DIFFERENCES BETWEEN SHR AND WKY FOLLOWING THE AIRPUFF STARTLE STIMULUS IN THE NUMBER OF FOS EXPRESSING, RVLM PROJECTING NEURONS

Abstract

The neurocircuitry responsible for excessive stress-induced cardiovascular responses in genetic hypertensive rats remains elusive. Prior studies detailed a differential cardiovascular response profile to airpuff startle stimuli between Spontaneously Hypertensive (SHR) and Wistar Kyoto (WKY) rats. We recently identified strain differential Fos expression in the rostroventrolateral medulla (RVLM) and several RVLM projecting sites following airpuff startle. The current study sought to define RVLM projecting neurons that also express Fos following placement in the test chamber and administration of the airpuff startle stimulus. Unilateral iontophoretic micro-injections of fluorogold were made into the RVLM of 9–10 week old SHR and WKY rats. Two to three weeks later, animals were subjected to a series of 60 airpuff startle stimuli. Brains were double labeled for Fos and fluorogold. Single fluorogold and single Fos cells, and double labeled cells were found in the nucleus tractus solitarius (NTS), caudal ventral lateral medulla (CVLM), Kölliker fuse (KF), ventral lateral, lateral, and dorsal central gray, lateral hypothalamus (LH), and paraventricular nucleus of the hypothalamus (PVN). These data are consistent with the notion that the RVLM receives differential excitatory and/or inhibitory input from higher brain centers, perhaps contributing to differential Fos expression in the RVLM, differential autonomic responding, or both.