bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of background illumination on the photoresponses of red and green cones.
Authors: Normann R A , Perlman I
Published: December 2014

1. The photoresponses of light‐ and dark‐adapted red and green cone photoreceptors were recorded intracellularly in the retina of the turtle, Pseduemys scripta elegans. Background illumination produced similar effects on both types of cones. 2. In response to the onset of a prolonged, steady background illumination the cone initially hyperpolarized to a peak which then sagged back to a steady‐state polarization that was typically about one half the initial peak amplitude. This sag was observed for all backgrounds studied (dim as well as bright). 3. A resensitization was observed concomitantly with this sag; both the maximum increment and decrement responses grew in amplitude as light‐adaptation proceeded. After about 2‐‐3 min of background illumination, the amplitudes of these responses stabilized. 4. The dark‐adapted cone produced graded responses to test pulses over a range of intensities spanning about 3.5 log units. The amplitudes of these responses were well fit by the relationship V = I.Vm/(I + sigma). 5. After 2‐‐3 min of background illumination, 500 msec test pulses either brighter or dimmer than the background intensity were substituted for the background. The light‐adapted intensity‐response curves constructed from this data were similar to the dark‐adapted curve but were shifted horizontally and slightly vertically, so that they still spanned about 3.5 log units of intensity. Thus, in the light‐adapted cone, graded responses were elicited by a range of bright test pulses which would have produced saturated responses when delivered to the dark‐adapted cone. 6. The 'off response' observed at the offset of the background became faster as the background intensity was increased. It also became faster with time following the onset of any particular background intensity. 7. It was concluded that cone sensitivity during any state of light‐adaptation is determined by two mechanisms; response compression resulting from the instantaneous non‐linearity between 'internal transmitter' concentration and membrane potential and a more active 'cellular adaptation' mechanism which is manifest as a shift in the intensity‐response curve. In the steady‐state condition of light‐adaptation, most of the sensitivity changes are a result of the cellular adaptation mechanism. 8. Photopigment bleaching caused by the backgrounds, negative feed‐back from horizontal cells and voltage dependent mechanisms in the cones could not account for this cellular adaptation. These effects of background illumination were interpreted in terms of the 'internal transmitter' hypothesis of phototransduction.
Motor unit organization of human medial gastrocnemius.
Authors: Garnett R A , O'Donovan M J , Stephens J A , Taylor A
Published: December 2014

1. The properties of fifty‐seven motor units in human medial gastrocnemius have been studied using controlled intramuscular microstimulation, glycogen depletion and muscle biopsy. 2. Motor units could be divided into three classes on the basis of their mechanical properties. Type S units were slow, small and fatigue resistant. Type FR units were fast, intermediate in size, and fatigue resistant. Type FF units were fast, large and fatigable. 3. Glycogen depletion of a number of type S and FF units revealed them to be composed of type 1 and type 2b muscle fibres respectively. 4. The results suggest that during slowly increasing voluntary contractions where units are recruited in order of size, type 1 and 2a muscle fibres would be employed at low force levels followed by type 2b muscle fibres in stronger contractions.
The effect of hypoxia on evoked potentials in the in vitro hippocampus.
Authors: Lipton P , Whittingham T S
Published: December 2014

1. We have studied the effect of hypoxia on transmission of electrical activity between the perforant path and the dentate granule cells in the in vitro guinea‐pig hippocampus. 2. Hypoxia abolishes the evoked field potential within about 3 min, a time similar to that occurring in vivo (Andersen, 1960). 3. The evoked potential is very rapidly abolished by extracellular K+ concentrations greater than 13.4 mM; it is abolished by ouabain concentrations greater than 10(‐5) M. The rate at which it is abolished increases with increasing ouabain concentrations: concentrations of about 8 x 10(‐5) M abolish the evoked potential at the same rate as does hypoxia. 4. The time required to abolish the evoked potential during hypoxia decreases markedly as the extracellular K+ concentration is elevated from 4.4 to 13.4 mM. The time to abolish the potential during hypoxia is also decreased by partial replacement of the Cl‐ in the bathing medium by less permeant anions and by the presence of a low (10(‐7) M) concentration of ouabain. All these are conditions which are expected to depolarize neuronal cell membranes. None of these alterations in the perfusing medium affect the concentrations of ATP or creatine phosphate in the hippocampal slice. Increasing extracellular Mg2+/Ca2+ to levels which reduce the evoked response by about 50% has no effect upon the time required to abolish the evoked potential during hypoxia at any concentration of extracellular [K+]. 5. These results provide evidence that the basis for the hypoxic block of the evoked potential is a depolarization of neuronal processes. They are consistent with the hypothesis that this depolarization is a result of inhibition of the Na+/K+ pump.
The physiology, pharmacology, and trophic effectiveness of synapses formed by autonomic preganglionic nerves on frog skeletal muscle.
Authors: Grinnell A D , Rheuben M B
Published: December 2014

1. Frog sartorius muscles, newly denervated and transplanted to the lymph sac of the back, are reinnervated by implanted cholinergic nerves (spinal somatic motor nerves or the preganglionic sympathetic splanchnic nerve), but not by nerves). 2. Foreign somatic motor nerves (s.m.n.s) form synapses that resemble normal sartorius neuromuscular junctions electrophysiologically. 3. Axons of the sympathetic preganglionic splanchnic nerve (s.p.n.) grow throughout the muscle, but only a small percentage of fibres form synapses. Most e.p.p.s are of low quantal content, generally subthreshold. Long onset latencies and multiple post‐synaptic responses indicate that innervation is multiple, multi‐terminal, and by unmyelinated axons. 4. Spontaneous miniature e.p.p.s at splanchnic junctions occur at an average rate under 0.1/sec. Their average amplitude and time course are about the same as for control muscles, but the variability of amplitudes is greater than for control muscles. 5. The amount of facilitation shown by s.p.n.‐evoked e.p.p.s is the same as by s.m.n. e.p.p.s, but the time course is almost twice as long. 6. S.p.n.‐reinnervated fibres show dramatic post‐tetanic potentiation preceded by depression, following as few as 20‐‐50 stimuli. 7. As judged by standard physiological and histochemical criteria, AChEsterase is absent at s.p.n. junctions. 8. The pharmacological responses of the s.p.n. junctions are similar to those of normal or foreign s.m.n. innervated neuromuscular junctions in their sensitivity to the cholinergic blocking agents D‐tubocurarine and hexamethonium. 9 The s.p.n. is capable of restricting ACh sensitivity to the sites of nerve contacts, although this restriction occurs more slowly and less completely than with s.m.n. reinnervation. The loss of extrajunctional ACh sensitivity can be correlated with effectiveness of innervation; but significant restriction occurs even in s.p.n. reinnervated fibres that probably never contract to nerve stimulation.
An estimation of intracranial blood flow in the new‐born infant.
Authors: Cross K W , Dear P R , Hathorn M K , Hyams A , Kerslake D M , Milligan D W , Rahilly P M , Stothers J K
Published: December 2014

1. A non‐invasive method for the estimation of the intracranial blood flow of the new‐born infant is described, and results obtained with it are presented. 2. The technique is a novel application of the principle of blood flow measurement by venous occlusion plethysmography. It is possible to apply a plethysmographic technique to the neonatal cranium because the presence of open sutures between the component bones permits small, but readily measurable, changes in intracranial volume to occur. 3. Skull volume changes are calculated from changes in the occipito‐frontal circumference of the cranium as recorded and measured with a mercury‐in‐Silastic strain gauge. 4. The jugular veins in the baby's neck are occluded by finger pressure and there follows an increase in skull volume, which is rapid at first, but which decreases exponentially as venous drainage diverts to non‐occluded channels such as the vertebral venous plexus. At the instant of jugular occlusion the rate of skull volume increase is representative of the rate of flow in the jugular vessels prior to occlusion, and so provides an index of the relative magnitude of the intracranial blood flow. The method thus allows changes in intracranial blood flow to be followed. When occlusion is released cranial volume decreases, initially rapidly, but slowing exponentially as resting volume is regained. 5. A theoretical model of the events occurring during the inflow and outflow phases has been developed, and a formula derived which allows an estimation to be made of the flow of blood through uncompressed channels. The measured value of jugular blood flow can then be augmented to an estimate of total intracranial flow. 6. The mean cerebral blood flow of sixteen normal babies was estimated to be 40 ml. 100 g‐1.min‐1 (S.D. = +/‐ 11.63).
Distribution of climbing fibres on cerebellar Purkinje cells in X‐irradiated rats. An electrophysiological study.
Authors: Crepel F , Delhaye-Bouchaud N
Published: December 2014

1. The distribution of climbing fibres on cerebellar Purkinje cells has been studied with intracellular recordings in X‐irradiated and normal rats. 2. In the treated rats, multiple steps in the post‐synaptic potential were elicited in 57% of the Purkinje cells by graded stimulation of the climbing fibres, the response was all‐or‐none in character in the other cells and in all Purkinje cells recorded in normal animals. In the neurones exhibiting the former type of response, no collision was seen along the afferent fibres during interaction experiments between just‐threshold juxtafastigial and maximal olivary stimulations, whereas a collision always occurred when all‐or‐none responses were recorded. 3. These results show that in X‐irradiated rats, the majority of Purkinje cells have a multiple innervation by two to four climbing fibres, instead of the one‐to‐one relationship seen normally. 4. Input resistances and total electrotonic lengths of Purkinje cells were measured in normal and treated rats. Mean values for these two parameters were higher than normal in multiply innervated cells. 5. Mean time course and mean current for reversal of the post‐synaptic potential elicited in Purkinje cells by stimulation of the climbing fibres were nearly the same in mono‐ and in multiply innervated neurones. In multiply innervated cells, time courses and currents for reversal were independent of the size of the response or varied slightly with it, suggesting that the climbing fibres involved innervated territories whose electrotonic distance from the recording site were either the same or slightly different. 6. Interactions between two all‐or‐none steps of the graded post‐synaptic potential evoked in multiply innervated cells by juxtafastigial and olivary stimulations revealed either a very weak or a very marked shunting effect between synapses of the two climbing fibres involved. 7. These results indicate that the over‐all distribution of climbing fibre synapses on multiply innervated Purkinje cells is not grossly abnormal and that two fibres contacting a given cell can be either intermingled on the same dendrites, or segregated on distinct dendritic branches. 8. In general, the present study does not suggest the existence of a strong competition among climbing fibres innervating each Purkinje cell during development at least when granule cells are absent.
Effects of nerve impulses on threshold of frog sciatic nerve fibres.
Authors: Raymond S A
Published: December 2014

1. The firing thresholds of single myelinated fibres of frog sciatic nerves were monitored as a function of impulse activity in the fibre. The threshold was given by the number of coulombs in current pulses that excited a particular fibre half the time when delivered to the whole nerve. Threshold was tracked by a device that incrementally decreased the number of coulombs in the current pulse whenever the fibre responded and increased the pulse if it did not respond. 2. There was a pattern to the after‐oscillations of threshold following activity. The fibres were briefly refractory, transiently superexcitable for about 1‐1.5 sec and then entered a phase of raised threshold or 'depression' that lasted for many minutes. 3. Activity produced little change in the threshold curve during the refractory period. Strong depressions following prolonged activity prevented the threshold from returning to the base‐line level within the time associated with the refractory period for the same fibre at rest. 4. After an impulse, superexcitability reached a maximum within 7‐20 msec. This peak was larger as the number of impulses in a preceding burst increased and as the intervals between the impulses became briefer. Each successive impulse of a burst contributed less to the growth of superexcitability, and after the burst had 6‐10 impulses additional impulses contributed nothing. 5. The depression phase was marked by the interaction between build‐up, which depended on the activity rate, and recovery, which required as long as an hour or more for the threshold to be completely restored to resting level. These two mechanisms, one causing build‐up and the other recovery, led to formation of dynamic equilibria. The threshold level at equilibrium increased monotonically with the activity rate. 6. The processes associated with superexcitability interact with those producing depression. In active fibres showing raised thresholds, impulses are followed by a relative superexcitability that persists for at least as long as an absolute superexcitability (with threshold below the resting level) can be measured in the same fibre at rest. 7. The duration of the superexcitable phase interpreted as a relative change in excitability was roughly the same regardless of the level of depression. 8. The magnitude of the oscillation in threshold was give to ten times larger than the grey region (the range of stimuli for which response is probabilistic). It is concluded that at regions of low conduction safety such as axonal branches, where weak forces can influence whether an impulse will pass, such pronounced and long‐lasting after‐effects of firing can be expected to modulate conduction of nerve impulses.
Electrophysiological and electron‐microscopical correlations with fluid and electrolyte secretion in rabbit ileum.
Authors: Holman G D , Naftalin R J , Simmons N L , Walker M
Published: December 2014

1. The effects of theophylline and triaminopyrimidine on the passive permeability of Na+ and Cl‐ across sheets of rabbit ileum treated with 0.1 mM‐ouabain were examined by determining the NaCl: mannitol dilution potentials, K+:Na+; choline: Na+ and SO24‐:Cl‐ biionic potentials. The results indicate (a) that triaminopyrimidine reduces paracellular Na+ and K+ permeability without affecting Cl‐ permeability and (b) that theophylline increases Cl‐ permeability without affecting Na+ permeability and (c) that neither theophylline nor triaminopyrimidine interfere with each other's action. This is further evidence consistent with separate routes for paracellular Na+ and Cl‐ movement. 2. Electrical resistance changes across sheets of actively transporting rabbit ileum were measured as a function of time in various conditions. Theophylline has a biphasic effect on resistance. Initially it decreases resistance from 56 omega cm2 (control) to 40 omega cm2. In the ensuing 30 min, resistance rises to 50 omega cm2; whereas it falls to 30 omega cm2 in controls. When theophylline is present, with triaminopyrimidine, or with galactose, no secondary rise in tissue resistance occurs. The initial decrease in resistance is consistent with a theophylline‐dependent increase in Cl‐ conductance and the secondary rise in resistance may be attributed to collapse of the lateral intercellular space following leakage of NaCl and fluid into the mucosal solution. 3. Electron microscopy of glutaraldehyde‐fixed tissue confirms the above views, since, with theophylline present, the lateral intercellular spaces are collapsed and with both triaminopyrimidine and theophylline, or both theophylline and 20 mM‐galactose present the spaces remain open. 4. It is shown in the Discussion that the theophylline‐ or choleragen induced increase in passive Cl‐ permeability of the mucosal border is the only requirement necessary to explain the increase in electrogenic Cl‐ secretion, the increase in short‐circuit current, as well as neutral secretion of NaCl and net fluid secretion.
Gastric emptying and secretion in the calf on duodenal infusion of tryptophan, tryptamine and 5‐hydroxytryptamine
Authors: Bell F. R. , Webber D. E.
Published: December 2014

1. Gastric emptying, gastric acid and pepsinogen secretion were assessed simultaneously in the conscious calf using the test meal and duodenal perfusion technique (Bell & Mostaghni, 1975).

2. When 60 m
M‐HCl was infused into the duodenum, gastric emptying was arrested but both acid and pepsinogen secretion continued at a low level. Duodenal infusion with isotonic NaHCO3 caused rapid exponential emptying of the test meal and acid and pepsinogen output was more than doubled.

3. Duodenal infusion of amino acids in isotonic NaHCO3 did not affect the rapid emptying, except infusion with tryptophan, which caused a measureable degree of inhibition of emptying, with concomitant effects on acid and pepsinogen secretion

4. Tryptamine and 5‐hydroxytryptamine (5‐HT) incorporated in low concentration into isotonic NaHCO3 also produced depression of gastric emptying, acid and pepsinogen levels comparable to the response initiated by acid infusate. Tryptophan was effective only in non‐physiological amounts while 5‐HT and tryptamine were active in smaller doses.

5. Our results suggest that the inhibition of gastric emptying following duodenal infusion of tryptophan noted by Stephens, Woolson & Cooke (1975) may be due to the duodenal synthesis of its biogenic amine derivatives tryptamine and 5‐HT.

6. The level of activity of the three gastric functions, emptying, acid secretion and pepsinogen secretion appears to be linked. A single stimulus, therefore, could evoke a duodenal receptor or receptors to mediate or suppress activity of the gastric smooth muscle and secretory cells through interrelated mechanisms. The effect of some duodenal infusates, however, produces some variability in response which suggests differential activation of different receptors with consequent variable motor activity on effector cells.
Responses of striate cortex cells to grating and checkerboard patterns.
Authors: De Valois K K , De Valois R L , Yund E W
Published: December 2014

1. Cells in visual cortex have been alternately considered as bar and edge detectors, or as spatial‐frequency filters responding to the two‐dimensional Fourier component of patterns. 2. The responses to gratings and to checkerboards allow one to test these alternate models: the Fourier components of a checkerboard pattern do not occur at the same orientation as the edges, nor do the checkerboard spatial frequencies correspond to the check widths. 3. Knowing the orientation tuning of a cell for gratings, one can precisely predict its orientation tuning to checkerboards from the orientation of the fundamental Fourier components of the patterns, not from the orientation of their edges. This was found for both square and rectangular checkerboards, and held for both simple and complex cortical cells. 4. Knowing the spatial tuning of a cell for sine‐wave gratings, one can precisely predict its spatial tuning to square and rectangular checkerboards from the spatial frequencies of the fundamental Fourier components of the patterns, not from the widths of their checks. 5. When presented with checkerboards in which not the fundamental but the upper harmonics were within its spatial bandpass, a cell's orientation tuning was found to be predictable from the (quite different) orientation of the higher Fourier harmonic components, but not from the orientation of the edges. 6. Knowing a cell's contrast sensitivity for gratings, one can predict the cell's contrast sensitivity for checkerboards much more accurately from the amplitudes of the two‐dimensional Fourier components of the patterns than from the contrasts of the patterns. 7. The orientation tuning, spatial‐frequency tuning and responsiveness of cells to a plaid pattern were also found to be predictable from the pattern's two‐dimensional Fourier spectrum. 8. Both simple and complex striate cortex cells can thus be characterized as two‐dimensional spatial‐frequency filters. Since different cells responsive to the same region in the visual field are tuned to different spatial frequencies and orientations, the ensemble of such cells would fairly precisely encode the two‐dimensional Fourier spectrum of a patch of visual space.
Sarcomere length‐tension relations of frog skinned muscle fibres during calcium activation at short lengths.
Authors: Moss R L
Published: December 2014

1. Single twitch fibres were isolated from anterior tibial muscles of the frog, Rana pipiens. The relationship between sarcomere length and steady tetanic tension at 5 degrees C was obtained from these living fibres in the range of sarcomere lengths between about 2.2 and 1.3 microns . These fibres were then either mechanically or chemically skinned. 2. Segments were cut from the skinned fibres and mounted in an experimental chamber using a technique designed to minimize segment compliance at the points of attachment. A piece approximately 1 mm in length remained exposed to the bathing solution. 3. The segments were photographed through a light microscope at magnifications of about 460 or 110 X during activation and relaxation, so that the sarcomere lengths could be determined from a part or the whole of the segment. Activations were done with solutions of pCa either 5.49 or 6.09 and at a temperature of 5 degrees C. Fibre segments which developed striation pattern irregularities during contraction were rejected. 4. The sarcomere length‐tension relation obtained from these segments in the sarcomere length range 1.3‐2.2 microns was similar to that obtained from the same fibres while still living. The results were similar at the two values of pCa used. 5. These results do not support the view that sarcomere length dependent variation in the amount of calcium which is released during tetanic stimulation is a major determinant of the form of the length‐tension relation in living muscle fibres at sarcomere lengths less than about 2.0 microns.
The electrical responses of the rabbit rectococcygeus following extrinsic parasympathetic nerve stimulation.
Authors: Blakeley A G , Cunnane T C , Muir T C
Published: December 2014

1. The responses of the rabbit rectococcygeus muscle to stimulation of the extrinsic pelvic nerves have been investigated using intracellular micro‐electrode recording techniques. 2. Submaximal pelvic nerve stimulation evoked a depolarization (e.j.p.) which was graded with stimulus strength and abolished by atropine (10(‐6) g/ml.) and tetrodotoxin (TTX). 3. Single supramaximal stimuli evoked action potentials associated with muscle contraction. 4. In the presence of atropine, to abolish the e.j.p.s, supramaximal stimulation of the pelvic nerves evoked hyperpolarizations (i.j.p.s) which were graded with stimulus strength and abolished by TTX. 5. The transmitter responsible for the i.j.p.s is unknown. Phentolamine (10(‐5) g/ml.) and propranolol (3 x 10(‐5) g/ml.) in concentrations which block respectively alpha and beta adrenoceptors and the adrenergic neurone blocking agent guanethidine (10(‐6) g/ml.) were ineffective in blocking the inhibitory response. 6. It is concluded that stimulation of the pelvic nerves to the rectococcygeus releases two transmitters, acetylcholine, responsible for the e.j.p. (and muscle contraction) and a non‐adrenergic non‐cholinergic transmitter which is the basis for the mechanical relaxation.
Distribution of inulin, sucrose and mannitol in rat brain cortex slices following in vivo or in vitro equilibration
Authors: Amtorp Ole
Published: December 2014

1. The distribution spaces of inulin, sucrose and mannitol in rat brain cortex slices were determined in tracer experiments. Tracer equilibration times of 5 hr were used with combined ventriculo‐cisternal perfusion and
I.V. infusion of tracers. After 5 hr of equilibration the distribution volumes (expressed as μl./100 mg wet wt.) obtained using the perfusion fluid as reference and after correction of tracer amount in residual blood were obtained. Information on cellular uptake was obtained by examining a slow component of wash‐out curves from brain slices after in vivo equilibration. Distribution spaces were corrected for intracellular penetration to obtain the extracellular volumes of distribution. Inulin was found to equilibrate with 13·3 μl. extracellular tissue water per 100 mg initial wet weight, sucrose with 16·6 μl. and mannitol with 19·5 μl.

2. Marker spaces in rat brain cortex slices were also analysed by compartmental analysis of efflux of tracer inulin, sucrose and mannitol following in vitro incubation in a balanced medium for 60 min. Following in vitro equilibration, inulin was found to equilibrate with 22·4 μl. extracellular tissue water per 100 mg of final wet weight, sucrose to equilibrate with 31·7 μl. extracellular tissue water and mannitol with 42·3 μl.

3. Inulin space in vitro when allowance is made for swelling produced during incubation of the slice was similar to the chemically delineated extracellular distribution volume in vivo. Sucrose and mannitol spaces in vitro, however, did not accord with in vivo determinations, most likely due to access of markers to areas of cell damage in the slice arisen during incubation.

4. Comparison of fluid spaces delineated by inulin in slices of rat cerebral cortex following in vivo and in vitro equilibration indicated that swelling produced during incubation in vitro mainly occurred in the extracellular space. Swollen glial cells may account for the small, but significant intracellular swelling in incubated slices.
Segmental and descending control of the external urethral and anal sphincters in the cat.
Authors: Mackel R
Published: December 2014

1. The present work concerns the contribution of the somatic central nervous system to two viscero‐somatic reflexes, micturition and defecation. Descending and segmental actions and properties of the motoneurones innervating the striated external urethral and external anal sphincters were studied with intracellular recording in male cats, under chloralose anaesthesia. 2. Motoneurones innervating the external urethral and external anal sphincters were intermingled and most strongly concentrated in the lateral part of the ventral horn in the S2 segment of the spinal cord. 3. Stimulation of the S1 to S3 ipsilateral dorsal roots or of the homonymous pudendal nerve branches showed that less than half of the sphincter motoneurons receive monosynaptic excitatory connexions from low threshold afferents. 4. The after‐hyperpolarization recorded in the external urethral and external anal sphincter motoneurones was relatively short lasting, not long lasting as would have been expected for motoneurones innervating slow‐twitch, tonic type muscles. 5. There was no evidence for recurrent inhibition in pudendal motoneurones innervating the external urethral and external anal sphincters. 6. Descending excitation and inhibition to the sphincter motoneurones originated in the nucleus reticularis gigantocellularis of the medullary reticular formation. The descending reticulospinal actions are comparable to those observed in hind limb motoneurones. 7. It is suggested that the segmental reflex connexions play a role in controlling bladder and rectal continence. The descending actions studied also modulate the segmental reflex actions and may provide voluntary control of the sphincter muscles.
Bicarbonate exchange through the human red cell membrane determined with [14C] bicarbonate.
Authors: Wieth J O
Published: December 2014

1. Bicarbonate transport across human red cell membranes was studied between 0 and 10 degrees C at alkaline pH values by determining the efflux of 14C‐labelled bicarbonate from resealed erythrocyte ghosts. Transfer of labelled CO2 was eliminated as a source of error, when formation of intracellular 14CO2 was inhibited with carbonic anhydrase inhibitors. The study showed that there are no fundamental differences between the characteristics of bicarbonate and of chloride self‐exchange as has been inferred from previous studies of chloride‐bicarbonate exchange. 2. Efflux of radioactivity could be reduced more than 99% by reversible and irreversible inhibitors of anion transport. Inhibition of both chloride and bicarbonate self‐exchange was linearly related to the binding of 4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid (DIDS) to the membranes. Complete (i.e. greater than 99%) inhibition was obtained after binding of 1.2 x 10(6) DIDS molecules per cell. 3. Bicarbonate self‐exchange proved a saturable function of bicarbonate concentration, with a maximum at external and internal concentrations of approximately 100 mM, showing self‐depression at higher bicarbonate concentrations, and half‐maximum exchange flux at a concentration of 10 mM. The results were consistent with the hypothesis that the exchange mechanism has two anion binding sites, one mediating ion transport and the other causing transport inhibition. 4. Maximum exchange flux of bicarbonate was about 30% larger thant that of chloride, and the affinity of bicarbonate for the transport site was about three times larger than that of chloride. The apparent activation energy of bicarbonate exchange was 28 kcal/mole, the same order of magnitude as found for other inorganic anions between 0 and 10 degrees C. 5. The ability of other inorganic anions to exchange with bicarbonate decreased in the sequence Cl greater than NO3 greater than F greater than Br greater than or equal to I, corresponding to the sequence of the rate of self‐exchange of halides. 6. Counter‐transport of bicarbonate could be driven by a chloride gradient, when ghosts containing KCl were suspended in a medium containing traces of labelled bicarbonate in addition to a non‐permeating anion. Concentration ratios (ci/co) up to about 1000 could be obtained. 7. It is concluded that bicarbonate is transported by the inorganic anion exchange mechanism of the erythrocyte membrane. The slight differences between the exchange kinetics of chloride and bicarbonate were explained by differing affinities of the two anions for the two anion binding sites of the transport system.
A mathematical model for conduction of action potentials along bifurcating axons.
Authors: Parnas I , Segev I
Published: December 2014

1. A mathematical model based on the Hodgkin‐Huxley equations is derived to describe quantitatively the propagation of action potentials in a branching axon. 2. The model treats the case of a bifurcating axon with branches of different diameters. The solution takes into account the changes in space constant in the different regions. 3. The model allows for investigating parameters leading to preferential conduction of action potentials in one daughter branch as seen experimentally. 4. Assuming that the only difference between the various daughter branches is in their diameters, conduction blocks should occur simultaneously rather than differentially into all daughter branches when the geometrical ratio is greater than 10. 5. In order to obtain differential conduction into the two branches changes in ionic concentrations due to the repetitive action potentials had to be introduced into the equations. 6. We find that conditions which allow differential buildup of K concentration around the two branches, produce differential conduction block. These conditions may be different periaxonal spaces around the branches or different time constant for recovery processes that eliminate K from the periaxonal space. 7. The effects of an inexcitable branch on conduction of action potentials in the second branch are described. 8. We find that the membrane current which is associated with the action potential is much more sensitive than the action potential itself and shows more distinct changes near regions of inhomogeneity such as a branch point, a step increase in diameter or an inexcitable branch.
Responses of visual cortical cells to periodic and non‐periodic stimuli.
Authors: Maffei L , Morrone C , Pirchio M , Sandini G
Published: December 2014

1. The activity of neurones of the visual cortex (area 17) has been recorded in anaesthetized cats in response to gratings of different profile and to single light and dark bars. 2. At very low spatial frequencies, outside the frequency response range to sinusoidal gratings, the response to square‐wave drifting gratings is obtainable from a combination of the response to the single bars of the grating presented in isolation. At higher spatial frequencies this is no longer true. 3. At very low spatial frequencies the responses to square‐wave gratings and to missing‐fundamental gratings (obtained by subtraction from the square‐wave grating of its fundamental gratings (obtained by subtraction from the square‐wave grating of its fundamental harmonic) are very similar. 4. At spatial frequencies near the peak of the spatial frequency tuning curve of the cell, the responses to square‐wave grating and to sinusoidal gratings are very similar. At these spatial frequencies the response to the missing‐fundamental grating is practically zero. 5. At spatial frequencies lower than that of best sensitivity for the cell, the response to square‐wave gratings is correlated with the 1st and 3rd harmonic of the stimulus. 6. We conclude that at very low spatial frequencies of the grating the response of cortical cells is correlated with the light or dark edges (or light or dark bars) of the stimulus, because the edges contain high frequencies within the range of sensitivity of the cells. At higher spatial frequencies the results are interpreted best by assuming that cortical cells respond to the harmonics of the visual periodic stimulus. 7. When a background of dynamic visual noise is added to increase the spontaneous discharge of simple cells, their response to visual stimuli becomes linear or quasi‐linear. The stimuli could be either single bars or gratings.
The morphology of group Ib afferent fibre collaterals in the spinal cord of the cat.
Authors: Brown A G , Fyffe R E
Published: December 2014

1. The enzyme horseradish peroxidase (HRP) was injected into single Ib muscle afferent fibres in anaesthetized cats. Subsequently, histochemistry allowed the morphology of the axons and their collaterals in the lumbosacral spinal cord to be determined. 2. Eleven Ib axons were stained, seven from lateral gastrocneminus‐soleus, one from medial gastrocnemius and three from muscles innervated by the posterior tibial nerve. Ten of the axons were traced into the dorsal roots and all but one (from the posterior tibial nerve) bifurcated upon entering the cord. Between 5.1 and 9.9 mm of each axon was stained and the fibres gave off eighty‐four collaterals at intervals of 100‐2300 micron, at an average spacing of about 900 micron. The spacing between collaterals on the (finer) descending axon branches was generally less than the intervals between collaterals on ascending branches. 3. All Ib collaterals had a characteristic morphology. The collaterals coursed cranially on a direct path through the dorsal horn to lamina IV or V before branching. They arborized widely in the intermediate region, mainly in lamina VI and in the dorsal part of lamina VII. Occasionally, less extensive arborizations were seen more dorsally in lamina IV and V. The rostro‐caudal extent of individual collateral arborizations was limited to 200‐400 micron and there was no overlap between adjacent collaterals. Each terminal arborization gave rise to 56‐384 boutons, mainly of them ‘en passant’ type. 4. The results are discussed in relation to previous anatomical and electrophysiological studies.
Chemical change, production of tension and energy following stretch of active muscle of frog.
Authors: Curtin N A , Woledge R C
Published: December 2014

1. Measurements were made of the tension and the heat + work produced during 6.5 s of tetanic stimulation at 0 degrees C. The muscle was stretched by 3 mm to 1.2 times rest length either 1 s before stimulation began of 1 s after it began. 2. The extent of ATP splitting during the period from 1.5 to 6.5 s after stimulation began was determined from observations of the levels of phosphocreatine, creatine and the sum of inorganic phosphate and glucose‐6‐phosphate and glucose‐1‐phosphate. (The creatine kinase reaction was taken to be in equilibrium.) 3. In agreement with earlier findings more active tension was produced following a stretch when the stretch occurred during stimulation than when it occurred before stimulation. This increase was large and statistically significant. 4. The mean splitting of ATP was greater following a stretch during stimulation, but this change was small and not statistically significant. 5. During the interval from 1.5 to 2.5 s after stimulation began, which is shortly after the stretch ended, the rate of heat production was significantly greater than in the isometric contraction. 6. From 2.5 s to the end of stimulation and during relaxation the heat + work was not significantly different in the two types of contraction.
Effect of measured calcium chloride injections on the membrane potential and internal pH of snail neurones.
Authors: Meech R W , Thomas R C
Published: December 2014

1. Ion‐sensitive micro‐electrodes were used to measure changes in intracellular pH (pHi) and internal chloride which resulted from the pressure injection of calcium chloride into identified Helix aspersa neurones. The internal chloride measurement allowed the quantity of calcium chloride injected to be estimated. 2. Application of the metabolic inhibitor carbonyl cyanide m‐chlorophenyl hydrazone (CCmP) to a calcium‐loaded cell caused an increase in the membrane potential comparable to the effect of injecting calcium itself. The effect was not observed in normal cells. 3. When injected in the presence of CCmp, calcium caused a much larger and longer‐lasting effect on the membrane potential than that observed in untreated cells. 4. The injection of ruthenium red can increase and/or prolong the hyperpolarization caused by a given quantity of injected calcium. The pHi changes following calcium injection were biphasic and slower than normal. 5. In seven experiments, both hydrogen chloride and calcium chloride were injected into the same cell. The relative changes in pHi corresponded to the production of one hydrogen ion for each calcium ion injected. 6. The relationship between the quantity of calcium injected and the size of the induced hyperpolarization suggested that at least three calcium ions acting cooperatively are required to activate a potassium ‘channel'. 7. Injection of barium chloride hyperpolarized the membrane after a delay of about 1 min. After several injections of barium the cell lost this response while retaining its normal response to calcium injection. Injection of barium also caused a slowly developing (biphasic) fall in pHi. 8. We conclude that injected calcium is normally rapidly taken up by mitochondria in exchange for hydrogen ions. If this uptake process is blocked by ruthenium red or CCmP, the calcium is taken up by a second, slower, process which also releases hydrogen ions. When pre‐loaded, but not otherwise, the mitochondria will release calcium ions on treatment with CCmP. Injection of barium does not directly affect the membrane conductance, but causes the release of calcium from intracellular binding sites.
Mechanical relaxation rate and metabolism studied in fatiguing muscle by phosphorus nuclear magnetic resonance.
Authors: Dawson M J , Gadian D G , Wilkie D R
Published: December 2014

1. We have used phosphorus nuclear magnetic resonance (31P NMR) to study muscular fatigue in anaerobic amphibian muscle. In this paper the biochemical and energetic changes that result from a series of tetani are related to the decrease in rate constant (1/tau) for the final, exponential, phase of relaxation. 2. Using 31P NMR we have measured the concentrations of phosphocreatine (PCr), inorganic phosphate (Pi) and ATP as well as the internal pH. From our measurements we have calculated [creatine], [free ADP], the free‐energy change (more precisely, the affinity A = ‐dG/d xi) for ATP hydrolysis and the rates of lactic acid production and of ATP hydrolysis. 3. We have found that 1/tau, the rate constant of relaxation, is correlated with each of the following, independently of the pattern of stimulation: isometric force production, all of the measured or calculated metabolite levels, pH and dG/d xi. 4. There is a clear dependence upon the pattern of stimulation of the relation between 1/tau and each of the following: total duration of the experiment, number of contractions, rate of lactic acid production and rate of ATP hydrolysis. 5. The rate of relaxation is linearly related to [PCr], [creatine], [Pi] and dG/d xi. It is nonlinearly related to isometric force, [ATP], [H+] and rate of ATP hydrolysis. 6. We conclude that the change in 1/tau, like that of isometric force, depends upon metabolic factors, and not upon any independent changes in the activation or deactivation of contraction. We suggest that 1/tau may depend upon the free‐energy change for ATP hydrolysis which in turn may be related to the rate of Ca2+ uptake into the sarcoplasmic reticulum.
The site of action of corticosteroid antipyresis in the rabbit.
Authors: Willies G H , Woolf C J
Published: December 2014

1. The antipyretic effects of corticosteroids on the fevers produced by bacterial and endogenous pyrogens in the rabbit were investigated. 2. Intravenous infusions of hydrocortisone and methyl prednisolone, when administered simultaneously with bacterial or endogenous pyrogens, failed to produce an antipyresis. 3. Pretreatment of rabbits with methyl prednisolone for 3 days diminished the febrile effect of both bacterial and endogenous pyrogens. 4. The fever produced by intrahypothalamic micro‐injections of endogenous pyrogen was significantly attenuated by the simultaneous micro‐injection of methyl prednisolone. 5. These results indicate that the antipyretic effect of steroids in the rabbit is the result not of a peripheral inhibition of endogenous pyrogen production, but rather of an action on the central nervous system.
Mechanisms of phasic and tonic actions of pentagastrin on canine gastric smooth muscle.
Authors: Morgan K G , Szurszewski J H
Published: December 2014

1. Pentagastrin increased the amplitude and frequency of spontaneous phasic contractions of gastric smooth muscle preparations from the antrum and corpus. Pentagastrin also increased the basal tone in the corpus but not in the antrum. 2. The increase in the amplitude of phasic contractions caused by pentagastri was associated with an increase in the amplitude and duration of the plateau of the action potential in both the antrum and corpus. 3. Voltage‐tension curves generated by graded potassium depolariztion of the membrane potential defined a mechanical threshold for the muscle. 4. Comparison of the effects of pentagastrin to the voltage‐tension curves indicated that the pentagastrin‐induced depolarization of the resting potential was below threshold for the production of a contraction. In contrast, the movement of the top of the plateau potential to more depolarized potentials by this agent exactly followed the voltage‐tension curve for the muscle, implying that both potassium and the plateau potential affected the same voltage‐sensitive mechanism. 5. Pentagastrin caused an increase in conductance of antral preparations during the plateau of the action potential but not between action potentials. In corporal preparations, pentagastrin increased conductance during action potentials, but in addition increased conductance between action potentials. 6. The data indicate that pentagastrin increases the force of phasic contractions in antral and corporal smooth muscle by a voltage dependent process, probably involving the opening of voltage dependent calcium channels. In contrast, the data indicate that pentagastrin increases tone by a voltage independent process, possibly involving a nonregenerative increase in calcium movements through voltage independent channels.
Long‐term effects of axotomy on neural activity during cat locomotion.
Authors: Gordon T , Hoffer J A , Jhamandas J , Stein R B
Published: December 2014

1. Neural activity was recorded from cats during locomotion on a treadmill using electrodes in Silastic cuffs placed around the sciatic nerve and the lateral gastrocnemius‐soleus, medial gastrocnemius, common peroneal and tibial nerve branches. Each branch gave characteristic patterns of activity which were studied before and after it was cut distal to the recording cuffs. Sensory and motor components were separated and measured using cross‐correlation techniques. The amplitude of the cross‐correlation peaks was compared with the amplitude of compound action potentials evoked by electrical stimulation and recorded from the same sites in the anaesthetized animal. 2. Sensory activity declined rapidly following axotomy and did not recover unless reinnervation occurred. Sensory activity even 5 months after nerve section and resuture had recovered to only a fraction of the control values. This reduction is attributed to a decline in the evoked compound potentials and to many fibres being unsuccessful in regenerating to appropriate sensory organs. 3. Motor activity declined more than could be accounted for by a decline in evoked potentials over the first month after axotomy. The extra reduction represents a decline in the number of impulses generated by alpha‐motoneurones after axotomy. If regeneration was permitted, motor activity recovered to higher levels than did the evoked potentials for the whole nerve. Even if regeneration was prevented by nerve ligation, motoneurones continued to generate activity at a stable level over a period of months during which whole nerve compound potentials continued to decline. 4. The modulation of motor activity in ligated nerves during the step cycle was still appropriate to the required movement. Thus, activity recorded from severed nerves in human amputees may be useful in controlling powered artificial limbs. The persistence of motor activity may be responsible for the lesser degree of atrophy found in motor fibres than in sensory fibres following ligation (Hoffer, Stein & Gordon, 1979b).