Effect of GABA applied onto ventral surface of medulla oblongata on respiratory function

Experiments were carried out on 32 rabbits anaesthetized with chloraloseurethane. Cervical vagi, sinus nerves and depressor nerves were cut bilaterally. The ventral surface of the medulla oblongata was exposed. Decreases in tide volume (VT) and frequency (f) were induced dose-dependently by mounting small pieces of filter paper soaked with either 6,12.5, 25, 50, 100 microg GABA or 2 microg GABA-agonist muscimol on the bilateral rostral, intermedial, caudal areas of the ventral surface. Increases in VT and f appeared when filter paper moistened with 25 microg GABA-antagonist picrotoxin was placed on the same three areas. No significant changes in slopes of VT, f-CO2 response curves were seen when 25 microg GABA or 25 microg picrotoxin was applied to the ventral surface. It is suggested that there are GABA receptors on the ventral surface of medulla oblongata in rabbit. Activation of GABA receptors exerts a tonic inhibitory effect on the normal central respiratory activities, but it does not affect the sensitivity of central chemoreceptors to CO2.