Anaesthetic neurotoxicity and neuroplasticity: an expert group report and statement based on the BJA Salzburg Seminar.

Although previously considered entirely reversible, general anaesthesia is now being viewed as a potentially significant risk to cognitive performance at both extremes of age. A large body of preclinical as well as some retrospective clinical evidence suggest that exposure to general anaesthesia could be detrimental to cognitive development in young subjects, and might also contribute to accelerated cognitive decline in the elderly. A group of experts in anaesthetic neuropharmacology and neurotoxicity convened in Salzburg, Austria for the BJA Salzburg Seminar on Anaesthetic Neurotoxicity and Neuroplasticity. This focused workshop was sponsored by the British Journal of Anaesthesia to review and critically assess currently available evidence from animal and human studies, and to consider the direction of future research. It was concluded that mounting evidence from preclinical studies reveals general anaesthetics to be powerful modulators of neuronal development and function, which could contribute to detrimental behavioural outcomes. However, definitive clinical data remain elusive. Since general anaesthesia often cannot be avoided regardless of patient age, it is important to understand the complex mechanisms and effects involved in anaesthesia-induced neurotoxicity, and to develop strategies for avoiding or limiting potential brain injury through evidence-based approaches.

Distinct long-term neurocognitive outcomes after equipotent sevoflurane or isoflurane anaesthesia in immature rats.

BACKGROUND: Many anaesthetics when given to young animals cause cell death and learning deficits that persist until much later in life. Recent attempts to compare the relative safety or toxicity between different agents have not adequately controlled for the relative dose of anaesthetic given, thereby making direct comparisons difficult. METHODS: Isoflurane or sevoflurane were given at 1 minimum alveolar concentration (MAC) for 4 h to postnatal day 7 (P7) rat pups. Beginning at P75 these animals underwent fear conditioning and at P83 Morris water maze testing to assess working memory, short-term memory and early long-term memory using delays of 1 min, 1 h, and 4 h. RESULTS: No difference between groups was seen in fear conditioning experiments. Morris water maze learning was equivalent between groups, and no difference was seen in working memory. Sevoflurane-treated animals had a deficit in early long-term memory, and isoflurane-treated animals had a deficit in both short-term and early long-term memory. CONCLUSIONS: Both isoflurane and sevoflurane delivered at 1 MAC for 4 h to immature rats caused a deficit in long-term memory. Isoflurane also caused a deficit in short-term memory. Isoflurane might be more detrimental than sevoflurane in very young animals.

A randomized comparison of a five-minute versus fifteen-minute lockout interval for PCEA during labor.

BACKGROUND: The best combination of bolus size and lockout interval for patient-controlled epidural analgesia (PCEA) is not known. This study compared a 5-min with a 15-min lockout interval. METHODS: Parturients were randomly assigned to receive PCEA with either a 5-min or a 15-min interval. All had a 15-mL loading dose, continuous background infusion 6 mL/h of 0.125% bupivacaine plus fentanyl 2 mug/mL, PCEA bolus volume 5 mL, maximum hourly dose 26 mL. Visual analogue scores for pain, nausea and pruritus, sensory levels to ice, sacral analgesia, motor power, blood pressure and fetal heart rate were assessed pre-epidural and regularly thereafter until delivery. The numbers of boluses and attempts and patient satisfaction were recorded. RESULTS: 29 patients were assigned to the 5-min group and 31 to the 15-min group, but the 15-min group contained twice as many nulliparous women. Side-effect and complication rates did not differ between groups. VAS pain scores were reduced from a median of 79 in the 15-min group and 82 in the 5-min group to a median of zero 30 min after epidural insertion. Bolus/attempt ratio was 0.88 in the 5-min vs. 0.70 in the 15-min group. The numbers of requests for physician intervention were similar. No differences in pain scores, side-effects, drug use or patient satisfaction were demonstrated. CONCLUSION: The 5-min lockout interval appears the more efficient and has been used safely in our practice for 15,000 parturients, although a larger study is required to confirm the relative efficacy, efficiency and safety of this regimen.

Cholinomimetics increase glutamate outflow via an action on the corticostriatal pathway: implications for Alzheimer's disease.

Physostigmine, the acetylcholinesterase inhibitor (0.3 mg/kg, i.m.), increased extracellular glutamate but not aspartate concentrations in the striatum of anaesthetised rats, determined using microdialysis and HPLC. The rise was both tetrodotoxin and calcium dependent. In contrast, neither physostigmine (10 microM) added to the perfusion fluid nor vehicle (injected intramuscularly) affected amino acid concentrations. To obtain evidence that the action of acetylcholine was to modulate positively cortical pyramidal neurone activity via the M1 receptor, the selective M1 agonist PD 142505-0028 (10 microM) was topically applied to the frontal cortex. Like physostigmine, PD 142505-0028 rapidly increased glutamate but not aspartate concentrations in the striatum. Moreover, the effect of intramuscular physostigmine was blocked by a topically applied M1 antagonist. These new data add to our hypothesis that cholinomimetics increase pyramidal neurone function.

NMDA-induced glutamate and aspartate release from rat cortical pyramidal neurones: evidence for modulation by a 5-HT1A antagonist.

1. We have investigated an aspect of the regulation of cortical pyramidal neurone activity. Microdialysis was used to assess whether topical application of drugs (in 10 microliter) to fill a burr hole over the frontal cortex, where part of the corticostriatal pathway originates, would change concentrations of the excitatory amino acids glutamate and aspartate in the striatum of the anaesthetized rat. 2. Topical application of N-methyl-D-aspartate (NMDA, 2 and 20 mM) dose-dependently increased glutamate and aspartate concentrations in the striatum. Coapplication of tetrodotoxin (10 microM) blocked the NMDA-evoked rise in these amino acids. A calcium-free medium, perfused through the probe also blocked the rise, indicating that it was due to an exocytotic mechanism in the striatum. 3. It was hypothesized that the rise observed was due to an increase in the activity of the corticostriatal pathway. As 5-hydroxytryptamine1A (5-HT1A) receptors are enriched on cell bodies of corticostriatal neurones, a selective 5-HT1A-antagonist (WAY 100135) was coapplied with the lower dose of NMDA. Compared to NMDA alone, coapplication of 50 microM WAY 100135 significantly increased glutamate release. This effect was sensitive to tetrodotoxin and calcium-dependent. Application of 50 microM WAY 100135 alone significantly enhanced glutamate release above baseline; this was also tested at 100 microM (not significant). 4. Compared to NMDA alone, coapplication of WAY 100135 (20 microM) significantly enhanced aspartate release; the mean value was also increased (not significantly) with 50 microM. This rise was calcium-dependent, but not tetrodotoxin-sensitive. WAY 100135 (100 microM) reduced NMDA-induced aspartate release. WAY 100135 (100 microM) reduced NMDA-induced aspartate release. Application of the drug alone had no effect on basal aspartate release.5. Coapplication of the 5-HT1A agonist, 8-OHDPAT (5 sanM) with NMDA did not affect the NMDA evoked increase in glutamate and aspartate.6. Topical application of high potassium (100 sanM) to the surface of the cortex did not result in a detectable rise in striatal glutamate or aspartate.7. Perfusion of WAY 100135 (tested at 50 microM) through the dialysis probe did not affect glutamate oraspartate concentrations.8. It was concluded that a selective 5-HT1A-antagonist can increase the activity of corticostriatal pyramidal neurones. As in Alzheimer's disease hypoactivity of pyramidal neurones almost certainly exists, a selective 5-HT1A-antagonist may be potentially useful in the treatment of the cognitive symptoms of this disease.

Postmortem brains reveal similar but not identical amyloid precursor protein-like immunoreactivity in Alzheimer compared with other dementias.

Concentrations of amyloid precursor protein (APP)-like immunoreactivity (APPLIR) have been determined by Western blotting in a soluble fraction and two membrane fractions of two areas of brain cortex from patients with Alzheimer's disease (AD) and other dementias. There were no significant differences between AD and other cases in species with the Kunitz protease inhibitor domain. However, the total soluble APPLIR was higher in AD and it was hypothesized that this relates to cholinergic hypoactivity.

Brain membrane serine protease activity in human cortex compared with rat: implication for Alzheimer's disease.

Cerebral cortex from humans and rats was extracted sequentially with detergent-containing and low-ionic-strength buffers. The resulting pellet was extracted with detergent/high-ionic-strength buffer to yield a soluble enzyme preparation. This was incubated with substrate prepared from rat cerebral cortical membranes containing amyloid precursor protein-like immunoreactivity (APPLIR) of 116 kD approximate apparent molecular mass. The effectiveness of various enzyme preparations to degrade APPLIR was: routine-post-mortem (pm)-delay human samples > rat pup > short-pm-delay human samples >> adult rat. In incubations with human samples only a 100-kD product accumulated. The activity in human brain was inhibited by phenylmethylsulphonylfluoride, insensitive to Ca2+, correlated with pyramidal neurone numbers but not those of astrocytes and was not significantly higher in Alzheimer's disease compared with controls. These data are discussed in terms of other approaches for studying proteolytic activity to explain the deposition of beta-amyloid protein in this disease.

beta-Amyloid precursor protein isoforms show correlations with neurones but not with glia of demented subjects.

Post-mortem cerebral cortex from 15 demented patients was specially collected to minimise autolysis and two membrane fractions and one soluble fraction were quantitatively examined for the major species of beta-amyloid precursor protein (APP) of high apparent molecular mass (> or = 80 kDa) together with the major mRNA species encoding APP isoforms. The number of pyramidal neurones and astrocytes, putative biochemical indices of interneurones and pyramidal neurones, and choline acetyl transferase activity were also determined. Multiple regression analysis has been used to investigate intercorrelations of APP species with biochemical and morphometric measures, free of any effects of confounding demographic variables. Subjects with Alzheimer's disease showed a loss of cholinergic activity and D-aspartate uptake compared with patients with other causes of dementia. The major finding of the study is that measures of neurones rather than astrocytes most closely correlate with the concentration of APP. Pyramidal cell numbers were positively correlated with mRNA for APP695. APP in the soluble fraction showed a negative correlation with pyramidal cell numbers and cholinergic activity. These results indicate that neurones within the cerebral cortex are the major source of APP, and that secretion of APP is dependent upon cortical pyramidal neuronal activity and cholinergic activity.

Neurotransmitters and second messengers in aging and Alzheimer's disease.

A substantial loss of cortical cholinergic nerve endings, along with a much more circumscribed cortical degeneration of pyramidal neurons, almost certainly causes glutamatergic hypoactivity in live Alzheimer's patients. These selective pathologies are discussed in terms of therapy. An additional effect of some proposed treatments is emerging as there is evidence that processing pathways for beta-amyloid precursor proteins in cortical pyramidal neurons, a target cell for acetylcholine, are affected by neuronal activity.

Independent mutation of arginine(3500)-->glutamine associated with familial defective apolipoprotein B-100.

Familial defective apolipoprotein B-100 (FDB) is characterized by a decreased affinity of low density lipoprotein (LDL) to the LDL receptor resulting in a dominantly inherited increase of plasma LDL. It is postulated that FDB is caused by a G to A mutation at nucleotide 10,708 in exon 26 of the apoB gene creating a substitution of glutamine for arginine in amino acid 3500. The arginine(3500)-->glutamine mutation has been identified on the same haplotype of the apoB gene in several populations from North America and Europe, suggesting that it occurred on a single ancestral gene. Independent mutations were not observed. The purpose of this paper is to report on a family where individuals show a dominantly inherited increase of plasma LDL associated with an independent arginine(3500)-->glutamine mutation as determined by haplotype analysis using polymorphic markers of the apoB gene. The identification of these individuals is strong evidence that the arginine(3500)-->glutamine mutation is causative for the defective binding of apoB-100.

Preliminary neurochemical findings in non-Alzheimer dementia due to lobar atrophy.

Non-Alzheimer's dementia due to lobar atrophy had choline acetyltransferase activities comparable with control rather than Alzheimer's disease values, based on 3 autopsy proven cases on Pick's disease and biopsies from 3 examples of dementia of frontal lobe type. Muscarinic cholinergic receptors were relatively spared only in Alzheimer's disease. Serotonin receptors were markedly reduced (based on Pick cases) whereas measures that reflected presynaptic serotonergic activity were either not affected or increased. Cerebrospinal fluid and brain tissue measurements suggested that inhibitory interneurones and dopamine release were relatively spared. There was no in vitro evidence of hypometabolism.

Changes of natural killer cells during acute psychological stress.

Emotional stress is often followed by increased susceptibility to infections. One major role in the immediate immune response to infection is played by natural killer (NK) cells. This study was designed to establish whether acute psychological stress influences cellular immune functions and to elucidate the role of endocrine parameters as potent mediators of stress induced alterations of the immune system. Forty-five first-time tandem parachutists were examined continuously for their plasma concentrations of cortisol and catecholamines from 120 min before to 60 min after jumping. Lymphocyte subsets, NK activity, and ADCC were determined 2 hr before, immediately after, and 1 hr after jumping. There was a significant increase in sympathetic-adrenal hormones during (adrenaline, noradrenaline) and shortly after jumping (cortisol). Lymphocyte subsets and the functional capacity of NK cells revealed an increase immediately after jumping followed by a decrease significantly below starting values 1 hr later. These changes were significantly correlated to plasma concentrations of noradrenaline. Thus, quick mobilization of NK cells is suggested as one major mechanism for this effective adaptation of the immune system to stress situations.

Psychophysiological, neuroendocrine and cellular immune reactions under psychological stress.

Emotional stress is often followed by increased susceptibility to infections. Natural killer (NK) cells play a major role in the immediate immune response controlling this susceptibility. In this study on 45 first-time parachutists, it is demonstrated that highly controlled psychological stress increased psychophysiological variables, enhanced the secretion of sympathetic-adrenal hormones and also led to a significant increase of NK cells and their cytotoxic activity followed by a decrease below starting values. This immunological alteration is correlated with the secretion of noradrenaline during the emotional strain. Quick mobilization of these cytotoxic effector cells is suggested as a major mechanism for the effective adaptation of the immune system to stress situations.

Serotonergic pathology is not widespread in Alzheimer patients without prominent aggressive symptoms.

Behavioural symptoms of Alzheimer's disease, such as aggression, may determine the care patients required. Most postmortem neurochemical studies have been of institutionalized patients and conclusions drawn from these may not be valid for all patients. We have shown that serotonin 2 receptors are not lost from 12 of the 13 areas of cerebral cortex examined in the patients assessed to be free of aggressive symptoms. This has been interpreted as representing the relative preservation of cortical interneurones. In contrast choline acetyltransferase activity was reduced in all areas whereas serotonin content was reduced in only 2 of the 4 areas examined.

Protease 'Clipsin' extract activity reflects demographic characteristics of human brain.

'Clipsin' and other peptide bond hydrolase activities that appear to be integral membrane proteins, including two implicated in the formation of the histological hallmarks of Alzheimer's disease, were assayed in the frontal and parietal cortex from a large (n = 45) series of postmortem human brains. Tissues were extracted sequentially with detergent-containing and low ionic strength buffers. The final extracts obtained with detergent-high ionic strength buffer were assayed for peptide-bond hydrolase activity using radiolabelled casein and four chromophore-linked peptide substrates. Hydrolysis of N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide and alpha-casein showed evidence of sensitivity to the presence of Alzheimer's disease (n = 22) and some of the seven other demographic features (postmortem delay; mode of death in the case of one substrate) of the brain samples considered. By contrast, activity towards carbobenzoxy(Z)-Leu-Leu-Glu-2-naphthylamide, Z-Val-Lys-Met-4-methyl-coumaryl-7-amide and Z-Val-Lys-Lys-Arg-4-methoxy-2-naphthylamide were independent of all factors. The results are discussed in terms of damage to a sub-population of protease-containing membranes.

5-Hydroxytryptamine1A but not 5-hydroxytryptamine2 receptors are enriched on neocortical pyramidal neurones destroyed by intrastriatal volkensin.

Experimental lesions followed by binding of [3H]8-hydroxy-2-(n-dipropylamino)tetralin (8-OH-DPAT) and [3H]ketanserin to cryostat sections and quantitative autoradiography were used to investigate the cellular localization of 5-hydroxytryptamine1A (5-HT1A) and 5-hydroxytryptamine2 (5-HT2) receptors in the neocortex of the rat. The lesions were produced by intrastriatal injections of either volkensin (2 and 6 ng) or ricin (10 ng): both are suicide transport agents, but only the former is retrogradely transported in the central nervous system. Only animals treated with volkensin showed cortical receptor changes and these were almost exclusively confined to the 5-HT1A site. The binding of [3H]8-OH-DPAT was significantly reduced in rats receiving 2 or 6 ng volkensin in the deeper cortical layers of areas Fr1/Fr2 of neocortex ipsilateral to the striatal lesion. Quantitative histological analysis of adjacent sections had previously revealed a significant loss of large infragranular pyramidal neurones with sparing of both interneurones and supragranular pyramidal neurones. There was no significant reduction in [3H]8-OH-DPAT binding in superficial layers. In cortical areas, Par1/Par2 [3H]8-OH-DPAT binding was significantly reduced (2 and 6 ng animals) in both superficial and deeper cortical layers, but quantitative histological analysis has not been performed. The binding of [3H] ketanserin was unaffected except for the most superficial layers of Par1/Par2, where binding was significantly reduced in only the 2 ng animals. There was no reduction in [3H]8-OH-DPAT binding after intrastriatal ricin injection, which caused as much cell loss in the striatum as 2 ng of volkensin, but did not destroy cortical pyramidal neurones.(ABSTRACT TRUNCATED AT 250 WORDS)

CD16- CD56+ natural killer cells after bone marrow transplantation.

Natural killer (NK) cells are phenotypically defined as lymphocytes expressing the antigens CD56 and mostly CD16 (Fc gamma RIII), but lacking CD3. A small CD3- CD16- CD56+ NK cell subset has been described in normal individuals representing less than 2% of peripheral blood lymphocytes. We analyzed here 70 patients for their reconstitution of the immune system during follow-up after autologous or allogeneic bone marrow transplantation. In 35% of these patients, two different NK cell subsets, namely CD56+dim and CD56+bright cells, were observed. The mean duration of these two subsets after transplant was 4 months. Sixty-five percent of the patients exhibited an increased number of NK cells, but only the typical CD16+ CD56+dim population. The CD56+bright subpopulation represented a particular CD3- CD16- NK subset, with posttransplant frequencies up to 70% of all NK cells and 40% of peripheral blood lymphocytes, respectively. In contrast to normal CD56+dim NK cells, CD56+bright cells coexpressed the activation antigens p75 beta-chain of interleukin-2 receptor (IL-2R), CD2R, and CD26, but were negative for CD16. NK and antibody-dependent cellular cytotoxicity activity of CD56+bright cells was low compared with CD56+dim NK cells. But using IL-2 and interferon gamma, their cytotoxicity could be enhanced even more than in CD56+dim lymphocytes. These different subsets may reflect distinct activation or differentiation steps of NK cells during reconstitution of the immune system. Their differential response to IL-2 may be of functional importance for posttransplant cytokine therapy.