Postnatal developmental trajectory of dopamine receptor 1 and 2 expression in cortical and striatal brain regions.

Healthy brain function requires a balance between the activity of dopamine receptor 1 (D1) and dopamine receptor 2 (D2). Alterations in this balance increase the risk for numerous developmental brain disorders. Indeed, D1 and D2 expression fluctuates throughout maturation, although there is conflicting evidence regarding the precise changes that occur. Here, we used stereology to investigate the developmental changes in the number of D1- or D2-expressing neurons in the prelimbic cortex, infralimbic cortex (IL), insula cortex, dorsal striatum, and ventral striatum of female and male mice with green fluorescent protein-tagged D1 or D2. Postnatal day 17, 25, 35, 49, and 70 were examined to cover juvenility to adulthood. In all regions, analysis of D1 density compared to D2 density within each sex seldom detected effects or interactions involving age. However, D1:D2 density ratio changed across age depending on sex. In the IL, D1:D2 density ratio increased in females from adolescence, whereas it was stable in males. In the insula cortex, D1:D2 ratio initially increased in males but decreased in females from juvenility to preadolescence. The ratio then increased in males and females from adolescence to adulthood, with males showing a more dramatic increase. In both the dorsal and ventral striatum, the ratio increased from adolescence. In all regions, females had a higher ratio compared to males throughout maturation except in the insula cortex at P25. These comprehensive observations are novel, and highlight how the maturational changes in the expression of these receptors may contribute to developmental disorders.