bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic secretion of quanta from visualized sympathetic nerve varicosities in mouse vas deferens.
Authors: Lavidis N A , Bennett M R
Published: December 2014

1. Sympathetic varicosities on the surface of smooth muscle cells of the mouse vas deferens were visualized with the fluorescent dye 3‐3 Diethyloxardicarbocyanine iodide (DiOC2(5)) and quantal secretion recorded from these with both small diameter (4‐6 microns) and large diameter (20‐50 microns) microelectrodes. Small diameter electrodes were placed over one to three varicosities and large diameter electrodes over three to seven varicosities. 2. The size and distribution of varicosities along individual terminal branches was about the same when these were fluoresced with DiOC2(5) (length 1.09 +/‐ 0.40 microns (mean +/‐ S.D.); intervaricosity distance 5.53 +/‐ 2.68 microns) as when they were stained for catecholamines using Faglu fluorescence (length 1.05 +/‐ 0.43 microns; intervaricosity distance 5.12 +/‐ 2.79 microns) suggesting that DiOC2(5) does allow for identification of the catecholamine‐containing varicosities. 3. The spontaneous excitatory junctional currents (EJCs) recorded from visualized varicosities with small diameter electrodes (amplitudes 59‐67 microV) were much larger than those recorded with large diameter electrodes (amplitudes 25‐29 microV). The frequency of evoked EJCs as well as the amplitude‐frequency distribution of these EJCs varied greatly between sets of visualized varicosities recorded along individual branches, either with a small or large diameter electrode. These amplitude‐frequency distributions typically followed Poisson statistics, in which the mean quantal content of the EJC (m) varied by over threefold for different sets of varicosities on the same branch (m was 0.07‐0.21 for small electrodes whereas m was 1‐3 for large electrodes). 4. Although m varied considerably for a constant number of varicosities beneath the electrode at different sites along a single branch, there was an overall correlation between m and the number of varicosities, m increasing on average 0.25 for each additional varicosity in a [Ca2+]o of 4.0 mM. 5. The frequency of evoked EJCs at visualized sets of varicosities along some branches was sufficiently high to allow binomial statistics to predict the amplitude‐frequency distributions of evoked EJCs. In these cases m was again shown to vary considerably along single terminal branches, and this was primarily due to variation in the probability of secretion (p) between sets of varicosities and not to variation in binomial parameter n. 6. In one case a relatively isolated varicosity, over 3 microns from adjacent varicosities, was recorded for 30 min with a 4 microns diameter electrode. The mean and variance of the evoked EJC was similar to that of the spontaneous EJCs suggesting that this varicosity secreted at most one quantum on arrival of the nerve impulse.(ABSTRACT TRUNCATED AT 400 WORDS)
Thermal and PGE2 sensitivity of the organum vasculosum lamina terminalis region and preoptic area in rat brain slices.
Authors: Matsuda T , Hori T , Nakashima T
Published: December 2014

1. The effects of local applications of prostaglandin E2 (PGE2) on the unit activity of fifty‐one neurones in the organum vasculosum lamina terminalis (OVLT) region and fifty‐eight neurones in the preoptic area (POA) were investigated in small tissue slices from the rat hypothalamus containing the OVLT and POA isolated from each other. 2. Of these, thirty OVLT and twenty‐eight POA neurones were warm sensitive and increased their discharge rate in response to a rise in tissue temperature. One OVLT neurone and one POA neurone were cold sensitive and showed the opposite type of responses to changes in temperature. The thermosensitivity of these neurones was still observed in a Ca2+ free‐high Mg2+ solution. 3. Perfusion with PGE2 in doses between 1 and 250 nM changed the discharge rate in forty‐two of fifty‐one OVLT neurones and in thirty‐two of fifty‐eight POA neurones in a dose‐dependent manner. The responses to PGE2 were not lost during synaptic blockade. The threshold dose of PGE2 to alter the discharge rate of the OVLT neurones (4.8 +/‐ 1.1 (S.E.M.) nM, n = 16) was significantly lower than that of the POA neurones (40.9 +/‐ 12.2 nM, n = 16). 4. Fifteen of forty‐two OVLT neurones exhibited the responses with a slower onset (latency 5‐13 min) and a longer duration (20 min to 3 h), but such responses were observed in only one of thirty‐two POA neurones. 5. The responses of OVLT and POA neurones to PGE2 (50‐250 nM) were reversibly blocked by a concurrent application of AH6809, a prostanoid EP1 and/or a DP receptor antagonist. 6. While there was no clear correlation between the type of thermosensitivity and the type of response to PGE2 among the POA neurones, a significantly higher incidence of inhibitory response to PGE2 was found among the warm‐sensitive neurones in the OVLT region. 7. The lower threshold responses to PGE2 and the higher incidence of PGE2 responsiveness among OVLT neurones are consistent with previous findings which showed that the highest density of PGE2 receptor binding and the highest pyrogenic sensitivity to microinjected PGE2 were observed in the OVLT region. The results provide further evidence for the critical involvement of the OVLT region in mediating the febrile responses to blood‐borne endogenous pyrogen through the local release of PGE2.
Simultaneous visualization of cortical barrels and horseradish peroxidase‐injected layer 5b vibrissa neurones in the rat.
Authors: Ito M
Published: December 2014

1. Using diaminobenzidine (DAB) as a chromagen, horseradish peroxidase‐injected neurones and cytochrome oxidase‐stained barrels were visualized simultaneously in the rat vibrissa cortex. Neurones were initially tested during extracellular recording for responses to whisker deflections. This was followed by intracellular injection of the soma with horseradish peroxidase (HRP) and histological processing to visualize the HRP‐stained neurone in an incubation solution which contained, in addition to DAB, cytochrome C for cytochrome oxidase (CO) reaction of the barrels. 2. Recording and intracellular staining were made in layer 5b under urethane anaesthesia. CO‐stained barrels were observed in layer 4. Physiologically and morphologically characterized neurones were mostly large pyramidal neurones that responded to more than one whisker and displayed transient‐type responses. 3. In tangential sections, the apical dendrite of the HRP‐filled neurone was followed from the soma level upward as it ascended through the barrelfield in layer 4. The cross‐section of the apical dendrite was found in the periphery of the CO‐stained barrel. Using the apical dendrite as a guide, the basal dendritic field of the layer 5b pyramidal neurone was aligned on the pattern of layer 4 barrels. The soma was seen to project basal dendrites in all directions, involving one or two neighbouring barrels/columns. 4. In sixteen neurones examined in tangential sections, a complete spatial tuning map constructed by measuring sensitivity of the neurone to different whiskers could be compared to the basal dendritic field in relation to the pattern of overlying layer 4 barrels. The mean receptive field size in terms of the number of effective whiskers was 5.8 whereas the mean dendritic field size in terms of the number of barrels/columns involved was 2.2. In addition to the well‐documented role of intracortical connectivity in elaboration of multi‐whisker receptor fields in the cortical neurones, the role played by direct inputs from multi‐whisker thalamic ventrobasal neurones was discussed.
Pacemaker current in single cells and in aggregates of cells dissociated from the embryonic chick heart.
Authors: Brochu R M , Clay J R , Shrier A
Published: December 2014

1. We have measured the time‐dependent pacemaker current, I(f), in single cells, or small clusters of two or three cells dissociated from embryonic chick hearts with the whole‐cell patch clamp technique, and in multicellular reaggregates of dissociated cells with the two‐microelectrode voltage clamp technique. 2. We observed time‐dependent current (I(f)) in the ‐90 to ‐60 mV range from aggregates of ventricular cells, as in our earlier results from this preparation, which we previously attributed to the potassium ion current mechanism, IK2. We also observed I(f) in single atrial cells and aggregates of atrial cells. 3. The range of activation of I(f) was ‐120 to ‐90 mV in atrial preparations (either single cells or aggregates). The activation range of I(f) in ventricular cells was also ‐120 to ‐90 mV which is approximately 30 mV negative to the I(f) activation range in ventricular cell aggregates. The reasons for this shift of I(f) in ventricular preparations are unknown. 4. The I(f) component clearly underlies the spontaneous pacemaker depolarization which is observed in ventricular heart cell aggregates during the first week of embryonic development. However, I(f) is not a significant factor underlying spontaneous activity in atrial preparations. The pacemaker current in these cells is a net inward background component, which is significantly reduced in amplitude with development, as is the I(f) component in the ventricle.
An internal viscous element limits unloaded velocity of sarcomere shortening in rat myocardium.
Authors: de Tombe P P , ter Keurs H E
Published: December 2014

1. Peak twitch force (F0) and sarcomere length (SL) were measured in trabeculae that had been dissected from the right ventricle of rat heart and that were superfused with a modified Krebs‐Henseleit solution at 25 degrees C. Sarcomere length was measured by laser diffraction techniques. Force was measured with a silicone strain gauge. Unloaded velocity of sarcomere shortening (V0) was measured by the ‘isovelocity release’ technique. 2. At [Ca2+]o = 1.5 mM and SL below 1.9 microns, V0 increased in proportion to SL, while V0 was independent of SL above 1.9 microns. At [Ca2+]o = 0.5 mM, V0 was proportional to SL up to 2.2 microns. At [Ca2+]o = 0.2 mM, V0 was proportional to SL up to 2.3 microns which is the longest SL that we were able to study in our trabeculae. 3. A unique relationship was observed between V0 and F0, irrespective of whether F0 was altered by variation of [Ca2+]o or sarcomere length above slack length. 4. Passive viscosity (Fv) was measured during the pause between contractions in the presence of 1.5 mM [Ca2+bdo and in the range SL = 2.0‐2.1 microns by applying 0.1 micron stretches at various velocities up to v = 30 microns s‐1. The force response to stretch, corrected for the contribution of parallel elastic force, showed viscoelastic characteristics with an exponential increase to a maximum (Fv) during stretch and an exponential decline after the end of the stretch. Fv increased, by 0.3%F0 microns‐1 s‐1, in proportion to v < 5 microns s‐1; the increase of Fv was smaller at higher v, suggesting non‐Newtonian viscous properties. 5. The time constant of the increase of force during the stretch decreased (tau rise congruent to 7 ms to tau rise congruent to 4 ms) with increases in v (congruent to 4 microns s‐1 to v congruent to 10 microns s‐1; P = 0.02). The time constant of decay of force at the end of the stretch also decreased with increases in v (tau decay congruent to 8 ms at v congruent to 4 microns s‐1 to tau decay congruent to 3 ms at v congruent to 30 microns s‐1; P < 0.001). Calculated stiffness of the elastic term of the viscoelastic element was independent of v, i.e. 45‐50 N mm‐3.(ABSTRACT TRUNCATED AT 400 WORDS)
Role of K+ channels in the modulation of cholinergic neural responses in guinea‐pig and human airways.
Authors: Miura M , Belvisi M G , Stretton C D , Yacoub M H , Barnes P J
Published: December 2014

1. Several agonists modulate cholinergic neurotransmission in airways raising the possibility that there may be a common inhibitory mechanism, such as the activation of a common K+ channel in the nerve ending. To test this hypothesis, we examined whether blockers of K+ channels are able to depress the prejunctional inhibitory modulation of cholinergic contractile responses by various agonists in guinea‐pig and human airways in vitro. 2. Electrical field stimulation (40 V, 0.5 ms) was applied to guinea‐pig (0.5 Hz) or human (1 Hz) tracheal strips every 4 min to elicit cholinergic neural responses. The effects of the K+ channel blockers, charybdotoxin (ChTX, 10 nM), apamin (100 nM) and glibenclamide (1 microM), on the prejunctional inhibition of cholinergic contraction evoked by neuropeptide Y (NPY, 100 nM), an alpha 2‐agonist, clonidine (10 nM), a mu‐opioid agonist, [D‐Ala2, NMePhe4, Gly‐ol5]‐enkephalin (DAMGO, 100 nM), and a KATP channel opener, lemakalim (300 nM) were tested in guinea‐pigs. In human tissues, the effect of ChTX (10 nM) on the mu‐opioid (DAMGO, 300 nM)‐induced inhibition of cholinergic nerves was examined. 3. In guinea‐pigs, ChTX (10 nM) significantly reversed the prejunctional inhibition of cholinergic contraction by NPY (84.2 +/‐ 16.2%), clonidine (71.9 +/‐ 22.4%), DAMGO (67.3 +/‐ 13.1%) and lemakalim (20.9 +/‐ 9.4%) (n = 5, P < 0.05, respectively), while apamin (100 nM) had no effect. Glibenclamide (10 microM) reduced only the lemakalim‐induced inhibitory modulation. ChTX (10 nM) itself potentiated cholinergic contraction (24.6 +/‐ 9.4%, n = 5, P < 0.05) without affecting exogenously applied acetylcholine dose‐response curves. Pretreatment with ChTX (10 nM) significantly reduced the inhibitory modulation of cholinergic nerves by NPY, clonidine and DAMGO, but not by lemakalim. 4. In human tissues, ChTX significantly reduced DAMGO‐induced prejunctional inhibition of cholinergic contraction (13.6 +/‐ 8.5% with and 46.5 +/‐ 5.5% without ChTX, respectively; n = 5, P < 0.05). 5. These results may support a hypothesis that the activation of ChTX‐sensitive K+ channels is involved in the inhibitory modulation of cholinergic neuro‐transmission by agonists acting on presynaptic receptors in guinea‐pig and human airways.
Dependence of electrical slow waves of canine colonic smooth muscle on calcium gradient.
Authors: Ward S M , Sanders K M
Published: December 2014

1. The ionic dependence of the upstroke and plateau components of slow waves of canine colonic circular muscles was studied. 2. Reduced extracellular Ca2+ caused a decrease in the amplitude of the upstroke and plateau components, a decrease in the depolarization velocity, and a decrease in frequency. The reduction in the upstroke phase per 10‐fold reduction in external Ca2+ was close to the value predicted by the Nernst relationship, suggesting that the membrane permeability to Ca2+ increases steeply during this phase. 3. Nifedipine (10(‐9)‐10(‐6)) reduced the plateau component, but concentrations of 10(‐6) M did not abolish the upstroke component. The data suggest that a nifedipine‐resistant component of Ca2+ current may be involved in the upstroke. 4. Inorganic Ca2+ channel blockers (Mn2+ and Ni2+) blocked spontaneous slow waves at concentrations of 1.0 mM or less. 5. The upstroke component was more sensitive to Ni2+ than to Mn2+; a concentration of 0.040 mM‐Ni2+ caused more than a 50% reduction in upstroke velocity. Ni2+ also reduced the plateau phase of slow waves. 6. The results suggest that the upstroke and plateau components of slow waves are dependent upon activation of voltage‐dependent Ca2+ currents. The current responsible for the upstroke is partially resistant to dihydropyridines (at least at 10(‐6) M). The current responsible for the plateau component is nifedipine‐sensitive.
Effects of n‐alkanols and a methyl ester on a transient potassium (IA) current in identified neurones from Helix aspersa.
Authors: Winpenny J P , Elliott J R , Harper A A
Published: December 2014

1. A two‐microelectrode voltage clamp was used to determine the effects of n‐butanol, n‐hexanol, n‐octanol, n‐decanol and methyl hexanoate on a transient potassium (IA) current in identified Helix aspersa neurones. Experiments were carried out at a temperature of 10‐12 degrees C. 2. Each n‐alkanol reversibly reduced the amplitude of the IA current. Logarithmic dose‐response curves for the current reduction by each homologue were sigmoidal and had slope factors of around four. The concentrations required to reduce the peak (with time) current at ‐30 mV by 50% (ED50 +/‐ fitted standard error) were: 57 +/‐ 5 mM (n‐butanol); 2.0 +/‐ 0.1 mM (n‐hexanol); 0.28 +/‐ 0.02 mM (n‐octanol) and 0.016 +/‐ 0.001 mM (n‐decanol). Methyl hexanoate also reduced the current amplitude, with an ED50 of 1‐2 mM. The Helix IA current thus showed a similar sensitivity to n‐alkanols to that of squid and rat sodium currents but was rather more sensitive than the squid delayed rectifier potassium current. 3. The n‐alkanol ED50 concentrations were used to calculate a standard free energy per methylene group for adsorption to a site of action in the cell of ‐3.1 +/‐ 0.2 kJ/mol. This suggested a hydrophobic site or sites of action. The regularity of the change in free energy with chain length was maintained up to, and including, n‐decanol. This implied that the site(s) could accommodate a ten‐carbon chain as readily as an eight‐carbon chain. 4. The voltage dependencies of IA current activation and steady‐state inactivation were not consistently altered by treatment with n‐alkanols at concentrations around or above their current suppression ED50 concentrations. 5. The kinetics of current activation and inactivation were affected, particularly by lower chain length compounds. At 60 mM n‐butanol reduced the time constant for development of inactivation of open channels (tau b) by 56%, while 0.016 mM n‐decanol produced only a 13% reduction. n‐Butanol (60 mM) also caused a substantial (76%) reduction in the time constant for development of inactivation in channels which were presumed to be closed. The effects of n‐alkanols on the current time‐to‐peak (tc) were complex, showing both increases and decreases, but these actions also declined with chain length. Methyl hexanoate (1 mM) reduced tau b by around 30% and tc by around 20%. 6. n‐Alkanols have now been shown to inhibit a number of voltage‐gated ion conductances.(ABSTRACT TRUNCATED AT 400 WORDS)
The effects of hypoxia on the ventilatory response to sudden changes in CO2 in newborn piglets.
Authors: Wolsink J G , Berkenbosch A , DeGoede J , Olievier C N
Published: December 2014

1. The ventilatory response to square‐wave challenges in end‐tidal partial pressure of CO2 (PCO2) was investigated at three levels of arterial PO2 (Pa,O2) in nineteen anaesthetized 2‐ to 11‐day‐old piglets. 2. The ventilatory responses, measured on a breath‐to‐breath basis, were separated into a peripheral and a central component using a two‐compartment model. Both components were described by a CO2 sensitivity, a time constant, a time delay and a single offset. 3. Fifty‐six responses were analysed against a background of normoxaemia (Pa,O2 = 12.70 +/‐ 0.72 kPa, mean +/‐ S.D.), fifty‐three against a background of moderate hypoxaemia (Pa,O2 = 8.63 +/‐ 0.34 kPa) and fifty‐one against a background of severe hypoxaemia (Pa,O2 = 4.98 +/‐ 0.30 kPa). 4. The sensitivity of the peripheral chemoreceptors in mediating the response to CO2 increased from 38.3 +/‐ 17.0 ml min‐1 kPa‐1 kg‐1 during normoxaemia to 48.8 +/‐ 15.3 ml min‐1 kPa‐1 kg‐1 during moderate hypoxaemia and to 72.9 +/‐ 24.0 ml min‐1 kPa‐1 kg‐1 at severe hypoxaemia. 5. As compared with the central CO2 sensitivity during moderate hypoxaemia and normoxaemia (104.0 +/‐ 39.0 and 100.8 +/‐ 41.6 ml min‐1 kPa‐1 kg‐1, respectively) it decreased to 85.9 +/‐ 54.1 ml min‐1 kPa‐1 kg‐1 at severe hypoxaemia. 6. We conclude that in newborn piglets there is a positive interaction between hypoxia and hypercapnia at the level of the peripheral chemoreceptors while severe hypoxaemia reduced the CO2 sensitivity centrally.
Phencyclidine block of calcium current in isolated guinea‐pig hippocampal neurones.
Authors: Ffrench‐Mullen J M , Rogawski M A
Published: December 2014

1. Phencyclidine (PCP) block of Ca2+ channel current in enzymatically dissociated neurones from the CA1 region of the adult guinea‐pig hippocampus was studied using whole‐cell voltage clamp techniques. Ca2+ channel current was recorded with 3 mM‐Ba2+ as the charge carrier. Na+ currents were blocked with tetrodotoxin and K+ currents were eliminated by using tetraethylammonium and N‐methyl‐D‐glucamine as the predominant extracellular and intracellular cations, respectively. 2. Peak Ca2+ channel current evoked by depolarization from ‐80 to ‐10 mV was reduced in a use‐dependent fashion by PCP. The apparent forward and reverse rate constants for block at the depolarized voltage were 10(6) s‐1 M‐1 and 11‐14 s‐1, respectively. These values were at least 60 times faster than the corresponding rates at the resting voltage. The steady‐state block produced by PCP increased in a concentration‐dependent fashion with an IC50 of 7 microM. Other dissociative anaesthetic drugs were substantially weaker inhibitors of the current (tiletamine > dizocilpine (MK‐801) > ketamine). 3. The Ca2+ channel current recorded under identical conditions in rat dorsal root ganglion neurones was less sensitive to blockade by PCP (IC50, 90 microM). 4. PCP block of the hippocampal Ca2+ channel current occurred in a voltage‐dependent fashion with the fractional block decreasing at positive membrane potentials. Analysis indicated that the PCP blocking site senses 56% of the transmembrane electric field. 5. Analysis of tail currents recorded at ‐80 mV demonstrated that PCP does not affect the voltage‐dependent or time‐dependent activation or deactivation of the Ca2+ channel current. 6. The rate and extent of inactivation of the Ca2+ channel current was maximal at ‐10 mV and diminished at more positive potentials. Experiments with Ba(2+)‐free external solution demonstrated that inactivation of the Ca2+ channels is largely voltage‐dependent and is not affected by Ba2+ influx. 7. PCP markedly increased the apparent extent of inactivation of the Ca2+ channel current during prolonged voltage steps. This increase in apparent inactivation was more pronounced at depolarized potentials. Inactivation at ‐10 mV proceeded in two exponential phases; PCP had little effect on the fast decay phase and caused a moderate speeding of the slow decay phase. Although block of the activated state evolved on the same time scale as inactivation, the apparent rate of inactivation was not increased in a concentration‐dependent fashion by PCP indicating that the block does not occur by a conventional open channel mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanisms of caffeine‐induced contraction and relaxation of rat aortic smooth muscle.
Authors: Watanabe C , Yamamoto H , Hirano K , Kobayashi S , Kanaide H
Published: December 2014

1. Using front‐surface fluorimetry and Fura‐2, we determined the effects of caffeine on cytosolic calcium concentration ([Ca2+]i) and on tension of strips of the rat thoracic aorta. We also determined the effects of caffeine on 45Ca2+ influx into the strips. The objective was to elucidate the mechanism of contraction and relaxation in vascular smooth muscle, as induced by caffeine. 2. In normal physiological salt solution (PSS), caffeine induced a transient tension development, while it induced a biphasic change in [Ca2+]i. The initial transient peak in [Ca2+]i which coincided with tension development was followed by a sustained increase. Thus, changes in tension did not follow changes in [Ca2+]i. In Ca(2+)‐free PSS, both the caffeine‐induced contraction and the increase in [Ca2+]i were transient. It was suggested that in both the presence and absence of extracellular Ca2+, the transient increase in [Ca2+]i was due to the release of Ca2+ from the intracellular store. Although the sustained increase in [Ca2+]i depended on extracellular Ca2+, it was not affected by diltiazem, a Ca2+ antagonist. 3. Caffeine inhibited the increase in [Ca2+]i and tension development during 118 mM‐K+ depolarization, in a concentration‐dependent manner. The extent of reduction in tension (relaxation) was greater than that expected from the reduction in [Ca2+]i based on the [Ca2+]i‐tension relationship observed with K+ depolarization. Pretreatment of the strips with ryanodine did not alter the inhibitory effects of caffeine. 4. Caffeine inhibited the increased [Ca2+]i and developed tension during stimulation by 10(‐5) M‐noradrenaline, in a concentration‐dependent manner. 5. Dibutyryl cAMP (10(‐4) M) inhibited both high K(+)‐induced and noradrenaline‐induced tension development. Inhibition of an increase in [Ca2+]i in relation to the inhibition of tension during noradrenaline stimulation was much greater than that in 118 mM‐K+ depolarization. 6. Although caffeine per se had no effect on 45Ca2+ influx in the strips in normal PSS, caffeine did inhibit the increase in 45Ca2+ influx stimulated by 118 mM‐K+ or by 10(‐5) M‐noradrenaline, to a similar extent and with similar IC50 values. 7. The characteristic features of the effects of caffeine on vascular smooth muscle, i.e. the transient nature of contraction and the relaxation of precontracted strips could be explained as follows: caffeine is able to reduce [Ca2+]i after releasing Ca2+ from intracellular stores; however, this may play a minor role. Independent of the [Ca2+]i reduction, the second messenger, cAMP, might directly influence the [Ca2+]i‐tension relationship, and if so, would play a major role.
A role for low‐frequency, rhythmic synaptic potentials in the synchronization of cat thalamocortical cells.
Authors: Soltesz I , Crunelli V
Published: December 2014

1. Low‐frequency, rhythmic synaptic potentials and their ability to evoke and modulate membrane potential oscillations in thalamocortical (TC) cells of the cat dorsal lateral geniculate nucleus (dLGN) were investigated using intracellular recordings in a brain slice preparation. Three types of rhythmic synaptic potentials were distinguished: EPSPs, IPSPs and ‘complex synaptic potentials’ consisting of an IPSP followed by an EPSP. 2. The frequency of all three types of synaptic potentials was insensitive to changes in the membrane potential. At potentials positive to ‐50 mV, the EPSPs and the complex potentials gave rise to action potentials, while between ‐65 and ‐80 mV all three types of synaptic potential evoked low‐threshold Ca2+ potentials. TC cells which displayed rhythmic synaptic potentials were either cells that showed spontaneous pacemaker oscillation or cells that were brought to oscillate by the rhythmic EPSPs or depolarizing (i.e. reversed IPSPs. 3. The low‐frequency (1.9 +/‐ 0.2 Hz), rhythmic EPSPs were observed in 23 (out of 192) cells, were abolished by tetrodotoxin (TTX; n = 4) and by the combined application of DL‐2‐amino‐5‐phosphonovaleric acid and 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (n = 3), and were insensitive to bicuculline (n = 4). Paired intracellular recordings (n = 32) demonstrated the presence of simultaneously occurring EPSPs in a pair of cells situated 75 microns apart. 4. The low‐frequency (2.2 +/‐ 0.3 Hz), rhythmic IPSPs were observed in 5 (out of 192) cells, were blocked by bicuculline (n = 3), and reversed in polarity at ‐65 mV. The low‐frequency (1.3 +/‐ 0.3 Hz), rhythmic ‘complex potentials’ were observed in 5 (out of 192) cells and were abolished by TTX (n = 2). 5. Intracellular depolarizing current pulses delivered at different phases of the pacemaker oscillations revealed the existence of two different types of phase resetting. Furthermore, a current pulse of critical amplitude and duration applied at a specific phase of the cycle abolished the pacemaker oscillations. 6. These results indicate that the low‐frequency, rhythmic synaptic potentials recorded in TC cells of the dLGN (i) originate from other TC cells that are in the pacemaker oscillating mode, (ii) are capable of driving other TC cells to oscillate rhythmically, or of modulating the frequency of pacemaker oscillations, and (iii) provide a means by which oscillatory activities of TC cells can be synchronized in the absence of sensory, cortical and reticular thalamic inputs.
Stellate cell inhibition of Purkinje cells in the turtle cerebellum in vitro.
Authors: Midtgaard J
Published: December 2014

1. The stellate cell‐mediated inhibition of Purkinje cells was studied by intracellular recordings in an in vitro slice preparation of the turtle cerebellar cortex. A graded inhibitory postsynaptic potential (IPSP) was recorded in Purkinje cells upon stimulation of the parallel fibre‐stellate cell pathway. 2. The IPSP was abolished by bicuculline, and had a reversal potential around ‐75 mV, consistent with a GABAA receptor‐operated Cl‐ conductance dominating the response investigated here. 3. Paired recordings from synaptically coupled stellate cells and Purkinje cells demonstrated that the inhibitory input from a single stellate cell is sufficient to reduce the firing in a Purkinje cell. 4. The extracellular‐evoked IPSP interacted with the active postsynaptic membrane properties in the Purkinje cell. Interaction with both the Na+ plateau and the IA prolonged the responses to an IPSP, making the net effect of the inhibitory response dependent on the membrane potential in each postsynaptic neurone. 5. A precisely timed IPSP was particularly efficient in reducing dendritic Ca2+ influx. 6. The voltage‐dependent Ca2+ component of a climbing fibre response (CFR) as well as of a parallel fibre (PF) input was reduced by the IPSP. 7. It is suggested that Ca2+ spike‐mediated reduction in Purkinje cell excitability may be prevented by the stellate cell IPSP‐mediated reduction in Ca2+ influx.
Differential effects of tetracaine on two kinetic components of calcium release in frog skeletal muscle fibres.
Authors: Pizarro G , Csernoch L , Uribe I , Ríos E
Published: December 2014

1. Intramembrane charge movements and changes in intracellular calcium concentration were recorded simultaneously in voltage clamped cut skeletal muscle fibres of the frog in the presence and absence of tetracaine. 2. Extracellular application of 20 microM tetracaine reduced the increase in myoplasmic [Ca2+]. The effect on the underlying calcium release flux from the sarcoplasmic reticulum was to suppress the peak of the release while sparing the steady level attained at the end of 100 ms clamp depolarizations. 3. While the peak of the release flux at corresponding voltages was reduced by 62% after the addition of tetracaine, the rate of inactivation was the same when the pulses elicited release fluxes of similar amplitude. 4. Higher concentrations of tetracaine, 0.2 mM, abolished the calcium signal in stretched fibres whereas in slack fibres this concentration left a non‐inactivating calcium release flux. 5. Lowering the extracellular pH antagonized the effect of the drug both on charge movements and on calcium signals. The permanently charged analogue tetracaine methobromide lacked effects on excitation‐contraction coupling. 6. These results imply that the two kinetic components of calcium release flux have very different tetracaine sensitivities. They are also consistent with an intracellular site of action of the drug at low concentration. Taken together they strongly suggest that the inactivating and non‐inactivating components of calcium release correspond to different pathways: one that inactivates, is sensitive to tetracaine and is controlled by calcium, and another that does not inactivate, is much less sensitive to tetracaine and is directly controlled by voltage.
Dynamics of the ventilatory response in man to step changes of end‐tidal carbon dioxide and of hypoxia during exercise.
Authors: MacFarlane D J , Cunningham D J
Published: December 2014

1. Four human subjects exercised in hypoxia (end‐tidal partial pressure of O2 (P(ET),O2) ca 55 Torr; heart rate ca 100‐130 beats min‐1), and the contribution to the respiratory drive of the peripheral and central chemoreflex pathways have been separated on the basis of the latencies and the time courses of the responses to sudden changes of stimulus. 2. The subjects were exposed to repeated end‐tidal step changes in PCO2 of ca 3‐3.5 Torr (at nearly constant P(ET),O2) and PO2 (between ca 55 and 230 Torr) at three regions along the expiratory ventilation VE‐P(ET),CO2 response line (hypocapnia, eucapnia, hypercapnia). The dynamics of the ventilatory responses were calculated using a two‐compartment non‐linear least‐squares optimization method. 3. The component of the response attributable to the peripheral chemoreflex loop may in some subjects contribute up to 75% of the ventilatory drive during mild hypocapnic hypoxic exercise and ca 72% of the total gain following steps of P(ET),CO2 during hypoxic exercise. These data support the notion that the effectiveness of the peripheral chemoreceptor pathway is enhanced in moderate exercise. 4. During hypoxic exercise, the time delays and time constants attributed to the peripheral chemoreflex pathways (ca 3.5 and 9 s respectively) and to the central chemoreflex pathways (ca 9.5 and 47 s respectively) are some of the shortest reported. 5. The dynamics of the peripheral and central chemoreflex pathways appeared to be largely independent of each other. 6. There was a notable absence of systematic change of inspiratory and expiratory durations during the step‐induced transients.
Voltage‐dependent ionic currents in dissociated paratracheal ganglion cells of the rat.
Authors: Aibara K , Ebihara S , Akaike N
Published: December 2014

1. Conventional whole‐cell voltage‐clamp technique was used to study the electrophysiological and pharmacological properties of voltage‐dependent Na+, K+ and Ca2+ channels in parasympathetic neurones enzymatically dissociated from the paratracheal ganglia of rat trachea. The voltage‐dependent Na+, K+ and Ca2+ currents (INa, IK and ICa) were separated by the use of ion subtraction and pharmacological treatments. 2. INa was activated by a step depolarization more positive than ‐50 mV and fully activated at positive potentials more than +10 mV. The inactivation phase of INa consisted of fast and slow exponential components (tau if and tau is, respectively). The tau if and tau is were voltage dependent and decreased with a more positive step pulse. 3. The time course for recovery of INa from the complete inactivation exhibited two exponential processes. 4. The reversal potential of INa was equal to the Na+ equilibrium potential (ENa) and resembled a simple Na+ electrode depending only on external Na+ concentration. 5. Tetrodotoxin (TTX) reduced INa without affecting the current kinetics in a concentration‐dependent manner, and the concentration of half‐maximal inhibition (IC50) was 6 x 10(‐9) M. There was no TTX‐resistant component of INa in any of the cells tested. 6. Scorpion toxin increased the peak amplitude of INa and prolonged the inactivation phase in a time‐ and concentration‐dependent manner. In the presence of toxin, both tau is and the fractional contribution of the slow current component to total INa increased concentration dependently. 7. High‐threshold (L‐type) ICa was activated by a step depolarization more positive than ‐30 mV and reached a peak at near 0 mV in the external solution with 2.5 mM Ca2+. The current was inactivated to only a small extent (< 10%) during 100 ms of depolarizing step pulse. There was no low‐threshold (T‐type) ICa in this preparation. 8. The maximum ICa in individual current‐voltage (I‐V) relationships was saturated by an increase in extracellular Ca2+ concentration ([Ca2+]o). The I‐V relationships were also shifted along the voltage axis to the more positive potential with increasing [Ca2+]o. 9. The inactivation process of the L‐type ICa was dependent on Ca2+ influxes (ICa‐dependent inactivation). 10. Relative maximum peak currents of divalent cations passing through the L‐type Ca2+ channels were in the order of IBa > ICa > ISr. 11. Organic and inorganic Ca2+ antagonists blocked the ICa in a concentration‐dependent manner.(ABSTRACT TRUNCATED AT 400 WORDS)
Responses of slowly adapting type II afferent fibres in cat hairy skin to vibrotactile stimuli.
Authors: Gynther B D , Vickery R M , Rowe M J
Published: December 2014

1. Slowly adapting type II (SAII) afferent fibres that supply the forelimb were isolated from the medial cutaneous nerve of anaesthetized cats and examined for their capacity to signal information about vibrotactile events in the hairy skin. 2. The SAII fibres had a single spot‐like receptive field focus where they were highly sensitive to steady indentation and vibration applied with probes normal to the skin surface. However, their sensitivity was affected profoundly by the size of the stimulus probe, its position in relation to the receptive field focus and, to a lesser extent, the magnitude of any pre‐indentation on which vibration was superimposed. Small stimulus probes (e.g. 250 microns diameter) were much more effective than larger (> or = 1‐2 mm) ones, and small shifts in the position of the perpendicularly applied probe away from the receptive field focus led to a marked decline in responsiveness. 3. With appropriate choice of stimulus parameters for vibratory stimuli applied at the receptive field focus, the SAII fibres could respond at low threshold (< 100 microns), with a tightly phase‐locked, regular 1:1 impulse pattern (one impulse per vibration cycle) that accurately signalled the vibration frequency over a bandwidth that extended to 600 Hz. Furthermore, their responses remained phase‐locked up to 1000 Hz. Phase‐locking in SAII fibres was marginally tighter than that in SAI fibres and comparable to that of Pacinian corpuscle fibres. 4. The sensitivity of forelimb SAII fibres to tangential skin stretch was directionally selective; stretch across the forelimb was much more effective than along its long axis. Vibration associated with tangential skin stretch led to a marked spatial expansion of the field of vibration sensitivity. SAII fibres could therefore signal information about natural stimuli that contain elements of skin stretch and vibration, as may be encountered when the forelimb brushes against textured surfaces. Should the SAII fibres fail to contribute to the sensory experience of vibrotactile stimuli, the explanation may be related to limitations imposed centrally on the processing of their signals. Nevertheless, the present results demonstrate that, with appropriate stimulus conditions, the SAII afferent fibres have much greater vibrotactile sensitivity than has been suggested by past studies.
Intracellular electrophysiological study of suprachiasmatic nucleus neurons in rodents: inhibitory synaptic mechanisms.
Authors: Kim Y I , Dudek F E
Published: December 2014

1. The mechanisms responsible for evoked and spontaneous fast inhibitory postsynaptic potentials (IPSPs) in the hypothalamic suprachiasmatic nucleus (SCN) were studied with intracellular recording. SCN neurons, primarily ones identified as receiving excitatory optic nerve input, were recorded in rat and guinea‐pig brain slice preparations maintained in vitro. 2. In normal medium, electrical stimulation of a site dorsocaudal to the SCN evoked IPSPs from thirty‐three of thirty‐six neurons. The evoked IPSPs rose to the peak quickly (8.7 +/‐ 0.9 ms, mean +/‐ S.E.M.; n = 15 neurons) and decayed gradually with a time constant of 25 +/‐ 3 ms. Spontaneous IPSPs were present in each of the thirty‐six neurons. These IPSPs had a rise‐to‐peak time of 7.2 +/‐ 1.0 ms (n = 6 neurons) and a decay time constant of 14 +/‐ 5 ms. 3. When recorded with potassium acetate‐filled electrodes, the evoked and spontaneous IPSPs were hyperpolarizing at resting membrane potential (less negative than ‐70 mV) and had a reversal potential of around ‐75 mV. On the other hand, when recorded with potassium chloride‐filled electrodes, the IPSPs were depolarizing at membrane potentials more negative than ‐50 mV and had an estimated reversal potential less negative than spike threshold. 4. Bath application of bicuculline (10‐50 microM), a gamma‐aminobutyric acidA (GABAA) receptor antagonist, resulted in a complete blockade of both the evoked (n = 16) and spontaneous (n = 13) IPSPs. The bicuculline effects were reversible, and were not associated with any significant and consistent change in baseline membrane potential or input resistance. The neurons impaled in bicuculline‐containing medium (n = 11) exhibited neither spontaneous IPSPs nor evoked IPSPs. 5. In some neurons bicuculline‐resistant hyperpolarizing potentials, which were similar to the fast IPSPs in time course, occurred spontaneously or were evoked by electrical stimulation of the optic nerve or the dorsocaudal site. A fast prepotential always preceded the hyperpolarizing potential, and hyperpolarizing currents blocked these events, indicating that they were not synaptic in origin. No slow IPSPs were detected. 6. The results suggest that fast IPSPs from non‐retinal afferents exist in virtually all SCN neurons receiving excitatory retinal input, and that GABAA receptors associated with Cl‐ channels mediate the fast IPSPs.
The inward rectifier K+ current underlies oscillatory membrane potential behaviour in bovine pigmented ciliary epithelial cells.
Authors: Stelling J W , Jacob T J
Published: December 2014

1. Fresh bovine, pigmented ciliary epithelial cells possess an inward rectifier current activated by hyperpolarization. This current was investigated using whole‐cell patch‐clamp techniques. At the holding potential of ‐70 mV, and with EK (potassium equilibrium potential) set at ‐84 mV, a small outward current flowed through the inward rectifier that was sensitive to external K+, becoming more outward in 0.5 mM K+ and progressively more inward in 20 and 50 mM K+. 2. The inward rectifier showed V‐EK dependence; increasing [K+]o increased the inward conductance from 1.28 nS in 5 mM K+ to 7.42 nS in 50 mM K+. The conductance at a given V‐EK was proportional to the square root of [K+]o. 3. It was blocked by external Cs+ but replacing K+ in the pipette with Cs+ blocked only outward ion movement through the inward rectifier. Inward rectification was also blocked by Ba2+ (85% with Ki (concentration giving half‐maximal inhibition) = 3.1 x 10(‐5) M) and TEA+ (74% with Ki = 2.9 x 10(‐4) M). 4. The activation time constant was voltage dependent, decreasing from 5 ms to 0.7 ms over the voltage range ‐90 to ‐170 mV. With increasing hyperpolarization the current exhibited time‐dependent decay. The time constant for this process was voltage sensitive but the steady‐state inactivation was independent of external [K+]. 5. The current disappeared in culture within 8 days. 6. Solution flow over the cell inactivated the inward rectifier, a property that may be related to [K+]o. 7. In current clamp the cells exhibited an unstable region at a potential of around ‐70 mV. Once in this region oscillations and regenerative hyperpolarizing potentials were observed. This behaviour was eliminated by treatments that blocked (Cs+, Ba2+) or removed (0.5 mM K+) active inward rectification. 8. It is suggested that these oscillations may represent a process of cation loading, the first step in the secretion of aqueous humour.
Adaptation of quantal content to decreased postsynaptic sensitivity at single endplates in alpha‐bungarotoxin‐treated rats.
Authors: Plomp J J , van Kempen G T , Molenaar P C
Published: December 2014

1. Rats were injected once every 48 h with alpha‐bungarotoxin (alpha BTX) for periods up to 6 weeks. Injections caused weakness of facial muscles which lasted about 8 h. Hemidiaphragms were dissected for biochemical and electrophysiological measurements. 2. In muscles from animals treated for 2‐3 weeks with toxin, the binding of 125I‐alpha BTX was reduced to 58%, and the ACh content to 81% of control values. Choline acetyltransferase activity was unchanged. ACh release evoked by 3 Hz nerve stimulation was increased to 175% of control values. 3. The use of mu‐conotoxin, which specifically blocks muscle action potentials, enabled the recording of full‐sized endplate potentials (EPPs) and miniature endplate potentials (MEPPs) at normal muscle membrane potentials (‐70 to ‐80 mV). The amplitude of MEPPs was decreased to 57% in muscles from animals treated for 3 weeks with alpha BTX. The mean of the quantal contents, calculated from the ratio of the corrected EPPs and the MEPPs, was increased to 154%. 4. Within individual muscles of both alpha BTX‐treated and control rats, there was an inverse relationship between the quantal content of an endplate and its MEPP amplitude. 5. The MEPP frequency of endplates from control muscles was positively correlated with the quantal content. However, this correlation was not found in alpha BTX‐affected muscles. 6. Three hours after a single injection of alpha BTX the amplitude of the MEPPs was reduced to about 60% of control values but no increase of the quantal content was found. During the first few days of alpha BTX treatment the quantal content gradually increased; it reached a plateau between 20 and 30 days. 7. The results suggest the existence of an adaptive mechanism, operating at individual endplates, in which retrograde signals at the motor nerve terminals modulate ACh release when neuromuscular transmission is endangered by block of acetylcholine receptors.
Depolarizing action of cholecystokinin on rat supraoptic neurones in vitro.
Authors: Jarvis C R , Bourque C W , Renaud L P
Published: December 2014

1. Cholecystokinin is co‐localized within the oxytocin‐ and, to a lesser extent, vasopressin‐synthesizing magnocellular neurones in the hypothalamic supraoptic and paraventricular nuclei. These nuclei are also prominent binding sites for cholecystokinin. In the present study we used intracellular current‐ and voltage‐clamp recordings from fifty‐seven supraoptic nucleus cells, maintained in superfused explants of rat hypothalamus, to assess their membrane responses to exogenous cholecystokinin and define the nature of their cholecystokinin receptors. 2. In a majority of the fifty‐seven cells tested, bolus infusions into the superfusion media of cholecystokinin fragments (maximum concentrations estimated at 0.3‐15 microM) were followed within 1‐5 s by a transient and reversible membrane depolarization. Active peptides included sulphated cholecystokinin octapeptide (26‐33) (28 of 33 cells responded), non‐sulphated cholecystokinin octapeptide (26‐33) (21 of 25 cells responded), cholecystokinin tetrapeptide (30‐33) (20 of 24 cells responded and caerulein (4 of 4 cells responded). None of five cells responded to cholecystokinin (26‐28). Depolarizing responses to cholecystokinin analogues persisted in the presence of tetrodotoxin (0.2‐0.4 microM), and in Ca(2+)‐free solutions containing MnCl2 (2.5 mM). 3. Under voltage clamp, cholecystokinin fragments evoked an inward current accompanied by an increase in membrane conductance. The amplitude of the inward current varied linearly as a function of membrane voltage, with an extrapolated reversal potential of approximately ‐15 mV. Reversal potentials were not altered by chloride injection. These features suggest that cholecystokinin activates a non‐selective cationic conductance. 4. Active cholecystokinin analogues were approximately equipotent in their depolarizing actions, a feature that supports the activation of cholecystokinin‐B type receptors. Moreover bath application of 200 nM L‐365,260, an antagonist with a high affinity for cholecystokinin‐B receptors, reversibly attenuated the cholecystokinin‐induced responses in four of six cells tested. 5. These observations indicate that cholecystokinin can directly influence the excitability of rat supraoptic nucleus neurones and provide evidence for an additional site where this peptide may act within the hypothalamo‐neurohypophysial axis.