DOPAMINERGIC ACCELERATION AND GABAERGIC INHIBITION IN EXTRINSIC NEURAL CONTROL OF THE HERMIT-CRAB HEART

The acceleratory and inhibitory cardio-regulatory nerves of hermit cra bs (Aniculus aniculus, Dardanus crassimanus) were studied using histoc hemical, immunocytochemical and pharmacological tests. Glyoxylic acid- induced fluorescence was observed in two of three axons of the dorsal cardiac nerve. One axon of the nerve showed gamma-aminobutyric acid-li ke immunoreactivity. Effects of stimulation of cardio-acceleratory axo ns were blocked by the dopaminergic antagonists, haloperidol and chlor promazine, but not by cholinergic, adrenergic or serotonergic blockers , suggesting that dopamine is the primary potential candidate for the neurotransmitter of cardio-accelerator neurons. Picrotoxin antagonized inhibition of the cardiac ganglion induced by gamma-aminobutyric acid and by cardio-inhibitory axons. Both small and large ganglionic cells may receive dopaminergic and GABAergic extrinsic neural control.