尽管大鼠和小鼠是研究听觉功能许多特征的首选动物模型之一,它们很少用于研究双耳听力的一个重要方面:动物通过检测耳间时差(ITD)来定位低频声音源的能力,那就是声音到达每只耳朵的时间差。在哺乳动物中,ITD主要编码在内侧上橄榄(MSO)中,上橄榄复合物(SOC)的主要核之一。由于它们的头小和高频听觉范围,大鼠和小鼠通常被认为不能使用ITDs进行声音定位。此外,与使用ITD定位声音的哺乳动物相比,它们的MSO经常被认为太小或微不足道,包括猫和沙鼠.然而,最近的研究表明,小鼠MSO神经元的大多数形态和生理特征与使用ITDs的哺乳动物的MSO神经元之间具有显着的相似性。在这种情况下,我们分析了大鼠MSO的结构和神经传入和传出连接,从未通过将神经解剖示踪剂注射到细胞核中进行过研究。大鼠MSO纵向跨越SOC。它的尾部相对较小,而是长成一个发育良好的堆叠双极神经元列。通过放置小,将双向示踪剂生物素化葡聚糖胺(BDA)精确注射到MSO中,我们表明,该核主要由两侧的前腹侧耳蜗核的最腹侧和头侧球形丛生细胞支配,以及梯形体同侧内侧核的最腹外侧主要神经元。相同的实验表明,MSO密集地支配下丘中央核的最背外侧区域,外侧背核的中央区域,以及其自身侧面的外侧圆面的中间核的最外侧区域。因此,MSO被选择性地支配,并发送预测,处理低频声音的神经元。大鼠MSO的结构和病理学特征与猫和沙鼠的MSO明显相似。虽然这些相似性提出了MSO执行ITD编码以外的其他功能的问题,他们还表明,大鼠MSO是未来以MSO为中心的研究的合适模型。
Although rats and mice are among the preferred animal models for investigating many characteristics of auditory function, they are rarely used to study an essential aspect of binaural hearing: the ability of animals to localize the sources of low-frequency sounds by detecting the interaural time difference (ITD), that is the difference in the time at which the sound arrives at each ear. In mammals, ITDs are mostly encoded in the medial superior olive (MSO), one of the main nuclei of the superior olivary complex (SOC). Because of their small heads and high frequency hearing range, rats and mice are often considered unable to use ITDs for sound localization. Moreover, their MSO is frequently viewed as too small or insignificant compared to that of mammals that use ITDs to localize sounds, including cats and gerbils. However, recent research has demonstrated remarkable similarities between most morphological and physiological features of mouse MSO neurons and those of MSO neurons of mammals that use ITDs. In this context, we have analyzed the structure and neural afferent and efferent connections of the rat MSO, which had never been studied by injecting neuroanatomical tracers into the nucleus. The rat MSO spans the SOC longitudinally. It is relatively small caudally, but grows rostrally into a well-developed column of stacked bipolar neurons. By placing small, precise injections of the bidirectional tracer biotinylated dextran amine (BDA) into the MSO, we show that this nucleus is innervated mainly by the most ventral and rostral spherical bushy cells of the anteroventral cochlear nucleus of both sides, and by the most ventrolateral principal neurons of the ipsilateral medial nucleus of the trapezoid body. The same experiments reveal that the MSO densely innervates the most dorsolateral region of the central nucleus of the inferior colliculus, the central region of the dorsal nucleus of the lateral lemniscus, and the most lateral region of the intermediate nucleus of the lateral lemniscus of its own side. Therefore, the MSO is selectively innervated by, and sends projections to, neurons that process low-frequency sounds. The structural and hodological features of the rat MSO are notably similar to those of the MSO of cats and gerbils. While these similarities raise the question of what functions other than ITD coding the MSO performs, they also suggest that the rat MSO is an appropriate model for future MSO-centered research.