TRPV1 receptor expression in cardiac vagal afferent neurons of infant rats

Abstract

We examined in infant rats whether cardiac afferent neurons in the nodose ganglia (NG) express transient receptor potential vanilloid 1 (TRPV1) receptors. Anesthetized rats (9–11 days old) were injected with 2 μl of a fluorescent retrograde tracer (Fluoro-Gold, FG) into the ventricular wall through the anterior epicardial surface. After 2 days, the NG were excised under anesthesia for identification of FG-labeled neurons and immunohistochemical analysis. Of 3858 NG neurons, 5% (202 neurons) were labeled with FG. Among the FG-labeled neurons, 180 (89%) were TRPV1 positive, of which 123 co-expressed 200-kDa neurofilaments (NF200), which is specific for myelinated nerve fibers. Among the FG-labeled neurons that expressed both TRPV1 and NF200, 37 had relatively large cell diameters (>26 μm) (range: 12–38 μm). In conclusion, in infant rats, most cardiac afferent neurons (both myelinated and unmyelinated) in the NG may express TRPV1 receptors. Although functional properties such as those related to the arterial baroreflex may vary among the neurons, our results suggest that, in immature animals, TRPV1 receptors help convey cardiac sensations and control autonomic reflexes.