Oliver D L, Ostapoff E M, Beckius G E
Department of Anatomy, University of Connecticut Health Center, Farmington 06030-3405, USA.
Neuroscience. 1999;93(2):643-58. doi: 10.1016/s0306-4522(99)00143-8.
The present study sought to identify tectothalamic neurons in the rat inferior colliculus that receive their innervation directly from the cochlear nuclei and to identify the axons that provide the innervation. A direct projection would bypass the binaural interactions of the superior olivary complex and provide the quickest route to the neocortex. Axons, primarily from the dorsal cochlear nucleus, were labeled with anterograde transport of dextran and terminated in the central nucleus of the inferior colliculus in a laminar pattern. Most labeled axons were thin and simply branched. Other axons were thicker, gnarly, less frequently observed and probably originated from the ventral cochlear nucleus. None had concentrated endbulbs or a nest of endings. Both types of axons terminated primarily in the central nucleus and layer 3 of the external cortex. This pattern suggests that the combination of these subdivisions in the rat are equivalent to the central nucleus as defined in other species. Tectothalamic neurons in the inferior colliculus in the same animals were identified by retrograde transport from the medial geniculate body and intracellular injection of Lucifer Yellow. A number of different cell types act as tectothalamic neurons and receive contacts from cochlear nucleus axons. These include flat cells (disc-shaped), less-flat cells and stellate cells. Two innervation patterns were seen: a combination of axosomatic and axodendritic contacts, and predominantly axodendritic contacts. Both patterns were seen in the central nucleus, but axosomatic contacts were seen less often in the other subdivisions. This is the first study to show direct connections between cochlear nuclear axons and identified tectothalamic neurons. The layers of axons from cochlear nuclei may provide convergent inputs to neurons in the inferior colliculus rather than the heavy inputs from single axons typical of lower auditory nuclei. Excitatory synapses made by axons from the cochlear nuclei on tectothalamic neurons may provide a substrate for rapid transmission of monaural information to the medial geniculate body.
本研究旨在识别大鼠下丘中直接接受来自耳蜗核神经支配的顶盖丘脑神经元，并确定提供这种神经支配的轴突。直接投射将绕过上橄榄复合体的双耳相互作用，并提供通往新皮层的最快途径。轴突主要来自背侧耳蜗核，通过葡聚糖的顺行运输进行标记，并以分层模式终止于下丘的中央核。大多数标记的轴突很细且分支简单。其他轴突较粗、扭曲，较少见，可能起源于腹侧耳蜗核。没有轴突有密集的终球或一团终末。这两种类型的轴突主要终止于中央核和外侧皮质的第3层。这种模式表明，大鼠中这些亚区的组合等同于其他物种中定义的中央核。通过从中脑内侧膝状体逆行运输和对荧光黄进行细胞内注射，确定了同一动物下丘中的顶盖丘脑神经元。许多不同类型的细胞充当顶盖丘脑神经元，并接受来自耳蜗核轴突的接触。这些细胞包括扁平细胞（盘状）、不太扁平的细胞和星形细胞。观察到两种神经支配模式：轴体和轴树突接触的组合，以及主要是轴树突接触。两种模式在中央核中均可见，但在其他亚区中轴体接触较少见。这是第一项显示耳蜗核轴突与已确定的顶盖丘脑神经元之间直接联系的研究。来自耳蜗核的轴突层可能为下丘中的神经元提供汇聚输入，而不是像较低听觉核那样由单个轴突提供大量输入。耳蜗核轴突在顶盖丘脑神经元上形成的兴奋性突触可能为单耳信息向内侧膝状体的快速传递提供了一个底物。
