The suprachiasmatic nucleus generates the diurnal changes in plasma leptinlevels

At present it is not clear which factors are responsible for the diurnal pa ttern of plasma leptin levels, although the timing of food intake and circu lating hormones such as glucocorticoids and insulin have both been proposed as independent determinants. In this study we show that ablation of the bi ological clock by thermal lesions of the hypothalamic suprachiasmatic nucle us (SCN) completely eliminates the diurnal pattern of plasma leptin levels. By contrast, removal of the diurnal corticosterone signal by adrenalectomy and corticosterone replacement did not affect diurnal plasma leptin levels . More importantly, removal of the nocturnal feeding signal by submitting t he animals to a regular feeding schedule of six meals per day did not aboli sh the diurnal plasma leptin levels. However, both SCN lesions and the regu lar feeding schedule did cause an increase in the 24-h mean plasma leptin l evels. As neither rhythmic feeding, insulin, or corticosterone signals can completely explain the diurnal plasma leptin rhythm, we conclude that biolo gical clock control of the sympathetic input to the adipocyte is essential for regulation of the daily rhythm in leptin release.