bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional caveolae are a prerequisite for CD40 signaling in human renal proximal tubule cells
Authors: Li Hongye , Nord Edward P.
Published: March 2004

The role of caveolae in CD40/CD154 activation of proinflammatory chemokines and their potential role in renal inflammatory disease were explored in primary cultures of human renal proximal tubule epithelial cells. With the use of a cell fractionation assay, caveolin-1 (Cav-1), the defining structural protein of caveolae, was detected exclusively in the cell membrane (detergent insoluble) component of resting and CD40-activated cells. In the unstimulated condition, CD40 was associated with Cav-1, and with activation of the receptor by its cognate ligand CD154, CD40 disassociated from Cav-1. Other previously identified components of the CD40 signaling pathway, namely, SAPK/JNK, p38, and ERK1/2 MAPKs, but not tumor necrosis factor receptor-associated factor 6 (TRAF-6), were also present within caveolae and dissociated from this structure with ligation of the CD40 receptor. Disruption of caveolae with filipin diminished CD40-mediated MAPK activation and blunted downstream monocyte chemoattractant protein-1 (MCP-1) and IL-8 production. Similarly, dislodgment of signaling proteins from their scaffolding with a peptide targeted to the Cav-1 scaffolding domain (CSD) resulted in blunted MAPK activation and augmented IL-8 and MCP-1 production. In contrast, epidermal growth factor (EGF)-mediated tyrosine phosphorylation of the EGF receptor and activation of ERK1/2 were not interrupted by the peptide. We conclude that in human renal proximal tubule epithelial cells, CD40 and its downstream MAPK signaling proteins are located in membrane rafts and that disruption of caveolae or dislodgment of signaling proteins from the CSD diminishes MAPK activation and IL-8 and MCP-1 production in these cells.
Insights into the molecular nature of magnesium homeostasis
Authors: Konrad Martin , Schlingmann Karl P. , Gudermann Thomas
Published: March 2004

Magnesium is an important cofactor for many biological processes, such as protein synthesis, nucleic acid stability, or neuromuscular excitability. Extracellular magnesium concentration is tightly regulated by the extent of intestinal absorption and renal excretion. Despite the critical role of magnesium handling, the exact mechanisms mediating transepithelial transport remained obscure. In the past few years, the genetic disclosure of inborn errors of magnesium handling revealed several new proteins along with already known molecules unexpectedly involved in renal epithelial magnesium transport, e.g., paracellin-1, a key player in paracellular magnesium and calcium reabsorption in the thick ascending limb or the γ-subunit of the Na+-K+-ATPase in the distal convoluted tubule. In this review, we focus on TRPM6, an ion channel of the “transient receptor potential” (TRP) gene family, which, when mutated, causes a combined defect of intestinal magnesium absorption and renal magnesium conservation as observed in primary hypomagnesemia with secondary hypocalcemia.
Action of EGF and PGE2on basolateral organic anion uptake in rabbit proximal renal tubules and hOAT1 expressed in human kidney epithelial cells
Authors: Sauvant C. , Hesse D. , Holzinger H. , Evans K. K. , Dantzler W. H. , Gekle M.
Published: March 2004

We recently showed that, in a proximal tubule cell line (opossum kidney cells), epithelial growth factor (EGF) stimulates basolateral organic anion transport (OAT) via ERK1/2, arachidonic acid, phospholipase A2, and generation of prostaglandins. PGE2binds the prostanoid receptor and, thus, activates adenylate cyclase and PKA, which stimulate basolateral organic anion uptake. In the present study, we investigated whether this regulatory cascade is also true 1) for ex vivo conditions in isolated renal proximal (S2) tubules from rabbit and 2) in a human renal epithelial cell line stably expressing human OAT1 (IHKE-hOAT1). EGF activated ERK1/2 in S2 tubules and IHKE-hOAT1, and, in both cases, inhibition of ERK activation (by U-0126) abolished this stimulation. In S2 tubules and IHKE-hOAT1, EGF led to an increase of organic anion uptake, which again was inhibited by U-0126. PGE2stimulated basolateral organic anion uptake in rabbit S2 tubules and IHKE-hOAT1. EGF- and PGE2-mediated stimulation of organic anion uptake was abolished by inhibition of PKA in rabbit S2 tubules and IHKE-hOAT1, respectively. We conclude that 1) stimulation of basolateral organic anion uptake by EGF or PGE2is a widespread (if not general) regulatory mechanism, 2) the signal transduction pathway involved seems to be general, 3) stimulation of basolateral organic anion uptake by EGF or PGE2is also present under ex vivo conditions and, thus, is not a cell culture artifact, 4) activation of OAT1 is sufficient to explain the stimulatory effects of EGF and PGE2in opossum kidney cells and rabbit S2 segments, and 5) stimulation of basolateral OAT1 by EGF or PGE2is also important in humans and, thus, may have clinical implications.
Differentiated human podocytes endogenously express an inhibitory isoform of vascular endothelial growth factor (VEGF165b) mRNA and protein
Authors: Cui Tai-Gen , Foster Rebecca R. , Saleem Moin , Mathieson Peter W. , Gillatt David A. , Bates David O. , Harper Steven J.
Published: March 2004

Despite production by podocytes of the proangiogenic molecule vascular endothelial growth factor-A (VEGF), the glomeruli are not sites of angiogenesis. We recently described mRNA expression of an inhibitory splice variant of VEGF (VEGF165b) in normal kidney (Bates DO, Cui TG, Doughty JM, Winkler M, Sugiono M, Shields JD, Peat D, Gillatt D, and Harper SJ. Cancer Res 62: 4123–4131, 2002). Available anti-VEGF antibodies do not distinguish stimulatory from inhibitory VEGF families. To assess the production of VEGF165(stimulatory) and VEGF165b (inhibitory) isoforms by human podocytes, we examined both primary cultured and conditionally immortalized human podocytes using family- and isoform-specific RT-PCR. In addition, VEGF protein production was analyzed in podocytes, using isoform-specific double-strand small-interference RNAs (siRNA). RT-PCR demonstrated the production of VEGF189mRNA by podocytes of both phenotypes. In contrast, on differentiation there was a splicing change from VEGF165to VEGF165b mRNA. In addition, VEGF protein in the supernatant of conditionally immortalized, differentiated podocytes was reduced by VEGF165b siRNA to 20 ± 11% of the level of mock-transfected cells ( P < 0.01). No reduction was seen with mismatch siRNA. Moreover, there was no reduction in VEGF protein concentration in the supernatant of primary cultured, dedifferentiated human podocytes (109 ± 8% of mismatch siRNA, P > 0.1). In conclusion, differentiated but not dedifferentiated human podocytes secrete significant amounts of VEGF165b protein. It is possible that this may explain the paradox of high VEGF production in the glomerulus but no angiogenesis. Furthermore, the existence of this splicing switch in relation to podocyte phenotype suggests that alternative splicing of the VEGF pre-RNA is a regulated process that is open to manipulation and therefore could be a target for novel cancer therapies.
Central control of renal sodium-phosphate (NaPi-2) transporters
Authors: Mulroney Susan E. , Woda Craig B. , Halaihel Nabil , Louie Brandon , McDonnell Kevin , Schulkin Jay , Haramati Aviad , Levi Moshe
Published: March 2004

Regulation of phosphate (Pi) reabsorption occurs through the up- and downregulation of the renal type-II sodium Pi cotransporters (NaPi-2). Recently, renal NaPi2-type expression has been identified in areas of the brain. The present study determined whether brain NaPi-2 is regulated by dietary Pi and whether the behavioral and renal adaptations to low-dietary Pi are controlled centrally. NaPi-2-like expression in the third ventricle (3V) and amygdala of juvenile Wistar rats was regulated by dietary Pi, as in the kidneys. When cerebrospinal fluid (CSF) Pi concentration was elevated by 3V injections of Pi in rats fed low-Pi diet (LPD), the behavioral and renal adaptations to LPD were abolished. Most importantly, NaPi-2 expression was markedly reduced not only in the brain, but also renal proximal tubules, despite the low plasma Pi milieu. This was confirmed by the significant reduction in the transport maximum for Pi (from 8.1 ± 0.2 in LPD + veh 3V to 1.7 ± 0.1 μmol Pi/ml glomerular filtration rate in LPD + 3V Pi, P < 0.001). These findings indicate that NaPi-2-like transporters in the brain are regulated by both dietary Pi and CSF Pi concentrations, and most significantly, that the central Pi milieu can regulate renal NaPi-2 expression. We hypothesize that central 3V NaPi-2 transporters may act as Pi sensors and help regulate both brain and whole body Pi homeostasis.
Regulation of renal NaPi-2 expression and tubular phosphate reabsorption by growth hormone in the juvenile rat
Authors: Woda Craig B. , Halaihel Nabil , Wilson Paul V. , Haramati Aviad , Levi Moshe , Mulroney Susan E.
Published: March 2004

Growth hormone (GH) is an important factor in the developmental adaptation to enhance Pi reabsorption; however, the nephron sites and mechanisms by which GH regulates renal Pi uptake remain unclear and are the focus of the present study. Micropuncture experiments were performed after acute thyroparathyroidectomy in the presence and absence of parathyroid hormone (PTH) in adult (14- to 17-wk old), juvenile (4-wk old), and GH-suppressed juvenile male rats. While the phosphaturic effect of PTH was blunted in the juvenile rat compared with the adult, suppression of GH in the juvenile restored fractional Pi excretion to adult levels. In the presence or absence of PTH, GH suppression in the juvenile rat caused a significant increase in the fractional Pi delivery to the late proximal convoluted (PCT) and early distal tubule, so that delivery was not different from that in adults. These data were confirmed by Pi uptake studies into brush-border membrane (BBM) vesicles. Immunofluorescence studies indicate increased BBM type IIa NaPi cotransporter (NaPi-2) expression in the juvenile compared with adult rat, and GH suppression reduced NaPi-2 expression to levels observed in the adult. GH replacement in the [ N-acetyl-Tyr1-d-Arg2]-GRF-(1-29)-NH2-treated juveniles restored high NaPi-2 expression and Pi uptake. Together, these novel results demonstrate that the presence of GH in the juvenile animal is crucial for the early developmental upregulation of BBM NaPi-2 and, most importantly, describe the enhanced Pi reabsorption along the PCT and proximal straight nephron segments in the juvenile rat.
Ablation of the Tamm-Horsfall protein gene increases susceptibility of mice to bladder colonization by type 1-fimbriatedEscherichia coli
Authors: Mo Lan , Zhu Xin-Hua , Huang Hong-Ying , Shapiro Ellen , Hasty David L. , Wu Xue-Ru
Published: March 2004

The adhesion of uropathogenic Escherichia coli to the urothelial surface of the bladder is a prerequisite for the establishment of bladder infections. This adhesion process relies on E. coli adhesins and their cognate urothelial receptors, and it also is influenced by an intricate array of defense mechanisms of the urinary system. In this study, we examined the in vivo role of Tamm-Horsfall protein (THP), the most abundant urinary protein, in innate urinary defense. We genetically ablated the mouse THP gene and found that THP deficiency predisposes mice to bladder infections by type 1-fimbriated E. coli. Inoculation of too few type 1-fimbriated E. coli to colonize wild-type mice caused significant bladder colonization in THP-knockout mice. In contrast, THP deficiency did not enhance the ability of P-fimbriated E. coli to colonize the bladder. Our results provide the first in vivo evidence indicating that under physiological conditions, the mannosylated THP can serve as an effective soluble “receptor,” binding to the type 1-fimbriated E. coli and competitively inhibiting them from adhering to the uroplakin Ia receptors present on the urothelial surface. These results suggest that potential THP defects, either quantitative or qualitative, could predispose the urinary bladder to bacterial infections. The generation of THP-deficient mice established the role of THP as a first line of urinary defense and should help elucidate other potential functions of this major protein in urinary tract physiology and diseases.
1α-Hydroxylase gene ablation and Pisupplementation inhibit renal calcification in mice homozygous for the disruptedNpt2agene
Authors: Tenenhouse Harriet S. , Gauthier Claude , Chau Hien , St.-Arnaud René
Published: March 2004

Disruption of the major renal Na-phosphate (Pi) cotransporter gene Npt2a in mice leads to a substantial decrease in renal brush-border membrane Na-Picotransport, hypophosphatemia, and appropriate adaptive increases in renal 25-hydroxyvitamin D3-1α-hydroxylase (1αOHase) activity and the serum concentration of 1,25-dihydroxyvitamin D3[1,25(OH)2D]. The latter is associated with increased intestinal Ca absorption, hypercalcemia, hypercalciuria, and renal calcification in Npt2-/-mice. To determine the contribution of elevated serum 1,25(OH)2D levels to the development of hypercalciuria and nephrocalcinosis in Npt2-/-mice, we examined the effects of 1α OHase gene ablation and long-term Pisupplementation on urinary Ca excretion and renal calcification by microcomputed tomography. We show that the urinary Ca/creatinine ratio is significantly decreased in Npt2-/-/1α OHase-/-mice compared with Npt2-/-mice. In addition, renal calcification, determined by estimating the calcified volume to total renal volume (CV/TV), is reduced by ∼80% in Npt2-/-/1α OHase-/-mice compared with that in Npt2-/-mice. In Npt2-/-mice derived from dams fed a 1% Pidiet and maintained on the same diet, we observed a significant decrease in urinary Ca/creatinine that was also associated with ∼80% reduction in CV/TV when compared with counterparts fed a 0.6% diet. Taken together, the present data demonstrate that both 1α OHase gene ablation and Pisupplementation inhibit renal calcification in Npt2-/-mice and that 1,25(OH)2D is essential for the development of hypercalciuria and nephrocalcinosis in the mutant strain.
Dual constrictor and dilator actions of ETB receptors in the rat renal microcirculation: interactions with ETA receptors
Authors: Just Armin , Olson Andrea J. M. , Arendshorst William J.
Published: March 2004

The vascular actions of endothelin-1 (ET-1) reflect the combination of vasoconstrictor ETA and ETB receptors on smooth muscle cells and vasodilator ETB receptors on endothelial cells. The present study investigated the contribution of ET receptor subtypes using a comprehensive battery of agonists and antagonists infused directly into the renal artery of anesthetized rats to evaluate the actions of each receptor class alone and their interactions. ET-1 (5 pmol) reduced renal blood flow (RBF) 25 ± 1%. ETA antagonist BQ-123 attenuated this response to a 15 ± 1% decrease in RBF ( P < 0.01), indicating net constriction by ETB receptors. Combined receptor blockade (BQ-123+BQ-788) resulted in a renal vasoconstriction of 7 ± 1% ( P = 0.001 vs. BQ-123), supporting a constrictor action of ETB receptors. In marked contrast, the ETB antagonist BQ-788 enhanced the ET-1 RBF response to 60 ± 5% ( P < 0.001), suggesting ETB-mediated net dilation. Consistent with ETA blockade, the ETB agonist sarafotoxin 6C (S6C) produced vasoconstriction, reducing RBF by 23 ± 5%. Dose-response curves for ET-1 and S6C showed similar degrees of constriction between 0.2 and 100 pmol. Both antagonists (BQ-123, BQ-788) were equally effective at threefold lower than the standard doses, suggesting complete inhibition. We conclude that ETB receptors alone exert a net constrictor effect but cause a net dilator influence when costimulated with ETA receptors. Such opposing actions indicate more complex than additive interaction between receptor subtypes. Model analysis suggests ETA-mediated constriction is appreciably greater without than with costimulation of ETB receptors. Possible explanations include ET-1 clearance by ETB receptors and/or a dilator ETB receptor function that counteracts constriction.
Role of vasopressin in diabetes mellitus-induced changes in medullary transport proteins involved in urine concentration in Brattleboro rats
Authors: Kim Dongun , Sands Jeff M. , Klein Janet D.
Published: March 2004

In rats with streptozotocin-induced diabetes mellitus for 10–20 days, we showed that the abundance of the major medullary transport proteins involved in the urinary concentrating mechanism, urea transporter (UT-A1), aquaporin-2 (AQP2), and the Na+-K+-2Cl-cotransporter (NKCC2/BSC1), is increased, despite the ongoing osmotic diuresis. To test whether vasopressin is necessary for these diabetes mellitus-induced changes in UT-A1, AQP2, or NKCC2/BSC1, we studied Brattleboro rats because they lack vasopressin. Brattleboro rats were given vasopressin (2.4 μg/day via osmotic minipump) for 5 or 12 days. At 5 days, vasopressin increased AQP2 protein abundance but decreased UT-A1 abundance compared with untreated Brattleboro rats. At 12 days, vasopressin increased the abundance of both UT-A1 and AQP2 proteins but did not alter NKCC2/BSC1. Next, untreated Brattleboro rats were made diabetic for 10 days by injecting them with streptozotocin (40 mg/kg). Diabetes mellitus increased the abundance of AQP2 and NKCC2/BSC1 proteins, but UT-A1 protein abundance did not increase. Third, vasopressin-treated Brattleboro rats were made diabetic with streptozotocin for 10 days. In vasopressin-treated Brattleboro rats, diabetes mellitus increased UT-A1, AQP2, and NKCC2/BSC1 protein abundances. Vasopressin significantly increased UT-A1 phosphorylation in vasopressin-treated diabetic Brattleboro rats but not in the other groups of Brattleboro rats. We conclude that 1) administering vasopressin to Brattleboro rats for 12 days, but not for 5 days, increases UT-A1 protein abundance and 2) vasopressin is necessary for the increase in UT-A1 protein in diabetic rats but is not necessary for the increase in AQP2 or NKCC2 proteins.
Na channels in the rat connecting tubule
Authors: Frindt Gustavo , Palmer Lawrence G.
Published: March 2004

Epithelial Na channels were investigated using patch-clamp techniques in connecting tubule (CNT) segments isolated from rat kidney. Cell-attached patches with Li+ in the patch pipette contained channels with conductances for inward currents of 13–16 pS and slow opening and closing kinetics, similar to properties of Na channels in the cortical collecting tubule (CCT). Macroscopic amiloride-sensitive currents ( INa) were also observed under whole cell clamp conditions. These currents were undetectable in cells from control rats but were large when the animals were infused with aldosterone (1,380 ± 340 pA/cell at a holding potential of -100 mV) or fed a high-K diet (670 ± 260 pA/cell) for 1 wk. Under both of these conditions, currents in cells of the CNT were two- to fourfold larger than currents in cells of the CCT of the same animals. In aldosterone-treated animals, currents in cells of the initial collecting tubule (iCT) were intermediate, such that the relative magnitude of INa was as follows: CNT > iCT > CCT. Quantitative analysis of the results suggests that the maximal capacity of the aggregate population of CNTs to reabsorb Na could be as high as 18 μmol/min, or ∼10% of the filtered load of Na. This capacity is ∼10 times higher than that of the CCT.
Glucocorticoids stimulate cation absorption by semicircular canal duct epithelium via epithelial sodium channel
Authors: Pondugula Satyanarayana R. , Sanneman Joel D. , Wangemann Philine , Milhaud Pierre G. , Marcus Daniel C.
Published: March 2004

The semicircular canal duct (SCCD) epithelium is a vestibular epithelial domain that was recently shown to actively contribute to endolymph homeostasis by Cl− secretion under control of β2-adrenergic stimulation. By analogy to other Cl− secretory epithelia, we hypothesized that SCCD also provides an active absorptive pathway for Na+ under corticosteroid control. Measurements of short-circuit current ( Isc) demonstrated stimulation (7–24 h) by the glucocorticoids hydrocortisone (EC50 13 nM), corticosterone (33 nM), prednisolone (70 nM), and dexamethasone (13 nM) over physiologically and therapeutically relevant concentrations and its block by amiloride (IC50 470 nM) and benzamil (57 nM), inhibitors of the epithelial sodium channel (ENaC). Isc was also partially inhibited by basolateral ouabain and Ba2+, indicating the participation of Na+-K+-ATPase and a K+ channel in Na+ transport. By contrast, aldosterone stimulated Isc only at unphysiologically high concentrations (EC50 102 nM). The action of all steroids was blocked by mifepristone (RU-486; Kd ∼0.3 nM) but not by spironolactone ( Kd ∼0.7 μM). Expression of mRNA for the α-, β-, and γ-subunits of ENaC was demonstrated in the presence and absence of glucocorticoids. These findings are the first to identify SCCD in the vestibular labyrinth as a site of physiologically significant ENaC-mediated Na+ absorption and osmotically coupled water flux. They further demonstrate regulation of Na+ transport by natural and therapeutic glucocorticoids. The results provide for the first time an understanding of the therapeutic benefit of glucocorticoids in the treatment of Meniere's disease, a condition that is associated with increased luminal fluid volume.
Effect of age on O2 uptake kinetics and the adaptation of muscle deoxygenation at the onset of moderate-intensity cycling exercise
Authors: DeLorey Darren S. , Kowalchuk John M. , Paterson Donald H.
Published: March 2004

Phase 2 pulmonary O2 uptake (V̇o2p) kinetics are slowed with aging. To examine the effect of aging on the adaptation of V̇o2p and deoxygenation of the vastus lateralis muscle at the onset of moderate-intensity constant-load cycling exercise, young (Y) ( n = 6; 25 ± 3 yr) and older (O) ( n = 6; 68 ± 3 yr) adults performed repeated transitions from 20 W to work rates corresponding to moderate-intensity (80% estimated lactate threshold) exercise. Breath-by-breath V̇o2p was measured by mass spectrometer and volume turbine. Deoxy (HHb)-, oxy-, and total Hb and/or myoglobin were determined by near-infrared spectroscopy (Hamamatsu NIRO-300). V̇o2p data were filtered, interpolated to 1 s, and averaged to 5-s bins. HHb data were filtered and averaged to 5-s bins. V̇o2p data were fit with a monoexponential model for phase 2, and HHb data were analyzed to determine the time delay from exercise onset to the start of an increase in HHb and thereafter were fit with a single-component exponential model. The phase 2 time constant for V̇o2p was slower ( P < 0.01) in O (Y: 26 ± 7 s; O: 42 ± 9 s), whereas the delay before an increase in HHb (Y: 12 ± 2 s; O: 11 ± 1 s) and the time constant for HHb after the time delay (Y: 13 ± 10 s; O: 9 ± 3 s) were similar in Y and O. However, the increase in HHb for a given increase in V̇o2p (Y: 7 ± 2 μM·l−1·min−1; O: 13 ± 4 μM·l−1·min−1) was greater ( P < 0.01) in O compared with Y. The slower V̇o2p kinetics in O compared with Y adults was accompanied by a slower increase of local muscle blood flow and O2 delivery discerned from a faster and greater muscle deoxygenation relative to V̇o2p in O.
Temporal Dynamics of Binocular Disparity Processing in the Central Visual Pathway
Authors: Menz Michael D. , Freeman Ralph D.
Published: March 2004

To solve the stereo correspondence problem (i.e., find the matching features of a visual scene in both eyes), it is advantageous to combine information across spatial scales. The details of how this is accomplished are not clear. Psychophysical studies and mathematical models have suggested various types of interactions across spatial scale, including coarse to fine, fine to coarse, averaging, and population coding. In this study, we investigate dynamic changes in disparity tuning of simple and complex cells in the cat's striate cortex over a short time span. We find that disparity frequency increases and disparity ranges decrease while optimal disparity remains constant, and this conforms to a coarse-to-fine mechanism. We explore the origin of this mechanism by examining the frequency and size dynamics exhibited by binocular simple cells and neurons in the lateral geniculate nucleus (LGN). The results suggest a strong role for a feed-forward mechanism, which could originate in the retina. However, we find that the dynamic changes seen in the disparity range of simple cells cannot be predicted from their left and right eye monocular receptive field (RF) size changes. This discrepancy suggests the possibility of a dynamic nonlinearity or disparity specific feedback that alters tuning or a combination of both mechanisms.
Functional Connectivity of Disparity-Tuned Neurons in the Visual Cortex
Authors: Menz Michael D. , Freeman Ralph D.
Published: March 2004

Different mechanisms have been proposed concerning how disparitytuned neurons might be connected to produce the signals for depth perception. Here we present neurophysiological evidence providing insight on this issue. We have recorded simultaneously from pairs of disparity-tuned neurons in the cat's striate cortex. The purpose was to determine the relationships between disparity tuning and functional connectivity revealed through neural cross-correlograms. Monosynaptic connections tend to be stronger between pairs of cells with similar disparity tuning. Pairs of complex cells tend to have either similar tuning or nearly opposite tuning with an absence of quadrature relations. Pairs with at least one simple cell do have some nearly quadrature relationships when they are recorded from the same electrode. Coarse-to-fine connections (i.e., the presynaptic cell has lower disparity frequency and larger disparity range) tend to be stronger but less frequent than those of a fine-to-coarse nature. Our results are consistent with a system that produces weighted averaging across cells that are tuned to similar disparities but different disparity scales to reduce false matches.
Hemispheric Differences in the Relationship Between Corticomotor Excitability Changes Following a Fine-Motor Task and Motor Learning
Authors: Garry Michael I. , Kamen Gary , Nordstrom Michael A.
Published: March 2004

Motor performance induces a postexercise increase in corticomotor excitability that may be associated with motor learning. We investigated whether there are hemispheric differences in the extent and/or time course of changes in corticomotor excitability following a manipulation task (Purdue pegboard) and their relationship with motor performance. Single- and paired-pulse (3 ms) transcranial magnetic stimulation (TMS) was used to assess task-induced facilitation of the muscle evoked potential (MEP) and intracortical inhibition (ICI) for three intrinsic hand muscles acting on digits 1, 2, and 5. Fifteen right-handed subjects performed three 30-s pegboard trials with left or right hand in separate sessions. TMS was applied to contralateral motor cortex before and after performance. Number of pegs placed was higher with the right hand, and performance improved (motor learning) with both hands over the three trials. MEP facilitation following performance was short-lasting (<15 min), selective for muscles engaged in gripping the pegs, and of similar magnitude in left and right hands. ICI was reduced immediately following performance with the right hand, but not the left. The extent of MEP facilitation was positively correlated with motor learning for the right hand only. We conclude that the pegboard task induces a selective, short-lasting change in excitability of corticospinal neurons controlling intrinsic hand muscles engaged in the task. Only left hemisphere changes were related to motor learning. This asymmetry may reflect different behavioral strategies for performance improvement with left and right upper limb in this task or hemispheric differences in the control of skilled hand movements.
Cloning and Expression of a Small-Conductance Ca2+-Activated K+ Channel From the Mouse Cochlea: Coexpression with α9/α10 Acetylcholine Receptors
Authors: Nie Liping , Song Haitao , Chen Mei-Fang , Chiamvimonvat Nipavan , Beisel Kirk W. , Yamoah Ebenezer N. , Vázquez Ana E.
Published: March 2004

Functional interactions between ligand-gated, voltage-, and Ca2+-activated ion channels are essential to the properties of excitable cells and thus to the working of the nervous system. The outer hair cells in the mammalian cochlea receive efferent inputs from the brain stem through cholinergic nerve fibers that form synapses at their base. The acetylcholine released from these efferent fibers activates fast inhibitory postsynaptic currents mediated, to some extent, by small-conductance Ca2+-activated K+ channels (SK) that had not been cloned. Here we report the cloning, characterization, and expression of a complete SK2 cDNA from the mouse cochlea. The cDNAs of the mouse cochlea α9 and α10 acetylcholine receptors were also obtained, sequenced, and coexpressed with the SK2 channels. Human cultured cell lines transfected with SK2 yielded Ca2+-sensitive K+ current that was blocked by dequalinium chloride and apamin, known blockers of SK channels. Xenopus oocytes injected with SK2 in vitro transcribed RNA, under conditions where only outward K+ currents could be recorded, expressed an outward current that was sensitive to EGTA, dequalinium chloride, and apamin. In HEK-293 cells cotransfected with cochlear SK2 plus α9/α10 receptors, acetylcholine induced an inward current followed by a robust outward current. The results indicate that SK2 and the α9/α10 acetylcholine receptors are sufficient to partly recapitulate the native hair cell efferent synaptic response.
Neural Correlates of Beauty
Authors: Kawabata Hideaki , Zeki Semir
Published: March 2004

We have used the technique of functional MRI to address the question of whether there are brain areas that are specifically engaged when subjects view paintings that they consider to be beautiful, regardless of the category of painting (that is whether it is a portrait, a landscape, a still life, or an abstract composition). Prior to scanning, each subject viewed a large number of paintings and classified them into beautiful, neutral, or ugly. They then viewed the same paintings in the scanner. The results show that the perception of different categories of paintings are associated with distinct and specialized visual areas of the brain, that the orbito-frontal cortex is differentially engaged during the perception of beautiful and ugly stimuli, regardless of the category of painting, and that the perception of stimuli as beautiful or ugly mobilizes the motor cortex differentially.
Body-Centered Visuomotor Adaptation
Authors: van den Dobbelsteen John J. , Brenner Eli , Smeets Jeroen B. J.
Published: March 2004

Previous research has shown that humans generalize distortions of visuomotor feedback in terms of egocentric rotations. We examined whether these rotations are linked to the orientation of the eyes or of the shoulder of the arm that was used. Subjects moved a hand-held cube between target locations in a sequence of adaptation and test phases. During adaptation phases, subjects received either veridical or distorted visual feedback about the location of the cube. The distortions were changes in azimuth either relative to the eyes or to the shoulder. During test phases subjects received no visual feedback. Test phases were performed either with the arm that was exposed to the distorted feedback or with the unexposed arm. We compared test movement endpoints after distorted feedback with ones after veridical feedback. For the exposed arm, the spatial layout of the changes in endpoints clearly reflected the small differences between a rotation around the shoulder and around the eyes. For the unexposed arm, the changes in endpoints were smaller for both types of distortions and were less consistent with the distortions. Thus although the adaptation closely matches the imposed distortion, it does not appear to be directly linked to the orientation of the eyes or of the exposed arm.
Internal Models of Target Motion: Expected Dynamics Overrides Measured Kinematics in Timing Manual Interceptions
Authors: Zago Myrka , Bosco Gianfranco , Maffei Vincenzo , Iosa Marco , Ivanenko Yuri P. , Lacquaniti Francesco
Published: March 2004

Prevailing views on how we time the interception of a moving object assume that the visual inputs are informationally sufficient to estimate the time-to-contact from the object's kinematics. Here we present evidence in favor of a different view: the brain makes the best estimate about target motion based on measured kinematics and an a priori guess about the causes of motion. According to this theory, a predictive model is used to extrapolate time-to-contact from expected dynamics (kinetics). We projected a virtual target moving vertically downward on a wide screen with different randomized laws of motion. In the first series of experiments, subjects were asked to intercept this target by punching a real ball that fell hidden behind the screen and arrived in synchrony with the visual target. Subjects systematically timed their motor responses consistent with the assumption of gravity effects on an object's mass, even when the visual target did not accelerate. With training, the gravity model was not switched off but adapted to nonaccelerating targets by shifting the time of motor activation. In the second series of experiments, there was no real ball falling behind the screen. Instead the subjects were required to intercept the visual target by clicking a mousebutton. In this case, subjects timed their responses consistent with the assumption of uniform motion in the absence of forces, even when the target actually accelerated. Overall, the results are in accord with the theory that motor responses evoked by visual kinematics are modulated by a prior of the target dynamics. The prior appears surprisingly resistant to modifications based on performance errors.
Sleep Deprivation Effects on Growth Factor Expression in Neonatal Rats: A Potential Role for BDNF in the Mediation of Delta Power
Authors: Hairston Ilana S. , Peyron Christelle , Denning Daniel P. , Ruby Norman F. , Flores Judith , Sapolsky Robert M. , Heller H. Craig , O'Hara Bruce F.
Published: March 2004

The sleeping brain differs from the waking brain in its electrophysiological and molecular properties, including the expression of growth factors and immediate early genes (IEG). Sleep architecture and homeostatic regulation of sleep in neonates is distinct from that of adults. Hence, the present study addressed the question whether the unique homeostatic response to sleep deprivation in neonates is reflected in mRNA expression of the IEG cFos, brain-derived nerve growth factor (BDNF), and basic fibroblast growth factor (FGF2) in the cortex. As sleep deprivation is stressful to developing rats, we also investigated whether the increased levels of corticosterone would affect the expression of growth factors in the hippocampus, known to be sensitive to glucocorticoid levels. At postnatal days 16, 20, and 24, rats were subjected to sleep deprivation, maternal separation without sleep deprivation, sleep deprivation with 2 h recovery sleep, or no intervention. mRNA expression was quantified in the cortex and hippocampus. cFos was increased after sleep deprivation and was similar to control level after 2 h recovery sleep irrespective of age or brain region. BDNF was increased by sleep deprivation in the cortex at P20 and P24 and only at P24 in the hippocampus. FGF2 increased during recovery sleep at all ages in both brain regions. We conclude that cortical BDNF expression reflects the onset of adult sleep-homeostatic response, whereas the profile of expression of both growth factors suggests a trophic effect of mild sleep deprivation.
In Vivo Multiphoton Microscopy of Deep Brain Tissue
Authors: Levene Michael J. , Dombeck Daniel A. , Kasischke Karl A. , Molloy Raymond P. , Webb Watt W.
Published: March 2004

Although fluorescence microscopy has proven to be one of the most powerful tools in biology, its application to the intact animal has been limited to imaging several hundred micrometers below the surface. The rest of the animal has eluded investigation at the microscopic level without excising tissue or performing extensive surgery. However, the ability to image with subcellular resolution in the intact animal enables a contextual setting that may be critical for understanding proper function. Clinical applications such as disease diagnosis and optical biopsy may benefit from minimally invasive in vivo approaches. Gradient index (GRIN) lenses with needle-like dimensions can transfer high-quality images many centimeters from the object plane. Here, we show that multiphoton microscopy through GRIN lenses enables minimally invasive, subcellular resolution several millimeters in the anesthetized, intact animal, and we present in vivo images of cortical layer V and hippocampus in the anesthetized Thy1-YFP line H mouse. Microangiographies from deep capillaries and blood vessels containing fluorescein-dextran and quantum dot-labeled serum in wild-type mouse brain are also demonstrated.
Does Head Rotation Contribute to Gaze Stability During Passive Translations?
Authors: Wei Min , Angelaki Dora E.
Published: March 2004

Active translations of human subjects are nearly perfectly compensated by a combined rotation of both the eyes and the head. Because vestibuloocular reflex (VOR) gain is less than perfect during passive translations with near targets in head-fixed subjects, there is a possibility that the compensatory head rotation observed during natural behavior represents a vestibularly driven head reflex [translational vestibulocollic reflex (TVCR)]. The TVCR could elicit a horizontal rotation of the head during lateral linear acceleration that contributes to gaze stabilization. To investigate this hypothesis, we examined whether a horizontal rotation of the head contributes to gaze stability during passive lateral translation in rhesus monkeys whose head was free to rotate in the horizontal plane. Motion frequency was varied between 0.5 and 5 Hz while animals fixated targets at distances of 12–102 cm. We did not find evidence supporting the existence of a TVCR. Specifically, during motion at frequencies between 0.5 and 2 Hz, horizontal head rotation was negligible. During 4- and 5-Hz oscillations, there was a clear and consistent horizontal rotation of the head, but responses were always anticompensatory to gaze stabilization; that is, the head rotated in the same direction as head translation and oppositely to the direction of gaze rotation. Furthermore, there was no difference in gaze stability between the head-free and head-fixed conditions. Thus we conclude that the compensatory head rotation observed in human studies of active gaze movements could represent a strategy and/or a motor command contribution to gaze stabilization, rather than a simple vestibularly driven reflex.
How Self-Initiated Memorized Movements Become Automatic: A Functional MRI Study
Authors: Wu Tao , Kansaku Kenji , Hallett Mark
Published: March 2004

We used functional magnetic resonance imaging (fMRI) and dual tasks to investigate the physiology of how movements become automatic. Normal subjects were asked to practice some self-initiated, self-paced, memorized sequential finger movements with different complexity until they could perform the tasks automatically. Automaticity was evaluated by having subjects perform a secondary task simultaneously with the sequential movements. Our secondary task was a letter-counting task where subjects were asked to identify the number of times a target letter from the letter sequences was seen. Only the performances that achieved high accuracy in both single and dual tasks were considered automatic. The fMRI results before and after automaticity was achieved were compared. Our data showed that for both conditions, sequential movements activated similar brain regions. No additional activity was observed in the automatic condition. There was less activity in bilateral cerebellum, presupplementary motor area, cingulate cortex, left caudate nucleus, premotor cortex, parietal cortex, and prefrontal cortex during the automatic stage. These findings suggest that most of the motor network participates in executing automatic movements and that it becomes more efficient as movements become more automatic. Our results do not provide evidence for any area to become more activated for automatic movements.
Spontaneous REM Sleep Is Modulated By the Activation of the Pedunculopontine Tegmental GABAB Receptors in the Freely Moving Rat
Authors: Ulloor Jagadish , Mavanji Vijayakumar , Saha Subhash , Siwek Donald F. , Datta Subimal
Published: March 2004

Considerable evidence suggests that the neurotransmitter γ-aminobutyric acid (GABA)-ergic system and pedunculopontine tegmentum (PPT) in the brain stem are critically involved in the regulation of rapid-eye-movement (REM) sleep. GABA and its various receptors are normally present in the PPT cholinergic cell compartment. The aim of this study was to identify the role of GABA and its receptors in the regulation of REM sleep. To achieve this aim, specific receptors were activated differentially by local microinjection of selective GABA receptor agonists into the PPT while quantifying its effects on REM sleep in freely moving chronically instrumented rats ( n = 21). The results demonstrated that when GABAB receptors were activated by local microinjection of a GABAB receptor selective agonist, baclofen, spontaneous REM sleep was suppressed in a dose-dependent manner. The optimum dose for REM sleep reduction was 1.5 nmol. In contrast, when GABAA and GABAC receptors were activated by microinjecting their receptor selective agonists, isoguvacine (ISGV) and cis-4-aminocrotonic acid (CACA), respectively, the total percentages of REM sleep did not change compared with the control values. In another eight freely moving rats, effects of baclofen application was tested on firing rates of REM-on cells ( n = 12). Of those 12 neurons, 11 stopped firing immediately after application of baclofen [latency: 50 ± 14 s (SD)] and remained almost silent for 130 ± 12 min. Findings of the present study provide direct evidence that the PPT GABAB receptors and REM-on cells are involved in the regulation of REM sleep.
Synthesis of Multiwhisker-Receptive Fields in Subcortical Stations of the Vibrissa System
Authors: Timofeeva Elena , Lavallée Philippe , Arsenault Dominique , Deschênes Martin
Published: March 2004

This study addresses the origins of multiwhisker-receptive fields of neurons in the thalamic ventral posterior medial (VPM) nucleus of the rat. We sought to determine whether multiwhisker-receptive field synthesis occurs in VPM through convergent projections from the principalis (PrV) and interpolaris (SpVi) nuclei, or in PrV by intersubnuclear projections from the spinal trigeminal complex. We tested these hypotheses by recording whisker-evoked responses in PrV and VPM before and after electrolytic lesion of the SpVi in lightly anesthetized rats. Before the lesion PrV cells responded, on average, to 3.2 ± 1.2 whiskers but responsiveness was reduced to 1.07 ± 0.31 whisker after the lesion. A similar reduction of receptive field size was observed in VPM, where neurons responded, on average, to 2.94 ± 0.95 whiskers before the lesion and to 1.05 ± 0.22 whisker after the lesion. Thus one can conclude that intersubnuclear projections mediate surround whisker-receptive fields in PrV, and therefore in VPM. However, it has previously been shown that parasagittal brain stem transection, which severed ascending projections from SpVi, but left intersubnuclear connections intact, rendered VPM cells monowhisker responsive. We wondered whether midline brain stem lesion modified receptive field properties in SpVi. In normal rats SpVi cells responded, on average, to 7.52 ± 4.25 whiskers, but responsiveness was dramatically reduced to 1.47 ± 1.07 whisker after the lesion. Together these results indicate that the synthesis of surround receptive fields in subcortical stations relies almost exclusively on intersubnuclear projections from the spinal trigeminal complex to the PrV.
Probability of Transmitter Release at Neocortical Synapses at Different Temperatures
Authors: Volgushev Maxim , Kudryashov Igor , Chistiakova Marina , Mukovski Mikhail , Niesmann Johannes , Eysel Ulf T.
Published: March 2004

The probability of transmitter release at synaptic terminals is one of the key characteristics of communication between nerve cells because it determines both the strength and dynamic properties of synaptic connections. To assess the distribution of the release probabilities at excitatory synapses on supragranular pyramidal cells in rat visual cortex, we have used the MK-801, a blocker of the open N-methyl-d-aspartate (NMDA) receptor-gated channels. With this method, the release probability can be calculated from the time course of the blockade of NMDA-receptor mediated postsynaptic currents in the presence of MK-801. At temperatures >32°C, the distribution of release probabilities covered the range from 0.05 to 0.43 [mean: 0.171 ± 0.012 (SE), n = 65], being skewed toward low values. When estimated at room temperature (22–25°C), the release probabilities were significantly lower (mean: 0.123 ± 0.009, n = 54), and almost the whole distribution was restricted to values <0.2. Furthermore, warming from room temperature to >32°C led to a pronounced overshooting increase of the release probability. Taken together, the results of the present study show that release probabilities at synapses formed onto layer 2/3 pyramidal cells in the visual cortex vary significantly, but values >0.3 are rare and the results obtained either at room or variable temperature differ significantly from those made under conditions of constant temperature in the physiological range.
Haphazard Wiring of Simple Receptive Fields and Orientation Columns in Visual Cortex
Authors: Ringach Dario L.
Published: March 2004

The receptive fields of simple cells in visual cortex are composed of elongated on and off subregions. This spatial arrangement is widely thought to be responsible for the generation of orientation selectivity. Neurons with similar orientation preferences cluster in “columns” that tile the cortical surface and form a map of orientation selectivity. It has been proposed that simple cell receptive fields are constructed by the selective pooling of geniculate receptive fields aligned in space. A recent analysis of monosynaptic connections between geniculate and cortical neurons appears to reveal the existence of “wiring rules” that are in accordance with the classical model. The precise origin of the orientation map is unknown, but both genetic and activity-dependent processes are thought to contribute. Here, we put forward the hypothesis that statistical sampling from the retinal ganglion cell mosaic may contribute to the generation of simple cells and provide a blueprint for orientation columns. Results from computer simulations show that the “haphazard wiring” model is consistent with data on the probability of monosynaptic connections and generates orientation columns and maps resembling those found in the cortex. The haphazard wiring hypothesis could be tested by measuring the correlation between the orientation map and the structure of the retinal ganglion cell mosaic of the contralateral eye.