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Biomedical subjects

J J Torres

Publications and source records attributed to J J Torres.

At least 19 recordsLinked to original sources
PubMed2006

Control of neural chaos by synaptic noise.

We study neural automata - or neurobiologically inspired cellular automata - which exhibits chaotic itinerancy among the different stored patterns or memories. This is a consequence of activity-dependent synaptic fluctuations, which continuously destabilize the attractor and induce irregular hopping to other possible attractors. The nature of these irregularities depends on the dynamic details, namely, on the intensity of the synaptic noise and the number of sites of the network, which are synchronously updated at each time step. Varying these factors, different regimes occur, ranging from regular to chaotic dynamics. As a result, and in absence of external agents, the chaotic behavior may turn regular after tuning the noise intensity. It is argued that a similar mechanism might be on the basis of self-controlling chaos in natural systems.

Algorithms↗
PubMed2006

Effects of fast presynaptic noise in attractor neural networks.

We study both analytically and numerically the effect of presynaptic noise on the transmission of information in attractor neural networks. The noise occurs on a very short timescale compared to that for the neuron dynamics and it produces short-time synaptic depression. This is inspired in recent neurobiological findings that show that synaptic strength may either increase or decrease on a short timescale depending on presynaptic activity. We thus describe a mechanism by which fast presynaptic noise enhances the neural network sensitivity to an external stimulus. The reason is that, in general, presynaptic noise induces nonequilibrium behavior and, consequently, the space of fixed points is qualitatively modified in such a way that the system can easily escape from the attractor. As a result, the model shows, in addition to pattern recognition, class identification and categorization, which may be relevant to the understanding of some of the brain complex tasks.

Animals↗
PubMed2005

Pulmonary tuberculosis in lung and heart-lung transplantation: fifteen years of experience in a single center in Spain.

The increase in the number of solid organ transplants has resulted in an increased incidence of opportunistic infections, including infection by typical and atypical mycobacteria, with risk of developing tuberculosis. Pretransplant chemoprophylaxis with isoniazid has become increasingly common in an attempt to prevent the disease. The source of infection in tuberculosis (TB) may be difficult to identify. Infection may be caused by reactivation of a primary infection in the recipient, reactivation of a lesion from the donor lung, or primary infection. There are few reports on TB in lung transplantation. Incidence in the reported series ranges from 6.5% to 10%. Our series of 7 patients out of a total 271 patients (2.58%) represents a rate higher than reported for the general Spanish population, 26.7/10(5) inhabitants and for lung transplant candidates (0.18%). Our aim was to evaluate the incidence, clinical signs, and outcome of TB in our series of patients undergoing lung transplantation in the 15 years since inception of the program (February 1990 to December 2004). Morbidity and mortality was high (42.8%), but limited to patients in whom treatment was not administered or could not be successfully completed. However, early detection and treatment are essential.

Adult↗
PubMed2004

Effects of static and dynamic disorder on the performance of neural automata.

We report on both analytical and numerical results concerning stochastic Hopfield-like neural automata exhibiting the following (biologically inspired) features: (1) Neurons and synapses evolve in time as in contact with respective baths at different temperatures; (2) the connectivity between neurons may be tuned from full connection to high random dilution, or to the case of networks with the small-world property and/or scale-free architecture; and (3) there is synaptic kinetics simulating repeated scanning of the stored patterns. Although these features may apparently result in additional disorder, the model exhibits, for a wide range of parameter values, an extraordinary computational performance, and some of the qualitative behaviors observed in natural systems. In particular, we illustrate here very efficient and robust associative memory, and jumping between pattern attractors.

Models, Neurological↗
PubMed2004

Dietary myo-inositol hexaphosphate prevents dystrophic calcifications in soft tissues: a pilot study in Wistar rats.

Myo-inositol hexaphosphate (InsP6) is an abundant component of plant seeds. It is also found in significant levels in blood and mammalian tissues, but they are totally dependent on their dietary intake. In the present paper, we describe studies on the effect of InsP6 on a model of dystrophic calcification, which was chemically induced by subcutaneous injection of a 0.1% KMnO4 solution. Male Wistar rats were randomly divided into four groups for treatment over 31 days. A: animals consuming a purified diet in which InsP6 was absent but to which 1% of InsP6 (as sodium salt) was added. In this group, the InsP6 plasma levels (0.393 +/- 0.013 microM) were similar to those observed in rats consuming a standard diet. B: animals consuming only the purified diet in which InsP6 was absent. In this case the InsP6 plasma levels decreased (0.026 +/- 0.006 microM); C: animals consuming the same purified diet as group B but received daily subcutaneous injections of 50 microg kg(-1) etidronate during the last 14 days. In this case the InsP6 plasma levels were also very low (0.025 +/- 0.007 microM); D: animals consuming the same diet as group B but a 6% of carob germ (InsP6 rich product) was added. The InsP6 plasma levels (0.363 +/- 0.035 microM) were also similar to those observed in rats consuming a standard diet. After 21 days plaque formation was induced. Calcification plaques were allowed to proceed for 10 days, after which the plaque material present was excised, dried and weighed. It was found that the presence of myo-inositol hexaphosphate (phytate) in plasma at normal concentrations (0.3-0.4 microM) clearly inhibited the development of dystrophic calcifications in soft tissues. These results demonstrates that myo-inositol hexaphosphate acts as an inhibitor of calcium salt crystallization.

Administration, Oral↗
PubMed2004

Modeling action potential generation and propagation in NRK fibroblasts.

Normal rat kidney (NRK) fibroblasts change their excitability properties through the various stages of cell proliferation. The present mathematical model has been developed to explain excitability of quiescent (serum deprived) NRK cells. It includes as cell membrane components, on the basis of patch-clamp experiments, an inwardly rectifying potassium conductance (G(Kir)), an L-type calcium conductance (G(CaL)), a leak conductance (G(leak)), an intracellular calcium-activated chloride conductance [G(Cl(Ca))], and a gap junctional conductance (G(gj)), coupling neighboring cells in a hexagonal pattern. This membrane model has been extended with simple intracellular calcium dynamics resulting from calcium entry via G(CaL) channels, intracellular buffering, and calcium extrusion. It reproduces excitability of single NRK cells and cell clusters and intercellular action potential (AP) propagation in NRK cell monolayers. Excitation can be evoked by electrical stimulation, external potassium-induced depolarization, or hormone-induced intracellular calcium release. Analysis shows the roles of the various ion channels in the ultralong ( approximately 30 s) NRK cell AP and reveals the particular role of intracellular calcium dynamics in this AP. We support our earlier conclusion that AP generation and propagation may act as a rapid mechanism for the propagation of intracellular calcium waves, thus contributing to fast intercellular calcium signaling. The present model serves as a starting point to further analyze excitability changes during contact inhibition and cell transformation.

Action Potentials↗
PubMed2003

Ionic basis for excitability of normal rat kidney (NRK) fibroblasts.

Ionic membrane conductances of normal rat kidney (NRK) fibroblasts were characterized by whole-cell voltage-clamp experiments on single cells and small cell clusters and their role in action potential firing in these cells and in monolayers was studied in current-clamp experiments. Activation of an L-type calcium conductance (GCaL) is responsible for the initiation of an action potential, a calcium-activated chloride conductance (GCl(Ca)) determines the plateau phase of the action potential, and an inwardly rectifying potassium conductance (GKir) is important for the generation of a resting potential of approximately -70 mV and contributes to action potential depolarization and repolarization. The unique property of the excitability mechanism is that it not only includes voltage-activated conductances (GCaL, GKir) but that the intracellular calcium dynamics is also an essential part of it (via GCl(Ca)). Excitability was found to be an intrinsic property of a fraction (approximately 25%) of the individual cells, and not necessarily dependent on gap junctional coupling of the cells in a monolayer. Electrical coupling of a patched cell to neighbor cells in a small cluster improved the excitability because all small clusters were excitable. Furthermore, cells coupled in a confluent monolayer produced broader action potentials. Thus, electrical coupling in NRK cells does not merely serve passive conduction of stereotyped action potentials, but also seems to play a role in shaping the action potential.

Animals↗
PubMed2003

Visceral leishmaniasis in lung transplantation.

Infection by intracellular microorganisms with a special geographic distribution, such as Leishmania spp, has been reported in a limited number of patients undergoing solid-organ transplant (SOT). No cases of Leishmania spp infection in lung transplant patients were found in a review of the literature. In our series of 222 lung or heart and lung transplantations performed from February 1990 to October 2002, two cases of visceral leishmaniasis (VL) were diagnosed and treated with liposomal amphotericin B. All cases reported to date in transplant patients, including the ones discussed here, occurred in people living in or traveling to countries in the Mediterranean area. We therefore consider it advisable to include serological testing for latent infection due to Leishmania spp in pretransplantation screening for our geographical setting, despite the limited return of this strategy.

Adult↗
PubMed2003

Cardiopulmonary transplantation: experience of a lung transplant group.

Cardiopulmonary transplantation (CPT) is indicated for patients eligible for heart transplantation (HT) or lung transplantation (LT) who have severe concomitant lung or heart disease. Only 2 groups perform CPT in Spain. We report our experience with 18 CPTs representing 8.2% and 5% compared with LT (220) and HT (362), respectively, from February 13, 1990 to October 15, 2002. The mean time on a waiting list was 138 days. The current number of surviving patients is 7 (39%), with a mean follow-up of 602 days (range, 3 to 4627 days). They all remain asymptomatic with normal respiratory function in 4 patients. No cardiac graft rejection has been detected. Two patients experienced sustained gastroparesis during the first year with spontaneous resolution. Death occurred within the first 3 months in 9 patients. These outcomes contrast with the early mortality associated with LT and HT in our series, namely 10.6% and 11%, respectively. The different causes of death were as follows: sepsis and multiorgan failure in 5 patients, hemorrhagic shock in 3 patients, and suture dehiscence and fungal aortic perforation in 1 patient. Late mortalities were recorded in 2 cases. Overall patient survival in our series is lower than that reported by the International Registry (IR), with an early mortality rate of 50% (30% IR). Nevertheless, our survival rate at 10 years after transplantation is 30% (26% IR). We conclude that CPT should be considered despite the greater early morbidity and mortality.

Adolescent↗
PubMed2003

Lung transplantation in patients with x-linked agammaglobulinemia.

Lung transplantation is an established procedure to treat patients with end-stage lung disease. The criteria for recipient selection are broadening to include patients with congenital defects of the immune system, such as X-linked hypogammaglobulinemia (XLA). We report 2 cases of successful double lung transplantation in patients with XLA. The 2 men had developed bronchiectasis and end-stage lung disease despite early institution of intravenous immunoglobulin (IVIG) replacement therapy. Before transplantation, hypogammaglobulinemia was well controlled with IVIG in both patients. After transplantation, IVIG was administered every 48 hours during the first 10 days and then tapered slowly in the following weeks until returning to an every 3 weeks schedule. One patient has been followed up for 12 months and the other for 6 months. Lung function normalized in the first case and showed a restrictive pattern in the second one. Lung transplantation may be considered as a therapeutic option for patients with XLA and end-stage lung disease. Regular administration of IVIG overcomes the high risk of infections due to the severe immunodeficiency and the intensive immunosuppressive therapy.

Adult↗
PubMed2003

[Esophageal tuberculosis in an immunocompetent patient].

We present the case of a 68-year-old man who presented dysphagia and weight loss over the previous three months. Esophageal transit showed extreme stenosis suspicious for neoplasia but which was revealed to be a granulomatous inflammatory lesion. Culture of the lesion revealed Mycobacterium tuberculosis. Chest x-ray showed pulmonary tuberculosis. Esophageal tuberculosis should be considered in patients with dysphagia and pulmonary tuberculosis.

Aged↗
PubMed2003

[Anterior uveitis and juvenile idiopathic arthritis].

PURPOSE: Anterior uveitis is one of the most important extraarticular manifestations of juvenile idiopathic arthritis (JIA). The aim of this study was to describe the frequency of uveitis, complications and ocular surgical procedures, to corroborate risk factors for the development of uveitis and to analyze its evolutive characteristics. METHODS: Retrospective review of 132 children diagnosed with JIA in our hospital from 1985 to 2000. Patients presenting anterior uveitis (Tyndall + or recent keratic precipitates) were studied. RESULTS: Uveitis was detected in 26 of 132 children (19%). All of them presented pauciarticular JIA. The patients received corticosteroid therapy for a mean time of 19.2 months, developing a mean of 4.5 episodes of uveitis. Patients diagnosed with uveitis before or within 1 year from the onset of arthritis required longer treatment (295 months versus 206) and suffered more episodes (73 versus 44) than those with uveitis found later on. Complications (cataract, band keratopathy, glaucoma, macular edema) developed in 27.9% of the affected eyes. Surgery was required in 10 eyes. CONCLUSIONS: The incidence of uveitis in our study is similar to recently reported rates. Female sex, pauciarticular onset, serum antinuclear antibodies (ANA) and early onset of uveitis seem to increase the development of chronic uveitis. Periodic slit-lamp ophthalmologic screenings in high risk patients are recommended (Arch Soc Esp Oftalmol 2003; 78: 561-566).

Arthritis, Juvenile↗
PubMed2001

Dynamics of two electrically coupled chaotic neurons: experimental observations and model analysis.

Conductance-based models of neurons from the lobster stomatogastric ganglion (STG) have been developed to understand the observed chaotic behavior of individual STG neurons. These models identify an additional slow dynamical process calcium exchange and storage in the endoplasmic reticulum as a biologically plausible source for the observed chaos in the oscillations of these cells. In this paper we test these ideas further by exploring the dynamical behavior when two model neurons are coupled by electrical or gap junction connections. We compare in detail the model results to the laboratory measurements of electrically-coupled neurons that we reported earlier. The experiments on the biological neurons varied the strength of the effective coupling by applying a parallel, artificial synapse, which changed both the magnitude and polar-of the conductance between the neurons. We observed a sequence of bifarctions that took the neurons from strongly synchronized in-phase behavior. through uncorrelated chaotic oscillations to strongly synchronized and now regular out-of-phase behavior. The model calculations reproduce these observations quantitatively, indicating that slow subcellular processes could account for the mechanisms involved in the synchronization and regularization of the otherwise individual chaotic activities.

Animals↗
PubMed1999

Indinavir crystallization and urolithiasis.

The crystallization of indinavir in synthetic urine at different pH values and indinavir concentrations was kinetically studied. It was found that precipitation time notably decreases at urinary pH values above 6.0. The effects of some products as potential crystallization inhibitors were studied. Some natural saponins such as escin and glycyrrhizic acid provoked a notable increase in the precipitation time of indinavir, this pointing out their possible use to prevent renal tubular solid deposition.

Chemical Precipitation↗
PubMed1999

Origin of coherent structures in a discrete chaotic medium.

Using as an example a large lattice of locally interacting Hindmarsh-Rose chaotic neurons, we disclose the origin of ordered structures in a discrete nonequilibrium medium with fast and slow chaotic oscillations. The origin of the ordering mechanism is related to the appearance of a periodic average dynamics in the group of chaotic neurons whose individual slow activity is significantly synchronized by the group mean field. Introducing the concept of a "coarse grain" as a cluster of neuron elements with periodic averaged behavior allows consideration of the dynamics of a medium composed of these clusters. A study of this medium reveals spatially ordered patterns in the periodic and slow dynamics of the coarse grains that are controlled by the average intensity of the fast chaotic pulsation.

Journal Article↗
PubMed1998

Vitamin A and urolithiasis.

The effects of vitamin A deficiency on urolithiasis were investigated in male rats. A vitamin A-deficient diet caused important changes in the composition of the urine of the treated rats when compared with controls. One of the main effects was a decrease in the concentration of urinary glycosaminoglycans and zinc in the rats receiving the vitamin A-deficient diet. Significant differences were also found in plasma vitamin E and in the relation of vit E/vit A between treated and control groups but, in general, with no important differences in vitamin A. Nevertheless, significant differences in kidney content of vitamin A were observed between both groups. On the other hand, lesions of the cuboidal epithelium that covers the papillae in rats treated with the vitamin A-deficient diet were severe when compared with controls. The vitamin A and E plasma levels in urolithiasic humans were also investigated and compared with those found in a control group. No significant differences were observed in plasma vitamin A levels; nevertheless a significant increase in vitamin E and in the vit E/vit A ratio was clearly observed. These results could be related to a possible deficit of vitamin A in kidneys of stone formers, this being one of the diverse factors that can contribute to urolith development. Moreover, the deficit of important urinary crystallization inhibitors normally found in stone-formers, such as pyrophosphate and phytate, can also be related to the presence of low levels of renal vitamin A which prevents the enzymatic degradation of such inhibitors.

Animals↗
PubMed1998

Effects of phytic acid on renal stone formation in rats.

The effects of phytic acid and phytic acid/zinc mixtures on renal urolith development in an animal model of nephrolitiasis were studied. Male rats were divided into four groups of 15, 10, 10 and 12 rats each. The rats of Group I were treated with ethylene glycol; of Group II with ethylene glycol plus zinc; of Group III with ethylene glycol phytic acid; and of Group IV with ethylene glycol plus a mixture of phytic acid/zinc. Urine analysis (24 h) was carried out to determine the levels of calcium, oxalate, citrate, zinc and phytic acid in each group. At the end of the experiment all kidneys were removed and examined macroscopically and microscopically for possible crystal/stone locations and the total calcium amount in the renal papillary tissue was evaluated. In the rats treated with the aqueous phytic acid and phytic acid/zinc mixture, the number of calcifications on the papillary tips and the total calcium amount of the papillary tissue were significantly reduced compared with the controls treated exclusively with ethylene glycol or ethylene glycol plus zinc. Consequently, phytic acid and mixtures of phytic acid/zinc may be a useful agent in the treatment of patients with calcic urolithiasis.

Animals↗