Electrophysiological properties of rostral ventrolateral medulla neurons in angiotensin II 1a receptor knockout mice

We compared the electrophysiological properties of neurons in the rostral ventrolateral medulla of neonatal angiotensin II type 1a receptor knockout mice and wild-type mice with responses to angiotensin II, its type-1 receptor blocker candesartan, and its type-2 receptor blocker PD123319. Using the whole-cell patch-clamp technique, we examined the characteristics of rostral ventrolateral medulla neurons in brain stem-spinal cord preparations in which the sympathetic neuronal network is preserved. Baseline membrane potential and firing rate were almost similar between angiotensin II type 1a receptor knockout mice and wild-type mice. Superfusion with angiotensin II depolarized rostral ventrolateral medulla bulbospinal neurons in wild-type mice, whereas it hyperpolarized those in angiotensin II type 1a receptor knockout mice. Because pretreatment with candesartan significantly prevented the angiotensin II-induced depolarization in wild-type mice, the angiotensin II type 1 receptor is crucial for this depolarization. Superfusion with PD123319 depolarized rostral ventrolateral medulla bulbospinal neurons in angiotensin II type 1a receptor knockout mice. PD123319 prevented the angiotensin II-induced hyperpolarization in angiotensin II type 1a receptor knockout mice, and, rather, it induced depolarization. These results suggest that the angiotensin II type 2 receptor in rostral ventrolateral medulla plays an antagonistic role against the angiotensin II type 1a receptor in controlling the neuronal activity of rostral ventrolateral medulla.