ENHANCED GAMMA-AMINOBUTYRIC ACID-MEDIATED RESPONSES IN NUCLEUS-TRACTUS-SOLITARIUS OF HYPERTENSIVE RATS

Previous studies demonstrated that stimulation of type B gamma-aminobutyric acid (GABA(B)) receptors but not type A (GABA(A)) receptors in the nucleus tractus solitarius of spontaneously hypertensive rats elicited a larger increase in arterial pressure compared with control rats of the Wistar-Kyoto strain. The present studies extended that observation by examining the cardiovascular response to injection into the nucleus tractus solitarius of a selective GABA(B) receptor antagonist, CGP 35348, in these strains as well as examining the cardiovascular responses to stimulation or blockade of GABA(B) receptors in the nucleus tractus solitarius in another model of hypertension, the rat treated with deoxycorticosterone acetate and salt. In both groups of hypertensive rats the presser response to injection into the nucleus tractus solitarius of the GABA uptake blocking drug nipecotic acid was significantly greater compared with control rats (P<.01 in each model). Similarly, in both models of hypertension, the depressor response elicited by blockade of GABA(B) receptors in the nucleus tractus solitarius by injection of CGP 35348 was approximately 75% greater compared with control rats (P<.05 in each model). These results suggest that alterations in GABA(B)-mediated neural transmission in the nucleus tractus solitarius may contribute to the elevated arterial pressure observed in these models of hypertension.