Differences in Quinpirole‐Induced Yawning Between Radiation Sensitive and Insensitive Rats

Abstract

A previous report noted that rats receiving head-only radiation exposure displayed neurobehavioral deficits on the rodent psychomotor vigilance test (rPVT), including changes in accuracy and premature responding. These changes were only apparent in a subset of irradiated rats, such that radiation-sensitive and radiation-insensitive groups emerged. Group specific changes in levels of the dopamine D2 receptor and dopamine transporter (DAT) protein were also evident. To better understand the DA system in radiation sensitivity, rats were trained on the rPVT, irradiated, and post-IR rPVT data were acquired. All rats were then observed for quinpirole-induced yawning under food-restricted and free-feeding conditions using a cumulative dosing procedure. The D2 receptor antagonist, L-741626 (0.32-1.0 mg/kg) was used to assess group differences in antagonism of the descending limb of the yawning curve. Since the hippocampus is sensitive to radiation, group differences in downstream hippocampal cholinergic mediation of quinpirole-induced yawning were assessed with the muscarinic antagonist, scopolamine (0.001-0.01 mg/kg). Quinpirole-induced hypothermia and its antagonism were assessed immediately following all yawning observations. Differences in quinpirole-induced yawning appear to be indicative of differential changes in D2/3 receptors between radiation-sensitive and insensitive rats following the highest dose of radiation exposure. Funding: NASA NCC 9-58-PF02602 and 9-58-NBPF02802; Mylan Internships program.