Dynamic Changes in Hindlimb Motor Cortex Neurons during Simulated Weightlessness Revealed by Miniature 2-Photon Microscopy.

Dysfunction of motor behavior during spaceflight is linked to alterations in neuronal activities. However, the longitudinal functional changes in the motor cortex triggered by simulated weightlessness remain ambiguous. In this study, we utilized a miniaturized 2-photon microscope to examine the dynamic shifts in neuronal activities within the hindlimb motor cortex during simulated weightlessness and its subsequent recovery period at the single-cell level. Our results demonstrated that simulated weightlessness led to a progressive decline in motor behavior during open-field and rotarod tasks, which was fully reversed after a 2-week recovery period. Single-cell analysis revealed that hindlimb motor neurons could be classified as activated, inhibited, or unchanged. During active locomotion in the open field, the activity of locomotion-activated neurons increased, while the activity of locomotion-inhibited neurons decreased, despite their numbers remaining constant. Conversely, during passive rotation on the rotarod test, the number of rotation-activated neurons decreased, while their activity increased, and the number of rotation-inhibited neurons increased along with their activity. These changes were largely restored after reloading. These findings elucidate motor dysfunction under simulated weightlessness and the heterogeneous changes in neuronal activities within the hindlimb motor cortex, offering valuable insights into understanding behavioral changes regulated by the motor cortex during spaceflight.