Physiological Society Symposium – Vagal Control: From Axolotl to Man

Milsom, William K.; Zimmer, M. Beth; Harris, Michael B.

doi:10.1111/j.1469-445x.2001.tb00046.x

Cited by 29 publications

(5 citation statements)

References 21 publications

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“…There remains some debate as to the control mechanisms behind the cardiac rhythms we see during torpor (Lyman and O'Brien, 1963;Milsom et al, 1999;Zosky and Larcombe, 2003;Braulke and Heldmaier, 2010). Although the autonomic nervous system plays an essential role in reducing f H at the onset of torpor, at low T b nervous input is reduced, partially related to the dampening effects of temperature on nerve function but also probably as a result of withdrawal of control (Milsom et al, 2001). While we did not directly measure neurotransmitters or experimentally test for nerve response at the heart, our results suggest that once thermoconforming bats are in steady-state torpor and the heart is cold, temperature becomes the driving factor behind the patterns that we observe.…”

Section: Discussionmentioning

confidence: 99%

“…During torpor at low T b , the heart must facilitate adequate blood supply under conditions of reduced blood flow and slow ventilation/ low oxygen intake (Milsom et al, 2001). In addition, to minimise metabolic costs during torpor, adequate perfusion is only retained in vital tissues and organs as a result of circulatory adjustments (Carey et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Cold-hearted bats: uncoupling of heart rate and metabolism during torpor at subzero temperatures

Currie

Stawski

Geiser

2017

Journal of Experimental Biology

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Many hibernating animals thermoregulate during torpor and defend their body temperature () near 0°C by an increase in metabolic rate. Above a critical temperature (), animals usually thermoconform. We investigated the physiological responses above and below for a small tree-dwelling bat (, ∼14 g) that is often exposed to sub-zero temperatures during winter. Through simultaneous measurement of heart rate () and oxygen consumption ( ), we show that the relationship between oxygen transport and cardiac function is substantially altered in thermoregulating torpid bats between 1 and -2°C, compared with thermoconforming torpid bats at mild ambient temperatures ( 5-20°C). for this species was at a of 0.7±0.4°C, with a corresponding of 1.8±1.2°C. Below, animals began to thermoregulate, as indicated by a considerable but disproportionate increase in both and The maximum increase in was only 4-fold greater than the average thermoconforming minimum, compared with a 46-fold increase in The differential response of and to low was reflected in a 15-fold increase in oxygen delivery per heart beat (cardiac oxygen pulse). During torpor at low, thermoregulating bats maintained a relatively slow and compensated for increased metabolic demands by significantly increasing stroke volume and tissue oxygen extraction. Our study provides new information on the relationship between metabolism and in an unstudied physiological state that may occur frequently in the wild and can be extremely costly for heterothermic animals.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Cold-hearted bats: uncoupling of heart rate and metabolism during torpor at subzero temperatures

Currie

Stawski

Geiser

2017

Journal of Experimental Biology

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“…The rate of cooling during onset of torpor is slower than during drug-induced hypothermia due to postural adjustments, decreases in respiratory frequency and profound vasoconstriction in the lower extremities (Drew et al, 2012; Milsom et al, 2001). This reduced cooling rate is consistent with decreased thermal conductance, which is reported to be lower for torpid animals than for euthermic animals (Jinka et al, 2011; Snyder and Nestler, 1990).…”

Section: Torpormentioning

confidence: 99%

Neuroprotection: Lessons from hibernators

Dave

Christian

Pérez-Pinzón

et al. 2012

Comparative Biochemistry and Physiology Part B: Biochemistry an

106

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Mammals that hibernate experience extreme metabolic states and body temperatures as they transition between euthermia, a state resembling typical warm blooded mammals, and prolonged torpor, a state of suspended animation where the brain receives as low as 10% of normal cerebral blood flow. Transitions into and out of torpor are more physiologically challenging than the extreme metabolic suppression and cold body temperatures of torpor per se. Mammals that hibernate show unprecedented capacities to tolerate cerebral ischemia, a decrease in blood flow to the brain caused by stroke, cardiac arrest or brain trauma. While cerebral ischemia often leads to death or disability in humans and most other mammals, hibernating mammals suffer no ill effects when blood flow to the brain is dramatically decreased during torpor or experimentally induced during euthermia. These animals, as adults, also display rapid and pronounced synaptic flexibility where synapses retract during torpor and rapidly re-emerge upon arousal. A variety of coordinated adaptations contribute to tolerance of cerebral ischemia in these animals. In this review we discuss adaptations in heterothermic mammals that may suggest novel therapeutic targets and strategies to protect the human brain against cerebral ischemic damage and neurodegenerative disease.

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“…When animals near the onset of torpor breathe, ventilation occurs in concert with increased electromyogram activity (either a result of shivering or postural changes) and tachycardia (100,157). Interestingly, ventilation during torpor decreases to a greater extent than does metabolic rate, leading to a slight respiratory acidosis (100,101), similar to what occurs during NREM sleep. mechanisms involved, such as adenosine signaling.…”

Section: Common Physiological Changes In Nrem Sleep and Torpormentioning

confidence: 99%

“…During entrance into torpor and during the bout of torpor, parasympathetic activity to the heart is markedly increased. During this time, heart rate slows, whereas its variability increases, with periodic increases in heart rate coupled to ventilation (60,101,102,183,184). The parasympathetic dominance during entry into torpor occurs as sympathetic activity withdraws (6).…”

Section: Common Physiological Changes In Nrem Sleep and Torpormentioning

confidence: 99%

Is Adenosine Action Common Ground for NREM Sleep, Torpor, and Other Hypometabolic States?

et al. 2018

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This review compares two states that lower energy expenditure: non-rapid eye movement (NREM) sleep and torpor. Knowledge on mechanisms common to these states, and particularly on the role of adenosine in NREM sleep, may ultimately open the possibility of inducing a synthetic torpor-like state in humans for medical applications and long-term space travel. To achieve this goal, it will be important, in perspective, to extend the study to other hypometabolic states, which, unlike torpor, can also be experienced by humans.

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Physiological Society Symposium – Vagal Control: From Axolotl to Man

Cited by 29 publications

References 21 publications

Cold-hearted bats: uncoupling of heart rate and metabolism during torpor at subzero temperatures

Cold-hearted bats: uncoupling of heart rate and metabolism during torpor at subzero temperatures

Neuroprotection: Lessons from hibernators

Is Adenosine Action Common Ground for NREM Sleep, Torpor, and Other Hypometabolic States?

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