Pharmacological studies of facial motoneurones in the rat

Experiments were performed on 39 male albino rats anaesthetized with pentobarbitone sodium and paralyzed with gallamine triethiodide. Facial motoneurones consistently showed a progressive alteration of spike shape and decrease in spike firing frequency during the continuous microelectrophoretic application of the excitant amino acids D,L-homocysteate, L-glutamate, L-aspartate, and kainate, but infrequently during that of N-methyl-D-aspartate. The relative potencies of these excitants on facial motoneurones are reported. The potential usefulness of N-methyl-D-aspartate to produce amino acid-evoked motoneurone action potentials is discussed. The microelectrophoretically-applied depressant amino acid antagonist strychnine selectively and reversibly blocked the depressant effects of glycine on facial motoneurones. The depression of amino acid-induced firing of facial motoneurones by stimuli to the lingual or glossopharyngeal nerves were reversibly antagonized by microelectrophoretically applied strychnine but not by bicuculline.