bluuebunny/crossref_metadata_2025 huggingface dataset:
The dependence of the action potential of the frog's heart on the external and intracellular sodium concentration
Authors: Niedergerke R. , Orkand R. K.
Published: December 2014

1. The overshoot of the action potential of the frog's heart was reduced when external sodium chloride was replaced by sucrose. However, the potential decrement was only 17·3 mV for a 10‐fold reduction of sodium as compared with 58 mV expected on the basis of the sodium hypothesis of excitation.

2. Replacement of up to 75% of the external sodium by choline did not reduce the overshoot, provided atropine was present in sufficient concentrations to suppress any parasympathomimetic action.

3. The maximum rate of rise of the action potential markedly declined in low sodium fluids whether sucrose or choline chloride was used to replace sodium chloride.

4. The maximum rate of rise was reduced to only a small extent when external sodium was replaced by lithium.

5. Increasing the intracellular sodium concentration in exchange for lost potassium caused overshoots to decline. The effects resembled those obtained in similar experiments with skeletal muscle fibres (Desmedt, 1953).

6. Action potentials occurring under certain conditions even in the presence of very low external sodium concentrations (≤ 5% normal) also declined in height when the intracellular sodium concentration was increased.

7. The behaviour of the action potential in low external sodium concentrations may be explained by an action of calcium on the excitable membrane.
Concentration of radioiodide by the uterus of the rat and the relationship to blastocyst implantation
Authors: Brown-Grant K.
Published: December 2014

1. When pregnant rats are ovariectomized early in pregnancy and treated with progesterone a raised uterus—plasma concentration ratio (U/P ratio) for radio‐iodide is observed at the usual stage of pregnancy (days 3, 4 and 5) but is not followed by implantation. When delayed implantation is induced by the administration of oestradiol it is not preceded by a rise in the U/P ratio for 131I.

2. Similar findings are obtained when implantation is delayed by concurrent lactation in rats mated at the post‐partum oestrus.

3. Ovariectomy early in pregnancy without progesterone treatment prevents the rise in U/P and oviduct—plasma (O/P) ratio for 131I that normally occurs.

4. Administration of progesterone to intact or ovariectomized non‐pregnant rats produces a raised U/P and O/P ratio for 131I; oestrogen may inhibit this response. The simplest explanation of these results is a direct action of progesterone on the uterus.

5. By gross dissection it was possible to show that the region of high iodide concentration in the rat uterus is the endometrium.

6. No evidence of a concentration of iodide in the uterus or oviduct of the pregnant rabbit was obtained.
Rod and cone interaction in dark‐adapted monkey ganglion cells
Authors: Gouras P. , Link Krista
Published: December 2014

1. Rod—cone interaction has been studied by analysing the response latency of large ganglion cells in the perifovea of dark‐adapted Rhesus monkey retina.

2. Both rod and cone signals have been found to converge on such cells. The cone system is less sensitive but much faster than that of the rods so that the cones determine latency whenever stimuli become suprathreshold for them. Responses to dimmer stimuli are determined entirely by the rods.

3. The earliest signals to excite the ganglion cell leave a transitory refractoriness in their wake. Therefore when both rods and cones are stimulated simultaneously, the earlier cone signal, arriving at the ganglion cell, has a greater chance of producing excitation than the later rod signals.
Onset of contractility in cardiac muscle
Authors: Brady Allan J.
Published: December 2014

1. A technique is described whereby (i) quick stretches and releases of controlled velocity, amplitude and time of onset can be applied to muscle. (ii) Releases from isometric to isotonic contraction can be performed at controlled delays relative to the stimulus, and displayed on a delayed expanded oscilloscope sweep. An isotonic lever system with an equivalent mass of 12·8 mg is described.

2. Quick stretch of rabbit or cat papillary muscle after excitation does not result in a level of tension equal to or greater than normal peak isometric tension appropriate to the stretched length. Stretches applied during the first half of the rising phase of tension development give responses nearly identical to the same stretches applied before the stimulus (indicating that Starling's Law of the heart holds until this time). Stretches applied in the later phase of tension development or during relaxation result in diminished peak isometric tensions or accelerated relaxation.

3. The rate of tension development following quick releases of isometrically contracting muscle to zero tension is not maximal until the releases are made 150‐200 msec after excitation.

4. Shortening velocity with light afterloads is not initially maximal nor constant for an appreciable period of time. The shortening velocity with heavy afterloads reaches its maximum more rapidly when the load is not lifted within the first 200 msec of a contraction which, if maintained isometric, would have required 400‐500 msec to reach peak tension. With these heavier loads, a period of 100‐200 msec of constant shortening velocity may occur.

5. Freeloaded isotonic contractions show an inflexion in their shortening curves occurring 150‐200 msec after excitation.

6. Maximum rate of isotonic shortening following releases from isometric to isotonic contraction with a given load is not maximal until the releases occur about 200 msec after the stimulus.

7. It is concluded that contractility in cardiac muscle is relatively slow in its onset with maximum capacity to shorten occurring about midway through the rising phase of isometric tension development.
Chemoreceptor reflexes in the new‐born infant: effects of varying degrees of hypoxia on heart rate and ventilation in a warm environment*
Authors: Brady June P. , Ceruti Eliana
Published: December 2014

1. We studied the effects of varying degrees of hypoxia for 3 min periods on the heart rate and respiration of thirty‐three healthy full‐term infants in a warm environment.

2. During the first 5 days of life a decrease in alveolar oxygen tension (PA, CO2) below 80 mm Hg induced hyperventilation, a decreased alveolar carbon dioxide tension (PA, CO2), and tachycardia during the first minute of hypoxia. During the second and third minute, while the decreased PA, CO2 and tachycardia persisted, ventilation fell. There was a further fall in ventilation when the baby breathed 21% O2 again. This response was also observed when the inspired gas was heated to 35° C.

3. During the first 5 days of life a decrease in PA, CO2 between 81 and 100 mm Hg did not affect ventilation or PA, CO2 during the first minute of hypoxia, but still induced a tachycardia and a fall in minute volume during the second and third minute.

4. When the PA, CO2 was elevated and maintained constant during hypoxia, ventilation increased during the first minute and fell during the second and third minutes, suggesting that hypocapnia did not explain the transient ventilatory response to hypoxia.

5. After the first week of life a greater and maintained increase in ventilation was seen during hypoxia. This response was potentiated by the addition of CO2.

6. The possibility that changes in the pulmonary circulation, associated with a functionally patent ductus arteriosus, may explain these differences, is discussed.
The effect of cortisol on the haematocrit values and serum electrolytes of the adult and foetal rat
Authors: Seller Mary J.
Published: December 2014

1. The serum sodium, potassium and chloride levels of the non‐pregnant rat, pregnant rat and foetus were estimated under normal circumstances and following the administration of 3 mg/kg cortisol to the non‐pregnant and pregnant rat.

2. Normally, the electrolytes and haematocrit value of the non‐pregnant rat and the electrolytes of the foetus were higher than those occurring in the pregnant rat.

3. After treatment with cortisol, the sodium, potassium and chloride content of the serum, and the haematocrit value of the non‐pregnant rat dropped significantly. There was no change in these values in the pregnant animals, but the foetus showed a significant decrease in sodium, potassium and chloride levels after maternal treatment.
Analysis of actions of 5‐hydroxytryptamine in pregnancy
Authors: Robson J. M. , Sullivan F. M.
Published: December 2014

1. When 5‐hydroxytryptamine creatinine sulphate is injected subcutaneously in a dose of 2 mg into mice during the second half of pregnancy, the foetuses die within 1 hr. The mode of action of 5‐hydroxytryptamine (5‐HT) in producing this effect has been studied.

2. It has been demonstrated that this is not a direct toxic effect of 5‐HT. Very little passes through the placenta into the foetus, and after the injection of much larger amounts directly into the foetus no lethal effect was observed.

3. It was shown that 5‐HT had little effect on uterine motility in vivo, and that the much larger contractions produced by oxytocin did not produce any effect on the foetus.

4. No constriction of the umbilical vessels was produced by 5‐HT injected into the mother, nor did the local application of 5‐HT to the cord produce any effect.

5. The administration of 5‐HT to the mother markedly reduced the passage of 22Na from the maternal circulation into the placenta and foetus. This was accompanied by a reduction in the blood supply to the placenta from a normal value of 87 μl./min/g to 4 μg/min/g.

6. It is suggested that the effect of 5‐HT in producing foetal death is a consequence of the reduction in the transfer function of the placenta.
The effect of previous stimulation of the adrenal cortex by adrenocorticotrophin on the function of the pituitary—adrenocortical axis in response to stress
Authors: Jones M. T. , Stockham M. A.
Published: December 2014

1. There appear to be at least two peripheral regulators affecting normal physiological adrenal function during repeated stimulation with adrenocorticotrophin (ACTH).

2. There is a tachyphylaxis to ACTH if the stimulation of the adrenal gland is frequent. This may be due to alteration or saturation of the trapping mechanism for acceptance of ACTH by the tissue. There also may be inhibitors at the adrenal level. The results obtained could also be explained on the basis of end product inhibition by corticosterone on the process of synthesis or by the presence of a destructive enzyme for ACTH.

3. If the amounts of ACTH released or injected are sufficiently great the gland is capable of synthesizing more steroid but adrenocortical dynamics do not allow an immediate release of the steroid into the peripheral circulation. Thereby high levels of steroid in the plasma are maintained for longer periods rather than increased.
The permeability of the gastric mucosa of dog
Authors: Altamirano M. , Martinoya C.
Published: December 2014

1. Tritiated water, [14C]urea, [14C]thiourea, [14C]sucrose and [59Fe]‐haemoglobin were used to study the permeability of a semi‐isolated piece of the great curvature of the canine stomach.

2. The osmotic pressure of the solutions placed in contact with the secretory surface of the epithelium was changed by means of dextrose or urea. The mucosa behaved as a semi‐permeable membrane, meaning that water flowed under gradients of osmotic pressure. Regardless of the solute used, about 45 × 10−6 ml. of water flowed/cm2/min under a gradient of one atmosphere.

3. The permeability constants of the probing molecules were determined under zero net volume flow obtained by placing isosmotic dextrose or isosmotic urea in the chamber. The constants decreased as the molecular volume of the probing molecules increased.

4. The transport of all the non‐electrolytes across the epithelium decreased significantly when the chamber contained isosmotic dextrose. Basically, this effect seems to be a result of the reduction of the area available for diffusion caused by the high molecular volume of dextrose.

5. The increased hindrance to diffusion of the probing molecules caused by the added solutes is considered as good evidence that the probing molecules diffuse by way of pores filled with water.

6. The equation derived by Renkin (1954) fits the results obtained if we assume that the equivalent membrane has pores of at least two different radii. The calculated radii vary somewhat with the solute placed in the chamber, though about 88% of the area available for diffusion consists of pores with radii smaller than 2·5 Å.

7. The equivalent pore radius, calculated from Kedem & Katchalsky's (1961) formula for pores of one single radius, contradicts some experimental findings. Once again, the results obtained would be reproduced more accurately by an equivalent membrane pierced by parallel pores of at least two different diameters.

8. A procedure is suggested for calculating the proportion of pores of different radii. It seems likely that the pore radii vary in a continuous distribution from the large pores which allow the diffusion of haemoglobin, to pores hardly permitting the passage of water. The wide pores would form a small fraction of the total area available for the diffusion of water.
Appearance of 5‐hydroxytryptamine and an unidentified pharmacologically active lipid acid in effluent from perfused cerebral ventricles
Authors: Feldberg W. , Myers R. D.
Published: December 2014

1. In cats anaesthetized with intraperitoneal pentobarbitone sodium, three regions of the cerebral ventricles, the third ventricle, the inferior or the anterior horn, were perfused with artificial c.s.f. and the effluent was tested on the fundus strip of the rat's stomach.

2. Effluent from all three regions contracted the fundus strip. The contractions were due to at least two substances as revealed by treatment of the strip with 2‐bromolysergic acid diethylamide (BOL). The contractions that were sensitive to BOL are attributed to 5‐hydroxytryptamine (5‐HT) whereas the BOL resistant contractions appear to be due to an unknown hydroxy acid related to irin or the prostaglandins.

3. The contractions produced by effluent collected from the third ventricle were due wholly or mainly to 5‐HT, those from the inferior horn to the unknown hydroxy acid, and those from the anterior horn to both substances in varying proportions. In addition, some samples of effluent from the third ventricle seemed to contain catecholamines as well.

4. The 5‐HT in the effluent from the third ventricle is thought to be derived from the hypothalamus. The amounts assayed in 1 ml. effluent—the volume collected during 10 or 20 min perfusion—varied between 0·4 and 12 ng 5‐HT. Output of 5‐HT was initially high, then usually decreased but sometimes increased again during prolonged perfusion when temperature began to rise as anaesthesia lightened or when additional pentobarbitone sodium was given intravenously.

5. When perfusion of the third ventricle was continued after death the 5‐HT content in the effluent increased 3 to 24‐fold during the first hour and then gradually declined. This post mortem rise in 5‐HT output suggests an abnormal state of release of 5‐HT from the hypothalamus. The theory is discussed that the same may happen in certain cases of brain injury and that the abnormal release of 5‐HT would explain the pyrexia and shivering seen in such cases.

6. The intraperitoneal injection of 5‐hydroxytryptophan greatly increased the output of 5‐HT in the effluent from the perfused third ventricle but only when this precursor of 5‐HT was injected in large doses which caused respiratory arrest thus necessitating artificial ventilation. Upon the injection of 150 mg/kg the output of 5‐HT rose to 90 ng/ml. and a further rise to 180 ng/ml. occurred when perfusion was continued after death.

7. It was not possible to establish a relation between the presence of the hydroxy acid in the effluent from the inferior horn and neuronal activity.

8. The 5‐HT detected in the effluent from the anterior horn is assumed to have been released from the caudate nucleus.
Nerve implants in botulinum poisoned mammalian muscle
Authors: Fex S. , Sonesson B. , Thesleff S. , Zelená Jirina
Published: December 2014

1. In albino rats the botulinum poisoned gastrocnemius muscle was supplied with an accessory motor nerve in order to investigate whether muscle fibres with structurally intact but non‐transmitting synapses would accept additional innervation. As a control similar operations were made in unpoisoned rats.

2. One to three months after nerve implantation the muscles were examined histologically for the presence of a new end‐plate zone. In botulinum treated muscles 1662 ± 165 (mean ±
S.D.) of new end‐plates were found. In the control animals only a few (90 ± 13) were observed in the immediate vicinity of the implanted nerve trunk.

3. Following recovery from the paralysing action of botulinum toxin electrical stimulation of both the implanted and the original motor nerve evoked strong mechanical twitches in the gastrocnemius muscle.

4. When the nerves were stimulated simultaneously little or no summation of tension occurred, indicating that presumably many of the muscle fibres with new end‐plates also had functionally intact junctions from the original nerve. The presence of two end‐plates in a muscle fibre was confirmed in a few experiments on single curarized fibres by intracellular recording of end‐plate potentials on stimulation of each nerve.
Sodium depletion of pregnant ewes and its effects on foetuses and foetal fluids
Authors: Phillips G. D. , Sundaram S. K.
Published: December 2014

1. Some effects of sodium depletion were investigated in sheep at different stages of pregnancy ranging from 55 to 139 days. Sodium depletion was induced by draining the saliva from one parotid gland for a period of 6 days. Foetal samples were collected at the end of the depletion period.

2. Sodium depletion of the ewe resulted in a fall in saliva Na+ level and a rise in saliva K+ level, a fall in plasma Na+ and K+ levels, a 35% reduction in plasma volume and a 16% reduction in body weight.

3. In the Na+ depleted ewes the sodium levels of the foetal plasma and amniotic fluid were lower and the volume of the allantoic fluid greater than those in the control ewes.

4. It is concluded that sodium depletion of the ewe leads to a deficiency of sodium in the foetus.

5. On the basis of these experiments and other reports it is postulated that a sodium deficient foetus, like a sodium deficient adult, responds to the deficiency by restricting sodium losses in the urine and by excreting water.
The influences of adrenolytic drugs and noradrenaline on the histamine release in cardiac anaphylaxis in vitro
Authors: Giotti A. , Guidotti A. , Mannaioni P. F. , Zilletti Lucilla
Published: December 2014

1. The regional distribution (auricles, ventricles and septum) of histamine and its release during anaphylaxis were studied in isolated perfused guinea‐pig hearts.

2. The highest value of histamine content was found in the right auricle, the lowest in the left ventricle and septum, both in normal hearts, and in the hearts subjected to anaphylaxis.

3. The fraction of the total histamine released in the course of 24 min by antigen was 50%. The fraction released from the different regions of the heart was similar. No evidence was found for release of 5‐hydroxytryptamine.

4. A relation was found between the distribution of mast cells and the tissue concentration of histamine. The highest number of mast cells per unit area was found in the right auricle; the lowest in the left ventricle.

5. The histamine release by antigen was reduced by previous treatment with (+)‐tubocurarine; the histamine release by (+)‐tubocurarine was depressed by previous challenge of the heart with antigen.

6. Reserpine reduces histamine release. Perfusion of reserpine‐treated hearts with noradrenaline partially restored histamine release.

7. β‐Adrenergic blocking agents (dichloroisoproterenol and pronethalol) reduced histamine release.

8. The drugs tested did not modify the tissue concentration of histamine.

9. The possibility of a modulating activity of catecholamines on histamine release in cardiac anaphylaxis is discussed.
The influence of thyroid gland on amino acid accumulation and protein synthesis by rat small intestine in vitro
Authors: Bronk J. R. , Parsons D. S.
Published: December 2014

1. A method is described for measuring the accumulation of amino acids and also the extent to which the absorbed amino acids are incorporated into the tissue protein of rings of rat intestine in vitro.

2. With this method rat jejunum was found to accumulate a mixture of amino acids to give a concentration in the tissue water which was 2‐3 times that in the medium after 8 min incubation. More than 10% of the absorbed amino acids were found to be incorporated into protein.

3. In surgically thyroidectomized animals there was no impairment of the capacity of the intestine to accumulate amino acids nor was there any loss of ability to incorporate these amino acids into protein. Similarly, treatment of the thyroidectomized animals with 3,5,3′‐triiodothyronine (T3) did not produce any significant change either in the rate of accumulation or in the extent of the incorporation of the amino acids.

4. The omission of glucose from the incubation medium was found to cause a large increase in the respiration of mucosal slices in the presence of the amino acid mixture. Thyroidectomy significantly reduced this high respiration rate. Treatment of thyroidectomized animals with T3 restored the respiration to high value.
Amino acid accumulation and incorporation in rat intestine in vitro
Authors: Bronk J. R. , Parsons D. S.
Published: December 2014

1. Rings of rat jejunum incubated in vitro accumulate a mixture of amino acids at a rate of about 3 μmoles/cm. hr. The rate of incorporation of the accumulated amino acid into the tissue protein corresponds to a rate of synthesis of 50% of the protein of the whole wall in five days.

2. Replacement of the Na+ in the NaCl of the incubation medium by choline or by Li+ did not prevent amino acid accumulation by the tissue. However, replacement of the Na+ by K+ prevented the accumulation.

3. The accumulation of amino acids by rat jejunum in vitro proceeded at normal rates not only in the presence in the incubation medium of oxygen tensions below 10 Torr but also in the presence of 2,4‐dinitrophenol. Reasons are given for supposing that the findings are compatible with the view that the energy upon which depend the processes of amino acid accumulation by the tissue could be derived from the movement of ions across cellular boundaries.

4. The amino acid incorporation into the tissue proteins was reduced to one tenth of the control rate in the presence of 2,4‐dinitrophenol or by hypoxia so that the processes of incorporation depend upon energy derived from oxidative metabolism. In the presence of oligomycin the tissue respiration was depressed but the amino acid incorporation into the tissue protein was not inhibited. The view that the amino acid incorporation may be able to function with energy intermediates other than ATP is discussed.
Experiments on the genesis of bubbles as a result of rapid decompression
Authors: Lever M. J. , Miller K. W. , Paton W. D. M. , Smith E. B.
Published: December 2014

1. The time course of intravascular bubble formation in mice after rapid decompression from 150 Lb/sq. in. has been followed in vivo in a flap preparation of thoracic and abdominal skin.

2. Gas appeared first in the arteries, moving distally after a latent period of 3 min or more. Then bubbles appeared, moving centrally, in the venous system.

3. The arterial bubbles could not be attributed to air forced into the circulation from the lungs or lumen of the gut.
The effects of arginine deficiency on the water and solute metabolism in weanling rats
Authors: Bentley P. J. , Ferguson D. R. , McGowan G. K.
Published: December 2014

1. Weanling rats fed on a synthetic diet, which was completely deficient in arginine, grew more slowly than rats fed on a similar diet which included arginine.

2. No differences in the haemoglobin level or plasma protein concentration or electrophoretic pattern were found in the two groups of rats.

3. The arginine‐deficient rats drank less water, and excreted less urine, which was more concentrated than that of the control animals, although the solute output was reduced, and the extrarenal water losses were the same.

4. The arginine‐deficient animals excreted less urea, non‐protein nitrogen, creatinine and total solutes. The blood urea concentration of the deficient animals was significantly higher than that of the controls, indicating that arginine deficiency had impaired the excretion of urea.

5. There was no difference between the renal weights of both groups of animals when related to total body weight, nor was there a difference in the histological appearance of the kidneys.

6. The amounts of arginine vasopression and oxytocin/kg body wt. stored in the neurohypophyses of both arginine‐deficient and control animals were the same.
Asphyxial potentials of spinal grey matter, and of ventral and dorsal roots
Authors: Biersteker P. A. , Collewijn H. , Van Harreveld A.
Published: December 2014

1. Asphyxial potentials of short latency (from a few to about 10 sec) were recorded with mono‐ and bipolar electrodes from the cat's spinal cord. Monopolarly, a zone of maximum negativity was found somewhat dorsal of the central canal in the dorsal horn. With bipolar leads potentials of opposite polarity were observed in the dorsal and ventral horns. In the dorsal horn the more ventral electrode tip became negative with respect to the more dorsal one, in the ventral horn the more ventral tip became more positive. In the centre of the cord where the monopolar potential showed a maximum the bipolar potentials were small in either direction, or reversed during asphyxiation.

2. These observations can be explained by the development of two independent dipoles of opposite polarity, located in the dorsal and ventral horn respectively, oriented with their negative poles towards the centre of the cord.

3. In the ventral as well as in the dorsal root a negativity of a proximal electrode with respect to a more distal one developed during asphyxiation after the same latency as the asphyxial cord potentials. The asphyxial root potentials continued to grow during periods of asphyxiation as long as 30 min, and recovered promptly upon re‐oxygenation.

4. Ventral and dorsal root potentials were abolished by asphyxiation of the cord for a period of 60 min, 2 weeks previously. This procedure destroys practically all the neurones, but not the dorsal root fibres. The dorsal root potential, but not the ventral one, was abolished by extradural sectioning of the roots, 2 weeks previously.

5. The asphyxial ventral and dorsal root potentials were interpreted as the result of depolarization of the intraspinal part of the motoneurones and primary afferent endings respectively, conducted electrotonically along the roots. The short latency of these potentials suggests that an early depolarization of motoneurone, and of the primary afferent end knobs occurs. The latter, which may have some relation to presynaptic inhibition, explains the early failure of synaptic conduction during acute asphyxiation.
Intracellular recording from spinal motoneurones in cats with post‐asphyxial rigidity
Authors: Collewijn H. , Van Harreveld A.
Published: December 2014

1. Intracellular recordings were obtained from lumbar spinal motoneurones in cats with post‐asphyxial rigidity of the hind limbs.

2. Membrane potentials, latencies and (or) appearance of excitatory post‐synaptic potentials, initial segment responses and soma‐dendritic spikes were not materially different from those observed in cells of normal cords.

3. Dorsal root stimulation activated all the motoneurones examined through monosynaptic pathways in contrast to cells in normal cords in which such a stimulus sometimes elicits only a post‐synaptic potential. In a number of cells subsequent polysynaptic activation caused a spike about 10 msec after the monosynaptic response, notwithstanding the serious interneuronal destruction which characterized these preparations.

4. In a few preparations the effects of acute asphyxiation could be examined. The soma depolarized at a rate of 3‐4 mV/min. Synaptic activation was more resistant to O2 lack than antidromic and direct excitation, in contrast to the experience with normal cells. Survival times of 8·5, 11 and 16 min were found. At certain levels of depolarization ‘spontaneous’ spikes were observed, which, since they were preceded by post‐synaptic potentials, could be considered as the result of synaptic activation.

5. To account for the enhanced reflex activity of rigid preparations, it was postulated that the substantial loss of interneurones in the cord had caused denervation supersensitivity of the motoneurones to the transmitter compound without materially changing their electrical excitability.

6. It was postulated that the early presynaptic failure during asphyxiation in normal preparations was dependent on a mechanism resembling presynaptic inhibition. The prolonged asphyxial survival of reflex activity in rigid preparations may be due to the destruction of interneurones involved in this form of inhibition.
Respiratory and circulatory effects of breathing 100% oxygen in the new‐born lamb before and after denervation of the carotid chemoreceptors*
Authors: Purves M. J.
Published: December 2014

1. Methods are described for measuring tidal volume and frequency, end‐tidal CO2, blood pressure and heart rate, and arterial gas tensions in the unanaesthetized new‐born lamb.

2. The resting values of minute ventilation (V̇)/kg body wt. and arterial oxygen and carbon dioxide tension, (Pa, o2) and (Pa, CO2) were similar to those which have been reported in the new‐born baby. There was a direct and significant relation between Pa, o2 and Pa, CO2 and the age of the lamb.

3. Thirty‐five unanaesthetized lambs aged 40 min to 10 days breathed 100% oxygen; minute ventilation fell by an average of 19% of control, end‐tidal CO2 increased and the ratio of change in tidal volume (ΔVT) to change in pressure (ΔP) (ΔVT/ΔP) remained constant. In a proportion of lambs, a small decrease in blood pressure and heart rate was observed. The effect of breathing 100% O2 on lung compliance was variable.

4. These changes in ventilation were virtually abolished after both sinus nerves had been cut.

5. The results therefore suggest that a significant hypoxic drive to ventilation exists in the new‐born lamb and that this drive is mediated by functioning and mature peripheral chemoreceptors.

6. Preliminary evidence suggested that, on 100% O2, the sensitivity of new‐born lambs to inhaled CO2 was reduced.
The respiratory response of the new‐born lamb to inhaled CO2 with and without accompanying hypoxia*
Authors: Purves M. J.
Published: December 2014

1. The respiratory response to inhaled CO2 was measured in twenty unanaesthetized new‐born lambs aged 4 hr‐10 days. Measurement of resting arterial pH, PCO2 and plasma bicarbonate showed a non‐respiratory acidosis immediately after birth which was corrected in the first 24‐28 hr: thereafter, the acid—base pattern was of a compensated respiratory alkalosis.

2. When CO2 was added to the inspired gases and resting arterial oxygen tension (Pa, O2) was controlled, the average increase in minute ventilation (V̇) was 0·075 l.min−1.kg−1.mm Hg, Pa, CO2−1 and duplicate responses in the same lamb differed by 6‐22·5%.

3. The slope of the V̇/Pa, CO2 line (S) varied inversely with Pa, O2. In one lamb, severe hypoxia (Pa, O2 = 21 mm Hg) caused a marked depression of the slope.

4. Neither the slope S nor the horizontal intercept B of the lines was related to the age of the lamb. B was not related to pHa and only slightly affected by acute hypoxia. B was related to arterial [HCO3−] and values for both were reduced with the acid—base disturbances seen in the first 10 days after birth. Evidence was given which suggested that the response of the new‐born lamb to inhaled CO2 was similar to that of man acclimatized to a Pa, O2 of 70‐75 mm Hg.

5. In the lightly anaesthetized lamb, bilateral section of the sinus nerves caused a small reduction in the sensitivity to inhaled 5% CO2 in air, an increase in the respiratory lag and a reduction in the rate at which V̇ increased.

6. It was concluded that, in the new‐born lamb, the carotid chemo‐receptors are involved in the response to inhaled CO2 and that hypoxia potentiates this response.
Competition between sodium and calcium ions in transmitter release at mammalian neuromuscular junction
Authors: Gage P. W. , Quastel D. M. J.
Published: December 2014

1. Frequencies of miniature end‐plate potentials (m.e.p.p.s) were recorded at neuromuscular junctions in rat diaphragm‐phrenic nerve preparations in vitro.

2. In the presence of raised [K] (15‐20 m
M) lowering [Na] caused a rapid increase in m.e.p.p. frequency whether [Ca] was low or normal. Raising [Na] towards the normal concentration (162 m
M) caused a slow fall in frequency and raising [Ca] in the range 0·32‐2 m
M caused a slow increase in frequency. These effects were less in the normal [K] (5 m
M).

3. Mean m.e.p.p. frequencies were determined for solutions containing 15 m
M‐K and combinations of [Ca] and [Na]. M.e.p.p. frequency varied inversely with [Na] when [Ca] was constant. In each of the three Na concentrations used (162, 113 and 65 m
M) raising [Ca] in the range 0·32‐2 m
M increased m.e.p.p. frequency but when raised above 2‐3 m
M, Ca depressed frequency.

4. A model was proposed in which Ca affected transmitter release by changing the concentration in the presynaptic membrane of a complex CaX to which the rate of transmitter release was directly proportional. Higher concentrations of Ca depressed transmitter release by inactivating CaX. Sodium ions competitively depressed release either by competing with calcium ions for association with X or by reducing the affinity of X for Ca.

5. When [Na] was lowered in solutions containing raised [Mg] and [Ca], the increase of mean m.e.p.p. frequency was greater than that observed in raised [Ca] and normal [Mg] and was of the same order as the increases seen in low [Ca]. The result was interpreted to indicate either that Na and Mg do not compete with Ca at the same site or that Mg affects the affinity of X for Ca and Na.

6. The effect of lowering [Na] on m.e.p.p. frequency was a specific effect of Na ions. When LiCl was substituted for NaCl, the increase of m.e.p.p. frequency persisted. Changes in [Cl] had no effect on m.e.p.p. frequency.

7. There was a linear relation between the mean logarithm of m.e.p.p. frequencies and [K], the slope of the relation increasing as [Na] was lowered. Conversely, lowering [Na] caused a greater increase in m.e.p.p. frequency as [K] was raised.

8. The variation of m.e.p.p. frequencies in a diaphragm was roughly proportional to a second or higher power of [Na] and inversely proportion to [Ca]. It was thought that this could be due to differences in chelation of Ca which were more apparent at low Ca concentrations.

9. The similarities between the effects of Na, Ca and K on m.e.p.p. frequency and the effects of these ions on Ca‐influx in heart muscle led to the suggestion that transmitter release is proportional to the concentration of a negatively charged complex of a carrier X with one calcium ion (CaX) at the internal surface of the membrane and that changes in membrane potential affect transmitter release by changing the distribution or location of CaX in the membrane.
An examination of the evidence for membrane pores in frog skin
Authors: Dainty J. , House C. R.
Published: December 2014

1. Measurements of the diffusional permeability, Pd, of tritiated water in isolated frog skin bathed in sulphate Ringer have been made under different stirring conditions.

2. The mean ±
S.E. values for Pd were found to be (6·5 ± 0·3), (7·9 ± 0·5), (9·7 ± 0·7) and (11·1 ± 0·8) × 10−5 cm sec−1 at 120, 300, 500 and 1000 rev/min. It is considered that these results indicate the existence of ‘unstirred layers’ associated with frog skin.

3. The hydraulic conductivity, Lp, of the skin in sulphate Ringer was found to be (2·36 ± 0·07) × 10−7 cm sec−1 atm−1 (±
S.E. of estimate), and no marked increase in this value for Lp was found when the stirring rate was increased from 0 to 500 rev/min.

4. It is considered that these results show that previous comparisons of the relative magnitudes of LpRT/V̄w (where V̄w is the partial molar volume of water) and Pd for frog skin have been in error because of the presence of ‘unstirred layers’.

5. The bearing of our results and other evidence on the question of pores in cell membranes has been discussed.
Skin histamine in cats: its depletion and subsequent recovery after injection of compound 48/80
Authors: Waton N. G. , West G. B.
Published: December 2014

1. The histamine content of the skin has been determined in untreated cats, in cats injected with the histamine liberator, compound 48/80, and in cats injected subcutaneously with an oily suspension of histamine or histidine after treatment with compound 48/80.

2. Skin histamine in cats varied from 2·2 to 37·5 μg/g. Apart from regional variations in the histamine content of the abdominal skin, lower values were obtained from cats kept on a laboratory diet which included aureomycin (mean 8·5 μg/g, range 2·2‐13·1) than from cats on a high protein diet without aureomycin (mean 17·5 μg/g, range 5·2‐37·5).

3. Compound 48/80 caused a depletion of skin histamine which was never complete, and a residue of 3‐7% remained; in cats which originally had a low histamine content of skin, depletion was even less and up to 20% of the original histamine remained.

4. Recovery of skin histamine in cats after injections of compound 48/80 was slow, at least 110 days being required for full restoration. The rate of recovery was not altered by daily subcutaneous injections of histidine, but an effect was found with daily subcutaneous injections of histamine. Histamine had no effect for the first 33 days, but at 55 days the percentage histamine content of the skin was greater than in the cats treated with histidine or the oily suspending vehicle, and at 110 days the histamine content was not only much greater than the other two groups but was greater than that before injection of compound 48/80.

5. No in vitro histamine formation was detected in the skin samples either before compound 48/80 treatment or at any time during the subsequent recovery of the histamine to control levels.

6. The results support the theory that the histamine found in skin tissues of the cat is not formed there but is taken up from the blood stream.
The inhibitory action of noradrenaline and other monoamines on spinal neurones
Authors: Engberg I. , Ryall R. W.
Published: December 2014

1.
L‐Noradrenaline (NA), 5‐hydroxytryptamine (5‐HT) and acetylcholine (ACh) were administered micro‐electrophoretically to feline lumbar neurones while recording their spike potentials extracellularly.

2. There was no evidence to suggest that NA acts as an excitatory transmitter in the spinal cord.

3. NA had potent inhibitory effects on some interneurones as revealed by a depression of spontaneous and synaptic firing and on the firing to a local application of an excitant amino acid. The effects on Renshaw cells and motoneurones were less marked.

4. The depressant actions of 5‐HT were less marked than those of NA. ACh and carbamylcholine had depressant effects on some NA‐sensitive interneurones but were invariably far less potent and on other NA‐sensitive cells were completely inactive.

5. NA had no detectable effect on the normal spike amplitude but when the action potentials were reduced by excessive depolarization then both NA and synaptic inhibition increased the spike amplitude; this effect could be due to a hyperpolarization of the cell membrane.

6. There was a correlation between the distribution of NA‐sensitive cells and the relative densities of NA‐containing terminals in various layers of the grey matter.

7. It was postulated that NA acts as an inhibitory transmitter released from the terminals of descending pathways in the spinal cord. Other possible mechanisms were discussed but lacked experimental support.
Observations on the isolated foetal sheep with particular reference to the metabolism of glucose and fructose
Authors: Alexander D. Pauline , Britton H. G. , Nixon D. A.
Published: December 2014

1. Isolated sheep foetuses of 72‐146 days conceptual age (155‐4840 g) have been maintained for periods up to 325 min on an artificial circuit where the placenta has been replaced by an oxygenator.

2. Measurements made during the period of observation included heart rate, femoral arterial pressure, umbilical blood flow, blood gases and pH; plasma and urine concentrations of glucose, fructose, lactic acid, urea, α amino nitrogen and electrolytes.

3. The circulatory, metabolic and renal conditions of the isolated foetus were found to be similar to those of the exteriorized foetus with intact placental connexions. However, in the later stages a terminal hypoxia developed. This was due to a progressive diminution in umbilical blood flow caused by umbilical arterial constriction.

4. The young foetuses removed glucose from the circulation and seemed unaffected by the consequent hypoglycaemia. If the glucose removed was completely oxidized it would account for much of the estimated oxygen consumption. The blood glucose concentration in the older foetuses, on the other hand, did not fall and sometimes rose. Renal excretion of glucose was very small.

5. Fructose was usually slowly removed from the circulation and under no conditions did a rapid removal occur. Renal excretion accounted for about half of the fructose disappearing from the apparent fructose space. It is therefore suggested that a small utilization of fructose occurs in foetal tissues but this could account for only a very small fraction of the estimated oxygen consumption.
Release of vasopressin and oxytocin from isolated pituitary glands of adult and new‐born rats
Authors: Dicker S. E.
Published: December 2014

1. Pituitary glands of adult rats of both sexes, of lactating female and of new‐born rats, incubated in a Locke solution, release both oxytocin and vasopressin. The amount of hormones released, during a measured period of incubation, is related to the actual hormone content of the gland.

2. Increasing the concentration of KCl in the incubation medium, with CaCl2 present and in concentration of at least 2·2 m
M, produces an enhanced release of both hormones from pituitary glands of adults, but does not affect the release of hormones from glands of new‐born animals.

3. Addition of ouabain to the incubation medium produces a marked increase of the release of the hormones from glands of both adult and new‐born rats. This is accompanied by an extrusion of K ion and an influx of Na ion. The effect of ouabain on the hormone release and the shift of ions can be reversed by subsequent addition of adenosine triphosphate.

4. The increased release of hormones produced by ouabain, in glands from new‐born rats, is unaffected by the presence or absence of CaCl2. In adults, however, the effect of ouabain, though present, is reduced in the absence of CaCl2.

5. It is suggested that in glands from adult animals, the hormones must be freed from their attachment on the protein‐carrier, neurophysin and that this can be achieved by the entry of calcium ion into the cell. The subsequent secretion of the ‘freed’ hormones appears to be accompanied by a shift of ions across the cell membrane.

6. In glands from neonates up to 3 weeks old, the absence of neurophysin, or its poor capacity for binding the hormones, explains the inability of calcium to operate in the same way as in the glands of adults. There is evidence suggesting that the secretion of the neurohypophysial hormones in the new‐born animal consists mainly of their diffusion from the cells, without previous elution of the hormones as in adults.
An excitatory action of adrenaline, noradrenaline, and 5‐hydroxytryptamine on the spinal cord
Authors: E Silva M. Rocha , Sproull D. H.
Published: December 2014

1. Fasciculation was produced in the trapezius and sternomastoid muscles of anaesthetized cats by adrenaline, noradrenaline and 5‐hydroxytryptamine (5‐HT) put into the cisterna magna. Isoprenaline, similarly applied, was ineffective.

2. Each of the three active amines was without effect when applied for a second time after the fasciculation in response to the first application had passed off, but 5‐HT was effective after adrenaline and, similarly, adrenaline after 5‐HT.

3. Fasciculation produced by adrenaline, but not by 5‐HT, was inhibited by ergotamine or phenoxybenzamine, given intravenously.

4. In producing fasciculation, the adrenaline appeared to be acting on or through the lateral aspect of the upper cervical cord, about the line of emergence of the roots of the spinal accessory nerve, mainly in C1 and C2.

5. The electromyograms of the fasciculation due to adrenaline and 5‐HT showed intermittent bursts of activity. After adrenaline, the bursts consisted of fewer spikes than after 5‐HT. The intervals between consecutive spikes were 3·75‐5 msec after either amine, and the bursts occurred irregularly, at frequencies between 7 and 12/sec.

6. It is suggested that adrenaline and 5‐HT have excitatory actions on the dendrites or somata of the spinal accessory motor neurones, and the possible role of these amines as synaptic transmitters in the spinal nucleus of the accessory nerve is discussed.
Presynaptic inhibition evoked by muscle contraction
Authors: Devanandan M. S. , Eccles Rosamond M. , Stenhouse D.
Published: December 2014

1. Contractions of flexor and extensor muscles of the knee and ankle were used to investigate presynaptic inhibition at the spinal level.

2. Contractions evoked dorsal root potentials, and increased the excitability of the central terminals of group Ia, Ib and low threshold cutaneous primary afferent fibres.

3. The monosynaptic reflexes recorded in response to stimulation of flexor or extensor muscle nerves were depressed, in the presence of strychnine hydrochloride 0·1 mg/kg
I.V., by the contractions.

4. It is suggested that these presynaptic inhibitory effects are largely due to the activation of Golgi tendon organs by contraction.
The origin of the glucose dependent increase in the potential difference across the tortoise small intestine
Authors: Wright E. M.
Published: December 2014

1. Experiments were carried out to investigate the origin of the glucose dependent increase in the potential difference (p.d.) across the isolated intestinal mucosa of the tortoise.

2. In addition to glucose, galactose, α‐methyl glucoside, 3‐0‐methyl glucopyranose and sucrose also increased the transepithelial potential difference. There was no increase with either fructose or mannose.

3. The use of micro‐electrodes demonstrated that the change in the p.d. due to the presence of glucose was wholly accounted for by the increase in the p.d. across the serosal face of the epithelial cells.

4. Diffusion potentials were produced across the isolated mucosa by varying the ionic composition of either the mucosal or serosal fluids. However, there was no reduction of the glucose dependent increase in the p.d. when the ionic concentration gradients across the serosal face of the cell were reversed.

5. These results suggest that the increase in the p.d. associated with the active transfer of sugars across the small intestine was due to the presence of an electrogenic ion pump at the serosal face of the epithelial cell.