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首页> 美国卫生研究院文献>Frontiers in Neuroanatomy >Ultrastructural examination of the corticocollicular pathway in the guinea pig: a study using electron microscopy neural tracers and GABA immunocytochemistry
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Ultrastructural examination of the corticocollicular pathway in the guinea pig: a study using electron microscopy neural tracers and GABA immunocytochemistry

机译：豚鼠皮质胶体通路的超微结构检查：使用电子显微镜神经示踪剂和GABA免疫细胞化学的研究

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Projections from auditory cortex (AC) can alter the responses of cells in the inferior colliculus (IC) to sounds. Most IC cells show excitation and inhibition after stimulation of the AC. AC axons release glutamate and excite their targets, so inhibition is presumed to result from cortical activation of GABAergic IC cells that inhibit other IC cells via local projections. However, it is not known whether cortical axons contact GABAergic IC cells directly. We labeled corticocollicular axons by injecting fluorescent dextrans into the AC in guinea pigs. We visualized the tracer with diaminobenzidine and processed the tissue for electron microscopy. We identified presumptive GABAergic profiles with post-embedding anti-GABA immunogold histochemistry on ultrathin sections. We identified dextran-labeled cortical boutons in the IC and identified their postsynaptic targets according to morphology (e.g., spine, dendrite) and GABA-reactivity. Cortical synapses were observed in all IC subdivisions, but were comparatively rare in the central nucleus. Cortical boutons contain round vesicles and few mitochondria. They form asymmetric synapses with spines (most frequently), dendritic shafts and, least often, with cell bodies. Excitatory boutons in the IC can be classified as large, medium or small; most cortical boutons belong to the small excitatory class, while a minority (~14%) belong to the medium excitatory class. Approximately 4% of the cortical targets were GABA-positive; these included dendritic shafts, spines, and cell bodies. We conclude that the majority of cortical boutons contact non-GABAergic (i.e., excitatory) IC cells and a small proportion (4%) contact GABAergic cells. Given that most IC cells show inhibition (as well as excitation) after cortical stimulation, it is likely that the majority of cortically-driven inhibition in the IC results from cortical activation of a relatively small number of IC GABAergic cells that have extensive local axons.
机译：听觉皮层（AC）的投影可以改变下丘脑（IC）中的细胞对声音的响应。大多数AC细胞在刺激AC后显示出激发和抑制作用。 AC轴突释放谷氨酸并激发其靶标，因此推测抑制作用是由GABA能IC细胞的皮质激活引起的，GABA能IC细胞通过局部投射抑制其他IC细胞。但是，尚不清楚皮质轴突是否直接接触GABA能IC细胞。我们通过向豚鼠的AC中注射荧光右旋糖酐标记皮质皮质轴突。我们用二氨基联苯胺使示踪剂可视化，并处理了组织用于电子显微镜检查。我们在超薄切片上鉴定了嵌入的抗GABA免疫金组织化学的推测性GABA能谱。我们在IC中鉴定了右旋糖酐标记的皮囊，并根据形态学（例如，脊柱，树突）和GABA反应性确定了它们的突触后靶标。在所有的IC细分中都观察到了皮质突触，但是在中央核中相对较少。皮质纽扣包含圆形囊泡和少量线粒体。它们与棘（最常见），树突状干以及至少与细胞体形成不对称突触。集成电路中的兴奋性按键可以分为大，中或小；大部分皮层钮扣属于轻度兴奋性类别，而少数（〜14％）属于中度兴奋性类别。大约4％的皮质靶标为GABA阳性；这些包括树突状干，棘和细胞体。我们得出的结论是，大多数皮质纽扣接触非GABA能的（即兴奋性）IC细胞，而一小部分（4％）接触GABA能的细胞。鉴于大多数IC细胞在皮质刺激后均显示出抑制作用（以及兴奋性），因此IC中大多数皮质驱动的抑制作用可能是由皮质激素激活的相对较少的具有大量局部轴突的IC GABA能细胞引起的。

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