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Chemoreceptor modulation of gill ventilation in the larval bullfrog Rana catesbeiana
Abstract
As free-living organisms, larval amphibia encounter changes in environmental conditions. Respiratory regulation is important for them to meet environmental challenges and metabolic demands. However, little is known about chemoreceptors modulating respiration in larval amphibia. This investigation provides the first direct proof of peripheral O$\sb2$-sensitive chemoreceptors modulating gill ventilation in larval bullfrogs, Rana catesbeiana. The changes of the receptors in sensitivity and location were also studied. The rapid response time to inspired hyperoxic or hypoxic water in gill ventilation frequency, buccal pressure, branchial water flow, and branchial stroke volume revealed the existence of O$\sb2$-sensitive chemoreceptors in larval bullfrogs of TK stage V-VII, IX-XI and XVII-XIX. Measurements of the blood circulation time and the response time to NaCN injected into inspired water or conus of the larvae provided evidence that the O$\sb2$-sensitive chemoreceptors may be located on the gills or branchial chamber in all three developmental groups, which monitor branchial water PO$\sb2.$ A second site of chemoreceptors is most likely located on the epithelium of the lungs in larval bullfrogs of stage IX-XI and XVII-XIX, but not likely in stage V-VII larvae. Surgical removal of the first gill arch eliminated the quick response of gill ventilation to changes of inspired water PO$\sb2,$ but did not abolish the slow response in all three developmental groups. These data indicated that the rapidly responding O$\sb2$-sensitive chemoreceptors are located on the first gill arch. In stage (V-VII) larvae, the removal of the first gill arch significantly increased gill ventilation frequency in normoxic water and caused a slow response to NaCN, which suggested that the input of O$\sb2$-sensitive chemoreceptors located on the first gill arch in some undetermined way has inhibitory effects over other sites of O$\sb2$-sensitive chemoreceptors in CNS in these larvae. In late stage (XVII-XIX) larvae, the sensitivity of the O$\sb2$-sensitive chemoreceptors located on the first gill arch decreased, but the second site chemoreceptors became more sensitive than other two groups.
Subject Area
Zoology|Physiology
Recommended Citation
Jia, Xixi, "Chemoreceptor modulation of gill ventilation in the larval bullfrog Rana catesbeiana" (1992). Doctoral Dissertations Available from Proquest. AAI9219452.
https://scholarworks.umass.edu/dissertations/AAI9219452