bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical mapping of the early development of the response pattern to vagal stimulation in embryonic chick brain stem.
Authors: Momose‐Sato Y , Sakai T , Komuro H , Hirota A , Kamino K
Published: December 2014

1. In both intact and slice preparations of vagus‐brain stem isolated from 3‐ to 8‐day‐old chick embryos, the spatial pattern of neural responses to vagal stimulation and its development were assessed by means of multiple‐site optical recording of electrical activity, using a voltage‐sensitive merocyanine‐rhodanine dye (NK2761) and a 12 x 12‐element photodiode array. 2. The first neural responses, viz. fast optical signals (related to the action potential), were recorded in the 4‐day‐old brain stem preparation, and slow optical signals (related to excitatory postsynaptic potentials) were detected from late 7‐ and 8‐day‐old brain stem preparations. 3. The evoked optical signals appeared to be concentrated longitudinally in the central region of the stimulated side of the intact brain stem preparation and in a limited dorsal area in the slice preparation. The signal size gradually increased and the response area expanded as development proceeded. 4. Based on the above results, we have constructed developmental maps of the spatial patterns of the fast and slow optical responses. In the maps, the positions of the peak‐size regions of the fast and slow signals were assessed and we have found that there were differences in the location of these areas for the fast vs. the slow signals in the late 7‐ and 8‐day‐old embryonic brain stem preparations. 5. In the maps for the late 7‐ and 8‐day‐old embryonic brain stems, the fast signal response area seems to correspond to the dorsal motor nucleus of the vagus nerve and the slow response area to the nucleus tractus solitarii.
A potassium current evoked by growth hormone‐releasing hormone in follicular oocytes of Xenopus laevis.
Authors: Yoshida S , Plant S
Published: December 2014

1. Electrophysiological properties of the growth hormone‐releasing hormone (GRH) receptor were studied in Xenopus oocytes with an intact follicle cell layer (i.e. follicular oocytes) by measuring whole‐cell current using the two‐electrode voltage‐clamp method. 2. A slow transient outward current was elicited in oocytes, clamped at ‐60 mV, by the application of rat GRH but not bovine, porcine, or human GRH. 3. The response to GRH was not suppressed by blockers known to inhibit other endogenous receptors present in follicular Xenopus oocytes; blockers used were timolol (2 microM; beta‐adrenergic blocker), theophylline (0.1 mM; purinergic blocker) and atropine (100 nM; muscarinic blocker). 4. The current response evoked by rat GRH occurred in a dose‐dependent manner. The concentrations of GRH for threshold and maximum responses were 1 and 100 nM respectively and the estimated EC50 (half‐maximal effective concentration) was approximately 7 nM. The amplitude and conductance of the response became larger and the latency, time‐to‐peak and half‐decay time were shortened when the concentration of GRH was increased. 5. The GRH response was reversibly inhibited by a K+ channel blocker, tetraethylammonium+ (TEA+; 20 mM). The reversal potential for the GRH response was around ‐100 mV and was compatible with the reported value for a K+ current in Xenopus oocytes. Furthermore, a depolarizing shift of 40 mV in the reversal potential was observed when the external K+ concentration was increased from 2 to 10 mM, agreeing with the Nernst equation. In contrast, no significant shift in the reversal potential was observed by changing the external concentration of Na+ or Cl‐. 6. The GRH response was not suppressed in oocytes treated with an acetoxy‐methyl ester of bis‐(o‐aminophenoxy)‐ethane‐N,N,N',N'‐tetraacetic acid (BAPTA/AM; 10 microM) which penetrates the cell membrane and chelates internal Ca2+. 7. The GRH response was potentiated by pre‐treatment with forskolin (0.4 microM; 5 min), which stimulates adenylate cyclase and increases the internal concentration of adenosine 3',5'‐cyclic monophosphate (cyclic AMP). 8. The GRH response was not obtainable when follicle cells surrounding oocytes were removed mechanically with forceps or enzymically with collagenase (i.e. denuded oocytes). The response was also suppressed when gap junctions, which electrically couple follicle cells and the oocyte, were blocked by 1‐octanol (1 mM). 9. The first amino acid is considered to be important for the binding of peptide ligands to their receptors.(ABSTRACT TRUNCATED AT 400 WORDS)
Intraperitoneal injections of prostaglandin E2 attenuate hyperthermia induced by restraint or interleukin‐1 in rats.
Authors: Long N C , Morimoto A , Nakamori T , Yamashiro O , Murakami N
Published: December 2014

1. The purpose of this study was to investigate the effect of the intraperitoneal (I.P.), intravenous (I.V.) or intrapreoptic area (POA) injection of prostaglandin E2 (PGE2) on the body temperature of restrained and unrestrained rats. The effect of I.P. PGE2 on the body temperature of rats during fever induced by I.P. injection of interleukin‐1 beta (IL‐1 beta) was also investigated. 2. Prior to injection, restrained rats had body temperatures of approximately 1 degree C higher than unrestrained rats. The I.P. injection of PGE2 (0.05 and 0.5 mg kg‐1) caused body temperature to fall towards the pre‐restraint levels in a dose‐dependent manner. This fall in body temperature was preceded by a sharp increase in tail skin temperature that was also dependent on dose. The I.P. injection of PGE2 had no effect on the body temperature of unrestrained animals. 3. The I.V. injection of PGE2 caused very little change in the body temperature of restrained rats. However, when injected I.V. into unrestrained animals, PGE2 caused dose‐dependent fevers. The injection of PGE2 (50 ng) into the POA resulted in fever in both restrained and unrestrained animals. 4. The I.P. injection of IL‐1 beta (10 micrograms kg‐1) caused a biphasic fever that lasted at least 420 min. The I.P. injection of PGE2 180 min after the injection of IL‐1 beta caused a transient decrease in the rats' body temperature. This drop in body temperature was not associated with a decrease in metabolic rate. 5. These data support the hypothesis that during restraint stress hyperthermia and IL‐1 beta fever, the I.P. injection of PGE2 acts peripherally to lower the body temperature of rats.
Muscarinic adrenal responses to acetylcholine in conscious calves.
Authors: Jones C T , Edwards A V
Published: December 2014

1. Adrenal responses to intra‐aortic infusions of acetylcholine (4.5 nmol min‐1 kg‐1 for 10 min) have been investigated in hypophysectomized conscious calves given exogenous adrenocorticotrophic hormone (ACTH) (2 ng min‐1 kg‐1 I.V.) in the presence and absence of hexamethonium. 2. Acetylcholine produced a significant increase in adrenal cortisol output and plasma cortisol concentration. In the absence of nicotinic blockade with hexamethonium this was apparently accounted for by an increase in adrenal ACTH presentation secondary to increased adrenal blood flow. However, administration of hexamethonium revealed a direct steroidogenic action of acetylcholine in the presence of exogenous ACTH. 3. Adrenal medullary responses to acetylcholine, including the release of catecholamines, enkephalins and corticotrophin‐releasing factor (CRF), were not significantly reduced by nicotinic blockade. 4. It is concluded that both adrenal medullary and cortical responses to intraaortic infusions of acetylcholine at a low dose are mediated mainly by muscarinic receptors, as it has previously been shown that they are substantially reduced in the presence of atropine.
Influence of perivascular peptides on endoneurial blood flow and microvascular resistance in the sciatic nerve of the rat.
Authors: Zochodne D W , Ho L T
Published: December 2014

1. A variety of vasoactive peptides has been identified in the axon terminals innervating vasa nervorum but their function is unknown. In mesenteric arterioles, substance P (SP) and calcitonin gene‐related peptide (CGRP) have been postulated to have a role in tonic vasodilatation. 2. We explored the effect of epineurial capsaicin, SP, CGRP, spantide (SP antagonist), and hCGRP (8‐37) (CGRP antagonist) on blood flow (EBF) and microvascular resistance (EMR) in the endoneurial compartment of the rat sciatic nerve, as measured by hydrogen clearance. 3. Epineurial capsaicin induced a prompt, intense and prolonged increase in EBF and lowering of EMR as compared to epineurial application of the carrier alone in a separate animal group. The hyperaemic response was also confirmed by studying serial clearance curves in individual animals. 4. Multifibre sciatic‐tibial motor conduction was not changed by epineurial capsaicin. 5. When co‐administered with capsaicin, hCGRP (8‐37) completely blocked the hyperaemic response and increased EMR above the pooled control range. Spantide also blocked the capsaicin response. 6. When administered alone, both epineurial hCGRP (8‐37) and spantide lowered EBF below and increased EMR above the control measurements in the same animals. 7. At 10(‐5) M epineurial CGRP, but not SP lowered EMR. Vasodilatation from intra‐arterial administration of CGRP was much greater and was more prolonged compared with that induced by SP. hCGRP (8‐37), but not spantide reduced the intra‐arterial response to CGRP. 8. The findings suggest that epineurial peptidergic terminals mediate a vasodilatory response (particularly through CGRP) that increases blood flow in the ‘downstream’ endoneurial compartment. Physiological peptide release (blocked by SP and CGRP receptor antagonism) may be important in maintaining tonic vasodilatation.
Different mechanisms underlie the long‐latency stretch reflex response of active human muscle at different joints.
Authors: Thilmann A F , Schwarz M , Töpper R , Fellows S J , Noth J
Published: December 2014

1. Stretch of voluntarily activated human muscle results in a reflex response consisting of short‐latency (M1) and delayed long‐latency (M2) components. The mechanism of the M2 response remains the subject of controversy. The present study tested the universality of the hypothesis that the M2 response results from the transmission of low‐threshold muscle afferent input travelling over a long‐loop supraspinal pathway. Muscle reflex responses resulting from imposed stretch were obtained from the first dorsal interosseus (FDI), biceps brachii (BB), triceps brachii (TB) and triceps surae (TS) muscles. 2. Patients suffering from Huntington's disease (HD) show a selective loss of FDI‐M2 responses, with sparing of the M1. This has been attributed to disruption of supraspinal pathways as a part of the disease pathology. Accordingly, HD has been used in the present study as a model to test the universality of the long‐loop hypothesis: if this is so, then HD patients with an absent FDI M2 should also fail to show an M2 response in other muscles. 3. It is shown that a group of HD patients in whom the FDI‐M2 response was absent or residual developed clear M2 responses in the TB, BB and TS muscles following stretch sufficient to invariably evoke this component in normal subjects. 4. It is thus concluded that longer‐latency stretch reflex components are not invariably mediated over long‐loop supraspinal pathways, but that this mode of control is dominant only in muscles, such as those of the hand, whose function depends largely on direct cortical control.
Differential activation of motor units in the wrist extensor muscles during the tonic vibration reflex in man.
Authors: Romaiguère P , Vedel J P , Azulay J P , Pagni S
Published: December 2014

1. Single motor unit activity was recorded in the extensor carpi radialis longus and extensor carpi radialis brevis muscles of five healthy human subjects, using metal microelectrodes. 2. Motor units were characterized on the basis of their twitch contraction times and their force recruitment thresholds during voluntary imposed‐ramp contractions. 3. The discharge patterns of forty‐three motor units were studied during tonic vibration reflex elicited by prolonged (150 s) trains of vibration (30 Hz) applied to the distal tendons of the muscles. The temporal relationships between the individual small tendon taps of the vibratory stimulus and the motor unit impulses were analysed on dot raster displays and post‐stimulus time histograms. 4. After tendon taps, the impulses of motor units with long twitch contraction times (mean +/‐ S.D., 47.2 +/‐ 10.7 ms) and low recruitment thresholds (0.88 +/‐ 0.6 N) formed a single narrow peak (P1) with a latency (22.7 +/‐ 1.4 ms) which was comparable to that of the tendon jerk in the extensor carpi radialis muscles. These motor units were named ‘P1 units’. On the other hand, the response of motor units with shorter twitch contraction times (31.1 +/‐ 3.3 ms) and higher recruitment thresholds (3.21 +/‐ 1.3 N) showed two peaks: a short latency (23.4 +/‐ 1.3 ms) P1 peak similar to the previous one and a P2 peak occurring 9.4 +/‐ 1.2 ms later. These motor units were named ‘P1‐P2 units’. 5. When the reflex contraction increased slowly, the P1 peaks of ‘P1‐P2 units’ were clearly predominant at the beginning of the contraction, during the rising phase of the motor unit discharge frequency, while the P2 peaks became predominant when the units had reached their maximal discharge frequency. 6. Increasing the tendon vibration frequency (35, 55, 75, 95 Hz) did not modify the ‘P1 unit’ discharge pattern. Due to interference between vibration period and peak latencies, increasing the vibration frequency caused the P1 and P2 peaks of ‘P1‐P2 units’ to overlap. 7. Superficial cutaneous stimulation of the dorsal side of the forearm during tendon vibration noticeably decreased the P1 peaks in both types of motor units. In the P2 peaks it could result in either a decrease or an increase but the average effect was a slight increase. 8. When applied 10 s before tendon vibration, cutaneous stimulation considerably suppressed the tonic vibration reflex.(ABSTRACT TRUNCATED AT 400 WORDS)
Muscle history dependence of responses to stretch of primary and secondary endings of cat soleus muscle spindles.
Authors: Proske U , Morgan D L , Gregory J E
Published: December 2014

1. Responses were recorded from both primary and secondary endings of soleus muscle spindles in the anaesthetized cat during slow stretches of the muscle after conditioning contractions at different lengths. 2. After a 5 mm length step and a fusimotor‐strength contraction given at the longer length, on return to the initial length the response to a slow test stretch (0.5 mm s‐1) showed a change in slope midway through the stretch which was attributed to taking up of slack in intrafusal fibres. 3. The onset of the change in slope during the test stretch depended on the size of the conditioning step. With no conditioning length change, just a fusimotor‐strength contraction, there was no slope change and the response consisted of an initial burst followed by a maintained high rate of discharge. 4. Following a conditioning length step, the point of onset of the slope change during the test stretch could be altered by stimulating single identified fusimotor fibres to the spindle. Stimulating some static axons produced large changes in the stretch response while other static axons and dynamic axons had only small effects. 5. Many secondary endings showed a delay in onset of their response to a test stretch, dependent on the size of the preceding conditioning step, signalling the presence of slack in much the same way as the primary endings. Other secondary endings, however, appeared to have stretch responses that were largely independent of muscle conditioning. 6. Muscle history‐independent responses of secondary endings were associated with low axonal conduction velocities. It is proposed that secondary endings which remain unaffected by muscle conditioning lie on more distal regions of nuclear chain fibres in the S2‐S5 position. Here they are stimulated during both the take‐up of slack and the subsequent direct stretch of the intrafusal fibres.
Impulses and resting membrane properties of small cultured rat hippocampal neurons.
Authors: Johansson S , Friedman W , Arhem P
Published: December 2014

1. The impulses and resting membrane parameters of small (soma diameter less than 10 microM) cultured hippocampal neurons from rat embryos were studied with the tight‐seal whole‐cell recording technique. 2. Mean resting potential was ‐47 mV, mean input resistance 3.3 G omega, mean capacitance 11 pF, and mean time constant 33 ms. 3. Rectangular suprathreshold current steps elicited regenerative potential responses. The amplitude and time course of the responses were clearly stimulus dependent: stronger current steps caused impulses of larger amplitude. 4. The current threshold was very low: rheobase current was less than 15 pA. 5. The potential response depended on the preceding holding potential, responses from more negative potentials showing sharper peaks than those from more positive potentials. 6. Spontaneous impulses with pre‐potentials similar to synaptically induced events were recorded from several cells. The amplitude of the spontaneous impulses varied similarly to that of the stimulus‐induced responses.
Computed potential responses of small cultured rat hippocampal neurons.
Authors: Johansson S , Arhem P
Published: December 2014

1. The potential responses of small hippocampal neurons were computed on the basis of a previous mathematical description of the currents recorded under voltage‐clamp conditions. 2. The computed action potentials were graded with respect to stimulus strength, in accordance with previous experimental findings. 3. The time course of the membrane currents and of the permeabilities and permeability variables during the impulse was computed for different stimulus intensities. 4. The effect of the membrane time constant on the impulse amplitude was investigated. It was concluded that the value of the time constant used was not per se sufficient to explain the amplitude variation of the impulse. 5. The effect of the magnitudes of the different potential‐dependent permeabilities on the impulse amplitude was investigated. A Na+ permeability within a certain range caused impulses of variable amplitude, and this variability was affected by the K+ permeability.
Mechanisms by which the pregnant ewe can sustain increased salt and water supply to the fetus.
Authors: Gibson K J , Lumbers E R
Published: December 2014

1. Nine chronically catheterized pregnant ewes were monitored before, during and after 1 week in which fetal urine was drained continuously, to determine whether they could compensate for the resulting loss of salt and water and increase net supply across the placenta to the fetus. 2. Fetal growth and urine and lung liquid production were not affected by loss of all fetal fluids. 3. When fetal urine was drained, the increase (P less than 0.05) in maternal drinking was greater than the extra amount of fluid lost. Thus, maternal plasma osmolality fell (P less than 0.01). When fetal urine again flowed into the amniotic and allantoic cavities, maternal drinking did not fall significantly and plasma osmolality remained low. Maternal urine flow rate increased (P less than 0.05) and its osmolality fell (P less than 0.02). 4. Maternal food intake increased (P less than 0.005) during fetal urine drainage. 5. Maternal plasma renin activity increased (P less than 0.05), her urinary sodium excretion fell (P less than 0.005) and the Na(+)‐K+ ratio in both her urine and faeces decreased (P less than 0.01 and P less than 0.05 respectively) when fetal urine was drained. Maternal urinary and faecal sodium conservation continued after drainage ceased because of continued loss of sodium in lung liquid. 6. It is concluded that the ewe can compensate for inappropriate loss of salt and water from the conceptus.
Electrical behaviour of myenteric neurones in the gastric antrum of the guinea‐pig.
Authors: Tack J F , Wood J D
Published: December 2014

1. Intracellular microelectrodes were used to study the electrical behaviour of ganglion cells in the myenteric plexus of the antrum of the guinea‐pig stomach. In the absence of any information on antral myenteric neurones, the aim was to characterize the electrical behaviour and identify biophysical properties of the neurones that could be related to specialized organization of the neural microcircuits in this physiologically important division of the stomach. 2. Myenteric neurones in the gastric antrum were classified into four subtypes based on electrophysiological properties. These were gastric I, II, III and AH/type 2 neurones. Gastric I neurones were characterized by repetitive spike discharge during intraneuronal injection of depolarizing current, by higher input resistances and by lower resting membrane potentials than the other cell types. Gastric II neurones did not discharge repetitively. They discharged one or two spikes only at the beginning of depolarizing current pulses. Gastric III neurones did not discharge action potentials in response to depolarizing pulses. These neurones had higher membrane potentials and lower input resistances than the other types. A fourth type of neurone discharged one or more spikes during depolarizing current pulses and had long‐lasting hyperpolarizing after‐potentials associated with the spikes. The behaviour of these neurones was like AH/type 2 neurones found elsewhere in the enteric nervous system. 3. Action potentials in gastric I and II neurones were abolished by tetrodotoxin. Spikes of the AH/type 2 cells were not abolished by tetrodotoxin due to a calcium component of the inward current. Application of tetraethylammonium broadened the spikes. This was reversed by removal of Ca2+ from the bathing medium. 4. The hyperpolarizing after‐potentials of AH/type 2 neurones were suppressed by removal of Ca2+ from the bathing medium. Treatment with 4‐aminopyridine decreased the amplitude and duration of the after‐hyperpolarization, whereas tetraethylammonium increased the duration and amplitude of the after‐potentials. The hyperpolarizing after‐potentials were unaffected by apamin. 5. Elevation of cyclic 3',5'‐adenosine monophosphate by forskolin resulted in excitation of all AH/type 2 neurones and some of the gastric III cells. Gastric I and II neurones were unaffected. 6. The electrophysiological behaviour of myenteric neurones in the antrum was similar in some respects and different in others from neurones in the gastric corpus and the small and large intestine of the same animal. The differences may reflect distinct organization of the microcircuits for the specialized neural control of the effector functions which characterize the gastric antrum.
Effect of digital nerve stimuli on responses to electrical or magnetic stimulation of the human brain.
Authors: Maertens de Noordhout A , Rothwell J C , Day B L , Dressler D , Nakashima K , Thompson P D , Marsden C D
Published: December 2014

1. Reflexes were elicited in the first dorsal interosseous muscle of seven normal subjects by electrical stimulation of the digital nerves of the index finger at 3 times perceptual threshold while subjects maintained a constant voluntary contraction of the muscle. The average response in the surface‐rectified electromyogram (EMG) consisted of an early inhibitory (I1) component followed by a later excitation (E2). 2. Low intensity anodal electrical or magnetic scalp stimuli were given over the motor cortex in order to elicit muscle responses within the period of the I1 and E2 reflex components. 3. Compared with control responses elicited in the absence of digital nerve stimulation, responses to electrical cortex stimulation were suppressed in the I1 period and facilitated during the E2 period of the reflex. In contrast, responses evoked by magnetic stimulation were suppressed during I1 and also for the first 10 ms or so of the E2 response. Magnetically evoked responses were facilitated during the later part of the E2 reflex. 4. Similar effects were seen when the probability of firing of single motor units was studied. 5. In three subjects, small taps were given to the abducted index finger in order to stretch the first dorsal interosseous muscle and evoke reflexes which were of comparable size to the E2 reflex evoked by digital nerve stimulation. In contrast to the experiments in which digital nerve stimuli were given, responses evoked by magnetic stimulation over motor cortex were facilitated at all times during the course of the reflex evoked when the muscle was stretched. 6. We conclude that single electrical stimuli applied to the digital nerves can reduce for a short period the excitability of motor cortex to magnetic stimulation. This occurs at a time when the same stimulus is evoking an excitatory (E2) reflex in the average surface‐rectified EMG.
Changes in the stretch reflex of the human first dorsal interosseous muscle during different tasks.
Authors: Doemges F , Rack P M
Published: December 2014

1. Subjects flexed the interphalangeal joint of the index finger against a lever which was mounted on the shaft of a torque motor. 2. There were two different tasks. In one, the subject attempted to maintain a constant finger position in the face of changing forces, whereas in the other the subject attempted to maintain a constant force while the motor moved the lever. 3. Each of the tasks was interrupted by ramp extensions. These evoked stretch reflexes which were recorded in the first dorsal interosseous (FDI) muscle electromyogram (EMG). 4. Long‐latency (55‐90 ms) reflex responses were larger during the ‘maintain position’ task than during the ‘maintain force’ task, although the ramp extensions began from a similar finger position, a similar flexing force, and with a similar amount of FDI EMG activity. 5. It is concluded that the nature of the task has an effect on the magnitude of the long‐latency stretch reflex.
Dihydropyridine‐sensitive and omega‐conotoxin‐sensitive calcium channels in a mammalian neuroblastoma‐glioma cell line.
Authors: Kasai H , Neher E
Published: December 2014

1. Pharmacological and kinetic properties of high‐voltage‐activated (HVA) Ca2+ channel currents were studied using the whole‐cell and perforated patch‐clamp methods in a mouse neuroblastoma and rat glioma hybrid cell line, NG108‐15, differentiated by dibutyryl cyclic AMP or by prostaglandin E1 and theophylline. 2. The HVA currents were separated into two components by use of two organic Ca2+ channel antagonists, omega‐conotoxin GVIA (omega CgTX) and a dihydropyridine (DHP) compound, nifedipine. One current component, IDHP, was blocked by nifedipine (Kd = 8.2 nM) and was resistant to omega CgTX. Conversely, the other component, I omega CgTX, was irreversibly blocked by omega CgTX and was resistant to DHPs. Thus, IDHP could be studied in isolation by a short application of omega CgTX, while I omega CgTX could be studied in the presence of nifedipine. 3. The voltage for half‐activation of IDHP was smaller than that of I omega CgTX by 13 mV. IDHP was activated at potentials that were subthreshold for voltage‐dependent K+ currents of the cell, whereas I omega CgTX was not. 4. Time courses of activation and deactivation of IDHP were faster than those of I omega CgTX. 5. Voltage‐dependent inactivation was small for both IDHP and I omega CgTX at any potential. 6. Ca(2+)‐dependent inactivation of IDHP was faster and more prominent than that of I omega CgTX. The time course of the Ca(2+)‐dependent inactivation of IDHP, but not I omega CgTX, was slowed as the membrane potential was made more positive between ‐20 and 30 mV, although amplitude of the current was increased. 7. Alkaline earth metal ions carried the two components of IHVA in the same order: Ba2+ greater than Sr2+ greater than Ca2+. 8. Metal ions blocked the two components of IHVA in the same order of potency: Gd3+ greater than La3+ greater than Cd2+ greater than Cu2+ greater than Mn2+ greater than Ni2+. 9. An alkylating agent, N‐ethylmaleimide (NEM, 0.1 mM), selectively augmented IDHP by 30%. 10. During the course of cellular differentiation induced by dibutyryl cyclic AMP, IDHP appeared earlier than I omega CgTX. 11. These results indicate that two classes of Ca2+ channels contribute to the HVA currents of this cell line. The DHP‐sensitive channel is more apt to generate Ca2+ spikes and Ca2+ plateau potentials than the omega CgTX‐sensitive channel.
Two types of steady‐state desensitization of N‐methyl‐D‐aspartate receptor in isolated hippocampal neurones of rat.
Authors: Chizhmakov I V , Kiskin N I , Krishtal O A
Published: December 2014

1. Whole‐cell voltage‐clamp recordings were made from rat isolated hippocampal neurones. Aspartate (Asp) and/or glycine (Gly) were applied by a method in which the external solution could be changed within 30 ms and thereafter held constant. 2. Asp and Gly applied together at maximal concentrations (5 mM and 10 microM, respectively) evoked an inward current due to activation of N‐methyl‐D‐aspartate (NMDA) receptors. The current peaked and then declined to a steady state during the application. The time constant of desensitization (tau) was about 1 s when the agonists were applied soon after the onset of whole‐cell recording. The desensitization became more rapid (tau = 0.3 s) and more complete during the first 15 min of recording, and thereafter remained stable; the amplitude of the peak response did not change throughout. In solutions containing 10 microM‐Gly, Asp had an apparent Kd of 51 microM at the peak of response and 20 microM measured at the steady state. The steady‐state current was 14% of the peak current. 3. Asp was applied after a conditioning exposure of the cell of Gly (from 1 to 50 microM), together with the same Gly concentration. The maximum current evoked by the application of Asp was increased while increasing Gly in the conditioning solution, with no change in the apparent Kd for Asp at the peak of Asp‐activated response. 4. Various concentrations of Asp (plus 10 microM‐Gly) were applied after a conditioning exposure to Asp (which alone was without effect). The maximum current induced by Asp applications was only 28% of that observed without conditioning Asp application, but the apparent Kd was unchanged (about 57 microM). 5. Test solution containing maximal concentrations of Asp and Gly was applied after conditioning exposure to both Asp (varying concentrations) and Gly (10 microM). Complete desensitization was caused by 200 microM‐Asp. The apparent Kd for Asp to induce desensitization (8.7 microM) was less than the Kd as an agonist (51 microM). 6. Test solution containing maximal concentrations of Asp and Gly was applied after conditioning exposure to both Gly (varying concentrations) and Asp (5 mM). Complete desensitization was caused by 1 microM‐Gly. The apparent Kd for Gly to induce desensitization (120 nM) was less than the Kd as a co‐agonist (about 1 microM).(ABSTRACT TRUNCATED AT 400 WORDS)
The effect of the stimulation pattern on the fatigue of single motor units in adult cats.
Authors: Bevan L , Laouris Y , Reinking R M , Stuart D G
Published: December 2014

1. The main purpose of this study was to examine the effects of two subtly different stimulus patterns on the force developed by fast‐twitch, fatiguable motor units in a cat hindlimb muscle during control (pre‐fatigue) and fatiguing contractions. 2. The peak force and the force‐time integral responses of nineteen high fatigue (FF) and three intermediate fatigue (FI) motor units of the tibialis posterior muscle in five deeply anaesthetized adult cats were measured at selected times during the course of a 360‐s fatigue test. 3. The fatigue test involved a pseudo‐random alternation of two patterns of stimulation. One pattern (regular) was composed of a train of stimuli with constant interpulse intervals, set at 1.8 x the twitch contraction time of each unit (interval range, 27‐51 ms), and delivered for 500 (or 400) ms. For the total (FF + FI) motor‐unit sample, the mean (+/‐ S.D.) stimulation frequency was 26 +/‐ 4 Hz (range, 19‐37 Hz). The other stimulus pattern (optimized) consisted of three initial stimuli with short (10 ms) interpulse intervals, followed by a constant interpulse‐interval train that was adjusted (interval range, 29‐62 ms; frequency, 23 +/‐ 5 Hz; frequency range, 16‐36 Hz) such that the total train had the same number of pulses, and the same average frequency and duration as the regular train. 4. The stimulus trains were delivered at 1 s‐1 for 360 s, using three‐train sequences of each pattern, randomly alternating with one another. The response of the third train in each sequence was selected for the force measurements. The force profile obtained from the fatigue test was subsequently decomposed into two profiles: one attributable to regular and one to optimized stimulation. 5. During the initial responses to the fatigue test, the optimized stimulus pattern produced significantly more force than the regular stimulus pattern. For FF units, the mean increase in peak force (141%) was significantly greater than the increase in the force‐time integral (59%). 6. All motor units exhibited an initial potentiation of peak force with the regular stimulation pattern, whereas peak force declined monotonically with the optimized pattern. In contrast, the force‐time integral potentiated in the first 30 s for both regular and optimized stimulus patterns. 7. Each motor unit maintained an increased force response to optimized stimulation during the fatigue test, with the greatest relative increase occurring about 120 s into the test, well after the potentiation effect had subsided.(ABSTRACT TRUNCATED AT 400 WORDS)
Cationic channels sensitive to extracellular ATP in rat lacrimal cells.
Authors: Vincent P
Published: December 2014

1. Responses of isolated rat lacrimal cells to local applications of ATP were studied using tight‐seal whole‐cell recording and/or Fura‐2‐derived calcium concentration measurements. 2. In cells where variations in Ca2+ concentration were prevented by use of a strong Ca2+ buffer, ATP was found to induce an inward current response at negative holding potentials. With 10 microM‐ATP, the current amplitude ranged between 20 and 200 pA. The reversal potential of this ATP‐induced current was close to 0 mV with normal external solution and shifted to ‐19 +/‐ 3 mV (mean +/‐ S.D.) when the concentration of external monovalent cations was halved. These results indicate that the channels have a cationic selectivity. The response amplitude decreased markedly from trial to trial, indicating a desensitization process which was irreversible on the time scale of the recordings. 3. Steady state I‐V curves for the ATP‐induced current in normal saline showed a marked inward rectification. This rectification appeared to be linked to a time‐dependent activation of the channels, as hyperpolarizing voltage jumps elicited a time‐dependent current increase. This relaxation could be fitted by a double‐exponential function, with time constants (at ‐120 mV) of 0.9 +/‐ 0.3 ms and 110 +/‐ 6.4 ms. 4. Variance analysis of the ATP‐induced current gave a single‐channel current value of 0.34 pA at ‐60 mV. The single‐channel current amplitude varied linearly with potential, with a slope close to 6 pS. The relation between noise covariance and time could be fitted by a double‐exponential function, with time constants (at ‐60 mV) of 0.8 +/‐ 0.4 ms and 6.8 +/‐ 3.4 ms (mean +/‐ S.D.). 5. In an isotonic Ca2+ solution, 10 microM‐ATP induced an inward current at ‐60 mV with a calculated single‐channel current amplitude obtained from noise analysis close to 0.2 pA. In an external solution containing 10 mM‐calcium and no sodium, 50 microM‐ATP elicited a current with a reversal potential of ‐19 mV. 6. Fura‐2 measurements were performed in intact cells or in cells dialysed with a low concentration of Ca2+ buffer (e.g. 0.5 mM‐EGTA). Under such conditions ATP induced increases of the internal Ca2+ concentration with very variable amplitudes. In some cells Ca2+ rises of 50 nM or lower were found. Minimal activation of Ca(2+)‐dependent channels was then observed. In other cells large Ca2+ rises (up to 500 nM) were observed and were then correlated with marked activation of Ca(2+)‐dependent channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Neural regulation of acetylcholine receptors in rat neonatal muscle.
Authors: Bambrick L L , Gordon T
Published: December 2014

1. The neuronal regulation of the developmental decline in skeletal muscle acetylcholine (ACh) receptors was studied by comparing the effects of sciatic nerve section or of neuromuscular blockade with botulinum toxin (BoTX) on this decline in neonatal and adult rats, using 125I‐alpha‐bungarotoxin (125I‐BTX) as a ligand for the receptor alpha‐subunit. 2. The decline in 125I‐BTX binding site concentration in neonatal rat triceps surae muscle homogenates towards low, adult levels followed a simple exponential with a time constant of 8 days. This decline occurred while the muscle is still rapidly growing, before the postnatal increase in numbers of sodium channels. It also preceded the decline in muscle ACh receptor alpha‐subunit mRNA, reported in other studies, suggesting that subunit levels are not regulated only by mRNA availability. 3. Muscle denervation in the first two weeks of life prevented this developmental decline. Denervation increased the concentration of 125I‐BTX binding sites but the magnitude of this increase became progressively smaller as the muscle matured, showing that removal of innervation during adult life does not revert the muscle, in toto, to its pre‐innervation state. 4. Blockade of neuromuscular activity with BoTX increased 125I‐BTX binding sites to a lesser extent than muscle denervation during neonatal life. This lesser effect of BoTX blockade contrasts with the equal effects of BoTX blockade and denervation in the adult.
Developmental changes in troponin T isoform expression and tension production in chicken single skeletal muscle fibres.
Authors: Reiser P J , Greaser M L , Moss R L
Published: December 2014

1. The Ca2+ sensitivity of tension development was characterized in single skinned fibres from the slow anterior latissimus dorsi (ALD), fast posterior latissimus dorsi (PLD), and fast pectoralis major (PM) muscles of the chicken at adult and neonatal (2 weeks post‐hatch) stages of development. In the adult, the PM was most sensitive, the ALD intermediate, and the PLD least sensitive to Ca2+. 2. PM and PLD fibres were less sensitive to Ca2+ at the neonatal stage of development than in the adult. However, ALD fibres exhibited no age‐dependent changes in Ca2+ sensitivity. 3. Characterization of regulatory protein composition indicated that the PM and PLD fibres had identical fast isoforms of troponin C and troponin I at each developmental stage examined, but there were muscle‐specific and age‐dependent expressions of troponin T isoforms in these fibres. 4. In the ALD fibres, identical slow isoforms of troponin C, troponin I and tropomyosin were found at each stage. In addition, the troponin T isoform that was present did not change with age. 5. The results suggest a relationship between the specific troponin T isoform composition of individual muscle fibres and their calcium sensitivities of tension development.
Ca2+ current in myotome cells of the lancelet (Branchiostoma lanceolatum).
Authors: Benterbusch R , Melzer W
Published: December 2014

1. By using the whole‐cell patch clamp method Ca2+ and Ba2+ currents were measured in the extremely thin twitch muscle cells of the protochordate Branchiostoma lanceolatum whose Ca2+ channels are likely to resemble the evolutionary ancestors of those found in vertebrate skeletal muscle. 2. When using 10 mM‐Ca2+ in the artificial external solution and 1 mM‐EGTA in the internal solution two kinetically different Ca2+ inward current components could be observed, showing very similar voltage dependence of activation and inactivation. 3. In solutions containing 10 mM‐Ba2+ as an external charge carrier the biphasic inward current turned into a single rapidly activated and slowly inactivating current. 4. Inspecting peak currents, the voltage dependence of fractional activation and inactivation was nearly the same in Ca2+ and in Ba2+. 5. A transformation into a single component of the Ca2+ current could also be observed after perfusing the intracellular lumen with 10 mM of either EGTA or BAPTA. In the case of EGTA this transformation required considerably more time. Probably a higher internal concentration of EGTA is necessary since it binds Ca2+ more slowly than BAPTA. 6. Soon after establishing the whole‐cell configuration a gradual increase of the second, slow inward current phase was observed relative to the fast component, indicating an enhancement of the slow component by intermediate intracellular buffer concentrations. 7. We conclude that the Branchiostoma myotome cells have only one Ca2+ channel system. The biphasic appearance of the inward current is caused by an unusually rapid inactivation due to Ca2+ ions, which enter the myoplasm during the current and temporarily bind to an inactivation site at the channel. The second phase probably reflects reactivation from the inactivated state upon dissociation of Ca2+ from the binding site.
Membrane hyperpolarization inhibits agonist‐induced synthesis of inositol 1,4,5‐trisphosphate in rabbit mesenteric artery.
Authors: Itoh T , Seki N , Suzuki S , Ito S , Kajikuri J , Kuriyama H
Published: December 2014

1. Effects of membrane hyperpolarization induced by pinacidil on Ca2+ mobilization induced by noradrenaline (NA) were investigated by measuring intracellular Ca2+ concentration ([Ca2+]i), isometric tension, membrane potential and production of inositol 1,4,5‐trisphosphate (IP3) in smooth muscle cells of the rabbit mesenteric artery. 2. Pinacidil (0.1‐10 microM) concentration dependently hyperpolarized the smooth muscle membrane with a reduction in membrane resistance. Glibenclamide (1 microM) blocked the membrane hyperpolarization induced by 1 microM‐pinacidil. NA (10 microM) depolarized the smooth muscle membrane with associated oscillations. Pinacidil (1 microM) inhibited this response and glibenclamide (1 microM) prevented the action of pinacidil on both the NA‐induced events. 3. In thin smooth muscle strips, 10 microM‐NA produced a large phasic and a subsequent small tonic increase in [Ca2+]i with associated oscillations. These changes in [Ca2+]i seemed to be coincident with phasic, tonic and oscillatory contractions, respectively. Pinacidil (0.1‐1 microM) inhibited the increases in [Ca2+]i and in tension induced by NA, but not by 128 mM‐K+. Glibenclamide inhibited these actions of pinacidil. Pinacidil (1 microM) also inhibited the contraction induced by 10 microM‐NA in strips treated with A23187 (which functionally removes cellular Ca2+ storage sites), suggesting that membrane hyperpolarization inhibits Ca2+ influxes activated by NA. 4. In Ca2(+)‐free solution containing 2 mM‐EGTA, NA (10 microM) transiently increased [Ca2+]i, tension and synthesis of IP3. Pinacidil (over 0.1 microM) inhibited the increases in [Ca2+]i, tension and synthesis of IP3 induced by 10 microM‐NA in Ca2(+)‐free solution containing 5.9 mM‐K+, but not in a similar solution containing 40 or 128 mM‐K+. Glibenclamide (1 microM) inhibited these actions of pinacidil. These inhibitory actions of pinacidil were still observed in solutions containing low Na+ or low Cl‐. These results suggest that pinacidil inhibits NA‐induced Ca2+ release from storage sites through an inhibition of IP3 synthesis resulting from its membrane hyperpolarizing action. 5. In beta‐escin‐treated skinned strips, NA (10 microM) or IP3 (20 microM) increased Ca2+ in Ca2(+)‐free solution containing 50 microM‐EGTA and 3 microM‐guanosine triphosphate (GTP) after brief application of 0.3 microM‐Ca2+, suggesting Ca2+ is released from intracellular storage sites. Heparin (500 micrograms/ml, an inhibitor of the IP3 receptor), but not pinacidil (1 microM) or glibenclamide (1 microM), inhibited the Ca2+ release from storage sites induced by NA or IP3. These results suggest that membrane hyperpolarization is essential for the inhibitory action of pinacidil on the NA‐induced Ca2(+)‐releasing mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)
Neuronal selectivity of ATP‐sensitive potassium channels in guinea‐pig substantia nigra revealed by responses to anoxia.
Authors: Murphy K P , Greenfield S A
Published: December 2014

1. Two sub‐populations of pars compacta substantia nigra neurones were identified with very different electrophysiological properties and rostral‐caudal distribution. Both cell types were identified by biocytin intracellular dye injection and found to be located within pars compacta containing tyrosine hydroxylase‐positive cells. These sub‐populations displayed distinctly different responses to transient anoxia. 2. The first group ('Phasic' neurones) exhibited a low threshold calcium conductance LTS gCa associated with bursts of action potentials, were located at the level of the mammillary bodies and were highly sensitive to anoxia. The second group ('rhythmic' neurones) fired in a rhythmic pattern, were located at the level of the accessory optic tract and were relatively insensitive to anoxia. 3. The anoxic response of phasic cells was characterized by membrane hyperpolarization (mean 12 mV), a decrease in input resistance (mean 36%) and cessation of action potential firing. The axonic response of these neurones was not blocked by TEA (5‐10 mM), haloperidol (100 microM), the removal of extracellular calcium or depletion of endogenous dopamine. However, this effect was blocked by both the sulphonylurea tolbutamide (50‐500 microM), and also by quinine (100 microM) and could be mimicked by application of diazoxide (1 mM). 4. Rhythmic cells displayed a variable response to anoxia consisting of either modest depolarization, hyperpolarization or no change in membrane potential, in all cases accompanied by little or no change in input resistance. The polarity of the membrane potential shift during anoxia was reversed by TEA (5‐10 mM) or the removal of calcium. These cells were also relatively insensitive to diazoxide (1 mM). 5. It is concluded from the neuronal responses to anoxia and the pharmacological modification of these responses, that the ATP‐sensitive potassium channel (KATP channel) is functionally operative in the substantia nigra and is primarily distributed on the phasically discharging cells of the rostral pars compacta. The relevance of this recently discovered ionic channel is discussed with regard to the normal and abnormal functioning of the substantia nigra.