Transmission and scanning electron-microscopic observations on tanycytes in the mediobasal hypothalamus and the median eminence of adrenalectomized rats.

Tanycytes in the median eminence (ME) of the rat exhibit morphological features suggesting their possible participation in transport phenomena. After adrenalectomy, which modifies the hypothalamo-hypophyseal axis, they undergo morphological changes characterized by an accumulation of lipid droplets, an increased number of bleb-like protrusions at their apex, as well as an increased pinocytosis of intraventricularly injected horseradish peroxidase (HRP). In addition, after adrenalectomy an increased number of vacuoles appears at the level of the tubero-infundibular sulci. Their intracellular location in the tanycytes is demonstrated by an intraventricular injection of HRP. The significance of these vacuoles is discussed in relation to the hydroelectrolytic modifications associated with the state of adrenalectomy.

The hypothalamus: anatomy and functions.

The neuroanatomy of the human hypothalamus is reviewed with special interest focused on its neuroendocrine role. The magnocellular neurons in the supraoptic and paraventricular nuclei are the site of synthesis of the nonapeptides antidiuretic hormone and oxytocin and their carriers, the neurophysins. They are in close relation with the posterior lobe of the pituitary which contains their axonal neurosecretory endings. The parvocellular neurons are scattered around the third ventricle, from the preoptic area towards the infundibulum. They control the adenohypophysis by the releasing hormones for thyrotropin (TRH), luteinizing hormone (LHGR), growth hormone (GHRH) and the inhibiting factor for growth hormone (somatostatin or SRIF) and prolactin (PIH). The mapping of the various hypothalamic structures responsible for these syntheses is still a problem although it progresses thanks to new techniques of immunocytochemistry. Recent so-called "hypothalamic" hormones like TRH and somatostatin for instance have been identified outside the hypothalamus. The posterior hypothalamus with other parts of the brain: the medial forebrain non myelinated bundle, in the lateral hypothalamus, connects the preoptic region to the midbrain. The stria terminalis connects the amygdala with the hypothalamus. Fibers of retinal origin terminate in the suprachiasmatic nuclei.