Experience-dependent modulation of olfactory representations and behavior in Drosophila

我们都出生在一个充满视觉、听觉、触觉、味觉和嗅觉刺激的世界，但并不是每个人都在相同的刺激环境中长大。例如，一个在面包店旁边长大的孩子每天醒来都能闻到新鲜面包的味道，而他住在花店旁边的朋友，无论何时回家都能闻到花香。这样的童年经历会影响成年人的嗅觉和气味偏好吗？动物研究表明，事实确实如此。早期生命的神经可塑性使神经系统能够适应动物出生的环境。这些神经适应反过来又塑造了动物成年后的行为：早期的刺激体验可以改变对刺激的偏好，它可以提高动物检测和识别刺激的能力。我们对早期刺激体验如何改变周围神经系统有基本的了解。然而，技术挑战在很大程度上阻止了我们深入了解对高级大脑区域的影响，特别是哺乳动物。因此，人们对周围神经系统的可塑性如何转化为动物行为的变化知之甚少。幸运的是，早期刺激暴露的影响不仅可以在哺乳动物中观察到，也可以在包括果蝇在内的一些昆虫中观察到。果蝇是研究早期刺激暴露诱导嗅觉可塑性现象的一个很好的模型系统，原因有三：首先，在果蝇早期生活中，气味预暴露对嗅觉回路中的外周神经元和气味驱动行为都有调制作用。其次，我们现在拥有新技术，使我们能够在参与驱动嗅觉行为的更高大脑结构中以单细胞分辨率捕获气味的完整神经元表征。最后，我们有工具可以让我们非常详细地分析单个苍蝇对气味的行为。因此，神经气味编码的经验依赖性变化可能与嗅觉行为方面的变化有关。了解果蝇早期气味体验引起的行为变化的神经基础，将揭示昆虫和人类之间可能共享的早期体验编码的原则。

We are all born into a world full of visual, auditory, tactile, gustatory and olfactory stimuli, but not everyone grows up in the same stimulus environment. For example, a child who grows up next to a bakery wakes up to the smell of fresh bread every day, while his friend who lives next to a flower shop is welcomed by the fragrance of flowers whenever he comes home. Do such childhood experiences affect the sense of smell and odor preferences of an adult? Animal studies suggest that this is indeed the case. Neural plasticity during early life allows the nervous system to adapt to the environment that the animal is born into. These neural adaptations in turn shape the animals’ behavior in adulthood: early experience with a stimulus can alter the preference for that stimulus, and it can improve the animals’ ability to detect and recognize it. We have basic knowledge about how the peripheral nervous system is altered by early stimulus experience. However technological challenges have largely prevented us from gaining deep understandings of the effects on higher brain regions, especially of mammals. As a consequence, little is known about how plasticity in the peripheral nervous system translates into changes in animal behavior. Fortunately, effects of early stimulus exposure can be observed not only in mammals, but also in some insects including the fruit fly Drosophila. Drosophila is an excellent model system for studying the phenomenon of early stimulus exposure induced plasticity in the context of olfaction for three reasons: First of all, both peripheral neurons in the olfactory circuit and odor-driven behaviors are modulated by odor pre-exposure during early life in Drosophila. Secondly, we are now in possession of new techniques which enable us to capture the complete neuronal representation of an odor with single cell resolution in a higher brain structure that is involved in driving olfactory behaviors. Lastly, we have tools that allow us to analyze the behavior of individual flies towards an odor in great detail. Thus, experience-dependent changes in neural odor encoding can be related to changes in aspects of olfactory behaviors. Understanding the neuronal basis for behavioral changes due to early odor experience in Drosophila will reveal principles of early experience encoding that may be shared between insects and humans.