Brain s reward system

Researchers begin to examine dopamine s role in the brain s reward system and in the reinforcing aspects of drugs of abuse. 

This question deserves a fuller treatment than I can give it here. The answer, I think, is connected with the fact that breathing is an automatic response, controlled by the autonomic nervous system. Appetites, acquired and unacquired, are sustained by reward.34 In contrast, I suppose, the desire to breathe and the discomfort of not breathing do not involve the brain s reward system in the same way, but I am not sure how to incorporate these observations into a satisfactory definition of the appetitive. 

Methadone, like all opiates, is a chemically simple compound that has a variety of effects on those who take it. But while other opiates exert powerful euphoric effects on a person by acting very much like chemicals called endorphins and enkephalins, methadone produces only a mild (or no) euphoria, to which patients quickly become tolerate. Endorphins and enkephalins are naturally produced inside the brain. When released in the brain s reward system, they produce a mind reward and users feel good as a result. Methadone and other opiates mimic these natural brain chemicals, which is why they are so addicting. 

Dopamine is also an important component of the brain s reward system and is believed to play a role in drug addiction. Increased levels of dopamine have been associated with cocaine, amphetamine, and marijuana use, as well as alcohol and nicotine addiction, see also Neurotransmitters. 

One of nicotine s effects is to increase the concentration of dopamine, a chemical in the brain s reward system. Release of this chemical makes smokers feel good and reinforces the need to smoke. 

A kind of (low-dose) dependence may also develop when alcohol is consumed daily, albeit in minor quantities. As a rule of thumb, alcohol always makes people dependent when consumed on a regular basis — no matter what the dose may be. Alcohol addiction comprises (1.) physical dependence including increased tolerance as well as the withdrawal syndrome and (2.) psychological dependence with an uncontrollable desire for permanent or intermittent alcohol consumption, reduced self-control as well as changes in behaviour, (s. tab. 28.1) Alcohol abuse includes addiction without actually being identical to it. Neither the brain s reward system (A. Herz et af, 1989) nor the addiction memory (X Boning, 1992) are stimulated by occasional alcohol consumption. Another explanation for this... 

The compelling and overwhelming nature of cocaine addiction is impressive and tells us something profound about how the brain is built. It is apparently comprised of critically important internal neural systems that can produce a powerful rewarding experience usually connected to activities that are the basis for the survival of our species eating and reproduction. Drugs such as cocaine can hijack these neural processes and stimulate the brain s reward centers so excessively and unnaturally that users will crave more stimulation, as they would normally crave food and sex. From the brain s perspective, there is no real... 

Both cocaine and the amphetamines act through the monoamine neurotransmitter systems, particularly by enhancing dopaminergic activity. This action in the brain s reward pathways may account for the highly addictive nature of cocaine. 

Gardner, Eliot L., and Joyce H. Lowinson. 1991. "Marijuana s Interaction with Brain Reward Systems Update 1991." Pharmacology Biochemistry and Behavior 40 571-80. 

These smoked substances interact with the brain s own cannabinoid receptors to trigger dopamine release from the mesolimbic reward system. There are two known cannabinoid receptors, CB1 (in the brain, which is coupled via G proteins and modulates adenylate cyclase and ion channels) and CB2 (in the immune system). The CB1 receptors may mediate not only marijuana s reinforcing properties, but also those of alcohol. There is also an endogenous cannabinoid system (the brain s own marijuana) capable of activating these cannabinoid receptors functionally. These ert-docannabinoids are synthesized by neurons and inactivated by reuptake systems and enzymes in both neurons and glia. 

In 2005, Mague et al. published more on their research, again finding that methylphenidate caused changes in the young rat s brain that persist into adulthood. They concluded, Reduced sensitivity to these various types of reward may reflect general dysfunctions of brain reward systems. None of this is good news for children and adolescents who have been treated with Ritalin products. 

Gardner EL, Lowinson JH (1991) Marijuana s interaction with brain reward systems— update 1991. Pharmacol Biochem Behav 40 571-580... 

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