Dept. of Zoology and Physiology, Univ. of Wyoming, 1000 E. Univ. Ave., Laramie, WY 82071, USA.
J Neurophysiol. 2011 Nov;106(5):2523-35. doi: 10.1152/jn.00569.2011. Epub 2011 Jul 20.
Multiple mechanisms have been shown to shape frequency-modulated (FM) selectivity within the central nucleus of the inferior colliculus (IC) in the pallid bat. In this study we focus on the mechanisms associated with sideband inhibition. The relative arrival time of inhibition compared with excitation can be used to predict FM responses as measured with a two-tone inhibition paradigm. An early-arriving low-frequency inhibition (LFI) prevents responses to upward sweeps and thus shapes direction selectivity. A late-arriving high-frequency inhibition (HFI) suppresses slow FM sweeps and thus shapes rate selectivity for downward sweeps. Iontophoretic application of gabazine (GBZ) to block GABA(A) receptors or strychnine (Strych) to block glycine receptors was used to assess the effects of removal of inhibition on each form of FM selectivity. GBZ and Strych had a similar effect on FM direction selectivity, reducing selectivity in up to 86% of neurons when both drugs were coapplied. FM rate selectivity was more resistant to drug application with less than 38% of neurons affected. In addition, only Strych could eliminate FM rate selectivity, whereas GBZ alone was ineffective. The loss of FM selectivity was directly correlated to a loss of the respective inhibitory sideband that shapes that form of selectivity. The elimination of LFI correlated to a loss of FM direction selectivity, whereas elimination of HFI correlated to a loss of FM rate selectivity. Results indicate that 1) although the majority of FM direction selectivity is created within the IC, the majority of rate selectivity is inherited from lower levels of the auditory system, 2) a loss of LFI corresponds to a loss of FM direction selectivity and is created through either GABAergic or glycinergic input, and 3) a loss of HFI corresponds to a loss of FM rate selectivity and is created mainly through glycinergic input.
多种机制已被证明可在苍白蝙蝠的下丘脑中核（IC）内塑造调频（FM）选择性。在这项研究中，我们专注于与边带抑制相关的机制。与兴奋相比，抑制的相对到达时间可用于预测使用双音抑制范式测量的 FM 响应。早期到达的低频抑制（LFI）可防止向上扫动的反应，从而形成方向选择性。晚期到达的高频抑制（HFI）抑制缓慢的 FM 扫动，从而形成向下扫动的速率选择性。应用加巴喷丁（GBZ）阻断 GABA(A)受体或士的宁（Strych）阻断甘氨酸受体的离子电泳，以评估去除抑制对每种 FM 选择性的影响。GBZ 和 Strych 对 FM 方向选择性有相似的影响，当两种药物同时应用时，多达 86%的神经元的选择性降低。FM 速率选择性对药物应用的抵抗力更强，受影响的神经元不到 38%。此外，只有 Strych 可以消除 FM 速率选择性，而单独使用 GBZ 则无效。FM 选择性的丧失与形成该选择性的相应抑制边带的丧失直接相关。LFI 的消除与 FM 方向选择性的丧失相关，而 HFI 的消除与 FM 速率选择性的丧失相关。结果表明：1）尽管大多数 FM 方向选择性是在 IC 内产生的，但大多数速率选择性是从听觉系统的较低水平继承而来的，2）LFI 的丧失对应于 FM 方向选择性的丧失，是通过 GABA 能或甘氨酸能输入产生的，3）HFI 的丧失对应于 FM 速率选择性的丧失，主要是通过甘氨酸能输入产生的。
