In-vitro circadian rhythm of murine bone marrow progenitor production

Hematopoietic processes display 24h rhythms both in rodents and in human beings. We hypothesized these rhythms to be in part generated by a circadian oscillator within the bone marrow. The ability of murine bone marrow granulo-monocytic (GM) precursors to form colonies following colony-stimulating factor (rm GM-CSF) exposure was investigated in liquid culture samples obtained every 3 h for a span of up to 198 h. The CFU-GM count varied rhythmically over the first 4 d of culture, with a reproducible maximum in the early morning hours, similar to that observed in vivo. These experiments provide the first evidence that bone marrow progenitors sustain in vitro circadian rhythmicity, and they demonstrate the presence of a circadian time-keeping system within these cells. The results support the potential usefulness of bone marrow cultures for investigating chronopharmacologic effects of anticancer drugs and cytokines on this target system.     

A simple method for separating cells of Microcystis aeruginosa for counting

Heat was used to break up the mucilage-bound colonies of the blue-green alga, Microcystis aeruginosa Kütz. emend. Elenkin, for cell counting. Samples were heated in a water bath at 80°C for 5–10 min, then agitated in a Vortex mixer for 30–60 s. The treatment separated cells completely and reaggregation of cells did not occur. There was no evidence that heating distintegrated the cells.     

Twelve-Hour Night Shifts of Healthcare Workers: A Risk to the Patients?

We assessed the impact of 12h fixed night shift (19:00–07:00h) work, followed by 36h of off-time, on the sleep–wake cycle, sleep duration, self-perceived sleep quality, and work-time alertness on a group composed of 5 registered and 15 practical nurses. Wrist actigraphy (Ambulatory Monitoring, Inc.), with data analysis by the Cole-Kripke algorithm, was applied to determine sleep/wake episodes and their duration. The sleep episodes were divided into six categories: sleep during the night shift (x¯=208.6; SD±90.6mins), sleep after the night shift (x¯=138.7; SD±79.6min), sleep during the first night after the night work (x¯=318.5; SD±134.6min), sleep before the night work (x¯=104.3; SD±44.1min), diurnal sleep during the rest day (x¯=70.5; SD±43.0min), and nocturnal sleep during the rest day (x¯=310.4; SD±188.9mins). A significant difference (p<.0001; T-test for dependent samples) was detected between the perceived quality of sleep of the three diurnal sleep categories compared to the three nocturnal sleep categories. Even thought the nurses slept (napped) during the night shift, their self-perceived alertness systematically decreased during it. Statistically significant differences were documented by one-way ANOVA (F=40.534 p<.0001) among the alertness measurements done during the night shift. In particular, there was significant difference in the level of perceived alertness (p<.0001) between the 7^th and 10^thh of the 12h night shift. These findings of decreased alertness during the terminal hours of the night shift are of concern, since they suggest risk of comprised patient care.     

Circadian response of annual weeds to glyphosate and glufosinate

Five field experiments were conducted in 1998 and 1999 in Minnesota to examine the influence of time of day efficacy of glyphosate [N-(phosphonomethyl)glycine] and glufosinate [2-amino-4-(hydroxymethyl-phosphinyl)butanoic acid] applications on the control of annual weeds. Each experiment was designed to be a randomized complete block with four replications using plot sizes of 3×9 m. Glyphosate and glufosinate were applied at rates of 0.421 kg ae/ha and 0.292 kg ai/ha, respectively, with and without an additional adjuvant that consisted of 20% nonionic surfactant and 80% ammonium sulfate. All treatments were applied with water at 94 L/ha. Times of day for the application of herbicide were 06:00h, 09:00h, 12:00h, 15:00h, 18:00h, 21:00h, and 24:00h. Efficacy was evaluated 14 d after application by visual ratings. At 14 d, a circadian response to each herbicide was found, with greatest annual weed control observed with an application occurring between 09:00h and 18:00h and significantly less weed control observed with an application at 06:00h, 21:00h, or 24:00h. The addition of an adjuvant to both herbicides increased overall efficacy, but did not overcome the rhythmic time of day effect. Results of the multiple regression analysis showed that after environmental temperature, time of day was the second most important predictor of percent weed kill. Thus, circadian timing of herbicide application significantly influenced weed control with both glyphosate and glufosinate.     

Diurnal modulation of visual motion prediction

Predicting the future position of moving objects is an essential cognitive function used for many daily activities, such as driving, walking and reaching. The experiments described in this paper show a marked diurnal modulation of motion prediction in inflating image perception. This motion prediction was shown to be more accurate in the afternoon than in the morning. In contrast, such modulation could not be found in deflating image perception. Such diurnal fluctuations may be mediated by circadian properties of retinal cone photoreceptors.     

Chronopharmacology and Chronotherapeutics: Definitions and Concepts

Most knowledge of medications has been derived from single- and multiple-dose investigations in which pharmacokinetic and pharmacodynamic phenomena have been evaluated following one, usually, daytime drug administration. Chronopharmacologic studies involving the evaluation of such phenomena after each of several different clock-hour treatments during the day- and nighttime reveal that biological rhythmic processes, such as those of 24 hr, can profoundly affect the kinetics and effects of various medications. Several new concepts have arisen based on findings from chronopharmacologic investigations, such as chronokinetics, chronesthesy and chronergy. These are defined and discussed herein using illustrative examples. A major goal of chronopharmacologic research is to devise chronotherapeutic interventions. Chronotherapeutics is the optimization of drug effects and/or minimization of toxicity by timing medications with regard to biological rhythms. Chronotherapeutics takes into account predictable administration-time-dependent variation in the pharmacokinetics of drugs as well as the susceptibility of target tissues due to temporal organization of physiochemical processes and functions of the body as circadian and other rhythms. The unequally divided and once-daily theophylline treatment schedules for the clinical management of nocturnal asthma, which are discussed in this issue, represent steps toward a chronotherapy.     

Daily Rhythms Related to Distinct Social Tasks inside an Eusocial Bee Colony

A bee colony is often compared to a multicellular organism, mainly because of its spatial organization. We propose that a temporal organization of equal importance is also present. To support this view, we studied the reproductive processes of two closely related species of stingless bees. Stingless bees enable observations of daily rhythms that are performed by distinct social classes. The emergent process, POP, is cyclic and consists of the building and provisioning of brood cells by the worker bees and egg‐laying by the queen. Colonies were kept in the laboratory under constant conditions with the exit tube opening to the environment; thus, foragers had direct access to environmental cycles. At a later stage of the experiment, the exit tube was closed by a sieve; in this case, bees had their own stock of food, but the environmental LD cycle could still be detected when they were inside the exit tube. Daily POP rhythms were present and showed distinct temporal patterns in each species. A third condition was imposed on one of the species only: the exit tube was closed by a sieve and maintained inside a box that was provided with constant illumination. In this colony, the POP rhythm was perturbed by the destruction of the brood cells. Restoration of POP consisted of a rapid reconstruction of cells followed by a late oviposition in the same day. As different rhythmic patterns were detected, but showed regular timings with respect to one another, an interpretation based upon the concept of an internal temporal order is suggested.     

Orcadian Variation in Human Stature

Thyroxine (T₄) and triiodothyronine (T₃) plasma concentrations have been determined during 24-hr sampling periods in six mongrels (age 12-36 months), six beagles (age 35-37 months), three labradors (age 3.5 months) and three beagles (age 5 months). The mean T₄ levels of the labradors were significantly lower than the values found for mongrels or older beagles (P < 0.05), whereas T₃ was higher in the 5 month old beagles compared to the mongrels (P < 0.001), young beagles (P < 0.05) or labradors (P < 0.01).

Circadian and ultradian rhythmicities have been evaluated by cosinor and Fourier analysis. Mongrels and older beagles did have a 12-hr rhythmicity in plasma T₄ (P < 0.05), whereas 5 month old beagles had a circadian one (P < 0.01). A 12-hr rhythmicity was also found for T₃ in the older Beagles (P < 0.05). However, Fourier analysis indicated that the daily variation in T₄ and T₃ plasma levels was inadequately mathematically described by single sinusoidal rhythm and that more harmonic components are to be taken into account.

The obtained data during a 24-hr period indicate that T₄ and T₃ concentrations in plasma may vary according to breed, age and sampling hour.     

Automatic data recording of circadian rhythms

This paper illustrates a method for automatic data recording using the printer port of personal computer and software designed ad hoc. The system was tested by measuring circadian rhythms of activity in the subterranean rodent Ctenomys talarum. Data is recorded in a text-only comma-delimited file, and displayed on screen.