Hypothalamus

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

Immunocytochemical localization of luteinizing hormone-releasing hormone (LHRH) pathways in the sheep brain during anestrus and the mid-luteal phase of the estrous cycle.

Abstract: The luteinizing hormone-releasing hormone (LHRH) system of the sheep brain was examined by light microscopic immunocytochemistry with thick, unembedded sections. We compared the distribution and morphology of LHRH cells and their fibers in intact and ovariectomized anestrous ewes, and in breeding season ewes during the mid-luteal phase of their estrous cycle. In all animals, a majority of LHRH neurons were found in the medial preoptic area adjacent to the organum vasculosum of the lamina terminalis. These cells formed a continuum rostrally with immunoreactive neurons in the diagonal band of Broca and medial septum and caudally with cells in the ventrolateral anterior hypothalamus and lateral hypothalamus. Relatively few cells (1-2%) were seen in the arcuate nucleus or its vicinity. Preoptic LHRH neurons project to the tubero-infundibular sulcus of the median eminence by at least two routes: a major ventrolateral projection above the optic tract in the anterior and lateral hypothalamus, and a less prominent periventricular pathway along the third ventricle. LHRH fibers were also observed in a number of extrahypothalamic regions, including the medial amygdala and the accessory olfactory bulb. Immunoreactive LHRH neurons in the sheep exhibited a complex light microscopic morphology unlike that seen in LHRH cells of any other species to date. LHRH cells with extensive, branching processes were frequently found in clusters with close somatic appositions between neighboring cells. Multiple thin protuberances emanated from the soma of many immunoreactive neurons. Immunoreactive fibers with beaded varicosities often were intimately associated with both cell bodies and their dendritic processes. Morphometric analyses revealed that preoptic LHRH neurons in three of four mid-luteal phase ewes had a shorter total dendritic length than those neurons in either intact or ovariectomized anestrous ewes, but this difference between breeding season and anestrous ewes was not statistically significant. Evidence for possible seasonal and/or steroid-induced alterations in the morphology of LHRH neurons must be documented by further studies, including immunocytochemical observations at an ultrastructural level.

Hypothalamic thyroid hormone catabolism acts as a gatekeeper for the seasonal control of body weight and reproduction.

Abstract: Seasonal adaptations in physiology exhibited by many animals involve an interface between biological timing and specific neuroendocrine systems, but the molecular basis of this interface is unknown. In this study of Siberian hamsters, we show that the availability of thyroid hormone within the hypothalamus is a key determinant of seasonal transitions. The expression of the gene encoding type III deiodinase (Dio3) and Dio3 activity in vivo (catabolism of T4 and T3) is dynamically and temporally regulated by photoperiod, consistent with the loss of hypothalamic T3 concentrations under short photoperiods. Chronic replacement of T3 in the hypothalamus of male hamsters exposed to short photoperiods, thus bypassing synthetic or catabolic deiodinase enzymes located in cells of the ependyma of the third ventricle, prevented the onset of short-day physiology: hamsters maintained a long-day body weight phenotype and failed to undergo testicular and epididymal regression. However, pelage moult to a winter coat was n...

Puberty in monkeys is triggered by chemical stimulation of the hypothalamus.

Abstract: Gonadal quiescence prior to puberty in primates results from a diminished secretion of the pituitary gonadotropic hormones, follicle-stimulating hormone and luteinizing hormone, which, in turn, is occasioned by an interruption of pulsatile release of gonadotropin-releasing hormone (GnRH) from the hypothalamus during this phase of development. A discharge of GnRH may be provoked from the hypothalamus of prepubertal monkeys, however, by an i.v. injection of N-methyl-D-aspartate (NMDA), an analog of the putative excitatory neurotransmitter, aspartate. Since this action of NMDA is blocked by the specific NMDA receptor antagonist, DL-2-amino-5-phosphonopentanoic acid, the release of GnRH is likely mediated by NMDA receptors located either on the GnRH neurons themselves or on afferents to the GnRH cells. We report here that prolonged intermittent NMDA stimulation of GnRH neurons within the hypothalamus of the juvenile monkey for 16-30 wk results, with surprising ease, in the onset of precocious puberty with full activation of the hypothalamic-pituitary-Leydig cell axis and initiation of spermatogenesis. These findings demonstrate that, in primates, the network of hypothalamic GnRH neurons, which in adulthood provides the drive to the gonadotropin-secreting cells of the anterior pituitary gland, must now be viewed together with the pituitary and gonads as a nonlimiting component of the control system that governs the onset of puberty in these species.

The central melanocortin system and the integration of short- and long-term regulators of energy homeostasis.

Abstract: The importance of the central melanocortin system in the regulation of energy balance is highlighted by studies in transgenic animals and humans with defects in this system Mice that are engineered to be deficient for the melanocortin-4 receptor (MC4R) or pro-opiomelanocortin (POMC) and those that overexpress agouti or agouti-related protein (AgRP) all have a characteristic obese phenotype typified by hyperphagia, increased linear growth, and metabolic defects Similar attributes are seen in humans with haploinsufficiency of the MC4R The central melanocortin system modulates energy homeostasis through the actions of the agonist, alpha-melanocyte-stimulating hormone (alpha-MSH), a POMC cleavage product, and the endogenous antagonist AgRP on the MC3R and MC4R POMC is expressed at only two locations in the brain: the arcuate nucleus of the hypothalamus (ARC) and the nucleus of the tractus solitarius (NTS) of the brainstem This chapter will discuss these two populations of POMC neurons and their contribution to energy homeostasis We will examine the involvement of the central melanocortin system in the incorporation of information from the adipostatic hormone leptin and acute hunger and satiety factors such as peptide YY (PYY(3-36)) and ghrelin via a neuronal network involving POMC/cocaine and amphetamine-related transcript (CART) and neuropeptide Y (NPY)/AgRP neurons We will discuss evidence for the existence of a similar network of neurons in the NTS and propose a model by which this information from the ARC and NTS centers may be integrated directly or via adipostatic centers such as the paraventricular nucleus of the hypothalamus (PVH)

Afferent and efferent connections of the A5 noradrenergic cell group in the rat.

Abstract: The supraspinal afferent and efferent connections of the A5 noradrenergic cell group were examined in rats. Very small deposits of HRP-WGA were made in the rostral A5 area. Catecholamine histofluorescence techniques were used to confirm that the deposits overlapped the A5 column. Retrogradely labeled cells were present in the perifornical area and paraventricular nucleus of the hypothalamus, the Kolliker-Fuse nucleus, dorsal parabrachial area, intermediate and caudal portions of the nucleus of the solitary tract, and the ventral medullary reticular formation in the areas of the A1 and B1 cell groups. Anterograde HRP-WGA labeling was found in several areas of the subcortical CNS. The contribution of A5 neurons to this labeling was confirmed with retrogradely transported fluorescent latex microspheres combined with catecholamine histofluorescence techniques. The A5 cell group was found to have significant projections to the central nucleus of the amygdala, perifornical area of the hypothalamus, midbrain periaqueductal gray, parabrachial area, and the nucleus of the solitary tract. Other A5 projections include the paraventricular nucleus of the thalamus, the bed nucleus of the stria terminalis, and possibly the zona incerta and lateral and dorsal hypothalamic areas. In addition, A5 neurons may innervate the ventrolateral reticular formation of the medulla. Virtually all of the areas innervated by A5 noradrenergic neurons are involved in cardiovascular regulation. In addition, the A5 area receives afferent input from major cardiovascular regulatory centers of the supraspinal CNS. Thus the A5 cell group has the potential to exert a significant influence on the cardiovascular regulatory system.