dizocilpine-maleate and 1-2-3-4-tetrahydroisoquinoline

1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), unlike several other tetrahydroisoquinolines, displays neuroprotective properties. To elucidate this action we compared the effects of 1MeTIQ with 1,2,3,4-tetrahydroisoquinoline (TIQ), a compound sharing many activities with 1MeTIQ (among them reducing free radicals formed during dopamine catabolism), but offering no clear neuroprotection. We found that the compounds similarly inhibit free-radical generation in an abiotic system, as well as indices of neurotoxicity (caspase-3 activity and lactate dehydrogenase release) induced by glutamate in mouse embryonic primary cell cultures (a preparation resistant to NMDA toxicity). However, in granular cell cultures obtained from 7-day-old rats, 1MeTIQ prevented the glutamate-induced cell death and 45Ca2+ influx, whereas TIQ did not. This suggested a specific action of 1MeTIQ on NMDA receptors, which was confirmed by the inhibition of [3H]MK-801 binding by 1MeTIQ. Finally, we demonstrated in an in vivo microdialysis experiment that 1MeTIQ prevents kainate-induced release of excitatory amino acids from the rat frontal cortex. Our results indicate that 1MeTIQ, in contrast to TIQ, offers a unique and complex mechanism of neuroprotection in which antagonism to the glutamatergic system may play a very important role. The results suggest the potential of 1MeTIQ as a therapeutic agent in various neurodegenarative illnesses of the central nervous system.

Topics: Analysis of Variance; Animals; Animals, Newborn; Calcium Isotopes; Caspase 3; Caspases; Cells, Cultured; Cerebellum; Dizocilpine Maleate; Dopamine; Dose-Response Relationship, Drug; Drug Interactions; Embryo, Mammalian; Free Radical Scavengers; Glutamic Acid; Glycine; L-Lactate Dehydrogenase; Male; Mice; Microdialysis; Neocortex; Neurons; Neuroprotective Agents; Protein Binding; Rats; Rats, Wistar; Tetrahydroisoquinolines; Time Factors