Search

El II Congreso Internacional de Ciencias Economicas y Administrativas “Desafios Globales para la innovacion en la gestion empresarial”, es un evento cientifico, liderado por la Division de Ciencias Economicas, Administrativas y Contables. El proposito es motivar la difusion de investigaciones realizadas por docentes, investigadores y semilleros. Asimismo, propiciar espacios de actualizacion, reflexion y disertacion en temas actuales y afines a las ciencias economicas, administrativas y contables. Para el presente evento cientifico fue imprescindible la participacion de ponentes nacionales e internacionales, quienes socializaron temas relacionados con los desafios globales a los que se enfrentan las empresas actuales, tales como la inclusion digital y financiera, la responsabilidad social y ambiental, la bioeconomia y sostenibilidad ambiental, integracion economica y comercio mundial, ademas de la inclusion economica y social, en coherencia a su experiencia laboral y academica, claramente contemporaneos. A su vez los ponentes en modalidad de poster compartieron adelantos en investigaciones desarrolladas en el seno de semilleros y grupos de investigacion.

Local blood flow/oxygen partial pressure (Po2) distributions and flow-Po2 relationships are physiologically relevant. They affect the pathophysiology and treatment of conditions like hemorrhagic shock (HS), but direct noninvasive measures of flow, Po2, and their heterogeneity during prolonged HS are infrequently presented. To fill this void, we report the first quantitative evaluation of flow-Po2 relationships and heterogeneities in normovolemia and during several hours of HS using noninvasive, unbiased, automated acquisition. Anesthetized rats were subjected to tracheostomy, arterial/venous catheterizations, cremaster muscle exteriorization, hemorrhage (40% total blood volume), and laparotomy. Control animals equally instrumented were not subjected to hemorrhage/laparotomy. Every 0.5 h for 4.5 h, noninvasive laser speckle contrast imaging and phosphorescence quenching were employed for nearly 7,000 flow/Po2 measurements in muscles from eight animals, using an automated system. Precise alignment of 16 muscle areas allowed overlapping between flow and oxygenation measurements to evaluate spatial heterogeneity, and repeated measurements were used to estimate temporal heterogeneity. Systemic physiological parameters and blood chemistry were simultaneously assessed by blood samplings replaced with crystalloids. Hemodilution was associated with local hypoxia, but increased flow prevented major oxygen delivery decline. Adding laparotomy and prolonged HS resulted in hypoxia, ischemia, decreased tissue oxygen delivery, and logarithmic flow/Po2 relationships in most regions. Flow and Po2 spatial heterogeneities were higher than their respective temporal heterogeneities, although this did not change significantly over the studied period. This quantitative framework establishes a basis for evaluating therapies aimed at restoring muscle homeostasis, positively impacting outcomes of civilian and military trauma/HS victims. NEW & NOTEWORTHY This is the first study on flow-Po2 relationships during normovolemia, hemodilution, and prolonged hemorrhagic shock using noninvasive methods in multiple skeletal muscle areas of monitored animals. Automated flow/Po2 measurements revealed temporal/spatial heterogeneities, hypoxia, ischemia, and decreased tissue oxygen delivery after trauma/severe hemorrhage. Hemodilution was associated with local hypoxia, but hyperemia prevented a major decline in oxygen delivery. This framework provides a quantitative basis for testing therapeutics that positively impacts muscle homeostasis and outcomes of trauma/hemorrhagic shock victims.

Background Many studies evaluating blood flow and oxygen partial pressure (PO2) do not directly measure both parameters, are confined to few locations/microvessels, and depend on investigator's selection of measuring sites. Moreover, clinically/physiologically relevant systemic parameters are not simultaneously recorded. We implemented an automated system for prolonged blood flow/PO2 acquisition in large areas while collecting relevant systemic information. Methods In anesthetized animals, cardiorespiratory parameters were continuously recorded. Other data were collected at baseline and hourly after 4 hours of hemorrhagic shock. A cremaster muscle was spread over a pedestal fixed to a motorized stage. One 2-dimensional tissue scan allowed 16 noninvasive PO2 measurements using oxygen-dependent phosphorescence quenching and fiber optics. Blood flow was estimated using laser speckle contrast imaging in the same areas used for PO2 measurements. At each timepoint, blood was sampled for extensive biochemistry/coagulation profile. Results The system was used successfully by different operators. A set of flow/PO2 measurements was completed in less than 90 seconds. Muscle flow and PO2 correlated with some but not several systemic parameters, emphasizing the importance of performing both local and systemic evaluations. Conclusion System advantages include integration between local and over 40 systemic parameters, unbiased data collection/analysis, improved performance/sampled area, easy expansion, implementation and maintenance, no customized programming, and simplified training. Combining this system with trauma/prolonged HS models will enhance our ability to investigate tissue stability and select better resuscitation strategies to improve outcomes and survival. Level of evidence Diagnostic test, level V.

Neurons of the subthalamic nucleus (STN) are very sensitive to applied currents, firing at 10–20/s during spontaneous activity, but increasing to peak firing rates of 200/s with applied currents + current. This current was independent of calcium or sodium entry and could be induced with long-duration voltage steps after blockade of action potentials. In addition to the adaptation current, driven firing produced slow inactivation of the persistent Na+ current, which also contributed to the reduced excitability of STN cells during and after driven firing.

Injecting white noise currents has been shown to increase mean firing rate in several types of neuron. This speed up is generally attributed to the fact that depolarizing currents on the tails of the noise distribution push cells past spike threshold sooner than they would have otherwise. As part of a larger effort to understand the dynamic properties of rat subthalamic (STN) neurons, we have performed perforated patch recordings of these tonically active neurons in brain slices, exposing them to contiguous sequences of brief current pulses drawn from a Gaussian distribution. Pulsed noise disrupted firing pattern with no significant change in rate over a wide range of noise amplitudes, so long as the pulse durations were brief (

We used phase resetting methods to predict firing patterns of rat subthalamic nucleus (STN) neurons when their rhythmic firing was densely perturbed by noise. We applied sequences of contiguous brief (0.5–2 ms) current pulses with amplitudes drawn from a Gaussian distribution (10–100 pA standard deviation) to autonomously firing STN neurons in slices. Current noise sequences increased the variability of spike times with little or no effect on the average firing rate. We measured the infinitesimal phase resetting curve (PRC) for each neuron using a noise-based method. A phase model consisting of only a firing rate and PRC was very accurate at predicting spike timing, accounting for more than 80% of spike time variance and reliably reproducing the spike-to-spike pattern of irregular firing. An approximation for the evolution of phase was used to predict the effect of firing rate and noise parameters on spike timing variability. It quantitatively predicted changes in variability of interspike intervals with variation in noise amplitude, pulse duration and firing rate over the normal range of STN spontaneous rates. When constant current was used to drive the cells to higher rates, the PRC was altered in size and shape and accurate predictions of the effects of noise relied on incorporating these changes into the prediction. Application of rate-neutral changes in conductance showed that changes in PRC shape arise from conductance changes known to accompany rate increases in STN neurons, rather than the rate increases themselves. Our results show that firing patterns of densely perturbed oscillators cannot readily be distinguished from those of neurons randomly excited to fire from the rest state. The spike timing of repetitively firing neurons may be quantitatively predicted from the input and their PRCs, even when they are so densely perturbed that they no longer fire rhythmically., Author Summary Most neurons receive thousands of synaptic inputs per second. Each of these may be individually weak but collectively they shape the temporal pattern of firing by the postsynaptic neuron. If the postsynaptic neuron fires repetitively, its synaptic inputs need not directly trigger action potentials, but may instead control the timing of action potentials that would occur anyway. The phase resetting curve encapsulates the influence of an input on the timing of the next action potential, depending on its time of arrival. We measured the phase resetting curves of neurons in the subthalamic nucleus and used them to accurately predict the timing of action potentials in a phase model subjected to complex input patterns. A simple approximation to the phase model accurately predicted the changes in firing pattern evoked by dense patterns of noise pulses varying in amplitude and pulse duration, and by changes in firing rate. We also showed that the phase resetting curve changes systematically with changes in total neuron conductance, and doing so predicts corresponding changes in firing pattern. Our results indicate that the phase model may accurately represent the temporal integration of complex patterns of input to repetitively firing neurons.

Synchrony among neurons is seen throughout the mammalian CNS, in particular within networks of GABAergic neurons. The globus pallidus (GP) consists of GABAergic neurons that project to neurons throughout the basal ganglia in addition to each other via local axon collaterals. The GP does not display synchronous rhythms and there are no clear correlations between neurons in healthy mammals. In contrast, strong correlations among GP neurons emerge in Parkinson’s disease patients and MPTP treated primates. Why GP neurons show no correlations in healthy animals is not known. GP neurons are autonomous pacemakers and are thought to discharge at a constant frequency. Theoretical work shows that the degree of synchrony in interconnected networks depends on the amount of heterogeneity in firing rate. We have observed in cell-attached recordings of GP neurons, in slices, that their firing rates are not stationary, but instead visit a range of rates over a period of one hour in a non-stereotypical fashion. The fluctuations in rate are stable for periods of minutes, can vary as much as 30 Hz, and appear to be unaffected by blocking synaptic inputs. HCN channels are a critical component of the GP neuron’s pacemaking mechanism, and their availability is positively correlated with the firing rate of GP neurons. Paired recordings revealed that these fluctuations in rate were neuron-independent. We hypothesized that these slow non-stereotypical fluctuations in firing rate could be attributed to regulation of HCN channels by cAMP. cAMP alters HCN availability by shifting the channel’s activation curve to depolarized potentials. Consistent with this, up-regulation of cAMP levels by bath application of 50 μM Forskolin increased the firing rate of GP neurons from 12.7 ± 1.3 to 20.5 ± 1.5 Hz. After the Forskolin induced increase in firing rate stabilized, there was a marked decrease in the amount of variability in interspike intervals (ISIs) observed over a one hour period of recording in the cell-attached configuration. In control conditions the average coefficient of variation of ISIs (CV), measured over one hour, was 0.43 ± 0.22 and was 0.09 ± 0.02 after exposure to Forskolin. Thus, fluctuations in cAMP can create heterogeneity in firing rate among GP neurons by altering the availability of the voltage-gated ion channels necessary to drive pacemaking. By this mechanism, activity independent intracellular signaling could potentially contribute to the absence of synchrony in the GP.