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

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 hormone Anterior 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 hormone Anterior 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