title: Dual effects of proctolin on the rhythmic burst activity of the cardiac ganglion.
abstract: The neuropeptide proctolin has distinguishable excitatory effects upon premotor cells and motorneurons of Homarus cardiac ganglion. Proctolin's excitation of the small, premotor, posterior cells is rapid in onset (5-10 s) and readily reversible (less than 3 min). Prolonged bursts in small cells often produce a "doublet" ganglionic burst mode via interactions with large motorneuron burst-generating driver potentials. In contrast to small cell response, proctolin's direct excitatory effects upon motorneuron are slow in onset (60-90 s to peak) and long-lasting (10-20 min). The latter include: a concentration-dependent (10(-9)-10(-7)M) depolarization of the somatic membrane potential; increases in burst frequency and enhancement of the rate of depolarization of the interburst pacemaker potential. Experiments on isolated large cells indicate: the slow depolarization is produced by a decrease in the resting GK and proctolin can produce or enhance motorneuron autorhythmicity . A two- tiered non-hierarchical network model is proposed. The differential pharmacodynamics exhibited by the two cell types accounts for the sequential modes of ganglionic burst activity produced by proctolin.
mesh_terms: D000818:Animals; D002319:Cardiovascular System / Q000294:innervation; D004305:Dose-Response Relationship, Drug; D005724:Ganglia / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects*; D008121:Nephropidae / Q000502:physiology*; D009479:Neuropeptides; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009842:Oligopeptides / Q000494:pharmacology*; D010507:Periodicity; D013329:Structure-Activity Relationship; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D009479:Neuropeptides; D018377:Neurotransmitter Agents; D009842:Oligopeptides; D013779:Tetrodotoxin; C011536:proctolin