A mouse model of neurobehavioural response to altered gravity conditions: an ontogenetical study.

To determine the influence of gravity during critical periods of development is important in the perspective of long-term spaceflight and exploration, data coming from this kind of studies providing insight into basical biological phenomena underlying the development of the nervous system and its plasticity. Aim of the present study was to evaluate neurobehavioural responses to hypergravity exposure in CD-1 mice at different stage of development. Early adolescent (postnatal day 28, PND 28), adolescent (PND 42) and young-adult (PND 60) male and female mice were exposed to acute 2g rotational-generated hypergravity. Motion sickness index and behavioural performances pre, during and after rotation were recorded, and long-lasting effects on exploratory behaviour (hole-board test) and emotional/anxiety-like responses (plus-maze test) were investigated. Furthermore, in order to correlate behavioural changes with alterations in central levels of neurotrophins, brain amounts of Nerve Growth Factor (NGF) and Brain Derived Neurotrophic Factor (BDNF) were also assessed on PND 90, following a re-exposure to hypergravity. Age and sex differences were observed, females being more vulnerable than males to motion sickness, and susceptibility to hypergravity increasing with age of exposure. Moreover, mice showed a general reduction in spontaneous activity during the rotation, while recovery time after rotation became progressively longer with increasing age of the experimental subjects. Long-term effects on exploratory behaviour and emotional/anxiety-like response were also observed, behavioural profiles mainly changing in those animals experiencing hypergravity as young-adults. Finally, major changes in brain levels of NGF and BDNF were detected in mice firstly exposed as young-adults.