Acute administration of angiotensin II improves long-term habituation in the crab Chasmagnathus

A shadow moving overhead acts as a danger stimulus and elicits an escape response in the crab Chasmagnathus granulatus that habituates after 15 trials and for a long period. A shorter training of ten trials fails to induce long-term habituation; however, a good retention of the habituated 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 administered. 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 might have emerged early in evolution.