Developmental regulation of leptin gene expression in rat brain and pituitary.

We have previously reported the expression of leptin mRNA and protein in adult rat brain and pituitary gland. We report here the presence of leptin and leptin receptor mRNA in neonatal female rat brain and pituitary using RT-PCR as well as leptin and leptin receptor immunoreactivity in neonatal rat brain. In addition, we describe age-related changes in leptin mRNA expression in female rat brain and pituitary from postnatal day 2 to 28, evaluated using semi-quantitative RT-PCR analysis. Age-related differences in leptin (ob) mRNA levels were tissue-dependent. The most striking developmental changes were noted in the pituitary and cerebral cortex. In the pituitary, ob mRNA levels were maximal during postnatal days 7-14 and fell sharply by postnatal day 22. In cortex, ob mRNA levels were low in neonatal pups (day 2-7) but increased significantly between postnatal days 14 and 28. Leptin mRNA was detectable at postnatal day 2 in hypothalamus and subcutaneous fat. No significant differences in the level of expression were observed between postnatal day 2 and 28. Serum leptin levels were highest at day 7-14 and decreased significantly by day 21-28, coincident with the fall in pituitary leptin expression. The high levels of leptin expression in the neonatal pituitary suggest that this gland may contribute to the circulating leptin levels during early postnatal development, when adipose deposits are minimal. These data indicate that regulation of leptin gene expression in the postnatal period is tissue-dependent, a finding, which suggests that local leptin expression may have important functional significance in the development of the brain-pituitary system.