bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thyroxine utilization in the new‐born lamb
Authors: Nathanielsz P. W. 
Published: December 2014

1. From previous studies on foetal thyroid function in various mammalian species it would appear that the foetal pituitary—thyroid axis is capable of function before birth. Few studies are available to indicate the level of function before birth and in the immediate post‐natal period.2. Plasma thyroxine levels, thyroxine pool and utilization rate of thyroxine have been followed in new‐born Welsh mountain lambs from birth to 39 days of age.3. Plasma thyroxine levels are high within the first hour of life after birth (18·2 ± 2·0 μg/100 ml.) and fall steadily to a minimum of 5·1 ± 1·1 on day 11 and 12 of post‐natal life. Thereafter they fluctuate about a mean of 6·1 μg/100 ml. The significance of these changes is discussed in respect to foetal thyroxine levels, placental permeability to thyroxine, and foetal and neonatal thyroid and pituitary function.4. Thyroxine utilization rate is high both in absolute terms and relative to unit body weight on days 1‐4 of post‐natal life. The utilization rate/kg remains fairly constant from days 10–39 of post‐natal life.5. Thyroxine utilization in the new‐born lamb is compared with that in the new‐born calf in which the post‐natal growth curve is very different.6. The various factors such as levels of free thyroxine, diet and environmental changes which influence thyroxine utilization are discussed and the rate of utilization is compared with other indices of thyroid function in new‐born and adult animals of different species.
Effect of stimulation and hyperpolarization on non‐electrolyte and sodium permeability in perfused axons of squid
Authors: Hidalgo Cecilia , Latorre Ramón 
Published: December 2014

1. The permeability for micro‐injected [3H]ethylene glycol was measured in resting state and during stimulation at 100/sec in squid giant axons. No detectable changes during electrical activity were observed.2. The influxes of urethane, tritiated water, ethylene glycol, urea and sodium were measured in internally perfused squid axons. Ethylene glycol and urea influxes were determined simultaneously with sodium influxes. The electrical stimulation of the fibre produced an increase in the influx of sodium but did not alter the influxes of the non‐electrolytes listed above.3. Experiments were done with the combined voltage clamp—perfusion technique. The influxes of ethylene glycol and sodium were simultaneously measured in resting state and during maximum sodium current under stimulation at 10/sec. The influx of sodium increased in these conditions but the influx of ethylene glycol remained constant. In some experiments, the fibre was hyperpolarized to 10 or 20 mV, above the resting potential and the influxes of ethylene glycol and sodium were measured. The sodium influx decreased to 60% at 20 mV above the resting potential whereas the influx of ethylene glycol remained constant.4. These results indicate that in the giant axons of the squid Dosidicus gigas, sodium and non‐electrolytes fluxes are not coupled.
The role of hypothalamic temperature in the control of panting in the chicken exposed to heat
Authors: Richards S. A. 
Published: December 2014

1. In unanaesthetized chickens, the temperatures of the hypothalamus, colon and skin have been recorded in relation to the onset and cessation of thermally induced panting.2. During control conditions, hypothalamic temperature showed fluctuations associated with arousal and movement. It was lower than colonic temperature by about 0·9° C but this difference generally decreased during exposure to heat.3. When the birds were exposed abruptly to 40° C, or to ambient temperatures increasing gradually from 20 to 52° C, there was a delay of 15–65 min and marked increases in both peripheral and central body temperatures before panting commenced.4. Infra‐red irradiation of the thorax and abdomen caused vasodilatation in the comb and toe before detectable increases in the deep body temperatures. Increasing the colonic temperature by up to 2° C did not cause panting until hypothalamic temperature was also raised. This inhibitory effect of normal hypothalamic temperature was enhanced by low ambient temperature.5. Infra‐red irradiation of the head increased hypothalamic temperature by up to 3·5° C and caused vasodilatation in the toe without changes in colonic temperature. Panting, however, did not occur so long as colonic temperature was within the normal range. The inhibitory effect of normal colonic temperature was again enhanced by low ambient temperature.6. In anaesthetized chickens, selective heating of the head and body caused panting only after increases in both the hypothalamic and colonic temperatures.7. Repeated exposure of birds to 40° C did not reduce the time delay before panting started.8. It is concluded that panting in the fowl requires an increase in some extracranial deep body temperature as well as in that of the hypothalamus.
The effect of progressive hypoxia on the respiratory and cardiovascular systems of the pigeon and duck
Authors: Butler P. J. 
Published: December 2014

1. During the initial stages of progressive hypoxia in ducks and pigeons (Pa, O2 100 → 60 mm Hg) there were no significant changes in heart rate, blood pressure or oxygen uptake, but respiratory frequency increased.2. As hypoxia became more profound (Pa, O2 60 → 30 mm Hg), there was a significant tachycardia, and blood pressure fell slightly in both animals. Respiratory frequency continued to increase in both species, and ducks were able to maintain their oxygen uptake at control levels at a lower Pa, O2 than pigeons.3. The response to progressive hypoxia of pigeons and ducks was compared with that of the domestic fowl. The former two birds could maintain control of their cardiovascular system at a lower environmental oxygen concentration than the latter. Arterial PO2 followed a similar course in all three birds in relation to environmental oxygen content. Pigeons and ducks were therefore able to endure a lower arterial PO2 than chickens.
The binding of thyroid hormones to phospholipid membranes
Authors: Hillier A. P. 
Published: December 2014

1. Thyroxine and tri‐iodothyronine are bound by liposomes (bimolecular phospholipid membranes produced by dispersing egg‐yolk lecithin in water). At pH 7·4 the ‘partition coefficient’ between water and the phospholipid is 1·2 × 104 for thyroxine and 2·2 × 104 for tri‐iodothyronine. The partition coefficient falls off rapidly in more alkaline solutions as the phenolic group on the hormones becomes ionized.2. The binding of thyroxine by membranes is very rapid, occurring at rates equivalent to those found in the binding of thyroxine by serum.3. Lecithin membranes are readily permeable to thyroxine (the oil:water partition coefficient is 1·7).4. The binding of thyroid hormones by perfused rat hearts and the binding of thyroid hormones by liposomes are similar in their sensitivity to pH. Simple alcoholic extracts of tissues have strong thyroxine‐binding activity.5. These results are discussed in relation to the nature and function of the tissue thyroxine‐binding reaction.
The range and scope of binocular depth discrimination in man
Authors: Blakemore Colin 
Published: December 2014

1. Depth discrimination, using disparity cues alone, was studied with a small fixation point and briefly exposed, vertical slit‐shaped targets.2. The upper limit for reliable qualitative localization of a slit as nearer or further than the fixation point is 4‐7 deg of absolute disparity in a convergent direction and 9–12 deg in a divergent direction. Even larger absolute disparities can be recognized in the peripheral visual field.3. Relative depth discrimination between two slit targets was measured as a function of their spatial position. The horopter (the locus of targets that appear to be fused binocularly) is the region of maximum stereoacuity and this does not necessarily coincide with the Vieth—Müller circle (the locus of zero geometric or absolute disparity). There is a gradual increase in stereo‐threshold as the targets are moved out along the horopter, away from the fixation point into the peripheral visual field. The relative disparity threshold also rises, approximately exponentially, as the targets are moved in depth or absolute disparity away from the horopter.4. Relative depth discrimination is, then, operative over a very wide band of visual space around the horopter (about 3 deg of absolute disparity in the centre of the visual field and even more in the periphery).5. The findings are discussed in relation to the neurophysiology of binocular neurones of the cat cortex. The dimensions of visual space under observation by the binocular apparatus of cat and man are rather similar. The sharper decline of stereo‐acuity with absolute disparity in the centre of the visual field may be related to the limits of bilateral representation of a central strip of retina in the human brain.
Slow changes in membrane permeability and long‐lasting action potentials in axons perfused with fluoride solutions
Authors: Chandler W. K. , Meves H. 
Published: December 2014

1. Voltage clamp experiments were carried out on squid giant axons which were perfused internally with 300 m
M‐NaF + sucrose and placed in K‐free artificial sea‐water at 16–17° C. On stepwise depolarization (V = −38·5 to 68 mV) the Na conductance gNa rapidly reached a peak value and then declined to a new level; this ‘maintained’ level was slowly inactivated in an exponential manner with a rate constant which varied from 0·3 to 1·1 sec−1. This process was not influenced appreciably by replacing 50 m
M‐NaF with KF.2. On repolarization to a potential which varied between −73 and −101 mV the slow inactivation was removed with a rate constant of 0·11–0·73 sec−1.3. Prolonged depolarization also produced a slow inactivation of the ability of the membrane to give a transient increase in gNa. This effect developed at a rate about ⅓‐½ that associated with the inactivation of the ‘maintained’ component; on repolarization, recovery of the peak gNa was 1–2 times as fast as recovery of the ‘maintained’ gNa.4. In experiments on fibres perfused with 300 m
M‐KF after internal NaF had removed the usual delayed K conductance, depolarization resulted in an outward current which developed in an exponential manner with a time constant of a fraction of a second. The equilibrium potential for this component was more negative than −50 mV.5. Long‐lasting action potentials were computed on the basis of the above slow changes and, except for the period of final repolarization, were found to be in satisfactory agreement with experimental records. The discrepancies suggest that there may be additional slow changes in permeability which could not be resolved in the present experiments.
Electrophysiological studies of neuromuscular transmission in hereditary ‘motor end‐plate disease’ of the mouse
Authors: Duchen L. W. , Stefani E. 
Published: December 2014

1. Studies have been made on isolated nerve—muscle preparations from mice with hereditary ‘motor end‐plate disease’.2. Spontaneous fibrillation was observed in the isolated preparation.3. Muscles gave only a weak twitch or failed to contract in response to nerve stimulation. Direct stimulation of muscles caused a twitch response which had a slower time course than normal. Peripheral nerve conduction was normal.4. Intracellular recording from single muscle fibres showed that with longer survival of the animal an increasing proportion of fibres failed to show end‐plate potentials or action potentials in response to nerve stimulation.5. Miniature end‐plate potentials (m.e.p.p.s) were recorded in almost all muscle fibres including those in which neuromuscular transmission had failed. The frequency of m.e.p.p.s was greater than normal, was not increased by tetanic stimulation of the nerve but was increased by a raised external potassium concentration.6. Muscle fibres were supersensitive to acetylcholine.7. The results suggest that the muscular weakness in this disease is due to the failure of nerve action potentials to invade motor nerve terminals so that muscle fibres become ‘functionally denervated’.
Effects of mecamylamine on responses of carotid body chemoreceptors in vivo to physiological and pharmacological stimuli
Authors: Sampson S. R. 
Published: December 2014

1. Effects of mecamylamine on the spontaneous discharge rate of afferent fibres of carotid body chemoreceptors in vivo and their responses to ACh, NaCN, HCl and hypoxia were studied in sixteen cats.2. Cats were anaesthetized with sodium pentobarbitone, paralysed with gallamine triethiodide and artificially ventilated. Chemoreceptor excitants were injected into the common carotid artery; mecamylamine was given intravenously.3. Mecamylamine, 230 μg/kg or greater, failed to diminish either the rate of spontaneous discharge of carotid body chemoreceptors at high arterial oxygen tensions (greater than 130 mm Hg), or the responses of these receptors to NaCN (0·5–25 μg), HCl or hypoxic blood.4. Responses of chemoreceptor afferent fibres to ACh (1·0–50 μg) in the same preparations were either completely abolished or considerably reduced by mecamylamine.5. These data do not support the hypothesis of a cholinergic mechanism for the initiation of chemosensory discharges in the carotid body, either at rest or in response to stimuli such as NaCN, acid or hypoxia.
Passive vasodilatation of the hind limb after sympathetic preganglionic stimulation
Authors: Lioy Franco , Polosa Canio 
Published: December 2014

1. The post‐vasoconstriction dilatation (PVCD) observed after release of carotid clamping has been attributed to baroreceptor stimulation. However, PVCD has been observed in baroreceptor deafferented animals following cessation of stimulation of the diencephalon or of chemoreceptor fibres.2. The effects of preganglionic (ventral roots) and post‐ganglionic (sciatic nerve) stimulation upon the vascular resistance of the hind limb of anaesthetized cats and dogs was investigated. The limb was vascularly isolated and perfused at constant flow with the animal's own arterial blood. The animals were atropinized and neuromuscular block was obtained with gallamine triethiodide.3. PVCD was observed upon cessation of stimulation of intact preganglionic fibres or of their peripheral stump.4. PVCD was dependent upon the existence of neurogenic vasomotor tone in the vessels, but independent from baroreceptor influences.5. PVCD was never observed after cessation of stimulation of the post‐ganglionic fibres.6. Similar results were obtained after removal of the skin of the perfused limb.7. The possibility that the post‐vasoconstriction dilatation observed in these experiments is due to the existence of a preganglionic inhibitory system is discussed.
Vasoactive hormones in endotoxin shock: A comparative study in cats and dogs
Authors: Hall R. C. , Hodge R. L. 
Published: December 2014

1. Entamoeba coli endotoxin was administered intravenously to cats and dogs.2. The changes in circulating levels of catecholamines and angiotensin following endotoxin were assayed by a continuous superfusion technique.3. The response of the dog was characterized by an immediate sustained rise in angiotensin levels and a later variable rise in catecholamine levels.4. The response of the cat was characterized by an early rise in catecholamine levels and a later rise in angiotensin levels.5. It is concluded that this species difference may reflect the relative importance of renin‐angiotensin and sympatho‐adrenal systems of dogs and cats, respectively.
Cardiovascular responses to salt‐loading in conscious domestic geese
Authors: Hanwell Ann , Linzell J. L. , Peaker M. 
Published: December 2014

1. The intravenous injection of large volumes of 0·5
M‐NaCl that are usually used to induce nasal gland secretion in marine birds has been shown in geese to increase greatly plasma volume, cardiac output, heart rate and stroke volume at the time secretion commences after 2‐8 min.2. There were no consistent changes in mean arterial blood pressure or in the distribution of the cardiac output to major organs except to the salt‐glands whose share increased approximately fourteenfold. Salt‐gland blood flow remained high for 10–20 min after cardiac output and heart rate had returned to nearly normal levels.3. The increases in plasma volume and venous return are unlikely to be the stimuli for salt‐gland secretion because secretion was also initiated by giving artificial sea water into the proventriculus and this produced no changes in these variables at the time secretion commenced, 5‐14 min later.4. At the start of secretion in orally loaded birds, the only detectable changes in the plasma were small increases in osmolality (from 1·3 to 4·6%), Na (from 0·3 to 6%) and Cl (from 1·3 to 7·1%) concentrations.
Experiments on the liberation of phosphate from the muscles of the human forearm during vigorous exercise and on the action of sodium phosphate on forearm muscle blood vessels
Authors: Barcroft H. , Foley T. H. , McSwiney R. R. 
Published: December 2014

1. During vigorous sustained or rhythmic exercise of the forearm muscles, plasma phosphate in the venous effluent from the active muscles increased by about 20%.2. The forearm muscles liberate phosphate during vigorous activity. This confirms observations made by Hilton & Vrbová (1970) on fast muscles in the cat.3. Infusions of sodium phosphate into the brachial artery which raised plasma phosphate in the venous effluent from the resting muscles by 400% had no effect upon the rate of the forearm blood flow.4. These results do not suggest that the liberation of phosphate plays any significant part in mediating the vasodilatation accompanying vigorous exercise of the muscles in the forearm.
Effects of hexoses and anions on the erythritol permeability of human red cells
Authors: Wieth Jens Otto 
Published: December 2014

1. The effect of hexoses and of the anions chloride, thiocyanate, and salicylate on the permeability of human red cells to [14C]erythritol has been studied.2. It was confirmed that erythritol competes with glucose, mannose, and galactose for the hexose transfer system of the red cell membrane. Approximately 25% of the erythritol influx was insensitive to the presence of hexoses or phloretin. Identical maximum degrees of inhibition were obtained with 0·3
M glucose and with phloretin (0·5 × 10−3
M). In the absence of competing inhibitors the erythritol permeability, P, was 1·2 × 10−7 cm/sec at 38° C. At maximum inhibition P was 0·3 × 10−7 cm/sec.3. Erythritol is able to penetrate the membrane by two pathways, only one of which is sensitive to hexoses. Both hexose‐sensitive and hexose‐insensitive erythritol influx are well described by first‐order diffusion kinetics. The affinity of erythritol for the hexose transfer system is very low, and the half saturation constants of hexoses can be determined from their ability to retard erythritol permeation. The following values were found for the half saturation of the transport system with hexoses at 38° C: glucose 6 m
M, mannose 11 m
M, and galactose 40 m
M.4. Thiocyanate and salicylate reduce the hexose‐sensitive fraction of erythritol influx, but the hexose‐insensitive erythritol permeability is not affected when chloride is replaced by the foreign anions. This applies to the whole temperature range between 0 and 38° C, where the ionic permeabilities of red cells have been shown to be profoundly changed by thiocyanate and salicylate.
The transformation of myosin in cross‐innervated rat muscles
Authors: Bárány M. , Close R. I. 
Published: December 2014

1. The characteristics of isometric twitch and tetanic contractions have been determined for normal (N‐EDL, N‐SOL), self‐innervated (S‐EDL, S‐SOL) and cross‐innervated (X‐EDL, X‐SOL) extensor digitorum longus (EDL) and soleus (SOL) muscles of the rat at 35° C. The muscles were then used for biochemical analyses of properties of myosin and actomyosin.2. The ATPase activities of myosin and actomyosin of X‐EDL decreased to the level of those of N‐SOL or S‐SOL, and the ATPase activities of X‐SOL approached those of N‐EDL or S‐EDL. Of the various ATPase activities, the actin‐ and Mg2+‐activated ATPase activity of myosin and the Mg2+‐activated ATPase activity of actomyosin showed the highest degree of correlation with the intrinsic speed of shortening of the muscles.3. Myosin of normal, self‐innervated, and cross‐innervated muscles combined with F‐actin superprecipitated at rates which were proportional to the speed of muscle contraction.4. The pH profile curve and the ATP‐induced dinitrophenylation reaction revealed that the structure of myosin of X‐EDL was altered to that of N‐SOL or S‐SOL, and the structure of myosin of X‐SOL was modified to that of N‐EDL or S‐EDL.5. No differences were found in the yield of myosin of normal, self‐innervated, and cross‐innervated extensor digitorum longus and soleus muscles.
The distribution of cutaneous receptors in the rabbit's hind limb and differential electrical stimulation of their axons
Authors: Brown A. G. , Hayden R. E. 
Published: December 2014

1. The receptive field properties and conduction velocities of single dorsal root axons, activated from the sural and cutaneous branches of the posterior tibial (medial plantar) nerves, were examined in anaesthetized rabbits.2. The sural nerve sample included all types of units previously recorded from the saphenous nerve (Brown & Iggo, 1967). In particular it was shown that electrical stimulation of the sural nerve at strengths up to 1·3T produced a volley of impulses in a pure population of slowly adapting units (Type I units).3. The medial plantar sample showed an absence of Type I slowly adapting units and Type T hair follicle units. Corresponding to this there were no touch corpuscles or tylotrich hairs in the skin of the hind foot and the fastest medial plantar axons conducted at 60–70 m/sec as opposed to 80–85 m/sec for the sural nerve. Stimulation of the medial plantar nerve at stimulus strengths close to threshold produced a volley of impulses in a nearly pure population of Type G hair follicle units.
Correlation between nerve terminal size and transmitter release at the neuromuscular junction of the frog
Authors: Kuno M. , Turkanis S. A. , Weakly J. N. 
Published: December 2014

1. End‐plate potentials were recorded intracellularly at the frog neuromuscular junction bathed in a solution containing a low concentration of calcium and a high concentration of magnesium.2. The muscle was subsequently subjected to ‘cholinesterase staining’, and the area of the individual end‐plates, studied with intracellular electrodes, was measured.3. A positive correlation was found between the end‐plate area and the diameter of muscle fibres.4. The mean quantum content (m) showed a positive correlation with the size of end‐plates.5. The frequency of spontaneous miniature end‐plate potentials was positively correlated with m as well as with end‐plate area.6. It is concluded that the amount of transmitter released following nerve stimulation is related to the size of nerve endings.