Hyperthermia Modulates Respiratory Pacemaker Bursting Properties

• Published in: Journal of neurophysiology Vol. 92; no. 5; pp. 2844 - 2852
• Main Authors: Tryba, Andrew K, Ramirez, Jan-Marino
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.11.2004
• Subjects: Animals; Animals, Newborn; Hyperthermia, Induced; In Vitro Techniques; Medulla Oblongata - physiology; Mice; Nerve Net - physiology; Neurons - physiology; Respiratory Burst - physiology; Respiratory Mechanics
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00752.2003

Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, Illinois 60637-1508 Submitted 5 August 2003; accepted in final form 1 June 2004 Most mammals modulate respiratory frequency (RF) to dissipate heat (e.g., panting) and avoid heat stroke during hyperthermic conditions. Respiratory neural network activity recorded in an isolated brain stem-slice preparation of mice exhibits a similar RF modulation in response to hyperthermia; fictive eupneic frequency increases while inspiratory network activity amplitude and duration are significantly reduced. Here, we study the effects of hyperthermia on the activity of synaptically isolated respiratory pacemakers to examine the possibility that these changes may account for the hyperthermic RF modulation of the respiratory network. During heating, modulation of the bursting frequency of synaptically isolated pacemakers paralleled that of population bursting recorded from the intact network, whereas nonpacemaker neurons were unaffected, suggesting that pacemaker bursting may account for the temperature-enhanced RF observed at the network level. Some respiratory neurons that were tonically active at hypothermic conditions exhibited pacemaker properties at approximately the normal body temperature of eutherian mammals (36.81 ± 1.17°C; mean ± SD) and continued to burst at 40°C. At elevated temperatures (40°C), there was an enhancement of the depolarizing drive potential in synaptically isolated pacemakers, while the amplitude of integrated population activity declined. Isolated pacemaker bursting ceased at 41–42°C ( n = 5), which corresponds to temperatures at which hyperthermic-apnea typically occurs in vivo. We conclude that pacemaker properties may play an important role in the hyperthermic frequency modulation and apnea, while network effects may play important roles in generating other aspects of the hyperthermic response, such as the decreased amplitude of ventral respiratory group activity during hyperthermia. Address for reprint requests and other correspondence: A. K. Tryba, Dept. of Organismal Biology and Anatomy, University of Chicago, 1027 E. 57th St., Chicago, IL 60637-1508 (E-mail: Andrew.Tryba{at}ttuhsc.edu ).