bluuebunny/crossref_metadata_2025_split huggingface dataset:
Activity‐dependent regulation of ‘on’ and ‘off’ responses in cat visual cortical receptive fields
Authors: Debanne Dominique , Shulz Daniel E. , Frégnac Yves 
Published: September 2004

A supervised learning procedure was applied to individual cat area 17 neurons to test the possible role of neuronal co‐activity in controlling the plasticity of the spatial ‘on‐off’ organization of visual cortical receptive fields (RFs).
Differential pairing between visual input evoked in a fixed position of the RF and preset levels of postsynaptic firing (imposed iontophoretically) were used alternately to boost the ‘on’ (or ‘off’) response to a ‘high’ level of firing (S+ pairing), and to reduce the opponent response (respectively ‘off’ or ‘on’) in the same position to a ‘low’ level (S− pairing). This associative procedure was repeated 50‐100 times at a low temporal frequency (0.1‐0.15 s−1).
Long‐lasting modifications of the ratio of ‘on‐off’ responses, measured in the paired position or integrated across the whole RF, were found in 44 % of the conditioned neurons (17/39), and in most cases this favoured the S+ paired characteristic. The amplitude change was on average half of that imposed during pairing. Comparable proportions of modified cells were obtained in ‘simple’ (13/27) and ‘complex’ (4/12) RFs, both in adult cats (4/11) and in kittens within the critical period (13/28).
The spatial selectivity of the pairing effects was studied by pseudorandomly stimulating both paired and spatially distinct unpaired positions within the RF. Most modifications were observed in the paired position (for 88 % of successful pairings).
In some cells (n= 13), a fixed delay pairing procedure was applied, in which the temporal phase of the onset of the current pulse was shifted by a few hundred milliseconds from the presentation or offset of the visual stimulus. Consecutive effects were observed in 4/13 cells, which retained the temporal pattern of activity imposed during pairing for 5‐40 min. They were expressed in the paired region only.
The demonstration of long‐lasting adaptive changes in the ratio of ‘on’ and ‘off’ responses, expressed in localized subregions of the RF, leads us to suggest that simple and complex RF organizations might be two stable functional states derived from a common connectivity scheme.
The responsiveness of isolated human hand vein endothelial cells in normal pregnancy and in pre‐eclampsia
Authors: Mahdy Z. , Otun H. A. , Dunlop W. , Gillespie J. I. 
Published: September 2004

Human hand vein endothelial cells were isolated from blood obtained by traumatic venepuncture. Cells were identified as endothelial by staining with endothelium‐specific antibodies. The subject groups studied were (i) non‐pregnant, (ii) pregnant (mean, 35 weeks gestation) and (iii) pre‐eclamptic women (mean, 36 weeks gestation).
Fura‐2 was used to measure agonist‐induced responses in intracellular Ca2+ in single endothelial cells isolated and maintained in vitro. All of the cells examined responded to adenosine triphosphate (ATP) with a large transient increase in Ca2+ followed by a sustained plateau.
The responses to ATP were significantly larger in the cells from pregnant women than in those from non‐pregnant and pre‐eclamptic women, but no other differences were observed. The amplitudes of the responses to ATP were (means ± s.e.m.) 0.56 ± 0.04, 1.42 ± 0.24 and 0.65 ± 0.09 fura‐2 ratio units for cells from non‐pregnant, pregnant and pre‐eclamptic subjects, respectively.
In cells isolated from non‐pregnant subjects, the amplitude of the responses to carbachol, histamine and bradykinin were all smaller than those activated by ATP: 5.1, 13.9 and 4.4 %, respectively. Not all cells responded to these agonists: 25 % responded to carbachol, 70.5 % responded to histamine and 12.5 % responded to bradykinin. Sixty‐five per cent of the cells from normotensive pregnant subjects responded to bradykinin compared with 25 % in the non‐pregnant and 13.9 % in the pre‐eclamptic subjects.
These data suggest that there may be differences in the responsiveness of venous endothelial cells in pregnancy and that pre‐eclamptic cells behave differently.
Muscular sense is attenuated when humans move
Authors: Collins D. F. , Cameron T. , Gillard D. M. , Prochazka A. 
Published: September 2004

Muscle receptors play an important role in our conscious perception of movement, but there are no published accounts of our ability to detect their signals during different motor tasks. The present experiments introduce a method to test muscular sense when humans move.
Muscle receptors were excited by an electrically induced twitch of the right extensor carpi ulnaris muscle. The muscle was stimulated via percutaneously inserted intramuscular electrodes or using surface stimulation through anaesthetized skin. Muscular sense was represented by the ability to detect the twitch and was compared between various tasks and stationary control trials.
Three hertz voluntary wrist movements significantly attenuated muscular sense to 37 % of control. This velocity‐dependent attenuation was present over a range of twitch amplitudes suggesting it does not simply reflect a masking of low intensity stimuli. Perceptual ratings of twitch amplitude during fast imposed passive movements were reduced by 40 %, though this did not quite reach statistical significance. However, perceptual ratings of twitches evoked up to 2 s after the termination of the passive movements were significantly different from control.
Reaching with the stimulated, but not the contralateral, arm also significantly reduced muscular sense (to 40 %).
Attenuation to 58 % of control during cyclic stretching of the skin on the dorsum of the hand showed that signals from peripheral receptors may play a role. Attenuation prior to a single wrist flexion movement indicated that central sources can also contribute.
The results are consistent with current findings of a general attenuation of sensory feedback during movement and raise questions regarding the role of muscular sense in movement control.
Hyperpolarization‐activated cationic currents (Ih) in neurones of the trigeminal mesencephalic nucleus of the rat
Authors: Khakh Baljit S. , Henderson Graeme 
Published: September 2004

We studied the voltage‐dependent current activated by membrane hyperpolarization in sensory proprioceptive trigeminal mesencephalic nucleus (MNV) neurones.
Membrane hyperpolarization (from ‐62 to ‐132 mV in 10 mV steps) activated slowly activating and non‐inactivating inward currents. The hyperpolarization‐activated currents could be described by activation curves with a half‐maximal activation potential (V½) of ‐93 mV, slope (k) of 8.4 mV, and maximally activated currents (Imax) of around 1 nA. The reversal potential of the hyperpolarization‐activated currents was ‐57 mV.
Extracellular Cs+ blocked hyperpolarization‐activated currents rapidly and reversibly in a concentration‐dependent manner with an IC50 of 100 μM and Hill slope of 0.8. ZD7288 (1 μM; 4‐(N‐ethyl‐N‐phenylamino)‐1,2‐dimethyl‐6‐(methylamino) pyridinium chloride), the compound developed as an inhibitor of the cardiac hyperpolarization‐activated current (If), also blocked the hyperpolarization‐activated currents in MNV neurones. Extracellular Ba2+ (1 mM) did not affect hyperpolarization‐activated currents. We tested whether the hyperpolarization‐activated currents contribute to the somatic membrane properties of MNV neurones by performing some experiments using current‐clamp recording. In such experiments application of Cs+ (1 mM) produced no effect on neuronal resting membrane potentials.
During the course of our experiments we noticed that activating ATP‐gated non‐selective cation channels (P2X receptors) caused an inhibition of Ih associated with a V½ shift of 10 mV in the hyperpolarizing direction. This P2X receptor‐mediated inhibition of Ih was blocked in recordings made with the rapid calcium chelator BAPTA (11 mM) in the pipette solution.
We conclude that the current activated by membrane hyperpolarization in MNV neurones is Ih on the basis of its similarity to Ih observed in other neuronal preparations. Activation of Ih can account for the anomalous time‐dependent inward rectification that has previously been described in MNV neurones.
Increased contribution of NR2A subunit to synaptic NMDA receptors in developing rat cortical neurons
Authors: Stocca Gabriella , Vicini Stefano 
Published: September 2004

Pharmacologically isolated miniature NMDA receptor‐mediated excitatory postsynaptic currents (mN‐EPSCs) were recorded in large visual cortical neurons in layer V of rat cortical slices. Haloperidol (100 μm) and CP101,606 (10 μm), two specific blockers of NMDA receptors comprising NR1/NR2B subunits, were tested on mN‐EPSCs in rats at postnatal days 7 and 8 (P7–P8) and P13–P15. At both ages tested, no significant effects of these drugs were seen in the whole population of neurons, although in few neurons at both ages changes in amplitude were observed with haloperidol. Other dopamine receptor antagonists, spiperone and clozapine, failed to decrease mN‐EPSCs in cortical neurons at P13–P15.
CP101,606 (10 μm) significantly decreased the amplitude of evoked N‐EPSCs (eN‐EPSCs) in visual cortical slices from rats at P3–P5, a developmental stage at which mRNA studies have indicated the virtual absence of NR2A mRNA. CP101,606 failed to significantly change evoked AMPA‐mediated EPSCs at P5 and eN‐EPSCs at P7–P8 and P13–P15.
NMDA receptor‐mediated currents were also studied in somatic outside‐out patches at P13–P15 with fast application of l‐glutamate (1 mm). Haloperidol (50 μm) and CP101,606 (10 μm) blocked these currents in all patches tested. The effect of CP101,606 was concentration dependent.
We suggest that rather early in development synaptic receptors comprising NR1/NR2B subunits could be associated with other subunits so that blockade by haloperidol and CP101,606 is prevented. Moreover, the consistent blockade seen in outside out patches might be ascribed to the confinement of NR1/NR2B receptors to an extrasynaptic population.
An allosteric interaction between the NMDA receptor polyamine and ifenprodil sites in rat cultured cortical neurones
Authors: Kew James N. C. , Kemp John A. 
Published: September 2004

The atypical NR2B subunit‐selective NMDA receptor antagonist ifenprodil was originally believed to act as a competitive antagonist at the polyamine binding site of the NMDA receptor. However, a number of studies have suggested that ifenprodil might bind to a distinct site.
Using whole‐cell voltage clamp recordings, we have studied the interaction of spermine with both ifenprodil and the related NR2B selective antagonist Ro 8–4304 at the NMDA receptor in rat cultured cortical neurones in the presence of saturating concentrations of glycine.
Ifenprodil and Ro 8‐4304 inhibited steady‐state currents evoked by 100 μm NMDA in the absence of spermine with IC50 values of 0.3 and 0.6 μm, respectively. In the presence of 1 and 3 mm spermine, IC50 values for ifenprodil were 1.4 and 1.8 μm and for Ro 8‐4304 they were 3.0 and 7.5 μm, respectively.
In the presence of spermine, the on‐time constant of receptor blockade by both antagonists was significantly slower than control and the off‐time constant of recovery from receptor blockade following removal of Ro 8‐4304 was significantly faster.
Fast application of spermine during an NMDA steady‐state current in the continuous presence of a subsaturating concentration of either antagonist resulted in a biphasic increase in the current, consistent with a fast increase upon spermine binding and a slow increase resultant from dissociation of antagonist due to spermine binding‐induced allosteric reduction in receptor antagonist affinity. In agreement with this, at higher, saturating concentrations of antagonist, the slow increase in current amplitude was markedly reduced or absent.
These observations are consistent with a non‐competitive, allosteric interaction between spermine and the antagonists, such that spermine binding to the NMDA receptor results in a reduction in receptor affinity for the antagonists and vice versa.
The effects of Mg2+ on the NMDA‐evoked currents and its interaction with ifenprodil were similar to those of spermine, supporting the suggestion that Mg2+ might be the physiological ligand acting at the spermine site mediating glycine‐independent stimulation.
Single‐channel currents of a peptide‐gated sodium channel expressed in Xenopus oocytes
Authors: Zhainazarov Aslbek B. , Cottrell Glen A. 
Published: September 2004

Single‐channel recordings were made from outside‐out membrane patches of Xenopus oocytes injected with the cDNA clone FaNaCh, which encodes a peptide‐gated Na+ channel from Helix aspersa.
The natural peptides FMRFamide and FLRFamide only activated unitary currents in oocytes injected with FaNaCh; the EC50 values were 1.8 and 11.7 μm, respectively.
The slope conductance of the channel was 9.2 pS for both peptides.
With FMRFamide, the open probability (Po) of the channel was 0.06 at 0.3 μm and 0.76 at 30 μm, whereas for FLRFamide the open probability increased from 0.04 at 1.8 μm to 0.49 at 50 μm. The Hill coefficient was greater than 1 for both peptides.
High concentrations of each peptide evoked very fast flickering between open and closed states which led to decreased unitary current amplitude.
At low doses, brief single openings and bursts of longer openings occurred. With higher doses, the occurrence of the brief openings declined and the number of longer openings increased; the duration of the longer openings was shorter with FLRFamide than with FMRFamide.
For each peptide, frequency distribution histograms of open events were best fitted by the sum of two exponential components, suggesting the existence of two open states of the channel. Closed events were fitted by the sum of three components, suggesting the existence of three closed states.
The data were analysed according to a five‐state model in which the brief openings correspond to a single liganded open form of the channel and the longer openings to a doubly liganded open form. According to this interpretation, the greater whole‐cell response observed with FMRFamide than with FLRFamide results mostly from a slower closing rate constant for the longer (doubly liganded) channel openings.
Calcium permeability and block at homomeric and heteromeric P2X2and P2X3receptors, and P2X receptors in rat nodose neurones
Authors: Virginio Caterina , North R. A. , Surprenant Annmarie 
Published: September 2004

Whole‐cell recordings were made from HEK 293 (human embryonic kidney) cells stably transfected with cDNAs encoding P2X2, P2X3or both receptors (P2X2/3) and from cultured rat nodose neurones. Nodose neurones all showed immunoreactivity for both P2X2and P2X3, but not P2X1, receptors.Reversal potentials were measured in extracellular sodium,N‐methyl‐D‐glucamine (NMDG) and NMDG containing 5 mM Ca2+; the values were used to compute relative permeabilities (PNMDG/PNaandPCa/PNa).PNMDG/PNawas not different for P2X2, P2X2/3and nodose neurones (0.03) but was significantly higher (0.07) for P2X3receptors.PCa/PNawas not different among P2X3, P2X2/3and nodose neurones (1.2‐1.5) but was significantly higher (2.5) for P2X2receptors.External Ca2+inhibited purinoceptor currents with half‐maximal concentrations of 5 mM at the P2X2receptor, 89 mM at the P2X3receptor and 15 mM at both the P2X2/3heteromeric receptor and nodose neurones. In each case, the inhibition was voltage independent and was overcome by increasing concentrations of agonist.These results may indicate that Ca2+permeability of the heteromeric (P2X2/3) channel is dominated by that of the P2X3subunit, while Ca2+block of the receptor involves both P2X2and P2X3subunits. The correspondence in properties between P2X2/3receptors and nodose ganglion neurones further supports the conclusion that the native α,β‐methylene ATP‐sensitive receptor is a P2X2/3heteromultimer.
Voltage change‐induced gating transitions of the rabbit skeletal muscle Ca2+ release channel
Authors: Zahradníková A. , Mészáros L. G. 
Published: September 2004

We used the planar lipid bilayer method to study single ryanodine receptor Ca2+ release channels (RyRCs) from fast skeletal muscle of the rabbit. We found that changes in membrane voltage directly induced gating transitions of the RyRC: (i) in the steady state, even at activating Ca2+ concentrations (20 μm), at a constant membrane potential the channels resided in a low open probability (Po) state (inactivated‐, I‐mode), and (ii) upon abrupt changes of voltage, the apparent inactivation of the RyRCs was relieved, resulting in a rapid and transient increase in Po.
The magnitude of the Po increase was a function of both the duration and the amplitude of the applied prepulse, but was independent of the channel activity during the prepulse.
The voltage‐induced Po increase probably involved major conformational changes of the channel, as it resulted in substantial alterations in the gating pattern of the channels: the voltage change‐induced increase in Po was accompanied by the rapid appearance of two types of channel activity (high (H) and low (L) open probability modes).
The response of the RyRC to voltage changes raises the interesting possibility that the activation of RyRC in situ might involve electrical events, i.e. a possible dipole‐dipole coupling between the release channel and the voltage sensor.
Effects of caffeine and adenine nucleotides on Ca2+ release by the sarcoplasmic reticulum in saponin‐permeabilized frog skeletal muscle fibres
Authors: Duke Adrian M. , Steele Derek S. 
Published: September 2004

The effect of caffeine and adenine nucleotides on the sarcoplasmic reticulum (SR) Ca2+ release mechanism was investigated in permeabilized frog skeletal muscle fibres. Caffeine was rapidly applied and the resulting release of Ca2+ from the SR detected using fura‐2 fluorescence. Decreasing the [ATP] from 5 to 0.1 mm reduced the caffeine‐induced Ca2+ transient by 89 ± 1.4 % (mean ± s.e.m., n= 16), while SR Ca2+ uptake was unaffected.
The dependence of caffeine‐induced Ca2+ release on cytosolic [ATP] was used to study the relative ability of other structurally related compounds to substitute for, or compete with, ATP at the adenine nucleotide binding site. It was found that AMP, ADP and the non‐hydrolysable analogue adenylyl imidodiphosphate (AMP‐PNP) partially substituted for ATP, although none was as potent in facilitating the Ca2+‐releasing action of caffeine.
Adenosine reversibly inhibited caffeine‐induced Ca2+ release, without affecting SR Ca2+ uptake. Five millimolar adenosine markedly reduced the amplitude of the caffeine‐induced Ca2+ transient by 64 ± 4 % (mean ± s.e.m., n= 11). The degree of inhibition was dependent upon the cytosolic [ATP], suggesting that adenosine may act as a competitive antagonist at the adenine nucleotide binding site.
These data show that (i) the sensitivity of the in situ SR Ca2+ channel to caffeine activation is strongly dependent upon the cytosolic [ATP], (ii) the number of phosphates attached to the 5′ carbon of the ribose ring influences the efficacy of the ligand, and (iii) removal of a single phosphate group transforms AMP from a partial agonist, to adenosine, which acts as a competitive antagonist under these conditions.
Osmosensitive Cl− currents and their relevance to regulatory volume decrease in human intestinal T84 cells: outwardly vs. inwardly rectifying currents
Authors: Bond Tamara D. , Ambikapathy Sujidra , Mohammad Samira , Valverde Miguel A. 
Published: September 2004

The swelling‐activated outwardly rectifying Cl− current (ICl(swell)) recorded in T84 human intestinal cells was completely blocked by 10 μM tamoxifen, while 300 μM Cd2+ had no effect.
A ClC‐2‐like, inwardly rectifying Cl− current was activated after strong hyperpolarization in T84 cells. This current was completely inhibited by 300 μM Cd2+, unaffected by 10 μM tamoxifen, and its magnitude increased slightly in response to cell swelling under hyposmotic conditions. However, the swelling‐dependent modulation occurred only after prior activation by hyperpolarizing voltages.
T84 cells behaved initially close to perfect osmometers in response to changes in external osmolalities between +20 and ‐30 %. The cells underwent full regulatory volume decrease (RVD) within 16 min when exposed to 30 or 10 % hyposmotic shocks.
Pharmacological tools were used to determine the anionic pathway(s) involved in RVD in T84 cells. Tamoxifen (10 μM), 1,9‐dideoxyforskolin (DDFSK; 100 μM) and 4,4′‐diisothiocyanatostilbene‐2,2′‐disulphonic acid (DIDS; 100 μM) blocked RVD while 300 μM Cd2+ had no effect upon RVD following a 30 % hyposmotic shock. The RVD response was similarly unaffected by Cd2+ when cells were exposed to a smaller (10 %) hyposmotic shock.
In conclusion, these data show that the anionic pathway primarily activated by cell swelling and relevant to RVD in T84 cells is the tamoxifen‐, DDFSK‐ and DIDS‐sensitive ICl(swell) and not the hyperpolarization‐activated, Cd2+‐sensitive Cl− current associated with the ClC‐2 Cl− channel.
Modulation of Ca2+ channel currents of acutely dissociated rat periaqueductal grey neurons
Authors: Connor Mark , Christie MacDonald J. 
Published: September 2004

The actions of the neuropeptide nociceptin on the calcium channel currents (IBa) of acutely dissociated rat periaqueductal grey (PAG) neurons were examined using whole‐cell patch clamp techniques. These effects were compared with those of opioid receptor agonists and the GABAB receptor agonist baclofen.
Neurons from young adult rats (23 to 56 days old) expressed predominantly ω‐conotoxin GVIA (N‐type)‐ and ω‐agatoxin IVA (P/Q‐type)‐sensitive IBa, together with smaller amounts of nimodipine‐sensitive current and current resistant to all three blockers. There was proportionately more N‐type IBa in neurons from female rats and proportionately more resistant current in neurons from male rats.
Nociceptin (EC50, 5 nm) and baclofen (EC50, 0.8 μm) inhibited IBa in all PAG neurons, while the opioid agonist methionine enkephalin (met‐enkephalin; 300 nm‐10 μm) inhibited IBa in 40 % of neurons. The effects of met‐enkephalin were reversed by the μ‐opioid antagonist CTAP, and mimicked by the μ‐opioid agonist DAMGO (300 nm‐3 μm). The δ‐opioid agonists DPDPE and deltorphin II, and the κ‐opioid agonist U69593, did not affect IBa in any neuron. The actions of nociceptin were not mimicked or blocked by the opioid antagonist naloxone or the nociceptin analogue [desPhe1]‐nociceptin.
The effects of nociceptin and baclofen on IBa were blocked by pretreatment of the neurons with pertussis toxin (500 ng ml−1, 8 h).
Nociceptin predominantly inhibited the N‐type (EC50, 2 nm; maximum inhibition, 50 %) and P/Q‐type (EC50, 7 nm; maximum inhibition, 33 %) IBa while having little effect on the L‐type and R‐type IBa.
These results are consistent with the previously described actions of nociceptin, baclofen and μ‐opioids in PAG slices, whereby they couple to increases in an inwardly rectifying K+ conductance. These agonists thus have the potential to modulate the function of PAG neurons via a number of different cellular effectors.