Developmental regulation of expression of the D-3 dopamine receptor in ratnucleus accumbens and Islands of Calleja

The dopamine D-3 receptor (D3R) belongs to the D-2 subfamily and is express ed in the rat brain in targets of the mesolimbic dopaminergic system. Littl e is known about its normal development and control by dopaminergic innerva tion. We studied developmental expression of D3R in the rat nucleus accumbe ns (NAC) and islands of Calleja (ISC). At postnatal day (P) 7, D-3 binding sites and mRNA were low in both areas. By P14, D3R and mRNA concentrations were close to adult levels in the ISC, whereas, in the NAG, binding increas ed until 3 months after birth. Cellular concentrations of D-3 mRNA in the I SC increased with age in conjunction with a decrease in the number of D-3 p ositive cells. In the NAC, the number of positive cells increased, whereas cellular levels of expression remained unchanged. Neonatal 6-hydroxydopamin e lesion caused age-dependent changes in D3R expression. D-3 binding sites did not change at P7 or P14, but there was a reduction in the number of D-3 mRNA positive neurons accompanied by an increase in cellular levels of D-3 mRNA at P14, suggesting that changes occurred in a subset of neurons. Up-r egulation of D-3 binding sites in NAC and ISC occurred 1 month after the le sion (P35) concomitant with a decrease in cellular levels of D-3 mRNA and t he number of D-3 mRNA positive cells. At 3 months (P90) after the lesion, a n increase in D-3 mRNA occurred with no change in D-3 binding sites. D3R sh ows region-specific dynamics in receptor/mRNA expression during development and is sensitive to loss of dopamine in early postnatal development.