Pulses of cholinergic receptor escape from atropine blocking reflect major natural periodicities

1. Semi-lunar variation in cardiac response to applied acetylcholine was reconfirmed. 2. Atropine completely blocked the effects of acetylcholine on the heart except for brief pulses of escape at 12-hr intervals which began at moonset and progressed through midday at 10 to 14-day intervals. 3. The direction of escape, i.e. inhibition or acceleration, reversed at the winter solstice and at both equinoxes. 4. Cholinergic receptors in the cardiac preparation seem to reflect the following: 12-hr intervals beginning at moonset, 24.8 hr. 10 to 14-day intervals, 14.8-day intervals and the equinoxes and solstices. 90-day intervals.     

Circadian rhythm resetting in sparrows: early response to doublet light pulses

Circadian responses were studied using the perching activity of house sparrows (Passer domesticus). The sparrows were subjected to single or double 4-hr light pulses (the single pulses or the second pulses of the doublets scanned 24 hr) in the first cycle after previous entrainment to a light-dark cycle (LD 12:12). The differences in times at which the birds commenced perch-hopping in LD 12:12 before the pulses and in the five cycles immediately following the pulses were determined (phase shifts). A 24-hr time profile for phase shifts in response to single light pulses replicated our previous study: Early-night pulses delayed the rhythm (-1.7 hr), while late-night pulses advanced the rhythm (+3.8 hr). After pretreatment with a light pulse that advanced the birds +2.7 hr, the resetting curve was advanced. There were no delays; the range of average shifts was +0.1 hr to +6.2 hr. After pretreatment with a light pulse that delayed the birds -1.7 hr, the resetting curve was delayed. Average delays as much as -1.1 hr and advances up to +2.1 hr were measured. The data for double pulses were interpreted from predictions made from single-pulse data.     

Diurnal Phototropism in Solar Tracking Leaves of Lavatera cretica

On a clear day, leaf laminas of Lavatera cretica tracked the solar position throughout the day. The laminar azimuth did not diverge from the solar azimuth by more than 12° from sunrise to sunset. Tracking of the solar elevation started 1 to 2 hours after sunrise and ceased 1 to 2 hours before sunset. On an overcast day, the laminas reoriented horizontally. After sunset, following a clear day, the laminas performed a nocturnal reorientation, with three well defined phases. During the initial phase the laminas relaxed their strained sunset-facing orientation to one perpendicular to their petioles. This equilibrium configuration was maintained throughout the following phase, which was apparently concerned with time-measuring. During the final phase, the laminas reoriented, before sunrise, to a position facing the direction of the anticipated sunrise. This directional information is phototropic and was retained for 3 to 4 diurnal cycles, probably in the pulvinus itself, which is the site of the response. Laminas of plants transferred from sunlight either to darkness, or to a simulated natural photoperiod under overhead illumination, were facing the originally anticipated direction of sunrise at the time of each of the three to four subsequent sunrises (after which they reverted to the dark orientation in darkness, or to the horizontal one with overhead illumination). Cotyledonary laminas required directional information for the nocturnal reorientation during 3 or 4 cycles of simulated sunrise to sunset transitions.     

Pulses of prolactin before, during, and after luteolysis and synchrony with pulses of a metabolite of prostaglandin F2α in heifers

Pulses of prolactin (PRL) and a metabolite of prostaglandin F2α (PGFM) were determined from hourly blood samples collected before, during, and after luteolysis (n=7 heifers). Progesterone concentrations were used to partition the results into six 12-h sets from 12h before to 36h after luteolysis. Pulses of PRL with a nadir-to-nadir interval of 4.4±0.2h were detected in each 12-h set. Pulses were rhythmic (P<0.05) in six heifers, beginning 12h before the end of luteolysis. The peak of a PRL pulse was greater (P<0.05) for the 12h after the end of luteolysis than for other 12-h sets, except for the last set of luteolysis. Area under the curve of a pulse was greater (P<0.05) for the 24h that encompassed the end of luteolysis than for two previous 12-h sets. Synchrony between the peaks of PRL and PGFM pulses was greater (P<0.03) during and after luteolysis (same hour for 29/39 pairs) than before luteolysis (0/12). Concentration of PRL centralized to the peak (Hour 0) of PGFM pulses was greater (P<0.05) at Hours 0 and 1 than at Hours -2, -1, and 3. Results supported the hypothesis that PRL is secreted in pulses in heifers. The pulses were most prominent and rhythmic during the last 12h of luteolysis and thereafter. The pulse peaks of PRL and PGFM were synchronized for most PRL pulses during and after luteolysis.     

Emergence behaviour of rabbits, Oryctolagus cuniculus, in Central Otago, New Zealand

The characteristic emergence behaviour of a rabbit population in Central Otago, New Zealand, involves a steady rise in the number of rabbits active throughout the afternoon to a peak near sunset. This differs from populations in Great Britain and Australia, where emergence occurs later and is more rapid. Young rabbits emerged slightly later than adults and were more susceptible to disturbances. Slightly earlier emergence by male rabbits, particularly between May and September, was possibly related to the increased levels of territoriality and social interaction just before and during the early stages of the breeding season. Three emergence indices (25% of the population feeding, 50% of the population emerged, and maximum number of rabbits emerged) were significantly correlated with season. Rabbits emerged earliest before sunset in winter and spring and latest in autumn. Daily variation in emergence times was considerable and was related to weather factors such as temperature and wind direction. A greater level of diurnal activity in New Zealand rabbit populations than in those in Great Britain and Australia is possibly associated with lower levels of diurnal predation in New Zealand.     

Concentrations of 13, 14-dihydro-15-keto prostaglandin F2 alpha after pulsatile progesterone administration at the time of luteolysis of heifers

Progesterone was administered in pulses to 12 dairy heifers from days 17.5 to 22.5 post-estrus in order to determine its ability to modify secretion of PGF2 alpha around the time of luteolysis. Control heifers exhibited pulses of PGFM concomitant with a sharp decline in progesterone concentrations and thus these pulses were temporally associated with luteolysis. Additional pulses of PGFM were observed in heifers receiving exogenous progesterone, but these were not statistically predictable by either dose of progesterone (50 or 100 micrograms) or time of administration (3 or 6 hour intervals). However, all heifers (4/4) treated with progesterone at 3 hour intervals had additional pulses of PGFM as compared to only one heifer (1/4) treated at 6 hour intervals. When pulses of PGFM were induced by exogenous progesterone there was a substantial lag time between the initiation of progesterone treatment and their occurrence. The limited response to progesterone administration and the lack of synchrony is not consistent with an ability of exogenous progesterone to directly stimulate secretion of PGF2 alpha at the time of luteolysis.     

农田作物层温度初步研究—以冬小麦、夏玉米为例

观测表明,充分供水的麦田作物层温度在一昼夜的大部分时间内,低于作物层顶以上1.5米处气温。8—10点叶温有时比气温稍高。叶温与气温差最大值出现在日落后至露出现前一段时间内,晴日无风天气大约出现在日落后一小时。白昼,夏玉米作物层温度高于气温,冬小麦作物层温度低于气温。夜间,小麦和玉米叶温都比气温低。土壤水分不足,蒸腾速率减小,叶温升高,叶温与气温差增大。叶温的变化反映了作物自身的水分状况。     

Locomotor activity of atlantic salmon parr (Salmo salar L.) in various light conditions and in weak magnetic fields

Locomotor activity studies in the laboratory under artificial light cycles co-ordinated with times of sunrise and sunset demonstrated that ten of sixteen Atlantic salmon parr were nocturnal, with an approximately twenty-four hour periodicity. The remaining six fish exhibited diurnal activity patterns or activity mainly after times of light change. Two fish immediately shifted their activity patterns to co-ordinate with a 6-hr shifted light cycle. Six fish retained no activity patterns in constant light, and only two of eleven fish had weak activity patterns in constant darkness. Results suggest that Atlantic salmon parr are dependent on a light-dark cycle for timing their activity rhythms. Three of twelve salmon in an imposed magnetic field four times the strength of the horizontal vector of the ambient field, increased their activity level and changed activity patterns in the increased field. The remaining fish showed no distinct change in locomotor activity.     

Effect of altering suckling intervals of early-weaned pigs on rebreeding performance of sows

Sows on two commerical farms were assigned to have their pigs weaned after a 3-week lactation (control, n=160) or after a 3-week lactation that included a 48-hr period of interrupted nursing before weaning (altered-suckling, n=122). Sows in the altered-suckling groups were paired, and each member of a pair was separated from both litters during the alternate 12-hr periods. Thus during the final 48 hr before weaning, each sow in the altered-suckling group had two 12-hr periods when no litters were present and two 12-hr periods when two litters were present. On farm 1, interval from weaning to estrus was 12.8 +/- 0.8 days for control sows compared to 8.4 +/- 1.0 days for sows in the altered-suckling group (P<.01). On farm 2, interval from weaning to estrus did not differ between sows in the control group and those in the altered-suckling group (6.2 vs 6.1 days, P>.05). Thus altered-suckling was effective in reducing the interval from weaning to estrus only when the normal rebreeding interval was prolonged (farm 1). Conception rates at first breeding and subsequent litter sizes did not differ between treatments. Altered-suckling may improve reproductive performance of sows in situations where prolonged postweaning anestrus is a problem.     

Integration of environmental stimuli in the migratory orientation of the savannah sparrow (Passerculus sandwichensis)

Two ‘cue-conflict’ experiments were designed to evaluate the role of (1) solar cues at sunset and stars, and (2) solar cues at sunset and geomagnetic stimuli, in the migratory orientation of the savannah sparrow (Passerculus sandwichensis). A sunset and stars experiment exposed birds in the experimental group to a mirror-reflected sunset followed by an unmanipulated view of stars. Experimental birds shifted their migratory activity in accordance with the setting sun despite exposure to a normal night sky. The sunset and geomagnetism experiment exposed birds in the experimental group to a simultaneous shift in both the position of sunset and the earth's magnetic field. Again experimentals shifted their activity in accordance with the setting sun rather than the artificially shifted magnetic field. Savannah sparrows probaly use stars as celestial landmarks to maintain a preferred direction and do not reorient their activity when exposed to an alternative cue once a direction is established. Moreover, savannah sparrows with experience of migration do not require geomagnetic information in order to use the solar cues available at sunset to select a migratory direction.     

Sunset and the orientation of European robins (Erithacus rubecula)

The migratory orientation of European robins (Erithacus rubecula) in autumn was tested immediately after sunset and also after the beginning of astronomical darkness. In twilight tests under clear skies, the birds selected an appropriate migratory direction. During the course of autumn, along with the shift of sunset azimuth, the orientation of birds also shifted, always in a counter-clockwise direction. Although this shift of orientation was not statistically significant, the difference between the mean direction and the sunset was the same for each autumn period. This suggests that the migratory direction was selected on the basis of menotactic orientation re the setting sun. Random directions were observed under solid overcast skies as well as during tests under starry skies, begun after all trace of the sunset position had disappeared.     

LH secretion around the time of the preovulatory gonadotrophin surge in the ewe

Blood samples were taken once an hour from 17 ewes starting on Day 15 of a natural oestrous cycle and continuing for 4 days or until 36 h after the onset of oestrus. On Days 12, 16, 17 and 18 of the cycle, blood samples were also taken every 5 min for 6 h, between 09:00 and 15:00 h. LH pulse frequency rose and amplitude fell between the luteal and follicular phase of the oestrous cycle ( ). In the period from 48 h before to 40 h past the peak of the preovulatory LH surge, LH pulse frequency did not change. LH pulse amplitude was similar prior to and following the LH surge. During the preovulatory LH surge, LH pulse amplitude rose markedly ( ), with the visible, discrete components of pulses ranging from twice to 20 times those seen prior to or following the surge. The amplitude of LH pulses on the downslope of the LH surge was greater than that on the upslope of the surge (P < 0.05). We conclude that the preovulatory LH surge may consist of an amalgamation of high frequency, high amplitude pulses of LH secretion.     

Effects of duration, concentration, and timing of ionomycin and 6-dimethylaminopurine (6-DMAP) treatment on activation of goat oocytes

The protocol of ionomycin followed by 6-dimethylaminopurine (6-DMAP) is commonly used for activation of oocytes and reconstituted embryos. Since numerous abnormalities and impaired development were observed when oocytes were activated with 6-DMAP, this protocol needs optimization. Effects of concentration and treatment duration of both drugs on activation and development of goat oocytes were examined in this study. The best oocyte activation (87-95%), assessed by pronuclear formation, was obtained when oocytes matured in vitro for 27 hr were treated with 0.625-20 microM ionomycin for 1 min before 6-hr incubation in 2 mM 6-DMAP. Progressional reduction of time for 6-DMAP-exposure showed that the duration of 6-DMAP treatment can be reduced to 1 hr from the second up to the fourth hour after ionomycin, to produce activation rates greater than 85%. Activation rates of oocytes in vitro matured for 27, 30, and 33 hr were higher (P < 0.05) than that of oocytes matured for 24 hr when treated with ionomycin plus 1-hr (the third hour) 6-DMAP, but a 4-hr incubation in 6-DMAP enhanced activation of the 24-hr oocytes. Goat activated oocytes began pronuclear formation at 3 hr and completed it by 5-hr post ionomycin. An extended incubation in 6-DMAP (a) impaired the development of goat parthenotes, (b) quickened both the release from metaphase arrest and the pronuclear formation, and (c) inhibited the chromosome movement at anaphase II (A-II) and telophase II (T-II), leading to the formation of one pronucleus without extrusion of PB2. In conclusion, duration, concentration, and timing of ionomycin and 6-DMAP treatment had marked effects on goat oocyte activation, and to obtain better activation and development, goat oocytes matured in vitro for 27 hr should be activated by 1 min exposure to 2.5 microM ionomycin followed by 2 mM 6-DMAP treatment for the third hour.     

Acoustic behaviour of Abudefduf luridus

Adult males Abudefduf luridus produced sounds during aggressive interactions, although not all aggressive interactions were associated with sounds. Such sounds were always related to characteristic swimming movements during an aggressive display or territorial defence. The sound was a combination of several sonic pulses, with most energy concentrated towards the low end of the spectrum (from <50 to 800 Hz), and was most frequently groups of two pulses. Analysis of the pulse structure suggested that these sounds are produced by muscles acting on the swimbladder. However, the mechanism of sound production has yet to be demonstrated. Sounds were emitted throughout the 24-h period with increased activity at sunrise and sunset.     

Effects of self-generated wind on compensational recovery of escape direction in unilaterally cercus-ablated crickets, Gryllus bimaculatus

The effects of self-generated wind on the compensational recovery of escape direction were investigated in unilaterally cercus-ablated crickets, Gryllus bimaculatus. To separate walking and self-generated wind during walking, unilaterally cercus-ablated crickets were placed on a styrofoam ball that was easily rotated by leg motion during walking. The stationary walking on the ball did not produce self-generated wind, because no body motion occurred. Crickets that were trained on the ball but given no artificial air puff for 14 days after cercal ablation did not show any compensational recovery of escape direction. Therefore, spontaneous walking itself was not sufficient to compensate the wind-evoked escape direction in the crickets. Artificial air puffs from the anterior direction synchronized with the stationary walking were effective for the compensational recovery of escape direction, but those from the posterior direction were not. As most of the spontaneous walking was directed to the forward direction, only an artificial air puff from the anterior direction coincided well with actual self-generated wind occurring during the onset of normal walking. Therefore, self-generated wind during walking seems essential for the compensational recovery of escape direction in unilaterally cercus-ablated crickets. When artificial air puffs were unsynchronized with walking, no compensational recovery was observed. This result suggests that artificial air puffs should be given just after the onset of spontaneous walking. Otherwise, the artificial air puffs may not be recognized as self-generated wind.     

The Paramecium circadian behavioral rhythm: light phase response curves and entrainment

The population of a ciliate protozoan, Paramecium multimicronucleatum, exhibits a circadian rhythm as measured by the number of the cells traversing an observation point ("traverse frequency," or TF). The present study examined phase shifting of the TF rhythm by administering 2-hr light pulses at different phases of the circadian cycle to cultures free-running in constant darkness (DD). The results were summarized in a phase response curve (PRC), categorized as Type 1. This PRC indicated a relatively narrow phase zone insensitive to the light pulse ("dead zone"). Entrainment of the rhythm to light pulses repeated at 24-hr intervals was also examined, and it was found that the rhythm gradually reached a steady state, following several transient cycles, with the pulses falling at a phase corresponding to the narrow dead zone. Such a steady-state rhythm, with a minimum at approximately 3 hr after the pulse and a maximum at approximately 12 hr after the pulse, was mathematically simulated by superimposing a response function to the pulse on a sinusoidal function representative of the free-running rhythm in DD.     

Luteinizing hormone secretion in hypophysial stalk-transected pigs given progesterone and pulsatile gonadotropin-releasing hormone

This study was conducted to determine whether progesterone inhibits luteinizing hormone (LH) secretion in female pigs by a direct action on the pituitary gland. Eight ovariectomized, hypophysial stalk-transected gilts were given 1-microgram pulses of gonadotropin-releasing hormone iv every 45 min from Day 0 to 12. On Days 5-12, each of four gilts received either progesterone or oil vehicle im at 12-hr intervals. Serum progesterone concentrations in steroid-treated gilts reached 70 +/- 6.8 ng/ml (mean +/- SE) by Day 8 and remained elevated thereafter, whereas serum progesterone concentrations in oil-treated controls were less than 1 ng/ml for the entire study. Daily serum LH concentrations were not different between gilts treated with progesterone or oil. The 1-microgram pulses of gonadotropin-releasing hormone reliably evoked pulses of LH in both treatment groups. The LH pulse frequency and amplitude, assessed from samples collected every 15 min for 6 hr on Day 12, were similar for progesterone- and oil-treated gilts. These results provide evidence that progesterone does not act at the pituitary gland to alter LH secretion in pigs.     

Endocrine alterations that underlie endotoxin-induced disruption of the follicular phase in ewes

Two experiments were conducted to investigate endocrine mechanisms by which the immune/inflammatory stimulus endotoxin disrupts the follicular phase of the estrous cycle of the ewe. In both studies, endotoxin was infused i.v. (300 ng/kg per hour) for 26 h beginning 12 h after withdrawal of progesterone to initiate the follicular phase. Experiment 1 sought to pinpoint which endocrine step or steps in the preovulatory sequence are compromised by endotoxin. In sham-infused controls, estradiol rose progressively from the time of progesterone withdrawal until the LH/FSH surges and estrous behavior, which began approximately 48 h after progesterone withdrawal. Endotoxin interrupted the preovulatory estradiol rise and delayed or blocked the LH/FSH surges and estrus. Experiment 2 tested the hypothesis that endotoxin suppresses the high-frequency LH pulses necessary to stimulate the preovulatory estradiol rise. All 6 controls exhibited high-frequency LH pulses typically associated with the preovulatory estradiol rise. As in the first experiment, endotoxin interrupted the estradiol rise and delayed or blocked the LH/FSH surges and estrus. LH pulse patterns, however, differed among the six endotoxin-treated ewes. Three showed markedly disrupted LH pulses compared to those of controls. The three remaining experimental ewes expressed LH pulses similar to those of controls; yet the estradiol rise and preovulatory LH surge were still disrupted. Our results demonstrate that endotoxin invariably interrupts the preovulatory estradiol rise and delays or blocks the subsequent LH and FSH surges in the ewe. Mechanistically, endotoxin can interfere with the preovulatory sequence of endocrine events via suppression of LH pulsatility, although other processes such as ovarian responsiveness to gonadotropin stimulation appear to be disrupted as well.     

Transforming growth factor beta (TGF-beta) inhibits hepatocyte DNA synthesis independently of EGF binding and EGF receptor autophosphorylation

Subpicomolar concentrations of human platelet-derived transforming growth factor beta (TGF-beta) inhibited growth factor-stimulated DNA synthesis in primary cultures of adult rat hepatocytes. This inhibition was not the result of changes in the size of intracellular pools of 3H-thymidine and was not dependent on the state of confluence of the cells. A 24-hr exposure to TGF-beta either before or after insulin/EGF stimulation was as inhibitory on DNA synthesis between 48 and 72 hr of culture as was TGF-beta present throughout 72 hr of culture. From 12 hr in culture to 24 hr, hepatocyte EGF binding sites dropped from about 230,000 to 85,000 per cell with no significant change in Kd, but with a loss in capacity for EGF-induced receptor down-regulation. Maximally inhibitory concentrations of TGF-beta did not compete with EGF for the EGF receptor, and a 4- to 24-hr exposure to TGF-beta did not alter subsequent EGF binding. Coincubation of hepatocytes with TGF-beta and EGF did not influence the 60% reduction in EGF binding sites produced by EGF alone. In addition, TGF-beta did not prevent EGF-induced autophosphorylation of the 170,000 dalton EGF receptor in membranes from whole liver. Our studies suggest that TGF-beta regulates hepatocyte growth independently of changes in EGF receptor number, ligand affinity, or postbinding autophosphorylation.     

Insect photoperiodism: diversity of results in night-break experiments, including nonresponsiveness to light

Three night-break experiment protocols were utilized in an attempt to help clarify the role of the circadian system in photoperiodic time measurement in the European corn borer, Ostrinia nubilalis. Larvae raised in a light-dark (LD) cycle consisting of 12 hr of light alternating with 12 hr of darkness (LD 12:12), at a constant temperature of 30 degrees C, enter a state of arrested growth and development known as diapause (Takeda and Skopik, 1985). In the present research (Experiment 1), the induction of diapause was prevented by 1-hr light pulses that systematically scanned the dark phase of LD 12:12. Thus, the importance of 12 hr of uninterrupted darkness for maximal induction of diapause is stressed. The same experimental protocol applied to larvae already in diapause (Experiment 2), however, resulted in a bimodal curve of diapause termination. Although this result is consistent with the proposition that a nonperiodic hourglass timer underlies this event (Skopik and Takeda, 1986), it does not rule out the circadian system. Like LD 12:12, a thermoperiod in constant darkness (12 hr at 4 degrees C alternating with 12 hr at 25 degrees C) also induces diapause. Scanning such a thermoperiod with 1-hr light pulses, however, resulted in only a small effect (reduction of diapause) when light fell in the early to middle part of the warm phase (Experiment 3). Thus, the time-measuring system, under these experimental conditions, showed only a weak response to light. This unexpected result is discussed with respect to Experiment 1 and two general models that have been proposed to account for photoperiodic time measurement in insects.