RESUMO
The effects of chronic administration of MK-801 (NMDA-receptor antagonist) and remacemide (sodium channel blocker) on monkey learning of several brain function tasks was assessed in juveniles (nine months old). Low (LO) and high (HI) doses of both drugs were given orally each day for 18 months. There were no adverse effects of any treatment on tests of short-term memory or motivation. HI doses of both MK-801 and remacemide delayed acquisition of a visual discrimination task (the remacemide effect was much greater). HI doses of remacemide alone severely disrupted learning task acquisition and this effect lasted for several months after dosing. Thus, in monkeys, chronic blockade of NMDA receptors is relatively well tolerated, whereas blockade of sodium channels (perhaps in conjunction with NMDA receptor blockade) has long-term-perhaps permanent-consequences. To further explore the roles of NMDA receptors and sodium channels in these effects, MK-801, phenytoin (sodium channel blocker), or both were administered to rats and the acquisition of tasks similar to those used in the monkey study were assessed. Dosing began at weaning and continued for nine months. Throughout the study, HI MK-801 subjects exhibited impaired performance in all tasks. Some effects of MK-801 were blocked completely by phenytoin. In the rat, blockade of sodium channels was well tolerated but blockade of NMDA receptors had significant and long-term (permanent?) adverse consequences. These data contrast markedly with those obtained for the monkey and suggest, at least for some drug classes, that the rat might not be a good predictor of effects in primates.
Assuntos
Acetamidas/farmacologia , Encéfalo/efeitos dos fármacos , Cognição/efeitos dos fármacos , Maleato de Dizocilpina/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Fármacos Neuroprotetores/farmacologia , Bloqueadores dos Canais de Sódio/farmacologia , Acetamidas/administração & dosagem , Animais , Encéfalo/crescimento & desenvolvimento , Antagonistas de Aminoácidos Excitatórios/administração & dosagem , Haplorrinos , Humanos , Aprendizagem/efeitos dos fármacos , Fármacos Neuroprotetores/administração & dosagem , Testes Neuropsicológicos , Ratos , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , Receptores de N-Metil-D-Aspartato/metabolismo , Bloqueadores dos Canais de Sódio/administração & dosagemRESUMO
The article highlighted in this issue is "Dizocilpine Improves Beneficial Effects of Cholinergic Antagonists in Anticholinesterase-Treated Mice," by Andrzej Dekundy, Rafal M. Kaminski, and Waldemar A. Turski (pp. 289-295). It explores the relationship between cholinergic and N-methyl-D-aspartate (NMDA) receptors as mediators of anticholinesterase toxicity. The following review summarizes these findings and discusses their broader implications for central nervous system pharmacology. Alzheimer's disease is discussed as an example of how knowledge of the interactions between NMDA and cholinergic receptors may lead to a better understanding of human disease.