Water uptake and energy metabolism in brain slices from the rat

Chronic inhibition of brain glycolysis initiates epileptogenesis

Metabolic abnormalities found in epileptogenic tissue provide considerable evidence of brain hypometabolism, while major risk factors for acquired epilepsy all share brain hypometabolism as one common outcome, suggesting that a breakdown of brain energy homeostasis may actually precede epileptogenesis. However, a causal link between deficient brain energy metabolism and epilepsy initiation has not been yet established. To address this issue we developed an in vivo model of chronic energy hypometabolism by daily intracerebroventricular (i.c.v.) injection of the nonmetabolizable glucose analog 2-deoxy-D-glucose (2-DG) and also investigated acute effects of 2-DG on the cellular level. In hippocampal slices, acute glycolysis inhibition by 2-DG (by about 35%) led to contrasting effects on the network: a downregulation of excitatory synaptic transmission together with a depolarization of neuronal resting potential and a decreased drive of inhibitory transmission. Therefore, the potential acute effect of 2-DG on network excitability depends on the balance between these opposing pre- and postsynaptic changes. In vivo, we found that chronic 2-DG i.c.v. application (estimated transient inhibition of brain glycolysis under 14%) for a period of 4 weeks induced epileptiform activity in initially healthy male rats. Our results suggest that chronic inhibition of brain energy metabolism, characteristics of the well-established risk factors of acquired epilepsy, and specifically a reduction in glucose utilization (typically observed in epileptic patients) can initiate epileptogenesis. © 2017 Wiley Periodicals, Inc.

Differential increase in cerebral cortical glucose oxidative metabolism during rat postnatal development is greater in vivo than in vitro

The steady-state rate of glucose oxidation through the mitochondrial TCA cycle (V(TCA)) was measured in acid extracts of 10- and 30-day-old cerebral cortex of rats receiving [1-13C]glucose intravenously and in neocortical slices superfused in vitro with the same isotope. TCA cycle flux was determined for each age group based on metabolic modeling analysis of the isotopic turnover of cortical glutamate and lactate. The sensitivity of the calculated rates to assumed parameters in the model were also assessed. Between 10 and 30 postnatal days, V(TCA) increased by 4.3-fold (from 0.46 to 2.0 micromol g(-1) min(-1)) in the cortex in vivo, whereas only a 2-fold (from 0.17 to 0.34 micromol g(-1) min(-1)) increase was observed in neocortical slices. The much greater increase in glucose oxidative metabolism of the cortex measured in vivo over that measured in vitro as the cortex matures suggests that function-related energy demands increase during development, a process that is deficient in the slice as a result of deafferentiation and other mechanisms.

Prediction of in vivo tissue distribution from in vitro data 1. Experiments with markers of aqueous spaces

PURPOSE

The aim of this study was to evaluate the ability of an in vitro method of tissue distribution to accurately predict total water and extracellular aqueous spaces using marker compounds urea and inulin.

METHODS

Slices (50-200 mg) of all the major tissues in the rat were incubated with Hanks/HEPES pH7.4 buffer containing 14C-urea and 3H-inulin for 2 h at 37 degrees C. Tissue weight was noted before and after incubation and the tissue-to-buffer ratios determined.

RESULTS

14C-Urea Kp estimates were generally greater than total tissue water due to tissue swelling, which varied widely among the tissues, up to 41% in muscle. In most cases, Kp values were much closer to in vivo values after correcting for the 14C-urea in the imbibed media (Kpcorr). The method was able to distinguish between 14C-urea and 3H-inulin Kp values and indicated that inulin occupied a smaller space than urea, which for the majority of tissues corresponded to the extracellular space.

CONCLUSIONS

The Kp(corr) values for 14C-urea and Kp for 3H-inulin were consistent with total tissue water and extracellular space for the majority of tissues studied, indicating their suitability as marker compounds for checking the viability of this in vitro method for estimating tissue distribution.

Cardiac cell volume: crystal clear or murky waters? A comparison with other cell types

The osmolarity of bodily fluids is strictly controlled so that most cells do not experience changes in osmotic pressure under normal conditions, but osmotic changes can occur in pathological states such as ischemia, septic shock, and diabetic coma. The primary effect of a change in osmolarity is to acutely alter cell volume. If the osmolarity around a cell is decreased, the cell swells, and if increased, it shrinks. In order to tolerate changes in osmolarity, cells have evolved volume regulatory mechanisms activated by osmotic challenge to normalise cell volume and maintain normal function. In the heart, osmotic stress is encountered during a period of myocardial ischemia when metabolites such as lactate accumulate intracellularly and to a certain degree extracellularly, and cause cell swelling. This swelling may be exacerbated further on reperfusion when the hyperosmotic extracellular milieu is replaced by normosmotic blood. In this review, we describe the theory and mechanisms of volume regulation, and draw on findings in extracardiac tissues, such as kidney, whose responses to osmotic change are well characterised. We then describe cell volume regulation in the heart, with particular emphasis on the effect of myocardial ischemia. Finally, we describe the consequences of osmotic cell swelling for the cell and for the heart, and discuss the implications for antiarrhythmic drug efficacy. Using computer modelling, we have summated the changes induced by cell swelling, and predict that swelling will shorten the action potential. This finding indicates that cell swelling is an important component of the response to ischemia, a component modulating the excitability of the heart.

In vivo 31P NMR study of early cellular responses to hyperosmotic shock in cultured glioma cells

Cell volume regulation in the face of osmotic stress is a fundamental homeostatic activity, and is most critical in brain, which is spatially constrained. Despite the importance of this phenomenon, little is known about volume regulation in the brain, primarily because of the cellular heterogeneity in the tissue. We describe here simultaneous in vivo 31P nuclear magnetic resonance (NMR) measurements of cell volume, intracellular pH and phosphate metabolites during early responses to hyperosmotic stress in C6 glioma cells perfused in NMR-compatible bioreactors. Cell volume was measured using dimethyl methylphosphonate (DMMP) as a probe which has an intracellular NMR resonance shifted upfield from the extracellular resonance. The sensitivity of these measurements allowed 31P NMR spectra to be collected every 30 s. Following an increase in osmolarity from 320 to 480 mOsm by addition of NaCl to the perfusate, C6 glioma cells shrank to 67% of their original volume. We also observed a simultaneous increase of intracellular pH coincident with the decrease in cell volume. The signals from ATP decreased by 10%, but those from phosphocreatine (PCr) increased by 31% after hyperosmotic shock. However, correcting the ATP signals for the decrease in cell volume indicated that its intracellular concentrations increased after treatment. Signals from glycerophosphorylcholine (GPC) and glycerophosphorylethanolamine (GPE) were not changed significantly. This is the first in vivo report of early cellular responses monitored by NMR spectroscopy following hyperosmotic shock in cultured cells.

Comparative effects of kainic, quisqualic, and ibotenic acids on phenylethanolamine-N-methyltransferase-containing cells of rat retina

Phenylethanolamine-N-methyltransferase (PNMT) activity is located in a subpopulation of amacrine cells in the inner nuclear layer of the rat retina. Kainic, quisqualic, and ibotenic acids, all of which are analogues of glutamic acid, were injected intravitreally to the right and saline to the contralateral left eyes of adult male rats in order to determine the effect of these agents upon retinal PNMT activity. Animals were sacrificed 1 week later for tissue removal. The effect of these agents was measured by radiometric assay for PNMT. The fall in PNMT activity was used to measure the sensitivity of the PNMT-containing cells to these agents. Kainic acid was the most potent, producing the greatest reduction in PNMT activity in the smallest doses. Quisqualic acid was intermediate in potency to that of kainic and ibotenic acids. Ibotenic acid reduced PNMT activity only in extremely high doses. The PNMT-containing cells are sensitive to the toxic actions of kainic and quisqualic acids, but relatively insensitive to the actions of ibotenic acid.

Utilization of the synthetic phosphagen cyclocreatine phosphate by a simple brain model during stimulation by neuroexcitatory amino acids

The ability of 1-carboxymethyl-2-imino-3-phosphonoimidazolidine (cyclocreatine-P), accumulated by a simple brain model, to function as a supplemental synthetic phosphagen and respond to the decreases in cytosolic ATP/free ADP ratios that occur during prolonged stimulation by various excitatory amino acids was investigated. Suspensions of chopped whole brain from 11- to 14-day-old chick embryos were incubated with 30 mM cyclocreatine for 90 min, resulting in accumulation of 100 mumol/g dry weight of cyclocreatine-P, and then incubated for up to 1 h with a series of excitatory amino acids of widely differing potencies. Under these conditions net utilization of cyclocreatine-P was detected in response to stimulation by the following neuroexcitatory compounds at the indicated threshold concentrations: kainate (20 microM), N-methyl-DL-aspartate (20 microM), L-homocysteate (20 microM), L-glutamate (200 microM), D-glutamate (200 microM), L-aspartate (2 mM), DL-2-amino-3-phosphonopropionate (2 mM), and DL-2-amino-4-phosphonobutyrate (2 mM). Significant increases in water content of chick embryo brain minces accompanied stimulation by excitatory amino acids. It is suggested that changes in water content or cyclocreatine-P levels in this sensitive brain model might be utilized in automatable screening procedures for detecting novel antagonists and/or new agonists of excitatory amino acids.

GABA release from Xenopus retina does not correlate with horizontal cell membrane potential

The relationship between horizontal cell membrane potential and the release of GABA was explored in the retina of Xenopus laevis. The intracellularly recorded membrane potential of horizontal cells was monitored while the retina was exposed to different concentrations of depolarizing agents. The dose-response curves obtained revealed a rise from 5 to 95% maximum depolarization in 0.5-1.5 log unit concentration change. The molar concentrations that elicited a 20 mV depolarization were 40 mM (potassium), 0.8 mM (glutamate), 0.8 mM (glycine), 5 microM (kainate) and 1.3 microM (quisqualate). Autoradiography revealed that radiolabel was accumulated almost exclusively by horizontal cells when isolated retinas were incubated in medium containing 1 microM [3H]GABA. Thus, retinal release of radioactivity was used as a measure of [3H]GABA release from horizontal cells. Endogenous GABA released from retinas was measured using high performance liquid chromatography and was taken to reflect both amacrine and horizontal cell GABA pools. The release of both [3H]GABA and endogenous GABA was stimulated by glutamate, kainate and potassium, but not by glycine or quisqualate. Similar dose-response curves for GABA release and for depolarization were obtained in the case of potassium and kainate but not for glutamate. Potassium-evoked release either of endogenous GABA or [3H]GABA was both calcium- and sodium-dependent, whereas kainate- or glutamate-evoked GABA release was sodium-dependent but calcium-independent. The results indicate that depolarization per se is not necessarily associated with transmitter release in Xenopus retinal horizontal cells. It is suggested that the action of a given neurotransmitter upon the efflux of GABA from horizontal cells may depend on the degree to which it modifies the sodium conductance of the horizontal cell.

Influence of Na+, K+, and Ca2+ on glutamine synthesis and distribution in rat brain cortex slices: a possible linkage of glutamine synthetase with cerebral transport processes and energetics in the astrocytes

The ouabain-induced suppression of glutamine synthesis and retention in incubating rat brain cortex slices was found to be mimicked by changes in the cationic content of the incubation medium, which cause an increase in the intracellular [Na+] and a decrease in the intracellular [K+]. The suppression of glutamine synthesis (and fixation of ammonia) was also found to take place when Ca2+ was omitted from the incubation medium. This occurred whether endogenous or exogenous glutamate was the substrate for glutamine synthesis. The suppressions cannot be due solely to an effect on glutamate uptake, because the uptake is not markedly affected by these conditions. The results show that Na+, K+, and Ca2+ influence the synthesis and distribution of glutamine in the brain. They suggest that Ca2+ and the Na+, K+ pump may serve a role in regulating the activity of ATP-dependent glutamine synthetase, a key enzyme of the glutamate-glutamine cycle, located in the astrocytes. This may be mediated via a direct effect on the enzyme or through an effect on the production of ATP.

Effects of temperature and general anesthesia on the water gain and the inulin space of the brain of the toad, Bufo arenarum Hensel

1. The water gain in vitro and the inulin space of the brain of the toad were measured under different experimental conditions. 2. There exists a highly positive correlation between water uptake by the brain and the acclimation-incubation temperature, 7 degrees-37 degrees C. 3. Regional differences in the water gain and inulin space were also demonstrated when measured at 20 degrees C. Higher gains were observed in hemispheres, mesodiencephalon and rhombencephalon. 4. The water gain was higher for whole brains obtained under deep anesthesia with ether or urethane but not under nembutal. The inulin space was also higher under ether but lower under urethane. Nembutal had no effect in this case either. 5. A hypothesis about the possible role of water and electrolyte movements in the mechanism of action of some general anesthetics is advanced.

Effect of excitatory amino acids on gamma-aminobutyric acid release from frog horizontal cells

The effects of excitatory amino acids, analogues and K on [3H]gamma-aminobutyric acid [3H]GABA) release from horizontal cells of the isolated superfused frog retina were studied. Exposure of the retina to medium containing high concentrations (25-100 mM) of KCl increased the release of [3H]GABA to a maximum which was 40 times the spontaneous resting release. The K-evoked release of [3H]GABA was almost abolished in high-Mg/low-Ca medium. Glutamate, aspartate, kainate and quisqualate also stimulated the release of [3H]GABA from horizontal cells, the maximum evoked release being similar to that produced by KCl. The release of [3H]GABA evoked by glutamate, aspartate, kainate and quisqualate was abolished in high-Mg/low-Ca medium and by Na-free medium. The evoked releases of [3H]GABA were not reduced by tetrodotoxin. N-Methyl-D-aspartate (NMDA) at concentrations up to 10 mM had virtually no effect on [3H]GABA release from horizontal cells. In Mg-free medium, NMDA stimulated [3H]GABA release, but the maximum release was only 10% of that produced by other agonists. Mg-free medium did not significantly affect the evoked release of [3H]GABA by other agonists. NMDA apparently possessed affinity for the kainate receptor, because in normal medium it antagonized the effects of kainate but not glutamate, aspartate or quisqualate. The non-selective antagonist of excitatory amino acids, (+/-)-cis-2,3-piperidine dicarboxylic acid (PDA) antagonized the action of glutamate, aspartate, kainate and quisqualate on horizontal cell [3H]GABA release. D(-)-2-Amino-4-phosphonobutyrate (APB) and D-gamma-glutamylglycine (D-gamma-GG) antagonized the actions of kainate on horizontal cell [3H]GABA release at concentrations which had little affect on quisqualate-evoked responses. Approximate estimates of pA2 values (Schild, 1947) showed that the specificity and potency of the antagonists was low. Nevertheless, the retinal 'non-NMDA' receptors can probably be subdivided into kainate and quisqualate types. Glutamate diethylester (GDEE) did not affect the action of any agonist. We conclude that glutamate (and aspartate) probably stimulate the release of [3H]GABA from frog horizontal cells by activating receptors of the non-NMDA type. This activation may trigger the opening of tetrodotoxin-insensitive Na channels, resulting in the depolarization of the cell membrane and an increase in the conductance of voltage-sensitive Ca-channels. An influx of Ca ions would then trigger the release of [3H]GABA. Our results are not consistent with previous suggestions that GABA release from horizontal cells involves an outwardly directed transport process.

Effects of metabolic inhibitors on evoked activity and the energy state of hippocampal slices superfused in vitro

The effects of the metabolic inhibitors, arsenate (1,10 mM), iodoacetate (1 mM), alpha-cyano-4-hydroxycinnamate (alpha C4HC: 0.05, 0.15, 0.5 mM), malonate (10 mM) and 2,4-dinitrophenol (10 microM) on granule cell evoked activity and levels of energy metabolites of superfused hippocampal slices were investigated. Every inhibitor tested decreased the amplitudes of the population spikes, and also to a lesser extent, the rates of rise of EPSP. The effects were essentially reversible except in the case of iodoacetate. Concentrations of inhibitors, sufficient to depress evoked activity by at least 75%, did not significantly decrease tissue levels of phosphocreatine, ATP or total K+, with the exception of 1 mM iodoacetate. In slices superfused with 10 mM arsenate, 0.5 mM alpha C4HC, 10 mM malonate or 10 micron 2,4-dinitrophenol, the threshold EPSP for population spike generation was significantly higher than in inhibitor-free medium. These results are discussed in relation to the potential importance of non-oxidative glucose metabolism in maintaining evoked activity, and the possibility that during metabolic insults, tissue ATP utilisation is decreased to match reduced cytoplasmic ATP supply.

Monosodium glutamate lesions in rat hypothalamus studied by immunohistochemistry for gonadotropin releasing hormone, neurotensin, tyrosine hydroxylase, and glutamic acid decarboxylase and by autoradiography for [3H] estradiol

Adult male and female rats treated neonatally with monosodium glutamate (MSG) exhibit lesions in the arcuate nucleus of the hypothalamus. Immunohistochemical analysis of the distribution of tyrosine hydroxylase (TH), glutamic acid decarboxylase (GAD), neurotensin (NT) and gonadotropin-releasing hormone (GnRH) reveals substantial destructions of tuberoinfundibular dopamine and NT systems accompanied by a marked reduction of immunoreactivity in the median eminence. GAD immunoreactivity in the arcuate nucleus and median eminence is greatly reduced, while GnRH containing structures in the mediobasal hypothalamus are not noticeably affected. Evaluation of autoradiograms after intravenously administered [3H] estradiol in the ventral hypothalamus indicate an almost complete loss of target neurons in the arcuate nucleus but not in the nearby ventromedial nucleus. The results suggest that: (a) NT- and dopamine-containing neurons of the arcuate nucleus project to the median eminence via tuberoinfundibular NT and dopaminergic pathways; (b) GABA in the median eminence originates to a major extent from neurons of the arcuate nucleus through a tuberoinfundibular GABAergic system; (c) GnRH is produced in the rat outside the arcuate nucleus; (d) the MSG-induced lesion in the basal tuberal region abolishes or strongly diminishes estradiol target neurons in the arcuate nucleus.

The differential effects of excitatory amino acids on uptake of 45CaCl2 by slices from mouse striatum

Exposure to L-glutamate (10 mM) or 60 mM K+ for 1 min significantly stimulated the uptake of 45Ca2+ in slices from mouse striatum. Glutamate-induced stimulation was antagonized by 30 mM Mg2+ and by 5 or 10 mM L-glutamic acid diethyl ester, but not by 5 microM tetrodotoxin. Under these 1-min incubation conditions, neither kainate nor N-methyl-D,L-aspartate significantly affected the uptake of 45Ca2+ ion. By contrast, following preincubation for 10 min, glutamate and the conformationally restricted analogues, ibotenate, quisqualate, and kainate significantly inhibited the 60 mM K+-induced stimulation of the uptake of 45Ca2+. These effects of glutamate and kainate were not significantly affected by the presence of 1 mM Ca2+ in the preincubation medium. These results suggest that glutamate may activate a receptor directly linked to Ca2+ channels, whereas kainate may indirectly modulate the intracellular disposition of Ca2+.

Effects of kainic acid on high-energy metabolites in the mouse striatum

Intrastriatal injection of either kainic acid (0.35 micrograms) or ibotenic acid (7.0 micrograms) in the mouse causes a profound and selective degeneration of striatal neurons accompanied by a secondary astrocytic response. The kainate injection (0.35 micrograms) resulted in significant decrements in the striatal levels of phosphocreatine and ATP by 30 min. a progressive reduction in adenosine phosphates between 30 min and 48 h, and a decrease in energy charge; whereas lactate levels increased by 44% at 2 h, glucose levels fell by 56%. Two hours after intrastriatal injection of ibotenic acid (7.0 micrograms) similar alternations in striatal high-energy phosphates and glucose disposition were found. Prior decortication protected against the neurotoxic effects of kainate in the mouse striatum and prevented the alterations in high-energy phosphates at 2 h although lactate levels increased by 212%. These findings in vivo are consistent with the hypothesis that the neurotoxic effects of acidic excitatory amino acids involve a profound activation of energy consumption by affected neurons.

Intracellular volume of osmotically regulated C-6 glioma cells

The intracellular volume of neoplastic brain cells was investigated with regard to the effects of hypo-osmolality and hyperosmolality utilizing double isotopic labeling with 3-0-methyl-D-glucose or tritiated water to measure the total volume of the pellet and inulin or polyethyleneglycol to measure the extracellular volume of the pellet. The cellular pellets were rapidly separated from the incubation medium by centrifugation after addition of an oil mixture. After 60 minutes incubation in Hanks balanced salt medium, the intracellular volume was 7.50 +/- 0.64, 8.48 +/- 0.19, and 2.97 +/- 0.18 ml H2O per 10(6) packed cells for C-6 glioma cells, N18TG-2 neuroblastoma cells, and NG108-15 neuroblastoma X glioma hybrid cells, respectively. The extracellular trapped space of these cultured cells was about one third of the intracellular volume. The intracellular volume of C-6 glioma cells was increased in hypotonic environment, whereas it was decreased with hyperosmolality. Both intracellular sodium and potassium were increased with increased osmolality of the incubation media. These data indicate iso-osmotic regulation by tumor cells, i.e., there is a good correlation between the intracellular volume, intracellular cations and lactate levels of C-6 glioma cells under various osmotic conditions.

Control of aerobic glycolysis in the brain in vitro

Protoveratrine-(5 microM) stimulated aerobic glycolysis of incubated rat brain cortex slices that accompanies the enhanced neuronal influx of Na+ is blocked by tetrodotoxin (3 microM) and the local anesthetics, cocaine (0.1 mM) and lidocaine (0.5 mM). On the other hand, high [K+]-stimulated aerobic glycolysis that accompanies the acetylcholine-sensitive enhanced glial uptakes of Na+ and water is unaffected by acetylcholine (2 mM). Experiments done under a variety of metabolic conditions show that there exists a better correlation between diminished ATP content of the tissue and enhanced aerobic glycolysis than between tissue ATP and the ATP-dependent synthesis of glutamine. Whereas malonate (2 mM) and amino oxyacetate (5 mM) suppress ATP content and O2 uptake, stimulate lactate formation, but have little effect on glutamine levels, fluoroacetate (3 mM) suppresses glutamine synthesis in glia, presumably by suppressing the operation of the citric acid cycle, with little effect on ATP content, O2 uptake, and lactate formation. Exogenous citrate (5 mM), which may be transported and metabolized in glia but not in neurons, inhibits lactate formation by cell free acetone-dried powder extracts of brain cortex but not by brain cortex slices. These results suggest that the neuron is the major site of stimulated aerobic glycolysis in the brain, and that under our experimental conditions glycolysis in glia is under lesser stringent metabolic control than that in the neuron. Stimulation of aerobic glycolysis by protoveratrine occurs due to diminution of the energy charge of the neuron as a result of stimulation of the sodium pump following tetrodotoxin-sensitive influx of Na+; stimulation by high [K+], NH4+, or Ca2+ deprivation occurs partly by direct stimulation of key enzymes of glycolysis and partly by a fall in the tissue ATP concentration.

Anion exchange and volume regulation during metabolic blockade of renal cortical slices

1. The development of swelling of rat and guinea-pig renal cortical slices was studied after metabolic blockade (hypoxia plus glycolytic blockade with iodo-acetic acid) and/or exposure to 'isotonic' high potassium, no sodium solution. 2. Swelling was greater after exposure to oxygenated high potassium solution than after metabolic blockade in physiologic Krebs-Henseleit solution. Swelling was reduced after metabolic blockade in high potassium solution compared to incubation in oxygenated high potassium solution. Increasing periods of transient metabolic blockade in Krebs-Henseleit solution progressively blunted swelling when slices were subsequently incubated in oxygenated high potassium solution. 3. Metabolic blockade in Krebs-Henseleit solution resulted in marked reductions in potassium and increases in sodium. Incubation in high potassium solution resulted in marked increases in potassium and similar low levels of sodium regardless of associated interventions. Metabolic blockade in both media resulted in significantly greater increases in renal cortical chloride than in monovalent cations (potassium plus sodium). Incubation in oxygenated high potassium solution was associated with similar increases in renal cortical chloride and total monovalent cations. 4. Renal cortical losses of solids and protein and increases in renal cortical inulin space were greater after metabolic blockade than after incubation under oxygenated conditions regardless of the incubation media. 5. These data support the conclusion that during metabolic blockade there is a significant replacement of larger intracellular anions by extracellular chloride. The loss of osmotically active intracellular anions limits the increase in renal cortical volume during metabolic inhibition and exposure to high potassium solution.

Electrolyte- and fluid-spaces of rat brain in situ after infusion with dinitrophenol

Chemical distribution measurements of radioactive sodium-thiosulfate (35S) and of the brain water indicate that infusion of 2.4-dinitrophenol into a carotid artery of rats caused a water uptake and fluid shifts from the extra- into the intracellular compartments in the central nervous system. The extracellular marker compound was administered to the brain via ventriculo-cisternal perfusion and intravenous injection yielding almost equal concentrations in plasma-water and perfusate. In order to prevent an active efflux of the label from the tissue, high concentrations were utilized in the perfusate to saturate potential outward transport mechanisms. The indicator space (based on total brain water) was 16% in controls and 12% in experimental animals when marker equilibrium had been attained, which is equivalent in reduction of the extracellular space of about 1/4. Intracellular water and Na+ rose after DNP, while K+ remained all but unchanged. The fluid shift into the intracellular compartment was found to relate closely with a cellular uptake of Na+. The Na+ concentration both in plasma and in the perfusion fluid leaving the ventricular system was consistently reduced in experimental animals. The K+ concentration was significantly elevated in the plasma of experimental animals but virtually unchanged in the cisternal effluate.

Energy state and glycolysis in human cerebral edema

✓ A new freeze-stop device using a liquid nitrogen reservoir and an automatic biopsy mechanism has been developed, suitable for rapid, sterile, and standardized sampling of cerebral tissue in man. In animal experiments a 200 mg piece of cerebral cortex was cooled from a room temperature of 18°C to −40°C within 7 sec which is twice as fast as when it was immersed in liquid N2. The method was then applied to metabolic tissue studies of perifocal edematous cortex from patients undergoing neurosurgery for intracranial tumors. Energy-rich phosphate compounds or parameters of the energy state were found to be less affected in this type of brain edema than the glycolytic activity which was markedly enhanced, indicated by lactic and pyruvic acid determinations. The tissue water content correlated closely with the lactic acid concentration, and very little with measurements of the energy state such as the energy charge potential or the adenosinetriphosphate-adenosinediphosphate (ATP/ADP) ratio. It is suggested that in perifocal brain edema increased levels of lactic acid are associated with mechanisms leading to an increased water uptake.

Control of synthesis and release of radioactive acetylcholine in brain slices from the rat. Effects of neurotropic drugs

1. Studies of the synthesis and release of radioactive acetylcholine in rat brain-cortex slices incubated in Locke-bicarbonate-[U-(14)C]glucose media, containing paraoxon as cholinesterase inhibitor, revealed the following phenomena: (a) dependence of K(+)-or protoveratrine-stimulated acetylcholine synthesis and release on the presence of Na(+) and Ca(2+) in the incubation medium, (b) enhanced release of radioactive acetylcholine by substances that promote depolarization at the nerve cell membrane (e.g. high K(+), ouabain, protoveratrine, sodium l-glutamate, high concentration of acetylcholine), (c) failure of acetylcholine synthesis to keep pace with acetylcholine release under certain conditions (e.g. the presence of ouabain or lack of Na(+)). 2. Stimulation by K(+) of radioactive acetylcholine synthesis was directly proportional to the external concentration of Na(+), but some synthesis and release of radioactive acetylcholine occurred in the absence of Na(+) as well as in the absence of Ca(2+). 3. The Na(+) dependence of K(+)-stimulated acetylcholine synthesis was partly due to suppression of choline transport, as addition of small concentrations of choline partly neutralized the effect of Na(+) lack, and partly due to the suppression of the activity of the Na(+) pump. 4. Protoveratrine caused a greatly increased release of radioactive acetylcholine without stimulating total radioactive acetylcholine synthesis. Protoveratrine was ineffective in the absence of Ca(2+) from the incubation medium. It completely blocked K(+) stimulation of acetylcholine synthesis and release. 5. Tetrodotoxin abolished the effects of protoveratrine on acetylcholine release. It had blocking effects (partial or complete) on the action of high K(+), sodium l-glutamate and lack of Ca(2+) on acetylcholine synthesis and release. 6. Unlabelled exogenous acetylcholine did not diminish the content of labelled tissue acetylcholine, derived from labelled glucose, suggesting that no exchange with vesicular acetylcholine took place. In the presence of 4mm-KCl it caused some increase in the release of labelled acetylcholine. 7. The barbiturates (Amytal, pentothal), whilst having no significant effects on labelled acetylcholine synthesis in unstimulated brain except at high concentration (1mm), diminished or abolished (at 0.25 or 0.5mm) the enhanced release of acetylcholine, due to high K(+) or lack of Ca(2+). The fall in tissue content of acetylcholine, due to lack of Ca(2+), was diminished or abolished by pentothal (0.25 or 0.5mm) or Amytal (0.25mm).

The relation of sodium and potassium ion transport to the respiration and adenine nucleotide content of liver slices treated with inhibitors of respiration

1. The dependence of the net transport of Na(+) and K(+) by rat liver on the respiration has been determined by incubating slices in the presence of varying concentrations of respiratory inhibitors. 2. Neither the rate of net transport nor the total amount of each ion transported was inhibited unless the rate of endogenous respiration was decreased below a critical value of about 330mmol of O(2)/h per kg of protein (i.e. 50% of the total endogenous respiration). 3. The uninhibited rate of respiration could be varied over a twofold range (380-770mmol of O(2)/h per kg of protein) by the use of different substrates, but the critical value for the onset of transport inhibition was quite constant (290-360mmol/h per kg of protein) under these different conditions. 4. Slices incubated at 38 degrees C without inhibitors showed an increase of their ATP content and the concentration ratio ATP/ADP. The final ATP content and concentration ratio, ATP/ADP, of slices treated with different concentrations of inhibitors were closely related to the rate of respiration. 5. The increased ATP content of the control slices during incubation was equal to the increase of total adenine nucleotides. At increasing degrees of respiratory inhibition the relative contributions of ADP and AMP to the total adenine nucleotide content increased. 6. The critical rate of respiration for the onset of inhibition of ion transport and the corresponding contents of adenine nucleotides provide estimates of the maximal values of certain parameters of energy metabolism required for the support of alkali-cation transport in the liver slices.

Locations of amino acids in brain slices from the rat. Tetrodotoxin-sensitive release of amino acids

1. Amino acids, particularly glutamate, gamma-aminobutyrate, aspartate and glycine, were released from rat brain slices on incubation with protoveratrine (especially in a Ca(2+)-deficient medium) or with ouabain or in the absence of glucose. Release was partially or wholly suppressed by tetrodotoxin. 2. Tetrodotoxin did not affect the release of glutamine under various incubation conditions, nor did protoveratrine accelerate it. 3. Protoveratrine caused an increased rate of formation of glutamine in incubated brain slices. 4. Increased K(+) in the incubation medium caused release of gamma-aminobutyrate, the process being partly suppressed by tetrodotoxin. 5. Incubation of brain slices in a glucose-free medium led to increased production of aspartate and to diminished tissue contents of glutamates, glutamine and glycine. 6. Use of tetrodotoxin to suppress the release of amino acids from neurons in slices caused by the joint action of protoveratrine and ouabain (the latter being added to diminish reuptake of amino acids), it was shown that the major pools of glutamate, aspartate, glycine, serine and probably gamma-aminobutyrate are in the neurons. 7. The major pool of glutamine lies not in the neurons but in the glia. 8. The tricarboxylic cycle inhibitors, fluoroacetate and malonate, exerted different effects on amino acid contents in, and on amino acid release from, brain slices incubated in the presence of protoveratrine. Fluoroacetate (3mm) diminished the content of glutamine, increased that of glutamate and gamma-aminobutyrate and did not affect respiration. Malonate (2mm) diminished aspartate and gamma-aminobutyrate content, suppressed respiration and did not affect glutamine content. It is suggested that malonate acts mainly on the neurons, and that fluoroacetate acts mainly on the glia, at the concentrations quoted. 9. Glutamine was more effective than glutamate as a precursor of gamma-aminobutyrate. 10. It is suggested that glutamate released from neurons is partly taken up by glia and converted there into glutamine. This is returned to the neurons where it is hydrolysed and converted into glutamate and gamma-aminobutyrate.