Molecular characterization of individual D3 dopamine receptor-expressing cells isolated from multiple brain regions of a novel mouse model

Among dopamine receptors, the expression and function of the D-3 receptor subtype is not well understood. The receptor has the highest affinity for dopamine and many drugs that target dopamine receptors. In this paper, we examined, at the single cell level, the characteristics of D-3 receptor-expressing cells isolated from different brain regions of male and female mice that were either 35 or 70 days old. The brain regions included nucleus accumbens, Islands of Calleja, olfactory tubercle, retrosplenial cortex, dorsal subiculum, mammillary body, amygdala and septum. The expression analysis was done in the drd3-enhanced green fluorescent protein transgenic mice that report the endogenous expression of D-3 receptor mRNA. Using single cell reverse transcriptase PCR, we determined if the D-3 receptor-expressing fluorescent cells in these mice were neurons or glia and if they were glutamatergic, GABAergic or catecholaminergic. Next, we determined if the fluorescent cells co-expressed the four other dopamine receptor subtypes, adenylate cyclase V (ACV) isoform, and three different isoforms of G protein-coupled inward rectifier potassium (GIRK) channels. The results suggest that D-3 receptor is expressed in neurons, with region-specific expression in glutamatergic and GABAergic neurons. The D-3 receptor primarily co-expressed with D-1 and D-2 dopamine receptors with regional, sex and age-dependent differences in the co-expression pattern. The percentage of cells co-expressing D-3 receptor and ACV or GIRK channels varied significantly by brain region, sex and age. The molecular characterization of D-3 receptor-expressing cells in mouse brain reported here will facilitate the characterization of D-3 receptor function in physiology and pathophysiology.