Fig. 23.Coronal sections (rostral to caudal) of rat hypothalamus showing the regional distribution of neurons that accumulate a retrogradely transported marker substance injected into the external zone of the median eminence. Cells of origin of both the tuberoinfundibular pathway and hypothalamic neurohypophysial tract are identified due to diffusion of the tracer into the internal zone of the median eminence. (A-F) Level of the paraventricular nucleus (PVN); (G-I) level of the arcuate nucleus (ARC). III = third ventricle, AH = anterior hypothalamus, M = magnocellular division of the PVN, ME = median eminence, ap = anterior parvocellular subdivision, dp = dorsal parvocellular subdivision, mp = medial parvocellular subdivision, pp = periventricular parvocellular subdivision, vp = ventral parvocellular subdivision of the PVN.