Neural Mechanism of Prey-catching Behavior in Anurans

视顶盖是低等脊椎动物的主要视觉中枢。一般认为，无尾两栖类的视觉信息，如猎物的运动，是在视顶盖中检测到的，并从那里发出捕食行为的“运动指令”。另一方面，我们已经表明，从视顶盖到舌肌运动神经元的神经通路，控制捕食行为的最后阶段，（舌翻转运动），由多突触兴奋和抑制通路组成（Satou et al.1984，1985）。本研究的目的是（1）阐明视顶盖中的神经元如何检测猎物对象，（2）识别介于视顶盖和舌肌运动神经元之间的中间神经元。结果表明：（1）蟾蜍视顶盖内的许多神经元具有“局部运动探测器”的特性，它们不是被视野内的“全局运动”选择性激活，而是被视野内的“局部运动”选择性激活。有人提出，这些顶盖的“局部运动检测器”参与的过程中的猎物对象的检测。(2)此外，我们还发现网状结构中接受视顶盖输入并投射到舌下神经和脊髓运动神经元池的神经元可能是上述抑制性中间神经元的候选者，从而阐明了蟾蜍捕食行为的神经过程，从感觉侧的猎物检测机制到运动侧的运动神经元突触通路。

The optic tectum is a major visual center in lower vertebrates. It has been considered that in anurans visual informations, such as motion of prey-objects, are detected in the optic tectum, and 'motor-commands' for prey-catching behavior are sent out from there. On the other hand, we have shown that neuronal pathways from the optic tectum to the tongue-muscle motoneurons, which control the final phase of prey-catching behavior (the tongue-flipping movement), are composed of polysynaptic excitatory and inhibitory pathways (Satou et al. 1984, 1985).The present research aimed to (1) clarify how the prey-objects are detected by neurons in the optic tectum, and (2) identify interneurons intervened between the optic tectum and the tongue-muscle motoneurons. The results showed that (1) many neurons in the toad's optic tectum show a property of 'local motion detectors' which are activated selectively not by 'global motion', but by 'local motion' within the animal's visual field. It was proposed that these tectal 'local motion detectors' are involved in process of detection of prey-objects. (2) Furthermore, we showed that neurons in the re ticular formation, which receive inputs from the optic tectum and project to the hypoglossal and spinal motoneuron pools, are likely candidates for inhibitory interneurons mentioned above.Thus, neural processes underlying the toad's prey-catching behavior, from detection mechanism of prey-objects at the sensory-side to synaptic pathways towards motoneurons at the motor-side, are now being clarified.