The role of stress in drug self-administration

Is love passion an addictive disorder?

AIMS

Inquiry regarding the relationship between passionate love and addiction has long been a topic of intense debate. Recent advances in neurobiology now allow for an examination between these two states.

METHODS

After describing the clinical distinctions between "love passion," "love addiction," and "sex addiction," we compare clinical, neuropsychological, neurobiological, and neuroimaging data on love, passion, pathological gambling (PG) and substance dependence.

RESULTS

There are no recognized definitions or diagnostic criteria for "love addiction," but its phenomenology has some similarities to substance dependence: euphoria and unrestrained desire in the presence of the love object or associated stimuli (drug intoxication); negative mood, anhedonia, and sleep disturbance when separated from the love object (drug withdrawal); focussed attention on and intrusive thoughts about the love object; and maladaptive or problematic patterns of behavior (love relation) leading to clinically significant impairment or distress, with pursuit despite knowledge of adverse consequences. Limited animal and human studies suggest that brain regions (e.g., insula, anterior cingulated [ACC], orbitofrontal [OFC]) and neurotransmitters (dopamine) that mediate substance dependence may also be involved with love addiction (as for PG). Ocytocin (OT), which is implicated in social attachment and mating behavior, may also be involved in substance dependence. There are no data on the epidemiology, genetics, co-morbidity, or treatment of love addiction.

CONCLUSION

There are currently insufficient data to place some cases of "love passion" within a clinical disorder, such as "love addiction," in an official diagnostic nomenclature or to firmly classify it as a behavioral addiction or disorder of impulse control. Further clinical and scientific studies are needed to improve our understanding and treatment of this condition. For these studies, we propose new criteria for evaluating addiction to love.

Age at menarche is associated with divergent alcohol use patterns in early adolescence and early adulthood

A cross-sectional retrospective design was employed to examine the relationship between age at menarche (AAM) and alcohol use patterns from middle childhood (age 7) to early adulthood in 265 University-aged women. Earlier menarche was associated with: (a) earlier ages at first drink and first intoxication, (b) greater use between ages 9 and 14 (i.e., frequency, amount, vomiting), and (c) binge drinking between ages 11 and 14. In contrast, late menarche was associated with greater current use in the adult women (i.e., frequency, amount, hangovers). Early timing of first intoxication relative to menarche (FIRM) strongly predicted higher current drinking. These findings suggest: (a) a link between AAM and alcohol use as early as age 9, (b) opposite relationships between AAM and alcohol use during two distinct developmental periods separated by a period of use unassociated with AAM, and (c) that the impact of early FIRM on adult consumption deserves further study.

About a snail, a toad, and rodents: animal models for adaptation research

Neural adaptation mechanisms have many similarities throughout the animal kingdom, enabling to study fundamentals of human adaptation in selected animal models with experimental approaches that are impossible to apply in man. This will be illustrated by reviewing research on three of such animal models, viz. (1) the egg-laying behavior of a snail, Lymnaea stagnalis: how one neuron type controls behavior, (2) adaptation to the ambient light condition by a toad, Xenopus laevis: how a neuroendocrine cell integrates complex external and neural inputs, and (3) stress, feeding, and depression in rodents: how a neuronal network co-ordinates different but related complex behaviors. Special attention is being paid to the actions of neurochemical messengers, such as neuropeptide Y, urocortin 1, and brain-derived neurotrophic factor. While awaiting new technological developments to study the living human brain at the cellular and molecular levels, continuing progress in the insight in the functioning of human adaptation mechanisms may be expected from neuroendocrine research using invertebrate and vertebrate animal models.

Adolescent social defeat alters neural, endocrine and behavioral responses to amphetamine in adult male rats

The mesocorticolimbic dopamine system, which governs components of reward and goal-directed behaviors, undergoes final maturation during adolescence. Adolescent social stress contributes to adult behavioral dysfunction and is linked to adult psychiatric and addiction disorders. Here, behavioral, corticosterone and limbic dopamine responses to amphetamine were examined in adult male rats previously exposed to repeated social defeat stress during mid-adolescence. Amphetamine (2.5mg/kg, ip) was administered after a novel environment test, with behavior observed in the same context for 90min thereafter. Adult rats that had been defeated in adolescence showed increased locomotion in the novel environment but reduced amphetamine-induced locomotion relative to non-defeated age matched controls. Monoamine and corticosterone responses to amphetamine were examined following a second amphetamine injection 3 days later. In previously defeated rats, corticosterone and medial prefrontal cortex dopamine responses to amphetamine were blunted while dopamine responses in the nucleus accumbens core were elevated. Our results suggest that experience of social defeat stress during adolescent development can contribute to altered behavioral and endocrine responses to amphetamine in adulthood. Furthermore, these effects are paralleled by changes in amphetamine-induced dopamine responses in corticolimbic systems implicated in addiction disorders.

Adolescence: a central event in shaping stress reactivity

The magnitude and duration of the hormonal stress response change dramatically throughout an organism's lifespan. Although much is known about the factors that modulate stress reactivity during adulthood and how neonatal development and aging influence stress responsiveness, we know relatively little about how stress reactivity changes during the juvenile to adult transition. Recent studies in adolescent boys and girls have suggested that stress is an important factor contributing to an individual's vulnerability to various neuropsychological dysfunctions, including anxiety, depression, and drug abuse. Thus, understanding how exposure to stressors during this crucial period of development lead to negative consequences is of paramount importance. A growing body of literature indicates that pubertal organisms react differentially, both physiologically and behaviorally, to a stressor compared to adults. The purpose of this review, therefore, is to discuss the recent findings regarding the pubertal maturation of stress reactivity, while also highlighting future research directions that will aid in our understanding of stress and adolescent mental health and development.

Toxic keratopathy due to abuse of topical anesthetic drugs

OBJECTIVE

To describe 8 cases of toxic keratopathy due to abuse of topical anesthetic drugs.

METHODS

Clinical findings from patients with toxic keratopathy were investigated retrospectively.

RESULTS

Two patients had toxic keratopathy bilaterally. Five of 8 patients had an ocular history of a corneal foreign body, 1 had basal membrane dystrophy, 1 had ultraviolet radiation, and 1 had chemical burn. All patients had undergone psychiatric consultation. Four patients had anxiety disorder and 1 had bipolar disease. Clinical signs were improved in all patients with discontinuation of topical anesthetic drug use along with adjunctive psychiatric treatment. Penetrating keratoplasty was performed in 2 patients.

CONCLUSION

Toxic keratopathy due to topical anesthetic abuse is a curable disease. Early diagnosis and prevention of topical anesthetic drug use are the most important steps in the treatment of this condition. As these patients commonly exhibit psychiatric disorders, adjunctive psychiatric treatment may help to break the chemical addiction.

Chronic stress enhances the corticosterone response and neurotoxicity to +3,4-methylenedioxymethamphetamine (MDMA): the role of ambient temperature

Stress facilitates drug abuse by humans. In rodents, stress enhances the neurochemical, neuroendocrine, and behavioral responses to psychostimulants. Although chronic unpredictable stress (CUS) enhances the acute hyperthermic and long-term monoamine-depleting effects of the psychostimulant +3,4-methylenedioxymethamphetamine (MDMA), the roles of hyperthermia and corticosterone (CORT) in mediating the stress-induced enhancement of MDMA-induced serotonin (5-HT) and dopamine (DA) depletions are unknown. Rats were exposed to 10 days of CUS and then challenged with MDMA (5 mg/kg i.p. once every 2 h for a total of four injections). Prior exposure to CUS augmented MDMA-induced hyperthermia and plasma CORT secretion and the long-term depletions in 5-HT content in striatum, hippocampus, and frontal cortex and DA content in striatum. A reduced ambient temperature of 21°C attenuated the hyperthermia, CORT secretion, and 5-HT decreases after MDMA in nonstressed rats. The lower ambient temperature also prevented the augmented hyperthermia, CORT secretion, and enhanced 5-HT and DA depletions after MDMA in chronically stressed rats to levels exhibited by nonstressed, MDMA-treated rats. To investigate the role of CORT on monoamine depletions in response to MDMA, stressed and nonstressed rats were treated with the CORT synthesis inhibitor metyrapone during exposure to MDMA. Metyrapone prevented CORT secretion in both stressed and nonstressed rats but did not modify 5-HT or DA depletions in any brain region examined. This study suggests that enhanced CORT is a consequence of enhanced hyperthermia and the CUS-induced enhancements of MDMA-induced monoamine depletions may be mediated by hyperthermia but not CORT.

Concurrent glucocorticoid and noradrenergic activity shifts instrumental behavior from goal-directed to habitual control

Stress modulates instrumental action in favor of habitual stimulus-response processes that are insensitive to changes in outcome value and at the expense of goal-directed action-outcome processes. The neuroendocrine mechanism underlying this phenomenon is unknown. Here, we tested the hypothesis that concurrent glucocorticoid and noradrenergic activity bias instrumental behavior toward habitual performance. To this end, healthy men and women received hydrocortisone, the alpha2-adrenoceptor antagonist yohimbine or both orally before they were trained in two instrumental actions leading to two distinct food outcomes. After training, one of the outcomes was devalued by inviting participants to eat that food to satiety. A subsequent extinction test revealed whether instrumental performance was goal-directed or habitual. Participants that received hydrocortisone or yohimbine alone decreased responding to the devalued action in the extinction test, i.e., they behaved goal-directed. The combined administration of hydrocortisone and yohimbine, however, rendered participants' behavior insensitive to changes in the value of the goal (i.e., habitual). These findings demonstrate that the concerted action of glucocorticoids and noradrenergic activity shifts instrumental behavior from goal-directed to habitual control.

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.

Social anxiety disorder and alcohol use disorder co-morbidity in the National Epidemiologic Survey on Alcohol and Related Conditions

BACKGROUND

To assess the prevalence and clinical impact of co-morbid social anxiety disorder (SAD) and alcohol use disorders (AUD, i.e. alcohol abuse and alcohol dependence) in a nationally representative sample of adults in the United States.

METHOD

Data came from a large representative sample of the US population. Face-to-face interviews of 43093 adults residing in households were conducted during 2001-2002. Diagnoses of mood, anxiety, alcohol and drug use disorders and personality disorders were based on the Alcohol Use Disorder and Associated Disabilities Interview Schedule - DSM-IV version.

RESULTS

Lifetime prevalence of co-morbid AUD and SAD in the general population was 2.4%. SAD was associated with significantly increased rates of alcohol dependence [odds ratio (OR) 2.8] and alcohol abuse (OR 1.2). Among respondents with alcohol dependence, SAD was associated with significantly more mood, anxiety, psychotic and personality disorders. Among respondents with SAD, alcohol dependence and abuse were most strongly associated with more substance use disorders, pathological gambling and antisocial personality disorders. SAD occurred before alcohol dependence in 79.7% of co-morbid cases, but co-morbidity status did not influence age of onset for either disorder. Co-morbid SAD was associated with increased severity of alcohol dependence and abuse. Respondents with co-morbid SAD and alcohol dependence or abuse reported low rates of treatment-seeking.

CONCLUSIONS

Co-morbid lifetime AUD and SAD is a prevalent dual diagnosis, associated with substantial rates of additional co-morbidity, but remaining largely untreated. Future research should clarify the etiology of this co-morbid presentation to better identify effective means of intervention.

Stress-induced changes in mood and cortisol release predict mood effects of amphetamine

BACKGROUND

Stress is thought to contribute to both initiation and relapse to drug abuse. However, the mechanisms by which stress influences drug use are unclear. Interestingly, responses to acute administration of stimulant drugs resemble certain neuronal and hormonal responses to acute stress, and there is accumulating evidence that individual variation in the positive reinforcing or euphorigenic effects of a drug is related to individual differences in responsivity to acute stress.

METHODS

In this study we evaluated relationships between physiological and subjective responses to a stressful task and to an oral dose of d-amphetamine in healthy adult volunteers (N=34). Individuals participated in four experimental sessions; two behavioral sessions involving a stressful task (i.e., public speech) or a non-stressful control task, and two drug sessions involving oral administration of d-amphetamine (20mg) or a placebo. The dependent measures included salivary cortisol, heart rate, mean arterial pressure, and subjective ratings of mood.

RESULTS

As expected, both stress and d-amphetamine increased cortisol, heart rate and blood pressure. Stress increased negative mood, whereas d-amphetamine induced prototypic stimulant effects and increased ratings of drug liking. Analyses revealed that increased negative mood states after stress were correlated with positive mood after amphetamine. In addition, increased cortisol after stress was correlated with positive mood responses to amphetamine. Finally, there were modest positive correlations between cortisol and heart rate increases after stress and mean arterial pressure after amphetamine.

CONCLUSIONS

These results support and extend previous observations that responses to acute stress are correlated with certain subjective, hormonal and cardiovascular effects of a stimulant drug.

Individual differences in prefrontal cortex function and the transition from drug use to drug dependence

Several neuropsychological hypotheses have been formulated to explain the transition to addiction, including hedonic allostasis, incentive salience, and the development of habits. A key feature of addiction that remains to be explored is the important individual variability observed in the propensity to self-administer drugs, the sensitivity to drug-associated cues, the severity of the withdrawal state, and the ability to quit. In this review, we suggest that the concept of self-regulation, combined with the concept of modularity of cognitive function, may aid in the understanding of the neural basis of individual differences in the vulnerability to drugs and the transition to addiction. The thesis of this review is that drug addiction involves a failure of the different subcomponents of the executive systems controlling key cognitive modules that process reward, pain, stress, emotion, habits, and decision-making. A subhypothesis is that the different patterns of drug addiction and individual differences in the transition to addiction may emerge from differential vulnerability in one or more of the subcomponents.

The dissection of transcriptional modules regulated by various drugs of abuse in the mouse striatum

BACKGROUND

Various drugs of abuse activate intracellular pathways in the brain reward system. These pathways regulate the expression of genes that are essential to the development of addiction. To reveal genes common and distinct for different classes of drugs of abuse, we compared the effects of nicotine, ethanol, cocaine, morphine, heroin and methamphetamine on gene expression profiles in the mouse striatum.

RESULTS

We applied whole-genome microarray profiling to evaluate detailed time-courses (1, 2, 4 and 8 hours) of transcriptome alterations following acute drug administration in mice. We identified 42 drug-responsive genes that were segregated into two main transcriptional modules. The first module consisted of activity-dependent transcripts (including Fos and Npas4), which are induced by psychostimulants and opioids. The second group of genes (including Fkbp5 and S3-12), which are controlled, in part, by the release of steroid hormones, was strongly activated by ethanol and opioids. Using pharmacological tools, we were able to inhibit the induction of particular modules of drug-related genomic profiles. We selected a subset of genes for validation by in situ hybridization and quantitative PCR. We also showed that knockdown of the drug-responsive genes Sgk1 and Tsc22d3 resulted in alterations to dendritic spines in mice, possibly reflecting an altered potential for plastic changes.

CONCLUSIONS

Our study identified modules of drug-induced genes that share functional relationships. These genes may play a critical role in the early stages of addiction.

Neuroplasticity in the mesolimbic system induced by natural reward and subsequent reward abstinence

BACKGROUND

Natural reward and drugs of abuse converge on the mesolimbic system, where drugs of abuse induce neuronal alterations. Here, we tested plasticity in this system after natural reward and the subsequent impact on drug responses.

METHODS

Effects of sexual experience in male rats on behavioral sensitization and conditioned place preference associated with d-amphetamine (AMPH) and Golgi-impregnated dendrites and spines of nucleus accumbens (NAc) cells were determined. Moreover, the impact of abstinence from sexual behavior in experienced males on these parameters was tested.

RESULTS

First, repeated sexual behavior induced a sensitized locomotor response to AMPH compared with sexually naive control subjects observed 1, 7, and 28 days after last mating session. Second, sexually experienced animals formed a conditioned place preference for lower doses of AMPH than sexually naive males, indicative of enhanced reward value of AMPH. Finally, Golgi-Cox analysis demonstrated increased numbers of dendrites and spines in the NAc core and shell with sexual experience. The latter two alterations were dependent on a period of abstinence of 7-10 days.

CONCLUSIONS

Sexual experience induces functional and morphological alterations in the mesolimbic system similar to repeated exposure to psychostimulants. Moreover, abstinence from sexual behavior after repeated mating was essential for increased reward for drugs and dendritic arbors of NAc neurons, suggesting that the loss of sexual reward might also contribute to neuroplasticity of the mesolimbic system. These results suggest that some alterations in the mesolimbic system are common for natural and drug reward and might play a role in general reinforcement.

Differences in negative mood-induced smoking reinforcement due to distress tolerance, anxiety sensitivity, and depression history

RATIONALE

Negative mood increases smoking reinforcement and may do so to a greater degree in smokers vulnerable to negative mood dysregulation.

METHODS

Adult smokers (N = 71) without current depression were randomly assigned to one of two smoking conditions (nicotine or denic cigarettes, presented blind) maintained across all sessions. Subjects completed one neutral mood session and four negative mood induction sessions. Negative mood inductions included one each of the following: 1) overnight smoking abstinence, 2) challenging computer task, 3) public speech preparation, 4) watching negative mood slides. In each session, subjects took 4 puffs on their assigned cigarette, rated it for "liking" (reward), and then smoked those cigarettes ad libitum (reinforcement) during continued mood induction. Affect was assessed intermittently before and after smoking. Differences in responses were examined as functions of self-reported history of major depression and levels of distress tolerance and anxiety sensitivity.

RESULTS

Smoking reinforcement, but not reward or negative affect relief, was greater in all sessions in those with a history of depression and greater after overnight abstinence in those with lower distress tolerance. Reward and affect relief, but not reinforcement, were greater during speech preparation among those high in anxiety sensitivity.

CONCLUSIONS

Low distress tolerance may enhance acute smoking reinforcement due to abstinence, while depression history may broadly increase acute smoking reinforcement regardless of mood. Neither smoking reward nor affect help explain these individual differences in smoking reinforcement.

Delineating the psychic structure of substance abuse and addictions: should anxiety, mood and impulse-control dysregulation be included?

Current "official" nosology (e.g. DSM IV) is largely limited to physical manifestations of addiction that can be objectively observed and are suited to the maintaining of an "atheoretical" perspective. However, addicted subjects display additional psychiatric symptoms that affect their well-being and social functioning and, in accordance with DSM IV, are typically relegated to the domain of psychiatric "comorbidity." We contend that the relationship of these psychiatric symptoms with addiction is very close, as demonstrated by the high frequency of association observed. We further assert that substance use may modify pre-existing psychic structures such as temperament and related subthreshold conditions and lead to addiction as a specific mental disorder, inclusive also of symptoms pertaining to mood/anxiety, or impulse-control dimensions. The present contribution addresses the weaknesses of the current DSM-based nosology of addiction-related mental comorbidity. We highlight the overlap of the biological substrates and the neurophysiology of addictive processes and psychiatric symptoms associated with addiction, and propose the inclusion of specific mood, anxiety, and impulse-control dimensions in the psychopathology of addictive processes. We postulate that addiction reaches beyond the mere result of drug-elicited effects on the brain and cannot be peremptorily equated only with the use of drugs despite the adverse consequences produced. We infer that mood, anxiety and impulse-control dysregulation is at the very core of both the origins and clinical manifestations of addiction and should be incorporated into the nosology of the same, emphasising how addiction is a relapsing chronic condition in which psychiatric manifestations play a crucial role. To conclude, addictionology cannot be severed from its psychopathological connotations, in view of the undeniable presence of symptoms, of their manifest contribution to the way addicted patients feel and behave, and to the role they play in maintaining the continued use of substances.

Genotype-phenotype associations in understanding the role of corticosteroid-binding globulin in health and disease animal models

Corticosteroid-binding globulin (CBG) is a plasma glycoprotein discovered more than 60 years ago for its high-affinity for glucocorticoids. Although its molecular structure and its biochemical properties have been described, its various biological roles and its importance are not yet fully understood. This review focuses first on studies that have used no-hypothesis-driven genetic approaches in animal models to reveal the higher than expected importance of CBG in particular in glucocorticoid stress responses. Then the dissection of some CBG physiological roles in an animal model of genetic CBG deficiency is reported. Finally, studies on the role of CBG genetic variability in human obesity traits are reviewed and discussed.

The locus coeruleus: A key nucleus where stress and opioids intersect to mediate vulnerability to opiate abuse

The interaction between the stress axis and endogenous opioid systems has gained substantial clinical attention as it is increasingly recognized that stress predisposes to opiate abuse. For example, stress has been implicated as a risk factor in vulnerability to the initiation and maintenance of opiate abuse and is thought to play an important role in relapse in subjects with a history of abuse. Numerous reports indicating that stress alters individual sensitivity to opiates suggest that prior stress can influence the pharmacodynamics of opiates that are used in clinical settings. Conversely, the effects of opiates on different components of the stress axis can impact on individual responsivity to stressors and potentially predispose individuals to stress-related psychiatric disorders. One site at which opiates and stress substrates may interact to have global effects on behavior is within the locus coeruleus (LC), the major brain norepinephrine (NE)-containing nucleus. This review summarizes our current knowledge regarding the anatomical and neurochemical afferent regulation of the LC. It then presents physiological studies demonstrating opposing interactions between opioids and stress-related neuropeptides in the LC and summarizes results showing that chronic morphine exposure sensitizes the LC-NE system to corticotropin releasing factor and stress. Finally, new evidence for novel presynaptic actions of kappa-opioids on LC afferents is provided that adds another dimension to our model of how this central NE system is co-regulated by opioids and stress-related peptides.

Role of CRF and other neuropeptides in stress-induced reinstatement of drug seeking

A central problem in the treatment of drug addiction is high rates of relapse to drug use after periods of forced or self-imposed abstinence. This relapse is often provoked by exposure to stress. Stress-induced relapse to drug seeking can be modeled in laboratory animals using a reinstatement procedure. In this procedure, drug-taking behaviors are extinguished and then reinstated by acute exposure to stressors like intermittent unpredictable footshock, restraint, food deprivation, and systemic injections of yohimbine, an alpha-2 adrenoceptor antagonist that induces stress-like responses in humans and nonhumans. For this special issue entitled "The role of neuropeptides in stress and addiction", we review results from studies on the role of corticotropin-releasing factor (CRF) and several other peptides in stress-induced reinstatement of drug seeking in laboratory animals. The results of the studies reviewed indicate that extrahypothalamic CRF plays a critical role in stress-induced reinstatement of drug seeking; this role is largely independent of drug class, experimental procedure, and type of stressor. There is also limited evidence for the role of dynorphins, hypocretins (orexins), nociceptin (orphanin FQ), and leptin in stress-induced reinstatement of drug seeking.

Role of innate and drug-induced dysregulation of brain stress and arousal systems in addiction: Focus on corticotropin-releasing factor, nociceptin/orphanin FQ, and orexin/hypocretin

Stress-like symptoms are an integral part of acute and protracted drug withdrawal, and several lines of evidence have shown that dysregulation of brain stress systems, including the extrahypothalamic corticotropin-releasing factor (CRF) system, following long-term drug use is of major importance in maintaining drug and alcohol addiction. Recently, two other neuropeptide systems have attracted interest, the nociceptin/orphanin FQ (N/OFQ) and orexin/hypocretin (Orx/Hcrt) systems. N/OFQ participates in a wide range of physiological responses, and the hypothalamic Orx/Hcrt system helps regulate several physiological processes, including feeding, energy metabolism, and arousal. Moreover, these two systems have been suggested to participate in psychiatric disorders, including anxiety and drug addiction. Dysregulation of these systems by chronic drug exposure has been hypothesized to play a role in the maintenance of addiction and dependence. Recent evidence demonstrated that interactions between CRF-N/OFQ and CRF-Orx/Hcrt systems may be functionally relevant for the control of stress-related addictive behavior. The present review discusses recent findings that support the hypotheses of the participation and dysregulation of these systems in drug addiction and evaluates the current understanding of interactions among these stress-regulatory peptides.

Roles of neural stem cells and adult neurogenesis in adolescent alcohol use disorders

This review discusses the contributions of a newly considered form of plasticity, the ongoing production of new neurons from neural stem cells, or adult neurogenesis, within the context of neuropathologies that occur with excessive alcohol intake in the adolescents. Neural stem cells and adult neurogenesis are now thought to contribute to the structural integrity of the hippocampus, a limbic system region involved in learning, memory, behavioral control, and mood. In adolescents with alcohol use disorders (AUDs), the hippocampus appears to be particularly vulnerable to the neurodegenerative effects of alcohol, but the role of neural stem cells and adult neurogenesis in alcoholic neuropathology has only recently been considered. This review encompasses a brief overview of neural stem cells and the processes involved in adult neurogenesis, how neural stem cells are affected by alcohol, and possible differences in the neurogenic niche between adults and adolescents. Specifically, what is known about developmental differences in adult neurogenesis between the adult and adolescent is gleaned from the literature, as well as how alcohol affects this process differently among the age groups. Finally, this review suggests differences that may exist in the neurogenic niche between adults and adolescents and how these differences may contribute to the susceptibility of the adolescent hippocampus to damage. However, many more studies are needed to discern whether these developmental differences contribute to the vulnerability of the adolescent to developing an AUD.

Plasma transcortin influences endocrine and behavioral stress responses in mice

Glucocorticoids are released after hypothalamus-pituitary-adrenal axis stimulation by stress and act both in the periphery and in the brain to bring about adaptive responses that are essential for life. Dysregulation of the stress response can precipitate psychiatric diseases, in particular depression. Recent genetic studies have suggested that the glucocorticoid carrier transcortin, also called corticosteroid-binding globulin (CBG), may have an important role in stress response. We have investigated the effect of partial or total transcortin deficiency using transcortin knockout mice on hypothalamus-pituitary-adrenal axis functioning and regulation as well as on behaviors linked to anxiety and depression traits in animals. We show that CBG deficiency in mice results in markedly reduced total circulating corticosterone at rest and in response to stress. Interestingly, free corticosterone concentrations are normal at rest but present a reduced surge after stress in transcortin-deficient mice. No differences were detected between transcortin-deficient mice for anxiety-related traits. However, transcortin-deficient mice display increased immobility in the forced-swimming test and markedly enhanced learned helplessness after prolonged uncontrollable stress. The latter is associated with an approximately 30% decrease in circulating levels of free corticosterone as well as reduced Egr-1 mRNA expression in hippocampus in CBG-deficient mice. Additionally, transcortin-deficient mice show no sensitization to cocaine-induced locomotor responses, a well described corticosterone-dependent test. Thus, transcortin deficiency leads to insufficient glucocorticoid signaling and altered behavioral responses after stress. These findings uncover the critical role of plasma transcortin in providing an adequate endocrine and behavioral response to stress.

Endocrine and metabolic effects of smoking cessation

BACKGROUND

Cardiovascular, pulmonary, and oncological hazards of tobacco smoking have been well studied. Smoking may also have multiple effects on endocrine and metabolic systems affecting pituitary, thyroid, and adrenal glands; testicular and ovarian function; as well as energy balance; lipid, and glucose metabolism; and insulin resistance. Less is known about hormonal and metabolic effects that patients may experience while quitting smoking.

SCOPE

The objective of this article is to review systematically data on the endocrine and metabolic effects of smoking cessation. Articles based upon clinical trials, randomised controlled trials, and meta-analyses were obtained via a MEDLINE search (articles published between 1 August 1998 and 31 July 2008, inclusive; English language; human subjects; including abstracts) using key search terms relating to smoking cessation and endocrine or metabolic parameters. Additional studies were identified from the bibliographies of reviewed literature. Studies related to the search criteria were reviewed, 199 papers were identified, and 57 pertinent to this review were included.

FINDINGS

Limited data are available on the short- and long-term effects of smoking cessation on hypothalamic- and thyroid-pituitary-adrenal axes, sex hormones, energy homeostasis, and lipid and glucose metabolism. Initial data indicate that smoking cessation is associated with decreased cortisol levels and in the short-term, smoking cessation does not correct the diminished adrenocortical responses to stress caused by chronic smoking. Cessation reverses smoking's effects on thyroid disorders and may reduce the risk of osteoporosis. Finally, smoking cessation increases transiently food intake and sustained weight gain and is associated with increases in high-density lipoprotein cholesterol levels that occur rapidly on cessation.

CONCLUSION

Further research may provide insight into post-cessation endocrine changes that may be caused by alterations to central and peripheral systems. Such research may increase the understanding of underlying biological mechanisms that lead to symptoms and clinical features of smoking cessation.

Maternal separation fails to render animals more susceptible to methamphetamine-induced conditioned place preference

The maternal separation (MS) paradigm is an animal model that has been successfully used to study the long term effects of child abuse and neglect. Experiments showed that animals subjected to trauma and stress early in life display behavioural, endocrinological and growth factor abnormalities at a later stage in life, results that mirrored clinical conditions. It is apparent that adverse events early in life may affect the development and maturation of the brain negatively. The purpose of the present study was to investigate whether the abnormal brain development occurring in separated animals would also enhance the development of a preference for psychostimulant drug usage. Rats were subjected to maternal deprivation and further exposed to methamphetamine-induced conditioned place preference (CPP) which primarily measures drug reward (ventral striatum) learning and memory. Apomorphine-induced locomotor activity was also assessed to investigate the effects of methamphetamine on the dorsal (primarily locomotor activity) striatal dopaminergic system. We found that four consecutive injections of methamphetamine resulted in CPP behaviour 24 h after the 4th injection. A further four injections yielded similar CPP results and this effect lasted for at least 7 days until the third CPP assessment. These animals also had decreased ACTH and corticosterone secretions, but the prolactin levels were increased. Prior exposure to maternal separation did not have any effect on the CPP test. The ACTH and corticosterone secretions were also similarly reduced. However maternal separation decreased the release of prolactin and this reduction was not evident in the separated group that received methamphetamine. There was no significant difference in the apomorphine-induced locomotor activity of normally reared animals whether they received methamphetamine or saline. Interestingly there was a significant difference in locomotor activity between the two groups of animals that were subjected to maternal deprivation. The separated animals that received methamphetamine displayed markedly reduced locomotor activity upon apomorphine administration when compared to those that were treated with saline. Taken together, we conclude that maternal deprivation differentially influences dorsal and ventral striatal regions implicating dopaminergic mechanisms.

Voluntary alcohol consumption alters stress-induced changes in dopamine-2 receptor binding in Wistar-Kyoto rat brain

The Wistar-Kyoto (WKY) rat has been proposed as an animal model of depressive behavior and exhibits hyper-responsiveness to stressful stimulation when compared to other rat strains. We have demonstrated that WKY rats consume 200% more alcohol under naïve conditions as compared to their outbred counterparts, Wistar (WIS) rats. The present study was designed to understand the influence of stress and alcohol consumption on central dopamine type-2 (D2) receptor sites in these two behaviorally distinct rat strains. The first part of this study examined the effects of chronic stress on alcohol consumption, while the second part examined the binding of [(125)I]-Iodosulpiride to D2 receptors in control, stressed or stress and alcohol co-treated WKY compared to WIS rats. Exposure to chronic stress led to an increase in the amount of alcohol consumed by both rat strains, with WKY rats consuming significantly more alcohol than WIS rats with or without stress exposure. Quantitative autoradiography experiments showed that chronic stress increased D2 receptor binding in the caudate putamen (CPu), nucleus accumbens (NAc), substantia nigra (SN) and ventral tegmental area (VTA) of WKY rats, and reduced receptor binding in the CPu and SN of WIS rats. Compared to the stressed animals, WKY rats co-treated with stress and alcohol demonstrated a reduction in D2 receptor sites in the cell body regions (SN and VTA), while WIS rats showed no changes in receptor binding. The observed changes in D2 receptor sites may indicate altered DA neurotransmission following stress and alcohol exposure. Since stressed WKY rats consumed more alcohol, it is possible that consumption of alcohol reverses the stress-induced D2 receptor alterations in the cell body regions, suggestive of a self medicating phenotype.

Neurobiological mechanisms contributing to alcohol-stress-anxiety interactions

This article summarizes the proceedings of a symposium that was presented at a conference entitled "Alcoholism and Stress: A Framework for Future Treatment Strategies." The conference was held in Volterra, Italy on May 6-9, 2008 and this symposium was chaired by Jeff L. Weiner. The overall goal of this session was to review recent findings that may shed new light on the neurobiological mechanisms that underlie the complex relationships between stress, anxiety, and alcoholism. Dr. Danny Winder described a novel interaction between D1 receptor activation and the corticotrophin-releasing factor (CRF) system that leads to an increase in glutamatergic synaptic transmission in the bed nucleus of the stria terminalis. Dr. Marisa Roberto presented recent data describing how protein kinase C epsilon, ethanol, and CRF interact to alter GABAergic inhibition in the central nucleus of the amygdala. Dr. Jeff Weiner presented recent advances in our understanding of inhibitory circuitry within the basolateral amygdala (BLA) and how acute ethanol exposure enhances GABAergic inhibition in these pathways. Finally, Dr. Brian McCool discussed recent findings on complementary glutamatergic and GABAergic adaptations to chronic ethanol exposure and withdrawal in the BLA. Collectively, these investigators have identified novel mechanisms through which neurotransmitter and neuropeptide systems interact to modulate synaptic activity in stress and anxiety circuits. Their studies have also begun to describe how acute and chronic ethanol exposure influence excitatory and inhibitory synaptic communication in these pathways. These findings point toward a number of novel neurobiological targets that may prove useful for the development of more effective treatment strategies for alcohol use disorders.

Stress-induced potentiation of cocaine reward: a role for CRF R1 and CREB

Both clinical and preclinical research have shown that stress can potentiate drug use; however, the underlying mechanisms of this interaction are unknown. Previously, we have shown that a single exposure to forced swim (FS) reinstates extinguished conditioned place preference (CPP) to cocaine and that cAMP response element binding protein (CREB) is necessary for this response. CREB can be activated by corticotropin releasing factor (CRF) receptor type 1 (CRF(R1)) binding, which mediates neuroendocrine and behavioral responses to stress as well as to drugs of abuse. The present experiments investigate whether changes in cocaine reward elicited by previous exposure to stress are mediated by CREB and/or CRF(R1). Chronic exposure to FS in advance of conditioning enhances cocaine CPP in wild-type mice, but this is blocked in CREB-deficient mice. In addition, pretreatment with the CRF(R1) antagonist, antalarmin, before FS exposure blocks this stress-induced enhancement of cocaine CPP. Furthermore, FS-induced increase in phosphorylated CREB (pCREB), specifically in the lateral septum (LS) and nucleus accumbens (NAc) is also blocked by antalarmin. Taken together, these studies suggest that both CREB and CRF(R1) activation are necessary for stress-induced potentiation of drug reward.

Ethanol and acetaldehyde action on central dopamine systems: mechanisms, modulation, and relationship to stress

There has been a great deal of activity in recent years in the study of the direct effects of ethanol on the dopamine reward system originating in the ventral tegmental area (VTA). In addition, recent evidence suggests that acetaldehyde formed from ethanol in the brain or periphery may be a crucial factor in the central effects of ethanol. This critical review examines the actions of ethanol and acetaldehyde on neurons of the VTA and the possible interactions with stress, with a focus on electrophysiological studies in vivo and in vitro. Ethanol has specific effects on dopamine neurons and there is recent evidence that some of the in vivo and in vitro effects of ethanol are mediated by acetaldehyde. Stress has some analogous actions on neuronal activity in the VTA, and the interactions between the effects of stress and alcohol on VTA neurons may be a factor in ethanol-seeking behavior. Taken together, the evidence suggests that stress may contribute to the activating effects of ethanol on dopamine VTA neurons, that at least some actions of ethanol on dopamine VTA neurons are mediated by acetaldehyde, and that the interaction between stress and alcohol could play a role in susceptibility to alcoholism. The link between acetaldehyde and ethanol actions on brain reward pathways may provide a new avenue for the development of agents to reduce alcohol craving.

Race and unhealthy behaviors: chronic stress, the HPA axis, and physical and mental health disparities over the life course

OBJECTIVES

We sought to determine whether unhealthy behaviors play a stress-buffering role in observed racial disparities in physical and mental health.

METHODS

We conducted logistic regressions by race on data from the first 2 waves of the Americans' Changing Lives Survey to determine whether unhealthy behaviors had buffering effects on the relationship between major stressors and chronic health conditions, and on the relationship between major stressors and meeting the criteria for major depression.

RESULTS

Among Whites, unhealthy behaviors strengthened the relationship between stressors and meeting major-depression criteria. Among Blacks, however, the relationship between stressors and meeting major-depression criteria was stronger among those who had not engaged in unhealthy behaviors than among those who had. Among both race groups there was a positive association between stressors and chronic health conditions. Among Blacks there was an additional positive association between number of unhealthy behaviors and number of chronic conditions.

CONCLUSIONS

Those who live in chronically stressful environments often cope with stressors by engaging in unhealthy behaviors that may have protective mental-health effects. However, such unhealthy behaviors can combine with negative environmental conditions to eventually contribute to morbidity and mortality disparities among social groups.

Neuronal adaptations, neuroendocrine and immune correlates of heroin self-administration

Opioid receptor-mediated action in the central nervous system (CNS) has been consistently shown to trigger changes in the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS) and suppress a variety of parameters of immune function in investigator-delivered paradigms. Overwhelming evidence supports the concept that the CNS undergoes numerous and complex neuronal adaptive changes in addicts, and in animal models of heroin addiction as a result of the training of drug stimuli to serve as reinforcers, altering the function of individual neurons and the larger neural circuits within which the neurons operate. Taken together, these advances suggest that since plastic neuronal changes occur in drug addiction and related animal model paradigms, profiles of neuroendocrine and immune function would differ in a rat model of heroin self-administration compared to passive infusion of drug. Self-administration of heroin induces neuronal circuitry adaptations in specific brain regions that may be related to alterations in neuroendocrine and T lymphocyte function also observed. Animals self-administering (SA) heroin exhibit increased mu-opioid receptor agonist ([D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO))-stimulated guanosine-5'-O-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) binding in the anterior hypothalamus (50% and 33%) and rostral medial thalamus (33% and 36%) compared with control animals receiving identical non-contingent injections of yoked-heroin (YH) or yoked-saline (YS), respectively. No changes in agonist-stimulated G-protein sensitization were observed in 14 other brain regions studied. No changes in mu-opioid receptor density, ((3)H-DAMGO binding) were seen in all brain regions examined. The neuronal changes in SA animals were correlated with elevated adrenocorticotrophic hormone (ACTH) (64% and 104%) and glucocorticoid production (198% and 79%) compared with YH and YS groups, respectively. Neuroendocrine adaptive changes in SA animals were associated with thymic hypoplasia. Splenic T lymphocytes from animals that had self-administered heroin showed a profoundly reduced ability to proliferate in response to concanavalin A (50% and 48% compared with YH and YS controls, respectively; Fig. 1A), or a monoclonal antibody (R73) to the CD3/T-cell receptor complex (anti-TCR) plus IL-2 (55% and 59% compared with YH and YS controls, respectively; Fig. 1B). Self-administration of heroin selectively alters T lymphocyte function, as no effects on natural killer cell activity or macrophage functions were observed. These findings may have relevance to the acquisition and documented increased incidence of infectious diseases, including HIV, in heroin addicts, due to a pre-existing T-cell immunodeficient state.

The neuropharmacology of relapse to food seeking: methodology, main findings, and comparison with relapse to drug seeking

Relapse to old, unhealthy eating habits is a major problem in human dietary treatments. The mechanisms underlying this relapse are unknown. Surprisingly, until recently this clinical problem has not been systematically studied in animal models. Here, we review results from recent studies in which a reinstatement model (commonly used to study relapse to abused drugs) was employed to characterize the effect of pharmacological agents on relapse to food seeking induced by either food priming (non-contingent exposure to small amounts of food), cues previously associated with food, or injections of the pharmacological stressor yohimbine. We also address methodological issues related to the use of the reinstatement model to study relapse to food seeking, similarities and differences in mechanisms underlying reinstatement of food seeking versus drug seeking, and the degree to which the reinstatement procedure provides a suitable model for studying relapse in humans. We conclude by discussing implications for medication development and future research. We offer three tentative conclusions: (1)The neuronal mechanisms of food-priming- and cue-induced reinstatement are likely different from those of reinstatement induced by the pharmacological stressor yohimbine. (2)The neuronal mechanisms of reinstatement of food seeking are possibly different from those of ongoing food-reinforced operant responding. (3)The neuronal mechanisms underlying reinstatement of food seeking overlap to some degree with those of reinstatement of drug seeking.

Anti-relapse medications: preclinical models for drug addiction treatment

Addiction is a chronic relapsing brain disease and treatment of relapse to drug-seeking is considered the most challenging part of treating addictive disorders. Relapse can be modeled in laboratory animals using reinstatement paradigms, whereby behavioral responding for a drug is extinguished and then reinstated by different trigger factors, such as environmental cues or stress. In this review, we first describe currently used animal models of relapse, different relapse triggering factors, and the validity of this model to assess relapse in humans. We further summarize the growing body of pharmacological interventions that have shown some promise in treating relapse to psychostimulant addiction. Moreover, we present an overview on the drugs tested in cocaine or methamphetamine addicts and examine the overlap of existing preclinical and clinical data. Finally, based on recent advances in our understanding of the neurobiology of relapse and published preclinical data, we highlight the most promising areas for future anti-relapse medication development.

mechanisms of disulfiram-induced cocaine abstinence: antabuse and cocaine relapse

The anti-alcoholism drug disulfiram (Antabuse), which is an inhibitor of aldehyde dehydrogenase, induces an aversive reaction to alcohol consumption and thereby helps patients reduce alcohol intake. Recent clinical trials, initiated to investigate whether disulfiram could be used to treat individuals who abuse both alcohol and cocaine, have indicated that disulfiram effectively decreases cocaine consumption. Yet the ability of disulfiram to curb cocaine intake cannot be explained by the disruption of ethanol metabolism. Here, we synthesize clinical and animal data that point to dopamine beta-hydroxylase inhibition as a mechanism underlying the efficacy of disulfiram in the treatment of cocaine dependence.

Novel environment and GABA agonists alter event-related potentials in N-methyl-D-aspartate NR1 hypomorphic and wild-type mice

Clinical and experimental data suggest dysregulation of N-methyl-d-aspartate receptor (NMDAR)-mediated glutamatergic pathways in schizophrenia. The interaction between NMDAR-mediated abnormalities and the response to novel environment has not been studied. Mice expressing 5 to 10% of normal N-methyl-d-aspartate receptor subunit 1 (NR1) subunits [NR1(neo)(-/-)] were compared with wild-type littermates for positive deflection at 20 ms (P20) and negative deflection at 40 ms (N40) auditory event-related potentials (ERPs). Groups were tested for habituation within and across five testing sessions, with novel environment tested during a sixth session. Subsequently, we examined the effects of a GABA(A) positive allosteric modulator (chlordiazepoxide) and a GABA(B) receptor agonist (baclofen) as potential interventions to normalize aberrant responses. There was a reduction in P20, but not N40 amplitude within each habituation day. Although there was no amplitude or gating change across habituation days, there was a reduction in P20 and N40 amplitude and gating in the novel environment. There was no difference between genotypes for N40. Only NR1(neo)(-/-) mice had reduced P20 in the novel environment. Chlordiazepoxide increased N40 amplitude in wild-type mice, whereas baclofen increased P20 amplitude in NR1(neo)(-/-) mice. As noted in previous publications, the pattern of ERPs in NR1(neo)(-/-) mice does not recapitulate abnormalities in schizophrenia. In addition, reduced NR1 expression does not influence N40 habituation but does affect P20 in a novel environment. Thus, the pattern of P50 (positive deflection at 50 ms) but not N100 (negative deflection at 100 ms) in human studies may relate to subjects' reactions to unfamiliar environments. In addition, NR1 reduction decreased GABA(A) receptor-mediated effects on ERPs while causing increased GABA(B) receptor-mediated effects. Future studies will examine changes in GABA receptor subunits after reductions in NR1 expression.

SUBSEQUENTLY ENHANCED CPP TO MORPHINE FOLLOWING CHRONIC BUT NOT ACUTE FOOTSHOCK STRESS ASSOCIATED WITH CORTICOSTERONE MECHANISM IN RATS

The purpose of this study was to determine the morphine-induced place preference in rats pre-exposed to footshock stress and corticosterone (CORT). The authors also studied the involvement of dopamine mechanisms in the CORT-induced place preference. The results showed that chronic footshock or CORT exposure but not acute footshock or CORT exposure similarly potentiated the conditioned place preference to morphine. The CORT-induced conditioned place preference were established only with high and middle dose (5, 3 mg/kg) CORT. The dopamine levels in NAc of rats injected with CORT (5, 3, 1 mg/kg, i.p.) increased significantly. The findings suggest that the increase of dopamine levels in NAc induced by CORT might be the medium between stress and morphine.

Behavioral sensitization to cocaine: cooperation between glucocorticoids and epinephrine

RATIONALE

Stressful life experiences facilitate responsiveness to psychostimulant drugs. While there is ample evidence that adrenal glucocorticoids mediate these effects of stress, the role of the sympatho-adrenal system in the effects of psychostimulants is poorly understood.

OBJECTIVES

The present study investigated the role of the two adrenal stress hormones, corticosterone and epinephrine, in sensitization to the locomotor stimulant effects of cocaine.

MATERIALS AND METHODS

The DBA/2 mouse strain was used, as behavioral sensitization in this strain critically depends on adrenal hormones. Animals were subjected to adrenalectomy ("ADX", surgical removal of the adrenals) or SHAM surgery, and ADX mice were given replacement of epinephrine (5 x 10(-3) mg/kg subcutaneously (s.c.) just prior to each drug administration), corticosterone (20%, s.c., pellet), or both. Mice were subjected to a cocaine sensitization regimen (15.0 mg/kg cocaine on nine consecutive days followed by a 7.5 mg/kg cocaine challenge after a 5-day withdrawal).

RESULTS

In agreement with our previous observations, ADX prevented initiation and expression of cocaine-induced locomotor sensitization. Whereas neither corticosterone nor epinephrine alone were sufficient to reverse the ADX effect, both hormones were necessary to fully restore initiation and retention of sensitization to levels observed in SHAM animals.

CONCLUSIONS

The present findings indicate that corticosterone and epinephrine cooperate to facilitate behavioral responsiveness to cocaine. These data emphasize that in addition to the hypothalamic-pituitary-adrenal axis, the sympathetic nervous system plays a critical role in psychostimulant sensitivity.

Gender differences in delay-discounting under mild food restriction

Impulsivity, a core symptom of attention-deficit hyperactivity disorder (ADHD), is tested in animal models by delay-discounting tasks. So far, mainly male subjects have been used in this paradigm at severe levels of food restriction. Here we studied the impulsive behaviour of CD-1 adult male and female mice at mild levels of food restriction. Mice maintained at 90 +/- 5% of ad libitum bodyweight, were tested in operant chambers provided with nose-poking holes. Nose poking in one hole resulted in the immediate delivery of one food pellet (small-soon, SS), whereas nose poking in the other hole delivered five food pellets after a delay (large-late, LL), which was increased progressively each day (0-150 s). Two subgroups emerged: individuals that shifted at short delays ("steep") and individuals that did not shift, even at the highest delays ("flat"). Analysis showed that "steep" females shifted at shorter delays than "steep" males, while no difference existed between males and females within the "flat" sub-population. In home-cage circadian activity as well as in a novelty-seeking test, females were more active than males. It can be concluded from these results that female mice are more impulsive than male mice under mild food restriction. This is in contrast with findings in earlier studies with more severe food restriction. Therefore, an alternative explanation is that females are more explorative, and that different features might be tested in delay-discounting paradigms, depending on restriction levels.

Subcellular plasticity of the corticotropin-releasing factor receptor in dendrites of the mouse bed nucleus of the stria terminalis following chronic opiate exposure

Chronic opiate administration alters the expression levels of the stress-responsive peptide, corticotropin-releasing factor (CRF), in the bed nucleus of the stria terminalis (BNST). This brain region contains CRF receptors that drive drug-seeking behavior exacerbated by stress. We used electron microscopy to quantitatively compare immunolabeling of the corticotropin-releasing factor receptor (CRFr) and CRF in the anterolateral bed nucleus of the stria terminalis (BSTal) of mice injected with saline or morphine in escalating doses for 14 days. We also compared the results with those in non-injected control mice. The tissue was processed for CRFr immunogold and CRF immunoperoxidase labeling. The non-injected controls had a significantly lower plasmalemmal density of CRFr immunogold particles in dendrites compared with mice receiving saline, but not those receiving morphine, injections. Compared with saline, however, mice receiving chronic morphine showed a significantly lower plasmalemmal, and greater cytoplasmic, density of CRFr immunogold in dendrites. Within the cytoplasmic compartment of somata and dendrites of the BSTal, the proportion of CRFr gold particles associated with mitochondria was three times as great in mice receiving morphine compared with saline. This subcellular distribution is consistent with morphine,- and CRFr-associated modulation of intracellular calcium release or oxidative stress. The between-group changes occurred without effect on the total number of dendritic CRFr immunogold particles, suggesting that chronic morphine enhances internalization or decreases delivery of the CRFr to the plasma membrane, a trafficking effect that is also affected by the stress of daily injections. In contrast, saline and morphine treatment groups showed no significant differences in the total number of CRF-immunoreactive axon terminals, or the frequency with which these terminals contacted CRFr-containing dendrites. This suggests that morphine does not influence axonal availability of CRF in the BSTal. The results have important implications for drug-associated adaptations in brain stress systems that may contribute to the motivation to continue drug use during dependence.

Chronic cocaine enhances corticotropin-releasing factor-dependent potentiation of excitatory transmission in ventral tegmental area dopamine neurons

Current concepts suggest that stress-induced release of neuromodulators such as corticotropin-releasing factor (CRF) can drive drug-dependent behaviors. Although previous drug exposure can enhance behavioral and neurochemical responses to stress, it is unclear how such drug exposure alters the CRF modulation of excitatory synapses onto ventral tegmental area (VTA) dopamine neurons, a key locus of drug- and stress-induced neuroadaptation. Here, we demonstrate that, after repeated cocaine exposure, the magnitude and duration of the CRF-induced potentiation of NMDA receptor (NMDAR)-mediated neurotransmission was significantly increased compared with naive and saline-treated mice. Furthermore, CRF enhanced AMPA receptor (AMPAR)-mediated transmission only in mice that were exposed to cocaine. Increased frequency of AMPAR-mediated spontaneous miniature EPSCs and the intracellular blockade of CRF potentiation of AMPAR-mediated transmission suggest both presynaptic and postsynaptic effects of CRF. Importantly, pharmacological experiments revealed that CRF receptor 1 and protein kinase A pathways were newly recruited after repeated cocaine for the enhancement of CRF-induced NMDAR potentiation and the appearance of AMPAR potentiation. Thus, enhanced CRF-induced potentiation of excitatory synaptic transmission onto VTA dopamine neurons after cocaine preexposure is likely to produce an abnormal increase in dopamine release during stressful events and could augment activation of addictive behaviors in response to stress.

Repeated stress prevents cocaine-induced activation of BDNF signaling in rat prefrontal cortex

In this report we provide evidence that repeated stress prevents cocaine-induced activation of BDNF expression and signaling in rat prefrontal cortex. A single injection of cocaine up-regulates BDNF expression in sham (i.e. unstressed) rats but not in repeatedly stressed rats. Similarly, the expression as well as trafficking of the high affinity BDNF receptor trkB promoted by the psychostimulant is impaired in chronically-stressed rats challenged with cocaine. Moreover, among the different intracellular signaling pathways that can be activated by the neurotrophin, i.e. ERK1/2-, Akt- and PLCgamma-pathway, we found that cocaine is able to selectively activate the ERK1/2 pathway in sham animals, but not in rats exposed to repeated stress. Notably, such changes take place in chronically-stressed animals although they still retain the ability to increase neuronal activity as measured by the enhancement of Arc gene expression. In summary, we have demonstrated that stress globally interferes with BDNF-mediated signaling responses to cocaine challenge, providing key insights into the molecular basis of stress-cocaine interaction and indicating the critical role of the prefrontal cortex in mediating such interaction.

Valproate treatment and cocaine cue reactivity in cocaine dependent individuals

Based on prior clinical trials indicating that gamma-aminobutyric acid (GABA)-based anticonvulsant medications reduce drug craving in cocaine dependent study participants, we tested the effects of valproate treatment on cue-induced cocaine craving. Crack cocaine dependent individuals (N=20) were tested in a randomized, placebo-controlled, within-subjects, crossover study design. Valproate treatment was titrated up to 1500 mg/day by Day 6 of treatment, cue testing was completed on Day 8 of treatment, and all study participants underwent a washout period of 5 days between active and placebo medication treatment periods. Testing included both cocaine and neutral cue exposure sessions, presented in a random and counterbalanced order. Main effects of cue exposure were found for subjective ratings of "desire to use cocaine now", the cocaine craving index, cocaine-like high, and cocaine withdrawal. Treatment interaction effects were found with "desire to use cocaine now", which underwent a greater increase following cocaine cue exposure in the valproate condition. Main effects of medication treatment were found, in which lower blood pressure and heart rate, and higher plasma cortisol levels, were associated with valproate treatment. Valproate treatment was also associated, at a trend level, with higher pre-test cocaine craving levels. The results demonstrate that cocaine cue reactivity is a robust phenomena across two assessment sessions, but fail to support the use of valproate as a means of reducing spontaneous and cue-induced cocaine craving. The use of valproate as a treatment for cocaine dependence is not supported.

Gambling pathology is associated with dampened cortisol response among men and women

Pathological gambling has many similarities to pharmacological addiction. Notably, both pathological gambling and drug addiction are characterized by aberrations in hypothalamic-pituitary-adrenal (HPA) axis responding. As well, there are indications that gender differences may play a role in these processes. Whether gender and/or HPA response are associated with pathological gambling was of interest. Recreational and pathological gamblers (15 men and 6 women per group) had the HPA factor, cortisol, assessed in saliva before and after watching a video of their preferred mode of gambling (slot machines, horse race betting, scratch-off tickets, blackjack, video poker, craps, sports betting, online casino games, or lottery tickets), and a video of neutral stimuli (a rollercoaster ride). Basal levels of salivary cortisol did not significantly differ among recreational and pathological gamblers. However, recreational gamblers demonstrated significantly increased salivary cortisol levels after the gambling and rollercoaster videos, whereas pathological gamblers demonstrated no salivary cortisol increase in response to either video stimulus. There was also a non-significant trend for women to have a greater cortisol response to video stimuli compared to men. These data suggest that pathological gambling is associated with hypoactive HPA response to gambling stimuli, similar to chronic drug exposure, and gender may contribute to this effect.

Effects of prenatal and postnatal maternal ethanol on offspring response to alcohol and psychostimulants in long evans rats

An important factor that may influence addiction liability is exposure during the early life period. Exposure to ethanol, early in life, can have long-lasting implications on brain function and drugs of abuse response later in life. In the present study we investigated the behavioral responses to ethanol and to psychostimulants in Long Evans rats that have been exposed to pre- and postnatal ethanol. Since a relationship between heightened drug intake and susceptibility to drug-induced locomotor activity/sensitization has been demonstrated, we tested these behavioral responses, in control and early life ethanol-exposed animals. The young adult male and female progeny were tested for locomotor response to alcohol, cocaine and d-amphetamine. Sedative, rewarding effects of alcohol and alcohol consumption were measured. Our results show that early life ethanol exposure behaviorally sensitized animals to subsequent ethanol and psychostimulants exposure. Ethanol-exposed animals were also more sensitive to the hyperlocomotor effects of all drugs of abuse tested and to those of the dopamine receptor agonist apomorphine. Locomotor sensitization to repeated injections of cocaine was facilitated in ethanol-exposed animals. Ethanol-induced conditioned place preference was also facilitated in ethanol-exposed animals. Ethanol consumption and preference were increased after early life ethanol exposure and this was associated with decreased sensitivity to the sedative effects of ethanol. The altered behavioral responses to drugs of abuse were associated with decreased striatal dopamine transporter and hippocampal NMDAR binding. Our results outline an increased vulnerability to rewarding and stimulant effects of ethanol and psychostimulants and support the epidemiological and clinical data that suggested that early chronic exposure to ethanol may increase the propensity for later self-administration of ethanol or other substances.

The contribution of the central nucleus of the amygdala to individual differences in amphetamine-induced hyperactivity

Rats classified as high responders (HR) based on their response to an inescapable novel environment self-administer more amphetamine and have greater amphetamine-induced sensitization than rats classified as low responders (LR). Recent research suggests that the central nucleus of the amygdala (ACe) contributes to the elevated self-administration in HR rats. Therefore, the current study examined the role of the ACe in the expression of both amphetamine-induced sensitization and conditioned hyperactivity in HR and LR rats. Male Sprague-Dawley rats were screened for their response to inescapable novelty and classified as HR or LR rats. Rats were implanted with bilateral cannulae into the ACe and received amphetamine (1.0 mg/kg, s.c.) or saline injections immediately prior to 1-h locomotor sessions. Following five training sessions, all rats received an infusion of muscimol (0.5 microg/0.5 microl) or phosphate buffered saline (PBS) followed by a saline injection to measure conditioned hyperactivity. HR rats displayed conditioned hyperactivity, while LR rats did not, suggesting that HR and LR rats differ in the expression of conditioned hyperactivity. While ACe inactivation attenuated the expression of conditioned hyperactivity, it did not differentially affect HR and LR rats. Following additional training and a 10-day rest period, all rats were then tested for amphetamine-induced sensitization (1.0 mg/kg) following an infusion of muscimol or PBS. Inactivation of the ACe attenuated the expression of sensitization only in HR rats. These results suggest the ACe contributes to the greater amphetamine sensitization in HR rats.

Mechanisms underlying the comorbidity between depressive and addictive disorders in adolescents: interactions between stress and HPA activity

OBJECTIVE

Depression may be a precursor to substance use disorder in some youngsters, and substance abuse might complicate the subsequent course of depression. This study examined whether hypothalamic-pituitary-adrenal (HPA) activity and stressful life experiences are related to the development of substance use disorder in depressed and nondepressed adolescents, and whether substance use disorder predicts a worsening course of depression.

METHOD

Urinary-free cortisol was measured for 3 nights in 151 adolescents with no prior history of substance use disorder (55 depressed, 48 at high risk for depression, and 48 normal subjects). Information was obtained on recent stressful life experiences. The participants were followed for up to 5 years to assess the onset of substance use disorder, course of depression, and stressful experiences. The relationships among depression, cortisol as a measure of HPA activity, stressful experiences, and substance use disorder were examined.

RESULTS

Elevated cortisol was associated with onset of substance use disorder. Stressful life experiences moderated this relationship. Cortisol and stress accounted for the effects of a history or risk of depression on the development of substance use disorder. Substance use disorder was associated with higher frequency of subsequent depressive episodes.

CONCLUSIONS

Higher cortisol prior to the onset of substance use disorder may indicate vulnerability to substance use disorder. Stressful experiences increase the risk for substance use disorder in such vulnerable youth. The high prevalence of substance use disorders in depressed individuals may be explained, in part, by high levels of stress and increased HPA activity.

Progesterone modulation of alpha5 nAChR subunits influences anxiety-related behavior during estrus cycle

Smokers often report an anxiolytic effect of cigarettes. In addition, stress-related disorders such as anxiety, post-traumatic stress syndrome and depression are often associated with chronic nicotine use. To study the role of the alpha5 nicotinic acetylcholine receptor subunit in anxiety-related responses, control and alpha5 subunit null mice (alpha5(-/-)) were subjected to the open field activity (OFA), light-dark box (LDB) and elevated plus maze (EPM) tests. In the OFA and LDB, alpha5(-/-) behaved like wild-type controls. In the EPM, female alpha5(-/-) mice displayed an anxiolytic-like phenotype, while male alpha5(-/-) mice were undistinguishable from littermate controls. We studied the hypothalamus-pituitary-adrenal axis by measuring plasma corticosterone and hypothalamic corticotropin-releasing factor. Consistent with an anxiolytic-like phenotype, female alpha5(-/-) mice displayed lower basal corticosterone levels. To test whether gonadal steroids regulate the expression of alpha5, we treated cultured NTera 2 cells with progesterone and found that alpha5 protein levels were upregulated. In addition, brain levels of alpha5 mRNA increased upon progesterone injection into ovariectomized wild-type females. Finally, we tested anxiety levels in the EPM during the estrous cycle. The estrus phase (when progesterone levels are low) is anxiolytic-like in wild-type mice, but no cycle-dependent fluctuations in anxiety levels were found in alpha5(-/-) females. Thus, alpha5-containing neuronal nicotinic acetylcholine receptors may be mediators of anxiogenic responses, and progesterone-dependent modulation of alpha5 expression may contribute to fluctuations in anxiety levels during the ovarian cycle.

Chronic unpredictable stress augments +3,4-methylenedioxymethamphetamine-induced monoamine depletions: the role of corticosterone

Exposure to stress alters the behavioral and neurochemical effects of drugs of abuse. However, it is unknown if chronic stress can affect the serotonergic depletions induced by the psychostimulant drug 3,4-methylenedioxymethamphetamine (MDMA). Rats were exposed to 10 days of chronic unpredictable stress (CUS) which resulted in the predicted elevation of basal plasma corticosterone concentrations. On the 11th day, rats received four challenge doses of MDMA (5 mg/kg every 2 h, i.p.) or saline. Five days later, rats were killed and serotonin (5-HT) and dopamine content were measured in the striatum, hippocampus, and frontal cortex. MDMA produced greater depletions of 5-HT in all three brain regions of rats pre-exposed to CUS compared to rats not exposed to CUS. CUS-exposed rats also had an augmented acute hyperthermic response but a similar increase in plasma corticosterone after challenge injections of MDMA compared with non-stressed rats similarly challenged with MDMA. Moreover, CUS-exposed rats exhibited an MDMA-induced depletion of striatal dopamine that was absent in non-stressed rats that received MDMA. To investigate the role of corticosterone in these effects, the corticosterone synthesis inhibitor, metyrapone (50 mg/kg i.p.), was administered prior to each stressor on each of the 10 days of CUS. Metyrapone blocked the chronic stress-induced elevation in basal plasma corticosterone, prevented the enhancement of MDMA-induced hyperthermia, and blocked the enhanced depletions of 5-HT and dopamine in CUS-exposed rats, but had no effect on the acute MDMA-induced increases in plasma corticosterone. These findings suggest that CUS alone can increase the basal level of corticosterone that in turn, plays an important role in enhancing the sensitivity of both 5-HT and dopamine terminals to the hyperthermic and monoamine depleting effects of MDMA without altering the acute corticosterone response to an MDMA challenge.

Stress, alcohol and drug interaction: an update of human research

A challenging question that continues unanswered in the field of addiction is why some individuals are more vulnerable to substance use disorders than others. Numerous risk factors for alcohol and other drugs of abuse, including exposure to various forms of stress, have been identified in clinical studies. However, the neurobiological mechanisms that underlie this relationship remain unclear. Critical neurotransmitters, hormones and neurobiological sites have been recognized, which may provide the substrates that convey individual differences in vulnerability to addiction. With the advent of more sophisticated measures of brain function in humans, such as functional imaging technology, the mechanisms and neural pathways involved in the interactions between drugs of abuse, the mesocorticolimbic dopamine system and stress systems are beginning to be characterized. This review provides a neuroadaptive perspective regarding the role of the hormonal and brain stress systems in drug addiction with a focus on the changes that occur during the transition from occasional drug use to drug dependence. We also review factors that contribute to different levels of hormonal/brain stress activation, which has implications for understanding individual vulnerability to drug dependence. Ultimately, these efforts may improve our chances of designing treatment strategies that target addiction at the core of the disorder.