Prolonged exposure to intermittent alcohol vapors blunts hypothalamic responsiveness to immune and non-immune signals

Background: We have previously shown that long-term alcohol treatment blunt s the ACI-H response to alcohol itself, as well as to other stresses, and i s accompanied by decreased pituitary responsiveness to vasopressin (VP), bu t nut corticotropin-releasing Factor (CRF). The present work aims to determ ine the relevance of changes in CRF and VP receptors in the pituitary gland and/or peptide stores of CRF neurons in the paraventricular nucleus (PVN) of the hypothalamus, the areas that are most directly involved in ACTH rele ase. Methods: intact male rats were exposed to alcohol using a new vapor deliver y system which enables individual rat housing in boxes. Alcohol treatment w as delivered for 6 hr once daily (0700-1300), after which the rats were ret urned to their home cages where they had free access to food and water. Con trol rats were kept in similar boxes, but not exposed to alcohol. Total tre atment time was 8 days. All animals were equipped with indwelling jugular c annulae that were used to monitor blood alcohol levels (BALs) as well as AC TH and corticosterone release throughout drug exposure. Due to the presence of a swivel, the animals' movements were not restricted or hindered by the presence of these cannulae. On the morning of day 9, the animals were deca pitated under basal conditions or exposed to a neurogenic (mild electrofoot shocks) or systemic [iv lipopolysaccharide (LPS)] stimulus. PVN neuronal re sponses, indicated by changes in mRNA concentrations of the immediate early genes (IEGs) c-fos and NGFI-B, and plasma ACTH levels were measured before and during endotoxemia or electrofootshocks. Results: In the absence of alcohol, plasma ACTH and corticosterone remained at basal levels, indicating the absence of environment-induced stress. In rats exposed to alcohol, BALs were consistent and predictable, and we targe ted peak values of about 200 mg%. At the end of the drug treatment period, there were no significant differences between CRF and VP receptor mRNA leve ls in the anterior pituitary of control and alcohol-treated rats. In contra st, alcohol treatment respectively decreased CRF and increased VP stores in the external zone of the median eminence. It also increased NGFI-B and c-f os transcripts in the magnocellular (m) portion of the PVN, but not the par vicellular (p) division of this nucleus under basal conditions (i.e., in th e absence of shocks or LPS). After exposure to these stressors, on the othe r hand, all groups of rats showed significant increases in plasma ACTH leve ls as well as up-regulation of their PVN neuronal response, as indicated by changes in pPVN IEGs transcripts. However, these hormonal and neuronal res ponses were significantly blunted in animals pretreated with alcohol. Conclusions: Collectively, our results suggest that decreased PVN neuronal activation represents an important mechanism of the ability of long-term al cohol treatment to blunt the ACTH response to shocks or endotoxemia. In add ition, the new system of alcohol delivery that we developed is practical an d reliable, and has the significant advantage that it enables measurement o f circulating hormone levels during drug exposure of the animals.