Respiratory Physiology & Neurobiology 141 (2004) 21–34 Expression of -7 nAChRs on spinal cord–brainstem neurons controlling inspiratory drive to the diaphragm Ozra Dehkordi a,b,∗ , Musa A. Haxhiu b,c , Richard M. Millis b , Gary C. Dennis a , Prabha Kc b , Anjum Jafri b , Mehran Khajavi b , C. Ovid Trouth b , Syed I. Zaidi b a Department of Surgery, Howard University Hospital, Washington, DC 20060, USA b Specialized Neuroscience Research Program, Department of Physiology & Biophysics, Howard University College of Medicine, 520 “W” St. N.W., Washington, DC 20059, USA c Department of Pediatrics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA Accepted 10 March 2004 Abstract In the present study, we determined whether -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. -7 Immunohisto- chemistry combined with cholera toxin B (CTB), a retrograde tracer was used to detect expression of -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 -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 -7 nAChR immunoreactivity. Of the peudorabies virus (PRV) labeled bulbospinal neurons in PMn, Gi, raphe and RVLM, 9–12% co-expressed -7 nAChRs. Immunoreactivity for -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. © 2004 Elsevier B.V. All rights reserved. Keywords: Brainstem; Pre-Botzinger complex; Control of breathing; Central; Mammals; Rat; Receptor; Nicotinic; ACh; Receptor; NK1 1. Introduction The role of nicotinic mechanisms in the control of breathing has been demonstrated by the stimulation of ventilation associated with administration of nicotine at the ventral surface of the medulla oblongata (VLM) ∗ Corresponding author. Tel.: +1-202-865-1978; fax: +1-202-865-1977. E-mail address: odehkordi@howard.edu (O. Dehkordi). (Mitchell et al., 1963). Injection of nicotine into the lateral ventricles or at the VLM also increases phrenic and hypoglossal nerve activities and stimulates the res- piratory muscles they innervate (Haxhiu et al., 1984). Microinjection of nicotine into the pre-Botzinger com- plex (pre-BotC), the putative site of respiratory rhythm generation, has been found to modulate the respiratory frequency and amplitude of inspiratory bursting (Shao and Feldman, 2001). Although these findings suggest a role for nicotinic mechanisms in the central control 1569-9048/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.resp.2004.03.006