title: Unilateral microdialysis of gabazine in the dorsal medulla reverses thermal prolongation of the laryngeal chemoreflex in decerebrate piglets.
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 approximately 2.5 degrees 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.
authors.affiliation: Dept. of Physiology, Dartmouth Medical School, Lebanon, NH 03756, USA.
authors.forename: Luxi
authors.initials: L
authors.lastname: Xia
authors.forename: Tracey
authors.initials: T
authors.lastname: Damon
authors.forename: Mary M
authors.initials: MM
authors.lastname: Niblock
authors.forename: Donald
authors.initials: D
authors.lastname: Bartlett
authors.forename: J C
authors.initials: JC
authors.lastname: Leiter
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001049:Apnea / Q000378:metabolism / Q000503:physiopathology*; D001831:Body Temperature / Q000187:drug effects; D002628:Chemoreceptor Cells / Q000187:drug effects* / Q000503:physiopathology; D003655:Decerebrate State; D018756:GABA Antagonists / Q000008:administration & dosage*; D058787:GABA-A Receptor Antagonists; D007036:Hypothermia, Induced; D007823:Laryngeal Nerves / Q000187:drug effects* / Q000503:physiopathology; D017551:Microdialysis; D009434:Neural Pathways / Q000187:drug effects; D010791:Phrenic Nerve / Q000187:drug effects / Q000503:physiopathology; D011724:Pyridazines / Q000008:administration & dosage*; D011963:Receptors, GABA-A / Q000378:metabolism; D012018:Reflex / Q000187:drug effects*; D015656:Respiratory Mechanics / Q000187:drug effects; D017552:Solitary Nucleus / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D013552:Swine; D013997:Time Factors