Shneiderman A, Oliver D L
Department of Anatomy, University of Connecticut Health Center, Farmington 06032.
J Comp Neurol. 1989 Aug 1;286(1):28-47. doi: 10.1002/cne.902860103.
The fine structure of the projection from the dorsal nucleus of the lateral lemniscus (DNLL) to the inferior colliculus is examined in the cat. Anterograde axonal transport of 3H-leucine and EM autoradiographic techniques are used to label axonal endings from DNLL. The primary finding is that axonal endings from DNLL contain pleomorphic synaptic vesicles and make symmetrical synaptic contacts. This morphology is associated with inhibitory synapses. The projection from DNLL is the source of approximately one-third of the axonal endings with pleomorphic vesicles in the central nucleus of the inferior colliculus. In the contralateral central nucleus, only labeled endings with pleomorphic vesicles are found. By comparison, on the ipsilateral side, both endings with pleomorphic vesicles and, to a lesser degree, endings with round vesicles are labeled. Endings from DNLL are more numerous per unit area on the contralateral side. About half of the labeled axonal endings from DNLL terminate upon small dendrites, and another third terminate upon more proximal dendrites and several types of cell bodies. Many axonal endings form multiple synaptic contacts, sometimes on more than one postsynaptic structure. Sites of termination for axonal endings include dendritic spines and branch points of dendrites. These data support the hypothesis that the DNLL pathway to the inferior colliculus may have an inhibitory function. Previous studies show that DNLL neurons exhibit immunoreactivity to GAD and GABA antibodies. The crossed projection of DNLL to the inferior colliculus forms tonotopically organized bands that terminate as endings with pleomorphic vesicles. These endings may supply GABAergic inputs to the inferior colliculus. Thus, bands from DNLL could provide inhibitory inputs and overlap with bands from other sources that provide excitatory inputs. Overlapping bands may form unique synaptic domains in the inferior colliculus. The uncrossed projections from DNLL may provide the inferior colliculus with a more diffusely organized projection that could include excitatory and inhibitory inputs. Since the DNLL on one side may inhibit the opposite DNLL and the inferior colliculus, the DNLL pathway may regulate ascending inhibition to the midbrain. Presumed inhibitory inputs from DNLL to the inferior colliculus could be involved in binaural information processing and contralateral dominance.
在猫身上研究了外侧丘系背核（DNLL）至下丘投射的精细结构。采用³H-亮氨酸的顺行轴突运输和电子显微镜放射自显影技术标记来自DNLL的轴突终末。主要发现是，DNLL的轴突终末含有多形性突触小泡，并形成对称性突触联系。这种形态与抑制性突触相关。DNLL的投射是下丘中央核中约三分之一有多形性小泡的轴突终末的来源。在对侧中央核中，仅发现有多形性小泡的标记终末。相比之下，在同侧，既有多形性小泡的终末，也有少量圆形小泡的终末被标记。DNLL的终末在对侧每单位面积更多。来自DNLL的约一半标记轴突终末终止于小的树突上，另外三分之一终止于更靠近近端的树突和几种类型的细胞体上。许多轴突终末形成多个突触联系，有时在不止一个突触后结构上。轴突终末的终止部位包括树突棘和树突分支点。这些数据支持这样的假说，即DNLL至下丘的通路可能具有抑制功能。先前的研究表明，DNLL神经元对谷氨酸脱羧酶（GAD）和γ-氨基丁酸（GABA）抗体表现出免疫反应性。DNLL至下丘的交叉投射形成了按音频拓扑组织的带，这些带以多形性小泡的终末形式终止。这些终末可能向下丘提供GABA能输入。因此，来自DNLL的带可提供抑制性输入，并与来自其他提供兴奋性输入的来源的带重叠。重叠的带可能在下丘形成独特的突触域。DNLL的不交叉投射可能为下丘提供组织更分散的投射，其中可能包括兴奋性和抑制性输入。由于一侧的DNLL可能抑制对侧的DNLL和下丘，DNLL通路可能调节向上至中脑的抑制。推测的从DNLL至下丘的抑制性输入可能参与双耳信息处理和对侧优势。
