bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of calcium in depolarization—secretion coupling at the motor nerve terminal
Authors: Cooke J. D. , Okamoto K. , Quastel D. M. J. 
Published: December 2014

1. The relation between m.e.p.p. frequency (F) and [Ca] was studied at the mouse neuromuscular junction, at varied concentrations of K+ and at nerve terminals depolarized by focal depolarization.2. Under all conditions the relation between log F and log [Ca] was sigmoid, with a maximum slope that increased with depolarization or raised [K+]. In addition, depolarization or raised K+ caused a progressive shift of the sigmoid curve upward and to the left (to reduced log [Ca]) and increased the range over which log F could be altered by [Ca].3. Reduction of osmotic pressure changed the relation between log F and log [Ca] in the same way as increase of depolarization, while increase of osmotic pressure did the opposite.4. Raised [Mg] acted in two ways: (a) to shift the curve of log F vs. log [Ca] to the right and (b) to reduce maximum Δ log F/Δ log [Ca] without altering the range of log F sensitive to [Ca].5. The relation between log quantal content of e.p.p.s and log [Ca] was similar to that between log m.e.p.p. frequency and log [Ca].6. Individual nerve terminals varied in both Ca‐dependent and Ca‐independent fractions of log F; a large Ca‐independent portion appears to be associated with a low Ca‐dependent portion and vice versa. With large prolonged depolarization the Ca‐independent portion was increased, apparently at the expense of the Ca‐dependent portion.7. The results of all experiments were summarized in terms of parameters found by fitting the observed log release —log [Ca] curves to two theoretical equations, each derived on the basis of a model: (a) all‐or‐nothing activation of release probability by Ca‐complex(es) and (b) graded activation of release probability by Ca complex(es).8. On the basis of the all‐or‐nothing model, from which follows alinear relation between F and amounts of Ca complex(es), the number of Ca2+ atoms that ‘cooperate’ to mediate release appeared to increase progressively with presynaptic depolarization, to a value of 4 or more with a presynaptic action potential.9. On the basis of the graded activation model, which predicts an exponential relation between F and amount of Ca complex, the number of Ca2+ atoms that combine with Ca receptor appears to be independent of presynaptic depolarization.10. Various models which could account for the data are discussed. It was concluded that all the data are consistent with a model in which:(i) quantal release probability is continuously graded with the amount of a simple Ca complex (CaX) inside the nerve terminal.(ii) Ca entry is governed by presynaptic membrane potential (increasing exponentially with depolarization) and by the amount of a Ca complex (Ca2Y) on or in the membrane.(iii) Mg2+ competes with Ca2+ at both receptors, X and Y.(iv) The internal Ca receptor X is also increased by presynaptic depolarization.
The effect of some molecules and ions on gastric function in the milk‐fed calf
Authors: Bell F. R. , Razig S. A. D. 
Published: December 2014

1. The abomasum of the milk‐fed calf has been examined using an adaptation of the Serial Test Meal method devised by Hunt & Spurrell (1951). The emptying process, acid secretion and pepsin secretion were studied.2. Using serial test meals of simple solutions instilled into the abomasum via a cannula, our investigation leaves no doubt that the osmolarity of the abomasal contents significantly modifies the rate of abomasal emptying.3. Hypotonic and isotonic solutions of sodium chloride and sodium bicarbonate increase abomasal emptying but bicarbonate is most effective.4. Increasing the concentration of solutes in the abomasal contents slows abomasal emptying. Sodium chloride, sodium bicarbonate, ammonium chloride and urea do not delay abomasal emptying until hypertonic concentrations are attained. Hypotonic solutions of potassium chloride, calcium chloride, glucose, lactose, hydrochloric acid and acetic acid delay abomasal emptying.5. The results obtained in the calf show that the abomasum is under restraint probably from duodenal receptors as is the simple stomach (Hunt & Knox, 1968) and that an osmoreceptor as postulated by Hunt (1956) is an important factor in this mechanism.6. Acid secretion is inhibited when hypertonic solutions are instilled into the abomasum.7. Pepsin secretion is not affected by simple solutions in the abomasum.8. Gastric function in the milk‐fed calf appears to be controlled by mechanisms essentially similar to those already demonstrated in the simple stomach.
Cortical and peripheral modification of cerebellar climbing fibre activity arising from cutaneous mechanoreceptors
Authors: Leicht Rolf , Rowe Mark J. , Schmidt Robert F. 
Published: December 2014

1. In cats anaesthetized with Nembutal climbing fibre (CF) responses evoked in individual cerebellar Purkyně cells by mechanical stimulation of the skin were conditioned by preceding stimuli both to the periphery and to the precruciate area of the cerebral cortex.2. Cortical stimulation, generally subthreshold for evoking a CF response itself, induced an inhibition of cutaneous evoked CF responses in 65% of all Purkyně cells tested. The maximum inhibition ranged from 40 to 100% of the control responses at conditioning‐testing intervals of 30–70 msec and the duration of the inhibition was usually 125 msec.3. In most cases the corticofugal inhibition of cutaneously evoked CF responses was mediated by inhibitory mechanisms outside the cerebellar cortex, probably at relays within the spino‐olivocerebellar pathways. Purkyně cells undergoing corticofugal inhibition were distributed widely within both the vermis and the pars intermedia of the anterior lobe.4. In 40% of all Purkyně cells tested, there was evidence for afferent inhibition of their peripherally evoked CF responses as revealed by conditioning stimuli applied to the skin outside the receptive field. Again it was found that the inhibition was exerted at levels prior to the cerebellum.5. It is concluded that the afferent input transmitted to Purkyně cells via climbing fibres can be modified by corticofugal and peripheral influences exerted on the relays of the CF pathways outside the cerebellar cortex.
Types of afferent nervous activity which may be measured in the vagus nerve of the sheep foetus
Authors: Ponte J. , Purves M. J. 
Published: December 2014

1. Afferent activity was measured in the vagus nerves in sixteen foetuses within 2–3 days of natural term and in two foetuses 130 and 135 days gestational age, exteriorized by hysterotomy from seventeen ewes given either a spinal anaesthetic (ten) or pentobarbitone sodium (seven).2. Activity from aortic chemoreceptors was observed which increased in rate with foetal hypoxia, NaCN or nicotine and temporary occlusion of the umbilical cord or veins. Activity was abolished or reduced with saline equilibrated with air.3. Activity from baroreceptors was observed which was synchronous with the arterial pulse and which followed changes in arterial pressure.4. Activity designated as arising from stretch receptors in the lungs or lower airways was observed which consisted of a regular discharge at 15–45 impulses sec−1, which varied with intra‐tracheal pressure, which increased with negative intrathoracic pressure generated by spontaneous respiratory movements, which, when the umbilical cord was occluded, at first increased in rate and then fell to zero at or about the occasion of the first breath. After breathing had been established, activity assumed the rhythmical pattern and showed evidence of slow adaptation of receptors seen in the adult. This activity was frequently modulated by the heart beat and after breathing had started it was reduced when carbon dioxide was raised.5. Respiratory movements with a frequency of 10–20/min occurred spontaneously in foetuses from ewes given a spinal anaesthetic and were associated with a modulation of the stretch receptor discharge. They could be induced by withdrawing fluid from the trachea and so lowering both intra‐tracheal pressure and receptor discharge and were abolished by raising intra‐tracheal pressure. These changes were abolished by sectioning the vagi just caudal to the nodose ganglion.6. These results indicate that there are excitatory and inhibitory pathways in the vagus nerves which are active in the foetus and which may well be concerned with the limitation of respiratory movements of the foetus and the onset of maintained respiration at birth.
An analysis of light‐induced admittance changes in rod outer segments
Authors: Falk G. , Fatt P. 
Published: December 2014

1. Measurements were made of the time course and amplitude of the change in real part of admittance, ΔG, of a suspension of frog rod outer segments, following a flash of light bleaching about 1% of the rhodopsin content of the rods. The measurements, based on the use of a specially designed marginal oscillator, covered the frequency range between 500 Hz and 17 MHz.2. The components of response, previously described for rods prepared by a method involving exposure to strongly hypertonic sucrose solutions, are present in similar form when rods are isolated and maintained in isotonic solutions made up with equi‐osmotic concentrations of NaCl and sucrose or with Na2SO4.3. Component I, identified as a slowly developing positive ΔG apparent at very low frequencies, is temperature‐independent up to the characteristic frequency of admittance for the suspension, fY (about 2 MHz for rods suspended in a solution having the conductivity of Ringer solution), but decreases at still higher frequencies.4. Component II, identified as a rapidly developing positive ΔG which appears only above a critical frequency about 2·5 decades below fY, increases approximately logarithmically with frequency to reach a limiting amplitude in the region of fY.5. The amplitude of component II, ΔGII, measured in the region of fY, varies linearly with the conductivity of the suspending medium, Go, under conditions in which the conductivity of the rod interior is also a linear function of the external conductivity. The relation for a flash bleaching 1% of the rhodopsin content of the dark‐adapted rod is [Formula: see text]6. Measurements made on rods suspended in a low‐conductivity solution, which has the effect of reducing the conductivity of the rod interior to about one ninth its value for rods suspended in Ringer solution, reveal a decline in component II for frequencies above 8 MHz.7. To explain the frequency dependence of component II and its dependence on conductivity, it is proposed that component II arises from a light‐induced increase in conductance of the disk membranes which obstruct the longitudinal flow of current through the rod interior except at very high frequencies.8. The disk‐membrane conductance increase for rods suspended in a solution having the conductivity of Ringer solution is calculated to be 4·3 × 10−11 mho/rhodpsin molecule bleached, a value which is similar to what has been found for ionic channels operated by membrane potential change in the nerve membrane and by synaptic transmitter in the postjunctional membrane.9. No component of response has been observed which could be reliably attributed to a surface membrane conductance decrease of the type observed in receptor cells in the retina.
Polyneuronal innervation of kitten skeletal muscle
Authors: Bagust J. , Lewis D. M. , Westerman R. A. 
Published: December 2014

1. Isometric contractions of kitten soleus and flexor hallucis longus (FHL) muscles have been examined for evidence of polyneuronal innervation. The sum of tetanic tensions of two almost equal divisions of the ventral roots was greater than the tetanic tension elicited by stimulating both the divisions simultaneously. The difference was large in kittens aged about 3 days, was less at 2 weeks and was small or absent at 6 weeks.2. A tetanus elicited from one division of the ventral root potentiated a twitch elicited from the other root division. The time course of this potentiation was similar to that of post‐tetanic potentiation induced from the same root from which the twitch was elicited.3. It is concluded that polyneuronal innervation exists in the kitten limb muscles.4. The observed degree of tension excess was less if the divisions of the root were not equal. The observations were compatible with a model which assumed a random distribution of nerve axons to the muscle fibres.
Ionic diffusion delays in the transverse tubules of frog twitch muscle fibres
Authors: Caputo Carlo , Dipolo Reinaldo 
Published: December 2014

1. The possibility of retarding the diffusional processes in the transverse tubules of frog single muscle fibres was explored by increasing the viscosity of the bathing medium. The viscosity was increased by adding Dextran 15 to the experimental solutions.2. The criterion used to test this possibility was the speed of repolarization of muscle fibre membranes produced by sudden reduction in [K]o in media of different viscosity.3. In fibres equilibrated in media containing 15% Dextran 15, and that had been depolarized with 80 m
M‐K for more than 5 sec, the repolarization caused by lowering the [K]o to 40 m
M proceeded more slowly than in fibres in Dextran‐free media.4. On the basis of the above results, it was deduced that high viscosity solutions would delay the diffusion of Na ions in the transverse tubules. Thus the effect of sudden changes in [Na]o on the twitch tension of single fibres could be studied.5. The recovery of twitches when the fibres were exposed from a solution containing no Na, to one that contained 46 m
M‐Na, occurred more slowly in high viscosity media.6. This result can be explained assuming that a Na regenerative process occurs at the level of the membrane of the transverse tubules.
A physiological study of chick myotubes grown in tissue culture
Authors: Harris J. B. , Marshall M. W. , Wilson P. 
Published: December 2014

1. A study has been made of some passive and active membrane properties of myotubes of different ages obtained in culture from explants of chick embryo thigh muscle.2. After 3 days in vitro the mean values for the myotube resting membrane potential and input resistance were ‐ 63·8 mV and 1·30 MΩ respectively. By 13 days these values had fallen to ‐ 51·0 mV and 0·80 MΩ.3. Current/voltage relations were measured in the presence of tetrodotoxin. The relations were linear for membrane potentials between ‐ 120 and ‐ 35 mV. Further depolarization usually resulted in a delayed increase in conductance which inactivated with time.4. All myotubes tested using anodal break excitation were capable of generating action potentials. Action potentials were blocked by tetrodotoxin, saxitoxin and procaine.5. All myotubes were sensitive to iontophoretically applied ACh. The potential change produced by ACh reversed polarity at a membrane potential between 0 and + 10 mV. The depolarization produced by ACh was unaffected by anticholinesterases.6. The ACh response was blocked by cobra neurotoxin,
D‐tubocurarine and atropine.7. The electrical properties of the myotubes appear to resemble those of normal adult twitch‐type skeletal muscle fibres.8. The pharmacological properties of the myotube cholinergic receptor have been compared with those of the neuromuscular junction and the denervated muscle fibre membrane.
Organization of on‐off cells in the retina of the turtle
Authors: Schwartz E. A. 
Published: December 2014

1. The organization of central and peripheral responses for one type of spike‐producing cell in the retina of the turtle (Pseudemys scripta elegans) has been studied. These cells produced a short burst of spikes following the onset and offset of a small spot of illumination (i.e.
ON—OFF cells). The effect of increasing the area of illumination was to include a peripheral inhibition. Intracellular
ON and
OFF responses were, however, affected differently.2.
ON—OFF cells marked intracellularly with Procion Yellow M4R had somata in the inner nuclear and ganglion cell layers.3. Peripheral inhibition could be evoked without a change in the membrane potential of horizontal cells.4. Passing 5 nA hyperpolarizing or depolarizing current through a micropipette within a horizontal cell elicited in
ON—OFF cells a transient excitation following the onset and offset of current.5. It is concluded that inhibition from the periphery of an
ON—OFF cell receptive field is not mediated by luminosity horizontal cells but more probably by peripheral bipolar cells.
The dorsal root potentials produced on both sides of the spinal cord by long‐lasting stimulation of the cutaneous afferents
Authors: Hołobut W. , Niechaj A. 
Published: December 2014

1. The dorsal root potentials (DRPs) produced on both sides of the spinal cord by prolonged repetitive stimulation of the alpha cutaneous afferents have been studied in spinal cats lightly anaesthetized by barbiturate.2. Ipsilateral depolarization produced by long‐lasting stimulation increases rapidly to maximum and then, in spite of a slight decline, it persists throughout the period of stimulation. Contralateral depolarization after its increase to maximum rapidly subsides to zero during continued stimulation.3. Depression of the contralateral DRP during long‐lasting stimulation depends on its frequency. It occurs at higher frequencies of tetanization (in excess of 20 c/s) while at low frequencies (3–15 c/s) contralateral DRP is maintained till the end of stimulation, displaying the pattern similar to depolarization of the ipsilateral dorsal root.4. The effect of temporal facilitation on the DRPs is much greater and of longer duration on the contralateral than on ipsilateral side of the spinal cord.5. After long‐lasting conditioning stimulation there is prolonged depression of the testing DRPs produced by a single volley in the same nerve, Since duration of this depression is prolonged beyond the known duration of presynaptic inhibitory action, it is suggested to be due to homosynaptic depression in interneuronal pathways producing primary afferent depolarization.6. More severe and prolonged depression of the contralateral DRPs evoked by preceding volleys indicates enhancement of homosynaptic depression on the other side of the spinal cord. It may be assumed that this increase depends on greater complexity of synaptic organization of the pathways producing contralateral depolarization of the primary afferent fibres.
The neural signal of angular head position in primary afferent vestibular nerve axons
Authors: Loe P. R. , Tomko David L. , Werner G. 
Published: December 2014

1. The relation between discharge frequency and angular head position was determined for a population of regularly discharging single first‐order vestibular neurones in the eighth nerve of the barbiturate anaesthetized cat.2. Each axon had a characteristic head position which was maximally excitatory to it, and a diametrically opposed head position which was minimally excitatory.3. After correction for phase shifts introduced by the orientation of preferred excitability, discharge rate in statoreceptor afferents varied as a power function of the sine of angular head position with exponents ranging from 0·9 to 1·6.4. Experimentally determined discharge rates were compared with the predictions of a computer simulation model incorporating the idea that shearing force acting on morphologically polarized receptors is the adequate stimulus for macular receptor cells.5. This approach permitted the identification of a population of first‐order vestibular afferents whose discharge frequency varied with head position as did the magnitude of shear force computed for individual receptors, each most excited in a particular head position.6. The majority of the spatial orientations of maximal sensitivity defined a surface which is tilted by approximately 30° with reference to the Horsley—Clarke horizontal plane, implying that most statoreceptor afferents are maximally sensitive to position changes when the cat's head is at or near its normal position.
Descending and segmental inhibition of transmission through the spinocervical tract
Authors: Brown A. G. , Kirk E. J. , Martin H. F. 
Published: December 2014

1. Micro‐electrode recordings were made from axons of the spinocervical tract in unanaesthetized decerebrate‐spinal cats.2. The effects of stimulation of (1) descending systems at the level of the upper cervical spinal cord and (2) hind limb cutaneous nerves, on discharges of spinocervical tract neurones were examined.3. Effects were obtained from bilateral spinal cord regions in the dorsolateral funiculi and the most medial and ventral parts of the ventral funiculi and also from the dorsal columns in the upper cervical region even though the columns had been transected at low thoracic and upper lumbar levels.4. Stimulation of either descending or segmental systems inhibited spontaneous and evoked responses. Facilitation was not seen. The inhibition had a time course of up to 250 msec, with maximal action at 20–40 msec and was greatest for polysynaptic responses or those evoked from the smaller myelinated cutaneous axons.5. It is suggested that the descending and segmental systems converge on to common inhibitory interneurones.
Possible screening of surface charges on crayfish axons by polyvalent metal ions
Authors: D'Arrigo J. S. 
Published: December 2014

1. The effect of different polyvalent metal ions in the external solution upon the threshold membrane potential for spike initiation in crayfish axons has been studied by means of intracellular micro‐electrodes. The metal ions tested included six divalent cations (Ca2+, Mg2+, Sr2+, Ba2+, Co2+, and Ni2+) and three trivalent cations (La3+, Y3+ and Eu3+).2. Identical extracellular concentrations of different cations with the same valence had essentially the same effect on threshold membrane potential. However, a very low concentration of trivalent cations (about 225 μ
M) was found to be equivalent to a much higher divalent cation concentration (13·5 m
M) as measured by their effects on threshold potential.3. Upon a tenfold increase in concentration, the threshold potential for spike initiation was shifted in a positive direction by 30·6 mV with divalent cations and by 20·8 mV with trivalent cations.4. It is shown that a hypothesis involving screening of negative charges at the axonal membrane surface, based on Gouy—Chapman theory, predicts these various experimental results rather closely.5. It is concluded that a high negative charge density, sufficient to render a screening mechanism possible, exists at the surface of crayfish axons in the region of the sodium ‘gates’.6. The density of surface charges is calculated to be approximately 1e−/43 Å2. This calculation is discussed in connexion with the possible molecular identity of the sodium ‘gates’ in crayfish axons and other excitable systems.