bluuebunny/crossref_metadata_2025_split huggingface dataset:
The electrical properties of the ectoderm in the amphibian embryo during induction and early development of the nervous system
Authors: Warner Anne E. 
Published: December 2014

1. The electrical properties of ectodermal cells have been studied in embryos of the axolotl Ambystoma mexicanum between gastrulation and the closure of the neural tube.2. At the time of neural induction by the underlying mesoderm the mean membrane potential recorded in ectoderm cells was −30 mV (± 1·5 mV
S.E. of mean) and in presumptive neural cells −27 mV (± 1·6 mV
S.E. of mean).3. At late neural fold stages, when specification of the neuroectoderm is complete, the membrane potential in presumptive nerve cells was −44 mV (± 1·7 mV
S.E. of mean). This is significantly greater than in cells of the surrounding ectoderm at the same developmental stage (−31 mV ± 1·5 mV
S.E. of mean).4. Current injected into an ectoderm cell spread freely throughout the neural and lateral ectoderm both before and after neural specification was complete.5. Voltage—current relations recorded at mid‐neural fold stages in the lateral ectoderm and neural plate rectified in opposite directions. In the neural plate the slope conductance rose as the internal potential was made less negative; in the lateral ectoderm the slope conductance fell with depolarization.6. At the time of closure of the neural tube ectoderm and presumptive neural cells lose their low resistance connexions with each other. At the same time low resistance contacts are established across the mid line between ectoderm cells originally separated by the neural plate.7. After the neural tube has closed low resistance connexions remain between presumptive neural cells, although the degree of current spread from one cell to the next is not very great.8. The voltage—current relation recorded in neural tube cells showed a rise in slope conductance as the cell was depolarized.9. Occasionally signs of regenerative activity were seen, but the mechanism for generating a fully fledged action potential does not differentiate until after complete closure of the neural tube.
The movement of amino acids between blood and skeletal muscle in the rat
Authors: Baños Guadalupe , Daniel P. M. , Moorhouse S. R. , Pratt O. E. 
Published: December 2014

1. The rates of entry of twenty of the blood amino acids into skeletal muscle of living rats were measured directly by means of a technique which ensured that a steady concentration of a radioactively labelled amino acid is reached rapidly and is maintained in the bloodstream.2. The rates of entry were measured in experiments of short duration to avoid possible artifacts caused by amino acids leaving the muscle or by their metabolism.3. The entry rate of each amino acid increased in direct proportion to its concentration in the blood plasma over the physiological range.4. The various amino acids had widely different rates of entry. These rates could not be correlated with the physicochemical properties of the amino acids.5. Two amino acids,
L‐lysine and
L‐threonine, enter muscle against a concentration gradient, while in the case of a third,
L‐arginine, the blood concentration was raised high enough to induce saturation of the entry mechanism.6. It is concluded that entry takes place in vivo by means of carrier‐mediated transport processes with a high degree of specificity.7. When the concentration of an amino acid in the bloodstream was increased to about twice normal the proportion of the additional amino acid that was taken up rapidly by the muscle was large enough, especially for the essential amino acids, to suggest that the tissue constitutes a quantitatively important storage system helping to regulate the concentrations of amino acids in the bloodstream.
The influence of androgens on enzymes (chymotrypsin‐ and trypsin‐ like proteases, renin, kallikrein and amylase) and on cellular structure of the mouse submaxillary gland
Authors: Bhoola K. D. , Dorey Gundula , Jones C. W. 
Published: December 2014

1. The effect of age and androgen level on enzyme activity and cellular structure has been determined in the mouse submaxillary gland.2. A new protease which resembles chymotrypsin in its substrate specificity has been characterized in the gland.3. Activity of the chymotrypsin‐ and trypsin‐like proteases and renin increased considerably in male mice concomitantly with proliferation of granules in the secretory tubules of the gland.4. The androgen dependence of the chymotrypsin‐ and trypsin‐like enzymes, renin and the organelles within the secretory tubules was confirmed in castrated male mice. The activity of these enzymes increased and correlated with the appearance of intracellular granules in the secretory tubules when the castrated male mice and in addition female mice were treated with testosterone preparations.5. Kallikrein, a closely related protease, and amylase increased in activity with age but showed no sex‐linked differences.6. The results suggest that kallikrein is sequestered in acinar cells whereas the androgen‐dependent enzymes (chymotrypsin, trypsin and renin) are located in the secretory tubules.
The onset of the effects of zinc and tetraethylammonium ions on action potential duration and twitch amplitude of single muscle fibres
Authors: Stanfield P. R. 
Published: December 2014

1. Single dissected muscle fibres were used to examine the rates of onset and reversal of the effects of zinc and tetraethylammonium (TEA) ions on the duration of the action potential and the amplitude of the twitch.2. The increases in fall time (100‐50%) of the action potential and in the amplitude of the twitch resulting from the application of zinc or TEA follow exponential time courses.3. The time constants for the onset of the effects of 0·1 m
M zinc were 11·03±0·71 sec (six fibres) and 9·24±0·77 sec (sixteen fibres) on action potential and twitch amplitude respectively. The values are not significantly different from each other.4. The onset of the effect of zinc on action potential duration was speeded up by ‘detubulation’ by glycerol treatment. The time constant was 3·88±0·68 sec (six fibres).5. The time constants for the onset of the effects of 25 m
M‐TEA were 3·48±0·69 sec (six fibres) and 3·81±0·26 sec (nine fibres) on action potential and twitch respectively. These values are not significantly different from each other.6. The results are consistent with the idea that zinc and TEA act as twitch potentiators by way of their effect on action potential duration. It seems likely that this effect is, in part at least, on the surface membrane, but an effect within the T‐system is not ruled out.
Mechanical studies on the retractor bulbi muscle and its motor units in the cat
Authors: Lennerstrand Gunnar 
Published: December 2014

1. For a description of some of the mechanical properties of the retractor bulbi muscle in the cat, the isometric tension development was studied in one of the four slips of the muscle and in single retractor bulbi motor units.2. The motor units and the muscle were activated by stimulating their motoneurones of origin in the abducens nucleus.3. All twenty‐eight motor units studied were of the same fast, twitch type, which fatigued quickly. Similarities between the motor units and the muscle with regard to isometric tension development strongly suggest that the retractor bulbi is composed exclusively of this type of motor unit.4. On an average the motor unit had a twitch rise time of 9·2 msec and a half‐decay time of 11·4 msec. The twitch tension was 36·7 mg. At stimulation with 175 pulses/sec or above the tetanus fused. The maximal tetanic tension developed was 440 mg and the maximal rate of tension rise was 24·5 g/sec. To prolonged tetanic stimulation most of the units fatigued completely within 10–15 sec.5. In a slip of the muslce similar values were obtained for contraction time, half‐decay time, fusion frequency and fatigability. Tetanic tension reached 11·7 g and the maximal speed of tetanic contraction was 255 g/sec.6. As in other extrinsic eye muscles a linear relation was found between length and tension in the activated retractor bulbi. An increase in activation induced a parallel shift in the curves to higher tension values but the slopes of the curves remained unchanged. The average slope value was 1·7 g/mm.
The spontaneous release of transmitter from insect nerve terminals as predicted by the negative binomial theorem
Authors: Rees D. 
Published: December 2014

1. In the retractor unguis muscles of Periplaneta americana and Blaberus giganteus, the rate of spontaneously occurring miniature potentials from nerve‐muscle synapses associated with the ‘white’ muscle fibres was greater than that observed in the ‘red’ muscle fibres.2. In 5% of the intracellular recordings, particularly from the ‘white’ fibres, short ‘bursts’ of relatively high (20‐100 sec−1) rates of m.e.p.p.s occurred infrequently in an unpredictable manner. This bursting phenomenon was not observed in extracellular recordings of the miniature potential discharge.3. Rigorous statistical analyses indicated that the spontaneous mode of transmitter release at cockroach retractor unguis muscle fibres was predictable by the negative binomial theorem with a 90% reliability.4. Perfusion of nerve‐muscle preparations with high Mg2+ salines resulted in low spontaneous discharge rates which were characterized by a negative binomial distribution.5. The fit of the data to the negative binomial theorem implied some mutual interaction between those processes responsible for the spontaneous release of transmitter from cockroach nerve terminals.
Effects of thymol on the electrical and mechanical properties of the guinea‐pig taenia coli
Authors: Ito Y. , Kuriyama H. 
Published: December 2014

Effects of thymol (0·02‐2 m
M) on the electrical and mechanical activities of the smooth muscle cells of the guinea‐pig taenia coli were investigated with either micro‐electrode or double sucrose gap methods.1. Thymol, in a concentration of more than 0·03 m
M, reduced the amplitude and maximum rate of rise of the spikes without any change of the membrane potential. When the concentration was increased to 0·3 m
M, thymol completely blocked the spontaneous and evoked spike activities. In a concentration of more than 0·1 m
M, thymol reduced the membrane resistance in proportion to the concentration without any change of the membrane potential.2. Ionic mechanisms involved in the effects of thymol on the membrane resistance were investigated in various ionic environments. The results showed that in concentrations below 0·5 m
M thymol might selectively increase the Cl‐conductance of the membrane. Participations of Na and K ion in the effects of thymol on the membrane resistance could be eliminated. However, at more than 1 m
M, thymol increased the membrane conductance non‐selectively. Excess Ca in the external solution partly suppressed the action of thymol on the taenia coli.3. Potentiation of the twitch tension was not observed on treatment with any concentration of thymol.4. After pre‐treatment with thymol (0·5 m
M), isotonic K Krebs solution depolarized the membrane and reduced the membrane resistance as observed in the absence of thymol. However, thymol completely suppressed the K‐induced contracture.5. Application of excess Ca and acetylcholine during the maintained contracture evoked by isotonic K Krebs solution induced further development of the contracture. However, on pre‐treatment with thymol, neither excess Ca nor acetylcholine could evoke a mechanical response in isotonic K Krebs solution.6. The results obtained from the present experiments are discussed in relation to the roles of Ca on the smooth muscle cells.
Responses of bipolar cells in the retina of the turtle
Authors: Schwartz E. A. 
Published: December 2014

The responses of bipolar cells in the retina of the turtle have been studied by intracellular recording. Two types of bipolar cell have been identified: one gave graded depolarizing and the other graded hyperpolarizing responses to small circles of light (100 μm diameter). The responses of both types of cell were similar in the following respects.1. Both were extremely sensitive to dim light; the amplitude of response to a small circle of light increased with light intensity more steeply than the cone response.2. Enlarging the diameter of a spot added an antagonistic effect which decreased response amplitude. This decrease in response amplitude was more apparent at dim than at bright light. Stimulating only distant areas of retina with an annulus produced a response of polarity opposite to that normally produced by a central spot. However, the responses of bipolar cells did not appear to be due to a simple summation of opposite polarity signals contributed from central and peripheral parts of their receptive fields.3. When small spots or annuli of light were turned off there frequently occurred an overshooting OFF transient. The occurrence of OFF transients depended on the duration of the stimulus. Cones recorded under similar conditions produced an OFF depolarization. The size of cone OFF depolarizations increased with increasing duration of the preceding light; following approximately 3 sec of illumination their maximum amplitude was roughly 1/10 the amplitude of the preceding hyperpolarization. The size of OFF responses in both cone and bipolar cells was increased when horizontal cells were hyperpolarized by light.It is concluded that bipolar cells produce large responses for very small cone responses, and, as a consequence, a small depolarization in cones following illumination produces large OFF transients in bipolar cells. Furthermore, the responses of bipolar cells do not appear to represent a simple summation of opposite polarity input from receptor and horizontal cells.
Thermoregulatory responses to the injection of monoamines, acetylcholine and prostaglandins into a lateral cerebral ventricle of the echidna
Authors: Baird J. A. , Hales J. R. S. , Lang W. J. 
Published: December 2014

1. The putative neurotransmitter substances 5‐hydroxytryptamine (5‐HT), noradrenaline (NA), acetylcholine (ACh) and prostaglandins E1 (PGE1) and E2 (PGE2) have been injected into a lateral cerebral ventricle of the conscious echidna (Tachyglossus aculeatus); thermoregulatory responses in thermoneutral (ambient dry bulb temperature, Tdb, of approximately 22° C), cool (Tdb of approximately 14° C) and warm (Tdb of approximately 26° C) environments were determined.2. Under all conditions, all of the drugs tested either caused deep body temperature to fall or else had no effect; the fall was brought about by peripheral vasodilatation and/or reduced metabolic rate due to a decrease in shivering or to general relaxation.3. Responses of the many placental mammals to 5‐HT, NA and ACh vary widely, and the echidna, a monotreme, appears to exhibit responses most like those of the rat.4. Placental mammals tested to date invariably exhibit a hyperthermic response to prostaglandins, and the hypothermic responses of this monotreme is therefore unique. The present study included the confirmation of a hyperthermic response to PGE1 and PGE2 in cats and rats.5. It is concluded that the concept of thermoregulation by amines and other substances in the hypothalamus of placental mammals may also be applicable to the monotremes which have evolved separately from the marsupials and placental mammals for about 180 million years.
Organization of corticofugal neurones in somatosensory area II of the cat
Authors: Atkinson D. H. , Seguin J. J. , Wiesendanger M. 
Published: December 2014

1. This investigation had two main objectives: first to determine whether or not motor activity could be elicited by localized intracortical stimulation in somatosensory area II of the cat, and secondly to identify, by antidromic stimulation, neurones which projected to subcortical structures and to study their afferent input.2. Although arm movements could be elicited in most cats by intracortical train stimulation with tungsten micro‐electrodes, the lowest motor thresholds were much higher than the lowest thresholds for the primary motor area under similar experimental conditions. Facial responses were evoked at lower stimulus thresholds, but the threshold decreased steadily as successive stimulation tracks approached the coronal face area. Previously observed responses to prolonged surface stimulation could have been caused by intracortical spread of excitation or by escape of stimulus to the primary area, especially the face area.3. Neurones with corticofugal axons projecting to bulbar and spinal levels were first identified by their antidromic response to stimulation of the cerebral peduncle. Each was further tested by stimulation of the cervical corticospinal tract, and the dorsal column nuclei. Their receptive fields were then recorded.4. It was possible to classify the neurones into four main categories: (i) non‐descending neurones: neurones not activated antidromically by any of the subcortical stimulating electrodes. The majority of these neurones had very small (lemniscal type) receptive fields, (ii) corticobulbar neurones: these were invaded antidromically by stimulation of the peduncle but not by spinal or dorsal column nuclei stimulation. They had ‘stocking‐like’ or larger receptive fields; (iii) cortico‐spinal neurones: neurones driven antidromically by stimulation of corticospinal fibres. Characteristically, these neurones had large confluent fields, often bilateral. Very few had receptive fields of the lemniscal type; (iv) neurones invaded by dorsal column nuclei stimulation: the number of such units was extremely low and their receptive fields were large or ‘stocking‐like’.5. The results indicate that somatosensory area II in the cat does not exert an independent motor control of spinal neurones, and it is thought that corticofugal neurones of SII are involved in the control of somatosensory transmission rather than having a direct motor function.
The properties of motor units in a fast and a slow twitch muscle during post‐natal development in the kitten
Authors: Bagust J. , Lewis D. M. , Westerman R. A. 
Published: December 2014

1. Motor units were functionally isolated from a fast and a slow twitch muscle of kittens: flexor digitorum longus (FDL) and soleus. Both muscles were examined in two groups: one aged about 2 weeks and the other 6 weeks.2. A clear division into α and γ axons could be made. The mean conduction velocity of α axons from FDL was higher than that of soleus axons at both ages.3. Tetanic tensions were expressed as a percentage of whole muscle tension. The distributions of motor unit tensions were symmetrical in soleus muscles but were skewed towards large values in FDL. In both types of muscle the scatter of motor unit tensions was greater at 2 weeks than at 6, the mean percentage tension also fell with age.4. The motor unit twitch times to peak were symmetrically distributed in soleus but skewed towards large values in FDL. The variance was less than in adults.5. Motor unit axonal conduction velocity was related to tetanic tension and twitch speed. The relationship between twitch time to peak and the ratio of twitch to tetanic tension varied with age but was not seen so clearly.
A study of the contractures induced in frog atrial trabeculae by a reduction of the bathing sodium concentration
Authors: Chapman R. A. 
Published: December 2014

1. The relationship between the [Ca]o, the [Na]o and the strength of the contracture evoked when the [Na]o is reduced has been investigated in isolated frog atrial trabeculae.2. The strength of the contracture varies by the [Ca]o2 and by 4√([Na]o) over the lower tension range.3. The contracture induced by reduction of [Na]o is not sustained, but relaxes spontaneously. The rate of this relaxation is only dependent on the [Na]o is the presence of strophanthidin.4. After the spontaneous relaxation of an Na‐free contracture, the ability of the trabecula to develop tension upon a second challenge with Na‐free solution returns in about 3 min if the muscle is perfused with Na‐containing fluid. This recovery process is slowed if the [Na]o is low during the recovery period, but the recovery is hastened by electrical stimulation of the preparation or by perfusion with K‐free or strophanthidin containing sodium‐Ringer.5. It is suggested that the influx of Ca2+ which induces the Na‐free contracture depends on the presence of Na+ inside the cells. When the intracellular Na concentration falls, the Ca influx falls, and the muscle relaxes as a result of the activity of an intracellular relaxing structure.
An estimate of sodium/potassium pump activity and the number of pump sites in the smooth muscle of the guinea‐pig taenia coli, using 3[H]ouabain
Authors: Brading Alison F. , Widdicombe J. H. 
Published: December 2014

1. Binding of tritiated ouabain to the smooth muscle of the guinea‐pig taenia coli showed two components, one saturable at lower glycoside concentrations and the other linear with increasing concentrations.2. The saturable component alone was affected by extracellular potassium concentrations. This component seems to be bound to sodium pumping sites, and when completely saturated binds 1·1 × 1011 molecules per mg fresh wt. of tissue, or 250–300 molecules per square micron of membrane, assuming a volume:surface area ratio of 1·5 μm.3. Only a fraction of 42K uptake by the cells can be blocked by ouabain at maximal concentrations. In normal Krebs solution two thirds can be blocked. The remaining one third is presumably passive uptake. The fraction blocked is reduced as the extracellular potassium concentration, and thus passive uptake, is increased.4. The amount of potassium pumped into the cells at various concentrations of extracellular potassium has been calculated. In normal Krebs solution the amount pumped in 45 min was 20·0 m‐mole/kg fresh wt., and this was increased at higher potassium concentrations.5. On the assumption of a stoichiometry of 3Na: 2K, the pump sites in normal Krebs solution have a turnover rate of 1320 min−1.6. Indirect calculations of sodium movements suggest that the sodium permeability may be about 0·9 × 10−8 cm sec−1 and the pump may generate a current of 0·9 × 10−7 A cm−2. This crossing an Ohmic membrane resistance of 30–60 kΩ cm2 would be equivalent to a potential difference of 3–5 mV.
Responses in the rat thalamus to whisker movements produced by motor nerve stimulation
Authors: Brown A. W. S. , Waite Phil M. E. 
Published: December 2014

1. The effect of electrical stimulation of the motor nerve supplying the whiskers on the activity of single cells in the vibrissal region of the ventrobasal complex of the thalamus has been studied in rats under urethane anaesthesia.2. The stimulation caused protraction of the ipsilateral whiskers. 60% of the cells which fired to mechanical movements of the whiskers were found to respond to this electrical stimulus with 1–2 impulses at short latency (average 7·7 msec), provided the stimulus was sufficient to move the whiskers.3. When the moving whiskers hit a barrier, 92% of the cells responded to the stimulus. The most effective position of the barrier was in front of the whiskers, although other positions often produced a response as well. Static displacement of the whiskers, particularly in the forward direction, could abolish the response or increase its latency.4. The following‐frequencies for these cells were 5–10 stimuli/sec. Combinations of electrical stimuli with mechanical ramp movements of the whiskers showed that similar recovery times followed both types of stimuli.5. These results are compared with those reported from studies in the afferent nerve fibres after electrical stimulation of the motor nerve and also with responses in the thalamus following mechanical movements of the whiskers. The possible importance of the latency of these sensory responses is considered.