Biphasic effect of quinolinate on frog spinal, but not rat cortical, neurones: [formula omitted] depolarisation and a novel type of hyperpolarisation

Abstract

Using grease seal techniques on rat cerebral cortical slices and on frog hemisected spinal cords, bath applied N- methyl- d-aspartate (NMDA; 10–160 μM) and quinolinate (0.25–8 mM) induced dose-dependent depolarisations. These depolarising responses, but not those to quisqualate or kainate, were reduced by 2-amino-5-phosphono-valerate (2-AP5; 10–100 μM), magnesium (0.1–10 mM) and ketamine (10–100 μM). A novel dose-dependent hyperpolarising response to quinolinate (0.1–2 mM) but not to NMDA was observed only on frog motoneurones, and this was not reduced by classical amino acid receptor antagonists.