bluuebunny/crossref_metadata_2025_split huggingface dataset:
The time and voltage dependence of the slow outward current in cardiac Purkinje fibres
Authors: McAllister R. E. , Noble D. 
Published: December 2014

1. In normal Tyrode solution the initial inward sodium current which is produced in Purkinje fibres in response to a sudden depolarization is followed by a very slow change in current in an outward direction. The magnitude and speed of onset of this slow change both increase with the strength of the depolarization.2. On repolarization, a transient outward current is observed (Deck & Trautwein, 1964). The initial magnitude of this outward current also increases with the strength and duration of the preceding depolarization, with a time course similar to the time course of the slow change in current during depolarization.3. Evidence is presented for the view that the slow change in current during depolarization represents the onset of delayed potassium rectification and that the decline in outward current following repolarization represents its decay.4. Removal of sodium ions greatly increases the threshold of the slow outward current. In the presence of sodium ions 15 mV depolarization is sufficient to produce an appreciable current. In the absence of sodium ions at least 50 mV depolarization is required and, in some fibres, no delayed rectification is observed even when the membrane potential is made positive.5. Prolonged depolarization of the membrane by outward current changes the quiescent membrane potential in a positive direction. This change in potential is attributed to an accumulation of potassium ions in a space immediately outside the cell membrane, which equilibrates slowly with the extracellular fluid. It is shown that this effect is very small during depolarizations of the magnitude and duration of the normal action potential.6. It is concluded that the results are consistent with the view that repolarization of the Purkinje fibre action potential is initiated by a slow increase in K conductance similar to, but much smaller and slower than, that observed in nerve fibres.
The effects of suxamethonium and acetylcholine on the behaviour of cat muscle spindles during dynamic stretching, and during fusimotor stimulation
Authors: Rack P. M. H. , Westbury D. R. 
Published: December 2014

1. The responses of primary and secondary afferent fibres from muscle spindles in cat soleus were studied during constant velocity stretching.2. Intravenous Suxamethonium (SCh) caused a large increase in the response of the primary afferents to the dynamic phase of stretching, and a smaller increase in their response to static extension. The effects of SCh were similar to the effects of dynamic fusimotor stimulation.3. Increasing doses of SCh increased the response of primary afferents to dynamic stretching up to a point, but a peak discharge frequency was encountered beyond which the afferent fibre could not be induced to discharge.4. Suxamethonium increased the response of the secondary afferent fibres by a smaller amount than the primaries, and in particular caused a smaller increase in the response to dynamic extension.5. Acetylcholine given by close arterial injection had an effect similar to the effect of SCh.6. The effects of static and dynamic fusimotor stimulation on the response of primary afferents summed with the effects of small doses of SCh. When large amounts of SCh were used fusimotor stimulation sometimes had no further effect on the afferent discharge. It was not possible to say whether the fusimotor activity was then inhibited, or submerged in the SCh activity.7. The actions of SCh and of acetylcholine emphasized the differences in response of primary and secondary afferent endings to dynamic stretching. The use of these drugs enabled us to classify fibres of intermediate conduction velocity.8. Suxamethonium is known to activate slow muscle fibre systems with distributed nerve endings. The similarity between dynamic fusimotor activity and the effect of SCh suggests that the dyanimic fusimotor fibres act on slow intrafusal muscle fibres through multiple distributed endings.
A comparison of the responses of frog skin receptors to mechanical and electrical stimulation
Authors: Catton W. T. 
Published: December 2014

1. The latencies of spike responses evoked alternatively by brief mechanical (M) and electrical (E) pulses applied to single mechanoreceptive terminals in frog skin were compared on the same receptor.2. Latency was found to be a maximum at threshold and to decrease with increased stimulus strength for both modes of excitation, but at all strengths M latency exceeded E latency. Mean maximum and minimum values for M latency were 4·8 and 2·85 msec; for E latency the maximum was 2·8 and minimum 2·3 msec.3. At high frequency and strength of E stimulation there was an abrupt and marked shortening of latency to a fixed minimum value which ranged from 0·5 to 1·2 msec (mean 0·8). This was taken to be the response of the parent myelinated axon excited directly. The gap (1·5 msec) between the minimum value for the receptor response (2·3 msec) and the axonal response (0·8 msec) was taken to represent conduction time in the terminal branches of the sensory axon.4. The response latency for excitation of the sensory terminal was also dependent on the duration of the stimulus pulse, but whereas the latency range for the M stimulus could be greatly extended that for the E stimulus was only slightly affected by increase in pulse duration.5. The responses evoked by direct currents were complex, and consisted of an early brief discharge at the start of a cathodal current followed after a delay of 5‐30 sec by a prolonged multi‐fibre discharge which out‐lasted the stimulus. It is proposed that the sensory terminal is rapidly accommodating to current flow and that the delayed discharge is due to release of chemical material.6. It is suggested that delay in mechanical excitation may be due to non‐rigid coupling of the receptor terminal to the skin tissues.
A visco‐elastic theory of mechanoreceptor adaptation
Authors: Catton W. T. , Petoe N. 
Published: December 2014

1. Physical analysis of two visco‐elastic models was performed, to afford a quantitative basis for examination of a theory of slip as applied to mechanoreceptor adaptation. In one model the coupling force between skin tissue and receptor was considered to be purely viscous; in another it was supposed to consist of parallel viscous and elastic forces, representing the properties of a gel.2. Predictions from the models were compared with experimental results from frog and rat skin receptors. Good fits with slope—latency and slope—amplitude curves were obtained, with the adjustment of two constants.3. The excitability changes during long subliminal stimuli showed dynamic and static phases, which developed at different rates as stimulus strength was increased. This behaviour could be explained qualitatively by the more complex model, but quantitative comparisons could not be achieved.4. Treatment of the skin with tissue‐destroying enzymes caused changes in stimulus‐response relationships consistent with predictions from the models. The effect of the enzymes seemed to be largely on the elastic coupling forces.5. The visco‐elastic model offers a satisfactory but not exclusive explanation of certain time‐ and amplitude‐dependent features of mechanoreceptor behaviour and also accounts for a specific delay in mechanical excitation.
The uptake and release of radioactive noradrenaline by the splenic nerves of cats
Authors: Gillespie J. S. , Kirpekar S. M. 
Published: December 2014

1.
DL‐[3H]noradrenaline was infused close‐arterially into the spleens of chloralosed cats at rates of 0·625 or 1·25 μg/min for 10 or 20 min and the recovery of noradrenaline and its metabolites in the venous blood measured during the infusion and after nerve stimulation at various times after the infusion.2. During the infusion 41% of the noradrenaline was recovered in the blood as such and 11% as metabolites. The remaining 48% was retained within the spleen.3. The noradrenaline retained in the spleen was slowly released to appear as metabolites in the blood stream. In normal animals the rate of loss from the spleen was 0·22% per minute. In animals given phenoxybenzamine after the end of the infusion this rate was several times greater.4. Splenic nerve stimulation in normal animals or in animals treated with phenoxybenzamine resulted in an increase in the radioactivity of the blood leaving the spleen. Paper chromatography showed this to be radioactive noradrenaline.5. In normal animals the specific activity of the transmitter liberated by nerve stimulation was less than that of the stores of noradrenaline within the spleen. In animals treated with phenoxybenzamine these two values were similar.6. It is suggested that the infused noradrenaline retained in the spleen is largely taken up into nerve fibres and is available for subsequent release by nervous activity.
The histological localization of noradrenaline in the cat spleen
Authors: Gillespie J. S. , Kirpekar S. M. 
Published: December 2014

1. The histological localization of noradrenaline in the cat spleen has been studied with a fluorescence technique and, after infusing
DL‐[3H] noradrenaline, both by the fluorescence technique and by autoradiography.2. In the normal cat spleen the specific fluorescence of catecholamines is confined to nerve fibres among the smooth muscle of the capsule, trabeculae, arteries and veins. These fluorescent fibres are not present after treating the animal with reserpine or after degeneration of the postganglionic splenic nerves.3. The splenic artery outside the spleen has few visible terminal adrenergic fibres. This is associated with the presence of an external elastic lamina. No terminal fibres were found in the walls of the main splenic vein.4. After infusing
DL‐[3H]noradrenaline 1·25 μg/min for 10 or 20 min fluorescence remained confined to the same sites as in normal cats, i.e. in fibres related to smooth muscle. The red and white pulp and the smooth muscle itself remained free of fluorescence. Autoradiography showed radioactivity in similar sites and with the same pattern as the fluorescent fibres. These results support the conclusion reached in the previous article that noradrenaline infused into the spleen is bound to adrenergic nerves.
Recovery of responsiveness of cells of lateral geniculate nucleus of rat
Authors: Burke W. , Sefton Ann Jervie 
Published: December 2014

1. Recovery of responsiveness of single cells in lateral geniculate nucleus of rat has been determined in both P and I cells. There are three types of recovery curve among P cells; (a) early recovery, (b) early partial recovery followed by depression and then complete recovery, (c) prolonged depression followed by cyclic recovery. Type (c) is by far the commonest recovery curve. In contrast to the spike in a P cell, the synaptic potential recovers to its full amplitude in about 20 msec. All I cells exhibit similar rapid recovery curves after a prolonged depression.2. Conditioning stimuli applied to visual cortex also produce a prolonged depression in most P cells but I cells can be re‐excited at short intervals from cortex. Decortication does not prevent the prolonged depression of the multineuronal response produced by optic nerve stimulation.3. A neuronal model is proposed to explain these observations. It is supposed that I cells (interneurones) are innervated by axon collaterals of the P cells (principal cells, projecting to visual cortex) and that the I cells exert an inhibitory influence on the P cells.
Inhibitory mechanisms in lateral geniculate nucleus of rat
Authors: Burke W. , Sefton Ann Jervie 
Published: December 2014

1. An examination was made of the mechanisms responsible for the inhibition of synaptic transmission through the lateral geniculate nucleus (LGN) of the rat following a single shock to the optic nerve.2. In the rat anaesthetized with paraldehyde we found no evidence that optic nerve stimulation produced any presynaptic inhibition in LGN. In agreement with other workers it was found that repetitive stimulation of visual cortex produced effects attributable to presynaptic inhibition. However, this was of small magnitude in the conditions of our experiments.3. Stimulation of the optic nerve elicited an action potential in a P cell (principal cell) which was followed by a wave of hyperpolarization lasting about 150 msec (inhibitory post‐synaptic potential, IPSP, wave).4. The IPSP wave was chloride‐dependent and was associated with inhibition of the P cell discharge. Occasional rippling on the IPSP wave suggests that it was produced by the repetitive discharge of I cells (interneurones).5. These observations support the model proposed previously wherein P cells are inhibited by I cells which in turn are excited by axon collaterals of P cells. There is evidence for diffuse interconnexions between P cells and I cells.6. The observation that the extracellularly recorded wave of hyperpolarization (P‐wave) is usually negative suggests that most of the inhibitory synapses are not on the soma of the P cell.
The effect of propranalol on the calorigenic response in brown adipose tissue of new‐born rabbits to catecholamines, glucagon, corticotrophin and cold exposure
Authors: Heim T. , Hull D. 
Published: December 2014

1. Experiments measuring the rate of oxygen consumption of unanaesthetized new‐born rabbits and the blood flow in brown adipose tissue of anaesthetized new‐born rabbits are described.2. The increase in rate of oxygen consumption caused by
I.V. infusion of noradrenaline, adrenaline and isoprenaline (2 μg/kg.min for 10 min) was blocked by propranalol (
I.V. 1 mg/kg) but the increase caused by cold exposure was not. A larger dose of propranalol (5 mg) blocked the calorigenic response to cold exposure as well.3. Infusion of glucagon (
I.V. 4 μg/kg.min for 10 min) caused a large increase in the rate of the rabbit's oxygen consumption and in blood flow through its brown adipose tissue. These responses, which reached a maximum within 10 min from the start of the infusion, were not blocked by propranalol (1 or 5 mg/kg).4. Infusion of corticotrophin (
I.V. 1 i.u./kg.min for 10 min) also caused a large increase in the rate of oxygen consumption of new‐born rabbits. The response reached a maximum about 20 min from the start of the infusion and it was not blocked by propranalol (5 mg/kg).5. These results support the conclusion that noradrenaline is released at sympathetic endings in brown adipose tissue and that the increase in blood flow caused by noradrenaline is secondary to its metabolic action on the tissue. They also suggest the possibility that glucagon and corticotrophin may act directly on brown adipose tissue and stimulate heat production during cold exposure.
A thermal component of excitation in the lateral eye of Limulus
Authors: Srebro R. 
Published: December 2014

1. The temperature dependence of the relative spectral sensitivity of the excised lateral eye of Limulus was examined using its electrical response to light.2. At wave‐lengths longer than 625 mμ lowering the temperature from 27 to 7° C reduced the relative spectral sensitivity, while no effect was measurable at shorter wave‐lengths.3. The reduction in relative sensitivity increased linearly with decreasing wave number.4. The observations support the hypothesis that a critical amount of energy (activation energy) must be supplied to the photopigment molecule in order that it excite the photoreceptor. Quanta with energy lower than the activation energy are effective only if the thermal energy of the molecule can supply the deficit.5. The lower limit of the activation energy for the photoreceptor of the lateral eye of Limulus determined from the results of this study is 44 kcal mole−1.
The rise in clotting factor VIII induced in man by adrenaline: effect of α‐ and β‐blockers
Authors: Ingram G. I. C. , Jones R. Vaughan 
Published: December 2014

1. Human subjects received intravenous infusions of adrenaline preceded by saline, phentolamine (an α‐blocker) or either pronethalol or propranalol (β‐blockers), in different experiments.2. Clinical measurements of blood pressure and pulse rate confirmed that α‐ or β‐blockade had been achieved.3. The rise in clotting factor VIII induced by adrenaline was blocked by pronethalol and propranalol but not by phentolamine. This indicated that the effect of adrenaline on factor VIII was mediated by β‐receptors.
Effects of saline loading on the perfused cat kidney
Authors: Lockett Mary F. 
Published: December 2014

1. Isolated cat kidneys perfused at constant pressure with blood from normal animals respond either to infusion or to injection of 0·9% NaCl (5‐20 ml./150 ml. blood) by diuresis, natriuresis, a fall of the Na concentration in the urine, a fall followed by a rise in urinary Na/K and a rise in renal blood flow. The filtration fraction remains unchanged (Figs. 1, 2).2. Kidneys perfused either with blood from intact donors at constant blood flow or with blood from hypophysectomized donors at constant pressure show no vascular response to dilution of the blood with 0·9% NaCl. Saline dilution still causes diuresis and natriuresis. The concentration of urinary Na rises, as does Na/K without an initial fall (Figs. 3, 4).3. Kidneys perfused with blood from headless animals are unable to respond to saline loading (Fig. 6).4. Extracts of posterior hypothalamus convert the modified response of the kidney perfused with blood from hypophysectomized animals on dilution of the blood with saline to the response given when blood from intact animals is used (Figs. 3‐5).5. Renal responses to saline loading are shown to be due to two hormones, and are dependent on the presence of an unidentified intracranial hormone, related to hypophysial hormones.
Activity of the human eccrine sweat gland during exercise in a hot humid environment before and after acclimatization
Authors: Peter J. , Wyndham C. H. 
Published: December 2014

1. Six unacclimatized African mine labourers were subjected to exercise for 4½ hr in a hot humid environment (90°‐93° F wet‐bulb/dry‐bulb (
W.B./D.B.); approximately 90% r.h.)2. The patterns of glandular activity and the densities of active glands on the chest and back were assessed half‐hourly from plastic impressions.3. Acclimatization increased and prolonged glandular activity. The increment in activity of the sweat glands on the back was greater than that on the chest.4. There was no significant increase in the maximum number of active glands on either site after acclimatization.5. Acclimatization greatly reduced the number of inactive glands, subsequent to the maximum count, on the back, but this was not observed on the chest.6. The increased sweat rates with acclimatization were due mainly to increased glandular activity.7. The decline in sweat rates and activity on prolonged exposure to hot humid environment was attributed to glandular fatigue. Other factors, such as increased body temperature, hydration of the skin and fatigue of the central nervous system, suggested by other investigators as possibly causing the decline in sweat rates, did not have support in this study.
Vasodilatation in the submaxillary gland of the rabbit
Authors: Morley J. , Schachter M. , Smaje L. H. 
Published: December 2014

1. In the rabbit, in contrast to the cat and dog, the vasodilatation and the secretion in the submaxillary gland which accompany parasympathetic nerve stimulation are correspondingly sensitive to atropine block.2. It is concluded that true vasodilator nerve fibres to the submaxillary gland exist in the chorda tympani nerve of the rabbit.3. The vasodilatation which follows sympathetic vasoconstriction in the submaxillary gland of the rabbit is small and variable. The possibility that this after‐dilatation is due to an adrenergic neurotransmitter agent acting on β‐vascular receptors is discussed.
Concealed glomerular filtration
Authors: Brewin E. G. , Ekins R. P. , Nashat F. S. , Portal R. W. 
Published: December 2014

1. An increase in apparent renal clearances is frequently observed on restoring urine flow after a period of anuria or on increasing it after oliguria. An analysis of such ‘peaks’ in clearance has been made in experiments on anaesthetized dogs, using two preparations of labelled vitamin B12 and urine collections of 1–2 min. [57Co]B12 was infused throughout the experiments, while [58Co]B12 was given as a single injection during periods of anuria or oliguria induced by noradrenaline infusion, haemorrhage or aortic obstruction.2. The apparent high clearance in the first minute or two of restored or increased flow is an artifact explained by inclusion in the peak of material filtered earlier, but not excreted. By means of the integrated plasma concentration ratio of the two B12 isotopes during the period of low or absent flow, the excess B12 in the peak may be reapportioned between the period before the 58Co was injected and the period after it.3. The findings indicate that filtration may temporarily continue during anuria, but this is concealed as a result of failure of onward flow of filtrate. In oliguria a similar concealment of filtration may result from the cessation of onward flow in some nephrons.
Motor responses of the urinary bladder and skeletal muscle in Botulinum intoxicated rats
Authors: Carpenter F. G. 
Published: December 2014

1. Type A or type D botulinum toxin administered to rats did not produce a generalized paralysis of skeletal muscles at the time of ventilatory arrest. However, if survival was extended by artificial ventilation complete blockade of neuromuscular transmission developed 6·5 hr after 100 MLD of type D and 5 hr after 1000 MLD of type A toxin. The onset of paralysis of a muscle was shortened by repetitive stimulation of the motor nerves.2. There was no consistent blockade of parasympathetically innervated viscera in animals dying after type A toxin. Animals given type D toxin displayed mydriasis and urinary retention before death.3. Motor responses to electrical stimulation, of bladder preparations in vitro were more vulnerable to type D than to type A toxin. When somatic paralysis was complete in animals treated with type A or type D toxin the excised bladders produced pressure elevations 45 and 25%, respectively, of control preparations.4. During electrical stimulation of bladder preparations nearly paralysed by either toxin, the ACh release was significantly diminished from controls. In the rat bladder botulinum toxin specifically disrupted the liberation of mediator from post‐ganglionic nerve endings.
The action of tubocurarine and atropine on the normal and denervated rat diaphragm
Authors: Beránek R. , Vyskočil F. 
Published: December 2014

1. The potency with which tubocurarine chloride (TC) and atropine sulphate (AS) influence the amplitude of the end‐plate potentials was measured in the rat diaphragm. This effect was compared with the action of these drugs on brief depolarizations evoked by iontophoretic application of ACh to end‐plate‐free spots of the chronically denervated fibre.2. TC and AS act similarly on e.p.p.s, but the concentrations necessary to cause the same effect are 2000‐times higher for AS.3. The dose—response curves for both inhibitors are unchanged by prostigmine.4. Ten to twenty‐five days after denervation the ACh‐potentials of the sensitized end‐plate‐free parts of the membrane are less responsive to curare than the normal e.p.p.s are. AS is as effective in blocking ACh potentials of denervated muscles as it is in blocking normal e.p.p.s. The curare/atropine coefficient (dose ratio for equal effect) is 0·0005 for e.p.p.s and 0·003 for ACh potentials of the denervated membrane.5. Both blocking drugs reduce the amplitude of ACh‐potentials evoked in the end‐plate region of normally innervated rat diaphragm fibres as effectively as they reduce the amplitude of e.p.p.s.6. Neither TC nor AS have a presynaptic action in concentrations markedly reducing the e.p.p. amplitude.