bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of the motion of organelles which undergo retrograde and anterograde rapid axonal transport in Xenopus
Authors: Koles Z. J. , McLeod K. D. , Smith R. S. 
Published: December 2014

1. Axonally transported organelles were detected optically in myelinated axons from Xenopus laevis at room temperature (21‐23 °C). Details of the motion of organelles which were transported in the retrograde and anterograde directions were studied using filmed records.2. A group of 133 organelles with a mean retrograde velocity of 0·91 μm/sec was compared with a group of thirty‐nine organelles with a mean anterograde velocity of 0·93 μm/sec.3. Averaged power spectra of the positional deviations about the mean positional change through time were constructed for organelles which travelled in the retrograde and anterograde directions. Most of the power in the two spectra was at frequencies below 0·2 Hz and each contained a single peak at 0·02‐0·04 Hz. The power spectrum for retrograde organelle motion had a magnitude about twice that for anterograde organelle motion.4. Estimates of the instantaneous velocity of organelles which travelled in either direction varied smoothly with time. Instantaneous velocity was not a smooth function of organelle position, (i.e. was ‘saltatory’).5. Histograms of the estimates for the groups of organelles whose major motion was retrograde or anterograde were broad, covering a range of about 3 μm/sec, were unimodal, and passed through zero to include a small group of values which indicated motion in the opposite (minor) direction.6. Organelles spent, on average, more time moving in the minor direction the lower their mean velocity.7. The variation in instantaneous velocity was greater for organelles which travelled in the retrograde direction than for those which travelled in the anterograde direction. No correlation was found between the variation of instantaneous velocity and the mean velocity of the organelles.8. Images of organelles occasionally appeared to rotate while the organelle continued to move in the major direction of travel.9. Evidence is presented that spatially related properties of the axon influence organelle velocity and that this influence is common to organelles which travel in the two major directions.10. A hypothesis is presented to account for the findings. This supposes that each organelle travels through a stationary axoplasm and is propelled by the resultant of two opposing driving forces whose relative magnitude fluctuates with time. Spatially dependent properties of the axoplasm modify the postulated time‐related cycle of motion.
Interstitial space of mouse skeletal muscle
Authors: Sheff Michael F. , Zacks Sumner I. 
Published: December 2014

1. A new preparation of mouse skeletal muscle, prepared from pectoral muscles, is described.2. The sorbitol space of this muscle, both in vivo and in vitro, has been measured with dynamic loading of the muscle in vitro as an experimental variable.3. The Na+ and K+ contents of the muscle have been determined and the apparent intracellular concentration for these ions calculated both in vivo and after incubation in vitro.4. Histological studies on the incubated muscle have been made so as to permit comparison of the changes in the chemical measurements with changes in the ultrastructure of the muscle.5. The results of these experiments show that there is an increase in the apparent extracellular space of the muscle following incubation. This increase is constant, and independent of the load, with the important exception that unloaded muscles do not reach an equilibrium during the period of incubation and have a much greater apparent extracellular space.6. Intracellular Na+ and K+ concentrations are consistent with the sorbitol being restricted to an extracellular phase in the loaded muscle; but the evidence implies that sorbitol in the unloaded muscle penetrates into a space from which Na+ is excluded.7. The total water content of the muscle per unit weight is unchanged by incubation, indicating that the apparent change in sorbitol space is in the ratio of intracellular space to extracellular space rather than by addition of water to the extracellular space.The significance of these results is discussed with reference to the use of such preparations for in vitro studies.
Sodium currents and sodium‐current fluctuations in rat myelinated nerve fibres
Authors: Neumcke B. , Stämpfli R. 
Published: December 2014

1. Sodium currents and fluctuations of sodium currents were measured in myelinated fibres of rat sciatic nerve under voltage clamp at 20 °C.2. Relaxations of sodium currents during various test potentials were recorded in the presence of 6 nM‐TTX in the extracellular solution. The activation of sodium currents at low depolarizations could be described with the m2 formulation. At increasing potentials higher powers of m up to 4 were required. The mid‐point of the PNa (E) curve was located near E = ‐32 mV. Sodium inactivation during various depolarizations developed in two phases.3. The resistance in series with the nodal membrane was calculated from peak sodium currents without and with 6 nM‐TTX in the extracellular solution. The resistance varied between different fibres and ranged between 190 and 620 kΩ.4. From peak sodium currents at the same mambrane potential without and in the presence of TTX an apparent equilibrium dissociation constant of 1·6 nM was calculated for TTX binding to sodium channels.5. The conductance γ and the number N0 (corrected for series‐resistance effects) of sodium channels were evaluated from ensemble average values of the mean sodium current and the variance of sodium‐current fluctuations at the beginning of a test pulse. The mean values were γ = 14·5 pS, N0 = 21,000 per node.6. The spectral density of stationary sodium‐current fluctuations exhibited two relaxation components whose time constants were comparable to those of sodium activation and inactivation. At low depolarizations the variance produced by inactivation fluctuations was larger than predicted by the m3. h formulation.7. It is concluded that individual sodium channels of rat and frog nerve have similar gating properties. In mammalian nodes the number of sodium channels is lower and the single‐channel conductance higher than in amphibian nodes.
Anion blockers inhibit impulse‐evoked quantal transmitter release at the crayfish neuromuscular junction
Authors: Niles Walter D. , Smith Dean O. 
Published: December 2014

1. The effects of the anion‐transport blocking reagents Probenecid, 4,4′diisothiocyanostilbene‐2,2′‐disulphonate (DIDS), and pyridoxal phosphate on the number of quanta released (m) and the time course of the probability of quantal release, α(t), following an action potential were studied at single synaptic sites on the opener muscle in the crayfish leg.2. Low concentrations (10‐50 μM) of DIDS or Probenecid produced decreases in m to about 30‐50% of the initial value; at higher concentrations (100 μM or greater), evoked release failed. Much greater concentrations (500 μM) of pyridoxal phosphate were necessary to produce decreases in m.3. Synaptic depression in 50 μM‐Probenecid was reversible by removing the agent; after treatment with 50 μM‐DIDS, however, m partially regained the initial value upon removal of the drug.4. The time course of α(t) after an action potential was unaffected by any of the reagents.5. It is concluded that the reagents decrease the number of quanta evoked by a nerve impulse by decreasing the magnitude, but not the time course, of the average rate of quantal release following an action potential; it is suggested that nerves and other secretory cells may share a common mechanism during exocytosis that is subject to modification by these agents.
Effects of sympathetic nerve stimulation on intra‐oral mechanoreceptor activity in the cat
Authors: Cash R. M. , Linden R. W. A. 
Published: December 2014

1. Micro‐electrode recordings were made from intra‐oral mechanoreceptor neurones in the trigeminal ganglion and mesencephalic nucleus of the fifth nerve in the cat.2. The effect of cervical sympathetic trunk stimulation on the discharge of the mechanoreceptors to a controlled force was observed.3. Almost half of the mechanoreceptor neurones studied were modulated by sympathetic stimulation. Sympathetic stimulation both decreased the impulse frequency to a controlled force application and raised the threshold in these receptors. The remainder were unaffected by sympathetic stimulation.4. In previous studies involving recordings from either the trigeminal ganglion or mesencephalic nucleus no spontaneously active slowly adapting intra‐oral mechanoreceptors have been observed, yet in peripheral alveolar nerve studies many workers have reported spontaneously discharging neurones. In the present study spontaneous activity has been recorded from intra‐oral mechanoreceptors both in the trigeminal ganglion and in the mesencephalic nucleus after cutting the cervical sympathetic trunk. The spontaneous activity could be abolished in all cases but one, by sympathetic stimulation. It is suggested that reported spontaneous activity from intra‐oral mechanoreceptors could be due to cutting the peripheral nerve and therefore the sympathetic supply, thus removing an inhibitory influence from the sensory unit. The means by which the sympathetic supply inhibits the sensory unit has not been resolved.
Muscle receptors in the cross‐reinnervated soleus muscle of the cat
Authors: Gregory J. E. , Luff A. R. , Proske U. 
Published: December 2014

1. Discharges have been recorded from afferents of the soleus muscle following reinnervation by the nerve of a fast twitch muscle, extensor digitorum longus. Recordings were made 227‐449 d post‐operatively.2. The gross afferent discharge from the cross‐reinnervated soleus suggested the presence of fewer mechanosensitive receptors than in normal muscles, as judged by discharges seen during a maximal muscle twitch.3. A comparison of receptors in the cross‐reinnervated muscle with afferents from a self‐reinnervated muscle showed that many of the responses in the self‐reinnervated muscle were also abnormal. It was concluded that much of the disruption resulted from the surgical interference and that rather less could be attributed to the foreign nerve.4. A detailed analysis of response characteristics of receptors in cross‐reinnervated soleus muscles of five cats showed that afferent conduction velocities of identified spindles and tendon organs were generally lower than normal and responses to muscle stretch or vibration were often atypical. A large number of afferents which could not be classified as muscle spindles or tendon organs included a group called contraction receptors. These responded generally only during maximal muscle contractions and with a rather feeble discharge. A second group consisted of afferents in which impulses could be elicited by electrical stimulation of the nerve but not by any mechanical activity in the muscle.5. In a further five animals a detailed study was made of the motor supply of muscle spindles. A fusimotor innervation was common, but invariably stimulation of the γ fibre had a static action on the spindle. No purely dynamic fusimotor fibres were encountered. There were many static β fibres (skeletofusimotor) no dynamic βs and three axons conducting in the α range, which developed no tension, yet produced specific intrafusal effects. Two of these had a mixed static—dynamic action while the third was purely static.6. It was concluded that in the cross‐reinnervated soleus muscle the majority of afferents were abnormal in one or other respect. The central action of such abnormal receptors would have to be taken into account when seeking explanations of the transformation of a muscle's mechanical properties following reinnervation by a foreign nerve.
Effects of β‐adrenergic stimulation on calcium movements in rabbit aortic smooth muscle: relationship with cyclic AMP
Authors: Meisher Kaushik D. , van Breemen Cornelis 
Published: December 2014

1. The effects of isoprenaline (10−6 M) on relaxation, unidirectional as well as net Ca2+ fluxes, and cyclic AMP levels were investigated in rabbit aorta under the condition of high‐K+ depolarization in the presence of phentolamine (10−5 M).2. Isoprenaline (10−6 M) caused significant inhibition of Ca2+ influx stimulated by 145 mM‐K+ (0 Na+) solution. The time courses of Ca2+ influx inhibition and relaxation by isoprenaline were parallel. Isoprenaline also caused a significant inhibition of high‐K+‐induced gain in net Ca2+ content.3. Ro 20‐1724 (1 mM), a phosphodiesterase inhibitor, also caused relaxation and Ca2+ influx inhibition in high‐K+‐depolarized rabbit aorta. Pre‐treatment with Ro 20‐1724 potentiated isoprenaline‐induced Ca2+ influx inhibition and relaxation.4. Isoprenaline and Ro 20‐1724 each alone increased cyclic AMP levels. Furthermore pre‐treatment with Ro 20‐1724 caused potentiation of isoprenaline‐induced increases in cyclic AMP levels.5. At submaximal concentration, D600 (10−7 M) caused partial inhibition of high‐K+‐stimulated Ca2+ influx and produced relaxation. However, unlike Ro 20‐1724, it did not potentiate isoprenaline‐induced Ca2+ influx inhibition and relaxation. D600 does not increase cyclic AMP levels in smooth muscle.6. Dibutyryl cyclic AMP (1 mM), a lipid‐soluble analogue of cyclic AMP, caused relaxation and inhibited high‐K+‐stimulated Ca2+ influx.7. Isoprenaline failed to cause stimulation of Ca2+ efflux in high‐K+‐depolarized rabbit aorta.8. It is concluded that the inhibition of Ca2+ influx may be one of the mechanisms by which β‐receptor stimulation can reduce intracellular free Ca2+ to promote relaxation of smooth muscle. The data support the involvement of cyclic AMP in this action of the β‐agonist.9. Since the experiments were conducted in 145 mM‐K+ (0 Na+) depolarizing conditions, the role of hyperpolarization or of a Na+—Ca2+ exchange mechanism in isoprenaline‐induced Ca2+ influx inhibition and/or relaxation can be excluded.
The action of puromycin and cycloheximide on the initiation of rapid axonal transport in amphibian dorsal root neurones
Authors: Nichols T. R. , Smith R. S. , Snyder R. E. 
Published: December 2014

1. Amphibian dorsal root ganglia—sciatic nerve preparations were incubated in vitro and the rapid axonal transport of radioactive labels was studied with a position‐sensitive detector and by conventional liquid scintillation analysis. Protein was labelled by exposure of the ganglia to [35S]methionine or [3H]leucine and lipid was labelled using [32P]orthophosphoric acid.2. Protein synthesis was interrupted by exposure of the ganglia to either cycloheximide or puromycin. When ganglia were exposed to either inhibitor prior to or simultaneously with a label, the somal export of both protein and lipid to the axon was reduced by two to three orders of magnitude.3. Using the position‐sensitive detector, [35S]methionine was observed to be exported from the ninth dorsal root ganglia of Rana catesbiana 3·49±1·56 h (± S.D.) after exposure, and [32P]phosphate 4·46±1·85 h after exposure.4. Export of [35S]methionine or [32P]phosphate was disrupted 3·32±1·21 h (± S.D.) or 1·93±1·04 h respectively after exposure of the ganglia to cycloheximide or puromycin.5. For a given preparation the time required for [35S]methionine to be exported was statistically equal to the time required for cycloheximide or puromycin to disrupt export. No such correlation was found to exist for the export of [32P]phosphate.6. Analysis revealed that materials labelled with either [35S]methionine or [32P]phosphate continue to be exported from the ganglia for several hours after the initial disruption in outflow caused by the inhibitors.7. The results do not provide support for the hypothesis of Ambron, Goldman & Schwartz (1975) that a ‘key’ newly synthesized, and non‐storable, polypeptide is added to an already assembled structure to allow rapid axonal transport to be initiated.
The influence of temporal frequency and adaptation level on receptive field organization of retinal ganglion cells in cat
Authors: Derrington A. M. , Lennie P. 
Published: December 2014

1. The discharges of single X and Y ganglion cells (distinguished by a test of linearity of spatial summation) were recorded in the optic tract of anaesthetized, paralysed cats.2. Fourier techniques were used to analyse the distribution of amplitudes of several component temporal frequencies in the maintained discharge. X and Y cells were distinguished by their mean rates, but not by the amplitude or variability of other component frequencies.3. Sensitivities to moving sinusoidal gratings were measured by an automatic procedure in which stimulus contrast was adjusted to give the smallest modulation of discharge that reliably exceeded that of the relevant component frequency in the maintained discharge.4. Spatial contrast sensitivity curves of X cells and of on‐centre Y cells could be described by a model of the receptive field as two concentric Gaussian sensitivity profiles representing the centre and the antagonistic surround.5. Changes in temporal frequency altered the shapes of the spatial contrast sensitivity curves of most units. For X cells sensitivity at the optimum spatial frequency was greater at a temporal frequency of 10·4 Hz than at lower or higher temporal frequencies. The relative sensitivity to low spatial frequencies improved as temporal frequency was raised from 0·16 to 20·8 Hz. The shapes of the contrast sensitivity functions of Y cells were less affected by changes in temporal frequency: at all spatial frequencies sensitivity was greater at 2·6 Hz than at lower or higher frequencies.6. The effect of temporal frequency upon the shape of the spatial contrast sensitivity curve could be explained by assuming that the centre and surround changed their sensitivities without changing their characteristic radii. A simple model, using a temporal R—C filter in the surround pathway, predicted qualitatively similar changes in the shape of contrast sensitivity curves but failed to provide acceptable fits to the observations. A second model, which assumed that surround signals are delayed by a fixed amount before being combined with those from the centre, fitted the observations of most, but not all, X cells.7. Dark adaptation produced changes in the shape of the spatial contrast sensitivity curve consistent with a reduction in the relative sensitivity of the surround, but did not bring about systematic changes in the space constants of the best‐fitting theoretical curves.8. The effects of adaptation level upon contrast sensitivity were expressed as plots of increment—threshold against mean illumination. The shallowest of these curves, obtained for the optimum spatial stimulus moving at about 10 Hz, had slopes averaging 0·77. Decreases in spatial or temporal frequency increased the slopes of the curves.
Presynaptic currents in mouse motor endings
Authors: Brigant J. L. , Mallart A. 
Published: December 2014

1. We used external electrodes placed under precise visual control on motor endings of the mouse to record electrical activity promoted by nerve stimulation.2. Three types of wave form have been observed in relation to well‐defined electrode emplacements: (i) at the transition between myelinated and non‐myelinated parts of the axon, the wave form consists of two negative deflexions preceded by a small positivity (preterminal response), (ii) at the main part of the terminal branches, we obtained a two component positive wave form (terminal response) and (iii) electrode positions in a narrow area between the former and the latter yielded triphasic (positive—negative—positive) wave forms (intermediate responses).3. Since these responses could not be readily interpreted in terms of classical description of membrane currents associated with propagating action potentials, we used specific channel blocking agents to identify wave form components.4. Bath application of tetraethylammonium or aminopyridines, or, better, a combination of both, suppressed delayed positive deflexions of terminal and intermediate responses and the late negative component of preterminal responses. Local inophoretic drug application showed that K channels are present only at the terminal part of the endings. K+ outflux promotes a local circuit whose sink is located at the preterminal part where it generates the late negative deflexion of the preterminal response.5. Local application of tetrodotoxin suppressed the first negative component of preterminal responses but failed to affect electrical activity at the terminal part of the endings. This indicates that Na channels, and, therefore, action potential generation, are restricted to the preterminal part.6. Suppression of K conductance revealed a slow inward current at the terminal part of the endings which could be identified as a Ca current. Ba2+ and Sr2+ could substitute for Ca2+ as inward current carriers.7. Activation of spatially separated Na channels, on one side, and of K and Ca channels, on the other, generated ionic currents and separated local circuit currents which flow between preterminal and terminal parts (and vice versa). Thus, the signals recorded at each point of motor endings correspond to the sum of ionic and passive currents entering (or leaving) the membrane at that point.8. The present results represent a further example of heterogeneity of axonal membrane.