Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.
Collaborative Research Center 889, University of Göttingen, Göttingen, Germany.
EMBO J. 2021 Mar 1;40(5):e106010. doi: 10.15252/embj.2020106010. Epub 2020 Dec 21.
The cochlea encodes sound pressures varying over six orders of magnitude by collective operation of functionally diverse spiral ganglion neurons (SGNs). The mechanisms enabling this functional diversity remain elusive. Here, we asked whether the sound intensity information, contained in the receptor potential of the presynaptic inner hair cell (IHC), is fractionated via heterogeneous synapses. We studied the transfer function of individual IHC synapses by combining patch-clamp recordings with dual-color Rhod-FF and iGluSnFR imaging of presynaptic Ca signals and glutamate release. Synapses differed in the voltage dependence of release: Those residing at the IHC' pillar side activated at more hyperpolarized potentials and typically showed tight control of release by few Ca channels. We conclude that heterogeneity of voltage dependence and release site coupling of Ca channels among the synapses varies synaptic transfer within individual IHCs and, thereby, likely contributes to the functional diversity of SGNs. The mechanism reported here might serve sensory cells and neurons more generally to diversify signaling even in close-by synapses.
耳蜗通过功能多样化的螺旋神经节神经元（SGN）的集体运作，对超过六个数量级的声压进行编码。使这种功能多样性成为可能的机制仍难以捉摸。在这里，我们想知道，包含在突触前内毛细胞（IHC）受体潜力中的声强信息是否通过异质突触进行分离。我们通过结合膜片钳记录与双荧光 Rhod-FF 和 iGluSnFR 成像，研究了单个 IHC 突触的传递功能，以测量突触前 Ca 信号和谷氨酸释放。突触在释放的电压依赖性方面存在差异：位于 IHC 柱状侧的突触在更超极化的电位下激活，并且通常通过少数 Ca 通道对释放进行紧密控制。我们得出的结论是，Ca 通道的电压依赖性和释放部位偶联的异质性在单个 IHC 内改变了突触传递，从而可能有助于 SGN 的功能多样性。这里报道的机制可能为感觉细胞和神经元提供服务，使其即使在附近的突触中也能多样化信号传递。
