Release of VEGF and FGF in the extracellular space following severe subarachnoidal haemorrhage or traumatic head injury in humans

Microdialysate fluid from 145 severely injured NSICU-patients, 88 with subarachnoidal haemorrage (SAH), and 57 with traumatic brain injury (TBI), was collected by microdialysis during the first 7 days following impact, and levels of the neurotrophins fibroblast growth factor-2 (FGF2) and vascular endothelial growth factor (VEGF) were analysed. The study illustrates both similarities and differences in the reaction patterns of the 2 inflammatory proteins. The highest concentrations of both FGF2 and VEGF were measured on Day 2 (mean (+/- SE) values being 47.1 +/- 15.33 and 116.9 +/- 41.85 pg/ml, respectively, in the pooled patient material). The VEGF concentration was significantly higher in TBI-patients, while the FGF2 showed a tendency to be higher in SAH-patients. This is the first report presenting in some detail the human cerebral response of FGF2 and VEGF following SAH and TBI. Apart from increasing the understanding of the post-impact inflammatory response of the human brain, the study identifies potential threshold values for these chemokines that may serve as monitoring indicators in the NSICU.

Differences in cerebral extracellular response of interleukin-1β, interleukin-6, and interleukin-10 after subarachnoid hemorrhage or severe head trauma in humans

BACKGROUND

Microdialysis has become a routine method for biochemical surveillance of patients in neurosurgical intensive care units.

OBJECTIVE

To analyze the intracerebral extracellular levels of 3 interleukins (ILs) during the 7 days after major subarachnoid hemorrhage or traumatic brain injury).

METHODS

Microdialysate from 145 severely injured neurosurgical intensive care unit patients (88 with subarachnoid hemorrhage, 57 with traumatic brain injury) was collected every 6 hours for 7 days. The concentrations of IL-1β and IL-6 were determined by fluorescence multiplex bead technology, and IL-10 was determined by enzyme-linked immunosorbent assay.

RESULTS

Presented are the response patterns of 3 ILs during the first week after 2 different types of major brain injury. These patterns are different for each IL and also differ with respect to the kind of pathological impact. For both IL-1β and IL-6, the initial peaks (mean values for all patients at day 2 being 26.9 ± 4.5 and 4399 ± 848 pg/mL, respectively) were followed by a gradual decline, with IL-6 values remaining 100-fold higher compared with IL-1β. Female patients showed a stronger and more sustained response. The response of IL-10 was different, with mean values less than 23 pg/mL and with no significant variation between any of the postimpact days. For all 3 ILs, the responses were stronger in subarachnoid hemorrhage patients. The study also indicates that under normal conditions, IL-1β, IL-6, and IL-10 are present only at very low concentrations or not at all in the extracellular space of the human brain.

CONCLUSION

This is the first report presenting in some detail the human cerebral response of IL-1β, IL-6, and IL-10 after subarachnoid hemorrhage and traumatic brain injury. The 3 ILs have different reaction patterns, with the response of IL-1β and IL-6 being related to the type of cerebral damage sustained, whereas the IL-10 response was less varied.

Changes in extracellular concentrations of some cytokines, chemokines, and neurotrophic factors after insertion of intracerebral microdialysis catheters in neurosurgical patients

OBJECTIVE

The extracellular levels of eight different inflammatory agents were analyzed during the initial 36 hours after insertion of microdialysis catheters in patients.

METHODS

Cerebral extracellular fluid from 38 patients who were treated in a neurosurgical intensive care unit for severe brain injury was collected every 6 hours for 36 hours. The concentration of interleukin (IL)-1 beta, IL-6, IL-8, macrophage inflammatory protein-1 beta, regulated on activation, normal T-cell expressed and secreted (RANTES), fibroblast growth factor-2, and vascular endothelial growth factor was determined by a multiplex assay, and IL-10 was determined by enzyme-linked immunosorbent assay.

RESULTS

This is the first report regarding the presence of IL-10, IL-8, macrophage inflammatory protein-1 beta, regulated on activation, T-cell expressed and secreted, vascular endothelial growth factor, and fibroblast growth factor-2 in the tissue level proper of the living human brain. The study also provides new information regarding the response of IL-1 beta and IL-6 after insertion of a microdialysis catheter. The study confirms that the intriguing patterns of interplay between different components of the inflammatory response studied in laboratory settings are present in the human brain. This was most clearly observed in the variations in response between the three different chemokines investigated, as well as in the rapid and transient response of fibroblast growth factor-2.

CONCLUSION

The data presented illustrate the opportunity to monitor biochemical events of possible importance in the human brain and indicate the potential of such monitoring in neurosurgical intensive care. The study also underlines that any analysis of events in the brain involving mechanical invasiveness needs to take into account biochemical changes that are directly related to the manipulation of brain tissue.

Potential use of quantitative bedside CBF monitoring (Xe-CT) for decision making in neurosurgical intensive care

During a 3-year period, mobile xenon-computerized tomography (Xe-CT) for bedside quantitative assessment of cerebral blood flow was used as an integrated tool for decision making during the care of complicated patients in our neurosurgical intensive care units (NSICU), in an attempt to make a preliminary evaluation regarding the usefulness of this method in routine work in the neurosurgical intensive care. With approximately 200 studies involving 75 patients, we identified six different categories where the use of bedside Xe-CT significantly influenced (or, with more experience, could have influenced) the decision making, or facilitated the handling of patients. These categories included identification of problems not apparent from other types of monitoring, avoidance of adverse effects from treatment, titration of standard treatments, evaluation of the vascular resistance reserve, assessment of adequate perfusion pressure and better utilization of resources from access to the bedside cerebral blood flow (CBF) technology. We conclude that quantitative bedside measurements of CBF could be an important addition to the diagnostic and monitoring arsenal of NSICU-tools.

Variations in the response of interleukins in neurosurgical intensive care patients monitored using intracerebral microdialysis

OBJECT

The aim of this study was to make a preliminary evaluation of whether microdialysis monitoring of cytokines and other proteins in severely diseased neurosurgical patients has the potential of adding significant information to optimize care, thus broadening the understanding of the function of these molecules in brain injury.

METHODS

Paired intracerebral microdialysis catheters with high-cutoff membranes were inserted in 14 comatose patients who had been treated in a neurosurgical intensive care unit following subarachnoidal hemorrhage or traumatic brain injury. Samples were collected every 6 hours (for up to 7 days) and were analyzed at bedside for routine metabolites and later in the laboratory for interleukin (IL)-l and IL-6; in two patients, vascular endothelial growth factor and cathepsin-D were also checked. Aggregated microprobe data gave rough estimations of profound focal cytokine responses related to morphological tissue injury and to anaerobic metabolism that were not evident from the concomitantly collected cerebrospinal fluid data. Data regarding tissue with no macroscopic evidence of injury demonstrated that IL release not only is elicited in severely compromised tissue but also may be a general phenomenon in brains subjected to stress. Macroscopic tissue injury was strongly linked to IL-6 but not IL- lb activation. Furthermore, IL release seems to be stimulated by local ischemia. The basal tissue concentration level of IL-lb was estimated in the range of 10 to 150 pg/ml; for IL-6, the corresponding figure was 1000 to 20,000 pg/ml.

CONCLUSIONS

Data in the present study indicate that catheters with high-cutoff membranes have the potential of expanding microdialysis to the study of protein chemistry as a routine bedside method in neurointensive care.

Bedside monitoring of CBF with xenon-CT and a mobile scanner: a novel method in neurointensive care

Combining previously independently established techniques our objective was to develop and evaluate a method for bedside qualitative assessment of cerebral blood flow in neurointensive care (NICU) patients. The CT-protocol was optimized using phantoms and comparing a mobile CT-scanner (Tomoscan-M, Philips) with two stationary CT scanners. Thirty-two per cent xenon was delivered with standard equipment (Enhancer 3000). Mean cortical flow in volunteers was 48 ml/min/100 g, with the mean vascular territorial flow varying between 45 and 66 ml/min/100 g. The potential clinical usefulness was illustrated in three patients with vasospasm following subarachnoid haemorrhage. Our conclusion is that quantitative bedside measurements of CBF can be repeatedly performed in an easy and safe way in a standard NICU-setting, using xenon-inhalation and a mobile CT-scanner. The method is useful for the decision-making, and is a good example of how the quality of multi-modality monitoring in the NICU can be developed and further diversified.

A microdialysis technique for routine measurement of macromolecules in the injured human brain

OBJECTIVE

To evaluate a new intracerebral microdialysis catheter with a high-cutoff membrane and its potential for the study of macromolecules in the human brain.

METHODS

Paired intracerebral microdialysis catheters were inserted in 10 patients who became comatose after subarachnoid hemorrhage or traumatic brain injury and were then treated in our neurosurgical unit. The only differences from the routine use of microdialysis in our clinic were the length (20 mm) and cutoff properties of the catheter membranes (100 kD) and the perfusion fluids used (standard perfusion fluid, 3.5% albumin, or Ringer-dextran 60). Samples were weighed (for net fluid fluxes) and analyzed at bedside (for routine metabolites) and later in the laboratory (for total protein and interleukin-6). The in vitro recovery of glucose, glutamate, and glycerol were also investigated under different conditions.

RESULTS

Even brief perfusion with standard perfusion fluid resulted in a significant loss of volume from the microdialysis system. For albumin and Ringer-dextran 60 fluid, recovery was comparable to standard settings. Interleukin-6 (highest value close to 25,000 pg/ml) was sampled from all catheters, and total protein was analyzed from catheters perfused with Ringer-dextran 60 (average concentration, 234 mug protein/ml). There were detectable patterns of variations in the concentration of interleukin-6, seemingly related to concomitant variations in intracerebral conditions. In the present study, no direct comparison was made with the standard CMA 70 catheter (CMA Microdialysis, Stockholm, Sweden), but in vivo, the measured mean concentrations of glucose, glycerol, lactate, and pyruvate were comparable to those previously reported from standard catheters. In vitro, the recovery of metabolites was better when using Ringer-dextran 60 compared with albumin.

CONCLUSION

Microdialysis catheters with high-cutoff membranes can be used in routine clinical practice, allowing for sampling and analysis of cytokines and other macromolecules.

Intracerebral microdialysis in neurosurgical intensive care patients utilising catheters with different molecular cut-off (20 and 100 kD)

OBJECTIVE

To compare the properties of a new intracerebral micro-dialysis catheter with a high cut-off membrane (molecular cut-off 100 kDalton) with a standard catheter (CMA70, molecular cut-off 20 kDalton).

METHODS

Paired intracerebral microdialysis catheters were inserted in fifteen comatose patients treated in a neurosurgical intensive care unit following subarachnoid haemorrhage or traumatic brain injury. The high-cut-off catheter (D(100)) differed from the CMA 70 catheter by the length (20 mm) and cut-off properties of the catheter membranes (100 kDalton) and the perfusion fluids used (Ringer-Dextran 60). Samples were collected every 4-6 hours, analyzed bedside (for glucose, glutamate, glycerol, lactate, pyruvate and urea) and later in the laboratory (for total protein).

RESULTS

Fluid recovery was similar for the two types of catheters, but significantly more protein was recovered by the D(100) catheter. The recovery of glycerol and pyruvate did not differ, while minor differences in recovery of glutamate and glucose were observed. The recovery of lactate was considerably lower in the D(100) catheter (p < 0.01), influencing the lactate/pyruvate-ratio. The patterns of concentration changes over time were consistent for all metabolites, and independent of type of catheter.

CONCLUSION

Microdialysis catheters with high cut-off membranes can be used in routine clinical practice in the NSICU, adding the possibility of macro-molecule sampling from the extracellular space during monitoring.

Local changes in cerebral energy metabolism due to brain retraction during routine neurosurgical procedures

PATIENTS AND INTERVENTIONS

Tissue damage caused by brain retraction was evaluated utilizing intracerebral microdialysis in six patients operated on subfrontally for pituitary adenoma. The microdialysis probes (membrane length 10 mm, cut-off 20 kDalton) were placed in cerebral cortex beneath the brain retractor and perfused with Ringer solution at 0.3 microl/min. The microdialysis vials were changed at intervals of 30 minutes and analysed for glucose, pyruvate, lactate, glutamate and glycerol.

RESULTS

During brain retraction regional intracerebral glucose was within normal range in cortical tissue and the levels of lactate, glutamate, and glycerol as well as the lactate/pyruvate ratio were considerably above normal range.

CONCLUSION

The biochemical analysis shows a pronounced incomplete cerebral ischemia due to brain retraction. The increases in glutamate and glycerol indicate tissue damage and degradation of cell membranes. Intracerebral microdialysis may be a valuable tool in the development of optimal techniques for brain retraction during neurosurgical procedures.

Intracerebral microdialysis and bedside biochemical analysis in patients with fatal traumatic brain lesions

BACKGROUND

Microdialysis with bedside biochemical analysis was used to monitor cerebral biochemical alterations that precede and accompany increase in intracranial pressure (ICP), resulting in a complete cessation of cerebral blood flow.

METHODS

Seven patients, who died due to an untreatable increase in ICP, were included. The patients originate from a large, consecutive series of severely head injured patients (n: 95) monitored with intracerebral microdialysis (perfusion rate 0.3 microl/min). One microdialysis catheter was inserted via a separate burr hole frontally to that used for the intraventricular catheter ("better" position) and one catheter was inserted into cerebral cortex surrounding an evacuated focal contusion or underlying an evacuated haematoma ("worse" position). Biochemical analyses of glucose, lactate, glycerol, urea, glutamate, and pyruvate were performed at the bedside. All samples were frozen for subsequent HPLC (high-performance liquid chromatography) analyses of amino acids and ions.

RESULTS

Decreases in glucose and pyruvate and increases in lactate, glycerol, glutamate, and lactate/pyruvate (la/py) ratio characterized cerebral ischaemia. The measured markers give information regarding substrate availability (glucose), redox state of the tissue (la/py ratio), degradation of glycerophospholipids in cell membranes (glycerol), and extracellular concentration of excitatory amino acids (glutamate). In the "worse" position biochemical deterioration occurred before the increase in ICP. In the "better" position biochemical deterioration was usually observed after the increase in ICP.

CONCLUSION

Changes of cerebral energy metabolism that accompany cerebral ischaemia follow a certain pattern and may be detected at the bedside by intracerebral microdialysis before the secondary damage causes an increase in ICP.

Intracerebral microdialysis in clinical practice: baseline values for chemical markers during wakefulness, anesthesia, and neurosurgery

OBJECTIVE

The study was undertaken to measure baseline values for chemical markers in human subjects during wakefulness, anesthesia, and neurosurgery, using intracerebral microdialysis.

METHODS

Microdialysis catheters were inserted into normal posterior frontal cerebral cortex in nine patients who were undergoing surgery to treat benign lesions of the posterior fossa. The perfusion rate was 1.0 microl/min during anesthesia/neurosurgery and the early postoperative course and 0.3 microl/min during the later course. Bedside biochemical analyses of glucose, pyruvate, lactate, glycerol, glutamate, and urea were performed before, during, and after neurosurgery. After the bedside analyses, all samples were frozen for subsequent high-performance liquid chromatographic analyses of amino acids.

RESULTS

The following baseline values were obtained during wakefulness (perfusion rate, 0.3 microl/min): glucose, 1.7+/-0.9 mmol/L; lactate, 2.9+/-0.9 mmol/L; pyruvate, 166+/-47 micromol/L; lactate/pyruvate ratio, 23+/-4; glycerol, 82+/-44 micromol/L; glutamate, 16+/-16 mmol/L; urea, 4.4+/-1.7 mmol/L. Marked increases in the levels of all chemical markers were observed at the beginning and end of anesthesia/surgery.

CONCLUSION

The study provides human baseline levels for biochemical markers that can presently be measured at the bedside during neurointensive care. In addition, some changes that occurred under varying physiological conditions are described.

Intracerebral microdialysis in clinical practice: baseline values for chemical markers during wakefulness, anesthesia, and neurosurgery

OBJECTIVE

The study was undertaken to measure baseline values for chemical markers in human subjects during wakefulness, anesthesia, and neurosurgery, using intracerebral microdialysis.

METHODS

Microdialysis catheters were inserted into normal posterior frontal cerebral cortex in nine patients who were undergoing surgery to treat benign lesions of the posterior fossa. The perfusion rate was 1.0 microl/min during anesthesia/neurosurgery and the early postoperative course and 0.3 microl/min during the later course. Bedside biochemical analyses of glucose, pyruvate, lactate, glycerol, glutamate, and urea were performed before, during, and after neurosurgery. After the bedside analyses, all samples were frozen for subsequent high-performance liquid chromatographic analyses of amino acids.

RESULTS

The following baseline values were obtained during wakefulness (perfusion rate, 0.3 microl/min): glucose, 1.7+/-0.9 mmol/L; lactate, 2.9+/-0.9 mmol/L; pyruvate, 166+/-47 micromol/L; lactate/pyruvate ratio, 23+/-4; glycerol, 82+/-44 micromol/L; glutamate, 16+/-16 mmol/L; urea, 4.4+/-1.7 mmol/L. Marked increases in the levels of all chemical markers were observed at the beginning and end of anesthesia/surgery.

CONCLUSION

The study provides human baseline levels for biochemical markers that can presently be measured at the bedside during neurointensive care. In addition, some changes that occurred under varying physiological conditions are described.

Operations and re-operations for chronic subdural haematomas during a 25-year period in a well defined population

In this retrospective study the hospital records of all patients being operated on for chronic subdural haematomas (CSD) at the Neurosurgical clinic in Lund in the years 1969, 1979, 1989, and 1993 were examined. 218 patients were operated on, 25 of whom had bilateral haematomas. During the 25-year period the incidence of surgically treated CSD rose from 2 to 5.3 per 100,000 inhabitants per year. The mean age (70.5 years) and the relationship males: females (2:1) did not significantly change. The clinical condition of the patients on admission steadily improved during the period. The relative proportion of patients with known chronic alcoholism decreased over the years, but the proportion of patients suffering from other complicating diseases increased, as did the proportion of patients treated with anticoagulants. There was no mortality directly related to surgery, but if defined as deaths within one month after surgery, the overall mortality rate was 3.2%. 84.2% of the patients improved following the first operation, in a majority of cases back to the premorbid state. The relative frequency of re-operations for CSD was 12.3% and did not significantly change during the period. No pre- or peri-operative variable could be identified which could predict who of the patients was at higher risk of re-operation. Surprisingly, the data suggest that the less experienced neurosurgeons had better operative results compared with their older collegues.

The influence of calcium transients on intracellular pH in cortical neurons in primary culture

The objective of this study was to assess the influence of Ca2+ influx on intracellular pH (pHi) of neocortical neurons in primary culture. Neurons were exposed to glutamate (100-500 microM) or KCl (50 mM), and pHi was recorded with microspectrofluorometric techniques. Additional experiments were carried out in which calcium influx was triggered by ionomycin (2 microM) or the calcium ionophore 4-Br-A23187 (2 microM). Glutamate exposure either caused no, or only a small decrease in pHi (delta pH approximately 0.06 units). When a decrease was observed, a rebound rise in pHi above control was observed upon termination of glutamate exposure. In about 20% of the cells, the acidification was more pronounced (delta pH approximately 0.20 units), but all these cells had high control pHi values, and showed gradual acidification. Exposure of cells to 50 mM KCl consistently increased pHi. Since this increase was similar in the presence and nominal absence of HCO3-, it probably did not reflect influx of HCO3- via a Na(+)-HCO3- symporter. Furthermore, since it occurred in the absence of external Ca2+ (or a measurable rise in Cai2+) it seemed independent of Ca2+ influx. It is tentatively concluded that the rise in pHi was due to reduced passive influx of H+ along the electrochemical gradient, which is reduced by depolarization. In Ca(2+)-containing solutions, depolarization led to a rebound increase in pHi above control. This, and the rebound found after glutamate transients, may reflect Ca(2+)-triggered phosphorylation and upregulation of the Na+/H+ antiporter which extrudes H+ from the cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracerebral temperature in neurosurgical patients: intracerebral temperature gradients and relationships to consciousness level

Information regarding human brain temperature is still rather sparse, which is surprising giving the no longer recent findings that the mammalian brain is very sensitive to minor variations in temperature. We therefore report the results of intracranial temperature monitoring in thirty neurosurgical patients. Intraventricular temperature was monitored with a thermocouple specifically designed for the purpose, and introduced through a plastic catheter used for monitoring of intracranial pressure, with simultaneous measurements of rectal and epidural temperature with commercially available thermocouples. Human intraventricular temperature is higher than central core temperature, and there is also a temperature gradient within the brain, with the central parts being warmer than the surface. The presence of an intracerebral temperature gradient was confirmed in two patients undergoing stereotactic thalatomy. We found no clear evidence for a correlation between consciousness level and brain temperature. Observations of brain temperature changes after clinical diagnosis of brain death are also reported.

Influence of acid-base changes on the intracellular calcium concentration of neurons in primary culture

The influence of changes in intra- and extracellular pH (pHi and pHe, respectively) on the cytosolic, free calcium concentration ([Ca2+]i) of neocortical neurons was studied by microspectrofluorometric techniques and the fluorophore fura-2. When, at constant pHe, pHi was lowered with the NH4Cl prepulse technique, or by a transient increase in CO2 tension, [Ca2+]i invariably increased, the magnitude of the rise being proportional to delta pHi. Since similar results were obtained in Ca(2+)-free solutions, the results suggest that the rise in [Ca2+]i was due to calcium release from intracellular stores. The initial alkaline transient during NH4Cl exposure was associated with a rise in [Ca2+]i. However, this rise seemed to reflect influx of Ca2+ from the external solution. Thus, in Ca(2+)-free solution NH4Cl exposure led to a decrease in [Ca2+]i. This result and others suggest that, at constant pHe, intracellular alkalosis reduces [Ca2+]i, probably by enhancing sequestration of calcium. When cells were exposed to a CO2 transient at reduced pHe, Ca2+ rose initially but then fell, often below basal values. Similar results were obtained when extracellular HCO3- concentration was reduced at constant CO2 tension. Unexpectedly, such results were obtained only in Ca(2+)-containing solutions. In Ca(2+)-free solutions, acidosis always raised [Ca2+]i. It is suggested that a lowering of pHe stimulates extrusion of Ca2+ by ATP-driven Ca2+/2H+ antiport.

Relationship between intra- and extracellular pH in primary cultures of rat astrocytes

We studied the influence of extracellular pH (pHe) on the mechanisms regulating intracellular pH (pHi) in astrocytes cultured from neonatal rat cortex, using single cell microspectrofluorometry and the pH-sensitive fluorophore 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. When pHe was maintained at control values of 7.35 during acid transients caused by an increased CO2 tension, pHi was rapidly regulated back to normal. However, at pHe 6.9 or below, there was no recovery of pHi. Steady-state pHi was also strongly dependent on pHe (pHi = 1.14 + 0.80 pHe). The pHi recovery after normalization of pHe was very rapid, indicating that a prolonged exposure to a low pH stimulates pH-regulating mechanisms, and was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and amiloride or the removal of Na+. Recovery was also slowed down by Cd2+. The pHe-dependent acidification was not critically influenced by DIDS or amiloride and was not inhibited by tetrodotoxin, tetraethylammonium, Ba2+,2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)-quinoxaline, kynurenic acid, 5-hydroxysaclofen, bicuculline, Cd2+, or albumin. The results emphasize the importance of pHe for pHi regulation and suggest that in astrocytes pHi is not regulated back to normal levels until pHe is normalized.

The influence of pH on glutamate- and depolarization-induced increases of intracellular calcium concentration in cortical neurons in primary culture

The present experiments, carried out on neocortical neurons in primary culture with measurements of cytosolic calcium concentrations ([Ca2+]i) by microspectrofluorometric techniques, were designed to study how changes in extra- and intracellular pH (pHe and pHi, respectively) modulate the rise in [Ca2+]i due to glutamate exposure or potassium (K+)-induced depolarization. Although a reduction in pHe/pHi per se increased [Ca2+]i, the acidosis attenuated both the peak rise in [Ca2+]i following exposure to glutamate, and the plateau level observed during prolonged exposure. As a result, cells exposed to solutions with low pH consistently had lower [Ca2+]i values upon glutamate exposure than cells studied at normal pH. Alkalosis, i.e., an increase in pHe/pHi, had the opposite effect, accentuating the glutamate-induced [Ca2+]i transients. Experiments designed to separate changes due to extra- and intracellular pH suggested that the decisive event was the change in pHe. These results are consistent with the known effect of pHe on calcium flux through NMDA-gated ion channels. However, lowering of pHe had an equivalent effect on the rise in [Ca2+]i triggered by exposure of the cells to a K+ concentration of 50 mM. Thus, acidosis reduces influx of calcium through both agonist-operated and voltage-sensitive channels to such an extent that efflux/sequestration mechanisms suffice to maintain a lower [Ca2+]i.

The regulation of intracellular pH is strongly dependent on extracellular pH in cultured rat astrocytes and neurons

We studied the mechanisms regulating intracellular pH (pHi) in cultured rat astrocytes and neurons, with particular reference to the influence of extracellular pH (pHe) on these mechanisms, using microspectrofluorometric monitoring from single cells, loaded with the pH-sensitive fluorophore BCECF. The pH regulatory mechanisms differ between neurons and astrocytes. The experimental data suggest the presence of a Na+/H+ and a Na(+)-independent HCO3-/Cl- exchanger in both types of cells, while astrocytes, in addition, utilise a Na(+)-dependent HCO3-/Cl- exchanger for regulating acid transients. In both cell types the pH regulatory mechanisms are strongly dependent on pHe. Thus, at pHe 6.85 or below, there was no recovery of pHi. Steady state pHi was also strongly dependent on pHe, in both astrocytes and neurons. The pHi recovery following normalisation of pHe was very rapid, (indicating that a prolonged exposure to a low pH stimulates pH regulating mechanisms), and was inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and amiloride, or in the absence of Na+. The results challenge the concept of a H(+)-regulatory site solely at the internal side of the exchanger regulating pHi to a constant value.

Monitoring of rectal, epidural, and intraventricular temperature in neurosurgical patients

We will report our accumulated experience in monitoring of brain temperatures in neurosurgical patients. The intraventricular temperature was monitored with a thermocouple designed for the purpose. This thermocouple was introduced through a plastic catheter, which was also used for monitoring intracranial pressure. The rectal and epidural temperature was simultaneously measured, with commercially available thermocouples. Human brain temperature is higher than the central core temperature, and there is also a temperature gradient within the brain, with the central parts being warmer than the surface. The relationship between rectal, epidural and intraventricular temperatures is maintained during anaesthesia. We have also shown that it is possible to lower the temperature of the human brain.

Regulation of intracellular pH in single rat cortical neurons in vitro: a microspectrofluorometric study

Intracellular pH (pHi) and the mechanisms of pHi regulation in cultured rat cortical neurons were studied with microspectrofluorometry and the pH-sensitive fluorophore 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. Steady-state pHi was 7.00 +/- 0.17 (mean +/- SD) and 7.09 +/- 0.14 in nominally HCO3(-)-free and HCO3(-)-containing solutions, respectively, and was dependent on extracellular Na+ and Cl-. Following an acid transient, induced by an NH1 prepulse or an increase in CO2 tension, pHi decreased and then rapidly returned to baseline, with an average net acid extrusion rate of 2.6 and 2.8 mmol/L/min, in nominally HCO3(-)-free and HCO3(-)-containing solutions, respectively. The recovery was completely blocked by removal of extracellular Na+ and was partially inhibited by amiloride or 5-N-methyl-N-isobutylamiloride. In most cells pHi recovery was completely blocked in the presence of harmaline. The recovery of pHi was not influenced by addition of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) or removal of Cl-. The rapid regulation of pHi seen following a transient alkalinization was not inhibited by amiloride or by removal of extracellular Na+, but was partially inhibited by DIDS and by removal of extracellular Cl-. The results are compatible with the presence of at least two different pHi-regulating mechanisms: an acid-extruding Na+/H+ antiporter, possibly consisting of different subtypes, and a passive Cl-/HCO3- exchanger, mediating loss of HCO3- from the cell.

Buffer capacity of rat cortical tissue as well as of cultured neurons and astrocytes

The primary objective of this work was to assess the intrinsic nonbicarbonate buffer capacity (beta i) of cultured neurons and astrocytes and to compare the beta i values obtained to those of neocortical tissue. A second objective was to determine the pH dependence of beta i. Titration of homogenates of whole-brain cortical tissue and cultured neurons with NaOH and HCl gave beta i values of 25-30 mmol.l-1 x pH-1. The buffer capacity was essentially constant in the pH range of 6-7. Astrocytes showed a higher buffer capacity and a clear relationship between beta i and pH. However, beta i decreased when pH was reduced from 7 to 6. The beta i values derived from microspectrofluorometric studies on neurons and astrocytes were surprisingly variable, ranging from 10 to 50 mmol.l-1 x pH-1. The ammonia "step method" suggested that beta i increased dramatically when pH was lowered from 7 to 6 but the propionic "step method" failed to reveal such a pH dependence. Some techniques obviously give erroneous values for beta i, presumably because changes in buffer base concentration (due to transmembrane fluxes of H+, HCO3-, NH4+ or anions of weak acids) violate the principles upon which the calculations are based. From the results obtained by direct titration and with the propionate technique, we tentatively conclude that beta i in neurons and astrocytes are approximately 20 and 30 mmol.l-1 x pH-1, respectively. We further suggest that the term "intrinsic buffer capacity", as commonly used, is redefined.

Intracellular pH regulation in cultured rat astrocytes in CO2/HCO3(-)-containing media

We studied the regulation of intracellular pH (pHi) and the mechanisms of pHi regulation in cultured rat astrocytes using microspectrofluorometry and the pH-sensitive fluorophore 2',7'-bis(carboxyethyl-)-5,6-carboxyfluorescein. Control pHi was 7.00 +/- 0.02 in HCO3(-)-containing solutions at an extracellular pH of 7.35. Addition of 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) or amiloride decreased pHi, as did removal of extracellular Na+, while removal of extracellular Cl- was followed by an increase in pHi. Following exposure to an acid transient induced by increasing the CO2 content from 5 to 15%, pHi rapidly returned to base line, with an average initial rate of recovery of 0.10 pH units min-1 (corresponding to a mean acid extrusion rate of 6.3 +/- 0.36 mmolo l-1 min-1). Regulation of pHi was impaired when either amiloride or DIDS was added or Cl- was removed. This inhibition was enhanced when both DIDS and amiloride were present, and pHi regulation was completely blocked in the absence of extracellular Na+. The rapid regulation of pHi normally seen following a transient alkalinisation was not inhibited by amiloride or removal of Na+, but was partially inhibited by DIDS and by the absence of extracellular Cl-. The results are compatible with the presence of at least three different pHi-regulating mechanisms: a Na+/H+ antiporter, a Na(+)-dependent HCO3-/Cl- exchanger (both regulating pHi during a transient acidification), and a passive Cl-/HCO3- exchanger (regulating pHi during transient alkalinisation). The results fail to provide firm evidence of the presence of an electrogenic Na+/HCO3- symporter.

Changes in human intracerebral temperature in response to different methods of brain cooling

The rectal, epidural, and intraventricular temperatures were continuously monitored in 10 seriously injured and unconscious patients admitted for neurosurgical intensive care. Different attempts were made to lower their brain temperatures. Isolated head cooling, whether with frozen liquid (Hypotherm Gel Kap; Flexoversal, Hilden, Germany) or a cooling helmet, had very limited effect. Nasopharyngeal cooling had no effect. During barbiturate coma, a considerable increase in brain temperature was observed. The administration of paracetamol was the single most effective method by which to lower brain temperature, at times by 2 degrees C and usually with a concomitant decrease in the temperature gradient between the rectum and the brain. However, in order to achieve a lasting reduction of brain temperature to 35 degrees C, we had to use a combination of head cooling and intensive whole-body cooling.

Human Brain Temperature During Anesthesia for Intracranial Operations

The intraventricular and rectal temperatures were registered in nine patients subjected to major surgery of the brain. Copper-constantan thermocouples were introduced into the lumen of an intraventricular catheter also used for perioperative monitoring of intracranial pressure. During anesthesia, the intraventricular temperature was higher than rectal temperature, the mean difference being 0.30 +/- 0.24 degrees C. No significant changes in intraventricular temperature were seen during different stages of the operations. It is concluded that during routine anesthesia rectal temperature can be relied on for a reasonable estimation of human brain temperature. It should be observed, however, that in the postoperative period, both rectal and intraventricular temperature rose considerably. In three patients, the intraventricular temperature rose as much as 2.5-4 degrees C, thus increasing the temperature gradient between rectum and brain. The relevance of these findings are discussed.

Intracerebral temperature in neurosurgical patients

Recent laboratory results have indicated that the ischemic brain is very sensitive to minor variations in temperature. This has created new interest in hypothermia and brain temperature. There is, however, very little information available regarding human intracerebral temperature and its relation to body core temperature during normal and pathological circumstances. We therefore made continuous measurements of the temperature of the lateral ventricle in 15 neurosurgical patients utilizing a newly developed technique with copper-constantan thermocouples introduced through a plastic catheter also used for monitoring intracranial pressure. The intraventricular temperature was higher than the rectal temperature during approximately 90% of all measurements. The largest temperature gradient measured was 2.3 degrees C. Usually the difference between the temperature of the rectum and the brain was much smaller, the mean value being 0.33 degrees C. For the patients in the most severe condition, the rectal temperature was sufficiently close to the brain temperature to afford a reliable basis for adequate clinical judgment.

Intracerebral Temperature in Neurosurgical Patients

Recent laboratory results have indicated that the ischemic brain is very sensitive to minor variations in temperature. This has created new interest in hypothermia and brain temperature. There is, however, very little information available regarding human intracerebral temperature and its relation to body core temperature during normal and pathological circumstances. We therefore made continuous measurements of the temperature of the lateral ventricle in 15 neurosurgical patients utilizing a newly developed technique with copper-constantan thermocouples introduced through a plastic catheter also used for monitoring intracranial pressure. The intraventricular temperature was higher than the rectal temperature during approximately 90% of all measurements. The largest temperature gradient measured was 2.3°C. Usually the difference between the temperature of the rectum and the brain was much smaller, the mean value being 0.33°C. For the patients in the most severe condition, the rectal temperature was sufficiently close to the brain temperature to afford a reliable basis for adequate clinical judgment.

A method for monitoring intracerebral temperature in neurosurgical patients

Current interest in brain temperature and selective brain cooling makes a method allowing for continuous monitoring of intracerebral temperature in humans desirable. The authors describe a safe, simple, and reliable technique using a thermocouple of copper and constantan in combination with intraventricular monitoring of intracranial pressure for measurement of brain temperature in neurosurgical patients.

A Method for Monitoring Intracerebral Temperature in Neurosurgical Patients

Current interest in brain temperature and selective brain cooling makes a method allowing for continuous monitoring of intracerebral temperature in humans desirable. The authors describe a safe, simple, and reliable technique using a thermocouple of copper and constantan in combination with intraventricular monitoring of intracranial pressure for measurement of brain temperature in neurosurgical patients.

Preservation of brain temperature during ischemia in rats

Our objectives were to study the loss of heat from ischemic brain and to devise a method of maintaining brain temperature. Reversible forebrain ischemia was induced by carotid clamping and exsanguination in 30 anesthetized and artificially ventilated rats. Rectal, skull, and brain temperatures were measured, confirming previous findings that brain temperature falls by 4-5 degrees C during 15 minutes of ischemia unless measures are taken to maintain head temperature by external heating. Temperature gradients developed within the ischemic brain, superficial tissues being cooler than deep ones. These temperature gradients were reversed when skull temperature was maintained at core body (rectal) temperature by external heating. With rectal and skull temperatures maintained at 38 degrees, 37 degrees, 35 degrees, or 33 degrees C, brain temperatures nonetheless decreased by approximately 1 degree C during ischemia. This decrease in brain temperature could be prevented by placing the rat in a Plexiglas box with circulating air at temperatures close to that of the body core and a relative humidity of approximately 100%. We also found that, unless special precautions are taken, a temperature gradient develops between the brain and body core during recirculation.

Epidural temperature and possible intracerebral temperature gradients in man

Although it has been known for a long time that pronounced hypothermia has a protective effect on the brain during ischemia, and that severe hyperthermia damages neuronal tissue, knowledge of human brain temperature is very limited. The recent findings by two independent research groups, that even small differences in brain temperature significantly influence the degree of neuronal damage following cerebral ischemia, became the incentive for measuring brain temperature in neurosurgical patients. The temperature of the lateral ventricle, epidural space, membrana tympani and rectum were measured with copper-constantan thermocouples. During the implantation of an intraventricular catheter for measuring intracranial pressure, a temperature gradient of 0.4-1.0 degrees C between the lateral ventricle and the epidural space was noted. Continuous measurements for 1-5 days showed that the rectal temperature usually adequately reflects the temperature of the epidural space, although the temperature of the membrana tympani followed changes in epidural temperature more closely. However, at times, and in one patient during most of the time, the temperature of the epidural space was up to 1 degree C above rectal temperature. The relevance of these findings for the care of neurosurgical patients is discussed in relationship to what is known about brain temperature from animal experiments.

Time course of early brain edema following reversible forebrain ischemia in rats

Cerebral ischemia is known to be accompanied by brain edema. This increase in brain tissue water content probably influences the final outcome of an ischemic insult negatively. Despite extensive investigations on different aspects of brain edema, information on edema development during the early recirculation period following ischemia is sparse. We assessed changes in brain water content, as reflected by changes in tissue density, during the early recirculation period following severe forebrain ischemia. Fasted rats were subjected to 5, 15, or 30 minutes of ischemia and 5 to 180 minutes of recirculation. The specific gravity of specimens from the caudoputamen, frontoparietal cortex, hippocampus, and mesencephalon were measured with a Percoll linear density gradient. Five minutes of ischemia followed by recirculation did not produce any significant regional brain edema. However, following 15 minutes of ischemia, transient edema developed in the caudoputamen, frontoparietal cortex, and hippocampus. This edema was maximal after 30 minutes of reperfusion and was normalized after 180 minutes of reperfusion. Similar edema was seen following 30 minutes of ischemia. In the mesencephalon (where blood flow is approximately 50% of control during the ischemic insult) no brain edema was noted following 5, 15, or 30 minutes of ischemia. We discuss to what extent this transient regional brain edema may influence the selective neuronal vulnerability and cell damage observed in rats subjected to reversible forebrain ischemia and how these findings may correlate with neurochemical alterations observed during the early recirculation period.

Regional and species differences in vascular reactivity to extracellular potassium

In-vitro vasoreactivity to extracellular potassium (Ko+) was tested in isolated human pial and mesenteric arteries as well as basilar and mesenteric arteries from rabbits and rats. Contractions were induced by stepwise increases in [K+]o and were measured isometrically with a force-displacement transducer, in small-volume organ baths. Significant differences between species as well as between regions were found. The threshold of [K+]o for eliciting contraction in human cerebral arteries in hyperosmotic solutions was 10 mM, in rabbit cerebral arteries 17 mM and in rat cerebral arteries 27 mM. The threshold concentration for contraction in mesenteric arteries was significantly higher compared to cerebral arteries in humans and rabbits, but lower in rats: 20 mM in humans, 26 mM in rabbits and 25 mM in rats. In all species the contractile amplitudes were significantly higher in both cerebral and mesenteric arteries when [K+]o was increased under isotonic conditions in the buffer solution than when hyperosomolality was created. This difference increased with increasing hyperosmolality. In hyperosmotic solutions, the EC50 for [K+]o was lower in cerebral and mesenteric arteries from man than in vessels from rabbit and rat. When the solutions were isotonic, this pattern was seen only in mesenteric arteries. It is concluded that significant species and regional differences in vascular responses to [K+]o exist. Considering that [K+]o is increased in cerebral ischaemia, the observed significantly lower threshold for K+-induced contractions in human cerebral arteries may be of importance, especially in human cerebral ischaemic events.

HLA-typing in a family with six intracranial aneurysms

The pedigree of a family where three of nine siblings had suffered from aneurysmal subarachnoid haemorrhage (SAH) was explored, by means of interviews and revisions of population and medical records. We thus found two nephews with previously ruptured intracranial aneurysms. Subsequently high resolution computerised tomography (CT) scans were performed in the remaining six siblings, one of which was shown to harbor an intracranial aneurysm. This individual was subjected to uncomplicated clipping of the aneurysm. Typing of human leukocyte antigen (HLA) was performed in 15 individuals of the pedigree. Three of the six HLA-antigens recently reported to occur in increased frequently in a series of (non-familial) patients with ruptured aneurysm were found, namely B7, DR2 and Cw2. Most noteable was the expression of the antigen B7 in five of the six individuals with aneurysm in the investigated family. At present HLA-typing is not a useful screening tool to identify individuals in the general population with an increased risk of developing intracranial aneurysms. The present study shows that HLA-typing could neither be used to predict the occurrence of intracranial aneurysms in the siblings in the investigated family. HLA-typing may provide further clues to our understanding of the etiology of intracranial aneurysms, especially concerning possible genetic factors. The authors thus would like to encourage HLA-typing in previously known and newly detected families with accumulation of intracranial aneurysms.

Management of ruptured intracranial aneurysm: a review

The discouraging history associated with management of aneurysmal subarachnoid haemorrhage (SAH) is reviewed along with improvements in outlook attributable to progress made within the past decade. Among the new developments is the introduction of microsurgical techniques that allow elective surgery in the acute stage thereby preventing repeat haemorrhages. Early operation also offers the possibility of a more aggressive pharmacological anti-ischaemic treatment. Notwithstanding the improved results of acute elective surgery and the fact that delayed ischaemic deterioration (symptomatic cerebral vasospasm) now may be almost eliminated, the overall outcome remains gloomy. Despite recent advances not more than one out of three individuals, who are struck by the rupture of an intracranial aneurysm, may be expected to make a good neurological and functional recovery. Hope for further improvements may depend on the development of techniques that can identify intracranial aneurysms before they rupture and increased knowledge of the aetiology of such arterial wall lesions.