bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of membrane potential on the voltage dependence of motility‐related charge in outer hair cells of the guinea‐pig
Authors: Santos‐Sacchi J. , Kakehata S. , Takahashi S. 
Published: September 2004

Isolated outer hair cells (OHCs) from the guinea‐pig were whole‐cell voltage clamped to study the influence of initial voltage on the voltage dependence of motility‐related gating current or, equivalently, on the voltage dependence of membrane capacitance.
Prepulse delivery caused changes in the magnitude of motility‐related gating currents, which are due predominantly to shifts in the voltage at peak capacitance (VpkCm). Depolarization shifts VpkCm in the hyperpolarizing direction, and hyperpolarization does the opposite. The mean shift between ‐120 and +40 mV prepulse states with long‐term holding potentials (> 2 min) at −80 mV was 14.67 ± 0.95 mV (n= 10; mean ± s.e.m.).
The effect of initial membrane potential is sigmoidal, with a voltage dependence of 23 mV per e‐fold change in VpkCm, and maximum slope within the physiological range of OHC resting potentials. This indicates that the cell is poised to respond maximally to changes in resting potential.
The kinetics of prepulse effects are slow compared with motility‐related gating current kinetics. High‐resolution measurement of membrane capacitance (Cm) using two voltage sinusoids indicates that shifts in VpkCm induce Cm changes with time courses fitted by two exponentials (τ0, 0.070 ± 0.003 s; τ1, 1.28 ± 0.07 s; A0, 1.54 ± 0.13 pF; A1, 1.51 ± 0.13 pF; means ± s.e.m.; n= 22; step from +50 to −80 mV). Recovery of prepulse effects exhibits a similar time course.
Prepulse effects are resistant to intracellular enzymatic digestion, to fast intracellular calcium buffers, and to intracellular pressure. Through modelling, we indicate how the effect may be explained by an intrinsic voltage‐induced tension generated by the molecular motors residing in the lateral membrane.
Interaction of platelet‐activating factor, spleen and atrial natriuretic peptide in plasma volume regulation during endotoxaemia in rats
Authors: Qu Xiao‐Wu , Rozenfeld Ranna A. , Huang Wei , Crawford Susan E. , Gonzalez‐Crussi F. , Hsueh Wei 
Published: September 2004

We studied endotoxin (lipopolysaccharide, LPS)‐induced platelet‐activating factor (PAF) production in various visceral organs, and the effect of PAF antagonists or splenectomy on LPS‐induced changes.
PAF production in response to LPS was highest in the spleen, followed by ileum, heart, lung and kidneys. None was found in the liver. The splenic response was rapid, reaching 10 times the basal level at 30 min. The increased PAF content in each organ was unrelated to the enzyme activity of either macrophages or neutrophils.
LPS‐induced hypotension and haemoconcentration were largely prevented by PAF antagonists and splenectomy.
Plasma volume fell, and plasma atrial natriuretic peptide (ANP) rose, after LPS administration. Splenectomy or pretreatment with PAF antagonists almost completely prevented these LPS‐induced changes at 30 min, but only partially reversed them at 90 min.
These results suggest that during endotoxaemia: (a) the spleen is the site of the highest endogenous PAF production; (b) the initial release of ANP is dependent on the production of endogenous PAF, and a PAF‐ANP interaction mediates the early plasma volume reduction; (c) plasma volume reduction as well as ANP release depend on the spleen; (d) PAF mediated the hypotensive response and its action in the spleen; and (e) sequestered neutrophils are probably not the main source of PAF in the spleen.
Monocularly programmed human saccades during vergence changes?
Authors: Enright J. T. 
Published: September 2004

When binocular fixation is shifted to a new target located at a different distance and in a different direction from initial fixation, a binocularly unbalanced saccade occurs at or near the onset of the composite eye movement. Those saccades typically produce good post‐saccadic foveation of the target by one eye or the other.
Following such saccades, the better‐aligned eye is typically as well aimed at the target as after pure versional saccades, but the partner eye deviates much more, thus requiring asymmetrical post‐saccadic vergence movement.
This phenomenon suggests that during binocular viewing, the retinal eccentricity of a new‐target's image from one of the eyes can be used to programme that eye's own saccade, so that it arrives reliably on target; and that the images of that target from both eyes participate in generating the saccadic excursion of the partner eye.
The ecologically useful result is rapid achievement of a high‐resolution monocular view of the new target, although full binocular foveation is achieved much later.
Protein kinase A induces recruitment of active Na+,K+‐ATPase units to the plasma membrane of rat proximal convoluted tubule cells
Authors: Carranza Maria Luisa , Rousselot Martine , Chibalin Alexander V. , Bertorello Alejandro M. , Favre Hervé , Féraille Eric 
Published: September 2004

The aim of this study was to investigate the mechanism of control of Na+,K+‐ATPase activity by the cAMP‐protein kinase A (PKA) pathway in rat proximal convoluted tubules. For this purpose, we studied the in vitro action of exogenous cAMP (10−3 M dibutyryl‐cAMP (db‐cAMP) or 8‐bromo‐cAMP) and endogenous cAMP (direct activation of adenylyl cyclases by 10−5 M forskolin) on Na+,K+‐ATPase activity and membrane trafficking.
PKA activation stimulated both the cation transport and hydrolytic activity of Na+,K+‐ATPase by about 40 %. Transport activity stimulation was specific to the PKA signalling pathway since (1) db‐cAMP stimulated the ouabain‐sensitive 86Rb+ uptake in a time‐ and dose‐dependent fashion; (2) this effect was abolished by addition of H‐89 or Rp‐cAMPS, two structurally different PKA inhibitors; and (3) this stimulation was not affected by inhibition of protein kinase C (PKC) by GF109203X. The stimulatory effect of db‐cAMP on the hydrolytic activity of Na+,K+‐ATPase was accounted for by an increased maximal ATPase rate (Vmax) without alteration of the efficiency of the pump, suggesting that cAMP‐PKA pathway was implicated in membrane redistribution control.
To test this hypothesis, we used two different approaches: (1) cell surface protein biotinylation and (2) subcellular fractionation. Both approaches confirmed that the cAMP‐PKA pathway was implicated in membrane trafficking regulation. The stimulation of Na+,K+‐ATPase activity by db‐cAMP was associated with an increase (+40 %) in Na+,K+‐ATPase units expressed at the cell surface which was assessed by Western blotting after streptavidin precipitation of biotinylated cell surface proteins. Subcellular fractionation confirmed the increased expression in pump units at the cell surface which was accompanied by a decrease (‐30 %) in pump units located in the subcellular fraction corresponding to early endosomes.
In conclusion, PKA stimulates Na+,K+‐ATPase activity, at least in part, by increasing the number of Na+‐K+ pumps in the plasma membrane in proximal convoluted tubule cells.
Importance of basolateral K+ conductance in maintaining Cl− secretion in murine nasal and colonic epithelia
Authors: MacVinish Lesley J. , Hickman Margaret E. , Mufti Dina A. H. , Durrington Hannah J. , Cuthbert Alan W. 
Published: September 2004

Epithelia lining the nasal passages and descending colon of wild‐type and cystic fibrosis (CF) mice were examined by the short‐circuit current technique. Additionally, intracellular Ca2+ ion determinations were made in nasal epithelial cells. Forskolin produced anion secretory currents in wild‐type and CF nasal epithelia. It produced similar effects in wild‐type colonic epithelia, but not in colonic epithelia from CF mice.
After electrogenic Na+ transport was blocked with amiloride and electrogenic Cl− secretion was stimulated with forskolin, the ability of K+ channel blockers to inhibit the forskolin‐induced Cl− current was determined. The order of efficiency for nasal epithelium was: Ba2+ > clofilium >>> TEA = azimilide >>> trans‐6‐cyano‐4‐(N‐ethylsulphonyl‐N‐methylamino)‐3‐hydroxy‐2,2‐dimethyl‐chromane (293B) = charybdotoxin, whereas for the colonic epithelium the order was: Ba2+= 293B >>> azimilide = TEA >>> clofilium = charybdotoxin.
1‐Ethyl‐2‐benzimdazolinone (1‐EBIO) was able to generate large Cl−‐secretory currents in colonic epithelia which were partially sensitive to charybdotoxin, with the remaining current being inhibited by 293B. In nasal epithelia 1‐EBIO produced only a small transient effect on current.
Forskolin released intracellular Ca2+ in nasal epithelial cells; this activity was attenuated when more powerful Ca2+‐releasing agents were applied first.
It is concluded that an action on basolateral cAMP‐sensitive K+ channels is an important determinant of the maintained responses to forskolin in nasal and colonic epithelia, in addition to the effects on the cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane. In CF nasal epithelia the activation of calcium‐activated chloride channels (CACs) substitutes for the effect on CFTR. On the basis of the different orders of potency of the blocking agents and the differential response to 1‐EBIO it is concluded that the cAMP‐sensitive K+ channels are different in the airways and the gut.
Contribution of Na+‐H+ exchange to sodium reabsorption in the loop of Henle: a microperfusion study in rats
Authors: Shirley D. G. , Walter S. J. , Unwin R. J. , Giebisch G. 
Published: September 2004

The contribution of apical Na+‐H+ exchange to sodium reabsorption in the thick ascending limb of the loop of Henle (TALH) in vivo was examined in anaesthetized rats by perfusing loops of Henle of superficial nephrons with solutions containing the Na+‐H+ exchange inhibitor, ethyl isopropyl amiloride (EIPA).
Using a standard perfusate, no statistically significant effect of EIPA on net sodium reabsorption (JNa) was detected. However, when sodium reabsorption in the pars recta of the proximal tubule was minimized by using a low‐sodium perfusate, EIPA reduced JNa from 828 ± 41 to 726 ± 37 pmol min−1 (P < 0.05), indicating that apical Na+‐H+ exchange can make a small contribution to net sodium reabsorption in the TALH in vivo. This contribution appears to be dependent on the bicarbonate load, since an increase in the latter led to an enhancement of EIPA‐sensitive sodium transport.
Addition of the Na+‐K+‐2Cl− cotransport inhibitor, bumetanide, to the low‐sodium perfusate reduced baseline JNa to 86 ± 27 pmol min−1. In this setting, EIPA reduced JNa further, to −24 ± 18 pmol min−1 (P < 0.05), an effect similar to that seen in the absence of bumetanide. This finding argues against previous suggestions (based on in vitro evidence) that inhibition of the Na+‐K+‐2Cl− cotransporter leads to an increase in apical Na+‐H+ exchange in the TALH.
Blockade of synaptic inhibition within the pre‐Bötzinger complex in the cat suppresses respiratory rhythm generation in vivo
Authors: Pierrefiche O. , Schwarzacher S. W. , Bischoff A. M. , Richter D. W. 
Published: September 2004

The role of synaptic inhibition in respiratory rhythm generation was analysed by microinjections of GABAA and glycine receptor antagonists into the bilateral pre‐Bötzinger complex (PBC) of anaesthetized cats. Central respiratory activity was monitored by phrenic nerve recordings.
Bilateral injections of bicuculline (50 or 100 μm) irreversibly slowed respiratory frequency and induced apneustic patterns.
Bilateral injections of strychnine (50 or 100 μm) greatly reduced phrenic burst amplitudes leading to increased burst frequency or irreversibly blocked rhythmic phrenic discharges. After unilateral tetrodotoxin (TTX) blockade in the PBC, strychnine injection into the contralateral PBC blocked rhythmic phrenic discharges.
Bilateral blockade of both GABAergic and glycinergic inhibition abolished rhythmic burst discharges and only tonic phrenic activity remained. Such tonic activity was blocked only by TTX (1 μm).
Potentiation of synaptic inhibition by the serotonin 1A receptor agonist 8‐hydroxydipropylaminotetralin (8‐OH‐DPAT; 50 μm) restored rhythmic activity only when given shortly after strychnine and bicuculline applications. It was, however, ineffective after blockade of synaptic inhibition was complete.
The study demonstrates the significance of synaptic inhibition in the process of respiratory generation in the adult cat in vivo .
The reliability of excitatory synaptic transmission in slices of rat visual cortex in vitro is temperature dependent
Authors: Hardingham Neil R. , Larkman Alan U. 
Published: September 2004

A total of twelve synaptic connections between pairs of pyramidal neurones in layer 2/3 of slices of rat visual cortex maintained in vitro was investigated using whole‐cell voltage recordings under visual control. The connections varied widely in strength, with the mean peak amplitudes of the resulting excitatory postsynaptic potentials (EPSPs) ranging between approximately 40 μV and 2 mV at 23°C. The smaller mean amplitudes included a substantial proportion of apparent failures of transmission.
The properties of these EPSPs were examined over a range of temperatures between 13 and 36°C. All the connections became more reliable, in that they showed fewer apparent failures of transmission, and showed less trial‐to‐trial variability at the higher temperatures. These changes appeared to be due primarily to an increase in the mean number of transmitter quanta released per presynaptic action potential.
At 36°C most connections were relatively reliable, with a mean failure rate of only 16%. Five connections showed virtually no failures (1% or fewer) at this temperature.
We conclude that quantal transmitter release is temperature dependent at these synapses, and that experiments performed at room temperature could lead to an exaggerated impression of the unreliability of transmission at central excitatory synapses.
Inhibitory influence of the ipsilateral motor cortex on responses to stimulation of the human cortex and pyramidal tract
Authors: Gerloff Christian , Cohen Leonardo G. , Floeter Mary Kay , Chen Robert , Corwell Brian , Hallett Mark 
Published: September 2004

The ability of the primary motor cortex (M1) to modulate motor responses in ipsilateral hand muscles seems to be important for normal motor control and potentially also for recovery after brain lesions. It is not clear which pathways mediate this ipsilateral modulation. Transcallosal connections have been proposed, but are known to be sparse between cortical hand motor representations in primates. The present study was performed to determine whether descending ipsilateral modulation of motor responses might also be mediated below the cortical level in humans.
A paired‐pulse protocol was used, in which motor‐evoked potentials (MEPs) were produced by cortical transcranial magnetic stimulation (cTMS) or by electrical stimulation of the pyramidal tract at the level of the pyramidal decussation (pdTES), in both preactivated and relaxed hand muscles. Paired stimuli were applied at various interstimulus intervals (ISIs) between 2 and 100 ms. The conditioning stimulus (CS) was always magnetic, and delivered to the M1 ipsilateral to the target hand, prior to the test stimulus (TS). The magnetic TS was delivered to the M1 contralateral to the target hand; the electrical TS was applied through electrodes placed over the mastoid process bilaterally. Further experiments included cortical electrical stimulation and H‐reflexes. The MEP amplitudes were averaged separately for each ISI and the control condition (no CS), and expressed as a percentage of the unconditioned response.
Conditioning stimulation of the ipsilateral M1 resulted in significant inhibition of magnetically evoked MEPs, and also of MEPs produced by pdTES. Inhibition occurred at ISIs between 6 and 50 ms, and was observed in preactivated and relaxed muscles. Higher CS intensities caused greater inhibition of both cTMS‐ and pdTES‐evoked MEPs.
While the conditioning effects on magnetically evoked muscle responses could be explained by a transcallosal mechanism, the effects on pdTES‐evoked MEPs cannot, because they are elicited subcortically and are therefore not susceptible to inhibitory mechanisms transmitted at the cortico‐cortical level.
In conclusion, the present results provide novel evidence that the inhibitory influence of the human M1 on ipsilateral hand muscles is to a significant extent mediated below the cortical level, and not only through cortico‐cortical transcallosal connections. They point to a concept of inhibitory interaction between the two primary motor cortices that is relayed at multiple levels along the neuroaxis, thus perhaps providing a structurally redundant system which may become important in case of lesions.
Muscle shortening induced by tenotomy does not reduce activity levels in rat soleus
Authors: Elder Geoffrey C. B. , Toner Lee V. 
Published: September 2004

A slow postural muscle was tenotomized to determine the role of muscle stretch on chronic recruitment patterns in freely moving animals.
Different amounts of muscle shortening were induced in the soleus muscles of ten rats by severing the tendon of insertion (n= 3), the whole Achilles' tendon (n= 4) or the origins and insertions (n= 3).
Bipolar wire electrodes were implanted on each muscle to record the electromyographic activity (EMG) under control and tenotomized conditions. The complex interference pattern was continuously analysed to determine the number and amplitude of peak potentials (called turns). The numbers of these ‘turns’ and their amplitudes were determined during 4 control and at least 5 experimental days. Sham‐operated controls and groups matched according to the type of tenotomy were analysed for length changes and pathological changes 5 and 10 days post‐tenotomy.
The total activity levels in all three tenotomy conditions were not significantly changed when compared with their own control levels. No differences in total activity level were found between the three tenotomized conditions.
The normal diurnal patterns of muscle recruitment were preserved during the tenotomized conditions, with the highest levels consistently occurring during the first 3 h of the dark cycle.
Tenotomy of the soleus, whether induced by distal (ST), distal and proximal (DT) or Achilles' tenotomy (AT) resulted in muscle shortening (9–26 %). No muscle pathology was found in the ST or AT groups. Degeneration was found in the DT group after 5 days, with further increases at 10 days.
These data suggest that the absence of stretch had no discernible influence on the aggregate activity levels in the slow postural soleus muscle. Whether tenotomy caused changes in recruitment within individual step cycles was not evaluated.
The arterial baroreceptor reflex of the rat exhibits positive feedback properties at the frequency of Mayer waves
Authors: Bertram Delphine , Barrès Christian , Cuisinaud Guy , Julien Claude 
Published: September 2004

Modelling studies have led to the proposal that Mayer waves (∼0.4 Hz in rats) could result from a resonance phenomenon in a feedback control loop. In this study, we investigated the presence of a resonance frequency in the arterial baroreceptor reflex loop, i.e. a particular frequency at which arterial pressure feeds back positively to the baroreceptors.
Frequency responses of mean arterial pressure (MAP) to aortic depressor nerve (ADN) stimulation were studied in fifteen urethane anaesthetized, ventilated rats with cardiac autonomic blockade. The ADN was stimulated using rectangular trains of impulses (2 ms, 100 Hz) delivered at frequencies ranging from 0.1 to 1 Hz. Phase angles between impulses and MAP were calculated using cross‐spectral analysis based on a fast Fourier transform algorithm.
Rhythmic ADN stimulation induced regular MAP oscillations at the expected frequencies that were attenuated by α‐adrenoceptor blockade and abolished after ganglionic blockade. The relationship between impulse and MAP oscillations was characterized by a strong coherence and a positive phase shift at low frequencies, indicating that impulses led MAP with respect to the out‐of‐phase pattern. Deviation of the phase from the out‐of‐phase behaviour was mainly due to the presence of a fixed time delay (∼0.8 s) between ADN stimuli and MAP changes. Phase angles fell to zero at 0.42 ± 0.02 Hz.
In rats, the arterial baroreceptor reflex exhibits a resonance frequency close to the frequency of spontaneously occurring Mayer waves. The reflex therefore seems the most likely origin for the Mayer waves.
Central projection of proprioceptive information from the wrist joint via a forearm ‘muscle’ nerve in the cat
Authors: Mackie P. D. , Rowe M. J. 
Published: September 2004

Peripheral nerves arising in joint capsules are known to contain a ‘contaminating’ contribution from muscle afferent fibres. In the present report we provide the first electrophysiological evidence that some joint afferent fibres may take an ‘ectopic’ path to the central nervous system via a nearby muscle nerve.
Experiments were conducted in anaesthetized cats in which a distal extension of the indicis proprius nerve was observed to project beyond its own muscle to the dorsal surface of the wrist joint capsule which is also supplied by the ‘classic’ wrist joint nerve, a branch of the dorsal interosseous nerve. Both the proximal and distal segments of the indicis proprius nerve were exposed for recording, by means of silver hook electrodes, while each segment remained in continuity.
Individual wrist joint afferent fibres with receptive fields on the dorsal surface of the joint capsule could be identified electrophysiologically within the distal segment of the indicis proprius nerve. In each of these cases the same fibre could also be identified at the proximal recording site. The identity of each of these simultaneously recorded units was established (1) by the short fixed interval between their times of spike occurrence, (2) from the exact correspondence of the capsular receptive field for the simultaneously recorded spikes, and (3) by the unfailing correlation in the presence, or absence, of the distally and proximally recorded spikes in association with either manual or controlled stimulation of the wrist joint capsule. Most joint afferent fibres identified with this projection path were in the group II range of conduction velocities and had conventional properties but group III fibres also appeared to be represented.
The present demonstration that some joint afferent fibres may be located within ‘muscle’ nerves emphasizes the importance of activating deep inputs, of joint or muscle origin, by adequate stimulation of the peripheral receptors in order to examine selectively the central actions of either source of input. Electrical stimulation of the peripheral nerves may lead to interpretative ambiguities.