Sleep Deprivation Alters the Cell Population Kinetics In the Jejunum of the Male Syrian Hamster (Mesocricetus auratus)

The proliferative and functional units of the jejunum were studied every 3 hr during 24 hr in groups of control and sleep-deprived hamsters. Peaks in kinetic parameters were evident during the sleep period in control hamsters; in the absence of sleep, peak values were significantly reduced. Sleep deprivation was associated with reduction of G₂ to M flux and reduction of the circadian rhythm in mitotic index from 74% to 25%. the reduction in the number of cells passing through M was reflected by a drop in labelling index 9 hr later. These findings are consistent with the theory that sleep promotes restorative processes.     

Homeostatic regulation of sleep in arrhythmic Siberian hamsters

Sleep is regulated by independent yet interacting circadian and homeostatic processes. The present study used a novel approach to study sleep homeostasis in the absence of circadian influences by exposing Siberian hamsters to a simple phase delay of the photocycle to make them arrhythmic. Because these hamsters lacked any circadian organization, their sleep homeostasis could be studied in the absence of circadian interactions. Control animals retained circadian rhythmicity after the phase shift and re-entrained to the phase-shifted photocycle. These animals displayed robust daily sleep-wake rhythms with consolidated sleep during the light phase beginning about 1 h after light onset. This marked sleep-wake pattern was circadian in that it persisted in constant darkness. The distribution of sleep in the arrhythmic hamsters over 24 h was similar to that in the light phase of rhythmic animals. Therefore, daily sleep amounts were higher in arrhythmic animals compared with rhythmic ones. During 2- and 6-h sleep deprivations (SD), it was more difficult to keep arrhythmic hamsters awake than it was for rhythmic hamsters. Because the arrhythmic animals obtained more non-rapid eye movement sleep (NREMS) during the SD, they showed a diminished compensatory response in NREMS EEG slow-wave activity during recovery sleep. When amounts of sleep during the SD were taken into account, there were no differences in sleep homeostasis between experimental and control hamsters. Thus loss of circadian control did not alter the homeostatic response to SD. This supports the view that circadian and homeostatic influences on sleep regulation are independent processes.     

Fertilizing ability in vitro of golden hamster spermatozoa after acute testicular X-irradiation]

The present study is concerned with the effect of radiation to the testis on fertilizing ability in vitro using golden hamster spermatozoa. Male hamsters at 6 and 8 weeks of age were given acute testicular X-irradiation (200 kVp, 20 mA, 0.47-0.48 Gy/min). Spermatozoa were collected from the cauda epididymides at different times after irradiation and then they were suspended in fertilization medium. After preincubation for 4-5 hr, the spermatozoa were cultured with the eggs collected from mature hamsters treated with PMSG-hCG. Fertilized eggs were examined for incidence of sperm penetration and formation of pronuclei at 4-5 hr after insemination. The fertilization rate (47.7%) at the 6th week after irradiation with a dose of 2 Gy was much lower in comparison with the control value (92.6%). However, the fertilization rates at the 3rd and 9th weeks after irradiation were 97.7 and 90.6%, respectively. In these period, no difference was found between the irradiated groups and the control groups. From the changes in sperm concentration after irradiation with a dose of 2 Gy, it was found that the fertilization rate was the lowest at the 6th week. The sensitive stage to radiation during spermatogenesis with reference to the reduction of fertilizing ability after irradiation coincides with that of decrease in the sperm concentration and sperm motility. The results of fertilization rate at the 6th week after different doses of X-irradiation (0.25-6 Gy) indicated that the reduction of fertilization rate is nearly expressed as a dose-response relationship.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sleep: sequential reduction of paradoxical (REM) and elevation of slow-wave (NREM) sleep by a non-convulsive dose of insulin in rats

Administration of a single non-convulsive dose of insulin (1.0, I.U./kg., I.P.) which produced no observable gross behavioral changes in rats, reduced rapid eye movement (REM) sleep time 100% in the first 3 hrs. and 82% by the 4th hr., reaching control subject levels (saline-treated) by the 6th hr. In contrast, slow-wave sleep (NREM) time in insulin treated animals exceeded control subject levels by 49% by the end of the 2nd hr., returning to normal by the 5th hr. Although there was no difference between insulin and saline treated rats for the total 8 hr. post-injection recording period for total percentage of time awake, or slow-wave sleep time, a 44% reduction in REM sleep time was observed in insulin treated animals compared to that of a saline treated control. The significance of these findings are discussed in terms of known neurochemical changes i.e., an increase of both brain tryptophan and serotonin in rats, induced by a subconvulsive dose of exogenous insulin.     

Diurnal Variation in Subjective and Objective Measures of Sleepiness: the Effects of Sleep Reduction and Circadian Type

In young, good sleepers the diurnal evolution of alertness was studied as a function of degree of morningness: (1) during habitual sleep routine and (2) in a 2-hr sleep reduction protocol. During habitual sleep routine, alertness was assessed using both the subjective evaluation based on Thayer's Activation Deactivation Adjective Checklist (43 subjects) and the objective measurement of sleep latency (Multiple Sleep Latency Test, MSLT). Self-alertness scored highest around midday. Later it showed a dip, then stayed on a plateau until about 2200 hr. On average, 77+ of the subjects fell asleep at the 1400 hr MSLT session while only 35.5+ did at 1000 hr and 25.8+ at 2000 hr. Morning-types (MT) and evening-types (ET) differed only during the morning: ET fell asleep more frequently at 1000 hr and 1200 hr and rated lower self-alertness on arising than did MT. Twelve subjects were given the protocol of a 2-hr sleep reduction (both in delayed bedtime and advanced rising time conditions). At 0700 hr, MT rated their alertness lower when they had only just gotten up (delayed bedtime condition) than when they had been awake for 2 hr (advanced rising time condition). In contrast, ET had the same low level of alertness at 0800 hr, independent of the time elapsed since arising. On average the advanced rising time condition affected the general pattern of alertness more than did delayed bedtime.     

Lipolytic and antilipolytic responses of the Siberian hamster (Phodopus sungorus sungorus) white adipocytes after weight loss induced by short photoperiod exposure

Short day photoperiod promotes thermogenesis and extensive weight loss in Siberian hamsters (Phodopus sungorus sungorus). To determine whether a change in hormone-sensitive lipolysis occurs after short-photoperiod exposure, some lipolytic responses were measured on white adipocytes isolated from animals exposed in warm conditions to short or Long daylight photoperiod. The body mass of male Siberian hamsters exposed during 11 weeks to short days (SD; light: dark, 6:18 hr) reached only 50% of those kept in long days (LD; 16: 8 hr). In SD-hamsters, adipose depot mass also represented approximately 50% of the LD group. A lower DNA content was observed in intra-abdominal fat pads of SD-hamsters. Lipolytic responses to noradrenaline, adrenaline, isoproterenol and ACTH were unchanged. However, sensitivity to the beta-3 adrenergic agonist, BRL 37344, was moderately increased. The major component of the adrenergic control of lipolysis was mediated by beta-3 adrenoceptors in both LD- and SD-Siberian hamsters. The limited antilipolytic effect of alpha-2 adrenergic agonists, PYY or insulin was rather surprising in Siberian hamsters since these inhibitory systems are efficient in hibernants and other photoperiod-sensitive rodents. Our results show that, after short photoperiod exposure, white adipose tissue mass and DNA content are reduced, especially in the epididymal fat pad, with only minor changes in the adipocyte sensitivity to lipolytic hormones.     

Diurnal Variation in Subjective and Objective Measures of Sleepiness: the Effects of Sleep Reduction and Circadian Type

In young, good sleepers the diurnal evolution of alertness was studied as a function of degree of morningness: (1) during habitual sleep routine and (2) in a 2-hr sleep reduction protocol. During habitual sleep routine, alertness was assessed using both the subjective evaluation based on Thayer's Activation Deactivation Adjective Checklist (43 subjects) and the objective measurement of sleep latency (Multiple Sleep Latency Test, MSLT). Self-alertness scored highest around midday. Later it showed a dip, then stayed on a plateau until about 2200 hr. On average, 77+ of the subjects fell asleep at the 1400 hr MSLT session while only 35.5+ did at 1000 hr and 25.8+ at 2000 hr. Morning-types (MT) and evening-types (ET) differed only during the morning: ET fell asleep more frequently at 1000 hr and 1200 hr and rated lower self-alertness on arising than did MT. Twelve subjects were given the protocol of a 2-hr sleep reduction (both in delayed bedtime and advanced rising time conditions). At 0700 hr, MT rated their alertness lower when they had only just gotten up (delayed bedtime condition) than when they had been awake for 2 hr (advanced rising time condition). In contrast, ET had the same low level of alertness at 0800 hr, independent of the time elapsed since arising. On average the advanced rising time condition affected the general pattern of alertness more than did delayed bedtime.     

Flow cytometric analysis of adriamycin-perturbed mouse mammary tumors.

The effects of a single intraperitoneal injection of adriamycin (10 mg/kg) on a fast-growing C3H mouse mammary tumor (S102F) have been analyzed volumetrically, biochemically, autoradiographically and flow cytometrically. Mathematical simulation of the data was also used to aid in the interpretation of the recovery kinetics. This dose of adriamycin did not induce regression in tumor volume but did inhibit the growth rate for 4-5 days. 3H-TdR incorporation was gradually inhibited to reach a low of 20% of control at 24 and 36 hr and then recovered back to control by 96 hr after adriamycin treatment. The flow cytometric analysis also showed a marked reduction in the relative fraction of cells in the S-phase with a minimum of 23% of control at 72 hr; however, in contrast to the 3H-TdR incorporation data, the fraction of cells in the S-phase was only at 39% of control at 96 hr after the adriamycin injection. Since the 3H-TdR incorporation data disagreed with the flow cytometry data, autoradiographic analysis was also done at selected times after the adriamycin injections, and qualitatively, this analysis confirms the flow cytometry data in that the labeling index was 29% of control at 96 hr after adriamycin. The mitotic index also dropped from 8 to 1%, respectively, for controls and at 96 hr posttreatment. The degenerate index was about 1% in control tumors and no increase was observed in treated tumors. Adriamycin-induced cell-cycle delay occurs predominately in G1 and G2 but there is also an apparent minor delay in the transit across the S-phase and some apparent cytotoxicity in G2 and/or M. The long delay in volumetric growth appears to be due to the extended cell-cycle delay rather than extensive cell killing.     

BK(Ca) channels compensate for loss of NOS-dependent coronary artery relaxation in cardiomyopathy

Previously, we showed that development of myocardial necrotic lesions is associated with impaired endothelium-dependent coronary artery relaxation in young cardiomyopathic hamsters. Since active necrosis declines with aging, this study was designed to determine whether coronary artery endothelium-dependent relaxation to ACh is restored and to identify the mechanisms mediating this effect. Intraluminal diameter was recorded in coronary arteries (150-250 micrometer) from control (C, 297 +/- 5 days old) and cardiomyopathic (M, 296 +/- 4 days old) hamsters. Relaxation to ACh (10(-9)-3 x 10(-5) M) was similar in vessels from C and M hamsters. However, mechanisms mediating relaxation to ACh were altered. Inhibition of nitric oxide synthase (NOS) activity with N-nitro-L-arginine (1 mM) had a greater inhibitory effect in vessels from C hamsters, indicating a reduction in NOS-dependent relaxation in vessels from M hamsters. Conversely, inhibition of large Ca(2+)-dependent K(+) (BK(Ca)) channels with charybdotoxin (CTX, 0.1 microM) had a greater inhibitory effect in vessels from M hamsters. In the presence of both N-nitro-L-arginine and CTX, relaxation to ACh was abolished in both groups. CTX (0.1 micrometer) produced a 50 +/- 4 and 30 +/- 3% contraction of vessels from M and C hamsters, respectively, indicating an enhanced role for BK(Ca) channels in regulation of coronary artery tone in M hamsters. Finally, vasodilatory cyclooxygenase products contributed to ACh-induced relaxation in vessels from M, but not C, hamsters. In conclusion, NOS-dependent relaxation of coronary small arteries is reduced in the late stage of cardiomyopathy. An increase in relaxation mediated by BK(Ca) channels and vasodilatory cyclooxygenase products compensates for this effect.     

Glucocorticoids and hypothermic induction and survival in the rat

Glucocorticoids (GC) are important for thermoregulatory responses to low environmental temperatures. Pretreatment of hamsters, which are capable of natural hibernation, with cortisone acetate has been demonstrated to improve carbohydrate homeostasis during hypothermia. The objectives of the current studies were to evaluate the effects of GC pretreatment of a nonhibernator, the rat, on (i) cooling time, (ii) carbohydrate homeostasis (in terms of liver and cardiac glycogen concentrations and plasma glucose concentration), and (iii) duration of survival in hypothermia. In addition, the effects of liver glycogen depletion on cooling times and survival were examined. Hypothermia was induced in rats by exposure to a helium:oxygen (80:20, Helox) atmosphere at 0 degree C. Pretreatment of rats with triamcinolone acetonide (1.5 mg/kg/day, sc, 48, 24, and 1 hr prior to induction) significantly (P less than 0.05) lengthened induction time, while fasting was associated with a significant decrement (25%). While liver and cardiac glycogen levels in control and GC-treated rats fell approximately 45% during cooling, this reduction occurred over a significantly greater period of time in treated rats and suggests a sparing of glycogen or increased capacity for its production in response to GC. Glycogen utilization was accompanied by a hyperglycemia in control, GC-treated, and fasted groups. Survival in hypothermia at a rectal temperature of 14-15 degrees C in GC-treated (9.5 +/- 1.2 hr) and fasted (10.9 +/- 0.9 hr) rats was not significantly different from control (10.5 +/- 1.1 hr) values. These findings suggest that treatment with GC can increase the thermogenic capacity of the rat (as evidenced by an increased induction time) and promote carbohydrate homeostasis, but does not contribute to an enhancement of survival in the hypothermic nonhibernator.     

EEG power density during nap sleep: reflection of an hourglass measuring the duration of prior wakefulness

The relation between the duration of prior wakefulness and EEG power density during sleep in humans was assessed by means of a study of naps. The duration of prior wakefulness was varied from 2 to 20 hr by scheduling naps at 1000 hr, 1200 hr, 1400 hr, 1600 hr, 1800 hr, 2000 hr, and 0400 hr. In contrast to sleep latencies, which exhibited a minimum in the afternoon, EEG power densities in the delta and theta frequencies were a monotonic function of the duration of prior wakefulness. The data support the hypothesis that EEG power density during non-rapid eye movement sleep is only determined by the prior history of sleep and wakefulness and is not determined by clock-like mechanisms.     

Photoperiodic variation of Leydig cell numbers in the testis of the golden hamster: a possible mechanism for their renewal during recrudescence

Golden hamster testes regress after short day exposure. The present study asks: 1) are Leydig cell numbers depleted during short days, and 2) if so, how are they replenished during recrudescence. Control hamsters were shown 14 h of light and 10 h of dark (LD 14:10) for 10 weeks (n = 12). Testicular regression was induced by LD 6:18 for 10 weeks (n = 4), and recrudescence by switching regressed hamsters to LD 14:10 for 3 and 5 weeks (n = 8 for each group). All hamsters were injected with [3H]thymidine [3 microCi/gm body wt., intraperitoneally (i.p.)] 1 h or 2 weeks before sacrifice. Leydig cell number per testis was determined by stereological analysis of sections of perfusion-fixed testes, and labeling indices were determined by autoradiography. Leydig cell numbers were reduced significantly from 18.2 X 10(6) in control to 9.0 X 10(6) in regressed testes (p less than 0.05); then increased to 14.0 X 10(6) and 17.9 X 10(6) in 3- and 5-week recrudesced hamsters. The labeling index was nondetectable (n.d.) for regressed hamsters. In control and recrudescing hamsters the labeling index was measured at two times (t1 = 1 h vs. t2 = 2 weeks post-injection): in controls, t1 = 0.22 +/- 0.15% (mean +/- SEM) vs. t2 = 0.28 +/- 0.22%; in 1 week recrudesced, n.d. vs. 1.92 +/- 0.77% (p less than 0.05); at 3 wk, n.d. vs. 4.58 +/- 1.74% (p less than 0.05); at 5 weeks, 1.92 +/- 0.61% vs. 2.25 +/- 0.59%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Melatonin or a melatonin agonist corrects age-related changes in circadian response to environmental stimulus

The effects of a melatonin agonist, S-20098, included in the diet were tested on a specific effect of aging in hamsters: the marked decline in the phase shifting effects of a 6-h pulse of darkness on a background of constant light. In contrast to young hamsters, old hamsters fed with the control diet showed little or no phase shifts in response to a dark pulse presented in the middle of their inactive or active period. Old hamsters fed with S-20098 showed phase shifts that were ~70% of the ones in young animals and significantly greater than those in old controls. The phase advancing response to a dark pulse presented during the inactive period was dose dependent and reversed after S-20098 discontinuation. Melatonin included in the diet showed comparable restorative effects on the phase shifting response to a dark pulse in old hamsters. Replacement therapy with melatonin or melatonin-related compounds could prove useful in treating, preventing, or delaying disturbances of circadian rhythmicity and/or sleep in older people.     

Effects of fasting and food restriction on brown adipose tissue composition in normal and dystrophic hamsters

Fasting for 36-48 h or food restriction (30% reduction of daily food intake for 6 weeks) caused brown adipose tissue (BAT) atrophy in hamsters. Fasting-induced atrophy was characterized by reductions in tissue mass, DNA, protein, and thermogenin. By contrast, food restriction had no effect on tissue cellularity (DNA) but markedly reduced the tissue protein and thermogenin contents. The concentration of thermogenin in isolated mitochondria was unchanged by fasting or food restriction. Dystrophic hamsters had a reduced BAT mass when compared with weight-matched control hamsters. This resulted from a reduction in tissue cellularity since BAT DNA, protein and thermogenin contents were all reduced. The extent of binding of [3H]guanosine diphosphate to isolated mitochondria and their content of thermogenin were similar in normal and dystrophic hamsters. In response to cold exposure, as in normal hamsters, BAT of dystrophic hamsters grew and the tissue thermogenin increased, but the mitochondrial concentration of thermogenin did not change. In response to fasting, in contrast with normal hamsters, there was no significant reduction in BAT DNA in dystrophic animals and the loss of tissue protein was reduced. However, the relative changes in BAT composition during chronic food restriction were similar in normal and dystrophic animals. Thus, reduction in hamster BAT thermogenic capacity during food deprivation may occur by loss of cells and (or)reduction in the tissue protein and thermogenin contents. The extent of protein and (or) DNA loss may be dependent upon the original tissue mass and the severity of food deprivation.     

A comparative study of adrenal progesterone secretion during the estrous cycles of hamsters and rats

Adrenal secretory rates and peripheral plasma levels of progesterone (PROG) were determined during the estrous cycles of hamsters and 4-day cyclic rats. In both species, the PROG concentrations in peripheral plasma were never more than 6% of those observed in adrenal venous plasma. In hamsters, adrenal PROG secretory rates varied from 3.8 ± 0.8 ng/min at 0800 hr on proestrus (P) to 8.5 ± 1 ng/min at 2000 hr on estrus (E). The rates noted on P were among the lowest observed and were similar to those noted at 0800 hr the following morning. In rats, adrenal PROG secretory rates varied from 57 ± 9 ng/min at 0800 hr on E to 130 ± 18 ng/min at 2000 hr on P. A significant decline occurred between 2000 hr on P and 0800 hr the following morning. Rats secreted 3 to 8 times more PROG than did hamsters when the secretory rates are expressed as ng/min/100 mg adrenal. In hamsters, the data suggest a relative lack of influence of female reproductive hormones on adrenal PROG secretion and in turn the latter may not be involved in reproductive hormonal changes leading to ovulation. In rats, the increased adrenal PROG secretion noted on P may be due to the influence of reproductive hormones on adrenocortical function. This elevated rate may in turn influence the hypothalamo-hypophyseal-ovarian axis.     

Age-related reduction in the maximal capacity for sleep--implications for insomnia

Sleep changes markedly across the life span and complaints about insomnia are prevalent in older people [1]. Whether age-related alterations in sleep are due to modifications in social factors, circadian physiology, homeostatic drive, or the ability to sleep remains unresolved. We assessed habitual sleep duration at home and then quantified daytime sleep propensity, sleep duration, and sleep structure in an inpatient protocol that included extended sleep opportunities covering 2/3 of the circadian cycle (12 hr at night and 4 hr in the afternoon) for 3-7 days in 18 older and 35 younger healthy men and women. At baseline, older subjects had less daytime sleep propensity than did younger subjects. Total daily sleep duration, which was initially longer than habitual sleep duration, declined during the experiment to asymptotic values that were 1.5 hr shorter in older (7.4 +/- 0.4 SEM, hour) than in younger subjects (8.9 +/- 0.4). Rapid-eye-movement sleep and non-rapid-eye-movement sleep contributed about equally to this reduction. Thus, in the absence of social and circadian constraints, both daytime sleep propensity and the maximal capacity for sleep are reduced in older people. These data have important implications for understanding age-related insomnia.     

Sleep and EEG spectra in the Syrian hamster (Mesocricetus auratus) under baseline conditions and following sleep deprivation

Summary Sleep was studied by continuous 24-h recordings in adult male Syrian hamsters, chronically implanted with EEG and EMG electrodes. Three vigilance states were determined using visual scoring and EEG power spectra (0.25–25 Hz) computed for 4-s episodes.The effects of two methods of total sleep deprivation (SD) were examined on vigilance states and the EEG power spectrum. The animals were subjected to 24 h SD by: (1) forced locomotion in a slowly rotating drum, (2) gentle handling whenever the hamsters attempted a sleeping posture. In addition, the hamsters were subjected to SD by handling during the first 3 h of the L period.Sleep predominated in the L period (78.2% of 12 h) and the D period (51.2%). The power spectra of the 3 vigilance states were similar during the L and D period. In NREM sleep, power density values in the low frequency range (0.25–6.0 Hz) exceeded those of REM sleep and W by a maximum factor of 8.3 and 2.8, respectively. At frequencies above 16 Hz, NREM and REM sleep power density values were significantly lower than during W. A progressive decrease in power density for low EEG frequencies (0.25–7 Hz) during NREM sleep was seen in the course of the L period. Power density values of higher frequencies (8–25 Hz) increased at the end of the L period and remained high during the first hours of the D period.The effect of prolonged SD on vigilance states and EEG spectra was similar by both methods and strikingly small compared to similar results in rats. In contrast, 3 h SD induced a large and more prolonged effect. The similarities and differences of sleep and sleep regulation are summarized for the hamster, rat and man.Abbreviations EEG electroencephalogram - LD light dark - REM rapid eye movements - NREM sleep non REM sleep - W waking - SD sleep deprivation - TST total sleep time - L light - D dark     

Diurnal Variations of Beta-Endorphin at Rest and After Moderate Intensity Exercise

To determine the effect of time of day on circulating beta-endorphin concentrations 14 men exercised at 75% of their maximal capacity at 0600, 1200, 1800 and 2400 hr. Each trial was separated by 3-5 days and preceded by a normal sleep cycle except for the 0600 hr trials which was preceded by 6 hr sleep. Resting physiological data indicated normal diurnal variations in heart rate, core temperature and oxygen uptake, being lowest during the 0600 hr trials and highest during the 1800 hr trials. Resting plasma beta-endorphin concentrations averaged 11.9 +/- 8.4 pmol/l during the 0600 hr trials, significantly greater than the 2400 hr trials (6.4 +/- 3.6 pmol/l; P less than 0.05). No other significant differences existed at rest. Post exercise beta-endorphin concentrations were elevated and found to be inversely related to time of day with the 0600 hr trials having the highest mean (25.7 +/- 14.7) and the 2400 hr trials the lowest (14.7 +/- 8.3). These data suggest that the plasma beta-endorphin concentrations at rest and after exercise are affected by the time of day. The results also suggest that the changes in beta-endorphin associated with exercise are not major contributors to cardiorespiratory control or changes in psychological effect associated with exercise.     

Auditory deprivation modifies biological rhythms in the golden hamster

To assess to what extent auditory sensory deprivation affects biological rhythmicity, sleep/wakefulness cycle and 24 h rhythm in locomotor activity were examined in golden hamsters after bilateral cochlear lesion. An increase in total sleep time as well as a decrease in wakefulness (W) were associated to an augmented number of W episodes, as well as of slow wave sleep (SWS) and paradoxical sleep (PS) episodes in deaf hamsters. The number of episodes of the three behavioural states and the percent duration of W and SWS increased significantly during the light phase of daily photoperiod only. Lower amplitudes of locomotor activity rhythm and a different phase angle as far as light off were found in deaf hamsters kept either under light-dark photoperiod or in constant darkness. Period of locomotor activity remained unchanged after cochlear lesions. The results indicate that auditory deprivation disturbs photic synchronization of rhythms with little effect on the clock timing mechanism itself.     

Circadian and Seasonal Variations of Plasma Insulin and Cortisol Concentrations in the Syrian Hamster, Mesocricetus Auratus

Circadian rhythms of plasma insulin, Cortisol, and glucose concentrations were examined in scotosensitive (reproductively sensitive to inhibitory effects of short daylengths) and scotorefractory male and female Syrian hamsters (Mesocricetus auratus) maintained on short (LD 10:14) and long (LD 14:10) daylengths. The baseline concentration (mean of all values obtained every 4 hr six times of day) of insulin was much greater in female than in male scotosensitive hamsters kept on short daylengths. These differences in insulin concentration may account for the observed heavy fat stores in female and low fat stores in male scotosensitive hamsters kept on short daylengths. The baseline concentrations of Cortisol were approximately equal in both scotosensitive and scotorefractory males held on short and long daylengths, but were relatively low in females held on short daylengths and especially high in scotorefractory females held on long daylengths.

The plasma concentrations of both cortisol and insulin varied throughout the day in many of the groups tested. However, the variations were not equivalent. The circadian variations of cortisol were similar irrespective of sex, seasonal condition and daylength. Peak concentrations generally occurred about 12 hr after light onset. In contrast, the circadian variations of insulin differed markedly. For example in male hamsters, robust daily variations were found in scotosensitive hamsters held on short daylengths but not on long daylengths and in scotorefractory hamsters held on long daylengths but not on short daylengths. Furthermore, the daily peak occurred during the light in the scotosensitive hamsters and during the dark in the scotorefractory animals. Neither the daily feeding pattern (about 60% consumed during dark) nor the daily variations of glucose concentration varied appreciably with seasonal condition or daylength. They do not appear to determine nor directly reflect the variations in cortisol and glucose concentrations. It is postulated that the daily rhythms of cortisol and insulin are regulated by different neural pacemaker systems and that changes in the phase relations of circadian systems account in part for seasonal changes in body fat stores.