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Animal models for investigating the central control of the Mammalian diving response.

McCulloch PF - Front Physiol (2012)

Bottom Line: Secondly, physiological recordings during natural and simulated diving indicate that both animals possess the same basic physiological responses to underwater submersion that occur in marine animals.Thirdly, the size and ease of housing of both animals makes them attractive laboratory research animals.Finally, the enormous amount of scientific literature regarding rodent brainstem autonomic control mechanisms, and the availability of brain atlases, makes these animals ideal choices to study the central control of the mammalian diving response.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Midwestern University Downers Grove, IL, USA.

ABSTRACT
Pioneering studies by Per Scholander indicated that the diving response consists of reflexly induced apnea, bradycardia and an alteration of blood flow that maintains perfusion of the heart and brain. More recently field physiological studies have shown that many marine animals can adjust cardiorespiratory aspects of their diving response depending upon the behavioral situation. This could suggest that the very labile heart rate during diving is under direct cortical control. However, the final control of autonomic nervous system functioning resides within the brainstem and not the cortex. Many physiologists regard the brain as a "black box" where important neuronal functioning occurs, but the complexity of such functioning leaves systematic investigation a daunting task. As a consequence the central control of the diving response has been under-investigated. Thus, to further advance the field of diving physiology by understanding its central neuronal control, it would be first necessary to understand the reflex circuitry that exists within the brainstem of diving animals. To do this will require an appropriate animal model. In this review, two animals, the muskrat and rat, will be offered as animal models to investigate the central aspects of the diving response. Firstly, although these rodents are not marine animals, natural histories indicate that both animals can and do exploit aquatic environments. Secondly, physiological recordings during natural and simulated diving indicate that both animals possess the same basic physiological responses to underwater submersion that occur in marine animals. Thirdly, the size and ease of housing of both animals makes them attractive laboratory research animals. Finally, the enormous amount of scientific literature regarding rodent brainstem autonomic control mechanisms, and the availability of brain atlases, makes these animals ideal choices to study the central control of the mammalian diving response.

No MeSH data available.


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Raw traces showing pulsatile arterial blood pressure during (A) swimming, (B) voluntary diving, and (C) forced diving in rats trained to dive. Period of swimming or diving is indicated by the bar underneath the trace. Breaks in trace indicate periods where the radiotelemetric signal was lost (Modified from McCulloch et al., 2010).
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Figure 5: Raw traces showing pulsatile arterial blood pressure during (A) swimming, (B) voluntary diving, and (C) forced diving in rats trained to dive. Period of swimming or diving is indicated by the bar underneath the trace. Breaks in trace indicate periods where the radiotelemetric signal was lost (Modified from McCulloch et al., 2010).

Mentions: Voluntarily diving rats have a substantial diving response that is qualitatively similar to that of muskrats. Comparable results in rats are found whether heart rate and blood pressure are recorded using trailing arterial cannulae (McCulloch et al., 1997; Ollenberger and West, 1998b) or implanted transmitters (McCulloch et al., 2010; Panneton et al., 2010b). In rats trained to dive 3 m through an underwater maze, heart rate, and mean arterial blood pressure decrease immediately upon submersion, heart rate by 78% (from 453 ± 12 to 101 ± 8 BPM) and mean arterial blood pressure by 25% (from 143 ± 1 to 107 ± 5 mmHg; McCulloch et al., 2010; Figure 5B). After its initial decrease, mean arterial blood pressure then increases, reaching a maximum of 174 ± 3 mmHg 4–5 s after submersion (McCulloch et al., 2010). Pre-existing chemoreceptor drive, achieved by altering arterial PO2 and/or PCO2, does not have any effect on the cardiovascular responses to voluntary diving (McCulloch et al., 1997). Additionally, during long duration (approximately 100 s) forced dives, rats do not attempt to breathe even though there are radical changes in arterial PO2, PCO2, and pH (Panneton et al., 2010a). Together these studies suggest that the chemoreceptor reflex in rats is not important in initiating the cardiovascular response to diving and is actually suppressed during diving. However, bilateral section of the carotid sinus nerve or destruction of the carotid body chemoreceptors attenuates the bradycardia response during forced submersion in conscious rats (Huang and Peng, 1976). Pretreatment with the muscarinic antagonist atropine eliminates the bradycardia associated with voluntary diving, and, even with the decrease in cardiac output due to the bradycardia, mean arterial blood pressure increases to 202 ± 5 mmHg during the dive (McCulloch et al., 1997). These results suggest that during voluntary diving in the rat there is both a parasympathetically mediated bradycardia and a sympathetically mediated peripheral vasoconstriction (McCulloch et al., 1997, 2010). Blood corticosterone levels indicate that rats not trained in the diving protocol find voluntary diving stressful, whereas repetitive daily training in rats decreases the stressfulness associated with voluntary diving (McCulloch et al., 2010). Trained rats find diving no more stressful than being handled daily by a human (McCulloch et al., 2010). However dive training has no effect on diving heart rate or mean arterial blood pressure, as quantitatively similar heart rate and blood pressure responses are found in both trained and untrained rats during voluntary diving (McCulloch et al., 2010).


Animal models for investigating the central control of the Mammalian diving response.

McCulloch PF - Front Physiol (2012)

Raw traces showing pulsatile arterial blood pressure during (A) swimming, (B) voluntary diving, and (C) forced diving in rats trained to dive. Period of swimming or diving is indicated by the bar underneath the trace. Breaks in trace indicate periods where the radiotelemetric signal was lost (Modified from McCulloch et al., 2010).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3362090&req=5

Figure 5: Raw traces showing pulsatile arterial blood pressure during (A) swimming, (B) voluntary diving, and (C) forced diving in rats trained to dive. Period of swimming or diving is indicated by the bar underneath the trace. Breaks in trace indicate periods where the radiotelemetric signal was lost (Modified from McCulloch et al., 2010).
Mentions: Voluntarily diving rats have a substantial diving response that is qualitatively similar to that of muskrats. Comparable results in rats are found whether heart rate and blood pressure are recorded using trailing arterial cannulae (McCulloch et al., 1997; Ollenberger and West, 1998b) or implanted transmitters (McCulloch et al., 2010; Panneton et al., 2010b). In rats trained to dive 3 m through an underwater maze, heart rate, and mean arterial blood pressure decrease immediately upon submersion, heart rate by 78% (from 453 ± 12 to 101 ± 8 BPM) and mean arterial blood pressure by 25% (from 143 ± 1 to 107 ± 5 mmHg; McCulloch et al., 2010; Figure 5B). After its initial decrease, mean arterial blood pressure then increases, reaching a maximum of 174 ± 3 mmHg 4–5 s after submersion (McCulloch et al., 2010). Pre-existing chemoreceptor drive, achieved by altering arterial PO2 and/or PCO2, does not have any effect on the cardiovascular responses to voluntary diving (McCulloch et al., 1997). Additionally, during long duration (approximately 100 s) forced dives, rats do not attempt to breathe even though there are radical changes in arterial PO2, PCO2, and pH (Panneton et al., 2010a). Together these studies suggest that the chemoreceptor reflex in rats is not important in initiating the cardiovascular response to diving and is actually suppressed during diving. However, bilateral section of the carotid sinus nerve or destruction of the carotid body chemoreceptors attenuates the bradycardia response during forced submersion in conscious rats (Huang and Peng, 1976). Pretreatment with the muscarinic antagonist atropine eliminates the bradycardia associated with voluntary diving, and, even with the decrease in cardiac output due to the bradycardia, mean arterial blood pressure increases to 202 ± 5 mmHg during the dive (McCulloch et al., 1997). These results suggest that during voluntary diving in the rat there is both a parasympathetically mediated bradycardia and a sympathetically mediated peripheral vasoconstriction (McCulloch et al., 1997, 2010). Blood corticosterone levels indicate that rats not trained in the diving protocol find voluntary diving stressful, whereas repetitive daily training in rats decreases the stressfulness associated with voluntary diving (McCulloch et al., 2010). Trained rats find diving no more stressful than being handled daily by a human (McCulloch et al., 2010). However dive training has no effect on diving heart rate or mean arterial blood pressure, as quantitatively similar heart rate and blood pressure responses are found in both trained and untrained rats during voluntary diving (McCulloch et al., 2010).

Bottom Line: Secondly, physiological recordings during natural and simulated diving indicate that both animals possess the same basic physiological responses to underwater submersion that occur in marine animals.Thirdly, the size and ease of housing of both animals makes them attractive laboratory research animals.Finally, the enormous amount of scientific literature regarding rodent brainstem autonomic control mechanisms, and the availability of brain atlases, makes these animals ideal choices to study the central control of the mammalian diving response.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Midwestern University Downers Grove, IL, USA.

ABSTRACT
Pioneering studies by Per Scholander indicated that the diving response consists of reflexly induced apnea, bradycardia and an alteration of blood flow that maintains perfusion of the heart and brain. More recently field physiological studies have shown that many marine animals can adjust cardiorespiratory aspects of their diving response depending upon the behavioral situation. This could suggest that the very labile heart rate during diving is under direct cortical control. However, the final control of autonomic nervous system functioning resides within the brainstem and not the cortex. Many physiologists regard the brain as a "black box" where important neuronal functioning occurs, but the complexity of such functioning leaves systematic investigation a daunting task. As a consequence the central control of the diving response has been under-investigated. Thus, to further advance the field of diving physiology by understanding its central neuronal control, it would be first necessary to understand the reflex circuitry that exists within the brainstem of diving animals. To do this will require an appropriate animal model. In this review, two animals, the muskrat and rat, will be offered as animal models to investigate the central aspects of the diving response. Firstly, although these rodents are not marine animals, natural histories indicate that both animals can and do exploit aquatic environments. Secondly, physiological recordings during natural and simulated diving indicate that both animals possess the same basic physiological responses to underwater submersion that occur in marine animals. Thirdly, the size and ease of housing of both animals makes them attractive laboratory research animals. Finally, the enormous amount of scientific literature regarding rodent brainstem autonomic control mechanisms, and the availability of brain atlases, makes these animals ideal choices to study the central control of the mammalian diving response.

No MeSH data available.


Related in: MedlinePlus