Fig. 31. Schematic representation of the regulatory system involved in establishing the set point for feedback regulation of TRH mRNA in hypophysiotropic neurons in the hypothalamic paraventricular nucleus in (A) fed and (B) fasted states. Insets in A and B arein situhybridization autoradiograms of coronal sections through the rat hypothalamus showing the effect of fasting to reduce TRH mRNA in the PVN. ARC = arcuate nucleus, PVN = paraventricular nucleus.