A relationship between increased voluntary alcohol preference and basal hypercorticosteronemia associated with an attenuated rise in corticosterone output during stress

Line- and sex-dependent effects of juvenile stress on contextual fear- and anxiety-related behavior in high- and low-alcohol-preferring mouse lines

Juvenile stress (JS) is a known risk factor for the development of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD), both of which are frequently co-morbid. Data suggest there may be common, genetically-influenced biological responses to stress that contribute to the development of both AUD and PTSD. The present study investigated the impact of JS on contextual fear learning and extinction, as well as corticosterone (CORT) responses before and after JS, before and after contextual fear conditioning (CFC), and after fear extinction in male and female high-alcohol-preferring (HAP2) and low-alcohol-preferring (LAP2) mouse lines. We also measured unconditioned anxiety-related behavior in the light-dark-transition test before CFC. HAP2 and LAP2 mice did not differ in fear acquisition, but HAP2 mice showed faster fear extinction compared to LAP2 mice. No effects of JS were seen in HAP2 mice, whereas in LAP2 mice, JS reduced fear acquisition in males and facilitated fear extinction in females. Females showed greater fear-related behavior relative to males, regardless of subgroup. HAP2 males demonstrated more anxiolytic-like responses than LAP2 males and LAP2 females demonstrated more anxiolytic-like responses than LAP2 males in the light-dark transition test. HAP2 and LAP2 mice did not differ in CORT during the juvenile stage; however, adult LAP2 mice showed greater CORT levels than HAP2 mice at baseline and after CFC and extinction testing. These findings build upon prior work in these unique mouse lines that differ in genetic propensity toward alcohol preference and provide new information regarding contextual fear learning and extinction mechanisms theorized to contribute to co-morbid AUD and PTSD.

Targeting the Glucocorticoid Receptor Reduces Binge-Like Drinking in High Drinking in the Dark (HDID-1) Mice

BACKGROUND

Chronic alcohol exposure can alter glucocorticoid receptor (GR) function in some brain areas that promotes escalated and compulsive-like alcohol intake. GR antagonism can prevent dependence-induced escalation in drinking, but very little is known about the role of GR in regulating high-risk nondependent alcohol intake. Here, we investigate the role of GR in regulating binge-like drinking and aversive responses to alcohol in the High Drinking in the Dark (HDID-1) mice, which have been selectively bred for high blood ethanol (EtOH) concentrations (BECs) in the Drinking in the Dark (DID) test, and in their founder line, the HS/NPT.

METHODS

In separate experiments, male and female HDID-1 mice were administered one of several compounds that inhibited GR or its negative regulator, FKBP51 (mifepristone [12.5, 25, 50, 100 mg/kg], CORT113176 [20, 40, 80 mg/kg], and SAFit2 [10, 20, 40 mg/kg]) during a 2-day DID task. EtOH consumption and BECs were measured. EtOH conditioned taste and place aversion (CTA and CPA, respectively) were measured in separate HDID-1 mice after mifepristone administration to assess GR's role in regulating the conditioned aversive effects of EtOH. Lastly, HS/NPT mice were administered CORT113176 during DID to assess whether dissimilar effects from those of HDID-1 would be observed, which could suggest that selective breeding had altered sensitivity to the effects of GR antagonism on binge-like drinking.

RESULTS

GR antagonism (with both mifepristone and CORT113176) selectively reduced binge-like EtOH intake and BECs in the HDID-1 mice, while inhibition of FKBP51 did not alter intake or BECs. In contrast, GR antagonism had no effect on EtOH intake or BECs in the HS/NPT mice. Although HDID-1 mice exhibit attenuated EtOH CTA, mifepristone administration did not enhance the aversive effects of EtOH in either a CTA or CPA task.

CONCLUSION

These data suggest that the selection process increased sensitivity to GR antagonism on EtOH intake in the HDID-1 mice, and support a role for the GR as a genetic risk factor for high-risk alcohol intake.

Prenatal Alcohol Exposure as a Case of Involuntary Early Onset of Alcohol Use: Consequences and Proposed Mechanisms From Animal Studies

Prenatal alcohol exposure has been found to be an important factor determining later consumption of this drug. In humans, despite the considerable diversity of variables that might influence alcohol consumption, longitudinal studies show that maternal alcohol intake during gestation is one of the best predictors of later alcohol use from adolescence to young adulthood. Experimental studies with animals also provide abundant evidence of the effects of prenatal alcohol exposure on later alcohol intake. In addition to increased consumption, other effects include enhanced palatability and attractiveness of alcohol flavor as well as sensitization to its sensory and reinforcing effects. Most of these outcomes have been obtained after exposing rats to binge-like administrations of moderate alcohol doses during the last gestational period when the fetus is already capable of detecting flavors in the amniotic fluid and learning associations with aversive or appetitive consequences. On this basis, it has been proposed that one of the mechanisms underlying the increased acceptance of alcohol after its prenatal exposure is the acquisition (by the fetus) of appetitive learning via an association between the sensory properties of alcohol and its reinforcing pharmacological effects. It also appears that this prenatal appetitive learning is mediated by the activation of the opioid system, with fetal brain acetaldehyde playing an important role, possibly as the main chemical responsible for its activation. Here, we review and analyze together the results of all animal studies testing these hypotheses through experimental manipulation of the behavioral and neurochemical elements of the assumed prenatal association. Understanding the mechanisms by which prenatal alcohol exposure favors the early initiation of alcohol consumption, along with its role in the causal pathway to alcohol disorders, may allow us to find strategies to mitigate the behavioral effects of this early experience with the drug. We propose that prenatal alcohol exposure is regarded as a case of involuntary early onset of alcohol use when designing prevention policies. This is particularly important, given the notion that the sooner alcohol intake begins, the greater the possibility of a continued history of alcohol consumption that may lead to the development of alcohol use disorders.

Toward a Unifying Account of Impulsivity and the Development of Self-Control

Impulsivity has traditionally been thought to involve various behavioral traits that can be measured using different laboratory protocols. Whereas some authors regard different measures of impulsivity as reflecting fundamentally distinct and unrelated behavioral tendencies (fragmentation approach), others regard those different indexes as analogue forms of the same behavioral tendency, only superficially different (unification approach). Unifying accounts range from mere intuitions to more sophisticated theoretical systems. Some of the more complete attempts at unifying are intriguing but have validity weaknesses. We propose a new unifying attempt based on theoretical points posed by other authors and supplemented by theory and research on associative learning. We then apply these assumptions to characterize the paradigms used to study impulsivity in laboratory settings and evaluate their scope as an attempt at unification. We argue that our approach possesses a good balance of parsimony and empirical and theoretical grounding, as well as a more encompassing scope, and is more suitable for experimental testing than previous theoretical frameworks. In addition, the proposed approach is capable of generating a new definition of impulsivity and outlines a hypothesis of how self-control can be developed. Finally, we examine the fragmentation approach from a different perspective, emphasizing the importance of finding similarities among seemingly different phenomena.

The FKBP5 Gene Affects Alcohol Drinking in Knockout Mice and Is Implicated in Alcohol Drinking in Humans

FKBP5 encodes FK506-binding protein 5, a glucocorticoid receptor (GR)-binding protein implicated in various psychiatric disorders and alcohol withdrawal severity. The purpose of this study is to characterize alcohol preference and related phenotypes in Fkbp5 knockout (KO) mice and to examine the role of FKBP5 in human alcohol consumption. The following experiments were performed to characterize Fkpb5 KO mice. (1) Fkbp5 KO and wild-type (WT) EtOH consumption was tested using a two-bottle choice paradigm; (2) The EtOH elimination rate was measured after intraperitoneal (IP) injection of 2.0 g/kg EtOH; (3) Blood alcohol concentration (BAC) was measured after 3 h limited access of alcohol; (4) Brain region expression of Fkbp5 was identified using LacZ staining; (5) Baseline corticosterone (CORT) was assessed. Additionally, two SNPs, rs1360780 (C/T) and rs3800373 (T/G), were selected to study the association of FKBP5 with alcohol consumption in humans. Participants were college students (n = 1162) from 21–26 years of age with Chinese, Korean or Caucasian ethnicity. The results, compared to WT mice, for KO mice exhibited an increase in alcohol consumption that was not due to differences in taste sensitivity or alcohol metabolism. Higher BAC was found in KO mice after 3 h of EtOH access. Fkbp5 was highly expressed in brain regions involved in the regulation of the stress response, such as the hippocampus, amygdala, dorsal raphe and locus coeruleus. Both genotypes exhibited similar basal levels of plasma corticosterone (CORT). Finally, single nucleotide polymorphisms (SNPs) in FKBP5 were found to be associated with alcohol drinking in humans. These results suggest that the association between FKBP5 and alcohol consumption is conserved in both mice and humans.

A family history of Type 1 alcoholism differentiates alcohol consumption in high cortisol responders to stress

BACKGROUND

The differentiation between high and low cortisol responders to stress is of interest in determining the risk factors which may, along with genetic vulnerability, influence alcohol intake.

STUDY 1

METHODS

Thirty-two healthy volunteers, family history positive to alcoholism (FHP, n = 16) and family history negative (FHN, n = 16) attended two laboratory sessions during which alcohol or placebo was offered.

RESULTS

There were no differences in consumption of alcohol or placebo between FHP and FHN subjects. STUDY 2:

METHODS

Fifty-eight healthy social drinkers, FHP (n = 27) and FHN (n = 31) attended two laboratory sessions. They were administered either alcohol or placebo in both sessions they attended. All subjects underwent either a stress task (the Trier Social Stress Test, TSST) or a stress-free period, at two separate occasions, before being offered beverage. After the salivary cortisol analysis, subjects in each group were divided into high (HCR) or low (LCR) cortisol responders.

RESULTS

After stress, subjects who were FHP-HCR consumed more alcohol than FHN-HCR. There were no differences in the placebo intake between FHP and FHN subjects regardless of their cortisol response.

CONCLUSIONS

This result indicates that stress promotes alcohol consumption only in subjects with a family history of Type 1 alcoholism who show an increase in cortisol response to stress. This behaviour is similar to that previously observed in alcohol dependent individuals after stress and thus could represent an endophenotype posing a risk for future development of alcohol use disorders.

Relation between corticosterone and fear-related behavior in mice selectively bred for high or low alcohol preference

Blunted cortisol responses to stress or trauma have been linked with genetic (familial) risk for both alcoholism and post-traumatic stress disorder (PTSD). Mouse lines selectively bred for high (HAP) or low (LAP) alcohol preference may be a relevant model of genetic risk for co-morbid alcoholism and PTSD in humans. HAP mice show greater fear-potentiated startle (FPS), a model used to study PTSD, than LAP mice. The relation between corticosterone (CORT) and FPS behavior was explored in four experiments. Naïve male and female HAP2 and LAP2 mice received fear-conditioning or control treatments, and CORT levels were measured before and immediately after fear-conditioning or FPS testing. In two other experiments, HAP2 mice received CORT (1.0, 5.0 or 10.0 mg/kg) or a glucocorticoid receptor antagonist (mifepristone; 25.0 and 50.0 mg/kg) 30 minutes before fear conditioning. HAP2 mice exposed to fear conditioning and to control foot shock exposures showed lower CORT after the fear-conditioning and FPS testing sessions than LAP2 mice. A trend toward higher FPS was seen in HAP2 mice pretreated with 10.0 mg/kg CORT, and CORT levels were the lowest in this group, suggesting negative feedback inhibition of CORT release. Mifepristone did not alter FPS. Overall, these results are consistent with data in humans and rodents indicating that lower cortisol/CORT levels after stress are associated with PTSD/PTSD-like behavior. These findings in HAP2 and LAP2 mice suggest that a blunted CORT response to stress may be a biological marker for greater susceptibility to develop PTSD in individuals with increased genetic risk for alcoholism.

Effects of Cagemate Gender and the Cagemate's access to ethanol on ethanol and water intake of the proximal male or the proximal female CD-1 mouse

The effects of social stimulation on ethanol drinking in humans may depend on the gender of the drinker, the gender of the social stimulus, and the availability of ethanol provided to the social stimulus. The present study employed the Proximal Cagemate Drinking (PCD) Procedures to evaluate the effects of the gender of the social stimulus Cagemate mouse and the effects of providing ethanol to the Cagemate mouse on the drinking of ethanol and water by the male or female CD-1 Drinker mouse. Twelve groups of subjects were arranged in a 3 × 2 × 2 factorial design with 3 levels of Cagemate Gender (Male vs. Female vs. None), 2 levels of Drinker Gender (Male vs. Female), and 2 levels of Cagemate Ethanol (Ethanol vs. No Ethanol). In the 8 groups assigned to social housing conditions, each Drinker mouse was housed with a Cagemate mouse on opposite sides of a clear plastic shoebox cage equipped with a clear plastic barrier that divided the cage lengthwise into 2 equal compartments. Six groups of Drinkers and 4 groups of Cagemates were provided with continuous access to 2 bottles (ethanol vs. water), while the 4 groups of Cagemates in the No Ethanol condition were provided with 2 bottles containing water. Results revealed that providing the Cagemate with ethanol elevated ethanol intake and ethanol preference but reduced water intake in Drinkers in Other-Gender Pairings (Male Drinker-Female Cagemate or Female Drinker-Male Cagemate) relative to Drinkers in Same-Gender Pairings (Male Drinker-Male Cagemate or Female Drinker-Female Cagemate). In contrast, when the Cagemate was not provided with access to ethanol, the opposite effects were observed. These novel PCD procedures reveal that the gender of the Cagemate and the Cagemate's access to ethanol influenced ethanol drinking in proximal-housed CD-1 Drinker mice.

Environmental manipulations alter age differences in attribution of incentive salience to reward-paired cues

Cues repeatedly paired with rewards often themselves become imbued with enhanced motivational value, or incentive salience. During Pavlovian conditioned approach procedures, a cue repeatedly preceding reward delivery often elicits conditioned responses at either the reward delivery location ("goal-tracking") or the cue itself ("sign-tracking"). Sign-tracking behavior is thought to reflect the individual differences in attribution of incentive salience to reward-paired cues that may contribute to addiction vulnerability. Adolescent rats typically demonstrate less sign-tracking behavior than adult rats, a surprising finding given that adolescence is hypothesized to be a time of heightened addiction vulnerability. Given evidence that adult sign-tracking behavior can be influenced by environmental conditions, the present study compared the effects of isolate housing and food deprivation on expression of sign-tacking and goal-tracking behavior in adolescent and adult male rats across eight days of a Pavlovian conditioned approach procedure. Pair-housed adults exhibited more sign-tracking behavior than pair-housed adolescents; however, this age difference was not apparent in isolate-housed subjects. Adolescents often appeared more sensitive than adults to both food restriction- and isolate housing-induced changes in behavior, with food restriction promoting an increase in sign-tracking among isolate-housed adolescents and an increase in goal-tracking among pair-housed adolescents. For adults, food restriction resulted in a modest increase in overall expression of both sign- and goal-tracking behavior. To the extent that sign-tracking behavior reflects attribution of incentive salience to reward-paired cues, results from the present study provide evidence that reactivity to rewards during adolescence is strongly related to the nature of the surrounding environment.

Glucocorticoid receptor antagonism blocks ethanol-induced place preference learning in mice and attenuates dopamine D2 receptor adaptation in the frontal cortex

The glucocorticoid receptor (GR) plays an important role in alcohol (EtOH) self-administration behaviour by its interaction with the dopaminergic (DA) system in the brain. Here we asked whether the GR is also involved in the establishment of EtOH-induced conditioned place preference (CPP) by an interaction with the DA systems in terminal projection areas. We found that the establishment of an EtOH (2 g/kg, i.p.)-induced CPP was paralleled by a decrease in frontal cortex DA D2 receptor mRNA expression, but not in local D2 gene promoter methylation rate. No effect in other brain areas, nor on DA transporter or DA receptor regulating factor mRNA was found. The GR antagonist, RU486 (20 mg/kg, i.p.) blocked the establishment of EtOH CPP and prevented DA D2 receptor adaptations. These data may suggest a role of glucocorticoid receptor mediated D2 adaptations in the establishment of the reinforcing effects of EtOH.

Amphetamine modifies ethanol intake of psychosocially stressed male rats

Studies of socially housed rodents have provided significant information regarding the consequences of exposure to stressors. Psychosocial stressors are known to alter the ingestion of ethanol and the activity of the dopaminergic neuronal system. Since both stressors and ethanol are known to affect the function of dopaminergic neurons, we employed amphetamine to assess the role of this neural system on the ingestion of ethanol by psychosocially stressed male rats. Male rats housed two per cage were designated as dominant or subdominant rats based on evaluations of agonistic behavior and body weight changes. The dyad-housed rats and a group of single-housed rats were sequentially assessed for ethanol intake after injections of saline or amphetamine (0.3, 0.9 or 2.7 mg/kg i.p.) both prior to dyad housing and subsequently again during dyad-housing. Prior to dyad housing ethanol intake of future subdominant rats was higher than that of future dominant rats. Dyad-housing significantly increased ethanol intake of dominant rats. Pre-dyad the highest dose of amphetamine potently depressed ethanol ingestion. Sensitivity to amphetamine's depressant effect on ethanol intake was higher at the dyad test in all subjects, most prominently in single-housed rats. In contrast to the single-housed rats, the dyad-housed rats displayed saccharin anhedonia. It can be concluded that dopaminergic system modulates, at least partially, the psychosocial stress-induced changes in ethanol intake. Furthermore, the level of ethanol ingestion at the pre-dyad test was predictive of future hierarchical status.

Sex hormone activity in alcohol addiction: integrating organizational and activational effects

There are well-known sex differences in the epidemiology and etiopathology of alcohol dependence. Male gender is a crucial risk factor for the onset of alcohol addiction. A directly modifying role of testosterone in alcohol addiction-related behavior is well established. Sex hormones exert both permanent (organizational) and transient (activational) effects on the human brain. The sensitive period for these effects lasts throughout life. In this article, we present a novel early sex hormone activity model of alcohol addiction. We propose that early exposure to sex hormones triggers structural (organizational) neuroadaptations. These neuroadaptations affect cellular and behavioral responses to adult sex hormones, sensitize the brain's reward system to the reinforcing properties of alcohol and modulate alcohol addictive behavior later in life. This review outlines clinical findings related to the early sex hormone activity model of alcohol addiction (handedness, the second-to-fourth-finger length ratio, and the androgen receptor and aromatase) and includes clinical and preclinical literature regarding the activational effects of sex hormones in alcohol drinking behavior. Furthermore, we discuss the role of the hypothalamic-pituitary-adrenal and -gonadal axes and the opioid system in mediating the relationship between sex hormone activity and alcohol dependence. We conclude that a combination of exposure to sex hormones in utero and during early development contributes to the risk of alcohol addiction later in life. The early sex hormone activity model of alcohol addiction may prove to be a valuable tool in the development of preventive and therapeutic strategies.

Stress and consumption of alcohol in humans with a Type 1 family history of alcoholism in an experimental laboratory setting

BACKGROUND

This paper investigates how stress interacts with alcohol consumption in subjects with a family history of alcoholism. One mechanism for increases in alcohol intake may be that stress alters the subjective effects produced by the drug.

METHODS

58 healthy volunteers, divided into two groups of family history positive (FHP) and two groups of family history negative (FHN) participated in two laboratory sessions, in which they performed in one out of two sessions a stress task. Then subjects were allowed to choose up to six additional drinks of ethanol or placebo depending on which session they were randomly assigned to start with.

RESULTS

It was found that FHP subjects increased their consumption of alcohol after stress.

CONCLUSIONS

It is possible that both stress and alcohol specifically exaggerate the feelings of the reward in the FHP individuals in such way that it may increase the likelihood of consuming more alcohol.

Autoshaping in adolescence enhances sign-tracking behavior in adulthood: impact on ethanol consumption

Autoshaping refers to a procedure during which a cue repeatedly paired with a reward elicits a conditioned response directed at either the reward delivery location ("goal-tracking") or the cue itself ("sign- tracking"). Individual differences in expression of sign-tracking behavior may be predictive of voluntary ethanol intake. The present study was designed to explore the development of differences in sign-tracking behavior in adolescent and adult male and female rats in an 8-day autoshaping procedure. Consistency of sign-tracking and goal-tracking across age was examined by retesting adolescents again in adulthood and comparing their adult data with animals tested only as adults to explore pre-exposure effects on adult responding. In order to assess the relationship between sign-tracking and ethanol intake, voluntary ethanol consumption was measured in an 8-day, 2-hr limited access drinking paradigm following the 8-day autoshaping procedure in adulthood. Animals tested as adolescents showed notably less sign-tracking behavior than animals tested as adults, and sign-tracking behavior was not correlated across age. Animals exposed to the autoshaping procedure as adolescents demonstrated greater sign-tracking behavior as adults when compared to control animals tested only in adulthood. When examining the relationship in adulthood between sign-tracking and ethanol intake, an increase in ethanol intake among sign-trackers was found only in animals pre-exposed to autoshaping as adolescents. Whether or not these results reflect an adolescent-specific experience effect is unclear without further work to determine whether comparable pre-exposure effects are seen if the initial autoshaping sessions are delayed into adulthood.

Corticosterone treatment before puberty sensitizes the effect of oral methylphenidate on locomotor activity in preadolescence and produces differential effects in adulthood

The first objective of this study was to examine the effects of early exposure to methylphenidate and then those of re-exposure in adulthood. The second was to analyze the effect of corticosterone treatment during pre-puberty on oral methylphenidate consumption and, consequently, the effect of this psychostimulant on locomotor activity in preadolescent and adult rats. Experiment 1: from 31 to 39 days of postnatal age (PA), Wistar rats were exposed to either oral methylphenidate or water. Experiment 2: from 24 to 39 days PA, the rats received either corticosterone (2.0 mg/kg/day/subject) or a saline solution. From 31 to 39 days PA, rats were exposed to either methylphenidate or water. During adulthood, all rats in experiments 1 and 2 were exposed to either methylphenidate or water, and subsequently exposed to a free-choice condition of the same two substances.

RESULTS

Experiment 1. Methylphenidate increased locomotor activity (LA) regardless of age. In adulthood, higher methylphenidate consumption was observed in the group that had not been exposed to this substance, compared to the early methylphenidate-exposed group. Experiment 2. Corticosterone did not affect methylphenidate consumption during preadolescence or adulthood; however, the LA induced by methylphenidate was higher in the preadolescents that had been treated with corticosterone+methylphenidate than in the animals treated only with methylphenidate. In adulthood, methylphenidate produced higher LA in the animals previously treated with corticosterone+methylphenidate than in those that had received previous treatment exclusively with corticosterone. These results suggest that preadolescent corticosterone exposure produced a sensitizing effect of methylphenidate on LA in preadolescence. The differential effect on LA in adulthood depended on whether the corticosterone was administered with or without methylphenidate in preadolescence, which would suggest an enduring effect of the early synergic action between these two substances.

Behavioral characteristics and neurobiological substrates shared by Pavlovian sign-tracking and drug abuse

Drug abuse researchers have noted striking similarities between behaviors elicited by Pavlovian sign-tracking procedures and prominent symptoms of drug abuse. In Pavlovian sign-tracking procedures, repeated paired presentations of a small object (conditioned stimulus, CS) with a reward (unconditioned stimulus, US) elicits a conditioned response (CR) that typically consists of approaching the CS, contacting the CS, and expressing consummatory responses at the CS. Sign-tracking CR performance is poorly controlled and exhibits spontaneous recovery and long-term retention, effects that resemble relapse. Sign-tracking resembles psychomotor activation, a syndrome of behavioral responses evoked by addictive drugs, and the effects of sign-tracking on corticosterone levels and activation of dopamine pathways resemble the neurobiological effects of abused drugs. Finally, the neurobiological profile of individuals susceptible to sign-tracking resembles the pathophysiological profile of vulnerability to drug abuse, and vulnerability to sign-tracking predicts vulnerability to impulsive responding and alcohol self-administration. Implications of sign-tracking for models of drug addiction are considered.

Increased ethanol intake after prenatal ethanol exposure: studies with animals

This review analyses the most relevant studies in which ethanol intake was measured after prenatal exposure to the drug. Despite the variety in methodology, in most such studies this prenatal experience induced a higher consumption of ethanol. Several variables that may affect the expression of this phenomenon are discussed, such as gender, age at testing, period of ethanol exposure, ethanol dose and conditions during the test. The mechanisms proposed in all these studies to explain the increased ethanol intake effect are also discussed. Some of these mechanisms are related to the teratological effects of the drug on the neurochemical systems involved in the reinforcing effects of abuse drugs, as well as on the regulatory systems of stress response. Another explanation of this phenomenon is also proposed in terms of associative learning. Specifically, the increased ethanol intake effect may be the result of a conditioned preference for ethanol acquired by the fetus when exposed to the drug during the last days of gestation.

From Malthus to motive: how the HPA axis engineers the phenotype, yoking needs to wants

The hypothalamo-pituitary-adrenal (HPA) axis is the critical mediator of the vertebrate stress response system, responding to environmental stressors by maintaining internal homeostasis and coupling the needs of the body to the wants of the mind. The HPA axis has numerous complex drivers and highly flexible operating characterisitics. Major drivers include two circadian drivers, two extra-hypothalamic networks controlling top-down (psychogenic) and bottom-up (systemic) threats, and two intra-hypothalamic networks coordinating behavioral, autonomic, and neuroendocrine outflows. These various networks jointly and flexibly control HPA axis output of periodic (oscillatory) functions and a range of adventitious systemic or psychological threats, including predictable daily cycles of energy flow, actual metabolic deficits over many time scales, predicted metabolic deficits, and the state-dependent management of post-prandial responses to feeding. Evidence is provided that reparation of metabolic derangement by either food or glucocorticoids results in a metabolic signal that inhibits HPA activity. In short, the HPA axis is intimately involved in managing and remodeling peripheral energy fluxes, which appear to provide an unidentified metabolic inhibitory feedback signal to the HPA axis via glucocorticoids. In a complementary and perhaps a less appreciated role, adrenocortical hormones also act on brain to provide not only feedback, but feedforward control over the HPA axis itself and its various drivers, as well as coordinating behavioral and autonomic outflows, and mounting central incentive and memorial networks that are adaptive in both appetitive and aversive motivational modes. By centrally remodeling the phenotype, the HPA axis provides ballistic and predictive control over motor outflows relevant to the type of stressor. Evidence is examined concerning the global hypothesis that the HPA axis comprehensively induces integrative phenotypic plasticity, thus remodeling the body and its governor, the brain, to yoke the needs of the body to the wants of the mind. Adverse side effects of this yoking under conditions of glucocorticoid excess are discussed.

Adolescence, glucocorticoids and alcohol

This review examines the evidence that glucocorticoids are involved, during both adolescence and adulthood, in the cognitive deficits caused by long-term alcohol consumption and in the mechanism(s) of alcohol dependence. During adolescence, the hypothalamopituitary-adrenal (HPA) axis undergoes well-characterized changes in basal activity and many of these are influenced by alcohol consumption. While the former have been fairly well studied, there is little information about whether alcohol effects on the HPA in adolescents differ from those in adults. The means by which glucocorticoids may influence alcohol-related neurotoxicity are presented, and potential differences between adolescence and adults in this regard noted. The substantial evidence for involvement of glucocorticoids in alcohol-induced cognitive deficits is described, with particular reference to the consequences of alcohol withdrawal. The use of immature organotypic cultures of rodent brain in the study of alcohol neurotoxicity is considered in detail, and the information obtained from this methodology concerning the role of glucocorticoid receptors and excitable membrane proteins in this neurotoxicity. The influence of glucocorticoids on alcohol consumption and possible contributions to alcohol dependence are then considered. In conclusion, more information concerning the effects of glucocorticoids on plasticity and alcohol neurotoxicity during the adolescent period is needed.

An inter-gender effect on ethanol drinking in rats: Proximal females increase ethanol drinking in males

Three groups of male Long-Evans hooded rats were assessed for effects of social opportunity on drinking of ethanol or water. The ethanol/female group received intermittent presentations of a sipper containing ethanol that was followed by 15 s of social interaction opportunity with a female rat. The ethanol/male group received similar training except the social interaction opportunity was with a male rat. The water/female group received training similar to the ethanol/female group except that the sipper contained water. For the ethanol groups, the concentration of ethanol [3%, 4%, 6%, 8% and 10% (vol/vol)] in the sipper was increased across sessions. With 10% ethanol in the sipper, social opportunity with females induced more drinking and ethanol intake than did social opportunity with males. Social opportunity with females induced more intake of ethanol than water. Post-session plasma samples revealed social opportunity with females induced higher corticosterone and testosterone levels than did social opportunity with males, irrespective of the sipper fluid. This study documents, for the first time, an inter-gender effect on ethanol drinking in rats.

The glucocorticoid receptor antagonist mifepristone reduces ethanol intake in rats under limited access conditions

There is a substantial amount of evidence indicating control over ethanol intake by steroid hormones, particularly adrenal glucocorticoids. Thus far, however, studies employing pharmacological methods have failed to find effects of glucocorticoid receptor blockade on voluntary ethanol consumption. Since length of ethanol access period can influence ethanol consumption levels as well as potential pharmacological effects in such studies, the present study was conducted to determine the effects of acute administration of the glucocorticoid receptor (GR) antagonist mifepristone on voluntary ethanol intake under limited access conditions. Rats were fluid restricted and given concurrent access to 10% ethanol and water in a two-bottle choice paradigm for 1 h/day, 5 days a week. Both fluids were available ad libitum during the remaining 2 days per week. Administration of mifepristone (1, 5 and 20 mg/kg i.p.) immediately prior to the limited access two-bottle access period dose-dependently suppressed ethanol intake (maximum 40% at 20 mg/kg). The mineralcorticoid receptor (MR) antagonist spironolactone (10, 25 and 50 mg/kg i.p.) was without effect on ethanol intake, and neither compound had an effect on water intake. These data confirm an active role of GRs in modulating voluntary ethanol consumption, particularly under conditions of limited access.

Effect of chronic alcohol consumption on the activity of the hypothalamic-pituitary-adrenal axis and pituitary beta-endorphin as a function of alcohol intake, age, and gender

BACKGROUND

Experimental evidence indicates that components of the hypothalamic-pituitary-adrenal (HPA) axis and of the endogenous opioid system, such as beta-endorphin (beta-END), influence alcohol consumption, whereas chronic alcohol abuse alters the activity of both systems. Furthermore, gender and age differences have been reported in the activity of the HPA axis under basal conditions, in response to stress and acute alcohol challenge. The objective of the present studies was to investigate the hypothesis that chronic alcohol consumption alters the activity of the HPA axis and pituitary beta-END as a function of severity of alcohol abuse, gender, and age.

METHODS

Three age groups of each gender (18-29, 30-44, and 45-60 years old) were recruited. Each age and gender group included four subgroups: (a) nondrinkers, (b) light drinkers, (c) heavy drinkers, and (d) alcoholics in treatment. Demographic characteristics, alcohol consumption, and presence of alcohol dependence were recorded by using a structured interview. Blood samples were taken on the day of the interview. The levels of plasma adrenal corticotropic hormone (ACTH), cortisol, and beta-END were estimated as an index of the activity of the HPA-axis and pituitary beta-END.

RESULTS

Plasma ACTH and beta-END levels were significantly lower in females than males of all age and drinking category groups. Plasma cortisol levels were higher in 18- to 29-year-old female subjects compared with the 18- to 29-year-old male subjects. The plasma ACTH and beta-END levels were lower whereas plasma cortisol levels were higher in heavy drinkers than nondrinkers. This decrease in plasma ACTH and beta-END levels with heavy drinking was more pronounced in female than male subjects of the 30-44 and 45-60 age groups.

CONCLUSIONS

Chronic drinking, gender, and age influence the activity of the HPA-axis and pituitary beta-END, which in turn may influence drinking behavior.

The impact of corticosteroids on the developing animal

Infants are subjected to both endogenous and exogenous corticosteroids in the pre- and postnatal periods. Stress to the mother before birth, or to the child postpartum, can give rise to high, chronic endogenous corticosteroid levels caused by activation of the hypothalamic-pituitary-adrenal (HPA) axis. Physician-administered exogenous corticosteroids are also used in the management of a wide spectrum of pre- and postnatal conditions. The long-term effects of corticosteroids in developing humans are not well known. Studies in animals, however, indicate that both natural stress and exogenous corticosteroids can have long-lasting and deleterious effects on the body, brain, behavior, and hypothalamic-pituitary-adrenal axis of developing infants. These data suggest that exogenous corticosteroids should be administered with caution, after careful benefit/risk analyses, and that, as far as possible, the developing brain should be protected against the effects of pre- and postnatal stress.

No effect of the cortisol-synthesis inhibitor metyrapone on alcohol drinking: a pilot study

Two bases for this study were the theory of stress as a provoking factor for high alcohol consumption in human being and findings that the stress hormones stimulate ethanol intake in rats. We therefore investigated whether the cortisol-synthesis inhibitor metyrapone could reduce high alcohol consumption in socially stable subjects who reported drinking mainly for relaxation purposes. Most of the investigated subjects were found to be alcohol dependent (81%), with moderately high levels of intake, yet they had not reported more severe life problems. All subjects reported their daily alcohol consumption during 2-week baseline, medication, and postmedication periods. Sixteen subjects were given 1 g of metyrapone orally daily for 14 days, and 15 subjects received placebo. Morning serum cortisol concentration was assessed four times in the course of the study period. Metyrapone treatment was not found to reduce alcohol consumption more than placebo. Serum cortisol concentrations remained within the laboratory reference interval during the study and did not differ between the study groups. In this study, we found that a cortisol-synthesis inhibitor had no effect on alcohol consumption. One reason may be that cortisol secretion has no role in the maintenance of high alcohol consumption. On the other hand, because this study is the first of its kind, further studies using other doses of treatment and treatment schedules are suggested.

Short or continuous social stress: suppression of continuously available ethanol intake in subordinate rats

We explored the effects of short, intermediate, and continuous social stress on daily ethanol and water intake in rats. The study was designed to: (1) detect increases in intake during hours when animals were not stressed; and (2) detect shifts in preference from solutions with high to low alcohol content. Male Long-Evans rats acquired ethanol self-administration using a sucrose-fading procedure, which was followed by continuous access to 10% and 3% ethanol solutions and water. After intake stabilized, rats were exposed to three periods of five consecutive days of social stress, with 8-10 days without stress in between. Short social stress consisted of being attacked and defeated by an aggressive opponent, followed by 30 min exposure to threats by the aggressive male while in a protective cage. Intermediate and continuous social stress consisted of a 6 h or 24 h 'threat of attack' exposure, respectively. All stress exposures reduced daily intake of 10% ethanol, did not cause changes in intake of 3% ethanol, and caused increases in water intake. No compensatory ethanol consumption was observed on stress days or after stress exposure was discontinued. These results are at variance with the hypothesis for increased alcohol consumption during or following social stress episodes.

Individual differences in pavlovian autoshaping of lever pressing in rats predict stress-induced corticosterone release and mesolimbic levels of monoamines

Pavlovian autoshaping CRs are directed and reflexive consummatory responses targeted at objects repeatedly paired with rewarding substances. To evaluate the hypothesis that autoshaping may provide an animal learning model of vulnerability to drug abuse, this study relates individual differences in lever-press autoshaping CR performance in rats to stress-induced corticosterone release and tissue monoamine levels in the mesolimbic dopamine tract. Long-Evans rats (n = 14) were given 20 sessions of Pavlovian autoshaping training wherein the insertion of a retractable lever CS was followed by the response-independent presentation of food US. Large between-subjects differences in lever-press autoshaping CR performance were observed, with group high CR frequency (n = 5) performing many more lever press CRs than group low CR frequency (n = 9). Tail-blood samples were obtained before and after the 20th autoshaping session, then 24 h later the rats were sacrificed and dissection yielded tissue samples of nucleus accumbens (NAC), prefrontal cortex (PFC), caudate putamen (CP), and ventral tegmental area (VTA). Serum levels of postsession corticosterone were elevated in group high CR frequency. HPLC revealed that group high CR frequency had higher tissue levels of dopamine and DOPAC in NAC, lower levels of DOPAC/DA turnover in CP, and lower levels of 5-HIAA and lower 5-HIAA/5-HT turnover in VTA. The neurochemical profile of rats that perform more autoshaping CRs share some features of vulnerability to drug abuse.

Behavioral responses to ethanol in rats perinatally exposed to low lead levels

Wistar rats were exposed to 220 ppm of lead (Pb) in the drinking water from conception to the end of the nursing period (postnatal day 25). Maternal blood Pb levels at this time were 25 microg/dl. Male offspring were tested at the age of 35 or 70 days. We studied the anxiolytic response to 0.5-2.0 g/kg ethanol in an elevated plus maze test and preference for increasing ethanol solutions (2%, 4%, and 6%, v/v) in a free-choice paradigm; we also determined basal blood levels of corticosterone. Results demonstrated that, at 35 days of age, experimental rats were hypersensitive to the anxiolytic effect of ethanol and showed greater voluntary intake of this drug. In addition, 35-day-old Pb-treated rats exhibited higher basal levels of corticosterone as compared with those of controls. These differences disappeared at 70 days. Our findings are discussed in terms of either Pb-induced alterations in the development of the CNS or higher levels of corticosterone in experimental animals. Possible Pb-ethanol effects interactions are also considered.

Long-term behavioral effects of repetitive pain in neonatal rat pups

Human preterm neonates are subjected to repetitive pain during neonatal intensive care. We hypothesized that exposure to repetitive neonatal pain may cause permanent or long-term changes because of the developmental plasticity of the immature brain. Neonatal rat pups were stimulated one, two, or four times each day from P0 to P7 with either needle prick (noxious groups N1, N2, N4) or cotton tip rub (tactile groups T1, T2, T4). In groups N2, N4, T2, T4 stimuli were applied to separate paws at hourly intervals;each paw was stimulated only once a day. Identical rearing occurred from P7 to P22 days. Pain thresholds were measured on P16, P22, and P65 (hot-plate test), and testing for defensive withdrawal, alcohol preference, air-puff startle, and social discrimination tests occurred during adulthood. Adult rats were exposed to a hot plate at 62 degrees C for 20 s, then sacrificed and perfused at 0 and 30 min after exposure. Fos expression in the somatosensory cortex was measured by immunocytochemistry. Weight gain in the N2 group was greater than the T2 group on P16 (p < 0.05) and P22 (p < 0.005); no differences occurred in the other groups. Decreased pain latencies were noted in the N4 group [5.0 +/- 1.0 s vs. 6.2 +/- 1.4 s on P16 (p < 0.05); 3.9 +/- 0.5 s vs. 5.5 +/- 1.6 s on P22 (p < 0.005)], indicating effects of repetitive neonatal pain on subsequent development of the pain system. As adults, N4 group rats showed an increased preference for alcohol (55 +/- 18% vs. 32 +/- 21%; p = 0.004); increased latency in exploratory and defensive withdrawal behavior (p < 0.05); and a prolonged chemosensory memory in the social discrimination test (p < 0.05). No significant differences occurred in corticosterone and ACTH levels following air-puff startle or in pain thresholds at P65 between N4 and T4 groups. Fos expression at 30 min after hot-plate exposure was significantly greater in all areas of the somatosensory cortex in the T4 group compared with the N4 group (p < 0.05), whereas no differences occurred just after exposure. These data suggest that repetitive pain in neonatal rat pups may lead to an altered development of the pain system associated with decreased pain thresholds during development. Increased plasticity of the neonatal brain may allow these and other changes in brain development to increase their vulnerability to stress disorders and anxiety-mediated adult behavior. Similar behavioral changes have been observed during the later childhood of expreterm neonates who were exposed to prolonged periods of neonatal intensive care.

Tryptophan pyrrolase gene expression in an alcohol preferring and non-preferring mouse strain

There is considerable evidence that the level of cerebral serotonin plays a key role in the volitional consumption of ethanol in both man and animals. Naive alcohol-preferring C57BL/6J mice have been shown to have a lower cerebral serotonin content compared to the non-preferring CBA/Ca mouse strain. This has been attributed to the enhancement of hepatic tryptophan pyrrolase activity in C57 mice. Activity and/or expression of tryptophan pyrrolase may be an important biological determinant of alcohol preference. We have investigated the possible mechanism/s underlying this strain difference in tryptophan pyrrolase activity by assaying both mRNA levels encoding for the tryptophan pyrrolase gene and by mutational analysis of tryptophan pyrrolase cDNA. We were unable to demonstrate any difference in tryptophan pyrrolase mRNA levels between naive C57 and CBA mice. Tryptophan pyrrolase mRNA levels were increased following starvation in C57 mice and following glucocorticoid administration in both C57 and CBA mice. Heteroduplex mutational analysis failed to detect any tryptophan pyrrolase cDNA sequence heterogeneity between these mice strains.

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.

Emerging themes in preclinical research on alcohol and aggression

Animal research into the alcohol-aggression relationship is based on a need to understand this relationship in people, and its success depends on the degree to which animal models can provide appropriate parallels to relevant human phenomena. Comparisons of human and animal literature suggest that parallels may be found for the following: alcohol enhances aggression in some, but not all individuals; consumption increases the probability of victimization (being attacked by a conspecific); alcohol reduces anxiety, and socially stressed individuals show increased voluntary consumption; alcohol reduces avoidance of threatening situations or stimuli and may place individuals at greater risk of being attacked; both anxiety reduction and decreased avoidance of threat may increase the probability of involvement in violent situations. These findings suggest that a variety of mechanisms may be involved in alcohol enhancement of aggression. Differences in effects of alcohol on human, as opposed to animal, aggression may reflect specific human capabilities. Although high doses of alcohol consistently reduce aggression in laboratory animals, this may reflect motoric and sedative effects that are not relevant for human behavior, in which verbal aggression and aggression involving the use of weapons make motor capability less important. Human voluntary alcohol consumption may also reflect response to stressors that also simultaneously promote aggression, a situation not paralleled by animal studies in which the drug is administered rather than voluntarily consumed. Nonetheless, obtained parallels suggest that animal experimentation using ecologically relevant situations can provide highly generalizable analyses of the alcohol-aggression relationship.

Facilitation of ethanol consumption by intracerebroventricular infusions of corticosterone

Male Wistar rats bearing intracerebroventricular (ICV) cannulae and with simultaneous access to 6% ethanol and water were subjected to adrenalectomy (ADX) or sham surgery. ADX decreased ethanol intake. Starting a few days later, the animals received ICV infusions with 100 micrograms corticosterone acetate (CORT) with 2-to 3-day intervals for 2 weeks. ICV CORT, but not SC CORT at the same dose, restored ethanol consumption in ADX rats to preoperative levels, whereas vehicle infusions (propylene glycol) did not. Adrenally intact animals, which normally consumed moderate amounts of ethanol (approximately 0.5 g/kg per day), also showed a robust effect of ICV infusions of CORT, whereas this facilitatory effect was not observed in high consumers (approximately 3.0 g/kg per day). The suppressive effect of ADX on ethanol intake was not reproduced by concurrent and repeated ICV infusions of intracellular mineralocorticoid (RU 28318) and glucocorticoid (mifepristone) receptor blockers. It is concluded that CORT stimulates alcohol consumption by acting in the brain, probably by way of neuronal membrane mechanisms.