Objective: To determine the effect of the most commonly abused drugs (tramadol and morphine), on acetylcholine esterase (AChE), Na+/K+-ATPase activities and related parameters, Na+ and K+ as biomarkers of neurotoxicity. 

Methods: Tramadol - as a weak µ opioid receptor agonist- and morphine - as opiate analgesic drugs, were chosen for the present study. Four series of experimental animals were conducted for either tramadol or morphine: control series; repeated single equal doses (therapeutic dose) series; cumulative increasing doses series and delay (withdrawal) series (96 hours withdrawal period after last administration), at time period intervals 7, 14 and 21 days. Acetylcholine esterase (AChE), Na+/K+-ATPase activities and related parameters, Na+ and K+ were measured in cerebral cortices of experimental rats. 

Results: Acetylcholine esterase (AChE) activity in the brain cerebral cortex increased after the administration of therapeutic repeated doses of either tramadol (20 mg/kg b.w.) or morphine (4 mg/kg b.w.) in different groups. The daily intraperitoneal injection of cumulative increasing dose levels of either tramadol 20, 40 and 80 mg/kg or morphine 4, 8 and 12 mg/kg revealed a significant increase in the mean of acetylcholine esterase activities. The withdrawal groups of either tramadol or morphine showed significant decreases in their levels. Na+/K+ ATPase activity in the brain cerebral cortex of either repeated therapeutic doses of tramadol (20 mg/kg) or morphine repeated therapeutic doses (4 mg/kg) for 21 consecutive days at different intervals 7, 14 and 21 days, induced a significant decrease in the levels of Na+/K+-ATPase in all groups. Withdrawal groups showed a significant decrease in Na+/K+-ATPase level. Furthermore, the daily intraperitoneal injection of cumulative increasing dose levels of either tramadol (20, 40 and 80 mg/kg b.w.) or morphine (4, 8 and12 mg/kg b.w.) induced significant decreases in Na+/K+-ATPase levels in all studied groups. Regarding Na+ and K+, concentrations of either repeated therapeutic doses or cumulative increasing doses at different time intervals, showed different fluctuations in their levels. 

Conclusion: The recorded data suggest that both drugs exert potent effects on AChE and Na+/K+-ATPase activities which could contribute to cerebral cortex malfunction including, memory deficits and the decline in cognitive function observed in chronic users.


Keywords: Morphine, Tramadol, Acetylcholine esterase (AChE), Na+/ K+-ATPase
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