Responses of the Single Sympathetic Ganglionic Neurones to Acetylcholine and to Dopamine

Abstract

The responses of the single superior cervical ganglion cells of the rabbits to acetylcholine (ACh) and to dopamine (DA) applied iontophoretically and in bulk were studied by the intracellular recording techniques. ACh elicited both nicotinic fast (f-) and muscarinic slow (s-) depolarization (DP) in about 30% of the principal ganglion cells perfused with d-tubocurarine. ACh elicited f-DP alone in about 20% of cells and s-DP in about 50%. ACh could elicit two forms of hyperpolarizing (HP) responses in the same cells that responded with f-DP and/or s-DP. Pretreatment with bethanechol (BCh) tended to reduce the short-latency HP response to ACh; pretreatment with bretylium eliminated the longer-latency HP response, while pretreatment with both BCh and bretylium essentially eliminated all HP responses to ACh. Neither f-DP nor longer-latency HP responses were observed in cells tested with BCh. It is suggested that the short-latency HP response is mediated by a muscarinic release of DA from SIF cell interneurones, and the longer-latency HP response is mediated by a non-muscarinic release of noradrenaline probably from dendrodendritic junctions between principal ganglion cells.

DA applied iontophoretically induced HP responses in many cells that exhibited no HP response to ACh and the DA-induced HP responses could be observed regardless of the depth of cells lying in the ganglion. DA added in bulk to the perfusing medium could apparently elicit an HP response in principal ganglion cells located in the outer 30 µm of the ganglion, but not in deeper-lying cells. The lack of response to DA of the deeper-lying cells may be due to the inactivation of diffusing DA by COMT.

That the receptors on the principal ganglion cells responsible for each type of response to ACh are distributed in a differential spatial manner relative to the position of the ACh delivery tip is suggested to explain the variability of responses to ACh of the principal ganglion cells.