Friday 6 July 2018

Physical exercise against addiction

Recent research into addiction, performed at the ‘Buffalo Research Institute on Addictions’, unravelled an important neurobiological mechanism. By influencing the dopamine metabolism, it has been found that aerobic physical exercise possibly helps to treat addictions.

Cardiovascular training, also known as aerobic training, accelerates the heart rate and respiration. During exercise of this type, the body consumes more oxygen. This type of exercise is associated with several health benefits. This improves the general condition (muscle strength and muscle stamina), the cardiovascular system and lung function. That helps to prevent all sorts of chronic disorders, including diabetes and cardiovascular disease. Mental health also benefits from physical exercise, because its helps to reduce stress and feelings of anxiety and depression. 


Functioning through neurotransmitter dopamine

More significantly, there is growing evidence that aerobic exercise helps to prevent and treat substance abuse and addiction. An increase in substance abuse (alcohol, nicotine, opioids) and relapse can also be prevented through regular aerobic physical exercise. The study, published in ‘Medicine and science in sports and exercise’, focussed on the neurobiological aspects of dopamine metabolism and how changes to this come about through physical exercise 


Functioning through mesolimbic pathway

Based on animal studies, the researchers discovered that daily aerobic physical exercise caused the mesolimbic dopamine pathway in the brain to change. The main function of the dopaminergic mesolimbic pathway is the regulation of emotional behaviour, particularly behaviour that is determined by reward and punishment. Dopamine is an important neurotransmitter that is associated with rewards, motivation and learning. 
The physiological effects of this neurotransmitter are brought about through binding to various subtypes of dopamine receptors; the D1 and D2 receptors are the best known. These receptors have various locations in the brain (e.g. D1 receptors in striatum and the neocortex; D2 receptors in striatum and the limbic system). 


Recycling of dopamine

Many drugs, such as cocaine or certain medications delay the recycling of dopamine, the consequence being an overstimulation of dopamine pathways, through the mesolimbic circuit. In addition, drugs stimulate opiate receptors as a result of which the inhibitory effect of certain neurotransmitters (gamma-aminobutyric acid, abbreviated GABA) is eliminated. Measurements of dopamine in addicted people show that the dopamine balance is often disrupted. 


Running on a wheel

To investigate the changes in the dopamine signalling through physical exercise, eight-week-old rats were divided into two groups. For a six-week period, half of the rats ran five times a  week on a wheel, at a speed of 10 metres a minute. The other half remained in the cage and had a more ‘sedentary’ lifestyle. After 6 weeks, the brain structures were examined by means of autoradiography and specific substances that bind to dopamine receptors. This can be used to determine the number of dopamine receptors. 


Changed binding capacity of dopamine receptors

The rats which exercised regularly on the wheel were compared to the animals that were subjected to a sedentary lifestyle. The active rats were found to have a lower binding capacity with the D1-like receptors, in comparison to the animals that were subjected to a sedentary lifestyle. That reduced binding capacity was seen in specific brain structures. 
In addition, the rats in the exercise groups demonstrated an increased binding capacity through D2-like dopamine receptors in other specific brain structures (including caudate putamen). Some of these structures play a crucial role through the mesolimbic dopamine pathways and/or in experiencing positive experiences, such as desires and motivation. The nuclei (cell bodies of nerve cells) react to the rewarding effects of behaviour, including addictive behaviour. 



In summary, it is found that aerobic physical exercise changes the mesolimbic dopamine route in the brain. It might be the case that this form of exercise can restore a disrupted dopamine balance in addicted people. A lot of research emphasises that addiction is a complex illness. Follow-up research would have to focus on people who are addicted or have a tendency to become addicted.