Infradian alteration of circadian rhythms in owl monkeys (Aotus lemurinus griseimembra): an effect of estrous?

Integration of biological clocks and rhythms

Animals, plants, and microorganisms exhibit numerous biological rhythms that are generated by numerous biological clocks. This article summarizes experimental data pertinent to the often-ignored issue of integration of multiple rhythms. Five contexts of integration are discussed: (i) integration of circadian rhythms of multiple processes within an individual organism, (ii) integration of biological rhythms operating in different time scales (such as tidal, daily, and seasonal), (iii) integration of rhythms across multiple species, (iv) integration of rhythms of different members of a species, and (v) integration of rhythmicity and physiological homeostasis. Understanding of these multiple rhythmic interactions is an important first step in the eventual thorough understanding of how organisms arrange their vital functions temporally within and without their bodies.

Seasonal variation of temporal niche in wild owl monkeys (Aotus azarai azarai) of the Argentinean Chaco: a matter of masking?

Among the more than 40 genera of anthropoid primates (monkeys, apes, and humans), only the South American owl monkeys, genus Aotus, are nocturnal. However, the southernmostly distributed species, Aotus azarai azarai, of the Gran Chaco may show considerable amounts of its 24-h activity during bright daylight. Due to seasonal changes in the duration of photophase and climatic parameters in their subtropical habitat, the timing and pattern of their daily activity are expected to show significant seasonal variation. By quantitative long-term activity recordings with Actiwatch AW4 accelerometer data logger devices of 10 wild owl monkeys inhabiting a gallery forest in Formosa, Argentina, the authors analyzed the seasonal variation in the temporal niche and activity pattern resulting from entrainment and masking of the circadian activity rhythm by seasonally and diurnally varying environmental factors. The owl monkeys always displayed a distinct bimodal activity pattern, with prominent activity bouts and peaks during dusk and dawn. Their activity rhythm showed distinct lunar and seasonal variations in the timing and daily pattern. During the summer, the monkeys showed predominantly crepuscular/nocturnal behavior, and a crepuscular/cathemeral activity pattern with similar diurnal and nocturnal activity levels during the cold winter months. The peak times of the evening and morning activity bouts were more closely related to the times of sunset and sunrise, respectively, than activity-onset and -offset. Obviously, they were better circadian markers for the phase position of the entrained activity rhythm than activity-onset and -offset, which were subject to more masking effects of environmental and/or internal factors. Total daily activity was lowest during the two coldest lunar months, and almost twice as high during the warmest months. Nighttime (21:00-06:00 h) and daytime (09:00-18:00 h) activity varied significantly across the year, but in an opposite manner. Highest nighttime activity occurred in summer and maximal daytime activity during the cold winter months. Dusk and dawn activity, which together accounted for 43% of the total daily activity, barely changed. The monkeys tended to terminate their nightly activity period earlier on warm and rainy days, whereas the daily amount of activity showed no significant correlation either with temperature or precipitation. These data are consistent with the dual-oscillator hypothesis of circadian regulation. They suggest the seasonal variations of the timing and pattern of daily activity in wild owl monkeys of the Argentinean Chaco result from a specific interplay of light entrainment of circadian rhythmicity and strong masking effects of various endogenous and environmental factors. Since the phase position of the monkeys' evening and morning activity peaks did not vary considerably over the year, the seasonal change from a crepuscular/nocturnal activity pattern in summer to a more crepuscular/cathemeral one in winter does not depend on a corresponding phase shift of the entrained circadian rhythm, but mainly on masking effects. Thermoregulatory and energetic demands and constraints seem to play a crucial role.

Procedures for numerical analysis of circadian rhythms

This article reviews various procedures used in the analysis of circadian rhythms at the populational, organismal, cellular and molecular levels. The procedures range from visual inspection of time plots and actograms to several mathematical methods of time series analysis. Computational steps are described in some detail, and additional bibliographic resources and computer programs are listed.

Physical activity of adult female rhesus monkeys (Macaca mulatta) across the menstrual cycle

Physical activity is an important physiological variable impacting on a number of systems in the body. In rodents and several species of domestic animals, levels of physical activity have been reported to vary across the estrous cycle; however, it is unclear whether such changes in activity occur in women and other primates across the menstrual cycle. To determine whether significant changes in activity occur over the menstrual cycle, we continuously measured physical activity in seven adult female rhesus monkeys by accelerometry over the course of one menstrual cycle. Monkeys were checked daily for menses, and daily blood samples were collected for measurement of reproductive hormones. All monkeys displayed ovulatory menstrual cycles, ranging from 23 to 31 days in length. There was a significant increase in estradiol from the early follicular phase to the day of ovulation (F(1.005,5.023) = 40.060, P = 0.001). However, there was no significant change in physical activity across the menstrual cycle (F(2,12) = 0.225, P = 0.802), with activity levels being similar in the early follicular phase, on the day of the preovulatory rise in estradiol and during the midluteal phase. Moreover, the physical activity of these monkeys was not outside the range of physical activity that we measured in 15 ovariectomized monkeys. We conclude that, in primates, physical activity does not change across the menstrual cycle and is not influenced by physiological changes in circulating estradiol. This finding will allow investigators to record physical activity in female primates without the concern of controlling for the phase of the menstrual cycle.

No time to eat: an adaptationist account of periovulatory behavioral changes

A comprehensive review of women's dietary behavior across the menstrual cycle suggests a drop in caloric intake around the time of ovulation; similar patterns occur in many other mammals. The periovulatory nadir is puzzling, as it is not explicable in terms of changes in the energy budget. Existing explanations in the animal literature operate wholly at the proximate level of analysis and hence do not address this puzzle. In this paper, I offer an ultimate explanation for the periovulatory feeding nadir, arguing that the decrease in the set point for satiation during the fertile period of the female cycle is an adaptation produced by natural selection in order to reduce the motivational salience of goals that compete with those directly or indirectly pertaining to mating. In support of this explanation, I adduce evidence of: a) periovulatory reductions in other ingestive behaviors, and b) periovulatory increases in motor activity and the psychological concomitants thereof.

Oestrogen receptor-alpha-immunoreactive neurones project to the suprachiasmatic nucleus of the female Syrian hamster

Ovarian steroid hormones regulate circadian period and phase, but classical receptors for these hormones are absent in the circadian pacemaker localized in the suprachiasmatic nucleus of the hypothalamus (SCN). In order to determine whether effects of oestrogen may be exerted through steroid-binding systems afferent to the SCN we have performed double label immunocytochemistry for oestrogen receptor-alpha(ER-alpha) and the retrograde tracer cholera toxin B subunit (CtB) after its application to the SCN. Most of the areas that contain ER-alpha-immunoreactive (ERalpha-ir) cells also contained cells afferent to the SCN. The percentage of neurones afferent to the SCN which show ERalpha-immunoreactivity varies between areas. As many as one-third of the neurones afferent to the SCN in some parts of the preoptic area and the corticomedial amygdala are ERalpha-ir. Very few of the afferent neurones from the septum and the central grey are ERalpha-ir, whereas an intermediate proportion of afferents from the bed nucleus of the stria terminalis and the arcuate nucleus are ERalpha-ir. Our retrograde tracing results were compared with results of anterograde tracing from some of the sites containing SCN afferents. Using a combined retrograde and anterograde tracing technique we tested the possibility that single ERalpha-ir neurones afferent to the SCN could receive reciprocal innervation by SCN efferents. Although we found SCN input to some SCN afferent neurones, we found no evidence of reciprocity between single ERalpha-ir cells and the SCN. Our results indicate the existence of oestrogen binding systems afferent to the SCN. These neuroanatomical pathways may mediate effects of gonadal steroid hormones on circadian rhythms.