Effects of gamma-aminobutyric acid on the Hering-Breuer inspiration-inhibiting reflex.

Acute experiments on rats were performed to study the effects of intraventricular microinjections of gamma-aminobutyric acid (GABA) on the volume-time parameters of external respiration and the inspiration-inhibiting Hering-Breuer reflex. The state of this reflex before and after GABA administration was assessed in terms of the extent of changes in the duration and amplitude of inspiratory oscillations in intrathoracic pressure in response to end-expiratory occlusion of the trachea. Administration of 20 microM GABA into the lateral ventricles of the brain decreased the minute ventilation (due to reductions in the respiratory frequency and respiratory volume), weakened respiratory muscle contractions, and decreased the peak airflow rate on inspiration and expiration. The response to end-expiratory occlusion decreased significantly after administration of GABA, demonstrating the involvement of GABAergic mechanisms in mediating the inspiration-inhibiting Hering-Breuer reflex.