Synaptically mediated potentials elicited by the stimulation of post-ganglionic trunks in the guinea-pig superior cervical ganglion.

Abstract

Stimulation of a post-ganglionic nerve trunk (internal carotid nerve) leads to synaptic activation of the majority of the sympathetic neurons in the superior cervical ganglion of the guinea-pig. Curarization of the ganglion and the section of the cervical sympathetic trunk eliminate any sign of synaptic activation in the ganglion cells produced by stimulating the internal carotid nerve. Stimulation of other post-ganglionic nerve trunks (superior cardiac nerve) gives rise only to pure antidromic responses in the cells. A compound action potential of considerable amplitude, which is completely cancelled by curarization of the ganglion, may be led off from the superior cardiac nerve after stimulating the internal carotid nerve; no propagated potential in the opposite direction was recorded at all. The conclusion is drawn that pre-ganglionic fibres projecting into the internal carotid nerve give rise to an elaborate system of collateral endings impinging onto most of the ganglion neurons and are responsible for synaptic activation of the ganglion cells observed after stimulating post-ganglionic nerves. The characteristics of action potentials evoked antidromically in the sympathetic neurons are also described.