bluuebunny/crossref_metadata_2025 huggingface dataset:
Expression of adrenomedullin in hypoxic and ischemic rat kidneys and human kidneys with arterial stenosis
Authors: Sandner Peter , Hofbauer Karl Heinz , Tinel Hanna , Kurtz Armin , Thiesson Helle C. , Ottosen Peter D. , Walter Steen , Skøtt Ole , Jensen Boye L.
Published: April 2004

To investigate regional aspects of hypoxic regulation of adrenomedullin (AM) in kidneys, we mapped the distribution of AM in the rat kidney after hypoxia (normobaric hypoxic hypoxia, carbon monoxide, and CoCl2 for 6 h), anemia (hematocrit lowered by bleeding) and after global transient ischemia for 1 h (unilateral renal artery occlusion and reperfusion for 6 and 24 h) and segmental infarct (6 and 24 h). AM expression and localization was determined in normal human kidneys and in kidneys with arterial stenosis. Hypoxia stimulated AM mRNA expression significantly in rat inner medulla (CO 13 times, 8% O2 6 times, and CoCl2 8 times), followed by the outer medulla and cortex. AM mRNA level was significantly elevated in response to anemia and occlusion-reperfusion. Immunoreactive AM was associated with the thin limbs of Henle's loop, distal convoluted tubule, collecting ducts, papilla surface epithelium, and urothelium. AM labeling was prominent in the inner medulla after CO and in the outer medulla after occlusion-reperfusion. The infarct border zone was strongly labeled for AM. In cultured inner medullary collecting duct cells, AM mRNA was significantly increased by hypoxia. AM mRNA was equally distributed in human kidney and AM was localized as in the rat kidney. In human kidneys with artery stenosis, AM mRNA was not significantly enhanced compared with controls, but AM immunoreactivity was observed in tubules, vessels, and glomerular cells. In summary, AM expression was increased in the rat kidney in response to hypoxic and ischemic hypoxia in keeping with oxygen gradients. AM was widely distributed in the human kidney with arterial stenosis. AM may play a significant role to counteract hypoxia in the kidney.
Fatigue and recovery of dynamic and steady-state performance in frog skeletal muscle
Authors: Syme Douglas A. , Tonks Dillon M.
Published: April 2004

Muscle fatigue reflects alterations of both activation and cross-bridge function, which will have markedly different affects on steady-state vs. dynamic performance. Such differences offer insight into the specific origins of fatigue, its mechanical manifestation, and its consequences for animal movement. These were inferred using dynamic contractions (twitches and cyclic work as might occur during locomotion) and steady-state performance with maximal, sustained activation (tetani, stiffness, and isokinetic force) during fatigue and then recovery of frog ( Rana pipiens) anterior tibialis muscle. Stiffness remained unaltered during early fatigue of force and then declined only 25% as force dropped 50%, suggesting a decline with fatigue in first the force-generating ability and then the number of cross bridges. The relationship between stiffness and force was different during fatigue and recovery; thus the number of cross bridges and force per cross bridge are not intimately linked. Twitch duration increased with fatigue and then recovered, with trajectories that were remarkably similar to and linear with changes in tetanic force, perhaps belying a common mechanism. Twitch force increased and then returned to resting levels during fatigue, reflecting a slowing of activation kinetics and a decline in cross-bridge number and force. Net cyclic work fatigued to the degree of becoming negative when tetanic force had declined only 15%. Steady-state isokinetic force (i.e., shortening work) declined by 75%, while cyclic shortening work declined only 30%. Slowed activation kinetics were again responsible, augmenting cyclic shortening work but greatly augmenting lengthening work (reducing net work). Steady-state measures can thus seriously mislead regarding muscle performance in an animal during fatigue.
The M2 muscarinic receptor mediates in vitro bladder contractions from patients with neurogenic bladder dysfunction
Authors: Pontari Michel A. , Braverman Alan S. , Ruggieri Michael R.
Published: April 2004

Bladder muscle specimens from seven patients with neurogenic bladder dysfunction were analyzed to determine whether the muscarinic receptor subtype mediating contraction shifts from M3 to the M2 subtype as found in the denervated, hypertrophied rat bladder. Seven bladder specimens were analyzed from six female and one male patients. Six of the patients had traumatic cervical spinal cord injuries (C4-C7), and the other patient had an L1 congenital myelomeningocele. This was compared with results from bladder specimens obtained from eight organ transplant donors. The affinities of three subtype-selective muscarinic receptor antagonists for inhibition of carbachol-induced contractions were determined. The affinity of the M3 selective antagonists darifenacin or p-fluoro-hexahydrosiladifenadol (p-F-HHSiD) was determined in six of the seven spinal injury patient specimens. The affinity was consistent with M2-mediated contractions in four of these six specimens, intermediate between M2 and M3 in one specimen, and within the M3 range in one specimen. The other specimen, tested only with the M2 selective antagonist methoctramine, showed an M3 affinity. In the organ donors, the affinity of p-F-HHSiD was within the M2 range for six of seven specimens, whereas the affinity of darifenacin was within the M3 range for five of six and intermediate between M2 and M3 for the other specimen tested. The affinity of methoctramine in both organ donor specimens tested was within the M3 range. Whereas normal detrusor contractions are mediated by the M3 receptor subtype, in patients with neurogenic bladder dysfunction as well as certain organ transplant donors, contractions can be mediated by the M2 muscarinic receptor subtype.
Hypoxic suppression ofE. coli-induced NF-κB and AP-1 transactivation by oxyradical signaling
Authors: Matuschak George M. , Lechner Andrew J. , Chen Zhoumou , Todi Subhash , Doyle Timothy M. , Loftis Laura L.
Published: April 2004

Transactivation of the DNA-binding proteins nuclear factor-κB (NF-κB) and activator protein (AP)-1 by de novo oxyradical generation is a stereotypic redox-sensitive process during hypoxic stress of the liver. Systemic trauma is associated with splanchnic hypoxia-reoxygenation (H/R) followed by intraportal gram-negative bacteremia, which collectively have been implicated in posttraumatic liver dysfunction and multiple organ damage. We hypothesized that hypoxic stress of the liver before stimulation by Escherichia coli serotype O55:B5 (EC) amplifies oxyradical-mediated transactivation of NF-κB and AP-1 as well as cytokine production compared with noninfectious H/R or gram-negative sepsis without prior hypoxia. Livers from Sprague-Dawley rats underwent perfusion for 180 min with or without 0.5 h of hypoxia (perfusate Po2, 40 ± 5 mmHg) followed by reoxygenation and infection with 109EC or 0.9% NaCl infusion. In H/R + EC livers, nuclear translocation of NF-κB and AP-1 was unexpectedly reduced in gel shift assays vs. normoxic EC controls, as were perfusate TNF-α and IL-1β levels. Preceding hypoxic stress paradoxically increased postbacteremic reduced-to-oxidized glutathione ratios plus nuclear localization of IκBα and phospho-IκBα, but not JunB/FosB profiles. Notably, xanthine oxidase inhibition increased transactivation as well as cytokine production in H/R + EC livers. Thus brief hypoxic stress of the liver before intraportal gram-negative bacteremia potently suppresses activation of canonical redox-sensitive transcription factors and production of inflammatory cytokines by mechanisms including xanthine oxidase-induced oxyradicals functioning in an anti-inflammatory signaling role. These results suggest a novel multifunctionality of oxyradicals in decoupling hepatic transcriptional activity and cytokine biosynthesis early in the posttraumatic milieu.
ANG II-induced downregulation of RBF after a prolonged reduction of renal perfusion pressure is due to pre- and postglomerular constriction
Authors: Sorensen Charlotte Mehlin , Leyssac Paul Peter , Salomonsson Max , Skott Ole , Holstein-Rathlou Niels-Henrik
Published: April 2004

Previous experiments from our laboratory showed that longer-lasting reductions in renal perfusion pressure (RPP) are associated with a gradual decrease in renal blood flow (RBF) that can be abolished by clamping plasma ANG II concentration ([ANG II]). The aim of the present study was to investigate the mechanisms behind the RBF downregulation in halothane-anesthetized Sprague-Dawley rats during a 30-min reduction in RPP to 88 mmHg. During the 30 min of reduced RPP we also measured glomerular filtration rate (GFR), proximal tubular pressure (Pprox), and proximal tubular flow rate (QLP). Early distal tubular fluid conductivity was measured as an estimate of early distal [NaCl] ([NaCl]ED), and changes in plasma renin concentration (PRC) over time were measured. During 30 min of reduced RPP, RBF decreased gradually from 6.5 ± 0.3 to 6.0 ± 0.3 ml/min after 5 min (NS) to 5.2 ± 0.2 ml/min after 30 min ( P < 0.05). This decrease occurred in parallel with a gradual increase in PRC from 38.2 ± 11.0 × 10-5to 87.1 ± 25.1 × 10-5Goldblatt units (GU)/ml after 5 min ( P < 0.05) to 158.5 ± 42.9 × 10-5GU/ml after 30 min ( P < 0.01). GFR, Pprox, and [NaCl]EDall decreased significantly after 5 min and remained low. Estimates of pre- and postglomerular resistances showed that the autoregulatory mechanisms initially dilated preglomerular vessels to maintain RBF and GFR. However, after 30 min of reduced RPP, both pre- and postglomerular resistance had increased. We conclude that the decrease in RBF over time is caused by increases in both pre- and postglomerular resistance due to rising plasma renin and ANG II concentrations.
Developmental regulation of prostaglandin E2synthase in porcine ductus arteriosus
Authors: Bouayad Asmàa , Fouron Jean-Claude , Hou Xin , Beauchamp Martin , Quiniou Christiane , Abran Daniel , Peri Krishna , Clyman Ronald I. , Varma Daya R. , Chemtob Sylvain
Published: April 2004

The synthesis of PGE2, the major vasodilator prostanoid of the ductus arteriosus (DA), is catalyzed by PGE2synthases (PGES). The factors implicated in increased PGE2synthesis in the perinatal DA are not known. We studied the developmental changes of PGES along with that of cyclooxygenase (COX)-2 and cytosolic phospholipase A2(cPLA2) in the DA of fetal (75-90% gestation) and immediately postnatal newborn (NB) piglets. Levels of microsomal PGES (mPGES), COX-2, and PGE2in the DA of NB were ∼7-fold higher than in fetus; activities of cytosolic PGES (cPGES) and cPLA2in DA of the fetus and NB did not differ. Because platelet-activating factor (PAF) could regulate COX-2 expression, the former was measured and found to be more abundant in the DA of the NB than of fetus. PAF elicited an increase in mPGES, COX-2, and PGE2in fetal DA to levels approaching those of the NB; cPGES, cPLA2, and COX-1 were unaffected. In perinatal NB DA, PAF receptor antagonists BN-52021 and THG-315 reduced mPGES, COX-2, and PGE2levels and were associated with increased DA tone. It is concluded that PAF contributes in regulating DA tone by governing mPGES, COX-2, and ensuing PGE2levels in the perinate.
CytochromeP-450 metabolites in endothelin-stimulated cardiac hormone secretion
Authors: Lee Sook Jeong , Landon Carol S. , Nazian Stanley J. , Dietz John R.
Published: April 2004

We examined the role of cytochrome P-450-arachidonate (CYP450-AA) metabolites in endothelin-1 (ET-1)-stimulated atrial natriuretic peptide (ANP) and pro-ANP-(1-30) secretion from the heart. 17-Octadecynoic acid (17-ODYA, 10-5M) significantly inhibited ANP secretion stimulated by ET-1 (10-8M) in the isolated perfused rat atria and inhibited pro-ANP-(1-30) secretion stimulated by ET-1 (10-8M) or 20-hydroxyeicosatetraenoic acid in cultured neonatal rat ventricular myocytes (NRVM). In NRVM, 17-ODYA significantly ( P < 0.05) increased secretion of cAMP but had no significant effect on the secretion of cGMP from NRVM. Staurosporine, an inhibitor of protein kinase C, completely blocked the inhibitory action of 17-ODYA, whereas a protein kinase A inhibitor, H-89 (5 × 10-5M), did not significantly attenuate the effects of 17-ODYA. The results show that the inhibitory action of 17-ODYA on ET-1-augmented ANP secretion is mediated through cAMP and suggest that CYP450-AA may play an important role in ET-1-induced cardiac hormone secretion.
Insulin-dependent diabetes impairs the inflammatory response and delays angiogenesis following Achilles tendon injury
Authors: Chbinou Nadia , Frenette Jérôme
Published: April 2004

Although impaired wound healing associated with type 1 diabetes mellitus has been well studied in skin tissue, the influence of this metabolic disorder on tendon healing and recovery has not been extensively investigated. Because tendons are known to have limited repair potential, we studied the tendon-healing process by using a diabetic rat tendonitis model. We tested the hypothesis that diabetes influences the inflammatory response, cell proliferation, and angiogenesis in injured Achilles tendons. Diabetes was induced by injecting streptozotocin at 45 mg/kg body wt. Non-diabetic rats as well as diabetic and insulin-treated diabetic animals were then injected with collagenase. The accumulation of inflammatory cells was quantified in transversal sections of Achilles tendon by using immunohistochemical staining at days 0, 1, 3, 7, 14, and 28 posttrauma. The number of proliferative cells and the extent of neovascularization was also quantified in the paratenon and the core of the tendon at days 0, 3, 7, 14, and 28 posttrauma. Relative to nondiabetic and insulin-treated diabetic animals, the numbers of accumulated neutrophils and ED1+and ED2+macrophages in diabetic rats decreased by 46, 43, and 52%, respectively, in the first 3 days after injury compared with levels in nondiabetic and insulin-treated diabetic animals. The density of newly formed blood vessels decreased by 35 and 29% in the paratenon and the core of tendon, respectively, at days 3 and 7 after injury. Lastly, the concentration of proliferative cells decreased by 34% in the paratenon at day 7 posttrauma in injured tendons from diabetic rats relative to nondiabetic rats. These results indicate that alterations in inflammatory, angiogenic, and proliferative processes occurred in the diabetic state that might eventually perturb tendon healing and remodeling.
Human cerebrovascular and autonomic rhythms during vestibular activation
Authors: Cooke William H. , Carter Jason R. , Kuusela Tom A.
Published: April 2004

Otolith activation increases muscle sympathetic nerve activity (MSNA), and MSNA activation may alter associations among autonomic oscillators, including those modulating cerebral hemodynamics. The purpose of this study was to determine the influence of vestibulosympathetic activation on cerebral and autonomic rhythms. We recorded the ECG, finger arterial pressure, end-tidal CO2, respiration, cerebral blood flow velocity, and MSNA in eight subjects. Subjects breathed at 0.25 Hz for 5 min in the prone and head-down positions. We analyzed data in time and frequency domains and performed cross-spectral analyses to determine coherence and transfer function magnitude. Head-down rotation increased MSNA from 7 ± 1.3 to 12 ± 1.5 bursts/min ( P = 0.001) but did not affect R-R intervals, arterial pressures, mean cerebral blood flow velocities ( Vmean), or their power spectra. Vestibular activation with head-down rotation had no effect on mean arterial pressure and Vmean transfer function magnitude. The two new findings from this study are 1) head-down rotation independently activates the sympathetic nervous system with no effect on parasympathetic activity or Vmean; and 2) frequency-dependent associations between arterial pressures and Vmean are independent of vestibular activation. These findings support the concept that vestibular-autonomic interactions independently and redundantly serve to maintain steady-state hemodynamics.
Secretin depolarizes nucleus tractus solitarius neurons through activation of a nonselective cationic conductance
Authors: Yang Bo , Goulet Martin , Boismenu Richard , Ferguson Alastair V.
Published: April 2004

The recent suggestion that secretin may be useful in treating autism and schizophrenia has begun to focus attention on the mechanisms underlying this gut-brain peptide's actions in the central nervous system (CNS). In vitro autoradiographic localization of125I-secretin binding sites in rat brain shows the highest binding density in the nucleus tractus solitarius (NTS). Recent evidence suggests that intravenous infusion of secretin causes fos activation in NTS, a relay station playing important roles in the central regulation of autonomic functions. In this study, whole cell patch-clamp recordings were obtained from 127 NTS neurons in rat medullary slices. The mean resting membrane potential of these neurons was -54.7 ± 0.3 mV, the mean input resistance was 3.7 ± 0.2 GΩ, and the action potential amplitude of these neurons was always >70 mV. Current-clamp studies showed that bath application of secretin depolarized the majority (80.8%; 42/52) of NTS neurons tested, whereas the remaining cells were either unaffected (17.3%; 9/52) or hyperpolarized (1.9%; 1/52). These depolarizing effects were maintained in the presence of 5 μM TTX and found to be concentration dependent from 10-12to 10-7M. Using voltage-clamp techniques, we also identified modulatory actions of secretin on specific ion channels. Our results demonstrate that while secretin is without effect on net whole cell potassium currents, it activates a nonselective cationic conductance (NSCC). These results show that NTS neurons are activated by secretin as a consequence of activation of a NSCC and support the emerging view that secretin can act as a neuropeptide within the CNS.
Phenotypical evidence for a gender difference in cardiac norepinephrine transporter function
Authors: Schroeder Christoph , Adams Frauke , Boschmann Michael , Tank Jens , Haertter Sebastian , Diedrich Andre , Biaggioni Italo , Luft Friedrich C. , Jordan Jens
Published: April 2004

Norepinephrine transporter (NET) function has a central role in the regulation of synaptic norepinephrine concentrations. Clinical observations in orthostatic intolerance patients suggest a gender difference in NET function. We compared the cardiovascular response to selective NET inhibition with reboxetine between 12 healthy men and 12 age-matched women. Finger blood pressure, brachial blood pressure, and heart rate were measured. The subjects underwent cardiovascular autonomic reflex testing and a graded head-up tilt test. In a separate study, we applied incremental concentrations of tyramine and isoproterenol through subcutaneous microdialysis catheters in eight men and in eight women. NET inhibition elicited a threefold greater increase in supine blood pressure in men than women ( P < 0.05). The pressor response was driven by an increased cardiac output. The orthostatic heart rate increase during NET inhibition was greater in men than women (56 ± 5 beats/min in men, 42 ± 4 beats/min in women, P < 0.001). In contrast, NET inhibition resulted in a similar suppression in the cold pressor and handgrip response, low-frequency blood pressure oscillations, and venous norepinephrine in the supine position. Men and women were similarly sensitive to the lipolytic effect of isoproterenol and tyramine. We conclude that NET inhibition results in more pronounced changes in cardiac regulation in men than women. Our observations suggest that the NET contribution to cardiac norepinephrine turnover may be decreased in women. The gender difference in NET function may not be expressed in tissues that are less NET dependent than the heart.
Obesity and hypertension: two epidemics or one?
Authors: Davy Kevin P. , Hall John E.
Published: April 2004

The association between obesity and hypertension is well documented, although the exact nature of this relation remains unclear. Sympathetic nervous and renin-angiotensin-aldosterone system activation appear to play an important role in the sodium and water retention, rightward shift in the pressure-natriuresis, and blood pressure elevation observed in obese individuals. Visceral obesity and the ectopic deposition of adipose tissue may be important in the activation of these systems and in the target organ damage that ensues. Weight loss is critical in the effective management of obesity hypertension and the accompanying target organ damage, although recidivism rates are high. However, prevention of weight gain should be the major priority for combating hypertension and its consequences in the future. The present review will provide an overview of our understanding of the etiology, pathophysiology, and treatment of obesity hypertension. Our focus is on the state of knowledge in humans. The potential role of abdominal obesity is considered throughout our review. We refer to relevant animal literature for supportive evidence and where little or no data in humans are available.
Seasonal and state-dependent changes of eIF4E and 4E-BP1 during mammalian hibernation: implications for the control of translation during torpor
Authors: van Breukelen Frank , Sonenberg Nahum , Martin Sandra L.
Published: April 2004

Mammalian hibernation involves cessation of energetically costly processes typical of homeostatic regulation including protein synthesis. To further elucidate the mechanisms employed in depressing translation, we surveyed key eukaryotic initiation factors [eIF2, eIF4B, eIF4E, eIF4GI and -II, and 4E-binding protein-1 (4E-BP1), -2, and -3] for their availability and phosphorylation status in the livers of golden-mantled ground squirrels (Spermophilus lateralis) across the hibernation cycle. Western blot analyses indicated only one significant locus for regulation of translational initiation in ground squirrel liver: control of eIF4E. We found seasonal variation in a potent regulator of eIF4E activity, 4E-BP1. Summer squirrels lack 4E-BP1 and apparently control eIF4E activity through direct phosphorylation. In winter, eIF4E is regulated through binding with 4E-BP1. During the euthermic periods that separate bouts of torpor (interbout arousal), 4E-BP1 is hyperphosphorylated to promote initiation. However, during torpor, 4E-BP1 is hypophosphorylated and cap-dependent initiation of translation is restricted. The regulation of cap-dependent initiation of translation may allow for the differential expression of proteins directed toward enhancing survivorship.
Regulation and identity of intracellular calcium stores involved in membrane cross talk in the early distal tubule of the frog kidney
Authors: Fowler Mark R. , Cooper Gordon J. , Hunter Malcolm
Published: April 2004

The early distal tubule (EDT) of the frog nephron, similar to the thick ascending limb in mammals, mediates the transepithelial absorption of NaCl. The continued absorption of NaCl in the face of varying Na+load is maintained by coordination of the activity of ion-transporting proteins in the apical and basolateral membranes, so-called pump-leak coupling. Previous studies identified intracellular Ca2+, originating from an intracellular Ca2+store, as playing a key role in pump-leak coupling in the EDT (Cooper GJ, Fowler MR, and Hunter M. Pflügers Arch 442: 243–247, 2001). The purpose of the experiments described in this paper was to identify the intracellular Ca2+storage pools in the renal diluting segment. Store Ca2+movements were monitored by the fluorescence of mag-fura 2 in permeabilized segments of frog EDTs. The presence of both ATP and Ca2+was required to maintain store Ca2+content. Removal of either of these substrates resulted in a passive leak of Ca2+from the stores. The uptake of Ca2+into the store was sensitive to the SERCA inhibitor 2,5-di( tert-butyl) hydroquinone, whereas Ca2+release from the store was stimulated by IP3but not cADPR. Store Ca2+was insensitive to the mitochondrial ATP synthase inhibitor oligomycin, and, under conditions that energized Δψm, the complex 1 inhibitor rotenone and the protonophore FCCP. Ionomycin was able to mobilize store Ca2+following exposure to IP3. These results suggest that the endoplasmic reticulum is a dominant Ca2+store in the frog EDT. A second pool, sensitive to ionomycin but not IP3, may overlap with the IP3-sensitve pool. The data also rule out any contribution by mitochondria to EDT Ca2+cycling.
Constrained sessile drop as a new configuration to measure low surface tension in lung surfactant systems
Authors: Yu Laura M. Y. , Lu James J. , Chan Yawen W. , Ng Amy , Zhang Ling , Hoorfar Mina , Policova Zdenka , Grundke Karina , Neumann A. Wilhelm
Published: April 2004

Existing methodology for surface tension measurements based on drop shapes suffers from the shortcoming that it is not capable to function at very low surface tension if the liquid dispersion is opaque, such as therapeutic lung surfactants at clinically relevant concentrations. The novel configuration proposed here removes the two big restrictions, i.e., the film leakage problem that is encountered with such methods as the pulsating bubble surfactometer as well as the pendant drop arrangement, and the problem of the opaqueness of the liquid, as in the original captive bubble arrangement. A sharp knife edge is the key design feature in the constrained sessile drop that avoids film leakage at low surface tension. The use of the constrained sessile drop configuration in conjunction with axisymmetric drop shape analysis to measure surface tension allows complete automation of the setup. Dynamic studies with lung surfactant can be performed readily by changing the volume of a sessile drop, and thus the surface area, by means of a motor-driven syringe. To illustrate the validity of using this configuration, experiments were performed using an exogenous lung surfactant preparation, bovine lipid extract surfactant (BLES) at 5.0 mg/ml. A comparison of results obtained for BLES at low concentration between the constrained sessile drop and captive bubble arrangement shows excellent agreement between the two approaches. When the surface area of the BLES film (0.5 mg/ml) was compressed by about the same amount in both systems, the minimum surface tensions attained were identical within the 95% confidence limits.
Effect of endurance exercise on the Ca2+pumps from transverse tubule and sarcoplasmic reticulum of rabbit skeletal muscle
Authors: Becker Viola , González-Serratos Hugo , Álvarez Rocío , Bäermann Michael , Irles Claudine , Ortega Alicia
Published: April 2004

The sarcoplasmic reticulum (SR) Ca2+pump is the main homeostatic regulatory mechanism in fast skeletal muscle that maintains intracellular Ca2+concentration ([Ca2+]i) at the nanomolar level at rest. The transverse tubule (TT) Ca2+pump transports cytosolic Ca2+to the extracellular space. During prolonged muscular activity, [Ca2+]imay increase. TT and SR isolated microsomal vesicles were highly purified, and the purity was checked by immunoblotting. The present study shows the effects of endurance exercise on the activities and structures of the TT and SR Ca2+pumps of fast skeletal muscle from rabbit at rest. The Ca2+pump activity increased manifolds in TT but did not change in SR. The protein denaturalization profiles obtained by differential scanning calorimetry showed 1) a shift in the transition temperature and an increase in the enthalpy of the TT Ca2+pump and 2) a significant change in the transition temperature of the SR Ca2+pump Ca2+-binding domain. We conclude that the TT Ca2+pump activity was upgraded in association with structural changes to handle the changes in [Ca2+]iand TT lumen Ca2+concentration that occur during endurance exercise.
Modulation of Dural Nociceptor Mechanosensitivity by the Nitric Oxide-Cyclic GMP Signaling Cascade
Authors: Levy Dan , Strassman Andrew M.
Published: April 2004

The role of the nitric oxide (NO)-cGMP signaling cascade in modulation of peripheral nociception is controversial. Although behavioral studies have suggested both pro- and anti-nociceptive effects, little is known about the direct action of this signaling cascade on primary afferent nociceptive neurons that mediate these behaviors. Here, using single-unit recordings, we examined the direct effect of NO-cGMP signaling on spontaneous activity and mechanical responses of nociceptive afferents that innervate the dura mater. We found that the NO donor sodium nitroprusside (SNP), when applied topically to the neuronal receptive field, induced both sensitization and inhibition of the mechanical responses, albeit in different populations of neurons, which could be distinguished based on their baseline mechanical thresholds. SNP, however, did not change the level of spontaneous activity. Administration of the cGMP analogue 8-pCPT-cGMP mimicked only the inhibitory effect. When SNP was co-applied with either an inhibitor of guanylyl cyclase or a cGMP blocker, sensitization never occurred, and the inhibitory effect of SNP could also be blocked. Our findings suggest that NO can either increase or decrease the mechanical responsiveness of nociceptors and that its action might depend, in part, on the baseline level of neuronal excitability. Our results also implicate cGMP in mediating the inhibitory effect of NO.
Nonneuronal Origin of CO2-Related DC EEG Shifts: An In Vivo Study in the Cat
Authors: Nita Dragos A. , Vanhatalo Sampsa , Lafortune Frantz-Daniel , Voipio Juha , Kaila Kai , Amzica Florin
Published: April 2004

We studied the mechanisms underlying CO2-dependent DC potential shifts, using epicranial, epidural, epicortical, intraventricular, and intraparenchymal (intraneuronal, intraglial, and field) recordings in ketamine–xylazine-anesthetized cats. DC shifts were elicited by changes in artificial ventilation, causing end-tidal CO2variations within a 2–5% range. Hypercapnia was consistently associated with negative scalp DC shifts (average shift −284.4 μV/CO2%, range −216 to −324 μV/CO2%), whereas hypocapnia induced positive scalp DC shifts (average shift 307.8 μV/CO2%, range 234 to 342 μV/CO2%) in all electrodes referenced versus the nasium bone. The former condition markedly increased intracranial pressure (ICP), whereas the latter only slightly reduced ICP. Breakdown of the blood–brain barrier (BBB) resulted in a positive DC shift and drastically reduced subsequent DC responses to hypo-/hypercapnia. Thiopental and isoflurane also elicited a dose-dependent positive DC shift and, at higher doses, hypo-/hypercapnia responses displayed reverted polarity. As to the possible implication of neurons in the production of DC shifts, no polarity reversal was recorded between scalp, various intracortical layers, and deep brain structures. Moreover, the membrane potential of neurons and glia did not show either significant or systematic variations in association with the scalp-recorded CO2-dependent DC shifts. Pathological activities of neurons during spike-wave seizures produced DC shifts of significantly smaller amplitude than those generated by hyper-/hypocapnia. DC shifts were still elicited when neuronal circuits were silent during anesthesia-induced burst-suppression patterns. We suggest that potentials generated by the BBB are the major source of epicortical/cranial DC shifts recorded under conditions affecting brain pH and/or cerebral blood flow.
Inter-Joint Coupling Strategy During Adaptation to Novel Viscous Loads in Human Arm Movement
Authors: Debicki D. B. , Gribble P. L.
Published: April 2004

When arm movements are perturbed by a load, how does the nervous system adjust control signals to reduce error? While it has been shown that the nervous system is capable of compensating for the effects of limb dynamics and external forces, the strategies used to adapt to novel loads are not well understood. We used a robotic exoskeleton [kinesiological instrument for normal and altered reaching movements (KINARM)] to apply novel loads to the arm during single-joint elbow flexions in the horizontal plane (shoulder rotation was allowed). Loads varied in magnitude with the instantaneous velocity of elbow flexion, and were applied to the shoulder in experiment 1 (interaction loads) and the elbow in experiment 2 (direct loads). Initial exposure to both interaction and direct loads resulted in perturbations at both joints, even though the load was applied to only a single joint. Subjects tended to correct for the kinematics of the elbow joint while perturbations at the shoulder persisted. Electromyograms (EMGs) and computed muscle torque showed that subjects modified muscle activity at the elbow to reduce elbow positional deviations. Shoulder muscle activity was also modified; however, these changes were always in the same direction as those at the elbow. Current models of motor control based on inverse-dynamics calculations and force-control, as well as models based on positional control, predict an uncoupling of shoulder and elbow muscle torques for adaptation to these loads. In contrast, subjects in this study adopted a simple strategy of modulating the natural coupling that exists between elbow and shoulder muscle torque during single-joint elbow movements.
Sodium Currents in Subthalamic Nucleus Neurons From Nav1.6-Null Mice
Authors: Do Michael Tri H. , Bean Bruce P.
Published: April 2004

In some central neurons, including cerebellar Purkinje neurons and subthalamic nucleus (STN) neurons, TTX-sensitive sodium channels show unusual gating behavior whereby some channels open transiently during recovery from inactivation. This “resurgent” sodium current is effectively activated immediately after action potential-like waveforms. Earlier work using Purkinje neurons suggested that the great majority of resurgent current originates from Nav1.6 sodium channels. Here we used a mouse mutant lacking Nav1.6 to explore the contribution of these channels to resurgent, transient, and persistent components of TTX-sensitive sodium current in STN neurons. The resurgent current of STN neurons from Nav1.6−/− mice was reduced by 63% relative to wild-type littermates, a less dramatic reduction than that observed in Purkinje neurons recorded under identical conditions. The transient and persistent currents of Nav1.6−/− STN neurons were reduced by ∼40 and 55%, respectively. The resurgent current present in Nav1.6−/− null STN neurons was similar in voltage dependence to that in wild-type STN and Purkinje neurons, differing only in having somewhat slower decay kinetics. These results show that sodium channels other than Nav1.6 can make resurgent sodium current much like that from Nav1.6 channels.
Neuronal Activity in the Rodent Dorsal Striatum in Sequential Navigation: Separation of Spatial and Reward Responses on the Multiple T Task
Authors: Schmitzer-Torbert Neil , Redish A. David
Published: April 2004

The striatum plays an important role in “habitual” learning and memory and has been hypothesized to implement a reinforcement-learning algorithm to select actions to perform given the current sensory input. Many experimental approaches to striatal activity have made use of temporally structured tasks, which imply that the striatal representation is temporal. To test this assumption, we recorded neurons in the dorsal striatum of rats running a sequential navigation task: the multiple T maze. Rats navigated a sequence of four T maze turns to receive food rewards delivered in two locations. The responses of neurons that fired phasically were examined. Task-responsive phasic neurons were active as rats ran on the maze (maze-responsive) or during reward receipt (reward-responsive). Neither mazenor reward-responsive neurons encoded simple motor commands: maze-responses were not well correlated with the shape of the rat's path and most reward-responsive neurons did not fire at similar rates at both food-delivery sites. Maze-responsive neurons were active at one or more locations on the maze, but these responses did not cluster at spatial landmarks such as turns. Across sessions the activity of maze-responsive neurons was highly correlated when rats ran the same maze. Maze-responses encoded the location of the rat on the maze and imply a spatial representation in the striatum in a task with prominent spatial demands. Maze-responsive and reward-responsive neurons were two separate populations, suggesting a divergence in striatal information processing of navigation and reward.
Temporal Properties of Responses to Broadband Noise in the Auditory Nerve
Authors: Louage Dries H. G. , van der Heijden Marcel , Joris Philip X.
Published: April 2004

Temporal information in the responses of auditory neurons to sustained sounds has been studied mostly with periodic stimuli, using measures that are based on Fourier analysis. Less information is available on temporal aspects of responses to nonperiodic wideband sounds. We recorded responses to a reference Gaussian noise and its polarity-inverted version in the auditory nerve of barbiturate-anesthetized cats and used shuffled autocorrelograms (SACs) to quantify spike timing. Two metrics were extracted from the central peak of autocorrelograms: the peak-height and the width at halfheight. Temporal information related to stimulus fine-structure was isolated from that to envelope by subtracting or adding responses to the reference and inverted noise. Peak-height and halfwidth generally behaved as expected from the existing body of data on phase-locking to pure tones and sinusoidally amplitude-modulated tones but showed some surprises as well. Compared with synchronization to low-frequency tones, SACs reveal large differences in temporal behavior between the different classes of nerve fibers (based on spontaneous rate) as well as a strong dependence on characteristic frequency (CF) throughout the phase-locking range. SACs also reveal a larger temporal consistency (i.e., tendency to discharge at the same point in time on repeated presentation of the same stimulus) in the responses to the stochastic noise stimulus than in the responses to periodic tones. Responses at high CFs reflect envelope phase-locking and are consistent with previous reports using sinusoidal AM. We conclude that the combined use of broadband noise and SAC analysis allow a more general characterization of temporal behavior than periodic stimuli and Fourier analysis.
Responses and Afferent Pathways of C1–C2 Spinal Neurons to Cervical and Thoracic Esophageal Stimulation in Rats
Authors: Qin Chao , Chandler Margaret J. , Jou Chuanchau J. , Foreman Robert D.
Published: April 2004

Because vagal and sympathetic inputs activate upper cervical spinal neurons, we hypothesized that stimulation of the esophagus would activate C1–C2 neurons. This study examined responses of C1–C2 spinal neurons to cervical and thoracic esophageal distension (CED, TED) and afferent pathways for CED and TED inputs to C1–C2 spinal neurons. Extracellular potentials of single C1–C2 spinal neurons were recorded in pentobarbital-anesthetized male rats. Graded CED or TED was produced by water inflation (0.1–0.5 ml) of a latex balloon. CED changed activity of 48/219 (22%) neurons; 34 were excited (E), 12 were inhibited (I), and 2 were E-I. CED elicited responses for 18/18 neurons tested after ipsilateral cervical vagotomy, for 12/14 neurons tested after bilateral vagotomy and for 9/11 neurons tested after bilateral vagotomy and C6–C7 spinal cord transection. TED changed activity of 31/190 (16%) neurons (28E, 3 I). Ipsilateral cervical vagotomy abolished TED-evoked responses of 5/12 neurons. Bilateral vagotomy eliminated responses of 2/4 neurons tested, and C6–C7 spinal transection plus bilateral vagotomy eliminated responses of 2/2 neurons. Thus inputs from CED to C1–C2 neurons most likely entered upper cervical dorsal roots, whereas inputs from TED were dependent on vagal pathways and/or sympathetic afferent pathways that entered the thoracic dorsal roots. These results supported a concept that C1–C2 spinal neurons play a role in integrating visceral information from cervical and thoracic esophagus.
Characterization of Neocortical Principal Cells and Interneurons by Network Interactions and Extracellular Features
Authors: Barthó Peter , Hirase Hajime , Monconduit Lenaïc , Zugaro Michael , Harris Kenneth D. , Buzsáki György
Published: April 2004

Most neuronal interactions in the cortex occur within local circuits. Because principal cells and GABAergic interneurons contribute differently to cortical operations, their experimental identification and separation is of utmost important. We used 64-site two-dimensional silicon probes for high-density recording of local neurons in layer 5 of the somatosensory and prefrontal cortices of the rat. Multiple-site monitoring of units allowed for the determination of their two-dimensional spatial position in the brain. Of the ∼60,000 cell pairs recorded, 0.2% showed robust short-term interactions. Units with significant, short-latency (<3 ms) peaks following their action potentials in their cross-correlograms were characterized as putative excitatory (pyramidal) cells. Units with significant suppression of spiking of their partners were regarded as putative GABAergic interneurons. A portion of the putative interneurons was reciprocally connected with pyramidal cells. Neurons physiologically identified as inhibitory and excitatory cells were used as templates for classification of all recorded neurons. Of the several parameters tested, the duration of the unfiltered (1 Hz to 5 kHz) spike provided the most reliable clustering of the population. High-density parallel recordings of neuronal activity, determination of their physical location and their classification into pyramidal and interneuron classes provide the necessary tools for local circuit analysis.
Low-Probability Transmission of Neocortical and Entorhinal Impulses Through the Perirhinal Cortex
Authors: Pelletier Joe Guillaume , Apergis John , Paré Denis
Published: April 2004

One model of episodic memory posits that during slow-wave sleep (SWS), the synchronized discharges of hippocampal neurons in relation to sharp waves “replay” activity patterns that occurred during the waking state, facilitating synaptic plasticity in the neocortex. Although evidence of replay was found in the hippocampus in relation to sharp waves, it was never shown that this activity reached the neocortex. Instead, it was assumed that the rhinal cortices faithfully transmit information from the hippocampus to the neocortex and reciprocally. Here, we tested this idea using 3 different approaches. 1) Stimulating electrodes were inserted in the entorhinal cortex and temporal neocortex and evoked unit responses were recorded in between them, in the intervening rhinal cortices. In these conditions, impulse transfer occurred with an extremely low probability, in both directions. 2) To rule out the possibility that this unreliable transmission resulted from the artificial nature of electrical stimuli, crosscorrelation analyses of spontaneous neocortical, perirhinal, and entorhinal firing were performed in unanesthetized animals during the states of waking and SWS. Again, little evidence of propagation could be obtained in either state. 3) To test the idea that propagation occurs only when large groups of neurons are activated within a narrow time window, we computed perievent histograms of neocortical, perirhinal, and entorhinal neuronal discharges around large-amplitude sharp waves. However, these synchronized entorhinal discharges also failed to propagate across the perirhinal cortex. These findings suggest that the rhinal cortices are more than a relay between the neocortex and hippocampus, but rather a gate whose properties remain to be identified.
An Integrative Neural Network for Detecting Inertial Motion and Head Orientation
Authors: Green Andrea M. , Angelaki Dora E.
Published: April 2004

The ability to navigate in the world and execute appropriate behavioral responses depends critically on the contribution of the vestibular system to the detection of motion and spatial orientation. A complicating factor is that otolith afferents equivalently encode inertial and gravitational accelerations. Recent studies have demonstrated that the brain can resolve this sensory ambiguity by combining signals from both the otoliths and semicircular canal sensors, although it remains unknown how the brain integrates these sensory contributions to perform the nonlinear vector computations required to accurately detect head movement in space. Here, we illustrate how a physiologically relevant, nonlinear integrative neural network could be used to perform the required computations for inertial motion detection along the interaural head axis. The proposed model not only can simulate recent behavioral observations, including a translational vestibuloocular reflex driven by the semicircular canals, but also accounts for several previously unexplained characteristics of central neural responses such as complex otolith–canal convergence patterns and the prevalence of dynamically processed otolith signals. A key model prediction, implied by the required computations for tilt–translation discrimination, is a coordinate transformation of canal signals from a head-fixed to a spatial reference frame. As a result, cell responses may reflect canal signal contributions that cannot be easily detected or distinguished from otolith signals. New experimental protocols are proposed to characterize these cells and identify their contributions to spatial motion estimation. The proposed theoretical framework makes an essential first link between the computations for inertial acceleration detection derived from the physical laws of motion and the neural response properties predicted in a physiologically realistic network implementation.
Gene expression profiling of potential PPARγ target genes in mouse aorta
Authors: Keen Henry L. , Ryan Michael J. , Beyer Andreas , Mathur Satya , Scheetz Todd E. , Gackle Barry D. , Faraci Frank M. , Casavant Thomas L. , Sigmund Curt D.
Published: April 2004

Diminished activity of peroxisome proliferator-activated receptor-γ (PPARγ) may play a role in the pathogenesis of hypertension and vascular dysfunction. To better understand what genes are regulated by PPARγ, an experimental data set was generated by microarray analysis, in duplicate, of pooled aortic mRNA isolated from mice treated for 21 days with a PPARγ agonist (rosiglitazone) or vehicle. Of the 12,488 probe sets present on the array (Affymetrix MG-U74Av2), 181 were differentially expressed between groups according to a statistical metric generated using Affymetrix software. A significant correlation was observed between the microarray results and real-time RT-PCR analysis of 39 of these genes. Cluster analysis revealed 3 expression patterns, 29 transcripts of moderate abundance that were decreased (−93%) to very low levels, 106 transcripts that were downregulated (−42%), and 46 transcripts that were upregulated (+70%). Functional groups that were decreased included inflammatory response (−93%, n = 6), immune response (−86%, n = 7), and cytokines (−82%, n = 7). There was an overall upregulation in the oxidoreductase activity group (+47%, n = 9). Individually, six transcripts in this group were increased (+72%), and three were decreased (−34%). Fourteen of the genes map to regions in the rat genome that have been linked to increased blood pressure, and of 142 upstream regions analyzed, sequences resembling the DNA binding site for PPARγ were identified in 101 of the differentially expressed genes.