ROLE OF NPY NEURONS IN GH-DEPENDENT FEEDBACK SIGNALING TO THE BRAIN

The neuroendocrine regulation of pulsatile growth hormone (GH) secreti on involves the reciprocal interactions between growth hormone-releasi ng hormone (GHRH)- and somatostatin-containing neurones, residing prim arily in the hypothalamic arcuate nucleus (ARC) and the periventricula r nucleus (PeN), respectively. Considerable evidence supports the conc ept that GH itself participates in the regulation of its own rhythmic secretion through a reciprocal feedback on GHRH and somatostatin neuro nes. The direct actions of GH are mediated through GH receptors, and i n the PeN, the majority of somatostatin neurones express this receptor . GH induces the expression of the immediate early gene c-fos in the A RC; however, few GHRH residing in the ARC express the GH receptor, sug gesting that the action of GH on GHRH cells must be indirect through a nother population of unidentified cells. NPY neurones express c-fos in response to GH, and preliminary results suggest that NPY neurones in the ARC express the GH receptor. These observations suggest that NPY n eurones play a physiological role in the feedback of regulation of GH secretion.