Regional Specificity of the Long-Term Variation of Tyrosine Hydroxylase Protein in Rat Catecholaminergic Cell Groups After Chronic Heat Exposure

Abstract: The present study was carried out to investigate the effect of chronic heat exposure on tyrosine hydroxy-lase (TH) protein content in catecholaminergic rat brain-stem areas such as the anterior (LCA) and posterior (LCP) locus coeruleus, the substantia nigra (SN), the ventral tegmental area, and the dorsomedial (DMM) and the ventrolateral medulla and in the adrenal gland (AG). Male Sprague-Dawley rats were exposed to 34°C during 3, 7, or 14 days. Controls were kept at 25°C for the same period. In the LCA, TH content was decreased on day 7 (-34%) and 14 (-37%) of heat exposure. In the SN, TH protein content was decreased on day 7 (-25%) and 14 (-20%) after 34°C. In the DMM cell group, 14 days at 34°C produced a decrease (-20%) of TH content. In all of these structures, TH content variations were correlated with body temperature variations. In the AG, TH content increased progressively to peak (+31%) after 14 days of chronic heat exposure. This increase was also associated with body temperature modification. The selective and body temperature-related response of long-term TH protein content variations following chronic heat exposure observed in the LCA, SN, DMM, and AG could represent an adaptive physiological response of these catecholaminergic cells.