Coincidence of pheromone and plant odor leads to sensory plasticity in the heliothine olfactory system

Male moths possess a highly specialized olfactory system comprised of two segregated sub-arrangements dedicated to processing information about plant odors and pheromones, respectively. Communication between these two sub-systems has been described at the peripheral level, but relatively little is known about putative interactions at subsequent synaptic relays. The male moth faces the challenge of seeking out the conspecific female in a highly dynamic odor world. The female-produced pheromone blend, which is a limited resource serving as guidance for the male, will reach his antennae in intermittent pockets of odor filaments mixed with volatiles from various plants. In the present study we performed calcium imaging for measuring odor-evoked responses in the uni-glomerular antennal-lobe projection neurons (analog to mitral cells in the vertebrate olfactory bulb) of Helicoverpa armigera. In order to investigate putative interactions between the two sub-systems tuned to plant volatiles and pheromones, respectively, we performed repeated stimulations with a selection of biologically relevant odors. We found that paired stimulation with a plant odor and the pheromone led to suppressed responses in both sub-systems as compared to those evoked during initial stimulation including application of each odor stimulus alone. The fact that the suppression persisted also after pairing, indicates the existence of a Hebbian-like plasticity in the primary olfactory center established by temporal pairing of the two odor stimulation categories.

雄蛾拥有一套高度特化的嗅觉系统，包含两个相互分离的亚通路，分别负责处理植物气味与信息素（pheromone）的相关信息。目前学界已在外周水平阐明了这两个亚系统间的通讯机制，但针对后续突触传递环节中的潜在相互作用，我们的认知仍较为有限。在高度动态的气味环境中寻觅同种雌蛾，是雄蛾必须应对的核心挑战。雌蛾分泌的信息素混合物作为引导雄蛾的有限信号源，会以间歇性气味丝束的形式抵达雄蛾触角，且这些丝束中混杂着多种植物的挥发性气味物质。本研究通过钙成像（calcium imaging）技术，检测了棉铃虫（Helicoverpa armigera）单肾小球触角叶投射神经元（其与脊椎动物嗅球中的僧帽细胞（mitral cells）同源）的气味诱发反应。为探究分别适配植物挥发性物质与信息素的两个亚系统间的潜在相互作用，我们选用多种生物学相关的气味开展重复刺激实验。研究结果显示，与单独施加植物气味或信息素的初始刺激相比，将植物气味与信息素联合刺激后，两个亚系统的反应均受到抑制。且该抑制效应在联合刺激结束后仍持续存在，这表明在初级嗅觉中枢中，存在由两类气味刺激的时序联合所建立的类赫布（Hebbian）可塑性。