Expression of alpha-7 nAChRs on spinal cord-brainstem neurons controlling inspiratory drive to the diaphragm

In the present study, we determined whether alpha-7 subunit containing nicotinic acetylcholine receptors (nAChRs) are expressed by neurons within the pre-Botzinger complex (pre-BotC), bulbospinal, and phrenic motor nuclei in the rat. alpha-7 Immunohistochemistry combined with cholera toxin B (CTB), a retrograde tracer was used to detect expression of alpha-7 nAChRs by phrenic motor and bulbospinal neurons. Neurokinin-1 receptor immunoreactivity was used as a marker for pre-BotC neurons. Of the CTB-positive neurons in the phrenic nuclei, 60% exhibited immunoreactivity for alpha-7 nAChRs. Of the bulbospinal neurons in the paramedian reticular nuclei (PMn), gigantocellular nuclei (Gi), raphe nuclei, rostral ventrolateral medulla (RVLM) and nucleus tractus solitarius, 20-50% were found to express alpha-7 nAChR immunoreactivity. Of the peudorabies virus (PRV) labeled bulbospinal neurons in PMn, Gi, raphe and RVLM, 9-12% co-expressed alpha-7 nAChRs. Immunoreactivity for alpha-7 nAChRs was also detected in 57% of the neurokinin-1 receptor containing neurons presumed to reside in pre-BotC. These findings suggest that nicotinic cholinergic regulation of the chest wall pumping muscles may occur at multiple levels of the central nervous system.