Corticotropin-releasing factor 1 receptor mediates the activity of the reward system evoked by morphine-induced conditioned place preference

The Role of Epigenetics and Contributing Impact of Stress, Multigenerational, and Developmental Factors in Opiate Addiction

Drug addiction is characterized by maladaptive neural plasticity, particularly in vulnerable individuals exposed to drugs of abuse. Epigenetic factors include environmental influences, events during development, and stress adaptations, which seem to play an important role in the neuropathogenesis of drug addiction. This critical review hypothesizes that epigenetic modulation increases an individual's susceptibility to opiate addiction in three key areas of epigenetic study: developmental, stress-related, and transgenerational effects. The widespread use of opioids for clinical and recreational purposes raises significant societal and scientific concerns. Despite the increasing prevalence of opioid abuse, there is limited comprehensive knowledge about the impact of epigenetic factors on opiate addiction manifestation. This review hypothesizes that epigenetic modulation increases susceptibility to opiate addiction, exploring three key areas of epigenetic study: developmental, stress-related, and transgenerational effects. Current literature reveals a correlation between epigenetic influences and vulnerability to drug addiction, specifically in the context of opioid use. Epigenetics, the modulation of genetic expression beyond genotypic predisposition, plays a crucial role in an individual's susceptibility to drug addiction. Studies suggest that epigenetic mechanisms, once considered static in the adult brain, continue to influence synaptic plasticity and long-term memory, particularly in the endogenous opioid system. This review examines the effects of opioids and stress on epigenetic modifications, providing evidence of increased vulnerability to opiate addiction. Animal studies demonstrate how developmental adversities and adolescent exposure to substances can induce persistent epigenetic changes, predisposing individuals to opiate addiction in adulthood. Moreover, the review explores the transgenerational effects of opioid exposure during adolescence, suggesting that functional epigenetic neuroadaptations within the nucleus accumbens can persist for multiple generations. The examination of DNA methylation patterns in opioid addicts reveals potential markers for identifying susceptibility to opiate vulnerability. A critical analysis of research reports supports the hypothesis that developmental, transgenerational, and stress-related epigenetic mechanisms have a profound role in increasing the risk of opioid addiction susceptibility. Each study confirmed that developmental, stress-related, or transgenerational epigenetic regulations have a correlation to increased opiate sensitization and vulnerability. Unfortunately, every study reviewed was unable to elucidate an epigenetic mechanism to explain a specific neuropathogenesis of opiate drug addiction vulnerability, emphasizing our lack of knowledge in the complex pathology of epigenetics.

Noradrenergic circuits and signaling in substance use disorders

The central noradrenergic system innervates almost all regions of the brain and, as such, is well positioned to modulate many neural circuits implicated in behaviors and physiology underlying substance use disorders. Ample pharmacological evidence demonstrates that α1, α2, and β adrenergic receptors may serve as therapeutic targets to reduce drug -seeking behavior and drug withdrawal symptoms. Further, norepinephrine is a key modulator of the stress response, and stress has been heavily implicated in reinstatement of drug taking. In this review, we discuss recent advances in our understanding of noradrenergic circuitry and noradrenergic receptor signaling in the context of opioid, alcohol, and psychostimulant use disorders.

The Antagonism of Corticotropin-Releasing Factor Receptor-1 in Brain Suppress Stress-Induced Propofol Self-Administration in Rats

Propofol addiction has been detected in humans and rats, which may be facilitated by stress. Corticotropin-releasing factor acts through the corticotropin-releasing factor (CRF) receptor-1 (CRF1R) and CRF2 receptor-2 (CRF2R) and is a crucial candidate target for the interaction between stress and drug abuse, but its role on propofol addiction remains unknown. Tail clip stressful stimulation was performed in rats to test the stress on the establishment of the propofol self-administration behavioral model. Thereafter, the rats were pretreated before the testing session at the bilateral lateral ventricle with one of the doses of antalarmin (CRF1R antagonist, 100–500 ng/site), antisauvagine 30 (CRF2R antagonist, 100–500 ng/site), and RU486 (glucocorticoid receptor antagonist, 100–500 ng/site) or vehicle. The dopamine D1 receptor (D1R) in the nucleus accumbens (NAc) was detected to explore the underlying molecular mechanism. The sucrose self-administration establishment and maintenance, and locomotor activities were also examined to determine the specificity. We found that the establishment of propofol self-administration was promoted in the tail clip treated group (the stress group), which was inhibited by antalarmin at the dose of 100–500 ng/site but was not by antisauvagine 30 or RU486. Accordingly, the expression of D1R in the NAc was attenuated by antalarmin, dose-dependently. Moreover, pretreatments fail to change sucrose self-administration behavior or locomotor activities. This study supports the role of CRF1R in the brain in mediating the central reward processing through D1R in the NAc and provided a possibility that CRF1R antagonist may be a new therapeutic approach for the treatment of propofol addiction.

Effect of early life social adversity on drug abuse vulnerability: Focus on corticotropin-releasing factor and oxytocin

Early life adversity can set the trajectory for later psychiatric disorders, including substance use disorders. There are a host of neurobiological factors that may play a role in the negative trajectory. The current review examines preclinical evidence suggesting that early life adversity specifically involving social factors (maternal separation, adolescent social isolation and adolescent social defeat) may influence drug abuse vulnerability by strengthening corticotropin-releasing factor (CRF) systems and weakening oxytocin (OT) systems. In adulthood, pharmacological and genetic evidence indicates that both CRF and OT systems are directly involved in drug reward processes. With early life adversity, numerous studies show an increase in drug abuse vulnerability measured in adulthood, along a concomitant strengthening of CRF systems and a weakening of OT systems. Mechanistic studies, while relatively few in number, are generally consistent with the theme that strengthened CRF systems and weakened OT systems mediate, at least in part, the link between early life adversity and drug abuse vulnerability. Establishing a direct role of CRF and OT in mediating the relation between early life social stressors and drug abuse vulnerability will inform clinical researchers and practitioners toward the development of intervention strategies to reduce risk among those suffering from early life adversities. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Naloxone-induced conditioned place aversion score and extinction period are higher in C57BL/6J morphine-dependent mice than in Swiss: Role of HPA axis

Intense associative memories develop between drug-paired contextual cues and the drug withdrawal associated aversive feeling. They have been suggested to contribute to the high rate of relapse. Our study was aimed to elucidate the involvement of hypothalamic-pituitary-adrenocortical (HPA) axis activity in the expression and extinction of aversive memory in Swiss and C57BL/6J (B6) mice. The animals were rendered dependent on morphine by i.p. injection of increasing doses of morphine (10-60 mg/kg). The negative state associated with naloxone (1 mg/kg s.c.) precipitated morphine withdrawal was examined by using conditioned place aversion (CPA) paradigm. B6 mice obtained a higher aversion score and took longer to extinguish the aversive memory than Swiss mice. In addition, corticosterone levels were increased after CPA expression. Moreover, corticosterone levels were decreased during CPA extinction in Swiss mice without changes in B6 mice. Pre-treatment with the selective CRF1 receptor antagonist CP-154,526 before naloxone, impaired morphine-withdrawal aversive memory acquisition and decreased the extinction period. CP-154,526 also antagonized the increased levels of corticosterone observed after CPA expression in Swiss mice, without any changes in B6 mice. These results indicate that HPA axis could be a critical factor governing opioid withdrawal memory storage and retrieval, but in a strain or stock-specific manner. The differences observed between Swiss and B6 mice suggest that the treatment of addictive disorders should consider different individual predisposition to associate the aversive learning with the context.

Drug-Induced Conditioned Place Preference and Its Practical Use in Substance Use Disorder Research

The conditioned place preference (CPP) paradigm is a well-established model utilized to study the role of context associations in reward-related behaviors, including both natural rewards and drugs of abuse. In this review article, we discuss the basic history, various uses, and considerations that are tied to this technique. There are many potential takeaway implications of this model, including negative affective states, conditioned drug effects, memory, and motivation, which are all considered here. We also discuss the neurobiology of CPP including relevant brain regions, molecular signaling cascades, and neuromodulatory systems. We further examine some of our prior findings and how they integrate CPP with self-administration paradigms. Overall, by describing the fundamentals of CPP, findings from the past few decades, and implications of using CPP as a research paradigm, we have endeavored to support the case that the CPP method is specifically advantageous for studying the role of a form of Pavlovian learning that associates drug use with the surrounding environment.

The number of lateral hypothalamus orexin/hypocretin neurons contributes to individual differences in cocaine demand

Lateral hypothalamus (LH) orexin neuron signaling has been implicated in the motivation to seek and take drugs of abuse. The number of LH orexin neurons has been shown to be upregulated with exposure to drugs of abuse. We sought to determine if the number of LH orexin neurons related to individual differences in motivation (demand) for cocaine in our behavioral economics (BE) paradigm, and whether knockdown of these cells predicted changes in economic demand. We quantified LH orexin cell numbers in animals immediately following our BE paradigm, as well as after a 2-week period of abstinence, to relate the number of LH orexin cells to economic demand for cocaine. We also knocked down LH orexin expression with an orexin morpholino antisense to determine how reduced orexin numbers impacted cocaine demand. We found that animals with greater baseline motivation for cocaine (lower demand elasticity) had more LH orexin neurons. Following a 2-week abstinence from cocaine, the number of LH orexin neurons predicted economic demand for cocaine prior to abstinence, indicating that orexin expression is a persistent marker for demand. Reducing LH orexin cell numbers with antisense decreased motivation for cocaine (increased demand elasticity) without affecting baseline consumption. In addition, the number of spared LH orexin neurons after antisense treatment correlated with individual motivation for cocaine. These studies point to a role for the endogenous number of LH orexin neurons in individual differences in motivation for cocaine.

Conditioned aversive memory associated with morphine withdrawal increases brain-derived neurotrophic factor in dentate gyrus and basolateral amygdala

Morphine has been shown to increase the expression of brain-derived neurotrophic factor (BDNF) in the brain. However, little is known about the effect of conditioned naloxone-precipitated morphine withdrawal on BDNF and its precursor protein, proBDNF. We used the conditioned place aversion (CPA) paradigm to evaluate the role of corticotropin-releasing factor (CRF)/CRF1 receptor signaling on the BDNF expression and corticosterone plasma levels after CPA expression and extinction. Male mice were rendered dependent on morphine and injected acutely with naloxone before paired to confinement in a naloxone-associated compartment. The expression of BDNF and proBDNF in the dentate gyrus (DG) and basolateral amygdala (BLA) was measured in parallel with the corticosterone plasma levels with and without CRF1 receptor blockade. Mice subjected to conditioned naloxone-induced morphine withdrawal showed an increased expression of BDNF (in DG and BLA) in parallel with an enhancement of corticosterone plasma levels. These results demonstrated that BDNF expression together with the increased activity of hypothalamic-pituitary-adrenocortical (HPA) axis are critical to the acquisition of aversive memory. However, we have observed a decrease in corticosterone plasma levels and BDNF expression after CPA extinction reaffirming the importance of BDNF in the maintenance of aversive memory. In addition, the pre-treatment with the CRF1 receptor antagonist CP-154 526 before naloxone conditioning session impaired morphine withdrawal-induced aversive memory acquisition, the increased corticosterone plasma levels, and the expression of BDNF observed after CPA expression in the DG and BLA. Altogether, present results are suggesting a clear connection between HPA axis and BDNF in the formation and extinction of aversive memory.

Conditioned Aversion and Neuroplasticity Induced by a Superagonist of Extrasynaptic GABAA Receptors: Correlation With Activation of the Oval BNST Neurons and CRF Mechanisms

THIP (gaboxadol), a superagonist of the δ subunit-containing extrasynaptic GABA_A receptors, produces persistent neuroplasticity in dopamine (DA) neurons of the ventral tegmental area (VTA), similarly to rewarding drugs of abuse. However, unlike them THIP lacks abuse potential and induces conditioned place aversion in mice. The mechanism underlying the aversive effects of THIP remains elusive. Here, we show that mild aversive effects of THIP were detected 2 h after administration likely reflecting an anxiety-like state with increased corticosterone release and with central recruitment of corticotropin-releasing factor corticotropin-releasing factor receptor 1 (CRF₁) receptors. A detailed immunohistochemical c-Fos expression mapping for THIP-activated brain areas revealed a correlation between the activation of CRF-expressing neurons in the oval nucleus of the bed nuclei of stria terminalis and THIP-induced aversive effects. In addition, the neuroplasticity of mesolimbic DA system (24 h after administration) and conditioned place aversion by THIP after four daily acute sessions were dependent on extrasynaptic GABA_A receptors (abolished in δ-GABA_A receptor knockout mice) and activation of the CRF₁ receptors (abolished in wildtype mice by a CRF₁ receptor antagonist). A selective THIP-induced activation of CRF-expressing neurons in the oval part of the bed nucleus of stria terminalis may constitute a novel mechanism for inducing plasticity in a population of VTA DA neurons and aversive behavioral states.

Increased Number and Activity of a Lateral Subpopulation of Hypothalamic Orexin/Hypocretin Neurons Underlies the Expression of an Addicted State in Rats

BACKGROUND

The orexin (hypocretin) system is important for reward-driven motivation but has not been implicated in the expression of a multiphenotype addicted state.

METHODS

Rats were assessed for economic demand for cocaine before and after 14 days of short access, long access, or intermittent access (IntA) to cocaine. Rats were also assessed for a number of other DSM-5-relevant addiction criteria following differential access conditions. Orexin system function was assessed by quantification of numbers and activity of orexin cells, pharmacological blockade of the orexin-1 receptor, and subregion-specific knockdown of orexin cell populations.

RESULTS

IntA produced a cluster of addiction-like behaviors that closely recapitulate key diagnostic criteria for addiction to a greater extent than long access or short access. IntA was accompanied by an increase in number and activity of orexin-expressing neurons within the lateral hypothalamic subregion. This increase in orexin cell number and activity persisted during protracted withdrawal from cocaine for at least 150 days and was accompanied by enhanced incubation of craving in the same rats. Selective knockdown of lateral hypothalamic orexin neurons reduced motivation for cocaine, and orexin-1 receptor signaling played a larger role in drug seeking after IntA.

CONCLUSIONS

We provide the first evidence that lateral hypothalamic orexin system function extends beyond general reward seeking to play a critical role in expression of a multiphenotype addiction-like state. Thus, the orexin system is a potential novel target for pharmacotherapies designed to treat cocaine addiction. In addition, these data point to the IntA model as a preferred approach to modeling addiction-like behavior in rats.

Peripubertal stress of male, but not female rats increases morphine-induced conditioned place preference and locomotion in adulthood

Animal studies demonstrate that peripubertal social stress markedly increases the risk for subsequent substance use in adulthood. However, whether non-social stress has a similar long-term impact is not clear, and whether male and female animals show different sensitivity to peripubertal non-social stress has not been examined. In the present study, we addressed these issues by introducing two non-social stressors (elevated platform and predator odor 2,5-Dihydro-2,4,5-trimethylthiazoline) to male and female Wistar rats during adolescence (postnatal days 28-30, 34, 36, 40, and 42), then tested reward-related behaviors during adulthood, including morphine-induced conditioned place preference (CPP, 1 mg/kg morphine or 5 mg/kg morphine) and hyperlocomotor activity (5 mg/kg morphine). We found that adult male rats, but not females who were exposed to peripubertal non-social stressors showed enhanced morphine-induced CPP. Moreover, morphine-induced increase in locomotor activity was also significantly increased in adult male rats, but not in females. These results indicate that peripubertal exposure to repeated non-social stress may enhance sensitivity to the rewarding effects of opioids in adulthood in a sex-dependent manner, with males being even more sensitive than females in this regard.

GABAB receptors modulate morphine antinociception: Pharmacological and genetic approaches

Previous studies in our laboratory showed an interaction between the GABAergic and opioid systems involved in the analgesic effect of baclofen (BAC). Furthermore, it is known that sex differences exist regarding various pharmacological responses of morphine (MOR) and they are related to an increased sensitivity to MOR effects in males. The aims of the present study were to evaluate the possible involvement of the GABA_B receptors in the antinociceptive responses induced by MOR (1, 3 and 9 mg/kg, s.c.) administration using both pharmacological (BAC 2 mg/kg, i.p.; and 2-OH-saclofen, SAC 0.3 mg/kg, intra cisterna magna) and genetic approaches (GABA_B1 knockout mice; GABA_B1 KO) in mice of both sexes. In addition, we explored the alterations in c-Fos expression of different brain areas involved in the antinociceptive effect of MOR using both approaches. The pharmacological approach showed a higher dose-dependent antinociceptive effect of MOR in male mice compared to female mice. BAC and SAC pretreatment potentiated and attenuated the antinociceptive effect of MOR, respectively, in both sexes. The genetic approach revealed a dose-dependent antinociceptive effect of MOR in the wild type mice, but not in the GABA_B1 KO mice and no sex differences were observed. Additionally, BAC and SAC pretreatment and the lack of GABA_B1 subunit of the GABA_B receptor prevented the changes observed in c-Fos expression in the cingulate cortex and nucleus accumbens of male mice. Our results suggest that the GABA_B receptors are involved in the MOR antinociceptive effect of both male and female mice.

Morphine exposure before conception affects anxiety-like behavior and CRF level (in the CSF and plasma) in the adult male offspring

It has been proven that exposure to some drugs even before gestation had transgenerational effects. To investigate the changes which induced by parental morphine exposure before gestation; mainly the anxiety-like behavior, Corticotropin Releasing Factor (CRF) level in the CSF and plasma, CRF Receptor 1 (CRFR1), and the level of protein kinase C (PKC-α) were evaluated in the male offspring. Male and female Wistar rats were exposed to morphine for 21 following days. Ten days after last drug exposure, animals were prepared for mating in 4 distinct groups as follow: drug-naïve female and male (used as control), drug-naïve female and morphine-abstinent male, drug-naïve male and morphine-abstinent female, and morphine abstinent male and female. Offspring were subjected to assess anxiety-like behavior (using elevated plus maze test). CSF and plasma were gathered, and the CRF level was evaluated by ELISA. Using real-time PCR, the CRFR1 level in the brain was evaluated. Results showed that anxiety-like behavior increased in the offspring of morphine-abstinent parent(s) compared with the control group. CRF level in the plasma and CSF also increased in the litter of morphine-abstinent parent(s). CRFR1 mRNA level was upregulated in the brain of offspring with one and/or two morphine-abstinent parent(s). Furthermore, the level of PKC-α was decreased in the brain of offspring which had one and/or two morphine-abstinent parent(s). Taken together, our findings indicated that morphine exposure even before gestation induced transgenerational effects via dysregulation of HPA axis which results in anxiety in the adult male offspring.

Orexins and stress

The neuropeptides orexins are important in regulating the neurobiological systems that respond to stressful stimuli. Furthermore, orexins are known to play a role many of the phenotypes associated with stress-related mental illness such as changes in cognition, sleep-wake states, and appetite. Interestingly, orexins are altered in stress-related psychiatric disorders such as Major Depressive Disorder and Anxiety Disorders. Thus, orexins may be a potential target for treatment of these disorders. In this review, we will focus on what is known about the role of orexins in acute and repeated stress, in stress-induced phenotypes relevant to psychiatric illness in preclinical models, and in stress-related psychiatric illness in humans. We will also briefly discuss how orexins may contribute to sex differences in the stress response and subsequent phenotypes relevant to mental health, as many stress-related psychiatric disorders are twice as prevalent in women.

The involvement of CRF1 receptor within the basolateral amygdala and dentate gyrus in the naloxone-induced conditioned place aversion in morphine-dependent mice

Drug withdrawal-associated aversive memories trigger relapse to drug-seeking behavior. Corticotrophin-releasing factor (CRF) is an important mediator of the reinforcing properties of drugs of abuse. However, the involvement of CRF1 receptor (CRF1R) in aversive memory induced by opiate withdrawal has yet to be elucidated. We used the conditioned-place aversion (CPA) paradigm to evaluate the role of CRF1R on opiate withdrawal memory acquisition, along with plasticity-related processes that occur after CPA within the basolateral amygdala (BLA) and dentate gyrus (DG). Male mice were rendered dependent on morphine and injected acutely with naloxone before paired to confinement in a naloxone-associated compartment. The CPA scores as well as the number of TH-positive neurons (in the NTS-A2 noradrenergic cell group), and the expression of the transcription factors Arc and pCREB (in the BLA and DG) were measured with and without CRF1R blockade. Mice subjected to conditioned naloxone-induced morphine withdrawal robustly expressed CPA. Pre-treatment with the selective CRF1R antagonist CP-154,526 before naloxone conditioning session impaired morphine withdrawal-induced aversive memory acquisition. CP-154,526 also antagonized the enhanced number of TH-positive neurons in the NTS-A2 that was seen after CPA. Increased Arc expression and Arc-pCREB co-localization were seen in the BLA after CPA, which was not modified by CP-154,526. In the DG, CPA was accompanied by a decrease of Arc expression and no changes in Arc-pCREB co-localization, whereas pre-treatment with CP-154,526 induced an increase in both parameters. These results indicate that CRF-CRF1R pathway could be a critical factor governing opiate withdrawal memory storage and retrieval and might suggest a role for TH-NA pathway in the effects of withdrawal on memory. Our results might indicate that the blockade of CRF1R could represent a promising pharmacological treatment strategy approach for the attenuation of the relapse to drug-seeking/taking behavior triggered by opiate withdrawal-associated aversive memories.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

A Decade of Orexin/Hypocretin and Addiction: Where Are We Now?

One decade ago, our laboratory provided the first direct evidence linking orexin/hypocretin signaling with drug seeking by showing that activation of these neurons promotes conditioned morphine-seeking behavior. In the years since, contributions from many investigators have revealed roles for orexins in addiction for all drugs of abuse tested, but only under select circumstances. We recently proposed that orexins play a fundamentally unified role in coordinating "motivational activation" under numerous behavioral conditions, and here we unpack this hypothesis as it applies to drug addiction. We describe evidence collected over the past 10 years that elaborates the role of orexin in drug seeking under circumstances where high levels of effort are required to obtain the drug, or when motivation for drug reward is augmented by the presence of external stimuli like drug-associated cues/contexts or stressors. Evidence from studies using traditional self-administration and reinstatement models, as well as behavioral economic analyses of drug demand elasticity, clearly delineates a role for orexin in modulating motivational, rather than the primary reinforcing aspects of drug reward. We also discuss the anatomical interconnectedness of the orexin system with wider motivation and reward circuits, with a particular focus on how orexin modulates prefrontal and other glutamatergic inputs onto ventral tegmental area dopamine neurons. Last, we look ahead to the next decade of the research in this area, highlighting the recent FDA approval of the dual orexin receptor antagonist suvorexant (Belsomra®) for the treatment of insomnia as a promising sign of the potential clinical utility of orexin-based therapies for the treatment of addiction.

Orexin/hypocretin-1 receptor antagonism reduces ethanol self-administration and reinstatement selectively in highly-motivated rats

The orexin/hypocretin (ORX) system regulates motivation for natural rewards and drugs of abuse such as alcohol. ORX receptor antagonists, most commonly OX1R antagonists including SB-334867 (SB), decrease alcohol drinking, self-administration and reinstatement in both genetically-bred alcohol-preferring and outbred strains of rats. Importantly, levels of alcohol seeking and drinking in outbred rats are variable, as they are in humans. We have shown that OX1R antagonism selectively decreases homecage alcohol drinking in high-, but not low-alcohol-preferring rats. It is unknown, however, whether this effect is selective to homecage drinking or whether it also applies to alcohol seeking paradigms such as self-administration and reinstatement following extinction, in which motivation is high in the absence of alcohol. Here we trained Sprague Dawley rats to self-administer 20% ethanol paired with a light-tone cue on an FR3 regimen. Rats were then extinguished and subjected to cue-induced reinstatement. Rats were segregated into high- and low-ethanol-responding groups (HR and LR) based on self-administration levels. During self-administration and cue-induced reinstatement, rats were given SB or vehicle prior to ethanol seeking. In both conditions, OX1R antagonism decreased responding selectively in HR, but not LR rats. There were no non-specific effects of SB treatment on arousal or general behavior. These data indicate that ORX signaling at the OX1R receptor specifically regulates high levels of motivation for alcohol, even in the absence of direct alcohol reinforcement. This implicates the ORX system in the pathological motivation underlying alcohol abuse and alcoholism and demonstrates that the OX1R may be an important target for treating alcohol abuse.

Orexin/hypocretin neuron activation is correlated with alcohol seeking and preference in a topographically specific manner

Orexin (ORX) (also known as hypocretin) neurons are located exclusively in the posterior hypothalamus, and are involved in a wide range of behaviours, including motivation for drugs of abuse such as alcohol. Hypothalamic subregions contain functionally distinct populations of ORX neurons that may play different roles in regulating drug-motivated and alcohol-motivated behaviours. To investigate the role of ORX neurons in ethanol (EtOH) seeking, we measured Fos activation of ORX neurons in rats following three different measures of EtOH seeking and preference: (i) context-induced reinstatement, or ABA renewal; (ii) cue-induced reinstatement of extinguished responding for EtOH; and (iii) a home cage task in which preference for EtOH (vs. water) was measured in the absence of either reinforcer. We found significant activation of ORX neurons in multiple subregions across all three behavioural tests. Notably, ORX neuron activation in the lateral hypothalamus correlated with the degree of seeking in context reinstatement and the degree of preference in home cage preference testing. In addition, Fos activation in ORX neurons in the dorsomedial hypothalamic and perifornical areas was correlated with context and home cage seeking/preference, respectively. Surprisingly, we found no relationship between the degree of cue-induced reinstatement and ORX neuron activation in any region, despite robust activation overall during reinstatement. These results demonstrate a strong relationship between ORX neuron activation and EtOH seeking/preference, but one that is differentially expressed across ORX field subregions, depending on reinstatement modality.

CP-154,526 Modifies CREB Phosphorylation and Thioredoxin-1 Expression in the Dentate Gyrus following Morphine-Induced Conditioned Place Preference

Corticotropin-releasing factor (CRF) acts as neuro-regulator of the behavioral and emotional integration of environmental and endogenous stimuli associated with drug dependence. Thioredoxin-1 (Trx-1) is a functional protein controlling the redox status of several proteins, which is involved in addictive processes. In the present study, we have evaluated the role of CRF1 receptor (CRF1R) in the rewarding properties of morphine by using the conditioned place preference (CPP) paradigm. We also investigate the effects of the CRF1R antagonist, CP-154,526, on the morphine CPP-induced activation of CRF neurons, CREB phosphorylation and Trx expression in paraventricular nucleus (PVN) and dentate gyrus (DG) of the mice brain. CP-154,526 abolished the acquisition of morphine CPP and the increase of CRF/pCREB positive neurons in PVN. Moreover, this CRF1R antagonist prevented morphine-induced CRF-immunoreactive fibers in DG, as well as the increase in pCREB expression in both the PVN and DG. In addition, morphine exposure induced an increase in Trx-1 expression in DG without any alterations in PVN. We also observed that the majority of pCREB positive neurons in DG co-expressed Trx-1, suggesting that Trx-1 could activate CREB in the DG, a brain region involved in memory consolidation. Altogether, these results support the idea that CRF1R antagonist blocked Trx-1 expression and pCREB/Trx-1 co-localization, indicating a critical role of CRF, through CRF1R, in molecular changes involved in morphine associated behaviors.