The pattern of retinoic acid receptor expression and subcellular, anatomic and functional area translocation during the postnatal development of the rat cerebral cortex and white matter.

Retinoic acid (RA), which is an important modulator of brain development, neural cell proliferation, neurite outgrowth, and synaptic plasticity, is regulated via changes in RA receptors. The pattern of RA receptor changes in the rat cerebral cortex and white matter during postnatal development has not been extensively studied. Therefore, we studied the mRNA expression patterns of 6 RA receptors in the postnatal rat cerebral cortex and white matter at 1, 3, 7, 10, 14, 21, 28, and 35days. We found that RARβ, RXRα and RXRβ mRNA levels gradually increased during postnatal development. RARα presented a nearly unimodal trend, but RARγ and RXRγ were generally bimodal. RARα, RARγ, and RXRγ mRNA levels peaked at postnatal day 21 (P21). The pattern of RARα expression was consistent with that of its mRNA levels. RARα and RXRγ mRNA levels were the highest among those of all RA receptors during postnatal development. Interestingly, RARα expression was mainly located in the cytoplasm in the postnatal development apart from P3d. We further showed that RARα is expressed mainly in layers 2 and 3, partly in layers 1 and 4, and in a limited manner in layers 5 and 6 in the parietal cortex. Most RARα expression occurs in layers 2, 3, and 4 in the temporal lobe cortex. We realized that the M1 S2 region of RARα is highly expressed and that the position of RARα changes dynamically to meet the needs of different regions during development. These results support the idea that the RA receptor plays an important role in the cerebrum during postnatal development and implementation of these functions may be mainly dependent on the non-transcriptional or post- transcriptional regulation.