bluuebunny/crossref_metadata_2025_split huggingface dataset:
A computer simulation of conduction in demyelinated nerve fibres
Authors: Koles Z. J. , Rasminsky M. 
Published: December 2014

1. The theoretical effects of demyelination on conduction of a propagated impulse have been examined in a computer simulated myelinated nerve fibre. Demyelination was simulated by increasing the capacitance and conductance of the myelin sheath of individual internodes or parts of internodes.2. Internodal conduction time increased as myelin thickness was decreased. The increase in internodal conduction time became more precipitous as the myelin became thinner. Propagation continued past a single demyelinated internode until myelin thickness was uniformly reduced to less than 2·7% of normal myelin thickness.3. Paranodal demyelination was more effective in slowing impulse conduction than was uniform demyelination of an entire internode with an equivalent rise in overall internodal capacitance and conductance.4. The effects on conduction of demyelination of two adjacent internodes or of two internodes separated by a normal internode were more than the sum of the effects of demyelination of each internode individually.5. Propagation across a severely demyelinated internode was blocked with an increase in internal sodium concentration which had a trivial effect on conduction in a normal fibre.6. Propagation across a severely demyelinated internode was blocked with increased temperature at a temperature at which propagation proceeds normally across normal internodes.7. The similarity between the findings of the computer simulations and the experimental findings in demyelinated fibres is discussed.
Changes in regional blood flow and cardiodynamics evoked by electrical stimulation of the fastigial nucleus in the cat and their similarity to orthostatic reflexes
Authors: Doba Nobutaka , Reis Donald J. 
Published: December 2014

1. Changes in regional blood flow and cardiodynamics were measured in anaesthetized paralysed cats during electrical stimulation of the rostral fastigial nucleus.2. Fastigial stimulation results in a graded, highly reproducible and stereotyped cardiovascular response characterized by (a) increased systolic, diastolic and mean arterial pressures without changes in central venous or occluded vein pressure, (b) decreased blood flow and increased vascular resistance in the axillary, renal, femoral and mesenteric arteries, increased flow without any change in vascular resistance in the common carotid artery, and increase in total peripheral resistance, (c) a small increase in heart rate and myocardial contractile force, decrease in calculated stroke volume, and no change in the cardiac output.3. Changes in regional arterial flow were abolished by transection of sympathetic nerves or blockade of α‐adrenergic receptors by systemic administration of phentolamine.4. Changes in heart rate and myocardial contractility were abolished by stellate ganglionectomy or blockade of β‐adrenergic receptors by propranolol.5. No changes in pupillary diameter or retraction of the nictitating membrane were seen during fastigial stimulation with stimuli producing substantial changes in blood pressure.6. The fastigial pressor response represents a highly reproducible, stereotyped, graded, and differentiated pattern of activation of sympathetic preganglionic neurones.7. The pattern of cardiovascular effects of fastigial stimulation simulates the compensatory (orthostatic) reflex response to maintenance of an upright posture.8. Fastigial stimulation appears to excite the neural network subserving orthostatic reflexes.
Pyrogen fever and prostaglandin‐like activity in cerebrospinal fluid
Authors: Feldberg W. , Gupta K. P. 
Published: December 2014

1. In the unanaesthetized cat, rectal temperature was recorded and c.s.f. was collected from a Collison cannula implanted into the third ventricle with its opening lying in close proximity to the anterior hypothalamus. Samples of c.s.f. were collected from the same cat, during normal temperature, during fever produced by Shigella dysenteriae injected into the third ventricle and during the fall in temperature which occurred when the antipyretic paracetamol was injected intraperitoneally during the pyrogen fever.2. The samples of c.s.f., when tested on the rat stomach fundus preparation, caused contractions which were not due, or at most to a small degree only, to 5‐hydroxytryptamine, as they were resistant to BOL. They were therefore probably due to a prostaglandin‐like substance.3. When assayed against PGE1, the activity of c.s.f. collected from cats when their body temperature was normal corresponded to between 1·3 and 10 ng/ml. The values, whether low or high, rose over 2·5‐4 times to between 4 and 35 ng/ml. in c.s.f. collected during pyrogen fever; they were again low, between 1·5 and 6 ng/ml., in samples collected when the fever had been brought down by paracetamol, but rose again with the return of fever.4. The results provide direct evidence for the theory that fever produced by pyrogens results from their ability to increase synthesis and release of prostaglandins, and that antipyretics bring down the fever because they inhibit the increased synthesis.
Sodium uptake by frog skin and its modification by inhibitors of transepithelial sodium transport
Authors: Erlij D. , Smith M. W. 
Published: December 2014

1. The suitability of inulin and mannitol as markers of the diffusional space that exists between the surface of frog skin and the outer barrier to sodium transport has been compared in experiments designed to measure the rapid uptake of sodium.2. Inulin and mannitol both equilibrate finally with the same space at the outer surface of the frog skin, but the rate at which this equilibration occurs is considerably faster for mannitol.3. The dependence of the rapid uptake of sodium on the concentration of sodium in the external medium, using mannitol to correct for extracellular sodium, can be described by simple saturation kinetics with an apparent Km for sodium entry of 24 mM and a maximal rate of uptake of 1·28 μequiv/cm2. hr.4. The effect of amiloride is to inhibit sodium uptake, the degree of inhibition depending both on the concentration of sodium in the external medium and on the level of transepithelial transport normally maintained by the skin.5. Ouabain inhibits sodium uptake when the tissue has been pre‐incubated in sodium containing medium. It has no effect on sodium uptake if the pre‐incubation takes place in sodium free medium.6. A short‐circuit current and potential difference can be elicited across frog skin in the presence of ouabain, by increasing the concentration of sodium bathing the outside surface. This potential and short‐circuit current is abolished by the presence of amiloride.7. These results provide direct evidence that amiloride acts to stop entry of sodium into the transport compartment and suggest that the ouabain inhibition of sodium uptake is mediated primarily through an increase of epithelial sodium concentration.
Sensory inputs to neurones in Clarke's column from muscle, cutaneous and joint receptors
Authors: Kuno M. , Muñoz‐Martinez E. J. , Randić Mirjana 
Published: December 2014

1. Discharge of neurones at the region of Clarke's column of the cat was recorded intracellularly or extracellularly in response to electrical stimulation of various hind limb nerves or to adequate stimuli applied to a variety of sensory receptors.2. According to the type of excitatory sensory input, the neurones were classified into four groups. Their relative proportions were: muscle group, 55–65%; cutaneous group, 15–25%; joint group, 5–15%; convergent group, 10–20%.3. The location of the neurone cell bodies was examined by marking the site of extracellular recording with fast green. The neurones of the muscle or cutaneous group were found to be within Clarke's column. One out of four neurones tested for the joint group and two out of six cells examined for the convergent group were found to be located outside the column.4. There was no difference in axonal conduction velocity among the neurones of different groups.5. The neurones of different groups could be distinguished in terms of the pattern of discharges recorded under ‘resting’ conditions and during activation of sensory receptors. It is suggested that information carried by dorsal spinocerebellar tract neurones to the cerebellum has a lower signal‐to‐noise ratio for cutaneous inputs than for muscle or joint inputs.
Synaptic action on Clarke's column neurones in relation to afferent terminal size
Authors: Kuno M. , Muñoz‐Martinez E. J. , Randić Mirjana 
Published: December 2014

1. Excitatory post‐synaptic potentials (e.p.s.p.s) were recorded intracellularly from Clarke's column neurones (DSCT neurones) of the cat in response to adequate stimuli applied to a variety of sensory receptors.2. The amplitude of e.p.s.p.s so produced varied from less than 0·2 mV to more than 2–3 mV. The amplitude distribution of e.p.s.p.s suggested that the mean number of ‘quanta’ of transmitter released by one impulse varied widely from one fibre to another arising from a given type of sensory receptor.3. The average amplitude of e.p.s.p.s evoked by single afferent impulses was significantly smaller for cutaneous inputs than for muscle or joint inputs. However, synaptic action on DSCT neurones produced by different sensory inputs was equally greater, on the average, than that on spinal motoneurones.4. Both small and large e.p.s.p.s in DSCT neurones failed to increase in amplitude during post‐synaptic hyperpolarization applied through the cell body. This failure could not be attributed to possible anomalous rectification in the post‐synaptic membrane.5. Small and large e.p.s.p.s were comparable in half‐decay time, but there was a positive correlation between amplitude and time‐to‐peak of e.p.s.p.s. It is suggested that the locations of synapses responsible for small and large e.p.s.p.s are intermingled on the dendrites and that large e.p.s.p.s are associated with a longer duration of transmitter action than small e.p.s.p.s.6. Degenerating terminals of primary afferent fibres on DSCT neurones and motoneurones were examined with the electron microscope after chronic section of the dorsal roots.7. Dendritic degenerating terminals showed no significant difference in size between motoneurones and DSCT neurones. Degenerating ‘giant’ terminals were found on DSCT neurones, but they were located only on or very close to the cell body.8. It is concluded that the major factor responsible for a large number of ‘quanta’ of transmitter released at synapses on DSCT neurones is the number of multiple synaptic contacts formed by one afferent fibre rather than the size of individual synapses.
The calcium pump of cardiac sarcoplasmic reticulum. Functional alterations at different levels of thyroid state in rabbits
Authors: Suko J. 
Published: December 2014

1. Cardiac sarcoplasmic reticulum (SR) was prepared by differential centrifugation from euthyroid, hyperthyroid, hypothyroid as well as 131I‐treated plus thyroxine‐substituted rabbits. The function of the isolated SR has been characterized by measuring the ATP‐dependent calcium uptake, the calcium storing capacity, the calcium concentrating ability and the calcium‐dependent ATP hydrolysis by the calcium‐activated ATPase in the presence of oxalate.2. The rate of calcium uptake and the rate of the calcium‐dependent ATP hydrolysis (calcium‐activated ATPase) by the SR were significantly increased in hyperthyroidism, whilst both activities were markedly reduced in hypothyroidism. Thyroxine administration to 131I‐treated animals prevented a decrease in the rate of calcium uptake as well as in the rate of the calcium‐dependent ATP hydrolysis by the calcium‐activated ATPase.3. The transport ratio (rate of calcium uptake divided by the rate of calcium‐dependent ATP hydrolysis) of SR preparations from euthyroid controls was 0·93, suggesting a stoicheiometry of calcium uptake and calcium‐activated ATP split of 1·0. The transport ratio was unchanged in one hyper‐ and hypothyroid group, whilst a small but significant decrease or increase was observed after an excessive thyroxine treatment of a prolonged state of hypothyroidism, respectively.4. The saturation kinetics of calcium transport by the SR were described by Michaelis—Menten kinetics. The maximum rate of calcium uptake (V) was 0·193±0·004, 0·223±0·002 and 0·124±0·003 μmole Ca2+/mg protein. min (means ±S.E.) for euthyroid, hyperthyroid and hypothyroid SR, respectively. The Michaelis constants (Km) were (2·87±0·30) × 10−7
M (2·68±0·15) × 10−7
M and (4·00±0·48) × 10−7
M for the euthyroid, hyperthyroid and hypothyroid SR, respectively (means ±S.E.). The Km values for the hyper‐ and hypothyroid SR were not significantly different from controls.5. The calcium storing capacity as well as the calcium concentrating ability of the SR was unaltered at different levels of thyroid activity.6. The steady‐state level of calcium was the same for SR isolated from euthyroid, hyperthyroid and hypothyroid rabbits, indicating that calcium influx and calcium efflux are strongly coupled at steady‐state filling of the SR.7. It is suggested that the increased or reduced rate of calcium transport by the SR in hyperthyroidism or hypothyroidism, respectively, found in vitro, might be at least partially responsible for the shortening of the relaxation time of cardiac muscle in the hyperthyroid state and the prolongation of the relaxation time in the hypothyroid state observed in vitro and in vivo.
Periodic vernier acuity
Authors: Tyler C. William 
Published: December 2014

1. Sinusoidal curvature was produced in a vertical stimulus line generated on an oscilloscope screen. Sensitivity to sinusoidal curvature (periodic vernier acuity) was measured by the method of adjustment as a function of spatial frequency of the curvature.2. Sensitivity was maximal at about 3 c/deg and reduced steeply for both higher and lower spatial frequencies of curvature.3. Sensitivity at 10° in the periphery was greatly reduced but showed very little low frequency reduction.4. The effect of number of cycles present was checked by reduction of the field size with spatial frequency such that a fixed number of cycles of the stimulus were visible. This procedure did not affect the decline in sensitivity at spatial frequencies below 0·3 c/deg but reduced sensitivity at higher spatial frequencies.5. The results were interpreted in terms of cortical orientation detectors. It is suggested that the low frequency sensitivity is limited by a fixed value for the maximum difference in orientation in the stimulus (i.e. 20 and 30′ for the present subjects). The high frequency sensitivity was limited by grating acuity and required spatial integration of the stimulus information over about 2·5°.
An upper limit to the number of sodium channels in frog skin epithelium
Authors: Cuthbert A. W. 
Published: December 2014

1. Binding of [14C]amiloride to the mucosal surface of frog skin epithelium has been measured in the presence and absence of an excess of unlabelled amiloride. Simultaneous records were obtained of the sodium transport through the skin as indicated by the short circuit current.2. The number of binding sites with affinities for amiloride of 5 × 107 l./mole was around 400/μm2.3. The relation between the binding sites and sodium channels is discussed.4. Making certain assumptions it is concluded that when frog skin epithelium is bathed in Ringer solution each sodium channel can handle 8000 sodium ions/sec.
Effects of noradrenaline and isoprenaline, in combination with α‐ and β‐receptor blocking substances, on the action potential of cardiac Purkinje fibres
Authors: Giotti A. , Ledda F. , Mannaioni P. F. 
Published: December 2014

1. The effects of noradrenaline and isoprenaline on the repolarization phase of the action potential have been studied in the Purkinje fibres of sheep heart, electrically driven at constant rates.2. Isoprenaline (2, 5 and 8 × 10−8 g/ml.) increases the slope of phase 2 of repolarization and decreases the plateau length; the resulting decrease in action potential duration is concentration dependent, but not rate dependent.3. The effect of isoprenaline on the action potential duration is entirely blocked by propranolol (10−7 g/ml.) and unaffected by phentolamine (5 × 10−7 g/ml.).4. In phentolamine (5 × 10−7 g/ml.) pretreated preparations the response induced by noradrenaline (5 × 10−8, 1 and 5 × 10−7 g/ml.) is very similar to that induced by isoprenaline.5. In propranolol (2·5 × 10−7 g/ml.) pretreated preparations noradrenaline causes a lengthening of the plateau phase and an increase in action potential duration.6. The relationship of these results to the presence of both α‐ and β‐receptors in cardiac Purkinje fibres is discussed.
The measurement of dog gastric mucosal blood flow by radioactive aniline clearance compared with amidopyrine clearance
Authors: Curwain B. P. , Holton Pamela 
Published: December 2014

1. Methods for the estimation of radioactive aniline in body fluids are described. The recovery of aniline added to blood, plasma and gastric juice was over 90% of the recovery from saline.2. In the doses used aniline caused methaemoglobinaemia of 5–11% of total haemoglobin. No other effect was detected. Gastric secretion was also unaffected.3. Aniline clearance increased in parallel with acid secretion from Heidenhain pouches in conscious dogs and in anaesthetized dogs. In conscious dogs the ratio of aniline clearance to acid secretion was significantly higher for histamine stimulation than for pentagastrin stimulation.4. Aniline and amidopyrine clearances were compared simultaneously in the same dogs. Aniline clearance was about 80% of amidopyrine clearance.5. The proportion of aniline bound to plasma proteins was measured by two methods and found to be 25%. When aniline clearance was corrected for plasma binding, aniline and amidopyrine clearances were equal.
An electrophysiological analysis of the storage and release of noradrenaline at sympathetic nerve terminals
Authors: Bennett M. R. 
Published: December 2014

1. An electrophysiological analysis has been made of the storage and release of noradrenaline (NAd) in the sympathetic nerve terminals of the isolated vas deferens of the mouse. The amplitude of the excitatory junction potentials (e.j.p.s) recorded intracellularly in smooth muscle cells was taken as a measure of the NAd output per impulse from the terminals of sympathetic axons.2. During short trains of impulses (< 100), the amplitude of the e.j.p. increased with successive impulses at the beginning of a train, and then either continued to increase until a steady‐state amplitude was reached (frequencies < 1 Hz), or decreased until a depressed steady amplitude was reached (frequencies > 1 Hz).3. During trains of impulses lasting for several minutes, the amplitude of the e.j.p. continually declined (frequencies > 1 Hz) until a steady‐state amplitude was reached after 8 min of stimulation. This steady‐state amplitude is smaller, the higher the frequency of stimulation.4. During short trains of impulses in the presence of high magnesium solutions, the amplitude of successive e.j.p.s increased until a steady state was reached, no matter what the frequency of stimulation. This growth of the e.j.p. amplitude during a train could be quantitatively predicted in terms of the linear summation of the individual facilitatory effects introduced by each impulse in the train.5. During trains of impulses lasting for several minutes, in the presence of a NAd synthesis blocker, the amplitude of the e.j.p. continually declined along a curve which could be described as the sum of two exponential components: one with a time constant of 1 min and the other of 10 min.6. These results suggest that NAd is released from a small pool of transmitter in sympathetic nerve terminals, which is replenished from two stores, which are in turn replenished by the synthesis of new NAd.
Metabolism and the electrical activity of anoxic ventricular muscle
Authors: McDonald Terence F. , MacLeod Don P. 
Published: December 2014

1. The action potential duration of anoxic guinea‐pig ventricular muscle was related to ATP generated by glycolysis. In 50 mM glucose medium the action potential duration was maintained; in 5 mM glucose medium the action potential duration shortened, the glycolytic rate declined and the ATP content was reduced.2. The action potential amplitude was related to the metabolic state of the muscle but not to the intracellular sodium concentration.3. It is suggested that changes in the action potential duration and overshoot in anoxic muscle may be due to an influence of metabolism on the slow inward current.4. Anoxic muscle incubated for 8 hr in 5 mM glucose medium had an Em of −77·1 mV compared to −81·1 mV in fresh muscle. The calculated Ek of anoxic muscle was −47·4 mV.5. The resting potential of anoxic muscle was separated into two components, one dependent on potassium distribution and the other on the activity of an electrogenic sodium pump.6. The electrogenic pump component was stimulated upon raising the glucose concentration of the medium or upon raising the external potassium concentration.7. The electrogenic pump component was inhibited by ouabain or by reduction of the temperature from 35 to 8° C.
Ionic transport and membrane potential of rat liver cells in normal and low‐chloride solutions
Authors: Claret Brigitte , Claret M. , Mazet J. L. 
Published: December 2014

1. The ouabain‐sensitive component of Na efflux and K influx amount to 58 and 72% respectively. Taking into account also (a) the diffusional passive fluxes of Na (5%) and K (13%), as estimated by Ussing's equation and (b) the ouabain‐insensitive Na‐Na exchange (28%), 85% (K) and 90% (Na) of the measured total fluxes can be accounted for.2. Na efflux is diminished when K is partially or totally removed from the medium. This effect is reversible, indicating probably activation of the Na pump by external K.3. The coupling ratio of Na and K ouabain‐sensitive fluxes is equal to 1·58, suggesting that three Na ions are removed from and two K ions are carried into the cell in one cycle of the pump. Hence, in liver cell membranes, the Na pump must be electrogenic.4. A tenfold decrease in [Cl]o by substitution with an impermeant anion results in a membrane hyperpolarization and a decrease in [Cl]i. Cl loss from the liver is compensated by an equivalent loss of intracellular K to preserve electroneutrality.5. The measurement of passive fluxes indicates that Cl removal from the perfusing solutions increases PK but does not alter PNa.6. Addition of ouabain brings about a depolarization which is three times greater in low‐Cl solutions (21·9 mV) than in normal‐Cl solutions (6·8 mV).7. It is concluded that hyperpolarization which develops when Cl ions are removed can be accounted for entirely by (a) the increase in PK, (b) the increase of the contribution of the electrogenic pump to membrane potential.