The mechanisms responsible for
cholinergic dysfunction associated learning and memory impairment during
hypoxia are not well-understood. However it is known that inflammatory mediators like
inducible nitric oxide synthase (iNOS) hamper the functions of cholinergic neurons. In this present experiment we made an effort to study the iNOS expression mediated retrograde and anterograde memory impairment in Balb/c mice following acute hypobaric
hypoxia (at an altitude of 23,000ft for 6h) using elevated plus maze and passive avoidance step-through tasks. Our results demonstrated that
hypoxia transiently impairs the retrograde memory without affecting the anterograde memory functions, accompanied with a substantial rise in iNOS expression and
nitric oxide levels in cerebral cortex on days 2 and 3 post
hypoxia. Treatment with
aminoguanidine (iNOS inhibitor ), resulted in down-regulation of the iNOS expression, attenuation of the surge of
nitric oxide (NO) in cerebral cortex and reversal of retrograde memory impairment due to
hypoxia. Moreover the reduced AChE activity and elevated lipid peroxidation in cerebral cortex were evident during post
hypoxia re-oxygenation period, which was not observed in the hippocampus. Additionally, NO donor
spermine NONOate could inhibit the AChE activity in brain homogenates in a concentration-dependent manner, which further substantiate that
nitric oxide produced during post
hypoxia re-oxygenation, primarily contributes to the observed inhibition of cortical AChE activity. Based on these experiments we hypothesize that the NO burst as a result of iNOS upregulation during
hypoxia interrupts the memory consolidation by altering the
cholinergic functions.