Experience-Dependent Plasticity of Periglomerular Cells in the Olfactory Bulb

The olfactory bulb (OB) serves as the first relay station that processes odor information. Within the OB, odor representations are dynamically modulated by reciprocal synapses between excitatory mitral and tufted (M/T) cells and local inhibitory interneurons. Among these interneurons, periglomerular cells (PGCs) are GABAergic neurons located in the glomerular layer that provide inhibitory inputs to M/T cells. Although their anatomical and molecular properties have been extensively characterized, the in vivo dynamics of PGCs during odor processing and learning remain poorly understood. To address this question, we performed in vivo two-photon calcium imaging of awake male mice to monitor the activity of individual PGCs during odor-associated tasks. PGCs exhibited robust and odor-specific responses that varied among individual odorants. Repeated passive odor exposure reduced the number of odor-responsive PGCs while preserving their odor selectivity. In contrast, active odor discrimination learning expanded the population of odor-responsive PGCs and enhanced response amplitude. Furthermore, discriminating highly similar odor mixtures recruited a broader ensemble of PGCs with lower selectivity, but this representation sharpened over training, resulting in fewer yet more selective PGCs. These findings demonstrate the experience-dependent features of PGCs and reveal their critical role in tuning olfactory processing. Our study provides fundamental insights into how inhibitory circuits regulate sensory representations underlying adaptive odor-guided behaviors.