Adolescent intermittent ethanol (AIE) produces lasting, sex-specific changes in rat body fat independent of changes in white blood cell composition

Early initiation of alcohol use during adolescence, and adolescent binge drinking are risk factors for the development of alcohol use disorder later in life. Adolescence is a time of rapid sex-dependent neural, physiological, and behavioral changes as well as a period of heightened vulnerability to many effects of alcohol. The goal of the present studies was to determine age-related changes in blood (leukocyte populations) and body composition across adolescence and early adulthood, and to investigate whether adolescent intermittent ethanol (AIE) exposure would alter the trajectory of adolescent development on these broad physiological parameters. We observed significant ontogenetic changes in leukocyte populations that were mirrored by an age-related increase in cytokine expression among mixed populations of circulating leukocytes. Despite these developmental changes, AIE did not significantly alter overall leukocyte numbers or cytokine gene expression. However, AIE led to sex-specific changes in body fat mass and fat percentage, with AIE-exposed male rats showing significantly decreased fat levels and female rats showing significantly increased fat levels relative to controls. These changes suggest that while AIE may not alter overall leukocyte levels, more complex phenotypic changes in leukocyte populations could underlie previously reported differences in cytokine expression. Coupled with long-term shifts in adipocyte levels, this could have long-lasting effects on innate immunity and the capacity of individuals to respond to later immunological and physiological threats.

Age-related decline in social interaction is associated with decreased c-Fos induction in select brain regions independent of oxytocin receptor expression profiles

Social behavior decreases with aging, and we have previously found a substantial decline in social investigative behavior of old female rats. In this study we examined the neural activation pattern (c-Fos mRNA) of young (3 month) and old (18 month) female rats after brief 10 min exposure to a novel female rat in order to identify forebrain regions that show selective age-related alterations in their neural response to social investigation. We also measured relative oxytocin receptor expression (Oxtr mRNA) as a possible factor in age-related declines in c-Fos induction after social interaction. Young rats exposed to a social partner had a greater c-Fos mRNA response than those exposed to novel context alone in the lateral septum and septohypothalamic area, with blunted increases evident in old rats. In addition, c-Fos mRNA levels in the lateral septum were positively correlated with social investigative behavior. Interestingly, age-related differences in c-Fos gene induction were unrelated to the local amount of Oxtr expression within specific brain regions, although we found an age-related decline in Oxtr expression in the ventromedial hypothalamus. This functional neuroanatomical characterization may point to certain brain regions that are especially sensitive to age-related declines associated with social interaction behavior.

Cues associated with a single ethanol exposure elicit conditioned corticosterone responses in adolescent male but not female Sprague-Dawley rats

It has been shown that ethanol-induced interleukin-6 (IL-6) in adult male Sprague-Dawley rats was sensitized by environmental stimuli paired with ethanol and was accompanied by a conditioned increase in corticosterone (CORT). Adolescent males showed ethanol-induced IL-6 conditioning more readily than adults. The present studies examined whether female adolescents display IL-6 conditioning and whether adolescents of either sex show CORT conditioning. Male and female (N = 212, n = 6-10) adolescent (postnatal day 33-40) rats were given ethanol (2 g/kg intraperitoneal injection; the unconditioned stimulus), either paired with a lavender-scented novel context (the conditioned stimulus) or explicitly unpaired from context. Rats were tested in the context without ethanol and brains/blood were collected. Adolescent females did not show signs of neuroimmune (Experiment 1) or CORT conditioning (Experiments 2-4). Paired males showed enhanced CORT to the scented context relative to unpaired counterparts when the interoceptive cue of a saline injection was used on test day (Experiment 2). Experiment 5 used a delayed conditioning procedure and showed that male paired adolescents showed significantly higher CORT in response to context, showing that classically conditioned CORT response was precipitated by environmental cues alone. These findings indicate that adolescent males may be predisposed to form conditioned associations between alcohol and environmental cues, contributing to adolescent vulnerability to long-lasting ethanol effects.

Examination of the role of adrenergic receptor stimulation in the sensitization of neuroinflammatory-based depressive-like behavior in isolated Guinea pig pups

Early-life attachment disruption appears to sensitize neuroinflammatory signaling to increase later vulnerability for stress-related mental disorders, including depression. How stress initiates this process is unknown, but studies with adult rats and mice suggest sympathetic nervous system activation and/or cortisol elevations during the early stress are key. Guinea pig pups isolated from their mothers exhibit an initial active behavioral phase characterized by anxiety-like vocalizing. This is followed by inflammatory-dependent depressive-like behavior and fever that sensitize on repeated isolation. Using strategies that have been successful in adult studies, we assessed whether sympathetic nervous system activity and cortisol contributed to the sensitization process in guinea pig pups. In Experiment 1, the adrenergic agonist ephedrine (3 or 10 mg/kg), either alone or with cortisol (2.5 mg/kg), did not increase depressive-like behavior or fever during initial isolation the following day as might have been expected to if this stimulation was sufficient to account for the sensitization process. In Experiment 2, both depressive-like behavior and fever sensitized with repeated isolation, but beta-adrenergic receptor blockade with propranolol (10 or 20 mg/kg) did not affect either of these responses or their sensitization. The high dose of propranolol did, however, reduce vocalizing. These results suggest sympathetic nervous system activation is neither necessary nor sufficient to induce the presumptive neuroinflammatory signaling underlying sensitization of depressive-like behavioral or febrile responses in developing guinea pigs. Thus, processes mediating sensitization of neuroinflammatory-based depressive-like behavior following early-life attachment disruption in this model appear to differ from those previously found to underlie neuroinflammatory priming in adults.

Intermittent Exposure to a Single Bottle of Ethanol Modulates Stress Sensitivity: Impact of Age at Exposure Initiation

Alcohol use during adolescence is a serious public health problem, with binge drinking and high-intensity drinking being particularly harmful to the developing adolescent brain. To investigate the adverse consequences of binge drinking and high-intensity adolescent drinking, adolescent rodents were intermittently exposed to ethanol through intragastric gavage, intraperitoneal injection, or vapor inhalation. These models revealed the long-lasting behavioral and neural consequences of adolescent intermittent ethanol (AIE) exposure. The present study was designed to characterize a different AIE model, namely, intermittent exposure to a single bottle of 10% ethanol as the only source of fluids on a 2 days on/2 days off (water days) schedule, and to determine whether this AIE exposure model would produce changes in hormonal and neuroimmune responsiveness to challenges of differing modalities. Assessments of ethanol intake as well as blood and brain ethanol concentrations (BECs and BrECs, respectively) in adult male and female rats (Experiment 1) revealed that BECs and BrECs peaked following access to ethanol for a 2 h period when assessed 1 h into the dark cycle. Experiment 2 revealed age differences in ethanol intake, BECs, and BrECs following a 2 h access to ethanol (1 h into the dark cycle), with adolescents ingesting more ethanol and reaching higher BECs as well as BrECs than adults. In Experiment 3, intermittent exposure to a single bottle of 10% ethanol for 10 cycles of 2 days on/2 days off was initiated either in early or late adolescence, followed by an acute systemic immune challenge with lipopolysaccharide (LPS) in adulthood. LPS increased corticosterone and progesterone levels regardless of sex and prior ethanol history, whereas an LPS-induced increase in cytokine gene expression in the hippocampus was evident only in ethanol-exposed males and females, with females who underwent early exposure to ethanol being more affected than their later-exposed counterparts. In Experiment 4, intermittent ethanol exposure in females was initiated either in adolescence or adulthood and lasted for 12 ethanol exposure cycles. Then, behavioral (freezing behavior), hormonal (corticosterone and progesterone levels), and neuroimmune (cytokine gene expression in the PVN, amygdala, and hippocampus) responses to novel environments (mild stressors) and shock (intense stressors) were assessed. More pronounced behavioral and hormonal changes, as well as changes in cytokine gene expression, were evident in the shock condition than following placement in the novel environment, with prior history of ethanol exposure not playing a substantial role. Interleukin (IL)-1β gene expression was enhanced by shock in the PVN, whereas shock-induced increases in IL-6 gene expression were evident in the hippocampus. Together, these findings demonstrate that our intermittent adolescent exposure model enhances responsiveness to immune but not stress challenges, with females being more vulnerable to this AIE effect than males.

A review on the reciprocal interactions between neuroinflammatory processes and substance use and misuse, with a focus on alcohol misuse

Background: The last decade has witnessed a surge of findings implicating neuroinflammatory processes as pivotal players in substance use disorders. The directionality of effects began with the expectation that the neuroinflammation associated with prolonged substance misuse contributes to long-term neuropathological consequences. As the literature grew, however, it became evident that the interactions between neuroinflammatory processes and alcohol and drug intake were reciprocal and part of a pernicious cycle in which disease-relevant signaling pathways contributed to an escalation of drug intake, provoking further inflammation-signaling and thereby exacerbating the neuropathological effects of drug misuse.Objectives: The goal of this review and its associated special issue is to provide an overview of the emergent findings relevant to understanding these reciprocal interactions. The review highlights the importance of preclinical and clinical studies in testing and validation of immunotherapeutics as viable targets for curtailing substance use and misuse, with a focus on alcohol misuse.Methods: A narrative review of the literature on drug and neuroinflammation was conducted, as well as articles published in this Special Issue on Alcohol- and Drug-induced Neuroinflammation: Insights from Pre-clinical Models and Clinical Research.Results: We argue that (a) demographic variables and genetic background contribute unique sensitivity to drug-related neuroinflammation; (b) co-morbidities between substance use disorders and affect dysfunction may share common inflammation-related signatures that predict the efficacy of immunotherapeutic drugs; and (c) examination of polydrug interactions with neuroinflammation is a critical area where greater research emphasis is needed.Conclusions: This review provides an accessible and example-driven review of the relationship between drug misuse, neuroinflammatory processes, and their resultant neuropathological outcomes.

Cues associated with repeated ethanol exposure facilitate the corticosterone response to ethanol and immunological challenges in adult male Sprague Dawley rats: implications for neuroimmune regulation

Background: We previously found a conditioned increase in central neuroinflammatory markers (Interleukin 6; IL-6) following exposure to alcohol-associated cues. Recent studies suggest (unconditioned) induction of IL-6 is entirely dependent on ethanol-induced corticosterone.Objectives: The goals of these present studies were to test whether alcohol-paired cues facilitated the hypothalamic-pituitary-adrenal (HPA) axis response to either a subthreshold priming alcohol dose or an immune or psychological stress challengeMethods: In Experiment 1 (N = 64), adult male Sprague Dawley rats were trained (paired or unpaired, four pairings total) with  either vehicle or 2 g/kg alcohol [intragastric (i.g.) or intraperitoneal (i.p.)] injections. In Experiments 2 (N = 28) and 3 (N = 30), male rats were similarly trained but with 4 g/kg alcohol i.g. intubations. On test day, all rats were either administered a 0.5 g/kg alcohol dose (i.p. or i.g. Experiment 1), a 100 µg/kg i.p. lipopolysaccharide (LPS) challenge (Experiment 2), or a restraint challenge (Experiment 3), and exposed to alcohol-associated cues. Blood plasma was collected for analysis.Results: Alcohol-associated cues facilitated the plasma corticosterone response to a subthreshold dose of alcohol (F1,28 = 4.85, p < .05) and an immune challenge (F8,80 = 6.23, p < .001), but not a restraint challenge (F2,27 = 0.18, p > .05).Conclusion: These findings reveal that the impact of the cues associated with alcohol intoxication on the HPA axis may be context-specific. This work illustrates how HPA axis learning processes form in the early stages of alcohol use and has important implications for how the HPA and neuroimmune conditioning may develop in alcohol use disorder in humans and facilitate the response to a later immune challenge.

Sex-specific effects of ethanol consumption in older Fischer 344 rats on microglial dynamics and Aβ(1-42) accumulation

Chronic alcohol consumption, Alzheimer's disease (AD), and vascular dementia are all associated with cognitive decline later in life, raising questions about whether their underlying neuropathology may share some common features. Indeed, recent evidence suggests that ethanol exposure during adolescence or intermittent drinking in young adulthood increased neuropathological markers of AD, including both tau phosphorylation and beta-amyloid (Aβ) accumulation. The goal of the present study was to determine whether alcohol consumption later in life, a time when microglia and other neuroimmune processes tend to become overactive, would influence microglial clearance of Aβ_(1-42), focusing specifically on microglia in close proximity to the neurovasculature. To do this, male and female Fischer 344 rats were exposed to a combination of voluntary and involuntary ethanol consumption from ∼10 months of age through ∼14 months of age. Immunofluorescence revealed profound sex differences in microglial co-localization, with Aβ_(1-42) showing that aged female rats with a history of ethanol consumption had a higher number of iba1+ cells and marginally reduced expression of Aβ_(1-42), suggesting greater phagocytic activity of Aβ_(1-42) among females after chronic ethanol consumption later in life. Interestingly, these effects were most prominent in Iba1+ cells near neurovasculature that was stained with tomato lectin. In contrast, no significant effects of ethanol consumption were observed on any markers in males. These findings are among the first reports of a sex-specific increase in microglia-mediated phagocytosis of Aβ_(1-42) by perivascular microglia in aged, ethanol-consuming rats, and may have important implications for understanding mechanisms of cognitive decline associated with chronic drinking.

Acute Ethanol Challenge Differentially Regulates Expression of Growth Factors and miRNA Expression Profile of Whole Tissue of the Dorsal Hippocampus

Acute ethanol exposure produces rapid alterations in neuroimmune gene expression that are both time- and cytokine-dependent. Interestingly, adolescent rats, who often consume binge-like quantities of alcohol, displayed reduced neuroimmune responses to acute ethanol challenge. However, it is not known whether growth factors, a related group of signaling factors, respond to ethanol similarly in adults and adolescents. Therefore, Experiment 1 aimed to assess the growth factor response to ethanol in both adolescents and adults. To test this, adolescent (P29-P34) and adult (P70-P80) Sprague Dawley rats of both sexes were injected with either ethanol (3.5 g/kg) or saline, and brains were harvested 3 h post-injection for assessment of growth factor, cytokine, or miRNA expression. As expected, acute ethanol challenge significantly increased IL-6 and IκBα expression in the hippocampus and amygdala, replicating our prior findings. Acute ethanol significantly decreased BDNF and increased FGF2 regardless of age condition. PDGF was unresponsive to ethanol, but showed heightened expression among adolescent males. Because recent work has focused on the PDE4 inhibitor ibudilast for treatment in alcohol use disorder, Experiment 2 tested whether ibudilast would alter ethanol-evoked gene expression changes in cytokines and growth factors in the CNS. Ibudilast (9.0 mg/kg s.c.) administration 1 h prior to ethanol had no effect on ethanol-induced changes in cytokine or growth factor changes in the hippocampus or amygdala. To further explore molecular alterations evoked by acute ethanol challenge in the adult rat hippocampus, Experiment 3 tested whether acute ethanol would change the miRNA expression profile of the dorsal hippocampus using RNASeq, which revealed a rapid suppression of 12 miRNA species 3 h after acute ethanol challenge. Of the miRNA affected by ethanol, the majority were related to inflammation or cell survival and proliferation factors, including FGF2, MAPK, NFκB, and VEGF. Overall, these findings suggest that ethanol-induced, rapid alterations in neuroimmune gene expression were (i) muted among adolescents; (ii) independent of PDE4 signaling; and (iii) accompanied by changes in several growth factors (increased FGF2, decreased BDNF). In addition, ethanol decreased expression of multiple miRNA species, suggesting a dynamic molecular profile of changes in the hippocampus within a few short hours after acute ethanol challenge. Together, these findings may provide important insight into the molecular consequences of heavy drinking in humans.

Adolescent intermittent ethanol exposure produces Sex-Specific changes in BBB Permeability: A potential role for VEGFA

Binge drinking that typically begins during adolescence can have long-lasting neurobehavioral consequences, including alterations in the central and peripheral immune systems. Central and peripheral inflammation disrupts blood-brain barrier (BBB) integrity and exacerbates pathology in diseases commonly associated with disturbed BBB function. Thus, the goal of the present studies was to determine long-lasting effects of adolescent intermittent ethanol (AIE) on BBB integrity. For AIE, male and female Sprague Dawley rats were repeatedly exposed to ethanol (4 g/kg, intragastrically) or water during adolescence between postnatal day (P) 30 and P50. In adulthood (∼P75), rats were challenged with fluorescein isothiocyanate (FITC)-tagged Dextran of varying molecular weights (4, 20, & 70 kDa) for assessment of BBB permeability using gross tissue fluorometry (Experiment 1). Experiment 2 extended these effects using immunofluorescence, adding an adult ethanol-exposed group to test for a specific developmental vulnerability. Finally, as a first test of hypothesized mechanism, Experiment 3 examined the effect of AIE on Vascular Endothelial Growth Factor A (VEGFA) and its co-localization with pericytes (identified through expression of platelet derived growth factor receptor beta (PDGFRβ), a key regulatory cell embedded within the BBB. Male, but not female, rats with a history of AIE showed significantly increased dextran permeability in the nucleus accumbens (NAc), cingulate prefrontal cortex (cPFC), and amygdala (AMG). Similar increases in dextran were observed in the hippocampus (HPC) and ventral tegmental area (VTA) of male rats with a history of AIE or equivalent ethanol exposure during adulthood. No changes in BBB permeability were evident in females. When VEGFa expression was examined, male rats exposed to AIE were challenged with 3.5 g/kg ethanol (i.p.) or vehicle acutely in adulthood to assess long-lasting versus acute actions of ethanol. Adult rats with a history of AIE showed significantly fewer total cells expressing VEGFa in the AMG and dHPC following the acute ethanol challenge in adulthood. They also showed a significant reduction in the number of PDGFRβ positive cells that also expressed VEGFa signal. The anatomical distribution of these effects corresponded with increased BBB permeability after AIE (i.e., differential effects in the PVN, AMG, and dHPC). These studies demonstrated sex-specific effects of AIE, with males, but not females, demonstrating long-term increases in BBB permeability that correlated with changes in VEGFa and PDGFRβ protein, two factors known to influence BBB permeability.

Circulating corticosterone levels mediate the relationship between acute ethanol intoxication and markers of NF-κB activation in male rats

Binge drinking is a harmful pattern of alcohol use that is associated with a number of serious health problems. Of particular interest are the rapid alterations in neuroimmune gene expression and the concurrent activation of the hypothalamic-pituitary-adrenal (HPA) axis activation associated with high intensity drinking. Using a rat model of acute binge-like ethanol exposure, the present studies were designed to assess the role of corticosterone (CORT) in ethanol-induced neuroimmune gene expression changes, particularly those associated with the NFκB signaling pathway, including rapid induction of IL-6 and IκBα, and suppression of IL-1β and TNFα gene expression evident after administration of moderate to high doses of ethanol (1.5-3.5 g/kg ip) during intoxication (3 h post-injection). Experiment 1 tested whether inhibition of CORT synthesis with metyrapone and aminoglutethimide (100 mg/kg each, sc) would block ethanol-induced changes in neuroimmune gene expression. Results indicated that rapid alterations in IκBα, IL-1β, and TNFα expression were completely blocked by pretreatment with the glucocorticoid synthesis inhibitors, an effect that was reinstated by co-administration of exogenous CORT (3.75 mg/kg) in Experiment 2. Experiment 3 assessed whether these rapid alterations in neuroimmune gene expression would be evident when rats were challenged with a subthreshold dose of ethanol (1.5 g/kg) in combination with 2.5 mg/kg CORT, which showed limited evidence for additive effects of low-dose CORT combined with a moderate dose of ethanol. Acute inhibition of mineralocorticoid (spironolactone) or glucocorticoid (mifepristone) receptors, alone (Experiment 4) or combined (Experiment 5) had no effect on ethanol-induced changes in neuroimmune gene expression, presumably due to poor CNS penetrance of these drugs. Finally, Experiments 6 and 7 showed that dexamethasone (subcutaneous; a GR agonist) recapitulated effects of ethanol. Overall, we conclude that ethanol-induced CORT synthesis and release is responsible for suppression of IL-1β, TNFα, and induction of IκBα in the hippocampus through GR signaling. Interventions designed to curb these changes may reduce drinking, and subdue detrimental neuroimmune activation induced by ethanol.

Adolescent neuroimmune function and its interaction with alcohol

Adolescence is an evolutionarily conserved developmental period associated with behavioral change, including increased risk-taking and alcohol use. Experimentation with alcohol typically begins in adolescence and transitions to binge-like patterns of consumption. Alcohol exposure during adolescence can alter normative changes in brain structure and function. Understanding mechanisms by which ethanol impacts neurodevelopmental processes is important for preventing and ameliorating the deleterious consequences of adolescent alcohol abuse. This review focuses on the neuroimmune system as a key contributor to ethanol-induced changes in adolescent brain and behavior. After brief review of neuroimmune system development, acute and chronic effects of ethanol on adolescent neuroimmune functioning are addressed. Comparisons between stress/immunological challenges and ethanol on adolescent neuroimmunity are reviewed, as cross-sensitization is relevant during adolescence. The mechanisms by which ethanol alters neuroimmune functioning are then discussed, as they may portend development of neuropathological consequences and thus increase vulnerability to subsequent challenges and potentiate addictive behaviors.

Alcohol, inflammation, and blood-brain barrier function in health and disease across development

Alcohol is the most commonly used drug of abuse in the world and binge drinking is especially harmful to the brain, though the mechanisms by which alcohol compromises overall brain health remain somewhat elusive. A number of brain diseases and pathological states are accompanied by perturbations in Blood-Brain Barrier (BBB) function, ultimately exacerbating disease progression. The BBB is critical for coordinating activity between the peripheral immune system and the brain. Importantly, BBB integrity is responsive to circulating cytokines and other immune-related signaling molecules, which are powerfully modulated by alcohol exposure. This review will highlight key cellular components of the BBB; discuss mechanisms by which permeability is achieved; offer insight into methodological approaches for assessing BBB integrity; and forecast how alcohol-induced changes in the peripheral and central immune systems might influence BBB function in individuals with a history of binge drinking and ultimately Alcohol Use Disorders (AUD).

Male, but not female, Sprague Dawley rats display enhanced fear learning following acute ethanol withdrawal (hangover)

The present studies investigated the effects of withdrawal from a single binge-like dose of ethanol (hangover) on fear conditioning in male and female Sprague Dawley rats. In Experiment 1, males and females were given 0 or 3.5 g/kg ethanol intraperitoneally (i.p.) and then conditioned to contextual fear 24 h post injection. Withdrawal from acute ethanol enhanced expression of the conditioned freezing response in males, but not in females. Experiment 2 demonstrated that in males, withdrawal from acute ethanol administered 24 h prior to conditioning enhanced contextual fear conditioning, but not auditory-cued fear conditioning. In Experiment 3, male and female rats were given 3.5 g/kg ethanol, and blood ethanol concentrations (BECs) were assessed at various time points for determination of ethanol clearance. Female rats cleared ethanol at a higher rate than males, with 10 h required for females and 14 for males to eliminate ethanol from their systems. Because females cleared ethanol faster than males, in Experiment 4, females were conditioned 18 h after ethanol administration to keep the interval between ethanol clearance and fear conditioning similar to that of males. Withdrawal from acute ethanol given 18 h prior to conditioning did not affect both contextual and auditory-cued fear conditioning in females. In summary, these results highlight sex differences in the impact of withdrawal from acute ethanol (hangover) on fear learning; suggesting that males are more sensitive to hangover-associated enhancement of negative affect than females.

Adolescent intermittent ethanol (AIE) produces sex specific alterations in adult neuroimmune gene expression and ethanol sensitivity that are independent of ethanol metabolism

The goal of the present studies was to determine long-lasting effects of adolescent intermittent ethanol (AIE), a rodent model of binge patterns of ethanol consumption, on (i) behavioral sensitivity to ethanol challenge in adulthood using the Loss of Righting Reflex (LORR) test; (ii) ethanol pharmacokinetics and ethanol-metabolizing enzyme expression when re-challenged with ethanol as adults; and (iii) induction of neuroimmune gene expression during an adult binge-like ethanol challenge. To evaluate the impact of AIE on ethanol sensitivity in adulthood, adult rats received a sedative ethanol dose of 3.5 g/kg and were tested for the LORR. Sexually dimorphic effects were observed, with AIE males showing more rapid recovery than vehicle exposed controls, an effect that was completely absent in females. Rats exposed to the same AIE procedure were challenged with 0.75, 1.5, or 3.0 g/kg i.p. ethanol in adulthood. Female rats with a history of AIE displayed a small increase in ethanol clearance rate when challenged with 0.75 g/kg, however no other significant differences in ethanol pharmacokinetics were noted. To assess persistent AIE-associated changes in neuroimmune gene expression, rats were challenged with 0 or 2.5 g/kg ethanol. Both male and female adult rats with a history of AIE displayed sensitized hippocampal IL-6 and IκBα gene expression in response to ethanol challenge. Changes in cytokine gene expression as well as ethanol sensitivity assessed by LORR were not shown to be the result of changes in ethanol pharmacokinetics and point to AIE altering other mechanisms capable of significantly altering the neuroimmune and behavioral response to ethanol.

Neuroendocrine and neuroimmune responses in male and female rats: evidence for functional immaturity of the neuroimmune system during early adolescence

Adolescence is a developmental period characterized by rapid behavioral and physiological changes, including enhanced vulnerability to stress. Recent studies using rodent models of adolescence have demonstrated age differences in neuroendocrine responses and blunted neuroimmune responding to pharmacological challenges. The present study was designed to test whether this neuroimmune insensitivity would generalize to a non-pharmacological stress challenge. Male and female adolescent (P29-33) and adult (P70-80) Sprague Dawley rats were exposed to intermittent footshock for one-, two-, or two-hours + recovery. Plasma corticosterone and progesterone levels as well as gene expression of several cytokines and c-Fos gene expression in the paraventricular nucleus of the hypothalamus (PVN), the medial amygdala (MeA), and the ventral hippocampus (vHPC) were analyzed. The results of the present study demonstrated differences in response to footshock, with these differences dependent on age, sex, and brain region of interest. Adult males and females demonstrated time-dependent increases in IL-1β and IL-1R2 in the PVN, with these changes not evident in adolescent males and substantially blunted in adolescent females. TNFα expression was decreased in all regions of interest, with adults demonstrating more suppression relative to adolescents and age differences more apparent in males than in females. IL-6 expression was affected by footshock predominantly in the vHPC of adolescent and adult males and females, with females demonstrating prolonged elevation of IL-6 gene expression. In summary, central cytokine responses to acute stressor exposure are blunted in adolescent rats, with the most pronounced immaturity evident for the brain IL-1 signaling system.

Assessment of neuroinflammation in the aging hippocampus using large-molecule microdialysis: Sex differences and role of purinergic receptors

Aging is associated with an enhanced neuroinflammatory response to acute immune challenge, often termed "inflammaging." However, there are conflicting reports about whether baseline levels of inflammatory markers are elevated under ambient conditions in the aging brain, or whether such changes are observed predominantly in response to acute challenge. The present studies utilized two distinct approaches to assess inflammatory markers in young and aging Fischer 344 rats. Experiment 1 examined total tissue content of inflammatory markers from hippocampus of adult (3 month), middle-aged (12 month), and aging (18 month) male Fischer (F) 344 rats using multiplex analysis (23-plex). Though trends emerged for several cytokines, no significant differences in basal tissue content were observed across the 3 ages examined. Experiment 2 measured extracellular concentrations of inflammatory factors in the hippocampus from adult (3 month) and aging (18 month) males and females using large-molecule in vivo microdialysis. Although few significant aging-related changes were observed, robust sex differences were observed in extracellular concentrations of CCL3, CCL20, and IL-1α. Experiment 2 also evaluated the involvement of the P2X7 purinergic receptor in neuroinflammation using reverse dialysis of the selective agonist BzATP. BzATP produced an increase in IL-1α and IL-1β release and rapidly suppressed the release of CXCL1, CCL2, CCL3, CCL20, and IL-6. Other noteworthy sex by aging trends were observed in CCL3, IL-1β, and IL-6. Together, these findings provide important new insight into late-aging and sex differences in neuroinflammation, and their regulation by the P2X7 receptor.

Corticosterone and progesterone differentially regulate HPA axis and neuroimmune responses to stress in male rats

In response to stressor exposure, expression of the inflammatory cytokine interleukin-1β (IL-1) is increased within the paraventricular nucleus of the hypothalamus (PVN). Surgical removal of the adrenal glands (ADX) potentiated stress-induced IL-1 expression, suggesting a role for adrenal-derived hormones in constraining stress-evoked increases in IL-1. While corticosterone (CORT) is a primary factor inhibiting IL-1 expression, progesterone (PROG) is also released by the adrenal glands in male rats in response to stress and also has potent anti-inflammatory properties. This series of studies first established doses of CORT and PROG that adequately recapitulate the normal stress-induced rise, and then tested for individual and combined roles of CORT and PROG in mitigating stress-induced expression of inflammatory genes. We found that CORT injection alone attenuated ADX-induced increases in IL-1 expression and normalized the HPA axis response to stress. In general, PROG replacement had little effect on changes in HPA axis responsivity or stress-induced inflammatory measures. When CORT and PROG were co-administered, a small effect on expression of the decoy receptor, IL-1R2 was observed, suggestive of an anti-inflammatory response. Overall, these results suggest that although CORT is likely to be the primary stress-related hormone responsible for constraining cytokine expression evoked by stress, CORT and PROG may exert certain combined actions that temper stress-induced neuroinflammation.LAY SUMMARYExposure to stress promoted expression of inflammation-related genes in the PVN and BNST. This inflammation was mainly suppressed by the adrenal hormone corticosterone, whereas progesterone had a smaller role in mitigating post-stress inflammation.

Lingering Effects of Prenatal Alcohol Exposure on Basal and Ethanol-Evoked Expression of Inflammatory-Related Genes in the CNS of Adolescent and Adult Rats

Emerging data suggest that alcohol’s effects on central inflammatory factors are not uniform across the lifespan. In particular, prenatal alcohol exposure (PAE) significantly alters steady-state levels of neuroimmune factors, as well as subsequent reactivity to later immune challenge. Thus, the current experiment investigated developmental sensitivities to, and long-lasting consequences of, PAE on ethanol-evoked cytokine expression in male and female adolescent and adult rats. Pregnant dams received either an ad libitum ethanol liquid diet (2.2% GD 6–8; 4.5% GD 9–10; 6.7% GD11–20; 35% daily calories from ethanol) or free-choice access to a control liquid diet and water. At birth, offspring were fostered to dams given free-choice access to the control liquid diet. Pups then matured until mid-adolescence [postnatal day (PD) 35] or adulthood (PD90), at which time they were challenged with either a binge-like dose of ethanol (4 g/kg; intragastrically) or tap water. During intoxication (3 h post-ethanol challenge), brains and blood were collected for assessment of neuroimmune gene expression (reverse transcription-polymerase chain reaction; RT-PCR) in the hippocampus, amygdala, and PVN, as well as for blood ethanol concentrations (BEC) and plasma corticosterone levels. Results revealed that rats challenged with ethanol at either PD35 or PD90 generally exhibited a characteristic cytokine signature of acute intoxication that we have previously reported: increased Il-6 andIkBα expression, with decreased Il-1β and Tnfα gene expression. With a few exceptions, this pattern of gene changes was observed in all three structures examined, at both ages of postnatal ethanol challenge, and in both sexes. While few significant effects of PAE were observed for ethanol-induced alterations in cytokine expression, there was a consistent (but nonsignificant) trend for PAE to potentiate the expression of Il-6 and IkBα in all groups except adult females. Although these data suggest that later-life ethanol challenge was a far greater driver of inflammatory signaling than PAE, the current results demonstrate PAE resulted in subtle long-term alterations in the expression of many key neuroinflammatory factors associated with NF-κB signaling. Such long-lasting impacts of PAE that may engender vulnerability to later environmental events triggering neuroinflammatory processes, such as chronic ethanol exposure or stress, could contribute to heightened vulnerability for PAE-related alterations and deficits.

Gene expression profiling reveals a lingering effect of prenatal alcohol exposure on inflammatory-related genes during adolescence and adulthood

Prenatal Alcohol Exposure (PAE) exerts devastating effects on the Central Nervous System (CNS), which vary as a function of both ethanol load and gestational age of exposure. A growing body of evidence suggests that alcohol exposure profoundly impacts a wide range of cytokines and other inflammation-related genes in the CNS. The olfactory system serves as a critical interface between infectious/inflammatory signals and other aspects of CNS function, and demonstrates long-lasting plasticity in response to alcohol exposure. We therefore utilized transcriptome profiling to identify gene expression patterns for immune-related gene families in the olfactory bulb of Long Evans rats. Pregnant dams received either an ad libitum liquid diet containing 35% daily calories from ethanol (ET), a pair-fed diet (PF) matched for caloric content, or free choice (FCL) access to the liquid diet and water from Gestational Day (GD) 11-20. Offspring were fostered to dams fed the FCL diet, weaned on P21, and then housed with same-sex littermates until mid-adolescence (P40) or young adulthood (P90). At the target ages of P40 or P90, offspring were euthanized via brief CO₂ exposure and brains/blood were collected. Gene expression analysis was performed using a Rat Gene 1.0 ST Array (Affymetrix), and preliminary analyses focused on two moderately overlapping gene clusters, including all immune-related genes and those related to neuroinflammation. A total of 146 genes were significantly affected by prenatal Diet condition, whereas the factor of Age (P40 vs P90) revealed 998 genes significantly changed, and the interaction between Diet and Age yielded 162 significant genes. From this dataset, we applied a threshold of 1.3-fold change (30% increase or decrease in expression) for inclusion in later analyses. Findings indicated that in adolescents, few genes were altered by PAE, whereas adults displayed an increase of a wide range of gene upregulation as a result of PAE. Pathway analysis predicted an increase in Nf-κB activation in adolescence and a decrease in adulthood due to prenatal ethanol exposure, indicating age-specific and long-lasting alterations to immune signaling. These data may provide important insight into the relationship between immune-related signaling cascades and long-term changes in olfactory bulb function after PAE.

Adolescent forced swim stress increases social anxiety-like behaviors and alters kappa opioid receptor function in the basolateral amygdala of male rats

Adolescence is a developmental period marked by robust neural alterations and heightened vulnerability to stress, a factor that is highly associated with increased risk for emotional processing deficits, such as anxiety. Stress-induced upregulation of the dynorphin/kappa opioid receptor (DYN/KOP) system is thought to, in part, underlie the negative affect associated with stress. The basolateral amygdala (BLA) is a key structure involved in anxiety, and neuromodulatory systems, such as the DYN/KOP system, can 1) regulate BLA neural activity in an age-dependent manner in stress-naïve animals and 2) underlie stress-induced anxiety in adults. However, the role of the DYN/KOP system in modulating stress-induced anxiety in adolescents is unknown. To test this, we examined the impact of an acute, 2-day forced swim stress (FSS - 10 min each day) on adolescent (~postnatal day (P) 35) and adult Sprague-Dawley rats (~P70), followed by behavioral, molecular and electrophysiological assessment 24 h following FSS. Adolescent males, but not adult males or females of either age, demonstrated social anxiety-like behavioral alterations indexed via significantly reduced social investigation and preference when tested 24 h following FSS. Conversely, adult males exhibited increased social preference. While there were no FSS-induced changes in expression of genes related to the DYN/KOP system in the BLA, these behavioral alterations were associated with alterations in BLA KOP function. Specifically, while GABA transmission in BLA pyramidal neurons from non-stressed adolescent males responded variably (potentiated, suppressed, or was unchanged) to the KOP agonist, U69593, U69593 significantly inhibited BLA GABA transmission in the majority of neurons from stressed adolescent males, consistent with the observed anxiogenic phenotype in stressed adolescent males. This is the first study to demonstrate stress-induced alterations in BLA KOP function that may contribute to stress-induced social anxiety in adolescent males. Importantly, these findings provide evidence for potential KOP-dependent mechanisms that may contribute to pathophysiological interactions with subsequent stress challenges.

Presence of mother prompts dissociation of sickness behavior, fever, and hypothalamic gene expression in lipopolysaccharide-injected guinea pig pups

During infection, sickness behaviors, such as a hunched stance with piloerection, can facilitate host resistance by supporting the generation and maintenance of fever. Fever, in turn, is mediated by hypothalamic neuroimmune signaling. Sickness behaviors, however, can also be influenced by social stimuli. In this study, guinea pig pups were injected with lipopolysaccharide to simulate a bacterial infection and then exposed to a novel, threatening environment while either with their mother or alone. We found that the presence of the mother suppressed sickness behavior, but enhanced fever, and had no measureable effect on gene expression of hypothalamic mediators of fever. This 3-way dissociation induced by the mother's presence is interpreted in terms of the differential adaptive consequences of behavioral and febrile responses for pups in this situation. The results contribute to a growing literature linking immunological and social processes.

Acute stress imposed during adolescence has minimal effects on hypothalamic-pituitary-adrenal (HPA) axis sensitivity in adulthood in female Sprague Dawley rats

Adolescence is a developmental epoch marked by maturation of stress-responsive systems including the Hypothalamic-Pituitary-Adrenal (HPA) axis. Emerging evidence has found sex-specificity in the long term behavioral and neural effects of stressors experienced during this sensitive period, though most studies have utilized chronic stress exposures that span much of the adolescent period. Using Sprague-Dawley rats, we examined how a single exposure to inescapable footshock (80 shocks, 5 s, 1.0 mA, 90 s variable ITI) applied during early adolescence (PND 29-31) affected the corticosterone (CORT) response to a later restraint stress challenge in adulthood. We found that females, but not males, displayed a marginally enhanced CORT response when challenged with restraint in adulthood. To further probe intrinsic sensitivity of the HPA axis in adolescent stressed females, subsequent studies utilized exogenous CRH and ACTH challenges to probe sensitivity of the pituitary and adrenal glands respectively, demonstrating that neither gland appears to be sensitized to hormone challenge as a result of adolescent stress history in females. A final experiment examined negative feedback regulation of the HPA axis through systemic administration of dexamethasone, showing that corticosteroid receptor-mediated negative feedback mechanisms were also intact in females with a history of adolescent stress. Together, these findings report that intrinsic regulatory elements of the HPA axis are fully intact in females exposed to footshock in adolescence, and that adolescent exposure to footshock had appreciably modest long-lasting effects on HPA axis sensitivity. These findings are discussed within the general context of stress resilience and vulnerability.

Rapid alterations in neuroimmune gene expression after acute ethanol: Timecourse, sex differences and sensitivity to cranial surgery

Prior work has established that that an acute ethanol challenge mimicking high intensity alcohol consumption increased IL-6 and suppressed IL-1β and TNFα mRNA in intoxication, with the opposite pattern seen in withdrawal. These experiments utilized Sprague-Dawley rats to further extend these results across time course (from 45 min to 6 h after ethanol), sex, and central versus peripheral expression. Furthermore, these data show that cannulation surgery may selectively modify the central neuroimmune response to ethanol. These findings highlight a unique plasticity of IL-6 that is specific to central structures and responsive to alterations by environmental factors.

The influence of central interleukin-6 on behavioral changes associated with acute alcohol intoxication in adult male rats

Recent studies have demonstrated brain cytokine fluctuations associated with acute ethanol intoxication (increased IL-6) and withdrawal (increased IL-1β and TNFα). The purpose of the present studies was to examine the potential functional role of increased central interleukin-6 (IL-6). We utilized two tests of ethanol sensitivity to establish a potential role for IL-6 after high (3.5-4.0 g/kg, intraperitoneally [i.p.]) or moderate (2.0 g/kg, i.p.) doses of ethanol: loss of righting reflex (LORR) and conditioned taste aversion (CTA), respectively. Briefly, guide cannulae were implanted into the third ventricle of adult male Sprague-Dawley rats. In the first experiments, rats were infused with 25, 50, 100, or 200 ng of IL-6; or 0.3, 3.0, or 9.0 μg of the JAK/STAT inhibitor AG490 30 min prior to a high-dose ethanol challenge. Although sleep time was not affected by exogenous IL-6, infusion of AG490 increased latency to lose the righting reflex relative to vehicle-infused rats. Next, we assessed whether IL-6 was sufficient to produce a CTA. Moderately water-deprived rats received intracerebroventricular (i.c.v.) infusions of 25, 50, or 100 ng IL-6 immediately after 60-min access to 5% sucrose solution. Forty-eight hours later, rats were returned to the context and given 60-min access to sucrose solution. IL-6 infusion had no significant effect on sucrose intake when all rats were considered together. However, a median split revealed that low sucrose-consuming rats significantly increased their drinking on test day, an effect that was not seen in rats that received 50 or 100 ng of IL-6. In the last study, AG490 had no effect on ethanol-induced CTA (2 g/kg). Overall, these studies suggest that IL-6 had only a minor influence on ethanol-induced behavioral changes, yet phenotypic differences in sensitivity to IL-6 were apparent. These studies are among the first to examine a potential functional role for IL-6 in ethanol-related behaviors, and may have important implications for understanding the relationship between acute ethanol intoxication and its associated behavioral alterations.

From adolescence to late aging: A comprehensive review of social behavior, alcohol, and neuroinflammation across the lifespan

The passage of time dictates the pace at which humans and other organisms age but falls short of providing a complete portrait of how environmental, lifestyle and underlying biological processes contribute to senescence. Two fundamental features of the human experience that change dramatically across the lifespan include social interactions and, for many, patterns of alcohol consumption. Rodent models show great utility for understanding complex interactions among aging, social behavior and alcohol use and abuse, yet little is known about the neural changes in late aging that contribute to the natural decline in social behavior. Here, we posit that aging-related neuroinflammation contributes to the insipid loss of social motivation across the lifespan, an effect that is exacerbated by patterns of repeated alcohol consumption observed in many individuals. We provide a comprehensive review of (i) neural substrates crucial for the expression of social behavior under non-pathological conditions; (ii) unique developmental/lifespan vulnerabilities that may contribute to the divergent effects of low-and high-dose alcohol exposure; and (iii) aging-associated changes in neuroinflammation that may sit at the intersection between social processes and alcohol exposure. In doing so, we provide an overview of correspondence between lifespan/developmental periods between common rodent models and humans, give careful consideration to model systems used to aptly probe social behavior, identify points of coherence between human and animal models, and point toward a multitude of unresolved issues that should be addressed in future studies. Together, the combination of low-dose and high-dose alcohol effects serve to disrupt the normal development and maintenance of social relationships, which are critical for both healthy aging and quality of life across the lifespan. Thus, a more complete understanding of neural systems-including neuroinflammatory processes-which contribute to alcohol-induced changes in social behavior will provide novel opportunities and targets for promoting healthy aging.

Acute stress imposed during adolescence yields heightened anxiety in Sprague Dawley rats that persists into adulthood: Sex differences and potential involvement of the Medial Amygdala

Stressors experienced during adolescence have been demonstrated to have a long-lasting influence on affective behavior in adulthood. Notably, most studies to date have found these outcomes after chronic stress during adolescence. In the present study we tested how exposure to a single episode of acute footshock during early adolescence would modify subsequent adult anxiety- and depressive-like behaviors in male and female Sprague-Dawley rats. Adolescent rats were exposed to inescapable footshock (80 shocks, 5 s, 1.0 mA, 90 sec variable inter-trial interval (ITI)) at Post-natal day (PND) 29-30 and remained undisturbed until adulthood where they were evaluated with several behavioral assays for anxiety as well as depressive-like behavior via forced swim. In addition, gene expression changes were assessed immediately after a 30 min forced swim challenge in adulthood among several stress-related brain regions including the Central Amygdala (CeA), Medial Amygdala (MeA), ventral Hippocampus (vHPC), and Paraventricular Nucleus (PVN). Studies used real-time RT-PCR to examine the cytokines Interleukin-1β (IL-1β) and Interleukin-6 (IL-6), corticotropin-releasing hormone (CRH), the immediate early genes c-Fos, c-Jun, Egr1 and Arc, and several genes relating to corticosteroid receptor function (glucocorticoid and mineralocorticoid receptor (GR and MR, respectively), Gilz (glucocorticoid-induced leucine zipper), Sgk1 (Serum and Glucocorticoid regulated Kinase 1)). Behaviorally, males displayed signs of increased anxiety, most notably in the light-dark box, whereas females did not. No notable depressive-like behavior was observed in forced swim as a result of adolescent stress history, but adolescent footshock exacerbated the c-Fos response in the MeA produced by swim in both sexes. Forced swim led to increased IL-1β expression in the PVN regardless of adolescent stress history, whereas most HPA (hypothalamic-pituitaryadrenal) axis-related genes were largely unaffected in the vHPC. To determine the potential for β-adrenergic receptors to contribute to the male-specific anxiety-like behavior, two further studies applied a β-adrenergic agonist (isoproterenol) or antagonist (propranolol) in male rats. These studies found that propranolol administered 2 h after footshock led to a reduction in some anxiety-like behaviors as compared to controls. Overall, these findings suggest that exposure to a single, intense stress challenge imposed during adolescence may have sex-specific consequences across the lifespan and may implicate the MeA in developmental plasticity.

Late aging-associated increases in L-DOPA-induced dyskinesia are accompanied by heightened neuroinflammation in the hemi-parkinsonian rat

Aging is a primary risk factor for the development of Parkinson's disease (PD), and aging differentially predicts the incidence of L-DOPA-induced dyskinesia (LID). The goal of this work was to establish whether late aging-associated exacerbation of LID would be related to neuroinflammation in the hemi-parkinsonian rat. Two studies were conducted in which adult (3 months) and aged (18 months) male Fischer 344 rats bearing unilateral 6-hydroxydopamine lesions of the medial forebrain bundle were injected acutely with vehicle or L-DOPA (6 mg/kg). LID was quantified, and neuroinflammation was assessed postmortem via gene expression markers in the striatum (experiment 1) or through concurrent large-molecule microdialysis (experiment 2). In addition to exacerbating LID despite similar levels of striatal dopamine loss, late aging was associated with persistently elevated IL-1β gene expression ipsilateral to lesion, as well as a trend toward greater extracellular concentrations of IL-1β in response to acute L-DOPA treatment. In contrast, aged sham-operated rats displayed greater extracellular IL-6. Taken together, these data demonstrate an age-related vulnerability to LID and highlight potential neuroinflammatory mediators associated with these effects.

Impact of housing conditions on social behavior, neuroimmune markers, and oxytocin receptor expression in aged male and female Fischer 344 rats

Aging is associated with a substantial decline in social behavior, whereas positive social interaction can improve overall health in aged individuals. In laboratory rodents, manipulations of the social environment across the lifespan have been shown to affect social behavior. Therefore, we examined the effects of long-term (5-6 weeks) housing conditions (alone, with one adult, or with two adults) on social behavior and the expression of neuroinflammation-related genes as well as oxytocin receptor (OXTR) gene expression in brain areas associated with social behavior regulation in aged male and female Fischer (F) 344 rats. Single-housed males and females exhibited increased social investigation, relative to pair-housed rats (one aged and one adult). Triple-housed (one aged and two adults) aged males exhibited lower levels of social investigation, relative to triple-housed aged females. Aged females were more socially active that their male counterparts. Although social housing condition significantly affected social behavior in males, it had no impact on cytokine gene expression in the paraventricular nucleus of hypothalamus (PVN), bed nucleus of the stria terminalis (BNST) or medial amygdala (MeA). However, in triple-housed aged females, who exhibited social behavior comparable to their single- and pair-housed counterparts, there was a significant increase in the expression of IL-1β and IL-6 mRNA in the MeA. No changes in cytokine gene expression were observed in the PVN or BNST, indicating that the increased expression of cytokines in the MeA was not a result of a generalized increase in neuroinflammation. Single-housed males and females exhibited elevated OXTR gene expression in the BNST. Taken together, these data indicate that manipulations of the social environment in late aging significantly influenced social interactions with a novel partner and gene expression in social behavior circuits and that these effects are sex-specific.

Conditioning the neuroimmune response to ethanol using taste and environmental cues in adolescent and adult rats

IMPACT STATEMENT

A combined odor and taste cue was paired with a binge-like ethanol exposure (4 g/kg intraperitoneal) using a single-trial learning paradigm. Re-exposure to the CS alone was sufficient to evoke a conditioned Interleukin (IL)-6 elevation in the amygdala in adolescents, an effect that was not observed in young adults. This demonstrates a particular sensitivity of adolescents to alcohol-associated cues and neuroimmune learning, whereas prior work indicated that adults require multiple pairings of ethanol to the CS in order to achieve a conditioned amygdala IL-6 response. While the role of immune conditioning has been studied in other drugs of abuse, these findings highlight a previously unknown aspect of alcohol-related learning. Given the emergent importance of the neuroimmune system in alcohol abuse, these findings may be important for understanding cue-induced reinstatement of alcohol intake among problem drinkers.

Assessment of Extracellular Cytokines in the Hippocampus of the Awake Behaving Rat Using Large-Molecule Microdialysis Combined with Multiplex Arrays After Acute and Chronic Ethanol Exposure

BACKGROUND

Studies have demonstrated persistent changes in central nervous system (CNS) cytokine gene expression following ethanol (EtOH) exposure. However, the low endogenous expression and short half-lives of cytokines in the CNS have made cytokine protein detection challenging. The goal of these studies was to establish parameters for use of large-molecule microdialysis and sensitive multiplexing technology for the simultaneous detection of brain cytokines, corticosterone (CORT), and EtOH concentrations in the awake behaving rat.

METHODS

Adult (P75+) male Sprague Dawley rats that were either naïve to EtOH (Experiment 1) or had a history of adolescent chronic intermittent EtOH (CIE; Experiment 2) were given an acute EtOH challenge during microdialysis. Experiment 1 examined brain EtOH concentrations, CORT and a panel of neuroimmune analytes, including cytokines associated with innate and adaptive immunity. The natural time course of changes in these cytokines was compared to the effects of an acute 1.5 or 3.0 g/kg intraperitoneal (i.p.) EtOH challenge. In Experiment 2, rats with a history of adolescent CIE or controls exposed to vehicle were challenged with 3.0 g/kg i.p. EtOH during microdialysis in adulthood, and a panel of cytokines was examined in parallel with brain EtOH concentrations and CORT.

RESULTS

The microdialysis procedure itself induced a cytokine-specific response that replicated across studies, specifically a sequential elevation of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and IL-10. Surprisingly, acute EtOH did not significantly alter this course of cytokine fluctuations in the hippocampus. However, a history of adolescent CIE showed drastic effects on multiple neuroimmune analytes when rechallenged with EtOH as adults. Rats with a history of adolescent EtOH displayed a severely blunted neuroimmune response in adulthood, evinced by suppressed IL-1β, IL-10, and TNF-α.

CONCLUSIONS

Together, these findings provide a methodological framework for assessment of cytokine release patterns, their modulation by EtOH, and the long-lasting changes to neuroimmune reactivity evoked by a history of adolescent CIE.

Circulating Levels of Brain-Derived Neurotrophic Factor and History of Suicide Attempts in Women

A growing body of research examining biological factors associated with suicidal behaviors highlights the role of brain-derived neurotropic factor (BDNF), involved in neurogenesis and synaptic plasticity. There is evidence suggesting that suicide attempters have lower BDNF levels than those with no history of suicide attempts. The key question addressed in the current investigation is whether differences in circulating BDNF levels persist beyond the current suicidal episode and would be observed in those with a past history of suicide attempts (SA). Plasma levels of BDNF were assessed in 73 women from the community. We found that women with a history of SA exhibited lower levels of BDNF than women with no SA history and this difference was maintained after statistically controlling for the influence of other potential psychiatric or demographic factors. These findings support and extend existing research by suggesting that circulating BDNF levels are decreased among individuals with a history of SA compared to individuals with no history of SA. This relation appeared to be specific to women's history of SA and was not explained by other potential psychiatric or demographic factors, which further highlights the role of BDNF as a promising biomarker for suicidal behavior.

A Pivotal Role for Thiamine Deficiency in the Expression of Neuroinflammation Markers in Models of Alcohol-Related Brain Damage

BACKGROUND

Alcohol-related brain damage (ARBD) is associated with neurotoxic effects of heavy alcohol use and nutritional deficiency, in particular thiamine deficiency (TD), both of which induce inflammatory responses in brain. Although neuroinflammation is a critical factor in the induction of ARBD, few studies have addressed the specific contribution(s) of ethanol (EtOH) versus TD.

METHODS

Adult rats were randomly divided into 6 conditions: chronic EtOH treatment (CET) where rats consumed a 20% v/v solution of EtOH for 6 months; CET with injections of thiamine (CET + T); severe pyrithiamine-induced TD (PTD); moderate PTD; moderate PTD during CET; and pair-fed controls. After the treatments, the rats were split into 3 recovery phase time points: the last day of treatment (time point 1), acute recovery (time point 2: 24 hours posttreatment), and delayed recovery (time point 3: 3 weeks posttreatment). At these time points, vulnerable brain regions (thalamus, hippocampus, frontal cortex) were collected and changes in neuroimmune markers were assessed using a combination of reverse transcription polymerase chain reaction and protein analysis.

RESULTS

CET led to minor fluctuations in neuroimmune genes, regardless of the structure being examined. In contrast, PTD treatment led to a profound increase in neuroimmune genes and proteins within the thalamus. Cytokine changes in the thalamus ranged in magnitude from moderate (3-fold and 4-fold increase in interleukin-1β [IL-1β] and IκBα) to severe (8-fold and 26-fold increase in tumor necrosis factor-α and IL-6, respectively). Though a similar pattern was observed in the hippocampus and frontal cortex, overall fold increases were moderate relative to the thalamus. Importantly, neuroimmune gene induction varied significantly as a function of severity of TD, and most genes displayed a gradual recovery across time.

CONCLUSIONS

These data suggest an overt brain inflammatory response by TD and a subtle change by CET alone. Also, the prominent role of TD in the immune-related signaling pathways leads to unique regional and temporal profiles of induction of neuroimmune genes.

Early Attachment Disruption, Inflammation, and Vulnerability for Depression in Rodent and Primate Models

Early experiments in nonhuman primates established the relation between disruption of filial attachment and depressive-like outcomes. Subsequent studies in rats and mice have been instrumental in linking depressive-like outcomes to disturbances in maternal behavior. Another aspect of attachment disruption, absence of the attachment object per se, may be studied more effectively in a different laboratory rodent-the guinea pig. Here, we discuss the rationale for using guinea pigs for this work. We then review guinea pig studies providing evidence for inflammatory mechanisms mediating both depressive-like behavior during separation as well as sensitization of stress responsiveness such as is thought to lead to increased vulnerability to depression at later ages. Finally, we discuss recent complementary work in adult monkeys that suggests cross-species generalizability of broad principles derived from the guinea pig experiments. Overall, the findings provide experimental support for human research implicating inflammatory mechanisms in the development of increased stress responsiveness and vulnerability to depression following attachment disruption and other forms of early-life stress. Specifically, the findings suggest inflammatory mechanisms may set in motion a cascade of underlying processes that mediate later increased stress responsiveness and, therefore, depression susceptibility.

Preface: Setting the stage for understanding alcohol effects in late aging: A special issue including both human and rodent studies

It is widely recognized that people worldwide are living longer than in previous decades, with formidable projections regarding the expansion of elderly age groups in the decades to come. Older individuals are also sustaining higher levels of alcohol consumption later in life, and binge drinking remains a prevalent pastime in a significant proportion of aged individuals. Older people are more sensitive to neurobehavioral effects of alcohol, and as individuals age, the cumulative impact of lifetime alcohol intake begins to emerge. This brief review provides a perspective on the emerging field of how alcohol interacts with the aging brain and sets the stage for understanding the relationship between alcohol and overall brain health. In doing so, we introduce a set of articles collected in this book series (all chapters available on PubMed) which spans human epidemiology and clinical outcomes, along with a series of neurobehavioral studies in preclinical (rodent) models. Because both natural aging as well as alcohol use and abuse include tell-tale signs of neuroinflammation (heightened expression of neuroimmune genes, activation of inflammatory signaling pathways, and signs of glial activation), particular emphasis is placed on the role of neuroinflammation in both aging- and alcohol-related alterations in neurobehavioral function, with special emphasis on the spectrum of cognitive dysfunction ranging from mild cognitive impairment to Alzheimer's associated brain pathology.

Stress, alcohol and infection during early development: A brief review of common outcomes and mechanisms

Although stress is an adaptive physiological response to deal with adverse conditions, its occurrence during the early stages of life, such as infancy or adolescence, can induce adaptations in multiple physiological systems, including the reproductive axis, the hypothalamic-pituitary-adrenal (HPA) axis, the limbic cortex and the immune system. These early changes have consequences in adult life, as seen in the physiological and behavioural responses to stress. This review highlights the impact of several stress challenges incurred at various stages of development (perinatal, juvenile, adolescent periods) and how the developmental timing of early-life stress confers unique physiological adaptations that may persist across the lifespan. In doing so, we emphasise how intrinsic sex differences in the stress response might contribute to sex-specific vulnerabilities, the molecular processes underlying stress in the adult, and potential therapeutic interventions to mitigate the effects of early stage stress, including the novel molecular mechanism of SUMOylation as a possible key target of HPA regulation during early-life stress.

Factors promoting vulnerability to dysregulated stress reactivity and stress-related disease

Effective coordination of the biological stress response is integral for the behavioural well-being of an organism. Stress reactivity is coordinated by an interplay of the neuroendocrine system and the sympathetic nervous system. The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in orchestrating the bodily responses to stress, and the activity of the axis can be modified by a wide range of experiential events. This review focuses on several factors that influence subsequent HPA axis reactivity. Some of these factors include early-life adversity, exposure to chronic stress, immune activation and traumatic brain injury. The central premise is that each of these experiences serves as a general vulnerability factor that accelerates future HPA axis reactivity in ways that make individuals more sensitive to stress challenges, therefore feeding forward into the exacerbation of ongoing (or greater susceptibility toward) future stress-related disease states, especially as they pertain to negative affect and overall brain health.

Late aging alters behavioral sensitivity to ethanol in a sex-specific manner in Fischer 344 rats

Responsiveness to ethanol (EtOH) differs as a function of age. Adolescent rodents are less sensitive than adults to the sedative effects of EtOH, whereas they show enhanced sensitivity to EtOH-induced social facilitation. Late aging is associated with a natural decline in social behavior and aging-related peculiarities in sensitivity to EtOH have been largely unexplored. Whether there are sex differences in the behavioral response to EtOH during late aging remains unknown. Thus, behavioral responses to EtOH in male and female Fischer (F) 344 rats aged 4-5 months (adult) and 19-20 months (aging) were examined. First, the effects of saline and EtOH (0.5 and 0.75 g/kg) on social interaction were assessed. Social investigation and contact behavior were lower in aging animals and higher in females. Interestingly, in aged females, social contact behavior was increased following a 0.5 g/kg EtOH dose, whereas the same dose suppressed social contact in aged males. Behavioral sensitivity to the sedative effects of 3.0 and 3.5 g/kg EtOH was assessed with the loss of righting reflex (LORR) test. Although latency to LORR did not differ as a function of age or sex, aged rats showed significantly greater LORR duration and significantly lower blood ethanol concentrations (BECs) at regaining of the righting reflex relative to adults. In addition, females had a lower LORR duration, regardless of age; no sex differences were evident in BECs at awakening. In a second experiment, blood ethanol concentrations (BECs) over time were assessed following 0.75, 1.5, and 3.0 g/kg EtOH in 3-, 12-, and 18-month-old male and female F344 rats. Aged rats had higher peak BECs following 3.0 g/kg EtOH, whereas few age or sex differences were apparent at lower doses. Taken together, these data indicate that late aging is associated with altered sensitivity to the social facilitating effects and sedative effects of EtOH.

Differential effects of acute versus chronic stress on ethanol sensitivity: Evidence for interactions on both behavioral and neuroimmune outcomes

Acute alcohol intoxication induces significant alterations in brain cytokines. Since stress challenges also profoundly impact central cytokine expression, these experiments examined the influence of acute and chronic stress on ethanol-induced brain cytokine responses. In Experiment 1, adult male rats were exposed to acute footshock. After a post-stress recovery interval of 0, 2, 4, or 24 h, rats were administered ethanol (4 g/kg; intragastric), with trunk blood and brains collected 3 h later. In non-stressed controls, acute ethanol increased expression of Il-6 and IκBα in the hippocampus. In contrast, rats exposed to footshock 24 h prior to ethanol demonstrated potentiation of hippocampal Il-6 and IκBα expression relative to ethanol-exposed non-stressed controls. Experiment 2 subsequently examined the effects of chronic stress on ethanol-related cytokine expression. Following a novel chronic escalating stress procedure, rats were intubated with ethanol. As expected, acute ethanol increased Il-6 expression in all structures examined, yet the Il-6 response was attenuated exclusively in the hippocampus in chronically stressed rats. Later experiments determined that neither acute nor chronic stress affected ethanol pharmacokinetics. When ethanol hypnosis was examined, however, rats exposed to chronic stress awoke at significantly lower blood ethanol levels compared to acutely stressed rats, despite similar durations of ethanol-induced sedation. These data indicate that chronic stress may increase sensitivity to ethanol hypnosis. Together, these experiments demonstrate an intriguing interaction between recent stress history and ethanol-induced increases in hippocampal Il-6, and may provide insight into novel pharmacotherapeutic targets for prevention and treatment of alcohol-related health outcomes based on stress susceptibility.

Stereological Analysis of Microglia in Aged Male and Female Fischer 344 Rats in Socially Relevant Brain Regions

Aging is associated with a substantial decline in the expression of social behavior as well as increased neuroinflammation. Since immune activation and subsequent increased expression of cytokines can suppress social behavior in young rodents, we examined age and sex differences in microglia within brain regions critical to social behavior regulation (PVN, BNST, and MEA) as well as in the hippocampus. Adult (3-month) and aged (18-month) male and female F344 (N = 26, n = 5-8/group) rats were perfused and Iba-1 immunopositive microglia were assessed using unbiased stereology and optical density. For stereology, microglia were classified based on the following criteria: (1) thin ramified processes, (2) thick long processes, (3) stout processes, or (4) round/ameboid shape. Among the structures examined, the highest density of microglia was evident in the BNST and MEA. Aged rats of both sexes displayed increased total number of microglia number exclusively in the MEA. Sex differences also emerged, whereby aged females (but not males) displayed greater total number of microglia in the BNST relative to their young adult counterparts. When morphological features of microglia were assessed, aged rats exhibited increased soma size in the BNST, MEA, and CA3. Together, these findings provide a comprehensive characterization of microglia number and morphology under ambient conditions in CNS sites critical for the normal expression of social processes. To the extent that microglia morphology is predictive of reactivity and subsequent cytokine release, these data suggest that the expression of social behavior in late aging may be adversely influenced by heightened inflammation.

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

Acute illness not only reduces the expression of social behavior by sick rodents, but can also lead to avoidance responses when detected by healthy, would-be social partners. When healthy animals interact with a sick partner, an intriguing question arises: does exposure to a sick conspecific elicit an anticipatory immune response that would facilitate defense against future infection? To address this question, healthy adult male Sprague-Dawley rats (N=64) were given a brief social interaction (30min) with a partner that was either sick (250μg/kg injection with lipopolysaccharide [LPS] 3h prior to test) or healthy (sterile saline injection). During this exposure, social behavior directed toward the healthy or sick conspecific was measured. Additionally, the impact of housing condition was assessed, with rats group- or isolate-housed. Immediately after social interaction, brains were harvested for cytokine assessments within socially-relevant brain structures (olfactory bulb, amygdala, hippocampus and PVN). As expected, behavioral results demonstrated that (i) there was a robust suppression of social interaction directed against sick conspecifics; and (ii) isolate-housing generally increased social behavior. Furthermore, examination of central cytokine expression in healthy experimental subjects revealed a modest increase in TNF-α in rats that interacted with a sick social partner, but only in the olfactory bulb. Among the LPS-injected partners, expected increases in IL-1β, IL-6, and TNF-α expression were observed across all brain sites. Moreover, IL-1β and IL-6 expression was exacerbated in LPS-injected partners that interacted with isolate-housed experimental subjects. Together, these data replicate and extend our prior work showing that healthy rats avoid sick conspecifics, and provide preliminary evidence for an anticipatory cytokine response when rats are exposed to a sick partner. These data also provide new evidence to suggest that recent housing history potently modulates cytokine responses evoked by LPS.

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

Sex differences in the expression of social behavior are typically apparent in adolescent and adult rats. While the neurobiology underlying juvenile social play behavior has been well characterized, less is known about discrete brain regions involved in adult responsiveness to a same sex peer. Furthermore, whether adult males and females differ in their responsiveness to a social interaction in terms of neuronal activation indexed via immediate early gene (IEG) expression remains to be determined. Thus, the present study was designed to identify key sites relevant to the processing of sensory stimuli (generally) or social stimuli (specifically) after brief exposure to a same-sex social partner by assessing IEG expression. Four-month-old male and female Fisher (F) 344 rats (N=38; n=5-8/group) were either left undisturbed in their home cage as controls (HCC), exposed to a testing context alone for 30min (CXT), or were placed in the context for 20min and then allowed to socially interact (SI) with a sex-matched conspecific for 10min. Females demonstrated greater levels of social behavior, relative to males. Analysis of c-Fos induction revealed that females exhibited greater c-Fos expression in the prefrontal cortex, regardless of condition. In many brain regions, induction was similar in the CXT and SI groups. However, in the bed nucleus of the stria terminalis (BNST), females exhibited greater c-Fos induction in response to the social interaction relative to their male counterparts, indicating a sex difference in responsivity to social stimuli. Taken together, these data suggest that the BNST is a sexually dimorphic region in terms of activation in response to social stimuli.

A multispecies approach for understanding neuroimmune mechanisms of stress

The relationship between stress challenges and adverse health outcomes, particularly for the development of affective disorders, is now well established. The highly conserved neuroimmune mechanisms through which responses to stressors are transcribed into effects on males and females have recently garnered much attention from researchers and clinicians alike. The use of animal models, from mice to guinea pigs to primates, has greatly increased our understanding of these mechanisms on the molecular, cellular, and behavioral levels, and research in humans has identified particular brain regions and connections of interest, as well as associations between stress-induced inflammation and psychiatric disorders. This review brings together findings from multiple species in order to better understand how the mechanisms of the neuroimmune response to stress contribute to stress-related psychopathologies, such as major depressive disorder, schizophrenia, and bipolar disorder.

Repeated exposure to two stressors in sequence demonstrates that corticosterone and paraventricular nucleus of the hypothalamus interleukin-1β responses habituate independently

A wide range of stress-related pathologies such as post-traumatic stress disorder are considered to arise from aberrant or maladaptive forms of stress adaptation. The hypothalamic-pituitary-adrenal (HPA) axis readily adapts to repeated stressor exposure, yet little is known about adaptation in neuroimmune responses to repeated or sequential stress challenges. In Experiment 1, rats were exposed to 10 days of restraint alone (60 minutes daily), forced swim alone (30 minutes daily) or daily sequential exposure to restraint (60 minutes) followed immediately by forced swim (30 minutes), termed sequential stress exposure. Habituation of the corticosterone (CORT) response occurred to restraint by 5 days and swim at 10 days, whereas rats exposed to sequential stress exposure failed to display habituation to the combined challenge. Experiment 2 compared 1 or 5 days of forced swim with sequential stress exposure and examined how each affected expression of several neuroimmune and cellular activation genes in the paraventricular nucleus of the hypothalamus (PVN), prefrontal cortex (PFC) and hippocampus (HPC). Sequential exposure to restraint and swim increased interleukin (IL)-1β in the PVN, an effect that was attenuated after 5 days. Sequential stress exposure also elicited IL-6 and tumour necrosis factor-α responses in the HPC and PFC, respectively, which did not habituate after 5 days. Experiment 3 tested whether prior habituation to restraint (5 days) would alter the IL-1β response evoked by swim exposure imposed immediately after the sixth day of restraint. Surprisingly, a history of repeated exposure to restraint attenuated the PVN IL-1β response after swim in comparison to acutely-exposed subjects despite an equivalent CORT response. Overall, these findings suggest that habituation of neuroimmune responses to stress proceeds: (i) independent of HPA axis habituation; (ii) likely requires more daily sessions of stress to develop; and (iii) IL-1β displays a greater tendency to habituate after repeated stress challenges compared to other stress-reactive cytokines.

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

Our work in Sprague Dawley rats has shown rapid alterations in neuroimmune gene expression (RANGE) in the hippocampus and paraventricular nucleus of the hypothalamus (PVN). These manifest as increased interleukin (IL)-6 and IκBα, and suppressed IL-1β and tumor necrosis factor alpha during acute ethanol intoxication. The present studies tested these effects across the lifespan (young adulthood at 2-3 months; senescence at 18 and 24 months), as well as across strain (Fischer 344) and sex. The hippocampus revealed age-dependent shifts in cytokine expression (IL-6, IL-1β, and monocyte chemoattractant protein 1), but no changes were observed in the PVN at baseline or following ethanol. RANGE in adults was similar across sex and comparable with effects seen in Sprague Dawley rats. Plasma corticosterone levels increased with age, whereas the blood ethanol concentrations and loss of righting reflex were similar in all groups older than 2 months. These findings indicate that the RANGE effect is largely conserved across strain and is durable across age, even in the face of a shifting neuroimmune profile that emerges during immunosenescence.

Adolescent Ethanol Exposure Leads to Stimulus-Specific Changes in Cytokine Reactivity and Hypothalamic-Pituitary-Adrenal Axis Sensitivity in Adulthood

Adolescent alcohol use comprises a significant public health concern and is often characterized by binge-like consumption patterns. While ethanol exposure in adulthood has been shown to alter the stress response, including the Hypothalamic–Pituitary–Adrenal (HPA) axis, few studies have examined whether binge-like ethanol exposure during adolescence results in enduring changes in HPA axis sensitivity in adulthood. In the present studies, adolescent Sprague-Dawley rats were given intragastric (i.g.) intubations of ethanol (4 g/kg) or vehicle once per day for three consecutive days, beginning on postnatal day (P) 30 (±1). This exposure was followed by a 2-day period of rest/withdrawal. Rats received a total of either two (Experiments 1, 2 and 3) or four (Experiment 4) cycles of ethanol exposure and were subsequently allowed to age normally until adulthood. In Experiment 1, adult, (P71–75), ethanol- or vehicle-exposed rats received a 60 min restraint stress challenge. In Experiment 2, rats received a 50 μg/kg injection of lipopolysaccharide (LPS). In Experiment 3, rats received a challenge of 2.5 g/kg ethanol (intraperitoneally; i.p.). In Experiment 4, male and female ethanol- or vehicle- exposed rats received a 50 μg/kg injection of LPS. In all experiments, blood samples were collected for later assessment of corticosterone (CORT), blood ethanol concentrations (BECs), and the cellular fraction of blood was analyzed for cytokine gene expression. As expected, all three challenges led to a time-dependent surge in CORT. Gene expression analyses of cytokines (Interleukin [IL]-6, IL-1β, and Tumor necrosis factor alpha [TNFα]) from the cellular fraction of blood revealed unique, time-dependent patterns of cytokine expression depending upon the nature of the adult challenge incurred (restraint, LPS, or EtOH). Importantly, adolescent ethanol exposure led to attenuated restraint and LPS-induced cytokine expression in males, whereas female rats displayed an absence of cytokine alterations, and a tendency toward heightened HPA axis reactivity. These findings suggest that adolescent ethanol exposure may cause lasting alterations in cytokine regulation and HPA axis sensitivity that (a) persist into adulthood; (b) may vary depending on the nature of the challenge incurred during adulthood; and that (c) are sex-specific.

A multispecies approach for understanding neuroimmune mechanisms of stress

The relationship between stress challenges and adverse health outcomes, particularly for the development of affective disorders, is now well established. The highly conserved neuroimmune mechanisms through which responses to stressors are transcribed into effects on males and females have recently garnered much attention from researchers and clinicians alike. The use of animal models, from mice to guinea pigs to primates, has greatly increased our understanding of these mechanisms on the molecular, cellular, and behavioral levels, and research in humans has identified particular brain regions and connections of interest, as well as associations between stress-induced inflammation and psychiatric disorders. This review brings together findings from multiple species in order to better understand how the mechanisms of the neuroimmune response to stress contribute to stress-related psychopathologies, such as major depressive disorder, schizophrenia, and bipolar disorder.

Conditioned effects of ethanol on the immune system

Several studies indicate that the immune system can be subjected to classical conditioning. Acute ethanol intoxication significantly modulates several pro-inflammatory cytokines (e.g. interleukins-1 and 6 [IL-1β and IL-6, respectively] and tumor necrosis factor alpha [TNFα])) in several brain areas, including amygdala (AMG), paraventricular nucleus (PVN), and hippocampus (HPC). It is unknown, however, whether cues associated with ethanol can elicit conditioned alterations in cytokine expression. The present study analyzed, in male Sprague-Dawley rats, whether ethanol-induced changes in the central cytokine response may be amenable to conditioning. In Experiments 1 and 2, the rats were given one or two pairings between a distinctive odor (conditional stimulus, CS) and the post-absorptive effects of a high (3.0 or 4.0 g/kg, Experiments 1 and 2, respectively) ethanol dose. Neither of these experiments revealed conditioning of IL-6, IL-1β, or TNFα, as measured via mRNA levels. Yet, re-exposure to the lemon-odor CS in Experiment 1 significantly increased C-Fos levels in the PVN. In Experiment 3, the rats were given four pairings between an odor CS and a moderate ethanol dose (2.0 g/kg), delivered intraperitoneally (i.p.) or intragastrically (i.g.). Re-exposure to the odor CS significantly increased IL-6 levels in HPC and AMG, an effect only evident in paired rats administered ethanol i.p. Overall, this study suggests that ethanol exposure can regulate the levels of IL-6 at HPC and AMG via classical conditioning mechanisms. These ethanol-induced, conditioned alterations in cytokine levels may ultimately affect the intake and motivational effects of ethanol. Impact statement This study examines, across three experiments, whether odor cues associated with ethanol exposure can condition changes in cytokine expression. The analysis of ethanol-induced conditioning of immune responses is a novel niche that can help understand the transition from social drinking to alcohol abuse and dependence. Ethanol-induced conditioning of the immune system could likely exacerbate neuroinflammation and drug-related toxicity, which in turn may facilitate further engagement in ethanol intake. The main new finding of the present study was that, after four pairings of ethanol's unconditioned effects and a distinctive odor, the latter CS increased IL-6 levels in HPC and AMG. This suggests that ethanol's effects upon IL-6 in HPC and AMG may come under conditioned control, particularly after repeated pairings between distinctive odor cues and ethanol's effects. This article advances our knowledge of conditioned increases in cytokine responses, which should help understand the mechanisms underlying alcohol use, abuse, and relapse.

A users guide to HPA axis research

Glucocorticoid hormones (cortisol and corticosterone - CORT) are the effector hormones of the hypothalamic-pituitary-adrenal (HPA) axis neuroendocrine system. CORT is a systemic intercellular signal whose level predictably varies with time of day and dynamically increases with environmental and psychological stressors. This hormonal signal is utilized by virtually every cell and physiological system of the body to optimize performance according to circadian, environmental and physiological demands. Disturbances in normal HPA axis activity profiles are associated with a wide variety of physiological and mental health disorders. Despite numerous studies to date that have identified molecular, cellular and systems-level glucocorticoid actions, new glucocorticoid actions and clinical status associations continue to be revealed at a brisk pace in the scientific literature. However, the breadth of investigators working in this area poses distinct challenges in ensuring common practices across investigators, and a full appreciation for the complexity of a system that is often reduced to a single dependent measure. This Users Guide is intended to provide a fundamental overview of conceptual, technical and practical knowledge that will assist individuals who engage in and evaluate HPA axis research. We begin with examination of the anatomical and hormonal components of the HPA axis and their physiological range of operation. We then examine strategies and best practices for systematic manipulation and accurate measurement of HPA axis activity. We feature use of experimental methods that will assist with better understanding of CORT's physiological actions, especially as those actions impact subsequent brain function. This research approach is instrumental for determining the mechanisms by which alterations of HPA axis function may contribute to pathophysiology.