Tanycytes in the infundibular nucleus and median eminence and their role in the blood-brain barrier (2023)


The existence of a specialized class of ependymolyal cells in the hypothalamus has been known since the early 20th century. Indeed, starting around 1909, both Santiago Ramón y Cajal and Giuseppe Sterzi independently described elongated cells resembling radial glia in the infundibular or tuberal region of vertebrates, including mammals, with cell bodies lining the ventricular wall and long processes extending out extend to the pial surface . Ramon y Cajal, 1909; Stezi, 1909). Because of this structure, named by Ernst Horstmann in 1954 after the Greek term for “stretched cells” (Horstmann, 1954), tanycytes are not just passive members of the neuroglial and neurovascular components of the hypothalamus, but dynamic, responsive cells, often with a permissive or regulatory function . Indeed, a growing body of studies underscores the versatility of these cells and their critical involvement in a wide range of biological processes, from energy homeostasis and metabolism to the control of reproduction and other hypothalamic-pituitary axes and more. Although most of the knowledge about tanycytes comes from animal models, neuroanatomical studies of the hypothalamus using postmortem tissue (Baroncini et al., 2007; Sidibe et al., 2010; Koopman et al., 2017; Pellegrino et al., 2018) as well as some imaging Studies of the brain in living patients (Baroncini et al., 2010; Denis et al., 2020) support the extrapolation of these physiological and pathological features to humans (reviewed in Prevot et al., 2018).

The center of the diverse function of tanycytes is their special location. In fact, they form a bridge between the cerebrospinal fluid (CSF) and the perivascular space bordering the middle hypothalamus (ME), one of the seven circumventricular organs (CVO) bordering the arcuate nucleus of the hypothalamus (ARH) in humans as the nucleus infundibularis, where they are in contact with the peripheral circulation via the fenestrated endothelium of the hypothalamic-pituitary portal capillaries (Fig. 16.1). This privileged position at the blood-brain and blood-CSF interfaces allows tanycytes to replace the traditional blood-brain barrier (BBB) ​​or to modulate its function. Their morphological plasticity in response to the physiological and hormonal environment allows them to relay metabolic signals and circulating hormones in the brain and modulate the brain's secretion of neuroendocrine factors into the circulation (reviewed in Prevot et al., 2018; Banks, 2019; García-Caceres et al., 2019). In recent years, several new roles have been added to the tanycytes' repertoire, often at the interface between energy metabolism and reproduction: (i) They appear to be actively involved not only in the transport but also in the sensing of metabolic signals and the transmission of this information to the neurons; (ii) possess the properties of neural stem cells (NSCs), adding adult hypothalamic neurogenesis to the mechanisms by which the brain maintains metabolic balance or reproductive capacity; and (iii) they can mediate inflammatory pathogenesis, including aging, in the brain in a variety of ways.

This chapter briefly summarizes the current knowledge of these fascinating cells and the cellular and molecular mechanisms underlying their potential role as a giant control panel that enables efficient, appropriate, and adaptive exchange of information between the brain and the periphery, and between the neural circuits that regulate various physiological functions.

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Origin and classification of tannycytes

Like Bergmann's cerebellar glia, tanycytes are residual radial glial cells in the mammalian brain whose typical structure and many of their features persist throughout life (Goodman and Hajihosseini, 2015; Rizzoti and Lovell-Badge, 2017). The traditional view classifies tanycytes into four subtypes: α1, α2, β1, and β2 based on their dorsoventral position along the ventricular wall, the trajectory of their processes, and their histological features (Akmayev et al.

tanyzytische Morphology

As mentioned above, the morphology and location of tanycytes are closely related to their various roles. Consistent with their ontogeny, tanycytes have a radial morphology with a cell body lining the wall of the third ventricle and long, sometimes branching, processes that cross the hypothalamic parenchyma to terminate in the traditional BBB capillaries or in the perivascular space of fenestrated capillaries end up. of the hypothalamic-pituitary portal system (Fig. 16.1F and G).

Functional specialization of tannycytes

Tanyocytes are at the crossroads of several physiological processes. As knowledge of their biology advances, overlapping molecules and signaling pathways emerge, both between the major physiological processes they are involved in (reproduction and energy homeostasis) and linking newly discovered functions, such as B. their role as stem / progenitor cells or their properties. flammable. . It is therefore necessary to consider the functions described below as parts of a whole and not as discrete functions.


At the interface between the peripheral bloodstream, the hypothalamic parenchyma, and the cerebrospinal fluid in a part of the brain extremely rich in hormone-producing and hormone-responsive elements, tanycytes are uniquely located to dynamically mediate and interconnect these various processes. . . These processes are all the more important since the hypothalamus itself is the coordination center for numerous homeostatic processes without which life cannot exist. While the subtypes of

expression of gratitude

We thank Dr. Rasika for editing the manuscript. The authors are supported by the European Research Council's Synergy Program under Grant Agreement No. 810331.

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What is the role of tanycytes? ›

Tanycytes, glial-like cells that line the third ventricle, are emerging as components of the hypothalamic networks that control body weight and energy balance. They contact the cerebrospinal fluid (CSF) and send processes that come into close contact with neurons in the arcuate and ventromedial hypothalamic nuclei.

What cell is responsible for the blood-brain barrier? ›

The blood-brain barrier (BBB) is a specialized structure of the central nervous system (CNS) that restricts immune cell migration and soluble molecule diffusion from the systemic compartment into the CNS. Astrocytes and microglia are resident cells of the CNS that contribute to the formation of the BBB.

Where are tanycytes? ›

Tanycytes are polarized cells, with cell bodies located in the wall of the third ventricle and elongated processes extending into the parenchyma and contacting the pial surface of the brain. Due to this peculiar morphology and their stem cell properties, tanycytes can be considered radial glia of the mature brain66.

How are tanycytes different from ependymal cells? ›

Tanycytes are special ependymal cells found in the third ventricle of the brain, and on the floor of the fourth ventricle and have processes extending deep into the hypothalamus. It is possible that their function is to transfer chemical signals from the cerebrospinal fluid to the central nervous system.

Where is the median eminence located? ›

The median eminence is the structure at the base of the hypothalamus where hypothalamic-releasing and –inhibiting hormones converge onto the portal capillary system that vascularizes the anterior pituitary gland.

What is the physiological role of hypothalamic tanycytes in metabolism? ›

Tanycytes are modulators of energy balance. By interacting with both neurons and vessels—locally in the mediobasal hypothalamus and globally through the cerebrospinal fluid—tanycytes modulate both orexigenic and anorexigenic pathways and participate in the regulation of glucose homeostasis and energy balance.

What causes blood-brain barrier breakdown? ›

Hypertension, diabetes, and hyperlipidemia are the major factors besides age that cause changes in the blood vessels responsible for the impairments in cerebral blood flow and oxygenation, along with increase in permeability.

How do T cells cross the blood-brain barrier? ›

Activated T cells can enter the subarachnoid space by migrating from blood vessels into the stroma of the choroid plexus and then crossing the blood–cerebrospinal fluid (CSF) barrier surrounding the choroid plexus stroma, which comprises epithelial cells joined by tight junctions.

Which of the following substances that the blood-brain barrier prevents from entering brain tissue? ›

Answer and Explanation: The best answer is (C): Pharmaceuticals. Nicotine and alcohol can cross the blood-brain barrier.

What are the different types of tanycytes? ›

Four subtypes of tanycytes (α1, α2, β1, β2) have been described along the 3V wall. In vivo and in vitro studies suggest that α2 tanycytes (also known as dorsomedial ARH tanycytes) (blue) that face the dorsal part of the ARH have NSC properties, while the other tanycyte populations (green) rather behave as NPCs.

Do tanycytes respond to glucose? ›

Both in vitro and in situ studies demonstrated that tanycytes sense and respond to extracellular glucose via a rapid, glucose-activated signal transduction pathway mediated by lactate and/or ATP.

What is the role of astrocytes microglia and tanycytes in brain control of systemic metabolism? ›

Astrocytes, microglia, and tanycytes play active roles in the regulation of hypothalamic feeding circuits. These non-neuronal cells are crucial in determining the functional interactions of specific neuronal subpopulations involved in the control of metabolism.

What cell types include Ependymocytes and tanycytes? ›

Ependymal Cells

As non-neuronal cells in the brain and derived from neuroectoderm, they are clearly defined as a subtype of glial cells. They include the ependymocytes, choroid plexus epithelial cells, tanycytes, and within the retina, Müller cells and retinal pigment epithelial cells.

What are the roles of the five types of neuroglia? ›

Terms in this set (5)
  • ependymal cells. move cerebrous spinal fluid around to keep it homogenous.
  • astrocytes. form the blood brain barrier.
  • microglia. they do phagocytosis to fight infection.
  • oligodendrocytes. bind the CNS neurons together and insulate the axons.
  • schwann cells. insulate PNS axons.

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