Phrenic and iliohypogastric nerve discharges during tussigenic stimulation in paralyzed and decerebrate guinea pigs and rats

Abstract

Although effects of antitussive drugs have been examined in inbred small animals using a whole body plethysmography, neuronal mechanisms underlying the cough reflex are not fully understood. The present study analyzed the reflex discharge patterns of the phrenic (PN) and iliohypogastric nerves (IHN) evoked in decerebrate and paralyzed guinea pigs and rats. In guinea pigs, electrical stimulation of the superior laryngeal nerve, chemical stimulation with capsaicin and mechanical stimulation to the intratracheal mucosa equally produced a serial PN-IHN response. This response was characterized by an increased PN discharge and following spindle-shaped burst of the IHN. The evoked discharges overlapped for 20 ms. In rats, by contrast, mechanical stimulation was without effect while capsaicin and electrical stimulation produced two types of responses, both of which differed from that observed in guinea pigs. The first type consisted of an augmented burst of the IHN that was immediately followed by an increased PN discharge. The second type was a large spindle-shaped burst of the IHN that occurred 80 ms after the end of the preceding PN discharge. Codeine (3 mg/kg i.v.) depressed all types of responses evoked in guinea pigs and rats. The present study demonstrated that the fictive cough comparable with those induced in other experimental animals was produced consistently in guinea pigs, but not in rats. Therefore, guinea pigs are suitable for investigation of the neuronal mechanisms underlying the cough reflex and assessment of antitussive drugs.