bluuebunny/crossref_metadata_2025 huggingface dataset:
Peripheral neural representation of the spatial frequency of a grating moving across the monkey's finger pad.
Authors: Darian‐Smith I , Oke L E
Published: December 2014

1. Responses in mechanoreceptive afferent fibres innervating the monkey's finger pads were examined when a ridged surface ("grating') was moved across the fibre's receptive field with a specified velocity and applied force. 2. The stimulus feature represented in single fibre responses was the temporal frequency of the moving grating (stimulus temporal frequency = velocity of moving surface/spatial period); information about the spatial period of the grating was represented equivocally. 3. Peripheral neural representation of the grating's spatial period (or spatial frequency) depended on information signalled by the responding fibre population rather than by individual fibres. 4. The three mechanoreceptive fibre populations responded differentially to a grating moving across the finger pad. Slowly adapting fibres coded best those stimulus combinations with a stimulus temporal frequency in the range 20‐60 Hz, rapidly adapting fibres coded best those with frequencies of 60‐200 Hz, and Pacinian fibres best defined those stimuli with a high temporal frequency (100‐300 Hz). 5. Applying the moving grating to the skin with varying radial forces in the range 20‐60 g wt. did not greatly modify the pattern of discharge in the responding fibre populations.
A study of tetanic and post‐tetanic potentiation of miniature end‐plate potentials at the frog neuromuscular junction.
Authors: Lev‐Tov A , Rahamimoff R
Published: December 2014

1. The involvement of calcium sodium, potassium and magnesium in tetanic and post‐tetanic potentiation of miniature end‐plate potential frequency was examined at the frog neuromuscular junction using conventional electrophysiological techniques. 2. Tetanic potentiation is larger in calcium containing solutions, than in solutions which generate reversed electrochemical gradient for calcium during nerve activity. 3. Tetanic potentiation increases with stimulation frequency and duration, under both inward and reversed electrochemical gradient for calcium conditions. This indicates that factors, other than calcium entry, participate in tetanic potentiation. 4. Addition of the potassium conductance blocking agent, 3‐aminopyridine (5 mM), increases tetanic potentiation in calcium containing media, while depressing it under reversed calcium gradient. 5. Electronic depolarization of the nerve terminal in tetrodotoxin‐containing Ringer solution, produces tetanic potentiation under inward gradient, but fails to do so under reversed gradient. This indicates that the entry of sodium ions participates in the generation of tetanic potentiation. 6. Addition of magnesium ions suppresses tetanic potentiation in calcium containing solution, but increases tetanic potentiation under reversed gradient. 7. The results are explained by the hypothesis that calcium entry and intracellular calcium translocation participate in the generation of tetanic potentiation. 8. Both the fast and the slow components (augmentation and potentiation respectively) of post‐tetanic potentiation increase in duration, with increase in the tetanic stimulation rate. 9. The decay of post‐tetanic potentiation increases: when [Ca]o is elevated by ionophoretic application during the decay phase only, when ouabain is present in the medium or when [Mg]o is elevated. These finding suggest that calcium, sodium and possibly magnesium take part in post‐tetanic potentiation.
Physiological role of endogenous amines in the modulation of ventricular automaticity in the guinea‐pig.
Authors: Hume J , Katzung B G
Published: December 2014

1. Current‐clamp experiments were carried out with guinea‐pig papillary muscles to determine the dependence of depolarization‐induced automaticity on endogenous catecholamines. 2. Catecholamine depletion was produced by pre‐treatment of animals with 6‐hydroxydopamine and confirmed by fluorimetric assay of right ventricular tissue. Papillary muscles from depleted animals demonstrated a marked suppression of depolarization‐induced automaticity for maximum diastolic potentials less negative than ‐55 mV. This suppression was completely reversed by noradrenaline but not by tyramine. 3. In normal tissue, noradrenaline and tyramine had much smaller effects on automaticity arising from maximum diastolic potentials negative to ‐55 mV than on repetitive activity arising positive to this level. 4. L‐propranolol in concentrations of 2‐3 x 10(‐7) M reduced repetitive activity in the less negative range of maximum diastolic potential. No evidence of direct membrane depression was observed at these doses and the effect was reversed by application of noradrenaline. 5. D‐propranolol, the isomer with much lower beta‐receptor blocking potency, required twentyfold higher concentrations to depress automaticity and this was accompanied by evidence of direct membrane depression, i.e. reduction of upstroke velocity of action potentials. 6. These results show that automaticity induced in guinea‐pig papillary muscles by depolarization positive to ‐55 mV is strongly dependent upon endogenous catecholamines. 7. The hypothesis that endogenous catecholamines facilitate depolarization‐induced automaticity through an increase in calcium conductance was modelled using numerical techniques. It was found that changes in calcium conductance caused changes in the model which closely parallelled the experimental effects of catecholamine depletion and beta‐blockade. The effects of changes in delayed rectification in the model did not accurately reproduce the experimental results.
Patterns of motor innervation in the pectoral muscle of adult Xenopus laevis: evidence for possible synaptic remodelling.
Authors: Haimann C , Mallart A , Ferré J T , Zilber‐Gachelin N F
Published: December 2014

1. An anatomical and electrophysiological study was performed on the pectoral muscle of Xenopus laevis. 2. Silver‐impregnated preparations revealed immature endings, collateral and terminal sprouting and signs of synaptic regression. 3. Twenty percent of the fibres received a dual innervation from two different nerves. The synapses of 25% of these fibres are formed in close vicinity. 4. Some of the singly innervated and most of the dually innervated end‐plates generated only subthreshold electrical activity. Synaptic efficacy in dually innervated muscle fibres with closely spaced or distant endings was, on the average, one third and two thirds, respectively, of that obtained in singly innervated fibres. 5. Fibres with subthreshold electrical activity displayed normal ACh sensitivity. 6. The existence of non‐transmitting synapses, of dually innervated end‐plate sites and of morphological signs of the sprouting of new endings and the degeneration of old ones suggests that synaptic remodelling may occur in normal adult muscles.
Experimental analysis of the gait and frequency of locomotion in the tortoise, with a simple mathematical description.
Authors: Williams T L
Published: December 2014

1. Voluntary locomotion of the tortoise Testudo graeca was investigated over a range of experimental conditions. 2. The swing and stance intervals of the step cycles of individual limbs and the interlimb intervals were shown to depend only upon the locomotor cycle duration independent of experimental conditions. 3. The gait is described by four simple equations, valid for all animals and conditions tested, with locomotor cycle duration as the only independent variable. 4. The observed frequency of locomotion was shown to be related to body weight, cloacal temperature, and walking surface ina manner which can be described by a single equation. 5. The implications of these findings for vertebrate locomotion are discussed.
Electrical activity from smooth muscle of the anal sphincteric area of the cat.
Authors: Bouvier M , Gonella J
Published: December 2014

1. The electrical activities of longitudinal and circular smooth muscle of the anal sphincteric area have been studied in the cat. 2. Electromyographic recordings were achieved with extracellular electrodes, in vivo on acute and chronic animals, and in vitro on the isolated organ. In addition, electrical and mechanical activities were recorded from muscle strips with the sucrose gap technique. 3. Circular muscle coat electrical activity consisted exclusively of slow variations of the membrane potential of the smooth muscle cells. Each slow potential variation was followed by a contraction. 4. The electrical activity and the concomitant contractions were tetrodotoxin resistant (10(‐6) g/ml.). Both disappeared in Ca‐free solution or in the presence of Mn ions (10(‐3) M). 5. On circular muscle, noradrenaline (10(‐8)‐10(‐7) g/ml. in vitro, or 0.1‐0.15 mg/kg in vivo) had an excitatory effect consisting in an increase of slow potential frequency. The action of noradrenaline was antagonized by phentolamine (10(‐6)‐10(‐5) g/ml. in vitro, or 0.2 mg/kg in vivo). 6. On circular muscle, acetylcholine (10(‐8)‐10(‐6) g/ml.), used exclusively on muscle strips, did never produce any clear cut effect. 7. Longitudinal muscle coat electrical activity consisted of spike potentials superimposed on slow time course depolarizations which were never observed alone. Each spike was followed by a contraction. This electrical activity was tetrodotoxin resistant (10(‐6) g/ml.). 8. Longitudinal muscle activity was abolished by noradrenaline (10(‐6) g/ml.) and enhanced by acetylcholine (10(‐8)‐10(‐6) g/ml.). The action of noradrenaline was antagonized by propranolol (0.2 mg/kg I.V.; 10(‐6) g/ml.) and that of acetylcholine by atropine (10(‐7) g/ml.). 9. Electrophysiological and pharmacological data indicate that electromechanical coupling is achieved (1) in circular muscle, through Ca dependent slow variations in membrane potential of the muscle cells and (2) in longitudinal muscle, through spike potentials. Noradrenaline has opposite effects on the two muscle coats: circular muscle is excited through alpha‐receptors located on muscle cells membrane; longitudinal muscle is inhibited through beta‐receptors. Acetylcholine excites longitudinal muscle through muscarinic receptors, but it has no effect on circular muscle.
Capillary increase in the skeletal muscle of trained young and adult rats.
Authors: Adolfsson J , Ljungqvist A , Tornling G , Unge G
Published: December 2014

1. Capillaries in skeletal muscle were studied before and after physical training by prolonged swimming, in young and adult rats. 2. The mean area of striated muscle fibres was unchanged in both young and adult rats after training. 3. Training increased the capillary vasculature of skeletal muscle in both young and adult rats, but proportionally less in the adults.
The effect of profound cooling on adrenergic neurotransmission in canine cutaneous veins.
Authors: Rusch N J , Shepherd J T , Vanhoutte P M
Published: December 2014

1. Experiments were performed to investigate how profound cooling affects adrenergic neurotransmission and vascular smooth muscle reactivity in isolated saphenous veins of the dog. 2. Cooling from 37 to 5 degrees C caused progressive depression of the contractile responses to high K+ solutions, illustrating the direct inhibitory effect of cooling on depolarization‐induced contraction of the venous smooth muscle cells. 3. During prolonged cooling to 20, 15 and 10 degrees C, the contractile response to exogenous norepinephrine (10(‐8)‐10(‐6) M) was augmented compared to that at 37 degrees C. At 5 degrees C responses up to 10(‐7) M were also augmented, but those at higher concentrations were depressed. When veins contracted with 2 x 10(‐6) M‐norepinephrine were cooled to 20, 15, 10 and 5 degrees C, there was a further increase in tension; this increase slowly subsided to control values at 5 degrees C but was sustained at the other temperatures. 4. Cooling to 20 and 15 degrees C augmented the contraction caused by low but not high frequencies of electrical stimulation of the adrenergic nerve endings. Further cooling to 10 degrees C depressed, and at 5 degrees C abolished the response, demonstrating that profound cooling interrupted adrenergic neurotransmission. 5. In rings stimulated electrically at a low frequency (0.5 Hz), warming from 7 to 9 degrees C or from 9 to 11 degrees C, caused marked increases in tension. This may be explained by the combination of resumption of adrenergic neurotransmission and the increased responsiveness of the cutaneous venous smooth muscle cells to adrenaline. 6. The combination of enhanced affinity for noradrenaline combined with inhibition of neurotransmitter disposition probably permits the cutaneous veins to remain constricted during exposure to severe cold.
Unitary current through sodium channel and anomalous rectifier channel estimated from transient current noise in the tunicate egg.
Authors: Ohmori H
Published: December 2014

1. The noise included in the Na current and the anomalous rectifier current was measured in intracellularly perfused eggs of Halocynthia roretzi Drashe under voltage clamp conditions. 2. The time‐dependent component of the point‐by‐point ratio between the ensemble mean and the variance of successive current traces was the mirror image of the time‐dependent component of the mean current itself. This can be explained by assuming an open or closed conductance state for each ionic channel, and permits estimation of unitary currents and channel number. 3. The unitary Na currents showed a potential dependence similar to that of the instantaneous currents. The unitary conductances (gamma) at zero membrane potential were 7.4 and 3.3 pmho in sea water with 400 and 100 mM‐Na, respectively, and 400 mM‐intracellular K. With 400 mM‐Na intracellular perfusate and 400 mM‐Na sea water, gamma was 15.7 pmho. In spite of the large differences in the unitary conductances, the single channel permeability for Na ions remained constant (1.15 x 10(‐14) cm3 sec‐1). The density of Na channels was 0.60/micrometer2. 4. The unitary currents calculated for the anomalous rectifier showed a potential dependence similar to that of the zero‐time extrapolated estimates of the K inward currents. The anomalous rectifier unitary conductance was 5.5 and 6.9 pmho for sea water with 50 and 100 mM‐K, respectively. The density of these channels was 0‐035/micrometer2.
The action of high hydrostatic pressure on the membrane currents of Helix neurones.
Authors: Harper A A , Macdonald A G , Wann K T
Published: December 2014

1. The actions of high hydrostatic pressure (10.4, 20.8 MPa) on the membrane currents of Helix neurones were examined under voltage clamp. 2. High hydrostatic pressure (20.8 MPa) reduced the maximum inward current to 0.78 and the delayed outward current, measured at the inward current reversal potential, to 0.75 of their value at atmospheric pressure. 3. High hydrostatic pressure shifted the curve relating the inward current conductance to membrane potential to more positive values but the maximum conductance was altered. 4. The rates of activation of the inward and delayed outward currents were slowed by pressure. 5. The steady‐state level and time course of inactivation of the inward current was unaffected by high pressure over the investigated range. 6. The effects of high hydrostatic pressure on the fast outward current identified in gastropod neurones by Connor & Stevens (1971) were also examined. 20.8 MPa reduced the current measured at ‐30 mV to 0.71 of its control value. 7. The rate of activation of the fast outward current was slowed by high pressure but the time constant of inactivation was unchanged. 8. The majority of the effects of high hydrostatic pressure were completely reversible upon decompression. 9. These results are discussed with reference to the known effects of high hydrostatic pressure on the action potential and discharge frequency of gastropod neurones. Possible sites and mechanisms of pressure action on the excitable cell are briefly discussed.
The involvement of histamine receptor subtypes in gastric acid secretion and mucosal blood flow in the anaesthetized rabbit.
Authors: Curwain B P , Turner N C
Published: December 2014

1. The involvement of histamine receptor subtypes in the gastric acid secretory and mucosal blood flow responses of the pentobarbitone‐anaesthetized rabbit to histamine were investigated. 2. Histamine produced a dose‐related increase in gastric acid secretion and mucosal blood flow. Maximal effects were stimulated further by mepyramine and inhibited by metiamide. Mepyramine had no effect on methacholine‐ or impromidine‐stimulated gastric acid secretion or mucosal blood flow. 3. Impromidine also produced a dose‐related increase in gastric acid secretion and mucosal blood flow. The maximal effect produced depended on the method of administration. The H1‐receptor agonist 2‐TEA inhibited impromidine‐stimulated blood flow but not gastric acid secretion. 4. It is concluded that, in addition to stimulating acid secretion by an action on H2‐receptors, histamine also exerts an inhibitory effect which is mediated by H1‐receptors and that this inhibitory effect operates via reduced blood flow resulting from vasoconstriction in the stomach.
Regeneration of barosensitivity in the aortic nerve of cats when severed and transposed on various vessels in the neck.
Authors: Arndt J O , Krossa M , Samodelov L F
Published: December 2014

1. In cats, regeneration of baroreceptors was studied in the aortic nerve after its peripheral end had been severed and sutured into an adventitial pouch of the common carotid artery (ten cats) on the wall of the external jugular vein (two cats) and into a cervical muscle (one cat). 2. Three weeks to four months after the initial operation, typical pulse synchronous baroreceptor activity was found in the whole desheathed nerve remnant in three of thirteen animals. This activity could be abolished by section of the vago‐sympathetic bundle distal to the implantation site. 3. In every cat, including the one with the nerve in cervical muscle, bursts of spikes could be repeatedly evoked in the whole nerve upon stroking or distortion of the neuroma formed at the site of implantation. 4. Additionally, single barosensitive fibres could be teased from the aortic nerves in seven of the ten cats whose nerves has been sutured into the arterial wall. 5. Finally, distension sensitive single afferents with predominantly phasic response characteristics were found in the nerves on jugular veins. 6. Transposed aortic nerves therefore, are apparently capable of reinnervating the originally severed endings in some cases while forming a mechanosensitive neuroma in every case. When in contact with a vessel wall some truly barosensitive endings can also develop which in most instances have a more phasic than tonic response to pressure changes.
The electrical basis for contraction and relaxation in canine fundal smooth muscle
Authors: Morgan Kathleen G. , Muir T. C. , Szurszewski J. H.
Published: December 2014

1. Mechanical and intracellular electrical activities were recorded simultaneously from canine fundal and antral smooth muscle preparations.

2. Most fundal preparations displayed no spontaneous electrical or mechanical activity. The tissue had a space constant of 1·5 mm and a time constant of 189 msec and showed outward rectification in response to depolarizing current.

3. Transmural nerve stimulation of fundal preparations demonstrated the presence of cholinergic excitatory and non‐cholinergic, non‐adrenergic inhibitory neural inputs to the tissue. The cholinergic nerve response consisted of a small, graded depolarization accompanied by a slow graded contraction; the inhibitory nerve response consisted of a graded hyperpolarization accompanied by a slow relaxation.

4. The excitatory fundal nerve response was abolished or greatly diminished by D600 and Mn2+. D600 and Mn2+ also decreased basal tone. The inhibitory nerve response was unaffected by either agent.

5. The excitatory nerve response in the fundus was contrasted with the excitatory nerve response in the antrum. In the fundus, stimulation of cholinergic motor nerves produced a depolarization which always produced a contraction. In the antrum, stimulation of cholinergic motor nerves between action potentials produced graded depolarizations of antral cells; however, there were no associated contractions. Stimulation of cholinergic motor nerves during spontaneous action potentials increased the amplitude and duration of the plateau phase of the action potential; this was associated with an augmentation of the spontaneous contractions.

6. Voltage—tension curves were determined for antral and fundal preparations using K+ depolarization as a means of controlling membrane potential. Antral preparations displayed a voltage threshold for contraction at a membrane potential approximately 30 m V positive to the resting potential. In cntrast, fundal resting potentials were at or more positive than their voltage thresholds.

7. These differences in electromechanical coupling provide an explanation for the marked differences in the responses of fundal and antral smooth muscles to nerve stimulation and account for their physiologic function in vivo.
Influence of the sympatho‐adrenal system and somatostatin on the secretion of insulin in the rat
Authors: Ahrén B. , Järhult J. , Lundquist I.
Published: December 2014

1. The effects of somatostatin on insulin secretion in anaesthetized rats subjected to different manipulations of the sympatho‐adrenal system have been investigated.

2. Somatostatin (0·1 μg/min) inhibited the secretion of insulin in intact rats both in the basal state and after inducing an enhanced insulin release by infusion of the α‐adrenoceptor‐blocker phentolamine.

3. Combined surgical splanchnicotomy and adrenalectomy caused an increase in the basal plasma insulin concentration. Somatostatin (0·1 μg/min) inhibited basal insulin release also in these rats. After infusion of phentolamine, however, the dose of somatostatin had to be raised five fold (0·5 μg/min) to achieve a comparable inhibition of insulin release. On the other hand, a similar rate of insulin secretion induced by glucose in intact rats could be inhibited by the lower dose of somatostatin.

4. Administration of the β‐adrenoceptor‐blocking agent propranolol to splanchnicotomized—adrenalectomized rats lowered basal insulin secretion to the same level as seen in intact rats. In these β‐adrenoceptor‐blocked rats somatostatin (0·1 μg/min) inhibited insulin release both in the presence and absence of α‐adrenoceptor blockade.

5. Rats subjected to chemical sympathectomy through pre‐treatment with 6‐hydroxydopamine together with adrenalectomy displayed plasma insulin concentrations slightly above the normal range, but the values were much lower than in splanchnicotomized—adrenalectomized rats. Infusion of phentolamine to the chemically sympathectomized rats did not further increase insulin secretion, and somatostatin (0·1 μg/min) depressed insulin release both in the absence and presence of α‐adrenoceptor blockade.

6. It is suggested that an inhibitory tone exerted by the splanchnic nerves modulates the basal insulin secretion in the rat. Somatostatin and the sympathoadrenal system show a complex interaction on the insulin cells in that the sensitivity to somatostatin in splanchnicotomized—adrenalectomized rats with intact β‐adrenoceptors is decreased in the presence of the α‐adrenoceptor‐blocker phentolamine. The exact mechanism behind this decreased sensitivity remains unclear.
The release of adenosine and inosine from canine subcutaneous adipose tissue by nerve stimulation and noradrenaline.
Authors: Fredholm B B , Sollevi A
Published: December 2014

1. Plasma and adipose tissue purine nucleosides were assayed by reversed phase high‐performance liquid chromatography after purification of the samples on phenylboronate affinity gel. 2. The adenosine content of unstimulated subcutaneous adipose tissue was close to 1 n‐mole/g. The concentrations of adenosine and inosine in canine arterial plasma were 0.26 +/‐ 0.03 and 0.16 +/‐ 0.03 microM, respectively. In venous plasma from the canine subcutaneous adipose tissue the corresponding values were 0.32 +/‐ 0.04 and 0.28 +/‐ 0.06 microM under basal conditions. The arterio‐venous concentration difference of adenosine was linearly dependent upon the arterial adenosine concentration. At arterial concentrations below 0.3 microM there was a net production of adenosine; above 0.3 microM there was a net extraction of approximately 77% of the adenosine. Adenosine was extensively eliminated in blood. The major part of this elimination could be accounted for by metabolism to inosine, hypoxanthine and uric acid. 3. Following sympathetic nerve stimulation (4 Hz for 20 min) the rate of adenosine outflow from adipose tissue increased from 0.33 +/‐ 0.22 to a peak value of 1.2 +/‐ 0.26 n‐mole/min. This corresponds to a net release of 8.7 +/‐ 3.0 n‐mole/100 g tissue. Inosine outflow rose from 0.64 +/‐ 0.37 to 5.3 +/‐ 1.4 n‐mole/min, corresponding to a net release of 24.6 4/‐ 8.7 n‐mole/100 g. Nerve stimulation also increased the release of [3H]purines from [3H]adenine pre‐labelled adipose tissue. The fractional release increased 15‐fold after stimulation. The radioactivity was mainly in the form of hypoxanthine, inosine and uric acid while adenosine was a minor component. When metabolism in blood was inhibited by dipyridamole and an adenosine deaminase inhibitor nerve‐stimulation‐induced release of [3H]purines was mainly in the form of adenosine. 4. Noradrenaline injection also induced a release of radioactive purines and of inosine. On the other hand, the outflow of endogenous adenosine was very small. 5. The present results demonstrate that under basal conditions adenosine is present in arterial and venous canine plasma. The free extracellular tissue level may be similar to the basal arterial adenosine concentration. Sympathetic nerve stimulation and noradrenaline induces a marked release of adenosine which is rapidly metabolized in the tissue and blood stream to inosine, hypoxanthine and uric acid. In adipose tissue the levels of adenosine reached after adrenergic stimulation appear high enough to be of physiological relevance.
Evidence for the presence of potassium channels in the paranodal region of acutely demyelinated mammalian single nerve fibres.
Authors: Chiu S Y , Ritchie J M
Published: December 2014

1. A study has been made of the ionic currents in voltage‐clamped single rabbit nodes of Ranvier at 22‐26 degrees C both under normal conditions, and after the nerve fibres had been acutely demyelinated by a variety of treatments designed to lossen the myelin from the axonal membrane. 2. The myelin‐loosening treatments included application of various combinations of: lysolecithin (to dissolve the myelin); collagenase (to loosen the connective tissue in the nodal region); high‐potassium Locke solution, hypertonic and hypotonic solutions (to induce axonal volume changes). 3. At a critical stage in such treatment (usually after 15‐45 min) a large outward current suddenly appeared. 4. There was no substantial change in the size of the measured inward sodium current when measured at this critical stage. 5. The outward current was blocked by internal TEA and caesium ions, had a reversal potential that became more positive when the external potassium concentration was increased, was kinetically similar to the known potassium current in frog fibres, and was therefore assumed to be a potassium current. 6. The phase of large outward current, whenever it appeared, was always accompanied by the appearance of a slow transient capacitative component in the leakage current, which indicated a marked increase in the effective nodal capacity (of 10‐ to 60‐fold). We suggest that the slow transient capacity current reflected charging of newly exposed axonal membrane, probably in the paranodal region, which was uncovered by the various acute demyelination treatments. This internodal membrane seems to contain mostly potassium channels and few, if any, sodium channels. 7. Newly dissected fibres occasionally showed large potassium currents before treatment, particularly if they were deliberately stretched during dissection; a marked slow capacity transient current was consistently present in these fibres. 8. The effects of acute paranodal demyelination on the sodium and potassium currents, and on the transient capacity currents, can be simulated by a model in which the node is coupled to a cable‐like paranode which contains Hodgkin‐‐Huxley type potassium channels and which has a much higher leakage resistance. 9. The functional significance of the presence of potassium channels in rhe internodal region (at least in the paranode) of mammalian fibres is discussed.
Stimulation by injected guanosine triphosphate of the sodium efflux in barnacle muscle fibres pre‐exposed to aldosterone.
Authors: Bittar E E , Nwoga J
Published: December 2014

1. A study has been made of the response of the Na efflux to injected guanosine triphosphate (GTP) in barnacle muscle fibres pre‐exposed to aldosterone. 2. (i) Injection of GTP into unpoisoned fibres causes a transitory stimulation. By contrast, injection of GTP into ouabain‐poisoned fibres causes a sustained stimulation. Little or no fall in Em is recorded following GTP injection. (ii) The stimulatory response to GTP of aldosterone pre‐exposed ouabain‐poisoned fibres differs from that seen in unexposed, ouabain‐poisoned fibres, in that its magnitude is greater and always sustained. 3. The magnitude of the response to GTP depends on external Ca and pH but not external Na. The response itself is not seen at 0 degrees C. 4. (i) Verapamil reduces the size of the response to GTP only if applied before GTP. Injection of EGTA, Fe, Zn and Co partially abolishes the residual response. (ii) Injection of MgCl2 almost completely reverses the response to GTP. KCl is ineffective. 5. These results are explained by supposing that removal of internal Mg and trace elements by GTP leads to activation of phosphoprotein phosphatase.
Electrophysiology of pig distal colon measured during early post‐natal development.
Authors: Cremaschi D , James P S , Meyer G , Smith M W
Published: December 2014

1. Brush border membrane (Vm) and transepithelial (Vms) potential differences, transepithelial resistance (Rep) and the brush border membrane/basolateral membrane resistance ratio (Rm/Rs) have been measured in distal colons taken from new‐born and 4‐day‐old pigs. 2. Vm remained independent of the age of the animal. Substituting choline or Tris for Na+ hyperpolarized Vm; substituting SO4(2‐) for Cl‐ or increasing the concentration of K+ depolarized Vm in colons taken from new‐born pigs. K+ depolarization was not seen using colons taken from 4‐day‐old animals. 3. The effect of Na+ or Cl‐ replacement on Vms and Rm/Rs was in agreement with the hypothesis that the brush border membrane of the distal colon possessed a conductance for both these ions. The brush border membrane of the new‐born, but not the 4‐day‐old pig colon possessed an additional conductance for K+. 4. These electrical measurements were repeated using 4‐day‐old pig distal colons in the presence of amiloride, to enable values for the electromotive force across the brush border membrane (Em) and the basolateral membrane (Es) to be calculated. The Em of the 4‐day‐old pig colon was found to be about 23 mV negative with respect to the mucosal solution. Cl‐ conductance appears to predominate in colons taken from these very young animals. 5. Separate experiments showed net transport of Na+ and measured short‐circuit current to be partly dependent upon the presence of Cl. Na+ transport measured in the absence of Cl‐ was approximately equal to that calculated from the measurement of short‐circuit current. 6. It is suggested that the brush border membrane of the neonatal pig colon is conductive to both Na+ and Cl‐, that the transport of these ions are partly coupled in some way and that this alone is sufficient to explain the discrepancies noted previously when measuring Na+ flux and short‐circuit current in Cl‐ ‐containing medium. The possible physiological importance of this transient transport function is discussed.
Sympathetically induced changes in the responses of guard hair and type II receptors in the cat.
Authors: Pierce J P , Roberts W J
Published: December 2014

1. Sympathetic effects on the activity of single guard hair receptors and slowly adapting, type II mechanoreceptors were studied in anaesthetized cats. 2. Spontaneous activity in type II receptors and mechanically evoked activity in both type II and guard hair receptors was recorded both without and with electrical stimulation of the lumbar sympathetic trunk. 3. Almost all guard hair receptors were desensitized by sympathetic stimulation, the mean effect being an increase in threshold to 2.2 times the unconditioned value. 4. One third of the more slowly adapting guard hair units showed sympathetically induced spontaneous activity. 5. These sympathetic effects on guard hair receptors appear not to be related to pilomotor responses or to changes in central arterial pressure. 6. Individual type II receptors were found to be excited by skin stretch along one of two axes: either parallel or perpendicular to the long axis of the leg. Intermediate orientations were not observed. 7. ‘Perpendicular’ units showed marked increases in resting discharge but no change in mechanical sensitivity during sympathetic stimulation. ‘Parallel’ units were unaffected. 8. The sympathetic effect appeared not to be related to changes in blood pressure or skin tension. 9. It is suggested that the location and orientation of stretch sensitivity of these receptors make them well suited for detection of limb movements; however, no satisfactory functional explanation was found for the pronounced sympathetic facilitation of only one subset of the receptors.
Calcium dependency of the inhibitory effect of antidiuretic hormone on in vitro renin secretion in rats.
Authors: Churchill P C
Published: December 2014

1. Synthetic arginine‐vasopressin (ADH or antidiuretic hormone) inhibited renin secretory rate of rat renal cortical slices. The response was concentration‐dependent and was maximal at 0.1 U . ml.‐1. 2. Ca depletion (incubation of slices in medium containing Na2EGTA and no added CaCl2) stimulated renin secretion and eventually abolished the inhibitory effect of ADH. Both these effects were reversible. 3. The Ca antagonist D‐600, at 0.5 microM, reversed the inhibitory effect of K depolarization on secretory rate but had no effect on secretory rate on on‐depolarized slices. In the presence of 0.5 microM‐D‐600, ADH inhibited the secretory rate of either depolarized or non‐depolarized slices. 4. These results confirm and extend previous observations suggesting that Ca plays an inhibitory coupling role in the control of renin secretion. Moreover they suggest that although Ca influx through voltage‐sensitive Ca channels influences the secretory activity of juxtaglomerular cells, ADH activates an independent pathway for Ca mobilization.
The recruitment order of gamma‐motoneurones in the decerebrate rabbit.
Authors: Murphy P R
Published: December 2014

1. The order of firing (i.e. recruitment order) of gastrocnemius medialis gamma‐motoneurones to natural stimulation of the limbs has been studied in the precollicular decerebrate rabbit. 2. Recruitment order was not invariable. However, when a fixed order occurred there was a significant tendency for neurones to be recruited in order of increasing axonal conduction velocity. The functional significance of this finding is discussed. 3. In the preparation used, many gamma‐motoneurones were spontaneously active. 4. Two types of gamma‐motoneurone were distinguished on the basis of their resting discharge characteristics and responses to natural stimulation. 5. A significant correlation between resting discharge frequency and axonal conduction velocity was found for gamma‐motoneurones that were predominantly excited by natural stimulation.
An ATP‐dependent sodium‐sodium exchange in strophanthidin poisoned dialysed squid giant axons.
Authors: Beaugé L , DiPolo R
Published: December 2014

1. Dialysed giant axons from the squid have been used to study some of the properties of the Na+ fluxes when the Na+ pump is fully inhibited by strophanthidin. 2. In axons which had been depleted of ATP, strophanthidin had no effect on Na+ efflux. Similar negative results were obtained in axons dialysed with and without internal or external K+, and with or without 100 microM‐internal Ca2+. 3. In the presence of 60 mM‐internal Na+, 440 mM‐external Na+ and strophanthidin, the fluxes of Na+ had the following characteristics. (i) ATP stimulated an efflux and an influx of Na+ of similar magnitude. The K1/2 for ATP, measured from its effect on Na+ efflux, was about 200 microM. (ii) The non‐hydrolysable ATP analogue adenylyl(beta, gamma‐methylene)‐diphosphonate (AMP‐PCP), at 2 mM concentration, either alone or in combination with 2 mM‐internal phosphate, failed to stimulate any efflux of Na+. (iii) The ATP‐dependent Na+ efflux was not affected by removal of internal or external K+, or external Mg2+ or Ca2+, and was not dependent on internal Ca2+. (iv) within the resolution of the method, all the ATP‐dependent Na+ influx required internal Na+, and all the ATP‐dependent Na+ efflux required external Na+. From the magnitude of the unidirectional Na+ fluxes the stoichiometry seemed to be a 1 to 1 Na+‐‐Na+ exchange. 4. The ATP‐internal Na+‐dependent influx of Na+ in the presence of strophanthidin was not affected by 1 mM‐vandate in the dialysis solution, a concentration which fully inhibits the Na+ efflux through the Na+ pump that is activated by external K+. 5. In the presence of external Na+, the external K+ sites of the Na+ pump are completely saturated with 100 mM‐external K+. In unpoisoned axons incubated with 100 mM‐external K+, replacement of external Na+ with Tris+ produced no change in the efflux of Na+. However, in axons poisoned with 50 microM‐strophanthidin, replacement of external Na+ with Tris+ resulted in a reversible inhibition of Na+ efflux. This could suggest that strophanthidin poisoning might induce Na+ (cations?) fluxes which are not present in normal conditions.
Electrophysiology of mammalian inferior olivary neurones in vitro. Different types of voltage‐dependent ionic conductances.
Authors: Llinás R , Yarom Y
Published: December 2014

The electrophysiological properties of guinea‐pig inferior olivary (I.O.) cells have been studied in an in vitro brain stem slice preparation. 1. Intracellular recordings from 185 neurones in this nucleus reveal that antidromic, orthodromic or direct stimulation generates action potentials consisting of a fast spike followed by an after‐depolarizing potential (ADP). The ADP had an amplitude of 49 +/‐ 8 mV (mean +/‐ S.D.) and a duration which varied over a wide range with the level of depolarization. This ADP is followed by an after‐hyperpolarizing potential (AHP) having an amplitude of 12 +/‐ 3 mV (mean +/‐ S.D.) from rest and lasting up to 250 msec. The AHP shows a rebound depolarization wave. 2. Synaptic activation may be obtained by peri‐olivary stimulation with a bipolar electrode located in the immediate vicinity of the I.O. nucleus. These potentials are a mixture of depolarizing and hyperpolarizing synaptic events which can be reversed by direct membrane polarization. 3. Addition of tetrodotoxin (TTX) to the bath, or removal of extracellular Na, abolishes the fast initial action potential but does not modify the ADP or the AHP. Blockage of Ca conductance by Co, Mn, Cd or D600, or replacement of Ca by Mg, abolishes the ADP‐‐AHP sequence. 4. Hyperpolarization of the neurone uncovers a low‐threshold Ca conductance which is inactivated at rest and has similar pharmacological properties to the ADP. This low‐threshold spike plays a central role in the rebound potential following the AHP. 5. Simultaneous impalement of I.O. neurone pairs demonstrated the presence of electrotonic coupling between neurones, which is especially prominent in the medial accessory olive.
The development of spatial‐frequency selectivity in kitten striate cortex.
Authors: Derrington A M , Fuchs A F
Published: December 2014

1. Single units were recorded in the striate cortex of kittens aged between 2 and 12 weeks. Contrast sensitivity measurements made using moving sinusoidal gratings were used to construct spatial‐frequency tuning curves. 2. In young kittens cells had low sensitivities, responded only to low spatial frequencies and were unselective for spatial frequency. In addition 30% of the cells recorded in the youngest kittens were unresponsive to visual stimuli. 3. Sensitivity improved to near‐adult values within 5‐6 weeks. 4. Best spatial frequency improved more gradually, so that even in the oldest kittens best spatial frequencies were lower than adult values. 5. Selectivity for spatial frequency, considered both in terms of the numbers of selective cells and the narrowness of their tuning curves, improved rapidly, and reached adult values within the first 6 weeks. 6. These results are discussed in relation to other developmental studies.
The effects of denervation on contractile properties or rat skeletal muscle.
Authors: Finol H J , Lewis D M , Owens R
Published: December 2014

1. Isometric contractions of fast and slow twitch muscles of rats were recorded 1‐42 days after denervation. 2. The major changes occurred over the period from 2 to 6 days after denervation. These changes were qualitatively similar in the two types of muscle. The most important effects were on the twitch: times to peak and half relaxation were prolonged, active tension and peak rate of rise of tension were increased. Tetanic tension per unit cross‐sectional area and the maximum rate of rise of tension decreased during this period but, in the second week, the tension recovered substantially and the maximum rate recovered completely. 3. Very small differences were seen between muscles denervated with short and long nerve stumps at day 4. 4. In the late stage of denervation (7‐42 days) twitch and tetanic tension fell more than cross‐sectional area, but this may have been due to greater atrophy of fibres compared with other muscle tissue. 5. Apart from this tension fall, there were only small changes in the fast muscle in the late stage of denervation. These were a fall in twitch‐tetanus ratio and a prolongation of relaxation. 6. In more than half of the soleus muscles there was a late reversal of some of the denervation changes, and these muscles showed a greater degree of atrophy. The less atrophied soleus muscles maintained a prolonged twitch and a low rate of development of tension. 7. It is concluded that denervation affects the contractile properties of muscle as early and as abruptly as it does the membrane properties, and that most of the contractile changes are a direct consequence of changes in excitation‐contraction coupling alone.
Recurrent inhibition of intercostal motoneurones in the cat.
Authors: Kirkwood P A , Sears T A , Westgaard R H
Published: December 2014

1. The external and internal intercostal nerves of a single intercostal space were stimulated in anaesthetized paralysed cats with dorsal roots cut in the corresponding spinal cord segment. 2. Extracellular recording in the ventral horn revealed single units which fired short high frequency bursts of spikes at short latency to stimulation of either or both of the two nerves at stimulus strengths appropriate to the activation of alpha motor axons. These units were deduced to be Renshaw cells. 3. Small (0.1‐0.2 mV) hyperpolarizing potentials of duration up to 50 msec were recorded intracellularly in both inspiratory and expiratory motoneurones of the same segment. Latencies and thresholds were appropriate for disynaptic i.p.s.p.s evoked by collaterals of alpha motor axons. 4. The changes in probability of firing following the stimuli were examined for inspiratory alpha motoneurones by constructing post‐stimulus histograms of efferent discharges recorded from filaments of the external intercostal nerve of the segment stimulated and from other segments. 5. A period of reduced probability of firing of up to 24 msec duration, corresponding in all respects to disynaptic inhibition from alpha motor axon collaterals, was seen in the segment stimulated and up to three segments distant, though declining in intensity with distance. Either nerve could evoke such inhibition although that evoked from the internal intercostal nerve was stronger, as were the intensities of the Renshaw cell discharges. 6. We conclude that recurrent inhibition, via Renshaw cells which have axons up to 30 mm in length, is present for intercostal motoneurones. Arguments are adduced to show that although the effects from stimulating any one segmental nerve may be relatively weak, the over‐all effect resulting from the widely spread projections of the Renshaw cells concerned is an inhibition comparable intensity with that seen in many hind limb motor nuclei.
Effects from fine muscle and cutaneous afferents on spinal locomotion in cats
Authors: Kniffki K.-D. , Schomburg E. D. , Steffens H.
Published: December 2014

1. The effects of chemically activated fine muscle afferents (groups III and IV) and electrically activated cutaneous afferents on motoneuronal discharges were studied before and during fictive locomotion induced pharmacologically by
i.v. administration of nialamide and
l‐DOPA in high spinal cats. Efferent activity was recorded simultaneously from nerve filaments to ipsi‐ and contralateral extensor and flexor muscles. In addition, intracellular recordings were made from lumbar α‐motoneurones.

2. After nialamide but before treatment with
l‐DOPA, in some cases, transient locomotor‐like discharges were induced by an increased activity in fine muscle afferents. The response pattern in nerves to both hind limbs could be different showing e.g. only transient alternating activity between knee flexor and extensor of one limb but not of the other one.

3. Treatment with
l‐DOPA did not always cause fictive locomotion. Often not all motoneurone pools showed rhythmic activity. In these cases stimulation of group III and IV muscle afferents usually caused transient periodic activity. In cases with apparent rhythmic activity, algesic stimulation of the gastrocnemius—soleus muscle caused an accentuation of the rhythm by a more abrupt transition from the active phase to the non‐active interval. Again, the response patterns on both sides were not uniform in all cases.

4. A second type of response to activation of fine muscle afferents had a quite different character: the rhythmic activity was more or less completely overridden by a strong transient tonic hyperactivity or the rhythm was transiently blocked. These phenomena did not occur in the same way in all nerves.

5. Electrical stimulation of cutaneous nerves of the hind limb generally induced the same response pattern as chemical stimulation of the group III and IV muscle afferents. The effects varied depending on the stimulus strength and the nerve.

6. The results revealed that cutaneous and fine muscle afferents not only have similar functions in the reflex control of a limb but also in evocation and modulation of locomotion. Therefore, it is assumed that both types of afferents may serve together as a peripheral feed‐back to the spinal locomotor centre.