Galantamine enhancement of long‐term potentiation is mediated by calcium/calmodulin‐dependent protein kinase II and protein kinase C activation

Abstract

Galantamine, a novel Alzheimer's drug, is known to inhibit acetylcholinesterase activity and potentiate nicotinic acetylcholine receptor (nAChR) in the brain. We previously reported that galantamine potentiates the NMDA-induced currents in primary cultured rat cortical neurons. We now studied the effects of galantamine on long-term potentiation (LTP) in the rat hippocampal CA1 regions. The field excitatory postsynaptic potentials (fEPSPs) were induced by stimulation of the Schaffer collateral/commissural pathways in the hippocampal CA1 region. Treatment with 0.01-10 microM galantamine did not affect the slope of fEPSPs in the CA1 region. Galantamine treatment increased calcium/calmodulin-dependent protein kinase II (CaMKII) and protein kinase Calpha (PKCalpha) activities with a bell-shaped dose-response curve peaked at 1 microM, thereby increasing the phosphorylation of AMPA receptor, myristoylated alanine-rich protein kinase C, and NMDA receptor as downstream substrates of CaMKII and/or PKCalpha. By contrast, galatamine treatment did not affect protein kinase A activity. Consistent with the bell-shaped CaMKII and PKCalpha activation, galantamine treatment enhanced LTP in the hippocampal CA1 regions with the same bell-shaped dose-response curve. Furthermore, LTP potentiation induced by galantamine treatment at 1 microM was closely associated with both CaMKII and PKC activation with concomitant increase in phosphorylation of their downstream substrates except for synapsin I. In addition, the enhancement of LTP by galantamine was accompanied with alpha7-type nAChR activation. These results suggest that galantamine potentiates NMDA receptor-dependent LTP through alpha7-type nAChR activation, by which the postsynaptic CaMKII and PKC are activated.