Dopamine D2 receptors in the cerebral cortex: distribution and pharmacological characterization with [3H]raclopride.

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Abstract
An apparent involvement of dopamine in the regulation of cognitive functions and the recognition of a widespread dopaminergic innervation of the cortex have focused attention on the identity of cortical dopamine receptors. However, only the presence and distribution of dopamine D1 receptors in the cortex have been well documented. Comparable information on cortical D2 sites is lacking. We report here the results of binding studies in the cortex and neostriatum of rat and monkey using the D2 selective antagonist [3H]raclopride. In both structures [3H]raclopride bound in a sodium-dependent and saturable manner to a single population of sites with pharmacological profiles of dopamine D2 receptors. D2 sites were present in all regions of the cortex, although their density was much lower than in the neostriatum. The density of these sites in both monkey and, to a lesser extent, rat cortex displayed a rostral-caudal gradient with highest concentrations in the prefrontal and lowest concentrations in the occipital cortex, corresponding to dopamine levels in these areas. Thus, the present study establishes the presence and widespread distribution of dopamine D2 receptors in the cortex.