bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency‐dependent synaptic depression modifies postsynaptic firing probability in cats
Authors: Clark B. D. , Cope T. C.
Published: September 2004

The influence of stimulus trains applied to single I a axons on the firing behaviour of single motoneurones was assessed in anaesthetized cats. The change in motoneurone firing probability associated with a single I a afferent spike was measured from short‐latency peaks in peristimulus time histograms or cross‐correlograms. Some synapses showed frequency‐dependent depression of the short‐latency peak, which is consonant with the frequency‐dependent depression reported for the I a‐motoneurone excitatory postsynaptic potential (EPSP).

Where they could be measured, EPSPs superimposed on the depolarizing ramps of potential recorded from motoneurones as they fired repetitively showed frequency‐dependent changes in amplitude that parallelled those of the simultaneously recorded histograms.

Thus it appears that at synapses with small EPSPs, which are typical in the mammalian CNS, modulation of the EPSP should result in similar modulation of cell firing.
Bilaterally evoked monosynaptic EPSPs, NMDA receptors and potentiation in rat sympathetic preganglionic neurones in vitro
Authors: Spanswick David , Renaud Leo P. , Logan Stephen D.
Published: September 2004

Whole‐cell patch clamp and intracellular recordings were obtained from 190 sympathetic preganglionic neurones (SPNs) in spinal cord slices of neonatal rats. Fifty‐two of these SPNs were identified histologically as innervating the superior cervical ganglion (SCG) by the presence of Lucifer Yellow introduced from the patch pipette and the appearance of retrograde labelling following the injection of rhodamine‐dextran‐lysine into the SCG.

Electrical stimulation of the ipsilateral (n= 71) or contralateral (n= 32) lateral funiculi (iLF and cLF, respectively), contralateral intermediolateral nucleus (cIML, n= 41) or ipsilateral dorsal horn (DH, n= 34) evoked EPSPs or EPSCs that showed a constant latency and rise time, graded response to increased stimulus intensity, and no failures, suggesting a monosynaptic origin.

In all neurones tested (n= 60), fast rising and decaying components of EPSPs or EPSCs evoked from the iLF, cLF, cIML and DH in response to low‐frequency stimulation (0.03‐0.1 Hz) were sensitive to non‐NMDA receptor antagonists.

In approximately 50 % of neurones tested (n= 29 of 60), EPSPs and EPSCs evoked from the iLF, cLF, cIML and DH during low‐frequency stimulation were reduced by NMDA receptor antagonists. In the remaining neurones, an NMDA receptor antagonist‐sensitive EPSP or EPSC was revealed only in magnesium‐free bathing medium, or following high‐frequency stimulation.

EPSPs evoked by stimulation of the iLF exhibited a sustained potentiation of the peak amplitude (25.3 ± 11.4 %) in six of fourteen SPNs tested following a brief high‐frequency stimulus (10‐20 Hz, 0.1‐2 s).

These results indicate that SPNs, including SPNs innervating the SCG, receive monosynaptic connections from both sides of the spinal cord. The neurotransmitter mediating transmission in some of the pathways activated by stimulation of iLF, cLF, cIML and DH is glutamate acting via both NMDA and non‐NMDA receptors. Synaptic plasticity is a feature of glutamatergic transmission in some SPNs where EPSPs are potentiated following a brief high‐frequency stimulus. Our data also suggest a differential expression of NMDA receptors by these neurones.
Low‐conductance intercellular coupling between mouse chromaffin cells in situ
Authors: Moser Tobias
Published: September 2004

Patch‐clamp experiments were used to compare membrane properties of mouse chromaffin cells in thin tissue slices and of isolated cells in primary culture. The mean membrane input resistance (Rin) and membrane capacitance were 3.1 ± 0.5 GΩ and 9.1 ± 0.5 pF in situ and 9.9 ± 1.8 GΩ and 8.2 ± 0.2 pF in isolated cells.

Spike‐like currents were observed on top of the calcium currents during depolarizations in thirty out of forty‐nine cells in situ. They were not seen in isolated cells nor after addition of Cd2+ (100 μM) and TTX (10 μM) to the perfusate of the slices. The mean Rin of cells which displayed current spikes (2.3 ± 0.18 GΩ) was significantly smaller than that of cells lacking spikes (3.9 ± 0.25 GΩ). It is suggested that the current spikes represent intercellular currents which result from action potential firing in neighbouring cells during the depolarization of the patch‐clamped cell.

Investigation of capacitative currents induced by square voltage pulses showed a slow component in twenty‐four out of twenty‐seven cells in situ.

It is concluded that a large fraction of mouse chromaffin cells in situ are electrically coupled. From the slow capacitative currents and the amplitude of the intercellular current spikes a junctional conductance between chromaffin cells of below 1 nS was deduced.

This junctional conductance appears to be too low to support spreading of electrical activity in cases where a single cell is stimulated by an action potential. However, the junctional conductance could allow longer depolarizations of one cell or simultaneous firing of several cells to trigger electrical activity in neighbouring cells.
Endogenous peptidergic modulation of perisynaptic Schwann cells at the frog neuromuscular junction
Authors: Bourque Marie‐Josée , Robitaille Richard
Published: September 2004

Although peptides are important modulators of synapses, their action on synapse‐glia interactions remain unclear. The amphibian neuromuscular junction (NMJ) was used to examine the effects of substance P (SP) on perisynaptic Schwann cells (PSCs), glial cells at the frog NMJ, by monitoring changes in intracellular Ca2+.

SP induced Ca2+ responses that were mimicked by the neurokinin 1 receptor (NK‐1) agonist septide and with a shorter delay by the SP fragment, SP(6–11). SP and SP(6–11) responses were blocked by NK‐1 antagonists SR140333 and LY303870.

Ca2+ responses remained unchanged when extracellular Ca2+ was removed but were blocked after pertussis toxin (PTX) treatment, indicating that the receptors were linked to internal stores of Ca2+ via a PTX‐sensitive G‐protein.

The slowly hydrolysable NK‐1 agonist [Sar9, Met(O2)11]‐SP only induced Ca2+ responses when applied for a long period of time and not during brief, local applications, suggesting the involvement of SP hydrolysis. Acetylcholinesterase (AChE) may not be involved in SP degradation since Ca2+ responses evoked by SP were unchanged in the presence of the cholinesterase inhibitor neostigmine.

Ca2+ responses induced by muscarine and nerve stimulations were almost abolished when preceded by SP applications, while those induced by ATP were significantly reduced. The rundown of the nerve‐evoked Ca2+ responses in PSCs was attenuated in the presence of SR140333.

These results indicate that endogenous SP is involved in the regulation of PSC activity and that SP is an important modulator of glial cell Ca2+ signalling and synapse‐glia communication.
Spontaneous electrical rhythmicity in cultured interstitial cells of Cajal from the murine small intestine
Authors: Koh Sang Don , Sanders Kenton M. , Ward Sean M.
Published: September 2004

Interstitial cells of Cajal (ICC) are pacemaker cells in the small bowel, and therefore this cell type must express the mechanism responsible for slow wave activity. Isolated ICC were cultured for 1–3 days from the murine small intestine and identified with c‐Kit‐like immunoreactivity (c‐Kit‐LI).

Electrical recordings were obtained from cultured ICC with the whole‐cell patch clamp technique. ICC were rhythmically active, producing regular slow wave depolarizations with waveforms and properties similar to slow waves in intact tissues.

Spontaneous activity of c‐Kit‐LI cells was inhibited by reduced extracellular Na+, gadolinium, and reduced extracellular Ca2+. The activity was not affected by nisoldipine. Voltage clamp studies showed rhythmic inward currents that were probably responsible for the slow wave activity. The current‐voltage relationship showed that the spontaneous currents reversed at about +17 mV. These observations are consistent with the involvement of a non‐selective cation current in the generation of slow waves, but do not rule out contributions from other conductances or transporters.

A Ba2+‐sensitive inwardly rectifying K+ current in c‐Kit‐LI cells that may be involved in slow wave repolarization and maintenance of a negative potential between slow waves was also found. Similar pharmacology was observed in studies of intact murine intestinal muscles.

Cultured ICC may be a useful model for studying the properties and pharmacology of some of the ionic conductances involved in spontaneous rhythmicity in the gastrointestinal tract.
Neuroeffector transmission in arterioles of the guinea‐pig choroid
Authors: Hashitani H. , Windle A. , Suzuki H.
Published: September 2004

Using conventional microelectrode techniques, membrane potentials were recorded from smooth muscle cells of guinea‐pig choroidal arterioles.

Transmural stimulation initiated excitatory junction potentials (EJPs) which were abolished by either guanethidine or α,β‐methylene‐ATP but not by phentolamine, indicating that they resulted from activation of purinoceptors.

Trains of stimuli evoked EJPs which were followed by a slow depolarization, an inhibitory junction potential (IJP) or a biphasic membrane potential change which consisted of an IJP and a subsequent slow depolarization.

Slow depolarizations were abolished by either phentolamine or guanethidine, indicating that they resulted from activation of α‐adrenoceptors.

IJPs were abolished by atropine but not by guanethidine, and were reduced by 50 % by apamin with the residual response being abolished by charybdotoxin, indicating that they resulted from the activation of muscarinic receptors which open two sets of Ca2+‐activated K+ channels.

Most responses were followed by slow hyperpolarizations. These were almost abolished by L‐nitroarginine, an effect which was partly overcome by L‐arginine, and were abolished by glibenclamide, indicating that they resulted from the release of NO and activation of ATP‐sensitive K+ channels.

Immunohistochemical analysis showed that arterioles were densely innervated by adrenergic nerve fibres. A population of fibres, likely to be cholinergic, was also identified. Furthermore, populations of nerve fibres immunoreactive to antibodies against either nitric oxide synthase (NOS) or substance P (SP) were also identified.

These findings indicate that choroidal arterioles of the guinea‐pig are innervated by at least three different populations of nerves, adrenergic nerves which evoke excitatory responses, cholinergic nerves which evoke inhibitory responses and a population of nerves which cause the release of NO.
Tetrodotoxin‐resistant impulses in single nociceptor nerve terminals in guinea‐pig cornea
Authors: Brock James A. , McLachlan Elspeth M. , Belmonte Carlos
Published: September 2004

Extracellular recording techniques have been used to study nerve impulses in single sensory nerve terminals in guinea‐pig cornea isolated in vitro.

Nerve impulses occurred spontaneously and were evoked by electrical stimulation of the ciliary nerves.

The nerve impulses were identified as originating in polymodal receptors, mechano‐receptors or ‘cold’ receptors. All three types are believed to be nociceptors.

Tetrodotoxin (TTX, 1 μm) blocked nerve impulses evoked by electrical stimulation of the ciliary nerves. However, ongoing and/or naturally evoked nerve impulses persisted in the presence of TTX in all three types of receptors. Lignocaine (lidocaine; 1 mm) blocked all electrical activity.

TTX‐resistant sodium channels therefore play a major role in generating the action potentials that signal pain to the brain.
Ionotropic and metabotropic activation of a neuronal chloride channel by serotonin and dopamine in the leech Hirudo medicinalis
Authors: Ali Declan W. , Catarsi Stefano , Drapeau Pierre
Published: September 2004

Cl− channels on the pressure‐sensitive (P) neuron in the leech are directly activated by synaptic release of serotonin (5‐HT) and are indirectly stimulated by the cAMP second messenger pathway, suggesting an unusual dual regulation of the channels. We have investigated the mode of action of 5‐HT and dopamine (DA) on a Cl− channel in adult P cells in culture by recording from cell‐attached patches.

5‐HT increased Cl− channel activity only when included in the recording pipette and not when applied in the bath.

Pipette or, more effectively, bath application of DA led to an increase in Cl− channel activity. This effect was blocked by the potent and specific dopaminergic (DA1) receptor blocker, SCH‐23390.

The stimulation by DA, but not by 5‐HT, was also blocked by the cAMP‐dependent protein kinase A (PKA) inhibitor Rp‐cAMP and was mimicked by the membrane‐permeant cAMP analogue dibutyryl cAMP (db‐cAMP).

Our results show that 5‐HT directly gates a Cl− channel that is also activated by DA via the cAMP pathway. This study demonstrates that a ligand‐gated channel can be independently operated by another transmitter acting via a second messenger pathway.
Chloride and non‐selective cation channels in unstimulated trout red blood cells
Authors: Egée Stéphane , Mignen Olivier , Harvey Brian J. , Thomas Serge
Published: September 2004

The cell‐attached and excised inside‐out configurations of the patch‐clamp technique were used to demonstrate the presence of two different types of ion channels in the membrane of trout red blood cells under isotonic and normoxic conditions, in the absence of hormonal stimulation. The large majority (93 %) of successful membrane seals allowed observation of at least one channel type.

In the cell‐attached mode with Ringer solution in the bath and Ringer solution, 145 mM KCl or 145 NaCl in the pipette, a channel of intermediate conductance (15‐25 pS at clamped voltage, Vp= 0 mV) was present in 85 % of cells. The single channel activity reversed between 5 and 7 mV positive to the spontaneous membrane potential. A small conductance channel of 5‐6 pS and +5 mV reversal potential was also present in 62 % of cells.

After excision into the inside‐out configuration (with 145 mM KCl or NaCl, pCa 8 in the bath, 145 mM KCl or NaCl, pCa 3 in the pipette) the intermediate conductance channel was present in 439 out of 452 successful seals. This channel was spontaneously active in 90 % of patches and in the other 10 % of patches the channel was activated by suction. The current‐voltage relationship showed slight inward rectification. The channel conductance was in the range 15‐20 pS between ‐60 and 0 mV and increased to 25‐30 pS between 0 and 60 mV, with a reversal potential close to zero. Substitution of K+ for Na+ in the pipette or in the bath did not significantly change the single channel conductance. Dilution of the bathing solution KCl concentration shifted the reversal potential towards the Nernst equilibrium for cations. Substitution of N‐methyl‐D‐glucamine (NMDG) for K+ or Na+ in the bath almost abolished the outward current whilst the divalent cation Ca2+ permeated the channel with a higher permeability than K+ and Na+. Inhibition of channel openings was obtained with flufenamic acid, quinine, gadolinium or barium. Taken together these data demonstrate that the intermediate conductance channel belongs to a class of non‐selective cation (NSC) channels.

In excised patches, under the same control conditions, the conductance of the small conductance non‐rectifying channel was 8·6 ± 0·8 pS (n= 12) between ‐60 and +60 mV and the reversal potential was close to 0 mV. This channel could be blocked by 5‐nitro‐2‐(3‐phenylpropylamino)‐benzoate (NPPB) but not by flufenamic acid, DIDS, barium or gadolinium. Selectivity and substitution experiments made it possible to identify this channel as a non‐rectifying small conductance chloride (SCC) channel.
Validation of the [1,2‐13C]acetate recovery factor for correction of [U‐13C]palmitate oxidation rates in humans
Authors: Schrauwen Patrick , van Aggel‐Leijssen Dorien P. C. , van Marken Lichtenbelt Wouter D. , van Baak Marleen A. , Gijsen Annemie P. , Wagenmakers Anton J. M.
Published: September 2004

The validity of estimations of plasma fatty acid oxidation using tracers has often been questioned. The appearance of isotopic markers in breath CO2 is delayed and incomplete. Recently suggestions have been made that substantial amounts of tracer are incorporated into products of the tricarboxylic acid cycle (e.g. glucose, glutamine and glutamate) and that an acetate correction factor can be used to correct for tracer fixation. In the present study we investigated whether the appearance of 13CO2 during a separate infusion of [1,2‐13C]acetate could be used for correction of [U‐13C]palmitate oxidation rates in studies lasting <2 h and we quantified the appearance of tracer in the glutamine, glutamate and glucose pools of the body.

An infusion of either [1,2‐13C]acetate (0.104 μmol min−1 kg−1) or [U‐13C]palmitate (0.013 μmol min−1 kg−1) was given to eight male subjects and continued for 2 h at rest. In six subjects the infusion of [1,2‐13C]acetate was repeated to determine reproducibility of the acetate recovery.

Fractional recovery in breath from [1,2‐13C]acetate gradually increased during the infusion period at rest from 14.1 ± 0.6 % at 60 min to 26.5 ± 0.5 % at 120 min after the start of the infusion. Intersubject coefficient of variance was 8.3 ± 0.6 % and intrasubject coefficient of variance of the acetate recovery tests was 4.0 ± 1.5 %. After 2 h of [1,2‐13C]acetate infusion, 12.4 ± 0.8 and 10.3 ± 0.9 % of infused 13C was incorporated in the glutamine and glutamate pools, respectively.

In conclusion, the [1,2‐13C]acetate recovery factor can be used for correcting the rate of [U‐13C]palmitate oxidation in infusing studies of 2 h in resting conditions. Failure to use this recovery factor leads to a substantial underestimation of the rate of plasma free fatty acid oxidation. The extent of label fixation could largely be explained by accumulation of tracer carbon in glutamine and glutamate, and the accumulation in glucose is negligible.
Potentiation of transmitter release by protein kinase C in goldfish retinal bipolar cells
Authors: Minami Naotoshi , Berglund Ken , Sakaba Takeshi , Kohmoto Hiromi , Tachibana Masao
Published: September 2004

We examined whether transmitter release could be modified by the activation of protein kinase C (PKC) of retinal bipolar cells. A bipolar cell with a large axon terminal was isolated from the goldfish retina. The presynaptic Ca2+ current was measured under whole‐cell voltage clamp, and the released transmitter (probably glutamate) was detected electrophysiologically by using the response of NMDA receptors of catfish horizontal cells as a reporter.

Transmitter release was potentiated by a PKC activator, phorbol 12‐myristate 13‐acetate (PMA), but not by an ineffective phorbol ester, 4α‐phorbol 12,13‐didecanoate. A PKC inhibitor, bisindolylmaleimide I, did not affect the transmitter release by itself but blocked the PMA‐induced potentiation of transmitter release. These results suggest that the actions of PMA were mediated via the activation of PKC.

Introduction of 5 mm EGTA into the presynaptic terminals of bipolar cells revealed two separate components of transmitter release. A rapid component was triggered immediately after depolarization while a slow component appeared with a delay. Application of PMA selectively potentiated the slow component without affecting the Ca2+ dependence of exocytosis.

We suggest that the activation of PKC may modify the recruitment process of synaptic vesicles in retinal bipolar cells.
Synaptic currents at individual connections among stellate cells in rat cerebellar slices
Authors: Kondo Satoru , Marty Alain
Published: September 2004

Unitary inhibitory synaptic connections among stellate cells were studied in rat cerebellar slices. Presynaptic action potentials and inhibitory postsynaptic currents (IPSCs) were simultaneously recorded by loose cell‐attached and tight‐seal whole‐cell recording, respectively.

Several types of synaptic connections were distinguished on the basis of the shape of the amplitude distribution of successfully evoked currents. For simple synapses, which presumably arise at single release sites, these histograms could be fitted to a single Gaussian (5 cases). In four additional cases a small amplitude component (< 50 pA) was superimposed to a single Gaussian peak. The small events had slow rise times and widely distributed amplitudes. Finally eleven histograms showed two or more Gaussian components and were classified as complex connections.

Failure rates ranged from 0.06 to 0.85 for unitary connections (n= 20) and from 0.59 to 0.78 for simple synapses (n= 5).

Coefficient of variation values derived from Gaussian fits to simple synapse histograms ranged between 0.20 and 0.38 (n= 5).

In simple synapses peak current amplitudes were positively correlated to both current rise time and decay half‐width.

Intervals between presynaptic action potentials were widely distributed. During stationary periods there was no correlation between interspike interval and amplitude size, success rate or latency. In some experiments, episodes with shorter interspike intervals were observed. During these periods, amplitude and success rate decreased, and the latency increased. Thus, IPSC characteristics depend on the mean frequency of presynaptic spikes, but not on random fluctuations of interspike intervals during stationary periods.
Differential oxygen sensitivity of the K+‐Cl− cotransporter in normal and sickle human red blood cells
Authors: Gibson J. S. , Speake P. F. , Ellory J. C.
Published: September 2004

K+ influx and efflux were measured in normal (HbA) and sickle (HbS) red blood cells to investigate the interaction of swelling, H+ ions and urea with O2 (0 to 150 mmHg O2) in the presence of ouabain and bumetanide (both 100 μM).

In HbA cells, K+‐Cl− cotransport was O2 dependent. At low oxygen tensions (PO2s) the transporter was inactive and refractory to low pH, swelling or urea.

Cl−‐independent K+ influxes in sickle cells were elevated at low PO2s, as previously reported. Cl−‐dependent K+ influxes were large at both high and low PO2s, whether stimulated by swelling, H+ ions or urea. In the absence of O2, Cl−‐dependent K+ influxes were similar in magnitude to those measured at high PO2s. The minimum for Cl−‐dependent K+ influx was observed at PO2s of about 40‐70 mmHg.

K+ efflux from HbS cells was stimulated by the addition of urea (500 mM). The rate constants were of similar magnitude whether measured at high PO2 or in the absence of O2, and were predominantly Cl− dependent under both conditions.

In HbS red blood cells, reduction of extracellular Ca2+, addition of 1 mM Mg2+ or nitrendipine (10 μM) to the saline had no effect. Inhibitors of K+‐Cl− cotransport, [(dihydroindenyl)oxy] alkanoic acid (DIOA; 100 μM) or calyculin A (0·1 μM), inhibited influxes by a similar magnitude to Cl− substitution.

Results are significant for the pathophysiology of sickle cell disease. Low pH and urea are able to stimulate KCl loss from sickle cells, leading to cellular dehydration, even in regions of low PO2.
The chronic effect of vascular endothelial growth factor on individually perfused frog mesenteric microvessels
Authors: Bates D. O.
Published: September 2004

Hydraulic conductivity (Lp) of the wall of perfused microvessels has previously been shown to be chronically increased 24 h after a 10 min perfusion with vascular endothelial growth factor (VEGF). In order to investigate this further, Lp and the effective oncotic pressure difference (σΔΠ) acting across the vessel walls was measured before exposure to VEGF and 24 h later after the mesentery had been replaced in the abdominal cavity.

Acute 10 min perfusion with VEGF did not chronically change σΔΠ despite chronically increasing Lp 6.8 ± 1.2‐fold. This suggests that pathways formed 24 h after perfusion with VEGF which increase hydraulic conductivity of the capillary walls have the same reflection coefficient as those present before VEGF.

Acute 10 min perfusion with VEGF significantly increased the diameter of vessels after 24 h by 48 ± 13 %. To determine whether this was due to changes in the compliance of the vessel wall, the distensibility of microvessels was measured before and 24 h after perfusion with VEGF. The distensibility was increased 45 ± 15 % by VEGF but this was not great enough to account for the increase in diameter.

The chronic increase in Lp could be attenuated by inhibition of nitric oxide synthase with l‐NAME. In addition, the chronic increase in permeability was correlated with the acute response to VEGF (r= 0.71, P < 0.01) suggesting that the acute and chronic changes may be related.

These results show that VEGF chronically increases Lp without affecting the oncotic reflection coefficient. This may be due to reduced pore path length, or increased small pore numbers, which are properties of fenestrated capillaries. They also show that VEGF increases microvascular distensibility and diameter.
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.