EFFECT OF ANESTHETIC ON SYMPATHETIC RESPONSES EVOKED FROM CEREBELLAR UVULA IN DECEREBRATE CATS

The sympathetic mechanisms involved in the conversion of the tachycardia-pressor response evoked by electrical stimulation of the uvula (lobule IX of the posterior cerebellar cortex) in the unanesthetized decerebrate cat to a bradycardia-depressor response in the same, but anesthetized preparation, were investigated. Sympathoexcitation was produced in the inferior cardiac and renal sympathetic nerves in response to short train stimulation (2-5 pulses, 100-500 Hz) of the uvula in the unanesthetized decerebrate cat, and when paired stimuli (conditioning and test) were applied, the test-evoked potential in both nerves was similar to the response elicited by the conditioning stimulus. Anesthetic administered to these same animals caused the test response in both sympathetic nerves to be greatly decreased, yet the conditioning response was unchanged. The attenuation of the test response by the conditioning stimulus diminished during recovery from anesthesia. The recovery of the test response paralleled the time course of the return of the tachycardia-pressor effect evoked by long train stimulation of the uvula. It appears that anesthesia does not block the sympathoexcitatory response but acts to augment sympathoinhibitory processes associated with uvula stimulation; some possible mechanisms are discussed.