Stress and corticosterone increase the readily releasable pool of glutamate vesicles in synaptic terminals of prefrontal and frontal cortex.

Stress and glucocorticoids alter glutamatergic transmission, and the outcome of stress may range from plasticity enhancing effects to noxious, maladaptive changes. We have previously demonstrated that acute stress rapidly increases glutamate release in prefrontal and frontal cortex via glucocorticoid receptor and accumulation of presynaptic SNARE complex. Here we compared the ex vivo effects of acute stress on glutamate release with those of in vitro application of corticosterone, to analyze whether acute effect of stress on glutamatergic transmission is mediated by local synaptic action of corticosterone. We found that acute stress increases both the readily releasable pool (RRP) of vesicles and depolarization-evoked glutamate release, while application in vitro of corticosterone rapidly increases the RRP, an effect dependent on synaptic receptors for the hormone, but does not induce glutamate release for up to 20 min. These findings indicate that corticosterone mediates the enhancement of glutamate release induced by acute stress, and the rapid non-genomic action of the hormone is necessary but not sufficient for this effect.

Effect of alternate energy substrates on mammalian brain metabolism during ischemic events.

Regulation of brain metabolism and cerebral blood flow involves complex control systems with several interacting variables at both cellular and organ levels. Quantitative understanding of the spatially and temporally heterogeneous brain control mechanisms during internal and external stimuli requires the development and validation of a computational (mathematical) model of metabolic processes in brain. This paper describes a computational model of cellular metabolism in blood-perfused brain tissue, which considers the astrocyte-neuron lactate-shuttle (ANLS) hypothesis. The model structure consists of neurons, astrocytes, extra-cellular space, and a surrounding capillary network. Each cell is further compartmentalized into cytosol and mitochondria. Inter-compartment interaction is accounted in the form of passive and carrier-mediated transport. Our model was validated against experimental data reported by Crumrine and LaManna, who studied the effect of ischemia and its recovery on various intra-cellular tissue substrates under standard diet conditions. The effect of ketone bodies on brain metabolism was also examined under ischemic conditions following cardiac resuscitation through our model simulations. The influence of ketone bodies on lactate dynamics on mammalian brain following ischemia is studied incorporating experimental data.

Methyl isobutyl amiloride delays normalization of brain intracellular pH after cardiac arrest in rats.

OBJECTIVE: The sodium/hydrogen ion (Na+/H+) antiporter system of brain cells is responsible for reducing intracellular acid loads and regulating cellular volume. Activation of this system during reperfusion following cardiac arrest may contribute to cerebral edema and subsequent brain damage. Therefore, we wished to determine whether administration of methyl isobutyl amiloride, a known inhibitor of the Na+/H+ antiporter system, would cross the blood brain barrier and delay the return of brain intracellular pH to normal values during reperfusion after cardiac arrest in rats. DESIGN: a) Prospective sequential evaluation of the regional brain blood flow and 3H-methyl isobutyl amiloride extraction fraction in rats; b) prospective sequential evaluation of brain intracellular pH in rats treated with methyl isobutyl amiloride compared with untreated control rats. SETTING: A research laboratory. SUBJECTS: Thirteen male Wistar rats: a) three rats to study regional brain blood flow and 3H-methyl isobutyl amiloride cerebral extraction; and b) ten rats to study the effect of methyl isobutyl amiloride on brain intracellular pH after cardiac arrest and reperfusion. INTERVENTIONS: a) Rats were injected with 14C iodoantipyrine and 3H-methyl isobutyl amiloride, and their brains were subsequently analyzed to determine regional cerebral blood flow and percent of cerebral extraction of methyl isobutyl amiloride. b) Cardiac arrest was induced with potassium chloride followed by resuscitation 7 mins later in untreated control rats and rats treated with methyl isobutyl amiloride. MEASUREMENTS AND MAIN RESULTS: a) Regional cerebral blood flow (mL/100 g/min) determined with 14C iodoantipyrine and percent of cerebral extraction of 3H-methyl isobutyl amiloride were evaluated in various regions of the brain. Mean +/- SD values were 167 +/- 15 and 7 +/- 1 for the frontal cerebral cortex; 159 +/- 10 and 7 +/- 2 for the parietal cerebral cortex, 130 +/- 17 and 8 +/- 1 for the hippocampus, 154 +/- 33 and 13 +/- 4 for the cerebellum and 166 +/- 27 and 6 +/- 1 for the striatum (mL/100 g/min). These values were determined by a dual label indicator fractionation method. b) Brain intracellular pH was measured by neutral red histophotometry after 15 mins of reperfusion following cardiac arrest. As compared with untreated control rats, methyl isobutyl amiloride-treated animals had significantly lower brain intracellular pH values after 15 mins of reperfusion. Mean +/- SD pH values were 6.78 +/- 0.18 for the rats treated with methyl isobutyl amiloride vs. normal intracellular pH of 7.11 +/- 0.07 for the untreated control rats. CONCLUSIONS: a) Methyl isobutyl amiloride crosses the blood brain barrier of rats. b) The Na+/H+ antiporter system is operative during reperfusion after cardiac arrest in rats.

Oxidation of cerebral cytochrome aa3 by oxygen plus carbon dioxide at hyperbaric pressures.

The reduction-oxidation level of cytochrome aa3 in the intact cerebral cortex of cerveau isolé or pentobarbital-anesthetized cats was monitored by means of dual-beam reflectance spectrophotometry. Respiratory gases containing varying fractions of carbon dioxide and oxygen were administered at increased pressures, allowing titration of the cytochrome redox state from maximum reduction during nitrogen ventilation to the completely oxidized state. We show that the fully oxidized state could be reached with about 5% CO2-95% O2 inspired at 4 ATA. Maximum oxidation was achieved only through the relaxation of oxygen-induced vasoconstriction of the cerebral vessels, as our data indicated that large blood volume responses accompanied the increases in inspired carbon dioxide. With out technique, we have established that under resting air-breathing conditions cytochrome aa3 is about 85% reduced in the cat cerebral cortex, and that the absorption peak for cytochrome aa3 in situ is located near 602 nm. A free energy change of an additional 8 kcal is calculated to occur with donation of an electron pair from 85% reduced cytochrome aa3 to oxygen as compared to a 1% reduction level.