Biomedical subjects

Danny Baranes

Publications and source records attributed to Danny Baranes.

3 recordsLinked to original sources

PubMed2006

SGP-1 increases dendritic and synaptic development dependent on synaptic activity.

Neurotrophic factors are a group of secreted proteins which generally regulate neurite outgrowth and synaptic development. SGP-1 has been reported as a neurotrophic factor, though little is known of its effect on neurite outgrowth, and it is unknown whether SGP-1 affects synaptic development. We report here that SGP-1 is distributed in vesicle-like puncta in somas and dendrites of primary neurons in culture, and that SGP-1 is secreted in culture and is taken up by endocytosis in dendrites. Endogenous extracellular activity of SGP-1 promotes dendritic, but not axonal outgrowth. Furthermore, endogenous activity of SGP-1 increases synaptogenesis in hippocampal neurons as determined by measuring the density and size of synaptophysin puncta and by determining the density of dendritic spines, their surface expression of GluR2 and their immunoreactivity for GluR1. The effect of SGP-1 on the amount of postsynaptic receptors in dendritic spines depends on synaptic activity and apparently on activation of MAPK, as inhibition of either of these abolished the affect. Hence, SGP-1 has neurotrophic effects, increasing dendritic growth and promoting synaptic development in an activity-dependent fashion.

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PubMed2005

Growth of neurites toward neurite- neurite contact sites increases synaptic clustering and secretion and is regulated by synaptic activity.

The integrative properties of dendrites are determined by several factors, including their morphology and the spatio-temporal patterning of their synaptic inputs. One of the great challenges is to discover the interdependency of these two factors and the mechanisms which sculpt dendrites' fine morphological details. We found a novel form of neurite growth behavior in neuronal cultures of the hippocampus and cortex, when axons and dendrites grew directly toward neurite-neurite contact sites and crossed them, forming multi-neurite intersections (MNIs). MNIs were found at a frequency higher than obtained by computer simulations of randomly distributed dendrites, involved many of the dendrites and were stable for days. They were formed specifically by neurites originating from different neurons and were extremely rare among neurites of individual neurons or among astrocytic processes. Axonal terminals were clustered at MNIs and exhibited higher synaptophysin content and release capability than in those located elsewhere. MNI formation, as well as enhancement of axonal terminal clustering and secretion at MNIs, was disrupted by inhibitors of synaptic activity. Thus, convergence of axons and dendrites to form MNIs is a non-random activity-regulated wiring behavior which shapes dendritic trees and affects the location, clustering level and strength of their presynaptic inputs.

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PubMedDate not supplied

Growth of primary hippocampal neuronal tissue on an aragonite crystalline biomatrix.

Tissue-like structures of hippocampal neurons were established in a crystalline three-dimensional (3D) aragonite biomatrix obtained from the exoskeleton of the coral Porites lutea. Cultures were maintained in vitro for up to 5 weeks. Cell viability and regeneration of neuronal properties were studied by immunocytochemical methods, light microscopy image analysis techniques, and scanning electron microscopy. Some portions of the cell population acquired the morphological characteristics of hippocampal pyramidal or granule neurons with axons and dendrites extending in a 3D manner along the surfaces of the crystalline biomatrix. The neurons usually grew on a sheet of glial cells. Within the pore void areas, multiple layers of neurons were formed, many of the neurons growing with no attachment to the crystalline surfaces. The neurons developed mature synaptic connections, with presynaptic sites expressing the synaptic vesicle protein 2 and postsynaptic sites having the shape of dendritic spines and expressing type 1 glutamate receptors, as these cells do under conventional culture conditions. The findings of the present study suggest that neuronal networks growing in a strong 3D aragonite support may find application as tissue replacement material for the central nervous system.

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