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 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 GABA(A) and GABA(B) 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 raphéobscurus with dominant role of GABA(A) receptors and neurons of rostral nucleus raphépallidus and caudal nucleus raphémagnus 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 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.

GABA-ergic neurotransmission in the nucleus of the solitary tract modulates cough in the cat.

GABA, muscimol, and baclofen were microinjected into the rostral (rNTS) and caudal solitary tract nucleus (cNTS) in 24 anesthetized cats. Electromyograms (EMGs) of diaphragm (DIA) and abdominal muscles (ABD), blood pressure and esophageal pressure (EP) were recorded and analysed. Bilateral microinjections of 1 mM GABA (total 66 ±â€¯4 nl), 1 mM baclofen (64 ±â€¯4 nl) and unilateral microinjections of 0.5 mM muscimol (33 ±â€¯1 nl) in the rNTS significantly reduced cough number (CN), amplitudes of ABD EMGs, expiratory EP, and prolonged the duration of the cough inspiratory phase. GABA microinjections decreased the amplitudes of cough-related DIA EMGs and inspiratory EP; muscimol microinjections decreased the cough DIA EMG on the contralateral side. Only microinjections of GABA into the cNTS suppressed CN. In some cases, microinjections prolonged the inspiratory phase, lowered respiratory rate, changed the depth of breathing, and increased blood pressure and heart rate. Our results confirm that GABA-ergic inhibitory mechanisms in the rNTS can regulate coughing in the anesthetized cat.