Corticosterone-dependent alterations in utilization of catecholamines in discrete areas of rat brain

Abstract

This study investigated the impact of chronic adrenalectomy (ADX), and subsequent corticosterone (CORT) replacement to ADX rats, on brain levels of norepinephrine (NE) and dopamine (DA) and their extent of depletion after α-methyl- p-tyrosine (α-MpT) administration. Seven discrete hypothalamic areas, namely, the paraventricular nucleus (PVN), medial preoptic nucleus (POM), dorsomedial nucleus (DMN), ventromedial hypothalamus (VMH), perifornical lateral hypothalamus (PLH), supraoptic nucleus (SON), and arcuate nucleus/median eminence (ARC-ME), were examined. The steady-state content of NE and DA in all areas remained essentially unaltered 7 days after ablation of the adrenal glands, as well as after subsequent CORT replacement therapy in ADX rats. However, ADX, which reduced circulating CORT levels to 0.3 μg% as compared to > 3.0 μg% in sham rats, caused a significant increase in the depletion of NE following α-MpT treatment, in 4 out of the 7 brain sites examined (PVN, PLH, DMN and ARC-ME). In these brain sites, the NE turnover rate (K,pg/μg protein/h) and rate constant (K,h −1) increased following ADX. The chronic subcutaneous CORT implant (200 mg), which raised circulating CORT levels of ADX rats to 11 μg%, prevented this enhancement of NE turnover in the PVN, PLH and ARC-ME, but not the DMN. Unlike NE, DA utilization in the 7 discrete hypothalamic areas of α-MpT-treated rats remained unaltered after ablation of the adrenal glands, as well as after the CORT replacement therapy in ADX rats. These results indicate that circulating CORT may have a modulatory role in the regulation of NE in specific discrete hypothalamic areas, and thereby have an impact on the control of various physiological responses.