DEPRESSION OF TRANSMISSION THROUGH SYMPATHETIC GANGLIA DURING GENERAL ANESTHESIA

¹ Jenkins Laboratories of Biophysics, Johns Hopkins University and Hospital, Baltimore, Maryland, and Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York

Previous observations on perfused and excised sympathetic ganglia of cats and rabbits showed that synaptic transmission was depressed in the presence of certain anesthetics in concentrations comparable to those found in the blood during surgical anesthesia. Experiments described in this paper were designed to determine whether similar effects occurred in ganglia retaining their natural circulation. Observations were made by measuring the height of the postganglionic action potential of the superior cervical ganglion in response to supramaximal stimulation of the preganglionic nerve.

When the preganglionic nerve was stimulated at frequencies exceeding 10 per second, fewer ganglion cells responded during plane iii than during plane i of surgical anesthesia induced by ether or chloroform. In general, the degree of this depression paralleled the depth of anesthesia. However, the postganglionic response was usually altered more quickly than the plane of anesthesia when the concentration of anesthetic in inspired air was suddenly changed. Thiopental anesthesia also depressed synaptic transmission during high frequency stimulation but to a lesser degree than did ether or chloroform.

The height of the postganglionic action potential was reduced more by deepening anesthesia when the frequency of stimulation was high than when it was low. At low frequencies the degree of depression observed during plane iii was variable, apparently because of differences in intensity of transynaptic excitation in different preparations. Differences were observed between the sensitivities of different groups of ganglion cells to anesthetics.