Regional density of glial cells in the rat corpus callosum

Axons and glial cells are the main components of white matter. The corpus callosum (CC) is the largest white matter tract in mammals; in rodents, 99% of the cells correspond to glia after postnatal day 5 (P5). The area of the CC varies through life and regional differences related to the number of axons have been previously described. Whether glial cell density varies accordingly is unknown; thus the aim of this study was to estimate glial cell density for the genu, body and splenium -the three main regions of CC-, of P6 and P30 rats. Here we report that the density of CC glial cells reduced by ~10% from P6 to P30. Even so, the density of astrocytes showed a slight increase (+6%), probably due to differentiation of glioblasts. Interestingly, glial cell density decreased for the genu (-21%) and the body (-13%), while for the splenium a minor increase (+5%) was observed. The astrocyte/glia ratio increased (from P6 to P30) for the genu (+27%), body (+17%) and splenium (+4%). Together, our results showed regional differences in glial cell density of the CC. Whether this pattern is modified in some neuropathologies remains to be explored.

Topography and axon arbor architecture in the visual callosal pathway: effects of deafferentation and blockade of TV-methyl-D-aspartate receptors

Visual callosal fibers link cortical loci in opposite hemispheres that represent the same visual field but whose locations are not mirror-symmetric with respect to the brain midline. Presence of the eyes from postnatal day 4 (P4) to P6 is required for this map to be specified. We tested the hypothesis that specification of the callosal map requires the activation of A'-methyl-D-aspartate receptors (NMDARs). Our results show that blockade of NMDARs with MK-801 during this critical period did not induce obvious abnormalities in callosal connectivity patterns, suggesting that retinal influences do not operate through NMDAR-mediated processes to specify normal callosal topography. In contrast, we found that interfering with NMDAR function either through MK801-induced blockade of NMDARs starting at P6 or neonatal enucleation significantly increases the length of axon branches and total length of arbors, without major effects on the number of branch tips. Our results further suggest that NMDARs act by altering the initial elaboration of arbors rather than by inhibiting a later-occurring remodeling process. Since the callosal map is present by P6, just as axonal branches of simple architecture grow into gray matter, we suggest that regulation of arbor development by NMDAR-mediated processes is important for maintaining the precision of this map.

Ventrículos laterales: valores longitudinales y edad / Lateral ventricle: longitudinal values and age: aing of the brain

La bibliografía muestra que los volúmenes de los ventrículos cerebrales se incrementan con la edad. Valores lineales relacionados podrían detectar las variaciones en un plano del espacio. El objetivo del trabajo es determinar en sujetos femeninos, en función de la edad, posibles variaciones lineales anteroposteriores y ventrodorsales de los ventrículos laterales.

La malnutrición prenatal proteica leve afecta el desarrollo del cuerpo callaso anterior / Mild protein prenatal malnutrition specifically affects development of the anterior corpus callosum

Ratas mal nutridas prenatalmente y durante la lactancia con una dieta isocalórica y baja en proteínas, presentaron un cuerpo calloso más pequeño que los controles, a los 45-52 días de edad, lo cual fue consistente con las diferencias en los pesos cerebrales. En cambio, ratas mal nutridas prenatalmente y rehabilitadas durante la lactancia con una dieta alta en proteínas, mostraron normalidad en el peso cerebral y en el desarrollo de los tercios medio y posterior del cuerpo calloso. Estas observaciones sugieren: 1) que las conexiones cortico-corticales (interhemisféricas) son vulnerables a la malnutrición proteica; y 2) el cuerpo calloso anterior, que conecta áreas frontales a través de la línea media, es particularmente afectado por este tipo de malnutrición, a pesar de una rehabilitación dietaria durante la vida postnatal.

Effect of monocular blockade of retinal activity on the development of visual callosal connections in the rat

It has been previously reported that neonatal monocular enucleation in rats and hamsters induces the development of an anomalous band of callosal connections in the middle of area 17 (primary visual cortex) in the hemisphere ipsilateral to the remaining eye. In order to determine whether this effect is due to elimination of retinal activity in one eye, we used the anatomical tracer horseradish peroxidase (HRP) to study the pattern of visual callosal connections in rats in which retinal activity had been blocked by intraocular injections of tetrodotoxin during the first two weeks of life. We found that the callosal pattern in the hemisphere ipsilateral to the eye not treated with tetrodotoxin was not distinguishable from the pattern present in normal rats. In particular, we did not observe the anomalous extra band of callosal connections that occurs in area 17 in the hemisphere ipsilateral to the remaining eye in monocularly enucleated rats. These results indicate that blockade of retinal activity in one eye is not sufficient to cause the marked changes in the pattern of visual callosal connections that are induced by neonatal monocular enucleation

The neurogenesis of the callosal population of cortical cells in hamsters

The neurogenesis of the callosal subpopulation of cortical cells was determined in hamsters by associating incorporation of [3H]- thymidine injected on different embryonic days with horseradish peroxidase retrograde labelling in adulthood. Despite the great radial dispersion of migratory destinations of neurons born simultaneously, it was found that callosal birthdates in cortical area 6 extend from day E13 to day E15, a period that corresponds to the neurogenesis of layers III-V, where most callosal neurons come to be located in adults