bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of excitatory amino acids and their antagonists on membrane and action potentials of cat caudate neurones.
Authors: Herrling P L , Morris R , Salt T E
Published: December 2014

The electrical activity of caudate neurones was recorded with intracellular electrodes in halothane anaesthetized cats. Agonists and antagonists of excitatory amino acid receptors were applied by micro‐ionophoresis and their effects on membrane‐ and action potentials and on cortically evoked synaptic potentials evaluated. The agonists, L‐aspartate (asp), L‐glutamate (glu), N‐methyl‐DL‐aspartate (NMA), quinolinate and quisqualate all depolarized the membrane, caused repetitive firing, reduced the apparent amplitude of the cortically evoked excitatory post‐synaptic potentials (e.p.s.p.s) and increased the amplitude of the associated inhibitory post‐synaptic potential. Two of the agonists, NMA and quinolinate, additionally caused the appearance of up to 500 ms long depolarizations (plateaus) on the falling phase of action potentials. These plateaus were seen in about two‐thirds of the cells in this sample while in the other third the excitatory effects of NMA and quinolinate were indistinguishable from those of glu and quisqualate. The N‐methyl‐D‐aspartate (NMDA) receptor antagonist D‐alpha‐aminoadipate (DAA) reversibly inhibited the effects of NMA and quinolinate but only on those cells where these two agents evoked action potential plateaus while on the same cells the effects of asp, glu and quisqualate were either only weakly antagonized or not affected. On cells not displaying plateaus to NMA or quinolinate none of the effects of the agonists could be antagonized by DAA. DAA applications that completely antagonized the effects of NMA never reduced the amplitudes of cortically evoked e.p.s.p.s. Cis‐2,3‐piperidine dicarboxylate also blocked the effects of NMA and asp at low application currents while at higher currents it enhanced the effects of glu or asp although still retaining its NMA antagonistic activity. High‐frequency stimulation of the cortico‐caudate pathway resulted in long‐lasting depolarizations and repetitive firing, but plateaus of the type caused by NMA or quinolinate were not seen.
Changes in motoneurone firing rates during sustained maximal voluntary contractions.
Authors: Bigland‐Ritchie B , Johansson R , Lippold O C , Smith S , Woods J J
Published: December 2014

Tungsten micro‐electrodes have been used to record the electrical activity of single motor units in the human adductor pollicis during maximal voluntary contractions. The potentials were characteristic of those from single muscle fibres. In brief maximal contractions, the firing rates of over 200 motor units were obtained from five normal subjects. Four subjects had a similar range (mean 26.4 +/‐ 6.5 Hz) while the fifth was slightly higher (35 +/‐ 7.4 Hz). When maximal voluntary force was sustained for 40‐120 s, there was a progressive decline in the range and mean rate of motor‐unit discharge. In the first 60 s, mean rates fell from about 27 Hz to 15 Hz. There was some evidence to suggest that those units with the highest initial frequencies changed rate most rapidly. It is suggested that this decline in motor unit discharge rates is not responsible for force loss, but that it may enable effective modulation of voluntary strength by rate coding to continue during fatigue.
Peptidergic and muscarinic excitation at amphibian sympathetic synapses.
Authors: Kuffler S W , Sejnowski T J
Published: December 2014

A single‐electrode voltage clamp was used to study the slow muscarinic and late slow peptidergic excitatory post‐synaptic currents (e.p.s.c.s) in B cells of the paravertebral sympathetic ganglia of the bull‐frog. Conductance decreases were measured during peptidergic e.p.s.c.s in nearly all cells at clamped potentials near the resting level. In about half of the cells the size of the peptidergic e.p.s.c.s increased with hyperpolarization and in some of these cells conductance increases were found at hyperpolarized levels. In the remaining cells conductance decreases occurred at all levels of membrane potential tested, and in a few of these the polarity of the e.p.s.c.s reversed at hyperpolarized potentials. A similar diversity was observed among muscarinic e.p.s.c.s. At least two simple ionic mechanisms are required to explain the heterogeneous voltage dependencies observed: a conductance decrease primarily to K+ that dominates at depolarized potentials and a conductance increase to other ions that is more prominent at hyperpolarized potentials. The proportion of these two mechanisms appears to differ among B cells. The two slow e.p.s.c.s recorded in the same neurone had the same voltage dependence and were accompanied by the same conductance changes in each of eight cells despite differences between cells. The muscarinic e.p.s.c. was reduced during the peptidergic e.p.s.c. in each of twenty‐five neurones tested over a range of membrane potentials. Externally‐applied luteinizing hormone releasing hormone (LHRH) produced currents with the same voltage dependence and conductance changes as the nerve‐evoked peptidergic e.p.s.c. in each of fifteen cells tested. Bethanechol, a muscarinic agonist, and LHRH produced currents with the same voltage dependence and conductance changes in each of the twelve cells studied. In several cells a saturating response to a prolonged application of LHRH completely occluded the response to bethanechol, and vice versa. Slow currents were recorded from dissociated cell bodies in response to bethanechol and LHRH; these responses exhibited the same diversity of voltage dependence and conductance changes as was observed in intact ganglia. Activation of muscarinic and peptidergic receptors may control shared ionic mechanisms in single ganglion cells.
An intracellular analysis of geniculo‐cortical connectivity in area 17 of the cat.
Authors: Ferster D , Lindström S
Published: December 2014

The latencies of excitatory and inhibitory post‐synaptic potentials (e.p.s.p.s and i.p.s.p.s) evoked by electrical stimulation of afferents from the lateral geniculate nucleus were recorded in neurones of area 17 of the cat visual cortex. After application of an extrapolation procedure to compensate for the conduction time of the afferent axons, a histogram of latencies formed three distinct peaks. Potentials in each of these were interpreted as being mediated by mono‐, di‐ and trisynaptic pathways. Characteristic laminar differences in the extracellular field potentials evoked from the lateral geniculate nucleus (l.g.n.) and in the antidromic activation of neurones from the l.g.n. and superior colliculus were used to determine the laminar position of recorded neurones. It was found that within a given layer, all cells maintained similar connexions with relay cells in the l.g.n. Cells in layers 3, 4, upper 5 and 6 were monosynaptically excited by geniculate afferents, while cells in layers 2 and lower 5 received only indirect excitation via other cortical neurones. Layer 3 cells were unique in receiving a prominent disynaptic e.p.s.p. in addition to the direct excitation from the l.g.n. Late, trisynaptic e.p.s.p. components were seen in many layer 5 and 6 cells. The orderly laminar arrangement of the connexions had the consequence that identified cortico‐geniculate neurones were monosynaptically excited and cortico‐collicular neurones di‐ and trisynaptically excited by geniculate afferents. Cortico‐cortical neurones in layers 2 and 3 received di‐ or mono‐ plus disynaptic excitation, depending on laminar position. Post‐synaptic inhibitory potentials were evoked in all impaled cells, following stimulation of the geniculo‐cortical pathway. Except for a few layer 2 cells, this inhibition was mediated through disynaptic pathways of the feed‐forward type. There was a good positive correlation between conduction times for monosynaptic e.p.s.p.s and disynaptic i.p.s.p.s in the same cells, suggesting that cortical neurones receive excitation and inhibition from the same type of geniculate afferents. The stimulating electrodes activated not only geniculo‐cortical afferents, but antidromically activated cortical efferent neurones from their extracortical axons. These neurones possess intracortical collaterals, and care must be taken to distinguish the resulting potentials from those mediated by orthodromic activation of geniculate afferents. In doing so, evidence was obtained for excitatory connexions from layers 2 and 3 to layer 5, from layer 5 to layer 6, and from layer 6 to layer 4. Typical recurrent inhibition was not observed.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of cooling on breathing and shivering in unanaesthetized fetal lambs in utero.
Authors: Gluckman P D , Gunn T R , Johnston B M
Published: December 2014

The effects of cooling have been studied in chronically instrumented unanaesthetized fetal lambs of 106‐132 days gestation. Cold stimulation of cutaneous thermoreceptors by means of a coil placed around the fetus in the amniotic cavity induced continuous breathing which was associated with high‐voltage electrocortical activity throughout the cooling period. Direct internal cooling by means of an intragastric cooling coil did not alter fetal breathing or sleep‐state patterns. Shivering occurred in response to both external and internal cooling, and this response was present as early as 106 days gestation, well before the appearance of high‐voltage sleep. In older fetuses there was evidence of a reduction in thermoregulatory responses during low‐voltage electrocortical activity, but not of the complete suspension of thermoregulation characteristic of low‐voltage (r.e.m.) sleep seen in mature animals. It is concluded that deep regular breathing associated with high‐voltage electrocortical activity can be induced by cold stimulation of cutaneous thermoreceptors, but not by a reduction in core temperature alone. Furthermore, fetal responses to cooling are present as early as 106 days gestation.
Blood flows within and among rat muscles as a function of time during high speed treadmill exercise.
Authors: Armstrong R B , Laughlin M H
Published: December 2014

The purpose of these experiments was to use radiolabelled microspheres to measure blood flow distribution patterns within and among rat hind‐limb skeletal muscles before, during, and after high speed treadmill running at 60 min‐1 to fatigue. Exercise blood flows were measured at the 0.5, 1, 2 and 3 min time points. Pre‐exercise blood flow was highest in physiological extensor muscles or muscle parts with large populations of slow‐twitch muscle fibres, e.g. soleus (197 ml min‐1 100 g‐1). Blood flows were lowest to muscles or muscle parts with high proportions of fast‐twitch glycolytic fibres, e.g. white gastrocnemius (15 ml min‐1 100 g‐1). The most rapid increases in blood flow at the beginning of exercise and the highest peak blood flows during exercise generally occurred in physiological extensor muscles with relatively high populations of fast‐twitch oxidative fibres. For example, red gastrocnemius muscle blood flow increased by 271 ml min‐1 100 g‐1 during the first 30 s of exercise, and attained a peak flow of 395 ml min‐1 100 g‐1 by the third minute of exercise. On the other hand, the slowest elevations in blood flow at the start of exercise and the lowest peak flows were observed in muscles with high populations of fast‐twitch glycolytic fibres. White gastrocnemius muscle, for example, increased its blood flow by 16 ml min‐1 100 g‐1 during the first 30 s of running, and had a peak flow of 76 ml min‐1 100 g‐1 by the end of 3 min exercise. These relationships between blood flows and fibre type populations were less consistent in physiological flexor muscle groups. Following exercise, blood flows in high‐oxidative muscles returned to the pre‐exercise levels within 30 s. However, in low‐oxidative muscles, return of blood flows to the pre‐exercise levels were slower. Thus, marked differences in the absolute magnitudes of blood flows and in the rates of change in blood flows were observed within and among the hind‐limb muscles before, during and after exercise. These differences were related to the fibre type compositions of the muscles.
Electrophysiology of neurones of the inferior mesenteric ganglion of the cat.
Authors: Julé Y , Szurszewski J H
Published: December 2014

Intracellular recordings were obtained from cells in vitro in the inferior mesenteric ganglia of the cat. Neurones could be classified into three types: non‐spontaneous, irregular discharging and regular discharging neurones. Non‐spontaneous neurones had a stable resting membrane potential and responded with action potentials to indirect preganglionic nerve stimulation and to intracellular injection of depolarizing current. Irregular discharging neurones were characterized by a discharge of excitatory post‐synaptic potentials (e.p.s.p.s.) which sometimes gave rise to action potentials. This activity was abolished by hexamethonium bromide, chlorisondamine and d‐tubocurarine chloride. Tetrodotoxin and a low Ca2+ ‐high Mg2+ solution also blocked on‐going activity in irregular discharging neurones. Regular discharging neurones were characterized by a rhythmic discharge of action potentials. Each action potential was preceded by a gradual depolarization of the intracellularly recorded membrane potential. Intracellular injection of hyperpolarizing current abolished the regular discharge of action potential. No synaptic potentials were observed during hyperpolarization of the membrane potential. Nicotinic, muscarinic and adrenergic receptor blocking drugs did not modify the discharge of action potentials in regular discharging neurones. A low Ca2+ ‐high Mg2+ solution also had no effect on the regular discharge of action potentials. Interpolation of an action potential between spontaneous action potentials in regular discharging neurones reset the rhythm of discharge. It is suggested that regular discharging neurones were endogenously active and that these neurones provided synaptic input to irregular discharging neurones.
Calcium dependence of open and shut interval distributions from calcium‐activated potassium channels in cultured rat muscle.
Authors: Magleby K L , Pallotta B S
Published: December 2014

The stochastic properties of single Ca‐activated K channels in excised patches of surface membrane from cultured rat muscle cells were studied using the patch‐clamp technique. The distribution of all open intervals was described by the sum of two exponential distributions of short and long mean open time, suggesting at least two major open‐channel states. Increasing the concentration of Ca at the inner membrane surface, [Ca]i, increased the mean duration of the long open distribution, while having little effect on the mean duration of the short open distribution. The frequency of openings to each distribution increased with [Ca]i. The rate of increase was a much steeper function of [Ca]i for openings in the long open distribution than for openings in the short open distribution; about 80% of the openings were to the long open distribution with 0.1 microM‐Cai, increasing to 97% with 1 microM‐Cai (+ 30 mV). These results suggest that openings in both open distributions are Ca‐dependent, with openings in the long open distribution requiring the binding of more Ca ions than openings in the short open distribution. The distribution of all shut intervals at 0.5 microM‐Cai and + 30 mV was described by the sum of three exponential distributions with mean durations of: 0.21 msec (short shut distribution), 1.90 msec (intermediate shut), and 44 msec (long shut). These results indicate that the channel typically enters at least three closed channel states during normal channel activity. In addition, a few longer shut intervals not accounted for by the above distributions suggested that there was a fourth infrequently occurring inactivated closed‐channel state. The mean duration of the distribution of long shut intervals decreased with a power of about 2 with increasing [Ca]i under conditions where most openings were to the long open state (+ 30 mV, 0.25‐1 microM‐Cai). This observation suggests that openings to the long open distribution typically require the binding of two or more Ca ions. The mean intermediate shut interval appeared to increase slightly with increasing [Ca]i while the mean short shut interval was relatively Cai‐independent. The percentage of all shut intervals that were short shut intervals increased with increasing [Ca]i while the percentage of long shut intervals decreased.(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of the canine popliteal node on the composition of lymph.
Authors: Knox P , Pflug J J
Published: December 2014

The composition of afferent lymph draining into the canine popliteal lymph node was compared with that of the efferent lymph leaving the node. Both the protein and cellular composition were studied. In twenty‐five greyhounds the protein concentration of efferent lymph was greater than that of afferent lymph collected from the same limb. Although the absolute level of protein varied greatly between dogs, in a particular animal there was a constant ratio between the protein content of afferent and efferent lymph. The concentration of protein in efferent lymph was approximately double that of afferent lymph. Chromatographic analysis of lymph and the use of radio‐iodinated canine albumin indicated that the reason for the increased level of protein in the efferent lymph is that the popliteal node concentrates the protein in afferent lymph. Afferent lymph contained less than 3 X 10(3) cells/ml; efferent lymph contained between 0.5 X 10(6) and 4.3 X 10(6) cells/ml, 98% of which were lymphocytes. In different dogs there was no correlation between efferent lymphocyte density and afferent or efferent protein concentration; however, when an afferent lymphatic was perfused with solutions of different protein concentration, the lymphocyte number in the efferent fluid became greater as protein concentration in the afferent perfusate was increased. The concentrating effect of the node is discussed in terms of its significance to both fluid balance and immunological surveillance.
Effect of changes in intra‐ and extracellular sodium on the inward (anomalous) rectification in salamander photoreceptors.
Authors: Bader C R , Bertrand D
Published: December 2014

Solitary rod inner segments were obtained by enzymic dissociation of the tiger salamander retina. Ih, an inward current activated by membrane hyperpolarization, was studied using the single‐pipette voltage‐clamp technique with patch pipettes. In order to investigate Ih in isolation from voltage‐dependent potassium and calcium currents, it was necessary to superfuse with a solution containing TEA and cobalt. When the solution in the patch pipette contained 45 mM‐KCl and 50 mM‐NaCl, the characteristics of Ih were indistinguishable from those previously described with fine‐tip micro‐electrodes: the reversal potential was near‐30 mV and Ih was blocked by extracellular caesium and enhanced by an increase in the extracellular potassium concentration. The increase in Ih observed when the extracellular potassium concentration is raised is due to an increase in conductance and in driving force. Replacement of sodium in the patch pipette with choline caused a 15 mV displacement of the reversal potential for Ih in the depolarized direction. When using sodium‐free patch pipettes, replacement of extracellular sodium displaced the reversal potential for Ih to ‐74 mV, a value in the range of the potassium equilibrium potential in solitary inner segments. Intracellular or intra‐ and extracellular sodium substitution affected neither the activation range of Ih nor the maximum conductance. From points 3‐6 it can be concluded that Ih is carried mainly, if not exclusively, by sodium and potassium and that the channel responsible for Ih is insensitive to modifications of the intra‐ or extracellular sodium concentration. The results of long‐term hyperpolarization, of partial block with caesium and of total sodium substitution are consistent with sodium and potassium permeating the same type of channel.
Control of sarcomere length in skinned muscle fibres of Rana temporaria during mechanical transients.
Authors: Goldman Y E , Simmons R M
Published: December 2014

A new technique is described for high‐speed measurement of striation spacing of single skinned muscle fibres. A galvanometer mirror directs helium‐neon laser light on to the muscle fibre at a variable angle. Light diffracted by the cross‐striations is collected by a position‐sensitive photodetector. The incident angle necessary to centre the diffracted light beam on to the photodetector is related to sarcomere length. The instrument was tested by comparison with measurements obtained with a compound microscope. Discrepancies of several nanometers per half sarcomere were observed between these two methods. When the incident angle of the laser beam was varied sinusoidally about its mean position the magnitude of the discrepancy was reduced. During steady passive shortening of the muscle fibres the output of the diffraction instrument often displayed pauses and brief periods of rapid shortening. These irregularities were eliminated by averaging the sarcomere length output over a range of illumination angles by oscillating the incident angle of the laser beam. The results suggest that at the spatial resolution of several nanometers per half sarcomere, volume diffraction effects can cause the apparent sarcomere length measured from the angle of coherent light diffraction to differ from the mean striation spacing. With incident‐angle oscillation the time and spatial resolution of the equipment were satisfactory for the sarcomere length signal to be fed back to a length controller for a 'sarcomere length clamp'. In active contractions, stiffness was closely related to steady developed tension at sub‐saturating calcium concentrations. Skinned fibres are less stiff than intact fibres at a given level of developed tension.
Synapse formation among developing sensory neurones from rat nodose ganglia grown in tissue culture.
Authors: Cooper E
Published: December 2014

Sensory neurones from new‐born rat nodose ganglia were grown in tissue culture, either with or without the ganglionic satellite cells, in order to investigate influences of satellite cells on sensory neurone development. To learn more about the post‐natal development of nodose ganglia in rats neuronal counts of the ganglion were made at three different developmental stages. There were no significant differences of neuronal number in nodose ganglia in new‐born rats, rats 3 weeks of age, and adult rats. Up to 60% of the neurones formed synapses with each other when they developed in culture without ganglion satellite cells. Pharmacological experiments indicated that the transmitter at these synapses was ACh and the post‐synaptic receptors were nicotinic. Neurones co‐cultured with satellite cells rarely formed functional synapses and most (85%) were not sensitive to ACh: 75% of neurones cultured without satellite cells were ACh sensitive. These results provide evidence that mammalian sensory neurones form synapses among each other in culture. The results also suggest that ganglionic satellite cells prevent functional synapses among these neurones from occurring, in part because the neurones do not express ACh sensitivity when co‐cultured with satellite cells.
Mechanisms of action of noradrenaline and carbachol on smooth muscle of guinea‐pig anterior mesenteric artery.
Authors: Bolton T B , Lang R J , Takewaki T
Published: December 2014

Membrane potential was recorded by micro‐electrode in segments of small (200‐500 microns o.d.) mesenteric arteries of guinea‐pig. Isotonic shortening was recorded in helical strips cut from these arteries. Raising the external potassium concentration, [K+]o, caused shortening and substantial depolarization. The threshold for contraction was about 30 mM which corresponded to a membrane potential of about ‐45 mV. Since high‐potassium contractions were abolished in calcium‐free solution it was suggested that they occur due to potential‐sensitive calcium channels opening positive to about ‐45 mV. Noradrenaline weakly depolarized the muscle and produced contractions resistant to calcium‐free conditions. It was suggested that noradrenaline contractions are mainly caused by mechanisms other than the opening of potential‐sensitive calcium channels, namely entry of calcium via other channels and release of stored calcium. Carbachol had no effect on basal tension but inhibited shortening by noradrenaline or by raising [K+]o. The inhibitory effect of carbachol on tension under various conditions was associated with hyperpolarization or depolarization in a range negative to ‐45 mV, or no effect on potential, so that modulation of the number of open potential‐sensitive calcium channels could not be evoked to explain its relaxant action. Removal or destruction of the endothelium by rubbing or by distilled water perfusion left tension responses to noradrenaline or raised [K+]o essentially unchanged. However, the inhibitory effect of carbachol on tension was attenuated and hyperpolarization of the resting artery was converted to a depolarization. It was concluded that carbachol has both a strong inhibitory and a weak excitatory effect on these vascular smooth muscle cells. Membrane potential changes are not essential to its inhibitory action but may, by closing potential‐sensitive calcium channels, sometimes reinforce it. Hyperpolarization by carbachol may be caused by a factor released by the action of carbachol on endothelial cells: in its absence carbachol may weakly depolarize but this alone is normally insufficient to generate tension.
Two‐component desensitization of nicotinic receptors induced by acetylcholine agonists in Lymnaea stagnalis neurones.
Authors: Andreev A A , Veprintsev B N , Vulfius C A
Published: December 2014

The kinetics of desensitization induced by different agonists of acetylcholine (ACh) as well as the kinetics of recovery from densensitization, have been studied using the voltage‐clamp technique in isolated, identified Lymnaea stagnalis neurones. Desensitization follows the sum of two exponentials: one fast and one slow. The time constant of the fast desensitization component (tau Ids) under ACh application is in the range of seconds at room temperature (18‐23 degrees C). It increases upon cooling (Q10 = 2.8 +/‐ 0.9), decreases with increasing ACh concentration and is independent of membrane voltage. The time constant of the slow component of densensitization (tau Ids) is in the range of tens of seconds. It decreases with increasing drug concentration and is weakly dependent upon temperature (Q10 = 1.3 +/‐ 0.4). The relative amplitude of the fast component, estimated by back extrapolation to the position of the peak current, increases with agonist concentration and decreases upon cooling. Recovery from desensitization follows the sum of two exponentials with time constants (tau Ir and tau IIr) of the order of seconds and minutes, respectively. Cooling prolongs the slow component (Q10 of tau IIr is approx. 3) and reduces its contribution during recovery. A comparison of the desensitization induced by various agonists indicates that for the small monoquaternary agonists the onset and recovery of desensitization resemble the onset and recovery observed with ACh. For more bulky agonists, like ethoxysebacylcholine, sebacylcholine and suberylcholine, the decay of the response during prolonged application of the agonist may involve an additional blocking process.
Calcium channel inactivation in frog (Rana pipiens and Rana moctezuma) skeletal muscle fibres.
Authors: Cota G , Nicola Siri L , Stefani E
Published: December 2014

The decay of the Ca2+ current (ICa) during a maintained depolarization was studied in intact twitch skeletal muscle fibres of Rana pipiens and Rana moctezuma with the three‐micro‐electrode voltage‐clamp technique. ICa was recorded at 23 degrees C, after blocking K+ currents, in TEA methanesulphonate saline with 10 mM‐Ca2+ made hypertonic by adding 350 mM‐sucrose. In two‐pulse experiments, ICa during the test pulse was reduced to about 80% (R. pipiens) or 50% (R. moctezuma) of the control value, without any detectable inward ICa during 7 s conditioning pre‐pulses. The experimental points of the steady‐state inactivation curve (h infinity) were fitted to h infinity = (1 + exp [Em ‐ Vh)/kh]‐1, where Em is the membrane potential and with Vh = ‐33 +/‐ 3 mV and kh = 6 +/‐ 1 mV for R. pipiens, and Vh = ‐44 +/‐ 3 mV and kh = 9.5 +/‐ 1.0 mV for R. moctezuma. The rate constant of decay for inactivated currents (range ‐8 to ‐47 mA cm‐3) and for control currents (range ‐23 to ‐62 mA cm‐3), was independent of ICa amplitude. The average rate constant of decay at 0 mV was 1.18 +/‐ 0.02 s‐1 (66). These results indicate that in intact fibres under hypertonic solution ICa decay can be explained by a voltage‐dependent inactivation process and not by depletion of tubular Ca2+. The absence of depletion could be due to a large fractional tubular volume or to the presence of a Ca2+ pump in the tubular system.
Low‐calcium field burst discharges of CA1 pyramidal neurones in rat hippocampal slices.
Authors: Haas H L , Jefferys J G
Published: December 2014

Incubation of rat hippocampal slices in solutions containing low Ca2+ and increased Mg2+ rapidly blocked synaptic responses and increased spontaneous firing of all the principal neurones. More remarkably, a rhythmic and synchronous bursting discharge developed, which was restricted to the CA1 population of pyramidal neurones. These 'field bursts' or 'spreading excitation' were rapidly abolished by restoring the Ca2+ to 2 mM, by increasing the Mg2+ to 6 mM or by decreasing K+ from 6 to 3 mM. The CA1 pyramidal cells depolarized after the change to the low‐Ca2+ solution by about 10‐20 mV. Individual field bursts were associated with a further depolarization of 10‐12 mV surmounted by a burst of action potentials at about 20/s. This transient depolarization shift, recorded extracellularly as a negative field, could be attributed to the increase of [K+]o during the bursts, reaching 9‐10 mM as measured by ion‐sensitive electrodes. The bursts were followed by a hyperpolarization, seen extracellularly as a small soma‐positive field, which was attributed to an electrogenic pump and/or a Ca2+‐activated K+ conductance. Stimulation of the tightly packed pyramidal cell axons in the alveus elicited a train of population spikes, instead of the single spike normally seen, and could trigger a full field burst. Recordings of the alvear tract volley suggested that the repeated spikes arose within the pyramidal cells. Multiple recordings from CA1 revealed that field bursts usually, but by no means always, started near the caudal (subicular) end of the area. They spread through the cell layer at 0.04‐0.12 m/s. The most rapid propagation was seen when the bursts had an abrupt onset; slower propagation (1‐10 mm/s) occurred when the bursts started gradually, which generally was the case near the sites of burst initiation and termination. Usually the action potentials within each burst were synchronized into population spikes which spread across CA1 at 0.04‐0.15 m/s. The site of initiation and the extent of the spread of these population spikes varied during each burst, as did their amplitude. The degree of spike synchronization was enhanced by various treatments expected to increase neuronal excitability. Measurements of transmembrane potential during the burst confirmed the role in the generation of population spikes of ephaptic or field interactions between the pyramidal cells. It is proposed that the increased firing of all neurones is due to the block of tonic inhibition, depression of after‐hyperpolarization and to increased membrane excitability.(ABSTRACT TRUNCATED AT 400 WORDS)
A comparison of spontaneous and nerve‐mediated activity in bladder muscle from man, pig and rabbit.
Authors: Sibley G N
Published: December 2014

Spontaneous activity in bladder muscle strips from man, pig and rabbit has been compared using an in vitro superfusion technique. Field stimulation was used to study nerve‐mediated activity. Bladder muscle strips from all areas of the rabbit bladder displayed rhythmic spontaneous activity. Spontaneous activity was regularly present in strips from the trigone region in man and pig, but was present in only 18 and 19% respectively of strips from the dome of the bladder. Strength‐duration curves in the presence of tetrodotoxin (10(‐7) g/ml) were constructed. The 'chronaxie' of the muscle was found to be considerably shorter than that of other smooth muscles, ranging from 6.1 ms in the rabbit to 12.9 ms in man. Frequency‐response curves were constructed using trains of stimuli. The responses were not antagonized by hexamethonium (10(‐4) M), but were markedly inhibited by tetrodotoxin (10(‐7) g/ml), indicating that the responses were mediated by excitation of post‐ganglionic nerves. Physostigmine (10(‐7)‐5 X 10(‐6) M) produced a dose‐related increase in the contractile response to field stimulation in all three species. Atropine (10(‐8)‐10(‐6) M) produced an inhibition of the contractile response, but the maximum degree of inhibition differed considerably between the species. In the rabbit, 58% of the control response was attained, whilst in the pig this was only 22%. Atropine completely abolished nerve‐mediated contractions in human bladder muscle. Phentolmaine (10(‐7)‐2.5 X 10(‐7) M) had no significant effect on the frequency‐response curve in any of the three species, and did not depress the atropine‐resistant component in rabbit and pig. It is concluded that nerve‐mediated activity in human bladder muscle is exclusively cholinergic, in contrast to most other mammals studied in which there is a significant non‐cholinergic component. The finding of a shorter chronaxie in bladder muscle than in other smooth muscles suggests important differences in its physiological properties that merit further investigation.
Release of neuropeptide Y in response to splanchnic nerve stimulation in the conscious calf.
Authors: Allen J M , Bircham P M , Bloom S R , Edwards A V
Published: December 2014

Plasma concentrations of neuropeptide Y were determined by means of a specific radioimmunoassay in the conscious calf. Significantly higher concentrations were found in the adrenal venous effluent (102 +/‐ 34 pmol/l) compared to systemic arterial plasma (11 +/‐ 7 pmol/l). Stimulation of the splanchnic nerves at 40 Hz in bursts for 1 s at 10 s intervals resulted in a slow sustained rise in plasma neuropeptide Y in both adrenal (peak 1124 +/‐ 217 pmol/l and peripheral (peak 771 +/‐ 182 pmol/l) samples. Experiments performed in adrenalectomized calves produced a closely similar release of neuropeptide Y when the nerves were stimulated intermittently in the same pattern and under the same conditions. Stimulation of the splanchnic nerves at 4 Hz continuously resulted in a smaller response. Pre‐treatment with hexamethonium completely abolished the rise in plasma neuropeptide Y concentrations.
Magnocellular red nucleus activity during different types of limb movement in the macaque monkey.
Authors: Gibson A R , Houk J C , Kohlerman N J
Published: December 2014

Three hundred and thirty‐four neurones located in the magnocellular division of red nucleus (r.n.m.) were studied in three alert macaque monkeys. These cells had low discharge rates at rest and produced high frequency bursts during movement. Single cells were selectively active for movement of one body part, and a motor somatotopy was evident. From dorsal to ventral we encountered cells related to movements of the face, contralateral upper limb, contralateral lower limb and, in one case, the tail. Free‐form tests indicated that 76% of upper‐limb cells were preferentially related to hand and finger movements, and 84% of lower limb cells were preferentially related to foot and toe movements. Quantitative tests of movement relations were based on depths of modulation in discharge rate recorded while the monkeys operated several devices that served as manipulanda in a tracking task; each device elicited a different movement. We conducted 220 tests on eighty‐one cells using eleven devices. The modulation in discharge rate exceeded a 50 pulses/s criterion level in seventy‐nine cases; eleven were well related to proximal movements, twenty‐two to movements of the digits and forty‐six to a co‐ordinated hand movement elicited by a device called the twister. Both unidirectional and bidirectional patterns of bursting were frequent. A few cells showed reciprocal patterns consisting of a large increase in rate for one direction of movement and a small decrease for the other. The bursts in discharge preceded movement onset (97% of 132 cases) by an average of 135 ms. Electromyographic activity in forearm muscles preceded movement by about 55 ms. In some cases we recorded from a single cell while the monkey operated two, three or four devices. Depth of modulation on the twister device was twice that on a proximal device in nine cases whereas one case showed a proximal device preference; five cases showed overlap. Comparison between twister and digits yielded ten cases of twister preference, four of digit preference and twenty cases of overlap. A directional preference was found for ten out of eleven cells responsive during active movement restricted to the metacarpo‐phalangeal joints, and in all cases the preferred direction was extension. Responses to natural somatosensory stimulation were weak or absent for the majority of cells. When present, sensory fields were confined to the same limb but were frequently out of register with motor fields.(ABSTRACT TRUNCATED AT 400 WORDS)
Simultaneous monitoring of electrical and secretory activity in peptidergic neurosecretory terminals of the crab.
Authors: Stuenkel E L
Published: December 2014

Intracellularly recorded responses of peptidergic neurosecretory terminals and somata were correlated with their secretory responsiveness to elevation of the external K concentration ([K+]o). The experiments were performed on in vitro X‐organ sinus gland neurosecretory systems from the eyestalk of the crab Cardisoma carnifex. Elevated‐K‐evoked release was followed in preparations exposed to a pulse‐chase radiolabelling regime. The release of [3H]leucine incorporated into neurosecretory peptides could be followed by collecting the separate perfusates of the somata and terminal regions. Elevation of the [K+]o evoked terminal depolarization, an increase in impulse firing frequency and a decrease (50%) in terminal input resistance. Impulse firing ceased (in ca. 2 min) as depolarization reached a sustained maximum level (‐17.6 +/‐ 3.57 mV, n = 9, absolute potential). The terminal depolarization and decreased input resistance were maintained throughout the period of elevated‐K treatment. Release from the terminal region of incorporated 3H label paralleled the simultaneously monitored terminal depolarization. Maintained exposure to elevated‐K saline was accompanied by sustained high levels of 3H release continuing beyond the loss of regenerative membrane responses. Release declined with a half‐time of 47.1 +/‐ 13.5 min (n = 7). In contrast, terminal release of red pigment concentrating hormone (RPCH) was transitory, reaching peak values and declining to base line within a 10 min period. Removal of external Ca or addition of the Ca antagonists, Cd or Mn, blocked the stimulated 3H release. Addition of Cd or Mn, prior to or during an elevated‐K‐evoked 3H release produced a reversible suppression of the secretory response. Stimulation in the absence of external Na, under normal Ca conditions, resulted in a normal secretory response. The amplitude and duration of the elevated‐K‐evoked terminal depolarization was unaffected by nominally Ca‐ or Na‐free saline or addition of Cd. Cd (1mM) and Na‐free saline were effective in removing a Ca and Na component, respectively, of spontaneous or evoked terminal action potentials. Somatic responses to direct application of elevated K exhibited membrane depolarization and an accompanying increase in impulse firing. In contrast to recordings from the terminals in elevated K, fast regenerative potentials, electrotonically conducted from the distal axon, persisted in the somatic records. Somatic secretion of RPCH was below detectable limits (less than 0.2 fmol min‐1). 3H release was an order of magnitude less than from the terminal region under similar conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechano‐electrical transduction currents in isolated vestibular hair cells of the chick.
Authors: Ohmori H
Published: December 2014

Properties of a mechano‐electrical transduction channel were studied in enzymatically dissociated chick vestibular hair cells by using a whole‐cell recording variation of the patch voltage‐clamp technique. The apical hair bundle was stimulated by a glass rod which moved along a one‐dimensional axis when stimulated by either a triangular or a trapezoidal command voltage. The motion of the glass rod was monitored optically using a photodiode. In response to triangular stimuli, the hair cell generated a current of triangular wave form with occasional step‐like spiky or zigzag‐appearing events. Control experiments confirmed that the current was generated only when the hair bundle was displaced towards the tallest stereocilium. The mechano‐sensitive current was blocked by streptomycin and by neomycin. The blockage by streptomycin was clearly voltage dependent: the reduction of the current became larger with hyperpolarization of the membrane. This suggests that the positively charged antibiotic molecules plug the mechanically gated channels. From the evidence presented in 3 and 4 above, the mechano‐sensitive current recorded here was identified as the mechano‐electrical transduction (m‐e.t.) current. The permeability of the m‐e.t. channel to various monovalent cations was determined from reversal potential measurements. Since a CsCl‐EGTA intracellular medium was used, all the permeabilities were calculated relative to PCs. The sequence of permeabilities was Li greater than Na greater than or equal to K greater than or equal to Rb greater than Cs greater than choline greater than TMA greater than TEA. External Ca ions were indispensable for the recording of transduction current and Sr ions could replace Ca ions without loss of the transduction activity. The minimum [Ca]o for stable generation of the m‐e.t. current was 20 microM in Cs saline. The addition of 50‐200 microM‐Ca to the isotonic Ba saline could maintain the m‐e.t. current. The m‐e.t. current was observed in isotonic Ca and in Sr salines. Isotonic Ba, Mg and Mn salines were enriched with 1‐2 mM‐Ca in order to generate the m‐e.t. current. The permeabilities of the divalent cations relative to Cs were calculated from the reversal potentials, and the sequence of permeabilities among divalent cations was Ca greater than Sr greater than Ba greater than Mn greater than Mg. Step‐like m‐e.t. currents were observed in Cs saline. The smallest step amplitude with clear resolution had a conductance of 49.7 +/‐ 4.5 pS (mean +/‐ S.D., n = 7 cells). This is likely to be an elementary m‐e.t. channel conductance.(ABSTRACT TRUNCATED AT 400 WORDS)
Two types of calcium channels in the somatic membrane of new‐born rat dorsal root ganglion neurones.
Authors: Fedulova S A , Kostyuk P G , Veselovsky N S
Published: December 2014

Ca2+ inward currents evoked by membrane depolarization have been studied by the intracellular dialysis technique in the somatic membrane of isolated dorsal root ganglion neurones of new‐born rats. In about 20% of the investigated cells a hump has been detected on the descending branch of the current‐voltage curve, indicating the presence of two populations of Ca2+ channels differing in their potential‐dependent characteristics. An initial less regular component of the Ca2+ current was activated at membrane potentials from ‐75 to ‐70 mV. Its amplitude reached 0.2‐0.9 nA at 14.6 mM‐extracellular Ca2+. The activation kinetics of this component could be approximated by the Hodgkin‐Huxley equation using the square of the m variable. tau m varied in the range from 8 to 1 ms at potentials between ‐60 and ‐25 mV ('fast' Ca2+ current). The second component of the Ca2+ current was activated at membrane depolarizations to between ‐55 and ‐50 mV. It could be recorded in all cells investigated and reached a maximum value of 1‐7 nA at the same extracellular Ca2+ concentration. This component decreased rapidly during cell dialysis with saline solutions. The decrease could be slowed down by cooling and accelerated by warming the extracellular solution. Intracellular introduction of 3',5'‐cAMP together with ATP and Mg2+ not only prevented the decrease but often restored the maximal current amplitude to its initial level. The activation kinetics of this component could also be approximated by a square function, tau m being in the range 16‐2.5 ms at membrane potentials between ‐20 and +3 mV ('slow' Ca2+ current). The fast Ca2+ current inactivated exponentially at sustained depolarizations in a potential‐dependent manner, tau h varying from 76 to 35 ms at potentials between ‐50 and ‐30 mV. The inactivation of the slow Ca2+ current studied in double‐pulse experiments was current‐dependent and developed very slowly (time constant of several hundreds of milliseconds). It slowed down even more at low temperature or after substitution of Ba2+ for Ca2+ in the extracellular solution. Both currents could also be carried by Ba2+ and Sr2+, although the ion‐selecting properties of the two types of channels showed quantitative differences. Specific blockers of Ca2+ channels (Co2+, Mn2+, Cd2+, Ni2+ or verapamil) exerted similar effects on them. The existence of metabolically dependent and metabolically independent Ca2+ channels in the neuronal membrane and their possible functional role are discussed.
Respiratory modulation of muscle sympathetic and vagal cardiac outflow in man.
Authors: Eckberg D L , Nerhed C , Wallin B G
Published: December 2014

We studied the influence of respiration on muscle sympathetic and cardiac vagal activities in twenty conscious, healthy young adult subjects. Efferent post‐ganglionic muscle sympathetic activity was measured directly with electrodes inserted percutaneously into a peroneal nerve, and vagal cardiac activity was measured indirectly from electrocardiographic changes of heart period. Muscle sympathetic activity waxed and waned with respiration; maximum activity occurred at end‐expiration and minimum activity occurred at end‐inspiration. Voluntary control of breathing did not alter the time course or magnitude of muscle sympathetic outflow. Spectral analyses showed that respiratory periodicities were present in sympathetic and vagal records. Average power at frequencies below respiratory frequencies exceeded or equalled that at respiratory frequencies in both muscle sympathetic and vagal cardiac records. A cardiac periodicity was present and conspicuous in muscle sympathetic recordings in all but one subject. Diastolic arterial pressure increased during inspiration and decreased during expiration. Heart period and muscle sympathetic activity paralleled each other and were related reciprocally to changes of diastolic pressure. Brief reductions of carotid baroreceptor afferent traffic provoked by neck pressure were more effective in increasing sympathetic activity in expiration than inspiration. We conclude that quiet respiration is associated with parallel phasic changes in activity of medullary vagal cardiac and spinal muscle sympathetic motonuclei in man; spontaneous activity and susceptibility to excitation or inhibition by autonomic inputs are greater in expiration than inspiration. Substantial power is present in both muscle sympathetic and cardiac vagal recordings at frequencies below respiratory frequencies.