Adrenal glucocorticoids as a required factor in the development of ethanol withdrawal seizures in mice

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.

Adrenalectomy prevents the development of alcohol preference in male rats

By forcing adrenalectomized (ADX) and sham-operated (SHAM) rats to chronically drink ethanol by mean of presentation of only one drinking bottle containing 10% ethanol, no differences occurred between both groups. ADX and SHAM rats were then exposed to chronic alcoholization using an inhalation procedure. After sejourning 3 weeks into the alcoholization chamber, rats were submitted to a free-choice paradigm [water vs. a 10% (v/v) ethanol solution]. The sham-operated rats presented an alcohol-induced behavioral preference towards alcohol whereas adrenalectomized animals never exhibited a preference to ethanol. In the adrenalectomized rats treatment with hydrocortisone (30 micrograms/ml) given orally during the pulmonary alcoholization failed to modify this preference whereas treatment with corticosterone (25 micrograms/ml) given orally abolished the difference with SHAM animals. These data showed that adrenalectomy prevented the development of ethanol preference and the clear involvement of the hypothalamo-pituitary-axis in alcohol preference.

Sensitivity of the circadian rhythm of kainic acid-induced convulsion susceptibility to manipulations of corticosterone levels and mineralocorticoid receptor binding

Increases in corticosterone levels have been associated with enhanced susceptibility and decreases in corticosterone levels have been associated with decreased susceptibility to convulsions in mice. The proconvulsant effects of corticosterone are believed to be mediated by central mineralocorticoid receptors (MR). Both convulsion susceptibility and plasma corticosteroid levels display circadian rhythmicity. When corticosterone levels are at their lowest, hippocampal MR binding is submaximal, whereas when corticosterone levels are at their circadian peak, hippocampal MR binding is maximal. In the present experiments the relationship between circadian rhythms of susceptibility to kainic acid-induced convulsions and plasma corticosterone levels was investigated. In addition, the effects of exogenously administered corticosterone and the MR antagonist spironolactone were examined at times of different convulsion susceptibility. In general, lower plasma corticosterone levels were associated with decreased convulsion susceptibility and higher plasma corticosterone levels were associated with greater convulsion susceptibility. Corticosterone, administered when endogenous levels were low, had a proconvulsant effect. Spironolactone, administered when corticosterone levels were higher and hippocampal MR were presumably maximally occupied, had an anticonvulsant effect. These results indicate that the circadian rhythm in susceptibility to kainic acid-induced convulsions is sensitive to manipulations of corticosterone levels and MR binding. Degree of central MR occupancy may, in part, mediate convulsion susceptibility in humans as well as laboratory animals.

Corticosterone increases severity of acute withdrawal from ethanol, pentobarbital, and diazepam in mice

It has been suggested that withdrawal from several subclasses of central nervous system (CNS) depressants involves common underlying mechanisms. For example, mice genetically selected for severe ethanol withdrawal convulsions (Withdrawal Seizure Prone or WSP) have also been found to express severe withdrawal following treatment with barbiturates and benzodiazepines. Corticosteroids appear to modulate severity of withdrawal from CNS depressants. Therefore, it was hypothesized that corticosterone would enhance withdrawal convulsions following acute ethanol, pentobarbital, and diazepam in WSP mice. Corticosterone (20 mg/kg) administered following each of these drugs significantly increased severity of handling-induced convulsions during withdrawal. Corticosterone did not affect pre-withdrawal convulsion scores or handling-induced convulsions of drug-naive mice. These results suggest that withdrawal convulsions following acute ethanol, pentobarbital, and diazepam are sensitive to modulation by corticosterone and they support the hypothesis that stress may increase drug withdrawal severity.

Are binge drinkers more at risk of developing brain damage?

Alcoholism is often associated with brain damage and cognitive deficits. Because drinking patterns can include periods of alcohol consumption followed by abstinence, binge drinking may enhance the possibility of brain damage. Chronic administration of ethanol leads to upregulation of N-methyl-D-aspartate (NMDA) and calcium receptors and increased release of glucocorticoids. NMDA-mediated mechanisms and glucocorticoid actions on the hippocampus are associated with brain damage. Thus, ethanol withdrawal may make the brain more vulnerable to damage from these mechanisms, especially with binge drinking. Therapeutic adjuncts for treating ethanol withdrawal, including NMDA, calcium, and glucocorticoid antagonists, may eventually prove useful in preventing further brain damage in alcoholism.

Type I corticosteroid receptors modulate PTZ-induced convulsions of withdrawal seizure prone mice

Corticosteroids have been shown to modulate convulsion expression in humans and animals. It is hypothesized that type I corticosteroid receptors mediate the excitatory effects of corticosteroids in vivo based on low-dose efficacy of corticosterone, and differential effects of mineralocorticoids vs. glucocorticoids on convulsions. In the present experiments, the effects of altering corticosterone levels, and the role of the type I receptor in mediating these effects, were examined using pentylenetetrazol (PTZ)-induced convulsions in ethanol withdrawal seizure prone (WSP) mice. It was hypothesized that stimulation of type I receptors partially mediates the expression of tonic hindlimb extensor (THE) convulsions produced by PTZ. Aminoglutethimide, a steroid synthesis inhibitor, increased latencies to PTZ-induced THE. This anticonvulsant effect was reversed by corticosterone and the type I agonist, deoxycorticosterone (DOC), but not by the type II agonist, dexamethasone. Furthermore, two type I receptor antagonists, spironolactone and RU26752, increased latencies to PTZ-induced THE, suggesting that they have anticonvulsant action. In summary, the results of these experiments suggest that type I corticosteroid receptors are important for expression of PTZ-induced convulsions.

Genetic differences in hypothalamic-pituitary-adrenal axis responsiveness to acute ethanol and acute ethanol withdrawal

There is a growing body of evidence suggesting that corticosteroids contribute to the increased neural excitability observed during ethanol withdrawal. In the present study, this was further investigated using mouse strains which differ in ethanol withdrawal severity. DBA/2 (DBA) mice were found to display more severe acute ethanol withdrawal seizures than C57BL/6 (C57) mice. Additionally, DBA mice showed a greater stress response than C57 mice, as measured by higher plasma concentrations of adrenocorticotropic hormone (ACTH) and corticosterone, to an acute dose of ethanol. Mimicking withdrawal plasma corticosterone levels by administering corticosterone to ethanol-naive mice resulted in increases in handling-induced convulsions in the range observed during withdrawal. There did not appear to be a strain difference in sensitivity to the excitatory effects of corticosterone. In summary, the greater stress response to ethanol by DBA mice may account, in part, for the more severe ethanol withdrawal syndrome of this strain.

Differential modulation by the stress axis of ethanol withdrawal seizure expression in WSP and WSR mice

Withdrawal from both acute and chronic ethanol (EtOH) exposure is associated with increased neural excitability and increased activity of the hypothalamic-pituitary-adrenal axis. There is some evidence that glucocorticoids are necessary for EtOH withdrawal seizure expression. Lines of mice that were selected for severe (WSP) and minimal (WSR) EtOH withdrawal (as estimated from handling-induced convulsion scores) have been shown to differ in their stress response following an acute dose of EtOH. In this study we provide evidence that these lines of mice also differ in their sensitivity to the excitatory effects of glucocorticoids. EtOH withdrawal seizures of WSP mice were significantly increased by chronic and acute corticosterone treatment, whereas those of the WSR mice were unaffected. Neural excitability was decreased in the WSP mice when aminoglutethimide, a glucocorticoid synthesis blocker, was administered. Thus, it appears that genetic differences in EtOH withdrawal seizure severity may be due, in part, to differences in sensitivity to the excitatory effects of glucocorticoids.

Pharmacological effects of phenylalanine on seizure susceptibility: an overview

The effects of excessive doses of phenylalanine on seizure susceptibility were examined in animal models in the past, primarily because of their relevance to phenylketonuria. It was thought that such effects might involve brain monoaminergic mechanisms. Recently, this issue has been pursued with a renewed interest but for a different reason. The dipeptide sweetener, aspartame, contains a phenylalanine residue. In the last three years, a number of studies involving as many as nine animal models of seizures have reexamined the effects of phenylalanine (and aspartame) on seizure thresholds. Data from these studies are in general agreement that aspartame at dosage levels below 1,000 mg/kg, or phenylalanine at equimolar doses, is without an effect on seizure susceptibility in animals. When the dosage level of aspartame reaches 1,000 mg/kg, the findings between various laboratories and from different animal models of seizures are inconsistent, showing either no effect or a proconvulsant effect. The Acceptable Daily Intake of aspartame in humans set by the Food and Drug Administration is 50 mg/kg/day. Thus, the data from the excessive bolus doses in rodents do not appear to be relevant to human use. This article provides a detailed review of the data from both early and recent studies and points out the methodological problems apparent at such high doses.

Benzodiazepines in the treatment of alcoholism

This chapter comprises three sections that cover the main aspects of benzodiazepines and alcohol: (1) the basic pharmacology of benzodiazepines; (2) use of benzodiazepines in the treatment of withdrawal; and (3) the use of benzodiazepines in treating alcoholics. The basic studies suggest that a major site of action of alcohol may be the GABA/benzodiazepine receptor complex and that compensatory alterations in this complex may underly withdrawal. In the section on alcohol withdrawal, interactions between the GABA/benzodiazepine receptor complex, sympathetic nervous system, and hypothalamic-pituitary-adrenal axis are discussed. Use of benzodiazepines in the treatment of the alcohol withdrawal syndrome are reviewed, including the possibility that the benzodiazepines may prevent withdrawal-induced "kindling." Lastly, we review indications for, and efficacy of, benzodiazepines in long-term treatment of patients with alcoholism. Benzodiazepines are not indicated for the treatment of alcoholism. Furthermore, they have very few indications in alcoholics and their dependency-producing potency has to be appreciated when they are used in patients with alcoholism.

A review of mouse mutants as genetic models of epilepsy

Here we review the major inherited convulsive disorders found in mice and discuss their possible relationship to specific clinical seizure disorders in humans. These mouse disorders include audiogenic seizures, the epilepsy (El) mutation, spontaneous seizures, the tottering/learner syndrome, cerebellar abnormalities, myelin disorders, and alcohol withdrawal seizures. Some of these disorders are symptomatic and others are idiopathic. We find that for many major types of epilepsy in humans there exists a similar counterpart in mice. Because the genetic constitution of the mouse is better known and more easily manipulated that that of other mammalian species, the mouse may serve as an excellent animal model for genetic and biochemical studies of epilepsy.

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

It has been shown that adrenal glucocorticoids have a permissive role in some of the actions of alcohol. To determine if an intact adrenal was necessary for the stimulation of locomotor activity, 24 female C3H mice were tested for open field activity with ethanol or saline. Two weeks after adrenalectomy or sham surgery, animals were tested for activity again with ethanol or saline. One week later, alcohol disappearance curves were generated for blood and brain. Adrenalectomy reduced but did not abolish the alcohol-stimulated locomotor activity. In addition, adrenalectomy significantly reduced estimated peak alcohol levels in blood and brain but significantly reduced the disappearance rate for alcohol only in brain. These data suggest that adrenalectomy significantly changes alcohol distribution, with greater impact on brain alcohol levels than on blood levels, and that this may be responsible, at least in part, for the reduction in stimulated locomotor activity.

Ethanol dependence and the pituitary-adrenal axis in mice. I. Genotypic differences in hormone levels

Resting pituitary levels of beta-endorphin-(beta-EP-IR), ACTH-(ACTH-IR), and alpha-MSH-(alpha-MSH-IR)-like immunoreactive material were found to differ among 16 inbred mouse strains. Hormone levels correlated genetically with severity of withdrawal from ethanol, which also differed among the strains. Ethanol dependence led to reduced pituitary beta-EP-IR in 4 of 5 strains studied. After 24 hr of withdrawal, 3 of those 4 showed elevated pituitary beta-EP-IR. These results are consistent with the hypothesis that genetically-determined difference in pituitary hormone functioning underlie some of the genetically-determined differences in ethanol withdrawal severity.

Cortexolone antagonizes development of alcohol tolerance in mice

Mice treated with cortexolone during a period of chronic ethanol feeding displayed significantly less tolerance to a challenge dose of ethanol than mice fed ethanol but not given cortexolone. This glucocorticoid receptor blocker did not alter the hypnotic effects of ethanol in animals not previously given ethanol and no differences were found in ethanol consumption or blood ethanol levels between ethanol-fed mice receiving daily injections of cortexolone and the vehicle-injected controls. It was concluded that cortexolone interferes with the development of tolerance to ethanol.

Endocrine effects of alcohol

A variety of effects of alcohol on endocrine function are now well documented. Clinically, the most important of these are alcohol-induced 'pseudo-Cushing's syndrome' and a syndrome of hypothalamic-pituitary-adrenocortical unresponsiveness, both of which result from long-term over-indulgence, and impairment of testosterone secretion which may occur following relatively short-term drinking. Evidence indicates that a number of different mechanisms are responsible for mediating the effects of alcohol on endocrine function. In a few instances (e.g. inhibition of vasopressin secretion and impairment of steroidogenesis resulting in a fall in testosterone production rate), alcohol appears to influence directly the release or synthesis of individual hormones. However, the majority of the endocrine effects of alcohol are probably indirect, resulting from either the stress of intoxication (stimulation of cortisol, catecholamines and possibly GH and prolactin), changes in the level of intermediary metabolites (e.g. a fall in circulating FFA stimulating GH secretion) or changes in the metabolism of hormones (e.g. catecholamines, oestrogens, androgens) resulting from alteration in intracellular redox state or tissue damage.

Corticosterone concentrations in mice during ethanol drinking and withdrawal

Consumption of an ethanol-containing diet by mice resulted in a significant increase in circulating concentrations of corticosterone which was maintained for 8 days. There were no changes in the concentrations of plasma corticosterone binding globulin. Ethanol withdrawal symptoms followed the removal of ethanol from the diet and circulating corticosterone concentrations were further increased. There was no correlation between blood ethanol and glucocorticoid concentrations during the chronic ethanol treatment. Stress related to ethanol consumption may be of greater importance than the circulating ethanol concentrations in producing the elevation in plasma glucocorticoids.

The permissive role of glucocorticoids in the development of ethanol dependence and tolerance

In mice chronically treated with ethanol (in a liquid diet containing 6% ethanol ad libitum for 2 weeks), brain tryptophan hydroxylase (TPH) activity was increased (by 30-45% in whole brain), while brain tyrosine hydroxylase activity remained unchanged. Such chronic ethanol treatment also induced susceptibility to audiogenic seizures during withdrawal (60% incidence). When ethanol treatment was given to adrenalectomized (Adx) mice, the increase of brain TPH activity and the development of withdrawal audiogenic seizures were both prevented. In Adx mice receiving daily injections of corticosterone (0.5 mg/mouse), the ethanol-induced increase of brain TPH activity and the occurrence of withdrawal audiogenic seizures were both restored. Similarly, the ethanol-induced increase of liver alcohol dehydrogenase activity (by 60%) was prevented in Adx mice and restored by corticosterone replacement. It was noted that in all three cases replacement with such large doses of the corticoid did not enhance the ethanol effects, but merely restored the effects to the levels observed in intact mice. Apparently, glucocorticoids are required in a permissive role in order for the ethanol effects to occur.

Glucocorticoids and development of audiogenic seizure susceptibility in DBA/1Bg mice

Metopyrone, an inhibitor of glucocorticoid synthesis, blocks the development of susceptibility to audiogenic seizures in C57BL/6Bg mice after either acoustic priming at 19 days of age or ethanol withdrawal at 70-80 days of age, whereas it has no effect on the development of genetic susceptibility in DBA/1Bg mice. This suggests that there may be similar developmental mechanisms for effects of acoustic priming and ethanol withdrawal on audiogenic seizure risk, which may be different from that for the genetic susceptibility of DBA/1Bg mice.

Long term reduction of male agonistic behavior in mice following early exposure to ethanol

A system was developed to study the ability of early (pre- and neonatal) ethanol input to induce long lasting neural and behavioral changes. Ethanol was administered to E7b1/10bg and DBA/1Bg offspring through their parents who received 10% ethanol as their only liquid supply either before and during pregnancy, or from delivery until 14 days post partum, or during both periods. Thus, the offspring received ethanol transplacentally and/or through the mother's milk. The present paper is concerned with the male agonistic behavior at age 50 days of the treated offspring as compared with their pair fed controls. Early ethanol input resulted in a 23% increase in latency to attack in C57 mice and 58% in DBA, as well as a 49% (C57) and 38% (DBA) decrease in time spent fighting. The sensitive period to ethanol effect was apparently postnatal. Prenatal administration had no effect on agonistic behavior. DBA offspring were more aggressive than C57 and the scores of C57 offspring were more variable, thus indicating a lower phenotypic buffering in this strain.

Changes in receptor sensitivity of the cerebral cortex and liver during chronic ethanol ingestion and withdrawal

The evidence was reviewed supporting the noradrenergic sub- and supersensitivity hypothesis of ethanol withdrawal pathogenesis. New data indicates that the cAMP generating system linked to noradrenergic receptor sensitivity is in a steady state in the brain during ethanol withdrawal since the cAMP levels were not different from controls in vivo. Propranolol blocking experiments indicated the beta-adrenergic receptor is a necessary link in the increased cAMP response induced by ethanol withdrawal. The changes in sensitivity observed in the ethanol withdrawn rats were reproduced by acute and chronic reserpinization.

Electroencephalographic correlates of audiogenic seizures during ethanol withdrawal in mice

C57BL/6Bg mice had silver bead electrodes chronically implanted on the surface of the cortex and had their cortical EEG recorded during audiogenic seizures following ethanol withdrawal. For 7 days, the experimental groups were fed a liquid diet containing 6% v/v ethanol ad lib as the only source of food and water. The control group was fed a similar diet containing an isocaloric amount of sucrose. The cortical EEG's of experimental and control groups before, during, and after treatment were virtually identical. Only the experimental group was susceptible to audiogenic seizures. During audiogenic seizures, the cortical EEG showed no sign of spike waves or paroxysmal activity. This is in contrast to picrotoxin convulsions with these same mice as well as to spontaneous convulsions in animals following ethanol withdrawal. Similar EEG observations have been reported on audiogenic seizures from genetic and acoustically primed susceptibilities. Consequently, we suggest that all audiogenic seizure responses, including those during ethanol withdrawal, are a type of subcortical epilepsy.

Increased sensitivity to chronic ethanol in isolated mice

Isolated C57BL/10 mice fed liquid diet as their only nutritional supply consumed 44% more diet than did grouped-housed mice. A similar increase due to isolation of 36% for C57BL/10 mice and 89% for DBA/1 mice was demonstrated when the sucrose in the liquid diet was replaced by an equicaloric (6% v/v) amount of ethanol. The ethanol-drinking isolated mice suffered a higher mortality rate than the grouped mice. When isolated mice were given a restricted amount of ethanol diet to match the consumption of the grouped mice, their death rate still remained higher. It was concluded that isolation increased the sensitivity to ethanol effects. The observed changes in the sensitivity to ethanol effects may have been mediated by the known isolation-induced changes in the levels of brain amines and corticosterone. Generally, DBA/1 mice were more susceptible to chronic ethanol than C57BL/10, and the young more susceptible than the adults.

Suppressant effects of alcohol on audiogenic seizures

Genetically seizure susceptible DBA/1/Bg mice fed 10% ethanol in their drinking water exhibited a marked diurnal variation in blood alcohol levels. At peak levels, sound-induced seizures were significantly reduced. At trough levels, seizures remained unaffected. Ethanol administered during early development enhanced seizures at post-weaning age. Such alcohol-augmented seizures were suppressed by ethanol feeding during the testing period, to the same base level as in animals not pretreated with ethanol in early life.