Addictions reward pathways

While activation of the reward pathways explains the pleasurable sensations associated with acute substance use, chronic use of abused substances resulting in both addiction and withdrawal may be related to neuroadaptive effects occurring within the brain. 

Outline how the mesolimbic reward pathway is implicated in addiction. 

These results are further evidence that inhalants, such as toluene, lead to addiction by activating the reward pathway. Answering the question of why this activation occurs is a current area of study. 

Inhalants are addictive because they activate the brain s reward pathway. 

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. 

Rimonabant may also alter reward pathways that promote addictive behaviors such as overeating. This drug has been shown to attenuate the rewarding effects of alcohol in a strain of alcohol-preferring rat s (161) and may similarly diminish the pleasurable effects of food and overeating that can often play important roles in the etiology of obesity. 

The illicit drug used most commonly by young people at parties and raves is 3,4-methylenedioxymethamphetamine (MDMA) or ecstasy. The mechanism of action of MDMA is not completely understood, but it is believed to inhibit the reuptake of serotonin, to facilitate serotonin release, and to a lesser extent enhance dopamine and norepinephrine release from presynaptic nerve terminals. The serotonin boost can produce a sense of emotional closeness, elation, and sensory delight, and, along with the potential of MDMA to increase dopamine transmission in the reward pathway, it might be associated with the addictive properties of the drug. 

A temporary form of drug-induced psychosis can occur in some cannabis users as a result of taking large doses. Cannabis has some addictive properties, but these are much less than amphetamines, for example. The addictive properties, of cannabis are due, probably, to its indirect capacity to enhance dopaminergic transmission in the reward pathway (i.e. by suppressing GABAergic neurons that modulate the dopaminergic pathway). ... 

Dopamine is the neurotransmitter that is most implicated in addictive behaviors. Drug addictions occur more readily in people who have inherited an abnormal dopamine receptor, for example. It is also a major transmitter in the reward pathway of the brain. Pleasurable activities such as eating and sex, release dopamine, so in terms of evolution, behaviors that promote human survival activate our built-in reward system. 

Reward Therapy. A similar (yet nonspecific) approach is to use a medication that stimulates the brain s reward centers. Reward medications usually do not work in quite the same way as the substance of abuse however, the net effect in the final common pathway (i.e., the reward centers) may be the same. For the most part, these reward centers are activated by either dopamine or endogenous opioid agonists. One common feature of most abused drugs is that they stimulate these reward centers. This lies at the heart of their addictive potential. Some attempts have been made to use medications that activate these reward centers in place of the abused substance. The hypothesis is that the addict will have less intense craving for his/her preferred substance of abuse in the presence of these other agents. This is, of course, a relatively nonspecific approach that could theoretically be used to treat the abuse of many different substances. It has not yet, however, demonstrated any utility in the treatment of substance abuse. 

Through the pathways of the mesolimbic system (a term introduced by Ungerstedt in 1971), the basal ganglia provide an interface with limbic brain regions. This interface has been repeatedly implicated in psychiatric diseases, such as schizophrenia and other affective disorders, as well as in reward and addiction. 

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