The endogenous rhythm of plasma melatonin and its regulation by light in the highveld mole-rat (Cryptomys hottentotus pretoriae): a microphthalmic, seasonally breeding rodent: Melatonin rhythm in C. hottentotus pretoriae (original) (raw)
Related papers
Journal of Zoology, 2003
Subterranean mammals inhabit an environment that is normally devoid of light and are therefore deprived of photoperiodic information that can be used to time important life-history events. An assessment was made of whether melatonin secretion in a strictly subterranean rodent, the Damaraland mole-rat Cryptomys damarensis, can be modified by photoperiod. In experiment 1, a clear diurnal rhythm of melatonin secretion in animals housed under a neutral photoperiod (12L:12D) was observed, with significantly higher melatonin concentrations in the dark compared to the light phase. The same diurnal melatonin rhythm was found 1 day after animals were transferred to either continuous light or continuous dark, suggesting that a circadian rhythm was maintained under acute exposure to light and dark. In experiment 2, melatonin secretion was monitored in a long (14L:10D) and short day (10L:14D) photoperiod and was found to be modified by the photoperiodic change. We therefore suggest that the Damaraland mole-rat possesses a circadian melatonin rhythm that can be physiologically modulated in response to photoperiod.
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
Physiology & …, 2006
The Lesotho mole-rat is a social subterranean rodent that occurs at altitude in the Drakensberg mountain range. As a consequence of living permanently underground these animals rarely if ever are exposed to light. The visual system of African mole-rats is particularly regressed whereas the circadian system is proportionately conserved. This study investigated the locomotor activity patterns of 12 Lesotho mole-rats maintained under a range of different lighting regimes. The majority (91.7%) of mole-rats entrained their activity patterns to a LD photoperiod of 12L/12D. The mole-rats displayed a monophasic nocturnal activity preference. Under constant dark (DD) most of the molerats (83.3%) showed a free running circadian activity pattern with a tau of 23.8 h to 24.4 h (mean ± S.E.M.: 24.07 h ± 0.07 h; n = 10). The phase of the activity rhythms each mole-rat exerted during the previous LD-cycle did not change when the animals started free-running after being placed in constant conditions. The duration of re-entrainment to a second bout of LD 12:12 amounted to 9.4 ± 2.03 days (mean ± S.E.M., n = 10). Eleven mole-rats (91.7%) adjusted their locomotor activity rhythms to an inversed light regime DL 12:12 and displayed significant nocturnal activity preference. The animals required 9.73 ± 2.01 days (mean ± S.E.M., n = 11) to adjust to the DL-photoperiod. The Lesotho mole-rat thus possesses a functional circadian clock that responds to a photic zeitgeber.
Clocks Ticking in the Dark: A Review of Biological Rhythms in Subterranean African Mole-Rats
Frontiers in Ecology and Evolution
Biological rhythms are rhythmic fluctuations of biological functions that occur in almost all organisms and on several time scales. These rhythms are generated endogenously and entail the coordination of physiological and behavioural processes to predictable, external environmental rhythms. The light-dark cycle is usually the most prominent environmental cue to which animals synchronise their rhythms. Biological rhythms are believed to provide an adaptive advantage to organisms. In the present review, we will examine the occurrence of circadian and seasonal rhythms in African mole-rats (family Bathyergidae). African mole-rats are strictly subterranean, they very rarely emerge aboveground and therefore, do not have regular access to environmental light. A key adaptation to their specialised habitat is a reduction in the visual system. Mole-rats exhibit both daily and seasonal rhythmicity in a range of behaviours and physiological variables, albeit to different degrees and with large ...
Journal of Experimental Zoology, 1986
Variations in pineal melatonin content throughout a %hour period and during different phases of the hibernation bout cycle were studied in the golden-mantled ground squirrel (Spermophilus lateralis). In addition to pineal melatonin, the circadian variation in the activities of pineal N-acetyltransferase (NAT) and hydroxyindole-0-methyltransferase (HIOMT) were also investigated in summer animals maintained at 22 f 2"C, on a 1ight:dark (L:D) schedule of 12:12 hr for 1 month (lights on at 08.00 hr). Pineal glands were collected from six animals in each group at 1200,1600,2000,2400,0200,0400, and 0800 hr. Changes in pineal melatonin content during the hibernation bout cycle were investigated in ground squirrels housed at 4 .05"C in relative darkness (1.9-3.4 lux; 10:14 LD). Pineal glands were obtained between 12:OO and 18:OO hr from 30 animals during one of three phases of the cycle (deep hibernation, euthermic interbout, and entrance into hibernation). Pineal melatonin was also measured for comparison in six winter euthermic animals that were housed at 22 f 2"C, on a L:D schedule of 10:14 hr. Melatonin was measured in individual pineal glands by radioimmunoassay. The daily melatonin rhythm in S. lateralis was characterized by a marked increase in pineal melatonin during the dark phase, in which peak nighttime values were nearly 20-fold greater than daytime basal levels. The daily rhythm for NAT activity Cheryl M.
Circadian rhythms of locomotor activity in the subterranean Mashona mole rat, Cryptomys darlingi
Physiology & …, 2005
The Mashona mole rat, Cryptomys darlingi, is a social, subterranean African rodent that is rarely, if ever, exposed to light, and that exhibits a regressed visual system. This study investigated locomotor activity patterns of Mashona mole rats (n=12) under different light cycles. Activity was measured using either infrared captors (n=8) or running wheels (n=4). The mole rats entrained their activity to a standard (LD 12:12) photoperiod. They displayed either a nocturnal or diurnal activity preference with one bout of activity and one bout of rest. Therefore, as a species, the Mashona mole rat did not show a clear nocturnal or diurnal activity preference. When the LD (12:12) light cycle was inversed, the animals switched their activity, too. Under constant dark (DD), most mole rats (73%) showed a free-running circadian activity rhythm, but under constant light (LL), only some (36%) did. The free-run period of the rhythm (s) ranged from 23.83 to 24.10 h. The remaining animals were arrhythmic. There was large interindividual and intraindividual variations in the rate and extent of entrainment, time of activity preference, and activity patterns. Possible reasons for the observed variations are discussed. It is concluded that the Mashona mole rat has an endogenous activity rhythm which approximates 24 h, that the mole rat can distinguish between light and dark, and that the endogenous clock utilises this photic information as a zeitgeber. D
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.
Frontiers in Physiology, 2021
Living organisms anticipate the seasons by tracking the proportion of light and darkness hours within a day—photoperiod. The limits of photoperiod measurement can be investigated in the subterranean rodents tuco-tucos (Ctenomys aff. knighti), which inhabit dark underground tunnels. Their exposure to light is sporadic and, remarkably, results from their own behavior of surface emergence. Thus, we investigated the endogenous and exogenous regulation of this behavior and its consequences to photoperiod measurement. In the field, animals carrying biologgers displayed seasonal patterns of daily surface emergence, exogenously modulated by temperature. In the laboratory, experiments with constant lighting conditions revealed the endogenous regulation of seasonal activity by the circadian clock, which has a multi-oscillatory structure. Finally, mathematical modeling corroborated that tuco-tuco’s light exposure across the seasons is sufficient for photoperiod encoding. Together, our results ...
European Journal of Neuroscience, 2007
In mammals, day length (photoperiod) is read and encoded in the main circadian clock, the suprachiasmatic nuclei (SCN). In turn, the SCN control the seasonal rhythmicity of various physiological processes, in particular the secretion pattern of the pineal hormone melatonin. This hormone then operates as an essential mediator for the control of seasonal physiological functions on some tissues, especially the pars tuberalis (PT). In the European hamster, both hormonal (melatonin) and behavioral (locomotor activity) rhythms are strongly affected by season, making this species an interesting model to investigate the impact of the seasonal variations of the environment. The direct (on SCN) and indirect (via melatonin on PT) effect of natural short and long photoperiod was investigated on the daily expression of clock genes, these being expressed in both tissues. In the SCN, photoperiod altered the expression of all clock genes studied. In short photoperiod, whereas Clock mRNA levels were reduced, Bmal1 expression became arrhythmic, probably resulting in the observed dramatic reduction in the rhythm of Avp expression. In the PT, Per1 and Rev-erba expressions were anchored to dawn in both photoperiods. The daily profiles of Cry1 mRNA were not concordant with the daily variations in plasma melatonin although we confirmed that Cry1 expression is regulated by an acute melatonin injection in the hamster PT. The putative role of such seasonal-dependent changes in clock gene expression on the control of seasonal functions is discussed.