bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of neurohypophysial hormones on renal function in the acutely hypophysectomized rat.
Authors: Balment R J , Brimble M J , Forsling M L , Musabayane C T
Published: December 2014

1. Renal function and the effect of neurohypophysial hormone replacement was investigated in anaesthetized, acutely hypophysectomized, male rats. 2. Although urine production was only slightly lower over the 8 h post‐operative study period in hypophysectomized rats, sodium excretion was greatly depressed reaching only 3.5 +/‐ 1.4 mumol/min compared with a peak of 13.2 +/‐ 1.0 mumol/min in intact animals. 3. In association with a decline in mean arterial blood pressure, glomerular filtration rate in hypophysectomized rats fell to 2.1 +/‐ 0.2 ml/min 8 h after operation by comparison with a mean rate in intact rats of 3.2 +/‐ 0.2 ml/min. 4. Plasma corticosterone levels were much lower in hypophysectomized (4 +/‐ 2 ng/ml) than in intact (36 +/‐ 4 ng/ml) rats, plasma aldosterone was reduced to a lesser extent (0.41 +/‐ 0.08 compared with 0.76 +/‐ 0.04 ng/ml). While oxytocin was not detectable in hypophysectomized rat plasma, trace levels of vasopressin (0.16 +/‐ 0.04 mu u./ml) were found. In intact unanaesthetized rats basal plasma levels of oxytocin were 0.32 +/‐ 0.13 mu u./ml and vasopressin were 0.85 +/‐ 0.19 mu u./ml. 5. Administration of oxytocin at 150 mu u./min, which produced plasma hormone levels (24.0 +/‐ 2.5 mu u./ml) greatly in excess of basal concentrations, increased renal sodium excretion but did not alter urine flow. Oxytocin administration at the lower rate of 15 mu u./min producing plasma hormone levels of 2.60 +/‐ 0.1 mu u./ml, did not alter renal sodium excretion. 6. Arginine vasopressin administered at 12 mu u./min induced plasma hormone levels of 1.54 +/‐ 0.09 mu u./ml and produced a large antidiuresis and small increase in the rate of sodium excretion. 7. The natriuretic response to vasopressin was potentiated by concurrent administration of oxytocin at 15 mu u./min. The peak sodium excretion of 5.8 +/‐ 1.0 mumol/min, however, remained well below that seen in intact rats. 8. It is concluded that, as restoration of posterior pituitary hormones at or above the physiological range only partially restored sodium excretion, the absence of anterior pituitary factors may also contribute directly or indirectly to the renal sodium retention of the hypophysectomized rat.
Organization of synaptic transmission in the mammalian solitary complex, studied in vitro.
Authors: Champagnat J , Denavit-Saubié M , Grant K , Shen K F
Published: December 2014

1. Synaptic transmission and neuronal morphology were studied in the nucleus tractus solitarius and in the dorsal vagal motor nucleus (solitary complex), in coronal brain‐stem slices of rat or cat, superfused in vitro. 2. Electrical stimulation of afferent fibres of the solitary tract evoked two different types of post‐synaptic response recorded intracellularly in different solitary complex neurones. Labelling with horseradish peroxidase showed that these two sorts of orthodromically evoked responses were correlated with different post‐synaptic neuronal morphologies. 3. The majority of recorded neurones (n = 93) showed a prolonged reduction in excitability following the initial solitary‐tract‐evoked excitatory post‐synaptic potential (e.p.s.p.). A smaller number of neurones (n = 53) showed a prolonged increase in excitability following solitary tract stimulation. In no case did the solitary tract stimulation induce a burst of action potentials at high frequency. 4. The time‐to‐peak and the half‐width of the initial solitary‐tract‐evoked e.p.s.p. were shorter in neurones with prolonged increased excitability than in those with prolonged reduced excitability. In neurones with prolonged reduced excitability, this e.p.s.p. was followed by a hyperpolarization lasting 60‐100 ms. The latency of this inhibitory post‐synaptic potential (i.p.s.p.) was 3‐5 ms longer than that of the initial e.p.s.p. and its reversal potential was 10 mV more negative than the reversal potential of the response measured following application of gamma‐aminobutyric acid or glycine. In neurones with prolonged increased excitability, at a membrane potential of ‐40 to ‐50 mV, the initial solitary tract e.p.s.p. was followed by a prolonged depolarization lasting 100‐400 ms. 5. Background synaptic activity was high in neurones with prolonged increased excitability, consisting of unitary e.p.s.p.s with an amplitude of more than 0.8 mV. This activity was increased for a period of 300‐800 ms following solitary tract stimulation. Spontaneous excitatory potentials of more than 0.5 mV were not seen in neurones with prolonged reduced excitability. In these neurones, after intracellular injection of choride ions, reversed unitary i.p.s.p.s formed a background activity which was increased following stimulation of the solitary tract. 6. Neurones with prolonged reduced excitability were found in the medial, ventral and ventrolateral part of the nucleus tractus solitarius and in the dorsal vagal motor nucleus where they were identified by their antidromic response to stimulation ventral and lateral to the tractus solitarius.(ABSTRACT TRUNCATED AT 400 WORDS)
The transport of pyrimidines into tissue rings cut from rat small intestine.
Authors: Bronk J R , Hastewell J G
Published: December 2014

1. At low concentrations (0.1 mM) the transport of uracil, 5‐fluorouracil and thymine into jejunal tissue rings is an active process. 2. The transport of 5‐fluorouracil into tissue rings cut from the duodenum and jejunum was greater than the transport into rings cut from the ileum. This difference was abolished by starving the rats for 48 h before the experiment. 3. The active transport can be abolished by replacing the Na+ in the incubation medium with either K+ or mannitol, or by increasing the concentration of the pyrimidine to 1.0 mM. 4. The accumulation of uracil or 5‐fluorouracil into the jejunal rings was identical when determined by radioactive tracer or by high‐performance liquid chromatography. 5. The apparent Michaelis constant (Km) for 5‐fluorouracil transport into jejunal rings was 0.074 mM in the standard Na+ bicarbonate Krebs‐Ringer solution and 0.394 mM in the K+‐substituted bicarbonate Krebs‐Ringer solution. 6. Both thymine and uracil inhibited the transport of 5‐fluorouracil into jejunal tissue rings: however, cytosine and orotic acid did not.
Activation of the human diaphragm from the motor cortex.
Authors: Gandevia S C , Rothwell J C
Published: December 2014

1. Rapidly conducting corticofugal pathways were activated by percutaneous electrical stimulation of the motor cortex in normal subjects. The electromyographic response produced in the diaphragm was assessed with recordings via a gastro‐oesophageal catheter and the mechanical response was measured as a change in transdiaphragmatic pressure. 2. The mean latency from the cortical stimulus to the muscle action potential in the diaphragm was 12.3 ms. The latency to the diaphragm from stimulation of the cervical spinal cord at the C4 level was 8.0 ms. The mean 'central conduction time' to the phrenic motor nucleus of 4.3 ms (range 4.0‐4.6 ms) was similar to that for the deltoid (mean 4.4 ms; range 4.0‐4.8 ms) recorded in the same subjects. 3. The largest twitch contractions of the diaphragm were evoked by cortical stimuli near the vertex during inspiration. The amplitude and duration of the electromyographic and mechanical responses often exceeded those produced by a supramaximal stimulus to both phrenic nerves simultaneously. 4. These results provide the first direct evidence that there is a rapidly conducting oligosynaptic pathway from the motor cortex to the human diaphragm.
Mechanism of anion permeation through channels gated by glycine and gamma‐aminobutyric acid in mouse cultured spinal neurones.
Authors: Bormann J , Hamill O P , Sakmann B
Published: December 2014

1. The ion‐selective and ion transport properties of glycine receptor (GlyR) and gamma‐aminobutyric acid receptor (GABAR) channels in the soma membrane of mouse spinal cord neurones were investigated using the whole‐cell, cell‐attached and outside‐out patch versions of the patch‐clamp technique. 2. Current‐voltage (I‐V) relations of transmitter‐activated currents obtained from whole‐cell measurements with 145 mM‐Cl‐ intracellularly and extracellularly, showed outward rectification. In voltage‐jump experiments, the instantaneous I‐V relations were linear, and the steady‐state I‐V relations were rectifying outwardly indicating that the gating of GlyR and GABAR channels is voltage sensitive. 3. The reversal potential of whole‐cell currents shifted 56 mV per tenfold change in internal Cl‐ activity indicating activation of Cl(‐)‐selective channels. The permeability ratio of K+ to Cl‐ (PK/PCl) was smaller than 0.05 for both channels. 4. The permeability sequence for large polyatomic anions was formate greater than bicarbonate greater than acetate greater than phosphate greater than propionate for GABAR channels; phosphate and propionate were not measurably permeant in GlyR channels. This indicates that open GlyR and GABAR channels have effective pore diameters of 5.2 and 5.6 A, respectively. The sequence of relative permeabilities for small anions was SCN‐ greater than I‐ greater than Br‐ greater than Cl‐ greater than F‐ for both channels. 5. GlyR and GABAR channels are multi‐conductance‐state channels. In cell‐attached patches the single‐channel slope conductances close to 0 mV membrane potential were 29, 18 and 10 pS for glycine, and 28, 17 and 10 pS for GABA‐activated channels. The most frequently observed (main) conductance states were 29 and 17 pS for the GlyR and GABAR channel, respectively. 6. In outside‐out patches with equal extracellular and intracellular concentrations of 145 mM‐Cl‐, the conductance states were 46, 30, 20 and 12 pS for GlyR channels and 44, 30, 19 and 12 pS for GABAR channels. The most frequently occurring main state was 46 pS for the GlyR and 30 pS for the GABAR channel. 7. Single‐channel conductances measured in equal 140 mM concentrations of small anions on both membrane faces revealed a conductance sequence of Cl‐ greater than Br‐ greater than I‐ greater than SCN‐ greater than F‐ for both channels. This is nearly the inverse sequence of that found for the permeability of these ions indicating the presence of binding sites for ions in the channel.(ABSTRACT TRUNCATED AT 400 WORDS)
Lung and cardiac reflex actions on the tracheal vasculature in anaesthetized dogs.
Authors: Sahin G , Webber S E , Widdicombe J G
Published: December 2014

1. With pentobarbitone‐anaesthetized dogs, the cranial tracheal arteries have been independently perfused on both sides, to measure vascular resistance. Blood pressure and contractions of tracheal muscle were also measured. 2. Capsaicin was injected intravenously to stimulate lung C‐fibre receptors. In breathing and in paralysed artificially ventilated dogs it decreased tracheal vascular resistance and blood pressure, and contracted tracheal muscle. The effects were abolished or far smaller after bilateral cervical vagosympathectomy. 3. Veratrine was injected intravenously to stimulate slowly adapting pulmonary stretch receptors and cardiac receptors. In breathing and in artificially ventilated dogs it lowered tracheal vascular resistance and blood pressure, and had variable effects on tracheal muscle tone. The vascular effects were prevented by vagotomy. 4. Veratrine injected into the left atrium caused similar vascular changes to intravenous administration. The changes were prevented by vagotomy. Veratrine causes a tracheal vasodilatation by action on cardiac receptors. 5. Inflation of the lungs in artificially ventilated dogs, to stimulate slowly adapting pulmonary stretch receptors, had no effect on tracheal vascular resistance but decreased blood pressure and tracheal muscle tone, the latter being prevented by vagotomy. 6. Bilateral carotid arterial occlusion, to decrease the discharge in carotid sinus baroreceptors, had no effect on tracheal vascular resistance but increased blood pressure and contracted tracheal muscle, the last two responses being greatly reduced by cutting the sinus nerves. 7. It is concluded that stimulation of lung C‐fibre and cardiac receptors causes a reflex tracheal vasodilatation, but that no changes in the tracheal vascular bed occur with stimulation of slowly adapting pulmonary stretch receptors or inhibition of carotid sinus baroreceptors.
Pre‐ and post‐junctional effects of adenosine triphosphate on noradrenergic transmission in the rabbit ear artery.
Authors: Miyahara H , Suzuki H
Published: December 2014

1. The effects of adenosine triphosphate (ATP), 5'‐adenylylimidodiphosphate (AMP‐PNP) or alpha,beta‐methylene ATP (mATP) on the excitatory junction potential (e.j.p.) and slow depolarization evoked by perivascular nerve stimulation were studied in smooth muscle cells of the rabbit ear artery. 2. ATP (above 10(‐6) M), AMP‐PNP (above 10(‐6) M) and mATP (above 10(‐8) M) transiently (10‐15 min) depolarized the membrane. The membrane remained depolarized after prolonged exposure (over 20 min) to ATP (above 3 X 10(‐5) M), AMP‐PNP (above 10(‐5) M) or mATP (above 3 X 10(‐8) M). 3. ATP (above 10(‐5) M), AMP‐PNP (above 5 X 10(‐6) M) or mATP (above 3 X 10(‐8) M) decreased the membrane resistance. Increasing the external K+ concentration (K+o) to 10.1 mM also decreased the membrane resistance, with an associated depolarization. 4. ATP (10(‐6)‐5 X 10(‐5) M) or AMP‐PNP (over 10(‐6) M) transiently decreased and then increased amplitudes of the e.j.p. and of the slow depolarization, the latter component increasing more than the former. 5. Depolarization of the membrane by 10.1 mM‐K+o solution or mATP (10(‐7) M) decreased the amplitude of e.j.p.s, with no change in the facilitation, and the slope of the relationship between amplitude of e.j.p. and that of slow depolarization decreased with mATP but not with 10.1 mM‐K+o solution. 6. The outflows of noradrenaline and 3,4‐dihydroxyphenylglycol (DOPEG) induced by perivascular nerve stimulation increased with ATP (above 10(‐6) M) or AMP‐PNP (above 10(‐5) M), while there was no change with mATP (10(‐8)‐10(‐5) M) or 10.1 mM‐K+o solution. 7. Pre‐treatment with mATP inhibited the ATP‐induced increase in the outflow of noradrenaline and DOPEG, and also the ATP‐induced enhancement of the amplitude of the e.j.p. 8. Therefore ATP and AMP‐PNP have predominantly excitatory actions on both pre‐ and post‐junctional membranes, while mATP has an excitatory action on the post‐junctional membrane but antagonizes the facilitatory action of ATP on release of noradrenaline from the nerve terminal.
Exercise during intermittent cold exposure prevents acclimation to cold rats.
Authors: Arnold J , Richard D
Published: December 2014

1. Energy balance and brown adipose tissue growth were examined in four groups of male Wistar rats: (i) sedentary, living at 24 degrees C (warm), (ii) exercise‐trained, 2 h daily, living at 24 degrees C, (iii) living at 24 degrees C but exposed to ‐5 degrees C, 2 h daily and (iv) living at 24 degrees C but exercise‐trained while being exposed to ‐5 degrees C, 2 h daily. 2. Cold exposure during exercise training appeared to have little additional influence on body composition following 28 days of treatment; body mass gain, in addition to protein and fat gains, of exercised cold‐exposed rats were similar to the gains observed in exercised warm‐exposed control animals. However, in sedentary cold‐exposed rats protein, fat and body mass gains were significantly lower than the gains measured in sedentary rats not exposed to cold. 3. Metabolizable energy intake, expressed mass‐independently, was similar in sedentary warm‐exposed rats and both groups of animals that were exercise‐trained. Metabolizable energy intake was increased almost 15% in sedentary cold‐exposed rats. 4. Energy expenditure (mass independent), excluding the net cost of exercise training, was not different in sedentary warm‐exposed and exercised rats; energy expenditure was almost 20% higher in sedentary cold‐exposed rats. 5. Total protein and deoxyribonucleic acid (DNA) contents of brown adipose tissue were more than doubled in sedentary rats exposed to cold; protein and DNA levels were similar among the other three groups of rats. 6. Treadmill running during daily, 2 h exposure at ‐5 degrees C appears to prevent the cold acclimation responses that occur in sedentary rats receiving similar cold exposure.
Augmented synaptic release by one excitatory axon in regions in which a synergistic axon was removed in lobster muscle.
Authors: Dudel J , Parnas I
Published: December 2014

1. In the lobster, every fibre of the lateral abdominal extensor muscle is innervated by two excitatory axons. When one of the excitatory axons (the common excitor) was removed chronically by intracellular injection of pronase, terminals of the remaining axon (the specific L1 excitor) showed augmented transmitter release. 2. Evidence as to the mechanism of this strengthening can be obtained taking advantage of the peculiar innervation pattern of the abdominal extensors. The L1 excitor axon of one segment sends a branch to part of the next posterior segment. The common excitor axon innervates only muscle fibres of its own segment. 3. 10‐20 days after removing the common excitor axon of segment II, the quantum content of release of terminals of the L1 excitor axon was measured in segments I, II and III. Terminals of the L1 excitor axon of segment I which innervate segment II released much more transmitter than controls, while the terminals of the same axon innervating segment I remained normal. Similarly, terminals of the L1 excitor axon of segment II became 'stronger' in segment II but remained normal in segment III. 4. It is concluded that only those terminals of one axon which innervate targets with reduced innervation increased the average release rate. It seems that the signal for synaptic strengthening, after removal of a synergistic axon, is generated and acts locally in partially denervated muscle fibres.
Myogenic adaptation of rabbit ear arteries to pulsatile internal pressures.
Authors: Speden R N , Warren D M
Published: December 2014

1. The effect of sinusoidal internal pressures on the constriction of in vitro, pressurized segments of ear arteries from rabbits has been examined. All arteries were constricted against a static transmural pressure of 60 mmHg to 35‐60% of maximal, using extraluminal noradrenaline, before being exposed to the sinusoidal pressures. 2. There was a short period of adaptation when active arteries were first exposed to physiological pulsatile pressures. This adaptation had two components: a small, largely transient distension, lasting about 1 min, and sustained suppression of the distension produced by individual pressure pulses. 3. Constriction of adapted arteries was insensitive to physiological changes in pulse frequency (3‐5 Hz), mean pulsatile pressure (60‐120 mmHg), pulse amplitude (20‐40 mmHg) and to alterations in pulse shape (sinusoidal, triangular and ramp). Over‐all distension was restricted to 3.6 +/‐ 1.0% (S.D. of an observation) when the mean of a 3 Hz sinusoidal pressure of 30 mmHg amplitude was increased in steps from 75 to either 115 or 120 mmHg. 4. An initial distension was needed to initiate suppression of pressure pulse distension. Distension by individual pressure pulses, within a train of rectangular 60‐90 mmHg pulses of 0.5 s duration, was maximally suppressed (85.6 +/‐ 1.3%; S.E. of mean, n = 9) at a pulse interval of 0.7 s. 5. Active ear arteries possess a myogenic mechanism capable of minimizing changes in constriction over the full physiological range of pulsatile internal pressures.
Transient tension changes initiated by laser temperature jumps in rabbit psoas muscle fibres.
Authors: Goldman Y E , McCray J A , Ranatunga K W
Published: December 2014

1. A technique was developed to generate 2‐8 degrees C step temperature perturbations (T‐jumps) in single muscle fibres to study the thermodynamics of muscle contraction. A solid‐state pulsed holmium laser emitting at 2.065 microns heated the fibre and surrounding solution in approximately 150 mus. The signal from a 100 microns thermocouple fed back to a heating wire maintained the elevated temperature after the laser pulse. 2. Tension of glycerol‐extracted muscle fibres from rabbit psoas muscle did not change significantly following T‐jumps when the fibre was relaxed. 3. In rigor, tension decreased abruptly on heating indicating normal (not rubber‐like) thermoelasticity. The thermoelastic coefficient (negative ratio of relative length change to relative temperature change) of the fibre was estimated to be ‐0.021 at sarcomere lengths of 2.5‐2.8 microns. Rigor tension was constant after the temperature step and returned to the original value on recooling. 4. In maximal Ca2+ activation, tension transients initiated by T‐jumps had several phases. An immediate tension decrease suggests that thermoelasticity during contraction is similar to that in rigor. Active tension then recovered to the value before the T‐jump with an apparent rate constant of approximately 400 s‐1 (at 10‐20 degrees C). This rate constant did not have an appreciable dependence on the final temperature. Finally, tension increased exponentially to a new higher level with a rate constant of approximately 20 s‐1 at 20 degrees C. This rate constant increased with temperature with a Q10 of 1.4. 5. At submaximal Ca2+ activation the tension rise was followed by a decay to below the value before the T‐jump. This decline was expected from the temperature dependence of steady pCa‐tension curves. The final tension decline occurred on the 1‐5 s time scale. 6. The value and amplitude dependence of the rate constant for the quick recovery following T‐jumps were similar to those of the quick recovery following length steps during active contractions. The enthalpy change associated with the quick tension recovery following temperature‐step perturbations was estimated to be positive suggesting that the recovery process is an endothermic reaction. Slower reaction steps on the 10‐30 ms timescale, as well as reactions corresponding to the quick recovery, may contribute to the cross‐bridge power stroke.
Post‐contraction errors in human force production are reduced by muscle stretch.
Authors: Hutton R S , Kaiya K , Suzuki S , Watanabe S
Published: December 2014

1. Based on findings from a previous study of plantar‐flexor muscles, the effect of a conditioning 25, 50 or 100% maximum voluntary contraction (m.v.c.) of elbow flexor muscles on the accuracy of reproducing a learned criterion muscle force (2% m.v.c.) was investigated. 2. Each conditioning contraction induced a significant error in reproducing the criterion muscle force under conditions of no visual feed‐back of force. As with plantar‐flexor muscles, the error was consistently in the direction of a positive bias. The magnitude of the error co‐varied with the magnitude of the previous contraction and, in all cases, decayed toward criterion force values over a 35 s period. 3. A brief muscle stretch, induced before subjects attempted the criterion force, reduced the size of the error but did not completely eliminate the bias. 4. The findings provide indirect evidence of post‐contraction potentiation of stretch reflex pathways. Residual post‐contraction errors in force production after muscle stretch may be attributed to other central or peripheral neural factors such as, for example, potentiating effects of prior activation on submaximal tension production in skeletal muscle.
Dexamethasone selectively increases sodium‐dependent alanine transport across neonatal piglet intestine.
Authors: James P S , Smith M W , Tivey D R , Wilson T J
Published: December 2014

1. Lysine and alanine uptake by pig enterocytes has been measured in piglet mid intestine both during normal development and 3 days after injection of dexamethasone and epidermal growth factor (EGF) into 3‐day‐old animals. 2. Alanine uptake measured in the presence of sodium increased markedly during the first 4 weeks of post‐natal life. Similar effects on alanine uptake could be produced through injection of dexamethasone, but not EGF, into 3‐day‐old piglets. Alanine uptake measured in the absence of sodium and lysine uptake measured in the presence of sodium remained unchanged during development and unaffected by injection of dexamethasone or EGF. 3. Enterocytes capable of transporting alanine in the presence of sodium were found, by quantitative autoradiography, to cover the top 400 micron of the villus in 6‐day‐old and 3‐4‐week‐old control pigs. Alanine concentrations in villus tip enterocytes in 3‐4‐week‐old pigs were four times those found in 6‐day‐old animals. Qualitative examination of selected villi, however, showed alanine uptake taking place over a considerably greater area of villus surface in 6‐day‐old compared with 3‐4‐week‐old animals. 4. Injection of dexamethasone and EGF into 3‐day‐old piglets caused an increase in crypt depth without apparent change in crypt cell proliferation. The rate at which enterocytes migrated out of the crypt and the length of individual villi also remained unchanged by dexamethasone or EGF injection. 5. Dexamethasone produces its effect on alanine uptake by acting on older enterocytes present on the upper part of the villus. These enterocytes can be shown, by calculations based on enterocyte migration rate, to have already been present on the villus at the time the pig was born. 6. The above findings are discussed in relation to the ability of villus as well as crypt enterocytes to change their programme of differentiation in response to external stimuli. The particular ability of dexamethasone to induce system A type carrier function is further discussed in relation to normal changes found to occur during neonatal development. It is finally suggested, as a working hypothesis, that endogenous glucagon might act as the final mediator of both developmentally controlled and dexamethasone‐induced changes in amino acid transport.
Disruption of the jejunal migrating motor complex by gastric distension and feeding in the dog.
Authors: Bull J S , Grundy D , Scratcherd T
Published: December 2014

1. The jejunal motor response to gastric distension has been quantified in the conscious dog and compared with that of feeding in order to determine the role of the physical bulk of a meal in the conversion from fasted to fed motor activity. 2. In six dogs gastric distension abolished the cyclical migrating motor complex (m.m.c.) and evoked a pattern of continuous irregular jejunal motility similar to that seen postprandially, but only after a latency of 21.5 +/‐ 2.7 min compared to that of 7.1 +/‐ 1.2 min for the response to feeding. Computer analysis of distension and fed jejunal motility revealed similar distributions of intervals between contractions and contraction amplitudes with comparable mean values for both. 3. In two dogs with antrum and corpus surgically divided distension of the corpus had a similar effect on jejunal motility although the latency to both distension and feeding were considerably less. 4. By varying the period of distension it has been possible to control accurately the duration of the jejunal motor response and so assess its effectiveness in disrupting the timing of the m.m.c. The return to m.m.c. cycling following deflation was independent of preceding complexes. The occurrence of the post‐distension activity front was closely related to the act of deflation itself (R = 0.94) following a latency of 26.2 +/‐ 2.1 min (n = 39). 5. It is concluded that the bulk of a meal contributes significantly to the early part of postprandial motility and is capable of disrupting the timing of subsequent migrating motor complexes.
Growth hormone releasing factor evokes rhythmic hyperpolarizing currents in rat anterior pituitary cells.
Authors: Nussinovitch I
Published: December 2014

1. The effect of human pancreatic growth hormone releasing factor (hpGHRF) on the electrical activity of dissociated rat anterior pituitary cells in culture was studied, using both the cell‐attached and whole‐cell modes of the patch‐clamp recording technique. 2. To avoid possible wash‐out of the responses, extracellular records were made from cell‐attached patches. Application of hpGHRF to the cells produced rhythmic inward currents through the patches, attributable to rhythmic hyperpolarizations of the cell membrane outside the patch. The amplitude of the current oscillations was 1‐8 pA and the frequency 0.05‐0.4 Hz. 3. Flooding the cells with K+ ions from a small pipette containing 50 mM or 100 mM‐K+ resulted in a reversible attenuation or block of the rhythmic inward currents evoked by hpGHRF, indicating that changes in K+ conductance were involved in the responses. 4. Flooding the cells with a solution containing 10 mM‐EGTA blocked these rhythmic inward currents reversibly, suggesting the involvement of Ca2+ in the responses. In addition, responses were blocked by adding Co2+ (5‐10 mM) to the bathing medium. The presence of tetrodotoxin (3 microM) had no effect, ruling out the participation of voltage‐gated Na+ channels. 5. With whole‐cell recording, the resting potential (‐41.46 +/‐ 7.78 mV) and input resistance (5.34 +/‐ 3.73 G omega) of anterior pituitary cells in culture were found to be similar to those previously reported for pituitary cells and chromaffin cells with the same recording method. 6. In whole‐cell experiments, application of hpGHRF (shortly prior to intracellular penetration) evoked rhythmic outward currents, associated with conductance increases, when the cells were clamped at their resting potential. The persistence of these currents in the 'voltage‐clamped' cell indicated that the rhythmicity was not related to voltage‐dependent phenomena. The currents disappeared within 4 min after breaking into the cell, presumably because of 'washout' of cell constituents into the pipette. 7. The reversal potential (‐60 mV) of the hpGHRF‐induced currents was negative to the resting potential of the cells (‐41 mV), further indicating that hpGHRF would evoke rhythmic hyperpolarizations in unclamped cells, possibly due to periodic increases in K+ conductance. 8. The possible relation of these rhythmic currents to hpGHRF‐induced secretion of growth hormone is discussed.
Characteristics of ongoing and reflex discharge of single splenic and renal sympathetic postganglionic fibres in cats.
Authors: Meckler R L , Weaver L C
Published: December 2014

1. Electrical discharge of thirty‐nine single splenic and renal postganglionic nerve fibres was recorded in artificially respired, chloralose‐anaesthetized cats. 2. Ongoing discharge rates, averaged over 10 s periods, did not differ between renal and splenic fibres. All neurones of both groups had irregular discharge frequencies. 3. Half of the splenic population and all renal fibres had cardiac‐related discharge patterns. Of those tested for respiratory‐related firing, 30% of the splenic fibres and 69% of the renal fibres exhibited this pattern. 4. Firing of splenic fibres was less inhibited than that of renal fibres by stimulation of pressoreceptors with phenylephrine‐induced increases in blood pressure. Firing of splenic fibres also was less excited than that of renal fibres by unloading pressoreceptors with depressor doses of sodium nitroprusside. 5. Chemical stimulation of splenic afferent nerves with bradykinin consistently elicited greater increases in splenic than renal nerve discharge by causing large increases in firing of all splenic fibres and smaller excitatory responses in 75% of the renal fibres. 6. Application of bradykinin to the intestinal serosa produced greater increases in renal than splenic nerve discharge by consistently causing increased firing of renal fibres and by causing excitation, inhibition, or no change in splenic fibre discharge. 7. Responses of splenic and renal fibres to stimulation of splenic and intestinal afferent nerves after spinal cord transection were similar to those responses elicited when the neuraxis was intact. 8. In conclusion, the differential reflex responses of splenic and renal neuronal populations can be due to the heterogeneity or to the intensity of responses within a neuronal population.
Sodium and water reabsorption in the proximal and distal nephron in conscious pregnant rats and third trimester women.
Authors: Atherton J C , Bielinska A , Davison J M , Haddon I , Kay C , Samuels R
Published: December 2014

1. Sodium and water reabsorption were determined in virgin controls and rats at 9 and 20 days of pregnancy during a water diuresis induced and maintained by infusion of 2.5% dextrose and in normally hydrated women during the third trimester and again 2‐3 months after delivery. 2. Reabsorption from the proximal tubules and distal nephron segments was assessed using the clearance of lithium as a marker of the sodium and water delivery from the proximal tubules to the loops of Henle. 3. Glomerular filtration rate and whole‐kidney reabsorption of sodium and water were significantly increased at both stages of pregnancy in rats and late in pregnancy in women when compared to the respective non‐pregnant control. Fractional reabsorption was unaltered in pregnant rats but increased in pregnant women. 4. Proximal tubule sodium and water reabsorption were increased in pregnant rats and women; fractional reabsorption was unaltered. 5. Absolute reabsorption of sodium and water in distal nephron segments were increased during pregnancy in both rats and women. Although increases in fractional reabsorption were detected in pregnant women, this was not the case at either stage of gestation in rats.
Primary afferent activity, putative excitatory transmitters and extracellular potassium levels in frog spinal cord.
Authors: Davidoff R A , Hackman J C , Holohean A M , Vega J L , Zhang D X
Published: December 2014

1. Changes in extracellular K+ activity were measured with ion‐selective microelectrodes in the grey matter of the isolated hemisected frog spinal cord. The magnitude of the elevation of [K+]o (delta[K+]o) produced by repetitive stimulation (25 Hz, 10 s) of afferent fibres in the sciatic nerve was monotonically related to the strength of the electrical stimuli applied to the sciatic nerve. Repetitive stimulation of the largest diameter A alpha and A beta fibres, which were found histologically to comprise only 11% of the afferent axons in the dorsal root, elevated [K+]o to approximately 60% of the maximum level seen when all afferent fibres were stimulated. 2. Addition of Mg2+ (20 mM) to Ringer solution devoid of Mg2+ reduced delta[K+]o by over 85% suggesting that about 15% of delta[K+]o results from action potentials in presynaptic primary afferents. When 20 mM‐Mg2+ was added to spinal cords bathed in Ringer solution containing a physiological (i.e. 1.0 mM) concentration of Mg2+, delta[K+]o was reduced by ca. 65‐75% indicating that in spinal cords bathed in medium containing 'physiological' concentrations of Mg2+ about 25‐35% of the K+ is released from primary afferent fibres. 3. Application of excitatory amino acids and agonists increased [K+]o with the following potency pattern: quisqualate greater than kainate greater than NMDA (N‐methyl‐D‐aspartate) greater than glutamate greater than aspartate. 4. D(‐)‐2‐Amino‐5‐phosphonovalerate (APV), an NMDA antagonist, reduced [K+]o by only about 50%, but kynurenate, an NMDA and non‐NMDA antagonist, reduced [K+]o by approximately 85%; i.e. the same levels observed when synaptic transmission was blocked with 20 mM‐Mg2+. These findings support the idea that synaptic release of excitatory amino acids such as L‐glutamate and/or L‐aspartate and subsequent activation of specific receptors by these putative transmitters are necessary for the postsynaptic component of delta[K+]o. 5. Addition of tachykinins elevated [K+]o but the effect appeared to require the participation of excitatory amino acids because it was blocked by APV and by kynurenate. 6. The finding that tetrodotoxin substantially reduced the ability of excitatory amino acid agonists and tachykinins to elevate [K+]o suggests that discharges in interneurones as a result of excitatory amino acid receptor activation are responsible for the postsynaptic component of delta[K+]o.
An electrophysiological and anatomical study of intestinal afferent fibres in the rat.
Authors: Cervero F , Sharkey K A
Published: December 2014

1. The afferent innervation of the distal ileum has been examined in normal rats and in rats treated at birth with capsaicin. Electrophysiological recordings were made using an in vitro preparation of distal ileum and its associated mesenteric nerves. The fibre composition of the mesenteric nerves was examined by electron microscopy and the numbers of primary afferent fibres innervating a segment of distal ileum was estimated using retrograde tracing. 2. Recordings were made from 120 single afferent units all of which showed some degree of background activity. The conduction velocities of sixty‐seven afferent units were estimated, and all were found to be in the C‐fibre range (less than 2 m/s). Eighty‐two units were sufficiently studied to allow their classification according to whether they responded to mechanical stimuli (M units), chemical stimuli (Ch units) or both mechanical and chemical stimuli (MCh units). In control rats 85.5% were classified as MCh units, 11.9% as M units and 2.6% as Ch units. In capsaicin‐treated rats six single and three multi‐units were MCh and one multi‐unit was classified as an M recording. 3. The effects of intraluminal distension were investigated in sixty‐seven units which were classified according to whether or not they adapted during the distension. About half the total units were classified as rapidly adapting, the other half were slowly adapting. This distribution was similar for the MCh‐units, but of the eight M units tested, seven adapted during distension. The distension thresholds were tested in thirty units, of which twenty‐eight responded at thresholds below 18 mmHg. There were no differences in the thresholds of units from control and capsaicin‐treated rats. 4. The chemosensitivity of units was tested in response to acetylcholine (ACh), bradykinin and substance P. Most units tested responded to ACh (78% of MCh units tested) and bradykinin (80% of MCh units), but fewer units responded to substance P (about 50% of MCh units). ACh produced an increased tension which outlasted the increase in afferent activity. Bradykinin gave long‐lasting afferent responses which were not always accompanied by increases in tension. The increases in afferent activity produced by substance P were often seen after an increase in tension. 5. The fluorescent dye True Blue injected into the wall of the ileum labelled cell bodies in the spinal and nodose ganglia, predominantly on the left side of an animal. The mean number of labelled cells per animal was eighty‐seven, of which the majority was in the T10‐T13 spinal ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)
The effects of atrial natriuretic peptide and glucagon on proximal glomerulo‐tubular balance in anaesthetized rats.
Authors: Harris P J , Skinner S L , Zhuo J
Published: December 2014

1. The renal actions of ANP (average dose 30 ng kg‐1 min‐1 and glucagon (50 ng kg‐1 min‐1) were compared using fractional lithium reabsorption as the index of proximal reabsorption in groups of seven rats. Doses were chosen to cause similar increases in glomerular filtration rate (GFR). Time controls were included. 2. Glucagon raised GFR 32% and absolute proximal reabsorption (APR) 26% producing 81% effective proximal glomerulo‐tubular balance (GTB) which was not significantly different from the 100% expected for perfect GTB. ANP raised GFR 33% and APR 10% indicating only 30% effective GTB (P less than 0.01). This was a significantly different effect from glucagon (P less than 0.005). 3. Sodium output increased 10‐fold with ANP and 3‐fold with glucagon. Filtration fraction increased 33% (P less than 0.04) above the pre‐treatment value with ANP but was unchanged with glucagon. Plasma renin concentration was suppressed similarly by each hormone (46 and 36%, P less than 0.05, compared with pre‐treatment values). 4. Despite a change in peritubular physical factors favouring reabsorption, there was almost complete attenuation of the increase expected in APR with the ANP‐induced increase in GFR. In contrast, a similar change in GFR with glucagon resulted in an almost parallel increase in APR demonstrating maintenance of proximal GTB. 5. It is concluded that in the anaesthetized rat, ANP but not glucagon profoundly inhibits the increase in proximal reabsorption that normally follows an increase in filtered load. Such an action would contribute to the more potent natriuretic activity of ANP compared with glucagon.
The functional significance of the sympathetic innervation of mucous glands in the bronchi of man.
Authors: Pack R J , Richardson P S , Smith I C , Webb S R
Published: December 2014

1. Pieces of human bronchi, from lung resected for carcinoma of the bronchus, were mounted in Ussing chambers and given [35S]sulphate as radiolabelled precursor of mucous glycoproteins (mucins). The release of 35S, bound to macromolecules, into the luminal half‐chamber was used as an index of mucin secretion. 2. Noradrenaline, at concentrations of 1, 10 and 100 microM, was given into both halves of the Ussing chamber. At the lowest concentration, noradrenaline failed to change mucin output, but at the two higher concentrations it stimulated output. 3. In other experiments the sympathetic nerves in the bronchial wall were labelled with 5‐hydroxydopamine and examined under the electron microscope. The distances between adrenergic nerve varicosities and submucosal glands were measured; some sympathetic nerve varicosities were seen within 1 microns of gland cells. 4. A simple mathematical model for the diffusion of noradrenaline was used to predict the concentrations of the transmitter likely to result at different distances from a nerve if one or more vesicles of noradrenaline were released. 5. The model predicts that the release of a single large vesicle of noradrenaline is likely to generate an effective concentration of transmitter provided that the nerve is within 1 micron of the target cell.
Activation of single ion channels from toad retinal rod inner segments by cyclic GMP: concentration dependence.
Authors: Matthews G , Watanabe S
Published: December 2014

1. Patch‐clamp recordings of single cyclic GMP‐activated channels from toad rod photoreceptors were made in inside‐out membrane patches containing only one such channel. Patches were obtained from the inner segment, where the density of cyclic GMP‐activated channels is lower than in the outer segment, making one‐channel patches possible. The dependence of channel gating on cyclic GMP concentration ([cyclic GMP]) was studied. At low [cyclic GMP] (5‐10 microM), channel openings were infrequent and occurred as bursts of rapid opening and closing. As [cyclic GMP] was increased, bursts became more frequent, until at 1 mM the activity fused into long bouts of rapid flicker between open and closed states. 2. The duration of brief openings and closings (flicker) within bursts was not affected by [cyclic GMP]. This suggests that the rapid flicker within bursts results from an intrinsic channel property not associated with agonist‐induced receptor activation. 3. At 10 microM‐cyclic GMP, the distribution of closed times was fitted by a sum of three exponential components. The briefest, with time constant averaging 0.29 ms, corresponded to the brief closings within bursts, while the two longer components, with time constants averaging 3.5 and 32 ms, corresponded to much longer closings between bursts. At 0.5 or 1 mM‐cyclic GMP (saturation), the longer components disappeared, and the distribution of closed times was fitted by a single‐exponential equation with the same time constant as the briefest component observed at lower concentrations. 4. Because the channel continued to flicker even at high [cyclic GMP], the maximal probability of being in the open state (Po) did not approach 1.0, averaging 0.30 +/‐ 0.05 (N = 8). The relation between Po and [cyclic GMP] was fitted by the Hill equation with an exponent of 3, suggesting that binding of cyclic GMP to multiple sites is required to open the channel.
Double‐hyperbolic force‐velocity relation in frog muscle fibres.
Authors: Edman K A
Published: December 2014

1. The relationship between force and velocity of shortening was studied at 2.10 micron sarcomere length during fused tetani (1‐3 degrees C) in single fibres isolated from the anterior tibialis muscle of Rana temporaria. The speed of shortening was recorded from the whole fibre and, in some experiments, simultaneously from a short (ca. 0.6 mm) segment, while the preparation was released to shorten isotonically at selected force levels (‘load‐clamp’ recording). The segment was defined by opaque markers of hair that were placed on the fibre surface. The distance between the markers was recorded by means of a photo‐electric detector system. 2. The force‐velocity relation had two distinct regions, each one exhibiting an upwards concave shape, that were located within the ranges 0‐78 and 78‐100% of the measured isometric force (P0), respectively. The two portions of the force‐velocity relation could be fitted well by hyperbolic functions or by single‐exponential functions. The curvature was more pronounced in the high‐force region than at low‐intermediate loads. The transition between the two portions of the force‐velocity relation (the ‘break point’ of the force‐velocity curve) occurred at 78.4 +/‐ 0.4% of P0 (mean +/‐ S.E. of mean, n = 12) corresponding to 10.9 +/‐ 0.4% of maximum velocity of shortening (Vmax). The general shape of the force‐velocity curve, and the appearance of a break point near 78% of P0, was the same when measurements were made from the whole fibre and from a short segment along the same fibre. 3. The ‘negative’ branch of the force‐velocity relation was delineated for loads ranging from P0 to 1.6‐1.8 P0 in five experiments. The negative branch formed a smooth continuation of the force‐velocity relation recorded between 0.78 P0 and P0. The force‐velocity relation was nearly flat between 0.90 P0 and 1.20 P0, the difference in speed of shortening or elongation being 1.8 +/‐ 0.3% (mean +/‐ S.E. of mean, n = 5) of Vmax over this range. 4. An increase in sarcomere length from 1.85 to 2.60 micron did not affect Vmax but caused a steady decrease in curvature of the force‐velocity relation, both at low‐intermediate loads and in the high‐force range. Similar changes in shape of the force‐velocity relation were produced by osmotic compression of the fibre in a Ringer solution made hypertonic by addition of 98 mM‐sucrose.(ABSTRACT TRUNCATED AT 400 WORDS)
Stimulation of breathing movements by L‐5‐hydroxytryptophan in fetal sheep during normoxia and hypoxia.
Authors: Fletcher D J , Hanson M A , Moore P J , Nijhuis J G , Parkes M J
Published: December 2014

1. In fetal lambs in late gestation, systemic infusion of L‐5‐hydroxytryptophan (L‐5‐HTP) during normoxia greatly increases the incidence of fetal breathing movements (FBM) and high‐voltage electrocortical activity (HV ECoG). It also induces FBM during HV ECoG and increases blood pressure. To investigate its mechanism of action, L‐5‐HTP was administered in conjunction with the 5‐hydroxy‐tryptamine (5‐HT) antagonists ketanserin or cyproheptadine. L‐5‐HTP was also infused with or without the antagonists during hypoxia, to test whether it would overcome the inhibition of FBM by hypoxia. 2. When L‐5‐HTP was given in normoxia, cyproheptadine blocked and ketanserin reduced the increase in blood pressure, both drugs blocked the stimulation of FBM, but neither drug prevented the induction of prolonged episodes of HV ECoG. 3. In hypoxia, L‐5‐HTP similarly stimulated FBM. This effect was also blocked by cyproheptadine and was delayed by ketanserin. 4. The antagonism of the effects of L‐5‐HTP on blood pressure and the incidence of FBM in normoxia and hypoxia is consistent with the action of L‐5‐HTP via 5‐HT receptors. At present there is no clear explanation of the mechanism by which L‐5‐HTP induces HV ECoG.