Casanova C, Molotchnikoff S
Département de Sciences Biologiques, Université de Montréal, Canada.
Exp Brain Res. 1990;80(2):387-96. doi: 10.1007/BF00228166.
The lateral posterior-pulvinar (LP-P) complex of mammals receives a major input from the superior colliculus (SC). We have studied the response properties of LP cells and investigated the effects of reversible inactivation of the colliculus on the visual responses of LP units in anesthetized and paralyzed rabbits. Cells in LP had large receptive fields responsive to either stationary or moving stimuli. One third of the motion-sensitive cells were direction selective. The size of the receptive fields increased with eccentricity and there was a retinotopic organization along the dorso-ventral axis. Comparison of the LP and superior colliculus properties revealed substantial differences in visual response characteristics of these two structures such as the size of the receptive fields and the number of direction-selective cells. Electrical stimulation of the LP evoked antidromic action potentials in tectal cells that were motion sensitive. We found a dorsoventral gradient in the projections of collicular cells. Units located more dorsally in the colliculus sent their axons to LP while cells lying more ventrally sent axons toward the region lying posterior to LP. A micropipette filled with lidocaine hydrochloride was lowered into the superficial layers of the superior colliculus in order to reversibly inactivate a small population of collicular cells. Rendering the superior colliculus inactive produced a sharp attenuation of visual responses in the majority of LP cells. Some neurons ceased all stimulus-driven activity after collicular blockade while a few cells exhibited increased excitability following collicular inactivation. These experiments also indicate that the tecto-LP path is topographically organized. An injection in the colliculus failed to influence the thalamic response when it was not in retinotopic register with the LP cells being recorded. Our results demonstrate that the superior colliculus input to LP is mainly excitatory in nature.
哺乳动物的外侧后丘脑-丘脑枕（LP-P）复合体主要接收来自上丘（SC）的输入。我们研究了LP细胞的反应特性，并在麻醉和瘫痪的兔子中研究了上丘可逆失活对LP单位视觉反应的影响。LP中的细胞具有对静止或移动刺激有反应的大感受野。三分之一的运动敏感细胞具有方向选择性。感受野的大小随离心率增加，并且沿背腹轴存在视网膜拓扑组织。LP和上丘特性的比较揭示了这两个结构在视觉反应特征上的显著差异，例如感受野的大小和方向选择性细胞的数量。电刺激LP会在对运动敏感的顶盖细胞中诱发逆向动作电位。我们发现顶盖细胞的投射存在背腹梯度。位于顶盖更靠背部的单位将其轴突发送到LP，而位于更腹侧的细胞则将轴突发送到LP后方的区域。将一根充满盐酸利多卡因的微吸管降低到上丘的表层，以便可逆地使一小部分顶盖细胞失活。使上丘失活会导致大多数LP细胞的视觉反应急剧减弱。一些神经元在顶盖阻断后停止了所有刺激驱动的活动，而少数细胞在顶盖失活后表现出兴奋性增加。这些实验还表明，顶盖-LP通路是按拓扑结构组织的。当注射到上丘的区域与所记录的LP细胞不在视网膜拓扑对应时，未能影响丘脑反应。我们的结果表明，上丘对LP的输入本质上主要是兴奋性的。
