Effect of gamma amino-butyric acid on spinal vascular reflex mechanisms.

Stimulation of sciatic nerve produced a rise in arterial blood pressure followed by a fall with an increase in the rate and depth of respiration in dogs under pentobarbitone anaesthesia. Application of cotton swabs soaked with GABA in 0.9 % saline to the spinal cord at Ll and L. segments did not change the basal arterial pressure and respiratory rate, but elicited only the pressor effect of sciatic nerve stimulation without changing the respiratory rate and depth. Injection of GABA at the same level in spinal cord had a similar effect. Control applications or injections with normal saline showed no effect. The effects of GABA were temporary and lasted for 45 minutes only. The depressor effect returned earlier than respiratory reflex changes which became prominent with the increase of depressor effect on stimulation of sciatic nerve. Section of spinal cord at the level of L. abolished the changes in arterial pressure and respiration on stimulation of sciatic nerve.