Evidence for GABAA receptor-mediated inhibition in ambiguous motoneurons.

Laryngeal motoneurons in the nucleus ambiguus were activated antidromically to ipsilateral recurrent nerve stimulation in urethane-chloralose anaesthetized rats. GABAA agonist muscimol and the antagonist bicuculline were applied separately or together with GABA iontophoretically with a multibarrel pipette glued with a recording electrode. The majority of neurons (119/155) which did not respond to the recurrent nerve stimulation exhibited activities mostly related to inspiration. Other 32 neurons were classified as laryngeal motoneurons, according to the criteria. Bicuculline application antagonized GABAA-mediated inhibition while muscimol or GABA reversed this effect significantly. Dose dependent changes were observed for administration of these GABAA-related agents. It can be concluded therefore that laryngeal motoneurons received GABAA-mediated inhibition.