Increased axonal bouton dynamics in the aging mouse cortex.

Aging is a major risk factor for many neurological diseases and is associated with mild cognitive decline. Previous studies suggest that aging is accompanied by reduced synapse number and synaptic plasticity in specific brain regions. However, most studies, to date, used either postmortem or ex vivo preparations and lacked key in vivo evidence. Thus, whether neuronal arbors and synaptic structures remain dynamic in the intact aged brain and whether specific synaptic deficits arise during aging remains unknown. Here we used in vivo two-photon imaging and a unique analysis method to rigorously measure and track the size and location of axonal boutons in aged mice. Unexpectedly, the aged cortex shows circuit-specific increased rates of axonal bouton formation, elimination, and destabilization. Compared with the young adult brain, large (i.e., strong) boutons show 10-fold higher rates of destabilization and 20-fold higher turnover in the aged cortex. Size fluctuations of persistent boutons, believed to encode long-term memories, also are larger in the aged brain, whereas bouton size and density are not affected. Our data uncover a striking and unexpected increase in axonal bouton dynamics in the aged cortex. The increased turnover and destabilization rates of large boutons indicate that learning and memory deficits in the aged brain arise not through an inability to form new synapses but rather through decreased synaptic tenacity. Overall our study suggests that increased synaptic structural dynamics in specific cortical circuits may be a mechanism for age-related cognitive decline.

Algebraic approach to spike-time neural codes in the hippocampus.

Although temporal coding through spike-time patterns has long been of interest in neuroscience, the specific structures that could be useful for spike-time codes remain highly unclear. Here, we introduce an analytical approach, using techniques from discrete mathematics, to study spike-time codes. As an initial example, we focus on the phenomenon of "phase precession" in the rodent hippocampus. During navigation and learning on a physical track, specific cells in a rodent's brain form a highly structured pattern relative to the oscillation of population activity in this region. Studies of phase precession largely focus on its role in precisely ordering spike times for synaptic plasticity, as the role of phase precession in memory formation is well established. Comparatively less attention has been paid to the fact that phase precession represents one of the best candidates for a spike-time neural code. The precise nature of this code remains an open question. Here, we derive an analytical expression for a function mapping points in physical space to complex-valued spikes by representing individual spike times as complex numbers. The properties of this function make explicit a specific relationship between past and future in spike patterns of the hippocampus. Importantly, this mathematical approach generalizes beyond the specific phenomenon studied here, providing a technique to study the neural codes within precise spike-time sequences found during sensory coding and motor behavior. We then introduce a spike-based decoding algorithm, based on this function, that successfully decodes a simulated animal's trajectory using only the animal's initial position and a pattern of spike times. This decoder is robust to noise in spike times and works on a timescale almost an order of magnitude shorter than typically used with decoders that work on average firing rate. These results illustrate the utility of a discrete approach, based on the structure and symmetries in spike patterns across finite sets of cells, to provide insight into the structure and function of neural systems.

Multi-synaptic boutons are a feature of CA1 hippocampal connections in the stratum oriens.

Excitatory synapses are typically described as single synaptic boutons (SSBs), where one presynaptic bouton contacts a single postsynaptic spine. Using serial section block-face scanning electron microscopy, we found that this textbook definition of the synapse does not fully apply to the CA1 region of the hippocampus. Roughly half of all excitatory synapses in the stratum oriens involved multi-synaptic boutons (MSBs), where a single presynaptic bouton containing multiple active zones contacted many postsynaptic spines (from 2 to 7) on the basal dendrites of different cells. The fraction of MSBs increased during development (from postnatal day 22 [P22] to P100) and decreased with distance from the soma. Curiously, synaptic properties such as active zone (AZ) or postsynaptic density (PSD) size exhibited less within-MSB variation when compared with neighboring SSBs, features that were confirmed by super-resolution light microscopy. Computer simulations suggest that these properties favor synchronous activity in CA1 networks.

A Distance-Dependent Distribution of Presynaptic Boutons Tunes Frequency-Dependent Dendritic Integration.

How presynaptic inputs and neurotransmitter release dynamics are distributed along a dendritic tree is not well established. Here, we show that presynaptic boutons that form onto basal dendrites of CA1 pyramidal neurons display a decrease in active zone (AZ) size with distance from the soma, resulting in a distance-dependent increase in short-term facilitation. Our findings suggest that the spatial distribution of short-term facilitation serves to compensate for the electrotonic attenuation of subthreshold distal inputs during repeated stimulation and fine-tunes the preferred input frequency of dendritic domains.

Long live the axon. Parallels between ageing and pathology from a presynaptic point of view.

All animals have to find the right balance between investing resources into their reproductive cycle and protecting their tissues from age-related damage. In higher order organisms the brain is particularly vulnerable to ageing, as the great majority of post-mitotic neurons are there to stay for an entire life. While ageing is unavoidable, it may progress at different rates in different individuals of the same species depending on a variety of genetic and environmental factors. Inevitably though, ageing results in a cognitive and sensory-motor decline caused by changes in neuronal structure and function. Besides normal ageing, age-related pathological conditions can develop in a sizeable proportion of the population. While this wide array of diseases are considerably different compared to physiological ageing, the two processes share many similarities and are likely to interact. At the subcellular level, two key structures are involved in brain ageing: axons and their synapses. Here I highlight how the ageing process affects these structures in normal and neurodegenerative states in different brain areas.

Systems genetics identifies Sestrin 3 as a regulator of a proconvulsant gene network in human epileptic hippocampus.

Gene-regulatory network analysis is a powerful approach to elucidate the molecular processes and pathways underlying complex disease. Here we employ systems genetics approaches to characterize the genetic regulation of pathophysiological pathways in human temporal lobe epilepsy (TLE). Using surgically acquired hippocampi from 129 TLE patients, we identify a gene-regulatory network genetically associated with epilepsy that contains a specialized, highly expressed transcriptional module encoding proconvulsive cytokines and Toll-like receptor signalling genes. RNA sequencing analysis in a mouse model of TLE using 100 epileptic and 100 control hippocampi shows the proconvulsive module is preserved across-species, specific to the epileptic hippocampus and upregulated in chronic epilepsy. In the TLE patients, we map the trans-acting genetic control of this proconvulsive module to Sestrin 3 (SESN3), and demonstrate that SESN3 positively regulates the module in macrophages, microglia and neurons. Morpholino-mediated Sesn3 knockdown in zebrafish confirms the regulation of the transcriptional module, and attenuates chemically induced behavioural seizures in vivo.

Organización y desarrollo de un programa de trasplante hepático en Mar del Plata: Resultados iniciales (2010-2018) / Organization and development of a liver transplant program in Mar del Plata: Initial Results (2010-2018)

Antecedentes: en los últimos 30 años, la creación de nuevos programas de trasplante hepático ha respondido a la difusión de esta terapéutica para el tratamiento de la insuficiencia hepática irreversible. Objetivo: describir la organización y el desarrollo de un Programa de Trasplante Hepático en una institución sanatorial de Mar del Plata, y sus resultados iniciales. Material y método: se constituyó un equipo profesional con especialistas en trasplante hepático en las disciplinas: cirugía, anestesia, terapia intensiva, hepatología, instrumentación, enfermería, hemoterapia y hematología, que se acreditaron ante los organismos fiscalizadores. La institución fue adecuada edilicia y tecnológicamente para este tipo de emprendimiento. Se trasplantaron con donante cadavérico completo 32 pacientes de localidades vecinas (55%) y de Mar del Plata (45%). Las etiologías más frecuentes de la cirrosis fueron hepatitis C y abuso de alcohol. Resultados: la mortalidad operatoria fue 12,5%. La supervivencia actuarial de los trasplantados fue 75% a los 55 meses. Seis pacientes desarrollaron de inmediato estenosis biliares , que fueron tratadas satisfactoriamente en forma conservadora. Conclusiones: el Programa de Trasplante Hepático de Mar del Plata asiste al área geográfica del sudeste de la provincia de Buenos Aires. Los resultados iniciales alcanzados encuadran en lo esperable para los estándares actuales en la materia.

Background: Over the past 30 years, new liver transplant programs have emerged as a response to the increasing use of this therapy to treat irreversible liver failure. Objective: the aim of this presentation is to describe the organization, development and initial results of a Liver Transplant Program in Mar del Plata. Material and methods: A team of professionals trained in liver transplantation was created, with specialists in surgery, anesthesiology, intensive care, hepatology, hemotherapy, hematology, and registered nurses and nurse scrubs granted by regulatory agencies. Building alterations, and technical and adaptations were implemented. Thirtytwo transplantations were performed with complete cadaveric donor in patients from neighboring localities (55%) and from Mar del Plata (45%). The most common etiologies of cirrhosis were chronic hepatitis C virus infection and alcohol abuse. Results: Operative mortality was 12.5%. Actuarial survival at 55 months of the 32 recipients was 75%. Six bile drug strictures late postoperative period which were treated successfully trated with a conservative approach Conclusions: the Liver Transplant Program in Mar del Plata provides care to the geographic area of the southeast of the province of Buenos Aires. The initial results are consistent with those expected for the current standards in liver transplantation.

Manejo percutáneo y endoscópico combinado de las estenosis benignas de la vía biliar / Combined endoscopic and percutaneous management of benign biliary strictures

Antecedentes: las estenosis benignas de la vía biliar (EBVB) tradicionalmente han sido tratadas con derivaciones biliodigestivas. En la actualidad existe una clara tendencia para resolverlas en forma mínimamente invasiva (endoscópica o percutánea o de ambos modos). Objetivo: describir el manejo y los resultados del tratamiento percutáneo y/o endoscópico de las estenosis biliares benignas. Material y métodos: período del estudio: enero de 2009 a junio de 2015. Etología de las EBVB: 8 lesiones quirúrgicas de la vía biliar (LQVB), 5 trasplantes hepáticos (TH), 5 hidatidosis hepáticas (HH), 2 quistes de colédoco (QC). Se realizaron 4 procedimientos promedio por paciente (r. 1-11). Se colocaron 3 stentis (endoprótesis) promedio por paciente (r. 1-5). Seguimiento promedio: 21 meses con una mediana de 13 meses. Resultados: mortalidad relacionada con los procedimientos: 0%. Morbilidad relacionada con los procedimientos: 35% (bacteriemia, colangitis, hemorragia digestiva, síndrome febril, hemoperitoneo leve, sepsis). Diecinueve pacientes (95%) evolucionaron con control satisfactorio de la estenosis; un paciente (5%) presentó recidiva de la estenosis y debió ser tratado nuevamente. Conclusiones: el tratamiento mininvasivo puede lograr resultados satisfactorios en un alto porcentaje de pacientes con estenosis benignas de la vía biliar.

Background: although benign strictures of the bile duct (BSBD) have traditonally been treated by constructon of a surgical biliodigestive anastomosis at present, there is a clear tendency to resolve them in a minimally invasive way (endoscopic or percutaneous or both). Objective: to describe the management and Results of percutaneous and / or endoscopic treatment of BSBD. Materials and methods: study period: January 2009 to June 2015. Etology of BSBD, 8 surgical injury to the bile duct (BDI), 5 liver transplantis (LT), 5 liver hydatidosis (LH), 2 choledochal cystis (CC). As an average, 4 procedures per patent were done (range, 1-11); and 3 stentis were placed (range, 1-5). Average and median follow up were 21 months, and 13 months, respectively. Results: mortality related to the procedure was 0%. Morbidity was 35% (bacteremia, cholangitis, gas-trointestinal bleeding, febrile syndrome, mild hemoperitoneum, and sepsis). 19 patentis (95%) had satisfactory outicome; one patentis (5%) developed a re-stricture that required a new procedure. Conclusions: mininmally invasive treatment can achieve satisfactory Results in a high percentage of patentis with benign stricture of the bile duct.

Regulation of bestrophins by Ca2+: a theoretical and experimental study.

Bestrophins are a recently discovered family of Cl(-) channels, for which no structural information is available. Some family members are activated by increased intracellular Ca2+ concentration. Bestrophins feature a well conserved Asp-rich tract in their COOH terminus (Asp-rich domain), which is homologous to Ca2+-binding motifs in human thrombospondins and in human big-conductance Ca2+- and voltage-gated K+ channels (BK(Ca)). Consequently, the Asp-rich domain is also a candidate for Ca2+ binding in bestrophins. Based on these considerations, we constructed homology models of human bestrophin-1 (Best1) Asp-rich domain using human thrombospondin-1 X-ray structure as a template. Molecular dynamics simulations were used to identify Asp and Glu residues binding Ca2+ and to predict the effects of their mutations to alanine. We then proceeded to test selected mutations in the Asp-rich domain of the highly homologous mouse bestrophin-2. The mutants expressed in HEK-293 cells were investigated by electrophysiological experiments using the whole-cell voltage-clamp technique. Based on our molecular modeling results, we predicted that Asp-rich domain has two defined binding sites and that D301A and D304A mutations may impact the binding of the metal ions. The experiments confirmed that these mutations do actually affect the function of the protein causing a large decrease in the Ca2+-activated Cl(-) current, fully consistent with our predictions. In addition, other studied mutations (E306A, D312A) did not decrease Ca2+-activated Cl(-) current in agreement with modeling results.