The CRF 1 and the CRF 2 receptor mediate recognition memory deficits and vulnerability induced by opiate withdrawal

Oral self-administration of pregabalin in a mouse model and the resulting drug addiction features

Prescription drug abuse is an issue that is rapidly growing globally. Pregabalin, an anticonvulsant, analgesic, and anxiolytic medication, is effective in the management of multiple neurological disorders; however, there is increasing concern regarding its widespread illicit use. It has been previously reported in mice that pregabalin can induce conditioned place preference. In this current investigation, the potential of pregabalin to elicit free-choice drinking in a mouse model of drug addiction, and its effect on recognition and withdrawal behaviors after forced abstinence, were studied. Twenty-two male BALB/c mice were randomly divided into three groups (n = 7-8/group); control, pregabalin-30, and pregabalin-60. The study had three phases: habituation (days 1-5) with free water access, free-choice drinking (days 6-13) with pregabalin groups receiving one water and one pregabalin bottle, and forced abstinence (days 14-21) with free water access. On day 13, the first open field test was conducted, followed by the Novel Object Recognition Test. On day 21, the second open field test was performed, followed by the Tail Suspension Test and Forced Swimming Test. Pregabalin elicited voluntary drinking in the higher-dose group, concurrently causing a decline in recognition memory performance in the novel object recognition test. Moreover, pregabalin induced withdrawal behavior after a period of forced abstinence in the forced swimming and tail suspension tests. This is the first report to establish an animal model of free-choice pregabalin drinking that may be used for further molecular studies and targeted therapy for pregabalin addiction.

Investigating the potential of mirtazapine to induce drug-seeking behavior in free-choice drinking mouse model

Addiction to various drugs and chemicals is a significant public health concern worldwide. Addiction to prescription medications has increased due to the psychoactive effects of these medications, their availability, low price, and the lack of legal consequences for abusers. One of such prescription medication is mirtazapine (MIRT). MIRT is an antidepressant that has recently been reported to be abused and could induce withdrawal symptoms in different case studies. No previous study has investigated its abuse potential in animal models of drug addiction. Here, we conducted a free-choice drinking paradigm to investigate voluntary drinking of MIRT at two different concentrations. Male BALB/c mice were given unlimited access to two water bottles for five days before being divided into three groups: the first group had free access to two water bottles. The second group (MIRT10) and the third group (MIRT20) was allowed unlimited choice to one bottle of water and one bottle of MIRT at concentrations of 0.03 and 0.06 mg/mL, respectively. The average daily MIRT intake in the MIRT20 group was significantly higher on all tested days than that in the MIRT10 group. Moreover, mice in the MIRT20 group preferred to self-administer MIRT over water, indicating that MIRT can induce drug-seeking behavior. To further investigate the addictive potential of MIRT and its possible deterioration of memory and recognition, as reported with several known drugs of abuse, animals underwent a novel object recognition test. Mice in the MIRT20 group demonstrated significant deterioration in memory and recognition, indicating its effects on different brain regions involved in recognition, similar to other known drugs of abuse. The forced swimming test and tail suspension test were used to test MIRT-induced withdrawal symptoms after forced abstinence. After eight days of abstinence, mice in the MIRT20 group demonstrated significant depression-like symptoms in both the TST and FST, manifested by a significant increase in immobility time. MIRT was shown to induce drug-seeking behavior, deteriorate recognition, and cause withdrawal symptoms. This might confirm that MIRT has the potential to induce drug dependence and further studies are warranted to explore the neurobiological basis of MIRT-induced drug-seeking behavior.

A role for the circadian transcription factor NPAS2 in the progressive loss of non-rapid eye movement sleep and increased arousal during fentanyl withdrawal in male mice

RATIONALE

Synthetic opioids like fentanyl are contributing to the rise in rates of opioid use disorder and drug overdose deaths. Sleep dysfunction and circadian rhythm disruption may worsen during opioid withdrawal and persist during abstinence. Severe and persistent sleep and circadian alterations are putative factors in opioid craving and relapse. However, very little is known about the impact of fentanyl on sleep architecture and sleep-wake cycles, particularly opioid withdrawal. Further, circadian rhythms regulate sleep-wake cycles, and the circadian transcription factor, neuronal PAS domain 2 (NPAS2) is involved in the modulation of sleep architecture and drug reward. Here, we investigate the role of NPAS2 in fentanyl-induced sleep alterations.

OBJECTIVES

To determine the effect of fentanyl administration and withdrawal on sleep architecture, and the role of NPAS2 as a factor in fentanyl-induced sleep changes.

METHODS

Electroencephalography (EEG) and electromyography (EMG) was used to measure non-rapid eye movement sleep (NREMS) and rapid eye movement sleep (REMS) at baseline and following acute and chronic fentanyl administration in wild-type and NPAS2-deficient male mice.

RESULTS

Acute and chronic administration of fentanyl led to increased wake and arousal in both wild-type and NPAS2-deficient mice, an effect that was more pronounced in NPAS2-deficient mice. Chronic fentanyl administration led to decreased NREMS, which persisted during withdrawal, progressively decreasing from day 1 to 4 of withdrawal. The impact of fentanyl on NREMS and arousal was more pronounced in NPAS2-deficient mice.

CONCLUSIONS

Chronic fentanyl disrupts NREMS, leading to a progressive loss of NREMS during subsequent days of withdrawal. Loss of NPAS2 exacerbates the impact of fentanyl on sleep and wake, revealing a potential role for the circadian transcription factor in opioid-induced sleep changes.

Recent advances in neuropeptide-related omics and gene editing: Spotlight on NPY and somatostatin and their roles in growth and food intake of fish

Feeding and growth are two closely related and important physiological processes in living organisms. Studies in mammals have provided us with a series of characterizations of neuropeptides and their receptors as well as their roles in appetite control and growth. The central nervous system, especially the hypothalamus, plays an important role in the regulation of appetite. Based on their role in the regulation of feeding, neuropeptides can be classified as orexigenic peptide and anorexigenic peptide. To date, the regulation mechanism of neuropeptide on feeding and growth has been explored mainly from mammalian models, however, as a lower and diverse vertebrate, little is known in fish regarding the knowledge of regulatory roles of neuropeptides and their receptors. In recent years, the development of omics and gene editing technology has accelerated the speed and depth of research on neuropeptides and their receptors. These powerful techniques and tools allow a more precise and comprehensive perspective to explore the functional mechanisms of neuropeptides. This paper reviews the recent advance of omics and gene editing technologies in neuropeptides and receptors and their progresses in the regulation of feeding and growth of fish. The purpose of this review is to contribute to a comparative understanding of the functional mechanisms of neuropeptides in non-mammalians, especially fish.

Enriched Environment Ameliorates Cognitive Deficits and Locomotor Sensitization in Morphine-Withdrawn Rats Receiving Methadone Maintenance Treatment

OBJECTIVE

This study was designed to examine whether enriched environments (EE) would attenuate object recognition and spatial learning and memory deficits and locomotor sensitization induced by methadone maintenance treatment (MMT) in morphine-withdrawn rats.

METHODS

Male Wistar rats (170 ± 10 g) were injected with bi-daily doses (10 mg/kg, 12-h intervals) of morphine for 14 days. Rats receiving MMT were reared in the standard environment (SE) or EE during 30 days of morphine withdrawal. Then, the rats were tested for object recognition (the object recognition memory test, ORMT) and spatial learning and memory (the water maze) and then challenged with morphine (1 mg/kg, i.p.) and evaluated for locomotor activity (open-field box).

RESULTS

The results revealed that the dependent/saline/EE (D/Sal/EE) and D/methadone/EE (D/Meth/EE) rats exhibited significant preference for the new object (p = 0.006 and p = 0.049), spent more time in the target zone (p = 0.045 and p = 0.005) on the water maze, and displayed a lower level of distance traveled (p = 0.002 and p = 0.0001) compared to their control groups reared in SE.

CONCLUSIONS

We conclude that exposure to EE could ameliorate the object recognition and spatial memory deficits and also decrease locomotor sensitivity in morphine-withdrawn rats receiving MMT. Thus, EE may be beneficial in the treatment of addiction during MMT.

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.

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.

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.

Concurrent Effects of Exercise and Curcumin on Spatial Learning and Memory in Sensitized Male Mice Following Morphine Administration

Background:

Exercise and Curcumin have positive effects on spatial memory and cognition independently. The present study aims to investigate whether the combination of ineffectual dosage of these factors can affect cognition and as a solvent if DMSO is involved in Curcumin effects.

Materials and Methods:

Male NMRI mice (1-month-old) swam (1 week) for 60 minutes (5days/week) and injected with morphine (2.5 mg/ml/kg, intraperitoneal) for five days. Spatial learning and memory were assessed by Moris Water Maze test on the 10th day after stopping morphine injection.

Results:

The findings revealed that exercise, dimethyl sulfoxide (DMSO), and Curcumin increased memory formation induced by 2.5 mg/ml/kg morphine. DMSO+exercise decreased memory formation induced by morphine, but curcumin +exercise could return the effect of DMSO on the cognition.

Conclusion:

As a solvent, DMSO had independent effects on memory, which lead to memory impairment in combination with exercise. Therefore, considering its unpredictable effects on cognitive performance, it should be replaced with another solvent or might be used carefully in behavioral experiments.

Anti-inflammatory agents for smoking cessation? Focus on cognitive deficits associated with nicotine withdrawal in male mice

Nicotine withdrawal is associated with cognitive deficits including attention, working memory, and episodic memory impairments. These cognitive deficits are a hallmark of nicotine abstinence which could be targeted in order to prevent smoking relapse. The underlying mechanisms, however, are poorly understood. In this study, memory impairment was observed in mice 4 days after the precipitation of nicotine withdrawal by the nicotinic antagonist mecamylamine. The presence of cognitive deficits correlated with microglial activation in the hippocampus and the prefrontal cortex. Moreover, an increased expression of neuroinflammatory markers including IL1β, TNFα and IFNγ was found in both memory-related brain regions. Notably, flow cytometric analysis also revealed an enhancement of TNFα and IFNγ plasmatic levels at the same time point during nicotine withdrawal. Impaired neurogenesis, as shown by reduction in the expression of the endogenous cell proliferation marker Ki67 and the early neuron marker doublecortin, was also associated with nicotine abstinence. Treatment with the non-psychoactive cannabinoid cannabidiol abolished memory impairment of nicotine withdrawal and microglia reactivity, reduced the expression of IL1β and IFNγ in the hippocampus and the prefrontal cortex, respectively, and normalized Ki67 levels. The nonsteroidal anti-inflammatory drug indomethacin also prevented cognitive deficits and microglial reactivity during withdrawal. These data underline the usefulness of anti-inflammatory agents to improve cognitive performance during early nicotine abstinence.

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: 2016

This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 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.