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NEUROREGULATION AND MOTILITY

Norepinephrine effects on identified neurons of the rat dorsal motor nucleus of the vagus

¹Department of Internal Medicine-Gastroenterology, and ³Department of Physiology, University of Michigan, Ann Arbor, Michigan 48109; and ²Laboratory of Autonomic Neuroscience, Pennington Biomedical Research Center, Baton Rouge, Louisiana 70808

Submitted 9 July 2003 ; accepted in final form 19 August 2003

The dorsal motor nucleus of the vagus (DMV) receives more noradrenergic terminals than any other medullary nucleus; few studies, however, have examined the effects of norepinephrine (NE) on DMV neurons. Using whole cell recordings in thin slices, we determined the effects of NE on identified gastric-projecting DMV neurons. Twenty-five percent of DMV neurons were unresponsive to NE, whereas the remaining 75% responded to NE with either an excitation (49%), an inhibition (26%), or an inhibition followed by an excitation (4%). Antrum/pylorus- and corpus-projecting neurons responded to NE with a similar percentage of excitatory (49 and 59%, respectively) and inhibitory (20% for both groups) responses. A lower percentage of excitatory (37%) and a higher percentage of inhibitory (36%) responses were, however, observed in fundus-projecting neurons. In all groups, pretreatment with prazosin or phenylephrine antagonized or mimicked the NE-induced excitation, respectively. Pretreatment with yohimbine or UK-14304 antagonized or mimicked the NE-induced inhibition, respectively. These data suggest that NE depolarization is mediated by ₁-adrenoceptors, whereas NE hyperpolarization is mediated by ₂-adrenoceptors. In 16 neurons depolarized by NE, amplitude of the action potential afterhyperpolarization (AHP) and its kinetics of decay () were significantly reduced vs. control. No differences were found on the amplitude and of AHP in neurons hyperpolarized by NE. Using immunohistochemical techniques, we found that the distribution of tyrosine hydroxylase fibers within the DMV was significantly different within the mediolateral extent of DMV; however, distribution of cells responding to NE did not show a specific pattern of localization.

brain stem; electrophysiology; gastrointestinal-receptive relaxation

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