Functional and neurochemical characterization of angiotensin type 1A receptor-expressing neurons in the nucleus of the solitary tract of the mouse.

Angiotensin II acts via two main receptors within the central nervous system, with the type 1A receptor (ATR) most widely expressed in adult neurons. Activation of the ATR in the nucleus of the solitary tract (NTS), the principal nucleus receiving central synapses of viscerosensory afferents, modulates cardiovascular reflexes. Expression of the ATR occurs in high density within the NTS of most mammals, including humans, but the fundamental electrophysiological and neurochemical characteristics of the ATR-expressing NTS neurons are not known. To address this, we have used a transgenic mouse, in which the ATR promoter drives expression of green fluorescent protein (GFP). Approximately one-third of ATR-expressing neurons express the catecholamine-synthetic enzyme tyrosine hydroxylase (TH), and a subpopulation of these stained for the transcription factor paired-like homeobox 2b (Phox2b). A third group, comprising approximately two-thirds of the ATR-expressing NTS neurons, showed Phox2b immunoreactivity alone. A fourth group in the ventral subnucleus expressed neither TH nor Phox2b. In whole cell recordings from slices in vitro, ATR-GFP neurons exhibited voltage-activated potassium currents, including the transient outward current and the M-type potassium current. In two different mouse strains, both ATR-GFP neurons and TH-GFP neurons showed similar ATR-mediated depolarizing responses to superfusion with angiotensin II. These data provide a comprehensive description of ATR-expressing neurons in the NTS and increase our understanding of the complex actions of this neuropeptide in the modulation of viscerosensory processing.