Analysis of brain metabolism changes induced by acute potassium cyanide intoxication by 31P NMR in vivo using chronically implanted surface coils

The two faces of cyanide: an environmental toxin and a potential novel mammalian gasotransmitter

Cyanide is traditionally viewed as a cytotoxic agent, with its primary mode of action being the inhibition of mitochondrial Complex IV (cytochrome c oxidase). However, recent studies demonstrate that the effect of cyanide on Complex IV in various mammalian cells is biphasic: in lower concentrations (nanomolar to low micromolar) cyanide stimulates Complex IV activity, increases ATP production and accelerates cell proliferation, while at higher concentrations (high micromolar to low millimolar) it produces the previously known ('classic') toxic effects. The first part of the article describes the cytotoxic actions of cyanide in the context of environmental toxicology, and highlights pathophysiological conditions (e.g., cystic fibrosis with Pseudomonas colonization) where bacterially produced cyanide exerts deleterious effects to the host. The second part of the article summarizes the mammalian sources of cyanide production and overviews the emerging concept that mammalian cells may produce cyanide, in low concentrations, to serve biological regulatory roles. Cyanide fulfills many of the general criteria as a 'classical' mammalian gasotransmitter and shares some common features with the current members of this class: nitric oxide, carbon monoxide, and hydrogen sulfide.

In vivo excitotoxicity induced by ouabain, a Na+/K+-ATPase inhibitor

The susceptibility of immature rat brain to neurotoxicity of N-methyl-D-aspartate (NMDA) has provided a widely used paradigm to study excitotoxicity relevant to acute neurodegenerative diseases such as cerebral ischemia. In this study, excitotoxicity was induced via injection of ouabain (1 mM/0.5 microL), a Na+/K+ -ATPase-inhibitor, into neonatal rat brain and compared with NMDA injection. The aim of the study was to induce excitotoxicity secondary to cellular membrane depolarization, thereby more closely mimicking the pathophysiologic processes of ischemia-induced brain injury where NMDA-receptor overstimulation by glutamate follows, not precedes, membrane depolarization. Na+/K+ -ATPase-inhibition caused an acute, 40% +/- 8% decrease of the apparent diffusion coefficient (ADC) of water, as measured using diffusion-weighted magnetic resonance imaging (MRI), and resulted in infarctlike lesions as measured using T2-weighted MRI and histology up to 2 weeks later. Localized one- and two-dimensional 1H-magnetic resonance spectroscopy (MRS) demonstrated that the early excitotoxic diffusion changes were not accompanied by an overall metabolic disturbance. Furthermore, 31P-MRS demonstrated that energy depletion is not a prerequisite for ADC decrease or excitotoxic cell death. Treatment with the NMDA-antagonist MK-801 (1 mg/kg) attenuated the volume of tissue exhibiting a decreased ADC (P < 0.005), demonstrating that the ouabain-induced injury is indeed excitotoxic in nature. The authors argue that, compared with NMDA-injection, ouabain-induced excitotoxicity elicits more appropriate glutamate-receptor overstimulation and is better suited to detect relevant neuroprotection in that it is more sensitive to attenuation of synaptic glutamate levels.

In vivo measurement of the size of lipid droplets in an intracerebral glioma in the rat

Pulsed field gradient NMR was used to measure the root mean square displacement lambda of the NMR visible lipid molecules in C6 brain tumors in the rat at different diffusion times. For a distribution of spherical droplets of diameter with volume fraction xi(Phi(i)), the mean characteristic droplet diameter Phi(c) = square root of Sigma(i)xi(Phi(i)Phi(i)(2) was shown to be related to the root mean square displacement at long diffusion times by the simple relationship Phi(c)(2) = 10 lambda(2). In the range of diffusion times 100--530 msec, lambda was found to be independent of the diffusion time and equal to 1.35 +/- 0.22 microm and Phi(c) to 4.27 +/- 0.71 microm. The data reinforce the notion that the presence of lipid resonances in NMR spectra of tumors is due to lipid droplets. Light microscopy of histologic slices showed the presence of lipid droplets mainly in the necrotic region and in a layer of tumor cells surrounding the necrosis. Magn Reson Med 45:409-414, 2001.

Lactate accumulation during moderate hypoxic hypoxia in neocortical rat brain

Neocortical metabolism was studied during moderate hypoxic hypoxia, reoxygenation, and postmortem periods in anesthetized normocapnic rats using 1H nuclear magnetic resonance (NMR) spectroscopic imaging. Rats were prepared with unilateral common carotid occlusion to determine the ipsilateral metabolic effects of inadequate cerebral blood flow (CBF) response to hypoxia. No difference in brain metabolism between the two hemispheres was found during the control period. Hypoxic hypoxia (PaO2 = 54.1 +/- 5.8 mm Hg) resulted in a significant rise in neocortical lactate peak in both hemispheres, with an additional marked rise in the clamped side compared to the unclamped side (53 +/- 27 vs. 22 +/- 13% of postmortem value, p < 0.001). These lactate changes were not reversible within 30 min of reoxygenation in the clamped hemisphere. No changes in neocortical lactate peak were observed while elevating arterial lactate via intravenous lactate infusion without hypoxia. In addition, hypoxic hypoxia resulted in an apparent decrease in neocortical water and N-acetyl aspartate (NAA) signals, which were related to a shortening in T2 relaxation times. It is concluded that neocortical lactate is an early metabolic indicator during moderate hypoxic hypoxia in normocapnic conditions.

Concurrent changes in intracranial pressure, cerebral blood flow velocity, and brain energy metabolism in rabbits with acute intracranial hypertension

The relationship between intracranial pressure or cerebral perfusion pressure (CPP), cerebral blood flow, and brain energy failure is unpredictable throughout the development of acute intracranial hypertension. The purpose of the present study was to correlate intracranial pressure with cerebral blood flow velocities and brain energy metabolism in adult rabbits. The acute intracranial hypertension was achieved by pressure transmission. Transcranial Doppler wave-forms were obtained from the basilar artery for monitoring cerebral blood flow velocities. 31P-Magnetic resonance spectroscopy was used to assess brain energy metabolism. The diastolic blood flow velocity began to decrease significantly (34.5%) when the intracranial pressure was equal to half the diastolic arterial pressure for a CPP of 36 +/- 18 mmHg. Circulatory cerebral resistances increased significantly (55%) for the same value of CPP. Diastolic frequency was near zero when intracranial pressure approached diastolic arterial pressure (51 +/- 12 mmHg), corresponding to a CPP of 30 +/- 15 mmHg. At the same time, only a tendency for brain energy metabolism to decrease was observed. Consequently, transcranial Doppler sonography could be proposed for the follow-up of intracranial hypertension. Magnetic resonance spectroscopy could help to monitor these patients and could be especially proposed in case of high intracranial pressure (near diastolic arterial pressure). The joint use of these two methods would help in making appropriate therapeutic decision in humans.

Cerebral metabolic changes induced by MK-801: a 1D (phosphorus and proton) and 2D (proton) in vivo NMR spectroscopy study

The dynamic effects of the non-competitive NMDA receptor antagonist, MK-801 on brain metabolism were investigated over 105 minutes in unanesthetized rats by proton and phosphorus NMR spectroscopy. MK-801 (0.5 and 5 mg/kg, i.p) induced no changes in intracellular pH, and in phosphocreatine, ATP, and inorganic phosphate levels, indicating that the drug preserved energy and intracellular pH homeostasis. There were transient increases in lactate after both doses of MK-801, suggesting early activation of glycolysis, which was not immediately matched by enhanced oxidative metabolism or by enhanced blood flow. Thereafter, lactate control level was not restored after 0.5 mg/kg whereas it was restored after 5 mg/kg in spite of a sustained metabolic activation. The low dose of MK-801 also caused a continuous decrease in cerebral aspartate level (-38%) which is thought to match the enhanced energy demand, whereas the high dose caused shorter and smaller changes. The intracerebral glucose level rose after MK-801 injection, indicating that brain tissue had an adequate or even excessive supply of glucose. Glucose time course seemed to closely match the changes in blood flow elicited by MK-801. This is the first study giving the metabolic pattern of a pharmacological activation. We demonstrate an excess of glycolysis over oxidative metabolism in the early time similar to that following physiological and pathophysiological states such as photic stimulation and seizures. The difference between the effects of the two doses of MK-801 suggests that the adjustment of cerebral metabolism to MK-801 activation is faster and greater with the high dose than with the low dose.

Effects of kainate-induced seizures on cerebral metabolism: a combined 1H and 31P NMR study in rat

The cerebral metabolic changes elicited by kainate-induced seizures in the rat were investigated by in vivo combined NMR spectroscopy of 31P and 1H. Systemic injection of kainate induced no significant changes in cerebral ATP or PCr levels during up to 90 min of continuous, generalised seizures, and the cerebral 31P spectra showed only a transient mild cerebral acidosis 30 min after kainate administration. In parallel with the changes in intracellular cerebral pH, the 1H spectra showed a significant increase in lactate, which remained elevated throughout the seizures. These findings indicate that oxidative metabolism does not completely match the increased glycolysis during seizures though the energy homeostasis is maintained. This suggests that oxidative metabolism has a limited capacity to satisfy the brain's energy needs during the kainate-induced seizures, but that the different pathways of energy production in the brain cells can overcome this limitation. Thus the brain damage associated with this experimental model of epilepsy is not due to extended major failure of the energy supply.

In vivo, ex vivo, and in vitro one- and two-dimensional nuclear magnetic resonance spectroscopy of an intracerebral glioma in rat brain: assignment of resonances

An in vivo study of intracerebral rat glioma using proton-localized NMR spectroscopy showed important modifications of the spectra in the tumor as compared with the contralateral brain. To carry out the assignment of the resonances of the glioma spectra, tumoral and normal rat brain tissues were studied in vivo, ex vivo, and in vitro by one-dimensional and two-dimensional proton spectroscopy. N-Acetylaspartate was found at an extremely low level in the glioma. The change of peak ratio total creatine/3.2 ppm peak was found to be due to a simultaneous decrease of the total creatine content and an increase of the 3.2 ppm peak. The 3.2 ppm resonance in the glioma spectra has been shown to originate from choline, phosphocholine, glycerophosphocholine, taurine, inositol, and phosphoethanolamine. The increase of the 3.2 ppm peak in the glioma was found to result from the increase of taurine and phosphoethanolamine contents. The peak in the 1.3 ppm region of the glioma spectra was due to both lactate and mobile fatty acids. Moreover, two-dimensional spectroscopy of excised tissues and extracts showed the presence of hypotaurine only in the tumor.

Phased spectroscopic images: application to the characterization of the 1H 1.3-ppm resonance in intracerebral tumors in the rat

Spectra obtained with phase-encoding techniques show phase-shifts varying from voxel to voxel. The procedure allowing voxel-dependent phase-shifts to be compensated is presented. The method has been applied to the characterization of the 1.3-ppm resonance observed in intracerebral tumors in the rat.

The effects of cyanide on brain mitochondrial cytochrome oxidase and respiratory activities

Brain mitochondrial cytochrome oxidase and respiratory activities were compared after in vivo and in vitro exposure to cyanide. For the in vivo studies, mice were exposed to a non-lethal (4 mg kg-1) or lethal (20 mg kg-1) dose of KCN. From these mice, purified brain mitochondria were prepared and cytochrome oxidase and respiratory activities measured. Results of these experiments revealed greater inhibition of cytochrome oxidase activity following a lethal (20 mg kg-1) than a non-lethal (4 mg kg-1) KCN dose (57 and 45% inhibition, respectively). Respiration states 3 and 4 of brain mitochondria prepared from mice that received 4 mg kg-1 KCN were inhibited by 15 and 20%, respectively. In mice that received a lethal 20 mg kg-1 KCN dose, respiration states 3 and 4 were each inhibited by ca. 30% (P < 0.05). In vitro, mitochondrial cytochrome oxidase activity was inhibited in a concentration-dependent fashion at cyanide concentrations of 10(-6)-10(-2) M. A biphasic inhibition of ADP-stimulated (state 3) respiration was observed. Cyanide concentrations of 10(-6)-10(-4) M produced only a 25% inhibition of respiration state 3, whereas 10(-3) M produced 80% inhibition. Because this dramatic inhibition only occurred at cyanide concentrations that caused > 50% inhibition of mitochondrial cytochrome oxidase activity, these findings suggest that a large proportion of cytochrome oxidase activity may be functional reserve and that cyanide poisoning likely involves other mechanisms in addition to inhibition of cytochrome oxidase.

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.

Comparative 31P and 1H NMR studies on rat astrocytes and C6 glioma cells in culture

Rat astroglial cells in primary culture (95% enrichment) and C6 glioma cells were adapted to grow on microcarrier beads. In vivo 31P NMR spectra were collected from cell-covered beads perfused in the NMR tube. The NMR-visible phosphorylated metabolite contents of both cell types were determined using saturation factors calculated from the values of longitudinal relaxation times determined for C6 cells using progressive saturation experiments. On the other hand, the amounts of phosphorylated metabolites in cells were determined from proton decoupled 31P NMR spectra of cell perchloric acid extracts. The results indicate that the NTP and Pi contents of the normal and tumoral cells were similar, whereas the PCr level was higher in C6 cells and the NDP and phosphomonoester levels higher in astrocytes. The comparison of 1H NMR spectra of cell perchloric acid extracts evidenced larger inositol and alanine contents in C6 cells, whereas larger taurine and choline (and choline derivatives) contents were found in astrocytes. The Glu/Gln ratio was very different, 3.5 and 1 in C6 cells and astrocytes, respectively. In both cases, the more intense resonance in the 1H NMR spectrum was assigned to glycine. Based on the comparison of the metabolite content of a tumoral and a normal cell of glial origin, this work emphasizes the usefulness of a multinuclear NMR study in characterizing intrinsic differences between normal and tumoral cells.

Proton spectroscopic imaging: a tool for studying intracerebral tumor models in rat

Water-suppressed 2D 1H spectroscopic imaging was used with surface coils to study in vivo the cerebral metabolism changes in rat brain induced by a glial tumor growing in situ. To achieve slice selection without a chemical-shift artifact, we exploited the depth pulse properties of a spin-echo sequence. In order to give a spectral response which is independent of the position, the water suppression was achieved by using a spin-locking excitation and a binomial refocusing pulse. Spectroscopic images were obtained with an in-plane resolution of 1.1 X 1.1 mm and a slice thickness of roughly 3 mm. The growing of the tumor induced dramatic modifications in the proton spectra, including a nearly complete loss of N-acetyl aspartate, an increase of the 1.3-ppm peak, an increase in choline, and a decrease in creatine. The results demonstrate the potential of spectroscopic imaging in the study of intracranial tumor models in rats.

Metabolic effects of kynurenate during reversible forebrain ischemia studied by in vivo 31P-nuclear magnetic resonance spectroscopy

The metabolic effects of kynurenate, an endogenous excitatory amino acid antagonist, were studied by in vivo 31P-NMR spectroscopy before, during and after reversible forebrain ischemia in the rat. Kynurenate had no effect on cerebral metabolism before ischemia. During a 30-min ischemia, kynurenate protected against the decrease in phosphocreatine (up to -55 +/- 3% vs -73 +/- 3% in the reference group) and the increase in inorganic phosphate (up to +479 +/- 39% vs +805 +/- 66%), whereas there was no statistical difference in the decrease in intracellular pH (up to 6.37 +/- 0.05 vs 6.30 +/- 0.03) and ATP (up to -60 +/- 3% vs -60 +/- 7%). The recovery of PCr, Pi, and pHi to control levels during recirculation was faster in the treated group than in the reference group, whereas the time course of ATP recovery was similar in both groups. We conclude that kynurenate protects against neuronal loss, as previously reported, by mechanisms other than metabolic protection.

Metabolic effects of R-phenylisopropyladenosine during reversible forebrain ischemia studied by in vivo 31P nuclear magnetic resonance spectroscopy

The metabolic effects of R-phenylisopropyladenosine (R-PIA), an agonist of adenosine A1 receptors, were studied by in vivo 31P NMR spectroscopy before, during, and after 30 min of reversible forebrain ischemia in the rat. R-PIA had no effect on cerebral metabolism before ischemia. During a 30-min ischemia, R-PIA reduced the decrease in phosphocreatine (43 +/- 11% of the control level at the end of ischemia vs. 27 +/- 9% in the reference group) and ATP (58 +/- 12% vs. 40 +/- 23%) and the increase in inorganic phosphate (672 +/- 210% vs. 905 +/- 229%). The intracellular acidosis elicited by ischemia was also less in the treated group (pH of 6.40 +/- 0.10 vs. 6.30 +/- 0.10). Recirculation was associated with a faster recovery of PCr, ATP, Pi, and pHi to control levels in the treated group than in the reference group. It is concluded that adenosine protects against ischemic injury by mechanisms that include metabolic protection.

Proton spectral editing in the inhomogeneous radiofrequency field of a surface coil using modified stimulated echoes

It is shown that the modified stimulated echo sequence, [theta](+/- x +/- y)-t1-[theta](+ x)-t2/2-[2 theta](+ x)-t2/2- [theta](+ x)-t1-Acq(+/- x +/- y), denoted as MSTE[2 theta]x according to the exciter phase of the 2 theta pulse, is able to perform proton spectral editing without difference spectra. On the other hand, this sequence appears to be suitable for spatial localization. Sensitivity and spatial selectivity of MSTE and conventional stimulated echo sequence (STE) are briefly compared. MSTE is applied to editing lactate in the rat brain using the locally restricted excitation of a surface coil.

Cerebral intracellular pH regulation during hypercapnia in unanesthetized rats: a 31P nuclear magnetic resonance spectroscopy study

The energy metabolism and the brain intracellular pH regulation under arterial CO2 tensions of 25-90 mm Hg were investigated in unanesthetized spontaneously breathing rats by in vivo phosphorus nuclear magnetic resonance spectroscopy (31P NMR). The 31P brain spectra, recorded with a high resolution spectrometer (AM 400 Brucker), allowed repeated non-invasive measurements of cerebral pH (pHi), phosphocreatine (PCr), inorganic phosphate (Pi) and adenosine triphosphate (ATP) levels in 15 rats breathing a gas mixture containing 21% O2, N2, and a varied percentage of CO2. The pHi decreased significantly when the paCO2 was increased by hypercapnia. The percentage of pH regulation, estimated from the linear regression analysis of pHi versus the logarithm of the paCO2 was 78%. This result indicates that spontaneously breathing unanesthetized animals have better pHi regulation under hypercapnia investigated than that estimated for higher levels of hypercapnia in previous studies on unanesthetized animals, suggesting that there is a threshold for this highly efficient regulation. Furthermore, there were no significant correlations between the PCr, ATP and Pi levels and the paCO2 levels during hypercapnia. This indicates that physiological variations of the CO2 tension in the blood, and consequently in the brain parenchyma, have little effect on cerebral energy metabolism in unanesthetized spontaneously breathing animals.

In vivo 1H NMR spectroscopy of an intracerebral glioma in the rat

High-resolution 1H surface coil NMR spectroscopy (MRS) was used to evaluate in vivo the cerebral metabolism changes in rat brain induced by a glial tumor growing in situ. Tumor cells (C6 glioma cells) were stereotaxically placed in the right hemisphere superficially. 1H MRS was performed using 5-mm surface coils implanted over the right hemisphere and the water was suppressed using a binomial sequence. As the intracerebral tumor size increased, there was a marked decrease in the N-acetyl aspartate level and an increase in the 1.3 ppm peak. Edition of this peak showed that lactate increased but lipids increased much more than lactate. Moreover the ratio between the choline-phosphocholine and creatine-phosphocreatine peaks changed. This study demonstrates that high-resolution surface coil 1H MRS can be used to monitor changes in metabolism associated with growth of an experimentally induced rat brain tumor in situ.

Correlation between intracellular pH and lactate levels in the rat brain during potassium cyanide induced metabolism blockade: a combined 31P-1H in vivo nuclear magnetic spectroscopy study

Female Sprague-Dawley rats were chronically implanted with nuclear magnetic resonance (NMR) surface coils tuned to both 31P and 1H NMR frequencies. Alternated 31P and 1H NMR spectra were recorded at 2.5 min intervals in waking rats or rats under pentobarbital or chloral hydrate anesthesia. After a reference period, the metabolic changes were observed following intraperitoneal injection of potassium cyanide (KCN, 5 mg/kg). Among previously observed changes typical of cellular anoxia, attention was specifically paid to the relationship between the intracellular pH values and the lactate levels. The results show a strong lactate-pH correlation in waking rats, a partial decoupling under nembutal anesthesia and a complete decoupling under chloral hydrate anesthesia.

Metabolic changes in rabbit spinal cord after trauma: magnetic resonance spectroscopy studies

Combined phosphorus and proton magnetic resonance spectroscopy (MRS), using double-tuned surface coils, was used to monitor certain metabolic changes in the L-3 spinal segment of anesthetized rabbits prior to and following experimental spinal cord trauma. Following severe trauma, resulting in spastic paraplegia, there was a delayed and progressive accumulation of lactic acid, a decline in intracellular pH, and a loss of high-energy phosphates. Maximal alterations occurred between 2 and 3 hours after the trauma, with little further change by 4 hours. Histological examination 2 weeks after trauma showed tissue necrosis and cavitation. These findings support the concept of secondary tissue injury after spinal cord trauma and suggest that early changes in metabolism, as shown by MRS, may predict irreversible tissue damage.

In vivo 31P nuclear magnetic resonance (NMR) study of cerebral metabolism during histotoxic hypoxia in mice

The alterations of cerebral energetic metabolism and intracellular brain pH that occur during histotoxic hypoxia were estimated in mice by in vivo 31P nuclear magnetic resonance (NMR) spectrometry. The brain spectra obtained by means of chronically implanted surface coils connected to a special designed probe were recorded sequentially and continuously before, during, and after histotoxic hypoxia induced by an injection of potassium cyanide. The levels of PCr, ATP, inorganic phosphate, and intracellular pH estimated from the records of the 31P cerebral spectra and the cerebral cortical activity allow noninvasive monitoring of both the energetic metabolism and the functional state of the brain in unanesthetized animals. The time courses of these different parameters are largely the same as those obtained previously by invasive methods, however, the simultaneous and continuous monitoring performed in this study exhibits several unexpected dissociations between, respectively, onset of coma, decrease in PCr level and intracellular pHi, and recovery of normal levels of PCr and intracellular pH. These dissociations indicate that tissue acidosis plays a minor role in the changes in PCr levels, compared with ATP, and they confirm that the thresholds of oxidative metabolism required for functional tissue activity and a normal rate of ATP are clearly different.

31P magnetic resonance spectroscopy of traumatic spinal cord injury

31P magnetic resonance spectroscopy (MRS) was applied in vivo to study metabolic changes in spinal cord after experimental traumatic injury. Severe trauma, resulting in spastic paraplegia, caused an early and sustained loss of high energy phosphates with profound intracellular acidosis. Early metabolic changes after traumatic spinal injury may predict irreversible tissue damage.

Effects of traumatic brain injury on cerebral high-energy phosphates and pH: a 31P magnetic resonance spectroscopy study

Traumatic injuries to the CNS produce tissue damage both through mechanical disruption and through more delayed autodestructive processes. Delayed events include various biochemical changes whose nature and time course remain to be fully elucidated. Magnetic resonance spectroscopy (MRS) techniques permit repeated, noninvasive measurement of biochemical changes in the same animal. Using phosphorus MRS, we have examined certain biochemical responses of rats over an 8-h period following lateralized brain injury (1.5-2.5 atmospheres) using a standardized fluid-percussion model recently developed in our laboratory. Following injury, the ratio of phosphocreatine to inorganic phosphate (PCr/Pi) showed a biphasic decline: The first decline reached its nadir (4.8 +/- 0.4 to 2.8 +/- 0.7) by 40 min post-trauma with recovery by 100 min, followed by a second decline by 2 h that persisted for the remaining 6-h observation period (mean 2.5 +/- 0.5). The first, but not the second, decrease in PCr/Pi was associated with tissue acidosis (pH 7.10 +/- 0.03 to 6.86 +/- 0.11). No changes in ATP occurred at any time during the injury observation period. Such changes may be indicative of altered mitochondrial energy production following brain injury, which may account for the reduced capacity of the cell to recover from traumatic injury.

31P nuclear magnetic resonance in vivo spectroscopy of the metabolic changes induced in the awake rat brain during KCN intoxication and its reversal by hydroxocobalamine

Radiofrequency surface coils were chronically implanted in rats, which were subsequently subjected to 31P nuclear magnetic resonance (NMR) investigations at 4.7 T. The implanted coil allowed study of the animals without need for anesthesia, which is a prerequisite for studies of normal brain metabolism. The animals may be kept in the NMR probe for several hours. During subsequent experiments, they may be placed in the same position, therefore allowing follow-up studies for periods as long as 2 months. This method has been used in the study of sublethal KCN intoxication. KCN, a cytochrome c oxidase inhibitor, induces a blockade of cell respiratory processes, which is reflected, in a dose-dependent manner, by a decrease in phosphocreatine content and pH and an increase in inorganic phosphate content, whereas ATP levels remain constant until high doses of KCN (6 mg/kg i.p.) are reached. 31P NMR allows the time course of these metabolic changes to be followed. For high KCN doses, a new peak, termed X, is observed, which is interpreted as being due to a pool of inorganic phosphate at very low pH (5.65), corresponding to a subset of cells that did not survive KCN injury. Hydroxocobalamine, a specific antidote of KCN, suppresses the metabolic changes due to 6 mg/kg of KCN.

In vivo 31P nuclear magnetic resonance studies of T1 and T2 relaxation times in rat brain and in rat brain tumors implanted to nude mice

31P NMR spin-lattice (T1) and spin-spin (T2) relaxation times of phosphocreatine, ATP, inorganic phosphate, and phosphomonoesters have been measured in vivo at 4.7 T in rat brain and rat brain tumors implanted on nude mice. The relaxation data were acquired using a phase-cycled saturation-recovery spin-echo sequence. The problems associated with the phase modulation of the ATP lines by the homonuclear coupling constants were overcome by using selective refocusing pulses for the T2 measurements. In all the metabolites, large differences (1 to 2 orders of magnitude) are observed between the two relaxation times. T1 values in rat brain tumors are 30 to 90% longer than their counterparts in normal rat brain. T2 values follow the same trend with smaller variations except for phosphocreatine values which seem much less sensitive to the metabolic state of the tissues.

Brain 31P NMR spectroscopy in the conscious rat

Using a home-built head-body holder (HBH) which enables in vivo 31P NMR spectroscopy measurements on conscious rats, no significant changes were observed in the cerebral relative concentrations of ATP, phosphocreatine, phosphomonoesters, inorganic phosphate and intracellular pH during pentobarbital anesthesia in normal rats as compared to their conscious state.

Natural-abundance 13C NMR of brain

In natural-abundance 13C NMR spectrum of excised rat brain 55 resonances were resolved. The chemical shifts of most of the resonances were well correlated with those of pure brain metabolites, determined under identical experimental conditions. These resonances were also found in the cytosol fraction and perchloric acid extract of the brain. Some brain resonances were not observed in the perchloric acid extract but only in the microsomes or cytosol.

In vivo solvent-suppressed localized hydrogen nuclear magnetic resonance spectroscopy: a window to metabolism?

Solvent-suppression NMR techniques are combined with a pulsed magnetic field gradient and surface coil detection method of spatial localization. The result is a technique that enables observation of metabolites in the hydrogen (1H) NMR chemical-shift spectra from preselected disk-shaped volumes of biological tissue in vivo. Localized spectra are recorded from the normal human brain and forearm and from a dog in acquisition periods of 2 s using a 1.5-T imaging/spectroscopy system. This is several hundred-fold faster than acquiring similar state-of-the-art 31P NMR spectra of brain metabolites in vivo. Spectroscopy experiments are followed by conventional surface coil imaging sequences to precisely define the selected volume. Contamination of spectra by lipid resonances is a problem.

Effect of hypoglycemic encephalopathy upon amino acids, high-energy phosphates, and pHi in the rat brain in vivo: detection by sequential 1H and 31P NMR spectroscopy

Metabolic alterations in amino acids, high-energy phosphates, and intracellular pH during and after insulin hypoglycemia in the rat brain was studied in vivo by 1H and 31P nuclear magnetic resonance (NMR) spectroscopy. Sequential accumulations of 1H and 31P spectra were obtained from a double-tuned surface coil positioned over the exposed skull of a rat while the electroencephalogram was recorded continuously. The transition to EEG silence was accompanied by rapid declines in phosphocreatine, nucleoside triphosphate, and an increase in inorganic orthophosphate in 31P spectra. In 1H spectra acquired during the same time interval, the resonances of glutamate and glutamine decreased in intensity while a progressive increase in aspartate was observed. Following glucose administration, glutamate and aspartate returned to control levels (recovery half-time, 8 min); recovery of glutamine was incomplete. An increase in lactate was detected in the 1H spectrum during recovery but it was not associated with any change in the intracellular pH as assessed in the corresponding 31P spectrum. Phosphocreatine returned to control levels following glucose administration, in contrast to nucleoside triphosphate and inorganic orthophosphate which recovered to only 80% and 200% of their control levels, respectively. These results show that the changes in cerebral amino acids and high-energy phosphates detected by alternating the collection of 1H and 31P spectra allow for a detailed assessment of the metabolic response of the hypoglycemic brain in vivo.