Martyn G Boutelle

Spreading and Synchronous Depressions of Cortical Activity in Acutely Injured Human Brain

Background and Purpose— Cortical spreading depression (CSD) has been much studied experimentally but never demonstrated unequivocally in human neocortex by direct electrophysiological recording. A similar phenomenon, peri-infarct depolarization, occurs in experimental models of stroke and causes the infarct to enlarge. Our current understanding of the mechanisms of deterioration in the days after major traumatic or ischemic brain injury in humans has not yielded any effective, novel drug treatment. This study sought clear evidence for the occurrence and propagation of CSD in the injured human brain. Methods— In 14 patients undergoing neurosurgery after head injury or intracranial hemorrhage, we placed electrocorticographic (ECoG) electrodes near foci of damaged cortical tissue. Results— Transient episodes of depressed ECoG activity that propagated across the cortex at rates in the range of 0.6 to 5.0 mm/min were observed in 5 patients; this rate of propagation is characteristic of CSD. We also observed, in 8 of the 14 patients, transient depressions of ECoG amplitude that appeared essentially simultaneous in all recording channels, without clear evidence of spread. Conclusions— These results indicate that CSD or similar events occur in the injured human brain and are more frequent than previously suggested. On the basis of these observations, we suggest that the related phenomenon, peri-infarct depolarization, is indeed likely to occur in boundary zones in the ischemic human cerebral cortex.

Dynamic changes in brain glucose and lactate in pericontusional areas of the human cerebral cortex, monitored with rapid sampling on-line microdialysis: relationship with depolarisation-like events

The pathophysiology of peri-lesion boundary zones in acute brain injury is highly dynamic, and it is now clear that spreading-depression-like events occur frequently in areas of cerebral cortex adjacent to contusions in the injured human brain. An automated method to assay microdialysate from peri-lesion cerebral cortex in 11 patients with intracranial haematomas requiring surgery was used. Perfusate (2 μL/min) flowed directly into a flow-injection system for assay of glucose and lactate at intervals typically of 30 secs each. Four channels of electrocorticogram (ECoG) were recorded from a subdural strip adjacent to the catheter. Several patterns of change in metabolites were identified in different time domains. Overall, the number of transient lactate events was significantly correlated with the number of glucose events (r2=0.48, P=0.027, n=10). Progressive reduction in dialysate glucose was very closely correlated with the aggregate number of ECoG events (r2=0.76, P=0.0004, n=11). It is proposed that the recently documented adverse impact of low dialysate glucose on clinical outcome may be because of recurrent, spontaneous spreading-depression-like events in the perilesion cortex.

The mechanisms controlling physiologically stimulated changes in rat brain glucose and lactate: a microdialysis study.

1. This study is concerned with the supply of metabolic substrates for neuronal metabolism. Experiments were carried out to investigate whether mechanisms demonstrated in cultured astrocytes also occurred in vivo; these were cAMP‐mediated breakdown of glycogen and glutamate uptake‐stimulated release of lactate. 2. In vivo microdialysis was used in freely moving rats. Lactate and glucose in the dialysate were assayed using enzyme‐based on‐line assays. Drugs were given locally through the dialysis probe. Regional cerebral blood flow was measured using the hydrogen clearance method. 3. There was an increase in dialysate glucose in response to the beta‐adrenoceptor agonist isoprenaline and to 8‐bromo‐cAMP, an analogue of cAMP, the second messenger of beta‐adrenoceptor stimulation. The effect of isoprenaline was blocked by the antagonist propranolol. Isoprenaline had no effect on dialysate lactate, which was increased by the glutamate uptake blocker beta‐D,L‐threohydroxyaspartate (THA). 4. Physiological stimulation of neuronal activity produced an increase in both lactate and glucose. The increase in lactate was depressed in the presence of THA but was unaffected by propranolol. The increase in glucose was blocked by propranolol. Regional cerebral blood flow was increased by physiological stimulation but was unaffected by propranolol. 5. These results demonstrate that physiologically stimulated increases in glucose and lactate in the brain are mediated by different mechanisms.

Transient Changes in Cortical Glucose and Lactate Levels Associated with Peri-Infarct Depolarisations, Studied with Rapid-Sampling Microdialysis

Peri-infarct depolarisations (PIDs) contribute to infarct expansion in experimental focal ischaemia; furthermore, depolarisations propagate in the injured human brain. Glucose utilisation is increased under both conditions, and depletion of brain glucose carries a poor prognosis. We studied dynamics of cerebral glucose and lactate in relation to PID patterns in experimental stroke. The middle cerebral artery was occluded for 3 h in 23 cats under terminal chloralose anaesthesia. We used fluorescence imaging to detect occurrence of PIDs, and rapid-sampling online microdialysis (rsMD), coupled to a flow-injection assay, to examine changes in cerebral cortical extracellular glucose and lactate at intervals of 30 sec each. After 30 min ischaemia, lactate had increased by 43.6±s.d. 45.9 μmol/L, and stabilised in that range for 3 h. In contrast, glucose fell only slightly initially (11.9±9.7 μmol/L), but progressively decreased to a reduction of 56.7±47.2 μmol/L at 3 h, with no evidence of stabilisation. There was a highly significant inverse relationship of frequency of PIDs with plasma glucose (P<0.001). The results also characterise a metabolic signature for PIDs for possible application in clinical work, and emphasise potential risks in the use of insulin to control plasma glucose in patients with brain injury.

An amperometric glucose-oxidase/poly(o-phenylenediamine) biosensor for monitoring brain extracellular glucose: in vivo characterisation in the striatum of freely-moving rats.

Amperometric glucose biosensors based on the immobilization of glucose oxidase (GOx) on Pt electrodes with electropolymerized o-phenylenediamine (PPD) were implanted in the right striatum of freely-moving rats. Carbon paste electrodes for the simultaneous monitoring of ascorbic acid (AA) and/or tissue O2 were implanted in the left striatum. A detailed in vivo characterization of the Pt/PPD/GOx signal was carried out using various pharmacological manipulations. Confirmation that the biosensor responded to changing glucose levels in brain extracellular fluid (ECF) was obtained by intraperitoneal (i.p.) injection of insulin that caused a decrease in the Pt/PPD/GOx current, and local administration of glucose (1 mM) via an adjacent microdialysis probe that resulted in an increase in the biosensor current. An insulin induced increase in tissue O2 in the brain was also observed. Interference studies involved administering AA and subanaesthetic doses of ketamine i.p. Both resulted in increased extracellular AA levels with ketamine also causing an increase in O2. No significant change in the Pt/PPD/GOx current was observed in either case indicating that changes in O2 and AA, the principal endogenous interferents, have minimal effect on the response of these first generation biosensors. Stability tests over a successive 5-day period revealed no significant change in sensitivity. These in vivo results suggest reliable glucose monitoring in brain ECF.

Extracellular glucose turnover in the striatum of unanaesthetized rats measured by quantitative microdialysis

1 Steady‐state and time‐resolved quantitative microdialysis was used to measure dialysate concentration, extracellular concentration and the in vivo recovery of glucose in rat striatum. 2 The extracellular concentration of glucose, determined by the zero net flux method of Lönnroth, was 350 ± 20 μm and the in vivo recovery was 39 ± 2%. 3 Veratridine caused a steep decrease in dialysate glucose after an initial delay of 7.5 min. When steady‐state glucose levels had been reached in the presence of veratridine the extracellular concentration was reduced to zero, but there was no significant change in in vivo recovery. 4 Measurement of the dynamic changes during the administration of veratridine showed an immediate decrease in extracellular glucose concentration and a steep rise in in vivo recovery, which accounted for the delay in the decrease in dialysate glucose. When extracellular concentration reached zero, in vivo recovery returned to control levels.

Measurement of brain tissue oxygen at a carbon paste electrode can serve as an index of increases in regional cerebral blood flow

Simultaneous monitoring of tissue O(2) and regional cerebral blood flow (rCBF) was performed in the striatum of freely-moving rats. Differential pulse amperometry and constant potential amperometry were used to monitor O(2) levels at a carbon paste electrode (CPE), while rCBF values were obtained using the H2 clearance technique. Two forms of behavioural activation were studied and the resultant changes in tissue O(2) and blood flow compared. Both tail pinch and induced grooming produced immediate and parallel increases in O(2) and blood flow which returned to baseline on cessation of activity. These findings indicate that under conditions of physiological stimulation the direct voltammetric measurement of O(2) in brain tissue with a CPE can be used as a reliable index of increases in rCBF, resulting in an improvement in time resolution from 5 min (H2 clearance) to <1 s (amperometry). Because tissue O(2) is a balance between supply by the blood stream and utilisation by the cells, increases in O(2) current are an index of increased blood flow only when supply significantly exceeds utilisation.

Resolving dynamic changes in brain metabolism using biosensors and on-line microdialysis

A tight coupling exists in the brain between the activity of neurons, the energetic consequences of this activity and the local blood flow. This makes the monitoring of the levels of energy metabolites, such as glucose and lactate, in the fluid surrounding the neurons a particularly effective means of studying brain function. This review outlines why rapid monitoring of brain metabolism in vivo is effective, and demonstrates how the in vivo techniques of implanted biosensors and on-line microdialysis can be used to study the brain in the laboratory and in brain-injury patients.

On-line monitoring in neurointensive care Enzyme-based electrochemical assay for simultaneous, continuous monitoring of glucose and lactate from critical care patients

This paper describes the development, verification and use of the first dual on-line electrochemical assay system for use with clinical microdialysis. The assay is a flow injection assay using mediated enzyme beds with electrochemical detection. The on-line assay has been specifically designed for use with head trauma patients in neurointensive care, allowing simultaneous measurement of the levels of glucose and lactate present in the dialysate with high time resolution (30 s sampling intervals). The assay is compared with the Yellow Springs 2300 glucose/lactate analyser in simple analyses and during zero net flux experiments. The on-line assay has greater accuracy and precision particularly at low concentrations of glucose and lactate. The rapid nature of this dual on-line system makes it valuable in studying the roles of energy metabolites in the brain extracellular fluid (ECF), and as an important new method for routine clinical monitoring of patients in the neurointensive care unit. Data is shown for monitoring during surgery and in intensive care.

Oxo-anion binding by metal containing molecular 'clefts'

Abstract A simple but effective route has been developed to produce a series of molecular clefts, [(η6-p-cymene)RuCl(1)2]PF6 (4a), [(dppe)Pd(1)2](BF4)2 (5a), [(dppe)Pd(2)2](BF4)2 (5b), [(dppe)Pt(1)2](BF4)2 (6a) and [(dppe)Pt(2)2](BF4)2 (6b), that contain either a redox active ferrocenyl or a photoactive anthracenyl side arm, attached to a ruthenium(II), palladium(II) or platinum(II) backbone. Compounds 4a, 5a, 5b and 6a act as hosts for oxo-anions. Anion recognition is achieved via convergent hydrogen bond interactions from secondary amine functionality on the side arms. The binding is also enhanced by the positive charge of the metal centres. The X-ray crystal structure of the related [PdCl2(1)2] (7) shows it to possess a trans geometry. The X-ray crystal structures of the monoadducts [(η6-p-cymene)RuCl2(1)] (3a) and [(η6-p-cymene)RuCl2(2)] (3b), which show contrasting behaviour in their hydrogen bonding to coordinated chloride, are also reported.