CONTRASTING EFFECTS OF THE GABA TRANSAMINASE INHIBITORS GAMMA-VINYLGABA AND AMINOOXYACETIC ACID ON ARTERIAL-PRESSURE FOLLOWING INJECTION INTO NUCLEUS-TRACTUS-SOLITARIUS

The effect of injection of inhibitors of GABA-transaminase into the nu cleus tractus solitarius (NTS) on arterial pressure was examined in an esthetized rats. Two typical GABA-transaminase inhibitors, gamma-vinyl GABA (GVG) and aminooxyacetic acid (AOAA), increased arterial pressure when injected into the NTS, a response similar to that elicited by di rect stimulation of GABA receptors in the NTS. However, with neither d rug was the response consistent with the action of inhibiting GABA-T. The response elicited by GVG, despite GVG acting as an irreversible in hibitor of GABA-T, could be reproduced with subsequent injections. Sti ll, the pressor response to GVG could be reversed by blockade of GABA( B)-receptors with CGP-35348, suggesting that GVG injection did increas e GABA-mediated neural transmission. In contrast, the pressor response to AOAA could not be antagonized by blockade of either GABA(A) or GAB A(B) receptors. These results suggest that acute inhibition of GABA-T does not necessarily result in an increase in GABA-mediated neural tra nsmission.