Dataset Information

Rapid induction of hypothalamic iodothyronine deiodinase expression by photoperiod and melatonin in juvenile Siberian hamsters (Phodopus sungorus).

ABSTRACT: Production of T(3) in the mediobasal hypothalamus is critical for regulation of seasonal reproductive physiology. Type 2 iodothyronine deiodinase (DIO2) and DIO3 enzymes catalyze the prohormone T(4) into biologically-active T(3) and biologically-inactive rT(3), respectively. In several seasonally-breeding vertebrates, DIO2 and DIO3 expression is implicated in photoperiod signal transduction in adulthood. These experiments tested the hypothesis that juvenile Siberian hamsters, which are highly responsive to photoperiod at weaning (postnatal day [PND]18), exhibit rapid and sustained changes in hypothalamic dio3 mRNA expression during photoperiod-induced and photoperiod-inhibited puberty. Hypothalamic dio2 and dio3 expression was measured via quantitative PCR in hamsters born and reared in a long-day photoperiod (15L:9D) and weaned on PND18 into short-day photoperiods (9L:15D). In SD males, hypothalamic dio3 mRNA was elevated 2.5-fold within 3 days (PND21) and continued to increase (>20-fold) through PND32; changes in dio3 mRNA preceded inhibition of gonadotropin (FSH) secretion and gonadal regression in SD. Females exhibited comparable dio3 responses to SD. In LD males, dio3 remained low and invariant from PND18-PND32. In contrast, dio2 mRNA rose conspicuously on PND21, independent of photoperiod, returning to basal levels thereafter. In LD, a single afternoon melatonin (MEL) injection on PND18 or PND20 was sufficient to increase hypothalamic dio3 mRNA, and dio3 increased in proportion to the number of successive days of MEL treatment. SD photoperiods and MEL exert rapid, sustained, and additive effects on hypothalamic dio3 mRNA, which may play a central role in inhibiting maturation of the peripubertal hypothalamo-pituitary-gonadal axis.

SUBMITTER: Prendergast BJ

PROVIDER: S-EPMC3548179 | biostudies-literature | 2013 Feb

REPOSITORIES: biostudies-literature

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Publications

Rapid induction of hypothalamic iodothyronine deiodinase expression by photoperiod and melatonin in juvenile Siberian hamsters (Phodopus sungorus).

Prendergast Brian J BJ Pyter Leah M LM Kampf-Lassin August A Patel Priyesh N PN Stevenson Tyler J TJ

Endocrinology 20130107 2

Production of T(3) in the mediobasal hypothalamus is critical for regulation of seasonal reproductive physiology. Type 2 iodothyronine deiodinase (DIO2) and DIO3 enzymes catalyze the prohormone T(4) into biologically-active T(3) and biologically-inactive rT(3), respectively. In several seasonally-breeding vertebrates, DIO2 and DIO3 expression is implicated in photoperiod signal transduction in adulthood. These experiments tested the hypothesis that juvenile Siberian hamsters, which are highly re ...[more]

PMID: 23295738

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Project description:To survive the Siberian winter, Djungarian hamsters (Phodopus sungorus) adjust their behavior, morphology, and physiology to maintain energy balance. The reduction of body mass and the improvement of fur insulation are followed by the expression of spontaneous daily torpor, a state of reduced metabolism during the resting phase to save additional energy. Since these complex changes require time, the upcoming winter is anticipated via decreasing photoperiod. Yet, the extent of adaptation and torpor use is highly individual. In this study, adaptation was triggered by an artificially changed light regime under laboratory conditions with 20°C ambient temperature and food and water ad libitum. Two approaches analyzed data on weekly measured body mass and fur index as well as continuously recorded core body temperature and activity during: (1) the torpor period of 60 hamsters and (2) the entire adaptation period of 11 hamsters, aiming to identify parameters allowing (1) a better prediction of torpor expression in individuals during the torpor period as well as (2) an early estimation of the adaptation extent and torpor proneness. In approach 1, 46 torpor-expressing hamsters had a median torpor incidence of 0.3, covering the spectrum from no torpor to torpor every day within one representative week. Torpor use reduced the body temperature during both photo- and scotophase. Torpor was never expressed by 14 hamsters. They could be identified by a high, constant body temperature during the torpor period and a low body mass loss during adaptation to a short photoperiod. Already in the first week of short photoperiod, approach 2 revealed that the hamsters extended their activity over the prolonged scotophase, yet with reduced scotophase activity and body temperature. Over the entire adaptation period, scotophase activity and body temperature of the scoto- and photophases were further reduced, later accompanied by a body mass decline and winter fur development. Torpor was expressed by those hamsters with the most pronounced adaptations. These results provide insights into the preconditions and proximate stimuli of torpor expression. This knowledge will improve experimental planning and sampling for neuroendocrine and molecular research on torpor regulation and has the potential to facilitate acute torpor forecasting to eventually unravel torpor regulation processes.

Dataset Information

Rapid induction of hypothalamic iodothyronine deiodinase expression by photoperiod and melatonin in juvenile Siberian hamsters (Phodopus sungorus).

Publications

Rapid induction of hypothalamic iodothyronine deiodinase expression by photoperiod and melatonin in juvenile Siberian hamsters (Phodopus sungorus).

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