bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective phototoxic destruction of rat Merkel cells abolishes responses of slowly adapting type I mechanoreceptor units.
Authors: Ikeda I , Yamashita Y , Ono T , Ogawa H
Published: December 2014

1. The fluorescent dye quinacrine which accumulates in Merkel cells in touch domes was administered to rats and the effects of excitation light irradiation on the mechanical responses of slowly adapting (SA) type I units innervating the touch domes were investigated. 2. Histological examination showed that after 10 min of irradiation degeneration was specifically localized to Merkel cells loaded with quinacrine. Nerve terminals associated with Merkel cells remained intact, even after treatment. 3. In SA type I units, responses to standard stimulation (a 100 ms ramp followed by a 2.9 s plateau of 400 microns constant displacement) decreased significantly after irradiation of the domes with quinacrine‐excitation light through a ‘B’ filter (‘B’ light). With 5 min irradiation, the response decreased to 52 +/‐ 7% (n = 10, mean +/‐ S.E.M.) of the pretreated value, to 17 +/‐ 4% with a 10 min treatment and practically disappeared within 20 min. 4. In SA type I units with non‐loaded Merkel cells, the response increased to 119 +/‐ 8% (n = 13) with 5 min irradiation and was 99 +/‐ 9% with the 10 min treatment. At around 15 min after the onset of irradiation there was a gradual decrease and within 60 min the response disappeared. 5. When responses were divided into phasic (0‐120 ms after the onset of stimulation) and tonic (120‐3000 ms) components, ‘tonic’ responses were more affected than ‘phasic’ ones in quinacrine‐loaded SA type I units. 6. Stimulus‐response curves shifted to the right and downwards in SA type I units with quinacrine‐loaded Merkel cells after irradiation, but no significant change was seen in SA type I units without quinacrine. 7. Our observations are consistent with the hypothesis that Merkel cells are responsible for mechanoelectric transduction in SA type I units.
Electrophysiological properties of neonatal mouse cardiac myocytes in primary culture.
Authors: Nuss H B , Marban E
Published: December 2014

1. The increasing utility of transgenic mice in molecular studies of the cardiovascular system has motivated us to characterize the ionic currents in neonatal mouse ventricular myocytes. 2. Cell capacitance measurements (30 +/‐ 1 pF, n = 73) confirmed visual impressions that neonatal mouse ventricular myocytes in primary culture are considerably smaller than freshly isolated adult ventricular myocytes. With the use of electron microscopy, mitochondria and sarcoplasmic reticulum were found in close association with myofibrils, but transverse tubules were not observed. 3. Action potential durations, measured at 50 and 90% repolarization, were 23 +/‐ 1 and 42 +/‐ 2 ms respectively (n = 46). Application of 4‐aminopyridine (4‐AP; 5 mM) prolonged action potential duration at 50% repolarization by 26 +/‐ 5% (n = 3). The brevity of the action potential is explained by the rapid activation of a transient outward K+ current upon voltage‐clamp depolarization to plateau potentials. 4. Potassium currents identified include an inward rectifier, a large 4‐AP‐sensitive transient outward, a slowly inactivating 4‐AP‐insensitive outward, a slowly activating delayed rectifier and a small rapidly activating E‐4031 (10 microM)‐sensitive delayed rectifier K+ current. 5. Sodium currents (‐305 +/‐ 50 pA pF‐1, n = 21) were recorded in 40 mM Na+ with Ni2+ (1 mM) to block Ca2+ currents and with K+ replaced by Cs+. The relative insensitivity of the Na+ current to block by tetrodotoxin (IC50 = 2.2 +/‐ 0.3 microM, n = 4) is distinctive of the cardiac Na+ channel isoform. 6. Nitrendipine‐insensitive (10 microM) Ba2+ currents elicited during steps from ‐90 to ‐30 mV measured ‐25 +/‐ 5 pA pF‐1 (n = 7, 30 mM Ba2+). Decay of these currents was complete during 180 ms depolarizations, even with Ba2+ as the charge carrier. These currents were not present when the holding potential was set at ‐50 mV. These data support the presence of a low threshold, T‐type Ca2+ current. 7. The maximal nitrendipine‐sensitive L‐type Ca2+ current density was ‐10 +/‐ 2 pA pF‐1 (n = 8) in 2 mM Ca2+ and ‐38 +/‐ 5 pA pF‐1 (n = 9) in 30 mM Ba2+. Exposure to isoprenaline (1 microM) resulted in an 82% increase (n = 3) in the amplitude of the Ba2+ currents elicited at 0 mV. 8. Neonatal mouse cardiac myocytes in primary culture possess surprisingly large inward currents given the brevity of their action potentials.(ABSTRACT TRUNCATED AT 250 WORDS)
The effect of intracellular anions on ATP‐dependent potassium channels of rat skeletal muscle.
Authors: McKillen H C , Davies N W , Stanfield P R , Standen N B
Published: December 2014

1. We have used excised inside‐out patches to study the effects of anions bathing the cytoplasmic surface of the membrane on ATP‐dependent K+ channels of rat flexor digitorum brevis muscle. Channels were closed by ATP applied to the cytoplasmic face of the patch with a concentration for half‐closure (Ki) of 14 microM, were highly selective for K+ and had unitary conductances of 62 pS in symmetrical 155 mM K+ and 27 pS in 5 mM [K+]o. 2. In 139 mM Cl‐ internal solution channel activity declined rapidly after excision of the patch. Inclusion of 40 mM potassium gluconate (substituted for KCl) in the solution both restored channel activity and greatly slowed its subsequent run‐down. 3. The action of gluconate was concentration dependent. The effect did not involve a change in ATP binding, since the Ki for ATP was not significantly changed by gluconate, and was specific for the cytoplasmic face of the patch. 4. The anions pyruvate, lactate and acetate were all able to restore channel activity after run‐down, though less well than gluconate, while sulphate and methylsulphate were without effect. 5. Analysis of single channel kinetics showed that gluconate did not affect mean open lifetime, but led to a decrease in the number and duration of long closings. 6. Anions are most likely to act by stabilizing the structure of the channel protein. Changes in the intracellular concentration of certain anions may play a role in regulating channel activity.
Changes in potassium channel activity following axotomy of B‐cells in bullfrog sympathetic ganglion.
Authors: Jassar B S , Pennefather P S , Smith P A
Published: December 2014

1. Whole‐cell and microelectrode voltage‐clamp techniques were used to investigate the changes in ionic currents and action potential shape that follow axotomy of bullfrog paravertebral sympathetic ganglion B‐cells. 2. Axotomy increased M‐conductance (gM; muscarine‐sensitive, voltage‐ and time‐dependent K+ conductance) by 35% at ‐30 mV and slowed its deactivation kinetics. 3. The delayed rectifier K+ current (IK; at +50 mV) was reduced in axotomized neurones to 61% of control without any change in activation or deactivation kinetics. Steady‐state intracellular Ca2+ levels and leak conductance were unchanged. 4. The fast, voltage‐sensitive, Ca(2+)‐activated K+ current (IC), evoked from ‐40 mV, was decreased to about 71% of control (at +30 mV) in axotomized neurones, whereas that evoked from ‐80 mV was largely unaffected. IC kinetics were also similar in control and axotomized neurones. This suggests that IC channels are not changed after axotomy. 5. In axotomized neurones, commands to +10 from ‐40 mV had to be extended by 16 ms to evoke voltage‐insensitive Ca(2+)‐dependent K+ current (IAHP) responses that were similar in magnitude to those observed in control cells. 6. The previously documented, axotomy‐induced decrease in Ca2+ current (ICa) due to increased resting inactivation can account for the reduction in IC and IAHP and for the change in the shape of the action potential.
Role of cell volume and protein kinase C in regulation of a Cl‐ conductance in single proximal tubule cells of Rana temporaria.
Authors: Robson L , Hunter M
Published: December 2014

1. The whole‐cell patch clamp technique was used to investigate Cl‐ currents in single proximal tubule cells isolated from kidneys of Rana temporaria. 2. Immediately following establishment of the whole‐cell clamp, the Cl‐ conductance (gCl) of the cells was low. However, with 2 mM ATP in the pipette there was a time‐dependent activation of gCl. Such activation was inhibited when the bath contained a hypertonic Ringer solution. 3. The Cl‐ conductance was not directly dependent on cell volume; gCl increased with hypotonic shock and decreased with hypertonic shock, but only in the presence of ATP. 4. Activation of gCl by ATP was dependent on extracellular Ca2+; however, the conductance was not directly Ca2+ sensitive. Activation was inhibited by Gd3+, which also had a direct inhibitory action on gCl. 5. Inhibition of protein kinase C (PKC), by 10 microM PKC pseudo‐substrate (PKC‐ps), completely abolished the ATP‐dependent activation of gCl, while stimulation of PKC, by the PKC activator 4 beta‐phorbol 12‐myristate, 13‐acetate (PMA), increased the degree of activation typically observed with ATP. 6. We propose that gCl is activated by PKC‐mediated phosphorylation and plays a role in volume regulation of the cells.
Phenylalanine transport in rabbit small intestine.
Authors: Munck B G , Munck L K
Published: December 2014

1. The proposal that rabbit small intestine possesses a separate, sodium‐dependent carrier of phenylalanine has been examined by measurements of the unidirectional influx of amino acids across the brush‐border membrane of the intact epithelium of the rabbit small intestine. 2. We demonstrate that, like alanine, glycine and leucine, phenylalanine shares sodium‐dependent as well as sodium‐independent transport with lysine. 3. Using the distal ileum we applied the A (phenylalanine)‐B (leucine)‐C (alanine) test on the sodium‐dependent, lysine‐resistant transport of phenylalanine. For phenylalanine, K1/2 (concentration required for half‐maximal transport) was 3.1 +/‐ 0.2 mM (n = 7) and Ki (inhibitor constant) against leucine transport was 3.1 +/‐ 0.2 mM (n = 4). For leucine, K1/2 was 1.1 +/‐ 0.1 mM (n = 4) and Ki against transport of phenylalanine was 1.1 +/‐ 0.1 mM (n = 4). For alanine, K1/2 was 12.6 +/‐ 1.1 mM (n = 3), Ki against phenylalanine was 13.1 +/‐ 1.8 mM (n = 4) and Ki against leucine was 11.0 +/‐ 0.4 mM (n = 4). 4. Using the jejunum we applied the A (phenylalanine)‐B (alanine)‐C (methionine) test on the lysine‐resistant, sodium‐dependent transport of phenylalanine. For phenylalanine, K1/2 was 4.7 +/‐ 0.2 mM (n = 7) and Ki against alanine was 4.8 +/‐ 0.2 mM (n = 4). For alanine, K1/2 was 15.6 +/‐ 0.8 mM (n = 7) and Ki against phenylalanine was 18.1 +/‐ 0.9 mM (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)
Sympathetic and parasympathetic interaction in vascular control of the nasal mucosa in anaesthetized cats.
Authors: Lacroix J S , Ulman L G , Potter E K
Published: December 2014

1. In cats anaesthetized with pentobarbitone sodium (45 mg kg‐1), electrical stimulation of the parasympathetic nerve fibres to the nasal mucosa evoked frequency‐dependent increases in nasal arterial blood flow whereas stimulation of the superior cervical sympathetic nerve induced marked vasoconstriction. 2. Sympathetic nerve stimulation for 3 min at 10 Hz evoked significant (P < 0.05) and prolonged (> 30 min) attenuation of the vasodilatory response to subsequent parasympathetic stimulation. 3. Combined pretreatment with adrenergic and cholinergic blockers reduced the vasoconstrictory effect of sympathetic stimulation by 28 +/‐ 4% (mean +/‐ S.E.M.) and the parasympathetically evoked vasodilatation by 20 +/‐ 5%. 4. The vasodilatory effects of exogenous vasoactive intestinal polypeptide, peptide histidine isoleucine and galanin, and the vasoconstrictory effects of exogenous neuropeptide Y (NPY) and alpha,beta‐methylene adenosine 5'‐triphosphate were not altered by adrenoceptor antagonists and atropine whereas the effects of exogenous noradrenaline and acetylcholine were virtually abolished. 5. The atropine‐resistant parasympathetic vasodilatation remained significantly attenuated for more than 30 min after the non‐adrenergic sympathetically evoked vasoconstriction. 6. Exogenous NPY (25 x 10(‐9) mol) mimicked the effect of sympathetic stimulation in attenuating subsequent parasympathetically evoked vasodilatation.
Dual modulation of unitary L‐type Ca2+ channel currents by [Ca2+]i in fura‐2‐loaded guinea‐pig ventricular myocytes.
Authors: Hirano Y , Hiraoka M
Published: December 2014

1. Single‐channel studies were performed to clarify how tonic changes in intracellular Ca2+ concentrations ([Ca2+]i) modulate cardiac L‐type Ca2+ channels. Currents were recorded from fura‐2‐loaded guinea‐pig ventricular myocytes in the cell‐attached configuration. Fura‐2 fluorescence signals were recorded simultaneously during pulses to elicit channel activity. 2. The myocyte [Ca2+]i was altered through changes in bath Ca2+ concentration during K+ depolarization. When [Ca2+]i exceeded approximately 2 times the resting level (estimated [Ca2+]i around 180‐400 nM), the activity of Ca2+ channels was reversibly potentiated without changes in unitary current amplitudes. 3. Increased channel open probability during Ca(2+)‐dependent potentiation resulted from increased availability and increased open probability during non‐blank sweeps. Closed time analysis revealed a distribution best fitted with two exponentials. Increased [Ca2+]i reduced the longer time constant, but had no effect on the shorter time constant. The open time constant was unchanged in most cases. Current records occasionally included sweeps with long openings (approximately 10 ms or more), whose appearance increased during potentiation. 4. When [Ca2+]i was increased after cAMP‐dependent upregulation of Ca2+ channels, the change in channel activity was diminished. Similar results were observed when Ca(2+)‐dependent potentiation was examined in myocytes exposed to a membrane‐permeant protein kinase inhibitor, H‐89. This suggests that channel phosphorylation may be responsible for Ca(2+)‐dependent potentiation. 5. When [Ca2+]i was further increased, but remained below the threshold for contraction (estimated [Ca2+]i above 600 nM), Ca2+ channel activity was suppressed. 6. Our results demonstrate directly at the single‐channel level that [Ca2+]i modulates the activity of cardiac L‐type Ca2+ channels, enhancing it with modest [Ca2+]i increases and decreasing it with greater [Ca2+]i increases.
Transient expression of a novel type of GABA response in rat CA3 hippocampal neurones during development.
Authors: Strata F , Cherubini E
Published: December 2014

1. Intracellular recordings were used to study the effects of gamma‐aminobutyric acid (GABA) on rat CA3 hippocampal neurones during the first two weeks of postnatal life. 2. In the presence of tetrodotoxin (TTX, 1 microM), from postnatal day 0 (P0) to P12 both associated with an increase in input conductance whereas baclofen (30‐100 microM) produced a membrane hyperpolarization. 3. Bicuculline (50 microM) reduced the effects of GABA and abolished the response to isoguvacine without affecting the response to baclofen. 4. This novel bicuculline‐insensitive GABA response was chloride dependent and was blocked by picrotoxin (10‐100 microM) in an uncompetitive way. In bicuculline and picrotoxin, a GABAB‐mediated hyperpolarization appeared. 5. Towards the end of the second postnatal week, bicuculline blocked the GABA‐induced depolarization and revealed a small hyperpolarizing response which was blocked by the GABAB antagonist CGP 35348 (0.5‐1 mM). 6. It is suggested that, during development, the GABA response was mediated through the conventional GABAA and GABAB receptors as well as a new bicuculline‐baclofen‐insensitive type of receptor.
Vascular bed‐dependent roles of the peptide CGRP and nitric oxide in acid‐evoked hyperaemia of the rat stomach.
Authors: Holzer P , Wachter C , Jocic M , Heinemann A
Published: December 2014

1. Acid back‐diffusion through a disrupted gastric mucosal barrier is known to increase gastric mucosal blood flow via a neural mechanism. The present study examined how the acid‐evoked change in the gastric microcirculation compares with blood flow changes in the left gastric artery, one of the major arteries supplying the stomach, and whether the dilator mediators in the left gastric artery are identical to those in the gastric mucosa. 2. The experiments were performed on rats anaesthetized with urethane. Blood flow in the left gastric artery was measured by the ultrasonic transit time shift technique, and blood flow in the gastric mucosa was assessed by the hydrogen gas clearance method. 3. Gastric acid back‐diffusion evoked by perfusion of the stomach with 15% ethanol in 0.15 M HCl increased blood flow in the left gastric artery by a factor of 4.7, which was significantly larger than the 2.9‐fold increase in blood flow through the gastric mucosa. Blood pressure and heart rate were not altered appreciably. 4. The acid‐evoked hyperaemia in the left gastric artery was left unaltered by atropine and the substance P receptor antagonist RP‐67580. 5. The calcitonin gene‐related peptide (CGRP) antagonist CGRP (8‐37) had no effect on gastric blood flow but prevented the dilator action of CGRP and inhibited the acid‐evoked hyperaemia in the gastric mucosa to a larger degree than the hyperaemia in the left gastric artery. 6. Blockade of nitric oxide synthesis by N omega‐nitro‐L‐arginine methyl ester (L‐NAME) caused constriction of the left gastric artery and the gastric mucosal microvessels. The acid‐evoked vasodilatation in the gastric mucosa was blocked by L‐NAME, whereas the dilator response in the left gastric artery was not significantly depressed. 7. The data show that the gastric hyperaemic response to acid back‐diffusion results from dilatation of mucosal microvessels and extramural arteries. The dilator mechanisms, however, differ between the two vascular beds. CGRP and nitric oxide are important vasodilator mediators in the gastric mucosa but are of less relevance in the left gastric artery.
Interdependence of respiratory and cardiovascular changes induced by systemic hypoxia in the rat: the roles of adenosine.
Authors: Thomas T , Marshall J M
Published: December 2014

1. In ten spontaneously breathing, Saffan‐anaesthetized rats (group I), respiratory and cardiovascular responses evoked by 10 min periods of hypoxia (arterial partial pressure of O2, Pa,O2, 33 mmHg) were recorded before and after the administration of the adenosine receptor antagonist 8‐phenyltheophylline (8‐PT, 10 mg kg‐1 i.v.). Similar experiments were performed on nine constantly ventilated rats (group II; Pa,O2, 29 mmHg) with arterial partial pressure of CO2 (Pa,CO2) held constant. 2. In group I, hypoxia induced an initial increase and a secondary fall in ventilation (VE) with an accompanying secondary fall in heart rate (HR), arterial pressure (ABP) fell and cerebral vascular conductance (CVC) increased progressively. Cerebral blood flow (CBF) tended to fall with time during hypoxia. 8‐PT abolished the secondary falls in VE and HR and reduced the fall in ABP and increase in CVC, while CBF was better maintained. 3. In group II, hypoxia induced a similar cardiovascular response to that in group I, but at the 1st minute of hypoxia, the HR was lower and the increase in CVC was greater. 8‐PT did not affect the hypoxia‐induced changes in HR, ABP, CVC or CBF. 4. These results indicate specific ways in which the ventilatory and cardiovascular responses induced by hypoxia in the spontaneously breathing rat are interdependent. They also indicate that the influences of 8‐PT on the cardiovascular changes induced by hypoxia during spontaneous ventilation are mainly a consequence of its ability to block the centrally mediated contribution of adenosine to the secondary fall in ventilation.
Concentration dependence of neurotransmitter effects on calcium current kinetics in frog sympathetic neurones.
Authors: Elmslie K S , Jones S W
Published: December 2014

1. Noradrenaline (NA) slows the activation kinetics of N‐type calcium channels, via G proteins. It has been suggested that the G proteins act by binding directly to the calcium channels. If the slow kinetics reflect binding and unbinding of G proteins, the rates should depend on the concentration of activated G protein. 2. We used different concentrations of NA, and increasing durations of intracellular dialysis with GTP‐gamma‐S, to vary the concentration of activated G protein. 3. At depolarized potentials (‐20 or ‐10 mV), the slow activation kinetics showed no detectable concentration dependence. This analysis required correction for effects of inactivation on the measured time constants. 4. At ‐80 mV, reinhibition of calcium channel current was more rapid for larger responses. Thus, the effect appears to be concentration dependent at ‐80 mV, but not at more depolarized voltages. 5. This voltage dependence is actually expected from kinetic principles: the binding step is rate limiting when the position of equilibrium is toward the bound state (at ‐80 mV), but not when equilibrium favours unbinding (when the channel is open). 6. During inhibition, the channel appears to ‘sense’ directly the concentration of the modulator, possibly active G proteins.
Lactate efflux from fatigued fast‐twitch muscle fibres of Xenopus laevis under various extracellular conditions.
Authors: Nagesser A S , van der Laarse W J , Elzinga G
Published: December 2014

1. Isolated, fast‐twitch, low‐oxidative muscle fibres from the iliofibularis muscle of Xenopus laevis were fatigued by intermittent tetanic stimulation at 20 degrees C in different Ringer solutions and the amount of lactate released was determined. 2. The rate of lactate efflux was constant during 10 min of intermittent stimulation while lactate in the fibres accumulated, and lactate efflux was not hampered by an unstirred layer surrounding the isolated muscle fibre. 3. The rate of lactate efflux at extracellular pH 7.2 was the same as that at pH 7.8, but depended on the type of buffer used; the highest efflux rate (mean +/‐ S.E.M., 7.4 +/‐ 2.2 mumol min‐1 (g dry weight)‐1, n = 8) was observed in bicarbonate‐buffered Ringer solution. This rate was about 2.5 times higher than the rate in phosphate‐buffered Ringer solution (2.9 +/‐ 1.3 mumol min‐1 (g dry weight)‐1, n = 8), indicating that lactate‐bicarbonate exchange is the most important route for lactate extrusion in vivo. 4. The highest rate of lactate efflux corresponds to a rate of glycolytic ATP production which is only about 30% of the oxidative rate of ATP production (calculated from the maximum rate of oxygen consumption determined previously). 5. In the presence of 5 mM alpha‐cyano‐4‐hydroxycinnamate (CHC) the lowest lactate efflux rate (1.5 +/‐ 0.6 mumol min‐1 (g dry weight)‐1, n = 16) was found. This rate was independent of the composition of the Ringer solution. Assuming that 5 mM CHC completely inhibits lactate transporters in the sarcolemma, the rate of lactate efflux in the presence of 5 mM CHC can be explained by passive diffusion, but only if most lactate is extruded via the T‐tubules.
Static sensitivity of tendon organs to tetanic contraction of in‐series motor units in feline peroneus tertius muscle.
Authors: Petit J , Davies P , Scott J J
Published: December 2014

1. The results of several studies have indicated an absence of any consistent relationship between the discharge of Ib Golgi tendon organ afferents and the steady‐state tetanic tension generated by activating motor units. This question has been re‐examined by recording the responses of individual tendon organs to tetanic, isometric contractions of one or more motor units from the peroneus tertius muscle of anaesthetized cats. 2. In three experiments, seventy‐three individual tendon organ‐motor unit interactions were recorded. The motor units were stimulated at 30‐150 s‐1 and for each tendon organ‐motor unit pair a linear relationship was found between steady‐state tetanic tension and Ib afferent discharge. The slopes of these relationships (the static sensitivities) were steepest for the weakest units. 3. When motor units were stimulated in combination, the relationship between discharge frequency and plateau tension was again linear but the static sensitivities were generally much lower than for single units and approached 1 impulse s‐1 g‐1. 4. Expression of these relationships in terms of the relative tensions generated revealed that the tendon organs were activated most strongly by the IIb muscle fibres, the static sensitivities being reduced by unloading effects. 5. The linear relationships observed during stimulation of single, and groups of, motor units suggest that the patterns of discharge from the tendon organs can mirror the steady‐state contractile tensions within the muscle.
Epileptic activity outlasts disinhibition after intrahippocampal tetanus toxin in the rat.
Authors: Whittington M A , Jefferys J G
Published: December 2014

1. A single dose of tetanus toxin, injected under anaesthesia into one dorsal hippocampus of the rat, produces chronic epileptic foci involving both hippocampi. Generalized seizures occurred 1‐6 weeks after injection and epileptic discharges were found in hippocampal slices in vitro. Here we measured the time course of decay of epileptic activity and the level of GABAA receptor‐mediated inhibition in hippocampal slices 1‐16 weeks after toxin injection in vivo. 2. Epileptic activity peaked in the dentate granule cell and CA3 pyramidal cell layers 2 weeks after toxin injection and at 4 weeks in CA1. Thresholds for evoking epileptic activity were lowest in the suprapyramidal blade of the dentate gyrus and area CA3c. Recovery from epileptic activity occurred more rapidly in the contralateral hippocampus. Polyspike activity ceased by 8 weeks and interictal activity by 16 weeks. Epileptic discharges could still be evoked from CA1 16 weeks after toxin injection. 3. The maximal monosynaptic fast inhibitory postsynaptic current (IPSC) conductance changes (gIPSC) decreased to < 10% of control values at the time of peak epileptic activity and remained lower than controls for 4 weeks ipsilaterally. In the contralateral hippocampus, gIPSC fell to ca 50% of control values for the first 2 weeks. Responses to exogenous GABA remained unchanged. 4. After 8 weeks dentate granule cells had gIPSC significantly larger than controls. No increase in gIPSC occurred in CA3. Epileptic activity persisted 8‐10 weeks after recovery from disinhibition ipsilaterally and 4 weeks contralaterally. 5. Epileptic activity was seen when monosynaptic GABAA receptor‐mediated IPSCs were normal or supranormal. At these times polysynaptic inhibition was still profoundly reduced. These observations provide strong evidence for long‐term changes in the pattern of synaptic excitation contributing to a chronic epileptic syndrome syndrome following disinhibitory insult, and are consistent with weakened excitation of inhibitory neurones.
An in vivo pharmacological study of single group Ia fibre contacts with motoneurones in the cat spinal cord.
Authors: Walmsley B , Bolton P S
Published: December 2014

1. Direct experimental evidence was obtained on the spatial distribution of active synaptic contacts from single Ia muscle afferents on the dendrites of lumbosacral motoneurones in anaesthetized cats. 2. An extracellular micropipette was used to pressure eject the AMPA/kainate receptor antagonists 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) or 2,3‐dihydroxy‐6‐nitro‐7‐sulphamoyl‐benzo(F)quinoxaline (NBQX) in close proximity to the intracellular recording site, in order to create an extracellular concentration gradient of the antagonist. The effect of antagonist ejection on the time course and amplitude of excitatory postsynaptic potentials (EPSPs) evoked in motoneurones by impulses in single group Ia fibres was examined. 3. Pressure ejection of NBQX resulted in a complete block of the monosynaptic group Ia EPSP in two cells, and a significant reduction to 23‐57% of control EPSP peak amplitudes in a further six cells (mean, 27%; n = 8). These effects were not associated with changes in membrane potential or membrane time constant. 4. The reduction in amplitude of these single group Ia fibre EPSPs following ejection of NBQX was usually accompanied by a pronounced slowing in the time course of the EPSPs. On average, the EPSP rise times and half‐widths were increased by 269 and 37%, respectively. This is most probably due to a considerable spatial spread of the synaptic contacts along the dendrites of motoneurones, with the most proximal synaptic contacts (producing the briefest synaptic potentials) subjected to a greater reduction in amplitude due to a higher local antagonist concentration. 5. An equivalent dendritic cable model of the motoneurone was used to interpret the observed changes in the time course of single fibre EPSPs. The time course of control single fibre EPSPs examined in the present study could be well matched using the cable model and assuming a single location for synaptic input. The observation of a slowed EPSP time course following antagonist ejection indicated that this assumption was not correct and that there was in fact considerable spatial spread in the synaptic contacts arising from these single afferent fibres. These results provide direct evidence that spatial spread of synaptic input may not be detected using the time course of a synaptic potential in conjunction with a neuronal cable model of the postsynaptic cell.
The discharge behaviour of single vasoconstrictor motoneurones in human muscle nerves.
Authors: Macefield V G , Wallin B G , Vallbo A B
Published: December 2014

1. The discharge behaviour of fourteen single sympathetic vasoconstrictor efferents was studied using a tungsten microelectrode inserted percutaneously into a motor fascicle of the radial or peroneal nerve in eight awake supine subjects. Units were classified as vasoconstrictor because their firing properties correlated appropriately to changes in cardiac interval and arterial pressure. 2. On average, individual vasoconstrictor units discharged in only 21% of heart beats, with an overall mean frequency of 0.47 Hz. Usually only one spike was generated per cardiac cycle. Calculated from cardiac cycles in which a unit fired from two to seven spikes, the mean within‐burst firing rate was 18.8 +/‐ 2.5 Hz (mean +/‐ S.E.M.); but instantaneous frequencies above 50 Hz were occasionally observed. 3. Measured from a defined R‐wave of the ECG, the spike onset latency varied over 358 +/‐ 33 ms, suggesting considerable variation of synaptic delays in the baroreflex arc. This latency had a relatively uniform temporal relationship with the burst onset or peak latency, compatible with a fixed recruitment order of individual sympathetic neurones. 4. In view of the low average firing rate of individual units we suggest that the variable instantaneous firing rates may optimize the contractile responses of vascular smooth muscle.
Fusimotor neurone responses to medial plantar nerve stimulation in the decerebrate cat.
Authors: Murphy P R , Martin H A
Published: December 2014

1. The effect of single shock electrical stimulation, up to 20 x threshold (T), of the medial plantar nerve on the discharges of single medial gastrocnemius static and dynamic gamma‐efferents has been investigated in the decerebrate cat. 2. The neurones were classified as static (15) or dynamic (8) indirectly on the basis of their locomotor and/or resting discharge characteristics. 3. All gamma‐efferents were affected by stimulation of the medial plantar nerve. Dynamic units showed net inhibition while facilitation dominated the responses of static neurones. 4. The responses of dynamic units consisted of powerful short latency (15 +/‐ 1.2 ms, mean +/‐ S.D.) spinal inhibition followed by weaker facilitation that was difficult to characterize due to concomitant rephasing of neuronal discharge. 5. Static neurones showed two patterns of response. Some units (7 of 15) were facilitated at medium latency (39.9 +/‐ 12.2 ms) while the remainder showed mixed effects in which short latency (18 +/‐ 3.6 ms) spinal inhibition was followed by stronger facilitation (latency, 38.1 +/‐ 5.3 ms). 6. Fusimotor facilitation and inhibition were generally present at 2T. The inhibition of dynamic and static gamma‐efferents, and the facilitation of the latter type, increased with stimulus intensity. Thus low and high threshold afferents contributed to the effects without changing their qualitative nature. 7. We conclude that low threshold cutaneous mechanoreceptors in the plantar surface of the foot are capable of influencing the discharges of medial gastrocnemius static and dynamic gamma‐efferents. Further, the cutaneous responses of fusimotor neurones appear to vary according to both the source of the afferent input and the type of unit involved. 8. The results are discussed in relation to the control and function of fusimotor neurones and the possible existence of subdivisions within the static system.
Human muscle spindle afferent activity in relation to visual control in precision finger movements.
Authors: Wessberg J , Vallbo A B
Published: December 2014

1. Impulse activities of muscle spindle afferents from the finger extensor muscles were recorded in the radial nerve of human subjects. In addition to single unit activity, surface EMG was recorded as well as finger joint position and angular velocity. 2. All units were studied under two conditions of voluntary finger movements. In the visual condition, the subject tracked ramp and hold sequences at a single metacarpophalangeal joint. In the non‐visual condition the subject was asked to produce the same movement while visual control was denied altogether. 3. With sixteen units, detailed statistical analyses failed to reveal significant differences in muscle spindle afferent activity between the visual and the non‐visual task. However, with two group Ia units, impulse rate was marginally but significantly higher in the visual task even when differences in average movement velocity, velocity variability and EMG level had been factored out. 4. The findings suggested that access to visual information for movement control did not produce any large‐scale differences in spindle afference, although a small effect of an increased and independent gamma‐activation emerged in the statistical analysis in 11% of the units.
AMPA receptors with high Ca2+ permeability mediate synaptic transmission in the avian auditory pathway.
Authors: Otis T S , Raman I M , Trussell L O
Published: December 2014

1. The permeability of AMPA (alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐ isoxazolepropionate) receptors in the chick cochlear nucleus, the nucleus magnocellularis (nMAG), was examined by measuring the shift in reversal potential (Erev) of current through glutamate or neurotransmitter‐gated channels in solutions of different ionic composition. 2. Outwardly rectifying glutamate‐activated currents in outside‐out membrane patches showed rapid activation and desensitization. The Erev of glutamate‐evoked current in zero sodium solutions was dependent on the extracellular Ca2+ concentration. The relation between Erev and Ca2+ ionic activities could be described by the Goldman‐Hodgkin‐Katz equation with a permeability ratio, PCa/PCs, of 3.3. The PNa/PCs was estimated as 0.66, indicating a PCa/PNa of 5. 3. Evoked excitatory postsynaptic currents (EPSCs) could be recorded during local perfusion of the auditory nerve‐nMAG synapse with isotonic Ca2+. The Erev of the EPSC shifted in the positive direction in high‐Ca2+ solution as predicted from the preceding analysis. The fraction of current carried by Ca2+ during the AMPA receptor EPSC was estimated as 18%.
Nicotinamide‐adenine dinucleotide regulates muscarinic receptor‐coupled K+ (M) channels in rodent NG108‐15 cells.
Authors: Higashida H , Robbins J , Egorova A , Noda M , Taketo M , Ishizaka N , Takasawa S , Okamoto H , Brown D A
Published: December 2014

1. The possible role of nicotinamide‐adenine dinucleotide (NAD+) and cyclic adenosine diphosphate ribose (cADPR) as regulators of M‐type K+ currents (IK(M)) has been studied in whole‐cell patch‐clamped NG108‐15 mouse neuroblastoma x rat glioma cells that had been transformed to express m1 muscarinic acetylcholine receptors (mAChRs). 2. Pre‐incubation of NG108‐15 cells for 6‐8 h with streptozotocin (2‐5 mM) reduced NAD+ levels by 40‐50%. Nicotinamide (2‐5 mM) increased NAD+ levels and prevented depletion by streptozotocin. 3. Streptozotocin pretreatment reduced the inhibition of IK(M) produced by 100 microM acetylcholine (ACh) from 51.6 +/‐ 7.0 to 29.1 +/‐ 7.5%. This was prevented by simultaneous pre‐incubation with 2 mM nicotinamide or by adding 2 mM NAD+ to the pipette solution. Neither procedure significantly affected the initial amplitude of IK(M). 4. Inclusion of 2 microM cADPR in the pipette solution induced a slow loss of IK(M) with a time constant of about 20 min. 5. It is concluded that mAChR‐induced inhibition of IK(M) requires intracellular NAD+. This might be needed for the formation of cADPR as a regulator or messenger for IK(M) inhibition.
Involvement of endothelin‐1 in hypoxic pulmonary vasoconstriction in the lamb.
Authors: Wang Y , Coe Y , Toyoda O , Coceani F
Published: December 2014

1. Using isolated pulmonary resistance vessels from mature fetal lamb and chronically instrumented lambs (8‐17 days old), we have examined whether hypoxic pulmonary vasoconstriction is sustained by activation of a constrictor mechanism or suppression of a dilator mechanism. 2. Hypoxia contracted both arteries and veins in vitro, and the contraction was greater with the former. After removing the endothelium, arteries responded faster to hypoxia, but the magnitude of the response remained unchanged. 3. Hypoxic arteries, unlike normally oxygenated arteries, did not contract with either indomethacin (2.8 microM) or N omega‐nitro‐L‐arginine methyl ester (L‐NAME, 100 microM). The same vessels relaxed with sodium nitroprusside (SNP, 0.001‐10 microM) but not with bradykinin (0.1‐100 nM). 4. Endothelin‐1 (ET‐1, 0.01‐10 nM) contracted isolated arteries and veins under normoxic and hypoxic conditions. In both vessels, the contraction was fast in onset and subsidence, and was inhibited by the ETA receptor antagonist BQ123 (1 microM). The ET‐1 precursor, big ET‐1 (100 nM), also contracted arteries and veins, but compared with ET‐1 its action was slower in development. Big ET‐1 contraction, unlike ET‐1 contraction, was curtailed by the inhibitor of the ET‐1‐converting enzyme, phosphoramidon (50 microM). 5. ET‐1 (0.1‐10 nM) had no effect on isolated arteries precontracted with a thromboxane A2 (TXA2) analogue (ONO‐11113) and treated with BQ123 (10 microM). Under the same conditions, ET‐1 relaxed the veins. Accordingly, in the absence of BQ123 treatment, the selective ETB receptor agonist IRL‐1620 (0.1‐100 nM) relaxed the contracted veins but not the arteries. 6. BQ123 (10 microM) inhibited the constriction of isolated arteries and veins to hypoxia. Likewise, in the conscious lamb a bolus of BQ123 (0.4 mg kg‐1, injected into the pulmonary artery) curtailed the rise in pulmonary vascular resistance (Rpa) brought about by alveolar hypoxia without changing significantly systemic vascular resistance (Rao). Under normoxia, Rpa was insignificantly affected by BQ123. 7. The results indicate that pulmonary resistance arteries are more susceptible to hypoxia than the veins, and that hypoxic vasoconstriction does not require an intact endothelium to occur. Hypoxic tone is ascribed primarily to intramural generation of ET‐1, while removal of the tonic action of a relaxant may only have an accessory role in the response.
Nitric oxide donors enhanced Ca2+ currents and blocked noradrenaline‐induced Ca2+ current inhibition in rat sympathetic neurons.
Authors: Chen C , Schofield G G
Published: December 2014

1. The effects of NO donors on Ca2+ channel currents and noradrenaline (NA)‐induced Ca2+ current inhibition were investigated in superior cervical ganglion (SCG) neurons using the whole‐cell patch‐clamp technique. 2. A 500 microM concentration of the NO donors, sodium nitroprusside (SNP) and S‐nitroso‐N‐acetylpenicillamine (SNAP), enhanced Ca2+ current amplitude after either extracellular or intracellular application. The magnitude of Ca2+ current enhancement induced by NO donors was greater after intracellular application than after extracellular application. 3. Intracellular application of 1 mM guanosine 3',5'‐cyclic monophosphate (cGMP) or 100 microM M&B 22948 (2‐O‐propoxyphenyl‐8‐azapurine‐6‐one), a cGMP phosphodiesterase inhibitor, or extracellular application of 1 mM 8‐bromoguanosine 3',5'‐cyclic monophosphate (8‐Br‐cGMP) also increased the amplitude of Ca2+ currents thus mimicking the effect of the NO donors on Ca2+ channels. In contrast, pretreatment with Methylene Blue (100 microM) decreased the SNP (500 microM)‐induced enhancement of Ca2+ currents. 4. Intracellular application of 500 microM SNP and SNAP, 100 microM M&B 22948 or 1 mM cGMP, or extracellular application of 200 microM 8‐Br‐cGMP reduced the magnitude of Ca2+ current inhibition induced by 5 microM NA. In addition, 500 microM SNP prevented the NA‐induced shift of tail current activation curves to more depolarized potentials. 5. Internal dialysis with 500 microM SNP and SNAP or 1 mM cGMP, or extracellular application of 200 microM 8‐Br‐cGMP, reduced Ca2+ current facilitation produced by a depolarizing conditioning pulse both in the absence and presence of 5 microM NA. 6. The results suggest that NO donors induce enhancement of Ca2+ currents and block NA‐induced Ca2+ current inhibition of SCG neurons via stimulation of cGMP formation.
Analysis of responses observed in mesenteric microcirculation of the rat during systemic hypoxia.
Authors: Langdown A J , Marshall J M
Published: December 2014

1. Direct observations were made of responses to systemic hypoxia (breathing 12 or 6% O2 for 3 min) evoked in terminal arterioles (TA, 14‐30 microns internal diameter), precapillary arterioles (PCA, 8‐18 microns), collecting venules (CV, 12‐30 microns) and small veins (SV, 20‐50 microns) of the mesenteric circulation of the anaesthetized rat. Changes in vessel diameter were recorded before and after local blockade of alpha‐adrenoreceptors with phentolamine when the mesentery was covered with Saran Wrap, which is impermeable to O2, and then after removal of the Saran Wrap, which would have kept local PO2 relatively high even during systemic hypoxia. 2. The majority of TA showed an initial decrease in diameter of 14 +/‐ 1% (mean +/‐ S.E.M.). These responses were reversed to increases in diameter (12 +/‐ 2%) after phentolamine, but virtually abolished after removal of the Saran Wrap (0.3 +/‐ 2%). 3. Some PCA showed similar behaviour to the TA; others showed an increase in diameter (11 +/‐ 1%). The increases in diameter were accentuated after phentolamine (16 +/‐ 1%), but were reduced after removal of the Saran Wrap (6 +/‐ 2%). 4. CV and SV showed either a decrease in diameter followed by relaxation towards control levels, or an increase in diameter that waned before hypoxia ceased (6 +/‐ 1% and 1 +/‐ 1%, respectively). The responses of CV were not altered by phentolamine (8 +/‐ 1%), but SV showed larger increases in diameter (5 +/‐ 1%).(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of baseline vascular tone on vasomotor responses in cat lip.
Authors: Karita K , Izumi H
Published: December 2014

1. Parasympathetic vasodilator and sympathetic vasoconstrictor responses were monitored using laser Doppler measurement of red cell flux in the lips of anaesthetized and artificially ventilated cats. 2. Three relationships were investigated: (i) that between the reflex parasympathetic vasodilator response induced by lingual nerve (LN) stimulation and baseline red cell flux (BRCF) levels adjusted by repetitive stimulation of the cervical sympathetic nerve (CSN) at various frequencies; (ii) that between the sympathetic vasoconstrictor response elicited by CSN stimulation and the adjusted BRCF levels; and (iii) that between the vasomotor response evoked by simultaneous stimulation of the LN and CSN and the adjusted BRCF levels. 3. The amplitude of the parasympathetic vasodilator response increased as BRCF decreased. In contrast, the amplitude of the sympathetic vasoconstrictor response increased in line with BRCF. 4. Simultaneous activation of the parasympathetic and sympathetic nerves induced a blood flow decrease at high BRCF levels but an increase at low levels. 5. The tendency for the skin of cold subjects to vasodilate and that of warm ones to vasoconstrict in response to various types of stimuli discussed in the light of the present findings.
A sustained inward current activated at the diastolic potential range in rabbit sino‐atrial node cells.
Authors: Guo J , Ono K , Noma A
Published: December 2014

1. After blocking both the hyperpolarization‐activated current and the membrane K+ conductance, depolarizations from ‐80 mV to between ‐70 and ‐50 mV induced a sustained current in sino‐atrial node cells. We have tentatively designated this current Ist. 2. Ist was blocked by both organic and inorganic Ca2+ channel blockers, but was insensitive to tetrodotoxin (30 microM). Isoprenaline increased Ist. 3. The peak of Ist (at about ‐50 mV) was increased to 149 +/‐ 13% (n = 8, P < 0.01) by lowering the external Ca2+ concentration ([Ca2+]o) from 1.8 to 0.1 mM, in contrast to the marked depression of the L‐type Ca2+ current. In 0.1 mM [Ca2+]o solution, the nicardipine‐sensitive current‐voltage relation showed the peak amplitude at about ‐50 mV and a reversal potential of +37.4 +/‐ 4.4 mV (n = 5). The isoprenaline‐sensitive component also showed a reversal potential of about +30 mV. 4. Reducing [Na+]o from 140 to 70 mM in 0.1 mM [Ca2+]o decreased Ist to 53 +/‐ 5% (n = 7, P < 0.01). Increasing [Ca2+]o or [Mg2+]o decreased the amplitude of Ist. The half‐maximum concentration of Mg2+ inhibition was 2.2 mM. 5. At 1.8 mM [Ca2+]o, Ist was inactivated by clamping for 5s at ‐10 mV, and gradually recovered after repolarization to ‐80 mV with a half‐time of 1.36 +/‐ 0.4 s (n = 6). 6. The transitional sino‐atrial node cell had minimal amplitude of Ist. 7. These characteristics of Ist are qualitatively comparable to those of the monovalent cation conductance of the L‐type Ca2+ channel induced by depleting external divalent cations to the micromolar range. We conclude that Ist is generated by a novel subtype of L‐type Ca2+ channel.
‘Non‐hypotensive’ hypovolaemia reduces ascending aortic dimensions in humans.
Authors: Taylor J A , Halliwill J R , Brown T E , Hayano J , Eckberg D L
Published: December 2014

1. The notion that small, ‘non‐hypotensive’ reductions of effective blood volume alter neither arterial pressure nor arterial baroreceptor activity is pervasive in the experimental literature. We tested two hypotheses: (a) that minute arterial pressure and cardiac autonomic outflow changes during hypovolaemia induced by lower body suction in humans are masked by alterations in breathing, and (b) that evidence for arterial baroreflex engagement might be obtained from measurements of thoracic aorta dimensions. 2. In two studies, responses to graded lower body suction at 0 (control), 5, 10, 15, 20 and 40 mmHg were examined in twelve and ten healthy young men, respectively. In the first, arterial pressure (photoplethysmograph), R‐R interval, and respiratory sinus arrhythmia amplitude (complex demodulation) were measured during uncontrolled and controlled breathing (constant breathing frequency and tidal volume). In the second, cross‐sectional areas of the ascending thoracic aorta were calculated from nuclear magnetic resonance images. 3. Lower body suction with controlled breathing resulted in an increased arterial pulse pressure at mild levels (5‐20 mmHg; ANOVA, P < 0.05) and a decreased arterial pulse pressure at moderate levels (40 mmHg; ANOVA, P < 0.05). Both R‐R intervals and respiratory sinus arrhythmia were negatively related to lower body suction level, whether group averages (general linear regression, r > 0.92) or individual subjects (orthogonal polynomials, 12 of 12 subjects) were assessed. 4. Aortic pulse area decreased progressively and significantly during mild lower body suction, with 47% of the total decline occurring by 5 mmHg. 5. These results suggest that small reductions of effective blood volume reduce aortic baroreceptive areas and trigger haemodynamic adjustments which are so efficient that alterations in arterial pressure escape detection by conventional means.