NMDA receptor NR2B subunit is expressed by NO-producing neurons in the preoptic region. Representative illustration of nNOS-expressing neurons (red) and NR2B subunit detection (green) by fluorescent immunocytochemistry in coronal brain sections from female rats showing progressively caudal sections of the preoptic region containing the vascular organ of the lamina terminalis (OV) (A), the MPO (B), and the MPN (C). V3, Third ventricle; ac, anterior commissure; oc, optic chiasm. Right, High magnifications of the areas delineated by rectangles. Arrowheads indicate double-labeled neurons expressing nNOS and NMDA receptor NR2B subunit. Arrows indicate NR2B single-labeled neurons. Scale bars: low magnification, 210 μm; high magnification, 60 μm.