Actualización en la fisiopatología de la hidrocefalia crónica del adulto idiopática: ¿nos enfrentamos a otra enfermedad neurodegenerativa? / Current concepts on the pathophysiology of idiopathic chronic adult hydrocephalus: Are we facing another neurodegenerative disease?

INTRODUCCIÓN: Desde la descripción hace 5 décadas de la hidrocefalia crónica del adulto idiopática (HCAi), su fisiopatología ha sido considerada básicamente relacionada con el efecto que la dilatación ventricular ejerce sobre las estructuras adyacentes al sistema ventricular. Sin embargo, las alteraciones en el flujo sanguíneo cerebral (FSC) y, sobre todo, la reducción en el recambio licuoral parecen emerger como componentes fisiopatológicos principales de esta enfermedad. DESARROLLO: En la HCAi se observa una compresión del tracto piramidal, de los circuitos cortico-subcorticales fronto-estriatales y fronto-reticulares, y de las fibras profundas del fascículo longitudinal superior. En el cuerpo calloso se objetiva un descenso en el número de fibras comisurales, que son reemplazadas por gliosis. El FSC se encuentra alterado, con un patrón de última pradera en la región subcortical adyacente a los ventrículos, correspondiente a la intersección entre las arterias subependimarias y las arterias perforantes dependientes de los grandes troncos arteriales de la circulación anterior. El recambio diario del LCR se ve disminuido en un 75%, lo que conlleva una reducción del aclaramiento de neurotóxicos y la interrupción de las señalizaciones neuroendocrinas y paracrinas que ocurren a través del LCR. CONCLUSIONES: La HCAi emerge como una entidad nosológica compleja, en la que los efectos de la microangiopatía subcortical y la disminución del recambio de LCR desempeñan un papel fundamental. Esta base fisiopatológica aleja la HCAi del concepto clásico de hidrocefalia y la acerca al perfil de otras enfermedades neurodegenerativas, como la enfermedad de Alzheimer o la enfermedad de Binswanger

INTRODUCTION: Since its description five decades ago, the pathophysiology of idiopathic chronic adult hydrocephalus (iCAH) has been traditionally related to the effect that ventricular dilatation exerts on the structures surrounding the ventricular system. However, altered cerebral blood flow, especially a reduction in the CSF turnover rate, are starting to be considered the main pathophysiological elements of this disease. DEVELOPMENT: Compression of the pyramidal tract, the frontostriatal and frontoreticular circuits, and the paraventricular fibres of the superior longitudinal fasciculus have all been reported in iCAH. At the level of the corpus callosum, gliosis replaces a number of commissural tracts. Cerebral blood flow is also altered, showing a periventricular watershed region limited by the subependymal arteries and the perforating branches of the major arteries of the anterior cerebral circulation. The CSF turnover rate is decreased by 75%, leading to the reduced clearance of neurotoxins and the interruption of neuroendocrine and paracrine signalling in the CSF. CONCLUSIONS: iCAH presents as a complex nosological entity, in which the effects of subcortical microangiopathy and reduced CSF turnover play a key role. According to its pathophysiology, it is simpler to think of iCAH more as a neurodegenerative disease, such as Alzheimer disease or Binswanger disease than as the classical concept of hydrocephalus

Current concepts on the pathophysiology of idiopathic chronic adult hydrocephalus: Are we facing another neurodegenerative disease? / Actualización en la fisiopatología de la hidrocefalia crónica del adulto idiopática: ¿nos enfrentamos a otra enfermedad neurodegenerativa?

INTRODUCTION: Since its description five decades ago, the pathophysiology of idiopathic chronic adult hydrocephalus (iCAH) has been traditionally related to the effect that ventricular dilatation exerts on the structures surrounding the ventricular system. However, altered cerebral blood flow, especially a reduction in the CSF turnover rate, are starting to be considered the main pathophysiological elements of this disease. DEVELOPMENT: Compression of the pyramidal tract, the frontostriatal and frontoreticular circuits, and the paraventricular fibres of the superior longitudinal fasciculus have all been reported in iCAH. At the level of the corpus callosum, gliosis replaces a number of commissural tracts. Cerebral blood flow is also altered, showing a periventricular watershed region limited by the subependymal arteries and the perforating branches of the major arteries of the anterior cerebral circulation. The CSF turnover rate is decreased by 75%, leading to the reduced clearance of neurotoxins and the interruption of neuroendocrine and paracrine signalling in the CSF. CONCLUSIONS: iCAH presents as a complex nosological entity, in which the effects of subcortical microangiopathy and reduced CSF turnover play a key role. According to its pathophysiology, it is simpler to think of iCAH more as a neurodegenerative disease, such as Alzheimer disease or Binswanger disease than as the classical concept of hydrocephalus.

Effect of ultraviolet-B radiation on salt marsh vegetation: Trends of the genus Salicornia along the Americas.

The effects of natural UV-B radiation on growth, photosynthetic and photoprotective pigment composition of different Salicornia species were analyzed in salt marshes at three different sites along the Americas (Puerto Rico, southern Brazil and Patagonia, Argentina). Plants were exposed to different levels of UV-B radiation for 1-2 years in situ as well as in outdoor garden UV-B exclusion experiments. Different UV-B levels were obtained by covering plants with UV-B opaque (blocked 93-100% of ambient UV-B) and UV-B attenuating (near-ambient) filters (reduced 20-25% of UV-B). Unfiltered plants were exposed to natural irradiance. UV-B filters had significant effects on temperature and photosynthetic pigments (due to changes in PAR; 400-700 nm). The growth of Salicornia species was inhibited after 35 to 88 days of exposure to mean UV-B radiation dosages between 3.6 and 4.1 kJ m(-2) day(-1). The highest number of branches on the main shoot (S. bigelovii and S. gaudichaudiana) and longest total length of the branches (S. gaudichaudiana) were observed in the UV-B opaque treatment. Salicornia species responded to increasing levels of UV-B radiation by increasing the amount of UV-B absorbing pigments up to 330%. Chromatographic analyses of seedlings and adult S. bigelovii plants found seven different UV-B absorbing flavonoids that are likely to serve as UV-B filtering pigments. No evidence of differential sensitivity or resilience to UV-B radiation was found between Salicornia species from low-mid latitudes and a previously published study of a high-latitude population.

The effect of natural UV-B radiation on a perennial Salicornia salt-marsh in Bahía San Sebastián, Tierra del Fuego, Argentina: a 3-year field study.

The Antarctic ozone hole and a general depletion of the stratospheric ozone layer cause increased levels of ultraviolet-B solar radiation (UV-B) over Tierra del Fuego, the southernmost tip of South America. For three consecutive growing seasons (1997-2000), we studied the biological impacts (morphology, physiology, demography and phenology) of natural UV-B radiation on a perennial Salicornia ambigua Michx. community in San Sebastian Bay (53 degrees S and 68 degrees W), Tierra del Fuego, Argentina. This is the first UV-B screening experiment on a subantarctic halophytic community. The shortwave UV-B spectrum (280 to 320 nm) was excluded by covering plots with UV-B blocking film (Mylar). These plots were compared to controls covered with UV-B transparent (Aclar) plastic screens, and unscreened plots. Shoot length in Salicornia was not affected by UV-B. Exposure to natural UV-B reduced biomass and density (by 17% and 38%, respectively). Concentration of UV-shielding pigments and cuticle thickness were both significantly higher (25-48% and 21-40%, respectively) in plants receiving ambient UV-B. The increase in cuticle thickness persisted throughout the growing season, whereas pigment concentration was higher at the beginning of the growing season. Also, the number of dead shoots was higher in plants exposed to UV-B. At the end of the growing season (March) shoot mortality was higher in plants exposed to ambient UV-B, and post-flowering senescence was 30 days earlier. Slight changes in the relative composition of Salicornia to Puccinellia were seen. The reduction observed in Salicornia shoot density under ambient UV-B was cumulative over time; 23% in the first growing-season, rising to 38% by the third growing-season. A similar incremental increase in pigment absorption at 305 nm was seen; 25% in the first and 48% in the third growing season.

Solar ultraviolet B radiation and photoproduction of vitamin D3 in central and southern areas of Argentina.

The incidence of nutritional rickets in the southern part of Argentina is 8-12 times higher than in the rest of the country. Winter 25(OH)D serum levels in normal population of southern areas are lower than in central and northern areas. To elucidate these differences, we compared the photoconversion of provitamin D3 (7-DHC) to previtamin D3 in two cities: Ushuaia (latitude 55 degrees S) and Buenos Aires (34 degrees S). Ampules containing 7-DHC were exposed to sunlight one day in the middle of each month either from 10:30 a.m. to 2:30 p.m. or from 8:00 a.m. to 5:00 p.m. The percentages of photoproducts formed were determined by high performance liquid chromatography (HPLC). Previous studies have proved that this is a valid model to assess "in vitro" the photoproduction of vitamin D3 in human skin. Previtamin D3 + vitamin D3 formed in Ushuaia were less (p < 0.02) than those found in Buenos Aires during all seasons: summer, (X +/- SEM) 6.4 +/- 0.8% vs. 13.2 +/- 1.8%; autumn, 1.2 +/- 0.7% vs. 6.3 +/- 1.3%; winter, 0.8 +/- 0.7% vs. 3.6 +/- 0.7%; spring, 3.4 +/- 0.5% vs. 9.1 +/- 1.1%. The photoproducts produced from 10:30 a.m. to 2:30 p.m. were similar for each month and latitude to those formed when the ampules were exposed from 8:00 a.m. to 5:00 p.m. We conclude that in Ushuaia there is a prolonged "vitamin D winter" during which cutaneous synthesis of vitamin D is absent, leading to lower serum values of 25(OH)D and contributing to the higher incidence of rickets.