Intensity-dependent phase-adjustments in the locomotor activity rhythm of the nocturnal field mouse Mus booduga

The locomotor activity rhythm of the nocturnal field mouse Mus booduga was monitored under constant darkness (DD) and free-running periods (tau) were estimated. Following a free-run of about 15 days in DD, the animals were exposed to periodic light pulses (LPs) of various intensities (1 lux, 10 lux, 50 lux, 100 lux, and 1,000 lux) and 15 minutes duration for 65 days at intervals of 24 hours to investigate the influence of intensity of light on the phase-angle-difference (psi) between the onset of locomotor activity and the time of LP administration. The experimentally observed values of psi and tau for a LP of 1,000 lux intensity used for 15 minutes every 24 hr, showed a sigmoid shaped relationship with tau. This relationship was similar to that predicted based on the nonparametric model of entrainment, which uses the tau and the LP phase response curve (PRC) constructed using LP of similar duration and intensity. The functional nature of the relationship between psi and tau was not found to change significantly with increasing intensities of LP used to entrain the locomotor activity rhythm. However, psi was significantly modulated by the intensity of LP. These results suggest that the periodic sensitivity of the circadian pacemaker underlying the locomotor activity rhythm in the nocturnal field mouse M. booduga to LPs plays an important role in maintaining a characteristic psi with the zeitgeber and the psi changes in a light intensity-dependent manner.     

Entrainment of the circadian locomotor activity rhythm in the Japanese newt by melatonin injections

We examined whether melatonin can act as a synchronizing agent within the circadian system of amphibians by testing the ability of melatonin injections to entrain the circadian locomotor activity rhythm of a newt (Cynops pyrrhogaster). Under constant darkness, all newts (13 cases) showing the free-running rhythms were subcutaneously injected with 10 g melatonin at the same time every other day for at least 30 days. Subsequently, they were injected with vehicle (1% ethanolic saline) instead of melatonin for at least another 30 days. In 10 of the 13 newts, the locomotor activity rhythms could be entrained to a period of 24 h by melatonin injections but not by vehicle injections. During the entrained steady-state, the active phase of an activity-rest cycle preceded the time of melatonin injections as previously reported in other diurnal species. These results suggest that the endogenous circadian rhythm of melatonin concentration may be involved in synchronizing circadian oscillator(s) within the newt's circadian system.     

Irradiance dependency of UV-A induced phase shifts in the locomotor activity rhythm of the field mouse Mus booduga

In the nocturnal field mouse Mus booduga, the responsiveness of the circadian system to UV-A light of 2.5 W/m² and 30 minutes duration is known to be phase dependent. The results of our experiments indicate that the phase shifts evoked by UV-A at the two phases, CT14 (circadian time 14) and CT20 increases nonlinearly with irradiance. (Chronobiology International, 17(6), 777-782, 2000)     

Melatonin enhances the sensitivity of circadian pacemakers to light in the nocturnal field mouse Mus booduga

The effect of exogenous melatonin (1 mg/kg) on light pulse (LP) induced phase shifts of the circadian locomotor activity rhythm was studied in the nocturnal field mouse Mus booduga. Three phase response curves (PRCs: LP, control, and experimental) were constructed to study the effect of co-administration of light and melatonin at various circadian times (CTs). The LP PRC was constructed by exposing animals free-running in constant darkness (DD) to LPs of 100-lux intensity and 15-min duration, at various CTs. The control and experimental PRCs were constructed by using a single injection of either 50% DMSO or melatonin (1 mg/kg dissolved in 50% DMSO), respectively, administered 5 min before LPs, to animals free-running in DD. A single dose of melatonin significantly modified the waveform of the LP PRC. The experimental PRC had significantly larger areas under advance and delay regions of the PRC compared to the control PRC. This was also confirmed when the phase shifts obtained at various CTs were compared between the three PRCs. The phase delays at three phases (CT12, CT14, and CT16) of the experimental PRCs were significantly greater than those of the control and the LP PRCs. Based on these results we conclude that phase shifting effects of melatonin and light add up to produce larger responses.     

Timely administration of melatonin accelerates reentrainment to phase-shifted light-dark cycles in the field mouse Mus booduga

The effect of melatonin on the rate of reentrainment after a 6h phase delay and a 6h phase advance in the light-dark (LD) cycle was assayed in the nocturnal field mouse Mus booduga. After a phase delay of 6h in the LD cycle, a single dose of melatonin (1 mg/kg) was administered for three consecutive days at about CT4 (circadian time 4). After a phase advance of 6h in the LD cycle, melatonin was administered for three consecutive days at about CT22. Melatonin was found to accelerate reentrainment in both cases. Melatonin-treated animals took significantly fewer cycles to reentrain compared to vehicle-treated (50% dimethylsulfoxide [DMSO]) and nontreated control animals.     

Effect of light intensity on the phase and period response curves in the nocturnal field mouse Mus booduga

The effect of light intensity on the phase response curve (PRC) and the period response curve (τRC) of the nocturnal field mouse Mus booduga was studied. PRCs and τRCs were constructed by exposing animals free-running in constant darkness (DD), to fluorescent light pulses (LPs) of 100 lux and 1000 lux intensities for 15min duration. The waveform of the PRCs and τRCs evoked by high light intensity (1000 lux) stimuli was significantly different compared to those constructed using low light intensity (100 lux). Moreover, a weak but significant correlation was observed between phase shifts and period changes when light stimuli of 1000 lux intensity were used; however, the phase shifts and period changes in the 100 lux PRC and τRC were not correlated. This suggests that the intensity of light stimuli affects both phase and period responses in the locomotor activity rhythm of the nocturnal field mouse M. booduga. These results indicate that complex mechanisms are involved in entrainment of circadian clocks, even in nocturnal rodents, in which PRC, τRC, and dose responses play a significant role.     

Effect of dieldrin on catalytic potential of field mouse Mus booduga brain acetylcholinesterase

Substrate kinetics of acetylcholinesterase (AChE) were investigated in control and dieldrin-treated Mus booduga brains. Non competitive inhibition with respect to activation by acetylcholine was indicated by decreased maximal velocity (V) without change in Michaelis-Menten constant (Km). Activation energies (delta E) were found to be increased suggesting decreased efficiency of enzyme in dieldrin-treated mouse brains. Fall in the activity potential of AChE may account for the interference of dieldrin or its metabolites with the acetylcholine (ACh)--AChE system and deserve consideration in contributing to the neurotoxicity.     

Serotonin phase-shifts the circadian rhythm of locomotor activity in the cockroach

Serotonin, a putative neurotransmitter in insects, was found to cause consistent phase shifts of the circadian rhythm of locomotor activity of the cockroach Leucophaea maderae when administered during the early subjective night as a series of 4-microliters pulses (one every 15 min) for either 3 or 6 hr. Six-hour treatments with dopamine also caused significant phase shifts during the early subjective night, but 3-hr treatments with dopamine had no phase-shifting effect. Other substances tested in early subjective night (norepinephrine, octopamine, gamma-aminobutyric acid, glutamate, carbachol, histamine, tryptophan, tryptamine, N-acetyl serotonin, or 5-hydroxyindole-3-acetic acid) did not consistently cause phase shifts. The phase-shifting effect of serotonin was found to be phase-dependent. The phase response curve (PRC) for serotonin treatments was different from the PRC for light. Like light, serotonin caused phase delays in the late subjective day and early subjective night, but serotonin did not phase-shift rhythms when tested at phases where light causes phase advances.     

Environmental enrichment exerts anxiolytic effects in the Indian field mouse (Mus booduga)

Environmental enrichment (EE) is known to have behavioral and physiological anxiolytic effects in several animal models. However, it is as yet unclear how EE modulates behavior of wild animals and the underlying molecular mechanisms. The adult male field mouse Mus booduga (n = 42) captured at agricultural field, were housed in non-enriched standard condition (SC) for 7 days and considered as directly from wild (DW). Another two groups of mice were housed in either EE or SC for 30 days. Behavioral testing was carried out to assess their anxiety-like behavior in the elevated plus-maze (EPM). We found that on EPM, mice housed in EE display less anxiety like behavior when compared to mice housed in SC. Exposure to plus-maze did not increase the levels of corticosterone (CORT) in prefrontal cortex (PFC) and circulating CORT, and adrenocorticotropic hormone (ACTH) in the mice housed in EE but not in the mice housed in SC. We observed a trend in the EE induced inhibition of expression of corticotropin releasing hormone (CRH), glucocorticoid receptor (GR), E2 ubiquitin-conjugating enzyme (Ubc9) and steroid receptor coactivator-1 (SRC-1) mRNA levels, which are all known to be involved in the stress response signaling pathway. Our study suggests that EE exerts therapeutic and anxiolytic effects against stressors.     

Limits of maternal entrainment of the activity rhythm in the field mouseMus booduga

Summary Cycles of 12 h presence and 12 h absence of motherMus booduga entrain the circadian rhythm in the locomotor activity of her pups such that the pups rest in her presence and are active in her absence. We wanted to determine whether this maternal entrainment arises because activity is inhibited by the mother's presence and enhanced by her absence (masking). We performed experiments with the period of the presence/absence cycles ranging from 20 to 28 h and find that only periods of 23–25 h allow entrainment while periods below 23 h and above 25 h do not allow entrainment. Our results speak against the involvement of masking and in favour of the involvement of a genuine circadian organization.Abbreviations PA presence and absence of mother - LD light and darkness - DD continuous darkness - T period of Zeitgeber - period of activity rhythm - phase angle difference     

Control of the circadian rhythm of locomotor activity in the house cricket

A detailed analysis was made of the locomotor activity of Acheta domesticus under conditions of 12 hr light and 12 hr darkness (LD 12 : 12) and of continuous darkness (DD). Under LD 12 : 12 it was found that there are three types of insects: (1) those beginning the period of increased locomotor activity immediately after darkness falls, (2) considerably before this time, and (3) considerably after this time. Under DD conditions the greater amount of the insects have a free-running rhythm shorter than 24 hr, while only a small percentage have a rhythm of more than 24 hr.Destruction of the neurosecretory cells of the pars intercerebralis by means of radio waves leads to the formation of hyperactivity and loss of locomotor activity rhythm when more than half of these cells are destroyed.Injection of reserpine into the insect's haemolymph with doses of 10 μg/g of body weight results in a reduction in locomotor activity and produces arrhythmicity for 2 to 3 days under LD 12 : 12 conditions. Under DD conditions, however, this same dose results in a total and irretrievable loss of free-running rhythm. Histological studies of the brain of crickets following injection of reserpine show a large degree of accumulation of neurosecretion in the cells of the pars intercerebralis as compared with control insects.A hypothesis is put forward as to the way in which the brain centres regulating locomotor rhythm act in crickets.     

Formal properties of the circadian rhythm of locomotor activity in Japanese quail

Summary Japanese quail have a circadian rhythm of locomotor activity whose free-run period () in constant darkness (DD) was 22.5±0.1 h (45). A phase response curve of typical form was obtained by illuminating the free-running rhythm with single 1 h light pulses. Using entrainment theory a derived phase response curve was calculated from the phase relationships between the locomotor rhythm and 1 h light periods in light-dark cycles of various lengths (T). Although the limits of entrainment to theseT cycles differed slightly from those predicted, there was a close correlation between the two phase response curves. The phase relationships between the locomotor rhythm and 1–9 h photoperiods in 24 h cycles were in general accord with a prediction based on the short free-run period and the relative sizes of the delay and advance portions of the phase response curve for 1 h light pulses.     

A circadian rhythm of locomotor activity in newly emerged Ceratophyllus sciurorum

Abstract Circadian rhythm in newly emerged individuals of the Red Squirrel ( Scuirus vulgaris ) flea C.s. sciurorum was studied in a constant environment, using an insect activity monitor. Trials were run over 7 days using two start times (08.00 and 17.00 hours). The results show that, regardless of start time, the fleas display a 24 h activity rhythm. The presence of a rhythm under constant conditions gives a strong indication that C. s.sciurorum has a self-sustaining clock which is started by disturbance and is most likely to be linked to host activity patterns.     

The circadian body temperature rhythm in the elderly: effect of single daily melatonin dosing

The present study is part of a more extensive investigation dedicated to the study and treatment of age-dependent changes/disturbances in the circadian system in humans. It was performed in the Tyumen Elderly Veteran House and included 97 subjects of both genders, ranging from 63 to 91 yrs of age. They lived a self-chosen sleep-wake regimen to suit their personal convenience. The experiment lasted 3 wks. After 1 control week, part of the group (n=63) received 1.5 mg melatonin (Melaxen) daily at 22:30 h for 2 wks. The other 34 subjects were given placebo. Axillary temperature was measured using calibrated mercury thermometers at 03:00, 08:00, 11:00, 14:00, 17:00, and 23:00 h each of the first and third week. Specially trained personnel took the measurements, avoiding disturbing the sleep of the subjects. To evaluate age-dependent changes, data obtained under similar conditions on 58 young adults (both genders, 17 to 39 yrs of age) were used. Rhythm characteristics were estimated by means of cosinor analyses, and intra- and inter-individual variability by analysis of variance (ANOVA). In both age groups, the body temperature underwent daily changes. The MESOR (36.38+/-0.19 degrees C vs. 36.17+/-0.21 degrees C) and circadian amplitude (0.33+/-0.01 degrees C vs. 0.26+/-0.01 degrees C) were slightly decreased in the elderly compared to the young adult subjects (p<0.001). The mean circadian acrophase was similar in both age groups (17.19+/-1.66 vs. 16.93+/-3.08 h). However, the inter-individual differences were higher in the older group, with individual values varying between 10:00 and 23:00 h. It was mainly this phase variability that caused a decrease in the inter-daily rhythm stability and lower group amplitude. With melatonin treatment, the MESOR was lower by 0.1 degrees C and the amplitude increased to 0.34+/-0.01 degrees C, a similar value to that found in young adults. This was probably due to the increase of the inter-daily rhythm stability. The mean acrophase did not change (16.93 vs. 16.75 h), although the inter-individual variability decreased considerably. The corresponding standard deviations (SD) of the group acrophases were 3.08 and 1.51 h (p<0.01). A highly significant correlation between the acrophase before treatment and the phase change under melatonin treatment indicates that this is due to a synchronizing effect of melatonin. Apart from the difference in MESOR, the body temperature rhythm in the elderly subjects undergoing melatonin treatment was not significantly different from that of young adults. The data clearly show that age-dependent changes mainly concern rhythm stability and synchronization with the 24 h day. A single daily melatonin dose stabilizes/synchronizes the body temperature rhythm, most probably via hypothermic and sleep-improving effects.     

Diazepam phase shifts the circadian clock of the field mouseMus booduga

Single 2h administration of diazepam (benzodiazepine) in 3.5% ethanol solution was found to evoke advance and delay phase shifts in the locomotor activity rhythm in the field mouseMus booduga. Through such pulsed administration of diazepam at various phases of circadian rhythm a phase response curve could be constructed. Phase advance occurred during early subjective day (CT 2) and phase delays were observed in the remaining phases. The shape of the diazepam phase response curve is similar to the general shape of the phase response curves generated by intraperitoneal injections of other benzodiazepines in hamsters. The phase shifting action of diazepam may be explained by its agonistic action on the neurotransmitter gamma-aminobutyric acid.     

Entrainment analysis of the circadian locomotor activity rhythm in specimens of the crayfish, Faxonella clypeata, having activity peaks at different times of the solar day.

Locomotor activity rhythms in the crayfish, Faxonella clypeata, were recorded under conditions of controlled light and temperature. In LD 12:12, dark active rhythms with a major activity onset at lights-off, and bimodally active rhythms with onsets at both lights-on and lights-off were recorded. In DD, most of the LD dark active rhythms retained the lights-off activity onset. However, among the majority of the LD bimodally active crayfish, only the lights-on activity peak persisted in DD. A small number of the LD bimodal rhythms remained bimodal in DD. DD records revealed free-running period lengths both greater and less than 24 hrs. An hypothesis stating that the two recorded LD rhythms represent two basically different rhythmic types is presented. The dark active crayfish appear to entrain to the lights-off position, but the bimodally rhythmic crayfish appear to entrain to the lights-on position.