Receptive fields and properties of a new cluster of mechanoreceptor neurons innervating the mantle region and the branchial cavity of the marine mollusk Aplysia californica.

The rostral LE cluster (rLE) is a new set of mechanoreceptor neurons of the abdominal ganglion innervating the mantle area, the branchial cavity, the gill and the siphon of the marine mollusk Aplysia californica Cooper. We have compared the organization of rLE cell receptive fields with that of three other clusters of sensory neurons in the abdominal ganglion (LE, RE and RF) that we have reanalysed. There is extensive overlap of receptive fields from the four populations of sensory cells, and the most exposed areas of the mantle are the most densely innervated. The sensory threshold is similar for all groups. The action potentials of the LE, rLE and RE neurons are broadened by serotonin and the peptide SCPB and narrowed by dopamine and FMRFamide. The RF group does not show the same kind of sensitivity to these neuromodulators. The synaptic outputs of the LE and rLE neurons undergo similar synaptic depression and homosynaptic and heterosynaptic facilitation. We estimate that 100 mechanoreceptor neurons innervate the entire mantle and siphon skin, gill and branchial cavity of Aplysia. The degree of their convergence onto various interneurons and motor neurons mediating the gill- and siphon-withdrawal reflex and other reflexes is under investigation.