Histochemical survey of transmitters in the central ganglia of the gastropod mollusc Phestilla sibogae.

The aeolid nudibranch Phestilla sibogae is well studied in terms of its larval nervous system and neuronal involvement in metamorphosis. Central neurones in the adult have also been identified anatomically and electrophysiologically. We describe the neurotransmitter contents of these neurones and provide details of neuritic projections and developmental changes during growth (3 to 18 mm body length). Central ganglia from specimens of all sizes contained 100-115 serotonin-immunoreactive neurones, some of which appeared to be homologues of cells identified in other gastropods. Tyrosine hydroxylase immunoreactivity and aldehyde-induced fluorescence marked a common set of 28-30 catecholaminergic neurones located anteriorly in the cerebropleural ganglia and laterally in the pedal ganglia. Ganglionic neuropile and nerve trunks also contained many catecholaminergic fibres. About 65-100 intensely labelled FMRFamide-immunoreactive neurones were located symmetrically throughout the central ganglia, although one population was located only in the right pedal ganglion. Another 40-45 FMRFamide-immunoreactive neurones were weakly or variably stained. Central ganglia also contained 27-29 intensely labelled pedalpeptide-immunoreactive neurones, including those that were apparently homologues of cells previously described in Tritonia diomedea, and 16-19 weakly labelled pedal-peptide-immunoreactive neurones, including giant cerebropleural neurones coexhibiting FMRFamide immunoreactivity. Little cell addition involving any transmitter phenotype occurred as animals grew in body length, body growth being accommodated by growth in the size of individual cells, consistent with an approximate doubling in the size of the ganglia themselves.