Neuroendocrine neurons Different groups of arcuate nucleus neuroendocrine neurons secrete various types or combinations of
neurotransmitters and
neuropeptides, such as
neuropeptide Y (NPY),
gonadotropin-releasing hormone (GnRH),
agouti-related peptide (AgRP),
cocaine- and amphetamine-regulated transcript (CART),
kisspeptin,
dopamine,
substance P,
growth hormone–releasing hormone (GHRH),
neurokinin B (NKB),
β-endorphin,
melanocyte-stimulating hormone (MSH), and
somatostatin.
Proopiomelanocortin (POMC) is a precursor
polypeptide that is cleaved into MSH, ACTH, and β-endorphin and expressed in the arcuate nucleus. 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
prolactin. 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 hormone, explaining in part why lactating (or otherwise
hyperprolactinemic) women experience oligomenorrhea or amenorrhea (infrequency or absence of menses). •
GHRH neurons help to control
growth hormone (GH) secretion in conjunction with somatostatin and NPY. •
NPY/AgRP neurons and
POMC/CART neurons make up two groups of neurons in the arcuate nucleus that are centrally involved in the neuroendocrine function of feeding. Medial neurons utilize NPY peptides as neurotransmitters to stimulate appetite, and lateral neurons utilize POMC/CART to inhibit appetite. •
GnRH neurons have also been found. 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. • Feeding regulatory neurons also activate oxytocin-containing neurons of the
periventricular nucleus (PVN), which projects to nucleus of
tractus solitarius in the
medulla oblongata. • The arcuate nucleus is also contacted by the processes of specialized
ependymal cells, called
tanycytes. •
Astrocytes in the arcuate nucleus hold high capacity glucose transporters that function as nutrient sensors for appetite controlling neurons • The diverse and specialized collections of neurons reside within a special compartment with
glial cells and have their own network of
capillaries and a membrane of
tanycytes that help create a blood brain barrier. Circulating or molecules such as hormones travel in the blood and can directly affect these neurons and their plasticity as evidence by adult neurogenesis. == References ==