Kathleen M. Ogilvie

Gender difference in hypothalamic–pituitary–adrenal axis response to alcohol in the rat: activational role of gonadal steroids

Alcohol administration activates the hypothalamic-pituitary-adrenal (HPA) axis of both male and female rats, with females secreting more adrenocorticotropin (ACTH) and corticosterone than males in response to the same dose of alcohol. Our earlier work suggested that this gender difference arises due to the activational effects of gonadal steroids. In particular, we hypothesized that both androgens and estrogens play a role, with androgens exerting an inhibitory influence while estrogens elevate activity of the HPA. In the present studies, we tested this hypothesis by manipulating steroidal milieu in male rats using surgical castration and chronic implantation of testosterone (T), dihydrotestosterone (DHT), or estradiol (E2). Intact male and female rats were included as controls. Injection of alcohol (3 g/kg b.wt., i.p.) resulted in elevation of blood alcohol levels, ACTH and corticosterone in all groups. However, the amount of ACTH secreted was greater in females and castrated males implanted with E2 than in intact males. In castrated males, regardless of androgen implantation, the ACTH response was intermediate, with mean levels between those of females and males, but not differing significantly from either. In contrast to the ACTH results, significantly higher corticosterone secretion was measured in females and castrated males which did not receive a steroid implant. Since there were no significant differences between groups in blood alcohol levels (BALs), these results are not due to steroid-dependent alterations in alcohol metabolism. Because the ACTH data confirmed an activational effect of E2, we sought to determine whether this steroid regulated levels of corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) mRNAs in the paraventricular nucleus of the hypothalamus (PVN). Four pretreatment groups were studied: intact males, intact females, castrated males, and castrated males implanted with E2. Two weeks after surgery, alcohol or vehicle was administered 3 h before brains were collected. In intact males, alcohol treatment elevated levels of both CRF and AVP mRNAs in the PVN, as previously reported. In contrast, this treatment decreased CRF mRNA in castrated males implanted with E2. In addition, steroid pretreatment alone elevated CRF mRNA levels in castrated males. Although we did not observe E2-dependent increases in CRF or AVP mRNAs, our data do support a complex effect of gonadal steroids on expression of these mRNAs in the PVN.

Role of arginine vasopressin and corticotropin-releasing factor in mediating alcohol-induced adrenocorticotropin and vasopressin secretion in male rats bearing lesions of the paraventricular nuclei

In male rats, lesions of the paraventricular nucleus (PVN) of the hypothalamus attenuate, but do not abolish, adrenocorticotropin (ACTH) secretion in response to acute alcohol injection. As the PVN is the major source of corticotropin-releasing factor (CRF) in the median eminence, this observation suggests that extra-PVN brain regions, and/or ACTH secretagogues other than CRF (e.g. arginine vasopressin (AVP)), mediate ACTH stimulation by alcohol. This hypothesis was tested by examining the effect of AVP immunoneutralization in PVN-lesioned (PVNx) rats. Removal of endogenous AVP diminished alcohol-evoked ACTH secretion in both sham-operated and PVNx animals, indicating that AVP from outside the PVN partially mediates the hypothalamic-pituitary-adrenal (HPA) axis response to alcohol. This led us to determine whether alcohol might also regulate AVP steady-state gene expression in the supraoptic nucleus (SON) and PVN, and/or CRF mRNA in the PVN and the central nucleus of the amygdala (AMY). In the magnocellular portion of the PVN, sham-operated animals showed significantly increased PVN levels of both CRF and AVP mRNAs 3 h after alcohol. In the SON, alcohol administration tended to decrease AVP gene expression in PVNx rats, while the drug increased AVP mRNA levels in the SON of sham-operated rats. AMY levels of CRF mRNA were unaffected by these manipulations. Finally, since the regulation of alcohol-induced AVP mRNA levels in the SON appeared to depend on the presence of the PVN, we measured peripheral levels of AVP in both sham-operated and PVNx animals after injection of vehicle or alcohol. Although AVP decreased in all groups, alcohol depressed AVP secretion to a greater extent in PVNx animals, suggesting that AVP systems are more sensitive to inhibition in the absence of the PVN. Our results demonstrate that although AVP of PVN origin may participate in regulating the stimulatory effect to AVP on ACTH secretion, AVP from areas other than the PVN also plays a role. Additionally, regulation of both AVP gene expression in the SON and secretion in the systemic circulation are altered in rats bearing lesions of the PVN.

The Intracerebroventricular Injection of Interleukin-1β Blunts the Testosterone Response to Human Chorionic Gonadotropin: Role of Prostaglandin- and Adrenergic-Dependent Pathways1

The present work extends our previous report that the intracerebroventricular (icv) injection of interleukin-1β (IL-1β, 80 ng) significantly blunted the testosterone response to 1 U/kg human CG (hCG), an effect that we attributed to the stimulation of inhibitory pathways connecting the hypothalamus to the testes. Systemic blockade of prostaglandin-dependent pathways with ibuprofen (α-methyl-4-[2-methyl-propyl]benzeneacetic acid; sodium salt), which did not, in itself, alter the stimulatory effect of hCG on testosterone release in control rats, modestly, but significantly (P < 0.05) reversed the inhibitory influence of IL-1β. In contrast, blockade of brain receptors for CRF was unable to alter the effect of IL-1β, as were lesions of the ventromedial hypothalamic nucleus, a brain area implicated in the control of ovarian function. Blockade of β-adrenergic receptors significantly prevented the decrease in testicular responsiveness induced by the icv injection of IL-1β. Finally, the central injection of the β...