Figure 8.

A model of leptin action on the TRH neuron. Shown is a proposed model of leptin action on the TRH neuron. After crossing the blood-brain barrier leptin can act either directly on the TRH neuron or via an indirect pathway by increasing the production of α-MSH in the POMC neuron in the arcuate nucleus. Also shown are the inputs of AGRP and NPY, both of which are known to project to the TRH neuron. Leptin, through the phosphorylation of Stat3, can directly activate the TRH promoter as can α-MSH through the activation of CREB. T3 can inhibit TRH gene expression, principally through the TRβ2 isoform. NPYR1/5, NPY receptor 1 or 5.