Age differences in the expression of acute and chronic tolerance to ethanol in male and female rats

Voluntary wheel running exercise rescues behaviorally-evoked acetylcholine efflux in the medial prefrontal cortex and epigenetic changes in ChAT genes following adolescent intermittent ethanol exposure

Adolescent intermittent ethanol (AIE) exposure, which models heavy binge ethanol intake in adolescence, leads to a variety of deficits that persist into adulthood-including suppression of the cholinergic neuron phenotype within the basal forebrain. This is accompanied by a reduction in acetylcholine (ACh) tone in the medial prefrontal cortex (mPFC). Voluntary wheel running exercise (VEx) has been shown to rescue AIE-induced suppression of the cholinergic phenotype. Therefore, the goal of the current study is to determine if VEx will also rescue ACh efflux in the mPFC during spontaneous alternation, attention set shifting performance, and epigenetic silencing of the cholinergic phenotype following AIE. Male and female rats were subjected to 16 intragastric gavages of 20% ethanol or tap water on a two-day on/two-day off schedule from postnatal day (PD) 25-54, before being assigned to either VEx or stationary control groups. In Experiment 1, rats were tested on a four-arm spontaneous alternation maze with concurrent in vivo microdialysis for ACh in the mPFC. An operant attention set-shifting task was used to measure changes in cognitive and behavioral flexibility. In Experiment 2, a ChIP analysis of choline acetyltransferase (ChAT) genes was performed on basal forebrain tissue. It was found that VEx increased ACh efflux in the mPFC in both AIE and control male and female rats, as well as rescued the AIE-induced epigenetic methylation changes selectively at the Chat promoter CpG island across sexes. Overall, these data support the restorative effects of exercise on damage to the cholinergic projections to the mPFC and demonstrate the plasticity of cholinergic system for recovery after alcohol induced brain damage.

Age-related differences in the effect of chronic alcohol on cognition and the brain: a systematic review

Adolescence is an important developmental period associated with increased risk for excessive alcohol use, but also high rates of recovery from alcohol use-related problems, suggesting potential resilience to long-term effects compared to adults. The aim of this systematic review is to evaluate the current evidence for a moderating role of age on the impact of chronic alcohol exposure on the brain and cognition. We searched Medline, PsycInfo, and Cochrane Library databases up to February 3, 2021. All human and animal studies that directly tested whether the relationship between chronic alcohol exposure and neurocognitive outcomes differs between adolescents and adults were included. Study characteristics and results of age-related analyses were extracted into reference tables and results were separately narratively synthesized for each cognitive and brain-related outcome. The evidence strength for age-related differences varies across outcomes. Human evidence is largely missing, but animal research provides limited but consistent evidence of heightened adolescent sensitivity to chronic alcohol's effects on several outcomes, including conditioned aversion, dopaminergic transmission in reward-related regions, neurodegeneration, and neurogenesis. At the same time, there is limited evidence for adolescent resilience to chronic alcohol-induced impairments in the domain of cognitive flexibility, warranting future studies investigating the potential mechanisms underlying adolescent risk and resilience to the effects of alcohol. The available evidence from mostly animal studies indicates adolescents are both more vulnerable and potentially more resilient to chronic alcohol effects on specific brain and cognitive outcomes. More human research directly comparing adolescents and adults is needed despite the methodological constraints. Parallel translational animal models can aid in the causal interpretation of observed effects. To improve their translational value, future animal studies should aim to use voluntary self-administration paradigms and incorporate individual differences and environmental context to better model human drinking behavior.

Interactive Effects of Ethanol and HIV-1 Proteins on Novelty-Seeking Behaviors and Addiction-Related Gene Expression

BACKGROUND

Novelty-seeking behavior is related to the reward system in the brain and can predict the potential for addiction. Alcohol use is prevalent in HIV-1-infected patients and adversely affects antiretroviral medication. The difference in vulnerability to alcohol addiction between HIV-1-infected and noninfected populations has not been fully investigated. This study was designed to determine whether HIV-1 proteins alter the effects of ethanol (EtOH) on novelty-seeking behavior using the HIV-1 transgenic (HIV-1Tg) rat as the study model and to examine the molecular mechanisms responsible for this behavior.

METHODS

Both HIV-1Tg and F344 control rats were tested for baseline novelty-seeking behavior, then received either EtOH (1 g/kg) at a concentration of 20% v/v or saline treatment for 13 days, and then were retested for novelty seeking. Quantitative real-time polymerase chain reaction was conducted to examine the differences in expression of 65 genes implicated in novelty seeking and alcohol addiction between strains and treatment groups.

RESULTS

The HIV-1 proteins significantly enhanced baseline novelty-seeking behaviors in both the hole-board and open-field tests. Chronic EtOH treatment significantly increased baseline novelty-seeking behavior in both strains, but the effects of EtOH appeared to be more robust and prominent in HIV-1Tg rats. Strain-specific patterns of altered gene expression were observed for dopaminergic, cholinergic, and glutamatergic signaling in the nucleus accumbens, suggesting the effects of HIV-1 proteins on the brain's reward system. Chronic EtOH treatment was shown to greatly modulate the effects of HIV-1 proteins in these neurotransmitter systems.

CONCLUSIONS

Taken together, our findings indicate that HIV-1 proteins could modify novelty-seeking behavior at the gene expression level, and EtOH treatment may enhance this behavior in both strains but to a greater extent in HIV-1Tg rats.

Sex, strain, and estrous cycle influences on alcohol drinking in rats

Although women appear to be more vulnerable to alcohol-induced pathophysiology than men, the neurobiological basis for sex differences is largely unknown, partially because most studies on alcohol drinking are conducted in male subjects only. The present study examined sex differences in alcohol consumption in two rat strains, Long Evans and Wistar, using multiple behavioral paradigms. The effects of the estrous cycle on alcohol consumption were monitored throughout the study. The results indicated that females drank more alcohol than males when given either continuous or intermittent access to alcohol (vs. water) in their home cages (voluntary drinking). Under operant conditions, no sex or strain differences were found in drinking prior to development of alcohol dependence. However, upon dependence induction by chronic, intermittent alcohol vapor exposure, Wistar rats of both sexes substantially escalated their alcohol intake compared with their nondependent drinking levels, whereas Long Evans rats only exhibited a moderate escalation of drinking. Under these conditions, the estrous cycle had no effect on alcohol drinking in any strain and drinking model. Thus, strain, sex, and drinking conditions interact to modulate nondependent and dependent alcohol drinking. The present results emphasize the importance of including sex and strain as biological variables in exploring individual differences in alcohol drinking and dependence.

Effects of acute ethanol exposure on anxiety measures and epigenetic modifiers in the extended amygdala of adolescent rats

Epigenetic mechanisms appear to play an important role in neurodevelopment. We investigated the effects of acute ethanol exposure on anxiety measures and function of histone deacetylases (HDAC) and DNA methyltransferases (DNMT) in the amygdala and bed nucleus of stria terminalis (BNST) of adolescent rats. One hour after ethanol exposure, rats were subjected to anxiety measures. A subset of adolescent rats was exposed to two doses (24 h apart) of ethanol (2 g/kg) to measure rapid ethanol tolerance to anxiolysis. The HDAC and DNMT activities and mRNA levels of DNMT isoforms were measured in the amygdala and BNST. The lower dose of ethanol (1 g/kg) produced neither anxiolysis, nor inhibited the HDAC and DNMT activities in the amygdala and BNST, except DNMT activity in BNST was attenuated. Anxiolysis by ethanol was observed at 2 and 2.25 g/kg, whereas higher doses (2.5 and 3 g/kg) were found to be sedative. DNMT activity in the amygdala and BNST, and nuclear HDAC activity in the amygdala, but not in the BNST were also inhibited by these doses of ethanol. A lack of tolerance was observed on ethanol-induced inhibition of DNMT activity in the amygdala and BNST, and nuclear HDAC activity in the amygdala, as well to anxiolysis produced by ethanol (2 g/kg). The DNMT1, DNMT3a, and DNMT3b mRNA expression in the amygdala was not affected by either 1or 2 doses of 2 g/kg. However, DNMT1 and DNMT3a expression in the BNST was increased, whereas DNMT3l mRNA was decreased in the amygdala, after 2 doses of 2 g/kg ethanol. These results suggest that reduced sensitivity to anxiolysis and the lack of rapid tolerance to the anxiolytic effects of ethanol and inhibition of HDAC and DNMT functions may play a role in engaging adolescents in binge drinking patterns.

The effects of an acute challenge with the NMDA receptor antagonists, MK-801, PEAQX, and ifenprodil, on social inhibition in adolescent and adult male rats

RATIONALE

NMDA antagonists consistently produce social inhibition in adult animals, although effects of these manipulations on social behavior of adolescents are relatively unknown.

OBJECTIVES

The aim of this study was to assess potential age differences in the socially inhibitory effects of the non-competitive NMDA antagonist, MK-801, as well as NR2 subunit selective effects, given the regional and developmental differences that exist for the NR2 subunit during ontogeny.

METHODS

In separate experiments, adolescent and adult male Sprague-Dawley rats were treated acutely with MK-801 (0, 0.05, 0.1, 0.2 mg/kg, i.p.), the NR2A antagonist, PEAQX (2.5, 5, 10, 20 mg/kg, s.c.), or the NR2B antagonist, ifenprodil (1.5, 3, 6, 12 mg/kg, i.p.), 10 min prior to a social interaction test.

RESULTS

Adolescents required higher doses of MK-801 (0.1 and 0.2 mg/kg) to induce social suppression, whereas adults demonstrated reductions in social activity after all doses. Likewise, adolescents required higher doses of ifenprodil (6 and 12 mg/kg) to produce social inhibitory effects relative to adults (all doses). In contrast, adults were less sensitive to PEAQX than adolescents, with adults showing social inhibition after 20 mg/kg whereas adolescents showed this effect following 10 and 20 mg/kg. Although locomotor activity was generally reduced at both ages by all drugs tested, ANCOVAs using locomotor activity as a covariate revealed similar patterns of social inhibitory effects.

CONCLUSIONS

Adolescents are less sensitive than adults to the disruption of social behavior by NMDA and NR2B-selective receptor antagonism, but not by an NR2A antagonist-age differences that may be related to different subunit expression patterns during development.

The developmental psychopathology of alcohol use and alcohol disorders: research achievements and future directions

The last 25 years have seen significant advances in our conceptualization of alcohol use and alcohol use disorders within a developmental framework, along with advances in our empirical understanding that have been potentiated by advances in quantitative methods. These include advances in understanding the heterogeneity of trajectories of alcohol outcomes; new insights about early childhood antecedents, and adolescence and emerging adulthood as important developmental periods for alcohol outcomes; a more nuanced understanding of the influences of developmental transitions, and their timing and contexts; a greater appreciation for the importance of considering multiple levels of analysis (including an increasing number of genetically informative studies); a continuing focus on studying multiple pathways underlying alcohol outcomes; and an increasing focus on studying the effects of alcohol exposure on future development. The current paper reviews these advances and suggests directions for future study.

The developmental psychopathology of alcohol use and alcohol disorders: research achievements and future directions

The last 25 years have seen significant advances in our conceptualization of alcohol use and alcohol use disorders within a developmental framework, along with advances in our empirical understanding that have been potentiated by advances in quantitative methods. These include advances in understanding the heterogeneity of trajectories of alcohol outcomes; new insights about early childhood antecedents, and adolescence and emerging adulthood as important developmental periods for alcohol outcomes; a more nuanced understanding of the influences of developmental transitions, and their timing and contexts; a greater appreciation for the importance of considering multiple levels of analysis (including an increasing number of genetically informative studies); a continuing focus on studying multiple pathways underlying alcohol outcomes; and an increasing focus on studying the effects of alcohol exposure on future development. The current paper reviews these advances and suggests directions for future study.

Heavy ethanol intoxication increases proinflammatory cytokines and aggravates hemorrhagic shock-induced organ damage in rats

Hemorrhagic shock (HS) following acute alcohol intoxication can increase proinflammatory cytokine production and induce marked immunosuppression. We investigated the effects of ethanol on physiopathology and cytokine levels following HS in acutely alcohol-intoxicated rats. Rats received an intravenous injection of 5 g/kg ethanol over 3 h followed by HS induced by withdrawal of 40% of total blood volume from a femoral arterial catheter over 30 min. Mean arterial pressure (MAP) and heart rate (HR) were monitored continuously for 48 h after the start of blood withdrawal. Biochemical parameters, including hemoglobin, ethanol, glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), blood urea nitrogen (BUN), creatinine (Cre), lactic dehydrogenase (LDH), and creatine phosphokinase (CPK), were measured at 30 min before induction of HS and 0, 1, 3, 6, 9, 12, 18, 24, and 48 h after HS. Serum tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels were measured at 1 and 12 h after HS. The liver, kidneys, and lungs were removed for pathology at 48 h later. HS significantly increased HR, blood GOT, GPT, BUN, Cre, LDH, CPK, TNF-α, and IL-6 levels and decreased hemoglobin and MAP in rats. Acute ethanol intoxication further increased serum levels of GOT, GPT, BUN, Cre, LDH, CPK, TNF-α and IL-6 elevation following HS. Acutely intoxicated rats exacerbated the histopathologic changes in the liver, kidneys, and lungs following HS.

Effects of the kappa opioid receptor antagonist, nor-binaltorphimine, on ethanol intake: impact of age and sex

The kappa opioid receptor (KOR) antagonist, nor-binaltorphimine (nor-BNI), was used to investigate the role of the KOR system in mediating ethanol intake. On P25 (adolescent) or P67 (adult) male and female rats were individually housed and given ad libitum access to food and water. The experimental procedure was initiated on P28 or P70: animals were given 30 min/day access to a 10% ethanol/supersaccharin solution every other day (3 baseline exposures). On the day after the final baseline test, rats were injected with nor-BNI (0, 2.5, 5, 10 mg/kg), with testing initiated 24 hr later (30-min access every other day, 3 test exposures). Nor-BNI (10 mg/kg) increased ethanol intake in adult males, whereas the same dose decreased intake in adult females, suggesting pronounced sex differences in KOR-associated mediation of ethanol intake in adulthood. There was no impact of nor-BNI in adolescent animals of either sex, suggesting that the KOR may play less of a role in modulating ethanol intake during adolescence.

Anxiolytic effects of the GABA(A) receptor partial agonist, L-838,417: impact of age, test context familiarity, and stress

The partial α2,3,5 GABA(A) receptor agonist, L-838,417 has been reported to have anxiolytic effects in adult rodents. Although maturational differences exist for the GABA(A) receptor subunits, the anxiolytic effects of L-838,417 have not been tested in younger animals. The goal of the present experiments was to determine whether L-838,417 reverses anxiety-like behavior induced by either an unfamiliar environment (Experiment 1) or repeated restraint stress (Experiment 2) differentially in adolescent and adult, male and female Sprague-Dawley rats using a modified social interaction test. In Experiment 1, rats were injected with 0, 0.5, 1.0, 2.0, or 4.0 mg/kg L-838,417, i.p. and tested 30 min later in an unfamiliar test context for 10 min. In Experiment 2, rats were exposed to restraint stress (90 min daily for 5 days). Immediately after the last restraint session, animals were injected with L-838,417 and placed alone for 30 min in the test apparatus to familiarize them to this context prior to the 10 min social interaction test. In Experiment 1, L-838,417 produced anxiolytic effects in adults at 1.0 mg/kg, as indexed by a transformation of social avoidance into preference and an increase in social investigation. In adolescents, a dose of 2.0 mg/kg eliminated social avoidance, but had no anxiolytic effects on social investigation. Testing under familiar circumstances (Experiment 2) after repeated restraint stress eliminated age differences in sensitivity to L-838,417, with 0.5 mg/kg reversing the anxiogenic effects of prior stress regardless of age, but with doses ≥ 1 mg/kg decreasing social investigation, an effect possibly due in part to locomotor-impairing effects of this compound. Although locomotor activity was suppressed in both experiments, higher doses of L-838,417 were necessary to suppress locomotor activity in Experiment 1. Thus, anxiolytic effects of L-838,417 were found to be context-, age-, and stress-dependent.

The influence of acute and chronic alcohol consumption on response time distribution in adolescent rhesus macaques

BACKGROUND

Analysis of the distribution of reaction times (RTs) in behavioral tasks can illustrate differences attributable to changes in attention, even when no change in mean RT is observed. Detrimental attentional effects of both acute and chronic exposure to alcohol may therefore be revealed by fitting RT data to an ex-Gaussian probability density function which identifies the proportion of long-RT responses.

METHODS

Adolescent male rhesus macaques completed a 5-choice serial reaction time task (5CSRT) after acute alcohol consumption (up to 0.0, 1.0 and 1.5 g/kg). Monkeys were next divided into chronic alcohol (N = 5) and control groups (N = 5); the experimental group consumed 1.5-3.0 g/kg alcohol for 200 drinking sessions. Unintoxicated performance in the 5CSRT task was determined systematically across the study period and the effect of acute alcohol was redetermined after the 180th drinking session. The effect of extended abstinence from chronic alcohol was determined across 90 days.

RESULTS

Acute alcohol exposure dose-dependently reduced the probability of longer RT responses without changing the mean or the standard deviation of the RT distribution. The RT distribution of control monkeys tightened across 10 months whereas that of the chronic alcohol group was unchanged. Discontinuation from chronic alcohol increased the probability of long RT responses with a difference from control animals observed after 30 days of discontinuation.

CONCLUSIONS

Alcohol consumption selectively affected attention as reflected in the probability of long RT responses. Acute alcohol consumption focused attention, chronic alcohol consumption impaired the maturation of attention across the study period and alcohol discontinuation impaired attention.

Effects of ethanol during adolescence on the number of neurons and glia in the medial prefrontal cortex and basolateral amygdala of adult male and female rats

Human adolescents often consume alcohol in a binge-like manner at a time when changes are occurring within specific brain structures, such as the medial prefrontal cortex (mPFC) and the basolateral nucleus of the amygdala (BLN). In particular, the number of neurons and glia is changing in both of these areas in the rat between adolescence and adulthood (Markham et al., 2007; Rubinow and Juraska, 2009). The current study investigated the effects of ethanol exposure during adolescence on the number of neurons and glia in the adult mPFC and BLN in Long-Evans male and female rats. Saline or 3g/kg ethanol was administered between postnatal days (P) 35-45 in a binge-like pattern, with 2days of injections followed by 1 day without an injection. Stereological analyses of the ventral mPFC (prelimbic and infralimbic areas) and the BLN were performed on brains from rats at 100 days of age. Neuron and glia densities were assessed with the optical disector and then multiplied by the volume to calculate the total number of neurons and glia. In the adult mPFC, ethanol administration during adolescence resulted in a decreased number of glia in males, but not females, and had no effect on the number of neurons. Adolescent ethanol exposure had no effects on glia or neuron number in the BLN. These results suggest that glia cells in the prefrontal cortex are particularly sensitive to binge-like exposure to ethanol during adolescence in male rats only, potentially due to a decrease in proliferation in males or protective mechanisms in females.