bluuebunny/crossref_metadata_2025 huggingface dataset:
Cellular localization and expression of insulin-like growth factors (IGFs) and IGF binding proteins within the epiphyseal growth plate of the ovine fetus: possible functional implications
Authors: de los Rios P , Hill D J
Published: April 2011

The insulin-like growth factors (IGFs) are important in the regulation of normal fetal musculoskeletal growth and development, and their actions have been shown to be modulated by IGF binding proteins (IGFBPs). Because the anatomical distribution of IGFBPs is likely to dictate IGF bioavailability, we determined the cellular distribution and expression of IGF-I, IGF-II, and IGFBP-1 to IGFBP-6 in epiphyseal growth plates of the fetal sheep, using immunocytochemistry and in situ hybridization. Little mRNA for IGF-I was detectable within the growth plates, but mRNA for IGF-II was abundant in germinal and proliferative chondrocytes, although absent from some differentiating chondrocytes and hypertrophic cells. Immunohistochemistry for IGF-I and IGF-II showed a presence of both peptides in all chondrocyte zones, including hypertrophic cells. Immunoreactive IGFBP-2 to -5 were localized within the germinal and proliferative zones of chondrocytes, but little immunoreactivity was present within the columns of differentiating cells. IGFBP immunoreactivity again appeared in hypertrophic chondrocytes. IGFBP mRNA in chondrocytes of the epiphyseal growth plate was below the detectable limit of in situ hybridization. However, low levels of mRNAs for IGFBP-2 to -6 were detected by the reverse transcriptase polymerase chain reaction. A co-localization of IGFBPs with IGF peptides in intact cartilage suggests that they may regulate IGF bioavailability and action locally. To test this hypothesis, monolayer cultures of chondrocytes were established from the proliferative zone of the growth plate, and were found to release immunoreactive IGF-II and to express mRNAs encoding IGFBP-2 to -6. Exogenous IGFBP-3, -4, and -5 had an inhibitory action on IGF-II-dependent DNA synthesis. IGFBP-2 had a biphasic effect, potentiating IGF-II action at low concentrations but inhibiting DNA synthesis at equimolar or greater concentrations relative to IGF-II. Long R3 IGF-I, which has a reduced binding affinity for many IGFBPs, was more potent than native IGF-I in promoting DNA synthesis by chondrocytes. Our findings suggest that locally produced IGF-II and IGF-I derived from the circulation can influence fetal epiphyseal chondrogenesis, and that this may be modulated locally by multiple IGFBP expression.Key words: epiphyseal growth plate, insulin-like growth factor, insulin-like growth factor binding protein, chondrocyte, cartilage.
Differential response of rat skeletal muscle glycogen metabolism to testosterone and estradiol
Authors: Ramamani A , Aruldhas M M , Govindarajulu P
Published: April 2011

Although reports on sex steroids have implicated them as promoting protein synthesis and also providing extra strength to the skeletal muscle, it remains unclear whether sex steroids affect glycogen metabolism to provide energy for skeletal muscle functions, since glycogen metabolism is one of the pathways that provides energy for the skeletal muscle contraction and relaxation cycle. The purpose of the current study was to show that testosterone and estradiol act differentially on skeletal muscles from different regions, differentially with reference to glycogen metabolism. To study this hypothesis, healthy mature male Wistar rats (90-120 days of age, weighing about 180-200 g) were castrated (a bilateral orchidectomy was performed to test the significance of skeletal muscle glycogen metabolism in the absence of testosterone). One group of castrated rats was supplemented with testosterone (100 µg/100 g body weight, i.m., for 30 days from day 31 postcastration onwards). To test whether estradiol has any effect on male skeletal muscle glycogen metabolism 17beta-estradiol (5 µg/100 g body weight, i.m., for 30 days from day 31 postcastration onwards) was administered to orchidectomized rats. To test whether these sex steroids have any differential effect on skeletal muscles from different regions, skeletal muscles from the temporal region (temporalis), muscle of mastication (masseter), forearm muscle (triceps and biceps), thigh muscle (vastus lateralis and gracilis), and calf muscle (gastrocnemius and soleus) were considered. Castration enhanced blood glucose levels and decreased glycogen stores in skeletal muscle from head, jaw, forearm, thigh, and leg regions. This was accompanied by diminished activity of glycogen synthetase and enhanced activity of muscle phosphorylase. Following testosterone supplementation to castrated rats, a normal pattern of all these parameters was maintained. Estradiol administration to castrated rats did not bring about any significant alteration in any of the parameters. The data obtained suggest a stimulatory effect of testosterone on skeletal muscle glycogenesis and an inhibitory effect on glycogenolysis. Estradiol did not play any significant role in the skeletal muscle glycogen metabolism of male rats.Key words: testosterone, estradiol, skeletal muscle, glycogen metabolism.
Two novel types of calcium release from skeletal sarcoplasmic reticulum by phosphatidylinositol 4,5-bisphosphate
Authors: Ohizumi Yasushi , Hirata Yutaka , Suzuki Atsuko , Kobayashi Masaki
Published: April 2011

In both the heavy and light fractions of fragmented sarcoplasmic reticulum (SR) vesicles from the fast skeletal muscle, about 27 min after beginning the active Ca2+uptake, the extravesicular Ca2+concentration suddenly increased to reach a steady level (delayed Ca2+release). Phosphatidylinositol 4,5-bisphosphate (PIP2) not only shortened the time to delayed Ca2+release but also induced prompt Ca2+release from the heavy fraction of SR. Delayed Ca2+release and prompt Ca2+release stimulated by 100 µM PIP2were not modified by ruthenium red. PIP2(>0.1 µM) markedly accelerated the rate of45Ca2+efflux from SR vesicles in a concentration-dependent manner. The PIP2-induced45Ca2+efflux was potentiated by ruthenium red but profoundly inhibited by La3+. The concentration-response curve for Ca2+or Mg2+in PIP2-induced45Ca2+release was clearly different from that in the Ca2+-induced Ca2+release. PIP2caused a concentration-dependent increase in Ca2+release from SR of chemically skinned fibers from skeletal muscle. Furthermore, [3H]ryanodine or [3H]methyl-7-bromoeudistomin D (MBED) binding to SR was increased by PIP2in a concentration-dependent manner. These observations present the first evidence that PIP2most likely activates two types of SR Ca2+release channels whose properties are entirely different from those of Ca2+-induced Ca2+release channels (the ryanodine receptor 1).Key words: phosphatidylinositol 4,5-bisphosphate, sarcoplasmic reticulum, calcium release, ryanodine receptor, ryanodine.
Gender difference in baroreflex-mediated bradycardia in young rats: role of cardiac sympathetic and parasympathetic components
Authors: Abdel-Rahman Abdel A
Published: April 2011

In a previous clinical study we have demonstrated a significantly lower baroreflex-mediated bradycardic response in young women compared with men. The present study determined whether sexual dimorphism in baroreflex sensitivity in young rats also covers the reflex tachycardic response. The study was then extended to test the hypothesis that an attenuated cardiac cholinergic component of the baroreflex heart rate response in females may account for the gender difference. Baroreflex sensitivity (BRS) was expressed as the regression coefficient of the reciprocal relationship between evoked changes in blood pressure and heart rate. BRS measured in conscious rats with phenylephrine (BRSPE) and nitroprusside (BRSNP) represented the reflex bradycardic and tachycardic responses, respectively. Female rats exhibited significantly lower BRSPE compared with male rats (-1.53 ± 0.1 vs. -2.36 ± 0.13 beats·min-1·mmHg-1; p < 0.05) but similar BRSNP (-2.60 ± 0.20 vs. -2.29 ± 0.17 beats·min-1·mmHg-1). Blockade of cardiac muscarinic receptors with atropine methyl bromide elicited greater attenuation of BRSPE in male than in female rats (72 ± 4.6 vs. 53 ± 6.7% inhibition; p < 0.01) and abolished the gender difference. In male rats cardiac muscarinic blockade attenuated BRSPE significantly more than did cardiac beta-adrenergic receptor blockade with propranolol (72 ± 4.6 vs. 43 ± 2.7; p < 0.01), which suggests greater dependence of BRSPE on the parasympathetic component. In females, muscarinic and beta-adrenergic blockade elicited similar attenuation of BRSPE. The findings suggest that (i) BRS is differentially influenced by gender; female rats exhibit substantially lower BRSPE but similar BRSNP compared with age-matched male rats and (ii) the sexual dimorphism in BRSPE results, at least partly, from a smaller increase in vagal outflow to the heart in response to baroreceptor activation.Key words: gender difference, baroreflex sensitivity, vagal outflow, conscious rats.
Pharmacological evidence for β2-adrenoceptor in right atria from stressed female rats
Authors: Spadari-Bratfisch R C , Santos I N , Vanderlei LCM , Marcondes F K
Published: April 2011

The purpose of the present study was to demonstrate a physiological response to TA2005, a potent β2-adrenoceptor (β2-AR) selective agonist, in right atria isolated from stressed female rats under the influence of the estrous cycle. We obtained concentration-response curves to the agonist in the presence and in the absence of selective antagonists in right atria isolated from female rats submitted to three daily foot-shock sessions (30 min duration, 120 pulses of 1.0 mA, 1.0 s, applied at random intervals of 5-25 s) and sacrificed at estrus or diestrus. Our results showed that the pD2 values of TA2005 were not influenced by estrous cycle phase or foot-shock stress. However, in right atria from stressed rats sacrificed during diestrus, the concentration-response curve to TA2005 was biphasic, with a response being obtained at concentrations of 0.1 nM, whereas during estrus no response was observed at doses lower than 3 nM. ICI118,551, a β2-AR antagonist, abolished the response to nanomolar concentrations of TA2005 in right atria from stressed rats at diestrus, with no changes in agonist pD2 values in right atria from control rats (7.47 ± 0.09, p > 0.05) but a 3-fold decrease in pD2 values of TA2005 in right atria from foot shock stressed rats (7.90 ± 0.07, p [Formula: see text] 0.05). Concentration-response curves to TA2005 in the presence of ICI118,551 were best fitted by a one-site model equation. The β1-AR antagonist, CGP20712A, shifted to the right only the second part of the concentration-response curves to the agonist, unmasking the putative β2-AR-mediated response to the agonist in tissues isolated from stressed rats at diestrus. Under this condition, concentration-response curves to the agonist were best fitted by a two-site model equation. pD2 and maximum response of TA2005 interaction with β1- and putative β2-adrenoceptor components were calculated. Schild analyses gave a pKB value for CGP20712A that was typical for the interaction with β1-AR in each experimental group. pKB values for ICI118,551 could not be obtained in stressed rats sacrificed at diestrus since Schild plot slopes were lower than 1.0. In right atria from control rats, ICI118,551 pKB values were similar to reported values for the interaction of the antagonist with β1-AR. These results confirm that a heterogenous β-AR population mediating the chronotropic response to catecholamines can be demonstrated in right atria from foot shock stressed female rats sacrificed at diestrus. The stress-induced response seems to be mediated by the β2-AR subtype. Right atria from rats sacrificed during estrus are protected against stress-induced alterations on the homogeneity of β-AR population.Key words: foot-shock stress, TA2005, ICI118,551, CGP20712A, estrus, diestrus.
Myocardial meta-[125I]iodobenzylguanidine uptake in awake genetically hypertensive rats at different ages: an autoradiographic study
Authors: Schwebel Carole , Durand Andrée , Godin-Ribuot Diane , Provendier Olivier , Demenge Pierre
Published: April 2011

The purpose of this work was to evaluate changes in myocardial meta-[125I]iodobenzylguanidine ([125I]MIBG) uptake and distribution with age in awake spontaneously hypertensive rats (SHR) with respect to Wistar-Kyoto (WKY) rats. Rats were randomly divided into two groups, one for measuring myocardial [125I]MIBG uptake and distribution 4 h after its injection and the second for evaluating myocardial catecholamine concentrations. Mean arterial blood pressure, cardiac hypertrophy index (heart/body weight ratio), and heart rate were significantly higher with increasing age in SHR compared with matched WKY rats. Myocardial catecholamine concentrations and turnover did not differ between the two strains and were significantly decreased with increasing age. Myocardial [125I]MIBG uptake determined by gamma counting was similar in WKY rats and SHR and did not vary significantly with age when expressed as uptake density. However, in both strains of rats, [125I]MIBG uptake determined by autoradiography was significantly greater at the base of the heart than at the apex and midventricular levels, and the uptake values of young rats were significantly higher than those of older rats. In 21-week-old WKY rats and SHR, the highest [125I]MIBG uptake values were found in the right ventricle. Thus, quantitative autoradiography allowed detection of significant changes in myocardial [125I]MIBG uptake and showed its heterogeneous distribution in the rat heart.Key words: spontaneously hypertensive rats (SHR), Wistar-Kyoto rats, myocardial meta-[125I]iodobenzylguanidine uptake, sympathetic drive.
Na+channel and Na+-K+ATPase involvement in norepinephrine- and veratridine-stimulated metabolism in perfused rat hind limb
Authors: Tong Alex CY , Maria Carla AD , Rattigan Stephen , Clark Michael G
Published: April 2011

In the constant flow perfused rat hind limb, norepinephrine (NE) evoked increases in oxygen uptake ([Formula: see text]o2) and lactate efflux (LE) were inhibited by the cardiac glycoside ouabain (1 mM), without interrupting the NE-mediated vasoconstriction. The membrane labilizer veratridine, previously shown to increase [Formula: see text]o2and LE, without increasing perfusion pressure, was also shown to be inhibited by the cardiac glycoside ouabain, as well as by the ouabain analogues digitoxin and digoxin. The stimulatory actions of veratridine on [Formula: see text]o2were inhibitable by low doses of the specific sodium channel blocker tetrodotoxin (TTX), while NE effects were unaffected, suggesting that NE may be acting via a TTX-insensitive sodium channel. It is concluded that agents such as NE (a vasoconstrictor) or veratridine (a membrane labilizer), which stimulate [Formula: see text]o2in the perfused rat hind limb, do so by increasing Na+influx. The observed increases in oxygen consumption and LE are due to Na+-K+ATPase activity to pump Na+out of the cell at the expense of ATP turnover. Energy dissipation due to Na+cycling may be a form of facultative thermogenesis attributable to NE that can be stimulated by membrane labilizers such as veratridine in the constant flow perfused rat hind limb.Key words: membrane labilizer, digitoxin, digoxin, cardiac glycosides, Na+-K+ATPase, ouabain.
Role of Na-Ca exchange in the action potential changes caused by drive in cardiac myocytes exposed to different Ca2+loads
Authors: Liu Qi-Ying , Vassalle Mario
Published: April 2011

The role of Na-Ca exchange in the membrane potential changes caused by repetitive activity ("drive") was studied in guinea pig single ventricular myocytes exposed to different [Ca2+]o. The following results were obtained. (i) In 5.4 mM [Ca2+]o, the action potentials (APs) gradually shortened during drive, and the outward current during a train of depolarizing voltage clamp steps gradually increased. (ii) The APs shortened more and were followed by a decaying voltage tail during drive in the presence of 5 mM caffeine; the outward current became larger and there was an inward tail current on repolarization during a train of depolarizing steps. (iii) These effects outlasted drive so that immediately after a train of APs, currents were already bigger and, after a train of steps, APs were already shorter. (iv) In 0.54 mM [Ca2+]o, the above effects were much smaller. (v) In high [Ca2+]oAPs were shorter and outward currents larger than in low [Ca2+]o. (vi) In 10.8 mM [Ca2+]o, both outward and inward currents during long steps were exaggerated by prior drive, even with steps (+80 and +120 mV) at which there was no apparent inward current identifiable as ICa. (vii) In 0.54 mM [Ca2+]o, the time-dependent outward current was small and prior drive slightly increased it. (viii) During long steps, caffeine markedly increased outward and inward tail currents, and these effects were greatly decreased by low [Ca2+]o. (ix) After drive in the presence of caffeine, Ni2+decreased the outward and inward tail currents. It is concluded that in the presence of high [Ca2+]odrive activates outward and inward Na-Ca exchange currents. During drive, the outward current participates in the plateau shortening and the inward tail current in the voltage tail after the action potential.Key words: ventricular myocytes, repetitive activity, outward and inward Na-Ca exchange currents, caffeine, nickel.
Intracellular calcium stores are involved in growth hormone-releasing hormone signal transduction in rat somatotrophs
Authors: Petit Audrey , Bleicher Catherine , Lussier Benoît T
Published: April 2011

In rat pituitary somatotrophs, the stimulation of growth hormone secretion by growth hormone-releasing hormone (GHRH) is a Ca2+-dependent event involving Ca2+influx. The presence of calcium-induced calcium release (CICR) Ca2+stores has been suggested in these cells. The aim of our study was to demonstrate the presence of CICR stores in rat somatotrophs and to determine their function in GHRH Ca2+signalling. To this end we measured cytosolic free Ca2+concentration ([Ca2+]i), using indo-1 in purified rat somatotrophs in primary culture, while altering intracellular Ca2+stores. Ionomycin (10 µM) or 4-bromo-A23187 (10 µM), used to mobilise organelle-bound Ca2+, raised [Ca2+]iin the absence of extracellular Ca2+. Caffeine (5 to 50 mM), used to mobilise Ca2+from CICR stores, transiently raised [Ca2+]iin 65% of cells tested. The response to 40 mM caffeine was abolished when Ca2+stores were depleted, with 1 µM thapsigargin or with 10 µM ryanodine. All cells that responded to 40 mM caffeine responded to 10 nM GHRH. The [Ca2+]iresponse to 10 nM GHRH was reversible and repeatable. However, the second response was 38% smaller than the first. Ryanodine treatment abolished the reduction in the second [Ca2+]iresponse, while thapsigargin increased the reduction by 67%. We conclude that rat somatotrophs possess CICR Ca2+stores and that they account for 30-35% of the GHRH-induced increase in [Ca2+]i, and that their partial depletion is involved in somatotroph desensitization.Key words: somatotrophs, growth hormone-releasing hormone, intracellular calcium, calcium stores, calcium-induced calcium release.
Intrarenal infusion of bradykinin elicits a pressor response in conscious rats via a B2-receptor mechanism
Authors: Hoagland Kimberly M , Maddox David A , Martin Douglas S
Published: April 2011

Bradykinin (BK) is a peptide known to activate afferent nerve fibers from the kidney and elicit reflex changes in the cardiovascular system. The present study was specifically designed to test the hypothesis that bradykinin B2 receptors mediated the pressor responses elicited during intrarenal bradykinin administration. Pulsed Doppler flow probes were positioned around the left renal artery to measure renal blood flow (RBF). A catheter, to permit selective intrarenal administration of BK, was advanced into the proximal left renal artery. The femoral artery was cannulated to measure mean arterial pressure (MAP). MAP, heart rate (HR), and RBF were recorded from conscious unrestrained rats while five-point cumulative dose-response curves during an intrarenal infusion of BK (5-80 µg·kg-1·min-1) were constructed. Intrarenal infusion of BK elicited dose-dependent increases in MAP (maximum pressor response, 26 ± 3 mmHg), accompanied by a significant tachycardia (130 ± 18 beats/min) and a 28% increase in RBF. Ganglionic blockade abolished the BK-induced increases in MAP (maximum response, -6 ± 5 mmHg), HR (maximum response 31 ± 14 beats/min), and RBF (maximum response, 7 ± 2%). Selective intrarenal B2-receptor blockade with HOE-140 (50 µg/kg intrarenal bolus) abolished the increases in MAP and HR observed during intrarenal infusion of BK (maximum MAP response, -2 ± 3 mmHg; maximum HR response, 15 ± 11 beats/min). Similarly, the increases in RBF were prevented after HOE-140 treatment. In fact, after HOE-140, intrarenal BK produced a significant decrease in RBF (22%) at the highest dose of BK. Results from this study show that the cardiovascular responses elicited by intrarenal BK are mediated predominantly via a B2-receptor mechanism.Key words: bradykinin, blood pressure, renal hemodynamics, B2 receptors, autonomic nervous system.
Lipoprotein lipase activity is stimulated by insulin and dexamethasone in cardiomyocytes from diabetic rats
Authors: Ewart H Stephen , Carroll Rogayah , Severson David L
Published: April 2011

Type 1 diabetes mellitus reduces lipoprotein lipase (LPL) activity in the heart. The diabetic phenotype of decreased LPL activity in freshly isolated cardiomyocytes persisted after overnight culture (16 h). Total cellular LPL activity was 311 ± 56 nmol oleate released·h-1·mg-1cell protein in diabetic cultured cardiomyocytes compared with 661 ± 81 nmol oleate released·h-1·mg-1cell protein for control cultured cells. Diabetes also resulted in lower heparin-releasable (HR) LPL activity compared with control cells (111 ± 25 vs. 432 ± 63 nmol·h-1·mg-1cell protein). In kinetic experiments, the reduction in total cellular LPL and HR-LPL activities in cultured cells from diabetic hearts was due to a decrease in maximal velocity, with no change in apparent Kmfor substrate (triolein). LPL activity in primary cultures of cardiomyocytes from control rats is stimulated by the combination of insulin (Ins) and dexamethasone (Dex). Overnight treatment of cultured cardiomyocytes from diabetic rats with Ins+Dex elicited an 84% increase in cellular LPL activity (to 572 ± 65 nmol·h-1·mg-1cell protein) and a 194% increase in HR-LPL activity (to 326 ± 46 nmol·h-1·mg-1cell protein). This stimulation occurred at subnanomolar concentrations of the hormones, but neither hormone was effective alone. The amount of immunoreactive LPL protein mass in cultured cardiomyocytes from diabetic hearts was unchanged by Ins+Dex treatment. Addition of oleic acid (60 µM) to the overnight culture medium inhibited the already reduced HR-LPL activity in diabetic cultured cells by 73% (to 30 ± 4 nmol·h-1·mg-1cell protein). The presence of oleic acid also reduced hormone-stimulated HR-LPL activity. Increasing the glucose concentration in the culture medium to 26 mM had no effect on total cellular LPL or HR-LPL activities.Key words: lipoprotein lipase, cardiomyocytes, diabetes.
Effects of enalaprilat on neointimal growth of cultured rabbit aorta following balloon injury
Authors: Dale William E , Blaine Edward H
Published: April 2011

Our objective was to determine if the ability of an angiotensin-converting enzyme (ACE) inhibitor to attenuate neointima formation in balloon-damaged vessel is expressed in an isolated organ culture model of neointimal growth. In vivo balloon angioplasty in combination with in vitro organ culture was used to produce a unique model of vascular neointima formation. Aortic segments were cultured in medium containing a broad concentration range of the ACE inhibitor enalaprilat (0-100 µM). Cell proliferative indices and neointima:media thickness ratios were determined from vessel segments after 1, 4, and 7 days in culture. We observed no significant effect on either parameter at any dose of enalaprilat. Linear regression analysis on the rate of increase in intima to media thickness ratios during the 7 days of culture also showed no effect of enalaprilat at any concentration. We conclude that enalaprilat has no effect on neointimal growth or cell proliferation in this vascular organ culture model, and it is suggested that ACE inhibitors may act by mechanisms other than local converting enzyme inhibition to attenuate neointimal growth in rabbits following vascular ballooning in vivo.Key words: angiotensin, restenosis, angiotensin-converting enzyme inhibitors, organ culture, aorta.
Functional comparison of the human isolated femoral artery, internal mammary artery, gastroepiploic artery, and saphenous vein
Authors: Cracowski Jean-Luc , Stanke-Labesque Françoise , Sessa Carmine , Hunt Mark , Chavanon Olivier , Devillier Philippe , Bessard Germain
Published: April 2011

Human femoral, internal mammary, and gastroepiploic arteries and saphenous veins are used as bypass grafts for coronary surgery or for reconstruction in arterial occlusive disease. We have characterized the contractile responses of these vessels to various agents that are liberated during cardiac or vascular surgery. In organ baths, U46619 (a stable thromboxane A2mimetic), norepinephrine, endothelin-1, angiotensin II, and KCl caused concentration-dependent contractions in all vessels tested. Leukotriene C4did not induce any contraction in the arteries, whereas a contraction was obtained in the saphenous vein rings. U46619 induced the most powerful contraction in all vessels tested. The pD2values for each agent did not differ among the different vessels. When responses were expressed as a percentage of KCl-induced contraction, the contraction of endothelin-1 (151 ± 5%) and leukotriene C4(43 ± 5%) was more significant on saphenous veins than on arteries. In conclusion, thromboxane A2appears to be the most potent endogenous constricting agent on different human vascular beds. Our second finding is that saphenous veins are more sensitive to contract to leukotriene C4and endothelin-1 than arteries. These properties may influence early and (or) long-term vein graft patency.Key words: femoral arteries, vascular reactivity, thromboxane A2, endothelin-1, leukotrienes.
Reflex changes in heart rate during chemoreceptor stimulation in monkeys
Authors: Ravi K , Singh M
Published: April 2011

The changes in heart rate induced by the stimulation of arterial chemoreceptors by apneic asphyxia and left atrial - intracarotid injections of sodium cyanide were investigated in anesthetized artificially ventilated and paralysed monkeys. Apneic asphyxia and sodium cyanide injection caused tachycardia, bradycardia, or both in monkeys paralysed with decamethonium bromide and tachycardia only, in monkeys paralysed with gallamine. In both groups, the tachycardia was abolished by prior administration of propranolol and the bradycardia, by atropine. Prior ventilation with 100% O2 abolished the heart rate responses produced by apnea. Recording of phrenic efferent activity showed that the neural discharge increased in response to apneic asphyxia and sodium cyanide injections. It remained so during the manifestation of tachycardia, bradycardia, or no change in heart rate, suggesting that even though "higher centres" may have an important influence in the heart rate responses elicited, central respiratory drive may not be the only mechanism. The present results show that in the nonhuman primate, arterial chemoreceptor stimulation elicits both cardioacceleratory and cardioinhibitory reflexes, and the net effect of their stimulation on heart rate depends upon the balance between these opposing mechanisms.Key words: chemoreceptors, heart rate, monkey.
Silent glutamatergic synapses in the mammalian brain
Authors: Isaac John TR , Nicoll Roger A , Malenka Robert C
Published: April 2011

Excitatory synaptic transmission in the mammalian brain is mediated primarily by α-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors that are thought to be co-localized at individual synapses. However, recent electrophysiological and anatomical data suggest that the synaptic localization of AMPA and NMDA receptors may be independently regulated by neural activity. These data are reviewed here and the implications of these findings for the mechanisms underlying synaptic plasticity are discussed.Key words: glutamate receptor, long-term potentiation (LTP), synaptic plasticity, hippocampus, cortex.
Effects of adenosine on Ca2+entry in the nerve terminal of the frog neuromuscular junction
Authors: Robitaille Richard , Thomas Sébastien , Charlton Milton P
Published: April 2011

This study aimed to test whether nerve-evoked and adenosine-induced synaptic depression are due to reduction in Ca2+entry in nerve terminals of the frog neuromuscular junction. Nerve terminals were loaded with the fluorescent Ca2+indicator fluo 3 (fluo 3-AM) or loaded with dextran-coupled Ca2+green-1 transported from the cut end of the nerve. Adenosine (10-50 µM) did not change the resting level of Ca2+in the presynaptic terminal, whereas it induced large Ca2+responses in perisynaptic Schwann cells, indicating that adenosine was active and might have induced changes in the level of Ca2+in the nerve terminal. Ca2+responses in nerve terminals could be induced by nerve stimulation (0.5 or 100 Hz for 100 ms) over several hours. In the presence of adenosine (10 µM), the size and duration of the nerve-evoked Ca2+responses were unchanged. When extracellular Ca2+concentration was lowered to produce the same reduction in transmitter release as the application of adenosine, Ca2+responses induced by nerve stimulations were reduced by 40%. This indicates that changes in Ca2+responsible for the decrease in release should have been detected if the mechanism of adenosine depression involved partial block of Ca2+influx. Ca2+responses evoked by prolonged high frequency trains of stimuli (50 Hz for 10 or 30 s), which caused profound depression of transmitter release, were sustained during the whole duration of the stimulation, and adenosine had no effect on these responses. These data indicate that neither adenosine induced synaptic depression nor stimulation-induced synaptic depression are caused by reductions in Ca2+entry into the presynaptic terminal in the frog neuromuscular junction.Key words: adenosine, Ca2+, nerve terminal, transmitter release, synaptic depression.
K+ transport in resting rat hind-limb skeletal muscle in response to paraxanthine, a caffeine metabolite
Authors: Hawke Thomas J , Willmets Robert G , Lindinger Michael I
Published: April 2011

This study tested the hypothesis that paraxanthine, a caffeine metabolite, stimulates skeletal muscle potassium (K+) transport by an increase in Na+-K+ ATPase activity. The unidirectional transport of K+ into muscle (JinK) was studied using a perfused rat hind limb technique. Using 12 hind limbs, we examined the response to 20 min of paraxanthine perfusion (0.1 mM), followed by 20 min perfusion with 0.1 mM paraxanthine and 5 mM ouabain (n = 5) to irreversibly inhibit Na+-K+ ATPase activity. Paraxanthine stimulated JinK by 23 ± 5% within 20 min. Ouabain abolished the paraxanthine-induced stimulation of JinK, suggesting the increase in K+ uptake was due to activation of the Na+-K+ ATPase. To confirm the role of the Na+-K+ ATPase, 14 hind limbs were perfused for 20 min with 5 mM ouabain prior to 20 min perfusion with 0.1 mM paraxanthine and 5 mM ouabain (n = 6). Ouabain alone resulted in a 41 ± 7% decrease in JinK within 15 min. Inhibition of ouabain-sensitive JinK prevented the paraxanthine-induced increase in JinK. Hind limbs (n = 3) were also perfused with 0.1 mM paraxanthine for 60 min to examine the response to longer duration paraxanthine perfusion. The paraxanthine-induced increase in JinK continued for the entire 60 min. In another series, hind limbs were perfused with 0.01 (n = 9), 0.1 (n = 9), or 0.5 (n = 6) mM paraxanthine for 15 min. There was no concentration-dependent relationship between JinK and paraxanthine concentration, and 0.01, 0.1, and 0.5 mM paraxanthine increased JinK similarly (25 ± 5, 22 ± 4, and 27 ± 6%, respectively). The effect of paraxanthine on JinK could not be reversed by subsequent perfusion with paraxanthine-free perfusate. Caffeine (0.05-1.0 mM) had no effect on K+ transport. It is concluded that paraxanthine increases JinK in resting skeletal muscle by stimulating ouabain-sensitive Na+-K+ ATPase activity.Key words: caffeine, methylxanthine, ouabain, potassium transport, sodium pump, Na-K ATPase, VO2, glycolysis.
Methionine sulfoximine shows excitotoxic actions in rat cortical slices
Authors: Shaw C A , Bains J S , Pasqualotto B A , Curry K
Published: April 2011

Methionine sulfoximine (MSO) is a rare amino acid. It occurs in nature or as a by-product of some forms of food processing. A notable example of the latter was a former method for bleaching wheat flour, using nitrogen trichloride, the "agene process," in use for most of the first 50 years of this century. "Agenized" flour was found to be responsible for various neurological disorders in animals, and MSO was identified as the toxic factor. The agene process was subsequently discontinued in the United States and the United Kingdom circa 1950. MSO inhibits the synthesis of both glutathione and glutamine, and it is possible that its actions on the nervous system arise from alterations in the amount or distribution of these molecules. Structurally, MSO resembles glutamate, an observation that has also raised the possibility that it might have more direct glutamate-like actions on neurons. In the present investigation, we report excitatory and toxic actions of MSO in an in vitro preparation of adult rat cortex. Field potential recordings in this preparation show that MSO application evokes a sustained depolarization, which can be blocked by the N-methyl-D-aspartate (NMDA) antagonist L-(+)-2-amino-5-phosphonovalerate (AP5). However, competition assays using MSO on [3H]CGP-39653 (DL-(E)-2-amino-4-propyl-1-phosphono-3-pentenoate) binding in rat cortical homogenates show only 20% displacement of total binding, suggesting that MSO is acting indirectly, perhaps by releasing glutamate. To investigate this possibility, we measured glutamate release during MSO application. Time course and dose-response experiments with MSO showed significant [3H]glutamate release, which was partially attenuated by AP5. To assess cellular toxicity, we measured lactate dehydrogenase (LDH) release from cortical sections exposed to MSO. MSO treatment led to a rapid increase in LDH activity, which could be blocked by AP5. These data suggest that MSO acts by increasing glutamate release, which then activates NMDA receptors, leading to excitotoxic cell death. These data suggest the possibility that MSO in processed flour had excitotoxic actions that may have been contributing factors to some human neuronal disorders.Key words: agene process, glutamate release, lactate dehydrogenase, methionine sulfoximine, N-methyl-D-aspartate (NMDA) receptor, neurological disorders.
Glucose refractoriness of β-cells from fed fa/fa rats is ameliorated by nonesterified fatty acids
Authors: Chan Catherine B , Surette Justin J
Published: April 2011

The aim of this study was to characterize the glucose responsiveness of individual β-cells from fa/fa rats under ad libitum feeding conditions. Enlarged intact islets from fed fa/fa rats had a compressed insulin response curve to glucose compared with smaller islets. Size-sorted islets from obese rats yielded β-cells whose glucose responsiveness was assessed by reverse hemolytic plaque assay to determine whether glucose refractoriness was caused by a decreased number of responsive cells or output per cell. In addition, the effects of palmitic acid on glucose-stimulated insulin secretion were assessed because of evidence that nonesterified fatty acids have acute beneficial effects. Two- to three-fold more β-cells from >250 µm diameter (large) islets than <125 µm diameter (small) or lean islets responded to low glucose. Increasing the glucose (8.3-16.5 mM) induced a >10-fold increase in recruitment of active cells from small islets, compared with only a 2.6-fold increase in large islets. This refractoriness was partially reversed by preincubation of the cells in low glucose for 2 h. In addition, secretion per cell of the large islet β-cell population was significantly reduced compared with lean β-cells, so that the overall response capacity of large but not small islet β-cells was significantly reduced at high glucose. Therefore, continued near-normal function of the β-cells from small islets of fa/fa rats seems crucial for glucose responsiveness. Incubation of β-cells from large islets with palmitic acid normalized the secretory capacity to glucose mainly by increasing recruitment and secondarily by increasing secretion per cell. In conclusion, these studies demonstrate refractoriness to glucose of β-cells from large islets of fa/fa rats under ad libitum feeding conditions. When acutely exposed to nonesterified fatty acids, islets from fa/fa rats have a potentiated insulin response despite chronic elevation of plasma lipids in vivo.Key words: Zucker rat, insulin secretion, palmitic acid, glucose, β-cells.
Specific binding of [3H]ketanserin to hypothalamus membranes of juvenile rainbow trout, Oncorhynchus mykiss?
Authors: Agrawal Smriti M , Omeljaniuk Robert J
Published: April 2011

This study examines the existence and pharmacological specificity of [3H]ketanserin binding in hypothalamus of juvenile rainbow trout. Hypothalamic membranes were incubated with [3H]ketanserin (selective 5HT2 antagonist) under several experimental conditions; reactions were terminated by filtration and bound radioactivity was counted by liquid scintillation spectroscopy. Tissue dilution experiments revealed that specific [3H]ketanserin binding (Bsp) was tissue dependent; 1 hypothalamus equivalent per tube (1100 ± 115 cpm/mg protein) was subsequently used throughout the rest of this study. In association experiments, Bsp increased progressively with time, achieved equilibrium binding levels (1192 ± 120 cpm/mg protein) within 80 min, and remained stable for at least 60 min thereafter; kobs, and k+1 were 0.032 and 0.048 min-1·nM-1, respectively. In dissociation experiments, Bsp completely dissociated within 20 min following addition of excess ketanserin; k-1 and t1/2 were 0.0803 min-1 and 8.7 min, respectively. Bsp was saturable (2500 ± 256 cpm/mg protein); Scatchard-calculated values for the equilibrium dissociation constant (KD) and capacity (Bmax) were 0.48 nM, and 125 fmol/mg protein, respectively. Bsp was differentially displaced by structurally related competitors, with a rank order of potency of ketanserin = mianserin > ritanserin > serotonin (5HT) = spiperone >> methiothepin mesylate > metergoline = DOI ((±)-2-5-dimethoxy-4-iodoamphetamine hyrobromide) > 2-methyl-5HT > alpha-methyl-5HT >>>> 5HIAA (5-hydroxyindole acetic acid) = reserpine. These findings provide pharmacological evidence for the presence of a 5HT2-like receptor subtype in the trout hypothalamus.Key words: hypothalamus, [3H]ketanserin, 5HT2 receptor subtype, rainbow trout.
Acute plasma volume expansion alters cardiovascular but not thermal function during moderate intensity prolonged exercise
Authors: Roy B D , Green H J , Grant S M , Tarnopolsky M A
Published: April 2011

To investigate the hypothesis that the increase in plasma volume (PV) that typically occurs with training results in improved cardiovascular and thermal regulation during prolonged exercise, eight untrained males (Vo2peak = 3.52 ± 0.12 L·min-1) performed 90 min of cycle ergometry at 62% Vo2peak before and after acute PV expansion. Subjects were infused with a PV-expanding solution (dextran (6%) or Pentaspan (10%)) equivalent to 6.7 mL·kg-1 body mass (PVX) or acted as their own control (CON) in a randomized order. PVX resulted in a calculated 15.8% increase in resting PV, which relative to CON, was maintained throughout the exercise (P < 0.05). During PVX, heart rate was lower (P < 0.05) and stroke volume and cardiac output were higher (P < 0.05) during the exercise. Mean arterial pressure and total peripheral resistance, although altered by exercise (P < 0.05), were not different between the two conditions. Core temperature, which was progressively increased by the exercise (P < 0.01), was not affected by PVX. A similar decrease in body weight was observed between the conditions as a result of the exercise (P < 0.01). These results indicate that acute PVX alters cardiovascular performance without affecting the thermoregulatory response to prolonged cycle exercise.Key words: cardiovascular, prolonged exercise, acute plasma volume expansion, thermoregulation, hypervolemia.
Nesting success and nest-site selection by a neotropical migrant in a fragmented landscape
Authors: Bisson Isabelle A , Stutchbury Bridget JM
Published: April 2011

Information on breeding-habitat requirements for neotropical migrants is important for managing remnant woodlots used by these species. In 1998, we examined nest-site selection and nesting success of hooded warblers (Wilsonia citrina) in seven woodlots of the highly fragmented Carolinian Forest in southwestern Ontario, Canada. We sampled and compared 23 nest and unoccupied sites. We recorded number of eggs, number of nestlings, and number of young fledged, as measures of productivity, and the presence of cowbird (Molothrus ater) parasitism. Nest sites had an overall higher percentage of vegetation cover than unoccupied sites (U [Formula: see text] 75.0, P < 0.04) and a lower basal area of trees with a diameter at breast height between 7.5 and 15 cm (U = 376.0, P = 0.014). Our best logistic regression model showed that the probability of a site being occupied by nesting hooded warblers increased with the height of the subcanopy and with the percentage of vegetation cover at the 1- to 2-m height interval. The model correctly classified 74.6% of the nest and unoccupied sites. Nest survivorship for the entire nesting period was estimated at 67.1%. Cowbird parasitism was low (18%). No nest-site characteristics were correlated with any of the productivity parameters (rs[Formula: see text] 0.663, P [Formula: see text] 0.536, n = 17). We conclude that canopy gaps and understory vegetation, rather than forest maturity, appear to be the limiting factors affecting the selection of a site by hooded warblers. Further research should focus on the use of gaps by breeding hooded warblers, and logging prescriptions should be formulated to include the creation of openings in the forest canopy.
Effect of osmolarity on in vitro responses of winter flounder (Pleuronectes americanus) melanophores
Authors: Linthorne K D , Burton D
Published: April 2011

No information is available on the effects of osmotic changes on winter flounder (Pleuronectes americanus) neurally regulated melanosome-aggregating responses within dermal or epidermal melanophores. The Na+ composition of balanced salt solution and the Na+ and K+ composition of K+-rich melanosome-aggregating fluid were varied to manipulate osmolarity in vitro to determine their effect on melanosome aggregation. It is evident that without previous acclimation the in vitro neuromelanophore system can tolerate a wide range of salinities equivalent to seasonal high and low levels of plasmatic osmolarity with little effect on responsiveness. In addition winter flounder neuromelanophore preparations can display attenuated responsiveness when molarities have been changed by up to 50% and without indications of cellular lysis in hypotonic media.
Histocompatibility analysis of clonal diversity in unisexual hybrids of the killifishesFundulus heteroclitusandFundulus diaphanus
Authors: Dawley Robert M , Yeakel Amy M , Beaulieu Keith A , Phiel Kristen L
Published: April 2011

Hybrids of the killifishes Fundulus diaphanus and Fundulus heteroclitus, found at two sites on the Atlantic coast of Nova Scotia, are unisexual diploid gynogens. Because there seemed to be many opportunities for the sexual progenitor species to hybridize and form new clones at these sites, we initially had expected that clonal diversity might be high among the hybrids. However, examination of their histocompatibility genomes, via inter-individual scale grafting, provides evidence, albeit not conclusive, that most of the hybrids at the two sites, which are separated by 125 km, comprise a single clone. Grafts made among F. diaphanus were rejected within an average of 16-20 days, establishing that sufficient diversity exists within the histocompatibility genomes of these fish to permit their immune systems to reject foreign melanophores. Grafts made from F. diaphanus to the hybrids were also rejected, within an average of 17-26 days, demonstrating that the hybrids possessed competent immune systems. Grafts made between hybrids were nearly always accepted. Those few that appeared to be rejected were usually accepted when regrafted. Melanophores carried on the graft remained visible for the duration of the study (90-180 days) or, if they slowly disappeared, they did so at a rate comparable with that of autograft scales.
Selective predation by brown bears (Ursus arctos) foraging on spawning sockeye salmon (Oncorhynchus nerka)
Authors: Ruggerone Gregory T , Hanson Renn , Rogers Donald E
Published: April 2011

Selective predation by and predation rates of brown bears (Ursus arctos) foraging on spawning sockeye salmon (Oncorhynchus nerka) in a small shallow creek in the Wood River lake system near Bristol Bay, Alaska, were quantified during 1986 and 19901992. Bears killed a high proportion of spawning salmon when few salmon entered the creek (92% of 505 fish) and a much smaller proportion when the spawning population reached a historical high (16% of 15 631 fish). Selective predation on salmon that differed in length, sex, and spawning condition was measured by tagging salmon at the mouth of the creek immediately prior to upstream migration and then recovering dead tagged fish during daily surveys of the entire creek. The relative frequencies of large, medium-sized, and small salmon killed by bears indicated that the risk of predation was more than 150% greater for large than for small salmon. A higher proportion of the male salmon population was killed and a greater proportion of male bodies were consumed than female salmon. Selectivity for male salmon increased as the spawning season progressed, possibly because male salmon weakened earlier and lived longer in a weakened state than female salmon. Male salmon were attacked mostly along the dorsal hump area, whereas female salmon tended to be attacked along the abdomen, where eggs could be exposed. Bears selectively killed female salmon prior to spawning during 1 of the 3 years, but only 6.17.8% of the female spawning populations were killed prior to spawning. These data support the hypothesis that selective predation by bears may influence the body morphology of spawning salmon.