Computational Reconstruction of Pacemaking and Intrinsic Electroresponsiveness in Cerebellar Golgi Cells

The Golgi cells have been recently shown to beat regularly in vitro (Forti et al., 2006. J. Physiol. 574, 711–729). Four main currents were shown to be involved, namely a persistent sodium current (I Na-p), an h current (I h), an SK-type calcium-dependent potassium current (I K-AHP), and a slow M-like potassium current (I K-slow). These ionic currents could take part, together with others, also to different aspects of neuronal excitability like responses to depolarizing and hyperpolarizing current injection. However, the ionic mechanisms and their interactions remained largely hypothetical. In this work, we have investigated the mechanisms of Golgi cell excitability by developing a computational model. The model predicts that pacemaking is sustained by subthreshold oscillations tightly coupled to spikes. I Na-p and I K-slow emerged as the critical determinants of oscillations. I h also played a role by setting the oscillatory mechanism into the appropriate membrane potential range. I K-AHP, though taking part to the oscillation, appeared primarily involved in regulating the ISI following spikes. The combination with other currents, in particular a resurgent sodium current (I Na-r) and an A-current (I K-A), allowed a precise regulation of response frequency and delay. These results provide a coherent reconstruction of the ionic mechanisms determining Golgi cell intrinsic electroresponsiveness and suggests important implications for cerebellar signal processing, which will be fully developed in a companion paper (Solinas et al., 2008. Front. Neurosci. 2:4)

Fast-Reset of Pacemaking and Theta-Frequency Resonance Patterns in Cerebellar Golgi Cells: Simulations of their Impact In Vivo

The Golgi cells are inhibitory interneurons of the cerebellar granular layer, which respond to afferent stimulation in vivo with a burst-pause sequence interrupting their irregular background low-frequency firing (Vos et al., 1999a. Eur. J. Neurosci. 11, 2621–2634). However, Golgi cells in vitro are regular pacemakers (Forti et al., 2006. J. Physiol. 574, 711–729), raising the question how their ionic mechanisms could impact on responses during physiological activity. Using patch-clamp recordings in cerebellar slices we show that the pacemaker cycle can be suddenly reset by spikes, making the cell highly sensitive to input variations. Moreover, the neuron resonates around the pacemaker frequency, making it specifically sensitive to patterned stimulation in the theta-frequency band. Computational analysis based on a model developed to reproduce Golgi cell pacemaking (Solinas et al., 2008 Front. Neurosci., 2:2) predicted that phase-reset required spike-triggered activation of SK channels and that resonance was sustained by a slow voltage-dependent potassium current and amplified by a persistent sodium current. Adding balanced synaptic noise to mimic the irregular discharge observed in vivo, we found that pacemaking converts into spontaneous irregular discharge, that phase-reset plays an important role in generating the burst-pause pattern evoked by sensory stimulation, and that repetitive stimulation at theta-frequency enhances the time-precision of spike coding in the burst. These results suggest that Golgi cell intrinsic properties exert a profound impact on time-dependent signal processing in the cerebellar granular layer

Can selectivity be functionally modulated in ion channels?

In a two-electrode voltage-clamp study on the rat sympathetic neuron, the properties of the subsynaptic native neuronal AChR (nAChR) in response to the physiologically released ACh were shown to be modified within a few hours after denervation (Sacchi et al., 2008), suggesting that the nAChR ion selectivity switched from preferential permeability to potassium ions to scarce selectivity between K+ and Na+; the changes regarded synaptic, but not extrasynaptic, receptors and revealed an unexpected flexibility of the nicotinic channel in its permeation properties. Subsequently, a number of quite simple experimental procedures in intact ganglia were also shown to produce changes in conductance and ion selectivity properties of the nAChR; unlike denervation, such procedures (resting membrane potential shifts within a voltage range of physiological interest, ionic modifications, and the action of \u3b1-bungarotoxin) were very unlikely to acutely produce modifications in nAChR subunit composition or steric conformation (Sacchi et al., 2011). Posttranslational modifications of the channel protein might have occurred, but the consistency of those results with the idea that impermeant Cl 12 ions might affect cation binding and/or penetration into the pore raised the aforementioned question of whether extrinsic factors might contribute, together with the structural organization of the pore, to determine the permeability and ion selectivity of the channel. Actually, any change in the potential profile along the pore (and/or at its mouths) is bound to affect both the thermodynamic aspects of ion permeation (local field profile and ion binding to sites within the pore) and the kinetic aspects (ease of ion displacement and traveling among subsequent sites). These appear to constitute two distinct factors in determining ion selectivity, but the two aspects are strictly related. The electrical field across the membrane, determined by the membrane potential (Vm), may well be constant and produce a linear change in free energy along the pore. However, the thermodynamic profiles in ion-selective channels display nonlinear variations in the local potential seen by each ion, so that the energetic profile, \u394G(x) = G(x) 12 G(0) (where 0 refers to the extracellular bulk solution), is not simply a result of the presence of the membrane potential. At equilibrium, the probability for an ion to be located at x, p(x), is proportional to exp(\u2013\u394G(x)/RT); this determines the ratio between forward and backward velocities. As a purely qualitative, numerical example, an arbitrary pore energy profile has been simulated for the Na+ and K+ ions. The profiles for the ions are arbitrarily designed, based on the suggested differential coordination of Na+ and K+ with the charges lining the pore (Nimigean and Allen, 2011). From the same energy profile in the presence of a constant electrical field (Vm = \u20133RT/zF 48 \u201375 mV) the relative occupancy along the pore for Na+ and K+ has been computed, and the resulting permeability derived. It is shown that simple modifications of the profiles by Ca- concentration could account for the observed changes in cation selectivit

Granule cell ascending axon excitatory synapses onto Golgi cells implement a potent feedback circuit in the cerebellar granular layer.

The function of inhibitory interneurons within brain microcircuits depends critically on the nature and properties of their excitatory synaptic drive. Golgi cells (GoCs) of the cerebellum inhibit cerebellar granule cells (GrCs) and are driven both by feedforward mossy fiber (mf) and feedback GrC excitation. Here, we have characterized GrC inputs to GoCs in rats and mice. We show that, during sustained mf discharge, synapses from local GrCs contribute equivalent charge to GoCs as mf synapses, arguing for the importance of the feedback inhibition. Previous studies predicted that GrC-GoC synapses occur predominantly between parallel fibers (pfs) and apical GoC dendrites in the molecular layer (ML). By combining EM and Ca(2+) imaging, we now demonstrate the presence of functional synaptic contacts between ascending axons (aa) of GrCs and basolateral dendrites of GoCs in the granular layer (GL). Immunohistochemical quantification estimates these contacts to be ∼400 per GoC. Using Ca(2+) imaging to identify synaptic inputs, we show that EPSCs from aa and mf contacts in basolateral dendrites display similarly fast kinetics, whereas pf inputs in the ML exhibit markedly slower kinetics as they undergo strong filtering by apical dendrites. We estimate that approximately half of the local GrC contacts generate fast EPSCs, indicating their basolateral location in the GL. We conclude that GrCs, through their aa contacts onto proximal GoC dendrites, define a powerful feedback inhibitory circuit in the GL.journal articleresearch support, non-u.s. gov't2013 Jul 24importe

Desenvolvimento de sistema de baixo custo para monitoramento de integridade estrutural

O Monitoramento da Integridade Estrutural (MIE) pode ser utilizado para avaliar as condições de integridadede uma estrutura, ou ainda para verificar modelos de comportamento da mesma. Os atuais sistemas de monitoramentoaplicados em grandes estruturas, contam com inúmeros sensores, dos mais variados tipos, queformam redes de comunicação, em alguns casos sem fio, até sistemas automatizados de aquisição de dados,do inglês data acquisition (DAQ) e processamento dos resultados, o que inclusive permite a realização de ummonitoramento em tempo real e remoto. Entretanto, muitas das tecnologias empregadas nestes sistemas, sãode custo relativamente alto, e carecem de conhecimento específico para operação, o que em alguns casos,torna sua utilização inviável. Neste contexto, foi desenvolvido um sistema DAQ com um hardware a partir daplataforma Arduino, associada a um software mobile para smartphones, que via Bluetooth, envia e recebeinformações do Arduino, para aquisição de dados de deformação, deslocamento e força, da estrutura monitorada,com transmissão de dados em tempo real via internet. Foram realizados ensaios de flexão em lâminasmetálicas e vigas de concreto armado, com o uso de extensômetros, transdutores de deslocamento e célula decarga, sendo os dados aquisitados por um equipamento comercial de referência e o sistema desenvolvido nestapesquisa, com a comparação entre os mesmos, onde se obtiveram resultados satisfatórios.Palavras-chave: Monitoramento da Integridade Estrutural; Deformação; Deslocamento; Sistema de BaixoCusto

Estudos numérico-experimentais de vigas de concreto armado com reforço de fibra de carbono

Em algumas construções são necessárias intervenções para restabelecer ou aumentar a capacidade de suporte da estrutura antes de atingir um estado limite. Os Polímeros Reforçados com Fibra de Carbono (CFRP) são um dos mais adequados como elemento de reforço estrutural por ser um material de alto desempenho mecânico e elevado módulo de elasticidade, resistência à fadiga e baixo peso específico. Este trabalho teve como objetivo analisar a eficiência de materiais compósitos de Polímeros Reforçados com Fibras de Carbono (CFRP) como reforço estrutural em vigas de concreto armado, por meio de ensaios experimentais e simulação numérica. Nos ensaios, a armadura da viga de concreto foi dimensionada com resistência insuficiente ao cisalhamento. Nas vigas de referência, inicialmente, surgiram fissuras de cisalhamento, e em seguida as vigas romperam-se à flexão. Nas vigas com CRFP, que foram dimensionadas como reforço ao cisalhamento, as vigas não apresentaram fissuras de cisalhamento e romperam à flexão. Não houve acréscimo significativo da carga máxima. Em apenas uma viga houve o descolamento da fibra de carbono em um dos bordos da estrutura, mostrando boa eficiência do adesivo utilizado. As simulações numéricas foram realizadas utilizando o Método dos Elementos Finitos (MEF) no software ANSYS 18.1. Os resultados obtidos no modelo numérico ficaram próximos aos resultados experimentais.Palavras-chave: Reforço estrutural, Fibra de carbono, Experimental, Simulação numérica.

"Delirium Day": A nationwide point prevalence study of delirium in older hospitalized patients using an easy standardized diagnostic tool

Background: To date, delirium prevalence in adult acute hospital populations has been estimated generally from pooled findings of single-center studies and/or among specific patient populations. Furthermore, the number of participants in these studies has not exceeded a few hundred. To overcome these limitations, we have determined, in a multicenter study, the prevalence of delirium over a single day among a large population of patients admitted to acute and rehabilitation hospital wards in Italy. Methods: This is a point prevalence study (called "Delirium Day") including 1867 older patients (aged 65 years or more) across 108 acute and 12 rehabilitation wards in Italian hospitals. Delirium was assessed on the same day in all patients using the 4AT, a validated and briefly administered tool which does not require training. We also collected data regarding motoric subtypes of delirium, functional and nutritional status, dementia, comorbidity, medications, feeding tubes, peripheral venous and urinary catheters, and physical restraints. Results: The mean sample age was 82.0 ± 7.5 years (58 % female). Overall, 429 patients (22.9 %) had delirium. Hypoactive was the commonest subtype (132/344 patients, 38.5 %), followed by mixed, hyperactive, and nonmotoric delirium. The prevalence was highest in Neurology (28.5 %) and Geriatrics (24.7 %), lowest in Rehabilitation (14.0 %), and intermediate in Orthopedic (20.6 %) and Internal Medicine wards (21.4 %). In a multivariable logistic regression, age (odds ratio [OR] 1.03, 95 % confidence interval [CI] 1.01-1.05), Activities of Daily Living dependence (OR 1.19, 95 % CI 1.12-1.27), dementia (OR 3.25, 95 % CI 2.41-4.38), malnutrition (OR 2.01, 95 % CI 1.29-3.14), and use of antipsychotics (OR 2.03, 95 % CI 1.45-2.82), feeding tubes (OR 2.51, 95 % CI 1.11-5.66), peripheral venous catheters (OR 1.41, 95 % CI 1.06-1.87), urinary catheters (OR 1.73, 95 % CI 1.30-2.29), and physical restraints (OR 1.84, 95 % CI 1.40-2.40) were associated with delirium. Admission to Neurology wards was also associated with delirium (OR 2.00, 95 % CI 1.29-3.14), while admission to other settings was not. Conclusions: Delirium occurred in more than one out of five patients in acute and rehabilitation hospital wards. Prevalence was highest in Neurology and lowest in Rehabilitation divisions. The "Delirium Day" project might become a useful method to assess delirium across hospital settings and a benchmarking platform for future surveys

The association of indwelling urinary catheter with delirium in hospitalized patients and nursing home residents: an explorative analysis from the "Delirium Day 2015"

Backround: Use of indwelling urinary catheter (IUC) in older adults has negative consequences, including delirium. Aim: This analysis, from the "Delirium Day 2015", a nationwide multicenter prevalence study, aim to evaluate the association of IUC with delirium in hospitalized and Nursing Homes (NHs) patients. Methods: Patients underwent a comprehensive geriatric assessment, including the presence of IUC; inclusion criteria were age > 65 years, being Italian speaker and providing informed consent; exclusion criteria were coma, aphasia, end-of-life status. Delirium was assessed using the 4AT test (score ≥ 4: possible delirium; scores 1-3: possible cognitive impairment). Results: Among 1867 hospitalized patients (mean age 82.0 ± 7.5 years, 58% female), 539 (28.9%) had IUC, 429 (22.9%) delirium and 675 (36.1%) cognitive impairment. IUC was significantly associated with cognitive impairment (OR 1.60, 95% CI 1.19-2.16) and delirium (2.45, 95% CI 1.73-3.47), this latter being significant also in the subset of patients without dementia (OR 2.28, 95% CI 1.52-3.43). Inattention and impaired alertness were also independently associated with IUC. Among 1454 NHs residents (mean age 84.4 ± 7.4 years, 70.% female), 63 (4.3%) had IUC, 535 (36.8%) a 4AT score ≥ 4, and 653 (44.9%) a 4AT score 1-3. The multivariate logistic regression analysis did not show a significant association between 4AT test or its specific items with IUC, neither in the subset of patients without dementia. Discussion: We confirmed a significant association between IUC and delirium in hospitalized patients but not in NHs residents. Conclusion: Environmental and clinical factors of acute setting might contribute to IUC-associated delirium occurrence

"Delirium Day": A nationwide point prevalence study of delirium in older hospitalized patients using an easy standardized diagnostic tool

Background: To date, delirium prevalence in adult acute hospital populations has been estimated generally from pooled findings of single-center studies and/or among specific patient populations. Furthermore, the number of participants in these studies has not exceeded a few hundred. To overcome these limitations, we have determined, in a multicenter study, the prevalence of delirium over a single day among a large population of patients admitted to acute and rehabilitation hospital wards in Italy. Methods: This is a point prevalence study (called "Delirium Day") including 1867 older patients (aged 65 years or more) across 108 acute and 12 rehabilitation wards in Italian hospitals. Delirium was assessed on the same day in all patients using the 4AT, a validated and briefly administered tool which does not require training. We also collected data regarding motoric subtypes of delirium, functional and nutritional status, dementia, comorbidity, medications, feeding tubes, peripheral venous and urinary catheters, and physical restraints. Results: The mean sample age was 82.0 \ub1 7.5 years (58 % female). Overall, 429 patients (22.9 %) had delirium. Hypoactive was the commonest subtype (132/344 patients, 38.5 %), followed by mixed, hyperactive, and nonmotoric delirium. The prevalence was highest in Neurology (28.5 %) and Geriatrics (24.7 %), lowest in Rehabilitation (14.0 %), and intermediate in Orthopedic (20.6 %) and Internal Medicine wards (21.4 %). In a multivariable logistic regression, age (odds ratio [OR] 1.03, 95 % confidence interval [CI] 1.01-1.05), Activities of Daily Living dependence (OR 1.19, 95 % CI 1.12-1.27), dementia (OR 3.25, 95 % CI 2.41-4.38), malnutrition (OR 2.01, 95 % CI 1.29-3.14), and use of antipsychotics (OR 2.03, 95 % CI 1.45-2.82), feeding tubes (OR 2.51, 95 % CI 1.11-5.66), peripheral venous catheters (OR 1.41, 95 % CI 1.06-1.87), urinary catheters (OR 1.73, 95 % CI 1.30-2.29), and physical restraints (OR 1.84, 95 % CI 1.40-2.40) were associated with delirium. Admission to Neurology wards was also associated with delirium (OR 2.00, 95 % CI 1.29-3.14), while admission to other settings was not. Conclusions: Delirium occurred in more than one out of five patients in acute and rehabilitation hospital wards. Prevalence was highest in Neurology and lowest in Rehabilitation divisions. The "Delirium Day" project might become a useful method to assess delirium across hospital settings and a benchmarking platform for future surveys