h. This facilitatory effect was not shown when a lower dose (5 mu M) was used. A post-training injection of 25 mu M, im mediately after a 5- or 15-trial session, induced retention when teste d at 24 or 72 h, respectively. Thus, the administration of CPT-cAMP+IB MX during acquisition of a habituated response or immediately after, i mproves long-term habituation, a result supporting the view that an in crease in the cAMP level is one of the steps in long-term memory conso lidation.