bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of phosphodiesterase inhibitors on the electrical activity of toad rods.
Authors: Capovilla M , Cervetto L , Torre V
Published: December 2014

The membrane potential of toad rods was recorded during addition of small amounts of phosphodiesterase inhibitors to the extracellular medium. Separate application of 3‐isobutyl‐1‐methylxanthine (IBMX), caffeine, theophylline, papaverine and RO 20‐1724 slowed down the time course of rod photo‐response to dim flashes of light. These changes were associated with a two to six‐fold increase in the amplitude of photoresponse. The effects on kinetics may be described simply by an expansion of the photoresponse time scale. When the drug concentration was raised above a certain level, the rods showed supralinear behaviour whereby doubling of the intensity of a dim flash could increase the response more than two‐fold. Under similar conditions rods also showed light sensitization whereby responses to dim flashes were enhanced in the presence of dim backgrounds. Taking the drug concentration that induced a two‐fold increase in the time‐to‐peak, IBMX was found the most effective compound, followed by papaverine, RO 20‐1724, theophylline and caffeine with relative effectivities 1, 1/2, 1/7, 1/40 and 1/100. Sensitivity, kinetics and supralinear behaviour may be restored to normal by steady background illumination while still in the presence of IBMX. However the intensity of the steady light, needed to restore the sensitivity to control levels, is not sufficient to accelerate the kinetics back to control values. In the presence of 50 microM‐IBMX a dim steady background of light enhanced the response to dim flashes. When the intensity of the light background was increased rods were desensitized and the supralinear behaviour disappeared. The antagonism between the effects of IBMX and the effects of background illumination on the kinetics of photoresponse suggests that phosphodiesterase activity controls the time course of light response in vertebrate rods.
Changes in fetal renal function in response to infusions of a hyperosmotic solution of mannitol to the ewe.
Authors: Lumbers E R , Stevens A D
Published: December 2014

In six pregnant ewes a reduction in transplacental water transfer was produced by increasing maternal osmolality (by infusion of 180 g of mannitol in 500 ml of 0.15 M‐sodium chloride) and the fetal renal responses to this reduction in water transfer were studied. These responses were compared with the renal responses of five other chronically catheterized fetal lambs whose mothers received I.V. infusions of 500 ml of 0.15 M‐sodium chloride. Intravenous infusion of 500 ml of 0.15 M‐sodium chloride to the ewe produced no changes in fetal plasma sodium, potassium or plasma renin activity and had no effect on fetal renal function. After I.V. infusion of mannitol to the ewe, fetal urinary flow rate fell from control levels of 0.69 +/‐ 0.12 ml/min to 0.32 +/‐ 0.04 ml/min (S.E. of mean, P less than 0.006). This fall in urinary flow rate was due to increased water reabsorption because there was no change in glomerular filtration rate and osmolar clearance. Fetal urinary sodium excretion increased from 16.2 +/‐ 2.0 mumol/min, to 34.2 +/‐ 6.9 mumol/min (S.E. of mean, P less than 0.04). This increase in fetal urinary sodium excretion was due to a fall in the fractional reabsorption of sodium which was related to this rise in fetal plasma sodium levels that occurred following infusion of mannitol to the ewe. The increases in fetal plasma sodium levels were also associated with reductions in fetal plasma renin activity.
Correlation of agonist structure with acetylcholine receptor kinetics: studies on the frog end‐plate and on chick embryo muscle.
Authors: Auerbach A , del Castillo J , Specht P C , Titmus M
Published: December 2014

The apparent lifetimes of frog end‐plate channels activated by several nicotinic agonists have been determined with voltage‐jump and fluctuation analysis techniques. The agonists were monoquaternary, N‐substituted derivatives of trimethylammonium (TMA). Methyl TMA activated channels which had apparent lifetimes about 3‐4 times shorter than acetylcholine (ACh)‐activated channels. This result was confirmed with single‐channel recordings from embryonic chick skeletal muscle. Channel conductance and voltage dependence of channel lifetime were similar for methyl TMA‐ and ACh‐activated channels. Methyl TMA showed no signs of blocking open end‐plate channels. Ethyl TMA, acetylthiocholine, cholinethiol and carbamylcholine all activated channels similar to methyl TMA‐activated channels with regard to lifetime. None of these agonists appeared to block end‐plate channels in the employed concentrations. 4‐ketopentyl TMA, which contains a methylene group in place of the ether oxygen of ACh, sometimes opened end‐plate channels with similar apparent lifetimes as those opened by ACh. Single‐channel recordings showed that bursts of current from channels activated by 4‐ketopentyl TMA have similar durations as do those activated by ACh. Pentyl TMA and benzyl TMA block open end‐plate channels even when delivered at doses which elicit very small currents. It is concluded that the ester moiety of ACh serves to stabilize the open conformation of the channel.
Development of sensory‐motor synapses in the spinal cord of the frog.
Authors: Frank E , Westerfield M
Published: December 2014

The development and specificity of monosynaptic sensory‐motor synapses were studied in the brachial spinal cord of bullfrog tadpoles. Intracellular and extracellular recordings were made from motoneurones innervating several different muscles of the forelimb. Excitatory synaptic potentials (e.p.s.p.s) were elicited by stimulation of various peripheral muscle nerves. Sensory and motor axons in the triceps brachii muscle nerves were electrically excitable at stage XIII, the earliest stage studied. Their conduction velocities were 0.2‐0.4 m/s. These velocities increased during subsequent development so that by stage XXII they were approximately 5 m/s. Before stage XVII, synaptic potentials evoked in motoneurones by stimulation of the triceps sensory fibres had a long central latency and fatigued easily. These potentials were probably mediated polysynaptically. At stage XVII, the first short‐latency triceps synaptic potentials appeared. They had central latencies of less than 3 ms and represented the direct, monosynaptic input from muscle sensory cells on to motoneurones. During subsequent development the percentage of triceps motoneurones innervated by triceps sensory fibres increased, while the number of long‐latency polysynaptic inputs decreased. Both the electrical and chemical components, characteristic of these monosynaptic e.p.s.p.s in adult frogs, were prominent from the time the e.p.s.p.s first appeared. The pattern of innervation of brachial motoneurones by triceps sensory afferents was specific from the beginning. Triceps sensory fibres innervated most triceps motoneurones but very few subscapular or pectoralis motoneurones, just as in adult frogs. At no time were there appreciable numbers of ‘aberrant’ connexions. The developmental time course of several different classes of sensory‐motor connexions was similar. Thus the synaptic specificity of this system cannot be explained by a differential timing of synaptogenesis.
Ventral medullary relay neurones in the pathway from the defence areas of the cat and their effect on blood pressure.
Authors: Hilton S M , Marshall J M , Timms R J
Published: December 2014

In cats anaesthetized with Althesin, the efferent descending pathway from the brain‐stem defence areas has been traced through the medulla by identifying sites at which electrical stimulation evoked the characteristic pattern of the visceral alerting (defence) response. This response includes an increase in arterial blood pressure resulting from increased heart rate and cardiac output and vasoconstriction in renal and splanchnic beds, accompanied by active vasodilation in skeletal muscle. The efferent pathway runs as a narrow strip, about 3 mm from the mid line, ventral to the superior olive and the nucleus of the trapezoid body, extending caudally to the rostral portion of the inferior olive where it lies ventral to the facial nucleus. It was found to lie very close to the ventral medullary surface just rostral to and within the area at which bilateral topical application of glycine results in a profound fall in arterial blood pressure and cessation of respiration. On bilateral application of glycine to the sensitive area of the ventral medulla, the visceral alerting response evoked by stimulation in the defence areas of the amygdalo‐hypothalamic complex, or the mid‐brain central grey or tegmentum, was attenuated in parallel with the fall in arterial pressure, the vasoconstrictor responses being most strongly reduced. As soon as arterial blood pressure had fallen to its lowest level the visceral alerting response was virtually abolished. A small radio‐frequency lesion made in the ventral medullary efferent pathway, in the rostral part of the ‘glycine‐sensitive area', had the same effect as that produced by unilateral application of glycine: it resulted in little respiratory or cardiovascular effect itself, but application of glycine to the contralateral area then produced the full effect otherwise seen only on bilateral application of glycine. It is suggested (1) that the effects of glycine result from blockade of a synaptic relay, close to the ventral surface of the medulla, in the efferent pathway from the defence areas to the preganglionic sympathetic neurones, and (2) that the neurones which receive an input from the alerting (defence) areas normally provide an essential, tonic excitatory drive to the sympathetic output and probably to respiration also. After sudden withdrawal of this drive, vasomotor tone and the normal level of arterial blood pressure are not maintained.
The intracellular pH of frog skeletal muscle: its regulation in isotonic solutions.
Authors: Abercrombie R F , Putnam R W , Roos A
Published: December 2014

The behaviour of intracellular pH (pHi) was studied with micro‐electrodes in frog semitendinosus muscle which was superfused with Ringer solution and with depolarizing solutions. The electrodes were introduced into the depolarized muscle about 40 min after contracture had subsided. All studies were done at external pH (pHo) of 7.35 and at 22 degrees C. The pHi in normal Ringer solution buffered with HEPES was 7.18 +/‐ 0.03 (S.E. of mean) (n = 10); the membrane potential, Vm, was ‐88 +/‐ 1.8 mV. When pHi was lowered to about 6.8 by replacing the HEPES by 5% CO2, 24 mM‐HCO3 (constant pHo), it recovered at a very slow rate of 0.025 +/‐ 0.011 delta pHi h‐1 (n = 6). When all the Na was replaced by N‐methyl‐D‐glucamine (initial pHi 7.20 +/‐ 0.04, initial Vm ‐89 +/‐ 1.5 mV, n = 8), this slow alkalinization was converted into a slow acidification at a rate of 0.069 +/‐ 0.024 delta pHi h‐1. In muscle depolarized in 15 mM‐K (Vm approximately ‐50 mV), the rate of recovery from CO2 acidification was not increased above that in normal Ringer solution (2.5 mM‐K). When, however, the muscle was depolarized in 50 mM‐K to about ‐20 mV, the rate of recovery increased to 0.33 +/‐ 0.07 delta pHi h‐1 (n = 6) when external Cl was kept constant, or to 0.21 +/‐ 0.03 (n = 9) when [K]. [Cl] product was kept constant. In the absence of Na, pHi recovery rate in 50 mM‐K was reduced by at least 90%. Enhanced recovery from CO2‐induced acidification was also observed in 2.5 mM‐K when the fibres were depolarized to about ‐20 mV in one of two ways: (a) by previous exposure for 60 min to 50 mM‐K at constant Cl, or (b) by reduction of external Cl to 5.9 mM in the presence of 0.5 mM‐Ba. When pHi of depolarized fibres (50 mM‐K) was lowered to about 6.8 by the weak acid dimethyl‐2,4‐oxazolidinedione (DMO), it recovered at a rate of 0.12 delta pHi h‐1 in two experiments. In fibres depolarized in 50 mM‐K and constant Cl, either 0.1 mM‐SITS or 0.5 mM‐amiloride slowed pHi recovery from CO2 exposure by about 50%. When the depolarization was achieved at constant [K]. [Cl] product, amiloride slowed pHi recovery by about 50%, while SITS had, at most, only a slight effect.(ABSTRACT TRUNCATED AT 400 WORDS)
Receptor potentials of lizard cochlear hair cells with free‐standing stereocilia in response to tones.
Authors: Holton T , Weiss T F
Published: December 2014

Intracellular potentials were recorded with micropipettes from hair cells with free‐standing stereocilia in the cochleae of anaesthetized alligator lizards. Wave forms of intracellular responses to click stimuli were classified into three types: hair cells, supporting cells, and untuned cells. We studied primarily the responses of hair cells to tonal stimuli. For most frequencies, f, and levels, P, of tone‐burst stimuli, the response envelope of the receptor potential increases monotonically at the tone‐burst onset, and decreases monotonically at tone‐burst offset. Overshoot in the envelope of the response at the onset and offset of tone bursts is observed only for tone bursts of low f, high P, and short (approximately equal to 1 msec) rise/fall time. The steady‐state response to tones consists of a positive (depolarizing) d.c. component, V0, plus a.c. components (e.g. a fundamental component, V1, second harmonic, V2, and third harmonic, V3). The magnitudes of a.c. and d.c. components are functions of f and P, and show three characteristics: frequency selectivity, non‐linearity, and low‐pass filtering. The receptor potential is frequency selective. The frequency selectivity of V0 and V1 components was measured by means of iso‐voltage (iso‐V0 and iso‐V1) contours. Iso‐V0 and iso‐V1 contours are V‐shaped: the maximum sensitivity occurs at a characteristic frequency (c.f.). The shapes of these contours near the c.f. depend on the values of V0 and V1 at which the contours were measured and are sharper for lower values of V0 and V1. The mean slopes of the low‐ and high‐frequency sides of these contours are: ‐45.0 and +85.1 dB/decade for iso‐V0 contours (n = 26), and ‐33.6 and +103.8 dB/decade for iso‐V1 contours (n = 28). The receptor potential has non‐linear properties. The magnitudes and phase angles of V0, V1, V2, and V3 receptor‐potential components were measured as a function of P for different f. The slopes of level functions (the dependence of log V0 and log magnitude of V1 on log P) were measured at low levels for different f. For values of f differing from c.f. by more than a half‐octave, the slope for V0 is between 1 and 2 with a mean of 1.3; the slope for V1 is about 1, i.e. magnitude of V1 increases approximately linearly with P. For frequencies near c.f., the slopes for V0 and V1 are approximately 0.8 and 0.5, respectively, indicating the presence of a compressive non‐linearity.(ABSTRACT TRUNCATED AT 400 WORDS)
The effects of low sodium solutions on intracellular calcium concentration and tension in ferret ventricular muscle.
Authors: Allen D G , Eisner D A , Lab M J , Orchard C H
Published: December 2014

Papillary muscles from the right ventricles of ferrets were micro‐injected with the photoprotein aequorin. Both tension and the light emitted by the aequorin, which is a measure of the free intracellular Ca concentration [( Ca2+]i), were monitored. Exposure of the papillary muscle to a solution in which all the Na had been replaced by K (0 Na(K) solution) resulted in an increase in tension which subsequently slowly decreased. This contracture was associated with a large increase in [Ca2+]i followed by a decrease to a steady‐state‐level which was often significantly greater than that in Na‐containing solutions. If choline, Li or Tris was used instead of K as a substitute for Na, both the contracture and the associated increase of [Ca2+]i were reduced. The effects of depolarization alone (by raising external K at constant Na concentration) were compared with those of Na removal alone (at constant external K concentration). Na removal contributes more than depolarization to the effects of a Na‐free, K‐containing solution on the contracture and rise of [Ca2+]i. Increasing intracellular Na concentration [( Na+]i), by exposure to strophanthidin (10 mumol/l), increased the magnitude of both the contracture and [Ca2+]i in 0 Na(K) solutions. Conversely, decreasing [Na+]i by exposure to a solution containing a decreased extracellular Na concentration [( Na+]o), decreased the contracture and [Ca2+]i. When contractures were produced by solutions with various [Na+]o, the size of the resulting contracture and [Ca2+]i were inversely related to [Na+]o. No contracture was seen unless [Na+]o was reduced to below 70 mmol/l. A decrease in the extracellular Ca concentration [( Ca2+]o) from 2 to 0.5 mmol/l or an increase to 8 mmol/l produced, respectively, large decreases and increases of the twitch and accompanying Ca transient. However, if [Ca2+]o was changed at the same time as Na was replaced by K there was little effect on either the contracture or the rise of [Ca2+]i. If [Ca2+]o was changed before replacing Na by K then increasing [Ca2+]o from 2 to 8 mmol/l decreased, and decreasing [Ca2+]o from 2 to 0.5 mmol/l increased, the rise of [Ca2+]i produced by replacing Na by K. The difference between this result and that obtained when [Ca2+]o was changed at the same time as Na was removed may be due to changes of [Na+]i produced by prolonged exposure to an altered [Ca2+]o.(ABSTRACT TRUNCATED AT 400 WORDS)
Interpretation of fusimotor activity in cat masseter nerve during reflex jaw movements.
Authors: Gottlieb S , Taylor A
Published: December 2014

Simultaneous recordings were made from fusimotor axons in the central ends of filaments of the masseter nerve, and from masseter and temporalis spindle afferents in the mesencephalic nucleus of the fifth cranial nerve in lightly anaesthetized cats. Fusimotor and alpha‐motor units in the masseter nerve were differentiated on the basis of their response to passive ramp and hold stretches applied to the jaw. Spindle afferents were identified as primary or secondary according to their dynamic index after administration of suxamethonium. The activity of a given fusimotor unit during reflex movements of the jaw followed one of two distinct patterns: so‐called ‘tonic’ units showed a general increase in activity during a movement, without detailed relation to lengthening or shortening, while ‘modulated’ units displayed a striking modulation of their activity with shortening, and were usually silent during subsequent lengthening. Comparison of the simultaneously recorded fusimotor and spindle afferent activity suggests that modulated units may be representative of a population of static fusimotor neurones, and tonic units of a population of dynamic fusimotor neurones. In these lightly anaesthetized animals, both primary and secondary spindle afferents showed increased firing during muscle shortening as well as during lengthening. This increase during shortening is not usually seen in conscious animals and reasons are given for the view that it is due to greater depression of alpha‐motor activity than of static fusimotor activity during anaesthesia. The results are discussed in relation to the theories of ‘alpha‐gamma co‐activation’ and of ‘servo‐assistance'; and it is suggested that static fusimotor neurones provide a ‘temporal template’ of the intended movement, while dynamic fusimotor neurones set the required dynamic sensitivity to deviations from the intended movement pattern.
Amiloride sensitive and insensitive sodium pathways and the cellular sodium transport pool of colonic epithelium in rats.
Authors: Edmonds C J , Mackenzie J
Published: December 2014

Methods for measurement of the epithelial Na transport pool (Nat) using epithelial scrapings and for analysing the transepithelial ionic fluxes of rat distal colon in vivo into transcellular and paracellular components have been used to study the amiloride sensitive (a.s.) and amiloride insensitive (a.i.) transcellular pathways in relation to variations of Nat. In the Na‐replete normal rats, substitution of SO4 for Cl in the lumen approximately halved the Na transported by a.i. pathways and reduced Nat by about 60%, but in the Na‐depleted rats, substitution of SO4 did not affect either the Na transported by a.s. pathways or Nat. The value of Nat for normal rats, with 150 mM‐NaCl in the lumen, was 6‐7 nmol Na mg‐1 dry weight (corresponding to about 2‐3 mmol kg‐1 cell water) and fell by about 60% when lumen Na concentration was reduced to 50 mM. Its turnover half‐time was 0.6 min. Nat was about threefold greater in the Na‐depleted than in the normal rats but became undetectable when amiloride was in the lumen. Amiloride did not affect Nat in normal rats. We conclude that the increased Na absorption in Na depletion depended on substitution of a.s. for a.i. apical membrane pathways allowing increased Na entry into the epithelial cells so expanding Nat and stimulating the basolateral Na pumps.
Canine oesophageal mechanoreceptors.
Authors: Satchell P M
Published: December 2014

The properties of slowly adapting oesophageal mechanoreceptors were determined in anaesthetized dogs in which the oesophagus had been isolated surgically. Changes in oesophageal pressure resulted in reproducible changes in oesophageal volume. Action potentials were recorded from thirty‐three oesophageal afferent nerve fibres in the cervical vagus. All the receptors were located in the thoracic oesophagus. The conduction velocities of the afferent fibres ranged from 9.3 to 27.7 m/s (mean, 17.2; S.D., 4.1). The receptors were of the 'in series' type. In the pressure range of 0‐1 mmHg, all units were tonically active with irregular firing rates that ranged from 0.2 to 13.0 Hz. Lung inflation altered the discharge rate in a variable manner depending upon the degree of distension of the oesophagus. The adapted discharge rate of eight units reached a maximum of 23‐44 Hz (mean, 35; S.D., 8) at an oesophageal pressure of 8‐15 mmHg (mean, 11; S.D., 3). The relationship between pressure and discharge rate was linear over a narrow pressure range. Ramps of similar gradient produced higher discharge rates in units whose afferent fibres had higher conduction velocities. In some units a large increase in firing rate occurred over a narrow pressure range and became more pronounced with ramps of increasing gradient. This increase in firing rate was called a 'burst'. Six out of thirty‐three units showed a 'burst' response. The conduction velocities of these six units ranged from 18.7 to 23.5 m/s. Slowly adapting oesophageal mechanoreceptors could be subdivided functionally into two types. Their discharge pattern was dominated by a narrow response range. These properties may be significant in an organ that is normally empty and has a low residual volume.
Neuronally mediated interactions between urinary bladder and internal anal sphincter motility in the cat.
Authors: Bouvier M , Grimaud J C
Published: December 2014

The effects of stimulation of vesical afferents on the electrical activity of the internal anal sphincter were studied in anaesthetized cats. Excitation of vesical afferents, either by electrical stimulation of nerves running at the vesico‐ureteral junction or by bladder distension, produced (1) an increase in the electrical activity of the internal anal sphincter which was abolished by the alpha‐blocker phentolamine (1.5 mg/kg, I.V.); (2) an inhibition of the excitatory response evoked in the internal anal sphincter by stimulation of one hypogastric nerve. This effect was blocked by naloxone (2 mg/kg, I.V.). These reflexes were abolished by hexamethonium (1 mg/kg, I.V.). Both reflexes were unaffected by section of sacral spinal roots (S1‐S3) or by administration of atropine (0.1 mg/kg, I.V.). This excludes any participation of the parasympathetic nervous system. The excitatory and inhibitory reflexes were only slightly affected by section of the lumbar dorsal spinal roots (L1‐L7) whereas they were strongly decreased after section of the corresponding ventral roots. The reflexes were abolished after section of the remaining hypogastric nerve. These results provide evidence for crossed reflexes between urinary bladder and internal anal sphincter which are achieved partly in the lumbar spinal cord and partly within the inferior mesenteric ganglion. Some of the vesical afferent nerve fibres responsible for these interactions presumably reach the spinal cord via the lumbar ventral spinal roots.
Neuroendocrine responses to stimulation of the splanchnic nerves in bursts in the conscious adrenalectomized calf.
Authors: Bloom S R , Edwards A V , Ghatei M A
Published: December 2014

Effects of stimulation of the peripheral ends of the splanchnic nerves below behavioural threshold at either 4 or 2 Hz continuously for 10 min, and at 40 or 20 Hz for 1 s at 10 s intervals for 10 min, have been compared in conscious calves. Cardiovascular responses were apparently unaffected by the pattern of the stimulus, whereas pancreatic neuroendocrine responses were significantly enhanced by stimulation in bursts, as was the rise in mean arterial plasma glucose concentration. Release of bombesin‐like immunoreactivity was substantially potentiated by intermittent stimulation at relatively high frequencies and the significance of this discovery is discussed in relation to the effects that this peptide is known to evoke in this species.
Evidence for sodium‐calcium exchange in the guinea‐pig ureter.
Authors: Aickin C C , Brading A F , Burdyga T V
Published: December 2014

The effects of high‐K and low‐Na solutions on the smooth muscle of the guinea‐pig ureter have been examined in both normal tissues, and tissues in which the Na pump had been blocked by exposure to K‐free solutions or ouabain (high‐Na tissues). Tension recording, membrane potential measurements and ion analysis were used. High‐K solutions depolarize normal tissues, leading to action potential generation and phasic contractions followed, at concentrations greater than 20‐30 mM, by cessation of action potentials and the development of a biphasic contracture which declines slowly during continuous exposure. The contracture is abolished by Ca‐antagonist drugs, procaine and Ca‐free solutions. Short exposures of normal tissues to Na‐free solutions do not result in tension development. Longer exposures may initiate tension, depending on the Na substitute used. Sucrose causes depolarization of the cells and spike development associated with phasic contractions, superimposed on a small contracture; Li depolarizes the cells but causes no tension generation; Tris hyperpolarizes the cells and a small increase in basal tone may be seen. On exposure to K‐free solutions or ouabain, the tissues do not develop significant tone but their response to short application of high‐K solutions grows with time. The tissues also develop the ability to contract on short applications of low‐Na solutions. The low‐Na contractures are resistant to concentrations of Ca antagonists that abolish the K responses of normal tissues, but are abolished in Ca‐free solutions. The ability of the tissues to contract in Na‐free solutions is accompanied by an increase in intracellular Na and loss of intracellular K. Even after several hours' exposure to ouabain, however, the tissues still contain significant amounts of K and the membrane potential is the same as, or more negative than that in normal tissues. Therefore it appears that another mechanism, apart from the Na pump, can regulate intracellular Na. On continuous exposure to Na‐free solutions, the contracture declines rapidly. The decline is associated with a loss of intracellular Na. The Na‐free contracture is larger when K rather than Tris is used as the substitute. This difference persists in the presence of a concentration of Mn that abolishes the K contracture of normal tissues but is abolished by high concentrations (10 mM) of procaine.(ABSTRACT TRUNCATED AT 400 WORDS)
Activity of putative oxytocin neurones during reflex milk ejection in conscious rabbits.
Authors: Paisley A C , Summerlee A J
Published: December 2014

Extracellular electrical recordings were taken from twenty antidromically identified paraventricular neurones in unanaesthetized, unrestrained rabbits. Neuronal activity was correlated with nursing behaviour of the doe and responses of the young during suckling. Magnocellular neurones were divided into two groups on the basis of their activity in suckling. Group 1 (n = 14) showed several discrete bursts of high‐frequency activity whilst neurones in group 2 (n = 6) did not. Neurones in group 1 showed 5‐9 bursts of high‐frequency activity in suckling. Each burst lasted 1‐4 s and represented a 3‐10‐fold rise in the discharge of the cell. These units were classified as oxytocinergic, as their stereotyped activation preceded bouts of sucking behaviour of the young indicative of milk ejection. All fourteen cells continued to show intermittent bursts of neurosecretory activity for up to 20 min after nursing terminated. This pattern of discharge followed grooming behaviour of the doe. In contrast, neurones in group 2 (n = 6) showed no high‐frequency activity in suckling. They showed a significant fall in their discharge frequency compared with pre‐suckling values (P less than 0.05; Student's t test) and a significant (P less than 0.05) lengthening of the modal interspike interval. They were classed as potential vasopressin‐producing cells. Control recordings were taken from thirty‐two neurones which could not be antidromically driven. The recording sites were shown histologically to be in the lateral hypothalamic area. These cells showed a significant fall in their discharge frequency (P less than 0.05) and a significant increase (P less than 0.01) in the modal interval during suckling. Cross‐correlation studies of the activity, recorded from one electrode, of groups of neurones clustered around a single hypothalamic neurone suggest that bursting discharge from the putative oxytocin neurones in suckling is accompanied by the synchronous activation of some of the surrounding magnocellular units.
Prostaglandin receptors and hormonal actions on water fluxes in cultured canine renal cells (MDCK line).
Authors: Martinez F , Reyes J L
Published: December 2014

An established cellular line (MDCK) derived from canine kidney showed specific binding for prostaglandin E2, both when the determination of specific binding was carried out in cells attached to a semipermeable support and when this binding was determined in suspended cells in a calcium‐free medium. Specific binding for tritiated prostaglandin F2 alpha was also observed, and it was inhibited by increasing concentrations of non‐radioactive PGF2 alpha in a dose‐related pattern. Cross‐reactivity between PGE2 binding and PGF2 alpha was present. Arginine‐vasopressin induced an increase in the apical‐to‐basal water flux when applied to the basolateral surface. No change was observed when the hormone was in contact with the apical surface of the monolayer. Prostaglandin E2 also induced an increase in water flux, with a slower time course than that of arginine‐vasopressin. The presence of PGE2 inhibited the increase in water flux induced by antidiuretic hormone. The results suggest that MDCK monolayers depict a physiological antagonism between ADH and prostaglandins which is similar to that observed in natural epithelia.
Inhibition from the brain stem of inhibitory interneurones of the cat's dorsal lateral geniculate nucleus.
Authors: Ahlsén G , Lindström S , Lo F S
Published: December 2014

Brain‐stem control of inhibitory circuits in the dorsal lateral geniculate nucleus (d.l.g.n.) of the cat was studied with extracellular recordings from functionally identified interneurones and with intracellular recordings from principal cells. Perigeniculate neurones, the recurrent inhibitory interneurones of the d.l.g.n., were inhibited by low‐threshold stimulation within a wide bilateral field of the brainstem reticular formation extending from the rostral mesencephalon to the caudal medulla oblongata. The inhibition had a latency of 10‐12 ms for stimulation sites in the mesencephalon and a duration of about 100 ms. The brain‐stem stimulation evoked large hyperpolarizing potentials in intracellularly recorded perigeniculate neurones, indicating that the effect was due to post‐synaptic inhibition. Intrageniculate interneurones, the feed‐forward inhibitory interneurones of the d.l.g.n., were inhibited with a similar time course from the same region of the brain stem. Both feed‐forward and recurrent inhibitory post‐synaptic potentials (i.p.s.p.s) in principal cells were depressed by a preceding stimulation of brain‐stem sites effective for the interneurones. The depression had about the same time course as the inhibition of the interneurones and it occurred without a concomitant change in the membrane potential of the recorded principal cells. A small depolarizing potential, with a latency of 10‐20 ms, was observed in some principal cells after brain‐stem stimulation. The potential reversed polarity when i.p.s.p.s were reversed by current injection into the recorded cell indicating that it was due to disinhibition of the principal cells. The possible neuronal pathway for the inhibition of the d.l.g.n. in interneurones is considered and it is proposed that the effect is mediated by a group of neurones located in the caudal mesencephalon and the rostral pons close to the fibres of the brachium conjunctivum.
Substance P in the bovine retina: localization, identification, release, uptake and receptor analysis.
Authors: Osborne N N
Published: December 2014

Substance P‐like immunoreactivity is restricted to at least three different cell types in the bovine retina. They are amacrine cells, displaced amacrine cells and interplexiform neurones. High performance liquid chromatography and radioimmunoassay have shown that the bovine retina substance P‐like immunoreactive material cannot be distinguished from authentic substance P. Isolated bovine retina does not take up exogenous [3H]substance P as revealed by autoradiography. By increasing the external K+ concentration it was shown that the release of endogenous substance P from the retina was stimulated. This release is Ca2+ dependent. The binding of [3H]substance P to crude membrane preparations of bovine retina was saturable and revealed a single population of binding sites with a KD value of 0.32 nM and a Bmax of 2.45 pmol/g wet wt. The characteristics of the binding site suggest the presence of substance P receptors. It is suggested that substance P is a likely neurotransmitter in the bovine retina.
Mechanical properties of toad slow muscle attributed to non‐uniform sarcomere lengths.
Authors: Morgan D L , Proske U
Published: December 2014

Tension changes have been measured during shortening or stretching movements applied to actively contracting motor units of the tonus bundle of the iliofibularis muscle of the toad Bufo marinus. During a slow, constant‐velocity release tension fell, initially rapidly and then more slowly. The size of the fall, particularly later in the movement, depended on a number of factors including the duration of the isometric contraction before the onset of shortening, the amount of tension developed by the motor unit and the length of the muscle. When an isometrically contracting motor unit was rapidly shortened, the rate of rise on re‐development of tension following the release was significantly slower than at the onset of the contraction. This effect was more marked if the release was preceded by a longer period of isometric contraction, if the experiment was carried out at shorter muscle lengths or if a smaller motor unit was used. If, following a period of isometric contraction, stimulation was interrupted, and a release‐stretch movement applied to quickly bring the level of force down to near zero, and then stimulation recommenced , the final level of re‐developed tension was less than that immediately before the release. The size of the tension deficit following re‐development was larger for small motor units and at short muscle lengths. When the duration of the contraction before release was increased the size of the deficit also increased. A deficit could be prevented if the muscle was allowed to relax passively before the shortening movement was commenced. Stretch of actively contracting slow muscle produced an initial steep tension rise followed at times by a transient fall before tension slowly rose again. The transient fall became larger at short muscle lengths, and after long‐duration contractions before stretch. Its tension dependence was less easy to establish because of complications involving changes in the relative series compliance. All of the above observations could be accounted for by an explanation based on the development of sarcomere non‐ uniformities in slow muscle fibres, produced as a result of non‐uniform activation of the fibre membrane through the distributed nerve supply.
Inhibition by papaverine of calcium movements and tension in the smooth muscles of rat vas deferens and urinary bladder.
Authors: Huddart H , Langton P D , Saad K H
Published: December 2014

Papaverine, up to 150 micron, was without effect on resting tension of vas deferens and urinary bladder smooth muscle strips, but caused a dose‐dependent inhibition of the phasic component of the 100 mM‐K contracture. At 150 micron, papaverine caused an 80 and 60% inhibition of phasic tension in vas deferens and urinary bladder muscle respectively. Papaverine caused a marked dose‐dependent reduction in the tonic component of 100 mM‐K contractures in both preparations. At 150 micron, papaverine often relaxed preparations below initial starting tension. Addition of 150 micron‐papaverine to incubation media caused a fall of 25‐30% in 45Ca uptake by both preparations. Papaverine at 150 micron caused a small fall in resting 45Ca efflux from vas deferens and a larger fall in efflux from bladder muscle. However, this papaverine concentration caused a large inhibition of the 45Ca uptake by and 45Ca efflux from both preparations when stimulated by high‐K depolarization. Papaverine at 150 micron was without significant effect on Ca binding by either microsomes or mitochondria isolated from both vas deferens and urinary bladder smooth muscle. The main site of papaverine action appears to be on the Ca‐influx mechanism responsible for regulating Ca entry during prolonged K depolarization.
Evidence that two sizes of ventromedial hypothalamic neurones project to the mesencephalic central grey matter in rats.
Authors: Sakuma Y , Tada K
Published: December 2014

The spatial spread of the extracellular antidromic action potentials was measured in eighty‐three neurones in the ventromedial nucleus region of the female rat hypothalamus following electrical stimulation of the mesencephalic central grey matter. The positive‐negative configuration of the antidromic action potentials across the extracellular field suggested that the potentials were generated predominantly by neuronal soma with simple geometries. When represented by the distance travelled by the electrode, at which peak‐to‐peak spike amplitude exceeded the half maximum value, the spatial spread of the extracellular field ranged from 25 to 174 micron. The frequency distribution for the field size was distinctively bimodal and could be divided into large and small groups at 85 micron. Antidromic action potentials with larger extracellular fields had significantly larger maximum spike amplitude and shorter duration, indicating that differences in field size were associated with neuronal size. At least 55% of the central grey projection of the ventromedial nucleus originated from small neurones. Taking into account the sampling bias, a much greater proportion of the central grey projection may arise from small neurones. The lack of a systematic difference in the antidromic spike latencies between large and small cells indicated that axonal thickness is not the major factor in determining the latency of the responses of the ventromedial hypothalamic neurones to stimulation of the central grey matter.
Different pattern of recovery of fast and slow muscles following nerve injury in the rat.
Authors: Lowrie M B , Vrbová G
Published: December 2014

The sciatic nerve was crushed in 5‐6‐day‐old rats and the time course of recovery and changes in physiological and morphological properties of reinnervated fast and slow muscles was compared. The maximal tetanic tension developed by the reinnervated muscles was recorded at different times from about 18 days of age, when functional recovery was first seen, until 2 months. The maximal indirectly elicited tetanic tension of the reinnervated slow soleus muscle gradually increased from 55% of normal at 18 days to 75% of normal at 2 months. In contrast, the tension of the reinnervated fast muscle extensor digitorum longus (e.d.l.) fell sharply from 70% of normal at 18 days to 40% at 21 days and remained at that level till the end of the study. The total number of muscle fibres in control, reinnervated and denervated e.d.l. muscles was counted. At 18 days the number of fibres in the reinnervated e.d.l. was similar to normal but by 1 month it had fallen to one‐third. This decrease did not take place in permanently denervated muscles until at least 35 days. Loss of fibres in the reinnervated soleus was small. During the early stages of reinnervation the contraction and relaxation of the fast muscles was very prolonged. By 1 month the time taken to reach peak twitch tension had decreased to normal values but the relaxation was still slower and remained so for several months. The study of fatigue resistance showed that at 18 days the reinnervated fast muscles were as fatigable as normal muscles from animals of the same age. The fatigability of normal muscles increased with age to adult levels, but the reinnervated muscles became more fatigue resistant and remained so. Our findings suggest that fast muscles become selectively impaired after nerve injury at 6 days because they lose a large number of fibres after reinnervation.
Charge movements near the mechanical threshold in skeletal muscle of Rana temporaria.
Authors: Adrian R H , Huang C L
Published: December 2014

Charge movement was investigated over a range of potentials close to the mechanical threshold in voltage‐clamped frog skeletal muscle. The delayed (q gamma) component of the charging currents appeared with a time course lasting well over 100 ms at around ‐50 to ‐40 mV, but the currents became larger and faster with further depolarization. The slow charging current was investigated using a 10 mV probe step intercepting the time course of these currents. This procedure showed that the charging currents could last as long as 100‐300 ms. The total charge was conserved when the charging current was small and prolonged. The results can be related directly to earlier findings concerning contractile activation of muscle by applied voltage steps to potentials near threshold ( Adrian , Chandler & Hodgkin, 1969).
The anionic basis of fluid secretion by the rabbit mandibular salivary gland.
Authors: Case R M , Hunter M , Novak I , Young J A
Published: December 2014

The role played by anions in salivary secretion has been studied in experiments on the isolated, perfused mandibular gland of the rabbit, in which perfusate Cl‐ and/or HCO3‐ were replaced by other anions. Replacement of Cl‐ with Br‐ had no significant effect on salivary secretion rate, but replacement with the other anions tested caused secretory rate to fall, by 38% (I‐), 50% (NO3‐), 61% (isethionate, ise ‐), and 66% ( CH3SO4 ‐), respectively. Replacement of perfusate Cl‐ with ise ‐ or CH3SO4 ‐ caused the salivary HCO3‐ concentration to rise up to 4‐fold. Replacement with Br‐ or I‐ seemed to have little effect on salivary HCO3‐ concentration but, in contrast to ise ‐, Br‐ and I‐ entered the saliva in concentrations comparable to those of Cl‐ during control perfusion. In glands perfused with HCO3‐ and ise ‐, the addition of methazolamide, an inhibitor of carbonic anhydrase, caused a further 60% drop in secretory rate, but the saliva remained rich in HCO3‐. Replacement of perfusate HCO3‐ with Cl‐ or ise ‐ had no effect on salivary secretion or composition. Replacement of both HCO3‐ and Cl‐ in the perfusate with ise ‐ reduced salivary secretion to less than 2% of control levels. In control glands (i.e. perfused with both HCO3‐ and Cl‐), administration of furosemide, an inhibitor of Na+/Cl‐ co‐transport, reduced the secretion rate and increased salivary HCO3‐ in a manner indistinguishable from that seen when perfusate Cl‐ was replaced with ise ‐. In control perfused glands, administration of SITS (4‐acetamido‐4'‐ isothio cyano‐2,2'‐disulphonic acid stilbene), an inhibitor of Cl‐/HCO3‐ antiports , did not cause any change in salivary HCO3‐ concentration. Unexpectedly, it induced a significant increase in salivary secretory rate. The results show that salivary secretion depends on two independent transport systems. One is a Cl‐ ‐dependent, furosemide‐sensitive system, probably a Na+/Cl‐ symport. The other is an HCO3‐ ‐dependent, methazolamide‐sensitive system, and is probably an Na+/H+ antiport.
Effects of chronic stimulation on the metabolic heterogeneity of the fibre population in rabbit tibialis anterior muscle.
Authors: Buchegger A , Nemeth P M , Pette D , Reichmann H
Published: December 2014

Chronic indirect stimulation (10 Hz) was performed on rabbit tibialis anterior muscle. Long‐term stimulation (52‐140 days) produced a transformation of the fast tibialis anterior into a slow red muscle as judged from the histochemistry of myofibrillar actomyosin ATPase, the pattern of myosin light chains and the thorough rearrangement of the enzyme activity pattern of energy metabolism. Activity levels of citrate synthetase (CS), malate dehydrogenase (MDH), succinate dehydrogenase (SDH), 3‐hydroxy‐acyl‐CoA dehydrogenase (HAD), and lactate dehydrogenase (LDH) were determined quantitatively by either microbiochemical assays (CS, MDH, HAD and LDH) on microdissected, single fibres or by kinetic microphotometry on cross‐sectioned fibres (SDH). The activity profiles of these enzymes displayed pronounced scattering in the fibre population of the unstimulated muscle. Despite a several fold increase in the activities of CS, MDH, SDH and HAD and a pronounced decrease in LDH, chronic stimulation failed to abolish the metabolic heterogeneity of the fibre population. It is possible that chronic indirect stimulation cannot produce uniformity of fibres because of continuing diverse natural activity of the motor units.