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PubMed1993

The role of Na(+)-Ca2+ exchange in paired pulse potentiation of ferret ventricular muscle.

1. Stimulation of cardiac muscle with pairs of stimuli ('paired pulse stimulation') results in a large inotropic effect and experiments have been carried out on ferret ventricular muscle to investigate the underlying mechanism. 2. Aequorin was used to measure sarcoplasmic Ca2+ in papillary muscles. During paired pulse stimulation the first aequorin light transient (i.e. Ca2+ transient) and contraction of the pair increased in amplitude, whereas the second aequorin light transient and contraction were small. When the interval between the pair was decreased, the second aequorin light transient and contraction of the pair were smaller, but the increase in the first aequorin light transient and contraction was greater. 3. The relationship between contraction and the aequorin light transient was the same during paired pulse stimulation and on raising the bathing Ca2+ concentration. It is concluded that there was no change in the myofilament sensitivity to Ca2+ during paired pulse stimulation. 4. The increase in the aequorin light transient and contraction during paired pulse stimulation was prevented by ryanodine, an inhibitor of the sarcoplasmic reticulum (SR). 5. During paired pulse stimulation of ventricular myocytes there was little change in the first action potential of the pair, but the second action potential was shorter than control when the interval between the pair was short. During paired pulse stimulation of ventricular myocytes under voltage clamp control there was little change in the first Ca2+ current (iCa) of the pair, but the second iCa was smaller than control when the interval between the pair was short. Because paired pulse potentiation was greatest when the interval between the pair was short, it is concluded that paired pulse potentiation was not the result of a prolongation of the action potential or increase in iCa. 6. During paired pulse stimulation of ventricular myocytes under voltage clamp control the increase in contraction was greater, the more positive the membrane potential during the second pulse of the pair. This voltage dependence is consistent with a role for the Na(+)-Ca2+ exchanger in paired pulse potentiation. 7. During paired pulse stimulation of ventricular myocytes under voltage clamp control, changes in putative Na(+)-Ca2+ exchange current were observed consistent with a decrease of Ca2+ efflux (or increase of Ca2+ influx) via the exchanger during the second pulse of the pair. 8. A computer model of excitation-contraction coupling (Harrison, McCall & Boyett, 1992) has been used to simulate paired pulse stimulation and the results described above.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed2000

Observer weighting of monaural level information in a pair of tone pulses.

A correlational analysis was used to assess the relative weight given to the levels of two monaurally presented tone pulses for interpulse intervals (IPIs) ranging from 2-256 ms. In three different experimental conditions, listeners were instructed to discriminate the level of the first pulse, the level of the second pulse, or the difference between the levels of the two pulses. The level of the target pulse was chosen randomly and independently from trial to trial from a Gaussian distribution. The level of the nontarget pulse was either fixed at 75 dB SPL or varied in the same manner as the level of the target. In the tasks in which one pulse was to be ignored, listeners gave increasing weight to the nontarget component as IPI decreased. Listeners weighted the level information in the pulses appropriately only when the IPI approached 256 ms. When the listeners were instructed to compare the pulse levels to one another, two of three listeners weighted the levels optimally at all IPIs, while the third listener did so only at the longest IPI. For the two listeners who weighted the pulses optimally, a minimum in performance was achieved at IPIs around 16-32 ms. Intensity discrimination thresholds were also measured for one pulse in the presence of a second fixed pulse for IPIs of 2-256 ms. Thresholds were higher in all the two-pulse conditions relative to a one-pulse condition, and were dependent on the level of the nontarget pulse but not on IPI. The results indicate that level information is integrated to some extent over fairly long durations, but not in a manner that is consistent with simple temporal integration.

Auditory Perception↗
PubMed2003

[Pulse oximetry in perioperative monitoring].

BACKGROUND: Monitoring with pulse oximetry might improve patient outcome by enabling an early diagnosis and consequently, correction of perioperative events that might cause postoperative complications or even death. Only a few randomised clinical trials of pulse oximetry have been performed during anaesthesia and in the recovery room which describe perioperative hypoxaemic events, postoperative cardiopulmonary complications and cognitive dysfunction. OBJECTIVES: To study the effect of perioperative monitoring with pulse oximetry to clearly identify the adverse outcomes that might be prevented or improved by the use of pulse oximetry. SEARCH STRATEGY: Trials were identified by computerised searches of the Cochrane Library, MEDLINE, EMBASE, and by checking the reference lists of trials and review articles. SELECTION CRITERIA: All controlled trials that randomised patients to either pulse oximetry or no pulse oximetry during the perioperative period, including the operating and recovery room. DATA COLLECTION AND ANALYSIS: We collected data in relation to events detectable by pulse oximetry, any serious complications that occurred during anaesthesia or in the postoperative period, intra- or postoperative mortality, and duration of recovery or intensive care stay. Formal statistical synthesis of individual trials was not performed in view of the variety of outcomes studied. MAIN RESULTS: Searching identified six reports; four studies with data from a total of 21,773 patients were considered eligible for analysis. Only two studies specifically addressed the outcomes in question; both found no effect on the rate of postoperative complications using perioperative pulse oximetry. Two studies used hypoxaemia detectable by pulse oximetry to assess the value of perioperative monitoring, although outcomes were not given. It was found that hypoxaemia was reduced in the pulse oximetry group both in the operating theratre and in the recovery room. During observation in the recovery room, the incidence of hypoxaemia in the pulse oximetry group was 1.5-3 times less. The postoperative cognitive function using the Wechsler memory scale and continuous reaction time was independent of perioperative monitoring with pulse oximetry. The other study showed that postoperative complications occurred in 10% of the patients in the oximetry group and in 9.4% in the control group. The two groups did not differ in cardiovascular, respiratory, neurologic, or infectious complications. The duration of hospital stay was a median of 5 days in both groups, and an equal number of in-hospital deaths was registered in the two groups. REVIEWERS' CONCLUSIONS: The studies confirmed that pulse oximetry can detect hypoxaemia and related events. However, we have found no evidence that pulse oximetry affects the outcome of anaesthesia. The conflicting subjective and objective results of the studies, despite an intense, methodical collection of data from a relatively large population, indicate that the value of perioperative monitoring with pulse oximetry is questionable in relation to improved reliable outcomes, effectiveness and efficiency.

Humans↗
PubMed1980

[On the reaction of finger pulse amplitude to noise (author's transl)].

1. Forty-three (30 male and 13 female) subjects were exposed to traffic noise of ca. 72dB. Their reactions concerning blood pressure, pulse pressure, finger pulse amplitude and radialis pulse amplitude, heart rate, breathing rate, and integrated EMG were analyzed. 2. Each of the circulatory parameters exhibited significant reactions in either direction in more than 40% of the subjects. The vasoconstrictive reaction in finger pulse amplitude was most outstanding. Moreover, pulse pressure, radioalis pulse amplitude and, heart rate also tended to decrease whereas diastolic blood pressure tended to increase. Breathing rate and EMG remained mainly unchanged. 3. Owing to the different direction of reactions the mean values of a sample can yield possible misleading information. Furthermore, it is suggested that the reaction of finger pulse amplitude should be related to the standard deviation of the prestimulus resting period instead of to the mean value of this period. 4. Male subjects react with a stronger decrease of heart rate than female subjects. Male subjects with higher diastolic casual blood pressure and heart rate values exhibit stronger decreases in finger pulse amplitude and heart rate. Older male subjects tend to react with an increase of heart rate. 5. Within the male subjects, the reaction of finger pulse amplitude correlated positively with the reactions of pulse pressure and heart rate, but not with the reaction of radialis pulse amplitude. The attempt to distinguish between vasoactive and pressure-dependent components in finger pulse amplitude means of radialis pulse amplitude failed, which is probably a consequence of artifacts in radialis pulse amplitude.

Adult↗
PubMed2004

Basic cardiac life support providers checking the carotid pulse: performance, degree of conviction, and influencing factors.

UNLABELLED: The American Heart Association recently abolished the carotid pulse check during cardiopulmonary resuscitation for lay rescuers, but not for health care providers. OBJECTIVES: The aim of the study was to evaluate health care providers' performance, degree of conviction, and influencing factors in checking the carotid pulse. METHODS: Sixty-four health care providers were asked to check the carotid pulse for 10 or 30 seconds on a computerized mannequin simulating three levels of pulse strength (normal, weak, and absent). Health care providers were asked whether they felt a pulse and how certain were they that they felt a pulse. Performance was evaluated, as well as degree of conviction about the answer, using a visual analog scale. Data were compared by using a general linear model procedure. RESULTS: In the pulseless situations, the answers were correct in 58% and 50% when checking the pulse for 10 and 30 seconds, respectively. In the situation with a weak pulse, the answer was correct in 83% when checking the pulse for 10 seconds. In situations with a normal pulse, the answers were correct in 92%, 84%, and 84%, respectively, when checking the pulse for 10 (twice) and 30 seconds. The exactitude of the answer was correlated with the pulse strength (p < 0.05). The degree of conviction about the answer was correlated with the exactitude of the answer (p < 0.01) and the pulse strength (p < 0.0001). CONCLUSIONS: These results question the routine use of the carotid pulse check during cardiopulmonary resuscitation, including for health care providers.

Adult↗
PubMed1994

Mechanisms of intraocular photodisruption with picosecond and nanosecond laser pulses.

Nd:YAG laser photodisruption with nanosecond (ns) pulses is an established method for intraocular surgery. In order to assess whether an increased precision can be achieved by the use of picosecond (ps) pulses, the plasma size, the shock wave characteristics, and the cavitation bubble expansion after optical breakdown with ps- and ns-laser pulses were investigated by time-resolved photography and acoustic measurements. Nd:YAG laser pulses with a duration of 30 ps and 6 ns, respectively, were focused into a water-filled glass cuvette. Frequency doubled light from the same laser pulses was optically delayed between 2 ns and 136 ns and used as illumination light source for photography. Since the individual events were well reproducible, the shock wave and bubble wall position could be determined as a function of time. From the slope of these r(t) curves, the shock wave and bubble wall velocities were determined, and the shock wave pressure was calculated from the shock velocity. The plasma size at various laser pulse energies was measured from photographs of the plasma radiation. The breakdown thresholds at 30 ps and 6 ns pulse duration were found to be 15 microJ and 200 microJ, respectively. At threshold, ps-plasmas are shorter than ns-plasmas, but at the same pulse energy they are always approximately 2.5 times longer. The initial shock pressures were 17 kbar after ps-pulses with an energy of 50 microJ, and 21 kbar after 1 mJ ns-pulses. The pressure amplitude decayed much faster after the ps-pulses. The maximum expansion velocity of the cavitation bubble was 350 m/s after a 50 microJ ps-pulse, but 1,600 m/s after a 1 mJ ns-pulse. The side effects of intraocular microsurgery associated with shock wave emission and cavitation bubble expansion can be considerably reduced by the use of ps-pulses, and new applications of photodisruption may become possible.

Eye↗
PubMed2006

Reducing contamination while closing the gap: BASSI RF pulses in PASL.

Bandwidth-modulated selective saturation and inversion (BASSI) pulses are a class of frequency- and gradient-modulated radiofrequency (RF) pulses, derived from the hyperbolic secant pulse by temporal variation of the bandwidth parameter. These pulses afford optimal amplitude modulation, achieving uniform and highly selective profiles at any effective flip angle. In this paper, BASSI pulses are parameterized to obtain low RF energy pulsed arterial spin labeling (PASL) label pulses with minimal contamination of static spins outside the label region and highly selective PICORE/QUIPSS II saturation pulses allowing for small label gaps. They are compared to frequency offset corrected inversion (FOCI) label pulses and sinc saturation pulses in simulations and a phantom experiment. Drawing on the outstanding selectivity of bandwidth-modulated saturation pulses, a new noninvasive method to measure in vivo the contamination effects due to direct and indirect saturation of static spins by the label pulse is presented. In an in vivo study on four subjects, contamination effects in a QUIPSS II PASL implementation based on BASSI pulses are compared to those present in a state-of-the-art Q2TIPS sequence employing a FOCI label pulse. Residual contamination in the QUIPSS II/BASSI sequence is shown to be reduced by a factor of 3, compared to the Q2TIPS/FOCI sequence. In vivo human perfusion images obtained with a label gap of only 2 mm are presented.

Adult↗
PubMed2004

Precipitation pulses and carbon fluxes in semiarid and arid ecosystems.

In the arid and semiarid regions of North America, discrete precipitation pulses are important triggers for biological activity. The timing and magnitude of these pulses may differentially affect the activity of plants and microbes, combining to influence the C balance of desert ecosystems. Here, we evaluate how a "pulse" of water influences physiological activity in plants, soils and ecosystems, and how characteristics, such as precipitation pulse size and frequency are important controllers of biological and physical processes in arid land ecosystems. We show that pulse size regulates C balance by determining the temporal duration of activity for different components of the biota. Microbial respiration responds to very small events, but the relationship between pulse size and duration of activity likely saturates at moderate event sizes. Photosynthetic activity of vascular plants generally increases following relatively larger pulses or a series of small pulses. In this case, the duration of physiological activity is an increasing function of pulse size up to events that are infrequent in these hydroclimatological regions. This differential responsiveness of photosynthesis and respiration results in arid ecosystems acting as immediate C sources to the atmosphere following rainfall, with subsequent periods of C accumulation should pulse size be sufficient to initiate vascular plant activity. Using the average pulse size distributions in the North American deserts, a simple modeling exercise shows that net ecosystem exchange of CO2 is sensitive to changes in the event size distribution representative of wet and dry years. An important regulator of the pulse response is initial soil and canopy conditions and the physical structuring of bare soil and beneath canopy patches on the landscape. Initial condition influences responses to pulses of varying magnitude, while bare soil/beneath canopy patches interact to introduce nonlinearity in the relationship between pulse size and soil water response. Building on this conceptual framework and developing a greater understanding of the complexities of these eco-hydrologic systems may enhance our ability to describe the ecology of desert ecosystems and their sensitivity to global change.

Carbon↗
PubMed1988

Prospective evaluation of initially ineffective defibrillation pulses on subsequent defibrillation success during ventricular fibrillation in survivors of cardiac arrest.

The effect of initially ineffective defibrillation pulses on subsequent defibrillation success is not known. Therefore, the voltage, current and energy at the defibrillation threshold were compared with the defibrillation rescue pulse voltage, current and energy that terminated ventricular fibrillation when an ineffective pulse just below the defibrillation threshold had been used initially. This lower amplitude ineffective pulse was termed a "subdefibrillation threshold" pulse. The pulse that restored sinus rhythm after the subdefibrillation threshold pulse was delivered was termed the "subdefibrillation threshold rescue pulse." This comparison was undertaken, intraoperatively, in 14 out-of-hospital cardiac arrest survivors using a sequential-pulse catheter-patch defibrillation system. Each of the 14 patients required higher voltage, current, delivered energy and stored energy for defibrillation with the subdefibrillation threshold rescue pulse than with the defibrillation threshold pulse. The defibrillation threshold voltage was 451 +/- 127 volts compared with a subdefibrillation threshold rescue voltage of 585 +/- 147 volts (p less than 0.00002). The defibrillation threshold current was 5.5 +/- 2.4 amps compared with a subdefibrillation threshold rescue current of 7.2 +/- 2.7 amps (p less than 0.00001). Delivered and stored energies were 10.9 +/- 7.4 and 12.3 +/- 7.2J, respectively, for the defibrillation threshold pulse and were 17.6 +/- 9.4 J (p less than 0.00002) and 20.5 +/- 9.3 J (p less than 0.00005), respectively, for the subdefibrillation threshold rescue pulse. It is concluded that the risk of requiring considerably higher energies than anticipated for defibrillation must be incurred, should defibrillation fail because of an initially insufficient defibrillation pulse.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Stimulus parameters affecting paired-pulse depression of dentate granule cell field potentials. I. Stimulus intensity.

Paired pulse stimulation of the perforant path provides a measure of inhibition of dentate granule cell field potentials that is reflected in the depression of the second (test) population spike (PS) relative to the first (conditioning) PS. The assumption that the strength of paired pulse depression is dependent upon the amplitude of the conditioning PS was investigated by increasing the stimulus intensity of both pulses (5-100% of maximum, Experiment 1), or by increasing the stimulus intensity of the conditioning pulse (5-100%) while maintaining a constant stimulus intensity of the test pulse (50%, Experiment 2). In both experiments, the threshold for early paired pulse depression (20 ms interpulse interval, IPI) was reached with moderate stimulation (30-40% of maximum). Above threshold, the test PS was depressed to a relatively constant amplitude in Experiment 1, in contrast to a nearly linear decrease observed in Experiment 2 with increasing strength of early paired pulse, relative to the conditioning reflects the lower stimulus intensity of the test pulse, relative to the conditioning pulse, in the second study, thereby allowing the increasing strength of early paired pulse depression to be detected more easily. The threshold for late paired pulse depression was reached near (20%, Experiment 1) or below (5%, Experiment 2) the PS threshold of dentate granule cells, and a paradoxical decrease in late paired pulse depression was detected with maximal stimulation in both studies. Together, these results suggest that early paired pulse depression exhibits a strong dependence upon the amplitude of the conditioning PS, whereas late paired pulse depression is marginally affected by the conditioning PS amplitude and is influenced by additional processes at both extremes of the stimulus intensity continuum.

Action Potentials↗
PubMed1998

Temporal relationships between oxytocin and 13,14-dihydro-15-keto-prostaglandin F2 alpha pulses in ovariectomized ewes.

The primary objective was to evaluate the role of non-ovarian oxytocin in the initiation of pulses of PGF2 alpha, as measured by peripheral concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM). A 2 x 2 factorial arrangement of estradiol and progesterone treatments was administered to groups of five ewes after ovariectomy on Day 12. Progesterone (10 mg) was administered at 0700 and 1900 hr on Day 12, and then either progesterone or its vehicle was administered on Days 13 and 14. Silastic implants, either empty or containing estradiol, was administered at ovariectomy. Oxytocin and PGFM were measured in jugular blood samples withdrawn from an indwelling catheter at 5-min intervals for 8 hr on Day 15. Statistically significant pulses of oxytocin, presumably of posterior pituitary origin, were detected in all ewes. Approximately one-half of the oxytocin pulses preceded a pulse in PGFM concentrations by 10 min or less. These pulses tended (P = 0.09) to have a longer duration than those not linked to pulses of PGFM. The number of PGFM pulses that followed or did not follow an oxytocin pulse by 10 min or less was similar (P > 0.2). The amplitude and duration of oxytocin-linked PGFM pulses were greater (P = 0.05) than non-linked pulses. Although several explanations for the lower than anticipated temporal relationship between oxytocin and PGFM pulses are possible, the finding that oxytocin-related PGFM pulses are distinguishable from other pulses is consistent with the concept that oxytocin initiates robust pulses in PGF2 alpha secretion.

Animals↗
PubMed2001

Non-invasive assessment of local arterial pulse pressure: comparison of applanation tonometry and echo-tracking.

OBJECTIVES: Pulse pressure is not constant throughout the arterial tree. Use of pulse pressure at one arterial site as surrogate for pulse pressure at another arterial site may be erroneous. The present study compares three non-invasive techniques to measure local pulse pressure: (i) internally calibrated readings from applanation tonometry, (ii) alternative calibration of pressure waves obtained with applanation tonometry and (iii) alternative calibration of arterial distension waves obtained with echo-tracking. Alternative calibration assumes mean and diastolic blood pressure constant throughout the large artery tree. DESIGN AND METHODS: Study 1 used invasive measurements in the ascending aorta as a reference method and internally calibrated tonometer readings and alternatively calibrated pressure waves at the common carotid artery as test methods. Study 2 used alternatively calibrated pressure waves as a reference method and alternatively calibrated distension waves and internally calibrated applanation tonometer readings as test methods. RESULTS: In study 1, pulse pressure from internally calibrated tonometer readings was 10.2+/-14.3 mmHg lower and pulse pressure from alternatively calibrated pressure waves was 1.8+/-5.2 mmHg higher than invasive pulse pressure. Pulse pressure from calibrated distension waves was 3.4+/-6.9 mmHg lower than pulse pressure from alternatively calibrated pressure waves. According to British Hypertension Society criteria, pulse pressure from the internally calibrated tonometer achieved grade D and pulse pressure from alternatively calibrated pressure waves achieved grade A. Pulse pressure from calibrated distension waves achieved grade B when alternatively calibrated pressure waves were used as a reference method. CONCLUSIONS: Pulse pressure obtained from alternatively calibrated tonometer-derived pressure waves and echo-tracking-derived distension waves demonstrates good accuracy. Accuracy of pulse pressure from internally calibrated applanation tonometer readings at the carotid artery is poor.

Adult↗
PubMed2002

Slow excitation supports propagation of slow pulses in networks of excitatory and inhibitory populations.

We study the propagation of traveling solitary pulses in one-dimensional networks of excitatory and inhibitory neurons. Each neuron is represented by the integrate-and-fire model, and is allowed to fire only one spike. Two types of propagating pulses are observed. During fast pulses, inhibitory neurons fire a short time before or after the excitatory neurons. During slow pulses, inhibitory cells fire well before neighboring excitatory cells, and potentials of excitatory cells become negative and then positive before they fire. There is a bistable parameter regime in which both fast and slow pulses can propagate. Fast pulses can propagate at low levels of inhibition, are affected by fast excitation but are almost unaffected by slow excitation, and are easily elicited by stimulating groups of neurons. In contrast, slow pulses can propagate at intermediate levels of inhibition, and are difficult to evoke. They can propagate without slow excitation, but slow excitation makes their propagation substantially more robust. Fast pulses can propagate in a wider parameter regime if inhibition decays slowly with time, whereas slow pulses can propagate in a wider parameter regime if the passive time constant of inhibitory cells is large. Strong inhibitory-to-inhibitory conductance eliminates the slow pulses and converts the fast traveling pulses into irregular pulses, in which the inhibitory neurons segregate into two groups that have different firing delays with respect to their neighboring excitatory cells. In general, the velocity of the fast pulse increases with the axonal conductance velocity c, but there are cases in which it decreases with c. We suggest that the fast and slow pulses observed in our model correspond to the fast and slow propagating activity observed in experiments on neocortical slices.

Biophysical Phenomena↗
PubMed1988

Internal cardiac defibrillation: single and sequential pulses and a variety of lead orientations.

A sequential pulse system for internal cardiac defibrillation incorporating catheter and patch electrodes with two current pathways has been shown to reduce defibrillation threshold in comparison to the single pulse technique. The relative advantage of the sequential pulse over the single pulse technique with other lead systems is not known. We compared defibrillation thresholds using sequential and single pulses delivered to a variety of lead orientations with the same electrode surface areas, when possible. Defibrillation threshold totals determined in halothane-anesthetized open-chest pigs averaged: For the single pulse shock passed between (1) superior vena cava (SVC) and left ventricular apical patch (LVA), 27.2 +/- 9.1 joules (J) and (2) LV epicardial patch (LVE) to right ventricular epicardial (RVE) patch leads, 16.5 +/- 2.1 J; and for the sequential pulse shock with two pulses passed between: (1) the SVC to RV intracavitary apex (RVA) and a quadripolar catheter in the coronary sinus to the RVA, 11.6 +/- 1.0 J; (2) the SVC to LVA and the LVE to RVE, 9.6 +/- 1.3 J and (3) the SVC to RVA and the LVE to RVA, 8.9 +/- 0.4 J. Defibrillation thresholds for sequential pulse shocks were all significantly lower than either of the defibrillation thresholds for single pulse shocks (p less than 0.001). We conclude that the sequential pulse system provides a substantial reduction in defibrillation threshold over the single pulse regardless of the lead system when the surface area and pulse characteristics are controlled. Sequential pulse technique may be valuable in the design of an implantable automatic defibrillator.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Resetting of the hamster circadian system by dark pulses.

Circadian rhythms of animals are reset by exposure to light as well as dark; however, although the parameters of photic entrainment are well characterized, the phase-shifting actions of dark pulses are poorly understood. Here, we determined the tonic and phasic effects of short (0.25 h), moderate (3 h), and long (6-9 h) duration dark pulses on the wheel-running rhythms of hamsters in constant light. Moderate- and long-duration dark pulses phase dependently reset behavioral rhythms, and the magnitude of these phase shifts increased as a function of the duration of the dark pulse. In contrast, the 0.25-h dark pulses failed to evoke consistent effects at any circadian phase tested. Interestingly, moderate- and long-dark pulses elevated locomotor activity (wheel-running) on the day of treatment. This induced wheel-running was highly correlated with phase shift magnitude when the pulse was given during the subjective day. This, together with the finding that animals pulsed during the subjective day are behaviorally active throughout the pulse, suggests that both locomotor activity and behavioral activation play an important role in the phase-resetting actions of dark pulses. We also found that the robustness of the wheel-running rhythm was weakened, and the amount of wheel-running decreased on the days after exposure to dark pulses; these effects were dependent on pulse duration. In summary, similarly to light, the resetting actions of dark pulses are dependent on both circadian phase and stimulus duration. However, dark pulses appear more complex stimuli, with both photic and nonphotic resetting properties.

Adaptation, Physiological↗
PubMed2000

Effects of light intensity and restraint on dark-pulse-induced circadian phase shifting during subjective night in Syrian hamsters.

Dark pulses presented on a background of constant light (LL) result in phase advances during midsubjective day and early subjective night, and phase delays during late subjective night, as shown in the dark-pulse phase response curve. In hamsters, the phase-shifting effects of dark pulses are thought to be mediated by increased activity, as previous studies have shown that restraining animals during dark pulses blocks the phase shifts observed in midsubjective day and late subjective night. This study focuses on dark-pulse-induced phase shifting during early subjective night, examining the influence of both LL intensity and restraint on the magnitude of these phase shifts. Syrian hamsters were maintained in LL of four different illumination levels (1, 10, 100, or 600 lux) and periodically presented with 6-h pulses (dark pulse alone, restraint alone, or dark pulse plus restraint) beginning at circadian time 11. Phase advances were observed in response to dark pulses alone, and the magnitude of these shifts was dependent on background illumination, with significantly larger advances seen under higher intensities. No relationship was found between the amount of activity displayed during dark pulses and phase shift magnitude. Six-hour periods of restraint resulted in phase delays, the magnitude of which was also dependent on background illumination. Restraining hamsters during dark pulses reduced the magnitude of phase advances, but the extent of this reduction could be predicted from the additive effects of the dark-pulse-alone and restraint-alone conditions. These results indicate that the phase-shifting effects of dark pulses during early subjective night are not mediated by behavioral activation and may instead reflect a mirror image of the phase-delaying effects of light pulses at this phase.

Animals↗
PubMed1992

Effect of gonadotropin-releasing hormone pulse frequency on gonadotropin secretion and subunit messenger ribonucleic acids in perifused pituitary cells.

Slow frequency GnRH pulses have been proposed to preferentially increase circulating FSH levels by increasing FSH synthesis and pulsatile release. Examination of this proposal using various in vivo models, however, has produced conflicting results. To examine directly the effects of GnRH pulse frequency on the pituitary, we compared the effects of 2.5-nM GnRH pulses administered every 1 h or every 4 h vs. no GnRH, using perifused rat pituitary cells. FSH secretion (total area under the response curve) was 2-fold greater (P less than 0.01) with every hour than with every 4 h GnRH pulses. This difference resulted from the increased number of GnRH pulses and increased (P less than 0.05) interpulse FSH secretion, whereas FSH pulse amplitude was unchanged. FSH beta mRNA levels at the completion of the 11-h perifusion were increased 4.5-fold by GnRH every h (P less than 0.01) and 3.3-fold by GnRH every 4 h (P less than 0.05) above levels in untreated cells. FSH beta mRNA levels were greater (P less than 0.05) at the faster GnRH pulse frequency. Because more frequent stimulation delivered more GnRH during the study, cells were next stimulated with 2.5 nM GnRH every 1 h for nine pulses, 7.5 nM GnRH every 4 h for three pulses to equalize the GnRH dose, or 2.5 nM GnRH every 4 h for three pulses. Interpulse FSH secretion and FSH beta mRNA levels were again greater (P less than 0.05) with every hour than every 4 h GnRH pulses. Interpulse LH secretion, FSH and LH pulse amplitude, and LH beta and alpha-subunit mRNA levels were not different between the groups. GnRH doses of 0.1-10 nM every hour increased FSH and LH pulsatile secretion dose-dependently, but FSH beta, LH beta, and alpha-subunit mRNA levels were similar. In conclusion, our data reveal that reducing the frequency of GnRH pulses from every hour to every 4 h reduces both FSH beta mRNA levels and FSH interpulse secretion, but does not change GnRH-stimulated FSH pulsatile release. We suggest that the finding by others that slow frequency GnRH pulses increase circulating FSH levels under certain experimental conditions in vivo may instead be explained by complex hormonal interactions or changes in FSH clearance.

Animals↗
PubMed1997

Differential effects of gonadotropin-releasing hormone (GnRH) pulse frequency on gonadotropin subunit and GnRH receptor messenger ribonucleic acid levels in vitro.

The hypothalamic hormone, GnRH, is released and transported to the anterior pituitary in a pulsatile manner, where it binds to specific high-affinity receptors and regulates gonadotropin biosynthesis and secretion. The frequency of GnRH pulses changes under various physiological conditions, and varying GnRH pulse frequencies have been shown to regulate differentially the secretion of LH and FSH and the expression of the gonadotropin alpha, LH beta, and FSH beta subunit genes in vivo. We demonstrate differential effects of varying GnRH pulse frequency in vitro in superfused primary monolayer cultures of rat pituitary cells. Cells were treated with 10 nM GnRH pulses for 24 h at a frequency of every 0.5, 1, 2, or 4 h. alpha, LH beta, and FSH beta messenger RNA (mRNA) levels were increased by GnRH at all pulse frequencies alpha and LH beta mRNA levels and LH secretion were stimulated to the greatest extent at a GnRH pulse frequency of every 30 min, whereas FSH beta mRNA levels and FSH secretion were stimulated maximally at a lower GnRH pulse frequency, every 2 h. GnRH receptor (GnRHR) mRNA levels also were increased by GnRH at all pulse frequencies and were stimulated maximally at a GnRH pulse frequency of every 30 min. Similar results were obtained when the dose of each pulse of GnRH was adjusted to maintain a constant total cumulative dose of GnRH over 24 h. These data show that gonadotropin subunit gene expression is regulated differentially by varying GnRH pulse frequencies in vitro, suggesting that the differential effects of varying GnRH pulse frequencies on gonadotropin subunit gene expression occur directly at the level of the pituitary. The pattern of regulation of GnRHR mRNA levels correlated with that of alpha and LH beta but was different from that of FSH beta. This suggests that alpha and LH beta mRNA levels are maximally stimulated when GnRHR levels are relatively high, whereas FSH beta mRNA levels are maximally stimulated at lower levels of GnRHR expression, and that the mechanism for differential regulation of the gonadotropins by varying pulse frequencies of GnRH may involve levels of GnRHR. Furthermore, these data suggest that the mechanisms whereby varying GnRH pulse frequencies stimulate alpha LH beta, and GnRHR gene expression are similar, whereas the stimulation of FSH beta mRNA levels may be different.

Animals↗