[3H]Aniracetam Binds to Specific Recognition Sites in Brain Membranes |
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Authors: | F Fallarino †A A Genazzani S Silla †M R L'Episcopo ‡O Camici ‡L Corazzi †F Nicoletti M C Fioretti |
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Institution: | Department of Experimental Medicine and Biochemical Sciences, Section of Pharmacology, and; Institute of Biological Chemistry, University of Perugia, Perugia;and; Institute of Pharmacology, University of Catania, Catania, Italy |
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Abstract: | Abstract: 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 KD 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 α-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 AMPA-sensitive glutamate receptors, specifically bound 3H]aniracetam could not be displaced by cyclothiazide or GYKI 52466, which act as a positive and negative modulator of AMPA receptors, respectively. |
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Keywords: | [3H]Aniracetam binding Glutamate GYKI 52466 Cyclothiazide |
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