Cyclical variations in the abundance of leptin receptors, but not in circulating leptin, correlate with NPY expression during the oestrous cycle

We have demonstrated previously that pharmacological doses of oestradiol de creased leptin receptor expression in the hypothalamus. We therefore analys ed leptin receptor expression during the oestrous cycle in the rat, to esta blish if acute changes in oestradiol affect leptin receptor expression unde r physiological conditions. Radioactive in situ hybridization histochemistr y was used to measure the gene expression under investigation. Total leptin receptor transcript levels were lowest in prooestrus in the choroid plexus , these changes correspond inversely with levels of circulating oestradiol in the rat 4-day oestrous cycle. In contrast full-length leptin receptor le vels in both arcuate and ventromedial nuclei did not correspond to the leve ls of total leptin receptor in the same areas of the hypothalamus or serum levels of oestradiol. Full-length leptin receptor expression in the arcuate nucleus was negatively correlated with neuropeptide Y (NPY) expression (r = 0.447, p < 0.05) in the same nucleus. Arcuate nucleus NPY expression did not correlate significantly with the expression of total leptin receptors i n the arcuate nucleus(r = 0.080) or serum leptin levels (r = 0.251). Our re sults demonstrate that leptin receptor expression is regulated during the o estrous cycle. The unchanged serum leptin levels during the oestrous cycle together with the correlation between the expression of leptin-RL and NPY p rovide circumstantial evidence that regulation of leptin receptor abundance in the hypothalamus governs the biological actions of leptin.