CYCLOHEXIMIDE INHIBITS CONTEXT MEMORY AND LONG-TERM HABITUATION IN THE CRAB CHASMAGNATHUS

A shadow moving over head elicits an escape response in the crab Chasm agnathus that habituates promptly and for a long period. The effect of the protein synthesis inhibitor cycloheximide (CY) on this long-term memory was analyzed. Two hours after injection, 10 mu g CY inhibited [ C-14]-amino acid incorporation into cerebral plus thoracic ganglia by 88% and 20 mu g by 92%, but no inhibition was found at 24 h. A single injection of 10-20 mu g CY given 30 min before training, failed to aff ect the short-term habituation. Similar doses impaired both context me mory (CM) and long-term habituation (LTH) when tested at 72 and 120 h but only CM at 24 h. Such a disparity was explained by an unspecific d epressing effect upon the response, attributed to an interaction betwe en CY and training. The hypothesis was confirmed, because CY injected immediately after training disclosed amnestic effect at 24 h on both C M and LTH. A similar effect was proven when animals were injected at 2 h but not at 6 h after training. Results from experiments with pretra ining and pretesting injections put aside a state-dependence or retrie val deficit effects of the drug. Taken together, findings of this arti cle argue strongly for de novo protein synthesis as a mechanism of LTH and for the close relation between CM and LTH.