bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformation of signals by interneurones in the barnacle's visual pathway
Authors: Oertel Donata , Stuart Ann E.
Published: December 2014

1. The photoreceptors of the median eye of the giant barnacle drive decrementally‐conducting neurones in the supraoesophageal ganglion termed ‘inverting cells’ (I‐cells) which in turn drive impulse‐producing neurones termed ‘amplifying cells’ (A‐cells). Using intracellular recording techniques we have studied the role of I‐cells in visual processing.

2. Horseradish peroxidase injections show that I‐cells are interneurones whose processes are confined to the regions of the photoreceptor terminals on both sides of the bilaterally symmetrical ganglion.

3. In the dark, I‐cell membrane potentials (‐45 mV) are considerably less negative than those of other ganglion cells (‐60 to ‐70 mV). At the onset of a maintained light, I‐cells undergo a transient peak hyperpolarization which declines to a steady‐state response. Both response components are graded with light intensity.

4. The reversal potential of the peak of the I‐cell light response depends on the external K+ concentration more strongly than does the dark resting potential (3‐30 m
m‐K+). This evidence indicates that the hyperpolarization results from an increase in the cell's permeability to K+ ions.

5. At the offset of light an I‐cell undergoes a transient depolarization that overshoots the dark membrane potential. Dimming of a background light can also cause the I‐cell membrane potential to overshoot its dark resting value. This overshoot is associated with a large depolarizing synaptic potential in A‐cells.

6. An overshoot of the dark resting potential can also be elicited by the break of a hyperpolarizing pulse of current injected into an I‐cell. The amplitude of this overshoot increases with pulse duration over a time course of seconds.

7. In the presence of external tetraethylammonium ion (TEA) and tetrodotoxin, (TTX), the break of a hyperpolarizing pulse or the onset of a depolarizing pulse can evoke in an I‐cell an action potential whose rate of rise and amplitude depend on the external Ca concentration. This action potential can be maintained by replacement of external Ca with Ba, or blocked by addition of 15 m
m‐Co to the saline. These observation's indicate that depolarizing potential changes in this cell activate a voltage‐sensitive Ca conductance.

8. When hyperpolarizing current pulses are injected into an I‐cell, the voltage during the pulse sags back slowly towards the dark resting potential. Thus, during hyperpolarization with light or current an I‐cell's membrane properties change over a time course of seconds.

9. The onset of a depolarizing pulse or the offset of a hyperpolarizing pulse of current injected into an I‐cell leads to a transient depolarization of a simultaneously impaled A‐cell. Synaptic transmission occurs when the I‐cell is depolarized to the vicinity of the dark resting potential. The amplitude of the response in an A‐cell depends on the rate of change of the I‐cell voltage.
Optical indications of pace‐maker potential and rhythm generation in early embryonic chick heart.
Authors: Fujii S , Hirota A , Kamino K
Published: December 2014

1. Pace‐maker type action potentials and rhythm generation in very early embryonic chick hearts have been monitored using a voltage‐sensitive merocyanine‐rhodanine dye. 2. Rhythmicity in recurrence of the spontaneous action potentials was evident at the 7 somite developmental stage, and the rhythm was completely organized by the early period of the 9 somite stage; just before the first contraction. The rhythmic recurrence of action potentials was increased in frequency as development proceeded from the 7 to the 9 somite stage, and presumably gives rise to the rhythm of the initial contractions. 3. Optical signals resembling the pace‐maker type action potential with a diastolic depolarization phase were first detected in embryonic hearts at the 8 somite stage. At this stage, pace‐maker type action potentials were detected from various regions, such as the ventricle and the unfused primordia at the atrium level. 4. Regionalization of pace‐maker type action signals was exhibited at the early period of the 9 somite stage. At this stage, the pace‐maker type signals were often evident at the atrium level, while the cardiac type signals were detected in the ventricular region. 5. Hence it is concluded (i) that the rhythmicity has already been generated at the 7 somite developmental stage, (ii) that the pace‐making cells are widely distributed in the embryonic hearts at the 7‐8 somite stages and (iii) that the appearance of the pace‐maker potential is initially localized to the atrium level at about the 9‐10 somite stages.
Phagocytic activity and hyperpolarizing responses in L‐strain mouse fibroblasts.
Authors: Okada Y , Tsuchiya W , Yada T , Yano J , Yawo H
Published: December 2014

1. Fibroblastic L cells not only respond with a slow hyperpolarizing potential change to a mechanical or electrical stimulus but also show spontaneous, repetitive hyperpolarizations (i.e. membrane potential oscillation). 2. Almost all the cells can actively take up latex beads whose surfaces were treated by U.V. irradiation. 3. Non‐phagocytic L cells hardly showed hyperpolarizing responses, while hyperpolarizing responses were obtained in all the phagocytic L cells. The exposure of the cell surface to beads, however, did not trigger the generation of hyperpolarizing responses. 4. Metabolic inhibitors, low temperature and cytochalasin B inhibited both the uptake of beads and the hyperpolarizing responses. 5. Increasing the external concentration of Ca2+ induced a remarkable stimulation of the phagocytosis of beads. Mg2+ and Ba2+, which inhibited hyperpolarizing responses due to competition for Ca2+ sites on the outer surface of the membrane, significantly suppressed the uptake of beads. 6. Verapamil, a Ca2+ channel blocker, inhibited not only hyperpolarizing membrane responses but also ingestion of beads. 7. It is concluded that the Ca2+ inflow on the hyperpolarizing membrane responses is closely associated with the phagocytic activity in L cells, probably through activation of the microfilament assembly.
Dielectric components of charge movements in skeletal muscle.
Authors: Huang C L
Published: December 2014

1. Voltage clamp experiments measured transients from 10 mV steps applied about different membrane potentials, VT. Their analysis employed the Fourier transform relationship between dielectric spectra of permittivity as a function of frequency, and the step transient admittance, as well as established methods. 2. The membrane capacitance measured between ‐85 mV and about ‐50 mV rose monotonically and was associated with simple decaying transients in both ‘on’ and ‘off’ steps. At more depolarized potentials the capacitance increased sharply and was associated with a charging current of complex form, before falling again beyond the transition potential. 3. Step‐transient responses for dielectric analysis were sampled in the above voltage range. Dielectric spectra of the non‐linear transients were obtained by subtracting Fourier transforms of transients at VC = ‐85 mV from test transforms at VT. 4. The imaginary transform coefficients represent a spectrum of dielectric loss against frequency. These showed two non‐linear components. The q beta component formed a broad peak, when charge movements were simple monotonic decays. A sharp low‐frequency q gamma peak became superimposed at particular voltages when charge‐movement kinetics became complex. 5. In contrast, ‘off’ transients were simple monotonic relaxations. Their transforms showed only one dielectric loss peak, whose frequency was relatively voltage‐independent when q gamma occurred in ‘on’ transforms. 6. Both altering holding potential from VH = ‐85 to ‐50 mV and adding 1 mM‐tetracaine to the bathing solution reduced the dependence of capacitance on voltage. The non‐linear polarization currents became simple monotonic relaxations at both the beginning and end of the voltage step. 7. It is concluded that charge movements are composed of at least two components: q beta, and the tetracaine and voltage‐inactivated q gamma. Any causal relationship between q beta and q gamma and the membrane processes they might underlie would be expected to be complex.
Motor units in cross‐reinnervated fast and slow twitch muscle of the cat.
Authors: Bagust J , Lewis D M , Westerman R A
Published: December 2014

1. Isometric contractile properties of motor units were measured in cross‐reinnervated fast (flexor digitorum longus) and slow (soleus) twitch muscles of the cat. All but one cross was at least 95% pure. 2. There was a reduction in the number of motor units in all muscles, but totals remained about equal in cross‐reinnervated soleus and flexor digitorum longus. 3. Motor unit tensions (mean and maximum values) were higher in cross‐reinnervated soleus than in cross‐reinnervated flexor digitorum longus, reversing the differences between normal muscles. This was due to increases in muscle mass and in the tension developed per unit cross‐sectional area. There were motor unit tensions larger and smaller than those seen in normal muscle, but the range was comparable with that seen in self‐reinnervated muscle. 4. The changes in twitch time to peak of whole muscle following cross‐reinnervations resulted from a change over the whole range of motor units. The conversion of soleus was less complete than that of flexor digitorum longus, and the time to peak of its fastest motor unit was twice as long as any seen in normal flexor digitorum longus. 5. In neither of the cross‐reinnervated muscles were the fast contracting motor units larger than the slow contracting ones, and in cross‐reinnervated soleus they were smaller. 6. Axonal conduction velocity was correlated with motor unit tension in both muscles and with twitch time to peak in cross‐reinnervated flexor digitorum longus, but in all cases less clearly than in normal muscles. 7. The ratio of twitch to tetanic tension increased with increasing twitch time to peak, as in normal muscles.
Motor unit firing and its relation to tremor in the tonic vibration reflex of the decerebrate cat.
Authors: Clark F J , Matthews P B , Muir R B
Published: December 2014

1. The discharge of single motor units has been recorded from the soleus muscle of the decerebrate cat during the tonic vibration reflex elicited isometrically, to further understanding of the tremor that is seen in the reflex contraction. The reflex was elicited by pulses of vibration of 50 micrometers amplitude at 150 Hz, and up to four units were studied concurrently. 2. Individual units fired rather regularly and at a low frequency (range 4‐14 Hz). The rate of firing of any unit normally fell within the frequency band of the tremor recorded at the same time. On comparing different preparations a higher frequency of tremor was associated with a higher frequency of motor firing. 3. The responses of pairs of motor units recorded concurrently during repeated production of the reflex were compared by cross‐correlation analysis; over 1000 spikes from each train were normally used for this. The major of the cross‐correlograms were flat with no overt sign of any synchronization between the units other than that due to the vibration. 4. Clear indications of correlated motor unit firing could be produced deliberately by modulating the amplitude of vibration at a frequency comparable to that of the normal tremor and thereby introducing a rhythmic component into the tonic vibration reflex. 5. About 20% of the cross‐correlograms obtained during normal tremor showed varying amounts of an irregular ‘waviness’ suggesting a possible correlation between the times of firing of a pair of units. But such waves never developed steadily throughout the period of analysis, in contrast to the comparable waves produced on modulating the vibration. Similar waves were seen on cross‐correlating a motor unit with an electronic oscillator, confirming that their occurrence does not necessarily demonstrate the existence of active neural interactions. 6. It is concluded that there is no strong and widespread neural synchronizing mechanism active during the tonic vibration reflex, although the possibility of some weak neural interactions has not been excluded. The findings favour the idea that the tremor in this preparation is simply the inevitable result of motor units discharging asynchronously, but at closely similar subtetanic frequencies.
Alterations in cat skeletal neuromuscular junctions following prolonged inactivity.
Authors: Eldridge L , Liebhold M , Steinbach J H
Published: December 2014

1. The distributions of acetylcholine (ACh) receptors, cholinesterase (ChE) activity and nerve terminals were studied on cat muscle fibres which had been inactive for 2‐3 years. 2. Neuromuscular junctions increased in size as a result of sprouting of terminal branches. In addition some fibres were multiply innervated at separate sites. 3. In muscles from two cats, some areas at the junction showed ChE activity but had only a relatively low density of ACh receptors. 4. The extrajunctional receptor density was higher than in normal muscles but lower than in muscles denervated for up to 10 months.
Signal transmission from rods to ganglion cells in rat retina after bleaching a portion of the receptive field.
Authors: Cicerone C M , Green D G
Published: December 2014

1. Recordings from single axons of retinal ganglion cells in the rat's optic tract in response to small flashing test lights were used to follow the course of dark adaptation after exposing half of the receptive field to a bleaching light. 2. The recovery of log sensitivity followed an exponential time course in the exposed and unexposed half‐fields. The curves had different time constants, with the exposed side taking longer to recover. 3. The time constants of recovery were increasing functions of exposure, but the rate of increase was different in the exposed and the unexposed half‐fields. Direct exposure increased the time constant at a greater rate than did indirect exposure. 4. Comparison of the time constants of recovery in the exposed half‐fields with those for pigment regeneration suggests that sensitivity recovers with the time course of rhodopsin regeneration. 5. Increment thresholds were determined using steady backgrounds which illuminated half of the receptive field. A greater threshold elevation was produced in the directly illuminated half‐field compared with the half‐field illuminated only by scattered light. Comparisons of the threshold‐raising capacity of direct and indirect illumination were used to establish an ‘upper bound’ on the magnitude of light scatter. The time courses of the recovery of sensitivity after two different bleaches were compared. First, thresholds were measured in the unexposed half‐field after a half‐field bleach. Secondly the recovery of sensitivity after direct bleaching‐exposure to the predetermined scatter upper bound’ was measured. Recovery was more rapid in the latter case than the former, thus indicating that adaptation spreads laterally via some process other than light scattering.
Studies of a gastric fundic mucosal factor which affects absorption from the antrum and jejunum in the rat.
Authors: Barmada S R , Burdett K , Elder J B
Published: December 2014

1. A rat bio‐assay has been developed in which the tracer ion technetium 99 m (99mTc) was used to monitor absorption from both the antrum and the jejunum of the rat. 2. Evidence has been obtained for the release of a humoral substance from the rat gastric fundus after alkalinization of the mucosa at pH 8, and this fundic factor has been shown to reduce the absorption of the tracer ion 99mTc from both the lumen of the antrum and of the jejunum in the rat. 3. Intravenous infusion of a neutral extract of porcine fundic mucosa, distension of the rat fundus with air or exposure of the fundic mucosa to alkaline buffer all decreased absorption of the tracer ion virtually to the same extent from the lumen of the antrum (P less than 0.001) and to a lesser extent from the lumen of the jejunum (P less than 0.05). This effect does not appear to be due to histamine. 4. Preliminary biochemical data have indicted that the biological activity in the mucosal extract is protein in nature and has a molecular weight of less than 10,000.
On the action of the anticonvulsant 5,5‐diphenylhydantoin and the convulsant picrotoxin in crayfish stretch receptor.
Authors: Aickin C C , Deisz R A , Lux H D
Published: December 2014

1. The effects of the anticonvulsant drug 5,5‐diphenylhydantoin (DPH) and the convulsant drug picrotoxin (PTX) on various membrane properties and GABA‐ergic inhibition were investigated in the slowly adapting neurone of the isolated crayfish stretch receptor. The soma was penetrated with two micro‐electrodes to allow accurate determination of membrane conductances. 2. Neither DPH nor PTX at 10(‐4) M had any significant effect on parameters of the anti‐ or orthodromic action potential or on the amplitude and duration of post‐tetanic hyperpolarization. This suggests that the pharmacological properties of the two drugs are unlikely to be mediated by effects on cationic movements in this preparation. 3. DPH increased the amplitude and duration of the inhibitory post‐synaptic potential (i.p.s.p.) within the range 10(‐9) to 10(‐4) M. The response to ionophoretically applied GABA was similarly prolonged. 4. PTX decreased the amplitude of the i.p.s.p. and prolonged its rising phase within the range 10(‐8) to 10(‐4) M. The response to ionophoretically applied GABA was similarly depressed. 5. A slow component of fluctuations in the resting potential was accentuated by DPH at 10(‐4) M and eliminated by PTX 10(‐4) M. This may reflect effects on the random opening and closing of inhibitory channels. 6. We conclude that the action of both drugs is post‐synaptic and suggest that DPH decreases the probability of closing, and PTX the probability of opening, of the transmitter‐activated channels. 7. The lack of any structural similarity between the two drugs suggests that they modify post‐synaptic inhibition at separate sites. These sites appear to be interdependent since analysis of the shift in the DPH dose‐response curve by PTX and vice versa, showed neither truly non‐competitive nor competitive interaction.
Effects of efferent stimulation on the saccule of goldfish.
Authors: Furukawa T
Published: December 2014

1. The effect of single or repetitive stimulation applied to efferent nerve fibres on afferent nerve activity and microphonic potentials was studied in the saccule of goldfish. 2. The sound‐evoked excitatory post‐synaptic potentials (e.p.s.p.s) recorded intracellularly from afferent eighth nerve fibres were reduced in size or completely abolished by efferent stimulation. The maximum inhibitory effect produced by repetitive efferent stimulation was equivalent to reducing the sound intensity by 10‐25 db. Spontaneous miniature e.p.s.p.s were also suppressed by efferent stimulation. 3. The effect of single efferent stimulation appeared with a delay of 607 msec and lasted for about 40 msec, reaching its peak at about 12 msec. The slow and prolonged time course makes a sharp contrast with the very fast time course of afferent synaptic action. 4. The application of hyperpolarizing current through the recording micro‐electrode revealed no sign of a post‐synaptic increase in membrane conductance during inhibition. Hence, the inhibition was mostly attributable to a presynaptic action, i.e. to a suppression of transmitter release from hair cells. 5. Individual e.p.s.p.s were evoked in response to each wave of sound without any change in latency, but reached their peak much earlier during inhibition than in the control period. A likely explanation for this finding is that transmitter is released from hair cells during inhibition only in the early part of the stimulatory phase of the sound wave. 6. The extracellularly recorded microphonic potentials showed a slight increase in amplitude during efferent stimulation. 7. The nature and site of action of efferent nerve action are discussed along with some drug effects.
The human ventilatory response to stimulation by transient hypoxia.
Authors: Jennett S , McKay F C , Moss V A
Published: December 2014

1. The detailed pattern of transient changes in breathing pattern has been studied following a brief hypoxic stimulus (three breaths of nitrogen) in nine healthy subjects. All showed an increase in ventilation of which the magnitude and relative contributions of volume and frequency varied between subjects. 2. Ventilation, tidal volume, inspiratory, expiratory and total breath time were recorded or derived breath‐by‐breath; for each of these variables, several test sequences were time‐averaged at half‐second intervals for each individual; similarly, time‐averages were obtained for percentage changes from base line over all nine subjects. 3. There ws an increase in inspiratory time accompanying the increasing tidal volume, in all but two subjects. This was statistically significant over all subjects, and in five individuals. Frequency changes were the resultant of alterations in the two phases; when total breath duration decreased it was always linked to a decrease in expiratory time. 4. Further analysis of the initial part of the response suggests that an increase of the duration of an inspiration may be the first change allowing an increase in tidal volume, before the ‘drive’ increases; this may be a dynamic feature of the control system whatever the nature and site of action of the stimulus.
The effect of external potassium on the removal of sodium inactivation in squid giant axons.
Authors: Gillespie J I , Meves H
Published: December 2014

1. The effect of external and internal electrolytes on the parameters of the Na conductance, in particular on the time constant of removal of Na inactivation, was studied in intact and perfused squid giant axons under voltage‐clamp conditions. 2. Adding 20‐40 mM‐KCl, ‐CsCl or ‐RbCl to K‐free sea water reversibly increased the time constant of removal of inactivation by a factor of about 1.3; adding 20 mM‐NaCl had no effect. The time constant of development of inactivation was decreased. The results are consistent with a ‐5 mV shift of the tau h(V) curve. The sodium activation (m infinity 3) and inactivation (h infinity) curves were shifted by the same amount. 3. Raising external Ca, by contrast, decreased the time constant of removal of inactivation and increased the time constant of development of inactivation, i.e. shifted the tau h(V) curve to more positive internal potentials. A free Ca concentration of 0.1 mM in the internal solution had no effect on Na inactivation. 3. The observations are compatible with the idea that external K, Cs or Rb interfere with the binding of Ca to negative fixed charges at the outer side of the membrane, thereby causing a shift in the opposite direction to the shift produced by raising external Ca. 5. Replacing two thirds of the internal K by Na reversibly increased the time constant of removal of sodium inactivation and moved the tau h(V) curve in the vertical direction.
The fatigue and voluntary discharge properties of single motor units in man
Authors: Grimby Lennart , Hannerz Jan , Hedman Björn
Published: December 2014

1. The discharge properties of single motor units during prolonged maximal voluntary effort have been studied using electromyographic recordings, mainly in the short big toe extensor muscle but also in the anterior tibial muscle.

2. The required selectivity of the e.m.g. recordings was achieved in the short big toe extensor muscle after previous mechanical lesions to the terminal nerve twigs and muscle fibres and consequent collateral sprouting, and in the anterior tibial muscle with the use of a high impedance wire electrode.

3. During the first few hundred milliseconds of sustained maximal effort the motor units fired at rates ranging from about 30‐60 Hz, and the tension was the same as that obtained on electrical tetanization of the nerve to the toe extensor muscles above 50 Hz.

4. During prolonged maximal effort the firing rates and the proportion of motor units firing successively decreased. Motor units initially firing at 30 Hz continued to fire tonically but at 15‐20 Hz. Motor units initially firing at 60 Hz ceased to fire tonically but could still be made to discharge phasically. The period of time during which all motor units responded tonically could be increased from some seconds up to 20 sec by long‐term training.

5. Motor units with a limited endurance fired at a lower tension in the early than in the late stages of maintained contraction.

6. It is suggested that motoneurones innervating slow twitch muscle fibres respond continuously to prolonged voluntary drive at rates sufficient for full fusion but that the threshold of motoneurones innervating fast twitch muscle fibres increases so that they finally mainly fire phasically thus protecting the peripheral excitation and contractile mechanisms from excessive exhaustion.
The sodium current underlying the responses of toad rods to light.
Authors: Capovilla M , Cervetto L , Pasino E , Torre V
Published: December 2014

1. Intracellular responses were recorded from single rods in the retina of the toads Bufo bufo and Bufo marinus during exposure to solutions in which sodium was replaced by equimolar amounts of choline. 2. Upon moderate reduction (80 and 50 mM) of the external sodium the size of responses to bright flashes decreased as a consequence of both an increase in the resting potential and a decrease of the membrane potential at the peak, while the level of the plateau remained fairly constant. 3. Upon reduction of the external sodium to 22 mM or less, rods hyperpolarized to about the plateau level and failed to respond to illumination. Under these circumstances, membrane depolarization induced by an increased external potassium did not restore the cell responsiveness. Addition of 2‐5 mM caesium hyperpolarized the membrane and partially restored the photoresponse. 4. Complete replacements of external sodium with potassium depolarized the rod by 40 +/‐ 10 mV, and no voltage responses to light could be detected. 5. In the presence of caesium, a nearly complete blockage of the photoresponses was obtained when the external sodium was 5 mM or less. Further reductions of the external sodium did not invert the photoresponses. Application of caesium when the external sodium was nominally zero induced a transient hyperpolarization followed by a slow decay. 6. During exposure to steady illumination, the dependence of the plateau level on the external sodium slowly increased. 7. These results indicate that the ionic current which is directly modulated by the light depends primarily on the external sodium. They suggest also that the current associated with the voltage‐ and time‐dependent process responsible for the sag from peak to plateau of the response to a bright flash of light may have multiple components.
Distinguishing transport systems having overlapping specificities for neutral and basic amino acids in the rabbit ileum.
Authors: Paterson J Y , Sepúlveda F V , Smith M W
Published: December 2014

1. The kinetic parameters of lysine and alanine uptake by rabbit ileal mucosa have been measured in the presence and absence of Na. 2. Using lysine as an inhibitor of part of alanine uptake in the absence of Na it has been possible to define two mediated systems for alanine entry. One of these systems (Km 14.2 mM; Jmax 41.3 n‐mole cm‐2 min‐1) is inhibited by lysine (Ki 0.96 mM) while the other (Km 115 mM; Jmax 323 n‐mole cm‐2 min‐1) is not. 3. Methionine is an effective inhibitor of both Na‐independent uptake mechanisms for alanine. 4. Na‐independent lysine uptake also takes place through two mediated systems. One of these systems (Km 1.0 mM; Jmax 12.8 n‐mole cm‐2 min‐1) is inhibited by alanine (Ki 4.3 mM) while the other (Km 108 mM; Jmax 194 n‐mole cm‐2 min‐1) is not. 5. The use of a naturally occurring basic amino acid to inhibit a portion of neutral amino acid uptake extends considerably the ability to distinguish multiple acid transport systems present in the same cell membrane. The physiological implications of these findings are discussed.
A comparative study of charge movement in rat and frog skeletal muscle fibres.
Authors: Hollingworth S , Marshall M W
Published: December 2014

1. The middle of the fibre voltage‐‐clamp technique (Adrian & Marshall, 1977), modified where necessary for electrically short muscle fibres, has been used to measure non‐linear charge movements in mammalian fast twitch (rat extensor digitorum longus), mammalian slow twitch (rat soleus) and frog (sartorius) muscles. 2. The maximum amount of charge moved in mammalian fast twitch muscle at 2 degrees C in hypertonic solution, was 3‐‐5 times greater than in slow twitch muscle. The voltage distribution of fast twitch charge was 10‐‐15 mV more positive when compared to slow twitch. 3. In both mammalian muscle types hypertonic Ringer solution negatively shifted the voltage distribution of charge some 6 mV. The steepness of charge moved around mechanical threshold was unaffected by hypertonicity. 4. The amount of charge in frog sartorius fibres at 2 degrees C in hypertonic solution was about half of that in rat fast twitch muscle; the voltage distribution of the frog charge was similar to rat soleus muscle. 5. Warming between 2 and 15 degrees C had no effect on either the amount of steady‐state distribution of charge in mammalian or frog muscles. 6. At 2 degrees C, the kinetics of charge movement in fast and slow twitch mammalian muscles were similar and 2‐‐3 times faster than frog muscle at the same temperature. In fast and slow mammalian fibres at 2 degrees C similar times were taken to shift the same fractions of the total amount of charge. The Q10 of charge movement kinetics was between 1.2 and 2.0 in the three muscles studied.
Intestinal control of gastric function in the calf: the relationship of neural and endocrine factors
Authors: Bell F. R. , Green A. R. , Wass J. A. H. , Webber D. E.
Published: December 2014

1. Gastric emptying and secretion were measured in conscious calves during alkaline or acid perfusion of the duodenum with simultaneous assessment of endogenous plasma somatostatin, gastrin and blood 5‐hydroxytryptamine (5‐HT).

2. Alkaline duodenal perfusion (isotonic NaHCO3) caused rapid gastric emptying and increased gastric acid secretion without any affect on basal levels of somatostatin, 5‐HT or gastrin.

3. Duodenal perfusion of 60 m
m‐HCl caused complete inhibition of gastric emptying, reduced gastric acid secretion considerably, and an associated elevation of somatostatin basal levels from 123.8 ± 11.2 to 281.9 ± 23.0 pg/ml. (P < 0.01) occurred.

4. These effects of duodenal perfusion were unimpaired by bilateral lumbar splanchnectomy.

5. On bilateral cervical vagotomy of the splanchnectomized calves, the inhibition of gastric function evoked by duodenal acidification persisted, and plasma somatostatin showed a further significant elevation to 506.9 ± 49.9 pg/ml. (P < 0.01) but gastrin and 5‐HT remained unchanged. The increased gastric function caused by alkaline duodenal function was significantly reduced following vagotomy but basal somatostatin, gastrin and 5‐HT in the blood remained unaffected.

6. These results suggest that the stimulatory effect on gastric emptying and acid secretion of isotonic NaHCO3 in the duodenum may be mediated, partially at least, through the vagal nerves but not the splanchnics.

7. The complete inhibition of gastric function which ensued on acidification of the duodenum and which continues after splanchnovagotomy, is not mediated by the autonomic nervous system. This inhibitory process appears to involve the endocrine system only, with somatostatin (but not gastrin or 5‐HT) fulfilling a main enterogastrone role.
The effects of single afferent impulses on the probability of firing of external intercostal motoneurones in the cat
Authors: Kirkwood P. A. , Sears T. A.
Published: December 2014

1. Recordings of afferent discharges from external intercostal muscle spindles were made from in‐continuity dorsal roots of anaesthetized, paralysed cats and the afferents were characterized as described in the preceding paper (Kirkwood & Sears, 1982).

2. The strengths and time courses of the raised probabilities of firing of external intercostal motoneurones evoked by the synaptic actions of impulses in the afferents were measured by constructing cross‐correlation histograms from the discharges of the individual afferents and the discharges of the motoneurones, which were simultaneously recorded from the cut central ends of intercostal nerve filaments. Other dorsal roots, apart from the rootlet containing the afferent fibre, were cut to prevent afferent synchronization from affecting the results.

3. Cross‐correlation histograms involving single efferent discharges showed narrow peaks (mean half‐width 0·99 msec) at monosynaptic latencies.

4. This mean half‐width is slightly longer than the mean rise‐time of the e.p.s.p.s described in the preceding paper, but much shorter than the mean half‐width of those e.p.s.p.s. These measurements, together with the shapes of individual histogram peaks thus confirm the prediction of Kirkwood & Sears (1978) that the shape of such a peak should be approximated by the time differential of the underlying e.p.s.p. plus the e.p.s.p. time course itself. Amplitudes of the peaks were also consistent with the predictions of Kirkwood & Sears (1978).

5. The cross‐correlation histograms involving multi‐unit efferent discharges were entirely consistent with those involving single efferent discharges and were used to demonstrate the patterns of projections of individual afferents to different groups of intercostal motoneurones.

6. Individual afferents excited α motoneurones of all spike sizes in the intercostal filament recordings but excitation of γ motoneurones was not detected.

7. Individual afferents excited motoneurones of the same segment and both adjacent segments, but no projection beyond these was detected.

8. The amplitude of the multi‐unit cross‐correlation peak was taken as a measure of the over‐all strength of the connexions to a given segment. When this amplitude was measured for motoneurones of the same segment as the afferent, for sixteen out of nineteen afferents there was a highly significant positive correlation with the conduction velocity of the afferent. The remaining three afferents gave a strength of connexion which appeared to be much stronger than would be expected from the rest of the population of afferents.

9. The strength of connexion to adjacent segments was generally lower than to the same segment.
Active groups of saxitoxin and tetrodotoxin as deduced from actions of saxitoxin analogues on frog muscle and squid axon.
Authors: Kao C Y , Walker S E
Published: December 2014

1. The actions of three saxitoxin (STX) analogues have been studied on the frog sartorius muscle fibre and the squid giant axon. One‐‐neosaxitoxin‐‐is a natural analogue, and two‐‐decarbamylsaxitoxin and reduced saxitoxin‐‐are synthetic. 2. The maximum dV/dt of the action potential in paired‐muscle protocol is reduced by the analogues with relative potencies: STX (1), tetrodotoxin (1), neo‐STX (1), decarbamyl‐STX (0.2) and reduced‐STX (0.01). 3. In constant‐current studies on frog muscle fibres and in voltage‐clamp studies on squid axons, all three analogues block only the sodium channel without affecting the potassium channel. 4. All three analogues bind to the same site as does STX in a competitive manner. 5. The experimental results suggest that the active groups in STX are the 7,8,9 guanidinium and the C‐12 hydroxy groups. The carbamyl group contributes to, but is not essential for activity. 6. Stereospecific groups in the tetrodotoxin (TTX) molecule are the 1,2,3 guanidinium and the C‐9, C‐10 hydroxy groups. C‐4 and C‐8 groups are also important. 7. As new view is proposed in which STX and TTX can bind to a receptor located in the outside surface of the membrane very close to the orifice of the sodium channel.
Pharmacological separation of charge movement components in frog skeletal muscle
Authors: Huang C. L.-H.
Published: December 2014

1. Charge movements to small 10 mV steps superimposed upon a wide range of closely spaced depolarizing voltage‐clamp pulses were studied in frog skeletal muscles under different pharmacological conditions in hypertonic solutions.

2. In control fibres, capacitance was strongly voltage‐dependent, especially between potentials of ‐60 and ‐20 mV, confirming earlier work. There was a sharp increase in capacitance at around ‐50 mV. The dependence of non‐linear charge on potential was asymmetrical and saturated at around 25 nC/μF.

3. The presence of tetracaine abolished the ‘hump’ in the non‐linear transients, which became simple monotonic decays. The dependence of capacitance upon potential was reduced. The maximum available amount of non‐linear charge fell to 10 nC/μF.

4. The presence of lidocaine abolished both the ‘hump’ as well as the monotonic part of the non‐linear transients. This resulted in capacitance falling with depolarization from ‐85 mV.

5. Comparing the steady‐state properties of the non‐linear charge under the different pharmacological conditions made it possible to deduce empirically the following components:

(i) A lidocaine‐resistant component (qα), which was responsible for the fall in observed capacitance with depolarization from the control voltage.

(ii) A component resistant to tetracaine yet abolished by lidocaine (qβ). This possesses quasi‐exponential kinetics, and a maximum charge of about 20 nC/μF.

(iii) A component abolished by both lidocaine and tetracaine (qγ), which possesses a maximum charge of 15 nC/μF. This has complex kinetics, and its steep dependence upon voltage resembles the potential‐dependence of the development of tension in skeletal muscle.
The effect of lesions in the neural crest on the formation of synaptic connexions in the embryonic chick spinal cord
Authors: Eide Anne‐Lill , Jansen Jan K. S. , Ribchester Richard R.
Published: December 2014

1. The pattern of synaptic activity in lateral gastrocnemius (l.g.) motoneurones in the lumbar spinal cord of chick embryos (Stage 44‐45, 19‐21 d of incubation) has been examined using intracellular recording. In the motoneurones of normal chick embryos, stimulation of different peripheral, sciatic nerve branches gave rise to characteristic synaptic responses. Stimulation of the lateral gastrocnemius nerve caused a monosynaptic e.p.s.p. which was graded by the intensity of nerve stimulation. Stimulation of synergistic muscle afferents also caused a brief latency e.p.s.p., followed by longer latency excitatory and inhibitory synaptic potentials. Stimulation of antagonistic muscle afferents or cutaneous afferents gave rise to longer latency inhibitory and excitatory synaptic potentials respectively.

2. The synaptic activity of l.g. motoneurones was also recorded in embryos in which short segments of the lumbar neural crest had been destroyed by microcautery at 3 d of incubation (Stage 18). The embryos developed without sensory ganglia and dorsal roots in the corresponding region.

3. At 19‐21 d of incubation, the amplitude of the l.g. e.p.s.p. of l.g. motoneurones in deafferented segments was on the average only a half to a third of the amplitude seen in motoneurones of intact spinal segments. However, both the l.g. and synergist e.p.s.p.s were larger than those seen in acutely deafferented segments of normal embryos.

4. In spite of the weak monosynaptic input from l.g. and synergistic afferents, the pattern of synaptic activity evoked by antagonistic muscle afferent or cutaneous afferent stimulation was not different from normal. This was even the case for gastrocnemius motoneurones in which no early e.p.s.p. could be evoked by stimulating the l.g. or synergistic muscle nerves.

5. No muscle spindles could be seen in sections of l.g. muscles from embryos with extensive lesions of the lumbosacral neural crest. Incomplete lesions of l.g. segments reduced the number of spindles in the muscle.

6. These results suggest that when motoneurones are deprived of part of their normal synaptic input before the formation of peripheral connexions, the identity of the motoneurones (in terms of the origin of their synaptic input) is preserved. Missing synaptic inputs are either replaced by appropriate afferent fibres, if they are available, or not at all. The chick sensory ganglion cells with monosynaptic connexions to motoneurones appear to be unable to compensate significantly for peripheral or central defects in the innervation of the hind limb. They behave as if their developmental possibilities were quite rigidly determined at an early embryonic stage.
A comparison of the structures of α‐ and γ‐spinal motoneurones of the cat
Authors: Westbury D. R.
Published: December 2014

1. The structures of seven γ‐motoneurones (axonal conduction velocities of 15‐48 m/sec) were compared with those of nine α‐motoneurones (axonal conduction velocities of 71‐91 m/sec) by using histochemical methods to reveal horseradish peroxidase which had previously been injected intracellularly into indentified motoneurones in the cat lumbosacral spinal cord.

2. The size of the cell bodies of the motoneurones, and the diameters of their intramedullary axons, were related to their axonal conduction velocities over the whole range studied.

3. Despite the smaller size of the cell bodies of the γ‐motoneurones, their dendritic trees extended as far as those of the α‐motoneurones. However, γ‐motoneurones had fewer main dendrites than the α‐motoneurones and these branched much less, so that the dendritic trees of the γ‐motoneurones were much simpler than those of α‐motoneurones. Although the extents of the dendritic trees were not related to axonal conduction velocity, the complexity of the dendritic trees was clearly related to axonal conduction velocity and to cell body size.

4. The total surface area of each cell, taken as an indication of the area available for synaptic contact, was much smaller for γ‐ than for α‐motoneurones, and was related to axonal conduction velocity.

5. Only one of the seven γ‐motoneurones studied had axon collaterals whereas five of the nine α‐motoneurones had well developed collaterals. This finding is consistent with the relative contribution that each group of motoneurone axons makes to recurrent inhibition.

6. One of the γ‐motoneurones had two axons, of different diameter, which emerged from the spinal cord at the same level but in different ventral rootlets.

7. These features of motoneurone structure are related to aspects of their physiological properties.
Local regulation of transmitter release from rodent sympathetic nerve terminals?
Authors: Blakeley A G , Cunnane T C , Petersen S A
Published: December 2014

1. Electrophysiological techniques were used to observe the release of transmitter from single release sites in the sympathetic neuro‐effector junction of the rodent vas deferens. Transmitter release produces transient peaks in the rate of depolarization of the smooth muscle cells, known as 'discrete events'. 2. The amplitude distributions of stimulus‐evoked discrete events in both mouse and guinea‐pig vas are multi‐modal. In the mouse, the distribution fits a Poisson with a 'quantal content' of about two. There are too many zeros in the amplitude distributions of guinea‐pig discrete events to fit a Poisson distribution, and it is likely that in this species there is a mechanism preceding the transmitter release process which may occasionally prevent it operating. 3. alpha‐adrenoreceptor agonists and antagonists produce, respectively, left and right shifts in the amplitude distributions of discrete events at a single latency, with no change in the amplitudes at the modes. 4. There is, however, no evidence of any inhibitory relationship between either discrete events evoked by successive stimuli, or early and late discrete events following a given stimulus. 5. Transmitter release at this junction is therefore packeted, with few quanta released by each stimulus. Release from single sites is affected in ways compatible with the 'alpha‐feed‐back' hypothesis by alpha‐adrenoreceptor agonists and antagonists, but in the absence of drugs we can find no evidence of any local feed‐back inhibition of transmitter release.
An enquiry into the mechanism by which substance P facilitates the phasic longitudinal contractions of the rabbit ileum
Authors: Holzer Peter
Published: December 2014

1. The effect of substance P on the phasic longitudinal contractions of the isolated rabbit ileum has been investigated. The contractions were recorded isotonically. Substance P in concentrations below those which cause tonic contraction (0·2‐2 nM) increased the height of the phasic contractions in a concentration‐dependent fashion without affecting their frequency (8‐12/min).

2. The effect of substance P was inhibited by verapamil, ouabain, noradrenaline, and isoprenaline, but was unaffected by tetrodotoxin, atropine, D‐2‐ala,5‐metenkephalin, somatostatin, and vasoactive intestinal polypeptide.

3. Tetraethylammonium, which blocks voltage‐dependent K+ channels, enhanced the phasic contractile activity of the rabbit ileum in a manner quite similar to substance P, but the maximal response to tetraethylammonium was larger than that to substance P.

4. The effect of matched concentrations of substance P and tetraethylammonium, which enhanced the phasic contractions to a similar extent, was investigated at various concentrations of K+, Na+, Ca2+ and Cl− in the bathing medium. Both substance P and tetraethylammonium lost their ability to enhance the phasic contractions when K+ was omitted from the medium or when its concentration therein was increased by a factor of 4, or when the NaCl concentration was reduced to less than 10%. The relative increase in phasic contractile activity evoked by substance P was smaller than that evoked by tetraethylammonium when more than 90% of the Cl− was replaced with propionate.

5. Noradrenaline, in a concentration which just abolished the spontaneous phasic contractions (200‐300 nM), reduced the enhancing effect of substance P on the phasic activity by 40‐50%, but did not influence the effect of tetraethylammonium.

6. These results indicate that substance P enhances the phasic longitudinal contractions of the isolated rabbit ileum by a direct action on the smooth muscle cells and that this effect is brought about by facilitation of the myogenically controlled action potential discharges in the ileum. Circumstantial evidence suggests that the underlying ionic mechanism of action of substance P is a decrease in K+ and Cl− conductances.
A pharmacological analysis of chloride transport across the amphibian cornea.
Authors: Bentley P J , McGahan M C
Published: December 2014

1. Active Cl, but not Na, transport across the toad cornea was inhibited by mepacrine, which is a phospholipase A2 inhibitor; trifluoperazine, which blocks the action of calmodulin; and meclofenamic acid, which inhibits synthesis of prostaglandins. Bumetanide and DIDS (4,4'‐diisothiocyano‐2,2'‐stilbene disulphonic acid) have previously been shown to inhibit this Cl transport. The interactions of these antagonists with several agonists that increase Cl transport were studied. 2. The effects of adrenaline, prostaglandin E2, dibutyryl cyclic AMP (DBcAMP) and the Ca ionophore A23187 were inhibited by mepacrine, trifluoperazine and bumetanide. 3. The inhibitory effects of high concentrations of DIDS, however, could be overcome by all of the agonists except DBcAMP. 4. Meclofenamic acid only blocked the effects of A23187. 5. A model is proposed to account for the observed actions and interactions of the various antagonists and agonists on Cl transport. This involves possible roles for Ca, calmodulin and phospholipase A2.