Photoperiod Regulates Growth, Puberty and Hypothalamic Neuropeptide and Receptor Gene Expression in Female Siberian Hamsters1

In seasonal mammals, both the growth and reproductive axes are regulated by photoperiod. Female Siberian hamsters were kept, for up to 12 weeks, in long-day (LD) or short-day (SD) photoperiod, from weaning at 3 weeks of age (Exp 1). LD hamsters had characteristically faster growth and higher asymptotic body weight, adiposity, and leptin gene expression in adipose tissue. Only LD females attained puberty. Gene expression in the hypothalamic arcuate nucleus for leptin receptor (OB-Rb), POMC, and melanocortin 3-receptor (MC3-R) was higher in LD but did not change from weaning levels in SD. In contrast, gene expression in the arcuate nucleus for cocaine and amphetamine-regulated transcript (CART) was higher in SD than LD, a difference that was apparent at 2 weeks post weaning. Transfer of SD females to LD at 15 weeks post weaning (Exp 2) increased body weight, leptin signal, and gene expression for POMC but failed to induce normal puberty onset or to increase gene expression for OB-Rb and MC3-R. Therefore, photoperiodic regulation of puberty may be modulated by age, by photoperiodic history, and by changes in leptin signaling and the activity of the leptin-sensitive hypothalamic melanocortin system (POMC, MC3-R). A role for CART in photoperiodic regulation of growth is suggested, because the changes in CART gene expression preceded significant divergence of growth trajectories in the opposite photoperiods.