Synaptic transmission in rat cardiac neurones

• Published in: Journal of the autonomic nervous system Vol. 39; no. 3; pp. 191 - 199
• Main Authors: Selyanko, A.A., Skok, V.I.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.1992; Elsevier Science
• Subjects: Action Potentials; Animals; Autonomic ganglia; Biological and medical sciences; Calcium; Cardiac neurone; Female; Fundamental and applied biological sciences. Psychology; Ganglia - physiology; Heart Atria - innervation; Heart Septum - innervation; Hexamethonium; Hexamethonium Compounds - pharmacology; Magnesium; Male; Neurons - drug effects; Neurons - physiology; Peripheral nervous system. Autonomic nervous system. Neuromuscular transmission. Ganglionic transmission. Electric organ; Rats; Rats, Inbred Strains; Synapses - physiology; Synaptic transmission; Trimethaphan - pharmacology; Tubocurarine - pharmacology; Vertebrates: nervous system and sense organs; Autonomic ganglia; Synaptic transmission; Cardiac neurone; Heart; Cardiac ganglion; Peripheral nervous system; Vertebrata; Mammalia; Rat; Autonomic nervous system; Rodentia; Isolated cell; Electrophysiology; Circulatory system
• ISSN: 0165-1838; 1872-7476
• DOI: 10.1016/0165-1838(92)90012-6

Intracellular recordings of spontaneous synaptic activity and synaptic responses to fibre tract stimulation were taken from neurones of ganglia isolated from the left atrium and interatrial septum of the rat. In six out of 57 neurones studied, spontaneous fast excitatory postsynaptic potentials (EPSPs) were recorded. Single stimulation of fibre tracts approaching the ganglion resulted in an all-or-none response consisting of an EPSP, from which an action potential abruptly appeared. This response disappeared in Ca 2+-free/high-Mg 2+ solution, indicating that it was orthodromic in origin. EPSPs were markedly exaggerated and prolonged by neostigmine (1–5 μM). EPSPs produced by high-frequency (0.1–20 Hz) fibre tract stimulation were markedly attenuated when compared with responses to single fibre tract stimulation, although they usually remained suprathreshold for spike initiation. High concentrations of hexamethonium (1 mM) and d-tubocurarine (300 μM) failed to inhibit responses to single fibre tract stimulation, although they completely abolished responses to high-frequency stimulation. Responses to single fibre tract stimulation were abolished by trimetaphan (≥ 100 μM). No slow synaptic responses were detected during single or high-frequency fibre tract stimulation. All cardiac neurones that responded orthodromically were highly excitable: they had a short post-spike after-hyperpolarization (AHP) and responded with multiple firing to prolonged membrane depolarization. It is concluded that cardiac neurones, in the region of the heart studied here, receive single ‘strong’ cholinergic inputs from some fibre tracts approaching the ganglion that elicit EPSPs accompanied by spikes. EPSPs are rather resistant to ganglion-blocking agents and subject to frequency modulation.