THE ACTIONS OF A RANGE OF EXCITATORY AMINO-ACIDS AT (1S,3R)-1-AMINOCYCLOPENTANE-1,3-DICARBOXYLIC ACID-DEPOLARIZING RECEPTORS ON NEONATAL RAT MOTONEURONS

Depolarizations induced by a range of amino acids including some sulph ur-containing excitatory transmitter candidates were evoked from moton eurones in the neonatal rat spinal cord under conditions that preclude d activation of known ionotropic glutamate receptors. The responses co uld be partially and differentially depressed by continuous applicatio n of several metabotropic glutamate receptor (mGluR) antagonists or by receptor desensitization with the mGluR agonist, (1S,3R)-1-aminocyclo pentane-1,3-dicarboxylic acid [(1S,3R)-ACPD]. In most cases [the excep tions being (1S,3R)-ACPD and to a lesser extent, quisqualate], the maj or component of these depolarizations was resistant to antagonism by p henylglycine-derived mGluR antagonists or desensitization of (1S,3R)-A CPD-sensitive receptors. Of the excitatory responses observed with the tested agonists, those evoked by L-glutamate itself were generally th e least affected by blockade of known glutamate receptors.