Daily Melatonin Injections Affect the Expression of Circadian Rhythmicity in Djungarian Hamsters Kept under a Long-Day Photoperiod

Puchalski, W.; Gr, Lynch

doi:10.1159/000125023

Cited by 44 publications

(26 citation statements)

References 26 publications

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“…In a related study, however, Puchalski and Lynch (1988b) found that refractoriness to daily melatonin injections (as determined by molt from a white to a greybrown pelt, body weight gain, and gonadal recrudescence) occurred at about weeks 26-32 of hormone treatment. Furthermore, they found that shifts in phase angle and a occurred simultaneously with changes in body weight, molt, and gonadal state.…”

Section: Discussionmentioning

confidence: 92%

Evidence for Independence of Circadian Characters and Extent of Photoresponsiveness in the Djungarian Hamster, Phodopus sungorus

Kliman

Lynch

1991

J Biol Rhythms

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Djungarian hamsters (Phodopus sungorus) exposed to a short-day photoperiod generally respond with a syndrome of physiological and behavioral changes, such as body weight loss and molt to a white pelage. The extent of the short-day-induced responses differs among individuals. Furthermore, some hamsters show no photoresponse. In this study, we sought to determine whether variation in the photoresponse would be associated with circadian function: whether phase angle or free-running period (tau) would differ between responsive and nonresponsive hamsters; and whether changes in these circadian characters would correlate with the extent of weight loss and molt (and the timing of molt onset) in photoresponsive hamsters. Adult hamsters were kept in a short-day photoperiod (9 hr light, 15 hr dark) for 14 weeks, during which time body weight and molt were measured biweekly. Hamsters were then transferred to cages equipped with running wheels; we measured the phase angle of activity onset under a short-day photoperiod and tau in constant dark. Hamsters exhibiting a short-day-induced molt had a significantly shorter tau and a less negative phase angle than nonmolting animals. Hamsters that exhibited weight loss also had a significantly less negative phase angle, but no difference in tau. No significant Pearson's or Spearman's correlation coefficients were found between extent (or timing) of the photoresponse and the circadian characters in responsive hamsters. Although these results indicate that threshold for photoresponsiveness is related to circadian function, the extent (and timing) of the photoresponse may not be.

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Section: Discussionmentioning

confidence: 92%

Evidence for Independence of Circadian Characters and Extent of Photoresponsiveness in the Djungarian Hamster, Phodopus sungorus

Kliman

Lynch

1991

J Biol Rhythms

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“…Pineal dependence of innate immunity has been inferred from a study which maintained hamsters in constant light, suppressing endogenous melatonin secretion (Yellon et al, 2005); pineal dependence of adaptive immunity has been inferred from an experiment which exposed pinealectomized hamsters to short days for 1 week prior to antigenic challenge (Yellon et al, 1999b). The interpretation of these studies is not straightforward, given that: (1) daily melatonin injections also render the circadian system in a SD-typical state (Puchalski and Lynch, 1988;Margraf and Lynch, 1993), (2) little is known regarding the significance of the amplitude of melatonin signals on immune function, and (3) constant light renders circadian rhythms in a free-running state, functions as a stressor, and can be immunosuppressive (Morimoto et al, 1975;Ramaley, 1977;Larsen et al, 1994;Liebmann et al, 1996). An alternative, and definitive, approach is to determine whether photoperiodic responses in the immune system endure following removal of the endogenous pineal melatonin signal (via surgical pinealectomy) and exposure to longer seasonal intervals of short days (>6 weeks).…”

Section: Introductionmentioning

confidence: 99%

Pineal-dependent and -independent effects of photoperiod on immune function in Siberian hamsters (Phodopus sungorus)

Wen

Dhabhar

Prendergast

2007

Hormones and Behavior

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Siberian hamsters (Phodopus sungorus) exhibit reproductive and immunological responses to photoperiod. Short (<10-h light/day) days induce gonadal atrophy, increase leukocyte concentrations, and attenuate thermoregulatory and behavioral responses to infection. Whereas hamster reproductive responses to photoperiod are dependent on pineal melatonin secretion, the role of the pineal in short-day induced changes in immune function is not fully understood. To examine this, adult hamsters were pinealectomized (PINx) or sham-PINx, and transferred to short days (9-h light/day; SD) or kept in their natal long-day (15-h light/day; LD) photoperiod. Intact and PINx hamsters housed in LD maintained large testes over the next 12 weeks; sham-PINx hamsters exhibited gonadal regression in SD, and PINx abolished this effect. Among pineal-intact hamsters, blood samples revealed increases in leukocyte, lymphocyte, CD62L+ lymphocyte, and T cell counts in SD relative to LD; PINx did not affect leukocyte numbers in LD hamsters, but abolished the SD increase in these measures. Hamsters were then treated with bacterial lipopolysaccharide (LPS), which induced thermoregulatory (fever), behavioral (anorexia, reductions in nest building), and somatic (weight loss) sickness responses in all groups. Among pineal-intact hamsters, febrile and behavioral responses to LPS were attenuated in SD relative to LD. PINx did not affect sickness responses to LPS in LD hamsters, but abolished the ameliorating effects of SD on behavioral responses to LPS. Surprisingly, PINx failed to abolish the effect of SD on fever. In common with the reproductive system, PINx induces the LD phenotype in most aspects of the immune system. The pineal gland is required for photoperiodic regulation of circulating leukocytes and neural-immune interactions that mediate select aspects of sickness behaviors.

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“…In the Djungarian hamster, gonadal regression or lengthening the duration of nocturnal locomotor activity requires repeated administration of melatonin for several weeks (Puchalski and Lynch, 1988). In the rat, more than a week of daily melatonin injections are needed to entrain or reinstate circadian locomotor activity under constant photoperiodic conditions .…”

Section: Introductionmentioning

confidence: 99%

Daily Melatonin Treatments Regulate the Circadian Melatonin Rhythm in the Adult Djungarian Hamster

Yellon

1996

J Biol Rhythms

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The present study tested the hypothesis that daily melatonin treatments influence the biological clock mechanism controlling the circadian melatonin rhythm. Adult male and female Djungarian hamsters in light:dark = 16L:8D (lights on 0300-1900 h) were administered melatonin subcutaneously (s.c.) each day (5 micrograms/0.2 ml saline) in the morning at 1000 h (AM) or late afternoon at 1700 h (PM); controls received a vehicle injection (CON). After 14 days, pineal and serum melatonin concentrations were determined at various times on the last day of treatment and the next day in constant darkness (no treatment). The rhythm in pineal gland melatonin content was similar in each of the three groups on the last day of treatment (about 6 h duration). On the next day in constant dark, the rising phase was advanced and duration extended by 2 h or more in melatonin-treated hamsters compared to that in CONs (ANOVA). In circulation, the melatonin rhythm in AM and PM groups was phase advanced (onset and peak) on both days of the study. Thus duration was extended by up to 4.5 h compared to that in saline-treated controls. Moreover, amplitude of the nighttime serum melatonin rise was elevated up to fivefold relative to that in the CON group (ANOVA and Accumulated Sums analysis). The effects of repeated melatonin treatments on amplitude and phase of the serum melatonin rhythm raise the possibility that the circadian clock that controls pineal gland production of melatonin may also regulate melatonin secretion. From this and another study, the apparent half-life of melatonin in circulation was estimated to be 7.5 min; the melatonin injection initially produced pharmacological concentrations that were followed by low serum melatonin levels within 2 h. Thus, in both melatonin treatment groups, the data suggest that two distinct periods of elevated serum melatonin were present each day. The cellular mechanism for melatonin action must take into consideration how a brief interruption in elevated melatonin in circulation (about 1 h in the PM group) is recognized as a continuous duration (short daylength), whereas a more extended baseline period is transduced as an abbreviated or long daylength (about 7 h in the AM group). These data further suggest that the biological clock mechanism that generates the circadian melatonin rhythm is responsive to the influence of daily melatonin treatments and presumably to the feedback action of endogenous melatonin on its own rhythm in the Djungarian hamster in long days.

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Daily Melatonin Injections Affect the Expression of Circadian Rhythmicity in Djungarian Hamsters Kept under a Long-Day Photoperiod

Cited by 44 publications

References 26 publications

Evidence for Independence of Circadian Characters and Extent of Photoresponsiveness in the Djungarian Hamster, Phodopus sungorus

Evidence for Independence of Circadian Characters and Extent of Photoresponsiveness in the Djungarian Hamster, Phodopus sungorus

Pineal-dependent and -independent effects of photoperiod on immune function in Siberian hamsters (Phodopus sungorus)

Daily Melatonin Treatments Regulate the Circadian Melatonin Rhythm in the Adult Djungarian Hamster

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