Immunoelectron microscopic analysis of neurotoxic effect of glutamate in the vestibular end organs during ischemia

Abstract

Conclusion: The excessive glutamate released from the type I and type II hair cells and the supporting cells injure the bouton-type endings and the nerve chalices in 30 min ischemia, and neuronal damage of glutamate was slight in 10 min ischemia. Objective: In the present study, we investigated by means of post-embedding immunoelectron microscopic analysis whether neuronal damage in the vestibular end organs is associated with the change of cellular glutamate concentration during ischemia. Methods: Transient local anoxia (10 min, 30 min) of guinea pig inner ear was induced by pressing the left labyrinthine artery. The right sides were used as controls. The morphological changes of the vestibular end organs and the areal gold particle densities representing glutamate were compared in the ischemia side and the control side. Results: The areal gold particle densities of the type I and type II hair cells and the supporting cells in the ischemic side were lower than those of the control side. There were no remarkable morphological changes compared to the control side in 10 min ischemia. In 30 min ischemia, the bouton-type endings were swollen and intercellular spaces between the type I hair cells and the nerve chalices were enlarged.

Keywords::

• Glutamatergic excitotoxicity
• morphological change
• vestibule
• labyrinthine artery
• electron microscope
• post-embedding immunogold labeling
• immunocytochemistry

Acknowledgments

We would like to thank Dr O.P. Ottersen for his generous gift of antibodies and test sandwich sections. We also extend our thanks to A. Obara for technical assistance.

Declaration of interest : The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.