SEROTONERGIC MODULATION OF SWIMMING SPEED IN THE PTEROPOD MOLLUSK CLIONE-LIMACINA .1. SEROTONIN IMMUNOREACTIVITY IN THE CENTRAL-NERVOUS-SYSTEM AND WINGS

Serotonin-immunoreactive ve somata in the pteropod mollusc Clione lima cina were restricted to the cerebral and pedal ganglia. 10-14 pairs of cells were consistently found in the cerebral ganglia, including one large pair that had soma positions and axon branching patterns reminis cent of those of the metacerebral cells of other molluscs. Two cluster s of somata were found on the midline near the cerebral commissure, on e on the anterio-lateral margin and one posterio-laterally, A distinct paired cluster of up to nine somata was found on the dorso-lateral ma rgin of the pedal ganglia, near the emergence of the pedal commissure. Up to five of these cells innervated the ipsilateral wing via the win g nerve. Dye-fills of these cells showed that they branch repeatedly i n the ipsilateral wing and innervate the swim musculature. Double-labe lling experiments indicated that the filled neurons were also serotoni n-immunoreactive. Neurobiotin fills that were processed for electron m icroscopy revealed two types of terminals associated with the swim mus culature: direct contacts and reactive terminals adjacent to non-label led presynaptic terminals, Additional immunoreactive neurons in the pe dal ganglia included the asymmetrical heart exciter neuron of the left pedal ganglion and up to nine ventral somata.