Olfactory Stimuli Affect Establishment of Behavioral Phenotype and Fate of Immature Neurons in the Developing Piriform Cortex of CD1 Mice

Control of the processes of survival and differentiation of immature neurons - non-newly generated immature neurons - nng-Ins - in the cortical areas of the brain is important for preventing the de-velopment of neurological dysfunction in disorders of brain development and physiological aging. We used olfactory stimuli (OS) in the dynamics of postnatal development (P21, P60) in CD1 mice. They have been exposed to the protocol of simulation and assessment of the piriform cortex activation upon olfactory stimuli presentation. Then, at 2 hours, 24 hours, and 7 days after stimuli presentation, we analyzed parameters of learning and memorization, social recognition, anxiety as well as the patterns of expression of nng-INs markers (DCX, PSA-NCAM), proliferation marker (Ki67), marker of postmitotic cortical neurons (Tbr1), and immediate early gene c-fos expression as a marker of neuronal activation. We found that in the period from 2 to 60 days of mice postnatal development, proliferating and non-proliferating cells co-expressing DCX and PSA-NCAM were present in the piriform cortex (PC) and responded to the presentation of olfactory stimuli. Activation of nng-INs (DCX+ PSA-NCAM+ Ki67-) in the OS-stimulated brain plasticity is more evident in the immature developing PC, whereas appearance of mitotically active neuroblasts (DCX+ PSA-NCAM+ Ki67+), presumably, coming from other neurogenic niches of the brain upon OS-driven PC activation as well as stimulus-induced differentiation of locally present nng-INs might dominate in the mature piriform cortex (P60).  Thus, immature neurons in the PC might contribute to the brain plasticity in the early ontogenesis.