bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction between responses in Purkinje cells evoked by climbing fibre impulses and parallel fibre volleys in the cat.
Authors: Campbell N C , Ekerot C F , Hesslow G
Published: December 2014

The plateau‐like depolarizing potentials evoked in Purkinje cell dendrites by impulses in climbing fibres (Ekerot & Oscarsson, 1981) were conditioned by single parallel fibre volleys and investigated by intra‐ and extracellular recording from cat cerebellar cortex. The conditioning parallel fibre volleys evoked predominantly inhibitory potentials of long duration in the Purkinje cell dendrites. Massive parallel fibre volleys, which may evoke plateau‐like depolarizing potentials (Campbell, Ekerot, Hesslow & Oscarsson, 1983) were avoided. In proximal dendrites parallel fibre volleys preceding climbing fibre responses reduced or abolished the plateau potential, whereas the initial spike‐like component of the climbing fibre responses was largely unaffected. Parallel fibre stimulation during already established plateau potentials immediately terminated the plateaus. In distal dendrites parallel fibre stimulation preceding climbing fibre responses reduced or abolished both the plateau potential and the initial component of the climbing fibre responses. Parallel fibre stimulation during established plateau potentials did not immediately terminate the plateau potentials but reduced their duration. The results of the present investigation suggest that single dendritic branches of Purkinje cells serve as independent integrators of mossy fibre and climbing fibre inputs.
The role of intracellular sodium activity in the anti‐arrhythmic action of local anaesthetics in sheep Purkinje fibres.
Authors: Eisner D A , Lederer W J , Sheu S S
Published: December 2014

The effects of lidocaine have been examined on the arrhythmogenic transient inward current (ITI) in voltage‐clamped sheep cardiac Purkinje fibres. Tension and intracellular Na activity (aiNa) were measured simultaneously. The addition of lidocaine (200‐300 microM) produced an immediate decrease of inward holding current and a gradual fall of aiNa. The relative magnitudes of the changes of current and aiNa were shown to be consistent with the outward shift of current representing principally a reduction of inward Na current. The Na pump was inhibited by reducing the external Rb concentration in a K‐free solution. This produced an after‐contraction and transient inward current (ITI) along with a rise of aiNa. The subsequent addition of lidocaine decreased the magnitude of ITI and the after‐contraction while decreasing aiNa. Tetrodotoxin (TTX) had qualitatively similar effects to lidocaine on inward holding current, aiNa, ITI and the after‐contraction. When aiNa was changed by (i) lidocaine, (ii) TTX or (iii) small changes of external Rb concentration, a hysteresis was seen in the relationship between aiNa and ITI or after‐contraction. The hysteresis was similar to that previously found between aiNa and contraction (Eisner, Lederer & Vaughan‐Jones, 1981). Despite this hysteresis, neither lidocaine nor TTX affected the relationship between magnitudes of ITI and the after‐contraction. It is suggested that the fall of aiNa is a major factor in the reduction of ITI by lidocaine. These results are discussed in relation to the anti‐arrhythmic actions of lidocaine.
Aspects of nasal heat exchange in resting reindeer.
Authors: Blix A S , Johnsen H K
Published: December 2014

Total respiratory heat loss (t.r.h.l.) in resting reindeer has been calculated from exhaled air temperature (Te) and respiratory minute volume (V) obtained during heat and cold stress in both summer and winter. Exhaled air temperature decreased with decreasing ambient temperature (Ta) in both summer and winter. The lowest Te recorded was +6 degrees C at a Ta of ‐45 degrees C in winter and the highest +38 degrees C at a Ta of + 29 degrees C in summer. At any Ta, Te was higher in winter than in summer. V was constant with increasing Ta up to +25 degrees C and ‐10 degrees C in summer and winter, respectively. Further increase in Ta resulted in thermal tachypnea. During summer t.r.h.l. did not change significantly in the ambient temperature range from ‐25 to +25 degrees C. In winter, however, t.r.h.l. increased linearly with increasing ambient temperature from ‐30 to +15 degrees C. Minimum t.r.h.l. was found to coincide with the animals' lower critical temperature. We suggest that the heat exchange in the upper respiratory tract of resting reindeer is actively regulated to attain fine tuning of thermal balance in this high arctic mammal undergoing great seasonal changes in fur insulation.
Patch‐clamp studies of slow potential‐sensitive potassium channels in longitudinal smooth muscle cells of rabbit jejunum
Authors: Benham C. D. , Bolton T. B.
Published: December 2014

1. The patch‐clamp technique was used to study single channel currents in membrane patches of longitudinal smooth muscle cells of rabbit jejunum dispersed by collagenase treatment. Recordings were made from both cell‐attached and isolated patches.

2. The predominant unit currents observed were outward at membrane potentials positive to the potassium equilibrium potential (EK) and they were rapidly and reversibly blocked by tetraethylammonium (TEA). Their size varied as EK was changed but was not noticeably affected by changing ENa, ECl or ECa; it was little altered in calcium‐free EGTA solution. Thus, these currents apparently result mainly, if not exclusively, from the movements of potassium ions through channels insensitive to the calcium ion concentration. The present study describes the properties of these potassium channels.

3. The unit conductance varied slightly with potential in most experiments; around zero potential it was about 50 pS. The conductance was dependent upon the potassium, but not the calcium, gradient. Sub levels of conductance of about two‐thirds and, less commonly, one‐third of the fully conducting channel state were sometimes seen.

4. Membrane patches were studied which showed one to about twelve levels of outward current which were presumed to result from the opening of up to twelve channels having the same characteristics. The probability of channel open state varied with membrane potential, increasing in the potential range ‐40 to +40 mV. Channel openings were rare negative to ‐40 mV. No inward currents through these potassium channels were observed as openings were not seen at membrane potentials negative to EK.

5. When the probability of channel opening was low, channel openings occurred in bursts which could be separated by several seconds. Analysis of the openings of a single channel revealed that open times and short closed times were exponentially distributed with mean durations of 15‐45 ms and about 6 ms at zero potential. In some patches regular cyclical openings of several channels occurred. In other patches openings of individual channels appeared to be independent events as they were reasonably fitted by a binomial distribution.

6. Following a step change from negative potentials, where channels were closed, to more positive potentials, channel openings increased during a period of 10 s to reach a steady state. No evidence of inactivation was observed.

7. These results suggest the existence of a population of potential‐sensitive potassium‐selective ion channels in the smooth muscle cell membrane which are closed at the resting membrane potential and which open upon depolarization with slow (seconds) kinetics; these may be involved in the slow potential (wave) activity of this muscle.
Release of two vasodilators, adenosine and prostacyclin, from isolated rabbit hearts during controlled hypoxia.
Authors: Edlund A , Fredholm B B , Patrignani P , Patrono C , Wennmalm A , Wennmalm M
Published: December 2014

The release of two locally formed vasodilators, adenosine and prostacyclin (PGI2), from hearts subjected to different degrees of hypoxia was investigated. Isolated rabbit hearts were perfused according to Langendorff with Tyrode solution, saturated with gas mixtures containing 8‐95% O2 and 5% CO2 in N2. Coronary flow rate, O2 extraction and uptake, and cardiac production of lactate, purines and 6‐keto‐PGF1 alpha (the stable metabolite of PGI2) were determined. During perfusion of the hearts with a solution saturated with 95% O2, release of lactate, 6‐keto‐PGF1 alpha and purines was very low: lactate was liberated at a rate of about 5 mumol/100 g . min, purine release corresponded to 2% of the total adenosine nucleotide content of the heart per hour and the release of 6‐keto‐PGF1 alpha was about 150 mumol/100 g . min. During hypoxia there was a graded release of lactate and purines from the heart, as well as a liberation of 6‐keto‐PGF1 alpha. Mild hypoxia (60% O2 in the gas mixture) elicited a 160% increase in the formation of lactate and a 40% increase in the release of purines. During severe hypoxia (8% O2 in the gas mixture) the release of lactate and purines increased by more than 2000%. In contrast, the release of 6‐keto‐PGF1 alpha never increased more than 80% at any degree of hypoxia, neither did it correlate to the severity of the hypoxia. From these data we conclude that of the two vasodilating agents formed in the heart, adenosine and prostacyclin, the former is probably more important in the regulation of coronary flow.
Time course of release of catecholamine and other granular contents from perifused adrenal chromaffin cells of guinea‐pig.
Authors: Ito S
Published: December 2014

Experiments were carried out to investigate the time course of the release of catecholamine, dopamine‐beta‐hydroxylase (DBH) and adenine nucleotides from isolated chromaffin cells of guinea‐pig adrenal gland. When the isolated chromaffin cells were incubated with medium containing acetylcholine (ACh) (0.1 mM), veratridine (0.1 mM) or scorpion (Leiurus quinquestriatus) venom, (10 micrograms/ml.), catecholamine was released into the medium. Catecholamine secretion induced by veratridine or scorpion venom was inhibited by tetrodotoxin (1 microM) but not by atropine (0.1 mM) plus hexamethonium (0.1 mM). On the other hand, the secretory response to ACh was abolished by the cholinergic blocking drugs but not by tetrodotoxin. DBH was released together with catecholamine into the medium in which cells were suspended with these drugs. The ratio of catecholamine (n‐mole) to DBH activity (n‐mole/hr) appearing in the supernatant was 7.08 +/‐ 0.55, 6.60 +/‐ 0.27 and 8.91 +/‐ 0.47 for ACh, veratridine and scorpion venom, respectively. These values were close to that found in the lysate of chromaffin granules obtained from guinea‐pig adrenal glands (7.37 +/‐ 0.39). The application of ACh or veratridine to perifused chromaffin cells was found to cause a parallel increase in catecholamine and DBH secretion in the perifusion medium without corresponding amounts of phenylethanolamine‐N‐methyltransferase leakage. However, DBH secretion tended to last for a longer period than catecholamine secretion. Adenine nucleotides were released from perifused chromaffin cells together with catecholamine, by ACh and veratridine. ATP added to the perifusion medium was metabolized to ADP and AMP, of which the ratio (ATP, 21.6%; ADP, 34%; AMP, 17.9%) was close to those of adenine nucleotides released from the cells. The secretion of adenine nucleotides induced by both secretagogues ceased much faster than the catecholamine secretion, so that molar ratio of catecholamine to adenine nucleotides was gradually increased during and after stimulation. The results indicate that catecholamine secretion is accompanied with a simultaneous release of DBH and ATP from adrenal chromaffin cells. Therefore, it is suggested that the delayed output of DBH, unlike catecholamine secretion, in perfused adrenal glands results from the presence of a diffusion barrier for this protein. The releasable secretory granules of isolated chromaffin cells are suggested to be heterogeneous with respect to the ratio of catecholamine to ATP.
beta‐Adrenoceptor alterations coupled with secretory response in rat parotid tissue.
Authors: Hata F , Ishida H , Kagawa K , Kondo E , Kondo S , Noguchi Y
Published: December 2014

Simultaneous studies on the secretory response of amylase and the neurotransmitter receptors of rat parotid gland, after brief treatment with agonists, showed selective alteration in beta‐adrenoceptors with specific change in amylase secretion, suggesting a regulatory role of the receptors in the secretory response. The beta‐adrenergic agonist (+/‐)‐isoprenaline (IPR) stimulated amylase secretion from rat parotid tissues much more than did the same concentration of an alpha‐adrenergic or cholinergic agonist. The stimulatory effects of IPR were studied by pre‐treating rat parotid tissues with IPR for 10 min and then incubating the tissue in fresh medium for 10 min. Pre‐treatment with 10 microM‐IPR for 10 min resulted in increased amylase secretion during further incubation with IPR and also in a lower EC50 value of amylase secretion for IPR. This treatment also resulted in selective changes in the number and affinity of beta‐adrenoceptors, assessed by measuring binding of [3H]dihydroalprenolol (DHA): the maximal binding sites increased from 286/357 f‐mole to mg protein and the IC50 value (the concentration for 50% inhibition of specific [3H]DHA binding) of beta‐agonists, not antagonists, decreased significantly. An increase in the period of pre‐treatment with IPR to 30 min resulted in a decrease in the maximal binding sites of beta‐adrenoceptors and a decrease in amylase secretion during further incubation with IPR. Experiments with other agonists showed that supersensitivity of the secretory response was induced specifically by beta‐agonists. Binding studies with [3H]WB‐4101 and [3H]quinuclidinyl benzilate showed that alpha‐adrenoceptors and muscarinic ACh receptors in rat parotid did not change under the conditions tested. The alteration in beta‐adrenoceptors was parallel with a change in amylase secretion after IPR pre‐treatment, but not with a change in cyclic AMP content.
Neural regulation on the active sodium‐potassium transport in hypokalaemic rat skeletal muscles.
Authors: Akaike N , Hirata A , Kiyohara T , Oyama Y
Published: December 2014

C.N.S.‐induced suppression of muscle Na‐pump activity was studied in fast ‘twitch’ muscle, extensor digitorum longus, of hypokalaemic rats which were fed a K‐deficient diet for 0‐9 weeks. The results were compared with those of slow ‘tonic’ muscle, soleus, reported previously. K‐deficient diet caused blood hypokalaemia and a considerable K+ loss and Na+ accumulation in the skeletal, heart and smooth muscles. The cellular K+ loss was in the order of soleus greater than extensor digitorum longus greater than diaphragm greater than duodenum greater than auricle greater than ventricle; C.N.S. organs such as cerebrum, cerebellum, medulla oblongata, spinal cord and liver were spared this K+ fall. Skeletal, heart and smooth muscles lost more K+ with prolongation of hypokalaemic periods, whereas plasma K+ concentration did not fall much below 1.6 mM during hypokalaemia. Peripheral nerve section, cervical and brain‐stem transection, decerebration and cortical spreading depression with 20% KCl, which activated the active Na+ and K+ transport in soleus muscles during hypokalaemia, could not enhance the pump activity in extensor digitorum longus muscles. Alpha‐adrenoreceptor antagonists such as phenoxybenzamine, phentolamine and dibenamine and a specific blocker of post‐synaptic alpha 1‐adrenoreceptor, prazosin, did not stimulate Na+ and K+ transport in the extensor digitorum longus muscles during hypokalaemia while the beta‐adrenoreceptor antagonist, propranolol, also had no effect. The sensitivity of the active Na+ and K+ transport system in rat muscles to ouabain applied intraperitoneally was greater in extensor digitorum longus muscles than in soleus muscles. The binding experiment with a radiolabelled ligand of alpha 1 adrenoreceptor antagonist, [3H]prazosin, demonstrated the presence of alpha 1‐adrenergic receptors on the soleus muscle membranes of hypokalaemic rats, but not of normal rats. alpha 1 Adrenergic receptors were not detected on the extensor digitorum longus muscle membranes prepared from either hypokalaemic or normal rats. The correlation between the C.N.S.‐induced inhibition on the Na pump in soleus muscle during hypokalaemia and the occurrence of alpha 1 adrenergic receptors on the muscle was discussed.
Effects of extracellular sodium on calcium efflux and membrane current in single muscle cells from the barnacle.
Authors: Lederer W J , Nelson M T
Published: December 2014

The actions of extracellular sodium (Nao) on membrane potential, membrane current, membrane conductance and Ca efflux were examined in single muscle cells from the giant barnacle, Balanus nubilus. The intracellular compartment was perfused to facilitate the control of intracellular constituents including calcium ions (Ca2i+). Changing Nao has no large effect on Ca efflux when free intracellular calcium activity, [Ca2+]i, is low (about 0.1 microM). However, increasing [Ca2+]i leads to the development of Nao‐dependent Ca efflux as well as to an augmentation in Nao‐independent Ca efflux. Reducing Nao (using Li+ as a substitute cation) leads to a depolarization of the membrane when [Ca2+]i is low (about 0.1 microM). Increasing [Ca2+]i causes the membrane to depolarize. With [Ca2+]i at about 10.0 microM, reduction of Nao produces a hyperpolarization of the membrane. Significant Nao‐dependent inward current is seen when [Ca2+]i is high. This current is large with respect to the Nao‐dependent changes in Ca efflux (about 1 microA per p‐mole/sec). The Ca2i+‐activated, Nao‐dependent changes in Ca efflux and membrane current are not sensitive to La3o+. However, Lao3+ does inhibit a fraction of the Cai2+‐activated changes in membrane current and Ca efflux which are not dependent on Nao. Over a limited range of membrane potential Ca efflux is not voltage‐dependent. Possible relationships between the Nao‐dependent changes in Ca efflux and Nao‐dependent changes in membrane potential or current are discussed. We find that these changes cannot be readily interpreted in terms of a single transport mechanism.
Modification by diet and environmental temperature of enterocyte function in piglet intestine.
Authors: Dauncey M J , Ingram D L , James P S , Smith M W
Published: December 2014

Intestinal morphology, enterocyte life span and alanine transport have been studied in the small intestine of piglets fed different amounts of food at high and low environmental temperatures. Villus height and crypt depth were both greater in pigs maintained on a high energy intake. Environmental temperature produced negligible effects on intestinal structure. Enterocyte life span increased from 45 h in pigs kept at 35 degrees C to about 70 h in animals living at 10 degrees C. A low energy intake prolonged enterocyte life span at an environmental temperature of 10 degrees C. The Na‐dependent fraction of alanine uptake, judged by analysis of autoradiographs and by measurement of alanine‐dependent short‐circuit current, was greater in intestines taken from pigs maintained on a restricted diet. This effect, which appeared to be due to changes in the number of carriers (Jm) rather than the apparent affinity of the carrier for the amino acid (Km) was most noticeable using intestines taken from pigs kept at 10 degrees C. The Na‐independent fraction of alanine uptake remained unchanged either by alterations in diet or in the environmental temperature at which pigs were kept. Restricting the diet of pigs at low environmental temperature leads to a relative increase in the capacity of the intestine to absorb alanine through an Na‐dependent process. This increase appears to be caused by an extension of enterocyte life span rather than by any change in the time of onset or rate of expression of carrier function in a single enterocyte.
Cyclic changes of plasma pancreatic polypeptide and pancreatic secretion in fasting dogs.
Authors: Chen M H , Joffe S N , Magee D F , Murphy R F , Naruse S
Published: December 2014

Fasting conscious dogs, each with a gastric fistula, Heidenhain pouch and Thomas duodenal fistula, were used. Basal pancreatic secretion showed periodic increases in phase with the periodic contraction of the stomach and duodenum. Periodic increases of plasma pancreatic polypeptide (PP), but not of gastrin, were observed in phase with the periodic contraction and secretion of the gut. Ganglion blockade abolished the cyclical activity, both secretory and motor, of the gut and of plasma PP. Intraduodenal infusion of lidocaine suppressed the spontaneous increase of pancreatic secretion and plasma PP. It is concluded both that the cyclical release of PP and the increase in pancreatic secretion are under the control of the intrinsic nerves of the duodenum.
Changes in breathing, electrocortical and muscle activity in unanaesthetized fetal lambs with age.
Authors: Clewlow F , Dawes G S , Johnston B M , Walker D W
Published: December 2014

Electrocortical and electro‐ocular activity, breathing movements and nuchal muscle activity were recorded continuously in the unanaesthetized lamb in utero (95‐135 days). Electrocortical activity was recorded simultaneously from various sites. The bi‐parietal electrocorticogram gave the clearest differentiation between high‐ and low‐voltage activity. The onset of cortical differentiation from 110 days gestation was attributed to the superimposition of high‐voltage electrocortical activity at 3‐10 Hz on existing low‐voltage activity. Three distinct patterns in the relationships between electrocortical activity, ocular activity breathing movements and nuchal muscle activity were observed at 95‐106, 107‐114 and 120‐135 days. Isocapnic hypoxia caused a diminution in fetal breathing from 95‐135 days gestation, quantitatively greater near term. After cortical differentiation, hypoxia caused the appearance of high‐voltage activity within 4 min, if low‐voltage electrocortical activity was present initially. The relationship, changing with age, between electrocortical activity, breathing movements, ocular and nuchal muscle activity is discussed.
Sodium and potassium transport in ferret red cells.
Authors: Flatman P W
Published: December 2014

Potassium movements into ferret red cells were measured with the tracer 86Rb. Equilibration of 86Rb between medium and cells could be resolved into two components. 70‐90% occurred rapidly with a rate constant of between 3.5‐5.5 h‐1. The remaining 10‐30% occurred slowly. The slow movement was equivalent to a potassium influx of about 1.2‐2.76 mmol l‐1 cell h‐1. Potassium influx was inhibited by 80‐90% by 0.1 mM‐bumetanide (a high‐ceiling, loop diuretic). This suggests that the sodium‐potassium co‐transport system has a high capacity for carrying potassium (estimated at about 17‐35 mmol l‐1 cell h‐1). After bumetanide (0.1 mM) remaining potassium movements (approximately 0.5 mmol l‐1 cell h‐1) are at a similar level to that found in red cells from other animals. The sodium pump makes a very small contribution to potassium flux into ferret red cells. Much of this pump activity may be attributed to reticulocytes present in cell samples. Sodium movements across the red cell membrane were measured with 22Na. Sodium equilibrated more slowly than potassium. 60‐70% of the sodium influx was inhibited by 0.1 mM‐bumetanide, indicating that most sodium influx in ferret red cells is also through the co‐transport system. The co‐transport system can transport up to 49 mmol sodium l‐1 cell h‐1 and is half maximally activated by 0.38 mM‐potassium in the external medium. In the presence of bumetanide, sodium influx (about 18 mmol l‐1 cell h‐1) is similar to that of other carnivore red cells. This is about five times greater than that of red cells from non‐carnivores. The possibility that there are two populations of ferret red cells with different potassium transport characteristics is discussed.
Effect of caffeine on intramembrane charge movement and calcium transients in cut skeletal muscle fibres of the frog
Authors: Kovács L. , Szűcs G.
Published: December 2014

1. The authors have studied the effect of caffeine in subthreshold concentration (0.5 mmol l−1 at 2‐4 °C) on the contraction threshold, on intramembrane charge movement and calcium transients in voltage‐clamped frog skeletal muscle fibres.

2. The single‐gap technique (Kovács & Schneider, 1978) was used for the voltage clamping of terminated segments of cut fibres. Ionic conductances were minimized by using caesium glutamate at the open end pool and tetraethylammonium sulphate and tetrodotoxin at the closed end pool.

3. Myoplasmic calcium transients evoked by depolarizing pulses were recorded by measuring the changes in absorbance of the fibres at 720 nm after the intracellular application of Antipyrylazo III dye.

4. The strength—duration curve for contraction threshold was shifted towards more negative membrane potentials in the presence of caffeine. Shift was more definite at shorter pulse durations than at the rheobase.

5. The total amount of charge moving during the depolarizing pulses at different membrane potentials was not changed by caffeine treatment, whereas the threshold amounts of charge moved during the critical periods of the contraction threshold decreased at different voltages (by about 23%).

6. In the presence of caffeine, calcium transients accompanying long (100 ms) depolarizing pulses showed increased voltage‐dependent peak amplitudes, rising phases and rate coefficients referring to calcium release, but a decreased voltage‐dependent re‐uptake rate either during or after the pulse.

7. Calcium transients evoked by depolarizing pulses along the strength—duration curve for contraction threshold gave the same peak amplitudes (ranging from 0.9 to 2.8 μmol l−1 free myoplasmic calcium on different fibres), but membrane‐potential‐dependent latency times and rising phases. The rate coefficients for declining phase did not depend on the preceding pulse voltage.

8. On applying caffeine, the calcium transients related to the contraction threshold also had equal but smaller peak amplitudes, shorter latency times and the same magnitude of voltage‐independent rate coefficients for the declining phase as in the control solution.

9. The twitch potentiating effect of caffeine can be explained by its facilitating calcium release from the sarcoplasmic reticulum, while the re‐uptake rate is not modified. The apparent inhibition of re‐uptake can be related to the enhanced release of calcium due to caffeine effect. Due to the sensitizing effect of caffeine on the sarcoplasmic reticulum membrane, smaller amounts of charge are needed to reach the contraction threshold than without caffeine.
Neurogenic vasodilatation in isolated bovine and canine penile arteries.
Authors: Bowman A , Gillespie J S
Published: December 2014

Field stimulation of isolated, perfused bovine or canine penile arteries produced dilatation, after the adrenergic motor component of the response had been blocked with guanethidine and the vessels had developed a background tone. The vasodilatation was blocked by tetrodotoxin but not by atropine. The vasodilator responses to field stimulation were compared with those produced by ATP, by vasoactive intestinal peptide (VIP), and by the inhibitory factor extracted from the bovine retractor penis muscle. Of the three putative transmitters, the inhibitory factor produced responses that most closely resembled those to field stimulation. Haemoglobin, which blocks non‐adrenergic, non‐cholinergic inhibitory transmission in the bovine and canine retractor penis muscles, did not impair the vasodilatations produced by ATP or VIP, but slowly reduced or abolished those produced by field stimulation or by the inhibitory factor. Haemoglobin itself produced a powerful constriction of the isolated penile arteries. The results are compatable with the possibility that the inhibitory factor from the bovine retractor penis muscle (which may be the inhibitory transmitter in that muscle) is, or closely resembles, the transmitter of non‐adrenergic, non‐cholinergic vasodilator fibres in the penile arteries of dog and ox.
Blockade of amino acid‐induced depolarizations and inhibition of excitatory post‐synaptic potentials in rat dentate gyrus.
Authors: Crunelli V , Forda S , Kelly J S
Published: December 2014

Excitatory post‐synaptic potentials (e.p.s.p.s) evoked by stimulation of the medial perforant path and depolarizations induced by excitatory amino acids were recorded from granule cells in the preparation of the hippocampal slice from the rat. The effects of (+/‐)‐2‐amino‐5‐phosphonovalerate (APV), gamma‐D‐glutamylglycine (gamma DGG) and cis‐2,3‐piperidinedicarboxylate (PDA), antagonists of excitatory amino acids on these phenomena were compared. gamma DGG was the most effective antagonist of the e.p.s.p. Its action was reversible and not associated with any change in the passive membrane properties of the granule cells or in the apparent reversal potential of the e.p.s.p. Quantal analysis showed that the reduction in the e.p.s.p. paralleled the decrease in quantal size rather than quantal content, confirming a post‐synaptic site of the action of gamma DGG. The potency of gamma DGG against the exogenous agonists was N‐methyl‐D‐aspartate greater than kainate greater than or equal to quisqualate. APV had very little effect on the e.p.s.p. but was a selective antagonist of N‐methyl‐D‐aspartate‐induced depolarizations. PDA depolarized granule cells and increased their membrane input resistance. Although gamma DGG was a potent antagonist of both glutamate‐ and aspartate‐induced depolarizations, no clear pattern of specificity could be found. The action of glutamate was unaffected by APV. These results indicate that the receptor for the transmitter at the synapses formed by the fibres of the perforant path with the granule cells is of the quisqualate and/or kainate type. The present data are consistent with the biochemical evidence that glutamate may be the endogenous transmitter at his synapse.
Chemical transmission in the rat interpeduncular nucleus in vitro.
Authors: Brown D A , Docherty R J , Halliwell J V
Published: December 2014

We have used a rat brain‐slice preparation to study the effects of some cholinomimetic and amino acid agonists and antagonists on the discharge frequency of neurones in the interpeduncular nucleus (i.p.n.), and on the response of these neurones to electrical stimulation of their main excitatory input, the fasciculus retroflexus of Meynert (f.r.m.). A high proportion of i.p.n. neurones were excited by carbachol, acetylcholine (ACh) and muscarine, but methacholine was less effective. The amino acids L‐glutamate and L‐aspartate were highly effective stimulants of i.p.n. neurones. The responses to ACh or carbachol were greatly reduced by the nicotinic blocking agents hexamethonium, d‐tubocurarine and mecamylamine but only slightly reduced by atropine. The response to muscarine was abolished by low doses of atropine. Alpha‐Bungarotoxin did not block the response of i.p.n. neurones to f.r.m. stimulation or to cholinomimetic agonists. The response of i.p.n. neurones to f.r.m. stimulation was not appreciably affected by high doses of nicotinic antagonists or atropine nor was there any enhancement of the response by physostigmine. The amino acid antagonists gamma‐D‐glutamylglycine (gamma DGG) and 2‐amino phosphonovalerate (2‐APV) were effective blockers of the response to f.r.m. stimulation and preferentially reduced responses to aspartate while having little effect on responses to glutamate or cholinomimetic agonists. It is concluded that ACh is an unlikely candidate for transmitter in this pathway despite abundant neurochemical evidence in its favour. It is more likely that the transmitter is an excitatory amino acid, probably an aspartate‐like substance.
Decerebration activates thermogenesis in the rat.
Authors: Rothwell N J , Stock M J , Thexton A J
Published: December 2014

Under fluothane anaesthesia, suction decerebration was performed at the immediate pre‐pontine level in adult, male, Sprague‐Dawley rats; this resulted in a large and sustained rise in rectal temperature from 35.6 +/‐ 0.2 (control) to 38.8 +/‐ 0.5 degrees C (decerebrate) following recovery from anaesthesia. Propranolol inhibited this rise. In a separate group of continuously (urethane) anaesthetized rats, brain transection at the immediate pre‐pontine level produced marked increases in rectal temperature and oxygen consumption, both of which were inhibited by injection of the beta‐adrenergic antagonist propranolol (10 mg/kg). The rise in rectal temperature (2.8 +/‐ 0.4 degrees C) after transection was preceded by a greater increase (3.6 +/‐ 0.3 degrees C) in the temperature of the interscapular brown adipose tissue (i.b.a.t.). Skin temperature on the tail showed no immediate response. In anaesthetized lean (+/?) male Zucker rats, rectal and i.b.a.t. temperatures showed similar responses to Sprague‐Dawley rats after decerebration, but in the genetically obese (fa/fa) Zucker rat, temperatures were not significantly altered by decerebration. The above results, together with macroscopic examination of the transected brains, suggest that descending pathways (possibly arising in the mid‐brain tegmentum) normally inhibit a sustained thermogenic drive from areas in the lower brain stem. Decerebration can release this inhibition and cause a large rise in body temperature and in metabolic rate, which apparently result from sympathetic activation of i.b.a.t. The genetically obese Zucker rat exhibits an impaired thermogenic response to decerebration.
Inhibition of dorsal spinocerebellar tract cells by interneurones in upper and lower lumbar segments in the cat.
Authors: Hongo T , Jankowska E , Ohno T , Sasaki S , Yamashita M , Yoshida K
Published: December 2014

The topographical distribution of interneurones mediating disynaptic inhibition of dorsal spinocerebellar tract (d.s.c.t.) cells from group I muscle afferents in the cat was investigated using both physiological and morphological techniques. Lesions of either the dorsal funiculi or of the lateral and ventral funiculi were made between L4 and L5 segments in two groups of cats. I.p.s.p.s. evoked from group I afferents were seen after both these lesions, showing that the i.p.s.p.s were evoked by interneurones located more caudally as well as by interneurones in the same segments as Clarke's column. Distribution of the caudally located interneurones in the lower lumbar segments was investigated after marking these interneurones with horseradish peroxidase retrogradely transported from Clarke's column. The horseradish peroxidase was injected along L3‐L4 segments of Clarke's column in two cats with transected dorsal funiculi. The marked cells were found in L5, L6, L7 and S1 segments, with a highest density in L6 and L7. They were seen in laminae V, VI and VII. A search was made for interneurones which could be antidromically invaded following stimuli applied in Clarke's column and were monosynaptically excited by group I afferents. Such interneurones were found at locations corresponding to laminae V‐VI of Rexed. The latencies of antidromic and orthodromic responses were within ranges allowing them to mediate disynaptic inhibition of d.s.c.t. cells.
Characterization of a chloride conductance activated by hyperpolarization in Aplysia neurones.
Authors: Chesnoy‐Marchais D
Published: December 2014

A voltage‐clamp study was made of some properties of the non‐synaptic hyperpolarization‐activated Cl‐ conductance recently described in Aplysia neurones loaded with Cl‐ ions (Chesnoy‐Marchais, 1982). The experiments were performed on an identified family of neurones, which present cholinergic responses allowing an easy measurement of the equilibrium potentials of Cl‐ (ECl) and K+ ions (EK). The Cl‐ selectivity of the hyperpolarization‐activated conductance was deduced from four observations: (1) the extrapolated reversal potential of the hyperpolarization‐activated current, Er, was close to the reversal potential of the cholinergic Cl‐ response, which is the equilibrium potential for Cl‐ ions, ECl. (2) Modifications of the intracellular or extracellular Cl‐ concentration induced changes of the reversal potential Er. (3) A prolonged and intense activation of the current lowered the intracellular Cl‐ concentration. (4) The current persisted after complete substitution of intracellular and extracellular cations by CS+ ions, as well as after replacement of extracellular Na+ ions by Tris. The steady‐state Cl‐ conductance (gss) increases steeply with hyperpolarization. The kinetics of activation and deactivation are exponential and are characterized by the same voltage‐dependent time constant (tau), of the order of a few seconds or fractions of seconds. The curves gss(V) and tau (V) can both be fitted by a two‐state model in which the rate constants are exponential functions of the membrane potential (e‐fold change for 12‐16 mV). The Cl‐ current is much more affected by changes of the intracellular Cl‐ concentration than predicted simply from the change in Cl‐ driving force. Both the conductance and the time constant of activation are strongly modified. Modifications of the extracellular Cl‐ concentration do not always alter the amplitude of the hyperpolarization‐activated Cl‐ current, but systematically affect its kinetics. The hyperpolarization‐activated current is abolished after prolonged exposure of the cell to an artificial sea water where NO3‐ ions replace Cl‐ ions, as well as after intracellular injections of NO3‐ ions. Increasing the external pH shifts the gss(V) and tau (V) curves to the left. Lowering the external pH has reverse but less pronounced effects. In cells which were not loaded with Cl‐ ions and did not present the hyperpolarization‐activated Cl‐ current, this current could be detected if the hyperpolarizing jump was preceded by short depolarizing pulses. In cells which were loaded with Cl‐ ions, the Cl‐ current became larger after a short depolarizing pulse. In the presence of extracellular Co2+ ions, depolarizing pulses no longer increased the Cl‐ current.(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for non‐cholinergic, non‐adrenergic nervous control of mucus secretion into the cat trachea.
Authors: Peatfield A C , Richardson P S
Published: December 2014

We have investigated the effects of electrical stimulation of the vagus nerves on the output of mucus glycoproteins (mucins), radiolabelled with 3H and 35S, into the trachea of anaesthetized cats. In five control experiments, stimulation of the vagus nerves on four successive occasions, separated by 1 h, caused significant rises in the output of radiolabelled mucins. In these experiments repetition of stimulation did not appear to lessen the response. In a parallel series of five experiments the vagus nerves were again stimulated on four occasions, but atropine was administered in increasing doses between the stimuli. Large responses, not significantly less than those seen in the corresponding control stimulations, were seen even in the presence of the highest dose of atropine. In this series of experiments, however, the effect of the last vagal stimulation (with the highest dose of atropine) was significantly less then the first (no atropine). Administration of phentolamine and l‐propranolol in addition to atropine failed to reduce the response to vagal stimulation significantly. We conclude that, while cholinergic nerves can probably explain part of the increase in mucin output which occurs with vagus nerve stimulation, there is a large response mediated by a non‐cholinergic, non‐adrenergic neurotransmitter. Possible neurotransmitters and the relationship of these findings to those of earlier studies are discussed.
Substance P is a functional neurotransmitter in the rat parotid gland.
Authors: Gallacher D V
Published: December 2014

The technique of electrical field stimulation was employed to stimulate the intrinsic nerves of isolated rat parotid gland fragments. Responses to field stimulation were recorded as changes in enzyme secretion (amylase release), radiolabelled ion fluxes (86Rb efflux) and electrophysiological effects (changes in acinar cell membrane potential and input resistance). All effects of field stimulation were abolished by the neurotoxin, tetrodotoxin (TTX). Selective use of pharmacological antagonists revealed that both the sympathetic and parasympathetic nerves to this tissue were being excited by field stimulation. Importantly a significant component of the response to field stimulation persisted in the presence of combined autonomic receptor blockade by atropine, phentolamine and propranolol, i.e. due to release of a non‐cholinergic, non‐adrenergic neurotransmitter. The non‐cholinergic, non‐adrenergic neurotransmitter evoked amylase release, 86Rb efflux and electrophysiological effects seen as changes in acinar cell membrane potential and conductance, i.e. stimulus‐permeability coupled. Two biologically active peptides, substance P (SP) and vasoactive intestinal polypeptide (VIP) were shown to evoke amylase release in the presence of combined autonomic blockade. VIP however did not evoke any increase in 86Rb efflux, i.e. not stimulus‐permeability coupled. All the effects of the non‐cholinergic, non‐adrenergic transmitter were mimicked by substance P which evokes 86Rb efflux and electrophysiological effects in addition to amylase release. The non‐cholinergic, non‐adrenergic field stimulus effects on amylase release and 86Rb efflux were abolished or markedly attenuated in tissues which had been desensitized by prior exposure to exogenous substance P. In the presence of VIP, however, the non‐cholinergic, non‐adrenergic effects persisted and were apparently potentiated. Acute application of the neurotoxin capsaicin first stimulated a transient release of amylase and subsequently abolished the non‐cholinergic, non‐adrenergic field stimulus‐evoked enzyme release. The putative substance P antagonist, D‐Pro2, D‐Trp7,9 substance P, reversibly blocked the response to both non‐cholinergic, non‐adrenergic nerve stimulation and exogenous substance P. It was demonstrated however that prolonged exposure to this antagonist is associated with non‐reversible and, importantly, non‐specific neurotoxic effects. It is concluded that substance P or a closely related peptide is a functional neurotransmitter in the rat parotid gland.
The response of the pancreas of the anaesthetized cat to secretin before, during and after reversible vagal blockade.
Authors: Grundy D , Hutson D , Scratcherd T
Published: December 2014

Cooling the cervical vagi of the anaesthetized splanchnectomized cat to 2 degrees C caused a 54.4 +/‐ 8.8% inhibition of pancreatic electrolyte secretion stimulated submaximally with pure secretin. On rewarming the vagi there was a prolonged increase in secretion rate over and above the control rate which existed before cooling. The increase lasted about 90 min. There were no changes in acid/base status due to interference of the lung inflation reflex which could account for the inhibition of secretion and the subsequent rebound. Cold block of the cervical vagi increased the transpancreatic electrical conductance, indicating that vasodilation had occurred and therefore eliminated a vasomotor cause for the inhibition. Electrolyte secretion was also inhibited by bilateral vagal section. Atropine only partially prevented the inhibitory response to vagal cooling. A cholinergic mechanism, therefore, accounted for some but not all of the response to vagal cooling. It is concluded that even in the fasted, anaesthetized animal vagal impulses facilitate the action of secretin on the pancreas. This facilitation is only partially cholinergic; the major part of the response is due to some non‐cholinergic transmitter substance. Such a mechanism may be necessary to potentiate the action of the very small amounts of secretin which appear to be released during a meal.
Sodium/calcium exchange in mammalian ventricular muscle: a study with sodium‐sensitive micro‐electrodes.
Authors: Chapman R A , Coray A , McGuigan J A
Published: December 2014

A method for mounting and rapidly perfusing small ventricular trabeculae (diameter around 250 micron) from either ferret or guinea‐pig is described. Tension, membrane potential (Em) and intracellular Na activity (aiNa) were measured. aiNa was measured using Na‐sensitive micro‐electrodes. At room temperature (22‐26 degrees C), [Na]o 155 mmol/l and [Ca]o 5.4 mmol/l, aiNa was 10.9 mmol/l +/‐ S.D. 4.2 mmol/l (n = 148). When [Na]o was reduced from 155 to 1.5 mmol/l contractures developed. These were about twitch height in guinea‐pig but less than the twitch height in ferret. Associated with the development of the contracture there was a decrease in aiNa. The aiNa halved within 30 s. The decrease in aiNa was not influenced by changing pHo from 7.4 to 9.5, K‐free solution or strophanthidin 50 mumol/l and was not passive since, even when the [Na]o was 1.5 mmol/l, the driving force for Na ions remained inward. The aiNa decreased if [Ca]o was increased and [Na]o decreased or vice versa. On the basis of these findings it is concluded that the decrease in aiNa is mainly due to Na/Ca exchange. Despite the large decrease in aiNa the [Ca]i, as monitored by tension changes, hardly increased. Since Ca uptake does occur in Na‐free conditions in heart muscle it is proposed that the mitochondria take up Ca ions and so prevent an excessive rise in cytoplasmic Ca. Strophanthidin increased both aiNa and the withdrawal contracture, but collected results from a number of experiments showed no clear correlation between the initial aiNa and contracture amplitude. Strophanthidin may, therefore, have actions additional to increasing aiNa.
Progression of age changes in synaptic transmission at mouse neuromuscular junctions.
Authors: Kelly S S , Robbins N
Published: December 2014

The progression of age‐related changes in neuromuscular function was investigated in muscles from CBF‐1 mice between 7 and 32 months of age. End‐plate potentials (e.p.p.s) were recorded in extensor digitorum longus (e.d.l.), soleus, and diaphragm muscles after neuromuscular transmission was blocked with either (+)‐tubocurarine chloride (curare) or high‐Mg/low‐Ca Krebs solutions. Between 10 and 31 months of age in e.d.l. and soleus but not in diaphragm, there was an increase in e.p.p. amplitude with age. In soleus this increase was approximately two‐fold in curare and three‐fold in high‐Mg solution. Increase in e.p.p. amplitude in curarized preparations took place between 20 and 28 months of age in e.d.l. and between 28 and 31 months of age in soleus. Indirectly elicited twitch responses were used to determine the time course of age‐related changes in sensitivity to Mg block. Increased resistance to block appeared between 15 and 19 months of age in both e.d.l. and soleus (in which the increase was more gradual). E.d.l. muscles from 25‐month‐old CFW mice also showed an increased resistance to Mg block compared to those from 7‐8‐month‐old animals. In Mg‐blocked preparations, increased quantum content (measured directly) accounted for the increased e.p.p. amplitude. Spontaneous miniature end‐plate potential (m.e.p.p.) frequency in old soleus muscles was not sensitive to low‐Ca/high‐Mg solutions although frequency in young soleus and young and old diaphragm was significantly reduced. It is concluded that age‐related changes in evoked transmitter release begin in mid life and take place more rapidly in e.d.l. than in soleus.(ABSTRACT TRUNCATED AT 250 WORDS)