bluuebunny/crossref_metadata_2025 huggingface dataset:
Stimulation of cat cutaneous nociceptive C fibres causing tonic and synchronous activity in climbing fibres.
Authors: Ekerot C F , Oscarsson O , Schouenborg J
Published: December 2014

1. The input from cutaneous nociceptors to climbing fibres projecting to the forelimb area of the C3 zone in the cerebellar anterior lobe was examined in barbiturate‐anaesthetized cats. Climbing fibre responses were simultaneously recorded in single Purkinje cells and as field potentials from the cerebellar surface close to these cells. 2. The cutaneous receptive field of the climbing fibres studied were located on the ipsilateral forelimb. All climbing fibres were activated by both non‐noxious tactile stimulation and noxious pinch of the skin. The location of the receptive field and the distribution of sensitivity in the receptive field appeared to be identical for noxious and tactile stimuli. 3. A phasic response in the climbing fibres was evoked by either short‐ or long‐lasting non‐noxious pressure applied to their cutaneous receptive field. By contrast, all climbing fibres studied were strongly and tonically activated (up to 4‐11 Hz for the duration of the stimulation) by sustained noxious pinch in the most sensitive area of their receptive fields. 4. Experiments with anodal block of impulse conduction in myelinated fibres indicated that a major input to climbing fibres during sustained noxious pinch originates from nociceptive C fibres. 5. Sustained noxious pinch of the skin evoked large field potentials on the cerebellar surface. These field potentials were evoked simultaneously with climbing fibre responses in single Purkinje cells and were due to synchronous activation of many climbing fibres. These field potentials and discharges in single climbing fibres were elicited from the same area of the skin suggesting that many of the synchronously discharging climbing fibres have the same receptive field on the skin.
Interaction between the vestibulo‐collic reflex and the cervico‐collic stretch reflex in the decerebrate cat.
Authors: Dutia M B , Price R F
Published: December 2014

1. Interactions between the sagittal vestibulo‐collic reflex (v.c.r.) and the cervico‐collic stretch reflex (c.c.r.) have been studied in the neck extensor muscles biventer cervicis (b.c.) in the decerebrate cat. The v.c.r. was evoked by a 'standard' vestibular stimulus consisting of a sinusoidal nose‐up, nose‐down head movement of 6‐8 deg amplitude at 1 Hz. The c.c.r. was evoked by sinusoidal stretching of the b.c. muscles at 1 Hz. The amplitude of muscle stretching, and its phase in relation to head movement, were systematically varied. 2. When muscle stretching was applied in phase with head movement (so that the muscles were stretched as the head moved in the nose‐down direction), the gain of the combined (v.c.r. + c.c.r.) reflex in the b.c. muscles increased above that of the v.c.r. If the muscle stretching was applied out of phase with head movement (so that the muscles shortened as the head moved downward), the gain of the combined reflex was reduced to a value below that of the v.c.r. 3. The effects on the gain of the combined reflex varied in proportion to the amplitude of muscle stretching. The gain and phase of the combined reflex is modelled reasonably well by a linear vectorial addition between the v.c.r. and the c.c.r. over a wide range of amplitudes of muscle stretching. The linear summation model contains a proportionality constant K, which may represent a factor by which the two reflexes are 'calibrated' against each other. 4. If one of the b.c. muscles was held at a fixed length and the other stretched sinusoidally, the c.c.r. was evoked only in the stimulated muscle. Vestibular stimulation then summed with the c.c.r in the stimulated muscle, while on the contralateral side the reflex response was the same as that of the v.c.r. alone. It would appear therefore that the motoneurone pools of the b.c. muscles are organized as independent entities without mutually excitatory or inhibitory reflex linkages. This arrangement presumably allows flexibility in the supraspinal control of the b.c. muscles, which are often used either as synergists during sagittal head movement or as antagonists during horizontal or roll movements of the head. 5. The interaction between the v.c.r. and the c.c.r. results in an apparent 'servo‐assistance' role for the muscle afferent feed‐back from the b.c. muscles, amplifying or attenuating the reflex response of the muscles to a given head movement.(ABSTRACT TRUNCATED AT 400 WORDS)
Contractile effects of perivascularly applied vasopressin on the pial artery of the cat brain.
Authors: Nakai M
Published: December 2014

1. The effects of perivascularly applied vasopressin on the diameter of pial arteries (control 298 +/‐ 14 S.E. micron) of the brain were examined after chronic implantation of a cranial window in fifteen anaesthetized cats. 2. Application of vasopressin resulted in a dose‐dependent contraction. The threshold concentration for contraction was 3 X 10(‐10) M, the half‐maximal effective concentration (ED50) (1.6 +/‐ 0.2) X 10(‐9) M, and the maximum reduction in artery diameter 37 +/‐ 2%. 3. The contraction was powerfully inhibited by perivascular application of a 10(‐7) M solution of the vasopressin antagonist, [1‐(beta‐mercapto‐beta,beta‐cyclopentamethylenepropionic acid),2‐(O‐methyl)tyrosine]arginine vasopressin. 4. Perivascular application of noradrenaline induced a dose‐dependent contraction of the pial artery. The ED50 was (8.9 +/‐ 2.5) X 10(‐7) M, and the maximum reduction in artery diameter was 33 +/‐ 2%. 5. Such noradrenaline‐induced contraction was not modified at all in the presence of a subthreshold dose (2 X 10(‐10) M) of vasopressin (P greater than 0.05, for the over‐all difference in size of the contraction, ED50 and maximum contraction). 6. In another experimental setting it was also found that neither the subthreshold nor a suprathreshold (10(‐9) M) dose of vasopressin modified the contraction induced by 10(‐6) M‐noradrenaline (P greater than 0.05, compared to the contraction in the absence of vasopressin). 7. Thus a powerful and sensitive contractile response of the pial arteries to perivascularly applied vasopressin was demonstrated. However, the modifying effect of vasopressin on the contraction induced by perivascularly applied noradrenaline was minimal.
Intramembrane charge movement in frog skeletal muscle fibres. Properties of charge 2.
Authors: Brum G , Rios E
Published: December 2014

1. Membrane currents were measured in cut skeletal muscle fibres voltage‐clamped in a double Vaseline gap in solutions that had impermeant ions substituted for Na+, K+ and Cl‐. The fibres were maintained at a holding potential of 0 mV. Pulses to positive voltages elicited outward currents that were proportional to voltage at all times; these were used to estimate linear capacitive currents, which in turn were used in the construction of non‐linear current transients. 2. Large negative‐going pulses elicited proportionally larger inward currents that decayed during the pulse with voltage‐dependent kinetics. A portion of the non‐linear current could be eliminated by solutions containing EGTA, as well as by large negative conditioning pulses of 200 ms or more. This portion was probably an inward Ca2+ current. 3. The non‐linear current remaining in EGTA‐containing solutions had characteristics of intramembrane charge movement ('charge 2'). This charge depended on voltage according to a two‐state Boltzmann function of average parameters Qmax = 47.7 nC/microF, V = ‐115 mV, K = 21.5 mV (seven fibres). 4. The charge movement current transients were single‐exponential decays (after a short rising phase) with time constants (tau) that depended on voltage (V). A single‐barrier Eyring rate model described well the dependence of time constant on voltage. This fit permitted an independent estimate of a transition voltage, V, and a slope parameter K related to apparent valence of the mobile particle. The values of V and K that best fitted the kinetic data were close to the corresponding values estimated from the charge vs. voltage distribution. 5. Effective capacitance was measured by the transfer of capacitive charge by a small pulse superimposed on a variable pre‐pulse. The capacitance was found to depend on pre‐pulse voltage. The voltage dependence of the capacitance was as expected from the properties of charge 2 measured independently in the same fibres. 6. The presence of charge 2, defined as charge that moves in a very negative voltage range, was compared on the same fibres in a depolarized and a normally polarized (holding potential = ‐100 mV) situation. All fibres had less charge 2 at a holding potential of ‐100 mV (14 nC/microF average reduction). In these fibres charge 1, explored with pulses from ‐70 mV to 0 mV, was greater at a holding potential of ‐100 mV (18 nC/microF average increase).(ABSTRACT TRUNCATED AT 400 WORDS)
Actions of gamma‐aminobutyric acid on rat supraoptic nucleus neurosecretory neurones in vitro.
Authors: Randle J C , Renaud L P
Published: December 2014

1. Intracellular recordings were obtained from thirty‐eight rat supraoptic nucleus (s.o.n.) neurosecretory neurones in perfused hypothalamic explants. Changes in membrane potential and conductance were monitored following application of gamma‐aminobutyric acid (GABA), and related agonists and antagonists. 2. GABA depressed action potential discharge of all of thirty‐five s.o.n. neurones tested and induced either membrane hyperpolarization or depolarization. Neurones that displayed membrane hyperpolarization in response to lower GABA concentrations (30‐300 microM) demonstrated a biphasic membrane voltage change with a later depolarizing phase as a response to higher concentrations (up to 3000 microM). 3. GABA (10‐3000 microM) induced a prominent concentration‐dependent increase in membrane conductance in all neurones. The critical slope for the log‐log plot of [GABA] vs. GABA‐induced membrane conductance was 1.7, indicating co‐operativity in the GABA receptor‐induced conductance change. 4. Muscimol (0.3‐30 microM) potently mimicked all the effects of GABA. Bicuculline (1‐100 microM) antagonized the effects of GABA and muscimol in a competitive manner. 5. Glycine and taurine (1‐10 mM) had weak effects, although comparatively similar to those of GABA. These actions were blocked both by bicuculline (100 microM) and by strychnine (1 microM). At higher concentrations (greater than 10 microM), strychnine also antagonized the actions of GABA. 6. In recordings with potassium‐acetate‐filled micropipettes, the reversal potential of hyperpolarizing membrane voltage responses to GABA was ‐72.5 +/‐ 1.5 mV in close agreement (+/‐ 5 mV) with the reversal potential of inhibitory post‐synaptic potentials (i.p.s.p.s) recorded in the same neurones. Depolarizing responses to GABA reversed polarity at ‐50 +/‐ 1.6 mV. In recordings with KCl‐filled micropipettes, voltage responses to GABA were always depolarizing and reversed near ‐40.0 +/‐ 4.3 mV. Similarly, reduction of the concentration of chloride ions in the perfusion medium from 134 to 10.4 mM induced a positive shift of the GABA reversal potential by 40‐50 mV. 7. From measurements of input resistance (Rin) and cell time constant (tau O), input capacitance (Cin; representing total membrane capacitance) was calculated as 78.9 +/‐ 2.1 pF. During responses to GABA or muscimol, decreased Rin was accompanied by a linearly related decrease in tau o indicating that these substances had no effect on the membrane capacitance of s.o.n. neurones.(ABSTRACT TRUNCATED AT 400 WORDS)
Relative displacements in muscle and tendon during human arm movements.
Authors: Amis A , Prochazka A , Short D , Trend P S , Ward A
Published: December 2014

1. X‐ray, cine and video recordings were made of the movement of radio‐opaque markers injected into the musculo‐tendinous junctions of biceps brachii muscle. 2. In strong isometric contractions, the distal tendon of the long head of biceps lengthened by about 2% of its estimated rest length. 3. During voluntary isotonic elbow flexion‐extension movements at frequencies up to 5.5 Hz there was no detectable phase shift between intramuscular and joint displacements. 4. In the fastest alternating movements (5.5‐6.7 Hz) small phase advances developed in the muscle. 5. We conclude that human tendons do stretch during muscle contraction, but not enough to cause intramuscular phase reversals in rapid unloaded movements. This in turn means that muscle spindles shorten and lengthen virtually in phase with joint movements under most conditions.
Change in optical activity of a lobster nerve associated with excitation.
Authors: Watanabe A
Published: December 2014

1. To record the change in optical rotation of a nerve fibre associated with excitation, an optical apparatus was constructed using a polarizer, a photo‐elastic modulator, an analyser and a lock‐in amplifier. The apparatus was calibrated with the sucrose solution as the standard. 2. When a lobster leg nerve was dissected and mounted on the sample stage of the apparatus, stimulation elicited a transient change in the lock‐in amplifier output. The signal (here called the 'R‐signal') had a rapid time course, formed a peak during the rising phase of the birefringence signal, and often quickly returned to the base line, but sometimes showed a long‐lasting later phase. 3. The R‐signal arose at about the time when the compound action potential of slowly conducting fibres passed through the window of the chamber for the optical experiment, suggesting that it originates mainly in the smaller fibres. 4. The R‐signal reversed its sign when the azimuth of the polarizer was changed by 90 deg, indicating that the R‐signal was not due to electrical artifacts. Simultaneously recorded changes in the intensity of the transmitted light had a different time course and an amplitude too small to explain the appearance of the R‐signal. 5. When the azimuth of the nerve was changed, the later phase of the R‐signal changed its amplitude and direction, but the initial phase of the R‐signal was much less influenced, suggesting that the birefringence signal was a component of the later phase. 6. The later phase of the R‐signal could be reconstructed as a sum of an R‐signal at a different azimuth and the birefringence signal, if the amplitude and direction of the latter were adjusted by multiplication of a factor. 7. Assuming that the nerve is a homogeneous, linearly and circularly birefringent and linearly and circularly dichroic material, the lock‐in output was described by mathematical equations. From one of them the birefringence signal could be deduced from a series of R‐signals observed at various nerve azimuths. The time course of the calculated birefringence signal agreed well with that of the experimentally recorded birefringence signals. 8. Utilizing the same equations, the contribution of the birefringence change to the R‐signal was estimated and subtracted. The remaining part was independent of the nerve azimuth, and could be regarded as representing the time course of the change in optical rotation of the nerve.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium in dark‐adapted toad rods: evidence for pooling and cyclic‐guanosine‐3'‐5'‐monophosphate‐dependent release.
Authors: Fain G L , Schröder W H
Published: December 2014

1. We have used laser micromass analysis (l.a.m.m.a.) to investigate Ca uptake and release in intact 'red' rod photoreceptors in the dark‐adapted retina of the toad, Bufo marinus. 2. With l.a.m.m.a. it is possible to measure separately the concentrations of each of the Ca isotopes. Rods normally containing almost exclusively 40Ca can be incubated in Ringer solution containing the stable isotopes 42Ca or 44Ca. In this way, the movements of Ca into and out of the rod can be separately determined. 3. When rods are incubated in darkness in high 44Ca (up to 20 mM), large amounts of 44Ca accumulate in the outer segment at a rate which increases with increasing external 44Ca concentration. However, this 44Ca appears not to exchange with the 40Ca originally present within the rod. This result suggests that the 40Ca may be sequestered within a pool which normally exchanges slowly with external Ca. 4. We explored Ca exchange in high‐Ca solutions in more detail with double‐isotope labelling. In these experiments, rods were first pre‐loaded with Ca of one isotope (42Ca) and then incubated in Ringer solution containing another (44Ca). We could then measure separately the rate of exchange of the pre‐loaded 42Ca with the 44Ca in the Ringer solution and with the 40Ca originally present within the rod in the sequestered pool. 5. These experiments show that the pre‐loaded‐Ca exchanges rapidly with Ca in the Ringer solution, at least in part by Ca‐Ca exchange, but much more slowly with the Ca originally present within the rod. Thus Ca in the outer segments can exist in (at least) two pools: one which exchanges rapidly across the plasma membrane and is probably Ca free or loosely bound within the cytosol, and another which exchanges slowly and is probably Ca within the disks. 6. Although Ca sequestered within the outer segment normally exchanges quite slowly, it can be rapidly released if the extracellular free Ca is buffered to low levels with EGTA. The rate‐limiting step for Ca release under these conditions appears not to be Na‐Ca exchange, since the rate of Ca efflux is unchanged if the Na in the Ringer solution is substituted with choline. 7. Ca can also be released from the sequestered pool if rods are incubated in Ringer solution containing 100 or 500 microM‐IBMX (3‐isobutyl‐1‐methylxanthine).(ABSTRACT TRUNCATED AT 400 WORDS)
Quantitative assessment of the permeability of the rat blood‐retinal barrier to small water‐soluble non‐electrolytes.
Authors: Lightman S L , Palestine A G , Rapoport S I , Rechthand E
Published: December 2014

1. The passive permeability of the blood‐retinal barrier (b.r.b.) to the water‐soluble non‐electrolytes, sucrose and mannitol, was determined using a multiple time point‐graphical approach as has been used in the assessment of blood‐brain barrier (b.b.b.) permeability. 2. The calculated permeability surface area product for the b.r.b. for sucrose was 0.44 (+/‐ 0.081 S.E. of mean) X 10(‐5) ml g‐1 s‐1 (n = 20) and for mannitol was 1.25 (+/‐ 0.30) X 10(‐5) ml g‐1 s‐1 (n = 18). These values are similar and comparable to those found for the capillaries in the brain (P greater than 0.05) and significantly different from zero (P less than 0.01). 3. Data on the concentrations of sucrose in different parts of the eye show that the permeability of the blood‐retinal barrier, rather than the more permeable blood‐aqueous barrier permeability, was being measured by our technique.
Cardiovascular, ventilatory and catecholamine responses to maximal dynamic exercise in partially curarized man.
Authors: Galbo H , Kjaer M , Secher N H
Published: December 2014

1. In ten young men the ventilatory, cardiovascular, catecholamine and metabolic responses to maximal dynamic leg exercise on a stationary bicycle were followed during partial neuromuscular blockade with tubocurarine. Maximal exercise was performed when the drug effect was at its maximum as well as during the subsequent reduction in the effect allowing a gradually increasing work intensity. The results were compared with those obtained during submaximal and maximal exercise performed without tubocurarine. Partial neuromuscular blockade decreased hand‐grip strength to 41 +/‐ 1.1% (S.E. of mean) and the maximal work load to 27 +/‐ 2.4% of control values. Voluntary effort was maximal and the rate of perceived exertion was high at all levels of exercise with tubocurarine indicating a maintained intense central nervous motor command. 2. During maximal action of the drug oxygen uptake was 1.67 +/‐ 0.11 l/min while only 0.91 +/‐ 0.13 l/min (P less than 0.01) at the same work intensity without neuromuscular blockade. This difference may reflect a dominant reliance on fast‐twitch muscle fibres when work was performed under the influence of tubocurarine. 3. Compared at a given oxygen uptake ventilation was higher during work with tubocurarine than during control exercise (e.g. 55 +/‐ 4.2 and 40 +/‐ 2.2 l/min, respectively (P less than 0.01), at a mean oxygen uptake of 1.9 l/min), while heart rate did not differ significantly (146 +/‐ 4.4 and 139 +/‐ 3.0 beats/min). With decreasing drug effect both variables increased towards the maximum values of 138 +/‐ 4.5 l/min and 183 +/‐ 3.9 beats/min, respectively, achieved in control experiments at an oxygen uptake of 3.8 +/‐ 0.2 l/min. Like heart rate the mean arterial blood pressure increased with increasing work load and was similar at a given oxygen uptake with and without tubocurarine. 4. During maximal exercise at peak tubocurarine effect plasma adrenaline and noradrenaline concentrations were smaller than during control maximum, 1.6 +/‐ 0.27 versus 3.4 +/‐ 0.55 nmol/l (P less than 0.01) and 7.5 +/‐ 1.3 versus 12.6 +/‐ 1.8 nmol/l (P less than 0.05), respectively. However, comparisons at identical oxygen uptake rates revealed that catecholamine responses were markedly enhanced during tubocurarine treatment. Also, blood lactate concentrations were smaller at peak tubocurarine action than during control maximum, 1.9 +/‐ 0.42 mmol/l and 6.1 +/‐ 0.49 mmol/l (P less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)
Ouabain augments calcium‐dependent potassium conductance in visceral primary afferent neurones of the rabbit.
Authors: Higashi H , Katayama Y , Morita K , North R A
Published: December 2014

1. The effects of ouabain (1 nM‐100 microM) on the membrane properties of rabbit visceral primary afferent neurones (nodose ganglion cells) were studied with intracellular recordings and voltage‐clamp techniques in vitro. 2. Ouabain (greater than or equal to 1 microM) often produced a membrane hyperpolarization associated with a fall of membrane resistance in type C neurones. The ouabain‐induced hyperpolarization reversed in polarity at about ‐90 mV. These suggest that the ouabain‐induced hyperpolarization is due to an increase in potassium conductance. 3. Both the peak amplitude and the duration of the after‐hyperpolarization following an action potential were reversibly increased with increasing concentration of ouabain. In tetraethylammonium (TEA, 10‐20 mM) and tetrodotoxin (TTX, 1‐10 microM), the duration of both the calcium‐dependent action potential and the after‐hyperpolarization following the action potential was prolonged by ouabain (greater than or equal to 10 nM). 4. A depolarizing command pulse evoked a slow outward current in TEA (10‐20 mM) and TTX (1‐10 microM). This was increased in amplitude and prolonged in duration by ouabain (100 nM‐1 microM). Such augmentation of the slow outward current by ouabain was usually associated with an increase in a slow inward current during the period of the depolarizing command pulse. 5. An outward current produced by the calcium ionophore A23187 was reversibly augmented by ouabain (greater than or equal to 10 nM). 6. An outward current caused by exchanging a potassium‐free superfusion solution for one containing 4.7 or 10 mM‐potassium was completely abolished by ouabain (greater than or equal to 10 nM). 7. The hyperpolarization elicited by intracellular injection of calcium was reversibly prolonged by either ouabain (1 microM) or caffeine (10 nM). 8. These results suggest that ouabain augments the after‐hyperpolarization both by an increase in calcium influx across the cellular membrane and by an increase in intracellular calcium concentration.
An interneuronal relay for group I and II muscle afferents in the midlumbar segments of the cat spinal cord.
Authors: Edgley S A , Jankowska E
Published: December 2014

1. The properties of interneurones located in the 4th lumbar segment of the cat spinal cord (L4 interneurones) have been investigated by intracellular and extracellular recording from individual neurones. The study focused on interneurones projecting to hind‐limb motor nuclei and/or interposed in pathways from group II muscle afferents. The projection to motor nuclei was assessed from antidromic activation of the neurones by stimuli applied in the motor nuclei of the 7th lumbar (L7) segment. 2. Interneurones which projected to gastrocnemius‐soleus or hamstring motor nuclei were found in laminae VI and VII and at the border between laminae VII and VIII. The dominant peripheral input to most of them was from group II muscle afferents, but they were also influenced by group I muscle afferents and by afferents in cutaneous, joint and interosseous nerves. Both excitatory post‐synaptic potentials (e.p.s.p.s) and inhibitory post‐synaptic potentials (i.p.s.p.s) were evoked from all of these fibre systems. 3. The same kind of multimodal input was also found in other interneurones in laminae VI and VII. However, their axonal projections were not identified and they might have included neurones projecting to motor nuclei (though outside the areas which were stimulated) as well as neurones with more local actions. 4. Interneurones located in laminae IV and V of the dorsal horn appeared to constitute a separate functional population since both their projections and their input differed from those of the more ventrally located interneurones; none of the dorsal horn interneurones were found to project to motor nuclei and none had input from group I afferents, although they were influenced by group II muscle afferents and by afferents in cutaneous, joint and interosseous nerves. 5. Many of the excitatory actions from group I and II afferents upon L4 interneurones were found to be evoked monosynaptically. A high proportion of L4 neurones synapsing upon motoneurones would thus be interposed in disynaptic reflex pathways from these afferents. In comparison to actions evoked via interneurones of the caudal lumbar segments, any post‐synaptic potentials (p.s.p.s) evoked via L4 interneurones would be delayed. These delays would amount to 0.4‐0.9 ms for p.s.p.s. from group I afferents and by 0.5‐2.5 ms for group II p.s.p.s. 6. In many interneurones, particularly those located ventrally, i.p.s.p.s. were evoked by group I and II muscle afferents at latencies which indicated that they were evoked disynaptically. They may therefore reflect inhibitory interactions between subpopulations of L4 interneurones.(ABSTRACT TRUNCATED AT 400 WORDS)
Properties of ion channels closed by light and opened by guanosine 3',5'‐cyclic monophosphate in toad retinal rods.
Authors: Matthews G , Watanabe S
Published: December 2014

1. In patch‐clamp recordings from outer segments of dark‐adapted rod photoreceptors, single‐channel recordings were obtained from the light‐sensitive conductance when divalent cations were omitted from the pipette solution bathing the extracellular face of the recorded patch of membrane. 2. Activity of the light‐sensitive channel was suppressed by light within the normal response range of the dark‐adapted rod. During dim, steady illumination, the rate of opening of the channel fluctuated dramatically, as expected qualitatively from statistical fluctuations in the number of photoisomerizations occurring within the effective collecting area of the recorded patch. 3. The light‐sensitive channel flickered rapidly in the open state, so that individual events appeared as a burst of openings and closings. The average duration of a burst was 0.78 +/‐ 0.03 ms (mean +/‐ S.E.). The average duration of an individual opening was 0.18 +/‐ 0.008 ms. The average closed duration within a burst was 0.37 +/‐ 0.02 ms. 4. Hyperpolarization of the recorded patch had no effect on average burst or open duration, although opening frequency increased slightly (+18.6 +/‐ 4.9%; n = 13; mean +/‐ S.E.). Average single‐channel current increased linearly with hyperpolarization, giving an estimated single‐channel conductance of 20.5 +/‐ 1.1 pS. By extrapolation of the relation between channel current and hyperpolarization, the dark driving force was estimated to be about 48 mV. 5. In addition to reducing the rate of channel events, dim non‐saturating light also reduced the average duration of a burst of openings and the average duration of openings within a burst. 6. About 50% of cell‐attached patches showed no channel activity in darkness. Light‐suppressable channel activity could be induced in these silent patches by perfusing the outer segment with low‐Ca2+ Ringer solution. Similarly, activity could be increased dramatically by low‐Ca2+ Ringer solution in patches that did show channel activity in the dark. From the maximal channel activity observed during low‐Ca2+ perfusion, the lower limit for the number of channels per patch was 20‐70, corresponding to an estimated channel density of 100‐350 channels micron‐2. 7. After recording light‐sensitive channel activity in the intact rod, the patch of membrane was excised, exposing the intracellular membrane face. Application of guanosine 3',5'‐cyclic monophosphate (cyclic GMP) to the intracellular face activated channels (Haynes, Kay & Yau, 1986; Zimmerman & Baylor, 1986; Matthews, 1986d, 1987) whose properties could then be compared directly with the light‐sensitive channels recorded earlier in the same patch of membrane.(ABSTRACT TRUNCATED AT 400 WORDS)
A non‐adrenergic, non‐cholinergic slow inhibitory post‐synaptic potential in neurones of the guinea‐pig submucous plexus.
Authors: Mihara S , Nishi S , North R A , Surprenant A
Published: December 2014

1. Intracellular recordings were made from neurones in the submucous plexus of guinea‐pig ileum and caecum. The responses to electrical stimulation of fibre strands entering the nodes of the plexus were studied. 2. Stimuli comprising trains of pulses (20 Hz, 1‐5 s) produced nicotinic excitatory post‐synaptic potentials (fast e.p.s.p.s), an adrenergic inhibitory post‐synaptic potential (i.p.s.p.), a slow excitatory post‐synaptic potential (slow e.p.s.p.) and a fourth, hitherto unnoticed, slow hyperpolarization which followed the slow e.p.s.p. All these responses were abolished by tetrodotoxin or solutions containing a low calcium concentration. 3. The slow hyperpolarization (slow i.p.s.p.) was examined in the presence of blockers of the nicotinic and adrenergic responses, and in conditions in which the slow e.p.s.p. was prevented by desensitizing concentrations of substance P or vasoactive intestinal polypeptide. The slow i.p.s.p. was unaffected by prazosin (0.1‐1 microM), propranolol (0.1‐1 microM), atropine (1 microM) or naloxone (1 microM). 4. The amplitude and duration of the slow i.p.s.p. increased with increasing numbers of stimulus pulses; it had an amplitude of 17 mV and a duration of 70 s when evoked by a stimulus of 20 Hz for 3 s. 5. The slow i.p.s.p. was associated with a decrease in the input resistance of the cell. It reversed polarity at ‐90 mV in 4.7 mM‐potassium and the extrapolated reversal potential in 0.47 mM‐potassium was ‐145 mV; these findings indicate that the slow i.p.s.p. results from an increase in membrane potassium conductance. 6. The slow i.p.s.p. could still be recorded from submucous plexus neurones in segments of ileum which had been extrinsically denervated 6‐11 days previously.(ABSTRACT TRUNCATED AT 250 WORDS)
Contractions of a human skeletal muscle at different temperatures.
Authors: Ranatunga K W , Sharpe B , Turnbull B
Published: December 2014

1. Influence of temperature on electrically evoked twitch contractions and maximal voluntary contractions was studied in human first dorsal interosseus muscle. The range of the muscle temperature was 35‐12 degrees C. 2. The maximal twitch tension decreased by about 50% in cooling from 35‐12 degrees C; the tension decrease was more pronounced below 25 degrees C. The temperature coefficients (Q10 values) estimated for muscle temperatures of 35‐25 degrees C were 1.43 for time‐to‐peak and 1.7 for half‐time of relaxation. 3. The maximum voluntary tension remained relatively constant on cooling to 25 degrees C but decreased by about 30% on cooling to 12‐15 degrees C. The normalized rate of tension rise in voluntary contractions was largely independent of temperature. 4. Results are discussed in relation to previous work on temperature and muscle contraction in humans and in animals.
Evidence favouring presynaptic inhibition between antagonist muscle afferents in the human forearm.
Authors: Berardelli A , Day B L , Marsden C D , Rothwell J C
Published: December 2014

1. A single motor‐threshold electrical stimulus to the radial nerve in the spiral groove produced three phases of inhibition in the H reflex of relaxed wrist and finger flexor muscles. The first phase of inhibition occurred with a conditioning‐test interval of ‐1 to 3 ms and represents disynaptic Ia reciprocal inhibition of flexor motoneurones by afferent input from extensor muscles. The second phase occurred with a conditioning‐test interval of 5‐40 ms. The characteristics of the second inhibitory phase have been investigated in the present study. 2. The threshold intensity of radial nerve stimulation required to produce the second phase of inhibition was 0.7 X motor threshold and was the same as that required to produce the first (disynaptic) phase of inhibition. 3. The time course of the effect of a radial nerve stimulus on the size of e.m.g. response to transcranial electrical stimulation of the motor cortex also was studied. The results were compared to those obtained with H reflex testing. The time course and depth of the first phase of inhibition were identical with both test inputs. The second phase of inhibition, however, was seen only with the H reflex test stimulus. When the corticospinal volley was timed to arrive at the cervical cord 30 ms after the radial nerve afferent volley, the flexor muscle response was facilitated rather than inhibited. 4. A single stimulus (2‐3 X sensory threshold) to the superficial (cutaneous) branch of the radial nerve at the wrist failed to produce inhibition of the flexor H reflex. Instead, the H reflex was facilitated when the median nerve Ia volley (for the H reflex) was timed to arrive at the cervical cord between 30‐40 ms after the radial nerve cutaneous afferent volley. In contrast to results using mixed nerve stimulation in the spiral groove, there was no difference between the effect of this cutaneous input on the cortically evoked e.m.g. response and the H reflex. 5. We conclude that the second phase of flexor H reflex inhibition is produced by activity in large‐diameter (group I) extensor muscle afferents which acts on the H reflex pathway at a premotoneuronal site.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium current in isolated neonatal rat ventricular myocytes.
Authors: Cohen N M , Lederer W J
Published: December 2014

1. Calcium currents (ICa) from neonatal rat ventricular heart muscle cells grown in primary culture were examined using the 'whole‐cell' voltage‐clamp technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). Examination of ICa was limited to one calcium channel type, 'L' type (Nilius, Hess, Lansman & Tsien, 1985), by appropriate voltage protocols. 2. We measured transient and steady‐state components of ICa, and could generally describe ICa in terms of the steady‐state activation (d infinity) and inactivation (f infinity) parameters. 3. We observed that the reduction of ICa by the calcium channel antagonist D600 can be explained by both a shift of d infinity to more positive potentials as well as a slight reduction of ICa conductance. D600 did not significantly alter either the rate of inactivation of ICa or the voltage dependence of f infinity. 4. The calcium channel modulator BAY K8644 shifted both d infinity and f infinity to more negative potentials. Additionally, BAY K8644 increased the rate of inactivation at potentials between +5 and +55 mV. Furthermore, BAY K8644 also increased ICa conductance, a change consistent with a promotion of 'mode 2' calcium channel activity (Hess, Lansman & Tsien, 1984). 5. We conclude that, as predicted by d infinity and f infinity, there is a significant steady‐state component of ICa ('window current') at plateau potentials in neonatal rat heart cells. Modulation of the steady‐state and transient components of ICa by various agents can be attributed both to specific alterations in d infinity and f infinity and to more complicated alterations in the mode of calcium channel activity.
Role of medullary inspiratory neurones in the control of the diaphragm during oesophageal stimulation in cats.
Authors: Altschuler S M , Davies R O , Pack A I
Published: December 2014

1. The effect of oesophageal distension and swallowing on the activity of medullary respiratory neurones was recorded in decerebrate, spontaneously breathing cats. The distension, produced by inflating a balloon in the thoracic portion of the oesophagus, was of sufficient magnitude to induce inhibition of the peri‐oesophageal part of the crural diaphragm, with little effect on the respiratory function of the diaphragm as measured by the activity in the C5 branch of the phrenic nerve. 2. 424 neurones were tested. They were located bilaterally, in the region of the nucleus tractus solitarius (dorsal respiratory group) or the ambiguous complex (ventral respiratory group). No cell exhibited a change in activity during periods of strong inhibition of crural electrical activity induced by distension or swallowing. The activity of all cells paralleled that of the C5 phrenic neurogram, which was unaffected by the tests. 3. We conclude that the reflex inhibition of the crural diaphragm during oesophageal distension does not result from an inhibition of medullary premotor inspiratory neurones of the dorsal and ventral groups. Additional central pathways must exist that inhibit motoneurones to the crural diaphragm during gastrointestinal reflexes.
The calcium current of mouse egg measured in physiological calcium and temperature conditions.
Authors: Peres A
Published: December 2014

1. Voltage‐clamp experiments have been performed on ovulated mouse eggs using the whole‐cell recording technique. 2. Whole‐cell recording offers improved signal‐to‐noise ratio and excellent stability over time. This allowed the study of the Ca2+ current of these eggs under physiological conditions (i.e. 1.7 mM‐external Ca2+ and 37 degrees C). 3. In these conditions a negative shift of the reversal potential of the current (about ‐25 mV) and also of the activation and inactivation parameters (about ‐10 mV) compared with those recorded in 20 mM‐external Ca2+ is found. 4. No significant diminution of the inward current was detected when external Na+ was substituted with impermeant cations, indicating no relevant participation of Na+ to the current in physiological conditions. 5. In a medium free of divalent cations a large inward current appeared, together with a large decrease in membrane resistance. 6. In Ca2+‐free medium containing 1.2 mM‐Mg2+ the inward current was largely suppressed, while an outward transient current appeared for depolarizations greater than +10 mV. 7. The 'outward surge current' previously described in this preparation appears to possess the same inactivation time constant and the same steady‐state inactivation curve as the inward Ca2+ current. This suggests that the two currents flow through the same channels. 8. The time constant of inactivation was the same for both inward and outward currents and was independent of the current amplitude. These observations exclude a Ca2+‐induced type of inactivation. 9. The channel which physiologically carries the Ca2+ current in mouse eggs belongs then to the class of Ca2+ channels that owe their selectivity to high‐affinity Ca2+ binding sites.
Extracellular potassium changes in the rat neurohypophysis during activation of the magnocellular neurosecretory system.
Authors: Leng G , Shibuki K
Published: December 2014

1. Potassium‐sensitive microelectrodes were used to measure extracellular [K+] in the isolated rat neurohypophysis maintained in vitro. Electrical stimulation of the neurohypophysial stalk (20 Hz 5 s) increased the inferred extracellular [K+] by 9.2 +/‐ 0.4 mM (mean +/‐ S.E. of mean; n = 21). 2. Veratridine (10 microM) enhanced the response to stalk stimulation, and at a higher concentration (50 microM) increased extracellular [K+] in the absence of stimulation. By contrast, tetrodotoxin (1 microM) blocked the [K+] increase completely and reversibly in each of five experiments, indicating that the increase was a consequence of action potential generation. 3. At the end of brief periods of stimulation, the raised extracellular [K+] returned to pre‐stimulation levels within 30 s. In the presence of ouabain (100 microM), the recovery was slower: the half‐decay time was extended by 150‐300% in each of three experiments. 4. Replacement of calcium in the medium with cobalt, cadmium or magnesium reduced the amplitude of the [K+] increase by 26‐30%, indicating that the [K+] increase was largely independent of events subsequent to evoked release of hormone and/or transmitters. 5. Potassium‐sensitive microelectrodes were placed in the neurohypophysis of rats anaesthetized with urethane. Electrical stimulation of the pituitary stalk (50 Hz, 5 s) produced transient voltage increases of 7.6 +/‐ 0.9 mV (mean +/‐ S.E. of mean of seven experiments). These voltage increases were similar in magnitude to the response of the electrodes to the addition of 7.6 +/‐ 1.0 mM‐K+ to rat plasma. 6. In seven lactating rats, the suckling of a litter of hungry pups evoked periodic reflex milk ejections, as detected by increases in intramammary pressure. Potassium‐sensitive microelectrodes in the neurohypophysis recorded transient voltage increases prior to each milk ejection (0.4‐5.5 mV). Each increase preceded an increase in intramammary pressure by 12‐30 s. 7. Thus synchronized high‐frequency activation of magnocellular neurones can produce large changes in extracellular [K+]. The implications of these findings for stimulus‐secretion coupling in the neurohypophysis are discussed in the light of previous reports that hormone release from the neurohypophysis is highly dependent on the frequency and pattern of electrical stimulation.
Effects of age on contractile and enzyme‐histochemical properties of fast‐ and slow‐twitch single motor units in the rat.
Authors: Edström L , Larsson L
Published: December 2014

1. Contractile, enzyme‐histochemical and morphometrical properties of muscle fibres were studied in single motor units of tibialis anterior (t.a.) and soleus muscles in young (3‐6 months) and old (20‐24 months) male albino rats. The technique of measuring glycogen depletion as a marker of previous muscle contraction was used for direct correlation of enzyme‐histochemical and contractile parameters within single motor units of the fast‐ and slow‐twitch type. 2. In t.a., the fast‐twitch motor units covered 18 +/‐ 9 and 22 +/‐ 16% (P = not significant, n.s.) of t.a. cross‐sections, included 148 +/‐ 65 and 162 +/‐ 63 muscle fibres per unit (P = n.s.) and had a cross‐sectional area of 0.50 +/‐ 0.32 and 0.44 +/‐ 0.22 mm2 (P = n.s.) in the young and old animals, respectively (means +/‐ S.D.). 3. In soleus, the slow‐twitch motor units covered 53 +/‐ 11 and 71 +/‐ 12% (P = n.s.), included 55 +/‐ 10 and 83 +/‐ 13 muscle fibres per unit (P less than 0.01) and had a total cross‐sectional area of 0.14 +/‐ 0.02 and 0.22 +/‐ 0.06 mm2 (P less than 0.01) in the young and the old animals, respectively. The calculated number of motor units in soleus accordingly decreased (P less than 0.01) from 49 +/‐ 10 in the young to 29 +/‐ 10 in the old animals resulting in a loss of muscle fibres and an increased innervation ratio in old age (mean +/‐ S.D.). 4. Clusters of more than three muscle fibres were rarely seen in any of the glycogen‐depleted motor units in either the young or the old animals. However, in the slow‐twitch motor units of old animals the muscle fibres were less randomly distributed within the motor unit territory (P less than 0.05), indicating a denervation‐reinnervation process. 5. The contraction and half‐relaxation times of the isometric twitch were significantly prolonged in old age. In 274 randomly isolated single motor units of t.a. the contraction time increased from 13 +/‐ 1 in young animals to 17 +/‐ 3 ms in old ones and the half‐relaxation time from 12 +/‐ 2 to 16 +/‐ 5 ms (P less than 0.01 in both cases). In 236 randomly isolated soleus single motor units, the contraction and half‐relaxation times increased (P less than 0.001) from 24 +/‐ 5 to 31 +/‐ 7 ms and from 26 +/‐ 8 to 35 +/‐ 9 ms, respectively (mean +/‐ S.D.).(ABSTRACT TRUNCATED AT 400 WORDS)
The discharges of cerebellar Golgi cells during locomotion in the cat.
Authors: Edgley S A , Lidierth M
Published: December 2014

1. Extracellular recordings have been obtained from 134 units in the paravermal cortex of lobule V in the anterior lobe of the cerebellum in free‐to‐move cats. Each unit discharged action potentials in a characteristic pattern with no complex spikes. Previous investigators have described such discharges and have assigned them to Golgi cells. We provide further evidence to support this identification. 2. In cats which were sitting quietly, each putative Golgi cell discharged tonically at a low rate (overall mean (+/‐ S.D.) was 14.5 +/‐ 7.3 spikes/s). Eighty‐one of the neurones were also recorded during steady walking on a moving belt and the discharge rate then averaged 17.7 (S.D. +/‐ 19.4) spikes/s. 3. All eighty‐one putative Golgi cells discharged rhythmically during locomotion. Many different patterns of discharge were seen but as a population the neurons were most active in early stance and at the onset of the swing phase of the step cycle in the ipsilateral forelimb. 4. Over a range of different walking speeds (0.5‐0.9 m/s) and of different uphill inclines (0‐25 deg), putative Golgi cells discharged with similar patterns and rates, despite large changes in the vigour of the locomotor movements and in the amplitude of limb muscle electromyograms. 5. Groups of putative Golgi cells and of Purkinje cells recorded from restricted cortical regions produced discharges which fluctuated approximately in parallel during locomotion. However, a comparison of the activity patterns of pairs of closely adjacent Golgi and Purkinje cells revealed a wide variety of phase relations. The possible role of Golgi cells in determining the Purkinje cell output is discussed in the light of these findings.