Ultradian Rhythms of Body Temperatures in Male Wistar Rats Maintained under Conditions of Constant Illumination

Ultradian Rest-activity Rhythms Induced by Quinpirole in Mice Using Wavelet Analysis

Objective

Ultradian rhythms are biological rhythms with periods of a few seconds to a few hours. Along with circadian rhythms, ultradian rhythms influence human physiology. However, such rhythms have not been studied as intensively as circadian rhythms. This study aimed to identify ultradian rest-activity rhythms induced by the dopamine D2/D3 agonist quinpirole in mice.

Methods

We used 10 mice from the Institute of Cancer Research. Quinpirole was administered at a dose of 0.5 mg/kg. We assessed free rest-activity using infrared detectors and conducted wavelet analysis to measure the period and its variation. We also used the paired t test to compare ultradian rhythm patterns.

Results

Quinpirole did not significantly change total 24-hour locomotor activity (p = 0.065). However, it significantly increased locomotor activity during the dark phase (p = 0.001) and decreased it during the light phase (p = 0.016). In the continuous wavelet transform analysis, the mean period was 5.618 hours before quinpirole injection and 4.523 hours after injection. The period showed a significant decrease (p = 0.040), while the variation remained relatively consistent before and after quinpirole injection.

Conclusion

This study demonstrated ultradian rest-activity rhythms induced by quinpirole using wavelet analysis. Quinpirole-induced ultradian rhythms exhibited rapid oscillations with shortened periods and increased activity during the dark phase. To better understand these changes in ultradian rhythms caused by quinpirole, it is essential to compare them with the effects of other psychopharmacological agents. Furthermore, investigating the pharmacological impact on ultradian rest-activity rhythms may have valuable applications in clinical studies.

A mathematical model for the role of dopamine-D2 self-regulation in the production of ultradian rhythms

Many self-motivated and goal-directed behaviours display highly flexible, approximately 4 hour ultradian (shorter than a day) oscillations. Despite lacking direct correspondence to physical cycles in the environment, these ultradian rhythms may be involved in optimizing functional interactions with the environment and reflect intrinsic neural dynamics. Current evidence supports a role of mesostriatal dopamine (DA) in the expression and propagation of ultradian rhythmicity, however, the biochemical processes underpinning these oscillations remain to be identified. Here, we use a mathematical model to investigate D2 autoreceptor-dependent DA self-regulation as the source of ultradian behavioural rhythms. DA concentration at the midbrain-striatal synapses is governed through a dual-negative feedback-loop structure, which naturally gives rise to rhythmicity. This model shows the propensity of striatal DA to produce an ultradian oscillation characterized by a flexible period that is highly sensitive to parameter variations. Circadian (approximately 24 hour) regulation consolidates the ultradian oscillations and alters their response to the phase-dependent, rapid-resetting effect of a transient excitatory stimulus. Within a circadian framework, the ultradian rhythm orchestrates behavioural activity and enhances responsiveness to an external stimulus. This suggests a role for the circadian-ultradian timekeeping hierarchy in governing organized behaviour and shaping daily experience through coordinating the motivation to engage in recurring, albeit not highly predictable events, such as social interactions.

Constant Light in Critical Postnatal Days Affects Circadian Rhythms in Locomotion and Gene Expression in the Suprachiasmatic Nucleus, Retina, and Pineal Gland Later in Life

The circadian clock regulates bodily rhythms by time cues that result from the integration of genetically encoded endogenous rhythms with external cycles, most potently with the light/dark cycle. Chronic exposure to constant light in adulthood disrupts circadian system function and can induce behavioral and physiological arrhythmicity with potential clinical consequences. Since the developing nervous system is particularly vulnerable to experiences during the critical period, we hypothesized that early-life circadian disruption would negatively impact the development of the circadian clock and its adult function. Newborn rats were subjected to a constant light of 16 lux from the day of birth through until postnatal day 20, and then they were housed in conditions of L12 h (16 lux): D12 h (darkness). The circadian period was measured by locomotor activity rhythm at postnatal day 60, and the rhythmic expressions of clock genes and tissue-specific genes were detected in the suprachiasmatic nuclei, retinas, and pineal glands at postnatal days 30 and 90. Our data show that early postnatal exposure to constant light leads to a prolonged endogenous period of locomotor activity rhythm and affects the rhythmic gene expression in all studied brain structures later in life.

Effect of Surgical Removal of Testicles and Adrenal Glands on Ultradian Rhythms of Body Temperature in Male Wistar Rats under Conditions of Constant Illumination

We have studied body temperature dynamics of mature male Wistar rats maintained under constant illumination after surgical removal of the testicles and adrenal glands. In gonadectomized animals, pronounced increases in body temperature (>0.9°C) were observed every 4-6 h; during the periods 03.35-04.30, 07.35-08.30, 11.35-12.30, 15.35-16.30, 19.35-20.30, and 23.35-00.30, they were recorded 1.5-fold more often than during the rest periods. These results do not significantly differ from the parameters of the control group. Combined removal of the testicles and adrenal glands led to shortening of main period of temperature oscillations to 4-4.5 h and a decrease in its amplitude; pronounced increase in body temperature (>0.5°C) was observed 2.1 times more often during the periods 03.35-04.30, 07.35-08.30, 11.35-12.30, 15.35-16.30, 19.35-20.30, and 23.35-00.30 than in other time intervals. Thus, the removal of the testicles and adrenal glands does not violate the 4-h intraday rhythm of body temperature.

Ultradian Biorhythms of C57BL/6 Mice Body Temperature under Constant Illumination or during Natural Day-Night Cycle

The study analyzed the dynamics of intraperitoneal body temperature in C57BL/6 mice during 39 days of uninterrupted measurements. When mice were exposed to constant illumination, the ultradian oscillations of body temperature demonstrated the rhythms with periods of 2 h, 60 min, and 12 min, which were the higher harmonics of the circadian temperature oscillations. In two mutually isolated groups exposed to constant illumination, the phases of revealed biorhythms coincided. When the mice maintained under natural illumination, the body temperature demonstrated the ultradian rhythms with the same periods, which indicated that constant illumination did not distort the parameters of ultradian biorhythms. Probably, there is an external biotropic factor with similar harmonic spectrum, which synchronizes these biorhythms.

Ultradian and Infradian Rhythms in the Dynamic of Testosterone Concentration in the Serum of the White-Breasted Hedgehog Erinaceus roumanicus

The aim of the study was to identify ultradian (intraday) and infradian (multi-day) rhythms in the dynamics of testosterone concentration in the blood serum of white-breasted hedgehogs. Blood sampling was performed from the femoral veins of 12 male hedgehogs. We found ultradian rhythms of testosterone on both sampling dates-March 7-8 (a day length of 11 hours and 15 minutes) and May 10-11 (a day length of 16 hours). An 8-hour rhythm of testosterone concentration has been established. The acrophases were at the same times in both photoperiods and thus independent of sunset times. The study of the infradian rhythms of testosterone was daily carried out on May 22-June 3, at 07:40 to 08:50 and from June 27 to July 7, at 16:15-16:50. It revealed an infradian rhythm of the testosterone concentration with a period of 4-days in both the morning and the evening sampling. According to our previous investigation, the infradian rhythms of testosterone among individual hedgehogs, rodents and primates have the same period. That indicates the common mechanisms for their formation. In case of experimental studies, the phase of ultradian and infradian biorhythms will need to be taken into account because the testosterone concentration in acrophase is 2-4 times higher than in bathyphase.