bluuebunny/crossref_metadata_2025 huggingface dataset:
Baroreceptor modulation of cutaneous vasodilator and sudomotor responses to thermal stress in humans.
Authors: Mack G , Nishiyasu T , Shi X
Published: December 2014

1. The influence of baroreceptor unloading on cutaneous vasodilatation was investigated in ten human subjects during dynamic supine cycle ergometer exercise at 28 degrees C. Increases in forearm skin blood flow (venous occlusion plethysmography) and arterial blood pressure (non‐invasive) were measured and used to calculate forearm vascular conductance while local chest sweating rate was measured by dew‐point hygrometry. Subjects performed two similar exercise protocols with and without baroreceptor unloading induced by application of ‐40 mmHg lower body negative pressure (LBNP). The LBNP condition was reversed (i.e. either removed or applied) after 15 min while exercise continued for an additional 20 min. 2. During exercise without LBNP, the body core temperature threshold for vasodilatation (measured as oesophageal temperature, Tc) averaged 37.06 +/‐ 0.12 degrees C (+/‐ S.E.M.) and increased to 37.30 +/‐ 0.09 degrees C (P < 0.05) during exercise with LBNP. The rate of rise of forearm vascular conductance (FVC) per unit increase in Tc (an expression of thermal sensitivity) and peak FVC at 15 min was significantly attenuated during baroreceptor unloading. These effects were rapidly reversed when LBNP was turned off. 3. Baroreceptor unloading during the first 15 min of exercise attenuated the local chest sweating rate, which was also reversed when LBNP was removed. 4. The time course and quickness in which baroreceptor unloading modulated thermoregulatory control of skin blood flow and local chest sweat rate suggests that the interaction between these two homeostatic mechanisms is primarily neurally mediated. The ability of baroreceptor activity to modulate both control of skin blood flow and sweating suggests a common site of interaction, more proximal than the effector organs, and involving the active vasodilator system.
Modulation by zinc ions of native rat and recombinant human inhibitory glycine receptors.
Authors: Laube B , Kuhse J , Rundström N , Kirsch J , Schmieden V , Betz H
Published: December 2014

1. The effect of the divalent cation Zn2+ on inhibitory glycine receptor (GlyR) currents was investigated in rat embryonic spinal cord neurons and Xenopus oocytes expressing recombinant GlyRs. 2. In cultured spinal neurons, Zn2+ potentiated glycine‐induced whole‐cell currents about 3‐fold when applied extracellularly at concentrations of 0.5‐10 microM. In contrast, higher concentrations (> 100 microM) of Zn2+ decreased the glycine response. 3. A similar biphasic modulation of glycine‐induced currents by Zn2+ was also found with recombinant homo‐ and hetero‐oligomeric GlyRs generated in Xenopus oocytes. Dose‐response analysis showed that both the potentiating and inhibitory effects of Zn2+ result from changes in apparent agonist affinity. 4. Analysis of chimeric constructs of the GlyR alpha 1‐ and beta‐subunits revealed that the positive and negative modulatory effects of Zn2+ are mediated by different regions of the alpha 1‐subunit. 5. Our data indicate the existence of distinct high‐ and low‐affinity Zn2+ binding sites on the ligand‐binding alpha‐subunits of the GlyR. These sites may be implicated in the regulation of synaptic efficacy within glycinergic pathways.
Subthreshold oscillations and resonant frequency in guinea‐pig cortical neurons: physiology and modelling.
Authors: Gutfreund Y , yarom Y , Segev I
Published: December 2014

1. Intracellular recordings were made from neurons in slices from guinea‐pig frontal cortex. In 50% of the cells, sustained subthreshold voltage oscillations were evoked by long (> 6 s) depolarizing pulses. The peak‐to‐peak amplitude of these oscillations was less than 5 mV and the frequency was voltage dependent, increasing with depolarization from 4 (near rest) to 20 Hz (at 30 mV depolarization). 2. The impedance‐frequency relationship of both oscillating and non‐oscillating cells was studied by intracellular injection of sinusoidal current with linearly changing frequency. In most cells, a peak in the impedance magnitude (resonant behaviour) was observed at depolarized levels. The frequency of the peak impedance (peak frequency) increased with depolarization from 3 (near rest) to 15 Hz (at 30 mV depolarization). 3. Application of TTX (10(‐6) M) significantly decreased the impedance magnitude near the peak frequency. The subthreshold oscillations, however, as well as the action potentials, were fully blocked by TTX. On the other hand, TEA (15 mM) and Cs+ (5 mM) abolished both the subthreshold oscillations and the resonant behaviour. Replacing Ca2+ with Co2+ (5 mM) or Ni2+ (1 mM) did not abolish the subthreshold oscillations. The peak in the frequency‐response curve was only slightly reduced. 4. An isopotential membrane model, consisting of a leak current, a fast persistent sodium current, a slow non‐inactivating potassium current (with the kinetics of the M‐current) and membrane capacitance, is sufficient to produce both voltage oscillations and resonant behaviour. The kinetics of the K+ current by itself is sufficient to produce resonance behaviour. The Na+ current amplifies the peak impedance magnitude and is essential for the generation of subthreshold oscillation. The model correctly predicted the behaviour of the frequency response before and after TTX and TEA application, as well as the relation between the expected passive impedance and the experimental impedance. 5. We speculate that the tendency of the neurons to generate voltage signals at a certain frequency (as a result of the subthreshold oscillations) and to preferentially respond to inputs arriving at the same frequency (the resonance behaviour) promotes population activity at that preferred frequency.
Vasoreactivity to prostaglandins of rat peripheral nerve.
Authors: Kihara M , Low P A
Published: December 2014

1. We evaluated the effect of the local superfusion of prostaglandins E1, I2 and F2 alpha (PGE1, PGI2 and PGF2 alpha, respectively) on rat sciatic nerve blood flow and microvascular resistance. 2. PGE1 increased nerve blood flow (NBF) in a dose‐dependent fashion with an EC50 of 10(‐6.7) M and an asymptote of 20.1 ml (100 g)‐1 min‐1. 3. PGI2 increased NBF in a linear dose‐dependent fashion, with an EC50 of 10(‐5.1) M. PGI2 appeared to be about 1.5 orders of magnitude less potent than PGE1. 4. PGF2 alpha also increased NBF in a dose‐dependent fashion. The threshold dose appeared to be identical with PGI2 but may have a reduced capacity of response. The EC50 of 10(‐5.8) M was slightly lower than that of PGI2.
Change of Na+ pump current reversal potential in sheep cardiac Purkinje cells with varying free energy of ATP hydrolysis.
Authors: Glitsch H G , Tappe A
Published: December 2014

1. The Na(+)‐K+ pump current, Ip, of cardioballs from isolated sheep cardiac Purkinje cells was measured at 30‐34 degrees C by means of whole‐cell recording. 2. Under physiological conditions Ip is an outward current. Experimental conditions which cause a less negative free energy of intracellular ATP hydrolysis (delta GATP) and steeper sarcolemmal gradients for the pumped Na+ and Cs+ ions evoked an Ip in the inward direction over a wide range of membrane potentials. The reversal of the Ip direction was reversible. 3. The inwardly directed Ip increased with increasingly negative membrane potentials and amounted to ‐0.13 +/‐ 0.03 microA cm‐2 (mean +/‐ S.E.M.; n = 6) at ‐95 mV. 4. The reversal potential (Erev) of Ip was studied as a function of delta GATP at constant sarcolemmal gradients of the pumped cations. 5. In order to vary delta GATP the cell interior was dialysed with patch pipette solutions containing 10 mM ATP and different concentrations of ADP and inorganic phosphate. The media were composed to produce delta GATP levels of about ‐58, ‐49 and ‐39 kJ mol‐1. 6. A less negative delta GATP shifted Erev to more positive membrane potentials. From measurements of Ip as a function of membrane potential Erev was estimated to be ‐195, ‐115 and ‐60 mV at delta GATP levels of approximately ‐58, ‐49 and ‐39 kJ mol‐1, respectively. The calculated Erev amounted to ‐224 mV at delta GATP approximately ‐58 kJ mol‐1, ‐126 mV at delta GATP approximately 49 kJ mol‐1 and ‐24 mV at delta GATP approximately ‐39 kJ mol‐1. 7. Possible reasons for the discrepancy between estimated and calculated Erev values are discussed. 8. Shifting delta GATP to less negative values not only altered Erev but also diminished Ip at each membrane potential tested. The maximal Ip (Ip,max), which can be activated by external Cs+ (Cs+o), decreased under these conditions, whereas [Cs+]o causing half‐maximal Ip activation remained unchanged. Similarly, the voltage dependence of Ip activation by Cs+o was unaffected. 9. It is concluded that Erev of Ip varies with delta GATP at constant sarcolemmal gradients of the pumped cations. This agrees with thermodynamic considerations.
Associative EPSP‐‐spike potentiation induced by pairing orthodromic and antidromic stimulation in rat hippocampal slices.
Authors: Jester J M , Campbell L W , Sejnowski T J
Published: December 2014

1. Pairing low‐frequency orthodromic stimulation with high‐frequency antidromic conditioning of pyramidal cells in area CA1 of the rat hippocampus resulted in long‐lasting potentiation of the extracellular population spike of the cells, without an accompanying increase in the extracellular excitatory postsynaptic potential (EPSP), indicating an increase in EPSP‐spike (E‐S) coupling, also called E‐S potentiation. 2. The amplitude of the antidromically conditioned E‐S potentiation took up to 60 min to reach its peak, much longer than synaptic long‐term potentiation (LTP) induced by orthodromic tetanic stimulation. 3. The population spike amplitude of a control orthodromic input, which stimulated a separate set of fibres and which was inactive during the pairing, was also increased in over half the slices tested. That it can affect a silent pathway suggests that antidromically conditioned E‐S potentiation is not generated locally at tetanized synapses. 4. Bath application of 50 microM D,L‐2‐amino‐5‐phosphonovaleric acid (AP5) blocked induction of antidromically conditioned E‐S potentiation. After washing out the AP5, the same stimulation resulted in population spike increases. This suggests that activation of the NMDA subtype of glutamate receptor is necessary for the induction of this form of E‐S potentiation. 5. Application of 10 microM picrotoxin and/or 10 microM bicuculline, which block inhibition mediated by gamma‐aminobutyric acid A (GABAA) receptors, did not reduce antidromically conditioned E‐S potentiation. Thus, plasticity in GABAA‐mediated inhibition cannot account for the increased population spike amplitude. 6. E‐S potentiation did not increase the amplitude of either extracellular or intracellular EPSPs recorded at the cell body.
Inhibition by 5‐hydroxytryptamine and noradrenaline in substantia gelatinosa of guinea‐pig spinal trigeminal nucleus.
Authors: Grudt T J , Williams J T , Travagli R A
Published: December 2014

1. Whole‐cell and intracellular recordings were made from neurons in slices of guinea‐pig spinal trigeminal nucleus pars caudalis. 2. 5‐Hydroxytryptamine (5‐HT) hyperpolarized 70% of neurons by activating 5‐HT1A receptors. The effect was mimicked by 5‐carboxamidotryptamine (5‐CT) and (+/‐)‐2‐dipropylamino‐8‐hydroxy‐1,2,3,4‐tetrahydronapthalene hydrobromide (8‐OH‐DPAT) and antagonized by 1‐(2‐methoxyphenyl)‐4‐[4‐(2‐phthalimido)‐butyl]‐piperazine hydrobromide (NAN 190) and pindobind‐5‐HT1A. Nine per cent of the neurons were depolarized by 5‐HT. 3. In about 20% of recordings, 5‐HT also evoked repetitive inhibitory postsynaptic potentials that were mediated by glycine. 4. Noradrenaline (NA) hyperpolarized 71% of neurons. This effect was mediated by activation of alpha 2‐adrenoceptors, since 5‐bromo‐N‐(4,5‐dihydro‐1H‐imidazol‐2‐yl)‐6‐quinoxalinamine (UK14304) also caused a hyperpolarization and idazoxan (1 microM) blocked the hyperpolarization to both NA and UK14304. Phenylephrine depolarized a subset of neurons and this depolarization was blocked by prazosin, suggesting an action mediated by activation of alpha 1‐adrenoceptors. 5. NA also evoked repetitive GABAA‐mediated inhibitory postsynaptic potentials in about 20% of recordings. The increase in synaptic activity was mimicked by phenylephrine and blocked by prazosin. 6. These results indicate that there are at least two mechanisms through which 5‐HT and NA inhibit neurons: (i) in many cells both 5‐HT and NA mediate a hyperpolarization through an increase of a potassium conductance; (ii) 5‐HT and NA also activated GABA‐ and glycine‐containing interneurons to cause IPSPs in separate groups of cells.
Voltage‐dependent clamp of intracellular pH of identified leech glial cells.
Authors: Deitmer J W , Schneider H P
Published: December 2014

1. The intracellular pH (pHi) was measured in voltage‐clamped, giant neuropile glial cells in isolated segmental ganglia of the leech Hirudo medicinalis, using double‐barrelled, pH‐sensitive microelectrodes and a slow, two‐electrode voltage‐clamp system. The potential sensitivity of the pHi regulation in these glial cells was found to be due to an electrogenic Na(+)‐HCO3‐ cotransporter (Deitmer & Szatkowski, 1990). 2. In the presence of 5% CO2 and 24 mM HCO3‐ (pH 7.4), pHi shifted by 1 pH unit per 110 mV, corresponding to a stoichiometry of 2HCO3‐: 1 Na+ of the cotransporter, while in Hepes‐buffered CO2‐HCO3(‐)‐free saline (pH 7.4), pHi changed by 1 pH unit per 274 mV. The potential sensitivity of pHi decreased at lower pHo, being 1 pH unit per 216 mV at external pH (pHo) 7.0. 3. Changing pHo between 7.8 and 6.6 induced pHi shifts with a slope of 0.72 pHi units per pHo unit in non‐clamped, and of 0.80 pHi units per pHo unit in voltage‐clamped cells, indicating that pHi largely followed pHo. The electrochemical gradient of H(+)‐HCO3‐ across the glial membrane was around 56 mV, and remained almost constant over this pHo range. 4. The membrane potential‐dependent and pHo‐sensitive shifts of pHi were unaffected by amiloride, an inhibitor of Na(+)‐H+ exchange. 5. The intracellular acidification upon lowering pHo could be reversed by depolarizing the membrane as predicted from a cotransporter, whose equilibrium follows the membrane potential by resetting pHi. 6. The results indicate that the pHi of leech glial cells is dominated by the electrogenic Na(+)‐HCO3‐ cotransporter, and is hence a function of the membrane potential, and the Na+ and H(+)‐HCO3‐ gradients, across the cell membrane.
Organization of inputs to motoneurone pools in man.
Authors: Gibbs J , Harrison L M , Stephens J A
Published: December 2014

1. Surface EMGs were recorded from pairs of muscles involved in movements of the wrist and/or digits in the upper limb and from pairs of intrinsic foot muscles in the lower limb during voluntary isometric contractions. 2. EMGs were also recorded from lower limb and trunk muscles during three different tasks: lying, standing and balancing. 3. To investigate if the co‐contraction of muscles was due to the presence of a common drive to each of the two motoneurone pools, cross‐correlation analysis of the two multiunit EMG signals was used. 4. Evidence for a common drive was seen between pairs of muscles that share a common joint or joint complex (such as the metacarpophalangeal joints); no evidence was found for a common drive to co‐contracting muscles that did not share a common joint. 5. When considering analogous hand and foot muscle pairs, the degree of synchrony was significantly greater for lower limb pairs. 6. Where a common drive was detected with lower limb muscle pairs, the degree of synchrony was significantly larger during balancing than during either lying or standing. 7. The origin of the common drive is discussed. It is concluded that activity in both last‐order branched presynaptic fibers and presynaptic synchronization is involved.
Electrophysiological evidence for mutual excitation of oxytocin cells in the supraoptic nucleus of the rat hypothalamus.
Authors: McKenzie D N , Leng G , Dyball R E
Published: December 2014

1. Using the ventral surgical approach in vivo, extracellular recordings were made from seventy‐nine cells in the supraoptic nucleus of urethane‐anaesthetized male, virgin female or lactating female rats while stimulating the pituitary stalk. Cells were classed according to their spontaneous firing activity as: continuous (putative oxytocin), phasic (putative vasopressin) and silent. 2. Stimulation of the neural stalk produced an excitation (up to 25 ms poststimulus) in eleven of the seventy‐nine antidromically identified magnocellular neurones, consistent with the existence of excitatory collaterals or dendritic contacts between such cells. In these recordings a second spike could frequently be seen, following the antidromic spike, with a variable latency. Such spikes consistently collided with subsequent antidromically evoked spikes. Poststimulus excitation was only seen in silent and continuously firing (putative oxytocin) cells, suggesting that oxytocin and vasopressin cells have different connections. 3. Excitatory connections were seen more frequently in lactating females (8 out of 22 cells) than in males (1 out of 15 cells) or virgin females (2 out of 10 cells), and thus may make an important contribution to the bursts of firing which precede reflex milk ejection.
Differential secretion of proteins by rat submandibular acini and granular ducts on graded autonomic nerve stimulations.
Authors: Anderson L C , Garrett J R , Zhang X , Proctor G B , Shori D K
Published: December 2014

1. The influence of graded parasympathetic and sympathetic nerve stimulations on the secretion of protein from rat submandibular gland was studied. Peroxidase was used as a marker for the acini and rat tissue kallikrein (official nomenclature rK1) as the marker for granular ducts. Tonin (rK2) was also measured, and the ratio of rK2:rK1 was calculated as an indication of the cellular route of secretion. 2. Continuous parasympathetic nerve stimulation caused a copious flow of saliva that had a low protein content. The secretion of peroxidase (acini) showed a gradual moderate increase as the frequency increased. However, the concentrations of rK1 and rK2 (granular ducts) showed little change throughout, and the ratio of rK2:rK1 remained relatively constant. 3. Graded sympathetic stimulation was applied against a background of parasympathetic stimulation. Secretion of peroxidase was increased by the addition of 0.1 Hz continuous sympathetic stimulation. The amount increased thereafter up to 2 Hz, but showed no further increase if the stimulation was applied as bursts of 10 or 20 Hz. In comparison, the secretion of proteinase activity showed little change with superimposed continuous sympathetic stimulation, and the rK2:rK1 ratio was similar to that in saliva produced by parasympathetic stimulation alone. Sympathetic stimulation applied in bursts, however, caused a large increase in the secretion of proteinase activity, and with 20 Hz burst stimulation the rK2:rK1 ratio was indistinguishable from that of sympathetic saliva per se. There was an augmented secretion of both peroxidase and kallikrein when 20 Hz burst stimulation was combined with parasympathetic stimulation. The effects of sympathetic stimulation were abolished by alpha‐ and beta‐adrenoceptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of renal medullary ionic hypertonicity by prostaglandins: data from tissue admittance studies in the rat.
Authors: Dobrowolski L , Kompanowska-Jezierska E , Sadowski J
Published: December 2014

1. Modulation of the cortico‐papillary electrolyte gradient by prostaglandins (PG) was studied in the kidney of anaesthetized rats. The intrarenal PG activity was varied by synthesis blockade with indomethacin (Ind) or meclophenamate (Me) and by intrarenal infusion of prostaglandin E2 (PGE2). 2. The interstitial electrolyte concentration in the medulla was continuously recorded in the kidney in situ as tissue electrical admittance (reciprocal impedance); the total renal blood flow (RBF), inulin clearance (Cin) and renal excretion were measured simultaneously. 3. Indomethacin and Me (15 mg kg‐1 h‐1) increased tissue admittance 15‐20% in the inner and 12‐15% in the outer medulla (P < 0.001) whereas PGE2 (300 ng kg‐1 min‐1) decreased admittance 14 and 8%, respectively (P < 0.01). 4. Renal blood flow and Cin were not affected by intrarenal PG activity changes. There was an increase in urine concentration after PG blockade and a delayed decrease after PGE2 infusion. 5. A joint analysis of the dynamics of medullary tissue admittance, renal haemodynamics and renal excretion provides evidence that PGs modify the medullary ionic hypertonicity by affecting NaCl transport in the ascending limb of the loop of Henle.
Modulation by magnesium of the affinity of NMDA receptors for glycine in murine hippocampal neurones.
Authors: Wang L Y , MacDonald J F
Published: December 2014

1. The effects of the divalent cation Mg2+ on NMDA currents recorded from cultured fetal mouse and acutely isolated neonatal rat hippocampal neurones were studied using the whole‐cell patch‐clamp technique. 2. Current‐voltage relations were measured in the presence or absence of applied Mg2+ and added glycine. NMDA‐evoked currents were studied in the absence or in a low concentration (0.2 mM) of applied Ca2+ in order to minimize Ca(2+)‐dependent inactivation of the responses. Mg2+ unexpectedly enhanced NMDA‐activated currents at positive membrane potentials. At negative membrane potentials Mg2+ caused a previously characterized voltage‐dependent block of inward NMDA‐activated currents. 3. The potentiation by Mg2+ of outward currents activated by NMDA was concentration dependent (EC50, approximately 3 mM; Hill coefficient, approximately 2). Mg2+ also reduced the desensitization of the NMDA receptor. The maximal enhancement of steady‐state NMDA‐activated currents was 2.7‐fold and at 6 mM the time constant of desensitization was doubled. 4. Comparisons of concentration‐response curves for glycine and 7‐chloro‐kynurenic acid demonstrated that Mg2+ significantly increased the affinity of the NMDA receptor for glycine. The EC50 for glycine was 380 nM in the absence of Mg2+ and 163 nM in 3 mM Mg2+. Mg2+ had little effect on the forward rate of the glycine response but halved the off‐rate (2.34 to 1.15 s‐1) and thus similarly reduced the apparent dissociation constant. 5. There was a good correlation between the concentration of extracellular Ca2+ and a reduction in the time constant of the glycine‐sensitive component of NMDA receptor desensitization. Ca2+ could enhance these NMDA‐activated currents briefly following exposure to high concentrations of Ca2+. These results are consistent with a Ca(2+)‐dependent enhancement of the affinity of the NMDA receptor for glycine. 6. Mg2+ can enhance NMDA‐mediated currents and reduce desensitization of this receptor by allosterically interacting with the glycine binding site. This interaction may be a key physiological mechanism through which modulation of the NMDA receptor is achieved.
Increased perinuclear Ca2+ activity evoked by metabotropic glutamate receptor activation in rat hippocampal neurones.
Authors: Phenna S , Jane S D , Chad J E
Published: December 2014

1. The effect of metabotropic glutamate receptor activation on intracellular Ca2+ activity (alpha Cai) of rat hippocampal pyramidal neurones in vitro was examined using ratiometric confocal laser scanning microscopy with the Ca(2+)‐sensitive fluorescent probe indo‐1 AM. 2. Metabotropic receptors were selectively activated with 1S,3R‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (1S,3R‐ACPD; 100 microM) in the presence of D‐2‐amino 5‐phosphonovaleric acid (D‐APV), 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and CdCl2. Most pyramidal neurones (77/84) responded with an elevation in Ca2+ activity, maximal after 3‐5 min. Fluorescence ratio responses were concentration dependent (EC50 approximately 10 microM) and were blocked by prior application of the antagonist (RS)‐4‐carboxy‐3‐hydroxyphenylglycine (RS‐CHPG, 300 microM). 3. Responses to 1S,3R‐ACPD (100 microM) also caused acidification of the neurones, from estimated control pH 7.2 to pH 6.6 (measured with the pH‐sensitive dye SNAFL‐calcein). The correction factor for indo‐1 determination of Ca2+ was estimated to be x 1.4. 4. Elevations in alpha Cai were greater within the perinuclear region (> 1000 nM), than in the cytoplasm (approximately 200 nM). This region was devoid of staining by the endoplasmic reticulum staining dye 3,3'‐dihexyloxacarbocyanine iodide (DiOC6(3)). 5. It is concluded that activation of metabotropic receptors in immature rat hippocampal pyramidal neurones leads to a large increase in perinuclear Ca2+ which would be well positioned to interact with the genome.
Erosion of inhibition contributes to the progression of low magnesium bursts in rat hippocampal slices.
Authors: Whittington M A , Traub R D , Jefferys J G
Published: December 2014

1. Bathing slices of rat hippocampus in media containing no magnesium ions results in epileptic discharges that originate in hippocampal area CA3. These discharges increase in severity gradually over periods of hours. 2. The progression of epileptic activity was much slower than the equilibration of extracellular magnesium activity and the resulting increase in strength of monosynaptic NMDA receptor‐mediated excitation. Its time course matched that of a progressive decrease in pharmacologically isolated, evoked GABAA receptor‐mediated inhibitory postsynaptic current (IPSC) in the CA3 pyramidal cells. Conductance decreased to 37 +/‐ 6% of control values after 4 h. Responses to exogenous GABA application decreased to 52 +/‐ 12%. 3. Maximal IPSC conductance in 0 mM extracellular Mg2+ ([Mg2+]o) also decreased gradually when epileptic activity was abolished by bath application of 20 microM 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) and 50 microM D‐2‐amino‐5‐phosphonovaleric acid (D‐APV) throughout the 4 h incubation period. It reached 61 +/‐ 8% of control values, a significantly smaller decline than that seen after 4 h of epileptic activity. 4. The decrease in mean IPSC conductance only partially reversed when the recording electrode contained 100 mM Mg2+. Complete recovery of IPSC strength occurred when electrodes also contained either 50 mM MgATP or 20 mM BAPTA. Reintroduction of 1 mM [Mg2+]o rapidly abolished epileptic activity and caused a slow, partial increase in IPSC conductance. 5. In the presence of 1 mM [Mg2+]o, GABAA receptor‐mediated inhibition had to decrease to 17 +/‐ 11% of control values, in the presence of 4‐7 microM bicuculline, to reach threshold for epileptic activity. 6. These data demonstrate a postsynaptic decrease in GABAA receptor‐mediated inhibition in the in vitro low magnesium model of epilepsy. We propose that the apparent leaching of intracellular Mg2+ ([Mg2+]i) from cells leads to loss of ATP and consequent partial dephosphorylation of the GABAA receptor and that this is exacerbated by epileptic activity.
KATP channel mediation of anoxia‐induced outward current in rat dorsal vagal neurons in vitro.
Authors: Trapp S , Ballanyi K
Published: December 2014

1. Thin brainstem slices (150 microns thickness) were taken from mature rats, and membrane potentials (Em) and currents (Im) in the dorsal vagal neurons (DVN) were analysed with whole‐cell patch clamp techniques during anoxia. 2. At a holding potential (Vh) of ‐50 mV, a sustained anoxia‐induced outward current (AOC) of 92 +/‐ 44 pA (reversal potential (Erev), ‐78 +/‐ 12 mV) and a concomitant increase of membrane conductance (gm) from 2.2 +/‐ 0.45 to 5.9 +/‐ 2.4 nS were revealed in 40% of 142 DVN analysed. The AOC led to a hyperpolarization of the cells by 14.4 +/‐ 6.1 mV from a mean resting Em of ‐51 +/‐ 6 mV, and to blockade of spontaneous action potential discharges. In the remaining DVN, anoxia had almost no effect on Em, Im or gm and did not block spontaneous action potential discharges. 3. The AOC was not affected by 0.5 microM tetrodotoxin (TTX), 2 mM Mn2+, 50 microM cyanonitroquinoxaline dione (CNQX) or 100 microM bicuculline. 4. Elevation of the extracellular [K+] from 3 to 10 mM resulted in a positive shift of Erev of the AOC by 23 mV, whereas an increase in the [Cl‐] of the patch pipette solution from 5 to 144 mM had no effect on Erev. 5. In DVN responding with an AOC, addition of 200 microM diazoxide, an activator of ATP‐sensitive K+ (KATP) channels, to oxygenated solutions elicited a similar outward current (Erev = ‐79 +/‐ 5.5 mV, n = 12) and increase in gm. Diazoxide did not affect Em, Im or gm in cells which did not show an AOC. 6. In a subpopulation of DVN (n = 26), spontaneous activation of a KATP current with an Erev of ‐80 +/‐ 6 mV was observed. As analysed in four of these cells, an AOC was revealed during the initial phase of development of the spontaneous outward current but not under steady‐state conditions. 7. The AOC, the diazoxide‐induced current, and the spontaneous outward current were completely blocked upon bath application of the KATP channel blocker tolbutamide (100‐200 microM). 8. The results indicate that the sustained anoxia‐induced outward current of dorsal vagal neurons is due to activation of KATP channels. A possible physiological role of functional inactivation of these cells during metabolic disturbances is discussed.
Synaptic GABAA activation induces Ca2+ rise in pyramidal cells and interneurons from rat neonatal hippocampal slices.
Authors: Leinekugel X , Tseeb V , Ben-Ari Y , Bregestovski P
Published: December 2014

1. Changes in intracellular Ca2+ concentration ([Ca2+]i) induced by activation of GABAA receptors (synaptic stimulation or application of the GABAA agonist isoguvacine) were studied on pyramidal cells and interneurons from hippocampal slices of rats from two age groups (postnatal days (P) 2‐5 and P12‐13) using the fluorescent dye fluo‐3 and a confocal laser scanning microscope. Cells were loaded with the dye either intracellularly, using patch pipettes containing fluo‐3 in the internal solution, or extracellularly, using pressure pulses applied to an extracellular pipette containing the permeant dye fluo‐3 AM. 2. Interneurons and pyramidal cells from P2‐5 slices loaded with fluo‐3 AM responded by an increase in [Ca2+]i to isoguvacine and to glutamate, in contrast to cells from P12‐13 slices which responded to glutamate but not to isoguvacine. 3. The isoguvacine‐induced rise in [Ca2+]i was reversibly blocked by bath application of the GABAA receptor antagonist bicuculline (20 microM), suggesting the specific involvement of GABAA receptors. The sodium channel blocker tetrodotoxin (TTX, 1 microM in the bath) did not prevent the isoguvacine‐induced rise in [Ca2+]i. 4. The isoguvacine‐induced rise in [Ca2+]i was reversibly blocked by bath application of the calcium channel blocker D600 (50 microM) suggesting the involvement of voltage‐dependent Ca2+ channels. 5. Electrical stimulation of afferent fibres induced a transient increase in [Ca2+]i in neonatal pyramidal cells and interneurons (P5) loaded non‐invasively with fluo‐3 AM. This elevation of [Ca2+]i was reversibly blocked by bicuculline (20 microM) but not by APV (50 microM) and CNQX (10 microM). 6. During simultaneous electrophysiological recording in the current‐clamp mode and [Ca2+]i monitoring from P5 pyramidal cells, electrical stimulation of afferent fibres, in the presence of APV (50 microM) and CNQX (10 microM), caused synaptic depolarization accompanied by a few action potentials and a transient increase in [Ca2+]i. In voltage clamp (‐70 mV) however, there was no increase in [Ca2+]i following synaptic stimulation, showing that it is depolarization dependent. 7. Using a non‐invasive method of [Ca2+]i monitoring, we demonstrate here that in neonatal (P2‐5) hippocampus, GABA is an excitatory neurotransmitter which can cause an elevation of [Ca2+]i in interneurons and pyramidal cells via activation of voltage‐dependent Ca2+ channels. This action may underlie the trophic role of GABA in hippocampal development.
The pattern of excitatory inputs to the nucleus tractus solitarii evoked on stimulation in the hypothalamic defence area in the cat.
Authors: Silva-Carvalho L , Dawid‐Milner M S , Spyer K M
Published: December 2014

1. In anaesthetized, paralysed and artificially ventilated cats, recordings have been made in the nucleus tractus solitarii (NTS) to assess further the role of this nucleus in mediating the cardiorespiratory responses that are elicited on stimulation within the hypothalamic defence area (HDA). 2. The responses of NTS neurones to stimulation in the hypothalamus were assessed, as were their patterns of evoked response to electrical stimulation of the sinus (SN), aortic (AN), superior laryngeal (SLN) and vagus (VN) nerves. 3. Stimulation in the HDA affected the activity of 110 NTS neurones (85 studied in intracellular and 25 studied in extracellular recordings). The present study focused on those sixty‐eight neurones that were excited by such stimulation (51 intracellular recordings and 17 extracellular recordings). 4. Of the sixty‐eight neurones that were excited by HDA stimulation, seven revealed no changes in membrane potential or evoked discharge (2 neurones) but the stimulus facilitated the excitatory effects of stimulating either (or both) the SN and SLN. An additional group of neurones showed powerful excitatory responses to HDA stimulation (15 studied with extracellular and 35 with intracellular recording). Evoked EPSPs had onset latencies in the range of 1‐30 ms. Of those thirty‐five neurones displaying EPSPs, twenty‐six were shown to receive convergent inputs on nerve stimulation. In nine neurones the early EPSP in response to HDA stimulation was followed by an IPSP. 5. In a further group of neurones HDA stimulation elicited a long‐lasting IPSP, but this was not analysed further because its features have been described in detail in earlier studies from this laboratory. 6. The patterns of response of several neurones excited by stimulation in the HDA are consistent with them forming a group of NTS interneurones that mediate the hypothalamically evoked cardiovascular responses, including modulation of reflex function, which is a major feature of cardiorespiratory control. This possibility is discussed in the light of the present physiological observations and descriptions of an intrinsic NTS group of GABA‐containing neurones that have been suggested to fulfil such a role.
Roles of arachidonic acid, lipoxygenases and phosphatases in calcium‐dependent modulation of M‐current in bullfrog sympathetic neurons.
Authors: Yu S P
Published: December 2014

1. M‐current (IM) is regulated by intracellular free Ca2+ ([Ca2+]i). Suppression and overrecovery of IM induced by muscarine and luteinizing‐hormone releasing hormone (LHRH) are also regulated by [Ca2+]i. The role of the arachidonic acid (AA) pathway in the Ca(2+)‐dependent modulation of IM was investigated using whole‐cell voltage clamp and intracellular perfusion in dissociated bullfrog sympathetic B neurons. 2. Quinacrine (10‐20 microM) and 4‐bromophenacyl bromide (4‐BPB; 4‐10 microM), the inhibitors of phospholipase A2, blocked the enhancement of IM evoked by raising [Ca2+]i. 3. AA (6‐120 microM) increased IM by about 50% of the control current in a Ca(2+)‐dependent manner. 4. Enhancements of IM by Ca2+ and AA were blocked by the lipoxygenase (LO) inhibitors nordihydroguaiaretic acid (NDGA; 1‐5 microM) and 5,8,11‐eicosatrynoic acid (ETI; 10 microM). The cyclo‐oxygenase inhibitor indomethacin (10 microM) had no effect. 5. Enhancement of IM by Ca2+ was abolished by the selective 12‐LO inhibitors baicalein (1‐2 microM) and 15(S)‐hydroxy‐5‐cis‐8‐cis‐11‐cis‐13‐trans‐eicosatetraenoic acid (15‐HETE; 6.5 microM). A 12‐LO product, 2(S)‐hydroxy‐5‐cis‐8‐cis‐10‐trans‐14‐cis‐ eicosatetraenoic acid (12‐HETE; 13‐20 microM), increased IM without Ca2+ requirement. 6. Enhancement of IM by Ca2+ was not affected by the selective 5‐LO inhibitors AA‐861 (10 microM), 5,6‐dehydroarachidonic acid (5,6‐DAA, 10 microM) and L‐651,896 (10 microM). The 5‐LO metabolites leukotriene C4 (1.5‐8 microM) and leukotriene B4 (1.5‐5 microM) showed no obvious effect on IM. 7. NDGA alone inhibited IM with an IC50 of 0.73 microM at 120 nM Cai(2+). 8. NDGA did not affect suppression of IM by muscarine or LHRH; however, overrecovery of IM upon removing these agonists was totally eliminated by 1 microM NDGA. 9. Inhibitors of phosphatases, calyculin A (0.1 microM) and okadaic acid (1 microM), completely abolished overrecovery of IM. Calyculin A also blocked the Ca(2+)‐induced IM enhancement. 10. It is suggested that Ca2+ enhances IM by stimulating the AA metabolic pathway. Dephosphorylation probably upregulates IM. Overrecovery of IM is probably a result of stimulation of the LO pathway and phosphatases by increased [Ca2+]i.
Paired‐pulse modulation of fast excitatory synaptic currents in microcultures of rat hippocampal neurons.
Authors: Mennerick S , Zorumski C F
Published: December 2014

1. Paired‐pulse modulation of excitatory non‐N‐methyl‐D‐aspartate (non‐NMDA) receptor‐mediated autaptic currents and conventional monosynaptic (interneuronal) excitatory postsynaptic currents (EPSCs) was investigated in microcultures of rat hippocampal neurons, where polysynaptic influences are eliminated. 2. Most autaptic currents and EPSCs exhibited paired‐pulse depression in response to paired stimuli. Depression was sensitive to the level of transmitter release, which was varied by manipulating extracellular Ca2+ and Mg2+ concentrations. Paired‐pulse facilitation emerged in many cells at low levels of transmitter release. 3. Paired‐pulse depression and facilitation could be differentially expressed at two distinct postsynaptic targets of a single presynaptic cell, and the form of modulation was not dependent upon the transmitter phenotype of the postsynaptic cell. 4. Paired‐pulse depression recovered exponentially with a time constant of approximately 5 s, although in most neurons a much faster component of recovery was detected. Recovery from paired‐pulse facilitation was well described by a single exponential of 380 +/‐ 57 ms. 5. Under conditions of robust paired‐pulse depression of evoked responses, spontaneous autaptic and postsynaptic currents (sEPSCs, presumed miniature EPSCs) occurred at an enhanced frequency immediately following evoked responses. The decay of the frequency increase mirrored the time course of recovery from paired‐pulse facilitation of evoked responses examined under conditions of reduced transmitter release. 6. Several lines of evidence suggested a large presynaptic component to paired‐pulse depression. In eight out of nine cells no depression in sEPSC amplitudes was detected following conditioning stimulation. Simultaneously recorded glial glutamate uptake currents showed depression similar to neuronal evoked EPSCs. Finally, NMDA receptor‐mediated EPSC paired‐pulse depression at positive potentials was similar to non‐NMDA EPSC depression. 7. Neither adenosine nor glutamate feedback onto presynaptic receptors is likely to mediate paired‐pulse depression, because neither competitive nor non‐competitive inhibitors of the actions of these agents diminished paired‐pulse depression.
Non‐linear relationship between O2 uptake and power output at high intensities of exercise in humans.
Authors: Zoladz J A , Rademaker A C , Sargeant A J
Published: December 2014

1. A slow component to pulmonary oxygen uptake (VO2) is reported during prolonged high power exercise performed at constant power output at, or above, approximately 60% of the maximal oxygen uptake. The magnitude of the slow component is reported to be associated with the intensity of exercise and to be largely accounted for by an increased VO2 across the exercising legs. 2. On the assumption that the control mechanism responsible for the increased VO2 is intensity dependent we hypothesized that it should also be apparent in multi‐stage incremental exercise tests with the result that the VO2‐power output relationship would be curvilinear. 3. We further hypothesized that the change in the VO2‐power output relationship could be related to the hierarchical recruitment of different muscle fibre types with a lower mechanical efficiency. 4. Six subjects each performed five incremental exercise tests, at pedalling rates of 40, 60, 80, 100 and 120 rev min‐1, over which range we expected to vary the proportional contribution of different fibre types to the power output. Pulmonary VO2 was determined continuously and arterialized capillary blood was sampled and analysed for blood lactate concentration ([lactate]b). 5. Below the level at which a sustained increase in [lactate]b was observed pulmonary VO2 showed a linear relationship with power output; at high power outputs, however, there was an additional increase in VO2 above that expected from the extrapolation of that linear relationship, leading to a positive curvilinear VO2‐power output relationship. 6. No systematic effect on the magnitude or onset of the ‘extra’ VO2 was found in relation to pedalling rate, which suggests that it is not related to the pattern of motor unit recruitment in any simple way.
Voltage‐dependent currents and modulation of calcium channel expression in zona fasciculata cells from rat adrenal gland.
Authors: Barbara J G , Takeda K
Published: December 2014

1. Whole‐cell voltage‐activated currents from single zona fasciculata (ZF) cells from rat adrenal glands were studied. T‐ and L‐type Ca2+ currents and a slowly inactivating A‐type K+ current were the three major currents observed. 2. In freshly isolated cells, the A‐type K+ current and the T‐type Ca2+ current were predominant. The A‐type current was activated at ‐50 mV and inhibited by 4‐amino‐pyridine with a half‐maximal block (IC50) at 130 microM while the T‐type current was activated at ‐70 mV and blocked by Cd2+, Ni2+ and amiloride with IC50 values of 24.1, 132.4 and 518.9 microM, respectively. 3. Under current clamp, depolarizing current pulses produced a single Ca2+ action potential with Cs+ in the pipette internal solution. Upon replacement of Cs+ by K+, the half‐amplitude width of the action potential was shortened and membrane potential oscillations were seen after the spike. 4. In freshly isolated cells and during the first 24 h after plating, the T‐type current was observed in all cells, with L‐type current being observed in < 2% of cells, even in the presence of (+)SDZ 202,791, a dihydropyridine Ca2+ channel agonist. With time in culture, the T‐type current disappeared, and a high‐voltage‐activated L‐type current became increasingly apparent. In cells tested after > 2 days in culture, (+)SDZ 202,791 potentiated L‐type current by 407 +/‐ 12% and the antagonist (‐)SDZ 202,791 blocked this increase. The L‐type current was activated between ‐30 and ‐20 mV and was sensitive to nitrendipine and omega‐conotoxin GVIA. 5. Pre‐incubation of cultured ZF cells with adrenocorticotrophic hormone (ACTH) or vasoactive intestinal peptide (VIP) for 3 days resulted in a high, sustained level of expression of T‐type current, with a mean amplitude of 34.2 +/‐ 5.5 pA pF‐1 for ACTH‐treated cells compared with 3.4 +/‐ 1.8 pA pF‐1 for untreated cells. Cycloheximide strongly inhibited this effect. Neither treatment affected L‐type current expression. 6. The expression of both Ca2+ current types was unaffected by pre‐incubation with 8‐bromo‐cAMP or forskolin. The protein kinase A antagonist, H89, did not inhibit the ACTH‐induced upregulation of T‐type Ca2+ currents. 7. It is concluded that the main voltage‐dependent currents involved in cell excitability and steroidogenesis in rat adrenal ZF cells are an A‐type K+ current and a T‐type Ca2+ current. The physiological role and control of expression of L‐type Ca2+ channels in rat ZF cells remain less clear.
Fatigue and heat production in repeated contractions of mouse skeletal muscle.
Authors: Barclay C J , Arnold P D , Gibbs C L
Published: December 2014

1. This study tested the hypothesis that moderate fatigue of skeletal muscle arises from a mismatch between energy demand and energy supply. Fatigue was defined as the decline in isometric force. Energy supply and demand were assessed from measurements of muscle heat production. 2. Experiments were performed in vitro (21 degrees C) with bundles of muscle fibres from mouse fast‐twitch extensor digitorum longus muscle and slow‐twitch soleus muscle. Fibre bundles were fatigued using a series of thirty isometric tetani. Cycle duration (time between successive tetani) was 5 s. The amount of fatigue that occurred during a series of tetani was varied by varying contraction duty cycle (tetanus duration/cycle duration) by varying tetanus duration. 3. Peak isometric force and total heat production in each cycle were measured. For each cycle, the amounts of initial heat (H(i)) and recovery heat (Hr) produced were calculated and used as indices of energy use and supply, respectively. H(i) and Hr were used to estimate the net initial chemical breakdown (in energy units) in each cycle (H(i,net)). 4. The magnitude of H(i,net) was greatest in the early stages of the contraction protocol when Hr was still increasing towards a steady value. The magnitude of decline in force between successive tetani was proportional to H(i,net) for both muscles. 5. The results are consistent with the idea that the development of moderate levels of fatigue at the start of a series of contractions is due to the rate of energy supply being inadequate to match the rate of energy use.
Heart rate responses to selective stimulation of cardiac vagal C fibres in anaesthetized cats, rats and rabbits.
Authors: Jones J F , Wang Y , Jordan D
Published: December 2014

1. The contribution of cardiac vagal C fibres to vagal chronotropic control in anaesthetized cats, rats and rabbits was analysed using electrical stimulation of the vagus nerve with a selective anodal block technique. 2. After bilateral vagotomy and pretreatment with atenolol, 10 Hz continuous selective stimulation of unmyelinated fibres in the cut peripheral end of the cervical vagus evoked a bradycardia in anaesthetized rats, cats and rabbits. With this stimulation protocol the three species exhibited a similar lengthening of the heart period (R‐R interval) when expressed as a percentage of their basal cardiac interval. 3. The mechanism of action of the selective blocking technique was analysed by recording eighty‐nine single A‐ (n = 12), B‐ (n = 22) and C‐fibre (n = 55) vagal‐projecting neurones in the medulla of the rat. This demonstrated that the technique can selectively block conduction in myelinated fibres and that ‘break excitation’ is seen mainly in unmyelinated fibres. Although thirty C fibres showed break excitation sixteen did not and this difference could not be correlated with their axonal conduction velocity, chronaxie or initial segment frequency following. 4. Using the anodal block technique the vagal effects on heart rate were reanalysed in the cat by incorporating a collision technique. B fibres were activated orthodromically to evoke cardioinhibition and simultaneously antidromically to collide with errant B‐fibre spikes activated at the electrode producing anodal block. With this protocol it was noted that the B‐ and C‐fibre bradycardias were not additive. Using a double anodal block and collision technique, it was demonstrated that this phenomenon was likely to be due to occlusion of the effects of B and C fibres. 5. In conclusion, in addition to the well‐defined effects of vagal B fibres on heart rate, selective stimulation of vagal C fibres also had a cardioinhibitory effect in all three species studied. However, since the effects of cardiac C fibres on heart rate was small, these neurones alone cannot account for the cardioinhibition of the pulmonary chemoreflex. It is likely that activation of both B‐ and C‐fibre cardiac vagal preganglionic neurones accounts for this reflex cardioinhibition.