Regional and temporal differences in leptin signaling in rat brain.

Leptin regulates energy homeostasis through activation of different hypothalamic pathways. Evidence indicates that leptin is a pleiotropic hormone that acts on many brain areas, altering food intake, metabolism, and locomotion, among other functions. Because short-term effects of leptin infusion and intracellular pathways in other brain areas involved in food regulation have not been thoroughly analysed, we have studied the acute effect of intracerebroventricular leptin administration on the levels of the long form of leptin receptor (Ob-Rb), as well as on activation of Janus kinase 2 (JAK2)-signal transducer and activator of transcription 3 (STAT3), protein kinase B (Akt), extracellular regulated kinases (ERKs) and levels of suppressor of cytokine signaling-3 (SOCS3) in the hypothalamus, hippocampus, frontal cortex and cerebellum of adult male Wistar rats at 15min, 1 and 6h. The levels of Ob-Rb increased at 6h in hypothalamus only. Leptin activated the JAK2/STAT3 pathway in all areas, although in a temporally specific pattern. In contrast, this hormone decreased Akt activation in hypothalamus, hippocampus and cerebellum and ERK activation in frontal cortex, while it increased ERK activation in hypothalamus and hippocampus. These differences in modulation of Ob-Rb levels and signaling indicate that the rapid effects of leptin in non-hypothalamic areas are mediated, at least in part, through the intracellular pathways involved in hypothalamic energy balance, but in a temporally specific manner.