Maturation of vulnerability to excitotoxicity: intracellular mechanisms incultured postnatal hippocampal neurons

Neuronal vulnerability to excitotoxicity changes dramatically during postna tal maturation. To study the intracellular mechanisms by which maturation a lters vulnerability in single neurons, we developed techniques to maintain hippocampal neurons from postnatal rats in vitro. After establishing their neuronal phenotype with immunohistochemistry and electrophysiology, we dete rmined that these neurons exhibit developmentally regulated vulnerability t o excitotoxicity. At 5 days in vitro, NMDA-induced cell death at 24 h incre ased from 3.6% in 3-day-old rats to >90% in rats older than 21 days. Time-l apse imaging of neuronal morphology following NMDA demonstrated increasingl y prevalent and severe injury as a function of postnatal age. Neither high- nor low-affinity calcium dyes demonstrated differences in peak NMDA-induce d [Ca2+](i) increases between neurons from younger and older animals. Howev er, neurons from older animals were uniformly distinguished from those from younger animals by their subsequent loss of [Ca2+](i) homeostasis. Because of the role of mitochondrial Ca2+ buffering in [Ca2+](i) homeostasis. we m easured NMDA-induced changes in mitochondrial membrane potential (Delta Psi ) as a function of postnatal age. NMDA markedly dissipated Delta Psi in neu rons from mature rats, but minimally in those from younger rats. These data demonstrate that, in cultures of postnatal hippocampal neurons, (a) vulner ability to excitotoxicity increases as a function of the postnatal age of t he animal from which they were harvested, and (b) developmental regulation of vulnerability to NMDA occurs at the level of the mitochondrion. (C) 2000 Elsevier Science B.V. All rights reserved.