Immunofluorescence photomicrographs of sections from two different levels of the rat hypothalamus after incubation with antiserum to LR. In the anterior hypothalamus, strong LR-LI is present in the magnocellular supraoptic nucleus (SON) and paraventricular nucleus (PVN). Weaker LR-IR cells are also encountered in the parvocellular PVN and in the periventricular nucleus (Pe). At a midhypothalamic level, strong LR-LI is present in the arcuate nucleus (Arc), the caudal extension of the SON, and the lateral hypothalamus (LH). Weaker LR-LI is seen in the ventromedial nucleus (VMN). f, Fornix; ME, median eminence; 3v, third ventricle. Scale bar, 100 μm.