bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transfer of alanine isomers by rat small intestine
Authors: de la Noüe J. , Newey H. , Smyth D. H. 
Published: December 2014

1. A study was made of the transfer of
L‐alanine,
D‐alanine and β‐alanine by sacs of everted small intestine of the rat.2.
D‐Alanine and β‐alanine are transported against a concentration gradient and in this respect resemble
L‐alanine.3. Transfer of all three isomers was stimulated in presence of glucose, but stimulation was much greater with
D‐alanine and β‐alanine.4. Transfer of all three isomers was inhibited by galactose.5. The effect of hexoses on amino acid transfer was relatively independent of the effect on fluid transfer.6.
L‐Methionine inhibited transfer of the three isomers in descending order,
L‐alanine,
D‐alanine and β‐alanine, while the magnitude of sarcosine inhibition was in the reverse order.7. At the concentration used (1 m
M),
L‐alanine was transferred mostly by the methionine carrier, and β‐alanine mostly by the sarcosine carrier.
D‐Alanine occupied an intermediate position.
Receptive fields of cones in the retina of the turtle
Authors: Baylor D. A. , Fuortes M. G. F. , O'Bryan P. M. 
Published: December 2014

1. Intracellular recordings have been made of the responses to light of single cones in the retina of the turtle. The shape of the hyperpolarizing response to a flash depends on the pattern of retinal illumination as well as the stimulus intensity.2. Although changes in the stimulus pattern can produce changes in the effective stimulus intensity, the responses to certain patterns cannot be matched by any adjustment of stimulus intensity.3. The initial portion of responses to large or small stimulating spots is proportional to light intensity; this allows comparison of responses when the amount of light on a cone is kept constant but the light on surrounding cones is changed. For equal light intensity on the cone, the response to a spot 2 or 4 μ in radius is smaller than that to a spot 70 μ in radius.4. Responses to spots 70 and 600 μ in radius coincide over their rising phases and peaks without any adjustment of stimulus intensity. The responses to the larger spot, however, contain a delayed depolarization not present with the smaller spot.5. During steady illumination of a cone with a small central spot, the response to transient illumination superimposed on the same area is greatly reduced. Illumination of cones in the near surround, however, produces a hyperpolarizing response, and illumination of cones in the more distant surround generates a delayed depolarization.6. The results described above suggested that synaptic signals might impinge on cones. This possibility was tested by electrically polarizing one retinal cell while recording from another.7. Currents passed through a cone within 40 μ of another cone can change the membrane potential of the latter. Not all cones within this distance show the interaction, however, and it has never been detected at distances greater than 50 μ.8. Hyperpolarization of a horizontal cell with applied current can produce a depolarization of a cone in the vicinity. During this depolarization, the response of the cone to a flash is reduced in size and altered in shape.9. It is concluded that the response of a cone to light may be modified by synaptic mechanisms which are activated by peripheral illumination.
Cardiovascular reflex responses to cutaneous and visceral stimuli in spinal man
Authors: Corbett J. L. , Frankel H. L. , Harris P. J. 
Published: December 2014

1. A study has been made of the effects of pinprick and a cold pack applied to the skin above and below the level of denervation, deep inspiration, squeezing the chest, and bladder percussion in non‐bedridden patients with chronic, closed, complete, localized transection of the cervical spinal cord. Variables studied were blood pressure, heart rate, calf blood flow, hand blood flow and occluded vein pressure in the hand and foot.2. Cutaneous stimuli above the lesion, mental arithmetic and noise from gunshot produced no response.3. Pinprick and cold applied below the lesion usually produced an increase in mean arterial pressure, little change in pulse pressure or heart rate, clear decreases in calf and hand blood flow, and occasional venoconstriction.4. Deep inspiration produced an initial rise in blood pressure and heart rate which was sometimes followed by a decrease in one or both. Squeezing the chest usually produced an increase in blood pressure and a decrease in heart rate. Both stimuli caused decreases in calf and hand blood flow and venoconstriction, the latter being more common after squeezing the chest.5. Bladder percussion produced contraction of the wall of the bladder and this was regularly associated with increased arterial mean and pulse pressures, a decreased heart rate and calf and hand blood flow, and venoconstriction. The responses occurred whether or not the bladder was full and whether or not a rise of intravesical pressure occurred.
The reflex nature of the pressor response to muscular exercise
Authors: Coote J. H. , Hilton S. M. , Perez‐Gonzalez J. F. 
Published: December 2014

1. In anaesthetized cats tetanic contraction of the hind‐limb muscles, elicited by stimulating the ventral roots L6—S1, caused a rise of arterial blood pressure, usually accompanied by small increases in heart rate and pulmonary ventilation: in decerebrate cats, all components of the response were much increased.2. With tetani of different strengths, obtained by stimulating with different intensities at the same frequency, the pressor response increased with increasing tension.3. When muscle contraction had been abolished by gallamine, or when dorsal roots L6—S1 had been sectioned, ventral root stimulation no longer caused a pressor response. The response is therefore a reflex, initiated in the exercising limb.4. The pressor response was not affected by section of all articular nerves to knee and ankle joints, or by section of the vagi. The stimulus therefore originates in the contracting muscles alone.5. The pressor response is potentiated by occluding the circulation through the working muscles. Reasons are discussed for concluding that the stimulus is chemical rather than mechanical, and that the ‘metabolic receptors’ for this exercise reflex are the free endings of group III and IV sensory nerve fibres located around the blood vessels.
The flow of juice from the pancreatic gland of the cat in response to vagal stimulation
Authors: Lenninger Sven , Ohlin P. 
Published: December 2014

1. Stimulation of the vagus nerve of the cat causes a pancreatic secretion in most animals. The volume of the secretion is about 20% of the maximal response of the gland to exogenous secretin.2. Maximal secretory effect of vagal stimulation is obtained with frequencies between 8 and 15 c/s.3. The effect of the nerve stimulation is direct on the pancreas and not mediated by gastro‐intestinal hormones.4. The secretion of water in response to vagal stimulation is not depressed by anticholinergic agents in doses which profoundly depress the secretion of enzymes.5. The secretion of water in response to submaximal vagal stimulation is not increased by eserinization of the gland, whereas the output of proteins is strongly augmented by this procedure.6. The significance of the finding that the watery and enzymic secretion can be dissociated pharmacologically is discussed.
Reflex effects on the heart of stimulating left atrial receptors
Authors: Furnival C. M. , Linden R. J. , Snow H. M. 
Published: December 2014

1. Stimulation of left atrial receptors, by distension of the pulmonary vein/left atrial junctions, is known to cause a reflex increase in heart rate; the efferent pathway is known to be solely in the sympathetic nerves.2. In expectation of a concomitant positive inotropic response the effect of stimulating the left atrial receptors on the inotropic state of the left ventricle was studied, using as a known sensitive index of inotropic changes the maximal rate of rise of pressure in the left ventricle (dP/dt max).3. Stimulation of left atrial receptors resulted in an increase in heart rate but there were no significant concomitant changes in dP/dt max.4. It is concluded that activity in this discrete efferent pathway does not include an inotropic effect on the left ventricle and therefore the reflex involves only those sympathetic nerves which innervate the sinu‐atrial node.5. The possible function of atrial receptors in the regulation of heart volumes is discussed.
Responses to visual contours: spatio‐temporal aspects of excitation in the receptive fields of simple striate neurones
Authors: Bishop P. O. , Coombs J. S. , Henry G. H. 
Published: December 2014

1. The properties of the receptive fields of simple cells in the cat striate cortex have been studied by preparing average response histograms both to moving slits of light of different width and to single light‐dark edges or contours.2. The movement of a narrow (< 0·3°) slit across the receptive field gives rise to average response histograms that are either unimodal, bimodal or multimodal. A slit of light has leading (light) and trailing (dark) edges. By increasing the width of the slit it was shown that a discharge peak in the histogram coincides with the passage of one or other of the two edges over a particular region (discharge centre) in the receptive field. Each edge has its own discharge centre which is fired when the edge has the correct orientation and direction of movement.3. The discharge centres in forty‐three simple cell receptive fields were located by using one or more of the following stimuli for each cell:(i) slits of different width;(ii) single light and dark edges;(iii) a wide (3°) slit moved over a range of different velocities.The same locations were obtained when all three procedures were used on the same cell.4. Most cells (79%) discharged to both edges though not necessarily in the same direction of movement. The majority (72%) fired in only one direction and most commonly (51%) the cells responded to both edges in this one direction. In only 16% of cells did both types of edge excite in both directions of movement. When the one type of edge, light or dark, was considered, 84% of the cells were direction selective and, for these cells, the other edge fired only in the same direction (51%), in both directions (7%), only in the opposite direction (5%) or not at all (21%).5. Cells responding in one direction with a unimodal average response histogram may be responding to both edges, the two responses being concealed in the one discharge peak. The two discharge centres are then either nearly coincident or, more usually, slightly offset with respect to one another. Most commonly the dark edge centre is slightly in advance of the light edge centre.6. The discharge peaks in the bimodal and multimodal types come from discharge centres that are spatially separate, each centre firing to only one type of edge. In the case of the bimodal type the light edge centre always lies ahead of the dark edge centre.7. When a cell responds to a single edge in both directions of movement, the type of contrast effective in one direction is always the reverse of that in the other. When the cell responded in both directions, whether to one or both edges, most commonly a light edge discharge centre in one direction occupied approximately the same location in space as the dark edge centre in the reverse direction and vice versa for the other edge.8. Temporal aspects of the discharge of simple cells have been examined by recording the responses to moving slits and single edges over a wide range of velocities.
Effect of temperature on muscle energy metabolism and endurance during successive isometric contractions, sustained to fatigue, of the quadriceps muscle in man
Authors: Edwards R. H. T. , Harris R. C. , Hultman E. , Kaijser L. , Koh D. , Nordesjö L-O. 
Published: December 2014

1. The effects of altered tissue temperature on muscle metabolism during successive isometric contractions, sustained to fatigue, have been studied in the quadriceps muscle of man by combining biochemical analyses of metabolites in needle biopsy samples with measurements of endurance time with a force of 2/3 maximum voluntary contraction. Fatigue and recovery were observed repeatedly in a series of seven contractions at intervals of 20 sec, following immersion of the test leg in water at 12, 26 or 44° C for 45 min. Muscle temperatures corresponding to these water temperatures were 22·5, 32·6 and 38·6° C respectively.2. Increased levels of several glycolytic intermediates at rest in the heated muscle suggested an increased rate of glycolysis. ATP and phosphoryl creatine were lower at the end of the first contraction and the calculated rate of ATP utilization (including the contribution from anaerobic glycolysis) was highest in the heated nuscle.3. Significantly shorter endurance times were found for the heated muscle. These could not be attributed to depletion of local energy resources in muscle. Fatigue may be due to a reduction in the rate of regeneration of ATP from anaerobic glycolysis below that needed to maintain the contraction force. Lower values for the ratio of fructose 1,6‐diphosphate: fructose 6‐phosphate at the end of contractions, particularly at the highest temperature, are compatible with the hypothesis that there is partial inhibition of the rate controlling enzyme phosphofructokinase, possibly due to the accumulation of hydrogen ions in muscle.
On the regulation of depth and rate of breathing
Authors: Clark F. J. , von Euler C. 
Published: December 2014

1. The relationships between the depth of a breath and the durations of the inspiratory and expiratory phases have been studied in cat and in man during rebreathing, and in cat using artificial inflations of different magnitudes and timings.2. In the cat, the apparent volume threshold for termination of inspiration (Hering—Breuer threshold) decreased with time from the onset of the inspiratory phase.3. Both in rebreathing experiments and with artificially imposed inflations in the cat, the inspiratory duration TI was dependent upon tidal volume VT, and this dependence could be expressed by a hyperbolic relationship of the form (VT‐V0) TI = C where V0 and C are constants.4. The time course of this ‘Hering—Breuer’ threshold was dependent on intact vagus nerves. After vagotomy the inspiratory duration remained essentially constant with changes in tidal volume produced either by artificial inflation or by the increased respiratory drive due to accumulation of CO2 during rebreathing.5. In man during rebreathing, the relation between volume and inspiratory duration typically showed two different characteristics. 1, at tidal volumes up to 1·5–2 times eupnoeic values, inspiratory duration did not change as tidal volume increased in response to increased PCO2. This range of operation has been designated range 1. 2, as tidal volume increased above this range 1 a second range designated range 2 was observed where inspiratory duration was volume dependent in the same manner as in the cat.6. In cat under pentobarbitone anaesthesia, a range 1 operation was not seen except after vagotomy. However, under urethane anaesthesia a range 1 plus a range 2 operation could be seen.7. The differences between cat and man appeared to be largely quantitative rather than qualitative.8. In both cat and man, expiratory duration was dependent on inspiratory duration, usually with a linear relationship.9. The experimental results were assembled in the form of an inspiratory characteristic and a timing relationship that serve as a model of the respiratory mechanisms controlling the depth and rate of breathing. The model predicts that the depth and duration of a breath are related in a definite manner fixed by the system characteristics and that ventilation is adjusted by setting the appropriate operating point on these characteristics. The operating point is determined primarily by how quickly lung volume increases, i.e. the rate of increase of inspiratory motor activity.
Voltage—clamp analysis of the early current in frog skeletal muscle fibre using the double sucrose‐gap method
Authors: Ildefonse Michèle , Rougier Oger 
Published: December 2014

1. The early membrane currents in skeletal muscle fibres have been studied with the double sucrose‐gap method, according to the experimental procedure used for the study of the giant axon of the squid.2. The earliest observable current is a capacitative transient. An equivalent circuit with two capacity‐resistance systems can account for such a current. The components of the electrical circuit are estimated from the records.3. The capacitative transient current is followed by an initial current, the time and voltage dependence of which are analogous to those of nerve fibres. During this phase of current, the membrane behaves like a sodium electrode for modifications of the external sodium concentration.4. Using tetrodotoxin, a specific inhibitor of the sodium permeability, it is possible to separate two current components, (i) a transient component, suppressed by tetrodotoxin, which reflects the modifications, with time and voltage, of the membrane permeability towards sodium ions; the larger the depolarization, the shorter the time to reach peak current. This current is inward for depolarizations (V) of about +30 mV to about +130 mV (VNa). There was some variation in these values between individual fibres. Beyond VNa, the current is outward. This current shows a small rectification — inward going — for high depolarizations which is comparable to the behaviour of the Ranvier node membrane. (ii) A quasi‐instantaneous outward component, only voltage dependent. The current—voltage relation of this current shows an outward going rectification for high depolarizations. This current can be considered as a ‘leak’ current, in which chloride ions could play an important role.5. A sodium tail current is observed when the imposed potential fall occurs during the time course of the initial current. It corresponds to the deactivation of the sodium current previously activated. Because of the large contemporary capacitative currents, it is difficult to measure accurately its maximum amplitude and its time course: yet, the instantaneous current—voltage relation seems to show a slight rectification for the largest depolarizations, as observed on the Ranvier node membrane.6. The inactivation properties of the sodium current are studied in experiments similar to those described by Hodgkin & Huxley. As in nerve fibres the ability of the membrane to undergo an increase of the sodium permeability depends on the membrane potential. In our experimental conditions, the availability of the sodium carrying system is 90 per cent at the resting potential; the half‐inactivation occurs for V = +11 mV. This potential value corresponds to the smallest value of τh−1, in agreement with the equations proposed by Hodgkin & Huxley (1952d) for the inactivation process.7. The activation parameters (m∞, τm) are determined by a fitting method, taking account of the values of τh previously established. The potential of half‐activation is near V = +40 mV.
An estimate of adenosine triphosphate release into the venous effluent from exercising human forearm muscle
Authors: Forrester T. 
Published: December 2014

1. Human subjects performed a sustained contraction of the forearm muscles for 4 min in the presence of arterial and venous occlusion.2. The contraction was maintained at 5% of the maximum voluntary contraction, a tension during which the muscle blood flow might be expected to increase by about three times (Lind & McNicol, 1967).3. Adenosine triphosphate (ATP) was identified in the venous effluent from occluded exercising forearm, but not in the venous effluent from occluded forearm without exercise.4. The rate of degradation of ATP was assessed in plasma at 37° C, with an estimate of the percentage loss occurring between sampling and testing. This enabled the rate of appearance of ATP in the blood at the time of exercise to be calculated as approximately 7·5–10·5 μg/min (14–20 n‐mole/min). These amounts are compared with 16 μg/min that was infused intra‐arterially into human forearm to cause a threefold increase in blood flow (Duff, Patterson & Shepherd, 1954).5. It is likely that the ATP detected in the venous effluent has active muscle as the source; if so, then the amounts calculated to be released could satisfy the vasodilator requirements of active skeletal muscle.6. The effects of circulating ATP on respiration and coronary blood flow during exercise is discussed, including the role it may play locally in the production of ischaemic pain.
Changes in light scattering that accompany the action potential in squid giant axons: potential‐dependent components
Authors: Cohen L. B. , Keynes R. D. , Landowne D. 
Published: December 2014

1. To obtain information about structural events that occur in axons, changes in light scattering from squid giant axons were measured during action potentials and voltage‐clamp steps.2. The scattering changes were measured at several scattering angles. Because the changes in scattering divided by the resting scattering were between 10−6 and 10−5, signal‐averaging techniques were used to increase the signal‐to‐noise ratio.3. The scattering changes during the action potential were different at different angles. Two types were found, one at 10–30° (forward angles) and the other at 60–120° (right angles).4. At forward angles, there was a transient scattering decrease during the action potential. The time course of the change was similar to that of the action potential; this change was thought to be potential‐dependent.5. At right angles, there was a transient scattering increase during the action potential followed later by a second, longer‐lasting increase. Indirect evidence indicated that neither component could be totally potential‐dependent.6. To further analyse these effects, scattering was measured during voltage‐clamp steps. The changes seen during hyperpolarizing steps were presumed to be potential‐dependent; again two different changes were found, one at forward angles and one at right angles.7. The potential‐dependent change at right angles occurred with a time course that could be approximated by a single exponential with a time constant τ = 24 μsec. The change at forward angles required two exponentials, τ1 = 23 μsec, τ2 = 900 μsec, to represent its time course.8. The size of both potential‐dependent changes was proportional to the square of potential. The change at right angles, but not that at forward angles, was increased in size by the addition of butanol or octanol to the bathing solution.
Effects of heating and cooling the spinal cord and medulla oblongata on thermoregulation in monkeys
Authors: Chai C. Y. , Lin M. T. 
Published: December 2014

1. In the unanaesthetized monkey (Macaca cyclopis), heating the spinal cord or the medulla oblongata from 38 to 42–43° C produced subcutaneous vasodilatation, respiratory acceleration (frequently interrupted with a period of apnoea in the medullary experiment), bradycardia and hypotension. The animal became drowsy and had a slight decrease of body temperature. Heating the medulla oblongata often induced retching and/or emesis.2. Cooling the spinal cord or medulla oblongata from 38 to 32–33° C produced subcutaneous vasoconstriction, slower respiration, tachycardia and hypertension. The animal became restless and had a slight increase of body temperature. Cooling the spinal cord induced shivering of the four limbs, while cooling the medulla oblongata induced only shivering of the jaws.3. The effects of heating or cooling of the spinal cord or the medulla oblongata were antagonized by simultaneous application of temperature displacement of the opposite nature in the same areas or vice versa.4. The data suggest that some thermosensitive elements possibly responsible for thermoregulation reside in the spinal cord and the medulla oblongata.