Glucocorticoids and vulnerability to psychostimulant drugs: toward substrate and mechanism

The Role of Estrogen Signaling and Exercise in Drug Abuse: A Review

BACKGROUND

Discovering how sex differences impact the efficacy of exercise regimens used for treating drug addiction is becoming increasingly important. Estrogen is a hormone believed to explain a large portion of sex differences observed during drug addiction, and why certain exercise regimens are not equally effective between sexes in treatment. Addiction is currently a global hindrance to millions, many of whom are suffering under the influence of their brain's intrinsic reward system coupled with external environmental factors. Substance abuse disorders in the U.S. alone cost billions of dollars annually.

REVIEW SUMMARY

Studies involving the manipulation of estrogen levels in female rodents, primarily via ovariectomy, highlight its impact regarding drug addiction. More specifically, female rodents with higher estrogen levels during the estrus phase increase cocaine consumption, whereas those in the non-estrus phase (low estrogen levels) decrease cocaine consumption. If estrogen is reintroduced, self-administration increases once again. Exercise has been proven to decrease relapse tendency, but its effect on estrogen levels is not fully understood.

CONCLUSIONS

Such findings and results discussed in this review suggest that estrogen influences the susceptibility of females to relapse. Therefore, to improve drug-abuse-related treatment, exercise regimens for females should be generated based on key sex differences with respect to males.

Two kinds of transcription factors mediate chronic morphine-induced decrease in miR-105 in medial prefrontal cortex of rats

Chronic morphine administration alters gene expression in different brain regions, an effect which may contribute to plastic changes associated with addictive behavior. This change in gene expression is most possibly mediated by addictive drug-induced epigenetic remodeling of gene expression programs. Our previous studies showed that chronic morphine-induced decrease of miR-105 in the medial prefrontal cortex (mPFC) contributed to context-induced retrieval of morphine withdrawal memory. However, how chronic morphine treatment decreases miR-105 in the mPFC still remains unknown. The present study shows that chronic morphine induces addiction-related change in miR-105 in the mPFC via two kinds of transcription factors: the first transcription factor is CREB activated by mu receptors-ERK-p90RSK signaling pathway and the second transcription factor is glucocorticoid receptor (GR), which as a negative transcription factor, mediates chronic morphine-induced decrease in miR-105 in the mPFC of rats.

Striatal miR-183-5p inhibits methamphetamine-induced locomotion by regulating glucocorticoid receptor signaling

MicroRNA (miRNA)-mediated striatal gene regulation may play an important role in methamphetamine (METH) addiction. This study aimed to identify changes in novel miRNAs and their target genes during METH self-administration and investigate their roles in METH-induced locomotion. RNA sequencing analysis revealed that mir-183-5p was upregulated in the striatum of METH self-administered rats, and target gene prediction revealed that the glucocorticoid receptor (GR) gene, Nr3c1, was a potential target gene for mir-183-5p. We confirmed that single and repeated METH administrations increased METH-induced locomotion and plasma corticosterone levels in rats. Additionally, increased miR-185-5p expression and decreased GR gene expression were observed only in the repeated-METH-injection group but not in the single-injection group. We then investigated the effects of miR-183-5p on METH-induced locomotion using a miR-183-5p mimic and inhibitor. Injection of a mir-183-5p mimic in the striatum of rats attenuated METH-induced locomotion, whereas injection of a miR-183-5p inhibitor enhanced the locomotor activity in METH-administered rats. Furthermore, the miR-183-5p mimic reduced the phosphorylation of tyrosine hydroxylase (TH) whereas the inhibitor increased it. Taken together, these results indicate that repeated METH injections increase striatal miR-183-5p expression and regulate METH-induced locomotion by regulating GR expression in rats, thereby suggesting a potential role of miR-183-5p as a novel regulator of METH-induced locomotion.

Prevention of relapse to methamphetamine self-administration by environmental enrichment: involvement of glucocorticoid receptors

RATIONALE

In rodents, environmental enrichment (EE) produces both preventive and curative effects on drug addiction, and this effect is believed to depend at least in part on EE's actions on the stress system.

OBJECTIVES

This study investigated whether exposure to EE during abstinence reduces methamphetamine seeking after extended self-administration. In addition, we investigated whether these effects are associated with alterations in the levels of glucocorticoid receptors (GR) in the brain and whether administration of GR antagonists blocks methamphetamine relapse.

METHODS

We allowed rats to self-administer methamphetamine for twenty 14-h sessions. After 3 weeks of abstinence either in standard (SE) or EE conditions, we measured methamphetamine seeking in a single 3-h session. Then, we used western blot techniques to measure GR levels in several brain areas. Finally, in an independent group of rats, after methamphetamine self-administration and abstinence in SE, we administered the GR antagonist mifepristone, and we investigated methamphetamine seeking.

RESULTS

Exposure to EE reduced methamphetamine seeking and reversed methamphetamine-induced increases in GR levels in the ventral and dorsal hippocampus. In addition, EE decreased GR levels in the amygdala in drug-naive animals, but this effect was prevented by previous exposure to methamphetamine. Administration of mifepristone significantly decreased methamphetamine seeking.

CONCLUSIONS

The anti-craving effects of EE are paralleled by restoration of methamphetamine-induced dysregulation of GR in the hippocampus. These results provide support for the hypothesis that the effect of EE on methamphetamine relapse is at least in part mediated by EE's action on the brain stress system.

Drugs and bugs: Negative affect, psychostimulant use and withdrawal, and the microbiome

BACKGROUND AND OBJECTIVES

A growing body of literature demonstrates that the human microbiota plays a crucial role in health and disease states, as well as in the body's response to stress. In addition, the microbiome plays a role in psychological well-being and regulating negative affect. Regulation of negative affect is a factor in psychostimulant abuse disorders. We propose a risk chain in which stress leads to negative affect that places an individual at risk to develop or relapse to psychostimulant abuse disorder. Stress, negative affect, and psychostimulant use all alter the gut microbiome.

METHODS

This review brings together the literature on affective disorders, stress, and psychostimulant abuse disorders to assess possible modulatory actions of the gut-brain axis to regulate these conditions.

RESULTS

Studies reviewed across the various disciplines suggest that the dysbiosis resulting from drug use, drug withdrawal, or stress may cause an individual to be more susceptible to addiction and relapse. Probiotics and prebiotics reduce stress and negative affect.

SCIENTIFIC SIGNIFICANCE

Treatment during the withdrawal phase of psychostimulant abuse disorder, when the microbiome is altered, may ameliorate the symptoms of stress and negative affect leading to a reduced risk of relapse to psychostimulant use.

From sign-tracking to attentional bias: Implications for gambling and substance use disorders

Sign-tracking behavior in Pavlovian autoshaping is known to be a relevant index of the incentive salience attributed to reward-related cues. Evidence has accumulated to suggest that animals that exhibit a sign-tracker phenotype are especially vulnerable to addiction and relapse due to their proneness to attribute incentive salience to drug cues, and their relatively weak cognitive and attentional control over their behavior. Interestingly, sign-tracking is also influenced by reward uncertainty in a way that may promote gambling disorder. Research indicates that reward uncertainty sensitizes sign-tracking responses and favors the development of a sign-tracker phenotype, compatible with the conditioned attractiveness of lights and sounds in casinos for problem gamblers. The study of attentional biases in humans (an effect akin to sign-tracking in animals) leads to similar observations, notably that the propensity to develop attraction for conditioned stimuli (CSs) is predictive of addictive behavior. Here we review the literature on drug addiction and gambling disorder, highlighting the similarities between studies of sign-tracking and attentional biases.

The corticosteroid prednisolone increases amygdala and insula reactivity to food approach signals in healthy young men

Short- and long-term treatment with glucocorticoids is widely used in clinical practice and frequently induces features of iatrogenic Cushing syndrome, such as abdominally centered weight gain. Despite decades of glucocorticoids usage, the mechanisms underlying these side effects are still only partly understood. One possibility is that glucocorticoids impact subcortical (hypothalamus, amygdala, insula) and cortical (orbitofrontal and cingulate cortex) brain regions involved in appetite regulation and reward processing. In the present study, we used functional magnetic resonance imaging (fMRI) to study the acute effects of a prednisolone infusion on reactivity of brain reward systems to food stimuli. Twenty healthy normal-weight men were tested in a randomized, double-blind, cross-over study. After an overnight fast and infusion of either 250 mg prednisolone or placebo (always administered between 8 and 9 A M), fMRI scans were taken while presenting food and object pictures in a Go/NoGo (GNG) task. At home, participants were asked to register what they had eaten. On the following morning they came back to the lab and had a supervised ad libitum breakfast at a standardized buffet. Food-Go in contrast to Object-Go pictures yielded increased blood oxygen level dependent (BOLD) activity in hippocampus, amygdala, orbitofrontal cortex, insula and anterior cingulate cortex. Prednisolone increased activation in the bilateral amygdala and right insula for approach-associated food pictures. The buffet test did not reveal significant differences in calorie consumption or preferences of different macronutrients. However, prednisolone-induced insula reactivity to Food-Go images was associated with greater caloric intake, both at home and in the standardized buffet. In sum, we observed a specific effect of prednisolone on the BOLD response of the amygdala and insula to approach-associated food stimuli. As these brain areas have previously been implicated in hedonic eating, the present pattern of results may reflect an increased anticipated reward value of food modulated by glucocorticoids. These effects might potentially drive increased food intake and weight gain under prolonged glucocorticoid treatment.

Differential effects of context on psychomotor sensitization to ethanol and cocaine

Repeated drug injections lead to sensitization of their stimulant effects in mice, a phenomenon sometimes referred to as drug psychomotor sensitization. Previous studies showed that sensitization to cocaine is context dependent as its expression is reduced in an environment that was not paired with cocaine administration. In contrast, the effects of the test context on ethanol sensitization remain unclear. In the present study, female OF1 mice were repeatedly injected with 1.5 g/kg ethanol to test for both the effects of context novelty/familiarity and association on ethanol sensitization. A first group of mice was extensively pre-exposed to the test context before ethanol sensitization and ethanol injections were paired with the test context (familiar and paired group). A second group was not pre-exposed to the test context, but ethanol injections were paired with the test context (nonfamiliar and paired group). Finally, a third group of mice was not pre-exposed to the test context and ethanol was repeatedly injected in the home cage (unpaired group). Control groups were similarly exposed to the test context, but were injected with saline. In a second experiment, cocaine was used as a positive control. The same behavioral procedure was used, except that mice were injected with 10 mg/kg cocaine instead of ethanol. The results show a differential involvement of the test context in the sensitization to ethanol and cocaine. Cocaine sensitization is strongly context dependent and is not expressed in the unpaired group. In contrast, the expression of ethanol sensitization is independent of the context in which it was administered, but is strongly affected by the relative novelty/familiarity of the environment. Extensive pre-exposure to the test context prevented the expression of ethanol sensitization. One possible explanation is that expression of ethanol sensitization requires an arousing environment.

HPA Axis Interactions with Behavioral Systems

Perhaps the most salient behaviors that individuals engage in involve the avoidance of aversive experiences and the pursuit of pleasurable experiences. Engagement in these behaviors is regulated to a significant extent by an individual's hormonal milieu. For example, glucocorticoid hormones are produced by the hypothalamic-pituitary-adrenocortical (HPA) axis, and influence most aspects of behavior. In turn, many behaviors can influence HPA axis activity. These bidirectional interactions not only coordinate an individual's physiological and behavioral states to each other, but can also tune them to environmental conditions thereby optimizing survival. The present review details the influence of the HPA axis on many types of behavior, including appetitively-motivated behaviors (e.g., food intake and drug use), aversively-motivated behaviors (e.g., anxiety-related and depressive-like) and cognitive behaviors (e.g., learning and memory). Conversely, the manuscript also describes how engaging in various behaviors influences HPA axis activity. Our current understanding of the neuronal and/or hormonal mechanisms that underlie these interactions is also summarized. © 2016 American Physiological Society. Compr Physiol 6:1897-1934, 2016.

Glutamatergic mechanisms of comorbidity between acute stress and cocaine self-administration

There is substantial comorbidity between stress disorders and substance use disorders (SUDs), and acute stress augments the locomotor stimulant effect of cocaine in animal models. Here we endeavor to understand the neural underpinnings of comorbid stress disorders and drug use by determining whether the glutamatergic neuroadaptations that characterize cocaine self-administration are induced by acute stress. Rats were exposed to acute (2 h) immobilization stress, and 3 weeks later the nucleus accumbens core was examined for changes in glutamate transport, glutamate-mediated synaptic currents and dendritic spine morphology. We also determined whether acute stress potentiated the acquisition of cocaine self-administration. Acute stress produced an enduring reduction in glutamate transport and potentiated excitatory synapses on medium spiny neurons. Acute stress also augmented the acquisition of cocaine self-administration. Importantly, by restoring glutamate transport in the accumbens core with ceftriaxone the capacity of acute stress to augment the acquisition of cocaine self-administration was abolished. Similarly, ceftriaxone treatment prevented stress-induced potentiation of cocaine-induced locomotor activity. However, ceftriaxone did not reverse stress-induced synaptic potentiation, indicating that this effect of stress exposure did not underpin the increased acquisition of cocaine self-administration. Reversing acute stress-induced vulnerability to self-administer cocaine by normalizing glutamate transport poses a novel treatment possibility for reducing comorbid SUDs in stress disorders.

MicroRNAs Modulate Interactions between Stress and Risk for Cocaine Addiction

Exposure to stress increases vulnerability to drug abuse, as well as relapse liability in addicted individuals. Chronic drug use alters stress response in a manner that increases drug seeking behaviors and relapse. Drug exposure and withdrawal have been shown to alter stress responses, and corticosteroid mediators of stress have been shown to impact addiction-related brain function and drug-seeking behavior. Despite the documented interplay between stress and substance abuse, the mechanisms by which stress exposure and drug seeking interact remain largely unknown. Recent studies indicate that microRNAs (miRNA) play a significant role in stress modulation as well as addiction-related processes including neurogenesis, synapse development, plasticity, drug acquisition, withdrawal and relapse. MiRNAs are short non-coding RNAs that function as bidirectional epigenetic modulators of gene expression through imperfect sequence targeted degradation and/or translational repression of mRNAs. They serve as dynamic regulators of CNS physiology and pathophysiology, and facilitate rapid and long-lasting changes to complex systems and behaviors. MiRNAs function in glucocorticoid signaling and the mesolimbic dopamine reward system, as well as mood disorders related to drug withdrawal. The literature suggests miRNAs play a pivotal role in the interaction between exposures to stress, addiction-related processes, and negative affective states resulting from extended drug withdrawal. This manuscript reviews recent evidence for the role of miRNAs in the modulation of stress and cocaine responses, and discusses potential mediation of the interaction of these systems by miRNAs. Uncovering the mechanism behind the association of stress and drug taking has the potential to impact the treatment of drug abuse and prevention of relapse. Further comprehension of these complex interactions may provide promising new targets for the treatment of drug addiction.

Neuronal correlates of depression

Major depressive disorder (MDD) is a common psychiatric disorder effecting approximately 121 million people worldwide and recent reports from the World Health Organization (WHO) suggest that it will be the leading contributor to the global burden of diseases. At present, the most commonly used treatment strategies are still based on the monoamine hypothesis that has been the predominant theory in the last 60 years. Clinical observations show that only a subset of depressed patients exhibits full remission when treated with classical monoamine-based antidepressants together with the fact that patients exhibit multiple symptoms suggest that the pathophysiology leading to mood disorders may differ between patients. Accumulating evidence indicates that depression is a neural circuit disorder and that onset of depression may be located at different regions of the brain involving different transmitter systems and molecular mechanisms. This review synthesises findings from rodent studies from which emerges a role for different, yet interconnected, molecular systems and associated neural circuits to the aetiology of depression.

Hypothalamic-pituitary-adrenal axis activity in patients with pathological gambling and internet use disorder

Alterations in secretion of stress hormones within the hypothalamic-pituitary-adrenal (HPA) axis have repeatedly been found in substance-related addictive disorders. It has been suggested that glucocorticoids might contribute to the development and maintenance of substance use disorders by facilitatory effects on behavioral responses to substances of abuse. The objective of this pilot study was to investigate HPA axis activity in patients with non-substance-related addictive disorders, i.e. pathological gambling and internet use disorder. We measured plasma levels of copeptin, a vasopressin surrogate marker, adrenocorticotropic hormone (ACTH) and cortisol in male patients with pathological gambling (n=14), internet use disorder (n=11) and matched healthy controls for pathological gambling (n=13) and internet use disorder (n=10). Plasma levels of copeptin, ACTH and cortisol in patients with pathological gambling or internet use disorder did not differ among groups. However, cortisol plasma levels correlated negatively with the severity of pathological gambling as measured by the PG-YBOCS. Together with our findings of increased serum levels of brain-derived neurotrophic factor (BDNF) in pathological gambling but not internet use disorder, these results suggest that the pathophysiology of pathological gambling shares some characteristics with substance-related addictive disorders on a neuroendocrinological level, whereas those similarities could not be observed in internet use disorder.

Activation of physiological stress responses by a natural reward: Novel vs. repeated sucrose intake

Pharmacological rewards, such as drugs of abuse, evoke physiological stress responses, including increased heart rate and blood pressure, and activation of the hypothalamic-pituitary-adrenal (HPA) axis. It is not clear to what extent the natural reward of palatable foods elicits similar physiological responses. In order to address this question, HPA axis hormones, heart rate, blood pressure and brain pCREB immunolabeling were assessed following novel and repeated sucrose exposure. Briefly, adult, male rats with ad libitum food and water were given either a single (day 1) or repeated (twice-daily for 14 days) brief (up to 30 min) exposure to a second drink bottle containing 4 ml of 30% sucrose drink vs. water (as a control for bottle presentation). Sucrose-fed rats drank more than water-fed on all days of exposure, as expected. On day 1 of exposure, heart rate, blood pressure, plasma corticosterone, and locomotion were markedly increased by presentation of the second drink bottle regardless of drink type. After repeated exposure (day 14), these responses habituated to similar extents regardless of drink type and pCREB immunolabeling in the hypothalamic paraventricular nucleus (PVN) also did not vary with drink type, whereas basolateral amygdala pCREB was increased by sucrose intake. Taken together, these data suggest that while sucrose is highly palatable, physiological stress responses were evoked principally by the drink presentation itself (e.g., an unfamiliar intervention by the investigators), as opposed to the palatability of the offered drink.

Cortisol administration induces global down-regulation of the brain's reward circuitry

Research in rodents and humans has shown divergent effects of the glucocorticoids corticosterone and cortisol (CRT) on reward processing. In rodents, administration of CRT increases reward drive by facilitating dopamine release in the ventral striatum. In humans, correspondingly, risky decision-making increases when CRT levels are elevated. Human stress studies contrariwise show that elevated CRT is accompanied by a decrease in reward-related brain activity. There are however no direct insights into how CRT acts on the reward system in the human brain. Accordingly, we used pharmacological functional magnetic resonance imaging (pharmaco-fMRI) to investigate the effects of CRT on the brain's reward system. In a randomized within-subject design we administered a high dose of CRT (40 mg) and placebo to twenty healthy male volunteers on separate days, and used a monetary incentive delay task to assess the effects of the hormone on the striatum and the amygdala in anticipation of potential reward. In contrast to animal studies, we show that this high dose of CRT strongly decreases activity of the striatum in both reward and non-reward conditions. Furthermore, we observed reductions in activity in the basolateral amygdala, a key regulator of the brain's reward system. Crucially, the overall down-regulation of the brain's reward circuit was verified on the subjective level as subjects reported significantly reduced reward preference after CRT. In sum, we provide here direct evidence in humans that CRT acts on brain regions involved in reward-related behavior, that is, the basolateral amygdala and the striatum. Our findings suggest that CRT in the quantity and time course presently used globally down-regulates the reward system, and thereby decreases motivational processing in general.

Endogenous cortisol levels are associated with an imbalanced striatal sensitivity to monetary versus non-monetary cues in pathological gamblers

Pathological gambling is a behavioral addiction characterized by a chronic failure to resist the urge to gamble. It shares many similarities with drug addiction. Glucocorticoid hormones including cortisol are thought to play a key role in the vulnerability to addictive behaviors, by acting on the mesolimbic reward pathway. Based on our previous report of an imbalanced sensitivity to monetary versus non-monetary incentives in the ventral striatum of pathological gamblers (PGs), we investigated whether this imbalance was mediated by individual differences in endogenous cortisol levels. We used functional magnetic resonance imaging (fMRI) and examined the relationship between cortisol levels and the neural responses to monetary versus non-monetary cues, while PGs and healthy controls were engaged in an incentive delay task manipulating both monetary and erotic rewards. We found a positive correlation between cortisol levels and ventral striatal responses to monetary versus erotic cues in PGs, but not in healthy controls. This indicates that the ventral striatum is a key region where cortisol modulates incentive motivation for gambling versus non-gambling related stimuli in PGs. Our results extend the proposed role of glucocorticoid hormones in drug addiction to behavioral addiction, and help understand the impact of cortisol on reward incentive processing in PGs.

Stress-mediated modulations in dopaminergic system and their subsequent impact on behavioral and oxidative alterations: an update

CONTEXT

Stress-induced changes in the dopaminergic system and subsequent enhancement of oxidative load and behavior are associated with a wide range of central and peripheral nervous disorders. Dopamine acts as a key neurotransmitter in the brain plays an important role in the regulation of motor and limbic functions.

OBJECTIVE

This article reviews the effect of stress on central dopaminergic system and its subsequent impact on the alterations in behavior and oxidative stress.

METHODS

A literature survey in PubMed (Bethesda, MD), Scopus (Philadelphia, PA), SciFinder (Columbus, OH) and Google Scholar (PMV, CA) was performed to gather information regarding the role of stress on central dopaminergic system and its associated behavioral and oxidative alterations.

RESULTS

Our collective data on behavioral studies and oxidative distress in stressful conditions show the functional reduction in dopaminergic neuronal system that could be one of the factors for the development of stress-induced motor suppression. Collectively, stress caused significant behavioral and oxidative alterations via suppression of neuronal functions of the central dopaminergic system.

CONCLUSIONS

This study provides an insight into the overall pathophysiological alterations in neuronal functions of the central dopaminergic system caused by acute and chronic unpredictable stress that, in our opinion, represent optimal utility as future therapeutic targets for neurodegenerative disorders.

The role of guanfacine as a therapeutic agent to address stress-related pathophysiology in cocaine-dependent individuals

The pathophysiology of cocaine addiction is linked to changes within neural systems and brain regions that are critical mediators of stress system sensitivity and behavioral processes associated with the regulation of adaptive goal-directed behavior. This is characterized by the upregulation of core adrenergic and corticotropin-releasing factor mechanisms that subserve negative affect and anxiety and impinge upon intracellular pathways in the prefrontal cortex underlying cognitive regulation of stress and negative emotional state. Not only are these mechanisms essential to the severity of cocaine withdrawal symptoms, and hence the trajectory of clinical outcome, but also they may be particularly pertinent to the demography of cocaine dependence. The ability of guanfacine to target overlapping stress, reward, and anxiety pathophysiology suggests that it may be a useful agent for attenuating the stress- and cue-induced craving state not only in women but also in men. This is supported by recent research findings from our own laboratory. Additionally, the ability of guanfacine to improve regulatory mechanisms that are key to exerting cognitive and emotional control over drug-seeking behavior also suggests that guanfacine may be an effective medication for reducing craving and relapse vulnerability in many drugs of abuse. As cocaine-dependent individuals are typically polydrug abusers and women may be at a greater disadvantage for compulsive drug use than men, it is plausible that medications that target catecholaminergic frontostriatal inhibitory circuits and simultaneously reduce stress system arousal may provide added benefits for attenuating cocaine dependence.

Cross-sensitization between cocaine and acute restraint stress is associated with sensitized dopamine but not glutamate release in the nucleus accumbens

Repeated administration of psychostimulant drugs or stress can elicit a sensitized response to the stimulating and reinforcing properties of the drug. Here we explore the mechanisms in the nucleus accumbens (NAc) whereby an acute restraint stress augments the acute locomotor response to cocaine. This was accomplished by a combination of behavioral pharmacology, microdialysis measures of extracellular dopamine and glutamate, and Western blotting for GluR1 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor (AMPAR). A single exposure to restraint stress 3 weeks before testing revealed that enduring locomotor sensitization to cocaine was paralleled by an increase in extracellular dopamine in the core, but not the shell subcompartment, of the NAc. Wistar rats pre-exposed to acute stress showed increased basal levels of glutamate in the core, but the increase in glutamate by acute cocaine was blunted. The alterations in extracellular glutamate seem to be relevant, as blocking AMPAR by 6-cyano-7-nitroquinoxaline-2,3-dione microinjection into the core prevented both the behavioral cross-sensitization and the augmented increase in cocaine-induced extracellular dopamine. Further implicating glutamate, the locomotor response to AMPAR stimulation in the core was potentiated, but not in the shell of pre-stressed animals, and this was accompanied by an increase in NAc GluR1 surface expression. This study provides evidence that the long-term expression of restraint stress-induced behavioral cross-sensitization to cocaine recapitulates some mechanisms thought to underpin the sensitization induced by daily cocaine administration, and shows that long-term neurobiological changes induced in the NAc by acute stress are consequential in the expression of cross-sensitization to cocaine.

Astrocytes are a neural target of morphine action via glucocorticoid receptor-dependent signaling

Chronic opioid use leads to the structural reorganization of neuronal networks, involving genetic reprogramming in neurons and glial cells. Our previous in vivo studies have revealed that a significant fraction of the morphine-induced alterations to the striatal transcriptome included glucocorticoid (GC) receptor (GR)-dependent genes. Additional analyses suggested glial cells to be the locus of these changes. In the current study, we aimed to differentiate the direct transcriptional effects of morphine and a GR agonist on primary striatal neurons and astrocytes. Whole-genome transcriptional profiling revealed that while morphine had no significant effect on gene expression in both cell types, dexamethasone significantly altered the transcriptional profile in astrocytes but not neurons. We obtained a complete dataset of genes undergoing the regulation, which includes genes related to glucose metabolism (Pdk4), circadian activity (Per1) and cell differentiation (Sox2). There was also an overlap between morphine-induced transcripts in striatum and GR-dependent transcripts in cultured astrocytes. We further analyzed the regulation of expression of one gene belonging to both groups, serum and GC regulated kinase 1 (Sgk1). We identified two transcriptional variants of Sgk1 that displayed selective GR-dependent upregulation in cultured astrocytes but not neurons. Moreover, these variants were the only two that were found to be upregulated in vivo by morphine in a GR-dependent fashion. Our data suggest that the morphine-induced, GR-dependent component of transcriptome alterations in the striatum is confined to astrocytes. Identification of this mechanism opens new directions for research on the role of astrocytes in the central effects of opioids.

The role of the glucocorticoids in developing resilience to stress and addiction

There is emerging evidence that individuals have the capacity to learn to be resilient by developing protective mechanisms that prevent them from the maladaptive effects of stress that can contribute to addiction. The emerging field of the neuroscience of resilience is beginning to uncover the circuits and molecules that protect against stress-related neuropsychiatric diseases, such as addiction. Glucocorticoids (GCs) are important regulators of basal and stress-related homeostasis in all higher organisms and influence a wide array of genes in almost every organ and tissue. GCs, therefore, are ideally situated to either promote or prevent adaptation to stress. In this review, we will focus on the role of GCs in the hypothalamic-pituitary adrenocortical axis and extra-hypothalamic regions in regulating basal and chronic stress responses. GCs interact with a large number of neurotransmitter and neuropeptide systems that are associated with the development of addiction. Additionally, the review will focus on the orexinergic and cholinergic pathways and highlight their role in stress and addiction. GCs play a key role in promoting the development of resilience or susceptibility and represent important pharmacotherapeutic targets that can reduce the impact of a maladapted stress system for the treatment of stress-induced addiction.

Stress-induced sensitization to cocaine: actin cytoskeleton remodeling within mesocorticolimbic nuclei

This study investigated the consequence of repeated stress on actin cytoskeleton remodeling in the nucleus accumbens (NAc) and prefrontal cortex (Pfc), and the involvement of this remodeling in the expression of stress-induced motor cross-sensitization with cocaine. Wistar rats were restrained daily (2 h) for 7 days and, 3 weeks later, their NAc and Pfc were dissected 45 min after acute saline or cocaine (30 mg/kg i.p.). F-actin, actin-binding proteins (ABP) and GluR1 were quantified by Western blotting, and dendritic spines and postsynaptic density (PSD) size measured by electron microscopy. In the NAc from the stress plus cocaine group we observed a decrease in the phosphorylation of two ABPs, cofilin and cortactin, and an increase in the PSD size and the surface expression of GluR1, consistent with a more highly branched actin cytoskeleton. The Pfc also showed evidence of increased actin polymerization after stress as an increase was observed in Arp2, and in the number of spines. Inhibiting actin cycling and polymerization with latrunculin A into the NAc, but not the Pfc, inhibited the expression of cross-sensitization to cocaine (15 mg/kg i.p.) and restored the expression of GluR1 to control levels. This study shows that a history of repeated stress alters the ability of a subsequent cocaine injection to modulate dendritic spine morphology, actin dynamics and GluR1 expression in the NAc. Furthermore, by regulating GluR1 expression in the NAc, elevated actin cycling contributes to the expression of cross-sensitization between stress and cocaine, while stress-induced changes in the Pfc were not associated with cross-sensitization.

Central dopaminergic system and its implications in stress-mediated neurological disorders and gastric ulcers: short review

For decades, it has been suggested that dysfunction of dopaminergic pathways and their associated modulations in dopamine levels play a major role in the pathogenesis of neurological disorders. Dopaminergic system is involved in the stress response, and the neural mechanisms involved in stress are important for current research, but the recent and past data on the stress response by dopaminergic system have received little attention. Therefore, we have discussed these data on the stress response and propose a role for dopamine in coping with stress. In addition, we have also discussed gastric stress ulcers and their correlation with dopaminergic system. Furthermore, we have also highlighted some of the glucocorticoids and dopamine-mediated neurological disorders. Our literature survey suggests that dopaminergic system has received little attention in both clinical and preclinical research on stress, but the current research on this issue will surely identify a better understanding of stressful events and will give better ideas for further efficient antistress treatments.

Immune system inflammation in cocaine dependent individuals: implications for medications development

OBJECTIVES

Cocaine dependence is a chronic stress state. Furthermore, both stress and substance abuse have robust and reciprocal effects on immune system cytokines, which are known to be powerful modulators of mood. We therefore examine basal and provoked changes in peripheral cytokines in cocaine dependent individuals to better understand their role in the negative reinforcing effects of cocaine.

METHODS

Twenty-eight (16 F/12 M) treatment-seeking cocaine dependent individuals and 27 (14 F/13 M) social drinkers were exposed to three 5-min guided imagery conditions (stress, drug cue, relaxing) presented randomly across consecutive days. Measures of salivary cortisol, tumor necrosis factor alpha (TNFα), interleukin-10 (IL-10), and interleukin-1 receptor antagonist (IL-1ra) were collected at baseline and various post-imagery time-points.

RESULTS

Cocaine abusers demonstrated decreased basal IL-10 compared with social drinkers. They also showed significant elevations in pro-inflammatory TNFα when exposed to stress compared with when they were exposed to relaxing imagery. This was not observed in the social drinkers. Conversely, social drinkers demonstrated increases in the anti-inflammatory markers, IL-10 and IL-1ra, following exposure to cue, which were not seen in the dependent individuals.

CONCLUSIONS

Cocaine dependent individuals demonstrate an elevated inflammatory state both at baseline and following exposure to the stress imagery condition. Cytokines may reflect potentially novel biomarkers in addicted populations for treatment development.

Neural Regulation of the Stress Response: The Many Faces of Feedback

The mammalian stress response is an integrated physiological and psychological reaction to real or perceived adversity. Glucocorticoids (GCs) are an important component of this response, acting to redistribute energy resources to both optimize survival in the face of challenge and restore homeostasis after the immediate threat has subsided. Release of GCs is mediated by the hypothalamo-pituitary-adrenocortical (HPA) axis, driven by a neural signal originating in the paraventricular nucleus (PVN). Stress levels of GCs bind to glucocorticoid receptors (GRs) in multiple body compartments, including brain, and consequently have wide-reaching actions. For this reason, GCs serve a vital function in feedback inhibition of their own secretion. Fast, non-genomic feedback inhibition of the HPA axis is mediated at least in part by GC signaling in the PVN, acting by a cannabinoid-dependent mechanism to rapidly reduce both neural activity and GC release. Delayed feedback termination of the HPA axis response is mediated by forebrain GRs, presumably by genomic mechanisms. GCs also act in the brainstem to attenuate neuropeptidergic excitatory input to the PVN via acceleration of mRNA degradation, providing a mechanism to attenuate future responses to stressors. Thus, rather than having a single defined feedback switch, GCs work through multiple neurocircuits and signaling mechanisms to coordinate HPA axis activity to suit the overall needs of multiple body systems.

Stress and cocaine interact to modulate Arc/Arg3.1 expression in rat brain

RATIONALE

The interaction between stress and drugs of abuse is a critical component of drug addiction, but the underlying molecular mechanisms remain elusive. Arc/Arg3.1 is an effector immediate early gene that may represent a bridge connecting short- and long-term neuronal modifications associated with exposure to stress and drugs of abuse.

OBJECTIVES

This research aims to study the modulation of Arc/Arg3.1 expression as a marker of neuronal changes associated with exposure to stress and cocaine.

MATERIALS AND METHODS

Rats exposed to either single or repeated stress sessions were subjected to a single intraperitoneal injection of cocaine hydrochloride (10 mg/kg) and sacrificed 2 h later. RNase protection assay was used to determine changes in Arc/Arg3.1 gene expression in different brain regions.

RESULTS

We found significant stress-cocaine interactions in the prefrontal cortex (p < 0.001) and hypothalamus (p < 0.05). In the prefrontal cortex, acute stress potentiated cocaine-induced Arc/Arg3.1 mRNA elevation, whereas prolonged stress attenuated the response to cocaine. In the hypothalamus, although markedly reduced by acute stress, Arc/Arg3.1 gene expression was still increased by cocaine. No interaction was observed following repeated stress. Notably, cocaine-induced Arc/Arg3.1 mRNA levels were not influenced by stress in striatum and hippocampus.

CONCLUSIONS

In our experimental model, stress interacted with cocaine to alter Arc/Arg3.1 expression in a regionally selective fashion and in a way that depended on whether stress was acute or repeated. These results point to Arc/Arg3.1 as a potential molecular target modulated by stress to alter cellular sensitivity to cocaine.

Stress- and glucocorticoid-induced priming of neuroinflammatory responses: potential mechanisms of stress-induced vulnerability to drugs of abuse

Stress and stress-induced glucocorticoids (GCs) sensitize drug abuse behavior as well as the neuroinflammatory response to a subsequent pro-inflammatory challenge. Stress also predisposes or sensitizes individuals to develop substance abuse. There is an emerging evidence that glia and glia-derived neuroinflammatory mediators play key roles in the development of drug abuse. Drugs of abuse such as opioids, psychostimulants, and alcohol induce neuroinflammatory mediators such as pro-inflammatory cytokines (e.g. interleukin (IL)-1β), which modulate drug reward, dependence, and tolerance as well as analgesic properties. Drugs of abuse may directly activate microglial and astroglial cells via ligation of Toll-like receptors (TLRs), which mediate the innate immune response to pathogens as well as xenobiotic agents (e.g. drugs of abuse). The present review focuses on understanding the immunologic mechanism(s) whereby stress primes or sensitizes the neuroinflammatory response to drugs of abuse and explores whether stress- and GC-induced sensitization of neuroimmune processes predisposes individuals to drug abuse liability and the role of neuroinflammatory mediators in the development of drug addiction.

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.

Social isolation and stress related hormones modulate the stimulating effect of ethanol in preweanling rats

Preweanling rats are highly sensitive to the locomotor stimulation induced by relatively high ethanol doses. In adult mice this ethanol effect is modulated by stress. The goal of the present study was to analyze the role of stress and corticosterone in the stimulating effect of ethanol in preweanling rats. In Experiment 1 15-day-old rats were separated from the mother during a period of 4h in which subjects remained isolated or paired with a littermate. In a third condition pups remained in the home-cage with the dam. After this isolation period pups were given ethanol (0 or 2.5 g/kg) and were tested in a novel environment. Previous data have shown that a similar period of isolation is enough to increase corticosterone levels in preweanling rats. Experiment 2 evaluated the effect of exogenous administration of corticosterone (0, 3 or 6 mg/kg) along with ethanol, and Experiment 3 tested ethanol-mediated locomotor activation in adrenalectomized preweanling rats. The last experiment aimed to test the role of corticotropic releasing factor 1 (CRF1) receptors in locomotion induced by ethanol in isolated pups. According to our results there is a synergism between stress or corticosterone and ethanol in preweanling rats. The interaction between stress (induced by social isolation) and ethanol seems to be mediated by CRF, since blockade of CRF1 receptors cancelled the effect of ethanol in isolated pups. This study highlights the importance of considering stress as a possible intervening variable in studies evaluating ethanol effects in developing animals when maternal separation is used in the experimental procedure.

BclI glucocorticoid receptor polymorphism and smoking in the general population

We studied the hypothesis that the BclI polymorphism of the glucocorticoid receptor gene is associated with an increased probability of being a (heavy) smoker and a decreased ability to quit smoking. The study cohort consisted of all subjects in the Rotterdam Study, a Dutch population-based cohort of people aged 55 years and older, for whom BclI genotyping and smoking status at baseline were available. In prospective analyses, the smoking status was reassessed during three additional examination rounds. Logistic regression analysis was used to study the association between BclI polymorphism and being a smoker or a heavy smoker at baseline. Furthermore, the relationship between BclI polymorphism and incident smoking cessation was tested with Cox proportional hazards analysis within those who smoked at baseline. In total, 6358 subjects were included in the study. The presence of a G-allele was not associated with current smoking at baseline [odds ratio (OR) = 0.96, 95%confidence interval (CI): 0.85-1.09] or with the incidence of smoking cessation during follow-up [hazard ratio (HR) = 0.98, 95%CI: 0.80-1.19]. Within current smokers, having a G-allele was not significantly associated with the risk of being a heavy smoker when measured by pack-years smoked (OR = 1.07, 95%CI: 0.85-1.35) or daily consumption of tobacco (OR = 1.10, 95%CI: 0.88-1.37). We were not able to replicate the earlier findings indicating that the proportion of current smokers is lower among carriers of the CC-genotype of the BclI glucocorticoid receptor. Furthermore, the BclI glucocorticoid receptor polymorphism did not predict the incidence of smoking cessation in the general elderly population.

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.

Effects of chronic stress on nicotine-induced locomotor activity and corticosterone release in adult and adolescent rats

We examined nicotine-induced locomotion and increase in corticosterone plasma levels in adolescent and adult animals exposed to chronic restraint stress. Adolescent [postnatal day (P) 28-37] and adult (P60-67) rats were restrained for 2 hours once daily for 7 days. Three days after the last exposure to stress, the animals were challenged with saline or nicotine (0.4 mg/kg subcutaneously). Nicotine-induced locomotion was recorded in an activity cage. Trunk blood samples were collected in a subset of adolescent and adult rats and plasma corticosterone levels were determined by radioimmunoassay. Exposure to stress did not affect the nicotine-induced locomotor- or corticosterone-activating effects in both ages.

Stress modulation of the memory retrograde-enhancing effects of the awakening drug modafinil in mice

PURPOSE

This study investigated the dose-effect relationship of modafinil administration on contextual memory processes, in parallel with the measurements of plasma corticosterone levels in acutely stressed mice.

MATERIALS AND METHODS

Memory was first evaluated in normal (nonstressed) mice either in contextual (CSD) or spatial (SSD) tasks. Thus, C57 Bl/6 Jico mice learned two consecutive discriminations (D1 and D2) in a four-hole board. The discriminations occurred on either distinct (CSD) or identical (SSD) floors (internal contextual cues). All mice received a vehicle intraperitoneal injection before learning and were injected 24 h later (20 min before the test session) either with vehicle or modafinil.

RESULTS

Results showed that modafinil-treated mice behaved similarly as vehicles in the spatial SSD task, whereas in contrast, memory of the first-learned discrimination (D1) in the CSD task was enhanced by a 32- but not a 16-mg/kg modafinil dose. Hence, we studied the effect of a pretest acute stress (electric footshocks) specifically on D1 performance in modafinil-treated subjects. Immediately after behavioral testing, blood was sampled to measure plasma corticosterone levels.

CONCLUSIONS

Results showed that: (1) stress significantly improved performance in vehicles, (2) stress decreased the efficiency threshold of modafinil, as performance was enhanced at the low dose (16 mg/kg), whereas this enhancement was obtained for the high dose (32 mg/kg) under nonstress conditions, (3) the performance was impaired at the high (32 mg/kg) dose, and (4) modafinil significantly reduced the magnitude of the stress-induced corticosterone secretion, mainly at the dose of 32 mg/kg.

Behavioral functions of the mesolimbic dopaminergic system: an affective neuroethological perspective

The mesolimbic dopaminergic (ML-DA) system has been recognized for its central role in motivated behaviors, various types of reward, and, more recently, in cognitive processes. Functional theories have emphasized DA's involvement in the orchestration of goal-directed behaviors and in the promotion and reinforcement of learning. The affective neuroethological perspective presented here views the ML-DA system in terms of its ability to activate an instinctual emotional appetitive state (SEEKING) evolved to induce organisms to search for all varieties of life-supporting stimuli and to avoid harms. A description of the anatomical framework in which the ML system is embedded is followed by the argument that the SEEKING disposition emerges through functional integration of ventral basal ganglia (BG) into thalamocortical activities. Filtering cortical and limbic input that spreads into BG, DA transmission promotes the "release" of neural activity patterns that induce active SEEKING behaviors when expressed at the motor level. Reverberation of these patterns constitutes a neurodynamic process for the inclusion of cognitive and perceptual representations within the extended networks of the SEEKING urge. In this way, the SEEKING disposition influences attention, incentive salience, associative learning, and anticipatory predictions. In our view, the rewarding properties of drugs of abuse are, in part, caused by the activation of the SEEKING disposition, ranging from appetitive drive to persistent craving depending on the intensity of the affect. The implications of such a view for understanding addiction are considered, with particular emphasis on factors predisposing individuals to develop compulsive drug seeking behaviors.

Gene-environment interactions in vulnerability to cocaine intravenous self-administration: a brief social experience affects intake in DBA/2J but not in C57BL/6J mice

RATIONALE

Individual differences in cocaine-taking behavior and liability to develop abuse are clearly observed, but underlying mechanisms are still poorly understood. A role for gene-environment interactions has been proposed but remains hypothetical.

OBJECTIVES

We investigated whether gene-environment interactions influence intravenous cocaine self-administration (SA) in mice. We tested the effect of a past short group housing experience on cocaine SA in two inbred strains of mice, the C57BL/6J (C57) and DBA/2J (DBA).

METHODS

Adult C57 and DBA mice were individually housed upon arrival in the laboratory. After 3 weeks, half of the animals of each strain were group housed for 19 days. One week after the end of group housing, cocaine SA or measurement of brain cocaine levels took place.

RESULTS

Individually and ex-group-housed C57 mice did not differ for cocaine SA. On the contrary, the ex-group-housed DBA mice showed an upward shift in the dose-response curve as compared to individually housed DBA. Differences in brain cocaine levels could not account for the observed behavioral differences.

CONCLUSIONS

These results demonstrate that vulnerability to cocaine reinforcing effects can be affected by gene-environment interactions. We propose a mouse model for the characterization of gene-environment interactions in the vulnerability to cocaine-taking behavior.

2006 Curt P. Richter award winner: Social influences on stress responses and health

Both positive and negative social interactions can modulate the hypothalamic-pituitary-adrenal (HPA) axis and influence recovery from injuries and illnesses, such as wounds, stroke, and cardiac arrest. Stress exacerbates neuronal death following stroke and cardiac arrest, and delays cutaneous wound healing, via a common mechanism involving stress-induced increases in corticosterone, acting on glucocorticoid receptors. In contrast, hamsters and mice that form social bonds are buffered against stress and heal cutaneous wounds more quickly than socially isolated animals, presumably because the physical contact experienced by the pairs releases oxytocin, which in turn suppresses the HPA axis and facilitates wound healing. Social housing also decreases stroke-induced neuronal death and improves functional recovery, but the mechanism appears to involve suppressing the inflammatory response that accompanies stroke, rather than alterations in HPA axis activity. An interaction between the HPA axis and immune system determines stroke outcome in neonatally manipulated mice that exhibit life-long dampening of the HPA axis. Taken together, these studies provide support for the detrimental effects of stress and identify potential mechanisms underlying the well-documented clinical observation that social support positively influences human health.

Association between the BclI glucocorticoid receptor polymorphism and smoking in a sample of patients with obstructive airway disease

Glucocorticoids seem to mediate the effect of stimulant drugs such as nicotine. Several studies have pointed to an association between the BclI polymorphism in the glucocorticoid receptor gene and increased glucocorticoid effects. We analysed the association of smoking behaviour and the BclI polymorphism using a case-control design within the framework of a larger pharmacogenetic study. A total of 327 Caucasian patients with asthma or chronic obstructive pulmonary disease from 39 German general practices gave informed consent to take part in the study. They filled in questionnaires concerning their smoking behaviour and were genotyped for the BclI polymorphism. The genotype frequencies for non-smokers (n = 251; CC, 0.42; CG, 0.46; GG, 0.12) as well as for smokers (n = 76; CC, 0.29; CG, 0.55; GG, 0.16) were consistent with the Hardy-Weinberg equilibrium. The proportion of smokers was significantly lower among carriers of the CC-genotype (22/127 = 17%) compared with carriers of the G-allele (54/200 = 27%; chi2 = 4.08; P = 0.04). Within the group of smokers, the proportion of heavy smokers (> 19 cigarettes/day; median) was reduced in C-homozygous patients when compared with carriers of the G-allele (7/22 = 32% versus 31/54 = 57%; chi2 = 4.09; P = 0.04). Stepwise logistic regression analysis also pointed to an association between the CC-genotype and a reduced probability of being a smoker (odds ratio = 0.55; 95% confidence interval = 0.30-1.00; P = 0.05) controlling for other predictors. In summary, this study provides evidence that the BclI polymorphism might play a role in the maintenance and severity of nicotine dependence.

Locomotor activity to nicotine and Fos immunoreactivity in the paraventricular nucleus of the hypothalamus in adolescent socially-stressed rats

We reported previously that social stressors in adolescence (SS: one-hour isolation and new cage partners daily for 16 days) increased locomotor activity to nicotine and to amphetamine in females, but not in males, when tested as adults. Here, we investigated whether effects of stressors in adolescence on locomotor responses to nicotine would be observed in both sexes if tested closer in time to the stressor exposure. We also tested whether social instability was necessary to alter nicotine's effects on locomotor activity by including a group that underwent daily isolation but was housed with the same partner (ISO). The locomotor-activating effects of nicotine were lower in SS rats compared to ISO and non-stressed control rats. In males, but not in females, there were effects of nicotine treatment and of stress condition on Fos immunoreactive (Fos-ir) cell counts in the paraventricular nucleus (PVN) of the hypothalamus: SS males had higher Fos-ir counts than did ISO and non-stressed control males, and higher Fos-ir counts in the PVN were found in repeated-nicotine groups than in acute-nicotine and saline groups. These results add to evidence that adolescents are uniquely vulnerable to stressors due to ongoing brain development, and also indicate that effects are sex- and stressor-specific.

Cocaine and amphetamine regulated transcript (CART) and the stress response

CART is expressed abundantly in the hypothalamic paraventricular nucleus and locus coeruleus, major corticotropin releasing factor (CRF) and noradrenaline sources, respectively. There is a bidirectional relation between CART and hypothalamo-pituitary-adrenal axis activity. CART stimulates CRF, adrenocorticotropic hormone and glucocorticoid secretion, whereas CRF and glucocorticoids increase the transcriptional activity of the CART gene; adrenalectomy declines CART expression in the hypothalamus. Stress exposure modulates CART expression in hypothalamus and amygdala in rat brain in a region and sex specific manner. CART may be a mediator peptide in the interaction between stress, drug abuse, and feeding. The review discusses the established role of CART as it relates to the stress response.

Role of glucocorticoids in dopamine-related neuropsychiatric disorders

'Psychoneuroendocrinology' is now quickly emerging as a hot interdisciplinary research field that addresses the interplay between neuronal and endocrine signaling in psychiatric diseases. Both glucocorticoid hormones and dopamine have an important role in maintaining normal brain functions. In this review, molecular and mechanistic aspects of glucocorticoid effects on brain function and behavior will be discussed with specific reference to dopamine signaling.

Differential behavioral and neuroendocrine effects of repeated nicotine in adolescent and adult rats

Despite the high prevalence of tobacco abuse among adolescents, the neurobiology of nicotine addiction has been studied mainly in adult animals. Repeated administration of this drug to adult rats induces behavioral sensitization. Nicotine activates the HPA axis in adult rats as measured by drug-induced increases in ACTH and corticosterone. Both behavioral sensitization and corticosterone are implicated in drug addiction. We examined the expression of behavioral sensitization induced by nicotine as well as the changes in corticosterone levels after repeated injections of nicotine in adolescent and adult animals. Adolescent and adult rats received subcutaneous (s.c.) injections of saline or 0.4 mg/kg of nicotine once daily for 7 days. Three days after the last injection animals were challenged with saline or nicotine (0.4 mg/kg; s.c.). Nicotine-induced locomotion was recorded in an activity cage. Trunk blood samples were collected in a subset of adolescent and adult rats and plasma corticosterone levels were determined by radioimmunoassay. Adult, but not adolescent, rats expressed behavioral sensitization. Pretreatment with nicotine abolished corticosterone-activating effect of this drug only in adult animals, indicating the development of tolerance at this age. Our results provide evidence that adolescent rats exposed to repeated nicotine display behavioral and neuroendocrine adaptations distinct from that observed in adult animals.