Daily Rise Research Articles

Evidence for RGS4 Modulation of Melatonin and Thyrotrophin Signalling Pathways in the Pars Tuberalis

In mammals, the pineal hormone melatonin is secreted nocturnally and acts in the pars tuberalis (PT) of the anterior pituitary to control seasonal neuroendocrine function. Melatonin signals through the type 1 Gi-protein coupled melatonin receptor (MT1), inhibiting adenylate cyclase (AC) activity and thereby reducing intracellular concentrations of the second messenger, cAMP. Because melatonin action ceases by the end of the night, this allows a daily rise in cAMP levels, which plays a key part in the photoperiodic response mechanism in the PT. In addition, melatonin receptor desensitisation and sensitisation of AC by melatonin itself appear to fine-tune this process. Opposing the actions of melatonin, thyroid-stimulating hormone (TSH), produced by PT cells, signals through its cognate Gs-protein coupled receptor (TSH-R), leading to increased cAMP production. This effect may contribute to increased TSH production by the PT during spring and summer, and is of considerable interest because TSH plays a pivotal role in seasonal neuroendocrine function. Because cAMP stands at the crossroads between melatonin and TSH signalling pathways, any protein modulating cAMP production has the potential to impact on photoperiodic readout. In the present study, we show that the regulator of G-protein signalling RGS4 is a melatonin-responsive gene, whose expression in the PT increases some 2.5-fold after melatonin treatment. Correspondingly, RGS4 expression is acutely sensitive to changing day length. In sheep acclimated to short days (SP, 8 h light/day), RGS4 expression increases sharply following dark onset, peaking in the middle of the night before declining to basal levels by dawn. Extending the day length to 16 h (LP) by an acute 8-h delay in lights off causes a corresponding delay in the evening rise of RGS4 expression, and the return to basal levels is delayed some 4 h into the next morning. To test the hypothesis that RGS4 expression modulates interactions between melatonin- and TSH-dependent cAMP signalling pathways, we used transient transfections of MT1, TSH-R and RGS4 in COS7 cells along with a cAMP-response element luciferase reporter (CRE-luc). RGS4 attenuated MT1-mediated inhibition of TSH-stimulated CRE-luc activation. We propose that RGS4 contributes to photoperiodic sensitivity in the morning induction of cAMP-dependent gene expression in the PT.

Short-term changes in zooplankton community in Paso Ancho basin (Strait of Magellan): functional trophic structure and diel vertical migration

Knowledge on community structure oriented to describe energy flow during late summer season in Paso Ancho basin (Strait of Magellan) is scarce and particularly affected by vertical diel migration (VDM). The main aim of this work is to identify the VDM patterns of selected species and functional feeding groups of mesozooplankton, collected by the electronic multinet BIONESS in 1995. Detailed studies were carried out on keystone components of the community: 7 species of copepods (Ctenocalanus citer, Drepanopus forcipatus, Metridia lucens, Clausocalanus brevipes, Scolecithricella minor, Paraeuchaeta antarctica, Calanus simillimus), one ostracod (Discoconchoecia elegans), one chaetognath (Sagitta tasmanica), one euphausiid (Euphausia vallentini), and two polychaetes (Pelagobia longicirrata, Tomopteris planktonis). Unexpected deviations from the classic pattern reported in literature were uncovered. The shallow layer mesozooplankton at night, although dominated by exclusively or preferentially herbivores, particularly by E. vallentini, was not represented by several species known as herbivores that remained in the deep layer throughout the day cycle. The deep-layer zooplankton throughout the day cycle was well represented by carnivores, detritivores, and omnivores. It is suggested that during low-chlorophyll summer conditions, the composition of functional groups and diet, and VDM patterns changed to take advantage of sinking phytoplankton and picoplankton in deep layers. Pelagic-benthic coupling would be strengthened due to animals that suppressed their vertical daily rise to the shallow layer at nights but remained in the deep layers to feed on a rain of particulate organic matter and other non-migrant zooplankton.

Influence of the impounding process of the Three Gorges Reservoir up to water level 172.5 m on water eutrophication in the Xiangxi Bay

The water level of the Three Gorges Reservoir (TGR) rose to 172.5 m in two stages from September to November, 2008. The hydrodynamic parameters and water quality parameters (e.g. flow velocity, temperature, turbidity and nutrient content) had been continuously monitored to reveal the influence of the impounding process of the TGR on the water eutrophication in the Xiangxi Bay (XXB). The maximal daily rise of the water level of the TGR was about 2.38 m. The water exchange between the mainstream (the Changjiang River) and the XXB of the TGR was enhanced by density current, and its main characteristics were a density-stratified flow in different directions. The water exchange reduced the differences of the water quality parameters (for example, temperature, turbidity, nutrient level, pH, etc.) between the mainstream and the XXB during the impounding process. Meanwhile, the water stability index in the mainstream remained small but it was lowered in the XXB. The main causes included the dilution by water of lower concentration of the chlorophyll a (Chl. a) entering from the mainstream, the decline of the water stability, and the increase of suspended silt, which induced the Chl.a to decrease in the XXB during the impounding process. The grade of the water eutrophication changed from middle eutrophic level to mesotrophic state in the process. However, as available nutrients were imported into the XXB from the mainstream during the impounding process the risk of water eutrophication increases in the XXB in the future.

Almost in a Day’s Work

Many plants coordinate their annual time of flowering with particular seasons of the year, and one indicator that they use to determine the change of seasons is day length. Sawa et al . (see the Perspective by Rubio and Deng) provide some insights into the molecular interactions that translate day length into flowering initiation. The day needs to be long enough for the blue-light stimulated expression of the proteins FKF1 (flavin-binding, kelch repeat, F-box1) and GIGANTIA (GI) to coordinate. The daily rise in expression of GI lags far enough behind the daily rise in expression of FKF1 that, in the shorter days of the year, daylight has waned by the time there is enough GI to form complexes with FKF1. With the longer days of spring and summer, there is enough time to form complexes and signal to the CONSTANS gene to trigger the flowering pathway. M. Sawa, D. A. Nusinow, S. A. Kay, T. Imaizumi, FKF1 and GIGANTEA complex formation is required for day-length measurement in Arabidopsis . Science 318 , 261-265 (2007). [Abstract] [Full Text] V. Rubio, X. W. Deng, Standing on the shoulders of GIGANTEA. Science 318 , 206-207 (2007). [Summary] [Full Text]

In-situ measurement of reactive hydrocarbons at Hohenpeissenberg with comprehensive two-dimensional gas chromatography (GC×GC-FID): use in estimating HO and NO<sub>3</sub>

Abstract. During a field campaign at the Meteorological Observatory Hohenpeissenberg (MOHp) in July 2004, volatile organic compounds (VOCs) were measured using comprehensive two-dimensional gas chromatography (GC×GC). Comparison to routinely made gas chromatography mass spectrometry (GC-MS) measurements showed good agreement for a variety of anthropogenic and biogenic ambient VOCs ranging in concentration from below the detection limit (0.1 pmol mol−1) to 180 pmol mol−1. Pronounced diurnal cycles were found for both the biogenic and anthropogenic compounds, driven for the most part by the daily rise and fall of the boundary layer over the station. For the reactive compounds (lifetimes <2 days), a significant, non-zero dependency of the variability on lifetime was found, indicating that chemistry (as opposed to transport alone) was playing a role in determining the ambient VOC concentrations. The relationship was exploited using a single-variate analysis to derive a daytime mean value of HO (5.3±1.4×106molecules cm−3), which compares well to that measured at the site, 3.2±2.3×106molecules cm−3. The analysis was extended to the night time data to estimate concentrations for NO3 (1.47±0.2×108molecules cm−3), which is not measured at the site. The feasibility of this approach for environments dominated by emissions of short-lived VOCs to estimate ambient levels of radical species is discussed.

Development of a bovine model to evaluate administration routines for endophyte-infected tall fescue

Fescue toxicosis in cattle is characterised by a reduction in feed intake and hyperthermia during the summer in Southeast to Midwest regions of the United States. Several studies were performed using these endpoints to evaluate different administration routines that might produce a reliable model for this condition. Endophyte-infected (E+) or uninfected (E- ) fescue seed was administered in the standard diet as ground or whole seed during thermoneutral and heat stress periods to determine which seed form produced the greater response in different thermal environments. Time of administration was also tested by comparing response to whole seed administered either before or during heat stress. In each study, a high and low level of ergovaline in the diet was evaluated to identify potential dose differences. Ground E+ seed at either level produced a rapid decrease in feed intake in both environments, with no effect on core body temperature. Whole E+ seed treatment prior to heat stress resulted in a greater daily rise in core body temperature than E- with no effect on feed intake. In contrast, whole E+ seed administration during heat stress produced a dose-dependant upward shift in body temperature and reduction in daily feed intake to suggest that this is the more reliable routine for generating these characteristics of fescue toxicosis in cattle. Keywords: fescue toxicosis, cattle, heat stress

Suprachiasmatic GABAergic inputs to the paraventricular nucleus control plasma glucose concentrations in the rat via sympathetic innervation of the liver.

Daily peak plasma glucose concentrations are attained shortly before awakening. Previous experiments indicated an important role for the biological clock, located in the suprachiasmatic nuclei (SCN), in the genesis of this anticipatory rise in plasma glucose concentrations by controlling hepatic glucose production. Here, we show that stimulation of NMDA receptors, or blockade of GABA receptors in the paraventricular nucleus of the hypothalamus (PVN) of conscious rats, caused a pronounced increase in plasma glucose concentrations. The local administration of TTX in brain areas afferent to the PVN revealed that an important part of the inhibitory inputs to the PVN was derived from the SCN. Using a transneuronal viral-tracing technique, we showed that the SCN is connected to the liver via both branches of the autonomic nervous system (ANS). The combination of a blockade of GABA receptors in the PVN with selective removal of either the sympathetic or parasympathetic branch of the hepatic ANS innervation showed that hyperglycemia produced by PVN stimulation was primarily attributable to an activation of the sympathetic input to the liver. We propose that the daily rise in plasma glucose concentrations is caused by an SCN-mediated withdrawal of GABAergic inputs to sympathetic preautonomic neurons in the PVN, resulting in an increased hepatic glucose production. The remarkable resemblance of the presently proposed control mechanism to that described previously for the control of daily melatonin rhythm suggests that the GABAergic control of sympathetic preautonomic neurons in the PVN is an important pathway for the SCN to control peripheral physiology.

A ground‐level ozone forecasting model for Santiago, Chile

AbstractA physically based model for ground‐level ozone forecasting is evaluated for Santiago, Chile. The model predicts the daily peak ozone concentration, with the daily rise of air temperature as input variable; weekends and rainy days appear as interventions. This model was used to analyse historical data, using the Linear Transfer Function/Finite Impulse Response (LTF/FIR) formalism; the Simultaneous Transfer Function (STF) method was used to analyse several monitoring stations together. Model evaluation showed a good forecasting performance across stations—for low and high ozone impacts—with power of detection (POD) values between 70 and 100%, Heidke's Skill Scores between 40% and 70% and low false alarm rates (FAR). The model consistently outperforms a pure persistence forecast. Model performance was not sensitive to different implementation options. The model performance degrades for two‐ and three‐days ahead forecast, but is still acceptable for the purpose of developing an environmental warning system at Santiago. Copyright © 2002 John Wiley & Sons, Ltd.

Long-term effects of the mammary carcinogen 7,12-dimethylbenz(a) anthracene on hypothalamic gonadotropin-releasing hormone and its pituitary receptor gene expression, during the promotion stage, in female Sprague-Dawley rats.

A single intragastric administration of 7,12-dimethylbenz(a)anthracene (DMBA) has been shown to induce mammary tumors in young cycling female Sprague-Dawley rats. The appearance of these tumors is preceded by a series of neuroendocrine disturbances, including attenuation of the preovulatory luteinizing hormone (LH) surge and amplification of the preovulatory 17beta-estradiol surge, and gonadotropin-releasing hormone (GnRH) released in vitro. In this study, we examined the hypothesis that DMBA administration decreases levels of GnRH mRNA in the preoptic area-anterior hypothalamus (POA-AH) and GnRH receptor (GnRH Rc) mRNA and protein in the anterior pituitary gland. Sprague-Dawley rats, 55-60 days of age with regular estrous cycles, received a single dose of 15 mg DMBA in 1 ml sesame oil delivered by intragastric intubation. A first series of experiments was performed for the measurement of hypothalamic GnRH mRNA and pituitary GnRH Rc mRNA levels. A second series of experiments was performed for the measurement of pituitary GnRH receptor. In both experiments, animals were sacrificed by decapitation at 11.00, 16.00, 18.00 and 20.00 h on each day of the 7th or 8th estrous cycle (28-32 days) after treatment. GnRH and GnRH receptor mRNAs were quantified using solution hybridization-RNase protection assay. The GnRH Rc was quantified using the 125I-D-Ala6-N-Met-Leu6-des-Gly10-ethylamide GnRH. DMBA-treatment produced no significant effect on the overall mean values of GnRH mRNA. GnRH mRNA levels in control rats rose significantly between 16.00 and 20.00 h on proestrus and between 18.00 and 20.00 h on diestrus I. DMBA-treated rats had a surge in GnRH mRNA levels at 18.00 h on proestrus, and showed additional surges at 18.00h on diestrus II and estrus. GnRH receptor mRNA content in the anterior pituitary gland surged at 16.00h on certain days of the cycle in both groups of rats. In control rats, only the surge on diestrus II proved significant, whereas DMBA-treated rats exhibited significant surges on diestrus I, diestrus II and proestrus. GnRH receptor mRNA values were significantly lower on both days of diestrus in DMBA-treated rats compared with controls. GnRH Rc peptide content, like GnRH receptor in RNA surged at 16.00h in both groups with the exception of a marked fall on proestrus day for DMBA treated rats. A reduction in the amplitude of the surge was also seen on the day of estrous and to a lesser extend on the day of diestrus DII in DMBA treated animal. Overall, there was a disruption of the GnRH Rc pattern which culminate on the day of proestrus in DMBA-treated animals. Interestingly, the daily rise between 11.00 and 16.00h which is the more pronounced on the day of proestrus in control animals, was completely blunted in DMBA-treated rats. Overall, the results are consistent with the hypothesis that the carcinogen attenuates, directly or indirectly, preovulatory biosynthesis of the GnRH receptor and LH release. Obviously, the changes in GnRH might occur simultaneously, independently from mammary tumorigenesis, but may play a role, in association with others DMBA-induced neuroendocrine disorders, in the promotion stage of mammary tumors in the Sprague-Dawley female rat.

The microclimate inside the Pollaiolo and Botticelli rooms in the Uffizi Gallery, Florence

To characterise the evolution of the internal climate in some of the rooms of the Uffizi Gallery (Florence), the main thermo-hygrometric parameters (air temperature, relative humidity, specific humidity, dew point, atmospheric stability) were measured automatically for some years, and also manually, with seasonal measuring surveys. Measurements were started in 1997 and are still continuing. The use of heating, air conditioning, ventilation and lighting and the daily flux of a huge number of visitors produce rapid changes and marked thermo-hygrometric gradients in the rooms. Sharp variations are found when the system is switched on in the morning, and switched off in the evening, instead of operating day and night, which is desirable for the preservation of the paintings. The humidifying system in the Pollaiolo room was found to be much too powerful, so that, instead of mitigating the relative humidity drop that is expected after a daily rise in air temperature, it increases it, forming an undesired excess of moisture. In the long run, all these cycles risk becoming harmful to the exhibits if air-temperature and air-humidity control is not regulated in accordance with the results of this study. These problems and the possible approaches to the installation of a new plant and the mitigation of these negative effects are discussed.

Indications for chlororespiration in relation to light regime in the marine diatom Thalassiosira weissflogii

The marine diatom Thalassiosira weissflogii was cultured under a light regime simulating the daily rise and fall of the sun. The light regime caused a daily cycle in non-photochemical quenching. Remarkable were the changes in fluorescence directly after a light-to-dark transition that occurred in addition to the changes induced by non-photochemical quenching. A transient non-photochemical reduction of PQ and of Q A was indicated by a transient increase in apparent F o and by changes in the shape of the fluorescence induction curve. The observed changes developed approximately the first 100–120 s after a light-to-dark transition and could be reversed by the application of far-red illumination. Chlororespiration is thought to cause the reduction of PQ and, as the PQ-pool is in equilibrium with Q A, also a reduction of Q A. The function and ecological relevance of chlororespiration are discussed.

Blunted rise in platelet count in critically ill patients is associated with worse outcome.

To test the hypothesis that a low rate of change of platelet counts (PCs) after admission to the intensive care unit (ICU) is associated with mortality. Low PCs are known to be associated with disease severity in critically ill patients, but the relevance of time-dependent changes of PCs has not been investigated. Retrospective study. A 12-bed surgical ICU of a university hospital. All adult patients admitted to the ICU for at least 4 days during a 7-yr period. At admission, Acute Physiology and Chronic Health Evaluation scores were calculated. PCs and leukocyte counts were analyzed from admission to day 10. The daily rise of the PCs (deltaPC/deltat from day 2 to day 10 was calculated. Rates for 30-day mortality as well as hospital mortality were determined. A total of 1,415 admissions were studied. Median PCs (interquartile range) initially decreased and subsequently increased, with a higher PC in 1,203 survivors than in 212 nonsurvivors from day 2 onward (302 [range,181-438] x 10(3)/mm3/day vs. 129 [range, 62-228] x 10(3)/mm3 at day 10; p < 0.001). After stratification of patients per type of surgery, within each group PC was also higher in survivors. Mean deltaPC/deltat was more than five times higher in survivors compared with nonsurvivors: 30 +/- 46 x 10(3)/mm3/day vs. 6 +/- 28 x 10(3)/mm3/day (p < 0.001). The area under the receiving operating characteristic curve of deltaPC/deltat for 30-day survival was 0.743 compared with 0.728 for the Acute Physiology and Chronic Health Evaluation. Leukocyte counts showed marginal differences between nonsurvivors and survivors. A blunted or absent rise in PCs in critically ill patients is associated with increased mortality. deltaPC/deltat is a readily available and simple parameter to improve assessment of critically ill patients.

Regulation of leptin secretion: effects of aging on daily patterns of serum leptin and food consumption

We have investigated the effects of age on the daily rise in serum leptin levels during the dark-phase of the light–dark cycle. The results show that in young 7-week-old rats, serum leptin levels increase significantly at 2300 h from the levels at 1500 h in association with increased food consumption. However, in middle-aged rats 25 weeks old, the dark-phase increase in serum leptin is absent despite retention of the daily dark-phase increase in food consumption. When compared to our earlier published results, these finding show that the loss of dark-phase rise in serum leptin occurred despite the daily increase in adipocyte leptin gene expression. These results are in accord with the view that the daily pattern in serum leptin is unlikely to be a contributor to the daily patterning of food consumption.

Hypoxic depression of circadian oscillations in sino-aortic denervated rats.

We hypothesized that hypoxia depresses the circadian oscillations of body temperature (T(b)) and oxygen consumption (V(O(2))) even in the absence of inputs from the peripheral chemoreceptors. Adult rats were sino-aortic denervated bilaterally (SAX, N=17) or sham-operated (Sham, N=17). Ten rats of each group were instrumented for measurements of T(b) and activity by telemetry. Animals were exposed to normoxia (21% O(2)), hypoxia (10.5% O(2)), and again normoxia, each for a 5-day duration, in constant light ('free-running') conditions. Hypoxia almost eliminated the T(b) circadian oscillations, mostly by abolishing the daily rise in T(b). Upon return to normoxia T(b) rapidly increased and the normal oscillation was reestablished at the expected phase of the cycle. The hypoxic effects did not differ between Sham and SAX. During hypoxia the amplitude of the circadian oscillation of activity was reduced by approximately 25%, and that of V(O(2)), measured by an open flow method in the remaining Sham and SAX rats (N=7 each), was reduced by almost 50%. In all cases there was no difference between the two groups. We conclude that activation of the peripheral chemoreceptors is not required for the manifestation of the hypoxic depression of the metabolic and temperature circadian oscillations. The results are compatible with the view that hypoxia depresses thermogenesis acting on the thermoregulatory centers of the hypothalamus.

Daily changes in hypothalamic gene expression of neuropeptide Y, galanin, proopiomelanocortin, and adipocyte leptin gene expression and secretion: effects of food restriction.

The participation of hypothalamic neuropeptide Y (NPY)-, galanin (GAL)-, and opioid-producing neurons in the restraint on food intake exerted by adipocyte leptin has recently been recognized. To further understand the interplay between the central appetite-stimulating- and peripheral appetite-inhibiting signals in the management of daily food intake, we have examined the daily patterns in expression of the hypothalamic neuropeptides and leptin receptor (R) and adipocyte leptin gene expression and secretion in freely feeding (FF) rats. These analyses were extended to determine the impact of food restriction (FR) to 4 h daily for 4 weeks. Groups of FF and FR rats were killed at 4-h intervals during a 24-h period, and hypothalamic NPY, GAL, POMC, and leptin-R gene expression and leptin gene expression were evaluated by RNase protection assays and serum leptin and corticosterone (CORT) levels were estimated by RIA. The following new findings emerged: 1) In FF rats, hypothalamic NPY messenger RNA (mRNA) levels fluctuated during the course of 24 h with high levels at 0700 h and 1100 h followed by a decrease at 1500 h during the lights-on phase that was sustained throughout the dark phase (1900 h-0500 h) of the light-dark cycle. Hypothalamic GAL and POMC mRNA also displayed daily patterns but with a different time course; GAL and POMC gene expression were elevated 4 h later than NPY mRNA at 1100 h and 1500 h. 2) Although FR to 4 h between 1100 h and 1500 h resulted in maintenance of body weight compared with a steady weight gain in FF rats, the daily patterns of fluctuations in hypothalamic neuropeptide gene expression were abolished. 3) In FF rats, hypothalamic leptin-R and adipocyte leptin gene expression and serum leptin levels displayed a daily pattern temporally different from that of hypothalamic neuropeptide gene expression. Adipocyte leptin mRNA remained low during the lights-on phase but increased at the onset of the lights-off phase (1900 h) and remained elevated through the dark phase. 4) Hypothalamic leptin-R gene expression, like that of adipocyte leptin gene expression, rose abruptly at the onset of nocturnal feeding behavior but receded progressively to low range thereafter. 5) On the other hand, a dichotomy in the daily rise in adipocyte leptin gene expression and leptin secretion was observed in FF rats. Unlike adipocyte leptin mRNA, serum leptin increased at 2300 h, 4 h after initiation of ingestive behavior. 6) In FR rats, adipocyte leptin gene expression fluctuated little over the 24-h period but, as in FF rats, leptin hypersecretion peaked 4 h after initiation of food intake. 7) In both FF and FR rats, increased serum CORT levels preceded serum leptin rise. Overall, these results show that in FF rats, gene expression of hypothalamic appetite stimulating peptides first rise and then fall to nadir during the lights-on phase when leptin levels are in low range; adipocyte leptin mRNA rises before impending ingestive behavior and increased leptin secretion reaching peak manifests itself during nocturnal feeding. The FR regimen, which curtailed the normal body weight gain, abolished these daily fluctuations in gene expression of hypothalamic orexigenic peptides and adipocyte leptin but permitted feeding-associated increased leptin secretion. Thus, it may be important to consider the daily patterns of gene expression and availability of hypothalamic orexigenic peptides in investigations aimed at elucidating the central mechanisms underlying the feedback action of the normal and altered leptin secretion patterns.

Interacting Appetite-Regulating Pathways in the Hypothalamic Regulation of Body Weight*

Various aspects of the complex spatio-temporal patterning of hypothalamic signaling that leads to the development of synchronized nocturnal feeding in the rat are critically examined. Undoubtedly, as depicted in Fig. 7, a distinct ARN in the hypothalamus is involved in the control of nocturnal appetite. At least four basic elements operate within this ARN. These are: 1) A discrete appetite-driving or orexigenic network of NPY, NE, GABA, GAL, EOP, and orexin transduces and releases appetite-stimulating signals. 2) Similarly, anorexigenic signal-producing pathways (e.g., CRH, GLP-1, alpha MSH, and CART) orchestrate neural events for dissipation of appetite and to terminate feeding, possibly by interrupting NPY efflux and action at a postsynaptic level within the hypothalamus. It is possible that some of these may represent the physiologically relevant "off" switches under the influence of GABA alone, or AgrP alone, or in combination with NPY released from the NPY-, GABA-, and AgrP-coproducing neurons. 3) Recent evidence shows that neural elements in the VMN-DMN complex tonically restrain the orexigenic signals during the intermeal interval; the restraint is greatly aided by leptin's action via diminution of orexigenic (NPY) and augmentation of anorexigenic (GLP-1, alpha MSH, and CART) signals. Since interruption of neurotransmission in the VMN resulted in hyperphagia and development of leptin resistance, it seems likely that the VMN is an effector site for the restraint exercised by leptin. The daily rhythms in leptin synthesis and release are temporally dissociable because the onset of daily rise in leptin gene expression in adipocytes precedes that in leptin secretion. Nevertheless, these rhythms are in phase with daily ingestive behavior because the peak in circulating leptin levels occurs during the middle of the feeding period. These observations, coupled with the fact that circulating levels of leptin are directly related to adiposity, pose a new challenge for elucidating the precise role of leptin in daily patterning of feeding in the rat. 4) A neural timing mechanism also operates upstream from the ARN in the daily management of energy homeostasis. Although the precise anatomical boundaries are not clearly defined, this device is likely to be composed of a group of neurons that integrate incoming internal and external information for the timely onset of the drive to eat. Evidently, this network operates independently in primates, but it is entrained to the circadian time keeper in the SCN of rodents. Apart from its role in the onset of drive to eat, the circadian patterns of gene expression of NPY, GAL, and POMC denote independent control of the timing device on the synthesis and availability for release of orexigenic signals. The VMN-DMN-PVN complex is apparently an integrated constituent of the timing mechanism in this context, because lesions in each of these sites result in loss of regulated feeding. The accumulated evidence points to the PVN and surrounding neural sites within this framework as the primary sites of release and action of various orexigenic and anorexigenic signals. A novel finding is the identification of the interconnected wiring of the DMN-mPVN axis that may mediate leptin restraint on NPY-induced feeding. The chemical phenotypes of leptin and NPY target neurons in this axis remain to be identified. These multiple orexigenic and anorexigenic pathways in the hypothalamic ARN appear to represent redundancy, a characteristic of regulated biological systems to provide a "fail-safe" neural mechanism to meet an organism's constant energy needs for growth and maintenance. Within this formulation, the coexisting orexigenic signals (NPY, NE, GAL, GABA, and AgrP) represent either another level of redundancy or it is possible that these signals operate within the ARN as reinforcing agents to varying degrees under different circumstances. (ABSTRACT TRUNCATED)

Ovarian steroid-independent diurnal rhythm in cyclic GMP/nitric oxide efflux in the medial preoptic area: possible role in preovulatory and ovarian steroid-induced LH surge.

The aim of this study was to evaluate the relationship between cyclic LH hypersecretion and nitric oxide (NO) release in the medial preoptic area (MPOA), the hypothalamic site implicated in induction of LH hypersecretion. The MPOA extracellular cyclic GMP (cGMP) efflux (an index of NO release), was monitored by microdialysis. Quite unexpectedly, we observed a daily afternoon rise in the MPOA cGMP efflux in cycling female rats on proestrus and diestrus II, in ovariectomized (ovx) rats and in ovx rats treated with ovarian steroids to induce the LH surge. The daily rise in cGMP efflux occurred earlier in diestrous and in estradiol benzoate (EB)-treated ovx rats than in ovx rats. Progesterone (P) injection to estrogen-primed ovx rats further advanced the onset of the rise close to the earliest time of rise as seen on proestrus. The afternoon increase in the cGMP efflux in proestrous rats was abolished by pentobarbital treatment that blocked the LH surge. Intracerebroventricular (i.c.v.) injection of 1 H-[1,2,4]oxadiazo[4,3-a]quinoxalin-one (ODQ), a selective inhibitor of soluble guanylyl cyclase, suppressed the P-induced LH surge in EB-primed ovx rats, but not basal LH secretion in unprimed ovx rats. Analysis of brain NOS (bNOS) levels in the POA by Western blotting showed that the morning bNOS levels were higher in the POA of EB-treated rats than in unprimed ovx rats. Further, with the exception of ovx rats treated with sequential EB and P treatment, the POA bNOS levels rose significantly in the afternoon in unprimed ovx and EB-treated ovx rats. Collectively, these findings reveal a diurnal rhythm in the MPOA cGMP/NO efflux that is ovarian steroid-independent. Ovarian steroids apparently shift the timing of the afternoon rise in cGMP/NO efflux to synchronize with the activation of steroid-dependent neuronal systems responsible for the LH surge.

Coarse bedload transport in a mountain river

Coarse bedload transport dynamics are investigated utilizing hydrodynamic and sediment transport data obtained in an extensively instrumented study reach located in Squaw Creek, Montana, USA. During 1991 and 1992, a number of discrete bedload transport events associated with the daily rise and fall in stream discharge were investigated. Data show that initiation of sediment transport was accompanied by a reduction in bed roughness and by changes in bulk hydraulic parameters. For larger discharges, coarser fractions of the bed material mobilized, and bedload transport rates and average hydraulic parameters stabilized. As discharge reduced, mobile coarse particles became less frequent and deposited fine particles were removed, resulting in an increase in bed roughness. These observations are attributed to the downstream translation of bar sediments during the passage of a hydrograph. Bedload pulses were aperiodic but spatially variable. Flow turbulence and velocity profile data obtained during low flows allowed comparison between average bed shear stress and apparent bed roughness estimates obtained using different approaches. © 1998 John Wiley & Sons, Ltd.

Coarse bedload transport in a mountain river

Coarse bedload transport dynamics are investigated utilizing hydrodynamic and sediment transport data obtained in an extensively instrumented study reach located in Squaw Creek, Montana, USA. During 1991 and 1992, a number of discrete bedload transport events associated with the daily rise and fall in stream discharge were investigated. Data show that initiation of sediment transport was accompanied by a reduction in bed roughness and by changes in bulk hydraulic parameters. For larger discharges, coarser fractions of the bed material mobilized, and bedload transport rates and average hydraulic parameters stabilized. As discharge reduced, mobile coarse particles became less frequent and deposited fine particles were removed, resulting in an increase in bed roughness. These observations are attributed to the downstream translation of bar sediments during the passage of a hydrograph. Bedload pulses were aperiodic but spatially variable. Flow turbulence and velocity profile data obtained during low flows allowed comparison between average bed shear stress and apparent bed roughness estimates obtained using different approaches. © 1998 John Wiley & Sons, Ltd.

Low Plasma Estradiol is Required for the Expression of Daily Increase in Plasma Gonadotropins in the Lactating Golden Hamster (Mesocricetus auratus).

Mechanisms responsible for a daily increase in plasma gonadotropins during lactation of golden hamsters (Mesocricetus auratus) were investigated. A daily afternoon (1700 h) increase in plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone was observed until at least day 15 of lactation (day 0 of lactation = day of parturition). On the other hand, plasma estradiol did not show any significant change at 1100, 1700 and 2300 h. Such increases occur in hamsters nursing 8 pups. In hamsters nursing 2 pups, however, only a daily increase in LH was noted on day 5 of lactation and the diurnal rhythm of LH was difficult to see because of the increase in basal levels of LH on day 10 and 15 of lactation. The diurnal increases in plasma LH and FSH disappeared within 2 days after removal of the litter on day 10 of lactation and by day 14 of lactation (4 days after litter removal) most animals had resumed ovulating. Ovariectomy on day 2 of lactation did not affect the profile of plasma LH on subsequent days. In contrast, the basal levels of plasma FSH increased, suggesting the absence of an inhibitory ovarian signal (probably inhibin). A negative relationship existed between plasma estradiol and the daily surges of LH and FSH at 1700 h; the daily rise in gonadotropins occurred when plasma levels of estradiol were low. The afternoon increases in plasma LH and FSH were prevented by treatment with physiological levels of estradiol, comparable to those observed in the cyclic hamster. Antiserum against LHRH injected at 1100 h on day 10 of lactation completely suppressed the daily rise of plasma LH and FSH. These results indicate that during lactation low levels of estradiol are required for the expression of diurnal increase in plasma LH and FSH in the hamster. Moreover, the low levels of estradiol results in the daily release of LHRH.