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ACETYLCHOLINE-CONTAINING NEUROEPITHELIAL CELLS IN FISH GILLS SUPPORT THE CHOLINERGIC HYPOTHESIS
OF O2 CHEMORECEPTION
Clinton Wanner, Mark L. Burleson
Department of Biological Sciences, College of Arts and Sciences
S UPPORT THE C HOLINERGIC H YPOTHESIS OF O 2 C HEMORECEPTION Clinton - - PowerPoint PPT Presentation
S UPPORT THE C HOLINERGIC H YPOTHESIS OF O 2 C HEMORECEPTION Clinton - - PowerPoint PPT Presentation
A CETYLCHOLINE -C ONTAINING N EUROEPITHELIAL C ELLS IN F ISH G ILLS S UPPORT THE C HOLINERGIC H YPOTHESIS OF O 2 C HEMORECEPTION Clinton Wanner, Mark L. Burleson Department of Biological Sciences, College of Arts and Sciences W HY IS O 2 IMPORTANT
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200 160 120 80 40 240
- xygen partial pressure (torr)
Environmental O2 Availability: Dissolved Oxygen in Trinity River, Ft. Worth
equivalent altitude (m)
9650 5280 2290 sea level
- 2000
Everest Dead Sea
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DISCOVERY OF O2 CHEMORECEPTORS
Corneille Heymans Nobel Prize in Physiology or Medicine in 1938 Chemoreceptors in cardio-aortic and carotid sinus
areas
Showed that chemical changes in arterial blood
elicited cardio-ventilatory responses.
Despite nearly 75 years of research, we still do not
understand how O2 chemoreceptors work!
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WHAT ARE O2 CHEMORECEPTORS?
O2 chemoreceptors are specialized cells that detect
changing levels of O2 availability and demand and initiate cardiovascular and ventilatory reflexes to maintain normal O2 uptake.
From Lahiri et al., 2001
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From Lahiri et al., 2001
WHAT ARE O2 CHEMORECEPTORS?
Hypoxia (low oxygen) depolarizes the O2 chemoreceptor causing the release of a neurotransmitter. The goal of this study is to identify that neurotransmitter using a non-mammalian animal model. The branchial neuroepithelial cells of fish gills are the evolutionary precursors to mammalian O2 receptors.
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Histochemical Profiles of O2 Chemoreceptor Cells
Mammals
serotonin dopamine norepinephrine acetylcholine epinephrine substance-P enkephalins nitric oxide neuron-specific enolase tyrosine hydroxylase
Birds
serotonin substance-P neuron-specific enolase tyrosine hydroxylase
Reptiles
serotonin enkephalins neuron-specific enolase tyrosine hydroxylase
Amphibians
serotonin enkephalins neuron-specific enolase tyrosine hydroxylase
Fish
serotonin enkephalins neuron-specific enolase tyrosine hydroxylase There is no consensus on the roles of any of these chemicals in the chemoreceptor control of ventilation in vertebrates!
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PHYLOGENY
Evolution of air-breathing was accompanied by
a reduction and internalization of O2-sensitive chemoreceptors and their loci.
IX X IX X X IX
Fish Amphibians Birds non-Chelonian Reptiles Mammals
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HYPOTHESIS : BRANCHIAL NEUROEPITHELIAL
CELLS CONTAIN ACETYLCHOLINE.
This hypothesis will be tested using
immunohistochemistry and laser confocal microscopy
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- Presence of the chemical within the cell. The chemical is either synthesized
by the neuron or is taken up from other cells that release it.2
- Stimulus-dependent release. It is released in appropriate quantities by the
neuron upon stimulation.
- Action on postsynaptic cell. Exogenous application of the substance in
appropriate amounts mimics the action of the endogenously-released substance on the postsynaptic cell or organ. Mechanism for removal. [Note, not always included as a criterion] A specific mechanism exists to remove the substance from the synaptic cleft, i.e., by degradation or reuptake.
CRITERIA FOR NEUROTRANSMITTER:
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PREVIOUS STUDIES:
Only acetylcholine consistently mimics the effects of
hypoxia and cyanide (histotoxic hypoxia) on cardio- ventilatory reflex responses and neural activity in mammals and fish.
Furthermore, the effects are mediated by the nicotinic
cholinergic receptor subtype.
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MATERIAL AND METHODS
Channel catfish (Ictalurus punctatus) obtained
from TP&W Dundee Fish Hatchery
Maintained in 100 gal tanks. On day of experiment, fish anesthetized (MS222),
heparinzed, cannulated and gills exsanguinated.
Pieces of gill with filaments removed with
scissors and fixed in buffered formadehyde
Processed, mounted, stained. Observed using Zeiss 200M inverted optical
microscope modified for confocal laser microscopy.
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GILL ANATOMY
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IMMUNOLABELING OF SEROTONIN RESULTS
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IMMUNOLABELING OF ACETYLCHOLINE
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IMMUNOLABELING OF ACETYLCHOLINE
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CONCLUSION
Branchial neuroepithelial of catfish
gills cells contain acetylcholine.
These data support previous reflex
and neural studies implicating acetylcholine as the principal neurochemical link between O2- sensitve chemoreceptor cells and primary sensory afferent nerves.
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