Interindividual differences in the pattern of melatonin secretion of the Wistar rat (original) (raw)
Behavioural Brain Research, 2002
The effect of exogenous melatonin (MEL) on the circadian system in nocturnal species has been extensively studied, but little is known about its chronobiotic effect in diurnal mammals. The present study investigated the effect of exogenous MEL on the circadian locomotor activity rhythm in the diurnal rodent Ar6icanthis ansorgei. Male animals (n= 34) were fitted with a subcutaneous catheter for daily infusion of MEL (1 h; 100 mg) and their running wheel activity was recorded. The results showed that administration of MEL to animals free-running in DD entrained their activity rhythm by phase advances at circadian time (CT) 10.62, and by phase delays at CT −0.40 (CT 0, activity onset). The range of entrainment was 17 and 11.5 min for advance and delay stimuli, respectively. Interestingly, in the nocturnal rat and the A. ansorgei, entrainment of the activity rhythm to exogenous MEL by phase advances occurs at exactly the same phase of the circadian cycle. In both nocturnal and diurnal species, the sensitivity window for exogenous MEL is located near the activity/rest transition points. It is concluded that the functional properties of entrainment to exogenous MEL are similar to those of other nonphotic stimuli. Furthermore, A. ansorgei might be an interesting animal model for studies on the chronobiotic effects of exogenous MEL in diurnal mammals including humans.
Journal of Neuroendocrinology, 1995
The pineal gland, via the daily pattern of melatonin (MEL) secretion, is directly involved in the conduction of photoperiodic information. The duration of MEL secretion is proportional to the duration of the dark period and, whatever the photoperiod is, MEL synthesis occurs 3 or 4 h after the dark onset in Syrian hamsters. In order to determine the relative importance of the duration or the coincidence hypothesis, a daily infusion protocol was used in sexually active pinealectomized hamsters. Long duration of MEL infusion (10 h) completely inhibit testes whereas short duration infusion (5 h) had no effect. When the animals were infused twice within 2 h 30 min separated by 3 h, they presented a complete gonadal atrophy, similar to the one observed with the 10 h infusion. Measurement of plasma MEL during the infusion and seperation periods revealed that MEL reached physiological nighttime values during the infusion period and fell to daytime values 1 h after the end of an infusion period. Thus, the results could not be due to a time additive action of the two MEL pulses. An intermediate response was observed when the 2 signals were applied across the Iightldark transition. Gonadal regression did not occur
Steroids, 1991
The major junction of the mammul~arl pineal gland appears to be its central role in ~~~otoperio~iism. The pineal hormone, me~atonin, is synt~tesi~ed and secreted primuri~y ut nig~~t, lander the control of a circadian oscillator that is entrained to the light-dark cycle. Both the circadian phase and the duration of the nocturnal peak of meiatonin secretion are established primarily by interactions between the endogenous circadian oscillator and the daily photic cycle. The duration of the melatonin peuk varies inversely with day length, and this relationship between day length and the durution of each circadian melatonin peak appears to be an integral part of the photoperiodic mechanism. When pinealectomized ani~nals are given daily rne~at[~nin infusions of long dt~ratioi~, they exhibit physiologic. re.~pon~~es that normally are observed during exposure to short day ph~~t~~period~~; when administered sh~~rt-duration melatonin infusions, the animals display longphotoperiod-type responses. In addition to the importance of the duration of each melatonin peak, certain other parameters appear to be sign$cant. If a longduration infusion of melatonin is interrupted by a period of 2 hours or more without melatonin (i.e., to produce two short duration infusions), the responses are those typical for long day-exposed animals. Thus, to elicit short day-type responses, each l~~ng-~~arat~on melatt)nin peak must be rel~~tiv~~iy continuous; responses are not determined simply by the total time of exposure to melatonin in euch ~ir~ad~a~~ cycle. Also, long-duration melatonin peaks may nor be effective to elicit photoperiod-type responses unless they are present at frequencies of nearly once every 24 hours or more.
Comparative effects of a melatonin agonist on the circadian system in mice and Syrian hamsters
Brain Research, 1997
S-20098 has potent and specific agonist properties on melatonin receptors both in vitro and in vivo. Behavioral studies on rodents already showed that repeated intraperitoneal administration of S-20098 could dose-dependently alter the functioning of the circadian clock. To determine whether single administration of S-20098 could alter the circadian rhythms of rodents, we first used the Ž . Ž . phase-response curve PRC approach in two different species: Syrian hamsters and mice C3HrHeJ . Our results show that the shape, circadian times and extent of the PRC to S-20098 look very similar in mice and hamsters. In both species, the phase advance portion of the PRC to S-20098 is limited to a 3 h window preceding the onset of locomotor activity, but the magnitude of phase shifts is larger in mice. We also tested the phase shifting effects of increasing doses of S-20098 during the interval of maximal sensitivity to this compound. Treatment with S-20098 induces dose-dependent phase shifts, with maximal shifts observed after injections of 20 and 25 mgrkg S-20098 i.p., respectively, in mice and hamsters. Those results are in agreement with the limited distribution of melatonin-binding sites within the circadian clock of adult Syrian hamsters, as compared to other rodents. q 1997 Elsevier Science B.V.
Journal of Pineal Research, 1989
Seasonal differences in daily patterns of plasma melatonin concentration were investigated in both free-living and captive mountain hares, in relation to reproductive activity. There was a marked increase in plasma melatonin concentrations at night at all times of the year. The period of elevation of plasma melatonin above the daytime values was longer in winter than in summer, correlating with the longer duration of darkness. The magnitude of the nighttime rise in melatonin concentrations did not differ significantly between seasons. There was no change in the plasma melatonin profile under similar photoperiods before the summer solstice when hares are sexually active or after the summer solstice when gonadal regression occurs, indicating that melatonin is not directly pro-or antigonadal. These field and laboratory observations support the view that the daily rhythm of melatonin secretion plays a role in the transduction of photoperiodic information in the mountain hare. Furthermore, they favor the hypotheses that the circadian melatonin rhythm transduces photoperiod information by means of the duration of nocturnal melatonin secretion or by the coincidence of elevated melatonin with a particular sensitive period, rather than by the amplitude of the nocturnal rise.
Melatonin secretion in the Mashona mole-rat, Cryptomys darlingi—influence of light on rhythmicity
Physiology & Behavior, 2005
The hormone melatonin is synthesised and secreted from the pineal gland in darkness and triggers the daily and seasonal timing of various physiological and behavioural processes. The Mashona mole-rat, Cryptomys darlingi, lives in subterranean burrows that are completely sealed and is therefore rarely, if ever, exposed to light under natural conditions. Hence, this species is of particular interest for studies on rhythms of melatonin secretion. We investigated how plasma melatonin concentrations of the Mashona mole-rat responded to exposure to a long-term standard photoperiod of 12 h light, 12 h dark (12:12 LD), constant light (LL) and constant dark (DD). In addition, we examined whether plasma melatonin concentration was coupled to locomotor activity. Mashona mole-rats displayed rhythms of plasma melatonin concentration that appeared entrained to the standard LD photoperiod, suggesting that the mole-rat is capable of perceiving and entraining to this photic zeitgeber. Furthermore, under chronic constant lighting conditions (DD, LL), circadian rhythms in plasma melatonin concentration were observed, suggesting the possible existence of an endogenous rhythm. Light suppressed melatonin secretion, but constant light did not abolish the rhythm of plasma melatonin concentration. Between active and non-active animals, no difference in plasma melatonin concentration was found for any of the sequential photoperiods (LD1 DD, LD2, LL), tentatively suggesting that the rhythm of melatonin secretion is uncoupled from that of locomotor activity. D
A non-invasive simple method for measurement of urinary excretion of melatonin in undisturbed mice
Journal of Pineal Research, 1993
Abstract: Melatonin is a hormone involved in neuroendocrine responses; its plasma concentrations display a circadian pattern which is modified by stress. Studies for determining the effects of stressors on melatonin levels in laboratory animals present the difficulty that the procedures for blood sampling are by themselves potential stressors capable of influencing the levels of the hormone measured. A simple non-stressful method for measuring urinary excretion of melatonin has been consequently developed. The method is applicable to single undisturbed mice kept in conventional cages, and consists of urine collection on chromatographic paper followed by extraction and melatonin assay by radioimmunoassay. The use of this method with BD2F1 mice indicates nocturnal excretion of melatonin significantly higher than during the day; nighttime melatonin levels were shown to be suppressed by constant illumination. A significant increase in nocturnal melatonin excretion was caused by the application of rotational stress applied as a mild experimental stressor.