Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
J Neurosci. 2010 Nov 3;30(44):14862-9. doi: 10.1523/JNEUROSCI.2734-10.2010.
Presynaptic inhibition is a widespread mechanism modulating the efficiency of synaptic transmission and in sensory pathways is coupled to primary afferent depolarizations. Axonal terminals of bush-cricket auditory afferents received 2-5 mV graded depolarizing inputs, which reduced the amplitude of invading spikes and indicated presynaptic inhibition. These inputs were linked to a picrotoxin-sensitive increase of Ca(2+) in the terminals. Electrophysiological recordings and optical imaging showed that in individual afferents the sound frequency tuning based on spike rates was different from the tuning of the graded primary afferent depolarizations. The auditory neuropil of the bush-cricket Mecopoda elongata is tonotopically organized, with low frequencies represented anteriorly and high frequencies represented posteriorly. In contrast graded depolarizing inputs were tuned to high-frequencies anteriorly and to low-frequencies posteriorly. Furthermore anterior and posterior axonal branches of individual afferents received different levels of primary afferent depolarization depending on sound frequency. The presence of primary afferent depolarization in the afferent terminals indicates that presynaptic inhibition may shape the synaptic transmission of frequency-specific activity to auditory interneurons.
突触前抑制是一种广泛存在的调节突触传递效率的机制，在感觉通路上与初级传入去极化耦联。蝉的听觉传入纤维的轴突末梢接受 2-5 mV 的分级去极化输入，这降低了入侵尖峰的幅度，并表明存在突触前抑制。这些输入与胡椒碱敏感的末梢内钙离子增加有关。电生理记录和光学成像显示，在单个传入纤维中，基于尖峰率的频率调谐与分级初级传入去极化的调谐不同。蝉的听觉神经原是音位组织的，低频在前，高频在后。相反，分级去极化输入在前部调谐到高频，在后部调谐到低频。此外，根据声音频率，单个传入纤维的前、后轴突分支接收到不同水平的初级传入去极化。传入末梢中的初级传入去极化表明，突触前抑制可能会影响特定频率的活动向听觉中间神经元的突触传递。
