bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐cholinergic nervous control of catecholamine secretion from perfused bovine adrenal glands.
Authors: Marley P D , Thomson K A , Smardencas A
Published: December 2014

1. Field stimulation of adrenal nerves was used to study nervous control of adrenal catecholamine secretion in isolated, retrogradely perfused, bovine adrenal glands. 2. Secretion of both adrenaline and noradrenaline was maximal at 10 Hz. Secretion at 2 Hz was < 10% of maximum. Stimulating with trains of pulses at ten times the average frequency for 1 s out of every 10 s gave 2‐fold greater secretion at 2 Hz average frequency, similar release at 5 Hz, and only half the secretion at 10 Hz, compared to continuous stimulation at the average frequency. 3. At 10 Hz, adrenaline and noradrenaline secretion was virtually abolished by tetrodotoxin (1 microM), but was only reduced by 75% by prolonged perfusion with a combination of mecamylamine (5 microM) and atropine (1 microM). Mecamylamine and atropine completely abolished the secretory response to 2 Hz stimulation. Tetrodotoxin had no significant effect on secretion induced by perfusing glands with nicotine (5 microM), while mecamylamine abolished this response. Mecamylamine and atropine had no effect on secretion induced by K+ depolarization. 4. The secretion of adrenaline and noradrenaline induced by 10 Hz stimulation was not inhibited by naloxone at either 1 or 30 microM. 5. The results suggest that bovine adrenal chromaffin cells, like those in the rat, receive a significant non‐cholinergic secretomotor innervation. In contrast to the rat, however, the non‐cholinergic component in the bovine adrenal is negligible at low‐frequency nerve stimulation and substantial at higher frequencies, and is not antagonized by naloxone. The identity of the non‐cholinergic transmitter remains to be determined.
Adrenal cortical and medullary responses to acetylcholine and vasoactive intestinal peptide in conscious calves.
Authors: Edwards A V , Jones C T
Published: December 2014

1. Adrenal responses to intra‐aortic infusions of acetylcholine and vasoactive intestinal peptide (VIP) have been investigated in functionally hypophysectomized calves given exogenous adrenocorticotrophic hormone (ACTH, 2 ng min‐1 kg‐1 I.V.). 2. Infusions of VIP at a dose of 0.13 micrograms min‐1 kg‐1 caused a small, but significant increase in adrenaline and noradrenaline output which was, however, far below the level recorded previously in response to acetylcholine (0.7 micrograms min‐1 kg‐1). In contrast, these doses of the two agonists produced closely similar rises in adrenal cortisol output. 3. The steroidogenic effects of acetylcholine and VIP were found to be strictly additive and no evidence of potentiation was obtained in relation to either cortical or medullary responses or in the case of any of the cardiovascular responses which were monitored. 4. Intra‐aortic infusions of VIP, at a dose which produced a substantial increase in adrenal steroidogenesis (0.065 micrograms min‐1 kg‐1), had no effect on the output of catecholamines, enkephalin‐like immunoreactivity or corticotrophin‐releasing factor, either in the presence or absence of acetylcholine. 5. It is concluded that VIP is unlikely to modulate adrenal medullary responses to muscarinic stimulation in this species as it has been claimed to do in the rat and does not potentiate adrenal steroidogenesis in response to acetylcholine as it does to ACTH.
Extracellular fluid translocation in perfused rabbit atria: implication in control of atrial natriuretic peptide secretion.
Authors: Cho K W , Kim S H , Hwang Y H , Seul K H
Published: December 2014

1. Transmural transport of 22Na+, 51Cr‐EDTA, [3H]inulin and [14C]Dextran (57 kDa) was measured in perfused rabbit atria. The radiolabelled extracellular space (ECS) markers and [14C]Dextran were introduced into the pericardial space or atrial lumen. Atrial volume changes were induced by steps up and down in atrial pressure. 2. Basal rates of transmural transport of radiolabelled ECS markers across the atrial wall were relatively stable up to 70 min. Atrial stretch and release resulted in a rapid but transient, and reversible increase in the ECS fluid (ECF) translocation. The increased translocation of the ECF into the atrial lumen occurred within 15 s of the reduction of atrial distension and returned to the baseline level within 60 s. 3. Transmural transport of [3H]inulin across the atrial wall was bidirectional. 4. The clearance of radiolabelled ECS markers was molecular‐size dependent. The transmural clearance of [3H]inulin was dependent on the distension‐reduction volume changes induced by atrial stretch and release. Little transport of [14C]Dextran across the atrial wall was observed. 5. The ECF translocation across the atrial wall was not influenced by changes in external Ca2+ but was suppressed by low temperature. 6. Dynamic changes in the ECS of the atrium were observed in response to atrial distension and reduction. The ECS of the atrium increased on distension and decreased on reduction of atrial distension. 7. Reduction in atrial distension resulted in an increase in the secretion of immunoreactive atrial natriuretic peptide (ANP) which coincided with an increase in the translocation of the ECF. The secretion of immunoreactive ANP was a function of the translocation of the ECF. 8. It is suggested that atrial stretch and release may play a role in driving fluid flow within the interstitium and fluid translocation out of the interstitium. This fluid movement presumably leads to convective transport of released ANP into the atrial lumen.
Characterization of Ca2+ signals induced in hippocampal CA1 neurones by the synaptic activation of NMDA receptors.
Authors: Alford S , Frenguelli B G , Schofield J G , Collingridge G L
Published: December 2014

1. A combination of confocal microscopy, whole‐cell patch‐clamp recording, intracellular dialysis and pharmacological techniques have been employed to study Ca2+ signalling in CA1 pyramidal neurones, within rat hippocampal slices. 2. In the soma of CA1 neurones, depolarizing steps applied through the patch‐pipette resulted in transient increases in the fluorescence emitted by the Ca2+ indicator fluo‐3. The intensity of the fluorescence transients was proportional to the magnitude of the Ca2+ currents recorded through the pipette. Both the somatic fluorescence transients and the voltage‐activated Ca2+ currents ran down in parallel over a period of between approximately 15‐45 min. The fluorescence transients were considered, therefore, to be caused by increases in cytosolic free Ca2+. 3. Under current‐clamp conditions, high‐frequency (tetanic) stimulation (100 Hz, 1 s) of the Schaffer collateral‐commissural pathway led to compound excitatory postsynaptic potentials (EPSPs) and somatic Ca2+ transients. The somatic Ca2+ transients were sensitive to the N‐methyl‐D‐aspartate (NMDA) receptor antagonist D‐2‐amino‐5‐phosphonopentanoate (AP5; 100 microM). These transients, but not the EPSPs, disappeared with a time course similar to that of the run‐down of voltage‐gated Ca2+ currents. Tetanus‐induced somatic Ca2+ transients could not be elicited under voltage‐clamp conditions. 4. Fluorescence images were obtained from the dendrites of CA1 pyramidal neurones starting at least 30 min after obtaining whole‐cell access to the neurone. Measurements were obtained only after voltage‐gated Ca2+ channel activity had run down completely. 5. Tetanic stimulation of the Schaffer collateral‐commissural pathway resulted in compound EPSPs and excitatory postsynaptic currents (EPSCs), under current‐ and voltage‐clamp, respectively. In both cases, these were invariably associated with dendritic Ca2+ transients. In cells voltage‐clamped at ‐35 mV, the fluorescent signal increased on average 2‐fold during the tetanus and decayed to baseline values with a half‐time (t1/2) of approximately 5 s. 6. The alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionate (AMPA) receptor antagonist, 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX; 10 microM) partially reduced the tetanus‐induced EPSC without affecting the Ca2+ transients. In contrast, AP5, which also depressed the EPSC, substantially reduced or eliminated the Ca2+ transients. 7. In normal (i.e. 1 mM Mg(2+)‐containing) medium, NMDA receptor‐mediated synaptic currents displayed the typical region of negative slope conductance in the peak I‐V relationship (between ‐90 and ‐35 mV). The dendritic tetanus‐induced Ca2+ transients also displayed a similar anomalous voltage dependence, decreasing in size from ‐35 to ‐90 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiological properties of cat reticular thalamic neurones in vivo.
Authors: Contreras D , Curró Dossi R , Steriade M
Published: December 2014

1. The electrophysiological properties of neurones of the reticular thalamic (RE) nucleus were studied in acutely prepared cats under urethane anaesthesia. 2. Two main types of neuronal firing were recorded. At the resting membrane potential (‐60 to ‐65 mV) tonic repetitive firing was elicited when the cell was activated synaptically or by current injection. From membrane potentials more negative than ‐75 mV, synaptic or direct stimulation generated a burst of action potentials. 3. The burst of RE cells consisted of a discharge of four to eight spikes riding on a slowly growing and decaying depolarization. The discharge rate during the burst showed a characteristic increase, followed by a decrease in frequency. 4. The burst response behaved as a graded phenomenon, as its magnitude was modulated by changing the intensity of the synaptic volley or the intensity of the injected current. 5. Spike‐like small potentials presumably of dendritic origin occurred spontaneously and were triggered by synaptic or direct stimulation. They were all‐or‐none, voltage‐dependent events. We postulate that these spikes originate in several hot spots in the dendritic arbor, with no reciprocal refractoriness and may generate multi‐component depolarizations at the somatic level. 6. Excitatory postsynaptic potentials (EPSPs) evoked by internal capsule stimulation consisted of two components, the late one being blocked by hyperpolarization. Such compound EPSPs were followed by a period of decreased excitability during which a second response was diminished in amplitude. 7. A series of depolarizing waves at the frequency range of spindle oscillations was triggered by internal capsule stimulation. The individual depolarizing waves constituting the spindle oscillation gradually decreased in amplitude when decreasing the intensity of the stimulation. 8. These results, showing that RE cells are endowed with an excitable dendritic tree and a graded bursting behaviour, support the proposed role of RE nucleus as the generator and synchronizer of spindle rhythmicity.
Direct comparison of corticospinal volleys in human subjects to transcranial magnetic and electrical stimulation.
Authors: Burke D , Hicks R , Gandevia S C , Stephen J , Woodforth I , Crawford M
Published: December 2014

1. The effects of graded transcranial magnetic and anodal electrical stimulation of the human motor cortex were compared in human subjects undergoing orthopaedic operations on the spine, before and after withdrawal of volatile anaesthesia. Corticospinal volleys were recorded from the spinal cord in the low‐cervical and low‐thoracic regions (six subjects) or the mid‐thoracic region (two subjects) using bipolar electrodes inserted into the epidural space. 2. Electrical stimuli were delivered using anode at the vertex and cathode 7 cm laterally. The corticospinal volley at threshold consisted of a single deflection with a mean latency to peak of 4.17 ms at the rostral recording site. With further increases in stimulus strength the latency of this D wave shortened in two steps, first by 0.89 ms (seven subjects) and then by a further 0.8 ms (two subjects), indicating that the site of activation of some corticospinal neurones had shifted to deep subcortical sites. 3. When volatile anaesthetics were given, a corticospinal volley could not be defined in three subjects with magnetic stimuli of 70, 80 and 100% maximal stimulator output with the coil at the vertex (Novametrix Magstim 200, round coil, external diameter 14 cm). In the remaining five subjects, the component of lowest threshold was a D wave recorded at the rostral site at 4.0 ms when stimulus intensity was, on average, 70%. With stimuli of 90‐100% a total of five small I waves could be defined in the five subjects (i.e. on average one I wave per subject). 4. After cessation of volatile anaesthetics in seven subjects, the thresholds for D and I waves were lower and their amplitudes were greater. The D wave remained the component of lowest threshold in all subjects, appearing at the low‐cervical level with magnetic stimuli of 50%. However, in three subjects I waves also appeared at D wave threshold, and the D wave was smaller than with electrical stimulation at I wave threshold. There was no consistent change in latency of the magnetic D wave as stimulus intensity was increased to 100%. 5. These findings suggest that the previously reported difference in latency of the EMG potentials produced in upper‐limb muscles by anodal stimulation and magnetic stimulation of the human motor cortex is not because the corticospinal volley induced by magnetic stimulation lacks a D wave.(ABSTRACT TRUNCATED AT 400 WORDS)
Lateral hypothalamic lesions alter baroreceptor‐evoked inhibition of rat supraoptic vasopressin neurones.
Authors: Nissen R , Cunningham J T , Renaud L P
Published: December 2014

1. Previous electrophysiological studies on rat hypothalamic supraoptic nucleus neurones have demonstrated that both the activation of peripheral baroreceptors (induced by a brief rise in arterial pressure consequent to an intravenous injection of an alpha‐adrenergic agonist, metaraminol) and electrical stimulation in the diagonal band of Broca evokes a GABA‐mediated postsynaptic inhibition which selectively involves the phasic‐firing (putative vasopressin‐secreting) neuronal population. Although baroreceptor‐triggered inhibitions are abolished after diagonal band lesions, anatomical data support the hypothesis that the GABAergic neurones mediating both the baroreflex and electrically induced inhibitions are not located in the diagonal band, but rather in the lateral hypothalamus adjacent to the supraoptic nucleus. To determine the validity of this hypothesis, excitotoxic lesions were placed in the lateral hypothalamus and their effects on both baroreceptor‐ and diagonal band‐evoked inhibitions were evaluated. 2. Male Long‐Evans rats were initially anaesthetized with intraperitoneal pentobarbitone, stereotaxically injected with an excitotoxin (ibotenic acid) or vehicle into the lateral hypothalamus on the left side and allowed to recover. Three or more days later, animals were again anaesthetized with pentobarbitone and the ventral surface of their hypothalamus was exposed for electrophysiological recording of neurones in the left supraoptic nucleus. In all injected animals, extracellular recordings from antidromically identified, phasically firing supraoptic neurones were evaluated for their response to activation of peripheral baroreceptors and to electrical stimulation in the diagonal band. 3. Increases in arterial pressure sufficient to activate peripheral baroreceptors were achieved by intravenous bolus infusions of metaraminol (10 micrograms/10 microliters). In vehicle control animals (n = 6), the activity of 34/39 neurones was inhibited by baroreceptor activation. In lesion control animals (n = 13) similar inhibitions were observed from 60/65 neurones. In the lateral hypothalamic lesioned group (n = 7), the activity of only 12/34 neurones were inhibited by similar elevations in blood pressure. 4. Ibotenic acid lesions in the lateral hypothalamus also disrupted the responsiveness of supraoptic neurones to electrical stimulation in the diagonal band. Whereas diagonal band stimulation in vehicle control and lesion control rats reduced the excitability in 7/9 cells and 15/19 cells respectively, only 1/7 cells responded in the lesioned animals. 5. Lesions having a significant effect on the responsiveness of vasopressin‐secreting neurones to baroreceptor activation extended laterally towards the nucleus of the lateral olfactory tract, dorsally into the striatum and medially to the fornix.(ABSTRACT TRUNCATED AT 400 WORDS)
Simultaneous oscillations in the membrane potential of pig coronary artery endothelial and smooth muscle cells.
Authors: von der Weid P Y , Bény J L
Published: December 2014

1. The effects of tetrabutylammonium (TBA) on the mechanical tension and on the electrical behaviour of endothelial and smooth muscle cells were studied in intact porcine coronary artery strips. 2. Superfusion of strips with TBA (2‐20 mM) induced mechanical oscillations, leading to an increase in tonic isometric tension. 3. TBA‐induced mechanical oscillations were correlated with fluctuations of the membrane potential of endothelial cells, which were identified by iontophoretic injection of Lucifer Yellow. 4. The endothelial cell membrane potential fluctuations appeared as action potentials or smaller amplitude slow waves, and were synchronized with electrical membrane potential fluctuations of the underlying coronary smooth muscle cells. 5. Oscillations induced by TBA in smooth muscle cells were not affected by removal of the endothelium, and depended on the presence of calcium in the external medium. 6. To our knowledge, this is the first description of action potential‐like fluctuations in the endothelium. It is concluded that the oscillations were generated in the smooth muscle and that they propagate to the endothelium. The question of the mode of propagation of the signal is discussed.
Space and time characteristics of transmitter release at the nerve‐electroplaque junction of Torpedo.
Authors: Girod R , Corrèges P , Jacquet J , Dunant Y
Published: December 2014

1. A loose patch electrode was used to stimulate axon terminals and to record evoked electroplaque currents (EPCs) in a limited area of innervated membrane of the electric organ of Torpedo marmorata. Electrophysiological signals were compared to the predictions of a semi‐quantitative model of synaptic transmission which was designed to simulate the release of several packets of neurotransmitter molecules, at the same or at different sites of the synapse, synchronously or with various temporal patterns. 2. The amplitude distribution of EPCs evoked by activation of nerve terminals showed quantal steps. The time to peak of EPCs was in most cases independent of amplitude, but in their decaying phase a positive correlation was seen between half‐decay time and amplitude. Comparison with the model suggested that (i) a dynamic interaction occurred at the end of the EPC between the fields of postsynaptic membrane activated by individual quanta, and (ii) the sites of quantal release in the electric organ are separated from each other by 600‐1000 nm. 3. Spontaneous miniature electroplaque potentials (MEPPs) were recorded externally with the same type of loose patch electrode. The majority (75%) of external MEPPs displayed a homogeneous and rapid time course. This fast MEPP population had a mean time to peak of 0.43 ms, a half‐decay time of 0.45 ms and a time constant of decay of 0.35 ms. 4. Despite homogeneous characteristics of time course, fast MEPPs exhibited a wide amplitude distribution with a main population which could be fitted by a Gaussian curve around 1 mV, and another population of small amplitude. Both the time‐to‐peak and the half‐decay time of fast MEPPs showed a positive correlation with the amplitude from the smallest to the largest events. Acetylcholinesterase was not blocked. 5. In addition to the fast MEPPs, spontaneous signals exhibiting a slow rate of rise, or a slow rate of decay, or both were observed. They occurred at any time during the experiment, independently of the overall frequency. Approximately 15% of the total number of events had a slow rise but their decay phase was nevertheless rapid and could be ascribed to the kinetics of receptors. These slow‐rising MEPPs exhibited a variety of conformations: slow but smooth rise, sudden change of slope and sometimes several bumps or inflexions. Their average amplitude was significantly smaller than that of the main population of fast MEPPs. 6. Composite MEPPs with multiple peaks as well as bursts of small MEPPs were often encountered, even during periods of low frequency.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanisms underlying enhanced responses of J receptors of cats to excitants in pulmonary oedema.
Authors: Anand A , Paintal A S , Whitteridge D
Published: December 2014

1. The responses of J receptors to certain excitants were recorded during pulmonary oedema produced by phosgene gas (320‐1080 p.p.m.) or alloxan, 150 mg kg‐1 i.v., in cats anaesthetized with sodium pentobarbitone, 35 mg kg‐1 I.P. 2. The responses of fourteen (out of fifteen) J receptors to phenyl diguanide (PDG) were greatly enhanced after phosgene, the enhancement being highly significant (P = < 0.01) in twenty‐one out of twenty‐six responses. The enhancements were also highly significant after alloxan in the case of another twelve receptors. Similar enhancements were observed in the case of responses to nicotine and capsaicin. This suggests that the enhancement of the responses of J receptors to excitants occurs in a non‐specific manner after phosgene and alloxan. 3. The enhanced responses occurred in the absence of any significant increase in the estimated concentration of the excitants in pulmonary artery blood. 4. The enhanced responses to PDG were not closely related to the oedema‐induced activity; several occurred during periods of silence of the receptors and in thirteen receptors the enhanced responses occurred before the increase in the oedema‐induced activity had begun. 5. A possible role of histamine, 5‐HT, prostaglandins and bradykinin in enhancing the responses to PDG after phosgene was excluded. 6. The results therefore suggest that the non‐specific enhancement of the responses of the J receptors to excitants must be due to the increased permeability of the capillaries produced by phosgene and alloxan leading to greater movement of the excitants to the J receptors. However, certain unidentified factors may also be involved.
Analysis of co‐ordination between breathing and exercise rhythms in man.
Authors: Bernasconi P , Kohl J
Published: December 2014

1. The purpose of the present study was to analyse the incidence and type of coordination between breathing rhythm and leg movements during running and to assess the effect of co‐ordination on the running efficiency, as well as to compare the results with those found during cycling. 2. The experiments were carried out on thirty‐four untrained volunteers exercising at two work loads (60 and 80% of subject's physical work capacity 170) on a treadmill. In addition nineteen of the subjects exercised at the same two work loads on a bicycle ergometer. The subjects were running at both work loads in three different modes in randomized order: with normal arm movements, without arm movements and with breathing paced by an acoustic signal which was triggered by the leg movement. 3. Respiratory variables, oxygen uptake and leg movements were continuously recorded and evaluated on‐line. The degree of co‐ordination was expressed as a percentage of inspirations and/or expirations starting in the same phase of the step or pedalling cycle. 4. The average degree of co‐ordination was higher during running (up to 40%) than during cycling (about 20%) during both work loads. The difference in the degree of co‐ordination between running and cycling is probably not due to the lack of arm movements during cycling since the degree of co‐ordination during running with and without arm movements was the same. 5. The degree of co‐ordination during running increased slightly but not significantly with increasing work load and could be increased significantly by paced breathing. 6. The co‐ordination between breathing and running rhythms occurred in three different patterns: (a) breathing was co‐ordinated all the time with the same phase of step, (b) co‐ordination switched suddenly from one phase of step to another and (c) co‐ordination ensued alternatively once on the right and once on the left leg movement. During cycling the pattern described in (a) occurred almost exclusively. 7. During running with a high degree of co‐ordination, oxygen uptake for a given work load was slightly but significantly lower than during running with weak co‐ordination.
Coupling between variations in strength and baroreflex latency of sympathetic discharges in human muscle nerves.
Authors: Wallin B G , Burke D , Gandevia S
Published: December 2014

1. Pulse‐synchronous multiunit muscle nerve sympathetic activity was recorded simultaneously from two nerves together with ECG in eleven healthy subjects; seven recordings were made from the two peroneal nerves during prolonged expiratory apnoeas and four from a radial and a peroneal nerve during lower body negative pressure of 10‐40 mmHg. The neural records were displayed in mean voltage neurograms (time constant 0.1 s) and for each mean voltage burst the following measures were taken and related to each other: amplitude, duration, rise time, decay time and baroreflex latency (from the appropriate R‐wave of the ECG to the peak of the burst). 2. Average baroreflex latencies were 1.3 s in the peroneal nerves and 0.9 s in the radial nerve. There were significant positive correlations between both the amplitudes and the baroreflex latencies of corresponding bursts in peroneal‐peroneal recordings and in radial‐peroneal recordings. 3. In all nerves baroreflex latency shortened significantly when burst amplitude increased. The correlation between burst amplitude and baroreflex latency was weaker in the radial than in the peroneal nerve. The average variation of baroreflex latency in peroneal‐peroneal recordings was 0.20 +/‐ 0.02 s in both legs, and in radial‐peroneal recordings the variation was 0.09 +/‐ 0.01 s in the radial nerve and 0.12 +/‐ 0.02 s in the peroneal nerve. 4. When peroneal burst amplitudes increased, burst duration increased. This was due to increases of both the rise time and the decay time of the burst, the latter being the greater.(ABSTRACT TRUNCATED AT 250 WORDS)
Separate activation of fast and slow inhibitory postsynaptic potentials in rat neocortex in vitro.
Authors: Benardo L S
Published: December 2014

Synaptic inhibition was investigated by stimulating inhibitory neurones with focal microapplications of glutamate, while recording from layer V pyramidal neurones of rat somatosensory cortical slices. One class of inhibitory postsynaptic potentials (IPSPs) thus elicited was characterized as a fast, chloride‐mediated, GABAA IPSP in part by its fast time‐to‐peak (mean 2.5 ms) and brief duration, but primarily on the basis of its reversal potential at ‐68 mV, and its blockade by picrotoxin. The average peak amplitude for these fast IPSPs was ‐1.5 mV, measured at ‐60 mV. The peak conductance calculated for these events was about 10 nS. The conductance change associated with the maximal fast inhibitory postsynaptic potential resulting from electrical stimulation of afferent pathways ranged up to 116 nS. A second class of IPSP was encountered much less frequently. These glutamate‐triggered events were characterized as slow, potassium‐mediated GABAB IPSPs partly because of their longer times‐to‐peak (mean, 45 ms) and duration, but especially because of their extrapolated equilibrium potential at about ‐89 mV and blockade by 2‐hydroxysaclofen. The average peak amplitude for these slow IPSPs was ‐2.3 mV, measured at ‐60 mV. The peak conductance for these events was about 8 nS. IPSPs resulting from the excitation of individual inhibitory interneurones were elicited by glutamate microapplication at particular locations relative to recording sites. Both fast and slow IPSPs were generated, but these occurred as separate events, and mixed responses were never seen. Thus, the two mechanistically distinct types of IPSPs which result from GABA interaction at GABAA and GABAB receptors on neocortical neurones may be mediated by separate classes of inhibitory neurones.
In vitro activation of cyclo‐oxygenase in the rabbit carotid body: effect of its blockade on [3H]catecholamine release.
Authors: Gómez‐Niño A , Almaraz L , González C
Published: December 2014

The release of prostaglandin E2 (PGE2) from rabbit carotid bodies (CBs) incubated in basal conditions (PO2 approximately 132 mmHg; PCO2 approximately 33 mmHg; pH = 7.42) amounts to 94.4 +/‐ 10.1 pg (mg protein)‐1 (10 min)‐1 (mean +/‐ S.E.M.). Incubation of the CB in a hypoxic solution (PO2 approximately 46 mmHg) produced a significant 40% increase (P < 0.05) in the release of PGE2. Indomethacin (2 microM) prevented the hypoxia‐induced release of PGE2. Sensory plus sympathetic denervation of the CB 4 days prior to the experiments did not modify either basal or low PO2‐induced PGE2 release, indicating that intraglomic nerve endings are not significant sources for the PGE2 released. Incubation of the CB in an acidic‐hypercapnic solution (PO2 approximately 132 mmHg; PCO2 approximately 132 mmHg; pH = 6.60) or in a high K(+)‐containing solution (35 mM) was also effective in promoting an increase in the outflow of PGE2 from the organs. The release of [3H]catecholamines ([3H]CA) from the CB elicited by incubating the organs in low PO2 solutions (PO2 ranged between 66 and 13 mmHg) was potentiated by two inhibitors of cyclo‐oxygenase, acetylsalicylic acid (ASA, 100 microM) and indomethacin (2 microM). The effect persisted after chronic denervation of the organ. The secretory response elicited by acidic stimuli was also augmented by cyclo‐oxygenase inhibitors. Thus, [3H]CA release elicited by incubating the CBs in the acidic‐hypercapnic solution increased by 300% in the presence of indomethacin (2 microM), and ASA (100 microM) more than doubled the release induced by dinitrophenol (100 microM), a protonophore that mimics an acidic stimulus. Indomethacin, but not ASA, moderately increased the high K(+)‐evoked [3H]CA release. The effect of indomethacin on the release of [3H]CA elicited by acidic and hypoxic stimuli was reversed by PGE2 in a dose‐dependent manner (0.3‐300 nM). These results show that low PO2 and high PCO2‐low pH, the natural stimuli to the CB, as well as high extracellular [K+], activate the cyclo‐oxygenase pathway in the CB, promoting an increase in the outflow of PGE2. The data also show that the blockade of this pathway activates the stimulus‐induced [3H]CA release from the CB, indicating that naturally released prostanoids exert an inhibitory control on chemoreceptor cells. The data lend support to the notion that the hyper‐reactivity of the ventilatory response to hypoxia in subjects under anti‐inflammatory drug treatment results from CB cycloxygenase inhibition.
Changes in mitochondrial function induced in isolated guinea‐pig ventricular myocytes by calcium overload.
Authors: Minezaki K K , Suleiman M S , Chapman R A
Published: December 2014

1. Changes in [Ca2+]i and pHi, mitochondrial membrane potential (psi m) and mitochondrial [NADH] have been measured independently using fluorescent techniques in single isolated guinea‐pig ventricular myocytes subjected to Ca2+ overload. 2. The changes in NADH autofluorescence on the inhibition or uncoupling of respiration are consistent with the signal emanating from the mitochondrial NADH. 3. Removal of Ca2+ and Mg2+ from the bathing Tyrode solution induced a modest fall in both [Ca2+]i and pHi, a small slowly developing depolarization of psi m and an initial fall followed by a rise in mitochondrial [NADH]. 4. In myocytes that maintained an intact sarcolemma, return to Ca(2+)‐containing fluid elicited a strong but brief intracellular acidification, a rise in [Ca2+]i which generally recovered more slowly to stabilize above the initial level in Tyrode solution, a steep fall in mitochondrial [NADH] and a brief transient recovery followed by a large sustained depolarization of psi m. NADH autofluorescence and mitochondrial depolarization often reached values that were not further increased by uncoupling respiration although recovery of NADH was elicited by inhibitors of respiration. 5. These changes were reduced when the Ca2+ overload was less severe as evidenced by a reduced hypercontracture upon Ca2+ repletion. A similar reduction could be routinely achieved by elevation of [Mg2+]o during the period of Ca2+ depletion. 6. These results suggest that the well‐established depletion of energy‐rich phosphates that occurs on Ca2+ overload is due to the combined effects of the failure of the citric acid cycle to provide sufficient mitochondrial NADH for the respiratory chain and an uncoupling of respiration from ATP production due to depolarization of psi m. The former effect could result from the depletion of sarcoplasmic amino acids and the latter from increased Ca2+ cycling across the mitochondrial wall provoked by the elevated [Na+]i and [Ca2+]i.
Acute ventilatory responses to hypoxia during voluntary and electrically induced leg exercise in man.
Authors: Pandit J J , Robbins P A
Published: December 2014

1. The acute ventilatory response to a brief period of hypoxia (AHVR) was measured in six subjects (a) at rest, (b) during electrically induced leg exercise (EEL), (c) during voluntary leg exercise at an external work rate matched to electrical exercise (EV1) and (d) during voluntary leg exercise at an internal work rate (i.e. metabolic rate) matched to electrical exercise (EV2). The end‐tidal PO2 during hypoxia was 50 mmHg and the end‐tidal PCO2 was held constant at 1‐2 mmHg above resting values throughout each of these four protocols. 2. EEL was produced by surface electrode stimulation of the quadriceps muscles so as to cause the legs to extend at the knee and lift a set of weights via a pulley system. During EV1, each subject lifted the same weight through the same height and at the same frequency as during his EEL protocol. During EV2, the weight, the height through which it was lifted and the frequency of voluntary contractions were altered to produce a similar O2 consumption and CO2 production as during EEL. 3. In each subject, end‐tidal PCO2 values showed no change between the four protocols, and in three subjects in whom they were measured, arterial PCO2 values were also similar between the protocols. Venous lactate levels did not increase after EEL or EV2. 4. The AHVR during EEL (14.1 +/‐ 1.42 l min‐1; mean +/‐ S.E.M) was significantly increased (Student's paired t test) compared with rest (7.55 +/‐ 1.10 l min‐1; P < 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)
A single aspartate residue is involved in both intrinsic gating and blockage by Mg2+ of the inward rectifier, IRK1.
Authors: Stanfield P R , Davies N W , Shelton P A , Sutcliffe M J , Khan I A , Brammar W J , Conley E C
Published: December 2014

1. We describe the effects on channel function of changing an aspartate residue (Asp172) in a membrane‐spanning alpha‐helix of the murine inward rectifier, IRK1, by site‐directed mutagenesis. 2. Alteration of Asp172 to Glu (charged) or to Gln or Asn (polar but uncharged) produced functional channels showing inward rectification, though rectification was weaker with Gln and Asn. 3. Intrinsic gating around the potassium equilibrium potential, EK, was conserved only if the charge on residue 172 was conserved. Currents through channels with Gln or Asn in this position showed no time dependence under hyperpolarization. 4. The change from Asp to Gln also reduced the affinity for internal Mg2+ at least fivefold, indicating that Asp172 also forms part of the site for Mg2+ blockage. 5. The consequences for channel structure of Asp172 lining the pore are discussed.
Stretch activation, unloaded shortening velocity, and myosin heavy chain isoforms of rat skeletal muscle fibres.
Authors: Galler S , Schmitt T L , Pette D
Published: December 2014

1. Contractile properties were investigated on single skinned‐fibre preparations from rat leg muscles. Following the mechanical measurements, the myosin heavy chain (HC) composition of the same fibre was analysed by gradient gel electrophoresis. 2. Fibres were typed according to their myosin HC isoform composition (HCI, type I; HCIIA, type IIA; HCIID, type IID; HCIIB, type IIB). Many fibres showed the co‐existence of two myosin HC isoforms (hybrid fibres). 3. A strong correlation was found between fibre type and time characteristics of stretch‐induced delayed force increase (stretch activation) of fully Ca(2+)‐activated fibres. 4. The maximal unloaded shortening velocity (Vmax), as measured with the slack test, was lowest in type I fibres. Within the type II group, a continuum of Vmax values was found, with large overlaps of the different fibre types. 5. The results suggest that the kinetics of stretch activation is determined by the myosin HCs whereas unloaded fibre shortening seems to be determined by other myofibrillar proteins in addition to the myosin HCs. Assuming that stretch activation represents certain steps of the cross‐bridge turnover under isometric conditions and Vmax reflects cross‐bridge detachment under unloaded conditions it can be deduced that different myofibrillar proteins are responsible for different steps within the cross‐bridge turnover.
Local, stochastic release of Ca2+ in voltage‐clamped rat heart cells: visualization with confocal microscopy.
Authors: López-López J R , Shacklock P S , Balke C W , Wier W G
Published: December 2014

1. Confocal microscopy and the fluorescent Ca2+ indicator fluo‐3 (K+ salt) were used to measure cytosolic free calcium ion concentration ([Ca2+]) during excitation‐contraction (E‐C) coupling in single, voltage‐clamped, rat cardiac ventricular cells. 2. Local [Ca2+]i transients were measured nearly simultaneously in different, separate, subcellular volumes of approximately 2.0 microns 3. During depolarization, local [Ca2+]i transients were distinctly different from each other and from whole‐cell [Ca2+]i transients. These differences were particularly apparent during small depolarizations, and were substantially reduced by ryanodine. 3. Components of the local [Ca2+]i transients, particularly those evoked by small depolarizations, were closely similar, in time course and amplitude, to spontaneous local [Ca2+]i transients, or ‘sparks’ (which have been shown previously to be Ca2+ released from sarcoplasmic reticulum). 4. Analysis of local [Ca2+]i transients in the spatial frequency domain (power spectrum) revealed that high power at spatial frequencies of 0.05‐0.2 microns‐1 was always associated with spontaneous calcium ‘sparks’ and with local [Ca2+]i transients evoked by small depolarizing pulses (e.g. to ‐31 mV). Evoked local [Ca2+]o transients in the presence of ryanodine, and those evoked by depolarization to very positive clamp‐pulse potentials (+45 mV), were associated with considerably lower power at this frequency. 5. The results suggest that whole‐cell [Ca2+]i transients evoked by voltage‐clamp depolarization, and thus by L‐type Ca2+ current, are comprised of local [Ca2+]i transients that are similar to the spontaneous calcium ‘sparks’. At very positive clamp‐pulse potentials, however, the electrically evoked local [Ca2+]i transients may be smaller, perhaps as a result of smaller unitary L‐type Ca2+ current.
Sensitization of insensitive branches of C nociceptors in human skin.
Authors: Schmelz M , Schmidt R , Ringkamp M , Handwerker H O , Torebjörk H E
Published: December 2014

1. Eighteen cutaneous mechanosensitive C nociceptors were recorded from the peroneal nerves of healthy human subjects. Their identity was continuously monitored by intracutaneous electrical stimulation, and their activation by mechanical or transcutaneous electrical stimulation was detected by slowing of conduction velocity during the relative refractory period. 2. Mechanoreceptive fields (mRFs) mapped with suprathreshold von Frey hair stimuli covered an area of 99 +/‐ 21 mm2 (mean +/‐ S.E.M.). Two of the units had separate mRFs, with borders about 0.5‐1.5 cm apart from each other and the largest of these units had a maximal diameter of 4.5 cm. 3. Successive topical application of mustard oil and capsaicin induced expansions of mRFs by 57 +/‐ 14 mm2 in eight of fifteen units. 4. In twelve units transcutaneous electrical stimulation delivered through a pointed electrode was used for mapping the electroreceptive fields (eRFs). The borders of the eRFs and the mRFs were identical for two of twelve units only. In the other ten units additional mechano‐insensitive areas (55 +/‐ 22 mm2) were detected from which transcutaneous electrical stimuli could activate the respective unit. 5. Application of mustard oil and capsaicin to these mechano‐insensitive areas sensitized five of eight units to mechanical stimuli. In these cases the mRF after sensitization exactly corresponded to the eRF. 6. It is concluded that there are insensitive branches in human mechanosensitive cutaneous C nociceptors that can be detected by transcutaneous electrical stimulation and sensitized by topical application of chemical irritants. Activation of those branches in the course of inflammatory processes may contribute to spatial summation at central synapses and hence to hyperalgesia.
Transcranial electrical stimulation of the motor cortex in man: further evidence for the site of activation.
Authors: Rothwell J , Burke D , Hicks R , Stephen J , Woodforth I , Crawford M
Published: December 2014

1. The motor cortex was stimulated electrically (vertex anode; cathode 6 cm lateral) in neurologically normal subjects undergoing surgery for scoliosis, and the evoked corticospinal volleys were recorded from the spinal cord using epidural electrodes. 2. Stimuli > 330 V produced a complex D‐wave volley containing three separate peaks, with high‐threshold components, 0.8 ms (D2) and 1.6 ms (D3), in advance of the lowest‐threshold component (D1). As stimuli increased up to 1500 V, D3 replaced the later components completely, but there was no further latency ‘jump’. 3. Brainstem stimulation using electrodes over each mastoid process produced a descending volley that had the same latencies as D3. At threshold, stimulation of the brainstem or spinal cord attenuated the D wave evoked by simultaneous cortical stimulation. 4. It is concluded that transcranial electrical stimulation of the motor cortex at high intensities can access corticospinal neurones at the pyramidal decussation, and that stimulation of the brainstem (and the spinal cord) preferentially accesses corticospinal axons. At threshold, motor cortex stimulation probably activates corticospinal neurones at or near the cerebral cortex.
Regulation of intracellular calcium and calcium buffering properties of rat isolated neurohypophysial nerve endings.
Authors: Stuenkel E L
Published: December 2014

1. Electrophysiological measurements of Ca2+ influx using patch clamp methodology were combined with fluorescent monitoring of the free intracellular calcium concentration ([Ca2+]i) to determine mechanisms of Ca2+ regulation in isolated nerve endings from the rat neurohypophysis. 2. Application of step depolarizations under voltage clamp resulted in voltage‐dependent calcium influx (ICa) and increase in the [Ca2+]i. The increase in [Ca2+]i was proportional to the time‐integrated ICa for low calcium loads but approached an asymptote of [Ca2+]i at large Ca2+ loads. These data indicate the presence of two distinct rapid Ca2+ buffering mechanisms. 3. Dialysis of fura‐2, which competes for Ca2+ binding with the endogenous Ca2+ buffers, reduced the amplitude and increased the duration of the step depolarization‐evoked Ca2+ transients. More than 99% of Ca2+ influx at low Ca2+ loads is immediately buffered by this endogenous buffer component, which probably consists of intracellular Ca2+ binding proteins. 4. The capacity of the endogenous buffer for binding Ca2+ remained stable during 300 s of dialysis of the nerve endings. These properties indicated that this Ca2+ buffer component was either immobile or of high molecular weight and slowly diffusible. 5. In the presence of large Ca2+ loads a second distinct Ca2+ buffer mechanism was resolved which limited increases in [Ca2+]i to approximately 600 nM. This Ca2+ buffer exhibited high capacity but low affinity for Ca2+ and its presence resulted in a loss of proportionality between the integrated ICa and the increase in [Ca2+]i. This buffering mechanism was sensitive to the mitochondrial Ca2+ uptake inhibitor Ruthenium Red. 6. Basal [Ca2+]i, depolarization‐induced changes in [Ca2+]i and recovery of [Ca2+]i to resting levels following an induced increase in [Ca2+]i were unaffected by thapsigargin and cyclopiazonic acid, specific inhibitors of intracellular Ca(2+)‐ATPases. Caffeine and ryanodine were also without effect on Ca2+ regulation. 7. Evoked increases in [Ca2+]i, as well as rates of recovery from a Ca2+ load, were unaffected by the extracellular [Na+], suggesting a minimal role for Na(+)‐Ca2+ exchange in Ca2+ regulation in these nerve endings. 8. Application of repetitive step depolarizations for a constant period of stimulation resulted in a proportional frequency (up to 40 Hz)‐dependent increase in [Ca2+]i. On the other hand, for a constant number of stimuli a reduction in the [Ca2+]i. On the other hand, for a constant number of stimuli a reduction in the [Ca2+]i increase per impulse was observed at higher frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)
Voltage‐clamp analysis of gap junctions between embryonic muscles in Drosophila.
Authors: Gho M
Published: December 2014

1. Intercellular communication between embryonic muscle fibres was examined in Drosophila melanogaster. 2. Injection of fluorescent dye revealed extensive coupling between muscle fibres which form a uniform communicating arrangement of cells without restriction at the segmental borders. 3. Dye transfer was blocked by octanol and membrane depolarization suggesting that it is mediated by gap junctions. 4. Double voltage‐clamp experiments from cell pairs in situ showed that the ionic coupling is sensitive to the voltage difference between the cytoplasm and the extracellular space (transmembrane voltage, Vi‐o) as well as between the cells (transjunctional voltage, Vj). 5. In steady‐state conditions, the gap conductance (gj) was maximal for hyperpolarized Vi‐o and decreased progressively to near zero as Vi‐o became more positive than ‐50 mV. 6. Gap conductance decreased from a maximal value as Vj increased either in the positive or negative direction (by depolarizing or hyperpolarizing, respectively, one of the cells from a holding potential of ‐60 mV). In both cases, gj asymptotically approached a non‐zero residual value which was different for negative and positive Vj (about 20% of the maximal conductance for negative transmembrane potentials and 10% for positive values). 7. Application of octanol (1 mM) resulted in an almost complete and reversible block of gj.