bluuebunny/crossref_metadata_2025 huggingface dataset:
The physiology and anatomy of long ranging afferent fibres within the spinal cord.
Authors: Wall P D , Werman R
Published: December 2014

The caudal extent of the terminal arborizations of dorsal root afferents was determined in adult cats. The method used micro‐electrode stimulation within the dorsal horn and the recording on a distant dorsal root filament of the antidromic action potentials evoked by the stimulation of axons within the spinal cord. 2. It was found that all filaments examined in the L2, 3 and 4 dorsal roots contained axons which projected at least as far as the S1 segment. The axons descended in or near the dorsal columns and from there penetrated into the grey matter. 3. The course of single fibres was followed to their apparent terminals. Thresholds, latencies and relative and absolute refractory periods were measured for single axons. These measurements confirmed that continuous axons ran from dorsal roots to distant segments and that the action potentials recorded were not dorsal root reflexes. 4. The majority of fibres with long range central arborizations were shown to have normal receptive fields in the dermatome of their parent dorsal root. They were not aberrant fibres leaving the spinal cord. 5. The long range afferents exist in substantial numbers since fifteen of eighty axons isolated by micro‐electrode recording in the L2 dorsal root sent their axons as far as the S1 segment. The presence of these afferents from five segments away does not fit the data published on the inhibitory and excitatory receptive fields or dorsal horn cells which appear adequately explained by afferents arriving over nearby dorsal roots up to two segments away.
Visual cells in the pontine nuclei of the cat.
Authors: Baker J , Gibson A , Glickstein M , Stein J
Published: December 2014

Two hundred and thirty‐two visually activated neurones were recorded in a small area of the rostral pontine nuclei of cats. The location of visually activated neurones was coextensive with the input from visual areas of cat's cortex as determined by degeneration studies. 2. Pontine visual cells could only be driven by visual stimuli. Cells responsive to somatosensory or auditory stimuli were also found in different regions in rostral pontine nuclei. They too responded to only one modality. 3. 96% of the cells were directionally selective. 4. Pontine visual cells were responsive to a wide range of stimulus speeds. Some cells responded to targets moving as fast as 1000 degrees/sec without losing directional selectivity. No pontine visual cells gave a clearly sustained response to a stationary stimulus. 5. Exact stimulus configurations were not critical. Large fields containing many spots were the most effective stimuli for 50% of the cells. Inhibition of responses depending upon stimulus dimensions, direction of movement, or location in the visual field was found for many cells. 6. Receptive field dimensions were large, ranging in size from 3 degrees X 4 degrees to more than an entire hemifield. 7. 94% of the cells had receptive fields which were centred in the contralateral hemifield. 8. 98% of the cells could be driven from both eyes. 9. The properties of the pontine visual cells suggest a corticopontocerebellar pathway sensitive to a wide range of speeds and directions of movement, but not sensitive to precise form.
Potassium and calcium conductance in slow muscle fibres of the toad.
Authors: Stefani E , Uchitel O D
Published: December 2014

Slow muscle fibres in isotonic potassium sulphate saline could be easily repolarized to ‐90 mV. From this membrane potential a regenerative response could be elicited with short depolarizing pulses. 2. This response is blocked by TEA, suggesting that potassium is the main ion involved. 3. In the presence of TEA, a transient depolarization is recorded when the steady hyperpolarization is withdrawn. This anode break response is dependent upon the external calcium and is blocked by cobalt, suggesting that it is due to a calcium conductance. 4. The membrane conductance change was continuously recorded with short pulses at the end of the hyperpolarization. The membrane conductance decayed with at least two components with an average t1/2 of 1‐2 and 6‐8 sec. TEA blocked the slow component, and the fast one was dependent upon calcium and was blocked by cobalt.
Acid secretion by guinea‐pig isolated stomach.
Authors: Holton P , Spencer J
Published: December 2014

An isolated stomach preparation from the guinea‐pig is described. 2. Both histamine acid phosphate (1‐4 mug/ml.) and theophylline hydrate (0‐2‐3‐2 mg/ml.) separately stimulated hydrochloric acid, HCl, secretion from the guinea‐pig stomach preparation. A linear dose‐response relationship was obtained for theophylline. 3. Addition of theophylline (0‐2 and 1‐6 mg/ml.) during maximal response to histamine increased the secretion further, whereas addition of histamine during maximal response to theophylline did not cause further secretion. 4. The secretory activities of Nalpha‐MeH (0‐3‐5‐0 muM), Nalpha‐Me2H (1‐2‐9‐5 muM) and 5‐MeH (1‐5‐12 muM) were compared with histamine (0‐9‐13 muM) on a threshold background secretion induced by theophylline (0‐2 mg/ml.). Linear log.‐dose response relationships were obtained for each test drug. The results confirm that Nalpha‐MeH is a more potent secretagogue than histamine. 5. Pentagastrin (0‐3‐1‐0 mug/ml.) stimulated HCl secretion in approximately half the experiments. The response was often transitory. In the other experiments, pentagastrin had no effect on HCl secretion although subsequent administration of histamine did stimulate HCl secretion.
Two components of the calcium current in the egg cell membrane of the tunicate.
Authors: Okamoto H , Takahashi K , Yoshii M
Published: December 2014

The Ca current of the egg cell membrane of a certain tunicate, Halocynthia roretzi Drasche, was studied by the voltage‐clamp technique. 2. The Ca current in the standard artificial sea water (ASW) was produced at the critical membrane potential of ‐10 mV after inactivating the Na current by conditioning depolarization, ‐30 to ‐15 mV. The Ca current was abolished by replacing Ca in ASW with Mg2+ or Mn2+. The Ca current was not significantly influenced by replacing Na in ASW with choline or Cs. 3. The relation of Ca current to the external Ca concentration was a monotonously increasing function, but was not linear. The current tended to saturate above 50 mM‐Ca. In 100 mM‐Ca ASW, the maximum peak inward current of Ca ranged from 1 to 7 X 10(‐9) A. 4. The kinetics of Ca current was accurately analysed because of the small contribution of K outward current and was found to be relatively slow in comparison with the Na current. The peak time and the half‐decay time of the maximum Ca current at about 25 mV were about 25 and 100 msec respectively in 100 mM‐Ca ASW at 15 degrees C. 5. Addition of 20 mM‐Co2+ to 100 mM‐Ca ASW reduced Ca current to one fourth and 1 mM‐La3+ to 100 mM‐Ca ASW abolished the current. 6. Sr and Ba could substitute for Ca in Ca channels. The selectivity ratios for the 'Ca channels's were Ca (1‐00):Sr(1‐17):Ba(0‐71) at a potential level of +40 mV. The Ca current in the egg cell membrane appeared to be essentially the same as the Ca current in the common excitable membranes, such as the crustacean muscle fibre. 7. The polyvalent cations including Ca ion and monovalent H+ ion showed the stabilizing effect upon both Na and Ca currents, by shifting V‐I relations along the voltage axis. From the prediction of a theory of the diffuse double layer, the shift in the V‐I relation induced by those cations should be directly related to their binding powers to the membrane. Thus, the sequence of the binding powers was inferred as H+ greater than La3+ greater than Co2+ greater than Mn2+ greater than Ca2+ greater than Sr2+ larger than or equal to Ba2+ greater than Mg2+. 9. In Na‐free ASW, such as isotonic Ca ASW, Ca current was composed of two components. The one component was the Ca current described in 1 to 6. The other was also dependent upon the external Ca concentration, but showed the more negative critical membrane potential and the faster kinetics. It was concluded that this component should be the Ca current through Na channels. 10. The selectivity among Ca, Sr and Ba for 'Ca' current through 'Na channels' was significantly different from that of 'Ca' current through 'Ca channels', being Ca greater than Sr larger than or equal to Ba = 0.
The effect of carbon dioxide on the intracellular pH and buffering power of snail neurones.
Authors: Thomas R C
Published: December 2014

1. Intracellular pH (pHi) was measured using pH‐sensitive glass micro‐electrodes. The effects on pHi of CO2 applied externally and HCO3‐, H+ and NH4+ injected iontophoretically, were investigated. 2. The transport numbers for iontophoretic injection into aqueous micro‐droples were found by potentiometric titration to be 0‐3 for HCO3‐ and 0‐94 for H+. 3. Exposure to Ringer, pH 7‐5, equilibrated with 2‐2% CO2 caused a rapid, but only transient, fall in pHi. Within 1 or 2 min pHi began to return exponentially to normal, with a time constant of about 5 min. 4. When external CO2 was removed, pHi rapidly increased, and then slowly returned to normal. The pHi changes with CO2 application or removal gave a calculated intracellular buffer value of about 30 m‐equiv H+/pH unit per litre. 5. Injection of HCO3‐ caused a rise in pHi very similar to that seen on removal of external CO2. 6. The pHi responses to CO2 application, CO2 removal and HCO3‐ injection were slowed by the carbonic anhydrase inhibitor acetazolamide. 7. H+ injection caused a transient fall in pHi. In CO2 Ringer pHi fell less and recovered faster than in CO2‐free Ringer. Calculation of the internal buffer value from the pHi responses to H+ and HCO3‐ injection gave very similar values. 8. The internal buffer value (measured by H+ injection) was greatly increased by exposure to CO2 Ringer. Acetazolamide reduced this effect of CO2, suggesting that the function of intracellular carbonic anhydrase may be to maximize the internal buffering power in CO2. 9. It was concluded that the internal HCO3‐ was determined primarily by the CO2 level and pHi, that internal HCO3‐ made a large contribution to the buffering power, and that after internal acidfication pHi was restored to normal by active transport of H+, OH‐ or HCO3‐ across the cell membrane. The active transport was much faster in CO2 than in CO2‐free Ringer.
The effect of parathyroidectomy and large doses of cholecalciferol on the ability of rats to adapt to changes in dietary intake of calcium.
Authors: Kemm J R
Published: December 2014

1. Adaptation to different dietary levels of calcium was produced by feeding a low (0‐2%) calcium diet or one of two high (1‐6 or 0‐8%) calcium diets for 4 or 6 weeks. Adaptive changes in true and apparent absorption of calcium, apparent absorption of phosphate and urinary excretion of calcium, were observed. 2. Parathyroidectomy performed prior to adaptation did not greatly impair the ability of rats to adapt to different levels of calcium in the diet. The response of the rats to parathyroidectomy was affected by their subsequent dietary history. 3. Six weeks after parathyroidectomy the plasma calcium was significantly higher than it had been immediately post‐operatively. This rise in plasma calcium was seen in the rats adapted to the 1‐6% calcium diet but not in those adapted to the 0‐2% calcium diet. 4. Parathyroidectomy performed after adaptation had taken place did not abolish the adaptive changes. The response of rats to parathyroidectomy was affected by their previous dietary history. 5. Large doses of cholecalciferol given for 8 days after adaptation had taken place increased the absorption of calcium in rats adapted to the 0‐8% calcium diet thereby abolishing or reducing the adaptive differences in absorption between these rats and rats adapted to the 0‐2% calcium diet. The cholecalciferol increased urinary calcium excretion but did not abolish adaptive differences in urinary excretion of calcium between rats adapted to diets with different calcium levels. 6. It is concluded that parathyroid hormone does not play a major role in mediating adaptation to different dietary intakes of calcium. The possible role of 1‐25 dihydroxycholecalciferol is discussed.
Reflex responses of gamma motoneurones to vibration of the muscle they innervate.
Authors: Fromm C , Noth J
Published: December 2014

1. High frequency vibration was applied to the tendon of the non‐contracting triceps surae muscle while recording the background discharges of single gamma fibres only small nerve bundles were cut, leaving most of the nerve supply to the triceps intact. 2. 22% out of a total of sixty‐three gamma efferents were tonically inhibited by vibration. The inhibition appeared between 25 and 50mum peak‐to‐peak amplitude of vibration and increased to a plateau for amplitudes of about 100mum. The dependence of the tonic vibration reflex of alpha‐efferents on the amplitude of vibration was found to be similar. Increasing the frequency of vibration from 150 to 300 Hz increased the degree of inhibition. 3. 33% of the fusimotor neurones investigated responded to muscle vibration with an increase in discharge rate. The threshold amplitudes of this reflex ranged from 20 to 50mum. Some features of the reflex, in particular the parallel post‐vibratory facilitation found in alpha and gamma efferents, pointed to a polysynaptic pathway organized in an alpha‐gamma linkage. 4. All gamma efferents inhibited by vibration showed inhibitory responses to antidromic stimulation of the parent ventral root, and most of them were inhibited by ramp stretch of the triceps. The gamma motoneurones facilitated by vibration, however, were excited by muscle stretch and were less susceptible to antidromic inhibition, some lacking it completely. 5. Cutting the nerves to triceps abolished the inhibitory as well as the excitatory responses of gamma efferents to muscle vibration. Both fusimotor reflexes were preserved after spinal section and subsequent administration of L‐DOPA. 6. It is concluded that both of the fusimotor reflex effects of vibration are caused by excitation of primary spindle endings within the triceps. The inhibition of fusimotor neurones is thought to be mediated by Renshaw cells activated during vibration. The significance of positive feed‐back on to gamma motoneurones as a result of autogenetic facilitation by Ia afferents is discussed in connexion with stability in the stretch reflex loop.
Synaptic transmission in parasympathetic ganglia in the urinary bladder of the cat.
Authors: DeGroat W C , Saum W R
Published: December 2014

1. Electrophysiological techniques were used to study the sacral para‐sympathetic input to pelvic ganglia located on the surface of the urinary bladder of the cat. 2. Synaptic transmission in pelvic ganglia was mediated primarily via nicotinic receptors although muscarinic excitatory receptors were present. 3. The most prominent characteristic of transmission in pelvic ganglia was the marked recruitment elicited by increasing frequencies of preganglionic nerve stimulation. Post‐ganglionic action potentials were of low amplitude at low frequencies of stimulation (0‐1‐0‐5c/s), but commonly increased to five to twenty times control amplitudes during continuous stimulation at frequencies between 5 and 10c/s. Thus, it is proposed that vesical ganglia may act as "filters" in the micturition pathway; blocking the excitatory input to the bladder when intravesical pressure and parasympathetic firing is low and facilitating the neural input to the bladder during micturition when preganglionic activity is high. 4. Information was also obtained about the characteristics of the parasympathetic post‐ganglionic neurones innervating the bladder. Stimulation of the preganglionic fibres in the pelvic nerve elicited a bimodal contraction consisting of an initial phasic response, which was atropine‐resistant and a tonic response which was blocked by atropine. This suggests that two types of neurones, cholinergic and non‐cholinergic, may mediate the sacral input to the vesical smooth muscle.
Plasma kininogen during the oestrous cycle, early pregnancy and pseudopregnancy in the rat.
Authors: Senior J , Whalley E T
Published: December 2014

1. Changes in the plasma kinin precursor, kininogen, occur following treatment with oestrogens and progestogens. This work was undertaken to attempt to relate plasma kininogen values to hormonal changes in various reproductive states. 2. During the oestrous cycle kininogen concentrations follow a nychthemeral rhythm, kininogen depletion occurring during the increase in general activity of the rat. 3. Superimposed on the nychthemeral changes in kininogen concentration are changes which may be related to the hormonal events of the oestrous cycle. 4. During early pregnancy and pseudopregnancy the kininogen level rises; this increase may be due to changes in the circulating levels of oestrogens and progestogens. 5. It is suggested that the changes in kininogen concentration may result from utilization of kinin which could be of functional significance.
Aspects of intestinal folate transport in the rat.
Authors: Blair J A , Johnson I T , Matty A J
Published: December 2014

1. In vitro preparations of rat jejunum were used to study the metabolic dependence, the structural specificity, and the pH sensitivity of the folic acid absorption process. 2. The presence of 2:4 dinitrophenol, and the absence of oxygen, in the muscosal bathing medium both led to a decrease in the tissue accumulation and serosal transfer of folic acid by everted sacs. 3. 10‐formylfolic acid, present in the mucosal medium at a molar ratio of 10:1 with labelled folic acid, appears to compete for tissue accumulation sites but has no significant effect on serosal transfer. 4. The efflux of folic acid from pre‐loaded jejunal sacs is stimulated by the presence in the mucosal medium of the folic acid and related compounds. Pteroyl‐L‐glutamic acid, 10‐formylfolic acid and methotrexate elicit a significant increase in the efflux rate; pteroyl‐D‐glutamic acid was significantly less effective and pteroic acid had no effect. 5. The uptake of folic acid by isolated jejunal cells prepared by enzymic disaggregation of the mucosa, was found to be influenced by the pH of the bathing medium, uptake being enhanced at a pH of between 5 and 6. 6. It is concluded that the effect of metabolic inhibitors and acid pH conditions on the uptake of folic acid in vitro is consistent with a passive absorption mechanism, influenced in intact preparations and in vivo by the jejunal pH microclimate. However the occurrence of competitive inhibition and stimulated efflux may indicate the existence of a structurally specific accumulation process at some site, or sites, within the mucosa.
Receptive fields of unmyelinated ventral root afferent fibres in the cat.
Authors: Clifton G L , Coggeshall R E , Vance W H , Willis W D
Published: December 2014

1. The receptive fields were determined for 118 afferent fibres in the S2, S3 and Ca (caudal) 1 ventral roots of the cat. Of these fibres, ninety‐three were unmyelinated, another eleven were probably unmyelinated, and fourteen were myelinated, according to estimates of their conduction velocities. 2. Confirmation that the recordings were from ventral root filaments came from electron microscopic inspection of ten of the filaments from which recordings of the activity of unmyelinated afferents were made. 3. Receptive fields were demonstrated for twelve unmyelinated afferent fibres in the distal stumps of the S2 and S3 ventral roots which had been sectioned 3 weeks previously, indicating that the cell bodies giving rise to these fibres were not in the spinal cord. 4. The action potentials of some of the unmyelinated ventral root afferent fibres were complex, suggesting branching of the afferents within the ventral root. 5. One third of the unmyelinated ventral root afferents had receptive fields in somatic structures: the skin and deep tissues. 6. Two thirds of the unmyelinated ventral root afferents had receptive fields in the viscera of the pelvis: the bladder, urethra, vagina, and lower bowel. 7. Many of the unmyelinated afferents in the ventral roots, especially those with cutaneous receptive fields, had high thresholds and may participate in nociception. 8. It is concluded that the cat ventral root contains a major sensory component and that the Law of Bell and Magendie is not an accurate description of the organization of the ventral root in this animal.
Servo action in the human thumb.
Authors: Marsden C D , Merton P A , Morton H B
Published: December 2014

1. The servo‐like properties of muscle in healthy human subjects have been studied by interfering unexpectedly with flexion movements of the top joint of the thumb. This movement is carried out by the flexor pollicis longus muscle only. 2. The movements were standardized in rate by giving the subject a tracking task. They started off against a constant torque load offered by an electric motor. 3. In some movements the load remained constant, but in others, in mid‐course, perturbations were introduced at random. Either the movement was halted, or released and allowed to accelerate by reducing the load, or reversed by suddenly increasing the current in the motor, so stretching the muscle. 4. Usually eight or sixteen responses to each kind of perturbation and a similar number of controls against a constant load were averaged. 5. Muscle activity was recorded as the electromyogram from surface electrodes over the belly of the long flexor in the lower forearm. Action potentials were usually full‐wave rectified and integrated. 6. About 50 msec after a perturbation the muscle's activity alters in such a sense as to tend to compensate for the perturbation, i.e. it increases after a halt or a stretch and decreases after a release. The latency is similar in each case. 7. These responses are interpreted as manifestations of automatic servo action based on the stretch reflex. They are considered to be too early to be voluntary. 8. This interpretation was supported by measuring voluntary reaction times to perturbations under tracking conditions. They were found to be 90 msec or longer. 9. When the initial load was increased by a factor of 10, the servo responses were all scaled up likewise. Thus to a first approximation the gain of the servo is proportional to initial load. 10. It follows that in relaxed muscle the gain should be zero. This was confirmed by showing that stretching a relaxed muscle gives no reflex, or only a small one. 11. Gain appears to be determined by the level of muscle activation as determined by the effort made by the subject, rather than by the actual pressure exerted by the thumb. 12. Thus in fatigued muscle gain is boosted as the muscle has to be activated more strongly to keep up the same force output. The net effect is to compensate for fatigue and maintain the performance of the servo. 13. The Discussion centres on the implications of gain control in the servo. For a start, if the gain of the stretch reflex arc is zero in relaxed muscle, contractions cannot be initiated via the stretch reflex by simply causing the spindles to contract, as proposed on the original ‘follow‐up’ servo theory.
Blockade by amino acid antagonists of neuronal excitation mediated by the pyramidal tract.
Authors: Stone T W
Published: December 2014

1.The responses to glutamate and amino acid antagonists of cells in the cuneate nucleus of anaesthetized rats have been examined.2. 1‐hydroxy‐3‐amino‐pyrrolidone‐2 (HA‐966) and glutamic acid diethylester applied by micro‐iontophoresis reduced glutamate excitation of the neurons. HA‐966 WAS EFFECTIVE ON MORE CELLS THAN GLUTAMIC ACID DIETHYLESTER AND WAS MORE POTENT. HA‐966 DID NOT AFFECT EXCITATORY RESPONSES TO ACETYLCHOLINE.3. Spike activity of cuneate cells was evoked by stimulating the cerebral cortex. Spikeswhich could be attributed to monosynaptic activation of the cells were studied. The pyramidal tract is the only corticofugal pathway known to be capable of short latency activation of dorsal column nucleus neurones.4. HA‐966 reversibly blocked the evoked activity in twenty‐eight (70%) of forty units in which monosynaptically evoked spikes were induced.5. The results raise the possibility that the neurotransmitter released by neurones of the pyramidal tract may be an excitatory amino acid.
Stimulus‐secretion coupling in pancreatic acinar cells: inhibitory effects of calcium removal and manganese addition on pancreozymin‐induced amylase release.
Authors: Kanno T , Nishimura O
Published: December 2014

The role of Ca ions in stimulus‐secretion coupling has been analysed in the isolated and perfused rat pancreas. 2. The omission of [Ca2+]O diminished but did not abolish the release of amylase in response to continuous stimulation with 5 m‐u. pancreozymin (Pz)/ml. The addition of Mn2+ (1‐0 mM) to this Ca‐deficient environment abolished the residual release of amylase. This was followed by a complete recovery of amylase output when the control [Ca2+]O was reestablished. 3. The addition of Mn2+ (1‐0 mM) to the extracellular environment containing 2‐5 mM‐Ca2+ reversibly inhibited the Pz‐induced release of amylase. 4. A kinetic scheme based on competition of Ca and Mn at a carrier in the acinar cell membrane could quantitatively explain the effects of Ca and Mn upon the Pz‐induced amylase release. 5. These results support the view that the Ca2+ influx into the acinar cells is the major contributor to the rise in [Ca2+]i which, in turn, mediates the processes in the stimulus‐secretion coupling in the exocrine pancreas, and suggest that the mode of Ca influx is a facilitated diffusion.
Long term changes in augmentation, potentiation, and depression of transmitter release as a function of repeated synaptic activity at the frog neuromuscular junction.
Authors: Magleby K L , Zengel J E
Published: December 2014

1. End‐plate potentials (e.p.p.s) were recorded from frog neuromuscular junctions under conditions of low quantal content to study the long‐term effects of repeated synaptic activity on transmitter release. 2. The nerve terminal was presented with 30‐100 successive conditioning‐testing trials applied once every 7‐10 min over a 4‐16 hr perod. Each conditioning‐testing trial consisted of a 200‐600 impulse conditioning train followed by a series of testing impulses. The magnitudes and time constants of decay of augmentation and potentiation following each successive conditioning train were determined by measuring the e.p.p. amplitudes resulting from the testing impulses. 3. The magnitude of augmentation immediately following the conditioning trains increased an average of 3‐4 times (range 1‐20) with sucessive trials. 4. As the magnitude of augmentation increased with successive trials the decay of augmentation deviated from a simple exponential, decaying faster immediately after the conditioning train. This faster decay led to a 20% decrease with successive trials in estimates of the time constant obtained from the first 10 or 20 sec of the decay of augmentation. The deviation of the decay of augmentation from a simple exponential could be accounted for if augmentation is related to the 4th power of some substance which decays with a simple exponential time course. Some alternative explantations for the non‐exponential decay of augmentation are also discussed. 5. The magnitude of potentiation increased or decreased about 25% with successive trials. 6. The time constant characterizing the decay of potentiation inceased an average of 1‐5 times (range 0‐8‐5 times) with successive trials. 7. The increase in the magnitude of augmentation with successive trials was accompanied by a similar increase in the magnitude of the e.p.p. amplitudes during the conditioning trains, suggesting that augmentation develops during the conditioning train. In some preparatons augmentation appeared to be the major factor acting to increase e.p.p. amplitudes during the conditioning train, having a greater effect than facilitation or potentiation. 8. If a sufficiently large number of successive trials were applied, a depression of e.p.p. amplitudes developed during the conditioning trains and estimates of the magnitude of potentiation following the depressed conditioning trains were reduced...
On the metabolism of the rod outer segments.
Authors: Carretta A , Cavaggioni A
Published: December 2014

1. The high energy phosphate esters available for the luminescent reaction of the firefly lantern extract correspond, in the dark adapted rods of the frog, to 7 X 10(‐16) mole of ATP per rod, corresponding to ca. 1‐4 mM. 2. Rods isolated from light adapted eyes contain a smaller amount. 3. The high energy phosphate esters are reduced spontaneously at a rate of 50% in 24 min, in the isolated rods in darkness. 4. Bleaching a few per cent of the rhodopsin molecules of a rod suspension induces a 60% decrease achieved in less than 12 sec. 5. The ionophore A23187 decreases the high energy phosphate esters when the extracellular free Ca concentration is greater than 10(‐7) M, suggesting that ATP is consumed in pumping Ca ions out of the rods, or into the disks contained in the rods, or both.
Differences in the metabolic and hormonal response to exercise between racing cyclists and untrained individuals.
Authors: Bloom S R , Johnson R H , Park D M , Rennie M J , Sulaiman W R
Published: December 2014

1. Six well‐trained cyclists and six untrained subjects were studied during and immediately after four successive 7 min periods of exercise at 30, 45, 60 and 75% of their maximal work capacity. 2. Venous blood samples were taken at rest, at the end of each exercise period and 5 min following the end of exercise, for estimation of metabolites in blood and plasma insulin, growth hormone, cortisol and catecholamines. 3. The results showed significant differences in the mobilization and utilization of muscle fuels between the athletically fit cyclists and the untrained group. In the cyclists, glucose, glycerol and free fatty acid concentrations were higher, but lactate, pyruvate and alanine were lower than in the untrained subjects during exercise. 4. Plasma catecholamines rose in both groups during exercise but the rise was significantly less in the racing cyclists. Plasma insulin was depressed to a greater extent in the untrained subjects during exercise and plasma glucagon rose to a greater extent during strenuous exercise and remained elevated after the end of exercise in the untrained group. Plasma human growth hormone rose to a greater extent during exercise and remained elevated after the end of exercise in the untrained group. Plasma cortisol fell at low and moderate exercise rates in both groups, but to a smaller extent in the cyclists. Cortisol values rose at higher workloads and were significantly higher in the cyclists at the end of exercise. 5. It is concluded that there are significant differences in the metabolic and hormonal responses to exercise between athletically trained and untrained individuals, even when the physically fit subjects work at the same percentage of their maximal capacity as the unfit subjects.
Sub‐miniature end‐plate potentials at untreated frog neuromuscular junctions.
Authors: Bevan S
Published: December 2014

1. Some properties of unusually small spontaneous miniature end‐plate potentials (sub‐min.e.p.p.s) at untreated end‐plates of adult frogs have been examined. 2. These small potentials, which show a fast time course, add a highly skewed component to the normal Gaussian distribution of min.e.p.p. amplitudes. 3. Sub‐min.e.p.p.s were not evoked by single nerve stimuli, though their frequency could be raised by tetanic nerve stimulation. 4. When min.e.p.p. rate was raised by addition of lanthanum, submin.e.p.p. frequency was also increased, though by a smaller factor than normal min.e.p.p.s. In contrast, sub‐min.e.p.p. frequency was unchanged when min.e.p.p. rates were raised by either ethanol or hypertonic solutions.
A pharmacological study of Renshaw cell inhibition.
Authors: Curtis D R , Game C J , Lodge D , McCulloch R M
Published: December 2014

1. In cats anaesthetized with pentobarbitone a pharmacological investigation was made of the inhibition of Renshaw cells by dorsal root afferent volleys and ventral root antidromic volleys, and of the inhibition of motoneurones by Renshaw cells. 2. The effects of strychnine, bicuculline and tetanus toxin indicate that both glycine and GABA operate as inhibitory transmitters released on Renshaw cells by dorsal root volleys. 3. The 'mutual' inhibition of Renshaw cells, and the recurrent inhibition of motoneurones by Renshaw cells, are suppressed by strychnine: Renshaw cells are thus glycinergic inhibitory neurones, a proposal consistant with recent evidence for strychnine‐sensitive inhibition of Ia interneurones by Renshaw cells. 4. The 'pause' which follows high frequency synaptic excitation of Renshaw cells is insensitive to strychnine, bicuculline and tetanus toxin, and is considered unlikely to be the consequence of synaptic inhibition.
Analysis of spontaneous activity of auditory neurones in the spiral ganglion of the guinea‐pig cochlea.
Authors: Manley G A , Robertson D
Published: December 2014

1. Spontaneous activity of single afferent neurones in the cochlea of the guinea‐pig was studied by measurement of mean rates and computation of interspike interval histograms. 2. The shapes of interval histograms agreed with those found in cat cochlear nerve fibres. Modes of the histograms were less than 7 msec for all cells with mean rates ranging from 20 to 150 spikes/sec. 3. The distribution of mean rates showed higher maximum rates than those found in cat. Cells from animals with abnormally high thresholds showed lower mean rates than those from sensitive animals. 4. No correlation was found between mean spontaneous rate and sensitivity to acoustic stimulation. No discrete populations of cells could be discerned on any of the criteria used. 5. The simultaneous effects of hypoxia on cell thresholds, mean spontaneous rate and scala media potentials are reported. These and other results are discussed in relation to possible sites of generation of spontaneous activity in primary auditory afferents.
The effect of temperature on potassium chloride contracture in cat myocardium.
Authors: Bassett A L , Wiggins J R
Published: December 2014

1. Contracture was induced in cat myocardium by exposure to 140 mM‐KC1 In isotonic Tyrode solution. Force of contracture expressed as mg/mm2 (muscle cross‐sectional area) falls with increasing cross‐sectional area. 2. The effect of temperature on isometric force developed during contracture was evaluated both in normal (untreated) atrial and ventricular muscle and following treatment with sympatholytic drugs. 3. The force of contracture was not significantly affected by sympatholytic drugs at 36 degrees C. 4. In normal atrial and ventricular muscle, force of contracture decreased when the muscle was cooled from 36 to either 29 or 20 degrees C. 5. In atrial muscle, the effect of temperature was not changed by sympatholytic drugs. In contrast, exposure to sympatholytic drugs increased contracture force developed by ventricular muscle at 20 degrees C. Also, contracture force was significantly greater at 20 than at 36 degrees C in ventricular muscle from reserpine‐pretreated cats. 6. It is suggested that ventricular muscle becomes more sensitive to the relaxing effects of endogenous catecholamines at temperature is lowered. 7. The differences shown between atrial and ventricular muscle with respect to the effect of temperature and sympatholytic drugs on contracture force may result from the differing amounts of sarcoplasmic reticulum found in these types of cardiac muscle and also from different mechanisms of "excitation‐contracture" coupling in atrial and ventricular muscle.
The effect of hormones and of an osmotic gradient on the structure and properties of mammalian foetal urinary bladder in vitro.
Authors: France V M , Stanier M W , Wooding F B
Published: December 2014

1. Water and isotope fluxes were measured by incubating urinary bladders of foetal pigs and sheep in vitro in the presence and absence of a concentration and osmotic gradient. The structure of the urinary bladder of foetal pigs under various conditions was studied by electron microscopy. Its ultrastructure was found to be closely similar to that of foetal sheep. 2. Antidiuretic hormone (ADH) (0‐2 U. ml‐1) enhanced the enlargement of intercellular spaces caused by dilute mucosal medium in pig bladders; prolactin (1 u. ml‐1) prevented osmotic dilatation of the intercellular spaces. 3. The hydraulic conductivity, Lp, was estimated to be 0‐5 X 10 (‐7) cm.s‐1atm‐1 in sheep and pigs at about 100 days gestation; the ratio of osomotic to diffusional permeability, (LpRT/VW)/PD, in the presence and absence of ADH, was 2‐1 and 1‐6 respectively. These are similar to the values found in fish gills. 4. Prolactin reduced bulk flow of water to zero in seven out of eight bladders investigated. Incubation with ADH or vasotocin (55 mu. ml‐1) in the presence of prolactin restored water flux to 22% and 45% of control values respectively. 5. There was no significant net flux of sodium from mucosa to serosa in pig bladder except in the presence of prolactin. No net flux of sodium occurred from mucosal to serosal side of pig or sheep bladders in the presence of an adverse electrochemical gradient, although in sheep the permeability ratio was significantly greater than one. 6. The diffusional flux ratio for water remained unity under all conditions; vasotocin increased unidirectional fluxes and prolactin reduced them. The flux ratios were unaffected by the direction of bulk fluid flow, probably because diffusion was rapid compared to flow: the ratio of diffusional flux to volume flow was between 11 and 18.
Potassium accumulation and depletion in frog atrial muscle.
Authors: Noble S J
Published: December 2014

1. In atrial wall trabeculae of Rana catesbeiana and R. ridibunda very slowly decaying membrane currents have been consistently observed in decay tails following voltage clamp depolarizing and hyperpolarizing pulses. It is not thought that these currents are carried by time‐dependent conductance channels but rather result from potassium ion accumulation or depletion. 2. Since voltage clamp techniques generally impose a non‐physiological situation on the membranes of excitable cells, evidence that potassium ion accumulation occurs in unclamped atrial tissue is presented. 3. When potassium ions accumulate, the reversal potentials for both atrial delayed conductance mechanisms, ixfast and ixslow, should be shifted in a positive direction, the magnitude of the shifts being a function of the charge transferred during depolarization. Experiments have been performed to test this prediction quantitatively, and as a result, a simple accumulation model is developed. 4. A second important effect of accumulation should be upon the time‐independent potassium conductance, iK1. It was found that this effect produces current tails whose decay becomes exponential when the amount of accumulation is small. The time constant of this exponential is shown to be equal to the time constant of decay of accumulation, tauacc. 5. One of the most important assumptions in the accumulation model is that the iK1(Em) relations for different values of [K]O 'cross‐over' one another as they do in skeletal muscle and mammalian Purkinje tissue. Experimental verification of this assumption is presented. This 'cross‐over' effect allows current changes due to accumulation to show an apparent 'reversal potential' and so to appear like a conductance mechanism. 6. Potassium depletion is shown to occur during hyperpolarizing pulses. This depletion process must be allowed for in a direct kinetic analysis of the pace‐maker current, ixslow, at potentials negative to the resting potential (ER).
The influence of non‐uniformity on the analysis of potassium currents in heart muscle.
Authors: Brown H F , Noble D , Noble S J
Published: December 2014

1. A method is described for determining the space constant gamma of heart muscle strips using a sucrose gap technique. 2. The average value of gamma for frog atrial trabeculae was found to be nearly 700 mum. This value is nearly twice the length of the test gap (400 mum). Near the resting potential, the voltage non‐uniformity should be about 10%. This was confirmed experimentally by comparing the membrane voltages recorded across the current‐passing and voltage‐recording sucrose gaps. 3. The non‐uniformity during large depolarizations was calculated using a computer model. This model includes the inward‐going rectification displayed by iK1 and the delayed rectification that occurs following depolarizations beyond ‐40mV. A single component of delayed rectification was included. 4. It is shown that even very large non‐uniformities have relatively small effects on the shape of the activation curve and on the time course of onset or decay of current. 5. It is comcluded that the fast component of current decay described in a previous paper (Brown, Clark & Noble, 1976b) is not attributable to a non‐uniformity artifact.
Temporal response patterns of the human sinus node to brief carotid baroreceptor stimuli.
Authors: Eckberg D L
Published: December 2014

1. A new technique, timed, quantitative neck suction was used to establish in normal man the temporal response patterns of the sinus node to brief baroreceptor stimuli. 2. Maximum sinus node inhibition occurred when stimuli were delivered about 0‐75 sec before the anticipated appearance of the subsequent P wave; less pulse interval prolongation occurred when stimuli were delivered earlier, or later in the cardiac cycle. 3. The timing of maximum sinus node responsiveness appeared to be independent of base‐line cardiac cycle length. 4. The duration of the baroreceptor‐cardiac reflex are (the time from the onset of baroreceptor stimulation until the earliest occurrence of pulse interval prolongation) averaged 0‐24 sec. 5. Pulse interval prolongation was proportional to baroreceptor stimulus strength and duration. 6. The results suggest that in man, sinus node responsiveness to baroreceptor stimuli depends critically upon the timing of stimuli within the cardiac cycle.
Functional and structural changes in mammalian sympathetic neurones following colchicine application to post‐ganglionic nerves.
Authors: Purves D
Published: December 2014

1. The effects of post‐ganglionic colchicine application on neurones of the guinea‐pig superior cervical ganglion were studied with intracellular recording and electron microscopy. 2. Local colchicine application for 30 min to one of the major post‐ganglionic nerves caused several electrophysiological changes after 4‐7 days in many neurones whose axons run in this nerve. These changes include: (a) a reduction in the amplitude of synaptic potentials elicited by supramaximal preganglionic stimulation; (b) a decrease in the number of preganglionic fibres innervating individual neurones; (c) the development of regenerative responses in dendrites; and (d) the failure of antidromic action potentials to fully invade the neuronal soma. These functional changes occurred in the absence of impaired impulse conduction or axon degeneration, and were not observed in nearby neurones whose axons ran in an untreated post‐ganglionic nerve. The effects of colchicine are similar to the changes produced by axotomy. 3. Counts of synapses in thin sections from the region of the ganglion where the affected neurones were located showed a reduction, compared to the number of synapses in other regions of the colchicine treated ganglia, or normal control ganglia. This finding indicates that synaptic depression after colchicine treatment, like that after axotomy, is due primarily to a loss of synaptic contacts from the dendrites of affected nerve cells. Unusual profiles containing numerous vesicular and tubular organelles frequently seen after interruption of the axons were also observed in thin sections after colchicine treatment. 4. The similarity of the electrophysiological and ultrastructural effects of colchicine treatment and axon interruption offers further support for the view that synaptic contacts on sympathetic neurones are normally regulated by an interaction of the neuronal soma with its axonal extension to the periphery.
Regulation of cerebrospinal fluid potassium by the cat choroid plexus.
Authors: Husted R F , Reed D J
Published: December 2014

1. The regulation of cerebrospinal fluid (c.s.f.) potassium concentration was studied using the cat choroid plexus isolated in a chamber in situ. 2. Hyperkalaemia (plasma potassium concentration greater than 6 m‐equiv/l.) caused relatively small increases in c.s.f. potassium concentration. 3. Alterations in c.s.f. potassium concentration (c.s.f. K = 0‐15 or 6‐56 m‐equiv/l.) were countered by changes in potassium concentration of the produced fluid or in the rate of potassium transport which returned c.s.f. potassium towards normal. 4. The data indicate that potassium concentration in c.s.f. secreted by the choroid plexus is actively regulated by the plexus whether the primary alteration in potassium occurs in plasma or c.s.f.
Sensitivity of renin secretion to volume depletion in the anaesthetized dog: comparison between urinary drainage and slow haemorrhage.
Authors: Bertoncello I , Naughton R J , Skinner S L
Published: December 2014

1. An experimental technique utilizing 'denervation diuresis' from one kidney with measurement of renin release from the contralateral innervated kidney was developed to study the sensitivity of renin secretion to volume depletion. 2. With urine excretion, release of renin increased progressively from the innervated kidney. The increase was significant at a sodium deficit of 0‐23 mole.kg‐1. At a sodium deficit of 0‐6 m‐mole.kg‐1 renin release had doubled. 3. Bilateral vagotomy did not alter this response. 4. Precise replacement of sodium loss with isotonic saline but without replacement of other urinary components returned renin release to control levels. 5. Slow haemorrhage causing a rate of volume and sodium loss equivalent to urinary drainage did not alter the rate of renin release. 6. With a single denervated kidney and contralateral nephrectomy, renin release fell progressively to minimal levels despite sodium deficits up to 2‐6 m‐mole.kg‐1. 7. It is concluded that renin secretion is sensitive to at most a 0‐5% change in body fluid volume and should be considered a primary response to volume depletion. The sensitivity of the response depends upon normal renal innervation but is not mediated via vascular volume receptors nor via receptors innervated by the vagus. 8. It is proposed that the extreme sensitivity of the renin‐secreting system in these experiments results from the combination of volume depletion and slight hypotonicity of extracellular fluid acting on the renal afferent arteriole without the mediation of the macula densa,
Unit responses in the medulla oblongata of rabbit to changes in local and cutaneous temperature.
Authors: Inoue S , Murakami N
Published: December 2014

1. In anaesthetized rabbits which were stereotaxically implanted with a thermode following decerebellation, thermal sensitivity of neurones in the medulla oblongata to local temperature changes was examined systematically. The medullary temperature was changed by circulating water at various temperatures through the thermode. 2. Eighty‐seven temperature‐responsive neurones were found in the medulla, especially in the medullary reticular formation. Out of these eighty‐seven, forty‐eight neurones were cold‐responsive neurones, while the rest were warm‐responsive. Both types of neurones included not only neurones with linear or continuous relations between discharge rate and local temperature but also neurones with non‐linear or discontinuous thermoresponse curves. 3. In the medulla a few of the temperature‐responsive neurones showed a dynamic reaction with static discharge rate changes to changes of local temperature. 4. Seven neurones out of the fifteen respiratory neurones encountered during the exploration had thermal sensitivity to respiratory alteration of the discharge. 5. with thermal stimulation of a limited area of the skin, over 50% of the temperature‐responsive neurones recorded in the medulla responded positively or negatively to changes in the skin temperature.