Breathing and upper airway CO2 in reptiles: role of the nasal and vomeronasal systems.
The ventilatory response of the garter snake, Thamnophis sirtalis, to 2% CO2 delivered to the upper airways (UA) was measured before and after the olfactory or vomeronasal nerves were transected. The UA (nasal cavities and mouth) were isolated from the gas source inspired into the lungs by inserting an endotracheal T tube into the glottis. CO2 was administered to the UA via a head chamber. The primary ventilatory response to UA CO2 was a significant decrease in ventilatory frequency (f) and minute ventilation. The decrease in f was caused by a significant increase in the pause duration. Tidal volume, expiratory duration, and inspiratory duration were not altered with UA CO2. The f response to UA CO2 was abolished with olfactory nerve transection, whereas vomeronasal nerve transection significantly increased the magnitude of the f depression. These results indicate that CO2-sensitive receptors are located in the nasal epithelium and that the olfactory nerves must be intact for the UA CO2 f response to be observed. In addition, the vomeronasal system appears to modulate the ventilatory response to UA CO2.
Coates
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Bioengineering Research Division, Lovelace Medical Foundation, Albuquerque, New Mexico 87131.
Ballam
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D000818:Animals; D002245:Carbon Dioxide / Q000032:analysis*; D005260:Female; D008297:Male; D009297:Nasal Mucosa / Q000502:physiology*; D009300:Nasal Septum / Q000502:physiology*; D009832:Olfactory Nerve / Q000502:physiology; D009833:Olfactory Pathways / Q000502:physiology; D011956:Receptors, Cell Surface / Q000378:metabolism; D012119:Respiration; D012911:Snakes / Q000502:physiology*; D013990:Tidal Volume
D011956:Receptors, Cell Surface; C054079:carbon dioxide receptor; D002245:Carbon Dioxide