bluuebunny/crossref_metadata_2025 huggingface dataset:
Decreased insulin-dependent glucose transport by chronic ethanol feeding is associated with dysregulation of the Cbl/TC10 pathway in rat adipocytes
Authors: Sebastian Becky M. , Nagy Laura E.
Published: August 2005

Heavy alcohol consumption is an independent risk factor for type 2 diabetes. Although the exact mechanism by which alcohol contributes to the increased risk is unknown, impaired glucose disposal is a likely target. Insulin-stimulated glucose disposal in adipocytes is regulated by two separate and independent pathways, the PI3K pathway and the Cbl/TC10 pathway. Previous studies suggest that chronic ethanol feeding impairs insulin-stimulated glucose transport in adipocytes in a PI3K-independent manner. In search of potential targets of ethanol that would affect insulin-stimulated glucose transport, we investigated the effects of 4-wk ethanol feeding to male Wistar rats on the Cbl/TC10 pathway in isolated adipocytes. Chronic ethanol feeding inhibited insulin-stimulated cCbl phosphorylation compared with pair feeding. Insulin receptor and Akt/PKB phosphorylation were not affected by ethanol feeding. Chronic ethanol exposure also impaired cCbl and TC10 recruitment to a lipid raft fraction isolated from adipocytes by detergent extraction. Furthermore, chronic ethanol feeding increased the amount of activated TC10 and filamentous actin in adipocytes at baseline and abrogated the ability of insulin to further activate TC10 or polymerize actin. These results demonstrate that the impairment in insulin-stimulated glucose transport observed in adipocytes after chronic ethanol feeding to rats is associated with a disruption of insulin-mediated Cbl/TC10 signaling and actin polymerization.
Steroidogenesis in human aldosterone-secreting adenomas and adrenal hyperplasias: effects of hypoxia in vitro
Authors: Raff Hershel , Bruder Eric D.
Published: August 2005

The synthesis of adrenal steroids requires molecular oxygen. Because arterial hypoxemia is a common clinical condition, the purpose of the present study was to examine steroidogenesis in vitro under physiological changes in O2tension (Po2) in cells from human adrenal glands with aldosterone-secreting adenomas (ASA; n = 3) or with bilateral adrenal hyperplasia causing Cushing's syndrome ( n = 4). A decrease in Po2from 150 mmHg (mild hyperoxia) to 80 mmHg had minimal effect on steroid production. A reduction to 40 mmHg (still well within the physiological range) significantly inhibited cAMP- and ACTH-stimulated aldosterone, cortisol, and dehydroepiandrosterone (DHEA) production from ASA. Furthermore, cortisol and DHEA production in cells from histologically normal tissue, adjacent to ASA and from bilateral adrenal hyperplasias, was also inhibited under a Po2of 40 mmHg. We conclude that physiological decreases in Po2to levels typical for adrenal venous Po2under mild hypoxia inhibit steroidogenesis. These studies may have implications for oxygen therapy in critically ill patients with functional adrenal insufficiency, as well as for therapeutic options in patients with adrenal neoplasms.
Mechanisms for abnormal postprandial glucose metabolism in type 2 diabetes
Authors: Woerle Hans J. , Szoke Ervin , Meyer Christian , Dostou Jean M. , Wittlin Steven D. , Gosmanov Niyaz R. , Welle Stephen L. , Gerich John E.
Published: August 2005

To assess mechanisms for postprandial hyperglycemia, we used a triple-isotope technique ([\3-3H]glucose and [14C]bicarbonate and oral [6,6-dideutero]glucose iv) and indirect calorimetry to compare components of glucose release and pathways for glucose disposal in 26 subjects with type 2 diabetes and 15 age-, weight-, and sex-matched normal volunteers after a standard meal. The results were as follows: 1) diabetic subjects had greater postprandial glucose release ( P < 0.001) because of both increased endogenous and meal-glucose release; 2) the greater endogenous glucose release ( P < 0.001) was due to increased gluconeogenesis ( P < 0.001) and glycogenolysis ( P = 0.01); 3) overall tissue glucose uptake, glycolysis, and storage were comparable in both groups ( P > 0.3); 4) glucose clearance ( P < 0.001) and oxidation ( P = 0.004) were reduced, whereas nonoxidative glycolysis was increased ( P = 0.04); and 5) net splanchnic glucose storage was reduced by ∼45% ( P = 0.008) because of increased glycogen cycling ( P = 0.03). Thus in type 2 diabetes, postprandial hyperglycemia is primarily due to increased glucose release; hyperglycemia overcomes the effects of impaired insulin secretion and sensitivity on glucose transport, but intracellular defects persist so that pathways of glucose metabolism are abnormal and glucose is shunted away from normal sites of storage (e.g., liver and muscle) into other tissues.
Coordinated alteration of hepatic gene expression in fatty acid and triglyceride synthesis in LCAT-null mice is associated with altered PUFA metabolism
Authors: Song Hui , Zhu Liping , Picardo Clive M. , Maguire Graham , Leung Vincent , Connelly Philip W. , Ng Dominic S.
Published: August 2005

Complete lecithin:cholesterol acyltransferase (LCAT) deficiency is associated with fasting hypertriglyceridemia (HTG). We recently reported that, in ldlr−/−×lcat−/−mice, fasting HTG is associated with hepatic triglyceride overproduction in association with an upregulation of the hepatic srebp1 gene and altered expression of its target genes in lipogenesis and gluconeogenesis. We further investigated the role of hepatic polyunsaturated fatty acid (PUFA) metabolism in the modulation of the lipid phenotypes. In the ldlr−/−×lcat−/−mice, using the ldlr−/−×lcat+/+littermate as controls, the hepatic level of cholesterol esters (CE) were reduced by 61.0% whereas the 20:4-CE and 22:6-CE contents were each reduced by >80%. In contrast, the hepatic levels of 20:4- and 22:6-containing phospholipid (PL) species were either unchanged or mildly elevated. Similar alterations of the hepatic PUFA in CE and in PL were also observed in the lcat−/−mice compared with their wild-type controls. In ldlr−/−×lcat−/−mice, hepatic mRNA level was markedly reduced for Δ-6 desaturase ( fads2) (70.2%) and acyl-CoA:cholesterol acyltransferase-2 ( soat2) (57.0%). A similar pattern of gene expression change was also observed in the lcat−/−single-knockout mice. In contrast, the acyl-CoA:diacylglycerol acyltransferase-2 ( dgat2) mRNA level was 1.7-fold upregulated in the double-knockout mice. In summary, we observed coordinated alterations in hepatic expression of the gene for fads2, soat2, and dgat2, resulting in a reduction in total hepatic PUFA pool and differentially in the PUFA-CE pool, in association with an increase in dgat2 gene expression for promoting triglyceride synthesis and secretion. Some of the phenotypes are not readily explained by known mechanisms and may represent novel regulatory pathways.
Regulation of muscle GLUT4 enhancer factor and myocyte enhancer factor 2 by AMP-activated protein kinase
Authors: Holmes Burton F. , Sparling David P. , Olson Ann Louise , Winder William W. , Dohm G. Lynis
Published: August 2005

As the primary glucose transporter in skeletal muscle, GLUT4 is an important factor in the regulation of blood glucose. We previously reported that stimulation of AMP-activated protein kinase (AMPK) with 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) increased GLUT4 expression in muscle. GLUT4 enhancer factor (GEF) and myocyte enhancer factor 2 (MEF2) have been shown to be important for normal GLUT4 expression because deletion or truncation of the consensus sequences on the promoter causes depressed GLUT4 mRNA expression. This led to the current study to investigate possible roles for GEF and MEF2 in mediating the activation of GLUT4 gene transcription in response to AMPK. Here we show that, although AMPK does not appear to phosphorylate MEF2A, AMPK directly phosphorylates the GEF protein in vitro. MEF2 and GEF are activated in response to AMPK as we observed translocation of both to the nucleus after AICAR treatment. Nuclear MEF2 protein content was increased after 2 h, and GEF protein was increased in the nucleus 1 and 2 h post-AICAR treatment. Last, GEF and MEF2 increase in binding to the GLUT4 promoter within 2 h after AICAR treatment. Thus we conclude that GEF and MEF2 mediate the AMPK-induced increase in transcription of skeletal muscle GLUT4. AMPK can phosphorylate GEF and in response to AICAR, GEF, and MEF2 translocate to the nucleus and have increased binding to the GLUT4 promoter.
Phosphorylation and binding of AUF1 to the 3′-untranslated region of cardiomyocyte SERCA2a mRNA
Authors: Blum Juliana L. , Samarel Allen M. , Mestril Ruben
Published: August 2005

Experimental animals and patients with cardiac hypertrophy and heart failure display abnormally slowed myocardial relaxation, which is associated with downregulation of sarco(endo)plasmic reticulum calcium ATPase 2a (SERCA2a), the cardiomyocyte sarcoplasmic reticulum Ca2+pump. We previously showed that SERCA2a downregulation can be simulated in cultured neonatal rat ventricular myocytes (NRVM) by treatment with the hypertrophic agonist phorbol myristate acetate (PMA) or by overexpression of the novel protein kinase C (PKC) isoenzymes PKCδ and PKCε. PKC activation, in turn, decreased SERCA2a promoter activity and destabilized the SERCA2a mRNA. Here we demonstrate by using an RSV β-galactosidase reporter system that a 609-nt fragment of the SERCA2a mRNA 3′-untranslated region (UTR), containing five adenylate-uridylate (AU)-rich regions, may be responsible for destabilizing the message following PMA treatment. UV cross-linking analysis demonstrated that several proteins found in the NRVM cell extracts bind to the 609-nt fragment. In addition, protein binding was transiently increased in response to PMA stimulation. 3′-UTR mRNA pull-down assays and Western blot analysis indicated that the AU binding protein AUF1 interacted with the SERCA2a 3′-UTR. AUF1 binding activity was predominantly found in the nuclear fraction, and PMA-induced AUF1 binding was associated with increased threonine phosphorylation of AUF1. These data suggest that the phosphorylation, binding, and location of AUF1 affect the posttranscriptional regulation of the SERCA2a message in NRVM.
Branching ducts similar to mesonephric ducts or ureteric buds in teratomas originating from mouse embryonic stem cells
Authors: Yamamoto Makoto , Cui Li , Johkura Kohei , Asanuma Kazuhiko , Okouchi Yasumitsu , Ogiwara Naoko , Sasaki Katsunori
Published: August 2005

Ureteric bud epithelial cells and metanephric mesenchymal cells that comprise the metanephric kidney primordium are capable of producing nephrons and collecting ducts through reciprocal inductive interaction. Once these cells are induced from pluripotent embryonic stem (ES) cells, they have the potential to become powerful tools in the regeneration of kidney tissues. In this study, we investigated these renal primordial cells and structures in mouse ES cell outgrowths and their transplants. Gene expression essential for early kidney development was examined by RT-PCR in embryoid body (EB) outgrowths and their transplants in adult mice. Histochemical detection of kidney primordial structures and gene expression analysis coupled with laser microdissection were performed in transplant tissues. RT-PCR analysis detected gene expression of Pax-2, Lim-1, c-Ret, Emx2, Sall1, WT-1, Eya-1, GDNF, and Wnt-4 in the EB outgrowths from days 6–9 of expansion onward, and also in the teratoma tissues 14 and 28 days after transplantation. Histochemical analysis 14 days after transplantation showed that some ducts were positive for Pax-2, endo A cytokeratin, kidney-specific cadherin, and Dolichos biflorus agglutinin and that dichotomous branching of these ducts had occurred. These staining patterns and morphological features are intrinsic for mesonephric ducts and ureteric buds. In long-term survival of 28 days, Pax-2-immunoreactivity disappeared in some renal primordia-like structures, indicating their differentiation. Some ducts were accompanied by mesonephric nephron-like convoluted tubules. RT-PCR analysis of those structures collected by microdissection confirmed that they expressed kidney development-related genes. In conclusion, these data suggest the potential of ES cells to produce renal primordial duct structures and provides an insight into the regeneration of kidney tissues.
Enhanced superoxide generation modulates renal function in ANG II-induced hypertensive rats
Authors: Kopkan Libor , Castillo Alexander , Navar L. Gabriel , Majid Dewan S. A.
Published: August 2005

This study was performed to examine the role of superoxide formation in the regulation of renal hemodynamic and excretory function and to assess its contribution in the pathogenesis of ANG II-dependent hypertension. Renal responses to acute intra-arterial infusion of the O2− scavenger tempol (50 μg·min−1·100 g body wt−1) with or without catalase (1,500 U·min−1·100 g−1; both native and polyethylene glycol-catalase), which reduces H2O2, were evaluated in anesthetized male Sprague-Dawley rats treated chronically with ANG II (65 ng/min) for 2 wk and compared with nontreated control rats. In ANG II-treated hypertensive rats, tempol caused increases in medullary (13 ± 2%), cortical (5 ± 2%), and total renal blood flow (9 ± 2%) without altering systemic arterial pressure. There were also increases in glomerular filtration rate (9 ± 2%), urine flow (17 ± 4%), and sodium excretion (26 ± 5%). However, tempol infusion in nontreated normotensive rats did not cause significant changes in any of these renal parameters. Coinfusion of catalase with tempol did not alter the responses observed with tempol alone, indicating that the observed renal responses to tempol in ANG II-treated rats were attributed to its O2− scavenging effects without the involvement of H2O2. Tempol infusion also significantly decreased 8-isoprostane excretion in ANG II-treated rats (39 ± 6%) without changes in H2O2 excretion. However, coinfusion of catalase reduced H2O2 excretion in both ANG II-treated (41 ± 6%) and nontreated rats (28 ± 5%). These data demonstrate that enhanced generation of O2− modulates renal hemodynamic and tubular reabsoptive function, possibly leading to sodium retention and thus contributing to the pathogenesis of ANG II-induced hypertension.
Expression and localization of N-domain ANG I-converting enzymes in mesangial cells in culture from spontaneously hypertensive rats
Authors: Camargo de Andrade Maria Claudina , Di Marco Giovana Seno , de Paulo Castro Teixeira Vicente , Mortara Renato Arruda , Sabatini Regiane Angélica , Pesquero João Bosco , Boim Miriam Aparecida , Carmona Adriana Karaoglanovic , Schor Nestor , Casarini Dulce Elena
Published: August 2005

The angiotensin-converting enzyme (ACE) profile in urine of hypertensive patients and spontaneously hypertensive rats (SHR; 90- and 65-kDa N-domain ACEs) is different from that of healthy subjects and Wistar rats (190 and 65 kDa). In addition, four ACE isoforms were purified from mesangial cells (MC) of Wistar rats in the intracellular compartment (130 and 68 kDa) and as secreted forms (130 and 60 kDa). We decided to characterize ACE forms from SHR MC in culture. Analysis of the ACE gene showed that SHR MC are able to express ACE mRNA. The concentrated medium and cell homogenate were separately purified by gel filtration and then subjected to lisinopril-Sepharose chromatography. The molecular masses of purified enzymes, 90 kDa for ACEm1A and 65 kDa for ACEm2A (secreted enzymes) and 90 kDa for ACEInth1A and 65 kDa for ACEInth2A (intracellular), were different from those of Wistar MC. The purified enzymes are Cl−dependent, inhibited by enalaprilat and captopril, and able to hydrolyze AcSDKP. Immunofluorescence and cell fractionation followed by Western blotting showed predominant immunoreaction of the 9B9 antiserum for N-domain ACE in the nuclei. The N-domain ACE was localized in the glomerulus from Wistar rats and SHR. ANG II and ANG-(1–7) were localized in the cell cytoplasm and nuclei. The 90-kDa N-domain ACE, described recently as a possible genetic marker of hypertension, was found inside the cell nuclei of SHR MC colocalized with ANG II and ANG-(1–7). The presence of ANG II in the cell nuclei could suggest an important role for this peptide in the transcription of new genes.
Bid deficiency ameliorates ischemic renal failure and delays animal death in C57BL/6 mice
Authors: Wei Qingqing , Yin Xiao-Ming , Wang Mong-Heng , Dong Zheng
Published: August 2005

Tubular cell apoptosis is involved in ischemic renal failure, but the underlying mechanism is unclear. Bid, a proapoptotic Bcl-2 family protein, may regulate the intrinsic as well as the extrinsic pathway of apoptosis. In vivo, Bid is most abundantly expressed in the kidneys. However, the role played by Bid in renal pathophysiology is unknown. Our recent work demonstrated Bid activation during renal ischemia-reperfusion. The current study has determined the role of Bid in ischemic renal injury and renal failure using Bid-deficient mice. In wild-type C57BL/6 mice, Bid was proteolytically processed into active forms during renal ischemia-reperfusion, which subsequently targeted mitochondria. This was accompanied by the development of tissue damage and severe renal failure, showing serum creatinine of 3.0 mg/dl after 48 h of reperfusion. The same ischemic insult induced acute renal failure in Bid-deficient mice, which was nonetheless less severe than the wild-type, showing 1.3 mg/dl serum creatinine. In addition, Bid deficiency attenuated tubular disruption, tubular cell apoptosis, and caspase-3 activation during 48 h of reperfusion. Compared with wild-type, animal death following renal ischemia was delayed in Bid-deficient mice. Collectively, the results suggest a role for Bid in ischemic renal injury and renal failure.
Cyclic arginine-glycine-aspartic acid peptide inhibits macrophage infiltration of the kidney and carotid artery lesions in apo-E-deficient mice
Authors: Elitok Saban , Brodsky Sergey V. , Patschan Daniel , Orlova Tatyana , Lerea Kenneth M. , Chander Praveen , Goligorsky Michael S.
Published: August 2005

Interactions of leukocytes with the vascular endothelium culminating in their diapedesis represent not only a crucial event in immune surveillance and defense but are also critically involved in the pathogenesis of many inflammatory diseases, including atherosclerosis. Our previous in vitro studies using atomic force microscopy measurement of monocyte-endothelial cell interaction have demonstrated that a cyclic arginine-glycine-aspartic acid peptide (cRGD) inhibited their adhesion through very late antigen (α4β1-integrin; VLA4)-vascular cell adhesion molecule-1 by 60% with the IC50= 100 nM. To elucidate the potential efficacy of this peptide in vivo in preventing atherogenesis, experiments were performed in apolipoprotein E (ApoE)-deficient (−/−) mice fed a Western diet and receiving chronic treatment with cRGD peptide for 2–4 wk. In addition, some animals were subjected to a temporary carotid artery ligation while receiving the above treatment. Formation of fatty streaks and infiltration of the vascular wall with macrophages were not affected by cRGD treatment. Infiltration of the carotid artery postligation was significantly reduced in the cRGD-treated animals, as was the lipid accumulation. Furthermore, cRGD-treated ApoE−/−mice exhibited significantly lesser macrophage infiltration and lipid accumulation in the kidneys, the site of the highest expression of VLA4. These data demonstrated that cRGD peptide is a potent inhibitor of monocyte/macrophage infiltration of the injured macrovasculature and of the renal microvasculature, where it results in the attenuation of lipid accumulation. Formation of fatty streaks in the aortic root was not inhibitable by this treatment.
Role of integrin α1β1in the regulation of renal medullary osmolyte concentration
Authors: Moeckel Gilbert W. , Zhang Li , Chen Xiwu , Rossini Michele , Zent Roy , Pozzi Ambra
Published: August 2005

The mechanism by which cells sense extracellular tonicity and trigger the accumulation of protective organic osmolytes is poorly understood. It has been proposed that changes in cell volume following alteration of extracellular toncity are important initiators of signaling events that lead to osmolyte accumulation. Because the extracellular matrix receptors integrins are linked to the cytoskeleton and can transduce signals that alter cell behavior, we investigated the role of these receptors in the modulation of osmolyte accumulation in the kidney medulla under different osmotic conditions. We show that integrin α1-null mice have impaired ability to accumulate organic osmolytes in the inner medulla due to altered signaling and decreased induction of osmolyte transporters or aldose reductase gene transcription. Utilizing inner medullary collecting duct cells, we demonstrate that the lack of integrin α1β1results in an impaired ability to induce the tonicity enhancer-binding protein TonEBP under hypertonic conditions. Furthermore, under the same conditions, integrin α1-null cells show prolonged ERK1/2 phosphorylation and decreased inositol uptake compared with control cells. The reduction of inositol uptake is significantly reversed by treatment with the MEK inhibitor PD-98059. Finally, integrin α1-null mice develop morphological changes of early tubular necrosis and increased apoptosis of renal medullary cells following dehydration. Together, these results show that integrin α1β1is an important mediator of the compatible osmolyte response in the medulla of the mammalian kidney.
Contribution of the basolateral isoform of the Na-K-2Cl−cotransporter (NKCC1/BSC2) to renin secretion
Authors: Castrop Hayo , Lorenz John N. , Hansen Pernille B. , Friis Ulla , Mizel Diane , Oppermann Mona , Jensen Boye L. , Briggs Josie , Skøtt Ole , Schnermann Jurgen
Published: August 2005

Acute administration of loop diuretics like furosemide leads to a stimulation of renin secretion, an effect thought to result from inhibition of Na-K-2Cl cotransporter (NKCC2)-mediated salt transport at the luminal surface of the macula densa (MD). However, loop diuretics also inhibit NKCC1, the second isoform of the Na-K-2Cl cotransporter, with similar potency. In the present study, we examined the influence of furosemide on renin secretion in NKCC1-deficient mice to distinguish between effects of the loop diuretic involving NKCC2 and, by implication, the MD pathway, and effects that might occur via inhibition of NKCC1. Baseline plasma renin concentration (PRC) was 1,212 ± 211 in NKCC1+/+ ( n = 13) and 3,851 ± 579 ng ANG I·ml−1·h−1in NKCC1−/− mice ( n = 14; P = 0.00024). Acute administration of furosemide (50 mg/kg i.p.) increased PRC significantly to 9,324 ± 1,018 ng ANG I·ml−1·h−1in NKCC1+/+ ( n = 13; P < 0.0001 compared with basal) and to 14,188 ± 2,274 ng ANG I·ml−1·h−1in NKCC1−/− mice [ n = 14; P = 0.0002 compared with basal; P = 0.034 compared with wild-type (WT) plus furosemide]. Renin mRNA expression was about threefold higher in NKCC1−/− compared with WT mice. There was considerable recruitment of granular cells to upstream regions of afferent arterioles in NKCC1−/− mice. Patch-clamp studies in single juxtaglomerular granular (JG) cells from WT mice showed an ∼10% increase in membrane capacitance during incubation with furosemide (10−4M), indicating a direct effect of the loop diuretic on renin secretion. No effect of furosemide on membrane capacitance was observed in JG cells from NKCC1-deficient mice. Furosemide (10−3M) significantly stimulated renin release from primary cultures of JG cells from WT mice, whereas no response was observed in NKCC1−/− mice. Our data suggest that a functional NKCC1 suppresses basal renin release, at least in part, through a direct effect on JG cells.
Silent Synapses in a Thalamo-Cortical Circuit Necessary for Song Learning in Zebra Finches
Authors: Bottjer Sarah W.
Published: August 2005

Developmental changes in synaptic properties may act to limit neural and behavioral plasticity associated with sensitive periods. This study characterized synaptic maturation in a glutamatergic thalamo-cortical pathway that is necessary for vocal learning in songbirds. Lesions of the projection from medial dorsolateral nucleus of the thalamus (DLM) to the cortical nucleus lateral magnocellular nucleus of the anterior nidopallium (LMAN) greatly disrupt song behavior in juvenile birds during early stages of vocal learning. However, such lesions lose the ability to disrupt vocal behavior in normal birds at 60–70 days of age, around the time that selective auditory tuning for each bird’s own song (BOS) emerges in LMAN neurons. This pattern has suggested that LMAN is involved in processing song-related information and evaluating the degree to which vocal motor output matches the tutor song to be learned. Analysis of reversed excitatory postsynaptic currents at DLM→LMAN synapses in in vitro slice preparations revealed a pronounced N-methyl-d-aspartate receptor (NMDAR)-mediated component in both juvenile and adult cells with no developmental decrease in the relative contribution of NMDARs to synaptic transmission. However, the synaptic failure rate at DLM→LMAN synapses in juvenile males during the sensitive period for song learning was significantly lower at depolarized potentials than at hyperpolarized potentials. In contrast, the failure rate at DLM→LMAN synapses did not differ at hyper- versus depolarized holding potentials in adult males that had completed the acquisition of a stereotyped song. This pattern indicates that juvenile cells have a higher incidence of silent (NMDAR-only) synapses, which are postsynaptically silent at hyperpolarized potentials due to the voltage-dependent gating of NMDARs. Thus the decreased involvement of the LMAN pathway in vocal behavior is mirrored by a decline in the incidence of silent synapses but not by changes in the relative number of NMDA and AMPA receptors at DLM→LMAN synapses. These findings suggest that a developmental decrease in silent synapses within LMAN may represent a neural correlate of behavioral plasticity during song learning.
Stimulus Induced Desynchronization of Human Auditory 40-Hz Steady-State Responses
Authors: Ross B. , Herdman A. T. , Pantev C.
Published: August 2005

The hypothesis that gamma-band oscillations are related to the representation of an environmental scene in the cerebral cortex after binding of corresponding perceptual elements is currently under discussion. One question is how the sensory system reacts to a fast change in the scene if perceptual elements are rigidly bound together. A reset of the gamma-band oscillation forced by a change in sensory input may dissolve the binding, which then would be re-established for the new sensation. We studied the reset of gamma-band oscillations on the 40-Hz auditory steady-state responses (ASSR) by means of whole-head magnetoencephalography (MEG). The rhythm of 40-Hz AM of a 500-Hz tone evoked the ASSR, and a short noise burst served as a concurrent stimulus. Possible direct interactions of the auditory stimuli were excluded by presenting the noise impulse in a different frequency channel (2,000–3,000 Hz) to the contralateral ear. The concurrent stimulus induced a considerable decrement in the amplitude of ASSR, which was localized in primary auditory cortices. This decrement lasted 250 ms and was significantly longer than the duration of the transient gamma-band response evoked by the noise burst. Thus it could not be explained by any linear superimposition of the responses. The time courses of ASSR amplitude and phase during recovery from the decrement resembled those after stimulus onset, indicating that a new ASSR was built up after the resetting stimulus. The results are discussed as reset of oscillations in human thalamocortical networks.
Neural Representation of Bitter Taste in the Nucleus of the Solitary Tract
Authors: Lemon Christian H. , Smith David V.
Published: August 2005

Based on the molecular findings that many bitter taste receptors (T2Rs) are expressed within the same receptor cells, it has been proposed that bitter taste is encoded by the activation of discrete neural elements. Here we examined how a variety of bitter stimuli are represented by neural activity in central gustatory neurons. Taste responses (spikes/s) evoked by bathing the tongue and palate with intensity-matched concentrations (in M) of 2 sugars (0.32 sucrose and 0.5 D-fructose), ethanol (40%), 4 salts (0.01 NaCl, 0.008 NaNO3, 0.01 MgCl2, and 0.05 KCl), 2 acids (0.003 HCl and 0.005 citric acid), and 10 bitter ligands (0.007 quinine-HCl, 0.015 denatonium benzoate, 0.003 l-cysteine, 0.001 nicotine, 0.005 strychnine-HCl, 0.04 tetraethylammonium chloride, 0.03 atropine-SO4, 0.005 brucine-SO4, 0.03 papaverine-HCl, and 0.009 sparteine) were recorded from 51 neurons in the nucleus of the solitary tract of anesthetized rats. Cluster analysis was used to categorize neurons into types based on responses to sucrose, NaCl, HCl, and quinine-HCl. Three groupings emerged: type S (responded optimally to sweets), type N (sodium-optimal), and type H/Q (responded robustly to bitters, acids, and salts). Multivariate analyses revealed that across-neuron patterns of response among bitter stimuli were strongly correlated. However, neural type H/Q, which was most responsive to bitter tastants, was not differentially sensitive to bitter stimuli and Na+ salts, which rats perceive as distinct. Thus central neurons most responsive to bitter substances receive significant input from receptors that mediate other tastes, indicating that bitter stimuli are not represented by activity in specifically tuned neurons.
SK Channel Regulation of Dendritic Excitability and Dendrodendritic Inhibition in the Olfactory Bulb
Authors: Maher Brady J. , Westbrook Gary L.
Published: August 2005

Small-conductance calcium-activated potassium channels (SK) regulate dendritic excitability in many neurons. In the olfactory bulb, regulation of backpropagating action potentials and dendrodendritic inhibition depend on the dendritic excitability of mitral cells. We report here that SK channel currents are present in mitral cells but are not detectable in granule cells in the olfactory bulb. In brain slices from PND 14–21 mice, long step depolarizations (100 ms) in the mitral cell soma evoked a cadmium- and apamin-sensitive outward SK current lasting several hundred milliseconds. Block of the SK current unmasked an inward N-methyl-d-aspartate (NMDA) autoreceptor current due to glutamate released from mitral cell dendrites. In low extracellular Mg2+ (100 μM), brief step depolarizations (2 ms) evoked an apamin-sensitive current that was reduced by d,l-2-amino-5-phosphonopentanoic acid. In current- clamp, block of SK channels increased action potential firing in mitral cells as well as dendrodendritic inhibition. Our results indicate that SK channels can be activated either by calcium channels or NMDA channels in mitral cell dendrites, providing a mechanism for local control of dendritic excitability.
Background Changes Delay the Perceptual Availability of Form Information
Authors: Huang Xin , Blau Seth , Paradiso Michael A.
Published: August 2005

In natural visual situations, unlike most psychophysical experiments, when a new stimulus appears in a portion of the visual field, the surrounding background changes simultaneously. In recordings from macaque V1, we found that a visual stimulus presented simultaneously with a background change evokes a response that is qualitatively different from the response to the same stimulus flashed on a static background. With the changing background, information about stimulus orientation and contrast is significantly delayed compared with the static-background situation. Our physiological results make several predictions that we test in the present paper with human psychophysical experiments. In a backward masking paradigm, a bar stimulus was either flashed onto a static background or presented simultaneously with a change in background luminance or pattern. Subjects discriminated bar orientation or detected that the scene changed before the mask. To achieve an equivalent contrast threshold for orientation discrimination, a longer stimulus-mask onset asynchrony (SOA) was needed in the changing than in the static-background condition; to match the orientation discrimination performance in the static and changing-background conditions at a fixed SOA, a higher bar contrast was needed when the background changed. Moreover, in the changing-background condition, a longer SOA was needed to discriminate bar orientation than to detect the scene change. These results suggest that orientation information is available more slowly when the background changes; orientation information is available earlier as stimulus contrast increases. The psychophysical findings are consistent with our physiological predictions. Compared with the common technique of flashing stimuli onto a static background, the changing-background paradigm may be more similar to natural vision in which saccades bring new stimuli and backgrounds into the visual field.
Gene expression analysis suggests that EBF-1 and PPARγ2 induce adipogenesis of NIH-3T3 cells with similar efficiency and kinetics
Authors: Åkerblad Peter , Månsson Robert , Lagergren Anna , Westerlund Simonetta , Basta Barbro , Lind Ulrika , Thelin Anders , Gisler Ramiro , Liberg David , Nelander Sven , Bamberg Krister , Sigvardsson Mikael
Published: August 2005

Differentiation of multipotent mesenchymal stem cells into lipid-accumulating adipocytes is a physiological process induced by transcription factors in combination with hormonal stimulation. We have used Affymetrix microarrays to compare the adipogenic differentiation pathways of NIH-3T3 fibroblasts induced to undergo in vitro differentiation by ectopic expression of early B cell factor (EBF)-1 or peroxisome proliferator-activated receptor (PPAR)γ2. These experiments revealed that commitment to the adipogenic pathway in the NIH-3T3 cells was not reflected in gene expression until 4 days after induction of differentiation. Furthermore, gene expression patterns at the earlier time points after stimulation indicated that EBF-1 and PPARγ2 induced different sets of genes, while the similarities increased upon differentiation, and that several genes linked to adipocyte differentiation were also transiently induced in the vector-transduced cells. These data suggest that the initial activation of genes associated with adipocyte development is independent of commitment to the adipogenic pathway and that EBF-1 and PPARγ2 induce adipocyte differentiation with comparable kinetics and efficiency.
Tools and strategies for physiological genomics: the Rat Genome Database
Authors: Twigger Simon N. , Pasko Dean , Nie Jeff , Shimoyama Mary , Bromberg Susan , Campbell Dan , Chen Jiali , Cruz Norberto dela , Fan Chunyu , Foote Cindy , Harris Glenn , Hickmann Brian , Ji Yuan , Jin Weihong , Li Dawei , Mathis Jedidiah , Nenasheva Nataliya , Nigam Rajni , Petri Victoria , Reilly Dorothy , Ruotti Victor , Schauberger Eric , Seiler Kathy , Slyper Ronit , Smith Jennifer , Wang Weiye , Wu Wenhua , Zhao Lan , Zuniga-Meyer Angela , Tonellato Peter J. , Kwitek Anne E. , Jacob Howard J.
Published: August 2005

The broad goal of physiological genomics research is to link genes to their functions using appropriate experimental and computational techniques. Modern genomics experiments enable the generation of vast quantities of data, and interpretation of this data requires the integration of information derived from many diverse sources. Computational biology and bioinformatics offer the ability to manage and channel this information torrent. The Rat Genome Database (RGD; http://rgd.mcw.edu ) has developed computational tools and strategies specifically supporting the goal of linking genes to their functional roles in rat and, using comparative genomics, to human and mouse. We present an overview of the database with a focus on these unique computational tools and describe strategies for the use of these resources in the area of physiological genomics.
Generalizations of principally quasi‐injective modules and quasiprincipally injective modules
Authors: Zhanmin Zhu , Zhangsheng Xia , Zhisong Tan
Published: August 2005

Let R be a ring and M a right R‐module with
S = End(MR). The module M is called almost principally
quasi‐injective (or APQ‐injective for short) if, for any m ∈ M, there exists an S‐submodule Xm of M such that
lMrR(m) = Sm ⊕ Xm. The module M is called almost
quasiprincipally injective (or AQP‐injective for short) if, for
any s ∈ S, there exists a left ideal Xs of S such that
lS(Ker(s)) = Ss ⊕ Xs. In this paper, we give some
characterizations and properties of the two classes of modules.
Some results on principally quasi‐injective modules and
quasiprincipally injective modules are extended to these modules,
respectively. Specially in the case RR, we obtain some results
on AP‐injective rings as corollaries.
A Wirsing‐type approach to some continued fraction expansion
Authors: Sebe Gabriela Ileana
Published: August 2005

Chan (2004) considered a certain continued fraction
expansion and the corresponding Gauss‐Kuzmin‐Lévy
problem. A Wirsing‐type approach to the Perron‐Frobenius operator of the associated
transformation under its invariant measure allows us to obtain a
near‐optimal solution to this problem.
Megaloblastosis: From Morphos to Molecules
Authors: Das K.C. , Das Monisha , Mohanty D. , Jadaon M.M. , Gupta A. , Marouf R. , Easow S.K.
Published: August 2005

Objective: Megaloblastosis (i.e., megaloblastic transformation of erythroid precursor cells in the bone marrow) is the cytomorphological hallmark of megaloblastic anemia resulting from vitamin B12 and folate deficiency. It is characterized by a finely stippled lacy pattern of nuclear chromatin, which is believed to be an expression of deranged cellular DNA synthesis. However, the molecular basis of these cytomorphological aberrations still remains obscure. The current presentation describes the results of our studies on some molecular events associated with the development of megaloblastosis. Methods: Transmission electron microscopy was used to study megaloblasts as well as DNA fibers extracted from megaloblastic and normoblastic bone marrows with and without treatment with proteinase K during the extraction procedure; cellular DNA synthesis in bone marrow cultures was studied by incorporation of 3H-thymidine and deoxyuridine suppression test, while histone biosynthesis in bone marrow cells was studied by in vitro incorporation of 3H-tryptophan, 3H-lysine and 3H-arginine into histones. Results: Derangement of DNA synthesis occurred due to an impaired de novo pathway of thymidylate synthesis in both vitamin-B12- and folate-deficient human megaloblastic bone marrows as well as in the bone marrows of rhesus monkeys and rats with experimentally induced folate deficiency. Interestingly, folate-deficient monkeys developed frank megaloblastic bone marrows, but folate-deficient rats did not. On the other hand, megaloblastic changes in the bone marrow of human patients with myelodysplastic syndrome and erythroleukemia were not associated with this DNA synthetic abnormality. Biosynthesis of predominantly arginine-rich histones in megaloblastic bone marrows was markedly reduced as compared to normoblastic bone marrows, which was consistently associated with elongation and despiralization of chromosomes and finely stippled nuclear chromatin in megaloblasts. Conclusion: The impaired biosynthesis of predominantly arginine-rich nuclear histones appeared to be a common molecular event (a denominator) underlying the development of megaloblastosis with or without abnormal DNA synthesis.
Sickle Cell Disease: A Multigenic Perspective of a Single-Gene Disorder
Authors: Kutlar Abdullah
Published: August 2005

Although significant progress has been made in our understanding of sickle cell disease (SCD) and in the development of new therapies, many questions are still unanswered, and a cure remains elusive. This is particularly evident in the clinical heterogeneity of the disease. Studies have shown the importance of high hemoglobin F determinants and α-thalassemia as modifiers of disease severity, but these alone do not explain the diversity that is seen. This paper focuses on recent advances on the effect of nonglobin genetic modifiers on the SCD phenotype. The roles of polymorphic variants of (1) methylenetetrahydrofolate reductase gene in the pathogenesis of avascular necrosis, (2) factor V R485K and risk of venous thrombosis, and (3) UDP glucuronosyltransferase-1 polymorphism on serum bilirubin levels in SCD are discussed. Mention is made of genetic polymorphisms that might predispose to stroke. The application of gene expression profiling to the study of SCD is very promising and some preliminary data are provided.
Molecular Techniques in the Diagnosis and Management of Infectious Diseases: Do They Have a Role in Bacteriology?
Authors: Poxton Ian R.
Published: August 2005

The diagnosis and management of bacterial diseases has been done by traditional methods for a century or more. With the advent of molecular methods, however, these traditional approaches are being challenged. This review examines the pros and cons of traditional versus modern methods and tries to answer the question: when are molecular methods useful or essential? The following topics are addressed with appropriate examples: diagnosis; identification, typing and fingerprinting; pathogenesis; patient management; susceptibility to disease, and resistance to antimicrobial agents. It was concluded that there is still a place for both traditional and modern molecular methods, and training of staff must include both methodologies. Innovation is encouraged – but new technologies must be thoroughly tested before introduction into the routine lab. Liaison between laboratory scientist and physician is important, but above all experience is paramount.
Mycobacterial Gene Cloning and Expression, Comparative Genomics, Bioinformatics and Proteomics in Relation to the Development of New Vaccines and Diagnostic Reagents
Authors: Mustafa A.S.
Published: August 2005

Recent advances in molecular and genomic techniques have facilitated research on several aspects of mycobacteriology, such as diagnosis and the identification of new vaccines and therapeutic targets for various diseases, including tuberculosis. The aim of this review was to analyze the implications of advances in molecular and genomic techniques on the development of new vaccines for tuberculosis as well as immunological reagents to diagnose the disease. Gene cloning and expression, DNA and protein sequencing, polymerase chain reaction, comparative genomics, bioinformatics, proteomics and DNA and peptide synthesis coupled with the application of cellular immunology techniques have led to the identification of several antigens of Mycobacterium tuberculosis, which have potential for diagnosis and vaccine applications. For example, cross-reactive mycobacterial antigens like heat shock proteins, MTB32 and MTB39, have been identified as new vaccine candidates, and antigens encoded by M. tuberculosis-specific genomic regions as new reagents for diagnosis.
Mechanisms of Drug Resistance in Cancer Chemotherapy
Authors: Luqmani Y.A.
Published: August 2005

The management of cancer involves procedures, which include surgery, radiotherapy and chemotherapy. Development of chemoresistance is a persistent problem during the treatment of local and disseminated disease. A plethora of cytotoxic drugs that selectively, but not exclusively, target actively proliferating cells include such diverse groups as DNA alkylating agents, antimetabolites, intercalating agents and mitotic inhibitors. Resistance constitutes a lack of response to drug-induced tumour growth inhibition; it may be inherent in a subpopulation of heterogeneous cancer cells or be acquired as a cellular response to drug exposure. Resistance varies. Although regulatory approval may require efficacy in as few as 20% of trial cohorts, a drug may subsequently be used in unselected patients displaying resistance to the treatment. Principal mechanisms may include altered membrane transport involving the P-glycoprotein product of the multidrug resistance (MDR) gene as well as other associated proteins, altered target enzyme (e.g. mutated topoisomerase II), decreased drug activation, increased drug degradation due to altered expression of drug-metabolising enzymes, drug inactivation due to conjugation with increased glutathione, subcellular redistribution, drug interaction, enhanced DNA repair and failure to apoptose as a result of mutated cell cycle proteins such as p53. Attempts to overcome resistance mainly involve the use of combination drug therapy using different classes of drugs with minimally overlapping toxicities to allow maximal dosages and with narrowest cycle intervals, necessary for bone marrow recovery. Adjuvant therapy with P-glycoprotein inhibitors and, in specific instances, the use of growth factor and protein kinase C inhibitors are newer experimental approaches that may also prove effective in abrogating or delaying onset of resistance. Gene knockout using antisense molecules may be another effective way of blocking drug resistance genes. Conversely, drug resistance may also be used to good purpose by transplanting retrovirally transformed CD34 cells expressing the MDR gene to protect the bone marrow during high-dose chemotherapy.
Molecular Mechanisms of Organelle Biogenesis and Related Metabolic Diseases
Authors: Dhaunsi Gursev S.
Published: August 2005

Organelle biogenesis is regulated by transcriptional networks that modulate expression of specific genes encoding organellar proteins. Structural and functional specificity of organelles requires not only the transcription of specific genes and translation of resulting mRNAs, but also the transfer of encoded polypeptides to their site of function through signaling peptides. A defect in targeting of proteins to their subcellular site of function may not necessarily prevent biogenesis of the organelle, but would definitely lead to formation of a defective organelle with respect to that specific function. Several metabolic diseases are associated with dysfunction or defects in organelle biogenesis; among these, peroxisome biogenesis disorders, mitochondrial biogenesis defects and lysosomal storage disorders are an extensively studied group of genetic diseases where biogenesis of the organelle is compromised either due to a defect in assembly of the organelle itself or impaired import of matrix proteins into the organelle. Recent advances in biochemical and molecular aspects of biogenesis of subcellular organelles have not only unraveled the mechanisms for organization of cellular networks, but have also provided new insights into the development of metabolic diseases that are caused by disruption of organelle biogenesis. This article reviews the molecular mechanisms of biogenesis of mitochondria, lysosomes and peroxisomes in relation to the metabolic diseases of genetic or nongenetic origin.