AUTHOR=Mori Kensaku , Sakano Hitoshi 

TITLE=Circuit formation and sensory perception in the mouse olfactory system

JOURNAL=Frontiers in Neural Circuits

VOLUME=Volume 18 - 2024

YEAR=2024

URL=https://www.frontiersin.org/journals/neural-circuits/articles/10.3389/fncir.2024.1342576

DOI=10.3389/fncir.2024.1342576

ISSN=1662-5110

ABSTRACT=In the mouse olfactory system, odorants are detected with odorant receptors (ORs) 
expressed by olfactory sensory neurons (OSNs) in the olfactory epithelium (OE). 
Each individual OSN expresses only one functional OR gene, and OSN axons 
expressing the same OR species converge to a specific projection site forming a 
glomerular structure in the olfactory bulb (OB). Thus, odor signals are converted to a 
topographic map of activated glomeruli in the OB. Although the arrangement of 
glomeruli is genetically determined, the glomerular structure is plastic and can be 
modified by environmental odor stimuli in neonates. If the pups are exposed to a 
particular odorant, responding glomeruli become larger recruiting the dendrites of 
connecting projection neurons and interneurons. This imprinting not only increases 
the sensitivity to the exposed odor, but also imposes the positive quality on imprinted 
odor memory. External odor information represented as an odor map in the OB is then 
transmitted to the olfactory cortex (OC) for decision making to elicit behavioral outputs
using two distinct neural pathways, innate and learned. Tufted cells (TCs) mediating 
learned decisions are activated earlier during inhalation, whereas mitral cells (MCs) for 
innate decisions are activated later in exhalation. Respiratory cycles are also 
correlated with processing of two types of olfactory signals, interoceptive and 
exteroceptive, using two pairs of mirror-symmetrical olfactory maps. In this paper, we 
will summarize the recent progress in the study of early olfactory inputs and neural 
circuit formation in mice.