Developmental changes in plasma leptin and hypothalamic leptin receptor expression in the rat : peripubertal changes and the emergence of sex differences

Leptin, the peptide hormone product of the ob gene, regulates food intake and energy expenditure at the hypothalamic level via the long-form of the leptin receptor (Ob-Rb). Leptin also plays a key role in determining the onset of puberty, but there is controversy as to whether leptin provides a trigger for puberty or is a permissive signal. Thus, although leptin administration can advance puberty onset in rodents, circulating leptin appears stable across puberty. While these data suggest a permissive role for leptin in rat puberty, it is possible that a change in hypothalamic response to leptin (e.g. via increased Ob-Rb expression) could enhance leptin action and thus trigger puberty without a rise in circulating leptin. In the present study we assessed developmental changes in hypothalamic Ob-Rb mRNA and protein expression in female and male rats from late fetal to postpubertal life. Quantitative RT-PCR showed that Ob-Rb mRNA increased (P