Contribution of medullary raphé to control of coughing-Codeine trials in cat

In order to determine if a codeine-sensitive control system for cough exists in the medullary raphé four microinjections of codeine (3.3 and 16.5 mM; 36.6 ± 0.7 nl 1.5 and 3 mm rostral to the obex at the depths 1.5 and 3 mm; the total dose 1.12 ± 0.3 nmol, 9 animals) were performed on pentobarbitone anesthetized spontaneously breathing cats. Amplitudes of abdominal muscle EMG moving averages during mechanically induced tracheobronchial cough decreased by 18% compared to control coughs (p < 0.05). The duration between maxima of cough diaphragm and abdominal muscle EMG discharge, cough expiratory phase duration and period of relative motor quiescence between coughs were increased (all p < 0.05). Cough number, other cough parameters, and cardiorespiratory characteristics were not altered significantly. Control microinjections of artificial cerebro-spinal fluid had no effect on coughing. Codeine sensitive neurons involved in the generation or modulation of motor pattern of tracheobronchial cough are located in the medullary midline raphé nuclei; however, their contribution to codeine induced cough suppression is limited.

► New insight in understanding of the role of medullary raphé in cough control. ► Limited contribution of medullary raphé in codeine induced cough suppression. ► Codeine sensitive mechanism in raphé involved in generation of cough motor pattern.