Laryngeal Motor Control in Frogs: Role of Vagal and Laryngeal Feedback Naoki Kogo, * Steven F. Perry, † John E. Remmers Department of Medical Physiology, Respiratory Research Group, Faculty of Medicine, University of Calgary, Health Science Centre, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada Received 30 January 1997; accepted 10 April 1997 tion followed by a long-lasting glottal constriction. The ABSTRACT: Using decerebrate frogs ( Rana first phase was inferred to be a direct (nonreflex) re- catesbeiana ), we investigated the role of vagal and sponse to the stimulus, whereas the second and third laryngeal sensory feedback in controlling motor acti- represent reflex responses to the activation of laryn- vation of the larynx. Vagal and laryngeal nerve affer- geal afferents. Intracellular recordings of membrane ents were activated by electrical stimulation of the potential of vagal motoneurons of lung and nonlung intact vagal and laryngeal nerves. Pulmonary affer- types revealed EPSPs in both types of neurons evoked ents were activated by lung inflation. Reflex responses by stimulation of Xm or X, indicating activation of were recorded by measuring efferent activity in the glottal dilator and constrictor motoneurons. In sum- laryngeal branch of the vagus (X ) and changes in mary, we have identified two novel reflexes producing glottal aperture. Two glottic closure reflexes were glottic closure, one stimulated by activation of pulmo- identified, one evoked by lung inflation or electrical nary receptors and the other by laryngeal receptors. stimulation of the main branch of the vagus (Xm), The former may be part of an inspiratory terminating and the other by electrical stimulation of X. Lung reflex and the latter may represent an airway inflation evoked a decrementing burst of X efferent protective reflex.  1997 John Wiley & Sons, Inc. J Neurobiol activity and electrical stimulation of Xm resulted in a 33: 213–222, 1997 brief burst of X action potentials. Electrical stimula- Keywords: amphibia; tadpole; neurobiology of breath- tion of X evoked a triphasic mechanical response, an ing; larynx; lung inflation abrupt glottal constriction followed by glottal dilata- INTRODUCTION respiratory functions: The first is to control lung volume and the second is to prevent aspiration of injurious substances into the lungs. Motor control of Pressure recordings in the oropharynx and in the both laryngeal functions is likely to involve reflexes lung of frogs evidence a dynamic flow of air be- arising in the periphery, and we speculate that re- tween these two chambers (de Jongh and Gans, flexes controlling lung volume arise in the lung 1969; West and Jones, 1975). The glottis, a valve (Milsom, 1990; Kogo et al., 1994) and that lung separating these two chambers, plays a pivotal role protection reflexes arise in the larynx. The objective in controlling airflow between the two chambers. of this article was to elucidate these two types of Neural regulation of glottic aperture has two major glottal reflexes in frogs. The respiratory cycle of mammals and reptiles is composed of three phases: inspiration, postinspi- * Present address: Department of Anatomy and Neurobiol- ration, and expiration ( Richter and Ballantyne, ogy, St. Louis University School of Medicine, St. Louis, Missouri 1983; Richter et al., 1986, 1987; Takeda et al., 63104 ² Present address: Abt. Morphologie und Systematik, Zoolog- 1986 ) . Similarly, the amphibian lung ventilatory isches Institut der Rheinisch Friedrich-Wilhelms-Universitat cycle is divided into three sequential phases: expira- Bonn 53115, Germany tion (E), inspiration (I), and breath hold (Brett Correspondence to: J. E. Remmers  1997 John Wiley & Sons, Inc. CCC 0022-3034/97/030213-10 and Shelton, 1979; Kogo et al., 1994). Muscles 213 8P27 1853 / 8P27$$1853 07-15-97 08:04:38 nbioal W: Neurobio