D3 and D2 dopamine receptors: Visualization of cellular expression patterns in motor and limbic structures

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Abstract
The distribution of the D3 and D2 dopamine receptor subtypes in forebrain regions of the basal ganglia and mesocorticolimbic system was determined. This was assessed through combined fluorescent visualization of subtype selective anti‐peptide antibodies for these cloned receptors and detection of their ligand recognition sites using the D2 subfamily antagonist, N‐(p‐aminophenethyl) spiperone (NAPS fluoroprobe). The double‐labeling technique enabled direct comparison of the cloned receptor proteins and NAPS fluoroprobe binding in vitro. The application of these two methods together produced results comparable to single‐labeling paradigms. Functional D3 receptors, defined as the coincident fluorescence of the D3 receptor antisera and fluoroprobe binding, were detected in the core region of the nucleus accumbens and exhibited a laminated expression pattern in the frontal cortex. D3 receptor protein was expressed robustly in neurons of the dorsolateral striatum, but showed an intense neuropil reaction in the globus pallidus. Functional D2 receptors, defined as the coincident fluorescence of the D2 receptor antisera and fluoroprobe binding, were detected in the frontal cortex and the medial shell of the nucleus accumbens. Thus, heterogeneities occurred in the cellular expression of functional D3 and D2 receptors in forebrain dopaminoceptive areas. D3 appears more related to basal ganglia and structures involved with motoric behavior, while D2 was associated with regions associated with cognitive/affective functions.