Prophylactic intravenous tranexamic acid and thromboembolism in non-cardiac surgery: a systematic review, meta-analysis and trial sequential analysis

Tranexamic acid is an antifibrinolytic drug that is widely used during surgery, but there are concerns about its thromboembolic effects. We aimed to investigate the effect of prophylactic intravenous tranexamic acid on thromboembolic outcomes in patients undergoing non-cardiac surgery. The MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials were searched. Randomised controlled trials comparing intravenous tranexamic acid with placebo or no treatment in patients undergoing non-cardiac surgery were included. The primary outcome was a composite of peri-operative cardiovascular thromboembolic events, defined as any deep vein thrombosis, pulmonary embolism, myocardial ischaemia/infarction or cerebral ischaemia/infarction. A total of 191 randomised controlled trials (40,621 patients) were included in the review. The primary outcome occurred in 4.5% of patients receiving intravenous tranexamic acid compared with 4.9% of patients in the control group. Our analysis showed that there was no difference between groups for composite cardiovascular thromboembolic events (risk ratio 1.02, 95%CI 0.94-1.11, p = 0.65, I² 0%, n = 37,512). This finding remained robust when sensitivity analysis was performed with continuity correction and in studies with a low risk of bias. However, in trial sequential analysis, our meta-analysis only achieved 64.6% of the required information size. There was no association between intravenous tranexamic acid and seizure rate or mortality rate within 30 days. Intravenous tranexamic acid was associated with a reduced blood transfusion rate compared with control (9.9% vs. 19.4%, risk ratio 0.46, 95%CI 0.41-0.51, p < 0.0001). It was encouraging to see the evidence that the administration of intravenous tranexamic in patients undergoing non-cardiac surgery was not associated with an increased risk of thromboembolic outcomes. However, our trial sequential analysis demonstrated that currently available evidence is not yet sufficient to reach a firm conclusion.

727 Robotic Assisted Versus Fluoroscopic Guided Approach in Pedicle Screw Insertion: A Systematic Review and Meta-Analysis

Aim

The robotic assisted surgery has become prevalent in most of the surgical subspecialty. The adaption of such technique in spine surgery has resulted in minimising several issues encountered with fluoroscopic guided approach. The aim of this study is to compare the outcomes of robotic assisted approach and fluoroscopic guided approach in pedicle screw insertion.

Method

PUBMED, EMBASE, MEDLINE and CENTRAL database were systematically searched from its inception until November 2020. All the studies comparing robotic assisted surgery and fluoroscopic guided approach in pedicle screw insertion were included for quantitative and qualitative analysis.

Results

Twenty-eight studies enrolling 2105 patients (robotic group: 1027, fluoroscopic: 1078) and total screws of 8668 screws (robotic group: 4217, fluoroscopic group: 4451) were eligible for inclusion, these studies consisted of 19 observational studies, 7 randomised controlled trials (RCTs) and 2 cadaveric study. Robotic assisted approach was associated with significantly higher accuracy (Grade A+B) (OR = 2.34; P &lt; 0.0001) and distance between pedicle and screw (MD: 1.69; P = 0.001), lower incident of facet joint violation (OR = 0.22; P &lt; 0.00001), screw revision (OR = 0.38; P = 0.009), intraoperative blood loss (MD: -116.95; P = 0.0006), shorter pedicle screw placement time (MD: -4.66; P &lt; 0.00001), radiation exposure time (MD:-5.27; P = 0.0001), radiation dose (MD:-22.30; P = 0.0002) and postoperative hospital stay (MD: -0.79; P = 0.02) compared to fluoroscopic guided approach. There was no significant difference in operative time and wound infection.

Conclusions

In this meta-analysis, robotic assisted approach is more effective in achieving better clinical outcomes compared to fluoroscopic guided technique in pedicle screw insertion. However, future adequately powered RCTs are warranted to generate standardised outcomes.

The Effect of Prehospital Epinephrine in Out-of-Hospital Cardiac Arrest: A Systematic Review and Meta-Analysis

INTRODUCTION

Epinephrine has been recommended for out-of-hospital cardiac arrest (OHCA) resuscitation for nearly one century, but its efficacy and safety remain unclear in the literature. The primary aim of this review was to determine whether epinephrine increases the return of spontaneous circulation in OHCA patients.

METHODS

A systematic review and meta-analysis were conducted using the following databases: MEDLINE, EMBASE, and CENTRAL, from their inception until October 2018. All the randomized controlled trials (RCTs) were included. Observational studies, case reports, case series, and non-systematic reviews were excluded.

RESULTS

Two trials including 8,548 patients were eligible for inclusion in the data synthesis. In patients who received epinephrine during OHCA, the incidence of return of spontaneous circulation was increased, with an odds ratio (95%CI) of 4.25 (3.79-4.75), P <.001, high-quality of evidence. The number of patients transported to hospital was increased in patients who had prehospital epinephrine, with an odds ratio (95%CI) of 2.31 (2.11-2.53), P <.001, high-quality of evidence. The prehospital use of epinephrine was associated with an increased survival to hospital discharge, the odds ratio (95%CI) being 1.43 (1.10-1.87), P = .008, moderate-quality of evidence. No significant effect was noted on the favorable neurologic state of patient at hospital discharge, with an odds ratio (95%CI) of 1.21 (0.90-1.64), P = .21, moderate-quality of evidence.

CONCLUSIONS

This meta-analysis suggests that the prehospital use of epinephrine increases return of spontaneous circulation, transport of patients to hospital, and survival to hospital discharge for OHCA. However, no significant effects on favorable neurologic function at hospital discharge were demonstrated. The general quality of evidence ranged from moderate to high.

Peri-implant inflammation and marginal bone level changes around dental implants in relation to proximity with and bone level of adjacent teeth

OBJECTIVES

This retrospective study assessed radiographic bone changes and prevalence of inflammation around teeth and neighbouring implants supporting a single-unit fixed dental prosthesis (FDP), in relation to implant- positioning and characteristics.

MATERIAL AND METHODS

Patients with an implant-supported FDP in function for at least 1 year were recruited. The radiographic horizontal and vertical position of the implants were identified. Probing depth (PD), bleeding on probing (BOP) and radiographic bone level around implants and adjacent teeth at the time of placement, prosthesis delivery, and the most recent review were assessed.

RESULTS

98 patients with 195 implants were evaluated for a mean of 37.8 months. Survival rate was 99.6% and success ranged from 31.3% to 91.3% when different success criteria were utilized. Significantly greater interproximal bone loss around teeth and higher prevalence of interproximal peri-implant inflammation occurred when the horizontal distance of BL implants was <1 mm, but not with TL implants. There was no significant impact of the corono-apical positioning of the implants on marginal bone loss.

CONCLUSION

Proximity of implants to adjacent teeth of <1 mm leads to increased prevalence of inflammation and interproximal bone resorption at the teeth adjacent to bone level implants.

Effect of nicotine replacement therapy on mortality, delirium, and duration of therapy in critically ill smokers: a systematic review and meta-analysis

Nicotine replacement therapy is widely used in critically ill smokers and its effect on delirium, mortality and duration of intensive care unit (ICU) admission is unknown. The aims of this review were to determine whether the management of nicotine withdrawal with nicotine replacement therapy reduces delirium, mortality or length of stay in critically ill smokers in ICU. The primary outcome was incidence of author-defined ICU delirium. Secondary outcomes were ICU or hospital mortality, ICU-free days at day 28, and ICU or hospital length of stay. We conducted a systematic review and meta-analysis of the data sources MEDLINE, EMBASE, CINAHL, and the Cochrane Database of Systematic Reviews for randomised controlled trials and observational studies. Clinical trials, observational studies and systematic reviews comparing nicotine replacement therapy with placebo or no treatment were included. Case reports, case series, non-systematic reviews and studies that involved children were excluded. Eight studies were eligible (n=2,636) for inclusion in the data synthesis. In a meta-analysis of observational studies, nicotine replacement therapy was associated with increased delirium (three studies; n=908; I²=0%; finite element method: odds ratio 4.03 [95% confidence interval 2.64, 6.15]; P <0.001). There was no difference in ICU mortality (three studies; n=1,309; P=0.10, I²=44%; finite element method: odds ratio 0.58; 95% confidence intervals 0.31-1.10) and hospital mortality or 28-day ICU-free days. In the absence of high-quality data, nicotine replacement therapy cannot currently be recommended for routine use to prevent delirium or to reduce hospital or ICU mortality in critically ill smokers.

High serum lactate as an adjunct in the early prediction of anastomotic leak following oesophagectomy

BACKGROUND

Anastomotic leak (AL) following oesophagectomy carries a high mortality and morbidity. Early detection and intervention is required for a successful outcome. We have examined the role of a high postoperative serum lactate in predicting which patients are at risk of developing an anastomotic leak(AL).

MATERIALS AND METHODS

All patients who underwent transthoracic oesophagectomy over a 3-year period were identified from a prospectively collected database. Medical records were reviewed to identify the highest serum lactate recorded from blood gas analysis over each 24hr post-operative period. Patients who underwent transhiatal and left thoraco-abdominal oesophagectomies were excluded. Patients who developed a chyle leak were excluded.

RESULTS

Of a total of 136 oesophagectomies included for analysis, 18 developed an AL (13.2%). Of these patients, 10 underwent thoracoscopic oesophageal mobilization with cervical anastomosis and the rest an Ivor Lewis procedure. Predictive factors for AL included neoadjuvant chemotherapy (15/18 83.3% vs 55/118 46.6% p = 0.0046) and number of positive lymph nodes (mean 4.2 vs control mean 2.3 p = 0.045). Overall net fluid balance was comparable between the 2 groups, although AL patients received slightly more fluid on Day 3. High lactate levels on days 1-3 were associated with an AL. Using a Day 2 lactate of 1.7 mmol/L, the sensitivity of predicting AL was 72% and specificity 88%. The mean lag time using existing diagnostic modalities was 7.9 days.

CONCLUSION

A serum lactate of >1.7 mmol/l on day 2 should raise the possibility of a potential AL. Such patients should be selected for more intensive monitoring, optimization and selective gastroscopy.

Deep sequencing of phage display libraries to support antibody discovery

The use of next generation sequencing (NGS) for the analysis of antibody sequences both in phage display libraries and during in vitro selection processes has become increasingly popular in the last few years. Here, our methods developed for DNA preparation, sequencing and data analysis are presented. A key parameter has also been to develop new software designed for high throughput antibody sequence analysis that is used in combination with publicly available tools. As an example of our methods, we provide data from the extensive analysis of five scFv libraries generated using different heavy chain CDR3 diversification strategies. The results not only confirm that the library designs were correct but also reveal differences in quality not easily identified by standard DNA sequencing approaches. The very large number of reads permits extensive sequence coverage after the selection process. Furthermore, as samples can be multiplexed, costs decrease and more information is gained per NGS run. Using examples of results obtained post phage display selections against two antigens, frequency and clustering analysis identified novel antibody fragments that were then shown to be specific for the target antigen. In summary, the methods described here demonstrate how NGS analysis enhances quality control of complex antibody libraries as well as facilitates the antibody discovery process.

Distinct mechanism of small-for-size fatty liver graft injury--Wnt4 signaling activates hepatic stellate cells

In this study, we aimed to investigate the significance of hepatic stellate cells (HSCs) activation in small-for-size fatty liver graft injury and to explore the underlying molecular mechanism in a rat liver transplantation model. A rat orthotopic liver transplantation model using fatty grafts (40% of fatty changes) and cirrhotic recipients was applied. Intragraft gene expression profiles, ultrastructure features and HSCs activation were compared among the rats received different types of grafts (whole vs. small-for-size, normal vs. fatty). The distinct molecular signature of small-for-size fatty graft injury was identified by cDNA microarray screening and confirmed by RT-PCR detection. In vitro functional studies were further conducted to investigate the direct effect of specific molecular signature on HSCs activation. HSCs activation was predominantly present in small-for-size fatty grafts during the first 2 weeks after transplantation, and was strongly correlated with progressive hepatic sinusoidal damage and significant upregulation of intragraft Wnt4 signaling pathway. In vitro suppression of Wnt4 expression could inhibit HSC activation directly. In conclusion, upregulation of Wnt4 signaling led to direct HSC activation and subsequently induced small-for-size fatty liver grafts injury. Discovery of this distinct mechanism may lay the foundation for prophylactic treatment for marginal graft injury in living donor liver transplantation.

The significance of proline-rich tyrosine kinase2 (Pyk2) on hepatocellular carcinoma progression and recurrence

Understanding the precise molecular mechanisms that trigger liver cancer cell migration and invasion could develop novel therapeutic strategies targeting cancer cell invasion to increase the sensitivity to current treatment modalities. In the current study, 49 patients with hepatocellular carcinoma (HCC) were included prospectively. Liver tumour and adjacent non-tumour tissues were detected for the expression of Proline-rich tyrosine kinase 2 (Pyk2), focal adhesion kinase (FAK), ezrin and fibronectin at protein and/or gene levels. Correlation between the expressions of Pyk2/FAK with the clinical pathological data was analysed. Protein expression of Pyk2 was also examined in a nude mice orthotopic liver tumour model with higher metastatic potential. There were 59% (29 out of 49) and 57% (28 out of 49) of HCC patients with higher levels of Pyk2 and FAK protein/gene expression, respectively. We observed a positive correlation between the protein and gene expression levels of Pyk2 and FAK (P=0.000, r=0.875). Overexpression of Pyk2 and FAK was significantly correlated with shorter disease-free survival. Patients with higher levels of Pyk2/FAK had larger tumour size and advanced Edmonson grading. In the animal studies, Pyk2 overexpression was found in infiltrative tumour cells and lung metastatic nodules. In conclusion, overexpression of Pyk2 and FAK was found in nearly 60% of HCC patients and was significantly correlated with poor prognosis. The significance of Pyk2 in HCC invasiveness was confirmed by animal studies.

HIV-1 protein gp120 rapidly impairs memory in chicks by interrupting the glutamate–glutamine cycle

Learning and memory impairments are frequently observed in patients suffering from AIDS Dementia Complex (ADC). These effects have been linked to the presence of gp120, an HIV viral coat glycoprotein. The present study investigated the possibility that gp120 prevents the uptake of extracellular glutamate by astrocytes, leading to an interruption of the glutamate-glutamine cycle and a subsequent impairment of memory. Ten microliters of 10nM gp120 was bilaterally injected into the region of the intermediate medial mesopallium of day-old chicks at various times before, or after, training using a single-trial passive avoidance task. Gp120 was found to significantly impair memory retention when injected 10-40 min after training. Memory impairments were evident within 5 min of gp120 administration and remained evident 24h later. Further, the amnestic effect of gp120 could be overcome with glutamine or with precursors of glutamate synthesis, but only weakly by glutamate. These results support the conclusion that the amnestic effect of gp120 is due to an impaired uptake of glutamate by astrocytes and a subsequent interruption of glutamine supply to neurones. The data indicate that the glutamate-glutamine cycle may be a useful therapeutic target in the treatment of ADC.

Clinicopathological significance of homeoprotein Six1 in hepatocellular carcinoma

Tumour recurrence and metastases of hepatocellular carcinoma (HCC) after hepatectomy are the major obstacles of long-term survival. The present study investigated the clinicopathological significance of a possible metastasis regulator Six1 in HCC patients who were undergone hepatectomy. Seventy-two pairs of RNA and 103 pairs of protein from tumour and adjacent nontumour liver tissues of HCC patients were examined. About 85 and 60% of HCC tumour tissues were found to overexpress Six1 mRNA and protein, respectively, compared with nontumour liver tissues. No Six1 protein was detected in HCC nontumour liver tissues and normal liver tissues. Increased Six1 protein expression in HCC patients was significantly correlated with pathologic tumour-node-metastasis (pTNM) stage (P=0.002), venous infiltration (P=0.004) and poor overall survival (P=0.0423). We concluded that Six1 is frequently overexpressed in HCC patients and elevated Six1 protein in HCC patients may be an indication of advanced stage and poor overall survival after hepatectomy.

Rapamycin attenuates liver graft injury in cirrhotic recipient--the significance of down-regulation of Rho-ROCK-VEGF pathway

To investigate whether rapamycin could attenuate hepatic I/R injury in a cirrhotic rat liver transplantation model, we applied a rat orthotopic liver transplantation model using 100% or 50% of liver grafts and cirrhotic recipients. Rapamycin was given (0.2 mg/kg, i.v.) at 30 min before graft harvesting in the donor and 24 h before operation, 30 min before total hepatectomy and immediately after reperfusion in the recipient. Rapamycin significantly improved small-for-size graft survival from 8.3% (1/12) to 66.7% (8/12) (p = 0.027). It also increased 7-day survival rates of whole grafts (58.3%[7/12] vs. 83.3%[10/12], p = 0.371). Activation of hepatic stellate cells was mainly found in small-for-size grafts during the first 7 days after liver transplantation. Rapamycin suppressed expression of smooth muscle actin, which is a marker of hepatic stellate cell activation, especially in small-for-size grafts. Intragraft protein expression and mRNA levels of vascular endothelial growth factor (VEGF) were down-regulated by rapamycin at 48 h both in whole and small-for-size grafts. Consistently, mRNA levels and protein expression of Rho and ROCK I were decreased by rapamycin during the 48 h after liver transplantation. In conclusion, rapamycin attenuated graft injury in a cirrhotic rat liver transplantation model by suppression of hepatic stellate cell activation, related to down-regulation of Rho-ROCK-VEGF pathway.

Fat-derived hormone adiponectin combined with FTY720 significantly improves small-for-size fatty liver graft survival

Owing to the discrepancy between organ donation and the demand for liver transplantation, expanding the liver donor pool is of vital importance. However, marginal liver grafts, such as small-for-size and/or fatty grafts, were associated with primary graft nonfunction or poor function. Therefore, novel combination therapies to rescue small-for-size fatty liver grafts should be investigated. In this study, we applied a combination therapy using a fat-derived hormone adiponectin (anti-steatosis) plus immunomodulator FTY720 (anti-inflammatory) in a rat liver transplantation model using small-for-size fatty liver grafts, and investigated the underlying protective mechanism such as anti-steatosis, intra-graft energy metabolism, hepatic microcirculatory changes, cell signaling cascades for survival, apoptosis and inflammation. The current study demonstrated that even a single treatment of adiponectin or FTY720 improved the 7-day graft survival from 0% to 62.5% (p = 0.001). The combination therapy significantly increased the 7-day graft survival rate to 100% by remarkable attenuation of graft steatosis and acute phase inflammatory response, significant activation of cell survival Akt pathway and maintenance of intra-graft adenosine triphosphate metabolism and improvement of hepatic microcirculation. In conclusion, the fat-derived hormone adiponectin combined with FTY720 might be a novel combination drug therapy for prevention of small-for-size fatty liver graft injury.

Inhibition of endogenous carbon monoxide production induces transient retention losses in the day-old chick when trained using a single trial passive avoidance learning task

Carbon monoxide (CO) is most often thought of as an exogenous toxin rather than as a possible endogenous nootrope. However, a limited number of studies have suggested that CO is necessary in memory processing for at least some tasks. While nitric oxide (NO) and CO are known activators of guanylyl cyclase (GC), only the effect of NO on GC has been extensively investigated as a mechanism underlying memory processing. The aim of the present study was to determine if inhibition of CO production would have an effect on memory processing. Using chicks trained on a single trial passive avoidance task, inhibition of CO production using zinc (II) deuteroporphyrin IX 2,4-bis ethylene glycol (ZnBG; 5 microM) resulted in two transient retention losses occurring at around 40 and 130 min post-training. The timing of these transient retention losses was similar to those observed following inhibition of GC, using the same species and task in a previous study. This supports the notion that CO is necessary in memory processing for this task and may act through a GC-dependent mechanism. As ZnBG also directly inhibits GC or nitric oxide synthase (NOS) at high concentrations, a second experiment was carried-out to confirm the specificity of ZnBG for heme oxygenase (HO) at the concentration used. The action of ZnBG was challenged with the HO agonist hemin (100 microM) and the transient deficits were abolished. This confirmed that the action of ZnBG on memory was through a CO-related mechanism rather than directly on GC or NOS. In this way the specificity of ZnBG (5 microM) for HO could be confirmed. The results support a role for endogenous CO in memory processing, possibly through activation of GC. In addition, the transient retention losses observed following administration of ZnBG suggest that CO may be necessary for memory retrieval and not formation as previously thought.

Noradrenaline involvement in the memory-enhancing effects of exposure to a complex rhythm stimulus following discriminated passive avoidance training in the young chick

Previous research in our laboratory has demonstrated a significant memory-enhancing effect of exposure to a complex rhythm stimulus following weakly-reinforced passive avoidance learning in chicks. The aim of this study was to explore whether noradrenaline mediates this process. Chicks were trained on a strongly-reinforced single-trial passive avoidance task involving discrimination between two coloured beads. Intracerebral administration of the protein synthesis blocker, anisomycin, revealed that a phase of memory formation sensitive to arousal levels was extended by approximately 35 min following exposure to the complex rhythm stimulus. Administration of 2,4-dinitrophenol showed that this extension occurred during phase B of intermediate-term memory. Finally, a higher dose of the beta-adrenergic receptor antagonist, propranolol, was required to inhibit long-term memory in the presence of the auditory stimulus than in its absence. These findings suggest that the memory-enhancing effects of the complex rhythm stimulus may be mediated by noradrenaline, possibly via an increase in physiological arousal.

Inhibition of short-term memory formation in the chick by blockade of extracellular glutamate uptake

Injection of monosodium glutamate (40nmol/hemisphere) into the intermediate hyperstriatum ventrale of the day-old chick inhibits the formation of short-term memory for a single trial learning that discriminates between colours of beads. These experiments showed that an excess of glutamate close to learning could be damaging to memory. In the present experiments we have blocked the normal reuptake of glutamate and suggest that glutamate release plays a role in normal learning. Removal of glutamate, released from presynaptic neurones during learning, is achieved by various neuronal and astrocytic glutamate transporters. By blocking the primarily astrocytic removal of glutamate by the injection of L-aspartic acid beta-hydroxamate, we effectively increased extrasynaptic levels of glutamate and inhibited short-term memory in a similar manner to central injection of 40nmol glutamate per hemisphere. These experiments suggest that glutamate release within 2.5min of the learning experience is an important feature of short-term memory formation.

Three-dimensional pseudospectral modelling of cardiac propagation in an inhomogeneous anisotropic tissue

Various investigators have used the monodomain model to study cardiac propagation behaviour. In many cases, the governing non-linear parabolic equation is solved using the finite-difference method. An adequate discretisation of cardiac tissue with realistic dimensions, however, often leads to a large model size that is computationally demanding. Recently, it has been demonstrated, for a two-dimensional homogeneous monodomain, that the Chebyshev pseudospectral method can offer higher computational efficiency than the finite-difference technique. Here, an extension of the pseudospectral approach to a three-dimensional inhomogeneous case with fibre rotation is presented. The unknown transmembrane potential is expanded in terms of Chebyshev polynomial trial functions, and the monodomain equation is enforced at the Gauss-Lobatto node points. The forward Euler technique is used to advance the solution in time. Numerical results are presented that demonstrate that the Chebyshev pseudospectral method offered an even larger improvement in computational performance over the finite-difference method in the three-dimensional case. Specifically, the pseudospectral method allowed the number of nodes to be reduced by approximately 85 times, while the same solution accuracy was maintained. Depending on the model size, simulations were performed with approximately 18-41 times less memory and approximately 99-169 times less CPU time.

Inhibition of guanylate cyclase and protein kinase G impairs retention for the passive avoidance task in the day-old chick

Nitric oxide (NO) is a highly labile chemical messenger which has previously been implicated in memory processes in a variety of learning paradigms and species. However, there is only limited evidence to suggest which enzymes are acted upon by NO during the formation of memory. The present study investigates the role of guanylate cyclase (GC) and protein kinase G (PKG) in a form of passive avoidance learning known to be dependent on nitric oxide activity. It was determined that in vivo pharmacological inhibition of GC using either 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one or 6-anilino-5,8-quinolinedione resulted in two transitory memory retention deficits centred around 40 and 120 min posttraining, respectively. In contrast, inhibition of PKG with N-[2-(methylamino)ehtyl]-5-isoquinoline-sulfornamide hydrochloride (H-8) resulted in a single temporary retention loss centered at 120 min posttraining. These temporary retention losses appear to be specific to memory since they were dose-dependent and could not be explained by nonspecific performance effects. Further, these results suggest that these agents inhibit memory retrieval rather than formation, since memory is subsequently available. The current findings indicate that guanylyl cyclase mediates two memory retrieval processes, the latter of which appears to be PKG-dependent. In contrast, since inhibition of NO results in a permanent retention loss, it is suggested that NO is required for memory formation through GC-independent processes.

Calibrated single-plunge bipolar electrode array for mapping myocardial vector fields in three dimensions during high-voltage transthoracic defibrillation

Mapping of the myocardial scalar electric potential during defibrillation is normally performed with unipolar electrodes connected to voltage dividers and a global potential reference. Unfortunately, vector potential gradients that are calculated from these data tend to exhibit a high sensitivity to measurement errors. This paper presents a calibrated single-plunge bipolar electrode array (EA) that avoids the error sensitivity of unipolar electrodes. The EA is triaxial, uses a local potential reference, and simultaneously measures all three components of the myocardial electric field vector. An electrode spacing of approximately 500 microm allows the EA to be direct-coupled to high-input-impedance, isolated, differential amplifiers and eliminates the need for voltage dividers. Calibration is performed with an electrolytic tank in which an accurately measured, uniform electric field is produced. For each EA, unique calibration matrices are determined which transform potential difference readings from the EA to orthogonal components of the electric field vector. Elements of the matrices are evaluated by least squares multiple regression analysis of data recorded during rotation of the electric field. The design of the electrolytic tank and electrode holder allows the electric field vector to be rotated globally with respect to the electrode axes. The calibration technique corrects for both field perturbation by the plunge electrode body and deviations from orthogonality of the electrode axes. A unique feature of this technique is that it eliminates the need for mechanical measurement of the electrode spacing. During calibration, only angular settings and voltages are recorded. For this study, ten EAs were calibrated and their root-mean-square (rms) errors evaluated. The mean of the vector magnitude rms errors over the set of ten EAs was 0.40% and the standard deviation 0.07%. Calibrated EAs were also tested for multisite mapping in four dogs during high-voltage transthoracic shocks.

Concentration-dependent effects of protein phosphatase (PP) inhibitors implicate PP1 and PP2A in different stages of memory formation

Numerous studies have demonstrated roles for protein phosphorylation and for specific kinases in memory formation; however, a role for specific protein phosphatases has not been established. Previous studies using pharmacobehavioral methods to implicate protein phosphatase activity in memory formation have been unable to discriminate between protein phosphatases 1 (PP1) and 2A (PP2A), as available cell-permeable agents generally inhibit both enzyme classes. To address this difficulty the present study exploited differences in the potency of the selective phosphatase inhibitor, okadaic acid, toward PP1 and PP2A. Within the context of a temporally precise animal model of memory, developed using the day-old chick (Gallus domesticus), acute administration of various concentrations of okadaic acid was found to disrupt two temporally distinct stages of memory formation. When administered bilaterally into an area of the chick brain implicated in memory formation, concentrations of okadaic acid known to selectively inhibit PP2A in vitro disrupted memory from 50 min posttraining. Higher concentrations, reported to inhibit both PP2A and PP1 in vitro, produced significant retention deficits from 20 min posttraining. Identical temporally specific effects were also obtained by varying the concentration and time of administration of calyculin A, a phosphatase inhibitor with equal potency toward both enzyme classes. Hence, different phosphatase enzymes may contribute to different stages of the enzymatic cascade believed to underlie memory formation.

Modification of a weak learning experience by memory retrieval in the day-old chick

Activation of memory retrieval after weak learning (WL), during either the short- or intermediate-term stages of memory in day-old chickens, resulted in the strengthening of the memory to levels normally associated with strong learning. Administration of the calcium channel antagonist lanthanum chloride, the glutamate receptor agonist monosodium glutamate, or the N-methyl-D-aspartate glutamatergic receptor antagonist AP5 prevented strengthening of a WL memory by reminder-activated memory retrieval. The results of this study are discussed in light of our recent findings suggesting two phases of memory retrieval in the day-old chick. The results are consistent with the proposition that a memory undergoing the processes of formation may be modified to include information gleaned at the time of memory retrieval and that a second phase of memory retrieval may be responsible for such modification.

Two-dimensional Chebyshev pseudospectral modelling of cardiac propagation

Bidomain or monodomain modelling has been used widely to study various issues related to action potential propagation in cardiac tissue. In most of these previous studies, the finite difference method is used to solve the partial differential equations associated with the model. Though the finite difference approach has provided useful insight in many cases, adequate discretisation of cardiac tissue with realistic dimensions often requires a large number of nodes, making the numerical solution process difficult or impossible with available computer resources. Here, a Chebyshev pseudospectral method is presented that allows a significant reduction in the number of nodes required for a given solution accuracy. The new method is used to solve the governing nonlinear partial differential equation for the monodomain model representing a two-dimensional homogeneous sheet of cardiac tissue. The unknown transmembrane potential is expanded in terms of Chebyshev polynomial trial functions and the equation is enforced at the Gauss-Lobatto grid points. Spatial derivatives are obtained using the fast Fourier transform and the solution is advanced in time using an explicit technique. Numerical results indicate that the pseudospectral approach allows the number of nodes to be reduced by a factor of sixteen, while still maintaining the same error performance. This makes it possible to perform simulations with the same accuracy using about twelve times less CPU time and memory.

Inhibition of the endothelial isoform of nitric oxide synthase impairs long-term memory formation in the chick

Previous studies with general inhibitors of nitric oxide synthase have yielded variable and contradictory results with respect to their effects on memory. This may have been due to differential effects of blocking the various isoforms of this enzyme. We show that day-old chicks trained on a single-trial passive-avoidance task suffered significant memory loss from approximately 40 min post-training following post-training intracranial administration of a potent inhibitor of eNOS. Administration of a specific nNOS or iNOS inhibitor at the same time had no effect on retention, although a role for either of these isoforms when administered at a different time after learning has yet to be fully investigated. The onset of memory loss following eNOS inhibition is the same as observed following general NOS inhibition, which suggests that amnestic effects observed in previous studies using nonspecific inhibitors may be attributable to blocking the function of eNOS. The findings indicate that eNOS may play a role in memory formation for this task, which is at least distinct from any role that may be played by nNOS.

Cognitive and behavioral outcome following mild traumatic head injury in children

OBJECTIVES

To investigate outcome in children with mild traumatic head injury (THI) at 1 week and 3 months postinjury and to identify factors associated with persisting problems.

DESIGN

Postconcussional symptomatology, behavior ratings, and neuropsychological test performance were examined at 1 week and 3 months postinjury.

SETTING

Participants were recruited from successive presentations to emergency departments of two major hospitals.

PARTICIPANTS

130 Children with mild THI were compared with 96 children having other minor injuries as controls.

RESULTS

Children with mild THI experienced headaches, dizziness, and fatigue but exhibited no cognitive impairments, relative to controls, at 1 week postinjury. By 3 months, symptoms had resolved. However, 17% of children showed significant ongoing problems. They were more likely to have a history of previous head injury, learning difficulties, neurological or psychiatric problems, or family stressors.

CONCLUSIONS

Persisting problems following mild head injury in children are more common in those with previous head injury, preexisting learning difficulties, or neurological, psychiatric, or family problems. These "at-risk" children should be identified in the emergency department and monitored.

Changes in phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in processing of short-term and long-term memories after passive avoidance learning

Characteristic autophosphorylation of calcium/ calmodulin-dependent protein kinase II (CaMKII) and its consequences have made this kinase an interesting target in studying the molecular pathway for important neuronal functions including learning and memory formation. In this article, we use immunoprecipitation and immunoblotting methods to detect changes in phosphorylation of CaMKII during memory formation in 1-day-old chicks trained in a single trial passive avoidance task. A 60-kDa protein has been immunoprecipitated from the chick brain with an anti-rabbit CaMKII antibody. This protein shows strong and specific immunoactivities with antibodies against the calmodulin binding site of CaMKII, and the N and C terminals of beta-CaMKII. Commercially available anti-phosphoserine and anti-phosphothreonine antibodies are shown to sensitively detect phosphorylation of purified CaMKII. The basal phosphorylation of CaMKII from the intermediate medial hyperstriatum ventrale (IMHV) and lobus parolfactorius (LPO) regions of the chick brain is shown to be largely right hemisphere-lateralized. When chicks are subjected to a passive avoidance training experience, a specific increase in CaMKII phosphorylation is induced in the IMHV and LPO of the left hemisphere from those chicks whose memory for the training experience is successfully retrieved. While this specific increase in CaMKII phosphorylation is seen in both the left IMHV and left LPO in short-term memory, it is detectable only in the left LPO associated with long-term memory retrieval. The present results provide evidence that in vivo changes in phosphorylation of CaMKII are associated specifically with processing of distinct memory stages, which take place in specific brain regions.

Peptidyl-prolyl-cis/trans-isomerase activity may be necessary for memory formation

At present, evidence for a plethora of physiological roles for the different classes of peptidyl-prolyl-cis/trans-isomerases (PPIases, EC 5.2.1.8) is emerging. Cyclosporin A (CyA) has been previously reported to disrupt memory formation in a temporally specific manner, when administered intracranially to day-old chicks trained on a single-trial, passive-avoidance task [Bennett, P.C., Zhao, W., Lawen, A. and Ng, K.T. (1996) Brain Res. 730, 107-1171. CyA is known to inhibit both the PPIase activity of cyclophilin and, indirectly, the protein phosphatase activity of calcineurin. Therefore to begin to distinguish between these two functions we studied the effects on memory formation of three non-immunosuppressive CyA analogues, in order to study the involvement of cyclophilins. These drugs retain the capacity to bind to and inhibit the PPIase activity of cyclophilin, but do not bind in the complex with cyclophilin to calcineurin and, therefore, do not inhibit its phosphatase activity. All three drugs exert effects on memory formation comparable to those induced by CyA, significantly inhibiting memory formation when injected intracranially (50 fmol per hemisphere) immediately following training. Brain extracts from chicks treated with [MeVal4]CyA show a strong inhibition of cyclophilin activity. These data show a requirement for the PPIase activity of a cyclophilin for successful memory formation and constitute the first set of data establishing a physiological role for a cyclophilin.

Further support for nitric oxide-dependent memory processing in the day-old chick

There is considerable evidence that nitric oxide activity is essential for memory formation, particularly from studies using inhibitors of nitric oxide synthase. The particular stage of memory formation requiring nitric oxide activity has not, however, been systematically investigated. In the current experiments, day-old black Australorp-white Leghorn chicks were trained on a passive avoidance task. Intracranial injections of the nitric oxide synthase inhibitor, l-NG-nitroarginine methylester (0.5 mM), were found to inhibit memory formation shortly after training, when injected pre- or posttraining. This effect was replicated with a second inhibitor, l-NG-nitroarginine (1 mM), and counteracted by the NO donor, sodium nitroprusside (150 microM). These findings provide covergent evidence that nitric oxide activity plays a critical role in the consolidation of memory in the day-old chick.

A new three-dimensional finite-difference bidomain formulation for inhomogeneous anisotropic cardiac tissues

Bidomain modeling of cardiac tissues provides important information about various complex cardiac activities. The cardiac tissue consists of interconnected cells which form fiber-like structures. The fibers are arranged in different orientations within discrete layers or sheets in the tissue, i.e., the fibers within the tissue are rotated. From a mathematical point of view, this rotation corresponds to a general anisotropy in the tissue's conductivity tensors. Since the rotation angle is different at each point, the anisotropic conductivities also vary spatially. Thus, the cardiac tissue should be viewed as an inhomogeneous anisotropic structure. In most of the previous bidomain studies, the fiber rotation has not been considered, i.e., the tissue has been modeled as a homogeneous orthotropic medium. In this paper, we describe a new finite-difference bidomain formulation which accounts for the fiber rotation in the cardiac tissue and hence allows a more realistic modeling of the cardiac tissue. The formulation has been implemented on the data-parallel CM-5 which provides the computational power and the memory required for solving large bidomain problems. Details of the numerical formulation are presented together with its validation by comparing numerical and analytical results. Some computational performance results are also shown. In addition, an application of this new formulation to provide activation patterns within a tissue slab with a realistic fiber rotation is demonstrated.

Tyrosine kinase inhibitors impair long-term memory formation in day-old chicks

The involvement of protein kinases in numerous neuronal cellular processes, including learning and memory, has been well established, particularly regarding serine/threonine kinases. In the present study, the role of protein kinases in learning was further examined through an investigation of the effects of inhibitors of tyrosine kinase activity on memory formation. The present findings reveal that the intracranial administration of the tyrosine kinase inhibitors genistein and lavendustin A produced retention deficits in day-old chicks trained on a single-trial passive avoidance task. These deficits were not apparent until 90 min after the training episode and were not observed at all in chicks administered control substances. The possibility that the tyrosine phosphorylation disrupted by the presence of the inhibitors is related to NMDA glutamate receptor activation is considered.

Anatomically constrained electrical impedance tomography for three-dimensional anisotropic bodies

As shown previously for two-dimensional geometries, anisotropy effects should not be ignored in electrical impedance tomography (EIT) and structural information is important for the reconstruction of anisotropic conductivities. Here, we will describe the static reconstruction of an anisotropic conductivity distribution for the more realistic three-dimensional (3-D) case. Boundaries between different conductivity regions are anatomically constrained using magnetic resonance imaging (MRI) data. The values of the conductivities are then determined using gradient-type algorithms in a nonlinear-indirect approach. At each iteration, the forward problem is solved by the finite element method. The approach is used to reconstruct the 3-D conductivity profile of a canine torso. Both computational performance and simulated reconstruction results are presented together with a detailed study on the sensitivity of the prediction error with respect to different parameters. In particular, the use of an intracavity catheter to better extract interior conductivities is demonstrated.

New finite difference formulations for general inhomogeneous anisotropic bioelectric problems

Due to its low computational complexity, finite difference modeling offers a viable tool for studying bioelectric problems, allowing the field behavior to be observed easily as different system parameters are varied. Previous finite difference formulations, however, have been limited mainly to systems in which the conductivity is orthotropic, i.e., a strictly diagonal conductivity tensor. This in turn has limited the effectiveness of the finite difference, technique in modeling complex anatomies with arbitrarily anisotropic conductivities, e.g., detailed fiber structures of muscles where the fiber can lie in any arbitrary direction. In this paper, we present both two-dimensional and three-dimensional finite difference formulations that are valid for structures with an inhomogeneous and nondiagonal conductivity tensor. A data parallel computer, the connection machine CM-5, is used in the finite difference implementation to provide the computational power and memory for solving large problems. The finite difference grid is mapped effectively to the CM-5 by associating a group of nodes with one processor. Details on the new approach and its data parallel implementation are presented together with validation and computational performance results. In addition, an application of the new formulation in providing the potential distribution inside a canine torso during electrical defibrillation is demonstrated.

Administration of DL-2-amino-5-phosphonovaleric acid (AP5) induces transient inhibition of reminder-activated memory retrieval in day-old chicks

DL-2-Amino-5-phosphonovaleric acid (50 microM) administered immediately after a visual reminder presented to day-old chickens between 7.5 min and 24 h following a single trial passive avoidance learning task produced transient losses of memory on retention test, an effect not observed in the absence of a reminder or when the reminder was given 48 h post learning. The duration of the transient deficits decreased with increasing interval between training and the reminder trial. The time of onset of memory loss after the reminder trial appeared to increase with increasing interval between the training and the reminder trials. The results suggest that, for a period of at least up to 24 h after passive avoidance training, retrieval of memory may lead to processes which are sensitive to inhibition by the NMDA receptor antagonist AP5, with the duration of sensitivity post retrieval decreasing as the period of memory consolidation increases. The results extend previously reported findings and suggest the possibility that consolidation of a stable memorial representation of a learning experience may take over several days and may entail the concurrent laying down of a stable retrieval mechanism.

Chicks injected with antisera to either S-100 alpha or S-100 beta protein develop amnesia for a passive avoidance task

The cellular expression of S-100 beta protein is upregulated in Alzheimer's disease and in Down's syndrome, and this protein has been implicated in memory-related processes in laboratory animals. However, the possibility that the alpha subunit of S-100 is also involved in memory has not yet been examined. In the present study, day-old black Australorp white Leghorn cockerel chicks (Gallus domesticus) received injections of monoclonal antisera to S-100 alpha (1:50) or S-100 beta (1:500) into each hemisphere immediately after training on a one-trial passive avoidance task. The chicks displayed significantly lower retention levels than control birds that had been injected with antisera to carbonic anhydrase, or with saline (p < .01). S-100 alpha antisera had an amnestic effect when injected between 0 and 20 min after training, with memory deficits occurring from 30 min post-learning, at the point of transition between the A and the B phases of the Gibbs-Ng intermediate memory stage. By contrast, the S-100 beta antisera needed to be injected either 5 min before or immediately after training and produced amnesia 10 min earlier, at the start of the A phase of the intermediate memory stage. We conclude that the two subunits of the S-100 protein are required at different points in the sequence of events leading to the consolidation of passive avoidance memory.

Inhibition of intermediate-term memory following passive avoidance training in neonate chicks by a presynaptic cholinergic blocker

The effects of a specific presynaptic cholinergic antagonist, toosendanin, on memory formation following a passive avoidance training experience in day-old chicks was investigated. Bilateral injection of toosendanin into the neostriatal/hyperstriatal region of the chick forebrain produced memory impairment in a dose-dependent manner. Retention deficits were apparent from 20 min following training in chicks treated with toosendanin, regardless of the injection time relative to training. Chicks that received injections of the drug at corresponding times prior to retention tests showed normal retention levels, suggesting that toosendanin has no effect on performance and memory retrieval. These results indicate an involvement of cholinergic transmission during an early stage of memory formation.

Electrical defibrillation optimization: an automated, iterative parallel finite-element approach

To date, optimization of electrode systems for electrical defibrillation has been limited to hand-selected electrode configurations. In this paper we present an automated approach which combines detailed, three-dimensional (3-D) finite-element torso models with optimization techniques to provide a flexible analysis and design tool for electrical defibrillation optimization. Specifically, a parallel direct search (PDS) optimization technique is used with a representative objective function to find an electrode configuration which corresponds to the satisfaction of a postulated defibrillation criterion with a minimum amount of power and a low possibility of myocardium damage. For adequate representation of the thoracic inhomogeneities, 3-D finite-element torso models are used in the objective function computations. The CPU-intensive finite-element calculations required for the objective function evaluation have been implemented on a message-passing parallel computer in order to complete the optimization calculations in a timely manner. To illustrate the optimization procedure, it has been applied to a representative electrode configuration for transmyocardial defibrillation, namely the subcutaneous patch-right ventricular catheter (SP-RVC) system. Sensitivity of the optimal solutions to various tissue conductivities has been studied. Results for the optimization of defibrillation systems are presented which demonstrate the feasibility of the approach.

Three-dimensional finite-difference bidomain modeling of homogeneous cardiac tissue on a data-parallel computer

In this paper, a data-parallel computer is used to provide the memory and reduction in computer time for solving large finite-difference bidomain problems. The finite-difference grid is mapped effectively to the processors of the parallel computer, simply by mapping one node to one (virtual) processor. Implemented on the connection machines (CM's) CM-200 and CM-5, the data-parallel finite-difference algorithm has allowed the solution of finite-difference bidomain problems with over 2 million nodes. Details on the algorithm are presented together with computational performance results.

Distribution of glutamine synthetase in the chick forebrain: implications for passive avoidance memory formation

The glial enzyme glutamine synthetase (GS) converts glutamate to glutamine; the latter is used by neurons for the resynthesis of glutamate and GABA. We have used a monoclonal antibody to GS to examine the regional distribution of this enzyme in the forebrains of day-old chicks. GS was detected in glia throughout the rostral and caudal regions of the forebrain and was particularly intense in the hippocampus, area parahippocampus and parts of the hyperstriatal and paleostriatal complex, regions widely considered to be involved in memory formation. Thus, our data provide an anatomical framework for the conclusion that neurons require the support of glia in order to restock their glutamate and/or GABA transmitter supplies during memory processing.

Complex roles of glutamate in the Gibbs-Ng model of one-trial aversive learning in the new-born chick

Glutamate is the most widespread excitatory transmitter in the CNS and is probably involved in LTP, a neural phenomenon which may be associated with learning and memory formation. Intracerebral injection of large amounts of glutamate between 5 min and 2.5 min after passive avoidance learning in young chicks inhibits short-term memory, which occurs between 0 and 10 min post-learning in a three-stage model of memory formation first established by Gibbs and Ng(25) [Physiol. Behav. 23:369-375; 1979]. This effect may be attributed to non-specific excitation. Blockade of glutamate uptake by L-aspartic and beta-hydroxamate also abolishes this stage of memory, provided the drug is administered within 2.5 min of learning. Interference with either production of percursors for transmitter glutamate in astrocytes or with glutamate receptors is also detrimental to memory formation, but the effects appear much later. After its release from glutamatergic neurons, glutamate is, to a large extent, accumulated into astrocytes where it is converted to glutamine, which can be returned to glutamatergic neurons and reutilized for synthesis of transmitter glutamate, and partly oxidized as a metabolic substrate. The latter process leads to a net loss of transmitter glutamate which can be compensated for by de novo synthesis of a glutamate precursor alpha-ketoglutarate (alpha KG) in astrocytes, a process which is inhibited by the astrocyte-specific toxin fluoroacetate (R. A. Swanson, personal communication). Intracerebral injection of this toxin abolishes memory during an intermediate stage of memory processing occurring between 20 and 30 min post-training (50) [Cog. Brain Res, 2:93-102; 1994]. Injection of methionine sulfoximine (MSO), a specific inhibitor of glutamine synthetase, which interferes with the re-supply of transmitter glutamate to neurons by inhibition of glutamine synthesis in astrocytes, has a similar effect. This effect of MSO is prevented by intracerebral injection of glutamate, glutamine, or a combination and alpha KG and alanine. MSO must be administered before learning, but does not interfere with acquisition since short-term memory remains intact. Administration of either the NMDA antagonist AP5, the AMPA antagonist DNQX, or the metabotropic receptor antagonist MCPF, also induces amnesia. Memory loss in each case does not occur until after 70 min post-training, during a protein synthesis-dependent long-term memory stage which begins at 60 min following learning. However, to be effective, AP5 must be administered within 60 s following learning, MCPG before 15 min post-learning, and DNQX between 15 and 25 min after learning. Together, these findings suggest that learning results in an immediate release of glutamate, followed by a secondary release of this transmitter at later stages of processing of the memory trace, and that one or both of these increases in extracellular glutamate concentration are essential for the consolidation of long-term memory. Since both fluoroacetate and MSO act exclusively on glial cells, the findings also show that neuronal-glial interactions are necessary during the establishment of memory.

Administration of lanthanum chloride following a reminder induces a transient loss of memory retrieval in day-old chicks

Lanthanum chloride (5.0 mM) administered immediately after a visual reminder presented to day-old chickens between 7.5 min and 48 h following a single trial passive avoidance learning task produced an immediate but transient loss of memory on retention test, an effect not observed in the absence of a reminder. The duration of the transient deficit was relatively stable with lanthanum chloride consistently inducing a loss of memory that was evident 5 min after the reminder, with recovery by 10-15 min. The results suggest that, for a period of at least up to 48 h after passive avoidance training, the activation of memory retrieval by a reminder stimulus may lead to processes which are sensitive to inhibition by the calcium channel antagonist lanthanum chloride. These results extend previously reported findings implicating the involvement of glutamate-sensitive channels in a transient memory process that is also activated as a result of a reminder stimulus, but that is no longer present 48 h after training. The glutamate-sensitive mechanism appears to be a secondary mechanism activated following memory retrieval and to be dependent on the level of memory consolidation that the memory for the original experience has undergone. The results presented here suggest that lanthanum chloride, a calcium channel antagonist, inhibits memory retrieval in the day-old chick. This effect implicates calcium channel mediated processes in immediate memory recall. Further, the results suggest the lanthanum inhibits a primary mechanism, that precedes that glutamate-sensitive mechanism identified previously and that both are dependent on the activation of memory retrieval by a reminder.

Cyclosporin A, an inhibitor of calcineurin, impairs memory formation in day-old chicks

Considerable evidence exists that changes in the phosphorylation state of neuronal proteins are correlated with learning and that inhibition of various protein kinases disrupts memory formation. Given the reversible nature of protein phosphorylation, a role for protein phosphatases in memory processing also seems likely. It has been shown recently that administration of the phosphatase inhibitor, okadaic acid, disrupts memory formation in day-old chicks, with retention deficits first appearing at approximately 40 min post-training [93]. In the present study the intracranial administration of the immunosuppressant cyclosporin A was also found to produce retention deficits in day-old chicks trained on a single-trial, passive-avoidance task, but the deficits were not significant until 85 min post-training. The difference could not be attributed to differences in the pharmacokinetics of the drugs. Since okadaic acid preferentially inhibits protein phosphatases 1 and 2A, while cyclosporin A is reported to inhibit only the Ca2+/calmodulin-dependent protein phosphatase, calcineurin, it is possible that different phosphatases may be involved in distinct stages of memory formation, as has been reported previously for protein kinases. The possibility that cyclosporin A may, in addition, act through inhibition of cyclophilin's peptidyl-prolyl-cis/transisomerase activity is also canvassed.

Prognostic factors of locoregionally recurrent nasopharyngeal carcinoma--a retrospective review of 182 cases

Locoregional relapse is the major cause of failure of nasopharyngeal carcinoma (NPC) after radical radiation therapy. The prognosis of such patients is dismal, and the factors related to the outcome are not well identified. Between January 1983 and December 1989, 1,168 new patients with biopsy-proven NPC were seen at this hospital. Eight hundred and eighty-three of these patients were treated uniformly with radical external irradiation and intracavitary treatment with or without chemotherapy. The clinical courses, retreatment outcomes, and prognostic factors for locoregional relapse and subsequent distant metastasis were analyzed. During the follow-up period of 3-10 years or until death, 182 patients (20.6%) developed locoregional relapses without distant metastasis initially. T stage and age were significant prognostic factors for locoregional recurrence. In contrast, histopathologic subtype, N stage, sex, and systemic chemotherapy were not. There were 36 patients (19.8%) who developed subsequent distant metastasis with or without retreatment. The median time from locoregional relapses to distant metastasis was 6 months in this study, and bone was the most frequent and the earliest site of distant metastasis. The N stage at diagnosis, the initial disease-free interval, the presence of neck nodal disease at relapse, and age were the significant factors for predicting the subsequent distant metastasis in locoregionally recurrent NPC patients. We recommend that additional systemic chemotherapy should be considered for retreatment of locoregional relapsed NPC, not only for enhancement of local control but also for eradicating microscopic metastasis as anticipated.

The involvement of Ca2+/calmodulin-dependent protein kinase in memory formation in day-old chicks

Day-old chicks trained on a single trial passive avoidance learning task showed a significant increase, relative to untrained controls, in activity of the Ca2+/calmodulin-dependent protein kinase (CaMK) in the particulate fraction from tissues from the intermediate medial hyperstriatum ventrale region of the forebrain. The increased kinase activity was observed within 10 min following training and persisted for at least 70 min posttraining. Amnesia for the task was induced by micromolar concentrations of the specific CAMK II antagonist, KN-62, administered into the neostriatal/hyperstriatal region of the forebrain. The effect of KN-62 was lateralized. In the right hemisphere, KN-62 induced amnesia only when injected within 2. 5 min following training, with memory loss evident by 5 min posttraining. In contrast, in the left hemisphere amnesia was induced by KN-62 administered as late as 5 min posttraining, with onset of amnesia occurring after 10 min posttraining. The findings were interpreted within the context of a three-stage model of memory formation.

Inhibition of glutamine synthetase activity prevents memory consolidation

Methionine sulfoximine, a specific inhibitor of the exclusively glial enzyme glutamine synthetase, was shown, at a concentration of 3.5-4.5 mM, to prevent consolidation of memory for a passive avoidance task in day-old chicks. Provided the drug was administered 5-20 min before the learning task, significant retention loss was observed from the normal time of onset of the second of three postulated stages in the memory formation sequence but the drug had to be administered considerably earlier. The amnestic effect of methionine sulfoximine was successfully counteracted by L-glutamine (10 mM) and monosodium glutamate (4 mM), and also by a cocktail of alpha-ketoglutarate (5 mM) and alanine (5 mM). This effect of methionine sulfoximine is attributed to its blockade of the production of glutamine via the glutamate-glutamine cycle, leading to a reduced capacity of neurons to replenish their transmitter glutamate.

Astrocyte-neuron interaction during one-trial aversive learning in the neonate chick

During two specific stages of the Gibbs-Ng model of one-trial aversive learning in the neonate chick, we have recently found unequivocal evidence for a crucial involvement of astrocytes. This evidence is metabolic (utilization of the astrocyte-specific energy store, glycogen, during normal learning and inhibition of memory formation by the astrocyte specific metabolic inhibitors, fluoroacetate and methionine sulfoximine) as well as physiological (abolition of memory formation in the presence of ethacrynic acid, an astrocyte-specific inhibitor of cellular reaccumulation of potassium ions). These findings are discussed in the present review in the framework of a more comprehensive description of metabolic and physiological neuronal-astrocytic interactions across an interstitial (extracellular) space bounded by minute processes from either cell type.

Control of high common mode voltage during transthoracic defibrillation

A high common mode voltage (Vcm) relative to earth ground is produced on the myocardium during the delivery of a defibrillator pulse and can generate a differential error signal when potential gradients are recorded with bipolar electrodes and isolation amplifiers. The error signal is proportional to Vcm, and therefore, a reduction in Vcm improves the accuracy of the potential gradient data. Experiments were conducted on 5 dogs to determine whether Vcm can be controlled using a bridge circuit. The bridge circuit consisted of a 5 k omega power rheostat in parallel with the transthoracic resistance of the dog. The variable contact of the rheostat was connected to earth ground, and by adjusting the rheostat, Vcm on the myocardium could be varied. In each dog, 20 A shocks were delivered through stainless steel transthoracic electrodes. Point contact electrodes sutured to the epicardium were used to measure Vcm. It was determined that Vcm could be reduced to approximately zero at a given electrode on the heart. In addition, for the 5 dogs studied, the maximum measured Vcm on the heart was only 10% of the transthoracic voltage when the bridge circuit was balanced for an interior point in the heart.

Administration of glutamate following a reminder induces transient memory loss in day-old chicks

Monosodium glutamate (4.0 mM) administered immediately after a visual reminder presented to day-old chickens between 7.5 min and 24 h following a single trial passive avoidance learning task produced transient losses of memory on retention test, an effect not observed in the absence of a reminder or when the reminder was given 48 h post-learning. The duration of the transient deficit decreased with increasing interval between the training and the reminder trial. The time of onset of memory loss after the reminder trial appeared to increase with increasing interval between the training and the reminder trials. The results suggest that, for a period of at least up to 24 h after passive avoidance training, retrieval of memory may lead to processes which are sensitive to inhibition by glutamate, with the duration of sensitivity post-retrieval decreasing as the period of memory consolidation increases. The results extend previously reported findings with rodents and suggest the possibility that consolidation of a stable memorial representation of a learning experience may take place over several days and may entail the concurrent laying down of a stable retrieval mechanism.

Glycogenolytic response of primary chick and mouse cultures of astrocytes to noradrenaline across development

Glycogen is the brain's largest energy store and it is mainly localised in astrocytes. Glycogen turnover is extremely rapid in the brain, especially during sudden increased demand when glucose supplies are insufficient. Previous culture studies have reported on the glycogenolytic effect of noradrenaline on 3--4 week-old primary mouse astrocyte cultures. This effect is believed to be mediated by the beta-adrenergic-cAMP signal transduction system. Recent evidence has shown a drop in forebrain glycogen levels at a specific time point during memory formation for a passive avoidance task in the day-old chick. This 'memory-related' glycogenolysis may be initiated by noradrenaline-induced rises in cAMP occurring around this point, but it is unknown whether astrocytic glycogenolysis is is stimulated by noradrenaline in day-old chicks. This question was approached in the present study and it was shown that noradrenaline is capable of stimulating both cAMP formation and glycogen breakdown in chick primary astrocyte cultures at developmental age (10-14 days in culture) comparable to the newborn chick. In contrast, noradrenaline did not have a corresponding glycogenolytic effect on 10-day-old mouse astrocyte cultures (equivalent to the 1-week mouse), although it induced a considerable amount of glycogen breakdown in older cultures (18 and 24-26 days).

Inhibitors of cAMP-dependent protein kinase impair long-term memory formation in day-old chicks

There is substantial evidence that protein kinases, through the phosphorylation of substrate proteins, play a significant role in information processing in the brain, including processes underlying memory formation. Inhibition of the activity of the cyclic-adenosine monophosphate-dependent protein kinase A by the highly specific inhibitor, halofantrine, resulted in impairment of memory formation in day-old chicks trained on a single-trial passive avoidance task. A dose of 9.6 ng/chick halofantrine induced amnesia at the beginning of a protein synthesis-dependent long-term memory stage, the last of three stages of memory postulated to underly memory formation in the chick following passive avoidance learning. The concentration of halofantrine required for 50% inhibition of chick brain protein kinase A was found to be similar to that observed for bovine heart and rat liver. The amnestic effect of halofantrine is tentatively attributed to interference with de novo protein synthesis necessary for long-term memory consolidation. Neither anthraquinone nor the anthraquinone derivative anthraflavic acid, which have little effect on protein kinase A activity, affected memory retention. On the other hand, two other anthraquinone derivatives, chrysophanic acid and purpurin, which inhibit PKA activity, at doses of 0.25 and 0.5 ng/chick also yielded retention deficits. In these cases, however, retention losses occurred earlier than observed with halofantrine, at about 30 min post-training. The earlier effects of these inhibitors may be due to the additional inhibitory action of these compounds on protein kinase C activity, which has been demonstrated in previous studies to be implicated, possibly through phosphorylation of the GAP43 phosphoprotein, in memory processing in the stage of memory immediately preceding the protein synthesis-dependent long-term stage.