Rodriguez-Contreras Adrian, Liu Xiao-Bo, DeBello William M
Department of Neurobiology, Physiology, and Behavior, Center for Neuroscience, University of California, Davis, Davis, California 95616, USA.
J Neurosci. 2005 Jun 8;25(23):5611-22. doi: 10.1523/JNEUROSCI.3972-04.2005.
In the owl midbrain, a map of auditory space is synthesized in the inferior colliculus (IC) and conveyed to the optic tectum (OT). Ascending auditory information courses through these structures via topographic axonal projections. Little is known about the molecular composition of projection neurons or their postsynaptic targets. To visualize axodendritic contacts between identified cell types, we used double-label immunohistochemistry, in vivo retrograde tracing, in vitro anterograde tracing, high-resolution confocal microscopy, three-dimensional reconstruction and fly-through visualization. We discovered a major class of IC neurons that strongly expressed calcium/calmodulin-dependent protein kinase type II, alpha subunit (CaMKII). The distribution of these cells within the IC was mostly restricted to the external nucleus of the IC (ICX), in which the auditory space map is assembled. A large proportion of ICX-OT projection neurons were CaMKII positive. In addition to being the principal outputs, CaMKII cells were in direct contact with axonal boutons emanating from the main source of input to ICX, the lateral shell of the central nucleus of the inferior colliculus (ICCls). Numerous sites of putative synaptic contact were found on the somata, proximal dendrites, and distal dendrites. Double-label immunoelectron microscopy confirmed the existence of synapses between ICCls axons and the dendrites of CaMKII cells. Collectively, our data indicate that CaMKII ICX neurons are a cellular locus for the computation of auditory space-specific responses. Because the ICCls-ICX projection is physically altered during experience-dependent plasticity, these results lay the groundwork for probing microanatomical rearrangements that may underlie plasticity and learning.
在猫头鹰中脑，听觉空间图谱在下丘（IC）合成，并传递到视顶盖（OT）。上行听觉信息通过地形轴突投射穿过这些结构。关于投射神经元或其突触后靶点的分子组成知之甚少。为了可视化已鉴定细胞类型之间的轴突-树突接触，我们使用了双标记免疫组织化学、体内逆行追踪、体外顺行追踪、高分辨率共聚焦显微镜、三维重建和飞行浏览可视化。我们发现了一大类强烈表达钙/钙调蛋白依赖性蛋白激酶II型α亚基（CaMKII）的IC神经元。这些细胞在IC内的分布大多局限于IC的外侧核（ICX），听觉空间图谱在此组装。很大一部分ICX-OT投射神经元是CaMKII阳性。除了作为主要输出外，CaMKII细胞还与来自ICX主要输入源——下丘中央核外侧壳（ICCls）的轴突终扣直接接触。在胞体、近端树突和远端树突上发现了许多假定的突触接触位点。双标记免疫电子显微镜证实了ICCls轴突与CaMKII细胞树突之间存在突触。总的来说，我们的数据表明CaMKII ICX神经元是计算听觉空间特异性反应的细胞位点。由于ICCls-ICX投射在经验依赖性可塑性过程中发生物理改变，这些结果为探究可能是可塑性和学习基础的微观解剖重排奠定了基础。
