Seasonal effects of central leptin infusion on secretion of melatonin and prolactin and on SOCS-3 gene expression in ewes

Recent studies have demonstrated photoperiodic changes in leptin sensitivity of seasonal mammals. Herein, we examined the interaction of season (long days (LD) versus short days (SD)) and recombinant ovine leptin (roleptin) on secretion of melatonin and prolactin (PRL) and on mRNA expression of suppressor of cytokine signaling-3 (SOCS-3) in the medial basal hypothalamus (MBH) in sheep. Twenty-four Polish Longwool ewes, surgically fitted with third ventricle (IIIV) cannulas, were utilized in a replicated switchback design involving 12 ewes per season. Within-season and replicate ewes were assigned randomly to one of three treatments (four ewes/treatment) and infused centrally three times at 0, 1 and 2 h beginning at sunset. Treatments were 1) control, Ringer–Locke buffer; 2) L1, roleptin, 0.5 μg/kg BW; and 3) L2, roleptin, 1.0 μg/kg BW. Jugular blood samples were collected at 15-min intervals beginning immediately before the start of infusions and continued for 6 h. At the end of blood sampling, a washout period of at least 3 days elapsed before ewes were re-randomized and treated with one of the treatments described above (four ewes/treatment). Ewes were then killed and brains were collected for MBH processing. Leptin treatments increased (P