Posted by Shawn. T. on October 7, 2003, at 23:44:18
In reply to diffrence between dopamine and serotoin, posted by superRitchie on October 7, 2003, at 21:44:11
I like this answer to the question of why drugs that affect dopamine lead to addiction:
Berridge KC, Robinson TE.
What is the role of dopamine in reward: hedonic impact, reward learning, or incentive salience?
Brain Res Brain Res Rev. 1998 Dec;28(3):309-69.
What roles do mesolimbic and neostriatal dopamine systems play in reward? Do they mediate the hedonic impact of rewarding stimuli? Do they mediate hedonic reward learning and associative prediction? Our review of the literature, together with results of a new study of residual reward capacity after dopamine depletion, indicates the answer to both questions is 'no'. Rather, dopamine systems may mediate the incentive salience of rewards, modulating their motivational value in a manner separable from hedonia and reward learning. In a study of the consequences of dopamine loss, rats were depleted of dopamine in the nucleus accumbens and neostriatum by up to 99% using 6-hydroxydopamine. In a series of experiments, we applied the 'taste reactivity' measure of affective reactions (gapes, etc.) to assess the capacity of dopamine-depleted rats for: 1) normal affect (hedonic and aversive reactions), 2) modulation of hedonic affect by associative learning (taste aversion conditioning), and 3) hedonic enhancement of affect by non-dopaminergic pharmacological manipulation of palatability (benzodiazepine administration). We found normal hedonic reaction patterns to sucrose vs. quinine, normal learning of new hedonic stimulus values (a change in palatability based on predictive relations), and normal pharmacological hedonic enhancement of palatability. We discuss these results in the context of hypotheses and data concerning the role of dopamine in reward. We review neurochemical, electrophysiological, and other behavioral evidence. We conclude that dopamine systems are not needed either to mediate the hedonic pleasure of reinforcers or to mediate predictive associations involved in hedonic reward learning. We conclude instead that dopamine may be more important to incentive salience attributions to the neural representations of reward-related stimuli. Incentive salience, we suggest, is a distinct component of motivation and reward. In other words, dopamine systems are necessary for 'wanting' incentives, but not for 'liking' them or for learning new 'likes' and 'dislikes'. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9858756&dopt=Abstract
See also
Kelley, Ann E., Berridge, Kent C.
The Neuroscience of Natural Rewards: Relevance to Addictive Drugs
J. Neurosci. 2002 22: 3306-3311
http://www.jneurosci.org/cgi/content/full/22/9/3306and
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8622814&dopt=Abstract
and
My own interpretation of dopamine's role in addiction varies slightly from Berridge's, but his is the best published interpretation currently available. The evolution of serotonin and dopamine systems within the human brain have resulted in different (and very complex) roles for both; one role of dopamine seems to involve motivation or "wanting." Drugs that affect dopamine receptors in certain areas of the brain basically disrupt the neural systems involved in "wanting" to control certain environmental variables (e.g. the availability of the drugs).
Shawn
poster:Shawn. T.
thread:266567
URL: http://www.dr-bob.org/babble/20031004/msgs/266612.html