Some effects of proctolin on the cardiac ganglion of the maine lobster, Homarus americanus (Milne Edwards)

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Abstract
The neuropeptide proctolin has excitatory effects on the isolated lobster cardiac ganglion. Selective application to the anterior cell body region produces a dose‐dependent (10−8–10−5M) prolonged depolarization of large anterior cells as well as marked increases in burst frequency and/or duration. In ganglia which have been silenced with tetrodotoxin, proctolin application to anterior cells elicits long‐lasting depolarizing responses which are accompained by a 10–30% increase of the apparent membrane input resistance. Higher proctolin concentrations produce high‐frequency trains of driver potentials. It is proposed that a proctolinlike peptide may serve a neurohumoral role in the lobster cardiac ganglion and that the anterior motor neurons exhibit endogenous rhythmicity in its presence.