Administration of nicotine and/or smoking has been shown to have important effects on gastric function. Evidence of others and our own data strongly indicate that these effects are due to nicotine acting on neuronal nicotinic acetylcholine receptors (nAChRs) in the dorsal motor nucleus of the vagus (DMV) and medial subnucleus of the tractus solitarius (mNTS). The goals of our proposed studies are to: (i) investigate the influence of DMV and mNTS nAChRs in the effects of systemically administered nicotine on gastric function and (ii) to use DMV and mNTS nAChRs as model systems to learn more about native CNS nicotinic receptors, their nature, their function and their regulation.
The Specific Aims of our research are to: (i) determine the subunit composition of nAChRs in the rat DMV and mNTS that mediate the effects of nicotine on gastric tone and motility; (ii) examine regulation of the function and density of nAChRs in rat DMV and mNTS after chronic administration of nAChR-stimulating doses of nicotine, and the agonist-induced responsiveness of nAChRs in the DMV and mNTS after acute exposure to sub-activating doses of nicotine; and (iii) test the hypothesis that nAChRs observed to exist in the DMV and mNTS as revealed by pursuing Specific Aims 1 & 2 play an important role in the gastric effects (DMV and mNTS) and cardiovascular effects (mNTS) of systemically administered nicotine. To achieve these Specific Aims, a focused but multidisciplinary approach will be used consisting of the following techniques: (i) pharmacological tools applied either in vivo by microinjection of drugs into the DMV and mNTS of anesthetized rats while monitoring gastric tone and motility, or in vitro to rat brain slice preparations containing the DMV and mNTS while monitoring electrophysiological events using the whole-cell patch-clamp recording method; (ii) in vitro autoradiography taking advantage of the high affinity epibatidine binding to nAChRs combined with selective denervation of efferent and afferent vagal fibers; (iii) immunofluorescent identification of nAChR subtypes in DMV and mNTS neurons; (v) fluorescent in situ hybridization technique to identify nAChR subunits associated with DMV neurons projecting to the fundus and antrum, (vi) knockout mice, in which one gene of interest is silenced, and the contribution of a particular nAChR subunit (e.g., a7 subunit) in eliciting a specific gastric response can be assessed. Findings made to date suggest that: (I) there are five different nAChRs in the DMV and mNTS that influence gastric function; (ii) there might be a viscerotopic organization of nAChR subunits on DMV motoneurons. That is a7 containing nAChRs might be located primarily on DMV neurons projecting to the fundus but not on DMV neurons projecting to the antrum; and (iii) iv. administered nicotine might act in the mNTS on a ct4B2-nAChR subtype to inhibit tonic contraction of the fundus. These and future data obtained from pursuing our Specific Aims will extend current understanding of the different receptor mediated effects of nicotine on parasympathetic nervous system control of the upper GI tract.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK056920-05
Application #
7049583
Study Section
Special Emphasis Panel (ZRG1-MDCN-5 (01))
Program Officer
May, Michael K
Project Start
2002-04-01
Project End
2008-03-31
Budget Start
2006-04-01
Budget End
2008-03-31
Support Year
5
Fiscal Year
2006
Total Cost
$230,849
Indirect Cost
Name
Georgetown University
Department
Pharmacology
Type
Schools of Medicine
DUNS #
049515844
City
Washington
State
DC
Country
United States
Zip Code
20057
Herman, Melissa A; Cruz, Maureen T; Sahibzada, Niaz et al. (2009) GABA signaling in the nucleus tractus solitarius sets the level of activity in dorsal motor nucleus of the vagus cholinergic neurons in the vagovagal circuit. Am J Physiol Gastrointest Liver Physiol 296:G101-11
Herman, Melissa A; Niedringhaus, Mark; Alayan, Alisa et al. (2008) Characterization of noradrenergic transmission at the dorsal motor nucleus of the vagus involved in reflex control of fundus tone. Am J Physiol Regul Integr Comp Physiol 294:R720-9
Pearson, Rebecca J; Gatti, Philip J; Sahibzada, Niaz et al. (2007) Ultrastructural evidence for selective noradrenergic innervation of CNS vagal projections to the fundus of the rat. Auton Neurosci 136:31-42
Cruz, Maureen T; Murphy, Erin C; Sahibzada, Niaz et al. (2007) A reevaluation of the effects of stimulation of the dorsal motor nucleus of the vagus on gastric motility in the rat. Am J Physiol Regul Integr Comp Physiol 292:R291-307
Nguyen, Henry N; Rasmussen, Bruce A; Perry, David C (2004) Binding and functional activity of nicotinic cholinergic receptors in selected rat brain regions are increased following long-term but not short-term nicotine treatment. J Neurochem 90:40-9
Tosaka, Toshimasa; Casimiro, Mathew C; Rong, Qi et al. (2003) Nicotine induces a long QT phenotype in Kcnq1-deficient mouse hearts. J Pharmacol Exp Ther 306:980-7
Nguyen, Henry N; Rasmussen, Bruce A; Perry, David C (2003) Subtype-selective up-regulation by chronic nicotine of high-affinity nicotinic receptors in rat brain demonstrated by receptor autoradiography. J Pharmacol Exp Ther 307:1090-7
Sahibzada, Niaz; Ferreira Jr, Manuel; Williams, Bernice et al. (2002) Nicotinic ACh receptor subtypes on gastrointestinally projecting neurones in the dorsal motor vagal nucleus of the rat. J Physiol 545:1007-16
Quesenberry, P; Habibian, M; Dooner, M et al. (1998) Chiaroscuro hematopoietic stem cell. Trans Am Clin Climatol Assoc 109:19-25;discussion 25-6