Institute of Neuroscience, Faculty of Medical Sciences, Newcastle University Newcastle upon Tyne, UK.
Front Neural Circuits. 2012 Dec 14;6:100. doi: 10.3389/fncir.2012.00100. eCollection 2012.
The auditory pathways coursing through the brainstem are organized bilaterally in mirror image about the midline and at several levels the two sides are interconnected. One of the most prominent points of interconnection is the commissure of the inferior colliculus (CoIC). Anatomical studies have revealed that these fibers make reciprocal connections which follow the tonotopic organization of the inferior colliculus (IC), and that the commissure contains both excitatory and, albeit fewer, inhibitory fibers. The role of these connections in sound processing is largely unknown. Here we describe a method to address this question in the anaesthetized guinea pig. We used a cryoloop placed on one IC to produce reversible deactivation while recording electrophysiological responses to sounds in both ICs. We recorded single units, multi-unit clusters and local field potentials (LFPs) before, during and after cooling. The degree and spread of cooling was measured with a thermocouple placed in the IC and other auditory structures. Cooling sufficient to eliminate firing was restricted to the IC contacted by the cryoloop. The temperature of other auditory brainstem structures, including the contralateral IC and the cochlea were minimally affected. Cooling below 20°C reduced or eliminated the firing of action potentials in frequency laminae at depths corresponding to characteristic frequencies up to ~8 kHz. Modulation of neural activity also occurred in the un-cooled IC with changes in single unit firing and LFPs. Components of LFPs signaling lemniscal afferent input to the IC showed little change in amplitude or latency with cooling, whereas the later components, which likely reflect inter- and intra-collicular processing, showed marked changes in form and amplitude. We conclude that the cryoloop is an effective method of selectively deactivating one IC in guinea pig, and demonstrate that auditory processing in the IC is strongly influenced by the other.
听觉通路在脑干中沿中线双侧呈镜像排列，并在几个水平上相互连接。最突出的连接点之一是下丘（IC）的联合。解剖学研究表明，这些纤维进行相互连接，遵循下丘的音调组织（IC），并且联合包含兴奋性纤维和尽管较少，但抑制性纤维。这些连接在声音处理中的作用在很大程度上是未知的。在这里，我们描述了一种在麻醉豚鼠中解决此问题的方法。我们使用放置在一个 IC 上的 cryoloop 来产生可逆失活，同时记录两个 IC 中声音的电生理反应。在冷却之前、期间和之后，我们记录了单个单元、多单元簇和局部场电位（LFPs）。用放置在 IC 和其他听觉结构中的热电偶测量冷却的程度和范围。足以消除放电的冷却仅限于与 cryoloop 接触的 IC。其他听觉脑干结构的温度，包括对侧 IC 和耳蜗，受影响最小。冷却至 20°C 以下会降低或消除与特征频率高达约 8 kHz 的深度相对应的频率层中动作电位的放电。冷却也会导致未冷却的 IC 中的神经活动发生调制，表现为单个单元放电和 LFPs 的变化。表示传入 IC 的 lemniscal 传入输入的 LFPs 成分的幅度或潜伏期随冷却变化很小，而可能反映 IC 内和 IC 间处理的后期成分则表现出明显的形式和幅度变化。我们得出结论，cryoloop 是一种在豚鼠中选择性失活一个 IC 的有效方法，并证明 IC 中的听觉处理受到另一侧的强烈影响。
