Hypothalamic tanycytes generate acute hyperphagia through activation of the arcuate neuronal network

Hypothalamic tanycytes are chemosensitive glial cells that contact the cerebrospinal fluid in the third ventricle and send processes into the hypothalamic parenchyma. To test whether they can activate neurons of the arcuate nucleus, we targeted expression of a Ca2+-permeable channelrhodopsin (CatCh) specifically to tanycytes. Activation of tanycytes ex vivo depolarized orexigenic (neuropeptide Y/agouti-related protein; NPY/AgRP) and anorexigenic (proopiomelanocortin; POMC) neurons via an ATP-dependent mechanism. In vivo, activation of tanycytes triggered acute hyperphagia only in the fed state during the inactive phase of the light–dark cycle

Annu Rev Physiol

Information processing imposes urgent metabolic demands on neurons, which have negligible energy stores and restricted access to fuel. Here, we discuss metabolic recruitment, the tissue-level phenomenon whereby active neurons harvest resources from their surroundings. The primary event is the neuronal release of K+ that mirrors workload. Astrocytes sense K+ in exquisite fashion thanks to their unique coexpression of NBCe1 and α2β2 Na+/K+ ATPase, and within seconds switch to Crabtree metabolism, involving GLUT1, aerobic glycolysis, transient suppression of mitochondrial respiration, and lactate export. The lactate surge serves as a secondary recruiter by inhibiting glucose consumption in distant cells. Additional recruiters are glutamate, nitric oxide, and ammonium, which signal over different spatiotemporal domains. The net outcome of these events is that more glucose, lactate, and oxygen are made available. Metabolic recruitment works alongside neurovascular coupling and various averaging strategies to support the inordinate dynamic range of individual neurons. Copyright © 2023 by the author(s)

Small is fast: astrocytic glucose and lactate metabolism at cellular resolution

Brain tissue is highly dynamic in terms of electrical activity and energy demand. Relevant energy metabolites have turnover times ranging from milliseconds to seconds and are rapidly exchanged between cells and within cells. Until recently these fast metabolic events were inaccessible, because standard isotopic techniques require use of populations of cells and/or involve integration times of tens of minutes. Thanks to fluorescent probes and recently available genetically-encoded optical nanosensors, this Technology Report shows how it is now possible to monitor the concentration of metabolites in real-time and in single cells. In combination with ad hoc inhibitor-stop protocols, these probes have revealed a key role for K(+) in the acute stimulation of astrocytic glycolysis by synaptic activity. They have also permitted detection of the Warburg effect in single cancer cells. Genetically-encoded nanosensors currently exist for glucose, lactate, NADH and ATP, and it is envisaged that other metabolite nanosensors will soon be available. These optical tools together with improved expression systems and in vivo imaging, herald an exciting era of single-cell metabolic analysis

A lifetime’s adventure in extracellular K+ regulation: the Scottish connection

In a career that has spanned 45 years and shows no signs of slowing down, Dr Bruce Ransom has devoted considerable time and energy to studying regulation of interstitial K+. When Bruce commenced his studies in 1969 virtually nothing was known of the functions of glial cells, but Bruce’s research contributed to the physiological assignation of function to mammalian astrocytes, namely interstitial K+ buffering. The experiments that I describe in this review concern the response of the membrane potential (Em) of in vivo cat cortical astrocytes to changes in [K+]o, an experimental manoeuvre that was achieved in two different ways. The first involved recording the Em of an astrocyte while the initial aCSF was switched to one with different K+, whereas in the second series of experiments the cortex was stimulated and the response of the astrocyte Em to the K+ released from neighbouring neurons was recorded. The astrocytes responded in a qualitatively predictable manner, but quantitatively the changes were not as predicted by the Nernst equation. Elevations in interstitial K+ are not sustained and K+ returns to baseline rapidly due to the buffering capacity of astrocytes, a phenomenon studied by Bruce, and his son Chris, published 27 years after Bruce’s initial publications. Thus, a lifetime spent investigating K+ buffering has seen enormous advances in glial research, from the time cells were identified as ‘presumed’ glial cells or ‘silent cells’, to the present day, where glial cells are recognised as contributing to every important physiological brain function

The effect of general anaesthetics on brain lactate release

The effects of anaesthetic agents on brain energy metabolism may explain their shared neurophysiological actions but remain poorly understood. The brain lactate shuttle hypothesis proposes that lactate, provided by astrocytes, is an important neuronal energy substrate. Here we tested the hypothesis that anaesthetic agents impair the brain lactate shuttle by interfering with astrocytic glycolysis. Lactate biosensors were used to record changes in lactate release by adult rat brainstem and cortical slices in response to thiopental, propofol and etomidate. Changes in cytosolic nicotinamide adenine dinucleotide reduced (NADH) and oxidized (NAD+) ratio as a measure of glycolytic rate were recorded in cultured astrocytes. It was found that in brainstem slices thiopental, propofol and etomidate reduced lactate release by 7.4 ± 3.6% (P < 0.001), 9.7 ± 6.6% (P < 0.001) and 8.0 ± 7.8% (P = 0.04), respectively. In cortical slices, thiopental reduced lactate release by 8.2 ± 5.6% (P = 0.002) and propofol by 6.0 ± 4.5% (P = 0.009). Lactate release in cortical slices measured during the light phase (period of sleep/low activity) was ~25% lower than that measured during the dark phase (period of wakefulness) (326 ± 83 μM vs 430 ± 118 μM, n = 10; P = 0.04). Thiopental and etomidate induced proportionally similar decreases in cytosolic [NADH]:[NAD+] ratio in astrocytes, indicative of a reduction in glycolytic rate. These data suggest that anaesthetic agents inhibit astrocytic glycolysis and reduce the level of extracellular lactate in the brain. Similar reductions in brain lactate release occur during natural state of sleep, suggesting that general anaesthesia may recapitulate some of the effects of sleep on brain energy metabolism

Current technical approaches to brain energy metabolism

Neuroscience is a technology‐driven discipline and brain energy metabolism is no exception. Once satisfied with mapping metabolic pathways at organ level, we are now looking to learn what it is exactly that metabolic enzymes and transporters do and when, where do they reside, how are they regulated, and how do they relate to the specific functions of neurons, glial cells, and their subcellular domains and organelles, in different areas of the brain. Moreover, we aim to quantify the fluxes of metabolites within and between cells. Energy metabolism is not just a necessity for proper cell function and viability but plays specific roles in higher brain functions such as memory processing and behavior, whose mechanisms need to be understood at all hierarchical levels, from isolated proteins to whole subjects, in both health and disease. To this aim, the field takes advantage of diverse disciplines including anatomy, histology, physiology, biochemistry, bioenergetics, cellular biology, molecular biology, developmental biology, neurology, and mathematical modeling. This article presents a well‐referenced synopsis of the technical side of brain energy metabolism research. Detail and jargon are avoided whenever possible and emphasis is given to comparative strengths, limitations, and weaknesses, information that is often not available in regular articles.Fondecyt, Grant Number: 1160317; MINECO, Grant Numbers: SAF2016‐78114‐R and RTC‐2015‐3237‐1; CIBERFES, Grant Numer: CB16/10/00282; SP3‐People‐MC‐ITN program, Grant Number: 608381; EU BATCure, Grant Number: 666918; FEDER (European regional development fund); Investissement d'Avenir, Grant Number: ANR‐11‐INBS‐0011; French State in the context of the “Investments for the future” Program IdEx and the LabEx TRAIL, Grant Numbers: ANR‐10‐IDEX and ANR‐10‐LABX‐57; French–Swiss ANR‐FNS, Grant Numer: ANR‐15‐ CE37‐0012. University of Nottingham; BBSRC, Grant Numers: BB/L019396/1 and BB/K009192/1; MRC, Grant Number: MR/L020661/1; Deutsche Forschungsgemeinschaft, Grant Numers: DFG SPP 1757, SFB 894, and FOR 2289; European Commission, Grant Number: H2020‐FETPROACT 732344; Neurofibres, Grant Number: H2020‐MSCA‐ITN‐722053 EU‐GliaPhD; US National Institutes of Health, Grant Number: R01NS087611; Teva Pharmaceuticals; Agilent Technologies. IdEx, Grant Number: ANR‐10‐IDEX‐03‐02; French–Swiss ANR‐FNS, Grant number: 310030E‐164271; National Institutes of Neurologic Disease and Stroke at the National Institutes of Health, Grant Numer: R01 NS077773; University of Zurich and the Swiss National Science Foundation; Comisión Nacional de Investigación Científica y Tecnológica, Grant Numer: PB 01; Fondo Nacional de Desarrollo Científico y Tecnológico, Grant Numer: 1160317; Ministerio de Economía y Competitividad, Grant Numer: RTC‐2015‐3237‐1,SAF2016‐78114‐R; Agence Nationale de la Recherche, Grant Numers: ANR‐10‐IDEX, ANR‐10‐IDEX‐03‐02, ANR‐10‐LABX‐57, ANR‐11‐INBS‐0011, and ANR‐15‐ CE37‐0012; Biotechnology and Biological Sciences Research Council, Grant Numers: BB/L019396/1 and BB/K009192/1; Medical Research Council, Grant Numer: MR/L020661/1.Peer reviewe

Effect of warming anesthetic on pain perception during dental injection: a split-mouth randomized clinical trial

Pedro Christian Aravena,1,2 Camila Barrientos,1 Catalina Troncoso,1 Cesar Coronado,3 Pamela Sotelo-Hitschfeld4 1Department of Dentistry, Universidad Austral de Chile, Valdivia, Chile; 2Department of Dental Implant Surgery, S&atilde;o Leopoldo Mandic School and Dental Institute, Campinas, SP, Brazil; 3Faculty of Health Science, School of Medicine, Universidad Aut&oacute;noma de Chile, Santiago, Chile; 4Department of Center for Interdisciplinary Studies on Nervous System (CISNe), Universidad Austral de Chile, Valdivia, Chile Background: The purpose of this study is to determine the effectiveness of warming anesthesia on the control of the pain produced during the administration of dental anesthesia injection and to analyze the role of Transient Receptor Potential Vanilloid-1 nociceptor channels in this effect.Patients and methods: A double-blind, split-mouth randomized clinical trial was designed. Seventy-two volunteer students (22.1&plusmn;2.45 years old; 51 men) from the School of Dentistry at the Universidad Austral de Chile (Valdivia, Chile) participated. They were each administered 0.9 mL of lidocaine HCl 2% with epinephrine 1:100,000 (Alphacaine&reg;) using two injections in the buccal vestibule at the level of the upper lateral incisor teeth. Anesthesia was administered in a hemiarch at 42&deg;C (107.6&deg;F) and after 1 week, anesthesia was administered by randomized sequence on the contralateral side at room temperature (21&deg;C&ndash;69.8&deg;F) at a standardized speed. The intensity of pain perceived during the injection was compared using a 100 mm visual analog scale (VAS; Wilcoxon test p&lt;0.05).Results: The use of anesthesia at room temperature produced an average VAS for pain of 35.3&plusmn;16.71 mm and anesthesia at 42&deg;C produced VAS for pain of 15&plusmn;14.67 mm (p&lt;0.001).Conclusion: The use of anesthesia at 42&deg;C significantly reduced the pain during the injection of anesthesia compared to its use at room temperature during maxillary injections. The physiological mechanism of the temperature on pain reduction could be due to a synergic action on the permeabilization of the Transient Receptor Potential Vanilloid-1 channels, allowing the passage of anesthetic inside the nociceptors. Keywords: pain, dental anesthesia, maxillary, lidocaine, trigeminal nerve, clinical trial, TRP channe

GABAergic disinhibition from the BNST to PNOCARC neurons promotes HFD-induced hyperphagia

Summary: Activation of prepronociceptin (PNOC)-expressing neurons in the arcuate nucleus (ARC) promotes high-fat-diet (HFD)-induced hyperphagia. In turn, PNOCARC neurons can inhibit the anorexic response of proopiomelanocortin (POMC) neurons. Here, we validate the necessity of PNOCARC activity for HFD-induced inhibition of POMC neurons in mice and find that PNOCARC-neuron-dependent inhibition of POMC neurons is mediated by gamma-aminobutyric acid (GABA) release. When monitoring individual PNOCARC neuron activity via Ca2+ imaging, we find a subpopulation of PNOCARC neurons that is inhibited upon gastrointestinal calorie sensing and disinhibited upon HFD feeding. Combining retrograde rabies tracing and circuit mapping, we find that PNOC neurons from the bed nucleus of the stria terminalis (PNOCBNST) provide inhibitory input to PNOCARC neurons, and this inhibitory input is blunted upon HFD feeding. This work sheds light on how an increase in caloric content of the diet can rewire a neuronal circuit, paving the way to overconsumption and obesity development

NH4+ triggers the release of astrocytic lactate via mitochondrial pyruvate shunting

Neural activity is accompanied by a transient mismatch between local glucose and oxygen metabolism, a phenomenon of physiological and pathophysiological importance termed aerobic glycolysis. Previous studies have proposed glutamate and K(+) as the neuronal signals that trigger aerobic glycolysis in astrocytes. Here we used a panel of genetically encoded FRET sensors in vitro and in vivo to investigate the participation of NH4(+), a by-product of catabolism that is also released by active neurons. Astrocytes in mixed cortical cultures responded to physiological levels of NH4(+) with an acute rise in cytosolic lactate followed by lactate release into the extracellular space, as detected by a lactate-sniffer. An acute increase in astrocytic lactate was also observed in acute hippocampal slices exposed to NH4(+) and in the somatosensory cortex of anesthetized mice in response to i.v. NH4(+). Unexpectedly, NH4(+) had no effect on astrocytic glucose consumption. Parallel measurements showed simultaneous cytosolic pyruvate accumulation and NADH depletion, suggesting the involvement of mitochondria. An inhibitor-stop technique confirmed a strong inhibition of mitochondrial pyruvate uptake that can be explained by mitochondrial matrix acidification. These results show that physiological NH4(+) diverts the flux of pyruvate from mitochondria to lactate production and release. Considering that NH4(+) is produced stoichiometrically with glutamate during excitatory neurotransmission, we propose that NH4(+) behaves as an intercellular signal and that pyruvate shunting contributes to aerobic lactate production by astrocytes