Tanycytes are highly specialized ependymal cells (also called ependymoglial cells) with long basal processes.[1][2] Tanycytes in adult mammals are found in theventricular system, and themedian eminence, acircumventricular organ. They are most numerous in thethird ventricle of the brain, are also found in thefourth ventricle, and can also be seen in thespinal cord radiating from thecentral canal (also known as the ependymal canal), to the spinal cord surface. The long processes extend through the layer ofastrocytes to cross the median eminence and formend-feet on neuropil, and blood vessels near the portal perivascular space.[1][3]
Along the process from each tanycyte are some unusual protrusions as spikes, and swellings, and at their end feet are boutons or claws. The different protrusions contain blood vessels, and contact different neurons, and cells.[4] The protrusions containribosomes,mitochondria, varied vesicles, and transporters.[4]
In the third ventricle four different subtypes of tanycte populations with differing structure, morphology, genetics, and function have been defined. These are named beta 2 (β2) and beta 1 (β1), and alpha 2 (α2) and alpha 1 (α1).[4]
β2 tanycytes line the median eminence; β1 tanycytes line part of theinfundibular recess.
α2 tanycytes line the dorsomedial arcuate nucleus; α1 tanycytes line the ventromedial nucleus and the dorsomedial nucleus.[4]
A tanycyte has a single long basal process that crosses into the hypothalamic parenchyma to make contact with blood vessels and an array of neurons.[5] The different components of the tanycyte process protrusions that include ribosomes, mitochondria, and transporters, indicate communication between the tanycytes and blood vessels, and between the tanycytes and neurons. These interactions are associated with the regulation of differentneuroendocrine functions.[4]
Studies suggests that tanycyte cells bridge the gap between the central nervous system (CNS) viacerebrospinal fluid (CSF) to thehypophyseal portal blood.[8][9] Tanycytes provide a link that is both structural and functional between the CSF and the perivascular space of the hypophyseal portal vessels.[3] Unlike regular ependymal cells there are tight junctions between them, and between their adjacent ependymal cells.[1] There are also desmosomes present which together with the tight junctions provide structural support.[1]
Role in the release of gonadotropin-releasing hormone
Prieto, M; Chauvet, N; Alonso, G (Jan 2000). "Tanycytes transplanted into the adult rat spinal cord support the regeneration of lesioned axons".Experimental Neurology.161 (1):27–37.doi:10.1006/exnr.1999.7223.PMID10683271.S2CID42078438.
