[The neuronal correlates of the serotonin-dependent behavior of the pteropod mollusk Clione limacina].

Predatory behaviour of the carnivorous marine pteropod mollusk Clione limacina is normally induced by contact with prey. In the absence of prey, a similar behaviour can be induced by injection of serotonin (5-HT) or its precursor, L-5-hydroxytroptophan (5-HTP). It consists of non-stop fast swimming, rapid extrusions of cephaloconi and other components of the actual prey capturing. Neuronal correlates of this phenomenon were investigated using histofluorescence and intracellular recordings. Prior to treatment with 5-HTP only green fluorescence of catecholamines has been revealed. In the CNS and periphery of 5-HTP-injected hunting animals yellow fluorescence of 5-HT is present as well. In isolated pedal ganglia 5-HTP induces characteristic changes in the activity of the swim generator neurones. An initial intermittent fictitious swimming of these neurones has been changed to sustained swimming of a higher frequency and enhanced spiking per cycle. Changes in activity of 5-HT-producing pedal neurones are also described.