Interganglionic axonal transport of neuropeptides in Aplysia.

The transport of neuropeptides between central ganglia was studied in Aplysia. Peptide transport was determined by incubating ganglia with 35S-methionine and measuring the appearance of labeled peptides in connected ganglia. Selected interganglionic connectives were left intact and passed through a diffusion barrier separating the ganglia. Labeled peptides transported between ganglia included FMRFamide, myomodulin, and pedal peptide. Each of these peptides has been shown to be physiologically active in Aplysia. In addition to these previously characterized neuropeptides, a number of other as yet uncharacterized labeled peptides were also transported. All the peptides were transported by fast axonal transport as judged by the distance transported and/or the sensitivity to colchicine. Overall, FMRFamide and several unidentified peptides were the predominant transported peptides. However, the nature and amount of the peptides transported differed for each ganglia. These results support the proposition that the labeled peptides have transmitterlike actions and suggest that there are a number of neuropeptides that are likely to have central actions that have not yet been characterized in Aplysia.