NOOTROPIC DRUGS POSITIVELY MODULATE ALPHA-AMINO-3-HYDROXY-5-METHYL-4-ISOXAZOLEPROPIONIC ACID-SENSITIVE GLUTAMATE RECEPTORS IN NEURONAL CULTURES

Micromolar concentrations of piracetam, aniracetam, and oxiracetam enhanced alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-stimulated Ca-45(2+) influx in primary cultures of cerebellar granule cells. Nootropic drugs increased the efficacy but not the potency of AMPA and their action persisted in the presence of the voltage-sensitive calcium channel blocker nifedipine. Potentiation by oxiracetam was specific for AMPA receptor-mediated signal transduction, as the drug changed neither the stimulation of Ca-45(2+) influx by kainate or N-methyl-D-aspartate nor the activation of inositol phospholipid hydrolysis elicited by quisqualate or (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid. Piracetam, aniracetam, and oxiracetam increased the maximal density of the specific binding sites for [H-3]AMPA in synaptic membranes from rat cerebral cortex. Taken collectively, these results support the view that nootropic drugs act as positive modulators of AMPA-sensitive glutamate receptors in neurons.