Abstract
Microgravity and sleep loss lead to cognitive and learning deficits. These behavioral alterations are likely to be associated with cytomorphological changes and loss of neurons. To understand the phenomenon, we exposed rats (225–275 g) to 14 days simulated microgravity (SMg) and compared its effects on CA1 hippocampal neuronal plasticity, with that of normal cage control rats. We observed that the mean area, perimeter, synaptic cleft, and length of active zone of CA1 hippocampal neurons significantly decreased while dendritic arborization and number of spines significantly increased in SMg group as compared with controls. The mean thickness of the postsynaptic density and total dendritic length remained unaltered. The changes may be a compensatory effect induced by exposure to microgravity; however, the effects may be transient or permanent, which need further study. These findings may be useful for designing effective prevention for those, including the astronauts, exposed to microgravity. Further, subject to confirmation, we propose that SMg exposure might be useful for recovery of stroke patients.
Highlights
Human astronauts who spent more than 400 days in space showed ataxia, perceptual illusions, neuromuscular weakness, and fatigue after landing
Microgravity exposure-associated impairments of cognitive functions are likely to be dependent on duration of exposure and the effects varied depending on the rate of recovery and degree of adaptation
As hippocampal neurons are involved in memory formation [20] and the latter is altered by exposure to microgravity [6, 8], we argued that exposure to simulated microgravity (SMg) under controlled experimental condition is likely to affect the hippocampal CA1 neurons
Summary
Human astronauts who spent more than 400 days in space showed ataxia, perceptual illusions, neuromuscular weakness, and fatigue after landing They tended to readapt with time under normal gravity condition after returning to the earth [1]. Independent studies have reported that exposure to microgravity alters levels of biomolecules [2,3,4], increase cortical spine density [5], induce impaired cognition as well as learning and memory [6, 7] These impairments are likely to be specific to exposure to microgravity because such microgravity exposure-associated loss of memory [8, 9] tended to reverse with time after their return to the earth under normal gravity condition [10]. On the other hand, isolated studies have shown that impaired learning and memory is associated with reduced spine density [15] and neuronal loss [16, 17]
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