bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cardiorespiratory and metabolic costs of continuous and intermittent exercise in man
Authors: Edwards R. H. T. , Ekelund L.-G. , Harris R. C. , Hesser C. M. , Hultman E. , Melcher A. , Wigertz O. 
Published: December 2014

1. Cardiorespiratory and metabolic responses to paired patterns of continuous and intermittent exercise with the same average power output were studied in eight men. Heart rate, ventilation and pulmonary gas exchange were measured during the different patterns of exercise performed on a cycle ergometer. The recovery oxygen volume was measured over 30 min of loadless pedalling. Needle biopsy samples of the vastus lateralis muscle were taken before, during and after completion of the exercise for measurement of muscle metabolites.2. Heart rate, ventilation, oxygen intake, respiratory exchange ratio, and blood lactate concentration were generally higher with intermittent compared with continuous exercise as were the accumulated totals for heart beats, ventilation and oxygen intake. Muscle biopsy samples tended to have higher lactate and lower phosphocreatine contents in intermittent exercise. The lactate concentration in muscle and blood water was the same during loadless pedalling before exercise but was significantly higher in muscle than blood during exercise. This concentration gradient was larger in intermittent than in continuous exercise.3. Work efficiency, calculated from the total oxygen cost of work in excess of a loadless pedalling control, was significantly lower in intermittent exercise. The explanation is thought to be connected with the observation that when the work was performed at a high rate in short bursts a large part of the oxidative recovery took place after the contraction during the rest periods, whereas in the low intensity continuous exercise the oxygen was mainly utilized while the work was being performed. This indicates that for part of the time in the intermittent exercise the muscle was working under anaerobic conditions. Although the possibility exists that the efficiency of resynthesis of phosphagen may be reduced in this form of activity, it is more likely that the result described is due to the greater amount of lactate formed in the intermittent exercise.
Physiological types and histochemical profiles in motor units of the cat gastrocnemius
Authors: Burke R. E. , Levine D. N. , Tsairis P. , Zajac F. E. 
Published: December 2014

1. A variety of physiological properties of single motor units have been studied in the gastrocnemius muscle (primarily in the medial head) of pentobarbitone‐anaesthetized cats. Intracellular stimulation of individual motoneurones ensured functional isolation of the muscle units innervated by them.2. A system for muscle unit classification was developed using a combination of two physiological properties. Almost all of the units studied could be classified into one of three major types, including two groups with relatively short twitch contraction times (types FF and FR, which were differentiable from one another on the basis of sensitivity to fatigue) and one group with relatively long contraction times (type S, which were extremely resistant to fatigue and were differentiable from FF and FR units on the basis of the shape of unfused tetani). Post‐tetanic potentiation of twitch responses was observed in all three muscle unit types. The distributions of axonal conduction velocities for motoneurones innervating FF and FR muscle units were essentially the same, while conduction velocities for motoneurones innervating type S units were, in general, slower.3. Histochemical profiles of muscle units representative of each of the physiological classes present in the gastrocnemius pool were determined using a method of glycogen depletion for muscle unit identification. Each of the physiological categories of muscle units exhibited a corresponding unique set of muscle fibre staining reactions, or histochemical profile. Within each physiological type, all of the units examined had the same histochemical profile. The results generally support the hypothesis that the histochemical characteristics of muscle fibres are meaningfully related to the physiological properties of the same fibres. However, certain limitations in the detailed application of the hypothesis were also apparent.4. Systematic assessment of the histochemical profiles of relatively large numbers of fibres belonging to single muscle units provided strong support for the hypothesis that all of the muscle fibres innervated by a single α‐motoneurone are histochemically identical.
Depolarization of sensory nerve endings and impulse initiation in common carotid baroreceptors
Authors: Matsuura S. 
Published: December 2014

1. Electrical events in the peripheral nerve terminals of baroreceptors were investigated following isolation and identification of receptive fields innervated by single baroreceptor fibres. A slow potential change, that is a local depolarization which had the characteristics of a generator (receptor) potential, was recorded from the common carotid baroreceptor fibres at a point close to the sensory terminals.2. The slow potential increased in amplitude with increasing stimulus strength and its time course increased with increasing duration of the mechanical stimulus. Action potentials were initiated from the slow potential when the applied mechanical stimulus was suprathreshold.3. The slow potentials evoked by a train of subthreshold stimuli summed to evoke action potentials.4. When a high‐frequency train of suprathreshold stimuli was applied to the baroreceptors, the slow potential following a preceding one from which an action potential was initiated failed to fire the nerve fibre.5. When the sodium content of the Ringer—Locke solution was decreased, the slow potential remained after blockage of the action potential.6. The slow potential remained after abolishing the spike potential by application of tetrodotoxin.
Ionic analysis of photoreceptor membrane currents
Authors: Zuckerman Ralph 
Published: December 2014

1. Membrane current was derived from simultaneous measurements of interstitial ‘dark’ voltages and conductivities along the radial axis of frog photoreceptor cells. Membrane current was subsequently resolved into its component ionic currents or fluxes by means of ionic substitution and by the use of inhibitors of active transport.2. The plasma membrane of the frog rod outer segment was found to be permeable to Na+ and Cl−, with a ratio of Na+ to K+ permeabilities higher than that found in most neuronal cells. A net inward flux of 1·5 × 108 Na+/sec.rod flows across the outer segment plasma membrane in the dark.3. The proximal portion of the rod receptor, extending from the proximal region of the inner segment to the synaptic terminal, is mainly permeable to K+, although some degree of Na+ permeability is also presumed.4. A hyperpolarizing electrogenic Na pump was localized to the base of the outer segment and inner segment of the cell. The pump transfers at least 108 charges/sec out of the cell at this level, the pump current dividing and re‐entering the cell at both the outer segment and proximal portion of the photoreceptor including the synaptic terminal.5. These findings have been incorporated into an ionic model of the photoreceptor, and its implications for cellular functioning considered.
Net placental transfer of free amino acids against varying concentrations
Authors: Hill Penny M. M. , Young Maureen 
Published: December 2014

1. The patterns of the free plasma amino acids in the pregnant guinea‐pig and her foetuses, near term, are described. The concentration of each amino acid was higher in the foetal plasma than in the maternal. The foetal:maternal gradients (F:M) varied for each amino acid; the straight chain amino acids had the highest F:M ratios.2. Net transfer of endogenous plasma amino acids, from the maternal circulation across the placental membrane, was studied. The foetus was removed and the foetal placenta perfused in situ via the umbilical arteries, with an artificial fluid containing varying concentrations of amino acids.3. All the amino acids, both essential and non‐essential, could be transferred from the maternal to the foetal circulation against the F:M gradients. With ‘closed circuit’ perfusion, this transport increased the concentration of total amino N in the perfusate until it was twice that of the normal F:M gradient of 5. The concentrations of the individual amino acids was increased to 1·7–4·2 times those normally present in foetal plasma, and the final values reached were similar to the concentrations of free amino acid found in placental tissue.4. The umbilical vein—artery differences were small, with the placenta perfused ‘open circuit’ in the steady state, using physiological flow rates and amino acid concentrations. The average net placental transfer of amino N found was 1·14 m‐mole min−1. This is about 60% of the calculated net rate of accumulation of N by the 60 g guinea‐pig foetus.5. The influence of foetal placental perfusion concentration on transfer was small but significant. In the steady state, the transfer of amino N, and each individual amino acid, was found to be inversely proportional to the concentrations in the perfusate when the placenta was perfused ‘open circuit’. The slopes of the regression of transfer on concentration had an average value of 0·13 n‐mole min−1 g−1 per μmole. No significant difference in the slopes was found between the three amino acid transport groups.6. Net transfer was independent of perfusate flow, within the physiological range, which suggests a secretory process across the membrane from maternal to foetal circulation.
Influence of eye movements on geniculo‐striate excitability in the cat
Authors: Adey W. Ross , Noda Hiroharu 
Published: December 2014

1. The excitability of the geniculo‐striate pathway during a saccadic eye movement was studied in alert cats with chronically implanted electrodes. Excitability was assessed by the amplitude of post‐synaptic components of field responses in both lateral geniculate nucleus and visual cortex to electrical stimulation of the optic chiasm. Modifications in amplitude were evaluated during the period following eye movements, by triggering a stimulator from potential shifts in the electrooculograms and altering delays in the stimulus pulse.2. The post‐synaptic component of the geniculate response was markedly depressed for about 150 msec, reaching a trough at approximately 100 msec after the initiation of an eye movement. This effect was dependent on the visual environment and was not observed in complete darkness. A similar depression occurred when the visual field was abruptly moved by retinal impulses generated by a quick displacement of the image of the visual world associated with an eye movement. The depression reflected a reduction of cellular discharge to the orthodromic volley and hence a suppression of the transmission of visual information through the lateral geniculate nucleus. This may be a mechanism for saccadic suppression.3. The post‐synaptic components of the cortical response were enhanced for about 200 msec, reaching a peak at approximately 150 msec after the initiation of an eye movement. Although this facilitation occurred also in complete darkness, it did not occur when the visual field was abruptly shifted while the eyes were stationary. The fact that it occurred with eye movements and exclusively in the post‐synaptic components suggests that it was caused by signals from a system closely related to eye movements. This may be a manifestation of the corollary mechanism.
Light‐induced resistance changes in retinal rods and cones of the tiger Salamander
Authors: Lasansky A. , Marchiafava P. L. 
Published: December 2014

1. The electrical properties of retinal rods and cones of the larval tiger salamander were investigated with intracellular electrodes, and the cells identified by means of dye injections.2. Both types of photoreceptors are hyperpolarized by illumination. Following stimulation with brief flashes of dim light, rod responses show a slower time course than cone responses; with bright flashes, rod responses can be recognized because of their long recovery time.3. Values of input resistance were derived from the voltage displacement induced by constant current pulses in darkness or at the peak of the photoresponse. The input resistance following illumination was also calculated from the effect of steady polarizing currents on the amplitude of the photoresponse.4. In darkness, the input resistance of the rod cells is time‐ and voltage‐dependent, but the voltage—current relations of most cells have a linear region which includes the physiological limits of membrane potential. At the peak of the photoresponse, the input resistance (slope of the linear region of the v—i relations) is decreased.5. Cone cells show approximately linear v—i relations. As reported by previous authors, illumination increases the input resistance.6. These results support the current view that the cone photoresponse is the consequence of a reduction in the permeability of channels which in darkness shunt the membrane. In rods, however, it appears that the main effect of illumination is to increase the permeability of the membrane to ions for which the equilibrium potential is more negative than the membrane potential in darkness.
Stochastic properties of spontaneous transmitter release at the crayfish neuromuscular junction
Authors: Cohen Ira , Kita Hiroshi , Van Der Kloot William 
Published: December 2014

1. Miniature excitatory junctional potentials (min.e.j.p.s) were recorded with an intracellular electrode from the adductor muscle of the dactyl of the first or second walking leg of the crayfish, Orconectes virilis.2. The intervals between the min.e.j.p.s were compared to the exponential prediction by five goodness of fit tests. The results indicate that the intervals are not exponentially distributed.3. The autocorrelogram of intervals shows that the intervals are unlikely to be independent.4. A stochastic analysis that includes the power spectrum of intervals, the variance—time curve, and the ln‐survivor curve suggest that there is a clustering of min.e.j.p.s. The results are similar to those on the frog neuromuscular junction.5. An autocorrelogram of the min.e.j.p. amplitudes suggests that sizes are not independently distributed.6. These results, which are similar to those previously reported from the frog neuromuscular junction, support the use of the branching Poisson process as a theoretical model for the stochastic properties of spontaneous quantal release of transmitter.
The kinetics of the reaction of carbon monoxide with fully oxygenated haemoglobin in solution and erythrocytes
Authors: Sirs John A. 
Published: December 2014

1. Spectrophotometric measurements, using a rapid mixing and stopped flow technique, have been made of the rate at which CO displaces O2 from its combination with haemoglobin.2. In haemoglobin solutions, buffered at pH 7·2 and 9·1, the reaction proceeds by a unimolecular dissociation as proposed by Gibson & Roughton (1955). In a Ringer—Locke solution, equilibrated with a PCO2 of 3 cmHg and at pH 7·4, the reaction of HbO2 with CO is a two‐stage process, with a transition from one form of Hb4O6 to another.3. An investigation of the reaction between CO and HbO2 in erythrocytes, suspended in Ringer—Locke solution, indicates that the rate is determined by the chemical reaction and this also is a two‐stage process.4. The transition is probably associated with the reaction of CO2 with Hb4O6, following the dissociation from fully saturated oxyhaemoglobin of an oxygen molecule. It alters the relative velocity constants of the reactions of O2 and CO with Hb4O6 by 100:1.5. The implications of these proposals of the equilibria of haemoglobin with CO and O2 are discussed. The difference between the sigmoid equilibria curves at high HbO2 and HbCO values can be explained as due to the different reaction pathways.
The influence of the splanchnic nerves on the external secretion, blood flow and electrical conductance of the cat pancreas
Authors: Barlow T. E. , Greenwell J. R. , Harper A. A. , Scratcherd T. 
Published: December 2014

1. Electrical stimulation of the cut peripheral end of the splanchnic nerves results in a biphasic change in electrical conductance measured across the tail of the pancreas. A phase of decreased conductance is followed by a more prolonged phase of increased conductance.2. Simultaneous measurements of pancreatic blood flow indicate that the phase of decreased conductance occurs as a result of vasoconstriction, whilst the phase of increased conductance is due to vasodilatation.3. The initial phase of decreased conductance and vasoconstriction is abolished by α‐receptor blocking agents such as phenoxybenzamine and the phase of increased conductance blocked by β‐receptor blocking agents such as pronethalol.4. Short periods of electrical stimulation applied to the splanchnic nerves result in a secretion of amylase and a reduction in the volume rate of secretion.5. When the vasoconstrictor response was abolished by phenoxybenzamine, nerve stimulation still reduced the rate of secretion, suggesting that the inhibitory effect is in part due to a direct action of the secretory cells.6. After bretylium tosylate, splanchnic nerve stimulation no longer produced vasomotor changes in the pancreas and the inhibitory effect on the volume response was converted to one of augmentation, but the secretion of enzymes was unaffected.7. The secretion of amylase on splanchnic stimulation was abolished by intravenous injection of atropine, suggesting that a cholinergic mechanism is involved.8. Noradrenaline did not mobilize pancreatic enzymes.
Lipogenesis and insulin sensitivity of single fat cells*
Authors: Gliemann J. , Vinten J. , Vølund Aa. 
Published: December 2014

1. A method for measuring the lipogenesis from [14C]glucose by single fat cells is described: (i) after incubation with ‘carrier‐free’ [U‐14C]glucose (0·55 μ‐mole/ml.), collagenase‐isolated fat cells were fixed with osmium tetroxide; (ii) similarly incubated pieces of epididymal fat pads were treated with osmium tetroxide for 90 sec, whereby only the superficial cells are fixed, and the tissue was then disintegrated by shaking with collagenase. The osmium‐fixed free cells were washed, sucked into a micropipette, measured under a microscope and assayed individually for 14C‐activity.2. There was a quantitative recovery of 14C‐lipid activity from osmium‐fixed single cells.3. Both collagenase‐isolated cells and in situ fixed surface cells were normally distributed with respect to diameters (for both cell groups from ad lib. fed rats of ca. 110 g; mean diameter, about 55 μm;
S.D. about 7 μm).4. Frequency distribution curves (number of fat cells versus 14C‐lipogenesis per cell) were asymmetric and very broad (coefficient of variation about 50%) for collagenase‐isolated cells incubated with insulin (103 μ‐u./ml.). Frequency distribution curves for surface cells obtained from similarly incubated pieces of epididymal fat pads showed a coefficient of variation of the same magnitude, whereas the mean lipogenesis of these cells was only about one third of that of the isolated cells.5. Collagenase‐isolated cells incubated in the presence of insulin (103 μ‐u./ml.) showed a weak but highly significant positive correlation between fat cell diameter and 14C‐lipogenesis (eight rats, r about 0·5 and P < 0·001 for each rat). Analysis of the relationship: lipogenesis = k × diameter to the exponent of β showed that the estimates of β varied significantly from rat to rat (range: 1·3–2·9). Similar correlations between cell size and lipogenesis were found both for cells incubated with insulin in various submaximal concentrations and for cells incubated without insulin.6. Small and large cells from the same rat were equally sensitive to insulin.7. Statistical analysis of frequency distribution curves (number of cells versus 14C‐lipogenesis per unit surface area) representing cells from the same rat incubated with insulin 0, 2·5, 5, 10, and 103 μ‐u./ml., respectively, suggests that insulin exerts a graded influence on the lipogenesis of each fat cell.
Functional organization of a visual area in the posterior bank of the superior temporal sulcus of the rhesus monkey
Authors: Zeki S. M. 
Published: December 2014

1. Anatomical studies have shown the cortex of the posterior bank of the superior temporal sulcus to receive a projection from visual cortical areas, including areas 17, 18 and 19. In this paper the response of single neurones in this area to simple visual stimulation is reported. Ten monkeys were studied.2. A clear but relatively crude topographic representation of the visual field was found. There was a large variation in the size of the receptive fields of individual cells, even in a single penetration. Some cells, with the central parts of their receptive fields located from between 1 and 5° from the centre of gaze had receptive fields averaging about 10° × 10° or even larger. Other cells with central receptive fields had much smaller field sizes.3. Two main types of neurones were encountered, with subdivisions within each type. The first type responded to movement irrespective of form. These could be subdivided into neurones which responded to movement in any direction within the receptive field and neurones which responded to movement in one direction only (directionally selective neurones). Another type of cell was responsive to both contour and movement, much like the complex and lower order hypercomplex cells. Almost all such neurones were directionally selective.4. In oblique penetrations through this cortical region, there tended frequently to be an orderly shift in preferred directions of motion, thus suggesting the possibility of a columnar organization for movement.5. Combined anatomical (degeneration) and electrophysiological experiments showed that these types of neurones are found in those regions of the posterior bank of the superior temporal sulcus receiving a direct projection from area 17.
Sensitization and centre‐surround antagonism in Necturus retina
Authors: Burkhardt Dwight A. 
Published: December 2014

1. The impulse discharge of ganglion cells and the proximal negative response were recorded with extracellular micro‐electrodes in Necturus retina and spatial influences of background illumination studied.2. When a steady background of constant illuminance was extended in diameter from 0·25 to 1 mm, the response to a small concentrically placed test flash was enhanced (sensitization).3. This sensitization was tonic, showed marked spatial summation, was also found by surrounding a central background with an annulus, and when quantified by threshold measurements, closely resembled the sensitization effect found psychophysically in human vision.4. Sensitization was prominent in intracellular recordings from bipolar cells and usually apparent in horizontal cells. In bipolar cells, a background change which produced sensitization evoked a large but predominantly transient potential whose polarity was opposite to that evoked by a central flash.5. The tonicity and large spatial extent of the sensitization effect strongly suggest that it is mediated by horizontal cells. They might do this by either acting upon receptors, bipolar cells, or both.