Ventilatory effects of impaired glial function in a brain stem chemoreceptor region in the conscious rat

1 Department of Biology, Allegheny College, Meadville, Pennsylvania 16335; and 2 Department of Biology, St. Lawrence University, Canton, New York 13617 Glia are thought to regulate ion homeostasis, including extracellular pH; however, their role in modulating central CO 2 chemosensitivity is unclear. Using a push-pull cannula in chronically instrumented and conscious rats, we administered a glial toxin, fluorocitrate (FC; 1 mM) into the retrotrapezoid nucleus (RTN), a putative chemosensitive site, during normocapnia and hypercapnia. FC exposure significantly increased expired minute ventilation ( E ) to a value 38% above the control level during normocapnia. During hypercapnia, FC also significantly increased both breathing frequency and expired E . During FC administration, maximal ventilation was achieved at ~4% CO 2 , compared with 8-10% CO 2 during control hypercapnic trials. RTN perfusion of control solutions had little effect on any ventilatory measures ( E , tidal volume, or breathing frequency) during normocapnic or hypercapnic conditions. We conclude that unilateral impairment of glial function in the RTN of the conscious rat results in stimulation of respiratory output. brain stem pH regulation; central chemoreception; control of breathing; retrotrapezoid nucleus; brain stem glia