The Study on the Mechanisms of Central Nervous System for Olfactory Behavior in Insects

家蚕雄蛾对接受性信息素的同种雌蛾的性信息素反应，表现出定向迎风摆动行走并伴有翅的振动。我们建议，翅膀的振动，以及走向信息素源的步行控制由一个自我生成的曲折转弯程序，这是由间歇性的信息素刺激施加到触角触发。为了了解这种先天行为的行为和神经机制，我们研究了信息素在大脑嗅觉神经系统中的加工过程，以及这些信息如何参与嗅觉行为的产生和控制。我们发现，位于高级嗅觉整合中心的前脑（PC）中的嗅觉神经元支配一个特定的神经元区域，外侧副叶（LAL）。每个LAL也通过LAL的连合彼此连接。在嗅觉信息传递的过程中，从一级嗅觉中枢（触角叶）经外侧PC到中间神经元（DNs），中间神经元经腹神经索（VNC）下行到胸运动中枢（TMC）。在两种状态之间来回切换发生在Olberg（1983）先前描述的顺序信息素刺激之后。结果发现，在两组（Ⅰ、Ⅱ组）的嗅神经元中，有两种触发器活动呈反相关系，它们分别从VNC下降到TMC，这些发现为了解触发器活动所需的嗅觉神经系统提供了一个基础，触发器活动可能是控制嗅觉行为的一个重要信号。

Male silkworm moth, Bombyx mori, display oriented upwind zigzagging walking accompanying wing vibration in response to the sex pheromones of receptive conspecific females. We suggested that the wing vibration as well as the walking toward the pheromone source are controlled by a self-generated zigzag turning program which is triggered by intermittent pheromonal stimulation applied to the antennae. In order to understand the behavioral and neural mechanisms of such an innate behavior, we have studied how information about the pheromones is processed in the olfactory neural system of the brain and how this information participates in generating and controlling the zigzagging behavior.we found that olfactory neurons in the protocerebrum (PC) , the higher olfactory integrative centers, innervate a particular neuropil region, the lateral accessory lobe (LAL). Each LAL is also linked with each other through the commissure of LALs. The LALs may be interposed in the pathways of olfactory information flow, from the first-order olfactory center, the antennal lobe, through the lateral PC to the interneurons descending (DNs) to the thoracic motor center (TMC) via the ventral nerve cord (VNC).Some LAL DNs showed state-dependent activities, like an electronic 'flip-flop', which have two distinct firing frequencies, high and low. Switching back and forth between the two states occurs upon sequential pheromonal stimulation previously characterized by Olberg (1983). Two clusters (group I,II) of DNs which have arborizations in the LAL were examined and two types of flip-flop activities, which have an antiphasic relationship, descending in each of the VNC to the TMC were found. These findings provide a substrate for understanding the olfactory neural system required to produce flip-flop activities, which may be an important signal to control zigzagging behavior.