bluuebunny/crossref_metadata_2025_split huggingface dataset:
Saturation of a shared mechanism which transports L‐arginine and L‐lysine into the brain of the living rat
Authors: Baños Guadalupe , Daniel P. M. , Pratt O. E. 
Published: December 2014

1. The rate of entry of
L‐arginine and
L‐lysine into the brain of the rat was measured in vivo by a direct method in which the amino acid concentration was at a constant level in the blood plasma over the period of the experiment.2. Both
L‐arginine and
L‐lysine enter the brain by a transport mechanism which can be saturated by a high concentration of the same amino acid in the bloodstream. The rate of entry can be explained by Michaelis—Menten kinetics.3. The entry into the brain of
L‐arginine can be inhibited by raised plasma concentrations of
L‐lysine or
L‐ornithine and the entry of
L‐lysine by raised concentrations of
L‐arginine.4. The inhibition of entry of an amino acid is most severe when its own concentration in the blood plasma is low and that of the inhibitor is high. The inhibition appears to be basically competitive in type, suggesting that common transport systems are shared by three dibasic amino acids.5. It is suggested that the raised levels of amino acids found in various disorders of amino acid metabolism are likely to reduce the rate of entry into the brain of other amino acids and a way is suggested in which the dietary treatment of hyperlysinaemia may be made more effective.
A study of single axons in the cat's medial lemniscus
Authors: Brown A. G. , Gordon G. , Kay R. H. 
Published: December 2014

1. A method was developed for locating the rostral part of the medial lemniscus in anaesthetized cats and then exploring it with a micro‐electrode selective for single axons. Records were made from 165 axons, all shown histologically to lie in the lemniscus.2. Almost all lemniscal axons responded at short latency to a shock through surface electrodes over the dorsal columns at C2. The great majority probably belonged to the dorsal column‐lemniscal system, though some may have belonged to other (e.g. spinocervicothalamic) systems.3. Resting discharge was seen in almost all axons in the absence of any stimulation, and must have been generated almost entirely in the relevant relay nuclei, particularly since in many axons it was easily depressed or totally inhibited by appropriately placed mechanical stimulation of skin or a shock to the dorsal columns.4. For each fibre held for an adequate length of time, the receptive field, if accessible, was classified as accurately as possible. Fifty‐two axons were precisely categorized in this way: many more were studied for long enough to yield useful information.5. One half (twenty‐six) of the best categorized axons had receptive fields suggesting excitation by only one type of receptor: fifteen by tylotrich hairs, four by rapidly adapting tactile foot pad receptors, two by claw movement, two by cutaneous touch corpuscles and three by Type II cutaneous receptors. Rigidly held probes driven by electromechanical transducers were used to establish stimulus/response relations. Adjacent or surround inhibition was seen in nearly all these fields, except for the Type II category.6. The other half (twenty‐six) of the best categorized axons showed various degrees of inter‐receptive excitatory convergence. Five responded to all types of hair, twelve to hair movement and foot‐pad displacement, and nine to hair movement combined with inputs from a variety of slowly adapting receptors in skin or deep tissues, thresholds for the latter ranging from light contact to noxious pressure.7. Forty axons responded with a slowly adapting discharge to joint movement, some with properties suggesting that their receptors did not lie in the joint capsule itself. The high threshold of most of these axons to dorsal column stimulation suggested that the relevant primary axons lay either deep in the dorsal column or in some other tract.8. Of axons whose receptive fields were accurately located, 88% lay in forelimb or upper trunk — the remainder in lower trunk, hind limb or tail. The forepaw accounted for 41% of the former group. Axons with receptively ‘pure’ properties tended to lie in central or deep parts of the main lemniscal mass at the level studied. Axons responding to joint movement tended to lie deep in the main mass and in the ventromedial lemniscal bundle. There was some clustering of axons with identical receptive properties.
The relationship of choline acetyltransferase activity at the neuromuscular junction to changes in muscle mass and function
Authors: Diamond Ivan , Franklin Gary M. , Milfay Dale 
Published: December 2014

1. The role of muscle mass and function in the regulation of choline acetyltransferase activity at the neuromuscular junction has been investigated in the rat.2. Choline acetyltransferase (ChAc) is located in presynaptic nerve terminals and is a specific enzymatic marker of cholinergic innervation in muscle.3. ChAc activity increased co‐ordinately with developmental growth of the soleus muscle. However, another form of muscle growth, work hypertrophy, did not produce an increase in ChAc.4. Growth arrest of muscle by hypophysectomy did not alter the normal development of ChAc activity, and cortisone‐induced muscle atrophy did not reduce ChAc activity in the soleus or plantaris.5. Tenotomy‐induced muscle atrophy provoked a significant fall in ChAc in the soleus and plantaris.6. The tonic soleus had significantly greater ChAc activity than the phasic plantaris.7. These observations suggest that muscle mass per se does not influence the development and regulation of ChAc in muscle but that the quality of muscle contraction may modulate enzyme activity.
Levels of prostaglandins in human endometrium during the normal menstrual cycle
Authors: Downie J. , Poyser N. L. , Wunderlich M. 
Published: December 2014

The levels of prostaglandins in the human endometrium throughout the normal menstrual cycle were measured by bioassay. The identity of prostaglandin F2α and prostaglandin E2 in endometrial tissue extracts was established by combined gas chromatography/mass spectrometry.The levels of prostaglandin F2α and prostaglandin E2 are low during the proliferative phase of the cycle (10–25 ng/100 mg tissue). Prostaglandin F2α rises significantly during the luteal phase to levels of 65–75 ng/100 mg of tissue. Prostaglandin E2 levels are similar to prostaglandin F2α levels in the proliferative phase but remain lower during the luteal phase. The prostaglandin E2 level is highest at menstruation (52 ng/100 mg tissue). The implications of these findings are discussed in relation to the menstrual process and to the steroid hormonal changes during the cycle.
An analysis of the role of calcium in facilitation at the frog neuromuscular junction
Authors: Younkin S. G. 
Published: December 2014

1. Under appropriate conditions stimulation of the neuromuscular junction by a single impulse or a brief train causes subsequent impulses to release increased amounts of transmitter. It has been proposed that this facilitation of transmitter release is due to calcium which remains on release sites following the conditioning stimuli. This residual calcium hypothesis is examined in frog cutaneous pectoris muscle in the present study.2. The second component of facilitation is shown to depend on the amount of calcium present during tetanization as required by the residual calcium hypothesis.3. The quantitative behaviour of the facilitation accompanying tetani of a number of frequencies and durations is found to be consistent with the residual calcium hypothesis.4. Quantitative analysis of facilitation leads to a description of the time course of removal of calcium from release sites which is discussed.
Characteristics, specificity, and efferent control of frog cutaneous cold receptors
Authors: Spray David C. 
Published: December 2014

1. Thermal stimulation of frog skin produces a discharge in afferents in the dorsocutaneous nerve. The characteristics of this response have been examined with regard to static and dynamic sensitivity to thermal stimuli and to mechanical sensitivity. Frog cutaneous receptors respond only to cooling, with no response to warming through the same thermal range.2. The static temperature at which these receptors are maximally active is about 24° C for Rana pipiens and about 27° C for R. catesbiana.3. The dynamic sensitivity of frog cutaneous receptors is linearly related to both stimulus slope and magnitude. Maximum dynamic sensitivity was between −90 and −120 impulses/° C.sec.4. Antidromic occlusion experiments demonstrate relative insensitivity of these receptors to tonic mechanical stimulation. At high stimulus intensities, however, larger fibres are recruited into the response; this recruitment of action potentials of larger amplitude is a linear function of both stimulus slope and magnitude.5. Spike heights are linearly related to conduction velocities in the dorsocutaneous nerve; tonic mechanoreceptors have a mean spike height of 28·4±0·6 μV and conduction velocities about 6–8 m/sec, whereas these temperature sensitive receptors have spike heights 15·8±0·4 μV and conduction velocities about 3–4 m/sec.6. Maximum dynamic sensitivity skin is increased following stimulation of the first or second sympathetic ganglion. This increase is both marked and progressive, reaching a maximal enhancement of about 150–160% control at a stimulus rate of 5 stimuli/train, each train delivered once every 5 sec.7. Static sensitivity of the cold receptors is also increased following sympathetic stimulation. This increased sensitivity is shown by both increased discharge rate within the same thermal range and by decreased temperature of maximum static sensitivity.8. Sympathetic modulation of dynamic thermal sensitivity is mimicked by epinephrine and norepinephrine in doses of 10−6‐10−7 g/ml. Ephedrine, another adrenergic agonist, also mimics the enhancement of cold receptors by sympathetic stimulation.9. Larger fibres are recruited to account for the increased sensitivity of thermoreceptors following sympathetic stimulation and epinephrine application.10. Propranolol and phentolamine both block the enhancement of the response by sympathetic stimulation, but propranolol blocks the response of the receptor to thermal stimulation as well. Reserpine pre‐treatment blocks the effect of sympathetic stimulation on the cold response.
The effect of visual experience on the development of stimulus specificity by kitten cortical neurones
Authors: Pettigrew J. D. 
Published: December 2014

1. 284 single cortical neurones were studied in area seventeen of twenty‐five normal kittens and of fifteen kittens, binocularly deprived, whose first visual experience had been delayed until the experiment by bilateral lid‐suture. Both normal and binocularly deprived kittens ranged in age from 1 to 6 weeks.2. The optimal, binocularly presented, visual stimulus and receptive fields were determined for each neurone by varying target configuration, speed and direction of movement and the prism‐induced alignment of both eyes. Repetitive, controlled stimulation in eighty‐four cases allowed quantitative estimates to be made of the response selectivity for the target configuration (spot vs. line), the direction of target motion and the prism‐induced disparity between the retinal images of the binocular target.3. Before the fourth post‐natal week neurones from both normal and binocularly deprived cortex showed similar properties: selectivity for direction of target motion was present in both preparations but both lacked binocular specificity and dependence on target configuration.4. After the fourth week, normal kittens had increasing numbers of neurones with selective responses which were dependent upon target configuration and the degree of binocular misalignment. The proportion of selective neurones approached the adult value after the fifth week.5. The cortex of binocularly deprived kittens failed to show an increase of selectivity with age, and of 150 neurones, sixty‐two were visually unresponsive, two showed selectivity which was dependent upon target configuration and none showed selectivity for prism‐induced retinal disparity.6. The data are not consistent with the hypothesis that the highly specific response properties of visual cortical neurones can develop without appropriate visual experience. Innate mechanisms appear to be sufficient for the development of the excitatory connexions producing motion sensitivity and receptive field location on both retinas, but patterned visual experience is necessary for the ‘fine‐tuning’ which vetoes responses to stimuli with non‐optimal configuration or binocular disparity.
The compliance of contracting skeletal muscle
Authors: Bressler B. H. , Clinch N. F. 
Published: December 2014

1. The method of controlled releases was used to obtain tension—extension curves in toad (Bufo bufo) sartorii under a variety of conditions at 0° C.2. The curves obtained were approximately linear over a considerable range of force (0·4P0 to P0) if the releases were given from the plateau of tetanic tension. The slope of this linear region was little affected by changes of release velocity in the range 10–120 mm/sec.3. Such changes as did occur with alterations in release velocity could be quantitatively accounted for in terms of the internal shortening predicted by A. V. Hill's two‐component model.4. As the muscles were stretched above l0, we found that the maximum stiffness of the tetanized muscles fell in much the same way as the maximum developed force, P0.5. In another series of experiments we found a rapid change in the overall shape of the tension—extension curve during the early phase of force development in an isometric tetanus. The stiffness of the muscle increased with increasing developed force during this period.6. The force—velocity curve in these muscles was measured by two methods, both giving a similar result. Surprisingly, toad muscle appears to have about the same intrinsic speed as frog muscle at 0° C. The a.b product from our experiments is considerably greater than the reported values for the maintenance heat rate at 0° C in these muscles.7. The probable site of the variable compliance in active muscle is discussed. It seems most likely that this is within the A‐band, perhaps in the cross‐bridges themselves.
The effects of the production of sodium depletion by peritoneal dialysis with 5% glucose on the volume and composition of the extracellular fluid of dogs
Authors: Rampton D. S. , Ramsay D. J. 
Published: December 2014

1. The volumes and compositions of the extracellular and peritoneal fluids were monitored in functionally nephrectomized dogs during a period of 4 hr of peritoneal dialysis with 5% glucose.2. The extracellular fluid volume ([14C]mannitol space), sodium, potassium and chloride concentrations decreased, while the peritoneal fluid volume, sodium, potassium and chloride concentrations increased.3. Movement of water from the e.c.f. to non‐extracellular sites occurred, reaching a maximum after 1 hr; thereafter, the movement of water was first reduced, and later reversed.4. From the volumes and compositions of the extracellular and peritoneal fluids, the total contents of solutes in the two compartments were calculated.5. There was a mobilization of sodium and chloride from non‐extra‐cellular sites, which became significant after 2 hr of dialysis, and increased throughout the remainder of the period of dialysis.6. The physiological significance of these changes is discussed.
The sodium‐transporting compartment of the epithelium of frog skin
Authors: Cereijido M. , Rabito C. A. , Boulan E. Rodríguez , Rotunno Catalina A. 
Published: December 2014

1. The abdominal frog skin was mounted between two chambers containing Ringer with 1 m
M‐Na on the outside and 115 m
M‐Na on the inside. When the Na concentration of the outer solution ([Na]o) is instantaneously raised from 1 to 50 m
M, the short circuit current (I) increases to a new value in less than a second, and becomes essentially time‐independent. Only in a few experiments was it observed to increase further, although at a much slower rate.2. At a time t after this increase, the addition of 10−4
M amiloride to the outer solution produces an exponential decrease of I. The area under this exponential curve is generally taken to reflect the existence of a Na‐ transporting compartment (NaTC).3. The amount of Na represented by NaTC is a function of t: it increases from 1·7 × 10−9 mole. cm−2, at t = 10 sec, to 22·8 × 10−9 mole. cm−2 at t = 10 min.4. In view of the fact that (a) I is not a function of the size of the ‘NaTC’ and (b) that whereas I reaches a steady value in a fraction of a second the size of NaTC keeps increasing for minutes, it is proposed that the ‘NaTC’ represents an amount of Na which is not located along the main route of transepithelial transport.5. On the assumption that the NaTC is located in a cellular compartment and that, in order to accumulate in this compartment Na should be accompanied by a permeable anion, a series of experiments were performed with Ringer in which Cl− was replaced by gluconate. It was observed as expected, that NaTC in gluconate is 164 times smaller than in Cl−, but I only decreases to one half its value in Cl− Ringer.
Membrane capacity measurements on frog skeletal muscle in media of low ion content. With an Appendix
Authors: Adrian R. H. , Almers W. , Chandler W. K. 
Published: December 2014

1. A voltage‐clamp technique for the measurement of effective membrane capacity is described and its theoretical basis given in an Appendix. Unlike most other methods used so far, the present technique does not depend on the assumption of a particular equivalent circuit for muscle membrane.2. With this technique, we have re‐examined the effect of media of low ion content on the effective membrane capacity Ceff. In fibres where potassium conductance is blocked by Rb, Ceff failed to show any appreciable dependence on ionic strength (between 0·015 and 0·29
M) or conductivity (between 0·86 and 13·4 mmho/cm) of the bathing medium.3. Low conductivity can reduce Ceff in fibres of moderately high K‐conductance. However, in all cases explored here, Ceff had values well above the 2 μF/cm2 found in glycerol‐treated fibres, indicating that passive spread of potential displacements from surface into the tubular system could still occur.4. The changes in Ceff observed under conditions of moderately high K‐conductance are explicable as a result of potential decrements in the transverse tubules, which would be expected when the wall conductance there is high, and the conductivity of the tubule lumen is low.
Analysis of non‐linearity observed in the current—voltage relation of the tunicate embryo
Authors: Miyazaki Shun‐Ichi , Takahashi Kunitaro , Tsuda Kazuko , Yoshii Mitsunobu 
Published: December 2014

1. In the gastrula of the tunicate (Halocynthia aurantium) the resting potential of the embryonic membrane was about −70 mV in both std ASW and Na‐free ASW.2. The potential responses to depolarizing current in the early gastrula embryo showed distinct potential jumps from about −50 to about +40 mV during the application of current and from about 0 to resting level after its cessation thus forming a plateau at about 0 mV. Those jumps were not altered significantly by the removal of both Na and Ca ions from ASW except for the duration of the plateau after the cessation of current.3. Blastomeres in an embryo were tightly coupled with each other electrotonically at the blastula and gastrula stages. The fact that the coupling ratio was nearly 1·0 made it reasonable to treat an embryo as one cell as far as electrical properties are concerned.4. The I—V relation of the embryonic membrane consisted of an inward rectifying region, outward rectifying region and transitional zone between the two, resulting in a S‐shaped curve as in the egg cell membrane. But in the gastrula embryo, the transitional zone actually included the discontinuous part of the I—V curve (from about −50 to about +40 mV) due to the potential jump.5. The ionic current (Ii) during the potential jump in Na‐free ASW was estimated from the slope of the potential response based on the assumption of constant capacitance during the membrane potential changes. The calculated Ii—V curve complemented the interrupted I—V curve smoothly and showed the existence of a negative resistance region from about −50 to about 0 mV in the steady‐state I—V relation.6. The steady‐state I—V relation was altered significantly by changing the K concentration in ASW, and the existence of the negative resistance can be reasonably explained by the marked inward‐going rectification or anomalous rectification of K conductance.7. The replacement of K with Rb in ASW produced the marked suppression of the inward‐going rectification of the embryonic membrane.
The influence of centrally applied noradrenaline on shivering and body temperature in the pigeon
Authors: Hissa R. , Rautenberg W. 
Published: December 2014

1. Noradrenaline (NA) was injected in a volume of 1·0 μl. through chronically implanted cannula into the hypothalamus of the unanaesthetized pigeon.2. In doses of 1–15 μg NA caused complete inhibition of shivering of dose‐dependent duration. Histological mapping of the brain showed that NA was exerting its inhibitor action in the region above the optic chiasma bordering on the posterior hypothalamus and the anterior preoptic nucleus.3. At low ambient temperature, the NA induced inhibition of the cold tremor caused a fall of core temperature which lasted as long as shivering was inhibited. Shivering induced by local cooling of the spinal cord, and by the combined cooling of the skin and the spinal cord, was likewise inhibited by the cerebral application of NA. There was no evidence of an adjustment of the temperature set‐point by NA.4. A rapid rise in skin temperature of the unfeathered feet, whenever NA was injected indicated a reduction in peripheral vasomotor tone.
Energetics of relaxation in frog muscle
Authors: Curtin Nancy A. , Woledge Roger C. 
Published: December 2014

1. Changes in the levels of phosphocreatine (PCr) and ATP during relaxation after tetanic contraction have been observed and compared with the heat + work production during the same period.2. The results were the same using 2 sec or 15 sec tetani and using 15 or 30 Hz stimulation.3. During relaxation the mean chemical change (of ATP + PCr) was −0·105 ± 0·078 μmol/g muscle (n = 53). This change is less than would be required to explain the heat + work produced.4. The PCr split during both 2 sec and 15 sec tetani (up to the last stimulus) was less than would be required to explain the heat + work produced. This confirms previous experiments.5. It is concluded that the discrepancy between chemical change and heat + work production does not diminish during relaxation but actually increases.