Survival and synaptogenesis of hippocampal neurons without NMDA receptor function in culture

Authors

  • Shigeo Okabe,

    1. Laboratory of Molecular Biology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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    • *

      Present Address: Laboratory of Molecular Neurobiology, National Institute of Bioscience and Human-Technology, Tsukuba, Ibaraki, Japan.

  • Carlos Vicario-Abejón,

    1. Laboratory of Molecular Biology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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  • Menahem Segal,

    1. Department of Neurobiology, The Weizmann Institute of Science, Rehovot 76100, Israel
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  • Ronald D. G. McKay

    1. Laboratory of Molecular Biology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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Correspondence: Shigeo Okabe, National Institute of Bioscience and Human-Technology, 1–1, Higashi, Tsukuba, Ibaraki 305, Japan. E-mail: sokabe@nibh.go.jp

Abstract

Physiological and morphological properties of cultured hippocampal neurons were measured to investigate whether NMDA receptors play a role in survival and differentiation. Neurons dissociated from mouse embryos with different NMDAR1 genotypes were grown in culture. Electrophysiological analysis verified the absence of NMDA receptor-mediated currents in neurons taken from homozygous mutant (NR1–/–) embryos. The number of surviving hippocampal neurons was 2.5-fold higher in cultures from the NR1–/– embryos compared with wild type (NR1 +/+) and heterozygous (NR1+/–) controls. Despite the lack of NMDA receptor function, NR1–/– neurons formed synapsin I-positive presynaptic boutons associated with MAP2ab-positive dendrites in culture. Confocal microscopic analysis of DiI labelled neurons confirmed the presence of dendritic spines on NR1–/– neurons with 80% of the density found in NR1 +/+ neurons. These results suggest that the NMDA receptor has little effect on general features of neuronal differentiation. In contrast, there is clear effect on neuronal survival. This finding establishes neuron number in standard culture conditions as a measure of NMDA receptor activity.

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