Ontogeny of dopamine D1 receptors in rat forebrain: a quantitative autoradiographic study.

The development of dopamine D1 receptors during the early postnatal period is examined in rat forebrain, using quantitative autoradiography and [3H]SCH 23390 as ligand. Dopamine D1 receptors are present in many regions at birth. In general, regions with the highest densities of D1 receptors in adults have the highest densities of receptors in neonates. For most regions in the forebrain there is a steady increase in the density of D1 receptors, as measured in fmol/mg tissue, from day 1 to day 28 of age. This is most obvious in the regions with the greatest number of receptors, such as the caudate-putamen, the nucleus accumbens, and the olfactory tubercles. The more caudal regions examined in this study had a relatively greater portion of their receptors present at day 1 compared to day 28 than more rostral regions. In general they had about 50% of their receptors present at birth, whereas most regions studied had receptor levels at day 1 about 20% of those found at day 28. In the most anterior regions, the development of receptors was somewhat slower. Receptor number in the frontal cortex region did not begin to increase until about 10 days of age. The present studies indicate that dopamine D1 receptors develop in the forebrain of the rat in a steady pattern. There are no dramatic increases or decreases in receptor number throughout the postnatal period.