Involvement of arginine vasopressin and V1b receptor in heroin withdrawal and heroin seeking precipitated by stress and by heroin

Incubation of methamphetamine craving in punishment-resistant individuals is associated with activation of specific gene networks in the rat dorsal striatum

Methamphetamine use disorder (MUD) is characterized by loss of control over compulsive drug use. Here, we used a self-administration (SA) model to investigate transcriptional changes associated with the development of early and late compulsivity during contingent footshocks. Punishment initially separated methamphetamine taking rats into always shock-resistant (ASR) rats that continued active lever pressing and shock-sensitive (SS) rats that reduced their lever pressing. At the end of the punishment phase, rats underwent 15 days of forced abstinence at the end of which they were re-introduced to the SA paradigm followed by SA plus contingent shocks. Interestingly, 36 percent of the initial SS rats developed delayed shock-resistance (DSR). Of translational relevance, ASR rats showed more incubation of methamphetamine craving than DSR and always sensitive (AS) rats. RNA sequencing revealed increased striatal Rab37 and Dipk2b mRNA levels that correlated with incubation of methamphetamine craving. Interestingly, Bdnf mRNA levels showed HDAC2-dependent decreased expression in the AS rats. The present SA paradigm should help to elucidate the molecular substrates of early and late addiction-like behaviors.

Abstinence from Escalation of Cocaine Intake Changes the microRNA Landscape in the Cortico-Accumbal Pathway

Cocaine administration alters the microRNA (miRNA) landscape in the cortico-accumbal pathway. These changes in miRNA can play a major role in the posttranscriptional regulation of gene expression during withdrawal. This study aimed to investigate the changes in microRNA expression in the cortico-accumbal pathway during acute withdrawal and protracted abstinence following escalated cocaine intake. Small RNA sequencing (sRNA-seq) was used to profile miRNA transcriptomic changes in the cortico-accumbal pathway [infralimbic- and prelimbic-prefrontal cortex (IL and PL) and nucleus accumbens (NAc)] of rats with extended access to cocaine self-administration followed by an 18-h withdrawal or a 4-week abstinence. An 18-h withdrawal led to differential expression (fold-change > 1.5 and p < 0.05) of 21 miRNAs in the IL, 18 miRNAs in the PL, and two miRNAs in the NAc. The mRNAs potentially targeted by these miRNAs were enriched in the following pathways: gap junctions, neurotrophin signaling, MAPK signaling, and cocaine addiction. Moreover, a 4-week abstinence led to differential expression (fold-change > 1.5 and p < 0.05) of 23 miRNAs in the IL, seven in the PL, and five miRNAs in the NAc. The mRNAs potentially targeted by these miRNAs were enriched in pathways including gap junctions, cocaine addiction, MAPK signaling, glutamatergic synapse, morphine addiction, and amphetamine addiction. Additionally, the expression levels of several miRNAs differentially expressed in either the IL or the NAc were significantly correlated with addiction behaviors. Our findings highlight the impact of acute and protracted abstinence from escalated cocaine intake on miRNA expression in the cortico-accumbal pathway, a key circuit in addiction, and suggest developing novel biomarkers and therapeutic approaches to prevent relapse by targeting abstinence-associated miRNAs and their regulated mRNAs.

Establishment of a biomarker of peripheral stress in opioid addicts based on the hypothalamic-pituitary-adrenal axis-The improvement effect of exercise

PURPOSE

This study aims to investigate the relationship between peripheral blood oxytocin (OT), vasopressin (AVP), and subjectively perceived stress and cortisol in male opioid addicts based on the hypothalamic-pituitary-adrenal (HPA) axis. We also investigate the impact of exercise on reducing subjectively perceived stress, craving level, negative reinforcement, anxiety, sleep quality, plasma OT, AVP, and cortisol levels.

METHODS

Participants were divided into 28 subjects in the low-stress control group (LSC group), 29 subjects in the medium-high stress control group (MTHSC group), and 28 subjects in the moderate-high-stress exercise group (MTHSE group), based on their subjectively perceived stress levels. Subjects in the MTHSE group performed 12 weeks of combined aerobic resistance training (60 min per day, 5 days per week). Plasma OT, AVP, and cortisol concentrations were analyzed via Elisa. PSQI was used to assess the subjective perceived stress, craving, negative reinforcement, anxiety, and sleep quality level, respectively. Mixed-effects ANOVA and Pearson correlation analysis were employed to explore the impact and correlation between different parameters.

RESULT

Plasma OT levels significantly increased (95% CI: -7.48, -2.26), while plasma AVP (95% CI: 2.90, 4.10), and cortisol (95% CI: 19.76, 28.17) levels significantly decreased in the MTHSE group after exercise. The PSS (95% CI: 1.756, 4.815), "Desire and Intention" (95% CI: 1.60, 2.71), and "Negative reinforcement" (95% CI: 0.85, 1.90) (DDQ), SAS (95% CI: 17.51, 26.06), and PSQI (95% CI: 1.18, 3.25) scores of the MTHSE group were significantly decreased after exercise. Plasma OT, plasma cortisol, craving, negative reinforcement and anxiety were negatively correlated. Plasma AVP was positively correlated with craving.

CONCLUSION

As an auxiliary treatment, exercise improves the plasma OT, AVP, and cortisol levels of opioid addicts, and reduces their subjective perceived stress level, desire, negative reinforcement level, anxiety level, and sleep quality. In addition, peripheral plasma OT, AVP, and cortisol may play a role as potential peripheral biomarkers to predict stress in male opioid addicts.

Role of Oxytocin and Vasopressin in Neuropsychiatric Disorders: Therapeutic Potential of Agonists and Antagonists

Oxytocin (OT) and vasopressin (AVP) are hypothalamic neuropeptides classically associated with their regulatory role in reproduction, water homeostasis, and social behaviors. Interestingly, this role has expanded in recent years and has positioned these neuropeptides as therapeutic targets for various neuropsychiatric diseases such as autism, addiction, schizophrenia, depression, and anxiety disorders. Due to the chemical-physical characteristics of these neuropeptides including short half-life, poor blood-brain barrier penetration, promiscuity for AVP and OT receptors (AVP-R, OT-R), novel ligands have been developed in recent decades. This review summarizes the role of OT and AVP in neuropsychiatric conditions, as well as the findings of different OT-R and AVP-R agonists and antagonists, used both at the preclinical and clinical level. Furthermore, we discuss their possible therapeutic potential for central nervous system (CNS) disorders.

Consideration of sex as a biological variable in the translation of pharmacotherapy for stress-associated drug seeking

Stress is a frequent precipitant of relapse to drug use. Pharmacotherapies targeting a diverse array of neural systems have been assayed for efficacy in attenuating stress-induced drug-seeking in both rodents and in humans, but none have shown enough evidence of utility to warrant routine use in the clinic. We posit that a critical barrier in effective translation is inattention to sex as a biological variable at all phases of the research process. In this review, we detail the neurobiological systems implicated in stress-induced relapse to cocaine, opioids, methamphetamine, and cannabis, as well as the pharmacotherapies that have been used to target these systems in rodent models, the human laboratory, and in clinical trials. In each of these areas we additionally describe the potential influences of biological sex on outcomes, and how inattention to fundamental sex differences can lead to biases during drug development that contribute to the limited success of large clinical trials. Based on these observations, we determine that of the pharmacotherapies discussed only α₂-adrenergic receptor agonists and oxytocin have a body of research with sufficient consideration of biological sex to warrant further clinical evaluation. Pharmacotherapies that target β-adrenergic receptors, other neuroactive peptides, the hypothalamic-pituitary-adrenal axis, neuroactive steroids, and the endogenous opioid and cannabinoid systems require further assessment in females at the preclinical and human laboratory levels before progression to clinical trials can be recommended.

Drug Addiction: Hyperkatifeia/Negative Reinforcement as a Framework for Medications Development

Compulsive drug seeking that is associated with addiction is hypothesized to follow a heuristic framework that involves three stages (binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation) and three domains of dysfunction (incentive salience/pathologic habits, negative emotional states, and executive function, respectively) via changes in the basal ganglia, extended amygdala/habenula, and frontal cortex, respectively. This review focuses on neurochemical/neurocircuitry dysregulations that contribute to hyperkatifeia, defined as a greater intensity of negative emotional/motivational signs and symptoms during withdrawal from drugs of abuse in the withdrawal/negative affect stage of the addiction cycle. Hyperkatifeia provides an additional source of motivation for compulsive drug seeking via negative reinforcement. Negative reinforcement reflects an increase in the probability of a response to remove an aversive stimulus or drug seeking to remove hyperkatifeia that is augmented by genetic/epigenetic vulnerability, environmental trauma, and psychiatric comorbidity. Neurobiological targets for hyperkatifeia in addiction involve neurocircuitry of the extended amygdala and its connections via within-system neuroadaptations in dopamine, enkephalin/endorphin opioid peptide, and γ-aminobutyric acid/glutamate systems and between-system neuroadaptations in prostress corticotropin-releasing factor, norepinephrine, glucocorticoid, dynorphin, hypocretin, and neuroimmune systems and antistress neuropeptide Y, nociceptin, endocannabinoid, and oxytocin systems. Such neurochemical/neurocircuitry dysregulations are hypothesized to mediate a negative hedonic set point that gradually gains allostatic load and shifts from a homeostatic hedonic state to an allostatic hedonic state. Based on preclinical studies and translational studies to date, medications and behavioral therapies that reset brain stress, antistress, and emotional pain systems and return them to homeostasis would be promising new targets for medication development. SIGNIFICANCE STATEMENT: The focus of this review is on neurochemical/neurocircuitry dysregulations that contribute to hyperkatifeia, defined as a greater intensity of negative emotional/motivational signs and symptoms during withdrawal from drugs of abuse in the withdrawal/negative affect stage of the drug addiction cycle and a driving force for negative reinforcement in addiction. Medications and behavioral therapies that reverse hyperkatifeia by resetting brain stress, antistress, and emotional pain systems and returning them to homeostasis would be promising new targets for medication development.

Opioid withdrawal and memory consolidation

It is well established that learning and memory are central to substance dependence. This paper specifically reviews the effect of opioid withdrawal on memory consolidation. Although there is evidence that opioid withdrawal can interfere with initial acquisition and retrieval of older memories, there are several reasons to postulate a facilitatory action on the consolidation of newly acquired memories. In fact, there is substantial evidence that memory consolidation is facilitated by the release of stress hormones, that it requires the activation of the amygdala, of central noradrenergic and cholinergic pathways, and that it involves long-term potentiation. This review highlights evidence that very similar neurobiological processes are involved in opioid withdrawal, and summarizes recent results indicating that naltrexone-precipitated withdrawal enhanced consolidation in rats. From this neurocognitive perspective, therefore, opioid use may escalate during the addiction cycle in part because memories of stimuli and actions experienced during withdrawal are strengthened.

Opioids and the hormone oxytocin

The neuropeptide Oxytocin (ΟΤ) is involved as a neurohormone, a neurotransmitter, or a neuromodulator in an extensive range of central and peripheral effects, complex emotional and social human behaviors, memory and learning processes. It is implicated in homeostatic, neuroadaptive processes associated with stress responses and substance use via interactions with the hypothalamic-pituitary-adrenal (HPA) axis and the dopamine mesolimbic reward stress system. This chapter reviews the preclinical and clinical literature on the complicated relationships between endogenous and exogenous opioids and ΟΤ systems and attempts to highlight key findings to date on the effectiveness of intranasal OT administration to treat opioid use disorders. OΤ seems to attenuate, even inhibit, the development of opioid use disorders in preclinical models but is still under clinical research as a promising pharmacological agent in the treatment of opioid use related behaviors. Evidence suggests a role for OT as an adjunctive or stand-alone treatment of behavioral, cognitive and emotional deficits associated with substance use, which may be responsible for seeking behavior and relapse. The mechanisms by which oxytocin acts to reverse the neural substrates of these deficits, partially due to substance induced alterations of the endogenous OT system, and thus modify the behavioral response to substance use are discussed. Other clinically relevant issues are also discussed.

Anti-stress neuropharmacological mechanisms and targets for addiction treatment: A translational framework

Stress-related substance use is a major challenge for treating substance use disorders. This selective review focuses on emerging pharmacotherapies with potential for reducing stress-potentiated seeking and consumption of nicotine, alcohol, marijuana, cocaine, and opioids (i.e., key phenotypes for the most commonly abused substances). I evaluate neuropharmacological mechanisms in experimental models of drug-maintenance and relapse, which translate more readily to individuals presenting for treatment (who have initiated and progressed). An affective/motivational systems model (three dimensions: valence, arousal, control) is mapped onto a systems biology of addiction approach for addressing this problem. Based on quality of evidence to date, promising first-tier neurochemical receptor targets include: noradrenergic (α1 and β antagonist, α2 agonist), kappa-opioid antagonist, nociceptin antagonist, orexin-1 antagonist, and endocannabinoid modulation (e.g., cannabidiol, FAAH inhibition); second-tier candidates may include corticotropin releasing factor-1 antagonists, serotonergic agents (e.g., 5-HT reuptake inhibitors, 5-HT3 antagonists), glutamatergic agents (e.g., mGluR2/3 agonist/positive allosteric modulator, mGluR5 antagonist/negative allosteric modulator), GABA-promoters (e.g., pregabalin, tiagabine), vasopressin 1b antagonist, NK-1 antagonist, and PPAR-γ agonist (e.g., pioglitazone). To address affective/motivational mechanisms of stress-related substance use, it may be advisable to combine agents with actions at complementary targets for greater efficacy but systematic studies are lacking except for interactions with the noradrenergic system. I note clinically-relevant factors that could mediate/moderate the efficacy of anti-stress therapeutics and identify research gaps that should be pursued. Finally, progress in developing anti-stress medications will depend on use of reliable CNS biomarkers to validate exposure-response relationships.

The role of the vasopressin system and dopamine D1 receptors in the effects of social housing condition on morphine reward

BACKGROUND

The association with opioid-abusing individuals or even the perception of opioid abuse by peers are risk factors for the initiation and escalation of abuse. Similarly, we demonstrated that morphine-treated animals housed with only morphine-treated animals (referred to as morphine only) acquire morphine conditioned place-preference (CPP) more readily than morphine-treated animals housed with drug-naïve animals (referred to as morphine cage-mates). However, the molecular mechanisms underlying these effects are still elusive.

METHODS

Mice received repeated morphine or saline while housed as saline only, morphine only, or cage-mates. Then, they were examined for the expression levels of D1 dopamine receptor (D1DR), D2 dopamine receptor (D2DR), dopamine transporter (DAT), oxytocin, and Arginine-vasopressin (AVP) in the striatum using qPCR. Additionally, we examined the effects of the AVP-V1b receptor antagonist, SSR149415, on the acquisition of morphine conditioned place-preference (CPP).

RESULTS

Increased striatal expression of D1DR and AVP was observed in morphine only animals, but not morphine cage-mates. No significant effects were observed on the striatal expression of D2DR, DAT, or oxytocin. Antagonizing the AVP-V1b receptors decreased the acquisition of morphine CPP in the morphine only mice, but did not alter the acquisition of morphine CPP in the morphine cage-mate mice.

CONCLUSIONS

Housing with drug-naïve animals protects against the increase in striatal expression of D1DR and AVP elicited by morphine exposure. Moreover, our studies suggest that the protective effect of housing with drug-naïve animals on the acquisition of morphine reward might be, at least partially, mediated by AVP.

Involvement of Activated Brain Stress Responsive Systems in Excessive and "Relapse" Alcohol Drinking in Rodent Models: Implications for Therapeutics

Addictive diseases, including addiction to alcohol, pose massive public health costs. Addiction is a chronic relapsing disease caused by both the direct effects induced by drugs and persistent neuroadaptations at the molecular, cellular, and behavioral levels. These drug-type specific neuroadaptations are brought on largely by the reinforcing effects of drugs on the central nervous system and environmental stressors. Results from animal experiments have demonstrated important interactions between alcohol and stress-responsive systems. Addiction to specific drugs such as alcohol, psychostimulants, and opioids shares some common direct or downstream effects on the brain's stress-responsive systems, including arginine vasopressin and its V1b receptors, dynorphin and the κ-opioid receptors, pro-opiomelanocortin/β-endorphin and the μ-opioid receptors, and the endocannabinoids. Further study of these systems through laboratory-based and translational research could lead to the discovery of novel treatment targets and the early optimization of interventions (for example, combination) for the pharmacologic therapy of alcoholism.

Effects of alcohol and psychostimulants on the vasopressin system: behavioral implications

Drug addiction is a chronic brain disease characterized by a compulsion to seek drugs, a loss of control with respect to drug consumption, and negative emotional states, including increased anxiety and irritability during withdrawal. Central vasopressin (AVP) and its receptors are involved in controlling social behavior, anxiety and reward, all of which are altered by drugs of abuse. Hypothalamic AVP neurons influence the stress response by modulating the hypothalamic-pituitary-adrenal (HPA) axis. The extrahypothalamic AVP system, however, is commonly associated with social recognition, motivational and anxiety responses. The specific relationship between AVP and drugs of abuse has been rarely reviewed. Here, we provide an overview of the interaction between the brain AVP system and psychostimulants and alcohol. We focus on the effects of alcohol and psychostimulants on AVP regulation of the HPA axis, their effect on the brain AVP system and their behavioral implications, the influence of the AVP system on addictive behaviors, AVP's organizational effects on the brain and consequently on behavior, and we highlight clinical studies on the relation between the AVP system and drug addiction. Finally, we discuss the data to address areas that need further research to support clinical trials and prevent drug-related disorders. This article is protected by copyright. All rights reserved.

V1b Receptor Antagonist SSR149415 and Naltrexone Synergistically Decrease Excessive Alcohol Drinking in Male and Female Mice

BACKGROUND

A recent clinical trial found that pharmacological blockade of V1b receptors reduces alcohol relapse in alcohol-dependent patients. SSR149415 is a selective V1b receptor antagonist that has potential for development as an alcohol dependency treatment. In this study, we investigated whether SSR149415 alone or in combination with the mu-opioid receptor (MOP-r) antagonist naltrexone (NTN) would alter excessive alcohol drinking in mice.

METHODS

Both sexes of C57BL/6J (B6) mice were subjected to a chronic intermittent access (IA) drinking paradigm (2-bottle choice, 24-hour access every other day) for 3 weeks. Sucrose and saccharin drinking were used as controls for alcohol-specific drug effects. Neuronal proopiomelanocortin (POMC) enhancer (nPE) knockout mice with hypothalamic-specific loss of POMC (including beta-endorphin, the main endogenous ligand of MOP-r) were used as a genetic control for the effects of NTN.

RESULTS

Acute administration of SSR149415 (1 to 30 mg/kg) reduced alcohol intake and preference in a dose-dependent manner in both male and female B6 mice after IA. To investigate potential synergistic effects between NTN and SSR149415, we tested 6 different combination doses of SSR149415 and NTN, and found that a combination of SSR149415 (3 mg/kg) and NTN (1 mg/kg) reduced alcohol intake profoundly at doses lower than the individual effective doses in both sexes of B6 mice. We confirmed the effect of SSR149415 on reducing alcohol intake in nPE-/- male mice, consistent with independent mechanisms by which SSR149415 and NTN decrease alcohol drinking.

CONCLUSIONS

The combination of V1b antagonist SSR149415 with NTN at individual subthreshold doses shows potential in alcoholism treatment, possibly with less adverse effects.

Bidirectional relationship between alcohol intake and sensitivity to social defeat: association with Tacr1 and Avp expression

While epidemiological studies show that alcohol abuse is often co-morbid with affective disorders, the causal direction of this association is unclear. We examined this relationship using mouse models including social defeat stress (SDS), social interaction (SI) and voluntary alcohol consumption. C57BL6/J mice exposed to SDS segregate into two subpopulations, those that express depressive-like phenotypes ('susceptible') and those that do not ('resilient'). First, we stratified SDS-exposed mice and measured their voluntary alcohol consumption. Next, we determined whether SI behavior in alcohol-naïve mice could predict alcohol intake. Finally, we assessed the effect of binge-like alcohol exposure on sensitivity to SDS. We quantified Tacr1 (neurokinin-1 receptor gene) and Avp (vasopressin peptide gene) mRNA in brain regions involved in depression, addiction and social behavior. We found that susceptible mice consumed more alcohol compared with resilient mice, suggesting that depression-like phenotypes associate with increased alcohol intake. Interestingly, we observed a negative correlation between SI and alcohol intake in stress- and alcohol-naïve mice, suggesting that individual differences in SI associate with alcohol preference. Finally, alcohol pre-treatment increased sensitivity to SDS, indicating that alcohol exposure alters sensitivity to social stress. Quantification of mRNA revealed that increased expression of Tacr1 and Avp generally associated with decreased SI and increased alcohol intake. C57BL6/J mice are an inbred strain; thus, it is likely that individual differences in behavior and gene expression are driven by epigenetic factors. Collectively, these results support a bidirectional relationship between alcohol exposure and susceptibility to stress that is associated with variations in neuropeptide expression.

Oprm1 A112G, a single nucleotide polymorphism, alters expression of stress-responsive genes in multiple brain regions in male and female mice

BACKGROUND

OPRM1 A118G, a functional human mu-opioid receptor (MOR) polymorphism, is associated with drug dependence and altered stress responsivity in humans as well as altered MOR signaling. MOR signaling can regulate many cellular processes, including gene expression, and many of the long-term, stable effects of drugs and stress may stem from changes in gene expression in diverse brain regions. A mouse model bearing an equivalent polymorphism (Oprm1 A112G) was previously generated and studied. Mice homozygous for the G112 allele show differences in opioid- and stress-related phenotypes.

APPROACH

The current study examines the expression of 24 genes related to drug and stress responsivity in the caudoputamen, nucleus accumbens, hypothalamus, hippocampus, and amygdala of drug-naïve, stress-minimized, male and female mice homozygous for either the G112 variant allele or the wild-type A112 allele.

RESULTS

We detected nominal genotype-dependent changes in gene expression of multiple genes. We also detected nominal sex-dependent as well as sex-by-genotype interaction effects on gene expression. Of these, four genotype-dependent differences survived correction for multiple testing: Avp and Gal in the hypothalamus and Oprl1 and Cnr1 in the hippocampus.

CONCLUSIONS

Changes in the regulation of these genes by mu-opioid receptors encoded by the G112 allele may be involved in some of the behavioral and molecular consequences of this polymorphism observed in mice.

Etiological theories of addiction: A comprehensive update on neurobiological, genetic and behavioural vulnerability

Currently, about 246 million people around the world have used an illicit drug. The reasons for this use are multiple: e.g. to augment the sensation of pleasure or to reduce the withdrawal and other aversive effects of a given substance. This raises the problem of addiction, which remains a disease of modern society. This review offers a comprehensive update of the different theories about the etiology of addictive behaviors with emphasis on the neurobiological, environmental, psychopathological, behavioural and genetic aspects of addictions, discussed from an evolutionary perspective. The main conclusion of this review is that vulnerability to drug addiction suggests an interaction between many brain systems (including the reward, decision-making, serotonergic, oxytocin, interoceptive insula, CRF, norepinephrine, dynorphin/KOR, orexin and vasopressin systems), genetic predisposition, sociocultural context, impulsivity and drugs types. Further advances in biological and psychological science are needed to address the problems of addiction at its roots.

Chronic treatment with the vasopressin 1b receptor antagonist SSR149415 prevents the dysphoria associated with nicotine withdrawal in rats

Nicotine addiction is a chronic brain disorder that is characterized by dysphoria upon smoking cessation and relapse after brief periods of abstinence. It has been hypothesized that the negative mood state associated with nicotine withdrawal is partly mediated by a heightened activity of brain stress systems. Animal studies suggest that blockade of vasopressin 1b (V1b) receptors diminishes high levels of drug intake in dependent animals and attenuates the emotional response to stressors. The goal of the present studies was to investigate the effect of acute and chronic treatment with the V1b receptor antagonist SSR149415 on the negative mood state associated with nicotine withdrawal in rats. An intracranial self-stimulation (ICSS) procedure was used to assess mood states and nicotine dependence was induced using minipumps. The nicotinic receptor antagonist mecamylamine was used to precipitate withdrawal. Mecamylamine elevated the brain reward thresholds of the nicotine dependent rats, which reflects a negative mood state. Mecamylamine did not affect the brain reward thresholds of the saline-treated control rats. Chronic treatment with SSR149415 completely prevented the elevations in brain reward thresholds associated with nicotine withdrawal while acute treatment only partly prevented nicotine withdrawal. These data suggest that chronic treatment with V1b receptor antagonists may prevent the dysphoria associated with smoking cessation and thereby improve relapse rates.

Stress, sex, and addiction: potential roles of corticotropin-releasing factor, oxytocin, and arginine-vasopressin

Stress sensitivity and sex are predictive factors for the development of neuropsychiatric disorders. Life stresses are not only risk factors for the development of addiction but also are triggers for relapse to drug use. Therefore, it is imperative to elucidate the molecular mechanisms underlying the interactions between stress and drug abuse, as an understanding of this may help in the development of novel and more effective therapeutic approaches to block the clinical manifestations of drug addiction. The development and clinical course of addiction-related disorders do appear to involve neuroadaptations within neurocircuitries that modulate stress responses and are influenced by several neuropeptides. These include corticotropin-releasing factor, the prototypic member of this class, as well as oxytocin and arginine-vasopressin that play important roles in affiliative behaviors. Interestingly, these peptides function to balance emotional behavior, with sexual dimorphism in the oxytocin/arginine-vasopressin systems, a fact that might play an important role in the differential responses of women and men to stressful stimuli and the specific sex-based prevalence of certain addictive disorders. Thus, this review aims to summarize (i) the contribution of sex differences to the function of dopamine systems, and (ii) the behavioral, neurochemical, and anatomical changes in brain stress systems.

Individual differences in gene expression of vasopressin, D2 receptor, POMC and orexin: vulnerability to relapse to heroin-seeking in rats

Individual vulnerability to stress-induced relapse during abstinence from chronic heroin exposure is a key feature of opiate addiction, with limited studies on this topic. Arginine vasopressin (AVP) and its V1b receptor, components of the brain stress responsive systems, play a role in heroin-seeking behavior triggered by foot shock (FS) stress in rats. In this study, we tested whether individual differences in the FS-induced heroin-seeking were associated with alterations of AVP and V1b, as well as other stress responsive systems, including pro-opiomelanocortin (POMC), orexin, plasma ACTH and corticosterone, as well as dopamine D2 receptor (D2) and plasma prolactin. Sprague-Dawley rats were subjected to 3-hour intravenous heroin self-administration (SA) and then tested in extinction, and FS-induced and heroin priming-induced reinstatements. The rats that self-administered heroin were divided into high and low reinstatement responders induced by FS (H-RI; L-RI). Over SA sessions, both the H-RI and L-RI displayed similar active lever responding, heroin infusion and total heroin intake. Compared to the L-RI, however, the H-RI showed greater active lever responses during stress-induced reinstatement, with higher AVP mRNA levels in medial/basolateral amygdala and lower D2 mRNA levels in caudate putamen. However, heroin priming resulted in similar reinstatement in both groups and produced similarly low POMC and high orexin mRNA levels in hypothalamus. Our results indicate that: 1) enhanced amygdalar AVP and reduced striatal D2 expression may be related to individual vulnerability to stress-induced reinstatement of heroin- seeking; and 2) heroin abstinence-associated alterations of hypothalamic orexin and POMC expression may be involved in drug priming-induced heroin-seeking.

Role of cues and contexts on drug-seeking behaviour

Environmental stimuli are powerful mediators of craving and relapse in substance-abuse disorders. This review examined how animal models have been used to investigate the cognitive mechanisms through which cues are able to affect drug-seeking behaviour. We address how animal models can describe the way drug-associated cues come to facilitate the development and persistence of drug taking, as well as how these cues are critical to the tendency to relapse that characterizes substance-abuse disorders. Drug-associated cues acquire properties of conditioned reinforcement, incentive motivation and discriminative control, which allow them to influence drug-seeking behaviour. Using these models, researchers have been able to investigate the pharmacology subserving the behavioural impact of environmental stimuli, some of which we highlight. Subsequently, we examine whether the impact of drug-associated stimuli can be attenuated via a process of extinction, and how this question is addressed in the laboratory. We discuss how preclinical research has been translated into behavioural therapies targeting substance abuse, as well as highlight potential developments to therapies that might produce more enduring changes in behaviour.

NF-κB signaling and vesicle transport are correlated with the reactivation of the memory trace of morphine dependence

BACKGROUND

Morphine has been widely used as a clinical anesthetic and analgesic. However, abuse of morphine might result in psychological and physiological dependence. Previous studies have indicated that memory mechanisms play critical roles in morphine dependence.

METHODS

Morphine dependence was established in mice utilizing place preference conditioning (CPP). We observed changes in the methylome and transcriptome of the nucleus accumbens during the reactivation of the memory trace. We also monitored for changes in the methylome and transcriptome of mice that were acutely exposed to morphine.

RESULTS

We detected 165 and 18 differentially expressed genes (DEGs) and 6 and 24 significant methyl-sensitive cut counting (MSCC) windows in the acute morphine treatment and the CPP model, respectively. The changes in the methylome and transcriptome during the acute treatment were mainly caused by a response to the morphine stimulus; most of the DEGs were correlated with hormone or transcription factor activity regulation. The expression levels of Lcn2 and Hspb1, which participate in the activation of NF-κB, were significantly decreased in the CPP morphine treatment model. Besides, the alternative splicing of the curtailed isoform of Caps1 was significantly increased in the CPP morphine-treated group, and the methylation levels of Arf4, Vapa, and Gga3 were decreased. These genes play critical roles in the regulation of the Golgi network.

CONCLUSIONS

The current study indicates that NF-κB signaling and vesicular transport are correlated with the reactivation of the memory trace in morphine-dependent mice. The results obtained in our study agree with previous observations and identify additional candidate genes for further research.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1196707364133126.

Alcohol: a stimulant activating brain stress responsive systems with persistent neuroadaptation

Addictive diseases, including addiction to alcohol, opiates or cocaine, pose massive public health costs. Addictions are chronic relapsing brain diseases, caused by drug-induced direct effects and persistent neuroadaptations at the molecular, cellular and behavioral levels. These drug-type specific neuroadapations are mainly contributed by three factors: environment, including stress, the direct reinforcing effects of the drug on the CNS, and genetics. Results from animal models and basic clinical research (including human genetic study) have shown important interactions between the stress responsive systems and alcohol abuse. In this review we will discuss the involvement of the dysregulation of the stress responsive hypothalamic-pituitary-adrenal (HPA) axis in alcohol addiction (Section I). Addictions to specific drugs such as alcohol, psychostimulants and opiates (e.g., heroin) have some common direct or downstream effects on several brain stress-responsive systems, including vasopressin and its receptor system (Section II), POMC and mu opioid receptor system (Section III) and dynorphin and kappa opioid receptor systems (Section IV). Further understanding of these systems, through laboratory-based and translational studies, have the potential to optimize early interventions and to discover new treatment targets for the therapy of alcoholism. This article is part of the Special Issue entitled 'CNS Stimulants'.

Chronic psychosocial stress causes delayed extinction and exacerbates reinstatement of ethanol-induced conditioned place preference in mice

RATIONALE

We have shown previously, using an animal model of voluntary ethanol intake and ethanol-conditioned place preference (EtOH-CPP), that exposure to chronic psychosocial stress induces increased ethanol intake and EtOH-CPP acquisition in mice.

OBJECTIVE

Here, we examined the impact of chronic subordinate colony (CSC) exposure on EtOH-CPP extinction, as well as ethanol-induced reinstatement of CPP.

METHODS

Mice were conditioned with saline or 1.5 g/kg ethanol and were tested in the EtOH-CPP model. In the first experiment, the mice were subjected to 19 days of chronic stress, and EtOH-CPP extinction was assessed during seven daily trials without ethanol injection. In the second experiment and after the EtOH-CPP test, the mice were subjected to 7 days of extinction trials before the 19 days of chronic stress. Drug-induced EtOH-CPP reinstatement was induced by a priming injection of 0.5 g/kg ethanol.

RESULTS

Compared to the single-housed colony mice, CSC mice exhibited increased anxiety-like behavior in the elevated plus maze (EPM) and the open field tests. Interestingly, the CSC mice showed delayed EtOH-CPP extinction. More importantly, CSC mice showed increased alcohol-induced reinstatement of the EtOH-CPP behavior.

CONCLUSION

Taken together, this study indicates that chronic psychosocial stress can have long-term effects on EtOH-CPP extinction as well as drug-induced reinstatement behavior and may provide a suitable model to study the latent effects of chronic psychosocial stress on extinction and relapse to drug abuse.

Escalation of drug self-administration as a hallmark of persistent addiction liability

Drug addiction is a progressive, relapsing disease comprised of interlocking stages of disordered motivation. Numerous animal models describing various stages of the addiction process have been developed over the past few decades, providing considerable advantages for the modeling of drug addiction compared with other complex psychiatric disease states. Escalation of drug self-administration has emerged as a widely accepted operant conditioning model of excessive drug intake. We further argue here that drug-escalated animals represent a comprehensive model of addiction according to the manifestations of behavioral neuroadaptations resulting directly or indirectly from excessive drug consumption. In particular, drug-escalated animals exhibit a host of symptoms in line with multiple Diagnostic and Statistical Manual of Mental Disorders criteria for substance dependence, which can be summarized as an emergence of uncontrollable drug-taking and drug-seeking behaviors as a consequence of within-circuit and between-circuit neuroadaptations. Such a transition from impulsive drug sampling to compulsive intake represents a highly valid conceptualization of the addiction timeline in humans, and further investigation of persistent or near-permanent (e.g. epigenetic) neuroadaptations generated by operant drug intake escalation models will continue to provide mechanisms and therapeutic interventions for reversing the aberrant neuroplasticity underlying addiction.

Effects of voluntary alcohol drinking on corticotropin-releasing factor and preprodynorphin mRNA levels in the central amygdala of Sardinian alcohol-preferring rats

The stress-response corticotropin-releasing factor (CRF) and dynorphin systems are critically involved in alcohol drinking and "anxiety"-related behaviors. Selectively bred Sardinian alcohol-preferring (sP) rats display high inherent "anxiety"-related behaviors, in comparison with their alcohol-nonpreferring counterpart (sNP rats). The present study was undertaken to investigate: (1) if there were genetically determined differences in basal gene expression levels of CRF, CRF-R1, preprodynorphin (ppDyn) and kappa opioid receptor (KOP-r) between sP and sNP rats; specifically, mRNA levels of the above genes were measured in the central amygdala (CeA), hypothalamus and other stress responsive and mesolimbic regions of alcohol-naive sP and sNP rats; and (2) if the above mRNA levels were altered by voluntary alcohol drinking in sP rats exposed to the standard, homecage 2-bottle "alcohol vs. water" choice regimen 24h/day for 17 days. Higher basal CRF mRNA levels were found only in CeA of alcohol-naive sP rats, compared with sNP rats; these levels were decreased after alcohol consumption. In contrast, ppDyn mRNA levels in CeA of sP rats were increased by alcohol consumption, but with no basal difference from sNP rats. Although higher basal ppDyn mRNA levels were found in hypothalamus of sP rats, compared with sNP rats, there was no alteration after alcohol drinking in sP rats. No difference for the above mRNA levels was observed in other regions, including nucleus accumbens shell or core, caudate-putamen, ventral tegmental area and medial/basolateral amygdala, between the two rat lines before or after alcohol consumption. Our results demonstrate the existence of genetically determined high basal CRF mRNA levels in CeA of sP rats. Alcohol consumption decreased CeA CRF mRNA levels with parallel increases in CeA ppDyn mRNA levels.

Atrial natriuretic peptide, arginine vasopressin peptide and cortisol serum levels in opiate-dependent patients

Preclinical studies suggest that chronic drug abuse profoundly alters stress-responsive systems. The best studied of the stress-responsive systems in humans is the hypothalamic-pituitary-adrenal (HPA) axis. Apart from cortisol, arginine vasopressin peptide (AVP), and atrial natriuretic peptide (ANP) are known to directly impact upon the HPA axis in addictive behavior. We investigated alterations in ANP, AVP and cortisol serum levels in opiate-dependent patients who received diacetylmorphine treatment within a structured opiate maintenance program. ANP serum levels were significantly increased in opiate-dependent patients as compared to healthy controls, whereas AVP and cortisol serum levels were reduced. The ANP, AVP and cortisol serum levels were not significantly associated with the psychometric dimensions of heroin craving. In conclusion, chronic drug abuse profoundly alters stress-responsive systems like the HPA axis. Alterations of AVP, ANP and cortisol appear to constitute an important component in the neurobiology of opiate-dependent patients.

Role of amygdala in drug memory

Drug addiction is a chronic brain disorder with the hallmark of a high rate of relapse to compulsive drug seeking and drug taking even after long-term abstinence. Addiction has been considered as an aberrant memory that has been termed "addiction memory." Drug-related memory plays a critical role in the maintenance of learned addictive behaviors and emergence of relapse. Disrupting these long-lasting memories by administering amnestic agents or other manipulations during specific phases of drug memory is a promising strategy for relapse prevention. Recent studies on the processes of drug addiction and relapse have demonstrated that the amygdala is involved in associative drug addiction learning processes. In this review, we focus on preclinical studies that used conditioned place preference and self-administration models to investigate the differential roles of the amygdala in each phase of drug-related memory, including acquisition, consolidation, retrieval, reconsolidation, and extinction. These studies indicate that the amygdala plays a critical role in both cue-associative learning and the expression of cue-induced relapse to drug-seeking behavior.

Suppression of hypothalamic-pituitary-adrenal axis by acute heroin challenge in rats during acute and chronic withdrawal from chronic heroin administration

It is known that heroin dependence and withdrawal are associated with changes in the hypothalamic-pituitary-adrenal (HPA) axis. The objective of these studies in rats was to systematically investigate the level of HPA activity and response to a heroin challenge at two time points during heroin withdrawal, and to characterize the expression of associated stress-related genes 30 min after each heroin challenge. Rats received chronic (10-day) intermittent escalating-dose heroin administration (3 × 2.5 mg/kg/day on day 1; 3 × 20 mg/kg/day by day 10). Hormonal and neurochemical assessments were performed in acute (12 h after last heroin injection) and chronic (10 days after the last injection) withdrawal. Both plasma ACTH and corticosterone levels were elevated during acute withdrawal, and heroin challenge at 20 mg/kg (the last dose of chronic escalation) at this time point attenuated this HPA hyperactivity. During chronic withdrawal, HPA hormonal levels returned to baseline, but heroin challenge at 5 mg/kg decreased ACTH levels. In contrast, this dose of heroin challenge stimulated the HPA axis in heroin naïve rats. In the anterior pituitary, pro-opiomelanocortin (POMC) mRNA levels were increased during acute withdrawal and retuned to control levels after chronic withdrawal. In the medial hypothalamus, however, the POMC mRNA levels were decreased during acute withdrawal, and increased after chronic withdrawal. Our results suggest a long-lasting change in HPA abnormal responsivity during chronic heroin withdrawal.

Attenuated effects of experimenter-administered heroin in adolescent vs. adult male rats: physical withdrawal and locomotor sensitization

OBJECTIVES

Early onset of heroin use during adolescence might increase chances of later drug addiction. Prior work from our laboratory suggests, however, that adolescent male rats are actually less sensitive than adults to some enduring effects of heroin self-administration. In the present study, we tested two likely correlates of sensitivity to behavioral reinforcement in rats: physical withdrawal and locomotor sensitization.

METHODS

Adolescent (35 days old at start) and adult (79 days old) male Sprague-Dawley rats were administered escalating doses of heroin, increasing from 1.0 to 8.0 mg/kg (i.p.) every 12 h, across 13 days. Somatic signs of spontaneous withdrawal were scored 12 and 24 h after the last injection, and then every 24 h for 5 days; locomotion was recorded concurrently. Challenge injections of heroin (1 mg/kg i.p.) were given at four points: as the first of the escalating doses (day 1), at days 7 and 13 during the escalating regimen, and after 12 days of forced abstinence. Body mass and food intake were measured throughout experimentation.

RESULTS

A heroin withdrawal syndrome was not observed among adolescents as it was among adults, including somatic signs as well as reduced locomotion, body mass, and food intake. On the other hand, heroin-induced locomotor sensitization did not differ across ages.

CONCLUSION

Reduced withdrawal is consistent with the attenuated reinforcing effects of heroin among adolescent male rats that we reported previously. Thus, it is possible that adolescent rats could reveal important neuroprotective factors for use in treatment of heroin dependence.

Proopiomelanocortin (POMC) expression and conditioned place aversion during protracted withdrawal from chronic intermittent escalating-dose heroin in POMC-EGFP promoter transgenic mice

In heroin-dependent individuals, the drive to avoid or ameliorate the negative affective/emotional state associated with the discontinuation of heroin contributes to the chronic relapsing nature of the disease. Here, we investigate changes in proopiomelanocortin (POMC) expression at three time points across an extended period of heroin withdrawal in a clinically relevant rodent model of addiction using conditioned place aversion (CPA) in POMC-EGFP (POMC-enhanced green fluorescent protein) bacterial artificial chromosome (BAC) transgenic mice. Neurons expressing POMC-EGFP were found in the medial nucleus of the amygdala (MeA), basomedial amygdala (BMA) and dentate gyrus of hippocampus (DG), as well as the arcuate nucleus of hypothalamus (ARC). Heroin-treated mice displayed robust CPA after acute spontaneous withdrawal (12h), which persisted across the extended (14days) withdrawal period. After 12-h withdrawal, heroin-treated mice showed lower signal intensity of POMC-EGFP-positive cells in the ARC, higher levels of POMC mRNA in the amygdala but lower levels in the hippocampus than saline controls. After 7-d withdrawal, heroin-treated mice showed fewer POMC-EGFP-positive cells in the MeA and lower POMC mRNA in the amygdala than saline controls. After extended (14days) withdrawal, heroin-treated mice showed more POMC-EGFP-positive cells in BMA and DG, increased intensity of POMC-EGFP signal in DG, and higher POMC mRNA levels in the hippocampus compared to controls. Our results show dynamic changes in POMC in hypothalamic and extra-hypothalamic regions that may contribute to the negative affective/emotional state of heroin withdrawal shown by CPA from acute to extended periods of heroin withdrawal.

Stress-dependent and gender-specific neuroregulatory roles of the apelin receptor in the hypothalamic-pituitary-adrenal axis response to acute stress

The neuropeptide apelin is expressed in hypothalamic paraventricular and supraoptic nuclei and mediates its effects via activation of the apelin receptor (APJ). Evidence suggests a role for apelin and APJ in mediating the neuroendocrine response to stress. To understand the physiological role of APJ in regulation of the hypothalamic-pituitary-adrenal (HPA) axis, we measured ACTH and corticosterone (CORT) plasma levels in male and female mice lacking APJ (APJ knockout, APJ KO) and in wild-type controls, in response to a variety of acute stressors. Exposure to mild restraint, systemic injection of lipopolysaccharide (LPS), insulin-induced hypoglycaemia and forced swim (FS) stressors, elevated plasma ACTH and CORT levels in wild-type mice. Acute mild restraint significantly increased plasma ACTH and CORT to a similar level in APJ KO mice as in wild-type mice. However, an intact APJ was required for a conventional ACTH, but not CORT, response to LPS administration in male mice and to insulin-induced hypoglycaemia in male and female mice. In contrast, APJ KO mice displayed an impaired CORT response to acute FS stress, regardless of gender. These data indicate that APJ has a role in regulation of the HPA axis response to some acute stressors and has a gender-specific function in peripheral immune activation of the HPA axis.

Tolerance and sensitization to chronic escalating dose heroin following extended withdrawal in Fischer rats: possible role of mu-opioid receptors

RATIONALE/OBJECTIVES

Heroin addiction is characterized by recurrent cycles of drug use, abstinence, and relapse. It is likely that neurobiological changes during chronic heroin exposure persist across withdrawal and impact behavioral responses to re-exposure. We hypothesized that, after extended withdrawal, heroin-withdrawn rats would express behavioral tolerance and/or sensitization in response to heroin re-exposure and that these responses might be associated with altered mu-opioid receptor (MOPr) activity.

METHODS

Male Fischer rats were exposed chronically to escalating doses of heroin (7.5-75 mg/kg/day), experienced acute spontaneous withdrawal and extended (10-day) abstinence, and were re-exposed chronically to heroin. Homecage behaviors and locomotor activity in response to heroin, as well as somatic withdrawal signs, were recorded. Separate groups of rats were sacrificed after extended abstinence and MOPr expression and G-protein coupling were analyzed using [(3)H]DAMGO and [(35)S]GTPγS assays.

RESULTS

The depth of behavioral stupor was lower during the initial days of heroin re-exposure compared to the initial days of the first exposure period. Behavioral responses (e.g., stereotypy) and locomotion were elevated in response to heroin re-exposure at low doses. Rats conditioned for heroin place preference during the chronic re-exposure period expressed heroin preference during acute withdrawal; this preference was stronger than rats conditioned during chronic heroin exposure that followed chronic saline and injection-free periods. Extended withdrawal was associated with increased MOPr expression in the caudate-putamen and frontal and cingulate cortices. No changes in G-protein coupling were identified.

CONCLUSIONS

Aspects of tolerance/sensitization to heroin are present even after extended abstinence and may be associated with altered MOPr density.

Desmopressin accelerates the rate of urinary morphine excretion and attenuates withdrawal symptoms in rats

AIM

The aim of this study was to examine the effects of desmopressin on morphine withdrawal symptoms and vasopressin level in morphine-dependent subjects.

METHODS

Wistar male rats were injected s.c. with morphine once per day for 5 consecutive days to induce morphine dependence. After morphine use ceased on day 5, an equal number of rats were assigned to one of four groups for either saline or desmopressin by either intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) injection. From days 5 to 10, urine was collected daily and tested for the presence of morphine, and withdrawal symptoms were monitored to assess the effects of desmopressin.

RESULTS

Significant weight loss occurred among all morphine-addicted rats during the withdrawal period. With both methods (i.p. and i.c.v.), the period of urinary morphine excretion was shorter for the two groups that were given desmopressin (experimental groups) than the two groups that were not given desmopressin (control groups), and no significant difference in urinary morphine excretion was found between the two experimental groups. During the early stage of withdrawal, the severity of the withdrawal symptoms in the experimental groups was significantly lower than that in the control groups.

CONCLUSION

Desmopressin decreases the extent of morphine withdrawal symptoms, indicating that this agent might be appropriate for treating morphine addiction. Desmopressin appears to reduce withdrawal symptoms not by exerting an anti-diuretic effect but rather by exerting an effect on the central nervous system.

Opiate addiction and cocaine addiction: underlying molecular neurobiology and genetics

Addictive diseases, including addiction to heroin, prescription opioids, or cocaine, pose massive personal and public health costs. Addictions are chronic relapsing diseases of the brain caused by drug-induced direct effects and persisting neuroadaptations at the epigenetic, mRNA, neuropeptide, neurotransmitter, or protein levels. These neuroadaptations, which can be specific to drug type, and their resultant behaviors are modified by various internal and external environmental factors, including stress responsivity, addict mindset, and social setting. Specific gene variants, including variants encoding pharmacological target proteins or genes mediating neuroadaptations, also modify vulnerability at particular stages of addiction. Greater understanding of these interacting factors through laboratory-based and translational studies have the potential to optimize early interventions for the therapy of chronic addictive diseases and to reduce the burden of relapse. Here, we review the molecular neurobiology and genetics of opiate addiction, including heroin and prescription opioids, and cocaine addiction.

Vasopressin V1a and V1b Receptors: From Molecules to Physiological Systems

The neurohypophysial hormone arginine vasopressin (AVP) is essential for a wide range of physiological functions, including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. These and other actions of AVP are mediated by at least three distinct receptor subtypes: V1a, V1b, and V2. Although the antidiuretic action of AVP and V2 receptor in renal distal tubules and collecting ducts is relatively well understood, recent years have seen an increasing understanding of the physiological roles of V1a and V1b receptors. The V1a receptor is originally found in the vascular smooth muscle and the V1b receptor in the anterior pituitary. Deletion of V1a or V1b receptor genes in mice revealed that the contributions of these receptors extend far beyond cardiovascular or hormone-secreting functions. Together with extensively developed pharmacological tools, genetically altered rodent models have advanced the understanding of a variety of AVP systems. Our report reviews the findings in this important field by covering a wide range of research, from the molecular physiology of V1a and V1b receptors to studies on whole animals, including gene knockout/knockdown studies.

Effects of cocaine on maternal behavior and neurochemistry

Drug addiction is a chronic relapsing disorder that involves drug seeking and abuse despite the negative social and health consequences. While the potential effects of cocaine on child development have been extensively studied over the last 30 years, few researchers have focused on the effects of cocaine on maternal behavior, which includes offspring care and maternal aggression towards an unfamiliar individual. In humans, maternal cocaine use can lead to child neglect, abuse, and disrupt the mother-child bond. While it has been argued the developmental effects of maternal cocaine use on children were initially overstated, it is clear that disruptions of typical maternal behavior (i.e. postpartum depression, anxiety disorders) are detrimental to the physical and emotional health of offspring. Cocaine use in mothers is commonly associated with psychological disorders, including depression and anxiety, and it is postulated that many of the negative effects of maternal cocaine use on offspring are mediated through changes in maternal behavior. This review will summarize research on cocaine and maternal behavior in animal and human studies, discuss potential mechanisms, and suggest therapeutic strategies for treating cocaine-affected maternal behavior which may improve the physical and behavioral health of both mother and child. The primary objective is to stimulate future communication, cooperation, and collaboration between researchers who use animals and humans to study cocaine and maternal behavior.

The effects of vasopressin and oxytocin on methamphetamine-induced place preference behaviour in rats

Methamphetamine is a highly addictive stimulant drug whose illicit use and resultant addiction has become an alarming global phenomenon. The mesolimbic dopaminergic pathway has been shown to be fundamental to the establishment of addictive behaviour. This pathway, as part of the reward system of the brain, has also been shown to be important in classical conditioning, which is a learnt response. Within the modulation of learning and memory, the neurohypophyseal hormones vasopressin and oxytocin have been reported to play a vital role, with vasopressin exerting a long- term facilitatory effect and oxytocin exerting an inhibitory effect. Therefore we adopted a conditioned place preference model to investigate whether vasopressin V1b receptor antagonist SSR 149415 or oxytocin treatment would cause a decrease in the seeking behaviour in a reinstatement paradigm. Behavioural findings indicated that methamphetamine induced a change in the place preference in the majority of our animals. This change in place preference was not seen when vasopressin was administered during the extinction phase. On the other hand the methamphetamine-induced change in place preference was enhanced during the reinstatement phase in the animals that were treated with oxytocin. Striatal dopamine levels were determined, as methamphetamine is known to increase dopamine transmission in this area. Significant changes in dopamine levels were observed in some of our animals. Rats that received both methamphetamine and oxytocin had significantly higher striatal dopamine than those that received oxytocin alone. Western blot analysis for hippocampal cyclic AMP response element binding protein (CREB) was also conducted as a possible indicator of glutamatergic NMDA receptor activity, a pathway that is important for learning and memory. The Western blot analysis showed no changes in hippocampal pCREB expression. Overall our data led us to conclude that methamphetamine treatment can change place preference behaviour in rats and that this change may be partially restored by vasopressin antagonism, but exaggerated by oxytocin.

Dose escalation and dose preference in extended-access heroin self-administration in Lewis and Fischer rats

RATIONALE

A genetic component may be involved in different stages of the progression of drug addiction. Heroin users escalate unit doses and frequency of self-administration events over time. Rats that self-administer drugs of abuse over extended sessions escalate the amount of drug infused over days.

OBJECTIVES

Using a recently developed model of extended-access self-administration allowing for subject-controlled dose escalation of the unit dose, thus potentially escalating the unit dose and number of infusions, we compared for the first time two genetically different inbred rat strains, Fischer and Lewis.

METHODS

Extended (18 h/day) self-administration lasted for 14 days. Rats had access to two active levers associated with two different unit doses of heroin. If a rat showed preference for the higher unit dose, then the available doses were escalated in the following session. Four heroin unit doses were available (20, 50, 125, 250 μg/kg per infusion).

RESULTS

Fischer rats did not escalate the unit dose of heroin self-administered; daily amount of heroin administered remained low, with a mean daily intake of 1.27 ± 0.22 mg/kg per session. In marked contrast, Lewis rats escalated the total daily amount of heroin self-administered from 3.94 ± 0.82 mg/kg on day 1 to 8.95 ± 2.2 mg/kg on day 14; almost half of the subjects preferred a higher heroin dose than Fischer rats.

CONCLUSION

These data are consistent with the hypothesis that Lewis rats are prone to opiate taking and escalation, and are in agreement with our previous data obtained with cocaine.

Measuring the incentive value of escalating doses of heroin in heroin-dependent Fischer rats during acute spontaneous withdrawal

RATIONALE/OBJECTIVES

Although continued heroin use and relapse are thought to be motivated, in part, by the positive incentive-motivational value attributed to heroin, little is understood about heroin's incentive value during the relapse-prone state of withdrawal. This study uses place preference to measure the incentive value attributed to escalating-dose heroin in the context of heroin dependence.

METHODS

Male Fischer rats were exposed chronically to escalating doses of heroin in the homecage and during place preference conditioning sessions. Conditioned preference for the context paired with escalating-dose heroin was tested after homecage exposure was discontinued and rats entered acute spontaneous withdrawal. Individuals' behavioral and locomotor responses to heroin and somatic withdrawal signs were recorded.

RESULTS

Conditioned preference for the heroin-paired context was strong in rats that received chronic homecage exposure to escalating-dose heroin and were tested in acute withdrawal. Behavioral responses to heroin (e.g., stereotypy) varied widely across individuals, with rats that expressed stronger heroin preference also expressing stronger behavioral activation in response to heroin. Individual differences in preference were also related to locomotor responses to heroin but not to overt somatic withdrawal signs.

CONCLUSIONS

Escalating doses of heroin evoked place preference in rats, suggesting that positive incentive-motivational value is attributed to this clinically relevant pattern of drug exposure. This study offers an improved preclinical model for studying dependence and withdrawal and provides insight into individual vulnerabilities to addiction-like behavior.

Evidence that vasopressin V1b receptors mediate the transition to excessive drinking in ethanol-dependent rats

Alcoholism is a devastating condition that represents a progression from initial alcohol use to dependence. Although most individuals are capable of consuming alcohol in a limited fashion, the development of alcohol dependence in a subset of individuals is often associated with negative emotional states (including anxiety and depression). Since the alleviation of this negative motivational state via excessive alcohol consumption often becomes a central goal of alcoholics, the transition from initial use to dependence is postulated to be associated with a transition from positive to negative reinforcement mechanisms. Vasopressin is a neuropeptide known to potentiate the effects of CRF on the HPA axis, and emerging evidence also suggests a role for centrally located vasopressin acting on V(1b) receptors in the regulation of stress- and anxiety-like behaviors in rodents. The present study determined state-dependent alterations in vasopressin/V(1b) R signaling in an animal model of ethanol dependence. The V(1b) R antagonist SSR149415 dose-dependently reduced excessive levels of ethanol self-administration observed in dependent animals without affecting the limited levels of ethanol drinking in non-dependent animals. Ethanol self-administration reduced V(1b) receptor levels in the basolateral amygdala of non-dependent animals, a neuroadaptation that could theoretically facilitate the positive reinforcing effects of alcohol. In contrast, V(1b) R levels were seemingly restored in ethanol-dependent rats, a switch that may in part underlie a transition from positive to negative reinforcement mechanisms with dependence. Together, our data suggest a key role for vasopressin/V(1b) R signaling in the transition to ethanol dependence.

Involvement of arginine vasopressin and V1b receptor in alcohol drinking in Sardinian alcohol-preferring rats

BACKGROUND

Recent animal studies have shown that the level of stress-responsive arginine vasopressin (AVP) gene expression in the amygdala is increased during early withdrawal from long-term heroin or cocaine administration. The selective AVP V1b receptor antagonist SSR149415 (capable of exerting antidepressant-like and anxiolytic effects in animal models) also blocked stress-induced reinstatement of drug-seeking behavior. This study was undertaken to investigate the effects of alcohol and to determine whether (i) there are genetically determined differences in basal AVP mRNA levels in the medial/central amygdala (Me/CeA) and medial hypothalamus (MH) between selectively bred Sardinian alcohol-preferring (sP) and alcohol-nonpreferring (sNP) rats; (ii) the AVP mRNA levels are altered by long-term alcohol drinking in sP rats; and (iii) the V1b receptor antagonist SSR149415 alters alcohol drinking in sP rats.

METHODS

In Experiment 1, AVP mRNA levels were measured in the Me/CeA and MH of alcohol-naïve sP and sNP rats, and sP rats exposed to the standard, homecage 2-bottle "alcohol versus water" choice regimen 24 h/d for 17 days. In Experiment 2, SSR149415 (0, 3, 10, or 30 mg/kg; intraperitoneal) was acutely administered 30 minutes before lights off to alcohol-experienced sP rats. Alcohol, water, and food intake were monitored 6 and 24 hours later.

RESULTS

We found higher basal AVP mRNA levels in both Me/CeA and MH of alcohol-naïve sP than sNP rats; alcohol consumption decreased AVP mRNA levels in both brain regions of sP rats, suggesting genetically determined differences between the 2 rat lines and in the effects of alcohol drinking in sP rats. Acute treatment with SSR149415 significantly reduced alcohol intake of sP rats.

CONCLUSION

The stress-responsive AVP/V1b receptor system is 1 component of the neural circuitry underlying high alcohol drinking in sP rats.

Persistent increase in hypothalamic arginine vasopressin gene expression during protracted withdrawal from chronic escalating-dose cocaine in rodents

Arginine vasopressin (AVP) from the paraventricular nucleus (PVN) of hypothalamus has important roles in regulation of the hypothalamic-pituitary-adrenal (HPA) axis and stress-related behaviors during chronic stress. It is unknown, however, whether AVP in the PVN is involved in the modulation of HPA activity after chronic cocaine exposure. Here, we examined the gene expression alterations of AVP in the hypothalamus, and V1b receptor and pro-opiomelanocortin (POMC) in the anterior pituitary, as well as HPA hormonal changes, in Fischer rats after chronic cocaine and withdrawal, using two different chronic (14-day) 'binge' pattern administration regimens: steady-dose cocaine (SDC, 45 mg/kg/day) and escalating-dose cocaine (EDC, 45 up to 90 mg/kg/day). There was a significant (7-fold) plasma adrenocorticotropic hormone (ACTH) elevation after chronic EDC (but not SDC), coupled with increased V1b and POMC mRNA levels in the anterior pituitary. From acute (1-day) to protracted (14-day) withdrawal from chronic EDC (but not from SDC), we found persistent elevations of both plasma ACTH and corticosterone levels and AVP mRNA levels in the PVN. Selective V1b antagonist SSR149415 (5 mg/kg) attenuated acute withdrawal-induced HPA activation after EDC. To study potential roles of endogenous opioids in modulating the AVP gene, we administered naloxone (1 mg/kg); we found that opioid receptor antagonism increased AVP mRNA levels in cocaine-naive rats, but not in cocaine-withdrawn rats, suggesting less tonic opioid inhibition of PVN AVP neurons after chronic EDC. To assess the effects of cocaine withdrawal on sub-populations of PVN AVP neurons, we utilized AVP-enhanced green fluorescent protein (EGFP) promoter transgenic mice and found that acute withdrawal following chronic EDC increased the number of AVP-EGFP neurons in the parvocellular PVN (pPVN). These results suggest that during protracted withdrawal, enhanced pPVN AVP gene expression is associated with persistent elevations of basal HPA activity; a hyposensitivity of PVN AVP gene expression to naloxone is indicative of reduced opioidergic tone. Our studies indicate that the AVP and its V1b receptor system may be a potential therapeutic target for treating anxiety and depressive symptoms associated with cocaine addiction.

Stress modulation of drug self-administration: implications for addiction comorbidity with post-traumatic stress disorder

Drug abuse and dependence present significant health burdens for our society, affecting roughly 10% of the population. Stress likely contributes to the development and persistence of drug use; for example, rates of substance dependence are elevated among individuals diagnosed with post-traumatic stress disorder (PTSD). Thus, understanding the interaction between stress and drug use, and associated neuroadaptations, is key for developing therapies to combat substance use disorders. For this purpose, many rodent models of the effects of stress exposure on substance use have been developed; the models can be classified according to three categories of stress exposure: developmental, adult nonsocial, and adult social. The present review addresses preclinical findings on the effect of each type of trauma on responses to and self-administration of drugs of abuse by focusing on a key exemplar for each category. In addition, the potential efficacy of targeting neuropeptide systems that have been implicated in stress responses and stress system neuroadaptation in order to treat comorbid PTSD and substance abuse will be discussed. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.