INFLUENCE OF GABA IN THE NUCLEUS OF THE SOLITARY TRACT ON BLOOD-PRESSURE IN BARORECEPTOR-DENERVATED RATS

We have previously reported that inhibition of the nucleus of the soli tary tract (NTS) in chronically sinoaortic baroreceptor-denervated (SA D) rats has no effect on blood pressure in contrast to the marked incr ease in blood pressure it elicits in baroreceptor-intact rats. This co uld result either from a lack of tonic excitatory input to this region or from overriding inhibition of NTS neurons involved in the control of blood pressure. The present study aimed to distinguish between thes e two possibilities by examining the changes in blood pressure elicite d by injection of bicuculline (Bic), a gamma-aminobutyric acid (GABA) antagonist, into the NTS of SAD and control rats. In chloralose-anesth etized baroreceptor-intact rats or acutely SAD rats, injection of 10 p mol Bic into the NTS elicited minimal changes in blood pressure. In co ntrast, in chronic SAD rats injection of Bic into the NTS elicited a l arge decrease in blood pressure. The maximal decrease in blood pressur e elicited by Bic in chronic SAD rats was equivalent to the maximal de crease in blood pressure that could be evoked by direct excitation of the NTS with L-glutamate. These results suggest that the lack of a ton ic role of the NTS in the regulation of blood pressure in chronic SAD rats is a result of maximal GABA-mediated inhibition of relevant NTS n eurons.