Chronotropic and Dromotropic Responses to Localized Glutamate Microinjections in the Rat $ Nucleus Ambiguus
brain research 1542 (2014) 93–103 Available online at www.sciencedirect.com www.elsevier.com/locate/brainres Research Report Chronotropic and dromotropic responses to localized glutamate microinjections in the rat $ nucleus ambiguus Karla N. Sampaio1,He´lder Mauad2, K. Michael Spyer, Timothy W. Fordn Division of Biosciences, Faculty of Life Sciences, University College London, Gower Street, London WC1E 6BT, UK article info abstract Article history: The cardioinhibitory effects of cardiac vagal motoneurons (CVMs) are mediated by Accepted 18 October 2013 activation of postganglionic neurons in the epicardial ganglia which have been shown to Available online 24 October 2013 exert functionally selective effects on heart rate and atrioventricular conduction in the rat. Here we investigate whether CVMs producing these responses may occupy different Keywords: rostrocaudal positions within the nucleus ambiguus. Excitation of CVMs was attempted Autonomic nervous system by microinjections of glutamate into the nucleus ambiguus of an arterially perfused Vagus nerve preparation in a grid extending over 2 mm in the rostrocaudal plane using the obex as a Nucleus ambiguus reference point. Microinjections were paired, one made during pacing to measure changes Heart rate in atrioventricular conduction (P-R interval) independent of changes in heart rate and the Glutamate other looking for changes in heart period (P-P interval) un-paced. Although evidence of a differential distribution was found in 7 cases, in the majority (13/20), sites producing maximal effects on both variables coincided. Maximal changes in atrioventricular conduc- tion resulted from more rostral sites in 6 cases and from a more caudal site in only one. Overall, the ratio of the change in atrioventricular conduction to the change in heart rate for a given site was significantly greater 1 mm rostral to the obex than at either end of the test grid.
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