Marín Gonzalo, Salas Carlos, Sentis Elisa, Rojas Ximena, Letelier Juan Carlos, Mpodozis Jorge
Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
J Neurosci. 2007 Jul 25;27(30):8112-21. doi: 10.1523/JNEUROSCI.1420-07.2007.
We describe the operation of a midbrain neural circuit in pigeons that may participate in selecting and attending to one visual stimulus from the myriad displayed in their visual environment. This mechanism is based on a topographically organized cholinergic signal reentering the optic tectum (TeO). We have shown previously that, whenever a visual stimulus activates neurons in a given tectal location, this location receives a strong bursting feedback from cholinergic neurons of the nucleus isthmi pars parvocellularis (Ipc), situated underneath the tectum. Here we show that, if a second visual stimulus is presented, even far from the first, the feedback signal to the first tectal location is diminished or suppressed, and feedback to the second tectal location is initiated. We found that this long-range suppressive interaction is mostly mediated by the nucleus isthmi pars magnocellularis, which sends a wide-field GABAergic projection to Ipc and TeO. In addition, two sets of findings indicate that the feedback from the Ipc modulates the ascending output from the TeO. First, visually evoked extracellular responses recorded in the dorsal anterior subdivision of the thalamic nucleus rotundus (RtDa), receiving the ascending tectal output, are closely synchronized to this feedback signal. Second, local inactivation of the Ipc prevents visual responses in RtDa to visual targets moving in the corresponding region of visual space. These results suggest that the ascending transmission of visual activity through the tectofugal pathway is gated by this cholinergic re-entrant signal, whose location within the tectal visual map is dynamically defined by competitive interactions.
我们描述了鸽子中脑神经回路的运作，该回路可能参与从其视觉环境中显示的无数视觉刺激中选择并关注其中一个。这种机制基于一种拓扑组织的胆碱能信号重新进入视顶盖（TeO）。我们之前已经表明，每当视觉刺激激活给定顶盖位置的神经元时，该位置会从位于顶盖下方的峡核小细胞部（Ipc）的胆碱能神经元接收到强烈的爆发性反馈。在这里我们表明，如果呈现第二个视觉刺激，即使离第一个很远，对第一个顶盖位置的反馈信号也会减弱或被抑制，并且会启动对第二个顶盖位置的反馈。我们发现这种远程抑制性相互作用主要由峡核大细胞部介导，它向Ipc和TeO发送广泛的GABA能投射。此外，两组研究结果表明，来自Ipc的反馈调节了TeO的上行输出。首先，在接受顶盖上行输出的丘脑圆核背侧前部分（RtDa）中记录的视觉诱发细胞外反应与该反馈信号紧密同步。其次，Ipc的局部失活会阻止RtDa对在视觉空间相应区域移动的视觉目标的视觉反应。这些结果表明，视觉活动通过顶盖传出通路的上行传递受这种胆碱能折返信号的门控，其在顶盖视觉图谱中的位置由竞争性相互作用动态定义。
