Various effects of angiotensin II on amygdaloid neuronal activity in normotensive control and hypertensive transgenic [TGR(mREN-2)27] rats

The effects: of iontophoretically ejected angiotensin II (Ang II) on the fi ring rate of neurons in the basolateral complex and the central and cortica l amygdala were investigated in two strains of urethane anesthetized rats. hi normotensive Sprague-Dawley rats, Ang II induced a significant increase in the discharge rate of responsive amygdaloid neurons. In contrast, in the hypertensive transgenic [TGR(mREN-2)27] rats with higher brain Ang II leve l, Ang II more often caused inhibitory effects on the amygdaloid firing rat e in comparison with controls. The distribution of nonresponsive, excited, and inhibited neurons differed significantly in the two rat strains. Moreov er, the responsiveness of amygdaloid neurons was significantly higher in tr ansgenic rats in comparison with controls. Both the increase and the decrea se in the firing rate caused by Ang II could be blocked either by angiotens in AT(1) or by AT(2) receptor-specific antagonists. In many cases, the Ang II-induced decrease in the firing rate was antagonized by bicuculline, a ga mma-aminobutyric acid (GABA(A)) antagonist. The higher responsiveness of am ygdaloid neurons in transgenic rats as well as the predominance of inhibito ry effects, presumedly mediated by GABAergic interneurons, could change the output of the amygdala and its influence on thirst, kidney, and cardiovasc ular function or on processes of learning and anxiety.