Neiman Alexander B, Yakusheva Tatyana A, Russell David F
Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA.
J Neurophysiol. 2007 Nov;98(5):2795-806. doi: 10.1152/jn.01289.2006. Epub 2007 Sep 12.
The response properties of ampullary electroreceptors of paddlefish, Polyodon spathula, were studied in vivo, as single-unit afferent responses to external electrical stimulation with varied intensities of several types of noise waveforms, all Gaussian and zero-mean. They included broadband white noise, Ornstein-Uhlenbeck noise, low- or high-frequency band-limited noise, or natural noise recorded from swarms of Daphnia zooplankton prey, or from individual prey. Normally the afferents fire spontaneously in a tonic manner, which is actually quasiperiodic due to embedded oscillators. 1) Weak noise stimuli increased the variability of afferent firing, but it remained tonic. 2) In contrast, stimulation with less-weak broadband noise led to a qualitative change of the firing patterns, to parabolic bursting, even though the mean firing rate was scarcely affected. 3) The transition to afferent bursting was marked by the development of two well-separated timescales: the fast frequency of spiking inside bursts at <or=250 spikes/s and the slow frequency of burst occurrences at about 9 (range 5-13) bursts/s. These two timescales were manifested as two regimes in afferent power spectra, bimodal interspike interval histograms, return maps, and autocorrelation functions of afferent spike trains. 4) The stochastic approximately 9-Hz bursts were not simply driven by similar-frequency components of noise stimuli because bursts could be dissociated from stimulus waveforms using high-pass filtered noise, or a 0.1-Hz sine-wave stimulus. 5) Arrhenius plots showed that the threshold noise intensity required to elicit bursting depended on the frequency content of a noise stimulus, being lowest, about 1.2 microV/cm, for stimuli matching the 1- to 20-Hz best response band of these cathodally excited ampullary electroreceptors. This is only slightly higher than previous behavioral estimates of the electrosensory threshold as 0.5 microV/cm. 6) Comparable threshold values for bursting came from an alternate analytical approach, based on correlation times of spike trains. 7) Simultaneous recordings from pairs of afferents showed that their bursting frequencies (bursts/s) always converged as the amplitude of a noise stimulus was raised. Thus the slow timescale of bursting is similar for different electroreceptors, even though their mean spiking rates can differ. In conclusion, the ampullary electroreceptors of paddlefish have two distinct modes of operation: their spontaneous tonic firing is modulated by the weakest stimuli, but they switch to bursting output for less-weak stimuli. We propose that afferent bursting may mediate close-range tracking of planktonic prey.
在活体状态下研究了匙吻鲟（Polyodon spathula）壶腹电感受器的反应特性，记录了其作为单单位传入神经对几种不同类型噪声波形（均为高斯分布且均值为零）的外部电刺激的反应，刺激强度各不相同。这些噪声波形包括宽带白噪声、奥恩斯坦 - 乌伦贝克噪声、低频或高频带限噪声，以及从浮游动物水蚤群或单个猎物记录的自然噪声。通常，传入神经以紧张性方式自发放电，由于嵌入的振荡器，这种放电实际上是准周期性的。1）弱噪声刺激增加了传入神经放电的变异性，但仍保持紧张性。2）相比之下，强度稍强的宽带噪声刺激导致放电模式发生质的变化，变为抛物线形爆发，尽管平均放电率几乎未受影响。3）向传入神经爆发的转变以两个明显分离的时间尺度的出现为标志：爆发内的快速放电频率小于或等于250次/秒，爆发出现的缓慢频率约为9次/秒（范围为5 - 13次/秒）。这两个时间尺度在传入神经功率谱、双峰峰间间隔直方图、返回映射以及传入神经冲动序列的自相关函数中表现为两种状态。4）随机的约9赫兹爆发并非简单地由噪声刺激的同频成分驱动，因为使用高通滤波噪声或0.1赫兹正弦波刺激可以使爆发与刺激波形分离。5）阿伦尼乌斯图表明，引发爆发所需的阈值噪声强度取决于噪声刺激的频率成分，对于匹配这些阴极兴奋的壶腹电感受器1至20赫兹最佳反应频段的刺激，阈值最低，约为1.2微伏/厘米。这仅略高于先前行为学估计的电感觉阈值0.5微伏/厘米。6）基于冲动序列相关时间的另一种分析方法得出了类似的爆发阈值。7）对成对传入神经的同步记录表明，随着噪声刺激幅度的增加，它们的爆发频率（次/秒）总是趋于一致。因此，尽管不同电感受器的平均放电率可能不同，但爆发的缓慢时间尺度相似。总之，匙吻鲟的壶腹电感受器有两种不同的运作模式：其自发的紧张性放电受最弱刺激调制，但对于强度稍强的刺激会切换为爆发性输出。我们认为传入神经爆发可能介导对浮游猎物的近距离追踪。
