2-3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline and 2-aminoethoxydiphenyl-borate

During development, dendrites, and in particular dendritic filopodia, undergo extensive structural remodeling, presumably to help establish synaptic contacts. Here, we investigated the role of calcium signaling in dendritic plasticity by simultaneously recording calcium dynamics and filopodial growth in rat hippocampal slice cultures. Local calcium transients occurred in dendritic filopodia and shafts, often at putative synaptic sites. These events were highly correlated with filopodial motility: comparatively rare when individual filopodia emerged from the dendrite, they became more frequent after filopodia started growing, finally causing them to halt. Accordingly, an experimental reduction of the frequency of local calcium transients elicited filopodial growth and, conversely, calcium uncaging reduced filopodial motility. Our observations suggest that low levels of local calcium transients facilitate filopodial outgrowth, whereas high levels inhibit the formation of filopodia and stabilize newly formed ones. This process may facilitate synapse formation and may serve as a homeostatic mechanism distributing synapses evenly along developing dendrites.

Topics: 2-Amino-5-phosphonovalerate; Animals; Animals, Newborn; Boron Compounds; Calcium; Calcium Signaling; Cell Movement; Cells, Cultured; Dendrites; Diagnostic Imaging; Drug Interactions; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; GABA Antagonists; Glycine; Hippocampus; Immunohistochemistry; In Vitro Techniques; Indoles; Pseudopodia; Pyramidal Cells; Pyridazines; Quinoxalines; Rats; Synapses; Time Factors

Intracellular ATP supply and ion homeostasis determine neuronal survival and degeneration after ischemic stroke. The present study provides a systematic investigation in organotypic hippocampal slice cultures of the influence of experimental ischemia, induced by oxygen-glucose-deprivation (OGD). The pathways controlling intracellular Na(+) and Ca(2+) concentration ([Na(+)](i) and [Ca(2+)](i)) and their inhibition were correlated with delayed cell death or protection. OGD induced a marked decrease in the ATP level and a transient elevation of [Ca(2+)](i) and [Na(+)](i) in cell soma of pyramidal neurons. ATP level, [Na(+)](i) and [Ca(2+)](i) rapidly recovered after reintroduction of oxygen and glucose. Pharmacological analysis showed that the OGD-induced [Ca(2+)](i) elevation in neuronal cell soma resulted from activation of both N-methyl-d-aspartate (NMDA)-glutamate receptors and Na(+)/Ca(2+) exchangers, while the abnormal [Na(+)](i) elevation during OGD was due to Na(+) influx through voltage-dependent Na(+) channels. In hippocampal slices, cellular degeneration occurring 24 h after OGD, selectively affected the pyramidal cell population through apoptotic and non-apoptotic cell death. OGD-induced cell loss was mediated by activation of ionotropic glutamate receptors, voltage-dependent Na(+) channels, and both plasma membrane and mitochondrial Na(+)/Ca(2+) exchangers. Thus, we show that neuroprotection induced by blockade of NMDA receptors and plasma membrane Na(+)/Ca(2+) exchangers is mediated by reduction of Ca(2+) entry into neuronal soma, whereas neuroprotection induced by blockade of AMPA/kainate receptors and mitochondrial Na(+)/Ca(2+) exchangers might result from reduced Na(+) entry at dendrites level.

Topics: Adenosine Triphosphate; Animals; Animals, Newborn; Boron Compounds; Calcium; Calcium Channel Blockers; Cell Death; Clonazepam; Dantrolene; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Fura-2; Glucose; Hippocampus; Hypoxia; In Situ Nick-End Labeling; Indoles; Intracellular Space; Ion Exchange; Lidocaine; Mibefradil; Nimodipine; Organ Culture Techniques; Quinoxalines; Rats; Rats, Wistar; Sodium; Sodium Channel Blockers; Thiazepines; Thiourea; Time Factors