Sustained alterations in neuroimmune gene expression after daily, but not intermittent, alcohol exposure

Abstract

Acute ethanol intoxication is associated with Rapid Alterations in Neuroimmune Gene expression (RANGE), including increased Interleukin (IL)-6 and nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα), and suppressed IL-1β and Tumor necrosis factor (TNF) α, yet little is known about adaptations in cytokines across the first few ethanol exposures. Thus, the present studies examined central cytokines during intoxication (3 h post-ethanol) following 2, 4 or 6 intragastric ethanol challenges (4 g/kg) delivered either daily or every-other-day (EOD). Subsequent analyses of blood ethanol concentrations (BECs) and corticosterone were performed to determine whether the schedule of ethanol delivery would alter the pharmacokinetics of, or general sensitivity to, subacute ethanol exposure. As expected, ethanol led to robust increases in IL-6 and IκBα gene expression in hippocampus, amygdala and bed nucleus of the stria terminalis (BNST), whereas IL-1β and TNFα were suppressed, thereby replicating our prior work. Ethanol-dependent increases in IL-6 and IκBα remained significant in all structures—even after 6 days of ethanol. When these doses were administered EOD, modest IL-6 increases in BNST were observed, with TNFα and IL-1β suppressed exclusively in the hippocampus. Analysis of BECs revealed a small but significant reduction in ethanol after 4 EOD exposures — an effect which was not observed when ethanol was delivered after 6 daily intubations. These findings suggest that ethanol-induced RANGE effects are not simply a function of ethanol load per se, and underscore the critical role that ethanol dosing interval plays in determining the neuroimmune consequences of alcohol.

A cross-sectional comparison of ethanol-related cytokine expression in the hippocampus of young and aged Fischer 344 rats

“…resulted in sustained IL-6 and IκBα expression in the hippocampus after as many as 6 once-daily exposures, whereas the amygdala and BNST showed signs of habituation. These alterations were independent of blood ethanol concentrations observed, and were seen after repeated daily administration as opposed to every-other-day exposure to the same dose, which did not produce changes in these brain regions, showing the schedule and site specificity of the RANGE effects (Gano et al, 2016). Interestingly, recent work indicated that adolescents display similar patterns of cytokine expression after acute ethanol challenge, though the effects were severely blunted relative to young adults in most structures (Doremus-Fitzwater et al, 2015).…”

“…The floor of assay sensitivity using the Analox is ~12–15 mg/dl, as evidenced by background BEC measurements obtained from rats never exposed to ethanol. As such, measurements at or below those observed in vehicle-injected rats should be interpreted as zero values (Gano et al, 2016). …”

“…or i.g. showed elevation of IL-6 and IκBα (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha; a reporter of Nf-κB activity) and suppression of TNFα and IL-1β during intoxication (Doremus-Fitzwater et al, 2014; 2015; Gano et al, 2016). More recent work has shown that repeated ethanol administration (4 g/kg i.g.)…”

Assessment of social behavior directed toward sick partners and its relation to central cytokine expression in rats

“…Samples were run in triplicate in a 384-well plate (BioRad Laboratories) using the BioRad CFX 384 Real Time System C1000 Thermal Cycler (BioRad Laboratories). Relative gene expression was quantified using the 2−ΔΔCT method [41], with target gene expression calculated relative to the reference gene, β-actin (see [42] for primer sequences). Before analyses of target genes, reference gene expression was first separately analyzed in each structure/tissue compartment to ensure stability across treatment groups.…”

“…Interleukin-1β, IL-6, and TNF-α were measured, as these three cytokines have been shown to be potently activated in brain in response to systemic infection (e.g., [43]), with other non-immune challenges such as stress (e.g., [44, 45]) or ethanol exposure (e.g., [42, 46]) also altering central expression of these targets. Additionally, expression of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) was also assessed, as this is considered a reporter of nuclear factor kappa-light-chain-enhancer of activated B cells (NK-κB) activation.…”