Nicotine-induced inhibition of neuronal phospholipase A2.

A protective effect of nicotine against glutamate-induced neurotoxicity has previously been reported in cultured striatal and cortical neurons. The aim of this study was to investigate whether nicotine also inhibits glutamate-evoked arachidonic acid release from cultured striatal neurons. (-)-Nicotine selectively inhibited the release of [3H]-arachidonic acid induced by the joint stimulation of alpha-amino-3-isoxazol-5-propionic acid and metabotropic receptors, whereas the response evoked by the sole activation of N-methyl-D-aspartate receptors remained unchanged. The inhibitory effect of (-)-nicotine was not mediated by nicotinic receptors because it was neither reproduced by acetylcholine (in the presence of atropine) or 1,1-dimethyl-4-phenyl piperazinium, nor reversed by dihydro-beta-erythroidine or hexamethonium, two central nicotinic receptor antagonists. (-)-Nicotine, which induced rapidly desensitizing inward currents in 17% of striatal neurons, did not alter the alpha-amino-3-isoxazol-5-propionic acid-evoked currents. Moreover, (-)-nicotine did not inhibit the accumulation of inositol phosphate derivatives induced by agonists of glutamate metabotropic receptors. In fact, using the fluorogenic phospholipase A2 substrate 1,2-bis-(1-pyrenedecanoyl)-sn-glycero-3-phosphocholine, (-)-nicotine was found to inhibit both particulate and soluble phospholipase A2 activities from striatal neurons. Therefore, (-)-nicotine can modulate a neuronal response (arachidonic acid release) evoked by glutamate but this process is not involved in the neuroprotective effect of the drug on glutamate-induced neurotoxicity.