Investigating the role of mouse olfactory dopaminergic cells in processing sexual odors

Olfaction is a crucial sense for many species, influencing behavioral responses like mating and reproduction. A significant dopaminergic (DA) population is found in the mouse main olfactory bulb (OB), with inhibitory interneurons identified by tyrosine hydroxylase (TH) expression and divided into two major groups (i.e., small and large cells) according to their shape, generation time, and biophysical characteristics. Although it is known that salient stimuli activate midbrain DA neurons, it is unclear if OB DA cells are involved in processing ethologically relevant odorants, especially those associated with sexual behaviors. Here we investigated how exposure to the scents found in opposite-sex urine affects the olfactory DA cell recruitment. Through whole-brain labelling of immediate early genes and light-sheet microscopy, we demonstrate that, in females, brief and acute exposure to male urine increases neuronal activation mainly in the most dorsal-posterior OB, where we detected a selective and strong TH+ cell recruitment not selective for small or large DA cells. Interestingly, however, this portion of OB shows enhanced basal recruitment of large TH+ neurons. By using a time-controlled Cre-lox approach to express the calcium indicator GCaMP selectively in the small or large cells, we aim in distinguishing the physiological responses of the two subpopulations to opposite-sex odors using in vivo 2-photon functional imaging. Furthermore, we are evaluating concurrent dopamine release utilizing dopamine sensors. The research aims at investigating how the two OB DA subpopulations contribute to processing opposite-sex odors and clarify the function of glomerular dopamine in relation to reproduction.