Catecholamine-containing cells in the central nervous system and peripheryof Aplysia californica

Previous studies have suggested the presence of numerous catecholamine-cont aining cells in both the central ganglia and peripheral tissues of Aplysia, but they often offered conflicting or incomplete accounts of numbers, loca tions, and morphologies. The current study combines aldehyde-induced histof luorescence and tyrosine hydroxylase-like immunoreactivity together with co nfocal microscopy to provide details of these cells. Approximately 35-50 ne urones in the cerebral ganglia, 4-8 neurones in the pedal ganglia, 5 neuron es in the buccal ganglia, and numerous small fibres in various nerve trunks exhibited both immunoreactivity and aldehyde-induced fluorescence. Approxi mately 20 cells in the pedal ganglia and 4 cells in the buccal ganglia exhi bited only immunoreactivity whereas 15-20 neurons in the cerebral ganglia e xhibited only aldehyde-induced fluorescence. No somata in the pleural or ab dominal ganglia exhibited aldehyde-induced fluorescence or immunoreactivity . Both aldehyde-induced histofluorescence and immunoreactivity also labelle d what appeared to be two classes of catecholamine-containing cells in the gill, siphon, oesophagus, rhinophore, tentacle, and reproductive organs. Th e more numerous, but smaller cells had subepithelial somata and processes p enetrating the overlying body wall, thus suggesting a sensory function. Ano ther class of neurones had larger somata, often located more deeply within the tissue, and occasionally appeared to be multipolar. Processes from thes e various peripheral cells appeared to comprise the major component of affe rent fibres and to form an extensive peripheral plexus, often associated wi th various muscles. The morphologies of the peripheral cells thus suggest i nvolvement in both local and centrally mediated reflexes and responses, but additional studies must test such hypothesised functions and determine the sensory modalities that the cells mediate. J. Comp. Neurol. 441:91-105, 20 01. (C) 2001 Wiley-Liss, Inc.