Centrally injected angiotensin II trans-synaptically activates angiotensin II-sensitive neurons in the anterior hypothalamic area of rats

Role of nitric oxide system in hydroxyl radical generation in rat striatum due to carbon monoxide poisoning, as determined by microdialysis

We explored the possible role of the nitric oxide (NO) system in hydroxyl radical (*OH) generation induced by carbon monoxide (CO) poisoning in rat striatum by means of microdialysis with the use of NO synthase (NOS) inhibitors, N(G)-nitro-L-arginine methyl ester (L-NAME) and N(G)-monomethyl-L-arginine (L-NMMA), as well as L-arginine (L-Arg; the NOS substrate) and D-arginine (D-Arg). The CO-induced *OH generation was suppressed by both L-Arg and D-Arg. It was also suppressed by L-NAME, which inhibits generation of reactive oxygen species (ROS) via neuronal NOS (nNOS) and inducible NOS, but not via endothelial NOS. In contrast, L-NMMA, which inhibits only ROS generation via inducible NOS, potentiated the *OH generation. L-Arg completely reversed the L-NAME effect and partly reversed the L-NMMA effect. D-Arg reversed the L-NAME effect more potently than did L-Arg, resulting in much more *OH generation than was observed with CO alone, and also potentiated the L-NMMA effect. On the other hand, W-7, an antagonist of calmodulin, which is critical for nNOS activity, had no effect on the CO-induced *OH generation. These findings suggest that complex mechanisms operate in *OH generation in rat striatum upon CO poisoning and that the NO system might not be included among those mechanisms.

Intracerebroventricular injection of losartan inhibits angiotensin II-sensitive neurons via GABA inputs in the anterior hypothalamic area of rats

Previously, we have demonstrated that pressure-ejected application of angiotensin II and losartan, an angiotensin AT1 receptor antagonist, onto some neurons in the anterior hypothalamic area (AHA) of the rat increases and decreases, respectively, the basal firing rate of the neurons. To investigate possible participation of these AHA neurons in the brain angiotensin system, we examined whether intracerebroventricular injection of the angiotensin AT1 receptor antagonist losartan inhibits the neuronal activity of angiotensin II-sensitive neurons via GABA inputs in the AHA of rats. Intracerebroventricular injection of losartan decreased the firing rate of AHA angiotensin II-sensitive neurons. However, the intracerebroventricular injection of losartan did not affect the increase in firing rate of AHA angiotensin II-sensitive neurons induced by pressure application of angiotensin II onto the same neurons, although losartan similarly injected abolished the increase in firing rate of AHA angiotensin II-sensitive neurons induced by intracerebroventricular injection of angiotensin II. The losartan-induced decrease of unit firing in AHA neurons was abolished by pressure application of the GABAA receptor antagonist bicuculline onto the same neurons. Bicuculline itself did not affect the basal firing rate of AHA neurons. These findings suggest that intracerebroventricular injection of losartan inhibits AHA angiotensin II-sensitive neurons via GABA inputs to the neurons.