Auditory Neuroscience Group, Department of Anatomy and Neurobiology, Northeast Ohio Medical University Rootstown, OH, USA.
Department of Physical Therapy, Arkansas State University Jonesboro, AR, USA.
Front Neuroanat. 2014 Jul 18;8:70. doi: 10.3389/fnana.2014.00070. eCollection 2014.
Experiments in several species have identified direct projections to the medial geniculate nucleus (MG) from cells in subcollicular auditory nuclei. Moreover, many cochlear nucleus cells that project to the MG send collateral projections to the inferior colliculus (IC) (Schofield et al., 2014). We conducted three experiments to characterize projections to the MG from the superior olivary and the lateral lemniscal regions in guinea pigs. For experiment 1, we made large injections of retrograde tracer into the MG. Labeled cells were most numerous in the superior paraolivary nucleus, ventral nucleus of the trapezoid body, lateral superior olivary nucleus, ventral nucleus of the lateral lemniscus, ventrolateral tegmental nucleus, paralemniscal region and sagulum. Additional sources include other periolivary nuclei and the medial superior olivary nucleus. The projections are bilateral with an ipsilateral dominance (66%). For experiment 2, we injected tracer into individual MG subdivisions. The results show that the subcollicular projections terminate primarily in the medial MG, with the dorsal MG a secondary target. The variety of projecting nuclei suggest a range of functions, including monaural and binaural aspects of hearing. These direct projections could provide the thalamus with some of the earliest (i.e., fastest) information regarding acoustic stimuli. For experiment 3, we made large injections of different retrograde tracers into one MG and the homolateral IC to identify cells that project to both targets. Such cells were numerous and distributed across many of the nuclei listed above, mostly ipsilateral to the injections. The prominence of the collateral projections suggests that the same information is delivered to both the IC and the MG, or perhaps that a common signal is being delivered as a preparatory indicator or temporal reference point. The results are discussed from functional and evolutionary perspectives.
在几个物种中的实验已经确定了来自亚丘脑中的细胞向内侧膝状体核（MG）的直接投射。此外，许多投射到 MG 的耳蜗核细胞向下丘（IC）发送侧支投射（Schofield 等人，2014 年）。我们进行了三项实验，以描述豚鼠中来自上橄榄核和外侧索状核的向 MG 的投射。对于实验 1，我们在 MG 中进行了大的逆行示踪剂注射。标记细胞在 SuperiorParaolivary 核、梯形体腹核、外侧上橄榄核、外侧索腹核、腹侧中脑盖核、旁索状区和 Sagulum 中数量最多。其他来源包括其他periollivary 核和内侧上橄榄核。这些投射是双侧的，具有同侧优势（66%）。对于实验 2，我们将示踪剂注射到单个 MG 亚区。结果表明，下丘的投射主要终止于内侧 MG，而背侧 MG 是次要靶标。投射核的多样性表明存在一系列功能，包括听觉的单耳和双耳方面。这些直接投射可以为丘脑提供有关声刺激的一些最早（即最快）信息。对于实验 3，我们在一个 MG 和同侧 IC 中进行了不同逆行示踪剂的大注射，以识别投射到两个靶标的细胞。这样的细胞数量众多，分布在上文列出的许多核中，大多数位于注射的同侧。侧支投射的突出表明相同的信息被传递到 IC 和 MG，或者可能是相同的信号被传递作为预备指标或时间参考点。结果从功能和进化的角度进行了讨论。
