Contribution of olfactory neurogenesis to the establishment of maternal behaviour in mammals – PLASTMATBEHAV

Motherhood induces profound behavioral changes in mammals. Besides suckling, which characterizes mammalian species, maternal behavior is defined by consumption of placental membranes and the immediate interest to and cleaning of the neonate. However, differences exist according to neonate maturity. Birth of immature neonates (rodents) is related to nest building. In species in which neonates are mature (ungulates), maternal behavior is characterized by an individual recognition and the establishment of an exclusive bonding. Brain plasticity, specifically at the level of olfactory structures, could account for these behavioral changes.
This proposal is aimed at understanding whether olfactory neurogenesis, a supply of brain plasticity, could be a mechanism by which olfaction can contribute to the onset of maternal behavior and the associated learning in mice and sheep, two mammalian species with different maternal styles
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The first objective (task 2) assesses, in both mice and sheep, whether olfactory neurogenesis is regulated by parturition and interactions with young and the relative importance of both factors will be considered. To this end, the number of Bromo-deoxyuridine positive cells (BrdU; a cell proliferation marker) in neuroblasts and mature neurons will be compared in parturient and non-gestant females with or without the first 24-hr period of contact with young.

The second objective (task 3) is aimed at testing the hypothesis that adult-generated olfactory neurons make a contribution to the processing of odors which are involved in attraction to any young (mice) and in memorization of olfactory offspring signature (sheep). We hypothesize that new olfactory interneurons will preferentially respond to pup odors in the early postpartum period. In addition, because sheep offers a unique possibility to scrutinize the mechanisms underlying olfactory memory, we hypothesize that new olfactory interneurons generated when mothers interact with their lambs will preferentially respond to odors of their own lamb as compared to alien lamb. For both species, immunofluorescent labelling of BrdU, the neuron-specific nuclear protein NeuN and the activity-dependent protein Fos will be assessed to see whether the formation of an olfactory trace within the MOB will specifically involve newborn olfactory neurons.

In task 4, the effects of neurogenesis ablation in maternal behavior of mice and sheep mothers will be evaluated using two different methodologies. In mice, optogenetic tool will be used to silence adult born neurons of the olfactory bulb at parturition whereas in sheep an antimitotic agent will be centrally infused several weeks before parturition to reduce the number of new neurons at the time of parturition.