bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical responses to frog taste cells to chemical stimuli.
Authors: Akaike N , Noma A , Sato M
Published: December 2014

1. Cells inside a fungiform papilla of the frog tongue were impaled with a glass capillary micro‐electrode filled with 3 M‐KCl. Cells considered to be taste cells showed a resting potential of about ‐35 mV and an input resistance of 17 Momega on the average. 2. Application of chemical stimuli such as salts, acids and quinine produced a sustained depolarization in a taste cell, the magnitude of depolarization being dependent on the stimulus concentration. Water and weak NaCl solution yielded a hyperpolarization. The thresholds for depolarization as well as the concentration‐response relationships for various chemical stimuli in taste cells are in approximate agreement with those determined from the glossopharyngeal nerve responses. 3. The magnitude of depolarization produced by 0‐1 M‐NaCl and 0‐03 M‐CaCl2 was dependent on the membrane potential level and reduced linearly with a rise in the latter. However, depolarizations generated by 0‐001 M‐HDl and 0‐02 M quinine changed little in magnitude by a membrane potential change over a wide range. 4. During depolarizations induced by NaCl and KCl a marked reduction in the input resistance of a cell was observed, the amount of the reduction depending on the stimulus concentration. The reduction was also produced by CaCl2 and HCl, but it is small compared with those by NaCl and KCl. Quinine produced an increase in the resistance associated with a depolarization. Water and weak NaCl solution produced an increase in the resistance associated with hyperpolarization. 5. The receptive mechanisms for various kinds of chemical stimuli are discussed in relation to changes in the membrane potential and the membrane conductance of taste cells.
Stoichiometry of sodium and potassium transport in erythrocytes from patients with myotonic muscular dystrophy.
Authors: Hull K L , Roses A D
Published: December 2014

1. 22Na and 42K radioisotopes were used to measure Na efflux and K influx in identical suspensions of fresh erythrocytes from myotonic dystrophy patients and matched controls under the same conditions and in the same time interval. K was present in concentration 10 mM in the suspending medium to prevent Na‐for‐Na exchange. Each flux was measured in the presence and absence of ouabain. The mean ouabain‐sensitive Na efflux rate in controls (2‐33+/‐0‐13, S.E. of mean, m‐equiv/1. cells.hr) was significantly greater (P less than 0‐001) than the corresponding rate in myotonic dystrophy (1‐64+/‐0‐09). 2. No significant differences between myotonic dystrophy and controls in mean ouabain‐insensitive Na efflux, mean ouabain‐sensitive K influx, or mean ouabain‐insensitive K influx were found. 3. The stoichiometric ratio (ouabain‐sensitive Na efflux)/(ouabain‐sensitive K influx) was determined for each flux experiment. The mean stoichiometric ratio determined in controls (1‐46+/‐0‐08) reconfirms extensive previous evidence favouring a 3Na‐for‐2K active exchange in controls. 4. The mean stoichiometric ratio determined in myotonic dystrophy (1‐01+/‐0‐06) is statistically significantly different (P less than 0‐001) from that in controls. These findings are interpreted as indication of 2Na‐for‐2K exchange in erythrocytes from patients with myotonic dystrophy.
Muscle responses during sudden falls in man.
Authors: Greenwood R , Hopkins A
Published: December 2014

1. E.m.g. activity in soleus during an unexpected fall is found to be more complex than that described by Melvill Jones & Watt (1971b). After a silent period of about 80 msec an initial peak of activity lasts until about 100 msec after release. In falls from sufficient heights a second peak of activity occurs before landing. 2. The initial peak of activity is found in muscles throughout the body and is absent during falls in which the subject releases himself. It is suggested that this initial peak is a startle response to release and on landing during the initial peak any deceleration due to tension in the leg muscles is in part coincidental. 3. The second peak of activity is found in muscles of the lower limbs. Its timing is related to the timing of landing. It is suggested that this is the activity concerned in thhe voluntary control of landing. 4. No initial peak of activity could be recorded in two patients with absent labyrinthine function.
Alterations of synapses on axotomized motoneurones.
Authors: Mendell L M , Munson J B , Scott J G
Published: December 2014

1. Properties of medial gastrocnemius motoneurones in cats were examined with intracellular electrodes 1‐77 days after partial transection of the medial gastrocnemius muscle nerve. 2. Three sequential stages of reaction were defined: (i) firstly, conduction velocity of axotomized motoneurones fell, but e.p.s.p. properties and Ia‐motoneurone connectivity were normal; (ii) secondly, e.p.s.p.s became characterized by prolonged rise times and half‐widths and by diminished amplitudes; (iii) finally, failures of connectivity were also seen, that is, Ia spindle afferent fibres connected with fewer axotomized than normal homonymous motoneurones. 3. The reason for the change of e.p.s.p. properties cannot be stated with certainty: among the factors may be (i) a change of motoneurone membrane properties and morphology; (ii) partial detachment of synaptic boutons before their total disconnexion, and (iii) detachment of Ia afferent branches terminating on the motoneurone soma before those on the dendrites. 4. The previous conclusion that alteration of e.p.s.p. profiles following motoneurone axotomy was due to total disconnexion of those Ia fibres making synapses on the soma and proximal dendrites ("somatic stripping") must be modified to account for the findings that e.p.s.p. changes are seen before connectivity changes.
Low resistance junctions between mesoderm cells during development of trunk muscles.
Authors: Blackshaw S E , Warner A E
Published: December 2014

1. Electrical connexions between mesoderm cells have been examined during the formation of somites in Xenopus laevis, Bombina orientalis and Ambystoma mexicanum. 2. In Xenopus the resting potentials of presumptive myotome cells (‐65 + 2 mV, S.E. of mean) and somite muscle cells (‐65 +/‐ 0‐6 mV S.E. of mean) were 40 mV, greater than dermatome cells (‐25 +/‐ 0‐6 mV, S.E. of mean). Similar differences were found in Bombina and Ambystoma. 3. In all three species cells of the dermatome layer of the mesoderm were electrically coupled to each other. Cells of the presumptive myotome layer in the unsegmented region of the mesoderm were also electrically coupled. 4. In Xenopus dermatome and myotome layers of the mesoderm were not electrically coupled to each other either before or after somite formation. In the other two species dermatome and myotome layers were uncoupled once the somites had formed. 5. In all three species the position of the intersomite border in the unsegmented mesoderm region is marked by the breaking of electrical contracts between those cells destined to form the next somite and the rest of the unsegmented mesoderm. 6. In the axolotl each somite remains electrically insulated from its neighbour. In Xenopus and Bombina electrical connexions are re‐established between somite muscle cells once the morphogenetic movements underlying somite formation are complete. 7. Presumptive myotome cells in Xenopus and Ambystoma acquire the membrane property of inward‐going rectification before incorporation into a somite. 8. Once Xenopus and Bombina embryos show spontaneous movements large end‐plate potentials are recorded from the head somites. Excitation spreads from somite to somite along the low resistance intercellular pathway allowing simultaneous contraction of several somites before extensive somite innervation. 9. The structure of developing somite muscle of Xenopus has been studied with the electron microscope. 10. Close membrane contacts of the gap junction type have been seen between undifferentiated presumptive myotome cells, muscle cells in the same somite and between muscle cells in adjacent somites. 11. Myofilament organization first begins in mesoderm cells when they are forming a new somite. Complete sarcomeres appear in the head somites when the embryo begins spontaneous flexion movements.
Two types of extrajunctional L‐glutamate receptors in locust muscle fibres.
Authors: Cull-Candy S G
Published: December 2014

L‐glutamate applied iontophoretically to the extrajunctional membrane of locust muscle produced a biphasic response, depolarization followed by hyperpolarization (i.e. DH‐response). Applying L‐glutamate and DL‐ibotenate from multibarrel micropipettes allowed comparison of their extrajunctional responses. While glutamate produced a two component response, ibotenate produced a single component H‐response. 2. The equilibrium values for the H‐responses to L‐glutamate and DL‐ibotenate applied at the same extrajunctional site were very similar. The equilibrium value was 59‐5 +/‐ 5‐4 mV indicating an increased Cl‐ conductance. The H‐response was reversed and abolished in Cl‐ free medium. Picrotoxin 10(‐3) M selectively blocked the H‐component of the DH‐response in a reversible manner. 3. The possibility that the D‐ and H‐responses arose from the activation of two distinct types of extrajunctional glutamate receptors was investigated. Desensitization of the glutamate H‐response by ibotenate and vice versa indicated the presence of an extrajunctional H‐receptor sensitive to glutamate and ibotenate and an extrajunctional D‐receptor sensitive to glutamate and insensitive to ibotenate. The junctional depolarizing response to glutamate was insensitive to ibotenate. 4. The presence of junctionally occurring H‐receptors could not be discounted, although, if present, they were not measurably activated by the excitatory transmitter. 5. Double logarithmic plots (coulomb dose vs. response) for the actions of glutamate and ibotenate on H‐receptors had values of 0‐75, indicating that both drugs act on the same receptors with similar mechanisms. The value for the action of glutamate on the D‐receptors was 1‐5. 6. While the extrajunctional D‐receptors show analogies to the extrajunctional ACh receptors in vertebrate muscle, the significance of the extrajunctional H‐receptors remains speculative.
Absorption from a mixture of seventeen free amino acids by the isolated small intestine of the rat.
Authors: Gardner M L
Published: December 2014

Absorption and secretion from a mixture of seventeen free amino acids has been measured in isolated perfused rat small intestine. 2. The absorption rate of an amino acid from this mixture is proportional to its concentration in the perfusate and independent of its chemical constitution. The constant of proportionality is the same as that previously observed when the perfusate contained peptides as well as amino acids. 3. Amino acids are concentrated, on average, sixfold during passage across the mucosa, and the free amino acid composition of the secretion into the tissue fluid is very similar to that of the luminal perfusate. 4. Peptides do not appear to be added to the tissue fluid during absorption of free amino acids. 5. It is concluded that the mechanisms for absorption of free amino acids are in general independent of those for absorption of peptides.
Permeability changes produced by L‐glutamate at the excitatory post‐synaptic membrane of the crayfish muscle.
Authors: Onodera K , Takeuchi A
Published: December 2014

1. Permeability changes produced by L‐glutamate at the neuromuscular junction of the crayfish (Cambarus clarkii) were investigated by application of the drug iontophoretically to the voltage‐clamped junction and measuring the resulting 'glutamate current'. 2. Reversal potentials were determined by measuring the glutamate current at different membrane potentials. They were +39‐1 +/‐ 3‐6 mV (mean +/‐ S.E. of mean) in normal solution and +16‐5 +/‐ 2‐0 mV in solutions made twice as hypertonic by the addition of sucrose. 3. Decreasing external Na+ concentration shifted the reversal potential in the negative direction; increased Na+ in the positive direction. 4. The relation between the amplitude of the glutamate current and extracellular Na+ concentration was approximately linear. 5. Alteration of the external K+ or Cl‐ concentration did not affect the amplitude or reversal potential of glutamate current. 6. In Na+‐free solution the application of L‐glutamate produced a small inward current at the resting potential and its amplitude was augmented by increasing the external Ca2+ concentration. 7. Increasing the Ca2+ concentration in the normal Na+ media produced no appreciable effect on the reversal potential but decreased the amplitude of glutamate current. 8. The results indicate that L‐glutamate increases the membrane permeability mainly to Na+ and slightly to Ca2+. 9. The time course of glutamate current was shorter than that of the concentration calculated from the diffusion equation and it was simulated more closely by the square of the concentration.
Dopamine evoked inhibition of single cells of the feline putamen and basolateral amygdala.
Authors: Ben-Ari Y , Kelly J S
Published: December 2014

1. In cats under pentobarbitone or halothane anaesthesia, neurones of the putamen and basolateral amygdala were inhibited with a similar time course by iontophoretic applications of dopamine and gamma‐aminobutyric acid (GABA), ejected with relatively short (20 sec) low intensity (less than 40 nA) pulses of positive current from five and seven barrelled extracellular micropipettes. The use of a stereotaxically positioned guide tube, sealed to the skull with dental cement, made it possible to obtain stable recording conditions and to correlate the stereotaxic position of the cells with the position of the micro‐electrode tracks determined histologically by the post‐mortem reconstruction of serial sections. 2. Since in cats anaesthetized with pentobarbitone none of the cells were found to be spontaneously active, the relative potency of dopamine and GABA were compared on glutamate excited cells. Approximately 2‐5 times more current was required to release sufficient dopamine to cause just submaximal inhibition, equal in magnitude and duration to that evoked by GABA. 3. In nitrous oxide/halothane anaesthetized cats, approximately one quarter of the cells were spontaneously active. Relative potency studies showed that for dopamine, currents 2‐0 and 1‐6 times larger than those used for GABA were required to inhibit glutamate excited and spontaneously active cells respectively. 4. When the depth distribution of the cells was compared with the sensitivity of the cells to dopamine and GABA, the most sensitive cells were found to lie within the putamen and the basolateral amygdala. 5. On more than one third of the cells tested, iontophoretic application of the neuroleptic, alpha‐flupenthixol of more than 3 or 4 min in duration, greatly reduced or abolished the inhibition of the cells by dopamine without impairing their sensitivity to GABA. 6. In four cats, large I.V. injections of alpha‐flupenthixol (10 mg/kg) and the more potent neuroleptic pimozide (1 mg/kg) had no significant effect on the dopamine or GABA sensitivity of seventy cells in the putamen and basolateral amygdala. 7. Our results are in keeping with the view that dopamine has a predominantly inhibitory action in the mammalian forebrain. However the failure of I.V. neuroleptics to modify the sensitivity of the cells to dopamine suggests that the dramatic effects of neuroleptics on animal behaviour may not be explicable simply in terms of a generalized blockade of dopamine receptors at post‐synaptic sites.
A mechanism for spike frequency adaptation
Authors: Partridge L. D. , Stevens C. F.
Published: December 2014

1. Spike frequency adaptation was studied in large neurones of the marine molluscs Archidoris montereyensis and Anisodoris nobilis. These cells respond to a current step with a rapid rise in spike frequency followed by a gradual decline to a new steady level.

2. An exponentially declining current, Is, was measured when the cell was voltage clamped following an adapting spike train. The initial amplitude of this current depended on the preceding number of spikes and on the voltage to which the cell was clamped. A reversal potential (Vs) for this current was obtained by clamping to various potentials following a spike train. The time constant (τs) of decay of the current was dependent upon the clamping potential.

3. Clamping the membrane potential to a constant test level from various initial levels initiates an exponentially decaying current of similar time constant. The voltage dependence of the steady‐state conductance (ḡsas(V, ∞)) associated with this current was determined using this technique.

4. Equations for neural repetitive firing (Connor & Stevens, 1971c) were modified by the addition of a term describing these slow membrane currents: [Formula: see text]. The solution to the modified equation was in good agreement with the spike frequency adaptation observed in these cells.
The relation between stimulus frequency and the relative size of the components of the biphasic response of the vas deferens to electrical stimulation at different temperatures.
Authors: Birmingham A T , Freeman M A
Published: December 2014

1. Electrical stimulation of the guinea‐pig or rat vas deferens (pre‐ or post‐ganglionically) at frequencies from 2‐5 to 40 Hz with trains of stimuli of 30 sec duration induced a biphasic response. A rapid contraction (component A) was followed after a brief relaxation by a slower contraction (component B); the two phases were seen most clearly with stimulation frequencies of less than 10 Hz. 2. The responses to post‐ganglionic stimulation were always larger than those to preganglionic stimulation. In general, at low frequencies component A exceeded component B whilst at high frequencies component B was the larger. Separation of the two components on the basis of their frequency response characteristics was better for rat than for guinea‐pig vasa. 3. Log. frequency‐response curves to transmural (post‐ganglionic) electrical stimulation and log dose‐response curves to noradrenaline were recorded for guinea‐pig and rat vasa deferentia at 32 degrees, 22 degrees and 12 degrees C. For the guinea‐pig reduction of bath temperature to 12 degrees C increased the amplitude of component A at 2‐5 and 5 Hz; component B could not confidently be distinguished at this temperature. At 22 degrees C there was potentiation of B at lower frequencies and depression of B at higher frequencies. There was no response to noradrenaline at 12 degrees C. At 22 degrees C the response to noradrenaline was increased except to doses at or near the maximum to which the response was reduced. 4. For the rat was deferens component A was little changed by reduction of temperature. Component B at 12 degrees C was greatly depressed at higher frequencies. The response to noradreanaline was increased to lower doses and decreased to higher doses as the temperature was lowered. 5. The B component of the response of guinea‐pig vasa at 22 degrees C and rat vasa at 32 degrees C was more sensitive than the A component to inhibition by thymoxamine. 6. Further analysis of the mechanisms underlying the A and B components of the biphasic response may be facilitated by relative isolation of each component by the appropriate selection of parameters of electrical stimulation and of temperature for the species being investigated. The contractions of the B component are similar to, if not identical with, those produced by exogenously applied noradrenaline.
Augmentation: A process that acts to increase transmitter release at the frog neuromuscular junction.
Authors: Magleby K L , Zengel J E
Published: December 2014

1. End‐plate potentials (e.p.p.s) were recorded from frog neuromuscular junctions bathed in Ringer solution containing increased Mg and decreased Ca to reduce transmitter release. Conditioning and testing stimulation was applied to the nerve to study a previously uncharacterized process which acts to increase e.p.p. amplitudes. We will refer to this process as augmentation. 2. Following repetitive stimulation augmentation decayed approximately exponentially over most of its time course with a mean time constant of about 7 sec (range 4‐10 sec) which is intermediate in duration between the time constants for the decay of facilitation and potentiation. 3 . The magnitude of agumentation increased with the duration of the conditioning stimulation. Assuming a multiplicative relationship between augmentation and potentiation, values of the magnitude of augmentation ranged from 0‐3 to 0‐6 following 50 impulses at 20/sec to 0‐5‐7‐8 following 600 impulses at 20/sec. (An augmentation of 0‐3 and 7‐8 would increase e.p.p. amplitudes 1‐3 and 8‐8 times, respectively.) 4. The time constant characterizing the decay of augmentation remained relatively constant as the duration of the conditioning stimulation was increased. 5. Augmentation as well as facilitation and potentiation resulted from an increase in the number of quanta of transmitter released from the nerve terminal. 6. Augmentation decayed faster at higher temperatures with a mean temperature coefficient, Q10, of about 3‐8. The corresponding Q10 for the decay of potentiation was found to be about 2‐4. 7. It is concluded that augmentation can be a significant factor in increasing transmitter release and will therefore have to be accounted for when studying the effects of repetitive stimulation on the function of the nerve terminal or when formulating models of transmitter release.
Catecholamine‐induced changes in ion transport in short‐circuited frog skin and the effect of beta‐blockade.
Authors: Tomlinson R W , Wood A W
Published: December 2014

1. A method for measuring bidirectional Cl fluxes has been used to estimate net Cl movements in short‐circuited frog skin and to compare these with the short‐circuit current (Isc) and Na fluxes. 2. In some experiments bidirectional fluxes of both Na and Cl were measured simultaneously. It was found that the algebraic sum of the net fluxes of these two ions did not differ significantly from the values of Isc, either in untreated or catecholamine‐treated skins, except for the half‐hour period immediately after catecholamine addition. 3. The net effluxes of Cl produced by noradrenaline (1‐6 X 10(‐5)M), isoprenaline (8 X 10(‐7)M) and adrenaline (6 and 15 X 10(‐6)M) were of similar magnitude for each catecholamine. The magnitude of the Cl response measured as a flux ratio was related to a certain extent to the precatecholamine Cl conductance. 4. The net Na influx was increased by isoprenaline and reduced by noradrenaline. 5. Addition of the beta‐adrenergic blocking agent oxprenolol (4‐5 X 10(‐5)M) to skins stimulated by catecholamine resulted in the disappearance of the net Cl movement and fall in skin conductance and Isc. This fall was similar in magnitude to, and correlated with the mean rise in Isc produced by isoprenaline, but of significantly greater magnitude in the case of noradrenaline. 6. The changes in Na influx were strongly associated with the changes in Isc following catecholamine addition. Similarly, the changes in Na efflux and Cl efflux were correlated, suggesting the Na fluxes to be dissociated, influx and efflux changes perhaps taking place at different loci. 7. Acetazolamide (1‐2 X 10(‐4)M), added either before or during the noradrenaline stimulation, had no effect on the Cl efflux response. 8. The tissue exchange of Cl from the outside bathing medium after 4 hr was greater in catecholamine‐stimulated skins than in those in which the response had been blocked by oxprenolol. 9. These findings were taken to support a model entailing a neutral NaCl pump resident in the mucous glands and an epithelial Na pump enhanced by beta‐ and inhibited by alpha‐adrenergic stimulation.
Activation of the contractile mechanism in the anterior byssal retractor muscle of Mytilus edulis.
Authors: Sugi H , Yamaguchi T
Published: December 2014

1. The electrical and mechanical responses of the anterior byssal retractor muscle (ABRM) of Mytilus edulis to acetylcholine (ACh), high [K]O or the removal of external Ca were examined under a variety of conditions. 2. ACh (10(‐6)‐‐10(‐3)M) produced contracture tensions larger than those produced by high [K]O (30‐300 mM) for a given amount of depolarization. In Ca‐free solution, the rate of decline of ACh‐contractures was much smaller than that of K contractures, though both ACh‐ and K‐contractures eventually disappeared. 3. 5‐HT (10(‐4)M) of procaine (1 mM) markedly reduced the height of ACh‐contractures, but had little or no effect on K‐contractures. The height of K contractures was markedly decreased by Mn ions (20 mM) or low pH (4‐5), while ACh‐contractures remained unaffected. 4. Partial replacement of [Na]o by choline (30‐100 mM) reduced both ACh‐induced depolarization and contracture tension, whereas K‐contractures remained unchanged even after total replacement of [Na]o by choline. 5. ACh could produce little or no tension when applied during the relaxation phase of K‐contractures, while high [K]o produced the maximal contracture tension when applied during the relaxation phase of ACh‐contractures. 6. Following the removal of external Ca from solutions containing less than 10 mM‐Mg, the ABRM showed a marked tension development associated with repetitive electrical activity superimposed on a gradual decline of membrane potential. 7. These results suggest that ACh‐contractures are mainly due to the release of intracellularly stored Ca, while K‐contractures are mainly associated with the inward movement of external Ca.
Induction of cholinergic enzymes in chick ciliary ganglion and iris muscle cells during synapse formation.
Authors: Chiappinelli V , Giacobini E , Pilar G , Uchimura H
Published: December 2014

1. In chick ciliary ganglia and irises, cholineacetyltransferase (ChAc) and acetylcholinesterase (AChE) activities were measured from the fifth day of incubation until 1 week after hatching. The changes in enzyme activity were correlated in time with previous electrophysiological and morphological findings of synapse formation in these tissues. 2. At Stage 26 (Hamburger & Hamilton, 1951; before synapse formation in the ganglia) low activities of ChAc (12 +/‐ 4 [mean +/‐ S.E.] p‐mole of ACh synthesized/hr) were measured in the iris nerve terminals, indicating that ganglion cells are biochemically differentiated, immediately after cell migration is completed. The specific acitivities of ChAc and AChE rose during development and these increases were closely related to the onset and maturation of ganglionic and iris synaptic transmission. These increases in enzyme activities can be used in cholinergic synapses as an index of synapse formation. 3. The 200‐fold specific increase of ChAc in iris nerve terminals which occurs at Stage 34 probably reflects an increase in synthesis of the enzyme in ganglion cells and suggests that the formation of the iris neuromuscular junction triggers the enzyme induction. It is implied that the cell responds to a signal ascending the axon from the terminal. 4. The initial increase of AChE specific activity in the ganglion occurs after transmission is established in all cells between Stage 30 and 34 and is mainly due to enzyme synthesis by the ganglion cells. In the iris there is a twofold increase in specific activity after the formation of neuromuscular junctions which probably reflects enzyme induction in the muscle subneural region. It is concluded that the specific induction of AChE in post‐junctional cells is due to an influence of the prejunctional element. 5. During synaptic formation in the ciliary ganglion, reciprocal interactions between the neurones and their targets result in the induction of ChAc in the prejunctional elements and AChE in the post‐junctional cells.
Re‐innervation of twitch and slow muscle fibres of the frog after crushing the motor nerves.
Authors: Schmidt H , Stefani E
Published: December 2014

1. The conduction velocities of individual motor axons innervating twitch and slow muscle fibres of the frog were determined by intracellular recording of junctional potentials elicited by stimulating the motor nerves at two different points. 2. In normal pyriformis muscles twitch and slow fibres were found to be innervated by two distinct populations of motor axons. Twitch fibre axons conducted at 10‐18‐7 m/sec, while the conduction velocities of slow fibre axons ranged from 0‐5 to 5 m/sec (at 7‐9 degrees C). The thresholds for electrical stimulation were significantly lower in the fast than in the slow axons population. 3. Following denervation by crushing the sciatic nerve fast axons which re‐innervated the muscle had lower conduction velocities than normal but could still be identified. These lower conduction velocities were measured proximal to the site of the crush and did not recover over a period of 446 days. 4. Fast motor axons regenerated more quickly than slow axons and re‐innervated twitch as well as slow muscle fibres non‐selectively. About 1 month later slow axons re‐established synaptic contacts with slow (and some twitch) muscle fibres. Simultaneous re‐innervation by fast and slow motor axons was occasionally observed in slow muscle fibres. Finally, the slow muscle fibres were innervated by slow axons only, while synapses of fast axons could no longer be found in this type of muscle fibre. 5. Action potentials were observed in denervated as well as in re‐innervated slow muscle fibres; they disappeared as re‐innervation progressed. 6. It is concluded that non‐selective re‐innervation of slow muscle fibres is present in the frog; it is, however, a transient phenomenon followed by restoration of the original innervation pattern.
Rectification in the smooth muscle cell membrane of rabbit aorta.
Authors: Mekata F
Published: December 2014

1. The current‐voltage relation of the smooth muscle cell membrane of rabbit aorta was determined by the partition method. 2. No anomalous rectification was observed in any of the following solutions: normal Krebs, Na free choline, Na sulphate, and high K‐Na free sulphate. 3. Delayed rectification was seen on application of depolarizing current in both normal Krebs solution and Na free choline solution. 4. High concentration of K made the steady‐state current‐voltage relation almost linear in a voltage range of about 0 to ‐20mV. This effect, and steady‐state cathodal rectification which was seen in physiological solution, could be explained qualitatively by constant field theory without involving channels capable of anomalous rectification. 5. A slow decrease in K conductance, during application of large and long‐lasting hyperpolarizing currents, which occurs in skeletal muscle and is attributed to the tubule system, was never observed in the arteries either in Krebs, Na‐free choline, or Na sulphate solution.
A quantitative description of end‐plate currents in the presence of two lidocaine derivatives.
Authors: Beam K G
Published: December 2014

1. Possible ways in which local anaesthetics may act to produce their characteristic alterations of end‐plate current (e.p.c.s) are considered. 2. Following Magleby & Stevens (1972b), it is proposed that when acetylcholine (ACh) binds to its end‐plate receptor it induces a conformational change which causes an increased ionic permeability and, thus, the measured e.p.c.; the reverse conformational change which returns the permeability to its resting state is postulated to be the rate‐limiting event for e.p.c. decay whether or not local anaesthetics are present. Moreover, it is proposed that the ACh receptor had multiple binding sites and the local anaesthetics can bind to one or more of these sites thereby altering the conformational changes induced when ACh binds to remaining sites. 3. Equations based on this proposal are developed and are shown to provide an accurate description of the entire e.p.c. time couse as modified by eith QX‐222 or QX‐314. 4. Other models are also discussed; models in which local anaesthetic molecules bind only after receptor activation appear to be ruled out.
The reduced responsiveness of neurones in nucleus reticularis gigantocellularis following their excitation by peripheral nerve stimulation.
Authors: Fox J E , Wolstencroft J H
Published: December 2014

1. Post‐stimulus histograms of neuronal activity, constructed from extracellular recordings in decerebrate, decerebellate cats, have been used to investigate the responsiveness of neurons in nucleus reticularis gigantocellularis following their excitation by a peripheral nerve stimulus. 2. The response to a testing stimulus applied to a peripheral nerve was depressed following the response to a conditioning stimulus applied to the same or a different peripheral nerve. This reduction in responsiveness was maximal within 50 msec of the peak of the response to the conditioning stimulus. Response latencies to the testing stimulus were increased during the period of reduced responsiveness. 3. Responsiveness to a peripheral nerve stimulus was also reduced following a spontaneous or an antidromically evoked spike, but this effect was weaker and much shorter‐lasting than that following a nerve‐evoked spike. Thus, the reduced responsiveness cannot be solely due to phenomena which are an inevitable consequence of an action potential in the neurone. 4. In spontaneously firing neurones, the duration of the reduced responsiveness to a testing stimulus generally outlasted the depression of spontaneous activity which often followed an excitation evoked by a peripheral nerve conditioning stimulus. 5. The reduction in responsiveness to a testing stimulus applied to the same nerve as the conditioning stimulus was greater and longer‐lasting than that to a testing stimulus applied to a different nerve. 6. When stimuli were applied to one nerve at a relatively high rate, the neurone became much less responsive to that input, but simultaneously became more responsive to low rate stimulation of other nerves. 7. It is concluded that the greater part of the reduced responsiveness is due to events occurring on the input pathway to a reticular neurone, or possibly in the region of the afferent endings on its dendrites. These processes may allow selective changes in responsiveness to different inputs, and enable the units to act as novelty detectors.
Endogenous prostaglandins, adenosine 3':5'‐monophosphate and sodium transport across isolated frog skin.
Authors: Hall W J , O'Donoghue J P , O'Regan M G , Penny W J
Published: December 2014

1. Sodium transport across isolated frog skin, as measured by the short‐circuit current, was decreased by acetylsalicylic acid, mefenamic acid, paracetamol and phenylbutazone. Indomethacin (6 X 10(‐6) M) had a biphasic effect on the short‐circuit current: a transient increase followed by a sustained decrease. 2. The release of prostaglandin‐like material from the skin was reduced by acetylsalicylic acid and indomethacin. Paracetamol caused a significant reduction in the short‐circuit current response of the skin to low doses of arachidonic acid, but the response to the highest dose tested was not significantly altered. 3. Indomethacin (6 X 10(‐6) M) increased the sensitivity of the skin to applied prostaglandin E1. The other prostaglandin synthetase inhibitors did not have this effect. Indomethacin (6 X 10(‐6) M) also enhanced the effect of antidiuretic hormone on the short‐circuit current. 4. Indomethacin (30 X 10(‐6) M) increased the short‐circuit current and diminished the response to applied prostaglandin E1. 5. In sulphate Ringer, theophylline increased the short‐circuit current and diminished the response to prostaglandin E1. 6. Prostaglandin E1 increased the levels of cyclic AMP in frog skin and these increases preceded the increases in short‐circuit current. There was a seasonal variation in the level of cyclic AMP in the skin: the levels in winter exceeded those in summer. There was also a seasonal variation in the cyclic AMP response to prostaglandin E1: the winter response was greater than that in summer. 7. Indomethacin (6 X 10(‐6) M) had a biphasic effect on cyclic AMP levels in the skin, an initial increase followed by a decrease. Indomethacin also potentiated prostaglandin E1 stimulated cyclic AMP accumulation. 8. Theophylline increased cyclic AMP levels in the skin and potentiated prostaglandin E1 stimulated cyclic AMP accumulation. 9. Pre‐treatment of the skin with theophylline reversed the effects of cyclic AMP on the short‐circuit current and open‐circuit potential. 10. It is concluded that endogenous prostaglandins help to maintain sodium transport across isolated frog skin and that the effects of E‐type prostaglandins on the short‐circuit current are mediated by increased cyclic AMP levels. The transient increase in short‐circuit current and the increased skin sensitivity caused by indomethacin (6 X 10(‐6) M) are attributed to inhibition of phosphodiesterase activity. The failure of theophylline to potentiate the short‐circuit current response of the skin to prostaglandin E1 is attributed to alteration of cyclic AMP action on the skin by theophylline.
Evidence for genetic control of glycine uptake in cultured cells, regulated by the amino acid concentration of the growth medium.
Authors: Hume S P , Lamb J F
Published: December 2014

1. Cultured cells were grown in various concentrations of amino acids for periods up to 3 days and the characteristics of the glycine transport system measured under fixed experimental conditions. During this time, the effect of enucleation, using cytochalasin B, and the effects of protein synthesis inhibitors (cycloheximide and actinomycin D) were investigated. 2. Glycine influx is regulated by the prior growth concentration of similarly transported amino acids. 3. The modification in transport involves primarily a change in Vmax (but also a change in Km in HeLa cells) and is effected within 2‐10 hr after media change. Increased transport activity is calculated to be sufficient to compensate for the reduction in extracellular amino acid concentration, so that nearly normal influx values from media are maintained. Regulation over the range of concentrations studied is shown to be very accurate. 4. The nucleus is essential for the regulatory mechanism to function. It seems probable that mRNA synthesis is required for acquisition of increased transport activity and mRNA translation required for maintenance of normal activity. 5. The controlling factor in the regulatory mechanism appears unlikely to be intracellular pool size. Other possible signals are discussed.
The formation of metarhodospin380 in the retinal rods of the frog.
Authors: Baumann C
Published: December 2014

1. The formation of metarhodopsin380 (metarhodopsin II) was studied in isolated frog retinas exposed to intense flashes of 120 mus duration. 2. A rapid increase in absorbance at 375 nm during the flash was followed by a slower absorbance increase in the subsequent dark period. The slower increase showed virtual completion after 5 ms. 3. The fast absorbance increase during the flash was due to the formation of metarhodopsin478. The rate of this reaction was dependent on the time course of the flash and on the decay rate of lumirhodopsin. 4. Kinetic analysis indicates that three consecutive reactions occur: the light‐controlled formation of lumirhodopsin, its first‐order decay to metarhodopsin478 and the conversion of metarhodopsin478 into metarhodopsin380. At 21 degrees C, the decay constants were 2 X 10(4) S‐1 (lumirhodopsin) and 1 X 10(3) S‐1 (metarhodopsin478), respectively.
Calcium conductance in relation to contractility in frog myocardium.
Authors: Horackova M , Vassort G
Published: December 2014

1. Ca inward current and the corresponding phasic component of tension were measured in frog atrial muscle under voltage‐clamp conditions in Na‐free (Li) Ringer solution with tetrodotoxin (TTX) added. 2. The quantity of Ca ions entering the cell upon depolarization, delta[Ca]i, was linearly related to peak phasic tension. 3. The voltage dependence of the steady‐state inactivation of the Ca‐carrying system, f infinity, against voltage yielded similar relationships whether determined directly from variations of Ca inward current or peak phasic tension. The Ca system was almost fully available at potentials more negative than ‐45 mV and almost fully inactivated at potentials more positive than +10 mV. 4. It was established that the time‐ and voltage‐dependence of Ca current and of phasic tension are directly related. The time constants of Ca activation, tau f, were comparable in the range of membrane potential investigated (‐20 to +25 mV), whether determined directly from the decay of Ca current or indirectly from peak phasic tension. 5. It was concluded that the Ca current, ICa, directly activates phasic contraction and that either parameter can be used as an indicator of the kinetics of the Ca‐carrying system. Peak phasic tension was used to determine tau f further in the membrane potential range in which interference by other membrane currents renders direct analysis of Ca current difficult. 6. The tau f against voltage relationship determined from phasic tension showed that the inactivation process of the Ca‐carrying system is slowest at membrane potentials around ‐13 mV (tau f = 55 msec) and that the rate of inactivation increases with both increasing and decreasing depolarizations. 7. It is suggested that normal repolarization in frog myocardium depends mainly on the decay of Ca inward current rather than on an increase of outward current.
Caudate stimulation and substantia nigra activity in the rat.
Authors: Dray A , Gonye T J , Oakley N R
Published: December 2014

1. The responses of spontaneously active single neurones in the substantia nigra and overlying mesencephalic reticular formation have been analysed during the electrical stimulation of the ipsilateral caudate nucleus. Experiments were performed in rats anaesthetized with urethane or pentobarbitone. All recordings were made extracellularly with multi‐barrelled glass micropipettes which were also used to test neuronal responsiveness to electrophoretically administered substances. The micropipette tip position was marked and the distribution of neurones studied has been analysed. 2. Single shock stimulation of the caudate nucleus inhibited neuronal activity in the substantia nigra (270/320 cells: mean latency 5‐4 msec) and in the mesencephalic reticular formation (62/72 cells: mean latency 16‐6 msec). However, these effects were often accompanied by periods of excitation. In pentobarbitone anaesthetized animals the latency and duration of these substantia nigra inhibitions was increased. 3. Compared with the zona reticulata, fewer neurones in the zona compacta of the substantia nigra responded to caudate stimulation in both urethane or pentobarbitone anaesthetized animals. 4. The activity of most cells was depressed by electrophoretically administered GABA or glycine and increased by acetylcholine or glutamate. Neurones of the mesencephalic reticular formation were less sensitive to GABA and glycine than substantia nigra neurones. Within the substantia nigra, both zona compacta and zona reticulata neurones were more sensitive to GABA than to glycine. Over‐all, glutamate was a more potent excitant than acetylcholine (ACh). 5. Electrophoretic bicuculline methochloride (BMC) consistently reduced GABA but not glycine depression of substantia nigra neurones. Approximately twice as much BMC was required to reduce the endogenous inhibition of the same substantia nigra neurones and the amplitude of concomitantly evoked positive field potential as was required to abolish exogenous GABA responses. Some evoked substantia nigra inhibitions were resistant to BMC. 6. Electrophoretic strychnine consistently reduced glycine but not GABA depression of substantia nigra neurones, and did not modify caudate evoked inhibition of these neurones or the accompanying field potential. 7. The results support the concept of a slowly conducting caudato‐nigral pathway which has both facilitatory and inhibitory components. The inhibitory pathway uses GABA as the neurotransmitter. The identity of the possible excitatory transmitter is unknown. The monosynaptic nature of this pathway is uncertain and the possible contribution of other bicuculline insensitive nigral inhibitory processes is discussed.
An analysis of the actions of low concentrations of ouabain on membrane currents in Purkinje fibres.
Authors: Cohen I , Daut J , Noble D
Published: December 2014

1. The influence of low concentrations (5 X 10(‐8) to 5 X 10(‐7) M) of ouabain on the K gradient in sheep cardiac Purkinje fibres was observed by measuring changes in the reversal potential for a K specific current iK2, and by measuring total steady‐state current‐voltage relations. 2. Provided that the bathing solution K concentration, [K]o was not too low, these doses of ouabain were often observed to increase the K gradient, i.e. the reversal potential was shifted in a negative direction. 3. The change in the reversal potential and in the current‐voltage relation could be mimicked by reducing the value of [K]o in the absence of ouabain. It is therefore suggested that ouabain may stimulate the Na+‐K+ exchange pump and so reduce the K concentration, [K]e, in the clefts of the preparation. 4. At sufficiently low values of [K]o, a dose of ouabain that was stimulatory may become inhibitory. The reversal potential for iK2 then shifts in a positive direction. 5. During either stimulation or inhibition, the speed of change of reversal potential is consistent with a change in [K]e, which may change fairly rapidly. It is not possible to account for the results solely by changes in intracellular concentration, [K]i. 6. Low concentrations of ouabain were found to have no effect on the activation curve, s infinity (Em), controlling iK2. It is concluded that the changes in iK2 are solely attributable to changes in reversal potential. 7. Since net stimulation of the Na+‐K+ exchange pump was observed to occur at doses of ouabain that exert a strong positive inotropic action on Purkinje fibres (Blood, 1975), it is not likely that the inotropic action is causally related to net pump inhibition.
Physiological and morphological effects of post‐ganglionic axotomy on presynaptic nerve terminals.
Authors: Brenner H R , Johnson E W
Published: December 2014

1. Electrophysiological and electron microscope studies were done on cells in the ciliary ganglion of chickens which had been axotomized on the day of hatching. 2. By the third day after post‐ganglionic axotomy both electrical and chemical transmission through the ganglion were severely depressed; by the fifth day ganglionic transmission had disappeared. 3. Action potential initiation and conduction in axotomized cells and in their associated presynaptic nerve terminals were unimpaired 3‐4 days after axotomy. 4. Depression of ganglionic transmission in 3‐4 day axotomized preparations was due to a reduction in amplitude of both the excitatory post‐synaptic potential (e.p.s.p.) and the electrical coupling potential in individual ganglion cells. 5. In addition to being reduced in amplitude, e.p.s.p.s in axotomized cells were more subject to fatigue during low frequency (1/sec) stimulation. 6. The reduction in e.p.s.p. amplitude was due to a reduction in both the mean quantal content of the e.p.s.p.s and the calculated depolarization produced by an individual quantum of transmitter. On the average the e.p.s.p. was reduced by a factor of about 4, the mean quantum content to about two thirds normal and the quantal size to about a third normal, compared with responses in unaxotomized cells of the same age. 7. Ultrastructural studies revealed a progressive maturation of pre‐synaptic terminals in normal ganglia between 0 and 9 days after hatching. Over this period the content of synaptic vesicles and mitochondria in the terminals increased and the background matrix became more dense. 8. After axotomy these signs of maturation was abolished or reversed, particularly from the third day onward. In addition there was an increase in the number of cell sections in which no synaptic terminals were observed. 9. It was concluded that loss of synaptic transmission was due to at least three factors: a reduction in release of transmitter from presynaptic terminals, a reduction in quantal size, probably due to a loss of post‐synaptic sensitivity, and a partial loss of presynaptic contact.