Diurnal patterns of scent-marking, serum testosterone concentration and heart rate in male Mongolian gerbils

The diurnal rhythms of scent marking behavior in an open-field test as well as the diurnal rhythms of serum testosterone concentration and heart rate under home cage conditions were investigated in male Mongolian gerbils. The behavioral measures of scent marking activity, sniffing frequency and locomotor activity in the open field showed a clear rhythm during the 24 hour period with a significant maximum during the dark. In contrast to this, the mean testosterone concentration was lower during the dark as compared to the light phase. The heart rate was not different during light and dark phase of the diurnal cycle, instead, bursts of increased frequency occurred approximately once per hour, both during light and dark phase.     

Nyctohemeral differences in response to restraint stress in CD-1 and C57BL/6 mice

Restraint represents psychological and physical stress. Methods used to model restraint stress in mice vary in duration, time of day during which restraint is applied, and the strain of mouse tested. The goals of this study were: (1) to identify the optimal daily time periods during which the stress response is maximized, and (2) to describe mouse strain differences, if any, in response to restraint. Groups of outbred CD-1 and inbred C57BL/6 mice were restrained for 3 h during three time points of the daily light-dark cycle: (1) the late light phase, (2) the transition between the light phase and the dark phase, and (3) the mid-dark phase. Additional mice served as control groups for food deprivation or were unhandled except for blood sampling. Mice of both strains lost significant body mass after 3 days of restraint. Unrestrained food-deprived mice lost body mass, particularly if food-deprived during transition periods. Corticosterone was elevated in restrained mice compared with control mice. Neither basal nor postrestraint corticosterone differed between strains. Corticosterone was elevated by food deprivation during transitional periods in CD-1 mice and during both transition and dark phases in C57 mice. Corticosterone response in restrained CD-1 mice was increased during the dark phase. These results suggest that the physiological response to restraint is similar in both strains. However, corticosterone responses to both restraint and food deprivation were highest during the transitional and dark phases.     

Circadian rhythms of blood pressure and heart rate in conscious rats: effects of light cycle shift and timed feeding

The aim of the present study was to evaluate the impact of a shift in the light cycle and of restricted food availability on circadian rhythms of blood pressure, heart rate, and behavioral activity in freely moving rats by radiotelemetry. In rats that were fed ad lib, a shift of the light cycle by 6 h (from lights on 0700-1900 h to lights on 1300 to 0100 h) induced an immediate, but from then on gradual, shift of the circadian rhythms of blood pressure, heart rate, and behavioral activity, which took 4-5 days to fully synchronize with the new light cycle. Rats on a normal light cycle receiving feeding for 1 h only during the light period rather than ad lib feeding, showed a suppressed circadian rhythm, with the dark period values reduced to values not significantly different from those observed in the light period. In addition, during the timed feeding blood pressure, heart rate, and behavioral activity peaked to levels that were normally seen during the dark period. These data show that environmental factors such as timed feeding or changes in the light cycle have a marked influence on the circadian rhythms of blood pressure and heart rate.     

Strain differences in sleep patterns of healthy and influenza-infected inbred mice

Influenza-infected C57BL/6J and BALB/cByJ mice respectively develop increased slow-wave sleep (SWS) during the dark phase and reduced SWS during the light phase of the 24 hour circadian cycle. To determine whether similar or alternative variations in SWS develop after influenza infection in other inbred strains of mice, we characterized the sleep patterns of additional strains both before and after influenza infection. Three strains (A/J, BALB/cByJ, and C3H/HeJ) showed light-phase SWS suppression, two strains (C57BL/6J and DBA/2J) showed dark-phase SWS enhancement, and one strain (A/J) showed dark-phase SWS suppression. Three strains (AKR/J, C57BR/cdJ, and FVB/NJ) did not show significant changes in SWS time on day two post-inoculation. Core temperatures were correlated to change in SWS time after infection, but were not correlated to SWS during the baseline period. These data support and expand the existing literature that indicates genetic modulation of sleep both in healthy mice and in mice undergoing viral infection.     

Patterns of maternal behavior in the spontaneously hypertensive rat

Maternal behavior of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats was assessed over the preweanling period (days 1-21). Ten litters of each strain were observed during the dark phase of the light:dark cycle using a scan sampling technique. Cages were observed periodically throughout the day and the momentary behavior of the dam was recorded on a checklist of 9 different behaviors. These behaviors included: nursing entire litter, nursing part of litter, contact with entire litter, contact with part of litter, pup carrying/retrieval, licking pups, sniffing pups, nest building, and away from litter. A second set of ten litters per strain was observed in the same manner during the light phase of the light:dark cycle thus providing around the clock data throughout the entire preweanling period. For purposes of data analysis, the 21-day preweanling period was divided into 7 3-day blocks. The mean relative frequency with which each behavior was observed from SHR and WKY mothers was determined for each block and for each phase of the light:dark cycle separately. SHR mothers were with their pups and nursing them more frequently than WKY mothers during the light phase of the circadian cycle. Complimentary to this finding, WKY mothers were observed away from their pups more frequently than SHR mothers during both light and dark phases. Finally, SHR mothers were observed to lick their pups more often than WKY mothers during both phases of the light:dark cycle. These findings were consistent across the entire preweanling period.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of reproductive state on circadian periodicity in the rat

The circadian activity rhythms of adult female rats maintained under a light-dark cycle of 14 hr light, 10 hr dark (LD 14:10) or constant dim illumination (dim LL) were recorded during their 4 or 5 day estrous activity cycles and when they were pseudopregnant. In LD 14:10 both the phase angle difference (ψ), which defines the temporal relationship between the onsets of activity and darkness, and the period (τ) of locomotor activity differed significantly among the days of the 4 and 5 day estrous cycle. Activity-time (α) varied reliably only over the days of the 5 day estrous cycle. The period of the free-running activity rhythm in dim LL also differed significantly among the days of the estrous cycle. In both LD and dim LL the most positive ψ, shortest τ and longest α were observed on the day of estrus. Pseudopregnancy diminished the amplitude and altered the daily pattern of the estrous activity rhythm. We conclude that the periodicity of circadian activity systematically varies as a function of the stage of the estrous cycle and in a manner that cannot be solely explained by corresponding alterations in endogenous estrogen.     

Circadian rhythms of activity and drinking in mice lacking angiotensin II 1A receptors.

Angiotensin II (ANG II) type 1 receptors are found in the mouse suprachiasmatic nucleus (SCN), the site of the circadian pacemaker, but their significance for circadian timekeeping is unknown. We examined circadian rhythms of wheel running and drinking in angiotensin AT(1a) receptor knockout (KO) mice. Mean daily running and drinking activity were elevated in KO mice under a light-dark (LD) cycle and in constant dark (DD). These increases were confined to the usual active (dark) period, thus, the 'amplitude' of running and drinking rhythms was higher in KO mice. The phase of entrainment to LD (measured by the onset of the daily active period) did not differ between groups, either in LD or on the first day of DD ('unmasked' phase). KO mice showed a modestly shorter free-running period (tau) in DD. The direction and magnitude of phase shifts to light pulses at two circadian times (CTs) in DD did not differ between groups. Core functions of the circadian system appear intact following AT(1a) receptor KO. The modestly shorter tau and increased rhythm amplitude in KO mice may be secondary to an effect of the mutation on the level of running and drinking activity.     

Circadian rhythms in ingestive behavior and responsiveness to glucoprivic and osmotic challenges in rats with rostral zona incerta lesions

Albino rats with lesions in the rostral zona incerta (ZI) displayed an exaggerated diurnal rhythm of ingestive behavior, consuming nearly all of their daily food and water during the dark portion of a 12-hr light/12-hr dark cycle. When tested during the light phase of the cycle, rats with ZI lesions ate little or nothing in response to 2-deoxy-D-glucose (2DG) while their response to insulin was only slightly impaired. When these tests were repeated during the dark phase of the cycle, the response to insulin was entirely normal but the response to 2DG was even more depressed than during daytime testing. During the light phase of the cycle, rats with ZI lesions also drank little or nothing in response to hypertonic saline. This impairment was ameliorated in some but not all experimental rats when these tests were repeated in the dark. A correlational analysis failed to establish a significant relation between changes in the diurnal distribution of ad lib food and water intake and feeding responses to 2DG or insulin or drinking responses to hypertonic saline in the light or dark phases of the cycle.     

不同光照制对雄性小鼠生殖影响的研究

目的 探讨不同光照制对雄性小鼠生殖的影响。方法 取昆明种雄性小鼠作短期持续光照、持续黑暗、反相光照3种光照制处理。观察小鼠睾丸、附睾重量及光镜下睾丸、附睾组织学变化、精子数量、精子活动度、精子畸形率。结果 各组小鼠睾丸、附睾重量无显著性差异,而且各实验组光镜下睾丸、附睾组织学均未见异常。与对照组相比,黑暗小鼠和反相光照组小鼠精子数量明显降低,此外,反相光照组小鼠精子畸形率显著增加。结论 异常光照周期可能影响雄性小鼠生殖能力。     

Polymorphonuclear leukocyte activation induces cerebral hypoperfusion in rats in the absence of previous ischemia-reperfusion damage

Lighting cycles can influence the expression of daily activity rhythms in two ways: by entraining the circadian pacemaker that normally drives this rhythm, and by directly affecting the expression of activity itself, thereby 'masking' the influence of the pacemaker. We describe a California mouse (Peromyscus californicus) in which these processes are dissociated. Circadian rhythms of wheel-running activity were recorded continuously while the animal was housed in a standard light/dark cycle and in constant darkness. This animal expressed a normal circadian rhythm that failed to entrain to the light/dark cycle, but was completely masked during the light phase. This animal's phenotype appears to have a genetic basis, since the progeny of selective crosses of his descendants showed similar abnormalities. These mice are the first example of animals expressing apparently normal circadian rhythms that are not entrained by light, but that still show potent masking responses to light exposure.     

Control of wheel running by near-ultraviolet light

Wheel running by mice was compared during incandescent and incandescent plus near-ultraviolet (UV) illumination in three experiments. During the daily 12-hour light period, running rates decreased with supplemental UV compared to previous incandescent only baselines. The decrements were systematically replicated in a second experiment using alternating UV exposure and recovery phases programmed across blocks of sessions. Again, running rates consistently decreased with supplemental UV irradiation of phases two and four compared to preceeding baselines of phases one and three. In comparison, running rates were inconsistently affected during the 12-hour dark period in both experiments. A third experiment compared the relative decremental effects of UV, blue and red illumination. Baseline running rates monotonically decreased as an inverse function of wavelength for all subjects. The data suggest that the spectral composition of ambient illumination may affect behavior.     

Rabbit antibodies to the cell wall polysaccharide of Streptococcus pneumoniae fail to protect mice from lethal challenge with encapsulated pneumococci.

A conjugate, composed of the cell wall polysaccharide (C polysaccharide) of Streptococcus pneumoniae and bovine serum albumin (BSA), was prepared with the bifunctional agent N-succinimidyl-3-(2-pyridyldithio)-propionate. Analysis with monoclonal antibodies provided evidence that the phosphocholine (PC) moiety of the C polysaccharide was retained during the conjugation procedure. The C polysaccharide-BSA conjugate elicited antibodies to C polysaccharide in rabbits; no PC-specific antibodies were detected in globulins prepared from these hyperimmune sera obtained early and late after a second immunization. Rabbit hyperimmune sera were taken after multiple intravenous injections of the pneumococcus strain SRC-2, which has a capsulelike structure composed of the C polysaccharide. Globulin prepared from these antisera had both C polysaccharide- and PC-specific antibodies. Antibodies to C polysaccharide elicited by the C polysaccharide-BSA conjugate failed to protect mice against intraperitoneal challenge with a strain of type 3 or type 6A pneumococci. The anti-SRC-2 globulin conferred protection against both of these pneumococcal strains. Absorption of the SRC-2 globulin with C polysaccharide, however, failed to change its protective activity. These data provide evidence that antibodies to the C polysaccharide do not confer immunity against infection of mice with encapsulated pneumococci inoculated by the intraperitoneal route.     

Light inhibits the release of both [Met5]enkephalin and [Met5]enkephalin-containing peptides in chicken retina, but not their syntheses

The levels of native and cryptic [Met5]enkephalin in the chicken retina were found to vary during a 12:12 h light-dark cycle, both rising in the light and falling during the dark. Such variations could conceivably arise from (a) changes in the rate of release and subsequent degradation of native and/or cryptic [Met5]enkephalin, (b) changes in the rate of proenkephalin A synthesis, or (c) changes in the rate of proenkephalin A processing. Measurement of the rate of release of native and cryptic [Met5]enkephalin in vitro indicated that the increased rate of release of both of these forms of [Met5]enkephalin during the dark quantitatively accounted for the fall in their retinal levels during the dark. This indicated that the biosynthesis of proenkephalin A was not activated during the light-dark cycle. Molecular weight fractionation of retinal extracts also supported this idea, since the pool of high molecular weight precursors did not vary in size, suggesting that processing was not modulated during the light-dark cycle. Instead, the fall in both cryptic and native [Met5]enkephalin during the dark was due to their increased rate of release together with a rate-limiting conversion of high molecular weight [Met5]enkephalin-containing peptides to low molecular weight [Met5]enkephalin-containing peptides. The enkephalinergic cells of the retina seem to cope with physiological variations in demand by accumulating a large pool of peptide during periods of low stimulation (light), so that when stimulation and release is high (dark), the decrease in pool levels does not compromise the function of the cells and their postsynaptic targets.     

Aging and cellular defense mechanisms: age-related changes in resistance of mice to Listeria monocytogenes.

Age-related changes in resistance of mice to infection with Listeria monocytogenes were investigated. One-month-old mice exhibited the least resistance, and the resistance level increased over the first few months to reach a maximum by 8 months. Increase in age thereafter was accompanied by a slow but progressive decrease in resistance. Thus, 50% lethal doses for 1-, 8-, and 24-month-old mice were 10(4.2), 10(6.6), and 10(5.2), respectively. In spite of differences in resistance, the growth of Listeria in the organs of mice of different age groups was identical during the first 48 h of infection, regardless of the size of the inoculum. Moreover, both young (3- to 8-month-old) and old (22-month-old or older) mice inoculated with a small dose of Listeria were equally capable of inactivating the bacterial load in their spleens and livers within 8 to 10 days of infection. However, a difference in bacterial growth after day 2 of infection was observed when different age groups of mice were inoculated with a large dose of Listeria. These results suggest that the decreased capacity of aged mice to resist infection with Listeria is not due to deficiency in the innate mechanisms of antibacterial resistance, but instead is due to age-related decline in the capacity to acquire immunologically specific antibacterial immunity.     

A Quantitative Genetic Analysis of Slow-Wave Sleep in Influenza-Infected CXB Recombinant Inbred Mice

Influenza-infected C57BL/6J mice spend increased amounts of time in slow-wave sleep (SWS) during the dark phase of the circadian cycle compared to healthy mice. In contrast, infected BALB/cByJ mice show a normal or reduced time in SWS, particularly during the light phase. To identify genetic loci with linkage to these traits, we measured sleep in 13 CXB recombinant inbred (RI) strains derived from a cross between C57BL/6ByJ and BALB/cByJ mice. The probability density distribution of sleep patterns of influenza-infected CXB RI mice showed modes that correspond roughly with the parental modes during the dark phase of the circadian cycle and are intermediate or C57BL/6-like during the light phase. These patterns are consistent with the presence of a low number of major effect quantitative trait loci (QTLs). Chromosomal regions with provisional association to strain variation in influenza-induced SWS patterns were identified. In particular, a 10- to 12-cM interval on Chr 6 between D6Mit74 and D6Mit188 contains a QTL (LRS = 16.6 at 1 cM proximal to D6Mit316; genomewide p<.05) that influences the SWS response to influenza infection during the light phase. We have provisionally named this QTL Srilp1 (sleep response to influenza, light phase 1). Candidate genes for mediation of this phenotype include Ghrhr (growth hormone releasing hormone receptor), Crhr2 (corticotropin releasing hormone receptor 2), and Cd8a (an epitope on cytotoxic T lymphocytes). Several other intervals achieved suggestive probability scores that are sufficient to warrant further analysis either with additional RI strains or with F₂ panels. The analysis also suggests that dark phase and light phase responses are regulated by different genetic factors.     

A novel quantitative trait locus on mouse chromosome 18, "era1," modifies the entrainment of circadian rhythms

STUDY OBJECTIVE: The mammalian circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus conveys 24-h rhythmicity to sleep-wake cycles, locomotor activity, and other behavioral and physiological processes. The timing of rhythms relative to the light/dark (LD12:12) cycle is influenced in part by the endogenous circadian period and the time of day specific sensitivity of the clock to light. We now describe a novel circadian rhythm phenotype, and a locus influencing that phenotype, in a segregating population of mice. METHODS: By crossbreeding 2 genetically distinct nocturnal strains of mice (Cast/Ei and C57BL/6J) and backcrossing the resulting progeny to Cast/Ei, we have produced a novel circadian phenotype, called early runner mice. RESULTS: Early runner mice entrain to a light/dark cycle at an advanced phase, up to 9 hours before dark onset. This phenotype is not significantly correlated with circadian period in constant darkness and is not associated with disruption of molecular circadian rhythms in the SCN, as assessed by analysis of period gene expression. We have identified a genomic region that regulates this phenotype-a major quantitative trait locus on chromosome 18 (near D18Mit184) that we have named era1 for Early Runner Activity locus one. Phase delays caused by light exposure early in the subjective night were of smaller magnitude in backcross offspring that were homozygous Cast/Ei at D18Mit184 than in those that were heterozygous at this locus. CONCLUSION: Genetic variability in the circadian response to light may, in part, explain the variance in phase angle of entrainment in this segregating mouse population.     

Activity rhythms and photoperiodism of Syrian hamsters in a simulated burrow system

Male Syrian hamsters were housed in simulated burrows in order to investigate (a) how these nocturnal, fossorial rodents entrain to the prevailing light:dark cycle in this semi-natural habitat and (b) the response of the reproductive system to environmental illumination. The burrow emergence activity of hamsters housed in simulated burrows was compared to the running wheel activity of animals maintained in standard cage conditions. The activity rhythm was similar in both measuring devices. The data suggested that in a natural environment hamsters are only exposed to light for short amounts of time each day. To determine whether brief photoperiodic stimulation could alter the phase angle of entrainment and/or the reproductive condition, burrow housed animals were exposed to a supplemental 30-second light pulse during specified clock hours of the dark period on a daily basis. These light pulses induced a phase shift and maintained a long day reproductive response in what was otherwise a short photoperiod.     

A pneumolysin-negative mutant of Streptococcus pneumoniae causes chronic bacteremia rather than acute sepsis in mice.

Pneumolysin is a cytoplasmic virulence factor of Streptococcus pneumoniae that can interfere with phagocyte function in vitro. We have examined the effects of pneumolysin in vitro and in vivo and have found that it protects intravenously injected pneumococci against infection-induced host resistance. We employed a virulent capsular type 2 pneumococcal strain, D39, and its isogenic pneumolysin-negative mutant, PLN. Strain D39 exhibited exponential net growth in mice (doubling time, 1.4 h); 24 to 28 h after infection with 10(4) CFU, the numbers of pneumococci reached 10(9) to 10(10) CFU/ml and the mice died. Strain PLN yielded identical net growth in mice until reaching 10(6) to 10(7) CFU/ml at 12 to 18 h postinfection. At this time, the increase in the level of PLN CFU per milliliter ceased and remained constant for several days. PLN exhibited wild-type growth kinetics in mice when coinfected simultaneously with strain D39. This observation suggests that pneumolysin exerts its effects at a distance. By 12 to 18 h postinfection with PLN, mice exhibited the following evidence of an induced inflammatory response: (i) elevated plasma interleukin-6, (ii) a halt in the net growth of PLN, and (iii) control of the net growth of pneumolysin-producing D39 pneumococci upon subsequent challenge. Our data suggest that pneumolysin plays a critical role in sepsis during the first few hours after infection by enabling pneumococci to cause acute sepsis rather than a chronic bacteremia. However, once chronic bacteremia was established, it appeared that pneumolysin was no longer able to act as a virulence factor.     

Comparative role of complement in pneumococcal and staphylococcal pneumonia.

To evaluate the role of complement in pneumococcal and staphylococcal pneumonia, we decomplemented rats with cobra venom factor and inoculated them intratracheally with Staphylococcus aureus or type 25 pneumococci. S. aureus produced a patchy bronchopneumonia in normal Sprague-Dawley or Lewis rats, and decomplementation did not increase the severity of staphylococcal infection in either rat strain as judged by quantitative cultures of the lungs and blood at 6, 24, and 48 h after inoculation. In contrast, decomplementation markedly increased the severity of pneumonia caused by type 25 pneumococci in Sprague-Dawley and Lewis rats. In Sprague-Dawley rats, decomplementation significantly increased the number of bacteria in the lungs at 3, 6, and 24 h of infection. Bacteremia developed early in decomplemented Sprague-Dawley rats, but the higher pulmonary bacterial counts did not appear to be caused by bacteremic seeding of the lungs. Decomplemented Sprague-Dawley rats inoculated intravenously with pneumococci failed to develop the very high levels of bacteria in the lungs that were observed when the rats were inoculated intratracheally. Moreover, decomplemented Lewis rats inoculated intratracheally with pneumococci developed significantly increased numbers of pneumococci in the lungs early in infection (3 and 6 h) when they had no detectable bacteremia. These data indicate that in murine models complement plays a major protective role against type 25 pneumococci in the lung, whereas complement is not important to host defense in staphylococcal pneumonia.     

Impaired behavioral suppression by light in metabotropic glutamate receptor subtype 6-deficient mice

The metabotropic glutamate receptor subtype 6 is localized on the dendrites of ON bipolar cells in mammalian retina, and is responsible for synaptic transmission from photoreceptors to ON bipolar cells. We have previously provided electrophysiological evidence that metabotropic glutmate receptor subtype 6-deficient mice have an impairment in the ON visual pathway. In this study, we compared, between metabotropic glutamate receptor subtype 6-deficient (n=9) and wild-type mice (n=7), their daily wheel-running activity in constant dark and light-dark cycle environments. There was no difference in their free-running rhythmicity in a constant dark environment nor in their ability to entrain their active/rest phase to the phase-shifted light-dark cycle environment, indicating that the circadian system in mutant mice was functioning normally. However, the wheel-running activity was suppressed immediately after light onset of the light-dark cycle in wild-type mice (suppressive effect), whereas that of mutant mice was prolonged for several hours in spite of light onset (very weak suppressive effect). The suppression of activity in wild-type mice is a "masking effect" of the endogenous circadian rhythm in response to light stimuli.The results indicate that the failure of mutant mice to suppress their activity upon light onset is not due to abnormality in their circadian system, but to their lack of response to light stimuli. This study clearly demonstrates that the dysfunction of the ON visual pathway in metabotropic glutamate receptor subtype 6-deficient mice impairs their behavioral responsiveness to light and yet preserves their circadian system.