Inhibition of Adrenergic Activity at a Locus Peripheral to the Brain and Spinal Cord

Abstract

This report confirms that adrenergic discharge can be neurogenically inhibited at a site outside of the central nervous system. Centers controlling peripheral inhibition are located in both the spinal cord and the brain. The inhibition is of the competitive-equilibrium type and can be surmounted by increasing the frequency of lumbar sympathetic stimulation. Inhibition of adrenergic discharge at an extraspinal locus occurs in the dog and in two species of monkey. Confirming evidence for central inhibition of vasomotor activity was also obtained in the cat and dog. Reflex dilatation can still be obtained after brain transections which abolish all neurogenic tone, confirming that reflex dilatation is in part active, and further showing that the centers that control active reflex dilatation and neurogenic tone can be differentiated by selected lesioning. The pathways in the spinal cord that mediate active reflex dilatation, adrenergic discharge, and inhibition of adrenergic discharge were explored. Sensitization (loss of accommodation) of pressoreceptors in the carotid sinus of the dog vvas noted within two hours of maintained hypotension. Reaccommodation of pressoreceptors occurred rapidly when the blood pressure was returned to normal. Marked sensitization of the vasomotor center to inhibitory input occurred in the same time period. Deaccommodation to inhibitory input also took place rapidly.