Redd E E, Pongstaporn T, Ryugo D K
Center for Hearing Sciences, Johns Hopkins University School of Medicine, Traylor Research Building, 5th Floor, 720 Rutland Avenue, Baltimore, MD 21205, USA.
Hear Res. 2000 Sep;147(1-2):160-74. doi: 10.1016/s0378-5955(00)00129-5.
It is well known that auditory deprivation affects the structure and function of the central nervous system. Congenital deafness represents one form of deprivation, and in the adult white cat, it has been shown to have a clear effect upon the synaptic interface between endbulbs of Held and spherical bushy cells. It is not known, however, whether all primary synapses are affected and/or whether they are affected in the same way and to the same extent. Thus, we studied a second neuronal circuit in the deaf white cat involving modified (small) endbulbs and globular bushy cells. Compared to normal hearing cats, modified endbulbs of congenitally deaf cats were 52.2% smaller but unchanged in structural complexity. There was also a striking loss of extracellular space between ending and cell body. The somata of postsynaptic globular bushy cells were 13.4% smaller and had enlarged postsynaptic densities. These data reveal that axosomatic synapses demonstrate abnormal structure as a consequence of deafness and that the extent of the abnormalities can vary with respect to the circuits involved. The implication of these observations is that synaptic anomalies would introduce differential delays within separate circuits, thereby desynchronizing neural activity from sound stimuli. This loss of synchronization could in turn disrupt temporal processing and compromise a host of related functions, including language comprehension.
众所周知，听觉剥夺会影响中枢神经系统的结构和功能。先天性耳聋是剥夺的一种形式，在成年白猫中，已证明它对Held终球与球状浓密细胞之间的突触界面有明显影响。然而，尚不清楚所有初级突触是否都受到影响，以及它们是否以相同的方式和程度受到影响。因此，我们研究了聋白猫中的第二个神经元回路，该回路涉及经过修饰的（小的）终球和球状浓密细胞。与正常听力的猫相比，先天性耳聋猫的修饰终球小52.2%，但结构复杂性未变。终末与细胞体之间的细胞外空间也明显减少。突触后球状浓密细胞的胞体小13.4%，且突触后致密物增大。这些数据表明，轴体突触因耳聋而表现出异常结构，且异常程度可能因所涉及的回路而异。这些观察结果的意义在于，突触异常会在不同回路中引入不同的延迟，从而使神经活动与声音刺激不同步。这种同步性的丧失反过来可能会扰乱时间处理，并损害包括语言理解在内的一系列相关功能。
