bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chloride conductance in normal and myotonic muscle fibres and the action of monocarboxylic aromatic acids
Authors: Bryant S. H. , Morales-Aguilera A. 
Published: December 2014

1. Cable parameters, component conductances, excitability and membrane potentials in isolated external intercostal fibre bundles at 38° C from normal and myotonic goats were measured in normal and low‐chloride Ringer, and in the presence of monocarboxylic aromatic acids that produce myotonic responses in mammalian muscle.2. The mean resting chloride conductance in μmho/cm2 of myotonic fibres (range 0–147) was significantly less than that of normal fibres (range 376–951). The mean resting potassium conductance was higher in myotonic fibres (range 123–285) than in normal fibres (range 44–132). Potassium conductance increased about 10 μmho/cm2 per mV increase in absolute resting potential.3. In normal fibres in normal Ringer 3‐chloro‐2,5,6‐trimethylbenzoic acid; 5,6‐dihydro‐5,5‐dimethyl‐7‐carboxybenz[c]acridine; phenanthrene‐9‐carboxylic acid; and anthracene‐9‐carboxylic acid at 10−5‐10−4
M decreased membrane conductance without consistently changing diameter or capacitance. In low‐chloride Ringer 3‐chloro‐2,5,6‐trimethylbenzoic acid (5 × 10−5
M) increased potassium conductance in myotonic and normal fibres. It is concluded that these compounds block chloride conductance.4. The carboxylic acids produced myotonia in normal fibres similar to that in untreated myotonic fibres.5. Anthracene‐9‐carboxylic acid intravenously (8 mg/kg) in normal goats produced acutely a condition resembling myotonia congenita. The carboxylic acids produced no myotonic effects in frog muscle.
Stimulation of tubero‐infundibular dopamine neurones and gonadotrophin secretion
Authors: Keller P. J. , Lichtensteiger W. 
Published: December 2014

1. In ovariectomized rats pre‐treated with oestrogen and progesterone, the intensity of the catecholamine fluorescence was determined by micro‐fluorimetry in the cell bodies of the tubero‐infundibular dopamine neurones (situated in the arcuate and periventricular hypothalamic nuclei). The concentrations of follicle‐stimulating (FSH) and luteinizing hormone (LH) in serum and pituitary were estimated by bio‐assay.2. The characteristic changes in fluorescence intensity of the tuberal catecholamine‐containing nerve cell group that are induced by unilateral intermittent electrical stimulation of the arcuate nucleus or of the medial preoptic area during 5‐60 min, were accompanied by a marked rise in serum LH concentration. With arcuate stimulation, the rise in serum LH paralleled the increase in the fluorescence intensity of the nerve cell bodies, whereas with preoptic stimulation, the initial increase in cellular fluorescence intensity preceded the rise in serum LH. Preoptic stimulation also caused a moderate fall in pituitary LH which was simultaneous with the increase in fluorescence intensity. No systematic changes in FSH concentration were observed during the time interval studied.3. Pre‐treatment with the tyrosine hydroxylase inhibitor α‐methyltyrosine completely blocked the increase in fluorescence intensity caused by electrical stimulation of the arcuate nucleus but did not prevent the rise in serum LH.4. It is concluded that the tubero‐infundibular dopamine neurones serve as an intermediary between the medial preoptic area (and possibly other forebrain structures) and neurones containing releasing factors. Under the present experimental conditions, stimulation of the tuberoinfundibular dopamine neurones increased the release of LH, probably by promoting the release of LH‐releasing factor.
The independence of the temporal integration properties of individual chromatic mechanisms in the human eye
Authors: Krauskopf J. , Mollon J. D. 
Published: December 2014

1. Since it has been shown by Stiles that the adaptive states of the primary chromatic (π) mechanisms of the human eye vary independently and since recent theories of visual function have postulated an intimate relation between sensitivity and the temporal characteristics of the retinal response, it is asked whether the temporal integration properties of the eye depend upon the state of adaptation of the retina as a whole or vary independently for each of the chromatic mechanisms.2. It is found that the critical duration, or limit of time‐intensity reciprocity, for the detection of monochromatic increments presented on monochromatic background fields depends only upon the adaptive state of the individual π mechanism mediating the detection. Our results support the hypothesis that each chromatic mechanism has its own automatic gain control.3. At both dark‐adapted and asymptotic levels the critical durations for the short wave‐length mechanisms appear to be greater than those for π4 and π5.4. When 500 nm test flashes are presented on 600 nm adaptation fields, critical durations increase at high background intensities. This anomaly adds further support to the hypothesis that the critical durations of different chromatic mechanisms vary independently, since 500 nm flashes are probably detected by π1, rather than by π4, when presented on long wave‐length adaptation fields of high energy.5. Our findings provide partial support for the suggestion that the Fechner—Benham subjective colours are due to differences in the time constants of the different colour mechanisms.6. It is concluded that the critical duration is principally determined at a very distal stage in the visual system before interactions occur between chromatic mechanisms.
Thermoregulatory effects of intrahypothalamic injections of adrenergic and cholinergic substances at different environmental temperatures
Authors: Avery David D. 
Published: December 2014

1. Rats were unilaterally implanted with chronic indwelling cannulae directed towards the medial preoptic area of the hypothalamus. Carbamylcholine chloride (carbachol), noradrenaline, and saline were microinjected in volumes of 0·5 μl. at each of three environmental temperatures, 5, 24, and 35° C.2. At an ambient temperature of 24° C injections of carbachol significantly raised core temperature, whereas injections of noradrenaline to the same sites significantly lowered temperature.3. Injections of carbachol did not affect core temperature at 35° C, but injections of noradrenaline defended against the normal hyperthermia observed in this environment.4. Hyperthermia resulted from hypothalamic injections of both substances at an ambient temperature of 5° C.5. The data generally support a neurochemical model for hypothalamic thermoregulatory mechanisms proposed by Myers & Yaksh (1969).According to their theory a cholinergically coded heat production pathway courses from the anterior to the posterior hypothalamus. This pathway is activated by 5‐HT and inhibited by noradrenaline in the anterior hypothalamus. The observation in the present experiments of hyperthermia following adrenergic stimulation at 5° C cannot be accounted for by this model and therefore an addition to the model is proposed. It is suggested that a heat loss mechanism is also located, at least partially, in the anterior hypothalamus and that this system is inhibited by noradrenaline. Thus a thermal balance is established via an interaction of the two systems.
The antagonistic actions of calcium and magnesium on the superfused ventricle of the snail Helix pomatia
Authors: Burton R. F. , Loudon J. R. 
Published: December 2014

1. The isolated, superfused half‐ventricle of the snail (Helix pomatia) maintains a degree of tonic activity even when not beating, since the membrane is depolarized beyond the tension threshold. Beating may be initiated by lateral stretch of the ventricle and by 5‐hydroxytryptamine.2. Ca and Mn each have a hyperpolarizing action, while K and to a lesser extent Na cause depolarization: the tonic activity of the ventricle is affected accordingly.3. An increase in the extracellular concentration of Mg also causes the tension to fall, but without change in membrane potential. It can also initiate beating.4. Contractures induced by 30 m
M‐K are steadily maintained, but start with a more‐or‐less distinct twitch‐like contraction. A contracture induced by a concentration of K above about 50 m
M is poorly sustained and is followed by a further brief contracture when the K concentration is reduced to normal.5. Relations between contracture tension and the concentrations of Ca and Mg accord with the hypothesis that the two ions compete for attachment to a binding site on the cell surface and that tension is proportional to the amount of bound Ca. On this hypothesis, the apparent dissociation constant of the Mg complex is 11·4 m
M and that of the Ca complex 0·15 m
M or less.6. This effect of Mg is like that of Na on frog ventricle and some of the differences in the behaviour of snail and frog ventricles are abolished by appropriate adjustment of the extracellular concentrations of these ions.
Membrane potentials recorded from the mucosa of the toad's tongue during chemical stimulation
Authors: Eyzaguirre C. , Fidone S. , Zapata P. 
Published: December 2014

An isolated stretch of tongue mucosa was obtained from the Chilean toad (Callyptocephalella gayi). The preparation was observed under transmitted illumination through a binocular microscope. The surface cells were impaled with micro‐electrodes and different chemical agents were applied to the area. The following results were obtained.1. The surface cells had resting potentials of −6 to −40 mV (mean of −17·6 mV) with the preparation bathed in Ringer solution.2. The cells underwent depolarization by application of different salts (NaCl, NaF, KCl, Na2SO4, CaCl2 and MgCl2) in concentrations of 0·25–1·0
M. The potentials evoked by the salt solutions often overshot the zero membrane potential level by several millivolts. The positive‐going potential change produced by application of salts was increased during hyperpolarization of the membrane by inward current and was decreased by current of the opposite sign. Application of salts during depolarization of the membrane to a certain positive level produced a negative‐going potential change. The potentials evoked by different salts were about the same, qualitatively, when recordings were made from different areas of the tongue, i.e. top of the fungiform and filiform papillae, doughnut‐shaped folds at the base of the fungiform papillae, areas between papillae and from the side of the tongue totally devoid of papillary structures.3. Quinine applied in concentrations of 2 × 10−2
M did not change the resting polarization of the surface epithelial cells. However, quinine applied to cells already depolarized by outward currents induced further depolarization. When it was delivered to cells hyperpolarized by inward current the substance induced further hyperpolarization.4. Sucrose (0·5–1·0
M) did not change the membrane potential of lingual cells regardless of the level of cell polarization induced by injected currents.5. Hydrochloric, sulphuric, nitric and acetic acids produced minimal biphasic effects: a brief hyperpolarization followed by a slower secondary depolarization.6. Water increased the membrane potential of the surface cells. Salts applied at the peak of the water‐evoked hyperpolarization induced cell depolarization which was much larger than that evoked during application of salts to cells bathed in Ringer solution.
An electrophysiological analysis of the storage of acetylcholine in preganglionic nerve terminals
Authors: Bennett M. R. , McLachlan Elspeth M. 
Published: December 2014

1. An electrophysiological analysis has been made of the storage of acetylcholine (ACh) in the preganglionic nerve terminals of the isolated superior cervical ganglion of the guinea‐pig. The mean amplitude of excitatory post‐synaptic potentials recorded intracellularly was taken as a measure of the ACh output per impulse from the terminals of a preganglionic axon.2. Prolonged repetitive stimulation of the cervical sympathetic trunk at 10 and 20 Hz in the presence of hemicholinium No. 3 led to an exponential decline of ACh output as the transmitter formed before the beginning of stimulation was depleted.3. The rate of decline of ACh output during stimulation at 20 Hz (τ = 0·83–1·95 min) was about twice as fast as that at 10 Hz (τ = 1·00–6·83 min).4. The results suggest that, during prolonged stimulation, ACh is released from a single store in the preganglionic nerve terminal and that each impulse releases a constant fraction of the store of the transmitter.
The composition of foetal and maternal blood during parturition in the ewe
Authors: Comline R. S. , Silver Marian 
Published: December 2014

1. Changes in the composition of foetal and maternal blood have been followed during the last 5–10 days of gestation and throughout parturition in the conscious sheep.2. Catheters were placed in the foetal inferior vena cava through a tarsal vein and in a maternal uterine vein in ten ewes under sodium pentobarbitone anaesthesia. In four of the foetuses blood pressure and heart rates were recorded before and during parturition from an arterial catheter.3. Foetal blood gas tensions, pH and PCV remained stable during the latter part of gestation and throughout labour until 15 min before delivery, when PO2 and pH fell while PCV and PCO2 rose in about 50% of the foetuses examined.4. Metabolite levels were also relatively stable at the end of gestation. Plasma glucose in both maternal and foetal blood rose during the hour before birth, while foetal plasma lactate was elevated as early as 4 hr before birth and was unrelated to any maternal changes. Foetal fructose levels were maintained until after delivery.5. Rises in foetal blood pressure before birth were associated with uterine contractions. Foetal heart rate changes during labour varied in different individuals. The heart rate either fell gradually before birth or there was little change until a sudden drop at delivery.6. The most striking changes in the lamb occurred at, or a few minutes after, birth; pH and PO2 fell, PCO2 and PCV rose, and bradycardia at delivery was succeeded by prolonged tachycardia. There were marked increases in plasma glucose and lactic acid at this time.7. PO2 rose rapidly once respiration was established, while pH and PCO2 levels were restored within ½–1 hr. Plasma FFA levels rose rapidly in the lambs 10–30 min after birth and remained high, while plasma glucose, lactate and fructose concentrations declined slowly in the 1–2 hr after birth, although suckling raised the plasma glucose levels. Considerable individual variation in the metabolite levels was found in both ewes and lambs.8. In the majority of ewes delivery was associated with an abrupt maternal hyperglycaemia, with a much smaller rise in lactate and virtually no change in maternal blood gases or pH.9. These findings are discussed in relation to existing information on new‐born lambs and the human infant during birth.
An extreme supernormal period in cerebellar parallel fibres
Authors: Gardner-Medwin A. R. 
Published: December 2014

1. The electrical responses produced by stimulation at the surface of the cerebellar cortex have been studied in anaesthetized cats.2. The propagation of the underlying activity is attributed to parallel fibres, but the mode of generation of the potential changes is less certain.3. The threshold for a second response is up to 40% lower following a conditioning stimulus, and the responses to test stimuli less strong than the conditioning stimulus are correspondingly potentiated.4. A second stimulus given 22 msec after the first produces a response which propagates 15–20% faster along the folium.5. The reduction of the threshold and the increase of the propagation velocity are as large with small (but above threshold) conditioning shocks as with large shocks.6. Both after‐effects are present from 5 to 100 msec after a conditioning stimulus, with maximal values at about 10–30 msec.7. The fibre conduction velocity inferred from collision experiments agrees with that inferred from the propagation velocity of the responses, and shows a similar increase after conditioning.8. A second shock does not recruit a new and faster population of parallel fibres.9. Under the conditions of electrical stimulation the after‐effects are probably restricted to those fibres which are active during conditioning.
Acetylcholine receptors: topographic distribution and pharmacological properties of two receptor types on a single molluscan neurone
Authors: Levitan Herbert , Tauc Ladislav 
Published: December 2014

1. The iontophoretic application of acetylcholine (ACh) on to identified neurones in the buccal ganglion of the mollusc Navanax produced a biphasic or monophasic membrane potential change which was a function of the current intensity and site of ACh application.2. Low iontophoretic currents, 200 msec in duration, applied to the somatic surface facing the neuropile, caused a monophasic potential change of 6–10 sec duration, which had a reversal potential of about − 50 mV, varied with changes in the [Cl]o of the bathing medium, and was not blocked by the cholinolytics tested.3. ACh applied more distal to the soma, in the neuropile, produced a 1‐3 sec monophasic response whose reversal potential was more positive than − 30 mV, varied in amplitude with changes in the [Na]o of the medium, and was blocked by cholinolytics such as tubocurarine, hexamethonium and atropine.4. With larger iontophoretic currents a biphasic response could be obtained, depolarization followed by hyperpolarization, which represented a superposition of the above monophasic potentials.5. The cholinomimetics propionylcholine and butyrylcholine caused a biphasic response like that to ACh. Carbamylcholine and tetramethylammonium also produced a biphasic response but with a more prominent Cl component than that to ACh. Acetyl‐β‐methylcholine, oxytremorine and pilocarpine only produced a response comparable to the chloride phase of the ACh response.6. Anticholinesterases prolonged both phases of the ACh response.7. It was concluded that each of the identified neurones possess two types of cholinoceptive sites, which are pharmacologically distinct, produced different changes in membrane permeability and are distributed differently over the axo‐somatic membrane complex.
A quantitative description of end‐plate currents
Authors: Magleby K. L. , Stevens C. F. 
Published: December 2014

1. End‐plate currents have been studied in glycerol‐treated frog sartorius nerve—muscle preparations with the voltage clamp technique.2. The effects of temperature on the decay rate of end‐plate currents were investigated over a temperature range from 10 to 30·5° C. The Q10 for the decay constant of end‐plate currents depends somewhat on membrane potential; at — 100 mV the decay constant has a Q10 of 2·7.3. Peak end‐plate current depends non‐linearly on membrane potential with a decreasing slope conductance associated with hyperpolarization.4. The ‘instantaneous’ voltage—current relationship for end‐plate channels was determined by causing step changes in membrane potential during end‐plate current flow. This relationship appears to be linear.5. The interaction of acetylcholine with its receptor is viewed as being analogous to the first step in enzymic catalysis. On this view, acetylcholine binds to its receptor and induces a conformational change which is responsible for opening end‐plate channels. By analogy to the first steps in the catalytic sequence of enzymes, the binding step is very rapid, almost diffusion‐limited, and the conformational change is rate‐limiting.6. Equations describing this process have been derived. Expressions for the rate constants have also been derived by considering changing dipole moments of the transmitter‐receptor complex associated with the conformational change. As the transmitter‐receptor complex is in the membrane field, different conformational states have different energies, and the rate of conformational change thus depends on membrane potential. The equations thus derived are shown to account adequately for the time course of end‐plate conductance change.
Foetal placental blood flow in the lamb
Authors: Faber J. Job , Green Thomas J. 
Published: December 2014

1. Fifteen sheep foetuses of 1·5–5·2 kg body weight were prepared with indwelling arterial and venous catheters for experimentation one to six days later.2. Unanaesthetized foetuses were found to have mean arterial and central venous blood pressures of 40 ± 1·5 (
S.E. of mean) and 2·0 ± 0·3 (
S.E. of mean) mm Hg respectively, compared to intra‐uterine pressure. Intra‐uterine pressure was 16 ± 0·8 (
S.E. of mean) mm Hg with respect to atmospheric pressure at mid‐uterine level.3. Mean placental blood flow of the foetuses was 199 ± 20 (
S.E. of mean) ml./(min.kg body wt.). Mean cardiac output in eleven of the foetuses was 658 ± 102 (
S.E. of mean) ml./(min.kg).4. Mean foetal and maternal colloid osmotic pressures were 17·5 ± 0·7 (
S.E. of mean) and 20·5 ± 0·6 (
S.E. of mean) mm Hg respectively at 38° C.5. Intravenous infusions into six ewes of 1·8 mole of mannitol and 0·4 mole of NaCl resulted in significant increases in foetal plasma osmolarity, sodium, potassium, and haemoglobin concentrations, without detectable transfer of mannitol to the foetal circulation.6. In the sheep placenta there is osmotic and hydrostatic equilibration of water. As a consequence, there should be an interaction between foetal placental blood flow and foetal water exchange with the maternal circulation. It was concluded that this interaction tends to stabilize foetal placental blood flow.
Dogfish ganglion cell discharge resulting from extrinsic polarization of the horizontal cells
Authors: Naka Ken-Ichi , Witkovsky Paul 
Published: December 2014

1. Ganglion cell discharges were evoked by extrinsic polarization of the horizontal cells in the retina of the smooth dogfish (Mustelus canis). Depolarization of the horizontal cell gave rise to a discharge similar to that evoked by a spot of light (centre type response) and hyperpolarization of the horizontal cell, a discharge similar to that by an annulus (surround type response).2. Procion dye injection established that the current‐passing electrode was sometimes located in the external horizontal cell. Other possibilities, such as middle and internal horizontal cells, were neither confirmed nor excluded.3. Activation of ganglion cells by current was possible under completely dark‐adapted conditions and for several log units above this level.4. Depolarizing current enhanced the ganglion cell response evoked by a light spot in the centre of its receptive field; hyperpolarizing current antagonized the response to the same flash.5. The results are consistent with the supposition that a potential change in the horizontal cell, irrespective of its polarity, or whether produced by light or current, spreads within a laminar layer (the S‐space). The effect of the potential change is to modulate the response of bipolar cells and their input into the ganglion cell.