Abstract

In the present study, immunohistochemistry combined with retrograde labeling techniques were used to determine if hypoglossal motoneurons (HMNs), retrogradely labeled after cholera toxin B subunit (CTB) injection to the genioglossus muscle in rats, show immunoreactivity for alpha-7 and alpha-4 subunits of nicotinic acetylcholine receptors (nAChRs). CTB-positive HMNs projecting to the genioglossus muscle were consistently labeled throughout the rostrocaudal extent of the hypoglossal nuclei with the greatest labeling at and caudal to area postrema. Alpha-7 subunit immunoreactivity was found in 39.44 ± 5.10% of 870 CTB-labeled motoneurons and the alpha-4 subunit in 51.01 ± 3.71% of 983 CTB-positive neurons. Rostrally, the number of genioglossal motoneurons demonstrating immunoreactivity for the alpha-7 subunit was 45.85 ± 10.04% compared to 34.96 ± 5.11% at and caudal to area postrema (P > 0.1). The number of genioglossal motoneurons that showed immunoreactivity for the alpha-4 subunit was 55.03 ± 4.83% at and caudal to area postrema compared to 42.98 ± 3.90% in rostral areas (P = 0.074). These results demonstrate that nAChR immunoreactivity is present in genioglossal motoneurons and suggest a role for alpha-7 and alpha-4 subunits containing nAChRs in the regulation of upper airway patency.

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