DIFFERENTIAL BRAIN-STEM FOS-LIKE IMMUNOREACTIVITY AFTER LARYNGEAL-INDUCED COUGHING AND ITS REDUCTION BY CODEINE

We used the expression of the immediate-early gene c-fos, a marker of neuronal activation, to localize brainstem neuronal populations functi onally related to fictive cough (FC). In decerebrate, paralyzed, and v entilated cats, the level of Fos-like immunoreactivity (FLI) was exami ned in five groups of animals: (1) controls, sham-operated unstimulate d animals; (2) coughing cats, including both animals in which FC was e licited by unilateral electrical stimulation of the superior laryngeal nerve (SLN) and (3) those in which FC was elicited by bilateral SLN s timulation; (4) stimulated-treated cats, in which bilateral SLN stimul ation was applied after selective blockade of FC by codeine; and (5) c odeine controls, sham-operated unstimulated cats subjected to administ ration of codeine. Fifteen brainstem structures were compared for numb ers of labeled cells. Because codeine selectively blocks FC, brainstem nuclei activated specifically during FC were identified as regions sh owing increased FLI after FC and significant reductions in FLI after F C suppression by codeine in stimulated-treated cats. In coughing anima ls, we observed a selective immunoreactivity in the interstitial and v entrolateral subdivisions of the nucleus of the tractus solitarius, th e medial part of the lateral tegmental field, the internal division of the lateral reticular nucleus, the nucleus retroambiguus, the para-am bigual region, the retrofacial nucleus, and the medial parabrachial nu cleus. FLI in all these nuclei was significantly reduced in stimulated -treated cats. Our results are consistent with the involvement of neur ons overlapping the main brainstem respiratory-related regions as well as the lateral tegmental field and the lateral reticular nucleus in t he neural processing of laryngeal-induced FC.