Postnatal ontogeny of dopamine D3 receptors in the mouse brain: Autoradiographic evidence for a transient cortical expression

The expression of dopamine D3 receptors is relatively low in the adult brain and is mainly restricted to the limbic region. We studied here the postnatal development of these receptors in the mouse brain by quantitative autoradiography using [H-3](+/-)-7-OH-DPAT as ligand, In all brain regions examined. there was a progressive increase in D3 receptor protein expression from birth to the weaning period, a pattern reminiscent of that of dopamine D2 rather than D1 receptors. In broad outline, the regional distribution of D3 receptors during brain ontogeny resembled that observed in adult animals, the labelling being detected Earlier in the structures with the higher density in the adult. The highest and earliest expression of D3 receptors was observed in the islands of Calleja and olfactory tubercle, where [H-3]7-OH-DPAT binding was already present at birth. D3 receptors appeared at postnatal day 4 in the nucleus accumbens, at postnatal day 8 in the substantia nigra, in the medial mamillary nucleus and in the anterior thalamic complex, and at postnatal day II in the archaeocerebellum. In contrast to other brain structures where the developmental pattern of D3 receptor expression parallelled its distribution and density in the adult brain, there was a transient cortical expression of [H-3]7-OH-DPAT binding between postnatal days 6 and 15, confined to a longitudinal strip in the dorso-lateral part of the parietal cortex. This expression had disappeared by postnatal day 21 and was not detected In adult mice. These developmental findings, and particularly the transient cortical expression of functional receptors, point to the involvement of D3 receptors in ontogenic processes.