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Am J Physiol Regul Integr Comp Physiol 286: R1069-R1076, 2004. First published February 5, 2004; doi:10.1152/ajpregu.00427.2003
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CARDIAC, RENAL, AND RESPIRATORY INTEGRATION

Chemical activation of C1-C2 spinal neurons modulates intercostal and phrenic nerve activity in rats

Fang Lu, Chao Qin, Robert D. Foreman, and Jay P. Farber

Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73190

Submitted 30 July 2003 ; accepted in final form 28 January 2004

Chemical activation of upper cervical spinal neurons modulates activity of thoracic respiratory interneurons in rats. The aim of the present study was to examine the effects of chemical activation of C1-C2 spinal neurons on thoracic spinal respiratory motor outflows. Electroneurograms of left phrenic (n = 23) and intercostal nerves (ICNs, n = 93) between T3 and T8 spinal segments were recorded from 36 decerebrated, vagotomized, paralyzed, and ventilated male rats. To activate upper cervical spinal neurons, glutamate pledgets (1 M, 1 min) were placed on the dorsal surface of the C1-C2 spinal cord. Glutamate on C1-C2 increased ICN tonic activity in 56/59 (95%) ICNs. The average maximal tonic activity of ICN was increased by 174% (n = 59). After spinal transection at rostral C1, glutamate on C1-C2 still increased ICN tonic activity in 33/35 ICNs. However, the effects of C1-C2 glutamate on ICN phasic activity were highly variable, with observations of augmentation or suppression of both inspiratory and expiratory discharge. C1-C2 glutamate augmented the average amplitude of phrenic burst by 20%, whereas the increases in amplitude of ICN inspiratory activity, when they occurred, averaged 120%. The burst rate of phrenic nerve discharge was decreased from 34.2 ± 1.6 to 26.3 ± 2.0 (mean ± SE) breaths/min during C1-C2 glutamate. These data suggested that upper cervical propriospinal neurons might play a role in descending modulation of thoracic respiratory and nonrespiratory motor activity.

glutamate; propriospinal modulation; cervical spinal cord; respiration


Address for reprint requests and other correspondence: J. P. Farber, Dept. of Physiology, Univ. of Oklahoma Health Sciences Center, PO Box 26901, Oklahoma City, OK 73190 (E-mail: jay-farber{at}ouhsc.edu).




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