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

家蚕雄蛾对同种雌虫性信息素的反应表现为迎风曲折行走伴翼振动。我们认为，翅膀的振动以及向信息素来源的行走是由一个自产生的Z字形转弯程序控制的，该程序是通过对天线施加间歇性信息素刺激来触发的。为了了解这种先天行为的行为和神经机制，我们研究了信息素信息是如何在大脑的嗅觉神经系统中处理的，以及这种信息是如何参与Z字形行为的产生和控制的。我们发现，前脑(PC)中的嗅觉神经元是高级嗅觉整合中心，支配着一个特定的神经纤维区，即外侧副叶(LAL)。每个LAL还通过LAL的合点相互链接。LAL可能存在于嗅觉信息流的通路中，从一级嗅觉中枢、触角叶，经外侧PC到中间神经元下行(NS)，再经腹神经索(VNC)到达胸部运动中枢(TMC)。一些LAL神经元表现出状态依赖的活动，就像电子触发器一样，有两种不同的放电频率，高和低。在Olberg(1983)之前描述的顺序信息素刺激下，在两种状态之间来回切换。我们观察了两个在LAL内有分支的DNs簇(组I和组II)，发现了两种类型的触发器活动，它们在每个VNC到TMC中都有逆相关系。这些发现为理解产生触发器活动所需的嗅觉神经系统提供了基础，这可能是控制之字形行为的重要信号。

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.