Intermittent hypoxia impairs performance of adult mice in the two‐way shuttle box but not in the Morris water maze

Abstract

We have previously found that neonatal intermittent hypobaric hypoxia exposure enhanced mouse spatial, but impaired associative, cognition. This study sought to investigate the effects of hypobaric hypoxia on adult mice cognition. Mice were exposed to 2, 5, 10, 15, or 25 days of intermittent hypoxia (IH; 4 hr/day) at 2 km (16.0% O2) or 5 km (10.8% O2) altitudes in a hypobaric chamber for the Morris water maze (MWM) test and exposed to IH for 2, 10, or 25 days for the shuttle-box test. Amino acid dynamics in vivo in the hippocampus and amygdala of mice exposed to 2 km hypoxia were analyzed by high-pressure liquid chromatography. The results in MWM task showed that IH-2d to -25d at 2 km or 5 km did not change the escape latencies of mice in the training test or the retention of platform in the probe test. In the shuttle-box task, however, IH-10d at 5 km significantly reduced mouse avoidances in the acquisition test on day 4, and IH-10d at 2 km reduced avoidances in the retention test; IH-25d at 5 km significantly reduced avoidances of mice throughout the acquisition days. Glutamate in the amygdala persisted in declining to 69% of baseline at 8 hr posthypoxia (P = 0.040 vs. GLU released during 30 min before hypoxia) during the posthypoxia stage. These results suggest that adult hypobaric IH impairs the hippocampal-independent, but not the hippocampal-dependent, task in mice. The different GLU releases in the hippocampus and amygdala in response to hypoxia are involved in the different behaviors.

Dim light at night interacts with intermittent hypoxia to alter cognitive and affective responses

“…Consistent with previous studies of IH (44,53) and patients with OSA (20, 37), we observed impaired learning and memory. The effects of IH and sleep deprivation were previously determined to have distinct effects on the central nervous system, although both have separately been associated with impaired memory function, specifically in spatial learning tasks (25)(26)(27).…”

“…The effects of IH and sleep deprivation were previously determined to have distinct effects on the central nervous system, although both have separately been associated with impaired memory function, specifically in spatial learning tasks (25)(26)(27). It was also reported that 3 days of IH exposure prior to acquisition decreased consolidation, consistent with other findings of IH impairing learning and memory after sustained exposure (48,53). Differences in learning and memory were only observed in the passive avoidance task.…”

“…Both tests require short durations of memory recall between 1 min and 1 h, whereas the passive avoidance task examined retention 24 h later. These results suggest that IH and dLAN may not affect shorter-term memory but might influence memory consolidation (48,53).…”

Hypoxic Preconditioning Improves Spatial Cognitive Ability in Mice

“…To our knowledge, our study is the first reporting that acute and repeated hypoxic exposure enhances performance of adult mice in a water maze. In contrast with our results, other results suggest that hypoxic exposure impairs, or does not affect, the ability of learning and memory in adult and neonatal animals [8,9,32] . This discrepancy could be explained by the differences in the methods for hypoxic exposure and differences in the development stage in which animals were exposed to hypoxia.…”

“…Compared with the control group, the spatial cognitive ability of mice exposed to hypoxia once was not changed. Zhang et al [24,32] have reported that intermittent hypoxia could enhance spatial cognitive ability in young mice but did not affect this ability in adult mice. Others also reported that brief hypobaric hypoxia enhanced animals' cognition.…”