Department of Biology, James Madison University, Harrisonburg, VA, United States.
Front Neural Circuits. 2022 Apr 7;16:882485. doi: 10.3389/fncir.2022.882485. eCollection 2022.
The lateral cortex of the inferior colliculus (LCIC) is a multimodal subdivision of the midbrain inferior colliculus (IC) that plays a key role in sensory integration. The LCIC is compartmentally-organized, exhibiting a series of discontinuous patches or modules surrounded by an extramodular matrix. In adult mice, somatosensory afferents target LCIC modular zones, while auditory afferents terminate throughout the encompassing matrix. Recently, we defined an early LCIC critical period (birth: postnatal day 0 to P12) based upon the concurrent emergence of its neurochemical compartments (modules: glutamic acid decarboxylase, GAD+; matrix: calretinin, CR+), matching Eph-ephrin guidance patterns, and specificity of auditory inputs for its matrix. Currently lacking are analogous experiments that address somatosensory afferent shaping and the construction of discrete LCIC multisensory maps. Combining living slice tract-tracing and immunocytochemical approaches in a developmental series of GAD67-GFP knock-in mice, the present study characterizes: (1) the targeting of somatosensory terminals for emerging LCIC modular fields; and (2) the relative separation of somatosensory and auditory inputs over the course of its established critical period. Results indicate a similar time course and progression of LCIC projection shaping for both somatosensory (corticocollicular) and auditory (intracollicular) inputs. While somewhat sparse and intermingling at birth, modality-specific projection patterns soon emerge (P4-P8), coincident with peak guidance expression and the appearance of LCIC compartments. By P12, an adult-like arrangement is in place, with fully segregated multimodal afferent arrays. Quantitative measures confirm increasingly distinct input maps, exhibiting less projection overlap with age. Potential mechanisms whereby multisensory LCIC afferent systems recognize and interface with its emerging modular-matrix framework are discussed.
下丘外侧核（LCIC）的外侧皮质是中脑下丘（IC）的一个多模态细分区域，在感觉整合中起着关键作用。LCIC 是分区组织的，表现出一系列不连续的斑块或模块，被一个模块外基质包围。在成年小鼠中，躯体感觉传入纤维靶向 LCIC 模块区，而听觉传入纤维则终止于整个包围的基质中。最近，我们根据其神经化学隔室（模块：谷氨酸脱羧酶，GAD+；基质：钙视网膜蛋白，CR+）的同时出现、Eph-ephrin 导向模式以及基质中听觉输入的特异性，定义了一个早期 LCIC 关键期（出生：出生后第 0 天至 P12 天）。目前还缺乏类似的实验来研究躯体感觉传入纤维的形成和离散 LCIC 多感觉图谱的构建。本研究在一系列 GAD67-GFP 敲入小鼠的发育系列中，结合活体切片示踪和免疫细胞化学方法，描述了：（1）新兴 LCIC 模块区的躯体感觉末端的靶向；（2）在其既定关键期内，躯体感觉和听觉输入的相对分离。结果表明，躯体感觉（皮质丘系）和听觉（丘系内）传入的 LCIC 投射形成具有相似的时间进程和进展。虽然在出生时有些稀疏和混杂，但特定模式的投射模式很快就会出现（P4-P8），与高峰导向表达和 LCIC 隔室的出现同时发生。到 P12 时，已经形成了类似于成年的排列，具有完全分离的多模态传入阵列。定量测量证实了随着年龄的增长，输入图谱越来越明显，与年龄相关的投射重叠越来越少。讨论了多感觉 LCIC 传入系统识别和与新兴的模块-基质框架接口的潜在机制。
