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

Acute aerobic exercise ameliorates craving and attentional function in individuals with methamphetamine use disorders

OBJECTIVE

Chronic methamphetamine use is frequently associated with impairments in the attentional network (alerting, orienting, conflict networks) and related brain regions, which significantly trigger METH-related cravings. The aim of this study is to investigate the effects of moderate-intensity acute aerobic exercise on cravings and attentional networks in individuals with methamphetamine use disorders (MUD).

METHODS

Using a cross-over design, this study recruited 32 male MUDs to randomly complete a 30min moderate-intensity aerobics exercise condition (65%-75% HRmax) and an assigned material reading control condition, with a 7-day washout interval. All participants completed Visual Analog Scales before, during, and after exercise, until the HR dropped to 110% of the resting heart rate, in preparation for the Attention Network Test (ANT).

RESULTS

The aerobic exercise significantly reduces the participants' cravings. There were no differences observed in the efficiency of alerting and orienting networks between the aerobic exercise and control conditions, however, the efficiency of conflict network was enhanced after exercise. Furthermore, the results showed a significant negative correlation between the enhancements in conflict network efficiency and the reductions in post-exercise craving scores for both conditions.

CONCLUSION

Moderate-intensity acute aerobic exercise significantly improves the attentional network, especially enhancing the conflict network in individuals with MUD. Additionally, the improvement of the conflict network is closely related to the reduction in cravings in individuals with MUD, suggesting that aerobic exercise may reduce cravings through improvements in cognitive function.

Comparison of forced and voluntary exercise types on male rat brain monoamine levels, anxiety-like behaviour, and physiological indexes under light and dark phases

PURPOSE

Physical exercise improves physical and mental health; however, the differences between voluntary and forced exercise protocols are unclear. In addition, knowledge regarding the consequences of differences in testing timing, such as light and dark phases, in response to exercise type is limited. We investigated the effects of chronic forced and voluntary wheel running on the changes in brain monoamine levels (5-HT: serotonin, DA: dopamine, NA: noradrenaline), anxiety-like behaviours, and physiological stress responses in the light and dark phases.

METHODS

Adult male Wistar rats were equally and randomly assigned to four groups: sedentary control, voluntary exercise (free running on a wheel, V-EX), voluntary limited exercise (wheel available only 1 h/day, VL-EX), and forced exercise (running on a motorised wheel, F-EX). Each group was further divided into dark- or light-experimental condition groups. After 4 weeks, the rats underwent an open-field test. The monoamines and their metabolite levels were measured in the major neural cell bodies and the projection areas related to behaviour, cognition, anxiety, and stress in the brain.

RESULTS

Adrenal hypertrophy and elevated body temperature, except during the exercise period, were observed in the F-EX rats that exhibited anxiety-like behaviour. The levels of monoamines and their metabolites, particularly the 5-HTergic and DAergic systems, in specific areas, were significantly altered in the rats in the V-EX group compared to those in the VL-EX and other groups. These differences were observed only in the dark phase.

CONCLUSION

The results suggest that V-EX mainly stimulates the 5-HTergic and DAergic systems, while F-EX induces physiological stress and increases anxiety-like behaviour during the dark phase. This study highlights the importance of accounting for exercise types and light/dark phases in behavioural neuroscience experiments.

Maintaining a Dynamic Brain: A Review of Empirical Findings Describing the Roles of Exercise, Learning, and Environmental Enrichment in Neuroplasticity from 2017-2023

Brain plasticity, also termed neuroplasticity, refers to the brain's life-long ability to reorganize itself in response to various changes in the environment, experiences, and learning. The brain is a dynamic organ capable of responding to stimulating or depriving environments, activities, and circumstances from changes in gene expression, release of neurotransmitters and neurotrophic factors, to cellular reorganization and reprogrammed functional connectivity. The rate of neuroplastic alteration varies across the lifespan, creating further challenges for understanding and manipulating these processes to benefit motor control, learning, memory, and neural remodeling after injury. Neuroplasticity-related research spans several decades, and hundreds of reviews have been written and published since its inception. Here we present an overview of the empirical papers published between 2017 and 2023 that address the unique effects of exercise, plasticity-stimulating activities, and the depriving effect of social isolation on brain plasticity and behavior.

Impact of high-access exercise prior to and during early adolescence on later vulnerability to opioid use and relapse in male rats

Middle- and high-school athletes participating in certain team sports are at greater risk of opioid misuse and addiction than those who do not. While this risk is thought to be due to increased access to opioids, in this study we explored the possibility that the sensitizing effects of discontinued high-intensity exercise may also contribute. Specifically, using male rat models with fentanyl, we tested the hypothesis that high-access exercise (24 h/day access to a running wheel) during pre/early adolescence (two weeks, postnatal-day 24-37) would enhance vulnerability to opioid use and relapse during late adolescence/adulthood. Rats with a history of high-access exercise showed stronger fentanyl-associated lever discrimination during acquisition, greater motivation to obtain infusions of fentanyl following acquisition, and had an enhanced sensitivity to the reinstating effects of fentanyl-associated cues following extended (24 h/day), intermittent-access self-administration and protracted abstinence (14 days) compared to sedentary controls. In contrast, sedentary rats had greater overall responding (active- and inactive-lever) during acquisition and greater non-specific (inactive-lever) responding during extended-access self-administration. Molecular markers associated with opioid seeking/relapse were also differentially expressed in the nucleus accumbens core of rats with versus without a history of high-access exercise following relapse testing (e.g., Bdnf-IV and Drd2 expression). Together, these findings demonstrate that high-access exercise prior to and throughout early-adolescence enhances vulnerability to the reinforcing and cue-induced reinstating effects of opioids during later adolescence/adulthood. Thus, it is possible that the discontinuation of high intensity exercise contributes to the enhanced vulnerability observed in middle- and high-school athletes.

A red nucleus-VTA glutamate pathway underlies exercise reward and the therapeutic effect of exercise on cocaine use

Physical exercise is rewarding and protective against drug abuse and addiction. However, the neural mechanisms underlying these actions remain unclear. Here, we report that long-term wheel-running produced a more robust increase in c-fos expression in the red nucleus (RN) than in other brain regions. Anatomic and functional assays demonstrated that most RN magnocellular portion (RNm) neurons are glutamatergic. Wheel-running activates a subset of RNm glutamate neurons that project to ventral tegmental area (VTA) dopamine neurons. Optogenetic stimulation of this pathway was rewarding, as assessed by intracranial self-stimulation and conditioned place preference, whereas optical inhibition blocked wheel-running behavior. Running wheel access decreased cocaine self-administration and cocaine seeking during extinction. Last, optogenetic stimulation of the RNm-to-VTA glutamate pathway inhibited responding to cocaine. Together, these findings indicate that physical exercise activates a specific RNm-to-VTA glutamatergic pathway, producing exercise reward and reducing cocaine intake.

The Influence of Moderate Physical Activity on Brain Monoaminergic Responses to Binge-Patterned Alcohol Ingestion in Female Mice

Monoamine neurotransmitter activity in brain reward, limbic, and motor areas play key roles in the motivation to misuse alcohol and can become modified by exercise in a manner that may affect alcohol craving. This study investigated the influence of daily moderate physical activity on monoamine-related neurochemical concentrations across the mouse brain in response to high volume ethanol ingestion. Adult female C57BL/6J mice were housed with or without 2.5 h of daily access to running wheels for 30 days. On the last 5 days, mice participated in the voluntary binge-like ethanol drinking procedure, “Drinking in the dark” (DID). Mice were sampled immediately following the final episode of DID. Monoamine-related neurochemical concentrations were measured across brain regions comprising reward, limbic, and motor circuits using ultra High-Performance Liquid Chromatography (UHPLC). The results suggest that physical activity status did not influence ethanol ingestion during DID. Moreover, daily running wheel access only mildly influenced alcohol-related norepinephrine concentrations in the hypothalamus and prefrontal cortex, as well as serotonin turnover in the hippocampus. However, access to alcohol during DID eliminated wheel running-related decreases of norepinephrine, serotonin, and 5-HIAA content in the hypothalamus, but also to a lesser extent for norepinephrine in the hippocampus and caudal cortical areas. Finally, alcohol access increased serotonin and dopamine-related neurochemical turnover in the striatum and brainstem areas, regardless of physical activity status. Together, these data provide a relatively thorough assessment of monoamine-related neurochemical levels across the brain in response to voluntary binge-patterned ethanol drinking, but also adds to a growing body of research questioning the utility of moderate physical activity as an intervention to curb alcohol abuse.