Glutamate, released at a majority of excitatory synapses in the central nervous system, depolarizes neurons by acting at specific receptors. Its action is terminated by removal from the synaptic cleft mostly via Na+-dependent uptake systems located on both neurons and astrocytes. Here we report that glutamate, in addition to its receptor-mediated actions on neuronal excitability, stimulates glycolysis-i.e., glucose utilization and lactate production-in astrocytes. This metabolic action is mediated by activation of a Na+-dependent uptake system and not by interaction with receptors. The mechanism involves the Na+/K+-ATPase, which is activated by an increase in the intraceliular concentration of Na+ cotransported with glutamate by the electrogenic uptake system. Thus, when glutamate is released from active synapses and taken up by astrocytes, the newly identified signaling pathway described here would provide a simple and direct mechanism to tightly couple neuronal activity to glucose utilization. In addition, glutamate-stimulated glycolysis is consistent with data obtained from functional brain imaging studies indicating local nonoxidative glucose utilization during physiological activation.Glutamate, the main excitatory neurotransmitter in the brain, profoundly affects neuronal activity by interacting with specific ionotropic and metabotropic receptors (1). The postsynaptic actions of glutamate are rapidly terminated by avid reuptake systems located on both neurons and astrocytes surrounding the synaptic cleft. Both neuronal and astrocytic glutamate transporters have been cloned and their properties studied in vitro (2). In astrocytes, the major glutamate transport is an electrogenic process by which one glutamate is cotransported with three Na+ (or two Na+ and one H+) in exchange for one K+ and one OH-(or one HCO3j (3). The consequence of this stoichiometry is an increase in the Na+ concentration within the astrocyte, accompanied by an intracellular acidification and extracellular alkalinization. Glutamate uptake is essential not only to terminate its effects as neurotransmitter, but also to prevent extracellular glutamate levels from reaching excitotoxic levels (4). In this study, we report that glutamate uptake into astrocytes also results in the stimulation ofglucose utilization and lactate production. This metabolic action ofglutamate, via a newly identified signaling mechanism, provides a simple and straightforward explanation for the coupling existing between neuronal activity and glucose utilization as observed both in animal experiments (5, 6) and in vivo in humans (7). MATERIALS AND METHODS 2-Deoxy-D-[1,2-3H]glucose ([3H]2DG) was purchased fromDuPont (specific activity, 30.6 Ci/mmol; 1 Ci = 37 GBq). D(-)-2-Amino-5-phosphonopentanoic acid, 6-cyano-7-nitroquinoxaline-2,3-dione, L(+)-2-amino-3-phosphonopropionic acid, L(+)-2-amino-4-phosphonobutyric acid, and (2S,3S,4R)-a-(carboxycyclopropyl)glycine (L-CCG III) were obtained from Tocris Neuramin (Bristol, U.K.). Fetal calf serum was purchased from...

The energy requirements of the brain are very high, and tight regulatory mechanisms operate to ensure adequate spatial and temporal delivery of energy substrates in register with neuronal activity. Astrocytes-a type of glial cell-have emerged as active players in brain energy delivery, production, utilization, and storage. Our understanding of neuroenergetics is rapidly evolving from a "neurocentric" view to a more integrated picture involving an intense cooperativity between astrocytes and neurons. This review focuses on the cellular aspects of brain energy metabolism, with a particular emphasis on the metabolic interactions between neurons and astrocytes.

SUMMARY We report that in the rat hippocampus learning leads to a significant increase in extracellular lactate levels, which derive from glycogen, an energy reserve selectively localized in astrocytes. Astrocytic glycogen breakdown and lactate release are essential for long-term but not short-term memory formation, and for the maintenance of long-term potentiation (LTP) of synaptic strength elicited in-vivo. Disrupting the expression of the astrocytic lactate transporters monocarboxylate transporter 4 (MCT4) or MCT1 causes amnesia, which, like LTP impairment, is rescued by lactate but not equicaloric glucose. Disrupting the expression of the neuronal lactate transporter MCT2 also leads to amnesia that is unaffected by either L-lactate or glucose, suggesting that lactate import into neurons is necessary for long-term memory. Glycogenolysis and astrocytic lactate transporters are also critical for the induction of molecular changes required for memory formation, including the induction of phospho-CREB, Arc and phospho-cofilin. We conclude that astrocyte-neuron lactate transport is required for long-term memory formation.

Summary Oligodendroglia support axon survival and function through mechanisms independent of myelination and their dysfunction leads to axon degeneration in several diseases. The cause of this degeneration has not been determined, but lack of energy metabolites such as glucose or lactate has been hypothesized. Lactate is transported exclusively by monocarboxylate transporters, and changes to these transporters alter lactate production and utilization. We show the most abundant lactate transporter in the CNS, monocarboxylate transporter 1 (MCT1), is highly enriched within oligodendroglia and that disruption of this transporter produces axon damage and neuron loss in animal and cell culture models. In addition, this same transporter is reduced in patients with, and mouse models of, amyotrophic lateral sclerosis (ALS), suggesting a role for oligodendroglial MCT1 in pathogenesis. The role of oligodendroglia in axon function and neuron survival has been elusive; this study defines a new fundamental mechanism by which oligodendroglia support neurons and axons.

A full list of affiliations appears at the end of the paper. 'N euroglia' or 'glia' are collective terms describing cells of neuroepithelial (oligodendrocytes, astrocytes, oligodendrocyte progenitor cells, ependymal cells), neural crest (peripheral glia), and myeloid (microglia) origin. Changes in neuroglia associated with diseases of the CNS have been noted, characterized, and conceptualized from the very dawn of neuroglial research. Rudolf Virchow, in a lecture to students and medical doctors in 1858, stressed that 'this very interstitial tissue [that is, neuroglia] of the brain and spinal marrow is one of the most frequent seats of morbid change... ' 1. Changes in the shape, size, or number of glial cells in various pathological contexts have been frequently described by prominent neuroanatomists 2. In particular, hypertrophy of astrocytes was recognized very early as an almost universal sign of CNS pathology: 'the protoplasmic glia elements [that is, astrocytes] are really the elements which exhibit a morbid hypertrophy in pathological conditions' 3. Neuroglial proliferation was thought to accompany CNS lesions, leading to early suggestions that proliferating glia fully replaced damaged neuronal elements 4. Thus, a historical consensus was formed that a change in 'the appearance of neuroglia serves as a delicate indicator of the action of noxious influences upon the central nervous system, ' and the concept of 'reactionary change or gliosis' was accepted 5. While the origin of 'gliosis' is unclear (glia + osis in Greek means 'glial condition or process'; in Latin the suffix-osis acquired the additional meaning of 'disease'; hence 'astrogliosis'

Targeted genome editing via engineered nucleases is an exciting area of biomedical research and holds potential for clinical applications. Despite rapid advances in the field, in vivo targeted transgene integration is still infeasible because current tools are inefficient1, especially for non-dividing cells, which compose most adult tissues. This poses a barrier for uncovering fundamental biological principles and developing treatments for a broad range of genetic disorders2. Based on clustered regularly interspaced short palindromic repeat/Cas9 (CRISPR/Cas9)3,4 technology, here we devise a homology-independent targeted integration (HITI) strategy, which allows for robust DNA knock-in in both dividing and non-dividing cells in vitro and, more importantly, in vivo (for example, in neurons of postnatal mammals). As a proof of concept of its therapeutic potential, we demonstrate the efficacy of HITI in improving visual function using a rat model of the retinal degeneration condition retinitis pigmentosa. The HITI method presented here establishes new avenues for basic research and targeted gene therapies.

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The energy demands of the brain are high: they account for at least 20% of the body's energy consumption. Evolutionary studies indicate that the emergence of higher cognitive functions in humans is associated with an increased glucose utilization and expression of energy metabolism genes. Functional brain imaging techniques such as fMRI and PET, which are widely used in human neuroscience studies, detect signals that monitor energy delivery and use in register with neuronal activity. Recent technological advances in metabolic studies with cellular resolution have afforded decisive insights into the understanding of the cellular and molecular bases of the coupling between neuronal activity and energy metabolism and point at a key role of neuron-astrocyte metabolic interactions. This article reviews some of the most salient features emerging from recent studies and aims at providing an integration of brain energy metabolism across resolution scales.