Brain: Hypothalamus
Location of the human hypothalamus
Illu diencephalon .jpg
Latin hypothalamus
Gray's subject #189 812
NeuroNames hier-358
MeSH Hypothalamus
NeuroLex ID birnlex_734


The hypothalamus is located below the thalamus, just above the brain stem. In the terminology of neuroanatomy, it forms the ventral part of the diencephalon. All vertebrate brains contain a hypothalamus. In humans, it is roughly the size of an almond.

The hypothalamus is responsible for certain metabolic processes and other activities of the autonomic nervous system. It synthesizes and secretes certain neurohormones, often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones. The hypothalamus controls body temperature, hunger, thirst,[1] fatigue, and circadian cycles.



Hypothalamus (Animation)

The hypothalamus is a complex region in the brain of humans, and even small nuclei within the hypothalamus are involved in many different functions. The paraventricular nucleus for instance makes oxytocin and the supraoptic nucleus makes vasopressin (also called antidiuretic hormone) neurons which project to the posterior pituitary, but also contains neurons that regulate ACTH and TSH secretion from the anterior pituitary, as well as gastric reflexes, maternal behavior, blood pressure, feeding, immune responses, and temperature.

The hypothalamus co-ordinates many hormonal and behavioural circadian rhythms, complex patterns of neuroendocrine outputs, complex homeostatic mechanisms,[2] and many important behaviours.

The hypothalamus must therefore respond to many different signals, some of which are generated externally and some internally. It is thus richly connected with many parts of the central nervous system, including the brainstem reticular formation and autonomic zones, the limbic forebrain (particularly the amygdala, septum, diagonal band of Broca, and the olfactory bulbs, and the cerebral cortex).

The hypothalamus is responsive to:

Olfactory stimuli


Blood-borne stimuli

Peptide hormones have important influences upon the hypothalamus, and to do so they must evade the blood-brain barrier. The hypothalamus is bounded in part by specialized brain regions that lack an effective blood-brain barrier; the capillary endothelium at these sites is fenestrated to allow free passage of even large proteins and other molecules. Some of these sites are the sites of neurosecretion - the neurohypophysis and the median eminence. However others are sites at which the brain samples the composition of the blood. Two of these sites, the subfornical organ and the OVLT (organum vasculosum of the lamina terminalis) are so-called circumventricular organs, where neurons are in intimate contact with both blood and CSF. These structures are densely vascularized, and contain osmoreceptive and sodium-receptive neurons which control drinking, vasopressin release, sodium excretion, and sodium appetite. They also contain neurons with receptors for angiotensin, atrial natriuretic factor, endothelin and relaxin, each of which is important in the regulation of fluid and electrolyte balance. Neurons in the OVLT and SFO project to the supraoptic nucleus and paraventricular nucleus, and also to preoptic hypothalamic areas. The circumventricular organs may also be the site of action of interleukins to elicit both fever and ACTH secretion, via effects on paraventricular neurons.


The hypothalamus functions as a type of thermostat for the body.[3] It sets a desired body temperature, and stimulates either heat production and retention to raise the blood temperature to a higher setting, or sweating and vasodilation to cool the blood to a lower temperature. All fevers result from a raised setting in the hypothalamus; elevated body temperatures due to any other cause are classified as hyperthermia.[3] Rarely, direct damage to the hypothalamus, such as from a stroke, will cause a fever; this is sometimes called a hypothalamic fever. However, it is more common for such damage to cause abnormally low body temperatures.[3]


The hypothalamus contains neurons that react strongly to steroids and glucocorticoids – (the steroid hormones of the adrenal gland, released in response to ACTH). It also contains specialised glucose-sensitive neurons (in the arcuate nucleus and ventromedial hypothalamus), which are important for appetite. The preoptic area contains thermosensitive neurons; these are important for TRH secretion.

Neural inputs




A cross section of the monkey hypothalamus displays 2 of the major hypothalamic nuclei on either side of the fluid-filled 3rd ventricle

Hypothalamic nuclei

The hypothalamic nuclei include the following:[4][5][6]

Hypothalamic nuclei
Region Area Nucleus Function[7]
Anterior Medial Medial preoptic nucleus
Supraoptic nucleus (SO)
Paraventricular nucleus (PV)
Anterior hypothalamic nucleus (AH)
Suprachiasmatic nucleus (SC)
Lateral Lateral preoptic nucleus
Lateral nucleus (LT)
  • thirst and hunger
Part of supraoptic nucleus (SO)
Tuberal Medial Dorsomedial hypothalamic nucleus (DM)
  • GI stimulation
Ventromedial nucleus (VM)
  • satiety
  • neuroendocrine control
Arcuate nucleus (AR)
  • Lutenizing Hormone R.H. release
  • Follicle Stimulating Hormone Releasing Factor
  • feeding
  • Dopamine
  • GHRH
Lateral Lateral nucleus (LT)
  • thirst and hunger
Lateral tuberal nuclei
Posterior Medial Mammillary nuclei (part of mammillary bodies) (MB)
Posterior nucleus (PN)
Lateral Lateral nucleus (LT)
See also: ventrolateral preoptic nucleus

Hypothalamic nuclei on one side of the hypothalamus, shown in a 3-D computer reconstruction



The outputs of the hypothalamus can be divided into two categories: neural projections, and endocrine hormones.[9]

Neural projections


Endocrine hormones

The hypothalamus affects the endocrine system and governs emotional behavior, such as anger and sexual activity. Most of the hypothalamic hormones generated are distributed to the pituitary via the hypophyseal portal system.[10] The hypothalamus maintains homeostasis; this includes a regulation of blood pressure, heart rate, and temperature.

Secreted hormone Abbreviation Produced by Effect
Thyrotropin-releasing hormone
(Prolactin-releasing hormone)
TRH, TRF, or PRH Parvocellular neurosecretory neurons Stimulate thyroid-stimulating hormone (TSH) release from anterior pituitary (primarily)
Stimulate prolactin release from anterior pituitary
(Prolactin-inhibiting hormone)
(growth hormone-inhibiting hormone)
Inhibit thyroid-stimulating hormone (TSH) release from anterior pituitary
Stimulate luteinizing hormone (LH) release from anterior pituitary
Corticotropin-releasing hormone CRH or CRF Parvocellular neurosecretory neurons Stimulate adrenocorticotropic hormone (ACTH) release from anterior pituitary
Oxytocin Magnocellular neurosecretory cells Uterine contraction
Lactation (letdown reflex)
(antidiuretic hormone)
ADH or AVP Magnocellular neurosecretory neurons Increases water permeability in the distal convoluted tubule and collecting duct of nephrons, thus promoting water reabsorption and increasing blood volume

See also: Hypocretin

Control of food intake


There are different hypotheses related to this regulation:[11]

  2. Gutpeptide hypothesis - gastrointestinal hormones like Grp, glucagons, CCK and others claimed to inhibit food intake. The food entering the gastrointestinal tract triggers the release of these hormones which acts on the brain to produce satiety. The brain contains both CCK-A and CCK-B receptors.
  4. Thermostatic hypothesis - according to this hypothesis, a decrease in body temperature below a given set point stimulates appetite, while an increase above the set point inhibits appetite.

Sexual dimorphism


Some differences are apparent even in gross neuroanatomy: most notable is the sexually dimorphic nucleus within the preoptic area, which is present only in males. However most of the differences are subtle changes in the connectivity and chemical sensitivity of particular sets of neurons.


Responses to ovarian steroids

Other striking functional dimorphisms are in the behavioral responses to ovarian steroids of the adult. Males and females respond differently to ovarian steroids, partly because the expression of estrogen-sensitive neurons in the hypothalamus is sexually dimorphic, i.e. estrogen receptors are expressed in different sets of neurons.



Gonadal steroids in neonatal life of rats


Androgens in primates


Human sexual orientation and the hypothalamus


Swaab first reported on the relationship between sexual orientation in males and the hypothalamus's "clock", the suprachiasmatic nucleus (SCN). In 1990, Swaab and Hofman[13] reported that the SCN of heterosexual men was significantly larger than in women, and the SCN of homosexual men was signifigantly larger than in heterosexual men. Then in 1995, Swaab et al.[14] linked brain development to sexual orientation by treating male rats both pre- and postnatally with ATD, an aromatase blocker in the brain. This produced an enlarged SCN and bisexual behavior in the adult male rats. In 1991, LeVay showed that part of the sexually dimorphic nucleus (SDN), the interstitial nuclei of the anterior hypothalamus (INAH) 3, is twice as large in HeM as HoM and HeW, in terms of volume but not number of neurons.

In 2004 and 2006, two studies by Berglund, Lindström, and Savic[15][16] used Positron Emission Tomography (PET) to observe how the hypothalamus responds to smelling common odors, the scent of testosterone found in male sweat, and the scent of estrogen found in female urine. These studies showed that the hypothalamus of HeM and HoW both respond to estrogen. Also, the hypothalamus of HoM and HeW both respond to testosterone. The hypothalamus of all four groups did not respond to the common odors, which produced a normal olfactory response in the brain.

Other influences upon hypothalamic development

Sex steroids are not the only important influences upon hypothalamic development; in particular, pre-pubertal stress in early life determines the capacity of the adult hypothalamus to respond to an acute stressor.[17] Unlike gonadal steroid receptors, glucocorticoid receptors are very widespread throughout the brain; in the paraventricular nucleus, they mediate negative feedback control of CRF synthesis and secretion, but elsewhere their role is not well understood.

See also

Additional images


  1. Definition of hypothalamus - NCI Dictionary of Cancer Terms
  2. hypothalamus
  3. 3.0 3.1 3.2 Fauci, Anthony, et al. (2008). Harrison's Principles of Internal Medicine (17 ed.). McGraw-Hill Professional. pp. 117–121. ISBN 9780071466332. 
  4. Diagram of Nuclei (psycheducation.org)
  5. Diagram of Nuclei (universe-review.ca)
  6. Diagram of Nuclei (utdallas.edu)
  7. Unless else specified in table, then ref is: Guyton Eight Edition
  9. Hypothalamus and ANS
  10. Overview of Hypothalamic and Pituitary Hormones
  11. Theologides A (1976). "Anorexia-producing intermediary metabolites". Am J Clin Nutr 29 (5): 552–8. PMID 178168. 
  12. Swaab DF (2008). ""Sexual orientation and its basis in brain structure and function"". PNAS 105 (30): 10273–10274. doi:10.1073/pnas.0805542105. PMID 18653758. 
  13. Swaab DF, Hofman MA (1990). "An enlarged suprachiasmatic nucleus in homosexual men". Brain Res. 537 (1-2): 141–8. doi:10.1016/0006-8993(90)90350-K. PMID 2085769. 
  14. Swaab DF, Slob AK, Houtsmuller EJ, Brand T, Zhou JN (1995). "Increased number of vasopressin neurons in the suprachiasmatic nucleus (SCN) of ‘bisexual’ adult male rats following perinatal treatment with the aromatase blocker ATD". Developmental Brain Research 85 (2): 273–279. doi:10.1016/0165-3806(94)00218-O. PMID 7600674. 
  15. Savic I, Berglund H, Lindström P (2005). "Brain response to putative pheromones in homosexual men". PNAS 102 (20): 7356–7361. doi:10.1073/pnas.0407998102. PMID 15883379. 
  16. Savic I, Berglund H, Lindström P (2006). "Brain response to putative pheromones in lesbian women". PNAS 103 (21): 8269–8274. doi:10.1073/pnas.0600331103. PMID 16705035. 
  17. Romeo, Russell D; Rudy Bellani, Ilia N. Karatsoreos, Nara Chhua, Mary Vernov, Cheryl D. Conrad and Bruce S. McEwen (2005). "Stress History and Pubertal Development Interact to Shape Hypothalamic-Pituitary-Adrenal Axis Plasticity". Endocrinology (The Endocrine Society) 147 (4): 1664–1674. doi:10.1210/en.2005-1432. PMID 16410296. http://endo.endojournals.org/cgi/content/short/147/4/1664. Retrieved 2007-10-16. 

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