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

We studied the effects of GABA receptor agonists microinjections in medullary raphe 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 GABA(A) and GABA(B) receptors. The data are consistent with inhomogeneous occurrence of GABA-ergic neurons in medullary raphe and their different involvement in the cough reflex control. Cells within rostral nucleus rapheobscurus with dominant role of GABA(A) receptors and neurons of rostral nucleus raphepallidus and caudal nucleus raphemagnus with dominant role of GABA(B) receptors participate in regulation of cough expiratory efforts. These cough control elements are distinct from cough gating mechanism. GABA-ergic inhibition in the raphe caudal to obex had insignificant effect on cough. Contradictory findings for GABA, muscimol and baclofen administration in medullary raphe suggest involvement of coordinated activity of GABA on multiple receptors affecting raphe neurons and/or the local neuronal circuits in the raphe modulating cough motor drive.