Abstract
The present study aimed to determine how the learning and memory gradually change with the prolonged hindlimb unloading (HU) treatment in rats. Different HU durations (7 d, 14 d, 21 d, and 28 d) in Sprague-Dawley (SD) rats were implemented. Cognitive function was assessed using the Morris water maze (MWM) and the shuttle box test. Additionally, parameters about cholinergic activity and oxidative stress were tested. Results showed that longer-than-14 d HU led to the inferior performances in the behavioral tasks. Besides, acetylcholine esterase (AChE) activity, malondialdehyde (MDA) level in brain, reactive oxygen species (ROS), and 8-hydroxy-2-deoxyguanosine (8-OHdG) concentrations of HU rats were significantly increased. Furthermore, choline acetyltransferase (ChAT), superoxide dismutase (SOD), and catalase (CAT) activity in brain were notably attenuated. Most of these effects were more pronounced after longer exposure (21 d and 28 d) to HU, although some indicators had their own characteristics of change. These results indicate that cholinergic dysfunction and oxidative damage were involved in the learning and memory impairments induced by longer-than-14 d HU. Moreover, the negative effects of HU tend to be augmented as the HU duration becomes longer. The results may be helpful to present possible biochemical targets for countermeasures development regarding the memory deficits under extreme environmental conditions.
Highlights
Microgravity, as a basic environmental factor in spaceflight, can influence the physiological conditions as well as psychological functions
The central cholinergic system plays a pivotal role in learning and memory process and has been the center of attention regarding diseases characterized by a cognitive deficit [17, 18]. These findings strongly suggest that cholinergic dysfunction and oxidative stress are closely associated with cognitive impairment
Average escape latency in each group was calculated to estimate the effect of various hindlimb unloading (HU) duration on memory
Summary
Microgravity, as a basic environmental factor in spaceflight, can influence the physiological conditions as well as psychological functions. Reports about nervous system function are relatively less, notably cognition. Few studies have evaluated cognitive function during space travel or parabolic flights. A few studies reported no effects [4, 5] or enhancement in cognitive function [6], whereas other results proved that cognitive function showed a certain degree of decline during the weightlessness [7,8,9]. A definite and deep understanding of the effects of microgravity on cognitive function is required as a predisposition to design efficient countermeasures to minimize the negative impact on human performance.
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