Effects of temperature, steroids and castration on daily torpor in the Djungarian hamster (Phodopus sungorus)

Ouarour, Ali; Kirsch, R.; Pévet, Paul

doi:10.1007/bf00199607

Cited by 29 publications

(22 citation statements)

References 30 publications

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“…Possible mechanisms for the action of PAS to influence testicular atrophy and recrudescence in LP hamsters have previously been discussed (8). Testes involution results in very low testosterone concentrations, which is a prerequisite for spontaneous torpor in male Siberian hamsters (18,30). Accordingly, a repressive effect on testes being greater for PAS than for OCT might explain both the enhancing effect of PAS on torpor expression in males as well as absence of torpor stimulation in OCT females.…”

Section: Discussionmentioning

confidence: 99%

Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

Scherbarth¹,

Diedrich²,

Dumbell³

et al. 2015

American Journal of Physiology-Regulatory, Integrative and Comp

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Scherbarth F, Diedrich V, Dumbell RA, Schmid HA, Steinlechner S, Barrett P. Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal. Am J Physiol Regul Integr Comp Physiol 309: R668 -R674, 2015. First published July 8, 2015 doi:10.1152/ajpregu.00191.2015 show spontaneous daily torpor only after ϳ2 mo in winter-like short photoperiods (SP). Although some SP-induced hormonal changes have been demonstrated to be necessary for the occurrence of seasonal torpor, the whole set of preconditions is still unknown. Recent findings provide evidence that the hypothalamic pituitary growth axis is involved in endocrine responses to SP exposure in the photoperiodic hamsters. To examine whether suppression of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) secretion affects the incidence of daily torpor, we used two somatostatin receptor agonists, pasireotide (SOM230) and octreotide, with different affinity profiles for receptor subtypes. Pasireotide strikingly increased the torpor frequency in male hamsters compared with sham-treated controls, and torpor duration was often increased, which in some cases exceeded 12 h. In contrast, administration of octreotide reduced the body weight of SP hamsters but had only a marginal effect on torpor frequency in males and no effect in females. Together with measured concentrations of circulating IGF-1, the present results strongly suggest that reduced activity of the GH/IGF-1 axis is not critical for stimulation of torpor expression but activation of specific somatostatin receptors is critical. This putative role for certain somatostatin receptor subtypes in torpor induction provides a promising new approach to unravel the endocrine mechanisms of torpor regulation.GH/IGF-1 axis; somatostatin receptors; torpor; seasonality; pasireotide (SOM230); octreotide SPONTANEOUS DAILY TORPOR REPRESENTS one trait of the substantial acclimation to winter-like short photoperiods (SP) in Siberian hamsters (Phodopus sungorus; a.k.a. Djungarian hamster; for review, see Ref. 26). Together with a considerably reduced body weight and improved insulative properties of the white winter fur, daily torpor contributes significantly to reduce energy demands (12). Unlike fasting-induced torpor, spontaneous daily torpor is not necessarily linked to food scarcity. Instead, Siberian hamsters show this energy-saving behavior after ϳ10 wk of SP exposure despite food abundance. Interestingly, the frequency of torpor varies largely between individuals, ranging from animals that show torpor almost every day to individuals that never enter torpor (23). Thus these hamsters exhibit an individual propensity to use this state of reduced metabolism and body temperature (T b ). Despite several decades of study, the underlying metabolic and/or hormonal factors that tip the balance in support of, or against, entry into torpor at the beginning of the (diurnal) resting phase are still unknown.SP-mediated loss of body weight appears to be a prerequisite for the occurrence of torpo...

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Section: Discussionmentioning

confidence: 99%

Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

Scherbarth¹,

Diedrich²,

Dumbell³

et al. 2015

American Journal of Physiology-Regulatory, Integrative and Comp

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“…Thus, while the animals were clearly responsive to the different photoperiods, the levels of FSH in the LD animals appear to have been insufficient to promote cyclicity. It is possible that additional environmental cues are necessary to promote full reproductive function in this species (Goldman 1991, Ouarour et al 1991, Puchalski & Lynch 1991, Badura & Goldman 1992, Debeljuk & Lasaga 1999, Drazen et al 2001, Horton & Yellon 2001, Pak et al 2001. The LD animals used were 7 weeks old and, based on previous studies, were thought to be sexually mature (Lerchl & Schlatt 1993.…”

Section: Long Photoperiod (Ld)mentioning

confidence: 99%

Photoperiod-dependent regulation of inhibin in Siberian hamsters: I. Ovarian inhibin production and secretion

Kenny

Bernard²,

Horton

et al. 2002

Journal of Endocrinology

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Follicle-stimulating hormone (FSH) stimulates ovarian follicle development and the production of protein hormones including inhibin A and inhibin B. The inhibins are dimeric proteins ( -A or -B ) secreted by growing follicles that suppress FSH in a classical endocrine negative feedback loop. Siberian hamsters, Phodopus sungorus, exhibit seasonal variation in FSH levels. Given the role of inhibin in FSH regulation, we hypothesized that ovarian inhibin expression differs between animals reared in long (16 h light:8 h darkness) and short (6 h light:18 h darkness) photoperiods. To examine inhibin expression in animals housed under long or short photoperiods, hamster inhibin -, A -, and B -subunits were cloned and used to detect and localize inhibin subunit mRNA in developing follicles. Ovarian inhibin -subunit mRNA levels were significantly higher in long day-exposed (LD) than in short day-exposed (SD) hamsters. In addition, dimeric inhibin, as well as inhibin -, A -, and B -subunit protein levels were higher in the LD than in the SD hamster ovaries.

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“…In the Djungarian hamster, torpor bouts appear when animals are exposed to SP for several weeks [12]. Castration, when per formed before or on the day of transfer to SP, reduces this duration [12], In the present study, we examined (1) the relationships be tween gonadal activity and daily torpor, (2) the presence of a T-dependent VP innervation in the LS.…”

Section: Introductionmentioning

confidence: 99%

“…It appears that gonadal regression in the Djun garian hamster is a necessary condition for the occurrence of daily torpor [12], Testosterone (T) implants completely inhibited daily tor por expression during SP. Inhibition by T was immediate and continued until the end of the daily torpor season orT capsule removal [12], The same relationship between T and hiber nation was demonstrated in other hibernating species [13][14][15][16][17][18][19][20]. In the European hamster (Cricetus cricetus), a T-dependent vasopres sin (VP) neurotransmitter system was shown to be involved in the action of gonadal hor mones on the expression of hibernation [18].…”

Section: Introductionmentioning

confidence: 99%

“…Interestingly, the annual cycle of daily torpor coincides with the seasonal variations of gonadal activity [11] which are also depen dent on changes in the photoperiod [8]. It appears that gonadal regression in the Djun garian hamster is a necessary condition for the occurrence of daily torpor [12], Testosterone (T) implants completely inhibited daily tor por expression during SP. Inhibition by T was immediate and continued until the end of the daily torpor season orT capsule removal [12], The same relationship between T and hiber nation was demonstrated in other hibernating species [13][14][15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

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Expression of Daily Torpor in the Djungarian Hamster <i>(Phodopus sungorus) </i>Is Correlated with the Testosterone-Driven Vasopressin Content in the Lateral Septum

Ouarour

Kirsch²,

Pévet³

1995

Neurosignals

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In the Djungarian hamster (Phodopus sungorus), torpor bouts appear after exposure to short photoperiods (SP) for 11 weeks. Castration accelerates the occurrence of daily torpor when performed between the 1st week before and the 4th week after transfer to SP. In animals castrated 8 weeks before transfer to SP, daily torpor was observed nearly at the same time as in the control group. Vasopressin-immunoreactivity (VP-ir) in the lateral septum (LS) of the Djungarian hamster was examined. Dense VP-ir was seen in sexually active and in sexually inactive hamsters implanted with testosterone (T) capsules. No VP-ir could be detected in sexually inactive animals. Thus, the presence of VP-ir in the LS depends on circulating T levels. In control animals exposed to SP, complete disappearance of VP-ir in the LS was observed after 8 weeks. Castration on the day of transfer to SP reduced this period to 6 weeks. In these animals, the early occurrence of daily torpor is related to the quick disappearance of VP-ir in the LS. When castrated animals were maintained under long photo-periods the disappearance of VP-ir was not complete. However, VP-ir disappeared completely after transfer to SP. The results suggest that the SP message acts on daily torpor indirectly via testicular regression but also ‘directly’ via VP septal innervation.

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Effects of temperature, steroids and castration on daily torpor in the Djungarian hamster (Phodopus sungorus)

Cited by 29 publications

References 30 publications

Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

Somatostatin receptor activation is involved in the control of daily torpor in a seasonal mammal

Photoperiod-dependent regulation of inhibin in Siberian hamsters: I. Ovarian inhibin production and secretion

Expression of Daily Torpor in the Djungarian Hamster <i>(Phodopus sungorus) </i>Is Correlated with the Testosterone-Driven Vasopressin Content in the Lateral Septum

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