Thyroid hormone excess secondary to global type 3 deiodinase (DIO3) deficiency leads to increased locomotor activity and reduced adiposity, but also to concurrent alterations in parameters of the leptin–melanocortin system that would predict obesity. To distinguish the underlying contributions to the energy balance phenotype of DIO3 deficiency, we generated mice with thyroid hormone excess targeted to pro-opiomelanocortin (POMC)-expressing cells via cell-specific DIO3 inactivation. These mice exhibit a male-specific phenotype of reduced hypothalamic Pomc expression, hyperphagia, and increased activity in brown adipose tissue, with adiposity and serum levels of leptin and thyroid hormones rem
