CRF2 Receptor Deficiency Eliminates the Long-Lasting Vulnerability of Motivational States Induced by Opiate Withdrawal

Differential effects of acute and prolonged morphine withdrawal on motivational and goal-directed control over reward-seeking behavior

Opioid addiction is a relapsing disorder marked by uncontrolled drug use and reduced interest in normally rewarding activities. The current study investigated the impact of spontaneous withdrawal from chronic morphine exposure on emotional, motivational, and cognitive processes involved in regulating the pursuit and consumption of natural food rewards in male rats. In Experiment 1, rats experiencing acute morphine withdrawal lost weight and displayed somatic signs of drug dependence. However, hedonically-driven sucrose consumption was significantly elevated, suggesting intact and potentially heightened emotional reward processing. In Experiment 2, rats undergoing acute morphine withdrawal displayed reduced motivation when performing an effortful response for palatable food reward. Subsequent reward devaluation testing revealed that acute withdrawal also disrupted their ability to exert flexible goal-directed control over their reward-seeking behavior. Specifically, morphine-withdrawn rats displayed insensitivity to reward devaluation both when relying on prior action-outcome learning and when given direct feedback about the consequences of their actions. In Experiment 3, rats tested after prolonged morphine withdrawal displayed heightened rather than diminished motivation for food rewards and retained their ability to engage in flexible goal-directed action selection. However, brief re-exposure to morphine was sufficient to impair motivation and disrupt goal-directed action selection, though in this case insensitivity to reward devaluation was only observed in the presence of morphine-paired context cues and in the absence of response-contingent feedback. We suggest that these opioid-withdrawal induced deficits in motivation and goal-directed control may contribute to addiction by interfering with the pursuit of adaptive alternatives to drug use.

Morphine reduces the interest for natural rewards

RATIONALE

Alongside a pathological, excessive, motivation for substances of abuse, substance use disorder (SUD) patients often show a dramatic loss of interest for naturally rewarding activities, such as positive peer social interaction and food intake. Yet, pre-clinical evidence of the latter SUD features remains scarce and inconsistent.

OBJECTIVES

In the current study, we investigated the effect of non-rewarding and rewarding doses of morphine upon social behaviour, motivation for and intake of palatable food, in male and female C57BL/6J mice.

METHODS

First, the rewarding effects of two relatively low morphine doses (1.25 and 2.5 mg/kg) were assessed using a newly established single substance administration/conditioning trial conditioned place preference (CPP) paradigm. Then, morphine (1.25 and 2.5 mg/kg) effects upon social behaviour, motivation for and intake of palatable food were examined by the three-chamber (3-CH), an operant behaviour and a palatable food preference test, respectively.

RESULTS

Morphine (2.5 mg/kg) induced CPP in both male and female mice, whereas morphine (1.25 mg/kg) induced CPP only in female mice. Both morphine doses (1.25 and 2.5 mg/kg) reduced sociability, motivation for and intake of palatable food in male and female mice, independently of cognitive function or locomotor activity.

CONCLUSIONS

Female mice were more sensitive than male mice to the rewarding effects of morphine. Moreover, both a non-rewarding and a rewarding dose of morphine impaired the interest for naturally rewarding activities, indicating that brain reward systems might be more sensitive to the deleterious than to the rewarding effects of substances of abuse.

Repeated cocaine or methamphetamine treatment alters astrocytic CRF2 and GLAST expression in the ventral midbrain

Dopamine neurons in the substantia nigra (SN) and ventral tegmental area (VTA) play a central role in the reinforcing properties of abused drugs including methamphetamine and cocaine. Chronic effects of psychostimulants in the SN/VTA also involve non-dopaminergic transmitters, including glutamate and the stress-related peptide corticotropin-releasing factor (CRF). In the SN/VTA, astrocytes express a variety of membrane-bound neurotransmitter receptors and transporters that influence neurotransmission. CRF receptor type 2 (CRF2) activity in the VTA is important for stress-induced relapse and drug-seeking behaviour, but the localization of its effects is incompletely understood. Here, we first identified CRF2 transcript in astrocytes of the SN/VTA using RNA-Seq in Aldh1l1;NuTRAP mice and confirmed it using in situ hybridization (RNAscope) in wild-type mice. We then used immunofluorescence to quantify the astrocytic marker protein S100β, glial-specific glutamate/aspartate transporter GLAST, and CRF2 in the SN/VTA following 12 days of treatment (i.p.) with methamphetamine (3 mg/kg), cocaine (10 mg/kg), or saline. We observed a significant decrease in GLAST immunofluorescence in brains of psychostimulant treated mice compared with saline controls. In addition, we observed increased labelling of CRF2 in drug treated groups, a decrease in the number of S100β positive cells, and an increase of co-staining of CRF2 with both S100β and tyrosine hydroxylase (dopamine neurons). Our results suggest a significant interaction between CRF2, GLAST, and astrocytes in the midbrain that emerges with repeated exposure to psychostimulants. These findings provide rationale for future investigation of astrocyte-based strategies for altering cellular and circuit function in response to stress and drug exposure.

The CRF1 receptor mediates social behavior deficits induced by opiate withdrawal

Poor sociability and aggressive behavior are key clinical features of opioid use disorders. The corticotropin-releasing factor (CRF) system may mediate behavioral effects of substances of abuse but its implication in substance-induced social behavior deficits and outward-directed hostility remains largely unknown. CRF signaling is mediated by two receptor types, termed CRF₁ and CRF₂ . The present study aimed at understanding the role for the CRF₁ receptor in social and aggressive behavior induced by withdrawal from repeated opiate administration. Thus, wild-type (CRF₁ +/+), CRF₁ receptor heterozygous (CRF₁ +/-), and null mutant (CRF₁ -/-) female and male mice were treated with saline or escalating doses of morphine (20-100 mg/kg, i.p.) during six consecutive days and tested in the three-chamber task for sociability (i.e., preference for an unfamiliar same-sex conspecific vs. an object) 7 days after the last administration. Moreover, aggressive biting behavior toward the unfamiliar conspecific was assessed during the three-chamber test. Opiate withdrawal disrupted sociability in CRF₁ +/+ and CRF₁ +/-, but not in CRF₁ -/-, female mice, without affecting aggressive biting behavior in any genotype. In contrast, opiate withdrawal did not affect sociability but increased aggressive biting behavior in male mice, independently of CRF₁ receptor-deficiency. Nevertheless, in opiate-withdrawn CRF₁ +/+, but not CRF₁ +/- and CRF₁ -/-, male mice, sociability directly correlated with aggressive biting behavior, suggesting a role for the CRF₁ receptor in hostility-linked social approach. These findings demonstrate the implication of the CRF₁ receptor in social behavior deficits associated with repeated opiate administration and withdrawal, revealing a new potential target for the treatment of opioid use disorders.

Sex-linked roles of the CRF1 and the CRF2 receptor in social behavior

Dysfunctional social behavior is a major clinical feature of mood, anxiety, autism spectrum, and substance-related disorders, and may dramatically contribute to the poor outcome of these diseases. Nevertheless, the mechanisms underlying social behavior deficits are still largely unknown. The corticotropin-releasing factor (CRF) system, a major coordinator of the stress response, has been hypothesized to modulate social behavior. CRF signaling is mediated by two receptor types, termed CRF₁ and CRF₂ . Using the three-chamber task for sociability (i.e., preference for an unfamiliar conspecific vs. an object), this study demonstrates that CRF₂ receptor null mutation (CRF₂ -/-) reduces sociability in female mice but increases it in male mice. Both female and male CRF₂ -/- mice display a preference for social odor cues over neutral cues, indicating that sex- and CRF₂ receptor-dependent sociability is not due to altered olfaction or impaired social cues discrimination. Moreover, treatment with the CRF₁ receptor-preferring antagonist, antalarmin, consistently induces sociability in non-social mice but disrupts it in social mice, independently of CRF₂ receptor deficiency. Sex, CRF₂ receptor deficiency, or antalarmin affect locomotor activity during the three-chamber test. However, throughout the study CRF₁ and CRF₂ receptor-linked sociability is independent of locomotor activity. The present findings highlight major functions for the CRF system in the regulation of social behavior. Moreover, they provide initial evidence of sex-linked roles for the CRF₁ and the CRF₂ receptor, emphasizing the importance of sex as a major biological variable to be taken into consideration in preclinical and clinical studies.

Anxiety-like behavior in acute and protracted withdrawal after morphine-induced locomotor sensitization in C57BL/6 male mice: The role of context

Contextual memory plays an important role in development and maintenance of drug addiction. However, little is known about of the role contextual memory in the emergence of a negative emotional state in the withdrawal period. Therefore, this study investigated anxiety-like behavior in acute and protracted morphine withdrawal of mice submitted to a locomotor sensitization protocol and the influence of contextual memory on this behavior. Male adult C57Bl6 mice were subjected to morphine locomotor sensitization and anxiety-like behavior was assessed by using the elevated plus maze test (EPM). To evaluate associative memory, the mice were re-exposed to the context of locomotor sensitization immediately before EPM. As expected, repeated morphine administrations promoted locomotor sensitization, seen as a gradual increase in the distance traveled during the acquisition phase. There was an increase in anxiety-like behavior upon acute withdrawal, as indicated by a decrease in open arms activity (OAA), but this effect dissipated over time. However, when the context was presented, mice in protracted withdrawal showed enhanced anxiety-like behavior, indicated by an increase in closed arms activity (CAA). This effect was context specific since re-exposure in an alternative context did not change the anxiety-like behavior. Treatment with diazepam counteracted the decrease in OAA in acute withdrawal and the increase in CAA induced by context re- exposure during protracted abstinence. Thus, repeated morphine administration induced a negative emotional state when the drug was discontinued. The context associated with drug exposure played a pivotal role in the appearance of anxiety-like behavior, even long after drug discontinuation. There were differences in the patterns of anxiety behaviors in acute (unconditioned anxiety-like behavior) and protracted (conditioned anxiety-like behavior) withdrawal since the former was characterized by a passive behavioral strategy and the latter by an active behavioral strategy.

Long-lasting pseudo-social aggressive behavior in opiate-withdrawn mice

Poor sociability and aggressive behavior are major clinical features of opiate use disorders that may contribute to the establishment and maintenance of these harmful diseases. The present study investigated the long-term effects of chronic morphine administration and withdrawal upon social and aggressive behavior as well as the interrelationship between these two behaviors. Thus, social behavior was measured in C57BL/6J male mice 7, 21, 35 and 49 days after cessation of escalating morphine doses (20-100 mg/kg, i.p.) administered during 6 consecutive days, using the three-chamber task for sociability (i.e., preference for an unfamiliar conspecific vs. an object) and social novelty preference (i.e., preference for a novel vs. a familiar conspecific). Moreover, aggressive biting behavior towards an unfamiliar conspecific was assessed throughout the three-chamber tests. Opiate withdrawal increased both social approach and aggressive biting behavior. Moreover, in morphine-withdrawn, but not in control, mice social approach and aggressive behavior followed a similar time-course and positively correlated one with each other, suggesting that social interest was mainly driven by aggressiveness. Aggressive biting behavior was still elevated 49 days after the last morphine administration, revealing that opiate withdrawal is followed by long-lasting aggressiveness. Throughout, opiate withdrawal did not affect social novelty preference, ruling out a role for olfactory or social discrimination dysfunction in the elevated social approach and aggressive behavior. The present findings of very long-lasting aggressive behavior and aggression-driven social approach in opiate-withdrawn mice might help understanding the behavioral and brain underpinnings of poor sociability and aggressiveness commonly observed in opiate use disorders patients.

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.

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.

CRF receptor type 1 (but not type 2) located within the amygdala plays a role in the modulation of anxiety in mice exposed to the elevated plus maze

The amygdala (Amy) is an important center that processes threatening stimuli. Among the neurotransmitters implicated in the control of emotional states, the corticotrophin releasing factor (CRF) is an important modulator, acting at CRF1 and CRF2 receptors. Few studies have investigated the role of CRF and its receptors in the Amy on anxiety in mice. Here, we investigated the effects of intra-Amy (aimed at the basolateral nucleus) injections of CRF (37.5 and 75pmol/0.1μl), urocortin 3 (UCn3, a selective CRF2 agonist; 4, 8, 16 or 24pmol/0.1μl), CP376395 (a selective CRF1 antagonist; 0.375, 0.75 or 1.5nmol/0.1μl), antisauvagine-30 (ASV-30, a selective CRF2 antagonist; 1 or 3nmol/0.1μl) on the behavior of mice exposed to the elevated plus maze (EPM). Both spatiotemporal (e.g., percentage of open-arm entries and percentage of open-arm time; %OE and %OT) and complementary [e.g., frequency of protected and unprotected stretched attend postures (pSAP and uSAP) and head dips (pHD and uHD); frequency and time spent on open arm end exploration (OAEE)] measures were recorded during a 5-min test in the EPM. While intra-Amy injections of CRF decreased %OE, %OT and OAEE, suggesting an anxiogenic-like action, UCn3 (all doses) did not change any behavior. In contrast, injections of CP376395 (0.75nmol) produced an anxiolytic-like effect, by increasing %OT and OAEE and decreasing pSAP and pHD. Neither spatiotemporal nor complementary measures were changed by intra-Amy ASV-30. These results suggest that CRF plays a marked anxiogenic role at CRF1 receptors in the amygdala of mice exposed to the EPM.