Hypothalamus NEU 257 3/3/2011

The diencephalon “between brain” Posterior part of embryonic forebrain Lies between brainstem and cerebral hemispheres Includes: thalamus, hypothalamus, subthalamus, epithalamus

Hypothalamus: General description Below rostral thalamus (hypo =“under”/”beneath) Vital regulatory functions include: temperature, heart rate, blood pressure, blood osmolarity, goal seeking behavior, emotional behavior, visceral nervous system, sexual activity, food & water intake, aggression Forms floor and lower walls of third ventricle Contains various classes of peptidergic neuroendocrine cells which control endocrine function Communicates with cortex via limbic system and also via direct projections

Involvement with 3 major systems Endocrine system (HPA: hypothalamo- pituitary-adrenal axis) Autonomic nervous system Motivation system ….Also adaptive emotional behavior

Gross anatomy of the Hypothalamus science.tjc.edu/ images/brain/Index.htm

PV = paraventricular A = anterior nucleus S = supraoptic & suprachiasmatic DM = dorsomedial VM = ventromedial ARC = arcuate P = posterior nuclei M = mammillary TC = tuber cinereum ME = median eminence INF = infundibulum Anatomical Organization of Hypothalamus

Main Inputs to Hypothalamus receives info on external and internal conditions: – specific sensory info (e.g., direct retinal projection) - input from visceral senses (NTS: nucleus of the solitary tract: taste ) –contains many neurons that are sensitive to local temperature, osmolarity, glucose, sodium –circulating hormones influence it via the circumventricular organs

SCN Retinohypothalamic tract SCN III

Circumventricular organs Brain regions near ventricles that lack a blood-brain barrier, e.g., subfornical organ, OVLT, median eminence, area postrema Highly vascularized Influenced by circulating hormones, osmotic changes, substances in CSF, afferent fibers from other parts of the nervous system

Peptidergic neuroendocrine cells: Magnocellular neurons “Large” neurons Located in paraventricular and supraoptic nuclei Secrete oxytocin and vasopressin into general circulation via posterior pituitary Oxytocin uterine contraction & milk secretion Vasopressin vasoconstriction, water resorption by the kidney

Brainmaps.org

Magnocellular Secretory System clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm

“small” neurons Located in medial basal region, arcuate and tuberal nuclei, periventricular region, preoptic and paraventricular nuclei Secrete releasing and inhibiting hormones into portal vasculature via anterior pituitary Nobel prize awarded to Guillemin (Salk), Schally and Yalow in 1977 for their (independent) work in proving the hypothesis that the hypothalamus releases hormones that regulate the pituitary Peptidergic neuroendocrine cells: Parvocellular neurons

Brainmaps.org

Hypothalamic Portal System clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm

Hypothalamic inhibitors Hypothalamic hormoneAnterior pituitary hormone Prolactin release-inhibiting hormone (PIH), dopamine Prolactin Growth hormone release-inhibiting hormone (GIH; somatostatin) GH, thyrotropin Melanocyte-stimulating hormone release inhibiting factor (MIF) MSH

Hypothalamic releasers Hypothalamic hormoneAnterior pituitary hormone Thyrotropin-releasing hormone (TRH) Thyrotropin, prolactin Corticotropin-releasing hormone (CRH) Adrenocorticotropin,  -lipotropin gonadotropin-releasing hormone (GnRH) LH, FSH Growth-hormone releasing hormone (GHRH) GH Prolactin-releasing factor (PRF)Prolactin Melanocyte-stimulating hormone- releasing factor (MRF) MSH,  -endorphin

Peripheral Influence of Hypothalamus clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm

Hypocretin From Thannickal et al., Neuron 27: 469, 2000 Also known as “orexin” Peptide involved in arousal and feeding behavior Project to thalamus, cortex and brainstem regions associated with arousal, cardiovascular control, and autonomic functions Few thousand neurons Loss of hypocretin neurons implicated in human narcolepsy