bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation patterns of embryonic chick hind limb muscles recorded in ovo and in an isolated spinal cord preparation.
Authors: Landmesser L T , O'Donovan M J
Published: December 2014

Muscle activation patterns of embryonic chick hind limb muscles were determined from electromyographic (e.m.g.) recordings in an isolated spinal cord/hind limb preparation of stage 34‐36 embryos, and were compared with in ovo e.m.g. activity from similarly staged embryos. Muscle activity in ovo consisted of periodically recurring sequences of bursts during which antagonistic muscles often alternated and synergistic muscles were co‐active, as compatible with their mature function. However, more variable behaviour was also observed. Burst sequences in ovo were often initiated by a short‐duration, high‐amplitude discharge that occurred synchronously in all muscles studied, and which was followed by a period of electrical silence that was longest in the flexor muscles. This type of activity has not been described previously in mature animals. In ovo movement sequences were generally initiated by extensor activity which progressively declined in duration and intensity throughout the sequence, while flexor activity progressively intensified. The onset of activity in extensor muscles was accompanied by an abrupt decrease in flexor activity, whereas the converse was not observed. Spontaneous movement sequences also occurred when the spinal cord and hind limb were isolated and maintained in oxygenated Tyrode solution for several hours. Deafferentation experiments indicated that the motor pattern in this preparation was generated centrally by circuits within the spinal cord. Activity from the isolated cord was less variable than that occurring in ovo, consisting of sequences of highly regular recurring bursts. Each burst began with a brief high‐amplitude discharge that occurred synchronously in all muscles and which was similar to that observed in ovo. This was followed by a silent period, which was longest in the flexors, and then by a more prolonged burst. Although its behaviour differs from that in ovo in some respects, it is concluded that the isolated cord maintained in vitro produces a spontaneous and patterned motor output.
Spatial contrast adaptation characteristics of neurones recorded in the cat's visual cortex.
Authors: Albrecht D G , Farrar S B , Hamilton D B
Published: December 2014

Spatial contrast adaptation, produced by prolonged exposure to high contrast grating patterns, has become an important psychophysical method for isolating spatial and orientation selective channels in the human visual system. It has been reasonably argued that this adaptation may be fundamentally dependent upon the activity of neurones in the striate cortex. To test the validity of this hypothesis, and several others, we measured the general adaptation characteristics of 144 striate neurones using a stimulus protocol comparable to the typical psychophysical methods. In general, during prolonged high contrast stimulation, the responses of most cells exponentially decayed from a transient peak response to a sustained plateau response; following adaptation, the responses to lower contrasts were depressed relative to the unadapted state but then gradually recovered from the transient depression to a sustained plateau. Such adaptation was a property common to both simple and complex cells (the distributions of the quantitative of adaptation were overlapping); there were however small but reliable differences. We compared the neurophysiological contrast adaptation with two psychophysical estimates of human contrast adaptation (threshold contrast elevation and apparent contrast reduction) and found that the time courses and the magnitudes were quite similar. The effect of contrast adaptation on the spatial frequency tuning was assessed by measuring the contrast response function at several different test spatial frequencies before and after adaptation at the optimum centre frequency. We found that the effect of adaptation decreased as the difference between test and adaptation frequency increased. Grating contrast adaptation has been alternatively described as 'constructive gain control' on the one hand and as 'deleterious fatigue' on the other. We tested the effect of contrast adaptation on the contrast response function and found (a) that adaptation shifts the curves vertically downward parallel to the response axis (thus reflecting a decrease in the maximum rate of firing and a deleterious compression of the response range) and (b) that adaptation shifts the curves horizontally to the right parallel to the contrast axis (thus reflecting a true sensitivity shift of the remaining response range for constructive maintenance of high differential sensitivity around the prevailing background level).(ABSTRACT TRUNCATED AT 400 WORDS)
A study of the action of tetanus toxin at rat soleus neuromuscular junctions.
Authors: Bevan S , Wendon L M
Published: December 2014

Tetanus toxin (TeTX) inhibits the evoked release of acetylcholine (ACh) at rat soleus end‐plates. The effects of various procedures which evoke ACh release by raising the level of free intracellular calcium have been investigated at various stages of tetanus intoxication. At all stages studied TeTX has little or no effect on either the frequency or the amplitude of spontaneous miniature end‐plate potentials (m.e.p.p.s). After TeTX poisoning, e.p.p. latency is more variable than normal and the slope of the relationship between ln m (quantal content) and ln [Ca]o is reduced from the control value of about 4. Plots of m‐1/n against 1/[Ca]o, for n = 1‐4, suggest that mmax, the maximum number of quanta releasable by nerve stimulation, is reduced at intoxicated end‐plates. Blocking delayed rectification with 3‐aminopyridine (1‐5 mM) increases m, but has little or no effect on either the slope of ln m‐ln [Ca]o plots or estimates of mmax. Several treatments which raise m.e.p.p. rate (high [Ca]o, hyperosmotic medium, addition of lanthanum) are less effective after TeTX poisoning. Some of the tested agents increase m.e.p.p. frequency by a mechanism which is thought to involve a mobilization of calcium from intracellular stores. The decline in m.e.p.p. rate after a period of high‐frequency nerve stimulation is different at normal and TeTX‐treated end‐plates. At tetanus‐intoxicated end‐plates, the decline differs from that expected if TeTX acted simply to block calcium entry into the terminal. In addition, the increase in m.e.p.p. frequency observed with a high rate of nerve stimulation suggests that considerable amounts of calcium can enter the terminal with each action potential. It is concluded that TeTX blocks transmitter release by acting at a step between calcium influx to the terminal and transmitter release such that the mechanism for ACh release shows a reduced sensitivity to intracellular calcium. The possibility of an additional effect on the presynaptic calcium conductance cannot be excluded. Some differences between the properties of end‐plates poisoned with TeTX and botulinum toxin are discussed.
In vivo development of cholinesterase at a neuromuscular junction in the absence of motor activity in Xenopus laevis.
Authors: Cohen M W , Greschner M , Tucci M
Published: December 2014

Embryos of Xenopus laevis were selected prior to the onset of innervation and were raised for 2 days in the anaesthetic tricaine methanesulphonate (200 micrograms/ml). The gross development of these tricaine‐reared animals appeared normal despite the absence of spontaneous motor activity and the lack of motor responses to prodding with a pin. Motor activity quickly appeared when the anaesthetic was withdrawn. Intracellular recording from the myotomes of intact, tricaine‐maintained animals failed to reveal any spontaneous muscle action potentials. Synaptic potentials increased in frequency and amplitude upon withdrawing tricaine, but resting potentials remained unchanged. Cholinesterase activity, detected histochemically, was observed at the ends of the myotomes, the main site of innervation. The intensity of the histochemical reaction product at these sites appeared to be about as great in the myotomes of tricaine‐reared animals as in control myotomes. Miniature end‐plate currents (m.e.p.c.s), examined by focal external recording, declined with a time constant of 2.9 +/‐ 0.2 ms (mean +/‐ S.E. of mean) in the myotomes of tricaine‐reared animals (stages 40‐41). The time constants in the myotomes of control animals were 1.8 +/‐ 0.1 ms at stages 40‐41 and 8.7 +/‐ 0.7 ms at stages 24‐26 (shortly after the onset of innervation). The anticholinesterase neostigmine doubled m.e.p.c. time constants in the myotomes of tricaine‐reared animals as well as in control myotomes at stages 40‐41. It is concluded that motor activity is not required for the in vivo development of physiological levels of synaptic cholinesterase in Xenopus myotomal muscle.
Relationship between peritubular membrane potential and net fluid reabsorption in the distal renal tubule of Amphiuma.
Authors: Cohen B , Giebisch G , Hansen L L , Teuscher U , Wiederholt M
Published: December 2014

Amphiuma kidneys were isolated and perfused with modified Ringer solution and peritubular and transepithelial membrane potentials (p.d.s) in distal tubules measured with micro‐electrodes during rapid changes of luminal electrolyte concentrations. Peritubular membrane potential and net fluid reabsorption (split‐oil‐droplet method) were also measured with and without application of various drugs known to alter transport. Raising the luminal sodium concentration from 10 to 100 mM reversibly increased the peritubular p.d. The magnitude of the peritubular p.d. was a saturable function of luminal sodium concentration. In the presence of chloride in the lumen the peritubular hyperpolarization following increased luminal sodium could be inhibited by luminal amiloride (10(‐4)M). Sodium‐induced hyperpolarization of the peritubular p.d. could be completely inhibited by 10(‐5)M‐ouabain. Adding amiloride (10(‐4)M) to the luminal fluid rapidly and reversibly depolarized the peritubular p.d. and inhibited fluid reabsorption. Addition of amphotericin B (20 micrograms/ml) to the luminal perfusion solution had no effect on peritubular p.d. at 100 mM‐luminal NaCl but at 10 mM‐NaCl, peritubular p.d. hyperpolarized. Fluid reabsorption was stimulated (with 100 mM‐NaCl in the lumen). Addition of amphotericin when the tubule was perfused on both sides with solutions containing a constant potassium concentration of 78 mM and a variable sodium concentration ranging from 7.8 to 34.5 mM revealed strong dependence of the peritubular hyperpolarization on the sodium concentration. Luminal furosemide (10(‐4)M) and chlorothiazide (10(‐4)M) and peritubular ethacrynic acid (10(‐4)M) all reduced fluid reabsorption but hyperpolarized the peritubular p.d. The data suggest the presence of an electrogenic sodium transport process in the peritubular membrane that directly contributes to the generation of the peritubular potential. In addition, chloride transport has an important role in determining this potential.
A bicuculline‐resistant inhibitory post‐synaptic potential in rat hippocampal pyramidal cells in vitro.
Authors: Newberry N R , Nicoll R A
Published: December 2014

Experiments were performed on rat hippocampal CA1 pyramidal cells in vitro in order to elucidate the origin of the late hyperpolarizing potential, which follows the gamma‐aminobutyric acid (GABA)‐mediated inhibitory post‐synaptic potential (GABA‐i.p.s.p.). The late hyperpolarizing potential could be evoked by orthodromic stimulation via stratum radiatum or stratum oriens but not by selective antidromic stimulation. The membrane soluble analogue of cyclic AMP, 8‐bromoadenosine 3',5'‐cyclic monophosphate (8‐Br cyclic AMP), which blocks calcium‐activated potassium hyperpolarizations (GK(Ca], did not reduce the late hyperpolarizing potential. The enkephalin analogue, (D‐ala2‐met5)‐enkephalinamide (DALA) reversibly reduced both the GABA‐i.p.s.p. and the late hyperpolarizing potential. The late hyperpolarizing potential and GABA‐i.p.s.p. were more sensitive to low doses of the calcium antagonist, cadmium, than the excitatory post‐synaptic potential (e.p.s.p.). The local application of cadmium to the pyramidal cell layer blocked the antidromic i.p.s.p. but the orthodromically evoked late hyperpolarizing potential was less affected. In contrast to the GABA‐i.p.s.p., the late hyperpolarizing potential was not reversed by chloride injection and was enhanced, rather than depressed, by bicuculline. We conclude that the late hyperpolarizing potential is a bicuculline‐resistant i.p.s.p. The unidentified transmitter for this i.p.s.p. is released from feed‐forward interneurones primarily onto the dendrites of the pyramidal cell and may act by increasing the potassium permeability of the membrane. The epileptiform burst after‐hyperpolarization evoked in the presence of GABA antagonists is composed of at least two components, a long‐duration hyperpolarization mediated GK(Ca) and an earlier and shorter late hyperpolarizing potential. Blockade of the GK(Ca) by 8‐Br cyclic AMP did not alter the duration of epileptiform bursts but did markedly increase the frequency of their occurrence. This suggests that GK(Ca) is involved in controlling the interval between bursts.
Evidence from the use of vibration that the human long‐latency stretch reflex depends upon spindle secondary afferents.
Authors: Matthews P B
Published: December 2014

The electromyographic activity of flexor pollicis longus has been recorded in normal human subjects on moving the tip of the thumb with the proximal phalanx clamped. Ramp and hold displacements (stretches) were compared with high‐frequency sinusoidal movement (vibration). The subject exerted a constant flexor force between stimuli and made no voluntary response to them. On stretching the muscle by forcibly extending the thumb at various constant velocities the usual combination of short‐latency (ca. 25‐30 ms) and long‐latency (ca. 40 ms) components of response were observed. The short‐latency response progressively predominated as the velocity was increased (60‐900 deg s‐1, 9 deg joint displacement). One subject still showed only a long‐latency response with the fastest stretch, arguing that it is a distinct reflex entity. On commencing vibration (143 Hz, 3 deg movement peak‐to‐peak) a short‐latency response was regularly obtained, but any long‐latency response was always small in relation to that elicited by stretch. This was equally so when the short‐latency responses to the two types of stimulation were matched by using appropriate parameters of stimulation. The time course of the vibration response did not change appreciably with change of amplitude of vibration, so that its temporal profile was always quite different from that of the stretch response. The observed differences are in accordance with the hypothesis that the spindle group II afferents produce the long‐latency excitation, with the time lost peripherally in afferent conduction rather than centrally. In relation to the strength of their Ia excitatory actions, stretch is known to excite secondary afferents more powerfully than does vibration. The findings are not readily accommodated on the hypothesis that the long‐latency response is a transcortical reflex elicited by the initial Ia input, since vibration should then also have had a powerful long‐latency action. Similar responses to vibration were obtained when it was applied percutaneously to the tendon of flexor pollicis longus 6 cm above the wrist. Also, those elicited by thumb vibration persisted largely unchanged when the thumb was anaesthetized. This confirms that they were dependent upon the excitation of receptors in flexor pollicis longus, presumably the Ia afferents, rather than upon cutaneous or joint receptors in the thumb. The stretch responses also depended upon muscle receptors, since they too survived anaesthesia.(ABSTRACT TRUNCATED AT 400 WORDS)
On the significance of monoamines and their metabolites in the cerebrospinal fluid of the sheep.
Authors: Ruckebusch M , Sutra J F
Published: December 2014

Assays capable of concurrently measuring small quantities of noradrenaline, dopamine, serotonin, and several of their metabolites in cerebrospinal fluid (c.s.f.) were developed by the use of high performance liquid chromatography with electrochemical detection. For comparison, cortical subarachnoid, ventricular, cisternal and lumbar c.s.f. were obtained by puncture under barbiturate anaesthesia in sheep. Basal concentrations related to the adrenergic system, including methoxyhydroxyphenylglycol (MHPG), were similar in ventricular, cisternal and lumbar c.s.f., and those of the serotoninergic metabolites, 5‐hydroxyindole‐3‐acetylacetic acid (5‐HIAA), were similar in ventricular and cisternal c.s.f. High concentrations of the dopamine metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were found only in ventricular c.s.f. Monoamine metabolites in ventricular c.s.f. under basal conditions and after various experimental manipulations were then determined over periods of 3 months in two different breeds of sheep fitted chronically with cannulae in lateral ventricles. A dose‐related accumulation of all the acidic monoamine metabolites was recorded during treatment with probenecid. The increase in 5‐HIAA was linear after administration of increased doses of tryptophan and 5‐hydroxytryptophan. The concentrations of dopamine, DOPAC and HVA in the ventricular c.s.f. reflected the response of the dopaminergic system to agents capable of crossing the blood‐brain barrier. It is concluded that cerebral metabolism in conscious sheep could be indirectly approached by recording the concentration of end‐products of dopamine metabolism in ventricular cerebrospinal fluid, obtained under conditions of minimal stress.
Excitatory amino acid receptors in Xenopus embryo spinal cord and their role in the activation of swimming.
Authors: Dale N , Roberts A
Published: December 2014

Bath application of N‐methyl‐D‐aspartate (NMDA), kainate or quisqualate to Xenopus embryos depolarized spinal cord motoneurones and reduced their input resistance in both normal salines and salines containing 20 mM‐Mn2+ and 0.5 mM‐Ca2+, or 2 X 10(‐6) M‐tetrodotoxin. This suggests that motoneurones possess all three types of excitatory amino acid receptor. These receptors have similar specificities to excitatory amino acid antagonists as those occurring in adult frog and cat spinal cords. Application of 30‐40 microM‐NMDA or 5‐6.5 microM‐kainate to the medium bathing spinalized embryos can cause a sustained patterned motor output similar to that of swimming evoked by natural stimulation of intact animals. At these concentrations NMDA and kainate depolarized motoneurones by 19.0 +/‐ 1.80 (mean +/‐ S.E. of mean) and 18.0 +/‐ 2.00 mV respectively and decreased their input resistance by 23.0 +/‐ 2.82% and 24.0 +/‐ 3.46%. These changes are similar to those associated with the tonic excitation which motoneurones receive during naturally evoked swimming. Bath application of 5‐8 microM‐quisqualate to spinal embryos can also cause a sustained motor output. However, this was different to that evoked by NMDA and kainate and was inappropriate for swimming. When applied to intact animals during swimming both 2‐3 mM‐cis‐2,3‐piperidine dicarboxylic acid (PDA) and 0.5 mM‐gamma‐D‐glutamylglycine (DGG) selectively blocked the tonic excitation of motoneurones and in doing so abolished the motor output of the spinal cord. 50‐200 microM‐2‐amino‐5‐phosphonovaleric acid reduced the tonic excitation but to a lesser extent than either PDA or DGG. The tonic excitation of motoneurones which occurs during swimming therefore appears to be mediated via an endogenous excitatory amino acid transmitter which acts on NMDA and kainate receptors.
Cooling dissociates glucose‐induced insulin release from electrical activity and cation fluxes in rodent pancreatic islets.
Authors: Atwater I , Goncalves A , Herchuelz A , Lebrun P , Malaisse W J , Rojas E , Scott A
Published: December 2014

Insulin release and beta‐cell membrane potentials in response to glucose at 37 and 27 degrees C have been measured simultaneously in single, micro‐dissected, perifused islets of Langerhans from normal mice. Insulin release and 45Ca outflow in response to glucose at 37 and 27 degrees C have been measured simultaneously from perfused islets isolated by collagenase digestion from normal rats. The effect of cooling on beta‐cell membrane potassium permeability was assessed by changes in measured membrane potential and input resistance (in the mouse) and by changes in 86Rb outflow (in the rat). Resting and active beta‐cell membrane parameters (i.e. membrane potential, spike frequency, input resistance, 45Ca outflow and 86Rb outflow), in both mouse and rat islets, were affected only slightly by cooling to 27 degrees C, with temperature coefficients of 2 or lower. At 27 degrees C glucose‐stimulated insulin release was inhibited completely in mouse islets and almost completely in rat islets. The temperature coefficients in both preparations were greater than 5. It is concluded that beta‐cell electrical activity and changes in membrane permeability induced by glucose are not consequences of insulin release.
Ionic basis for the electro‐responsiveness and oscillatory properties of guinea‐pig thalamic neurones in vitro.
Authors: Jahnsen H , Llinás R
Published: December 2014

The ionic requirements for electro‐responsiveness in thalamic neurones were studied using in vitro slice preparations of the guinea‐pig diencephalon. Analysis of the current‐voltage relationship in these neurones revealed delayed and anomalous rectification. Substitution of Na+ with choline in the bath or addition of tetrodotoxin (TTX) abolished the fast spikes and the plateau potentials, described in the accompanying paper. Ca2+ conductance blockage with Co2+, Cd2+ or Mn2+, or replacement of Ca2+ by Mg2+ abolished the low‐threshold spikes (l.t.s.). Substitution with Ba2+ did not significantly increase the duration of the l.t.s., suggesting that under normal conditions the falling phase of this response is brought about by inactivation of the Ca2+ conductance. The after‐hyperpolarization (a.h.p.) following fast spikes was markedly reduced in amplitude and duration by bath application of Cd2+, Co2+ or Mn2+, indicating that a large component of this response is generated by a Ca2+‐dependent K+ conductance (gK[Ca]). Following hyperpolarizing current pulses, the membrane potential showed a delayed return to base line. This delay is produced by a transient K+ conductance as it can be modified by changing the drive force for K+. Presumptive intra‐dendritic recording demonstrated high‐threshold Ca2+ spikes (h.t.s.s.) which activate a gK[Ca]. Such h.t.s.s. were also seen at the somatic level when K+ conductance was blocked with 4‐aminopyridine. It is proposed that the intrinsic biophysical properties of thalamic neurones allow them to serve as relay systems and as single cell oscillators at two distinct frequencies, 9‐10 and 5‐6 Hz. These frequencies coincide with the alpha and theta rhythms of the e.e.g. and, in the latter case, with the frequency of Parkinson's tremor.
Dark noise in the outer segment membrane current of green rod photoreceptors from toad retina.
Authors: Matthews G
Published: December 2014

The outer segment membrane current of single green rods from toad retina was recorded with a suction electrode, and the rate of spontaneous noise events similar to single‐photon responses was measured at different temperatures. The activation energy, Gibbs free energy of activation, and entropy of activation for the process producing spontaneous events were similar to the values reported for thermal isomerization of free 11‐cis‐retinal (Hubbard, 1966), suggesting that thermal isomerization of the chromophore may be the trigger for the spontaneous events. The apparent rate constant for thermal activation of the green rod photopigment was about 4 times higher than in red rods but about 1000 times lower than for free 11‐cis‐retinal. Thus, both red and green rod opsin appear to stabilize 11‐cis‐retinal against thermal isomerization, but green rod opsin is somewhat less effective. The speed of the average dim‐flash response increased as temperature was raised, as reported previously in both cone and rod photoreceptors. The reciprocal of the time‐to‐peak of the dim‐flash response had an average Q10 of 3.3 between 20 and 30 degrees C. Changing temperature shifted the time scale of the response without altering response wave form, suggesting that all delay stages shaping the light response were approximately equally affected by temperature. At temperatures greater than 25 degrees C, flash responses were sometimes biphasic, i.e. inward dark current first decreased after a flash, then transiently increased beyond the resting dark level.
A study of the submaxillaris muscle of the frog.
Authors: Miledi R , Uchitel O D
Published: December 2014

The characteristics of muscle fibres in the submaxillaris muscle of the frog were studied using electrophysiological and anatomical techniques. The muscle fibres were capable of eliciting action potentials and their passive membrane properties were similar to those of fast muscle fibres. Composite end‐plate potentials, due to polyneuronal innervation, were observed in most muscle fibres. Acetylcholinesterase staining of the whole muscle revealed multiple end‐plate areas, and several end‐plates of different size and shape were observed in single teased fibres. It is concluded that the submaxillaris muscle of the frog is composed of a distinctive population of muscle fibres (intermediate muscle fibres) with electrical properties like those of fast muscle fibres and multiple innervation like that of slow muscle fibres.
Light and electron microscopic identification of nerve terminal sprouting and retraction in normal adult frog muscle.
Authors: Anzil A P , Bieser A , Wernig A
Published: December 2014

A combined light and electron microscopic study was performed on neuromuscular junctions of normal adult frogs. In a previous investigation signs of new synapse formation, as well as abandoned former synaptic sites, have been observed in normal muscles (Wernig, Pécot‐Dechavassine & Stöver, 1980a, b). Here we performed a detailed light and electron microscopic correlation to investigate those parts of junctions which, after staining for cholinesterase (ChE) and presynaptic axon terminals, were suspected either to be newly formed or sites abandoned by the presynaptic nerve and the Schwann cell. Thin presynaptic nerve branches, enclosed by Schwann cell sheaths along most of their length, formed synaptic contacts with the muscle fibre only at small circumscribed areas. In these regions post‐synaptic secondary folds (invariably present at mature synapses) were either missing or were less well developed. At these small contacts, binding sites for fluorescein‐labelled alpha‐bungarotoxin were usually present. At other sites the ChE reaction product was present but an axon could not be detected in silver‐stained preparations. Electron microscopic observation revealed post‐synaptic secondary folds filled with ChE reaction product while the presynaptic axon and Schwann cell were missing. The sites with ChE remnants can thus be regarded as abandoned former synaptic contacts. No binding of fluorescein‐labelled alpha‐bungarotoxin could be detected at such sites. These findings confirm earlier suggestions that synaptic contacts in frog muscle are normally undergoing continual remodelling. The lack of binding sites for fluorescein‐labelled alpha‐bungarotoxin at abandoned synaptic sites suggests that a neural or Schwann cell factor is important for the maintainance of synaptic acetylcholine receptors.
Sites and mechanisms of actions of enkephalin in the feline parasympathetic ganglion.
Authors: Katayama Y , Nishi S
Published: December 2014

Intracellular recordings were made in vitro from neurones of the cat parasympathetic ciliary ganglion with a current‐ or voltage‐clamp technique. (Met5)enkephalin and (leu5)enkephalin (10 nM to 10 microM) were applied by superfusion. Both caused a membrane hyperpolarization which persisted in a calcium‐free/high‐magnesium solution, and both reduced the amplitude of excitatory post‐synaptic potentials (e.p.s.p.s). These actions of enkephalin were antagonized by naloxone. The enkephalin‐induced hyperpolarization was associated with an increase in membrane conductance, reversed in polarity at ‐90 mV and was not altered by changing external sodium and chloride concentrations. This indicates that the enkephalin hyperpolarization is due mainly to activation of potassium conductance. Enkephalin decreased the mean quantal content of e.p.s.p.s recorded in low‐calcium/high‐magnesium solution, without changing quantal size. Furthermore, the increase in the frequency of miniature e.p.s.p.s after tetanic preganglionic stimulations was inhibited by enkephalin. Acetylcholine potentials were not altered by enkephalin. These findings suggest that enkephalin reduces transmitter release. The experiments suggest that enkephalin may inhibit ganglionic transmission by both pre‐ and post‐synaptic actions in a mammalian parasympathetic ganglion.
Interactions between splanchnic and vagus nerves in the control of mean intragastric pressure in the ferret.
Authors: Andrews P L , Lawes I N
Published: December 2014

To determine whether splanchnic nerves relax the stomach by direct or indirect mechanisms, ramp inflations of the stomach, section and electrical stimulation of the vagus and greater splanchnic nerves, and step inflations of the duodenum were used. A high threshold, sustained inhibition of the gastric pressure response to ramp inflation was mediated by the vagus. Prior splanchnectomy increased vagal inhibition. The greater splanchnic nerves had no effect on gastric responses to inflation, although after vagotomy they were shown to be mediators of a low threshold, powerful but transient inhibition of the stomach. This was not dependent on intrinsic neurones with nicotinic receptors. Electrical stimulation of the greater splanchnic nerves produced a relaxation of the stomach, the magnitude of which was determined by resting pressure. Splanchnically mediated relaxation was not abolished by atropine, nor was it reduced by concurrent vagal stimulation. At submaximal levels of vagal stimulation the two nerves had a partially additive effective on relaxation. Duodenal inflation had an effect on intracorpus pressure similar to that of electrical stimulation of the greater splanchnic nerves on intragastric pressure. Reflex relaxation of the corpus evoked by duodenal distension was decreased by atropine but greatly increased by atropine coupled with vagotomy. These changes were caused by variations in resting pressure. It was concluded that the principal effect of splanchnic nerves on mean gastric pressure is direct and does not depend on inhibition of cholinergic neurones either centrally or peripherally. Evidence is presented for central interactions between the vagus and the greater splanchnic nerves in the anaesthetized ferret.
The force‐velocity relation of rat fast‐ and slow‐twitch muscles examined at different temperatures.
Authors: Ranatunga K W
Published: December 2014

The steady‐state force‐velocity relation was examined at temperatures between 35 and 10 degrees C in rat fast‐twitch (extensor digitorum longus, e.d.l.) and slow‐twitch (soleus) muscle preparations in vitro, with direct stimulation, and employing the isotonic release technique. The curvature of the force‐velocity relation increased with cooling in both muscles; the increase was more pronounced below 25 degrees C. The maximum shortening velocity of e.d.l. muscle decreased with a Q10 (temperature coefficient) of 1.8 in cooling from 35 to 25 degrees C; it decreased with a Q10 of 2.4 in cooling below 20 degrees C. The shortening velocity of slow muscle was more temperature sensitive. The Q10 values for soleus muscle were 2.0 at 35‐25 degrees C and 3.5 below 20 degrees C. The maximum rate of isometric tetanic tension rise had a temperature sensitivity similar to the maximum velocity of shortening in each muscle type.
Sensitivity of guinea‐pig hippocampal granule cell field potentials to hexoses in vitro: an effect on cell excitability?
Authors: Bachelard H S , Cox D W , Drower J
Published: December 2014

Evoked granule cell field potentials, and levels of tissue metabolites, in superfused guinea‐pig hippocampal slices have been studied in the presence of low glucose and an alternative glycolytic substrate (D‐fructose). The effects of glucose analogues (5‐thio‐D‐glucose, 2‐deoxy‐D‐glucose or 3‐O‐methyl‐D‐glucose) in the presence of glucose were also tested. Concentrations of glucose or fructose in excess of 2 mM and 10 mM respectively were required to maintain normal evoked activity. 5‐Thioglucose (15 mM) in the presence of 5 mM‐glucose decreased the amplitude of the population spike by 60% with little effect on population excitatory post‐synaptic potential (e.p.s.p.). Tissue levels of phosphocreatine and ATP were essentially unchanged under all conditions tested, with the exception of 10 mM‐fructose. The decrease in rates of lactate efflux from superfused tissue during and after superfusion with 3‐O‐methylglucose, 2‐deoxyglucose or 5‐thioglucose was found to be positively correlated with the extent of attenuation of field potentials. Analysis of the relationship between population spike amplitude and rates of rise of e.p.s.p., under conditions where field potentials were attenuated, showed that the population spike was always more sensitive to metabolic perturbation than was the e.p.s.p., thus indicating an effect on cell excitability. It is suggested that some aspect of non‐oxidative glucose metabolism is important in maintaining this granule cell excitability.
Autoradiography of benzodiazepine receptor binding in the central nervous system of the normal C57BL6J mouse.
Authors: Biscoe T J , Fry J P , Rickets C
Published: December 2014

[3H]flunitrazepam has been used as a photoaffinity label for the specific, clonazepam‐displaceable 1,4‐benzodiazepine binding sites in sections of normal C57BL6J mouse brain and spinal cord. Binding was visualized by light microscope autoradiography and quantified by a simple microdensitometric procedure. Specific flunitrazepam binding was seen to be highest in the colliculi, cerebral cortex, hippocampal formation, interpeduncular nucleus, mamillary body, hypothalamus, olfactory tubercle, and in the molecular layer and deep nuclei of the cerebellum. The distribution of specific flunitrazepam binding sites in mouse brain and spinal cord is discussed in terms of the known actions of the benzodiazepines.
Stretch‐activated single ion channel currents in tissue‐cultured embryonic chick skeletal muscle.
Authors: Guharay F , Sachs F
Published: December 2014

The membrane of tissue‐cultured chick pectoral muscle contains an ionic channel which is activated by membrane stretch. Nicotinic channels and Ca2+‐activated K+ channels are not affected by stretch. In 150 mM‐external K+ and 150 mM‐internal Na+ the channel has a conductance of 70 pS, linear current‐voltage relationship between ‐50 and ‐140 mV and a reversal potential of +30 mV. Kinetic analysis of single‐channel records indicates that there are one open (O) and three closed (C) states. The data can be fitted by the reaction scheme: C1‐C2‐C3‐O. Only the rate constant that governs the C1‐C2 transition (k1,2) is stretch‐sensitive. None of the rates are voltage‐sensitive. The rate constant k1,2 varies with the square of the tension as k1, 2 = k0 X e alpha T2, where alpha is a constant describing the sensitivity to stretch and T is the tension. A typical value of alpha is 0.08 (dyn cm‐1)‐2. Following exposure to cytochalasin B the channel becomes more sensitive to stretch. The stretch‐sensitivity constant, alpha, increases from 0.08 to 2.4 (dyn cm‐1)‐2. The probability of the channel being open is strongly dependent upon the extracellular K+ concentration. With a suction of 2 cmHg the probability increases from 0.004 in normal saline (5 mM‐K+) to 0.26 in 150 mM‐K+. The channel appears to gather force from a large area of membrane (greater than 3 X 10(5) A2), probably by a cytochalasin‐resistant cytoskeletal network.
Birefringence signal and early mechanical changes at normal and increased tonicities in frog skeletal muscle.
Authors: Oetliker H , Schümperli R A
Published: December 2014

Simultaneous measurements of the time course of early mechanical events and the early large birefringence signal were performed during activation of isolated frog skeletal muscle fibres bathed in iso‐ and hypertonic media. A piezo‐electric transducer was used which had a resonance frequency of 3.3 kHz and a sensitivity of 740 mV/mN (0.5 mV noise peak to peak) and a compliance of 0.6 mu/mN. The delay from stimulus onset to the onset of the birefringence signal was estimated to be 0.78 +/‐ 0.03 ms in normal Ringer solution at room temperature (20‐23 degrees C). The beginning of latency relaxation appeared subsequent to the birefringence signal after a delay of 0.36 +/‐ 0.03 ms. Increasing the tonicity retarded the time course of both birefringence signal and latency relaxation. In solutions of twofold greater tonicity an increase in tension (denoted pre‐relaxation contraction) was observed to precede latency relaxation. Pre‐relaxation contraction became more prominent with increasing tonicity and appeared to coincide with its onset with the onset of the birefringence signal. The pre‐relaxation contraction was shown not to be a stimulus artifact and was not reduced in amplitude by D 600 or calcium‐poor solutions. Lowering the temperature to 2.2 degrees C in normal Ringer solution delayed the onsets of the birefringence signal and latency relaxation, and increased the interval between the two signals but did not result in a tension increase before latency relaxation. The coincidence of the birefringence signal onset with the onset of pre‐relaxation contraction suggests a common aetiology. The aetiology remains speculative but seems to require hypertonicity for expression of the mechanical signal.
Mixed‐agonist action of excitatory amino acids on mouse spinal cord neurones under voltage clamp.
Authors: Mayer M L , Westbrook G L
Published: December 2014

Neurones from the ventral half of mouse embryo spinal cord were grown in tissue culture and voltage clamped with two micro‐electrodes. The current‐voltage relation of responses evoked by brief pressure applications of excitatory amino acids was examined over a membrane potential range of ‐100 to +70 mV. Three types of current‐voltage relation were observed. Responses to kainic and quisqualic acids were relatively linear within +/‐ 20 mV of the resting potential. N‐methyl‐D‐aspartate (NMDA) and L‐aspartic acid responses had a negative slope conductance at membrane potentials more negative than ‐30 mV. In contrast, over the same potential range the slope conductance of responses evoked by L‐glutamic and L‐homocysteic acids was close to zero. The membrane potential‐chord conductance relation of the ionic mechanism activated by excitatory amino acids, derived using the driving force for ionic current, showed two types of behaviour. The conductance linked to NMDA receptors was highly voltage sensitive and increased on depolarization; a much weaker voltage sensitivity was observed for responses evoked by kainic and quisqualic acids. L‐glutamic and L‐homocysteic acid responses behaved as though due to simultaneous activation of both NMDA and either kainate or quisqualate receptors. In the presence of the NMDA receptor antagonist (+/‐)‐2‐aminophosphonovaleric acid (2‐APV) the response to L‐glutamate became less voltage sensitive and resembled responses evoked by kainate or quisqualate. Simultaneous activation of both conductance mechanisms by mixtures of kainate and NMDA produced current‐voltage and membrane potential‐chord conductance relations similar to those of L‐glutamate. The voltage sensitivity of the L‐glutamate response was inversely related to the dose; for low doses of L‐glutamate the slope conductance of responses recorded near the resting potential was close to zero. However, larger doses of L‐glutamate evoked responses with a voltage sensitivity similar to that of kainate. We suggest that L‐glutamate acts as a mixed agonist at both NMDA and non‐NMDA receptors. This can explain the results of previous experiments that failed to demonstrate a membrane resistance change during L‐glutamate‐induced depolarizations.
Cortical projection of afferent information from tendon organs in the cat.
Authors: McIntyre A K , Proske U , Rawson J A
Published: December 2014

In cats anaesthetized with chloralose, evidence has been sought for the projection of information from tendon organs to the sensory receiving areas of the cerebral cortex. Selective stimulation of afferent fibres from tendon organs has been achieved by raising the threshold to electrical stimulation of the fibres from primary endings of muscle spindles. The method uses longitudinal vibration at 200‐250 Hz to elicit, over a period of 20 min, one impulse for each excursion of the vibrator from all of the spindles in the test muscle, soleus or medial gastrocnemius. The accumulated post‐spike positivities following passage of the impulses are thought to be responsible for the rise in threshold. Segmental monosynaptic reflex testing after a bout of vibration was used to confirm that the residual Group I volley no longer contained impulses from muscle spindles. The volley in response to stimulating the nerve of the test muscle was timed to facilitate the monosynaptic reflex of a synergist. Before vibration 5‐ to 10‐fold facilitation of reflex amplitude could be produced; however, after vibration, if all the spindle primary endings had been effectively engaged by the stimulus, no detectable facilitation remained. This test was found to be sensitive and reproducible. An afferent volley containing only activity of tendon organ afferents evoked small‐amplitude potentials from the post‐sigmoid gyrus of the contralateral pericruciate cortex. The field was highly localized and lay caudal to the main receiving area for activity from the sural nerve and from afferents of hip flexor muscles. Recordings with tungsten micro‐electrodes revealed that the surface‐evoked activity took origin in cellular discharges in the internal pyramidal layer of area 3a. Recent psychophysical experiments have provided evidence for a sense of muscle tension, as distinct from a sense of effort, and the tendon organ has been suggested as the likely receptor of origin. Our electrophysiological observations now provide a firm experimental basis for such a proposal.
Is the voluntary control of exercise in man necessary for the ventilatory response?
Authors: Adams L , Garlick J , Guz A , Murphy K , Semple S J
Published: December 2014

The ventilatory response to electrically induced exercise (EEL) was studied in eighteen normal subjects and compared with the response to performing the same exercise voluntarily (EV). EEL was produced by surface electrode stimulation of the quadriceps and hamstring muscles so as to cause a pushing movement at 1 HZ against a spring load; this produced no pain or discomfort. Matching of EV to EEL was achieved by subjects copying a tension signal recorded during EEL and displayed on a storage oscilloscope. There were no differences between the resting states measured before either form of exercise. The ventilatory response (change in ventilation as a ratio of the change in CO2 elimination) was similar in the two types of exercise. The increases in ventilation and CO2 elimination were greater with EEL. Small but significant increases in the gas exchange ratio and serum lactate were found for EEL but not for EV, suggesting an increase in anaerobic metabolism in EEL. End‐tidal PCO2 showed little change in either form of exercise. In some runs end‐tidal PCO2 rose, but insufficiently to account for the ventilatory response as judged by the response to inhaled CO2. In two subjects arterial blood samples showed small and inconsistent changes in both Pa,CO2 and PaO2 for EV and EEL. pH and base excess changes also were consistent with more anaerobiosis with EEL compared to EV. The first ten breaths of exercise were used to study the on transient. In EV, expiratory duration shortened and ventilation increased significantly on the first breath but CO2 elimination did not increase until the second breath; in EEL, these variables did not change significantly until the second breath. For the remainder of the on transient the pattern of the ventilatory response was similar for EV and EEL. By the end of the on transient both EV and EEL had reached approximately 80% of their final steady‐state values. These results suggest that a normal ventilatory response can occur in the absence of a drive to exercise from the cortex.
Interaction of inactivity and nerve breakdown products in the origin of acute denervation changes in rat skeletal muscle.
Authors: Cangiano A , Magherini P C , Pasino E , Pellegrino M , Risaliti R
Published: December 2014

The action of nerve breakdown products on innervated fibres of soleus and extensor digitorum longus muscles was investigated with the following procedures: partial denervation, sensory or sympathetic denervation, section of a previously transplanted foreign nerve. Each procedure was performed either in isolation or combined with chronic muscle inactivity obtained by blocking impulse conduction along the sciatic nerve. Silastic cuffs containing tetrodotoxin (TTX) and sodium chloride were utilized for the block. Partial denervation induced extrajunctional sensitivity to acetylcholine (ACh) and resistance to tetrodotoxin not only in the denervated but also in the innervated fibres. The effects in the innervated fibres were equal in magnitude to those in the denervated fibres, provided they were paralysed. The onset of the membrane changes was synchronous in the two classes of fibres and their amount correlated with the extent of partial denervation. If the innervated fibres were normally active, the membrane changes were still detectable, but considerably smaller than in the denervated fibres. Sensory denervation (removal of dorsal root ganglia L4 and L5) was followed by the development of moderate ACh supersensitivity and TTX resistance in chronically paralysed muscles. Furthermore, section of radicular nerves (total denervation, i.e. efferent plus afferent) induced larger membrane changes than those observed following section of ventral roots alone (efferent denervation). Sympathetic denervation was ineffective even when associated with chronic muscle paralysis. Section of a previously transplanted mixed nerve (superficial fibular) was ineffective if the soleus muscle was normally active, while it induced marked extrajunctional ACh sensitivity and TTX resistance when combined with chronic paralysis of the muscle. Section of a transplanted sensory nerve (sural) also induced extrajunctional membrane changes in paralysed soleus muscles, but their magnitude was much smaller than after section of mixed nerves. We conclude that products of nerve destruction, especially those of motor axons, induce membrane changes of striking magnitude when potentiated by muscle inactivity. Such an action may also explain the greater efficacy of denervation vs. pure inactivity, at least at early times after their onset.