Oliver D L, Beckius G E, Shneiderman A
Department of Anatomy, University of Connecticut Health Center, Farmington 06030-3405, USA.
J Comp Neurol. 1995 Sep 11;360(1):17-32. doi: 10.1002/cne.903600103.
The superior olivary complex is the first site in the central auditory system where binaural interactions occur. The output of these nuclei is direct to the central nucleus of the inferior colliculus, where binaural inputs synapse with monaural afferents such as those from the cochlear nuclei. Despite the importance of the olivary pathways for binaural information processing, little is known about their synaptic organization in the colliculus. The present study investigates the structure of the projections from the lateral and medial superior olivary nuclei to the inferior colliculus at the electron microscopic level. Stereotaxic placement and electrophysiological responses to binaural sounds were used to locate the superior olive. Anterograde axonal transport of 3H-leucine was combined with light and electron microscopic autoradiography to reveal the location and morphology of the olivary axonal endings. The results show that the superior olivary complex contributes different patterns of synaptic input to the central nucleus of the inferior colliculus. Each projection from the superior olivary complex to the colliculus differs in the number and combinations of endings. Axonal endings from the ipsilateral medial superior olive were exclusively the round (R) type that contain round synaptic vesicles and make asymmetrical synaptic junctions. This morphology is usually associated with excitatory synapses and neurotransmitters such as glutamate. Endings from medial superior olive terminate densely in the central nucleus. The projection from the contralateral lateral superior olive also terminates primarily as R endings. This projection also includes small numbers of pleomorphic (PL) endings that contain pleomorphic synaptic vesicles and usually make symmetrical synaptic junctions. The PL morphology is associated with inhibitory synapses and transmitters such as gamma-aminobutyric acid and glycine. All endings from the contralateral lateral superior olive terminate much less densely than endings from the medial olive. In contrast, the projection from the ipsilateral lateral superior olive contributes both R and PL endings in roughly equal proportions. These ipsilateral afferents are heterogeneous in density and can terminate in lower or higher concentrations than endings from the contralateral side. These data show that the superior olive is a major contributor to the synaptic organization of the central nucleus of the inferior colliculus. The ipsilateral projections of the medial and lateral superior olive may produce higher concentrations of R endings than other inputs to the central nucleus. Such endings may participate in excitatory synapses. The highest concentrations of PL endings come from the ipsilateral lateral superior olive.(ABSTRACT TRUNCATED AT 400 WORDS)
上橄榄复合体是中枢听觉系统中双耳相互作用发生的首个部位。这些核团的输出直接至下丘中央核，在该部位双耳输入与诸如来自蜗神经核的单耳传入纤维形成突触。尽管橄榄体通路对双耳信息处理很重要，但对其在下丘的突触组织却知之甚少。本研究在电子显微镜水平研究了外侧和内侧上橄榄核向下丘的投射结构。采用立体定位放置以及对双耳声音的电生理反应来定位上橄榄体。将³H - 亮氨酸的顺行轴突运输与光镜和电镜放射自显影相结合，以揭示橄榄体轴突终末的位置和形态。结果表明，上橄榄复合体向下丘中央核贡献了不同模式的突触输入。从上橄榄复合体到下丘的每个投射在终末数量和组合上都有所不同。来自同侧内侧上橄榄体的轴突终末均为圆形（R）型，含有圆形突触小泡并形成不对称突触连接。这种形态通常与兴奋性突触以及诸如谷氨酸的神经递质相关。内侧上橄榄体的终末密集地终止于中央核。来自对侧外侧上橄榄体的投射也主要以R终末终止。该投射还包括少量多形性（PL）终末，其含有多形性突触小泡且通常形成对称突触连接。PL形态与抑制性突触以及诸如γ - 氨基丁酸和甘氨酸的递质相关。来自对侧外侧上橄榄体的所有终末的终止密度远低于来自内侧橄榄体的终末。相比之下，来自同侧外侧上橄榄体的投射贡献的R和PL终末比例大致相等。这些同侧传入纤维在密度上是异质性的，其终止浓度可能低于或高于对侧的终末。这些数据表明，上橄榄体是下丘中央核突触组织的主要贡献者。内侧和外侧上橄榄体的同侧投射可能比中央核的其他输入产生更高浓度的R终末。此类终末可能参与兴奋性突触。PL终末的最高浓度来自同侧外侧上橄榄体。（摘要截短至400字）
