Synchronization and Oscillatory Dynamics in Heterogeneous, Mutually Inhibited Neurons

We study some mechanisms responsible for synchronous oscillations and loss of synchrony at physiologically relevant frequencies (10–200 Hz) in a network of heterogeneous inhibitory neurons. We focus on the factors that determine the level of synchrony and frequency of the network response, as well as the effects of mild heterogeneity on network dynamics. With mild heterogeneity, synchrony is never perfect and is relatively fragile. In addition, the effects of inhibition are more complex in mildly heterogeneous networks than in homogeneous ones. In the former, synchrony is broken in two distinct ways, depending on the ratio of the synaptic decay time to the period of repetitive action potentials (_s/T), where T can be determined either from the network or from a single, self-inhibiting neuron. With _s/T > 2, corresponding to large applied current, small synaptic strength or large synaptic decay time, the effects of inhibition are largely tonic and heterogeneous neurons spike relatively independently. With _s/T < 1, synchrony breaks when faster cells begin to suppress their less excitable neighbors; cells that fire remain nearly synchronous. We show numerically that the behavior of mildly heterogeneous networks can be related to the behavior of single, self-inhibiting cells, which can be studied analytically.     

Effect of variation in photoperiod and light intensity on oxygen consumption, lactate concentration and behavior in crayfish Procambarus clarkii and Procambarus digueti

The effects of light intensity and duration on metabolic and behavioral parameters of two species of crayfish, Procambarus clarkii and Procambarus digueti, were studied. Sixty animals of each species were submitted to high irradiance conditions of two different photoperiod lengths, one normal light/dark (LD) 12:12 and one extreme LD 20:4 for 2 weeks. Hemolymph, lactate and oxygen consumption were determined throughout the experimental period. Simultaneously in 18 additional animals of each species, motor activity was individually recorded under the same control and experimental conditions. Both species showed a decrease in oxygen uptake and an increase in hemolymph lactate concentration. The statistical significance of this finding was higher for LD 20:4. This extreme condition evoked a significant decrease of motor activity in P. clarkii and a high mortality rate in P. digueti. P. digueti did not survive after the experiment, whereas P. clarkii survived and adapted to the laboratory conditions. Changes in metabolic and behavioral parameters could indicate different adaptation abilities in these species.     

Comparative study of microbiological and histopathological techniques used for the detection of Helicobacter pylori

This study evaluates the sensitivity, specificity and predictive values of several techniques commonly used for the detection of Helicobacter pylori in an analysis of 105 biopsy specimens (gastric and duodenal). For comparative purposes, the techniques investigated were divided into 2 groups: histopathological and microbiological. The former included hematoxylin-eosin and Giemsa stains, a Gram stain modified for use in tissue, and immunohistochemical techniques. Microbiological analysis was performed using culture, the urease test and the conventional Gram stain. The immunohistochemical techniques proved to be the most sensitive (93%). The modified Gram stain was sufficiently sensitive (92%) and specific (97%) for the detection of the bacterium. When combined with a microbiological technique such as the urease test, this stain showed increased sensitivity (96%) but its specificity was reduced to 94%. This combination of tests is recommended for the detection of H. pylori in biopsy specimens since it is easily performed at low cost and gives excellent results. For economical reasons, it is suggested that the use of immunohistochemical techniques should be restricted to specific cases.     

Prevalence of oral lesions by Candida sp.: Their varieties and serotypes in a population of patients with AIDS under a highly active antiretroviral therapy.

The aim of this study has been to determine the prevalence of oral candidiasis and oral Candida carriers in an AIDS population under highly active antiretroviral therapy. Eighty-six AIDS patients treated with an antiretroviral combination (indinavir o ritonavir o saquinavir + zidovudine [AZT] + lamivudine [3TC]). Patients were grouped attending the predisposing factors for HIV infection in: intravenous drug users (IDU), heterosexuals, homosexuals, patients using hematological products or having unknown factors. Oral cavity was examined and an oral specimen was inoculated in a chromogenic culture medium (Albicans ID, bioMérieux, France). The prevalence of oral Candida lesions was 30.2% and Candida was isolated from 54.7% of patients. The predominant species was C. albicans serotype A in all the groups with the exception of homosexual patients, were C. albicans serotype B was the predominant. The IDU group showed the higher prevalence of Candida lesions and oral yeasts colonization, followed by the group of heterosexuals and homosexuals. An association was found between the presence of lesions and/or Candida spp. and the clinical stage or the viral concentration. The species Candida dubliniensis was isolated in the oral samples of two patients with candidosis and in two individuals without oral candidosis. The finding of this species in Spanish patients can be added to the data obtained in epidemiological studies in other countries.     

Trichophyton simii in a "Caí" monkey (Cebus apella) colony in the province of Corrientes, Argentina.

The objective is to describe an outbreak of Trichophyton simii in a Cebus apella monkey colony in Argentine. During summer, alopecic zones appeared on dorsal regions from head to base of the tail of the animals. The hair and skin of nine animals were streaked onto Sabouraud dextrose with cloramphenicol and incubated at 25 degrees C. By the 10th day, white, filamentous colonies, which turned pale pink, developed from simples of four animals. Microscopical examinations were carried out and, because of colony and macroconidia morphology, were classified as Trichopyton simii. Although infection with T. simii is considered a zoonosis, we did not find human cases.     

D-Aminoacylase from a novel producer: Stenotrophomonas maltophilia ITV-0595

A novel bacterial strain producing D-aminoacylase was isolated from organic waste and identified as Stenotrophomonas maltophilia ITV-0595. The isolation was performed using N-acetyl-D-phenylglycine (NAcDPG) as the sole source of C and N. The optimum pH for enzyme expression was 8 at 37°C. Using N-Ac-DPG concentrations from 0.5 up to 3% w/v, it was observed that at the 1% level, the microorganism showed acceptable responses in both enzyme activities and cell growth. From the different tested compounds N-acetyl-D-methionine (1%) was the best enzyme inducer (Sp. act. = 4.14 U mg⁻¹ protein, Vol. act. = 0.17 U ml⁻¹) and the only one that increased cell growth. Received 13 June 1997/ Accepted in revised form 29 October 1998     

Podophyllotoxin and nocodazole counter the effect of IKP104 on tubulin decay

Tubulin, the subunit protein of microtubules, undergoes a time-dependent loss of functional properties known as decay. We have previously shown that the drug 2-(4-fluorophenyl)-1-(2-chloro-3,5-dimethoxyphenyl)-3-methyl-6-phenyl-4(1H)-pyridinone (IKP104) accelerates decay, but that in the presence of colchicine, IKP104 becomes a stabilizer of tubulin. To see if this is due to conformational effects specific to colchicine or simply to occupancy at the colchicine site, we examined the effects of nocodazole and podophyllotoxin, two well-known competitive inhibitors of colchicine for binding to tubulin, on IKP104’s acceleration of decay. We found that podophyllotoxin abolished IKP104’s accelerating effect and, like colchicine, turned it into a stabilizer of tubulin. Nocodazole’s effects were similar to those of podophyllotoxin and colchicine, in that it abolished IKP104-induced enhancement of decay; however, in the presence of nocodazole, IKP104 caused little or no stabilization of tubulin. Since colchicine, nocodazole, and podophyllotoxin have very different interactions with tubulin, but all inhibit the IKP104-induced enhancement of decay, our findings suggest that this inhibition arises from occupancy of the colchicine site rather than from a direct conformational effect of these two drugs.     

Screening of larval/pupal P-element induced lethals on the second chromosome in Drosophila melanogaster: clonal analysis and morphology of imaginal discs

We have carried out screens for lethal mutations on the second chromosome of Drosophila melanogaster that are associated with abnormal imaginal disc morphologies, particularly in the wing disc. From a collection of 164 P element-induced mutations with a late larva/pupa lethal phase we have identified 56 new loci whose gene products are required for normal wing disc development and for normal morphology of other larval organs. Genetic mosaics of these 56 mutant lines show clonal mutant phenotypes for 23 cell-viable mutations. These phenotypes result from altered cell parameters. Causal relationships between disc and clonal phenotypes are discussed.     

patufet, the gene encoding the Drosophila melanogaster homologue of selenophosphate synthetase, is involved in imaginal disc morphogenesis

Proliferation in imaginal discs requires cell growth and is linked to patterning processes controlled by secreted cell-signalling molecules. To identify new genes involved in the control of cell proliferation we have screened a collection of P-lacW insertion mutants that result in lethality in the larval/pupal stages, and characterized a novel gene, patufet (ptuf). Inactivation of ptuf by a P element insertion in the 5′ untranslated region leads to aberrant imaginal disc morphology characterized by a reduction in mass of discs and disorganisation of disc cells where no folding or patterning can be detected. Moreover, apoptotic cells can be observed in these small and abnormal mutant discs. To examine the role of ptuf we have studied its clonal behaviour in genetic mosaics generated by mitotic recombination. The mutation causes reduced cell viability, smaller cell size and stops vein differentiation. Non-autonomous effects, such as abnormal differentiation of wild-type cells surrounding the clones, are also observed. We have cloned the ptuf gene of Drosophila melanogaster and found that it encodes a selenophosphate synthetase, which is the first identified in insects. Mutant flies transformed with the full-length cDNA show complete reversion of lethality and disc phenotype. Northern blot analysis and in situ hybridization indicate that the ptuf gene is expressed in imaginal discs as well as at different stages of development. The synthesis of selenoproteins by the selenophosphate synthetase, the role of selenoproteins in the maintenance of the oxidant/antioxidant balance of the cell and its possible implications in imaginal disc morphogenesis are discussed.