<正> Experiments were performed on 19 vagotomized

curareparalyzed andartificially ventilated rabbits.3-5 barrel glass micropipettes were used torecord the extracellular discharges and to apply the ionized substances tested.Medullary respiratory units located in the region of Nucleus Treactus Soli-tarius were tested for their responsiveness to iontophoretically appliedGABA.GABA tended to inhibit not only inspiratory units but also expi-ratory ones.Of 60 units tested

49 were inhibited and the inhibitoryeffect of GABA had much to do with its quantity ejected.Phrenic nervedischarges were unchanged while the discharges of respiratory units weredepressed by GABA.The inhibitory effect of GABA could be blocked bypicrotoxin.Our results indicate that GABA may be one of the importantinhibitory neurotransmitters in the medullary“respiratory center”.