Postnatal development of dopamine D4-like receptors in rat forebrain regions: comparison with D2-like receptors.

Development of dopamine D4-like receptors in rat caudate-putamen (CPu), nucleus accumbens (NAc), frontal cortex, hippocampus, and entorhinal cortex was assessed at seven points between postnatal days 7 and 60 by computed in vitro receptor autoradiography, and compared with dopamine (DA) D2-like receptors. Density of radioligand binding to both receptor types increased from day 7 to a peak at day 28 in caudate-putamen (D4, 3.3-fold; D2, 4.3-fold) and nucleus accumbens (2.9- and 3.6-fold), then declined by 28%-33% over days 35-60 to adult levels in both brain regions. In hippocampus, frontal and entorhinal cortex, both receptor types increased by 3.8- to 5.8-fold from day 7 to maximal levels at day 35 that remained unchanged to day 60. These findings suggest: (1) D4- and D2-like receptors follow a similar course of development in several cortical, extrapyramidal, and limbic regions of rat forebrain; (2) elimination of excessive receptors of both types occurred in caudate-putamen and nucleus accumbens but not in the other brain regions.