Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA.
Adv Exp Med Biol. 2012;739:93-106. doi: 10.1007/978-1-4614-1704-0_6.
Evolutionally, chemosensation is an ancient but yet enigmatic sense. All organisms ranging from the simplest unicellular form to the most advanced multicellular creature possess the capability to detect chemicals in the surroundings. Conversely, all living things emit some forms of smells, either as communicating signals or as by-products of metabolism. Many species (from worms, insects to mammals) rely on the olfactory systems which express a large number of chemoreceptors to locate food and mates and to avoid danger. Most chemoreceptors expressed in olfactory organs are G-protein coupled receptors (GPCRs) and can be classified into two major categories: odorant receptors (ORs) and pheromone receptors, which principally detect general odors and pheromones, respectively. In vertebrates, these two types of receptors are often expressed in two distinct apparatuses: The main olfactory epithelium (MOE) and the vomeronasal organ (VNO), respectively. Each olfactory sensory neuron (OSN) in the MOE typically expresses one type of OR from a large repertoire. General odors activate ORs and their host OSNs (ranging from narrowly- to broadly-tuned) in a combinatorial manner and the information is sent to the brain via the main olfactory system leading to perception of smells. In contrast, pheromones stimulate relatively narrowly-tuned receptors and their host VNO neurons and the information is sent to the brain via the accessory olfactory system leading to behavioral and endocrinological changes. Recent studies indicate that the functional separation between these two systems is blurred in some cases and there are more subsystems serving chemosensory roles. This chapter focuses on the molecular and cellular mechanisms underlying odor and pheromone sensing in rodents, the best characterized vertebrate models.
从进化的角度来看，化学感觉是一种古老但神秘的感觉。从最简单的单细胞形式到最先进的多细胞生物，所有生物都具有检测周围化学物质的能力。相反，所有生物都会发出某种形式的气味，无论是作为交流信号还是作为代谢的副产物。许多物种（从蠕虫、昆虫到哺乳动物）依赖于嗅觉系统，该系统表达大量的化学感受器来定位食物、配偶和避免危险。嗅觉器官中表达的大多数化学感受器是 G 蛋白偶联受体（GPCR），可分为两大类：气味受体（OR）和信息素受体，它们主要分别检测一般气味和信息素。在脊椎动物中，这两种类型的受体通常在两个不同的器官中表达：主要嗅觉上皮（MOE）和犁鼻器（VNO）。MOE 中的每个嗅觉感觉神经元（OSN）通常表达来自大量库的一种类型的 OR。一般气味以组合方式激活 OR 和其宿主 OSN（从窄调谐到宽调谐），信息通过主要嗅觉系统传递到大脑，导致嗅觉感知。相比之下，信息素刺激相对窄调谐的受体及其宿主 VNO 神经元，信息通过副嗅觉系统传递到大脑，导致行为和内分泌变化。最近的研究表明，这两个系统之间的功能分离在某些情况下是模糊的，并且有更多的子系统发挥化学感觉作用。本章重点介绍了啮齿动物（研究最充分的脊椎动物模型）中气味和信息素感知的分子和细胞机制。
