Integrative analysis of multiple pathways in the honeybee olfactory system

跨物种的一个显著共性是平行嗅觉系统的反复出现，如哺乳动物的主嗅觉系统、犁鼻系统、鼻中隔器官和格林伯格器官。同样，两栖动物、鱼类和昆虫中也存在不同的子系统，这表明并行系统具有很高的适应价值。我们用蜜蜂研究了一个物种，在这个物种的主要嗅觉系统中发现了两个大小相等的不同嗅觉子系统：l-APT和m-APT途径。此外，蜜蜂提供了大量的知识和丰富的范式来研究嗅觉解剖、生理和行为，包括与认知能力接近的学习和记忆。在第一个资助期，我们发现了这种双嗅觉通路的重要的新的解剖学和生理学特征。在感觉输入端，基本感受器是性别特异性的，在雌性中主要局限于m-APT子系统，而在雄性雄蜂中则较少。对蘑菇体花萼输出突触的超微结构分析揭示了这两个子系统突触可塑性的新方面。最重要的是，通过光生理记录和实时双束多单元电生理，我们发现两个天线瓣输出束对类似的气味反应，表明真正的并行处理。我们发现，在联想气味学习之后，l-APT子系统中至少有两种突触可塑性机制的证据。因此，我们当前和未来的生理实验将通过使用扩展的气味刺激面板来关注这些并行编码特性及其可塑性。未来的分析主要集中在使用不同气味浓度和混合物的空间和时间响应特性（延迟和巧合码）上。此外，我们将继续探索属于这两种通路的神经元的神经化学特征和内在特性，并测试它们的行为相关性。我们期望提高我们对平行嗅觉编码机制和平行通路在感觉系统中的意义的理解。

A striking commonality across species is the recurring presence of parallel olfactory systems, such as the main olfactory system, the vomeronasal system, the septal organ and the Grueneberg organ in mammals. Similarly, different subsystems are present in amphibians, fish and insects, suggesting that parallel systems have a highly adaptive value. We use the honeybee Apis mellifera to study a species where two distinct olfactory subsystems of about equal size have been found within the main olfactory system: the l-APT and the m-APT pathway. In addition, the honeybee offers a large body of knowledge and a wealth of paradigms to study olfactory anatomy, physiology and behavior, including learning and memory with close to cognitive capacities. In the first funding period we found important new anatomical and physiological characteristics of this dual olfactory pathway. At the sensory input side, basiconic sensilla are sex-specific and mostly restricted to the m-APT subsystem in females, which is reduced in male drones. Ultrastructural analyses of output synapses in the mushroom body calyx revealed new aspects of synaptic plasticity in the two subsystems. Most importantly, using optophysiological recordings and real-time dual tract multiunit electrophysiology we show that both antennal-lobe output tracts respond to a similar panel of odors indicating true parallel processing. We found evidence for at least two mechanisms of synaptic plasticity in the l-APT subsystem following associative odor learning. Consequently, our current and future physiological experiments focus on these parallel coding properties and their plasticity by using an expanded panel of odor stimuli. Future analyses largely focus on spatial and temporal response properties (latency and coincidence code) using different odor concentrations and mixtures. In addition, we will continue to probe the neurochemical characteristics and intrinsic properties of neurons belonging to the two pathways and test their behavioral relevance. We expect to improve our understanding of parallel olfactory coding mechanisms and of the significance of parallel pathways in sensory systems in general.