bluuebunny/crossref_metadata_2025 huggingface dataset:
The contrast sensitivity, spatial resolution and velocity tuning of the cat's optokinetic reflex.
Authors: Donaghy M
Published: December 2014

1. Optokinetic nystagmus has been evoked from two cats using horizontally moving vertical grating patterns with sinusoidally modulated wave forms (mean luminance 8.5 cd/m2). Eye movements were recorded by DC electro‐oculography. 2. The velocity ‘tuning’ of the slow phase response was measured for high‐contrast (0.8) gratings with spatial frequencies ranging from 0.18 to 2.8 cycles/deg. Irrespective of spatial frequency, the gain of slow phase tracking always declined as the stimulus velocity exceeded 5‐8 deg/sec. 3. The effect of variations in grating contrast on the gain of slow phase tracking was investigated for spatial frequencies ranging from 0.04 to 2.8 cycles/deg. These gratings always moved at a velocity of 3 deg/sec. Reductions in grating contrast produced a fall in the gain of slow phase tracking. At any given contrast, the extent of the fall in gain depended on spatial frequency. At no value of spatial frequency was an optokinetic response demonstrable when the contrast fell below 0.02. 4. The above results have been used to derive the threshold contrast for evoking an optokinetic response at each spatial frequency tested. A contrast sensitivity function is plotted from these threshold contrasts, and this is compared with previous estimates of the cat's contrast sensitivity function derived from measurements of visual discrimination and cortical evoked potentials.
Effects of synaptic and antidromic stimulation on tyrosine hydroxylase activity in the rat superior cervical ganglion.
Authors: Chalazonitis A , Zigmond R E
Published: December 2014

1. The effects of orthodromic and antidromic stimulation of the rat superior cervical ganglion on the specific activity of the enzyme tyrosine hydroxylase have been studied. 2. Orthodromic stimulation of the ganglion via the sympathetic trunk produced an increase in the activity of tyrosine hydroxylase when measured 3 days later while causing no change in the protein content of the ganglion. This increase in the specific activity of tyrosine hydroxylase was blocked by administration of the nicotinic antagonist, hexamethonium. 3. Antidromic stimulation of the superior cervical ganglion by stimulating the internal carotid nerve, the external carotid nerve or both nerves simultaneously produced no change in the specific activity of tyrosine hydroxylase. 4. Parallel increases in tyrosine hydroxylase activity and protein content per ganglion were seen when the internal carotid nerve was stimulated but similar changes were seen in "sham‐stimulated" animals. These "non‐specific" changes were apparently produced by the trauma involved in the extensive dissection necessary to position electrodes on this nerve trunk. 5. We conclude that an increase frequency of firing in post‐ganglionic neurones is not a sufficient stimulus to elevate the specific activity of tyrosine hydroxylase. Rather some other aspect of nicotinic receptor stimulation seems to be required.
Alpha‐drenergic inhibition of calcium‐dependent potentials in rat sympathetic neurones.
Authors: Horn J P , McAfee D A
Published: December 2014

1. Post‐ganglionic neurones of the rat superior cervical ganglion were studied in vitro (21‐26 degrees C) using single intracellular micro‐electrode methods. 2. Three Ca2+‐dependent potentials were studied: the shoulder on the normal action potential, the hyperpolarizing afterpotential (h.a.p.), and th Ca2+ spike. 3. Bath‐applied noradrenaline reversibly inhibited these Ca2+‐dependent potentials. The EC50 for inhibition of peak h.a.p. amplitude was about 1 microM. The order of catetholamine potency was: L‐adrenaline > L‐noradrenaline > D‐noradrenaline congruent to dopamine > DL‐isoprenaline. Phentolamine (10 microM), an alpha‐blocker, but not MJ‐1999 (10 microM), a beta‐blocker, antagonized the action of noradrenaline. 4. Noradrenaline (10 microM) hyperpolarized most neurones (1‐6 mV) studied, with no detectable change in resting membrane conductance. 5. Superfusion with low external Ca2+ and high Mg2+ mimicked the effect of noradrenaline. Either procedure alone antagonized the h.a.p. conductance increase but did not alter the h.a.p. reversal potential. However, in the presence of low Ca2+, high Mg2+, the remaining action potential and h.a.p. were not further reduced by noradrenaline. 6. The Ca2+‐dependent shoulder of the action potential did not appear dependent upon GK. Noradrenaline and low Ca2+ antagonized the shoulder when enhanced by TEA+ or Ba2+. 7. Both the rate of rise and amplitude of the Ca2+ spike were antagonized by noradrenaline. 8. We propose that activation of an alpha‐adrenoceptor inhibits a voltage‐sensitive Ca2+ conductance (GCa(V)), thereby reducing the inward Ca2+ current which may generate the noraml action potential shoulder and the rising phase of the Ca2+ spike. Reduction of Ca2+ current would also reduce the Ca2+‐dependent portion of outward K+ current underlying the h.a.p.
The effect of raised intramammary pressure on mammary function in the goat in relation to the cessation of lactation.
Authors: Peaker M
Published: December 2014

1. The effects of raising intramammary pressure on mammary function have been studied in conscious goats. 2. When intramammary pressure was raised to levels which normally occur following cessation of milking (by infusing isosmotic sucrose into the lumen of the gland) the rate of milk secretion fell within 6 hr, but in short‐term studies at these pressures, there was no reduction in mammary blood flow (in fact there was a significant increase) and no change in oxygen consumption or glucose uptake. 3. At pressures more than twofold higher than those which occur under physiological conditions, there was a decrease in mammary blood flow within 5 min; in addition the arterio‐venous difference for oxygen, but not for glucose, fell. The changes were reversed when pressure was lowered. Similar results were obtained in autotransplanted (denervated) glands. 4. Intramammary pressure‐volume curves were determined 3 days before cessation of milking. By determining the rate of secretion after cessation it was evident that the rate of secretion fell as the pressure‐volume curve steepened. 5. A positive correlation was found between empty gland volume and functional capacity of the gland (volume of liquid needed to raise intramammary pressure to 30 mmHg at the tip of the teat) in goats of the Saanen breed. 6. No apparent effect on blood‐milk potential difference was obtained at pressures within the range observed after cessation of milking. At higher pressures, the potential difference fell, eventually to zero. 7. It is concluded that in the goat the arrest of milk secretion following cessation of milking is caused by mammary distension but is not due to a primary effect of mammary distension on blood flow, and that the loss of integrity of the mammary epithelium, which also occurs, is not due simply to mechanical rupture. 8. From present and previous studies, a scheme is proposed to account for the control of mammary function after the cessation of milking in late lactation in the goat.
Slow synaptic potentials in neurones of the myenteric plexus.
Authors: Johnson S M , Katayama Y , North R A
Published: December 2014

1. Intracellular recordings were made in vitro from neurones in the myenteric plexus of the guinea‐pig ileum. Potential changes were recorded in response to focal stimulation of the surface of the myenteric ganglion at a distance of 30‐100 microM from the impaled cell. 2. Stimuli comprising single pulses evoked cholinergic excitatory post‐synaptic potentials ('fast' e.p.s.p.s) in S cells. In a small proportion (20%) of both S and AH cells such stimuli also evoked depolarizing potentials with a time course about 1000 times slower than that of the fast e.p.s.p. 3. Stimuli comprising repeated pulses (up to 20 Hz for 2 sec) evoked the slow depolarizing potentials in a higher proporton of neurones (42%). These stimuli caused a hyperpolarizing potential change in 9% of cells, and in a very few cells biphasic changes i membrane potential were observed. 4. Both the slow depolarizing and the slow hyperpolarizing responses persisted in atropine (up to 5 microM) and hexamethonium (up to 200 microM), but were reversibly abolished by changing to calcium‐free solutions. 5. Evidence is presented which suggests that the slow depolarizing response is caused by inactivation of the membrane potassium conductance, and the slow hyperpolarizing response is due to activaton of the potassium conductance.
The effects of partial denervation at birth on the development of muscle fibres and motor units in rat lumbrical muscle.
Authors: Betz W J , Caldwell J H , Ribchester R R
Published: December 2014

1. Two aspects of nerve‐muscle development were studied in neonatal rats, the role of competition between motor neurones during the elimination of polyneuronal innervation, and the dependence of muscle fibre production upon the number of motor neurones innervating the muscle. 2. Rat lumbrical muscles were partially denervated at birth by cutting the lateral plantar nerve. Many muscles remained innervated by a single motor axon from the sural nerve. These motor units developed in the complete absence of competition from other motor units. In the adult muscles the number of innervated muscle fibres was approximately the same as at birth (about 120 muscle fibres). 3. In muscles that were totally denervated at birth, the normal post‐natal production of muscle fibres was arrested. In partially denervated muscles, the production of new muscle fibres depended on the number of remaining motor units. The relationship between the total number of muscle fibres and the number of remaining motor units was fitted by a simple model. 4. The results suggest that in the lumbrical muscle, the decrease in motor unit size that occurs during normal development can be accounted for entirely by competition between motor nerve terminals. 5. The results also suggest that the normal post‐natal increase in the total number of muscle fibres depends on a trophic interaction between the muscle and its innervation.
Sprouting of active nerve terminals in partially inactive muscles of the rat.
Authors: Betz W J , Caldwell J H , Ribchester R R
Published: December 2014

1. Certain muscles in the hind foot of rats were partially paralysed by applying tetrodotoxin to part of their motor innervation. In these muscles motor nerve sprouting occurred from the terminals of the unblocked axons. The extent of sprouting was compared with that seen in totally paralysed and in partially denervated muscles. 2. Action potentials were blocked in the medial and lateral plantar nerves of adult rats for 5‐13 days by continuous superfusion with a solution containing tetrodotoxin. The drug was delivered through a tube and nerve cuff from an osmotic pump placed intraperitoneally. Control experiments showed that nerve block was complete and that signs of nerve damage were absent in the animals included in the study. 3. Two muscles (the second lumbrical and flexor digitorum brevis), which received innervation only from the medial plantar nerve, were totally paralysed by the nerve block. Two different muscles (the fourth lumbrical and flexor digitorum quinti brevis) were only partially paralysed, since they received their innervation from the lateral plantar nerve and, in addition, from the sural nerve which was not blocked. One day before the final experiment, the lateral plantar nerve was cut, and its terminals degenerated. Thus in the partially paralysed muscles only the unblocked terminals from the sural nerve remained. These terminals were observed after staining with zinc iodide and osmium tetroxide. Similarly, terminals from the medial plantar nerve were examined in the totally blocked muscles from the same animal. 4. In other experiments, muscles were partially denervated by cutting the lateral plantar nerve in order to compare effects of nerve block and nerve section. 5. Sprouting occurred under all three conditions. Active terminals in the muscles partially paralysed for 5‐7 days sprouted to the same extent as terminals in muscles totally blocked during the same period: about 35% of the terminals had sprouts, and their average length was about 13 micron. Sprouting was more pronounced in partially denervated muscles: about 65% of the terminals had sprouts and they averaged 24 micron in length. Collateral (preterminal) sprouts were seen only after partial denervation. 6. Physiological and histological observations suggested that sprouts in paralysed muscles, unlike those in partially denervated muscles, seldom if ever made new synapses on neighbouring muscle fibres, even after 12‐13 days of nerve block. 7. The results show that inactive muscle fibres cause active nerve terminals on neighbouring fibres to sprout, perhaps by releasing a diffusible, sprout‐promoting factor, which is part of the stimulus for motor nerve sprouting in partially denervated muscles.
Phasic secretion of acetylcholine at a mammalian neuromuscular junction.
Authors: Datyner N B , Gage P W
Published: December 2014

1. The transient increase in secretion of quanta of acetylcholine (phasic secretion) produced by an action potential or brief depolarizing current pulse in mouse phrenic nerve terminals was examined. 2. Following an activating stimulus, there was a brief delay (minimum latency) followed by a sigmoidal increase in secretion which then decayed exponentially. 3. The minimum latency, rise time and rate of decay of phasic secretion, whether elicited by action potentials or electrotonic depolarization, were all extremely sensitive to temperature, with Q10s as high as 4 at temperatures of 5‐15 degrees C. Arrhenius plots of results showed a change in slope with temperature, the change appearing most marked at 20‐25 degrees C. 4. Phasic secretion in response to action potentials prolonged by inhibitors of K conductance (4‐aminopyridine, uranyl, tetraethylammonium or Zn ions) showed an increase in minimum latency but no other change in time course. 5. Depolarizing pulses of varying width (0.2‐2 msec) applied to nerve terminals (in the presence of tetrodotoxin and 4‐aminopyridine) affected minimum latency, but had no great effect on the time course of phasic secretion. 6. Neither an increase in extracellular K ion concentration nor a decrease in pH had any effect on the time course of phasic secretion nor was any change produced by ethanol or octanol. 7. Variations in extracellular Ca concentration, substitution of Sr ions for Ca ions and repetitive stimulation, while producing changes in the magnitude of secretion, produced no change in the time course of phasic secretion.
The action of serotonin in the rat hippocampal slice preparation.
Authors: Segal M
Published: December 2014

1. Intracellular activity was recorded from neurones in the CA1 pyramidal layer of slices of rat hippocampus maintained in vitro. 2. Application of 5‐HT in a droplet or via ionophoresis produced a 3‐5 mV hyperpolarization associated with a 30% decrease in input resistance. 3. The response to 5‐HT was minimal with a drop concentration of 1 microM and maximal with 100 microM. The responses appeared to be blocked by methysergide applied in the superfusion medium. 4. The responses to 5‐HT were minimal when the drug was applied in the apical dendritic region and maximal when it was applied near the soma. 5. 5‐HT produced no substantial changes in e.p.s.p.s evoked by stimulation of the Schaffer collateral‐commissural system or in i.p.s.p.s which were occasionally encountered following stimuli to the stratum radiatum. 6. The responses to 5‐HT are true post‐synaptic responses and are not indirect effects since they are present in a Ca2+‐deficient Mg2+‐enriched medium which blocks synaptic transmission. 7. The responses to 5‐HT were not dependent on extracellular Cl‐ concentration. 8. These experiments indicate that 5‐HT produces its effects in the rat hippocampus by activating K+ channels.
Release of inorganic phosphate during activity in mammalian non‐myelinated nerve fibres
Authors: Maire J. C. , Straub R. W.
Published: December 2014

1. The efflux of labelled phosphate was measured in desheathed rabbit vagus nerve at rest and during activity.

2. In solutions with 2 m
M‐phosphate and 1 m
M‐K the rate constant of the resting efflux was 2·7 × 10−3 min−1; stimulation caused an extra fractional loss of 2·8 × 10−6 impulse−1.

3. Lowering the phosphate concentration decreased the resting and the stimulated efflux; with 0·2 m
M‐phosphate the corresponding values were 1·9 × 10−3 min−1 and 1·8 × 10−6 impulse−1, respectively.

4. Increasing the K to 5·6 m
M decreased both resting and stimulated efflux.

5. Lowering the temperature decreased the resting efflux with a Q10 of 2·9 and the stimulated efflux with a Q10 of 8·1.

6. Chromatography of the effluent showed that at rest and during activity at least 96% of the radiophosphate was in the orthophosphate fraction.

7. Replacing the Na of the solution by Li lowered the rate constant of the resting efflux to 0·8 × 10−3 min−1 and abolished the extra release during activity, without reduction of the action potential.

8. The presence of ouabain did not affect the resting efflux, except at 100 μ
M, when a transient reduction was found. The extra fractional loss was not affected with 0·001 μ
M; with 0·01‐0·5 μ
M, it was reduced without much change in the action potential, and abolished at higher concentrations.

9. The results agree with the hypothesis that the extra release results from an increase in internal inorganic phosphate caused by increased break‐down of ATP during recovery.

10. Comparison with the O2 consumption shows that about 1% of the inorganic phosphate liberated at the inside of the axons escapes to the outside.
Membrane‐potential effects on an inhibitory post‐synaptic conductance in Aplysia buccal ganglia.
Authors: Gardner D
Published: December 2014

1. Inhibitory post‐synaptic currents (i.p.s.c.s) were recorded under voltage clamp using two electrodes placed in neuronal somas of the buccal ganglia of Aplysia, in order to study the effects of membrane potential (Vm) on decay time constant (tau). 2. From ‐175 to ‐40 mV, tau did not vary with Vm. At Vm more depolarized than ‐40 mV, tau decreased. Also at depolarized Vm, cell input resistance (Rin) decreased and many cells showed non‐exponential i.p.s.c. decay, including undershoot. These results suggest that the apparently faster tau is an artifact of remote membrane poorly clamped at the low Rin of depolarized levels, rather than a Vm‐dependent i.p.s.c. relaxation. 3. Injected current pulses produced voltage relaxations which decayed faster including undershoot, when Vm was depolarized beyond ‐40 mV. 4. Step commands across the reversal potential were delivered during i.p.s.c.s. Currents reversed direction, relaxing consistent with the new Vm, thus showing that recorded current decay repressants the true time course of i.p.s.c. relaxation, rather than uncontrolled slow axonal charging from a fast remote synaptic current. 5. I conclude that clamp control is poor at depolarized Vm, due to decreased Rin, and the faster, non‐exponential decay seen includes a superimposed nonsynaptic current. Tetraethylammonium injected into the presynaptic neurone produces only slight effect on the i.p.s.c. decay time constant, suggesting that the non‐synaptic current is unlikely to be due to a voltage‐dependent K conductance.
Thermoregulatory noradrenergic and serotonergic pathways to hypothalamic units
Authors: Brück K. , Hinckel P.
Published: December 2014

1. In guinea‐pigs hypothalamic single units were extracellularly tested for their response to thermal stimulation of the skin and to electrical stimulation of two different pontine areas, the nucleus raphé magnus and the dorsomedial reticular formation. Furthermore, thermoregulatory control actions were measured during the stimulations.

2. Electrical stimulation of those reticular formation areas containing noradrenaline cells caused an increase of oxygen uptake, electrical muscle activity and body temperature, while stimulation of the nucleus raphé magnus, known to contain serotonin cells, brought about inhibition or had no effect.

3. The recorded units could be subdivided into three groups.

Cell type a. Neurones on the boundary of preoptic and anterior hypothalamic regions which increased their firing rate when the skin was cooled and decreased it when the nucleus raphé magnus was stimulated.

Cell type b. Neurones in the anterior hypothalamus which did not respond to brain‐stem stimulation.

Cell type c. More posterior neurones which increased their firing rate when the skin was warmed or when the nucleus raphé magnus was stimulated and decreased their firing rate when the reticular formation was stimulated.

4. Cell type a seems to represent interneurones which are connected to the ascending serotonergic thermoregulatory pathway. As for cell type c, it is inferred that it could represent interneurones which control the threshold for shivering and non‐shivering thermogenesis.
Divalent ion currents and the delayed potassium conductance in an Aplysia neurone.
Authors: Adams D J , Gage P W
Published: December 2014

1. In Na‐ and Ca‐free external solutions, Sr or Ba (but not Mg) could act as carriers of inward current during action potentials in the neurone, R15 of the Aplysia abdominal ganglion. These action potentials exhibited a prolonged plateau phase, the duration of which was dependent on the concentration and species of divalent cation and activity of the neurone. 2. Depolarization of the soma membrane in Na‐free Ba solution generated a prolonged, ‘late’ inward current the amplitude of which was dependent on the external Ba concentration. The Ba current was insensitive to tetrodotoxin but could be blocked by Mn2+ and Co2+ ions. 3. The peak current‐voltage relation and threshold for activation of the late inward current was shifted to more negative potentials on replacement of Ca with Ba. The zero‐current (reversal) potentials for both Sr and Ba were more negative than for Ca, indicating that the ‘Ca’ channel is less permeable to Sr2+ or Ba2+ ions than to Ca2+ ions. 4. Inactivation of the ‘Ca’ channel is slower in Ba than in Ca solution. The time course of Ba currents during a maintained depolarization of 2 sec could be reasonably described by the expression, I'Ba(t) = I'Ba (infinity) [1‐exp(‐t/tau M)]2exp(‐t/tau H). 5. Time constants for activation (tau M) and inactivation (tau H) were voltage‐dependent. In the range ‐10 to +30 mV, tau M varied from 15 to 5 msec and tau H from 2.0 to 0.5 sec (12 degrees C). Steady‐state Ba conductance (corrected for inactivation) was voltage‐dependent, increasing sigmoidally with depolarization to a maximum of approximately 12 microS at potentials beyond +15 mV. 6. Steady‐state inactivation of Ba conductance (hBa(infinity)) varied with holding potential (VH). Conditioning holding potentials more negative than the resting potential (‐40 to ‐50 mV) produced depression of Ba currents. Complete inactivation of Ba currents occurred at holding potentials more positive than 0 mV or with repetitive activation at frequencies greater than 1 Hz. 7. The divalent ions, Ba2+ and Sr2+, reversible depressed the total delayed K+ current at a rate dependent on the frequency of activation. Ba and Sr shifted the delayed K+ current‐voltage curve to more positive voltages and depressed the delayed outward current at all membrane potentials. 8. Comparison of the effect of Ba on delayed K+ currents with those obtained in the presence of Mn2+ ions indicated that Ba2+ ions depress both the voltage‐dependent and Ca‐dependent components of the delayed K+ current. However, the mechanism by which Ba acts to inhibit the two components of the delayed K+ current appears to be different.
Activation of cat muscle spindle primary, secondary and intermediate sensory endings by suxamethonium.
Authors: Dutia M B
Published: December 2014

1. These experiments were based on the recent observation of Gladden (1976), that acetylcholine (ACh) when applied to the isolated cat muscle spindle caused contraction of the dynamic and the static nuclear bag fibres, and not of the nuclear chain fibres, and that the dynamic nuclear bag fibre had the lower threshold to ACh than the static nuclear bag fibre. Subsequently, suxamethonium (SCh) has been shown to have similar effects on the intrafusal muscle fibres (Gladden & McWilliam, 1977). 2. In these experiments, the response of cat soleus muscle spindle primary, secondary and ‘intermediate’ sensory endings to repetitive ramp stretches during continuous slow infusions of SCh were studied. The changes observed are interpreted on the basis of the known action of SCh on the intrafusal muscle fibres of the isolated spindle. 3. Primary sensory endings, with afferent axon conduction velocities above 80 m/sec, were activated during SCh infusion in three stages. In Phase I of excitation, a gradual facilitation of the discharge of the Ia endings was seen, without potentiation of the dynamic or length sensitivity to stretch. In Phase II of excitation, the dynamic sensitivity of the Ia endings increased very markedly. In Phase III of excitation, an increase in length sensitivity was superimposed on the already enhanced dynamic sensitivity. 4. Secondary sensory endings, with afferent axon conduction velocities below 60 m/sec, only experienced a gradual facilitation of their discharge during SCh infusion, similar to the Phase I effects of SCh on primary endings. 5. The majority of ‘intermediate’ sensory endings, with afferent axon conduction velocities between 60 and 80 m/sec, were activated by SCh either in the same way as primary endings, or in the same way as secondary endings. However, a significant number of these sensory endings behaved in a truly intermediate manner during SCh infusion (cf. Rack & Westbury, 1966), and may represent an intermediate form of spindle sensory ending. 6. The afferent axon conduction velocities of these truly intermediate sensory endings were restricted to the range 69‐77 m/sec. All the ‘intermediate’ endings which were activated in a primary‐like manner had afferent axons conducting at velocities greater than 74 m/sec. ‘Intermediate’ endings which were activated in a secondary‐like manner had afferent axon conduction velocities below 72 m/sec. 7. The probable contribution of the static and dynamic nuclear bag fibres to the discharge of each type of spindle sensory ending is discussed.
Rubidium block and rubidium permeability of the inward rectifier of frog skeletal muscle fibres.
Authors: Standen N B , Stanfield P R
Published: December 2014

1. A three‐electrode voltage clamp method was used to investigate the Rb block of inward rectification in frog sartorius muscle fibres. 2. In a solution containing 80 mM‐K+, the potassium conductance increased with increasing hyperpolarization to 3.18 +/‐ 0.11 mS. cm‐2 (n = 17) when (V ‐ VK) was ‐150 mV. In the presence of Rb+, the conductance increased, fell and increased again with increasing hyperpolarization, i.e. the Rb block was first increased and then reduced by increasing hyperpolarization. Increasing [Rb]o increased the block at all voltages. 3. In a solution containing 80 mM‐Rb+ (zero K+) inward currents were recorded when the membrane was hyperpolarized beyond about ‐60 mV. These currents, which were < 10% the amplitude of those in 80 mM‐K solution, were blocked by tetraethylammonium ions. 4. Experiments were carried out in solutions either where both [K]o and [K]i were increased, or where [K]o only was increased. The form of the relation between K conductance and membrane potential appeared to depend on [K]o. The magnitude of the conductance appeared to depend on [K]o and on [K]i. 5. So far as the block by Rb+ is concerned, increasing [K]o appeared to enhance the release of Rb block under large hyperpolarizations. Increasing [K]o and [K]i reduced the Rb block at all membrane potentials. 6. The results of experiments in the presence of Rb+ and Cs+ suggest that these two ions do not compete with each other for a site at which they block inward rectification. Rather, over a range of membrane potentials from ‐25 to ‐65 mV, the presence of Cs+ enhances the Rb block and vice versa. 7. Single dissected muscle fibres (from semitendinosus) were used to measure sarcoplasmic resistivity in 80 mM‐K solution and 160 mM‐K (hyperosmotic) solution. The measured values were 163.2 +/‐ 11.7 omega x cm and 136.1 +/‐ 16.0 omega x cm, respectively (n = 7). 8. A semi‐empirical model is presented, supposing that Rb interacts with a site in the membrane to produce its blocking effect, but is able to move on through into the sarcoplasm. Internal K+ is supposed to reduce the affinity of the site for Rb+; external K+ is able to enhance the moving on of Rb+ into the sarcoplasm. 9. The implications of our experiments for the nature of the permeability mechanism inward rectification are discussed.
Phase relationship between normal human respiration and baroreflex responsiveness.
Authors: Eckberg D L , Kifle Y T , Roberts V L
Published: December 2014

1. We studied the influences of phase of respiration and breathing frequency upon human sinus node responses to arterial baroreceptor stimulation. 2. Carotid baroreceptors were stimulated with brief (0.6 sec), moderate (30 mmHg) neck suction during early, mid, and late inspiration or expiratin at usual breathing rates, or, during early inspiration and expiration at breathing rates of 3, 6, 12, and 24 breaths/min. 3. Baroreceptor stimuli applied during early and mid inspiration and late expiration provoked only minor sinus node inhibition; stimuli begun during late inspiration and early expiration provoked maximum sinus node inhibition. 4. At breathing rates of 3, 6 and 12 breaths/min, expiratory baroreflex responses were significantly greater than inspiratory responses; at 24 breaths/min, however, inspiratory and expiratory baroreceptor stimuli produced comparable degrees of sinus node inhibition. 5. Our results delineate an important central biological rhythm in normal man: human baroreflex responsiveness oscillates continuously during normal, quiet respiration. The phase shift of baroreflex responsiveness on respiration suggests that this interaction cannot be ascribed simply to gating synchronous with central inspiratory neurone activity. Regularization of heart rate during rapid breathing is associated with loss of the differential inspiratory‐expiratory baroreflex responsiveness which is present at usual breathing rates.
Effects of sugars, amino acids and inhibitors on electrolyte transport across hen colon at different sodium chloride intakes.
Authors: Lind J , Munck B G , Olsen O , Skadhauge E
Published: December 2014

1. The isolated colonic mucosa from adult hens has been studied in vitro under short‐circuit conditions. Colonic mucosa was prepared from hens fed either a NaCl‐poor or a NaCl‐rich diet. 2. The unidirectional transmucosal fluxes of chloride, K and Na were measured. For the high NaCl colon the fluxes of lysine were also measured. The effects of galactose, glucose, leucine, lysine, amiloride (10(‐4) M) and acetazolamide (5 X 10(‐4) M) on the short‐circuit current (Isc) were examined. 3. The Isc of the high NaCl colon was stimulated by galactose, glucose, leucine and lysine in a manner which suggests that these substances were transported by the epithelium in co‐transport with Na. The Isc was in most cases insensitive to amiloride (mucosal side), but moderately stimulated by acetazolamide (serosal side). The Isc was closely matched by the sum of the net transmucosal fluxes of chloride, lysine, K and Na. The effects of galactose, leucine and lysine on the Isc were maintained only when glucose was present on the serosal side of the preparations. 4. The Isc of the low NaCl colon depended on the presence of glucose on the serosal (or mucosal) side. It was not stimulated by galactose or by lysine, but leucine did stimulate when added to the mucosal solution. Adding amiloride on the mucosal side invariably eliminated or, in most cases, led to an inversion of the Isc. Acetazolamide markedly stimulated the Isc; and, when added after amiloride, acetazolamide caused the Isc to become positive again. The data on Isc and net fluxes of chloride, lysine, K and Na are consistent with the presence of a process of bicarbonate absorption or H ion secretion. 5. There is a net secretion of K across both the high and the low Na colon, which is highest in the former although both Isc and net absorption of Na are highest in the latter. 6. The results from both types of colon suggest that the transport of chloride differs with the functional status of tissues.
Hypothalamo‐pituitary‐adrenocortical function in rats with inherited diabetes insipidus.
Authors: Buckingham J C , Leach J H
Published: December 2014

1. Hypothalamo‐pituitary‐adrenocortical activity in male homozygous and heterozygous Brattleboro rats was compared with that in normal (Long Evans) controls in an attempt to elucidate the role of vasopressin the control of the secretion of corticotrophin. 2. The concentrations of corticosterone and corticotrophin in the plasma, corticotrophin in the adenohypophyses and corticotrophin releasing factor in the hypothalami were lower in the heterozygotes than in the controls and lower still in the homozygotes. 3. The capacities of adenohypophyses and hypothalami to secrete in vitro corticotrophin and corticotrophin releasing factor respectively in response to trophic stimuli were also reduced in the heterozygotes and, to an even greater extent, in the homozygotes. 4. The results suggest that vasopressin is not the corticotrophin releasing factor but they do not exclude the possibility that it may be involved in the sequence of events which leads to the secretion of corticotrophin in the rat.
Sensitization in voltage clamped barnacle photoreceptors.
Authors: Bolsover S R
Published: December 2014

1. The light response of Balanus lateral eye photoreceptor was studied using intracellular recording and voltage clamp techniques. 2. The effect upon the light response of a prior depolarization was studied. Two effects were observed: a transient sensitization which appeared not to involve a change in time course, and a long‐lived desensitization which was accompanied by a reduction in response time course. 3., The sensitizing effect of depolarizing prepulses increased monotonically with prepulse duration; it was maximal for pulses to around +20 mV. 4. Sensitization was inhibited by perfusion with salines containing cobaltous ions or with calcium‐free saline. 5. It is concluded that while desensitization is an effect upon the transduction mechanism, sensitization is a direct influence of a prior depolarization on the light‐activated channels.
Potassium transfer from brain to blood during sustained hyponatraemia in the calf.
Authors: Gardiner R M
Published: December 2014

1. The effects of hyponatraemia on cerebral blood flow, oxidative metabolism, and transfer of Na and K from the brain‐‐c.s.f. compartment to blood have been examined in anaesthetized calves 2‐‐6 weeks after birth. 2. Dilutional hyponatraemia was produced by administration of a long‐acting antidiuretic hormone analogue (desmopressin) and the infusion of hexose solutions of various concentrations. Cerebral blood flow was measured using a hydrogen clearance technique, and metabolism and cation transfer quantified by simultaneous determination of arterio‐cerebral venous concentration differences. 3. Sustained hyposmolar hyponatraemia (plasma osmolality, 232 +/‐ 1 m‐osmole/kg; plasma Na, 117 . 1 +/‐ 0 . 5 m‐mole/l.) was associated with a fall in cerebral blood flow, and increase in measured net transfer of K from the brain‐c.s.f. compartment to the circulation. C.s.f. Na concentration and osmolality were both decreased. 4. No alterations in these variables occurred during sustained isosmolar hyponatraemia (plasma osmolality, 284 +/‐ 2 m‐osmole/kg; plasma Na, 119 . 9 +/‐ 0 . 2 m‐mole/l). 5. The results are discussed in relation to the route, mechanism and time course of K loss from brain during hyponatraemia.
Nodal and terminal sprouting from motor nerves in fast and slow muscles of the mouse.
Authors: Brown M C , Holland R L , Ironton R
Published: December 2014

1. A study of nodal and terminal sprouting in fast and slow muscles of the mouse hind limb has been made using the zinc iodide and osmium tetroxide stain. 2. The terminal sprouting normally elicited by botulinum toxin injection can be prevented by regular and frequent direct electrical stimulation of the muscle fibres. But the number of end‐plates innervated by nodal sprouts in partly denervated spinal preparations was not reduced by direct muscle stimulation. 3. In leg muscles given varying doses of botulinum toxin the amount of terminal sprouting was linearly related to the degree of paralysis. In partly denervated muscles neither the amount of terminal sprouting nor the amount of nodal sprouting was correlated with the degree of denervation. 4. Partial denervation causes relatively more nodal sprouting in the fast muscles peroneus tertius and extensor digitorum longus than in the slower soleus muscle, which itself has considerably more terminal sprouting than the others. The fast muscles can develop as much terminal sprouting as the soleus only in response to full paralysis with botulinum toxin. 5. No evidence could be found for a sprouting signal generated or spreading within the spinal cord. 6. It is concluded in confirmation of earlier work (Duchen & Strich, 1968; Brown & Ironton, 1977 a) that the source of the signal for terminal sprouting is denervated or otherwise inactivated muscle fibres, whose action is boosted by the presence of degenerating nervous tissues. It is suggested that fast muscles probably have less terminal sprouting when partly denervated than slow muscles (a) because of the longer time it takes a fast muscle to undergo the changes associated with inactivity and (b) because of their higher resistance to the effects of nerve degeneration. It does not seem that the signal for nodal sprouting comes from the muscle fibres but further experimentation is needed to establish this firmly.
The effect of suxamethonium on the response to stretch of Golgi tendon organs in the cat.
Authors: Dutia M B , Ferrell W R
Published: December 2014

1. The effects of intra‐arterial infusion of suxamethonium (succinylcholine, SCh) on the response to stretch of Golgi tendon organs in the soleus muscle of the cat have been studied. 2. SCh infusion produced a gradual facilitation of the discharge of tendon organs with low thresholds to passive muscle stretch, but had no detectable effect on tendon organs with high thresholds to stretch. 3. The time course of excitation and recovery of low‐threshold tendon organs after SCh infusion was much longer than that of muscle spindle primary and secondary sensory endings. 4. Control experiments showed that there was no change in the passive tension of the soleus muscle during SCh infusion, thus excluding the possibility that the excitation of the low‐threshold tendon organs is caused by an increase in passive muscle tension. 5. These findings complement recent observations that SCh can excite receptors other than those in muscle spindles, and indicate that SCh activation on its own may not be a sufficient criterion on the basis of which to identify muscle spindle afferent axons.
Effect of acetylcholine on membrane currents in guinea‐pig papillary muscle.
Authors: Hino N , Ochi R
Published: December 2014

1. The effect of acetylcholine (ACh) on the membrane current components in guinea‐pig papillary muscle was studied by the single sucrose gap voltage clamp method. 2. The slow inward current (is) elicited by various depolarizations from the holding potential of ‐40 mV was evidently diminished by ACh greater than 5 x 10(‐7) M. The amplitude of is, estimated as the difference between the peak of is and the current at 150 msec, was reduced to 56.8 +/‐ 12.9% (mean +/‐ S.D., n = 34) by 2 x 10(‐8) M‐ACh when estimated at the membrane potential where the amplitude was maximal. 3. is was suppressed almost completely by 2 mM‐Co2+, is obtained by subtracting the current remaining in 2 mM‐Co2+ was also diminished to the same extent by 2 x 10(‐6) M‐Ach with little change in its time course; the degree of decrease was not dependent on the membrane potential. 4. The time‐dependent outward current during the depolarizing pulse was also diminished by 2 x 10(‐6) M‐Ach. Correspondingly, the positive tail current obtained when the membrane was repolarized to the holding potential of ‐40 mV after various 1 sec depolarizations was reduced in a proportionate manner to 68.6 +/‐ 7.3% (n = 10). 5. The time‐independent inward rectifying outward current was not affected by 2 x 10(‐6) M‐Ach. 6. Atropine (10(‐6) M) restored is and the time‐dependent outward current which had been previously depressed by 2 x 10(‐6) M‐ACh. 7. ACh may decrease tension development by depressing is, thereby preserving the duration of the action potential with relatively little change, since, different from atrial muscle, ACh does not increase the outward current in mammalian ventricular muscle.
Projections from Pacinian corpuscles and rapidly adapting mechanoreceptors of glabrous skin to the cat's spinal cord.
Authors: Brown A G , Fyffe R E , Noble R
Published: December 2014

1. Single axons innervating Pacinian corpuscles and rapidly adapting mechanoreceptors of the foot and toe pads were injected with horseradish peroxidase near their entrance to the lumbosacral spinal cord in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. Subsequent histochemistry revealed the morphology of the intra‐spinal parts of the axons. 2. All Pacinian corpuscle axons that could be traced into the dorsal root bifurcated upon entering the cord into ascending and descending branches. All Pacinian corpuscle axons gave rise to collaterals that entered the dorsal horn. 3. The collaterals of Pacinian corpuscle afferent fibres had a distinctive morphology. They provided two regions of termination, a larger dorsal region in laminae III and IV and a smaller ventral region in laminae V and VI. Within the dorsal region the terminal axons ran mainly in the longitudinal axis of the cord and carried many boutons en passant. Within the ventral region the axons ran dorso‐ventrally in the transverse plane of the cord and although carrying some boutons en passant also gave rise to clusters of boutons. 4. The collaterals of rapidly adapting afferent fibres had a distinctive morphology different from that of the Pacinian corpuscle afferent fibre collaterals. The termination region of rapidly adapting afferents was limited almost exclusively to lamina III, with only slight extension into lamina IV. Boutons were mainly of the en passant type and terminal axons were generally orientated within the longitudinal axis of the cord. 5. The morphology of the afferent fibre collaterals is discussed in relation to the physiology of the dorsal horn.
The effect of somatostatin on pancreatic endocrine responses mediated via the parasympathetic innervation in the conscious calf.
Authors: Bloom S R , Edwards A V , Järhult J
Published: December 2014

1. The effect of somatostatin on the responses to moderate insulin hypoglycaemia and to 2‐deoxyglucose has been examined in 2‐‐3 week‐old calves with cut splanchnic nerves. 2. Intravenous infusions of somatostatin (150 p‐mole . kg‐1 . min‐1) completely suppressed release of glucagon, pancreatic polypeptide (PP) and insulin from the pancreas in response to 2‐deoxyglucose (1.1 m‐mole/kg I.V.). 3. The same dose of somatostatin completely blocked the rise in plasma PP concentration that normally occurs in response to moderate insulin hypoglycaemia and significantly delayed the rise in plasma pancreatic glucagon concentration. The hypoglycaemic response to insulin was also found to be intensified by the administration of somatostatin. 4. It is concluded that each of the pancreatic neuroendocrine responses, that are now known to be mediated via the parasympathetic innervation, is suppressed in the presence of somatostatin in the young calf.
Calcium dependence of evoked transmitter release at very low quantal contents at the frog neuromuscular junction.
Authors: Andreu R , Barrett E F
Published: December 2014

1. The relationship between the rate of evoked transmitter release and the extra‐cellular concentration of Ca ions, [Ca2+]o, was studied at surface neuromuscular junctions of the frog cutaneous pectoris muscle. The average quantal content of the end‐plate potential was reduced to low levels by reducing [Ca2+]o and adding 2 mM‐Mn2+, 45 MM‐Co2+ or 10 mM‐Mg2+. 2. When the motor nerve was stimulated at a low frequency (0.5‐‐2 Hz) in 2 mM‐Mn2+ or 4 mM‐Co2+, the average quantal content of evoked release was proportional to the fourth power of [Ca2+]o down to the lowest measurable quantal contents, around 2‐‐4 quanta per 1000 stimuli. Combined with previous studies, this result indicates that evoked transmitter release has a steep, nonlinear dependence on [Ca2+]0 over our orders of magnitude of evoked release. 3. Calculations predict that if evoked and spontaneous release have the same fourth power dependence on intracellular [Ca2+], then the curve relating evoked release and [Ca2+]o should become much less steep as the evoked release rate approaches the spontaneous release rate. Our observation that the relationship between evoked release and [Ca2+]o remains fourth power down to very low release rates suggests that most spontaneous quantal release does not have the same dependence on intracellular [Ca2+], or does not use the same intracellular Ca2 pool, as evoked release. 4. In 2‐‐10 mM‐Mg2+, the lowest average quantal contents were markedly higher than the fourth power prediction. This discrepancy may occur either because Mg2+ somehow elevates intracellular [Ca2+], or because Mg2+ is itself a weak activator of transmitter release. 5. Even at very low rates of evoked release, increasing the stimulus frequency to 5‐‐50 Hz caused a progressive increase in both evoked release and the rate of ‘background’ quantal release during the interstimulus interval. The frequency‐dependent enhancement of both evoked and background release was more pronounced in solutions containing 10 mM‐Mg2+ than in solutions containing 2 mM‐Mn2+.
Voltage sensitive calcium entry in frog motoneurones.
Authors: Alvarez‐Leefmans F J , Miledi R
Published: December 2014

1. The electrical properties of motoneurone membrane were investigated in the isolated and hemisected spinal cord of frogs, using intracellular recording techniques. 2. TTX (1 x 10(‐6) g/ml.) blocked action potentials produced either by intracellular depolarizing current pulses or ventral root stimuli. Voltage‐‐current relations from these cells showed a diminishing slope for depolarizing current pulses of increasing intensity. 3. If TEA (5‐‐10 mM) was added to the media containing TTX, intracellular depolarizing pulses elicited prolonged regenerative depolarizations characterized by a peak of variable amplitude and a repolarizing phase preceded by a prolonged plateau of variable duration. 4. During the plateau of the response, the membrane conductance was increased above its resting value. 5. The response was shortened during repetitive stimulation and could be curtailed by applying a hyperpolarizing pulse during the plateau. 6. The response depended on the presence of external Ca2+ and increased in size and duration with increasing Ca2+ concentration. Sr2+ substituted effectively for Ca2+. Sr2+‐dependent responses were considerably longer than the Ca2+‐dependent ones. Ca2+ or Sr2+ dependent responses persisted in Na+‐free media containing isotonic TEA, and were abolished by addition of Co2+. 7. Ca2+ or Sr2+‐dependent regenerative responses were followed by a hyperpolarization which could last several seconds. The current responsible for this after‐hyperpolarization was TTX and TEA resistant. 8. It is concluded that the TTX‐resistant regenerative response is probably generated in the soma‐dendritic membrane, and is due to influx of Ca2+ or Sr2+ through voltage sensitive channels different to those through which Na+ permeates during generation of ‘normal’ action potentials. In addition it is shown that the hyperpolarization following ‘Ca spikes’, and which might be due to an increase in K+ conductance can also be triggered by Sr2+.