Drugs abused by humans preferentially increase synaptic dopamine concentrations in the mesolimbic system of freely moving rats.

TLDR

Brain dialysis in freely moving rats measured how drugs alter extracellular dopamine in the nucleus accumbens septi and dorsal caudate nucleus. Abused drugs (opiates, ethanol, nicotine, amphetamine, cocaine) raise dopamine in both the nucleus accumbens and caudate, especially the accumbens, and trigger hypermotility, whereas aversive drugs lower dopamine and induce hypomotility, haloperidol raises dopamine without preference and causes sedation, and non‑abused drugs have no effect, supporting the idea that limbic dopamine stimulation underlies drug abuse.

Abstract

The effect of various drugs on the extracellular concentration of dopamine in two terminal dopaminergic areas, the nucleus accumbens septi (a limbic area) and the dorsal caudate nucleus (a subcortical motor area), was studied in freely moving rats by using brain dialysis. Drugs abused by humans (e.g., opiates, ethanol, nicotine, amphetamine, and cocaine) increased extracellular dopamine concentrations in both areas, but especially in the accumbens, and elicited hypermotility at low doses. On the other hand, drugs with aversive properties (e.g., agonists of kappa opioid receptors, U-50,488, tifluadom, and bremazocine) reduced dopamine release in the accumbens and in the caudate and elicited hypomotility. Haloperidol, a neuroleptic drug, increased extracellular dopamine concentrations, but this effect was not preferential for the accumbens and was associated with hypomotility and sedation. Drugs not abused by humans [e.g., imipramine (an antidepressant), atropine (an antimuscarinic drug), and diphenhydramine (an antihistamine)] failed to modify synaptic dopamine concentrations. These results provide biochemical evidence for the hypothesis that stimulation of dopamine transmission in the limbic system might be a fundamental property of drugs that are abused.