Abstract
Nicotine is a major cough‐promoting component of cigarette smoke due to its excitatory effects on pulmonary afferents. There is no information on the central actions of nicotine on the cough reflex. We speculated that central administration of nicotine would enhance cough. Electromyograms (EMG) of parasternal and transversus abdominis (TA) muscles were recorded in anesthetized spontaneously breathing cats. Repetitive coughing was elicited by mechanical stimulation of the intrathoracic trachea. (−) Nicotine (0.1–30 μg/kg) was administered via the vertebral artery and significantly reduced cough number and TA EMG in a dose‐dependent manner. (+) Nicotine (0.1–30 μg/kg, ia) also inhibited cough in a dose‐dependent manner but was approximately 30 fold less potent than the (−) isomer. In a separate group of animals, (−) nicotine (38±6 nL, 1.6 mM, 63±10 picomole) was unilaterally microinjected into the expiratory region of the caudal ventral respiratory column (cVRC). Microinjection of nicotine into the cVRC significantly reduced cough number and TA EMG amplitude during cough. The results support stereo‐selective inhibition of cough by nicotine at one or more brainstem sites. The effects of systemic administration of nicotine on the cough reflex may represent a complex balance between peripheral excitatory and central inhibitory actions. Supported by James and Esther King Biomedical Research grant 06TSP‐01.
Published Version
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