3H-aniracetam binds to specific recognition sites in brain membranes

[ 3H]Aniracetam bound to specific and saturable recognition sites in membranes prepared from discrete regions of rat brain . In crude membrane preparation from rat cerebral cortex, specific binding was Na+independent, was still largely detectable at low temperature(4°C), and underwent rapid dissociation . Scatchard analysis of [ 3H]aniracetam binding revealed a single population of sites with an apparent Kp value of -70 nM and a maximal density of 3 .5 pmol/mg of protein . Specifically bound [ 3H]aniracetam was not displaced by various metabolites of aniracetam, nor by other pyrrolidinone-containing nootropic drugs such as piracetam or oxiracetam. Subcellular distribution studies showed that a high percentage of specific [ 3H]aniracetam binding was present in purified synaptosomes or mitochondria, whereas specific binding was low in the myelin fraction . The possibility that at least some [ 3H]aniracetam binding sites are associated with glutamate receptors is supported by the evidence that specific binding was abolished when membranes were preincubated at 37°C under fast shaking (a procedure that substantially reduced the amount of glutamate trapped in the membranes) and could be restored after addition of either glutamate or alfa-amino-3-hydroxy- 5-methyl-4-isoxazolepropionate (AMPA) but not kainate . The action of AMPA was antagonized by DNQX, which also reduced specific [ 3H]aniracetam binding in unwashed membranes. High levels of [ 3H]aniracetam binding were detected in hippocampal, cortical, or cerebellar membranes, which contain a high density of excitatory amino acid receptors . Although synaptosomal aniracetam binding sites may well be associated with AMPAsensitive glutamate receptors, specifically bound [H]- aniracetam could not be displaced by cyclothiazide or GYKI 52466, which act as a positive and negative modulator of AMPA receptors, respectively .