Fast axonal transport of modulatory neuropeptides from central ganglia to components of the feeding system in Aplysia

Abstract

The transport of neuropeptides from central ganglia to components of the feeding system was studied in Aplysia. Peptide transport was determined by incubating buccal or cerebral ganglia with 35S-methionine and measuring the appearance of labeled peptides by high-pressure liquid chromatography (HPLC) of extracts of target tissues. Selected nerves were left intact and passed through a Vaseline diffusion barrier separating the ganglia and their targets. Five major labeled peptides were observed to be transported from the buccal ganglia to feeding muscles. They were buccalin, FMRFamide, myomodulin, and 2 small cardioactive peptides. Each of these peptides has been shown to modulate the responses of these muscles to their motor neurons. The peptides were transported by fast axonal transport, as judged by the distance transported and the sensitivity to colchicine. When normalized to correct for differences in total incorporation, the patterns of peptide transport were reproducible between animals. The nature and amount of the peptides transported were different for different muscles. The nature of peptide transport also varied for different nerve groups. These results support the proposition that these 5 peptides act as modulatory transmitters at feeding muscles. No transport of neuropeptides from the cerebral ganglia to feeding muscles was observed, although myomodulin was specifically transported to the buccal ganglia. This suggests that this peptide may play an important role in the previously observed regulation of buccal ganglia activity by neurons in the cerebral ganglia.