Schweitzer L, Cecil T, Walsh E J
Department of Anatomical Sciences and Neurobiology, University of Louisville School of Medicine, KY 40292.
Hear Res. 1993 Feb;65(1-2):240-52. doi: 10.1016/0378-5955(93)90217-o.
Physiologic and pharmacologic evidence suggests that inhibitory influences are active in the mammalian dorsal cochlear nucleus (DCN) by the onset of hearing, while anatomical evidence suggests that inhibitory synapses are not present until days or weeks later. One inhibitory neurotransmitter in the DCN is gamma aminobutyric acid (GABA) and its presence can be indexed by immunohistochemical localization of its synthetic enzyme glutamic acid decarboxylase (GAD). The present study investigated the ingrowth and synapse formation of GAD-immunoreactive inputs in the DCN of cat and hamster. GAD-immunoreactive puncta are present in the DCN of the cat at birth and of the hamster on postnatal day (PND) 3. Thus, the present data correlate well with the physiologic and pharmacologic evidence. In both species the first labelled puncta are near the dorsal acoustic stria and may originate from efferent axons in the stria. Several days later a band of labelled puncta is found in the fusiform cell layer. This location is equivalent to the termination zone of cartwheel cells, GAD-immunoreactive interneurons in the DCN. Based on this spatiotemporal sequence in the appearance of GAD-immunoreactive puncta, we suggest that sources of GABA extrinsic to the DCN mature first, followed by intrinsic sources.
生理学和药理学证据表明，在哺乳动物的背侧耳蜗核（DCN）中，抑制性影响在听力开始时就已活跃，而解剖学证据表明，抑制性突触直到数天或数周后才出现。DCN中的一种抑制性神经递质是γ-氨基丁酸（GABA），其存在可通过其合成酶谷氨酸脱羧酶（GAD）的免疫组织化学定位来确定。本研究调查了猫和仓鼠DCN中GAD免疫反应性输入的向内生长和突触形成。GAD免疫反应性小点在猫出生时的DCN中以及在出生后第3天（PND 3）的仓鼠DCN中都存在。因此，目前的数据与生理学和药理学证据密切相关。在这两个物种中，最初标记的小点都靠近背侧听纹，可能起源于听纹中的传出轴突。几天后，在梭形细胞层中发现了一条标记小点带。这个位置相当于车轮状细胞（DCN中的GAD免疫反应性中间神经元）的终止区。基于GAD免疫反应性小点出现的这种时空顺序，我们认为DCN外部的GABA来源首先成熟，随后是内部来源。
