Effetto della separazione materna sulla plasticità dei neuroni nell’ippocampo delle mamme e della prole

Neuronal plasticity is the capability of neurons to change the structure, function and organization of neurons in response to new experiences. Behavioral studies in rodents, have shown that changes in the environment, in different periods of life, can lead to profound and lasting effects on neuronal plasticity as reflected by increased vulnerability or resilience to stress. Post-natal stress, such as maternal separation, have a deep impact not only for the offspring, but also for mothers, and lead to neuroendocrine, behavioral and structural changes in the brain. Neuroplasticity was evaluated both in mothers and offspring. Mothers were killed 21 days after delivery the day of the weaning and we analized density and morphology of dendritic spines and arborization of the dendritic tree in granule cells of hippocampus. Another goal of our study is to verify on the offspring, if stress induced by insufficient maternal care in the first 15 days of life increases the vulnerability to chronic stress conditions in adulthood. In this research, we used two experimental protocols of maternal separation, a) one group of pups was separated from their mothers for 15 min (short maternal separation), b) pups from the second group were separated for 3h (long maternal separation), every day from the 3rd to day 15th after birth respectively. The weaning day half of the rats belonging to the different groups was isolated for 60 days, while another group was isolated for 30 days then re-grouped for another 30 days. The results obtained were compared with those of rats never separated from their mothers (control), but subjected or not to social isolation. After sacrifice of offspring, we studied the density and morphology of dendritic spines, the arborization of dendritic tree and neurogenesis in the hippocampus. The results obtained in mothers showed that maternal separation reduced dendritic arborization in granule cells of hippocampus, and density of hippocampal dendritic spines is decreased in mothers after maternal separation. The results obtained in the offspring showed that social isolation induced a reduction of the arborization of the dendritic tree, variation of morphology and a reduction of the density of the dendritic spines, and a decrease of neurogenesis in animals not separated from the mother and in the separated ones. In rats subjected to re-group after 30 days of social isolation stress, the morphology and density of dendritic spines, arborization of the dendritic tree and the neurogenesis were completely reverted when compared to animals that have never been separated from their mothers (controls). In contrast, in animals subjected to maternal separation for 3 h, the social enrichment (re-grouped) failed to revert the effects of social isolation stress. In rats exposed to maternal separation for 15 min, social isolation for 60 days did not induce any change in the parameters studied. These results demonstrate that in the offspring, a short maternal separation of the animals in the first 15 days of life increase resilience to chronic stress during adult life. These data suggest that, in the offspring, high maternal care that result from a short maternal separation, increase resilience to chronic stress during adulthood. On the contrary, a lower maternal care as a consequence of a long maternal separation, reduce resilience and increase vulnerability to chronic stress, impairs neuronal plasticity and effect cognitive functions and emotional state. These results show that maternal separation during early post-natal period, have a negative effects on neuronal plasticity, both in mothers and offspring