Adrenalectomy reduces alcohol-stimulated activity: Blood and brain alcohol content

Role of adrenal glucocorticoid signaling in prefrontal cortex gene expression and acute behavioral responses to ethanol

BACKGROUND

Glucocorticoid hormones modulate acute and chronic behavioral and molecular responses to drugs of abuse including psychostimulants and opioids. There is growing evidence that glucocorticoids might also modulate behavioral responses to ethanol ( EtOH ). Acute EtOH activates the hypothalamic-pituitary-adrenal axis, causing the release of adrenal glucocorticoid hormones. Our prior genomic studies suggest that glucocorticoids play a role in regulating gene expression in the prefrontal cortex (PFC) of DBA2/J (D2) mice following acute EtOH administration. However, few studies have analyzed the role of glucocorticoid signaling in behavioral responses to acute EtOH . Such work could be significant, given the predictive value for the level of response to acute EtOH in the risk for alcoholism.

METHODS

We studied whether the glucocorticoid receptor (GR) antagonist, RU-486, or adrenalectomy (ADX) altered male D2 mouse behavioral responses to acute (locomotor activation, anxiolysis, or loss-of-righting reflex [LORR]) or repeated (sensitization) EtOH treatment. Whole-genome microarray analysis and bioinformatics approaches were used to identify PFC candidate genes possibly responsible for altered behavioral responses to EtOH following ADX.

RESULTS

ADX and RU-486 both impaired acute EtOH (2 g/kg)-induced locomotor activation in D2 mice without affecting basal locomotor activity. However, neither ADX nor RU-486 altered the initiation of EtOH sensitization (locomotor activation or jump counts), EtOH -induced anxiolysis, or LORR. ADX mice showed microarray gene expression changes in PFC that significantly overlapped with acute EtOH -responsive gene sets derived by our prior microarray studies. Q-rtPCR analysis verified that ADX decreased PFC expression of Fkbp5 while significantly increasing Gpr6 expression. In addition, high-dose RU-486 pretreatment blunted EtOH -induced Fkbp5 expression.

CONCLUSIONS

Our studies suggest that EtOH 's activation of adrenal glucocorticoid release and subsequent GR activation may partially modulate EtOH 's acute locomotor activation in male D2 mice. Furthermore, because adrenal glucocorticoid basal tone regulated PFC gene expression, including a significant set of acute EtOH -responsive genes, this suggests that glucocorticoid-regulated PFC gene expression may be an important factor modulating acute behavioral responses to EtOH .

The impact of gonadectomy and adrenalectomy on acute withdrawal severity in male and female C57BL/6J and DBA/2J mice following a single high dose of ethanol

BACKGROUND

Steroid hormones can influence neuronal excitability and subsequent seizure susceptibility through genomic and nongenomic mechanisms. For example, there are proconvulsant steroids such as estradiol and corticosterone and anticonvulsant steroids such as testosterone, progesterone, and their GABAergic metabolites. Recent findings indicated that a single, acute administration of ethanol increased levels of GABAergic steroids and that the source of this increase was peripheral organs such as the adrenals and gonads. Thus, the purpose of the present study was to determine the impact of removal of the adrenals and/or gonads on withdrawal severity following a single high dose of ethanol in 2 genotypes that differ in ethanol withdrawal severity.

METHOD

Male and female C57BL/6J (B6) and DBA/2J (D2) mice were either left intact (SHAM), adrenalectomized (ADX), gonadectomized (GDX), or underwent ADX/GDX surgery. Seven days following surgery, baseline handling-induced convulsions (HICs) were measured prior to administration of a 4 g/kg dose of ethanol. HICs were assessed following the ethanol injection, then hourly for 12 hours and at 24 hours. A separate group of mice were used to measure the impact of surgical status on ethanol metabolism at 30, 60, 120, and 240 minutes after a single 4 g/kg dose of ethanol.

RESULTS

ADX and ADX/GDX treatments in male B6 and D2 mice increased ethanol withdrawal severity following a single dose of ethanol, measured by area under the withdrawal curve and peak HIC scores. Acute ethanol withdrawal also was increased in female D2 mice that had undergone ADX/GDX. In contrast, surgical status did not alter ethanol withdrawal severity in female B6 mice. Surgical status had only minor effects on ethanol metabolism.

CONCLUSIONS

Removal of peripherally derived steroids with anticonvulsant properties significantly increased HIC scores during acute ethanol withdrawal following a single dose of ethanol in male and female D2 mice and in male B6 mice. These increases were not due to changes in ethanol metabolism.

Behavioral sensitization to ethanol: genetics and the effects of stress

Some aspects of drug abuse syndromes may be influenced by sensitization to some drug effects. This enhancement of drug effect has been associated with prior drug exposure and with exposure to stressful stimuli. It has been postulated that sensitization to psychomotor stimulant drug effects influences sensitivity to drug reward. The drugs of abuse best characterized for sensitization phenomena include cocaine, amphetamine, and morphine. In general, ethanol's molecular mechanisms of action have been difficult to define relative to drugs with known receptor or transporter binding sites and, likewise, ethanol sensitization has been less thoroughly examined. Evidence supporting the existence of behavioral sensitization to ethanol, for genetic differences in the occurrence of ethanol sensitization, and for the influence of corticosterone on the development of ethanol sensitization is reviewed herein. There appear to be different genetic determinants of acute drug sensitivity and sensitization. Cross-sensitization between stress and ethanol suggest a potential role for hypothalamic-pituitary-adrenal (HPA) axis associated changes in ethanol sensitization, consistent with mechanisms likely contributing to sensitization to other abused drugs. Furthermore, glucocorticoid receptors appear to mediate both ethanol- and stress-induced sensitization to ethanol. A biological link between drug reward and drug sensitization involving HPA axis hormones may exist and, thus, study of the sensitization process may elucidate mechanisms relevant to drug abuse.

The effects of acute stress on ethanol absorption in LS and SS mice

Previously, our laboratory demonstrated that naive long-sleep (LS) mice absorb ethanol faster than short-sleep (SS) mice when administered 6.0 g/kg ethanol intragastrically (IG). We also demonstrated that the removal of the adrenal glands results in decreased absorption in both lines of mouse. The present study was designed to assess whether acute short-term elevations of corticosterone produced by exposure to a mild stressor could also alter ethanol absorption in LS and SS mice. Because a difference in ethanol absorption rates was observed in LS mice as a function of time of day, all stress experiments were performed in the morning. CCS elevation was induced by exposure to an elevated plus-maze for 45 min. LS mice demonstrated greater CCS release in response to this stressor than SS mice. This exposure to a mild stressor produced an increase in ethanol absorption in both lines of mice receiving a 6.0 g/kg intragastric dose of ethanol. Although this effect of stress on ethanol absorption could be prevented by adrenalectomy in SS mice, adrenalectomy alone did not completely block these effects of stress on ethanol absorption in LS mice. Dexamethasome treatment at the time of adrenalectomy was required to block the effects of stress on ethanol absorption in LS mice. These results suggest that exposure to mild stressors may alter ethanol pharmacokinetic parameters but that genetic factors may play a role in this response via regulation of the hypothalamic-pituitary-adrenal axis.

The rate of ethanol absorption is influenced by corticosterone in long-sleep and short-sleep mice

Ethanol was administered by intragastric (IG) injection and absorption was measured in long-sleep (LS) and short-sleep (SS) mice under various conditions that alter levels of adrenal steroids. In naive mice, LS mice absorbed ethanol more quickly than SS mice. Ethanol absorption was slower in both lines of mice after adrenalectomy (ADX). Short-term inhibition of corticosterone synthesis had no effect on ethanol absorption in either line of mice. The effect of ADX was most pronounced in SS mice at 24 hr after surgery and at 168 hr after surgery in LS mice. Therefore, the effects of various steroid replacements were examined at these times. At 24 hr after ADX, ethanol absorption was replaced to SHAM-operated values in SS mice receiving corticosterone treatments. Likewise, in LS mice at 168 hr after ADX, corticosterone implants reversed the effects of ADX while dexamethasome was ineffective. These results support a role for corticosterone in regulation of gastric ethanol absorption and suggest that the lack of repeatability for pharmacokinetic measures of ethanol absorption and metabolism in previous human and animal studies may relate to environmental impact on stress responses.

Aging: modulation of GABAA binding sites by ethanol and diazepam

Modulation of gamma-aminobutyric acid (GABA) binding to the GABAA recognition site by ethanol and/or diazepam appears to change with the age of the animal. Brain tissue above the cerebellum of young, mature, and old rats was examined for an age-related change in the GABAA recognition sites 5 min after the rat was last habituated or received a single injection of the vehicle, ethanol and/or diazepam. The dose of ethanol injected was reduced in the senescent rats, so the brain levels of ethanol did not vary with age. An injection of ethanol and/or diazepam (180 micrograms/kg) did not significantly alter the GABAA recognition site in any age group relative to the habituated or vehicle-injected rats of that age group. However, the affinity of the GABAA recognition site was decreased by ethanol in mature and old rats relative to the affinity of the GABAA site after diazepam pretreatment in the presence and absence of ethanol, respectively. Finally, the combination of ethanol and diazepam elicited an increase in the number of GABAA binding sites relative to diazepam pretreatment in only the young rats. The present results indicate that the GABAA binding site is modulated by ethanol and diazepam in an age-dependent manner.

Morphometric changes in alcoholic mice of neurons of areas 6 and 17 and ependyma of the subcommissural organ

We have performed a karyometric study of the postnatal development of the subcommissural organ (SOC), the subjacent thalamic ependyma, and the pyramidal neurons of layer V of the motor and visual cortical areas, in alcoholic male albino mice, aged 25-100 days. Ethyl alcohol was added to the drinking water at a concentration of 20%, from birth until the day of sacrifice. Our results show that alcoholism affects the SOC ependyma and the motor cortex, and, apparently, does not affect the ventricular thalamic ependyma and the visual cortex. We suggest a neuroendocrine mechanism to explain the SOC answer, and a functional deprivation to explain the changes in the motor cortex.