Deschênes Martin, Timofeeva Elena, Lavallée Philippe, Dufresne Caroline
CRULRG, Université Laval, Quebec, QC, G1J 2G3, Canada.
Prog Brain Res. 2005;149:31-40. doi: 10.1016/S0079-6123(05)49003-2.
The highly segregated organization of the vibrissal system of rodents offers a unique opportunity to address key issues about thalamic operations in primary sensory and second order thalamic nuclei. In this short review, evidence showing that reticular thalamic neurons and relay cells with receptive fields on the same vibrissa form topographically closed loop connections has been summarized. Within whisker-related thalamic modules, termed barreloids, reticular axons synapse onto the cell bodies and dendrites of residing neurons as well as onto the distal dendrites of neurons that are located in adjacent barreloids. This arrangement provides a substrate for a mechanism of lateral inhibition whereby the spread of dendritic trees among surrounding barreloids determines whisker-specific patterns of lateral inhibition. The relay of sensory inputs in the posterior group, a second order nucleus associated with the vibrissal system is also examined. It is shown that in lightly anesthetized rats posterior group cells are tonically inhibited by GABAergic neurons of the ventral division of zona incerta. These observations suggest that a mechanism of disinhibition controls transmission of sensory signals in the posterior group nucleus. We further propose that disinhibition operates in a top-down manner, via motor instructions sent by cortex to brainstem and spinal cord. In this way posterior group nucleus would forward to the cerebral cortex sensory information that is contingent upon its action.
啮齿动物触须系统高度分隔的组织形式为解决有关初级感觉丘脑核和二级丘脑核中丘脑运作的关键问题提供了独特的机会。在这篇简短的综述中，总结了表明网状丘脑神经元和在同一触须上具有感受野的中继细胞形成拓扑闭环连接的证据。在与触须相关的丘脑模块（称为桶状体）内，网状轴突与驻留神经元的细胞体和树突以及位于相邻桶状体内的神经元的远端树突形成突触。这种排列为侧抑制机制提供了一个基础，即树突在周围桶状体之间的扩散决定了触须特异性的侧抑制模式。还研究了与触须系统相关的二级核——后组中感觉输入的中继情况。结果表明，在轻度麻醉的大鼠中，后组细胞受到未定带腹侧部的GABA能神经元的紧张性抑制。这些观察结果表明，去抑制机制控制后组核中感觉信号的传递。我们进一步提出，去抑制通过皮层向脑干和脊髓发送的运动指令以自上而下的方式运作。通过这种方式，后组核会将取决于其动作的感觉信息转发到大脑皮层。
