Sanes D H
Department of Otolaryngology, New York University Medical Center, New York 10016.
J Neurosci. 1990 Nov;10(11):3494-506. doi: 10.1523/JNEUROSCI.10-11-03494.1990.
One way in which animals localize sounds along the horizon is by detecting the level differences at the 2 ears. Neurons in the lateral superior olive (LSO) encode this cue by integrating the synaptic drive from ipsilateral excitatory and contralateral inhibitory connections. This synaptic integration was analyzed in 400-500-microns brain slices through the gerbil superior olive. Intracellular recordings from LSO neurons were obtained during the application of independent or conjoint electrical stimuli to the excitatory afferent and inhibitory afferent pathways. Stimulation of ascending fibers from the ipsilateral cochlear nucleus reliably evoked EPSPs and action potentials. Stimulation of the medial nucleus of the trapezoid body (MNTB) consistently evoked IPSPs. The evoked postsynaptic potentials differed in that IPSPs were 2 times the duration of EPSPs. An electrophysiological estimate of convergence indicated approximately 10 excitatory and 8 inhibitory afferents per LSO neuron. MNTB stimulation suppressed synaptically evoked action potentials. When stimulus amplitude was increased to the excitatory pathway, it was generally found that a greater MNTB stimulus was necessary to suppress the action potential. A similar commensurate rise in ipsilateral and contralateral acoustic stimulation was also found to be necessary to give the same criterion response. These results confirm that the LSO can integrate evoked action potentials and IPSPs to encode interaural level. Increasing stimulus voltage was found to decrease both action potential and IPSP latency, suggesting that intensity information may be encoded with temporal cues in the nervous system. It was also found that an evoked burst of action potentials could be inhibited in such a way as to yield intermediate discharge rates, dependent on contralateral stimulus level. Taken together, these results suggest that certain properties related to level-difference coding may be available for intracellular analysis using the brain-slice preparation. Several temporal characteristics of the synaptic potentials, including latency and duration, may play a critical role in this simple computation.
动物沿地平线定位声音的一种方式是通过检测两耳处的声级差异。外侧上橄榄核（LSO）中的神经元通过整合来自同侧兴奋性和对侧抑制性连接的突触驱动来编码这一线索。通过沙鼠上橄榄核在400 - 500微米的脑片中分析这种突触整合。在对兴奋性传入和抑制性传入通路施加独立或联合电刺激期间，获得了LSO神经元的细胞内记录。刺激来自同侧耳蜗核的上行纤维可靠地诱发了兴奋性突触后电位（EPSP）和动作电位。刺激梯形体内侧核（MNTB）始终诱发抑制性突触后电位（IPSP）。诱发的突触后电位的不同之处在于，IPSP的持续时间是EPSP的两倍。收敛的电生理估计表明，每个LSO神经元约有10个兴奋性传入纤维和8个抑制性传入纤维。MNTB刺激抑制了突触诱发的动作电位。当刺激幅度增加到兴奋性通路时，通常发现需要更大的MNTB刺激来抑制动作电位。还发现同侧和对侧听觉刺激也需要类似的相应增加才能给出相同的标准反应。这些结果证实，LSO可以整合诱发的动作电位和IPSP来编码双耳声级。发现增加刺激电压会缩短动作电位和IPSP的潜伏期，这表明强度信息可能在神经系统中通过时间线索进行编码。还发现诱发的一串动作电位可以被抑制，从而产生取决于对侧刺激水平的中间放电率。综上所述，这些结果表明，某些与声级差异编码相关的特性可用于使用脑片制备进行细胞内分析。突触电位的几个时间特征，包括潜伏期和持续时间，可能在这种简单的计算中起关键作用。
