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M K Chandrashekaran

Publications and source records attributed to M K Chandrashekaran.

At least 19 recordsLinked to original sources
PubMed1998

Age-dependent modulation of circadian parameters in the field mouse Mus booduga.

The locomotor activity of the field mouse Mus booduga was monitored under continuous darkness (DD) for extended periods of 275 to 388 days. Free-running period (tau), activity time (alpha) and rest time (rho) were computed from the activity records for all the animals (n = 10). Decreases in the circadian period (tau) with age were observed in some of the animals at an early age (< ca. 100 days) and then tau remained relatively constant for rest of their life span. The activity time (alpha), rest time (rho), and their ratio (alpha/rho), however, did not show any consistent trend of increase/decrease. The initial decrease in tau is consistent with previous models suggesting a time-dependent increase in the number of cells generating oscillations in the suprachiasmatic nucleus (SCN) and/or increase in the strength of coupling between these cells. In such models, after an optimal number of cells launch themselves into a state of self-sustained oscillation, tau stabilizes, achieving relative constancy, a pattern similar to the one observed in our study.

Aging↗
PubMed1997

Correlations between sleep and wake in internally synchronized and desynchronized circadian rhythms in humans under prolonged isolation.

The authors report the results of their experiments performed on the sleep-wake and rectal temperature rhythms of human subjects, who were held in prolonged social isolation for periods of 15-43 days in a specially constructed facility. Of 13 experiments performed with 11 subjects, the sleep-wake and rectal temperature rhythms free ran with circadian periods, remaining internally synchronized for the entire duration of the experiments in 9 subjects. The relationship between sleep and wake that is highlighted in this article is a trend that clearly and significantly expresses itself in four long-term experiments performed on a male subject and a female subject in separate experiments. There was clear-cut positive correlation between episodes of sleep and preceding episodes of wake. In all four experiments, the circabidian sleep-wake cycle and circadian rectal temperature rhythms, were in a state of internal desynchronization. The authors therefore attribute the differences reported in the literature and this article in the quality of correlation between sleep and wake to the phenomenon of internal desynchronization. However, they do not find significant correlation between sleep and wake episodes in 8 of their 9 subjects; in 1 35-year-female, there is a strong negative correlation between sleep and (preceding or following) wake episodes. It is of much physiological significance that the phenomenon of internal desynchronization should so radically alter the "quality of correlation" between sleep and wake and may be of interest for models of sleep regulation.

Adult↗
PubMed1997

Relationship between free-running period and minimum tolerable light pulse interval of skeleton photoperiods in field mice Mus booduga.

The entrainment of the circadian rhythm of locomotor activity was studied in the field mouse Mus booduga in order to examine the relationship between the free-running period (tau) and minimum tolerable light pulse interval of the skeleton photoperiods. The animals were entrained under three different light/dark (LD) schedules, each out of phase with the other. They were then subjected to various skeleton photoperiods created by two repeated light pulses (LPs) interrupting darkness. Animals that selected the shorter interval between the LPs as their "subjective night" had significantly shorter tau (23.13 +/- 0.38 h) as compared to those that selected the longer dark interval as subjective night (tau = 23.87 +/- 0.18 h). When the longer dark interval was 12 h, animals selecting that interval as their subjective night included both long-tau and short-tau individuals. When both intervals of darkness were of equal duration, no difference in the selection of subjective night was seen between short and long-tau animals. When the "dusk" LP for the animals that selected the longer dark interval as subjective night was advanced by 2 h to create a new skeleton photoperiod, the number of transient cycles appearing before steady-state entrainment was found to depend on the duration of the photoperiods. When the night defined by the two LPs was reduced below 6h, a dramatic "phase jump" in the activity rhythm was observed, and the initial phase relationship was restored after a relaxation in the night duration. We observed considerable interindividual variation in the "minimum tolerable light pulse interval of skeleton photoperiods," which we suggest may be due to the observed variation in tau among individuals.

Animals↗
PubMed1997

Rapid phase resetting of a mammalian circadian rhythm by brief light pulses.

The phase-shift (delta phi) responses of the circadian rhythm in the field mouse Mus booduga to brief light pulses (LPs) of 15 minutes duration and 1000 lux intensity were measured in 90 experiments. In each experiment, a resetting light pulse LP1 was administered at CT14 (CT, circadian time), and a scanning light pulse LP2 was then variously administered in separate experiments at CT16, CT20, and CT22 in the same and in the next circadian cycle. The delta phi obtained in all these two-pulse experiments did not differ significantly from theoretical values computed on the assumption that LP1 reset the phase response curve (PRC) rapidly. In each case, the steady-state delta phi observed after LP1 and LP2 differed significantly from the delta phi obtained at the same CT in determination of the single-pulse PRC (control) and also differed significantly from the values on the assumption of no delta phi in the PRC following LP1. These results indicate that the circadian pacemaker of M. booduga, as measured by its PRC, is substantially reset within 2h after a light pulse at CT14.

Animals↗
PubMed1996

Responses of the circadian locomotor activity rhythm of Mus booduga to shifts in LD schedules.

The responses of the field mouse Mus booduga to shifts in schedules of LD cycles were monitored and the results were interpreted with the help of a PRC constructed for the same species. The results reveal that, M. booduga reentrained faster with a lesser number of transients after delay shifts than advance shifts, thus exhibiting "asymmetry effect." A positive correlation was observed between the number of transients and the number of hours of shift. In most of the shifts, the sign of the transients (negative for delaying transients and positive for advancing transients) coincided with the direction of the shift. Interestingly, 11 and 12 h of advance shifting resulted in delaying transients. An 11-h advance shift can also be interpreted as a 13-h delay. Reentrainment through delaying transients is faster as compared to reentrainment through advancing transients. Thus, this animal might have taken a "shorter route," as proved by the fact that an 11-h advance shift has evoked delaying transients. But a 13-h advance shift evoked only advancing transients. This prompts us to speculate that there may be a "phase jump" in M. booduga. Further, irrespective of whether L or D has been doubled in a 12-h shift, both evoked only delaying transients.

Animals↗
PubMed1986

Light and dark pulse response curves in a day active palm squirrel Funambulus palmarum.

Light pulses (L-pulses 1 h, 1000 1x) and dark pulses (D-pulses, 2 h) reset the phases of the circadian rhythm of locomotor activity in the day active palm squirrel Funambulus palmarum. The phase response curves (PRCs) constructed from steady-state phase shifts (delta phi s) thus caused conformation to the generalization that the time course and wave form of the light pulse PRC (LP-PRC) and dark pulse PRC (DP-PRC) should be opposite in sign. No consistent correlations could be detected in the wake of L- and D-perturbations between the direction of transients, changes in the period length (tau) and the direction of steady state delta phi s.

Animals↗
PubMed1985

Light flashes of different durations (0.063-3.33 msec) phase shift the circadian flight activity of a bat.

The phase-response curve (PRC) for the circadian rhythm in the flight activity of a cave-dwelling bat, Hipposideros speoris, constructed with 0.063-msec light flashes, reported here is the first of its kind for any circadian system and is unlike any other phase-response curves constructed for other nocturnal animals. The phase responding with maximal advances (90 degrees) and the phase responding with maximal delays (0 degree) of this PRC were exposed to light flashes of systematically varying durations from 0.083 to 3.33-msec. For 0 degree phase, the flashes of 0.063-3.33 msec effected delay phase shifts of comparable magnitude. For 90 degrees phase, the flashes of 0.063-1.0 msec effected advance phase shifts, whereas 3.33-msec flashes effected unmistakable delay phase shifts with advancing transients. Phase shifts evoked with such light flashes are further compared with phase shifts evoked with pulses of longer durations (15 min to 2.8 hr) for H. speoris.

Animals↗
PubMed1985

Entrainment of the circadian rhythm in the locomotor activity of Mus booduga by red and white light.

The role of red light (greater than 610 nm) and white incandescent light in entraining the circadian locomotor activity rhythm of the field mouse Mus booduga has been studied using different light intensities. Red light of less than 150 microW/cm2 caused negative masking and greater than 150 microW/cm2 caused entrainment. Such intensity dependent masking and entrainment were also obtained with white incandescent light.

Animals↗
PubMedDate not supplied

Cycles of presence and absence of mother mouse entrain the circadian clock of pups.

Recent findings on neural and endocrine rhythms in infant mice and rats show that maternal coordination has an important role in setting the phase of the developing circadian clock both in the fetus and soon after birth. However, less information is available about the influence of the mother on activity/rest cycles of infants. Separation of the mother from infants in guinea pigs, monkeys and rats results in an increase in sleep disturbance (enhanced activity?). In this context it may be a common feature that during the postnatal period there is enhanced activity of pups during the hours when the mother is not nearby. Conversely, the social influences exerted by the mother while present with her young possibly leads to a relative rest stage. We have now tested this assumption in the night-active mouse Mus booduga. Our study addressed the postulate that the circadian activity/rest cycles of the pups are controlled by cyclic(?) presence and absence of the mother. The results reported here clearly indicate that the circadian locomotor activity of pups kept under continuous illumination or continuous darkness do entrain them to a regime of imposed 12:12-h cyclic presence and absence of the mother. The characteristics of this entrainment confer on the mother mouse the role of zeitgeber.

Animals↗
PubMedDate not supplied

Temperature sensitive events between photoreceptor and circadian clock?

The phase shifting action of low temperature pulses of 6 degrees C and 2 h duration administered to the various phases of the Drosophila pseudoobscura circadian rhythm and the action of light pulses given 30 min after the beginning of these low temperature pulses have been investigated. The phase response curve obtained from experiments with light pulses during low temperature cannot be explained on the basis of a straightforward and sequential phase shifting of the oscillation by the various transitions in the pulses. The response curve, after the slight phase shifting action of the temperature pulses is corrected for, resembles the standard phase response curve4 for light pulses (at 20 degrees C) in its wave form but not in its time course. Our curve is shifted in time in a manner that indicates that the light pulses accompanying the low temperature pulses arrived at phase points 1.5 h later than the actual phases at which they were given. We attribute this delay to a slowing down of the information that is apparently transmitted by a process that is temperature dependent.

Animals↗