Neuronal domains in developing neocortex.

The mammalian neocortex consists of a mosaic of columnar units whose development is poorly understood. Optical recordings of brain slices labeled with the fluorescent calcium indicator fura-2 revealed that the neonatal rat cortex was partitioned into distinct domains of spontaneously coactive neurons. In tangential slices, these domains were 50 to 120 micrometers in diameter; in coronal slices they spanned several cortical layers and resembled columns found in the adult cortex. In developing somatosensory cortex, domains were smaller than, and distinct from, the barrels, which represent sensory input from a single vibrissa. The neurons within each domain were coupled by gap junctions. Thus, nonsynaptic communication during cortical development defines discrete multicellular patterns that could presage adult functional architecture.

Stereotyped position of local synaptic targets in neocortex.

The microcircuitry of the mammalian neocortex remains largely unknown. Although the neocortex could be composed of scores of precise circuits, an alternative possibility is that local connectivity is probabilistic or even random. To examine the precision and degree of determinism in the neocortical microcircuitry, we used optical probing to reconstruct microcircuits in layer 5 from mouse primary visual cortex. We stimulated "trigger" cells, isolated from a homogenous population of corticotectal pyramidal neurons, while optically detecting "follower" neurons directly driven by the triggers. Followers belonged to a few selective anatomical classes with stereotyped physiological and synaptic responses. Moreover, even the position of the followers appeared determined across animals. Our data reveal precisely organized cortical microcircuits.

Efficacy of Direct-acting Antivirals to Improve Clinical Condition, Fibrosis, and Liver Function in Liver Transplant Recipients Infected by Hepatitis C.

BACKGROUND: Direct-acting antivirals (DAAs) have revolutionized the treatment of hepatitis C, including transplant recipients with an advanced fibrosis stage. Our aim in this study was to assess the clinical and functional benefits and improvement in liver fibrosis after treatment with DAAs in liver transplant recipients with chronic hepatitis C virus who achieved sustained virologic response (SVR). METHODS: We retrospectively analyzed 42 patients who underwent liver transplantation (LT) at our institution and were treated with DAAs from June 2014 to December 2015. Two patients died, so we ultimately included 40 transplant patients with chronic hepatitis C who received DAAs and achieved SVR. We assessed liver function, fibrosis stage, and clinical features at the start of the treatment, and then at 6 and 12 months after SVR. The indication for LT was hepatocellular carcinoma in 8 patients (20%) and Child-Pugh score B/C in 32 patients (80%). RESULTS: The DAAs regimens were sofosbuvir plus daclatasvir (45.0%), simeprevir plus sofosbuvir (42.5%), sofosbuvir plus ledipasvir (7.5%), and ombitasvir/paritaprevir/ritonavir (5%). The mean Modified End-stage Liver Disease (MELD) score pretreatment was 10.78, and was 8.46 at 1 year after treatment (P < .05). In addition, fibrosis stage decreased significantly from 14.81 kPa to 9.07 kPa (FibroScan) at 12 months after SVR. Clinically, there was a significant improvement, including control of ascites and chronic hepatic encephalopathy. CONCLUSION: DAAs were used successfully in the treatment of hepatitis C after orthotopic liver transplantation and resulted in significant improvement in liver function as measured by MELD score, fibrosis level, and cirrhotic clinical condition, even in patients with very advanced disease.

Control of postsynaptic Ca2+ influx in developing neocortex by excitatory and inhibitory neurotransmitters.

We assessed the pathways by which excitatory and inhibitory neurotransmitters elicit postsynaptic changes in [Ca2+]i in brain slices of developing rat and cat neocortex, using fura 2. Glutamate, NMDA, and quisqualate transiently elevated [Ca2%]i in all neurons. While the quisqualate response relied exclusively on voltage-gated Ca2+ channels, almost all of the NMDA-induced Ca2+ influx was via the NMDA ionophore itself, rather than through voltage-gated Ca2+ channels. Glutamate itself altered [Ca2+]i almost exclusively via the NMDA receptor. Furthermore, synaptically induced Ca2+ entry relied almost completely on NMDA receptor activation, even with low-frequency stimulation. The inhibitory neurotransmitter GABA also increased [Ca2+]i, probably via voltage-sensitive Ca2+ channels, whereas the neuromodulator acetylcholine caused Ca2+ release from intracellular stores via a muscarinic receptor. Low concentrations of these agonists produced nonperiodic [Ca2+]i oscillations, which were temporally correlated in neighbouring cells. Optical recording with Ca2(+)-sensitive indicators may thus permit the visualization of functional networks in developing cortical circuits.

Linear summation of excitatory inputs by CA1 pyramidal neurons.

A fundamental problem in neurobiology is understanding the arithmetic that dendrites use to integrate inputs. The impact of dendritic morphology and active conductances on input summation is still unknown. To study this, we use glutamate iontophoresis and synaptic stimulation to position pairs of excitatory inputs throughout the apical, oblique, and basal dendrites of CA1 pyramidal neurons in rat hippocampal slices. Under a variety of stimulation regimes, we find a linear summation of most input combinations that is implemented by a surprising balance of boosting and shunting mechanisms. Active conductances in dendrites paradoxically serve to make summation linear. This "active linearity" can reconcile predictions from cable theory with the observed linear summation in vivo and suggests that a simple arithmetic is used by apparently complex dendritic trees.

Extensive dye coupling between rat neocortical neurons during the period of circuit formation.

A low molecular weight intracellular tracer, Neurobiotin, was injected into single neurons in living slices of rat neocortex made at postnatal days 5-18. Between days 5 and 12, 66% of single-neuron injections labeled clusters of up to 80 neurons surrounding the injected cell. Coupling between neurons occurred primarily through dendrites. Injections done in the presence of halothane, a gap junction blocker, abolished the spread of tracer to surrounding neurons, implying that gap junctions mediate coupling. Injections done after day 16 resulted in little or no dye coupling. We conclude that transient local coupling via gap junctions in developing cortex may provide a pathway for communicating intercellular signals, including subthreshold electrical activity, and thereby enable temporal coordination of local neuronal ensembles during circuit formation.

Ca2+ accumulations in dendrites of neocortical pyramidal neurons: an apical band and evidence for two functional compartments.

Apical dendrites constitute a prominent feature of the microcircuitry in the neocortex, yet their function is poorly understood. Using fura-2 imaging of layer 5 pyramidal neurons from slices of rat somatosensory cortex, we have investigated the Ca2+ influx into dendrites under intracellular, antidromic, synaptic, and receptor-agonist stimulation. We find three spatial patterns of Ca2+ accumulations: an apical band in the apical dendrite approximately 500 microns from the soma, an accumulation restricted to the basal dendrites, soma, and proximal apical dendrite, and a combination of both of these. We show that the apical band can be activated antidromically and synaptically and that, under blocked Na+ and K+ conductances, it generates Ca2+ spikes. Thus, the apical band may serve as a dendritic trigger zone for regenerative Ca2+ spikes or as a current amplifier for distal synaptic events. Our results suggest that the distal apical dendrite should be considered a separate functional compartment from the rest of the cell.

Dynamics of spontaneous activity in neocortical slices.

The flow of activity in the cortical microcircuitry is poorly understood. We use calcium imaging to reconstruct, with millisecond and single-cell resolution, the spontaneous activity of populations of neurons in unstimulated slices from mouse visual cortex. We find spontaneous activity correlated among networks of layer 5 pyramidal cells. Synchronous ensembles occupy overlapping territories, often share neurons, and are repeatedly activated. Sets of neurons are also sequentially activated numerous times. Network synchronization and sequential correlations are blocked by glutamatergic antagonists, even though spontaneous firing persists in many "autonomously active" neurons. This autonomous activity is periodic and depends on hyperpolarization-activated cationic (H) and persistent sodium (Na(p)) currents. We conclude that the isolated neocortical microcircuit generates spontaneous activity, mediated by a combination of intrinsic and circuit mechanisms, and that this activity can be temporally precise.

Neuronal domains in developing neocortex: mechanisms of coactivation.

The mammalian neocortex consists of columnar circuits, whose development may be controlled by patterns of spontaneous activity. Columnar domains of spontaneously coactive neurons were previously described using Ca2+ imaging of slices from developing rat neocortex. We have now investigated the cellular mechanisms responsible for the coactivation of these domains. The activation starts in the center of a domain and spreads at speeds of approximately 100 microns/s. Domains occur in the presence of tetrodotoxin but are blocked by the gap junction blockers halothane and octanol. Simultaneous intracellular and optical recordings from dye-coupled cells reveal functional coupling between developing neocortical neurons. These data support the hypothesis that a neuronal domain results from the spontaneous excitation of one or a few trigger neurons that subsequently activate, either electrically or biochemically, the rest of the cells via gap junctions.

Networks of coactive neurons in developing layer 1.

Spontaneous neuronal activity plays an important role in the development of cortical circuitry, yet its spatio-temporal dynamics are poorly understood. Cajal-Retzius (CR) neurons in developing layer 1 are necessary for correct cortical lamination and are strategically located to coordinate early circuit activity. To characterize the spontaneous activity of CR and other layer 1 neurons during cortical development, we imaged calcium transients in populations of layer 1 neurons in hemispheres and slices from postnatal rat somato-sensory neocortex. The spontaneous activity in layer 1 had complex spatio-temporal patterns. Groups of non-CR cells showed synchronous activations and formed networks of correlated neurons superimposed in the same territory. Correlated activity among non-CR cells was mediated by a depolarizing effect of GABA and was modulated by glutamate, probably released by CR cells. Our findings demonstrate that developing layer 1 can sustain complex patterns of correlated activity and reveal a circuit mechanism that can mediate this patterned activity.

From form to function: calcium compartmentalization in dendritic spines.

Dendritic spines compartmentalize calcium, and this could be their main function. We review experimental work on spine calcium dynamics. Calcium influx into spines is mediated by calcium channels and by NMDA and AMPA receptors and is followed by fast diffusional equilibration within the spine head. Calcium decay kinetics are controlled by slower diffusion through the spine neck and by spine calcium pumps. Calcium release occurs in spines, although its role is controversial. Finally, the endogenous calcium buffers in spines remain unknown. Thus, spines are calcium compartments because of their morphologies and local influx and extrusion mechanisms. These studies highlight the richness and heterogeneity of pathways that regulate calcium accumulations in spines and the close relationship between the morphology and function of the spine.

[Testicular carcinoid tumor associated with teratoma: with regard to a case]. / Tumor carcinoide testicular asociado a teratoma: a propósito de un caso.

We report a case of a carcinoid tumor originated in testicle associated with mature teratoma in a 31 years old male. Primary gonadal location of this tumor is unusual, moreover when associated with teratoma. Early diagnosis and treatment determine the prognostic of the patients affected of this neoplasm since the only curative potential treatment is surgery. Follow up must be extent for years due to the possibility of late relapse.

Non-synaptic dendritic spines in neocortex.

A long-held assumption states that each dendritic spine in the cerebral cortex forms a synapse, although this issue has not been systematically investigated. We performed complete ultrastructural reconstructions of a large (n=144) population of identified spines in adult mouse neocortex finding that only 3.6% of the spines clearly lacked synapses. Nonsynaptic spines were small and had no clear head, resembling dendritic filopodia, and could represent a source of new synaptic connections in the adult cerebral cortex.

Imaging calcium dynamics in dendritic spines.

Recent advances in optical imaging technology have enabled the measurement of Ca2+ dynamics in individual synaptic spines with high time resolution. Results from work using this new technology have confirmed the view that individual synaptic spines can act as functional chemical compartments with independent dynamics of second-messenger concentration. In particular, the ability of Ca2+ to directly mediate Hebbian coincidence detection has been confirmed.

Density and morphology of dendritic spines in mouse neocortex.

Dendritic spines of pyramidal cells are the main postsynaptic targets of cortical excitatory synapses and as such, they are fundamental both in neuronal plasticity and for the integration of excitatory inputs to pyramidal neurons. There is significant variation in the number and density of dendritic spines among pyramidal cells located in different cortical areas and species, especially in primates. This variation is believed to contribute to functional differences reported among cortical areas. In this study, we analyzed the density of dendritic spines in the motor, somatosensory and visuo-temporal regions of the mouse cerebral cortex. Over 17,000 individual spines on the basal dendrites of layer III pyramidal neurons were drawn and their morphologies compared among these cortical regions. In contrast to previous observations in primates, there was no significant difference in the density of spines along the dendrites of neurons in the mouse. However, systematic differences in spine dimensions (spine head size and spine neck length) were detected, whereby the largest spines were found in the motor region, followed by those in the somatosensory region and those in visuo-temporal region.

Metabolic Syndrome After Liver Transplantation: Five-Year Prevalence and Risk Factors.

Survival after orthotopic liver transplantation (OLT) has increased over the last decades, focusing on the metabolic complications that contribute to patient morbidity and mortality. The aim of our study was to describe the prevalence of metabolic syndrome (MS), its components, and its associated factors in patients who underwent OLT in a hospital in Spain. From November 2001 to January 2014, we performed 415 transplantations in 386 patients. We analyzed 204 patients with a minimum follow-up of 1 year (77.6% were male and the mean age was 54.2+/-9.5 years). The most frequent etiology was alcohol (41%), followed by hepatitis C virus (29.1%). The indication was decompensated cirrhosis in 51.8% and hepatocellular carcinoma in 34%. According to modified National Cholesterol Education Program-Adult Treatment Panel-III (NCEP-ATP III) criteria, 5 years post-transplantation MS was diagnosed in 38.2% of patients. Significant independent predictors of post-transplantation MS on logistic regression analysis were as follows: pretransplantation obesity (odds ratio [OR], 3.09; P = .056), 1-year post-transplantation obesity (OR, 3.95; P = .009), pretransplantation diabetes (OR, 4.63; P = .001), 1-year post-transplantation diabetes (OR, 3.01; P = .015), 1-year post-transplantation hypertension (OR, 1.85; P = .176), and hypertriglyceridemia at the first year after transplantation (OR, 2.32; P = .063). In our center the prevalence of MS at 5 years after OLT is slightly lower than published. The most important risk factors were obesity and diabetes (both pretransplantation and the first year post-transplantation).

Regulation of spine calcium dynamics by rapid spine motility.

Dendritic spines receive most excitatory inputs in the CNS and compartmentalize calcium. Spines also undergo rapid morphological changes, although the function of this motility is still unclear. We have investigated the effect of spine movement on spine calcium dynamics with two-photon photobleaching of enhanced green fluorescent protein and calcium imaging of action potential-elicited transients in spines from layer 2/3 pyramidal neurons in mouse visual cortex slices. The elongation or retraction of the spine neck during spine motility alters the diffusional coupling between spine and dendrite and significantly changes calcium decay kinetics in spines. Our results demonstrate that the spine's ability to compartmentalize calcium is constantly changing.

Mechanisms of calcium decay kinetics in hippocampal spines: role of spine calcium pumps and calcium diffusion through the spine neck in biochemical compartmentalization.

Dendritic spines receive most excitatory inputs in the CNS and compartmentalize calcium. Although the mechanisms of calcium influx into spines have been explored, it is unknown what determines the calcium decay kinetics in spines. With two-photon microscopy we investigate action potential-induced calcium dynamics in spines from rat CA1 pyramidal neurons in slices. The [Ca(2+)](i) in most spines shows two decay kinetics: an initial fast component, during which [Ca(2+)](i) in spines decays to dendritic levels, followed by a slower decay phase in which the spine follows dendritic kinetics. The correlation between [Ca(2+)](i) in spine and dendrite at the breakpoint of the decay kinetics demonstrates diffusional equilibration between spine and dendrite during the slower component. To explain the faster initial decay, we rule out saturation or kinetic effects of endogenous or exogenous buffers and focus instead on (1) active calcium extrusion and (2) buffered diffusion of calcium from spine to dendrite. The presence of an undershoot in most spines indicates that extrusion mechanisms can be intrinsic to the spine. Supporting the two mechanisms, pharmacological blockade of smooth endoplasmic reticulum calcium (SERCA) pumps and the length of the spine neck affect spine decay kinetics. Using a mathematical model, we find that the contribution of calcium pumps and diffusion varies from spine to spine. We conclude that dendritic spines have calcium pumps and that their density and kinetics, together with the morphology of the spine neck, determine the time during which the spine compartmentalizes calcium.

Involvement of cajal-retzius neurons in spontaneous correlated activity of embryonic and postnatal layer 1 from wild-type and reeler mice.

Cajal-Retzius (CR) cells are a transient population of neurons in developing cortical layer 1 that secrete reelin, a protein necessary for cortical lamination. Combining calcium imaging of cortical hemispheres and cross-correlation analysis, we previously found spontaneous correlated activity among non-CR neurons in postnatal rat layer 1. This correlated activity was blocked by GABAergic and glutamatergic antagonists, and we postulated that it was controlled by CR cells. We now investigate the correlated activity of embryonic and postnatal layer 1 in wild-type and reeler mice, mutant in the production of reelin. We find that mouse layer 1 also sustains patterned spontaneous activity and that CR cells participate in correlated networks. These networks are present in embryonic marginal zone and are blocked by GABAergic and glutamatergic antagonists. Surprisingly, network activity in reeler mice displays similar characteristics and pharmacological profile as in wild-type mice, although small differences are detected. Our results demonstrate that the embryonic marginal zone has correlated spontaneous activity that could serve as the scaffold for the development of intracortical connections. Our data also suggest that reelin does not have a major impact in the development of specific synaptic circuits in layer 1.

On the function of dendritic spines.

Dendritic spines occupy a strategic position in the central nervous system, yet their function is still under debate. Over the past decades, many hypotheses have been put forward to explain the specific function of spines. Recently, imaging experiments have demonstrated that spines compartmentalize calcium, a role that appears necessary for input-specific forms of synaptic plasticity. In addition, it has been discovered that spine morphology is plastic over fast time scales and can be controlled by specific biochemical pathways. Also, several aspects of the spine's morphology appear to be intricately linked to its function. The authors review these recent data and incorporate them into a model for the function of dendritic spines in CNS circuits. In their proposal, spines serve to specifically connect sparse inputs and therefore minimize the wiring necessary in the CNS while maximizing connectivity. By virtue of the same design, spines isolate inputs and thus implement local learning rules. These rules appear only necessary with sparse inputs so these two functions are intimately related. Spines therefore would play a crucial circuit role, remarkably analogous to synaptic matrix elements of associative neural networks. This model highlights the economical, yet elegant, design of CNS circuits.