Control and interaction of the cardiovascular and respiratory systems in anuran amphibians.

In anuran amphibians, respiratory rhythm is generated within the central nervous system (CNS) and is modulated by chemo- and mechanoreceptors located in the vascular system and within the CNS. The site for central respiratory rhythmogenesis and the role of various neurotransmitters and neuromodulators is described. Ventilatory air flow is generated by a positive pressure, buccal force pump driven by efferent motor output from cranial nerves. The vagus (cranial nerve X) also controls heart rate and pulmocutaneous arterial resistance that, in turn, affect cardiac shunts within the undivided anuran ventricle; however, little is known about the control of central vagal motor outflow to the heart and pulmocutaneous artery. Anatomical evidence indicates a close proximity of the centers responsible for respiratory rhythmogenesis and the vagal motoneurons involved in cardiovascular regulation. Furthermore, anurans in which phasic feedback from chemo- and mechanoreceptors is prevented by artificial ventilation exhibit cardiorespiratory interactions that appear similar to those of conscious animals. These observations indicate interactions between respiratory and cardiovascular centers within the CNS. Thus, like mammals and other air-breathing vertebrates, the cardio-respiratory interactions in anurans result from both feedback and feed-forward mechanisms.