Temporal relationships of blood pressure, heart rate, baroreflex function, and body temperature change over a hibernation bout in Syrian hamsters

Abstract

Hibernating mammals undergo torpor during which blood pressure (BP), heart rate (HR), metabolic rate, and core temperature (TC) dramatically decrease, conserving energy. While the cardiovascular system remains functional, temporal changes in BP, HR, and baroreceptor-HR reflex sensitivity (BRS) over complete hibernation bouts and their relation to TC are unknown. We implanted BP/temperature telemetry transmitters into Syrian hamsters to test three hypotheses: H-1) BP, HR, and BRS decrease concurrently during entry into hibernation and increase concurrently during arousal; H-2) these changes occur before changes in TC; and H-3) the pattern of changes is consistent over successive bouts. We found: 1) upon hibernation entry, BP and HR declined before TC and BRS, suggesting baroreflex control of HR continues to regulate BP as the BP set point decreases; 2) during the later phase of entry, BRS decreased rapidly whereas BP and TC fell gradually, suggesting the importance of TC in further BP declines; 3) during torpor, BP slowly increased (but remained relatively low) without changes in HR or BRS or increased TC, suggesting minimal baroreflex or temperature influence; 4) during arousal, increased TC and BRS significantly lagged increases in BP and HR, consistent with establishment of tissue perfusion before increased TC/metabolism; and 5) the temporal pattern of these changes was similar over successive bouts in all hamsters. These results negate H-1, support H-2 with respect to BP and HR, support H-3, and indicate that the baroreflex contributes to cardiovascular regulation over a hibernation bout, albeit operating in a fundamentally different manner during entry vs. arousal.

Cell Death Patterns Due to Warm Ischemia or Reperfusion in Renal Tubular Epithelial Cells Originating from Human, Mouse, or the Native Hibernator Hamster

“…Interestingly, like human RPTECs, mouse RPTECs were extremely sensitive to reoxygenation, yet less sensitive to anoxia. These results indicate that although Syrian hamster drops body temperature during hibernation [28,29], its RPTECs are resistant to warm ischemia and reperfusion as well. Similar results in the kidney and other organs were obtained by other studies too [11,12,13].…”

Opposing Activity Changes in AMP Deaminase and AMP-Activated Protein Kinase in the Hibernating Ground Squirrel

“…The overall response to temperature changes in a circannual hibernator involve local adaptations from multiple central and peripheral organs including the skeletal muscle[ 12 ], adipose tissue-brown and white-[ 13 , 14 , 15 ], heart[ 16 ], kidney[ 17 ] and liver[ 18 , 19 , 20 ]. In this regard, in both daily torpor and hibernation, there is a general decrease in metabolic rate allowing animals to cope with cold environments and/or limited food.…”

Extreme Neuroplasticity of Hippocampal CA1 Pyramidal Neurons in Hibernating Mammalian Species

“…That AMPARs do so is obvious because brainstem cardiorespiratory controllers rely on glutamatergic neurons to maintain homeostasis in awake and in hibernating hamsters. That is, telemetry recordings of blood pressure in unrestrained Syrian hamsters directly confirm that the baroreflex operates to regulate systolic pressure at ~96 mm Hg in euthermic hamsters and at ~39 mm Hg during torpor (Horwitz et al, 2013). The first neuron on this reflex is a glutamatergic neuron that responds to pressure (baroreceptors in the aortic arch) and excites second order neurons in the nucleus tractus solitarious (NTS), a brainstem nucleus.…”