Leslie L. Devaud

Gender Impacts Behavioral and Neurochemical Adaptations in Ethanol-Dependent Rats

Previous investigations have found gender differences in the effects of chronic ethanol exposure on ethanol withdrawal behaviors as well as GABA(A) receptor gene expression. The present investigation extended these studies with additional behavioral and neurochemical measures of ethanol dependence and withdrawal. No significant gender differences in the elevated plus-maze assessment of ethanol withdrawal anxiety behaviors were found. However, the neuroactive steroid, 3alpha,5alpha-THP, increased exploratory behavior in ethanol withdrawn female, but not male, rats. GABA(A) receptor binding assays showed potent competition of [35S]TBPS binding by 3alpha,5alpha-THP. Control females displayed a decreased affinity for 3alpha,5alpha-THP compared to control males, as evidenced by a nearly 30% increase in the IC50 value. There was no significant effect of ethanol withdrawal on 3alpha,5alpha-THP modulation of [35S]TBPS binding. However, gender differences were observed in the effects of chronic ethanol exposure on GABA(A) receptor subunit peptide levels in the hypothalamus. Female rats had a significant increase in peptide levels for the alpha2 and alpha3 but not alpha4 subunit, whereas male rats displayed a significant increase in alpha4 and alpha3 but not alpha2 subunits compared to pair-fed control levels. Chronic ethanol-induced alterations in gene expression in the hypothalamus did not coincide with previous findings in the cerebral cortex. In particular, male rats showed an increase in alpha1 subunit peptide levels in the hypothalamus, whereas significant decreases in this subunit have been observed in the cerebral cortex. Both female and male rats showed significant increases in the alpha3 subunit in the hypothalamus but not the cerebral cortex. Taken together, these studies provide additional support for gender-selective effects of chronic ethanol-elicited adaptations at the molecular level.

Gender-selective effects of ethanol dependence on NMDA receptor subunit expression in cerebral cortex, hippocampus and hypothalamus

Previous investigations have shown subunit-selective alterations in NMDA receptors in ethanol dependent male rats. In the present study, we found pronounced gender differences in the effects of ethanol dependence on NMDA receptor subunit expression in all brain regions investigated. Ethanol dependent female rats exhibited increased NR1 subunit levels in cerebral cortex and hypothalamus, whereas males displayed increased NR1 levels only in hippocampus. NR2A subunit levels were significantly increased only in hippocampus from ethanol dependent male rats, whereas NR2B subunit levels significantly increased in cerebral cortex of both female and male rats. These findings suggest that gender influences neuroadaptations elicited by ethanol dependence at the level of NMDA receptor subunit expression.

Differential Effects of Chronic Ethanol Administration and Withdrawal on γ‐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.

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 patients gender and hormonal status.

Differential effects of mild repeated restraint stress on behaviors and GABAA receptors in male and female rats

We previously reported that the very mild stress of individual housing influenced seizure risk and gamma-amino butyric acid (GABA(A)) receptor activity differentially between male and female rats. The aim of the present set of studies was to assess sex differences in behavioral responses to a more pronounced type of stressor, repeated restraint stress. We also wanted to determine the role of GABA(A) receptors in effects of this stressor. Our data suggest that repeated restraint stress afforded short-term protection against seizure induction in both male and female rats. Moreover, this protection was more persistent in female than male rats. This stress paradigm also elicited a reduction in general activity in male rats, whereas female rats displayed prolonged increased activity following the repeated restraint stress exposure. However, there were limited effects on anxiety-like behaviors, as determined by time spent in the open arms on the elevated plus maze. Sex differences in stress-induced increases in plasma corticosterone levels were observed, which generally correlated with sex differences in behavioral measures. There were no significant effects of the repeated restraint stress exposure on benzodiazepine/GABA(A) receptor density or affinity nor on receptor function. Taken together, these findings provide additional evidence to support the important influences of sex in responding to stress and highlight the need to consider this context when addressing the role of stress in health issues for women and men.

Sex differences in effects of mild chronic stress on seizure risk and GABAA receptors in rats.

Social stress is a common occurrence in our society that can negatively impact health. Therefore, we wanted to study the effects of a mild stressor designed to model social stress on seizure susceptibility and GABAA receptors in male and female rats. The mild chronic stress of individual housing consistently decreased bicuculline (but not pentylenetetrazol, PTZ) seizure thresholds by 10-15% in both sexes. Housing conditions did not alter the anticonvulsant activity of diazepam or ethanol, although the anticonvulsant effect of ethanol was significantly greater against PTZ-induced seizures. Experiments testing the addition of an acute restraint stress unmasked sex differences in seizure induction. The acute stress also selectively decreased the potency of GABA to modulate GABAA receptor-mediated chloride uptake in group-housed females. There were additional sex differences by housing condition for GABAA receptor-gated chloride uptake but no differences in [3H]flunitrazepam binding. We also found significant effects of sex and housing on ethanol-induced increases in corticosterone (CORT) levels. In summary, there were complex and sex-selective effects of mild chronic stress on seizure induction and GABAA receptors. Gaining a better understanding of mechanisms underlying interactions between sex and stress has important implications for addressing health concerns about stress in men and women.

Sex Differences in Acoustic Startle Responses and Seizure Thresholds between Ethanol-Withdrawn Male and Female Rats

AIMS We have found consistent and significant sex differences in recovery from the increased seizure susceptibility observed during ethanol withdrawal (EW) in our rat model system. The main objective of the present study was to determine if sex differences in EW generalized to an additional behavioral measure startle reactivity. METHODS Acoustic startle or seizure threshold responses were measured in separate groups of rats at 1 day or 3 days of EW. RESULTS Both pair-fed control and EW males showed greater increases in acoustic startle responses than either the female or ovariectomized female (OVX) counterparts. There was a selective effect of pregnanolone on acoustic startle in that it reduced peak force of response only at 3 days EW in male rats. Unexpectedly, it modestly increased startle reactivity in control female and OVX rats. Acute treatment with low-dose ethanol trended toward reducing startle responses in control animals, as expected, while generally enhancing startle responses during EW. All sex conditions showed an enhanced startle response during EW following administration of the higher dose of estradiol compared to control animals. Estradiol did not alter seizure thresholds in control animals. However, it was anticonvulsant for males at 3 days EW, females and OVX at 1 day EW. CONCLUSIONS Observed sex differences in the startle reactivity during EW were consistent with earlier findings comparing EW seizure risk in male and female rats. Responses of OVX suggested that both hormones and differences in brain structures between males and females have a role in these sex differences. Our findings add weight to recommendations that treatment of alcohol withdrawal in humans should consider hormonal status as well as withdrawal time.

Ovariectomy has minimal effects on neuroadaptations associated with ethanol dependence in female rats.

We previously found gender selective alterations in gene expression for GABA(A) and NMDA receptors associated with the development of ethanol dependence. Males and females have a differing hormonal environment, including steroid hormone derivatives (neuroactive steroids) that exert effects at GABA(A) and NMDA receptors. Therefore, we explored whether the removal of ovarian steroids would alter gender differences in response to chronic ethanol exposure. We found that ovariectomy reduced ethanol drinking levels by 15%, comparable to earlier observations between intact female and male rats. However, investigation of the effects of chronic ethanol exposure on intact versus ovariectomized female rats uncovered few differences in chronic ethanol-induced alterations in selected GABA(A) or NMDA receptor subunit peptide levels. In general, findings for both groups of females were similar to previous observations. There was no reduction in GABA(A) receptor alpha1 subunit levels in cerebral cortex in either intact or ovariectomized female rats, in contrast to the significant reduction observed in male rats. In addition, both intact and ovariectomized female rats had increased levels of the NMDA NR1 subunit in cerebral cortex and hypothalamus, but not in hippocampus, whereas ethanol dependent male rats displayed significant increases in the NR1 subunit only in hippocampus. Radioligand binding analysis with [35S]TBPS found no differences in modulation of the GABA(A) receptor by neuroactive steroids between ethanol dependent male, intact female or ovariectomized female rats. Seizure susceptibility was not different between intact or ovariectomized female rats during ethanol withdrawal. We did observe differential effects on brain allopregnanolone and plasma corticosterone levels between ethanol dependent intact and ovariectomized female rats, suggesting that ovarian steroids influence HPA axis adaptations to prolonged ethanol exposure. Overall, these data suggest that ovarian steroids do not significantly impact the gender selective alterations of GABA(A) and NMDA receptors associated with ethanol dependence.

Altered responses to dizocilpine maleate administration in ethanol-withdrawn male and female rats

Dizocilpine maleate (MK-801) is a highly potent, noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist. Although it has been suggested that dizocilpine may be beneficial in alleviating some symptoms of ethanol withdrawal, a rigorous evaluation of beneficial versus detrimental (phencyclidine-like) actions has not been done. The objective of the present investigation was to explore whether dizocilpine protects against ethanol withdrawal-induced increases in seizure susceptibility without being compromised by its phencyclidine-like behavioral actions. The effects of dizocilpine were assessed by using seizure threshold determinations and scoring of open field behaviors. Low dose dizocilpine administration preferentially protected against bicuculline seizure induction in ethanol-withdrawn female rats when compared with findings in ethanol-withdrawn male rats. In contrast, we found dramatic reductions in dizocilpine-induced open field behaviors during ethanol withdrawal in both male and female rats compared with findings for pair-fed control animals. [3H]MK-801 binding analysis ruled out changes in cerebral cortex or hippocampus receptor density or affinity as having a primary role in these differential responses. Taken together, our findings from these studies indicate that there are complex neuroadaptations in NMDA receptor systems after persistent ethanol exposure, manifested as either enhanced or reduced responses, depending on the measure used.

Influence of hormonal status on behavioral responses to an acute ethanol challenge during ethanol withdrawal in male and female rats

We previously reported significant sex differences in ethanol withdrawal (EW) recovery as well as in sensitivity to GABA(A) receptor modulators during EW. The aim of the present study was to determine if hormonal status moderated behavioral responses to an acute ethanol challenge in EW animals comparing two different behaviors. An initial set of experiments explored motor-incoordinating effects of the acute ethanol injection during EW at either 1 day or 3 days of withdrawal. EW male, but not female, rats showed a decrease in coordination compared to controls that persisted through 3 days EW. Female rats displayed tolerance to the motor-incoordinating actions of the acute ethanol challenge at 1 day EW whereas tolerance was more evident in EW male rats at 3 days. In contrast, EW animals generally remained responsive to the anticonvulsant actions of ethanol, irrespective of hormonal status. While EW by itself did not significantly alter seizure latency, duration or severity, it increased seizure-induced mortality especially at 3 days EW. There was some evidence of tolerance to the anticonvulsant effect of the acute ethanol challenge at the lowest dose employed (0.62 g/kg), which varied by sex condition and time of EW. All sex conditions displayed marked sensitivity to the anticonvulsant effects of the ethanol challenge at the two higher doses studied. Overall, ovariectomized females showed the greatest response to the acute ethanol administration. These findings provide additional evidence of a divergence in behavioral responses during EW and suggest that multiple neuroadaptations moderate various responses to ethanol during EW, with minor contributions of hormonal status.