Role of the GABAA system in behavioral, motoric, and cerebellar protection by estrogen during ethanol withdrawal

A sex difference in oxidative stress and behavioral suppression induced by ethanol withdrawal in rats

Ethanol withdrawal (EW) is referred to the abrupt termination of long-term heavy drinking, and provokes oxidative brain damage. Here, we investigated whether the cerebellum and hippocampus of female rats are less affected by prooxidant EW than male rats due to the antioxidant effect of 17β-estradiol (E2). Female and male rats received a four-week ethanol diet and three-week withdrawal per cycle for two cycles. Some female rats were ovariectomized with E2 or antioxidant (Vitamin E+Co-Q10) treatment. Measurements were cerebellum (Rotarod) and hippocampus (water-maze)-related behaviors, oxidative markers (O2(-), malondialdehyde, protein carbonyls), mitochondrial membrane swelling, and a key mitochondrial enzyme, cytochrome c oxidase (CcO). Separately, HT22 (hippocampal) cells were subjected to ethanol-exposure and withdrawal for two cycles to assess the effect of a CcO inhibitor on E2's protection for mitochondrial respiration and cell viability. Ethanol-withdrawn female rats showed a smaller increase in oxidative markers in cerebellum and hippocampus than male rats, and E2 treatment decreased the oxidative markers. Compared to male counterparts, ethanol-withdrawn female rats showed better Rotarod but poorer water-maze performance, accompanied by more severe mitochondrial membrane swelling and CcO suppression in hippocampus. E2 or antioxidant treatment improved Rotarod but not water-maze performance. In the presence of a CcO inhibitor, E2 treatment failed to protect mitochondrial respiration and cell viability from EW. These data suggest that antioxidant E2 contributes to smaller oxidative stress in ethanol-withdrawn female than male rats. They also suggest that EW-induced severe mitochondrial damage in hippocampus may blunt E2's antioxidant protection for hippocampus-related behavior.

Sex and gender-related differences in alcohol use and its consequences: Contemporary knowledge and future research considerations

AIMS

To review the contemporary evidence reflecting male/female differences in alcohol use and its consequences along with the biological (sex-related) and psycho-socio-cultural (gender-related) factors associated with those differences.

METHODS

MEDLINE, PubMed, Web of Science, SCOPUS, PsycINFO, and CINAHL databases were searched for relevant publications, which were subsequently screened for the presence/absence of pre-specified criteria for high quality evidence.

RESULTS

Compared to men, more women are lifetime abstainers, drink less, and are less likely to engage in problem drinking, develop alcohol-related disorders or alcohol withdrawal symptoms. However, women drinking excessively develop more medical problems. Biological (sex-related) factors, including differences in alcohol pharmacokinetics as well as its effect on brain function and the levels of sex hormones may contribute to some of those differences. In addition, differences in alcohol effects on behavior may also be driven by psycho-socio-cultural (gender-related) factors. This is evident by variation in the magnitude of differences in alcohol use between countries, decreasing difference in the rates of alcohol consumption in recent generations and other findings. Evidence indicates that both sex and gender-related factors are interacting with alcohol use in complex manner, which differentially impacts the risk for development of the behavioral or medical problems and alcohol use disorders in men and women.

CONCLUSIONS

Discovery of the mechanisms underlying biological (sex-related) as well as psycho-socio-cultural (gender-related) differences in alcohol use and related disorders is needed for development of personalized recommendations for prevention and treatment of alcohol use disorders and related problems in men and women.

The cerebellum as a target for estrogen action

This review focuses on the effects of estrogens upon the cerebellum, a brain region long ignored as a site of estrogen action. Highlighted are the diverse effects of estradiol within the cerebellum, emphasizing the importance of estradiol signaling in cerebellar development, modulation of synaptic neurotransmission in the adult, and the potential influence of estrogens on various health and disease states. We also provide new data, consistent with previous studies, in which locally synthesized estradiol modulates cerebellar glutamatergic neurotransmission, providing one underlying mechanism by which the actions of estradiol can affect this brain region.

The effects of pre-pubertal gonadectomy and binge-like ethanol exposure during adolescence on ethanol drinking in adult male and female rats

The pubertal surge in gonadal hormones that occurs during adolescence may impact the long-term effects of early alcohol exposure and sex differences in drinking behavior in adulthood. We investigated this hypothesis by performing sham or gonadectomy surgeries in Long-Evans rats around post-natal day (P) 20. From P35-45, males and females were given saline or 3.0 g/kg ethanol using a binge-like model of exposure (8 injections total). As adults (P100), they were trained to self-administer ethanol via a sucrose-fading procedure and then given access to different unsweetened concentrations (5-20%, w/v) for 5 days/concentration. We found that during adolescence, ethanol-induced intoxication was similar in males and females that underwent sham surgery. In gonadectomized males and females, however, the level of intoxication was greater following the last injection compared to the first. During adulthood, females drank more sucrose per body weight than males and binge-like exposure to ethanol reduced sucrose consumption in both sexes. These effects were not seen in gonadectomized rats. Ethanol consumption was higher in saline-exposed females compared to males, with gonadectomy reversing this sex difference by increasing consumption in males and decreasing it in females. Exposure to ethanol during adolescence augmented ethanol consumption in both sexes, but this effect was statistically significant only in gonadectomized females. Together, these results support a role for gonadal hormones during puberty in the short- and long-term effects of ethanol on behavior and in the development of sex differences in consummatory behavior during adulthood.

Alcohol withdrawal and brain injuries: beyond classical mechanisms

Unmanaged sudden withdrawal from the excessive consumption of alcohol (ethanol) adversely alters neuronal integrity in vulnerable brain regions such as the cerebellum, hippocampus, or cortex. In addition to well known hyperexcitatory neurotransmissions, ethanol withdrawal (EW) provokes the intense generation of reactive oxygen species (ROS) and the activation of stress-responding protein kinases, which are the focus of this review article. EW also inflicts mitochondrial membranes/membrane potential, perturbs redox balance, and suppresses mitochondrial enzymes, all of which impair a fundamental function of mitochondria. Moreover, EW acts as an age-provoking stressor. The vulnerable age to EW stress is not necessarily the oldest age and varies depending upon the target molecule of EW. A major female sex steroid, 17β-estradiol (E2), interferes with the EW-induced alteration of oxidative signaling pathways and thereby protects neurons, mitochondria, and behaviors. The current review attempts to provide integrated information at the levels of oxidative signaling mechanisms by which EW provokes brain injuries and E2 protects against it.

Ethanol withdrawal acts as an age-specific stressor to activate cerebellar p38 kinase

We investigated whether protein kinase p38 plays a role in the brain-aging changes associated with repeated ethanol withdrawal (EW). Ovariectomized young, middle-age and older rats, with or without 17β-estradiol (E2) implantation, received a 90-day ethanol with repeated withdrawal. They were tested for active pP38 expression in cerebellar Purkinje neurons and whole-cerebellar lysates using immunohistochemistry and enzyme-linked immunosorbent assay, respectively. They were also tested for the Rotarod task to determine the behavioral manifestation of cerebellar neuronal stress and for reactive oxygen species (ROS) and mitochondrial protein carbonyls to determine oxidative mechanisms. Middle-age EW rats showed higher levels of pP38-positive Purkinje neurons/cerebellar lysates, which coincided with increased mitochondrial protein oxidation than other diet/age groups. Exacerbated motor deficit due to age-EW combination also began at the middle-age. In comparison, ROS contents peaked in older EW rats. E2 treatment mitigated each of the EW effects to a different extent. Collectively, pP38 may mediate the brain-aging changes associated with pro-oxidant EW at vulnerable ages and in vulnerable neurons in a manner protected by estrogen.

Sex differences in the effect of finasteride on acute ethanol withdrawal severity in C57BL/6J and DBA/2J mice

The neurosteroid allopregnanolone (ALLO) is a potent positive modulator of GABAA receptors that can modulate ethanol (EtOH) withdrawal. The 5alpha-reductase inhibitor finasteride can block the formation of ALLO and other GABAergic neurosteroids and also reduce certain effects of EtOH. Treatment with finasteride during chronic EtOH exposure decreased EtOH withdrawal severity and blood EtOH concentrations (BECs), suggesting an additional effect of finasteride on EtOH pharmacokinetics. Thus, the purpose of the present study was to determine the effect of finasteride on acute EtOH withdrawal severity, to minimize the effect of finasteride on EtOH metabolism. Male and female C57BL/6J and DBA/2J mice received a pretreatment of finasteride (50 mg/kg i.p.) or vehicle 24 h prior to an injection of EtOH (4 g/kg i.p.) or saline. Handling-induced convulsions (HICs) were scored at baseline, and then over a 24 h period after EtOH or saline injection. In another experiment, plasma estradiol and corticosterone levels were assessed at selected time points (0, 2, 8, and 24 h). In a final study, retro-orbital blood samples were collected at 30, 60, 120, and 240 min post-EtOH administration to access finasteride's effects on EtOH clearance parameters. Pretreatment with finasteride increased acute EtOH withdrawal severity in female C57BL/6J and DBA/2J mice but decreased withdrawal severity in male mice of both strains. Finasteride did not alter BECs, EtOH clearance, estradiol, or corticosterone concentrations in a manner that appeared to contribute to the sex difference in finasteride's effect on acute EtOH withdrawal severity. These findings suggest that male and female C57BL/6J and DBA/2J mice differ in their sensitivity to changes in ALLO or other GABAergic neurosteroid levels during acute EtOH withdrawal. Sex differences in the modulation of GABAergic 5alpha-reduced steroids may be an important consideration in understanding and developing therapeutic interventions in alcoholics.

Sex differences in steroid modulation of ethanol withdrawal in male and female rats

We investigated the actions of the neuroactive steroid, pregnanolone [corrected] and the ovarian steroid, 17beta-estradiol, on seizure expression during two time points of ethanol withdrawal (EW). Both steroids can exert rapid, nongenomic actions on the brain that include modulation of seizure activity. Because their basal levels differ in adult males and females and a major symptom of EW is increased seizure risk, we wanted to determine whether these steroids were anticonvulsant during EW. Rats were made ethanol-dependent by administration of 6% ethanol in a nutritionally complete liquid diet for 14 days. After removal of the ethanol-containing diet, EW and paired control rats were tested at 1 or 3 days for seizure responses to pentylenetetrazol. Consistent with previous reports, females seemed to have recovered from EW more quickly than males. We observed significant sex differences in responses to the steroids, primarily at 3 days EW. Pregnanolone afforded protection against seizures with larger effects during EW than in control conditions and greater effects in female than male rats. In contrast, effects of estradiol were mixed. Some responses of ovariectomized female rats were similar to intact females, whereas other responses were more similar to males. Our behavioral findings are consistent with observed EW-induced changes in plasma corticosterone levels, showing persistent elevations in male but not female rats. These results support and extend earlier findings suggesting that although the hormonal milieu influences EW, innate differences in brain structure between the sexes also contribute to sex differences in EW.

Impact of the Hormonal Milieu on the Neurobiology of Alcohol Dependence and Withdrawal

Alcoholism, or alcohol dependence, is a complex disorder with withdrawal symptoms that are often problematic for those trying to recover from their dependence. As researchers attempt to elucidate the neurobiological underpinnings of alcohol dependence and withdrawal, it is becoming clear that numerous factors, including the hormonal environment, impact the manifestations of this disorder. Of particular interest is the observation that women have fewer and less severe withdrawal symptoms than do men even though they tend to suffer greater physiological harm from excessive alcohol consumption. In this article, the authors present an overview of their understanding of how gonadal and stress hormones interact with alcohol, which results in differential neurobiological responses between males and females. Thus far, data generated from representative animal models have shown significant differences between the sexes in behavioral responses and neuroadaptations to chronic alcohol consumption and withdrawal. Accumulating evidence suggests that treatment of alcoholism, including withdrawal, should be tailored to the patient's gender and hormonal status.

Role of parvalbumin in estrogen protection from ethanol withdrawal syndrome

BACKGROUND

Parvalbumin (PA) is a calcium-binding protein that has been implicated in protecting neurons from hyperexcitability by sequestering intracellular calcium. This study examined whether ethanol exposure and/or ethanol withdrawal (EW) alter the levels of PA in a manner that is protected by 17beta-estradiol (E2).

METHODS

Ovariectomized rats implanted with E2 (EW/E2) or oil pellets (EW/Oil) received chronic ethanol (7.5% w/v, 5 weeks) or control dextrin (Dex/Oil and Dex/E2) diets. At 0 hr, 24 hr, and 2 weeks of EW, three brain areas (the cerebellum, hippocampus, and cortex) were prepared for immunoblotting and immunohistological assessment of PA.

RESULTS

At 24 hr of EW, the EW/Oil group showed reduced levels of PA protein and PA-positive neurons in the cerebellum and hippocampus compared with the dextrin control and the EW/E2 groups. At 2 weeks of EW, the reduced levels of PA persisted in the cerebellum but recovered toward the control levels in the hippocampus. The cortex showed no change in PA levels in any of the treatment groups. When tested at 24 hr of EW, the magnitude of EW signs inversely correlated with the levels of PA in the cerebellum and hippocampus. Ethanol exposure itself did not affect PA levels.

CONCLUSION

These data suggest that EW, rather than ethanol exposure, reduces PA levels in a manner that is brain region specific and that is protected by estrogen. Disturbed PA homeostasis is hypothesized to play a role in the hyperexcitability of EW signs.

Differential adaptations in GABAergic and glutamatergic systems during ethanol withdrawal in male and female rats

BACKGROUND

There are significant and consistent sex differences in recovery from ethanol withdrawal in our animal model of ethanol dependence. We have also observed significant and varied sex differences in subunit protein levels of gamma-aminobutyric acid A (GABAA) and the N-metheyl-D-aspartate subtype of glutamate receptors occurring with ethanol dependence and withdrawal. Considering the major role of these two systems as targets of ethanol, we wanted to explore additional possible mechanisms underlying changes in GABAergic and glutamatergic responses after chronic ethanol exposure. Therefore, the objective of the present study was to examine GABAergic- and glutamatergic-associated proteins at three days of ethanol withdrawal, when female rats appear to have largely recovered but male rats still display robust signs of withdrawal.

METHODS

Male and female rats were fed 6% ethanol in a nutritionally complete liquid diet for 14 days according to a pair-fed design; withdrawal was initiated by replacement of the diet with chow. At three days of withdrawal, the cerebral cortex and hippocampus were dissected for use in Western blot analysis. The paired design was maintained throughout all experimental procedures.

RESULTS

At three days of ethanol withdrawal, we found region-specific and sex-selective alterations in levels of GAD (glutamic acid decarboxylase, GABA synthetic enzyme), GABA and glutamate transporters, and the synapse-associated proteins HSP70, PSD-95, and synaptophysin. There were also several significant differences in transporter function at this time that varied between males and females.

CONCLUSIONS

Taken together, these findings show differential adaptations of GABAergic and glutamatergic neurotransmission between female and male rats that are associated with withdrawal recovery. This suggests that selective withdrawal-induced neuroadaptations in regulation of these systems' activities underlie, at least in part, sex differences in withdrawal recovery between male and female rats.

Anxiety, memory impairment, and locomotor dysfunction caused by a mutant thyroid hormone receptor alpha1 can be ameliorated by T3 treatment

The transcriptional properties of unliganded thyroid hormone receptors are thought to cause the misdevelopment during hypothyroidism of several functions essential for adult life. To specifically determine the role of unliganded thyroid hormone receptor alpha1 (TRalpha1) in neuronal tissues, we introduced a mutation into the mouse TRalpha1 gene that lowers affinity to thyroid hormone (TH) 10-fold. The resulting heterozygous mice exhibit several distinct neurological abnormalities: extreme anxiety, reduced recognition memory, and locomotor dysfunction. The anxiety and memory deficiencies were relieved by treatment with high levels of TH in adulthood, an effect that correlated with a normalization of GABAergic inhibitory interneurons in the hippocampal CA1 region. In contrast, a post-natal TH treatment was necessary and sufficient for ameliorating the adult locomotor dysfunction. Here, the hormone treatment normalized the otherwise delayed cerebellar development. The data thus identify two novel and distinct functions of an unliganded TRalpha1 during development and adulthood, respectively.

Role of the GABA-A system in estrogen-induced protection against brain lipid peroxidation in ethanol-withdrawn rats

BACKGROUND

Our previous study showed that 17 beta-estradiol (E2) treatment protects against cerebellar neuronal death and related motor deficits in ethanol-withdrawn rats, in part through the GABAergic system. In this study, we examined the effect of the GABA-A antagonist bicuculline on the neuroprotective effect of E2 by assessing the oxidative marker thiobarbituric acid reactive substances (TBARS) during ethanol withdrawal (EW).

METHODS

Ovariectomized animals that had implants of E2 (EW/E2) or oil (EW/Oil) pellets received liquid ethanol (7.5% w/v) or dextrin for 7 days by gavage. The GABA-A antagonist bicuculline (1.25 mg/kg) was administered (three times a day intraperitoneally) for 4 days starting 3 days before the onset of EW. After testing for overt EW signs at 7 hr of EW, one set of the animals was immediately killed for the collection of the cerebellum, hippocampus, and cortex. The brain homogenates were further processed for TBARS assay to detect TBARS in the presence or absence of FeCl(3). For assessing motor capacity, the other set of animals was tested for the latency to fall from a rotarod after 1 week of EW.

RESULTS

The EW/Oil animals had enhanced endogenous and FeCl(3)-stimulated TBARS levels in the cerebellum and the hippocampus in a manner potentiated by bicuculline but inhibited by E2. Bicuculline counteracted the protective effect of E2 when administered along with E2. Pearson correlation coefficients indicated that the latency to fall from the rotarod covaried with TBARS levels in the cerebellum and the hippocampus.

CONCLUSION

These data suggest that E2 protects against lipid peroxidation in vulnerable brain areas of ethanol-withdrawn rats, in part through the GABAergic system.

Ethanol withdrawal reduces cerebellar parvalbumin expression in a manner reversed by estrogens

Parvalbumin (PA) is a calcium-binding protein that has been implicated in neuroprotection. We examined whether the stimulus effect of ethanol withdrawal (EW) alters the expression of PA in a manner that is prevented by 17beta-estradiol (E2). Ovariectomized rats implanted with E2 (EW/E2) or oil (EW/Oil) pellets received chronic ethanol (7.5%, w/v, 5 weeks) or control dextrin diets (Dex/Oil). At 24h of EW, rats were tested for overt EW signs, and the cerebellum was prepared for immunoblotting and immunohistological assessment for PA. The EW/Oil group showed a higher EW sign score, a lower PA expression, and fewer PA-positive Purkinje neurons than the dextrin control group. In the EW/E2 group, EW sign scores, PA expression, and PA-positive Purkinje neurons were not significantly different from those in the control dextrin group. These data suggest that E2 treatment protects against the PA-suppression associated with EW toxicity.

Estrogen neuroprotection against the neurotoxic effects of ethanol withdrawal: potential mechanisms

Ethanol withdrawal (EW) produces substantial neurotoxic effects, whereas estrogen is neuroprotective. Given observations that both human and nonhuman female subjects often show less impairment following EW, it is reasonable to hypothesize that estrogens may protect females from the neurotoxic effects of ethanol. This article is based on the assumption that the behavioral deficits seen following EW are produced in part by neuronal death triggered by oxidative insults produced by EW. The EW leads to activation of protein kinase C, especially PKCepsilon, which subsequently triggers apoptotic downstream events such as phosphorylation of nuclear factor-kappaB (NFkappaB) complex. On phosphorylation, active NFkappaB translocates to the nucleus, binds to DNA, and activates caspases, which trigger DNA fragmentation and apoptosis. In contrast, estrogens are antioxidant, inhibit overexpression of PKCepsilon, and suppress expression of NFkappaB and caspases. Estrogen treatment reduces the behavioral deficits seen during EW and attenuates molecular signals of apoptosis. The effects of ethanol and estrogen on each step in the signaling cascade from ethanol exposure to apoptosis are reviewed, and potential mechanisms by which estrogen could produce neuronal protection against the neurotoxicity produced by EW are identified. These studies serve as a guide for continuing research into the mechanisms of the neuroprotective effects of estrogen during EW and for the development of potential estrogen-based treatments for male and female alcoholics.

Estrogen protects against brain lipid peroxidation in ethanol-withdrawn rats

This study examined whether 17beta-estradiol (E2) administration protects against ethanol withdrawal (EW)-associated oxidative insults by assessing oxidative markers thiobarbituric-acid-reacting-substances (TBARS). Ovariectomized rats implanted with E2 (EW/E2) or oil pellets (EW/Oil) received chronic ethanol (7.5% wt./vol., 5 weeks) or control dextrin diet (Dextrin/Oil). At 24 or 48 h of EW, rats were tested for overt EW signs and the cerebellum, hippocampus, and cortex were prepared for TBARS assessment in the presence and absence of FeCl3. For control experiments, we assessed E2 effects on blood ethanol concentrations and TBARS levels during ethanol exposure prior to EW. The EW/Oil group showed enhanced endogenous- and FeCl3-stimulated membrane TBARS levels in the cerebellum and hippocampus in a manner inhibited by E2 treatment. There was a relationship between the severity of EW and elevation of TBARS levels, particularly in the cerebellum. The enhanced TBARS levels at 24 h of EW appeared to diminish at 48 h in the hippocampus, but persisted in the cerebellum. E2 treatment did not alter blood ethanol concentrations and ethanol exposure alone did not enhance TBARS levels. These data suggest that EW rather than ethanol enhances brain lipid peroxidation that is transient and brain-region specific. Estrogens protect against the brain lipid peroxidation in a manner independent of blood ethanol concentrations.

Differential effects of chronic ethanol administration and withdrawal on gamma-aminobutyric acid type A and NMDA receptor subunit proteins in male and female rat brain

BACKGROUND

Investigations have shown that chronic ethanol exposure results in selective alterations in levels of gamma-aminobutyric acid (GABA)A and NMDA receptor subunits. We previously reported significant sex differences in these chronic ethanol-induced adaptations. Because we have more recently found important sex differences in timing for the development of and recovery from ethanol dependence, we wanted to ascertain whether there were associations between overt expression of withdrawal and neuroadaptations at the level of GABAA and NMDA receptors.

METHODS

Western blot analysis was used to assay protein levels for several GABAA and NMDA receptor subunits in rat cerebral cortex and hippocampus by using subunit-selective antibodies. Rats were fed 6% ethanol in a liquid diet with pair-fed controls. Feeding, harvesting of tissue, and Western blot experiments were all conducted while maintaining the paired design. Tissue was harvested after 3 days of ethanol exposure, 9 days of ethanol exposure, or 3 days of ethanol withdrawal after 14 days of liquid diet administration.

RESULTS

We again found sex-, subunit-, and brain region-selective effects of ethanol administration and withdrawal for GABAA and NMDA receptors. There was a strong association between increased GABAA receptor alpha4 subunit levels and previously determined withdrawal-induced changes in seizure susceptibility, highlighted by the sex differences in ethanol exposure length required to cause withdrawal signs. In addition, results obtained after 9 days of ethanol administration were in general agreement with previous findings after 14 days of ethanol administration.

CONCLUSIONS

These data further support the suggestion that alterations in subunit assembly of GABAA and NMDA receptors may have some mechanistic role in neuroadaptations underlying ethanol dependence and withdrawal. Furthermore, significant sex differences in these adaptations suggest that multiple types of adaptations may be elicited, depending on innate differences in the actions/effects of ethanol.