bluuebunny/crossref_metadata_2025 huggingface dataset:
Myoblasts and myoblast‐conditioned medium attract the earliest spinal neurites from frog embryos.
Authors: McCaig C D
Published: December 2014

A study was made of the capacity of newly segmented somites, unsegmented mesoderm and medium conditioned by each of these tissues to attract the growth of the earliest spinal neurites from the neural tube of Xenopus laevis in tissue culture. When presented with segmented somitic myoblasts or sheets of skin, spinal neurites grew selectively towards the somitic myoblasts. Neurites were not attracted specifically to somitic myoblasts from their own rostrocaudal level. A variable proportion of myoblasts from unsegmented caudal mesoderm differentiated and elongated in co‐culture with neural tube and skin. These myoblasts also attracted neural outgrowths, but only if present in sufficient numbers. An agar slab containing medium conditioned by the presence of segmented myoblasts for 1 day attracted neurite outgrowths. A source of medium conditioned by the presence of undifferentiated, unsegmented myotomal mesoderm alone did not attract neurite outgrowths. Nerve growth factor (NGF) at a range of concentrations in the agar source (500‐10,000 ng/ml) did not attract the earliest neurite outgrowths. It is concluded that the earliest skeletal myoblasts from Xenopus laevis embryos may attract neural outgrowths by releasing a soluble factor. Myoblasts may have to develop to the stage of somite segmentation before secretion of such an agent begins. The release of a myoblast‐derived factor so early in development may assist directed nerve growth in vivo.
Dynamic aspects of amphibian neurite growth and the effects of an applied electric field.
Authors: McCaig C D
Published: December 2014

The dynamics of growth of earliest spinal neurites from Xenopus laevis have been studied in vitro in the presence and absence of an applied d.c. electric field. Control and cathode‐directed neurites grew at a rate of about 30 micron/h: growth of anodal‐facing neurites was 8 times slower. Periods of arrested growth were common in cultured neurones; these lasted 2‐3 times longer in an applied electric field. The likelihood and the severity of neurite reabsorption was greatest in neurites directed towards the anode. Many neurites turned to direct their growth towards the cathode. As this happened their rate of growth increased 2‐3‐fold. The electric field further shaped neurite morphology by increasing the number of filopodia at the growth cone and by increasing the number of cytoplasmic spines along a neurite shaft. The electric field induced an asymmetry in the distribution of these cytoplasmic projections; greater numbers being found on the cathodal‐facing than on the anodal‐facing side. Implications of these data for nerve growth in development and in regeneration are discussed.
The transduction channel of hair cells from the bull‐frog characterized by noise analysis.
Authors: Holton T , Hudspeth A J
Published: December 2014

Receptor currents in response to mechanical stimuli were recorded from hair cells in the excised epithelium of the bull‐frog sacculus by the whole‐cell, gigohm‐seal voltage‐clamp technique. The stimulus‐dependent transduction current was separated from the cell's stimulus‐independent K+ and Ca2+ currents; the K+ currents were blocked with an internal solution containing Cs+ while the Ca2+ current was reduced by holding the membrane potential below ‐70 mV. The temperature of the preparation was maintained at about 10 degrees C to slow the kinetics of the cells' transduction channels. Calibrated displacements of hair bundles of individual hair cells were made with a probe coupled by suction to the kinociliary bulb and moved with a piezoelectricbimorph stimulator. The root mean square noise of probe motion was less than 2 nm. The mean, I, and the variance, sigma 2, of the receptor current were measured from the response to saturating (+/‐ 0.5 micron) displacements of the hair bundle. I was corrected for current offsets and sigma 2 for the transduction‐independent background variance. The relation between sigma 2 and I is consistent with the predictions of a two‐conductance‐state model of the transduction channel, a model having only one non‐zero conductance state. The relation between sigma 2 and I was fitted by the equation sigma 2 = Ii‐I2/N, where N is the number of transduction channels in the cell and i is the current through a single open channel. The conductance of the transduction channel is approximately ohmic with a reversal potential near 0 mV. The estimated conductance of a single transduction channel, gamma, is 12.7 +/‐ 2.7 pS (mean +/‐ S.D.; n = 18) at 10 degrees C. gamma is independent of the maximum transduction conductance of the cell, Gmax. The number of transduction channels, N, is proportional to Gmax. N ranges from 7 to 280 in cells with Gmax ranging from 0.08 to 2.48 nS. The largest values of N correspond to a few, perhaps four, active transduction channels per stereocilium. Control experiments show that transduction by the hair cell of two artifactual sources of hair‐bundle stimulation, noisy or discontinuous motion of the probe, do not contribute substantially to the measured variance, sigma 2. Displacement‐response curves are generally sigmoidal and symmetrical; they reasonably fit the predictions of a two‐kinetic‐state model, comprising one open state and one closed state. The estimated displacement‐sensitive free energy, Z, is 5.7 +/‐ 1.1 kcal/mol micron (mean +/‐ S.D., n = 18).(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanism of action of acetylcholine on calcium current in single cells from frog ventricle.
Authors: Fischmeister R , Hartzell H C
Published: December 2014

Ca currents (ICa) were measured by whole‐cell patch clamp in single cells isolated from frog ventricle in which K currents were blocked with intracellular (120 mM) and extracellular (20 mM) Cs. Inward currents elicited by depolarizing voltage steps from a holding potential of ‐80 mV were blocked completely by 0.5 mM‐Cd. The quality of the voltage clamp was assessed using two patch electrodes on a single cell. One electrode was used in the voltage‐clamp mode to measure membrane currents and the other in current‐clamp to measure membrane potential. Ca currents as large as 2 nA were well clamped in cells as long as 210 micron. Acetylcholine (ACh) had no effect on ICa in the absence of beta‐adrenergic stimulation but reduced to control levels ICa elevated by isoprenaline. Nanomolar concentrations of ACh were able to reduce significantly ICa elevated by 2 microM‐isoprenaline. ACh had no effect on the shape of the I‐V curve, on the reactivation (recovery from inactivation), or on the inactivation of ICa. Although isoprenaline increased ICa by an average of 6.5‐fold, it had no effect on the shape of the I‐V curve or on the inactivation at test potentials negative to +40 mV. However, isoprenaline slowed the half‐reactivation time from a control value of 120 +/‐ 10 ms (mean +/‐ S.D.) to 153 +/‐ 12 ms at ‐80 mV. The effect of cyclic AMP on ICa was investigated using two patch electrodes, one filled with cyclic AMP. Maximal effects of cyclic AMP were observed with 5 microM‐cyclic AMP in the pipette. Maximal ICa was recorded several minutes after breaking the patch with the second electrode. After removing the cyclic‐AMP‐containing electrode, ICa declined to control levels after approximately 10 min. 5 microM‐cyclic AMP in the patch electrode increased ICa by an average of 6.9‐fold, but had no effect on the shape of the I‐V curve or on inactivation. Cyclic AMP had a slowing effect on reactivation (half‐reactivation time = 155 +/‐ 24 ms) similar to that of isoprenaline. ACh (1‐10 microM) did not reduce ICa elevated with cyclic AMP (0.1‐20 microM‐cyclic AMP in the pipette). With low concentrations of cyclic AMP in the pipette (0.1 microM), isoprenaline augmented ICa, but with 5 microM‐cyclic AMP in the pipette, isoprenaline was incapable of increasing ICa further. These results suggest that the decrease of ICa produced by ACh can be explained solely by decreases in cyclic AMP levels.
The role of amiloride‐blockable sodium transport in adrenaline‐induced lung liquid reabsorption in the fetal lamb.
Authors: Olver R E , Ramsden C A , Strang L B , Walters D V
Published: December 2014

Adrenaline was infused intravenously at rates of 0.1‐1.0 microgram/min into chronically catheterized fetal lambs (125‐141 days gestation) to induce slowing of secretion or reabsorption of lung liquid. There was an electrical potential difference (p.d.) of ‐0.3 to ‐9.5 mV (mean ‐3.4 mV) between lung liquid and plasma (lung liquid negative) during control lung liquid secretion. In response to adrenaline infusion, the p.d. increased (lung lumen more negative) and this change was greatest (1.8 +/‐ 0.3 mV) in experiments in which reabsorption occurred. Measurements were made of bidirectional fluxes of Na+ and Cl‐ across the pulmonary epithelium during control lung liquid secretion and during adrenaline infusion. Adrenaline‐induced reabsorption of lung liquid was associated with an increase in Na+ flux from lung lumen to plasma. Similar but smaller changes occurred when the adrenaline response was slowing of secretion. The difference between measured flux ratios and those predicted from the forces determining passive flux provided evidence for active transport of Cl‐ from plasma to lung lumen, as previously demonstrated by Olver & Strang (1974). When adrenaline was infused, there was evidence of active Na+ transport in the direction lung lumen to plasma and an associated decrease in active Cl‐ transport in the opposite direction. These changes were greatest when the response to adrenaline was reabsorption. Amiloride, when mixed into the lung liquid to give a calculated concentration of 10(‐4) M, abolished the changes in p.d. and ion flux induced by adrenaline. In experiments using amiloride concentrations between 10(‐8) and 10(‐4) M it was shown that 50% inhibition of the reabsorptive response to adrenaline (KI) was induced by 4 X 10(‐6) M‐amiloride in the lung lumen. Thus adrenaline‐induced slowing of secretion or reabsorption of lung liquid is mediated by active Na+ transport from lung lumen to plasma and depends on amiloride‐inhibitable Na+ channels on the luminal surface of the pulmonary epithelium.
Low frequency chronic electrical stimulation of normal and dystrophic chicken muscle.
Authors: Barnard E A , Barnard P J , Jarvis J C , Lai J
Published: December 2014

The fast‐twitch posterior latissimus dorsi muscle of normal and genetically dystrophic chickens was subjected to continuous indirect electrical stimulation at 10 Hz for periods of 4‐8 weeks. To sustain this in vivo nerve stimulation an internally implantable miniature stimulator device was designed. This regime of stimulation caused complete fatigue of the normal muscle within 5 min of its initiation. The dystrophic muscles maintained a very small degree of contractile activity during this initial phase. Tangible twitching of the muscle returned in 5 week birds between 3 and 5 days and in 10 week birds between 11 and 16 days after implantation. After 4 weeks of stimulation, no significant change was measured in the time‐to‐peak of the isometric twitch response, nor in the half‐relaxation time. The resistance to fatigue was significantly increased in the stimulated muscles when tested with a series of tetani at 40 Hz. The mean fibre area was decreased, in all muscles stimulated for longer than 3 weeks, in comparison to their contralateral controls, except where fibre splitting in dystrophic birds abnormally reduced the control value. The majority fibre type of the muscle was changed from type IIB to IIA. The histochemical reactions for both NADH‐linked oxidation and phosphorylase were distinctly increased in the stimulated muscles. In normal muscle, stimulation increased somewhat the number of nuclei per unit area and changed their intracellular distribution, so that a greater proportion was found adjacent to the sarcolemma. The normal posterior latissimus dorsi muscle responded to chronic stimulation with increases of 3‐6‐fold in its acetylcholinesterase (AChE) activity. The maximum change in AChE occurred after 2 weeks stimulation; a steady level, 3 times that of the control unstimulated muscle, persisted at later times. Chronic stimulation suppressed the over‐production of AChE that is characteristic of dystrophic chicken fast‐twitch muscle, to attain a level comparable to the AChE activity in a stimulated normal muscle. Stimulation exerted a strong normalizing influence on dystrophic muscle, as assessed morphologically. The characteristic fibre rounding, fibre hypertrophy and myonuclear proliferation were reduced. This influence was most marked where the stimulation was initiated before the major pathological changes had occurred, but was also significant when commenced in strongly affected birds of 10‐11 weeks.
The time course and magnitude of blood flow changes in the human quadriceps muscles following isometric contraction.
Authors: Wesche J
Published: December 2014

Blood velocities in the human femoral artery were measured using pulsed bidirectional Doppler‐ultrasound equipment before, during and after single isometric contractions of the quadriceps muscle group. After contraction periods lasting more than 20 s (long) and of tensions from 10% up to 75% of maximal voluntary contraction (m.v.c.), an increase in blood velocities of seven to eight times the resting level was observed. Estimated maximal volume flow to the whole leg during the post‐contraction hyperaemic phase calculated from these blood velocity measurements and vessel diameter (measured with echo‐ultrasound equipment) was in two of the subjects 2.4 l/min (female) and 4.4 l/min (male), respectively. In the latter, this estimate fitted very well with results obtained using a venous thermo‐dilution method. When using computer tomography to estimate the volume of the quadriceps muscle group, the calculated maximum flow to this muscle group in the post‐contraction hyperaemic phase was approximately 175 (female) and 185 (male) ml/min. 100 ml muscle, respectively. This was about forty times the estimated resting volume flow to this muscle of 4.7 (female) and 4.5 (male) ml/min. 100 ml muscle. The length of the post‐contraction hyperaemia after short (less than 10 s) contraction periods was 12‐13 s, by which time velocities had reached 25% above the precontraction level. After long contractions, the corresponding values were 23‐25 s. By contrast, previous plethysmographic observations by others indicate that postcontraction hyperaemias following long contractions last 10‐15 min. There was a marked difference between the times taken to reach maximal velocity in the hyperaemic phase when comparing short and long contractions. Maximal velocity was reached four to six cardiac cycles following short periods of contraction but during the very first heart beat after long periods of contractions. The present observations are compatible with the hypothesis that locally released metabolites or hormones play a dominant role in the regulation of the post‐contraction hyperaemia. Since during the short contraction periods maximal velocity was reached only after some seconds, whereas with the longer contraction periods it was reached during the first heart beat, it is suggested that these metabolites are released at some distance from the resistance vessels and that some time is needed for diffusion.
Heterogeneous kinetic properties of acetylcholine receptor channels in Xenopus myocytes.
Authors: Auerbach A , Lingle C J
Published: December 2014

We have used the cell‐attached patch‐clamp technique to examine the kinetic and conductance properties of acetylcholine receptor channel currents in cultured Xenopus myocytes. At high agonist concentrations (5‐100 microM) the currents occurred in bursts of openings. The probability that a channel existed in an ion‐conducting conformation during a burst (Po) was adopted as an empirical measure of channel kinetic behaviour. All openings within a given burst were to the same mean current amplitude. However, different bursts could have openings with a mean conductance of either 46 pS (gamma 40) or 64 pS (gamma 60). For gamma 40 bursts there were three predominant populations which could be distinguished by their mean Po values (approximately 0.9, approximately 0.3, and less than 0.01 at 20 microM‐acetylcholine). Po values increased as the acetylcholine concentration within the micropipette was increased. About 80% of bursts were from the highest Po population. gamma 60 bursts also occurred in three predominant modes. The highest Po population accounted for greater than 80% of all bursts and had a mean Po of approximately 0.6 at 20 microM‐acetylcholine. For both gamma 40 and gamma 60 channels, bursts from the highest Po population had open‐interval durations which were approximately 4 times longer than those from bursts from the medium Po population. Closed intervals from gamma 40, high Po bursts were approximately 4 times shorter than those from medium Po bursts. Occasional examples of switching between different kinetic modes were observed, suggesting that the Po populations may represent different activity patterns of a homogeneous channel population.
Calcium and long‐term transmission damage following anoxia in dentate gyrus and CA1 regions of the rat hippocampal slice.
Authors: Kass I S , Lipton P
Published: December 2014

The mechanism of long‐term anoxic damage in brain tissue is investigated using the rat hippocampal slice as a model system. The effects of short durations of anoxia on subsequent transmission through two neural pathways are studied. 10 min of anoxia irreversibly abolishes transmission between the perforant path and the dentate granule cells while only 7 min of anoxia irreversibly abolishes transmission between the Schaeffer collaterals and the CA1 pyramidal cells. We examine the involvement of Ca2+ in this irreversible transmission damage and, also, the differential sensitivities of the dentate gyrus and CA1 regions. Substitution of a buffer containing 0 Ca2+ and 10 mM‐Mg2+ during the anoxic period substantially improves the recovery of synaptic transmission in both regions of the slice. Dentate gyrus transmission recovers completely after 20 min of anoxia and CA1 transmission survives 10 min of anoxia. These results suggest that Ca2+ influx during anoxia may be an important cause of the long‐term damage. The uptake of 45Ca2+ into the intracellular space of the slice is increased during anoxia. This effect is approximately twice as large in CA1 as in the dentate gyrus. Thus, in the dentate gyrus the calculated exchangeable pool of Ca2+ is increased 30% by anoxia and in the CA1 it is increased by 70%. Two incubating conditions which decrease the amount of 45Ca2+ uptake during anoxia protect transmission against long‐term damage. (a) Pre‐incubation of the slices with 25 mM‐creatine elevates tissue phosphocreatine and attenuates the fall in adenosine 5'‐triphosphate (ATP) during anoxia. This is associated with partial protection against transmission damage and an approximate 50% attenuation of the anoxic uptake of 45Ca2+. (b) Inclusion of 2 mM‐cobalt in the buffer reduces the normoxic uptake of 45Ca2+ so that the uptake during anoxia is no greater than normoxic uptake in the absence of cobalt. This is associated with a complete protection against long‐term transmission damage following 10 min of anoxia in the dentate gyrus. A kinetic analysis of the 45Ca2+ uptake shows that the anoxic uptake results primarily from inhibition of the unidirectional efflux of Ca2+ from the cells; there is no calculable increase in the undirectional influx. This suggests that anoxia increases Ca2+ uptake by inhibiting one or more Ca2+‐extrusion processes and not by opening depolarization‐sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Human fixation and pursuit in normal and open‐loop conditions: effects of central and peripheral retinal targets.
Authors: Collewijn H , Tamminga E P
Published: December 2014

Eye movements were recorded precisely with a scleral‐coil method under three experimental conditions: fixation of a central, stationary target; pursuit of a central, moving target; pursuit of eccentric, moving targets. Subjects were instructed to attend to and fixate the target and to pursue it when it moved. The target was presented either in darkness (no visible background), on a diffusely lighted background, or on a large, structured background. Target and/or background could be moved independently with single sinusoids, pseudo‐random mixtures of sinusoids or triangular waves. The target was usually presented under normal viewing conditions, but in some measurements (interleaved with normal ones) retinal target motion was uncoupled from eye motion by electronical addition of the eye position to the target position (open‐loop conditions). The gain and phase relations of eye movements induced by motion of the target and/or background were calculated for the total, composite (smooth and saccadic) eye movement and for the reconstructed cumulative smooth component separately. Horizontal motion of a large, structured background induced correlated smooth eye movements while subjects fixated a stationary point target. The induced horizontal movements were very small (gain about 0.05) when the target was seen normally, and larger (gain about 0.20) when the target was horizontally stabilized on the retina. The phase lag of the induced eye movements relative to the background movements was usually smaller than 90 deg. When the target moved vertically and the background horizontally, vertical pursuit was similar to that with a stationary background, but in addition horizontal smooth eye movements, correlated with the background movements, were elicited with a gain of about 0.1 and a phase lag which was usually smaller than 90 deg. Imposed pseudo‐random retinal motion of a central target under open‐loop conditions (retinal image motion uncoupled from eye movements) elicited highly idiosyncratic responses which varied too much among subjects to allow any general conclusions, other than that open‐loop stimulation seems unsuitable as a tool for analysing the response characteristics of the smooth pursuit system. In the absence of a background, an eccentric target configuration (two vertically aligned arrows with the points localized 5 deg above and 5 deg below the fovea) in horizontal motion was pursued equally well as a central target.(ABSTRACT TRUNCATED AT 400 WORDS)
Ionic regulation of sea urchin sperm motility, metabolism and fertilizing capacity.
Authors: Christen R , Schackmann R W , Shapiro B M
Published: December 2014

In order to pursue the significance of the ionic regulation of sea urchin sperm behaviour, alterations in the cation composition of sea water were tested for their effects on sperm fertilizing capacity. Nearly all changes which resulted in lowered sperm intracellular pH, including lowered sea‐water pH, inclusion of the divalent ion chelator EGTA, addition of dithiothreitol, or removal of sea‐water Na+, enhanced sperm viability for periods of up to a week. These conditions caused decreased cell motility and elevated ATP concentrations, and prevented the acrosome reaction. Conversely, changes which increased the intracellular pH, decreased sperm ATP concentrations, or induced the acrosome reaction, reduced sperm viability. A single medium, high sea‐water K+ concentrations (greater than 100 mM), provided an exception to these general trends. At elevated K+ concentrations sperm were quiescent but became completely infertile. These data show that sperm fertilizing capacity is generally extended by maintenance of the sperm in an inactive state, and the results suggest that decreased cellular energy levels contribute to decreased fertility.
Extravasation in the knee induced by antidromic stimulation of articular C fibre afferents of the anaesthetized cat.
Authors: Ferrell W R , Russell N J
Published: December 2014

Electrical stimulation of the cut distal end of the posterior articular nerve (p.a.n.) of the cat knee joint resulted in significant extravasation of plasma proteins and erythrocytes into the synovial cavity of the knee. This effect was mediated by group IV afferents (C fibres) since stimulation of p.a.n. suprathreshold for group II or III afferents but subthreshold for group IV afferents did not produce extravasation. Unmyelinated sympathetic efferent fibres in the joint nerve did not contribute to the extravasation and were responsible for a diminution of this response as shown by the enhanced extravasation occurring after adrenergic blockade. Plasma and erythrocyte extravasation was mediated by afferents containing substance P (SP), as demonstrated by the reversible abolition of extravasation when the substance P antagonist (D‐Pro4,D‐Trp7,9,10)‐SP (4‐11) was injected into the synovial cavity. In some animals it was observed that electrical stimulation of the cut distal end of p.a.n. in one limb resulted in extravasation in the contralateral knee joint. It is suggested that articular C fibre afferents could make a significant neurogenic contribution to the initiation or maintenance of inflammatory joint disease.
Tachykinins and bombesin excite non‐pyramidal neurones in rat hippocampus.
Authors: Dreifuss J J , Raggenbass M
Published: December 2014

The effects of substance P, eledoisin and physalaemin‐‐which are structurally similar and all belong to the tachykinin family‐‐and of bombesin, a gastrin‐releasing peptide, on non‐pyramidal neurones were studied using unitary extracellular recordings from rat hippocampal slices. The peptides were added to the perifusion solution, or locally applied by pressure ejection from a micropipette, at concentrations ranging from 10(‐8) to 10(‐6) M. 104 out of 115 non‐pyramidal neurones responded to tachykinins, and 26 out of 27 responded to bombesin, by a reversible, concentration‐dependent increase in firing. The responsive neurones retained their sensitivity to the tachykinins and to bombesin under the condition of synaptic blockade. A synthetic peptide known to antagonize the effects of oxytocin on hippocampal non‐pyramidal neurones did not affect the excitations induced by the tachykinins or bombesin. The action of the tachykinins was not blocked by the muscarinic antagonist, atropine. These results indicate that hippocampal non‐pyramidal neurones‐‐which were previously shown to possess oxytocin receptors and mu‐type opiate receptors‐‐bear receptors for peptides of the tachykinin and of the gastrin‐releasing families. The hippocampal effects of tachykinins and of bombesin, however, were not blocked by synthetic structural analogues of substance P, known to antagonize the action of these peptides on some non‐nervous tissues. The possibility must be considered that brain receptors for tachykinins and for gastrin‐releasing peptides may be distinct from the peripheral receptors for these peptides.
Reflex origin for the slowing of motoneurone firing rates in fatigue of human voluntary contractions.
Authors: Bigland-Ritchie B R , Dawson N J , Johansson R S , Lippold O C
Published: December 2014

During fatigue from a sustained maximal voluntary contraction (m.v.c.) the mean motoneurone discharge rates decline. In the present experiments we found no recovery of firing rates after 3 min of rest if the fatigued muscle was kept ischaemic, but near full recovery 3 min after the blood supply was restored. Since 3 min is thus sufficient time for recovery of any central changes in excitability, the results support the hypothesis that, during fatigue, motoneurone firing rates may be regulated by a peripheral reflex originating in response to fatigue‐induced changes within the muscle.
Quantal release of acetylcholine evoked by focal depolarization at the Torpedo nerve‐electroplaque junction.
Authors: Dunant Y , Muller D
Published: December 2014

To analyse evoked acetylcholine (ACh) release in the electric organ of Torpedo marmorata, a loose patch‐clamp technique was used that allowed with a single extracellular electrode both focal depolarization of nerve endings and recording of the post‐synaptic currents produced by the released transmitter. Two different types of post‐synaptic response could be evoked by depolarizing pulses of increasing intensity: a graded response appearing with a delay of 0.6 ms (pulses of 0.2 ms duration), and an all‐or‐none response characterized by a mean delay of 1.4 ms. Both responses had a similar maximal amplitude and a similar rise time of 0.6 ms. The graded response was evoked in all places where spontaneous miniature electroplaque currents (m.e.e.s) could be recorded. It was not modified by 1 microM‐tetrodotoxin (TTX), but was Ca2+ dependent and was abolished by Cd2+ (0.2 mM) or Mg2+ (10 mM). The all‐or‐none response could be evoked in only 30% of places where m.e.c.s. were recorded, it was highly TTX sensitive, Ca2+ dependent, and abolished by Cd2+ (0.2 mM) or Mg2+ (10 mM). K+ channel blocking agents, such as 4‐aminopyridine (4‐AP) or tetraethylammonium (TEA), which are known to prolong the duration of action potentials, prolonged the delay of the all‐or‐none response, but not that of the graded response. At low strength stimulation, the graded response was clearly evoked in a quantal way, with the quantum corresponding to the amplitude of spontaneous m.e.c.s. The amplitude distribution of the evoked responses closely followed a Poisson distribution. The maximum synchronous release of transmitter was found to be approximately 1.3 quanta/micron2 of presynaptic membrane and a mean quantal size of about 7000 ACh molecules was estimated from the charge transfer of m.e.c.s. The nerve terminal time constant was calculated from strength‐duration curves obtained with depolarizing pulses just able to evoke either the all‐or‐none response or the first few quanta of the graded response. Respective mean values of 0.22 and 0.40 ms were found. Increasing the duration of the depolarizing pulse had two consequences: it differently affected the delay of the all‐or‐none response and that of the graded response; it increased the mean quantal content of the graded response. Both effects could not simply be accounted for by the influence of the nerve terminal time constant.(ABSTRACT TRUNCATED AT 400 WORDS)
Potentiation by 4‐aminopyridine of quantal acetylcholine release at the Torpedo nerve‐electroplaque junction.
Authors: Muller D
Published: December 2014

The effects of 4‐aminopyridine (4‐AP) on electrophysiological post‐synaptic responses evoked by field stimulation or evoked focally using a loose patch‐clamp technique, and on radiolabelled transmitter release were studied in the Torpedo electric organ. In this preparation, 4‐AP had three major effects: it greatly potentiated the amount of acetylcholine (ACh) released by a nerve impulse, it prolonged the duration of the post‐synaptic electroplaque current (e.c.) by several hundreds of milliseconds, and it increased the delay of responses triggered by a presynaptic action potential. Noise analysis performed at different times during the focally recorded giant response showed that it was made of a sustained release of ACh quanta. The maximum synchronous release of transmitter, expressed as the maximum number of quanta simultaneously delivered/micron2 of presynaptic membrane, was apparently not modified by 4‐AP. A slightly different dose dependence was found for the effects of 4‐AP on the potentiation of transmitter release and on the prolongation of the synaptic delay. The effects of tetraethylammonium (TEA) and other K+ channel blockers on these parameters were similar to those of 4‐AP. Strong depolarizing pulses applied focally to a nerve ending were able to evoke a giant response even in the presence of 1 microM‐tetrodotoxin (TTX). The prolongation of the discharge by 4‐AP was therefore not caused by repetitive re‐excitation of the nerve branches. Both the amplitude and the time course of the giant response were Ca2+ dependent. At a low Mg2+ concentration, the Ca2+ dependence of transmitter release was identical in the presence or absence of 4‐AP. Paradoxically, in the presence of 4‐AP, addition of 4 mM‐Mg2+ considerably increased the Ca2+ dependence of release, whereas in the absence of 4‐AP, Mg2+ blocked transmitter release by decreasing its sensitivity to Ca2+. This potentiating interaction between Mg2+ and 4‐AP was not seen with TEA or guanidine. In conclusion, 4‐AP potentiates ACh release in two different ways in the Torpedo electric organ: it promotes a sustained quantal release of transmitter during several hundreds of milliseconds without any significant change in the maximal synchronous release, it interacts with Mg2+ in such a manner that the sensitivity to Ca2+ of the nerve terminals is increased.
Electrophysiological properties and glucose responsiveness of guinea‐pig ventromedial hypothalamic neurones in vitro.
Authors: Minami T , Oomura Y , Sugimori M
Published: December 2014

The membrane properties of neurones in the guinea‐pig ventromedial hypothalamic nucleus (v.m.h.) were studied in in vitro brain slice preparations. The average resting potential was ‐62.9 +/‐ 5.4 mV (mean +/‐ S.D.), input resistance was 155 +/‐ 58 M omega, and action potential amplitude was 69.9 +/‐ 6.3 mV. Three types of neurone were identified. The type A neurones were characterized by a short membrane time constant (7.3 +/‐ 2.0 ms) and a small after‐hyperpolarization (a.h.p.) (2.0 +/‐ 1.2 mV) with a short half decay time of 67 +/‐ 55 ms after stimulation with a long outward current pulse. Type B had a long time constant (18.8 +/‐ 5.7 ms) and a large a.h.p. (6.9 +/‐ 2.4 mV) with a medium half decay time of 203 +/‐ 90 ms. Type C was characterized by a long time constant (14.3 +/‐ 2.3 ms) and a large a.h.p. (6.5 +/‐ 1.5 mV) with a long half decay time of 478 +/‐ 230 ms. The slopes of the frequency‐current (f‐I) plots of the three types were different, particularly for the first spike interval. The slopes for the type A (414 +/‐ 102 impulses s‐1 nA‐1) and type B neurones (480 +/‐ 120 impulses s‐1 nA‐1) were steeper than that for the type C neurones (178 +/‐ 41 impulses s‐1 nA‐1). This difference is probably related to the relatively long first interval observed in the type C neurones. In all type B and a few type C neurones, when the membrane potential was hyperpolarized beyond‐‐65 mV the application of orthodromic or direct stimulation generated a burst of spikes, consisting of a low‐threshold response (l.t.r.) of low amplitude and superimposed high‐frequency spikes. At the original resting potential, outward current pulses produced a train of low‐frequency spikes. In type C neurones maintained in a depolarized state (about ‐50 mV), inward current pulses produced a specific delay of the return to the original membrane potential. This delayed return was thought to be generated by activation of a transient K+ (IA) conductance. Stimulation at the lateral edge of the v.m.h. produced excitatory post‐synaptic potentials (e.p.s.p.s) in type A neurones, e.p.s.p.s with l.t.r. in type B neurones and e.p.s.p.‐inhibitory post‐synaptic potential sequences in type C neurones. About 20% of v.m.h. neurones, particularly the type C cells, were depolarized by glucose application with an associated increase in the input membrane resistance.(ABSTRACT TRUNCATED AT 400 WORDS)
On the mechanism by which changes in extracellular pH affect the electrical activity of the rabbit sino‐atrial node.
Authors: Satoh H , Seyama I
Published: December 2014

1. The effect of altering the extracellular pH (pHo) on the electrical activity of the isolated rabbit sino‐atrial (s.a.) node was studied using the two‐micro‐electrode voltage‐clamp technique. 2. Alkalinization of the perfusate increased the maximum rate of rise and amplitude of the nodal action potential, and also the frequency of spontaneous beating of the s.a. node; acidification produced opposite effects. 3. A change in the extracellular pH from a value of 6.5 to 8.5 caused increases of the maximal conductance for both the slow inward current and the steady‐state outward current systems without affecting the gating processes of the channels. 4. H+ could modify the electrical activity of s.a. nodal cells, not through altering the membrane surface potential but through the protonation of the ionic channels themselves. From the titration curves, the apparent pKa values for the slow inward current and the steady‐state outward current were estimated to be 6.4 and 6.0, respectively.
Spontaneous transient outward currents in single visceral and vascular smooth muscle cells of the rabbit.
Authors: Benham C D , Bolton T B
Published: December 2014

1. Whole‐cell membrane current recordings under voltage clamp were made at room temperature from dispersed single cells of longitudinal smooth muscle of rabbit jejunum and dispersed single smooth muscle cells of rabbit ear artery using patch pipettes containing up to 10 mM‐EGTA Ca buffer. 2. Spontaneous transient outward currents (s.t.o.c.s) up to 250 pA in size and about 100 ms in duration were observed in conditions which might lead to an elevated internal Ca concentration. The amplitude distribution in some cells and form of the currents suggested that they were evoked by a quantal stimulus. 3. S.t.o.c. amplitude was voltage dependent and reversed at the K equilibrium potential. S.t.o.c.s. were blocked by 1 mM‐tetraethylammonium or 10 mM‐Ba applied externally or by perfusing Cs inside the cell. 4. Removing external Ca abolished s.t.o.c. activity in the jejunal cells but not in arterial cells. Increasing EGTA buffering within the cells from 1 mM or less to 10 mM abolished activity in both cell types. 5. Caffeine (5 mM) applied to the bathing solution stimulated rapid discharge of transient outward currents and then a prolonged period of inhibition. The stimulated discharge was sensitive to external Ca in jejunal cells but much less so in arterial cells. ACh applied by ionophoresis to jejunal cells or noradrenaline bath‐applied onto arterial cells also stimulated discharge of transients followed by a prolonged inhibitory phase. 6. It was suggested that s.t.o.c.s represent the simultaneous opening of up to 75‐100 Ca‐activated K channels at ‐40 mV in response to sudden discharge of Ca from internal stores when these became overloaded, and that this process may occur cyclically.
Effects of hypoxia on rat hippocampal neurones in vitro.
Authors: Fujiwara N , Higashi H , Shimoji K , Yoshimura M
Published: December 2014

1. The effects of hypoxia on the rat hippocampal CA1 neurones in tissue slices of the rat brain were studied in vitro by intracellular recording. 2. In response to superfusion of a hypoxic medium equilibrated with 95% N2‐5% CO2, a majority of the neurones showed a hyperpolarization of 5‐15 mV in amplitude and 4‐12 min in duration. The hyperpolarization was, in turn, followed by a slow depolarization which within 20 min of hypoxic exposure reached a plateau level of about 25 mV above the pre‐hypoxic resting potential. Both the initial hyperpolarization and subsequent depolarization were associated with a reduction in membrane resistance. 3. The hyperpolarization reversed in polarity at a membrane potential of ‐83 mV. There was an almost linear relationship between amplitude of the hyperpolarization and membrane potential. The hyperpolarization was markedly enhanced in potassium‐free media and was depressed in high‐potassium solutions. 4. The hyperpolarization was not significantly affected by low‐chloride or low‐sodium medium or by solution containing tetraethylammonium (10 mM), 4‐aminopyridine (1.5 mM) or caesium (3 mM). Moreover, intracellular injection of ethyleneglycol‐bis‐(beta‐aminoethylether)N,N‐tetraacetic acid (EGTA) did not alter the hyperpolarization. On the other hand, barium (0.5 mM)‐containing medium reduced the amplitude of the hyperpolarization by 20‐40%. 5. Superfusion of ouabain (5‐7 microM)‐containing medium in normoxic conditions produced hyperpolarizing and depolarizing responses similar to those elicited by hypoxic exposure. The slow depolarization was also mimicked by elevation of the extracellular potassium concentration to 10‐20 mM. 6. Evoked i.p.s.p.s were abolished within 4 min of hypoxic exposure while evoked e.p.s.p.s were maintained for about 20 min of hypoxic superfusion. Soma spikes of the neurones elicited by a depolarizing pulse were also well preserved. Their threshold was, however, raised, concomitant with a decrease in the peak amplitude. 7. When the slice was reoxygenated after 20‐40 min of hypoxic exposure, the neurones immediately began to repolarize and showed a transient hyperpolarization of 5‐10 mV in amplitude and 1‐2 min in duration. The membrane potential, input resistance and action potential returned to the pre‐hypoxic levels after 15‐20 min of reoxygenation. The amplitude of the reoxygenation‐induced hyperpolarization was not significantly changed when the membrane was hyperpolarized or depolarized. The hyperpolarization was eliminated by potassium‐free medium or solution containing ouabain (1 microM).(ABSTRACT TRUNCATED AT 400 WORDS)
Interhemispheric transfer of visual information in humans: spatial characteristics.
Authors: Berardi N , Fiorentini A
Published: December 2014

1. The problem of the interhemispheric transfer of visual information in humans has been approached psychophysically, making use of a visual discrimination task that shows a clear left field advantage and is subject to the phenomenon of perceptual learning. 2. For this task (discrimination of complex gratings differing only by the relative spatial phase of their harmonic components) there is a left field advantage and a lack of interhemispheric transfer of learning effects at all spatial frequencies tested for stimuli removed at least 5 deg from either side of the vertical meridian. 3. For stimuli close to the vertical meridian, the left field advantage disappears and there is a complete transfer of learning effects, provided the fundamental spatial frequency is 2 cycles/deg or lower. 4. At higher spatial frequencies the left field advantage is maintained and the learning effects do not transfer from one visual hemifield to the other, even at +/‐ 0.5 deg from the vertical meridian, unless the contrast is very high. 5. The transfer of learning effects obtained for spatial frequencies of 2 cycles/deg or lower is peculiar to regions placed close to the vertical meridian and symmetrically located on either side of it. No transfer is obtained between non‐overlapping regions on the same side of the vertical meridian. 6. These findings are consistent with an interhemispheric transfer of visual information, preferential for low spatial frequencies and high contrasts, in agreement with that found for callosal transfer in the cat (Berardi, Bisti & Maffei, 1987).
Current activation by membrane hyperpolarization in the slowly adapting lobster stretch receptor neurone.
Authors: Edman A , Gestrelius S , Grampp W
Published: December 2014

1. A polarization‐induced membrane current, IQ, was investigated in the slowly adapting lobster stretch receptor neurone using conventional electrophysiological techniques including intracellular ion measurements. 2. The current was readily blocked by Cs+ in a voltage‐dependent manner, but proved to be unaffected by tetrodotoxin, tetraethylammonium and 4‐aminopyridine. 3. From an analysis of the ionic basis of IQ, it appeared that the current is carried by both Na+ and K+ through a membrane channel whose permeability for K+ is about six times larger than that for Na+ in a normal ionic environment. In the presence of reduced external Na+ concentration the Q‐channel increases its permeability for both Na+ and K+, but more so for Na+ than for K+. 4. Kinetically, IQ was found to be characterized by a steep sigmoidal relationship between membrane voltage and steady‐state current activation, and by a bell‐shaped relationship between membrane voltage and the time constant of the exponential phase of current activation or deactivation. A significant feature of the latter relationship is a tendency to level off at finite time‐constant values in both strongly hyperpolarizing and strongly depolarizing voltage regions. 5. From the experiments a mathematical IQ model was inferred. This model was based on constant‐field and channel‐gating kinetics involving a voltage‐dependent reaction step in series with a voltage‐independent reaction step. The model was found to successfully reproduce IQ behaviour in the living preparation. 6. Functionally, the activation of IQ was found to play a role in setting the cell's resting polarization and membrane excitability. This function was inferred from experiments on unimpaled cells in which it was possible to demonstrate some overlap between the voltage ranges of IQ activation and impulse initiation. In addition, in impaled cells the activation of IQ was found to cause some shortening of post‐tetanic membrane hyperpolarization and to accelerate, thereby, the post‐tetanic restoration of membrane excitability to control levels.
Statistics of neuromuscular transmitter release in young and old mouse muscle.
Authors: Kelly S S , Robbins N
Published: December 2014

1. It was reported previously that in limb muscles of old (27‐30 months) CBF‐1 mice, quantal content (m) of evoked transmitter release was increased compared to that in young (9‐12 months) mice. In diaphragm muscles there was no change with age. The object of the present study was to determine whether the age‐related increase in transmitter release was due to increase in the binomial parameter n or the parameter p. The analysis also involved consideration of goodness‐of‐fit between observed and expected binomial distribution of the data. 2. Spontaneous miniature end‐plate potentials (m.e.p.p.s) and evoked end‐plate potentials (e.p.p.s) were recorded with intracellular techniques from soleus and diaphragm muscles bathed in low‐Ca high‐Mg medium. The goodness‐of‐fit between the observed e.p.p amplitude distribution and that expected from a binomial distribution was evaluated by chi 2 test. 3. In different muscles and at different ages, the percentage of fibres with binomial e.p.p. distributions varied from 17 to 44%, even though in all fibres there was a similar proportionality between direct quantal content and the reciprocal of the square of the coefficient of variation of e.p.p. amplitudes. In addition, apparent graphical agreement between observed and theoretical binomial e.p.p. distributions was often not substantiated by the chi 2 criterion. 4. In soleus muscles from young mice, lowering the stimulus frequency from 10 to 0.5 Hz and shortening the train length from 250 to 100 pulses increased the prevalence of binomial e.p.p. distributions, but the same result was not obtained in diaphragm or soleus muscles from old mice. If the mean amplitude of groups of 10 e.p.p.s in any train showed any drift (greater than 10%) then that train was excluded from the results. Thus, in order to make valid age comparisons, only fibres with binomial e.p.p. distributions were analysed further. 5. There was no change with age in m, n or p in diaphragm muscles, but in soleus muscles from old animals a nearly 2‐fold increase in n entirely accounted for the increase in m. 6. If, as proposed by others, n represents the number of release sites, then the ageing soleus neuromuscular junction may have increased numbers or length of active zones or associated membrane components.