Selective dependence of intracerebroventricular neuropeptide Y-elicited effects on central glucocorticoids

It has been reported that hyperphagia and excessive body weight gain of gen etically obese rodents were abolished by adrenalectomy. High hypothalamic l evels of neuropeptide Y (NPY) were found in obese rodents. A chronic intrac erebroventricular (icv) infusion of NPY in normal fats was shown to produce most hormone-metabolic abnormalities of genetically obese animals, and to be inefficient in doing so in adrenalectomized (ADX) rats. The combined pre sence of NPY and of glucocorticoids thus appeared to be necessary for induc ing obesity. This study, therefore, was aimed at determining the consequenc es of a chronic icy NPY infusion in ADX rats receiving or not icy glucocort icoids. It was found that the combined icy infusion of NPY and dexamethason e in ADX rats increased food intake, body weight, plasma insulin, leptin, a nd triglyceride levels relative to vehicle-infused ADX controls. The infusi on of NPY alone, or of dexamethasone alone in ADX rats failed to produce th ese effects. In contrast, the icy infusion of NPY alone greatly decreased t he expression of brown adipose tissue uncoupling protein-1 and -3. This was not modified by the superimposed infusion of dexamethasone. It is conclude d that, although many of centrally elicited NPY effects require the central presence of glucocorticoids, those bearing on the inhibition of uncoupling proteins expression (energy dissipation) do not require central glucocorti coids.