ACUTE ADMINISTRATION OF ANGIOTENSIN-II IMPROVES LONG-TERM HABITUATIONIN THE CRAB CHASMAGNATHUS

A shadow moving overhead acts as a danger stimulus and elicits an esca pe response in the crab Chasmagnathus granulatus that habituates after 15 trials and for a long period. A shorter training of ten trials fai ls to induce long-term habituation; however, a good retention of the h abituated response is manifest after a 24-h interval when angiotensin II (AII) (10(-6) M, 3 ng/g) is injected post-training. By contrast, no amnestic effect of AII was found even though high doses were administ ered. The facilitatory effect of AII is suppressed by saralasin (10(-7 ) M, 0.3 ng/g), a specific angiotensin II receptor antagonist. Results are considered as suggesting that angiotensin on memory processes mig ht have emerged early in evolution.