Mechanisms of vestibular compensation

为了弄清哪些类型的前庭核神经元在前庭代偿期改变了它们的活动，我们必须了解完整大鼠前庭神经元的电生理膜特性。在我们先前使用全细胞膜片钳技术在大鼠脑干切片上的研究中，我们研究了前庭内侧核(MVN)神经元的三种膜特性：后超极化(AHP)、放电模式和对超极化电流脉冲的反应模式。然而，在体内，膜的性质尚未确定，其功能意义也尚未阐明。为了解决这些问题，我们将全细胞膜片钳记录方法应用于幼年成年大鼠的活体制备，并研究了膜和自发放电特性。我们在体内的MVN神经元中发现了三种AHP图谱、三种放电模式和三种对超极化电流脉冲的反应模式，这在我们之前的体外研究中是有特征的。这表明这三种膜性质在体内都是适用的。对体内外MVN神经元放电特性的分析表明，AHP伴慢成分[AHP(S+)]和AUP后除极后慢成分[AHP(S+)+ADP]的神经元放电间期的变异系数小于不含慢成分的AHP(S+)和AUP(S+)。结果表明，表现为S+的神经元为规则放电神经元，表现为S-和S+的神经元为不规则放电神经元。

To clarify which types of vestibular nucleus neurons change their activity during the period of the vestibular compensation, we must know electrophysiological membrane properties of vestibular neurons in intact rats. In our previous study using the whole-cell patch clamp technique in rat brainstem slices, we characterized three membrane properties of neurons in the medial vestibular nucleus (MVN) : afterhyperpolarization (AHP) profiles, firing patterns, and response patterns to hyperpolarizing current pulses. However, the membrane properties have not been ascertained in vivo and their functional significance has not been clarified. To address these issues, we applied the whole-cell patch clamp recording method to in vivo preparations of young adult rats and investigated the membrane and spontaneous discharge properties. We found three AHP profiles, three firing patterns, and three response patterns to hyperpolarizing current pulses in MVN neurons in vivo, which were characterized in our previous in vitro study. This indicates that the three membrane properties are applicable in vivo. The analysis of discharge properties of MVN neurons both in vivo and in vitro revealed that the coefficient of variation of interspike intervals was smaller in neurons exhibiting AHP with a slow component [AHP(s+)] than in those exhibiting AHP without a slow component [AHP(s-)] and AUP with afterdepolarization followed by a slow component [AHP(s+) with ADP]. The result indicates that neurons exhibiting AHP(s+) are regular discharging neurons, whereas neurons exhibiting AHP(s-) and AHP(s+) with ADP are irregular discharging neurons.