bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsatile release of acetylcholine by nerve terminals (synaptosomes) isolated from Torpedo electric organ.
Authors: Girod R , Eder‐Colli L , Medilanski J , Dunant Y , Tabti N , Poo M M
Published: December 2014

1. Electrophysiological detection of acetylcholine (ACh) release by synaptosomes from the electric organ of Torpedo was searched for by laying the isolated nerve terminals on a culture of Xenopus embryonic muscle cells (myocytes), and by recording the ACh‐induced inward currents in the myocytes. 2. Whole‐cell recording in one of the myocytes revealed rapid inward currents that where generated soon after synaptosome application. These pulsatile events strongly resembled those occurring normally during the early phase of synaptogenesis after nerve‐muscle contact in Xenopus cell cultures. They were called spontaneous synaptic currents (SSCs). 3. The SSCs produced by the synaptosomes had a rapid time course, with mean time‐to‐peak and half‐decay times of 2.6 +/‐ 0.4 ms and 6.0 +/‐ 1.1 ms, respectively. Most events had a falling phase that could be fitted with a single exponential. The mean time constant of decay was 6.2 +/‐ 1.1 ms. More than half of the SSCs (approximately 60%) constituted a rather homogenous population in which the time‐to‐peak versus amplitude showed a positive relationship, the smallest events displaying a shorter time course. The rest of the SSCs had a more variable and slower time course. Such events are also observed in young and mature junctions in situ. 4. The amplitudes of SSCs had a wide distribution which was skewed towards the smallest values. The mean amplitude was 65.2 +/‐ 16.1 pA. 5. During the minutes following an application of synaptosomes, the frequency of the SSCs tended to decrease, but their mean amplitude remained constant. Such behaviour could be reproduced during several successive additions of synaptosomes while recording in the same myocyte. 6. Just after synaptosome application, the SSCs were superposed to a noisy inward current that lasted for 20‐60 s. Noise analysis of this current gave the values of 0.7 +/‐ 0.1 pA for the mean amplitude of the elementary event, and 4.7 +/‐ 0.2 ms for its mean duration, values that compare well with those reported for the activation of frog embryonic nicotinic receptor. This suggests that the noisy current was due to ACh molecules set free by synaptosomes which were either damaged or which released ACh at some distance. This view was strengthened by biochemical analysis of ACh release by synaptosomes in vitro. 7. Tubocurarine reversibly abolished the appearance of both the noise and the synaptosome‐generated SSCs, showing that these currents were due to the action of ACh.(ABSTRACT TRUNCATED AT 400 WORDS)
Presynaptic inhibitory effects of the peptides NPY, PYY and PP on nicotinic EPSPs in guinea‐pig gastric myenteric neurones.
Authors: Schemann M , Tamura K
Published: December 2014

1. Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) affect gastrointestinal effector systems. Although their precise mode of action is unknown it is suggested that their effects are partly mediated by enteric neurones. Therefore, the aim of this study was to investigate the effects of NPY, PYY, avian PP (aPP) and bovine PP (bPP) on the electrophysiological behaviour of gastric myenteric neurones using intracellular recording methods. 2. In all thirty‐one neurones tested, electrical stimulation of interganglionic fibre tracts evoked cholinergic, nicotinic fast excitatory postsynaptic potentials (fEPSPs). NPY, PYY and bPP (10‐500 nM) inhibited the fEPSPs in a concentration‐dependent manner. Additionally, these peptides reversibly abolished spontaneously occurring nicotinic fEPSPs. None of the peptides exhibited any effect on the response to exogenously applied acetylcholine or on the postsynaptic excitability of the neurones. The inhibitory effects on the fEPSPs could not be reversed by perfusion of the alpha‐adrenoceptor antagonist, phentolamine (1 microM). 3. In contrast, aPP had no significant effect on fEPSPs even when perfused at the high concentration of 1 microM. 4. The results suggest that NPY, PYY and bPP, but not aPP, act presynaptically to inhibit acetylcholine release from myenteric neurones of the gastric corpus, thereby suppressing fEPSPs. The study indicates a modulatory role for NPY, PYY and bPP in synaptic interactions within the enteric nervous system.
Comparison of the actions of baclofen at pre‐ and postsynaptic receptors in the rat hippocampus in vitro.
Authors: Thompson S M , Gähwiler B H
Published: December 2014

1. Intracellular microelectrode recordings were used to study the cellular location, pharmacology, and mechanism of action of gamma‐aminobutyric acidB (GABAB) receptors on pyramidal cells and presynaptic axonal endings in area CA3 of organotypic hippocampal slice cultures. 2. Baclofen (bath applied at 10 microM) caused a 10‐15 mV hyperpolarization of CA3 cells and a 75‐100% decrease in the amplitude of excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs). Baclofen reduced the amplitude of monosynaptic IPSPs elicited in the presence of excitatory amino acid receptor antagonists, as well as the amplitude of EPSPs elicited after blocking GABAA receptors and reducing subsequent epileptic bursts with excitatory amino acid receptor antagonists. These data indicate that GABAB receptors are located on both excitatory and inhibitory presynaptic elements. 3. The GABAB receptor antagonist CGP 35 348 blocked the postsynaptic action of baclofen, the late IPSP, and the reduction of EPSPs and monosynaptic IPSPs by baclofen. 3‐Aminopropylphosphinic acid (3‐APA) mimicked all the pre‐ and postsynaptic actions of baclofen, and its effects were fully antagonized by CGP 35 348. 4. Incubation of cultures with pertussis toxin (500 ng/ml for 48 h) prevented both the postsynaptic hyperpolarization and the block of monosynaptic IPSPs induced by baclofen. The action of baclofen on isolated EPSPs, however, was not affected by pertussis toxin treatment. Stimulation of protein kinase C with phorbol ester (phorbol 12, 13 dibutyrate, 1 microM for 10 min) reduced all pre‐ and postsynaptic effects of GABAB receptor activation. 5. Barium (bath applied at 1 mM) prevented both the baclofen‐induced hyperpolarization of pyramidal cells and the block of monosynaptic IPSPs by baclofen. In the presence of barium, however, baclofen was fully capable of blocking EPSPs. 6. We conclude that pre‐ and postsynaptic GABAB receptors are pharmacologically indistinguishable, at present, and that all actions of GABAB receptors are inhibited by stimulation of protein kinase C. Both the postsynaptic action of baclofen and the block of GABA release from interneurons are mediated by pertussis toxin‐sensitive G proteins which can be inactivated by stimulation of protein kinase C. Baclofen acts at postsynaptic sites and on the axon terminals of inhibitory interneurons by activating the same barium‐sensitive K+ conductance. GABAB receptors on excitatory axons must, however, work through some other mechanism.
Comparison of the actions of adenosine at pre‐ and postsynaptic receptors in the rat hippocampus in vitro.
Authors: Thompson S M , Haas H L , Gähwiler B H
Published: December 2014

1. Intracellular microelectrode recordings were used to study the cellular location, the receptor pharmacology, and the mechanism of action of adenosine on pyramidal cells and presynaptic axonal endings in area CA3 of organotypic hippocampal slice cultures. 2. Adenosine (bath applied at 50 microM) caused a 10‐15 mV hyperpolarization of CA3 cells, as well as a 75‐100% decrease in the amplitude of excitatory and polysynaptic inhibitory postsynaptic potentials (EPSPs and IPSPs). Adenosine had no effect on the amplitude of monosynaptic IPSPs elicited in the presence of excitatory amino acid receptor antagonists, but did reduce the amplitude of isolated EPSPs, elicited after blocking GABAA receptors and reducing subsequent epileptic bursts with excitatory amino acid receptor antagonists. These data indicate that adenosine receptors are located on excitatory, but not inhibitory, presynaptic elements. 3. The A1 receptor antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX, bath applied at 200 nM) blocked the pre‐ and postsynaptic actions of adenosine. DPCPX had no effect on the amplitude of control synaptic responses, suggesting that there is no tonic activation of adenosine receptors in hippocampal slice cultures under control conditions. The A1 receptor agonists R‐N6‐phenylisopropyladenosine (R‐PIA) mimicked all pre‐ and postsynaptic actions of adenosine. 4. Pertussis toxin pretreatment (500 ng/ml for 48 h) prevented adenosine from activating postsynaptic K+ conductance, but not from inhibiting EPSPs. In contrast, stimulation of protein kinase C with phorbol ester (phorbol 12, 13‐dibutyrate, 1 microM for 10 min) reduced the presynaptic, but not the postsynaptic, actions of adenosine. 5. Barium (bath applied at 1 mM) blocked the adenosine‐activated K+ conductance, but not the inhibition of isolated EPSPs by adenosine. 6. Adenosine at 0.03‐1 microM reduced the frequency of, or blocked, spontaneous epileptiform bursting produced by bicuculline. DPCPX (200 nM) increased the rate of spontaneous bursting, consistent with a tonic activation of adenosine receptors during hyperactivity, and led to the development of prolonged ictal‐like bursts, suggesting that the endogenous release of adenosine may contribute to the termination of epileptic bursts. 7. We conclude that adenosine acts at pre‐ and postsynaptic receptors which are pharmacologically indistinguishable. Postsynaptically, adenosine increases a barium‐sensitive K+ conductance via a pertussis toxin‐sensitive GTP‐binding protein. The presynaptic action of adenosine must, however, be mediated by some other mechanism.
Three components in the light‐induced current of the Limulus ventral photoreceptor.
Authors: Deckert A , Nagy K , Helrich C S , Stieve H
Published: December 2014

1. Light‐induced currents were measured in Limulus ventral nerve photoreceptors using a two‐electrode voltage clamp. Three kinetically distinct components in the light‐induced current could be distinguished by varying the light adaptation state of the photoreceptor and the intensity of the stimulus light. 2. The components could be partly separated by choosing appropriate stimulus intensities and dark adaptation time. Thus the properties of the components could be separately studied. The first component is the first to recover after a light adaptation, appears temporally first in the light‐induced response, has the lowest activation threshold and is the smallest. The second component needs a longer time to recover after an adapting illumination and its kinetics differ from that of the other components. Applying a bright stimulus to a dark‐adapted cell a third component can be observed late in the response. 3. The time to peak of the first and the third components depended on the stimulus intensity, but not on the dark adaptation time. The time to peak of the second component became shorter the longer the dark adaptation time. For a constant adaptation state the time to the maximum of component 2 was independent, but those of components 1 and 3 were dependent on the membrane voltage. 4. To exclude the possibility of the contribution of voltage‐gated currents, light‐activated currents were measured at clamp potentials more negative than ‐50 mV after adding 4‐aminopyridine into the bath solution or injecting tetraethyl‐ammonium chloride into the cell. The properties of the three components remained unchanged under these conditions. 5. The I‐V curve of the first component was flat at negative membrane potentials and had a strong outward rectification at positive membrane potentials. The I‐V curve of component 3 showed a negative resistance at potentials more negative than about ‐30 mV. In contrast, the I‐V curve for the second component was always nearly linear. 6. No membrane potential was found where the light‐induced current was zero. Instead, current traces close to the reversal potential showed a complex waveform indicating different reversal potentials for the three components. 7. The results indicate that the current components are caused by three different populations of light‐sensitive channels. The different activations, deactivations and recovery kinetics of the components suggest that the three types of channels are activated by distinct intracellular transmitters.
Voltage‐dependent gating mechanism for single fast chloride channels from rat skeletal muscle.
Authors: Weiss D S , Magleby K L
Published: December 2014

1. A voltage‐dependent gating mechanism for the fast Cl‐ channel was developed from the analysis of single‐channel current records obtained with the patch clamp technique from primary cultures of rat skeletal muscle. Up to 10(6) open and shut intervals were analysed from each of five different excised patches of membrane containing a single fast Cl‐ channel. 2. Rate constants for a kinetic scheme with six closed and two open states (scheme I) were estimated at a given voltage by maximum likelihood fitting of open and closed dwell‐time distributions obtained at that voltage. This procedure was then repeated for data obtained at each of three to eight different membrane potentials for each channel. 3. Plots of the estimated rate constants against membrane potential typically appeared linear on semilogarithmic co‐ordinates, consistent with rate constants that are exponentially dependent on voltage. 4. Regression analysis of these plots yielded two parameters for each rate constant: the value of the rate constant at ‐50 mV (B) and its voltage sensitivity (A). The dwell‐time distributions predicted with these parameters and scheme I gave a good description of the experimental dwell‐time distributions at all the studied voltages, lending further support for an exponential dependence of rate constants on membrane potential. 5. Estimates of A and B were also obtained by simultaneously fitting dwell‐time distributions obtained at three to eight different voltages, in order to better define these parameters. Predicted dwell‐time distributions obtained with these estimates and scheme I could approach the theoretical best description of the data for discrete‐state Markov models. 6. Eight to twelve of the fourteen rate constants in scheme I appeared voltage sensitive, with effective gating charges ranging from about ‐1.5 to +1.0 units of electronic charge. 7. The estimated rate constants and their voltage sensitivities for the five analysed channels were generally similar, but showed some heterogeneity. 8. Gating mechanisms which had fewer kinetic states than scheme I, or equal and opposite effective gating charges over each transition barrier, or four or five identical and independent voltage‐dependent subunits, all gave poorer descriptions of the data than scheme I. These simpler mechanisms were also ranked below scheme I by the Schwarz criterion, which applies a heavy penalty for additional free parameters. 9. These findings indicate that the voltage dependence of the fast Cl‐ channel is consistent with a kinetic scheme with six closed and two open states, in which a majority of transitions among the states are voltage dependent.(ABSTRACT TRUNCATED AT 400 WORDS)
Sympathetic activity is influenced by task difficulty and stress perception during mental challenge in humans.
Authors: Callister R , Suwarno N O , Seals D R
Published: December 2014

1. Our aim was to determine the influence of the type of task, the absolute and relative difficulty of the task, and the perceived stress associated with performance of the task on sympathetic circulatory regulation during cognitive challenge in humans. 2. Sympathetic nerve activity to skeletal muscle (MSNA) determined from peroneal microneurography, heart rate and arterial blood pressure were recorded continuously in twelve subjects during a modified Stroop colour word test (CWT) and mental arithmetic (MA), each performed over six levels of increasing absolute task difficulty. Performance (percentage correct) on each task was assessed and ratings of perceived stress obtained. Responses to CWT and MA were compared at similar levels of performance and perceived stress. 3. MSNA decreased at task onset, remained below baseline levels at low levels of difficulty which were not perceived as stressful, increased above baseline levels at higher levels of difficulty which were perceived as stressful, and increased further during recovery. Thus, the regulation of MSNA was stress dependent. At similar levels of stress perception there were no differences in MSNA between CWT and MA. Although performance declined as task difficulty increased, there was no particular ‘threshold’ level of performance associated with the stimulation of MSNA. 4. Arterial pressure and heart rate were elevated above baseline levels throughout the mental tasks. Arterial pressure increased over the first 3‐4 levels of each task and then plateaued whereas heart rate did not vary across increasing levels of task difficulty. Heart rate and arterial pressure responses to CWT were higher than those to MA. 5. These data demonstrate that during cognitive challenge the stimulation of MSNA is governed primarily by perceived stress which is dependent, in part, on the absolute level of task difficulty. In contrast, neither performance nor the type of cognitive task appear to be important determinants of MSNA. Arterial pressure is influenced by the task and level of difficulty. Heart rate is independent of task difficulty but may be task dependent.
Calcium sensitizing action of carnosine and other endogenous imidazoles in chemically skinned striated muscle.
Authors: Lamont C , Miller D J
Published: December 2014

1. The imidazole‐containing compounds carnosine and homocarnosine, endogenous to skeletal and cardiac muscle, have been tested for effect on the contractile behaviour of chemically skinned (saponin or Triton X‐100) skeletal and cardiac muscle. 2. Carnosine, at millimolar concentrations which are near physiological for many skeletal fibres, and in a concentration‐dependent fashion, shifts the curve relating [Ca2+] to steady‐state tension to lower [Ca2+] in both skeletal (frog but not crab) and cardiac (rat) muscle preparations. 3. Of other imidazoles endogenous to heart, homocarnosine is somewhat more effective, while N‐acetyl L‐histidine is much less so. 4. The maximum level of Ca(2+)‐activated force is increased significantly by homocarnosine in cardiac trabeculae. 5. We propose that the cellular imidazoles related to carnosine are natural ‘Ca2+ sensitizers’ in striated muscle. Alterations in their levels as a result of disease or training, and between different fibre types, may contribute to differences in contractile performance of the intact tissues.
Cortical modulation of transmission in spinal reflex pathways of man.
Authors: Iles J F , Pisini J V
Published: December 2014

1. The motor actions in the lower limb of transcranial electrical stimulation of the motor cortex have been studied in sitting human subjects. 2. Cortical stimulation induced a short latency inhibition of H reflexes evoked in soleus motoneurones both at rest and during small voluntary contractions of soleus. 3. Spatial interaction between cortical inhibition of soleus motoneurons and inhibition evoked through identified spinal reflex machinery was investigated. 4. Interactions were found between cortically evoked inhibition and spinal Ia reciprocal inhibition, group I non‐reciprocal inhibition and higher threshold components of longer latency reciprocal inhibition (D1 and D2 inhibitions). 5. Interactions were facilitatory when cortical and spinal inhibitory actions were weak and reversed to occlusion when both actions were strong. 6. It is concluded that the corticospinal pathway converges on the interneurones which subserve Ia reciprocal, group I non‐reciprocal, D1 and D2 inhibition of soleus motoneurones. 7. No significant interaction was found under the present experimental conditions between cortical stimulation and group Ia‐Ia presynaptic inhibition of soleus afferents. 8. The statistical significance of spatial interactions observed with H reflex conditioning was investigated using a control experiment.
Luminal Ca2+ promoting spontaneous Ca2+ release from inositol trisphosphate‐sensitive stores in rat hepatocytes.
Authors: Missiaen L , Taylor C W , Berridge M J
Published: December 2014

1. Spontaneous Ca2+ release from the inositol 1,4,5‐trisphosphate (InsP3)‐sensitive stores in permeabilized hepatocytes was monitored using Fluo‐3 to measure the free [Ca2+] of the medium bathing the cells. 2. Permeabilized cells rapidly sequestered Ca2+, reducing the [Ca2+] to 103 +/‐ 5 nM. Under conditions that depended critically upon cell density and the amount of Ca2+ in the medium, this was followed by a slow increase in [Ca2+] culminating in a substantial Ca2+ spike representing synchronous discharge from the InsP3‐sensitive stores. 3. During the latency preceding the Ca2+ spike, the stores increased their sensitivity to InsP3. This sensitization seemed to be an all‐or‐none phenomenon. 4. Oxidized glutathione and thimerosal promoted the spontaneous release by sensitizing the InsP3 receptor. 5. An increase in the [Ca2+] within the stores was required for both the increased sensitivity to InsP3 and the subsequent spike. 6. Caffeine (6 mM) antagonized the effect of very low InsP3 concentrations and abolished the Ca2+ spike, without itself releasing Ca2+. 7. Our results suggesting that luminal Ca2+ may sensitive InsP3‐sensitive stores leading to spontaneous Ca2+ mobilization will be discussed in the light of a modified version of the two‐pool model for explaining cytosolic Ca2+ oscillations.
Receptive field organization of retinal ganglion cells in the spastic mutant mouse.
Authors: Stone C , Pinto L H
Published: December 2014

1. We examined the receptive field properties of retinal ganglion cells in the isolated, superfused retinae of spastic mutant mice (B6C3Fe‐spa/spa) that did not have the retinal degeneration (rd) phenotype. Glycine receptor density in the spastic mutant is greatly reduced in all areas of the CNS that have been examined. Phenotypically normal litter‐mates were used as controls. Radial sections from the retinae of both spastic and normal animals were examined with light and electron microscopy and no differences were observed. The planimetric density of the cell bodies in the inner nuclear layer did not differ between the normal and mutant animals, about 400 cm‐2. The absolute dark‐adapted sensitivity of spastic ganglion cells was greater (271 +/‐ 69.0 impulses quanta‐1 rod‐1) than that of normal ganglion cells (47.7 +/‐ 10.4 impulses quanta‐1 rod‐1; P < 0.01). 2. Extracellular recordings of retinal ganglion cell responses to circular and annular stimuli, centred on the receptive field, were used to construct peri‐stimulus‐time histograms. In normal retinae, an annular stimulus elicited a response that was characteristic of the surround response mechanism of receptive fields with antagonistic centre‐surround organization. In the mutant retina, annular stimuli did not elicit a surround‐type response; instead, a centre‐type response was recorded. 3. Illumination of the receptive field periphery attenuated centre‐type responses in ganglion cells from both spastic and normal retinae. Centred circular stimuli of various areas (14, 35, 78, 122, 235, 783 deg2) were presented to the receptive fields. For mutant and normal ganglion cells, the response to the largest stimulus was smaller than that to an intermediate‐sized stimulus. 4. The effect of strychnine, a glycine receptor antagonist, on the response to circular stimuli was examined. Very low concentrations of strychnine attenuated the light response in mutant retinae (apparent inhibitory binding constant KI = 8.1 x 10(‐13) M). In normal animals, the light response was also attenuated by strychnine, but the apparent KI was much higher (apparent KI = 1 x 10(‐7) M). 5. In normal ganglion cells, the sustained component of the light response was much more attenuated by strychnine than was the transient component. Interestingly, ganglion cells from spastic retinae did not exhibit a sustained component, even at stimulus luminances that evoked responses near threshold.(ABSTRACT TRUNCATED AT 400 WORDS)
ATP dependence of Na(+)‐K+ pump of cold‐sensitive and cold‐tolerant mammalian red blood cells.
Authors: Marjanovic M , Willis J S
Published: December 2014

1. The ATP concentration of intact, cold‐tolerant (ground squirrel) red cells and cold‐sensitive (guinea‐pig and human) red cells was monitored by use of the firefly tail, luciferin‐luciferase assay. ATP kinetics of the pump in intact red blood cells was investigated by altering cell [ATP] by progressive depletion of ATP in the presence of 2‐deoxy‐D‐glucose and then by measurement of ouabain‐sensitive K+ influx at each level of [ATP] at various temperatures between 37 and 5 degrees C. Na(+)‐K(+)‐ATPase activity of broken membranes was also determined in parallel experiments using ouabain‐sensitive release of 32P from [gamma‐32P]ATP as a measure of activity. 2. Without depletion, there is no immediate decrease in [ATP] of intact cold‐sensitive cells at low temperature (5 degrees C) at times when there are marked differences in the activities of the Na(+)‐K+ pump of cold‐tolerant and cold‐sensitive cells. 3. At 37 degrees C Na(+)‐K(+)‐ATPase of all three species exhibited two components of ATP dependence at 37 degrees C, one with high velocity, low affinity, the other with low velocity, high affinity. Affinities of both components rose with cooling. 4. A similar, two component pattern was observed in intact guinea‐pig and human red cells at 37 degrees C, except that the segment corresponding to the high affinity component had an apparent Km (Michaelis‐Menten constant) 3‐ to 4‐fold higher than that of the broken membrane preparation. 5. Cooling intact guinea‐pig and human red cells decreased the apparent affinity of the high velocity, low affinity component for ATP, so that at 20 degrees C the value of Km approached or exceeded the levels of physiological ATP concentration. Below 20 degrees C only one component with values corresponding to that of the low velocity, high affinity component could be observed. 6. In intact ground squirrel cells only the low affinity, high velocity component was apparent between 37 and 5 degrees C. Its affinity for ATP rose with cooling between 37 and 5 degrees C.
Convergence of visceral and somatic inputs onto subnucleus reticularis dorsalis neurones in the rat medulla.
Authors: Roy J C , Bing Z , Villanueva L , Le Bars D
Published: December 2014

1. In anaesthetized rats, recordings were made within the medullary subnucleus reticularis dorsalis (SRD) from neurones that exhibited convergence of nociceptive inputs from the entire surface of the body. Neurones with total nociceptive convergence responded to supramaximal percutaneous electrical stimuli (2 ms duration) with early and late peaks due to the activation of A delta and C fibres, respectively, no matter which part of the body was stimulated. Neurones with partial nociceptive convergence responded to identical stimuli with an A delta peak of activation regardless of which part of the body was stimulated and with a C peak of activation from some, mainly contralateral, parts of the body. The characteristics of the responses of these neurones to graded colo‐rectal distension (< or = 100 mmHg) were analysed. 2. The majority of neurones with total nociceptive convergence (n = 13 out of 16) responded to colo‐rectal distension by increasing their firing rates. Although these neurones were virtually unresponsive to the lowest pressure employed (12.5 mmHg), they increased their discharges monotonically for distensions in the 26‐100 mmHg range and these responses were sometimes followed by after‐discharges. One of these neurones, which exhibited a high level of spontaneous activity, was inhibited during colo‐rectal distension. None of the neurones with partial nociceptive convergence recorded (n = 10) ever changed its firing rate during increases of intracolonic pressure up to 100 mmHg. 3. It is concluded that neurones with total nociceptive convergence give monotonic stimulus‐response relationships for colo‐rectal distensions. Thus, neurones with total nociceptive convergence can encode the strength of visceral stimuli, probably within the noxious range, just as they have previously been shown to do for thermal and mechanical cutaneous stimuli. Together with previous electrophysiological and neuroanatomical findings, this study provides further evidence for the convergence of noxious inputs onto single SRD neurones. 4. It is suggested that neurones with total nociceptive convergence could be a link in spino‐bulbospinal loops involved in autonomic reactions to strong visceral stimulation. In addition, SRD neurones could be an important supraspinal relay in the mechanisms of visceral pain.
Exercise‐induced diaphragmatic fatigue in healthy humans.
Authors: Johnson B D , Babcock M A , Suman O E , Dempsey J A
Published: December 2014

1. Twelve healthy subjects (33 +/‐ 3 years) with a variety of fitness levels (maximal oxygen uptake (VO2, max) = 61 +/‐ 4 ml kg‐1 min‐1, range 40‐80), exercised at 95 and 85% VO2, max to exhaustion (mean time = 14 +/‐ 3 and 31 +/‐ 8 min, expired ventilation (VE) over final minute of exercise = 149 +/‐ 9 and 126 +/‐ 10 l min‐1). 2. Bilateral transcutaneous supramaximal phrenic nerve stimulation (BPNS) was performed before and immediately after exercise at four lung volumes, and 400 ms tetanic stimulations were performed at 10 and 20 Hz. The coefficients of variation of repeated measurements for the twitch transdiaphragm pressures (Pdi) were +/‐ 7‐10% and for compound muscle action potentials (M wave) +/‐ 10‐15%. 3. Following exercise at 95% of VO2, max, group mean Pdi twitch values were reduced at all lung volumes (range ‐8 +/‐ 3 to ‐32 +/‐ 5%) and tetanically stimulated Pdi values were reduced at both 10 and 20 Hz (‐21 +/‐ 3 and ‐13 +/‐ 2%, respectively) (P = 0.001‐0.047). Following exercise at 85% VO2, max, stimulated Pdi values were reduced at all lung volumes and stimulating frequencies, but only significantly so with the twitch at functional residual capacity (‐15 +/‐ 5%). Stimulated Pdi values recovered partially by 30 min post‐exercise and almost completely by an average time of 70 min. 4. The fall in stimulated Pdi values post‐exercise was significantly correlated with the percentage increase in diaphragmatic work (integral of Pdi min‐1) from rest to end‐exercise and the relative intensity of the exercise. 5. The integral of Pdi min‐1 and the integral of Po min‐1 (Po, esophageal pressure) rose together from rest through the fifth to tenth minute of exercise, after which integral of Pdi min‐1 plateaued even though integral of Po min‐1, VE and inspiratory flow rate all continued to rise substantially until exercise terminated. Thus, the relative contribution of the diaphragm to total respiratory motor output was progressively reduced with exercise duration. 6. We conclude that significant diaphragmatic fatigue is caused by the ventilatory requirements imposed by heavy endurance exercise in healthy persons with a variety of fitness levels. The magnitude of the fatigue and the likelihood of its occurrence increases as the relative intensity of the exercise exceeds 85% of VO2, max.
Metabolic acidosis and breathlessness during exercise and hypercapnia in man.
Authors: Lane R , Adams L
Published: December 2014

1. A previous study showed that when combined with exercise in normal subjects, hypercapnic and hypoxic ventilatory stimuli did not have a specific effect on the intensity of the sensation of breathlessness in addition to their stimulation of ventilation. The aim of the present study was to assess the significance of another reflex ventilatory stimulus, metabolic acidosis, in the genesis of this sensation. 2. Six subjects performed progressive exercise tests (mean workload, 103 W; range, 88‐125 W) with normal acid‐base status. Following NH4Cl‐induced metabolic acidosis (mean change in base excess, ‐3.6 mmol l‐1; range, ‐0.3 to ‐6.8 mmol l‐1) exercise was repeated (mean workload, 91 W; range, 53‐116 W) such that the combined ventilatory stimulation resulted in levels of ventilation (mean maximum, 65 l min‐1) ‘matched’ to those resulting from exercise alone. A third, ‘matched ventilation’, exercise test was performed during metabolic acidosis but with end‐tidal PCO2 controlled to a normal level (mean workload, 56 W; range, 17‐103 W). Breathlessness was assessed using a visual analogue scale (VAS). 3. Progressive hypercapnic ventilatory stimulation was given before (mean maximum end‐tidal PCO2 (PET,CO2), 61 mmHg) and during metabolic acidosis (mean maximum PET,CO2, 57 mmHg) to achieve the same peak level of ventilation (mean maximum, 59 l min‐1). Breathlessness was assessed with the VAS. 4. As ventilation increased during a test, there were no statistically significant differences in the increasing breathlessness scores with metabolic acidosis compared to control, for either exercise (mean VAS, 22 mm vs. 24 mm) or progressive hypercapnia (mean peak VAS, 31 mm vs. 32 mm). 5. These results do not support the idea that metabolic acidosis is associated with a change in the relationship between the intensity of breathlessness and ventilation; this is similar to results found with other reflex ventilatory stimuli. 6. These findings are consistent with the hypothesis that the degree of reflex ventilatory activation is an important determinant of the intensity of the sensation of breathlessness in healthy humans, irrespective of the exact nature of ventilatory stimulus.
Regional cerebral blood flow during volitional expiration in man: a comparison with volitional inspiration.
Authors: Ramsay S C , Adams L , Murphy K , Corfield D R , Grootoonk S , Bailey D L , Frackowiak R S , Guz A
Published: December 2014

1. Positron emission tomographic (PET) imaging of regional cerebral blood flow (rCBF), using a new 3‐dimensional technique of data collection, was used to identify areas of neuronal activation associated with volitional inspiration and separately with volitional expiration in five normal male subjects. A comparison of the activated areas was also undertaken to isolate regions specific for one or other active task. 2. Scans were performed during intravenous infusion of H2(15)O under conditions of (a) volitional inspiration with passive expiration, (b) passive inspiration with volitional expiration and (c) passive inspiration with passive expiration. Four measurements in these three conditions were performed in each subject. Breathing pattern was well matched between conditions. 3. Regional increases in brain blood flow, due to increased neural activity associated with either active inspiration or active expiration, were derived using a pixel by pixel comparison of images obtained during the volitional and passive ventilation phases. Data were pooled from all runs in all subjects and were then processed to detect statistically significant (P < 0.05) increases in rCBF comparing active inspiration with passive inspiration and active expiration with passive expiration. 4. During active inspiration significant increases in rCBF were found bilaterally in the primary motor cortex dorsally just lateral to the vertex, in the supplementary motor area, in the right lateral pre‐motor cortex and in the left ventrolateral thalamus. 5. In active expiration significant increases in rCBF were found in the right and left primary motor cortices dorsally just lateral to the vertex, the right and left primary motor cortices more ventrolaterally, the supplementary motor area, the right lateral pre‐motor cortex, the ventrolateral thalamus bilaterally, and the cerebellum. 6. Using this modified and more sensitive PET technique, these findings essentially replicate those for volitional inspiration obtained in a previous study. For volitional expiration the areas activated are more extensive, but overlap with those involved in volitional inspiration. 7. The technique used has been successful in demonstrating the regions of the brain involved in the generation of volitional breathing, and probably in the volitional modulation of automatic breathing patterns such as would be required for the production of speech.
Calcium clamp in isolated neurones of the snail Helix pomatia.
Authors: Belan P , Kostyuk P , Snitsarev V , Tepikin A
Published: December 2014

1. Intracellular free calcium concentration ([Ca2+]i) in isolated non‐identified Helix pomatia neurones has been clamped at different physiologically significant levels by a feedback system between the fluorescent signal of fura‐2 probe loaded into the cell and ionophoretic injection of Ca2+ ions through a CaCl2‐loaded microelectrode. The membrane potential of the neurone has also been clamped using a conventional two‐microelectrode method. 2. Special measurements have shown that the transport indices of injecting microelectrodes filled with 50 mM CaCl2 are quite variable (0.11 +/‐ 0.06, mean +/‐ S.D.). However, for each electrode the transport indices remained stable during several injection trials into a solution drop having the size of a neurone. The spread of calcium ions from the tip of the microelectrode across the cytosol of the neurone terminated within 2‐4 s. The spatial difference in [Ca2+]i at this time did not exceed 10%. 3. Clamping of [Ca2+]i at a new increased level was accompanied by a transient of the Ca(2+)‐injecting current. To increase [Ca2+]i by 0.1 microM, the amount of calcium ions injected during this stage had to be 36 +/‐ 20 microM Ca2+ per cell volume. Obviously, this transient represents the filling of a fast cytosolic buffer which has to be saturated to reach a new increased level of [Ca2+]i. It was followed by a steady component of Ca(2+)‐injecting current, which was quite low (corresponding to injection of 0.39 +/‐ 0.20 microM s‐1 for a 0.1 microM change of [Ca2+]i). This may represent the functioning of Ca(2+)‐eliminating systems and corresponds to a similar amount of Ca2+ extruded from the cytoplasm. 4. Changes in the injection current also developed when Ca2+ influx through the membrane was triggered by the activation of voltage‐gated calcium channels. The amount of Ca2+ entering the cell during the first seconds of depolarization to‐‐15 mV was equal to 0.59 +/‐ 0.31 microM s‐1 per cell volume. 5. No activation of Ca(2+)‐dependent potassium current was observed during the changes in [Ca2+]i to levels exceeding the basal one by several times. Obviously, to activate this current, a much stronger increase in [Ca2+]i is needed in the immediate vicinity of the corresponding channels.
Characterization of TTX‐sensitive and TTX‐resistant sodium currents in small cells from adult rat dorsal root ganglia.
Authors: Elliott A A , Elliott J R
Published: December 2014

1. The whole‐cell patch‐clamp technique was used to investigate the characteristics of two types of sodium current (INa) recorded at room temperature from small diameter (13‐25 microns) dorsal root ganglion (DRG) cells, isolated from adult rats and maintained overnight in culture. 2. Sodium currents were isolated pharmacologically. Internal Cs+ and external tetraethylammonium (TEA) ions were used to suppress potassium currents. A combination of internal EGTA, internal F‐, a low (10 microM) concentration of external Ca2+ and a relatively high (5 mM) concentration of internal and external Mg2+ was used to block calcium channels. The remaining voltage‐dependent currents reversed direction at the calculated sodium equilibrium potential. Both the reversal potential and magnitude of the currents exhibited the expected dependence on the external sodium concentration. 3. INa subtypes were characterized initially in terms of their sensitivity to tetrodotoxin (TTX). TTX‐sensitive (TTXs) currents were at least 97% suppressed by 0.1 microM TTX. TTX‐resistant (TTXr) INa were recorded in the presence of 0.3 microM TTX and appeared to be reduced in amplitude by less than 50% in 75 microM TTX (n = 1). 4. As in earlier studies, the peak of the current‐voltage relationship, the mid‐point of the normalized conductance curve and the potential (Vh) at which the steady‐state inactivation parameter (h infinity) was 0.5 were found to be significantly more depolarized for the TTXr INa (by ca 10, 14 and 37 mV respectively). There was little difference in the slope at the mid‐point of the normalized conductance curves (the mean slope factors were 5.1 mV for the TTXs INa and 4.9 mV for the TTXr current) but the h infinity curves for TTXr currents were significantly steeper than those for TTXs currents (mean slope factors of 3.8 and 11.5 mV respectively). Both the time to peak and the decay time constant of the peak current recorded from a holding potential of ‐67 mV were more than a factor of three slower for the TTXr INa than for the TTXs current. 5. However, in direct contrast to the difference in activation and decay kinetics, 'slow’ TTXr INa recovered from inactivation at ‐67mV, or reprimed, more than a factor of ten faster than ‘fast’ TTXs INa. 6. The differences apparent in both the repriming kinetics of TTXs and TTXr INa at ‐67 mV and the kinetics of the decay phase of the peak INa are shown to be explicable largely in terms of the voltage dependence of their respective inactivation systems.(ABSTRACT TRUNCATED AT 400 WORDS)
Ca(2+)‐dependent inactivation of Ca2+ current in Aplysia neurons: kinetic studies using photolabile Ca2+ chelators.
Authors: Fryer M W , Zucker R S
Published: December 2014

1. The kinetics and sensitivity of the Ca(2+)‐dependent inactivation of calcium current (ICa) were examined in intact cell bodies from the abdominal ganglion of Aplysia californica under two‐electrode voltage clamp. 2. Rapid changes in the level of intracellular free calcium ([Ca2+]i) were generated at the cell surface by photolytic release of Ca2+ (nitr‐5 and dimethoxy nitrophen) or Ca2+ buffer (diazo‐4). 3. Diazo‐4 increased ICa by 10‐15% and slowed the rate of ICa decay when photolysed before a test pulse or between a prepulse and a test pulse. The predominant effect of further light flashes was to increase the amount of non‐inactivating current (I infinity) remaining at the end of long (> 1 s) depolarizing pulses. 4. A rapid increase in [Ca2+]i buffering during ICa inactivation did not cause a rapid recovery of current but merely reduced the rate and extent of subsequent inactivation. This effect was not seen when Ba2+ was the charge carrier. 5. Photolytic release of Ca2+ from nitr‐5 produced estimated Ca2+ jumps of 3‐4 microM at the front surface of the cell but failed to augment inactivation either before or during ICa. In contrast, photolysis of DM‐nitrophen 10‐90 ms before the test pulse decreased peak ICa by about 30%. A flash given during ICa rapidly blocked 41 +/‐ 3% of peak current with a time constant of 3‐4 ms at 17 degrees C. Similar results were seen with the barium current (IBa). 6. Microinjection of the potent phosphatase inhibitor microcystin‐LR (5 microM) had variable effects on ICa inactivation and augmented the cyclic AMP‐induced depression of the delayed rectifier (IK(V) by forskolin (100 microM) and 3‐isobutyl‐1‐methylxanthine (IBMX; 200 microM). 7. Full recovery from inactivation measured in two‐pulse experiments took at least 20 s. This slow recovery process was unaffected by increases in intracellular cyclic AMP elicited by direct injection or by bath application of forskolin and IBMX. It was also unaffected by decreases in cyclic AMP induced by injecting 2',5'‐dideoxyadenosine (1 mM) or bath application of the Rp isomer of cyclic adenosine 3',5'‐monophosphothioate (Rp‐cAMPS; 200 microM). 8. A 'shell’ model relating submembrane Ca2+ to inactivation was inconsistent with the experimental results since it greatly overestimated the effects of diazo‐4 and predicted significant inactivation by nitr‐5 photolysis. 9. A model linearly relating [Ca2+]i in a single Ca2+ channel ‘domain’ to inactivation more closely matched the experimental results with diazo‐4 and DM‐(ABSTRACT TRUNCATED AT 400 WORDS)
Roles of sympathetic nervous system in the suppression of cytotoxicity of splenic natural killer cells in the rat.
Authors: Katafuchi T , Take S , Hori T
Published: December 2014

1. We previously demonstrated that a central injection of interferon‐alpha in rats induced a suppression of cytotoxicity of splenic natural killer cells which depended upon intact splenic sympathetic innervation, suggesting the important role of the splenic nerve in immunosuppression. To further study the mechanisms of this phenomenon, we investigated: (1) the effects of a central injection of recombinant human interferon‐alpha on the electrical activity of the splenic nerve, and (2) the responses of splenic natural killer cytotoxicity on the electrical stimulation of the splenic nerve in urethane with alpha‐chloralose anaesthetized rats. 2. An injection of recombinant human interferon‐alpha (1.5 x 10(3) and 6.0 x 10(3) units (u) per rat) into the third cerebral ventricle produced a sustained and long lasting (at least for more than 60 min) increase in the electrical activity of splenic sympathetic nerve filaments in a dose‐dependent manner. Following an intra‐third‐ventricular injection of recombinant human interferon‐alpha at a dose of 6.0 x 10(3) u, the efferent discharges were elevated 2‐6 times that of the pre‐injection level with a mean onset latency of 12 min (8‐16 min). No changes in the arterial blood pressure and body temperature were observed after injections of recombinant human interferon‐alpha. 3. The excitation of the nerve activity induced by intra‐ventricular recombinant human interferon‐alpha was reversibly suppressed by an intravenous injection of an opioid antagonist, naloxone (1 mg/kg in 0.1 ml saline), whereas the injection of naloxone alone did not affect either the baseline level of the nerve activity or the systemic blood pressure. 4. The cytotoxicity of natural killer cells in the spleen measured by a standard chromium release assay was reduced 20 min after the laparotomy alone in anaesthetized rats. The reduced natural killer activity then recovered significantly when the splenic nerve was cut immediately after the laparotomy. When the peripheral cut end of the splenic nerve was subsequently stimulated (0.5 mA, 0.5 ms, 20 Hz for 20 min), a further suppression of natural killer cytotoxicity was observed. 5. The reduction of natural killer cytotoxicity produced by the stimulation of the splenic nerve was completely blocked by an intravenous injection of nadolol (a peripherally acting beta‐adrenergic receptor antagonist), but not by that of prazosin (an alpha‐antagonist). 6. These results indicate that a central injection of recombinant human interferon‐alpha activates the splenic sympathetic nerve through brain opioid receptors and thereby suppresses the natural killer cytotoxicity by beta‐adrenergic mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)