Brain-Selective Expression of Exogenous Angiotensin (AT1) Receptors Causes Enhanced Cardiovascular Sensitivity.

Abstract

19 To examine the functional consequences of overexpression of AT1 receptors selectively in brain of both normal mice and in mice otherwise lacking endogenous AT1 receptors, we generated a novel transgenic model with AT1 receptors targeted selectively to neurons in the CNS. A fusion transgene consisting of 2.8 Kb of rat neuron-specific enolase(NSE) 5’ flanking region, and a cDNA encoding the full open reading frame of the AT1A receptor was constructed and transgenic mice (NSE-AT1) were generated. Of the six transgenic founder lines identified, two exhibited overexpression of the transgene selectively in brain. Using both immunohistochemistry and a high affinity fluorescently labeled angiotensin II (AngII) probe, we observed high levels of transgenic AT1A receptors in brain of both lines. Distribution of the receptors was particularly prominent in regions involved in cardiovascular regulation, including brainstem and lamina terminalis nuclei. Focusing on NSE-AT1 line 6085/2, direct recording of baseline blood pressure in conscious freely moving mice revealed no difference between transgenic and wildtype controls. However, intracerebroventricular injection of AngII (50, 100, 200 ng, 200 nL) in conscious NSE-AT1 mice (n=5) caused an increased pressor response (Δ17±2, 22±4, 33±5) and a profoundly enhanced bradycardia (Δ-48±6, -92±27, -114±17) compared to wildtypes (n=8) (BP: Δ7±2, 17±2, 21±1; HR: Δ-15±12, -23±7, -34±10). Our data show that brain-selective overexpression of exogenous AT1 receptors results in enhanced cardiovascular sensitivity to central AngII. This model, along with a model harboring this transgene but lacking AT1 receptors elsewhere (NSE-AT1 mice bred with AT1 knockouts), provide a new approach and important tools for identifying the cardiovascular regulatory roles of brain AT1 receptors relative to those in peripheral tissues.