Descending forebrain projections targeting respiratory control areas in the midbrain and brainstem of rats

Abstract

We locally microinjected the conventional retrograde tracer cholera toxin subunit B (CT‐B, 100–150nL) into the BötC, KF, the pre‐Bötzinger complex (pre‐BötC), the midline raphé nuclei and the midbrain periaqueductal gray (PAG). Twelve days after unilateral CT‐B injections, brains were sectioned (40μm) and immunohistochemically stained with an anti‐CT‐B antibody. The strength of descending projections was qualitatively assessed: as strong (+++), moderate (++) or weak (+) numbers of CT‐B labeled cell bodies. Retrogradely labelled neurons after unilateral injections into the lateral PAG confirmed the predominantly ipsilateral location of strong and moderate descending projection neurons i..