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TRANSLATIONAL PHYSIOLOGY

Unilateral microdialysis of gabazine in the dorsal medulla reverses thermal prolongation of the laryngeal chemoreflex in decerebrate piglets

Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire

Submitted 14 May 2007 ; accepted in final form 5 September 2007

ABSTRACT

The laryngeal chemoreflex (LCR) is elicited by water in the larynx and leads to apnea and respiratory disruption in immature animals. The LCR is exaggerated by the elevation of brain temperature within or near the nucleus of the solitary tract (NTS) in decerebrate piglets. Thermal prolongation of reflex apnea elicited by superior laryngeal nerve stimulation is reduced by systemic administration of GABA_A receptor antagonists. Therefore, we tested the hypothesis that microdialysis within or near the NTS of gabazine, a GABA_A receptor antagonist, would reverse thermal prolongation of the LCR. We examined this hypothesis in 21 decerebrate piglets (age 3–13 days). We elicited the LCR by injecting 0.1 ml of water into the larynx before and after each piglet's body temperature was elevated by 2.5°C and before and after 2–5 mM gabazine was dialyzed unilaterally and focally in the medulla. Elevated body temperature failed to prolong the LCR in one piglet, which was excluded from analysis. Elevated body temperature prolonged the LCR in all the remaining animals, and dialysis of gabazine into the region near the NTS (n = 10) reversed the thermal prolongation of the LCR even though body temperature remained elevated. Dialysis of gabazine in other medullary sites (n = 10) did not reverse thermal prolongation of the LCR. Gabazine had no consistent effect on baseline respiratory activity during hyperthermia. These findings are consistent with the hypothesis that hyperthermia activates GABAergic mechanisms in or near the NTS that are necessary for the thermal prolongation of the LCR.

sudden infant death syndrome; laryngeal chemoreflex; hyperthermia; gamma-aminobutyric acid; gabazine; microdialysis; nucleus of the solitary tract

This article has been cited by other articles:

				L. Xia, J. C. Leiter, and D. Bartlett Jr. Laryngeal apnea in rat pups: effects of age and body temperature J Appl Physiol, January 1, 2008; 104(1): 269 - 274. [Abstract] [Full Text] [PDF]