Location of central respiratory chemoreceptors in the developing tadpole.
The location of central respiratory chemoreceptors in amphibian larvae may change as the central chemoreceptive function shifts from driving gill to driving lung ventilation during metamorphosis. We examined this possibility in the in vitro brain stem of the pre- and postmetamorphic Rana catesbeiana tadpole by microinjecting hypercapnic artificial cerebrospinal fluid (aCSF) while recording fictive lung ventilation. The rostral and caudal brain stem were separately explored systematically using injections of 11 nl of aCSF equilibrated with 100% CO2 that transiently acidified a 500-microm region, producing a maximum reduction in pH of 0.23 +/- 0.06 at the site of injection. In postmetamorphic tadpoles, chemoreceptive sites were concentrated in the rostral compared with the caudal brain stem. No such segregation was observed in the premetamorphic tadpole. We conclude that, as in lung rhythmogenic function, respiratory chemosensitivity emerges rostrally in the amphibian brain stem during development.
Respiratory Research Group, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 4N1.
C S
CS
Torgerson
M J
MJ
Gdovin
R
R
Brandt
J E
JE
Remmers
D000818:Animals; D001933:Brain Stem / Q000254:growth & development / Q000502:physiology*; D002245:Carbon Dioxide / Q000493:pharmacokinetics; D002628:Chemoreceptor Cells / Q000502:physiology*; D004058:Diffusion; D004525:Efferent Pathways / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007814:Larva; D008168:Lung / Q000254:growth & development / Q000502:physiology*; D008675:Metamorphosis, Biological / Q000502:physiology*; D010507:Periodicity; D011892:Rana catesbeiana / Q000254:growth & development / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*
D002245:Carbon Dioxide