Journal zyxwvutsrqponmlk of Neurochemistry zyxwvutsrqpon Raven Press, Ltd., New York zyxwvutsrqp 0 I992 International Society for Neurochemistry Nootropic Drugs Positively Modulate a-Amino-3-Hydroxy- 5-Methyl-4-Isoxazolepropionic Acid-Sensitive Glutamate Receptors in Neuronal Cultures A. Copani, A. A. Genazzani, G. Aleppo, G. Casabona, *P. L. Canonico, U. Scapagnini, and F. Nicoletti Institute zyxwvutsrqp of Pharmacology, University of Catania School of Medicine, Catania; and *Chair of Pharmacology. University of Pavia School of Dentistry, Pavia. Italy Abstract: Micromolar concentrations of piracetam, anira- cetam, and oxiracetam enhanced a-amino-3-hydroxy-5- zyxwvu methyl-4-isoxazolepropionic acid (AMPA)-stimulated 4sCaZ+ influx in primary cultures of cerebellar granule cells. Noo- tropic drugs increased the efficacy but not the potency of AMPA and their action persisted in the presence of the volt- age-sensitive calcium channel blocker nifedipine. Potentiation by oxiracetam was specific for AMPA receptor-mediated sig- nal transduction, as the drug changed neither the stimulation of 45CaZ+ influx by kainate or N-methyl-D-aspartate nor the activation of inositol phospholipid hydrolysis elicited by quisqualate or zyxwvutsrq (+)- 1 -aminocyclopentane-trans- 1,3-dicar- boxylic acid. Piracetam, aniracetam, and oxiracetam in- The nootropic agents piracetam, aniracetam, and oxiracetam are widely used for the treatment of im- paired cognitive functions, including various forms of dementia and mental disorders associated with alco- holism (Giurgea, 1982; Branconnier et al., 1983; Vil- lardita et al., 1986). The mechanism underlying the clinical efficacy of piracetam and its derivatives is un- known. Repeated injections of piracetam or oxiracetam to aged rats increase acetylcholinesynthesis and release, and restore the number and function of muscarinic receptors (Pedata et al., 1984; Mueller, 1988). However, cholinergic transmission is not a primary target for the action of nootropic drugs, as piracetam and its deriv- atives are inactive on [3H]quinuclidinylbenzilate bind- ing as well as on other markers of cholinergic trans- mission when applied in vitro to brain slices or mem- brane preparations (Bering and Muller, 1985). creased the maximal density of the specific binding sites for [3H]AMPA in synaptic membranes from rat cerebral cortex. Taken collectively, these results support the view that noo- tropic drugs act as positive modulators of AMPA-sensitive glutamate receptors in neurons. Key Words: Nootropic drugs-Oxiracetam-Piracetam-Aniracetam-a-Amino-3- hydroxy-5-methyl-4-isoxazolepropionic a~id-'~Ca'+ in- flux-cw-[3H]amino-3-hydroxy-5-methyl-4-isoxazolepro- pionic acid binding. Copani A. et al. Nootropic drugs posi- tively modulate cw-amino-3-hydroxy-5-methyl-4-isoxazole- propionic acid-sensitive glutamate receptors in neuronal cul- tures. J. Neurochem. 58, 1199-1204 (1992). Recently, Ito et al. (1990) have found that anirace- tam increases current responses to quisqualate or a- amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) in amphibian oocytes injected with rat brain mRNA, as well as in rat hippocampal CAI neurons. We now report that nootropic drugs positively mod- ulate AMPA receptors in cultured neurons and increase specific [3H]AMPA binding in crude synaptic mem- branes from rat brain. MATERIALS AND METHODS Measurement of 45CaZ+ influx, inositol phospholipid hydrolysis, and b[3H]aspartate release in cultured neurons Primary cultures of cerebellar granule cells were prepared from 8-day-old rats, as described previously by Nicoletti et ~ ~~ ~ ~ Received March 5, 199 zyxwvutsr 1 ; revised manuscript received June 23, Address correspondence and reprint requests to Dr. F. Nicoletti 1,3-dicarboxylicacid; AMPA, a-amino-3-hydroxy-5-methyl-4-isox- 1991; accepted July 31, 1991. azolepropionicacid; CNQX, 6-cyano-7-nitroquinoxaline-2,3-dione; Con A, concanavalin A; InsP, inositol monophosphate; LTP, long- at Institute of Pharmacology, University of Catania, Viale A. Doria, term potentiation; MK-801, (+)-5-methyI-lO,ll-dihydro-5H-di- 6,95125, Catania, Italy. benzo[a,d]cyclohepten-5,1O-imine maleate; NMDA, N-methyl-D- Abbreviations zyxwvutsrqp used: trans-ACPD, (+>l-aminocyclopentane-trans- aspartate. I199