Spine motility with synaptic contact.
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Animals↗
Biomedical subjects
R Blazeski
Publications and source records attributed to R Blazeski.
Neuron death in the substantia nigra of weaver mouse occurs late in development and is not apoptotic.
Weaver is a spontaneous mutation in mice characterized by the postnatal loss of external granule cells in the cerebellum and dopaminergic neurons of the midbrain, especially in the substantia nigra. We have shown previously that natural cell death with the morphology of apoptosis occurs in the substantia nigra of normal rodents during postnatal development. We therefore sought to determine whether the loss of dopaminergic neurons in homozygous weaver mice occurs during the period of natural cell death in the substantia nigra and whether it has the morphology of apoptosis. We have found, using a silver stain technique, that although apoptotic cell death does occur early postnatally in homozygous weaver substantia nigra, it also does so with equal magnitude in wild-type and heterozygous weaver littermates. Unique to homozygous weavers is the occurrence of degenerating neurons in the nigra that are not apoptotic. These degenerating neurons are observed at postnatal day 7, and they are most abundant on postnatal days 24-25. The nonapoptotic nature of this cell death is confirmed by negative in situ end labeling of nuclear DNA fragmentation and by ultrastructural analysis. Ultrastructural studies reveal irregular chromatin aggregates in the nucleus, as well as marked cytoplasmic changes, including the formation of vacuoles and distinctive stacks of dilated cisternae of endoplasmic reticulum. We interpret these changes as indicative of either a variant morphology of programmed cell death or a pathological degenerative process mediated by an as yet unknown mechanism related to the recently described mutation in the GIRK2 potassium channel.
Aging↗
Optical microscopy. 3. Tracking fluorescently labeled neurons in developing brain.
For decades, time-lapse microscopy has been used to track dynamic events associated with biological phenomena. Time-lapse studies of the developing nervous system have been restricted to analysis of dissociated cell cultures or of a series of static images from living organisms. The advent of new fluorescent dyes and video imaging technology has produced novel views of the behavior of neurons in the context of the developing nervous tissue, such as migrations within and away from proliferative zones and navigation of axonal processes to synaptic targets. After fixation of the tissue preparation, time-lapse monitoring can be followed by other analytical techniques and forms of microscopy, e.g., immunocytochemistry or electron microscopy, producing information on the interactions of individual cells whose behavioral histories are known. The power of video time-lapse microscopy of living brain tissue lies in the firsthand documentation of developmental patterning, which in turn can serve as an experimental assay.
Animals↗
Retinal axon divergence in the optic chiasm: uncrossed axons diverge from crossed axons within a midline glial specialization.
A long-standing question is how fiber pathways in the mammalian CNS project to both sides of the brain. Static and real-time analyses of dye-labeled retinal axons (Godement et al., 1990, 1994) have demonstrated that at embryonic day 15-17 in the mouse, crossed and uncrossed axons from each eye diverge in a zone 100-200 microns proximal to the midline of the optic chiasm. In this study, we identify cellular specializations in this zone that might serve as cues for retinal axon divergence. Second, using growth cone morphology as an indicator of growth cone destination, we analyzed how crossed and uncrossed retinal growth cones related to these cellular components. Monoclonal antibody RC2, a marker for radial glia in embryonic mouse CNS, revealed a palisade of radial glia straddling the midline. At the midline, a thin raphe of cells that appear morphologically distinct from the radial glia express a free carbohydrate epitope, stage-specific embryonic antigen 1 (SSEA-1). Sections containing Dil-labeled axons and immunolabeled cells indicated that all axons enter the radial glial palisade. Uncrossed axons turn within the palisade, but never beyond the raphe of SSEA-1-positive cells. In addition, ultrastructural analysis indicated that all growth cones contact radial glia, with projections of the growth cone interdigitating with glial fibers. These results demonstrate that retinal axons diverge within a cellular specialization centered around the midline of the developing optic chiasm, consistent with the hypothesis that cues for divergence are located in this zone.
Animals↗
Cell-cell interactions influence survival and differentiation of purified Purkinje cells in vitro.
To determine the role of cell-cell interactions in Purkinje cell survival and dendritic differentiation, perinatal mouse Purkinje cells were purified, and their development was analyzed in vitro. In isolation at low density, Purkinje cell survival was poor, improved by neuronal contacts, either with purified granule neurons or with Purkinje cells themselves. Moreover, coculture with specific cell populations led to widely different degrees of Purkinje cell differentiation. Purified Purkinje cells cultured alone or with an inappropriate afferent, the mossy fibers, did not progress beyond immature forms. With astroglia, Purkinje cells had thin smooth processes. Proper Purkinje cell differentiation was driven only by coculture with granule cells, resulting in dendrites with spines receiving synapses. These results suggest that Purkinje cell differentiation is regulated by local epigenetic factors, provided in large part by the granule neuron.
Afferent Pathways↗