MR imaging of ventriculus terminalis of the conus medullaris: A report of two operated patients and review of the literature

We report on 2 patients in whom a cystic dilation of the conus medullaris was incidentally found at MR imaging carried out in the work-up for sciatica. The cysts were well circumscribed and had signal intensity identical to the CSF on both T1- and T2-weighted images. There was no evidence of contrast enhancement. None of the patients had specific symptoms related to the spinal cord. At surgery, no evidence of malignancy was seen in any of the patients. A benign cystic dilation, also called dilated ventriculus terminalis, occasionally can be seen in the conus medullaris as an incidental finding at thoracolumbar MR imaging. Unless the expansion per se indicates cyst drainage, these patients may be monitored by clinical and MR follow-up, avoiding surgery in a substantial number of cases.

Cranioplasty with autologous cryopreserved bone after decompressive craniectomy: complications and risk factors for developing surgical site infection

Background

Renewed interest has developed in decompressive craniectomy, and improved survival is shown when this treatment is used after malignant middle cerebral artery infarction. The aim of this study was to investigate the frequency and possible risk factors for developing surgical site infection (SSI) after delayed cranioplasty using autologous, cryopreserved bone.

Methods

This retrospective study included 74 consecutive patients treated with decompressive craniectomy during the time period May 1998 to October 2010 for various non-traumatic conditions causing increased intracranial pressure due to brain swelling. Complications were registered and patient data was analyzed in a search for predictive factors.

Results

Fifty out of the 74 patients (67.6 %) survived and underwent delayed cranioplasty. Of these, 47 were eligible for analysis. Six patients (12.8 %) developed SSI following the replacement of autologous cryopreserved bone, whereas bone resorption occurred in two patients (4.3 %). No factors predicted a statistically significant rate of SSI, however, prolonged procedural time and cardiovascular comorbidity tended to increase the risk of SSI.

Conclusions

SSI and bone flap resorption are the most frequent complications associated with the reimplantation of autologous cryopreserved bone after decompressive craniectomy. Prolonged procedural time and cardiovascular comorbidity tend to increase the risk of SSI.

Sevoflurane and propofol depolarize mitochondria in rat and human cerebrocortical synaptosomes by different mechanisms

BACKGROUND AND OBJECTIVES

The mitochondrial membrane potential drives the main functions of the mitochondria. Sevoflurane depolarizes neural mitochondria. There is still, however, limited information concerning the effect of anaesthetics on neural mitochondria in humans. The effect of sevoflurane and propofol on the intracellular Ca(2+) concentration [Ca(2+)](i) and the mitochondrial membrane potential (DeltaPsi(m)) was therefore compared in rat and human synaptosomes, and the changes were related to interventions in the electron transport chain.

METHODS

Synaptosomes from rat and human cerebral cortex were loaded with the fluorescent probes fura-2 ([Ca(2+)](i)) and JC-1 (DeltaPsi(m)) before exposure to sevoflurane 1 and 2 minimum alveolar concentration (MAC), and propofol 30 and 100 microM. The effect on the electron transport chain was investigated by blocking complex V.

RESULTS

Sevoflurane and propofol decreased DeltaPsi(m) in rat synaptosomes in a dose-dependent manner, and to the same extent by equipotent doses. Inhibition of complex V enhanced the depolarizing effect of sevoflurane 2 MAC, but not of propofol 100 microM. Neither sevoflurane nor propofol affected [Ca(2+)](i) significantly. Sevoflurane and propofol decreased DeltaPsi(m) in human synaptosomes to the same extent as in the rat experiments.

CONCLUSIONS

Sevoflurane and propofol at equipotent doses depolarize the mitochondria in rat and human nerve terminals to the same extent. The depolarizing effect of propofol on Psi(m) was more rapid in onset than that of sevoflurane. Whereas sevoflurane inhibits the respiratory chain sufficiently to cause ATP synthase reversal, the depolarizing effect of propofol seems to be related to inhibition of the respiratory chain from complex I to V.

Isoflurane-induced depolarization of neural mitochondria increases with age

BACKGROUND AND OBJECTIVES

The mitochondrial membrane potential (DeltaPsi(m)) drives the three fundamental functions of mitochondria, namely adenosine triphosphate (ATP) generation, Ca(2+) uptake/storage, and generation/detoxification of ROS. Isoflurane depolarizes neural mitochondria. The sensitivity for general anesthetics increases with age, but the mechanism for this age-related sensitivity is still unknown. We compared the effect of isoflurane on [Ca(2+)](i) and DeltaPsi(m) in isolated pre-synaptic terminals (synaptosomes) from neonatal, adolescent, and adult rats and the influence of interventions in the respiratory chain was assessed.

METHODS

Synaptosomes were loaded with the fluorescent probes fura-2 ([Ca(2+)](i)) and JC-1 (DeltaPsi(m)) and exposed to isoflurane 1 and 2 minimum alveolar concentration (MAC). The effect on the electron transport chain was investigated by blocking complexes I and V.

RESULTS

In neonatal rats isoflurane had no significant effect on DeltaPsi(m). In adolescent and adult synaptosomes, however, isoflurane 1 and 2 MAC decreased DeltaPsi(m). Isoflurane 2 MAC increased [Ca(2+)](i) in neonatal and adolescent rats, but not in adult synaptosomes. In Ca(2+)-depleted medium, isoflurane still decreased DeltaPsi(m), while [Ca(2+)](i) remained unaltered. By blocking complex V of the respiratory chain, the isoflurane-induced mitochondrial depolarization was enhanced in all age groups. Blocking complex I depolarized the mitochondria to the same extent as isoflurane 2 MAC, but without any additive effect.

CONCLUSIONS

The depolarizing effect of isoflurane on neural mitochondria is more pronounced in the adolescent and adult than in neonatal synaptosomes. The increased mitochondrial sensitivity with age seems to be related to the reversed function of the ATP synthase of the electron transport chain.

Volatile anaesthetics depolarize neural mitochondria by inhibiton of the electron transport chain

BACKGROUND

The mitochondrial membrane potential (DeltaPsim) controls the generation of adenosine triphosphate (ATP) and reactive oxygen species, and sequesteration of intracellular Ca2+[Ca2+]i. Clinical concentrations of sevoflurane affect the DeltaPsim in neural mitochondria, but the mechanisms remain elusive. The aim of the present study was to compare the effect of isoflurane and sevoflurane on DeltaPsim in rat pre-synaptic terminals (synaptosomes), and to investigate whether these agents affect DeltaPsim by inhibiting the respiratory chain.

METHODS

Synaptosomes were loaded with the fluorescent probes JC-1 (DeltaPsim) and Fura-2 ([Ca2+]i) and exposed to isoflurane or sevoflurane. The effect of the anaesthetics on the electron transport chain was investigated by blocking complex I and complex V.

RESULTS

Isoflurane 1 and 2 minimum alveolar concentration (MAC) decreased the normalized JC-1 ratio from 0.92 +/- 0.03 in control to 0.86 +/- 0.02 and 0.81 +/- 0.01, respectively, reflecting a depolarization of the mitochondrial membrane (n = 9). Isoflurane 2 MAC increased [Ca2+]i. In Ca2+-depleted medium, isoflurane still decreased DeltaPsim while [Ca2+]i remained unaltered. The effect of isoflurane was more pronounced than for sevoflurane. Blocking complex V of the respiratory chain enhanced the isoflurane- and sevoflurane-induced mitochondrial depolarization, whereas blocking complex I and V decreased DeltaPsim to the same extent in control, isoflurane and sevoflurane experiments.

CONCLUSIONS

Isoflurane and sevoflurane may act as metabolic inhibitors by depolarizing pre-synaptic mitochondria through inhibition of the electron transport chain, although isoflurane seems to inhibit mitochondrial function more significantly than sevoflurane. Both agents inhibit the respiratory chain sufficiently to cause ATP synthase reversal.

Sevoflurane depolarizes pre-synaptic mitochondria in the central nervous system

BACKGROUND

Volatile anaesthetics protect the heart from ischaemic injury by activating mitochondrial signalling pathways. The aim of this study was to test whether sevoflurane, which is increasingly used in neuroanaesthesia, affects mitochondrial function in the central nervous system by altering the mitochondrial membrane potential (DeltaPsi(m)).

METHODS

In order to correlate free cytosolic Ca(2+) ([Ca(2+)](i)) and DeltaPsi(m), rat neural presynaptic terminals (synaptosomes) were loaded with the fluorescent probes fura-2 and JC-1. During sevoflurane exposure, 4-aminopyridine (4-AP) 500 micro M to induce pre-synaptic membrane depolarization or carbonylcyanide-p-(trifluoromethoxy)-phenylhydrazone (FCCP) 1 micro M to induce maximum mitochondrial depolarization was added. In order to block mitochondrial ATP-regulated K(+)-channels (mitoK(ATP)), the antagonist 5-hydroxydecanoate (5-HD) 500 micro M was added.

RESULTS

In Ca(2+)-containing medium, both sevoflurane 1 and 2 MAC gradually decreased the normalized JC-1 ratio from 0.96 +/- 0.01 in control to 0.92 +/- 0.01 and 0.89 +/- 0.01, representing a depolarization of DeltaPsi(m) (n = 9, P < 0.05). Sevoflurane 2 MAC increased [Ca(2+)](i). In Ca(2+)-depleted medium, sevoflurane 1 and 2 MAC depolarized DeltaPsi(m), while [Ca(2+)](i) remained unaltered. Sevoflurane 2 MAC attenuated the 4-AP-induced depolarization of DeltaPsi(m). When mitoK(ATP) was blocked, the sevoflurane-induced depolarization of DeltaPsi(m) was attenuated, but not blocked. The depolarizing effect of sevoflurane on DeltaPsi(m) compared with FCCP was calculated to 13.2 +/- 1.3% in Ca(2+)-containing and 15.1 +/- 1.2% in Ca(2+)-depleted medium (n = 7).

CONCLUSIONS

Sevoflurane depolarizes DeltaPsi(m) in rat synaptosomes, and the effect is not dependent on Ca(2+)-influx to the cytosol. Opening of mitoK(ATP) is partly responsible for the depolarizing effect of sevoflurane.

MR imaging of ventriculus terminalis of the conus medullaris. A report of two operated patients and a review of the literature

We report on 2 patients in whom a cystic dilation of the conus medullaris was incidentally found at MR imaging carried out in the work-up for sciatica. The cysts were well circumscribed and had signal intensity identical to the CSF on both T1- and T2-weighted images. There was no evidence of contrast enhancement. None of the patients had specific symptoms related to the spinal cord. At surgery, no evidence of malignancy was seen in any of the patients. A benign cystic dilation, also called dilated ventriculus terminalis, occasionally can be seen in the conus medullaris as an incidental finding at thoracolumbar MR imaging. Unless the expansion per se indicates cyst drainage, these patients may be monitored by clinical and MR follow-up, avoiding surgery in a substantial number of cases.

The in vitro effects of crystalloids and colloids on coagulation

Classically haemodilution is regarded as causing coagulopathy. However, haemodilution with saline seems to cause a hypercoagulable state both in vivo and in vitro. The aim of the present study was to measure the effect of mild to severe haemodilution using thrombelastography. Blood samples were taken in 12 healthy volunteers and divided into seven aliquots. One aliquot was undiluted and acted as control. The other six were diluted with normal saline, Ringer Acetate, 4% albumin, Dextran 70, 6% and 10% hydroxyethylstarch to 10%, 20%, 40%, 50% and 60% dilution. The dilution was checked by measuring the haemoglobin concentration. Each aliquot was placed in a temperature-controlled thrombelastography channel. Increased coagulation activity, as measured by thrombelastography changes, was detected at low and medium levels of dilution with all the tested solutions. At more than 40% dilution, coagulation returned to normal while in the case of dextran and hydroxyethylstarch coagulopathy developed. For crystalloids and albumin,dilution had to exceed 50% before coagulation was impaired. If these findings can be reproduced in vivo, they may have implications for transfusion practice and prophylaxis against thrombosis.

The effect of sevoflurane on glutamate release and uptake in rat cerebrocortical presynaptic terminals

BACKGROUND

Volatile anaesthetics exert their effect in the brain mainly by reducing synaptic excitability. Isoflurane abates excitation by reducing the release and increasing the uptake of transmitter glutamate into the presynaptic terminal. The exact molecular mechanisms exerting these effects, however, are not clear. Voltage-gated calcium channels have been proposed as the pharmacological target. The present study examines the effect of sevoflurane on synaptic glutamate release and free cytosolic calcium and the effect on high- and low-affinity uptake of L-glutamate using isolated presynaptic terminals prepared from rat cerebral cortex.

METHODS

Released glutamate was measured fluorometrically in a spectrophotometer as the fluorescence of NADPH and calcium as the fluorescence of fura-2. 4-aminopyridine was used to induce membrane depolarization. Glutamate uptake was measured in a series of different concentrations of L-glutamate corresponding to the high- and the low- affinity uptake systems adding a fixed concentration og radiolabelled glutamate. The labelling was measured by counting disintegrations per min in a beta-scintillation counter.

RESULTS

Sevoflurane reduced the calcium-dependent glutamate release in a dose-dependent manner as sevoflurane 1.5, 2.5 and 4.0% reduced the release by 58, 69 and 94%, respectively (P<0.05). Membrane depolarization induced an increase in free cytosolic calcium by 25%. Sevoflurane did not affect this increase. Neither the high- nor the low-affinity uptake transporter systems are affected by the anaesthetic.

CONCLUSION

These results indicate that different volatile anaesthetics may act differently on the presynaptic terminal. The exact modes of action have to be further investigated.

Measured increase in intracellular Ca(2+) during stimulated release of endogenous glutamate from human cerebrocortical synaptosomes

Presynaptic terminals (synaptosomes) prepared from guinea pig and rat cerebral cortex release endogenous glutamate in a Ca(2+)-dependent manner in response to membrane depolarisation. In the present study, synaptosomes were prepared from human cerebral cortex removed in association with temporal lobe resections in epileptic patients. The cytosolic free Ca(2+) concentration increased from 474+/-66 before to 649+/-89 nM after 2 min depolarisation. The basal level of free cytosolic Ca(2+) is higher and the increase in response to depolarisation is more pronounced in human synaptosomes than observed in animal experiments. The Ca(2+)-dependent glutamate release, estimated as the difference between total - and the Ca(2+)-independent glutamate release, increased from 0 to 5.4+/-1.9 nmol/mg protein. The released amount of glutamate is larger than reported in animal models. These results demonstrate that membrane depolarisation of synaptosomes from human brain evokes a rapid rise in cytosolic free Ca(2+) and a more prolonged rise in synaptic, Ca(2+)-dependent glutamate release.

[Early postoperative complications in carotid surgery]

Carotid endarterectomy has a documented stroke preventing effect in symptomatic high-grade carotid stenosis when the rate of serious complications is below 6%. In the period 1986-96, 160 procedures were performed on 150 patients at the Department of Neurosurgery, Ullevål Hospital. Oslo. The indication for surgery was hemispheric transient ischemic attack and/or amaurosis fugax in 137 patients and/or minor stroke in 49 in addition to a high-grade stenosis. Mean age was 61 years (42-74 years). One patient (0.6%) died four hours after surgery. Three patients (1.9%) suffered disabling postoperative stroke. The rate of serious complications was thus 2.5%. In addition, nine patients experienced minor and temporary paresis. Three patients were reoperated for haematoma and one for wound infection. Our surgical morbidity and mortality rate is comparable to larger series.

[Continuous intrathecal infusion of baclofen. A new therapeutic method for spasticity]

Intrathecal administration of baclofen is now generally accepted as a powerful treatment of spasticity caused by spinal lesions. 35 patients with severe spasticity, 29 of spinal origin and six of supraspinal origin resistant to conservative treatment, had a programmable pump (Synchromed, Medtronic) for continuous intrathecal baclofen infusion implanted. The patients were followed-up for an average of 29 months (0-68). The initial effect of the treatment was positive for all patients; spasms were less frequent, there was remission of pain caused by cramps, and in some cases improved ambulation. In five patients, however, the pump was later removed: in two patients the pump ceased to be effective, two patients became infected, and one experienced multiple catheter problems. Problems with the catheter was the most common complication experienced, and this was seen in nine patients. Three patients died of the underlying disease. The majority of patients became accommodated to intrathecal baclofen and it was necessary to administer increasingly larger doses to maintain the clinical effect. Long-term control of spinal spasticity by intrathecal baclofen can be achieved in most patients, but close follow-up is necessary for assessing efficacy and refilling the pump.

The effect of isoflurane on brain amino acid release and tissue content induced by energy deprivation

This article describes the effect of isoflurane on amino acid release and tissue content induced by energy deprivation in slices of rat hippocampus. Energy deprivation (95% N2 / 5% CO2 and glucose free medium) (ED) induced an increase in the release of all amino acids measured, with the exception of glutamine. The tissue content of all amino acids except gamma-aminobutyric acid (GABA) and arginine was concomitantly reduced. Isoflurane (1.5% and 3.0%) reduced glutamate release during ED by 27% and 28% (p < 0.05 as compared with release without isoflurane), respectively, whereas the tissue content was slightly increased. Similarly, GABA release was reduced by 25% and 25% (p < 0.05 as compared with release without isoflurane) accompanied by an insignificant enhancement in tissue content as compared with ED without isoflurane. Isoflurane reduced the release of taurine and most of the other amino acids. The total amount of all amino acids (both released and retained) was not significantly altered by the anesthetic. These observations demonstrate that isoflurane can modify the changes in amino acid handling induced by energy deprivation.

Effect of isoflurane on release and uptake of gamma-aminobutyric acid from rat cortical synaptosomes

We have studied the effect of isoflurane on potassium-evoked release and high-affinity uptake of gamma-aminobutyric acid (GABA) in rat cortical synaptosomes. Isoflurane 1.5% and 3% increased calcium-dependent release by 38% and 36% of control values, respectively (P < 0.05). Calcium-independent release was reduced correspondingly by 24% and 26% (P < 0.05). High-affinity uptake of GABA was not affected by isoflurane. The findings of increased synaptic GABA release combined with unaltered uptake suggest that isoflurane increases GABA in the synaptic cleft and thus may enhance inhibition.

Chloride influx during cerebral energy deprivation

The purpose of the present study was to investigate the possible role of chloride influx and GABA release during cerebral energy deprivation (ED). The functional activity measured by evoked activity (population spike) in hippocampal slices was recorded during nine minutes of ED and 60 minutes recovery. Treatment groups were exposed to ED following administration of the GABAA antagonist penicillin G (pc G) or substitution of extracellular chloride. The release of glutamate and GABA was measured by HPLC. The efflux of 36Cl from preloaded slices was measured during ED with and without blocking the GABAA receptor. The population spike disappeared during ED, and there was a marked release of GABA and glutamate. During recovery the population spike recovered partially. Both application of pc G and substitution of extracellular chloride during ED improved population spike recovery. Uptake of radiolabeled chloride was significantly reduced by pc G. Glutamate release, but not GABA, was significantly reduced by chloride substitution. These results indicate a possible role of chloride mediated injury during ED, and suggest that chloride entry may partly occur through ligand-operated channels. Furthermore there may be an early chloride dependent release of glutamate during cerebral ischemia, whereas later release seems to be chloride independent.

Isoflurane reduces synaptic glutamate release without changing cytosolic free calcium in isolated nerve terminals

The molecular mechanism of volatile anaesthetic action on presynaptic glutamate release is not clear. An inhibitory effect on voltage-gated calcium channels has been proposed. The present study examines the effect of isoflurane on cytosolic free calcium and synaptic glutamate release from isolated nerve terminals. Synaptosomes from rat cerebral cortex were used. Glutamate was measured with a continuous fluorometric measurement in a spectrophotometer as the fluorescence of NADPH and calcium as the fluorescence of fura-2. Isoflurane reduced the calcium-dependent glutamate release evoked by membrane depolarization with 4-aminopyridine in an inversely dose-dependent manner. The glutamate release was reduced by 56, 43 and 36% in response to isoflurane 0.5, 1.5 and 3.0%, respectively (for all: P < 0.05). Membrane depolarization evoked a rise in cytosolic free calcium of approximately 34%. Addition of isoflurane (0.5, 1.5 and 3.0%) produced no significant change in cytosolic free calcium. These results indicate that the isoflurane-induced reduction in presynaptic glutamate release is caused by other mechanisms than blocking voltage-gated calcium channels. As the release is inversely dose-dependent, two or more mechanisms could be involved.

[Intraspinal hematoma after thoracic epidural analgesia]

In one year three patients were operated on for spinal haematomas following thoracic epidural analgesia. All three patients experienced back pain and developed progressive paraparesis, one in connection with insertion of the catheter and two after its removal. A spinal block was visualized using MRI in two patients and myelography in one. The patients were operated on with posterior decompression. In two patients an epidural haematoma was evacuated. Both patients recovered neurologic function, one completely. The third patient, who had a subarachnoidal hemorrhage and an intramedullar haematoma, remained paralytic.

Survival, prognostic factors, and therapeutic efficacy in low-grade glioma: a retrospective study in 379 patients

PURPOSE

We report survival, prognostic factors, and treatment efficacy in low-grade glioma.

PATIENTS AND METHODS

A total of 379 patients with histologic intracranial low-grade glioma received post-operative radiotherapy (n = 361) and intraarterial carmustine (BCNU) chemotherapy (n = 153). Overall survival and prognostic factors were evaluated with the SPSS statistical program (SPSS Inc, Chicago, IL).

RESULTS

Median survival (all patients) was 100 months (95% confidence interval [CI], B7 to 113); in age group 0 to 19 years (n = 41), 226 months; in age group 20 to 49 years (n = 263), 106 months; in age group 50 to 59 years (n = 49), 76 months; and for older patients (n = 26), 39 months. Projected survival at 10 and 15 years was 42% and 29%, respectively. Patient age, World Health Organization (WHO) performance status, tumor computed tomography (CT) contrast enhancement, mental changes, or initial corticosteroid dependency were significant independent prognostic factors (p < .05), while histologic subgroup, focal deficits, presence of seizures, prediagnostic symptom duration, tumor category, and tumor stage were not. Patients aged 20 to 49 years with no independent negative prognostic factors (n = 132) had a median survival time of 139 months versus 41 months in patients with two or more factors (n = 33). Patients who presented with symptoms of expansion (n = 97) survived longer when resected (P < .03); otherwise no survival benefit was associated with initial tumor resection compared with biopsy. Intraarterial chemotherapy and radiation doses more than 55 Gy were not associated with prolonged survival. Among 66 reoperated patients, 45% progressed to high-grade histology within 25 months.

CONCLUSION

Prognosis in low-grade glioma following postoperative radiotherapy seems largely determined by the inherent biology of the glioma and patient age at diagnosis.

Isoflurane increases the uptake of glutamate in synaptosomes from rat cerebral cortex

We have studied the effect of increasing concentrations of isoflurane on high- and low-affinity uptake of L-glutamate using synaptosomes from rat cerebral cortex. In the high-affinity uptake range, 0.5% isoflurane had no effect on uptake velocity, while 1.5% and 3.0% isoflurane caused an increase in mean Vmax to 131 (SEM 54) and 210 (103)% of control, respectively. There was no significant change in the K(m) value. Vmax and K(m) values for low-affinity uptake of L-glutamate were unchanged by 1.5% isoflurane. These results provide evidence for an isoflurane-induced increase in high-affinity uptake of glutamate into presynaptic terminals. This effect may contribute to a reduction of transmitter in the synaptic cleft and thereby decreased excitatory synaptic transmission.

[Embolization of cerebral aneurysms. A new therapeutic possibility]

Treatment of cerebral aneurysms with Guglielmi Detachable Coils (GDC) was performed for the first time in Scandinavia in 1992. The experience at Ullevål University Clinic from 1994 to 1996 comprises 27 surgically inoperable aneurysms. Successful embolization was performed in 20 patients. No complications were seen during the procedure. However, renewed bleeding with fatal outcome occurred in one patient. In accordance with other colleagues we consider this treatment to be unsuitable for wide neck aneurysms (> 5 mm). For this reason seven patients were not treated. We conclude that GDC embolization seems to be an effective therapy for selected inoperable aneurysms. In the near future the method will probably be used to treat some of the surgically operable aneurysms as well.

[Prognosis in primary tumors of the central nervous system. A patient material from the Norwegian Radium Hospital 1960-94]

We present the results of a retrospective survey of 1,218 patients treated at the Norwegian Radium Hospital during the years 1980-94 for primary tumours of the central nervous system. Median survival for patients with glioblastoma (n = 492) was 12 months, for patients with anaplastic astrocytoma (n = 83) 25 months, astrocytoma (n = 260) 95 months, oligodendroglioma (n = 85) 74 months, mixed glioma (n = 68) 65 months, and medulloblastoma (n = 53) 109 months. Median survival for patients with brain stem tumours (n = 37) was nine months, while 74% of patients with tumours in the pineal region (n = 38) survived for five years. The histology and localisation of the tumour, as well as age and functional status, are important prognostic factors for survival in patients with primary CNS tumours.

Amino-acid release from human cerebral cortex during simulated ischaemia in vitro

The aim of the present study was to investigate the release of amino-acids in human cerebral cortex during membrane depolarization and simulated ischaemia (energy deprivation). Superfluous tissue from temporal Iobe resections for epilepsy was cut into 500 microns thick slices and incubated in vitro. Membrane depolarization with 50 mM K+ caused a release of glutamate, aspartate, GABA and glycine, but not glutamine or leucine. The release of glutamate and GABA was Ca(++)-dependent. Slices were exposed to simulated ischaemia (energy deprivation; ED) by combined glucose/oxygen deprivation. This caused a Ca(++)-independent release of glutamate, aspartate, GABA, glycine, and taurine which started after 8 min, peaked at the end or shortly after the 27 min period of ED, and returned to control levels within 11 min following termination of ED. Preloaded D-[3H]aspartate was released both during K(+)-stimulation and ED. Release of D-[3H]aspartate during ED was delayed compared to glutamate supporting an initial phase of synaptic glutamate release. Uptake of L-[3H]glutamate was increased during the period of glutamate release, suggesting passive diffusion across the cell membrane or enhanced transport efficacy in cellular elements with functioning uptake mechanisms.

Changes in amino acid release and membrane potential during cerebral hypoxia and glucose deprivation

Excessive release of glutamate is believed to play a major role in the susceptibility of neurons to ischaemia. Whether the glutamate release is the primary event or occurs in response to electrophysiologic alterations has not been clarified. In the present study, the amino acid release was therefore correlated to changes in electrophysiological parameters and energy status during conditions of low oxygen tension and varying glucose concentrations in rat hippocampal slices. Plain hypoxia failed to produce glutamate release. All neurons underwent, however, a slow depolarization causing most of the neurons to lose their membrane potential within 10 minutes. By restoring the membrane potential to resting level by current injection, the neurons could still be activated synaptically and respond to transmitter application. Following reoxygenation most of the cells regained their resting membrane potential, but showed reduced excitability. When the slices were exposed to hypoxia combined with glucose deprivation (simulated ischaemia), there was a pronounced increase in the glutamate release. This glutamate release was always preceded by a fast anoxic depolarization. Whereas hypoxia reduced the ATP content only to approximately 50%, ATP was depleted in slices exposed to simulated ischaemia. The results demonstrate that although the neurons lose their membrane potential completely during hypoxia, there is no glutamate release. A fast anoxic depolarization provoked by simulated ischaemia, however, is always followed by glutamate release, probably due to a more severe ATP depletion.

[Fatal cerebral hemorrhage in young amphetamine addicts]

Abuse of amphetamine, cocaine and related compounds has become an important risk factor for intracerebral haemorrhage in young adults. Five fatal cases of intracerebral haemorrhage following use of amphetamine are described. The symptoms occurred few hours after amphetamine intake, and all patients had considerably increased blood pressure upon admission. Autopsy was performed on four of the patients and did not reveal any predisposing factors for haemorrhage, such as trauma, vascular malformations or vasculitis. Cerebral CT should always be performed when severe headache and/or altered consciousness occur in relation to abuse of amphetamine-like compounds. Intracerebral haemorrhage in young adults may indicate abuse of psychoactive drugs.

Volatile anaesthetics: cellular mechanisms of action

The mechanisms by which volatile anaesthetics act in the central nervous system are reviewed. The main cellular targets are excitatory synapses and the cell membrane of the neuronal cell body/dendrite, although there also appears to be a significant effect on thin unmyelinated fibres. Experiments quantifying these effects have shown that 1 MAC isoflurane reduces the activity in afferent fibres by 18%, excitatory synapses by 27% and postsynaptic neurones by 24%. Two important effects observed when recording from individual neurones are hyperpolarization of the cell membrane by an enhanced potassium conductance and increased threshold for initiation of action potentials. Excitatory synaptic transmission is most probably reduced due to a decreased release of transmitter from presynaptic terminals. Antagonistic and biphasic effects are often seen, for instance depression of both inhibitory and excitatory transmission and depolarization-hyperpolarization of the postsynaptic membrane.

Changes in evoked potentials and amino acid content during fluorocitrate action studied in rat hippocampal cortex

Fluorocitrate inhibits the glial tricarboxylic acid cycle and thereby the synthesis of glutamine, which is the main precursor for transmitter glutamate. We investigated the possibility that there is a functional correlate to fluorocitrate action by recording evoked field potentials in rat hippocampal slices. The excitatory postsynaptic potential (field-EPSP) was markedly depressed after 7-8 h of fluorocitrate action. The population spike was also reduced, but a major part of the reduction may be the result of weaker synaptic activation rather than reduced excitability of the postsynaptic cells. The activity of thin unmyelinated fibres was only slightly affected. Preceding the changes in the field-EPSP there was a decrease in the glutamine content in the fluorocitrate treated slices relative to controls. Only a small decrease in tissue glutamate was seen concomitantly with the synaptic failure, probably because the transmitter pool of glutamate in those fibres stimulated makes little contribution to the total tissue glutamate.

Redistribution of glutamate and glutamine in slices of human neocortex exposed to combined hypoxia and glucose deprivation in vitro

This study was undertaken to elucidate the roles of neurons and glial cells in the handling of glutamate and glutamine, a glutamate precursor, during cerebral ischemia. Slices (400-600 microns) from human neocortex obtained during surgery for epilepsy or brain tumors were incubated in artificial cerebrospinal fluid and subjected to 30 min of combined hypoxia and glucose deprivation (an in vitro model of brain ischemia). These slices, and control slices that had not been subjected to "ischemic" conditions, were then fixed and embedded. Ultrathin sections were processed according to a postembedding immunocytochemical method with polyclonal antibodies raised against glutamate or glutamine, followed by colloidal gold-labeled secondary antibodies. The gold particle densities over various tissue profiles were calculated from electron micrographs using a specially designed computer program. Combined hypoxia and glucose deprivation caused a reduced glutamate immunolabeling in neuronal somata, while that of glial processes increased. Following 1 h of recovery, the glutamate labeling of neuronal somata declined further to very low values, compared to control slices. The glutamate labeling of glial cells returned to normal levels following recovery. In axon terminals, no consistent change in the level of glutamate immunolabeling was observed. Immunolabeling of glutamine was low in both nerve terminals and neuronal somata in normal slices and was reduced to nondetectable levels in nerve terminals upon hypoxia and glucose deprivation. This treatment was also associated with a reduced glutamine immunolabeling in glial cells. Reversed glutamate uptake due to perturbations of the transmembrane ion concentrations and membrane potential probably contributes to the loss of neuronal glutamate under "ischemic" conditions. The increased glutamate labeling of glial cells under the same conditions can best be explained by assuming that glial cells resist a reversal of glutamate uptake, and that their ability to convert glutamate into glutamine is compromised due to the energy failure. The persistence of a nerve terminal pool of glutamate is compatible with recent biochemical data indicating that the exocytotic glutamate release is contingent on an adequate energy supply and therefore impeded during ischemia.

[Action mechanisms of intravenous anesthetics]

Intravenous anaesthetic agents depress the activity of the brain by acting on receptor-operated ion channels. Barbiturates enhance gamma-aminobutyric acid (GABA)-mediated inhibition, depress glutamate-mediated excitation, and hyperpolarize the membrane by increased potassium conductance. Benzodiazepines facilitate GABA-mediated inhibition by binding to a benzodiazepine recognition site on the GABA receptor complex, and affect potassium channels. Opioids bind to opioid receptors and hyperpolarize the membrane by enhanced potassium and calcium conductances. Ketamine depresses excitatory synaptic transmission by acting on glutamate receptors of the N-methyl-D-aspartate (NMDA) subtype. Propofol acts at a recognition site on the GABA receptor, which differs from the binding sites of both barbiturates and benzodiazepines.

Changes in inhibitory synaptic transmission induced by isoflurane studied in rat hippocampal slices

The effect of isoflurane on inhibitory postsynaptic potentials (IPSPs) was studied in rat hippocampal slices by intracellular recordings from pyramidal neurons (n = 34). The amplitude of the IPSP was transiently increased and subsequently reduced in a dose-dependent manner. The duration of the IPSP was increased. The reduction in the IPSP persisted after correction was made for the anesthetic-induced hyperpolarization. The reversal potential for the IPSP was slightly displaced in the depolarizing direction. The depolarizing gamma-aminobutyric acid (GABA) response was unaltered, while the hyperpolarizing GABA response was reduced, suggesting a postsynaptic action. The reduction in the IPSP produced by isoflurane is at least partly due to an altered reversal potential for the IPSP (EIPSP).

An experimental study of the effect of isoflurane on epileptiform bursts

The effect of isoflurane on penicillin- and picrotoxin-induced epileptiform activity was tested using hippocampal slice preparations. Isoflurane reduced both the frequency of spontaneous epileptiform bursts and the number of population spikes within each burst in a dose-dependent manner. The last population spikes in the burst were most sensitive to the anesthetic, whereas the first 4-6 spikes were quite resistant and persisted until spontaneous activity was abolished at 3% isoflurane. Isoflurane increased the stimulus current required to evoke epileptiform bursts and shifted the relationship between stimulus current and population spike amplitude to the right. At 3% isoflurane, a dose that usually causes iso-electric EEG and abolishes all spontaneous epileptiform activity, responses could still be evoked, and then invariably had an epileptiform pattern. The maximum response was reduced compared to control and 1.5% isoflurane. With isoflurane there was a reduced tendency for activity to be transmitted from one region within the hippocampus to the other. This effect was also dose-dependent. However, transmitted activity always retained a typical epileptiform character, although the number of population spikes within a train to some extent decreased with increasing concentrations of isoflurane.

The effect of isoflurane on excitatory synaptic transmission in the rat hippocampus

The purpose of this investigation was to study the effect of isoflurane on excitatory synaptic transmission. Rat hippocampal slices maintained in vitro were used as a model. Isoflurane caused a dose-dependent reduction of the excitatory postsynaptic potential (EPSP); 1.5% isoflurane reduced the EPSP by 35 +/- 9% (mean +/- s.d.) and 3% by 57 +/- 11%. Neither spontaneous nor potassium-stimulated efflux of the glutamate analogue D-(3H)aspartate was changed, but the content of D-(3H)aspartate in slices loaded during isoflurane was reduced to 83 +/- 12% of control (P less than 0.05). The intracellularly recorded response to direct application of glutamate increased by 37 +/- 20% during isoflurane (3%) and 50 +/- 5% during halothane (2%). Isoflurane (3%) enhanced the response to the glutamate receptor agonist quisqualate by 44 +/- 19%, whereas the N-methyl-D-aspartate response was unchanged. Isoflurane enhanced the tetanic depression of the population spike. The present results suggest that isoflurane reduces excitatory synaptic transmission by a presynaptic mechanism.

Temperature sensitivity of thin unmyelinated fibers in rat hippocampal cortex

The effect of changes in temperature on the activity of thin intracortical unmyelinated fibers was investigated in rat hippocampal slices. The amplitude of the presynaptic volley was increased by 40% when the temperature was raised from 23 degrees C to 30 degrees C, whereas the area of the presynaptic volley was reduced. Increasing the temperature above 30 degrees C was without further effect on the amplitude. The conduction velocity was 0.3 m.s-1 at 35 degrees C and 0.1 m.s-1 at 12 degrees C. The Q10 of velocity (25 degrees C-35 degrees C) was 1.6.

Failure of allopurinol to protect against cerebral injury when given after the start of hypoxia

One cause of ischemic brain injury is free radical formation during recirculation. Allopurinol inhibits xanthine oxidase, an important source of free oxygen radicals. It is known that allopurinol pre-treatment has a protective action during cerebral ischemia. In the present study we exposed slices from the rat hippocampus to 9 minutes of hypoxia to test whether it is sufficient that allopurinol is present in the tissue at the time of reoxygenation. Forty-six slices loaded with allopurinol (10(-5) M) prior to reoxygenation (during hypoxia) were compared to 34 control slices. The response of the pyramidal cell population to orthodromic stimulation was reduced in both groups and there was not a significant difference between the two groups.

Mechanisms concerned in the direct effect of isoflurane on rat hippocampal and human neocortical neurons

The effect of isoflurane on postsynaptic neurons was studied by intracellular recordings from rat hippocampus and human neocortex in vitro. Isoflurane caused a hyperpolarization of the cell membrane. The hyperpolarization was reversed (although incompletely in some neurons) by increasing the membrane potential. The reversal potential was -80 +/- 12 mV (mean +/- S.D.) or 12 +/- 6 mV negative to the resting membrane potential. Potassium channel blockers reduced the isoflurane-induced hyperpolarization, while chloride loading was without effect. The transient depolarization preceding the hyperpolarization in some of the neurons was not reversed by hyperpolarization. The action potential was prolonged by 19 +/- 3% due to a slower rate of rise. The rise time was almost doubled. Firing threshold was increased by 4 +/- 3 mV (relative to the reference electrode). Subthreshold inward rectification was reduced or abolished. Some cells showed subthreshold outward rectification during isoflurane administration. These results suggest that isoflurane depressed neuronal excitability by (1) hyperpolarizing the cell membrane, at least partly by an increase in potassium conductance, (2) slowing the rate of rise of the action potential, presumably due to interference with the fast sodium channel, (3) decreasing subthreshold inward rectification and (4) increasing firing threshold.

Intracellular recordings from neurones in rat cerebral cortex during hypoxia

Neurones in rat hippocampal cortex were exposed to hypoxia while their membrane properties and responses to different kinds of stimuli were recorded with an intracellular electrode. The initial changes consisted of a small depolarization followed by a hyperpolarization. Following these early events the neurones lost their membrane potential through a large depolarization. Similar changes were observed in neurones where the Na/K-ATPase was blocked by ouabain. Responses to direct application of the transmitters GABA and glutamate, which was lost at this point, were restored by passive reestablishment of the membrane potential with current through the intracellular electrode.

Isoflurane hyperpolarizes neurones in rat and human cerebral cortex

The effect of the anaesthetic gas isoflurane was studied by intracellular recordings in neurones from rat hippocampal cortex and neurones from human neocortex in vitro. Anaesthetic concentrations of isoflurane abolished spontaneous activity and reduced synaptically evoked activity without rendering individual cells inexcitable or preventing evoked synaptic activity to increased afferent input. Induced epileptiform activity was not observed. Isoflurane reversibly hyperpolarized the cell membrane in a dose-dependent manner, isoflurane 1.5, 3 and 5% causing 4 +/- 1, 6 +/- 2 and 8 +/- 2 mV (mean +/- SD) hyperpolarization, respectively. The hyperpolarization was accompanied by a reduction in the input resistance, 18 +/- 3% for 3% isoflurane. The effects remained unchanged after synaptic transmission was blocked. Five experiments with intracellular recordings from human cortical neurones in vitro showed identical results.

Reduced hippocampal field potentials during administration of fluoropyrimidines in vitro

Toxic effects on the central nervous system have been reported in patients treated with fluoropyrimidines for cancer. In the present study we have investigated the earliest effects of these drugs at the cellular level using slices of hippocampal cortex maintained in vitro. Doxyfluridine (5'-dFUrd; 50 mg/l and 500 mg/l) caused a dose dependent, reversible depression of neuronal activity. The main effect was on the pyramidal cells (population spike reduced by 14 and 25% respectively) and the afferent unmyelinated fibres (afferent fibre volley reduced by 7 and 12% respectively). Excitatory synaptic transmission was affected only by the highest concentration (field-EPSP reduced by 10%). 5-FU caused similar but less marked changes. The drugs did not cause epileptiform activity.

Isoflurane effects in rat hippocampal cortex: a quantitative evaluation of different cellular sites of action

In order to evaluate quantitatively the effects of an inhalation anaesthetic on neuronal excitability and on synaptic transmission in the central nervous system, we have examined the action of isoflurane on slices from rat hippocampal cortex. Isoflurane 1.5% (1.38% anaesthetize 50% of tested rats (MAC)) reduced orthodromically evoked activity in pyramidal cells by 62%. This was due to the combined effects on afferent fibres, excitatory synapses and pyramidal cells. The effect on the postsynaptic neurones was almost as strong as the effect on the excitatory synapses: the population spike evoked by a given synaptic current was reduced by 24%, and the field-EPSP in response to a given afferent fibre volley by 27%. The presynaptic fibre volley was reduced by 17%.

The effect of isoflurane on unmyelinated and myelinated fibres in the rat brain

The effect of isoflurane on unmyelinated and myelinated fibres of the rat brain was investigated in vitro. The amplitude of the unmyelinated fibre potential (the prevolley of the hippocampal CA1 region) was reduced in a dose-dependent manner with increasing isoflurane concentrations (up to 5%). The conduction velocity was slightly decreased. The minimal alveolar concentration (MAC) anesthetizing 50% of the animals is 1.38%. At this concentration the presynaptic volley was reduced by 18% and the conduction velocity was decreased by about 1%. The effect on myelinated fibres (fimbria) was small and significantly different from the effect on unmyelinated fibres (P = 0.03 and 0.005 at 1 and 2% isoflurane, respectively.