ROLE OF GABA(B) RECEPTORS IN THE CONTROL OF HYPOGLOSSAL MOTONEURONS IN-VIVO

THERE is little information on GABA(B) receptor-mediated effects on or ofacial motoneurons. We recorded the inspiratory activity from both hy poglossal (XII) nerves in urethane-anesthetized, paralyzed, vagotomize d and artificially ventilated rats. A GABA(B) receptor agonist, baclof en, or antagonist, CGP-35348, was microinjected into one XII nucleus. Baclofen rapidly reduced the XII nerve activity in a dose-dependent ma nner by over 50%. The antagonist caused a delayed suppression of activ ity by 40%. We conclude that: (1) GABA(B) receptors within the XII nuc leus may suppress the activity of inspiratory XII motoneurons, but the y are not tonically active under the conditions of our experiment; (2) there is a net endogenous excitatory effect in XII motoneurons that i s mediated by GABA(B) receptors located in the reticular formation sur rounding the XII nucleus.