Physical exercise modifies behavioral and molecular parameters related to opioid addiction regardless of training time

Treadmill exercise training inhibits morphine CPP by reversing morphine effects on GABA neurotransmission in D2-MSNs of the accumbens-pallidal pathway in male mice

Relapse is a major challenge in the treatment of drug addiction, and exercise has been shown to decrease relapse to drug seeking in animal models. However, the neural circuitry mechanisms by which exercise inhibits morphine relapse remain unclear. In this study, we report that 4-week treadmill training prevented morphine conditioned place preference (CPP) expression during abstinence by acting through the nucleus accumbens (NAc)-ventral pallidum (VP) pathway. We found that neuronal excitability was reduced in D2-dopamine receptor-expressing medium spiny neurons (D2-MSNs) following repeated exposure to morphine and forced abstinence. Enhancing the excitability of NAc D2-MSNs via treadmill training decreased the expression of morphine CPP. We also found that the effects of treadmill training were mediated by decreasing enkephalin levels and that restoring opioid modulation of GABA neurotransmission in the VP, which increased neurotransmitter release from NAc D2-MSNs to VP, decreased morphine CPP. Our findings suggest the inhibitory effect of exercise on morphine CPP is mediated by reversing morphine-induced neuroadaptations in the NAc-to-VP pathway.

Analysis of physical activity and prescription opioid use among US adults: a cross-sectional study

BACKGROUND

Opioid crisis has become a global concern, but whether physical activity (PA) can effectively reduce prescription opioid use remains unclear. The study aimed to examine the relationship of different domains of PA (e.g., occupation-related PA [OPA], transportation-related PA [TPA], leisure-time PA [LTPA]) with prescription opioid use and duration of prescription opioid use.

METHODS

This cross-sectional study was conducted on 27,943 participants aged ≥ 18 years from National Health and Nutrition Examination Survey (NHANES, 2007- March 2020). We examined the relationship of different domains of PA with prescription opioid use and duration of prescription opioid use using multivariable logistic regression. Stratified analysis and a series of sensitivity analysis were used to elevate robustness. All analyses were conducted using appropriate sampling weights.

RESULTS

Of the 27,943 participants, the mean age was 45.10 years, with 14,018 [weighted, 50.0%] females and 11,045 [weighted, 66.0%] non-Hispanic White. After multivariable adjustment, inverse associations between PA and prescription opioid use were observed for sufficient (≥ 150 min/week) total PA (OR,0.68 95%CI [0.56-0.81]), TPA (OR,0.73 95%CI [0.58-0.92]), and LTPA (OR,0.60 95%CI [0.48-0.75]) compared with insufficient PA(< 150 min/week), but not for sufficient OPA (OR,0.93 95%CI [0.79-1.10]). In addition, the associations were dose-responsive, participants had 22-40%, 27-36%, and 26-47% lower odds of using prescription opioids depending on the duration of total PA, TPA, and LTPA, respectively. Nevertheless, the impact of PA on prescription opioid use varied by duration of opioid use. Sufficient total PA was associated with elevated odds of short-term use of prescription opioids (< 90 days). Comparatively, sufficient total PA, TPA, and LTPA had different beneficial effects on reducing long-term use of prescription opioids (≥ 90 days) depending on the strength of opioids.

CONCLUSIONS

This study demonstrated sufficient total PA, TPA, and LTPA were inversely associated with prescription opioid use and varied depending on the duration and strength of prescription opioid use. These findings highlight PA can provide policy guidance to address opioid crisis.

Physical Exercise Promotes Beneficial Changes on Neurotrophic Factors in Mesolimbic Brain Areas After AMPH Relapse: Involvement of the Endogenous Opioid System

Addiction is a serious public health problem, and the current pharmacotherapy is unable to prevent drug use reinstatement. Studies have focused on physical exercise as a promising coadjuvant treatment. Our research group recently showed beneficial neuroadaptations in the dopaminergic system related to amphetamine-relapse prevention involving physical exercise-induced endogenous opioid system activation (EXE-OS activation). In this context, additional mechanisms were explored to understand the exercise benefits on drug addiction. Male rats previously exposed to amphetamine (AMPH, 4.0 mg/kg) for 8 days were submitted to physical exercise for 5 weeks. EXE-OS activation was blocked by naloxone administration (0.3 mg/kg) 5 min before each physical exercise session. After the exercise protocol, the rats were re-exposed to AMPH for 3 days, and in sequence, euthanasia was performed and the VTA and NAc were dissected. In the VTA, our findings showed increased immunocontent of proBDNF, BDNF, and GDNF and decreased levels of AMPH-induced TrkB; therefore, EXE-OS activation increased all these markers and naloxone administration prevented this exercise-induced effect. In the NAc, the same molecular markers were also increased by AMPH and decreased by EXE-OS activation. In this study, we propose a close relation between EXE-OS activation beneficial influence and a consequent neuroadaptation on neurotrophins and dopaminergic system levels in the mesolimbic brain area, preventing the observed AMPH-relapse behavior. Our outcomes bring additional knowledge concerning addiction neurobiology understanding and show that EXE-OS activation may be a potential adjuvant tool in drug addiction therapy.

Amelioration of Nicotine-Induced Conditioned Place Preference Behaviors in Mice by an FABP3 Inhibitor

We previously demonstrated that fatty acid-binding protein 3 null (FABP3−/−) mice exhibit resistance to nicotine-induced conditioned place preference (CPP). Here, we confirm that the FABP3 inhibitor, MF1 ((4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy) butanoic acid), successfully reduces nicotine-induced CPP scores in mice. MF1 (0.3 or 1.0 mg/kg) was orally administered 30 min before nicotine, and CPP scores were assessed in the conditioning, withdrawal, and relapse phases. MF1 treatment decreased CPP scores in a dose-dependent manner. Failure of CPP induction by MF1 (1.0 mg/kg, p.o.) was associated with the inhibition of both CaMKII and ERK activation in the nucleus accumbens (NAc) and hippocampal CA1 regions. MF1 treatment reduced nicotine-induced increases in phosphorylated CaMKII and cAMP-response element-binding protein (CREB)-positive cells. Importantly, the increase in dopamine D2 receptor (D2R) levels following chronic nicotine exposure was inhibited by MF1 treatment. Moreover, the quinpirole (QNP)-induced increase in the level of CaMKII and ERK phosphorylation was significantly inhibited by MF1 treatment of cultured NAc slices from wild type (WT) mice; however, QNP treatment had no effect on CaMKII and ERK phosphorylation levels in the NAc of D2R null mice. Taken together, these results show that MF1 treatment suppressed D2R/FABP3 signaling, thereby preventing nicotine-induced CPP induction. Hence, MF1 can be used as a novel drug to block addiction to nicotine and other drugs by inhibiting the dopaminergic system.

The Role of Physical Exercise in Opioid Substitution Therapy: Mechanisms of Sequential Effects

It is generally accepted that chronic opioid use is associated with structural and functional changes in the human brain that lead to an enhancement of impulsive behavior for immediate satisfaction. Interestingly, in recent years, physical exercise interventions have been used as an adjunctive treatment for patients with opioid use disorders (OUDs). Indeed, exercise has positive effects on both the biological and psychosocial basis of addiction, modifying neural circuits such as the reward, inhibition, and stress systems, and thus causing behavioral changes. This review focuses on the possible mechanisms that contribute to the beneficial effects of exercise on the treatment of OUDs, with emphasis placed on the description of a sequential consolidation of these mechanisms. Exercise is thought to act initially as a factor of internal activation and self-regulation and eventually as a factor of commitment. This approach suggests a sequential (temporal) consolidation of the functions of exercise in favor of gradual disengagement from addiction. Particularly, the sequence in which the exercise-induced mechanisms are consolidated follows the pattern of internal activation-self-regulation-commitment, eventually resulting in stimulation of the endocannabinoid and endogenous opioid systems. Additionally, this is accompanied by modification of molecular and behavioral aspects of opioid addiction. Overall, the neurobiological actions of exercise in combination with certain psychological mechanisms appear to promote its beneficial effects. Given the positive effects of exercise on both physical and mental health, exercise prescription is recommended as a complement to conventional therapy for patients on opioid maintenance treatment.

Tactile Stimulation in Adult Rats Modulates Dopaminergic Molecular Parameters in the Nucleus accumbens Preventing Amphetamine Relapse

Amphetamine (AMPH) is a psychostimulant drug frequently related to addiction, which is characterized by functional and molecular changes in the brain reward system, favoring relapse development, and pharmacotherapies have shown low effectiveness. Considering the beneficial influences of tactile stimulation (TS) in different diseases that affect the central nervous system (CNS), here we evaluated if TS applied in adult rats could prevent or minimize the AMPH-relapse behavior also accessing molecular neuroadaptations in the nucleus accumbens (NAc). Following AMPH conditioning in the conditioned place preference (CPP) paradigm, male rats were submitted to TS (15-min session, 3 times a day, for 8 days) during the drug abstinence period, which were re-exposed to the drug in the CPP paradigm for additional 3 days for relapse observation and molecular assessment. Our findings showed that besides AMPH relapse, TS prevented the dopamine transporter (DAT), dopamine 1 receptor (D1R), tyrosine hydroxylase (TH), mu opioid receptor (MOR) increase, and AMPH-induced delta FosB (ΔFosB). Based on these outcomes, we propose TS as a useful tool to treat psychostimulant addiction, which is subsequent to clinical studies; it could be included in detoxification programs together with pharmacotherapies and psychological treatments already conventionally established.

Exercise can restore behavioural and molecular changes of intergenerational morphine effects

In our previous studies, the offspring of morphine-exposed parents (MEO) showed pharmacological tolerance to the morphine's reinforcing effect. According to the role of exercise in treatment of morphine addiction, the current study was designed to utilize exercise to improve the effect of parental morphine exposure on the morphine's reinforcing effect. Male and female rats received morphine for 10 days and were drug-free for another 10 days. Each morphine-exposed animal was allowed to mate either with a drug-naïve or a morphine-exposed rat. The offspring were divided into two groups: (1) offspring that were subjected to treadmill exercise and (2) offspring that were not subjected to exercise. The reinforcing effect of morphine was evaluated using conditioned place preference (CPP) and two-bottle choice (TBC) tests. Levels of dopamine receptors (D1DR and D2DR), μ-opioid receptor (MOR), and ΔFosB were evaluated in the nucleus accumbens. The MEO obtained lower preference scores in CPP and consumed morphine more than the control group in TBC. After 3 weeks of exercise, the reinforcing effect of morphine in the MEO was similar to the control. D1DR, D2DR, and MOR were increased in MEO compared with the controls before exercise. Levels of D1DR and MOR were decreased after exercise in the MEO; however, D1DR was increased in control. D2DR level did not change after exercise in MEO, but it increased in control group. Moreover, the level of ΔFosB was decreased among MEO while it was increased after exercise. In conclusion, exercise might modulate the reinforcing effect of morphine via alteration in levels of D1DR, MOR, and ΔFosB.

Machine-learning model successfully predicts patients at risk for prolonged postoperative opioid use following elective knee arthroscopy

PURPOSE

Recovery following elective knee arthroscopy can be compromised by prolonged postoperative opioid utilization, yet an effective and validated risk calculator for this outcome remains elusive. The purpose of this study is to develop and validate a machine-learning algorithm that can reliably and effectively predict prolonged opioid consumption in patients following elective knee arthroscopy.

METHODS

A retrospective review of an institutional outcome database was performed at a tertiary academic medical centre to identify adult patients who underwent knee arthroscopy between 2016 and 2018. Extended postoperative opioid consumption was defined as opioid consumption at least 150 days following surgery. Five machine-learning algorithms were assessed for the ability to predict this outcome. Performances of the algorithms were assessed through discrimination, calibration, and decision curve analysis.

RESULTS

Overall, of the 381 patients included, 60 (20.3%) demonstrated sustained postoperative opioid consumption. The factors determined for prediction of prolonged postoperative opioid prescriptions were reduced preoperative scores on the following patient-reported outcomes: the IKDC, KOOS ADL, VR12 MCS, KOOS pain, and KOOS Sport and Activities. The ensemble model achieved the best performance based on discrimination (AUC = 0.74), calibration, and decision curve analysis. This model was integrated into a web-based open-access application able to provide both predictions and explanations.

CONCLUSION

Following appropriate external validation, the algorithm developed presently could augment timely identification of patients who are at risk of extended opioid use. Reduced scores on preoperative patient-reported outcomes, symptom duration and perioperative oral morphine equivalents were identified as novel predictors of prolonged postoperative opioid use. The predictive model can be easily deployed in the clinical setting to identify at risk patients thus allowing providers to optimize modifiable risk factors and appropriately counsel patients preoperatively.

LEVEL OF EVIDENCE

III.

Oxytocin prevents cue-induced reinstatement of oxycodone seeking: Involvement of DNA methylation in the hippocampus

Oxycodone is one of the most commonly used analgesics in the clinic. However, long-term use can contribute to drug dependence. Accumulating evidence of changes in DNA methylation after opioid relapse has provided insight into mechanisms underlying drug-associated memory. The neuropeptide oxytocin is reported to be a potential treatment for addiction. The present study sought to identify changes in global and synaptic gene methylation after cue-induced reinstatement of oxycodone conditioned place preference (CPP) and the effect of oxytocin. We analyzed hippocampal mRNA of synaptic genes and also synaptic density in response to oxycodone CPP. We determined the mRNA levels of DNA methyltransferases (Dnmts) and ten-eleven translocations (Tets), observed global 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) levels, and measured DNA methylation status of four synaptic genes implicated in learning and memory (Arc, Dlg1, Dlg4, and Syn1). Both synaptic density and the transcription of 15 hippocampal synaptic genes significantly increased following cue-induced reinstatement of oxycodone CPP. Oxycodone relapse was also related to markedly decreased 5-mC levels and decreased transcription of Dnmt1, Dnmt3a, and Dnmt3b; in contrast, 5-hmC levels and the transcription of Tet1 and Tet3 were increased. Oxycodone exposure induced DNA hypomethylation at the exons of the Arc, Dlg1, Dlg4, and Syn1 genes. Intracerebroventricular (ICV) administration of oxytocin (2.5 μg/μl) specifically blocked oxycodone relapse, possibly by inhibition of Arc, Dlg1, Dlg4, and Syn1 hypomethylation in oxycodone-treated rats. Together, these data indicate the occurrence of epigenetic changes in the hippocampus following oxycodone relapse and the potential role of oxytocin in oxycodone addiction.

Impaired Acquisition of Nicotine-Induced Conditioned Place Preference in Fatty Acid-Binding Protein 3 Null Mice

Nicotine causes psychological dependence through its interactions with nicotinic acetylcholine receptors in the brain. We previously demonstrated that fatty acid-binding protein 3 (FABP3) colocalizes with dopamine D2 receptors (D2Rs) in the dorsal striatum, and FABP3 deficiency leads to impaired D2R function. Moreover, D2R null mice do not exhibit increased nicotine-induced conditioned place preference (CPP) following chronic nicotine administration. To investigate the role of FABP3 in nicotine-induced CPP, FABP3 knockout (FABP3^-/-) mice were evaluated using a CPP apparatus following consecutive nicotine administration (0.5 mg/kg) for 14 days. Importantly, nicotine-induced CPP was suppressed in the conditioning, withdrawal, and relapse phases in FABP3^-/- mice. To resolve the mechanisms underlying impaired nicotine-induced CPP in these mice, we assessed c-Fos expression and Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) signaling in both dopamine D1 receptor (D1R)- and D2R-positive neurons in the nucleus accumbens (NAc). Notably, 64% of dopamine receptor-positive neurons in the mouse NAc expressed both D1R and D2R. Impaired nicotine-induced CPP was correlated with lack of responsiveness of both CaMKII and ERK phosphorylation. The number of D2R-positive neurons was increased in FABP3^-/- mice, while the number of D1R-positive neurons and the responsiveness of c-Fos expression to nicotine were decreased. The aberrant c-Fos expression was closely correlated with CaMKII but not ERK phosphorylation levels in the NAc of FABP3^-/- mice. Taken together, these results indicate that impaired D2R signaling due to lack of FABP3 may affect D1R and c-Fos signaling and underlie nicotine-induced CPP behaviors.

The Effect of High-Frequency Electrical Stimulation of Bilateral Nucleus Accumbens on the Behavior of Morphine-Induced Conditioned Place Preference Rats at Extinction and Reinstatement Phases

Objective

To explore the optimal time points for deep brain stimulation (DBS) on the treatment of morphine addiction and its possible mechanisms by investigating how high-frequency stimulation (HFS) in bilateral nucleus accumbens (NAc) at different time points influences the addictive behaviors of rats with drug addiction.

Methods

The rats were randomly divided into extinction stimulation group (n = 20) and postextinction stimulation group (n = 20). Ten rats in the extinction stimulation group were treated using 120 Hz HFS during extinction stage while another 10 rats with pseudostimulation were served as control group. The CPP scores were evaluated at the second day after intervention, with total 9 sections accomplished. The CPP scores were evaluated at the second day of the intervention. In the postextinction stimulation group, 120 Hz HFS was intervened during the postextinction stage in 10 experimental rats and pseudostimulation was performed in 10 control rats. Stimulation was performed for 7 days continuously, and a small dose of morphine was administrated to induce relapse after the postextinction period.

Results

During the extinction phase, CPP scores after HFS were significantly higher. During the postextinction phase, relapse CPP scores after HFS were dramatically lower.

Conclusion

HFS of bilateral NAc inhibits the extinction of addictive behavior during the extinction phase, and HFS during the postextinction period suppresses relapse of drug seeking behavior.

Involvement of the endogenous opioid system in the beneficial influence of physical exercise on amphetamine-induced addiction parameters

Psychostimulant drugs addiction is a chronic public health problem and individuals remain susceptible to relapses increasing public expenses even after withdrawal and treatment. Our research group has focused on finding new therapies to be employed in drug addiction treatment, suggesting the physical exercise as a promising tool. This way, it is necessary to know the mechanisms involved in the beneficial influences of physical exercise observing the pathway that could be explored in drug addiction treatment. Male Wistar rats were conditioned with amphetamine (AMPH) following the conditioned place preference (CPP) protocol and subsequently submitted to swimming for 5 weeks (1 h per day, 5 days per week). Half of the animals were injected with Naloxone (0.3 mg/mL/kg body weight, i.p.) 5 min prior each physical exercise day. After AMPH-CPP re-exposure, our outcomes showed that physical exercise, in addition to minimizing the relapse behavior in the CPP, it increased D1R, D2R and DAT in the Ventral Tegmental Area (VTA), but not in the Nucleus accumbens (NAc). Interestingly, while naloxone inhibited the partial beneficial influence of the exercise on drug-relapse behavior, exercise-induced changes in the dopaminergic system were not observed in the group administered with naloxone as well. Based on these evidences, besides reinforcing the beneficial influence of the physical exercise on AMPH-induced drug addiction, we propose the involvement of endogenous opioid system activation, not as a single one, but as a possible mechanism of action resulting from the physical activity practice, thus characterizing an important therapeutic approach, which may contribute to drug withdrawal consequently preventing relapse.