Under conditions of scarce food availability and cool ambient temperature, the mouse (Mus Musculus) enters into torpor, a state of transient metabolic suppression mediated in part by the autonomic nervous system. Hypothalamic orexins are involved in the coordination of behaviors and autonomic function. We tested whether orexins are necessary for the coordinated changes in physiological variables, which underlie torpor and represent its physiological signature. We performed simultaneous measurements of brain temperature, electroencephalographic, and electromyographic activity allowing objective assessment of wake–sleep behavior, and cardiovascular, respiratory, and metabolic variables in orexin knockout mice (ORX-KO) and wild-type mice (WT) during torpor bouts elicited by caloric restriction and mild cold stress. We found that torpor bouts in WT are characterized by an exquisitely coordinated physiological signature. The characteristics of torpor bouts in terms of duration and rate of change of brain temperature and electromyographic activity at torpor entrance and exit did not differ significantly between ORX-KO and WT, and neither did the cardiovascular, respiratory, and metabolic characteristics of torpor. ORX-KO and WT also had similar wake–sleep state changes associated with torpor bouts, with the exception of a significantly higher rapid-eye movement sleep time in ORX-KO at torpor entrance. Our results demonstrate that orexins are not necessary either for the normal physiological adaptations occurring during torpor in mice or for their coordination, suggesting that mechanisms different from orexin peptide signaling may be involved in the regulation and the coordination of these physiological responses.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
Tax calculation will be finalised during checkout.
Alam MN, McGinty D, Szymusiak R (1995) Preoptic/anterior hypothalamic neurons: thermosensitivity in rapid eye movement sleep. Am J Physiol 269(5 Pt 2):R1250–R1257. https://doi.org/10.1152/ajpregu.1995.269.5.R1250
Amici R, Bastianini S, Berteotti C, Cerri M, Del Vecchio F, Lo Martire V, Luppi M, Perez E, Silvani A, Zamboni G, Zoccoli G (2014) Sleep and bodily functions: the physiological interplay between body homeostasis and sleep homeostasis. Arch Ital Biol 152(2–3):66–78. https://doi.org/10.12871/000298292014232
Baiula M, Bedini A, Spampinato SM (2015) Role of nociceptin/orphanin FQ in thermoregulation. Neuropeptides 50:51–56. https://doi.org/10.1016/j.npep.2015.03.005
Bastianini S, Silvani A (2018) Clinical implications of basic research: The role of hypocretin/orexin neurons in the central autonomic network. Clin Transl Neurosci. https://doi.org/10.1177/2514183X18789327
Bastianini S, Silvani A, Berteotti C, Elghozi JL, Franzini C, Lenzi P, Lo Martire V, Zoccoli G (2011) Sleep related changes in blood pressure in hypocretin-deficient narcoleptic mice. Sleep 34(2):213–218. https://doi.org/10.1093/sleep/34.2.213
Bastianini S, Silvani A, Berteotti C, Lo Martire V, Cohen G, Ohtsu H, Lin JS, Zoccoli G (2015) Histamine transmission modulates the phenotype of murine narcolepsy caused by orexin neuron deficiency. PLoS ONE 10(10):e0140520. https://doi.org/10.1371/journal.pone.0140520
Berntson GG, Cacioppo JT, Quigley KS (1995) The metrics of cardiac chronotropism: biometric perspectives. Psychophysiology 32(2):162–171. https://doi.org/10.1111/j.1469-8986.1995.tb03308.x
Bonnavion P, Mickelsen LE, Fujita A, de Lecea L, Jackson AC (2016) Hubs and spokes of the lateral hypothalamus: cell types, circuits and behaviour. J Physiol 594(22):6443–6462. https://doi.org/10.1113/JP271946
Borbély AA, Achermann P (2011) Sleep homeostasis and models of sleep regulation. In: Kryger MHRT, Dement WC (eds) Principles and practice of sleep medicine. Elsevier Saunders, Philadelphia, pp 431–434
Cerri M, Mastrotto M, Tupone D, Martelli D, Luppi M, Perez E, Zamboni G, Amici R (2013) The inhibition of neurons in the central nervous pathways for thermoregulatory cold defense induces a suspended animation state in the rat. J Neurosci 33(7):2984–2993. https://doi.org/10.1523/jneurosci.3596-12.2013
Cerri M, Luppi M, Tupone D, Zamboni G, Amici R (2017) REM sleep and endothermy: potential sites and mechanism of a reciprocal interference. Front Physiol 8:624. https://doi.org/10.3389/fphys.2017.00624
Chemelli RM, Willie JT, Sinton CM, Elmquist JK, Scammell T, Lee C, Richardson JA, Williams SC, Xiong Y, Kisanuki Y, Fitch TE, Nakazato M, Hammer RE, Saper CB, Yanagisawa M (1999) Narcolepsy in orexin knockout mice: molecular genetics of sleep regulation. Cell 98(4):437–451
Cui Y, Lee TF, Wang LC (1996) State-dependent changes of brain endogenous opioids in mammalian hibernation. Brain Res Bull 40(2):129–133. https://doi.org/10.1016/0361-9230(96)00038-x
Daan S, Barnes BM, Strijkstra AM (1991) Warming up for sleep? Ground squirrels sleep during arousals from hibernation. Neurosci Lett 128(2):265–268
Deboer T, Tobler I (1994) Sleep EEG after daily torpor in the Djungarian hamster: similarity to the effect of sleep deprivation. Neurosci Lett 166(1):35–38
Deboer T, Tobler I (1995) Temperature dependence of EEG frequencies during natural hypothermia. Brain Res 670(1):153–156. https://doi.org/10.1016/0006-8993(94)01299-w
Deboer T, Tobler I (2000) Slow waves in the sleep electroencephalogram after daily torpor are homeostatically regulated. NeuroReport 11(4):881–885
Deboer T, Tobler I (2003) Sleep regulation in the Djungarian hamster: comparison of the dynamics leading to the slow-wave activity increase after sleep deprivation and daily torpor. Sleep 26(5):567–572
Deboer T, Tobler I (1996) Natural hypothermia and sleep deprivation: common effects on recovery sleep in the Djungarian hamster. Am J Physiol 271(5 Pt 2):R1364–1371. https://doi.org/10.1152/ajpregu.1996.271.5.R1364
Elvert R, Heldmaier G (2005) Cardiorespiratory and metabolic reactions during entrance into torpor in dormice, Glis glis. J Exp Biol 208(Pt 7):1373–1383. https://doi.org/10.1242/jeb.01546
Futatsuki T, Yamashita A, Ikbar KN, Yamanaka A, Arita K, Kakihana Y, Kuwaki T (2018) Involvement of orexin neurons in fasting- and central adenosine-induced hypothermia. Sci Rep 8(1):2717. https://doi.org/10.1038/s41598-018-21252-w
Geiser F (2004) Metabolic rate and body temperature reduction during hibernation and daily torpor. Annu Rev Physiol 66:239–274. https://doi.org/10.1146/annurev.physiol.66.032102.115105
Glotzbach SF, Heller HC (1976) Central nervous regulation of body temperature during sleep. Science 194(4264):537–539. https://doi.org/10.1126/science.973138
Harding EC, Yu X, Miao A, Andrews N, Ma Y, Ye Z, Lignos L, Miracca G, Ba W, Yustos R, Vyssotski AL, Wisden W, Franks NP (2018) A neuronal hub binding sleep initiation and body cooling in response to a warm external stimulus. Curr Biol 28(14):2263–2273. https://doi.org/10.1016/j.cub.2018.05.054
Harris DV, Walker JM, Berger RJ (1984) A continuum of slow-wave sleep and shallow torpor in the pocket mouse Perognathus longimembris. Physiol Zool 57(4):428–434
Heldmaier G, Klingenspor M, Werneyer M, Lampi BJ, Brooks SP, Storey KB (1999) Metabolic adjustments during daily torpor in the Djungarian hamster. Am J Physiol 276(5 Pt 1):E896–906
Heldmaier G, Ortmann S, Elvert R (2004) Natural hypometabolism during hibernation and daily torpor in mammals. Respir Physiol Neurobiol 141(3):317–329. https://doi.org/10.1016/j.resp.2004.03.014
Hitrec T, Luppi M, Bastianini S, Squarcio F, Berteotti C, Lo Martire V, Martelli D, Occhinegro A, Tupone D, Zoccoli G, Amici R, Cerri M (2019) Neural control of fasting-induced torpor in mice. Sci Rep 9(1):15462. https://doi.org/10.1038/s41598-019-51841-2
Kakizaki M, Tsuneoka Y, Takase K, Kim SJ, Choi J, Ikkyu A, Abe M, Sakimura K, Yanagisawa M, Funato H (2019) Differential roles of each orexin receptor signaling in obesity. iScience 20:1–13. https://doi.org/10.1016/j.isci.2019.09.003
Kuwaki T (2015) Thermoregulation under pressure: a role for orexin neurons. Temperature (Austin) 2(3):379–391. https://doi.org/10.1080/23328940.2015.1066921
Li H, Hua T, Wang W, Wu X, Miao C, Huang W, Xiao Y, Yang J, Bradley JL, Peberdy MA, Ornato J, Dix TA, Beck T, Tang W (2019) The effects of pharmacological hypothermia induced by neurotensin receptor agonist ABS 201 on outcomes of CPR. Shock 51(5):667–673. https://doi.org/10.1097/SHK.0000000000001178
Lo Martire V, Valli A, Bingaman MJ, Zoccoli G, Silvani A, Swoap SJ (2018) Changes in blood glucose as a function of body temperature in laboratory mice: implications for daily torpor. Am J Physiol Endocrinol Metab. https://doi.org/10.1152/ajpendo.00201.2018
Lyman CP, O'Brien RC (1963) Autonomic control of circulation during the hibernating cycle in ground squirrels. J Physiol 168:477–499. https://doi.org/10.1113/jphysiol.1963.sp007204
Melvin RG, Andrews MT (2009) Torpor induction in mammals: recent discoveries fueling new ideas. Trends Endocrinol Metab 20(10):490–498. https://doi.org/10.1016/j.tem.2009.09.005
Milsom WK, Zimmer MB, Harris MB (1999) Regulation of cardiac rhythm in hibernating mammals. Comp Biochem Physiol A Mol Integr Physiol 124(4):383–391
Mochizuki T, Klerman EB, Sakurai T, Scammell TE (2006) Elevated body temperature during sleep in orexin knockout mice. Am J Physiol Regul Integr Comp Physiol 291(3):R533–540. https://doi.org/10.1152/ajpregu.00887.2005
Nakamura A, Zhang W, Yanagisawa M, Fukuda Y, Kuwaki T (2007) Vigilance state-dependent attenuation of hypercapnic chemoreflex and exaggerated sleep apnea in orexin knockout mice. J Appl Physiol (1985) 102(1):241–248. https://doi.org/10.1152/japplphysiol.00679.2006
Ortmann S, Heldmaier G (2000) Regulation of body temperature and energy requirements of hibernating alpine marmots (Marmota marmota). Am J Physiol Regul Integr Comp Physiol 278(3):R698–704. https://doi.org/10.1152/ajpregu.2000.278.3.R698
Parmeggiani PL (2003) Thermoregulation and sleep. Front Biosci 8:s557–s567
Parmeggiani PL, Azzaroni A, Cevolani D, Ferrari G (1983) Responses of anterior hypothalamic-preoptic neurons to direct thermal stimulation during wakefulness and sleep. Brain Res 269(2):382–385. https://doi.org/10.1016/0006-8993(83)90152-x
Patel S, Hutson PH (1996) Effects of galanin on 8-OH-DPAT induced decrease in body temperature and brain 5-hydroxytryptamine metabolism in the mouse. Eur J Pharmacol 317(2–3):197–204. https://doi.org/10.1016/s0014-2999(96)00716-9
Peyron C, Tighe DK, van den Pol AN, de Lecea L, Heller HC, Sutcliffe JG, Kilduff TS (1998) Neurons containing hypocretin (orexin) project to multiple neuronal systems. J Neurosci 18(23):9996–10015
Sakurai T (2007) The neural circuit of orexin (hypocretin): maintaining sleep and wakefulness. Nat Rev Neurosci 8(3):171–181. https://doi.org/10.1038/nrn2092
Sellayah D, Bharaj P, Sikder D (2011) Orexin is required for brown adipose tissue development, differentiation, and function. Cell Metab 14(4):478–490. https://doi.org/10.1016/j.cmet.2011.08.010
Shirasaka T, Nakazato M, Matsukura S, Takasaki M, Kannan H (1999) Sympathetic and cardiovascular actions of orexins in conscious rats. Am J Physiol 277(6):R1780–1785. https://doi.org/10.1152/ajpregu.1999.277.6.R1780
Silvani A, Bastianini S, Berteotti C, Franzini C, Lenzi P, Lo Martire V, Zoccoli G (2009) Sleep modulates hypertension in leptin-deficient obese mice. Hypertension 53(2):251–255. https://doi.org/10.1161/HYPERTENSIONAHA.108.125542
Silvani A, Bastianini S, Berteotti C, Cenacchi G, Leone O, Lo Martire V, Papa V, Zoccoli G (2014a) Sleep and cardiovascular phenotype in middle-aged hypocretin-deficient narcoleptic mice. J Sleep Res 23(1):98–106. https://doi.org/10.1111/jsr.12081
Silvani A, Berteotti C, Bastianini S, Cohen G, Lo Martire V, Mazza R, Pagotto U, Quarta C, Zoccoli G (2014b) Cardiorespiratory anomalies in mice lacking CB1 cannabinoid receptors. PLoS ONE 9(6):e100536. https://doi.org/10.1371/journal.pone.0100536
Silvani A, Cerri M, Zoccoli G, Swoap SJ (2018) Is adenosine action common ground for NREM sleep, torpor, and other hypometabolic states? Physiology (Bethesda) 33(3):182–196. https://doi.org/10.1152/physiol.00007.2018
Swoap SJ, Gutilla MJ (2009) Cardiovascular changes during daily torpor in the laboratory mouse. Am J Physiol Regul Integr Comp Physiol 297(3):R769–774. https://doi.org/10.1152/ajpregu.00131.2009
Terada J, Nakamura A, Zhang W, Yanagisawa M, Kuriyama T, Fukuda Y, Kuwaki T (2008) Ventilatory long-term facilitation in mice can be observed during both sleep and wake periods and depends on orexin. J Appl Physiol (1985) 104(2):499–507. https://doi.org/10.1152/japplphysiol.00919.2007
Trachsel L, Edgar DM, Heller HC (1991) Are ground squirrels sleep deprived during hibernation? Am J Physiol 260(6 Pt 2):R1123–1129. https://doi.org/10.1152/ajpregu.1991.260.6.R1123
Tupone D, Madden CJ, Cano G, Morrison SF (2011) An orexinergic projection from perifornical hypothalamus to raphe pallidus increases rat brown adipose tissue thermogenesis. J Neurosci 31(44):15944–15955. https://doi.org/10.1523/JNEUROSCI.3909-11.2011
Vicent MA, Borre ED, Swoap SJ (2017) Central activation of the A1 adenosine receptor in fed mice recapitulates only some of the attributes of daily torpor. J Comp Physiol B 187(5–6):835–845. https://doi.org/10.1007/s00360-017-1084-7
Vyazovskiy VV, Palchykova S, Achermann P, Tobler I, Deboer T (2017) Different effects of sleep deprivation and torpor on EEG slow-wave characteristics in Djungarian Hamsters. Cereb Cortex 27:950–961
Walker JM, Glotzbach SF, Berger RJ, Heller HC (1977) Sleep and hibernation in ground squirrels (Citellus spp): electrophysiological observations. Am J Physiol 233(5):R213–221. https://doi.org/10.1152/ajpregu.1977.233.5.R213
Walker JM, Garber A, Berger RJ, Heller HC (1979) Sleep and estivation (shallow torpor): continuous processes of energy conservation. Science 204(4397):1098–1100
Withers PC (1977) Metabolic, respiratory and haematological adjustments of the little pocket mouse to circadian torpor cycles. Respir Physiol 31(3):295–307
The authors wish to thank Prof. Gerard Heldmaier for generously providing the CaloBox system and its analysis software.
This research was supported by the University of Bologna (Grants for Fundamental Oriented Research, RFO2017/18, attributed to CB, AS, and GZ) and the European Space Agency (Research agreement collaboration 4000123556 attributed to MC).
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the EU Directive 2010/63/EU for animal experiments and were approved by the Committee on the Ethics of Animal Experiments of the University of Bologna (prot. n. 30209) and of the Italian Ministry of Health (prot. n. 141/2018-PR).
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Communicated by G. Heldmaier.
About this article
Cite this article
Lo Martire, V., Berteotti, C., Bastianini, S. et al. The physiological signature of daily torpor is not orexin dependent. J Comp Physiol B 190, 493–507 (2020). https://doi.org/10.1007/s00360-020-01281-6
- Metabolic rate