bluuebunny/crossref_metadata_2025 huggingface dataset:
Tension transients during steady shortening of frog muscle fibres.
Authors: Ford L E , Huxley A F , Simmons R M
Published: December 2014

Single intact fibres from frog muscle at 0‐1 degrees C were stimulated to produce isometric tetani at a sarcomere length of about 2.25 micron, using a spot‐follower apparatus to control the length of the central part of a fibre. When the plateau of the tetanus was reached the fibre was forced to shorten by applying a step and ramp length change in an approximation to an isotonic release. When tension had reached a steady level, Ti, during shortening, tension transients were elicited by applying step changes of length, complete within 0.2 ms, ranging from a stretch of 1.5 nm per half‐sarcomere to a release of 6 nm per half‐sarcomere. The tension transients recorded during shortening were qualitatively similar to those previously recorded in isometric tetani. There were four phases: phase 1, the change of tension during the step; phase 2, a rapid partial recovery of tension; phase 3, a delay or reversal of recovery; phase 4, a slower recovery of tension to the level before the step was applied. Measurements were made of the extreme tension, T1, attained during a step, and the level, T2, to which tension recovers in phase 2. The excursion of tension, [T1‐Ti], during a small step of given size, fell with increase of shortening velocity, reaching about 40% of the isometric value near the maximum velocity of shortening. T2 fell as shortening velocity was increased and the fraction of steady tension recovered, T2/Ti, also decreased, so that the proportion of tension recovery in phase 4 increased. All the recovery phases became progressively more rapid with increase of shortening velocity. The early tension response was matched with a delay‐line simulator so as to estimate the value of the instantaneous stiffness. Stiffness during shortening was found to decrease approximately linearly with tension, reaching about 35% of the isometric value as tension approached zero. It was impossible to match the early tension response in a rapidly shortening fibre without assuming decreased stiffness. The decline of stiffness is interpreted as due largely to reduced number of attached cross‐bridges, but quantitative estimates would be affected by possible filament compliance and non‐linearity of cross‐bridge stiffness. The decrease in T2 also suggests fewer cross‐bridges are attached as shortening velocity increases, but uncertainties about the processes determining phase 2 during shortening do not permit a precise estimate of stiffness to be made.(ABSTRACT TRUNCATED AT 400 WORDS)
Sources of input to interneurones mediating group I non‐reciprocal inhibition of motoneurones in the cat.
Authors: Harrison P J , Jankowska E
Published: December 2014

Intracellular recordings have been made from laminae V‐VI interneurones interposed in pathways of non‐reciprocal inhibition of motoneurones from group I afferents of triceps surae and/or plantaris. A comparison of actions of brief stretches of triceps surae and plantaris with actions of electrical stimulation of nerves of these muscles revealed that I a afferents influenced about a half of the interneurones excited by I b afferents. Electrical stimulation of seven muscles nerves, three cutaneous nerves, posterior knee joint and interosseous nerves, the red nucleus and the pyramidal tract, evoked excitatory post‐synaptic potentials (e.p.s.p.s) in various proportions of interneurones. Most of the interneurones were excited monosynaptically, or both monosynaptically and disynaptically by group I afferents. This, together with a very small proportion of interneurones in which e.p.s.p.s were evoked only disynaptically, indicates that the same last‐order interneurones may subserve di‐ and trisynaptically evoked inhibition of motoneurones. Other fibre systems excited these interneurones monosynaptically (interosseal, rubro‐ and corticospinal), disynaptically (cutaneous, rubro‐ and corticospinal) and polysynaptically. The coupling of the earliest e.p.s.p.s from group II and joint afferents could not be established, but was consistent with their mediation by only one or two interposed interneurones. Inhibition was evoked from all fibre systems with excitatory input to the same or to other interneurones of the sample, except from group II afferents, the effects of which were found in a much smaller number of cells and may not be fully representative.
Ionic and electrophysiological properties of retinal Müller (glial) cells of the turtle.
Authors: Conner J D , Detwiler P B , Sarthy P V
Published: December 2014

The ionic and electrophysiological properties of Müller cells, the principal glial element of the vertebrate retina, were investigated. The membrane potential of enzymatically dissociated and in situ Müller cells was about ‐80 mV and depended on external K+ concentration in a manner that was described by the Goldman‐Hodgkin‐Katz equation with a Na+‐K+ permeability ratio of 0.037. The current‐voltage relation showed marked inward rectification, with the input resistance at the resting potential being about 30 M omega for dissociated cells and about 3 M omega for in situ cells. In situ Müller cells were found to be electrically coupled to each other which could explain their lower resistance. We conclude that Müller cells are similar to other types of glia. In spite of a finite Na+ permeability their membrane potential is determined mainly by K+, they are electrically inexcitable and form an electrically coupled network in the retina.
Stepwise shortening in unstimulated frog skeletal muscle fibres.
Authors: Granzier H L , Pollack G H
Published: December 2014

We investigated the dynamics of sarcomere length change during imposed stretches and releases of unstimulated single fibres of frog skeletal muscle. Three independent methods were used: an on‐line method in which sarcomere length is computed from the striation pattern; laser diffraction; and a segment length tracking device. During steady ramp releases and stretches, both sarcomere and segment length changes occurred in stepwise fashion; i.e. periods of pause were interspersed between periods of rapid shortening. The above result indicates that activation of the fibre is not required to elicit stepwise length changes. Increasing the ramp velocity caused the steps to increase in size and the pauses to decrease in duration. Ramp releases and stretches were imposed at each of several initial sarcomere lengths up to 4.0 microns. Stepwise length changes were observed at all lengths, and their size was independent of initial sarcomere length. The observation of stepwise length changes beyond overlap indicates that the underlying mechanism probably does not lie in synchronous action of cross‐bridges; an alternative hypothesis is advanced.
The respiratory activity of human levator costae muscles and its modification by posture.
Authors: Goldman M D , Loh L , Sears T A
Published: December 2014

The activation of the levator costae, a set of axial muscles inserted between each rib and the vertebra immediately rostral, has been studied electromyographically in a human subject, standing upright, with head erect ('neutral' posture). Caudal levator costae muscles (T9, and T10) are active during eupnoea. Periodic activity in phase with inspiration occurs in admixture with different levels of tonic activity that is strongly influenced by posture. Postural changes and various voluntary respiratory manoeuvres which should lengthen or shorten the levator costae muscles increase and decrease, respectively, their activity in the 'neutral' posture. The tonic activity was most readily enhanced by contralateral flexion of the spine, and this could bring to threshold phasic activity not otherwise present. Conversely, ipsilateral flexion could abolish both phasic and tonic components. Active expiratory efforts and static voluntary relaxation of the respiratory muscles could diminish or abolish levator costae activity. Paradoxically, chest‐directed inspiratory efforts maintained at elevated lung volume with open glottis could also diminish or abolish levator costae activity. We attribute this to shortening of the levator costae muscles and unloading of their muscle spindles by the elevation of the ribs due to the action of the external intercostal and parasternal muscles. The results are discussed in relation to the mechanical coupling between the diaphragm and the lower rib cage; emphasis is given to the possible independent motions of the lower two or three ribs and the abductor action of their corresponding levator costae muscles, based on anatomico‐physiological considerations.
Discharge in muscle spindle afferents related to direction of slow precision movements in man.
Authors: Hulliger M , Nordh E , Vallbo A B
Published: December 2014

Single‐unit activity was recorded with needle electrodes in eighteen muscle spindle afferents (eleven primaries, seven secondaries) from finger extensor muscles in the radial nerve of awake human subjects. The discharge rate of the afferents was determined during precisely controlled voluntary movements. The subjects performed a standardized visual ramp‐and‐hold tracking task, which included very slow finger extension and flexion movements (2.5 deg/s) with an amplitude of 20 deg. Throughout the tracking task a constant torque load of small or intermediate size, i.e. less than 30% of maximum voluntary contraction force, opposed finger extension. Altogether, 131 trials were studied. For most units the discharge rate was lower during shortening compared with active position holding, and it was higher during lengthening contractions. Thus, the majority of units responded to phasic stretch during the active movements, although the size of the movement response varied considerably between units and was never large. A few units even exhibited a reversed stretch response pattern. Hence, when estimated from pooled data, movement responses of the unit sample as a whole were small, around 1 impulse/s. The over‐all response pattern of an individual afferent during the tracking task was very similar between successive tests. Although the discharge rate of most units increased with the load during movements as well as during position holding, the presence as well as the magnitude of movement responses depended only little on the size of the load. However, a few afferents exhibited a stretch response pattern with small loads and a reversed stretch response pattern with larger loads. In spite of the predominant increase of afferent firing during muscle lengthening there was no systematic modulation of the discharge rate in relation to the joint angle during the active movements, either in the primary or in the secondary afferents. The present findings suggest that human muscle spindles provide information about the occurrence as well as the direction of slow isotonic movements at low velocities in a precision motor task. This is in contrast to the lack of accurate position response which has previously been demonstrated.
Ionic permeabilities of the gill lamina cuticle of the crayfish, Astacus leptodactylus (E).
Authors: Avenet P , Lignon J M
Published: December 2014

The cuticle of the gill lamina of the crayfish Astacus leptodactylus (E), mechanically isolated, was mounted in an Ussing chamber and examined for its electrical properties. The cuticle of the gill lamina obtained from exuviae had similar properties. When perfused with artificial fresh water (AFW) outside and Van Harreveld solution (VH) inside, the transcuticular potential Voi was negative with respect to the inside, and close to the equilibrium potential for Cl‐ (ECl‐). CH3COO‐, HCO3‐, SO4(2‐) and cations (Na+, K+, Ca2+, Mg2+ and NH4+) behaved as impermeant ions with respect to Cl‐. A decrease of pH (brought about with CO2) from 8.5 to 6.0 in AFW, VH or both had no effect on the potential. The cuticle area specific conductance was 20‐30 mS/cm2 when superfused with AFW outside and VH inside. The conductance decreased linearly with log [Cl‐] when Cl‐ was replaced by CH3COO‐. Rectification was obvious when internal Cl‐ was reduced to 5 mmol/l. The Cl‐ selectivity of the cuticle could also be demonstrated in perfusing the cuticle with a single salt (NaCl, KCl, CaCl2, MgCl2 or LaCl3) and in diluting that salt on one side of the preparation or in replacing Cl‐ by CH3COO‐, SO4(2‐) and HCO3‐. The potential changed almost linearly with log [Cl‐] and was close to ECl‐. The inner face of the cuticle was found to be slightly less selective than the outer face. The relative permeabilities were calculated to be: PCl‐ = 1, PNa+ = 0.001, PHCO3‐ = 0.0006, PCH3COO‐ = 0.0002. The dilution of a Cl‐ ‐free salt resulted in a cationic potential. The relative permeabilities of cations (NH4+, K+, Na+, Ca2+ and Mg2+) were found to range within a factor 2. The permeability of the cuticle to HCO3‐, CH3COO‐ and SO4(2‐) was 2‐5 times lower. The cuticle conductance was linearly related to the activity of the salt perfusing the two sides of the preparation at equal concentrations. The molar area specific conductance to chloride salts was 14 (mS/cm2)/(mmol/l). That of Cl‐ ‐free salts ranged from 1 to 20 (microS/cm2)/(mmol/l) depending on the salt used. It was deduced that PCl‐ is 2 X 10(‐3) cm/s and that all the other ions tested have permeabilities of 10(‐7)‐10(‐6) cm/s. With large intensity current pulses the cuticle exhibited rectifying properties and an asymmetrical behaviour. Increasing the pH of the perfusing solution reduced the transcuticular potential established with a Cl‐ gradient.(ABSTRACT TRUNCATED AT 400 WORDS)
Dependence on calcium of potassium‐ and agonist‐induced changes in potassium permeability of rabbit ear artery.
Authors: Casteels R , Droogmans G
Published: December 2014

The effect of K+ depolarization and agonists on the 86Rb+ efflux from rabbit ear artery has been investigated. K+ depolarization with 59 mM‐K+ induces an increase of the 86Rb+ efflux rate, which is dependent on [Ca2+]o and is correlated with the concomitant force development. This effect is largely reduced by Ca2+ antagonists, such as D‐600 and Mn2+. The residual increase of the 86Rb+ efflux rate is much smaller than that predicted by the constant‐field equations. Stimulation with 10(‐5) M‐noradrenaline or 10(‐4) M‐histamine induces a biphasic increase of the efflux rate. The initial transient effect is reduced in low [Ca2+]o solutions, whereas the maintained component is largely independent of [Ca2+]o. Stimulation with noradrenaline during depolarization of the tissues with K+ induces, after a transient increase of the efflux rate, an inhibition of the K+‐induced increase of the efflux rate. Both phases of the noradrenaline action are due to activation of alpha‐adrenoreceptors. Exposure to Ca2+‐free medium induces a progressive increase of the 86Rb+ efflux rate, which reaches a new steady‐state value after about 60 min. Stimulation with noradrenaline after this 60 min exposure to Ca2+‐free solution no longer induces a significant effect. Stimulation with noradrenaline after shorter exposures to Ca2+‐free solution immediately increases the 86Rb+ efflux to a value close to the steady‐state value obtained after prolonged exposure to Ca2+‐free medium. Washing out the agonist has no effect on the rate constant. It will only return to its control value after exposure to solutions containing Ca2+. This recovery of the rate constant by external Ca2+ also occurs in the presence of 1 mM‐Mn2+ in the perfusion fluid. On re‐exposure of the tissues in the presence of 1 mM‐Mn2+ to Ca2+‐free solution the rate constant of the 86Rb+ efflux increases at once to the steady‐state value observed in Ca2+‐free solution. This increase proceeds gradually if the tissues have been re‐exposed in the absence of Mn2+. It is concluded that K+ permeability might be regulated by [Ca2+]i and that this relationship can be affected by agonists. In order to explain the effects of Ca2+‐free medium on the 86Rb+ efflux we have to assume that at very low values of [Ca2+]o and [Ca2+]i the membrane permeability for K+ is modified by a different mechanism.
Noradrenaline and functional plasticity in kitten visual cortex: a re‐examination.
Authors: Adrien J , Blanc G , Buisseret P , Frégnac Y , Gary-Bobo E , Imbert M , Tassin J P , Trotter Y
Published: December 2014

A quantitative re‐examination was made of the influence of noradrenergic depletion on the epigenesis of kitten visual cortex. Two methods were used to deplete noradrenaline at the cortical level: stereotaxically controlled injection of 6‐hydroxydopamine (6‐OHDA) in the coeruleus complex, from which the noradrenergic input to visual cortex arises; intraventricular injection of 6‐OHDA. The latter chemical lesion also depleted dopamine levels in the brain. Lesion of the noradrenergic or catecholaminergic systems was performed neonatally or at an age of 3‐4 weeks in kittens submitted to five different rearing procedures: normal rearing, dark rearing, monocular rearing, monocular exposure following dark rearing and monocular deprivation following normal rearing. Forty‐two kittens between 3 and 12 weeks of age were used for this biochemical and electrophysiological study. Noradrenaline and dopamine levels were measured by a radioenzymatic method in the primary visual cortex of twenty‐six kittens. A total of 1263 cells were recorded in area 17 of twenty‐six kittens. Combined biochemical and electrophysiological data were obtained in ten 6‐OHDA‐lesioned kittens. Whatever the mode of chemical lesion used, cortical noradrenergic depletion failed to block either maturation or vision‐dependent processes which are known to affect orientation selectivity and/or ocular dominance during the critical period. However, in some cases, the amplitude of the epigenetic functional modifications was slightly reduced in 6‐OHDA‐treated kittens. The cortical effects of monocular deprivation starting from the age of 5 weeks were studied quantitatively both in lesioned and intact kittens. Disappearance of noradrenaline in area 17 did not prevent the loss of binocularity in cortical cells. However, even when monocular occlusion had been maintained for 2 or 3 weeks in 6‐OHDA‐treated kittens, ocular dominance shifts were limited to a stage equivalent to that observed in the intact kitten after 5‐8 days of monocular occlusion. The amplitude of this partial protective effect was found to be unrelated either to the delay following the chemical lesion, or to the level of noradrenaline remaining in lesioned kitten cortex. Although a putative gating role of noradrenaline cannot be excluded in the development of the intact animal, this report shows that its presence is not required for functional plasticity to occur in kitten area 17.
Mediation of the fastigial pressor response and a somatosympathetic reflex by ventral medullary neurones in the cat.
Authors: McAllen R M
Published: December 2014

In chloralose‐anaesthetized, artificially ventilated cats, the effects have been studied of inactivating neurones of the 'glycine‐sensitive area' of the rostral ventrolateral medulla on evoked renal sympathetic and vasomotor responses. Glycine applied topically and bilaterally to the 'glycine‐sensitive area' besides markedly lowering blood pressure and heart rate, reversibly abolished or severely attenuated both the pressor response and the renal nerve volley produced by electrical stimulation of the fastigial nucleus as well as the tibial to renal nerve somatosympathetic reflex. Bilateral radio‐frequency lesions of the 'glycine‐sensitive area' similarly lowered blood pressure and heart rate, blocked the fastigial pressor response and abolished renal nerve responses to fastigial nucleus or tibial nerve stimulation. Effective lesions extended greater than or equal to 1 mm deep from the medullary surface. These results are discussed with reference to the view that the 'glycine‐sensitive area' contains neurones constituting a final descending bulbo‐spinal pathway to preganglionic vasomotor neurones.
Diffusible sodium, potassium, magnesium, calcium and phosphorus in frog skeletal muscle.
Authors: Maughan D , Recchia C
Published: December 2014

A microvolumetric analytical method has been developed to measure the endogenous concentrations of diffusible elements in muscle cells. Single twitch fibres from frog muscle were skinned under oil and 0.2 nl drops of isosmotic sucrose solution, held in the tips of specially constructed pipettes, were placed in contact with the skinned fibres. After 0‐10 min, the microdrops were removed and analysed with a wave‐length dispersive X‐ray spectrometer. The uptake of Na, K, Mg, and P into the microdrops was well fitted by a single exponential function, while the uptake of Ca was better represented by the sum of two exponential functions. All elements analysed except Ca reached diffusional equilibrium within 5 min of placing the microdrop on the fibre, while Ca was still not equilibrated at 10 min. For freshly isolated muscle fibres, diffusible element concentrations in the microdrops at equilibrium were (in mM, mean +/‐ S.D.): Na, 7.6 +/‐ 7.2; K, 82 +/‐ 36; Mg, 5.8 +/‐ 3.0; P, 51 +/‐ 19. Diffusible Ca concentration (at 10 min elapsed sampling time) was 0.7 +/‐ 0.4 mM. Results from experiments in which microdrops were equilibrated with skinned fibres pre‐soaked in an artificial (Ca‐free) solution support the notion that the exogenous solutes can replace the endogenous diffusible contents of a skinned fibre by soaking the skinned fibre in a relatively large volume of the artificial solution. Total Na, K, Mg, Ca, and P content of whole muscle was measured by electron probe analysis of muscle extracts. In freshly isolated muscle, whole muscle element content was (in mmol/kg wet weight, mean +/‐ S.D.): Na, 21 +/‐ 8; K, 120 +/‐ 26; Mg, 9.7 +/‐ 2.6; Ca, 2.2 +/‐ 0.5; P, 76 +/‐ 18. Extracellular fluid volumes of freshly isolated whole muscles were estimated by compartmental analysis of Na efflux. Extracellular element concentrations were measured by electron probe analysis of frog plasma. Using the extracellular fluid volume and concentration estimates, extracellular contributions were subtracted from measurements of the element content of whole muscle to yield estimates of total intracellular element concentration (in mmol/l myoplasmic water). Based on the values for the intracellular total and diffusible element concentrations, the diffusible/total content fraction in freshly isolated muscle is estimated to be: Na, 0.38; K, 0.48; Mg, 0.42; Ca, 0.22; and P, 0.47.
The roles of paracellular and transcellular pathways and submucosal space in isotonic water absorption by rabbit ileum.
Authors: Naftalin R J , Tripathi S
Published: December 2014

Water movements have been studied in sheets of isolated rabbit ileum using a method which measures net volume flows across the mucosal and serosal surfaces of the tissue continuously with high resolution. At 35 degrees C, with the tissues incubated in isotonic Ringer solution containing D‐glucose (25 mM) on both sides, there is a steady net inflow of fluid at the rate of 24 +/‐ 2 microliter cm‐2 h‐1 across the mucosal surface (Jm) and an outflow of 8 +/‐ 1 microliter cm‐2 h‐1 across the serosal surface (Js) (n = 16). The stable transepithelial p.d. across these tissues is 2.7 +/‐ 0.2 mV, serosa positive. Jm can be reversibly inhibited by anoxia. Ouabain (0.1 mM) added to the serosal solution inhibits inflow across the mucosal and serosal surfaces by 75% (n = 7) within 30 min. If phlorizin (0.1 mM) is added to the mucosal Ringer solution containing glucose (20 mM) within 30 min of the commencement of in vitro absorption, Jm is reduced from 37 +/‐ 3 to 28 +/‐ 2 microliter cm‐2 h‐1 (n = 3). Dilution of the mucosal Ringer solution by 50 mosmol kg‐1 (with the serosal solution kept isosmolar) results in a rapid transient increase in mucosal inflow. An increase of 50 mosmol kg‐1 in the mucosal Ringer solution with NaCl, sucrose or mannitol causes a transient reversal of mucosal flow, followed by a return of inflow at a reduced level. Rabbit ileum can transport water against gradients of approximately 75 mosmol kg‐1 of sucrose, NaCl, or mannitol. Addition of polyethylene glycol (mol. wt. 20000; 3 mosmol kg‐1) causes a sustained reversal of mucosal inflow; inflow can be restored only by removing polyethylene glycol from the mucosal Ringer solution. The tissue can absorb water against an osmotic gradient of 200 mM‐glycerol. The above data have been incorporated into a new model to explain isotonic flow of fluid by this epithelium. The main features are that the hydraulic conductivity (Lp) of the mucosal boundary of the lateral intercellular space is approximately 1 X 10(‐8) cm s‐1 cmH2O‐1. This Lp is too low to sustain isotonicity of the flow emerging from the lateral intercellular space at the observed rates. Hypertonic fluid emerging from the lateral intercellular space is diluted by transcellular water flow generated by the hypertonicity of the submucosa and back‐diffusion of solute via mucosal shunt channels.(ABSTRACT TRUNCATED AT 400 WORDS)
The actions of some general anaesthetics on the potassium current of the squid giant axon.
Authors: Haydon D A , Urban B W
Published: December 2014

A number of small organic molecules with general anaesthetic action have been examined for their effects on the voltage‐dependent potassium current of the squid giant axon. They include representatives of the three classes of anaesthetics examined in previous studies on the sodium current (Haydon & Urban, 1983a, b, c), i.e. the non‐polar molecules n‐pentane, cyclopentane and CCl4, several n‐alkanols and the inhalation anaesthetics chloroform, halothane, diethyl ether and methoxyflurane. Potassium currents under voltage clamp were recorded in intact and in intracellularly perfused axons before, during and after exposure to the test substances, and the records were fitted with equations similar to those proposed by Hodgkin & Huxley (1952). Shifts in the curves of the steady‐state activation against membrane potential and reductions in the potassium conductance at 60 or 70 mV membrane potential have been tabulated. On the same intact axons, all the anaesthetics with the exception of methoxyflurane reduced potassium currents less than sodium currents by about a factor of two or more. For the n‐alkanols, butanol to decanol, the concentrations required to reduce the potassium current at 60 mV membrane potential by 50% were determined. For n‐butanol to n‐heptanol, the standard free energy per CH2 for adsorption to the site of action was estimated to be ‐2.91 kJ mol‐1 as compared with ‐3.04 kJ mol‐1 for reduction of the sodium current. The magnitude of the free energy decreased for alkanols with longer chain lengths. At anaesthetic concentrations that reduce the sodium current by 50%, the hydrophobic substances n‐pentane and cyclopentane reduced the maximal sodium conductance, gNa, and the potassium conductance at 70 mV, gK70, equally by about a third, while the n‐alkanols reduced both parameters by less than 10%. By contrast, diethyl ether and methoxyflurane were more effective in reducing the maximal potassium conductance. All of the test substances examined, except n‐pentane and n‐hexane, shifted the voltage dependence of the potassium steady‐state activation in the depolarizing direction. A broad qualitative correlation was found between the shifts in the activation curves for sodium and potassium currents but, quantitatively, the agreement between the two shifts was poor. In n‐decanol and methoxyflurane solutions, the voltage‐clamped potassium currents exhibited pronounced inactivation‐like behaviour. These currents can be fitted by the Hodgkin‐Huxley formalism if an inactivation term analogous to the sodium current inactivation is added.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects on shortening velocity of rabbit skeletal muscle due to variations in the level of thin‐filament activation.
Authors: Moss R L
Published: December 2014

The effect of Ca2+ upon maximum shortening velocity (Vmax) has been investigated in skinned single fibres from rabbit psoas muscles. Vmax was obtained at 15 degrees C by measuring the amounts of time (delta t) required to take up various amounts of slack (delta l) imposed at one end of the fibre. During maximal activation with Ca2+, plots of delta l vs. delta t were well fitted by a single straight line. Calculation of Vmax from the slopes of the fitted lines yielded a Vmax of 4.44 +/‐ 0.15 (S.E. of mean) muscle lengths per second (m.l./s). However, at lower levels of Ca2+ activation, plots of delta l vs. delta t were biphasic, containing an initial phase of steady high‐velocity shortening and a subsequent phase of steady low‐velocity shortening. The transition between these two phases occurred following active shortening equivalent to 60‐80 nm/half‐sarcomere. Vmax during the high‐velocity phase was relatively insensitive to Ca2+ concentration between pCas (i.e. ‐log [Ca2+]) of 4.5 and 6.0; however, Vmax fell to 3.58 +/‐ 0.40 m.l./s at pCa 6.1 and further to 1.02 +/‐ 0.30 m.l./s at pCa 6.2. Vmax during the low‐velocity phase decreased as Ca2+ was lowered within the entire range of pCas studied to a minimum value of 0.35 +/‐ 0.09 m.l./s at pCa 6.2. The degree of thin‐filament activation at a particular pCa was varied by partial extraction of troponin‐C, which resulted in a permanent though reversible inactivation of parts of the thin filaments. Partial extraction of troponin‐C altered the plots of delta l vs. delta t obtained at pCa 4.5 to a biphasic form. In addition, Vmax during the high‐ and low‐velocity phases of shortening was reduced at each pCa greater than 4.5. Vmax values obtained in control fibres at low Ca2+ concentrations and extracted fibres were in good agreement when generated isometric tensions were equivalent. This was the case for both the high‐ and low‐velocity phases of shortening. Fibres were also activated in the absence of Ca2+ by partial removal of total troponin complexes. These fibres developed steady tensions less than 30% of maximum and underwent biphasic shortening, indicating that this phenomenon cannot be the result of shortening‐induced dissociation of Ca2+ from troponin‐C.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of excitatory amino acid antagonists on evoked and spontaneous excitatory potentials in guinea‐pig hippocampus.
Authors: Cotman C W , Flatman J A , Ganong A H , Perkins M N
Published: December 2014

Evoked and spontaneous excitatory post‐synaptic potentials (e.p.s.p.s) at the mossy fibre input to CA3 pyramidal neurones were recorded intracellularly in slices from the guinea‐pig hippocampus. The effects of several amino acid antagonists on these responses were examined. L‐2‐amino‐4‐phosphonobutyrate (L‐AP4), L‐serine‐O‐phosphate (L‐SOP), kynurenate, and N‐(p‐bromobenzoyl)piperazine‐2,3‐dicarboxylate (pBB‐PzDA) reduced the amplitude of evoked mossy fibre e.p.s.p.s without affecting membrane potential or input resistance. Antagonism of mossy fibre spontaneous miniature e.p.s.p.s (m.e.p.s.p.s) by these compounds fell into two groups. L‐AP4 and L‐SOP applied at concentrations that blocked evoked e.p.s.p.s did not affect amplitude distributions of spontaneous m.e.p.s.p.s. Kynurenate and pBB‐PzDA significantly affected the amplitude distributions and reduced the mean amplitude of spontaneous m.e.p.s.p.s. These results are consistent with a presynaptic site of action for L‐AP4 and L‐SOP and a post‐synaptic site of action for kynurenate and pBB‐PzDA as antagonists of e.p.s.p.s at the guinea‐pig mossy fibre‐CA3 pyramidal neurone synapse.
Mossy fibres sending retinal‐slip, eye, and head velocity signals to the flocculus of the monkey.
Authors: Noda H
Published: December 2014

Discharges of mossy fibres were recorded from the cerebellar flocculus of monkeys trained to fixate a small visual target and to track the target when it moved slowly. The experimental paradigms used were designed to study neural responses to retinal‐slip velocity, eye velocity, or head velocity, individually or in combination. Among 485 mossy‐fibre units recorded from the flocculus, sixty‐four units (or 13%) responded to movement of the visual stimulus in the horizontal plane. Two distinct groups of visual mossy fibres were found: they were designated 'visual units' (thirty‐nine/sixty‐four units or 61%) and 'visuomotor units' (twenty‐five/sixty‐four units or 39%). The visual units responded exclusively to the retinal‐slip velocity. Stationary fixation was necessary for clear cyclic modulation of activity. Their responses declined when the retinal‐slip velocity was reduced by eye movements in the same direction. The responses of the visual units were directionally selective and lagged behind the occurrence of 'turnabouts' (changes in direction of stimulus movement) and their peak discharges also lagged the occurrence of peak velocity. Each visual unit had a limited range of velocity sensitivity; in some units the range covered the velocity range of smooth‐pursuit eye movements. The visuomotor units had visual receptive fields in the peripheral retina (outside of the central 10 deg); they received also oculomotor and vestibular signals. When the head was stationary, the visuomotor units responded to the target velocity (or visual stimulus velocity) which is the algebraic sum of the retinal‐slip velocity and the eye velocity. Their responses reflected the retinal‐slip velocity during stationary fixation and the eye velocity during smooth‐pursuit eye movements. The responses to stimulus movements were, therefore, almost identical regardless of whether the eyes remained stationary or moved with the stimulus. In response to sinusoidal stimulus movements, the responses of the visuomotor units frequently preceded the stimulus velocity, and the phase lead relative to the velocity curve increased when the frequency of sinusoidal movements was increased. This reflected a relatively constant lead of neural discharges (circa 125 ms) during various frequencies. When the head was moved, the responses of the visuomotor units were dominated by the head velocity, and discharges in response either to the retinal‐slip velocity or to the eye velocity (both in the direction opposite to the head velocity) were occluded.(ABSTRACT TRUNCATED AT 400 WORDS)
Presynaptic opioid delta‐receptors in the rabbit mesenteric artery.
Authors: Illes P , Ramme D , Starke K
Published: December 2014

Excitatory junction potentials (e.j.p.s) evoked by nerve stimulation were recorded from muscle cells of the rabbit isolated mesenteric artery. At 0.03 Hz the e.j.p. amplitudes were stable. When a train of fifteen pulses was applied at 0.25 Hz or at higher frequencies (0.5, 1 and 2 Hz), e.j.p.s showed an initial facilitation followed by depression. [Met5]enkephalin 0.1 and 1 mumol/l, [D‐Ala2,D‐Leu5]enkephalin 0.1 and 1, but not 0.01 mumol/l, and [D‐Pen2, L‐Pen5]enkephalin 3 mumol/l all depressed the e.j.p.s evoked by trains of fifteen pulses at 1 Hz. When more than one concentration was used ([Met5]enkephalin, [D‐Ala2,D‐Leu5]enkephalin), the inhibition was concentration dependent. It was always greater for the first few e.j.p.s than for the later ones in a train. [Met5]enkephalin 1 mumol/l reduced the first e.j.p. at 1 Hz and the e.j.p.s evoked by 0.03 Hz to a similar extent. The inhibitory effect of [Met5]enkephalin 1 mumol/l on e.j.p.s persisted in the presence of yohimbine 0.3 mumol/l. Naloxone 1 mumol/l did not interfere with the effect of [Met5]enkephalin 1 mumol/l. Naloxone 10 mumol/l depressed some e.j.p.s and prevented the inhibition by [Met5]enkephalin 1 mumol/l. Neither ICI 154129 10 mumol/l nor ICI 174864 0.3 mumol/l had any effect of their own and both compounds antagonized the action of [Met5]enkephalin 1 mumol/l. Normorphine 10 mumol/l, fentanyl 1 mumol/l, ethylketocyclazocine 0.1 mumol/l, and dynorphin A(1‐13) 1 mumol/l were all ineffective. Ethylketocyclazocine 1 mumol/l did not change the e.j.p.s either, but antagonized [Met5]enkephalin 1 mumol/l. [Met5]enkephalin 1 mumol/l failed to influence both the resting membrane potential of the muscle cells and the depolarizing effect of noradrenaline 3 and 30 mumol/l. We suggest that the axon terminals of post‐ganglionic sympathetic neurones in the rabbit mesenteric artery possess opioid delta‐, but not mu‐ or kappa‐receptors. The activation of presynaptic delta‐receptors inhibits the release of the neuroeffector transmitter. There is no evidence for any effect of co‐released endogenous opioid peptides under our experimental conditions.
Motoneurones of the submucous plexus regulate electrical activity of the circular muscle of canine proximal colon.
Authors: Sanders K M , Smith T K
Published: December 2014

The hypothesis that the circular muscle of the canine proximal colon receives motor input from neurones in the submucous plexus was tested. Circular muscle cells were impaled with micro‐electrodes and submucous plexus neurones were stimulated by electrical field stimulation and microejection of acetylcholine (ACh). In the presence of atropine to block the direct muscarinic effects, microejection of ACh onto the submucosa where intact submucous ganglia were suspended evoked: (i) an inhibitory junction potential (i.j.p.) that reduced the amplitude, duration and rate of rise of the subsequent slow wave; (ii) a slow wave of increased duration following the initial inhibitory response. These responses were enhanced by increasing the volume of ACh administered. Responses to ACh were blocked by hexamethonium, 10(‐4) M; d‐tubocurarine, 10(‐4) M; or tetrodotoxin (TTX), 10(‐6) M, suggesting they were neural in origin. Both inhibitory and excitatory responses were the result of non‐cholinergic and non‐adrenergic nerves. The transmitters mediating these effects are unknown. Removal of the longitudinal muscle, myenteric plexus, and the serosal portion of the circular muscle had no apparent effect on the responses to application of ACh to submucosal ganglia. In these preparations the responses to field stimulation were identical to those produced by ACh. The submucous plexus also provides cholinergic input to the circular muscle. When ACh was discretely applied to the submucosa cholinergic responses were elicited at the muscle cell which were significantly reduced by hexamethonium or TTX. These findings suggest that the cholinergic responses were the result of ACh release by neurones at the effector and not by overflow of the exogenous ACh. Cholinergic responses were also elicited in preparations in which the myenteric plexus had been removed. Slow waves in circular muscle of the proximal colon yield excitation‐contraction coupling in the absence of Ca2+ action potentials. Therefore the influence of submucous neurones on electrical slow waves has direct consequences on motor activity. Reduction in the amplitude and duration of slow wave by i.j.p.s. results in reduction in the amplitude and duration of phasic contractions. Excitatory inputs enhance contractions. The data support a new concept: motoneurones emanating from submucous ganglia innervate the circular muscle and provide inhibitory and excitatory inputs to regulate slow wave activity.(ABSTRACT TRUNCATED AT 400 WORDS)
Organization and post‐natal development of the monkey's lateral geniculate nucleus.
Authors: Blakemore C , Vital-Durand F
Published: December 2014

We have studied the properties of neurones in the lateral geniculate nucleus (l.g.n.) of Old World monkeys, both in mature animals and throughout post‐natal development. Cells were classified as X (linear) or Y (non‐linear) on the basis of their responses to contrast‐reversing achromatic gratings ('null position test'). In older animals virtually all parvocellular neurones and the majority of magnocellular units were X cells; only about 15% of magnocellular neurones displayed highly non‐linear spatial summation, with no 'null position', typical of Y cells. X cells could not reliably be distinguished from Y cells, nor magnocellular from parvocellular, on the basis of their temporal patterns of discharge. Some Y cells responded transiently to contrast reversal of a grating far from the receptive field but X cells showed little or no such 'shift effect'. The spatial resolution of mature l.g.n. cells varied with the eccentricity of their receptive fields such that the best of them, at each point in the visual field, resolved drifting achromatic gratings about as well as a human observer. X cells in parvocellular and magnocellular layers had similar 'acuities', even in the central foveal representation, but Y cells generally had poorer resolution. Receptive fields in the temporal retina tended to have lower resolution than those at comparable eccentricities in the nasal retina. Even on the day of birth all cells we studied responded to visual stimulation and virtually all could be classified as X or Y. The laminar distribution of cell types and the general morphological appearance of the nucleus seemed very similar to those in the adult, but neurones in very young animals had low spontaneous activity, sluggish responses, and latencies to visual stimulation longer than any we saw in the adult. Until 3 weeks of age or so, many neurones suffered cumulative 'fatigue' when visually stimulated over several minutes. Visual latency was essentially mature by about 10 weeks. In the l.g.n. of the neonatal monkey there was little variation in neuronal 'acuity' with eccentricity: even in the foveal area the best cells could resolve only about 5 cycles/deg. Over the first year or more of life there is a gradual increase in responsiveness and about a 7‐fold improvement in spatial resolution for foveal l.g.n. cells, correlating roughly with the behavioural maturation of visual acuity.
Muscarinic slow excitation and muscarinic inhibition of synaptic transmission in the rat neostriatum.
Authors: Dodt H U , Misgeld U
Published: December 2014

Intracellular recording from neurones in rat neostriatal slices was used to compare the muscarinic effects of endogenous acetylcholine (ACh) released from cholinergic neostriatal synapses with the action of exogenously applied muscarinic agonists. Repetitive electrical stimulation in the neostriatum evoked a series of fast excitatory post‐synaptic potentials (e.p.s.p.s) followed by a short, variable period of input resistance decrease. In the presence of the acetylcholinesterase (AChE) inhibitor, physostigmine, these potentials were followed by a slow e.p.s.p. which lasted about 60 s. Higher stimulus intensities were needed to elicit the slow e.p.s.p. than the fast e.p.s.p. The slow e.p.s.p. could not be observed after a single stimulus. Its amplitude was graded and increased with stimulus strength. The slow e.p.s.p. was blocked by the muscarinic antagonist atropine (10 microM) and by Ba2+ (100 microM). Input resistance increased during the slow e.p.s.p. Depolarization of the cell increased the size of the slow e.p.s.p. and hyperpolarization decreased it. Simultaneously, resting input resistance increased with membrane depolarization and decreased with membrane hyperpolarization. Repetitive intrastriatal stimulation was followed by a hyperpolarization instead of the depolarization at membrane potentials negative to ‐75 mV. Input resistance increased during this hyperpolarization as it did during the slow e.p.s.p. The slow e.p.s.p. persisted at membrane potentials of ‐70 to ‐80 mV if K+ concentration in the saline was reduced from 5 to 2 mM. In 10 mM‐K+, the repetitive stimulation was followed by a hyperpolarization even at membrane potentials as low as ‐60 to ‐50 mV. Bath perfusion of high concentrations (100 microM) of muscarine or carbachol induced a sustained increase in the input resistance. The muscarinic agonists also reduced the amplitude of intrastriatally evoked fast e.p.s.p.s; however, this effect was transient and compensated by the increase in input resistance. The effects of the muscarinic agonists on input resistance and e.p.s.p. amplitude were antagonized by atropine (10 microM). Sustained decreases of e.p.s.p. amplitude were induced by the bath application of low doses (0.5‐10 microM) of muscarine or carbachol. Input resistance was not altered. Atropine (1‐10 microM) antagonized this effect. A sustained reduction of fast e.p.s.p. amplitude resulted also from inhibition of AChE by application of physostigmine (1‐100 microM). Input resistance and neuronal excitability were not affected by AChE blockade.(ABSTRACT TRUNCATED AT 400 WORDS)
A calcium‐activated sodium conductance produces a long‐duration action potential in the egg of a nemertean worm.
Authors: Jaffe L A , Kado R T , Kline D
Published: December 2014

1. The egg of the nemertean worm Cerebratulus lacteus produced an action potential having a duration of about 9 min. We investigated the ionic conductances which accounted for this long‐duration action potential. 2. The peak of the action potential was about +50 mV and depended on extracellular Ca2+, while the plateau potential was about +25 mV and depended on extracellular Na+. 3. Under voltage‐clamp conditions, depolarization produced two temporally separate inward currents: a fast current which reached a peak at about 10 ms, and a slow current which took up to 1 min to reach its peak and lasted for several min. 4. The fast current was independent of extracellular Na+, but was blocked by removal of extracellular Ca2+. 5. The slow current was not seen when extracellular Na+ was replaced by choline+ or K+. 6. The slow current did not develop in Ca2+‐free sea water, and was reduced to about half if Ca2+ was removed after the current had been initiated. 7. Microinjection of EGTA blocked the slow current, and reduced the action potential duration to about 1 min. 8. We concluded that a voltage‐activated Ca2+ conductance produced the peak of the action potential, while a Ca2+‐activated Na+ conductance produced its plateau.
Competition between segmental nerves at end‐plates in rat gastrocnemius muscle during loss of polyneuronal innervation.
Authors: Bennett M , Ho S , Lavidis N
Published: December 2014

1. The segmental innervation of the rat lateral gastrocnemius (l.g.) muscle is from lumbar nerves L4 and L5. A study has been made of changes in the innervation of the l.g. muscle by nerves L4 and L5 before and after removal of L4 during the loss of polyneuronal innervation which occurs over the first 2 weeks postnatal. 2. The rat l.g. muscle is a complex of three unipennate muscles; the lateral, intermediate and medial heads. Each of these has a characteristic distribution of type I and type II muscle fibres of different diameter by 12 days postnatal. Following the removal of nerve L4 at birth there is no change in the distribution of fibre types in the different heads of the l.g. muscle at 12 days postnatal. 3. The number of fibres in the l.g. muscle doubled between birth and 12 days postnatal and the maximum tetanic force generated by the muscle increased by fourfold. Removal of nerve L4 at birth did not alter the increase in fibre number and there was no difference between the tension generated by the l.g. muscle in the ipsilateral and contralateral limbs of operated animals. 4. The number of detectable motor units in a extracellular calcium concentration [( Ca]o) of 2 mM remained constant in L4 at about fifteen between birth and 12 days postnatal; the number of detectable motor units in L5 declined over this period from about fifteen to six in a [Ca]o of 2 mM. Following the removal of L4 at birth, the number of motor units in L5 increased to twenty by 3 days postnatal and remained there for at least 12 days in a [Ca]o of 2 mM. 5. The mean size of motor units and the range of motor unit sizes declined for both L4 and L5 during the postnatal period. Following the removal of L4, the mean size of motor units and the range of motor unit sizes in L5 failed to decline. 6. The number of motor units detected at birth in a raised [Ca]o of 3‐5 mM increased in L4 and L5 to about twenty; this estimate in high [Ca]o remained constant during the postnatal period. Estimates of the size of the large, low threshold motor units declined whether these were made in low or high [Ca]o.(ABSTRACT TRUNCATED AT 400 WORDS)