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KMID : 0960220030020010078
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Journal of the Korean Balance Society
2003 Volume.2 No. 1 p.78 ~ p.85
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Ionic mechanisms underlying spontaneous firing in isolated type B medial vestibular nucleus neurons
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천상우/Sang Woo Chun
최정희/김권수/이형재/김승록/이문영/박병림/Jeong Hee Choi/Kwon Soo Kim/Hyong Jae Lee/Seung Rok Kim/Moon Young Lee/Byung Rim Park
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Abstract
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Medial vestibular nucleus (MVN) neurons are found to have spontaneous electrical activity in the absence of any detectable synaptic input. To investigate the contributions of intrinsic mechanisms to the spontaneous activity of type B MVN neurons, we
examined the effects of various channel blockers on spontaneous firing by means of patch clamp recordings. Coronal slice (400 micro m) of the vestibular nucleus region was sequentially treated with pronase 0.2 mg/ml and thermolysin 0.2 mg/ml, then
single neurons were mechanically dissociated. MVN neurons recorded in neonatal rat were shown to have either a single deep afterhyperpolarization (AHP; type A cells), or an early fast and a delayed slow AHP (type B cells). In 300 nM TTX, spontaneous
firing was blocked in type B cells tested. In 8 of 11 cells, underlying fluctuation or oscillations in membrane potential was not remained, and hyperpolarization did not produce rebound low-threshold calcium spikes. Although type B MVN neurons possessed
hyperpolarization activated cation current (Ih), cesium had no effect on firing rates. The spike AHP is calcium dependent. When Ca(2+) influx was blocked in external Ca(2+) free solution, repetitive firing was abolished and the cell rested at
depolarized membrane potentials. Application of apamin (300 nM) caused a profound reduction in the amplitude of the AHP and produced rhythmic burst firing. These findings suggest that the spontaneous activity of type B MVN neurons is regulated by
interactions between the membrane depolarization mainly due to a persistent sodium conductances and hyperpolarization due to the calcium-activated potassium conductances.
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