bluuebunny/crossref_metadata_2025 huggingface dataset:
Sympathetically evoked secretory potentials in the parotid gland of the cat.
Authors: Emmelin N , Grampp W , Thesleff P
Published: December 2015

1. In cats under chloralose anaesthesia micro‐electrodes were inserted into parotid gland cells. 2. The average resting potential was found to be ‐35 . 6 +/‐ 4 . 7 (S.D.) mV. 3. Stimulation of the auriculo‐temporal nerve caused hyperpolarizing, or occasionally depolarizing, secretory potentials of 5‐‐10 mV, which were abolishable with atropine. 4. Stimulation of the cervical sympathetic trunk regularly caused, after long latency (several seconds), slow depolarizations of 15‐‐20 mV, accompanied by a decrease in input resistance. They were antagonized by practolol and therefore assumed to be mediated by beta 1‐adrenoceptors. Occasionally hyperpolarization, ascribed to an effect on alpha‐adrenoceptors, was observed. 5. In many units the slow depolarization on sympathetic stimulation was preceded by short‐lasting hyperpolarizing (sometimes depolarizing) transients. They resembled the evoked cholinergic responses but could be abolished not only by atropine but also by guanethidine.
Evolution of cholinergic proteins in developing slow and fast skeletal muscles in chick embryo.
Authors: Betz H , Bourgeois J P , Changeux J P
Published: December 2015

1. The cholinergic differentiation of two phenotypically muscles of the chick, the slow multiply innervated anterior latissimus dorsi (a.l.d.) and the fast focally innervated posterior latissimus dorsi (p.l.d.), was investigated during embryonic life and after hatching using both autoradiographical and biochemical methods. 2. The contents in total protein and in acetylcholinesterase activity follow similar development patterns in both muscles, but, after the 15th day in ovo, the accumulation of choline acetyltransferase activity and of acetylcholine nicotinic receptor sites as determined by alpha‐bungarotoxin binding occurs at a faster rate in a.l.d. than in p.l.d. 3. In muscle of the p.l.d., a rapid increase of the total number of acetylcholine receptor clusters takes place after the 11th day of embryonic life although some clusters could be observed on myofibres as soon as the 4th day in ovo. 4. The rate of degradation of cholinergic receptor sites in chick muscle is constant around 28 hr up to the 10th day after hatching; thus the different rates of accumulation of acetylcholine receptor in a.l.d. and p.l.d., respectively, after the 15th day of embryonic life must be due to different rates of receptor synthesis. 5. The role of muscle activity in the biochemical differentiation of the developing motor end‐plate was investigated in chick embryos which had been paralysed by repeated injections into the yolk sac of a curare‐like agent, Flaxedil (May & Baker). 6. The total content in acetylcholinesterase of both a.l.d. and p.l.d. muscles is not significantly modified by paralysis. However, the histochemical staining of end‐plates for acetylcholinesterase as well as the heavy form of this enzyme (19 . 5 S) are consistently reduced after Flaxedil injection. 7. In muscles from Flaxedil‐treated embryos, the total content in acetylcholine receptor sites as determined by alpha‐bungarotoxin binding is higher than in those from control embryos, whereas the rate of degradation of these sites is not significantly altered. 8. The localization of the acetylcholine receptors under the motor nerve terminals is not prevented by blocking muscle activity at the postsynaptic level. Clusters of receptor are still present, and there is no significant change in the number and distribution of these clusters along the myofibres of a.l.d. and p.l.d. muscles. 9. These results are discussed with respect to motor end‐plate formation in multiply and focally innervated embryo muscles, and in relation to the control of cholinergic proteins distribution and synthesis by muscle activity.
Rheogenic sodium transport in a tight epithelium, the amphibian skin.
Authors: Nagel W
Published: December 2015

1. Intracellular potentials from frog and toad skins were measured to identify rheogenic components of active Na transport across the basolateral membrane. Transcellular current flow and associated R . I‐drops were blocked with amiloride or Na‐free mucosal solution. 2. The potential difference across the basolateral membrane was found to be hyperpolarized by 18 . 5 +/‐ 1 . 6 mV above the steady‐state value immediately after blockage of apical membrane Na conductance. The hyperpolarization disappeared within 15‐‐25 min. 3. The final steady‐state value of 93 . 1 +/‐ 2 . 5 mV was slightly less than reasonable estimates of the K equilibrium potential. 4. The hyperpolarization could not be observed 3‐‐5 min after addition of ouabain (10(‐4) M). 5. Both the magnitude and duration of the hyperpolarization correlate directly with the amount of Na accumulated in the intracellular space. 6. A fraction of the intracellular potential was missing when Na transport was re‐established after long term blockage of apical membrane Na entry. It reappeared within 10‐‐20 min. 7. It is suggested that the hyperpolarization is due to rheogenic Na transport across the basolateral membranes. This transport mechanism may contribute some 30‐‐50% of the electrical gradient for passive Na entry across the mucosal membrane. 8. A coupling ratio between pumped fluxes of Na and K of about 2:1 is calculated from the data.
Hyperpolarization of frog primary afferent fibres caused by activation of a sodium pump.
Authors: Davidoff R A , Hackman J C
Published: December 2015

1. In the isolated frog spinal cord repetitive stimulation of a lumbar dorsal root produced a sustained negative potential recorded from an adjacent inactive dorsal root by sucrose gap techniques. This negative potential was followed by a positive potential, an indication that the dorsal root terminals were hyperpolarized. Increasing the duration of the tetanus applied to the active root increased the amplitude and duration of the after‐hyperpolarization which could be up to 6 mV and 3 min respectively. 2. The hyperpolarization presumably reflected an increased rate of active sodium pumping. Since it was reversibly reduced by metabolic inhibitors (dinitrophenol, NaCN) and cooling (Q10, 2 . 6) it was clearly dependent upon intact metabolic activity. In addition, a variety of procedures used to inhibit sodium pumps (including application of ouabain, elimination of potassium from the superfusate, and partial substitution of lithium for sodium ions) significantly and reversibly decreased the potential. 3. The hyperpolarization was not dependent upon intact chemical synaptic transmission since it could survive prolonged immersion of the cord in Ringer solution containing manganese or magnesium ions. 4. It is suggested that the hyperpolarization of inactive fibres resulted from a decreased extracellular potassium concentration in the dorsal horn produced as a result of a pumping mechanism which extruded sodium and transported potassium inwards by dorsal root fibres directly activated by the tetanus.
Glycogen depletion of bag1 fibers elicited by stimulation of static gamma axons in cat peroneus brevis muscle spindles.
Authors: Emonet‐Dénand F , Jami L , Laporte Y , Tankov N
Published: December 2015

1. The distribution of static fusimotor axons to intrafusal muscle fibres in cat peroneus brevis spindles has been studied with the glycogen depletion method. 2. In each of six experiments three to seven static axons were stimulated. The muscle was subsequently quick‐frozen and cut in serial transverse sections that were stained for glycogen. In each muscle, nearly all the spindles were examined for depletion. 3. Intrafusal muscle fibres displaying zones of complete glycogen depletion were observed in fifty‐two whole spindles and seven half‐spindles. Chain fibres were depleted in forty‐eight (92%) of the whole spindles, bag2 fibres in thirty‐five spindles (67%) and bag1 fibres in nineteen spindles (36%). 4. Seven other experiments were performed to test whether small amplitude sinusoidal stretching (30‐‐100 Hz) of the muscle might produce glycogen depletion in bag1 fibres. Two hundred and seven spindles were examined. In nearly all of them the glycogen content of the intrafusal muscle fibres was normal. Two muscles had limited atrophic portions within which a few depleted spindles were found. 5. These experiments show that the intrafusal distribution of static gamma axons is not restricted to chain and bag2 fibres but that in a significant number of spindles the bag1 fibres are also supplied by static gamma axons.
Electrophysiological studies of paraventricular and supraoptic neurones recorded in vitro from slices of rat hypothalamus.
Authors: Haller E W , Wakerley J B
Published: December 2015

1. In slices (300 micrometer) of rat hypothalamus maintained in vitro in isotonic (298 +/‐ 4 m‐osmol/kg) medium, the median firing rate of twenty‐four supraoptic (s.o.) neurones was 0 . 05 spikes/s, compared to 0 . 66 spikes/s for twenty‐eight paraventricular (p.v.) units (P < 0 . 01) and 0 . 79 spikes/s for forty‐three anterior hypothalamic area a.h.a. units (P < 0 . 001). 2. One hundred and two p.v. and s.o. units incubated in hypertonic medium (311‐‐343 m‐osmol/kg, achieved by adding NaCl) showed no correlation with osmotic pressure and displayed a similar level of spontaneous activity to units recorded in isotonic medium. Recordings from nineteen p.v. and s.o. units during rapid changes from iso‐ to hypertonic (338 +/‐ 4 m‐osmol/kg) medium confirmed this lack of osmo‐sensitivity. 3. Excitation of s.o. units in vitro with glutamate resulted in firing patterns similar to those found in previous in vivo studies on activated s.o. cells. Thus out of thirty‐two glutamate‐excited units, twelve (37%) fired in repetitive bursts, giving a phasic pattern and thirteen (41%) showed fast continuous activity. The remaining seven (22%) units showed ambiguous patterns that were neither continuous nor clearly phasic. 4. Mean durations of bursts and silent periods in phasic cells excited by perifused glutamate were 16 . 6 s and 13 . 2 s (calculated from normalized distributions of thirty values), compared to means of 41 . 7 s and 33 . 9 s (thirty‐six values, P < 0 . 001 for each parameter) for cells excited by glutamate ionophoresis. The periodicity of phasic firing in vitro was unaffected by a change to hypertonic (340 m‐osmol/kg) medium. 5. From these in vitro results it is proposed that the excitation associated with osmotic stimuli in vivo does not originate within the p.v. and s.o. neurosecretory cells, but that it involves a separate osmoreceptor. However, the control of phasic firing, which is commonly found during osmotic excitation, would seem to involve a mechanism which lies within or in close proximity to, the neurosecretory neurones.
The gastric motility patterns induced by direct and reflex excitation of the vagus nerves in the anaesthetized ferret.
Authors: Andrews P L , Scratcherd T
Published: December 2015

1. Under urethane anaesthesia the ferret has a stomach which exhibited spontaneous contractions. The amplitude of the contractions was reduced, but never abolished, by vagotomy, atropine or hexamethonium. 2. Electrical stimulation of the cut peripheral end of the cervical or abdominal vagus nerves activated both excitatory and inhibitory fibres, whereas reflex activation by stomach distension or by cytoglucopenia was predominantly excitatory on gastric motility. The magnitude of the response to electrical stimulation was dependent upon the stimulus frequency, duration and voltage. Stimulation for periods longer than 10 sec at 10 Hz caused an increase in tone and motility which declined almost to control values if it was sufficiently prolonged. 3. Short duration stimulation, 10 sec or less, at 10 Hz produced a single gastric contraction. An identical response could only be produced if a period of rest from 30 to 120 sec separated two such stimuli. 4. The frequency of gastric contractions was independent of the frequency of nerve stimulation. 5. Using a divided stomach, vagal non‐cholinergic, non‐adrenergic fibres were shown to cause mainly relaxation of the corpus region. Similar fibres supplied the antrum and their activation caused inhibition of spontaneous contractions. The transmitter may be ‘purinergic’ as rebound contractions were observed.
Attenuation of the diving reflex in man by mental stimulation.
Authors: Ross A , Steptoe A
Published: December 2015

1. A study was made of the effects of mental arithmetic, and of listening to prose, on the bradycardia produced by breath holding with and without immersion of the face in cold water. 2. Bradycardia was produced in both air and water, but the response was significantly greater on face immersion. The reaction was attenuated by mental arithmetic in both air and water. In contrast external distraction by listening to prose had no effect on cardiac response. 3. It was concluded that the diving reflex can be modified by higher nervous stimulation. The effect is apparently dependent on mental challenge, such as that provoked by arithmetic.
Absorption by the colon during prolonged infusions in conscious, unrestrained rats.
Authors: Edmonds C J , Thompson B D
Published: December 2015

1. Colonic absorption was studied in conscious, unrestrained rats during prolonged infusions through implanted cannulae. During infusion of predominantly NaCl‐containing solution at rates up to 0.7 ml h‐1 per 100 g body wt., absorption of fluid and Na increased considerably without significant change of transmucosal p.d.; diarrhoea did not occur. 2. Exclusion of the distal colon by colostomy showed that the proximal part of the colon was chiefly responsible for the increased absorption and inspection during the infusion showed it to be much dilated. Removal of the caecum showed that it contributed considerably to absorption by the proximal part. The distal colon influenced Na concentration in the faeces but absorbed little volume while direct infusion into this region rapidly produced diarrhoea. 3. The addition of Na deoxycholate (5 mmol/l) to the infusion solution impaired absorption provoking diarrhoea with mucus loss; there was no evidence that fluid secretion was stimulated. Substitution of SO4 for Cl in the infused solution produced only small changes of transmucosal p.d. but considerably impaired absorption and diarrhoea resulted. 4. The findings indicate that the proximal colon and caecum possess a considerable potential for increasing fluid and Na absorption and suggest the possibility that a neutral Na‐Cl coupled absorptive mechanism is stimulated by loading the colon with fluid and NaCl.
Effects of calcium ions on outward membrane currents in rat uterine smooth muscle.
Authors: Mironneau J , Savineau J P
Published: December 2015

1. The outward membrane current underlying delayed rectification in uterine smooth muscle has been studied by means of a double sucrose gap apparatus with particular reference to the effects of the external calcium. 2. The outward current was reversibly reduced in calcium‐free solution and in the presence of manganese (5 mM), or increased in high‐calcium solution. 3. In reference solution, when depolarizing steps activated the outward current to its maximal value, the current tails measured at the end of the pulse were made up of two exponentially declining components. The slower of the two components was suppressed in calcium‐free solution. The fast component reached full, steady‐state activation at about +75 mV and the slow one at less positive potentials, i.e. +50 mV. Altering the external calcium did not shift the activation curves of the outward current along the voltage axis. 4. The reversal potential of the outward current was not affected by alterations of the external calcium concentration. 5. The outward current components can also be separated on the basis of their sensitivity to 4‐aminopyridine (4‐AP) and tetracethylammonium (TEA). The fast component was selectively blocked by externally applied 4‐AP. TEA blocked both fast and slow components. 6. It is suggested that two sets of potassium channels contribute to the outward current in myometrium and that these channels can be separated pharmacologically.
Motoneurone projection patterns in the chick hind limb following early partial reversals of the spinal cord.
Authors: Lance‐Jones C , Landmesser L
Published: December 2015

1. The development of motoneurone projection patterns in the chick hind limb from reversed spinal cord segments was studied from the onset of axonal outgrowth (St. 24) to the establishment of mature connectivity patterns (St. 36). Approximately the first three lumbosacral cord segments were reversed along the anterior‐posterior axis at St. 15‐16. 2. Projection patterns from reversed cord segments were assessed electrophysiologically by direct spinal cord and spinal nerve stimulation and anatomically by retrograde horseradish peroxidase (HRP) labelling of motoneurones in St. 30‐36 embryos. In younger embryos, paths taken by reversed axons were characterized by orthograde HRP labelling of motoneurones in specific reversed cord segments. 3. Lumbosacral motoneurones formed appropriate functional connexions with individual limb muscles in spite of anterior‐posterior shifts in their spinal cord position aned consequent shifts in their spinal nerve entry point into the limb bud. Reversed motoneurones supplying individual hind limb muscles formed discrete nuclei in the transverse plane of the cord. Each nucleus and the lateral motor column as a whole showed reversed topographical characteristics when compared to control embryos. These observations were made before (St. 30) and after (St. 35‐36) the major period of motoneurone cell death. 4. Correct connectivity resulted from specific alterations in axonal pathways within the plexus or major nerve trunks proximal to the branching of individual muscle nerves. Further such directed outgrowth was present from the earliest times that axons could be traced into the limb which is before the onset of motoneurone cell death and muscle cleavage. 5. It is concluded that motoneurones are specified to project to individual muscles or to follow particular pathways prior to motoneurone birthdays and limb bud formation. The establishment of specific motoneurone connectivity can not be accounted for by passive or mechanical guidance models alone. Rather, motoneurones must also actively respond to cues within the limb or interact among themselves on the basis of an early central specification.
The effect of dantrolene sodium on intrafusal muscle fibres in the rat soleus muscle.
Authors: Leslie G C , Part N J
Published: December 2015

1. The action of the skeletal muscle relaxant drug, dantrolene sodium, given intravenously, on the intrafusal fibres of the soleus muscle of the urethane‐anaesthetized rat has been investigated. The experiments were made on functionally single spindle afferents and gamma fusimotor fibers isolated in dorsal and ventral roots respectively. 2. Dantrolene sodium was without effect on the discharge of primary and secondary afferents from the passive muscle spindle, nor were the dynamic indices of these endings affected. 3. Intrafusal muscle contraction was measured indirectly by means of the spindle afferent discharge. 4. The intrafusal muscle twitch contraction, as measured by means of the amplitude of the frequencygram, was depressed more slowly to a lesser extent than was the twitch of the extrafusal contraction. 5. Intrafusal contraction resulting from tetanic stimulation of the gamma fibre was depressed by dantrolene sodium to an extent dependent upon the stimulation frequency. At frequencies of 10, 25 and perhaps 50 Hz the depression was complete, that is, no afferent response was evoked; at 200 Hz stimulation, the depression was minimal (or non‐existent). 6. For a muscle spindle primary ending under dynamic gamma activation dantrolene sodium caused a reduction of dynamic index whereas for the ending under static activation it caused an increase. 7. The significance of the findings in terms of the clinical use of the drug is considered.
Potassium and caffeine contractures in fast and slow muscles of the chicken.
Authors: Huerta M , Stefani E
Published: December 2015

1 K+ contractures, caffeine contractures and electrical properties were studied in slow (posterior latissimus dorsi; p.l.d.) and fast (anterior latissimus dorsi; a.l.d.) chicken muscles. 2. P.l.d. K+ contractures show a transient increase of tension that relaxes spontaneously. Contractures in a.l.d. show an initial component followed by a maintained tension. 3. A.l.d. K+ contractures of similar amplitude and time course were reproduced at 4 min intervals. In p.l.d., the interval needed for full recovery is about 30 min. In Cl‐free saline p.l.d. and a.l.d. K+ contractures can be reproduced at 4 min intervals. 4. The time course of repolarization after a short exposure to 160 mM‐KCl was much slower in p.l.d. than in a.l.d. In Cl‐free saline the time course of repolarization becomes faster in p.l.d. 5. The membrane resistance was not modified in a.l.d. and was increased in p.l.d. by Cl‐free saline. The calculated Cl‐ conductance in p.l.d. was about 70% of the total membrane conductance. 6.In a.l.d., Mn2+, D600 and external Ca2+ reduction greatly diminishes the maintained phase of the K+ contracture leaving the initial phase almost unmodified. Under similar conditions p.l.d. K+ contractures were slightly reduced. 7. P.l.d. caffeine contractures (10‐40 mM) were not maintained and they were not modified by Ca‐free saline, Cd2+, Co2+, Mn2+ and D600. 8. A.l.d. caffeine contractures (2‐15 mM) were maintained and were highly dependent on external Ca2+. In addition they were greatly reduced by Cd2+, Co2+, Mn2 and D600. 9. It is suggested that caffeine contractures of a.l.d. are elicited by a Ca2+ entry into the muscle from the external fluid.
Electrogenic responses induced by neutral amino acids in endoderm cells from Xenopus embryo.
Authors: Bergman C , Bergman J
Published: December 2015

1. Membrane potential measurements were carried out on endoderm cells from early Xenopus embryos in order to study neutral amino acid transport in non‐excitable cells. 2. The electrical properties of the cell membrane were studied under normal conditions, then in the presence of various Na/K‐pump inhibitors and at different Na, K and Cl concentrations in Ringer solution. Blockade of the Na/K‐pump by ouabain, Li, cooling to 10 degrees C or low [Na]0 induces similar depolarizations of about 40 mV. 3. External application of various neutral L‐amino acids induces reversible membrane depolarizations. The D‐isomeric forms are found to be ineffective. The amino acid induced depolarizations are not accompanied by changes in membrane resistance. They do not show voltage dependence for potential changes of less than 40 mV. 4. The amino acid depolarization increases with increasing concentration and follows first order Michaëlian kinetics. Both the size and the time course of the amino acid depolarization depend on [Na]0. Increasing [Na]0 markedly increases the apparent affinity of the membrane receptor for amino acid. 5. Increasing [k]0 reduces the size of the amino acid response. Short exposures to either ouabain or Li do not alter the amino acid depolarization. However, p time course of the amino acid depolarization depend on [Na]0. Increasing [Na]0 markedly increases the apparent affinity of the membrane receptor for amino acid. 5. Increasing [k]0 reduces the size of the amino acid response. Short exposures to either ouabain or Li do not alter the amino acid depolarization. However, p time course of the amino acid depolarization depend on [Na]0. Increasing [Na]0 markedly increases the apparent affinity of the membrane receptor for amino acid. 5. Increasing [k]0 reduces the size of the amino acid response. Short exposures to either ouabain or Li do not alter the amino acid depolarization. However, prolonged exposure to pump inhibitors or marked alteration of the Na concentration gradient leads to a complete inhibition of amino acid responses. 6. The results are in good agreement with the notion that the amino acid induced responses reflect the activation of an electrogenic amino acid carrier, very likely co‐transporting Na and amino acid.
Pancreatic endocrine function in cortisol‐treated thyroidectomized calves.
Authors: Bloom S R , Edwards A V , Fielding A S
Published: December 2015

1. Pancreatic endocrine function has been investigated in thyroidectomized calves given exogenous cortisol (2.0 mg.kg‐1.day‐1) in order to produce overt signs of diabetes. 2. Whenever this diabetic syndrome was induced it was associated with falling plasma insulin concentrations. A few days later, there was a significant rise in the post‐absorptive concentration of both pancreatic glucagon and pancreatic polypeptide (PP) in the arterial plasma. Elevated levels of both hormones invariably persisted until the animals were given thyroxine. 3. Each of the pancreatic endocrine responses to cortisol was reversed by daily administration of thyroxine (25 microgram.kg‐1. day‐1) and the plasma glucose concentration was restored to normal within a few days. 4. Starvation was found to be an extremely effective way of reducing both the plasma glucose and glucagon concentration of diabetic calves without apparently affecting the concentration of either insulin of PP. 5. Neurally mediated release of insulin in response to 2‐deoxyglucose, but not of either pancreatic glucagon or PP, was found to be defective in diabetic calves and recovered in response to thyroxine. 6. These results suggest that the primary defect that leads to the development of this diabetic syndrome in cortisol‐treated thyroidectomized calves is failure of insulin release but that this is associated with consequential changes in the rates at which both glucagon and PP are released from the pancreas.
Responses of isolated Golgi tendon organs of the cat to muscle contraction and electrical stimulation.
Authors: Fukami Y
Published: December 2015

1. Responses of Golgi tendon organs isolated from cat tail muscles to contraction of muscle fibers inserting directly into the receptor (GTO‐muscle fibres) as well as to pulses of electrical current applied extracellularly through the sensory axon were studied. 2. Analysis of the responses to GTO‐muscle fibre contraction indicated that the active force developed by each muscle fibre constituted an equally potent input to the receptor in proportion to the developed force. 3. The sensitivity of a Golgi tendon organ remained almost constant with changes in muscle length up to a length where maximum active tension was developed (lo). Beyond lo, the sensitivity tended to decrease. 4. The absolute force threshold (passive + active) at 1o for initiating an impulse in the afferent nerve was estimated for five preparations to be 4.5‐14 mg. It was also demonstrated that the contraction of a single GTO‐muscle fibre may initiate impulse discharge from the receptor. 5. A constant depolarizing current applied extracellularly to a GTO through its axon initiated a train of impulses, probably originating from a site near or within the receptor capsule. Analysis of responses to constant currents of various intensities suggested that a single impulse initiation site was involved. 6. During combined stimulation, responses of a tendon organ to GTO‐muscle fibre contraction simply added to the response initiated by a constant current pulse, suggesting that the impulse initiation sites activated by each mode of stimulation were identical, or situated very close to each other in the nerve terminal.
Circulatory effects in healthy young men of atrial pacing at rest and during isometric handgrip.
Authors: Bergenwald L , Eklund B , Freyschuss U
Published: December 2015

1. The influence of a fixed heart rate and cardiac output on the cardiovascular response to isometric handgrip at one third of maximal voluntary contraction has been studied by means of atrial pacing. 2. At rest, atrial pacing with a mean heart rate of 109 beats/min increased cardiac output and forearm blood flow while total systemic and forearm vascular resistance decreased. 3. During handgrip, total systemic resistance increased both with and without pacing. A slow lowering of forearm vascular resistance was noted in the former situation, no change in the latter. 4. It is concluded that atrial pacing per se increases cardiac output in healthy, young volunteers. Handgrip elicits a vasoconstriction on other vascular beds than the resting forearm.
Function and distribution of three types of rectifying channel in rat spinal root myelinated axons.
Authors: Baker M , Bostock H , Grafe P , Martius P
Published: December 2015

1. The nature, distribution and function of rectifying channels in rat spinal root myelinated axons has been assessed with selective blocking agents and a variety of intracellular and extracellular recording techniques. 2. The electrotonic responses of roots poisoned with tetrodotoxin (TTX) to constant current pulses had fast (rise time much less than 1 ms) and slow components, which were interpreted in terms of Barrett & Barrett's (1982) revised cable model for myelinated nerve. Depolarization evoked a rapid outward rectification (time constant, tau approximately 0.5 ms), selectively blocked by 4‐aminopyridine (4AP, 1 mM), and a slow outward rectification (tau approximately 15 ms), selectively blocked by tetraethylammonium (TEA, 1 mM) or Ba2+ (0.5 mM). Hyperpolarization evoked an even slower inward rectification, selectively blocked by Cs+ (3 mM) but not by Ba2+. 3. From the different effects of the blocking agents on the fast and slow components of electrotonus, it was deduced (a) that the inward rectification is a property of the internodal axon, (b) that the slow outward rectifier is present at the nodes, and probably the internodes as well, and (c) that the 4AP‐sensitive channels have a minor nodal and a major internodal representation. 4. TEA and Ba2+ reduced the accommodation of roots and fibres not poisoned with TTX to long current pulses, whereas 4AP facilitated short bursts of impulses in response to a single brief stimulus. 5. TEA and Ba2+ also abolished a late hyperpolarizing after‐potential (peaking at 20‐80 ms), while 4AP enhanced the depolarizing after‐potential in normal fibres, and abolished an early hyperpolarizing after‐potential (peaking at 1‐3 ms) in depolarized fibres. Corresponding to the later after‐potentials were post‐spike changes in excitability and conduction velocity, which were affected similarly by the blocking agents. Cs+ increased the post‐tetanic depression attributable to electrogenic hyperpolarization. 6. The physiological roles of the three different rectifying conductances are discussed. It is also argued that the prominent ohmic 'leak conductance', usually ascribed to the nodal axon, must arise in an extracellular pathway in series with the rectifying internodal axon.
In vitro effects of dexamethasone on sodium transport across rat colon.
Authors: Bridges R J , Rummel W , Schreiner J
Published: December 2015

1. The in vitro effects of dexamethasone on Na+ transport across the colon descendens from normal rats was investigated. Amiloride was used at two concentrations, 10 microM and 1 mM, to differentially inhibit the transport of Na+ across the colon. The colon descendens from each rat was divided into four segments and Na+ unidirectional fluxes before and 7 h after the addition of dexamethasone (10(‐6) M) were determined under short‐circuit conditions. 2. Base‐line JnetNa (net flux of Na+) was twice as high in the proximal segment as in the distal segment. The two middle segments had intermediate rates of Na+ transport. JnetNa in control tissue was unaffected by 10 microM‐amiloride but was completely inhibited by 1 mM‐amiloride. In control tissue, amiloride at either 10 microM or 1 mM had no effect on the transmural potential difference (p.d.), the transmural conductance (Gt) or the short‐circuit current (Isc). 3. Dexamethasone caused a time‐dependent increase in the p.d. and in the Isc in all four segments of the colon. The increase in the p.d. and Isc was greatest in the most distal segment and less in each of the successive more proximal segments. This segmental difference along the colon was observed in tissue from all animals studied (n greater than 30). 4. The increase in p.d. and Isc caused by dexamethasone was accompanied by an increase in JnetNa to the same maximum rate of 14 mu equiv cm‐2 h‐1 in each segment.(ABSTRACT TRUNCATED AT 250 WORDS)
Presynaptic inhibition of synaptic potentials evoked in cat spinal motoneurones by impulses in single group Ia axons.
Authors: Clements J D , Forsythe I D , Redman S J
Published: December 2015

1. Single‐fibre group Ia excitatory post‐synaptic potentials (e.p.s.p.s) were evoked in triceps surae motoneurones. These e.p.s.p.s were reduced by conditioning stimulation of group I axons in posterior biceps‐semitendinosus nerves. 2. The investigation concentrated on e.p.s.p.s of somatic origin, because the amplitude of these e.p.s.p.s is not reduced by post‐synaptic conductance increases. Any reduction in these e.p.s.p.s could therefore be attributed to presynaptic inhibition. 3. The reduction in somatic e.p.s.p. amplitude was greatest when the conditioning stimulus preceded the e.p.s.p. by 30 ms, and was negligible when the conditioning interval was extended to 200‐300 ms. 4. The percentage reduction of somatic e.p.s.p.s was independent of their unconditioned peak amplitude. 5. E.p.s.p.s of somatic origin were reduced by the same amount, on average, as e.p.s.p.s of dendritic origin. 6. E.p.s.p.s evoked in the same motoneurone by impulses in different Ia axons were reduced by different amounts and e.p.s.p.s evoked in different motoneurones by impulses in the same Ia axon were also reduced by different amounts. 7. Analysis of fluctuations in e.p.s.p.s before and after conditioning indicated that after conditioning, larger discrete amplitudes became less probable, while smaller discrete amplitudes became more probable. The average increment between discrete amplitudes did not alter; nor were the discrete amplitudes reduced. 8. The probabilities of transmitter release at synaptic boutons were calculated before and during presynaptic inhibition. The maximum decrease in release probability was 0.64, suggesting a reduction in calcium influx of 10‐15%.
Dendritic activities of spinal motoneurones in pigs and rabbits enhanced through chronic stimulation of a dorsal root.
Authors: Fujita Y , Harada H , Kitamura T , Minami S , Sato T
Published: December 2015

1. The L6 or L7 dorsal root in 7‐10‐day‐old pigs was chronically stimulated for 3 or 4 h a day for 4 days/week. The stimuli were 50 or 500 Hz pulse trains delivered at 0.5/s. The induced movements were limited to the hip and hind leg on the stimulated side without any sign of pain. There was evidence that not only the monosynaptic, but also polysynaptic pathways to the motoneurones were chronically stimulated. After 2‐6 days of chronic stimulation, all pigs were studied in acute experiments either under pentobarbitone (Nembutal) anaesthesia or in the decerebrated state. Normal (unstimulated) 15‐28‐day‐old pigs were also studied in acute experiments under similar conditions, as the controls. 2. In thirty‐three out of fifty‐six motoneurones of normal pigs there were all‐or‐none potentials of 2‐6 ms duration and 1‐5 mV amplitude. These have been named D‐spikes. They occurred in response to tibial nerve and/or dorsal root stimulation and/or spontaneously. They could be abolished by injection of a hyperpolarizing current. These results show that D‐spikes are different from any of the well‐established all‐or‐none events of the motoneurone, i.e. the spikes of the axon, initial segment, soma and unitary excitatory post‐synaptic potentials. Several kinds of D‐spikes could exist in the same motoneurone, as judged from their wave forms and thresholds. This argues for the dendrites as the sites of origin for D‐spikes, because only the dendrites can have multiple sites for spike generation. D‐spikes were shown to summate to form a larger depolarization. 3. In pigs chronically stimulated with 500 Hz pulses seventy‐five motoneurones were studied in acute experiments. In sixty‐one motoneurones D‐spikes were observed. This indicated that D‐spike occurrence was enhanced in the chronically stimulated motoneurones as compared with controls. 4. Characteristic of the chronically stimulated motoneurone was the presence of a depolarization of all‐or‐none nature which was more than 10 ms in duration and 2‐12 mV in amplitude. The depolarization is referred to as the D‐wave. The D‐wave was similar in properties to the D‐spike described above, except that it was of longer duration. Consequently, it is assumed that the D‐wave is summed D‐spikes. D‐waves were observed in nineteen motoneurones.(ABSTRACT TRUNCATED AT 400 WORDS)
Oscillatory chloride current evoked by temperature jumps during muscarinic and serotonergic activation in Xenopus oocyte.
Authors: Miledi R , Parker I , Sumikawa K
Published: December 2015

1. Membrane currents were recorded from voltage‐clamped oocytes of Xenopus laevis, during temperature jumps imposed by a heating light. Resting oocytes usually showed little response, but large oscillatory membrane currents developed in response to cooling steps applied during activation of 'native' muscarinic receptors. 2. Similar temperature jump (Tjump) currents were seen during activation of oscillatory chloride currents mediated by muscarinic acetylcholine (ACh), serotonin, glutamate and noradrenaline receptors, expressed in the oocyte following injection with messenger ribonucleic acid (mRNA) from rat brain. The Tjump response during muscarinic activation was selectively blocked by atropine, and that during serotonergic activation by methysergide. In contrast, the 'smooth' membrane currents elicited by nicotinic ACh, kainate and gamma‐aminobutyric acid (GABA) were not accompanied by Tjump responses. 3. Rapid cooling of the oocyte gave larger Tjump currents than a gradual cooling over a few seconds. The size of the Tjump current elicited by a fixed cooling step increased linearly with the preceding time of warming, becoming maximal at intervals greater than about 100 s. 4. The Tjump current was inward at a clamp potential of ‐60 mV and reversed direction at about ‐22 mV, which corresponds to the chloride equilibrium potential in the oocyte. In low‐chloride solution the reversal potential was shifted to more positive potentials, but it was almost unchanged by changes in potassium and sodium concentration. The size of the Tjump current decreased as the membrane potential was made more negative than about ‐40 mV. 5. The period of oscillation of the Tjump current increased with decreasing temperature, following a Q10 of 3.15. Depolarization also caused a small increase in period. 6. The Tjump current was not abolished in calcium‐free solution, or by addition of manganese or lanthanum to the bathing solution. However, it was abolished by intracellular injection of the calcium‐chelating agent EGTA. 7. Intracellular injection of inositol 1,4,5‐trisphosphate evoked an oscillatory membrane current, during which Tjump responses developed similar to those after muscarinic activation. Intracellular injection of calcium evoked a chloride current, but this was not accompanied by Tjump responses. 8. We conclude that the oscillatory currents evoked by temperature jumps arise from chloride channels activated by intracellular calcium. This calcium is probably mobilized from intracellular stores by inositol trisphosphate which is liberated as a result of activation of muscarinic receptors, and also receptors for serotonin and glutamate.(ABSTRACT TRUNCATED AT 400 WORDS)
Properties of an electrogenic sodium‐potassium pump in isolated canine Purkinje myocytes.
Authors: Cohen I S , Datyner N B , Gintant G A , Mulrine N K , Pennefather P
Published: December 2015

1. Purkinje myocytes were isolated from canine Purkinje strands by collagenase exposure and gentle trituration. The myocytes were studied by a switched single‐micro‐electrode voltage‐clamp technique at 37 degrees C in Tyrode solution containing 8 mM‐K+ and 2 mM‐Ca2+. 2. The dose‐response relation for the cardiotonic steroid dihydroouabain (DHO) was obtained by measuring the change in membrane current caused by application of concentrations of 1‐100 microM. The KD obtained in fourteen experiments was 3.7 +/‐ 1.1 microM (mean +/‐ S.E. of mean). 3. We employed 100 microM‐DHO (a concentration more than 25‐fold greater than the KD) to estimate the resting pump current (Ip) in the isolated myocytes. A value of 0.27 +/‐ 0.02 microA microF‐1 (mean +/‐ S.E. of mean, n = 32) was obtained. 4. Myocytes were also exposed to K+‐free solution for a period of 200 s. On return to K+‐containing Tyrode solution there was a slowly decaying outward current. The time constant of decay of this pump current transient was 87 +/‐ 8 s (mean +/‐ S.E. of mean, n = 8). The integral beneath this transient was used to obtain a second estimate of the resting pump current. In four preparations where exposures in DHO and in K+‐free solutions were employed the ratio Ip, DHO/Ip, K‐free was 1.76 +/‐ 0.15 (mean +/‐ S.E. of mean). 5. From the magnitude of resting pump current, in the presence of total pump blockade the Na+ activity should rise at a rate of 1.3 mM min‐1. 6. Reducing [K+]o from 8 to 1 mM reduced Ip by more than 40% initially. Ip then slowly increased over the next 30 min. These results suggest that the steady‐state inward background current is not greatly altered by changes in [K+]o, and that [Na+]i rises to a new level. The changes in Ip obtained at early times following reduction of [K+]o to 1 or 0.5 mM (t less than 1.75 min) were used to estimate the Km for external K+; a value of 0.8 mM was obtained. 7. The results suggest that the properties of the Na+‐K+ pump in isolated canine Purkinje myocytes are similar to those in canine Purkinje strands. This argues against major distortions of measured pump properties in the canine Purkinje strand and for the physiological state of the Na+‐K+ pump in the isolated Purkinje myocyte.
Recurrent inhibitory connexions among neck motoneurones in the cat.
Authors: Brink E E , Suzuki I
Published: December 2015

1. Intracellular recordings were made from motoneurones innervating neck muscles in the cat. Dorsal roots were cut and muscle nerves electrically stimulated to activate alpha motor axons. 2. Recurrent inhibitory post‐synaptic potentials (i.p.s.p.s) evoked by antidromic volleys in homonymous or heteronymous nerves were found in the majority of motoneurones studied, including those to dorsal neck muscles (biventer cervicis, splenius and complexus) as well as to occipitoscapularis and levator scapulae ventralis. 3. Central latencies of the recurrent i.p.s.p.s indicate disynaptic transmission. Amplitudes ranged from 100 microV (criterion level) to 2.2 mV. Average amplitudes were less than 0.6 mV. 4. The recurrent i.p.s.p.s were distributed to non‐synergistic as well as to synergistic motoneurones. Analysis of relative strength of recurrent inhibition indicates influence of proximity of motoneurone pools, functional relatedness of muscles, as well as other factors. Variation in intrinsic motoneuronal properties probably underlies positive correlations (independent of variation in resting potential) between recurrent i.p.s.p.s evoked from different sources in motoneurones of a single pool. 5. Recordings (mainly extracellular) were also made from interneurones (Renshaw cells), located in the C3 and C4 segments of the spinal cord, that were excited by antidromic volleys in muscle nerves. The response varied from a single action potential to a burst of up to nineteen action potentials. Central latencies to the first response indicate monosynaptic transmission. Many Renshaw cells were excited by antidromic volleys in several muscle nerves, though this was restricted to nerves of the same segmental level as the Renshaw cell. All the muscle nerves studied were effective in activating Renshaw cells. 6. The results indicate that in many ways the recurrent i.p.s.p.s and the responses of Renshaw cells recorded in the neck segments resemble those in the hind‐limb segments. Thus, the basic organization of recurrent inhibition in the neck segments resembles that occurring elsewhere in the spinal cord. A difference is the tendency for recurrent i.p.s.p.s in neck motoneurones to be relatively small in amplitude and Renshaw cell responses to be less strong than those recorded in the hind‐limb segments. It is suggested that this is related to the segmentation of neck muscles and their motoneurone pools. 7. It is concluded that recurrent inhibition is a prominent feature of spinal organization governing neck muscles. It can therefore be expected to participate in control of head movements.
Spinal cord influences on the colonic myoelectrical activity of fed and fasted rats.
Authors: Du C , Ferré J P , Ruckebusch Y
Published: December 2015

1. The myoelectrical activity of the large intestine of fed and fasted rats was recorded with chronically implanted nichrome wire electrodes after destruction of the spinal cord, after spinal cord transection, and after spinal anaesthesia. 2. After spinal cord ablation, the cyclical organization of the colonic electrical spiking activity, as well as the gastrocolic reflex and accompanying postprandial enhancement of the cyclical pattern of activity, persisted on the proximal and distal colon. On the transverse colon, however, the spiking activity was considerably increased. This latter effect obliterated the gastrocolic response due to feeding but not the subsequent postprandial enhancement of the cyclical pattern of activity. 3. After spinal cord transection, the level of spiking activity also increased on both the transverse and distal colon, but no major changes in cyclical activity or in postprandial responses were recorded. 4. Spinal anaesthesia produced by intrathecal lidocaine increased the motility of the transverse colon to a level which masked the gastrocolic reflex. 5. These results suggest a prevertebral ganglia and/or a local control mechanism for the cyclical organization of the spiking activity of the colon. The central control mechanisms involve mostly spinal inhibitory influences on the transverse colon and supraspinal inhibitory influences on the distal colon.
The control of potassium concentration in the cerebrospinal fluid and brain interstitial fluid of developing rats.
Authors: Jones H C , Keep R F
Published: December 2015

1. In situ measurements of plasma, cerebrospinal fluid (CSF) and brain interstitial fluid (ISF) K+ concentrations have been made in anaesthetized rats aged between 19 days gestation and 30 days after birth using K+‐selective micro‐electrodes. 2. Under control conditions, plasma, CSF and ISF [K+] did not vary significantly with age, the over‐all mean concentrations being 3.8, 3.1 and 3.2 mM respectively. The CSF and ISF [K+] were significantly lower than plasma [K+] at all ages. 3. It is concluded that young rats, from the age of 19 days gestation, can normally maintain plasma‐to‐CSF and plasma‐to‐ISF gradients similar to those in the adult, presumably by action of the blood‐CSF and blood‐brain barriers. 4. During acute plasma hyperkalaemia there was very little regulation of CSF [K+] at 21 days gestation, but after birth there was a gradual improvement in CSF K+ homeostasis until by 30 days after birth a normal CSF [K+] could be maintained. 4. There was no regulation of ISF [K+] during hyperkalaemia at 21 days gestation, although after birth there was a rapid improvement in ISF K+ homeostasis. 1‐day‐old neonates were able to maintain a normal forebrain ISF [K+] during hyperkalaemia. 6. It is concluded that the onset of both CSF and ISF K+ homeostasis takes place at around birth in rats. However, K+ homeostasis matures more rapidly in the ISF than in the CSF. This suggests that, at least in the neonatal period, the CSF is not essential for ISF [K+] regulation.