Isoflurane enhances spontaneous Ca2+ oscillations in developing rat hippocampal neuronsin vitro

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Abstract

Background:

During the nervous system development, spontaneous synchronized Ca2+ oscillations are thought to possess integrative properties because their amplitude and frequency can influence the patterning of neuronal connection, neuronal differentiation, axon outgrowth, and long-distance wiring. Accumulating studies have confirmed that some drugs such as volatile anesthetic isoflurane produced histopathologic changes in the central nervous system in juvenile animal models. Because the hippocampus plays an important role in learning and memory, the present work was designed to characterize the Ca2+ oscillations regulated by volatile anesthetic isoflurane in primary cultures of developing hippocampal neurons (5-day-cultured).

Methods:

Primary cultures of rat hippocampal neurons (5-day-cultured) were loaded with the Ca2+ indicator Fluo-4AM (4 μM) and were studied with a confocal laser microscope.

Results:

Approximately 22% of 5-day-cultured hippocampal neurons exhibited typical Ca2+ oscillations. These oscillations were dose-dependently enhanced by isoflurane (EC50 0.5 MAC, minimum alveolar concentration) and this effect could be reverted by bicuculline (50 μM), a specific γ-aminobutyric acid (GABAA) receptor antagonist.

Conclusion:

Unlike its depressant effect on the Ca2+ oscillations in adult neurons in previous researches, isoflurane dose-dependently enhanced calcium oscillations in developing hippocampal neurons by activating GABAA receptors, a major excitatory receptor in synergy with N-methyl-D-aspartate receptors at the early stages of development. It may be involved in the mechanism of an isoflurane-induced neurotoxic effect in the developing rodent brain.

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