Neuronal correlates of 5-hydroxytryptophan-induced sustained swimming in Aplysia fasciata

Abstract

1. 1. Bathing the isolated CNS of A. fasciata in a 5-hydroxytryptophan (5HTP)-containing saline (50–120 μg/ml) induces sustained patterned rhythmic bursts in initially non-bursting neurones of the pedal ganglia. 2. 2. The neurones have been found within a specific area reportedly occupied by motor cells which supply locomotor muscles. 3. 3. The latency of the effect is 20–45 min and corresponds to that of actual swimming in whole animals injected with 5HTP. 4. 4. The frequency of bursts corresponds to that of cyclic swim movements. 5. 5. The rhythm is intrinsic to an, as yet unidentified, source of excitatory input. 6. 6. It is concluded from this evidence that metabolization of 5HTP results in release of a central program for locomotion, the fictitious swimming. 7. 7. Other 5HTP-induced changes include a considerable enhancement in firing of serotonin-containing neurones of the pedal ganglia. 8. 8. The 5HTP-treated isolated CNS is suggested to provide a favourable preparation to reveal the neuronal mechanisms of locomotor program generation in Aplysia.