Hypothalamus

About: Hypothalamus is a research topic. Over the lifetime, 22301 publications have been published within this topic receiving 1085925 citations.

Developmental Time Course of Estradiol, Testosterone, and Dihydrotestosterone Levels in Discrete Regions of Male and Female Rat Brain

Abstract: The prevailing view of sexual differentiation of mammalian brain is that androgen synthesized in the fetal and neonatal testis and aromatized centrally during a perinatal sensitive period is the sole source of brain estradiol and the primary determinant of sex differences. Subregions of the diencephalon are among the most sexually dimorphic in the brain, and there are well-established sex differences in the amount of testosterone and estradiol measured in the hypothalamus and preoptic area during the perinatal period. We previously reported unexpectedly high estradiol in the hippocampus and cortex of both male and female newborn rat. This prompted a thorough investigation of the developmental profile of steroids in the rat brain using RIA to quantify the level of estradiol, testosterone, and dihydrotestosterone in discrete subregions of the brain from embryonic d 19 to adulthood. Plasma estradiol levels from individual animals were assessed when sufficient sample was available. A significant sex differenc...

The kisspeptin system of the human hypothalamus: sexual dimorphism and relationship with gonadotropin-releasing hormone and neurokinin B neurons.

Abstract: Kisspeptin signaling via the kisspeptin receptor G-protein-coupled receptor-54 plays a fundamental role in the onset of puberty and the regulation of mammalian reproduction. In this immunocytochemical study we addressed the (i) topography, (ii) sexual dimorphism, (iii) relationship to gonadotropin-releasing hormone (GnRH) neurons and (iv) neurokinin B content of kisspeptin-immunoreactive hypothalamic neurons in human autopsy samples. In females, kisspeptin-immunoreactive axons formed a dense periventricular plexus and profusely innervated capillary vessels in the infundibular stalk. Most immunolabeled somata occurred in the infundibular nucleus. Many cells were also embedded in the periventricular fiber plexus. Rostrally, they formed a prominent periventricular cell mass (magnocellular paraventricular nucleus). Robust sex differences were noticed in that fibers and somata were significantly less numerous in male individuals. In dual-immunolabeled specimens, fine kisspeptin-immunoreactive axon varicosities formed axo-somatic, axo-dendritic and axo-axonal contacts with GnRH neurons. Dual-immunofluorescent studies established that 77% of kisspeptin-immunoreactive cells in the infundibular nucleus synthesize the tachykinin peptide neurokinin B, which is known to play crucial role in human fertility; 56 and 17% of kisspeptin fibers in the infundibular and periventricular nuclei, respectively, contained neurokinin B immunoreactivity. Site-specific co-localization patterns implied that kisspeptin neurons in the infundibular nucleus and elsewhere contributed differentially to these plexuses. This study describes the distribution and robust sexual dimorphism of kisspeptin-immunoreactive elements in human hypothalami, reveals neuronal contacts between kisspeptin-immunoreactive fibers and GnRH cells, and demonstrates co-synthesis of kisspeptins and neurokinin B in the infundibular nucleus. The neuroanatomical information will contribute to our understanding of central mechanisms whereby kisspeptins regulate human fertility.

A diurnal rhythm of stimulatory input to the hypothalamo-pituitary-adrenal system as revealed by timed intrahypothalamic administration of the vasopressin V1 antagonist

Abstract: The mammalian suprachiasmatic nuclei (SCN) contain an endogenous pacemaker that generates daily rhythms in behavior and secretion of hormones. We hypothesized that the SCN imposes its circadian rhythm on the rest of the brain via a rhythmic release of its transmitters in its target areas. Previously, we demonstrated a pronounced inhibitory effect of vasopressin (VP), released from SCN terminals in the dorsomedial hypothalamus, on the release of the adrenal hormone corticosterone. In the present study, microdialysis-mediated intracerebral administration of the VP V1-receptor antagonist was used to pursue the study of the mechanisms underlying the circadian control of basal corticosterone release. Using timed administrations of the VP antagonist divided equally over the day/night cycle, we were able to uncover the existence of an additional stimulatory input from the SCN to the hypothalamopituitary-adrenal (HPA) axis. Peak activity of this stimulatory SCN input takes place during the second half of the light period, after the daily peak of VP secretion, with a delay of approximately 4-6 hr. In all likelihood, the inhibitory and stimulatory circadian input via separate mechanisms affects corticosterone release. Together, these two opposing circadian control mechanisms of the HPA axis enable a precise timing of the circadian peak in corticosterone release.