Stress-related effects of ethanol in mammals

Alcohol impairs predation risk response and communication in zebrafish

The effects of ethanol exposure on Danio rerio have been studied from the perspectives of developmental biology and behavior. However, little is known about the effects of ethanol on the prey-predator relationship and chemical communication of predation risk. Here, we showed that visual contact with a predator triggers stress axis activation in zebrafish. We also observed a typical stress response in zebrafish receiving water from these conspecifics, indicating that these fish chemically communicate predation risk. Our work is the first to demonstrate how alcohol effects this prey-predator interaction. We showed for the first time that alcohol exposure completely blocks stress axis activation in both fish seeing the predator and in fish that come in indirect contact with a predator by receiving water from these conspecifics. Together with other research results and with the translational relevance of this fish species, our data points to zebrafish as a promising animal model to study human alcoholism.

Role of novelty and ethanol history in locomotor stimulation induced by binge-like ethanol intake

BACKGROUND

The acute locomotor effects of voluntary ethanol (EtOH) intake in mice (stimulation/sedation) might be important behavioral indicators of an animals' propensity to engage in EtOH consumption and/or EtOH seeking behaviors. Using a binge-like EtOH intake model dubbed "Drinking-in-the-Dark (DID)," we recently observed home cage locomotor stimulation in C57BL/6J mice during an acute EtOH intake session, but acute home cage locomotor sedation following repeated EtOH exposures. To determine the role of novelty and/or EtOH history on these previously described locomotor effects, and to determine the relationship between these variables on locomotor activity immediately following DID intake, we conducted 2 separate experiments.

METHODS

In experiment 1, mice were given access to either EtOH or water, and locomotor activity was monitored immediately afterwards. In experiment 2, mice were given 13 days access to EtOH or water solution while home cage locomotor activity was monitored. On the 14th day, half of the water consuming animals received EtOH access for the first time. On the 15th day, all animals received EtOH access, and locomotion was assessed afterwards in locomotor activity testing chambers.

RESULTS

In experiment 1, locomotor activity following DID was positively associated with EtOH intake and blood EtOH concentrations (BECs). In experiment 2, the group that received EtOH for the first time on the 14th day did not display locomotor stimulation. Locomotor activity following DID EtOH intake was positively associated with BECs in all groups regardless of EtOH history.

CONCLUSIONS

These results suggest that (i) DID-induced locomotor stimulation in the home cage may involve relative familiarity with the DID procedures, and (ii) locomotor stimulation immediately following DID is directly related to the relative concentration of EtOH in blood; an effect that is not altered by prior EtOH history. These data add new evidence of the pharmacological actions of binge-like EtOH intake, and provide a basis by which we may explore the motivation and consequences of such binge consumption.

Stress and alcohol drinking

The concept of stress-relief by alcohol has led to many investigations in order to elucidate the mechanisms of interactions of stress and alcohol, and the stress-reducing effect of alcohol as a motivation for alcohol consumption. The hypothalamo-pituitary-adrenocortical (HPA) system is one of the biological systems affected by both stress and alcohol. However, there is a high individual variation in the response of the HPA axis to either stress or alcohol. Factors like quality, severity and duration of stress, dose of alcohol and frequency of stress or alcohol exposure add to the individual response to stress or alcohol. The individual response is determined by interactions of genetic, environmental and experiential factors. Facing that complexity, with even more factors to be named, the often reported inconsistencies in both human and animal studies are not only attributable to methodological differences. Nevertheless, there are studies showing an influence of stress on alcohol consumption which most likely depends on the sample of probands examined. To our view, the concept of stress-relief by alcohol as a basic motivation for developing alcohol drinking habits is only applicable to subgroups of drinkers. Individuals with a dysfunctional HPA axis, inherited and/or acquired, might represent such a subgroup of stress-motivated drinkers.

Effect of neurogenic stress and ethanol on nitric oxide synthase and cyclooxygenase activities in rat adrenals

Repeated restraint stress (RRS) in male rats activated the pituitary adrenal system, as indicated by increases in adrenal weight and plasma corticosterone concentration that were accompanied by a decrease in constitutive nitric oxide synthase (cNOS), but not inducible NOS (iNOS). iNOS activated cyclooxgenase, causing elevated prostaglandin E(2) (PGE(2)) and F(2 alpha) in the adrenals, but had no effect on lipoxygenase. Administration of ethanol (ETOH) was also associated with elevated adrenal weight and a slight increase in corticosterone coupled with a decrease in both cNOS and iNOS and PGs in the adrenal. When ETOH was administered together with RRS, a decrease in iNOS and PGE release was noted consequent to a reduction in iNOS. Thus, ETOH probably reduced RRS-induced adrenocorticotropic hormone release. Adrenals were incubated in vitro to further evaluate the role of NO in these processes. Results indicated that NO released by sodium nitroprusside increased corticosterone release presumably by activating guanylyl cyclase with production of cyclic guanosine monophosphate (cGMP), because although NO also increased PGE release, PGE(2) (10(-5)-10(-9) M) decreased corticosterone release, an effect that was highly significant at a concentration of 10(-7) M PGE(2). ETOH (100 mM) had no effect on corticosterone release and did not block the increase in corticosterone caused by NO; however, ETOH reduced PGE release into the medium and blocked PGE(2) release induced by NO. Consequently, NO activated corticosterone release not by PGs, but by activation of guanylyl cyclase and release of cGMP. PGs have a negative feedback to suppress corticosterone release.

Effects of ethanol on the stress-induced expression of NGFI-A mRNA in the rat brain

We investigated expression of NGFI-A/zif268 mRNA, reliable marker for neuronal activation in response to stress in the brain of rats pretreated with ethanol. The rats were orally administrated with either 25% sucrose or 20% ethanol (20 ml of kg body weight) 10 min before the onset of the stress. The rats were exposed to immobilization stress for 20 min and quickly decapitated. The brains were extracted and immediately frozen. The level of NGFI-A mRNA was evaluated by in situ hybridization histochemistry. Prior ethanol administration attenuated the immobilization stress-induced upregulation of NGFI-A mRNA level in the neocortex and hippocampus. However, in the paraventricular hypothalamic nucleus, prior administration of ethanol did not affect the upregulation of this gene. These data suggest that ethanol abolishes the forebrain component of the stress response while it fails to attenuate the stress response on a region of the brain that regulates the autonomic nervous system and the hypothalamo-pituitary-adrenal axis. Regional differences in the expression of NGFI-A mRNA may be important for the complex interactions between ethanol and stress.

Mechanism of suppressed neutrophil mobilization in a mouse model for binge drinking: role of glucocorticoids

The goals of this study were to determine if suppression of neutrophil accumulation and TNF-alpha production in the peritoneal cavity occurs in mice exposed to a chemical stressor [ethanol (EtOH)], to evaluate the role of EtOH-induced increases in endogenous glucocorticoids in any such suppression, and to determine if decreased tumor necrosis factor-alpha (TNF-alpha) production is responsible for decreases in neutrophil accumulation in EtOH-treated mice. An inflammatory response induced in the peritoneal cavity of mice by administration of heat-killed Propionibacterium acnes (P. acnes) was suppressed by a single dose of EtOH given 1 h before administration of the bacteria, as indicated by decreased accumulation of neutrophils in the peritoneal cavity. The concentration of TNF-alpha in the peritoneal cavity was also decreased by EtOH, but exogenous TNF-alpha did not prevent the suppression of neutrophil accumulation. The glucocorticoid antagonist RU-486 did not prevent the suppression of neutrophil accumulation in mice treated with EtOH, but RU-486 did block suppression of neutrophil accumulation caused by administration of exogenous corticosterone. The suppression of neutrophil accumulation caused by exogenous corticosterone was less than produced by EtOH. These observations suggest that the increase in endogenous corticosterone induced by EtOH may explain some of the suppression of neutrophil accumulation, but other neuroendocrine mediators (or EtOH per se) are sufficient to cause the full suppressive effect when the action of corticosterone is blocked by RU-486. The results also demonstrate that EtOH decreases TNF-alpha production, but this is not the mechanism by which neutrophil accumulation is decreased in this model.

Endogenous glucocorticoids induced by a chemical stressor (ethanol) cause apoptosis in the spleen in B6C3F1 female mice

Stress-induced increases in glucocorticoid levels can cause-apoptosis in immature thymocytes, but it is not known if glucocorticoids at these levels can also cause apoptosis in peripheral lymphocytes. In the present study, mice were exposed to ethanol (EtOH) in a model designed to represent binge drinking. This induces a substantial stress response, including an increase in corticosterone levels. Apoptosis in the spleen was evaluated using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) with fluorescein-labeled dUTP. Flow cytometric analysis demonstrated a significant increase in the percentage of apoptotic cells in the spleen 2-6 h after administration of EtOH (3-6% apoptotic cells in treated mice vs 0.2-2% in controls). This increase was blocked by the glucocorticoid antagonist, RU 486, and administration of exogenous corticosterone in a manner that produced similar blood levels and kinetics as noted in EtOH-treated mice produced similar levels of apoptosis. Fluorescein-labeled Annexin V was used to confirm increased numbers of apoptotic cells in the spleen in EtOH-treated mice. These results indicate that stress-induced glucocorticoids are sufficient to induce apoptosis in the spleen, and this may be one mechanism by which stress responses cause immunosuppression.

The role of ethanol availability on stress-induced increases in ethanol consumption

Exposure to stressors can increase ethanol consumption and ethanol can attenuate the behavioral and biochemical effects of stressors. This study determined whether the availability of ethanol during the period of exposure to repeated restraint alters the poststress increase in ethanol intake. Seven days of restraint increased ethanol intake on the first poststress test only in animals deprived of ethanol during the restraint period. These results indicate that the availability of ethanol during exposure to restraint can attenuate the impact of restraint on ethanol intake. Ethanol intake was also positively related to novelty-induced locomotion and restraint eliminated this relationship. However, amphetamine-induced locomotion was not altered by either restraint or EtOH intake. These results indicate that voluntary ethanol intake can attenuate the impact of restraint stress and that restraint stress can alter the influence of ethanol on novelty-induced locomotion. It is suggested that this symmetrical relationship between ethanol intake and restraint stress may be involved in an interactive manner that determines stress-induced ethanol consumption.

Antidepressants suppress bulbectomy-induced augmentation of voluntary alcohol consumption in C57B1/6j but not in DBA/2j mice

Bulbectomy has been previously shown to produce the specific antidepressant-sensitive syndrome in C57Bl/6j, but not DBA/2j mice. The present study examined the effect of the depression on voluntary alcohol consumption. Alcohol consumption and alcohol preference (% of alcohol solution in total liquid) in a free-choice, two-bottle situation was measured in C57BL/6j and DBA/2j mice after sham-operation, anosmia with 10% ZnSO4, or bulbectomy. Both anosmic and bulbectomized mice of both strains consumed more alcohol and showed stronger preference for alcohol than sham-operated mice. In DBA/2j mice both operations altered alcohol consumption of the whole population, and the effect of bulbectomy was stronger. In C57Bl/6j mice bulbectomy and, to a less degree, anosmia seemed to affect predominantly the low-drinking animals. Chronic treatment with antidepressants amitriptyline (20 mg/kg), trazodone (20 mg/kg), and imipramine (10 mg/kg), did not change alcohol consumption in sham-operated C57Bl/6j mice. In anosmic mice antidepressants decreased alcohol preference, but only amitryptyline also decreased alcohol consumption. All antidepressants decreased both alcohol consumption and preference in bulbectomized C57Bl/6j mice. In DBA/2j mice antidepressant treatment either increased, or did not alter alcohol consumption and preference in all groups, though the effects varied among individual antidepressants. The possible connection between the bulbectomy-induced behavioral syndrome and elevated ethanol consumption in C57Bl/6j mice is discussed.