EFFECTS OF PRESSURE AND ANESTHETICS ON CONDUCTION AND SYNAPTIC TRANSMISSION

Abstract

The antagonism observed between pressure and anesthesia in intact animals suggests that pressure antagonism may be a promising criterion for identifying the effects of anesthetics which are important to loss of responsiveness. The effects of pressure and anesthesia on conduction and on synaptic transmission, which have often been proposed as possible alternative cellular sites of anesthesia are compared. The model used is the isolated rat superior cervical ganglion. He pressure (35-103 atm) antagonized partial conduction block of the preganglionic nerve by halothane (0.5 and 1 mM). He pressure failed to antagonize the depressant effects of halothane (0.25-0.5 mM) on nicotinic transmission and of halothane or methoxyflurane (0.24 mM) on muscarinic transmission in the ganglion. Pressure itself severely depressed synaptic transmission and added to the depressant effects of the anesthetics. Conduction block as a possible cellular mechanism of anesthesia meets the proposed criterion of pressure reversibility. In contrast pressure does not antagonize anesthetic depression of excitatory synaptic transmission in the rat superior cervical ganglion.