bluuebunny/crossref_metadata_2025 huggingface dataset:
Synaptic depression related to presynaptic axon conduction block.
Authors: Hatt H , Smith D O
Published: December 2014

1. The depression of synaptic transmission, which occurs during prolonged repetitive activation, was examined in the opener muscle of the crayfish walking leg. 2. Excitatory post‐synaptic potentials (e.p.s.p.s) initially facilitated but then declined to low amplitudes after about 4000 stimulus pulses had been delivered; this depression is presynaptic in origin; 3. Axon conduction blocks occured at points of bifurcation along the entire length of the presynaptic nerve. This resulted in failure of the nerve impulse to invade some branches of the terminal arborization. 4. Nerve terminal invasion failure caused either intermittent or complete inactiviation of some synaptic release sites; this was associated with depression of the post‐synaptic response. 5. The statistics of transmitter release during prolonged repetitive stimulation were examined by focal extracellular recording methods. Transmitter release could be described by binomial statistics, and depression involved a drop in m, n and p. 6. The rate of spontaneous quantal release did not decrease, however, arguing against transmitter depletion. 7. It is concluded that repetitive stimulation eventually leads to depolarization of the axon membrane. This causes impulse propagation failure which reduces the number of synaptic release sites that are activated and mimics a drop in the effective stimulation rate; both effects cause synaptic depression.
Non‐uniform probabilities of quantal release at the crayfish neuromuscular junction.
Authors: Hatt H , Smith D O
Published: December 2014

1. Transmitter release at the neuromuscular junction of the crayfish walking leg has been found to deviate from binomial predictions immediately after the onset of repetitive stimulation of the presynaptic nerve at frequencies of at least 15 Hz. 2. After several minutes of continuous stimulation, and at lower rates of stimulation, however, the number of quanta released could be described quite well by binomial or Poisson statistics. 3. Deviations from the theoretical expectations were characterized by (a) fewer release failures than predicted, (b) occasions in which the number of quanta released was more than the estimated number of quanta available for release, and (c) a tendency for the data to be underdispersed. 4. Each of these three characteristics are consistent with the hypothesis that different releasable quanta may have different probabilities of responding to a nerve impulse. 5. Using two different methods, different values of the non‐uniform probabilities were estimated from the data. At each synaptic site at least one of the estimated probabilities was very high. 6. The need for caution in interpreting statistical description of quantal release is emphasized.
Strain sensitivity and directionality in cat atrial mechanoreceptors in vitro.
Authors: Chapman K M , Pankhurst J H
Published: December 2014

1. Afferent discharges from single atrial mechanoreceptors were studied in vitro in isolated, perfused cat hearts, by balloon inflation and by localized endocardial stretching with step and ramp wave forms. 2. Receptor excitability could be maintained for several hours with perfusion, but failed reversibly within a half hour without it. 3. Responses to pure step stimuli were purely phasic, adapting within a few seconds as negative fractional powers of time. Ramp responses showed corresponding behaviour; 4. Median discharge sensitivities were 12 Hz ml.‐1 for step balloon inflation and 110 Hz strain‐1 for step local stretching, so that 1 ml. balloon expansion was equivalent to 10% local stretch. 5. Ramp stimulation indicated two distinct receptor groups, a 'high‐pass latency' (HPL) group for which threshold decreased with increasing ramp velocity, and a larger 'low‐pass latency' (LPL) group with the opposite behaviour. 6. The endocardial deformation due to local stretching comprised about half simple extension and half shear, so that half the effective lineal stretch would occur in end filaments oriented within 20 degrees of the stretch axis. 7. Of five receptors tested for directionality by local stretching in two perpendicular directions, four showed significant directionality in step sensitivity and/or ramp response latency, indicating the capability of receptive fields to encode changes in endocardial shape.
The influence of gastric distension and the duodenal infusate on the pattern of stomach (abomasal) emptying in the preruminant calf.
Authors: Bell F R , Watson D J
Published: December 2014

1. In the conscious calf it is possible to use duodenal re‐entrant cannulae to measure the output of a gastric test meal directly from the proximal cannula placed near the pylorus. At the same time the duodenum can be isolated from the stomach and maintained under constant stimulus by a continual infusion at regulated pressure, volume and temperature into the distal cannula. 2. Under these experimental conditions the pattern of gastric emptying is exponential in form. Thus direct recording of gastric emptying validates indirect methods, such as the serial test meal, where volume markers are used. It appears likely that the exponential pattern of gastric emptying is common to man, dog, cat and calf. 3. When the isolated duodenum was infused with water, the exponential pattern of gastric emptying was maintained even when the volume of meal instilled was increased substantially from 1 to 41. 4. Distension of the stomach by larger test meals did not affect the relative rate of emptying so that the half‐time of emptying of all meals was about the same. 5. When the isolated duodenum was infused with 0‐06 M‐HCl gastric emptying of the smaller meals was almost completely inhibited. The inhibition of gastric evacuation was accompanied by inhibition of the gastric e.m.g. 6. Infusion of the duodenum with acid also produced marked, but not complete, inhibition of emptying the larger test meals but the distension produced by the larger meals appeared to partially overcome the inhibitory effect of the acid duodenal infusate so that a small efflux occurred from the stomach. This small efflux was usually associated with some slight degree of gastric e.m.g. activity. 7. We are still investigating the mechanisms whereby the duodenum affects gastric emptying, but it is clearly demonstrable from our present results that the inhibitory effects of acid duodenal infusate are sufficiently powerful to overcome the forces, both physical and reflex, which normally aid gastric evacuation.
The dark adaptation curve of rods measured by their after‐image.
Authors: Gosline C J , MacLeod D I , Rushton W A
Published: December 2014

1. The common dark adaptation curve exhibits two branches; the course of the rod branch cannot normally be measured at early times since it lies above the observed cone thresholds. In this paper we measure it. 2. this is done by observing the negative after‐image against a uniform background critically adjusted in luminance. 3. adjacent to the bleached area to be studied is a second area more strongly bleached. If the background intensity is below threshold for the less bleached area it will not be seen there; but if the background is above that threshold, this area will be seen brighter than the other. 4. the dark adapted threshold on the less bleached area is therefore the background luminance which just permits the two areas to be distinguished in the after‐image. 5. after 5 min cones have quite recovered, and thus have no after‐image to contaminate the rod image. 6. the rod curve measured by after‐image is traced over 5 units of log threshold: it is an exponential with half life of 4.5 min, and coincides with the time course of regeneration of rhodopsin in man.
The effect of polarizing currents on unitary Ia excitatory post‐synaptic potentials evoked in spinal motoneurones.
Authors: Edwards F R , Redman S J , Walmsley B
Published: December 2014

1. Depolarizing and hyperpolarizing currents were applied to motoneurones in which unitary Ia e.p.s.p.s were evoked. The results concentrate on those e.p.s.p.s which had time courses which were compatible with somatically located synapses. 2. No reversal of these e.p.s.p.s was observed. Depolarizing currents up to 150 nA simply reduced the peak amplitude. 3. Hyperpolarizing currents caused little, if any, increase in the peak amplitude of the e.p.s.p. The time course of decay became briefer as the membrane was hyperpolarized. 4. Changes in decay time course of the e.p.s.p. which accompanied depolarization and hyperpolarization could be attributed to changes in membrane conductances, rather than to changes in synaptic current time course. 5. The failure of the e.p.s.p. to increase with hyperpolarization was shown to be due to the failure of the synaptic current to increase, rather than to the shunting of anomalous rectification. 6. Chemical and electrical transmission are evaluated against these results and those of the preceding papers.
Lithium transport by the colon of normal and sodium‐depleted rats.
Authors: Dolman D E , Edmonds C J
Published: December 2014

1. The transport of Li by colonic epithelium has been examined in normal and Na‐depleted rats. 2. Substitution of Li for Na with lumen of the conon causes the transepithelial electrical potential difference (p.d.) and short‐circuit current to fall to low levels and the electrical resistance of fall moderately. Recovery occurs by fairly slowly after removal of Li. 3. Li absorption increases linearly with increasing concentration in the lumen and is significantly faster in Na‐depleted rats. Increasing the luminal Na concentration reduces Li absorption from solutions of low Li concentration. 4. Comparison of absorption rates with secretion rates in rats given Li systemically, together with measurements of Li distribution across the epithelium in relationship to the transepithelial p.d. indicate that Li transport is predominatly or entirely passive. Interference with Li absorption by Na suggests, however a mucosal membrane carrier which, since Li absorption rises after Na depletion, may be increased in the Na‐depleted state.
Conductances, diffusion and streaming potentials in the rat proximal tubule.
Authors: De Mello G B , Lopes A G , Malnic G
Published: December 2014

1. Transtubular potential differences and specific resistances were measured in rat proximal tubules by means of single and double barrelled glass micro‐electrodes. 2. Tip localization was made by observation of effective resistance changes measured with double barrelled micro‐electrodes upon passage of oil droplets, and by perfusion with choline C1. 3. Mean early proximal p.d.s. of the order of ‐1 to ‐2 mV, and late values of +0‐5 to +1mV were found. Mean specific resistances ranged from 12 to 15 omega cm2. 4. Diffusion potentials and single ion relative conductances were evaluated, perfusing the lumen with solutions differing only with respect to one salt concentration. Na and K conductances were similar and greater than those of C1. 5. Luminal and peritubular perfusions with hypotonic solutions showed the occurrence of streaming potentials in this structure suggesting the existence of pores lined with negative charges. The effective diameter of these pores appeared to be reduced by hypotonic perfusion, as evidenced by a significant increase in resistance, indicating that the main ion path across this structure is represented by intercellular spaces.
Progressive enhancement in the secretory functions of the digestive system of the rat in the course of cold acclimation.
Authors: Harada E , Kanno T
Published: December 2014

1. The secretory function of the exocrine pancreas and the stomach have been studied in the course of cold acclimation of rats that had been fed at an ambient temperature of 1 degree C in a climatic room. 2. The secretory responses of pancreatic enzymes evoked by continuous infusion of pancreozymin (PZ, 2‐5 mu./kg. hr) and a rapid single injection of PZ (1.7 mu./kg) reached a maximum in the group of rats fed at 1 degree C for 4 weeks, and fell to the control levels after 8 weeks. The increase in the flow of pancreatic juice evoked by single injection of PZ was maximal at 4 weeks and slightly decreased after 8 weeks. 3. The insulin (3‐0 i.u./kg) evoked secretion of pancreatic enzymes gradually increased after cold exposure, reached a maximum at 4 weeks and fell to the control levels after 8 weeks. The flow of pancreatic juice after insulin injection was almost the same in every group throughout the course of cold exposure. 4. The ratio of amylase to the total amount of the protein in the pancreatic juice decreased abruptly, in contrast to an increase in the ratio of protease in the process of cold acclimation. The change in the ratio of enzyme activity in the pancreatic juice may reflect parallel changes in enzyme activity in the exocrine pancreas. 5. The gastric secretion in response to insulin and bile secretion in the group fed at 1 degree C for 7 weeks was significantly higher than that in the control group. 6. It was thus concluded that the secretory activities of digestive system were enhanced by prolonged cold exposure and then returned to control level, and that the activites of the pancreatic enzymes were altered in the process of cold acclimation in rats.
The morphology of spinocervical tract neurones in the cat.
Authors: Brown A G , House C R , Rose P K , Snow P J
Published: December 2014

1. The morphology of physiologically identified spinocervical tract (SCT) neurones was studied using the intracellular injection of Procion dyes in anesthetized and decerebrate cats. 2. Extracellular recordings were made from SCT neurones at depths between 1000 and 2850 mum from the cord surface but neurones were only stained at depths between 1100 and 2400 mum. 3. The dendritic trees of stained SCT neurones were reconstructed in the transverse plane of the spinal cord. All SCT neurones had well developed dorsal dendrites but despite this it is not possible to consider the twenty‐two SCT cells in out sample as consituting a morphologically homogenous population. 4. There was no correlation between the form of the dendritic trees and the depth of SCT neurones in the dorsal horn as determined both from measurements from the dorsal grey‐white border and the position of cells with respect to the border between Rexed's laminae II and III. 5. Six types of SCT neurones were identified on the basis of the form of their dendritic trees as viewed in the transverse plane: (1) radially symmetrical, (2) semicircular, (3) large elliptical, (4) bilobed, (5) triangular, (6) small elliptical. Each of these types was found only in a certain region across the dorsal horn although any one region could contain more than one type. 6. Spinocervical tract neurones with small elliptical dendritic trees always had receptive fields encompassing part of the hip or thigh and were unique in being located in the lateral portions of the horn. 7. There was no correlation between the morphology of SCT neurones and their excitatory cutaneous inputs, receptive field size, axonal conduction velocity or depth in the dorsal horn.
The effect of aminoacetonitrile on calcium metabolism and bone in the rat.
Authors: Kemm J R
Published: December 2014

1. The effect of the osteolathyrogen aminoacetonitrile (AAN) on plasma calcium, phosphate and alkaline phosphatase, on bone, on growth rates, on absorption of calcium and phosphate in the gut and on their urinary excretion, has been examined in rats. 2. AAN caused a general deterioration in the health of the rat and reduced its rate of growth. 3. AAN reduced plasma calcium and increased plasma alkaline phosphatase but did not affect plasma phosphate. 4. AAN caused obvious deformity of the long bones with large exostoses. The femurs of the lathyritic rats had an increased fat‐free weight and increased fat‐free weight to ash weight ratio. 5. AAN increased true and apparent absorption of calcium but did not consistently affect urinary excretion of phosphate or apparent absorption of phosphate. 6. AAN did not produce a significant reduction in the plasma calcium of parathyroidectomized or thyroparathyroidectomized rats. 7. Absorption of calcium from ligated jejunal loops was increased in AAN‐treated parathyroidectomized rats. 8. In some experiments parathyroidectomy or thyroparathyroidectomy protected the bones from the effect of AAN.
Reversal of the behavioural effects of monocular deprivation in the kitten.
Authors: Movshon J A
Published: December 2014

1. Eighteen kittens were monocularly deprived of vision until the age of 5, 6 or 7 weeks. Their eyes were then reverse‐sutured, and they were allowed to survive for 3‐63 days, before physiological recording from area 17. 2. At the time the reverse‐suture was performed, and immediately before the recording session, each kitten was tested separately in the two eyes to elicit five simple behavioural responses: optokinetic nystagmus, visual startle reaction, visually‐guided paw placing, visual following and negotiation of a "visual cliff". 3. Following the opening of their initially deprived eye, all kittens appeared behaviourally blind when forced to use that eye; their performance through the initially open eye was then perfect on all tests. After the period of reversed lid‐suture, however, their performance when using the initially deprived eye had improved, while that through the initially open eye deteriorated. This complementary improvement and deterioration was most rapid in kittens reverse‐sutured at the age of 5 weeks, and less rapid when reverse‐suturing was delayed until the age of 6 or 7 weeks. 4. Most of the kittens showed gross abnormalities of interocular alignment, and exhibited marked exotropia or esotropia. 5. The results of these tests were well correlated with the changes seen in cortical ocular dominance in the same animals.
Biphasic changes in body temperature produced by intracerebroventricular injections of histamine in the cat.
Authors: Clark W G , Cumby H R
Published: December 2014

1. Intracerebroventricular administration of histamine to cats caused hypothermia followed by a rise in body temperature. 2‐Methylhistamine caused a similar biphasic response, while 3‐methylhistamine had no effect on body temperature and 4‐methylhistamine produced a delayed hyperthermia. Some tolerance to the hypothermic activity developed when a series of closely spaced injections of histamine was given. 2. Doses of histamine and 2‐methylhistamine which altered body temperature when given centrally were ineffective when infused or injected I.V. 3. Pyrilamine, an H1‐receptor antagonist, prevented the hypothermic response to histamine. 4. Hypothermic responses to histamine at an environmental temperature of 22 degrees C were comparable to responses in a cold room at 4 degrees C in both resting animals and animals acting to depress a lever to escape an external heat load. A change in error signal from the thermostat could account for these results. However, lesser degrees of hypothermia developed when histamine was given to animals in a hot environment. In some, but not all animals, this smaller response could be attributed to inadequate heat loss in spite of maximal activation of heat‐loss mechanisms. 5. The hyperthermic response to histamine was antagonized by central, but not peripheral, injection of metiamide, an H2‐receptor antagonist. 6. The results indicate that histamine and related agents can act centrally to cause both hypothermia, mediated by H1‐receptors, and hyperthermia, mediated by H2‐receptors.
The secretory characteristics of dehydrocholate in the dog: comparison with the natural bile salts.
Authors: O'Máille E R , Richards T G
Published: December 2014

1. During dehydrocholate administration in the taurine replete dog, the maximum excretory rate of total bile salt (almost entirely dehydrocholate derivative, mostly conjugated) was 3‐84 +/‐ 0‐53 (S.D.) mumole/min. kg body wt. (eleven experiments). This was much less than the excretory maximum previously obtained for taurocholate (8‐64 +/‐ 1‐31 (S.D.) mumole/min. kg total cholate, mostly conjugated). 2. The superimposition of taurocholate infusion did not cause any significant change in the 'dehydrocholate' maximum but taurocholate itself was excreted into bile at no more than about half its normal maximum. When taurocholate maximum excretion was established first, it was reduced by dehydrocholate administration. In both types of experiment the joint bile salt excretory maximum was of the same order as that of taurocholate alone, provided taurocholate made up at least 40‐50% of the total bile salt. 3. When taurocholate administration was stopped, the maximum excretory rate of 'dehydrocholate' rose to values up to 63% above the initially determined excretory maximum; the enhanced 'dehydrocholate' excretory maximum, when calculated for optimal conditions, approached that of actively conjugated vholate, even though the effective 'dehydrocholate' concentration in bile was ten to twenty times the critical micellar concentration of taurocholate. This suggests that the effective bile salt concentration in bile is not an important determinant of the secretory performance of a bile salt. 4. To explain findings (2) and (3) it is necessary to postulate that taurocholate has both a facilitatory and an inhibitory action on 'dehydrocholate' excretion. The facilitatory action, which persists after taurocholate has left the animal, may consist either of an increase in the maximum rate at which modification of dehydrocholate takes place within the liver cell, or an increase in the number of functioning 'carriers' for 'dehydrocholate' transfer. The data suggest that the inhibitory effect is due to the competitive interaction that also appears to exist between the two bile salts. 5. The increase in bile flow rate per unit increase in 'dehydrocholate' excretion (15 ml./m‐mole) was about twice that obtained for taurocholate. There was no significant formation of micellar aggregates during 'dehydrocholate' excretion, as judged from the total electrolyte concentration of bile and its osmalality. 6. During the excretion of 'dehydrocholate'‐taurocholate mixtures (approximately 1:1) at submaximal rates the associated bile flow rate was not less than the sum of the separate components, thus suggesting that 'dehydrocholate' was not being incorporated in taurocholate mixed micelles.
The direct effect on pulmonary stretch receptor discharge produced by changing lung carbon dioxide concentration in dogs on cardiopulmonary bypass and its action on breathing.
Authors: Bradley G W , Noble M I , Trenchard D
Published: December 2014

1. Single fibre pulmonary stretch receptor discharge was recorded in dogs on cardiopulmonary bypass. 2. Inhalation of CO2 depressed pulmonary stretch receptor discharge despite the absence of changes in arterial PCO2. This effect was particularly marked with airway CO2 levels below 5%. 3. Changing arterial PCO2, without changing airway CO2, had only small and insignificant effects on pulmonary stretch receptor discharge. 4. The effect of changes in airway CO2 on pulmonary stretch receptor discharge was rapid and correlated well in time with the reflex tachypnoea produced when CO2 was inhaled in conditions of cardiopulmonary bypass. 5. Stimulation of the central end of the cut vagus nerve was triggered from simultaneously recorded action potentials from a single pulmonary stretch receptor. 6. In these conditions, the reflex response to CO2 could be simulated provided that the pulmonary stretch receptor had an end‐expiratory discharge. 7. It is suggested that the vagally mediated tachypnoeic response to changes in airway CO2 seen in conditions of cardiopulmonary bypass is due to the effect of CO2 on the end‐expiratory discharge of pulmonary stretch receptors.
Respiratory and thermoregulatory responses of rabbits breathing carbon dioxide during heat exposure.
Authors: Maskrey M , Nicol S C
Published: December 2014

1. Rabbits were clipped and exposed in turn to three environmental conditions: control (C), cold exposure (CE) and water deprivation (WD). Following each type of treatment, the rabbits were exposed to an ambient temperature (Ta) of 35 degrees C for 1 hr. Throughout this period they breathed either normal atmospheric air or 6% CO2 in air. 2.During heat exposure, measurements were made of the respiratory responses and of the O2 consumption (Vo2) of the rabbits. Rectal temperature (Tre) was measured immediately before and again immediately after heat exposure. 3. When subjected to cold exposure or water deprivation the rabbits showed an initial decrease in respiratory frequency (RF) and an initial increase in VT when compared with controls. There was no difference in VE. Rabbits breathing 6% CO2 showed an increase in VT and VE and a decrease in RF when compared with rabbits breathing atmospheric air. In all cases a change in VT or RF was associated with a reciprocal change in the other parameter. 4. The respiratory responses to breathing 6% CO2 were essentially similar in treated and control rabbits, from which it is concluded that neither cold exposure nor water deprivation alter the sensitivity of the medullary respiratory centre to the respiratory drive from the central chemosensors. 5. The increase in Tre during heat exposure was significantly less in rabbits breathing 6% CO2 than in rabbits breathing atmospheric air. However, there was no significant over‐all difference in VO2 between rabbits breathing CO2 and those breathing air. From this it is concluded that increased ventilation induced by CO2 causes a greater dissipation of heat than does thermally‐induced panting. 6. It is concluded that VT is controlled by the level of blood PCO2 whereas RF is controlled by thermoregulatory requirements. It is further concluded that the reciprocal relationship between VT and RF is regulated in such a way as to maintain VE at the appropriate level for effecting gaseous exchange and evaporative heat loss.
The possible mechanism for the 'fade' in acid gastric secretion during continuous infusions of pentagastrin.
Authors: Sanyal A K , Waton N G
Published: December 2014

1. The 'fade' phenomenon seen in acid gastric secretion in response to a continuous intravenous infusion of pentagastrin has been studied in anaesthetized cats. Whereas acid secretion to a continuous infusion of histamine steadily increased for 3 hr, that to pentagastrin infusion rose steeply to a maximum at 45 min and then decreased gradually to reach about 60% of maximum after 2 hr. 2. Pre‐treatment of the cats with the 5‐hydroxytryptamine (5‐HT) blocking drugs, methysergide and cyproheptadine or with the 5‐hydroxytryptamine‐depleting drug reserpine completely altered the pattern of secretion to pentagastrin such that the response was similar to that seen during an infusion of histamine. These drugs did not affect secretion stimulated by histamine. 3. It is suggested from these results that pentagastrin releases 5‐hydroxytryptamine which at first potentiates and then inhibits the resulting stimulated secretion.
Non‐random distribution of cell types in the preoptic and anterior hypothalamic areas.
Authors: Dyer R G , Ellendorff F , MacLeod N K
Published: December 2014

1. Single units were recorded extracellularly from the preoptic and anterior hypothalamic areas of male and female rats anaesthetized with urethane. 2. The effect of single shock stimulation of both the mediobasal hypothalamus and corticomedial amygdala upon unit activity was assessed for all cells. Neurones were designated either antidromically invaded, orthodromically excited or inhibited, or non‐responsive. 3. The distribution of responses among recorded cells was analysed for two groups of neurones. In one group the intercell distance was less than 100 mum and in the second group the distance was more than 1 mm. 4. For widely separated cells the connexions with the corticomedial amygdala and mediobasal hypothalamus were distributed at random. 5. In the groups of cells clustered closely together a marked structuring of connexions was apparant. In particular, there was a significant correlation between orthodromic responses from the amygdala (P less than 0‐05) and cells antidromically activated and orthodromically excited by stimulation of the mediobasal hypothalamus were frequently adjacent to one another (P less than 0‐02. 6. A complimentary analysis demonstrated that cells in the ventral half of the recording zone received significantly more inhibitory inputs from both the mediobasal hypothalamus (P less than 0‐001) and the corticomedial amygdala (P less than 0‐02) than those situated more dorsally. 7. The data provide evidence for structuring and orderliness in hypothalamic connexions that is often not apparent from descriptions of electrophysiological experiments.
Sialotonin: vasopressor substance in saliva and submandibular gland of the cat.
Authors: Barton S , Karpinski E , Moriwaki C , Schachter M
Published: December 2014

1. The large molecular pressor agent, sialotonin, present in cat saliva, has been separated from kallikrein and characterized further. 2. Sialotonin is present in saliva produced by parasympathetic (ch8da) but not in that produced by sympathetic nerve stimulation. After degenerative preganglionic parasympathetic nerve section, both sialotonin and kallikrein disappear completely, or nearly so. Sympathetic nerve section, however, fails to affect the concentration of these substances in chorda saliva. 3. The sialotonin activity is saliva is unaffected by ligation of Wharton's duct for 3‐‐4 days whereas the kallikrein concentration is greatly reduced. 4. Although normally present in chorda saliva, sialotonin cannot be detected in aqueous extracts of the submandibular gland. It is present, however, in extracts of glands which have previously been subjected to prolonged sympathetic nerve stimulation or to ligation of the duct for 3‐4 days. 5. The intravenous or close‐aterial injection of sialotonin causes marked but brief reductions of blood flow in the submaxillary gland and intestine.
Frequency of tendon organ discharges elicited by the contraction of motor units in cat leg muscles.
Authors: Jami L , Petit J
Published: December 2014

1. The responses elicited in individual tendon organs by the contraction of single motor units were studied in peroneus longus, peroneus brevis, tibialis anterior and soleus muscles. 2. No simple relation was found between the discharge frequency of a tendon organ and the tension produced in the muscle tendon by the contraction of individual motor units. 3. The sensitivity of a given tendon organ to contractile tension was not the same for each of the motor units which elicited its discharge. There was no correlation between the sensitivity of the receptor and the strength of the motor units. 4. Upon repetitive stimulation of a tendon‐organ‐activating motor unit at increasing rates, the frequency of the receptor sustained discharge reached a maximal value for rates of stimulation eliciting submaximal tetanic tension. Higher rates only produced an increase in the dynamic component of the tendon organ response. 5. These observations show that the contractile tension sensed by a tendon organ is not a simple fraction of the tension which appears at the muscle tendon. They might be accounted for as consequences of the fine structure of tendon organs and of variations in the number of muscle fibres contributed by different motor units to the bundle inserted on each receptor. The location of most tendon organs at musculo‐aponeurotic junctions rather than in the tendon proper, could also be responsible for some of the observed discrepancies.
Methionine transport by pig colonic mucosa measured during early post‐natal development.
Authors: James P S , Smith M W
Published: December 2014

New‐born pig proximal colon, incubated in vitro, transports methionine with a Km of 0‐33 mM and a Vmax of 0‐62 mumole cm‐2h‐1. There is still a net transport of methionine on day 4, but the Km now increases to 10 mM and the Vmax falls to 0‐15 mumole cm‐2h‐1. There is no net transport of methionine across proximal colons taken from 10‐day‐old pigs. 2. The mean intramucosal concentration of methionine, following incubation in medium containing 1 mM methionine, is 7‐18+/‐0‐8 mM for the new‐born, 0‐55+/‐0‐05 mM for the 4‐day‐old and 0‐31+/‐0‐06 mM for the 10‐day‐old pig. 3. Both methionine and glucose cause an immediate increase in the short‐circuit current of new‐born and 1‐day‐old pig colons. The kinetics for this interaction with methionine gives a Km for methionine of 0‐24 mM and a maximum effect of 27 muA cm‐2. This effect is not seen in 4‐ or 10‐day‐old pigs. 4. Net Na+ transport across the new‐born pig proximal colon, measured in the absence of methionine, is about three times that calculated from the measured short‐circuit current. Methionine increases the mucosal to serosal flux of Na+ by an amount roughly equal to that predicted from the increase in short‐circuit current. The ability of glucose and methionine to affect short‐circuit current is lost by day 4. 5. Short‐circuit current, measured in the absence of methionine or glucose, increases between day 1 and 2 of post‐natal life. This increased electrogenicity is maintained for up to at least 10 days after birth. 6. The pig proximal colon has many of the properties of a small intestine at birth. It actively transports methionine and the presence of methionine stimulates the absorption of Na+. These effects could be physiologically important in the pig, where the normal absorptive function of the intestine is temporarily inhibited at birth by the intestinal transmission of immune globulins.
L‐glutamate as an excitatory transmitter at the Drosophila larval neuromuscular junction.
Authors: Jan L Y , Jan Y N
Published: December 2014

The possibility that L‐glutamate is the excitatory transmitter at the Drosophila larval neuromuscular junction and the ionic basis of its action on the muscle membrane are examined. 2. Iontophoretically applied L‐glutamate causes muscle depolarization (L‐glutamate potential) if and only if the L‐glutamate pipette is within a few mum of the nerve ending. D‐glutamate, substance P, ACh and GABA are ineffective. 3. Bath‐applied L‐glutamate produces similar changes in the time course and amplitude of miniature excitatory junctional potential (m.e.j.p.), excitatory junctional potential (e.j.p.) and the L‐glutamate potential. 4. Neuromuscular transmission and excitation‐contraction coupling are operative in a haemolymph‐like solution containing 1 mM L‐glutamate. 5. The reversal potentials of the e.j.p. and the L‐glutamate potential are identical to each other, changing similarly with changes in the ionic compositions of the external medium (twelve solutions). 6. The ionic dependence of the reversal potentials is predicted from an extended constant‐field equation using a ratio of sodium:potassium permeabilities of PNa/PK=1‐3, and a ratio of magnesium:potassium permeabilities of PMg/PK=4‐7. 7. It is concluded that L‐glutamate is, or is an agonist of, the excitatory transmitter at certain Drosophila larval neuromuscular junctions.
Atrial receptors in the cat.
Authors: Kappagoda C T , Linden R J , Mary D A
Published: December 2014

Action potentials were recorded from slips of the cervical vagi in anaesthetized cats. Single functional units with atrial patterns of discharge (type A, B and Intermediate) were first obtained and then attempts were made to alter (i.e. convert) their patterns of discharge. Finally the points of origin of their action potentials were located. The investigations were done in five stages. 2. In the first series, thirty unselected units were investigated in thirty cats. Twenty‐five of these were located in the endocardium of vein‐atrial system and consisted of two type A, fifteen type B and eight Intermediate type units. The remaining five units were located elsewhere in the chest Conversion of the pattern of discharge was achieved in sixteen of the twenty‐five atrial units. Both atrial type A units were converted. 3. In the second series, eight type A units were selectively studied in twelve cats. Five were located in the atrial endocardium and all were converted. Of the other three units which were located at other sites in the chest, one could not be converted. 4. In the third series, four type A units which could not be converted were selectively studied in twenty cats. All were located outside the atria. 5. In the fourth series, three type B units which could not be converted were selectively studied in six cats. These units were located in the pulmonary veins and in the lateral walls of the atria. 6. In the fifth series, fifty‐five units were investigated in three anaesthetized spontaneously breathing cats. The proportion of the types of units were similar to that obtained in the artificially respired cats (first series). 7. The present study has shown that atrial receptors with a type A pattern of discharge are relatively rare in the cat and that conversion of the patterns of discharge is a common phenomenon. Evidence is presented which suggests that there is one basic type of atrial receptor whose pattern of discharge is determined by their precise location in the vein‐atrial system.
Sugars and sugar derivatives which inhibit the short‐circuit current of the everted small intestine of the rat.
Authors: Muflih I W , Widdas W F
Published: December 2014

1. The short‐circuit current of everted rat intestine supported on a perforated cannula proved to be stable for up to 3 hr and has been used to study competition between transportable and non‐transportable sugars. 2. 4,6‐O‐Ethylidene‐alpha‐D‐glucopyranose (ethylidene glucose) and 4,6‐O‐benzylidene‐e alpha‐D‐glucopyranos (benzylinene glucose), two nontransportable inhibitors of the hexose transfer system in human erythrocytes, were found to reduce the short‐circuit current generated by transportable sugars such as galactose or 3‐O‐methyl glucose. 3. These compounds were also found to reduce the basal short‐circuit current established by the everted intestine in a sugar‐free Krebs solution. Both types of inhibition approached saturation at the higher concentrations used. 4. Similar inhibitory properties were shown by mannose, a non‐actively accumulated monosaccharide, and by the beta‐disaccharides lactose and cellobiose. 5. It is suggested that this common pattern of behaviour is due to the ability of these compounds to react with the sites for active hexose transfer but without translocation by the system. The significance of the inhibition of the basal short‐circuit current is briefly discussed in this context.
An evaluation of the membrane constants and the potassium conductance in metabolically exhausted muscle fibres.
Authors: Fink R , Lüttgau H C
Published: December 2014

1. The membrane characteristics of metabolically poisoned and mechanically exhausted frog skeletal muscle fibres were investigated with intracellular micro‐electrodes. 2. When cyanide plus iodoacetate were applied as metabolic poisons twitch tension declined towards zero after 150‐300 stimuli (0‐3 Hz; temperature = 0 degrees C). At the beginning of stimulation the mean resting potenial fell from ‐75 to ‐69 mV; it rose subsequently to ‐83 mV. The membrane resistance decreased during this stimulation period along a sigmoid time course to 4‐6% of the original value. 3. In completely exhausted fibres the following membrane constants were estimated (23 degrees C): length constant, 0‐31 mm; input resistance, 31 komega; membrane resistance, 58 omega.cm2. These values were calculated under the assumption of a constant internal resistivity of 170 omega. cm. The Q10 values of these constants were similar to those in normal fibres. Afew experiments revealed that the membrane capacity remained roughly constant under these conditions. 4. The current‐voltage relation of exhausted fibres was approximately linear in the range between ‐60 and ‐100 mV. At less negative potentials the conductance increased slightly while at more negative potentials it decreased. The latter, in particular, became more evident when the imput current was converted into membrane current density by applying Cole's theorem. 5TEA+ and Rb+ in the external solution increased the membrane resistance of exhausted fibres by more than one order of magnitude. The major part of the membrane conductance induced by exhaustion, however, could not be blocked by these ions or Zn2+. 6. Chloride‐free test solutions were used to measure the relative contributions of potassium and chloride ions to the membrane conductance. The relation GK:GC1 changed from 2:3 in normal fibres to 5:1 in exhausted ones. In absolute terms GK rose from ca. 130 to 14,300 mumho/cm2 and GC1 from ca. 200 to 2900 mumho/cm2. The discrimination between K+ and Na+ by the resting membrane in exhausted fibres was probably equal to or even higher than that under normal conditions. 7. In normal fibres the input resistance decreased by up to 20% after the external application of 1‐2 mM caffeine, which is known to release calcium ions from internal stores. The elevation in internal Ca2+ by direct injection caused a small and, as a rule, irreversible decrease in input resistance which was probably partly due to local damage to the surface membrane. 8. It is concluded that in metabolically exhausted muscle fibres the surface and tubular membranes are still intact and that the observed decrease in membrane resistance is mainly due to an increase in potassium conductance. In addition, the results indicate that the gating mechanism of the potassium channels (presumably those with the characteristics of the slow component) is affected when energy reserves diminish.
Short‐term synchronization of intercostal motoneurone activity.
Authors: Sears T A , Stagg D
Published: December 2014

1. The hypothesis is advanced that the joint occurrence of unitary excitatory post‐synaptic potentials e.p.s.p.s) evoked in motoneurones by branches of common stem pre‐synaptic fibres causes short‐term synchronization of their discharge during the rising phases of the unitary e.p.s.p.s. 2. This hypothesis was tested using the pre‐ and post‐stimulus time (PPST) histogram to detect synchronized firing among groups of intercostal motoneurones discharging in response to their natural synaptic drives. 3. Motor nerve action potentials were recorded monophasically from nerve filaments of the external intercostal muscles of anaesthetized, paralysed cats maintained on artificial ventilation. 4. Computer methods were used to measure peak spike amplitude, spike amplitude, spike interval and filament identification for simultaneous recordings from four filaments. The spike amplitude histograms were derived for each filament and groups of spikes were selected for analysis. 5. With spikes of one group designated as 'stimuli' (occurring at zero time) and those of a second as 'response' the PPST histogram was computed with different time bin widths. 6. With bin widths of 100 and 10 msec the central respiratory periodicity was apparent in the PPST histogram. With 1.0 msec bins the PPST histogram showed a narrow central peak extending to +/‐ 3.0 msec at its base. This 'short‐term synchronization' supports the hypothesis of joint firing due to common presynaptic connectivity. 7. It was shown that detection of short‐term synchronization was critically dependent on a sufficient quantity of data but that provided a simple criterion of adequate counts per bin in the PPST histogram was met, short‐term synchronization could be detected between intercostal motoneurones of the same and adjacent segments.
An analysis of the influence of membrane potential and metabolic poisoning with azide on the sodium pump in skeletal muscle.
Authors: Beaugé L A , Sjodin R A
Published: December 2014

1. Activation of the Na pump in muscle by the external K concentration, [K]O, is independent of the membrane potential (Em) as shown by experiments in which Em was either stabilized during variation of [K]O or varied by application of azide at constant or zero [K]O. 2. Application of azide to Na‐enriched muscles causes a transient increase in 22Na efflux which occurs either in the presence or in the absence of external K. 3. The increased 22Na efflux induced by azide is abolished by addition of ouabain and is greatly reduced by removal of almost all of the external Na concentration, [Na]o. 4. Azide‐treated muscles show a rather normal K sensitivity of 22Na efflux and [K]O induces a net Na extrusion from Na‐enriched muscles in the presence of azide. 5. Azide reduces ouabain‐sensitive K influx to low values thus interfering with K pump but not with the ability of K to activate the Na pump. 6. The experiments provide evidence that azide promotes a ouabainsensitive Na‐Na exchange in Na‐enriched muscles and that it partially uncouples the Na‐K exchange normally observed.
The Bohr effect on the reaction of carbon monoxide with fully oxygenated haemoglobin.
Authors: Sirs J A
Published: December 2014

1. The rate at which CO displaces O2 from its combination with haemoglobin in solution, has been measured spectrophotometrically, using a rapid‐mixing stopped‐flow technique. 2. In the presence of CO2, the reaction proceeds by a unimolecular dissociation, with a rate constant r. 3. The relationship of the reciprocal of r to the ratio PO2/PCO is nonlinear, and a different curve is obtained at each CO concentration. 4. Measurements were made of the rate of the reaction when the pH was varied, with constant or varying PCO2. In both situations the value of r was found to have a miximum, for a given PO2/PCO ratio and CO cencentration, at pH 7.2. 5. An analysis of these results suggest that the Bohr effect, of pH and PCO2, is a dynamic equilibrium between four stable tertiary states of each of the alpha and beta chains. Each intermediatory complex has different rate constants for CO and O2.
Calcium absorption in diphosphonate‐treated rats: effect of parathyroid function, dietary calcium and phosphorus.
Authors: Bonjour J P , Fleisch H , Trechsel U
Published: December 2014

1. The role of parathyroid hormone (PTH) and 1, 25‐dihydroxy‐cholecalciferol (1,25‐(OH)2D3) in modulation of intestinal Ca absorption was studied in rats, using disodium ethane‐1‐hydroxy‐1,1‐diphosphonate (EHDP), which is known to reduce 1,25‐(OH)2D3 formation. 2. EHDP decreased intestinal Ca absorption. This effect could be abolished by small amounts of 1,25‐(OH)2D3, whereas even large doses of PTH were ineffective. EHDP also decreased Ca absorption in thyroparathyroidectomized (TPTX) rats. Therefore the effect of EHDP on 1,25‐(OH)2D3 production is unlikely to be mediated through PTH. 3. The correction by PTH of the decreased Ca absorption in TPTX rats was inhibited by EHDP. Since EHDP inhibits formation of 1,25‐(OH)2D3 the effect of PTH on Ca absorption is likely to be mediated through this vitamin D3 metabolite. 4. In normal rats both a low Ca and a low P diet stimulated Ca absorption. In EHDP‐treated intact rats low Ca still stimulated Ca absorption, whereas the effect of low P abolished. This indicates that low Ca and low P diets affect Ca absorption through different mechanisms. 5. Intestinal adaptation to a low Ca diet was still observed in EHDP‐treated TPTX rats. Thus, in the rat, intestinal adaptation to low Ca diet can occur without PTH.