Development of morphine-induced tolerance and withdrawal: involvement of the clock gene mPer2

Atp1a2 and Kcnj9 are candidate genes underlying oxycodone behavioral sensitivity and withdrawal in C57BL/6 substrains

Opioid use disorder is heritable, yet its genetic etiology is largely unknown. Analysis of addiction model traits in rodents (e.g., opioid behavioral sensitivity and withdrawal) can facilitate genetic and mechanistic discovery. C57BL/6J and C57BL/6NJ substrains have extremely limited genetic diversity, yet can show reliable phenotypic diversity which together, can facilitate gene discovery. The C57BL/6NJ substrain was less sensitive to oxycodone (OXY)-induced locomotor activity compared to the C57BL/6J substrain. Quantitative trait locus (QTL) mapping in an F2 cross identified a distal chromosome 1 QTL explaining 7-12% of the variance in OXY locomotor sensitivity and anxiety-like withdrawal in the elevated plus maze. We identified a second QTL for withdrawal on chromosome 5 near the candidate gene Gabra2 (alpha-2 subunit of GABA-A receptor) explaining 9% of the variance. Next, we generated recombinant lines from an F2 founder spanning the distal chromosome 1 locus (163-181 Mb), captured the QTL for OXY sensitivity and withdrawal, and fine-mapped a 2.45-Mb region (170.16-172.61 Mb). There were five striatal cis-eQTL transcripts in this region (Pcp4l1, Ncstn, Atp1a2, Kcnj9, Igsf9), two of which were confirmed at the protein level (KCNJ9, ATP1A2). Kcnj9, a.k.a., GIRK3, codes for a potassium channel that is a major effector of mu opioid receptor signaling. Atp1a2 codes for a subunit of a Na+/K+ ATPase enzyme that regulates neuronal excitability and shows adaptations following chronic opioid administration. To summarize, we identified genetic sources of opioid behavioral differences in C57BL/6 substrains, two of the most widely and often interchangeably used substrains in opioid addiction research.

Ameliorating effects of Acanthopanax koreanum extract and components on nicotine dependence and withdrawal symptoms

Tobacco smoking is a serious health problem in society. While smoking rates are declining, smoking remains a serious risk to national health. Currently, there are several medications available to aid in smoking cessation. However, these medications have the disadvantages of low success rates in smoking cessation and various side effects. Therefore, natural-based smoking cessation aids are being suggested as a good alternative due to their accessibility and minimal side effects. The roots and stems of Acanthopanax koreanum (AK) Nakai, a plant that is native to Jeju Island, South Korea, have traditionally been used as tonic and sedatives. Moreover, eleutheroside B and chlorogenic acid are the main components of AK stem extract. In the present study, we investigated the effect of 70% ethanol AK extract and its components on ameliorating nicotine dependence and withdrawal symptoms by using behavioural tests in mice. In addition, alterations in the dopaminergic and DRD1-EPAC-ERK-CREB pathways were observed using dopamine ELISA and western blotting using mouse brains. Our findings demonstrate that the AK extract and its components effectively mitigated the effects of nicotine treatment in behavioural tests. Furthermore, it normalized the dopamine concentration and the expression level of nicotine acetylcholine receptor α7. Additionally, it was observed that AK extract and its components led to the normalization of DRD1, ERK and CREB expression levels. These results indicate that AK extract exhibits effects in ameliorating nicotine dependence behaviour and alleviating withdrawal symptoms. Moreover, EB and CGA are considered potential marker components of AK extract.

The disruptive relationship among circadian rhythms, pain, and opioids

Pain behavior and the systems that mediate opioid analgesia and opioid reward processing display circadian rhythms. Moreover, the pain system and opioid processing systems, including the mesolimbic reward circuitry, reciprocally interact with the circadian system. Recent work has demonstrated the disruptive relationship among these three systems. Disruption of circadian rhythms can exacerbate pain behavior and modulate opioid processing, and pain and opioids can influence circadian rhythms. This review highlights evidence demonstrating the relationship among the circadian, pain, and opioid systems. Evidence of how disruption of one of these systems can lead to reciprocal disruptions of the other is then reviewed. Finally, we discuss the interconnected nature of these systems to emphasize the importance of their interactions in therapeutic contexts.

Sex-specific role of the circadian transcription factor NPAS2 in opioid tolerance, withdrawal and analgesia

Opioids like fentanyl remain the mainstay treatment for chronic pain. Unfortunately, opioid's high dependence liability has led to the current opioid crisis, in part, because of side-effects that develop during long-term use, including analgesic tolerance and physical dependence. Both tolerance and dependence to opioids may lead to escalation of required doses to achieve previous therapeutic efficacy. Additionally, altered sleep and circadian rhythms are common in people on opioid therapy. Opioids impact sleep and circadian rhythms, while disruptions to sleep and circadian rhythms likely mediate the effects of opioids. However, the mechanisms underlying these bidirectional relationships between circadian rhythms and opioids remain largely unknown. The circadian protein, neuronal PAS domain protein 2 (NPAS2), regulates circadian-dependent gene transcription in structure of the central nervous system that modulate opioids and pain. Here, male and female wild-type and NPAS2-deficient (NPAS2-/-) mice were used to investigate the role of NPAS2 in fentanyl analgesia, tolerance, hyperalgesia and physical dependence. Overall, thermal pain thresholds, acute analgesia and tolerance to a fixed dose of fentanyl were largely similar between wild-type and NPAS2-/- mice. However, female NPAS2-/- exhibited augmented analgesic tolerance and significantly more behavioral symptoms of physical dependence to fentanyl. Only male NPAS2-/- mice had increased fentanyl-induced hypersensitivity, when compared with wild-type males. Together, our findings suggest sex-specific effects of NPAS2 signaling in the regulation of fentanyl-induced tolerance, hyperalgesia and dependence.

Regulation of clock and clock-controlled genes during morphine reward and reinforcement: Involvement of the period 2 circadian clock

BACKGROUND

Morphine abuse is a devastating disorder that affects millions of people worldwide, and literature evidence indicates a relationship between opioid abuse and the circadian clock.

AIM

We explored morphine reward and reinforcement using mouse models with Per2 gene modifications (knockout (KO); overexpression (OE)).

METHODS

Mice were exposed to various behavioral, electroencephalographic, pharmacological, and molecular tests to assess the effects of morphine and identify the underlying mechanisms with a focus on reward and reinforcement and the corresponding involvement of circadian and clock-controlled gene regulation.

RESULTS

Per2 deletion enhances morphine-induced analgesia, locomotor sensitization, conditioned place preference (CPP), and self-administration (SA) in mice, whereas its overexpression attenuated these effects. In addition, reduced withdrawal was observed in Per2 KO mice, whereas an augmented withdrawal response was observed in Per2 OE mice. Moreover, naloxone and SCH 23390 blocked morphine CPP in Per2 KO and wild-type (WT) mice. The rewarding (CPP) and reinforcing effects (SA) observed in morphine-conditioned and morphine self-administered Per2 KO and WT mice were accompanied by activated μ-opioid and dopamine D1 receptors and TH in the mesolimbic (VTA/NAcc) system. Furthermore, genetic modifications of Per2 in mice innately altered some clock genes in response to morphine.

CONCLUSION

These findings improve our understanding of the role of Per2 in morphine-induced psychoactive effects. Our data and those obtained in previous studies indicate that targeting Per2 may have applicability in the treatment of substance abuse.

Dorsal Striatum Transcriptome Profile Profound Shift in Repeated Aggression Mouse Model Converged to Networks of 12 Transcription Factors after Fighting Deprivation

Both aggressive and aggression-deprived (AD) species represent pathologic cases intensely addressed in psychiatry and substance abuse disciplines. Previously, we reported that AD mice displayed a higher aggressive behavior score than the aggressive group, implying the manifestation of a withdrawal effect. We employed an animal model of chronic social conflicts, curated in our lab for more than 30 years. In the study, we pursued the task of evaluating key events in the dorsal striatum transcriptome of aggression experienced mice and AD species compared to controls using RNA-Seq profiling. Aggressive species were subjected to repeated social conflict encounters (fights) with regular positive (winners) experience in the course of 20 consecutive days (A20 group). This led to a profoundly shifted transcriptome expression profile relative to the control group, outlined by more than 1000 differentially expressed genes (DEGs). RNA-Seq cluster analysis revealed that elevated cyclic AMP (cAMP) signaling cascade and associated genes comprising 170 differentially expressed genes (DEGs) in aggressive (A20) species were accompanied by a downturn in the majority of other metabolic/signaling gene networks (839 DEGs) via the activation of transcriptional repressor DEGs. Fourteen days of a consecutive fighting deprivation period (AD group) featured the basic restoration of the normal (control) transcriptome expression profile yielding only 62 DEGs against the control. Notably, we observed a network of 12 coordinated DEG Transcription Factor (TF) activators from 62 DEGs in total that were distinctly altered in AD compared to control group, underlining the distinct transcription programs featuring AD group, partly retained from the aggressive encounters and not restored to normal in 14 days. We found circadian clock TFs among them, reported previously as a withdrawal effect factor. We conclude that the aggressive phenotype selection with positive reward effect (winning) manifests an addiction model featuring a distinct opioid-related withdrawal effect in AD group. Along with reporting profound transcriptome alteration in A20 group and gaining some insight on its specifics, we outline specific TF activator gene networks associated with transcriptional repression in affected species compared to controls, outlining Nr1d1 as a primary candidate, thus offering putative therapeutic targets in opioid-induced withdrawal treatment.

Molecular Mechanism of Neuroprotective Effect of Melatonin on Morphine Addiction and Analgesic Tolerance: an Update

Drug addiction is a global health problem and continues to place an enormous financial burden on society. This addiction is characterized by drug dependence sensitization and craving. Morphine has been widely used for pain relief, but chronic administration of morphine causes analgesic tolerance, hyperalgesia, and addiction, all of which limit its clinical usage. Alterations of multiple molecular pathways have been reported to be involved in the development of drug addiction, including mitochondrial dysfunction, excessive oxidative stress and nitric oxide stress, and increased levels of apoptosis, autophagy, and neuroinflammation. Preclinical and clinical studies have shown that the co-administration of melatonin with morphine leads to a reversal of these affected pathways. In addition, murine models have shown that melatonin improves morphine-induced analgesic tolerance and addictive behaviors, such as behavioral sensitization, reward effect, and physical dependence. In this review, we attempt to summarize the recent findings about the beneficial effect and molecular mechanism of melatonin on mitochondrial dysfunction, uncontrolled autophagy, and neuroinflammation in morphine addiction and morphine analgesic tolerance. We propose that melatonin might be a useful supplement in the treatment opiate abuse.

Gene Expression Profiling in the Striatum of Per2 KO Mice Exhibiting More Vulnerable Responses against Methamphetamine

Drug addiction influences most communities directly or indirectly. Increasing studies have reported the relationship between circadian-related genes and drug addiction. Per2 disrupted mice exhibited more vulnerable behavioral responses against some drugs including methamphetamine (METH). However, its roles and mechanisms are still not clear. Transcriptional profiling analysis in Per2 knockout (KO) mice may provide a valuable tool to identify potential genetic involvement and pathways in enhanced behavioral responses against drugs. To explore the potential genetic involvement, we examined common differentially expressed genes (DEGs) in the striatum of drug naïve Per2 KO/wild-type (WT) mice, and before/after METH treatment in Per2 KO mice, but not in WT mice. We selected 9 common DEGs (Ncald, Cpa6, Pklr, Ttc29, Cbr2, Egr2, Prg4, Lcn2, and Camsap2) based on literature research. Among the common DEGs, Ncald, Cpa6, Pklr, and Ttc29 showed higher expression levels in drug naïve Per2 KO mice than in WT mice, while they were downregulated in Per2 KO mice after METH treatment. In contrast, Cbr2, Egr2, Prg4, Lcn2, and Camsap2 exhibited lower expression levels in drug naïve Per2 KO mice than in WT mice, while they were upregulated after METH treatment in Per2 KO mice. qRT-PCR analyses validated the expression patterns of 9 target genes before/after METH treatment in Per2 KO and WT mice. Although further research is required to deeply understand the relationship and roles of the 9 target genes in drug addiction, the findings from the present study indicate that the target genes might play important roles in drug addiction.

Can chronopharmacology improve the therapeutic management of neurological diseases?

The importance of circadian rhythm dysfunctions in the pathophysiology of neurological diseases has been highlighted recently. Chronopharmacology principles imply that tailoring the timing of treatments to the circadian rhythm of individual patients could optimize therapeutic management. According to these principles, chronopharmacology takes into account the individual differences in patients' clocks, the rhythmic changes in the organism sensitivity to therapeutic and side effects of drugs, and the predictable time variations of disease. This review examines the current literature on chronopharmacology of neurological diseases focusing its scope on epilepsy, Alzheimer and Parkinson diseases, and neuropathic pain, even if other neurological diseases could have been analyzed. While the results of the studies discussed in this review point to a potential therapeutic benefit of chronopharmacology in neurological diseases, the field is still in its infancy. Studies including a sufficiently large number of patients and measuring gold standard markers of the circadian rhythmicity are still needed to evaluate the beneficial effect of administration times over the 24-hour day but also of clock modulating drugs.

Circadian rhythms and substance use disorders: A bidirectional relationship

The circadian system organizes circadian rhythms (biological cycles that occur around 24 h) that couple environmental cues (zeitgebers) with internal functions of the organism. The misalignment between circadian rhythms and external cues is known as chronodisruption and contributes to the development of mental, metabolic and other disorders, including cancer, cardiovascular diseases and addictive disorders. Drug addiction represents a global public health concern and affects the health and well-being of individuals, families and communities. In this manuscript, we reviewed evidence indicating a bidirectional relationship between the circadian system and the development of addictive disorders. We provide information on the interaction between the circadian system and drug addiction for each drug or drug class (alcohol, cannabis, hallucinogens, psychostimulants and opioids). We also describe evidence showing that drug use follows a circadian pattern, which changes with the progression of addiction. Furthermore, clock gene expression is also altered during the development of drug addiction in many brain areas related to drug reward, drug seeking and relapse. The regulation of the glutamatergic and dopaminergic neurocircuitry by clock genes is postulated to be the main circadian mechanism underlying the escalation of drug addiction. The bidirectional interaction between the circadian system and drug addiction seems to be mediated by the effects caused by each drug or class of drugs of abuse. These studies provide new insights on the development of successful strategies aimed at restoring/stabilizing circadian rhythms to reduce the risk for addiction development and relapse.

The circadian gene, Per2, influences methamphetamine sensitization and reward through the dopaminergic system in the striatum of mice

Drug addiction is a chronic and relapsing brain disorder, influenced by complex interactions between endogenous and exogenous factors. Per2, a circadian gene, plays a role in drug addiction. Previous studies using Per2-knockout mice have shown a role for Per2 in cocaine, morphine and alcohol addiction. In the present study, we investigated the role of Per2 in methamphetamine (METH) addiction using Per2-overexpression and knockout mice. We observed locomotor sensitization responses to METH administration, and rewarding effects using a conditioned place preference test. In addition, we measured expression levels of dopamine and dopamine-related genes (monoamine oxidase A, DA receptor 1, DA receptor 2, DA active transporter, tyrosine hydroxylase and cAMP response element-binding protein 1) in the striatum of the mice after repeated METH treatments, using qRT-PCR. Per2-overexpressed mice showed decreased locomotor sensitization and rewarding effects of METH compared to the wildtype mice, whereas the opposite was observed in Per2 knockout mice. Both types of transgenic mice showed altered expression levels of dopamine-related genes after repeated METH administration. Specifically, we observed lower dopamine levels in Per2-overexpressed mice and higher levels in Per2-knockout mice. Taken together, Per2 expression levels may influence the addictive effects of METH through the dopaminergic system in the striatum of mice.

Emerging relevance of circadian rhythms in headaches and neuropathic pain

Circadian rhythms of physiology are the keys to health and fitness, as dysregulation, by genetic mutations or environmental factors, increases disease risk and aggravates progression. Molecular and physiological studies have shed important light on an intrinsic clock that drives circadian rhythms and serves essential roles in metabolic homoeostasis, organ physiology and brain functions. One exciting new area in circadian research is pain, including headache and neuropathic pain for which new mechanistic insights have recently emerged. For example, cluster headache is an intermittent pain disorder with an exceedingly precise circadian timing, and preliminary evidence is emerging linking several circadian components (eg, Clock and Nr1d1) with the disease. In this review, we first discuss the broad metabolic and physiological relevance of the circadian timing system. We then provide a detailed review of the circadian relevance in pain disease and physiology, including cluster headache, migraine, hypnic headache and neuropathic pain. Finally, we describe potential therapeutic implications, including existing pain medicines and novel clock-modulating compounds. The physiological basis for the circadian rhythms in pain is an exciting new area of research with profound basic and translational impact.

The Intertwined Roles of Circadian Rhythms and Neuronal Metabolism Fueling Drug Reward and Addiction

Drug addiction is a highly prevalent and devastating disorder with few effective treatments, resulting in enormous burdens on family and society. The cellular and behavioral effects of drugs of abuse are related to their abilities to elevate synaptic dopamine levels. Midbrain dopaminergic neurons projecting from the ventral tegmental area to the nucleus accumbens play crucial roles in substance-induced neural and behavioral plasticity. Significantly, increasing work suggests that interplay between the brain circadian system and the cellular bioenergetic machinery in these dopamine neurons plays a critical role in mediating the actions of drugs of abuse. Here, we describe recent progress in elucidating the interconnections between circadian and metabolic systems at the molecular and cellular levels and their relationships to modulation of drug reward and addiction.

Neurobiological Functions of the Period Circadian Clock 2 Gene, Per2

Most organisms have adapted to a circadian rhythm that follows a roughly 24-hour cycle, which is modulated by both internal (clock-related genes) and external (environment) factors. In such organisms, the central nervous system (CNS) is influenced by the circadian rhythm of individual cells. Furthermore, the period circadian clock 2 (Per2) gene is an important component of the circadian clock, which modulates the circadian rhythm. Per2 is mainly expressed in the suprachiasmatic nucleus (SCN) of the hypothalamus as well as other brain areas, including the midbrain and forebrain. This indicates that Per2 may affect various neurobiological activities such as sleeping, depression, and addiction. In this review, we focus on the neurobiological functions of Per2, which could help to better understand its roles in the CNS.

Drosophila: An Emergent Model for Delineating Interactions between the Circadian Clock and Drugs of Abuse

Endogenous circadian oscillators orchestrate rhythms at the cellular, physiological, and behavioral levels across species to coordinate activity, for example, sleep/wake cycles, metabolism, and learning and memory, with predictable environmental cycles. The 21st century has seen a dramatic rise in the incidence of circadian and sleep disorders with globalization, technological advances, and the use of personal electronics. The circadian clock modulates alcohol- and drug-induced behaviors with circadian misalignment contributing to increased substance use and abuse. Invertebrate models, such as Drosophila melanogaster, have proven invaluable for the identification of genetic and molecular mechanisms underlying highly conserved processes including the circadian clock, drug tolerance, and reward systems. In this review, we highlight the contributions of Drosophila as a model system for understanding the bidirectional interactions between the circadian system and the drugs of abuse, alcohol and cocaine, and illustrate the highly conserved nature of these interactions between Drosophila and mammalian systems. Research in Drosophila provides mechanistic insights into the corresponding behaviors in higher organisms and can be used as a guide for targeted inquiries in mammals.

mPer1 promotes morphine-induced locomotor sensitization and conditioned place preference via histone deacetylase activity

RATIONALE

Previous studies have shown that repeated exposure to drugs of abuse is associated with changes in clock genes expression and that mice strains with various mutations in clock genes show alterations in drug-induced behaviors.

OBJECTIVE

The objective of this study is to characterize the role of the clock gene mPer1 in the development of morphine-induced behaviors and a possible link to histone deacetylase (HDAC) activity.

METHODS

In Per1 ^Brdm1 null mutant mice and wild-type (WT) littermates, we examined whether there were any differences in the development of morphine antinociception, tolerance to antinociception, withdrawal, sensitization to locomotion, and conditioned place preference (CPP).

RESULTS

Per1 ^Brdm1 mutant mice did not show any difference in morphine antinociception, tolerance development, nor in physical withdrawal signs precipitated by naloxone administration compared to WT. However, morphine-induced locomotor sensitization and CPP were significantly impaired in Per1 ^Brdm1 mutant mice. Because a very similar dissociation between tolerance and dependence vs. sensitization and CPP was recently observed after the co-administration of morphine and the HDAC inhibitor sodium butyrate (NaBut), we studied a possible link between mPer1 and HDAC activity. As opposed to WT controls, Per1 ^Brdm1 mutant mice showed significantly enhanced striatal global HDAC activity within the striatum when exposed to a locomotor-sensitizing morphine administration regimen. Furthermore, the administration of the HDAC inhibitor NaBut restored the ability of morphine to promote locomotor sensitization and reward in Per1 ^Brdm1 mutant mice.

CONCLUSIONS

Our results reveal that although the mPer1 gene does not alter morphine-induced antinociception nor withdrawal, it plays a prominent role in the development of morphine-induced behavioral sensitization and reward via inhibitory modulation of striatal HDAC activity. These data suggest that PER1 inhibits deacetylation to promote drug-induced neuroplastic changes.

Clock genes × stress × reward interactions in alcohol and substance use disorders

Adverse life events and highly stressful environments have deleterious consequences for mental health. Those environmental factors can potentiate alcohol and drug abuse in vulnerable individuals carrying specific genetic risk factors, hence producing the final risk for alcohol- and substance-use disorders development. The nature of these genes remains to be fully determined, but studies indicate their direct or indirect relation to the stress hypothalamo-pituitary-adrenal (HPA) axis and/or reward systems. Over the past decade, clock genes have been revealed to be key-players in influencing acute and chronic alcohol/drug effects. In parallel, the influence of chronic stress and stressful life events in promoting alcohol and substance use and abuse has been demonstrated. Furthermore, the reciprocal interaction of clock genes with various HPA-axis components, as well as the evidence for an implication of clock genes in stress-induced alcohol abuse, have led to the idea that clock genes, and Period genes in particular, may represent key genetic factors to consider when examining gene × environment interaction in the etiology of addiction. The aim of the present review is to summarize findings linking clock genes, stress, and alcohol and substance abuse, and to propose potential underlying neurobiological mechanisms.

Circadian rhythms and addiction: mechanistic insights and future directions

Circadian rhythms are prominent in many physiological and behavioral functions. Circadian disruptions either by environmental or molecular perturbation can have profound health consequences, including the development and progression of addiction. Both animal and humans studies indicate extensive bidirectional relationships between the circadian system and drugs of abuse. Addicted individuals display disrupted rhythms, and chronic disruption or particular chronotypes may increase the risk for substance abuse and relapse. Moreover, polymorphisms in circadian genes and an evening chronotype have been linked to mood and addiction disorders, and recent efforts suggest an association with the function of reward neurocircuitry. Animal studies are beginning to determine how altered circadian gene function results in drug-induced neuroplasticity and behaviors. Many studies suggest a critical role for circadian rhythms in reward-related pathways in the brain and indicate that drugs of abuse directly affect the central circadian pacemaker. In this review, we highlight key findings demonstrating the importance of circadian rhythms in addiction and how future studies will reveal important mechanistic insights into the involvement of circadian rhythms in drug addiction.

The ClockΔ19 mutation in mice fails to alter the primary and secondary reinforcing properties of nicotine

BACKGROUND

Clock genes have been demonstrated to play a role in behavioral responses to a variety of drugs of abuse, including cocaine, amphetamine, morphine, and ethanol. However, no studies to date have examined the role of Clock genes on nicotine-mediated behaviors. We examined the involvement of Clock, one of several Clock genes, on the effects of nicotine by examining mice with the ClockΔ19 mutation in behaviors commonly used to assess drug effects in rodents.

METHODS

We first measured the locomotor effects of nicotine in mutants and wild type mice in response to repeated nicotine injections (0.175 mg/kg, IP). To assess the secondary properties of nicotine, we measured the ability of nicotine (0.175 mg/kg, IP) to induce a conditioned place preference. Finally, we measured the primary reinforcing properties of nicotine at two doses (0.01 and 0.03 mg/kg/infusion, IV) using the self-administration paradigm.

RESULTS

Mutant mice demonstrated no difference in magnitude of the sensitized response to nicotine as compared to wild-type controls. In the conditioned place preference paradigm, mutant and wild-type mice demonstrated a similar preference for a nicotine-paired environment. And finally, mutant and wild-type mice demonstrated a similar acquisition of nicotine self-administration, as indicated by the number of responses on a nicotine-paired lever and the number of nicotine reinforcers achieved during sessions.

CONCLUSIONS

The ClockΔ19 mutation appears to have no effect on the reinforcing properties of nicotine, in contrast to its demonstrated role in cocaine reinforcement. Further studies are needed to determine the effect of other Clock genes on nicotine reinforcement.

Differential regulation of the period genes in striatal regions following cocaine exposure

Several studies have suggested that disruptions in circadian rhythms contribute to the pathophysiology of multiple psychiatric diseases, including drug addiction. In fact, a number of the genes involved in the regulation of circadian rhythms are also involved in modulating the reward value for drugs of abuse, like cocaine. Thus, we wanted to determine the effects of chronic cocaine on the expression of several circadian genes in the Nucleus Accumbens (NAc) and Caudate Putamen (CP), regions of the brain known to be involved in the behavioral responses to drugs of abuse. Moreover, we wanted to explore the mechanism by which these genes are regulated following cocaine exposure. Here we find that after repeated cocaine exposure, expression of the Period (Per) genes and Neuronal PAS Domain Protein 2 (Npas2) are elevated, in a somewhat regionally selective fashion. Moreover, NPAS2 (but not CLOCK (Circadian Locomotor Output Cycles Kaput)) protein binding at Per gene promoters was enhanced following cocaine treatment. Mice lacking a functional Npas2 gene failed to exhibit any induction of Per gene expression after cocaine, suggesting that NPAS2 is necessary for this cocaine-induced regulation. Examination of Per gene and Npas2 expression over twenty-four hours identified changes in diurnal rhythmicity of these genes following chronic cocaine, which were regionally specific. Taken together, these studies point to selective disruptions in Per gene rhythmicity in striatial regions following chronic cocaine treatment, which are mediated primarily by NPAS2.

The long-term abnormalities in circadian expression of Period 1 and Period 2 genes in response to stress is normalized by agomelatine administered immediately after exposure

In mammals, the circadian and stress systems are involved in adaptation to predictable and unpredictable stimuli, respectively. A series of experiments examined the relationship between stress-induced posttraumatic stress (PTSD)-like behavioral response patterns in rats and brain levels of genes related to circadian rhythms. The effects of agomelatine, administered immediately after exposure, on stress-related behavior and on local expression of Per1 and Per2 were assessed. Animals were exposed to predator scent stress. The outcome measures included behavior in an elevated plus-maze (EPM) and acoustic startle response (ASR) 7days after the exposure. Pre-set cut-off behavioral criteria classified exposed animals according to behavioral responses in EPM and ASR paradigms as those with 'extreme behavioral response' (EBR), 'minimal behavioral response (MBR),' or 'partial behavioral response' (PBR). Per1 and Per2 expression in hippocampal subregions, frontal cortex and suprachiasmatic nucleus (SCN) 8days after exposure were evaluated using immunohistochemical and RT-PCR techniques at zeitgeber-times 19 and 13. The effects of agomelatine, on behavioral tests were evaluated on Day 8. Local brain expression of Per1 and Per2 mRNA was subsequently assessed. Data were analyzed in relation to individual behavior patterns. Animals with extreme behavioral response (EBR) displayed a distinct pattern of Per1 and Per2 expression in the SCN, which was the opposite of that observed in the control and MBR animals. In the DG, no variation in Per2 expression was observed in the EBR and PBR animals. Immediate post-exposure treatment with agomelatine significantly reduced percentage of extreme-responders and normalized the expression of Per1 and Per2 as compared to controls. Stress-induced alterations in Per genes in the EBR animals may represent an imbalance between normally precisely orchestrated physiological and behavioral processes and psychopathological processes. These findings indicate that these circadian-related genes play a role in the neurobiological response to predator scent stress and provide supportive evidence that the use of agomelatine immediately after traumatic experience may be protective against the subsequent development of PTSD.

Endogenous opiates and behavior: 2010

This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

When brain clocks lose track of time: cause or consequence of neuropsychiatric disorders

Patients suffering from neuropsychiatric disorders often exhibit a loss of regulation of their biological rhythms which leads to altered sleep/wake cycle, body temperature rhythm and hormonal rhythms. Whereas these symptoms have long been considered to result from the pathology of the underlying disease, increasing evidence now indicates that the circadian system may be more directly involved in the etiology of psychiatric disorders. This emerging view originated with the discovery that the genes involved in the generation of biological rhythms are expressed in many brain structures where clocks function-and perhaps malfunction. It is also due to the interesting phenotypes of clock mutant mice. Here we summarize recent reports showing that alteration of circadian clocks within key brain regions associated with neuropsychiatric disorders may be an underlying cause of the development of mental illness. We discuss how these alterations take place at both systems and molecular levels.

Daily morphine injection and withdrawal disrupt 24-h wheel running and PERIOD2 expression patterns in the rat limbic forebrain

Symptoms of opiate withdrawal include disturbances in circadian rhythms. We examined in male Wistar rats (n=48) the effects of a daily, mid-morning morphine injection (5-40 mg/kg, i.p.) and its withdrawal on 24-h wheel-running activity and on the expression of the clock protein, PERIOD2 (PER2), in the suprachiasmatic nucleus (SCN), oval nucleus of the bed nucleus of the stria terminalis (BNSTov), central amygdala (CEA), and dorsal striatum. Rats were killed over 2 days at 10, 22, 46, and 58 h after the last daily morphine injection at zeitgeber times (ZT) 1 or ZT13. Daily morphine injections and their withdrawal suppressed nighttime wheel running, but did not entrain any increase in activity in advance of the injection. Neither morphine injection nor its withdrawal affected PER2 expression in the SCN, whereas the normal daily peaks of PER2 in the BNSTov, CEA, and dorsal striatum were blunted both during morphine administration and its withdrawal. Treatment with a dopaminergic agonist (the D2/3 agonist, quinpirole, 1.0 mg/kg) or a noradrenergic agonist (alpha2 agonist, clonidine, 0.1 mg/kg) in morphine withdrawal did not restore normal PER2 patterns in each affected region; however, both quinpirole and clonidine themselves altered normal daily PER2 expression patterns in morphine-naive rats. These findings confirm and extend previous observations that opiates disrupt daily patterns of clock gene expression in the limbic forebrain. Furthermore, catecholaminergic drugs, which have been previously found to alleviate symptoms of opiate withdrawal, do not alleviate the effects of morphine withdrawal on PER2, but do modulate daily patterns of PER2 expression in saline controls.