Laboratório de Psicobiologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo (USP), Ribeirão Preto, SP 14040-901, Brazil.
Brain Res. 2011 Nov 3;1421:20-9. doi: 10.1016/j.brainres.2011.09.013. Epub 2011 Sep 16.
The central nucleus of the inferior colliculus (CIC) is an important relay station for acoustic information that has an aversive connotation. γ-Aminobutyric acid (GABA) mechanisms exert tonic inhibitory control over the neural substrates of aversion in the midbrain tectum. Recent evidence obtained in this laboratory showed that low- (LA) and high-anxiety (HA) rats selected in the elevated plus maze (EPM) exhibit low and high auditory-evoked potential (AEP) amplitudes, respectively, recorded in the CIC when subjected to loud click noises. The present study investigated the eventual top-down regulation exerted by GABA mechanisms in the basolateral (BLA) and central (CeA) nuclei of the amygdala on aversive information processing at the level of the CIC. The GABA inhibitors bicuculline (10 ng/0.2 μl) and semicarbazide (7 μg/0.2 μl) and GABA agonist muscimol (1 nmol/0.2 μl) were locally infused into the CeA and BLA in rats subjected to an AEP recording procedure that used electrodes implanted in the CIC. Freezing behavior induced by these intra-amygdala injections was also measured. The results confirmed that the processing of aversive acoustic information depends on anxiety levels in LA and HA rats. Freezing behavior and the increased AEPs induced by intra-CeA injections of bicuculline and semicarbazide were more pronounced in HA than in LA animals. Intra-CeA injections of muscimol did not change either the basal levels of freezing or AEP amplitudes in LA and HA rats. However, freezing and the enhanced AEPs were of small magnitude following intra-BLA injections of bicuculline and semicarbazide. An unexpected magnitude of freezing and enhanced AEPs was observed following muscimol infusions into the BLA in HA rats. GABA mechanisms in the CeA appear to play a regulatory role in aversive states, and inactivation of the BLA with muscimol produced pro-aversive effects, suggesting that inactivation of the BLA removed the descending inhibitory control of the neural substrates of aversion in the CIC exerted by the BLA. Because the latter effects were observed only in HA rats, a dysfunctional BLA may underlie the differences between trait and state anxiety.
下丘中央核（CIC）是听觉信息的重要中继站，具有厌恶的内涵。γ-氨基丁酸（GABA）机制对中脑顶盖的厌恶神经基质施加紧张性抑制控制。本实验室最近的证据表明，在高架十字迷宫（EPM）中选择的低（LA）和高焦虑（HA）大鼠分别在受到大声点击噪音时在 CIC 中记录到低和高听觉诱发电位（AEP）幅度。本研究探讨了 GABA 机制在杏仁核的基底外侧（BLA）和中央（CeA）核对 CIC 水平上的厌恶信息处理的自上而下的调节作用。GABA 抑制剂荷包牡丹碱（10ng/0.2μl）和半卡巴肼（7μg/0.2μl）和 GABA 激动剂 muscimol（1nmol/0.2μl）被局部输注到接受 AEP 记录程序的大鼠的 CeA 和 BLA 中，该程序使用植入 CIC 的电极。还测量了这些内侧杏仁核注射引起的冻结行为。结果证实，厌恶声信息的处理取决于 LA 和 HA 大鼠的焦虑水平。与 LA 动物相比，CeA 内注射荷包牡丹碱和半卡巴肼引起的冻结行为和增加的 AEP 更为明显。CeA 内注射 muscimol 既不会改变 LA 和 HA 大鼠的基础冻结水平，也不会改变 AEP 幅度。然而，BLA 内注射荷包牡丹碱和半卡巴肼后，冻结和增强的 AEP 幅度较小。在 HA 大鼠中，BLA 内注射 muscimol 会引起出乎意料的冻结和增强的 AEP。CeA 中的 GABA 机制似乎在厌恶状态中发挥调节作用，而用 muscimol 失活 BLA 会产生促进厌恶的作用，这表明失活 BLA 消除了 BLA 对 CIC 中厌恶神经基质的下行抑制控制。由于这些影响仅在 HA 大鼠中观察到，因此功能失调的 BLA 可能是特质焦虑和状态焦虑之间差异的基础。
