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In neonates, transient exposure to glutamate produced large Ca<jats:sup>2+<\/jats:sup>increases throughout neurons, including distal dendrites (primary Ca<jats:sup>2+<\/jats:sup>responses). Repeated exposures resulted in sustained Ca<jats:sup>2+<\/jats:sup>increases in apical dendrites (secondary Ca<jats:sup>2+<\/jats:sup>responses) that were independent of continued glutamate exposure. These responses propagated and invaded the soma, resulting in irrecoverably high Ca<jats:sup>2+<\/jats:sup>elevations. In neurons from adults, identical glutamate exposure evoked primary Ca<jats:sup>2+<\/jats:sup>responses only in somata and proximal apical dendrites. Repeated glutamate exposures in the adult neurons also led to secondary Ca<jats:sup>2+<\/jats:sup>responses, but they arose in the peri-somatic region and then spread outward to distal apical dendrites, again without recovery. More stimuli were required to initiate secondary responses in neurons from adult versus neonates. Block of GABA<jats:sub>A<\/jats:sub>receptors in adults caused the primary and secondary responses to revert to the spatial pattern seen in the neonates and greatly increased their vulnerability to glutamate. These findings suggest that neurodegenerative secondary Ca<jats:sup>2+<\/jats:sup>events may be important determinants of susceptibility to HI injury in the developing CNS and that immature CA1 neurons may be more susceptible to excitotoxic injury due at least in part to insufficient development of GABAergic inputs to their dendrites.<\/jats:p>","DOI":"10.1152\/jn.01082.2005","type":"journal-article","created":{"date-parts":[[2006,4,20]],"date-time":"2006-04-20T00:48:16Z","timestamp":1145494096000},"page":"299-308","source":"Crossref","is-referenced-by-count":5,"title":["GABAergic Protection of Hippocampal Pyramidal Neurons Against Glutamate Insult: Deficit in Young Animals Compared to Adults"],"prefix":"10.1152","volume":"96","author":[{"given":"Aryan","family":"Azimi-Zonooz","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"C. 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