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β-catenin is one of the main proteins of adherens intercellular junctions, which are important for maintaining tissue integrity and the formation of apical-basal cell polarization. In the brain, adherens junctions are also important for maintaining the physiological integrity of the barriers formed by the ventricular lining cells. The purpose of this study was to analyse the distribution of β-catenin in ependymocytes and tanycytes of the third ventricle of the rat brain during postnatal development. It was found that the distribution pattern of adherens junctions in the lining cells of the third ventricle differs in the areas occupied by ependymocytes and tanycytes, as well as changing during postnatal development. In ependymocytes, this type of cell contact performs a mechanical function, participating in the formation of a continuous ependymal layer, and is also important for maintaining its integrity in early postnatal development and during aging, which is characterized by an increase in the size of the ventricles. In tanycytes, in addition to the formation of intercellular contacts, adherens junctions are important for the formation of bundles of processes and their stabilization. Thus, β-catenin, as part of adherens junctions in the lining of the third ventricle, performs several functions, including a mechanical function, uniting cells into a single layer, and is important for the stabilization of processes. [ABSTRACT FROM AUTHOR]

The central control of energy homeostasis is a regulatory axis that involves the sensing of nutrients, signaling molecules, adipokines, and neuropeptides by neurons in the metabolic centers of the hypothalamus. However, non-neuronal glial cells are also abundant in the hypothalamus and recent findings have underscored the importance of the metabolic crosstalk and horizontal lipid flux between glia and neurons to the downstream regulation of systemic metabolism. New transgenic models and high-resolution analyses of glial phenotype and function have revealed that glia sit at the nexus between lipid metabolism and neural function, and may markedly impact the brain's response to dietary lipids or the supply of brain-derived lipids. Glia comprise the main cellular compartment involved in lipid synthesis, lipoprotein production, and lipid processing in the brain. In brief, tanycytes provide an interface between peripheral lipids and neurons, astrocytes produce lipoproteins that transport lipids to neurons and other glia, oligodendrocytes use brain-derived and dietary lipids to myelinate axons and influence neuronal function, while microglia can remove unwanted lipids in the brain and contribute to lipid re-utilization through cholesterol efflux. Here, we review recent findings regarding glial-lipid transport and highlight the specific molecular factors necessary for lipid processing in the brain, and how dysregulation of glial-neuronal metabolic crosstalk contributes to imbalanced energy homeostasis. Furthering our understanding of glial lipid metabolism will guide the design of future studies that target horizontal lipid processing in the brain to ameliorate the risk of developing obesity and metabolic disease. • Lipid processing in the brain involves metabolic crosstalk and horizontal lipid flux between neurons and non-neuronal glia. • Disruption of this complex neuron-glia interplay has effects on neuronal function, and systemic energy balance. • Exposure to high-fat diets cause a shift towards a more inflammatory glial phenotype and away from metabolic support. • Sexual dimorphism in glial metabolism and phenotype could contribute to metabolic disease susceptibility. [ABSTRACT FROM AUTHOR]

Objectives: In Western society, high-caloric diets rich in fats and sugars have fueled the obesity epidemic and its related disorders. Disruption of the body-brain communication, crucial for maintaining glucose and energy homeostasis, arises from both obesogenic and genetic factors, leading to metabolic disorders. Here, we investigate the role of hypothalamic tanycyte shuttles between the pituitary portal blood and the third ventricle cerebrospinal fluid in regulating energy balance. Methods: We inhibited vesicle-associated membrane proteins (VAMP1-3)-mediated release in tanycytes by expressing the botulinum neurotoxin type B light chain (BoNT/B) in a Cre-dependent manner in tanycytes. This was achieved by injecting either TAT-Cre in the third ventricle or an AAV1/2 expressing Cre under the control of the tanycyte-specific promoter iodothyronine deiodinase 2 into the lateral ventricle of adult male mice. Results: In male mice fed a standard diet, targeted expression of BoNT/B in adult tanycytes blocks leptin transport into the mediobasal hypothalamus and results in normal-weight central obesity, including increased food intake, abdominal fat deposition, and elevated leptin levels but no marked change in body weight. Furthermore, BoNT/B expression in adult tanycytes promotes fatty acid storage, leading to glucose intolerance and insulin resistance. Notably, these metabolic disturbances occur despite a compensatory increase in insulin secretion, observed both in response to exogenous glucose boluses in vivo and in isolated pancreatic islets. Intriguingly, these metabolic alterations are associated with impaired spatial memory in BoNT/B-expressing mice. Conclusions: These findings underscore the central role of tanycytes in brain-periphery communication and highlight their potential implication in the age-related development of type 2 diabetes and cognitive decline. Our tanycytic BoNT/B mouse model provides a robust platform for studying how these conditions progress over time, from prediabetic states to full-blown metabolic and cognitive disorders, and the mechanistic contribution of tanycytes to their development. The recognition of the impact of tanycytic transcytosis on hormone transport opens new avenues for developing targeted therapies that could address both metabolic disorders and their associated cognitive comorbidities, which often emerge or worsen with advancing age.

Tanycytes are stem/progenitor cells that reside in the hypothalamus of the adult vertebrate brain. Tanycytes can be cultured as free-floating neurospheres in vitro but tend to spontaneously differentiate over time. Here we asked whether morphological cues provided by engineered polymer scaffolds can modify spontaneous differentiation. Tanycyte-derived neurospheres were cultured on electrospun scaffolds, prepared with either random or aligned fiber morphologies. Cells dispersed widely on the scaffolds, and - on aligned scaffolds - were highly organized, orientated parallel to the fibers. Immunocytochemical analysis showed that cells cultured on aligned scaffolds showed significantly greater expression of the neural stem/progenitor cell marker, NrCAM and reduced expression of differentiated cell markers in comparison to those cultured on random scaffolds. Together this shows that tanycytes respond to local engineered cues, and that a morphologically constrained environment can better maintain tanycytes as stem cells. The aligned scaffold culture system provides a powerful tool to better investigate this novel stem/progenitor cell population.

Neurogenesis continues throughout adulthood in the subventricular zone, hippocampal subgranular zone, and the hypothalamic median eminence (ME) and the adjacent medio‐basal hypothalamus. The ME is one of the circumventricular organs (CVO), which are specialized brain areas characterized by an incomplete blood–brain barrier and, thus, are involved in mediating communication between the central nervous system and the periphery. Additional CVOs include the organum vasculosum laminae terminalis (OVLT) and the subfornical organs (SFO). Previous studies have demonstrated that the ME contains neural stem cells (NSCs) capable of generating new neurons and glia in the adult brain. However, it remains unclear whether the OVLT and SFO also contain proliferating cells, the identity of these cells, and their ability to differentiate into mature neurons. Here we show that glial and mural subtypes exhibit NSC characteristics, expressing the endogenous mitotic maker Ki67, and incorporating the exogenous mitotic marker BrdU in the OVLT and SFO of adult rats. Glial cells constitutively proliferating in the SFO comprise NG2 glia, while in the OVLT, both NG2 glia and tanycytes appear to constitute the NSC pool. Furthermore, pericytes, which are mural cells associated with capillaries, also contribute to the pool of cells constitutively proliferating in the OVLT and SFO of adult rats. In addition to these glial and mural cells, a fraction of NSCs containing proliferation markers Ki67 and BrdU also expresses the early postmitotic neuronal marker doublecortin, suggesting that these CVOs comprise newborn neurons. Notably, these neurons can differentiate and express the mature neuronal marker NeuN. These findings establish the sensory CVOs OVLT and SFO as additional neurogenic niches, where the generation of new neurons and glia persists in the adult brain. [ABSTRACT FROM AUTHOR]

Tanycytes are stem/progenitor cells that reside in the hypothalamus of the adult vertebrate brain. Tanycytes can be cultured as free-floating neurospheres in vitro but tend to spontaneously differentiate over time. Here we asked whether morphological cues provided by engineered polymer scaffolds can modify spontaneous differentiation. Tanycyte-derived neurospheres were cultured on electrospun scaffolds, prepared with either random or aligned fiber morphologies. Cells dispersed widely on the scaffolds, and - on aligned scaffolds - were highly organized, orientated parallel to the fibers. Immunocytochemical analysis showed that cells cultured on aligned scaffolds showed significantly greater expression of the neural stem/progenitor cell marker, NrCAM and reduced expression of differentiated cell markers in comparison to those cultured on random scaffolds. Together this shows that tanycytes respond to local engineered cues, and that a morphologically constrained environment can better maintain tanycytes as stem cells. The aligned scaffold culture system provides a powerful tool to better investigate this novel stem/progenitor cell population. [ABSTRACT FROM AUTHOR]

Background: Tanycytes are specialized glial cells within the mediobasal hypothalamus that have multiple functions, including hormone sensing and regulation of hypophysiotropic hormone secretion. There are ongoing discussions about the role of tanycytes in regulating the supply of hypothalamic thyroid hormones (THs) through the expression of TH transporters (Slc16a2, Slco1c1) and deiodinases (Dio2, Dio3). In this study, we investigated the potential feedback effect of thyrotropin (TSH) on the transcription of these gatekeeper genes on tanycytes. Methods: We analyzed the changes in the expression of TH-gatekeeper genes, in TSH-stimulated primary tanycytes, using quantitative polymerase chain reaction (qPCR). We also used RNAScope® in brain slices to further reveal the local distribution of the transcripts. In addition, we blocked intracellular pathways and used small-interfering RNA (siRNA) to elucidate differences in the regulation of the gatekeeper genes. Results: TSH elevated messenger RNA (mRNA) levels of Slco1c1, Dio2, and Dio3 in tanycytes, while Slc16a2 was mostly unaffected. Blockade and knockdown of the TSH receptor (TSHR) and antagonization of cAMP response element-binding protein (CREB) clearly abolished the increased expression induced by TSH, indicating PKA-dependent regulation through the TSHR. The TSH-dependent expression of Dio3 and Slco1c1 was also regulated by protein kinase C (PKC), and in case of Dio3, also by extracellular signal-regulated kinase (ERK) activity. Importantly, these gene regulations were specifically found in different subpopulations of tanycytes. Conclusions: This study demonstrates that TSH induces transcriptional regulation of TH-gatekeeper genes in tanycytes through the Tshr/Gαq/PKC pathway, in parallel to the Tshr/Gαs/PKA/CREB pathway. These differential actions of TSH on tanycytic subpopulations appear to be important for coordinating the supply of TH to the hypothalamus and aid its functions. [ABSTRACT FROM AUTHOR]

Objective: The liver releases glucose into the blood using the glucose-6-phosphatase (G6Pase) system, a multiprotein complex located in the endoplasmic reticulum (ER). Here, we show for the first time that the G6Pase system is also expressed in hypothalamic tanycytes, and it is required to regulate energy balance. Methods: Using automatized qRT-PCR and immunohistochemical analyses, we evaluated the expression of the G6Pase system. Fluorescent glucose analogue (2-NBDG) uptake was evaluated by 4D live-cell microscopy. Glucose release was tested using a glucose detection kit and high-content live-cell analysis instrument, Incucyte s3. In vivo G6pt knockdown in tanycytes was performed by AAV1-shG6PT-mCherry intracerebroventricular injection. Body weight gain, adipose tissue weight, food intake, glucose metabolism, c-Fos, and neuropeptide expression were evaluated at 4 weeks post-transduction. Results: Tanycytes sequester glucose-6-phosphate (G6P) into the ER through the G6Pase system and release glucose in hypoglycaemia via facilitative glucose transporters (GLUTs). Strikingly, in vivo tanycytic G6pt knockdown has a powerful peripheral anabolic effect observed through decreased body weight, white adipose tissue (WAT) tissue mass, and strong downregulation of lipogenesis genes. Selective deletion of G6pt in tanycytes also decreases food intake, c-Fos expression in the arcuate nucleus (ARC), and Npy mRNA expression in fasted mice. Conclusions: The tanycyte-associated G6Pase system is a central mechanism involved in controlling metabolism and energy balance.

Neural progenitor cells (NPCs) are multipotent neural stem cells (NSCs) capable of self-renewing and differentiating into neurons, astrocytes and oligodendrocytes. In the postnatal/adult brain, NPCs are primarily located in the subventricular zone (SVZ) of the lateral ventricles (LVs) and subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). There is evidence that NPCs are also present in the postnatal/adult hypothalamus, a highly conserved brain region involved in the regulation of core homeostatic processes, such as feeding, metabolism, reproduction, neuroendocrine integration and autonomic output. In the rodent postnatal/adult hypothalamus, NPCs mainly comprise different subtypes of tanycytes lining the wall of the 3rd ventricle. In the postnatal/adult human hypothalamus, the neurogenic niche is constituted by tanycytes at the floor of the 3rd ventricle, ependymal cells and ribbon cells (showing a gap-and-ribbon organization similar to that in the SVZ), as well as suprachiasmatic cells. We speculate that in the postnatal/adult human hypothalamus, neurogenesis occurs in a highly complex, exquisitely sophisticated neurogenic niche consisting of at least four subniches; this structure has a key role in the regulation of extrahypothalamic neurogenesis, and hypothalamic and extrahypothalamic neural circuits, partly through the release of neurotransmitters, neuropeptides, extracellular vesicles (EVs) and non-coding RNAs (ncRNAs). [ABSTRACT FROM AUTHOR]

Adult neurogenesis is a striking example of neuroplasticity, which enables adaptive network remodelling in response to all forms of environmental stimulation in physiological and pathological contexts. Dysregulation or cessation of adult neurogenesis contributes to neuropathology negatively affecting brain functions and hampering regeneration of the nervous tissue while targeting adult neurogenesis may provide the basis for potential therapeutic interventions. Neural stem cells in the adult mammalian brain are at the core and the entry point of adult neurogenesis. By their origin and properties, these cells belong to astroglia, and are represented by stem radial astrocytes (RSA) which exhibit multipotent "stemness". In the neurogenic niches, RSA interact with other cellular components, including protoplasmic astrocytes, which in turn regulate their neurogenic activity. In pathology, RSA become reactive, which affects their neurogenic capabilities, whereas reactive parenchymal astrocytes up‐regulate stem cell hallmarks and are able to generate progeny that remain within astrocyte lineage. What makes RSA special is their multipotency, represented by self‐renewing capacity capability to generate other cellular types as progeny. A broad understanding of the cellular features of RSA and parenchymal astrocytes provides an insight into the machinery that promotes/suppresses adult neurogenesis, clarifying principles of network remodelling. In this review, we discuss the cellular hallmarks, research tools, and models of RSA and astrocytes of the subventricular zone along the lateral ventricle and dentate gyrus of the hippocampus. We also discuss RSA in ageing, which has a great impact on the proliferative capacity of RSA, as well as the potential of RSA and astrocytes in therapeutic strategies aimed at cell replacement and regeneration. [ABSTRACT FROM AUTHOR]

The third ventricle (3 V) wall of the tuberal hypothalamus is composed of two types of cells; specialized ependymoglial cells called tanycytes located ventrally and ependymocytes dorsally, which control the exchanges between the cerebrospinal fluid and the hypothalamic parenchyma. By regulating the dialogue between the brain and the periphery, tanycytes are now recognized as central players in the control of major hypothalamic functions such as energy metabolism and reproduction. While our knowledge of the biology of adult tanycytes is progressing rapidly, our understanding of their development remains very incomplete. To gain insight into the postnatal maturation of the 3 V ependymal lining, we conducted a comprehensive immunofluorescent study of the mouse tuberal region at four postnatal ages (postnatal day (P) 0, P4, P10, and P20). We analyzed the expression profile of a panel of tanycyte and ependymocyte markers (vimentin, S100, connexin‐43 [Cx43], and glial fibrillary acidic protein [GFAP]) and characterized cell proliferation in the 3 V wall using the thymidine analog bromodeoxyuridine. Our results show that most changes in marker expression occur between P4 and P10, with a switch from a 3 V mostly lined by radial cells to the emergence of a tanycytic domain ventrally and an ependymocytic domain dorsally, a drop in cell proliferation and increased expression of S100, Cx43, and GFAP that acquire a mature profile at P20. Our study thus identifies the transition between the first and the second postnatal week as a critical time window for the postnatal maturation of the 3 V wall ependymal lining. [ABSTRACT FROM AUTHOR]

The proliferative properties of tanycyte subpopulations during postnatal development and aging were studied. Using immunohistochemical markers, we described the distribution of proliferative markers and markers of neural stem cells (NSC) in 4 tanycyte subpopulations (α1-, α2-, β1-, and β2-tanycytes). During the first postnatal week, all tanycyte subpopulations exhibit proliferative activity. During aging, β-tanycytes lose their proliferative activity and retain a limited set of NSC markers, whereas α-tanycytes maintain both the ability to proliferate and the properties of NSC throughout the entire postnatal development including aging. The data obtained significantly improve modern understanding of the proliferative potential of tanycytes and their subpopulation differences in early postnatal period and during aging. [ABSTRACT FROM AUTHOR]

The conceptualization of polycystic ovary syndrome (PCOS) has primarily focused on hormonal alterations driven by changes within the hypothalamus and ovarian granulosa cells, with treatment by the contraceptive pill and weight loss. However, a growing body of data implicates wider systemic and central nervous system (CNS) changes in the pathoetiology and pathophysiology of PCOS, with consequent implications for targeted treatments. It is proposed that there is a significant role for night-time interactions of factors acting to regulate whether the rising level of cortisol over the night and during the morning cortisol awakening response (CAR) is able to induce the nuclear translocation of the glucocorticoid receptor (GR), thereby influencing how the immune and glial systems regulate cellular function in preparation for the coming day. Factors affording protection in PCOS also inhibit GR nuclear translocation including gut microbiome-derived butyrate, and pineal/local melatonin as well as melatonin regulated bcl2-associated athanogene (BAG)-1. A significant pathophysiological role in PCOS is attributed to the aryl hydrocarbon receptor (AhR), which shows heightened levels and activity in PCOS. The AhR is activated by ligands of many systemic processes, including white adipocyte-derived kynurenine, implicating obesity in the pathophysiological changes occurring in the hypothalamus and ovaries. AhR activation has consequences for the physiological function in the hypothalamic paraventricular nucleus, granulosa cells and adipocytes, partly mediated by AhR upregulation of the mitochondrial N-acetylserotonin/melatonin ratio, thereby decreasing melatonin availability whilst increasing local stress plasticity in the paraventricular nucleus. This article reviews in detail the wider systemic and CNS changes in PCOS highlighting interactions of local and pineal melatonergic pathway, gut microbiome-derived butyrate, white adipocyte-derived kynurenine, the hypothalamic paraventricular nucleus tanycytes/astrocytes, and the hypothalamus-pituitary-adrenal (HPA) axis driven glucocorticoid receptor activation in PCOS pathophysiology. This integrates a wide array of previously disparate data on the biological underpinnings of PCOS, including how PCOS associates with many other currently classified medical conditions, such as depression, bipolar disorder, type 1 diabetes mellitus and the autism spectrum. Numerous future research and treatment implications are detailed.

Nervous system is segregated from the body by the complex system of barriers. The CNS is protected by (i) the blood–brain and blood-spinal cord barrier between the intracerebral and intraspinal blood vessels and the brain parenchyma; (ii) the arachnoid blood-cerebrospinal fluid barrier; (iii) the blood-cerebrospinal barrier of circumventricular organs made by tanycytes and (iv) the choroid plexus blood-CSF barrier formed by choroid ependymocytes. In the peripheral nervous system the nerve-blood barrier is secured by tight junctions between specialised glial cells known as perineural cells. In the CNS astroglia contribute to all barriers through the glia limitans, which represent the parenchymal portion of the barrier system. Astroglia through secretion of various paracrine factors regulate the permeability of endothelial vascular barrier; in pathology damage or asthenia of astrocytes may compromise brain barriers integrity.

Summary: Background: Polycystic ovary syndrome (PCOS) is the most common reproductive-endocrine disorder affecting between 5 and 18% of women worldwide. An elevated frequency of pulsatile luteinizing hormone (LH) secretion and higher serum levels of anti-Müllerian hormone (AMH) are frequently observed in women with PCOS. The origin of these abnormalities is, however, not well understood. Methods: We studied brain structure and function in women with and without PCOS using proton magnetic resonance spectroscopy (MRS) and diffusion tensor imaging combined with fiber tractography. Then, using a mouse model of PCOS, we investigated by electron microscopy whether AMH played a role on the regulation of hypothalamic structural plasticity. Findings: Increased AMH serum levels are associated with increased hypothalamic activity/axonal-glial signalling in PCOS patients. Furthermore, we demonstrate that AMH promotes profound micro-structural changes in the murine hypothalamic median eminence (ME), creating a permissive environment for GnRH secretion. These include the retraction of the processes of specialized AMH-sensitive ependymo-glial cells called tanycytes, allowing more GnRH neuron terminals to approach ME blood capillaries both during the run-up to ovulation and in a mouse model of PCOS. Interpretation: We uncovered a central function for AMH in the regulation of fertility by remodeling GnRH terminals and their tanycytic sheaths, and provided insights into the pivotal role of the brain in the establishment and maintenance of neuroendocrine dysfunction in PCOS. Funding: INSERM (U1172), European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement n° 725149), CHU de Lille, France (Bonus H).

Introduction: During hypothalamic development, the germinative neuroepithelium gives birth to diverse neural cells that regulate numerous physiological functions in adulthood. Methods: Here, we studied the ontogeny of ependymal cells in the mouse mediobasal hypothalamus using the BrdU approach and publicly available single-cell RNAseq datasets. Results: We observed that while typical ependymal cells are mainly produced at E13, tanycyte birth depends on time and subtypes and lasts up to P8. Typical ependymocytes and β tanycytes are the first to arise at the top and bottom of the dorsoventral axis around E13, whereas α tanycytes emerge later in development, generating an outside-in dorsoventral gradient along the third ventricle. Additionally, α tanycyte generation displayed a rostral-to-caudal pattern. Finally, tanycytes mature progressively until they reach transcriptional maturity between P4 and P14. Discussion: Altogether, this data shows that ependyma generation differs in time and distribution, highlighting the heterogeneity of the third ventricle. [ABSTRACT FROM AUTHOR]

IntroductionDuring hypothalamic development, the germinative neuroepithelium gives birth to diverse neural cells that regulate numerous physiological functions in adulthood.MethodsHere, we studied the ontogeny of ependymal cells in the mouse mediobasal hypothalamus using the BrdU approach and publicly available single-cell RNAseq datasets.ResultsWe observed that while typical ependymal cells are mainly produced at E13, tanycyte birth depends on time and subtypes and lasts up to P8. Typical ependymocytes and β tanycytes are the first to arise at the top and bottom of the dorsoventral axis around E13, whereas α tanycytes emerge later in development, generating an outside-in dorsoventral gradient along the third ventricle. Additionally, α tanycyte generation displayed a rostral-to-caudal pattern. Finally, tanycytes mature progressively until they reach transcriptional maturity between P4 and P14.DiscussionAltogether, this data shows that ependyma generation differs in time and distribution, highlighting the heterogeneity of the third ventricle.

• Hypothalamic astrogenesis persists throughout life, unlike in other brain regions. • Multiple cellular sources contribute to hypothalamic astrogenesis. • Astrogenesis in the hypothalamus is closely coordinated with neuronal maturation. • Hypothalamic astrogenesis exhibits unique features in its dynamics and regulation. Astrocytes are now recognized as integral components of neural circuits, regulating their maturation, activity and plasticity. Neuroendocrinology has provided fertile ground for revealing the diverse strategies used by astrocytes to regulate the physiological and behavioural outcomes of neural circuit activity in response to internal and environmental inputs. However, the development of astrocytes in the hypothalamus has received much less attention than in other brain regions such as the cerebral cortex and spinal cord. In this review, we synthesize our current knowledge of astrogenesis in the hypothalamus across various life stages. A distinctive feature of hypothalamic astrogenesis is that it persists all throughout lifespan, and involves multiple cellular sources corresponding to radial glial cells during early development, followed by tanycytes, parenchymal progenitors and locally dividing astrocytes. Astrogenesis in the hypothalamus is closely coordinated with the maturation of hypothalamic neurons. This coordination is exemplified by recent findings in neurons producing gonadotropin-releasing hormone, which actively shape their astroglial environment during infancy to integrate functionally into their neural network and facilitate sexual maturation, a process vulnerable to endocrine disruption. While hypothalamic astrogenesis shares common principles with other brain regions, it also exhibits specific features in its dynamics and regulation, both at the inter- and intra-regional levels. These unique properties emphasize the importance of further exploration. Additionally, we discuss the experimental strategies used to assess astrogenesis in the hypothalamus and their potential bias and limitations. Understanding the mechanisms of hypothalamic astrogenesis throughout life will be crucial for comprehending the development and function of the hypothalamus under both physiological and pathological conditions. [ABSTRACT FROM AUTHOR]

Estrogen secretion by the ovaries regulates the hypothalamic-pituitary-gonadal axis during the reproductive cycle, influencing gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion, and also plays a role in regulating metabolism. Here, we establish that hypothalamic tanycytes—specialized glia lining the floor and walls of the third ventricle—integrate estrogenic feedback signals from the gonads and couple reproduction with metabolism by relaying this information to orexigenic neuropeptide Y (NPY) neurons. Using mouse models, including mice floxed for Esr1 (encoding estrogen receptor alpha, ERα) and those with Cre-dependent expression of designer receptors exclusively activated by designer drugs (DREADDs), along with viral-mediated, pharmacological and indirect calorimetric approaches, we evaluated the role of tanycytes and tanycytic estrogen signaling in pulsatile LH secretion, cFos expression in NPY neurons, estrous cyclicity, body-weight changes and metabolic parameters in adult females. In ovariectomized mice, chemogenetic activation of tanycytes significantly reduced LH pulsatile release, mimicking the effects of direct NPY neuron activation. In intact mice, tanycytes were crucial for the estrogen-mediated control of GnRH/LH release, with tanycytic ERα activation suppressing fasting-induced NPY neuron activation. Selective knockout of Esr1 in tanycytes altered estrous cyclicity and fertility in female mice and affected estrogen's ability to inhibit refeeding in fasting mice. The absence of ERα signaling in tanycytes increased Npy transcripts and body weight in intact mice and prevented the estrogen-mediated decrease in food intake as well as increase in energy expenditure and fatty acid oxidation in ovariectomized mice. Our findings underscore the pivotal role of tanycytes in the neuroendocrine coupling of reproduction and metabolism, with potential implications for its age-related deregulation after menopause. Our investigation reveals that tanycytes, specialized glial cells in the brain, are key interpreters of estrogen signals for orexigenic NPY neurons in the hypothalamus. Disrupting tanycytic estrogen receptors not only alters fertility in female mice but also impairs the ability of estrogens to suppress appetite. This work thus sheds light on the critical role played by tanycytes in bridging the hormonal regulation of cyclic reproductive function and appetite/feeding behavior. This understanding may have potential implications for age-related metabolic deregulation after menopause. • Hypothalamic tanycytes provide estradiol-weighed information to orexigenic NPY neurons in females • ERα in tanycytes links estrogen signaling to appetite and fertility in cycling females • ERα expression in female tanycytes is required for estrogens to exert its anorexigenic effect • Tanycytic ERα signaling is required for fasting-induced cFos expression in NPY neurons and refeeding in females. [ABSTRACT FROM AUTHOR]

In Western society, high-caloric diets rich in fats and sugars have fueled the obesity epidemic and its related disorders. Disruption of the body-brain communication, crucial for maintaining glucose and energy homeostasis, arises from both obesogenic and genetic factors, leading to metabolic disorders. Here, we investigate the role of hypothalamic tanycyte shuttles between the pituitary portal blood and the third ventricle cerebrospinal fluid in regulating energy balance. We inhibited vesicle-associated membrane proteins (VAMP1-3)-mediated release in tanycytes by expressing the botulinum neurotoxin type B light chain (BoNT/B) in a Cre-dependent manner in tanycytes. This was achieved by injecting either TAT-Cre in the third ventricle or an AAV1/2 expressing Cre under the control of the tanycyte-specific promoter iodothyronine deiodinase 2 into the lateral ventricle of adult male mice. In male mice fed a standard diet, targeted expression of BoNT/B in adult tanycytes blocks leptin transport into the mediobasal hypothalamus and results in normal-weight central obesity, including increased food intake, abdominal fat deposition, and elevated leptin levels but no marked change in body weight. Furthermore, BoNT/B expression in adult tanycytes promotes fatty acid storage, leading to glucose intolerance and insulin resistance. Notably, these metabolic disturbances occur despite a compensatory increase in insulin secretion, observed both in response to exogenous glucose boluses in vivo and in isolated pancreatic islets. Intriguingly, these metabolic alterations are associated with impaired spatial memory in BoNT/B-expressing mice. These findings underscore the central role of tanycytes in brain-periphery communication and highlight their potential implication in the age-related development of type 2 diabetes and cognitive decline. Our tanycytic BoNT/B mouse model provides a robust platform for studying how these conditions progress over time, from prediabetic states to full-blown metabolic and cognitive disorders, and the mechanistic contribution of tanycytes to their development. The recognition of the impact of tanycytic transcytosis on hormone transport opens new avenues for developing targeted therapies that could address both metabolic disorders and their associated cognitive comorbidities, which often emerge or worsen with advancing age. [Display omitted] • Blockade of tanycytic transcytosis abrogates access of blood-borne signals to the hypothalamus. • Obstructing tanycytic shuttles promotes intra-abdominal fat accumulation and carbohydrate consumption. • Expression of botulinum toxin in tanycytes alters peripheral lipid homeostasis. • Hindering tanycytes transports promotes glucose intolerance and insulin resistance. • Impairing tanycytic transcytosis leads to normal-weight central obesity and cognitive alterations. [ABSTRACT FROM AUTHOR]

The median eminence (ME) is part of the neuroendocrine system (NES) that functions as a crucial interface between the hypothalamus and pituitary gland. The ME contains many non-neuronal cell types, including oligodendrocytes, oligodendrocyte precursor cells (OPCs), tanycytes, astrocytes, pericytes, microglia and other immune cells, which may be involved in the regulation of NES function. For example, in mice, ablation of tanycytes (a special class of ependymal gliawith stem cell-like functions) results in weight gain, feeding, insulin insensitivity and increased visceral adipose, consistent with the demonstrated ability of these cells to sense and transport both glucose and leptin, and to differentiate into neurons that control feeding and metabolism in the hypothalamus. To give a further example, OPCs in the ME of mice have been shown to rapidly respond to dietary signals, in turn controlling composition of the extracellular matrix in the ME, derived from oligodendrocyte-lineage cells, which may contribute to the previously described role of these cells in actively maintaining leptin-receptor-expressing dendrites in the ME. In this review, we explore and discuss recent advances such as these, that have developed our understanding of how the various cell types of the ME contribute to its function in the NES as the interface between the hypothalamus and pituitary gland. We also highlight avenues of future research which promise to uncover additional functions of the ME and the glia, stem and progenitor cells it contains. [ABSTRACT FROM AUTHOR]

In adult mammals, neural stem cells are localized in three neurogenic regions, the subventricular zone of the lateral ventricle (SVZ), the subgranular zone of the dentate gyrus of the hippocampus (SGZ) and the hypothalamus. In the SVZ and the SGZ, neural stem/progenitor cells (NSPCs) express the glial fibrillary acidic protein (GFAP) and selective depletion of these NSPCs drastically decreases cell proliferation in vitro and in vivo. In the hypothalamus, GFAP is expressed by α-tanycytes, which are specialized radial glia-like cells in the wall of the third ventricle also recognized as NSPCs. To explore the role of these hypothalamic GFAP-positive tanycytes, we used transgenic mice expressing herpes simplex virus thymidine kinase (HSV-Tk) under the control of the mouse Gfap promoter and a 4-week intracerebroventricular infusion of the antiviral agent ganciclovir (GCV) which kills dividing cells expressing Tk. While GCV significantly reduced the number and growth of hypothalamus-derived neurospheres from adult transgenic mice in vitro , it causes hypogonadotropic hypogonadism in vivo. The selective death of dividing tanycytes expressing GFAP indeed results in a marked decrease in testosterone levels and testicular weight, as well as vacuolization of the seminiferous tubules and loss of spermatogenesis. Additionally, GCV-treated GFAP-Tk mice show impaired sexual behavior, but no alteration in food intake or body weight. Our results also show that the selective depletion of GFAP-expressing tanycytes leads to a sharp decrease in the number of gonadotropin-releasing hormone (GnRH)-immunoreactive neurons and a blunted LH secretion. Overall, our data show that GFAP-expressing tanycytes play a central role in the regulation of male reproductive function. [ABSTRACT FROM AUTHOR]

In adult mammals, neural stem cells are localized in three neurogenic regions, the subventricular zone of the lateral ventricle (SVZ), the subgranular zone of the dentate gyrus of the hippocampus (SGZ) and the hypothalamus. In the SVZ and the SGZ, neural stem/progenitor cells (NSPCs) express the glial fibrillary acidic protein (GFAP) and selective depletion of these NSPCs drastically decreases cell proliferation in vitro and in vivo. In the hypothalamus, GFAP is expressed by α-tanycytes, which are specialized radial glia-like cells in the wall of the third ventricle also recognized as NSPCs. To explore the role of these hypothalamic GFAP-positive tanycytes, we used transgenic mice expressing herpes simplex virus thymidine kinase (HSV-Tk) under the control of the mouse Gfap promoter and a 4-week intracerebroventricular infusion of the antiviral agent ganciclovir (GCV) which kills dividing cells expressing Tk. While GCV significantly reduced the number and growth of hypothalamus-derived neurospheres from adult transgenic mice in vitro, it causes hypogonadotropic hypogonadism in vivo. The selective death of dividing tanycytes expressing GFAP indeed results in a marked decrease in testosterone levels and testicular weight, as well as vacuolization of the seminiferous tubules and loss of spermatogenesis. Additionally, GCV-treated GFAP-Tk mice show impaired sexual behavior, but no alteration in food intake or body weight. Our results also show that the selective depletion of GFAP-expressing tanycytes leads to a sharp decrease in the number of gonadotropin-releasing hormone (GnRH)-immunoreactive neurons and a blunted LH secretion. Overall, our data show that GFAP-expressing tanycytes play a central role in the regulation of male reproductive function.

Genomes of higher eukaryotes encode many uncharacterized proteins, and the functions of these proteins cannot be predicted from the primary sequences due to a lack of conserved functional domains. In this study, we focused on a poorly characterized protein UGS148 that is highly expressed in a specialized cell type called tanycytes that line the ventral wall of the third ventricle in the hypothalamus. Immunostaining of UGS148 revealed the fine morphology of tanycytes with highly branched apical ER membranes. Immunoprecipitation revealed that UGS148 associated with mitochondrial ATPase at least in vitro, and ER and mitochondrial signals occasionally overlapped in tanycytes. Mutant mice lacking UGS148 did not exhibit overt phenotypes, suggesting that UGS148 was not essential in mice reared under normal laboratory conditions. We also found that RNA probes that were predicted to uniquely detect UGS148 mRNA cross‐reacted with uncharacterized RNAs, highlighting the importance of experimental validation of the specificity of probes during the hybridization‐based study of RNA localization. [ABSTRACT FROM AUTHOR]

In addition to the hypophysiotropic thyrotropin‐releasing hormone (TRH)‐synthesizing neurons, a glial cell type, the tanycytes, also play a role in the regulation of the hypothalamic‐pituitary‐thyroid (HPT) axis. Tanycytes modulate the feedback regulation of the axis by regulating the local thyroid hormone availability in the median eminence where the hypophysiotropic axons terminate. Recently, we showed that tanycytes produce diacylglycerol lipase alpha (DAGLα), the synthesizing enzyme of the endocannabinoid 2‐arachidonoylglycerol (2‐AG) that inhibits the release of TRH from the hypophysiotropic terminals in median eminence explants. To determine the importance of the endocannabinoid production of tanycytes, adult male Rax‐CreERT2//DAGLαfl/fl mice were treated with tamoxifen to induce a tanycyte specific decrease of DAGLα expression (T‐DAGLα KO). The effect of this genetic manipulation on the activity of the HPT axis was determined. Tanycyte specific decrease of DAGLα expression resulted in an approximately 2‐fold increase of TSHβ mRNA level that was accompanied by increased levels of circulating free T4. The TRH mRNA level was, however, not influenced by the genetic manipulation. In addition to the effects on the HPT axis, the T‐DAGLα KO mice showed increased fat mass ratio and decreased blood glucose levels. These data indicate that when endocannabinoid release of tanycytes is decreased, the disinhibition of the TRH release induces increased TSH synthesis and higher circulating T4 levels. Thus it suggests that in wild‐type mice, tanycytes exert a tonic inhibitory effect on the TRH release of hypophysiotropic axons. Furthermore, the endocannabinoid release of tanycytes also influences glucose homeostasis and fat deposition. [ABSTRACT FROM AUTHOR]

Tanycytes are hypothalamic radial glial-like cells with an important role in the regulation of neuroendocrine axes and energy homeostasis. These cells have been implicated in glucose, amino acids, and fatty acid sensing in the hypothalamus of rodents, where they are strategically positioned. While their cell bodies contact the cerebrospinal fluid, their extensive processes contact neurons of the arcuate and ventromedial nuclei, protagonists in the regulation of food intake. A growing body of evidence has shown that purinergic signaling plays a relevant role in this homeostatic role of tanycytes, likely regulating the release of gliotransmitters that will modify the activity of satiety-controlling hypothalamic neurons. Connexin hemichannels have proven to be particularly relevant in these mechanisms since they are responsible for the release of ATP from tanycytes in response to nutritional signals. On the other hand, either ionotropic or metabotropic ATP receptors are involved in the generation of intracellular Ca2+ waves in response to hypothalamic nutrients, which can spread between glial cells and towards neighboring neurons. This review will summarize recent evidence that supports a nutrient sensor role for tanycytes, highlighting the participation of purinergic signaling in this process. [ABSTRACT FROM AUTHOR]

Objectives: Glucokinase (GCK) is critical for glucosensing. In rats, GCK is expressed in hypothalamic tanycytes and appears to play an essential role in feeding behavior. In this study, we investigated the distribution of GCK-expressing tanycytes in mice and their role in the regulation of energy balance. Methods: In situ hybridization, reporter gene assay, and immunohistochemistry were used to assess GCK expression along the third ventricle in mice. To evaluate the impact of GCK-expressing tanycytes on arcuate neuron function and mouse physiology, Gck deletion along the ventricle was achieved using loxP/Cre recombinase technology in adult mice. Results: GCK expression was low along the third ventricle, but detectable in tanycytes facing the ventromedial arcuate nucleus from bregma −1.5 to −2.2. Gck deletion induced the death of this tanycyte subgroup through the activation of the BAD signaling pathway. The ablation of GCK-expressing tanycytes affected different aspects of energy balance, leading to an increase in adiposity in mice. This phenotype was systematically associated with a defect in NPY neuron function. In contrast, the regulation of glucose homeostasis was mostly preserved, except for glucoprivic responses. Conclusions: This study describes the role of GCK in tanycyte biology and highlights the impact of tanycyte loss on the regulation of energy balance.

The subfornical organ (SFO) is a sensory circumventricular organ located along the anterodorsal wall of the third ventricle. SFO lacks a complete blood-brain barrier (BBB), and thus peripherally-circulating factors can penetrate the SFO parenchyma. These signals are detected by local neurons providing the brain with information from the periphery to mediate central responses to humoral signals and physiological stressors. Circumventricular organs are characterized by the presence of unique populations of non-neuronal cells, such as tanycytes and fenestrated endothelium. However, how these populations are organized within the SFO is not well understood. In this study, we used histological techniques to analyze the anatomical organization of the rat SFO and examined the distribution of neurons, fenestrated and non-fenestrated vasculature, tanycytes, ependymocytes, glia cells, and pericytes within its confines. Our data show that the shell of SFO contains non-fenestrated vasculature, while fenestrated capillaries are restricted to the medial-posterior core region of the SFO and associated with a higher BBB permeability. In contrast to non-fenestrated vessels, fenestrated capillaries are encased in a scaffold created by pericytes and embedded in a network of tanycytic processes. Analysis of c-Fos expression following systemic injections of angiotensin II or hypertonic NaCl reveals distinct neuronal populations responding to these stimuli. Hypertonic NaCl activates ∼13% of SFO neurons located in the shell. Angiotensin II-sensitive neurons represent ∼35% of SFO neurons and their location varies between sexes. Our study provides a comprehensive description of the organization of diverse cellular elements within the SFO, facilitating future investigations in this important brain area.

There is accumulating evidence that an obesogenic Western diet causes neuroinflammatory damage to the brain, which then promotes further appetitive behaviour. Neuroinflammation has been extensively studied by analysing the translocator protein of 18 kDa (TSPO), a protein that is upregulated in the inflamed brain following a damaging stimulus. As a result, there is a rich supply of TSPO-specific agonists, antagonists and positron emission tomography ligands. One TSPO ligand, etifoxine, is also currently used clinically for the treatment of anxiety with a minimal side-effect profile. Despite the neuroinflammatory pathogenesis of diet-induced obesity, and the translational potential of targeting TSPO, there is sparse literature characterizing the effect of TSPO on appetite. Therefore, in this review, the influence of TSPO on appetite is discussed. Three putative mechanisms for TSPO's appetite-modulatory effect are then characterized: the TSPO–allopregnanolone–GABAAR signalling axis, glucosensing in tanycytes and association with the synaptic protein RIM-BP1. We highlight that, in addition to its plethora of functions, TSPO is a regulator of appetite. This review ultimately suggests that the appetite-modulating function of TSPO should be further explored due to its potential therapeutic promise.

This work was aimed at studying the structural organization of nucleolus and constitutive heterochromatin in different types of tanycytes during postnatal development and aging of rats. The distribution of nucleolus argentophilic proteins (nucleolin and nucleophosmin) and heterochromatin aggregates in tanycytes at various stages of postnatal development have been described for the first time using immunohistochemical methods and confocal laser microscopy. The heterogeneity of the size and number of nucleoli was demonstrated both in different tanycytes subpopulations and at different ages of an animal. This may indicate different levels of the tanycyte synthetic activity and the ability to proliferate during early postnatal development and aging. During aging, the distribution of heterochromatin aggregates varies among tanycyte subpopulations: α-tanycytes undergo intense heterochromatization, while β-tanycytes are characterized by a stable organization of the studied compartments of the cell nucleus. The data obtained significantly supplement the modern understanding of organization of the structure of the cell nucleus of tanycytes during normal development and aging. This can subsequently serve as a basis for establishing the role of these subnuclear structures in pathological processes. [ABSTRACT FROM AUTHOR]

The subfornical organ (SFO) is a sensory circumventricular organ located along the anterodorsal wall of the third ventricle. SFO lacks a complete blood-brain barrier (BBB), and thus peripherally-circulating factors can penetrate the SFO parenchyma. These signals are detected by local neurons providing the brain with information from the periphery to mediate central responses to humoral signals and physiological stressors. Circumventricular organs are characterized by the presence of unique populations of non-neuronal cells, such as tanycytes and fenestrated endothelium. However, how these populations are organized within the SFO is not well understood. In this study, we used histological techniques to analyze the anatomical organization of the rat SFO and examined the distribution of neurons, fenestrated and non-fenestrated vasculature, tanycytes, ependymocytes, glia cells, and pericytes within its confines. Our data show that the shell of SFO contains non-fenestrated vasculature, while fenestrated capillaries are restricted to the medial-posterior core region of the SFO and associated with a higher BBB permeability. In contrast to non-fenestrated vessels, fenestrated capillaries are encased in a scaffold created by pericytes and embedded in a network of tanycytic processes. Analysis of c-Fos expression following systemic injections of angiotensin II or hypertonic NaCl reveals distinct neuronal populations responding to these stimuli. Hypertonic NaCl activates ∼13% of SFO neurons located in the shell. Angiotensin II-sensitive neurons represent ∼35% of SFO neurons and their location varies between sexes. Our study provides a comprehensive description of the organization of diverse cellular elements within the SFO, facilitating future investigations in this important brain area. [ABSTRACT FROM AUTHOR]

The arcuate nucleus of the hypothalamus is central in the regulation of body weight homeostasis through its ability to sense peripheral metabolic signals and relay them, through neural circuits, to other brain areas, ultimately affecting physiological and behavioural changes. The early postnatal development of these neural circuits is critical for normal body weight homeostasis, such that perturbations during this critical period can lead to obesity. The role for peripheral regulators of body weight homeostasis, including leptin, insulin and ghrelin, in this postnatal development is well described, yet some of the fundamental processes underpinning axonal and dendritic growth remain unclear. Here, we hypothesised that molecules known to regulate axonal and dendritic growth processes in other areas of the developing brain would be expressed in the postnatal arcuate nucleus and/or target nuclei where they would function to mediate the development of this circuitry. Using state‐of‐the‐art RNAscope® technology, we have revealed the expression patterns of genes encoding Dcc/Netrin‐1, Robo1/Slit1 and Fzd5/Wnt5a receptor/ligand pairs in the early postnatal mouse hypothalamus. We found that individual genes had unique expression patterns across developmental time in the arcuate nucleus, paraventricular nucleus of the hypothalamus, ventromedial nucleus of the hypothalamus, dorsomedial nucleus of the hypothalamus, median eminence and, somewhat unexpectedly, the third ventricle epithelium. These observations indicate a number of new molecular players in the development of neural circuits regulating body weight homeostasis, as well as novel molecular markers of tanycyte heterogeneity. [ABSTRACT FROM AUTHOR]

The liver releases glucose into the blood using the glucose-6-phosphatase (G6Pase) system, a multiprotein complex located in the endoplasmic reticulum (ER). Here, we show for the first time that the G6Pase system is also expressed in hypothalamic tanycytes, and it is required to regulate energy balance. Using automatized qRT-PCR and immunohistochemical analyses, we evaluated the expression of the G6Pase system. Fluorescent glucose analogue (2-NBDG) uptake was evaluated by 4D live-cell microscopy. Glucose release was tested using a glucose detection kit and high-content live-cell analysis instrument, Incucyte s3. In vivo G6pt knockdown in tanycytes was performed by AAV 1 -shG6PT-mCherry intracerebroventricular injection. Body weight gain, adipose tissue weight, food intake, glucose metabolism, c-Fos, and neuropeptide expression were evaluated at 4 weeks post-transduction. Tanycytes sequester glucose-6-phosphate (G6P) into the ER through the G6Pase system and release glucose in hypoglycaemia via facilitative glucose transporters (GLUTs). Strikingly, in vivo tanycytic G6pt knockdown has a powerful peripheral anabolic effect observed through decreased body weight, white adipose tissue (WAT) tissue mass, and strong downregulation of lipogenesis genes. Selective deletion of G6pt in tanycytes also decreases food intake, c-Fos expression in the arcuate nucleus (ARC), and Npy mRNA expression in fasted mice. The tanycyte-associated G6Pase system is a central mechanism involved in controlling metabolism and energy balance. [Display omitted] • Tanycytes express the G6Pase system. • Tanycytes sequester G6P in the ER. • Tanycytes release glucose in hypoglycaemia through GLUTs. • Tanycytes-expressing G6Pase system regulate the energy balance. [ABSTRACT FROM AUTHOR]

Chronic metabolic diseases, including diabetes and obesity, have become a major global health threat of the twenty-first century. Maintaining glucose homeostasis is essential for survival in mammals. Complex and highly coordinated interactions between glucose-sensing mechanisms and multiple effector systems are essential for controlling glucose levels in the blood. The central nervous system (CNS) plays a crucial role in regulating glucose homeostasis. Growing evidence indicates that disruption of glucose sensing in selective CNS areas, such as the hypothalamus, is closely interlinked with the pathogenesis of obesity and type 2 diabetes mellitus. However, the underlying intracellular mechanisms of glucose sensing in the hypothalamus remain elusive. Here, we review the current literature on hypothalamic glucose-sensing mechanisms and discuss the impact of alterations of these mechanisms on the pathogenesis of diabetes. [ABSTRACT FROM AUTHOR]

Zucker diabetic fatty (ZDF) rats that harbor a mutation in the leptin receptor innately develop type 2 diabetes (T2D) with obesity. Transcutaneous auricular vagal nerve stimulation (taVNS) has an antidiabetic effect in ZDF rats. However, the underlying mechanisms of the weight-gain attenuating effect in ZDF rats by taVNS is still unclear. This study aimed to assess whether the weight-gain attenuating effect of taVNS in ZDF rats is associated with changes in the central nervous system (CNS) expression of P2Y1 receptors (P2Y1R). Adult male ZDF rats were subjected to taVNS and transcutaneous non-vagal nerve stimulation (tnVNS). Their food intake and body weight were recorded daily and weekly, respectively. P2Y1R expression in the hypothalamus, amygdala, and hippocampus was evaluated by western blotting. Hypothalamic P2Y1R expressing cells were detected using immunohistochemistry. Naïve ZDF rats were much heavier (p < 0.05) than their lean littermates (ZL rats), with elevated hypothalamic P2Y1R expression (p < 0.05). Further, taVNS but not tnVNS attenuated weight gain (p < 0.05) without decreasing food intake (p > 0.05) and suppressed hypothalamic P2Y1R expression in ZDF rats (p < 0.05). Moreover, P2Y1R showed major expression in astrocytes of ZDF rats' hypothalamus. ZDF rats innately develop obesity associated with elevated hypothalamic P2Y1R expression. taVNS attenuates weight gain in ZDF rats without changes in food intake, suggesting increased energy expenditure. Whether the reduced hypothalamic P2Y1R expression in response to taVNS is mechanistically linked to the increased energy expenditure remains to be determined. [ABSTRACT FROM AUTHOR]

Tanycytes are highly specialized ependymal cells that line the bottom and the lateral walls of the third ventricle. In contact with the cerebrospinal fluid through their cell bodies, they send processes into the arcuate nucleus, the ventromedial nucleus, and the dorsomedial nucleus of the hypothalamus. In the present work, we combined transgenic and immunohistochemical approaches to investigate the neuroanatomical associations between tanycytes and neural cells present in the hypothalamic parenchyma, in particular in the arcuate nucleus. The specific expression of tdTomato in tanycytes first allowed the observation of peculiar subcellular protrusions along tanycyte processes and at their endfeet such as spines, swelling, en passant boutons, boutons, or claws. Interestingly, these protrusions contact different neural cells in the brain parenchyma including blood vessels and neurons, and in particular NPY and POMC neurons in the arcuate nucleus. Using both fluorescent and electron microscopy, we finally observed that these tanycyte protrusions contain ribosomes, mitochondria, diverse vesicles, and transporters, suggesting dense tanycyte/neuron and tanycyte/blood vessel communications. Altogether, our results lay the neuroanatomical basis for tanycyte/neural cell interactions, which will be useful to further understand cell‐to‐cell communications involved in the regulation of neuroendocrine functions. [ABSTRACT FROM AUTHOR]

Hibernation is an extreme state of seasonal energy conservation, reducing metabolic rate to as little as 1% of the active state. During the hibernation season, many species of hibernating mammals cycle repeatedly between the active (aroused) and hibernating (torpid) states (T-A cycling), using brown adipose tissue (BAT) to drive cyclical rewarming. The regulatory mechanisms controlling this process remain undefined but are presumed to involve thermoregulatory centres in the hypothalamus. Here, we used the golden hamster (Mesocricetus auratus), and high-resolution monitoring of BAT, core body temperature and ventilation rate, to sample at precisely defined phases of the T-A cycle. Using c-fos as a marker of cellular activity, we show that although the dorsomedial hypothalamus is active during torpor entry, neither it nor the pre-optic area shows any significant changes during the earliest stages of spontaneous arousal. Contrastingly, in three non-neuronal sites previously linked to control of metabolic physiology over seasonal and daily time scales - the choroid plexus, pars tuberalis and third ventricle tanycytes - peak c-fos expression is seen at arousal initiation. We suggest that through their sensitivity to factors in the blood or cerebrospinal fluid, these sites may mediate metabolic feedback-based initiation of the spontaneous arousal process., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Objectives: Infections, cancer, and systemic inflammation elicit anorexia. Despite the medical significance of this phenomenon, the question of how peripheral inflammatory mediators affect the central regulation of food intake is incompletely understood. Therefore, we have investigated the sickness behavior induced by the prototypical inflammatory mediator IL-1β. Methods: IL-1β was injected intravenously. To interfere with IL-1β signaling, we deleted the essential modulator of NF-κB signaling (Nemo) in astrocytes and tanycytes. Results: Systemic IL-1β increased the activity of the transcription factor NF-κB in tanycytes of the mediobasal hypothalamus (MBH). By activating NF-κB signaling, IL-1β induced the expression of cyclooxygenase-2 (Cox-2) and stimulated the release of the anorexigenic prostaglandin E2 (PGE2) from tanycytes. When we deleted Nemo in astrocytes and tanycytes, the IL-1β-induced anorexia was alleviated whereas the fever response and lethargy response were unchanged. Similar results were obtained after the selective deletion of Nemo exclusively in tanycytes. Conclusions: Tanycytes form the brain barrier that mediates the anorexic effect of systemic inflammation in the hypothalamus.