Illuminating odors: when optogenetics brings to light unexpected olfactory abilities

Abstract

For hundreds of years, the sense of smell has generated great interest in the world literature, oenologists, and perfume makers but less of scientists. Only recently this sensory modality has gained new attraction in neuroscience when original tools issued from physiology, anatomy, or molecular biology were available to decipher how the brain makes sense of olfactory cues. However, this move was promptly dampened by the difficulties of developing quantitative approaches to study the relationship between the physical characteristics of stimuli and the sensations they create. An upswing of olfactory investigations occurred when genetic tools could be used in combination with devices borrowed from the physics of light (a hybrid technique called optogenetics) to scrutinize the olfactory system and to provide greater physiological precision for studying olfactory-driven behaviors. This review aims to present the most recent studies that have used light to activate components of the olfactory pathway, such as olfactory receptor neurons, or neurons located further downstream, while leaving intact others brain circuits. With the use of optogenetics to unravel the mystery of olfaction, scientists have begun to disentangle how the brain makes sense of smells. In this review, we shall discuss how the brain recognizes odors, how it memorizes them, and how animals make decisions based on odorants they are capable of sensing. Although this review deals with olfaction, the role of light will be central throughout.

Olfactory Optogenetics: Light Illuminates the Chemical Sensing Mechanisms of Biological Olfactory Systems

“…However, although optogenetics has been widely applied in the research of the olfactory sensing mechanism, the important applications of optogenetics in the olfactory system have rarely been outlined and discussed. Grimaud et al, reviewed the contributions of optogenetics in the study of olfactory learning and memory, but in recent years, scientists have made many outstanding advances in olfactory research using optogenetics [ 25 ]. Here, we first introduce optogenetic tools in the olfactory system, and then mainly focus on the findings in OB that use optogenetics as a tool, including the transmission of sensory input, the perception of odor information, and functional neuronal circuits in OB.…”