Saturday, December 24, 2011

The Genetics of Drug Addiction


     Drug addiction is a chronic disease associated with alterations in the brain that result in compulsive behaviour and the urge to use one or more particular drugs. Whether the drug involved is cocaine, amphetamines, narcotics (opioids), cannabis, alcohol or even nicotine, the affliction can be a chronic, relapsing disorder in which these compulsive drug-seeking and drug-taking behaviours persist despite serious negative consequences.
The Effects of Drug Abuse

     Even the tobacco smoker, well aware of the potentially deadly effects and faced with gruesome pictures of the results of smoking ignores, overlooks or 'blanks out' these warnings, overwhelmed by the need for nicotine.
     All these addictive substances induce pleasant states or relieve distress, effects that contribute to their recreational use (see post: Altered States of Consciousness). There really is a 'reward center' in the brain. It sits centrally, in the deep brain structures and is responsible for our feelings of motivation and reward. Performing healthy activities such as eating, drinking and sex, activities that aid in survival, results in stimulation of this central area of the brain. 
Dopamine Pathways and Central Reward Center of the Brain

     Bombarded by the senses of smell, touch, taste, and sight of a morsel of food, for instance, results in the release of the neurotransmitter dopamine, producing the sensation of pleasure and 'wiring' the brain to seek out this same pleasure again.    

     Dopamine has many functions in the brain including roles in motivation, regulation of body temperature, memory, voluntary movement (it is the neurotransmitter that is low in certain areas of the brain in cases of Parkinson's Disease), mood, learning, punishment and reward.
     Nature has programmed us to repeat behaviours that maximize rewards and thus, in a perverse way, it is dopamine that is critically involved in the drug addiction process.
Parkinson's Disease with Forward-Stooped Posture

     A neurotransmitter (such as dopamine, GABA, epinephrine, norepinephrine) is a chemical substance that is released from a nerve ending that then attaches itself to contact points on the next nerve cell(s). These contact points are called receptors but, to add to the confusion, there is often more than one receptor type for the various different neurotransmitters and even more than one receptor site for any one specific neurotransmitter, such as dopamine.
     The role(s) of the various dopamine receptor subtypes on brain cells has been difficult to precisely delineate.
     And then, of course there are two important questions:
1. Are the receptors for the 'reward neurotransmitter' (ie dopamine) different in the addict as compared to the non-addicted individual?
2. Is there a genetic 'predisposition' (a marker? a subtle difference in the gene(s) that codes for these receptors?) in the 'addictively-predisposed' individual?
Chemical Structure of Dopamine

     A great deal of research has looked at the genetics of addiction, mostly focusing on the differences in the genes that code for dopamine receptors in the brain. These studies, which examined families, identical and non-identical twin subjects and control subjects who differed in their drug use habits suggest that there is indeed a significant difference in the make-up of specific dopamine receptors, most markedly at the specific 'DRD2' gene site that codes for dopamine receptors.
Neurotransmitter at Nerve Ending (Synapse)

     Unfortunately, nothing in science is ever quite this simple and these research findings do not hold true in all studies. It seems evident that drug addiction certainly has a genetic component but environment as well as social factors also play important roles.
     One key aspect to addiction however seems to be that it is the neurotransmitter, dopamine that plays a central role in addiction, this scourge of many in today's society.

     An interesting 'mouse party' that demonstrates the brain's activity in drug use has been produced by the Department of genetics at the University of Utah. Click on the link below:
   
     *The genetics of drug addiction: subject of research for the novel Whip the Dogs - Amazon Kindle

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