Phase-shifting effects of dusklike and dawnlike light pulses on the circadian activity rhythms of Syrian hamsters

This study tested whether light pulses with a dusklike offset or a dawnlike onset caused phase shifts of different sizes in the circadian wheel-running activity of Syrian hamsters, Mesocricetus auratus. Six experiments were conducted, each with 30 hamsters; the hamsters received first one type of pulse and then the other type a few weeks later, allowing a paired comparison. The six experiments represented the combination of two maximum light intensities (150 and 250 lux) and three zeitgeber times (ZTs) at which the pulses were given (ZT13.5, ZT14.5, and ZT20). Pulses were 30 minutes long, a relatively short duration to minimize circadian time effects. Aschoff's type II method of measuring phase shifts was used. In none of the six experiments did a two-tailed paired t test detect a significant difference in the size of phase shifts caused by dusklike versus dawnlike pulses. A three-way analysis of variance (ANOVA) on the combined data from all six experiments (with pulse type, pulse intensity, and ZT as factors) also failed to detect a significant effect of pulse type. Statistical power was calculated and found to be reasonably good. These negative results are in line with those of a previous study in which a different methodology was used. (Chronobiology International, 18(3), 413-421, 2001)     

Circadian rhythm of motor activity of the Brazilian rock cavy (Kerodon rupestris) under artificial photoperiod

Kerodon rupestris, a Brazilian caviidae rodent, lives in dry stony places. In a first experiment, seven animals were kept in LD (250:0 lux and 400:0 lux) during 40 days in each condition. In the second, four animals were kept in LD (470 lux: red dim light) for 47 days, then in LL (470 lux) for 18 days and in DD (red dim light) for 23 days. Motor activity was continuously recorded by infrared sensors. Animals showed entrained rhythms to the LD cycle being light and dark active, with higher values in phase transitions. When the light intensity was increased, four animals increased and two reduced the activity. In LL, three animals expressed an endogenous tau of 24.4, 26.5 and 24.6 h and one was arrhythmic; in DD, two expressed tau of 23.6 and 23.7 h and one was arrhythmic. Results indicate that Kerodon rupestris circadian rhythm is affected by light intensity but it is not yet possible to determine its habit.     

The precision of circadian clocks: assessment and analysis in Syrian hamsters

Locomotor activity recordings of Syrian hamsters were systematically analyzed to estimate the precision of the overt circadian activity rhythm in constant darkness. Phase variation, i.e., the standard deviation of phase markers around the regression line, varied with the definition of phase. Smallest phase variation was found in the onset of wheel running activity defined by 1h running means of the raw data. Both lower and higher degrees of smoothing lead to decreased precision measured in the overt rhythm. With passive infrared recordings, the midpoint of activity defined by 3h running means was the least variable. This demonstrates that the choice of phase marker should vary between recording methods. Phase variation decreased with increasing activity and was larger in females than in males. By calculating the average cycle variation and serial covariance of consecutive cycles, we estimated the contribution of 'clock' and 'non-clock' related processes to the overt rhythm variability. Variance in precision between phase markers could be shown to be attributable mainly to nonclock processes. Variance in pacemaker cycle length appeared reduced in wheel running activity records compared with passive infrared sensing records, suggesting feedback from running activity onto pacemaker function.     

Effect of light on the development of the circadian rhythm of motor activity in the mouse

In previous experiments, we found that rats raised in constant light (LL) manifested a more robust circadian rhythm of motor activity in LL and showed longer phase shifts after a light pulse in constant darkness (DD) than those raised under constant darkness. In addition, we observed that the effects produced by constant light differed depending on the time of postnatal development in which it was given. These results suggest that both sensitivity to light and the functioning of the circadian pacemaker of the rat could be affected by the environmental conditions experienced during postembryonic development. Thus, the present experiment aimed to study whether postnatal exposure to light could also affect the circadian system of the mouse. Three groups of mice were formed: One group was raised under constant darkness during lactation (DD group), the second under constant light (LL group), and the third under light-dark cycles (LD group). After lactation, the three groups were submitted first to constant light of high intensity, then to LD cycles, and finally to constant darkness. In the DD stage, a light pulse was given. Finally, mice were submitted to constant light of low intensity. We observed that the circadian rhythm of the DD group was more disturbed under constant light than the rhythm of the LL group, and that, when light intensity increased, the period of the rhythm of the DD group lengthened more than that of the LL group. No significant differences among the groups were found in the phase shift induced by the light pulse. Therefore, it appears that DD mice are more sensitive to light than their LL counterparts. However, at present there is no evidence to affirm that the light environment experienced by the mouse during postnatal development affects the circadian pacemaker. (Chronobiology International, 18(4), 683-696, 2001)     

Masking of locomotor activity in hamsters

The inhibition of locomotion by light (masking) was investigated in Syrian hamsters. When 1-h pulses of light were presented in the early night, activity was strongly suppressed by irradiances of about 1 lx or greater. Ultradian light-dark cycles were used as another way to study masking. Hamsters were unable to entrain to 3.5:3.5-h light-dark cycles, thus permitting the masking and the entraining effects of light to be distinguished. Light had greater suppressive effects on activity in home cages than on activity in novel running wheels. Moreover, in home cages activity remained very low for about 30 min after lights were turned off. Post-pulse suppression of activity was not simply a consequence of reduced running, as shown by experiments in which running was temporarily prevented by locking the wheels. A phase response curve for masking was obtained by placing hamsters in novel wheels for 3-h periods at various times throughout their circadian cycles, and then superimposing a 30-min light pulse. The suppressive effect of light was maximal around the onset of activity, which normally coincides with dusk in hamsters. This may have adaptive value in limiting foraging to the hours of darkness. Accepted: 8 February 1999     

Effect of cage enrichment on the daily use of running wheels by Syrian hamsters

Institutional animal care committees may one day require for the welfare of captive hamsters more floor space and the introduction of tunnels and toys. As hamsters are popular animal subjects in chronobiological research, and as clock phase is usually measured through running wheel activity, it is important to determine what effect cage enrichment might have on daily wheel use. Here the daily number of wheel revolutions, the daily duration of the running activity phase, the phase relationship between lights-off and onset of running activity, and the free-running period of circadian activity rhythms were measured in Syrian hamsters, Mesocricetus auratus, housed in single cages or in multiple cages linked by tunnels and supplied with commercial wooden toys. Free-running periodicity was not affected by cage enrichment. In multiple-cage systems, there were fewer daily revolutions, shorter wheel-running activity phases, and delayed running activity onsets. These effects, however, were small as compared to interindividual and week-to-week variation. They were statistically significant only under a light:dark cycle, not in constant darkness, and only when interindividual variation was eliminated through a paired design or when the number of cages was increased to five (the maximum tested). Daily wheel use is thus affected by cage enrichment, but only slightly.     

Pathophysiological studies of trinitrobenzene sulfonic acid-induced colitis in Syrian hamsters (Mesocricetus auratus)

We developed a colitis model in Syrian hamsters (Mesocricetus auratus) to investigate the relationship between colitis and neutrophil elastase (NE). Colitis was induced by a single intracolonic dose of trinitrobenzene sulfonic acid (TNBS; 90 mg/ml) dissolved in 15% (vol/vol) ethanol. The ulcer area, tissue myeloperoxidase (MPO) activity, and luminal NE activity all were increased on Days 1 and 5, corresponding with the acute inflammatory histopathological changes. These acute inflammatory parameters subsequently decreased by Day 14, and chronic inflammatory histopathological changes became evident. Recurrence of inflammation was not observed during the period up to Day 28. To evaluate our colitis model, the effects of prednisolone were examined. Prednisolone was administered orally once on the day before induction of colitis, and animals were treated twice daily thereafter. Although prednisolone had little effect on the tissue MPO activity, prednisolone inhibited the ulcer area and NE activity. In addition, the effects of an NE-specific inhibitor (ONO-6818) on our TNBS-induced colitis model were examined. In the subcutaneous treatment study, ONO-6818 was administered once before the induction of colitis. Although ONO-6818 had little effect on the tissue MPO activity, the ulcer area and NE activity were decreased in the ONO-6818-treated group. The inhibitory effects on the ulcer area and NE activity were confirmed after oral treatment with ONO-6818 after induction of colitis. We conclude that our colitis model is useful for investigating the relationship between colitis and NE, and inhibition of NE activity can prevent the progression of ulceration.     

Acute effects of light on body temperature and activity in Syrian hamsters: influence of circadian phase

Light exposure at night causes an acute increase in human body temperature, which normally falls during the night. This change is largely attributable to the suppression by light of the nocturnal rise in melatonin levels. Little is known, however, about the effects of light on body temperature in nocturnally active mammals in which the nightly peak in melatonin secretion coincides with the circadian phase of elevated, rather than decreased, body temperature. We investigated the effects of a 1-h exposure to light on body temperature and activity of Syrian hamsters, Mesocricetus auratus, at two phases during the night and at two phases during the projected day. Brain or abdominal temperature was recorded continuously using implanted radio transmitters while locomotor activity was monitored simultaneously using a passive infrared movement detector. Responses to light exposure were strongly circadian phase dependent; light during the night caused elevations in both brain and core body temperature, whereas light during the projected day did not. Temperature increases at night could not be attributed solely to activity increases at the onset of light pulses, indicating a contribution from nonbehavioral mechanisms of thermogenesis. These results provide the first evidence for circadian modulation of acute temperature responses to light in a nocturnal mammal.     

DSIP/DSIP-P and circadian motor activity of rats under continuous light

Daily intravenous injection of 30 nmol/kg DSIP (delta sleep-inducing peptide) in rats under constant illumination produced marked changes of their motor activity as compared to saline controls. Similar marked but distinctly different effects on the circadian pattern of locomotor behavior partially abolished by constant illumination were also obtained after repeated administration of 0.1 nmol/kg DSIP-P (the phosphorylated analogue of DSIP) which enhanced overall motor activity. In both instances the results additionally differed from those reported for a normal 12 hr light:dark cycle. The present results support the hypothesis that DSIP might primarily act by influencing circadian rhythmicity.     

Circadian changes in synaptic ribbons and spherules in pinealocytes of the Syrian hamster (Mesocricetus auratus)

Summary In the present study, synaptic ribbons were studied morphologically and quantitatively in hamster pineal gland. The number of ribbons and spherules of hamster pinealocytes was counted over a 24-h period. The 24-h variations in the quantity of synaptic ribbons were found to parallel fluctuations in pineal melatonin concentrations. No significant circadian changes were observed for synaptic spherules, indicating different roles for these two structures.     

Illuminance threshold for maintenance of testes in Syrian hamsters (Mesocricetus auratus) is higher in continuous light than in long photoperiods

The illuminance threshold for maintenance of testicular function was found to be considerably higher in Syrian hamsters kept in continuous light (LL) than in hamsters on long-day (14-hr) photoperiods (LD 14:10), or in a similar-length skeleton photoperiod (LDSK); the threshold lay between 3 and 30 lux in LL and at approximately 0.3 lux in LD 14:10 or LDSK. The threshold for testicular maintenance in LL was related to the capacity of LL to suppress nocturnal melatonin secretion: 400 lux totally suppressed, 30 or 3 lux partially suppressed, and 0.3 lux failed to suppress melatonin secretion. Hamsters in the LD and LDSK groups, whose locomotion was entrained into a pattern characteristic of long-day exposure, maintained full testicular function; those whose locomotion free-ran or assumed a pattern of entrainment characteristic of short-day exposure underwent testicular regression. These results suggest that light signals entrain the circadian rhythms of locomotion and melatonin secretion in a similar manner, and that LL is less effective than LD or LDSK in shortening the duration of melatonin secretion. For hamsters in LL, a direct relationship was seen between the free-running period (tau) of locomotion and log10 illuminance at 0.3, 3.0, and 30 lux, but tau at 400 lux was no longer than tau at 30 lux. Splitting of locomotion did not occur at 0.3 or 3.0 lux, and occurred in 43% and 62% of hamsters in 30 and 400 lux, respectively.     

Effects of a circadian mutation on seasonality in Syrian hamsters (Mesocricetus auratus).

In Syrian hamsters, exposure to short photoperiods or constant darkness induces a decrease in gonadotrophin secretion and gonadal regression. After 10-12 weeks, animals undergo spontaneous gonadal reactivation, gonadotrophin concentrations rise, and in males, testes size increases and spermatogenesis resumes. The tau mutation shortens the period of circadian wheel-running activity by 4 h in the homozygote. Here, we examine the impact of this mutation on the reproductive response to photoperiod change. Seventeen adult tau mutant and nine adult wild-type males were housed in complete darkness for 25 weeks and testes size determined at weekly intervals. Gonadal regression and subsequent recrudescence occurred in both groups of animals. Regression occurred more rapidly in tau mutants, with a nadir significantly earlier than wild-types but after a similar number of circadian cycles. Rates of testicular recrudescence were similar in both groups. Our data suggest that an acceleration of the circadian period increases the rate of reproductive inhibition in animals exposed to inhibitory photoperiods. Once initiated, the rate of spontaneous reactivation may be independent of the circadian axis.     

Suprachiasmatic nuclei may regulate the rhythm of leptin hormone release in Syrian hamsters (Mesocricetus auratus)

The suprachiasmatic nuclei (SCN) generate the circadian rhythm of many hormones. The hormone leptin is a metabolic signal that informs the brain about fat and energy stores of the body. We investigated whether the rhythm of leptin hormone release in Syrian hamsters is directly controlled by the SCN. Three experiments were performed: in the first, hamsters were SCN-lesioned; in the second, hamsters were exposed to different feeding regimes; and in the third, hamsters were adrenalectomized and implanted with cortisol capsules to maintain constant glucocorticoid release. Blood samples were collected before and after the experiments at different clock times and examined for leptin levels by enzyme-linked immunosorbant assay (ELISA). Different feeding regimes and constant glucocorticoid release did not alter the rhythm of leptin release; whereas, SCN lesions abolished the rhythm. The results of the present study suggest the rhythm in leptin release in Syrian hamsters may be controlled by the SCN.     

Entrainment to light of circadian activity rhythms in tench (Tinca tinca)

The present article analyzes locomotor activity rhythms in Tinca tinca. To that end, three different experiments were conducted on 24 animals (20 g body weight) kept in pairs in 60-liter aquaria fitted with infrared sensors connected to a computer to continuously record fish movements. The first experiment was designed to study the endogenous circadian clock under free-running conditions [ultradian 40:40 min LD pulses and constant dark (DD)] and after shifting the LD cycle. Our results demonstrate that tench has a strictly nocturnal activity pattern, an endogenous rhythm being evident in 45.8% of the fish analyzed. The second experiment was conducted to test the influence of different photoperiods (LD 6:18, 12:12, 18:6, and 22:2) on locomotor activity, the results showing that even under an extremely long photoperiod, tench activity is restricted to dark hours. The third experiment examined the effect of light intensity on locomotor activity rhythms. When fish were exposed to decreasing light intensities (from 300:0 lux to 30:0, 3:0, and 0.3:0 lux) while maintaining a constant photoperiod (LD 12:12), the highest percentage of locomotor activity was in all cases associated with the hours of complete darkness (0 lux). In short, our results clearly show that (a) tench is a species with a strictly nocturnal behavior, and (b) daily activity rhythms gradually entrain after shifting the LD cycle and persist under free-running conditions, pointing to their circadian nature. However, light strongly influences activity rhythms, since (c) the length of the active phase is directly controlled by the photophase, and (d) strictly nocturnal behavior persists even under very dim light conditions (0.3 lux). The above findings deepen our knowledge of tench behavior, which may help to optimize the aquacultural management of this species, for example, by adjusting feeding strategies to their nocturnal behavior.     

Short days and exogenous melatonin increase aggression of male Syrian hamsters (Mesocricetus auratus)

Many nontropical rodent species rely on photoperiod as a primary cue to coordinate seasonally appropriate changes in physiology and behavior. Among these changes, some species of rodents demonstrate increased aggression in short, "winter-like" compared with long "summer-like" day lengths. The precise neuroendocrine mechanisms mediating changes in aggression, however, remain largely unknown. The goal of the present study was to examine the effects of photoperiod and exogenous melatonin on resident-intruder aggression in male Syrian hamsters (Mesocricetus auratus). In Experiment 1, male Syrian hamsters were housed in long (LD 14:10) or short (LD 10:14) days for 10 weeks. In Experiment 2, hamsters were housed in long days and half of the animals were given daily subcutaneous melatonin injections (15 microg/day in 0.1 ml saline) 2 h before lights out for 10 consecutive days to simulate a short-day pattern of melatonin secretion, while the remaining animals received injections of the vehicle alone. Animals in both experiments were then tested using a resident-intruder model of aggression and the number of attacks, duration of attacks, and latency to initial attack were recorded. In Experiment 1, short-day hamsters underwent gonadal regression and displayed increased aggression compared with long-day animals. In Experiment 2, melatonin treatment also increased aggression compared with control hamsters without affecting circulating testosterone. Collectively, the results of the present study demonstrate that exposure to short days or short day-like patterns of melatonin increase aggression in male Syrian hamsters. In addition, these results suggest that photoperiodic changes in aggression provide an important, ecologically relevant model with which to study the neuroendocrine mechanisms underlying aggression in rodents.     

Auditory brainstem responses in Golden Syrian hamsters (Mesocricetus auratus) affected with the Wh gene.

BACKGROUND AND PURPOSE: The anophthalmic white (Wh) gene in Golden Syrian hamsters (Mesocricetus auratus) is autosomal semi-dominant and causes several developmental defects, including hearing loss. The Wh mutation is thought to be homologous to Waardenburg syndrome in humans, apparently affecting similar developmental processes. The purpose of this study was to assess the hearing of hamsters in the AN/As-Wh strain. METHODS: Using auditory brainstem responses, electrophysiologic activity was determined in 20 hamsters of the AN/As-Wh strain, with the aim of elucidating hearing status. Hamsters were classified into five genotypes and were evaluated by use of click stimuli. RESULTS AND CONCLUSION: Hamsters assigned to the genotypes differed in their hearing sensitivity and could be classified into categories of normal hearing, moderate hearing loss, and profound hearing loss.     

Synchronization by light of the circadian rhythm of motor activity in the crayfish

Abstract

We have studied the pattern for resetting the circadian rhythm in the spontaneous motor activity of the crayfish. Spontaneous motor activity was recorded continously at a constant temperature and under free running conditions in complete darkness. The effect of single light pulses applied at different circadian times, on the circadian rhythm of motor activity was measured in both transient stage and steady state. The results led us to construct a phase‐transition curve and phase‐response curve which were analyzed to obtain information about the oscillators which underlie the circadian rhythm of motor activity.     

The effect of pinealectomy, melatonin and leptin hormones on ovarian follicular development in female Syrian hamsters (Mesocricetus auratus)

We studied the effects of melatonin and leptin hormones on ovarian follicular development in intact and pinealectomized female Syrian hamsters. We first monitored the oestrous cycle of the hamsters by the vaginal smear samples throughout a ten day period to start the injections simultaneously in all groups and performed saline, melatonin and leptin hormone injection groups for both control and pinealectomized hamsters. Then the injections were applied for four days starting the oestrus phase of the cycle and the ovaries were removed for preparation of histological analysis. We measured the diameters and the numbers of the follicles and we classified the follicles according to the number of the granulosa cell layer. Leptin hormone injection increased melatonin hormone injection decreased the number and the diameter of the follicles. The stimulating effect of the leptin hormone was more pronounced in the pinealectomized group. The results of the present study indicate that the removal of the pineal gland and leptin hormone administration are playing a stimulatory while melatonin hormone administration is playing an inhibitory role on the follicular development in female Syrian hamsters.     

The influence of aging on renal response to cadmium in Syrian hamsters

To determine the renal effects of cadmium (Cd) in older animals, we administered subcutaneously a single dose of cadmium, 3.0 mg/kg/BW, to Syrian hamsters aged 16 wk (“young”) and 60 wk (“old”). Marked morphologic changes in the kidney and renal dysfunction were observed, especially in the older animals. The concentration of MDA in the renal cortex was significantly increased only in young hamsters treated with cadmium. Concentrations of glutathione (GSH) in the renal cortex were increased in the old hamsters on d 6. Increased levels of renal MDA after cadmium treatment may induce the production of GSH in the kidney thus preventing renal damage. Aging can increase the susceptibility to the renal effects of cadmium.