The Human Hypothalamus
4C: LEVEL 4 CELLS: The large ventromedial hypothalamic nucleus is prominent at this level. Between the ventromedial nuclei and the third ventricle are the tiny cells of the periventricular "nuclei" which cannot be seen in these sections. Above and below small cells similar those of the periventricular nuclei accumulate in larger numbers as, respectively, the dorsomedial nuclei and the arcuate (or infundibular) nuclei. Cells of the arcuate nuclei extend into the infundibulum, which has been torn away. (The infundibulum leads to the pituitary which is enclosed in the bony sella turcica, these cannot be preserved during the rapid extraction necessary to obtain good brain fixation, which in turn is necessary to obtain adequate cell staining.) The dorsomedial nucleus is difficult to distinguish from neighboring regions in the human hypothalamus, particularly the diffuse cells of the lateral hypothalamic area. Dorsomedial, periventricular, and arcuate nuclei contain many dopaminergic cells, and many cells which influence the production of hormones in the pituitary. The lateral hypothalamic area is traversed by the largely unmyelinated fibers of the medial forebrain bundle, as well as the well-myelinated fibers of the fornix. Both of these fiber bundles run antero-posteriorly through this part of the hypothalamus.