Peptidergic modulation of patterned motor activity in identified neurons of Helisoma.

The neuroactive peptides SCP(B) (small cardioactive peptide B) and FMRFamide (Phe-Met-Arg-Phe-NH(2)), both originally isolated from molluscs, have potent modulatory effects upon the production of patterned motor activity in identified neurons (e.g., B5 and B19) in the buccal ganglia of the snail Helisoma. Such patterned motor activity has previously been shown to underlie feeding behavior. Micromolar concentrations of SCP(B) initiate patterned motor activity in quiescent ganglia and increase the rate of activity in ganglia that are spontaneously active. Micromolar concentrations of FMRFamide inhibit patterned motor activity in Helisoma buccal ganglia, and 10 muM FMRFamide completely suppresses such activity. In addition, there are both anti-SCP(B)-and anti-FMRFamide-immunoreactive neurons in Helisoma buccal ganglia. Our results suggest that peptides may play a prominent role in the regulation of feeding behavior in Helisoma.