Developmental regulation of expression of the D3 dopamine receptor in rat nucleus accumbens and islands of Calleja.

The dopamine D3 receptor (D3R) belongs to the D2 subfamily and is expressed in the rat brain in targets of the mesolimbic dopaminergic system. Little is known about its normal development and control by dopaminergic innervation. We studied developmental expression of D3R in the rat nucleus accumbens (NAC) and islands of Calleja (ISC). At postnatal day (P) 7, D3 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 NAC, binding increased until 3 months after birth. Cellular concentrations of D3 mRNA in the ISC increased with age in conjunction with a decrease in the number of D3 positive cells. In the NAC, the number of positive cells increased, whereas cellular levels of expression remained unchanged. Neonatal 6-hydroxydopamine lesion caused age-dependent changes in D3R expression. D3 binding sites did not change at P7 or P14, but there was a reduction in the number of D3 mRNA positive neurons accompanied by an increase in cellular levels of D3 mRNA at P14, suggesting that changes occurred in a subset of neurons. Up-regulation of D3 binding sites in NAC and ISC occurred 1 month after the lesion (P35) concomitant with a decrease in cellular levels of D3 mRNA and the number of D3 mRNA positive cells. At 3 months (P90) after the lesion, an increase in D3 mRNA occurred with no change in D3 binding sites. D3R shows region-specific dynamics in receptor/mRNA expression during development and is sensitive to loss of dopamine in early postnatal development.