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First published online December 16, 2008
Journal of Experimental Biology 212, 145-151 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.024042

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The unequal influences of the left and right vagi on the control of the heart and pulmonary artery in the rattlesnake, Crotalus durissus

E. W. Taylor^1,2,*, Denis V. Andrade¹, Augusto S. Abe¹, Cleo A. C. Leite¹ and Tobias Wang^1,3

¹ Departmento de Zoologia, Universidade Estadual Paulista, Rio Claro, SP, Brazil
² School of Biosciences, The University of Birmingham, Edgbaston B15 2TT, UK
³ Institute of Biology, Aarhus University, 8000 Aarhus C, Denmark

^* Author for correspondence (e-mail: E.W.Taylor{at}bham.ac.uk)

Accepted 28 August 2008

Autonomic control of the cardiovascular system in reptiles includes sympathetic components but heart rate (f_H), pulmonary blood flow (_pul) and cardiac shunt patterns are primarily controlled by the parasympathetic nervous system. The vagus innervates both the heart and a sphincter on the pulmonary artery. The present study reveals that whereas both the left and right vagi influence f_H, it is only the left vagus that influences pulmonary vascular resistance. This is associated with the fact that rattlesnakes, in common with some other species of snakes, have a single functional lung, as the other lung regresses during development. Stimulation of the left cervical vagus in anaesthetised snakes slowed the heart and markedly reduced blood flow in the pulmonary artery whereas stimulation of the right cervical vagus slowed the heart and caused a small increase in stroke volume (V_S) in both the systemic and pulmonary circulations. Central stimulation of either vagus caused small (5–10%) reductions in systemic blood pressure but did not affect blood flows or f_H. A bilateral differentiation between the vagi was confirmed by progressive vagotomy in recovered snakes. Transection of the left vagus caused a slight increase in f_H (10%) but a 70% increase in _pul, largely due to an increase in pulmonary stroke volume (V_S,pul). Subsequent complete vagotomy caused a 60% increase in f_H accompanied by a slight rise in _pul, with no further change in V_S,pul. By contrast, transection of the right vagus elicited a slight tachycardia but no change in V_S,pul. Subsequent complete vagotomy was accompanied by marked increases in f_H, _pul and V_S,pul. These data show that although the heart receives bilateral vagal innervation, the sphincter on the pulmonary artery is innervated solely by the left vagus. This paves the way for an investigation of the role of the cardiac shunt in regulating metabolic rate, as chronic left vagotomy will cause a pronounced left–right shunt in recovered animals, whilst leaving intact control of the heart, via the right vagus.

Key words: cardiovascular, nervous control, reptile

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