The
arcuate nucleus (or infundibular nucleus) is an aggregation of
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
s in the mediobasal
hypothalamusThe hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland ....
, adjacent to the
third ventricleThe third ventricle is one of four connected fluid-filled cavities comprising the ventricular system within the human brain...
and the
median eminenceThe median eminence is part of the inferior boundary for the hypothalamus part of the human brain. A small swelling on the tuber cinereum posterior to the infundibulum - atop the pituitary stalk - the median eminence lies in the area roughly bounded on its posterolateral region by the cerebral...
. The arcuate nucleus includes several important populations of neurons, including: Neuroendocrine neurons, Centrally-projecting neurons and Others.
- Neuroendocrine neurons
Neuroendocrinology is the study of the interactions between the nervous system and the endocrine system. The concept arose from the recognition that the secretion of hormones from the pituitary gland is closely controlled by the brain, especially by the hypothalamus.-Pioneers of...
with nerve endings in the median eminence, which release dopamineDopamine is a neurotransmitter occurring in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this phenethylamine functions as a neurotransmitter, activating the five types of dopamine receptors — D
1, D
2, D
3, D
4, and...
into the hypophysial portal blood. These are sometimes called the "tuberoinfundibular dopamine" (TIDA) neurons.
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The
arcuate nucleus (or infundibular nucleus) is an aggregation of
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
s in the mediobasal
hypothalamusThe hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland ....
, adjacent to the
third ventricleThe third ventricle is one of four connected fluid-filled cavities comprising the ventricular system within the human brain...
and the
median eminenceThe median eminence is part of the inferior boundary for the hypothalamus part of the human brain. A small swelling on the tuber cinereum posterior to the infundibulum - atop the pituitary stalk - the median eminence lies in the area roughly bounded on its posterolateral region by the cerebral...
. The arcuate nucleus includes several important populations of neurons, including: Neuroendocrine neurons, Centrally-projecting neurons and Others.
Neuroendocrine neurons
- Neuroendocrine neurons
Neuroendocrinology is the study of the interactions between the nervous system and the endocrine system. The concept arose from the recognition that the secretion of hormones from the pituitary gland is closely controlled by the brain, especially by the hypothalamus.-Pioneers of...
with nerve endings in the median eminence, which release dopamineDopamine is a neurotransmitter occurring in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this phenethylamine functions as a neurotransmitter, activating the five types of dopamine receptors — D
1, D
2, D
3, D
4, and...
into the hypophysial portal blood. These are sometimes called the "tuberoinfundibular dopamine" (TIDA) neurons. In lactating females, TIDA neurons are inhibited by the stimulus of suckling. Dopamine released from their nerve endings at the median eminence is transported to the anterior pituitary gland, where it regulates the secretion of prolactinProlactin or Luteotropic hormone is a peptide hormone discovered by Dr. Henry Friesen, primarily associated with lactation. In breastfeeding, the act of an infant suckling the nipple stimulates the production of prolactin, which fills the breast with milk via a process called lactogenesis, in...
; dopamine inhibits prolactin secretion, so, when the TIDA neurons are inhibited, there is increased secretion of prolactin, which stimulates lactogenesis (milk production). Prolactin acts in a short-loop negative feedback manner to decrease its levels by stimulating the release of dopamine. Dopaminergic neurons of the arcuate also inhibit the release of gonadotropin-releasing hormoneGonadotropin-releasing hormone , also known as Luteinizing-hormone releasing hormone and luliberin, is a tropic peptide hormone responsible for the release of FSH and LH from the anterior pituitary...
, explaining in part why lactating (or otherwise hyperprolactinemic) women experience oligomenorrhea or amenorrhea (infrequency or absence of menses).
- Neuroendocrine neurons, mainly in the ventrolateral part of the nucleus, that make growth hormone-releasing hormone (GHRH). Like the TIDA neurons, these neurons have nerve endings in the median eminence. GHRH released into the hypophysial portal blood is transported to the anterior pituitary gland, where it regulates the secretion of growth hormone
Growth hormone is a protein-based poly-peptide hormone. It stimulates growth and cell reproduction and regeneration in humans and other animals. It is a 191-amino acid, single-chain polypeptide hormone that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of...
; GHRH stimulates growth hormone secretion. These neurons are inhibited by somatostatinSomatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.Somatostatin...
. The reciprocal relationship between the electrical activity of GHRH neurons and somatostatin neurons leads to pulsatile secretion of growth hormone, a pattern of secretion that is important for its biological effectiveness.
Centrally-projecting neurons
- Centrally-projecting neurons that contain neuropeptide Y
Neuropeptide Y is a 36 amino acid peptide neurotransmitter found in the brain and autonomic nervous system.NPY has been associated with a number of physiologic processes in the brain, including the regulation of energy balance, memory and learning, and epilepsy. The main effect is increased food...
(NPY), agouti-related protein (AGRP), and the inhibitory neurotransmitter GABAGabâ or gabaa, for the Cebuano people , is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...
. These neurons, in the most ventromedial part of the nucleus, project strongly to the lateral hypothalamusThe lateral hypothalamus or lateral hypothalamic area is a part of the hypothalamus.It is concerned with hunger. Damage to this area can cause reduced food intake...
and to the paraventricular nucleusThe paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...
of the hypothalamus, and are important in the regulation of appetiteThe appetite is the desire to eat food, felt as hunger. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain metabolic needs. It is regulated by a close interplay between the digestive tract, adipose tissue and the brain. Decreased desire to eat is...
. When activated, these neurons can produce ravenous eating. These neurons are inhibited by leptinLeptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
and activated by ghrelinGhrelin is a hormone produced mainly by P/D1 cells lining the fundus of the human stomach and epsilon cells of the pancreas that stimulates hunger. Ghrelin levels increase before meals and decrease after meals. It is considered the counterpart of the hormone leptin, produced by adipose tissue,...
.
- Centrally-projecting neurons that contain peptide
Peptides are short polymers formed from the linking, in a defined order, of α-amino acids. The link between one amino acid residue and the next is called an amide bond or a peptide bond....
products of pro-opiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcriptCocaine and amphetamine regulated transcript also known as CART is a protein which in humans is encoded by the CARTPT gene. CART appears to have roles in reward, feeding, and stress, and it has the functional properties of an endogenous psychostimulant.- Function :CART is a neuropeptide which also...
(CART). These neurons have widespread projections to many brain areas, including to all nuclei in the hypothalamus. These cells are also important in the regulation of appetiteThe appetite is the desire to eat food, felt as hunger. Appetite exists in all higher life-forms, and serves to regulate adequate energy intake to maintain metabolic needs. It is regulated by a close interplay between the digestive tract, adipose tissue and the brain. Decreased desire to eat is...
, and, when activated, they inhibit feeding. These neurons are also activated by circulating concentrations of leptinLeptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...
, and they are directly innervated and inhibited by the NPY neurons. POMC neurons that project to the medial preoptic nucleus are also involved in the regulation of sexual behavior in both males and females. The expression of POMC is regulated by gonadal steroids. The release of a POMC product, beta-endorphin is regulated by NPY.
- Centrally-projecting neurons that make somatostatin; the neurosecretory somatostatin neurons that regulate growth hormone secretion are a different population, located in the periventricular nucleus.
Other
- A small population of neurons that synthesise ghrelin
Ghrelin is a hormone produced mainly by P/D1 cells lining the fundus of the human stomach and epsilon cells of the pancreas that stimulates hunger. Ghrelin levels increase before meals and decrease after meals. It is considered the counterpart of the hormone leptin, produced by adipose tissue,...
. The role of this population is not known; many neurons in the arcuate nucleus express receptors for ghrelin, but these are thought to be respond mainly to blood-borne ghrelin.
The arcuate nucleus also contains a population of specialized ependymal cells, called
tanycytesTanycytes are special ependymal cells located in the floor of the third ventricle having processes extending deep into the hypothalamus. It is possible that their function is to transfer chemical signals from CSF to CNS....
.