Intracortical pathways determine breadth of subthreshold frequency receptive fields in primary auditory cortex
Intracortical pathways determine breadth of subthreshold frequency receptive fields in primary auditory cortex
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DOI：
10.1152/jn.01121.2003
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发表时间：
2004-06-01
影响因子：
2.5
通讯作者：
Metherate, R
中科院分区：
文献类型：
--
作者：
Kaur, S;Lazar, R;Metherate, R
为了研究听觉皮层(ACX)频率感受场的基础，我们在麻醉大鼠上记录了细胞内(全细胞)和细胞外(局域场电位，LFP)对音调的反应。兴奋性突触后电位(EPSP)和来自同一部位的LFP的频率感受野在特征频率(Cf)和调谐幅度方面具有相似性，提示LFP反映局部突触(包括阈值以下)的活动。阈值下EPSP和LFP的感受野非常宽，通常跨越五个八度(测试的最大值)，中等强度(高于阈值40-50分贝)。为了识别皮层内产生的感受野特征，我们向ACX内微量注射GABA(A)受体激动剂Muscimol(0.2-5.1 mM，1-5mul)。Muscimol显著降低了LFP幅度和感受野带宽，这意味着皮质内对这些功能的贡献，但对CF反应阈值或起始潜伏期的影响较小，提示丘脑皮质输入的损失最小。通过从记录吸管扩散GABA(A)受体拮抗剂印防己毒素(0.01-100微米)，比起对光谱遥远的非CF刺激的反应，更多地抑制了对CF刺激的反应，从而逆转了苍蝇酚在记录部位的抑制作用。我们认为，丘脑皮质通路和皮质内通路分别优先参与CF刺激和非CF刺激引起的反应，皮质内投影连接频率表征决定了初级ACX中感受野的宽度。宽广的阈值下感受野可以区分ACX和皮质下听觉中继核，促进对复杂刺激的整合反应，并为皮质感受野和MAP的可塑性提供底物。
To examine the basis of frequency receptive fields in auditory cortex (ACx), we have recorded intracellular (whole cell) and extracellular (local field potential, LFP) responses to tones in anesthetized rats. Frequency receptive fields derived from excitatory postsynaptic potentials (EPSPs) and LFPs from the same location resembled each other in terms of characteristic frequency (CF) and breadth of tuning, suggesting that LFPs reflect local synaptic ( including subthreshold) activity. Subthreshold EPSP and LFP receptive fields were remarkably broad, often spanning five octaves ( the maximum tested) at moderate intensities (40-50 dB above threshold). To identify receptive-field features that are generated intracortically, we microinjected the GABA(A) receptor agonist muscimol (0.2-5.1 mM, 1-5 mul) into ACx. Muscimol dramatically reduced LFP amplitude and reduced receptive-field bandwidth, implicating intracortical contributions to these features but had lesser effects on CF response threshold or onset latency, suggesting minimal loss of thalamocortical input. Reversal of muscimol's inhibition preferentially at the recording site by diffusion from the recording pipette of the GABA(A) receptor antagonist picrotoxin (0.01-100 muM) disinhibited responses to CF stimuli more than responses to spectrally distant, non-CF stimuli. We propose that thalamocortical and intracortical pathways preferentially contribute to responses evoked by CF and non-CF stimuli, respectively, and that intracortical projections linking frequency representations determine the breadth of receptive fields in primary ACx. Broad, subthreshold receptive fields may distinguish ACx from subcortical auditory relay nuclei, promote integrated responses to spectrotemporally complex stimuli, and provide a substrate for plasticity of cortical receptive fields and maps.