Brain pH Research Articles

Effect of superhypercapnia on cortical pHi and cortical blood flow

In vivo panoramic imaging of regional cortical blood flow and intracellular brain pH with umbelliferone fluorescence was performed in fasted New Zealand White rabbits (n = 30) subjected to constant or stepwise increases in arterial PCO2 (PaCO2) up to 160 mmHg under 1.0% halothane anesthesia. At a PaCO2 of 40 mmHg, baseline brain pHi measured 7.03 +/- 0.04, while regional cortical blood flow was 47.0 +/- 4.3 ml.100 g-1.min-1. With an immediate but constant exposure to a PaCO2 of 60, 80, or 120 mmHg, at 15 min pHi fell to 6.94 +/- 0.03, 6.89 +/- 0.03, and 6.90 +/- 0.03 and recovered over 20, 80, and 120 min, respectively. At 160 mmHg PaCO2, pHi fell to 6.68 +/- 0.04 and remained acidotic. With stepwise increases in PaCO2 up to 80 mmHg, brain pHi decreased from 7.01 +/- 0.02 to 6.99 +/- 0.02, not significantly different despite a severe systemic acidosis of 7.022 +/- 0.034. At a PaCO2 of 120 and 160 mmHg, pHi dropped to 6.97 +/- 0.02 and 6.93 +/- 0.02, respectively. The difference in brain pHi between an immediate and stepwise exposure to a PaCO2 of 160 mmHg was significant (P < 0.005). These results demonstrate that brain pHi is tightly regulated across the cortical surface and resistant to profound changes in extracellular pH. The difference in pHi between the constant and incremental increases in PaCO2 suggests that there is upregulation of pH homeostatic mechanisms.

Calcium–hydrogen exchange by the plasma membrane Ca-ATPase of voltage-clamped snail neurons

The submicromolar levels of free Ca(2+) ions in animal cells are believed to be maintained in the long term by two different plasma membrane transport mechanisms. These are Na-Ca exchange, driven by the sodium gradient, and a Na-independent Ca pump, driven by ATP. There is good evidence from red blood cells, and indirect evidence from other non-neuronal preparations, that the Ca-ATPase exchanges internal Ca(2+) for external H(+). Although Ca extrusion from nerve cells is inhibited by high external pH, there as yet is no evidence for the counter-transport of H(+). We have used both pH- and calcium-sensitive microelectrodes on the cell surface, and the Ca indicator fura-2 intracellularily, to investigate how snail neurons regulate cytoplasmic free Ca(2+). We now report that in snail neurons the recovery of intracellular Ca(2+) after an increase coincides with both the expected increase in surface Ca(2+) and a decrease in surface H+. Recovery of intracellular Ca and the changes in surface pH and Ca are all blocked by intracellular vanadate. We conclude that snail neurons regulate intracellular Ca mainly by a Ca-H ATPase, and suggest that this Ca-H exchange may account for many of the reported extracellular pH changes seen with neuronal excitation.

Brain lactate and pH dissociation in edema: 1H- and 31P-NMR in collagenase-induced hemorrhage in rats

Brain edema has been shown to increase brain lactate, but the effect on pH is unclear. We used in vivo nuclear magnetic resonance (NMR) spectroscopy to measure lactate and pH in a region of brain edema. Ninety-five anesthetized rats underwent proton and 31P-NMR spectroscopy with a 7-T 89-mm vertical bore spectrometer, using a surface coil over the edematous regions and distant from a hemorrhage produced by the injection of bacterial collagenase. Brain water content was measured from multiple regions after the NMR measurements in all rats. Lactate was significantly increased 4 h after the hemorrhage and remained elevated for 48 h, but brain pH was unaffected. The increase in lactate correlated (P < 0.01) with the increase in water content in the measured region. We conclude that lactate and pH are dissociated in a region of primarily vasogenic edema.

Guanidinoethane sulfate: brain pH alkaline shifter.

A new category of agents, brain pH alkaline shifters, is described. Using the prototype agent, guanidinoethane sulfate (GES), the actual alkaline shift in pH was demonstrated in adult mice brain by 31-phosphorus (31P) nuclear magnetic resonance (NMR) in vivo spectroscopy. This alkaline shift was also shown to effectively reduce the extent of brain intracellular lactic acidosis brought about by anoxic insult. These findings support the notion that a pH alkaline shift may protect the brain against the deleterious effects of lactic acidosis. Since higher pH has been shown to significantly reduce beta-amyloid deposition, alkaline shifters may also have therapeutic potential in Alzheimer's disease.

Acute elevation and recovery of intracellular [Mg 2+ ] following human focal cerebral ischemia

We used 31P magnetic resonance spectroscopy (MRS) to investigate changes in brain intracellular [Mg2+] following human focal cerebral ischemia. Mean brain pMg (where pMg = -log[Mg2+]) was significantly lower in the ischemic focus of all stroke patients (pMg = 3.34 +/- 0.28, n = 45, p < 0.01) when compared with normal controls (pMg = 3.50 +/- 0.08, n = 25). Ischemic brain pMg was also significantly reduced when the pH of the stroke region was acidotic (pH < 6.90, pMg = 3.07 +/- 0.44, n = 11, p < 0.01) and when the phosphocreatine index (PCrI = PCr/[PCr+Pi (inorganic phosphate)]) was reduced (PCrI < 0.47, pMg = 3.12 +/- 0.42, n = 13, p < 0.01). Mean brain pMg was significantly reduced at days 0 to 1 (acute) poststroke (pMg = 3.32 +/- 0.28, n = 26, p < 0.01) and at days 2 to 3 (subacute) poststroke (pMg = 3.38 +/- 0.28, n = 21, p = 0.03). There was also a significant (p < 0.01) correlation between decreased pMg and increased relative signal intensity of Pi (normalized by total phosphate signal, Pi/TP) for all stroke groups studied. During the temporal evolution of stroke, pH returned to normal levels by days 2 to 3, and pMg returned to normal by days 4 to 10 (subacute). PCrI and Pi/TP returned toward normal levels after 10 days (chronic), at a time when ischemic brain pH had become significantly alkalotic (pH = 7.10 +/- 0.24, n = 15, p < 0.01). Elevation of ischemic brain [Mg2+] is temporally linked to the acidotic phase of human stroke as well as the breakdown of energy metabolism. These acute changes in [Mg2+] may contribute to, or be a marker for, cellular injury.

Widespread sites of brain stem ventilatory chemoreceptors

We produced local tissue acidosis in various brain stem regions with 1-nl injections of acetazolamide (AZ) to locate the sites of central chemoreception. To determine whether the local acidosis resulted in a stimulation of breathing, we performed the experiment in chloralose-urethan anesthetized vagotomized carotid-denervated (cats) paralyzed servo-ventilated cats and rats and measured phrenic nerve activity (PNA) as the response index. Measurements of extracellular brain tissue pH by glass microelectrodes showed that AZ injections induced a change in pH at the injection center equivalent to that produced by an increase in end-tidal PCO2 of approximately 36 Torr and that the change in brain pH was limited to a tissue volume with a radius of < 350 microns. We found AZ injections sites that caused a significant increase in PNA to be located 1) within 800 microns of the ventrolateral medullary surface at locations within traditional rostral and caudal chemosensitive areas and the intermediate area, 2) within the vicinity of the nucleus tractus solitarii, and 3) within the vicinity of the locus coeruleus. Single AZ injections produced increases in PNA that were < or = 69% of the maximum value observed with an increase in end-tidal PCO2. We conclude that central chemoreceptors are distributed at many locations within the brain stem, all within 1.5 mm of the surface, and that stimulation of a small fraction of all central chemoreceptors can result in a large ventilatory response.

Effect of acute and chronic hyponatremia on brain buffering in rats.

The present studies evaluated whether previously observed impairments in brain buffering during acute hyponatremia were maintained during chronic hyponatremia as well and whether the impairment was due in part to changes in brain water, brain perfusion, or activation of arginine vasopressin (AVP) V1 receptors. Acute (1 and 2 day) and chronic (7 and 14 day) hyponatremia was induced in male Sprague-Dawley rats by constant desmopressin administration in combination with a liquid diet. Brain pH was determined by 31P nuclear magnetic resonance (NMR) in rats anesthetized with N2O and paralyzed with pancuronium. Brain buffering was evaluated by the response to CO2 loading, and brain perfusion was evaluated by 19F-NMR using trifluoromethane washout. Compared with normonatremic controls fed the same diet, brain pH in both acute and chronic hyponatremics was 0.12 pH units lower after 55 min ventilation with 20% CO2 despite identical decreases of approximately 0.35 units in all groups during the first 15 min. Moreover, in the recovery period brain pH overshot basal levels only in normonatremic controls. Brain water content in chronic hyponatremic rats was equal to controls, and brain perfusion was identical in the five groups during CO2 exposure. These results are analogous to those reported during acute hyponatremia induced with AVP and show that the impairment of active brain buffering is maintained during chronic hyponatremia and is unrelated to brain water content, perfusion, tissue catabolism, or AVP V1 receptor activation.

Effect of acute and chronic hyponatremia on blood-brain barrier function in the rat.

To study whether acute or chronic hyponatremia alters blood-brain barrier (BBB) permeability, rats made hyponatremic by constant desmopressin acetate infusion were studied by NMR spectroscopy and imaging. On constant volume ventilation and nitrous oxide, acute (1- and 2-day) and chronic (7- and 14-day) hyponatremic and normonatremic controls were infused with 0.25 M HCl. Despite reducing blood pH by at least 0.35 in < 50 min, brain pH, measured by 31P NMR, was unaffected in any group. As a second test of BBB function, gadolinium-DTPA (Gd-DTPA) was injected intravenously in these five groups. Coronal slice 1H NMR images obtained before and after Gd-DTPA showed image intensity changes in multiple areas outside brain, but neither control nor hyponatremic rats showed any differences in cortex, white matter or cerebellum. To ascertain whether the threshold for BBB disruption was altered, hypertonic mannitol (1.5, 2.0 or 3.0 mL) was injected rapidly into one internal carotid artery and pre- and post-Gd-DTPA images obtained. In both control and hyponatremic rats only the largest dose caused detectable Gd-DTPA leakage into brain. Thus, BBB function appears intact in both acute and chronic hyponatremia since neither H+ nor GD-DTPA penetrated the barrier and resistance to mannitol disruption was unaffected by hyponatremia.

Brain pHi, cerebral blood flow, and NADH fluorescence during severe incomplete global ischemia in rabbits.

The aim of this experiment was to study the serial changes in brain intracellular pH, cerebral blood flow, and the oxidation/reduction level of intramitochondrial nicotinamide adenine dinucleotide fluorescence across the cortical surface during severe incomplete global ischemia. Reduced nicotinamide adenine dinucleotide fluorescence and brain intracellular pH using the pH-sensitive indicator umbelliferone were measured with in vivo panoramic fluorescence imaging of the cortical surface. Cerebral blood flow was measured with the clearance of both umbelliferone and xenon-133. Fifteen minutes of severe incomplete global ischemia was produced by temporary occlusion of the innominate, left carotid, and subclavian arteries in five fasted New Zealand White rabbits. Baseline brain intracellular pH was homogeneous over the exposed cortex, measuring 7.00 +/- 0.02, while cerebral blood flow was 48.0 +/- 2.6 ml/100 g/min. During 15 minutes of ischemia, cerebral blood flow measured 6.3 +/- 1.8 ml/100 g/min and brain pH declined to 6.61 +/- 0.02 (p < 0.005); in addition, there were acidotic foci with pH measuring 6.40 +/- 0.10. During reperfusion, there was an initial normalization of brain intracellular pH without an alkaline shift followed by a recurrent cortical acidosis of pH 6.88 +/- 0.06. There was a heterogeneous pattern of fluorescence that increased significantly following 60 minutes of reperfusion, coinciding with a postischemic hypoperfusion. The hypoperfusion was a uniform reduction in cerebral blood flow over the brain's surface, with reductions of 42.5% and 44.2% at 30 and 45 minutes, respectively. During incomplete global ischemia there is a heterogeneous pattern of brain intracellular pH and reduced nicotinamide adenine dinucleotide changes that do not correlate with changes in cortical blood flow. The acidotic foci that were approximately 0.2 pH units more acidotic than the surrounding cortex may be the result of continued glucose delivery under anaerobic conditions. The degree of reduced nicotinamide adenine dinucleotide fluorescence suggests that the cortex is most vulnerable to metabolic failure after 60 minutes of reperfusion following severe incomplete global ischemia. The heterogeneous pattern of brain intracellular pH and reduced nicotinamide adenine dinucleotide changes suggest that there may be a selective vulnerability of cortical tissue to an ischemic challenge.

Effect of arterial blood pressure and serum glucose on brain intracellular pH, cerebral and cortical blood flow during status epilepticus in the white New Zealand rabbit

Generalized seizures can induce both hypertension and hyperglycemia which may aggravate preexisting cerebral or medical conditions in patients. In vivo fluorescent imaging of regional cortical blood flow and brain intracellular pH (pH i) was performed in fasted New Zealand rabbits (n=35) in which either mean arterial blood pressure (MABP) or serum glucose was the covaried factor during pentylenetetrazole induced status epilepticus under 1.5% inspired halothane. Baseline brain pH i and regional cortical blood flow were 7.02±0.02 and 51.1±1.7 ml/100 g/min, respectively. Following seizure induction, MABP increased to 105 mm Hg and brain pH i fell to 6.79±0.03 within 15 min and remained at this level for 1 h ( P<0.001). With normalization of MABP during ongoing seizures, there was no worsening in brain pH i despite a significant decrease in regional cortical blood flow. Hyperglycemia decreased pH i to 6.71±0.02 compared to 6.84±0.04 in normoglycemic animals ( P<0.001). Using pH i as a cerebral metabolic index, these data suggest that normalization of MABP does not increase metabolic injury while hyperglycemia does significantly worsen brain acidosis. Therefore, administration of glucose to patients with status epilepticus should be avoided unless there is documented hypoglycemia.

Creatine kinase-catalyzed reaction rate in the cyanide-poisoned mouse brain.

Brain creatine kinase (CK)-catalyzed phosphorus flux from phosphocreatine (PC) to ATP was measured in vivo in young adult mice made reversibly hypoxic by injection of cyanide. Phosphorus spectra and saturation transfer measurements of CK-catalyzed flux were acquired using a high-field (8.45 T) nuclear magnetic resonance (NMR) spectrometer. After low cyanide doses (1-3 mg/kg of body weight), there were no measurable changes in brain pH or in concentrations of PC, the nucleoside triphosphates (including ATP), and Pi. The CK-catalyzed phosphorus flux increased about 75% after the low cyanide dose. Higher doses (4-6 mg/kg) produced a transient 30-40% decrease in PC concentration, doubling of Pi, and a 0.2 unit decrease in pH. The CK-catalyzed phosphorus flux decreased 50-80% after the higher cyanide doses. This decrease in phosphorus flux was present long after reactant concentrations returned to precyanide values. It is proposed that the increase in brain CK-catalyzed phosphorus flux with the lower cyanide doses is due to an increase in ADP concentration. The large, prolonged decrease in CK-catalyzed reaction rate in the moderately poisoned brain may be due to loss of activity of the mitochondrial CK isoform.

Post-ischemic brain tissue alkalosis suppressed by U74006F

We monitored chronically (for 1 week) the effect of the 21-aminosteroid U74006F, a potent lipid peroxidation inhibitor, on the pH profile of the rat brain following transient forebrain ischemia. Eight rats were treated initially with 3 mg/kg i.v. of U74006F 1 min after reperfusion. A second dose of 1.5 mg/kg i.v. was given 60 min after reperfusion. A vehicle group ( n = 9) was treated in the same manner, using the same volume of the vehicle solution, 20 mM citric acid, 3 mM sodium citrate, and 8 mM NaCl. Statistically significant interaction between group and time ( P = 0.003) was detected for pH. Brain pH of the vehicle treated animals were significantly higher than the U74006F treated group at 24 h ( P = 0.009) and 48 h ( P = 0.009) of reperfusion. Chronic post-ischemic brain tissue alkalosis at 24 h (pH 7.22 ± 0.12) and 48 h (pH 7.25 ± 0.11) post-ischemia, observed among the vehicle treated animals (and untreated animals), was suppressed by treatment with U74006F. These results suggest a coupling between post-ischemic brain tissue alkalosis and free radical induced lipid peroxidation.

Human focal cerebral ischemia: evaluation of brain pH and energy metabolism with P-31 NMR spectroscopy.

The authors investigated early human focal ischemia with phosphorus-31 nuclear magnetic resonance spectroscopy at 1.89 T to characterize the temporal evolution and relationship of brain pH and phosphate energy metabolism. Data from 65 symptomatic patients were prospectively studied; none of the patients had had ischemic stroke in the internal carotid artery territory before. Twenty-eight neurologically normal individuals served as control subjects. Serial ischemic brain pH levels indicated a progression from early acidosis to subacute alkalosis. When acidosis was present there was a significant elevation in the relative signal intensity of inorganic phosphate (Pi) and significant reductions in signal intensities of alpha-adenosine triphosphate (ATP) and gamma-ATP compared with those of control subjects. Ischemic brain pH values directly correlated with the relative signal intensity of phosphocreatine (PCr) and the PCr index and inversely correlated with the signal intensity of Pi. There was a general lack of correlation between either ischemic brain pH or phosphate energy metabolism and the initial clinical stroke severity. The data suggest a link between high-energy phosphate metabolism and brain pH, especially during the period of ischemic brain acidosis, and the authors propose that effective acute stroke therapy should be instituted during this period.

Panoramic imaging of brain pH i and CBF during penicillin and metrazole induced status epilepticus

Using real-time in vivo umbelliferone fluorescent imaging, cortical intracellular brain pH (pH i) and cortical blood flow (CBF) were measured in New Zealand white rabbits during generalized seizures induced by intravenous metrazole or sodium penicillin. In the former, brain pH i declined from 7.04 ± 0.07 to 6.78 ± 0.07 within 15 min of generalized seizures and remained at this level for 1 h. In the penicillin group, pH i fell from 7.05 ±0.10 to 6.81 ±0.07 and also remained at this level over 60 min. This brain acidosis was uniform across the brain's surface. With the onset of status epilepticus there was a hyperemia which occurred in a heterogeneous pattern with blood flow appearing to be greater adjacent to cortical vasculature and slower in border zones between surface blood vessels. In the metrazole group, there was evidence of vasomotor paralysis with loss of autoregulation involving both cortical surface vasculature and penetrating arterioles with their capillary beds.

Brain pH and lactic acidosis: quantitative analysis of taurine effect

A quantitative analysis of taurine effect (facilitation of acid handling capacity of brain in response to anoxia/hypoxia by high levels of cytosolic taurine) was performed utilizing multinuclear ( 1H, 31P) in vivo nuclear magnetic resonance (NMR) spectroscopy and in vitro titration analysis. Taurine effects observed in vivo showed excellent quantitative agreement with the predicted values estimated based on brain taurine levels. The study confirmed that high levels of cytosolic taurine indeed facilitate acid buffering capacity of brain and this taurine effect can be readily explained by the physical, and need not involve metabolic, properties of taurine. Taurine appears to be a key component of the brain cytosol system in the fetus.

Forebrain ischemia in diabetic and nondiabetic BB rats studied with 31P magnetic resonance spectroscopy.

In spontaneously diabetic BB rats, the effect of chronically maintained blood glucose levels on the degree of energy failure and brain pH change during an ischemic insult, and on subsequent recovery after reperfusion, was studied with in vivo 31P magnetic resonance spectroscopy. Short duration forebrain ischemia (10-min carotid occlusion plus hypotension of 50 mmHg) was induced in diabetic and nondiabetic male BB rats whose blood glucose levels were maintained with insulin. Spectra were obtained in 1-min blocks before, during, and for 1 h after ischemia. Before ischemia, hypoglycemic (blood glucose less than 3 mM) diabetic rats had an increased Pi peak intensity, with no significant pH change, compared with other groups. During ischemia, the rate and extent of hydrolysis of high-energy phosphate metabolites (as measured by an increase in Pi) decreased, and the severity of tissue acidosis increased as preischemia blood glucose concentration increased. Among hyperglycemic BB rats, similar ischemia-induced changes were found for subgroups with blood glucose levels of 13.7 +/- 1.2 and 20.3 +/- 0.6 mM, in keeping with the known decrease in hexose binding sites associated with chronic hyperglycemia. Decline in PCr level during ischemia was not significantly different between groups. With reperfusion, both Pi and pH values rapidly returned to preischemia values. PCr levels, however, did not recover in hyperglycemic diabetic animals, with the degree of residual impairment dependent on the preischemia glucose level. Results suggest that optimal management of diabetes may lessen the degree of injury within the ischemic penumbra in diabetic patients who suffer a stroke.

Brain cytochrome oxidase in Alzheimer's disease.

A recent demonstration of markedly reduced (-50%) activity of cytochrome oxidase (CO; complex 4), the terminal enzyme of the mitochondrial enzyme transport chain, in platelets of patients with Alzheimer's disease (AD) suggested the possibility of a systemic and etiologically fundamental CO defect in AD. To determine whether a CO deficiency occurs in AD brain, we measured the activity of CO in homogenates of autopsied brain regions of 19 patients with AD and 30 controls matched with respect to age, postmortem time, sex, and, as indices of agonal status, brain pH and lactic acid concentration. Mean CO activity in AD brain was reduced in frontal (-26%: p less than 0.01), temporal (-17%; p less than 0.05), and parietal (-16%; not significant, p = 0.055) cortices. In occipital cortex and putamen, mean CO levels were normal, whereas in hippocampus, CO activity, on average, was nonsignificantly elevated (20%). The reduction of CO activity, which is tightly coupled to neuronal metabolic activity, could be explained by hypofunction of neurons, neuronal or mitochondrial loss, or possibly by a more primary, but region-specific, defect in the enzyme itself. The absence of a CO activity reduction in all of the examined brain areas does not support the notion of a generalized brain CO abnormality. Although the functional significance of a 16-26% cerebral cortical CO deficit in human brain is not known, a deficiency of this key energy-metabolizing enzyme could reduce energy stores and thereby contribute to the brain dysfunction and neurodegenerative processes in AD.

Focal cortical distribution of blood flow and brain pHi determined by in vivo fluorescent imaging.

A technique was developed for panoramic imaging of intracellular focal brain pH (pHi) and focal cortical blood flow to measure the pattern of changes in these parameters during arterial PCO2 (PaCO2) and arterial PO2 (PaO2) alterations. Eleven overnight-fasted New Zealand White rabbits were operated and studied under 2.0 and 1.0% halothane anesthesia, respectively. The exposed cortex was imaged by a 512 x 512 pixel image intensifier system with a resolution of 10 microns2/pixel. Focal brain pHi and focal cortical blood flow were measured by umbelliferone fluorescence. The mean focal cortical blood flow was 49 +/- 4.5 ml.100 g-1.min-1, and focal brain pHi was 7.05 +/- 0.02 during normocapnia. At a stable PaCO2, focal cortical blood flow and focal brain pHi within 10 microns of surface-conducting vessels were 2-50% greater and 0.02 pH units lower than that observed in the border-zone regions between vessels. Focal cortical blood flow demonstrated a significant heterogeneity of 51% among various cortical regions, despite a stable PaCO2. Alternatively, focal brain pHi was homogeneous, varying no more than 0.05 pH units. These results demonstrate the dependence of focal cortical blood flow on topical locations from surface conducting vessels and the tight regulation of brain pHi.

Cerebral acid buffering capacity at different ages measured in vivo by 31P and 1H nuclear magnetic resonance spectroscopy.

Cerebral acidosis occurring during ischemia has been proposed as one determinant of tissue damage. Newborn animals appear to be less susceptible to ischemic tissue damage than adults. One possible component of ischemic tolerance could derive from maturational differences in the extent of acid production and buffering in newborns compared to adults. The purpose of this study was to measure the dependency of acid production on the blood plasma glucose concentrations and acid buffering capacity of piglets at different stages of development. Complete ischemia was induced in 29 piglets ranging in postconceptual age from 111 to 156 days (normal term conception, 115 days). Brain buffering capacity during the first 30 min of ischemia was quantified in vivo, via 31P and 1H nuclear magnetic resonance (NMR) spectroscopy, by measuring the change in intracellular brain pH for a given change in the concentration of compounds that contribute to the production of hydrogen ions. Animals from all four age groups showed a similar linear correlation between preischemia blood glucose concentration and intracellular pH after 30 min of ischemia. For each animal the slope of the plot of intracellular pH versus cerebral buffer base deficit was used to calculate the buffer capacity. Using data obtained over the entire 30 min of ischemia, there was no difference in the mean buffer capacity of the different age groups, nor was there a significant correlation between buffer capacity and age. However, there was a significant increase in buffer capacity for the intracellular pH range 6.6-6.0, compared to 7.0-6.6, for all age groups. No significant differences in buffer capacity for these two pH ranges were observed between any of the age groups. Acid buffering capacity was also measured by performing pH titrations on brain tissue homogenized in the presence of inhibitors of glycolysis and creatine kinase. Plots of homogenate pH versus buffer base deficit showed a nonlinear trend similar to that seen in vivo, indicating an increase in buffer capacity as intracellular pH decreases. A comparison of newborn and 1-month-old brain tissue frozen under control conditions or after 45 min of ischemia revealed no differences that could be attributed to age and a slight decrease in buffer capacity of ischemic brain compared to control brain tissue homogenates. There was no difference between the brain buffering capacity measured in vivo using 31P and 1H NMR and that measured in vitro using brain homogenates.

Intracellular pH in rat brain in vivo and in brain slices.

Intracellular pH can be measured quantitatively in rat brain in vivo and in vitro using spectrophotometric detection of the vital dye neutral red. This method preserves spatial information and is compatible with microhistochemistry. The intracellular pH indicated by this method is in close agreement with that indicated by 31P-NMR spectroscopy. During ischemia, intracellular acidification is correlated with tissue lactate accumulation. The spatial distribution of pH values becomes more heterogeneous as the tissue becomes more acidic. Resuscitation from total cerebral ischemia produced by cardiac arrest results in rapid intracellular realkalinization. This realkalinization is at least partially inhibited by amiloride pretreatment. Some neuronal populations, especially in the hippocampal CA1 and CA4 regions, may become more acidic during ischemia and realkalinize more slowly after reperfusion than other tissue regions. The intracellular pH of hippocampal brain slice preparations is more alkaline than expected from in vivo studies. The intracellular pH of the brain slice can be acidified to near neutrality by specific inhibitors of the sodium/hydrogen ion exchanger.