Oliver D L, Shneiderman A
Department of Anatomy, University of Connecticut Health Center, Farmington 06032.
J Neurosci. 1989 Mar;9(3):967-82. doi: 10.1523/JNEUROSCI.09-03-00967.1989.
The dorsal nucleus of the lateral lemniscus (DNLL) and its connections constitute one of the ascending auditory pathways to the inferior colliculus. One notable feature of this nucleus is the heavy commissural connections between DNLL on opposite sides of the midbrain. These commissural connections may have a significant impact on the ascending pathway. In this study, the fine structure of DNLL in the cat and its commissural connections were examined. Both anterograde and retrograde transport methods were used simultaneously at the EM level. Injections of 3H-leucine mixed with WGA-HRP were made in one DNLL. After axonal transport, EM autoradiographic methods were used to identify the anterogradely labeled axonal endings from the opposite DNLL. In the same location, retrogradely labeled neurons with crossed connections were identified with HRP histochemistry. Two types of axonal endings were found in DNLL, those with round synaptic vesicles forming asymmetrical synaptic junctions and those with pleomorphic vesicles and symmetrical synapses. Both types were equally common. However, only endings with pleomorphic vesicles were labeled after injections in the contralateral DNLL. The labeled endings from the opposite DNLL appeared to represent a homogeneous population, even though a number of variations in the 2 types of endings were found. Labeled endings were presynaptic to all parts of neurons in DNLL, but a large proportion of the synapses were on cell bodies and large dendrites. Two patterns of nuclear morphology and distribution of rough endoplasmic reticulum were identified and may represent different cell types. Examples of both cell types were observed to project to the contralateral side and received labeled synaptic endings. The major finding of this study is that the crossed connections between DNLL exhibit the morphology associated with inhibitory function. Since neurons in DNLL are thought to use GABA as a neurotransmitter, the crossed connections could provide inhibitory inputs to DNLL on each side. Since some neurons receive numerous axosomatic inputs from the contralateral DNLL and also project to the opposite side, they may participate in direct reciprocal, inhibitory connections between the nuclei. Crossed inhibitory connections in the DNLL pathway may be important in regulating the flow of ascending auditory information.
外侧丘系背核（DNLL）及其连接构成了通向中脑下丘的一条听觉上行通路。该核的一个显著特征是中脑两侧DNLL之间存在大量的连合连接。这些连合连接可能对上行通路有重大影响。在本研究中，对猫的DNLL的精细结构及其连合连接进行了检查。在电子显微镜水平同时使用了顺行和逆行运输方法。将3H-亮氨酸与WGA-HRP混合注射到一侧的DNLL中。轴突运输后，使用电子显微镜放射自显影方法来识别来自对侧DNLL的顺行标记的轴突终末。在同一位置，用HRP组织化学方法识别具有交叉连接的逆行标记神经元。在DNLL中发现了两种类型的轴突终末，一种是具有圆形突触小泡形成不对称突触连接的，另一种是具有多形性小泡和对称突触的。两种类型同样常见。然而，在对侧DNLL注射后，只有具有多形性小泡的终末被标记。来自对侧DNLL的标记终末似乎代表一个同质群体，尽管在这两种类型的终末中发现了一些变化。标记终末位于DNLL中神经元的所有部分的突触前，但大部分突触位于细胞体和大的树突上。识别出了两种核形态和粗面内质网分布模式，可能代表不同的细胞类型。观察到这两种细胞类型的例子都投射到对侧并接受标记的突触终末。本研究的主要发现是，DNLL之间的交叉连接表现出与抑制功能相关的形态。由于DNLL中的神经元被认为使用GABA作为神经递质，交叉连接可以为两侧的DNLL提供抑制性输入。由于一些神经元从对侧DNLL接收大量的轴体输入并且也投射到对侧，它们可能参与核之间直接互惠的抑制性连接。DNLL通路中的交叉抑制性连接在调节听觉上行信息的流动中可能很重要。
