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Biomedical subjects

M L Moline

Publications and source records attributed to M L Moline.

32 records · Page 2Linked to original sources
PubMed1989

Circadian determinants of subjective alertness.

Four healthy male subjects each experienced a temporal isolation experiment lasting several months. During part of each experiment (2-5 weeks), the subject's entire imposed daily routine (including light-dark, rest-activity, and meal routines) was either stretched (two subjects: T = 25.8 hr, 26.0 hr) or reduced (two subjects: T = 22.8 hr, 23.1 hr) to beyond the range of entrainment of the endogenous circadian pacemaker (ECP), which then ran at a different period (tau). Subjective alertness was measured approximately three times per hour (during wakefulness), using a computerized visual analogue scale technique. Circadian rhythms in subjective alertness were then plotted both at tau, the period length of the ECP, and at T, the period length of the imposed sleep-wake cycle (SWC) and light-dark cycle. At tau, the alertness rhythm was closely in phase with the temperature rhythm. At T, the alertness rhythm showed an "inverted-U" function with a peak toward the middle of the subjective day, upon which was superimposed a "postlunch dip" for one subject. Thus, subjective alertness would appear to be under the control fo both ECP and SWC mechanisms, which combine to produce the composite time-of-day function normally observed in a diurnal setting.

Arousal↗
PubMed1988

Response of circadian locomotor activity and the proestrous luteinizing hormone surge to phase shifts of the light-dark cycle in the hamster.

Female hamsters with regular 4 day estrous cycles were exposed to either a 3 hour phase advance or delay of the 14:10 light-dark (LD) cycle on the first, second or third day before proestrus. Blood samples were taken on proestrus to characterize the LH surge, and locomotor activity onset was recorded. Both the LH surge and activity onset phase delayed more quickly than they advanced, which can be explained by the free-running period of the hamster (longer than 24 hours). Higher estradiol levels were correlated with more rapid advances of activity onset.

Animals↗
PubMed1988

Removal of temporal constraints in the middle-aged and elderly: effects on sleep and sleepiness.

Ten healthy middle-aged and elderly subjects (44-81 years old; 4 men and 6 women) were studied in time isolation experiments involving: (a) entrainment to the subject's habitual routine (EN condition) and (b) removal of all temporal constraints or "free-running" (FR condition) with the subjects able to choose their own bed and meal times. Subjective day lengths and circadian temperature cycle periods were longer under FR than under EN, but not by an equal amount. Perhaps as a consequence, although time-in-bed (TIB) fractions were greater under FR than under EN, actual sleep fractions were not, reflecting a decline in sleep efficiency. Neither was there an increase in slow-wave sleep (SWS) under FR compared with EN. Daytime subjective alertness did, however, increase upon release into FR, also showing a slightly earlier peak than that observed under the EN condition. The results point to the need to regard sleep and sleepiness as rhythmic, as well as homeostatic, processes.

Aged↗
PubMed1988

Inducing jet lag in the laboratory: patterns of adjustment to an acute shift in routine.

Eight middle-aged males were studied in a temporal isolation experimental lasting 15 d. After 5 d and nights of entrainment to his own habitual routine, each subject experienced an acute, unheralded 6-h phase advance in routine, accomplished by truncating his sixth sleep episode. For the remaining 10 d of the study, subjects were held to a routine 6-h phase advanced to the original. Significant symptoms of jet lag appeared in mood, performance efficiency, sleep, and circadian temperature rhythms. When plotted as a function to "days post-shift," some variables (temperature phase, percent rapid eye movement sleep) showed a fairly monotonic recovery to baseline levels. However, other variables (actual sleep duration, percent slow wave sleep, motivation loss, subjective sleepiness) showed a zig-zag recovery pattern, suggesting the interaction of two competing processes, and reinforcing the need for greater sophistication in the development of jet lag coping strategies.

Adult↗
PubMed1986

Estrogen modifies the circadian timing and amplitude of the luteinizing hormone surge in female hamsters exposed to short photoperiods.

LH surges occur 3 h later in intact anovulatory hamsters exposed to nonstimulatory photoperiods (6L:18D) for 8 wk than the proestrous LH surges from the same hamsters housed in 6L:18D for 3 weeks. In ovariectomized hamsters housed in 6L:18D for 3 wk, the LH surge was observed at the same time of day as in intact anovulatory hamsters at 8 wk. Implanting Silastic capsules containing estradiol benzoate (EB) advanced the timing of the daily surge of LH in ovariectomized hamsters housed in 6L:18D for 8 wk. EB also affected the magnitude of the LH surge in hamsters housed in 6L:18D for 8 wk. Two days after receiving EB implants, daily LH surges in anovulatory hamsters were suppressed by 75% and in ovariectomized "regressed" hamsters by 37%. This difference between groups was probably due to ovarian progesterone in intact animals. Estrogen is not required for LH surges in anovulatory hamsters but suppresses LH release when administered exogenously. The delay in the timing of the LH surge in anovulatory hamsters may result from the decline in estrogen resulting from short photoperiod exposure.

Animals↗
PubMed1985

Circadian rhythms and photoperiodism.

The circadian timing system plays a critical role in the regulation of seasonal modifications in reproductive function. By detecting and transducing changes in the day-length (photoperiod), the neural substrates of the circadian system, including the supra-chiasmatic nuclei of the hypothalamus, trigger reproductive activity or quiescence at the appropriate seasons of the year in photoperiodic species. The circadian system also plays a role in the expression of endocrine changes that occur with seasonal breeding. Surges in luteinizing hormone secretion in female hamsters, for example, are either expressed daily during reproductive quiescence or suppressed on three out of the four days of the cycle during the breeding season. By such mechanisms a daily timer can be used in the regulation of cyclic events of much longer period.

Animals↗
PubMed1985

Diurnal variation in mood and performance in a time-isolated environment.

In order to document circadian rhythmicity in various psychological functions under the chronobiologically 'pure' condition of temporal isolation, a battery of mood and performance tests were administered about 6 times per day to a heterogeneous group of 18 subjects (ages 19-81, 5 female). Each subject spent about 5 days in temporal isolation, entrained to a routine equivalent to his/her own habitual sleep/wake cycle. Average time of day functions were obtained for the mood and performance variables, and compared to rectal temperature data subjected to exactly the same statistical analysis. Significant time of day effects were found in the mood variables of alertness, sleepiness, weariness, effort required, happiness and well-being. Times of 'best' mood were different from the time of peak temperature. Moreover, the minima of sleepiness, weariness and effort occurred earlier in the day than the maximum of alertness. Significant time of day effects were also found in the speed with which search and dexterity tasks were completed. Only the dexterity tasks showed a complete parallelism with the temperature rhythm.

Adult↗
PubMed1984

Sex differences in circadian control of LH secretion.

Sex differences in the hourly values of serum LH were examined in male and female Syrian hamsters exposed to either long photoperiods (14 h light: 10 darkness; 14L: 10D) or short photoperiods (6L: 18D). In long photoperiods, females exhibited a pro-oestrous surge of LH in response to high levels of circulating oestradiol (1047.36 +/- 90.68 pmol/l), while LH values in male hamsters remained essentially constant. In females housed in short photoperiods oestradiol levels were reduced by fivefold; however, a discrete surge in serum LH, similar to that seen at pro-oestrus in females exposed to long photoperiods, was observed. Although exposure to a short photoperiod eliminates the requirement of a positive feedback of oestrogen for the expression of an afternoon surge in LH, male hamsters housed in short photoperiods showed no indication of an afternoon surge in serum LH. These observations indicate that sex differences in the neural control of LH release are not the result of sex differences in oestrogen sensitivity or responsiveness.

Animals↗
PubMed1982

Chronobiology of aging: temperature, sleep-wake rhythms and entrainment.

Studies were carried out on a group of six young (ages 23-30) and six older (ages 53-70) normal men who lived under conditions of temporal, but not social isolation, from three to eight weeks. During entrained and non-entrained (free-running) conditions, comparative measurements were made of sleep-wake cycles, sleep stages and rectal temperature rhythms for these two age groups. Results demonstrated a reduction in the period and amplitude of the body temperature rhythms during free-running in the older group. Sleep efficiency, total sleep time, REM sleep latency, REM episode length, percent REM in the last 2 hours of sleep, the length and frequency of arousals during sleep, and the terminal wake latency were all age related and dependent on entrainment. The period of the sleep-wake cycle, terminal awakenings from REM and percent REM in the first 3 hours of sleep were not age related but were dependent on entrainment. Sleep stages as percents of total sleep time were found to be age related but independent of entrainment, while sleep latency, mid-REM to mid-REM cycle length and the ratio of sleep to total time were neither age related nor dependent on entrainment. In addition, individual chronobiological differences were prominent in the older group. Changes of period and of the phase relationship of sleep-wake and temperature rhythms occurred in several subjects during the non-entrained condition.

Adult↗
PubMedDate not supplied

Task variables determine which biological clock controls circadian rhythms in human performance.

There are circadian (approximately 24 h) rhythms for a wide range of human physiological and psychological functions including mood and performance efficiency. These rhythms are self-sustaining in conditions of temporal isolation, indicating that internal oscillators (or biological clocks) control them. Recent research has proposed an endogenous two-oscillator model of the human circadian system, with one oscillator indicated by the core body temperature rhythm and a second oscillator responsible for the daily cycle of sleep and wakefulness. The present study was designed to produce a desynchronization in period between the two oscillators, to assess directly the behaviour of the rhythms of different performance tasks. The results, reported here, indicate that a simple manual dexterity task is almost entirely under the control of the temperature rhythm oscillator, whereas a more complex cognitive task demonstrates a periodicity which appears to be influenced by those oscillators controlling temperature and the sleep/wake cycle.

Adult↗
PubMedDate not supplied

Human growth hormone release is decreased during sleep in temporal isolation (free-running).

Growth hormone (hGH) secretion was measured during sleep in 10 healthy male subjects isolated from all time cues. HGH concentrations following sleep onset were compared between scheduled sleep episodes (entrainment) and self-selected sleep episodes (free-running). Peak sleep-related hGH values were decreased significantly during free-running. The duration of the first slow wave sleep (SWS) episode and the latency to the first REM sleep episode also decreased significantly during free-running. The latencies from sleep onset to SWS and to peak hGH secretion did not differ between entrainment and free-running. These results suggest that sleep-related hGH secretion begins 'on time' during free-running, but is terminated earlier. Thus, while sleep onset facilitates hGH release, the timing of other stages of sleep such as REM may alter the magnitude of sleep-related hGH secretion.

Adult↗
PubMedDate not supplied

Circadian rhythms in human performance efficiency under free-running conditions.

A series of four experiments is described in which two men and two women (age range 22-79 years) were allowed to 'free-run' under conditions of isolation from all time cues. The circadian rhythms of performance efficiency were studied for three tasks: serial search, verbal reasoning, and manual dexterity (left and right hand versions). Strong evidence was obtained to suggest that different tasks are under the control of different circadian oscillators. The circadian rhythm in verbal reasoning performance tends to run at a shorter circadian period than that in more simple repetitive tasks, and slight differences in circadian behavior can occur between left- and right-handed dexterity.

Adult↗