bluuebunny/crossref_metadata_2025_split huggingface dataset:
The kidneys and arterial pressure in immature and adult rabbits
Authors: Mott Joan C. 
Published: December 2014

1. The effect of stepwise haemorrhage on arterial pressure in adult and immature (9–15 days old) rabbits lightly anaesthetized with sodium pentobarbitone is described.2. Bethanidine (1 or 3 mg/kg) lowered initial arterial pressure but did not impair the maintenance of arterial pressure in immature or adult rabbits during stepwise haemorrhage.3. Arterial pressure was only slightly lower in nephrectomized than in intact adult rabbits; in some immature rabbits nephrectomy caused a substantial fall of resting arterial pressure. This fall was largest in animals of low body weight and low haematocrit. Nephrectomy reduced the ability of both immature and adult rabbits to maintain arterial pressure during haemorrhage.4. Arterial pressure fell more precipitately on stepwise haemorrhage in adult rabbits in which the carotid sinus and depressor nerves had been cut than in intact rabbits. No such difference was seen in immature rabbits despite the fact that initial arterial pressure was higher in denervated animals at all ages.5. The responses to stepwise haemorrhage were compared in dummy operated and nephrectomized immature and adult rabbits with carotid sinus and depressor nerves cut to minimize changes of sympathetic tone. Under these conditions the presence or absence of kidneys made no significant difference in the response to stepwise bleeding in adult rabbits. In immature rabbits maintenance of arterial pressure was greatly impaired in the absence of the kidneys.6. The results suggest that a pressor mechanism of renal origin may be relatively more important in the maintenance of arterial pressure in the face of haemorrhage in immature than in adult rabbits.7. Resting arterial pressure in small and anaemic immature rabbits may partly depend on the presence of the kidneys. At birth arterial pressure is higher in rabbits of higher haematocrit but this relationship reverses in the second week of life when the haematocrit level is falling.
Ion movements in human red cells independent of the sodium pump
Authors: Lubowitz H. , Whittam R. 
Published: December 2014

1. A study was made of the dependence on external Na of the movements of Na and K in human red cells. Special attention was given to ouabain‐insensitive movements. The effect of internal Na on Na influx, and the influence of some sulphydryl inhibitors on ion movements and metabolism was also investigated.2. External Na stimulated ouabain‐insensitive Na efflux and K influx. There was also a ouabain‐insensitive component of Na influx that was raised on increasing the internal Na concentration. Exchange diffusion of Na appears to occur in the presence of ouabain and external K.3. Net transport of Na and K in the presence of ouabain was independent of external Na, as was also lactate production.4. Ethacrynic acid partially inhibited the Na pump; the Na‐dependent components of Na efflux and K influx in the presence of ouabain were completely inhibited by ethacrynic acid. Both ouabain‐sensitive and ouabain‐insensitive adenosinetriphosphatase activities were inhibited by ethacrynic acid indicating a non‐specific effect of this compound. Iodoacetamide decreased only the ouabain‐insensitive ATPase activity.5. The results suggest that when the Na pump is blocked by ouabain, part of the residual ion movements can be attributed to exchange diffusion.
A reappraisal of reflex stepping in the cat
Authors: Egger M. David , Wyman Robert J. 
Published: December 2014

1. In re‐evaluating Sherrington's experiment in which deafferented muscles in decerebrated cats ‘stepped’, we recorded from L5 ventral roots, a chief supplier of the major extensors of the hind legs, during stimulation of the common peroneal nerves. The extensor muscles had been denervated by appropriate dorsal root sections; the cats had been paralysed with a neuromuscular blocking agent.2. Response versus interval curves were constructed using 1 Hz stimulation. When stimulation of one peroneal preceded another, the responses ipsilateral to the second stimulation were facilitated at testing intervals of −2 to 10 msec, and inhibited at intervals of 30–400 msec.3. Responses from the L5 ventral roots mimicked ‘stepping’, waxing and waning at 1 Hz, only when 1 Hz was the best frequency for stimuli delivered to the two common peroneals (e.g. 24 and 25 Hz). When both sides were stimulated at the same frequency, no periodic changes in response amplitudes were seen.4. It was concluded that the apparent ‘stepping’ in deafferented muscles seen by Sherrington may have been due to differences in frequency of the two inductoria he used to stimulate the peroneals. We found no evidence of central timing of a pattern corresponding to walking.
The release of vasopressin in response to haemorrhage and its role in the mechanism of blood pressure regulation
Authors: e Silva M. Rocha , Rosenberg Manuela 
Published: December 2014

1. The release of vasopressin in response to haemorrhage and the effects of vasopressin infusions on blood pressure and heart rate have been investigated in anaesthetized dogs. Haemorrhage was produced by the method of Lamson & de Türk (1945), which allows for a precise control of the changes in arterial blood pressure.2. Blood samples were collected from an external jugular vein, from a femoral vein or from a femoral artery and extracted with alcohol; blood extracts were assayed for antidiuretic activity.3. Haemorrhage experiments showed that vasopressin secretion is increased when the fall in diastolic blood pressure (diastolic ΔP) is 25 mm Hg or more. Mild hypotensions (diastolic ΔP ranging from 21 to 30 mm Hg) produce an average fourfold increase in the concentration of vasopressin in blood. Such increase is maintained throughout the oligaemic period. Severe hypotensions produce, in most cases, a biphasic secretory response, with an initial high peak followed by a lower, constant, secretory plateau. In all experiments, the retransfusion of blood restored vasopressin to control levels.4. Vasopressin infusion experiments showed that the amounts of hormone secreted in response to haemorrhage are sufficient to cause vasopressor response, provided that the buffering action of blood pressure regulation mechanisms is suppressed. It was also found that the amounts of vasopressin secreted in response to haemorrhage are apparently adequate, if the function of such secretion is to combat the hypotension which follows haemorrhage.5. The effect of hypophysectomy on the blood pressure of animals previously submitted to bilateral division of the vagi and sinus nerves (deafferented animals) was also investigated. It was found that hypophysectomy is followed by a fall in arterial blood pressure which is positively correlated to the previous existing amounts of vasopressin. The time course of this hypotension is similar to that following the stopping of an infusion in a deafferented hypophysectomized animal. In some experiments it was shown that, following hypophysectomy, blood pressure can be restored to its pre‐hypophysectomy level by an adequate infusion of vasopressin.6. It is proposed that the release of vasopressin in response to stimuli arising from cardiovascular sensory receptors plays a part in the mechanism of blood pressure regulation.
The redistribution of cardiac output on cold exposure in new‐born rabbits
Authors: Járai I. 
Published: December 2014

1. In anaesthetized new‐born rabbits isotope‐labelled microspheres were injected into the left ventricle to investigate the distribution of cardiac output.2. On cold exposure the proportion of radioactivity (and hence of cardiac output) distributed to brown adipose tissue rose from 6 to 19%. Similar results were obtained in ten rabbits in which the distribution of microspheres labelled with two different isotopes was examined both in a neutral thermal and cold environment.3. The perirenal, inguinal, pectoral and axillary adipose tissue deposits showed a trivial increase in the proportion of cardiac output (from 1·2 to 1·9%) on cold exposure as compared with the cervical and interscapular deposits.4. The small intestine of new‐born rabbits received 24% of the cardiac output while renal flow was only 8%. There were large changes in the proportions of body weight and in the distribution of cardiac output with age from 1 to 6 days from birth.5. The results support the contention that brown adipose tissue is the principal site of additional thermogenesis in anaesthetized new‐born rabbits exposed to cold.
Changes in the maintained discharge with adaptation level in the cat retina
Authors: Barlow H. B. , Levick W. R. 
Published: December 2014

1. The mean rate, impulse interval distribution, and pulse number distribution of the maintained discharge of ganglion cells in the retina of the cat have been studied after prolonged adaptation at different luminance levels.2. From a state of complete dark adaptation up to a luminance of about 5 × 10−3 cd/m2 (viewed through a 7 mm2 pupil) the mean rate of on‐centre units increases. From darkness up to a somewhat higher luminance the mean rate of some off‐centre units decreases, but others show little change.3. Above 10−2 cd/m2 the mean rate ceases to show a regular relation with adaptation level. On units often decrease and then increase again at a higher level. Rhythmical fluctuations are common near 10−2 cd/m2, especially if the retina is not in first class condition. Mean rates above 70/sec and below 1/sec are very rare at any adaptation level.4. Over the range where mean rate increases monotonically with adaptation level, it is shown that the surround of on‐centre units does not inhibit and off responses cannot be elicited. When the monotonic increase is slowed or reversed it becomes possible to elicit responses from the surround. We suspect that the surround exerts a sustained, tonic, inhibiting effect at higher adaptation levels, thus holding down the maintained discharge.5. There are rare units, forming less than 1% of those isolated, that show a regularly increasing frequency with increase of adaptation level above 10−2 cd/m2. These units have concentric ‘on’ and ‘off’ zones in their receptive fields, but the responses to rapidly changing stimuli are sluggish and they have an unusually regular maintained discharge. They have been tentatively called ‘luminance units’.6. The impulse‐interval and pulse‐number distributions of on‐centre units change predictably with adaptation level; the variance of the pulse number distribution is usually several times the mean at very low adaptation levels, but only a fraction of the mean at high levels. Off‐centre units do not show predictable changes. Luminance units fire more regularly, and have narrower pulse‐number and impulse interval distributions than other concentric units.7. A simple model is proposed to account for the statistical characteristics of the maintained discharge of on‐centre units.
A comparison of sweat gland activity in eight species of East African bovids
Authors: Robertshaw D. , Taylor C. R. 
Published: December 2014

1. The pattern and control of the sweat glands of eight species of wild bovids has been studied.2. Heat exposure resulted in changes in cutaneous moisture loss which showed considerable species variation. Duiker, Grant's gazelle, Thomson's gazelle and oryx all demonstrated periodic discharges of moisture on to the surface of the skin. Defassa waterbuck and eland exhibited discharges which were accompanied by a gradual rise in basal level. Buffalo showed an immediate large increase which was sustained during the period of heat exposure. Three wildebeest displayed small fluctuations whilst a fourth animal showed a step‐wise increment in cutaneous moisture loss.3. The intravenous infusion of adrenaline into the buffalo and one wildebeest caused an increase in cutaneous moisture loss, the magnitude of which was directly related to the size of the dose administered. In three other wildebeest, and all other animals tested, a single injection of adrenaline was necessary to cause a discharge of moisture on to the surface of the skin. Noradrenaline was without effect.4. Heat‐induced but not adrenaline‐induced sweating was inhibited by the intravenous administration of an adrenergic neurone blocking agent, bethanidine.5. It is concluded that the sweat glands of the wild bovids studied are under adrenergic neurone control, in common with the domestic bovids previously studied, and that there is no correlation between the pattern of sweating and the phylogenetic position of the species.
The yellow colour of the lens of the grey squirrel (Sciurus carolinensis leucotis)
Authors: Cooper G. F. , Robson J. G. 
Published: December 2014

1. The absorption spectrum of the lens of the grey squirrel (Sciurus carolinensis leucotis) has been measured, revealing an absorption maximum at 370 nm. Peak densities in the intact lens ranged from 12 to 20.2. This peak is not present in the lenses of horse, cow, pig, dog, cat, ferret (Mustelo furo), or guinea‐pig (Cavia porcellus).3. The pigment responsible for this absorption is water‐soluble and aqueous extracts have been examined. Protein‐free aqueous extracts show an additional maximum at 265 nm, which can only partially be accounted for by the presence of ascorbic acid.4. The absorption spectrum of extracts of lens material from the ground squirrel (Citellus mexicanus) also had maxima at 265 and 370 nm.5. Chromatography of the protein‐free solution separated two yellow components, both of which had a yellow fluorescence. The faster component had a very similar absorption spectrum to the original protein‐free solution.6. Possible functions of the yellow pigment are discussed.
Light scattering and birefringence changes during activity in the electric organ of Electrophorus electricus
Authors: Cohen L. B. , Hille B. , Keynes R. D. 
Published: December 2014

1. In an attempt to obtain information about structural changes related to electrical activity in Electrophorus electroplates, we have determined the size and time course of the changes in light scattering and in bire‐fringence that occur during and after the discharge of the electric organ.2. The changes in light intensity detected with a photomultiplier were never greater than 0·2% for a single discharge, and were often much smaller than this, but records with an acceptable ratio of signal to noise could be obtained by signal‐averaging techniques.3. A single stimulus led to a decrease, then an increase, and finally another decrease in the light scattered by slices of the main electric organ. These three phases were designated E1, E2 and E3.4. E1 started at the beginning of the action potential, and its peak was reached at the same time as the completion of repolarization, even when the repolarization was delayed by cooling or hastened by drawing larger currents from the tissue.5. E2 was proportional to the integral of the current flowing through the slice of electric organ, and may arise from the swelling and shrinking of the tubules that stud the faces of the electroplates. It developed within a millisecond or two of the start of an applied current, and lasted for about 100 msec.6. E3 was a variable decrease in scattering that lasted for some seconds.7. A stimulus also led to a transient increase in the birefringence of the electric organ. The optical change followed the change in electrical potential across the innervated faces of the electroplates with a delay of somewhat under 50 μsec.8. This voltage‐dependent change in birefringence may arise from a Kerr effect (electric birefringence) in the membrane or from compression of the membrane.
Kinetics of potassium in colonic mucosa of normal and sodium‐depleted rats
Authors: Edmonds C. J. 
Published: December 2014

1. The transport of K across the mucosal epithelium of the colon of normal and Na‐depleted rats has been investigated in vivo by methods involving
I.V. administration of solutions containing 42K and by labelling the mucosa with 42K from the lumen and observing the ‘soaking‐out’ rates into radionucleide‐free solutions.2. During the infusions, the specific activity of the mucosal K was always less than the simultaneous specific activity of the secreted K. On stopping the infusion the specific activity of the mucosal K fell although the plasma specific activity remained at all times greater than that of the mucosa. The blood flow rate to the mucosa estimated from these results was 0·95 ml./min.g wet wt.3. Experiments with 42K in the lumen showed that the steady‐state specific activity of the mucosal K was considerably less than expected if the K had been in a single compartment. The 42K efflux curves were also consistent in showing two components. The curves were analysed on the basis of a model having two compartments in the mucosa with half‐times of 6 and 33 min.4. Na depletion produced two significant changes, (a) K secretion rate doubled, (b) the steady‐state specific activity of the mucosal K after luminal exposure to 42K was increased. The half‐times of the compartments were unaffected.5. The results were discussed in terms of a working hypothesis which represented the mucosal K in two compartments. Most of the K exchanges across the mucosa took place through the smaller compartment which probably contained 5% or less of the mucosal K, but which had a rapid turnover rate. The change of K permeability of the luminal face produced by Na depletion and probably due to increased aldosterone action, may well be an important factor in producing the rise of K secretion rate.
After‐effects of nerve impulses on signalling in the central nervous system of the leech
Authors: Baylor D. A. , Nicholls J. G. 
Published: December 2014

A long‐lasting hyperpolarization has been observed in sensory neurones of the
C.N.S. of the leech following natural stimulation applied to their receptive fields. The underlying mechanism of this hyperpolarization and its effects on signalling were investigated by intracellular recording.1. The amplitude and duration of the hyperpolarization depended on the number of action potentials. Whereas a brief burst of impulses had little effect, a prolonged sensory discharge was followed by a hyperpolarization of up to 30 mV that gradually declined over a period of several minutes.2. The hyperpolarization was abolished by ouabain, reversibly inhibited by strophanthidin or cooling, unaffected by Mg and accompanied by an increase in membrane resistance. These observations suggest that the hyperpolarization is the result of membrane current generated by an electrogenic pump.3. A hyperpolarization similar to that recorded in the cell body also occurred in the neuronal processes within the neuropile, where synaptic contacts are made. This led to significant changes in integrative activity, such as an increase in the amplitude of excitatory synaptic potentials, a reversal of inhibitory synaptic potentials or a conduction block in parts of the neurones. All of these effects could be mimicked by injecting hyperpolarizing currents into resting cells, or abolished by injecting a depolarizing current into a cell hyperpolarized by previous impulses.4. During neuronal hyperpolarization the sensitivity of the membrane potential to small increments of external K was enhanced by a factor of about three. This effect varied with the magnitude of the hyperpolarization produced by preceding impulses and could not be mimicked by applying K to a neurone hyperpolarized by the injection of current into its cell body.5. These findings are discussed in relation to possible effects that changes in the intracellular and extracellular concentrations of ions produced by activity might have on integration in the
C.N.S.
Dynamic properties of fast and slow skeletal muscles of the rat after nerve cross‐union
Authors: Close R. 
Published: December 2014

1. The properties of self‐innervated (S‐EDL, S‐SOL) and cross‐innervated (X‐EDL, X‐SOL) extensor digitorum longus (EDL) and soleus (SOL) muscles have been determined at various times between 25 and 490 days after operations, and these are compared with the properties of normal muscles from unoperated animals of about the same age.2. The muscle fibres of X‐SOL were 1·15 times longer than fibres of N‐SOL and S‐SOL at about 480 days after operations but the diameter of fibres was the same in the three muscles.3. The length of muscle fibres was the same in X‐EDL, N‐EDL and S‐EDL 480 days after operations but the fibres of X‐EDL failed to grow in cross‐sectional area after innervation by soleus nerve fibres.4. The twitch: tetanus ratio was altered transitorily in both X‐EDL and X‐SOL but returned to near normal values within about 300 days after operations.5. The time courses of isometric contractions and the force: velocity properties were virtually the same in normal and self‐innervated muscles 480 days after operations. The isometric twitch contraction time was about 13 msec for N‐EDL, 25 msec for X‐EDL, 34 msec for N‐SOL and 15 msec for X‐SOL, and the intrinsic speed of shortening of sarcomeres was about 45·1 μ/sec for N‐EDL, 22·5 μ/sec for X‐EDL, 19·8 μ/sec for N‐SOL and 33·8 μ/sec for X‐SOL; in these respects there was incomplete transformation of EDL to a slow muscle and of SOL to a fast muscle.6. There was a high degree of correlation between the intrinsic speed of shortening of sarcomeres and the isometric twitch contraction time but there was no correlation between isometric twitch contraction time and twitch: tetanus ratio of self‐innervated and cross‐innervated muscles 200–480 days after operations, and normal muscles from unoperated animals of the same age.7. The relation between intrinsic speed of shortening of sarcomeres and isometric twitch contraction time was approximately hyperbolic for normal, self‐innervated and cross‐innervated EDL and SOL muscles 480 days after operations.8. The maximum speed of shortening of whole muscle fibres was the same for X‐SOL, S‐EDL and N‐EDL, and the same for X‐EDL, S‐SOL and N‐SOL. The possibility that a neural influence determines the speed of shortening of whole fibres is discussed.