Electrophysiology of neurones of the inferior mesenteric ganglion of the cat.

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Abstract
Intracellular recordings were obtained from cells in vitro in the inferior mesenteric ganglia of the cat. Neurons were classified into 3 types: non-spontaneous, irregular discharging and regular discharging neurons. Non-spontaneous neurons had a stable resting membrane potential and responded with action potentials to indirect preganglionic nerve stimulation and to intracellular injection of depolarizing current. Irregular discharging neurons were characterized by a discharge of excitatory post-synaptic potentials (EPSP) which sometimes gave rise to action potentials. This activity was abolished by hexamethonium bromide, chlorisondamine and d-tubocurarine chloride. Tetrodotoxin and a low Ca2+-high Mg2+ solution also blocked on-going activity in irregular discharging neurons. Regular discharging neurons were characterized by a rhythmic discharge of action potentials. Each action potential was preceded by a gradual depolarization of the intracellularly recorded membrane potential. Intracellular injection of hyperpolarizing current abolished the regular discharge of action potential. No synaptic potentials were observed during hyperpolarization of the membrane potential. Nicotinic, muscarinic and adrenergic receptor blocking drugs did not modify the discharge of action potentials in regular discharging neurons. A low Ca2+-high Mg2+ solution also had no effect on the regular discharge of action potentials. Interpolation of an action potential between spontaneous action potentials in regular discharging neurons reset the rhythm of discharge. Evidently, regular discharging neurons were endogenously active and provided synaptic input to irregular discharging neurons.