Mean Pulse Frequency Research Articles

Sensitivity Analysis on the Parameters of Lithium-Ion Battery DC Pulse Preheating under Low Temperature

Lithium-ion batteries (LIBs) require to be preheated under cold weather to restore performance, while DC pulse discharging is often considered a promising approach. Applying a larger pulse current can shorten the heating time, but it may lead to battery decay and demand additional cost. To keep the current lower in preheating, it is necessary to explore the effects of pulse current on the cell temperature rise and make full use of the battery’s heat-generating potential. This paper experimentally compared the effects of DC pulse, average (AVG) current, root mean square (RMS) current, pulse frequency, and state of charge (SOC) of the LIBs on its temperature rise rate, respectively. It is found that within the frequency of 1 kHz~10 kHz, the heat generation is affected by all factors above, among which the frequency has less impact while AVG current has the highest impact. During DC pulse discharging, it is shown that there is more entropy heat produced than the Joule heat in some SOC ranges. Therefore, entropy heat cannot be overlooked in the heat generation model. Moreover, as the thermal coefficient of entropy varies greatly with the SOC, the battery temperature rise rate will be inconsistent during the DC pulse discharging, which might cause an inconsistent warm-up time.

Perceived tactile intensity at a fixed primary afferent spike rate varies with the temporal pattern of spikes.

The perceived intensity of a vibrotactile stimulus is thought to depend on single-neuron firing rates (rate coding) and the number of active afferents (population coding). Unaddressed until now is whether the temporal relation of individual spikes also conveys information about tactile intensity. We used cutaneous electro-tactile stimulation to investigate how the temporal structure of a fixed number of spikes in a 1-s train influenced the perception of intensity. Four mean spike rates spanning the flutter and vibratory hum range (36 Hz, 60 Hz; 120 Hz, 180 Hz) were tested, with spikes grouped into a regular pattern, or bursts of 2-6 spikes spaced 3 ms apart. To link a putative neural code to perception, perceived intensity was assessed in 16 human participants (aged 20-45; 4 females) using the psychophysical paradigm of magnitude estimation. Compound sensory nerve action potentials were recorded to assess any stimulus variation in afferent recruitment. The temporal structuring of a fixed number of spikes into periodic bursts of multiple spikes altered perceived intensity as a function of burst spike count. The largest increase was seen at 36 Hz, where the bursts of six spikes were rated 2.1 times stronger than the regularly spaced spikes [95% confidence interval (CI): 1.9-2.3]. The true increase is likely larger as temporal structuring of spikes into bursts had some negative effect on afferent recruitment. We conclude that the perceived intensity can be modulated by changing temporal features of afferent discharge even when normalized for the number of recruited afferents.NEW & NOTEWORTHY Structuring a fixed number of spikes into temporal burst patterns evoke gradations of perceived intensity with burst spike count, emphasizing the importance of spike timing in primary afferents for shaping perception. This forms the basis for new strategies in communicating a range of intensity information to users of neural interfaces by simply varying the timing of spikes in nonspecific primary afferents using fixed-charge electric pulses, without requiring alterations in stimulation current or mean pulse frequency.

Bifurcations in the Firing of Neuronal Population Caused by a Small Difference in Pulse Parameters During Sustained Stimulations in Rat Hippocampus in Vivo.

The bifurcation of neuronal firing is one of important nonlinear phenomena in the nervous system and is characterized by a significant change in the rate or temporal pattern of neuronal firing on responding to a small disturbance from external inputs. Previous studies have reported firing bifurcations for individual neurons, not for a population of neurons. We hypothesized that the integrated firing of a neuronal population could also show a bifurcation behavior that should be important in certain situations such as deep brain stimulations. The hypothesis was verified by experiments of rat hippocampus in vivo. Stimulation sequences of paired-pulses with two different inter-pulse-intervals (IPIs) or with two different pulse intensities were applied on the alveus of hippocampal CA1 region in anaesthetized rats. The amplitude and area of antidromic population spike (APS) were used as indices to evaluate the differences in the responses of neuronal population to the different pulses in stimulations. During sustained paired-pulse stimulations with a high mean pulse frequency such as ∼130 Hz, a small difference of only a few percent in the two IPIs or in the two intensities was able to generate a sequence of evoked APSs with a substantial bifurcation in their amplitudes and areas. Small differences in the excitatory inputs can cause nonlinearly enlarged differences in the induced firing of neuronal populations. The novel dynamics and bifurcation of neuronal responses to electrical stimulations provide important clues for developing new paradigms to extend neural stimulations to treat more diseases.

Vibrational courtship disruption of Nilaparvata lugens using artificial disruptive signals.

The brown planthopper (BPH), Nilaparvata lugens (Stål; Hemiptera: Delphacidae) is a piercing-sucking pest that causes serious damage to rice plants by sucking the phloem sap from the plants and transmitting viruses. During courtship, the BPH vibrates its abdomen to produce signals that are transmitted to rice plants through its legs. Male BPHs search, locate, and mate with female BPHs after they exchange courtship signals with each other. Currently, spraying chemical pesticides is still the primary method for controlling BPH populations in paddy fields, although this approach has led to severe environmental pollution. A physical control method based on BPH courtship disruption to reduce the mating rate is a promising strategy for cutting environmental pollution. To acquire effective courtship disruptive signals, we developed a vibration signal recording, monitoring, and playback system for BPHs. Using this system, BPH courtship signals and male competition signals were collected and analyzed to obtain their frequency spectra. Results show that the mean main vibration frequency of female courtship signals is 234 Hz and the mean pulse rate is 23 Hz. The mean main vibration and pulse frequencies of the male courtship signals are 255 Hz and 82 Hz, respectively. Besides, the mean main vibration frequency of the male competition signal is 281 Hz. Seven different forms and frequencies of artificial signals were played back to male BPHs, then the courtship and behavioral responses of male BPHs were analyzed. Results indicate that a pure tone of 225 Hz prevents the males from recognizing female courtship signals. The male reply rate fell from 95.6 to 33.3% and the mean reply delay time increased from 5.3 s to 9.1 s. The reply rates of the other six artificial signals ranged from 42.9 to 83.7%, and the mean reply delays were between 5.0 s and 9.3 s. Therefore, the courtship behavior of BPHs can be disrupted by using specific artificial disruptive signals.

Design and application of neural electrical stimulation system with time-varying parameters

Currently, commercial devices for electrical neural stimulations can only provide fixed stimulation paradigms with preset constant parameters, while the development of new stimulation paradigms with time-varying parameters has emerged as one of the important research directions for expanding clinical applications. To facilitate the performance of electrical stimulation paradigms with time-varying parameters in animal experiments, the present study developed a well-integrated stimulation system to output various pulse sequences by designing a LabVIEW software to control a general data acquisition card and an electrical stimulus isolator. The system was able to generate pulse sequences with inter-pulse-intervals (IPI) randomly varying in real time with specific distributions such as uniform distribution, normal distribution, gamma distribution and Poisson distribution. It was also able to generate pulse sequences with arbitrary time-varying IPIs. In addition, the pulse parameters, including pulse amplitude, pulse width, interphase delay of biphasic pulse and duration of pulse sequence, were adjustable. The results of performance tests of the stimulation system showed that the errors of the parameters of pulse sequences output by the system were all less than 1%. By utilizing the stimulation system, pulse sequences with IPI randomly varying in the range of 5~10 ms were generated and applied in rat hippocampal regions for animal experiments. The experimental results showed that, even with a same mean pulse frequency of ~130 Hz, for neuronal populations, the excitatory effect of stimulations with randomly varying IPIs was significantly greater than the effect of stimulations with fixed IPIs. In conclusion, the stimulation system designed here may provide a useful tool for the researches and the development of new paradigms of neural electrical stimulations.

Effects of different input pressure waveforms on the carotid sinus baroreflex-mediated sympathetic arterial pressure response in rats.

Although the pulsatility of an input pressure is an important factor that determines the arterial baroreflex responses, whether the difference in the input waveforms can meaningfully affect the baroreflex function remains unknown. This study aimed to compare baroreflex responses between two distinct pressure waveforms: a forward saw wave (FSW) and a backward saw wave (BSW). In seven anesthetized rats, carotid sinus pressure was exposed to the FSW or the BSW with a mean of 120 mmHg, pulse pressure of 40 mmHg, and pulse frequency of 1 Hz. Changes in efferent sympathetic nerve activity (SNA) and arterial pressure (AP) during six consecutive saw wave trials (FSW1, BSW1, FSW2, BSW2, FSW3, and BSW3) were examined. The steady-state SNA value during FSW1 was 91.1 ± 1.9%, which was unchanged during FSW2 and FSW3 but significantly increased during BSW1 (106.6 ± 3.4%, P < 0.01), BSW2 (110.6 ± 2.5%, P < 0.01), and BSW3 (111.6 ± 2.3%, P < 0.01). The steady-state AP value during FSW1 was 98.2 ± 8.1 mmHg, which was unchanged during FSW2 and FSW3 but significantly increased during BSW1 (106.7 ± 7.4 mmHg, P < 0.01), BSW2 (105.6 ± 7.8 mmHg, P < 0.01), and BSW3 (103.8 ± 7.2 mmHg, P < 0.05). In conclusion, the FSW was more effective than the BSW in reducing mean SNA and AP. The finding could be applied to designing an artificial pulsatile pressure such as that generated by left ventricular assist devices.NEW & NOTEWORTHY This study examined whether the waveforms of an input pressure alone can affect the baroreflex function by using a forward saw wave and a backward saw wave with the same mean pressure, pulse pressure, and pulse frequency. The forward saw wave was more effective than the backward saw wave in reducing sympathetic nerve activity and arterial pressure. The finding could be applied to designing an artificial pulsatile pressure such as that generated by left ventricular assist devices.

Effects of long-acting GnRH antagonist, degarelix acetate, on plasma insulin-like peptide 3, testosterone and luteinizing hormone concentrations, and scrotal circumference in male goats

We recently reported that plasma insulin-like peptide 3 (INSL3) concentrations increased soon after endogenous and exogenous stimulations of LH in male goats and bulls. However, the effects of LH suppression on INSL3 secretion are unknown in domestic animals. Here, we examined the effects of a long-acting GnRH antagonist (degarelix acetate; 4 mg/kg) on the secretions of plasma INSL3 and testosterone in two phases, an immediate and a long-term phase in male goats (n = 6; aged, 13–16 months). During the immediate phase, blood was taken at 15-minute intervals for 8 hours on Days −5, 0, and 3. The GnRH antagonist was administered after 2-hour sampling of Day 0. Moreover, a daily blood sample was taken from Day 0 to Day 7, followed by twice a week until 9 weeks and finally at week 10. The scrotal circumference was recorded before treatment and continued biweekly until week 10. Concentrations of LH, INSL3, and testosterone in plasma were determined by EIA and the pulsatile nature of secretion analyzed using pulse XP software. The mean concentrations, pulse frequency (per hour), and pulse amplitude (peak-nadir) of plasma LH and testosterone reduced from pretreatment to posttreatment Day 0 and Day 3 (P < 0.05). A decline in mean concentrations, pulse frequency, and pulse amplitude of INSL3 was exhibited on posttreatment Day 3 compared with pretreatment (P < 0.01). During long-term sampling, a decline (P < 0.01) in plasma testosterone and INSL3 concentrations was observed 1 day after treatment and remained lower until 8.5 weeks after treatment, and thereafter returned to pretreatment levels. A reduction in scrotal circumference was recorded 4 weeks after treatment and remained lower until 10 weeks after treatment (P < 0.05). In conclusion, the acute regulation of INSL3 by LH was confirmed by reduction of plasma INSL3 levels within 3 days after GnRH antagonist treatment in male goats. Although the onset of suppression of testosterone was more rapid than that of INSL3, the low levels persisted for 8.5 weeks for both hormones, and subsequently the concentrations returned to pretreatment levels. A significant reduction in testicular size was also observed. The quick, long-lasting, and transient suppression of testosterone and INSL3 after a single injection implies a potential application of this antagonist in reversible long-term chemical castration in male goats.

An experimental investigation of pulsed laser-assisted machining of AISI 52100 steel

Abstract Grinding and hard turning are widely used for machining of hardened bearing steel parts. Laser-assisted machining (LAM) has emerged as an efficient alternative to grinding and hard turning for hardened steel parts. In most cases, continuous-wave lasers were used as a heat source to cause localized heating prior to material removal by a cutting tool. In this study, an experimental investigation of pulsed laser-assisted machining of AISI 52100 bearing steel was conducted. The effects of process parameters (i.e., laser mean power, pulse frequency, pulse energy, cutting speed and feed rate) on state variables (i.e., material removal temperature, specific cutting energy, surface roughness, microstructure, tool wear and chip formation) were investigated. At laser mean power of 425 W with frequency of 120 Hz and cutting speed of 70 m/min, the benefit of LAM was shown by 25% decrease in specific cutting energy and 18% improvement in surface roughness, as compared to those of the conventional machining. It was shown that at constant laser power, the increase of laser pulse energy causes the rapid increase in tool wear rate. Pulsed laser allowed efficient control of surface temperature and heat penetration in material removal region. Examination of the machined subsurface microstructure and microhardness profiles showed no change under LAM and conventional machining. Continuous chips with more uniform plastic deformation were produced in LAM.

Gonadotropin-Inhibitory Hormone (GnIH) Secretion into the Ovine Hypophyseal Portal System

GnIH was first identified in avian species, and there is now strong evidence that it is operant in mammals as an inhibitor of reproduction. Mammalian gonadotropin-inhibitory hormone (GnIH)-3 is encoded by the RFRP gene in neurons of the dorsomedial nucleus. These neurons project to the median eminence, predicting a role as a secreted neurohormone and regulation of the pituitary gonadotropes. To determine whether GnIH-3 is a secreted neurohormone, we measured its concentration in hypophyseal portal blood in ewes during the nonbreeding (anestrous) season and during the luteal and follicular phases of the estrous cycle in the breeding season. Paired portal and jugular blood samples were collected and plasma prepared for RIA using an ovine GnIH-3 antibody. Pulsatile GnIH-3 secretion was observed in the portal blood of all animals. Mean GnIH-3 pulse amplitude and pulse frequency was higher during the nonbreeding season. GnIH-3 was virtually undetectable in peripheral blood plasma. There was a lack of association between secretory pulses of GnIH-3 (portal) and LH (peripheral). To determine the role of secreted GnIH-3, we examined its effects on GnRH-stimulated LH secretion in hypothalamo-pituitary-disconnected ewes; a significant reduction in the LH response to GnRH was observed. Finally, to identify cellular targets in the pituitary, the expression of GnIH receptor [G protein-coupled receptor 147 (GPR147)] in fractions enriched for gonadotropes somatotropes, and lactotropes was examined; expression was observed in each cell type. These data show GnIH-3 is secreted into portal blood to act on pituitary gonadotropes, reducing the action of GnRH.

Developmental Increase in Kisspeptin-54 Release in Vivo Is Independent of the Pubertal Increase in Estradiol in Female Rhesus Monkeys (Macaca mulatta)

Kisspeptin (KP) signaling has been proposed as an important regulator in the mechanism of puberty. In this study, to determine the role of KP in puberty, we assessed the in vivo release pattern of KP-54 from the basal hypothalamus/stalk-median eminence in prepubertal and pubertal ovarian-intact female rhesus monkeys. We found that there was a developmental increase in mean KP-54 release, pulse frequency, and pulse amplitude, which is parallel to the developmental changes in GnRH release that we previously reported. Moreover, a nocturnal increase in KP-54 release becomes prominent after the onset of puberty. Because the pubertal increase in GnRH release occurs independent of the pubertal increase in circulating gonadal steroids, we further examined whether ovariectomy (OVX) modifies the release pattern of KP-54. Results show that OVX in pubertal monkeys enhanced mean KP-54 release and pulse amplitude but not pulse frequency, whereas OVX did not alter the release pattern of KP-54 in prepubertal monkeys. Estradiol replacement in OVX pubertal monkeys suppressed mean KP-54 release and pulse amplitude but not pulse frequency. Estradiol replacement in OVX prepubertal monkeys did not alter the KP-54 release pattern. Collectively these results suggest that the pubertal increase in KP release occurs independent of the pubertal increase in circulating estradiol. Nevertheless, the pubertal increase in KP release is not likely responsible for the initiation of the pubertal increase in GnRH release. Rather, after puberty onset, the increase in KP release contributes to further increase GnRH release during the progression of puberty.

Variation of Arterial Blood Pressure in Clinically Healthy and Conscious Cats Measured by Oscillometric Method

The purpose of this study was to assess the variation of arterial blood pressure depending on site of measurement, age, gender and body condition, respectively. The study was carried out on 67 outpatient healthy cats, age between 1 and 14 years, of different breeds. The blood pressure was measured using oscillometric blood pressure monitor, that was previously validated for use in dog and cats. This automatic oscillometric device indirectly measures systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and pulse frequency. For each cat, a cuff width of between 30-40% of the measurement site was chosen and the systemic blood pressure value was calculated as the mean of five readings, with interval of 20 to 30 seconds between consecutive readings. In a subgroup of 46 cats was evaluated the arterial blood pressure measured, for each cat, both at the base of the tail and the thoracic limb.

Magnetic Stimulation and Depression of Mammalian Networks in Primary Neuronal Cell Cultures

For transcranial magnetic stimulation (TMS), the coupling of induced electric fields with neurons in gray matter is not well understood. There is little information on optimal stimulation parameters and on basic cellular mechanisms. For this reason, magnetic stimulation of spontaneously active neuronal networks, grown on microelectrode arrays in culture, was employed as a test environment. This allowed use of smaller coils and the continual monitoring of network action potential (AP) activity before, during, and for long periods after stimulation. Biphasic, rectangular, and 500 micros long pulses were used at mean pulse frequencies (MPFs) ranging from 3 to 100 Hz on both spinal cord (SC) and frontal cortex (FC) cultures. Contrary to stimulation of organized fiber bundles, APs were not elicited directly. Responses were predominantly inhibitory, dose dependent, with onset times between 10 s and several minutes. Spinal networks showed a greater sensitivity to activity suppression. Under pharmacological disinhibition, some excitation was seen at low pulse frequencies. FC cultures showed greater excitatory responses than SC networks. The observed primary inhibitory responses imply interference with synaptic exocytosis mechanisms. With 20,000 pulses at 10 Hz, 40% inhibition was maintained for over 30 min with full recovery, suggesting possible application to nonchemical, noninvasive pain management.

Endocrine responses in mares undergoing abrupt changes in nutritional management

Leptin, a protein hormone secreted by adipocytes, plays an important role in energy homeostasis and regulation of body composition. We previously observed that acute feed restriction resulted in a rapid decline in concentrations of leptin in obese pony mares. This acute response prompted us to characterize the temporal changes in concentrations of leptin, GH, and insulin in obese pony mares during the transition between fed and feed-restricted conditions. Nine obese pony mares of mixed breed, previously maintained on fescue pasture, were randomly allotted to 2 groups. Treatments consisted of a 48-h feed restriction, a 48-h refeeding, and a 24-h feed restriction (RFR; n = 4), or 48 h of alfalfa hay ad libitum, a 48-h feed restriction, and a 24-h refeeding (FRF; n = 5). Blood samples were taken every 15 min during restriction and feeding transitions (0600 to 1400 on d 2 and 4), and every 30 min thereafter until 0830 of the following days (d 3 and 5). In the FRF treatment, plasma concentrations of leptin declined precipitously 6 h after the removal of feed (sample by treatment interaction; P < 0.01), and remained low and unresponsive to refeeding. Similarly, in the RFR group, plasma concentrations of leptin were initially low, and did not respond to feeding during the second (refeeding) sampling period. After feed restriction in each of the 2 treatment sequences, plasma insulin decreased and GH mean concentration, pulse frequency, pulse amplitude, and area under the curve increased (P < 0.05). Refeeding reversed these effects on insulin and GH. These data provide evidence that peripheral concentrations of insulin and GH are dynamically responsive to feed removal (decrease in insulin; increase in GH) and replacement (increase in insulin; decrease in GH), whereas leptin decreases in response to feed restriction but is slow to recover from a transient nutritional insult.

Etomidate Versus Propofol for Electroconvulsive Therapy in Patients With Schizophrenia

Among drugs used for the anesthesia of electroconvulsive therapy (ECT), propofol reduces seizure duration to a greater degree than etomidate. The perceived difference between the 2 anesthetics is smaller in patients with schizophrenia than in patients who suffer depression. In this study, propofol and etomidate were compared during the ECT of patients with schizophrenia, on the basis of their impact on seizure activity and on seizure-induced hemodynamic reactions. Schizophrenics (n = 34) who were treated with ECT participated in this randomized crossover study. Propofol (1 mg/kg) and etomidate (0.2 mg/kg) were used alternately. The 2 drugs were compared on the basis of EEG- and EMG-registered seizure duration, mean arterial pressure (MAP), pulse frequency, energy index, and postictal suppression. We also analyzed the number of necessary restimulations. In case of anesthesia with etomidate, both EEG- (61.29 +/- 22.4 s, 47.9 +/- 21.3 s P = 0.014) and EMG- (46.3 +/- 23.8 s, 33.6 +/- 15.9 s P = 0.006) registered seizure durations were significantly longer than in case of propofol. When using propofol, the increase in MAP was significantly lower than when etomidate was used (8.1 +/- 10.2 mm Hg, 18.3 +/- 11.2 mm Hg, P = 0.001). There were no significant differences found in the postseizure increase in pulse frequency, in postictal suppression, or in the energy index, nor did the numbers of necessary restimulations differ significantly. Propofol was found to reduce seizure duration to a significantly greater extent than etomidate. At the same time, in electrophysiological parameters that show a correlation with clinical efficacy, there was no significant difference found between the 2 anesthetics. However, the seizure-induced increase in MAP was reduced by propofol to a significantly greater degree than by etomidate.

Restoration patterns for luteinising hormone and ovarian function following treatment with GnRH agonist implants (deslorelin) for 7, 14 or 21 days in cycling dairy cows

Continuous GnRH agonist treatment of cows results in downregulation of GnRH responsiveness and a state of induced anoestrus. Inducing anoestrus in a precisely controlled manner could have several potential applications in dairy herd management. However, relatively little is known regarding the processes involved in restoring reproductive normality following an induced anoestrus. This study describes an experiment that was conducted to examine patterns of recovery of LH release and follicle growth in non-lactating Holstein cows immediately following cessation of treatment for 7, 14 or 21 days with a deslorelin implant. Oestrus cycles were synchronized at 7 days intervals and a deslorelin implant inserted in every cow 13 days after detected oestrus so that a group had implants for either 21 days ( n = 9), 14 days ( n = 10) or 7 days ( n = 9). On the day of implant removal every ovarian follicle greater than 4 mm in diameter was ablated using ultrasound guided vacuum needle aspiration in an attempt to standardize follicle sizes. Daily ovarian ultrasound examinations were performed on each cow until 35 days after implant removal and again at 45, 59 and 74 days. A subgroup of four cows randomly selected from each treatment group had frequent serial blood samples collected over 8 h at 4 and 10 days after implant removal for LH profiling. There was no significant effect of treatment duration on any LH parameter and results were pooled. Mean LH pulse amplitude increased by 67% between 4 and 10 days after implant removal (0.34 ng/ml versus 0.57 ng/ml; 4 days versus 10 days post-implant, P < 0.001). Mean pulse frequency remained unchanged between the two samplings (5.9 pulses versus 6.9 pulses per 8 h; 4 days versus 10 days post-implant, P > 0.1). Smoothed mean LH concentrations were unaffected by treatment duration or time (0.36 ng/ml versus 0.41 ng/ml; 4 days versus 10 days post-implant, P > 0.1). The pattern of follicle growth and ovulation did not differ significantly between treatment durations and pooled means were used for comparative descriptions. The emergence of a new follicle wave could be detected beginning at 4 days after implant removal (mean 7.9 ± 0.8 days). After emergence, a period of rapid follicle growth generally ensued with signs of oestrus occurring when the follicle reached 12.3 ± 0.5 mm and ovulation when mean follicle diameter was 13.1 ± 0.7 mm at 13.6 ± 1.5 days after implant removal. Oestrus preceded ovulation in all cases where ovulation subsequently occurred. The mean interovulatory interval after implant removal was similar amongst groups (18.2 ± 1.3 days). Follicle growth could be categorized into three groups based on the time to emergence and fate of the first wave DF. Spontaneous recovery was characterised by ovulation of the newly emerged DF. Failure to ovulate the first DF was associated with the formation of a persistent follicle by 35 days after implant removal with some 25% (7/28) of cows showing persistent follicles. Delayed emergence (>14 days after implant removal) was detected in 11% (3/28) of cows, but when a follicle did eventually emerge it was seen to ovulate normally. The correlation between number of days to first oestrus expression and LH pulse amplitude on 4 days post-implant removal was significant ( R 2 = 44%, P < 0.05). A model was then proposed for the restoration of reproductive function following GnRH agonist removal. In conclusion, duration of deslorelin treatment was associated with only small changes in LH and follicle parameters. The formation of persistent follicles delayed the recovery of more cows than delayed emergence of a new follicle wave after implant removal.

Circadian Gene Expression Regulates Pulsatile Gonadotropin-Releasing Hormone (GnRH) Secretory Patterns in the Hypothalamic GnRH-Secreting GT1-7 Cell Line

Although it has long been established that episodic secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus is required for normal gonadotropin release, the molecular and cellular mechanisms underlying the synchronous release of GnRH are primarily unknown. We used the GT1-7 mouse hypothalamic cell line as a model for GnRH secretion, because these cells release GnRH in a pulsatile pattern similar to that observed in vivo. To explore possible molecular mechanisms governing secretory timing, we investigated the role of the molecular circadian clock in regulation of GnRH secretion. GT1-7 cells express many known core circadian clock genes, and we demonstrate that oscillations of these components can be induced by stimuli such as serum and the adenylyl cyclase activator forskolin, similar to effects observed in fibroblasts. Strikingly, perturbation of circadian clock function in GT1-7 cells by transient expression of the dominant-negative Clock-Delta19 gene disrupts normal ultradian patterns of GnRH secretion, significantly decreasing mean pulse frequency. Additionally, overexpression of the negative limb clock gene mCry1 in GT1-7 cells substantially increases GnRH pulse amplitude without a commensurate change in pulse frequency, demonstrating that an endogenous biological clock is coupled to the mechanism of neurosecretion in these cells and can regulate multiple secretory parameters. Finally, mice harboring a somatic mutation in the Clock gene are subfertile and exhibit a substantial increase in estrous cycle duration as revealed by examination of vaginal cytology. This effect persists in normal light/dark (LD) cycles, suggesting that a suprachiasmatic nucleus-independent endogenous clock in GnRH neurons is required for eliciting normal pulsatile patterns of GnRH secretion.

Ultradian rhythmicity of ghrelin secretion in relation with GH, feeding behavior, and sleep-wake patterns in rats.

Ghrelin, an endogenous ligand for the GHS receptor, stimulates GH secretion and gastrointestinal motility and has orexigenic effects. In this study, the relationships between ghrelin, GH secretion, feeding behavior, and sleep-wake patterns were investigated in adult male rats. The half-life of exogenous ghrelin (10 microg i.v.) in plasma was about 30 min. Repeated administration of ghrelin at 3- to 4-h intervals (one during lights-on and two during lights-off periods) increased GH release and feeding activity, and decreased rapid eye movement sleep duration. Endogenous plasma ghrelin levels exhibited pulsatile variations that were smaller and less regular compared with those of GH. No significant correlation between GH and ghrelin circulating levels was found, although mean interpeak intervals and pulse frequencies were close for the two hormones. In contrast, ghrelin pulse variations were correlated with food intake episodes in the lights off period, and plasma ghrelin concentrations decreased by 26% in the 20 min following the end of the food intake periods. A positive correlation between ghrelin levels and active wake was found during the first 3 h of the dark period only. In conclusion, ghrelin, in addition to affecting GH secretion, gastrointestinal motility, and feeding activity, also modifies sleep-wake patterns. However, a direct action of ghrelin per se or the indirect effects of feeding (and all of its attendant metabolic sequelae) on sleep cannot be differentiated. Moreover, ghrelin secretion is pulsatile and directly related to feeding behavior only.

Dose‐dependent effects of melengestrol acetate (MGA) on plasma levels of estradiol, progesterone and luteinizing hormone in cycling heifers and influences on oestrogen residues in edible tissues

Melengestrol acetat (MGA) is widely used as a growth promoting feed additive in cattle breeding in the USA and several other non‐European countries. To explore the physiological effects of MGA four heifers were fed during 8 weeks with 0.5 mg MGA daily as registered in the USA and two heifers each received 0, 1.5 or 5 mg/day, respectively. Plasma samples were collected twice a week and concentrations of MGA, progesterone (P4) and estradiol‐17β (E2‐17β) were quantified. The pulsatile secretion of luteinizing hormone (LH) was investigated in 6‐hour profiles before and during treatment. After slaughter the reproductive organs were examined and oestrogen residues in edible tissues were measured. Four days after the beginning of MGA feeding MGA concentrations in plasma reached levels of 30 and 100–400 pg/mL depending on the dose received. Three weeks after the beginning of MGA feeding P4 plasma concentrations had dropped to base levels below 0.3 ng/mL in all three treatment groups. Mean plasma E2‐17β levels increased in physiological range from 1 to 5 pg/mL during 0.5 mg MGA/day feeding with many acyclic peaks. Overdosed MGA decreased E2 levels and suppressed cyclic peaks. Number and size of ovarian follicles were not altered by any treatment. Mean LH levels and pulse frequencies increased significantly during labelled treatment (0.5 mg/day), while higher doses had reducing effects. The development of corpus luteum was suppressed. E2‐17β residues in fat increased about 300% following labelled MGA treatment.

Gonadotropin-releasing hormone in third ventricular cerebrospinal fluid of the heifer during the estrous cycle.

The release profile of GnRH in cerebrospinal fluid (CSF) and its correlation with LH in peripheral blood of ovary-intact heifers during the estrous cycle were investigated. A silicon catheter was placed into the third ventricle of six heifers using ultrasonography. During the mid-luteal phase, the heifers were injected with prostaglandin F(2alpha) to induce luteolysis. Surges of CSF GnRH (66.7 h after prostaglandin F(2alpha) administration) and peripheral LH (66.3 h) occurred simultaneously and were coincident with the onset of estrus (67.0 h). Duration of elevated GnRH concentration considerably overlapped with the estrous phase in each of the heifers. Mean pulse frequencies of both GnRH and LH were significantly higher during the proestrous and early luteal phases than during the mid-luteal phase, while mean concentration and pulse amplitude of both GnRH and LH were not different between these three phases. Of all the GnRH pulses identified, more than 80% were accompanied by an LH pulse during the proestrous and early luteal phases. However, the proportion of GnRH pulses that were coincident with an LH pulse during the mid-luteal phase decreased to 60%. The results clearly demonstrate that a dynamic (pulse) and longer-term (surge) changes of GnRH release into CSF are physiologically expressed during the estrous cycle in heifers, and the pattern of pulsatile GnRH secretion in heifers depends upon their estrous cycle.

The role of LH pulse frequency in ACTH-induced ovarian follicular cysts in heifers

The aim of the present study was to induce ovarian cysts experimentally in cattle using ACTH and to closely examine the role of LH pulse frequency in ovarian cyst formation. Five regularly cycling Holstein–Friesian heifers (15–18-month-old) were used. Ovaries were scanned daily using an ultrasound scanner with a 7.5MHz rectal transducer. Daily blood samples were obtained via tail venepuncture for hormone analyses. Additional blood samples (for FSH and LH pulses) were obtained through an indwelling jugular vein catheters every 15min for 8h on Days 2 (early luteal phase; ELP), 12 (mid-luteal phase; MLP) and 19 (follicular phase; FP) of control estrous cycle and on alternate days during follicular cyst (FC) formation and persistence. Cysts were induced using subcutaneous injections of ACTH (Cortrosyn® Z; 1mg) every 12h for 7 days beginning on Day 15 of the subsequent estrous cycle. Plasma concentrations of progesterone (P4), estradiol-17β, FSH and LH were determined by double antibody radioimmunoassay while cortisol concentration was determined by enzyme immunoassay (EIA). Ovarian follicular and endocrine dynamics were normal during the control estrous cycles. Ovarian follicular cysts were induced in four of the five heifers. Mean maximum size of cysts was larger (P<0.05) than that of ovulatory follicles (26.78±3.65 versus 14.1±0.90mm), respectively. Cortisol levels were increased during ACTH treatment. High concentrations of estradiol and low progesterone were observed after cyst formation. LH pulse frequency was significantly reduced (P<0.05) during cyst formation and persistence compared to ELP (7.5±0.75) and FP (6.5±0.58), but was not significantly (P=0.23) different from MLP (2.8±0.29) pulses. Mean LH pulse amplitude and concentrations were not different. Similarly, the mean pulse frequency, amplitude and concentration of FSH were not different between control study and cystic heifers. These results suggest that the LH pulse frequency observed following ACTH treatment may interact with high estradiol concentration to induce ovarian cyst formation in heifers.