Oxytocin Reduces Cocaine Cued Fos Activation in a Regionally Specific Manner

The Relationship Between Oxytocin and Alcohol Dependence

The hypothalamic neuropeptide oxytocin (OT) is well known for its prosocial, anxiolytic, and ameliorating effects on various psychiatric conditions, including alcohol use disorder (AUD). In this chapter, we will first introduce the basic neurophysiology of the OT system and its interaction with other neuromodulatory and neurotransmitter systems in the brain. Next, we provide an overview over the current state of research examining the effects of acute and chronic alcohol exposure on the OT system as well as the effects of OT system manipulation on alcohol-related behaviors in rodents and humans. In rodent models of AUD, OT has been repeatedly shown to reduce ethanol consumption, particularly in models of acute alcohol exposure. In humans however, the results of OT administration on alcohol-related behaviors are promising but not yet conclusive. Therefore, we further discuss several physiological and methodological limitations to the effective application of OT in the clinic and how they may be mitigated by the application of synthetic OT receptor (OTR) agonists. Finally, we discuss the potential efficacy of cutting-edge pharmacology and gene therapies designed to specifically enhance endogenous OT release and thereby rescue deficient expression of OT in the brains of patients with severe forms of AUD and other incurable mental disorders.

Peer-induced cocaine seeking in rats: Comparison to nonsocial stimuli and role of paraventricular hypothalamic oxytocin neurons

The purpose of this study was to determine if social vs nonsocial cues (peer vs light/tone) can serve as discriminative stimuli to reinstate cocaine seeking. In addition, to assess a potential mechanism, an oxytocin (OT) promoter-linked hM3Dq DREADD was infused into the paraventricular nucleus of the hypothalamus to determine whether peer-induced cocaine seeking is decreased by activation of OT neurons. Male rats underwent twice-daily self-administration sessions, once with cocaine in the presence of one peer (S+) and once with saline in the presence of a different peer (S-). Another experiment used similar procedures, except the discriminative stimuli were nonsocial (constant vs flashing light/tone), with one stimulus paired with cocaine (S+) and the other paired with saline (S-). A third experiment injected male and female rats with OTp-hM3Dq DREADD or control virus into PVN and tested them for peer-induced reinstatement of cocaine seeking following clozapine (0.1 mg/kg). Although acquisition of cocaine self-administration was similar in rats trained with either peer or light/tone discriminative stimuli, the latency to first response was reduced by the peer S+, but not by the light/tone S+. In addition, the effect of the conditioned stimulus was overshadowed by the peer S+ but not by the light/tone S+. Clozapine blocked the effect of the peer S+ in rats receiving the OTp-hM3Dq DREADD virus, but not in rats receiving the control virus. These results demonstrate that a social peer can serve as potent trigger for drug seeking and that OT in PVN modulates peer-induced reinstatement of cocaine seeking.

Oxytocin Attenuates the Stress-Induced Reinstatement of Alcohol-Seeking in Male Rats: Role of the Central Amygdala

Factors such as stress and anxiety often contribute to alcohol-dependent behavior and can trigger a relapse of alcohol addiction and use. Therefore, it is important to investigate potential pharmacological interventions that may alleviate the influence of stress on addiction-related behaviors. Previous studies have demonstrated that the neuropeptide oxytocin has promising anxiolytic potential in mammals and may offer a pharmacological target to diminish the emotional impact on reinstatement of alcohol-seeking. The purpose of the present study was to investigate the effect of oxytocin on stress-induced alcohol relapse and identify a neural structure mediating this effect through the use of an ethanol self-administration and yohimbine-induced reinstatement paradigm. While yohimbine administration resulted in the reinstatement of ethanol-seeking behavior, the concurrent administration of yohimbine and oxytocin attenuated this effect, suggesting that oxytocin may disrupt stress-induced ethanol-seeking behavior. The central amygdala (CeA) is a structure that drives emotional responses and robustly expresses oxytocin receptors. Intra-CeA oxytocin similarly attenuated the yohimbine-induced reinstatement of ethanol-seeking behavior. These results demonstrate that oxytocin has the potential to attenuate stress-induced relapse into ethanol-seeking behavior, and that this mechanism occurs specifically within the central amygdala.

Complex Interactions Between Sex and Stress on Heroin Seeking

Rationale: Stress plays a dual role in substance use disorders as a precursor to drug intake and a relapse precipitant. With heroin use at epidemic proportions in the United States, understanding interactions between stress disorders and opioid use disorder is vital and will aid in treatment of these frequently comorbid conditions. Objectives: Here, we combine assays of stress and contingent heroin self-administration (SA) to study behavioral adaptations in response to stress and heroin associated cues in male and female rats. Methods: Rats underwent acute restraint stress paired with an odor stimulus and heroin SA for subsequent analysis of stress and heroin cue reactivity. Lofexidine was administered during heroin SA and reinstatement testing to evaluate its therapeutic potential. Rats also underwent tests on the elevated plus maze, locomotor activity in a novel environment, and object recognition memory following stress and/or heroin. Results: A history of stress and heroin resulted in disrupted behavior on multiple levels. Stress rats avoided the stress conditioned stimulus and reinstated heroin seeking in response to it, with males reinstating to a greater extent than females. Lofexidine decreased heroin intake, reinstatement, and motor activity. Previous heroin exposure increased time spent in the closed arms of an elevated plus maze, activity in a round novel field, and resulted in object recognition memory deficits. Discussion: These studies report that a history of stress and heroin results in maladaptive coping strategies and suggests a need for future studies seeking to understand circuits recruited in this pathology and eventually help develop therapeutic approaches.

Oxytocin Attenuates Expression, but Not Acquisition, of Sucrose Conditioned Place Preference in Rats

Maladaptation of reward processing for natural rewards, such as sucrose or sugar, may play a role in the development of diseases such as obesity and diabetes. Furthermore, uncovering mechanisms to disrupt or reverse maladaptation of reward-seeking behaviors for natural reinforcers can provide insight into treatment of such diseases, as well as disorders such as addiction. As such, studying the effects of potential pharmacotherapeutics on maladaptive sugar-seeking behavior offers valuable clinical significance. Sucrose conditioned place preference (CPP) paradigms can offer insight into aspects of reward processes as it provides a way to assess acquisition and expression of context-reward associations. The present study examined the effect of peripheral oxytocin injections on sucrose CPP in rats. Oxytocin, when administered prior to CPP test, attenuated expression of sucrose CPP. However, oxytocin, when administered during sucrose conditioning, did not affect subsequent place preference. These findings suggest oxytocin sufficiently attenuates expression of sucrose-associated place preference.

Long-term impact of acute restraint stress on heroin self-administration, reinstatement, and stress reactivity

RATIONALE

There is a robust relationship between anxiety disorders, including post-traumatic stress disorder (PTSD) and substance abuse. In fact, 30-50% of people seeking treatment for substance abuse have a comorbid diagnosis for PTSD. Heroin use is at epic proportions in the USA and is commonly used by people with co-occurring PTSD symptoms and substance use disorder.

OBJECTIVES

Here, we combined animal assays of acute restraint stress and contingent heroin self-administration (SA) to study comorbidity between stress disorders and opioid use disorder and identify shifts in anxiety-like behaviors following stress and/or heroin in response to a stress-conditioned cue. Our objective for this approach was to determine the long-term impact of acute restraint stress and heroin self-administration on stress reactivity and basic reward processes.

METHODS

We used 2-h acute restraint stress paired with an odor stimulus to condition a stress cue (CS) for testing of subsequent stress reactivity in a burying task and reinstatement and extinction to heroin seeking. Rats were also tested for social place preference for measures of social reward and anxiety-like behaviors.

RESULTS

Stress rats exhibited multiple levels of disrupted behavior including enhanced acquisition of heroin intake and reinstatement in response to the stress CS, as well as delayed extinction in response to the stress CS. All rats developed a social place preference, but stress rats spent more time in nose-to-nose contact with the unfamiliar rat while heroin rats spent time exploring the chamber. In the burying task, stress shortened latencies to bury the CS and increased burying and immobility in male and female rats relative to sham counterparts.

CONCLUSIONS

Acute restraint stress results in anxiety-like behaviors and a stress-associated cue is sufficient to reinstate extinguished heroin seeking. This project has the potential to elucidate the complex relationship between stress/anxiety disorders, including some PTSD-like characteristics, and the onset, maintenance, and relapse to heroin seeking.

Oxytocin attenuates stress-induced reinstatement of alcohol seeking behavior in male and female mice

RATIONALE

The neuropeptide oxytocin (OXT) has emerged as a potential therapeutic intervention in the treatment of both alcohol use disorder (AUD) and stress-related psychiatric illnesses.

OBJECTIVES

The present study evaluates the effects of systemically administered (intraperitoneal (i.p.)) OXT treatment on alcohol relapse-like behavior in male and female mice.

METHODS

Adult male and female C57BL/6J mice were trained to lever respond in operant conditioning chambers for alcohol in daily self-administration sessions. Once lever responding and alcohol intake stabilized, mice were tested under extinction conditions for 14 days before reinstatement testing. All mice underwent stress-induced reinstatement testing using either predator odor (2,3,5-trimethyl-3-thiazoline (TMT)) or the α-2 adrenergic receptor agonist yohimbine. In study 1, mice were exposed to TMT for 15 min and then immediately placed into operant conditioning chambers to examine alcohol-seeking behavior under extinction conditions. At 30 min prior to test session, separate groups of mice were injected with vehicle or OXT (0.1, 0.5, 1 mg/kg). In study 2, mice were injected with yohimbine (0.3, 0.625 mg/kg) 1 h prior to reinstatement testing. At 30 min post-yohimbine injection, mice are injected (i.p.) with vehicle or OXT (1 mg/kg).

RESULTS

OXT attenuated alcohol-seeking behavior in a dose-related manner in male and female mice in response to acute challenge with a predator odor. Additionally, OXT administration produced a similar decrease in alcohol relapse-like behavior triggered by the pharmacological stressor yohimbine in both sexes.

CONCLUSIONS

Systemic oxytocin administration attenuates stress-induced reinstatement of alcohol seeking in male and female mice.

Post Traumatic Stress Disorder and Substance Use Disorder as Two Pathologies Affecting Memory Reactivation: Implications for New Therapeutic Approaches

In the present review, we provide evidence indicating that although post traumatic stress disorder (PTSD) and substance use disorder (SUD) are two distinct pathologies with very different impacts on people affected by these chronic illnesses, they share numerous common characteristics, present high rates of co-morbidity, and may result from common physiological dysfunctions. We propose that these pathologies result from hyper reactivity to reminders, and thus should be considered as two disorders of memory, treated as such. We review the different possibilities to intervene on pathological memories such as extinction therapy and reconsolidation blockade. We also introduce new therapeutic avenues directly indicate by our recent proposal to replace the consolidation/reconsolidation hypothesis by the integration concept. State dependency and emotional remodeling are two innovative treatments that have already provided encouraging results. In summary, this review shows that the discovery of reactivation-dependent memory malleability has open new therapeutic avenues based on the reprocessing of pathological memories, which constitute promising approaches to treat PTSD and SUD.

Prelimbic cortex is a common brain area activated during cue-induced reinstatement of cocaine and heroin seeking in a polydrug self-administration rat model

Many preclinical studies examined cue-induced relapse to heroin and cocaine seeking in animal models, but most of these studies examined only one drug at a time. In human addicts, however, polydrug use of cocaine and heroin is common. We used a polydrug self-administration relapse model in rats to determine similarities and differences in brain areas activated during cue-induced reinstatement of heroin and cocaine seeking. We trained rats to lever press for cocaine (1.0 mg/kg per infusion, 3-hr/day, 18 day) or heroin (0.03 mg/kg per infusion) on alternating days (9 day for each drug); drug infusions were paired with either intermittent or continuous light cue. Next, the rats underwent extinction training followed by tests for cue-induced reinstatement where they were exposed to either heroin- or cocaine-associated cues. We observed cue-selective reinstatement of drug seeking: the heroin cue selectively reinstated heroin seeking and the cocaine cue selectively reinstated cocaine seeking. We used Fos immunohistochemistry to assess cue-induced neuronal activation in different subregions of the medial prefrontal cortex, dorsal striatum, nucleus accumbens, and amygdala. Fos expression results indicated that only the prelimbic cortex (PL) was activated by both heroin and cocaine cues; in contrast, no significant cue-induced neuronal activation was observed in other brain areas. RNA in situ hybridization indicated that the proportion of glutamatergic and GABAergic markers in PL Fos-expressing cells was similar for the heroin and cocaine cue-activated neurons. Overall, the results indicate that PL may be a common brain area involved in both heroin and cocaine seeking during polydrug use.

Oxytocin and Rodent Models of Addiction

Interest for the use of oxytocin as a treatment for addiction began over 40years ago. Better known for its roles in parturition, lactation and pair bonding, oxytocin also has anxiolytic properties, reduces immune and inflammatory responses, and has a role in learning and memory. In this chapter, oxytocin effects on addiction processes are described by highlighting research findings that have used oxytocin within current preclinical animal models of addiction, relapse, or craving. First, we provide a brief background of the endogenous oxytocin system followed by descriptions of the behavioral models used to study addiction, including models of drug taking and seeking. Then we review recent preclinical studies that have used oxytocin as a therapeutic intervention throughout multiple stages of the addiction cycle from a behavioral and neurobiological perspective. These models encompass the entire range of the addiction cycle including acquisition and maintenance of drug taking, withdrawal and craving during periods of drug abstinence, and ultimately relapse. We then posit several theories about how oxytocin interacts with both drug and social reward, as well as presenting a mechanistic account of how specific oxytocin receptor localization may contribute to oxytocin's efficacy as an addiction therapeutic.

Attenuated cocaine-seeking after oxytocin administration in male and female rats

RATIONALE

Initial drug abstinence (modeled here as Extinction Day 1, ED1) is a critical time point in the progression of addiction that is strongly influenced by stress and sex. ED1 induces corticosterone release in both sexes, and cocaine-seeking during ED1 can be mitigated by corticotrophin-releasing factor (CRF) antagonists more effectively in female rats. Oxytocin (OXT) is a neuropeptide that has several biological functions, including regulation of stress pathways.

METHODS

To investigate a relationship between OXT, sex, and cocaine-seeking, we examined Fos on ED1 in OXT neurons of paraventricular (PVN) and supraoptic nuclei (SON) compared to homecage (cocaine experienced) or naïve male and female rats. We also administered OXT 30 min prior to ED1 testing or cued reinstatement testing.

RESULTS

OXT neurons had decreased activity (as reflected by Fos protein) in PVN and SON on withdrawal day 1 (homecage) compared to naïve rats. Fos in OXT neurons was further decreased on ED1, compared to homecage controls, in both males and females even though in SON, cocaine exposure increased the number of OXT-expressing neurons. In addition, systemically administered OXT reduced cocaine-seeking during ED1 and cue-induced reinstatement of cocaine-seeking but delayed extinction, similarly among male and female rats.

CONCLUSIONS

These data indicate that OXT neurons in PVN and SON may be involved in cocaine-seeking during ED1 and support OXT as a possible therapeutic to decrease cocaine-seeking during initial abstinence and in response to cocaine-associated cues.

Regionally Specific Effects of Oxytocin on Reinstatement of Cocaine Seeking in Male and Female Rats

BACKGROUND

Oxytocin reduces cued reinstatement of cocaine seeking in male and female rats, but the underlying neurobiology has not been uncovered. The majority of effort on this task has focused on oxytocin and dopamine interactions in the nucleus accumbens core. The nucleus accumbens core is a key neural substrate in relapse, and oxytocin administration in the nucleus accumbens core reduces reinstatement to methamphetamine cues. Further, the nucleus accumbens core has strong glutamatergic innervation from numerous regions including the prefrontal cortex. Thus, we hypothesize that oxytocin regulates presynaptic glutamate terminals in the nucleus accumbens core, thereby affecting reinstatement.

METHODS

To begin to evaluate this hypothesis, we examined the effects of intra-nucleus accumbens core oxytocin on extracellular glutamate levels in this region. We next determined if direct infusion of oxytocin into the nucleus accumbens core could attenuate cued reinstatement of cocaine seeking in a manner dependent on metabotropic glutamate 2/3 receptors. Finally, we tested if site-specific application of oxytocin in the prefrontal cortex reduced cued reinstatement of cocaine seeking.

RESULTS

We found an increase in nucleus accumbens core extracellular glutamate for several minutes following reverse dialysis of oxytocin. In male and female rats with a history of cocaine self-administration, site-specific application of oxytocin in the nucleus accumbens core and prefrontal cortex had opposing effects, decreasing and increasing cued reinstatement, respectively. The mGlu2/3 antagonist LY-341495 reversed oxytocin's ability to attenuate cued reinstatement.

CONCLUSIONS

While the precise mechanism by which oxytocin increases nucleus accumbens core glutamate is yet to be determined, the present results clearly support oxytocin mediation of glutamate neurotransmission in the nucleus accumbens core that impacts cued cocaine seeking.

Corticotropin-releasing factor receptor 2-deficiency eliminates social behaviour deficits and vulnerability induced by cocaine

BACKGROUND AND PURPOSE

Poor social behaviour and vulnerability to stress are major clinical features of stimulant use disorders. The corticotropin-releasing factor (CRF) system mediates stress responses and might underlie substance use disorders; however, its involvement in social impairment induced by stimulant substances remains unknown. CRF signalling is mediated by two receptor types, CRF₁ and CRF₂ . In the present study we investigated the role of the CRF₂ receptor in social behaviour deficits, vulnerability to stress and related brain alterations induced by cocaine administration and withdrawal.

EXPERIMENTAL APPROACH

CRF₂ receptor-deficient (CRF₂ -/-) and littermate wild-type mice were repeatedly tested in the three-chamber task for sociability (i.e. preference for an unfamiliar conspecific vs. an object) and social novelty preference (SNP; i.e. preference for a novel vs. a familiar conspecific) before and after chronic cocaine administration. An in situ hybridization assay was used to assess gene expression of the stress-responsive arginine vasopressin (AVP) and oxytocin (OT) neuropeptides in the hypothalamus.

KEY RESULTS

CRF₂ receptor deficiency eliminated the sociability deficit induced by cocaine withdrawal. Moreover, CRF₂ -/- mice did not show either the stress-induced sociability deficit or the increased AVP and OT expression associated with long-term cocaine withdrawal, indicating resilience to stress. Throughout, wild-type and CRF₂ -/- mice displayed SNP, suggesting that cocaine withdrawal-induced sociability deficits were not due to impaired detection of social stimuli.

CONCLUSIONS AND IMPLICATIONS

These findings demonstrate a central role for the CRF₂ receptor in social behaviour deficits and biomarkers of vulnerability induced by cocaine withdrawal, suggesting new therapeutic strategies for stimulant use disorders.

Antagonism of mGlu2/3 receptors in the nucleus accumbens prevents oxytocin from reducing cued methamphetamine seeking in male and female rats

Methamphetamine (meth) addiction is a prevalent health concern worldwide, yet remains without approved pharmacological treatments. Preclinical evidence suggests that oxytocin may decrease relapse, but the neuronal underpinnings driving this effect remain unknown. Here we investigate whether oxytocin's effect is dependent on presynaptic glutamatergic regulation in the nucleus accumbens core (NAcore) by blocking metabotropic glutamate receptors 2/3 (mGluR2/3). Male and female Sprague-Dawley rats self-administered meth or sucrose on an escalating fixed ratio, followed by extinction and cue-induced reinstatement sessions. Reinstatement tests consisted of systemic (Experiment 1) or site-specific application of the drugs into the NAcore (Experiments 2 and 3). Before reinstatement sessions, rats received LY341495, an mGluR2/3 antagonist, or its vehicle followed by a second infusion/injection of oxytocin or saline. As expected, both males and females reinstated lever pressing to meth associated cues, and LY341495 alone did not impact this behavior. Oxytocin injected systemically or infused into the NAcore decreased cued meth seeking. Importantly, combined LY341495 and oxytocin administration restored meth cued reinstatement. Interestingly, neither oxytocin nor LY341495 impacted sucrose-cued reinstatement, suggesting distinct mechanisms between meth and sucrose. These findings were consistent between males and females. Overall, we report that oxytocin reduced responding to meth-associated cues and blocking presynaptic mGluR2/3 reversed this effect. Further, oxytocin's effects were specific to meth cues as NAcore oxytocin was without an effect on sucrose cued reinstatement. Results are discussed in terms of oxytocin receptor localization in the NAcore and modulation of presynaptic regulation of glutamate in response to drug associated cues.