integrazione e attivazione dipendente dall'esperienza sensoriale di neuroni neo-generati nel bulbo olfattivo accessorio di topi femmine

The Accessory Olfactory Bulb (AOB) is the first brain region of the accessory olfactory system. This system mainly detects pheromones. Into the AOB of adult mammals, new-born neurons migrate and undergo differentiation and sensory imput play a prominent role for neuronal survival. The exixtence of critical periods for early integration of new neurons and their later activation in response to sensory stimulation, has been proposed.Specific aim of this work is to analyse haow AOB newborn neurons react to peripheral pheromonal stimulation in such critical periods, in term of both cell survival and functional activity. This is evaluated in females after stud male pheromonal exposure. Result obtained indicate that between 7 and 14 days after their genesis, newly-born cells are more sensitive to extrinsic stimuli, increasing their number and cell-density in the AOB.Furthermore, this study indivcate the existence of a temporal-window in which newborn neurons activation by pheromonal stimuli is higher. This functional response is specific to previously sensed pheromonal stimuli. By quantifying the co-expression of the immediate early gene c-fos in BrdU-positive cells in the AOB layers, we found that stimulatoion with a previously experienced odor specifically increases c-Fos expression, compared to exposures with odors never smelt before. At 4 weeks of age AOB newborn cells result to be more active (higher c-Fos expression) in comparison to more mature and immature neurons. This confirms that, at that age, AOB interneurons are more susceptible to be recruited by pheromonal stimulation. Such specific age-dependent involvement of newborn cells in bulbar activity could feed speculations about the possible role of new neurons in several AOB dependent task, such as individual recognition after mating. In this peculiar case, the experience of pheromones from the stud-male shapes AOB circuitry inducing LTP on reciprocal synapses between those mitral and granule cells activated by such pheromones. This is necessary to change the way pheromones are perceived in order to avoid the estrous-inducing effects of male pheromones during pregnency.