bluuebunny/crossref_metadata_2025 huggingface dataset:
Tension, stiffness, unloaded shortening speed and potentiation of frog muscle fibres at sarcomere lengths below optimum.
Authors: Julian F J , Morgan D L
Published: December 2014

1. Unloaded shortening velocity, stiffness, and the effects of potentiators were studied to understand the basis for the shallow ascending limb (1.65‐2.0 micrometers sarcomere length) of the sarcomere length‐tension diagram of from single fibres. 2. The velocity of externally unloaded shortening was found to be constant over most of the range. It is therefore unlikely that this part of the sarcomere length‐tension diagram results from an internal force opposing shortening. 3.Stiffness was found not to vary in proportion with tension between sarcomere lengths 1.65 and 2.0 micrometers, nor to be constant between 2.0 and 2.2 micrometers, where tension is constant. By assuming a small filament compliance, the observations could be adequately modelled on the hypothesis that the variation in tension in the range of sarcomere lengths 1.65‐20 micrometers was caused by variations in the number of attached cross‐bridges. 4. The twitch potentiators Zn2+, tetraethylammonium (TEA), nitrate and caffeine were found not to change the shape of the sarcomere length‐tension diagram. Potentiation in a tetanus was less than 3% in all experiments. 5. Contractures induced by raised [K+] in the bathing solution were found to produce more tension than a tetanus beyond optimum length, insignificantly different tension near optimum length, and less tension at sarcomere lengths near 1.7 micrometer. An explanation is proposed for these results in terms of inhomogeneous activation and internal motion. 6. It is concluded that there is no evidence from this work that a tetanized fibre is other than maximally activated over the range of sarcomere lengths spanned by the shallow ascending limb.
Action potential synchrony in embryonic precontractile chick heart: optical monitoring with potentiometric dyes.
Authors: Fujii S , Hirota A , Kamino K
Published: December 2014

1. Using an optical method for monitoring membrane potential, we recorded spontaneous action potentials simultaneously in several different areas of the 7‐9 somite embryonic chick hearts. 2. Absorption signals resembling spontaneous action potentials were well synchronized among the different areas in the prebeating embryonic heart during the 7‐9 somite stages of development, and the synchronization spread over the entire area of the heart. From these experimental results, it is evident that there is electrical coupling among embryonic chick heart cells even in the early stages of cardiogenesis. 3. When an embryonic heart was separated into right and left or anterior and posterior parts, the action potential synchrony between the two halves was completely blocked; however, the synchrony and the intrinsic rhythmicity in action potential recurrence remained in each part.
Evidence that histamine and carbachol may open the same ion channels in longitudinal smooth muscle of guinea‐pig ileum
Authors: Bolton T. B. , Clark J. P. , Kitamura K. , Lang R. J.
Published: December 2014

1. Membrane potential was recorded intracellularly by micro‐electrode in separated longitudinal muscle of guinea‐pig ileum. Electrotonic potentials were evoked in longitudinal strips by passing current between large external electrodes in the partition chamber.

2. Histamine increased the frequency of action potential discharge at low concentrations and depolarized the membrane. At higher concentrations it caused substantial depolarization and action potential discharge was abolished. Carbachol had similar actions but the maximal depolarization by carbachol (using 10−4
m) was some 4‐5 mV greater than maximal depolarization by histamine (using 10−4
m).

3. The change in size of evoked electrotonic potentials was used to estimate the effects of carbachol and histamine on the conductance of the smooth muscle membrane. The equilibrium potentials for histamine and carbachol depolarizations were estimated from their relative effects on potential and conductance and were found to be not significantly different; measurements of the effects on conductance showed that 10−4
m‐histamine increased conductance about 8‐fold whilst 10−4
m‐carbachol had a much greater effect on conductance. This difference could explain the differing maximal depolarizing effects of these agents if both were assumed to open channels having the same ionic selectivity (i.e. equilibrium potential).

4. The efflux of 42K was studied in separated strips of longitudinal ileal muscle from guinea‐pig. In the presence of a concentration of carbachol (2 × 10−5
m or 10−4
m) having a maximal effect on 42K efflux rate, histamine (10−4
m) did not increase efflux further although 120 m
m‐potassium did so. Experiments with the irreversible muscarinic receptor blocker, propylbenzilylcholine mustard, indicated that the number of muscarinic receptors did not limit the 42K efflux response to carbachol and it was suggested that the response was limited by the availability of ion channels which could be opened by activated muscarinic receptors.

5. Contractions to histamine and carbachol in 120 m
m‐potassium depolarizing solution were followed upon washing by a relaxation below basal tension. Carbachol, but not histamine, showed a pronounced and long lasting secondary contraction following this relaxation.

6. These results are consistent with the idea that activated histamine and activated muscarinic receptors open the same ion channels in the smooth muscle membrane to produce depolarization, increased action potential discharge and contraction, although muscarinic receptors can open more of these. However, there was evidence that the opening of these channels is not the only pathway between receptor activation and contraction.
Glycine transport in human erythrocytes.
Authors: Ellory J C , Jones S E , Young J D
Published: December 2014

1. Glycine transport in human erythrocytes was resolved into five separate components of uptake. The first and major component of uptake was transport by a high‐affinity (apparent Km 25 microM) Na+‐ and Cl‐ ‐dependent system. This system was specific for glycine, sarcosine and proline; Br‐ but not I‐ was able to substitute for Cl‐. Uptake by this route was inhibited less than 20% by the loop diuretics, bumetanide and furosemide (10(‐4) M), suggesting that it was distinct from the Cl‐ ‐dependent system responsible for Na+/K+ transport. Its properties closely resembled those of the gly transport system described previously in avian erythrocytes. 2. The second uptake route was transport by the Na+‐dependent, Cl‐ ‐independent small neutral amino acid transport system (designated ASC). Neither NA+‐dependent uptake route was present in sheep erythrocytes. 3. Two Na+‐independent uptake mechanisms were also identified; first, uptake by the amino acid transport system (designated L), and secondly, SITS‐sensitive uptake by the anion‐exchange (band 3) transport mechanism (SITS is 4‐acetamido‐4'‐iso‐thiocyanatostilbene‐2,2'‐disulphonic acid, an effective inhibitor of anion transport by this route). Uptake by the latter route was increased markedly when fluxes were measured in isotonic SO42‐ medium or when the pH was increased. 4. At 0.2 mM extracellular glycine, the relative contributions of each of these uptake routes to the total glycine flux were 42, 11, 15 and 16% for the gly, ASC, L and band 3 systems, respectively. 5. Finally, there was a residual Na+‐independent component of glycine uptake which contributed 16% of the total flux. With the exception of the gly system, all uptake routes showed a linear concentration dependence up to 2 mM‐glycine.
Functional maturation of motor nerve terminals in the avian iris: ultrastructure, transmitter metabolism and synaptic reliability
Authors: Pilar Guillermo , Tuttle Jeremy , Vaca Ken
Published: December 2014

1. The transformation of easily fatigued embryonic neuromuscular junctions into highly reliable mature terminals was examined by studying functional and morphological changes during development of the avian iris. The mature ability to follow repetitive electrical nerve stimulation was correlated with the rate of acetylcholine (ACh) synthesis and choline uptake, and with the fine structure of the nerve terminals and the post‐synaptic elements.

2. The terminals of the ciliary nerve of the chick initially form functional synaptic contacts with the iris muscle at embryonic St. 34‐40. At the onset of this period, no Na+‐dependent high affinity choline uptake can be demonstrated, and the low level of ACh synthesis present is sensitive to Na+ removal. At St. 36 [3H]ACh synthesis begins to increase, the increment being Na+‐dependent.

3. ACh synthesis in the embryonic iris was insensitive to a conditioning [K+]o depolarization even as late as St. 43. Just before hatching, depolarization elicits some augmentation in synthesis, but by 2 days ex ovo this release‐induced response has increased by an order of magnitude.

4. Concurrently with the acquisition of the ability to respond to depolarization with accelerated synthesis, neuromuscular transmission in the iris becomes reliable and secure during stimulation at 20 Hz. Embryonic junctions rapidly block during such stimulation, and the failure is shown to be presynaptic in origin, resulting most probably from failure to sustain adequate levels of transmitter release.

5. Ultrastructural examination of the developing ciliary terminals revealed few synaptic vesicles at early stages, and a dearth of other specializations. The sequence of development from these small structurally undistinguished endings to large en plaque junctions completely filled with vesicles was reconstructed and compared to other neuromuscular junctions. Morphological maturation appears progressive with little evidence of discontinuity signalling functional status, but it is only after the terminals enlarge and become closely packed with vesicles that mature synaptic reliability is found.

6. The temporal correlation between responsiveness of transmitter synthesis to depolarization and reliable neuromuscular transmission suggests that modulation of neurotransmitter metabolism in response to demand signals the achievement of junctional maturity.
Calcium current inactivation in identified neurones of Helix aspersa.
Authors: Plant T D , Standen N B
Published: December 2014

1. A two‐electrode voltage clamp method was used to study Ca inward currents in identified Helix aspersa neurones bathed in 25 mM‐Ca, Na‐free saline with TEA and 4‐AP. 2. Inward currents were blocked by CdCl2. In Cd delayed outward currents appeared at +30 mV. When two identical depolarizations were separated by a gap inward current turned off to the same level during the two pulses up to +20 mV; above this potential the records cross over. 3. The turn‐off of inward current at potentials up to +20 mV was not affected by 0.2 mM‐quinine, which reduced outward currents at more depolarized potentials. Inward currents declined exponentially over the first 100 msec with a time constant around 60 msec at 0 mV. Double‐pulse experiments gave the same time course of turn‐off. 4. When Ca inward current was reduced by lowering [Ca]o or by partial block by Cd the rate and extent of turn‐off was reduced. 5. The inactivation curve (obtained using a double pulse with gap method) was U‐shaped. The curve was not significantly changed by addition of quinine (0.2 mM) or by changing test pulse size. 6. Recovery of inward currents after a depolarizing prepulse was a double‐exponential process, with time constants of 120 msec and 9.4 sec at 10‐‐11 degrees C. 7. Our results are discussed in terms of possible Ca‐dependent Ca inactivation and in terms of the possibility of development of an outward Ca‐dependent K current.
Effects of endogenous and exogenous noradrenaline on the smooth muscle of guinea‐pig mesenteric vein
Authors: Suzuki Hikaru
Published: December 2014

Membrane responses of smooth muscles of the guinea‐pig mesenteric vein to noradrenaline released from perivascular nerves or applied exogenously were investigated.

1. Exogenously applied noradrenaline depolarized the muscle membrane at concentrations of over 10−6
m, and generated slow waves or action potentials. Application of phentolamine but not propranolol suppressed the depolarization.

2. The depolarization induced by exogenous noradrenaline was associated with increase in the membrane resistance. The level of the membrane depolarization was modified by changing [K]o, but not by [Na]o or [Cl]o.

3. Repetitive but not single stimulation of the nerves produced slow depolarization of the membrane. The amplitude of the slow depolarization was dependent on the frequency or number of stimuli within a certain range, but beyond this an increased frequency or an increased number of stimulating pulses produced no further increase in amplitude of the slow depolarization.

4. The slow depolarization induced by nerve stimulation was analysed in relation to the diffusion of transmitter. The rising phase of the slow depolarization fitted well with the theoretically predicted one, while the falling phase did not.

5. Stimulation of nerves with a high frequency and a large number of pulses produced slow waves or action potentials superimposed on the slow depolarization of the membrane.

6. Membrane responses induced by nerve stimulation did not appear in the presence of TTX or phentolamine. TEA enhanced the nerve‐induced responses.

7. Myogenic electrical activities insensitive to TTX and phentolamine were recorded from the mesenteric vein. These activities were induced by nerve stimulation only in the fresh tissues, were usually irregular in shape, size and frequency, and lasted for 5‐20 min.

8. It was concluded that alpha‐adrenergic receptors on the muscle membrane reacted in a similar manner to noradrenaline either released from the nerves or applied exogenously. Noradrenaline depolarized the muscle membrane by the decrease in potassium conductance of the membrane.
Quantal analysis of a decremental response at hair cell‐afferent fibre synapses in the goldfish sacculus.
Authors: Furukawa T , Kuno M , Matsuura S
Published: December 2014

1. On application of a step decrement in the sound intensity, the amplitude of excitatory post‐synaptic potentials (e.p.s.p.s) recorded intracellularly from large afferent auditory fibres in goldfish's sacculus showed a decremental response in which the amplitude of the e.p.s.p.s was temporarily reduced to a very low level, but soon returned to a new steady level appropriate to the decreased sound intensity. This response seems to underlie the temporary reduction in the rate of afferent discharge observed in the mammalian cochlea upon cessation of sound or upon reduction of its intensity 2. A statistical analysis revealed that reduction in the size of the mean quantal content (m) during the decremental response was associated with reduction in the size of binomial population (n), but not that of the probability (p) of any one of the available quanta actually being used. 3. The temporary reduction in the size of n during the decremental responses can be explained if it is assumed that replenishment to vacant release sites was channelled to high threshold sites and that the low threshold sites were bypassed. The mechanism underlying this special type of replenishment is discussed in relation to the ultrastructural features of presynaptic sites in the hair cell.
Evidence for the presence of potassium channels in the internode of frog myelinated nerve fibres.
Authors: Chiu S Y , Ritchie J M
Published: December 2014

1. The central portion of single frog internodes under voltage‐clamp conditions was acutely demyelinated with lysolecithin to resolve whether potassium channels are normally present only in the paranode (Chiu & Ritchie, 1980, 1981) or are in fact present throughout the entire internode of a myelinated nerve fibre. 2. The experiments were performed in the absence of nodes of Ranvier to ensure that all currents observed originated from the internode. 3. The demyelinating internodal segment showed a steady increase in the capacity and leakage for the first 40‐‐50 min, after which a delayed outward current was revealed. This delayed current, which was blocked by TEA and caesium and exhibited a potassium‐dependent reversal potential, seems to be a potassium current similar to that normally present in the frog node and in squid nerve. 4. The present method of acute demyelination revealed no detectable sodium currents in the internodal segments. 5. These results suggest that potassium channels, but virtually no sodium channels, are normally present throughout a frog internode covered by the myelin.
Role of presynaptic calcium ions and channels in synaptic facilitation and depression at the squid giant synapse.
Authors: Charlton M P , Smith S J , Zucker R S
Published: December 2014

1. The roles of presynaptic calcium influx and calcium accumulation in synaptic facilitation and depression were explored at the giant synapse in the stellate ganglion of the squid. 2. Calcium currents were recorded in the presynaptic terminal, using a three‐electrode voltage clamp and blocking sodium and potassium currents pharmacologically. The calcium influx was constant during pairs or trains of brief depolarizing pulses that elicited facilitating or depressing excitatory post‐synaptic potentials (e.p.s.p.s). 3. The relationship between calcium influx and transmitter release during brief depolarizing pulses of varying amplitude resembled a power function with exponent of about 2. 4. Presynaptic calcium concentration transients were measured by injecting the dye arsenazo III and detecting absorbance changes microspectrophotometrically. Increments in intracellular free calcium accompanying single action potentials appeared constant for repeated action potentials that elicited facilitating e.p.s.p.s. 5. The presynaptic calcium concentration remains elevated for several seconds following action potentials. 6. Presynaptic injection of calcium ions by interbarrel ionophoresis evokes a postsynaptic depolarization, apparently reflecting a large increase in miniature e.p.s.p. frequency. Presynaptic action potentials remain unaffected by this treatment, but e.p.s.p.s triggered by them are facilitated for several seconds, and then depressed. 7. The results are consistent with the hypothesis that synaptic facilitation is due to the action of residual calcium or a calcium complex remaining in the presynaptic terminal after electrical activity. The late depression of release during calcium injection may be a result of the continual release of transmitter and consequent depletion of a presynaptic store.
Interactions between three slow potassium responses controlled by three distinct receptors in Aplysia neurones
Authors: Ascher Philippe , Chesnoy‐Marchais Dominique
Published: December 2014

1. A voltage clamp study was made of the K+ permeability increases produced in certain identifiable neurones of the cerebral ganglion of Aplysia by any one of three distinct agonists (carbachol, histamine and dopamine).

2. The three K+ responses involve three distinct receptors, as shown by the selective effects of reversible antagonists (Gruol & Weinreich, 1979a) as well as by the differential, irreversible effects of trimethyloxonium (TMO) ions.

3. Prolonged exposure of the neurones to one of the agonists reduces the response to the same agonist (desensitization) and, over the low concentration range, doubling the concentration of an agonist leads to supra‐linear summation (potentiation).

4. Prolonged exposure of the neurones to one of the agonists also reduces the response to the other agonists (cross‐desensitization) and combined application of two agonists reveals cross‐potentiation.

5. The time course of desensitization (onset and decay) was the same for the histamine and carbachol responses and, except at very high concentration, was indistinguishable from that of cross‐desensitization. Likewise, potentiation was similar in the two agonist systems and did not differ significantly from cross‐potentiation.

6. The results can be interpreted by assuming that the responses to the three agonists involve specific steps followed by common reaction steps, and that some of the common reaction steps control both potentiation and desensitization.

7. The responses to carbachol and histamine differ in their voltage sensitivity. This suggests that one or more of the specific steps are voltage‐sensitive.

8. Although an increase of the intracellular Ca2+ concentration can itself open K+ channels, and also inhibit the responses to the three agonists, an increase of internal Ca2+ does not appear to play an important role either in the development of the response or in the desensitization process.
Central gating of developmental plasticity in kitten visual cortex
Authors: Singer W. , Tretter F. , Yinon U.
Published: December 2014

1. In nine 4‐week‐old, dark‐reared kittens we sutured one eye closed and rotated the other surgically. The kittens then grew up in a normally lighted animal colony with adequate room to play.

2. For about two weeks after surgery their visual‐motor co‐ordination did not differ from that of kittens with conventional monocular deprivation; then severe disturbance of visually guided behaviour became progressively more apparent until, after another two to three weeks, all the kittens stopped responding to most visual stimuli entirely. At that point their behaviour in an unfamiliar environment closely resembled that of binocularly deprived cats exposed to light for the first time.

3. Four weeks (n = 3) and 6 months (n = 6) after surgery, we examined the visual cortex with single‐unit recordings, and with evoked potentials elicited by electrical stimuli and patterned lights. We obtained the single‐unit recordings from 586 neurones of the striate cortex in both hemispheres, both ipsi‐ and contralateral to the deprived eye.

4. The single‐unit recordings and the evoked potentials showed a clear relation between the kitten's abnormal visual behaviour and the functioning of the striate cortex. Only about half the normal percentage of cells responded to light, and most of those which did react had abnormal receptive field properties: they responded only sluggishly even when the light stimuli were aligned optimally.

5. We also evoked cortical potentials with phase alternating square wave gratings of variable contrast and spatial frequency. The amplitude of the potentials indicated that contrast‐sensitivity was reduced at all spatial frequencies.

6. In the kittens tested 4 weeks after surgery, ocular dominance had shifted toward the open rotated eye but this shift was considerably less pronounced than in control kittens monocularly deprived for a comparable period of time.

7. In the kittens tested 6 months after surgery fewer cells than normal were binocular; ocular dominance had not shifted towards the open eye.

8. Numerous control experiments indicated that these abnormalities did not result from transitory immobilization of the eye alone nor from lesions of the retina or of the optic nerve.

We infer that a central mechanism prevents the inappropriate signals from the rotated eye from influencing the consolidation of central pathways.
Non‐cholinergic excitatory transmission in inferior mesenteric ganglia of the guinea‐pig: possible mediation by substance P.
Authors: Dun N J , Jiang Z G
Published: December 2014

1. Repetitive stimulation of guinea‐pig hypogastric nerves elicited, in addition to the fast cholinergic excitatory potential, a slow depolarization lasting for seconds to minutes in neurones of the isolated inferior mesenteric ganglion. 2. The slow depolarization which could be elicited at a frequency as low as 1‐2 Hz for several seconds was not blocked by cholinergic antagonists, but was eliminated in a low Ca2+ solution; it was termed henceforth the non‐cholinergic excitatory potential. 3. When the membrane potential was manually clamped, the non‐cholinergic potential was associated with three types of membrane resistance change: an increase, a delayed increase and a biphasic change consisting of an initial decrease followed by an increase. 4. In the majority of neurones, conditioning hyperpolarization augmented the non‐cholinergic depolarization; in a few neurones, moderate hyperpolarization depressed the latter, whereas stronger hyperpolarization unmasked a low depolarization. 5. The non‐cholinergic response was markedly attenuated in the presence of exogenously applied substance P; it was partially suppressed by luteinizing hormone‐releasing hormone. 6. Non‐cholinergic depolarization could be elicited in the same neurone by stimulation of all four nerve trunks associated with the ganglion. 7. It is suggested that substance P, a peptide, may be the transmitter responsible for the generation of the non‐cholinergic potential and that it may be released from collateral endings of primary sensory neurones, thus providing a functional connexion between sensory and autonomic neurones.
Action of caffeine in excitation‐contraction coupling of frog skeletal muscle fibres.
Authors: Kumbaraci N M , Nastuk W L
Published: December 2014

1. Frog sartorius muscle bathed in 1 mM‐caffeine generates brief asynchronous contraction of individual sarcomeres, 'sarcomeric oscillations', and propagated contractile waves. 2. Analysis of cinematographic records shows that during sarcomeric oscillations the sarcomere length decreases and the distribution of sarcomere lengths is wider than in controls. 3. Caffeine can produce sarcomeric oscillations in K depolarized muscle fibres and, to a limited extent, in glycerol‐treated muscle fibres. 4. Treatment of muscle with dantrolene sodium blocks production of sarcomeric oscillations by caffeine. 5. In caffeine‐treated muscle fibres, electrically produced depolarization could initiate or increase the frequency of sarcomeric oscillations, and electrical hyperpolarization diminishes the frequency or stops sarcomeric oscillations. 6. Caffeine solution bathing a muscle undergoing sarcomeric oscillations (the perfusate), when applied to a fresh muscle, initiates sarcomeric oscillations with a relatively short latency. 7. An U.V.‐absorbance peak at 245 nm develops in the caffeine solution bathing a muscle undergoing sarcomeric oscillations. 8. It was found that a contraction‐regulating substance (oscillogen) is released from a muscle undergoing sarcomeric oscillations. From results of selective dialysis and gel permeation chromatography, the molecular weight of the oscillogen is estimated to be between 700‐1000 daltons. 9. It is proposed that the oscillogen is a normally occurring substance which functions in excitation‐contraction coupling at the T‐tubule terminal cistern junction in skeletal muscle.
Excitation of hippocampal pyramidal cells by glutamate in the guinea‐pig and rat.
Authors: Hablitz J J , Langmoen I A
Published: December 2014

1. The mechanism by which L‐glutamic acid depolarizes hippocampal CA1 pyramidal neurones was investigated by using the in vitro slice and ionophoretic techniques. 2. Two types of responses were seen. One (in 85% of cells) consisted of spike discharges that outlasted the glutamate‐induced depolarization. In the other (the rest of the cells), spikes were produced only during the rising phase of the depolarization. 3. The effect was highly localized; it disappeared when the ionophoretic electrode was moved vertically by as little as 20 micrometers. 4. The effect of glutamate persisted after synaptic transmission was blocked; this probably was due to a direct effect of glutamate on the cell membrane. 5. Small doses of glutamate produced either no change or an apparent increase in input resistance. With larger doses, the input resistance invariably decreased. The apparent increase in input resistance was not seen in cells treated with Mn2+ and TTX and is believed to be an effect of the depolarization rather than a direct effect of glutamate. 6. By extrapolation, the reversal potential for the glutamate response (EGlu) was found to ‐3.6 mV. 7. Following intracellular injection of Cs+, neurones could be depolarized to a range of +20 to +50 mV. The glutamate response could then be reversed. EGlu in these cells was ‐1.5 mV. 8. Using the Cs+‐injection technique, it was also possible to reverse the e.p.s.p. E.e.p.s.p. was similar to EGlu. 9. When the external sodium concentration was reduced, the size of the glutamate response decreased, and EGlu became more negative.
Voltage‐clamp studies of transient inward current and mechanical oscillations induced by ouabain in ferret papillary muscle
Authors: Karagueuzian Hrayr S. , Katzung Bertram G.
Published: December 2014

1. We studied the effects of a toxic concentration of ouabain on transmembrane electrical activity and on mechanical behaviour of right ventricular papillary muscles from ferrets in a single sucrose‐gap using current clamp and voltage clamp.

2. Ouabain (1·4‐1·8 μM) induced oscillatory after‐potentials and after‐concentrations in current‐clamp experiments. Voltage clamp showed that the oscillatory after‐potential was caused by a transient inward current, similar to that in Purkinje fibres.

3. The transient current had a sigmoidal dependence on the preceding (activating) voltage step V1, with a treshold around ‐13 mV and a plateau between +10 and 20 mV. There was a decline in current amplitude for more positive clamps. When activated by a fixed V1 voltage step, and measured at different repolarization levels V2, the transient current manifested an inverse dependence on V2 between ‐50 and ‐10 mV. No outward transient current could be detected. Total replacement of Na in the bathing medium by Tris or by sucrose abolished the transient current.

4. Ouabain caused an increase of phasic (twitch) tension responses to voltage steps at all potentials without shifting the curve relating these variables on the voltage axis. The drug evoked an even greater increase in the tonic tension responses.

5. After prolonged exposure, oscillatory mechanical responses were frequently recorded during positive voltage steps. Unlike the after‐contraction, these mechanical fluctuations were not consistently damped and were not accompanied by detectable synchronous current fluctuations. Catecholamines and dibutyryl cyclic AMP markedly reduced the amplitude of the tonic contraction and the mechanical oscillations but increased their frequency. Caffeine had no effect on the tonic contraction amplitude but abolished the fluctuations.

6. These results support the proposal that Ca is transiently released from the overloaded sarcoplasmic reticulum in ouabain‐intoxicated muscle and may evoke oscillatory responses in nearby contractile fibrils. When these transient increases of sarcoplasmic free Ca are large enough, they may induce the transient transmembrane current described above.
Rapid restoration of functional input to the visual cortex of the cat after brief monocular deprivation
Authors: Blakemore Colin , Hawken M. J.
Published: December 2014

1. We recorded extracellularly from 1045 neurones in area 17 of seven monocularly deprived kittens and we employed careful sampling techniques to examine the effects of removing the signals from the non‐deprived eye on the proportion of cells responding to stimulation of the deprived eye.

2. Monocular deprivation itself produced a pronounced over‐all change in the ocular dominance of neurones in favour of the experienced eye, but both between animals and even between different samples of cells in individual animals there were marked variations in the magnitude of the effect.

3. Monocular deprivation starting immediately at the time of natural eye opening and lasting for several weeks reduced to about 10% the proportion of cortical neurones influenced through the deprived eye. Enucleation of the experienced eye did not then produce a significant increase in the proportion of cells responsive to the deprived eye.

4. Monocular deprivation lasting 3 days or more and beginning at 5 weeks of age, after normal binocular vision, also shifted ocular dominance substantially: 11‐27% of neurones responded through the deprived eye. Enucleation of the experienced eye or topical anaesthesia of the optic nerve resulted in a substantial recovery of input from the deprived eye: up to 78% of the cells responded.

5. In such animals the majority of neurones that recovered input from the deprived eye had receptive field properties qualitatively similar to those of normal cortical cells. Recording in a single penetration both before and after enucleation (or optic nerve block) suggested that the orientation preferences of cells with recovered input followed the same sequence as was originally present for the non‐deprived eye.

6. Recovery of input occurred in all cortical laminae in which cells were recorded, even in layer IV, and mainly took the form of an expansion of already existing clusters of cells driven by the deprived eye.

7. Spontaneous activity tended to increase after enucleation.

8. The results indicate that monocular deprivation after a period of normal binocular vision leaves subthreshold but functionally organized synaptic input from the deprived eye on cortical cells, which is revealed when activity arising in the retina of the non‐deprived eye is abolished.
Brief monocular deprivation leaves subthreshold synaptic input on neurones of the cat's visual cortex
Authors: Blakemore Colin , Hawken M. J. , Mark R. F.
Published: December 2014

1. We have examined neurones in area 17 of monocularly deprived kittens for subthreshold input in response to visual stimulation through the deprived eye during reversible abolition of activity from the non‐deprived eye and during increased excitability of cortical neurones induced by ionophoresis of DL‐homocysteic acid (DL‐H).

2. After two or three days of monocular deprivation, beginning five weeks post‐natally, most cortical neurones were dominated by the non‐deprived eye. From a sample of forty‐three neurones, from three kittens, driven exclusively by the non‐deprived eye, only 16% developed responses to stimulation through the deprived eye as a result of reversible pressure blinding of the non‐deprived eye. The responses through the deprived eye during pressure blinding usually developed over a period of several minutes and were always transitory: in no cases did the response persist for more than a few minutes after the return of the normal response through the non‐deprived eye. Occasionally cells became responsive through the deprived eye during a short period of heightened general excitability after the release of pressure.

3. Ionophoretic application of DL‐H usually increased the spontaneous activity of cortical neurones. From two kittens monocularly deprived for three days during the fourth or fifth week of life, out of a sample of sixteen cortical neurones initially responsive only through the non‐deprived eye, 63% showed responses to visual stimulation through the deprived eye during DL‐H application. From a kitten monocularly deprived for 12 d from post‐natal day 38, 28% of eighteen initially monocular neurones developed responses through the deprived eye during DL‐H application.

4. Preliminary results from intracellular recording showed apparently monocular neurones with excitatory input from the deprived eye producing subthreshold synaptic activity in response to moving bars of the same orientation that gave a suprathreshold response through the non‐deprived eye.
Response latency of brisk‐sustained (X) and brisk‐transient (Y) cells in the cat retina
Authors: Bolz J. , Rosner G. , Wässle H.
Published: December 2014

1. Several methods for evaluating light‐evoked response latency and its variability in brisk‐sustained (X) and brisk‐transient (Y) retinal ganglion cells were tested. The most accurate procedure proved to be that described by Levick (1973), in which the time of the occurrence of the fourth impulse after stimulus onset is taken as an estimate of the latency.

2. The shortest response latencies are obtained when the stimuli are the same size as the receptive field centre. At medium and high response amplitudes (> 150 impulses/sec) the response of brisk‐transient (Y) cells to these optimal stimuli is 10‐15 msec faster than that of adjacent brisk‐sustained (X) cells.

3. The response latency of brisk‐sustained (X) cells for stimuli larger than the receptive field centre increases, whereas that of brisk‐transient (Y) cells remains constant. Brisk‐sustained (X) cells respond faster than do brisk‐transient (Y) cells to stimuli smaller than the receptive field centre.

4. No systematic difference exists between brisk‐sustained (X) and brisk‐transient (Y) cells in regard to the temporal variability of the response. The standard deviation of the latency for stimuli of optimal size decreases from 2·0‐8·0 msec at medium stimulus contrast to 0·6‐2·0 msec at high stimulus contrast.

5. The response of OFF‐centre cells to the disappearance of a light spot is always slower than that of an ON‐centre cell of the same class to the onset of this stimulus. However, when OFF‐centre cells are stimulated with dark spots, their response latency does not differ from that of ON‐centre cells of the same class.

6. No simple relationship exists between the response latency and the response amplitude. At medium and high discharge rates, most brisk‐transient (Y) cells respond faster than an adjacent brisk‐sustained (X) cell with equal response. At the same response amplitude, the latencies become shorter as the background illumination is raised. The same discharge rate can be obtained with stimuli of sub‐optimal and supra‐optimal size, but the latency for the larger stimulus is shorter than that for the smaller one. Latency, therefore, is an additional parameter characterizing the light‐evoked response.
Voltage‐ and stage‐development uncoupling of Rohon‐Beard neurones during embryonic development of Xenopus tadpoles
Authors: Spitzer Nicholas C.
Published: December 2014

1. Electrical coupling of Rohon‐Beard neurones in the spinal cord of Xenopus laevis has been studied from the time of closure of the neural tube (stage 20, 22h after fertilization of the egg) to the free swimming tadpole (stage 49, 12d old). Pairs of cells were examined by impaling both simultaneously with single micro‐electrodes having current‐passing and voltage‐recording capabilities.

2. At the earliest time studied (stage 20), before Ca2+ action potentials are detected, cells are electrically coupled. Coupling coefficients as high as 0·6 can be recorded. Tests with small hyperpolarizing and depolarizing current pulses demonstrate that the coupling does not show rectification.

3. The coupling is voltage‐dependent: depolarization or hyperpolarization of one cell with respect to another, above a threshold, causes relative uncoupling of the cells. The coupling coefficient falls to ∼10% of its initial value when the difference in potential between the two cell bodies is ∼75 mV. Cells usually become recoupled at the termination of the current pulse. Other, unidentified cells in the spinal cords of the same embryos show coupling that is not voltage‐dependent.

4. Voltage‐dependent uncoupling and recoupling persist when cells are depolarized by high K+, and in the presence of 30 mM‐Co2+, suggesting that chemical synapses are not involved. They are also unaffected by addition of Rb+, Cs+ or TEA+ to the extracellular solution, elevated levels of Ca2+, or replacement of Na+ with Tris or Cl− with isethionate, suggesting that conductance changes in the surface membrane, such as anomalous rectification, are not responsible.

5. Lowering the intracellular pH with CO2‐HCO3− buffered saline does not abolish electrical coupling but appears to eliminate its voltage dependence.

6. Slightly later (e.g. stage 21), cells that do not yet produce Ca2+ action potentials while coupled will do so when their input resistance is increased by uncoupling them from their neighbours.

7. Later still (e.g. stage 23), cells make Ca2+ action potentials while coupled, and an action potential in one cell can trigger an action potential in other cells to which it is coupled. Ca2+ action potentials that do not bring other coupled cells to threshold for impulse initiation can transiently reduce the strength of coupling. Repetitive firing of these Ca2+ action potentials at a low frequency does not cause permanent uncoupling of the cells.

8. Rohon‐Beard neurones become electrically uncoupled about stage 25 (early tail‐bud, 28h old). Coupling disappears around the time of appearance of the Na+ component of the action potential, although coupling that is voltage‐dependent or independent can still be seen between other, unidentified cells. No electrical coupling of Rohon‐Beard cells was detected at later stages of development.
Recovery of slow and fast muscles following nerve injury during early post‐natal development in the rat.
Authors: Lowrie M B , Krishnan S , Vrbová G
Published: December 2014

1. The sciatic nerve was crushed in 5‐6‐day‐old rats and the recovery of function of slow and fast muscles was studied. The first signs of recovery of function were seen 10‐12 days after the operation. 2. Maximal tetanic tension developed by the reinnervated muscles was recorded and taken as an indication of their recovery. Two months after nerve crush, slow soleus muscles developed only slightly less tension than the control unoperated soleus muscles. The reinnervated fast muscles tibialis anterior (t.a.) and extensor digitorum longus (e.d.l.) developed only about 50% of the tension of the unoperated controls. 3. The fast muscles never recovered, remaining weaker and smaller throughout the animals' life. 4. The number of muscle fibres in the reinnervated fast muscles was substantially reduced and their fibre composition altered in that they contained mainly muscle fibres with high levels of oxidative enzymes. 5. The reinnervated fast muscles became much more fatigue resistant than the unoperated controls. 6. The possibility that these changes are due to motoneurone death was examined. The motoneurones innervating the fast muscles were labelled by retrograde transport of HRP. No significant reduction in the number of motoneurones innervating the operated muscles was found. 7. These results show that nerve injury during early post‐natal life causes permanent changes in fast muscles that are not caused by motoneurone death.
The temporal properties of rod vision.
Authors: Conner J D
Published: December 2014

1. Profiles which represent rod thresholds for flickering fields seen against backgrounds of various intensity have shapes which depend on flicker frequency. Low frequency profiles rise smoothly as background intensity is increased. High frequency profiles are only affected by bright backgrounds, which cause them to rise steeply. Intermediate frequency profiles contain two distinct branches which resemble separate increment threshold functions. 2. The high intensity branches of two‐branched threshold profiles cannot be attributed to cone intrusion. Instead, both branches of such profiles are mediated by visual mechanisms which have the spectral properties, the dark adaptation properties and the directional insensitivity of rod vision. Thus, the stimuli are detected by rods. 3. Plots of critical flicker frequency (c.f.f.) as a function of intensity contain two rising branches which are separated by a plateau (when modulation depth is large), or they form two enclosed lobes so that only intermediate frequencies, but neither high nor low ones, are seen (when modulation depth is small). C.f.f. is profoundly depressed by very bright light (above 100 scotopic trolands) which saturates rod vision. 4. In dim light rod modulation sensitivity functions resemble those of low‐pass filters, but in bright light they resemble those of band‐pass filters. 5. Several forms of rod mediated interference occur at moderate intensities, where rod vision's temporal properties ordinarily improve abruptly. With certain stimuli, rod signals conveying temporal information disrupt one another so completely that suprathreshold flicker cannot be seen within a ten‐fold intensity range. 6. Many of these observations can be explained by the hypothesis that rod vision comprises two temporal channels which have different properties.
Redistribution by 5‐hydroxytryptamine of carotid arterial blood at the expense of arteriovenous anastomotic blood flow
Authors: Saxena Pramod R. , Verdouw Pieter D.
Published: December 2014

1. The effects of 5‐hydroxytryptamine by intravenous (1, 5 and 10 μg kg−1 min−1 in cats) and intracarotid (0·5 and 2 μg kg−1 min−1 in pigs) routes were studied on the complete distribution of common carotid artery blood flow, measured with radioactive microspheres (15 μm). In addition, the amine was also infused (0·75‐3 μg kg−1 min−1) into the carotid artery of cats to observe its influence on the shunting of microspheres in the jugular venous blood.

2. The basal total common carotid blood flow was distributed ipsilaterally mainly to extracerebral tissues and only little blood entered the brain. As shown by the presence of microspheres in the lungs after injection into the carotid artery (52% in cats; 82% in pigs), a major fraction of the carotid blood by‐passed the capillary bed through arteriovenous anastomoses in the head (non‐nutrient fraction).

3. 5‐Hydroxytryptamine redistributed the blood in favour of the nutrient compartment at the expense of arteriovenous anastomotic fraction. In cats, tissue blood flow did not significantly change but, in the pig, blood flow to all tissues, particularly to skin and ears, was substantially increased despite a reduction in total carotid blood flow. This reduction was entirely due to a change in the non‐nutrient fraction.

4. Intracarotid infusion of 5‐hydroxytryptamine in vagosympathectomized intact or spinal cats decreased the number of microspheres appearing in the jugular venous blood, again indicating a reduction in arteriovenous anastomotic flow due to a constriction of these non‐nutrient vessels.

5. Cyproheptadine (1 mg kg−1) completely reversed the effect of 5‐hydroxytryptamine on the total carotid blood flow. However, the vasoconstriction of arteriovenous anastomoses was only partially attenuated and the vasodilatatory response was either unchanged (muscle) or even enhanced (skin, ear and bones).

6. It is suggested that 5‐hydroxytryptamine causes vasoconstriction of the large arteries via D‐receptors which are only partly involved in the constriction of arteriovenous anastomoses. A part of the vasoconstriction in these non‐nutrient vessels and the vasodilatation in extracerebral tissues are mediated by atypical 5‐hydroxytryptamine receptors that are yet to be fully characterized.