bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of the milk ejection reflex in the rat.
Authors: Dyball R E , Leng G
Published: December 2014

Extracellular recordings were made from neurones in or near the supraoptic nucleus in suckled lactating rats under urethane anaesthesia to investigate the mechanism by which the firing of oxytocin cells is synchronized during reflex milk ejection. Cells synaptically driven but not antidromically activated by neural stalk stimulation, which thus probably receive an afferent input from supraoptic neurones, were classified as 'regular' or 'bursters' on the basis of their spontaneous electrical activity. The majority (twelve out of eighteen) of synaptically excited cells (o.d.+) were bursters and the majority of inhibited (o.d.‐) cells (eleven out of nineteen) were regular, but only one o.d.+ burster showed any change of activity (inhibition) before milk ejection. Putative oxytocin cells in suckled lactating rats showed a firing pattern between milk‐ejection bursts which could not be distinguished from that of putative oxytocin cells in male animals. The mode interspike interval between milk ejections was 47.1 +/‐ 3.1 ms (mean +/‐ S.E. of mean) compared with 47.3 +/‐ 3.3 ms in male rats, and fewer than 1.4% of interspike intervals were less than 20 ms in duration. By contrast, within milk‐ejection bursts 40% of interspike intervals were in the range 8‐20 ms. Short trains (10 or 20) of pulses applied to the neural stalk at regular (5 min) intervals, in an attempt to simulate the initial part of the milk ejection burst, failed to trigger bursts. In only 2 of 150 tests was the interval between train and milk‐ejection burst less than 10 s, and after the pulse train all but one cell showed reduced activity for 1‐3 s. The trains of pulses were however not without effect: they significantly (P less than 0.01) enhanced the chance of a milk‐ejection burst occurring within the next 2.5 min. Our observation that pulse trains do not trigger bursts suggests that local positive feed‐back mechanisms are not responsible for orchestrating the activation of oxytocin cells during the milk‐ejection reflex. Moreover, because spontaneous tiring pattern is the same in lactating and non‐lactating rats, we found no evidence that the anatomical changes in the synaptic organization within the supraoptic nuclei in lactation have any influence on the firing of oxytocin cells. It is likely, however, since pulse trains alter the timing of milk ejections, that oxytocin released locally in the region of the supraoptic nucleus can influence reflex milk ejection.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of airflow on mucus secretion into the trachea of the cat.
Authors: Peatfield A C , Richardson P S , Wells U M
Published: December 2014

We have investigated the effects of the passage of air and of instillation of hyperosmolal solutions in a segment of trachea of the pentobarbitone‐anaesthetized cat on the release of radiolabelled mucus glycoproteins (mucins) into that segment. Ambient air passed through the segment at 11 min‐1 increased the output of both 35S‐ and 3H‐labelled mucins. It also stimulated the output of mucins measured chemically. Passage of ambient air warmed to body temperature caused a similar effect on the output of radiolabelled mucins unless the air had also been saturated with water vapour at that temperature. Instillation of cold Krebs‐Henseleit solution into the tracheal segment had no effect on the release of radiolabelled mucins. The action of warmed dry air persisted after extrinsic nerves (sympathetic and parasympathetic) to the trachea had been cut. Hyperosmolal solutions placed in the tracheal segment also increased the output of both 35S‐ and 3H‐labelled mucins. We conclude that passage of ambient air through the trachea of the cat increases mucin output. This is probably by its drying action rather than by the mechanical disturbance from the flow or by cooling. The response might occur during eupnoea but is more likely to be important during hyperpnoea such as occurs during exercise. We discuss the relevance of the response to exercise‐induced asthma.
Gamma loop contributing to maximal voluntary contractions in man.
Authors: Hagbarth K E , Kunesch E J , Nordin M , Schmidt R , Wallin E U
Published: December 2014

A local anaesthetic drug was injected around the peroneal nerve in healthy subjects in order to investigate whether the resulting loss in foot dorsiflexion power in part depended on a gamma‐fibre block preventing 'internal' activation of spindle end‐organs and thereby depriving the alpha‐motoneurones of an excitatory spindle inflow during contraction. The motor outcome of maximal dorsiflexion efforts was assessed by measuring firing rates of individual motor units in the anterior tibial (t.a.) muscle, mean voltage e.m.g. from the pretibial muscles, dorsiflexion force and range of voluntary foot dorsiflexion movements. The tests were performed with and without peripheral conditioning stimuli, such as agonist or antagonist muscle vibration or imposed stretch of the contracting muscles. As compared to control values of t.a. motor unit firing rates in maximal isometric voluntary contractions, the firing rates were lower and more irregular during maximal dorsiflexion efforts performed during subtotal peroneal nerve blocks. During the development of paresis a gradual reduction of motor unit firing rates was observed before the units ceased responding to the voluntary commands. This change in motor unit behaviour was accompanied by a reduction of the mean voltage e.m.g. activity in the pretibial muscles. At a given stage of anaesthesia the e.m.g. responses to maximal voluntary efforts were more affected than the responses evoked by electric nerve stimuli delivered proximal to the block, indicating that impaired impulse transmission in alpha motor fibres was not the sole cause of the paresis. The inability to generate high and regular motor unit firing rates during peroneal nerve blocks was accentuated by vibration applied over the antagonistic calf muscles. By contrast, in eight out of ten experiments agonist stretch or vibration caused an enhancement of motor unit firing during the maximal force tasks. The reverse effects of agonist and antagonist vibration on the ability to activate the paretic muscles were evidenced also by alterations induced in mean voltage e.m.g. activity, dorsiflexion force and range of dorsiflexion movements. The autogenetic excitatory and the reciprocal inhibitory effects of muscle vibration rose in strength as the vibration frequency was raised from 90 to 165 Hz. Reflex effects on maximal voluntary contraction strength similar to those observed during partial nerve blocks were not seen under normal conditions when the nerve supply was intact.(ABSTRACT TRUNCATED AT 400 WORDS)
Tetrodotoxin‐sensitive and ‐insensitive relaxations in the rat oesophageal tunica muscularis mucosae.
Authors: Akbarali H I , Bieger D , Triggle C R
Published: December 2014

1. Relaxation responses were produced by vagal and field stimulation, respectively, of the whole oesophagus preparation from the rat and of the isolated tunica muscularis mucosae (t.m.m.) preparation from the rat. These relaxation responses persisted in the presence of antagonists of histamine, serotonin, noradrenaline and acetylcholine. 2. Unlike vagally evoked relaxation, that evoked by low‐frequency field stimulation, i.e. field‐stimulated relaxation (f.s.r.) was generally resistant to tetrodotoxin (TTX). 3. Both types of relaxations exhibited remarkable temperature sensitivity and were abolished by lowering the bath temperature from 37 to 28 degrees C. 4. TTX‐resistant relaxations were also produced by scorpion (Leiurus quinquestriatus) venom, the calcium ionophore, A23187 (calimycin) and by increasing the extracellular potassium by 2 mM. The failure of these agents to inhibit f.s.r. is inconsistent with a releasing and/or depleting action on any endogenous mediator. 5. Relaxations produced by vasoactive intestinal peptide (VIP) could be blocked by alpha‐chymotrypsin which, however, failed to abolish f.s.r., suggesting that VIP is not the mediator of f.s.r. 6. F.s.r. was completely blocked by the calcium channel antagonists, verapamil (10(‐6) M), nifedipine (10(‐7) M), and by magnesium (20 mM). 7. Our results indicate that TTX‐insensitive relaxations in the isolated t.m.m. are dependent upon extracellular calcium, are due to activation of potential‐operated calcium channels and are not mediated by VIP.
The order of addition of sodium and release of potassium at the inside of the sodium pump of the human red cell.
Authors: Sachs J R
Published: December 2014

1. Inhibition of Na,K‐adenosine 5'‐triphosphatase (Na,K‐ATPase) activity of human red cell membranes by vanadate rapidly reaches a steady‐state level and is rapidly reversible. 2. In K‐free cells vanadate inhibits the Na‐K exchange at low concentrations, the uncoupled Na efflux at higher concentrations, and has little effect on the Na‐Na exchange even at high concentrations. Increasing intracellular K concentration increases the sensitivity of the Na‐Na exchange to vanadate. 3. Vanadate inhibition of the Na‐K exchange is uncompetitive with extracellular K and inhibition of the K‐K exchange is partially uncompetitive with intracellular K. Na‐Li exchange is less sensitive to vanadate inhibition than Na‐K exchange. The results indicate that vanadate inhibits by combining with an enzyme form which occurs between the addition of K at the outside and its release to the inside. 4. Inhibition by vanadate is non‐competitive with Na at low adenosine 5'‐triphosphate (ATP) concentrations and high concentrations of K. At high ATP and low K, vanadate inhibition becomes partially uncompetitive with Na. At high or at low ATP and in the absence of cell K, inhibition is strictly uncompetitive with cell Na. 5. These results are consistent with a ping‐pong model for the reaction mechanism of the Na pump, but they are not consistent with a sequential mechanism or with a branched‐chain mechanism in which Na adds after the release of K in one branch and before in the other.
Stimulation of raphe (obscurus) nucleus causes long‐term potentiation of phrenic nerve activity in cat.
Authors: Millhorn D E
Published: December 2014

1. The respiratory response, measured as integrated phrenic nerve activity, during and for up to an hour following 10 min of continuous electrical stimulation of raphe obscurus was quantitated in anaesthetized, artificially ventilated cats whose carotid sinus nerves and vagus nerves had been cut. End‐tidal PCO2 and body temperature were kept constant with servocontrollers. 2. Stimulation of raphe obscurus caused a significant increase in both phrenic tidal activity and respiratory frequency that persisted following cessation of the stimulus. This persistent facilitation is referred to as 'long‐term potentiation' of respiration. 3. Control stimulations in the parenchyma of the medulla oblongata failed to stimulate respiration and cause the long‐term potentiation. 4. Both the direct facilitatory effects of raphe obscurus stimulation on phrenic nerve activity and the long‐term potentiation of respiration following the stimulus were prevented by pre‐treating cats with methysergide, a serotonin receptor antagonist. 5. The results are discussed in terms of the raphe obscurus being the potential source of the long‐term potentiation of respiration that occurs following stimulation of carotid body afferents (Millhorn, Eldridge & Waldrop, 1980a, b).
A permissive role for the vagus nerves in the genesis of antro‐antral reflexes in the anaesthetized ferret.
Authors: Grundy D , Hutson D , Scratcherd T
Published: December 2014

1. The role of the vagus nerves in the genesis of antro‐antral reflexes was investigated in the urethane‐anaesthetized, splanchnectomized ferret. 2. Antral distension stimulated antral contractions with a threshold volume of 3.5 +/‐ 0.9 ml (corresponding to an intra‐antral pressure of 0.27 +/‐ 0.11 kPa) by a vagal‐dependent mechanism as indicated by the attenuated response seen during vagal blockade by cooling. Atropine (1 mg/kg) abolished the antral response to distension. 3. In vagotomized animals, close arterial infusions of acetylcholine at a dose sufficient to return antral motility to basal levels led to the reappearance of the reflex. Low‐frequency electrical stimulation of the preganglionic vagal neurones had a similar effect. These effects were also abolished by atropine (1 mg/kg). 4. Hexamethonium (10‐25 mg/kg) suppressed the potentiating effect of acetylcholine, indicating a ganglionic site of action. The attenuated response to antral distension seen in vagotomized animals in the absence of exogenous acetylcholine or electrical vagal stimulation was not sensitive to hexamethonium but abolished by atropine (1 mg/kg). 5. The results are consistent with the vagus performing a permissive role in the genesis of antro‐antral reflexes mediated through local enteric pathways.
Steady‐state analysis of ion fluxes in Necturus gall‐bladder epithelial cells.
Authors: Hill A E , Hill B S
Published: December 2014

1. The steady‐state fluxes of Na, K and Cl ions have been measured in Necturus gall‐bladder epithelium by a technique that involves labelling the cells with tracer ions from the mucosal bath only, whilst the serosa is kept at low specific activity. After removing tracer, the efflux is followed into the serosal bath, revealing two exponential components. 2. The time constant of the fast component lies between 0.03 and 0.04 s‐1 and corresponds to that of the extracellular space. The slow component closely matches the cellular efflux, with constants which lie between 0.14 and 0.46 X 10(‐2) s‐1. 3. Full unstirred‐layer calculations have been performed to determine the specific activities in the mucosal solution, the cell and the corium (subepithelium). These involved measuring the diffusion coefficients of Na and Cl in the isolated corium: they are restricted by factors of 0.17 and 0.11. 4. The partial flux equations for this double‐membrane system have been solved to obtain the cellular fluxes for all three ions. The results indicate that: (i) the net transcellular Na flux is 190 pmol cm‐2 s‐1, equivalent to the transepithelial salt flux during fluid secretion; (ii) the net transcellular K flux is effectively zero because this ion recirculates across the serosal membrane; (iii) the net transcellular Cl flux is 27 pmol cm‐2 s‐1, or 15% of the net transepithelial salt flux. 5. The permeability of the paracellular pathway to Cl is 1.65 X 10(‐5) cm s‐1 and the available driving forces will allow a maximum net electrodiffusive Cl transport of 10% through the shunt pathway. 6. 1:1 coupling of Na and Cl net fluxes at the mucosal membrane of this epithelium cannot be present, and processes other than simple electrodiffussion are required to effect net Cl transport by another route. 7. The serosal fluxes of K and Cl do not obey the flux‐ratio equation. A component of these fluxes must be present which is neither active (pumped) nor passive (electrodiffusive and independent). If they are symmetrical in the steady state then the ratio of these exchange fluxes lies between 2:1 and 3:1 depending upon the size of the pump flux. They support the view that a mode of coupled K and Cl transport may be operating at the basolateral membrane of these cells.
Effects of impulse blockade on the contractile properties of rat skeletal muscle.
Authors: Kowalchuk N , McComas A
Published: December 2014

1. Pressure was used to produce a localized block of impulse conduction in motor nerve fibres supplying rat plantaris and soleus muscles. After 1 week of inactivity both muscles exhibited marked atrophy of type I and type II muscle fibres. 2. In treated plantaris and soleus muscles the specific tetanic tensions were reduced to approximately half those of untreated control muscles; the specific twitch tensions were unchanged. The fall in specific tetanic tension in the nerve‐blocked muscles was not associated with impaired excitation of muscle fibres during repetitive stimulation. 3. In nerve‐blocked plantaris muscles the contraction and half‐relaxation times became significantly prolonged whereas no change could be demonstrated in similarly treated soleus muscles. In both muscles the maximum rates of tetanic tension development increased following nerve block. 4. It is concluded that, in the rat, most of the changes in contractile properties and in muscle fibre size which follow denervation may be attributed to disuse rather than to interruption of axoplasmic transport.
Excitatory actions of single impulses in single hair follicle afferent fibres on spinocervical tract neurones in the cat.
Authors: Brown A G , Koerber H R , Noble R
Published: December 2014

1. In cats under chloralose anaesthesia single dorsal root ganglion cells with axons innervating hair follicles were stimulated intracellularly to produce single impulses. At the same time single spinocervical tract (s.c.t.) neurones were recorded extracellularly, from their axons in the upper lumbar cord. 2. When the receptive field of the afferent fibre was contained within the impulse firing zone of the s.c.t. cell, a single afferent impulse increased the probability of firing of the neurone. In thirty‐nine pairs of units, where the afferent fibre had a group II conduction velocity, coupling was very efficient and for seventeen pairs the single afferent impulse produced one or more impulses in the s.c.t. cell in at least 90% of trials. The mean number of impulses evoked in s.c.t. cells by a single group II afferent impulse was 1.47. The latencies of the impulses ranged from 1.5 to 14.0 ms, with times to peak and total durations of 2.5‐17.5 ms and 4.5‐28.0 ms respectively. For two pairs of units where the afferent fibre had a group III conduction velocity the effectiveness of single afferent impulses was much less and the latencies, but not the durations, of the impulses were longer (12 and 17 ms). 3. When the receptive field of the hair follicle afferent fibre was outside, but close to, the firing zone of the s.c.t. neurone there was no indication that single afferent impulses affected the probability of neuronal discharge for thirteen of fifteen pairs of units. Weak excitation was observed in two pairs and this was clear only when two or more afferent impulses were employed. 4. There was a tendency for hair follicle afferent fibres with their receptive fields at or near the centre of the s.c.t. cell's firing zone to be most effective, producing shorter latency responses with more impulses at higher frequencies. When the afferent's field was peripherally located in the s.c.t. neurone's firing zone there was a wide range of responses but these included those with the longest latencies and very few impulses. 5. The results are discussed with reference to previous work on the spinocervical tract and to the known actions of single impulses on other neuronal types. Suggestions are made for the possible excitatory neuronal circuits linking hair follicle afferent fibres to the s.c.t. neurones.
Inhibition of reticulo‐ruminal motility by volatile fatty acids and lactic acid in sheep.
Authors: Gregory P C
Published: December 2014

1. A study was made of the influence on reticulo‐ruminal motility, recorded by electromyography, of ruminal infusions of volatile fatty acids (VFAs) and lactic acid in twenty‐four sheep maintained by intragastric infusion of a complete liquid diet, in three sheep fed grass pellets, and in nine chronically vagotomized sheep; abomasal and duodenal infusions of VFA and lactic acid were tested in five sheep fed grass pellets. 2. Ruminal infusions of VFAs and lactic acid progressively inhibited the amplitude of the reticulo‐ruminal contractions. In many experiments there was no effect on contraction frequency until the cessation of all reticulo‐ruminal contractions at which point the maximal concentration of VFA recorded in the abomasum was 28 mM, and that of lactic acid was 20 mM. 3. The concentrations of undissociated VFAs causing cessation of reticulo‐ruminal contractions in the vagus‐intact sheep were very similar to the concentrations causing abolition of the organized intrinsic motility of the chronically vagotomized sheep. 4. The inhibition of reticulo‐ruminal motility with ruminal infusions of mixtures of VFAs and of lactic acid together with VFAs could largely be explained by the sum of the effects of the individual acids present. 5. Abomasal infusion of VFA or lactic acid inhibited the amplitude of ruminal, especially primary ruminal, contractions at concentrations of undissociated acid of 60 mM and above and increased the frequency of reticulum and primary ruminal contractions at about 80 mM. 6. Duodenal infusion of VFAs and lactic acid (100 mM, 5 ml/min) strongly inhibited abomasal motility without affecting reticulo‐ruminal motility, and at a higher rate (100 mM, 10 ml/min) abolished motility and inhibited both the amplitude and frequency of reticulo‐ruminal contractions. 7. It is concluded that the initial inhibition of reticulo‐ruminal motility in ruminal acidosis is unlikely to involve any significant influence from duodenal, or abomasal receptors. The final cessation of reticulo‐ruminal motility with ruminal acidosis could involve local effects of VFAs in the reticulo‐rumen as well as through excitation of acid‐sensitive reticulo‐ruminal receptors.
Supraspinal morphine and descending inhibitions acting on the dorsal horn of the rat.
Authors: Dickenson A H , Le Bars D
Published: December 2014

1. Recordings were made from thirty‐nine convergent neurones in the lumbar enlargement of the rat spinal cord. These neurones were activated by both innocuous and noxious stimuli applied to their excitatory receptive fields located on the extremity of the ipsilateral hind paw. Transcutaneous application of suprathreshold 2 ms square‐wave pulses to the centre of the receptive field resulted in responses to A‐ and C‐fibre activation being observed; a mean of 18.8 +/‐ 1.8 C‐fibre latency spikes was evoked per stimulus. This type of response was inhibited by applying noxious conditioning stimuli to heterotopic body areas; immersing the tail in a 52 degrees C water‐bath caused a mean 54.5 +/‐ 2.3% inhibition of the C‐fibre‐evoked response; such inhibitory processes have been termed diffuse noxious inhibitory controls (d.n.i.c.). 2. The effects of microinjections of morphine (5 micrograms; 0.2 microliter) on both the unconditioned C‐fibre‐evoked response and inhibitory processes triggered from the tail were investigated in an attempt to answer two questions: (a) does morphine increase tonic descending inhibitory processes and (b) what are the effects of morphine on descending inhibitory processes triggered by noxious stimuli? 3. The predominant effect of periaqueductal grey matter (p.a.g.) morphine on the C‐fibre‐evoked responses was a facilitation: 51% of cells had their C‐fibre‐evoked responses increased by morphine (by roughly 50%); 31% of cells were not influenced while the remaining 18% of units were depressed; however the cells classified as depressed were only marginally so. No clear relationships were found either between the microinjection sites in the p.a.g. and their corresponding effects or between the number of C‐fibre‐spikes evoked in the control sequences and the subsequent effect of morphine. 4. While d.n.i.c. was not altered by morphine in 56% of cases, it was clearly reduced in the remaining cells. The effects were immediate but peaked at 40 min following the microinjection (a mean 77% reduction) and then returned towards control values. All but three of the corresponding microinjection sites were such as to include the medio‐ventral p.a.g. including the nucleus raphé dorsalis. In contrast none of the cases where d.n.i.c. was unaltered included microinjection sites in this region. 5. No relationship was found between the changes in d.n.i.c. and the number of spikes evoked in the control sequences, or the changes in the C‐fibre responses. 6. Autoradiographic controls using [3H]morphine showed a large diffusion of the drug within an area of about 0.75 mm around the tip of the cannula.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of glucose on insulin release and ion movements in isolated pancreatic islets of rats in old age.
Authors: Ammon H P , Fahmy A , Mark M , Wahl M A , Youssif N
Published: December 2014

1. The effect of glucose on 86Rb+ efflux, 45Ca2+ net uptake and insulin secretion of pancreatic islets from 3‐ and 24‐month‐old rats was studied. 2. Raising the glucose concentration from 3 to 5.6 and 16.7 mM had no effect on 86Rb+ efflux from islets of 24‐month‐old male rats whereas that from 24‐month‐old female rats was decreased. 3. At 16.7 mM‐glucose, net uptake of 45Ca2+ was significantly diminished in islets of 24‐month‐old rats compared to islets of 3‐month‐old rats. 4. In the presence of 16.7 mM‐glucose, islets of 24‐month‐old rats exhibited only 60‐70% of the insulin release obtained with islets from 3‐month‐old rats. 5. Neither net uptake of 45Ca2+ nor insulin secretion appear to differ between the sexes. 6. These data suggest that the decreased insulin secretory response to glucose during old age is due, at least in part, to inadequate inhibition of K+ efflux and diminished net uptake of Ca2+.
Respiratory sinus arrhythmia in new‐born infants.
Authors: Hathorn M K
Published: December 2014

1. Ventilation was measured in eleven healthy term infants during both quiet and active sleep, using the trunk plethysmograph, and instantaneous heart rate was derived from the electrocardiogram. Variations in individual respiratory and cardiac cycles were compared in each sleep state, and cross‐correlations between ventilation and heart rate were used in the analysis of the data. 2. It was found that heart rate and respiratory rate were higher and more variable during active than during quiet sleep, with a small reduction in tidal volume. 3. Cross‐correlations showed that respiratory sinus arrhythmia was present in both sleep states, but was more marked during quiet sleep. 4. Running cross‐correlations using a 5 s window showed that phase relationships between ventilation and heart rate, were, on the whole, stable during quiet sleep, but markedly unstable during active sleep. 5. It is concluded that in the investigation of respiratory sinus arrhythmia in the new‐born, it is important to take account of sleep state, the methods of measuring ventilation and heart rate, and to use analytical techniques suited to the specific purpose of the study. 6. Respiratory sinus arrhythmia is considered to be due to an interaction between systems controlling breathing and those controlling the cardiovascular system, and that this interaction is affected by sleep state.
Water deprivation: effects on fluid and electrolyte handling and plasma biochemistry in Long‐Evans and Brattleboro rats.
Authors: Bennett T , Gardiner S M
Published: December 2014

1. Intakes and urine outputs of fluid and electrolytes were measured before, during and after water deprivation in normal rats (Long‐Evans strain) and in vasopressin‐deficient rats (Brattleboro strain). 2. In a parallel experiment it was confirmed that the water‐deprivation schedule used (Long‐Evans rats 53 h, Brattleboro rats 14 h), and previously shown to cause similar percentage reductions in plasma volumes in the two strains, did produce more marked hypernatraemia and hyperosmolality and a greater percentage reduction in body weight in Brattleboro than in Long‐Evans rats. 3. In Long‐Evans rats, water deprivation caused a gradual reduction in urine output, a reduction in food intake and, during the first 24 h, increases in Na+ and K+ output. In Brattleboro rats, the reduction in urine output was more pronounced, but despite this total water losses were greater than from Long‐Evans rats. Brattleboro rats showed a greater reduction in food intake. Their urinary Na+ and K+ losses were elevated during the first 9 h of water deprivation; thereafter these variables fell but remained above the level of intake. 4. The cumulative Na+ losses during water deprivation were similar in the two strains but the cumulative K+ losses in the Brattleboro rats were greater than in the Long‐Evans rats. Thus the relative hypernatraemia and hyperkalaemia in water‐deprived Brattleboro rats compared to water‐deprived Long‐Evans rats cannot be explained simply on the basis of differences in renal fluid and electrolyte handling. 5. There were significant increases in plasma angiotensin II and aldosterone levels at the end of the water deprivation periods in both strains of rat, and after the drinking water was returned there was a marked anti‐natriuresis consistent with an expression of one of the renal actions of aldosterone.
Influence of chloride concentration and pH on the 36Cl efflux from depolarized skeletal muscle of Rana temporaria.
Authors: Skydsgaard J M
Published: December 2014

1. 36Cl‐ efflux rates were measured in depolarized fibre bundles (predominantly fast fibres) from m. semitendinosus of Rana temporaria in order to investigate the influence of chloride concentration (20‐400 mM) and external pH (pHo, 5.5‐11.6) on chloride self‐exchange. Usually, the bundles were depolarized to a membrane potential of virtually zero ([Cl‐]i = [Cl‐]o = [Cl‐]) in 140 mM‐K+ and 20 mM‐Cl‐ combined with either 60 mM‐SO4(2‐) (+52 mM‐sucrose) or 120 mM‐methyl sulphate, gluconate or glucuronate. Various values of [Cl‐] were obtained by adding KCl to the medium, keeping constant the concentration of relatively impermeant solutes and thus the fibre volume. 2. The chloride permeability, PCl, at pH 7.5 decreased with increasing [Cl‐] above 50 mM. At [Cl‐] less than 50 mM, PCl was about 4 X 10(‐6) cm s‐1. 3. PCl at pHo 7.5 and 5.6 was a hyperbolic function of [Cl‐1] (greater than or equal to 50 mM), consistent with saturation kinetics of chloride self‐exchange. 4. Methyl sulphate inhibited chloride self‐exchange and may enter depolarized fibre membranes slowly. Comparison of PCl estimates in SO4(2‐), gluconate, and glucuronate suggested that SO4(2‐) and gluconate may interfere with chloride self‐exchange at low [Cl‐], and that glucuronate interferes the least. 5. A change from chloride equilibrium to an inward KCl gradient increased the 36Cl‐ efflux rate in acid media (pH less than 6.5) and decreased the efflux rate at pHo greater than or equal to 7. The effects were not due to changes of membrane potential and demonstrate a change of transport mode consistent with single‐filing at high pH and dominant exchange diffusion at low pH. This result makes interpretation of the saturation kinetics difficult. 6. At constant [Cl‐], PCl showed a bell‐shaped dependence on pHo with a maximum around pH 8.5. The decrease of chloride permeability as the pH is decreased below 8.5 showed an apparent pK of about 7. PCl fell at very alkaline pH with an apparent pK of about 10. 7. The results are in agreement with previous observations of an external pH‐sensitive control of PCl (pK approximately 7) and suggest that, in conditions close to chloride equilibrium, this control includes a transition between a dominant conductive channel conformation at high pH and a dominant non‐conductive conformation at low pH.(ABSTRACT TRUNCATED AT 400 WORDS)
Inhibition of monosynaptic reflexes in the human lower limb.
Authors: Iles J F , Roberts R C
Published: December 2014

1. Presynaptic inhibition of muscle spindle Ia afferents by afferents from the same and other muscles has been studied in the human lower limb. The experiments have utilized conditioning of test monosynaptic reflexes by vibration of both the test and other muscles. 2. The pattern of inhibition invariably includes autogenetic actions. 3. There are powerful effects from flexor to extensor Ia afferents. Actions from flexor to flexor, and from extensor to extensor, are weaker. Actions from extensors to flexors are very weak. 4. The strength of presynaptic inhibition from one muscle type to another weakens as the muscles considered become more anatomically distant. 5. The inhibition studied both by vibration and by electrical conditioning stimulation of nerves becomes weaker during voluntary isometric contraction of the test muscle. It is strongest at rest and during antagonist contraction. 6. Evidence is provided suggesting that descending control is the primary cause of this modulation of inhibition during contraction. 7. Stimulation of afferents in cutaneous nerves reduces group I presynaptic inhibition of Ia afferents.
Paracellular ionic and transcellular water diffusions across rabbit corneal endothelium.
Authors: Hodson S A , Wigham C G
Published: December 2014

1. Corneal endothelial cell membrane electrical resistance is estimated at about 400 M omega by using intracellular micro‐electrodes. 2. If all ion diffusion across the endothelium were transcellular, electrical resistance of the endothelial monolayer would be about 1300 omega cm2, as there are about 3000 cells mm‐2. 3. Measured endothelial monolayer resistance is 12.7 +/‐ 0.8 omega cm2 (mean +/‐ S.E., n = 6), which indicates that about 99% of ion diffusion does not cross the transcellular pathway, but must pass through the paracellular route. Arguments are presented which suggest that the proportion may be even higher. 4. Endothelial passive ion permeabilities are about the same as corneal stromal passive ion permeabilities. 5. Stromal water diffusional permeability is about the same as stromal ion permeability, after allowance is made for free diffusion coefficients. In contrast, endothelial water diffusional permeability is so high as to be unmeasurable. 6. It is concluded that ions diffuse across the corneal endothelium through the paracellular route, and that water diffuses across the endothelium mainly through the transcellular route.
The apparent reflexion coefficient of the leaky corneal endothelium to sodium chloride is about one in the rabbit.
Authors: Hodson S A , Lawton D M
Published: December 2014

1. Rabbit corneal thickness changes were measured after some of the NaCl in the bathing Ringer solution was substituted by a neutral sugar. 2. The response had three phases which could be closely modelled by three exponentials of different amplitudes and rate constants, originating from the time of the substitution. 3. The first, fastest, phase was interpreted as being driven by the pure osmotic pressure difference developed across the corneal endothelium by the difference between the removed NaCl and the added sugar in the bathing Ringer solution; the second was driven by the diffusion of NaCl out of the stroma; and the third, slowest, phase was driven by the diffusion of the added sugar into the stroma. 4. Consistent with the interpretation, only the third, slowest, phase had its rate constant dependent upon the nature of the substituting neutral sugar. 5. The amplitude of the pure osmotic phase was a linear function of the added sugar. Its amplitude was zero when an equal osmolarity of sugar was substituted for NaCl. 6. It was concluded that the reflexion coefficient of rabbit corneal endothelium to NaCl is the same as that to sucrose, raffinose and stachyose, i.e. about 1. 7. The calculated hydraulic conductivity of the endothelium plus stroma was about the same as that of stroma alone, and it was concluded that the hydraulic conductivity of corneal endothelium is large compared to corneal stroma. 8. It is proposed that most of the hydraulic flow in response to osmotic gradients passes through the cells, whereas salt diffuses through the paracellular route, resulting in an apparent reflexion coefficient of 1. 9. Thus, corneal endothelium is a 'leaky' (12 omega cm2) salt‐permeable epithelium and, according to the present study, simultaneously a semi‐permeable membrane. To resolve the terminology, we suggest the term 'bi‐permeable' for such epithelia which have a high salt permeability but such a very high water permeability as to give apparent reflexion coefficients of 1.
The role of N‐methylaspartate receptors in mediating responses of rat and cat spinal neurones to defined sensory stimuli.
Authors: Headley P M , Parsons C G , West D C
Published: December 2014

1. Single‐cell recordings were made from neurones in various spinal laminae in anaesthetized or decerebrated, spinalized or intact rats and cats. Cells were activated by controlled peripheral sensory stimuli which mimicked natural conditions and with some cells also by micro‐electrophoretically administered excitatory amino acid analogues. Such responses were tested with amino acid antagonists administered both micro‐electrophoretically and intravenously. 2. With cells in the dorsal horn, the dissociative anaesthetic ketamine, administered either micro‐electrophoretically or intravenously at doses which selectively reduce responses to N‐methylaspartate, had no consistent effect on any of the sensory responses examined. 3. The non‐selective amino acid antagonist cis‐2,3‐piperidine dicarboxylate was somewhat more effective at reducing sensory responses. 4. With motoneurones, intravenous N‐methylaspartate‐blocking doses of ketamine consistently reduced nociceptive responses. Non‐nociceptive responses were less affected. 5. With ventral horn interneurones, intravenous but not micro‐electrophoretic ketamine reduced nociceptive responses on about half the cells tested. 6. These results are interpreted in terms of the physiological role of the N‐methylaspartate class of excitatory amino acid receptor in mediating responses in the ventral but not dorsal horn of the spinal cord to peripheral somatic stimuli.
Anterior pretectal stimulation alters the responses of spinal dorsal horn neurones to cutaneous stimulation in the rat.
Authors: Rees H , Roberts M H
Published: December 2014

1. The behavioural effects of stimulating sites in the anterior pretectal nucleus (a.p.t.n.) were studied in unanaesthetized rats; 1‐2 weeks later these rats were anaesthetized with Fluothane and the effects of similar electrical stimulation determined on the responses of spinal neurones to cutaneous stimuli. 2. Stimulation of the a.p.t.n. for 15 s with 35 microA r.m.s. sine‐wave current inhibited the tail‐flick response to noxious heat of unanaesthetized animals for up to 1 h. 3. Stimulation of the same sites in anaesthetized rats inhibited the responses to noxious heat of forty‐two multireceptive and two high‐threshold neurones located deep in the spinal dorsal horn. 4. The high‐threshold responses of seven cells were unaffected or slightly potentiated by pretectal stimulation. These seven cells were all recorded from the dorsal margin of the dorsal horn, were not multireceptive neurones and could be made to discharge only by water above 50 degrees C. 5. The responses of twelve multireceptive cells to low‐threshold stimulation were not affected by pretectal stimulation. All these cells were recorded from deep within the dorsal horn. 6. On ten occasions, cells deep in the dorsal horn were identified as projection neurones which were driven antidromically by high‐frequency (300 Hz) stimulation of the contralateral anterolateral tract at cervical levels. The high‐threshold responses of all these cells were reduced by pretectal stimulation. No cells were driven antidromically by pretectal stimulation. 7. Ipsilateral lesions of the dorsolateral funiculus abolished the inhibitory effects of prectectal stimulation. Lesions of the dorsal columns were without effect. 8. It is concluded that stimulation of the a.p.t.n. inhibits the tail‐flick reflex of unanaesthetized rats and inhibits the high‐threshold discharge of deep dorsal horn cells to cutaneous stimuli in anaesthetized rats. Cells recorded from the dorsal margin of the dorsal horn are not affected. The inhibition is mediated via the dorsolateral funiculus and affects cells which project rostrally in the contralateral anterolateral funiculus.
Dynamics of medullary hydrogen ion and respiratory responses to square‐wave change of arterial carbon dioxide in cats.
Authors: Eldridge F L , Kiley J P , Paydarfar D
Published: December 2014

1. The dynamics of changes of medullary extracellular fluid (ECF) hydrogen ion concentration ([H+]) and respiration, measured as integrated phrenic nerve activity, were determined in anaesthetized, paralysed, vagotomized and glomectomized cats. ECF [H+] was measured directly by means of a small (2 mm diameter) glass pH electrode placed on the ventral surface of the medulla. The variables were measured continuously after a step change of arterial PCO2 produced by abruptly starting or stopping an infusion of hypercapnic fluid into the aortic arch. 2. Alteration of pH in the descending thoracic aorta at the onset or offset of infusion was complete within 1.5 s after the change began, indicating that it was nearly square wave in form. 3. In sixteen experiments, ECF [H+] began to fall within 2 s of offset of infusion, reflecting aortic‐medullary circulation time. Thereafter, ECF [H+] decreased to a stable level over the next 5 min; the curve describing the decrease consisted of two exponential functions, one with a time constant (tau) of 9.5 +/‐ 0.6 s and a second with a tau of 53 +/‐ 3 s. 4. We interpret the findings at the offset of CO2 infusion in terms of CO2 wash‐out from the medullary ECF. The slow function is associated with wash‐out during stable medullary blood flow that develops after 1 min. The early fast function is associated with the decreasing medullary blood flow that occurs during the first minute after change from arterial hypercapnia to normocapnia. 5. We have estimated medullary blood flow using a mathematical model incorporating the two functions. The values obtained are consistent with those in the literature where other methods have been used. Changes of blood flow following the step change of CO2 are fairly rapid, half of the response occurring in 13 s. 6. The change of respiratory activity lags the change of stimulus expressed by [H+], throughout the recovery period and respiration requires up to 8 min to reach a stable level. We attribute this slow response to slow central neural respiratory dynamics, the respiratory after‐discharge.
Voltage‐clamp analysis of a crayfish rectifying synapse.
Authors: Giaume C , Kado R T , Korn H
Published: December 2014

1. The rectifying crayfish giant motor synapse has been studied in the second abdominal ganglion, using the double‐voltage‐clamp technique which allowed direct measurements of junctional current at various fixed transjunctional potentials. 2. The transjunctional potential (Vj), defined as the difference between the voltages recorded in the lateral giant axon and the giant motor fibre, was varied from ‐70 to +50 mV, the minimum and maximum junctional chord conductances (gmin and gmax, respectively) were found to be 1.2 +/‐ 1.3 microS (n = 10) and 22.9 +/‐ 6.3 microS (n = 10), respectively. 3. For a given Vj, changes in the lateral giant axon or giant motor fibre membrane potential over a range of +/‐ 30 mV around their resting levels did not influence the junctional permeability (gj), indicating that the inside‐outside potential of the junctional channel does not control gj. 4. Therefore, the steady‐state junctional chord conductances were dependent only upon Vj. 5. The voltage dependence of the chord conductance was well fitted by a modified Boltzmann relation given by the equation (Formula: see text) with the constants: A = 0.15 +/‐ 0.03 mV‐1 (n = 10) and V0 = 28 +/‐ 4 mV (n = 10); the latter two parameters were also found to be independent of both transmembrane potentials. 6. The junctional currents were already constant 1 ms after step changes in the junctional voltage; this was three orders of magnitude faster than the other known examples of voltage‐controlled gap junctions between embryonic cells. 7. Our results may be interpreted by a highly voltage‐dependent probability of opening of the junctional channels. They also suggest that the gap‐junction channels forming the giant motor synapse respond very rapidly to potential and that the hemi‐channels which constitute them may not be symmetric.
Rat muscle during post‐natal development: evidence in favour of no interconversion between fast‐ and slow‐twitch fibres.
Authors: Jones S P , Ridge R M , Rowlerson A
Published: December 2014

1. It was confirmed that in the fourth deep lumbrical muscle of the rat the number of muscle fibres at birth is about half that in the adult. 2. The average number of slow‐myosin‐containing (S) fibres (as determined by specific antibody binding) remains constant from birth to adulthood. Therefore it is likely that all the muscle fibres generated post‐natally are type F (i.e. slow‐myosin‐free). 3. A comparison in the electron microscope between transverse mid‐belly sections from new‐born (day 0) and 4 day muscles showed many muscle fibres or myotubes to be intimately associated with other fibres and cells of other types in the new‐born, but to be much less closely grouped at 4 days. 4. A full cell count was obtained from electron microscopy of a mid‐belly section of a lumbrical muscle at birth. 5. Cross‐sectional area measurements in the light microscope at 3‐5 days and in the adult showed that at 3‐5 days on average the S fibres have a greater cross‐sectional area than the F fibres. This is reversed in the adult where the S fibres are the smaller. At 3‐5 days the range of cross‐sectional areas of F fibres is much wider than for S fibres. Some F fibres are among the largest fibres in the muscle. 6. It is argued from the data that the motor units of adult muscle, which are homogeneous with respect to muscle‐fibre types, are produced by selective withdrawal of neonatal motor‐unit contacts during developmental synapse elimination.
Lung reflexes and nasal vascular resistance in the anaesthetized dog.
Authors: Lung M A , Widdicombe J G
Published: December 2014

1. In pentobarbitone‐anaesthetized dogs the nasal vasculature was perfused on both sides, and nasal vascular and airflow resistances were measured together with blood pressure, heart rate and tidal airflow. 2. Capsaicin was injected intravenously to stimulate lung C‐fibre receptors, and veratrine to stimulate pulmonary stretch receptors and cardiac receptors. Injections with both drugs were repeated after pulmonary denervation and after cervical vagosympathectomy. 3. Intravenous capsaicin caused hypotension, bradycardia and rapid shallow breathing, together with a decrease in nasal vascular resistance and little change in nasal airways resistance. Denervation showed that these effects came from lung reflexes, presumably from C‐fibre receptors. 4. Intravenous veratrine caused similar effects to capsaicin before denervations, presumably due to stimulation of slowly adapting pulmonary stretch receptors. Left atrial injections of veratrine caused hypotension, bradycardia and hyperpnoea, together with an increase in nasal vascular resistance and little change in nasal airways resistance. Thus cardiac receptors seem to increase nasal vascular resistance. 5. Injections of capsaicin and veratrine into the nasal circulation decreased nasal vascular resistance, with a stimulation of breathing and changes in blood pressure. Denervations indicated that these were a combination of local and reflex actions.
The effects of in vitro application of purified botulinum neurotoxin at mouse motor nerve terminals.
Authors: Dolly J O , Lande S , Wray D W
Published: December 2014

1. Purified botulinum neurotoxin type A (10 nM) was applied in vitro to mouse diaphragm muscles. Intracellular micro‐electrode recordings were made continuously in single fibres. 2. This treatment reduced end‐plate potential (e.p.p.) amplitudes with a time to half‐maximal effect of about 75 min at 22‐25 degrees C. E.p.p. rise‐times remained fast and unaffected by the toxin. 3. Miniature end‐plate potential (m.e.p.p.) frequency was reduced by the toxin to less than 5% of control frequency, and followed a similar time course to the block of e.p.p. amplitudes. The m.e.p.p. rise‐time and coefficient of variation (c.v.) of m.e.p.p. amplitude distributions both increased, but the time course of these increases lagged significantly behind the change in frequency. 4. A population of slow rise‐time m.e.p.p.s was present in controls at low frequency. This population was found to be unaffected by the toxin. 5. The above‐detailed in vitro changes could be explained by the toxin acting by a single common mechanism to inhibit the release process underlying both fast rise‐time m.e.p.p.s and e.p.p.s. A distinct release process, which leads to slow rise‐time m.e.p.p.s, was unaffected by the toxin.