Expression of angiotensin type 1A receptors in C1 neurons restores the sympathoexcitation to angiotensin in the rostral ventrolateral medulla of angiotensin type 1A knockout mice

Abstract

In adult mice we determined whether expression of angiotensin II (Ang II) type 1A receptors (AT1ARs) in C1 neurons mediates the excitation of the rostral ventrolateral medulla (RVLM) by Ang II. Blood pressure, heart rate, and sympathetic nerve activity were measured in anesthetized, artificially ventilated wild-type (n=15) and AT1AR knockout (AT1A-/-; n=9) mice. Microinjection of Ang II (50 nL of 0.1 to 1.0 mmol/L) into the RVLM induced a dose-related, sympathetically mediated pressor response (maximum of 17±2 mm Hg) in wild-type mice. These microinjections had no effect in AT1A-/- mice. Endogenous AT1Rs occur on catecholaminergic C1 neurons in the RVLM. We induced AT1A-/-R or green fluorescent protein expression in C1 neurons of AT1A-/- mice through bilateral microinjection of replication-deficient lentiviruses, with transgene expression under the control of a phox2 transcription factor binding promoter (PRSx8) (Lv-PRSx8-AT1A-/-, n=10, and Lv-PRSx8-GFP, n=5). Transgene expression was observed in a significant proportion of RVLM C1 neurons. In anesthetized Lv-PRSx8-AT1A-/- injected mice, unilateral RVLM microinjection of Ang II (50 nL of 1 mmol/L) increased blood pressure (17±4 mm Hg) and sympathetic nerve activity (155±32%). No response to Ang II occurred in Lv-PRSx8-GFP microinjected mice. These results show that Ang II-mediated excitation of RVLM neurons in adult mice depends on the AT1A-/-R with little or no effect of type 1B or 2 receptors. Expression of the AT1A-/-R predominantly in C1 catecholamine neurons restores the response to Ang II in the AT1A-/- mouse and demonstrates that these neurons are sympathoexcitatory in the mouse. © 2010 American Heart Association, Inc.