bluuebunny/crossref_metadata_2025_split huggingface dataset:
Motor units in cat soleus muscle: physiological, histochemical and morphological characteristics
Authors: Burke R. E. , Levine D. N. , Salcman M. , Tsairis P. 
Published: December 2014

1. Physiological properties of motor units in the soleus muscle were studied in anaesthetized cats using intracellular stimulation of motoneurones to ensure functional isolation of single units. The muscle fibres belonging to 6 units were identified by glycogen depletion following prolonged stimulation, permitting analysis of their histochemical profiles and anatomical organization.2. The studied units in soleus were all classed as type S and were extremely resistant to fatigue during prolonged stimulation. Twitch contraction times ranged from 64 to 131 msec (mean 97·1 msec) and tetanic tensions ranged from 3·5 to 36 g (mean 10·5 g). Most units exhibited depression of twitch tension in the wake of a short high‐frequency tetanus and few of the units showed any significant degree of post‐tetanic twitch potentiation.3. Muscle fibres belonging to single soleus motor units were found to be scattered through territorial volumes occupying a large fraction of the total muscle volume. The available data suggest that different soleus motoneurones may innervate from less than 50 to more than 400 muscle fibres, with an average innervation ratio between 140 and 190 muscle fibres per unit.4. The results were compared with observations on type S motor units in the synergist gastrocnemius, obtained under similar conditions. The evidence suggests that soleus units are not equivalent to the type S units of the mixed gastrocnemius but rather constitute a unique population.
Opponent‐colour cells in different layers of foveal striate cortex
Authors: Gouras Peter 
Published: December 2014

1. The majority of cells in layer 4B have opponent‐colour properties indicating that colour opponency plays an important role in the early stages of visual processing in foveal striate cortex. In contrast to cells in the lateral geniculate nucleus many of these cells receive centre—surround antagonism from the same cone mechanism. Some cells show this spatial antagonism at threshold; others require suprathreshold stimuli for its demonstration.2. The majority of cells in layer 4B do not show orientation or directional selectivity. The proportion of cells with orientation and directional selectivity increases and the proportion of opponent‐colour cells decreases with increasing distance above and below layer 4B so that the majority of cells in the outer layers exhibit considerable spatial selectivity without apparent colour opponency. These changing proportions suggest that the latter cells may be receiving their inputs from different types of opponent‐colour cells making them sensitive to different types of colour contrast but not to colour per se.3. More opponent‐colour cells receive inputs from the red‐ and green‐ sensitive cone mechanisms than from the blue‐sensitive one. This difference is more marked in layer 4B than 3B suggesting that the latter cortical layer may be more involved in colour vision than the former.
Effect of stretching on the elastic characteristics and the contractile component of frog striated muscle
Authors: Cavagna Giovanni A. , Citterio G. 
Published: December 2014

1. The force—velocity relationship and the stress—strain curve of the so‐called series elastic component (s.e.c.) of frog sartorius, semitendinosus and gastrocnemius have been determined during shortening against a given force (isotonic quick‐release) and at high speed (controlled release): (a) from a state of isometric contraction and (b) after stretching of the contracted muscle. In both cases the muscle was released from the same length: this was usually slightly greater than the muscle's resting length.2. The muscle released immediately after being stretched is able to shorten against a constant force, P, equal to or even greater than the isometric force, P0, at the same length. When the force P applied to the muscle is reduced below P0 the velocity of shortening is greater after stretching, and the force—velocity curve is therefore shifted along the velocity axis: the shift is maximal when P is near to P0 and it decreases rapidly with decreasing P.3. The extent of shortening of the s.e.c. required to make the force fall from P0 to zero is 50–100% greater when the muscle is released immediately after stretching than when it is released from a state of isometric contraction. This difference is found by using either the controlled release method or the isotonic quick‐release method.4. If a time interval is left between the end of stretching and the onset of shortening of the contracted muscle (controlled release method), the length change of the s.e.c., for a given fall of the force, is reduced and approaches that taking place when the muscle is released from a state of isometric contraction.5. Curare does not affect the results described above, indicating that these do not depend on modification of the neuromuscular transmission.6. It is concluded that stretching a contracted muscle modifies temporarily: (a) its elastic characteristics, as shown by the greater amount of mechanical energy released for a given fall of the force at the muscle's extremities, and (b) its contractile machinery, as it is suggested by the change of the force—velocity relationship.
Observations on the action of type A botulinum toxin on frog neuromuscular junctions
Authors: Boroff D. A. , del Castillo J. , Evoy W. H. , Steinhardt R. A. 
Published: December 2014

1. Progressive block of neuromuscular transmission in frog sartorius and gastrocnemius preparations by haemagglutinin‐free crystalline Type A botulinum toxin (BTX) was investigated by in vitro application and by injection of the toxin into living animals.2. Neuromuscular block was characterized by (a) decline in amplitude of evoked twitch contractions, (b) decline in amplitudes of end‐plate potentials (e.p.p.s) and (c) changes in statistical characteristics of spontaneous miniature end‐plate potentials (m.e.p.p.s).3. Progress of the block was enhanced by nerve stimulation.4. A decrease in frequency to less than 0·1/sec and decreased average amplitudes of m.e.p.p.s preceded observable impairment of neuromuscular transmission. These changes occurred as early as 3 hr after injection of the toxin into dorsal lymph sacs.5. The amplitude distributions of m.e.p.p.s changed from a normal distribution to one that showed an increased skewness toward smaller amplitudes as the block progressed. These changes were first detectable as early as 75 min following addition of the toxin to the bath.6. At later stages of toxin action, e.p.p.s began to decrease in amplitude and eventually failed altogether. E.p.p.s showed a normal quantal variation at very early stages in the block in Mg2+‐treated preparations. At later stages of the block, it was not possible to test the quantal make‐up of the e.p.p.7. At all stages before complete failure it was possible to obtain normal or greater than normal degrees of synaptic facilitation with paired stimuli to the nerve. This aspect of the coupling of nerve terminal depolarization to transmitter release appears to be relatively unaffected by BTX.8. Electrical depolarization of nerve terminals in partially blocked preparations evoked a maintained discharge of m.e.p.p.s with an amplitude distribution similar to that of the spontaneous m.e.p.p.s; hyperpolarization of the terminals evokes a distinctly larger class of m.e.p.p.s. In fully blocked preparations, depolarization of the terminals does not evoke transmitter release whereas hyperpolarization continues to yield the larger class of m.e.p.p.s.9. It is proposed that the neuromuscular block caused by BTX is due to impairment of a process by which vesicles become charged with transmitter before release.
Spontaneous and neurally evoked release of labelled noradrenaline from rabbit olfactory bulbs in vivo
Authors: Brenells Ann B. 
Published: December 2014

1. Rabbit olfactory bulbs were labelled with either [3H]noradrenaline (NA) and [14C]urea, or [14C]NA and [3H]inulin. The labelled substances released were collected by a modified cortical cup technique and estimated by liquid scintillation spectrometry.2. In many experiments only total radioactivity originating from labelled NA was measured. In such cases the term NA radioactivity is used.3. The spontaneous release of both NA radioactivity and marker radioactivity followed a multiphasic course. After 140 min the rate of efflux of NA radioactivity was significantly slower than that of the labelled marker.4. Stimulation of one medial olfactory tract, one lateral olfactory tract or the surface of one bulb resulted in a selective increase in release of NA radioactivity. The size of the increase was dependent on the intensity, frequency and duration of stimulation.5. There was a characteristic delay in the increased release of NA radioactivity following electrical stimulation. Acute lesioning of the olfactory tracts caudal to the stimulating electrode not only abolished this delay, but also resulted in a larger increase in release following stimulation.6. The radioactivity attributable to unchanged NA was initially 91%, but decreased to 66% after 4½ hr of sample collection. Stimulation did not affect significantly the relative amounts of NA and metabolites released.7. Replacement of calcium in the Krebs solution by magnesium did not affect measurably the spontaneous release of NA radioactivity. However, after 1 hr; stimulation failed to increase the efflux of NA radioactivity.8. It is suggested that the results provide further evidence for a role for NA in synaptic transmission in the olfactory bulbs.
Glucose metabolism and lipid mobilization by adipocytes from mice selected for growth
Authors: Mears G. J. , Mendel V. E. 
Published: December 2014

1. Experiments were conducted to compare the abilities of epididymal adipocytes from mice selected for growth (line G) and from unselected mice (line C) to: (a) incorporate glucose, (b) respond to insulin, and (c) mobilize lipids, and to relate these abilities to the food intake of the donors.2. During the 3‐week pre‐experimental period, line G mice gained body weight 78% faster and ate 35% more food than line C mice; both lines had similar intakes per unit of metabolic body size.3. Line G epididymal fat pads weighed 227% more than those of line C and contained adipocytes which were 38% larger; it was estimated that they contained approximately 65% more cells.4. The basal rate of glucose incorporated into lipids (per unit protein) was highest in line C adipocytes, whereas the basal rates of glucose oxidation to CO2 and the total glucose incorporation (uptake) were similar for adipocytes from both lines.5. Insulin (1000 μu./ml.) caused adipocytes from both lines of mice to increase significantly the incorporation of glucose into CO2 and lipids; the largest elevation occurred when the incubation medium contained 0·1 mg glucose/ml. At this concentration of glucose, the minimum effective dose (MED) of insulin to produce a significant increase in glucose oxidation was similar for both lines. However, the MED of insulin necessary to significantly increase glucose incorporation into lipids and into the sum of CO2 and lipids was highest in the larger, line G adipocytes. Furthermore, the magnitude of the insulin‐induced increase in glucose incorporation was much less for line G than for the line C adipocytes.6. Epinephrine significantly elevated the rates of NEFA and glycerol release and NEFA re‐esterification. The highest rates of NEFA and glycerol release occurred in line C adipocytes, whereas the highest rate of NEFA re‐esterification occurred in the line G adipocytes.7. Glucose had no effect on NEFA release but significantly elevated the rates of glycerol release (in most instances) and NEFA re‐esterification.8. The larger number of adipocytes in line‐G adipose tissue allows for more total incorporation of glucose and a greater overall release of glycerol by this tissue. Consequently, a greater reduction of glucose concentration and a larger elevation of glycerol concentration in the blood can occur; either of these could be the feed‐back signal which resulted in the larger long‐term food intake by the line G mice.
The role of arterial chemoreceptors in the breath‐by‐breath augmentation of inspiratory effort in rabbits during airway occlusion or elastic loading
Authors: Callanan D. , Read D. J. C. 
Published: December 2014

1. The breath‐by‐breath augmentation of inspiratory effort in the five breaths following airway occlusion or elastic loading was assessed in anaesthetized rabbits from changes of airway pressure, diaphragm e.m.g. and lung volume.2. When the airway was occluded in animals breathing air, arterial O2 tension fell by 20 mmHg and CO2 tension rose by 7 mmHg within the time of the first five loaded breaths.3. Inhalation of 100% O2 or carotid denervation markedly reduced the breath‐by‐breath progression but had little or no effect on the responses at the first loaded breath.4. These results indicate that the breath‐by‐breath augmentation of inspiratory effort following addition of a load is mainly due to asphyxial stimulation of the carotid bodies, rather than to the gradual emergence of a powerful load‐compensating reflex originating in the chest‐wall, as postulated by some workers.5. The small residual progression seen in animals breathing 100% O2 or following carotid denervation was not eliminated (a) by combining these procedures or (b) by addition of gas to the lungs to prevent the progressive lung deflation which occurred during airway occlusion.6. Bilateral vagotomy, when combined with carotid denervation, abolished the residual breath‐by‐breath progression of inspiratory effort.
Selective glycogen depletion in skeletal muscle fibres of man following sustained contractions
Authors: Gollnick P. D. , Karlsson J. , Piehl Karin , Saltin B. 
Published: December 2014

1. Six healthy males performed sustained contractions with different tensions related to their maximal voluntary contraction (MVC). The isometric exercise consisted of efforts to extend the knee when flexed at an angle of 90°.2. Biopsy samples were taken from the lateral portion of M. quadriceps femoris before and after different periods (6–45 min) during a series of sustained contractions. Total glycogen content was determined on each muscle sample. In order to evaluate whether the glycogen depletion occurred preferentially in slow twitch (ST) or fast twitch (FT) fibres, serial sections of the muscle samples were stained for myofibrillar ATPase and glycogen (PAS reaction).3. In all experiments a selective glycogen depletion was observed. At low tensions, the ST fibres and at higher tensions the FT fibres became glycogen depleted. The critical tension at which this conversion in glycogen depletion from ST to FT fibres took place was 20% MVC.4. It is concluded that at sustained contractions of less than 20% MVC there is a major reliance upon ST fibres and above that level a primary dependence upon FT fibres. It is further suggested that restriction of blood flow and thus availability of oxygen at forces higher than 20% MVC may be the explanation for the present findings.
Crayfish neuromuscular facilitation activated by constant presynaptic action potentials and depolarizing pulses
Authors: Zucker Robert S. 
Published: December 2014

1. Experiments were conducted to test the hypothesis that facilitation of transmitter release in response to repetitive stimulation of the exciter motor axon to the crayfish claw opener muscle is due to an increase in the amplitude or duration of the action potential in presynaptic terminals. No consistent changes were found in the nerve terminal potential (n.t.p.) recorded extracellularly at synaptic sites on the surface of muscle fibres.2. Apparent changes in n.t.p. are attributed to three causes.(i) Some recordings are shown to be contaminated by non‐specific muscle responses which grow during facilitation.(ii) Some averaged n.t.p.s exhibit opposite changes in amplitude and duration which suggest a change in the synchrony of presynaptic nerve impulses at different frequencies.(iii) Some changes in n.t.p. are blocked by γ‐methyl glutamate, an antagonist of the post‐synaptic receptor, which suggests that these changes are caused by small muscle movements.3. The only change in n.t.p. believed to represent an actual change in the intracellular signal is a reduction in n.t.p. amplitude to the second of two stimuli separated by a brief interval.4. Tetra‐ethyl ammonium ions increase synaptic transmission about 20% and prolong the n.t.p. about 15%. This result suggests that an increase in n.t.p. large enough to increase transmission by the several hundred per cent occurring during facilitation would be detected.5. The nerve terminals are electrically excitable, and most synaptic sites have a diphasic or triphasic n.t.p., which suggests that the motor neurone terminals are actively invaded by nerve impulses.6. When nerve impulses are blocked in tetrodotoxin, depolarization of nerve terminals increases the frequency of miniature excitatory junctional potentials (e.j.p.s), and a phasic e.j.p. can be evoked by large, brief depolarizing pulses. Responses to repetitive or paired depolarizations of constant amplitude and duration exhibit a facilitation similar to that of e.j.p.s evoked by nerve impulses.7. It is concluded that facilitation in the crayfish claw opener is not due to a change in the presynaptic action potential, but is due to some change at a later step in the depolarization—secretion process.
Characteristics of crayfish neuromuscular facilitation and their calcium dependence
Authors: Zucker Robert S. 
Published: December 2014

1. A quantitative description of facilitation in the crayfish claw opener muscle is presented. The facilitation of a test response following one or more conditioning stimuli, and the growth of facilitation during a tetanus, are measured.2. In superficial central fibres facilitation following one or more impulses can be described as the sum of two components which are both maximum at the end of the conditioning train and decline simultaneously and exponentially with different time constants thereafter.3. During a tetanus, facilitation to successive stimuli grows more rapidly than is predicted by assuming that each impulse adds a constant facilitative effect to an accumulating total state of facilitation.4. Sufficiently large values of tetanic facilitation are predicted by a model which assumes that transmitter release is proportional to the nth power of a substance or factor accumulating in nerve terminals. But no single value of n predicts the correct rise of facilitation in a tetanus and the time course of its subsequent decline from the facilitation following a single spike.5. A model which assumes that the facilitative effects of successive spikes multiply in a tetanus predicts responses that are larger than those observed.6. The effects of varying the calcium concentration ([Ca2+]) on transmitter release and facilitation were studied. When a magnesium‐EDTA buffering system is used to vary [Ca2+], transmitter release is found to be nearly linearly related to [Ca2+] in the range 0·1–13·5 m
M.7. The magnitude and time course of facilitation during and following a tetanus are unaffected by varying [Ca2+] between 1·0 and 40 m
M.8. The relation between ‘steady‐state’ facilitation and stimulus frequency is also unaffected by changing [Ca2+], except that in high [Ca2+] transmitter release appears to saturate at high frequencies (above 30 Hz).9. The results are discussed in terms of the ‘calcium accumulation’ hypothesis of facilitation. The findings in crayfish appear to be qualitatively consistent with this hypothesis if certain modifications are made in the hypothesis.
Ion fluxes across the pulmonary epithelium and the secretion of lung liquid in the foetal lamb
Authors: Olver R. E. , Strang L. B. 
Published: December 2014

1. Experiments were done on exteriorized foetal lambs of 123–144 days gestation to measure bidirectional ion fluxes through the pulmonary epithelium and to compare them with those predicted from the sum of the measured forces determining passive flux according to the Ussing flux‐ratio equation. Fluxes of Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, Cl−, Br− and I− were measured and permeability constants obtained by following concentrations of their labelled isotopes in lung liquid and plasma after injection into either. Activity ratios were obtained from chemical measurements or tracer distributions, electrical potential differences by placing KCl‐agar bridges, connected to calomel half‐cells, in blood and lung liquid. Lung liquid volume and secretion rate were measured by adding an impermeant tracer (inulin or [125I]albumin) to lung liquid.2. The permeability sequence of the pulmonary epithelium for alkali metals was, Na+ > K+ > Rb+ > Li+ > Cs+ and that for halides I− ≈ Br− > Cl−. Permeabilities to alkaline earths were lower than for the other ions, no definite sequence being established.3. There was an electrical potential difference of −1 to −10 mV (mean −4·3 mV) between lung liquid and plasma (lung liquid negative). Plasma/lung liquid chemical activity ratios were less than unity for the halides (Cl−, Br−, I−), and for K+ and Rb+, whereas the ratio of one‐way fluxes (plasma → lung liquid)/(lung liquid → plasma) was in each case greater than unity. From the difference between the measured flux ratios and those predicted from the forces determining passive flux, it was concluded that the halides, K+ and Rb+ were actively transported from plasma to lung liquid, Cl− being quantitatively the most important. Na+ and Ca2+ appeared to move passively down a gradient of electrochemical potential.4. When alveolar liquid [HCO3−] was artificially raised, a net flux of HCO3− from lung liquid against a gradient of electrochemical activity was observed, suggesting active transport of that ion out of lung liquid.5. The addition of KCN to lung liquid stopped the secretion of liquid and absorption took place.
Further studies on the role of prostaglandin in fever
Authors: Dey P. K. , Feldberg W. , Gupta K. P. , Milton A. S. , Wendlandt Sabine 
Published: December 2014

1. Experiments were carried out in unanaesthetized cats to find out if a prostaglandin is the mediator (a) for the long lasting fever which often follows injections of phsyiological salt solutions into the cerebral ventricles or into the cisterna magna, as well as their perfusions through the cerebral ventricles, and (b) for the sodium fever which occurs during a perfusion of the cerebral ventricles with calcium‐free artificial c.s.f. A fever mediated by prostaglandin should be accompanied by an increase of prostaglandin activity in cisternal c.s.f., and be abolished or prevented by antipyretics like paracetamol or indomethacin which inhibit prostaglandin synthesis. Both criteria were applied.2. The fever which follows injections or perfusions of physiological salt solutions appears to be mediated by a prostaglandin of the E series, probably E2 (PGE2) because it was accompanied by increased prostaglandin E‐like activity in the c.s.f. and abolished by paracetamol and indomethacin. During the first few days after pre‐treatment of the cats with intramuscular chloramphenicol the injections were rarely followed by fever.3. The fever which occurs during a perfusion with calcium‐free artificial c.s.f. appears not to be mediated by prostaglandin, because it was not associated with increased prostaglandin activity in the cisternal effluent, and not prevented by paracetamol or indomethacin, although these antipyretics usually attenuated the fever.4. A perfusion of the cerebral ventricles with artificial c.s.f. containing calcium in an abnormally high concentration (6·25 m
M) brought down fever produced by PGE1, or PGE2, or bacterial pyrogen.