HIGHLIGHTED TOPIC: Central CO2 Chemoreception in Cardiorespiratory Control Cardiorespiratory and neural consequences of rats brought past their aerobic dive limit
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چکیده
Panneton WM, Gan Q, Dahms TE. Cardiorespiratory and neural consequences of rats brought past their aerobic dive limit. J Appl Physiol 109: 1256–1269, 2010. First published August 12, 2010; doi:10.1152/japplphysiol.00110.2010.—The mammalian diving response is a dramatic autonomic adjustment to underwater submersion affecting heart rate, arterial blood pressure, and ventilation. The bradycardia is known to be modulated by the parasympathetic nervous system, arterial blood pressure is modulated via the sympathetic system, and still other circuits modulate the respiratory changes. In the present study, we investigate the submergence of rats brought past their aerobic dive limit, defined as the diving duration beyond which blood lactate concentration increases above resting levels. Hemodynamic measurements were made during underwater submergence with biotelemetric transmitters, and blood was drawn from cannulas previously implanted in the rats’ carotid arteries. Such prolonged submersion induces radical changes in blood chemistry; mean arterial PCO2 rose to 62.4 Torr, while mean arterial PO2 and pH reached nadirs of 21.8 Torr and 7.18, respectively. Despite these radical changes in blood chemistry, the rats neither attempted to gasp nor breathe while underwater. Immunohistochemistry for Fos protein done on their brains revealed numerous Fos-positive profiles. Especially noteworthy were the large number of immunopositive profiles in loci where presumptive chemoreceptors are found. Despite the activation of these presumptive chemoreceptors, the rats did not attempt to breathe. Injections of biotinylated dextran amine were made into ventral parts of the medullary dorsal horn, where central fibers of the anterior ethmoidal nerve terminate. Labeled fibers coursed caudal, ventral, and medial from the injection to neurons on the ventral surface of the medulla, where numerous Fos-labeled profiles were seen in the rats brought past their aerobic dive limit. We propose that this projection inhibits the homeostatic chemoreceptor reflex, despite the gross activation of chemoreceptors.
منابع مشابه
Cardiorespiratory and neural consequences of rats brought past their aerobic dive limit.
The mammalian diving response is a dramatic autonomic adjustment to underwater submersion affecting heart rate, arterial blood pressure, and ventilation. The bradycardia is known to be modulated by the parasympathetic nervous system, arterial blood pressure is modulated via the sympathetic system, and still other circuits modulate the respiratory changes. In the present study, we investigate th...
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HYPERCAPNIA, largely through the direct influence of CO2 on proton production, but possibly also via a direct effect of molecular CO2, is the primary chemical stimulus for alveolar ventilation. Small deviations in arterial CO2 in either direction elicit integrated cardiorespiratory reflexes that quickly restore CO2 levels in various tissue and cellular compartments, thereby providing the body w...
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Mulkey DK, Wenker IC, Kréneisz O. Current ideas on central chemoreception by neurons and glial cells in the retrotrapezoid nucleus. J Appl Physiol 108: 1433–1439, 2010. First published January 21, 2010; doi:10.1152/japplphysiol.01240.2009.—Central chemoreception is the mechanism by which CO2/pH-sensitive neurons (i.e., chemoreceptors) regulate breathing in response to changes in tissue pH. A re...
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