A study of amino acid-activated currents recorded from frog motoneurones in vitro.

Superfusion of the excitatory amino acids glutamate (1-2 mM), quisqualate (15-30 microM) and N-methyl-D-aspartate (NMDA: 15-30 microM) induced inward currents in voltage-clamped motoneurones, in vitro. Typically the NMDA and quisqualate currents had prolonged time courses relative to glutamate currents. No desensitization was apparent during repeated agonist application. D-2-Amino-5-phosphonovalerate (10 microM) selectively antagonized the NMDA current without affecting the quisqualate current; the glutamate current was partially reduced reflecting its mixed agonist properties.