bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conductance changes, an electrogenic pump and the hyperpolarization of leech neurones following impulses
Authors: Jansen J. K. S. , Nicholls J. G. 
Published: December 2014

Following trains of impulses, sensory neurones in the C.N.S. of the leech show a prolonged hyperpolarization, which lasts for seconds or minutes. In the present investigation the mechanisms that underly this hyperpolarization have been studied by recording intracellularly. Two factors have been found to be responsible. One is the activity of an electrogenic pump (see Baylor & Nicholls, 1969b); the other is a long‐lasting change in K conductance.1. Additional evidence that an electrogenic pump contributes to a slow after‐hyperpolarization of leech sensory neurones is provided by the effects of injecting Na intracellularly. This leads to an increase in membrane potential that is blocked by the cardiac glycoside strophanthidin. Furthermore, after a train of impulses, reducing the K concentration in the external fluid characteristically reduces the hyperpolarizing action of the pump.2. The hyperpolarization following impulses is associated with a reduction of the cell membrane resistance that can persist for several minutes.3. Several lines of evidence suggest that the reduction in input resistance during the hyperpolarization is mainly due to an increased permeability to K. Thus, when the K concentration in Ringer fluid is reduced, the peak amplitude of the hyperpolarization following a train becomes larger. Furthermore, the conductance dependent part of the after‐hyperpolarization has a reversal potential close to the equilibrium potential for K (EK). Substitution of Cl by SO4 has little effect either on the after‐hyperpolarization or on the conductance change following a train.4. Increased external Ca concentrations lead to a marked increase in the hyperpolarization that follows impulse activity. The enhanced hyperpolarization in high Ca is associated with a corresponding reduction in input resistance. The amplitude and duration of the hyperpolarization following a brief train of impulses can be increased by a factor of 5 or more in Ringer fluid containing 10 mM‐Ca instead of the usual 1·8 mM. The hyperpolarization and resistance changes still occur in solutions containing 20 mM‐Mg.5. To augment the hyperpolarization the increased concentration of Ca must be present during the train of impulses.6. The relative contributions of the K conductance increase and of the electrogenic pump for generating the hyperpolarization after impulse activity are different in the three types of sensory cell responding to touch, pressure and noxious stimulation.
The influence of exogenous steroids on macromolecule uptake by the small intestine of the new‐born rat
Authors: Daniels V. G. , Hardy R. N. , Malinowska K. W. , Nathanielsz P. W. 
Published: December 2014

1. Plasma concentrations of cortisol and corticosterone measured by competitive protein binding in rats between 5 and 28 days after birth have been related to the intestinal uptake of [125I]polyvinyl pyrrolidone (PVP).2. Plasma cortisol concentration was consistently low throughout the period studied, but there was an increase in plasma corticosterone concentration at the time (18–21 days) when PVP uptake declined to zero (closure).3. Injection of a large dose of cortisone acetate 5 days after birth resulted in precocious closure; PVP uptake declined progressively to zero during the 6 days following the injection. Injection of this steroid at 12 days of age caused closure within 4 days.4. Precocious closure induced by cortisone acetate was closely comparable histologically with natural closure; the decline in PVP uptake was associated with the progressive displacement of vacuolated cells from the villi of the terminal intestine.5. Injection of corticosterone at either 5 or 12 days after birth also reduced PVP uptake. However, the reduction was transient and uptake returned to control levels some days after the injection.6. The temporary reduction in PVP uptake following corticosterone injection was not associated with any change in the histological appearance of the small intestine at the light microscope level.7. The injection of either cortisone acetate or corticosterone was followed by a period of impaired body growth and also a reduction of adrenal weight in animals injected at 12 days but not in animals injected at 5 days.
The contrast sensitivity of the cat
Authors: Campbell F. W. , Maffei L. , Piccolino M. 
Published: December 2014

1. The experiments were carried out on pretrigeminal cats.2. By recording potentials evoked from the visual cortex by a grating stimulus, it was established that there was a linear relation between the voltage generated and the logarithm of the contrast of the grating.3. The voltage evoked by the grating was independent of the orientation of the grating.4. It has previously been shown in man that, if the contrast is determined by an extrapolation to the point at which a zero voltage occurs, this value corresponds to the psychophysical threshold. On the assumption that the threshold of the cat also occurs at zero voltage, thresholds for a number of spatial frequencies and orientations were determined.5. When the threshold sensitivity function for the cat is compared with man it is found to be displaced to lower spatial frequencies by a factor of about ten. This means that while the cat cannot see such high spatial frequencies as man, it can see lower frequencies better than man.
Uptake of calcium and magnesium by rat duodenal mucosa analysed by means of competing metals
Authors: O'Donnell J. M. , Smith M. W. 
Published: December 2014

1. The short‐term uptake of Ca and Mg by rat duodenal mucosa consisted of two parts, one apparently complete within 1 min (uptake I) and a second which increased linearly with time from 1 to 12 min (uptake II).2. Uptake II for both Ca and Mg showed a curvilinear dependence on concentration. Uptake I was related linearly to concentration up to the highest concentration tested.3. Mg caused a significant inhibition of Ca uptake II. Ca was without effect on Mg uptake.4. Mn reduced significantly both uptakes I and II for Ca; Ba and Sr were without effect on Ca uptake.5. Two lanthanides, La and Pr, both inhibited uptakes I and II for Ca. Inhibition by Pr could be reversed by increasing the concentration of Ca. Some uptake II for Ca still persisted when uptake I was completely abolished by 3 m
M‐La.6. It is suggested that a small part of Ca uptake I may be associated with the subsequent mediated entry into the mucosa, since inhibition of Ca uptake consistently involves both forms of uptake. However, since some Ca still enters the mucosa when uptake I is completely inhibited, it appears that some entry of Ca can occur by diffusion.
Two types of luminosity horizontal cells in the retina of the turtle
Authors: Simon Elliott J. 
Published: December 2014

1. Two classes of luminosity horizontal cells have been identified in the retina of the turtle by intracellular recording. These cells differ in the area of retinal surface over which they are sensitive to light. For moderate light intensities the maximum response amplitude of ‘type I’ cells increases progressively as the radius of a circle of light is enlarged to over 750 μm. Responses of ‘type II’ cells instead reach maximum amplitude with circular illumination of about 300 μm radius.2. Both types are maximally sensitive to red light and have similar action spectra.3. The cells from which these responses originated were identified by intracellular marking with Procion Yellow dye. Both types were located in the inner nuclear layer. Type I cells had asymmetric, thick, tuberous processes and no apparent discrete somata. Type II cells had thin processes radiating symmetrically from rounded cell bodies.4. The different properties of the two types of cells can be simply explained assuming that the cells of type I are coupled by low‐resistance electrical junctions while in cells of type II the junctional resistance is higher.5. Since type I and type II cells differ both morphologically and physiologically, they may have different functions.
The parasympathetic secretory nerves of the nose of the cat
Authors: Eccles R. , Wilson H. 
Published: December 2014

1. A flow of watery nasal secretion can be induced in the anaesthetized cat either by electrical stimulation of the brain stem or by the simpler procedure of stimulating the cut peripheral end of the Vidian nerve. In both instances the rate of flow of secretion was dependent on the stimulation frequency. Because brain stem stimulation caused an increase in arterial blood pressure, nasal secretion was evoked in subsequent experiments by Vidian nerve stimulation.2. The application of nicotine to the sphenopalatine ganglion shows that the secretory fibres in the Vidian nerve relay in this ganglion and reach the nasal mucosa by way of the posterior nasal nerve.3. Inhibition by atropine of the secretion induced by Vidian nerve stimulation indicates that the secretory fibres are cholinergic.4. It is suggested that the induction of nasal secretion by Vidian nerve stimulation may be useful in assessing the effects of drugs on this secretion.
The effects of fibre length and calcium ion concentration on the dynamic response of glycerol extracted insect fibrillar muscle
Authors: Abbott R. H. 
Published: December 2014

1. The property of insect fibrillar muscle which enables it to oscillate continuously when it is connected to a resonant load is the delayed activation by stretch of contractile activity. The dynamic response has been measured at different fibre lengths and at different calcium ion concentrations, to see what effects these conditions have on the magnitude and rate constant of the delayed tension.2. Bundles of ten fibres of the dorsal longitudinal muscle of the water bug, Lethocerus cordofanus, which had been in glycerol for less than 5 days were used. Graded activation was obtained with buffered calcium ion concentrations between 10−7 and 10−5
M.3. A computer‐controlled apparatus was used to measure the dynamic mechanical properties of the muscle fibres. This allowed many measurements to be made on the same preparation. Further computer programs analysed the Nyquist plots produced by the experiment.4. When the mean length of a fibre bundle was increased, the magnitude of the delayed tension was increased (for a constant amplitude of sinusoidal length change), the rate constant was unaltered, and the stiffness of the fibres was increased. When the calcium ion concentration was raised, the magnitude of the delayed tension was increased, the rate constant increased, and the stiffness of the fibres fell. Calcium activation and stretch activation are thus clearly separable in their effects, and so the mechanisms must be separate.5. The various different effects of calcium cannot be explained by any simple model of activation, for example, an on‐off switch mechanism controlling the number of bridges in action.6. The stretch‐induced activity is proportional to a power of the length of two or greater and this non‐linearity aids the efficient operation of the oscillatory mechanism.
The gustatory sense in foetal sheep during the last third of gestation
Authors: Bradley R. M. , Mistretta Charlotte M. 
Published: December 2014

1. Histological studies revealed that presumptive taste buds are present in the foetal sheep tongue at 50 days. By 100 days the taste buds appear morphologically mature.2. To determine if foetal taste buds are functional, electrophysiological recordings were made of activity in the chorda tympani nerve of sheep foetuses. Single and multi‐fibre preparations were studied in foetuses aged 100 days to term.3. Responses were recorded to lingual stimulation with salts, acids, glycerol, glycine, sodium saccharin, quinine HCl and amniotic fluid. Responses of the foetal chorda tympani to lingual stimulation with a series of monochloride salts and with increasing concentrations of one salt were similar to responses recorded in lambs and adults.4. The peripheral gustatory system of the foetal sheep is functional for at least the last third of gestation. Foetal taste experiences may influence the formation of adult taste preferences or may aid the foetus in monitoring its environment.
The membrane effects, and sensitivity to strychnine, of neural inhibition of the Mauthner cell, and its inhibition by glycine and GABA
Authors: Diamond J. , Roper S. , Yasargil G. M. 
Published: December 2014

1. Anionic conductance changes in Mauthner neurones of goldfish were measured during synaptically evoked inhibition and inhibition caused by iontophoretic application of the putative inhibitory transmitters glycine and γ‐aminobutyric acid (GABA).2. The effects of either amino acid were indistinguishable from those of the neural inhibitory transmitter(s). The membrane permeability during the neural or drug response was increased to Br−, Cl−, I−, SCN−, NO3−, ClO3−, and formate (HCOO−), but not to HCO3−, BrO3−, IO3−, SO4−, HPO4−, H2PO4−, acetate and citrate.3. Strychnine was injected intramuscularly, iontophoretically, or applied topically to the exposed brain in order to compare quantitatively its ability to prevent inhibition evoked by synaptic activation and by pharmacological means. Inhibitions were measured by the increase in membrane conductance.4. Strychnine, at concentrations just adequate to block completely the late collateral inhibition (LCI) and crossed VIII nerve inhibition, had little effect on the pharmacological inhibition caused by glycine, and sometimes there was no detectable effect at all. In one experiment even a local iontophoretic application of strychnine in a sufficient dose to diffuse over the cell and block the LCI almost completely, merely halved the effect of a small dose of glycine applied to the same localized region of the membrane.5. Higher concentrations of strychnine than those necessary to block synaptically evoked inhibition would reduce the effect of glycine but not that of GABA. The evidence indicated that any apparent effect of strychnine upon GABA could be explained by displacement of the GABA‐containing iontophoretic pipette.6. The glycine‐blocking action of iontophoretic pulses of strychnine was of relatively very slow onset and long duration compared to the effects of pulses of glycine and GABA.7. These findings can be interpreted as either (1) strychnine has a presynaptic action, preventing the release of inhibitory neurotransmitter, in addition to its less potent post‐synaptic one in blocking pharmacological inhibition, or (2) strychnine acts entirely post‐synaptically, but the physiological transmitter action differs from that of glycine and GABA in being considerably more sensitive to strychnine antagonism. In either case, the use of strychnine as evidence for the claim that glycine is an inhibitory neurotransmitter at the Mauthner cell is questionable.
Relationships between luminance and visual acuity in the rhesus monkey
Authors: Cavonius C. R. , Robbins D. O. 
Published: December 2014

1. The ability of rhesus monkeys to detect the gap in Landolt ring test‐objects that were presented against background luminances between 5 × 10−5 cd/m2 and 5 × 103 cd/m2 was compared with similar human data.2. At high luminance‐levels the acuity of human observers is slightly better than that of rhesus, but rhesus have better acuity at scotopic luminance‐levels. Both species have distinct photopic and scotopic acuity functions that cross at 6 × 10−3 cd/m2.3. The threshold for light detection is estimated to be the same for both species when specified in quanta incident on the retina.4. It is concluded that the receptor and neural mechanisms that mediate visual‐acuity function similarly in rhesus and man, and that the differences in acuity that were measured in the two species may be attributed to optical rather than to physiological factors.
Long‐lasting potentiation of synaptic transmission in the dentate area of the unanaesthetized rabbit following stimulation of the perforant path
Authors: Bliss T. V. P. , Gardner‐Medwin A. R. 
Published: December 2014

1. Potential changes evoked by stimulation of the perforant path have been recorded in the dentate area of the hippocampal formation in chronically prepared unanaesthetized rabbits.2. Components attributed to excitatory synaptic current flow and to action potentials in the granule cell population were distinguishable, with characteristics largely the same as in anaesthetized rabbits.3. Stimulation at 15/sec for several seconds usually led to the granule cells being more effectively activated by the individual stimuli of the train (‘frequency potentiation’). Single stimuli then commonly produced multiple discharges in the granule cell population.4. After single periods of stimulation at 15/sec for 15–20 sec there was on 26% of the occasions (41% of those on which there was good frequency potentiation) a long‐lasting potentiation of the responses to subsequent stimuli, lasting from 1 hr to 3 days.5. After a further 20% of the periods of repetitive stimulation there was a shorter lasting potentiation, and after 8% there was a short lasting depression.6. The potentiation, when present, was characterized by some or all of the following changes: increases in the amplitudes of the synaptic wave and population spike, reduction in the latency of the population spike, and reductions in the variability of the characteristics of the population spike.7. During the long‐lasting potentiation there was an increase in the excitability of the post‐synaptic cells and, on some but not all occasions, an increase in the extracellular current flow produced directly by synaptic action.
The time course of cardiovascular changes in lactation in the rat
Authors: Hanwell Ann , Linzell J. L. 
Published: December 2014

1. Cardiovascular changes in lactating rats have been traced from the first day post‐partum to the end of the third week of lactation. The pattern of changes showed three phases.2. Between days 1 and 5 of lactation there were sharp rises in both cardiac output and in the blood flow/g tissue for most organs, but little change in the distribution of the cardiac output.3. Between days 5 and 15 of lactation cardiac output remained steady. The blood flow to tissues actively involved in the body's response to lactation (mammary glands, liver, gastrointestinal tract) also remained at high steady levels, but the blood flow to other tissues declined due to a redistribution of the cardiac output away from them and towards the growing mammary glands and splanchnic organs.4. Between days 15 and 22 of lactation there were further rises in both cardiac output and in the blood flow/g tissue for most organs.5. It is suggested that the increases in organ blood flows that occurred in the first few days after parturition (days 1–5) and at the end of lactation (days 15–22) were largely dependent on increases in cardiac output and may represent the maternal response to rapidly rising demands from the young at these times.
The effects of engorgement with milk and of suckling on mammary blood flow in the rat
Authors: Hanwell Ann , Linzell J. L. 
Published: December 2014

1. Mammary blood flow was estimated in rats by measuring the cardiac output and the proportion of it received by the mammary glands.2. When the young were removed on the 10th day of lactation the mammary glands began to fill with milk and mammary blood flow fell from 78 ml./min. 100 g tissue to 45 ml./min. 100 g within 8 hr and decreased further to 34 ml./min. 100 g within 8 hr and decreased further to 34 ml./min. 100 g in the next 16 hr. These changes were associated with both a fall in cardiac output and a fall in the proportion of the cardiac output taken by the mammary glands.3. When the young were allowed to continue suckling, but milk removal was prevented by sealing the teat ducts with adhesive, more milk collected in the mammary glands within 8 hr and mammary blood flow was unchanged (74 ml./min. 100 g).4. In rats which had been separated from their young for 24 hr, milk was removed from the engorged glands by allowing the pups to suckle again. Mammary blood flow did not rise immediately following the removal of milk but only after 4 hr of suckling, and was associated largely with an increase in cardiac output.5. Upon resumption of suckling mammary blood flow was the same in emptied glands, and in full glands with the teats sealed.6. When the young were removed from 15–day lactating rats mammary blood flow after 24 hr was directly related to the volume of milk in the glands.7. It is concluded that the accumulation of milk in the mammary gland does not mechanically restrict the flow of blood through the tissue and that, in the rat, mammary blood flow and milk secretion are strongly dependent on a continually applied suckling stimulus.
Background configuration and rod threshold
Authors: Lennie P. , MacLeod D. I. A. 
Published: December 2014

1. This paper investigates the variation in rod threshold when a small test flash is seen against backgrounds of different sizes. Over a substantial range of luminances above absolute threshold, the test flash is less easily seen against small backgrounds than large. This confirms earlier results.2. If an annular surround is added to a small circular background, threshold is reduced when background and annulus are equiluminous (uniform field), but rises rapidly as the annulus is made brighter or dimmer than the background. This cannot be explained by the threshold‐elevating effects of light scattered on to the background from the surround, for threshold rises with annulus luminance faster than it does on uniform fields of equal luminance.3. If the surround is not a complete annulus but a windmill‐shaped cross, threshold is higher than on a uniform field, no matter what the windmill luminance. Thus it is not the addition of light per se to the surround which reduces threshold.4. This conclusion is reinforced by the results of another experiment. The test flash is seen on a large uniform field. When superimposed on this field, a thin ring, light or dark, which causes only a small change in mean luminance, produces an appreciable rise in threshold.5. The addition of an equiluminous red surround to a small red background so as to create a uniform field causes a marked drop in test flash threshold, but a scotopically equal blue surround, that creates a uniform field for rods, does not alter the threshold. Since the test flash is seen only by rods it follows that signals from cones can alter rod threshold.6. Known or probable behaviour of retinal mechanisms cannot account for our results. All the operations which elevate threshold above its level on a large uniform field produce contours in the vicinity of the test flash. This we take as evidence that signals from the test stimulus are suppressed or reduced by other signals present only when the background is locally non‐uniform.
Cortical pyramidal tract interneurones and their sensitivity to L‐glutamic acid
Authors: Stone T. W. 
Published: December 2014

1. Pyramidal tract interneurones, defined as neurones which are activated synaptically as a result of pyramidal tract stimulation, have been identified in the rat cerebral cortex. The number of evoked spikes depended upon stimulus strength, and stimulation in a specific thalamic nucleus produced a burst of activity lasting for up to 1 sec.2. These cells are readily excited by a brief (50 msec) pulse of glutamate applied by micro‐iontophoresis. Other, unidentified cells are not so responsive.3. Synaptically evoked spikes resulting from pyramidal tract stimulation can be blocked by the iontophoretic and
I.P. administration of substances shown to antagonize glutamate excitation of cells.4. The results support suggestions that glutamic acid is a neurotransmitter in the cerebral cortex. The evidence presented further indicates that glutamic acid could be the transmitter released by the pyramidal tract.