bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recruitment order of human spindle endings in isometric voluntary contractions
Authors: Burke David , Hagbarth Karl-Erik , Skuse Nevell F. 
Published: December 2014

1. The responses of twenty‐two spindle endings in the anterior tibial and toe extensor muscles of human subjects were studied during isometric voluntary contractions of the receptor‐bearing muscle with the ankle joint fixed in 25° plantar flexion.2. The discharge of eighteen endings accelerated in voluntary contractions when the contraction strength exceeded a threshold level which differed for different endings but was reproducible for the same ending.3. With contractions of slow onset the latency to spindle acceleration varied with the speed of onset of the contraction. Endings with a background discharge were often unloaded by contractions until the contraction strength exceeded the threshold for activation of the ending.4. No correlation was found between the sensitivity of a spindle to external length changes and its ease of activation in a voluntary contraction. For two spindle endings with a background discharge there was no change in either discharge frequency or the regularity of spindle discharge during contractions which were below the threshold for activation of the endings. It is concluded that the threshold for activation of a spindle ending in an isometric voluntary contraction is determined by its fusimotor innervation, and that fusimotor neurones probably have a recruitment order, much as do skeletomotor neurones.5. Once activated, the discharge of spindle endings fluctuated with changes in skeletomotor activity but the relationship for some endings contained non‐linearities. Such non‐linearities were not as apparent in multi‐unit recordings from a number of spindle endings in the contracting muscle. It is concluded that the fusimotor drive to a muscle is proportional to the skeletomotor drive to the muscle, and that skeletomotor and fusimotor neurones are subjected to similar if not identical descending command signals. From the work of Evarts (1968), it seems likely that these command signals are related more to desired muscle force than to desired muscle length.
Mechanism of the vibration paradox: excitatory and inhibitory effects of tendon vibration on single soleus muscle motor units in man
Authors: Desmedt John E. , Godaux Emile 
Published: December 2014

1. The parameters of presynaptic inhibition of the Ia spindle afferents from soleus muscle by vibration have been investigated. The inhibitory effects increase with the amplitude of vibration, but decrease when the vibration frequency is increased.2. The monosynaptic reflex threshold of twenty‐one single soleus motor units activated in the H (Hoffmann) reflex by a single electrical stimulus to the posterior tibial nerve was estimated quantitatively and expressed in relation to the size of the simultaneously recorded H reflex.3. A parametric study of the effects of various Achilles tendon vibrations on the reflex threshold of the single soleus motor units indicated that their order of derecruitment is concordant with their rank order for activation in the phasic reflexes of the soleus. The last recruited motoneurones are the most susceptible to being silenced by steady vibration.4. Muscle vibration progressively recruits single motor units according to the motoneurone size principle through polysynaptic proprioceptive pathways. However the presynaptic inhibition of Ia spindle afferents simultaneously induced by the vibration works in reverse on the same rank order of motoneurones of the soleus spinal pool, thereby limiting the polysynaptic recruitment of units in the tonic vibration reflex while depressing the autogenic phasic proprioceptive reflexes. These mechanisms elucidate the so‐called vibration paradox and extend the size principle of Henneman to presynaptic inhibitory effects.
Evidence of a neurotransmitter role for aspartate and γ‐aminobutyric acid in the rat olfactory cortex
Authors: Collins G. G. S. 
Published: December 2014

1. Using a cortical cup technique, the release of seven endogenous amino acids from the isolated rat olfactory cortex slice has been monitored.2. Electrical stimulation of the lateral olfactory tract at a frequency of 4 min−1 was accompanied by a significant increase in the release of aspartate, GABA and taurine; the release of GABA and aspartate but not that of taurine was Ca2+‐dependent.3. Chronic unilateral bulbectomy was accompanied by a specific, significant fall in the aspartate content of the olfactory cortex which reached a maximum 5 days after surgery and persisted for at least a further 5 days. Electrical stimulation of the lateral olfactory tract of such preparations did not release any of the amino acids under investigation.4. When slices from the unoperated side were exposed to solutions containing 25 m
M‐K+ or stimulated with electrodes placed directly on the cortex enclosed by the cup there was a Ca2+‐dependent release of aspartate and GABA accompanied by a Ca2+‐independent release of taurine. Following chronic bulbectomy, these procedures failed to evoke significant release of aspartate whereas the characteristics of GABA and taurine release were unaltered.5. It is concluded that aspartate may be the excitatory transmitter of some of the terminals of the lateral olfactory tract fibres and that GABA may be a transmitter at some inhibitory synapses of the rat olfactory cortex.
Influence of sex and age on febrile responses to peripheral and central administration of pyrogens in the rabbit
Authors: Lipton J. M. , Ticknor C. B. 
Published: December 2014

1. Intravenous injections of leucocytic pyrogen in doses of 15, 30 and 60 μl./kg caused febrile reactions in male rabbits that were related to age of the animal: rabbits under 2 yr of age developed fevers that were related to dose of pyrogen, while rabbits 2‐3 yr old showed large febrile responses which were not dose‐related.2. Female rabbits of comparable ages generally showed smaller febrile reactions to
I.V. leucocytic pyrogen, and still older females (3‐5 yr) developed fever only after the largest dose.3. Dose‐related febrile responses to 2·5, 5 and 10 μl. leucocytic pyrogen given intracerebroventricularly (
I.C.V.) were greater in male rabbits 1‐3 yr old than in females of comparable age. Female rabbits 3‐5 yr old showed dose‐related fevers that were smaller than those of younger animals of both sexes.4. There were no major differences in response to 125, 250 and 500 ng PGE2, given
I.C.V., between male and female rabbits under 2 yr of age. Females 2‐3 yr of age had greater responses to PGE2 than males of comparable age whilst the oldest females showed smaller responses.5. It is concluded that the febrile response of the rabbit to peripheral and central leucocytic pyrogen varies with both age and sex. Differences in sensitivity of central fever controls to endogenous pyrogen in animals of different ages and sexes may account for the different responses to peripheral pyrogen.
The equilibrium between different conformations of the unphosphorylated sodium pump: effects of ATP and of potassium ions, and their relevance to potassium transport
Authors: Beaugé L. A. , Glynn I. M. 
Published: December 2014

1. Changes in the intrinsic fluorescence of Na, K‐ATPase protein have been used to monitor the interconversion of E1 (low fluorescence) and E2 (high fluorescence) forms of the unphosphorylated enzyme.2. In media lacking sodium and nucleotides, 1 m
M‐potassium was sufficient to convert practically all of the enzyme into the E2 form. In media containing 1 m
M‐potassium, 1 m
M‐EDTA, and no sodium or magnesium, the addition of ATP, or its β, γ‐imido or methylene analogues, converted the enzyme back into the E1 form. The relation between nucleotide concentration and the fraction of the enzyme that was in the E1 form could be described by a rectangular hyperbola, with a K½ of about 15 μ
M for ATP, 65 μ
M for adenylyl‐imidodiphosphate (AMP‐PNP) and 180 μ
M for adenylyl (β, γ‐methylene)‐diphosphonate (AMP‐PCP). ADP also converted the enzyme back into the E1 form, with a K½ of about 25 μ
M, but the relation between concentration and fraction converted was not well described by a rectangular hyperbola.3. In similar media containing 50 m
M‐potassium, much higher concentrations of ATP were required to convert the enzyme back into the E1 form, and the conversion was probably incomplete.4. If we assume that ATP and potassium ions affect each other's binding solely by altering the equilibrium between E1 and E2 forms of the enzyme, we are able to conclude (i) that potassium ions bind to the E1 form with a moderately low affinity, (ii) that, in the absence of nucleotides, the equilibrium between E1K and E2K is poised strongly in favour of E2K, (iii) that the binding of ATP to a low‐affinity site alters the equilibrium constant for the interconversion of E1K and E2K by two to three orders of magnitude, so that, at saturating levels of ATP, the equilibrium is probably slightly in favour of E1K, and (iv) that in sodium‐free, potassium‐containing media, ATP will appear to bind to the enzyme more tightly than would be expected from the dissociation constant of the E2K. ATP complex.5. The pattern of the equilibrium constants for the various reactions between E1, E2, ATP and potassium is compatible with the hypothesis that the ATP‐accelerated conversion of E2K into E1K, and the subsequent release of potassium ions from low‐affinity inward‐facing sites, are part of the normal sequence of events during potassium influx in physiological conditions.
Paired‐pulse and frequency facilitation in the CA1 region of the in vitro rat hippocampus
Authors: Creager Robert , Dunwiddie Thomas , Lynch Gary 
Published: December 2014

1. Several types of facilitation of evoked synaptic responses were investigated in the CA1 region of the in vitro rat hippocampus. Homosynaptic paired‐pulse facilitation and heterosynaptic frequency facilitation were characterized and found to be differentiable processes on the basis of several characteristics.2. Paired‐pulse facilitation, which occurs when the same input is stimulated twice in rapid succession, is manifested as an increase in both the extracellularly recorded population spike and the field e.p.s.p., and is specific to the set of afferents excited by the first impulse. Responses to other excitatory afferents show no facilitation by a heterosynaptic conditioning pulse.3. At intervals less than 200 msec, the degree of facilitation produced by a preceding impulse appears to decline as a first order exponential function of time. Facilitation is increased by lowering calcium or raising magnesium concentrations in the bathing medium, with no apparent change in the time constant of the decay process.4. The phenomenon that has sometimes been termed frequency facilitation, and which occurs during the early phase of repetitive stimulation, appears to be an extension of paired‐pulse facilitation. It is seen as an increase in amplitude of both the e.p.s.p. and population spike in response to stimulation of homosynaptic inputs, can be predicted with fair accuracy by assuming that the residual paired‐pulse facilitation produced by each impulse adds linearly with that from previous impulses, and is affected by calcium and magnesium ions in the same manner as is paired‐pulse facilitation. These two types of facilitation, which apparently share a common mechanism, are termed synaptic or primary facilitation.5. Another type of facilitation, which we suggest might more properly be called frequency facilitation, develops slowly during the course of repetitive stimulation. It is the result of an increase in cell firing in response to any excitatory input, either homo‐ or heterosynaptic, at time points at which the field e.p.s.p. is typically depressed.6. Increases in the potassium concentration of the perfusion medium produce effects similar to those observed with frequency facilitation; stimulation‐evoked increases in the extracellular concentration of this ion are hypothesized to underlie this type of generalized facilitation.
Effects of autonomic stimulation on the release of vasoactive intestinal peptide from the gastrointestinal tract in the calf
Authors: Bloom S. R. , Edwards A. V. 
Published: December 2014

1. The effects of autonomic stimulation on the release of vasoactive intestinal peptide (VIP) from the gastrointestinal tract have been investigated in adrenalectomized claves 2‐5 weeks after birth.2. Stimulation of the peripheral ends of the splanchnic nerves (10 Hz for 10 min) caused a small fall in the concentration of VIP in portal and arterial plasma, together with a rise in the concentration in intestinal lymph. None of these changes achieved statistical significance.3. The effects of stimulation of the peripheral ends of the thoracic vagi, below the heart (10 Hz for 10 min), were found to depend in part upon the integrity of the splanchnic sympathetic innervation. A substantial rise in the concentration of VIP in intestinal lymph occurred whether or not the splanchnic nerves had been cut whereas an associated rise in arterial plasma VIP was only observed in calves in which the splanchnic nerves had been sectioned.4. The rise in the concentration of VIP in intestinal lymph, in response to vagal stimulation, was unaffected by concomitant stimulation of the splanchnic nerves, although the associated rise in arterial plasma VIP concentrations was suppressed. The response was also found to be resistant to atropine.5. The minimum estimated concentration of VIP in the extracellular fluid of the gastrointestinal tract was estimated to be about 60 p‐mole/l. at rest and to rise by 70‐120 p‐mole/l. in response to vagal stimulation.6. Intravenous infusions of VIP at a dose of 50 ng kg−1 min−1 (16 p‐mole kg−1 min−1), which raised the minimum estimated concentration of VIP in the gastro‐intestinal tract to the highest range encountered during stimulation, produced no significant changes in the concentrations of glucose, insulin, pancreatic glucagon or pancreatic polypeptide in the arterial plasma.7. It is concluded that a small amount of VIP is released from the gastrointestinal tract in response to vagal stimulation. In contrast, release of VIP is unaffected by stimulation of the splanchnic nerves except in so far as the rate at which the peptide passes into the circulation is reduced by adrenergic vasoconstriction.
The nature of the atrial receptors responsible for a reflex decrease in activity in renal nerves in the dog
Authors: Linden R. J. , Mary D. A. S. G. , Weatherill D. 
Published: December 2014

1. In dogs anaesthetized with chloralose, distension of small balloons in the pulmonary vein—atrial junctions and left atrial appendage, to stimulate left atrial receptors, caused a reduction in activity in efferent renal nerves. This response was maintained during distension of the balloons for 30 min periods.2. In a second group of dogs, cooling the cervical vagi in steps reduced the magnitude of the response in renal nerves. In seven dogs, the response in fourteen preparations of renal nerves was slightly reduced with the vagi at 18 °C and markedly reduced or abolished at 12 °C. The effect of cooling the vagi was the same as the previously shown effect of cooling on the increase in activity in myelinated afferent vagal fibres during similar stimulation of atrial receptors.3. In a third group of dogs, the cervical vagi were cooled to 9 °C. In six dogs, fifty‐four preparations of renal nerves showed no significant response to distension of the balloons.4. In a fourth group of dogs, both vagi were sectioned in the neck. In three dogs, twenty‐four preparations of renal nerves then showed no response to distension of the balloons.5. It is concluded that the reduction in activity in efferent renal nerves during distension of small balloons in the pulmonary vein—atrial junctions and left atrial appendage involves only atrial receptors discharging into myelinated vagal fibres.
Three types of acetylcholine response in bivalve heart muscle cells
Authors: Elliott Ellen J. 
Published: December 2014

1. The acetylcholine (ACh) responses of cardiac muscle cells from three species of bivalves were studied by intracellular recording and ACh ionophoresis. Heart muscle contraction was abolished by bathing in artificial sea water in which Mn2+ had been substituted for Ca2+.2. Three different types of membrane potential changes were observed in response to ACh pulses: a slow hyperpolarization in the clam Mercenaria mercenaria, a rapid depolarization which was sometimes followed by a slower hyperpolarization in the muscle Mytilus edulis, and a biphasic response consisting of both a rapid depolarization and slower hyperpolarization in the oyster Crassostrea virginica. All responses were accompanied by an increase in membrane conductance, as measured by passing constant current pulses with an extracellular suction electrode.3. The hyperpolarizing response in all three species was blocked most effectively by methylxylocholine and not very effectively by tubocurarine or hexamethonium. The depolarizing response in Mytilus was blocked preferentially by tubocurarine and hexamethonium, while the depolarizing response in Crassostrea was blocked effectively by tubocurarine only.4. The hyperpolarizing response in all three species was not altered by Cl−‐free or Na+‐free sea water, but was affected by changes in external K+. The rate of change of the inversion potential of this response with change in [K+]o was 59 mV per tenfold concentration change. The depolarizing response of Mytilus was not altered by changes in external Cl− or K+, but was abolished in Na+‐free sea water. The depolarizing response of Crassostrea was insensitive to external Na+ or K+, inverted at ‐31 mV in normal sea‐water, and was altered by changes in [Cl−]o. Substituting for Cl− with sulphate shifted the inversion potential at a rate of 56‐61 mV per tenfold Cl− concentration change.5. The three types of ACh response seen in bivalve heart muscle are similar with respect to time course, pharmacological sensitivity and ionic mechanism to the three types of ACh response described in Aplysia central neurones. Analogies can also be drawn with vertebrate ACh responses.
The density, distribution and topographical organization of spinocervical tract neurones in the cat
Authors: Brown A. G. , Fyffe R. E. W. , Noble R. , Rose P. K. , Snow P. J. 
Published: December 2014

1. In acute experiments, detailed grids of micro‐electrode recordings were made from spinocervical tract (s.c.t.) cells in the lumbosacral cord of anaesthetized cats. These grids provided electrophysiological data on the location, distribution, density and somatotopic organization of s.c.t. neurones.2. In acute experiments lasting up to 48 hr, retrograde labelling of s.c.t. cells was carried out by injecting horseradish peroxidase into the lateral cervical nucleus in anaesthetized cats. The aim was to flood the nucleus with the enzyme so that all s.c.t. neurones would be labelled in order to provide an independent check on the location, density and distribution data obtained in the electrophysiological experiments.3. The electrophysiological and the anatomical experiments were sometimes performed on the same animal.4. The electrophysiological and anatomical results were in excellent agreement. (a) S.c.t. cells are located mainly in ipsilateral laminae III, IV and V. About 25% are in lamina III, 60% in lamina IV and 10% in lamina V. There are a few cells in laminae I, II and VI making up the remaining 5%. (b) There are about 550‐800 s.c.t. cells in the lumbosacral enlargement (L4—S2 inclusive) on each side of the cord. Most cells are in L7—S1 where there are twenty to forty s.c.t. neurones in each millimetre length of cord.5. Many marginal (lamina I) cells were labelled with the retrograde horseradish peroxidase method and a few cells on the contralateral side in laminae III—V and VII—VIII were also labelled. The marginal cells formed 12‐18% of labelled cells on the side of injection and, in addition, a similar absolute number of marginal cells was labelled on the side contralateral to the injection. The possible identity of these neurones is discussed.6. S.c.t. cells form a sheet of neurones across the dorsal horn. The sheet is organized somatotopically in a way which resembles the representation of the hind limb dermatomes in the dorsal columns (Werner & Whitsel, 1967). There is a relative enlargement of the L6—S1 dermatomes which encroach upon their neighbouring cord segments. The gradient of the map is very steep in the mediolateral direction but gradual in the rostrocaudal direction. The detailed somatotopic maps generated in the present work have revealed that s.c.t. cells are arranged so that their receptive fields form longitudinal columns and cells within the columns have overlapping fields.
Effects of acetylcholine on ion fluxes and chlorotetracycline fluorescence in pancreatic islets
Authors: Gagerman E. , Sehlin J. , Täljedal I.-B. 
Published: December 2014

1. Acetylcholine potentiated glucose‐stimulated insulin release from ob/ob‐mouse islets in salt‐balanced bicarbonate buffer and to a lesser extent in Tris buffer; basal insulin release at 3 m
M-D‐glucose was not affected. Potentiation required the presence of Ca2+.2. In bicarbonate buffer, ACh stimulated the islet uptake of 45Ca2+ at 3 m
M‐glucose but not significantly at 11 m
M; no effect was seen in Tris buffer.3. At 11 m
M‐glucose, ACh increased the fluorescence from Ca2+‐chlorotetracycline in dispersed islet cells; the effect was inhibited by atropine.4. At both 3 and 11 m
M‐glucose, ACh stimulated the islet uptake of 22Na+ in 60 min. At 11 m
M‐glucose, 22Na+ uptake in 5 min was also enhanced significantly, and this effect was inhibited by atropine.5. At 3 m
M‐glucose, ACh probably stimulated the islet uptake of 86Rb+ in 10 min.6. ACh had no effect on 36Cl− retention at 3 or 11 m
M‐glucose, or on the oxidation of
D‐[U‐14C]glucose (11 m
M).7. The insulin secretory potentiator, ACh, does not act by accelerating glucose oxidation and does not induce the same ionic effects as the secretory initiator,
D‐glucose. Increased Na+ permeability and altered interaction of Ca2+ with the plasma membrane may play roles in the cholinergic depolarization of β‐cells and potentiation of insulin release.
Effect of calcium antagonism or chelation on rabbit lacrimal gland secretion and membrane potentials
Authors: Botelho Stella Y. , Dartt Darlene A. 
Published: December 2014

1. ACh‐induced secretion from the main excretory duct, as well as ACh‐induced hyperpolarizations and resting membrane potentials of superficial, probably acinar, cells were recorded from the rabbit lacrimal gland perfused in vivo with either control or test solutions.2. During perfusion with test solution containing a Ca antagonist, verapamil (10−5 to 10−3
M), or a Ca chelator EGTA (10−4 or 10−3
M), ACh‐induced secretion was only 30% of the control value, whereas the magnitude of the ACh‐induced hyperpolarization was unchanged.3. With 10−5
M‐verapamil, but not with 10−3
M‐verapamil or EGTA‐containing solutions, the inhibition of ACh‐induced flow was completely reversed either by replacing the test with control solution or by increasing the Ca concentration of the test solution twofold.4. In addition, EGTA (10−4
M) solution containing the normal extracellular Ca2+ concentration inhibited secretion by 30%.5. During perfusion with verapamil or EGTA test solutions the mean resting membrane potential of superficial, probably acinar, cells was depolarized by 15%.6. It is concluded that although extracellular Ca is required for the major portion of ACh‐induced secretion, the magnitude of the ACh‐induced hyperpolarization of cells, which are most likely acinar, is independent of extracellular Ca.