Respiratory Physiology & Neurobiology 140 (2004) 63–76 Interactive effects of mechano- and chemo-receptor inputs on cardiorespiratory outputs in the toad T. Wang a,b,∗ , E.W. Taylor c , S.G. Reid b , W.K. Milsom b a Department of Zoophysiology, University of Aarhus, Building 131, Universitetsparken, 8000 Aarhus C, Denmark b Department of Zoology, University of British Columbia, Vancouver BC, Canada c Biosciences, The University of Birmingham, Edgbaston, UK Accepted 7 January 2004 Abstract Arterial blood pressure (P b ), pulmocutaneous blood flow ( ˙ Q pc ), heart rate (f H ), and fictive ventilation (motor activity in the Vth cranial nerve, V int ), were recorded from decerebrated, paralysed toads receiving unidirectional ventilation with experimental gas mixtures over a range of lung inflation. At the onset of spontaneous bouts of fictive ventilation, ˙ Q pc and P b increased immediately, often with changes in heart rate, implying central cardiorespiratory interactions. Inflation of the lungs with different gas mixtures revealed that the effect of hypercarbia on V int was reduced by lung inflation and that feedback from pulmonary stretch receptors may summate with central feedforward control of f H and ˙ Q pc in an interactive fashion. The results of bolus injections of cyanide into the carotid or the pulmonary circulations suggest there are oxygen sensitive receptors in both circuits that affect the cardiovascular system directly and respiratory activity by complex central interactions with inputs from central chemoreceptors and pulmonary stretch receptors. © 2004 Elsevier B.V. All rights reserved. Keywords: Amphibian, toad (Bufo marinus); Blood flow, pulmocutaneous; Control of breathing, interaction mechano-, chemosensors; Hypercapnia, pattern of breathing; Hypoxia, pattern of breathing; Pattern of breathing, hypoxia, hypercapnia; Receptors, pulmonary stretch; Arterial chemo 1. Introduction Frogs and toads commonly exhibit intermittent ventilatory patterns where pulmonary ventilation is associated with an increase in heart rate (f H ) and pul- mocutaneous blood flow ( ˙ Q pc )(Shelton, 1970; West and Burggren, 1984; Gamperl et al., 1999). On the ∗ Corresponding author Tel.: +45-89-42-26-94; fax: +45-86-19-41-86. E-mail address: tobias.wang@biology.au.dk (T. Wang). efferent side, these cardiorespiratory interactions are the result of a release of vagal tone on the heart and pulmonary artery, and possibly an increase in sympa- thetic tone (Wang et al., 1999a). The factors that may contribute to this tight coupling between respiratory and cardiovascular function are: (1) central communi- cation between the respiratory centres and the cardiac vagal motorneuron pools within the medulla; (2) reflex effects following pulmonary stretch receptor stimulation; (3) mechanical effects associated with the movements of the pleuro-peritoneal cavity influencing 1569-9048/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.resp.2004.01.002