Immunocytological localization of pedal peptide in the central nervous system and periphery of Aplysia

Immunocytology using antisera raised to conjugated pedal peptide (Pep) was used to localize the peptide in the CNS and periphery of Aplysia. A total of over 200 neurons in the CNS exhibited Pep-like immunoreactivity. As expected from results presented in the previous paper, immunoreactive neurons were heavily concentrated in the pedal ganglia, primarily in a broad ribbon comprised of about 60 large contiguous neurons on the dorsal side of each ganglion. Smaller and less numerous immunoreactive neurons were found in the other ganglia. A number of neurons primarily located in the abdominal ganglia had dense networks of immunoreactive varicose fibers surrounding their cell bodies. Many immunoreactive axons were observed in peripheral nerves, particularly those nerves leaving the pedal ganglia. Analyses of sections of body wall indicated that Pep-like immunoreactivity was localized to a series of varicose axons that appeared to be associated with vascular spaces, muscle fibers, and other large cells. These axons likely arise from pedal ganglion nerves that were shown to transport large amounts of 35S-labeled Pep to the periphery. These results suggest that Pep is a transmitter-like neuropeptide that is likely to have a number of important physiological actions in Aplysia.