COMPLEX AVOIDANCE-BEHAVIOR AND ITS NEUROCHEMICAL REGULATION IN THE LAND SNAIL CEPAEA-NEMORALIS

1. In hot plate experiments, the pulmonate land snail Cepaea nemoralis displays a biphasic passive/active avoidance behaviour composed of re traction and subsequent searching mediated by antagonistic muscular sy stems. The switch, between the behaviours, is under neuronal control. 2. Leu- and met-enkephalin, as well as FMRFamide-antiserum, attenuated the retraction response and potentiated the searching behaviour. Oppo site effects were achieved by injection of antisera to the enkephalins . 3. Both retraction and searching behaviours were potentiated by 5-HT . Methysergide antagonized the effects of the enkephalins on the searc hing behaviour. 4. We conclude that endogenous opioids act antagonisti c to FMRFamide in the neuronally controlled switch between passive and active avoidance behaviour.