Modulation of Cough Reflex by Gaba-Ergic Inhibition in Medullary Raphé of the Cat

Abstract

We studied the effects of GABA receptor agonists microinjections in medullary raphé on the mechanically induced tracheobronchial cough response in anesthetized, unparalyzed, spontaneously breathing cats. The results suggest that GABA-ergic inhibition significantly contributes to the regulation of cough reflex by action of both GABAA and GABAB receptors. The data are consistent with inhomogeneous occurrence of GABA-ergic neurons in medullary raphé and their different involvement in the cough reflex control. Cells within rostral nucleus raphé obscurus with dominant role of GABAA receptors and neurons of rostral nucleus raphé pallidus and caudal nucleus raphé magnus with dominant role of GABAB receptors participate in regulation of cough expiratory efforts. These cough control elements are distinct from cough gating mechanism. GABA-ergic inhibition in the raphé caudal to obex had insignificant effect on cough. Contradictory findings for GABA, muscimol and baclofen administration in medullary raphé suggest involvement of coordinated activity of GABA on multiple receptors affecting raphé neurons and/or the local neuronal circuits in the raphé modulating cough motor drive.