Oxidation of 14C-labeled substrates by hippocampal slice cultures
Program in Neural and Behavioral Science, State University New York-Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, New York 11203, USA.Brain Research Protocols (Impact Factor: 1.82). 10/2005; 15(3):135-41. DOI: 10.1016/j.brainresprot.2005.06.002
In vitro studies of glucose and lactate utilization have been performed in acute hippocampal slices or dissociated neurons and glia. While some studies concluded that lactate and glucose are equivalent substrates to support evoked synaptic activity, others showed decreased synaptic activity in the presence of lactate as compared to glucose. We found diminished neural activity in the presence of lactate in hippocampal slice cultures. We developed a method to examine the oxidation rates of 14C-labeled substrates by hippocampal slice cultures. The rate of 14CO2 production from either 14C-glucose or 14C-lactate remained unchanged for 6 h suggesting that slice cultures are metabolically stable. While the glucose oxidation rate saturated between 2.8 and 10 mM, lactate oxidation rate had not saturated at 10 mM. These data suggest that organotypic slice cultures provide a method to examine elements of cerebral metabolism in vitro.
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ABSTRACT: Glucose is well accepted as the major fuel for neuronal activity, while it remains controversial whether lactate also supports neural activity. In hippocampal slice cultures, synaptic transmission supported by glucose was reversibly suppressed by lactate. To test whether lactate had a similar inhibitory effect in vivo, lactate was perfused into the hippocampi of unanesthetized rats while recording the firing of nearby pyramidal cells. Lactate perfusion suppressed pyramidal cell firing by 87.5+/-8.3% (n=6). Firing suppression was slow in onset and fully reversible and was associated with increased lactate concentration at the site of the recording electrode. In vivo suppression of neural activity by lactate occurred in the presence of glucose; therefore we tested whether suppression of neural firing was due to lactate interference with glucose metabolism. Competition between glucose and lactate was measured in hippocampal slice cultures. Lactate had no effect on glucose uptake. Lactate suppressed glucose oxidation when applied at an elevated, pathological concentration (10 mM), but not at its physiological concentration (1 mM). Pyruvate (10 mM) also inhibited glucose oxidation but was significantly less effective than lactate. The greater suppressive effect of lactate as compared to pyruvate suggests that alteration of the NAD(+)/NADH ratio underlies the suppression of glucose oxidation by lactate. ATP in slice culture was unchanged in glucose (1 mM), but significantly reduced in lactate (1 mM). ATP in slice culture was significantly increased by combination of glucose (1 mM) and lactate (1 mM). These data suggest that alteration of redox ratio underlies the suppression of neural discharge and glucose metabolism by lactate.Brain Research 11/2006; 1117(1):213-23. DOI:10.1016/j.brainres.2006.07.107 · 2.84 Impact Factor
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ABSTRACT: Presenilin 1 (PS1) regulates environmental enrichment (EE)-mediated neural progenitor cell (NPC) proliferation and neurogenesis in the adult hippocampus. We now report that transgenic mice that ubiquitously express human PS1 variants linked to early-onset familial Alzheimer's disease (FAD) neither exhibit EE-induced proliferation, nor neuronal lineage commitment of NPCs. Remarkably, the proliferation and differentiation of cultured NPCs from standard-housed mice expressing wild-type PS1 or PS1 variants are indistinguishable. On the other hand, wild-type NPCs cocultured with primary microglia from mice expressing PS1 variants exhibit impaired proliferation and neuronal lineage commitment, phenotypes that are recapitulated with mutant microglia conditioned media in which we detect altered levels of selected soluble signaling factors. These findings lead us to conclude that factors secreted from microglia play a central role in modulating hippocampal neurogenesis, and argue for non-cell-autonomous mechanisms that govern FAD-linked PS1-mediated impairments in adult hippocampal neurogenesis.Neuron 09/2008; 59(4):568-80. DOI:10.1016/j.neuron.2008.07.033 · 15.05 Impact Factor
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ABSTRACT: Lactate uses an unknown mechanism to induce panic attacks in people and panic-like symptoms in rodents. We tested whether intraperitoneal (IP) lactate injections act peripherally or centrally to induce panic-like symptoms in rats by examining whether IP lactate directly affects the CNS. In Long-Evans rats, IP lactate (2 mmol/kg) injection increased lactate levels in the plasma and the cerebrospinal fluid. IP lactate also induced tachycardia and behavioral freezing suggesting the production of panic-like behavior. To enter intermediate metabolism, lactate is oxidized by lactate dehydrogenase (LDH) to pyruvate with co-reduction of NAD(+) to NADH. Therefore, we measured the ratio of NADH/NAD(+) to test whether IP lactate altered lactate metabolism in the CNS. Lactate metabolism was studied in the hippocampus, a brain region believed to contribute to panic-like symptoms. IP lactate injection lowered the ratio of NADH/NAD(+) without altering the total amount of NADH and NAD(+) suggesting oxidation of hippocampal redox state. Lactate oxidized hippocampal redox since intrahippocampal injection of the LDH inhibitor, oxamate (50mM) prevented the oxidation of NADH/NAD(+) by IP lactate. In addition to oxidizing hippocampal redox, IP lactate rapidly increased the firing rate of hippocampal neurons. Similar IP pyruvate injections had no effect. Neural discharge also increased following intrahippocampal lactate injection suggesting that increased discharge was a direct action of lactate on the hippocampus. These studies show that oxidation of brain redox and increased hippocampal firing are direct actions of lactate on the CNS that may contribute to the production of lactate-induced panic.Neuroscience Letters 05/2009; 453(3):219-24. DOI:10.1016/j.neulet.2009.02.041 · 2.03 Impact Factor
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