| Summary: | Time domains of the hypoxic ventilatory response (HVR) are time dependent changes in ventilation that take place without changes in metabolic rate or arterial PCO2. Time domains of the HVR have been described in mammals along with their underlying mechanisms. Each time domain reflects a different change in the various steps in the control of breathing. Peripheral chemoreceptors are necessary for the expression of all time domains in mammals and changes in their sensitivity (reflected in release of different neurotransmitters) are involved in several of the time domains.
I demonstrated that neuroepithelial cells (NECs) in the gills of trout (Oncorhynchus mykiss) and goldfish (Carassius auratus) contain serotonin, but not acetylcholine or catecholamines. Acetylcholine was expressed in bipolar neurons in the filaments, and nerve bundles near the efferent filament arteries (eFA) in trout and goldfish and evidence suggests that they may play a key role in producing the HVR in these species.
In bowfin (Amia calva), I found five different types of serotonin containing NECs in the gills (identified as Type I to V). Three of these cell types (I - III) had the potential to be oxygen chemoreceptors. Time domains were evident in the HVR of bowfin during moderate exposure to hypoxia but only when they did not have access to air. In these fish, all three putative chemoreceptors increased in size during sustained hypoxia. The NECs found in the basal lamina near the eFA responded exclusively to hypoxaemia (by changing cell size and shape) while the other two NEC types responded to aquatic hypoxia as well.
Exposure to sustained hypoxia also caused changes within the oxygen transport cascade: the gill ventilatory sensitivity to hypoxia increased and the Hb-O₂ binding affinity decreased suggesting that acclimation to hypoxia in Amia elicits changes that both increase oxygen uptake and enhance oxygen delivery to the tissues.
This thesis focused primarily on a time domain in bowfin similar to the ventilatory acclimatization to hypoxia seen in mammals and highlights the importance of changes in both the peripheral oxygen chemoreceptors as well as in the oxygen transport cascade in establishing this time dependent change. === Science, Faculty of === Zoology, Department of === Graduate
|
|---|
