The Effect of the Acetylcholine Esterase Inhibitor, Eserine, on ERK Phosphorylation in Area CA1 of Rat Hippocampus

Carol Harden; Lori McMahon, Ph.D.; and Krystyna Kolasa, Ph.D. University of Alabama at Birmingham, Birmingham, AL

CarolHardenABRCMS

Cholinergic and adrenergic innervation are critical for normal hippocampal dependent learning and memory processing. It is known that hippocampal signaling from cholinergic and adrenergic innervation degenerates in aging and Alzheimer’s disease (AD), causing memory deficits in affected patients. These cholinergic and adrenergic mechanisms are targets for the pharmacological treatment of AD. One of many drugs used for the treatment of neurodegenerative diseases, such as Alzheimer’s diseases, is eserine. Eserine is an acetylcholine esterase inhibitor, preventing the hydrolysis of acetylcholine by acetylcholine esterase. This inhibition enhances the activity of acetylcholine on acetylcholine muscarinic receptors, making it useful in the treatment of cholinergic disorders. M1 and M3 are the most abundant G protein coupled muscarinic acetylcholine receptors in both rat and human hippocampus. A signaling molecule downstream of these G- coupled receptors is the mitogen activated kinase, ERK. Phosphorylation of ERK is essential for enhancing synaptic function, which determines the ability of the hippocampus to acquire and retain new memories. After ten minute incubation with carbachol (50µM), a muscarinic receptor agonist, we were able to detect two isoforms (42kDa and 44kDa) of phosphorylated ERK (pERK) from 20µg of protein per 25µl of rat CA1 homogenate with Western blot analysis. The increase in pERK levels were normalized to total ERK to confirm carbachol’s agonistics abilities resulting in a 30 percent increase from basal levels. In this study, we hypothesize that eserine will also increase ERK phosphorylation, by allowing endogenous acetylcholine to accumulate in the hippocampus thereby activating M1 muscarinic receptors and increasing levels of pERK. In conclusion, we expect eserine’s effect on pERK to mimic that of carbachol, and this increase in pERK will be an important factor for improving memory and learning in hippocampal cholinergic degeneration, as observed in AD.