Inactivation of the GR in the nervous system affects energy accumulation

The homeostatic regulation of body weight protects the organism from the negative consequences of starvation and obesity. Glucocorticoids (GCs) modulate this regulation, although the underlying mechanisms remain unclear. To address the role of central GRs in the regulation of energy balance, we studied mice in which GlIs have selectively been inactivated in the nervous system. Mutant mice display marked growth retardation. During suckling age this is associated with normal fat deposition causing a 60% temporary increase of percent body fat, compared with control Iittermates. After weaning, fat and protein depositions are reduced so that adults are both smaller and leaner than their controls. Decreased food intake and, after weaning, reduced metabolic efficiency account for these developmental disturbances. Plasma levels of leptin and insulin, two important energy balance regulators, are elevated in young mutants but normal in adults. Leptin/body fat ratio is higher at all ages, suggesting disturbed control of circulating leptin as a consequence of chronically elevated GC levels in mutant animals. Adult mutants display increased hypothalamic CRH and NPY levels, but peptide levels of melanin concentrating hormone and Orexin A and B are unchanged. The increased levels of plasma GCs and hypothalamic CRH may act as catabolic signals most likely leading to persistently reduced energy accumulation.