Role of cholinergic markers on memory function of rats exposed to hypobaric hypoxia

Hypobaric hypoxia is encountered at high altitude. It has a deleterious effect on cognitive functions. An important cause of memory impairment at high altitude is the impairment of neurotransmission. The present study investigates the role of cholinergic markers in hypobaric hypoxia-induced memory impairment. Rats were exposed to hypobaric hypoxia at 6,100 m for 7 days in a simulated-decompression chamber. Memory performance was assessed using the Morris water maze task. Cholinergic markers such as acetylcholine, acetylcholinesterase, choline acetyltransferase, α-7-nicotinic acetylcholine receptor and M(1) muscarinic acetylcholine receptor were also evaluated along with neuronal morphology and DNA fragmentation. We found impairment in memory function along with a decrease in acetylcholine levels, increase in acetylcholinesterase activity, down regulation of choline acetyltransferase, α-7-nicotinic acetylcholine receptor and M(1) muscarinic acetylcholine receptor. We also found that cellular damage is associated with a significant increase in DNA fragmentation. However, administration of acetylcholinesterase inhibitors, such as physostigmine and galantamine, resulted in amelioration of the hypobaric hypoxia induced deleterious effects. It improved acetylcholine level, decreased acetylcholinesterase activity and increased the synthesis of acetylcholine by increasing choline acetyltransferase activity. Also, the acetylcholinesterase inhibitors improved neuronal morphology, perhaps by increasing the expression of α-7-nicotinic acetylcholine receptor and by reducing the acetylcholinesterase level in the cortex and the hippocampus. Therefore, our results suggest cholinergic dysfunction is one of the mechanisms involved in hypobaric hypoxia-induced memory impairment and that acetylcholinesterase inhibitors were able to restore cholinergic function and thus improve memory function.