Abstract
Chronic exposure to hypobaric hypoxia (HH) causes memory impairment and prolonged state of mental confusion. However, effect of high altitude exposure on mood state and its underlying mechanisms have been poorly studied. Present study was undertaken to investigate the mood state alteration following chronic exposure to HH. Male Sprague Dawley rats were divided into five groups and exposed to hypoxia for 3, 7, 14 and 21 days in an animal decompression chamber at an altitude of 25,000ft. Anxiety-and depression-like behaviors were assessed by using various mazes along with changes in serotonin and glutamate level. Our study revealed a decrease in exploratory, grooming and rearing behavior in open field test following initial exposure to HH for 7 days without affecting the locomotory behavior. Initial exposure to HH-decreased time spent in open arm of elevated plus maze indicating induction of anxiety-like behavior which normalized on prolonged hypoxic exposure for 21 days. Hypoxic exposure for 7 days induced anhedonia and increased despair behavior in rat while there was steady improvement in these behaviors when exposed for 21 days. Decrease in serotonin level was noted in hippocampus along with elevated corticosterone and glutamate level which gradually decreased on prolonged exposure to HH. These findings suggest that initial exposure to HH increases transient anxiety-like behavior in rats followed by gradual improvement in mood state on prolonged exposure. Further, the study also indicates the involvement of serotonergic system in mood state alteration at high altitude following chronic exposure and reoxygenation.
Highlights
A significant portion of the world population resides at high altitude regions
Exposure to hypobaric hypoxia (HH) for 3 and 7 days significantly decreased the time spent in open arm with corresponding increase in time spent in closed arm compared to normoxic group
Chronic exposure to HH for 7 days induces anxiety-like behaviors in rats
Summary
A significant portion of the world population resides at high altitude regions. Apart from natives, natural beauty of the snow-clad peaks attracts a huge population of tourists every year to explore the high altitude. High altitude regions are important for its strategic locations, for sojourners, mountaineers and defense personnel. All of them face extreme climatic conditions like severe cold, high wind velocity, UV irradiation and most importantly, hypobaric hypoxia due to reduced partial pressure of oxygen. Exposure to HH is known to cause adaptive physiological changes that enable the organisms to cope up with severity of this environmental stress. Mal-acclimatisation to extreme altitudes results in many pathological manifestations like High Altitude Pulmonary
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