bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic properties of NMDA receptor‐mediated synaptic currents in rat hippocampal pyramidal cells versus interneurones.
Authors: Perouansky M , Yaari Y
Published: December 2014

1. Whole‐cell tight‐seal recordings were obtained from visually identified pyramidal cells (PCs) and interneurones (INs) in the CA1 field of thin hippocampal slices from 13‐ to 23‐day‐old rats. The INs sampled were classified according to their location either in the molecular layer (M‐INs) or in the oriens layer and alveus (OA‐INs). PCs and INs differed in their mode of firing when depolarized by a prolonged current pulse. Whereas PCs fired a single action potential, most INs responded with non‐accommodating high frequency spike firing. 2. In the presence of 1 microM tetrodotoxin (TTX), bath application of either 50 microM L‐glutamate with 10 microM 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) or 2.5 microM N‐methyl‐D‐aspartate (NMDA), induced a similar conductance increase in PCs and INs that was completely blocked by 200 microM DL‐2‐amino‐5‐phosphonovaleric acid (APV). The NMDA receptor‐mediated currents reversed around 4 mV and exhibited an area of negative slope conductance at potentials more negative than ‐20 to ‐30 mV in the presence of 1‐2 mM Mg2+. 3. Dual‐component excitatory postsynaptic currents (EPSCs) were evoked in PCs and INs by stimulating afferent fibres close to the neurone. The NMDA receptor‐mediated component of the EPSCs (NMDA EPSC) was isolated by adding 10 microM CNQX to block non‐NMDA receptors. The NMDA EPSCs in all cell types reversed around 1.5 mV and were abolished by 50 microM APV. 4. In saline containing 1 mM Mg2+, the peak current‐voltage (I‐V) relationship of NMDA EPSCs in PCs and INs showed an area of negative slope conductance at voltages more negative than ‐20 to ‐30 mV. In nominally Mg(2+)‐free saline, the peak I‐V relation was linear over a much wider voltage range in both cell types. 5. The 10‐90% rise times of NMDA EPSCs at ‐60 mV ranged from 4.5 to 16 ms in PCs (mean 8.7 ms; n = 25) and in M‐INs (mean 9.1 ms; n = 10). Their decay could be best fitted with the sum of two exponentials. The decay of NMDA EPSCs in PCs was significantly slower than that recorded in INs. The average fast (tau f) and slow (tau s) time constants of decay were, respectively, 66.5 and 353.9 ms in PCs, and 34.4 and 212.5 ms in M‐INs.(ABSTRACT TRUNCATED AT 400 WORDS)
Inward sodium current involvement in regenerative bursting activity of rat magnocellular supraoptic neurones in vitro.
Authors: Inenaga K , Nagatomo T , Kannan H , Yamashita H
Published: December 2014

1. The rat hypothalamic slice preparation was used to investigate the involvement of inward Na+ currents as well as inward Ca2+ currents in the generation of bursting activity by supraoptic (SON) neurones. Intracellular records were made from thirty‐two SON neurones which showed regenerative bursting activity. The bursting activity consisted of spontaneous, intermittent bursts of action potentials with subsequent silent periods. During the bursts, plateau potentials on which action potentials were superimposed were frequently observed. 2. Perfusion of a low‐Na+ medium, a tetrodotoxin (TTX)‐containing medium or a Ca(2+)‐free medium suppressed the regenerative bursting activity. 3. Addition of 3‐10 microM veratridine to Ca(2+)‐free medium elicited regenerative bursting activity and spontaneous plateau potentials. The veratridine‐induced regenerative bursting activity and plateau potentials were blocked by 1 microM TTX. Addition of 5 mM TEA allowed regenerative bursting activity to persist in Ca(2+)‐free medium. 4. These results suggest that TTX‐sensitive Na+ inward currents as well as Ca2+ inward currents contribute to the generation of bursting activity in rat SON cells.
Behaviour of short and long latency reflexes in fatigued human muscles.
Authors: Duchateau J , Hainaut K
Published: December 2014

1. The human abductor pollicis brevis (APB) and first dorsal interosseus (FDI) were fatigued by sustained maximal voluntary contractions and, in the case of the APB also by electrically induced (30 Hz) contractions, until the loss of force reached 50% of control. The short latency or Hoffmann reflex (H reflex) and the long latency reflex (LLR) were evoked during weak voluntary contractions by the electrical stimulation of the median nerve at the wrist in control, during and after the fatigue experiments. 2. As compared to control, the normalized H reflex amplitude in the two fatigue modalities was found to have decreased by 30% without any significant change in the LLR. This finding and the observation that the LLR was enhanced by 46% in simultaneous recordings, in which the APB remained at rest during FDI fatigue, could be explained by a stronger descending fatigue‐induced central drive which spreads to neighbouring non‐fatigued muscles. 3. A comparison of the H reflex and the LLR behaviour during fatigue indicates that motoneurone activation threshold is not affected but that changes in peripheral drive are present, which possibly induce presynaptic inhibition of Ia afferents and/or inhibition of interneurones in the oligosynaptic pathways. Our observation of a rather slow time course for the H reflex decrease during fatigue supports the point of view that these inhibitions are activated by metabolic and/or chemical changes in the fatigued muscle. 4. It is concluded from the results of this study that muscle fatigue induces an enhanced descending supraspinal drive which compensates for a loss of excitation from the peripheral afferents on motoneurones.
Changes in the short‐ and long‐latency stretch reflex components of the triceps surae muscle during ischaemia in man.
Authors: Fellows S J , Dömges F , Töpper R , Thilmann A F , Noth J
Published: December 2014

1. In order to establish the afferent source responsible for the M1 and M2 stretch reflex components of the voluntarily activated human triceps surae muscle, mechanical reflex testing was applied before and during ischaemic blockade of the lower limb. This procedure is known to affect large, fast conducting afferent fibres earliest, specifically Ia afferents arising from muscle spindle afferents. 2. It was found that both the M1 and M2 components were eliminated at the same time, at a point when the P40 peak in the somatosensory evoked potential, produced from stimulation of fast conducting peripheral afferents, was also abolished. This evidence indicates that both reflex components are mediated by information carried by muscle spindle Ia afferents. 3. The M1 component was selectively increased in the early stages of ischaemia. The M2 response did not increase during this period, but showed a tendency to reduce in amplitude. This effect may arise as the result of increased recruitment of motor units in the M1 component reducing the number of units available for activation in the M2 response. 4. These results do not support the view that the M2 reflex component of the triceps surae muscle is mediated by secondary afferent information, but indicate, rather, that both the M1 and M2 components are mediated by Ia afferent information acting on spinal pathways.
Active forearm blood flow adjustments to handgrip exercise in young and older healthy men.
Authors: Jasperse J L , Seals D R , Callister R
Published: December 2014

1. Our purpose was to test the hypothesis that ageing impairs the active muscle hyperaemia consequent to dynamic exercise in humans. 2. Eleven young (19‐29 years) and eleven older (60‐74 years) healthy, non‐obese men with similar chronic physical activity levels and forearm size performed two protocols of dynamic handgrip exercise: (a) brief (1 min), incremental loads to exhaustion, and (b) sustained (8 min), submaximal loads. Active forearm blood flow (FBF) was measured at rest and during a brief period of relaxation at the end of each minute of exercise. Arterial blood pressure was recorded to calculate active forearm vascular conductance (FVC). Sustained forearm ischaemia plus handgrip was used to elicit a peak forearm vasodilatatory response. 3. There were no differences in pre‐exercise levels of any variable between the young and older men. During exercise, ratings of perceived effort, the peak workload attained, and the ability to sustain submaximal workloads were all similar for the two groups. 4. During brief exercise, both submaximal and peak levels of FBF were similar in the two groups; however, the peak increases in FVC were greater in the older men. During sustained exercise, FBF and FVC were not different in the two groups at the lowest loads, but the increases became relatively greater in the older men with increasing workloads. 5. Peak levels of FBF and FVC in response to the peak vasodilatatory stimulus were similar in the young and older men. 6. These findings fail to support the postulate that ageing results in impaired active muscle hyperaemia and vasodilatation during small‐muscle dynamic exercise.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of single hyperpolarization‐activated channels (i(f)) by cAMP in the rabbit sino‐atrial node.
Authors: DiFrancesco D , Mangoni M
Published: December 2014

1. The hyperpolarization‐activated ‘pacemaker’ current (i(f)) was recorded in inside‐out patches excised from rabbit sino‐atrial (SA) node cell membranes. 2. Single‐channel activity could be resolved in patches containing only a few channels; the voltage dependence of single‐channel size and single‐channel conductance (0.97 pS) were similar to those measured previously in cell‐attached conditions. 3. Perfusion of the intracellular side of the patch membrane with 10 microM cAMP facilitated the opening of single i(f) channels on hyperpolarization. The cAMP‐induced i(f) current activation occurred without modification of the single‐channel conductance. 4. Modification by cAMP of the probability of channel opening was investigated with respect to the latency to first opening during hyperpolarization and in patches containing a large number of channels (macro‐patches). First‐latency histograms showed that cAMP shifts the probability curve of first openings to shorter times, in agreement with a cAMP‐induced facilitation of channel opening. In macro‐patches, measurement of the voltage dependence of the open probability by a slow voltage ramp protocol showed that cAMP shifts the probability curve to more positive voltages without modifying its shape. 5. In cell‐free macro‐patches the normalized open probability curve in control solutions was centred around ‐121.9 mV, a voltage some 30 mV more negative than in cell‐attached macro‐patches. Negative shifting of the curve after patch excision could only partly be explained by the removal of intracellular cAMP, and progressed with time during the ramp protocol, suggesting the presence of a run‐down process independent from cAMP.
Mechanisms of GABA and glycine depolarization‐induced calcium transients in rat dorsal horn neurons.
Authors: Reichling D B , Kyrozis A , Wang J , MacDermott A B
Published: December 2014

1. The mechanisms and effects of GABA‐ and glycine‐evoked depolarization were studied in cultured rat dorsal horn neurons using indo‐1 recordings of [Ca2+]i and patch clamp recordings in conventional whole‐cell or perforated‐patch mode. 2. Application of GABA to unclamped neurons caused [Ca2+]i increases that were dose dependent and exhibited GABAA receptor pharmacology. Calcium entered the neurons via high‐threshold voltage‐gated calcium channels (conotoxin and nimodipine sensitive). 3. In perforated‐patch recordings employing cation‐selective ionophores, GABAA receptor activation depolarized 123 of 132 cells to membrane potentials as depolarized as ‐33 mV (mean ‐50 mV in all 132 cells, +12 mV above resting potential). The ionic basis of the depolarization was determined by extracellular ion substitution; increased anionic conductance could account fully for the results. 4. Glycine, acting at a strychnine‐sensitive receptor, also caused Ca2+ entry into these neurons through voltage‐gated Ca2+ channels. Glycine and GABA both evoked [Ca2+]i responses in the same cells and the responses were highly correlated in amplitude. Glycine also depolarized all five cells tested with perforated recording. Each of the five cells was also depolarized by muscimol to a value similar to that obtained for glycine. 5. Both the depolarization and the increases in [Ca2+]i caused by GABA and glycine could potentially play a role in processes of development and differentiation and sensory transmission in the spinal cord dorsal horn.
Carotid sinus nerve section and the increase in plasma cortisol during acute hypoxia in fetal sheep.
Authors: Giussani D A , McGarrigle H H , Moore P J , Bennet L , Spencer J A , Hanson M A
Published: December 2014

1. We studied the effects of acute isocapnic hypoxia on plasma concentrations of adrenocorticotrophic hormone (ACTH) and cortisol in sixteen sheep fetuses at 118‐125 days of gestation (term is 147 days). Eight fetuses had their carotid sinus nerves cut (denervation); the remaining eight had these nerves left intact. 2. There were no differences in the plasma concentrations of ACTH or cortisol between intact and denervated fetuses during normoxia. 3. Whilst plasma cortisol increased in early (after 15 min) and late (after 45 min) hypoxia in intact fetuses, the rise in cortisol in denervated fetuses was delayed, increasing significantly only by late hypoxia. 4. In contrast, plasma ACTH concentrations were increased in early and late hypoxia in both intact and denervated fetuses. The rise was smaller in denervated fetuses, but was not significantly different from that in intact fetuses. 5. Our results indicate that, in the sheep fetus, carotid sinus nerve section delays the rise in plasma cortisol in response to acute hypoxia without affecting the ACTH response. Further work is needed to establish the mechanism underlying this effect of denervation.
The influence of single monkey cortico‐motoneuronal cells at different levels of activity in target muscles.
Authors: Bennett K M , Lemon R N
Published: December 2014

1. This study assessed the facilitation by cortico‐motoneuronal (CM) cells of hand and forearm muscles at different levels of EMG activity. 2. Twenty‐three CM cells were recorded in six hemispheres of four trained monkeys. CM cells were identified by the presence of post‐spike facilitation (PSF) in spike‐triggered averages (STAs) of their target muscles. Cell and muscle activity was recorded during performance of a low force (0.2‐1.5 N) precision grip task between the index finger and thumb. The hold periods of this task lasted 1‐1.5 s and provided segments of steady EMG activity. 3. The discharge activity of each CM cell, and the amplitude of the PSF produced in one or two target muscles, were compared across two to six different levels of EMG activity during the hold periods. 4. Of the forty‐two CM cell‐muscle combinations tested, twenty (48%) showed a significant increase in CM cell discharge rate with increased target muscle EMG activity (P < 0.001); three (7%) showed significant negative correlation; and no correlation was found for nineteen combinations (45%). 5. From a low to a high level of EMG activity (0.3‐8.65% of the maximum EMG activity recorded), the absolute amount of facilitation produced by each CM cell increased by a factor of 1.2‐32 (median value 3.7). This increase in facilitation occurred irrespective of the presence or absence of correlation between CM cell discharge rate and target muscle activity. 6. For thirty cell‐muscle combinations in which a significant PSF could be measured at more than one level of EMG activity, the relative degree of facilitation remained constant in nine, increased in thirteen and decreased in seven combinations. In some cases saturation effects were evident. For ten combinations PSF was observed at high but not at low levels of EMG activity. 7. The changes in PSF amplitude with level of EMG activity were also present in STAs compiled from only those spikes with long interspike intervals (20‐25 ms or greater). The results suggested that spikes with short interspike intervals did not make a significant contribution to the increase in PSF amplitude observed at the higher levels of EMG activity. 8. The changes in PSF amplitude with target muscle activity are probably explained best by changes at the spinal motoneuronal level, which set the response to the CM input. These changes may also reflect differences in the strength of synaptic connectivity made by a CM cell within the motoneurone pool of the target muscle.
Task‐dependent reflex responses and movement illusions evoked by galvanic vestibular stimulation in standing humans.
Authors: Fitzpatrick R , Burke D , Gandevia S C
Published: December 2014

1. To identify the vestibular contribution to human standing, responses in leg muscles evoked by galvanic vestibular stimulation were studied. Step impulses of current were applied between the mastoid processes of normal subjects and the effects on the soleus and tibialis anterior electromyograms (EMGs), ankle torque, and body sway were identified by post‐stimulus averaging. The responses were measured when subjects stood on a stable platform or on an unstable platform and the effects of eye closure were also assessed. Responses were also recorded during voluntary contraction of the leg muscles and when subjects balanced a load equivalent to their own body in a situation where vestibular postural reflexes would not be useful. 2. At a mean post‐stimulus latency of 56 ms, there were reciprocal changes in soleus and tibialis anterior muscle activity followed, at 105 ms, by larger responses of opposite sign. These were termed the short‐ and middle‐latency responses, respectively. Both responses increased with stimulus intensity, but the short‐latency response had a higher threshold. The early response had a similar latency to EMG responses evoked by rapid postural perturbations. Both responses were larger when the eyes were closed, but eye closure was associated with increased sway and EMG activity, and the responses were of similar magnitude when scaled to background EMG level. 3. Both short‐ and middle‐latency EMG responses in soleus and tibialis anterior muscles produced small transient postural sways. The transient changes in EMG activity were followed by a larger prolonged sway which was not attributable to the activity in these muscles but rather to reflex or volitional adjustments to movements at other body segments. When subjects were prevented from swaying, the galvanic stimulus produced illusory movements in the opposite direction to the sway evoked when standing, and it is possible that the prolonged sway is a reaction to the illusion of sway. 4. The short‐ and middle‐latency responses were modified during different postural tasks according to the dependence on vestibular reflexes. When the support platform was unstable, the EMG responses to galvanic stimulation were larger. There were no vestibular‐evoked responses when seated subjects made voluntary contractions of the leg muscles or when they stood upright with the trunk supported, using the ankles to balance a body‐like load.(ABSTRACT TRUNCATED AT 400 WORDS)
Alpha 1‐adrenoceptors in rat dorsal raphe neurons: regulation of two potassium conductances.
Authors: Pan Z Z , Grudt T J , Williams J T
Published: December 2014

1. alpha 1‐Adrenoceptor activation caused two separate effects in rat dorsal raphe neurons: a depolarization and an increase in the duration of the after‐hyperpolarization following the action potential. The depolarization often resulted in repetitive action potentials. The alpha 1‐adrenoceptor antagonists prazosin and WB 4101 blocked the depolarization induced by phenylephrine. The concentration‐response curve to phenylephrine was shifted to the right by WB 4101. 2. Under voltage clamp, alpha 1‐adrenoceptor agonists caused an inward current at ‐60 mV, which often became smaller at negative potentials but rarely reversed polarity even at strongly negative potentials. Using whole‐cell recording, the inward current reversed polarity at the equilibrium potential for potassium in the majority of cells. Intracellular Cs+ decreased or abolished the alpha 1‐mediated inward current. The inward current was dependent on external calcium, but not on the degree of internal calcium buffering. Removal of external calcium or addition of MgCl2, CoCl2 or CdCl2 reduced or blocked the effects of alpha 1‐adrenoceptor agonists. Barium and strontium supported and even augmented the inward current induced by alpha 1‐adrenoceptor agonists, whereas nifedipine and omega‐conous toxin had no effect. In contrast, internal dialysis with the calcium chelator 1,2‐bis(O‐aminophenoxy)ethane‐N,N,N'N'‐tetraacetic acid (BAPTA) did not inhibit the inward current. 3. The alpha 1‐induced depolarization was blocked (or occluded) by the inclusion of GTP‐gamma‐S (100 microM) in the recording pipette. The phorbol‐ester 4‐phorbol 12,13‐dibutyrate (PDBu) had no action on the membrane potential and depressed the phenylephrine‐induced depolarization. This depression was reversed by the non‐selective protein kinase inhibitor staurosporin. 4. Phenylephrine and noradrenaline increased a late component of the after‐hyperpolarization (late‐AHP) that followed a single action potential. The alpha 1‐sensitive late‐AHP was blocked by apamine suggesting that it is a calcium‐dependent potassium conductance. 5. Thapsigargin reduced the duration of the late‐AHP and blocked the phenylephrine‐mediated prolongation. Caffeine also augmented the late‐AHP and ryanodine blocked the augmentation induced by caffeine. The augmentation induced by phenylephrine was not occluded by caffeine and was still present after the caffeine‐induced augmentation was blocked by ryanodine. 6. In slices pretreated with manoalide the depolarization induced by alpha 1‐agonists was not changed; however, the late‐AHP was reduced in duration and the alpha 1‐receptor‐mediated augmentation of the late‐AHP was decreased.(ABSTRACT TRUNCATED AT 400 WORDS)
Direct patch recording from identified presynaptic terminals mediating glutamatergic EPSCs in the rat CNS, in vitro.
Authors: Forsythe I D
Published: December 2014

1. An in vitro brainstem slice preparation of the superior olivary complex has been developed permitting patch recording from a presynaptic terminal (calyx of Held) and from its postsynaptic target‐‐the principal neurone of the medial nucleus of the trapezoid body (MNTB). 2. The fluorescent stain DiI (1,1'‐dioctadecyl‐3,3,3',3'‐tetramethylindocarbocyanine perchlorate) was used in fixed tissue and Lucifer Yellow in living slices, to identify calices enclosing single MNTB neuronal somata. 3. Whole‐cell recording from the MNTB neurone shows evoked EPSCs preceded by a prespike, corresponding to the presynaptic action potential (AP). In some cases one patch pipette recorded from both pre‐ and postsynaptic elements, but confirmation of exclusively presynaptic recording was obtained using pipettes containing Lucifer Yellow in a further eleven cases. 4. Under current clamp, the pre‐ and postsynaptic sites could be distinguished by their response to step depolarizations; presynaptic terminals generated a train of APs at frequencies up to 200 Hz, while MNTB neurones gave a single AP. Each presynaptic AP had an after‐hyperpolarization lasting less than 2 ms. 5. Under voltage clamp, step depolarizations of presynaptic terminals generated a tetrodotoxin‐sensitive inward current followed by rapidly activating outward potassium currents at potentials more positive than ‐60 mV. The outward current exhibited little inactivation over the 150 ms steps and 4‐aminopyridine (200 microM) blocked 63.0 +/‐ 14.5% (mean +/‐ S.D., n = 3) of the sustained current at 0 mV. Like the squid giant synapse, mammalian terminals express rapidly activating ‘delayed rectifier’‐type potassium currents.
Inputs to group II‐activated midlumbar interneurones from descending motor pathways in the cat.
Authors: Davies H E , Edgley S A
Published: December 2014

1. Connections from descending motor pathways to group II‐activated interneurones in the midlumbar segments of the spinal cord have been examined by intracellular recording. Interneurones, many of which had axonal projections to the hindlimb motor nuclei, were tested for inputs from rubro‐, reticulo‐, vestibulo‐ or corticospinal fibres. 2. Of 138 cells, 113 were monosynaptically excited by electrical stimulation of at least one of the descending motor pathways. Monosynaptic excitation from reticulo‐, vestibulo‐ and rubrospinal pathways was common. Monosynaptic corticospinal EPSPs were identified in fewer neurones. 3. Convergent monosynaptic inputs from pathways which descend in the ventrolateral and ventral funiculi were common. Although few neurones with monosynaptic input from the corticospinal tract were identified, most also had monosynaptic rubrospinal input. In contrast, few neurones (4.3%) had convergent monosynaptic input both from pathways in the dorsolateral funiculus and from fibres in the ventral/ventrolateral funiculi. 4. The patterns of convergence from the different descending motor pathways differ from the patterns expected if the descending connections were distributed independently. Thus there is a significant segregation between rubrospinal and reticulo‐ or vestibulospinal inputs, and a significant association of reticulo‐ and vestibulospinal inputs. 5. Since descending motor pathways make monosynaptic connections with most group II‐activated midlumbar neurones, many of which project to the hindlimb motor nuclei, some of these neurones provide a disynaptic pathway for the supraspinal control of hindlimb movements. The distribution of descending connections is consistent with the hypothesis that pathways descending in the dorsal part of the lateral funiculus and those descending in the ventrolateral or ventral funiculi contact different sets of interneurones.
Effect of dynamic exercise on left atrial function in conscious dogs.
Authors: Nishikawa Y , Roberts J P , Tan P , Klopfenstein C E , Klopfenstein H S
Published: December 2014

1. Dynamic changes in left atrial (LA) function during treadmill exercise were studied in ten conscious dogs instrumented to measure left ventricular (LV) pressure and diameter, LA pressure and diameter, and pulmonary venous blood flow (PVF, transit time flowmeter). 2. Systolic PVF volume (reservoir volume; a measure of LA reservoir function) increased from 38 +/‐ 4% of total PVF volume at baseline to 52 +/‐ 8% of total PVF volume during exercise, and diastolic PVF volume (conduit volume; a measure of LA conduit function) decreased from 62 +/‐ 5% at baseline to 48 +/‐ 8% during exercise (P < 0.005). 3. The increases in reservoir volume and the decrease in conduit volume were due not only to a greater decrease in diastolic interval than systolic interval but were also caused by a significantly greater increase (P < 0.05) in the mean systolic filling rate (93%) than in the mean diastolic filling rate (51%). 4. During exercise the pattern of LV filling derived from changes in LV diameter showed that a greater percentage of LV filling occurred during the second half of diastole at the time of atrial contraction (P < 0.05), suggesting that LA booster function was enhanced. 5. Changes in LA dimension revealed that during exercise more blood volume was reserved in the LA during systole and that this change was associated with an increase in the LA dimension at the beginning of LA contraction (r = 0.61, P < 0.05). 6. We conclude that LA reservoir and booster functions were augmented during exercise, whereas conduit function was not. Increased reservoir function may play an important role in accelerating LV filling by helping to maintain an enhanced atrioventricular pressure gradient during diastole and also by increasing LA booster function through an increase in LA preload.
The simple frequency response of human stretch reflexes in which either short‐ or long‐latency components predominate.
Authors: Matthews P B
Published: December 2014

1. The stretch reflexes of the human abductor digiti minimi (ADM) and biceps brachii muscles were compared using small‐amplitude sinusoidal stretching at 10‐50 Hz and recording the surface EMG. The stimulus was applied either to the relevant proximal phalanx or to the biceps tendon while the muscle studied was contracting; the same amplitude was used for all frequencies (range 0.5‐2 mm for ADM, 0.1‐1 mm for biceps). 2. As the frequency increased, the response of ADM decreased while that of biceps increased. Neither muscle showed a minimum at 20‐25 Hz, as previously found for wrist muscles and attributed to an interaction between short‐ and long‐latency components of the reflex. 3. For both muscles, the phase of the response lagged behind the stimulus by an amount which increased approximately linearly with frequency, without the gross inflexion found for wrist muscles. Such linearity would be found for a system dominated by a fixed time delay; its value sets the slope. The slope for biceps was half that for ADM. The values of reflex delay calculated from the slope of the phase plots agreed reasonably with the absolute latencies of the responses evoked by tap or ramp stimulation. Part of the difference between the muscles was due to differences in peripheral conduction time, since ADM lies more distally. Most of it, however, was due to different reflexes being involved, with biceps being predominantly controlled by short‐latency pathways and ADM by long‐latency pathways. 4. For both muscles, the phase lag at any given frequency was less than that expected from the reflex latency, determined from the slope of the phase plot. Thus, sensory transduction and central transmission had produced a phase advance in the reflex. The ‘neural phase advance’ of biceps was appreciably larger than that of ADM, and more than would be expected from the behaviour of its spindle afferents. The excess is suggested to be due to the action of Renshaw inhibition, which ADM may lack. 5. The results were substantiated by recording from single motor units in biceps. Stretching at the present amplitudes had rather little effect on the overall rhythmic behaviour, as shown by interspike interval histograms. However, cycle histograms showed that the discharge was modulated reasonably sinusoidally by the stretching, whatever its frequency (i.e. the probability of the occurrence of a spike varied over the cycle). Cyclic changes were also found in autocorrelograms and amplitude spectra of the spike trains.(ABSTRACT TRUNCATED AT 400 WORDS)
The influence of hypoxia on transvascular leakage in the isolated rat heart: quantitative and ultrastructural studies.
Authors: al‐Haboubi H A , Tomlinson D R , Ward B J
Published: December 2014

1. The multiple indicator dilution method was used to study the transvascular movement of gamma‐globulin, bovine serum albumin, insulin and cyanocobalamin in the isolated rat heart. 2. Perfusion of the heart with well‐oxygenated solution for 75 min (constant flow) did not produce a significant change either in the total area under the dilution curve or the ‘leakage index’ (an arbitrary measure of transvascular flux) for all the tracers. 3. Perfusion of the heart with hypoxic solution produced a significant increase in leakage of gamma‐globulin of 38.6 +/‐ 18, 48.5 +/‐ 17.6, 60.5 +/‐ 24 and 58 +/‐ 20% after 15, 30, 45 and 60 min, respectively, compared with the well‐oxygenated equilibration period. Permeability‐ surface area products (PS) for the smaller diffusible solutes, therefore, could not be estimated. 4. The flux of albumin, insulin and cyanocobalamin in response to hypoxia was similar to that of gamma‐globulin. 5. Ultrastructural examination of well‐oxygenated hearts revealed that Monastral Blue‐labelled albumin remained within the lumen and that endothelial integrity remained intact. 6. Conversely biopsies from hypoxic hearts showed that the labelled albumin had passed to the interstitium through gaps (approximately 3 microns) in venular endothelium. 7. The results showed that, in intact hearts, hypoxia produced gaps in the endothelium of venules and that these gaps could be the possible route for transvascular leakage of macromolecules.
Characterization of Ca2+ channel currents in cultured rat cerebellar granule neurones.
Authors: Pearson H A , Sutton K G , Scott R H , Dolphin A C
Published: December 2014

1. High‐threshold voltage‐gated calcium channel currents (IBa) were studied in cultured rat cerebellar granule neurones using the whole‐cell patch clamp technique with 10 mM Ba2+ as the charge carrier. The putative P‐type component of whole‐cell current was characterized by utilizing the toxin omega‐agatoxin IVA (omega‐Aga IVA) in combination with other blockers. 2. omega‐Aga IVA (100 nM) inhibited the high voltage‐activated (HVA) IBa by 40.9 +/‐ 3.4% (n = 27), and the dissociation constant Kd was 2.7 nM. Maximal inhibition occurred within a 2‐3 min time course, and was irreversible. The isolated omega‐Aga IVA‐sensitive current was non‐inactivating. 3. omega‐Aga IVA exhibited overlapping selectivity with both N‐ and L‐channel blockers; omega‐conotoxin GVIA (omega‐CTX GVIA) (1 microM) and the dihydropyridine (‐)‐202‐709 (1 microM), respectively. Together these toxins reduced the omega‐Aga IVA‐sensitive component to just 4.5 +/‐ 1.4% (n = 3). Thus only a small proportion of the current can be unequivocally attributed to P‐type current. Inhibition of the HVA IBa by omega‐Aga IA also reduced the proportion of omega‐Aga IVA‐sensitive current to 28.0 +/‐ 3.2% (n = 3). 4. Application of omega‐Aga IVA and a synthetic form of funnel‐web toxin, N‐(7‐amino‐4‐azaheptyl)‐L‐argininamide (sFTX‐3.3; 10 microM), produced an additive block of the HVA IBa. Consequently these two toxins do not act on the same channel in cerebellar granule neurones. 5. omega‐Aga IVA inhibition of low voltage‐activated (LVA) IBa was studied in the ND7‐23 neuronal cell line. omega‐Aga IVA (100 nM) reduced the LVA current by 41.3 +/‐ 3.2% (n = 17) in a fully reversible manner with no shift in the steady‐state inactivation of the channel. 6. A component of current insensitive to N‐, L‐ and P‐channel blockers remained unclassified in all our studies. This component, and also that remaining following block by omega‐Aga IVA and omega‐Aga IA, exhibited relatively rapid, although incomplete, inactivation compared to the other currents isolated in this study. 7. In conclusion, omega‐Aga IVA inhibits a component of current in cultured cerebellar granule neurones which overlaps almost completely with that inhibited by L‐ and N‐channel blockers. In addition, a large component of whole‐cell current in these neurones still remains unclassified.
GABAA receptor activation and the excitability of nerve terminals in the rat posterior pituitary.
Authors: Zhang S J , Jackson M B
Published: December 2014

1. The activation of GABAA receptors in nerve terminal membranes gates a Cl‐ channel. Experiments were conducted to determine how the activation of this receptor influences membrane potentials, action potentials and voltage‐activated Na+ and K+ channels. 2. When activation of the GABAA receptor produced only conductance changes and no voltage changes, action potentials changed only slightly. The threshold for action potential generation increased by 15%. GABA reduced the broadening of action potentials caused by high frequency stimulation by only 7%. These results indicate that membrane shunting by GABA‐gated Cl‐ channels plays a relatively minor role. 3. By recording changes in the current through K+ channels in cell‐attached patches, the activation of GABAA receptors was shown to depolarize the nerve terminal membrane from rest by 14 mV. The GABAB receptor agonist baclofen produced no change in resting membrane potential as measured by this same technique. 4. In whole‐terminal recordings under current clamp, with pipettes containing various Cl‐ concentrations, the GABA‐induced depolarization increased with Ecl. The variation with Ecl provided a basis for evaluating the contributions of leak and K+ current in the balance of currents that determines the magnitude of the GABA‐induced depolarization. 5. Based on the GABA‐induced voltage change and an evaluation of the other currents of significance in the relevant voltage range, an estimate was obtained for ECl of ‐48 mV to give an estimate for the intracellular Cl‐ ion concentration of 20 mM. 6. Under conditions allowing both conductance and voltage to change during Cl‐ channel gating, GABA prevented action potential responses to current injection. Comparable depolarizations produced by adjusting a steady holding current also blocked action potential responses. 7. A depolarization from ‐60 to ‐45 mV under voltage clamp inactivated approximately 90% of the Na+ channels and activated a small amount of K+ current. This suggests that inactivation of Na+ channels makes a major contribution to the inhibition of action potentials by GABA. 8. These results are consistent with the hypothesis that GABA inhibits neurosecretion by retarding impulse propagation into the terminal arborization. These results support a depolarization block mechanism for the inhibition of secretion, in which depolarization inactivates Na+ channels sufficiently to block action potentials.
Receptive field characteristics of tactile units with myelinated afferents in hairy skin of human subjects.
Authors: Vallbo A B , Olausson H , Wessberg J , Kakuda N
Published: December 2014

1. Impulses in single nerve fibres from the lateral antebrachial cutaneous nerve were recorded using the microneurography technique in human subjects. 2. In a sample of fifty‐five mechanoreceptive units with fast‐conducting nerve fibres, five types were identified, i.e. SAI (slowly adapting type I, Merkel), SAII (slowly adapting type II, Ruffini), hair units, field units and Pacinian‐type units. The latter three unit types were all rapidly adapting. 3. The detailed structure of thirty‐five receptive fields of SAI, SAII, hair and field units was explored with a method which was objective and independent of the experimenter's skill and experience. A lightweight probe was used to scan the receptive field area in a series of tracks 0.23 mm apart while single‐unit activity was recorded. 4. SAI fields were small and composed of two to four well‐separated high‐sensitivity spots and often, in addition, one minor spot of lower sensitivity. SAII units typically fired spontaneously at a low and regular rate. Most fields consisted of one single spot of high sensitivity with diffuse borders. The hair units innervated ten to thirty‐three (or more) hairs, which were evenly distributed over a large area. The field units were characterized by a number of small and closely packed high‐sensitivity spots with diffuse borders. A conservative estimate indicated eleven spots per unit. 5. The findings indicate that the sheet of mechanoreceptors on the skin of the forearm is distinctly different from that on the dorsum of the hand and in the face. It seems reasonable to assume that the former is more representative for the hairy skin covering the main parts of the body.
Modulation by different GABAB receptor types of voltage‐activated calcium currents in rat thalamocortical neurones.
Authors: Guyon A , Leresche N
Published: December 2014

1. The effects of the GABAB receptor agonist baclofen on the voltage‐dependent Ca2+ currents were studied in rat thalamocortical neurones with the use of whole cell voltage‐clamp recordings in brain slices. 2. The contribution of N‐, L‐ and P‐types of Ca2+ channels to the total high voltage‐activated Ca2+ (HVA Ca2+) current was assessed by the use of omega‐conotoxin, nifedipine and omega‐agatoxin IVA, respectively. No P‐type current could be detected. Thus, the HVA Ca2+ current contained an N‐ and an L‐type current (23 and 15% of the total current, respectively) and a residual current, which will be referred to as the ‘R’ component. 3. Baclofen (1‐50 microM) had no effect on the low voltage‐activated (LVA) Ca2+ current (IT). 4. At low concentrations (0.5‐10 microM), baclofen decreased the HVA Ca2+ currents by about 10‐20% without a marked modification on the kinetics, whereas 50 microM baclofen decreased the HVA Ca2+ currents by about 40% with a pronounced slowing down of the kinetics. 5. The 10‐20% decrease of the total HVA Ca2+ currents produced by the low concentrations of baclofen occurred as the result of a 30% block of the ‘R’ component. The additional decrease observed with the dose of 50 microM was due to a full block of the N‐type current. The L‐type was unaffected by baclofen. 6. The effect of baclofen on the total HVA Ca2+ current was partially blocked by GABAB receptor antagonists indicating that it occurred through stimulation of GABAB receptors. 7. The effect of baclofen on the N‐type current was abolished by CGP 35348 (100 microM) and CGP 55845A (100 nM). The effect on the ‘R’ component was also antagonized by CGP 55845A (100 nM) although with a lower potency, but was not blocked by CGP 35348 (100 microM). 8. We conclude that the effects of baclofen on the various components of the HVA Ca2+ currents occur through different types of GABAB receptors. One receptor has a high affinity for baclofen (i.e. saturated by concentrations as low as 0.5 microM), is insensitive to CGP 35348, is coupled to the ‘R’ component and is responsible for a maximum 20% decrease in the total HVA Ca2+ current. The other receptor has a lower affinity for baclofen (i.e. affected by a concentration of 50 microM), is sensitive to CGP 35348, is coupled to the N‐type Ca2+ current and is responsible for the additional 20‐30% decrease in the HVA Ca2+ current observed with 50 microM baclofen.
Tyrosine phosphorylation during synapse formation between identified leech neurons.
Authors: Catarsi S , Ching S , Merz D C , Drapeau P
Published: December 2014

1. We have examined whether tyrosine phosphorylation is required for synapse formation between identified neurons from the central nervous system of the leech in culture. 2. Within a few hours of contact with the cell body of the serotonergic Retzius neuron (R cell), the soma of the postsynaptic pressure‐sensitive neuron (P cell), but not the R cell, could be labelled intracellularly with an antibody against phosphotyrosine residues. The labelling seemed specific for P cells contacted by R cells, as it was greatly reduced in pairs of either R or P cells and in single cells. Genistein (20 microM) and lavendustin A (10 microM), selective inhibitors of tyrosine kinases, blocked the labelling of contacted P cells, whereas their ineffective analogues (genistein and lavendustin B) had no effect on labelling. 3. R cell contact also induced the loss of an extrasynaptic, depolarizing response (due to modulation of cation channels) to serotonin (5‐HT) in the P cell within a few days of juxtaposing cell bodies and within an hour of contact with growth cones. Treatment of the neurons with the tyrosine kinase inhibitors (but not the ineffective analogues) prevented the loss of the depolarizing response and of single cation channel modulation by 5‐HT. 4. R cells formed inhibitory, Cl(‐)‐dependent synapses with P cells. Synapse formation was prevented by the tyrosine kinase inhibitors but not by their ineffective analogues. These compounds had no obvious effect on neurite outgrowth or cell adhesion. We conclude that tyrosine phosphorylation is a signal during the formation of this synapse.
Characterization of spontaneous excitatory synaptic currents in salamander retinal ganglion cells.
Authors: Taylor W R , Chen E , Copenhagen D R
Published: December 2014

1. Spontaneous excitatory postsynaptic currents (sEPSCs) were recorded under voltage‐clamp conditions. Consistent with activation of non‐NMDA‐type glutamate receptors, the sEPSCs reversed at potentials above 0 mV, were blocked by 1 microM CNQX and prolonged by 2 mM aniracetam. 2. The peak conductance of the averaged sEPSCs (n = 70‐400) was 130 +/‐ 60 pS (mean +/‐ S.D.; 17 cells, ranging from 70 to 290 pS). Amplitude distributions were skewed towards larger amplitudes. 3. The decay of individual and mean sEPSCs was exponential with a mean time constant (tau d) of 3.75 +/‐ 0.84 ms (n = 13), which was voltage independent. The 10‐90% rise time of the sEPSCs was 1.30 +/‐ 0.44 ms (n = 13). There was no correlation between sEPSC rise time and tau d suggesting that dendritic filtering alone did not shape the time course of sEPSCs. 4. Light‐evoked EPSCs in these retinal ganglion cells are mediated by concomitant activation of NMDA and non‐NMDA receptors; however, no NMDA component was discerned in the sEPSCs, even when recording at ‐96 mV in Mg(2+)‐free solutions. The decay time course was not altered by 20 microM AP7, an NMDA antagonist, nor was an NMDA component unmasked by adding glycine or D‐serine. These results suggest that NMDA and non‐NMDA receptors are not coactivated by a single vesicle of transmitter during spontaneous release, and thus are probably not colocalized in the postsynaptic membrane at the sites of spontaneous release. 5. The sEPSCs were an order of magnitude faster than the non‐NMDA receptor‐mediated EPSCs evoked by light stimuli, and it is proposed that the EPSC time course is determined largely by the extended time course of release of synaptic vesicles from bipolar cells. The quantal content of a light‐evoked non‐NMDA receptor‐mediated EPSC in an on‐off cell is about 200 quanta.
Contribution of SK and BK channels in the control of catecholamine release by electrical stimulation of the cat adrenal gland.
Authors: Montiel C , López M G , Sánchez-García P , Maroto R , Zapater P , García A G
Published: December 2014

1. Transmural electrical stimulation (10 Hz, 1 ms, 40 V for 10 s) of cat adrenal glands perfused at room temperature with Krebs‐Hepes solution produced catecholamine secretory responses which were reproducible when stimulations were applied at 5 min intervals. Such responses were inhibited about 20% by atropine (1 microM) and 80% by hexamethonium (30 microM). Apamin (100 nM) increased the secretory response 2.5‐fold in the presence of atropine and 8‐fold in the presence of hexamethonium. 2. Potentiation by apamin of secretory responses evoked by 100‐pulse trains was similar at 5, 10 and 20 Hz (about 2‐fold). When glands were continuously stimulated at 3 Hz, apamin increased 4‐fold the initial secretion plateau. Continuous stimulation at a higher frequency (20 Hz) produced a sharp secretory peak followed by a small, sustained plateau; apamin did not alter this plateau. Apamin also enhanced the secretory responses obtained with sustained stimulation with acetylcholine (10 or 200 microM). 3. Secretion peaks induced by brief acetylcholine pulses (10 microM for 10 s) applied to isolated and superfused cat adrenal chromaffin cells were enhanced more than 3‐fold by 100 nM apamin. Charybdotoxin (10 nM) did not enhance these secretory peaks. 4. In perfused cat adrenal glands, charybdotoxin (10 nM) affected neither the secretion evoked by trains of electrical stimulation applied at different frequencies nor the secretion evoked by acetylcholine pulses. 5. In 0.5 mM [Ca2+]o, apamin enhanced 3‐fold the secretion evoked by electrical stimulation trains of 100 pulses (10 Hz, 10 s) and almost 6‐fold the acetylcholine (10 microM for 10 s)‐induced secretion. In 5 mM Ca2+, apamin enhanced the secretory responses to electrical stimulation and acetylcholine 2‐ and 10‐fold, respectively. Charybdotoxin enhanced 2.5‐fold the secretory response to electrical stimulation in 0.5 mM Ca2+, although this effect was not statistically significant. A synergistic interaction between the two toxins on catecholamine release induced by electrical stimulation was observed at low but not at high [Ca2+]o. 6. Simultaneous release of acetylcholine and catecholamines upon electrical stimulation was achieved in glands in which the endogenous acetylcholine stores in the splanchnic nerve terminals had been prelabelled by perfusion with [3H]choline. While apamin enhanced more than 2‐fold the postsynaptic release of catecholamines, the presynaptic release of acetylcholine remained unaffected. 7. The results are compatible with the hypothesis that, under physiological conditions, Ca(2+)‐activated SK channels present in chromaffin cells control the firing patterns of action potentials induced by the acetylcholine released from splanchnic nerves during stress.(ABSTRACT TRUNCATED AT 400 WORDS)