Effects of dynamic synapses on noise-delayed response latency of a single neuron

The noise-delayed decay (NDD) phenomenon emerges when the first-spike latency of a periodically forced stochastic neuron exhibits a maximum for a particular range of noise intensity. Here, we investigate the latency response dynamics of a single Hodgkin-Huxley neuron that is subject to both a suprathreshold periodic stimulus and a background activity arriving through dynamic synapses. We study the first-spike latency response as a function of the presynaptic firing rate f. This constitutes a more realistic scenario than previous works, since f provides a suitable biophysically realistic parameter to control the level of activity in actual neural systems. We first report on the emergence of classical NDD behavior as a function of f for the limit of static synapses. Second, we show that when short-term depression and facilitation mechanisms are included at the synapses, different NDD features can be found due to their modulatory effect on synaptic current fluctuations. For example, an intriguing double NDD (DNDD) behavior occurs for different sets of relevant synaptic parameters. Moreover, depending on the balance between synaptic depression and synaptic facilitation, single NDD or DNDD can prevail, in such a way that synaptic facilitation favors the emergence of DNDD whereas synaptic depression favors the existence of single NDD. Here we report the existence of the DNDD effect in the response latency dynamics of a neuron.

Ungulate vehicle collisions in a peri-urban environment: consequences of transportation infrastructures planned assuming the absence of ungulates

Ungulate vehicle collisions (UVC) provoke serious damage, including human casualties, and a large number of measures have been developed around the world to avoid collisions. We analyse the main factors involved in UVC in a road network built in the absence of ungulates, where mitigation structures to avoid UVC were not adequately considered. Ungulate population greatly increased during the last two decades and now Roe Deer and Wild Boars are widely distributed over the study area, but even after this increase, the road network was not adapted to avoid UVC. A total of 235 Roe Deer (RDVC) and 153 Wild Boar vehicle collisions (WBVC) were recorded between January 2008 and December 2011. We randomly selected 289 sample points (87 RDVC, 60 WBVC and 142 controls) separated by at least 500 metres from the next closest point and measured 19 variables that could potentially influence the vehicle collisions. We detected variations in the frequency of RDVC on a monthly basis, and WBVC was higher at weekends but no significant differences were detected on a monthly basis. UVC were more likely to occur at locations where sinuosity of the road, velocity, surface of shrub and deciduous forest area were greater, the presence of fences entered with positive relationship and distance to the nearest building was less. RDVC were more likely to occur at locations where timber forest area increased and distance to the nearest building decreased and WBVC was related to open fields cover and also to the presence of fences. Sinuosity and velocity entered in both cases as significant factors. Major roads, in which the traffic volume is greater and faster, caused more accidents with ungulates than secondary roads. Nowadays, the high frequency of ungulate road-kills deserves a new strategy in order to adapt infrastructure and adopt mitigation measures.

Unstable dynamics, nonequilibrium phases, and criticality in networked excitable media

Excitable systems are of great theoretical and practical interest in mathematics, physics, chemistry, and biology. Here, we numerically study models of excitable media, namely, networks whose nodes may occasionally be dormant and the connection weights are allowed to vary with the system activity on a short-time scale, which is a convenient and realistic representation. The resulting global activity is quite sensitive to stimuli and eventually becomes unstable also in the absence of any stimuli. Outstanding consequences of such unstable dynamics are the spontaneous occurrence of various nonequilibrium phases--including associative-memory phases and one in which the global activity wanders irregularly, e.g., chaotically among all or part of the dynamic attractors--and 1/f noise as the system is driven into the phase region corresponding to the most irregular behavior. A net result is resilience which results in an efficient search in the model attractor space that can explain the origin of some observed behavior in neural, genetic, and ill-condensed matter systems. By extensive computer simulation we also address a previously conjectured relation between observed power-law distributions and the possible occurrence of a "critical state" during functionality of, e.g., cortical networks, and describe the precise nature of such criticality in the model which may serve to guide future experiments.

Antarctic mesopelagic micronekton: evidence from seabirds that pack ice affects community structure

Through a multidisciplinary project (AMERIEZ), with an unusual complement of components, previously unknown temporal and spatial dimensions to the structure of Antarctic epipelagic and mesopelagic communities were revealed. In late spring, an abundance of crustacean species thought to occur only below 300 meters was detected in ice-covered surface waters. Evident in ice-free waters were the expected occurrence patterns of these normally nonmigratory mesopelagic organisms. Where the pack was consolidated and little light penetrated to depth, primary and secondary production was confined to ice floes, and the physical environment immediately beneath the ice was reminiscent of a mesopelagic one. This suite of characteristics possibly explains why the crustaceans resided at the surface.

Instabilities in attractor networks with fast synaptic fluctuations and partial updating of the neurons activity

We present and study a probabilistic neural automaton in which the fraction of simultaneously-updated neurons is a parameter, rhoin(0,1). For small rho, there is relaxation towards one of the attractors and a great sensibility to external stimuli and, for rho > or = rho(c), itinerancy among attractors. Tuning rho in this regime, oscillations may abruptly change from regular to chaotic and vice versa, which allows one to control the efficiency of the searching process. We argue on the similarity of the model behavior with recent observations, and on the possible role of chaos in neurobiology.

Is hormone therapy a protective factor for late hematuria after high-dose radiotherapy in prostate cancer?

OBJECTIVES

To identify potential clinical and dosimetric factors predictive of a higher risk of grade 2 or higher late hematuria in patients with prostate cancer treated with high-dose radiotherapy.

METHODS

For this purpose, we have analyzed 229 T1c-T3b prostate cancer patients treated with 3-dimensional conformal radiotherapy (3DCRT) in a prospective dose escalation study and with a minimum follow-up of 1 year. The mean radiation dose was 79 Gy (range 72.1 to 84.14 Gy) and the mean follow-up was 47 months (range 14 to 95). One hundred eighteen patients also received androgen deprivation (AD) for high-risk disease. Univariate and multivariate analysis (MVA) were performed to identify variables significantly associated with late hematuria.

RESULTS

Of the 31 (14%) patients with grade 2 or higher genitourinary toxicity, hematuria was the main symptom in 24 (10.5%) with only 1 patient (0.5%) experiencing grade 3 hematuria. On statistical analysis, all the dosimetric parameters failed to show a significant correlation with grade 2 or higher hematuria. On MVA, prior transurethral resection of the prostate (TURP) was significantly associated with a higher risk of late hematuria (relative risk [RR] = 2.8; P = 0.026), whereas long-term AD was correlated with a significantly decreased risk (RR = 0.21; P = 0.019).

CONCLUSIONS

TURP was a relevant factor increasing 3 times the risk of late hematuria in prostate cancer patients treated with 3DCRT. Conversely, long-term AD resulted in a protective factor decreasing 5 times the risk of late hematuria. To our knowledge, this is the first study reporting a protecting effect of long-term hormones in late toxicity after radiotherapy.

Competition between synaptic depression and facilitation in attractor neural networks

We study the effect of competition between short-term synaptic depression and facilitation on the dynamic properties of attractor neural networks, using Monte Carlo simulation and a mean-field analysis. Depending on the balance of depression, facilitation, and the underlying noise, the network displays different behaviors, including associative memory and switching of activity between different attractors. We conclude that synaptic facilitation enhances the attractor instability in a way that (1) intensifies the system adaptability to external stimuli, which is in agreement with experiments, and (2) favors the retrieval of information with less error during short time intervals.

Amniotic membrane transplantation for conjunctival epithelization of exposed dermis-fat [corrected] graft

We report the use of amniotic membrane over dermis-fat graft to improve conjunctival epithelization when fat is exposed. A 38-year-old male with previous history of orbital implant extrusion managed with a dermis-fat graft, presented with exposed fat secondary to dermis retraction in its central area. This caused difficulty with the conjunctival growth. Eighteen days after the amniotic membrane graft placement, a complete conjunctival reepithelization and an appropriate ocular prosthesis adaptation were achieved. Therefore, the amniotic membrane graft is a useful method to improve conjunctival growth in cases of dermis-fat grafts with fat exposure and limited conjunctiva, are present.

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.

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.

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.

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.

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 ( GKir), an L-type calcium conductance ( GCaL), a leak conductance ( Gleak), an intracellular calcium-activated chloride conductance [ GCl(Ca)], and a gap junctional conductance ( Ggj), coupling neighboring cells in a hexagonal pattern. This membrane model has been extended with simple intracellular calcium dynamics resulting from calcium entry via GCaLchannels, 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 (∼30 s) NRK cell AP and reveals the particular role of intracellular calcium dynamics in this AP. We support our earlier conclusion (De Roos A, Willems PH, van Zoelen EJ, and Theuvenet AP. Am J Physiol Cell Physiol 273: C1900–C1907, 1997) 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.

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.

[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).

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.

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.

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.

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.

Tuberculosis esofágica en paciente inmunocompetente

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.

Regularization mechanisms of spiking-bursting neurons

An essential question raised after the observation of highly variable bursting activity in individual neurons of Central Pattern Generators (CPGs) is how an assembly of such cells can cooperatively act to produce regular signals to motor systems. It is well known that some neurons in the lobster stomatogastric ganglion have a highly irregular spiking-bursting behavior when they are synaptically isolated from any connection in the CPG. Experimental recordings show that periodic stimuli on a single neuron can regulate its firing activity. Other evidence demonstrates that specific chemical and/or electrical synapses among neurons also induce the regularization of the rhythms. In this paper we present a modeling study in which a slow subcellular dynamics, the exchange of calcium between an intracellular store and the cytoplasm, is responsible for the origin and control of the irregular spiking-bursting activity. We show this in simulations of single cells under periodic driving and in minimal networks where the cooperative activity can induce regularization. While often neglected in the description of realistic neuron models, subcellular processes with slow dynamics may play an important role in information processing and short-term memory of spiking-bursting neurons.

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.

Leptocephalus energetics: metabolism and excretion

Leptocephali are the unusual transparent larvae that are typical of eels, bonefish, tarpon and ladyfish. Unlike the larvae of all other fishes, leptocephali may remain in the plankton as larvae for several months before metamorphosing into the juvenile form. During their planktonic phase, leptocephali accumulate energy reserves in the form of glycosaminoglycans, which are then expended to fuel metamorphosis. The leptocephalus developmental strategy is thus fundamentally different from that exhibited in all other fishes in two respects: it is far longer in duration and energy reserves are accumulated. It was anticipated that the unusual character of leptocephalus development would be reflected in the energy budget of the larva. This study describes the allocation of energy to metabolism and excretion, two important elements of the energy budget. Metabolic rates were measured directly in four species of leptocephali, Paraconger caudilimbatus, Ariosoma balearicum, Gymnothorax saxicola and Ophichthus gomesii, using sealed-jar respirometry at sea. Direct measurements of metabolic rates were corroborated by measuring activities of lactate dehydrogenase and citrate synthase, two key enzymes of intermediary metabolism, in addition to that of Na(+)/K(+)-ATPase, a ubiquitous ion pump important in osmotic regulation. Excretion rates were determined by subsampling the sea water used in the respiratory incubations. The entire premetamorphic size range for each species was used in all assays. Mass-specific oxygen consumption rate, excretion rate and all enzyme activities (y) declined precipitously with increasing mass (M) according to the equation y=aM(b), where a is a species-specific constant and −1.74<b<-0.44. In leptocephali, the highly negative slope of the familiar allometric equation describing the relationship between mass-specific metabolic rate and mass, normally between −0.33 and 0, showed that a massive decline in metabolic rate occurs with increasing size. The result suggests that the proportion of actively metabolizing tissue also declines with size, being replaced in large measure by the metabolically inert energy depot, the glycosaminoglycans. Leptocephali can thus grow to a large size with minimal metabolic penalty, which is an unusual and successful developmental strategy.

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.

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.

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.

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.