High performance computing for three-dimensional agent-based molecular models.

Agent-based simulations are increasingly popular in exploring and understanding cellular systems, but the natural complexity of these systems and the desire to grasp different modelling levels demand cost-effective simulation strategies and tools. In this context, the present paper introduces novel sequential and distributed approaches for the three-dimensional agent-based simulation of individual molecules in cellular events. These approaches are able to describe the dimensions and position of the molecules with high accuracy and thus, study the critical effect of spatial distribution on cellular events. Moreover, two of the approaches allow multi-thread high performance simulations, distributing the three-dimensional model in a platform independent and computationally efficient way. Evaluation addressed the reproduction of molecular scenarios and different scalability aspects of agent creation and agent interaction. The three approaches simulate common biophysical and biochemical laws faithfully. The distributed approaches show improved performance when dealing with large agent populations while the sequential approach is better suited for small to medium size agent populations. Overall, the main new contribution of the approaches is the ability to simulate three-dimensional agent-based models at the molecular level with reduced implementation effort and moderate-level computational capacity. Since these approaches have a generic design, they have the major potential of being used in any event-driven agent-based tool.

A simplified chromatin dispersion (nuclear halo) assay for detecting DNA breakage induced by ionizing radiation and chemical agents.

Methods for visualizing DNA damage at the microscopic level are based on treatment of cell nuclei with saline or alkaline solutions. These procedures for achieving chromatin dispersion produce halos that surround the nuclear remnants. We improved the fast halo assay for visualizing DNA breakage in cultured cells to create a simplified method for detection and quantitative evaluation of DNA breakage. Nucleated erythrocytes from chicken blood were selected as a model test system to analyze the production of nuclear halos after treatment with X-rays or H(2)O(2). After staining with ethidium bromide or Wright's methylene blue-eosin solution, nuclear halos were easily observed by fluorescence or bright-field microscopy, respectively, which permits rapid visualization of DNA breakage in damaged cells. By using image processing and analysis with the public domain ImageJ software, X-ray dose and H(2)O(2) concentration could be correlated well with the size of nuclear halos and the halo:nucleus ratio. Our results indicate that this simplified nuclear halo assay can be used as a rapid, reliable and inexpensive procedure to detect and quantify DNA breakage induced by ionizing radiation and chemical agents. A mechanistic model to explain the differences between the formation of saline or alkaline halos also is suggested.

[AIDS in children. 8 years experience at La Raza Medical Center Infectology Hospital, Mexican Social Security Institute]. / Síndrome de inmunodeficiencia adquirida en niños. Experiencia de 8 años en el Hospital de Infectología del Centro Médico "La Raza", Instituto Mexicano del Seguro Social.

The objective for this work was to describe the transmission mechanisms and the clinical behavior of 60 HIV-infected pediatric patients. We studied children from newborn to 15 years old according to the CDC criteria. From January 1985 to February 1992, were evaluated 60 patients, 40 males and 20 females; 25 with perinatal transmission (23 transplacental and 2 breast-feeding), 22 hemophiliacs, 12 by blood transfusion and 1 by intramuscular injection with contaminated needle. The disease was symptomatic in 50 patients, asymptomatic in 5 and indeterminate in 5 cases. Up to date, 28 children are in phase P2, 10 in P0 and P1, and 22 patients have died. The clinical manifestations in 50 patients were: altered growth and development in 50, generalized lymphadenopathy in 30, severe infections in 23, fever in 15, hepatosplenomegaly in 15, chronic diarrhea in 10, and HIV-encephalopathy in one. It is concluded what at present time perinatal transmission is the main mechanism.

Sindrome coqueluchoide en pacientes desnutridos. / Pertussis syndrome in malnourished patients

En este trabajo se hace un analisis de 207 casos de sindrome coqueluchoide en pacientes atendidos en el Hospital de Infectologia del Centro Medico La Raza del IMSS, de enero de 1978 a agosto de 1980. Se comentan las principales complicaciones observadas, asi como varios aspectos relacionados con: edad, grado de desnutricion, antecedente de contacto con enfermos con tos paroxistica y esquema de vacunacion previo Se hace mencion de la dificultad para obtener cultivos para Bordetella pertussis en cultivo de exudado nasofaringeo

[Meningitis caused by Salmonella]. / Meningitis por Salmonella.

The clinical and laboratory characteristics of eleven cases of bacterial meningitis due to Salmonella, are reviewed. Meningitis was more common in children under the age of 13 months. In younger children the symptoms and neurological signs were not evident. Convulsive disorders and neurological coma were the most frequent complications in 4 and 5 cases respectively. The mortality ratio was high, 36% (4 patients) and the neurological sequelae were very important: two patients presented spastic paralytic alterations and other two had hydrocephalia. The main findings in the cerebral spinal fluid were: increased leukocytes and proteins with low glucose determinations; comparing with other purulent meningitis, mononuclear cells were predominant over polymorphonuclear cells in 7 cases (64%). Salmonella was isolated in all cases; Salmonella typhi was recovered in 3 cases; one had group "C" Salmonella and 7 cases Salmonella group "B". These cases were treated with either chloramphenicol or ampicillin.

[Fulminant hepatitis in children. Treatment by exchange transfusion]. / Hepatitis fulminante en niños. Tratamiento con exsanguinotransfusión.

Fulminant hepatitis is a potentially fatal clinical form of viral hepatitis. The experience at the Infectious Disease Hospital of the I.M.S.S. in Mexico City is presented. Twenty-two children with encephalopathy, grade III or IV managed with exchange transfusion were included. Results between these patients and a similar control group treated conservatively were compared. The mortality rates for the exchange transfusion and the control group were 91 and 100% respectively. A review of the literature revaled great differences in results obtained by several other authors. We conclude that well controled, prospective studies should be done, before the true efficiency of exchange transfusion can be properly evaluated.