Methylene blue (MB) is currently used to treat methemoglobinemia, a blood disorder.
But because high concentrations of methylene blue were known to damage the brain,
no one thought to experiment with low concentrations. The study aimed to evaluate
the possible protective effect of methylene blue against scopolamine induced- amnesia
in adult rats. Methylene blue (2 and 5mg/kg, i.p.) was administered separately or
concurrently with scopolamine administration (1mg/kg, i.p). Results showed that
scopolamine induced amnesia in passive avoidance task, increased the catalytic
activity of total cholinesterase and decreased content of acetylcholine depressed the
level of reduced glutathione (GSH) and total antioxidant activity in the hippocampus
and brain cortex. Methylene blue dose-dependently inhibited the enzymatic activity of
total cholinesterase and increased the acetylcholine content, increased GSH content
and total antioxidant activity in the hippocampus and brain cortex. Concurrent
treatment of MB dose-dependently minimized both amnesic and anti-cholinergic
effect of scopolamine. The study indicated that MB could protect against the
scopolamine effects at low doses through its enhancing effect on cholinergic
pathways and anti-oxidative activities. Methylene blue with its neuroprotective effects
and could thus act as disease modifiers in patients, slowing the progression of
behavioral deterioration since acetylcholinesterases themselves could contribute to
the degenerative process.