bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of antidiuretic hormone and state of potassium balance on the renin‐angiotensin system in rats with diabetes insipidus.
Authors: Fernández‐Repollet E , Maldonado M M , Opava‐Stitzer S
Published: December 2014

1. The influence of ADH and the state of potassium balance on the renin‐angiotensin system was studied in rats with hereditary diabetes insipidus (DI rats). 2. Plasma renin concentration in DI rats was higher than in control Long‐Evans rats. 3. Spontaneous reversal of the hypokalaemia normally found in DI rats did not reduce plasma renin concentration (p.r.c.), suggesting that potassium deficiency does not contribute significantly to the elevation of p.r.c. in DI rats. Similarly, a low potassium diet failed to further increase p.r.c. in DI rats. 4. In contrast, the p.r.c. of DI rats was significantly diminished by a high potassium intake both in the presence and absence of ADH. A highly significant inverse correlation was found between p.r.c. and urinary potassium excretion in both ADH‐treated and untreated DI rats on low, normal and high potassium diets. 5. Plasma renin concentration was significantly lower in ADH‐treated than in untreated DI rats on a high potassium intake, suggesting that the inhibitory effects of ADH and potassium are additive. 6. ADH consistently reduced p.r.c. in DI rats independent of the state of potassium balance. 7. ADH and potassium may inhibit renin secretion via different mechanisms of action.
Trophic action of epidermal growth factor on the pancreas and gastroduodenal mucosa in rats.
Authors: Dembiński A , Gregory H , Konturek S J , Polański M
Published: December 2014

1. Epidermal growth factor (EGF) infused subcutaneously in a dose of 10 micrograms/kg . h but not 1 microgram/kg . h inhibited spontaneous gastric acid and pepsin secretion, whereas when given intragastrically in a dose of 10 micrograms/kg . h it failed to affect this secretion. 2. EGF injected intraperitoneally at 8 h intervals for 24 h significantly stimulated DNA synthesis in the gastroduodenal mucosa and the pancreas, whereas when administered intragastrically it stimulated DNA synthesis only in the gastroduodenal mucosa but not in the pancreas. 3. Chronic parenteral administration of EGF significantly increased the DNA and RNA contents of the gastroduodenal mucosa and the pancreas. 4. This study demonstrates that parenteral EGF is a potent inhibitor of gastric secretion and trophic agent for the gastroduodenal mucosa and pancreas, and that the gastric inhibitory and trophic effects of EGF are the results of two separate mechanisms.
Reduced ATP concentration as a basis for synaptic transmission failure during hypoxia in the in vitro guinea‐pig hippocampus
Authors: Lipton Peter , Whittingham Tim S.
Published: December 2014

1. Experiments were performed to determine whether a decrease in tissue ATP contributes to the rapid failure of cerebral synaptic transmission during hypoxia. Transmission between the perforant path and the dentate granule cells in the in vitro hippocampus was studied.

2. Hippocampal slice ATP is decreased by ∼ 15% at the time that the evoked response begins to diminish in standard Krebs bicarbonate buffer. This is about 2 min after the onset of hypoxia.

3. When transmission failure is accelerated by increasing extracellular K+ from 4·4 to 13·4 mM, the evoked response begins to decay about 30 sec after exposure to hypoxia. There is no decrease in hippocampal slice ATP at this time.

4. However, ATP in the molecular layer (the synaptic region of the tissue) is decreased by ∼ 15% at the time the evoked response begins to decay in the slices exposed to elevated K+ concentration.

5. Exposing the hippocampal slice to 25 mM‐creatine for 3 hr elevates molecular layer phosphocreatine fourfold. Synaptic transmission during hypoxia survives three times as long as it does in the absence of creatine.

6. In the creatine fortified medium, molecular layer ATP no longer declines within 30 sec of hypoxia. However the molecular layer ATP does decline within 90 sec of hypoxia, the time at which the evoked response begins to decay in this creatine‐fortified buffer.

7. The results establish that ATP in the region of the active synapses is lowered when the first signs of electrophysiological failure appear during hypoxia. They also show that maintaining ATP for longer than normal during hypoxia is associated with a prolonged maintenance of the evoked response. They thus suggest that a decline in ATP is one factor causing hypoxic block of synaptic transmission.

8. It is further suggested that the very rapid failure of the electroencephalogram during anoxia may also result from a decline in ATP.
A quantitative study of skeletofusimotor innervation in the cat peroneus tertius muscle.
Authors: Jami L , Murthy K S , Petit J
Published: December 2014

1. Physiological tests were used to identify skeletofusimotor or beta axons to the cat peroneus tertius muscle in order to assess the proportion of beta axons in the motor supply to this muscle. 2. Static beta axons (beta S) were identified by: (a) observation of a delay between the complete block of extrafusal contraction and the failure of spindle activation upon prolonged stimulation, (b) increase of spindle excitation with stimulation frequencies above that eliciting maximal extrafusal contraction, (c) observation of 'unfused' frequencygram of spindle primary afferent discharge during stimulation of the axon at frequencies above that eliciting complete fusion of extrafusal contraction and (d) static action exerted on the response of the spindle afferent to ramp stretch. 3. Dynamic beta axons (beta D) were identified by the persistence of spindle activation after selective block of extrafusal neuromuscular junctions and by their dynamic action on spindle primary endings. 4. The actions of 116 motor axons (conduction velocity 56‐104 m/sec) on ninety‐five spindle afferents (fifty‐seven from primary and thirty‐eight from secondary endings) were examined in ten experiments. Thirty‐six beta axons (31% of the total sample) were identified: twenty‐four beta S (conduction velocity 69‐104 m/sec) and twelve beta D (conduction velocity 56‐91 m/sec). 5. Twenty (35%) primary endings were activated by a beta S and sixteen (28%) by a beta D axon. Nineteen (45%) secondary endings were activated by a beta S and five (13%) by a beta D axon. Convergence of beta D and beta S axons on the same spindle occurred in 10% of instances. beta‐innervated spindles were also supplied by gamma axons. 6. Most of the beta S motor units were of the fast‐fatigue resistant (FR) type, with a few units of the fast‐fatigable (FF) type, and nearly all the beta D motor units were of the slow (S) type.
Effects of environmental salinity on branchial permeability of rainbow trout, Salmo gairdneri.
Authors: Isaia J
Published: December 2014

1. The gill fluxes of various non‐electrolytes were measured in fresh‐water‐ and sea‐water‐adapted trout (Salmo gairdneri). The studies were performed in vitro with a ‘perfused‐head’ preparation. 2. The results allow one to specify different transepithelial pathways according to the physico‐chemical characteristics of the permeant molecules: (1) for hydrophilic the physico‐chemical characteristics of the permeant molecules: (1) for hydrophilic and lipophilic molecules of small molecular radius, a transcellular pathway in the respiratory cells of the secondary lamellae, (2) for hexose, all paracellular pathways in the gill epithelium, and (3) for hexose polymers (inulin, dextran), a transcellular pathway in the chloride cells of the primary lamellae. 3. The selectivity of the respiratory cells as a function of the liposolubility of the molecules tested is low. The decrease of this selectivity in the course of salt‐water adaptation taken together with the modification of lipid composition of membranes and the effect of adrenaline on the branchial permeability suggests that non‐electrolytes diffuse through a lipid phase able to form hydrogen bonds. 4. The high permeability of gills to hexose polymers of high molecular weight suggests a vesicular transport, especially in fish adapted to fresh water.
Ionic mechanism for the osmotically‐induced depolarization in neurones of the guinea‐pig supraoptic nucleus in vitro.
Authors: Abe H , Ogata N
Published: December 2014

1. Effects of hypertonic solutions prepared by adding NaCl or sucrose to Krebs solution on intracellular potentials were observed in neurones of the supraoptic nucleus using brain slices of the guinea‐pig hypothalamus. 2. Hypertonic solutions (306‐488 m‐osmole/kg) depolarized the membrane, increased the input resistance and augmented the spontaneous firing rate in supraoptic neurones, whereas cells in the hippocampus and anterior or ventromedial hypothalamus were not affected by the hypertonic solutions. 3. The excitatory action of hypertonic solutions on supraoptic neurones was retained in the medium containing 0 mM‐Ca2+ and 12 mM‐Mg2+. 4. Amplitude of the depolarization induced by superfusion of hypertonic solutions was voltage‐dependent. The reversal potential for the depolarization was about ‐90 mV. 5. The reversal potential for the depolarization induced by hypertonic solution shifted as a function of [K+]0. 6. These results suggest that the supraoptic neurones are themselves osmosensitive and that the local osmotic‐related information is transduced to neural signals in these cells by alteration in the membrane ionic permeability, probably due to suppression of K+ conductance.
Electrophysiological analysis of neuronal thermosensitivity in rat preoptic and hypothalamic tissue cultures.
Authors: Baldino F , Geller H M
Published: December 2014

1. Ninety‐six neurones in forty‐six explant tissue cultures of rat medial basal hypothalamus (m.b.h.) and preoptic area (p.o.a.h.) were subjected to thermal stimulation. 2. Neuronal response to temperature was determined on the basis of an extrapolated Q10 calculated from the regression line relating mean spontaneous activity to bath temperature. 3. Thermal stimulation (28‐41 degrees C) of p.o.a.h. cultures resulted in the identification of three distinct groups of neurones: (1) temperature‐insensitive (0.5 less than or equal to Q10 less than or equal to 2), (2) warm‐sensitive (Q10 greater than 2), and (3) cold‐sensitive (Q10 less than 0.5). 4. No temperature‐sensitive neurones were identified in m.b.h. cultures. 5. In the presence of a medium which effectively blocks synaptic transmission (12 mM‐Mg2+ and 0.25 mM‐Ca+) the sensitivity of both warm‐ and cold‐sensitive neurones was preserved. 6. These data indicate that thermosensitivity is a characteristic not only of the preoptic neuronal network in vitro but also is an intrinsic characteristic of individual neurones.
Peptidergic transmission in sympathetic ganglia of the frog.
Authors: Jan L Y , Jan Y N
Published: December 2014

1. A slow synaptic potential recorded in neurones of sympathetic ganglia of bullfrog, the late slow e.p.s.p., is probably mediated by a peptide resembling luteinizing hormone‐releasing hormone (LHRH), because (1). a LHRH‐like peptide is contained in preganglionic nerve terminals and is released upon nerve stimulation, (2) application of LHRH to ganglion cells mimics the effects of the natural transmitter for the late slow e.p.s.p., and (3) the pharmacological properties of LHRH and the natural transmitter for the late slow e.p.s.p. are similar. 2. Neurones in frog sympathetic ganglia are also depolarized by substance P. The substance P receptors, unlike the LHRH receptors or the post‐synaptic receptors for the late slow e.p.s.p., are not blocked by antagonist of LHRH. No cross‐desensitization was found between the substance P‐induced response and the LHRH‐induced response or the late slow e.p.s.p. 3. Substance P‐like immunoreactivity is contained in bundles of axons passing through the ganglia. This distribution is distinct from the distribution of LHRH‐like immunoreactivity in preganglionic nerve terminals. Thus, substance P receptors and substance P‐containing fibers are distinct from the post‐synaptic receptors and preganglionic fibers responsible for the late slow e.p.s.p. 4. Physiological and anatomical evidence is presented which indicates that the peptidergic transmitter for the late slow e.p.s.p. can diffuse for many micrometres before acting on ganglion cells.
The effects of atropine on [3H]acetylcholine secretion from guinea‐pig myenteric plexus evoked electrically or by high potassium
Authors: Alberts P. , Bartfai T. , Stjärne L.
Published: December 2014

1. The myenteric plexus‐longitudinal muscle preparation of the guinea‐pig ileum was incubated with [3H]choline (1·125‐1·5 μM), and then superfused with Tyrode solution containing hemicholinium‐3 (10 μM). Secretion of [3H]acetylcholine ([3H]ACh) was evoked either (a) by electrical field stimulation (0·5‐15 Hz, 150 shocks per period, 0·5 msec), used to ‘indirectly’ depolarize the varicosities of nerve terminals, or (b) by high potassium (40 mM with 1 μM‐tetrodotoxin, for 6 min, or 80 mM without tetrodotoxin, for 1 min), to ‘directly’ depolarize varicosities.

2. With these stimulation parameters, which yielded about the same fractional secretion of [3H]ACh, and with eserine (10 μM) present in the medium, atropine (1 μM) enhanced the ‘indirectly’, electrically evoked secretion 3·65±0·34 (n = 6) fold, and that caused by 40 mM or 80 mM‐potassium 1·82±0·06 (n = 6) or 1·55±0·09 (n = 10) fold, respectively. Atropine thus enhanced ‘indirectly’, electrically evoked secretion 4‐fold more than that caused by ‘direct’ depolarization of varicosities with high potassium (P < 0·001).

3. This difference is not likely to be caused by depression of the sensitivity of the presynaptic muscarinic receptors to ACh released by nerve stimulation, caused by the hypertonicity of the medium in the potassium stimulation experiments. The medium made hypertonic by addition of Tris‐HEPES (80 mM) did lower the binding affinity of membrane preparations of (pre‐ and post‐synaptic) muscarinic receptors, to carbamylcholine, and also the contractile responsiveness of the longitudinal muscle to this agent, in both cases to about one half. But it did not appear to alter the responsiveness of either pre‐ or post‐synaptic muscarinic receptors to endogenous ACh, released by nerve stimulation.

4. The results support a dual‐mode model for the muscarinic negative feed‐back control of ACh secretion from the nerve terminals of this preparation, mainly operating by restriction of the invasion of terminals, and only secondarily by depression of the efficiency of depolarization—secretion coupling in invaded varicosities.

5. Since this model has earlier been proposed to apply for the control of secretion of [3H]noradrenaline from the micro‐anatomically similar nerve terminals of noradrenergic nerves, the present findings suggest that the model may have a wider biological significance, and possibly apply to the control of the secretory activity of boutons‐en‐passant nerve terminals in general.
Control scheme governing concurrently active human motor units during voluntary contractions
Authors: de Luca C. J. , LeFever R. S. , McCue M. P. , Xenakis A. P.
Published: December 2014

1. The electrical activity of up to eight concurrently active motor units has been recorded from the human deltoid and first dorsal interosseous muscles. The resulting composite myoelectric signals have been decomposed into their constituent motor‐unit action potential trains using a recently developed technique.

2. A computer cross‐correlation analysis has been performed on motor‐unit firing rate and muscle‐force output records obtained from both constant‐force and triangular force‐varying isometric contractions performed by normal subjects, and three groups of highly trained performers (long‐distance swimmers, powerlifters and pianists).

3. The temporal relationships between firing rate activity and force output have provided evidence that the deltoid of long‐distance swimmers has a significantly higher percentage of slowly fatiguing fibres than that of normal subjects.

4. Results showed that both muscles are incapable of producing a purely isotonic contraction under isometric conditions. Small, possibly compensatory force variations at 1‐2 Hz result from a common drive to all active motoneurones in a single muscle pool.

5. Rapid force reversals during triangular, force‐varying isometric contractions appear to be accomplished through a size‐related motor‐unit control scheme. All firing rates decline prior to the force peak, but small motor units with slow‐twitch responses tend to decrease their firing rates before large, fast‐twitch motor units. This mechanism is not visually controlled, and does not depend on force rate in non‐ballistic contractions.
Effect of glutamate, aspartate and related derivatives on cerebellar Purkinje cell dendrites in the rat: an in vitro study
Authors: Crepel F. , Dhanjal S. S. , Sears T. A.
Published: December 2014

1. The responses of Purkinje cells to short duration (pulse) ionophoretic applications of L‐aspartate (L‐asp), L‐glutamate (L‐glu), N‐methyl DL‐aspartate (NMDLA) and quisqualic acid in their dendritic fields were studied in vitro on sagittal slices of lobules IX and X of the adult rat cerebellum.

2. Pulse application of L‐asp or L‐glu evoked transient and dose‐dependent increases in the firing rate of the simple spikes recorded extracellularly as single units. When the ionophoretic electrode was positioned in the dendritic field of the Purkinje cells, the lowest thresholds for L‐glu and L‐asp mediated excitations of the cells were as low as 25 and 35 pC respectively, with a latency for maximal responses as brief as 7 ms.

3. In intracellular recordings these excitatory responses consisted of depolarizations of up to 18 mV in amplitude and with depolarizing slopes up to 0·52 mV/ms. They were generally unaccompanied by changes in cell input resistance in contrast to the marked decrease which occurred in response to steady applications of large doses of L‐asp and L‐glu.

4. The spatial distribution of the excitatory sites confirmed that the dendritic sensitivity to L‐glu was greater than that of the soma and showed that the same was true for L‐asp. In 34% of cells the sensitivity for L‐asp declined markedly in the upper region of the molecular layer, whereas it remained high for L‐glu; no such differential sensitivity was detected in the remaining 66% of cells.

5. Inhibitory responses, antagonized by 10−5 M‐bicuculline in the bath, were also induced in Purkinje cells by L‐glu and L‐asp when the ionophoretic electrode was withdrawn from the excitatory sites by as little as 8 μm and up to 40 μm upward or downward along the track of parallel fibres or positioned as far as 250 μm laterally.

6. Whenever it was applied in the molecular layer, the pulse application of NMDLA elicited no excitatory response in Purkinje cells recorded extra or intracellularly. However, slow depolarizations accompanied by a slight increase in cell input resistance were obtained with steady applications of 20‐50 nA of the drug for 20‐30 s.

7. In contrast, pulse application of quisqualic acid appeared to have the same type of fast excitatory effect on Purkinje cells as L‐asp and L‐glu, but its potency was greater and its action more prolonged. Furthermore, its steady application led to an abrupt and marked decrease in cell membrane resistance.

8. The excitatory effects of L‐asp, L‐glu and quisqualic acid were antagonized by L‐glutamic acid diethyl ester more consistently than by D‐α‐aminoadipate, suggesting together with previous observations that L‐asp and L‐glu act on Purkinje cells via quisqualic acid rather than via NMDLA receptors.
Ano‐rectal activity in man during rectal infusion of saline: a dynamic assessment of the anal continence mechanism.
Authors: Haynes W G , Read N W
Published: December 2014

1. Anal and rectal pressures and the external anal sphincter electromyogram were recorded in eighteen normal subjects at rest and during rectal infusion of 1500 ml. saline at a rate of 60 ml./min. 2. During saline infusion, the recordings described a pattern of regular relaxations of the internal sphincter associated with contractions of the rectum and the external anal sphincter. The frequency of ano‐rectal pressure fluctuations increased as the infusion progressed. 3. The peaks in rectal pressure were always lower than the lowest anal pressure in all normal subjects tested. 4. External sphincter contractions only occurred in association with 60% of internal anal sphincter relaxations and did not prevent the maximum decrease in anal pressure. These observations suggest that phasic contraction of the external anal sphincter does not play a major role in maintaining continence.
X and Y cells in the lateral geniculate nucleus of macaque monkeys.
Authors: Kaplan E , Shapley R M
Published: December 2014

1. Cells of the lateral geniculate nucleus (l.g.n.) in macaque monkeys were sorted into two functional groups on the basis of spatial summation of visually evoked neural signals. 2. Cells were called X cells if their responses to contrast reversal of fine sine gratings were at the fundamental temporal modulation frequency with null positions one quarter of a cycle away from positions for peak response. Cells were called Y cells if their responses to such stimuli were at twice the modulation frequency and were approximately independent of spatial phase. 3. Ninety‐nine percent of the cells in the four dorsal parvocellular layers of the l.g.n. were X cells; about seventy‐five percent of the cells in the two ventral magnocellular layers were also X cells. The remainder were Y cells. 4. We confirmed previous findings that magnocellular cells had a shorter latency of response to electrical stimulation of the optic chiasm. 5. Magnocellular cells had much higher contrast sensitivities than did parvocellular cells. 6. Therefore, two distinct classes of X cells exist in the macaque l.g.n.: parvocellular X cells and magnocellular X cells. The great difference in their properties suggests that they have different functions in vision. The Y cells in the magnocellular layers form a third functional group with spatial properties distinctly different from the X cells. 7. We propose that the magnocellular layers of the macaque monkey's l.g.n. may be homologous to the A and A1 layers of the cat's l.g.n.
The effects of substance P on histamine and 5‐hydroxytryptamine release in the rat
Authors: Fewtrell C. M. S. , Foreman J. C. , Jordan C. C. , Oehme P. , Renner H. , Stewart J. M.
Published: December 2014

1. Substance P (SP) induces histamine release from isolated rat peritoneal mast cells at concentrations of 0·1‐10 μM.

2. Inhibitors of glycolysis and oxidative phosphorylation prevent the release of histamine induced by SP.

3. Cells heated to 47 °C for 20 min release histamine when treated with an agent causing cell lysis but fail to release in response to SP.

4. SP does not release histamine by interacting with cell‐bound IgE.

5. Histamine release by SP is rapid, with more than 90% of the response occurring within 1 min of the addition of the peptide to mast cells at 37 °C.

6. Substance P, unlike antigen—antibody or compound 48/80, does not show enhanced release of histamine when calcium (0·1‐1 mM) is present in the extracellular medium but calcium increases the response to SP when the ion is added after the peptide. Extracellular calcium (0·1‐1 mM), magnesium (1‐10 mM) and cobalt (0·01‐0·1 mM) all inhibit SP‐induced histamine release when added before the peptide. Pre‐treatment of the cells with EDTA (10 mM) and washing in calcium‐free medium inhibits the histamine release induced by SP.

7. Histamine release induced by SP was optimum at an extracellular pH of 7·2.

8. A number of peptides structurally related to SP were examined for histamine‐releasing activity. At the concentrations tested, the N‐terminal dipeptides Lys‐Pro and Arg‐Pro, tuftsin, physalaemin, eledoisin, SP3-11, SP4-11 and [p‐Glu6, p‐amino Phe7]‐SP6-11 were all found to be inactive. The relative activities of the other peptides were: [Formula: see text]

9. Rat basophilic leukaemia cells (RBL‐2H3) fail to respond to SP at concentrations which activate rat mast cells. Release of 5‐hydroxytryptamine by immunological activation of RBL cells is not changed by the presence of SP.

10. The mechanism of action of SP on mast cells and the nature of the SP receptor on mast cells is discussed in relation to SP receptors in other cell types.
The contents of high‐energy phosphates in different fibre types in skeletal muscles from rat, guinea‐pig and man.
Authors: Edström L , Hultman E , Sahlin K , Sjöholm H
Published: December 2014

1. The contents of high‐energy phosphates at rest have been measured in skeletal muscles with different fibre‐type composition from rat, guinea‐pig and man. All muscles studied biochemically have been characterized histochemically. 2. Fast‐twitch muscles had a higher ATP/ADP ratio than slow‐twitch muscles and, with the exception of the tongue in the rat, higher contents of ATP and phosphocreatine. 3. There was an inverse relationship between the content of phosphocreatine and the stainability for succinyl dehydrogenase, which is a marker enzyme for oxidative capacity. 4. The biochemical and histochemical data are discussed in relation to known morphological and functional properties of the different muscle‐fibre types. It is concluded that fast‐twitch fibres have a high ATP/ADP ratio favouring a fast acceleration of energy production. The content of phosphocreatine seems to be related to the glycolytic capacity but not to the contraction time. In addition to being an immediate energy source, phosphocreatine functions as a buffer against lactic acidosis.
Forces generated at the thumb interphalangeal joint during imposed sinusoidal movements
Authors: Brown T. I. H. , Rack P. M. H. , Ross H. F.
Published: December 2014

1. A method is described for driving the interphalangeal joint of the thumb through repeated sinusoidal flexion—extension movements, while immobilizing other joints of the wrist and hand.

2. The joint met the sinusoidal movement with a force that fluctuated in an approximately sinusoidal manner. This paper is concerned with the relationship between the position and force sinusoids.

3. When the thumb was relaxed the forces were small, but when the flexor pollicis longus was tetanically stimulated there was a large force change in response to each cycle of the movement. In either case, the maximum resistance to extension occurred during the later part of the extension movement, some 20°‐45° in advance of maximum extension. A similar result was obtained when the subject exerted a maximal voluntary flexing force.

4. The resistance to movement can conveniently be displayed as a stiffness vector, the amplitude of which is the force/displacement, and the phase is the angle by which the force sinusoid leads the position sinusoid.

5. When the subject maintained a continuous, though sub‐maximal, flexing effort the timing of the force fluctuations changed with changing frequency of movement in a characteristic way, and the stiffness vectors described a C‐shaped or spiral path. With increasing frequency the stiffness vectors moved round this path in a clockwise direction.

6. For descriptive purposes the resistance to movement can usefully be regarded as the vector sum of a reflex and a non‐reflex component. Since the reflex pathway involves significant conduction delays, the reflex force can be expected to appear later in the cycle of a higher frequency movement, and give rise to a vector which moves round in a clockwise direction as the frequency increases. The non‐reflex stiffness, however, changes much less with frequency.

7. It is concluded that the size of the C‐shaped or spiral vector path gives an indication of the strength of the reflex activity, while the position of the high frequency points gives an indication of the non‐reflex resistance to the movement.
Selective depression of motion sensitivity during saccades.
Authors: Burr D C , Holt J , Johnstone J R , Ross J
Published: December 2014

1. Horizontal gratings flashed for 20 ms were used to compare visual contrast sensitivity during horizontal saccades with sensitivity during normal vision, at three luminance levels, 4 X 10(2), 4 X 10(‐2), and 4 X 10(‐4) cd/m2. 2. Greatest sensitivity loss during saccades was found at low spatial frequencies. There is little or no loss at high spatial frequencies. 3. As luminance level is decreased there is a decrease in the spatial frequency below which saccadic sensitivity loss occurs. This shift in spatial frequency with luminance level, considered in conjunction with measurements of stationary and drifting gratings, indicates the functional involvement of movement sensitive mechanisms in saccadic sensitivity loss. 4. At the two lower luminance levels (4 X 10(‐2) and 4 X 10(‐4) cd/m2) sensitivity during saccades is greater than normal at high spatial frequencies. This enhancement of sensitivity was confirmed by forced choice measurements. 5. It was also shown that sensitivity to abrupt changes in the trajectory of moving gratings is lowered during saccades. 6. It is concluded that mechanisms sensitive to movement and transients are damped during saccades, so preventing perception of image motion during saccades and thereby preserving visual stability.
Ionic basis of the resting potential of submucosal arterioles in the ileum of the guinea‐pig.
Authors: Hirst G D , van Helden D F
Published: December 2014

1. The changes in the resting membrane potential of arterioles produced by rapid and brief changes in external ionic concentrations were measured. 2. The resting membrane potential was insensitive to changes in the external concentrations of both sodium and chloride ions but sensitive to changes in the external concentration of potassium ions. 3. Increasing the external concentrations of potassium ions produced depolarizations that were well described by the Nernst equation. 4. Decreased external concentrations of potassium ions produced membrane depolarizations which appeared to result not from inhibition of an electrogenic sodium pump but rather from a change in the resting conductance of the arteriolar membrane to potassium ions. 5. Ouabain caused both membrane depolarization and an increase in membrane resistance. 6. It is suggested that at rest, arteriolar smooth muscle is permeant predominantly to potassium ions, with only small contributions from chloride and sodium ions. No evidence was obtained which would support the idea that an appreciable proportion of the resting membrane potential depended upon current flow from an electrogenic sodium pump.
Denervation changes in normal and myasthenia gravis human muscle fibres during organ culture
Authors: Cull‐Candy S. G. , Miledi R. , Uchitel O. D.
Published: December 2014

1. Human intercostal nerve‐muscle obtained from normal and myasthenia gravis affected patients has been organ cultured for up to 5 weeks at 23 °C. In addition normal nerve‐muscle has been cultured for up to 2 weeks at 36 °C. Muscle fibres had normal resting and overshooting action potentials. Input resistances dropped markedly after 21 days at 23 °C or 10 days at 36 °C.

2. Muscle fibre action potentials became partially resistant to tetrodotoxin (10−7 g/ml.) after culturing for 8 days at 36 °C.

3. Extrajunctional acetylcholine (ACh) sensitivity was compared in fresh and cultured muscle. Fresh normal fibres possessed extrajunctional ACh sensitivity covering several hundred micrometres around the end‐plate and at the muscle—tendon junction. Myasthenia gravis affected fibres had reduced extrajunctional sensitivity at the end‐plate and no detectable ACh sensitivity near the tendon.

4. Less than one third of normal muscle bundles showed an increased area of ACh sensitivity after several days in organ culture. Under the same conditions myasthenic muscle bundles did not show an increase in extrajunctional ACh sensitivity,

5. M.e.p.p.s were present for 2‐4 days in normal fibres cultured at 36 °C. In normal and myasthenic muscles cultured at 23 °C m.e.p.p.s disappeared after 6‐8 days and re‐appeared in some fibres (50%) after approximately two weeks in organ culture. These m.e.p.p.s were abolished by curare and increased in frequency by hypotonic solution suggesting they are due to the release of ACh‐packets from Schwann cells.

6. Electron microscopic examination of cultured human muscle indicates that the disappearance of m.e.p.p.s corresponds with degeneration of nerve terminals.

7. In muscle bundles shown to possess m.e.p.p.s after 13‐14 days, the synaptic gutter, which had been vacated by the nerve terminal, was usually occupied by a Schwann cell or projections of Schwann cell cytoplasm. This indicates that the Schwann cell at denervated human end‐plates may be capable of releasing packets of ACh.

8. It is concluded that the organ culture system described here is suitable for studying normal and diseased human muscle fibres. Using this system we find that the denervation changes which follow nerve transection appear to be similar in most respects at normal and myasthenic end‐plates.
Effects of sarcomere length on the force—pCa relation in fast‐ and slow‐twitch skinned muscle fibres from the rat
Authors: Stephenson D. G. , Williams D. A.
Published: December 2014

1. Steady‐state force—pCa relations were determined for mechanically skinned fibres of fast‐ and slow‐twitch rat skeletal muscle, extensor digitorum longus (e.d.l.) and soleus respectively, at varied sarcomere lengths and temperatures (3‐35 °C).

2. This relation was different for the two fibre types at all sarcomere lengths, with soleus fibres having lower Ca2+ concentration threshold for activation and requiring a wider Ca2+ concentration range to reach force saturation.

3. An increase in sarcomere length within the range 2·2‐3·6 μm reversibly shifted the steady‐state force—pCa curves for both fast‐ and slow‐twitch fibres toward lower Ca2+ without affecting the steepness of the curves.

4. The results are consistent with the idea that the sensitivity of the contractile apparatus to Ca2+ is increased with increasing sarcomere length.

5. The change in apparent Ca2+ sensitivity (measured as the change in pCa corresponding to 50% Ca‐activated force (ΔpCa50)) was approximately proportional to the change in sarcomere length (ΔSL) at all temperatures for both types of muscle fibre.

6. The proportionality coefficient (ΔpCa50/ΔSL) was higher for slow‐twitch fibres than for fast‐twitch fibres by a factor of 1·5‐2·0 at all temperatures investigated.

7. The force—pCa relation was less affected by changes in sarcomere length at lower (3‐5 °C) than at higher temperatures (22‐35 °C).

8. The sarcomere length—maximum force relation obtained with skinned fibres for sarcomere lengths between 2·10 and 4·05 μm was similar for both fibre types at all temperatures despite large temperature dependent variations in maximum Ca‐activated force response. Maximum force decreased linearly to zero between ca. 2·8 and 3·95 μm; remained high and essentially constant between ca. 2·40 and 2·80 μm, and decreased significantly below 2·40 μm.

9. Myofilament‐generated tension oscillations produced by partially activated soleus skinned fibres are highly length dependent, disappearing completely when sarcomere length is increased above 3·15 μm.
Voltage‐dependent activation of potassium current in Helix neurones by endogenous cellular calcium.
Authors: Akaike N , Brown A M , Dahl G , Higashi H , Isenberg G , Tsuda Y , Yatani A
Published: December 2014

1. The effect of endogenous Ca on potential‐dependent K current IKD, was examined in identifiable neurones of Helix aspersa. The suction pipette method of internal perfusion was used along with a combined voltage‐clamp method in which the membrane potential was measured by a separate glass micro‐electrode and the current was passed by the suction pipette. Activation of the potential‐dependent A current, IA, was prevented by using holding potentials of ‐40 mV where IA is inactivated and by the addition of the A‐current blocker 4‐aminopyridine. Activation of K currents by transmembrane Ca current, IKCa, was suppressed by Co substitution for Ca ion extracellularly. 2. Under these conditions, IKD rose to a peak value and then subsided to a steady level. The current‐voltage (I‐V) relationship for peak IKD had an upward bump at about +50 mV that gave it an S‐shape. The I‐V curve for steady IKD rose continuously. Peak and steady IKD were reduced by perfusing with EGTA or F ions intracellularly. The EGTA effect occurred at intracellular Ca activity levels below 10(‐7) M. Increases in the concentration of EGTAi at constant Cai had no additional effect; however, recovery experiments do not allow us to rule out some direct action of EGTA on IKD. 3. Prolonged extracellular perfusion with Co‐substituted solutions also reduced IKD and the effects occurred more quickly when the solutions were made hypertonic or caffeine was added to them. The peak transient was abolished, and the small remaining steady IKD (about 5‐10% of normal peak IKD) was blocked by tetraethylammonium. IKD could be restored by the temporary reintroduction of Ca in the extracellular solution. 4. The S‐shape of the peak I‐V relationship for IKD may be due to Ca released from an endogenous site by membrane depolarization. The reduction of steady and peak IKD to very low values by Ca chelators or prolonged perfusion with Ca‐free solutions indicates that Cai is important for activation of these K channels. 5. Three cellular structures were identified in electron micrographs of freeze‐fractured neurones that could be involved in potential‐dependent endogenous Ca release. These were a restricted extracellularly space, an intracellular membrane system of endoplasmic reticulum that may be fused to the internal face of the plasma membrane (the subsurface cisterns of Henkart & Nelson, 1979), and intracellular vesicles that also may be fused to the plasma membrane.
Recovery from decamethonium in rat muscle and denervated guinea‐pig diaphragm.
Authors: Creese R , Humphrey P P , Mitchell L D
Published: December 2014

1. In denervated guinea‐pig diaphragm the depolarization produced by decamethonium (100 microM) was followed by an initial phase of recovery, and then by a slow restoration of membrane potential in the presence of the drug, with hyperpolarization. Membrane potentials were measured by repeated insertions. The slow phase of spontaneous recovery was not found in the absence of potassium or in the presence of ouabain (100 microM). 2. With 1 microM‐decamethonium the net loss of potassium from denervated muscle was 17% by wet weight in 20 min as compared with controls, which represents a loss of over 30 mM in internal concentration. Similar results were obtained with 100 microM‐decamethonium. Spontaneous recovery of potassium occurred in the succeeding 2 h in the presence of 1 microM and 100 microM‐decamethonium. With 5 nM‐decamethonium muscles exposed for 20 min had a potassium content which was not reduced as compared with controls. 3. In rat diaphragm decamethonium (100 microM) also produced depolarization and slow spontaneous recovery which was not seen in the absence of potassium or the presence of ouabain. With 3 mM‐decamethonium spontaneous recovery of potential was complete in 5 min. 4. Change from 5 mM‐potassium to potassium‐free solution produced consistent hyperpolarization in denervated guinea‐pig diaphragm. In rat diaphragm at 38 degrees C the results were variable, with some fibres showing hyperpolarization while others showed depolarization.
Temperature and end‐plate currents in rat diaphragm.
Authors: Head S D
Published: December 2014

1. Spontaneous miniature end‐plate currents (m.e.p.c.s.) were recorded in rat diaphragm at 7, 22 and 37 degrees C at ‐80 mV. The onset rate, measured as 20‐80% rise time, was sensitive to temperature with activation energy 14 kcal mol‐1 deg‐1, and was not sensitive to membrane voltage between ‐60 and ‐130 mV. 2. The rise time recorded by external electrodes was 144 microseconds at 37 degrees C (6) and was similar to that found by internal electrodes. 3. The fall time was temperature‐sensitive with activation 18 kcal, and was prolonged when the end‐plate was hyperpolarized. 4. With acetylcholine (10 microM) the current increased to a peak and then fell within 30 s to a value which declined slowly. From fluctuation analysis the channel open time of 237 microseconds (7) at 37 degrees C was estimated. External recording gave comparable values (4). Comparison of the initial estimates with those obtained after 3‐6 min of continued application showed no consistent change. The channel conductance was 26 pS at 37 degrees C. 5. The time constant of m.e.p.c. decay was consistently longer than the channel open time obtained from noise analysis. 6. With carbachol (40 microM) the current increased to a peak and then declined to a steady value. Fluctuation analysis by internal and external recording gave an increase of 5% in root mean square current with channel open time of 83 microseconds (6) at 37 degrees C, and channel conductance 17 pS.
Neuromuscular transmission in crustaceans is enhanced by a sodium ionophore, monensin, and by prolonged stimulation.
Authors: Atwood H L , Charlton M P , Thompson C S
Published: December 2014

A sodium ionophore, monensin, was applied to crustacean neuromuscular preparations to determine whether increased intracellular sodium could lead to enhancement of transmitter release similar to that observed with prolonged stimulation. Following a single application of monensin (3‐13 microM), the excitatory postsynaptic potential (e.p.s.p.) increased in amplitude by 50‐800%. The increase was entirely due to a presynaptic effect that resulted in higher quantal content of transmission and increased frequency of spontaneous miniature potentials. A second application of monensin was less effective than the first. Application of monensin in calcium‐free solutions led to rapid, marked enhancement of the e.p.s.p. upon restoration of the normal physiological solution, indicating that monensin can produce its effects in the absence of external calcium. Spontaneous miniature potentials often occurred more frequently in calcium‐free solution after monensin had been applied. The extent of enhancement of e.p.s.p. amplitude depended on the concentration of external sodium, being smaller in solutions of low sodium. Prolonged stimulation of the motor axon usually enhanced the e.p.s.p. to a greater extent than application of monensin alone, but the time course of recovery of e.p.s.p. amplitude was similar in both cases. We conclude that the increase in e.p.s.p. amplitude promoted by monensin can be attributed to increased transmitter output resulting from influx of sodium into the nerve terminal. Increased intracellular sodium may lead to a rise in intracellular calcium ion concentration. Some features of long‐term facilitation of transmitter release can be attributed to build‐up of intracellular sodium during stimulation.
Comparison of antidromic and orthodromic action potentials of identified motor axons in the cat's brain stem.
Authors: Gogan P , Gueritaud J P , Tyc‐Dumont S
Published: December 2014

Recordings were made from identified central axons at a known distance from their somata, to compare the action potentials resulting from antidromic and synaptic excitation. By taking advantage of the anatomical configuration within the brain stem of the motoneurones innervating the retractor bulbi muscle in the orbit, their axons were penetrated in the VIth nucleus and labelled by electrophoretic injection of horseradish peroxidase. Excitatory post‐synaptic potentials recorded in the retractor bulbi axons at about 3 mm from the soma were six times smaller than in the soma. The space constant of the axonal segment between the retractor bulbi and the abducens nucleus was estimated to be 1.7 mm. When the axons propagated action potentials the attenuation was increased to eighteen times due to the nodes of Ranvier intercalated between the soma and the site of recording. Antidromic action potentials displayed stepwise changes in amplitude and shape when stimuli were applied at intervals decreasing from 5 ms to 0.7 ms. The changes were related to the different lengths of refractoriness of the soma, initial segment and axon. Orthodromic action potentials evoked by synaptic excitation displayed similar changes in amplitude and shape. These observations lead to the conclusion that the soma, initial segment and neighbouring nodes of Ranvier contribute significantly to the shape of the action potential. Contrary to the generally accepted view, it appears that the efferent discharge along motor axons can be initiated without a simultaneous activation of the somato‐dendritic or even the initial segment membrane, as revealed by the lack of somato‐dendritic and/or initial segment contribution to the shape of the synaptically evoked action potentials.
Effects of ouabain on carotid body chemoreceptor activity in the cat.
Authors: McQueen D S , Ribeiro J A
Published: December 2014

The effects of infusions of ouabain on chemoreceptor activity recorded from the peripheral end of a sectioned carotid sinus nerve were studied in cats anaesthetized with pentobarbitone. Ouabain caused a marked increase in chemoreceptor discharge followed by a decline in discharge to frequencies near or below the pre‐ouabain level; during the latter period further administration of ouabain had no effect. Infusion of ouabain during hypoxia further increased the chemoreceptor discharge, but this effect was short‐lasting. On intracarotid administration ouabain was less effective in cats with the ganglioglomerular (sympathetic) nerves cut, whereas on intravenous administration no significant difference was observed. Following intravenous administration of ouabain the chemoreceptor peak discharge occurred with dose levels similar to those needed to cause cardiac arrhythmias, but following intracarotid administration the chemoreceptor discharge peaked at doses about 40% of those causing arrhythmias. During ouabain‐induced excitation the stimulatory action of NaCN, CO2‐equilibrated Locke solution and acetylcholine was potentiated, as was the chemo‐inhibition induced by dopamine. During the post‐excitatory period the responses evoked by these substances were reduced or abolished. Neither mecamylamine, a nicotinic antagonist, nor physostigmine, an anti‐cholinesterase, affected the response of the carotid chemoreceptors to ouabain. The major finding of this study was that ouabain initially ‘sensitizes’ the carotid body chemoreceptors and then ‘desensitizes’ them. The most likely mechanism responsible for these effects is the well established Na+‐‐K+‐ATPase‐inhibiting property of ouabain.
Effects of stretching and stirring on water and glucose absorption by canine mucosal membrane.
Authors: Lee J S
Published: December 2014

A ‘mini’ canine mucosal membrane preparation permitting simultaneous determination of water (Jv) and glucose (Jg) absorption rates, microscopic examination or micropuncture of the villi was used in this study. The small membranes were more stretched than the large ones, with more than a one‐fold increase in both Jv and Jg, apparently due to a change in architectural orientation between the villi and subvillous supporting tissue so as to facilitate water transport via the lymphatic system. During stirring of the bathing solution, the villi in the small membranes were widely separated from each other with more to‐and‐fro swaying movements than in the large ones. Stirring was seen to cause up‐and‐down movements of the loosely suspended large membranes but not the small ones. In the small membranes stirring caused no change in Jv but an increase in Jg due to the increase in glucose concentration in the absorbate, while in the large membranes both Jv and Jg were greatly increased. It is thus considered that the increase in absorption in the large membranes caused by stirring is mainly due to the increased membrane movements promoting lymph flow.