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 qua ntitative autoradiography using [H-3](+/-)-7-OH-DPAT as ligand, In all brain regions examined. there was a progressive increase in D3 recept or protein expression from birth to the weaning period, a pattern remi niscent of that of dopamine D2 rather than D1 receptors. In broad outl ine, the regional distribution of D3 receptors during brain ontogeny r esembled that observed in adult animals, the labelling being detected Earlier in the structures with the higher density in the adult. The hi ghest and earliest expression of D3 receptors was observed in the isla nds of Calleja and olfactory tubercle, where [H-3]7-OH-DPAT binding wa s already present at birth. D3 receptors appeared at postnatal day 4 i n the nucleus accumbens, at postnatal day 8 in the substantia nigra, i n the medial mamillary nucleus and in the anterior thalamic complex, a nd at postnatal day II in the archaeocerebellum. In contrast to other brain structures where the developmental pattern of D3 receptor expres sion parallelled its distribution and density in the adult brain, ther e was a transient cortical expression of [H-3]7-OH-DPAT binding betwee n postnatal days 6 and 15, confined to a longitudinal strip in the dor so-lateral part of the parietal cortex. This expression had disappeare d by postnatal day 21 and was not detected In adult mice. These develo pmental findings, and particularly the transient cortical expression o f functional receptors, point to the involvement of D3 receptors in on togenic processes.