bluuebunny/crossref_metadata_2025 huggingface dataset:
Disparity of motoneurone and muscle differentiation following spinal transection in the kitten.
Authors: Gallego R , Huizar P , Kudo N , Kuno M
Published: December 2014

1. The spinal cord of kittens, 3‐‐5 days of age, was transected at the lower thoracic level. Isometric contractions of the medial gastrocnemius and soleus muscles as well as intracellular potentials of their motoneurones were recorded after varying post‐operative periods of up to 110 days. Similar observations were made 52‐‐59 days after cord transection in adult cats. 2. In cord‐transected kittens, contraction time of the gastrocnemius muscle showed normal development, whereas the soleus muscle failed to maintain slow contraction. In adult cats, cord transection increased the speed of contraction in the soleus muscle without significant changes in contraction times of the gastrocnemius muscle. 3. Soleus motoneurones showed a normal post‐natal increase in the duration of afterhyperpolarization (a.h.p.) up to a certain stage (61‐‐71 days in age) following cord transection. However, the subsequent increase in the duration of a.h.p. of soleus motoneurones observed in normal kittens was lacking in cord‐transected kittens. It is suggested that soleus motoneurones show two stages of differentiation in terms of the duration of a.h.p. 4. In adult cats, cord transection caused a decrease in the duration of a.h.p. of soleus motoneurones approximately to the value observed at the end of the first stage of differentiation in kittens. 5. The duration of a.h.p. of gastrocnemius motoneurones remained virtually unchanged follwoing cord transection in both kittens and adult cats. 6. The positive correlation between the duration of a.h.p. of soleus motoneurones and contraction time of the innervated muscle fibres normally observed in kittens and adult cats was absent following cord transection. 7. It was assumed that alteration s in contraction time of the muscle following cord transection are due to virtual elimination of motoneurone discharge and that the duration of a.h.p. reflects the discharge pattern of motoneurones under normal conditions. Based on these assumptions, a possible process for normal post‐natal differentiation of motoneurone and muscle is proposed.
A voltage‐clamp study of the permeability change induced by quanta of transmitter at the mouse end‐plate.
Authors: Linder T M , Quastel D M
Published: December 2014

1. Miniature end‐plate currents (m.e.p.c.s) were recorded from mouse diaphragm using a point voltage‐clamp. The relation between m.e.p.c. amplitude and membrane potential was determined in bathing solutions of varied composition. 2. In solution containing normal sodium the relation between m.e.p.c. height and membrane potential (Im.e.p.c./Vm relation) was always linear, at least in the range +30 to ‐100 mV; the reversal potential (Vr) at which Im.e.p.c. was zero was close to 0. The slope of the Im.e.p.c./Vm line varied little between junctions (coefficient of variation about 20%) and was about 50 nS, or 1nA per 20 mV. The Im.e.p.c./Vm relation was not altered by withdrawal of Ca2+, addition of ethanol, or substitution of NO‐3 or SO2‐(4) for Cl‐. 3. Alteration of K+ concentration in the bathing medium, in the range 10 to 1 mM, had no apparent effect on the Im.e.p.c./Vm relation. 4. Reduction of Na+ concentration, with isosmotic substitution of sucrose, caused rapid alteration of the Im.e.p.c./Vm relation, which became rectifying, with a slope at negative Vm less than at positive Vm. Vr was shifted in the negative direction. Quantitatively these changes were close to those predicted by the Goldman‐Hodgkin‐Katz formulation for permeation of monovalent ions through a membrane with constant field. 5. In solution with low Na+ (2 mM) and partial substitution of K+ for Na+, the Im.e.p.c./Vm relation was indistinguishable from that in solutions with Na" as the predominant extracellular cation. With complete substitution of K+ for Na+ the Im.e.p.c./Vm relation was a little less steep (at negative Vm) than in Na+ solution and Vr was shifted slightly in the negative direction. 6. With substitution of NH+4 for Na+, the Im.e.p.c./Vm relation was little changed (about 10% steeper at negative Vm). With substitution of Li+ for Na+, the Im.e.p.c./Vm relation remained linear, but was made less steep, at positive as well as negative Vm, and Vr was shifted slightly in the positive direction. 7. These results indicate that the permeability change associated with generation of the m.e.p.c. (i.e., evoked by a quantum of transmitter) corresponds to the opening of a single species of membrane channel that allows the free movement of K+, Na+, NH+4, AND Li+ ions along their electrochemical gradients. The channel discriminates little between these ions. The apparent order of permeability is Li+ greater than NH+4 greater than Na+ greater than or equal to K+. The apparent permeability per channel corresponds to that expected for channels of about 6.4 A diameter, 100 A length, and ionic mobility the same as in dilute solution.
Studies on neurotrophic regulation of murine skeletal muscle
Authors: Mathers D. A. , Thesleff S.
Published: December 2014

1. A quantitative comparison was made of the effects of the paralysis caused by botulinum toxin (BoTx) type A with those of surgical denervation on the development of tetrodotoxin (TTX) resistant action potentials and of extrajunctional acetylcholine (ACh) receptors in rat and mouse skeletal muscle.

2. After surgical denervation, TTX resistant action potentials were present in all fibres on the third day and their rate of rise and amount of overshoot reached peak values at the fifth day. BoTx poisoning failed, despite causing complete paralysis, to induce TTX resistant action potentials in all fibres and their average rate of rise was at all times (4‐12 days) only about half that in denervated fibres. Similarly BoTx poisoning induced a smaller increase than surgical denervation in the number of extrajunctional ACh receptors, measured as 3H‐labelled Naja naja siamensis α‐neurotoxin binding sites.

3. Surgical denervation of BoTx poisoned muscles induced TTX resistant action potentials in all fibres and their rate of rise and amount of overshoot were 2‐3 times those in BoTx poisoned muscles only. Denervation also significantly increased the binding of labelled α‐neurotoxin. These effects of denervation were prevented by the administration of actinomycin D, a blocker of protein synthesis.

4. Administration of the α‐neurotoxin to BoTx poisoned animals resulted in the appearance of TTX resistant action potentials in all fibres and in a significant increase in their rate of rise and overshoot.

5. The results show that, despite causing complete paralysis, BoTx is less effective than surgical denervation in inducing denervatory changes in skeletal muscle. This suggests that the BoTx poisoned nerve has an influence which suppresses the appearance of denervation signs. Since the α‐neurotoxin blocked this influence remaining release of ACh, quantal or non‐quantal, may be responsible for this neurotrophic action.
A role for extraocular afferents in post‐critical period reversal of monocular deprivation.
Authors: Crewther D P , Crewther S G , Pettigrew J D
Published: December 2014

1. In order to investigate the phenomenon of acute reversibility of cortical ocular dominance, pressure block of the retinal ganglion cells and local anaesthetic block of the extraocular afferents were applied to the normal eye of six monocularly deprived cats. 2. Neither pressure blinding nor retrobulbar anaesthesia alone produced a significant increase in the proportion of single neurones recorded from area 17 which could be driven by the deprived eye. 3. Following combined pressure blinding and retrobulbar blockade, sixty‐four cells (54% of all encountered) could be stimulated through the deprived eye. 4. Of the sixty‐four cells driven by the deprived eye following both treatments a number showed direction (thirty) and orientation (thirteen) selectivity, but the majority showed non‐specific receptive field properties. 5. In four separate cases, out of the nine where the experiment could be carried out, it was possible to observe an individual neurone shift its ocular dominance. In the presence of a retrobulbar block, the four neurones could be driven first by the experienced eye alone, then by the deprived eye alone, and finally by the experienced eye again, all within a few minutes of the introduction and removal of pressure blinding. 6. These findings support previous studies which have revealed the presence of significant numbers of potentially functional cortical inputs from the deprived eye. Our new finding is that removal of tonic activity from the experienced eye, while it seems to be necessary to reveal these inputs, is not sufficient. An additional role in this phenomenon is played by extraocular afferents, possibly those involved in proprioception from the eye muscles.
Control of water content of respiring kidney slices by sodium chloride and polyethylene glycol
Authors: Robinson J. R.
Published: December 2014

1. Cortical slices from kidneys of adult rats were incubated for 1 and 2 hr at 25 °C in oxygenated solutions containing 5 m
M‐K, 2·5 m
M‐Ca and Mg, 0·007
M‐phosphate buffer (pH 7·4) and 5 m
M‐glucose, together with 1, 2, 4 and 6% polyethylene glycol (PEG 6000) and 46, 92, 123, 154 and 231 m
M‐NaCl.

2. There were no significant differences in water content between slices incubated for 1 and for 2 hr.

3. The slices contained more water when the concentration either of NaCl or of PEG 6000 was lower.

4. Larger increases in the contribution of NaCl to total osmolarity were required to prevent increases in water content accompanying relatively small reductions in the contribution of PEG 6000. At a physiological salt concentration around 300 m‐osmole/l., it took 10 m‐osmole/l. of additional NaCl to compensate for the loss of 1 m‐osmole/l. PEG 6000 and keep the volume of cell water normal.

5. The much greater contribution, osmole for osmole, which PEG 6000 made to tonicity suggests that metabolic activity failed to make the cell membranes effectively semipermeable; they were still substantially permeable to NaCl.

6. Comparison with earlier results suggested that ionic strength affected colloid osmolarity similarly in respiring and in non‐metabolizing cells; and that respiration at 25 °C somehow kept the concentration of diffusible solutes in the cells sufficiently lower than outside to compensate for a swelling effect of intracellular colloid osmolarity which, in the absence of metabolism, could be balanced by 20 m‐osmole/l. PEG 6000 added to the medium.
Two types of vagal preganglionic motoneurones projecting to the heart and lungs
Authors: McAllen R. M. , Spyer K. M.
Published: December 2014

1. A study has been made of eighty‐four cells in the cat's nucleus ambiguus whose axons projected to the cardiac (seventy‐four) and pulmonary (ten) branches of the right vagus. Their axonal conduction velocities were all in the range of B fibres (2·8‐15·5 m/sec).

2. Pulmonary branch projecting neurones were usually spontaneously active (nine out of ten) and fired in phase with inspiration. Their activity showed no pulse modulation.

3. Ten cardiac branch projecting neurones had properties indistinguishable from those of pulmonary branch projecting neurones. Inspiratory‐firing cells projecting to either branch are believed to be bronchoconstrictor in function.

4. The remaining sixty‐four cells that projected to the cardiac branch had properties expected of cardioinhibitory neurones. Most (fifty‐four) were silent until activated by ionophoresis of excitant amino acids. All showed an expiratory discharge when active, and of twenty‐seven tested twenty‐three showed a cardiac modulation of their discharge. When the aortic baroreceptors were denervated, the cardiac rhythm was always abolished reversibly by carotid occlusion.

5. Ionophoretic activation of expiratory firing (presumed cardioinhibitory) cells slowed the heart (fifteen out of eighteen neurones tested). Excited inspiratory‐firing cells never had this effect (eleven tested).

6. Both types of neurones were found in the nucleus ambiguus, but presumed cardioinhibitory cells tended to be found more caudally and ventrally than presumed bronchoconstrictor neurones.
Spontaneous multiquantal release at synapses in guinea‐pig hypogastric ganglia: evidence that release can occur in bursts.
Authors: Bornstein J C
Published: December 2014

1. A study was made of some properties of the spontaneous synaptic potentials recorded in cells of the hypogastric ganglia of guinea‐pigs. 2. The distribution of the amplitudes of the spontaneous synaptic potentials arising from a single preganglionic fibre was found to be multimodal, with peaks at roughly integral multiples of a unit peak. 3. It was found that the amplitudes of the larger spontaneous potentials were consistent with them being the result of synchronous or near‐synchronous release of two or more unit‐sized quanta (multiquantal release). 4. The proportion of multiquantal potentials observed was found to be dependent on the extracellular calcium ion concentration. 5. When the stochastic properties of the spontaneous potentials were examined, it was found that the spontaneous release process was not random and independent but appeared to be clustered. Indeed, the probability of occurrence of a unit spontaneous synaptic potential was greatly enhanced during the 40‐‐60 msec immediately following any given spontaneous synaptic potential. 6. When unit spontaneous potentials were excluded from the analysis, the multiquantal potentials were still found to be clustered although the clustering was less marked than that seen in the over‐all process. 7. These results suggested that the multiquantal spontaneous potentials arose from the release of unit quanta in short high frequency bursts and it was found that a mathematical model incorporating such a mechanism could describe the spontaneous quantal release process.
Observations on the elimination of polyneuronal innervation in developing mammalian skeletal muscle.
Authors: O'Brien R A , Ostberg A J , Vrbová G
Published: December 2014

1. The mechanism responsible for the elimination of polyneuronal innervation in developing rat soleus muscles was studied electrophysiologically and histologically. 2. Initially all the axons contacting a single end‐plate have simple bulbous terminals. As elimination proceeds one axon develops terminal branches while the other terminals remain bulbous and may be seen in contact with, or a short distance away from, the end‐plate. It is suggested that the branched terminal remains in contact with the muscle fibre while the other terminals withdraw. 3. At a time when polyneuronal innervation can no longer be detected electrophysiologically, the histological technique still shows the presence of end‐plates contacted by more than one nerve terminal. 4. The effect of activity on the disappearance of polyneuronal innervation was examined. Activity was increased by electrical stimulation of the right sciatic nerve. This procedure also produced reflex activity in the contralateral limb. In both cases polyneuronal innervation was eliminated more rapidly in the active muscles. 5. The finding that proteolytic enzymes are released from muscles treated with acetylcholine (ACh), and the observation of the more rapid elimination of supernumerary terminals at the end‐plates of active muscles, lead to the suggestion that superfluous nerve‐muscle contacts are removed by the proteolytic enzymes in response to neuromuscular activity. The selective stabilization of only one of the terminals is discussed in the light of these results.
Receptive field organization of complex cells in the cat's striate cortex.
Authors: Movshon J A , Thompson I D , Tolhurst D J
Published: December 2014

1. All complex cells in the cat's striate cortex exhibit gross non‐linearities of spatial summation when tested with sinusoidal grating stimuli. Their responses to moving gratings of all but the lowest spatial frequencies are usually dominated by a component that is not modulated by the passage of the bars of the grating across the receptive field. They give responses to temporally modulated stationary gratings that consist mostly of even harmonics of the stimulus frequency and that vary little in amplitude or wave form as the spatial phase of the grating is varied. 2. We compared complex cells' receptive fields with their sensitivity to sinusoidal gratings of different spatial frequencies. Qualitatively, the receptive fields are usually two to five times wider than the bars of the gratings that stimulate them most effectively. Quantitatively, the receptive field profiles of complex cells are invariably broader than those predicted by Fourier synthesis of their spatial frequency tuning curves, and in particular lack predicted spatially antagonistic regions. 3. We further examined the receptive field organization of these cells, using pairs of stationary lines flashed synchronously on their receptive fields. If both lines are of the same polarity (bright or dark), complex cells respond to the paired stimulus much less well than they do to either of its component bars, unless the bars are separated by less than about one quarter of the width of the receptive field. If the lines are of opposite polarity, one bright and one dark, the opposite situation obtains: closely spaced bars elicit small responses, while paired bars of larger separation are much more effective. In either case, the results are independent in general character of the absolute positions of the stimuli within the receptive field; rather, they depend in a manner characteristic of each cell on the relative positions of the two bars. 4. The two‐line interaction profile that plots the change in a complex cell's response to one bar as a function of the position of a second added bar corresponds closely to the receptive field profile predicted from Fourier synthesis of the cell's spatial frequency tuning curve. These profiles may thus reveal the spatial characteristics of subunits within complex cell‐receptive fields. We examined the nature of the interaction between these subunits by performing several two‐line interaction experiments in which the onset of the second bar was delayed some time after the onset of the first. The results suggest that neighbouring subunits interact in a facilitatory fashion: for an interval after the presentation of one bar, responses to neighbouring bars are enhanced. 5. The subunits of a complex receptive field may, by their spatial properties, determine the spatial selectivities of complex cells, while the nature of the interaction among the subunits may determine these cells' sensitivity and selectivity for moving visual stimuli...
Spatial and temporal contrast sensitivity of neurones in areas 17 and 18 of the cat's visual cortex.
Authors: Movshon J A , Thompson I D , Tolhurst D J
Published: December 2014

1. We have examined the spatial and temporal tuning properties of 238 cortical neurones, recorded using conventional techniques from acutely prepared anaesthetized cats. We determined spatial and temporal frequency tuning curves using sinusoidal grating stimuli presented to each neurone's receptive field by a digital computer on a cathode ray tube. 2. We measured tuning curves either by determining response amplitude as a function of spatial or temporal frequency, or by measuring contrast sensitivity (the inverse of the contrast of the grating that just elicited a detectable response). The two measures give very similar tuning curves in all cases. 3. We recorded from 184 neurones in area 17; of these 156 had receptive fields within 5 degrees of the area centralis. The range of preferred spatial frequency for these neurones was 0.3‐‐3 c/deg, and their spatial frequency tuning band widths varied from 0.7 to 3.2 octaves at half‐amplitude. The most common band width was roughly 1.3 octaves. Simple and complex cells in area 17 did not differ in their distributions of preferred spatial frequency, although complex cells were, on average, slightly less selective for spatial frequency than simple cells. 4. We recorded from fifty‐four neurones from area 18, and performed several experiments in which we recorded from corresponding portions of both area 17 and area 18 in the same electrode penetration. Neurones in area 18 preferred spatial frequencies that were, on average, one third as high as those preferred by area 17 neurones at the same retinal eccentricity. Thus the range of preferred spatial frequency in area eighteen cells having receptive fields within 5 deg of the area centralis was between less than 0.1 and 0.5 c/deg. The distributions of optimum spatial frequency in the two areas were practically non‐overlapping at eccentricities as high as 15 deg, the greatest eccentricity we examined. Neurones in area 18 were about as selective for spatial frequency as were neurones in area 17. 5. We determined temporal frequency tuning characteristics for some neurones from each area, using gratings that moved steadily across the screen. Neurones from area 17 all responded well to low temporal frequencies, and less well to higher frequencies (in excess of, usually, 2 or 4 Hz). In contrast, neurones recorded from area 18 sometimes had similar tuning properties, but more commonly showed a pronounced reduction in response as the temporal frequency was moved either above or below some optimum value (usually 2‐‐8 Hz). 6. We conclude from these results that areas 17 and 18 act in parallel to process different aspects of the visual information relayed from the retina via the lateral geniculate complex. Some or all of the differences between the areas may be attributable to the predominance of Y cell input to area 18 and the predominance of X cell input to area 17...
Gastrins in cat and dog: evidence for a biosynthetic relationship between the large molecular forms of gastrin and heptadecapeptide gastrin.
Authors: Rehfield J F , Uvnäs-Wallensten K
Published: December 2014

1. Extracts of antral, duodenal and jejunal mucosa contained the same concentrations and molecular forms of gastrin in cat and dog. In both species component III constituted 93%, component II 4% and components I and IV each 1% of the total immunoreactivity. 2. During electrical vagal stimulation or feeding in (a) anaesthetized cats with ligated kidney vessels and resected jejunum and ileum, (b) anaesthetized normal cats or (c) conscious normal cats, release of the large molecular forms of gastrin, components I and II, was not detectable. 3. Luminal perfusates of cat antrum contained only component III and occasionally less than 2% of component IV. 4. Intravenous injections into conscious cats of components I, II and III isolated from cat antrum revealed a significantly slower elimination of the large components (t1/2 approximately 4.2 and 4.0 min respectively) than of component III (t1/2 approximately 1.1 min). Thus the absence of components I and II in cat blood cannot be due to rapid degradation. 5. During feeding, components I and II constituted 20% of the total gastrin immunoreactivity in antral venous blood of dogs. This amount is sufficient to account for the predominance of large components in peripheral venous blood in dogs considering their slow metabolic clearance rates. 6. Luminal perfusates of dog antrum contained components I, II and III in proportions corresponding to those found in antrum. 7. The results indicate that components I and II are synthesized in the same proportions in gastrin cells of cat and dog. In the cat, components I and II are, however, never released from the cells. Since these components contain heptadecapeptide gastrin within their sequeaces, they probably represent biosynthetic precursors of the principal gastrin, the heptadecapeptide (component III). The predominance of component III in gastric juice suggests that the feline gastrin cell secretes only component III, which degrades to component IV in blood.
A quantitative analysis of the effects of 2,3‐diphosphoglycerate, adenosine triphosphate and inositol hexaphosphate on the oxygen dissociation curve of human haemoglobin.
Authors: Goodford P J , St-Louis J , Wootton R
Published: December 2014

1. Oxygen dissociation curves have been measured for human haemoglobin solutions with different concentrations of the allosteric effectors 2,3‐diphosphoglycerate, adenosine triphosphate and inositol hexaphosphate. 2. Each effector produces a concentration dependent right shift of the oxygen dissociation curve, but a point is reached where the shift is maximal and increasing the effector concentration has no further effect. 3. Mathematical models based on the Monod, Wyman & Changeux (1965) treatment of allosteric proteins have been fitted to the data. For each compound the simple two‐state model and its extension to take account of subunit inequivalence were shown to be inadequate, and a better fit was obtained by allowing the effector to lower the oxygen affinity of the deoxy conformational state as well as binding preferentially to this conformation.
A comparison of current‐voltage relations for full and partial agonists.
Authors: Adams P R , Sakmann B
Published: December 2014

1. Local conductance changes produced by various bath‐applied agonists at frog end‐plate membrane were measured using focal recording of extracellular potential in voltage‐clamped muscle fibres. The potential difference between a focal micropipette placed on the nerve terminal and another micro‐pipette placed on or near inactive membrane was taken as proportional to the agonist‐induced current through a small patch of an end‐plate membrane. 2. The current‐voltage (I‐‐V) relation of active membrane was obtained directly by increasing the membrane potential in a ramp fashion. The change in membrane potential was slow enough for post‐synaptic gating processes to reach equilibrium during the ramp. 3. During application of sufficiently low concentrations of full agonists (carbachol, (ACh) and partial agonists (choline and decamethonium) the I‐‐V relation of end‐plate membrane showed strong curvature in the range of ‐60 to ‐130 mV. The slope of I‐‐V relations increased exponentially with membrane hyperpolarization, an e‐fold change in conductance occurring for about 50 mV potential shift. 4. The curvature of the I‐‐V relation of end‐plate‐membrane activated by the partial agonists choline and decamethonium became less as the agonist concentration was increased, and with high concentrations (choline 15 mM; decamethonium 250 micrometer) the I‐‐V relation became almost straight. 5. When end‐plate currents produced by high concentrations of partial agonists were matched by application of equi‐active concentrations of carbachol, the carbachol‐activated membrane still showed as much curvature in its I‐‐V relation as when low concentrations of carbachol were used. 6. Choline and decamethonium concentrations for which the I‐‐V relation was straight produced much greater depression of miniature end‐plate currents than did carbachol concentrations which produced the same membrane current at the holding potential. 7. I‐‐V relations for full agonists at high concentrations were obtained after alpha‐bungarotoxin pre‐treatment. During application of carbachol (400‐‐500 micrometer) and ACh (30‐‐40 micrometer; after complete inhibition of acetylcholinesterase activity) the I‐‐V relation of end‐plate membrane is much less curved than during application of low concentrations. 8. It is concluded that either the voltage sensitivity of agonist‐induced end‐plate conductance reflects voltage sensitivity of agonist binding, or the partial agonists used can exert a voltage‐dependent 'local anaesthetic' action in addition to their agonist activity.
Amino acid and peptide absorption from partial digests of proteins in isolated rat small intestine.
Authors: Gardner M L
Published: December 2014

1. Absorption of each of sixteen amino acids, free and peptide‐bound, has been measured in isolated rat small intestine perfused with five partial digests of proteins. 2. At low concentrations net absorption of each amino acid was proportional to its luminal concentration and independent of the nature of the amino acid. 3. A series of first‐order multiple regressions was found to describe well the characteristics of absorption. 4. Rate constants for disappearance of free and peptide‐bound amino acids from the lumen were closely similar. However, substantial back‐flux occurred of amino acids derived from peptide hydrolysis. Hence 60‐70% of the amino‐N entering the serosal tissue fluid probably had left the lumen as free amino acids. 5. Intact peptides crossed the mucosa during absorption from a soy bean hydrolysate and in substantial quantities during absorption from one casein digest but not from another. With other hydrolysates there was no evidence for passage of peptides to the serosa. 6. In several cases there was a serious discrepancy between the amount of amino‐N absorbed from the lumen and the amount accounted for as peptide or free amino acid in the serosal secretion. 7. The characteristics of absorption were similar (apart from the exceptions in 5 above) for all the digests studied except for soy bean hydrolysate.
A comparison of threshold and suprathreshold appearance of gratings with components in the low and high spatial frequency range
Authors: Campbell F. W. , Howell E. R. , Johnstone J. R.
Published: December 2014

1. The appearance of square gratings with some of their Fourier components missing has been investigated for both threshold and suprathreshold contrasts.

2. If high frequency components are removed from a square grating there is only a very small effect on the detection threshold, or suprathreshold appearance, unless the components are visible by themselves.

3. If the fundamental frequency is removed from a square‐wave grating which has a spatial frequency lower than 1 cycle per degree (c/d) the contrast sensitivity is not altered. This is a generalisation of the Craik‐Cornsweet illusion. If the contrast is raised above the detection threshold the grating is indistinguishable from a square grating, unless the contrast is high enough to see the fundamental when it is presented alone.

4. If the fundamental is removed from a square grating which has a spatial frequency higher than 1 c/d the contrast threshold and the appearance at all contrasts are changed. At threshold it appears as a sinusoidal grating of three times the fundamental frequency. The threshold is dictated solely by the amplitude of the third harmonic. If the contrast is further raised, so that the fifth harmonic also reaches threshold, the periodictiy of the fundamental is seen.

5. Therefore, gratings of many different luminance profiles (including the Craik‐Cornsweet profile) all produce the perception of a square grating simply because those missing components which would be required in each case to produce a perfect square are by themselves undetectable. The visual system responds as though hardwired to detect square gratings and edges by means of quasi‐Fourier analysis.

6. These results are analagous to the missing fundamental, or residue, effect in hearing.
Nucleoside and glucose transport in erythrocytes from new‐born lambs
Authors: Mooney Nuala A. , Young J. D.
Published: December 2014

1. Glucose and inosine transport by erythrocytes from new‐born lambs and adult sheep were compared. Uptake of both permeants was considerably faster in the new‐born. Inosine uptake by erythrocytes from nucleoside‐permeable and impermeable lambs were not significantly different at birth. The difference between the two phenotypes was first apparent 30 days after birth.

2. The post‐natal changes in glucose and inosine transport activity closely paralleled the progressive decrease in the percentage of fetal erythrocytes (i.e. cells containing fetal haemoglobin) in the circulation. Cell fractionation studies confirmed that the permeability changes were directly related to changes in the relative proportions of fetal and adult haemoglobin containing erythrocytes.

3. The results demonstrate that fetal cells are highly permeable to both glucose and inosine. These cells are replaced by erythrocytes which contain adult haemoglobin and which have a much lower, but still significant, glucose permeability and either low or negligible inosine transport activity depending on the genotype of the animal.

4. Inosine transport by fetal erythrocytes from both nucleoside‐permeable and impermeable animals was mediated by a nucleoside transport system which had similar properties to that responsible for nucleoside transport in adult nucleoside‐permeable cells. Glucose transport in both fetal and adult cells was highly stereo‐specific, indicating the presence of a selective transport system.

5. It is suggested that the regulatory mechanism responsible for initiating the switch from fetal to adult haemoglobin synthesis may also be responsible for the changes in glucose and nucleoside transport activity.
Further observations on back‐firing in the motor nerve fibres of a muscle during twitch contractions.
Authors: Buller A J , Proske U
Published: December 2014

1. The tension developed by a muscle in response to a single supramaximal nerve volley is often the sum of two contractions, the second resulting from re‐excitation of some nerve terminals during the first contraction. Re‐excitation or back‐firing can be prevented if the muscle nerve is stimulated twice with the second volley arriving in the muscle at a time when muscle fibres are still refractory following the first volley (Brown & Matthews, 1960). 2. Back‐firing has been studied here in the medial gastrocnemius muscle of the spinal cat and responses have been recorded, either representing the summed activity of the muscle's motor supply or discharges of single functional motor axons. 3. When stimulating at a distance from the muscle, the second of two shocks is effective in suppressing back‐firing over a narrower range of stimulus intervals than when stimulating close to the muscle. 4. The amount of back‐firing can be reduced by stretching the muscle. At a length corresponding to the optimum for a twitch little if any back‐firing remains. 5. Measurements of threshold to electrical stimulation of single functional motor axons suggests that low threshold axons are more likely to show back‐firing. In the majority of cases, most or all of the motor units in the muscle have to be active before back‐firing can be observed.
Acid secretion by isolated canine gastric mucosa.
Authors: Kuo Y J , Shanbour L L
Published: December 2014

1. An isolated gastric mucosal preparation from the dog stomach which is capable of acid secretion is described. Average values for normal resting potential difference (p.d.) was 49 +/‐ 2 mV (mucosal side negative with respect to the serosal side), short‐circuit current (Isc) was 172 +/‐ 4 muA and resistance (R) was 285 +/‐ 6 omega.cm2. Low rates of spontaneous acid secretion (0‐0.58 muequiv/cm2.hr) were present initially but following short‐circuiting of the tissue these values decreased to low levels (less than 0.1 muequiv/cm2.hr) within an hour. 2. Histamine in doses exceeding 10(‐6)M stimulated acid secretion, increased Isc and decreased R. Concentrations ranging from 10(‐5) to 8 X 10(‐4)M produced maximal secretion. The maximal secretory rate achieved was 4.24 +/‐ 0.35 muequiv/cm2.hr. 3. Pentagastrin (10(‐8)M) and acetylcholine (10(‐6)‐‐10(‐5)M) also stimulated acid secretion with a lower maximal secretion as compared to histamine stimulation. These concentrations of pentagastrin and acetylcholine did not alter histamine stimulated acid secretion. Higher concentrations of pentagastrin (10(‐6)M) and acetylcholine (10(‐4) M) reversibly inhibited acid secretion of histamine stimulated mucosa. 4. These results demonstrate that there are many similarities between in vitro and in vivo findings on the dog stomach, indicating the great potential of the in vitro dog gastric mucosa for studies on the mechanism of action and interaction of gastric secretagogues.
The effect of distension of the pulmonary vein‐atrial junction on activity of left atrial receptors
Authors: Kidd C. , Ledsome J. R. , Linden R. J.
Published: December 2014

1. In anaesthetized dogs, the activity from left atrial receptors with vagal afferent fibres has been examined during distension of small balloons in the pulmonary veins or the application of pulsatile pressures to an isolated perfused pouch of the left atrium.

2. Eleven fibres were found in nineteen dogs. The receptors discharging into these fibres were located, post mortem, to the atrial endocardium and reasons are given for believing that these fibres were myelinated and the receptors were B or Intermediate.

3. Distension of small balloons induced significant increases in the discharge of action potentials from the receptors, the increases were similar to those after infusions of saline or dextran.

4. In the perfused pouch the ‘dynamic’ thresholds for pulsatile pressure were high as were the mean and pulsatile pressures required to induce bursts of action potentials similar to those observed from atrial receptors in the atrium of normal size. Restoration of the atrium to its normal size resulted in ‘dynamic’ thresholds and responses to changes in pressure within the normal range. The changes could be explained assuming the Laplace relationship.

5. This evidence supports the conclusion from previous investigations in which these techniques were used, that the increase in discharge in atrial receptors with myelinated vagal fibres could be the cause of the increase in heart rate and urine flow.
Relation of potassium transport to oxidative metabolism in isolated brain capillaries
Authors: Goldstein Gary W.
Published: December 2014

1. The uptake of K by a capillary suspension isolated from rat brain was studied with the radioactive analogue 86Rb.

2. Rb uptake was dependent upon the presence of oxygen and could be markedly inhibited with ouabain.

3. The ouabain sensitive Rb uptake was measured at varying external concentrations of K. Uptake of K (as 86Rb) was half‐maximal when the K concentration was 3·0 m
M. This in vitro affinity of the transport carrier for K is similar to that found in previous in vivo studies of K efflux from brain to blood.

4. I propose that the ouabain sensitive K pump is located on the antiluminal plasma membrane of brain capillary endothelial cells and that this pump contributes to the maintenance of a constant concentration (i.e. 3 m
M) of K in brain interstitial fluid.

5. Glucose and palmitate were tested as possible energy substrates for the support of active Rb uptake by isolated brain capillaries. The rate of Rb uptake increased 40% when 0·25 m
M‐palmitate was added to a capillary suspension containing 5 m
M‐glucose. This stimulation of Rb uptake could be blocked by 1 m
M‐4‐pentenoic acid, an inhibitor of fatty acid oxidation. In contrast, the fraction of Rb uptake supported by glucose was not altered by 4‐pentenoic acid.

6. The rates of [U‐14C]glucose and [U‐14C]palmitate oxidation to CO2 were measured in isolated brain capillaries and compared to their oxidation by brain slices and synaptosomes. Palmitate was the source of 28% of the 14CO2 produced by the capillaries but only 0·5% of the 14CO2 produced by the brain slices and synaptosomes.

7. It is concluded that brain capillaries are similar to renal tubules in their polar distribution of ouabain sensitive K transport carriers, dependence on oxidative metabolism for active ion transport, and use of fatty acids as energy substrates. These features may underlie the vulnerability of brain capillaries in several metabolic diseases that cause brain oedema.
An analysis of the inhibitory post‐synaptic current in the voltage‐clamped crayfish muscle.
Authors: Onodera K , Takeuchi A
Published: December 2014

1. Inhibitory post‐synaptic currents (i.p.c.s) were recorded from the feed‐back current through a wire electrode inserted longitudinally into the opener muscle fibre of the claw in the crayfish (Cambarus clarkii). 2. I.p.s.c. rose to its peak in about 3‐4 msec and decayed approximately exponentially. The decay time constant at ‐100 mV was 9.4 msec. 3. The decay time constant decreased as the membrane was hyperpolarized and increased during depolarization. The time constant (tau) depends on voltage (V) according to the relation tau = a exp (AV), with a = 18.6 msec and A = 0.0065 mV‐1. Voltage dependence was opposite in direction to that seen at frog end‐plates, but in the same direction as that of e.p.s.c. in crayfish muscle. 4. At lower temperatures, the rise and fall times of i.p.s.c.s were prolonged. Q10 for the decay time constant was 2.4 between 22.6 and 12.5 degrees C. 5. When pH was decreased from 7.2 to 5.5, the decay time constant increased by about 50%, with little change in the voltage dependence of the time course. 6. When chloride in the solution was changed to iodide, the decay time constant was increased by a factor of 3, while voltage dependence of the time course was not changed. In bromide solution the decay time constant increased by about 50%. 7. Peak amplitudes of i.p.s.c.s were approximately linear as the membrane was depolarized, but they levelled off as the membrane was hyperpolarized beyond reversal potential. The non‐linear I‐V relation did not result from inadequate voltage clamping, nor from a change in the inside concentration of chloride. After equilibration with iodide solution the I‐V relation was approximately linear. 8. The decay time constant was increased after repetitive nerve stimulation. This prolongation became more pronounced at lower temperatures. 9. The kinetic process of the transmitter action is discussed. It is suggested that the rate limiting process for i.p.s.c. is binding and unbinding of the transmitter to the receptor.
Ion‐concentration dependence of the reversal potential and the single channel conductance of ion channels at the frog neuromuscular junction.
Authors: Lewis C A
Published: December 2014

1. The acetylcholine‐sensitive ionic channels at the neuromuscular junction were studied in voltage‐clamped single muscle fibres from a monolayer preparation of the cutaneous pectoris muscle from Rana pipiens. The experimental observations were of three types: (a) reversal potential as a function of external Na and Ca concentrations, (b) the single channel conductance (gamma) from noise analysis as a function of these same concentrations, and (c) gamma as a function of membrane potential. 2. The reversal potential in normal Na Ringer was ‐3.8 +/‐ 0.5 mV (+/‐ S.E. of mean, n = 22) and decreased approximately linearly as the logarithm of the outside Na activity as this activity decreased to 10% of normal. 3. The single channel conductance in normal Na Ringer was 27.5 +/‐ 0.7 pS (n = 28) and reached a limiting value close to 10 pS as Na was replaced with sucrose. 4. Increasing [Ca]o from 2 to 10 mM made the reversal potential more positive and decreased the single channel conductance. Mg caused similar effects. 5. Various theories that have been used to describe the mechanism of ion permeation through e.p.c. channels were tested. Constant field theory (eqns. (3), (4) and (5)), a modified Takeuchi approach (eqn. (6)), and a single barrier theory (eqns. (8), (9) and (10)) could not account for all of the experimental observations. 6. In particular, constant field theory, with no surface charge density, could account for the following: (a) the reversal potential measurements for solutions containing 2 mM‐Ca (with PK/PNa = 1.2 and PCa/PNa = 1.02), (b) the single channel conductance values for solutions containing 2 mM‐Ca and Na concentrations down to 20% of normal, (c) that gamma has little voltage dependence. 7. However, constant field theory, with no assumed surface charge density, could not account for the following: (a) the reversal potential observed for Ringer containing 80 mM‐Ca, (b) the gamma values observed for very low Na concentrations, (c) the observation that increasing Ca from 2 to 10 mM in a solution containing 75% normal Na results in a decrease in gamma. 8. From the failure of the Takeuchi approach (eqn. (6)), it is argued that ion interactions must occur at e.p.c. channels because ion flux independence is the only asumption in the derivation of eqn. (6) without experimental verification. 9. The ion interactions at e.p.c. channels probably include both surface charge effects and competition for a binding site.
Signal transmission from red cones to horizontal cells in the turtle retina.
Authors: Normann R A , Perlman I
Published: December 2014

1. Intracellular recordings were made from L‐type horizontal cells in the retina of the turtle Pseudemys scripta elegans. The responses were evoked by 500 msec pulses of 'white' light. 2. L‐type horizontal cells were classified as either, 'small receptive field' s.r.f. or 'large receptive field' l.r.f. based upon (1) receptive field size and (2) kinetics of responses to test flashes covering small and big spots. 3. Constant illumination of the entire receptive field, with any intensity studied, evoked a response that reached a peak and then slowly sagged back to a steady‐state level that was about half the peak response. 4. Termination of backgrounds resulted in a very fast recovery of the membrane potential that overshot the dark‐adapted potential. This 'off' response had faster kinetics in horizontal cells than in red cones. 5. The intensity‐response curve measured around any background intensity was shifted along the log intensity axis toward higher test intensities. The curves obtained under light‐adapted conditions were sharper than the curve measured in the dark‐adapted state. 6. The photoresponses of red cones and s.r.f. horizontal cells were compared under similar states of adaptation. In the dark‐adapted state of the gain, expressed as the millivolt change in the horizontal cell per millivolt change in the cone, was not linearly related to cone potential, and was highest for dim stimuli. Light‐adaption modified the synaptic transmission to make the horizontal cells most sensitive to light modulation around the background illumination. 7. The mechanisms by which signal transmission can be modified by light‐adaptation are discussed in terms of transmitter release by the presynaptic terminals and its binding to post‐synaptic sites.
The measurement and dynamic implications of thin filament lengths in heart muscle.
Authors: Robinson T F , Winegrad S
Published: December 2014

1. The lengths of the thin filaments in amphibian and mammalian cardiac muscle have been determined from electron micrographs of serial transverse sections. Thin filament lengths in frog atrial trabeculae range from 0.8 to greater than 1.3 micrometers, with a maximum possible error of 0.14‐‐0.15 micrometer. In rat atrial tissue the span is from 0.6 to more than 1.1 micrometer, whereas in rat papillary muscle the breadth of the distribution is much narrower, from 0.9 to greater than 1.1 micrometer. Double overlap of thin filaments should, therefore, exist over a wide range of sarcomere lenghts. Thin filaments from opposite halves of a sarcomere accommodate each other by flexing up to an angle of about 2 degrees and moving from the trigonal position among the thick filaments to the centre of the region between two thick filaments. Such rearrangement probably contributes to the internal resistance to shortening in the muscle. 2. Except for the variation in thin filament lengths, the over‐all morphology of the cardiac sarcomere is generally similar to that found in skeletal muscle. Thick filaments in heart muscle are uniform in length, and their profiles change along their lengths. They are generally round in the M band, triangular adjacent to the M band, round again in the overlap region, and either round or triangular near the tapered tips. The M bridges in rat cardiac tissue link neighbouring thick filaments to form a symmetric hexagonal array, whereas in the frog atrium, the M bridge connexions are incomplete and often form isolated triangular clusters. 3. Computed sarcomere length‐developed tension curves were calculated using the thin filament length distributions and the assumptions basic to the sliding filament theory of muscle contraction. The curves for atrial tissue have plateau regions approximately as wide as the one‐half micron variation in thin filament length. 4. Work done against the internal loads during systole may be stored as potential energy and released during diastole to produce sarcomeric re‐extension.