Comparative studies of huperzine A, donepezil, and rivastigmine on brain acetylcholine, dopamine, norepinephrine, and 5-hydroxytryptamine levels in freely-moving rats.
OBJECTIVE
To assess the effects of cholinesterase inhibitors huperzine A, donepezil and rivastigmine on cerebral neurotransmitters in the cortex and hippocampus in freely-moving rats.


METHODS
Double-probe cerebral microdialysis and HPLC with electrochemical detection were used to detect neurotransmitters.


RESULTS
Our results showed that huperzine A (0.25, 0.5, and 0.75 micromol/kg, po) dose-dependently elevated extracellular acetylcholine (ACh) levels in the medial prefrontal cortex (mPFC) and hippocampus. Oral administration of donepezil (5.4 micromol/kg) or rivastigmine (1 micromol/kg) also elicited significant increases in ACh in the mPFC and hippocampus. The time course of cortical acetylcholinesterase (AChE) inhibition with the 3 inhibitors mirrored the increases of ACh at the same dose. The marked elevation of ACh after oral administration of huperzine A (0.5 micromol/kg) and donepezil (5.4 micromol/kg) was associated with a significantly increased release of dopamine (DA) in the mPFC or hippocampus. None of the 3 inhibitors affected norepinephrine (NE) and 5-hydroxytryptamine (5-HT) levels in the mPFC and hippocampus. The effects of huperzine A and rivastigmine did not depend on the route of administration, but donepezil was less efficacious by the oral route than by ip injection. The ability of huperzine A to increase ACh levels was unchanged when tests were performed after multiple oral administration of the drug at 0.5 micromol/kg, once per day for 30 d.


CONCLUSIONS
The present findings showed that, in molar terms, huperzine A had similar potency on increasing mPFC ACh and DA levels as compared to the 11- and 2-fold dosages of donepezil and rivastigmine, respectively, and had longer lasting effects after oral dosing.
Liang
Yan-qi
YQ
State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Instituties for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 201203, China.
Tang
Xi-can
XC
D000109:Acetylcholine / Q000378:metabolism*; D000284:Administration, Oral; D000470:Alkaloids; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002800:Cholinesterase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D000077265:Donepezil; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006624:Hippocampus / Q000378:metabolism; D007189:Indans / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D018696:Neuroprotective Agents / Q000008:administration & dosage / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D048448:Phenylcarbamates / Q000008:administration & dosage / Q000494:pharmacology*; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology*; D017397:Prefrontal Cortex / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D000068836:Rivastigmine; D012701:Serotonin / Q000378:metabolism; D012717:Sesquiterpenes / Q000008:administration & dosage / Q000494:pharmacology*
D000470:Alkaloids; D002800:Cholinesterase Inhibitors; D007189:Indans; D018696:Neuroprotective Agents; D048448:Phenylcarbamates; D010880:Piperidines; D012717:Sesquiterpenes; C050426:huperzine A; D012701:Serotonin; D000077265:Donepezil; D000109:Acetylcholine; D000068836:Rivastigmine; D004298:Dopamine; D009638:Norepinephrine