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Volume 17, Number 20, Issue of October 15, 1997 pp. 7988-7994
Copyright ©1997 Society for NeuroscienceD1-D2 Interaction in Feedback Control of Midbrain Dopamine Neurons
Received April 21, 1997; revised July 22, 1997; accepted July 30, 1997.
Wei-Xing Shi, Paula L. Smith, Chen-Lun Pun, Barbara Millet, and Benjamin S. Bunney Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut 06510
Dopamine (DA) D1-like receptors are present in pathways implicated in feedback control of midbrain DA neurons. However, stimulation of these receptors either produces no effect on DA cells, or the effect is inconsistent. It is possible that the expression of a D1 feedback effect requires co-activation of D2-like receptors. To test this hypothesis, we recorded extracellularly the spontaneous activity of nigral DA cells in a low cerveau isolé rat preparation. SKF38393 and dyhydrexidine, two D1 agonists, were administered systemically to animals pretreated with different doses of the D2 agonist quinpirole. Supporting the hypothesis, the two D1 agonists consistently inhibited DA cells in animals given high doses of quinpirole (
40 µg/kg, i.v.). However, no significant D1 effect was observed in animals pretreated with only low doses (
20 µg/kg) of quinpirole. Because low doses of D2 agonists preferentially act on DA autoreceptors, and because the D1 inhibition persisted in animals whose DA autoreceptors were blocked by intranigral application of raclopride, our results suggest that the expression of D1 feedback inhibition requires co-activation of D2-like receptors on DA target neurons, instead of DA neurons themselves. These results, together with the finding that chloral hydrate completely blocked the D1 inhibition, may explain why previous studies have failed to show a consistent D1 effect on DA cells and suggest that drugs designed to act specifically on one subtype of DA receptor may, via feedback pathways, influence the action of endogenous DA on other DA receptor subtypes as well.
Key words: DA neuron; feedback pathway; D1; D2; synergistic; SKF38393; dyhydrexidine; substantia nigra; striatonigral; single-unit recording
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