Daily treadmill exercise attenuates cocaine cue-induced reinstatement and cocaine induced locomotor response but increases cocaine-primed reinstatement

A historical perspective on clonidine as an alpha-2A receptor agonist in the treatment of addictive behaviors: Focus on opioid dependence

Clonidine operates through agonism at the alpha-2A receptor, a specific subtype of the alpha-2-adrenergic receptor located predominantly in the prefrontal cortex. By inhibiting the release of norepinephrine, which is responsible for withdrawal symptoms, clonidine effectively addresses withdrawal-related conditions such as anxiety, hypertension, and tachycardia. The groundbreaking work by Gold et al. demonstrated clonidine's ability to counteract the effects of locus coeruleus stimulation, reshaping the understanding of opioid withdrawal within the field. In the 1980s, the efficacy of clonidine in facilitating the transition to long-acting injectable naltrexone was confirmed for individuals motivated to overcome opioid use disorders (OUDs), including physicians and executives. Despite challenges with compliance, naltrexone offers sustained blockade of opioid receptors, reducing the risk of overdose, intoxication, and relapse in motivated patients in recovery. The development of clonidine and naltrexone as treatment modalities for OUDs, and potentially other addictions, including behavioral ones, underscores the potential for translating neurobiological advancements from preclinical models (bench) to clinical practice (bedside), ushering in innovative approaches to addiction treatment.

Potential Link Between Exercise and N-Methyl-D-Aspartate Glutamate Receptors in Alcohol Use Disorder: Implications for Therapeutic Strategies

Alcohol use disorder (AUD) is a significant risk factor, accounting for approximately 13% of all deaths in the US. AUD not only destroys families but also causes economic losses due to reduced productivity, absenteeism, and healthcare expenses. Statistics revealing the sustained number of individuals affected by AUD over the years underscore the need for further understanding of the underlying pathophysiology to advance novel therapeutic strategies. Previous research has implicated the limbic brain regions N-methyl-D-aspartate glutamate receptors (NMDAR) in the emotional and behavioral effects of AUD. Given that aerobic exercise can modulate NMDAR activity and sensitivity to alcohol, this review presents a summary of clinical and basic science studies on NMDAR levels induced by alcohol consumption, as well as acute and protracted withdrawal, highlighting the potential role of aerobic exercise as an adjunctive therapy for AUD. Based on our findings, the utility of exercise in the modulation of reward-linked receptors and AUD may be mediated by its effects on NMDA signaling. These data support further consideration of the potential of aerobic exercise as a promising adjunctive therapy for AUD.

Effect of exercise duration on toluene-induced locomotor sensitization in mice: a focus on the Renin Angiotensin System

RATIONALE

Exercise attenuates addictive behavior; however, little is known about the contribution of exercise duration to this positive effect. The Renin Angiotensin System (RAS) has been implicated both in addictive responses and in the beneficial effects of exercise; though, its role in the advantageous effects of exercise on toluene-induced addictive responses has not been explored.

OBJECTIVES

To evaluate the impact of different exercise regimens in mitigating the expression of toluene-induced locomotor sensitization and to analyze changes in RAS elements' expression at the mesocorticolimbic system after repeated toluene exposure and following voluntary wheel running in toluene-sensitized animals.

METHODS

Toluene-induced addictive-like response was evaluated with a locomotor sensitization model in mice. Toluene-sensitized animals had access to running wheels 1, 2, 4 or 24 h/day for 4 weeks; thereafter, locomotor sensitization expression was evaluated after a toluene challenge. RAS elements (ACE and ACE2 enzymes; AT1, AT2 and Mas receptors) expression was determined by Western blot in the VTA, NAc and PFCx of toluene-sensitized mice with and without exercise.

RESULTS

Individual differences in toluene-induced locomotor sensitization development were observed. Access to wheel running 1 and 2 h/day reduced but 4 and 24 h/day completely blocked locomotor sensitization expression. Repeated toluene exposure changed RAS elements' expression in the VTA, NAc and PFCx, while exercise mainly modified ACE and AT1 in air-exposed and toluene-sensitized mice.

CONCLUSIONS

Inhalant-exposed animals show different sensitization phenotypes. Exercise duration determined its efficacy to attenuate the addictive-like response. Toluene exposure and exercise each modified RAS, the latter also modifying toluene-induced changes.

Exercise Influences the Brain's Metabolic Response to Chronic Cocaine Exposure in Male Rats

Cocaine use is associated with negative health outcomes: cocaine use disorders, speedballing, and overdose deaths. Currently, treatments for cocaine use disorders and overdose are non-existent when compared to opioid use disorders, and current standard cocaine use disorder treatments have high dropout and recidivism rates. Physical exercise has been shown to attenuate addiction behavior as well as modulate brain activity. This study examined the differential effects of chronic cocaine use between exercised and sedentary rats. The effects of exercise on brain glucose metabolism (BGluM) following chronic cocaine exposure were assessed using Positron Emission Tomography (PET) and [18F]-Fluorodeoxyglucose (FDG). Compared to sedentary animals, exercise decreased metabolism in the SIBF primary somatosensory cortex. Activation occurred in the amygdalopiriform and piriform cortex, trigeminothalamic tract, rhinal and perirhinal cortex, and visual cortex. BGluM changes may help ameliorate various aspects of cocaine abuse and reinstatement. Further investigation is needed into the underlying neuronal circuits involved in BGluM changes and their association with addiction behaviors.

Selenoprotein P in a Rodent Model of Exercise; Theorizing Its Interaction with Brain Reward Dysregulation, Addictive Behavior, and Aging

Exercise promotes health and wellness, including its operation as a protective factor against a variety of psychological, neurological, and chronic diseases. Selenium and its biomarker, selenoprotein P (SEPP1), have been implicated in health, including cancer prevention, neurological function, and dopamine signaling. SEPP1 blood serum levels were compared with a one-way ANOVA between sedentary (SED), moderately exercised (MOD) [10 m/min starting at 10 min, increasing to 60 min], and high-intensity interval training (HIIT) exercised rats [30 min in intervals of 2-min followed by a 1-min break, speed progressively increased from 10 to 21 m/min]. HIIT rats showed significantly higher serum SEPP1 concentrations compared to MOD and SED. More specifically, HIIT exercise showed an 84% increase in SEPP1 levels compared to sedentary controls. MOD rats had greater serum SEPP1 concentrations compared to SED, a 33% increase. The results indicated that increased exercise intensity increases SEPP1 levels. Exercise-induced increases in SEPP1 may indicate an adaptive response to the heightened oxidative stress. Previous studies found a significant increase in dopamine D2 receptor (D2R) binding in these same rats, suggesting a potential association between SEPP1 and dopamine signaling during exercise. Modulating antioxidants like SEPP1 through personalized therapies, including exercise, has broad implications for health, disease, and addiction.

High intensity interval training exercise increases dopamine D2 levels and modulates brain dopamine signaling

Background

Previous research has outlined the health benefits of exercise including its therapeutic potential for substance use disorders (SUD). These data have already been utilized and it is now common to find exercise as part of SUD treatment and relapse prevention programs. However, we need to better understand different exercise regimens and determine which would be the most beneficial for SUDs. Recently, high intensity interval training (HIIT) has gained attention in comparison with aerobic and resistance exercise. Little is known regarding the neurobiological mechanisms of HIIT, including its effects on dopamine signaling and receptor levels in the brain. The present study examined the effects of chronic HIIT exercise on dopamine signaling as measured by dopamine type 1-like receptor (D1R)-like, dopamine type 2-like receptor (D2R)-like, and tyrosine hydroxylase (TH) quantification in the brains of male and female rats as measured by [3H] SCH 23390 and [3H] spiperone autoradiography, and TH-immunoreactive optical density values.

Methods

Rats were separated in two groups: sedentary and HIIT exercise. Exercise was on a treadmill for 30 min daily (10 3 min cycles) for six weeks with progressive speed increased up to 0.8 mph (21.5 m/min).

Results

Results showed for D2R-like binding, a significant effect across the ventral caudate putamen (V CPU) between sexes, such that mean D2R-like binding was 14% greater for males than females. In the nucleus accumbens shell (Nac Shell), the HIIT Exercise rats showed 16% greater D2R-like binding as compared to the sedentary rats. No significant effects of HIIT exercise were found across groups for brain D1R-like binding levels or TH expression.

Conclusion

These results suggest that HIIT exercise can modulate dopamine signaling by way of increased D2R. These findings support the premise that HIIT exercise plays an important role in dopamine signaling and, may provide a potential mechanism for how HIIT exercise can impact the brain and behavior.

Exercise Modifies the Brain Metabolic Response to Chronic Cocaine Exposure Inhibiting the Stria Terminalis

It is well known that exercise promotes health and wellness, both mentally and physiologically. It has been shown to play a protective role in many diseases, including cardiovascular, neurological, and psychiatric diseases. The present study examined the effects of aerobic exercise on brain glucose metabolic activity in response to chronic cocaine exposure in female Lewis rats. Rats were divided into exercise and sedentary groups. Exercised rats underwent treadmill running for six weeks and were compared to the sedentary rats. Using positron emission tomography (PET) and [18F]-Fluorodeoxyglucose (FDG), metabolic changes in distinct brain regions were observed when comparing cocaine-exposed exercised rats to cocaine-exposed sedentary rats. This included activation of the secondary visual cortex and inhibition in the cerebellum, stria terminalis, thalamus, caudate putamen, and primary somatosensory cortex. The functional network of this brain circuit is involved in sensory processing, fear and stress responses, reward/addiction, and movement. These results show that chronic exercise can alter the brain metabolic response to cocaine treatment in regions associated with emotion, behavior, and the brain reward cascade. This supports previous findings of the potential for aerobic exercise to alter the brain's response to drugs of abuse, providing targets for future investigation. These results can provide insights into the fields of exercise neuroscience, psychiatry, and addiction research.

Transcriptional Profile of Exercise-Induced Protection Against Relapse to Cocaine Seeking in a Rat Model

Background

Exercise has shown promise as a treatment for cocaine use disorder; however, the mechanism underlying its efficacy has remained elusive.

Methods

We used a rat model of relapse (cue-induced reinstatement) and exercise (wheel running, 2 hours/day) coupled with RNA sequencing to establish transcriptional profiles associated with the protective effects of exercise (during early withdrawal [days 1-7] or throughout withdrawal [days 1-14]) versus noneffective exercise (during late withdrawal [days 8-14]) against cocaine-seeking and sedentary conditions.

Results

As expected, cue-induced cocaine seeking was highest in the sedentary and late-withdrawal exercise groups; both groups also showed upregulation of a Grin1-associated transcript and enrichment of Drd1-Nmdar1 complex and glutamate receptor complex terms. Surprisingly, these glutamate markers were also enriched in the early- and throughout-withdrawal exercise groups, despite lower levels of cocaine seeking. However, a closer examination of the Grin1-associated transcript revealed a robust loss of transcripts spanning exons 9 and 10 in the sedentary condition relative to saline controls that was normalized by early- and throughout-withdrawal exercise, but not late-withdrawal exercise, indicating that these exercise conditions may normalize RNA mis-splicing induced by cocaine seeking. Our findings also revealed novel mechanisms by which exercise initiated during early withdrawal may modulate glutamatergic signaling in dorsomedial prefrontal cortex (e.g., via transcripts associated with non-NMDA glutamate receptors or those affecting signaling downstream of NMDA receptors), along with mechanisms outside of glutamatergic signaling such as circadian rhythm regulation and neuronal survival.

Conclusions

These findings provide a rich resource for future studies aimed at manipulating these molecular networks to better understand how exercise decreases cocaine seeking.

Effects of exercise of different intensities on withdrawal symptoms among people with substance use disorder: a systematic review and meta-analysis

Background: Exercise can effectively attenuate withdrawal symptoms and reduce relapse, but it is unknown whether exercise of different intensities produces different results. This study aimed to systematically review the effects of different exercise intensities on withdrawal symptoms among people with substance use disorder (SUD). Methods: Systematic searches for randomized controlled trials (RCTs) on exercise, SUD, and abstinence symptoms were conducted via electronic databases, including PubMed, up to June 2022. Study quality was evaluated using the Cochrane Risk of Bias tool (RoB 2.0) for assessment of risk of bias in randomized trials. The meta-analysis was performed by calculating the standard mean difference (SMD) in outcomes of interventions involving light-, moderate-, and high-intensity exercise for each individual study using Review Manager version 5.3 (RevMan 5.3). Results: In total, 22 RCTs (n = 1,537) were included. Overall, exercise interventions had significant effects on withdrawal symptoms, but the effect size varied with exercise intensity and by outcome measure (i.e., for different negative emotions). Light-, moderate-, and high-intensity exercise reduced cravings after the intervention [SMD = -0.71, 95% CI = (-0.90, -0.52)], and there were no statistical differences between the subgroups (p > 0.05). Light-, moderate-, and high-intensity exercise reduced depression after the intervention [light, SMD = -0.33, 95% CI = (-0.57, -0.09); moderate, SMD = -0.64, 95% CI = (-0.85, -0.42); high, SMD = -0.25, 95% CI = (-0.44, -0.05)], with moderate-intensity exercise producing the best effect (p < 0.05). Only light- and moderate-intensity exercise relieved anxiety after the intervention [light, SMD = -0.48, 95% CI = (-0.71, -0.26); moderate, SMD = -0.58, 95% CI = (-0.85, -0.31)]. Only high-intensity exercise worked in alleviating stress [SMD = -1.13, 95% CI = (-2.22, -0.04)]. Both irritability and restlessness could be improved by light- and moderate-intensity exercise [irritability, SMD = -0.74, 95% CI = (-0.98, -0.50); restless, SMD = -0.72, 95% CI = (-0.98, -0.47)], and there were no statistical differences between the subgroups (p > 0.05). Moderate- and high-intensity exercise decreased withdrawal syndrome after the intervention [moderate, SMD = -0.30, 95% CI = (-0.55, -0.05); high, SMD = -1.33, 95% CI = (-1.90, -0.76)], with high-intensity exercise producing the best effects (p < 0.01). Conclusion: Overall, exercise leads to improvements in withdrawal symptoms in individuals with SUD, but these effects vary significantly between the exercise of different intensities and according to the type of withdrawal symptoms. Moderate-intensity exercise has the greatest benefits in improving depression and anxiety; high-intensity exercise has the greatest benefits in improving withdrawal syndrome. Systematic Review Registration: www.crd.york.ac.uk/PROSPERO/, identifier, CRD42022343791.

Effects of Exercise on Testosterone and Implications of Drug Abuse: A Review

OBJECTIVE

Research points to exercise having a positive effect in fighting relapse and use of drugs of abuse. Through conducting this research, differences have been observed in the effects of exercise on drug abuse between sexes. Many of the studies found that exercise tends to cause a more profound effect in blocking drug relapse or reinstatement in males when compared with females.

METHODS

Our hypothesis is that these differences in response to drugs of abuse after an exercise regimen could in part be attributed to variations in testosterone levels between males and females.

RESULTS

Testosterone has been shown to have a modulatory impact on the dopaminergic activity in the brain, causing an effect on the brain's response to drugs of abuse. Exercise has demonstrated a causal effect on increasing testosterone levels in males, whereas drugs of abuse decrease testosterone levels in males.

CONCLUSIONS

Thus, exercise raising testosterone levels in males helps to decrease the dopaminergic response in the brain to drugs of abuse causing attenuation to drugs. To find sex-specific exercise treatments for drugs of abuse, it is important to continue researching exercise's efficacy against drugs of abuse.

Reducing short- and long-term cocaine craving with voluntary exercise in male rats

BACKGROUND

In a previous study in female rats, voluntary wheel running attenuated incubation of cocaine craving after 30 but not 3 days (Zlebnik and Carroll Zlebnik and Carroll, Psychopharmacology 232:3507-3413, 2015). The present study in male rats, using the same procedure, showed that wheel running reduced incubated craving after both 30 and 3 days of abstinence.

METHODS

Male rats self-administered i.v. cocaine (0.4 mg/kg) during 6-h sessions for 10 days. They were then moved from the operant chamber to a home cage with an attached running wheel or stationary wheel, for 6 h daily for a 3- or 30-day period when cocaine craving was hypothesized to incubate. Rats were then returned to the operant chamber for a 30-min test of cocaine seeking, or "craving," indicated by responses on the former "drug" lever was formerly associated with drug stimulus lights and responses (vs. no drug stimuli), and lever responding was compared to responses on the "inactive" that was illuminated and counted lever pressing.

RESULTS

Mean wheel revolutions were similar across the 3- and 30-day incubation groups, when both groups of rats were given access to wheel running vs. access to a stationary wheel in controls. Subsequently, when rats were tested in the operant chamber for "relapse" responding (drug-lever responding) on the lever formerly associated with drug access, cocaine craving was reduced by recent running wheel access (vs. stationary wheel access) in both the 3- and 30-day wheel exposure groups.

CONCLUSION

Voluntary, self-initiated, and self-sustained physical exercise reduced cocaine craving after short- (3 days) and long-term (30 days) abstinence periods in male rats that previously self-administered cocaine. This was contrasted with reduction of cocaine seeking in females after 30-day, but not 3-day, incubation periods under the wheel running vs. stationary wheel conditions in a previous study (Zlebnik and Carroll Zlebnik and Carroll, Psychopharmacology 232:3507-3413, 2015). These initial findings suggest males may be more sensitive to incubated craving for cocaine than females.

Exercise Modulates Brain Glucose Utilization Response to Acute Cocaine

Exercise, a proven method of boosting health and wellness, is thought to act as a protective factor against many neurological and psychological diseases. Recent studies on exercise and drug exposure have pinpointed some of the neurological mechanisms that may characterize this protective factor. Using positron emission tomography (PET) imaging techniques and the glucose analog [¹⁸F]-Fluorodeoxyglucose (¹⁸F-FDG), our team sought to identify how chronic aerobic exercise modulates brain glucose metabolism (BGluM) after drug-naïve rats were exposed to an acute dose of cocaine. Using sedentary rats as a control group, we observed significant differences in regional BGluM. Chronic treadmill exercise treatment coupled with acute cocaine exposure induced responses in BGluM activity in the following brain regions: postsubiculum (Post), parasubiculum (PaS), granular and dysgranular insular cortex (GI and DI, respectively), substantia nigra reticular (SNR) and compact part dorsal tier (SNCD), temporal association cortex (TeA), entopenduncular nucleus (EP), and crus 1 of the ansiform lobule (crus 1). Inhibition, characterized by decreased responses due to our exercise, was found in the ventral endopiriform nucleus (VEn). These areas are associated with memory and various motor functions. They also include and share connections with densely dopaminergic areas of the mesolimbic system. In conclusion, these findings suggest that treadmill exercise in rats mediates brain glucose response to an acute dose of cocaine differently as compared to sedentary rats. The modulated brain glucose utilization occurs in brain regions responsible for memory and association, spatial navigation, and motor control as well as corticomesolimbic regions related to reward, emotion, and movement.

Aerobic exercise as a promising nonpharmacological therapy for the treatment of substance use disorders

Despite the prevalence and public health impact of substance use disorders (SUDs), effective long-term treatments remain elusive. Aerobic exercise is a promising, nonpharmacological treatment currently under investigation as a strategy for preventing drug relapse. Aerobic exercise could be incorporated into the comprehensive treatment regimens for people with substance abuse disorders. Preclinical studies of SUD with animal models have shown that aerobic exercise diminishes drug-seeking behavior, which leads to relapse, in both male and female rats. Nevertheless, little is known regarding the effects of substance abuse-induced cellular and physiological adaptations believed to be responsible for drug-seeking behavior. Accordingly, the overall goal of this review is to provide a summary and an assessment of findings to date, highlighting evidence of the molecular and neurological effects of exercise on adaptations associated with SUD.

Brain Mapping the Effects of Chronic Aerobic Exercise in the Rat Brain Using FDG PET

Exercise is a key component to health and wellness and is thought to play an important role in brain activity. Changes in brain activity after exercise have been observed through various neuroimaging techniques, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). The precise impact of exercise on brain glucose metabolism (BGluM) is still unclear; however, results from PET studies seem to indicate an increase in regional metabolism in areas related to cognition and memory, direction, drive, motor functions, perception, and somatosensory areas in humans. Using PET and the glucose analog [18F]-Fluorodeoxyglucose (18F-FDG), we assessed the changes in BGluM between sedentary and chronic exercise in rats. Chronic treadmill exercise treatment demonstrated a significant increase in BGluM activity in the following brain regions: the caudate putamen (striatum), external capsule, internal capsule, deep cerebellar white matter, primary auditory cortex, forceps major of the corpus callosum, postsubiculum, subiculum transition area, and the central nucleus of the inferior colliculus. These brain regions are functionally associated with auditory processing, memory, motor function, and motivated behavior. Therefore, chronic daily treadmill running in rats stimulates BGluM in distinct brain regions. This identified functional circuit provides a map of brain regions for future molecular assessment which will help us understand the biomarkers involved in specific brain regions following exercise training, as this is critical in exploring the therapeutic potential of exercise in the treatment of neurodegenerative disease, traumatic brain injury, and addiction.

Factors modulating the incubation of drug and non-drug craving and their clinical implications

It was suggested in 1986 that cue-induced cocaine craving increases progressively during early abstinence and remains high during extended periods of time. Clinical evidence now supports this hypothesis and that this increase is not specific to cocaine but rather generalize across several drugs of abuse. Investigators have identified an analogous incubation phenomenon in rodents, in which time-dependent increases in cue-induced drug seeking are observed after abstinence from intravenous drug or palatable food self-administration. Incubation of craving is susceptible to variation in magnitude as a function of biological and/or the environmental circumstances surrounding the individual. During the last decade, the neurobiological correlates of the modulatory role of biological (sex, age, genetic factors) and environmental factors (environmental enrichment and physical exercise, sleep architecture, acute and chronic stress, abstinence reinforcement procedures) on incubation of drug craving has been investigated. In this review, we summarized the behavioral procedures adopted, the key underlying neurobiological correlates and clinical implications of these studies.

Substances of abuse and the blood brain barrier: Interactions with physical exercise

Substance use disorders pose a common medical, social and financial problem. Among the pathomechanisms of substance use disorders, the disruption and increased permeability of the blood-brain barrier has been recently revealed. Physical exercise appears to be a relatively inexpensive and feasible way to implement behavioral therapy counteracting the blood-brain barrier impairment. Concomitantly, there are also studies supporting a potential protective role of selected substances of abuse in maintaining the blood-brain barrier integrity. In this review, we aim to provide a summary on the modulatory influence of physical exercise, a non-pharmacological intervention, on the blood-brain barrier alterations caused by substances of abuse. Further studies are needed to understand the precise mechanisms that underlie various effects of physical exercise in substance use disorders.

Physical activity and the prevention, reduction, and treatment of alcohol and other drug use across the lifespan (The PHASE review): A systematic review

The aim of this review is to systematically describe and quantify the effects of PA interventions on alcohol and other drug use outcomes, and to identify any apparent effect of PA dose and type, possible mechanisms of effect, and any other aspect of intervention delivery (e.g. key behaviour change processes), within a framework to inform the design and evaluation of future interventions. Systematic searches were designed to identify published and grey literature on the role of PA for reducing the risk of progression to alcohol and other drug use (PREVENTION), supporting individuals to reduce alcohol and other drug use for harm reduction (REDUCTION), and promote abstinence and relapse prevention during and after treatment of alcohol and other drug use (TREATMENT). Searches identified 49,518 records, with 49,342 excluded on title and abstract. We screened 176 full text articles from which we included 32 studies in 32 papers with quantitative results of relevance to this review. Meta-analysis of two studies showed a significant effect of PA on prevention of alcohol initiation (risk ratio [RR]: 0.72, 95%CI: 0.61 to 0.85). Meta-analysis of four studies showed no clear evidence for an effect of PA on alcohol consumption (Standardised Mean Difference [SMD]: 0.19, 95%, Confidence Interval -0.57 to 0.18). We were unable to quantitatively examine the effects of PA interventions on other drug use alone, or in combination with alcohol use, for prevention, reduction or treatment. Among the 19 treatment studies with an alcohol and other drug use outcome, there was a trend for promising short-term effect but with limited information about intervention fidelity and exercise dose, there was a moderate to high risk of bias. We identified no studies reporting the cost-effectiveness of interventions. More rigorous and well-designed research is needed. Our novel approach to the review provides a clearer guide to achieve this in future research questions addressed to inform policy and practice for different populations and settings.

Differential effects of chronic voluntary wheel-running on morphine induced brain stimulation reward, motor activity and striatal dopaminergic activity

Physical exercise could be a protective factor against the development of substance use disorders; however, a number of preclinical studies report reward-enhancing effects of exercise for various drugs of abuse. We examined the effects of chronic wheel-running on brain reward sensitivity, reaction to novelty, reward-facilitating and locomotor-stimulating effects of morphine, using the intracranial self-stimulation (ICSS) and the open field test (OFT). Male Sprague-Dawley rats were randomly assigned to a sedentary or exercised group. For the ICSS procedure, rats were implanted with electrodes and trained to respond for electrical stimulation. Several indices were recorded in the training phase to estimate brain reward sensitivity. Once responding was stable, the animals of both groups received systemic injections of morphine and their ICSS thresholds were measured with the curve-shift paradigm. Employing the OFT, basal and morphine-induced locomotor activity was measured. Finally, basal and morphine-evoked tissue levels of dopamine and its metabolites were determined in the striatum using gas chromatography/mass spectrometry. Chronic wheel-running decreased brain reward sensitivity and subsequently increased the reward-facilitating effect of morphine. Exercised animals demonstrated a decreased reaction to novelty and reduced morphine-induced locomotion. Lastly, dopaminergic activity was decreased in the striatum of exercised animals under basal conditions, whereas morphine administration led to an increase in dopamine turnover. These findings indicate that chronic voluntary exercise exerts divergent effects on reward function, psychomotor activity and the reward-facilitating and locomotor-activating effects of opioids during adulthood. Our results provide insights into the increased non-medical use of opioids among young athletes reported in the literature.

Chronic aerobic exercise: Autoradiographic assessment of GABA(a) and mu-opioid receptor binding in adult rats

Exercise programs have shown great potential for both the prevention and treatment of substance use disorder (SUD). As exercise has been shown to have potent effects on physical and psychological health, it is reasonable to examine the mechanism of how exercise can be used as an adjunct treatment for addiction. The present study examined the effects of chronic aerobic (treadmill) exercise on both GABA(a) and mu-opioid receptor levels in the brains of male and female rats. GABA(a) receptor binding, measured by [³H] Flunitrazepam, was increased in the cingulate cortex following exercise, but only in females. Mu-opioid receptor expression, measured by [³H] ([D-Ala², N-MePhe⁴, Gly-ol]-enkephalin) (DAMGO), showed no effect of exercise while showing an effect of sex, with increased [³H] DAMGO binding in the brains of sedentary males compared to that of sedentary females. Our findings support the potential role for GABA(a) signaling in the cingulate cortex as part of the mechanism of action of aerobic exercise. These data, along with prior reports, aid our understanding of the neurochemical impact and mechanism of chronic aerobic exercise on neuropsychiatric disease, particularly regarding addiction.

The therapeutic potential of exercise for neuropsychiatric diseases: A review

Exercise is known to have a myriad of health benefits. There is much to be learned from the effects of exercise and its potential for prevention, attenuation and treatment of multiple neuropsychiatric diseases and behavioral disorders. Furthermore, recent data and research on exercise benefits with respect to major health crises, such as, that of opioid and general substance use disorders, make it very important to better understand and review the mechanisms of exercise and how it could be utilized for effective treatments or adjunct treatments for these diseases. In addition, mechanisms, epigenetics and sex differences are examined and discussed in terms of future research implications.

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.

Mechanisms underlying the efficacy of exercise as an intervention for cocaine relapse: a focus on mGlu5 in the dorsal medial prefrontal cortex

RATIONALE

Exercise shows promise as a treatment option for addiction; but in order to prevent relapse, it may need to be introduced early in the course of treatment.

OBJECTIVE

We propose that exercise, by upregulating dorsal medial prefrontal cortex (dmPFC)-nucleus accumbens (NAc) transmission, offsets deficits in pathways targeting glutamate, BDNF, and dopamine during early abstinence, and in doing so, normalizes neuroadaptations that underlie relapse.

METHODS

We compared the effects of exercise (wheel running, 2-h/day) during early (days 1-7), late (days 8-14), and throughout abstinence (days 1-14) to sedentary conditions on cocaine-seeking and gene expression in the dmPFC and NAc core of male rats tested following 24-h/day extended-access cocaine (up to 96 infusions/day) or saline self-administration and protracted abstinence (15 days). Based on these data, we then used site-specific manipulation to determine whether dmPFC metabotropic glutamate receptor5 (mGlu5) underlies the efficacy of exercise.

RESULTS

Exercise initiated during early, but not late abstinence, reduced cocaine-seeking; this effect was strongly associated with dmPFC Grm5 expression (gene encoding mGlu5), and modestly associated with dmPFC Grin1 and Bdnf-IV expression. Activation of mGlu5 in the dmPFC during early abstinence mimicked the efficacy of early-initiated exercise; however, inhibition of these receptors prior to the exercise sessions did not block its efficacy indicating that there may be redundancy in the mechanisms through which exercise reduces cocaine-seeking.

CONCLUSION

These findings indicate that addiction treatments, including exercise, should be tailored for early versus late phases of abstinence since their effectiveness will vary over abstinence due to the dynamic nature of the underlying neuroadaptations.

Exercise Reduces Dopamine D1R and Increases D2R in Rats: Implications for Addiction

INTRODUCTION

Exercise has been shown to be effective for preventing and treating substance abuse in both clinical and preclinical studies. Less is known, however, regarding the underlying neurobiological mechanisms driving these changes in drug-seeking behavior. One possibility is that exercise may alter the mesolimbic dopamine pathway in such a way that makes drugs of abuse less salient and/or rewarding.

METHODS

To examine possible exercise-induced changes in dopamine signaling, male and female Lewis rats were split into exercise and sedentary groups at 8 wk of age. Exercise rats were run on a treadmill at 10 m·min, 5 d·wk, for 6 wk, whereas sedentary rats remained in their home cage. Rats were killed after the 6 wk of treatment, and their brains were used for in vitro autoradiography using [H]SCH 23,390, [H]Spiperone, and [H]WIN55,428 ligands to quantify dopamine type 1-like receptor (D1R)-like, dopamine type 2-like receptor (D2R)-like, and dopamine transporter binding, respectively.

RESULTS

Exercised rats had 18% and 21% lower D1R-like binding levels compared to sedentary rats within the olfactory tubercle and nucleus accumbens shell, respectively. In addition, male and female exercise rats showed greater D2R-like binding levels within the dorsomedial caudate putamen (30%), ventrolateral caudate putamen (24%), and ventromedial caudate putamen (27%), as well as the olfactory tubercle (19%). Greater D2R-like binding in the nucleus accumbens core (24%) and shell (25%) of exercised rats compared with sedentary rats approached significance. No effects were found for dopamine transporter binding.

CONCLUSIONS

These findings support the hypothesis that aerobic exercise results in changes in the mesolimbic pathway that could mediate exercise-induced attenuation of drug-seeking behavior.

Chronic forced exercise inhibits stress-induced reinstatement of cocaine conditioned place preference

Stress increases the likelihood of cocaine relapse in humans and animals, even following a prolonged extinction/abstinence period. Exercise has previously been shown to reduce stress and decrease the likelihood of drug dependence, while also reducing cravings in humans and inhibiting relapse behaviors due to other risk factors in rodents. The present study evaluated the efficacy of exercise to reduce stress-induced relapse to cocaine in a rodent model. Young adult female Sprague Dawley rats were tested for cocaine conditioned place preference (CPP), then split into sedentary or exercise (six weeks of one-hour daily treadmill running, five days per week) groups. Following cocaine CPP, rats were tested for extinction behavior, and then tested for stress-primed reinstatement (15 min immobilization) following the six-week intervention period. Exercise inhibited stress-induced reinstatement of cocaine CPP despite increasing serum corticosterone levels following 15 min of immobilization, suggesting that chronic aerobic exercise intervention may result in adaptations of stress pathways. These findings suggest that exercise may help prevent stress-induced drug relapse, adding to a growing body of evidence supporting the utility of exercise to combat substance abuse.

Wheel running during chronic nicotine exposure is protective against mecamylamine-precipitated withdrawal and up-regulates hippocampal α7 nACh receptors in mice

BACKGROUND AND PURPOSE

Evidence suggests that exercise decreases nicotine withdrawal symptoms in humans; however, the mechanisms mediating this effect are unclear. We investigated, in a mouse model, the effect of exercise intensity during chronic nicotine exposure on nicotine withdrawal severity, binding of α4β2*, α7 nicotinic acetylcholine (nAChR), μ-opioid (μ receptors) and D2 dopamine receptors and on brain-derived neurotrophic factor (BDNF) and plasma corticosterone levels.

EXPERIMENTAL APPROACH

Male C57Bl/6J mice treated with nicotine (minipump, 24 mg·kg-1 ·day-1 ) or saline for 14 days underwent one of three concurrent exercise regimes: 24, 2 or 0 h·day-1 voluntary wheel running. Mecamylamine-precipitated withdrawal symptoms were assessed on day 14. Quantitative autoradiography of α4β2*, α7 nAChRs, μ receptors and D2 receptor binding was performed in brain sections of these mice. Plasma corticosterone and brain BDNF levels were also measured.

KEY RESULTS

Nicotine-treated mice undertaking 2 or 24 h·day-1 wheel running displayed a significant reduction in withdrawal symptom severity compared with the sedentary group. Wheel running induced a significant up-regulation of α7 nAChR binding in the CA2/3 area of the hippocampus of nicotine-treated mice. Neither exercise nor nicotine treatment affected μ or D2 receptor binding or BDNF levels. Nicotine withdrawal increased plasma corticosterone levels and α4β2* nAChR binding, irrespective of exercise regimen.

CONCLUSIONS AND IMPLICATIONS

We demonstrated for the first time a profound effect of exercise on α7 nAChRs in nicotine-dependent animals, irrespective of exercise intensity. These findings shed light onto the mechanism underlining the protective effect of exercise on the development of nicotine dependence.

LINKED ARTICLES

This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc.

Physical activity and the prevention, reduction, and treatment of alcohol and/or substance use across the lifespan (The PHASE review): protocol for a systematic review

BACKGROUND

Alcohol and substance use results in significant human and economic cost globally and is associated with economic costs of £21 billion and £15billion within the UK, respectively, and trends for use are not improving. Pharmacological interventions are well researched, but relapse rates across interventions for substance and alcohol use disorders are as high as 60-90%. Physical activity may offer an alternative or adjunct approach to reducing rates of alcohol and substance use that is associated with few adverse side effects, is easily accessible, and is potentially cost-effective. Through psychological, behavioural, and physiological mechanisms, physical activity may offer benefits in the prevention, reduction, and treatment of alcohol and substance use across the lifespan. Whilst physical activity is widely advocated as offering benefit, no systematic review exists of physical activity (in all forms) and its effects on all levels of alcohol and substance use across all ages to help inform policymakers, service providers, and commissioners.

METHODS

The objectives of this mixed methods systematic review are to describe and evaluate the quantitative and qualitative research obtained by a diverse search strategy on the impact of physical activity and its potential to: 1. Reduce the risk of progression to alcohol and/or substance use (PREVENTION) 2. Support individuals to reduce alcohol and/or substance use for harm reduction (REDUCTION), and 3. Promote abstinence and relapse prevention during and after treatment for an alcohol and/or substance use disorder (TREATMENT). With the input of key stakeholders, we aim to assess how what we know can be translated into policy and practice. Quantitative, qualitative, service evaluations, and economic analyses will be brought together in a final narrative synthesis that will describe the potential benefits of physical activity for whom, in what conditions, and in what form.

DISCUSSION

This review will provide details of what is known about physical activity and the prevention, reduction, and treatment of alcohol and/or substance use. The synthesised findings will be disseminated to policymakers, service providers, and commissioners in the UK.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO number: CRD42017079322 .

Does exercise augment operant and Pavlovian extinction: A meta-analysis

BACKGROUND

Exposure therapy, a behavioral approach to reduce symptomology in fear, anxiety, and drug-related psychiatric disorders, is based on learning and memory principles of extinction, and is subject to relapse. As such, it is important to find ways to enhance outcomes. One such way is through exercise.

OBJECTIVES

Identify if exercise augments extinction behavior, and whether this depends on the experimental paradigm used (i.e. operant or Pavlovian) and/or stimulus (i.e. appetitive or aversive). Additionally, determine which moderating variables influence the effects of exercise on extinction learning.

METHODS

A literature search was conducted and a Hedges' g calculation was employed to conduct a meta-analysis (metaSEM) using a structural equation modeling approach. This approach was chosen because of its ability to account for dependencies in effect sizes.

RESULTS

We found a significant effect of exercise as an augmentation over extinction alone (g = 0.37, p < 0.001), with extinction paradigm (but not stimulus) producing a moderating effect (B = 0.43, p = 0.030). Data were then split by extinction paradigm, with operant extinction models having a significant effect (g = 0.55, p < 0.001), and number of extinction sessions moderating aggregate effects. Pavlovian models did not have significant overall effects (g = 0.11, p = 0.3976), but were moderated by the number of animals housed together and exercise after extinction.

CONCLUSIONS

The effects of exercise on extinction learning are differentially modulated by the type of paradigm used, the number of extinction sessions, the timing of when exercise treatment was applied (after extinction), and the housing conditions.

Exercise as a Sex-Specific Treatment for Substance Use Disorder

PURPOSE OF REVIEW

Exercise is a promising treatment for substance use disorder that may reduce withdrawal symptoms and prevent relapse. In this review, we discuss recent evidence from clinical and preclinical studies for its efficacy, from a behavioral to a molecular level, in order to understand the exercise conditions that lead to beneficial effects. We also highlight the few recent findings of sex-specific differences.

RECENT FINDINGS

Clinical and preclinical findings show that exercise decreases withdrawal symptoms, including craving, in both males and females. Evidence from clinical studies support the efficacy of exercise to prevent relapse to smoking, although further research is needed to examine sex differences, establish long-term efficacy, and to determine if effects extend to other substance use disorders. Preclinical findings also support the potential utility of exercise to prevent relapse with evidence suggesting that its efficacy is enhanced in males, and mediated by blocking drug-induced adaptations that occur during early abstinence.

SUMMARY

Sex differences and timing of exercise availability during abstinence should be considered in future studies examining exercise as an intervention for relapse. A better understanding of the neurobiological mechanisms underlying the efficacy of exercise to reduce withdrawal symptoms and prevent relapse is needed to guide its development as a sex-specific treatment.

Treadmill exercise improves fitness and reduces craving and use of cocaine in individuals with concurrent cocaine and tobacco-use disorder

Exercise may be a useful treatment for substance use disorders. Participants (N=24) included treatment-seeking individuals with concurrent cocaine and tobacco-use disorder (cigarette smokers). Participants were randomized to either running or walking (30min per session, 3 times per week) or sitting (control condition) for 4 consecutive weeks. Several metrics indicated significant differences among runners, walkers, and sitters during sessions, including mean distance covered and calories burned. In addition, remote physiological monitoring showed that the groups differed significantly according to mean maximum heart rate (HR), respiration, and locomotor activity. Across the 4-week study, exercise improved fitness measures including significantly decreasing resting HR. Though not statistically significant, exercise improved abstinence from cocaine and increased self-reports of no cocaine use in last 24h. In general, reductions in tobacco use and craving were not as robust. To our knowledge, this is the first study to evaluate the effects of a multi-week exercise program in individuals with concurrent cocaine and tobacco-use disorder. The data clearly show significant improvements in basic fitness measures and several indices reveal that exercise improved both self-report and biochemically verified reports of cocaine abstinence. Taken together, the data from this study provide preliminary evidence for the efficacy of exercise for improving fitness and reducing cocaine use.

Environmental enrichment as a potential intervention for heroin seeking

BACKGROUND

Heroin-related cues can trigger craving and relapse in addicts or heroin seeking in rats. In the present study we investigated whether environmental enrichment (EE) implemented after heroin exposure can reduce cue-induced reinstatement of heroin seeking and expression of heroin conditioned place preference.

METHODS

In Experiment 1, male Long Evans rats that already acquired a heroin self-administration habit, were housed in enriched or non-enriched environments, underwent extinction training and later were tested for cue-induced reinstatement of heroin seeking. In Experiment 2, rats were conditioned with heroin in one compartment of a CPP apparatus and saline in the other, exposed to 30days of enrichment or no enrichment and were later tested for heroin CPP.

RESULTS

The results showed that exposure to EE significantly reduced responding during the reinstatement test (Experiment 1) and prevented the expression of heroin CPP (Experiment 2).

CONCLUSION

Our findings suggest that EE can be an effective behavioral approach to diminish the effects of conditioned cues on heroin seeking.

m-Trifluoromethyl-diphenyldiselenide as a pharmacological tool to treat preference symptoms related to AMPH-induced dependence in rats

Amphetamine (AMPH) abuse is a world concern and a serious public health problem. Repeated administration of high doses of AMPH induces neuropsychiatric consequences, including addiction, reward and psychosis, whose pharmacological treatment has shown limited effectiveness. The m-trifluoromethyl-diphenyldiselenide [(m-CF3-PhSe)2] has been documented as a promising pharmacological agent in different animal models related to oxidative damage. In this study, we examined the influence of (m-CF3-PhSe)2 on withdrawal following re-exposure to AMPH. Wistar rats received d,l-AMPH or saline in the conditioned place preference (CPP) paradigm for 8days. Then, half of each initial (AMPH or saline) experimental group was treated with (m-CF3-PhSe)2 or vehicle, resulting in four final groups: i) Saline/vehicle; ii) (m-CF3-PhSe)2/saline; iii) AMPH/vehicle; and iv) AMPH/(m-CF3-PhSe)2. After fourteen days of (m-CF3-PhSe)2 treatment, animals were re-exposed to AMPH or vehicle in the CPP paradigm for three more days in order to assess drug re-conditioning and memory/locomotor activity, performed 24h after AMPH re-exposure in the CPP and the Y maze, respectively. Subsequently, ex-vivo assays were carried out in samples of the prefrontal cortex (PFC) of the animals. The (m-CF3-PhSe)2 treatment was able to prevent AMPH-induced re-conditioning symptoms in rats. Behavioral observations in the Y maze task showed no significant changes. AMPH exposure was able to increase 5-HT uptake as well as oxidative damage in the PFC, whereas (m-CF3-PhSe)2 treatment exerted a preventative effect against these alterations. The current findings suggest that (m-CF3-PhSe)2 might be considered a promising therapeutic tool for AMPH-induced addiction.

Exercise during early, but not late abstinence, attenuates subsequent relapse vulnerability in a rat model

Exercise has shown promise as a nonpharmacological intervention for addiction, with evidence suggesting a potential utility for relapse prevention. In humans, exercise as an intervention is typically introduced well after the initiation of abstinence, yet neurobiological data from preclinical studies suggest that it may be more effective if initiated during early abstinence. Here, using rat models, we determined whether the beneficial effects of exercise on relapse vulnerability depends on when exercise is first initiated, during early versus late abstinence. Once rats (n=47) acquired cocaine self-administration, they were given 24-h access to cocaine (1.5 mg/kg per infusion) under a discrete trial procedure (four infusions per hour) for 10 days. The rats then began a 14-day abstinence period in which they had access (2 h per day) to a locked wheel throughout abstinence (sedentary) or an unlocked wheel during early (days 1-7), late (days 8-14) or throughout (days 1-14) abstinence (n=10-14 per group). Cocaine seeking, as assessed under an extinction/cued-induced reinstatement procedure, was examined on day 15 of abstinence. Exercise beginning during early abstinence robustly attenuated subsequent cocaine seeking, and this effect persisted even when exercise ended on the seventh day of abstinence. In contrast, exercise during late abstinence was not effective and these animals displayed high levels of cocaine seeking similar to those observed in sedentary animals. These results indicate that the timing of exercise availability differentially impacts cocaine seeking with results suggesting that exercise during early, but not late, abstinence may provide long-term protection against cocaine relapse.

Sex differences in drug addiction and response to exercise intervention: From human to animal studies

Accumulated research supports the idea that exercise could be an option of potential prevention and treatment for drug addiction. During the past few years, there has been increased interest in investigating of sex differences in exercise and drug addiction. This demonstrates that sex-specific exercise intervention strategies may be important for preventing and treating drug addiction in men and women. However, little is known about how and why sex differences are found when doing exercise-induced interventions for drug addiction. In this review, we included both animal and human that pulled subjects from a varied age demographic, as well as neurobiological mechanisms that may highlight the sex-related differences in these potential to assess the impact of sex-specific roles in drug addiction and exercise therapies.

Does physical activity protect against drug abuse vulnerability?

BACKGROUND

The current review examined recent literature to determine our state of knowledge about the potential ability of physical activity serve as a protectant against drug abuse vulnerability.

METHODS

Both preclinical and clinical studies were examined using either associational or random assignment study designs. In addition to examining drug use as an outcome variable, the potential neural mediators linking physical activity and drug abuse vulnerability were examined.

CONCLUSIONS

Several important conclusions may be drawn. First, the preclinical evidence is solid in showing that physical activity in various forms is able to serve as both a preventive and treatment intervention that reduces drug use, although voluntary alcohol drinking appears to be an exception to this conclusion. Second, the clinical evidence provides some evidence, albeit mixed, to suggest a beneficial effect of physical activity on tobacco dependent individuals. In contrast, there exists only circumstantial evidence that physical activity may reduce use of drugs other than nicotine, and there is essentially no solid information from random control studies to know if physical activity may prevent initiation of problem use. Finally, both preclinical and clinical evidence shows that various brain systems are altered by physical activity, with the medial prefrontal cortex (mPFC) serving as one potential node that may mediate the putative link between physical activity and drug abuse vulnerability. It is concluded that novel neurobehavioral approaches taking advantage of novel techniques for assessing the physiological impact of physical activity are needed and can be used to inform the longitudinal random control studies that will answer definitively the question posed.

Impact of physical exercise on substance use disorders: a meta-analysis

OBJECTIVE

The goal of this meta-analysis was to examine whether long-term physical exercise could be a potential effective treatment for substance use disorders (SUD).

METHODS

The PubMed, Web of Science, Elsevier, CNKI and China Info were searched for randomized controlled trials (RCT) studies in regards to the effects of physical exercise on SUD between the years 1990 and 2013. Four main outcome measures including abstinence rate, withdrawal symptoms, anxiety, and depression were evaluated.

RESULTS

Twenty-two studies were integrated in the meta-analysis. The results indicated that physical exercise can effectively increase the abstinence rate (OR = 1.69 (95% CI: 1.44, 1.99), z = 6.33, p < 0.001), ease withdrawal symptoms (SMD = -1.24 (95% CI: -2.46, -0.02), z = -2, p<0.05), and reduce anxiety (SMD = -0.31 (95% CI: -0.45, -0.16), z  =  -4.12, p < 0.001) and depression (SMD  =  -0.47 (95% CI: -0.80, -0.14), z = -2.76, p<0.01). The physical exercise can more ease the depression symptoms on alcohol and illicit drug abusers than nicotine abusers, and more improve the abstinence rate on illicit drug abusers than the others. Similar treatment effects were found in three categories: exercise intensity, types of exercise, and follow-up periods.

CONCLUSIONS

The moderate and high-intensity aerobic exercises, designed according to the Guidelines of American College of Sports Medicine, and the mind-body exercises can be an effective and persistent treatment for those with SUD.

Chronic wheel running-induced reduction of extinction and reinstatement of methamphetamine seeking in methamphetamine dependent rats is associated with reduced number of periaqueductal gray dopamine neurons

Exercise (physical activity) has been proposed as a treatment for drug addiction. In rodents, voluntary wheel running reduces cocaine and nicotine seeking during extinction, and reinstatement of cocaine seeking triggered by drug-cues. The purpose of this study was to examine the effects of chronic wheel running during withdrawal and protracted abstinence on extinction and reinstatement of methamphetamine seeking in methamphetamine dependent rats, and to determine a potential neurobiological correlate underlying the effects. Rats were given extended access to methamphetamine (0.05 mg/kg, 6 h/day) for 22 sessions. Rats were withdrawn and were given access to running wheels (wheel runners) or no wheels (sedentary) for 3 weeks after which they experienced extinction and reinstatement of methamphetamine seeking. Extended access to methamphetamine self-administration produced escalation in methamphetamine intake. Methamphetamine experience reduced running output, and conversely, access to wheel running during withdrawal reduced responding during extinction and, context- and cue-induced reinstatement of methamphetamine seeking. Immunohistochemical analysis of brain tissue demonstrated that wheel running during withdrawal did not regulate markers of methamphetamine neurotoxicity (neurogenesis, neuronal nitric oxide synthase, vesicular monoamine transporter-2) and cellular activation (c-Fos) in brain regions involved in relapse to drug seeking. However, reduced methamphetamine seeking was associated with running-induced reduction (and normalization) of the number of tyrosine hydroxylase immunoreactive neurons in the periaqueductal gray (PAG). The present study provides evidence that dopamine neurons of the PAG region show adaptive biochemical changes during methamphetamine seeking in methamphetamine dependent rats and wheel running abolishes these effects. Given that the PAG dopamine neurons project onto the structures of the extended amygdala, the present findings also suggest that wheel running may be preventing certain allostatic changes in the brain reward and stress systems contributing to the negative reinforcement and perpetuation of the addiction cycle.

Exercise modifies amphetamine relapse: behavioral and oxidative markers in rats

Exercise has been reported to attenuate rewarding symptoms related to addictive drugs mainly by affecting the brain neuroplasticity and neurotransmission. In this study, we investigated the influence of physical exercise on the behavioral and enzymatic status related to drug relapse in rats. Animals were primarily treated with amphetamine (AMPH; 4.0 mg/kg, i.p.) or vehicle (C; NaCl 0.9% solution) in the conditioned place preference (CPP) paradigm for 14 days. Half of each experimental group was then submitted to swimming sessions (60 min/day, 5 days/week) for 5 weeks. Animals were re-exposed to AMPH- or vehicle-CPP paradigm for another 3 days, in order to observe drug relapse and anxiety-like symptoms, which were observed 24h after AMPH reconditioning in CPP, and elevated plus maze (EPM), respectively, and brain biochemical evaluations were carried out subsequently. While AMPH was related to place preference and anxiety, indicating drug addiction and abstinence symptoms, respectively, physical activity was able to prevent relapse symptoms after AMPH reconditioning, as observed through consecutive decreased CPP and anxiety-like symptoms. In addition, AMPH exposure increased reactive species (RS) generation and protein carbonyl (PC) levels together with decreased activity of catalase- and Na(+)K(+)-ATPase in hippocampus. On the other hand, while all AMPH-induced effects were prevented by physical activity, there was a negative correlation between PC levels (r=0.65; p<0.003) and CAT activity, and a positive correlation between RS generation and PC levels (r=0.54; r=0.52, p<0.05) with AMPH-CPP after exercise. These results indicate that exercise has a clear beneficial influence on the prevention of psychostimulant drug relapse.

Exercise as a novel treatment for drug addiction: a neurobiological and stage-dependent hypothesis

Physical activity, and specifically exercise, has been suggested as a potential treatment for drug addiction. In this review, we discuss clinical and preclinical evidence for the efficacy of exercise at different phases of the addiction process. Potential neurobiological mechanisms are also discussed focusing on interactions with dopaminergic and glutamatergic signaling and chromatin remodeling in the reward pathway. While exercise generally produces an efficacious response, certain exercise conditions may be either ineffective or lead to detrimental effects depending on the level/type/timing of exercise exposure, the stage of addiction, the drug involved, and the subject population. During drug use initiation and withdrawal, its efficacy may be related to its ability to facilitate dopaminergic transmission, and once addiction develops, its efficacy may be related to its ability to normalize glutamatergic and dopaminergic signaling and reverse drug-induced changes in chromatin via epigenetic interactions with brain-derived neurotrophic factor (BDNF) in the reward pathway. We conclude with future directions, including the development of exercise-based interventions alone or as an adjunct to other strategies for treating drug addiction.

Effect of wheel-running during abstinence on subsequent nicotine-seeking in rats

RATIONALE

Exercise appears to be a promising non-pharmacological treatment for nicotine addiction that may be useful for the vulnerable adolescent population.

OBJECTIVES

The aim of this study is to determine if wheel-running, an animal model of aerobic exercise, during an abstinence period would decrease subsequent nicotine-seeking in rats that had extended access to nicotine self-administration during adolescence.

METHODS

Male adolescent rats (n = 55) were trained to self-administer saline or nicotine infusions (5 or 10 μg/kg) under a fixed ratio 1 schedule with a maximum of 20 infusions/day beginning on postnatal day 30. After 5 days, access was extended to 23 h/day with unlimited infusions for a total of 10 days. After the last self-administration session, rats were moved to polycarbonate cages for a 10-day abstinence period where they either had access to a locked or unlocked running wheel for 2 h/day. Nicotine-seeking was examined following the 10th day of abstinence under a within-session extinction/cue-induced reinstatement paradigm.

RESULTS

Intake was higher at the 10 μg/kg dose as compared to the 5 μg/kg dose; however, intake did not differ within doses prior to wheel assignment. Compared to saline controls, rats that self-administered nicotine at either dose showed a significant increase in drug-seeking during extinction, and consistent with our hypothesis, exercise during abstinence attenuated this effect. Nicotine led to modest but significant levels of cue-induced reinstatement; however, in this adolescent-onset model, levels were variable and not affected by exercise.

CONCLUSIONS

Exercise may effectively reduce relapse vulnerability for adolescent-onset nicotine addiction.