bluuebunny/crossref_metadata_2025 huggingface dataset:
Correspondence between climbing fibre input and motor output in eyeblink‐related areas in cat cerebellar cortex.
Authors: Hesslow G
Published: December 2014

The purpose of the present work was to identify sites in the cerebellar cortex which are likely to control eyeblink. This work was motivated by findings suggesting that the cerebellum is involved in the learning and/or performance of the classically conditioned eyeblink response. The identification was based on climbing fibre input to the cortex and on the effects of electrical stimulation of the cerebellar cortex in cats decerebrated rostral to the red nucleus. The cerebellar surface was searched for areas receiving short latency climbing fibre input on periorbital electrical stimulation. Four such areas were found in the c1 and c3 zones of lobules VI and VII in the anterior lobe of the cerebellum and in the c3 zone in the paramedian lobule. Electrical stimulation of the cerebellar cortex with trains (150‐400 Hz) of at least 10 ms duration evoked two types of EMG response in the orbicularis oculi muscle. An early response, time‐locked to the onset of the stimulation, was unrelated to climbing fibre input and a delayed response, time‐locked to the termination of the stimulation, could only be evoked from areas which received short latency climbing fibre input from the eye, that is, the c1 and c3 zones. The delayed responses had long latencies (up to 50 ms) after the termination of the stimulus train and could be delayed further by prolonging the stimulation. Both types of response were abolished by injections of small amounts of lignocaine into the brachium conjunctivum. A number of characteristics of the delayed responses are described. They could be inhibited by a further shock to the same area of the cerebellar cortex. Their latency could be increased by increasing the stimulation frequency. The period between stimulation and appearance of the response often showed a decrease in spontaneous EMG activity. There was a close topographical correspondence between input and output. Delayed responses could be evoked from all four of the areas in the c1 and c3 zones which have climbing fibre input from the periorbital area. They could not be evoked from other areas. In contrast, early responses were only evoked from areas without such climbing fibre input. It is proposed that the delayed responses were generated by activation of Purkinje cell axons leading to hyperpolarization and a subsequent rebound depolarization and activation of cells in the interpositus nucleus. The cortical areas are therefore probably involved in the control of the orbicularis oculi muscle.(ABSTRACT TRUNCATED AT 400 WORDS)
Facilitation of the arterial baroreflex by the ventrolateral part of the midbrain periaqueductal grey matter in rats.
Authors: Inui K , Murase S , Nosaka S
Published: December 2014

1. The effects of stimulation of the ventrolateral part of the midbrain periaqueductal grey matter (PAG) on the arterial baroreflex were investigated in urethane‐chloralose anaesthetized and artificially ventilated rats. 2. Both electrical and chemical stimulation of the ventrolateral PAG provoked hypotension, vagal bradycardia and marked facilitation of baroreflex vagal bradycardia (BVB), which was induced by stimulation of the aortic depressor nerve. The magnitude of ventrolateral PAG facilitation of BVB was 328 +/‐ 193% (n = 34) for electrical stimulation and 243 +/‐ 224% (n = 13) for chemical stimulation. Baroreflex hypotension was slightly augmented during either electrical or chemical stimulation of the ventrolateral PAG in vagotomized rats. 3. Stimulation of the nucleus raphe magnus (NRM) also provoked hypotension, vagal bradycardia and facilitation of BVB. The magnitude of BVB facilitation was 234 +/‐ 132% (n = 8) for electrical stimulation and 328 +/‐ 170% (n = 7) for chemical stimulation. After microinjection of kainic acid into the NRM region, baroreflex facilitation, as well as hypotension and vagal bradycardia, produced by ventrolateral PAG stimulation, was almost abolished. 4. In conclusion, the ventrolateral PAG, besides producing hypotension and bradycardia, facilitates arterial baroreflexes. These effects are exerted via the NRM, sharply contrasting with effects of the dorsal PAG.
K+ shifts of skeletal muscle during stepwise bicycle exercise with and without beta‐adrenoceptor blockade.
Authors: Hallén J , Gullestad L , Sejersted O M
Published: December 2014

1. K+ efflux rate and control of K+ reuptake rate in exercising muscle cells was examined in six healthy female volunteers. 2. A K(+)‐selective electrode in the femoral vein continuously monitored K+ concentration ([K+]fv) during bicycling. Power was increased stepwise 5‐6 times by 30‐40 W every fourth minute until exhaustion before and after I.V. administration of propranolol. Leg blood flow was measured by bolus injections of Cardiogreen. 3. [K+]fv increased from about 4.3 to 6.8 mmol l‐1 at exhaustion both before and after propranolol administration, but after drug infusion endurance was reduced from 22.2 +/‐ 0.6 to 19.7 +/‐ 1.1 min, so [K+]fv rose more rapidly. 4. The exercise‐induced efflux rate of K+ from the muscle cells was estimated to be about 11 mumol kg‐1s‐1 at exhaustion both before and after propranolol administration. 5. As an indicator of rate of net loss of K+ from the leg, veno‐arterial concentration differences ([K+]fv‐a) during first, fourth and fifth power increments were high after 15 and 40 s, but declined toward the end of each power step. Propranolol accentuated [K+]fv‐a only after 15 and 40 s of the first and fourth increments. 6. The exercise‐induced increase in reuptake rate of K+ in the muscle, estimated at exhaustion, was not significantly changed by propranolol and was about 10 mumol kg‐1s‐1, corresponding to about 15% of maximum Na(+)‐K+ pump capacity in man. 7. Extracellular accumulation and loss of K+ from muscle during bicycle exercise is due to Na(+)‐K+ pump lag. The higher [K+]fv during propranolol is mainly due to impaired redistribution outside the exercising muscles. In addition at low powers, beta‐adrenoceptor blockade caused a transiently increased net loss due to an accentuated Na(+)‐K+ pump lag.
Changes in MEPP frequency during depression of evoked release at the frog neuromuscular junction.
Authors: Zengel J E , Sosa M A
Published: December 2014

1. Endplate potentials (EPPs) and miniature endplate potentials (MEPPs) were recorded from frog neuromuscular junctions bathed in Ringer solutions containing normal (1.8 mM) or high (3.6 mM) Ca2+. The peptide toxin mu‐conotoxin GIIIA was added to the Ringer solution to prevent muscle action potentials and contraction. 2. The nerve was stimulated with conditioning trains of 200‐4800 impulses applied at 20 impulses s‐1 to characterize the effects of repetitive stimulation on changes in EPP amplitude and MEPP frequency under high quantal conditions. 3. MEPP frequency was dramatically increased during and immediately following repetitive stimulation under high quantal conditions, whereas EPP amplitude was greatly depressed. There was no effect of repetitive stimulation on MEPP amplitude. 4. Following the conditioning stimulation the increase in MEPP frequency decayed back to the control level with a time course that could be described by four exponentials. The time constants of these exponentials were very similar to those that describe the components of stimulation‐induced increases in EPP amplitude and MEPP frequency observed under low quantal conditions when depression is absent. 5. The results of this study indicate that depression and the components of stimulation‐induced increases in release (facilitation, augmentation and potentiation) can be present at the same time, suggesting that the mechanism of depression involves different underlying factors from the mechanism(s) responsible for increases in release. They also indicate either that depression selectively affects only those quanta destined to be released in direct response to the nerve action potential, which would suggest that EPPs and MEPPs arise from different pools of transmitter, or that depression in some way affects a step in the release process involved only in evoked release, and not asynchronous (spontaneous) release.
Muscarinic M‐current inhibition via G alpha q/11 and alpha‐adrenoceptor inhibition of Ca2+ current via G alpha o in rat sympathetic neurones.
Authors: Caulfield M P , Jones S , Vallis Y , Buckley N J , Kim G D , Milligan G , Brown D A
Published: December 2014

1. Microinjection of selective antibodies into superior cervical ganglion (SCG) neurones has identified the G‐protein alpha‐subunits mediating muscarinic receptor inhibition of M‐type K+ current (IK(M)) and alpha‐adrenoceptor inhibition of Ca2+ current (ICa). 2. Antibodies specific for G alpha q/11, but not those for G alpha o, reduced M‐current inhibition by the muscarinic agonist oxotremorine‐M, whereas anti‐G alpha o antibodies, but not anti‐G alpha q/11 or anti‐G alpha i1‐3 antibodies, reduced calcium current inhibition by noradrenaline. 3. Immunoblots with specific anti‐G‐protein antibodies demonstrated the presence of both G alpha q and G alpha 11, while G alpha o1 (but virtually no G alpha o2) was present. 4. We conclude that M1 muscarinic receptor inhibition of IK(M) is transduced by G alpha q and/or G alpha 11, and that G alpha o transduces alpha‐adrenoceptor inhibition of ICa.
Regional fibre stress‐fibre strain area as an estimate of regional blood flow and oxygen demand in the canine heart.
Authors: Delhaas T , Arts T , Prinzen F W , Reneman R S
Published: December 2014

1. In the present study the relation between regional left ventricular contractile work, regional myocardial blood flow and oxygen uptake was assessed during asynchronous electrical activation. 2. In analogy to the use of the pressure‐volume area for the estimation of global oxygen demand, the fibre stress‐fibre strain area, as assessed regionally, was used to estimate regional oxygen demand. The more often used relation between the pressure‐sarcomere length area and regional oxygen demand was also assessed. 3. Experiments were performed in six anaesthetized dogs with open chests. Regional differences in mechanical work were generated by asynchronous electrical activation of the myocardial wall. The ventricles were paced from the right atrium, the left ventricular free wall, the left ventricular apex or the right ventricular outflow tract. Regional fibre strain was measured at the epicardial anterior left ventricular free wall with a two‐dimensional video technique. 4. Regional fibre stress was estimated from left ventricular pressure, the ratio of left ventricular cavity volume to wall volume, and regional deformation. Total mechanical power (TMP) was calculated from the fibre stress‐fibre strain area (SSA) and the duration of the cardiac cycle (tcycle) using the equation: TMP = SSA/tcycle. Regional myocardial blood flow was measured with radioactive microspheres. Regional oxygen uptake was estimated from regional myocardial blood flow values and arteriovenous differences in oxygen content. 5. During asynchronous electrical activation, total mechanical power, pressure‐sarcomere length area, myocardial blood flow and oxygen uptake were significantly lower in early than in late activated regions (P < 0.05). 6. Within the experiments, the correlation between the pressure‐sarcomere length area and regional oxygen uptake was not significantly lower than the one between total mechanical power (TMP) and regional oxygen uptake (VO2,reg). However, variability of this relation between the experiments was less for total mechanical power. Pooling all experimental data revealed: VO2,reg = k1 TMP+k2, with k1 = 4.94 +/‐ 0.31 mol J‐1 k2 = 24.2 +/‐ 1.9 mmol m‐3 s‐1 (means +/‐ standard error of the estimate). 7. This relation is in quantitative agreement with previously reported relations between the pressure‐volume area and global oxygen demand. The results indicate that asynchronous electrical activation causes a redistribution of mechanical work and oxygen demand and that regional total mechanical power is a better and more general estimate of regional oxygen demand than the regional pressure‐sarcomere length area.
Inhibition by 5‐HT7 receptor stimulation of GABAA receptor‐activated current in cultured rat suprachiasmatic neurones.
Authors: Kawahara F , Saito H , Katsuki H
Published: December 2014

1. Whole‐cell voltage‐clamp recordings were made from postnatal rat suprachiasmatic (SCN) neurones to investigate possible modulation by 5‐hydroxytryptamine (5‐HT) of gamma‐aminobutyric acid (GABA)‐activated current (IGABA). 2. 5‐HT reversibly inhibited IGABA in a concentration‐dependent manner (10(‐10) to 10(‐6) M). (+/‐)‐8‐Hydroxy‐2‐N,N‐dipropylaminotetralin (8‐OH‐DPAT, 10(‐10) to 10(‐5) M) and 5‐carboxamidotryptamine (10(‐6) M) also inhibited IGABA, whereas 1‐(2,5‐dimethyl‐4‐iodophenyl)‐2‐aminopropane (DOI, 10(‐6) M) had no significant effect. 3. The effect of 8‐OH‐DPAT (10(‐7) M) was blocked by ritanserin (10(‐7) M), but not by pindolol (10(‐7) M). The effect of 5‐HT was also suppressed by ritanserin, but not by pindolol, ketanserin (10(‐7) M) or ICS 205‐930 (10(‐6) M). 4. 8‐Bromo‐cAMP (10(‐3) M) or forskolin (5 x 10(‐5) M) suppressed IGABA. The effects of forskolin and 5‐HT were not additive. Furthermore, the effect of 5‐HT (10(‐7) M) was significantly reduced by N‐[2‐(methylamino)ethyl]‐5‐isoquinoline sulphonamide (H‐8, 10(‐6) M). 5. It is concluded that 5‐HT inhibits IGABA in the SCN neurones, which involves the activation of 5‐HT7 receptors and cAMP‐coupled systems.
Synaptic responses of substantia gelatinosa neurones to dorsal column stimulation in rat spinal cord in vitro.
Authors: Baba H , Yoshimura M , Nishi S , Shimoji K
Published: December 2014

1. To study the mechanism of dorsal column stimulation‐induced depression of nociceptive transmission in the spinal cord, synaptic responses evoked in dorsal horn neurones by dorsal column and dorsal root stimulations were examined in a horizontal spinal cord slice of the adult rat. Intracellular recordings were made from substantia gelatinosa (SG) neurones. 2. All SG neurones examined received monosynaptic inputs and/or polysynpatic inputs from both dorsal column and dorsal root. A delta fibres were probably responsible for the synaptic responses. The responses evoked by dorsal column stimulation were similar to those evoked by primary afferent A delta fibre stimulation. 3. Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked by dorsal column A delta fibres were depressed by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione, suggesting that these fibres released L‐glutamate or a related amino acid as a transmitter. 4. In 38 of 101 SG neurones, dorsal column stimulation evoked an initial EPSP followed by fast and/or slow inhibitory postsynaptic potentials (IPSPs). These IPSPs reversed polarity at a membrane potential of ‐73 +/‐ 2 mV. The fast IPSPs observed in 16 of the SG neurones (42%) that received inhibitory inputs were depressed by strychnine, while the slow IPSPs observed in 22 SG neurones were depressed by bicuculline. In a few cells, a long‐lasting slow IPSP with a much slower time course was detected; this IPSP was insensitive to strychnine and bicuculline, and reversed polarity at a membrane potential near ‐90 mV. 5. Repetitive stimulation of the dorsal column depressed the amplitude of monosynaptic EPSPs evoked by dorsal root stimulation. 6. The responses of SG neurones to dorsal column stimulation had configurations and durations similar to responses to dorsal root stimulation, and may be mediated largely by the same A delta fibres. However, a C fibre‐mediated response could not be detected in SG neurones from dorsal column stimulation, although dorsal root stimulation could evoke C fibre‐mediated monosynaptic EPSPs in 18 of 88 SG neurones (20%). 7. These observations suggest that SG neurones receive abundant A delta but not C fibre inputs from the dorsal column and that dorsal column stimulation inhibits primary afferent transmission in the spinal cord both by reducing transmitter release from primary A delta fibres and by hyperpolarizing SG neurones.
Nicotinic and muscarinic ACh receptors in rhythmically active spinal neurones in the Xenopus laevis embryo.
Authors: Perrins R , Roberts A
Published: December 2014

1. Intracellular recordings were made from presumed motoneurones in the Xenopus embryo spinal cord, and their response to cholinergic agents was investigated. Nicotine and 1,1‐dimethyl‐4‐phenylpiperazinium (DMPP; both 1‐10 microM) strongly depolarized, and muscarine and oxotremorine (2‐20 microM) weakly hyperpolarized, these neurones. Tetrodotoxin (1 microM), which blocks action potentials in Xenopus neurones, did not affect either of these responses. 2. The extrapolated reversal potential of the nicotinic depolarization was ‐12.1 +/‐ 8.3 mV (mean +/‐ S.E.M.) suggesting the opening of a mixed conductance. The nicotinic response was antagonized by dihydro‐beta‐erythroidine, d‐tubocurarine and mecamylamine (10‐20 microM) but not by alpha‐bungarotoxin (10 microM). 3. The muscarinic response was not reversed when recorded with electrodes filled with potassium chloride but was antagonized by atropine (0.1 microM). 4. Acetylcholine (ACh, 10 microM) caused a strong depolarization of the neurones which was blocked by d‐tubocurarine and dihydro‐beta‐erythroidine, suggesting that its effects are mediated predominantly by nicotinic ACh receptors. 5. ACh and nicotinic agonists applied to the spinal cord produced a barrage of IPSPs that were blocked by TTX and strychnine.
Ionophoretically applied acetylcholine and vagal stimulation in the arrested sinus venosus of the toad, Bufo marinus.
Authors: Bramich N J , Brock J A , Edwards F R , Hirst G D
Published: December 2014

1. The effects of acetylcholine (ACh), applied by ionophoresis, on the isolated arrested sinus venosus of the toad, Bufo marinus, were examined. 2. At each position where ACh was applied across the surface of sinus venosus preparations, a hyperpolarization was produced. These responses were abolished by hyoscine, indicating that muscarinic cholinoceptors are widely distributed over the surface of these muscle cells. 3. Vagal stimulation produced hyperpolarizations which were mimicked, to some extent, by ionophoretically applied ACh. 4. The responses to ionophoretically applied ACh were abolished by adding barium ions to the perfusion fluid, whereas responses to vagal stimulation persisted. 5. The responses to ionophoretically applied ACh were consistently slower than those to vagal stimulation. It is argued that the pathways activated by neural and applied ACh have different kinetics of activation.
Relationships between morphology and physiology of pyramid‐pyramid single axon connections in rat neocortex in vitro.
Authors: Deuchars J , West D C , Thomson A M
Published: December 2014

1. Double intracellular recordings were made from 1163 pairs of pyramidal neurones in layer V‐VI of the rat somatomotor cortex in vitro using sharp electrodes filled with biocytin. Monosynaptically connected pairs of cells were identified when an action potential in one could elicit a constant latency excitatory postsynaptic potential (EPSP) in the other and the cells were filled with biocytin. Labelled cells were subsequently identified histologically with avidin‐horseradish peroxidase. 2. Thirty‐four pairs of cells were found to be monosynaptically connected. Fifteen of these pairs were sufficiently stable for electrophysiological recordings and three of these were recovered sufficiently to permit full morphological reconstruction. 3. The EPSP recorded between the first pair of pyramids varied in amplitude between 0 and 3 mV (mean 1.33 +/‐ 1.06 mV) and fluctuated considerably (coefficient of variation, 0.796). This was largely due to a high incidence of apparent failures of transmission. On reconstruction two boutons from the presynaptic pyramid axon were in close apposition to the proximal portions of basal dendrites of the postsynaptic cell. 4. In the second pair of pyramids the EPSP had a mean amplitude of 1.06 mV, and displayed a 10‐90% rise time of 2.8 ms and a width at half‐amplitude of 23 ms. This EPSP did not alter significantly with changes in membrane potential at the soma. The presynaptic axon closely apposed the distal apical dendrite of the postsynaptic cell in eight places. 5. In the third pair of pyramids, the EPSPs, recorded at a relatively depolarized membrane potential, were long lasting and could elicit slow dendritic spikes with long and variable latencies. These slow spikes suggested that the postsynaptic recording site was dendritic and on reconstruction a possible location was identified on the apical dendrite. A total of five presynaptic boutons closely apposed three separate, proximal branches of the postsynaptic apical dendrite. 6. These results provide the first illustration of a morphological basis for variations in functional properties of pyramid‐pyramid connections in the neocortex.
Mechanism of action of a K+ channel activator BRL 38227 on ATP‐sensitive K+ channels in mouse skeletal muscle fibres.
Authors: Hussain M , Wareham A C , Head S I
Published: December 2014

1. Investigations were made into the effects of BRL 38227, a potassium channel activator, on ATP‐sensitive potassium channels (K+ATP channels) in single fibres dissociated from the flexor digitorum brevis muscle of C57BL/6J mice. 2. In cell‐attached patches BRL 38227 (100 microM) caused activation of a glibenclamide‐sensitive potassium current. Linear slope conductance of the inward current, partial rectification of the outward current and glibenclamide sensitivity indicate that K+ATP channels are the site of action of BRL 38227. 3. In the absence of ATP at the cytoplasmic side of excised inside‐out patches, BRL 38227 caused direct and magnesium‐dependent activation of K+ATP channels. The degree of activation diminished with successive applications of BRL 38227. 4. BRL 38227 also caused activation of K+ATP channels in the presence of low (< 100 microM) but not high (1.0 mM) ATP, particularly in patches containing large numbers of channels. 5. BRL 38227 and 5 microM MgATP failed to activate channels following complete run‐down. 6. Results show that BRL 38227 caused direct activation of K+ATP in skeletal muscle and that this was mediated through a magnesium‐dependent binding site rather than alleviation of inhibition by competitive displacement of ATP from the inhibitory site.
Intercostal muscle compensation for parasternal paralysis in the dog: central and proprioceptive mechanisms.
Authors: De Troyer A , Yuehua C
Published: December 2014

1. Denervation of the parasternal intercostal muscles in the dog is known to cause a substantial reduction in the inspiratory cranial displacement of the ribs and a compensatory increase in the activation of the other inspiratory intercostal muscles, namely the external intercostals and the levator costae. The present studies were designed to assess the mechanism(s) of that compensation. 2. Denervating the parasternal intercostals bilaterally caused a reduction in tidal volume and an increase in arterial PCO2 (Pa, CO2). Severing the parasternal intercostals selectively produced similar changes. The concomitant increases in external intercostal and levator costae activity, however, were much greater than predicted on the basis of the increased Pa, CO2. 3. Denervating the parasternal intercostals on one side of the chest produced large increases in ipsilateral, but not contralateral external intercostal activity. 4. Manipulating the ribs after the parasternal intercostals were inactivated so as to reproduce the normal inspiratory cranial displacement of the ribs elicited immediate, clear‐cut reductions in external intercostal and levator costae activities. 5. The increases in external intercostal and levator costae activities that occur after inactivation of the parasternal intercostals thus result partly from the increased hypercapnic drive but mostly from proprioceptive reflexes, presumably muscle spindle reflexes.
Regulation of intracellular pH in smooth muscle cells of the guinea‐pig femoral artery.
Authors: Aickin C C
Published: December 2014

1. Intracellular pH (pHi) of smooth muscle cells in isolated strips of guinea‐pig femoral artery was measured using double‐barrelled pH‐sensitive microelectrodes. 2. In modified Krebs solution equilibrated with 5% CO2, pHi was 7.26 +/‐ 0.14 (n = 36; mean +/‐ S.D. of an observation) and the membrane potential (Em) was ‐60.5 +/‐ 5.5 mV. Removal of CO2 from the superfusing solution caused an immediate transient alkalosis before pHi stabilized at much the same value (7.28 +/‐ 0.14; n = 16) as in the presence of CO2. 3. The rate of recovery of pHi from experimentally induced acidosis was not measurably affected by the presence or nominal absence of CO2‐HCO3‐. 4. Application of amiloride (100 microM) blocked recovery from acidosis in the nominal absence of CO2‐HCO3‐ and caused a progressive fall in pHi. In the presence of CO2‐HCO3‐, application of amiloride allowed a slow recovery to pHi 6.7‐7.0, but completely prevented full recovery to the normal pHi. 5. Removal of extracellular Na+ (Na+o) caused a dramatic, progressive fall in pHi in both the presence and nominal absence of CO2‐HCO3‐. 6. The amiloride‐insensitive extrusion of acid equivalents observed in the presence of CO2‐HCO3‐ to pHi 6.7‐7.0 was inhibited by removal of Na+o but was not affected by preequilibration with DIDS (see Methods). 7. It is concluded that Na(+)‐H+ exchange is largely responsible for the effective extrusion of acid equivalents in these arterial cells, at least from relatively small perturbations. A DIDS‐insensitive, Na(+)‐ and HCO3(‐)‐dependent mechanism provides some recovery from acidosis to a relatively low pHi. 8. Comparison with data obtained in exactly the same manner in smooth muscle cells of the guinea‐pig ureter indicates that there are significant differences in the regulation of pHi in different smooth muscles.
Modifications of A‐current kinetics in mammalian central neurones induced by extracellular zinc.
Authors: Bardoni R , Belluzzi O
Published: December 2014

1. Whole‐cell voltage clamp recordings were used to study the action of the transition ion zinc on the A‐current kinetics in granule cells from rat cerebellar slices. 2. The effects of zinc have been tested in the concentration range from 1 microM to 1 mM, and fully characterized on all kinetic parameters at 100 and 300 microM. All the effects observed were rapid, concentration dependent and fully reversible. 3. Steady‐state inactivation curves are strongly shifted towards depolarized potentials, with activation curves much less so. These shifts lead to an increase of the peak current amplitude around physiological resting membrane potentials and to a decrease at hyperpolarized potentials. 4. The forward ‘on’ rate constants are slowed by Zn2+ at a concentration of 100‐300 microM by a factor from 1.5 to 4. The backward ‘off’ rate constants are unaffected by Zn2+. 5. The development of IA inactivation, as measured from the current decay, is not affected by Zn2+ up to 1 mM. Removal of inactivation is, on the contrary, significantly slowed. 6. The results are neither compatible with the theory of the surface charge screening effect nor with a mechanism involving channel block. It seems more likely that Zn2+ interferes with the channel gating by binding to a specific domain of the channel protein. 7. After treatment with Hg2+, which is irreversible, Zn2+ still maintains its effects, which suggest that the two divalents act at different sites. 8. In view of the widespread distribution of zinc throughout the brain, its actions on the A‐current could play an important role in physiological function.
Fusimotor reflexes in relaxed forearm muscles produced by cutaneous afferents from the human hand.
Authors: Gandevia S C , Wilson L , Cordo P J , Burke D
Published: December 2014

1. This study was designed to determine whether cutaneous receptors in the hand exert reflex effects on fusimotor neurones innervating relaxed muscles. Recordings were made from fifty‐four muscle spindle afferents in the radial nerve while the arm was held relaxed in a supporting frame. Cutaneous afferents were activated by trains of stimuli at non‐noxious levels to the superficial radial nerve or to the palmar surface of the fingers. 2. For the population of muscle spindle afferents, the mean discharge rate was 7.1 +/‐ 6.4 Hz (range 0‐24 Hz). Thirty‐three per cent had no background discharge, and this occurred significantly more often in finger extensors than wrist extensors. 3. Trains of cutaneous stimuli produced no change in the discharge rates of the majority of spindle endings irrespective of whether the spindle afferent had a background discharge or was given one by muscle stretch. However, with two of forty afferents, the stimuli produced an increase in discharge at latencies of 135 and 155 ms. 4. With a further fourteen muscle spindle endings, the dynamic responses to stretch were measured 100‐400 ms after the trains of cutaneous stimuli. For four spindle afferents there was a statistically significant change in the dynamic response to stretch occurring at conditioned‐stretch intervals of 100‐200 ms. For two afferents the dynamic response decreased by 17 and 26% and for two others it increased by about 24 and 37%. 5. While these results support the view that the level of background fusimotor drive is low in the relaxed state, they suggest that there is some dynamic fusimotor drive to completely relaxed muscles operating on the human hand, and that this drive can be altered reflexly by cutaneous afferent inputs from the hand.
The importance of hand use to discharge of interpositus neurones of the monkey.
Authors: van Kan P L , Horn K M , Gibson A R
Published: December 2014

1. Monkey interpositus neurones show large discharge modulations during reaching to grasp, however, the same neurones show little or no modulation during operation of devices that exercise individual forelimb joints. We tested the hypothesis that grasping during the reach‐to‐grasp is necessary for eliciting high discharge modulation. 2. Three monkeys (Macaca mulatta) moved an articulated lever between low and high target zones. While in the lower zone the monkey's hand was at its waist, in the upper zone its hand was in a position that required forelimb extension at right‐angles to the body axis. Small drawers adjacent to the target zones contained raisins, and the drawers could be remotely opened. Thus, we could elicit two types of reaches having similar trajectories: one reach involved limb transport while holding the lever handle, and the other involved limb transport while forming the hand to grasp a raisin. 3. Eighty‐one neurones from two monkeys, mostly from interpositus with some from adjacent regions of dentate, were tested during device use and reaching to grasp: 93% of the neurones discharged at high rates during at least one of the tasks. Of these, about half increased discharge rate solely during reaching to grasp; the other half showed some increase during device use but only discharged strongly during reaching to grasp. Overall, discharge modulations during the reach‐to‐grasp averaged twice as high as during the corresponding device movement (112 versus 56 impulses s‐1). 4. Individual neurones consistently discharged with characteristic patterns during the reach‐to‐grasp with rates often exceeding 300 impulses s‐1. Discharge during the reach‐to‐grasp was independent of reach trajectory: discharge patterns and amplitudes were similar when reaching from either the lower or upper target zone to the upper raisin drawer as when reaching from the upper target zone to the upper raisin drawer. Reach direction also made little difference: reaches from the upper target zone to the lower drawer typically elicited similar discharge modulation as those from the lower target zone to the upper drawer. 5. High discharge rates associated with grasping were independent of the item being grasped: typically, grasping the device handle elicited as high discharge rates as grasping a raisin. 6. The hypothesis was confirmed that grasping is critical for eliciting high discharge modulation in interpositus during reaching to grasp. Discharge pattern and modulation do not vary with reach direction or amplitude of the reach and, therefore, it is unlikely that intermediate cerebellum controls these features of the reach‐to‐grasp.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of angiotensin II on intracellular Ca2+ and pH in isolated beating rabbit hearts and myocytes loaded with the indicator indo‐1.
Authors: Ikenouchi H , Barry W H , Bridge J H , Weinberg E O , Apstein C S , Lorell B H
Published: December 2014

1. Angiotensin II increases myocardial contractility in several species, including the rabbit and man. However, it is controversial whether the predominant mechanism is an increase in free cytosolic [Ca2+]i or a change in myofilament Ca2+ sensitivity. To address this question, we infused angiotensin II in isolated perfused rabbit hearts loaded with the Ca2+ indicator indo‐1 AM and measured changes in beat‐to‐beat surface transients of the Ca2+i‐sensitive 400:500 nm ratio and left ventricular contractility. The effects of angiotensin II were compared with the response to a Ca(2+)‐dependent increase in the inotropic state produced by a change in the perfusate [Ca2+] from 0.9 to 3.6 nM. 2. In the isolated beating heart, an increase in perfusate [Ca2+] caused an increase in left ventricular pressure +dP/dt in association with an increase in peak systolic [Ca2+]i. Angiotensin II perfusion caused a similar increase in left ventricular +dP/dt in the absence of any increase in peak systolic [Ca2+]i. 3. To exclude any contribution of non‐myocyte sources of Ca(2+)‐sensitive fluorescence which may be present in the intact heart, we also compared the effects of angiotensin II and a change in superfusate [Ca2+] in collagenase‐dissociated paced adult rabbit ventricular myocytes loaded with indo‐1 AM. In the isolated rabbit myocytes a change in perfusate [Ca2+] from 0.9 to 3.6 mM caused an increase in peak systolic cell shortening coincident with an increase in peak systolic [Ca2+]i. In contrast, angiotensin II caused a similar increase in peak systolic cell shortening whereas there was no increase in peak systolic [Ca2+]i. There was also no change in inward Ca2+ current (ICa) in response to angiotensin II. 4. To investigate further the mechanism of the positive inotropic action of angiotensin II, its effects on intracellular pH were studied in isolated rabbit myocytes loaded with the fluorescent H+ probe SNARF 1. These experiments demonstrated that angiotensin II induced a 0.2 pH unit increase coincident with the development of a positive inotropic effect in isolated rabbit myocytes. 5. In summary, angiotensin II has a direct positive inotropic effect in beating rabbit hearts and in isolated paced rabbit myocytes. These experiments provide support for the hypothesis that the predominant mechanism is not an increase in free cytosolic Ca2+ but is due in part to an increase in myofilament Ca2+ sensitivity due to intracellular alkalosis.
Regulation of K+ conductance by histamine H1 and H2 receptors in neurones dissociated from rat neostriatum.
Authors: Munakata M , Akaike N
Published: December 2014

1. The effects of histamine on dissociated neostriatal neurones of the rat were investigated in the whole‐cell mode using the nystatin‐perforated patch recording technique. 2. Histamine evoked a net inward current accompanied by a decrease in the membrane conductance at a holding potential (Vh) of ‐44 mV. This response was observed in neurones considered to be interneurones based on morphology, membrane properties and the responsiveness to acetylcholine. 3. A net inward current evoked by 10(‐8) to 10(‐6) M histamine was inhibited in a concentration‐dependent manner by the H1 receptor antagonists, pyrilamine and triprolidine. The H1 receptor agonists, 2‐methylhistamine and 2‐thiazolylethylamine, mimicked the histamine response, indicating that this response was mediated by the H1 receptor. 4. Histamine, at high concentrations between 10(‐6) and 10(‐5) M, evoked an additional net inward current with a decrease in the membrane conductance, which was inhibited by the H2 receptor antagonists, cimetidine, ranitidine and famotidine. The H2 receptor agonist, impromidine, partially mimicked the response. Thus, this additional current was considered to be mediated by the H2 receptor. 5. The reversal potentials for H1 and H2 receptor‐operated currents shifted 56.9 and 59.3 mV for a 10‐fold change in [K+]o, respectively, suggesting that these currents were carried by K+. 6. An analysis of change in current fluctuations mediated by H1 and H2 receptors suggested that the unitary current amplitudes of K+ channels linked to H1 and H2 receptors were 0.29 +/‐ 0.06 (n = 4) and 0.27 +/‐ 0.07 pA (n = 4), respectively. There was no significant difference between these values. The estimated mean life times (tau) for both channels were also identical (1.1 ms). 7. It was concluded that histamine reduces K+ currents in neostriatal interneurones and that both H1 and H2 receptors are involved in the response.
Na+ channel mis‐expression accelerates K+ channel development in embryonic Xenopus laevis skeletal muscle.
Authors: Linsdell P , Moody W J
Published: December 2014

1. The normal developmental pattern of voltage‐gated ion channel expression in embryonic skeletal muscle cells of the frog Xenopus laevis was disrupted by introduction of cloned rat brain Na+ channels. 2. Following injection of channel mRNA into fertilized eggs, large Na+ currents were observed in muscle cells at the earliest developmental stage at which they could be uniquely identified. Muscle cells normally have no voltage‐gated currents at this stage. 3. Muscle cells expressing exogenous Na+ channels showed increased expression of at least two classes of endogenous K+ currents. 4. This increase in K+ current expression was inhibited by the Na+ channel blocker tetrodotoxin, suggesting that increased electrical activity caused by Na+ channel mis‐expression triggers a compensatory increase in K+ channel expression. 5. Block of endogenous Na+ channels in later control myocytes retards K+ current development, indicating that a similar compensatory mechanism to that triggered by Na+ channel mis‐expression operates to balance Na+ and K+ current densities during normal muscle development.
Desynchronization of epileptiform activity by extracellular current pulses in rat hippocampal slices.
Authors: Durand D M , Warman E N
Published: December 2014

1. A single cathodic current pulse applied in the somatic CA1 region of the hippocampus was found to induce a large decrease in the amplitude of the population spike. 2. Intracellular recordings showed intense cellular firing suggesting the amplitude decrease could not be attributed to a decrease in neuronal firing. 3. Simultaneous intracellular and extracellular potentials were recorded to analyse the synchronization of neuronal firing in the CA1 region. Action potentials were synchronized with the first population spike but this synchronization decreased with subsequent spikes. Histograms of the phase of the action potentials displayed a normal distribution. 4. Histograms of the phases of the action potentials following the application of the ‘singular stimulus’ (one producing a singular response) revealed a uniform distribution of the phases suggesting that the neuronal population was desynchronized. 5. This desynchronization effect of the singular stimulus was verified by double intracellular recordings. The simultaneous firing of two neurons could be desynchronized by the application of the singular stimulus. 6. These findings indicate that it is possible to desynchronize a neuronal pool with the application of a single current pulse. In addition, the results show that it is possible for a neuronal population to fire a large number of action potentials with no resulting evoked potentials in the extracellular space.
Block of stretch‐activated atrial natriuretic peptide secretion by gadolinium in isolated rat atrium.
Authors: Laine M , Arjamaa O , Vuolteenaho O , Ruskoaho H , Weckström M
Published: December 2014

1. Isolated superfused rat atrial preparations were used to study the mechanism of stretch‐induced atrial natriuretic peptide (ANP) secretion. The stretch of the atrial myocytes was induced by raising the intra‐atrial pressure. The secretion rates were analysed by measuring ANP concentrations from the superfusate fractions by radioimmunoassay. 2. The effect of gadolinium, a blocker of stretch‐activated ion channels, on stretch‐induced and basal ANP secretion was investigated by superfusing the atrial preparation with 5, 20 or 80 microM GdCl3. Gadolinium decreased stretch‐induced ANP secretion in a dose‐dependent manner, but did not affect basal secretion. 3. Because high concentrations of gadolinium may block voltage‐gated calcium channels, we tested whether the selective blockers of L‐type (diltiazem) and T‐type (NiCl2) calcium channels affect the stretch‐stimulated ANP release. Neither diltiazem at 3 microM nor NiCl2 at 50 microM affected stretch‐induced ANP release in paced atrial preparation. 4. Gadolinium, but not diltiazem, also inhibited stretch‐stimulated ANP secretion in non‐paced, quiescent atria. 5. The findings that ANP release is inhibited by Gd3+, but not by diltiazem or NiCl2, and that the stretch‐induced secretion in quiescent atria is also inhibited by Gd3+, suggest that stretch‐activated ion channels are involved in the regulation of stretch‐induced ANP release.
Oxygen deprivation inhibits a K+ channel independently of cytosolic factors in rat central neurons.
Authors: Jiang C , Haddad G G
Published: December 2014

1. K+ channel modulation has been shown to be an integral and important cellular response to O2 deprivation. Although part of this modulation occurs as a result of changes in concentrations of several cytosolic factors such as ATP and Ca2+, it is unknown whether there are mechanisms other than those originating from the cytosol. To test the hypothesis that membrane‐delimited mechanisms participate in the O2‐sensing process and are involved in the modulation of K+ channel activity in central neurons, we performed experiments using patch‐clamp techniques and dissociated cells from the rat neocortex and substantia nigra. 2. Whole‐cell outward currents were studied in voltage‐clamp mode using Na(+)‐free or low‐Na+ (5 mM, with 1 microM tetrodotoxin) extracellular medium plus 0.5 mM Co2+. O2 deprivation produced a biphasic response in current amplitude, i.e. an initial transient increase followed by a pronounced decrease in outward currents. The reduction in outward currents was a reversible process since perfusion with a medium of PO2 > 100 mmHg (1 mmHg = 133 Pa) led to a complete recovery. 3. In cell‐free excised membrane patches, we found that a specific K+ current (large conductance, inhibited by micromolar concentrations of ATP and activated by Ca2+) was reversibly inhibited by lack of O2. This was characterized by a marked decrease in channel open‐state probability and a slight reduction in unitary conductance. The magnitude of channel inhibition by O2 deprivation was closely dependent on O2 tension. The PO2 level for 50% channel inhibition was about 10 mmHg with little or no inhibition at PO2 > or = 20 mmHg. 4. Single‐channel kinetic analysis showed that channel open times consisted of two components and closed times were composed of three. The hypoxia‐induced inhibition of K+ channel activity was mediated by selective suppression of the longer time constant channel openings without significantly affecting closed time constants. This led to an increase in frequency of opening and closing and rapid channel flickerings. 5. Our data showed that O2 deprivation had no effect on another K+ current characterized by a much smaller conductance and Ca2+ independence. This provides evidence for the selective nature of the hypoxia‐induced inhibition of some species of K+ channels. 6. These results therefore provide the first evidence for regulation of K+ channel activity by O2 deprivation in cell‐free excised patches from central neurons.
Development of stiffness precedes cross‐bridge attachment during the early tension rise in single frog muscle fibres.
Authors: Bagni M A , Cecchi G , Colomo F , Garzella P
Published: December 2014

1. Force responses to ramp stretches were recorded in single muscle fibres isolated from the lumbricalis muscle of the frog. Stretches were applied at rest and at progressively increasing times after a single stimulus. 2. The increase of fibre stiffness that precedes tension development has a ‘static’ component that accounts for the whole fibre stiffness increase during the latent period and at very low tension at the beginning of the twitch. 3. Static stiffness increase was not affected by 2,3‐butanedione‐2‐monoxime, a drug that almost completely inhibited twitch tension. 4. Static stiffness increased approximately 5‐fold as the sarcomere length was increased from 2.1 to 2.84 microns. 5. These results suggest that static fibre stiffness increase is not attributable to the formation of non‐force‐generating cross‐bridges.
Kinetic separation of charge movement components in intact frog skeletal muscle.
Authors: Huang C L
Published: December 2014

1. Procedures for a complete charge movement separation employed a combination of its steady‐state inactivation and activation properties in intact frog skeletal muscle fibres in gluconate‐containing solutions. 2. Holding potential shifts from ‐70 to ‐50 mV reduced the total charge available between ‐90 and ‐20 mV from 16.76 +/‐ 1.70 nC microF‐1 (mean +/‐ S.E.M.; n = 4 fibres) to 9.25 +/‐ 1.43 nC microF‐1 without significant loss of tetracaine‐resistant charge (q beta). 3. The steady‐state and kinetic properties of tetracaine‐sensitive charge (q gamma) persisted through holding potential changes from ‐90 to ‐70 mV in the presence of gluconate and generally resembled activation properties established hitherto in sulphate‐containing solutions. 4. Further holding potential displacement to ‐50 mV abolished q gamma charge movements and depressed the charge‐voltage curve. 5. Test voltage steps applied from a ‐70 mV prepulse level gave rapid monotonic q beta decays and similarly depressed activation functions in 2 mM tetracaine unchanged by holding potential shifts between ‐70 and ‐50 mV. 6. The isolated ‘on’ q gamma charge movements, I(t), always included early transients that preceded any prolonged charging phases and which increased with depolarization. They decayed to stable baselines in the absence of prolonged time‐dependent or inward‐current phases and yielded integrals, Q(t), that monotonically increased with test voltage. 7. ‘Off’ steps always elicited rapid monotonic q gamma decays that fully returned the ‘on’ charge. 8. ‘On’ and ‘off’ q gamma currents, I(t), following voltage steps from fixed conditioning to varying test levels mapped onto topologically distinct higher‐order phase‐plane trajectories, I(Q), that steeply varied with test voltage. 9. In contrast, voltage steps to fixed test potentials of either ‐70 or ‐20 mV elicited identical q gamma phase‐plane trajectories independent of prepulse history. 10. The q gamma current thus reflects an independent, capacitative process driven uniquely by higher‐order dependences upon charge distribution, Q(t), and test voltage, V(t), autonomous of prepulse history or time, t.