Evidence from models of traumatic brain injury implicates excitotoxicity as an integral process in the ultimate neuronal damage that follows. Concentrations of the excitatory amino acid glutamate were serially measured in the cerebrospinal fluid (CSF) of patients with traumatic brain injuries and in control patients for comparison. The purpose of the study was to determine whether glutamate concentrations were significantly elevated following traumatic brain injury and, if so, whether they were elevated in a time frame that would allow the use of antagonist therapy. Cerebrospinal fluid was sampled fresh from ventricular drains every 12 hours and analyzed using high-performance liquid chromatography for the excitatory amino acids. The peak concentrations of glutamate in the CSF of the 12 brain-injured patients ranged from 14 to 474 microM and were significantly higher than those in the three control patients, 4.9 to 17 microM (Mann-Whitney U-test, p < 0.02). Glutamate concentrations in five of the eight patients who were still being sampled on Day 3 were beyond the control group range. The implication of this study is that severely head-injured patients are exposed to high concentrations of a neurotoxic amino acid for days following injury and thus may benefit from antagonist intervention.

Intracellular pH in the brain was evaluated by the bicarbonate-carbonic acid method and from the creatine phosphokinase equilibrium, in rats exposed to 6-40 % COz for 45 min. There was a very good agreement between the two methods, indicating that the creatine phosphokinase equilibrium in vivo shows the pH dependence predicted from previous in vitro studies. The stepwise increase in the tissue CO, tension from 45 to 265 mm Hg resulted in a lowering of the intracellular pH from 7.04 to 6.68. The regulation of intracellular pH in hypercapnia was far better than that which can be predicted from physicochemical buffering alone, and calculations indicate that the intracellular buffer base concentration increased by more than 10 mequiv./kg at the maximal Pco2 values encountered.THE EFFECTS of increased C 0 2 tensions upon the brain are varied and often profound and some of these effects suggest that CO, as such, or the pH changes which accompany hypercapnia, significantly influence cerebral metabolism (WOODBURY and KARLER, 1960; WYKE, 1963; SCHAEFER, 1963; see also POSNER and PLUM, 1967). It has been shown in experiments on rats that brain excitability, as tested by the threshold for electrically-and chemically-induced seizures, decreases continuously with the inspired CO, concentration up to about 15 per cent. At still higher concentrations the excitability again increases and at 30 % CO, in the inspired air, spontaneous seizures have been reported to occur. However, when the CO, concentration is increased to 40 per cent, anaesthesia is induced (see WOODBURY and KARLER, 1960).Although the physiological effects of CO, suggest that it may affect the energy metabolism of the tissue, neither the overall oxidative metabolism of the brain (KETY and SCHMIDT, 1948) nor the energy state of the tissue (SIESJO, FOLBERGROVA and MESSETER, 1972) is altered by moderate hypercapnia. However, such results do not exclude an effect of higher C 0 2 concentrations, or of intracellular pH or [HC03-] changes which correspond to such concentrations. Thus, changes in the CO, tension or HCO,-concentration may influence many reactions which are energetically important. Molecular CO, (or HCO,-) enters into carboxylation reactions which may be essential in replenishing Krebs cycle intermediates and which possibly

The energy state of brain tissue was evaluated from the tissue concentrations of ATP, ADP and AMP and the cytoplasmic NADH/NAD + ratio from the tissue, CSF and blood concentrations of lactate and pyruvate, and from the intracellular pH', in rats exposed to carbon dioxide concentrations of 6 4 0 per cent. The hypercapnia had no significant effect on the energy state of the tissue. Hypercapnia of increasing severity gave rise to a progressive decrease in the pyruvate concentration ; the lactate concentration fell at low COz concentrations, but no further decrease was observed at COz concentrations greater than 20 per cent. There was a progressive rise in the intracellular lactate/pyruvate ratio at increasing COz concentrations, corresponding to the fall in intracellular pH, i.e. the calculated NADH/NAD+ ratios remained normal. It is therefore concluded that hypercapnia does not affect the cytoplasmic redox state.As REMARKED in a previous communication (SIESJO, FOLBERGROVA and MACMILLAN, 1972u), carbon dioxide has profound effects upon the function of the brain, ranging from seizure activity to anaesthesia. These effects raise the question whether or not CO, directly affects the energy metabolism of the tissue. Several reports demonstrate that moderate concentrations of CO, do not change the overall oxygen consumption of the human brain (KETY and SCHMIDT, 1948), and recent studies (SIESJO, FOLBER-GROVA and MESSETER, 19726; see also BAIN and KLEIN, 1949) have shown that such CO, concentrations are without effects on the energy state of the tissue, as evaluated from the tissue concentrations of ATP, ADP and AMP. However, since seizure activity or anaesthesia are elicited at much higher COz concentrations (WOODBURY and KARLER, 1960), it remains a possibility that the energy state of the tissue is affected first at extreme hypercapnia. In this connection it should be mentioned that CO, has been found to interfere with oxidative phosphorylation in liver mitochondria (FANESTIL, HASTINGS and MAHOWALD, 1963 ;KASBEKAR, 1966).We have recently reported that administration of about 11 % C 0 2 to rats for periods ranging from 15 min to 72 h was without effect upon the energy state of the tissue (SIESJO et al., 19726), but that acute hypercapnia (15 min-3 h) was associated with a small rise in the calculated cytoplasmic NADH/NAD+ ratio (MESSETER and SIESJO, 1971). In the present experiments, the energy state of the tissue and the cytoplasmic NADH/NAD+ ratio were studied in rats exposed to 6-40% CO, for 45 min.

The accumulation of cerebral 5-hydroxytryptophan after decarboxylase inhibition was decreased in rats maintained at arterial O(2) tensions below 60 mm-Hg. In contrast, brain lactate was stable above 40 mm-Hg and brain adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate were unchanged above 30 mm-Hg. There was a linear correlation of brain 5-hydroxytryptophan accumulation to cerebral venous O(2) tension. Cerebral tryptophan hydroxylase appears to have a poor affinity for oxygen and to be affected by slight hypoxia. The resultant decreases in monoamine neurotransmitter metabolism may explain the behavioral changes of mild oxygen deprivation.

In order to study the influence of intracellular pH on the carbohydrate metabolism of brain tissue, the concentrations of glucose, glucose-6-phosphate, pyruvate, lactate, citrate, a-oxoglutarate, malate, glutamate, aspartate and ammonia were measured in rats exposed to &40% CO, for 45 min. Hypercapnia of increasing severity gave rise to progressive increases in the concentrations of glucose, glucose-6-phosphate and ammonium ion and to progressive decreases in the concentrations of all metabolic acids measured. The results fit with a H + inhibition of a rate-limiting step between glucose-6-phosphate and pyruvate, and by inference from the results published by others it may be assumed that this step is the phosphofructokinase reaction. Since the proportionally largest decrease occurred in a a-oxoglutarate, the results might be compatible either with an inhibition of a second rate-limiting step such as isocitrate dehydrogenase, or with a loss of a-oxoglutarate through carboxylation to citrate.ACID-BASE changes in tissues are known to affect enzymes which exert rate-limiting control upon metabolic reactions. The best known of these reactions is the activation of glycolysis of muscle tissue which occurs in alkalotic situations (DELCHER and SHIPP, 1966; SCHEUER and BERRY, 1967; DANFORTH, 1968), an effect which seems to be due to a pH-activation of phosphofructokinase (LOWRY and PASSONNEAU, 1966).Since this activation occurs without any accompanying increase in the rate of oxidative metabolism (DELCHER and SHIPP, 1966), the end result is an increase in the steadystate levels of glycolytic intermediates distal to the phosphofructokinase step (see SCHEUER and BERRY, 1967). In the brain, alkalosis due to hyperventilation is known to Iead to increases in the steady-state contents of lactate and pyruvate (LEUSEN, LACROIX and DEMEESTER, 1967; POSNER and PLUM, 1967; GRANHOLM and SIESJO, 1969;KJALLQUIST, NARDINI and SIESJO, 1969), as well as of a-oxoglutarate and glutamate (SIESJO and MESSETER, 1971 ; SIESJO, FOLBERGROVA and MESSETER, 19723). The effect of hyperventilation in releasing metabolic acids seems to provide an efficient mechanism which prevents an excessive increase in intracellular pH' ( SIESJO and MESSETER, 1971 ; SIESJO et al., 19723) and it would appear that the sensitivity to pH of ratelimiting glycolytic enzymes like phosphofructokinase therefore provides metabolic control of pH',.There are several reports which show that the fall in pH', elicited by hypercapnia leads to a decrease in the steady-state tissue contents of lactate, pyruvate, a-0x0glutarate and glutamate (BAIN and KLEIN, 1949; LEUSEN et al., 1967; GRANHOLM and SIESJO, 1969; MESSETER and S I E S J~, 1971; WEYNE and LEUSEN, 1971; SIESJO el al.,

This study documents the Na+,K+-ATPase activity as well as selected parameters of oxidative metabolism and electrophysiological function in rat brain exposed to ischemia produced by electrocautery of the vertebral arteries and reversible occlusion of the carotid arteries. During a 0.5-h ischemic exposure in which the electroencephalograph (EEG) was abolished and energy metabolism severly compromised the Na+,K+-ATPase showed a capability for enhanced activity (120-140% of control). On recirculation, the Na+,K+-ATPase activity showed a phasic pattern, which was characterized by normal values at 0.25-2 h, increased values (115-125% of control) at 3-24 h, and, finally, normal values at 72 h of recirculation, respectively. The maintenance of Na+,K+-ATPase integrity was correlated with a gradual return of EEG activity and virtually complete restitution of the cerebral energy state during the 72 h of recirculation. Measurements of thiobarbituric acid reactive material and water soluble antioxidant during ischemia and recirculation gave no evidence of the presence of significant free radical lipid peroxidation in this model. It is concluded that Na+,K+-ATPase and its associated membrane lipids are not irreversibly damaged by ischemia in which the tissue lactacidosis is limited to less than 20 mumol g-1.

A modified procedure is described for quantification of gangliosides in a mixture using thin-layer chromatography. Using this procedure, the gangliosides in human peripheral nerve were quantified, and compared with those in cerebral cortex and white matter.

Abstract— In order to evaluate the influence of hypocapnia upon the energy metabolism of the brain, lightly anaesthetized rats were hyperventilated to arterial CO2 tensions of 26, 15 and 10 mm Hg respectively, with subsequent measurements of intracellular pH and of tissue concentrations of carbohydrate substrates, amino acids and organic phosphates. At Pco1= 26 there was a moderate increase in the intracellular pH but when the Pco2 was reduced further to 10 mm Hg the intracellular pH returned to normal, or slightly subnormal, values. The reduction in PCo2 was accompanied by increased cerebral cortical concentrations of lactate, pyruvate, citrate, α‐ketoglutarate, malate and glutamate and by decreased aspartate concentrations. It is concluded that the accumulation of metabolic acids explains the normal value for intracellular pH at very low CO2 tensions. Previous results obtained in man indicate that there is an increased anaerobic production of lactic acid in the brain in extreme hypocapnia. At comparable CO2 tensions the present results showed a small fall in phosphocreatine and a small rise in ADP. However, since the ammonia concentrations were normal or decreased and since there was an increase in citrate, the results give no direct support to the hypothesis of an activation of phosphofructokinase. Since the cerebral venous Po2 was reduced to 20 mm Hg at an arterial CO2 tension of 10 mm Hg the accumulation of acids was probably secondary to tissue hypoxia. However, since there was no, or only a very small, increase in the calculated cytoplasmic NADH/NAD+ ratio, it appears less likely that acids accumulated due to lack of NAD+.