Male adolescent rats display blunted cytokine responses in the CNS after acute ethanol or lipopolysaccharide exposure

Abstract

Alcohol induces widespread changes in cytokine expression, with recent data from our laboratory having demonstrated that, during acute ethanol intoxication, adult rats exhibit consistent increases in interleukin (IL)-6 mRNA expression in several brain regions, while showing reductions in IL-1 and TNFα expression. Given evidence indicating that adolescence may be an ontogenetic period in which some neuroimmune processes and cells may not yet have fully matured, the purpose of the current experiments was to examine potential age differences in the central cytokine response of adolescent (P31–33 days of age) and adult (69–71 days of age) rats to either an acute immune (lipopolysaccharide; LPS) or non-immune challenge (ethanol). In Experiment 1, male Sprague-Dawley rats were given an intraperitoneal (i.p.) injection of either sterile saline, LPS (250 µg/kg), or ethanol (4-g/kg), and then trunk blood and brain tissue were collected 3 hr later for measurement of blood EtOH concentrations (BECs), plasma endotoxin, and central mRNA expression of several immune-related gene targets. In Experiment 2, the response to intragastrically (i.g.) administered ethanol was examined and compared to animals given tap water (i.g.). Results showed that LPS stimulated robust increases in expression of IL-1, IL-6, TNFα, and IκBα in the hippocampus, PVN, and amygdala, and that these increases were generally less pronounced in adolescents relative to adults. Following an i.p. EtOH challenge, IL-6 and IκBα expression were significantly increased in both ages in the PVN and amygdala, and adults exhibited even greater increases in IκBα than adolescents. I.g. administration of ethanol also increased IL-6 and IκBα expression in all three brain regions, with hippocampal IL-6 expression elevated even more so in adults compared to adolescents. Furthermore, assessment of plasma endotoxin concentrations revealed (i) whereas robust increases in plasma endotoxin were observed in adults injected with LPS, no corresponding elevations were seen in adolescents after LPS; and (ii) neither adolescents nor adults demonstrated increases in plasma endotoxin concentrations following i.p. or i.g. ethanol administration. Analysis of BECs indicated that, for both routes of exposure, adolescents exhibited lower BECs than adults. Taken together, these data suggest that categorically different mechanisms are involved in the central cytokine response to antigen exposure versus ethanol administration. Furthermore, these findings confirm once again that acute ethanol intoxication is a potent activator of brain cytokines, and calls for future studies to identify the mechanisms underlying age-related differences in the cytokine response observed during ethanol intoxication.

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

“…Consistent with this, the present data show that IκBα expression was positively correlated with IL-6 (r = 0.86), whereas the relationship of IκBα to both TNFα and IL-1β was not significant (r = 0.02, 0.03 respectively). This intriguing finding suggests a significant departure from the simple expectation that NF-κB signaling (reported by increased IκBα gene expression) would show a strong positive correlation with all 3 of these cytokines, and is consistent with our previous work examining acute ethanol effects (Doremus-Fitzwater et al, 2015). Based on our present data, therefore, future studies examining more specific features of NF-κB signaling are of high priority for elucidating the seemingly paradoxical dissociation between IκBα and TNF/IL-1β.…”

“…More recently, data from our own laboratory has shown that acute ethanol administration (4 g/kg) elicits a robust and significant elevation in IL-6 and nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα) gene expression in the hippocampus, paraventricular nucleus of the hypothalamus (PVN) and amygdala during acute intoxication (i.e., 3 h after exposure), whereas IL-1β and TNFα tend to be suppressed during intoxication in most structures (Doremus-Fitzwater et al, 2014, 2015). For convenience, we now refer to these highly reproducible cytokine changes observed during acute intoxication (increased IL-6 and IκBα, decreased IL-1β and TNFα) as Rapid Alterations in Neuroimmune Gene Expression (RANGE) effects.…”

Analysis of c-Fos induction in response to social interaction in male and female Fisher 344 rats

“…HSP-3805) and the reaction was captured in real-time with a PCR detection system (BioRad, Model No. CFX384) (Doremus-Fitzwater et al, 2015). The first step in the PCR reaction was a 3-min hot start (95° C), followed by denaturation (30 s at 95° C), annealing (30 s at 60° C), and finally an extension step (30 s at 72° C) for 50 cycles.…”

Transgenic mice with increased astrocyte expression of IL-6 show altered effects of acute ethanol on synaptic function

“…Thus, results from this model are likely to be most relevant to alcohol use that starts in the juvenile or adolescent stage of life, a pattern of alcohol use that has significant risk for developing alcohol dependence and is currently an important societal issue (Foltran et al, 2011; Hingson et al, 2006). Studies in animal models have shown that ethanol exposure increases IL-6 levels in the CNS of adolescents as well as adults (Doremus-Fitzwater et al, 2015). …”