Modeling realistic synaptic inputs of CA1 hippocampal pyramidal neurons and interneurons via Adaptive Generalized Leaky Integrate-and-Fire models

Computational models of brain regions are crucial for understanding neuronal network dynamics and the emergence of cognitive functions. However, current supercomputing limitations hinder the implementation of large networks with millions of morphological and biophysical accurate neurons. Consequently, research has focused on simplified spiking neuron models, ranging from the computationally fast Leaky Integrate and Fire (LIF) linear models to more sophisticated non-linear implementations like Adaptive Exponential (AdEX) and Izhikevic models, through Generalized Leaky Integrate and Fire (GLIF) approaches. However, in almost all cases, these models are tuned (and can be validated) only under constant current injections and they may not, in general, also reproduce experimental findings under variable currents. This study introduces an Adaptive GLIF (A-GLIF) approach that addresses this limitation by incorporating a new set of update rules. The extended A-GLIF model successfully reproduces both constant and variable current inputs, and it was validated against the results obtained using a biophysical accurate model neuron. This enhancement provides researchers with a tool to optimize spiking neuron models using classic experimental traces under constant current injections, reliably predicting responses to synaptic inputs, which can be confidently used for large-scale network implementations.

Mathematical generation of data-driven hippocampal CA1 pyramidal neurons and interneurons copies via A-GLIF models for large-scale networks covering the experimental variability range

Efficient and accurate large-scale networks are a fundamental tool in modeling brain areas, to advance our understanding of neuronal dynamics. However, their implementation faces two key issues: computational efficiency and heterogeneity. Computational efficiency is achieved using simplified neurons, whereas there are no practical solutions available to solve the problem of reproducing in a large-scale network the experimentally observed heterogeneity of the intrinsic properties of neurons. This is important, because the use of identical nodes in a network can generate artifacts which can hinder an adequate representation of the properties of a real network. To this aim, we introduce a mathematical procedure to generate an arbitrary large number of copies of simplified hippocampal CA1 pyramidal neurons and interneurons models, which exhibit the full range of firing dynamics observed in these cells - including adapting, non-adapting and bursting. For this purpose, we rely on a recently published adaptive generalized leaky integrate-and-fire (A-GLIF) modeling approach, leveraging on its ability to reproduce the rich set of electrophysiological behaviors of these types of neurons under a variety of different stimulation currents. The generation procedure is based on a perturbation of model's parameters related to the initial data, firing block, and internal dynamics, and suitably validated against experimental data to ensure that the firing dynamics of any given cell copy remains within the experimental range. A classification procedure confirmed that the firing behavior of most of the pyramidal/interneuron copies was consistent with the experimental data. This approach allows to obtain heterogeneous copies with mathematically controlled firing properties. A full set of heterogeneous neurons composing the CA1 region of a rat hippocampus (approximately 1.2 million neurons), are provided in a database freely available in the live paper section of the EBRAINS platform. By adapting the underlying A-GLIF framework, it will be possible to extend the numerical approach presented here to create, in a mathematically controlled manner, an arbitrarily large number of non-identical copies of cell populations with firing properties related to other brain areas.

Efficacy and Safety of Direct Oral Anticoagulants (DOACs) Versus Warfarin in Atrial Fibrillation Patients with Prior Stroke: a Systematic Review and Meta-analysis

BACKGROUND

The purpose of this meta-analysis was to compare efficacy and safety of direct oral anticoagulants (DOACs) to warfarin for secondary stroke prevention among adult patients with atrial fibrillation and prior stroke.

METHODS

Major repositories were screened for randomized controlled trials (RCTs), RCT subgroups, and observational studies (OBSs, divided in claims and non-claims). Occurrences of ischemic stroke or transient ischemic attack, systemic embolism, all-cause mortality, intracranial hemorrhage (ICH), and major bleeding were outcomes of interest. Hazard ratios (HRs) and their confidence intervals (95%CIs) were pooled using random-effects models for each study design. Claims studies were analyzed separately from non-claims, while RCT subgroups were grouped with OBSs (non-claims) as the randomization was broken.

RESULTS

Of 8647 articles, 20 were included (one RCT, six RCT subgroups, nine claims, and four non-claims). Comparing DOACs to warfarin, pooled HRs (95%CI) were consistently in favor of DOACs although some did not reach statistical significance: for ischemic stroke, 0.84 (0.66-1.07) in claims; 0.90 (0.77-1.06) in non-claims and RCT subgroups; for systemic embolism, 0.77 (0.62-0.96) in claims; 0.86 (0.77-0.96) in non-claims and RCT subgroups; for all-cause mortality, 0.57 (0.33-0.99) in claims; 0.87 (0.79-0.96) in non-claims and RCT subgroups; for ICH, 0.72 (0.39-1.33) in claims; 0.51 (0.38-0.67) in non-claims and RCT subgroups; and for major bleeding, 0.86 (0.71-1.03) in claims; 0.90 (0.76-1.08) for non-claims and RCT subgroups.

CONCLUSION

DOACs were associated with better efficacy and safety profiles than warfarin in atrial fibrillation patients with prior stroke, more specifically a lower risk of systemic embolism, all-cause mortality, and ICH.

The influence of anastomotic techniques on postoperative anastomotic complications: Results of the Oesophago-Gastric Anastomosis Audit

BACKGROUND

The optimal anastomotic techniques in esophagectomy to minimize rates of anastomotic leakage and conduit necrosis are not known. The aim of this study was to assess whether the anastomotic technique was associated with anastomotic failure after esophagectomy in the international Oesophago-Gastric Anastomosis Audit cohort.

METHODS

This prospective observational multicenter cohort study included patients undergoing esophagectomy for esophageal cancer over 9 months during 2018. The primary exposure was the anastomotic technique, classified as handsewn, linear stapled, or circular stapled. The primary outcome was anastomotic failure, namely a composite of anastomotic leakage and conduit necrosis, as defined by the Esophageal Complications Consensus Group. Multivariable logistic regression modeling was used to identify the association between anastomotic techniques and anastomotic failure, after adjustment for confounders.

RESULTS

Of the 2238 esophagectomies, the anastomosis was handsewn in 27.1%, linear stapled in 21.0%, and circular stapled in 51.9%. Anastomotic techniques differed significantly by the anastomosis sites (P < .001), with the majority of neck anastomoses being handsewn (69.9%), whereas most chest anastomoses were stapled (66.3% circular stapled and 19.3% linear stapled). Rates of anastomotic failure differed significantly among the anastomotic techniques (P < .001), from 19.3% in handsewn anastomoses, to 14.0% in linear stapled anastomoses, and 12.1% in circular stapled anastomoses. This effect remained significant after adjustment for confounding factors on multivariable analysis, with an odds ratio of 0.63 (95% CI, 0.46-0.86; P = .004) for circular stapled versus handsewn anastomosis. However, subgroup analysis by anastomosis site suggested that this effect was predominantly present in neck anastomoses, with anastomotic failure rates of 23.2% versus 14.6% versus 5.9% for handsewn versus linear stapled anastomoses versus circular stapled neck anastomoses, compared with 13.7% versus 13.8% versus 12.2% for chest anastomoses.

CONCLUSIONS

Handsewn anastomoses appear to be independently associated with higher rates of anastomotic failure compared with stapled anastomoses. However, this effect seems to be largely confined to neck anastomoses, with minimal differences between techniques observed for chest anastomoses. Further research into standardization of anastomotic approach and techniques may further improve outcomes.

Textbook outcome following oesophagectomy for cancer: international cohort study

Background

Textbook outcome has been proposed as a tool for the assessment of oncological surgical care. However, an international assessment in patients undergoing oesophagectomy for oesophageal cancer has not been reported. This study aimed to assess textbook outcome in an international setting.

Methods

Patients undergoing curative resection for oesophageal cancer were identified from the international Oesophagogastric Anastomosis Audit (OGAA) from April 2018 to December 2018. Textbook outcome was defined as the percentage of patients who underwent a complete tumour resection with at least 15 lymph nodes in the resected specimen and an uneventful postoperative course, without hospital readmission. A multivariable binary logistic regression model was used to identify factors independently associated with textbook outcome, and results are presented as odds ratio (OR) and 95 per cent confidence intervals (95 per cent c.i.).

Results

Of 2159 patients with oesophageal cancer, 39.7 per cent achieved a textbook outcome. The outcome parameter ‘no major postoperative complication’ had the greatest negative impact on a textbook outcome for patients with oesophageal cancer, compared to other textbook outcome parameters. Multivariable analysis identified male gender and increasing Charlson comorbidity index with a significantly lower likelihood of textbook outcome. Presence of 24-hour on-call rota for oesophageal surgeons (OR 2.05, 95 per cent c.i. 1.30 to 3.22; P = 0.002) and radiology (OR 1.54, 95 per cent c.i. 1.05 to 2.24; P = 0.027), total minimally invasive oesophagectomies (OR 1.63, 95 per cent c.i. 1.27 to 2.08; P &lt; 0.001), and chest anastomosis above azygous (OR 2.17, 95 per cent c.i. 1.58 to 2.98; P &lt; 0.001) were independently associated with a significantly increased likelihood of textbook outcome.

Conclusion

Textbook outcome is achieved in less than 40 per cent of patients having oesophagectomy for cancer. Improvements in centralization, hospital resources, access to minimal access surgery, and adoption of newer techniques for improving lymph node yield could improve textbook outcome.

Textbook outcome following oesophagectomy for cancer: international cohort study

BACKGROUND

Textbook outcome has been proposed as a tool for the assessment of oncological surgical care. However, an international assessment in patients undergoing oesophagectomy for oesophageal cancer has not been reported. This study aimed to assess textbook outcome in an international setting.

METHODS

Patients undergoing curative resection for oesophageal cancer were identified from the international Oesophagogastric Anastomosis Audit (OGAA) from April 2018 to December 2018. Textbook outcome was defined as the percentage of patients who underwent a complete tumour resection with at least 15 lymph nodes in the resected specimen and an uneventful postoperative course, without hospital readmission. A multivariable binary logistic regression model was used to identify factors independently associated with textbook outcome, and results are presented as odds ratio (OR) and 95 per cent confidence intervals (95 per cent c.i.).

RESULTS

Of 2159 patients with oesophageal cancer, 39.7 per cent achieved a textbook outcome. The outcome parameter 'no major postoperative complication' had the greatest negative impact on a textbook outcome for patients with oesophageal cancer, compared to other textbook outcome parameters. Multivariable analysis identified male gender and increasing Charlson comorbidity index with a significantly lower likelihood of textbook outcome. Presence of 24-hour on-call rota for oesophageal surgeons (OR 2.05, 95 per cent c.i. 1.30 to 3.22; P = 0.002) and radiology (OR 1.54, 95 per cent c.i. 1.05 to 2.24; P = 0.027), total minimally invasive oesophagectomies (OR 1.63, 95 per cent c.i. 1.27 to 2.08; P < 0.001), and chest anastomosis above azygous (OR 2.17, 95 per cent c.i. 1.58 to 2.98; P < 0.001) were independently associated with a significantly increased likelihood of textbook outcome.

CONCLUSION

Textbook outcome is achieved in less than 40 per cent of patients having oesophagectomy for cancer. Improvements in centralization, hospital resources, access to minimal access surgery, and adoption of newer techniques for improving lymph node yield could improve textbook outcome.

Postoperative outcomes in oesophagectomy with trainee involvement

BACKGROUND

The complexity of oesophageal surgery and the significant risk of morbidity necessitates that oesophagectomy is predominantly performed by a consultant surgeon, or a senior trainee under their supervision. The aim of this study was to determine the impact of trainee involvement in oesophagectomy on postoperative outcomes in an international multicentre setting.

METHODS

Data from the multicentre Oesophago-Gastric Anastomosis Study Group (OGAA) cohort study were analysed, which comprised prospectively collected data from patients undergoing oesophagectomy for oesophageal cancer between April 2018 and December 2018. Procedures were grouped by the level of trainee involvement, and univariable and multivariable analyses were performed to compare patient outcomes across groups.

RESULTS

Of 2232 oesophagectomies from 137 centres in 41 countries, trainees were involved in 29.1 per cent of them (n = 650), performing only the abdominal phase in 230, only the chest and/or neck phases in 130, and all phases in 315 procedures. For procedures with a chest anastomosis, those with trainee involvement had similar 90-day mortality, complication and reoperation rates to consultant-performed oesophagectomies (P = 0.451, P = 0.318, and P = 0.382, respectively), while anastomotic leak rates were significantly lower in the trainee groups (P = 0.030). Procedures with a neck anastomosis had equivalent complication, anastomotic leak, and reoperation rates (P = 0.150, P = 0.430, and P = 0.632, respectively) in trainee-involved versus consultant-performed oesophagectomies, with significantly lower 90-day mortality in the trainee groups (P = 0.005).

CONCLUSION

Trainee involvement was not found to be associated with significantly inferior postoperative outcomes for selected patients undergoing oesophagectomy. The results support continued supervised trainee involvement in oesophageal cancer surgery.

The role of network connectivity on epileptiform activity

A number of potentially important mechanisms have been identified as key players to generate epileptiform activity, such as genetic mutations, activity-dependent alteration of synaptic functions, and functional network reorganization at the macroscopic level. Here we study how network connectivity at cellular level can affect the onset of epileptiform activity, using computational model networks with different wiring properties. The model suggests that networks connected as in real brain circuits are more resistant to generate seizure-like activity. The results suggest new experimentally testable predictions on the cellular network connectivity in epileptic individuals, and highlight the importance of using the appropriate network connectivity to investigate epileptiform activity with computational models.

Mortality from esophagectomy for esophageal cancer across low, middle, and high-income countries: An international cohort study

BACKGROUND

No evidence currently exists characterising global outcomes following major cancer surgery, including esophageal cancer. Therefore, this study aimed to characterise impact of high income countries (HIC) versus low and middle income countries (LMIC) on the outcomes following esophagectomy for esophageal cancer.

METHOD

This international multi-center prospective study across 137 hospitals in 41 countries included patients who underwent an esophagectomy for esophageal cancer, with 90-day follow-up. The main explanatory variable was country income, defined according to the World Bank Data classification. The primary outcome was 90-day postoperative mortality, and secondary outcomes were composite leaks (anastomotic leak or conduit necrosis) and major complications (Clavien-Dindo Grade III - V). Multivariable generalized estimating equation models were used to produce adjusted odds ratios (ORs) and 95% confidence intervals (CI95%).

RESULTS

Between April 2018 to December 2018, 2247 patients were included. Patients from HIC were more significantly older, with higher ASA grade, and more advanced tumors. Patients from LMIC had almost three-fold increase in 90-day mortality, compared to HIC (9.4% vs 3.7%, p < 0.001). On adjusted analysis, LMIC were independently associated with higher 90-day mortality (OR: 2.31, CI95%: 1.17-4.55, p = 0.015). However, LMIC were not independently associated with higher rates of anastomotic leaks (OR: 1.06, CI95%: 0.57-1.99, p = 0.9) or major complications (OR: 0.85, CI95%: 0.54-1.32, p = 0.5), compared to HIC.

CONCLUSION

Resections in LMIC were independently associated with higher 90-day postoperative mortality, likely reflecting a failure to rescue of these patients following esophagectomy, despite similar composite anastomotic leaks and major complication rates to HIC. These findings warrant further research, to identify potential issues and solutions to improve global outcomes following esophagectomy for cancer.

P527Ultrasound-guided serratus anterior plane block for S-ICD implantation using the intermuscular technique

Funding Acknowledgements

NONE

Background

operative anesthetic requirements and peri-operative discomfort are barriers to wide adoption of the subcutaneous implantable cardioverter defibrillator (S-ICD) system expecially when the intermuscular technique is used due to the greater amount of tissue dissection. The procedure is most commonly performed under general anesthesia (GA). There is growing interest in transitioning away from the routine use of GA and towards several alternative anesthesia modalities implifying the anesthetic management of the S-ICD implant procedure without the involvement of an anesthesiologist.

Purpose

we assessed the feasibility of ultrasound-guided serratus anterior plane block (US-SAPB) in patients undergoing S-ICD implantation with the intermuscular two-incision technique. Methods: the study population included 38 consecutive patients (84% male; median, 53 [46-62] years) who received S-ICD implantation using the intermuscular two-incision technique. All procedures were performed under US-SAPB and sedoanalagesia without the involvement of an anesthesiologist.

Results

the average procedure time was 67 ± 14 minutes.No patient experienced significant hemodynamic changes or oxygen desaturation during the period of US- SAPB procedure and sedation; there was no need for pharmacological interventions. The whole procedute was well tollerated without discomfort and complications in the absence of needing GA except in one (2.6%) patient who required GA with laryngeal mask airway. Patients remained always able to respond appropriately to neurological monitoring during S-ICD implantation procedure. There were no procedure-related complications.

Conclusion

US-SAPB and the intermuscular two-incision technique may be a safe and feasible promising combination for S-ICD implantation overcoming potential barrier to wieder S-ICD adoption in the clinical practice.

Characterization of β-turns by electronic circular dichroism spectroscopy: a coupled molecular dynamics and time-dependent density functional theory computational study

Electronic circular dichroism is one of the most used spectroscopic techniques for peptide and protein structural characterization. However, while valuable experimental spectra exist for α-helix, β-sheet and random coil secondary structures, previous studies showed important discrepancies for β-turns, limiting their use as a reference for structural studies. In this paper, we simulated circular dichroism spectra for the best-characterized β-turns in peptides, namely types I, II, I' and II'. In particular, by combining classical molecular dynamics simulations and state-of-the-art quantum time-dependent density functional theory (with the polarizable embedding multiscale model) computations, two common electronic circular dichroism patterns were found for couples of β-turn types (namely, type I/type II' and type II/type I'), at first for a minimal di-peptide model (Ace-Ala-Ala-NHMe), but also for all sequences tested with non-aromatic residues in the central positions. On the other hand, as expected, aromatic substitution causes important perturbations to the previously found ECD patterns. Finally, by applying suitable approximations, these patterns were subsequently rationalized based on the exciton chirality rule. All these results provide useful predictions and pave the way for a possible experimental characterization of β-turns based on circular dichroism spectroscopy.

Molecular Dynamics Study of a KCl Aqueous Solution: Dynamical Results

In this paper we report on dynamical properties of a 2.2 molal aqueous KCl solution as obtained from an 8.7 ps MD simulation at an average temperature of 289 K. Velocity autocorrelation functions, self-diffusion coefficients and spectral densities of the hindered translational and librational motions of the ions and the water molecules assigned to three subsystems - hydration water of the cations, hydration water of the anions and bulk water - are discussed.

Pharmacophore model of the quercetin binding site of the SIRT6 protein

SIRT6 is a histone deacetylase that has been proposed as a potential therapeutic target for metabolic disorders and the prevention of age-associated diseases. We have previously reported on the identification of quercetin and vitexin as SIRT6 inhibitors, and studied structurally related flavonoids including luteolin, kaempferol, apigenin and naringenin. It was determined that the SIRT6 protein remained active after immobilization and that a single frontal displacement could correctly predict the functional activity of the immobilized enzyme. The previous study generated a preliminary pharmacophore for the quercetin binding site on SIRT6, containing 3 hydrogen bond donors and one hydrogen bond acceptor. In this study, we have generated a refined pharmacophore with an additional twelve quercetin analogs. The resulting model had a positive linear behavior between the experimental elution time verses the fit values obtained from the model with a correlation coefficient of 0.8456.

Anterior, extracanalar, cervical spine osteochondroma associated with DISH: description of a very rare tumor causing bilateral vocal cord paralysis, laryngeal compression and dysphagia. Case report and review of the literature

INTRODUCTION

Osteochondromas are common benign bone tumors, rarely involving the spine.

BACKGROUND

Osteochondroma account for about 35% of bone benign tumors and 9% of all bone tumors. Spinal involvement is described in 1%-4% of cases and their origin from the anterior surface of cervical vertebral bodies is exceedingly rare.

AIM

We describe the rare case of an osteochondroma arising from the anterior surface of the C4 and C5 vertebral bodies, and not involving the spinal canal, in a 68-year-old male patient suffering from Diffuse Idiopathic Skeletal Hyperostosis (DISH).

MATERIALS AND METHODS

The patient presented with acute onset of respiratory distress due to laryngeal compression exerted by the lesion, dysphagia and paralysis of left vocal cord. Imaging revealed the unusual lesion compressing and dislocating the air ways. An anterior approach to cervical spine was performed to remove the tumor.

RESULTS

Postoperatively, the patient sustained a progressive improvement of respiratory function and recovery of the vocal cord paralysis.

DISCUSSION

We believe that this case holds some interesting peculiarities: firstly, the anterior location of a cervical osteochondroma could be considered exceptional; yet, the resulting clinical picture should be remembered for differential diagnosis. Secondly, we hypothesized a possible correlation between the tumorigenesis of osteochondroma and the co-existence of DISH. Indeed, the abnormal bone turnover in cervical segments due to DISH could explain the unusual occurrence of osteochondromas in adult age.

CONCLUSIONS

The occurrence of an osteochondroma should be considered in patients suffering from DISH and harbouring large osteophytes.

Preterm delivery and premature rupture of membranes after conization in 80 women. Preliminary data

AIM

Cervical intraepithelial neoplasia is most frequently in young women in reproductive age. Cold knife conization, laser ablation, laser conization and large loop excision are conservative methods of treatment to remove the transformation zone and preserve the cervical function. Previous studies have shown conflicting results on the outcomes of pregnancy following these therapies that might increase the risk of preterm delivery. The purpose of this study was to evaluate the outcome of pregnancy after conization and its role as predictive risk factor.

METHODS

A retrospective study was performed. The study group comprised 80 women who had a conization and that had a subsequent singleton pregnancy. Variables considered includes maternal excision date, surgery procedure, previous surgery treatments, time interval between excisional procedure and subsequent pregnancy; duration and week of pregnancy, mode of delivery, histological grading (no cervical intraepithelial neoplasia [CIN], CIN 1, CIN 2-3) and cone excised depth.

RESULTS

In group study 45 women underwent loop electrosurgical excision procedure (LEEP) conization, 32 cold knife conization and 3 laser CO2. The authors found 11 cases of cone tissue depth<1 cm, and remaining one>1 cm. Eight preterm delivery have been reported to data: 5 between 28 and 34 weeks, 2 lower than 28 weeks and 1 between 34 and 37 weeks.

CONCLUSION

In these preliminary data the percentage of preterm birth appears as 10% and in range 6-15% evaluated for women not submitted to excisional procedures.

Learning mechanism for column formation in the olfactory bulb

Sensory discrimination requires distributed arrays of processing units. In the olfactory bulb, the processing units for odor discrimination are believed to involve dendrodendritic synaptic interactions between mitral and granule cells. There is increasing anatomical evidence that these cells are organized in columns, and that the columns processing a given odor are arranged in widely distributed arrays. Experimental evidence is lacking on the underlying learning mechanisms for how these columns and arrays are formed. To gain insight into these mechanisms, we have used a simplified realistic circuit model to test the hypothesis that distributed connectivity can self-organize through an activity-dependent dendrodendritic synaptic mechanism. The results point to action potentials propagating in the mitral cell lateral dendrites as playing a critical role in this mechanism. The model predicts that columns emerge from the interaction between the local temporal dynamics of the action potentials and the synapses that they activate during dendritic propagation. The results suggest a novel and robust learning mechanism for the development of distributed processing units in a cortical structure.

Realistic simulations of neuronal activity: a contribution to the debate on direct detection of neuronal currents by MRI

Many efforts have been done in order to preview the properties of the magnetic resonance (MR) signals produced by the neuronal currents using simulations. In this paper, starting with a detailed calculation of the magnetic field produced by the neuronal currents propagating over single hippocampal CA1 pyramidal neurons placed inside a cubic MR voxel of length 1.2 mm, we proceeded on the estimation of the phase and magnitude MR signals. We then extended the results to layers of parallel and synchronous similar neurons and to ensembles of layers, considering different echo times, voxel volumes and neuronal densities. The descriptions of the neurons and of their electrical activity took into account the real neuronal morphologies and the physiology of the neuronal events. Our results concern: (a) the expected time course of the MR signals produced by the neuronal currents in the brain, based on physiological and anatomical properties; (b) the different contributions of post-synaptic potentials and of action potentials to the MR signals; (c) the estimation of the equivalent current dipole and the influence of its orientation with respect to the external magnetic field on the observable MR signal variations; (d) the size of the estimated neuronal current induced phase and magnitude MR signal changes with respect to the echo time, voxel-size and neuronal density. The inclusion of realistic neuronal properties into the simulation introduces new information that can be helpful for the design of MR sequences for the direct detection of neuronal current effects and the testing of bio-electromagnetic models.

Dendritic action potentials connect distributed dendrodendritic microcircuits

Lateral inhibition of cells surrounding an excited area is a key property of sensory systems, sharpening the preferential tuning of individual cells in the presence of closely related input signals. In the olfactory pathway, a dendrodendritic synaptic microcircuit between mitral and granule cells in the olfactory bulb has been proposed to mediate this type of interaction through granule cell inhibition of surrounding mitral cells. However, it is becoming evident that odor inputs result in broad activation of the olfactory bulb with interactions that go beyond neighboring cells. Using a realistic modeling approach we show how backpropagating action potentials in the long lateral dendrites of mitral cells, together with granule cell actions on mitral cells within narrow columns forming glomerular units, can provide a mechanism to activate strong local inhibition between arbitrarily distant mitral cells. The simulations predict a new role for the dendrodendritic synapses in the multicolumnar organization of the granule cells. This new paradigm gives insight into the functional significance of the patterns of connectivity revealed by recent viral tracing studies. Together they suggest a functional wiring of the olfactory bulb that could greatly expand the computational roles of the mitral-granule cell network.

Parallel network simulations with NEURON

The NEURON simulation environment has been extended to support parallel network simulations. Each processor integrates the equations for its subnet over an interval equal to the minimum (interprocessor) presynaptic spike generation to postsynaptic spike delivery connection delay. The performance of three published network models with very different spike patterns exhibits superlinear speedup on Beowulf clusters and demonstrates that spike communication overhead is often less than the benefit of an increased fraction of the entire problem fitting into high speed cache. On the EPFL IBM Blue Gene, almost linear speedup was obtained up to 100 processors. Increasing one model from 500 to 40,000 realistic cells exhibited almost linear speedup on 2,000 processors, with an integration time of 9.8 seconds and communication time of 1.3 seconds. The potential for speed-ups of several orders of magnitude makes practical the running of large network simulations that could otherwise not be explored.

Input-output relations in the entorhinal cortex-dentate-hippocampal system: evidence for a non-linear transfer of signals

In the current study we analyzed the input-output relations in the entorhinal-dentate-hippocampal system, a major network involved in long-term memory. In anesthetized guinea pigs, the system was driven by activation of perforant path neurons in the entorhinal cortex (ENT), via presubicular fibers directly stimulated in the dorsal psalterium. Perforant path neuron discharge activated in parallel the dentate gyrus (DG) and hippocampal field CA2. Whereas the output from the DG activated hippocampal field CA3, the output from the sole field CA2 was sufficient for activation of field CA1. Signals from field CA3 operated in concert with CA2, likely contributing to discharge field CA1. These findings indicate the existence of two in parallel disynaptic systems: an ENT-CA2-CA1 and an ENT-DG-CA3 system. The convergence of the latter with the former gives origin the classical trisynaptic circuit, the ENT-DG-CA3-CA1 system. The input-output relations between the population excitatory postsynaptic potentials (pEPSP) evoked in the DG, CA3, CA2 and CA1 and the population spike (PS) evoked in the structure upstream (the input) were described by smooth sigmoid curves. In contrast, the input-output relations of the PS versus the pEPSP within each structure were described by steep sigmoid curves. The net input-output functions of the DG (ENT-DG system), field CA2 (ENT-CA2 system), field CA3 (ENT-DG-CA3 system) and field CA1 (ENT-CA2-CA1&ENT-DG-CA3-CA1 system) were described by sigmoid curves. While the DG and field CA2 exhibited steep sigmoids, fields CA3 and CA1 had less steep sigmoid functions. The present study demonstrates that all structures downstream to the ENT operate according to sigmoid input-output functions, characterized by specific parameters. These different behaviors may contribute to different memory processes. We additionally demonstrate that field CA1 can be activated by field CA2, independently from field CA3. This functional dissociation between CA3 and CA1 may subserve specific roles of each field in memory encoding/retrieval.

The role of distal dendritic gap junctions in synchronization of mitral cell axonal output

One of the first and most important stages of odor processing occurs in the glomerular units of the olfactory bulb and most likely involves mitral cell synchronization. Using a detailed model constrained by a number of experimental findings, we show how the intercellular coupling mediated by intraglomerular gap junctions (GJs) in the tuft dendrites could play a major role in sychronization of mitral cell action potential output in spite of their distal dendritic location. The model suggests that the high input resistance and active properties of the fine tuft dendrites are instrumental in generating local spike synchronization and an efficient forward and backpropagation of action potentials between the tuft and the soma. The model also gives insight into the physiological significance of long primary dendrites in mitral cells, and provides evidence against the use of reduced single compartmental models to investigate network properties of cortical pyramidal neurons.

Dendritic Ih selectively blocks temporal summation of unsynchronized distal inputs in CA1 pyramidal neurons

The active dendritic conductances shape the input-output properties of many principal neurons in different brain regions, and the various ways in which they regulate neuronal excitability need to be investigated to better understand their functional consequences. Using a realistic model of a hippocampal CA1 pyramidal neuron, we show a major role for the hyperpolarization-activated current, Ih, in regulating the spike probability of a neuron when independent synaptic inputs are activated with different degrees of synchronization and at different distances from the soma. The results allowed us to make the experimentally testable prediction that the Ih in these neurons is needed to reduce neuronal excitability selectively for distal unsynchronized, but not for synchronized, inputs.

The place of Belsey Mark IV fundoplication in the era of laparoscopic surgery☆

OBJECTIVES

Laparoscopic fundoplication to correct or avoid gastroesophageal reflux decreased Belsey Mark IV fundoplication (BMIV) dramatically worldwide. The purpose of this paper was to determine the role of BMIV and its current indications.

METHODS

We reviewed all patients who underwent fundoplication between April 1997 and December 2001. All patients underwent a complete work-up included barium meal, endoscopy, 24-h pH-metry and manometry preoperatively.

RESULTS

Sixty-two consecutive fundoplications were performed. There were 23 males and 39 females. Forty-six patients were treated by laparoscopic approach (37 patients with total and nine patients with partial fundoplication). BMIV was preferred in 16 patients with the following indications: reoperations for failed oesophageal surgery (5), hiatal hernia fixed in the chest (4), epiphrenic oesophageal diverticula (3), diffuse oesophageal spam (2), hiatal hernia associated with bullous emphysema (1), leiomyoma of the oesophago-gastric junction (1). Excellent to good results were reported in 14 patients and poor in two. Follow-up was completed in all patients.

CONCLUSIONS

BMIV remains a valid fundoplication although the current indications are now limited. The technique is to be considered an additional, but necessary, weapon for thoracic surgeons with interest in oesophageal disease.

Quantitative modeling of perception and production of time intervals

The accurate perception/production of durations in the seconds and minutes range is important in a number of everyday activities, but the lack of direct experimental evidence on the neural circuits that could be involved has precluded the detailed elucidation of the underlying physiological mechanisms. We show, using a basic biophysical model of a timekeeping system and experimental data on time intervals produced or estimated under different conditions, that experimental values, variability, and distributions can be quantitatively explained in terms of a background synaptic activity such as that generated by attention. The model provides a plausible neural substrate for encoding time intervals, and the findings suggest how it may interplay at the single neuron level with the attentional system, to elaborate a subjective representation of the elapsing time.

[Recent concepts regarding the treatment of traumatic hemopneumothorax]

BACKGROUND

The aim of the study was to examine the different therapeutic options for traumatic hemopneumothorax and in particular the latest concepts (videothoracoscopy).

METHODS

A retrospective study was performed on a group of 20 patients with post-traumatic hemothorax and/or pneumothorax attending the emergency department at Ospedale Vittorio Emanuele in Catania over the past 10 years where 2500 patients with abdominal and/or thoracic trauma were treated during the same period. The patients included 18 males and 2 females with a mean age of 35 years (range 13-70). The cause of injury was a gunshot wound in 8 patients, a blunt trauma following a road accident in 9 and a stab wound in 3 patients. A drainage tube was inserted in 15 patients (a videothoracoscopic approach was used in 2 cases); 3 patients required a diaphragmatic suture and 2 thoracotomy (inferior lobectomy and repair of the main left bronchus).

RESULTS

Three out of 20 patients died with an overall mortality rate of 15%. Two patients died respectively from severe brain and abdominal injuries associated with thoracic trauma, while the third patient died from septic complications.

CONCLUSIONS

In the past few years videothoracoscopy has allowed a different approach to be used in patients affected by hemo-pneumothorax since it allows a more accurate diagnosis (extent and origin of bleeding, identification of associated diaphragmatic lesion) and the possibility of treating pleuro-pulmonary injuries without performing extensive thoracotomies.

A single-trocar technique for minimally-invasive surgery of the chest

BACKGROUND

In thoracic surgery, the classic thoracoscope is used to perform simple maneuvers in the chest. We have devised a minimally invasive technique that requires only a single trocar. This technique is used in our department to diagnose and treat a wide range of thoracic pathologies.

METHODS

Between October 1998 and August 1999, 37 patients underwent surgery prospectively for a thoracic disease through a single trocar. There were 19 men and 18 women with a mean age of 60 years (range, 40-85). The trocar was flexible or soft and had a diameter of 15-20 mm. A 2-cm skin incision was made in the planned intercostal space. The chest drain was always inserted under video control.

RESULTS

The mean operative time was 53 +/- 5 min. One patient developed intraoperative bleeding that required intubation and a 5-cm mini-thoracotomy. In one patient with stage II empyema, it was necessary to insert another trocar. Chest tubes were removed after 77.7 +/- 7 h. Hospital stay was 4 +/- 1 days (range, 2-14). Histologic examination revealed malignant disease in 26 cases and benign disease in 11. Two patients (5.4%) developed wound infections. None of the patients had port site metastasis. There were no hospital deaths.

CONCLUSION

Because of its simplicity, we recommend the use of this mini-invasive technique in place of the classic thoracoscope or video-mediastinoscope.

A model of the effects of cognitive load on the subjective estimation and production of time intervals

How and where the brain calculates elapsing time is not known, and one or more internal pacemakers or others timekeeping systems have been suggested. Experiments have shown that the accuracy in estimating or producing time intervals depends on many factors and, in particular, both on the length of the intervals to be estimated and on the additional, and unrelated, cognitive load required during the task. The psychological 'attentional approach' is able to explain the experimental data in terms of perturbations of a cognitive timer. However, the basic biophysical mechanisms that could be involved at the single neuron level are still not clear. Here we propose a computational model suggesting how the process to focus the attention on a non-temporal task could alter the perception of time intervals as observed in the experiments. The model suggests that an attention-based excitatory and/or inhibitory background synaptic noise, impinging on the pacemaker circuit, could represent both qualitative and quantitative features of the cognitive load. These effects are predicted to be independent of the number, location or specific implementations of the internal timing systems.

[Systemic neoadjuvant chemotherapy in locally advanced gastric carcinoma: phase II study with 5-fluorouracil, epirubicin and etoposide]

Locally advanced gastric adenocarcinomas have a poor prognosis, particularly when the tumours are bulky, located in the cardia or when they present local/regional lymph node involvement. Neoadjuvant chemotherapy for locally advanced gastric cancer is an experimental treatment strategy that may increase resectability and improve survival in patients suffering from an almost uniformly fatal neoplasm. At our institution 11 patients younger than 70 years of age in good physical and mental condition with non-resectable adenocarcinomas of the stomach as determined by endoscopy, computed tomography scans and pathology examinations, were treated with combination chemotherapy [5-fluorouracil (375 mg/m2 i.v. for 5 days, epirubicin (60 mg/m2 i.v. on day 1), etoposide 80 mg/m2 on days 1, 2 and 3, leucovorin 100 mg/m2 for 5 days] every 4 weeks as neoadjuvant chemotherapy. The response to chemotherapy was evaluated after three courses. After three courses, we had one complete response, 8 partial responses or stable disease, and no response in two cases. One patient was still alive 36 months postoperatively. These preliminary results suggest that this protocol is an effective form of neoadjuvant chemotherapy for locally advanced gastric carcinoma.

Dendritic potassium channels in hippocampal pyramidal neurons

Potassium channels located in the dendrites of hippocampal CA1 pyramidal neurons control the shape and amplitude of back-propagating action potentials, the amplitude of excitatory postsynaptic potentials and dendritic excitability. Non-uniform gradients in the distribution of potassium channels in the dendrites make the dendritic electrical properties markedly different from those found in the soma. For example, the influence of a fast, calcium-dependent potassium current on action potential repolarization is progressively reduced in the first 150 micrometer of the apical dendrites, so that action potentials recorded farther than 200 micrometer from the soma have no fast after-hyperpolarization and are wider than those in the soma. The peak amplitude of back-propagating action potentials is also progressively reduced in the dendrites because of the increasing density of a transient potassium channel with distance from the soma. The activation of this channel can be reduced by the activity of a number of protein kinases as well as by prior depolarization. The depolarization from excitatory postsynaptic potentials (EPSPs) can inactivate these A-type K+ channels and thus lead to an increase in the amplitude of dendritic action potentials, provided the EPSP and the action potentials occur within the appropriate time window. This time window could be in the order of 15 ms and may play a role in long-term potentiation induced by pairing EPSPs and back-propagating action potentials.

Computational model of the effects of stochastic conditioning on the induction of long-term potentiation and depression

The long-term potentiation (LTP) or long-term depression (LTD) of synaptic strength are currently considered to be the first microscopic steps leading to learning and memory. The great majority of experiments (both in vitro and in vivo) studying the basic mechanisms of LTP and LTD induction use conditioning protocols in which the presynaptic stimuli are delivered at constant frequencies. This is not, however, what is commonly found in vivo, where a highly irregular spiking activity seems to drive most of the neuronal functions. Thus, some important aspects of the induction characteristics of LTP and LTD expressed in vivo might have been overlooked by the experiments. Using a simple schematic model for a synapse we show here that, in fact, the statistical properties of a presynaptic conditioning signal could change the probability to induce LTP and/or LTD, suggesting a new and faster operating mode for a synapse.

Clinical features and oesophageal motility in patients with tight fundoplication

OBJECTIVE

Tight fundoplication is a well known complication of surgery for gastroesophageal reflux. We have noted, in clinical experience, that some patients operated for gastro-oesophageal reflux develop pharyngo-oesophageal dysphagia. This study was undertaken to elucidate, by comparing motility data in patients with and without tight fundoplication, the pathophysiologic characteristics of the swallowing mechanism and to clarify the cause of dysphagia in these patients.

METHODS

Sixteen patients with postoperative persistent dysphagia following a fundoplication have been studied, of those 10 presented a lower oesophageal sphincter resting pressure above or equal to 30 mmHg (group A). Clinical work-up included a questionnaire, oendoscopy, manometry and barium meal or video-roentgenography. Oesophageal manometry was performed using a slow pull through technique while the stationary pull through technique was used for the pharyngo-oesophageal segment. The following parameters were evaluated: (a) amplitude of pharyngeal contraction; (b) upper oesophageal sphincter resting pressure; (c) amplitude of upper oesophageal sphincter contraction; (d) amplitude of oesophageal contraction; (e) lower oesophageal sphincter resting pressure. The results were compared to those of 21 patients who had a fundoplication with normal lower oesophageal sphincter pressure (group B).

RESULTS

in group A there were three males and seven females, with a mean age of 51 years (ranging from 28 to 60 years). Previous operations were Nissen in two and Nissen Rossetti in eight patients. Three out of 10 patients of group A presented pharyngo-oesophageal dysphagia. Mean lower oesophageal sphincter 36 versus 21 mmHg and upper oesophageal sphincter 86 versus 42 mmHg resting pressure, pharyngeal 147 versus 76 mmHg and oesophageal amplitude, upper oesophageal contraction 251 versus 103 mmHg were significantly higher in patients of group A versus group B. An increased number of repetitive contractions was also found in group A. The presence of a strong correlation was demonstrated between the pharyngeal amplitude and the closing tone of the upper oesophageal sphincter (R2 0.742 and R2 0.739) in both groups.

CONCLUSION

Tight fundoplication is, in our experience, always associated with total fundoplication. The appearance of pharyngo-oesophageal dysphagia in the postoperative period in patients operated on to correct gastroesophageal reflux using a total fundoplication, should not be under-estimated because it suggests an obstruction of the distal oesophagus.

Long-term potentiation and depression induced by a stochastic conditioning of a model synapse

Protracted presynaptic activity can induce long-term potentiation (LTP) or long-term depression (LTD) of the synaptic strength. However, virtually all the experiments testing how LTP and LTD depend on the conditioning input are carried out with trains of stimuli at constant frequencies, whereas neurons in vivo most likely experience a stochastic variation of interstimulus intervals. We used a computational model of synaptic transmission to test if and to what extent the stochastic fluctuations of an input signal could alter the probability to change the state of a synapse. We found that, even if the mean stimulation frequency was maintained constant, the probability to induce LTD and LTP could be a function of the temporal variation of the input activity. This mechanism, which depends only on the statistical properties of the input and not on the onset of additional biochemical mechanisms, is not usually considered in the experiments, but it could have an important role to determine the amount of LTP/LTD induction in vivo. In response to a change in the distribution of the interstimulus intervals, as measured by the coefficient of variation, a synapse could be easily adapted to inputs that might require immediate attention, with a shift of the input thresholds required to elicit LTD or LTP, which are restored to their initial conditions as soon as the input pattern returns to the original temporal distribution.

Role of an A-type K+ conductance in the back-propagation of action potentials in the dendrites of hippocampal pyramidal neurons

Action potentials elicited in the axon actively back-propagate into the dendritic tree. During this process their amplitudes can be modulated by internal and external factors. We used a compartmental model of a hippocampal CA1 pyramidal neuron to illustrate how this modulation could depend on (1) the properties of an A-type K+ conductance that is expressed at high density in hippocampal dendrites and (2) the relative timing of synaptic activation. The simulations suggest that the time relationship between pre- and postsynaptic activity could help regulate the amplitude of back-propagating action potentials, especially in the distal portion of the dendritic tree.

Energy efficient modulation of dendritic processing functions

The voltage dependent ionic conductances and the passive properties of the neural membrane determine how external inputs are processed by the dendritic tree, and define the computational characteristics of neurons. However, what controls these characteristics and how they are implemented at the single neuron level, in such a way that an external input results in the coding of the appropriate output, is essentially unknown. We show here that a slow inactivation of the Na+ channel, involved in the attenuation and/or failure of APs in the dendrites, acts as an active and energy efficient filter of synaptic input, and results in an activity-dependent control of the properties of individual neurons. Thus, the activation or expression of this mechanisms could be an efficient way to selectively modulate the input/output processing properties of dendrites, and could be needed to limit or suppress the onset of a number of pathological brain disorders.

Pedunculated intraluminal oesophageal fibrolipoma. A case report

Benign tumours of the oesophagus are rare. A patient with a pedunculated intraluminal tumour presented with dysphagia of recent onset and the tumour resected at open operation and histology was confirmed as a benign vascular fibrolipoma. We discuss the management and review the relevant literature.

Neuropsychological outcome of operated cerebral aneurysms: prognostic factors on 148 patients

OBJECTIVES

To analyse prognostic factors in patients operated upon for cerebral aneurysms. A previous investigation by our group showed that patients operated later than 10 days after bleeding have a worse neuropsychological prognosis, but the number of patients operated upon within 3 days was not sufficient. Here, a new sample of patients with early surgery is included in the analyses.

MATERIAL AND METHODS

Patients numbered 148 (65 with ACoA, 39 with MCA, and 44 with PCoA aneurysms): 56 were operated within 3 days, 44 within 4-10 days, and 48 after at least 10 days from bleeding. A standardized battery of 13 neuropsychological tests was adopted: we considered both the number of defective scores and the average performance.

RESULTS

Patients operated later than 10 days after bleeding had a worse prognosis than the 2 groups with early and intermediate surgery, which were not different. Aneurysm site was not relevant. Old age and low education were associated with a worse prognosis. Hunt and Hess scores at operation and post operation were also predictive of the outcome.

CONCLUSION

On the whole, patients operated upon later than 10 days after bleeding have a less favourable prognosis than those with earlier operation timing.

Possible roles of retrograde messengers on LTP, LTD, and associative memory

There are still no clear biophysical models for Associative Long-Term Potentiation (LTP) and Depression (LTD) in the hippocampus, where two populations of synapses targeted to the same receptive field are involved. Here we propose a model that allows an interpretation of the experiments in terms of the molecular processes that may be involved in associative memory. The model suggests that retrograde messengers could have a critical role in the induction and maintenance of associative LTP and LTD, by controlling the coupling between the two populations of synapses.

Modeling the attenuation and failure of action potentials in the dendrites of hippocampal neurons

We modeled two different mechanisms, a shunting conductance and a slow sodium inactivation, to test whether they could modulate the active propagation of a train of action potentials in a dendritic tree. Computer simulations, using a compartmental model of a pyramidal neuron, suggest that each of these two mechanisms could account for the activity-dependent attenuation and failure of the action potentials in the dendrites during the train. Each mechanism is shown to be in good qualitative agreement with experimental findings on somatic or dendritic stimulation and on the effects of hyperpolarization. The conditions under which branch point failures can be observed, and a few experimentally testable predictions, are presented and discussed.

Postoperative pain in neurosurgery: a pilot study in brain surgery

The incidence, magnitude, and duration of acute pain experienced by neurosurgical patients after various brain operations are not precisely known, because of a lack of well-designed clinical and epidemiological studies. We assessed these important pain variables in 37 consecutive patients who underwent various brain neurosurgical procedures. Postoperative pain was more common than generally assumed (60%). In two-thirds of the patients with postoperative pain, the intensity was moderate to severe. Pain most frequently occurred within the first 48 hours after surgery, but a significant number of patients endured pain for longer periods. Pain was predominantly superficial (86%), suggesting somatic rather than visceral origin and possibly involving pericranial muscles and soft tissues. Subtemporal and suboccipital surgical routes yielded the highest incidence of postoperative pain. Age and sex were significantly associated with the onset of pain, with female and younger patients reporting higher percentages of postoperative pain. Psychological Minnesota Multiphasic Personality Inventory profiles of patients with and without pain significantly differed on the Hypochondriasis scale, with patients without pain scoring unexpectedly higher than patients with pain. It is possible that hypochondriasis serves as a defense mechanism against pain, at least in some patients. Results of this pilot study indicate that postoperative pain after brain surgery is an important, although neglected, clinical problem, that deserves greater attention by surgical teams, to provide better and more appropriate treatment.

Pharyngo-oesophageal dysphagia: surgery based on clinical and manometric data

High or pharyngo-oesophageal dysphagia (PD) is defined as difficulty in initiating the act of swallowing within 1s. It involves the mechanisms controlling the tongue, pharynx and upper oesophageal sphincter (UOS) and is associated with a wide variety of local, neurologic and muscular disorders, and can also occur after surgery in the area and in response to gastro-oesophageal reflux (GOR). Our study aims at defining the criteria for surgery in PD and to evaluate the clinical results of such treatment. Twenty-three patients who underwent surgery were evaluated with pharyngo-oesophageal motility and ambulatory 24-hr pH-metry. The following parameters were measured: 1) pharyngeal contraction amplitude, 2) duration, 3) repetitive pharyngeal contractions, 4) UOS tone, 5) percentage of UOS relaxation, 6) duration of relaxation, 7) UOS closing pressure, 8) UOS closing duration, 9) co-ordination of UOS closing pressure and upper oesophageal (UO) contractions. Preoperative manometry showed a variety of abnormalities in several of the parameters, such as prolonged pharyngeal contraction ("spasm"), unco-ordinated pharyngeal contractions and UOS relaxation, low amplitude pharyngeal contractions, unco-ordinated UOS closing tone and UO contractions and hypotonic UO. Surgery was directed at the specific abnormality in each patient taking into consideration the presence or absence of GOR. Seventeen patients (74%) had excellent results. Three other patients (13%), who had improved swallowing but who continued to have GOR complicated by some oesophageal dysmotility, oesophagitis and an oesophageal web, underwent subsequent anti-reflux surgery with relief of symptoms. In conclusion, pharyngo-oesophageal motility measurement is mandatory in PD, especially when a diverticulum is absent. Cricopharyngeal myotomy with or without diverticulectomy as indicated produces excellent results. Associated oesophageal problems have to be dealt with appropriately.