DISSOCIATION OF HYPOTHALAMIC NPY FROM BAT UNCOUPLING PROTEIN MESSENGER-RNA IN RATS EXPOSED TO 24-H THERMONEUTRALITY

Neuropeptide Y (NPY) is increasingly considered to be involved in the central regulation of energy balance. Our previous studies suggest tha t hypothalamic NPY neurons of the arcuatoparaventricular (ARC-PVN) pro jection are inhibited in association with the marked increases in brow n adipose tissue (BAT) thermogenesis and uncoupling protein (UCP) gene expression in rats exposed to cold. We therefore hypothesized that th e NPYergic ARC-PVN system would be activated in a thermoneutral enviro nment, when energy expenditure falls to a minimum, and that this activ ation could mediate the fall in BAT activity. We measured regional hyp othalamic NPY concentrations, hypothalamic NPY receptor binding, and N PY mRNA together with UCP mRNA levels in rats exposed to thermoneutral ity (29 degrees C) for 24 h. At thermoneutrality, UCP mRNA levels fell to 42% of those in controls maintained at 22 degrees C, but there wer e no significant changes in hypothalamic NPY or NPY mRNA levels or in NPY receptor binding. We conclude that the fall in UCP mRNA expression occurring under short-term thermoneutral condition is mediated by neu roendocrine mechanisms other than increased activity of hypothalamic N PY neurons.