More about dopamine: The August issue of JAMA (Journal of the American Medical Association) news section had an article on various recent findings about dopamine, cocaine, ritalin and ADHD. Evidently, the target of action of cocaine and ritalin is the same: synaptic dopamine transporters, which recycle released dopamine into the synapse. It blocks them; dopamine action is heightened. The dopaminergic system is the reward and pleasure circuit, but the reason cocaine is highly addictive and ritalin much less so is the kinetics - orally taken, ritalin takes an hour to reach peak concentration in the synapse. Cocaine acts in seconds. (Injected ritalin does produce a high). People with ADHD seemingly have many more dopamine transporters, so dopamine does not stick around in the synapse. Two consequences - normally interesting activities produce fewer rewards, and at the same time, against a subdued signal the "noise" of random neural firing becomes more prominent, interfering with concentration. I seem to remember reading at one point that one of the first correlations of genes and personality traits involved dopamine receptor variants and the personality trait of novelty seeking behaviour - don't know whether preliminary results were borne out.
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