Acute copper exposure induces oxidative stress and cell death in lateral line hair cells of zebrafish larvae.

Numerous physical and chemical agents can destroy mechanosensory hair cells in the inner ear of vertebrates, a process that is irreversible in mammals. Few experimental systems allow the observation of hair cell death mechanisms in vivo, in the intact animal, one of these being the lateral line system in the zebrafish. In this work we characterize the behavior of dying lateral line hair cells in fish exposed to low doses of copper in the water. The concentration of copper used in our study kills hair cells in a few hours, but removal of the metal is followed by robust regeneration of new hair cells. We use a combination of membrane and nuclear live stains, ultrastructural analysis and measurement of reactive oxygen species to characterize the events leading to the death of hair cells under these conditions. Our results show that a combination of necrotic cell death, accompanied by apoptotic features such as rapid DNA fragmentation, lead to the loss of these cells. We also show that hair cells exposed to copper undergo oxidative stress and that antioxidants can protect these cells from the effects of the metal. The study of this process in the zebrafish lateral line allows rapid morphological analysis of hair cell death and may be used as an efficient end point for molecule screens aimed at preventing these effects.

Regeneration in zebrafish lateral line neuromasts: expression of the neural progenitor cell marker sox2 and proliferation-dependent and-independent mechanisms of hair cell renewal.

Mechanosensory hair cells are essential for audition in vertebrates, and in many species, have the capacity for regeneration when damaged. Regeneration is robust in the fish lateral line system as new hair cells can reappear after damage induced by waterborne aminoglycoside antibiotics, platinum-based drugs, and heavy metals. Here, we characterize the loss and reappearance of lateral line hair cells induced in zebrafish larvae treated with copper sulfate using diverse molecular markers. Transgenic fish that express green fluorescent protein in different cell types in the lateral line system have allowed us to follow the regeneration of hair cells after different damage protocols. We show that conditions that damage only differentiated hair cells lead to reappearance of new hair cells within 24 h from nondividing precursors, whereas harsher conditions are followed by a longer recovery period that is accompanied by extensive cell division. In order to characterize the cell population that gives rise to new hair cells, we describe the expression of a neural stem cell marker in neuromasts. The zebrafish sox2 gene is strongly expressed in neuromast progenitor cells, including those of the migrating lateral line primordium, the accessory cells that underlie the hair cells in neuromasts, and in interneuromastic cells that give rise to new neuromasts. Moreover, we find that most of the cells that proliferate within the neuromast during regeneration express this marker. Thus, our results describe the dynamics of hair cell regeneration in zebrafish and suggest the existence of at least two mechanisms for recovery of these cells in neuromasts.

Sub-lethal concentrations of waterborne copper are toxic to lateral line neuromasts in zebrafish (Danio rerio).

In teleosts, the lateral line system is composed of neuromasts containing hair cells that are analogous to those present in the inner ear of all vertebrates. In the zebrafish embryo and early larva, this system is composed of the anterior lateral line (ALL), which covers the head, and the posterior lateral line (PLL), present in the trunk and tail. The mechanosensory hair cells found in neuromasts can be labeled in vivo using fluorescent dyes such as 4-di-2-Asp (DiAsp) or FM1-43. We have studied the effects of water-borne copper exposure on the function of the lateral line system in zebrafish larvae. Our results show that transient incubation of post-hatching larvae for 2h with non-lethal concentrations of copper (1-50 microM CuSO4) induces cellular damage localized to neuromasts, apoptosis, and loss of hair cell markers. This effect is specific to copper, as other metals did not show these effects. Since hair cells in fish can regenerate, we followed the reappearance of viable hair cells in neuromasts after copper removal. In the PLL, we determined that there is a threshold concentration of copper above which regeneration does not occur, whereas, at lower concentrations, the length of time it takes for viable hair cells to reappear is dependent on the amount of copper used during the treatment. The ALL behaves differently though, as regeneration can occur even after treatments with concentrations of copper an order of magnitude higher than the one that irreversibly affects the PLL. Regeneration of hair cells is dependent on cell division within the neuromasts as damage that precludes proliferation prevents reappearance of this cell type.

[Causes of the crisis of medical profession in Chile]. / Causas de la crisis de la profesión médica en Chile.

There is a growing dissatisfaction among physicians towards their professional practice. This article tries to identify causes of this dissatisfaction and to explain the fears that physicians experience during their practice. The authors pose the hypothesis that physicians have non resolved internal problems with the application of technological advances and that medical practice has not changed along with the dramatic social changes that have occurred in the last decades. Medical organizations work in a confusing environment. Considering the main characteristics of medical work, the causes of difficulties and the reasons to explain the slowness of physicians to identify the problems and react, are analyzed. Finally some solutions are proposed to overcome this crisis.

Crecimiento físico y morbilidad en el primer año de vida según peso de nacimiento / Physical growth and morbidity in the 1st year of life according to birth weight

En este estudio se analizan retrospectivamente, durante el primer año de vida 123 niños de peso bajo de nacimiento (NPBN, peso inferior a 2.500 g), 51 niños de peso de nacimiento insuficiente (NPIN, peso entre 2.500 y 2.990 g) y 53 niños de peso de nacimiento normal, (NPNN, peso entre 3.000 y 4.490 g) inscritos en un Consultorio de atención primaria del Servicio de Salud Metropolitano Norte durante los años 1980 y 1981. Para cada grupo se extrajeron, desde la historia clínica, antecedentes maternos, perinatales, duración de lactancia materna exclusiva, frecuencia de cuadros mórbidos, porcentaje de hospitalizaciones e incremento de peso y talla y se compararon con los estimados normales según Sempé. No hubo diferencias significativas entre los grupos, según los antecedentes maternos, en cambio, fue significativamente mayor, entre los niños de bajo peso o peso insuficiente, la proporción con apgar menor de 7, parto distócico y menor número de semanas de gestación. La duración de la lactancia materna exclusiva es menor cuanto más bajo es el peso al nacer. La mediana fue de un mes en los NPBN, dos meses en los NPIN y tres meses en los NPNN. La frecuencia de morbilidad y hospitalizaciones es mayor a menor peso al nacer. El promedio de cuadros mórbidos fue de 3.8 en los NPBN; 3,5 en los NPIN y 2,5 en los NPNN. La tasa de hospitalizaciones de los NPBN fue de 21,7% mientras que en los niños de 2.500 g o más fue de 8.7%. El promedio de incremento de peso y talla al año fue de 6.236g y 25.6 cm para los NPBN. PEG; 6.496 g y 26,2 cm. para los NPBN. AEG; 6.023 g y 24,5 cm para los NPIN y 6.295 g y 24.1 cm para los NPNN. Entre grupos estos aumentos no difieren significativamente aún cuando todos los grupos, excepto los NPIN, aumentaron de peso más que lo esperado según Sempé cuyo promedio es 6.190 g. En talla todos los grupos superaron dicho promedio que es de 23.3 cm

Preparación de solución hidratante oral en el hogar / Preparation of oral rehydration solution at home

Para determinar la conveniencia de entregar una solución hidratante oral - en la forma de solutos por diluir - en el manejo del síndrome diarreico agudo en el hogar y establecer la forma más adecuada de entregar los contenidos educativos, se estudiaron dos grupos de 50 madres cada uno, del consultorio La Pincoya, comparando la mera instrucción (Grupo I) con la demostración práctica (Grupo 2). Seproporcionó a las madres, glucosa en sobres de polietileno conteniendo 20 g, para ser disuelta en 1 litro de agua y generar una concentración de 111 mmol/l. El 95% de las muestras estuvo dentro del margen definido como de seguridad (cifra esperada +/- 20%). Las preparaciones erróneas, correspondieron exclusivamente a diluciones excesivas, lo que representaría una eventual disminución en rendimiento, pero no un riesgo mayor. La composición de las soluciones obtenidas, no variío con la edad y escolaridad materna, ni con el número de hijos. Se destaca la importancia de suministrar los contenidos educativos, recurriendo a la demostración, ya que si bien los grupos 1 y 2 no mostraron diferencias significativas desdeel punto de vista de los promedios de concentración de glucosa logrados, las varianzas señalaron que el segundo tiene una dispersión de valores claramente menor(p<0.05). Se comenta la posibilidad de incorporal el uso de una solución hidratante oral, en forma de sales para disolver, en el manejo ambulatorio del síndromediarreico agudo en nuestro medio