31 phosphorous nuclear magnetic resonance spectroscopy of rat brain with temporary global cerebral ischemia--methodology

Hemodilution with liposome-encapsulated low-oxygen-affinity hemoglobin does not attenuate hypothermic cerebral ischemia in rats

Hypothermia decreases cerebral metabolism and increases hemoglobin oxygen affinity. A hypothesis that the reversal of increased oxygen affinity would further attenuate hypothermic cerebral ischemia was tested by evaluating the effects of liposome-encapsulated hemoglobin (LipoHb) with low oxygen affinity (P50 = 40-50 mmHg) on hypothermic incomplete cerebral ischemia. Wistar rats were randomly assigned to one of the following two groups: (A) exchange transfusion with LipoHb solution (Hb = 6 g/dl) (LipoHb, n = 5), (B) no exchange transfusion (control, n = 5). After surface cooling to 22 degrees C, forebrain ischemia was induced for 15 min by bilateral carotid artery occlusion combined with a decrease in the mean arterial pressure (MAP) to 40 mmHg. (31)P-magnetic resonance spectroscopy was performed during ischemia and 45 min of reperfusion. After reperfusion, MAP was significantly higher in the control group than in the LipoHb group (P < 0.01), although there were no significant differences during ischemia. Intracellular pH and phosphocreatine (PCr) levels decreased during ischemia and returned to the preischemic level in both groups following reperfusion. The LipoHb group had a significantly larger decrease and smaller recovery in PCr than the control group (P < 0.0001). Althouth beta-adenosine triphosphate decreased during ischemia in the LipoHb group, it increased in the control group (P < 0.0001). Inorganic phosphate (Pi) increased during ischemia and decreased to the normal value after reperfusion. The LipoHb group experienced a significantly larger production of Pi than the control group (P = 0.02). Hemodilution with high-P50 LipoHb does not reduce ischemic energy depletion induced by hypothermic incomplete forebrain ischemia in rats.

13C NMR spectroscopy study of cortical nerve cell cultures exposed to hypoxia

Primary cultures of cerebral cortical GABA-ergic neurons growing on top of a preformed layer of astrocytes (co-cultures) were incubated with [1-13C]glucose and exposed to a low oxygen atmosphere (2% O2) for 17 hr. 13C, 1H, and 31P nuclear magnetic resonance (NMR) spectroscopy was performed on perchloric acid (PCA) extracts of cells and of media collected from these cultures. In the control groups incorporation of 13C label into glutamine, citrate, and lactate could be demonstrated in both cell extracts and culture media. Labeled GABA and glutamate were only observed in cell extracts. During hypoxia high energy phosphates decreased but lactate production and glucose consumption increased. There was a decreased amount of citrate and glutamine in cell extracts and media of the hypoxic co-cultures. There was a change in distribution of the 13C label within the GABA molecule, with an increase of labeling in the C-2 position. This change in 13C distribution was not found in glutamine present in the media where it is a precursor for GABA in neurons. Instead a decrease in the corresponding C-4 position was observed. These results suggest that energy depletion during hypoxia leads to reduced export from the astrocytic tricarboxylic acid (TCA) cycle as demonstrated by a decreased amount of citrate and changed distribution of 13C in glutamine. The change in the distribution of label in GABA from cell extracts as compared to glutamine in the medium may indicate that neurons are synthesizing GABA using precursors supplied from their own TCA cycle and not from precursors supplied by astrocytes.

NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) did not affect recovery of high energy phosphates and pH in early reperfusion in a rat model of transient forebrain ischemia. Or: an in vivo 31P NMR spectroscopy study

The new non-NMDA (N-methyl-D-aspartate) receptor antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline) has previously been shown to exert a neuroprotective effect in animal models of cerebral ischemia when administered in the post-ischemic phase. In this investigation the effect of NBQX on acidosis and energy recovery in early reperfusion after 10 min of transient forebrain ischemia with the 2-vessel occlusion model in the rat was studied with 31P NMR spectroscopy. In the intervention group the animals received a bolus dose of NBQX 30 mg.kg-1 i.v. at the start of reperfusion. 31P NMR spectroscopy was used to measure intracellular pH, ATP and phosphocreatine continuously in-vivo during, and after, the ischemic event. The recovery of high energy phosphates and pH was followed during 30 min of reperfusion. Pre-ischemic levels of phosphocreatine were reached after approximately 9-10 min in both groups. Although a slight improvement could be seen in the intervention group there was no significant difference in the rate of recovery between the two groups. ATP reached 90% of preischemic levels after about 8 min without significant difference between the two groups. With respect to the recovery of intracellular pH, no difference could be shown. Our results do not contradict previously published results, but suggest that the potential protective effect of NBQX is not mediated through improved recovery of energy metabolism in early reperfusion.

The effects of brain temperature on temporary global ischaemia in rat brain. A 31-phosphorous NMR spectroscopy study

31-Phosphorus magnetic resonance spectroscopy was used in a rat model of 10 min severe incomplete forebrain ischaemia (2-vessel occlusion with hypotension) to assess the effect of mild brain hypo- and hyperthermia (+/- 2 degrees C) on intracellular pH and high energy phosphates. In three experimental groups intracerebral temperature was maintained at levels of 34, 36 and 38 degrees C during ischaemia and early reperfusion. The steady level of intracellular pH during ischaemia was 6.63, 6.58 and 6.53 in the 34, 36, and 38 degrees C groups, respectively. The rate of initial recovery of intracellular pH in reperfusion was 0.046 +/- 0.012 pH units per min (+/- s.d.) in the 36 degrees C group compared to 0.056 +/- 0.010 (+/- s.d., P less than 0.05) in the 34 degrees C group and 0.032 +/- 0.009 (+/- s.d., P less than 0.01) in the 38 degrees C group. The recovery in early reperfusion of phosphocreatine and ATP was slower in the 38 degrees C group compared to the other groups. The findings were consistent with recent studies, suggesting that even mild hypothermia may afford protection to the ischaemic brain, and furthermore indicate that mild hyperthermia as fever or even subfebricity may be deleterious for the outcome in stroke patients.

Hyperglycemia in global cerebral ischemia and reperfusion: a 31-phosphorous NMR spectroscopy study in rats

31-phosphorous magnetic resonance spectroscopy was used in a rat model of 10 min severe incomplete forebrain ischemia (two-vessel occlusion with hypotension) to assess the effect of hyperglycemia on intracellular pH and high energy phosphates during ischemia and early reperfusion. One group (n = 8) with preischemic hyperglycemia (serum glucose 20 mmol.l-1) showed an increased intracellular acidosis (pH 6.35) during ischemia compared to 6.55 in the normoglycemic control group (n = 7, P less than 0.001), but the recovery of phosphocreatine and ATP in early reperfusion was the same in the two groups. Another group (n = 7) was normoglycemic during ischemia, but received an i.v. bolus of glucose during the first minute of reperfusion. In this group the recovery of intracellular pH in early reperfusion was slower than in the control group (0.034 +/- 0.006 pH units per minute compared to 0.052 +/- 0.11 in the controls, +/- s.d. and P less than 0.01).

Quicker metabolic recovery after forebrain ischemia in rats treated with the antioxidant U74006F

We used phosphorus-31 nuclear magnetic resonance spectroscopy in a rat model of 10 minutes' severe incomplete forebrain ischemia (two-vessel occlusion with hypotension) to study the effects of preischemic and postischemic treatment with 3 mg/kg i.v. U74006F on the recovery of high-energy phosphates and intracellular pH during early reperfusion. The mean +/- SD time to 85% recovery of phosphocreatine was 14.1 +/- 8.4 minutes in the control group (n = 10) compared with 6.6 +/- 3.5 minutes (p less than 0.05) in the preischemic (n = 8) and 4.2 +/- 1.0 minutes (p less than 0.001) in the postischemic (n = 11) treatment groups. The mean +/- SD time to 80% recovery of adenosine triphosphate was 15.4 +/- 8.5 minutes in the control group compared with 6.3 +/- 1.8 (p less than 0.005) and 5.4 +/- 2.8 (p less than 0.001) minutes in the preischemic and postischemic treatment groups, respectively. There were no differences in intracellular pH between the control and either of the treatment groups. We conclude that U74006F led to quicker recovery of high-energy phosphates during early reperfusion, and this beneficial effect was also seen with postischemic treatment.

The NMDA antagonist MK-801 improved metabolic recovery after 10 minutes global cerebral ischaemia in rats measured with 31 phosphorous magnetic resonance spectroscopy

The blockade of postsynaptic receptors for excitatory amino acids is a promising new field for the possible treatment of cerebral ischaemia. The most important receptor seems to be the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptors and MK-801 is a potent non-competitive antagonist to the NMDA receptor. 31P NMR Spectroscopy was used to measure the recovery of intracellular pH and the high energy phosphates Phosphocreatine (PCr) and ATP after ten minutes of temporary global cerebral ischaemia in the rat. Cerebral ischaemia was obtained by combining bilateral carotid ligation and systemic hypotension (2 vessel occlusion model). Two intervention groups with intravenous injection of MK-801 in doses of 0.25 mg/kg and 0.5 mg/kg 15 minutes before onset of ischaemia were compared to a control group. Both intervention groups showed a more rapid recovery of PCr and ATP than the control group, but there were no significant differences for intracellular pH.