Environmental enrichment decreases the rewarding but not the activating effects of heroin

Physical exercise and synaptic protection in human and pre-clinical models of multiple sclerosis

In multiple sclerosis, only immunomodulatory and immunosuppressive drugs are recognized as disease-modifying therapies. However, in recent years, several data from pre-clinical and clinical studies suggested a possible role of physical exercise as disease-modifying therapy in multiple sclerosis. Current evidence is sparse and often conflicting, and the mechanisms underlying the neuroprotective and antinflammatory role of exercise in multiple sclerosis have not been fully elucidated. Data, mainly derived from pre-clinical studies, suggest that exercise could enhance long-term potentiation and thus neuroplasticity, could reduce neuroinflammation and synaptopathy, and dampen astrogliosis and microgliosis. In humans, most trials focused on direct clinical and MRI outcomes, as investigating synaptic, neuroinflammatory, and pathological changes is not straightforward compared to animal models. The present review analyzed current evidence and limitations in research concerning the potential disease-modifying therapy effects of exercise in multiple sclerosis in animal models and human studies.

Neighborhood Vigilance in Terms of Abstinence Expectancies for Smoking and Severity of Problems When Quitting

Background: Although social determinants of health (SDoH) have increasingly been understood as clinically important factors in the onset, maintenance, and relapse of substance use behavior, little research has evaluated neighborhood vigilance in terms of smoking. Objectives: The present investigation sought to evaluate the role of neighborhood vigilance in terms of smoking abstinence expectancies (i.e., perceived consequences of refraining from smoking, including negative mood, somatic symptoms, harmful consequences, and positive consequences) and severity of problems when trying to quit among adults who smoke. Results: Participants included 93 treatment-seeking people who smoke (45.2 years of age and 29% identified as female). Results: indicated that greater levels of neighborhood vigilance were associated with negative mood and harmful consequences abstinence expectancies. No effect was evident for somatic symptom abstinence expectancies after Bonferroni correction. Conclusions: As expected, neighborhood vigilance was not predictive of positive abstinence expectancies, offering explanatory specificity. Neighborhood vigilance was also associated with more severe problems when trying to quit smoking. The current findings suggest neighborhood vigilance represents an important contextual factor involved in certain negative beliefs about abstinence and challenges in quitting.

Gestational environmental enrichment prevents chronic social stress induced anxiety- and ethanol-related behaviors in offspring

Epidemiological surveys have shown a strong relationship between maternal stress and offspring's mood disorders. Growing evidence suggested that environmental enrichment (EE) improves cognitive function in models of psychiatric and neurological disorders. However, the potential protective effects of gestational EE on social stress-elicited mood disorders in offspring have not been studied. Knowing that the undeveloped brain is more sensitive to gestational environmental stimuli, we hypothesized that initiating cognitive stimulation, during gestation, would protect against social stress-induced behavioral alterations in adulthood. Therefore, the present study aimed to investigate the effects of gestational EE on social stress-elicited anxiety- and ethanol-related behaviors in adult offspring. EE consisted of free access, of dams, to tubular devices of different shapes, colors, and sizes that were changed regularly. After birth and weaning, young adult offspring were exposed to 19 days of social stress and anxiety-like behavior was evaluated by elevated plus maze, open field, and marbles burying tests. The two-bottle choice (TBC) drinking paradigm was used to assess stress-induced ethanol intake. Results showed that gestational EE prevented social stress-elicited anxiogenic-like effects with no differences in spontaneous locomotor activity. Moreover, in the TBC paradigm, mice pre-exposed to EE consistently showed a significantly decreased consumption and preference for ethanol with no effects on tastants' intakes. Interestingly, gestational EE increased serum BDNF levels, which showed a correlation with measures of anxiety- and ethanol-related behaviors. These findings indicate that some neurodevelopmental changes associated with prenatal EE may counteract adult social stress-induced behavioral alterations through a BDNF mechanism. Therefore, we propose that gestational EE has significant protective and beneficial effects on social stress-induced cognitive impairment. It can also alleviate anxiety-like behavior and subsequent excessive alcohol consumption.

Esketamine Inhibits Cocaine-Seeking Behaviour Subsequent to Various Abstinence Conditions in Rats

BACKGROUND

Cocaine use disorder (CUD) is a relapsing brain disease caused by a chronic drug intake that involves neural mechanisms and psychological processes, including depression. Preclinical and clinical studies have demonstrated the promise of pharmacological drugs in controlling the reinstatement of cocaine by targeting the N-methyl-D-aspartate (NMDA) receptor. Recent evidence has revealed that esketamine, a (S) enantiomer of ketamine, shows a high affinity to NMDA receptors and has been used in clinical trials to treat moderate-to-severe depression.

METHODS

In the present paper, we investigated the effects of esketamine in regulating cocaine-seeking behaviour induced through the use of cocaine (10 mg/kg) or the cocaine-associated conditioned cue after a short (10 days)-lasting period of drug abstinence with extinction training, home cage or enrichment environment conditions in male rats. Furthermore, we investigated the acute effects of esketamine on locomotor activity in drug-naïve animals.

RESULTS

Esketamine (2.5-10 mg/kg) administered peripherally attenuated the reinstatement induced with cocaine priming or the drug-associated conditioned cue after different conditions of abstinence.

CONCLUSIONS

These results seem to support esketamine as a candidate for the pharmacological management of cocaine-seeking and relapse prevention; however, further preclinical and clinical research is needed to better clarify esketamine's actions in CUD.

The systemic effects of the enriched environment on the conditioned fear reaction

In this review, a hypothesis is proposed to explain the beneficial effect of an enriched environment (EE) on the conditioned fear reaction (CFR) from the perspective of a functional system of behavioral control. According to the hypothesis, the EE affects all behavioral act components, including the processing of sensory information, memory, motivational and reinforcing systems, and motor activities, which weakens the CFR. Animals raised in the EE have effects that are comparable to those of context (CTX) and CS pre-exposures at latent inhibition. An abundance of stimuli in the EE and constant contact with them provide the formation of CS-noUS and CTX-noUS connections that later, during CFR learning, slow down and diminish fear. The EE also contributes to faster processing of information and habituation to it. As a result, many stimuli in the context lose their significance, and subjects simply ignore them. And finally, the EE affects the motivational and reinforcing brain mechanisms, induces an impairment of search activity, and worsens memory consolidation, which leads to a reduction of CFR.

MSK1 is required for the beneficial synaptic and cognitive effects of enriched experience across the lifespan

Positive experiences, such as social interaction, cognitive training and physical exercise, have been shown to ameliorate some of the harms to cognition associated with ageing. Animal models of positive interventions, commonly known as environmental enrichment, strongly influence neuronal morphology and synaptic function and enhance cognitive performance. While the profound structural and functional benefits of enrichment have been appreciated for decades, little is known as to how the environment influences neurons to respond and adapt to these positive sensory experiences. We show that adult and aged male wild-type mice that underwent a 10-week environmental enrichment protocol demonstrated improved performance in a variety of behavioural tasks, including those testing spatial working and spatial reference memory, and an enhancement in hippocampal LTP. Aged animals in particular benefitted from enrichment, performing spatial memory tasks at levels similar to healthy adult mice. Many of these benefits, including in gene expression, were absent in mice with a mutation in an enzyme, MSK1, which is activated by BDNF, a growth factor implicated in rodent and human cognition. We conclude that enrichment is beneficial across the lifespan and that MSK1 is required for the full extent of these experience-induced improvements of cognitive abilities, synaptic plasticity and gene expression.

Claustral neurons projecting to frontal cortex restrict opioid consumption

The synthetic opioid fentanyl is a major contributor to the current opioid addiction crisis. We report that claustral neurons projecting to the frontal cortex limit oral fentanyl self-administration in mice. We found that fentanyl transcriptionally activates frontal-projecting claustrum neurons. These neurons also exhibit a unique suppression of Ca²⁺ activity upon initiation of bouts of fentanyl consumption. Optogenetic stimulation of frontal-projecting claustral neurons, intervening in this suppression, decreased bouts of fentanyl consumption. In contrast, constitutive inhibition of frontal-projecting claustral neurons in the context of a novel, group-housed self-administration procedure increased fentanyl bout consumption. This same manipulation also sensitized conditioned-place preference for fentanyl and enhanced the representation of fentanyl experience in the frontal cortex. Together, our results indicate that claustrum neurons exert inhibitory control over frontal cortical neurons to restrict oral fentanyl intake. Upregulation of activity in the claustro-frontal projection may be a promising strategy for reducing human opioid addiction.

Neurobehavioral effects of environmental enrichment and drug abuse vulnerability: An updated review

Environmental enrichment consisting of social peers and novel objects is known to alter neurobiological functioning and have an influence on the behavioral effects of drugs of abuse in preclinical rodent models. An earlier review from our laboratory (Stairs and Bardo, 2009) provided an overview of enrichment-specific changes in addiction-like behaviors and neurobiology. The current review updates the literature in this extensive field. Key findings from this updated review indicate that enrichment produces positive outcomes in drug abuse vulnerability beyond just psychostimulants. Additionally, recent studies indicate that enrichment activates key genes involved in cell proliferation and protein synthesis in nucleus accumbens and enhances growth factors in hippocampus and neurotransmitter signaling pathways in prefrontal cortex, amygdala, and hypothalamus. Remaining gaps in the literature and future directions for environmental enrichment and drug abuse research are identified.

Bored at home?—A systematic review on the effect of environmental enrichment on the welfare of laboratory rats and mice

Boredom is an emotional state that occurs when an individual has nothing to do, is not interested in the surrounding, and feels dreary and in a monotony. While this condition is usually defined for humans, it may very well describe the lives of many laboratory animals housed in small, barren cages. To make the cages less monotonous, environmental enrichment is often proposed. Although housing in a stimulating environment is still used predominantly as a luxury good and for treatment in preclinical research, enrichment is increasingly recognized to improve animal welfare. To gain insight into how stimulating environments influence the welfare of laboratory rodents, we conducted a systematic review of studies that analyzed the effect of enriched environment on behavioral parameters of animal well–being. Remarkably, a considerable number of these parameters can be associated with symptoms of boredom. Our findings show that a stimulating living environment is essential for the development of natural behavior and animal welfare of laboratory rats and mice alike, regardless of age and sex. Conversely, confinement and under-stimulation has potentially detrimental effects on the mental and physical health of laboratory rodents. We show that boredom in experimental animals is measurable and does not have to be accepted as inevitable.

Valuing the Diversity of Research Methods to Advance Nutrition Science

The ASN Board of Directors appointed the Nutrition Research Task Force to develop a report on scientific methods used in nutrition science to advance discovery, interpretation, and application of knowledge in the field. The genesis of this report was growing concern about the tone of discourse among nutrition professionals and the implications of acrimony on the productive study and translation of nutrition science. Too often, honest differences of opinion are cast as conflicts instead of areas of needed collaboration. Recognition of the value (and limitations) of contributions from well-executed nutrition science derived from the various approaches used in the discipline, as well as appreciation of how their layering will yield the strongest evidence base, will provide a basis for greater productivity and impact. Greater collaborative efforts within the field of nutrition science will require an understanding that each method or approach has a place and function that should be valued and used together to create the nutrition evidence base. Precision nutrition was identified as an important emerging nutrition topic by the preponderance of task force members, and this theme was adopted for the report because it lent itself to integration of many approaches in nutrition science. Although the primary audience for this report is nutrition researchers and other nutrition professionals, a secondary aim is to develop a document useful for the various audiences that translate nutrition research, including journalists, clinicians, and policymakers. The intent is to promote accurate, transparent, verifiable evidence-based communication about nutrition science. This will facilitate reasoned interpretation and application of emerging findings and, thereby, improve understanding and trust in nutrition science and appropriate characterization, development, and adoption of recommendations.

Environmental Enrichment Components Required to Reduce Methamphetamine-Induced Behavioral Sensitization in Mice: Examination of Behaviors and Neural Substrates

Environmental enrichment (EE) involves the presentation of various sensory, physical, social, and cognitive stimuli in order to alter neural activity in specific brain areas, which can ameliorate methamphetamine (MAMPH)-induced behavioral sensitization and comorbid anxiety symptoms. No previous studies have comprehensively examined which EE components are critical for effectively reducing MAMPH-induced behavioral sensitization and anxiety. This study examined different housing conditions, including standard housing (SH, No EE), standard EE (STEE), physical EE (PEE), cognitive EE (CEE), and social EE (SEE). In the beginning, mice were randomly assigned to the different combinations of housing conditions and injections, consisting of No EE/Saline, No EE/MAMPH, STEE/MAMPH, PEE/MAMPH, CEE/MAMPH, and SEE/MAMPH groups. Then, the mice received intraperitoneal injections of 1 mg/kg MAMPH or normal saline daily for 7 days, followed by a final injection of 0.5 mg/kg MAMPH or normal saline. After behavioral tests, all mice were examined for c-Fos immunohistochemical staining. The results showed that MAMPH induced behavioral sensitization as measured by distance traveled. MAMPH appeared to induce lowered anxiety responses and severe hyperactivity. All EE conditions did not affect MAMPH-induced lowered anxiety behaviors. STEE was likely more effective for reducing MAMPH-induced behavioral sensitization than PEE, CEE, and SEE. The c-Fos expression analysis showed that the medial prefrontal cortex (i.e., cingulate cortex 1 (Cg1), prelimbic cortex (PrL), and infralimbic cortex (IL)), nucleus accumbens (NAc), basolateral amygdala (BLA), ventral tegmental area (VTA), caudate-putamen (CPu), and hippocampus (i.e., CA1, CA3, and dentate gyrus (DG)) contributed to MAMPH-induced behavioral sensitization. The Cg1, IL, NAc, BLA, VTA, CPu, CA3, and DG also mediated STEE reductions in MAMPH-induced behavioral sensitization. This study indicates that all components of EE are crucial for ameliorating MAMPH-induced behavioral sensitization, as no individual EE component was able to effectively reduce MAMPH-induced behavioral sensitization. The present findings provide insight into the development of non-pharmacological interventions for reducing MAMPH-induced behavioral sensitization.

Environmental enrichment reduces heroin seeking following incubation of craving in both male and female rats

BACKGROUND

Contemporary treatments for heroin use disorder demonstrate only limited efficacy when the goals are long term abstinence and prevention of relapse. We have demonstrated that environmental enrichment (EE) reduces cue-induced heroin reinstatement in male rats. The present study is an attempt to extend the "anti-relapse" effects of EE to female rats and to periods where incubation of craving is hypothesized to occur.

METHODS

This experiment implemented a 3-phase procedure. In Phase 1, male and female rats were trained to self-administer heroin for 15 days. Phase 2 consisted of a 3- or 15-day forced abstinence (FA) period. In Phase 3 half of the rats were placed into EE and the other half in non-EE housing and subsequently tested for responding in extinction (no heroin or cues) for 15 days followed by a cue-induced reinstatement test.

RESULTS

We found that rats in the 15 days FA condition showed significantly enhanced drug seeking during extinction, irrespective of sex. We also found that EE significantly reduced this effect. During reinstatement, EE significantly reduced drug seeking in male and female rats and in both 3- and 15-day FA groups.

CONCLUSIONS

EE, with or without prolonged FA, effectively reduced heroin seeking in male and female rats. These findings indicate that EE can reduce drug-seeking in males and females and when putative incubation of craving (i.e., prolonged abstinence period) has occurred and suggest that it may aid in the development of future long-term behavioral treatments for individuals at risk for heroin relapse.

Is It Possible to Shift from Down to Top Rank? A Focus on the Mesolimbic Dopaminergic System and Cocaine Abuse

Impaired social behavior is a common feature of many psychiatric disorders, in particular with substance abuse disorders. Switching the preference of the substance-dependent individual toward social interaction activities remains one of the major challenges in drug dependence therapy. However, social interactions yield to the emergence of social ranking. In this review, we provide an overview of the studies that examined how social status can influence the dopaminergic mesolimbic system and how drug-seeking behavior is affected. Generally, social dominance is associated with an increase in dopamine D_2/3 receptor binding in the striatum and a reduced behavioral response to drugs of abuse. However, it is not clear whether higher D₂ receptor availability is a result of increased D₂ receptor density and/or reduced dopamine release in the striatum. Here, we discuss the possibility of a potential shift from down to top rank via manipulation of the mesolimbic system. Identifying the neurobiology underlying a potential rank switch to a resilient phenotype is of particular interest in order to promote a positive coping behavior toward long-term abstinence from drugs of abuse and a protection against relapse to drugs. Such a shift may contribute to a more successful therapeutic approach to cocaine addiction.

Mirtazapine-induced decrease in cocaine sensitization is enhanced by environmental enrichment in rats

Several studies have reported that mirtazapine attenuated the induction and expression of cocaine-induced locomotor sensitization. Animals placed in enriched housing environments have shown a decrease in cocaine-induced locomotor activity and sensitization. In addition, it has been suggested that a pharmacological treatment combined with a behavioral intervention increases the efficacy of the former. Thus, the objective of this study was to determine if dosing of mirtazapine in an enriched housing environment enhanced the mirtazapine-induced decrease on the induction and expression of cocaine-induced locomotor sensitization. Wistar male rats were dosed with cocaine (10 mg/kg, i.p.). During the drug-withdrawal phase, mirtazapine (30 mg/kg, i.p.) was administered under standard and enriched housing environmental conditions. The environmental enrichment consisted of housing the animals in enclosures with plastic toys, tunnels, and running wheels. After each administration, locomotor activity for each animal was recorded for 30 min. The study found that treatment with mirtazapine in an enriched housing environment produced an enhanced and persistent attenuation of the induction and expression of cocaine-induced locomotor sensitization. Additionally, it reduced the duration of cocaine-induced locomotor activity in the expression phase of locomotor sensitization. Dosing of mirtazapine in an enriched housing environment enhanced the effectiveness of mirtazapine to decrease cocaine-induced locomotor sensitization. This suggests the potential use of enriched environments to enhance the effect of mirtazapine.

Opioid-induced structural and functional plasticity of medium-spiny neurons in the nucleus accumbens

Opioid Use Disorder (OUD) is a chronic relapsing clinical condition with tremendous morbidity and mortality that frequently persists, despite treatment, due to an individual's underlying psychological, neurobiological, and genetic vulnerabilities. Evidence suggests that these vulnerabilities may have neurochemical, cellular, and molecular bases. Key neuroplastic events within the mesocorticolimbic system that emerge through chronic exposure to opioids may have a determinative influence on behavioral symptoms associated with OUD. In particular, structural and functional alterations in the dendritic spines of medium spiny neurons (MSNs) within the nucleus accumbens (NAc) and its dopaminergic projections from the ventral tegmental area (VTA) are believed to facilitate these behavioral sequelae. Additionally, glutamatergic neurons from the prefrontal cortex, the basolateral amygdala, the hippocampus, and the thalamus project to these same MSNs, providing an enriched target for synaptic plasticity. Here, we review literature related to neuroadaptations in NAc MSNs from dopaminergic and glutamatergic pathways in OUD. We also describe new findings related to transcriptional, epigenetic, and molecular mechanisms in MSN plasticity in the different stages of OUD.

Early Growth Response Gene Upregulation in Epstein-Barr Virus (EBV)-Associated Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic multisystem disease exhibiting a variety of symptoms and affecting multiple systems. Psychological stress and virus infection are important. Virus infection may trigger the onset, and psychological stress may reactivate latent viruses, for example, Epstein-Barr virus (EBV). It has recently been reported that EBV induced gene 2 (EBI2) was upregulated in blood in a subset of ME/CFS patients. The purpose of this study was to determine whether the pattern of expression of early growth response (EGR) genes, important in EBV infection and which have also been found to be upregulated in blood of ME/CFS patients, paralleled that of EBI2. EGR gene upregulation was found to be closely associated with that of EBI2 in ME/CFS, providing further evidence in support of ongoing EBV reactivation in a subset of ME/CFS patients. EGR1, EGR2, and EGR3 are part of the cellular immediate early gene response and are important in EBV transcription, reactivation, and B lymphocyte transformation. EGR1 is a regulator of immune function, and is important in vascular homeostasis, psychological stress, connective tissue disease, mitochondrial function, all of which are relevant to ME/CFS. EGR2 and EGR3 are negative regulators of T lymphocytes and are important in systemic autoimmunity.

Environmental enrichment during forced abstinence from cocaine self-administration opposes gene network expression changes associated with the incubation effect

Environmental enrichment (EE) is a robust intervention for reducing cocaine-seeking behaviors in animals when given during forced abstinence. However, the mechanisms that underlie these effects are not well-established. We investigated the adult male rat transcriptome using RNA-sequencing (RNA-seq) following differential housing during forced abstinence from cocaine self-administration for either 1 or 21 days. Enriched, 21-day forced abstinence rats displayed a significant reduction in cocaine-seeking behavior compared to rats housed in isolation. RNA-seq of the nucleus accumbens shell revealed hundreds of differentially regulated transcripts between rats of different forced abstinence length and housing environment, as well as within specific contrasts such as enrichment (isolated 21 days vs. enriched 21 days) or incubation (isolated 1 day vs. isolated 21 days). Ingenuity Pathway Analysis affirmed several pathways as differentially enriched based on housing condition and forced abstinence length including RELN, the Eif2 signaling pathway, synaptogenesis and neurogenesis pathways. Numerous pathways showed upregulation with incubation, but downregulation with EE, suggesting that EE may prevent or reverse changes in gene expression associated with protracted forced abstinence. The findings reveal novel candidate mechanisms involved in the protective effects of EE against cocaine seeking, which may inform efforts to develop pharmacological and gene therapies for treating cocaine use disorders. Furthermore, the finding that EE opposes multiple pathway changes associated with incubation of cocaine seeking strongly supports EE as a therapeutic intervention and suggests EE is capable of preventing or reversing the widespread dysregulation of signaling pathways that occurs during cocaine forced abstinence.

Endogenous Opioids at the Intersection of Opioid Addiction, Pain, and Depression: The Search for a Precision Medicine Approach

Opioid addiction and overdose are at record levels in the United States. This is driven, in part, by their widespread prescription for the treatment of pain, which also increased opportunity for diversion by sensation-seeking users. Despite considerable research on the neurobiology of addiction, treatment options for opioid abuse remain limited. Mood disorders, particularly depression, are often comorbid with both pain disorders and opioid abuse. The endogenous opioid system, a complex neuromodulatory system, sits at the neurobiological convergence point of these three comorbid disease states. We review evidence for dysregulation of the endogenous opioid system as a mechanism for the development of opioid addiction and/or mood disorder. Specifically, individual differences in opioid system function may underlie differences in vulnerability to opioid addiction and mood disorders. We also review novel research, which promises to provide more detailed understanding of individual differences in endogenous opioid neurobiology and its contribution to opioid addiction susceptibility.

Opposite regulation of conditioned place preference and intravenous drug self-administration in rodent models: Motivational and non-motivational examples

Although developed from a common antecedent, conditioned place preference (CPP) and intravenous drug self-administration (SA) represent different behavioral paradigms, each with strong face validity. The field has treated results from these studies largely interchangeably; however, there is considerable evidence of opposite modulation of CPP vs. SA. This review outlines four manipulations that differentially affect CPP and SA based on alterations of motivation. These examples are contrasted with one example of differential CPP and SA results that can be explained by simple parallel shifts in dose-response functions. The final two examples have yet to be classified as motivation-based or parallel shifts. Important aspects, including motivation, volitional control of drug administration, reward, and the role of cues are discussed. One major conclusion of this paper is that explanations for apparent discrepancies between CPP and SA require full dose effect functions and assessment of PR breakpoints. Overall, this manuscript offers a more nuanced insight into how CPP and SA can be used to study different aspects of substance use disorders.

Environmental enrichment decreases chronic psychosocial stress-impaired extinction and reinstatement of ethanol conditioned place preference in C57BL/6 male mice

RATIONALE

During the last few decades, alcohol use disorders (AUD) have reached an epidemic prevalence, yet social influences on alcoholism have not been fully addressed. Several factors can modulate alcohol intake. On one hand, stress can reinforce ethanol-induced behaviors and be an important component in AUD and alcoholism. On the other hand, environmental enrichment (EE) has a neuroprotective role and prevents the development of excessive ethanol intake in rodents. However, studies showing the role of EE in chronic psychosocial stress-impaired ethanol-conditioned rewards are nonexistent.

AIM

The purpose of the current study is to explore the potential protective role of EE on extinction and reinstatement of ethanol-conditioned place preference (EtOH-CPP) following chronic psychosocial stress.

METHODS

In the first experiment and after the EtOH-CPP test, the mice were subjected to 15 days of chronic stress, then housed in a standard (SE) or enriched environment (EE) while EtOH-CPP extinction was achieved by repeated exposure to the CPP chambers without ethanol injection. In the second experiment and after the EtOH-CPP test, extinction was achieved as described above. Mice were then exposed to chronic stress for 2 weeks before being housed in a SE or EE. EtOH-CPP reinstatement was induced by a single exposure to the conditioning chambers.

RESULTS

As expected, stress exposure increased anxiety-like behavior and reduced weight gain. More importantly, we found that EE significantly shortened chronic stress-delayed extinction and decreased the reinstatement of EtOH-CPP.

CONCLUSION

These results support the hypothesis that EE reduces the impact of alcohol-associated environmental stimuli, and hence it may be a general intervention for reducing cue-elicited craving and relapse in humans.

Methylation in Syn and Psd95 genes underlie the inhibitory effect of oxytocin on oxycodone-induced conditioned place preference

Oxycodone (Oxy) is one of the most effective analgesics in medicine, but is associated with the development of dependence. Recent studies demonstrating epigenetic changes in the brain after exposure to opiates have provided an insight into possible mechanisms underlying addiction. Oxytocin (OT), an endogenous neuropeptide well known for preventing drug abuse, is a promising pharmacotherapy to counteract addiction. Therefore, we explored the mechanism of Oxy addiction and the role of OT in Oxy-induced epigenetic alterations. In this study, drug-induced changes in conditioned place preference (CPP), i.e. the expression of synaptic proteins and synaptic density in the ventral tegmental area (VTA) were measured. We also sought to identify DNA methyltransferases (DNMTs), ten-eleven translocations (TETs), global 5-methylcytosine (5-mC), and DNA methylation of two genes implicated in plasticity (Synaptophysin, Syn; Post-synaptic density protein 95, Psd95). Oxy (3.0 mg/kg, i.p.) induced CPP acquisition in Sprague-Dawley rats. Oxy down-regulated DNMT1 and up-regulated TET1-3, leading to a decrease in global 5-mC levels and differential demethylation at exon 1 of Syn and exon 2 of Psd95. These changes in DNA methylation of Syn and Psd95 elevated the expression of synaptic proteins (SYN, PSD95) and synaptic density in the VTA. Pretreatment with OT (2.5 µg, i.c.v.) via its receptor specifically blocked Oxy CPP, normalized synaptic density, and regulated DNMT1 and TET2-3 causing reverse of DNA demethylation of Syn and Psd95. DNA methylation is an important gene regulation mechanism underlying Oxy CPP, and OT - via its receptor - could specifically inhibit Oxy addiction.

Understanding Addiction Using Animal Models

Drug addiction is a neuropsychiatric disorder with grave personal consequences that has an extraordinary global economic impact. Despite decades of research, the options available to treat addiction are often ineffective because our rudimentary understanding of drug-induced pathology in brain circuits and synaptic physiology inhibits the rational design of successful therapies. This understanding will arise first from animal models of addiction where experimentation at the level of circuits and molecular biology is possible. We will review the most common preclinical models of addictive behavior and discuss the advantages and disadvantages of each. This includes non-contingent models in which animals are passively exposed to rewarding substances, as well as widely used contingent models such as drug self-administration and relapse. For the latter, we elaborate on the different ways of mimicking craving and relapse, which include using acute stress, drug administration or exposure to cues and contexts previously paired with drug self-administration. We further describe paradigms where drug-taking is challenged by alternative rewards, such as appetitive foods or social interaction. In an attempt to better model the individual vulnerability to drug abuse that characterizes human addiction, the field has also established preclinical paradigms in which drug-induced behaviors are ranked by various criteria of drug use in the presence of negative consequences. Separation of more vulnerable animals according to these criteria, along with other innate predispositions including goal- or sign-tracking, sensation-seeking behavior or impulsivity, has established individual genetic susceptibilities to developing drug addiction and relapse vulnerability. We further examine current models of behavioral addictions such as gambling, a disorder included in the DSM-5, and exercise, mentioned in the DSM-5 but not included yet due to insufficient peer-reviewed evidence. Finally, after reviewing the face validity of the aforementioned models, we consider the most common standardized tests used by pharmaceutical companies to assess the addictive potential of a drug during clinical trials.

Therapeutic efficacy of environmental enrichment for substance use disorders

Addiction to drug and alcohol is regarded as a major health problem worldwide for which available treatments show limited effectiveness. The biggest challenge remains to enhance the capacities of interventions to reduce craving, prevent relapse and promote long-term recovery. New strategies to meet these challenges are being explored. Findings from preclinical work suggest that environmental enrichment (EE) holds therapeutic potential for the treatment of substance use disorders, as demonstrated in a number of animal models of drug abuse. The EE intervention introduced after drug exposure leads to attenuation of compulsive drug taking, attenuation of the rewarding (and reinforcing) effects of drugs, reductions in control of behavior by drug cues, and, very importantly, relapse prevention. Clinical work also suggests that multidimensional EE interventions (involving physical activity, social interaction, vocational training, recreational and community involvement) might produce similar therapeutic effects, if implemented continuously and rigorously. In this review we survey preclinical and clinical studies assessing the efficacy of EE as a behavioral intervention for substance use disorders and address related challenges. We also review work providing empirical evidence for EE-induced neuroplasticity within the mesocorticolimbic system that is believed to contribute to the seemingly therapeutic effects of EE on drug and alcohol-related behaviors.

DRD2 and ANKK1 genes associate with late-onset heroin dependence in men

Objectives: Dopamine plays an important role in reward system of heroin dependence (HD), and dopaminergic D2 receptor (DRD2) gene is a candidate for the aetiology of HD. Ankyrin repeat and kinase domain containing 1 (ANKK1) gene is proximal to DRD2 and may influence its expression. We explored whether DRD2 and ANKK1 associate with occurrence of HD, and whether the genetic variants influence personality traits in male patients with HD.Methods:DRD2/ANKK1 polymorphisms were analysed in 950 unrelated Han Chinese male participants (601 HD patients and 349 healthy controls). All participants were screened using the same assessment tools and all patients met the diagnostic criteria of HD. Personality traits were assessed in 274 patients and 142 controls using the Tridimensional Personality Questionnaire.Results: According to the allele, genotype and haplotype frequency analysis, we observed an association between HD and several DRD2/ANKK1 polymorphisms (rs1800497, rs1800498, rs1079597 and rs4648319); this was most notable in the late-onset HD subgroup. However, these DRD2/ANKK1 polymorphisms did not associate with specific personality traits in HD patients and controls.Conclusions:DRD2/ANKK1 may play an important role in occurrence of late-onset HD, but does not mediate the relationship between personality traits and HD in Han Chinese male population.

Alternation in dopamine D2-like and metabotropic glutamate type 5 receptor density caused by differing housing conditions during abstinence from cocaine self-administration in rats

BACKGROUND

Environmental conditions have an important function in substance use disorder, increasing or decreasing the risks of relapse. Several studies strongly support the role of the dopamine D₂-like and metabotropic glutamate type 5 receptors in maladaptive neurobiological responses to cocaine reward and relapse.

AIMS

The present study employed cocaine self-administration with yoked-triad procedure in rats to explore whether drug abstinence in different housing conditions affects the drug-seeking behaviour and the dopamine D₂-like and metabotropic glutamate type 5 receptor density and affinity in several regions of the animal brain.

METHODS

Rats were trained to self-administer cocaine and later they were forced to abstain either in: (a) enriched environment or (b) isolation cage conditions to evaluate the effect of housing conditions on the drug-seeking behaviour and to assess changes concerning receptors in animals brain.

RESULTS

Our results show that exposure to enriched environment conditions strongly reduced active lever presses during cue-induced drug-seeking. At the neurochemical level, we demonstrated a significant increase in the dopamine D₂-like receptor density in the prefrontal cortex in animals following drug abstinence in isolation cage or enriched environment conditions, and the reduction in their density in the dorsal striatum provoked by isolation cage conditions. The metabotropic glutamate type 5 receptor density decreased only in the prefrontal cortex after isolation cage and enriched environment abstinence.

CONCLUSIONS

This study shows the different impacts caused by the type of housing conditions during abstinence from cocaine self-administration on drug-seeking behaviour in rats. The observed changes in the dopamine D₂-like and metabotropic glutamate type 5 receptor B_max and/or K_d values were brain-region specific and related to either pharmacological and/or motivational features of cocaine.

Treatment with 1-benzylpiperazine (BZP) during adolescence of male and female hooded rats exposed to environmental enrichment: Subsequent behavioral outcomes

From 30 days after birth until the completion of the study, male and female rats were caged in same-sexed twos or threes either with (enriched cages, EC) or without several objects for them to explore (standard cages, SC). From 41 to 50 days of age (late adolescence), they received a daily intraperitoneal injection of saline, or 10 or 20 mg/kg of the monoaminergic agonist drug of abuse, 1-benzylpiperazine (BZP). Ten days later (PND60+), their behavior was observed over several days in an open field, an elevated plus maze, a light-dark box and (to assess short-term memory) a Y maze in which one of the arms had been changed in brightness between two trials. These tests were repeated from 40 days after PND60+, namely PND100+. While open-arm occupancy at PND100+ in the plus maze was lower following both doses of the drug for SC rats only, other examples of BZP-related heightened anxiety were confined to EC rats. This suggested that enrichment had enhanced rather than reduced any anxiogenic effects of the drug treatment. There was no plausible evidence of BZP-associated impaired spatial memory required to recognize the changed novel Y-maze arm. Instead, changes in novelty preferences or neophobia-related anxiety were most likely. While there were also some examples of sex and age differences in the later effects of BZP, in most cases these were evident at both ages following treatment with both BZP doses. A number of overall BZP, cage, sex and age differences, independent of enrichment effects, were also observed.

Dopamine and addiction: what have we learned from 40 years of research

Among the neurotransmitters involved in addiction, dopamine (DA) is clearly the best known. The critical role of DA in addiction is supported by converging evidence that has been accumulated in the last 40 years. In the present review, first we describe the dopaminergic system in terms of connectivity, functioning and involvement in reward processes. Second, we describe the functional, structural, and molecular changes induced by drugs within the DA system in terms of neuronal activity, synaptic plasticity and transcriptional and molecular adaptations. Third, we describe how genetic mouse models have helped characterizing the role of DA in addiction. Fourth, we describe the involvement of the DA system in the vulnerability to addiction and the interesting case of addiction DA replacement therapy in Parkinson's disease. Finally, we describe how the DA system has been targeted to treat patients suffering from addiction and the result obtained in clinical settings and we discuss how these different lines of evidence have been instrumental in shaping our understanding of the physiopathology of drug addiction.

Expression of immediate early genes in brain reward circuitries: Differential regulation by psychostimulant and opioid drugs

Although some of the clinical manifestations of substance use disorders might be superficially similar, it is highly likely that different classes of abused drugs including opioids (heroin, morphine, and oxycodone, other opioids) and psychostimulants (cocaine and amphetamines) cause different neuroadaptations in various brain regions dependent in the distribution and concentration of their biochemical sites of actions. In fact, different molecular networks are indeed impacted by acute and chronic administration of addictive substances. Some of the genes whose expression is influenced by the administration of these substances are immediate-early genes (IEGs). IEGs include classes of low expression genes that can become very highly induced within seconds or minutes of activation by endogenous or exogenous stimuli. These IEGs might play important roles in activating target genes that regulate adaptations implicated in the behavioral manifestations diagnosed as addiction. Therefore, the purpose of this review is to provide an overview of recent data on the effects of psychostimulants and opioids on IEG expression in the brain. The review documents some contrasting effects of these classes of drugs on gene expression and indicates that further studies are necessary to identify the specific effects of each drug class when trying to predict clinical responses to therapeutic agents.

Environmental Enrichment Modulates Drug Addiction and Binge-Like Consumption of Highly Rewarding Substances: A Role for Anxiety and Compulsivity Brain Systems?

Drug addiction is a chronic disorder comprising components of both impulsivity and compulsivity in the so called “addiction cycle” which develops over time from early non-dependent, repetitive, binge-consumption to later post-dependent compulsive consumption. Thus, frequent binge-like intake is a typical pattern of excessive drug intake characteristic of the pre-dependent phase of the addiction cycle, which represent an important risk factor to develop addiction in vulnerable individuals. In this framework, it is of paramount interest to further understand the earliest stage of the addiction cycle so novel approaches would emerge aimed to control repetitive episodes of binge-consumption in non-dependent subjects, protecting vulnerable individuals from transition to dependence. Environmental enrichment (EE) is a preclinical animal model in which animals are housed under novel, social enriched conditions, which allows exercising and provides sensory and cognitive stimulation. EE promotes important improvements for a variety of cognitive processes and clear therapeutic and protective effects preventing ethanol (EtOH) and drug addiction as well. Interestingly, recent observations suggest that EE might additionally modulate binge-like intake of highly palatable caloric substances, including EtOH, which suggests the ability of EE to regulate consumption during the initial stage of the addiction cycle. We have proposed that EE protective and therapeutic effects on binge-consumption of palatable substances might primarily be mediated by the modulatory control that EE exerts on anxiety and impulsivity/compulsivity traits, which are all risk factors favoring transition to drug addiction.

Exploiting the Multifaceted Effects of Cannabinoids on Mood to Boost Their Therapeutic Use Against Anxiety and Depression

The endocannabinoid system (ECS) has been recently recognized as a prominent promoter of the emotional homeostasis, mediating the effects of different environmental signals including rewarding and stressing stimuli. The ECS modulates the rewarding effects of environmental stimuli, influencing synaptic transmission in the dopaminergic projections to the limbic system, and mediates the neurophysiological and behavioral consequences of stress. Notably, the individual psychosocial context is another key element modulating the activity of the ECS. Finally, inflammation represents an additional factor that could alter the cannabinoid signaling in the CNS inducing a "sickness behavior," characterized by anxiety, anhedonia, and depressive symptoms. The complex influences of the ECS on both the environmental and internal stimuli processing, make the cannabinoid-based drugs an appealing option to treat different psychiatric conditions. Although ample experimental evidence shows beneficial effects of ECS modulation on mood, scarce clinical indication limits the use of cannabis-based treatments. To better define the possible clinical indications of cannabinoid-based drugs in psychiatry, a number of issues should be better addressed, including genetic variability and psychosocial factors possibly affecting the individual response. In particular, better knowledge of the multifaceted effects of cannabinoids could help to understand how to boost their therapeutic use in anxiety and depression treatment.

Exposure to environmental enrichment attenuates addiction-like behavior and alters molecular effects of heroin self-administration in rats

Environmental factors profoundly affect the addictive potential of drugs of abuse and may also modulate the neuro-anatomical/neuro-chemical impacts of uncontrolled drug use and relapse propensity. This study examined the impact of environmental enrichment on heroin self-administration, addiction-related behaviors, and molecular processes proposed to underlie these behaviors. Male Sprague-Dawley rats in standard and enriched housing conditions intravenously self-administered similar amounts of heroin over 14 days. However, environmental enrichment attenuated progressive ratio, extinction, and reinstatement session responding after 14 days of enforced abstinence. Molecular mechanisms, namely DNA methylation and gene expression, are proposed to underlie abstinence-persistent behaviors. A global reduction in methylation is reported to coincide with addiction, but no differences in total genomic methylation or repeat element methylation were observed in CpG or non-CpG (CH) contexts across the mesolimbic circuitry as assessed by multiple methods including whole genome bisulfite sequencing. Immediate early gene expression associated with drug seeking, taking, and abstinence also were examined. EGR1 and EGR2 were suppressed in mesolimbic regions with heroin-taking and environmental enrichment. Site-specific methylation analysis of EGR1 and EGR2 promoter regions using bisulfite amplicon sequencing (BSAS) revealed hypo-methylation in the EGR2 promoter region and EGR1 intragenic CpG sites with heroin-taking and environmental enrichment that was associated with decreased mRNA expression. Taken together, these findings illuminate the impact of drug taking and environment on the epigenome in a locus and gene-specific manner and highlight the need for positive, alternative rewards in the treatment and prevention of drug addiction.

Environmental Enrichment During Adolescence Acts as a Protective and Therapeutic Tool for Ethanol Binge-Drinking, Anxiety-Like, Novelty Seeking and Compulsive-Like Behaviors in C57BL/6J Mice During Adulthood

Repetitive drug/ethanol (EtOH) binge-like consumption during pre-addictive stages favors a transition to addiction in vulnerable organisms. Experimental evidence points to the therapeutic and preventive effects of environmental enrichment (EE) on drug and EtOH addiction; however, little is known regarding EE modulation of binge-like consumption in non-dependent organisms. Here, we explore the impact of early EE on binge-like EtOH consumption: (1) we test whether early EE exposure prevents binge-like EtOH intake (20% v/v) in adult mice under an intermittent drinking in the dark (iDID) schedule; (2) we evaluate the therapeutic effects of EE housing conditions on binge-like EtOH consumption in adult animals; and (3) we compare novelty-seeking and compulsive-like behaviors, and anxiety-like behavior, as measured by the Hole Board (HB) and Elevated Plus Maze (EPM) tests, respectively, in adult EE/standard environment (SE) animals. Adolescent (postnatal day 28; PND28) mice were randomly allocated to two housing conditions (4 animals/cage): EE or SE. At PND67 all the animals were exposed to a schedule of EtOH binge-like iDID. On PND92 half of the animals in each environmental condition (EE and SE) were randomly allocated to two subgroups in a crossover design, where environmental conditions were kept similar to those previously experienced or switched, finally leading to four experimental conditions: EE-EE, EE-SE, SE-SE, and SE-EE. EtOH binge-like consumption continued until PND140, when EPM and HB tests were finally conducted. The main observations were: (1) EE-reared mice showed lower EtOH binge-like intake than SE-reared mice during adulthood, which supports a protective role for EE. (2) when adult EtOH drinking SE-reared mice were switched to EE conditions, a reduction in EtOH binge-like consumption was observed, suggesting a therapeutic role for EE; however, losing EE during adulthood triggered a progressive increase in EtOH binge-like intake. Moreover, (3) EE-housed adult animals with long-term exposure to EtOH binge-drinking showed lower anxiety-like, compulsive-like, and novelty-seeking behaviors than SE-housed mice, irrespective of the specific housing conditions during adolescence. We discuss the primary impact of EE on anxiety-like neurobehavioral brain systems through which it secondarily modulates EtOH binge-like drinking.

NGF gene polymorphisms are not associated with heroin dependence in a Taiwanese male population

BACKGROUND AND OBJECTIVES

Heroin dependence (HD) is a chronic relapsing brain illness with substantial heritability. Nerve growth factor (NGF) is a crucial modulator in the neurodevelopment, and may be a key mediator of reward processes in HD. The purpose of this genetic study was to investigate whether NGF gene polymorphisms associate with the occurrence of HD and the specific personality traits of patients with HD.

METHODS

We selected a homogeneous Han Chinese male population to overcome possible confounding effects of population and gender. For the study, 272 HD patients and 141 controls completed the Tridimensional Personality Questionnaire to evaluate their personality traits. In addition, a further sample 303 HD patients and 204 controls was added (with totally 920 participants) for the gene association and genotype-phenotype interaction studies.

RESULTS

Patients with HD had higher novelty seeking (NS) and harm avoidance (HA) scores than healthy subjects. Nonetheless, NGF gene polymorphisms did not associate with specific personality traits in HD patients and controls. There is no significant difference in NGF gene polymorphisms between patients with HD and controls.

DISCUSSION AND CONCLUSIONS

The NGF gene may neither contribute to the risk of development of HD, nor mediate the relationship between specific personality traits and HD in Han Chinese male population.

SCIENTIFIC SIGNIFICANCE

Patients with HD had higher novelty seeking (NS) and harm avoidance (HA) scores than healthy subjects. However, none of the polymorphisms in the NGF gene affected the NS and HA scores in both patients and healthy subjects. (Am J Addict 2018;27:516-523).

Social Influences in Animal Models of Opiate Addiction

Opiate addiction has reached an epidemic prevalence in recent years, yet social influences on the use and abuse of opiates has been widely understudied. In particular, the neurobiological substrates of opiate addiction and their modulation by social influences are largely unknown, perhaps due to the lack of widespread incorporation of social variables into animal models of opiate addiction. As reviewed here, animal models such as oral and intravenous drug self-administration, conditioned place preference, behavioral sensitization, and the effects of various stressors, have been useful in identifying some of the neurochemical circuitry that mediate social influences on opiate addiction. However, it is clear from our review that newer paradigms that incorporate various social elements are greatly needed to provide more translational insights into the neurobiological basis of opiate addiction. These elements include social and environmental enrichment, presence of conspecifics, and procedures that require subjects to exert effort to engage in prosocial behavior. A wider implementation of social variables into animal models of opiate addiction will help inform neurobehavioral strategies to increase the efficacy of treatment.

Environmental enrichment enhances conditioned place preference to ethanol via an oxytocinergic-dependent mechanism in male mice

Environmental conditions, such as stress and environmental enrichment (EE), influence predisposition to alcohol use/abuse; however, the underlying mechanisms remain unknown. To assess the effect of environmental conditions on the initial rewarding effects of alcohol, we examined conditioned place-preference (CPP) to alcohol following exposure to EE in mice. Since social context is a major factor contributing to initial alcohol-drinking, we also assessed the impact of EE on the levels of the "social neuropeptide" oxytocin (OT) and its receptor, OTR. Finally, we assessed the effect of pharmacological manipulations of the oxytocinergic system on EE-induced alcohol CPP. While EE increased sociability and reduced anxiety-like behaviors, it caused a ∼3.5-fold increase in alcohol reward compared to controls. EE triggered profound neuroadaptations of the oxytocinergic system; it increased hypothalamic OT levels and decreased OTR binding in the prefrontal cortex and olfactory nuclei of the brain. Repeated administration of the OT analogue carbetocin (6.4 mg/kg/day) mimicked the behavioral effects of EE on ethanol CPP and induced similar brain region-specific alterations of OTR binding as those observed following EE. Conversely, repeated administration of the OTR antagonist L,369-899 (5 mg/kg/day) during EE exposure, but not during the acquisition of alcohol CPP, reversed the pronounced EE-induced ethanol rewarding effect. These results demonstrate for the first time, a stimulatory effect of environmental enrichment exposure on alcohol reward via an oxytocinergic-dependent mechanism, which may predispose to alcohol abuse. This study offers a unique prospective on the neurobiological understanding of the initial stages of alcohol use/misuse driven by complex environmental-social interplay.

Environmental enrichment modulates the response to chronic stress in zebrafish

Several studies have shown that manipulations to the housing environment modulate the susceptibility to stress in laboratory animals, mainly in rodents. Environmental enrichment (EE) is one such manipulation that promotes neuroprotection and neurogenesis, besides affecting behaviors such as drug self-administration. Zebrafish are a popular and useful animal model for behavioral neuroscience studies; however, studies evaluating the impact of housing conditions in this species are scarce. In this study, we verified the effects of EE on behavioral (novel tank test) and biochemical (cortisol and reactive oxygen species (ROS)) parameters in zebrafish submitted to unpredictable chronic stress (UCS). Consistent with our previous findings, UCS increased anxiety-like behavior, cortisol and ROS levels in zebrafish. EE for 21 or 28 days attenuated the effects induced by UCS on behavior and cortisol, and prevented the effects on ROS levels. Our findings reinforce the idea that EE exerts neuromodulatory effects across species, reducing vulnerability to stress and its biochemical impact. Also, these results indicate that zebrafish is a suitable model animal to study the behavioral effects and neurobiological mechanisms related to EE.

Effects of environmental enrichment on self-administration of the short-acting opioid remifentanil in male rats

BACKGROUND

Opioid abuse is a major problem around the world. Identifying environmental factors that contribute to opioid abuse and addiction is necessary for decreasing this epidemic. In rodents, environmental enrichment protects against the development of low dose stimulant self-administration, but studies examining the effect of enrichment and isolation (compared to standard housing) on the development of intravenous opioid self-administration have not been conducted. The present study investigated the role of environmental enrichment on self-administration of the short-acting μ-opioid remifentanil.

METHODS

Rats were raised in an enriched condition (Enr), standard condition (Std), or isolated condition (Iso) beginning at 21 days of age and were trained to lever press for 1 or 3 μg/kg/infusion remifentanil in young adulthood. Acquisition of self-administration and responding during increasing fixed ratio requirements were assessed, and a dose-response curve was generated.

RESULTS

In all phases, Enr rats lever pressed significantly less than Std and Iso rats, with Enr rats pressing between 9 and 40% the amount of Iso rats. Enr rats did not acquire remifentanil self-administration when trained with 1 μg/kg/infusion, did not increase responding over increasing FR when trained at either dose, and their dose-response curves were flattened compared to Std and Iso rats. When expressed as economic demand curves, Enr rats displayed a decrease in both essential value (higher α) and reinforcer intensity (Q ₀) compared to Std and Iso rats at the 1 μg/kg/infusion training dose.

CONCLUSION

Environmental enrichment reduced remifentanil intake, suggesting that social and environmental novelty may protect against opioid abuse.

Effects of environmental enrichment upon ethanol-induced conditioned place preference and pre-frontal BDNF levels in adolescent and adult mice

Environmental enrichment (EE) provides a non-pharmacological tool to alter drug-induced reward, yet its effects on ethanol-induced reward remain controversial. We analyzed adolescent vs. adult (mice) differences in the influence of EE on ethanol-induced conditioned place preference (CPP). The effects of these treatments on brain-derived neurotrophic factor (BDNF) levels in the prefrontal cortex were examined in a separate group of animals. Ethanol-induced CPP was found in adults, and it was similar in EE and in animals reared under standard housing conditions (SC). Adolescents kept under EE, but not those in SC, exhibited CPP. Among SC, but not among EE, adolescents, BDNF levels were significantly lower in those treated with ethanol than in those given vehicle. These results indicate that, compared to adults, adolescent exhibited reduced sensitivity to ethanol’s rewarding effects, yet the youth but not the adults exhibited sensitivity to the promoting effect of EE upon CPP by ethanol. Ethanol significantly reduced BDNF levels in adolescents reared under standard housing conditions, but not in adult mice nor in adolescents given EE housing conditions. The present results add to the plethora of adolescent-specific responses to ethanol or to environmental stimuli that may put the youth at risk for escalation of ethanol intake.

Environmental enrichment reduces chronic psychosocial stress-induced anxiety and ethanol-related behaviors in mice

Previous research from our laboratory has shown that exposure to chronic psychosocial stress increased voluntary ethanol consumption and preference as well as acquisition of ethanol-induced conditioned place preference (CPP) in mice. This study was done to determine whether an enriched environment could have "curative" effects on chronic psychosocial stress-induced ethanol intake and CPP. For this purpose, experimental mice "intruders" were exposed to the chronic subordinate colony (CSC) housing for 19 consecutive days in the presence of an aggressive "resident" mouse. At the end of that period, mice were tested for their anxiety-like behavior using the elevated plus maze (EPM) test then housed in a standard or enriched environment (SE or EE respectively). Anxiety and ethanol-related behaviors were investigated using the open field (OF) test, a standard two-bottle choice drinking paradigm, and the CPP procedure. As expected, CSC exposure increased anxiety-like behavior and reduced weight gain as compared to single housed colony (SHC) controls. In addition, CSC exposure increased voluntary ethanol intake and ethanol-CPP. Interestingly, we found that EE significantly and consistently reduced anxiety and ethanol consumption and preference. However, neither tastants' (saccharin and quinine) intake nor blood ethanol metabolism were affected by EE. Finally, and most importantly, EE reduced the acquisition of CPP induced by 1.5g/kg ethanol. Taken together, these results support the hypothesis that EE can reduce voluntary ethanol intake and ethanol-induced conditioned reward and seems to be one of the strategies to reduce the behavioral deficits and the risk of anxiety-induced alcohol abuse.

The Role of Early Growth Response 1 (EGR1) in Brain Plasticity and Neuropsychiatric Disorders

It is now clearly established that complex interactions between genes and environment are involved in multiple aspects of neuropsychiatric disorders, from determining an individual's vulnerability to onset, to influencing its response to therapeutic intervention. In this perspective, it appears crucial to better understand how the organism reacts to environmental stimuli and provide a coordinated and adapted response. In the central nervous system, neuronal plasticity and neurotransmission are among the major processes integrating such complex interactions between genes and environmental stimuli. In particular, immediate early genes (IEGs) are critical components of these interactions as they provide the molecular framework for a rapid and dynamic response to neuronal activity while opening the possibility for a lasting and sustained adaptation through regulation of the expression of a wide range of genes. As a result, IEGs have been tightly associated with neuronal activity as well as a variety of higher order processes within the central nervous system such as learning, memory and sensitivity to reward. The immediate early gene and transcription factor early growth response 1 (EGR1) has thus been revealed as a major mediator and regulator of synaptic plasticity and neuronal activity in both physiological and pathological conditions. In this review article, we will focus on the role of EGR1 in the central nervous system. First, we will summarize the different factors influencing its activity. Then, we will analyze the amount of data, including genome-wide, that has emerged in the recent years describing the wide variety of genes, pathways and biological functions regulated directly or indirectly by EGR1. We will thus be able to gain better insights into the mechanisms underlying EGR1's functions in physiological neuronal activity. Finally, we will discuss and illustrate the role of EGR1 in pathological states with a particular interest in cognitive functions and neuropsychiatric disorders.

Reduction of Cocaine-Induced Locomotor Effects by Enriched Environment Is Associated with Cell-Specific Accumulation of ΔFosB in Striatal and Cortical Subregions

BACKGROUND

Early exposure to enriched environments has been shown to decrease the locomotor effects induced by repeated injections of cocaine and modify basal and cocaine-induced total protein levels of the transcription factor ΔFosB in the whole striatum of mice. In this study, we aimed at characterizing whether the profile of ΔFosB accumulation induced by enriched environments and cocaine would be similar or different in terms of brain areas and cell type.

METHODS

We used mice expressing the eGFP protein in D1 receptor positive (D1R(+)) neurons to determine whether Δ FosB induced by enriched environment or cocaine injections (5×15 mg/kg) would occur in selective subpopulations of neurons in several subregions of the striatum and prefrontal cortex.

RESULTS

We found that: (1) exposure to enriched environment reduces cocaine-induced locomotor activation, confirming our previous findings; (2) exposure to enriched environment by itself increases the accumulation of Δ FosB mostly in D1R(-) cells in the shell part of the nucleus accumbens and dorsal striatum, whereas in the nucleus accumbens core, Δ FosB accumulates in both D1R(+) and D1R(-) neurons; (3) in standard environment mice, cocaine induces accumulation of Δ FosB selectively in D1R(+) cells in the nucleus accumbens, dorsal striatum, and infralimbic cortex; and (4) the effects of enriched environments and cocaine on accumulation of Δ FosB were reciprocally blocked by their combination.

CONCLUSIONS

Altogether, these results suggest that the enriched environment-induced reduction in behavioral effects of cocaine might result from 2 distinct effects on ΔFosB in striatal medium-sized spiny neurons belonging to the direct and indirect pathways.

Sensitive periods of substance abuse: Early risk for the transition to dependence

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Early substance use dramatically increases the risk of substance use disorder (SUD).

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Although many try drugs, only a small percentage transition to SUD.

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High reactivity of reward, habit, and stress systems increase risk.

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Identification of early risk enables targeted, preventative interventions for SUD.

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Prevention must start before the sensitive adolescent period to maximize resilience.

Early adolescent substance use dramatically increases the risk of lifelong substance use disorder (SUD). An adolescent sensitive period evolved to allow the development of risk-taking traits that aid in survival; today these may manifest as a vulnerability to drugs of abuse. Early substance use interferes with ongoing neurodevelopment to induce neurobiological changes that further augment SUD risk. Although many individuals use drugs recreationally, only a small percentage transition to SUD. Current theories on the etiology of addiction can lend insights into the risk factors that increase vulnerability from early recreational use to addiction. Building on the work of others, we suggest individual risk for SUD emerges from an immature PFC combined with hyper-reactivity of reward salience, habit, and stress systems. Early identification of risk factors is critical to reducing the occurrence of SUD. We suggest preventative interventions for SUD that can be either tailored to individual risk profiles and/or implemented broadly, prior to the sensitive adolescent period, to maximize resilience to developing substance dependence. Recommendations for future research include a focus on the juvenile and adolescent periods as well as on sex differences to better understand early risk and identify the most efficacious preventions for SUD.

Rearing environment differentially modulates cocaine self-administration after opioid pretreatment: A behavioral economic analysis

BACKGROUND

Research has shown that previous experiences during development, especially if stressful, can alter an organism's response to opioids later in life. Given the previous literature on opioid modulation of cocaine self-administration, the current study raised rats in either an enriched condition (EC) or isolated condition (IC) and employed behavioral economics to study the effects of naltrexone and morphine on cocaine self-administration.

METHODS

EC and IC rats were trained to lever press for cocaine using a within-session demand procedure. This procedure measured cocaine consumption under changing cocaine price by decreasing the dose of cocaine earned throughout a session. Rats were able to self-administer cocaine on a FR1; every 10min the cocaine dose was systematically decreased (0.75-0.003mg/kg/infusion cocaine). After reaching stability on this procedure, rats were randomly pretreated with 0, 0.3, 1, or 3mg/kg naltrexone once every 3days, followed by random pretreatments of 0, 0.3, 1, or 3mg/kg morphine once every 3days. Economic demand functions were fit to each rat's cocaine consumption from each pretreatment, and appropriate mathematical parameters were extracted and analyzed.

RESULTS

Naltrexone decreased the essential value of cocaine in IC rats only. However, morphine decreased the essential value of cocaine and the consumption of cocaine at zero price in both EC and IC rats.

CONCLUSION

These results indicate that environmental experiences during development should be considered when determining the efficacy of opioid drugs, especially for the treatment of substance abuse.

Parameters for abolishing conditioned place preference for cocaine from running and environmental enrichment in male C57BL/6J mice

RATIONALE

Evidence suggests that 4 weeks of voluntary wheel running abolishes conditioned place preference (CPP) for cocaine in male C57BL/6J mice.

OBJECTIVES

To determine the duration and timing of exposure to running wheels necessary to reduce CPP, and the extent to which the running per se influences CPP as compared to environmental enrichment without running.

METHODS

A total of 239 males were conditioned for 4days twice daily with cocaine (10mg/kg) and then split into 7 intervention groups prior to 4days of CPP testing. Experiment 1 consisted of two groups housed as follows: short sedentary group (SS; n=20) in normal cages for 1 week; the short running group (SR; n=20) with running wheels for 1 week. Experiment 2 consisted of five groups housed as follows; short 1 week of running followed by a 3 week sedentary period (SRS; n=20); a 3 week sedentary period followed by 1 week of running (SSR; n=20); long sedentary group (LS; n=66) in normal cages for 4 weeks; long running group (LR; n=66) with running wheels for 4 weeks; and long environmental enrichment group (EE; n=27) with toys for 4 weeks.

RESULTS

Levels of running were similar in all running groups. Both running and environmental enrichment reduced CPP relative to sedentary groups.

CONCLUSIONS

Results suggest that the abolishment of cocaine CPP from running is robust and occurs with as low as 1 week of intervention but may be related to enrichment component of running rather than physical activity.