Ding J, Voigt H F
Department of Biomedical Engineering, Boston University, Massachusetts 02215-2407, USA.
J Neurophysiol. 1997 May;77(5):2549-72. doi: 10.1152/jn.1997.77.5.2549.
Intracellular recording experiments on the dorsal cochlear nuclei of unanesthetized decerebrate gerbils were conducted. Acceptable recordings were those in which resting potentials were -50 mV or less and action potentials (APs) were > or = 40 mV. Responses to short-duration tones and noise, and to current pulses delivered via recording electrodes, were acquired. Units were classified according to the response map scheme (types I-IV). Ninety-two acceptable recordings were made. Most units had simple APs (simple-spiking units); nine units had both simple and complex APs, which are bursts of spikes embedded on slow, transient depolarizations (complex-spiking units). Of 83 simple-spiking units, 46 were classified as follows: type I/III (9 units), type II (9 units), type III (25 units), type IV (2 units), and type IV-T (1 unit). One complex-spiking unit was classifiable (a type III unit); six were unclassifiable because of weak acoustic responses. Classifying 39 other simple-spiking units and 2 complex-spiking units was impossible, because they were either injured or lost before sufficient data were acquired. Many simple-spiking units showed depolarization or hyperpolarization (approximately 5-10 mV) during acoustic stimulation; some were hyperpolarized during the stimulus-off period. Type I/III units were not hyperpolarized during off-best-frequency (off-BF) stimulation. In contrast, many type II units were hyperpolarized by off-BF frequencies, suggesting that they received strong inhibitory sideband inputs. When inhibited, some type III units were hyperpolarized. Type IV units were hyperpolarized during inhibition even at low levels (<60 dB SPL); sustained depolarizations occurred only at higher levels, suggesting that they receive strong inhibitory and weak excitatory inputs. Several intracellular response properties were statistically different from those of extracellularly recorded units. Intracellularly recorded type II units had higher thresholds and lower maximum BF-driven and noise-driven rates than their extracellularly recorded counterparts. Type I/III units recorded intracellularly had lower maximum BF-driven rates. Type III units recorded intracellularly had higher maximum noise rates compared with those recorded extracellularly. Weaker acoustic responses most likely result from membrane disruption, but heightened responses may be related to weakened chloride-channel-dependent inhibition due to altered driving forces resulting from KCl leakage. Firing rates of simple-spiking units increased monotonically with increasing levels of depolarizing current pulses. In contrast, many complex-spiking units responded nonmonotonically to depolarizing current injection. The monotonic rate-versus-current curves and the nonmonotonic rate-versus-sound level curves of type IV and III units suggest that the acoustic behavior is the result of extrinsic inhibitory inputs and not due solely to intrinsic membrane properties.
在未麻醉的去大脑沙鼠的背侧耳蜗核上进行了细胞内记录实验。可接受的记录是指静息电位为-50mV或更低且动作电位（APs）≥40mV的记录。获取了对短持续时间音调、噪声以及通过记录电极施加的电流脉冲的反应。根据反应图谱方案（I-IV型）对神经元进行分类。共进行了92次可接受的记录。大多数神经元具有简单动作电位（简单放电神经元）；9个神经元同时具有简单动作电位和复杂动作电位，复杂动作电位是嵌入在缓慢、短暂去极化上的一串尖峰（复杂放电神经元）。在83个简单放电神经元中，46个分类如下：I/III型（9个）、II型（9个）、III型（25个）、IV型（2个）和IV-T型（1个）。1个复杂放电神经元可分类（III型）；6个由于听觉反应较弱而无法分类。另外39个简单放电神经元和2个复杂放电神经元无法分类，因为在获取足够数据之前它们就已受损或丢失。许多简单放电神经元在听觉刺激期间表现出去极化或超极化（约5-10mV）；有些在刺激结束期超极化。I/III型神经元在最佳频率外（off-BF）刺激期间不会超极化。相比之下，许多II型神经元被off-BF频率超极化，这表明它们接受了强烈的抑制性边带输入。当受到抑制时，一些III型神经元会超极化。IV型神经元即使在低水平（<60dB SPL）抑制期间也会超极化；仅在较高水平时才会出现持续去极化，这表明它们接受强烈的抑制性输入和较弱的兴奋性输入。一些细胞内反应特性在统计学上与细胞外记录的神经元不同。细胞内记录的II型神经元比细胞外记录的对应神经元具有更高的阈值以及更低的最大BF驱动率和噪声驱动率。细胞内记录的I/III型神经元具有更低的确最大BF驱动率。与细胞外记录的相比，细胞内记录的III型神经元具有更高的最大噪声率。较弱的听觉反应很可能是由于膜破坏，但增强的反应可能与KCl泄漏导致驱动力改变从而使氯离子通道依赖性抑制减弱有关。简单放电神经元的放电率随着去极化电流脉冲水平的增加而单调增加。相比之下，许多复杂放电神经元对去极化电流注入的反应是非单调的。IV型和III型神经元的单调放电率-电流曲线和非单调放电率-声压级曲线表明，听觉行为是外在抑制性输入的结果，而不仅仅是由于内在膜特性。
