Rübsamen R, Neuweiler G, Marimuthu G
Lehrstuhl für Allgemeine Zoologie und Neurobiologie, Ruhr-Universität Bochum, Federal Republic of Germany.
J Comp Physiol A. 1989 Oct;165(6):755-69. doi: 10.1007/BF00610874.
The postnatal development of midbrain tonotopy was investigated in the inferior colliculus (IC) of the south Indian CF-FM bat Hipposideros speoris. The developmental progress of the three-dimensional frequency representation was determined by systematic stereotaxic recordings of multiunit clusters from the 1st up to the 7th postnatal week. Additional developmental measures included the tuning characteristics of single units (Figs. 3f; 4f; 5f), the analysis of the vocalised pulse repertoire (Figs. 3e, 4e, 5e), and morphometric reconstructions of the brains of all experimental animals (Fig. 1). The maturation of auditory processing could be divided into two distinct, possibly overlapping developmental periods: First, up to the 5th week, the orderly tonotopy in the IC developed, beginning with the low frequency representation and progressively adding the high frequency representation. With regard to the topology of isofrequency sheets within the IC, maturation progresses from dorsolateral to ventromedial (Figs. 3c, 4c). At the end of this phase the entire IC becomes specialised for narrowly tuned and sensitive frequency processing. This includes the establishment of the 'auditory fovea', i.e. the extensive spatial representation of a narrow band of behaviorally relevant frequencies in the ventromedial part of the IC. In the 5th postnatal week the auditory fovea is concerned with frequencies from 100-118 kHz (Fig. 4c, d). During subsequent development, the frequency tuning of the auditory fovea increases by 20-25 kHz and finally attains the adult range of ca. 125-140 kHz. During this process, neither the bandwidth of the auditory fovea (15-20 kHz) nor the absolute sensitivity of its units (ca. 50 dB SPL) were changed. Further maturation occurred at the single unit level: the sharpness of frequency tuning increased from the 5th to the 7th postnatal weeks (Q-10-dB-values up to 30-60), and upper thresholds emerged (Figs. 4f, 5f). Although in the adult the frequency of the auditory fovea matches that of the vocalised pulses, none of the juvenile bats tested from the 5th to the 7th weeks showed such a frequency match between vocalisation and audition (Figs. 4e, 5e). The results show that postnatal maturation of audition in hipposiderid bats cannot be described by a model based on a single developmental parameter.
在南印度食果蝠（Hipposideros speoris）的下丘（IC）中，研究了中脑音频定位的产后发育情况。通过对出生后第1周到第7周的多单元簇进行系统的立体定位记录，确定了三维频率表征的发育进程。其他发育测量包括单个单元的调谐特性（图3f、4f、5f）、发声脉冲库的分析（图3e、4e、5e）以及所有实验动物大脑的形态计量重建（图1）。听觉处理的成熟过程可分为两个不同的、可能重叠的发育阶段：首先，到第5周时，IC中有序的音频定位开始发育，从低频表征开始，逐渐增加高频表征。关于IC内等频片的拓扑结构，成熟过程从背外侧向腹内侧推进（图3c、4c）。在这个阶段结束时，整个IC变得专门用于窄调谐和敏感的频率处理。这包括“听觉中央凹”的建立，即在IC腹内侧部分对行为相关窄带频率的广泛空间表征。在出生后第5周，听觉中央凹涉及100 - 118 kHz的频率（图4c、d）。在随后的发育过程中，听觉中央凹的频率调谐增加了20 - 25 kHz，最终达到约125 - 140 kHz的成年范围。在此过程中，听觉中央凹的带宽（15 - 20 kHz）及其单元的绝对灵敏度（约50 dB SPL）均未改变。在单个单元水平上发生了进一步的成熟：频率调谐的锐度从出生后第5周到第7周增加（Q - 10 - dB值高达30 - 60），并且出现了上限阈值（图4f、5f）。尽管在成年个体中，听觉中央凹的频率与发声脉冲的频率匹配，但从第5周到第7周测试的所有幼年蝙蝠均未表现出发声与听觉之间的这种频率匹配（图4e、5e）。结果表明，蹄蝠科蝙蝠听觉的产后成熟不能用基于单一发育参数的模型来描述。
