bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non‐transmitting neuromuscular junctions during an early stage of end‐plate reinnervation
Authors: Dennis M. J. , Miledi R. 
Published: December 2014

1. Electrophysiological studies were made on regenerating motor end‐plates in frog cutaneous pectoris muscle after crushing the motor nerve.2. The pattern of degenerative and regenerative changes is similar to that already described for the frog sartorius, although it occurs more quickly in the cutaneous pectoris. Resumption of synaptic transmission first occurs after 9 days, in muscle fibres closest to the nerve crush. During the subsequent 12 days synaptic contact is progressively re‐established across the muscle.3. During the period of regeneration muscle fibres can be found which have been reinnervated, but which do not produce an end‐plate potential in response to stimulation of the nerve trunk. This is referred to as the ‘non‐transmitting’ stage of regeneration.4. Increases in extracellular potassium, addition of lanthanum to the bath and focal extracellular stimulation all indicate that the axon terminals at non‐transmitting junctions do have a releasable supply of neurotransmitter. Focal stimulation occasionally sets up active responses in these nerve terminals.5. It is concluded that this ‘non‐transmitting’ stage results from failure of action potential propagation in the regenerating neurone proximal to the end‐plate region.
Characteristics of transmitter release at regenerating frog neuromuscular junctions
Authors: Dennis M. J. , Miledi R. 
Published: December 2014

1. A study was made of the onset of transmission and the characteristics of transmitter release from regenerating nerve terminals in frog muscle fibres.2. Soon after transmission had been restored, some junctions were found which responded to nerve stimulation with only subthreshold end‐plate potentials.3. The evoked transmitter release had a non‐linear dependence on the external calcium concentration, like that seen at normal junctions.4. The synaptic delay was only slightly longer than normal, and the amplitudes of single quantum potentials evoked by nerve stimulation seemed to have a normal distribution.5. The mean amplitude of the spontaneous miniature end‐plate potentials was often substantially smaller than the mean amplitude of the evoked quantal potentials at a given end‐plate. Some of these small spontaneous potentials were due to transmitter release from the axon terminal. Possible explanations for this discrepancy in size of spontaneous and evoked potentials are discussed. Two to three weeks after reinnervation began, the amplitude of the spontaneous miniature end‐plate potentials returned to normal.
The transamination of glutamate and aspartate during absorption in vitro by small intestine of chicken, guinea‐pig and rat
Authors: Parsons D. S. , Volman‐Mitchell Hetty 
Published: December 2014

1. Procedures are described for direct measurement of the extent and rate of transamination of glutamate and aspartate over periods of up to 90 min, during absorption in vitro by the small intestine of chicken, guinea‐pig, and rat.2. During absorption of dicarboxylic amino acids by rat small intestinal segments circulated through the lumen in vitro, alanine contributed up to 85% of the amino acids appearing in the fluid secreted at the serosal surface. In guinea‐pig and chicken intestine, the proportion of alanine in the secreted amino acids did not exceed 60%.3. For the different species studied, a relationship was found between the extent to which the dicarboxylic amino acids were transaminated to alanine and the total amount of GPT found in other studies to be present in the intestinal mucosa. In both rat and guinea‐pig small intestine, the proportion of alanine in the total amino acids appearing at the serosal surface was similar in the jejunum and ileum. The rate of appearance of alanine in serosal fluid was greater in the ileum than in the jejunum of the rat.4. Reasons are given for supposing that for all the species studied there is a limit to the capacity of the small intestinal mucosa to subject free dicarboxylic amino acids to transamination. It is concluded, however, that it is unlikely that this capacity will be exceeded under in vivo conditions.
The effects of cortisone acetate on stomach evacuation and the absorption of 125I‐labelled globulins in young rats
Authors: Morris B. , Morris R. 
Published: December 2014

1. After short exposure (3–5 hr) to
I.P. cortisone acetate (5 mg), the reduced transmission of labelled globulin to the circulation in 14‐day‐old rats is due to the slow release of the oral dose from the stomach. The ability of the small intestine to absorb and transmit globulin to the circulation is comparable in control and experimental animals.2. About 26 hr after cortisone acetate treatment (5 mg), the greatly reduced absorption of labelled globulin from oral doses administered to rats aged 15 days is due to the combined effects of the slower release of the dose from the stomach and to changes which have occurred in the small intestine.3. About 50 hr after the administration of 5 mg cortisone acetate the effect on the rate of stomach evacuation is minimal in rats aged 16 days. When labelled globulin is introduced directly into the duodenum of these animals virtually no absorption occurs.4. The results obtained from the experiments in which labelled globulin was injected into the duodenum support the contention that the proximal half of the small intestine is an important site for macromolecular transport.
Storage and release of acetylcholine in a sympathetic ganglion
Authors: Birks R. I. , Fitch S. J. G. 
Published: December 2014

1. The hypotheses of preferential release of newly synthesized acetylcholine (ACh) and two compartment storage of transmitter in the cat superior cervical ganglion have been re‐examined by testing, first, the assumption that ganglionic ACh stores do not alter during a 20 min rest following 60 min preganglionic nerve stimulation at 20/s, and secondly, the implication that the rate of ACh release should be high near the onset of activity and decline to a lower rate with time irrespective of the frequency of stimulation.2. The ganglionic ACh stores were found to increase by 38 ± 8% within 20 min following 60 min preganglionic nerve stimulation at 20/s, and this extra ACh was releasable.3. The rate of ACh release from ganglia perfused with cat plasma and stimulated at 4/s increased over the first 5 min of stimulation to reach a 27% higher rate that was maintained.4. Correction of the original data to allow for the post‐activation increase in ACh stores suggests that newly synthesized ACh equilibrates with most of the preformed stores. The time course of ACh release at 4/s does not support the two compartment model as currently formulated.5. These findings resolve in part a conflict between the physiological data and a recent hypothesis for ACh storage based on ganglion morphology.
Comparison of the effects of stimulation of the sympathetic vasomotor nerves and the adrenal medullary catecholamines on the hind limb blood vessels of the rabbit
Authors: Powis D. A. 
Published: December 2014

1. The responses to sympathetic nerve stimulation and to the adrenal medullary hormones have been studied in the hind limb vascular beds of the anaesthetized rabbit.2. Simultaneous measurements of femoral arterial blood pressure and of femoral venous blood flow indicate that stimulation of the sympathetic nerves decreases the calculated vascular conductance in both the intact and skinned hind limbs. Evidence is presented to show that these changes are due to vasoconstriction.3. The vasoconstriction in both skin and muscle vascular beds reaches a maximum at frequencies of stimulation around 15 Hz. No vasodilatation is obtained at any frequency of stimulation.4. The rabbit adrenal gland secretes only adrenaline during splanchnic nerve stimulation at frequencies between 3 and 60 Hz. The amounts liberated from both glands over this frequency range are 25–500 ng.kg body wt.−1 min−1.5. Intravenous infusions of adrenaline in concentrations similar to those liberated by the adrenal glands during splanchnic nerve stimulation, and of noradrenaline, cause only vasoconstrictor responses in skin and muscle.6. Simultaneous stimulation of the sympathetic nerves to the hind limb and infusion of adrenaline in quantities that could be liberated by splanchnic nerve stimulation at equivalent frequencies shows that the vasoconstrictor effects exerted by the individual components are additive, though the effects produced by the direct sympathetic nerve supply overshadow those produced by the catecholamine.7. The results are discussed in the context of the possible vascular role of the adrenal medullary hormones in the rabbit.
Responses of rostral hypothalamic neurones to peripheral temperature and to amines
Authors: Jell Ralph M. 
Published: December 2014

1. Five‐barrelled micropipettes have been used to record extracellularly the activity of neurones in the rostro‐medial hypothalamus of methoxyflurane‐anaesthetized cats, and to apply acetylcholine (ACh), noradrenaline (NA) and 5‐hydroxytryptamine (5‐HT) by micro‐iontophoresis to the vicinity of each neurone encountered. Peripheral thermal stimulation was achieved by blowing warm (42° C) and cold (4° C) air in the face of the animal, and thermoresponsiveness was compared with amine responsiveness.2. One hundred and twenty‐two neurones were obtained from ten cats. Eleven (9%) were warm‐responsive and sixteen (13%) were cold‐responsive. The rest did not respond to facial warming or cooling.3. No consistent relationship was observed between amine responses and responsiveness to facial temperature. Warm‐responsive neurones were mainly depressed or unaffected by amines. Cool‐responsive neurones were excited, depressed or unaffected by amines with the exception that no 5‐HT excitations were seen. Thermoresponsive neurones were more likely to be amine depressed than non‐thermoresponsive neurones.4. Six thermoresponsive neurones responded to peripheral temperature and to amines in a way which fitted the amine model of Myers (1971). Fifteen thermoresponsive neurones fitted the model of Bligh, Cottle & Maskrey (1971), according to the same criteria.5. The results lend little support to the amine model, as predicted from amine micro‐injection and release studies in primates, but support more strongly the model of Bligh et al. (1971) which is based on intraventricular injections of amines in sheep, goats and rabbits. On the basis of the latter model, functional identification was possible in 63% of the thermoresponsive rostral hypothalamic neurones tested.
The effects of load and force on tremor at the normal human elbow joint
Authors: Joyce G. C. , Rack Peter M. H. 
Published: December 2014

1. Spontaneous flexion‐extension tremor of the elbow was recorded in normal human subjects while they exerted a flexing force against different loads.2. Increases in the flexing force up to ½ or ¾ of the subject's maximum were accompanied by increases in the amplitude of the tremor. A further increase to very large forces was associated with a decrease in tremor.3. When the subject flexed against a spring, the frequency of the tremor was related to the properties of the spring; with increasingly stiff springs the tremor frequency increased up to about 12 Hz. With the stiffest springs, however, the tremor became irregular and very small in amplitude.4. Weights added to the limb at the wrist reduced the frequency of tremor.5. By using appropriate combinations of spring and mass, the principal tremor frequency could be adjusted between 2 and 12 Hz, higher in some subjects. Within this range the frequency2 was approximately proportional to the spring stiffness/mass, just as it is in a spring‐mass system, though the forearm provided some of this mass, and some of the spring‐like resistance was in the flexor muscles.6. When by suitable loading the tremor frequency was brought between 8 and 12 Hz, and the subject forcibly flexed his elbow, the tremor became regular and large in amplitude. This was a form of limited instability in the stretch reflex which arose because a powerful reflex response to extension of the elbow acted back on the flexor muscles after a delay.7. When the limb was so loaded that its natural frequency was outside this 8–12 Hz range, it behaved as a filter, and in response to any disturbing noise it oscillated mainly at frequencies close to the natural frequencies of either the mechanical system or the stretch reflex.8. This filtering function of the limb with its stretch reflex probably plays an important part in the control of normal movement and tremor.9. The large flexing forces that were here associated with vigorous tremor normally occur when a limb supports a large mass. Such a mass would give the mechanical system within the limb a low natural frequency; inconveniently large oscillations in the 8–12 Hz range would therefore seldom occur.
Dependence of intestinal glucose absorption on sodium, studied with a new arterial infusion technique
Authors: Fisher R. B. , Gardner M. L. G. 
Published: December 2014

1. A new preparation of isolated rat jejunum plus ileum (ca. 100 cm) is described in which a saline infusate is pumped into the superior mesenteric artery, the superior mesenteric vein having been ligated.2. The arterial infusate washes out the tissue spaces: the lumen is perfused in a single pass with a segmented flow as by Fisher & Gardner (1974).3. At an arterial infusion rate of 3 ml./min, steady states are set up in the tissue fluid within 10–15 min: the compositions of the fluids bathing both sides of the mucosa can therefore be controlled.4. The rate of glucose absorption from the lumen falls only gradually when the luminal sodium is replaced by choline abruptly while the tissue fluid sodium is maintained at 144 m‐equiv/l. by arterial infusion.5. The rate of glucose absorption from the lumen is unaffected by replacement of sodium in the arterial infusate by choline.6. Ouabain (10−4 M) in an arterial infusate containing sodium 144 m‐equiv/l. causes inhibition of glucose and water absorption from the lumen. There is no effect of ouabain when the arterial infusate contains sodium, 0 or 72 m‐equiv/l.7. Arterial ouabain does not reverse the effects of depletion of luminal sodium. Simultaneous removal of luminal sodium and application of arterial ouabain causes faster inhibition of glucose absorption than does either treatment alone.8. Glucose absorption is more likely to depend on rate of efflux of sodium from mucosal cell to tissue fluid than on a sodium gradient at the brush border or on intracellular sodium concentration.
Sodium—calcium sites in smooth muscle and their accessibility to lanthanum
Authors: Burton Josiane , Godfraind T. 
Published: December 2014

1. The Na, K, Ca, and Mg contents were determined in longitudinal smooth muscles of the guinea‐pig ileum incubated in various physiological solutions with or without ouabain or in a solution containing LaCl3 10 m
M instead of CaCl2.2. The Na and K contents were dependent upon the K concentration of the physiological solution. A decrease in [K]o below 6 m‐mole/l. increased tissue Na.3. A rise in [Na]i was followed by an increase of total cell Ca preceding a secondary decrease of total Ca, as well as by an increased 45Ca content occurring even when total Ca was decreased.4. Muscles washed in the lanthanum solution contained less Ca and Na than those incubated in the physiological solution. The Mg content was not significantly modified in the presence of La.5. In the La solution, the 45Ca diffusion space was not different from the [14C]inulin diffusion space, indicating that there was no Ca entry within the cell nor Ca binding at superficial sites. 45Ca content of preloaded muscles decreased; this decrease was blocked after 30 min washout in the La solution: this arrest lasted a further 45 min.6. The cell Ca fraction displaced by increased [Na]i originated from a Ca compartment which was not blocked by La.
Relationship between blood pressure alterations and bursts of panting in the conscious dog: a comparison of the effects of exercise and heat exposure
Authors: Dampney R. A. L. , Hales J. R. S. 
Published: December 2014

1. Continuous recordings of the arterial blood pressure and intrathoracic pressure of conscious dogs have been taken, in each animal, under two different conditions: (a) during mild exercise on a treadmill in a thermoneutral environment (19–22° C Tdb, 13·5–17·5° C Twb); (b) at rest in conditions of mild heat stress (35–40° C Tdb, 20–26° C Twb), and of severe heat stress (35–40° C Tdb, 30–34° C Twb).2. Under all conditions, panting occurred, but there were differences in its pattern. During exercise, panting usually occurred in short regular bursts of about 10 sec duration, whereas during both mild and severe heat stress it occurred in bursts of irregular but usually longer duration. At comparable rectal temperatures, the intensity of panting (as measured by the amplitude of intrathoracic pressure variations) was markedly greater during exercise than during heat stress; the frequency, however, was lower.3. During exercise, the bursts of panting were associated with striking oscillations in mean blood pressure, whereas during mild and severe heat stress they were associated with much smaller changes in mean blood pressure. In addition, cross‐correlation analysis revealed that blood pressure changes were far more strongly correlated with bursts of panting during exercise than during mild or severe heat stress.4. In view of the present and previous results, it is suggested that both the bursts of panting and the associated cardiovascular changes during exercise are stimulated primarily by metabolic rather than thermoregulatory factors. During heat stress, bursts of panting are solely thermally induced, and are therefore not associated with similar cardiovascular alterations.
Intracellular sodium and potassium concentrations in oocytes of Bufo bufo at the beginning of maturation
Authors: Dick D. A. T. , Ho‐Yen D. O. 
Published: December 2014

1. During the first phase of maturation in oocytes of Bufo bufo, after the growth phase but before ovulation, intracellular Na rises to 120 m‐mole/l. cell water while K falls to 15 m‐mole/l. cell water.2. At the same time, the ouabain‐insensitive Na efflux and total Na influx both increase while the ouabain‐sensitive Na efflux is unchanged.
Ornithine decarboxylase activity, nucleic acids and cell turnover in the livers of pregnant rats
Authors: Campbell Rosa M. , Fell B. F. , Mackie W. S. 
Published: December 2014

1. Comparisons were made between the livers of pregnant and non‐pregnant rats, all of which were fed on a ration of 20 g food per day.2. In the second half of pregnancy there were marked increases in the weight of the liver and in its total content of protein, RNA and DNA. RNA concentration increased from the 15th day of gestation.3. Between the 12th and 18th day of pregnancy liver weight, total RNA, totla DNA and mean liver cell nuclear volume increased in parallel at approximately the same rate of 6–10% per day.4. Ornithine decarboxylase activity was enhanced in pregnancy by the 5th day of gestation and rose to peak activity at the 18th day.5. The mitotic index of hepatic parenchymal cells was elevated in the first and last stages of pregnancy. The later peak in mitosis was associated with a rapid fall in mean nuclear volume.6. There was histological evidence of cell turnover in the liver of pregnant rats; enlargement of the liver was associated with both hyperplasia and cell deletion.
Methionine accumulation in villi isolated from maturing rat intestine
Authors: Fondacaro Joseph D. , Nathan Paul , Wright Walter E. 
Published: December 2014

1. This study compares the absorption rates of methionine in 15‐day‐old rats (preweaned) and 30‐day‐old rats (post‐weaned), and the effect of varying initial substrate concentration on the absorption rate of methionine in tissue removed from specific sites in the small intestine.2. The experiments utilize a new in vitro method, the villus technique, permitting evaluation of the mucosal (villus) absorptive cells separated from the relatively non‐transporting muscle and connective tissue components (non‐villus tissue).3. When the villus technique was used in a comparative age study of absorption by jejunal and duodenal tissue, it was found that at initial methionine concentrations below 1·0 m
M, no difference in the transport rate between preweaned and post‐weaned animals was observed.4. However, in preweaned animals, methionine transport is faster in the ileum than in the jejunum or duodenum.5. With initial methionine concentration greater than 1·0 m
M, duodenal and jejunal villi from preweaned animals transport methionine better than villi from older animals.6. At these higher methionine concentrations there is a slightly better transport by ileal villi from 30‐day‐old rats than in the younger group.7. With increasing initial concentration of methionine, physiological changes are shown to occur during maturation because transport rates into villi of mature duodenal and jejunal tissues are slower than into similar tissue from preweaned rats.8. The underlying physiological changes responsible for the transport rate differences are not known.9. The results reported indicate that following maturation, the absorbing mucosal cells from the duodenum, jejunum and ileum have an equal capacity for methionine accumulation.10. The apparent localization of the major amino acid transport to the ileum as reported by others may be an artifact reflecting the inclusion of an undetermined amount of non‐absorbing muscle mass in the calculation of intestinal transport.
The effect of glycine‐conjugated bile acids on net transport and potential difference across isolated rat jejunum and ileum
Authors: Wingate D. L. 
Published: December 2014

1. Five m
M glycodeoxycholate and glycochenodeoxycholate inhibit net fluid transport across isolated rat jejunum and ileum; 5 m
M glycocholate does not affect jejunal segments, but arrests fluid transport across ileal segments.2. Inhibition of fluid transport is accompanied by some diminution of mucosal glucose uptake, but translocation of glucose to the serosal surface of jejunal segments persists in the presence of dihydroxy conjugated bile acids.3. Inhibition of fluid transport is accompanied by a marked fall in the glucose‐stimulated transmural electropotential difference, within 5 min of mucosal exposure to the bile acids.4. The lactate concentration gradient normally maintained across isolated intestine is abolished when fluid transport is inhibited by conjugated bile acids, even though lactate formation is not greatly reduced.5. These results suggest that inhibition of intestinal fluid transport is reproducible in vitro, and that the inhibition is not associated with increased permeability of the mucosa, but may be associated with altered permeability of the mucosal pole of the enterocyte.6. Although in vitro and in vivo effects of dihydroxy bile acids on fluid transport are similar, the assumption that the mode of action is likewise similar is not justified on present evidence.