bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sodium chloride transport across the chicken coprodeum. Basic characteristics and dependence on sodium chloride intake
Authors: Choshniak I. , Munck B. G. , Skadhauge E. 
Published: December 2014

1. The transport characteristics of the chicken coprodeum have been examined in vitro using the isolated mucosa. The short‐circuit current (Isc), the transepithelial electrical potential difference (p.d.), the unidirectional transmural fluxes (Jms, Jsm) of sodium and chloride measured in the short‐circuited state, and the unidirectional influx of sodium and chloride across the brush border membrane measured under open‐circuit conditions have been studied. The effect of the sodium chloride contents of the diet on these parameters have been investigated.2. The isolated mucosa depends functionally on the presence of glucose in the incubation media. This dependence reflects the need of glucose as a fuel. There is no indication of coupling between transport of sugars and sodium across the brush border membrane. For preparations from chickens on a low sodium diet a very high and stable Isc can quantitatively be accounted for by the net transport of sodium. Influx of sodium across the brush border membrane is not significantly different from the net flux of sodium. By feeding the chickens a high sodium diet the Isc is reduced by more than 95%, the net transport of sodium is abolished, and the transepithelial electrical conductance is reduced by more than 50%.3. Both unidirectional transepithelial fluxes of chloride, and the serosa to mucosa flux of sodium appear to proceed through a paracellular shunt.4. Under the conditions of the low sodium diet the paracellular pathway appears to be anion selective. Whereas, under the conditions of the high sodium regimen the paracellular route appears to be cation selective. After adaptation to a high sodium diet the influx of sodium across the brush border membrane is only moderately reduced. Consequently the decisive event in the adaptation must be localized elsewhere.
The natural discharges of Purkinje cells in paravermal regions of lobules V and VI of the monkey's cerebellum
Authors: Harvey R. J. , Porter R. , Rawson J. A. 
Published: December 2014

1. Conscious monkeys were trained with food rewards to perform movement tasks with the left hand and to accept manipulation of the joints and muscles and natural non‐noxious stimulation of the skin of both forelimbs.2. Recordings were made from 230 Purkinje cells situated in the paravermal region of lobules V and VI or immediately adjacent folia of the left cerebellum in a region from 2 to 7 mm from the mid line. These neurones were all in a zone which was demonstrated to receive inputs from the ipsilateral hand and which is known to receive projections, via the pontine nuclei from the ‘arm area’ of motor cortex in the right hemisphere.3. Modulation of the natural activity of 182 of these 230 Purkinje cells (79%) occurred in a reproducible manner in temporal association, each with a particular phase of the self‐paced movement tasks performed by the animal using the ipsilateral arm and hand. The patterns of modulation of Purkinje cell firing in this limited zone of cerebellar cortex could be classified into one of four groups, and each cell's discharge was associated with a particular aspect of movement such as general arm flexion, shoulder retraction, elbow extension or elbow flexion whenever it occurred.4. The cells were spontaneously active at rest. Most commonly, marked accelerations of the discharge were related to one direction of the particular aspect of movement and a reduction of activity or even total silence accompanied movement in the opposite direction.5. Variation of the amount of discharge demonstrated during a movement performance with which this discharge was characteristically associated could be related to the range of the movement or its duration, more activity being characteristic of more prolonged movement performance through larger angles of joint displacement.6. Both simple spikes and complex spikes of some cells showed characteristic modulation of their activity during the monkey's self‐initiated movements. Cells whose simple spikes did not change in frequency during the movement task, also showed no modification of complex spike discharge.7. Of the 182 neurones whose discharges changed during active movement performance, 105 (roughly 60%) were demonstrated to be in receipt of an input from peripheral receptors in the hand which could be activated by brisk tapping of the skin or brushing of hairs. In contrast, none of the Purkinje cells whose discharges were unchanged during arm movements could be demonstrated to receive such an input.8. Movement of joints through their full range and prodding of muscles were completely ineffective stimuli for causing changes in Purkinje cell firing in this zone of the cerebellar cortex while the animal was passive and relaxed. Imposed perturbations of movement performance injected unexpectedly during the execution of a movement task were also ineffective in modifying the discharge of these Purkinje cells in relation to the task.
Cation movements in normal and short‐term denervated rat fast twitch muscle
Authors: Robbins Norman 
Published: December 2014

1. The earliest known change in rat fast muscle following denervation is a fall in resting membrane potential unaccompanied by change in membrane resistance. The present study tested the hypothesis that increased Na permeability (PNa) accounted for this early depolarization.2. In all experiments, rat extensor digitorum longus muscles were studied in vitro at 25° C. Li uptake in vitro, used as a measure of PNa, was greater in 1‐ and 2‐day denervated muscles (and in 2‐day denervated diaphragm) than in paired controls.3. The extra Li taken up by denervated muscle was not sequestered in an extracellular or freely exchangeable compartment, nor was it irreversibly bound.4. Measurements of resting membrane potential and of internal Na, K, and Li in Krebs solution before and 2 hr after replacement of NaCl by LiCl, were used to compute the ratios PNa/PK and PLi/PK for normal or denervated muscles. PNa and PLi were similar relative to PK within each class of muscle.5. Both PNa/PK and PLi/PK ratios were elevated more than twofold in denervated muscle, as were most estimates of relative PLi approximated by the flux equation.6. These data, and measurement of resting membrane potential of normal muscle in 1 m
M external K‐Krebs solution, support the view that an electrogenic Na—K pump does not substantially contribute to this potential of normal or denervated muscle, and that the early depolarization after denervation results from increased PNa.7. The Na—K pump of denervated muscle was as sensitive to ouabain as normal muscle. An effect of ouabain on PNa may explain previously noted differential effects of ouabain on normal and denervated muscle.
The effect of calcium ions and temperature on the binomial parameters that control acetylcholine release by a nerve impulse at amphibian neuromuscular synapses
Authors: Bennett M. R. , Fisher C. , Florin T. , Quine M. , Robinson J. 
Published: December 2014

1. A study has been made of the effects of changing the external calcium concentration, [Ca]o, and the temperature on both the number of quanta available for release by the nerve impulse (n) as well as the increase in release probability of a quantum p(t) during the release period (from 0 to T) following a nerve impulse at synapses in amphibian striated muscle.2. When [Ca]o was increased in the low range from 0·25 to 0·4 m
M at 18 °C, the average quantal content of the e.p.p. (m̄) increased as the fourth power of [Ca]o and this was primarily due to a third power dependence of n on [Ca]o; the dissociation constants and power dependence of n on calcium determined in the [Ca]o range from 0·25 to 1·0 m
M were successfully used to predict the changes in size of the e.p.p. in the very high [Ca]o range from 1 to 10 m
M. When the temperature was increased from 7 to 18 °C in a [Ca]o of 0·6 m
M or 0·35 m
M, n increased with a Q10 of 2·5.3. When [Ca]o was increased in the range from 0·25 to 1·0 m
M at 18 °C, the probability that a quantum initially available for release is released during the release period (p(T)) was very sensitive to [Ca]o, increasing as the third power of [Ca]o and with a dissociation constant of 0·13 m
M. When the temperature was increased from 7 to 18 °C in a [Ca]o of 0·6 m
M or 0·35 m
M, p(T) decreased.4. The histograms of latencies of individual quanta following a nerve impulse was very temperature dependent: the time to peak of the histograms (i.e. the interval in which most quanta fell) had a Q10 of over 4 as did the time constant of decline of the histograms in the temperature range from 7 to 18 °C.5. The average number of quanta released up to time t during the release period following a nerve impulse, namely np(t), was well described by a stochastic process in which p(t) was determined by two reactions; one of these reactions released available quanta from the nerve terminal whilst the other made some of the available quanta unavailable for release by the nerve impulse.
Synaptic excitation and inhibition resulting from direct action of acetylcholine on two types of chemoreceptors on individual amphibian parasympathetic neurones
Authors: Hartzell H. Criss , Kuffler Stephen W. , Stickgold Robert , Yoshikami Doju 
Published: December 2014

1. Synaptic transmission was studied in visually identified parasympathetic ganglion cells that modulate the heart beat of the mudpuppy Necturus maculosus).2. The brief pulse of acetylcholine (ACh) released from terminals of the vagus nerve after each impulse can produce two distinct post‐synaptic responses in individual principal cells of the ganglion: (i) within a milli‐second of release, ACh generates a rapid and strong excitatory post‐synaptic potential (e.p.s.p.) that normally initiates a post‐synaptic impulse; (ii) this excitation is usually followed by a slow hyperpolarizing inhibitory post‐synaptic potential (i.p.s.p.) that lasts for several seconds. The magnitude and time course of the i.p.s.p. depends on the frequency and number of vagal stimuli. When the hydrolysis of ACh is inhibited by prostigmine, a train of nerve stimuli may be followed by an i.p.s.p. lasting half a minute or longer.3. The rapid e.p.s.p. and slow i.p.s.p. result from the direct action of ACh on two different types of chemoreceptors in the post‐synaptic membrane of the principal cell. The e.p.s.p. can be preferentially blocked by the nicotinic antagonist dihydro‐β‐erythroidine (5 × 10−7
M), while the i.p.s.p. is selectively blocked by the muscarinic antagonist atropine (5 × 10−9
M).4. Potentials resembling nerve‐evoked e.p.s.p.s and i.p.s.p.s can be produced by iontophoretic release of ACh from micropipettes onto the post‐synaptic membrane. Application of the muscarinic agonist bethanechol generates exclusively inhibitory responses.5. The reversal potential for the i.p.s.p. is about ‐105 mV, which is approximately the equilibrium potential for potassium (EK). When the external K+ concentration is altered, the reversal potential for inhibition is shifted to the new value of EK as expected from the Nernst equation. Changes in the external Na+ and Cl− concentrations have no appreciable effect on the reversal potential. Thus, the i.p.s.p. is the result of a conductance increase for K+.6. The conductance change producing the i.p.s.p. is voltage sensitive. When the membrane potential is shifted from ‐40 to ‐60 mV, the i.p.s.p becomes larger and longer. Beyond ‐60 mV the inhibitory response decreases in proportion to the driving force on K+ without any further change in time course.7. The inhibitory response produced by an iontophoretically applied pulse of bethanechol has a delayed onset of about 150 msec at 24 °C. The early portion of this response, including the delay, is proportional to t3, where t is time. The proportionality factor (the apparent rate constant) decreases elevenfold when the temperature is lowered by 10 °C. This suggests that a multi‐step process is involved in the activation of the conductance increase that leads to the inhibitory response. Inhibitory responses with similar kinetics were produced in heart muscles of the mudpuppy upon application of ACh.
Passive signal propagation and membrane properties in median photoreceptors of the giant barnacle
Authors: Hudspeth A. J. , Poo Mu Ming , Stuart Ann E. 
Published: December 2014

1. The light‐induced electrical responses of barnacle photoreceptors spread decrementally along the cells' axons. The decay of the depolarizing and hyperpolarizing components of the visual signal was studied by recording intracellularly from single receptor axons of the median ocellus of the giant barnacle.2. The resistance of the photoreceptor neurone decreases markedly when the cell is depolarized with respect to its dark resting potential of ‐60 mV. This rectification results in differential attenuation of the depolarizing and hyperpolarizing components of the visual signal as they spread down the axon. Consequently, the visual signal entering the synaptic region is conspicuously distorted.3. Bathing the photoreceptor axons in sodium‐free or calcium‐free saline or in isotonic sucrose does not significantly affect the spread of the visual signal to the terminals. Thus the signal is not amplified by an ionic mechanism along the axon.4. Membrane characteristics of the photoreceptor for hyperpolarizing voltage changes were estimated from (a) the ratio of the amplitudes of the visual signals recorded simultaneously in the axon and in the soma, (b) the time constant, and (c) the input resistance of the cell. All three independent measurements are consistent with a length constant 1 to 2 times the total length of the cell (λ = 10‐18 mm) and an unusually high membrane resistivity of about 300 kΩ cm2. This resistivity enables the receptor potential to spread passively to the terminal region.5. Electron microscopic examination of receptor axons reveals an investment of glial lamellae, but demonstrates neither unusual structures which would lead to a high apparent membrane resistivity, nor junctions between cells which would seal off the extracellular space. Thus the observed high resistivity appears to be an intrinsic property of the receptor membrane.
Properties of different functional types of neurones in the cat's rostral trigeminal nuclei responding to sinus hair stimulation
Authors: Gottschaldt K.-M. , Young D. W. 
Published: December 2014

1. Properties of neurones in the trigeminal nuclei principalis and oralis responding to movements of facial sinus hairs were studied in cats anaesthetized by I. V. infusion of pentobarbitone.2. Using electrophysiological methods trigeminal neurones were classified into primary afferent fibres, trigeminothalamic relay neurones, interneurones and other unspecified higher order neurones.3. When receptive fields of synaptically activated neurones were compared with those of primary afferent fibres, an often extensive convergence from first order on to higher order neurones was established. Out of 119 relay neurones six received input from one sinus hair only. Spontaneous activity was encountered about twice as often in synaptically activated neurones than in primary afferent fibres.4. The responsiveness of single neurones was unstable over time in about one fifth of the population and then the total number of impulses discharged in successive responses could vary by as much as 500%. Unstable responsiveness occurred sometimes alone but was often accompanied by marked changes in the size or the configuration of the receptive field. Such instabilities were observed in all kinds of synaptically activated neurones but not in primary afferent fibres.5. Afferent inhibition in relay neurones could be elicited from within the excitatory receptive field and appeared to be related to the activation of distinct receptor populations responding to specific stimulus parameters. Inhibition was also seen in interneurones following both mechanical stimulation of the skin and electrical stimulation of lemniscal fibre terminals in the contralateral ventromedial thalamus.6. The results are discussed and compared with previous findings about sinus hair representation in the trigeminal nucleus and the ascending lemniscal projection. The findings indicate that the concept of the ‘static properties’ of relay neurones is not adequate for all trigeminothalamic relay neurones and may require a critical reconsideration.7. It is suggested that the afferent input from sinus hairs is effectively controlled at the level of the rostral trigeminal nuclei. This control may affect the spatial input to relay neurones, the temporal components of their responses and the intensity dimension of their transmission capacity. It is postulated that by these mechanisms tactile information from the sinus hair system is modulated according to the instantaneous sensory requirements of the behaving cat.
A comparison of ion concentrations, potentials and conductances of amphibian, bovine and cephalopod lenses
Authors: Delamere N. A. , Duncan G. 
Published: December 2014

1. The concentrations of sodium, potassium and chloride in frog and bovine lenses showed a normal intracellular ion distribution with the sum of the internal cations approximately equal to the external sum. In the cephalopod lens, however, the sum inside was much lower than that outside.2. The membrane potentials of frog, Sepiola and bovine lenses were ‐63, ‐63 and ‐23 mV respectively. A comparison of the electrical data with the Nernst potentials predicted from ion concentration data indicated that sodium and chloride ions as well as potassium contributed to the membrane potential in frog and bovine. In contrast, the membrane and Nernst potentials for potassium were equal in Sepiola.3. Substituting potassium for sodium in the external medium depolarized lens potentials in all three species. Estimates of the relative permeabilities of sodium, potassium and chloride were obtained by fitting the Goldman‐Hodgkin‐Katz equation to the potential data.4. The potassium permeability was determined directly by 42K efflux measurements and values of 2·99, 9·83 and 3·13 (× −8 m sec−1) were obtained for frog, Sepiola and bovine lenses respectively.5. The effect of raising external potassium on the efflux rate constant was determined and there was reasonable agreement between experiment and theory (Kimizuka‐Koketsu) in frog and bovine lenses, but the Sepiola data indicated that the potassium permeability decreased by a factor of 2·6 when the external potassium was raised from 10 to 120 m
M‐K+.6. The measured specific conductances, obtained using two internal micro‐electrodes, were 7·7, 15·9 and 9·9 (Sm−2) for frog, cephalopod and bovine lenses respectively. These data compare with computed values (Kimizuka‐Koketsu theory) of 7·5, 14·1 and 17·2 (Sm−2).7. The effect of increasing external potassium on the conductance was also tested and there was good agreement between experiment and theory (assuming constant permeabilities) only in the amphibian lens. However, when the cephalopod data were corrected assuming a 2·6‐fold decrease in PK for a twelvefold increase in potassium, then there was excellent agreement between experiment and theory.8. The bovine measured conductances were much lower than the theoretical values throughout the range of external potassium concentrations and several explanations were proposed to account for the discrepancies.
Analysis of electrical noise in turtle cones
Authors: Lamb T. D. , Simon E. J. 
Published: December 2014

1. Properties of the light‐sensitive voltage noise in cones in the retina of the turtle, Pseudemys scripta elegans, have been studied by intracellular recording.2. Suppression of the noise by light was a function of the hyperpolarizing response of a cone but not of the size or pattern of illumination.3. Power density spectra of the noise were fitted in many cones by the product of two Lorentzians with characteristic time constants τ1 and τ2 averaging 40 and 7 msec respectively. The spectra of some cells were peaked and could be fitted by a resonance curve.4. Spectra in dim light exhibited decreased low frequency power. They could often be fitted by a product of two Lorentzians using the same value of τ2 as used in darkness but decreasing τ1 and the zero frequency asymptote. An e‐fold reduction in τ1 occurred with lights which hyperpolarized by 4‐7 mV.5. Injection of hyperpolarizing currents of about 0·1‐0·2 nA into weakly coupled cones reduced the noise, and also reduced the sensitivity to dim flashes.6. The variance‐voltage relation during steady illumination of different intensities differed from cone to cone. Dim lights increased the noise in some cells and decreased it in others, but moderately bright lights which gave steady responses of more than about one third maximal reduced the noise in all cells.7. When the cell was transiently depolarized during the differentiated component following steady illumination, the noise was less than it was after prolonged darkness.8. In the after‐effect of bright light, the time course of recovery of noise was the same as that of flash sensitivity and voltage. The noise was reduced e‐fold for hyperpolarizations averaging 3 mV while for sensitivity this reduction occurred for 1·3 mV. For a given hyperpolarization the noise was lower during the after‐effect than during steady dim illumination.9. When a series of dim flashes was delivered to a cone, no significant increase in variance over the dark noise was detected during the photo‐response. This implies that each photoisomerization evokes no more than about 1·5 μV at the peak of the response in a coupled cone, corresponding to about 50 μV in an isolated cone.10. The elementary shot events underlying the noise are about 100 μV in amplitude in an isolated cone, have a characteristic time constant of 16‐60 msec and reflect unit conductance fluctuations of about 16 pS (S, Siemen ≡ Ω−1).11. It is concluded that the noise source is internal to the cones. We postulate that the noise arises from opening and closing of the light‐sensitive ionic channels in the outer segment, and that in darkness there is a residual concentration of the blocking substance which on average closes up to about one third of the channels. It seems likely that the unit event involves a considerable number of blocking molecules and ionic channels.