bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of a phosphorylation‐activated Cl‐selective channel in isolated Necturus enterocytes.
Authors: Giraldez F , Murray K J , Sepúlveda F V , Sheppard D N
Published: December 2014

1. The cell‐attached and excised inside‐out configurations of the patch‐clamp technique were employed to probe isolated enterocytes of Necturus maculosus for the presence of Cl(‐)‐selective channels. 2. Chloride‐selective channels were rarely observed unless cells were previously stimulated by agonists that raise cyclic AMP. In cell‐attached patches forskolin (20 microM) or dibutyryl cyclic AMP 2 mM) evoked single‐channel activity that reversed, depending on the cell, between 9 and 27 mV positive to the spontaneous membrane potential. This is close to the Cl‐ equilibrium potential in those cells; the single‐channel current‐voltage relationship was linear with a unitary slope conductance between 17 and 25 pS (pipettes filled with 100 mM‐NaCl). 3. Large depolarizing voltage steps also activated Cl‐ channels in excised inside‐out membrane patches that were previously quiescent. This mode of activation produced a distinctive single‐channel current‐voltage relationship with strong outward rectification at depolarizing membrane potentials. Single‐channel cord conductance at negative potentials was 15‐18 pS and increased to 45 pS at + 100 mV. 4. Altering the Cl‐ concentration in the bathing solution of excised inside‐out patches displaced the observed reversal potential (Erev) to values predicted for Cl‐ equilibrium potential. Replacement of K+ for Na+ was without effect. 5. The effect of different anions upon Erev was used to determine the channel anion selectivity in excised inside‐out patches. The permeability sequence was SCN‐ greater than I‐ greater than Br‐ greater than Cl‐ greater than F‐ greater than HCO3‐ greater than gluconate which corresponds to Eisenman's sequence 1. Neither ionic size nor diffusion rates determine the permeation of ions through the channel. 6. In channels activated by depolarization the open probability (Po) was insensitive to changes in the Ca2+ concentration (less than 10(‐8)‐10(‐3) M) bathing the cytoplasmic face of excised inside‐out patches. Depolarization was also without marked effect on Po. 7. Chloride channels in excised inside‐out patches were inhibited by stilbene and diphenylamine‐2‐carboxylate derivatives. 4‐Acetamido‐4'‐isothiocyanatostilbene‐2,2'‐disulphonic acid (SITS, 5 x 10(‐5) M) and 5‐nitro‐2‐(3‐phenylpropylamino) benzoic acid (NPPB, 1 x 10(‐5) M) caused an irreversible ‘flickery’ blockade without altering single‐channel current. 3'5‐Dichlorodiphenylamine‐2‐carboxylic acid (DDPC, 5 x 10(‐5) M) reduced the currents at every voltage without apparent effects on gating properties of the channel.(ABSTRACT TRUNCATED AT 400 WORDS)
Potassium currents in submucous neurones of guinea‐pig caecum and their synaptic modification.
Authors: Akasu T , Tokimasa T
Published: December 2014

1. Intracellular recordings were made from submucous neurones of the guinea‐pig caecum. In most experiments, membrane currents were measured using a single‐electrode voltage clamp. 2. A potassium current dependent on calcium influx occurred at rest (approximately equal to 200 pA at ‐60 mV). The amplitude of the current was increased up to 1 nA at ‐35 mV and decreased to zero at ‐100 mV; when fully activated the current did not show any inactivation. An inward calcium current, of 15‐25 pA in amplitude near ‐60 mV and insensitive to omega‐conotoxin (0.5 microM), probably activated the potassium current. 3. Step depolarizations from potentials negative to ‐80 mV evoked a transient (less than or equal to 200 ms at ‐40 mV) potassium current which was blocked by 4‐aminopyridine (1‐3 mM). Hyperpolarizing commands to potentials negative to ‐87 mV evoked an inwardly rectifying potassium current which was selectively blocked by caesium (1‐2 mM). The residual cell current between ‐100 and ‐40 mV in calcium‐free solution containing tetraethylammonium (20 mM), caesium (2 mM) and 4‐amino‐pyridine (3 mM) conformed to constant field assumptions. This current was called a background potassium current. 4. Decrease in membrane conductance during the slow excitatory postsynaptic current (EPSC) was due predominantly (greater than or equal to 90%) to a reduction in the calcium‐activated potassium current at ‐35 mV, but due almost exclusively to a reduction in the background potassium current at potentials more negative than ‐100 mV. The relative contribution of the two currents to the slow EPSC was entirely dependent on the relative contribution of the currents to the membrane conductance at given potentials. 5. The transient potassium current was unaffected or slightly enhanced during the slow EPSC. The inwardly rectifying potassium current was unaffected during the slow EPSC. 6. Three tachykinins (substance P, substance K and neurokinin B; 3‐800 nM), forskolin (1‐30 microM), 8‐bromoadenosine 3':5'‐cyclic monophosphate (8‐bromo cyclic AMP; 1‐3 mM), 3‐isobutyl‐1‐methylxanthine (0.3‐1 mM) mimicked the conductance changes during the slow EPSC in a concentration‐dependent manner. 7. It is concluded that the slow excitatory synaptic potential in the submucous plexus, presumably mediated by peptidergic transmitters, results from an inactivation of two distinct potassium currents, at least one of which is controlled by intracellular calcium ions.
Membrane currents elicited by prostaglandins, atrial natriuretic factor and oxytocin in follicle‐enclosed Xenopus oocytes.
Authors: Miledi R , Woodward R M
Published: December 2014

1. Membrane currents were recorded from voltage clamped Xenopus laevis oocytes, still surrounded by follicular cells, theca and enveloping inner ovarian epithelia (ovarian follicles). 2. Superfusing follicles with frog Ringer solution containing E‐series prostaglandins (PGE1 or PGE2) or oxytocin (0.5‐2 microM) generated slow membrane currents arising from an increase in membrane conductance to K+. 3. Follicles taken from different frogs varied greatly in responsiveness to PGE and oxytocin. For example, enclosed oocytes with good sensitivity to prostaglandins responded to 1 nM‐PGE, whereas follicles from some frogs failed to respond at 5 microM. 4. Oocytes with good responsiveness to PGE also produced K+ currents to PGA1, PGA2, PGB1, 11‐deoxy‐PGE1 and 11‐beta‐PGE2, whereas PGF2 alpha, PGI2, PGD2 and 8‐iso‐PGE1 generally failed to elicit membrane currents. 5. Responses to PGE and oxytocin were mimicked by the adenylate cyclase activator forskolin or by intraoocyte pressure injection of cyclic nucleotides. Responses were potentiated by the phosphodiesterase inhibitors theophylline and 3‐isobutyl‐1‐methylxanthine (IBMX). In IBMX (0.5 mM), human atrial natriuretic factor (ANF) (10‐60 nM) elicited a similar K+ conductance. This all implied that cyclic nucleotides played a role in the receptor‐channel coupling mechanism of these responses. 6. Defolliculating oocytes effectively abolished responses to prostaglandins, oxytocin and ANF, suggesting that the currents arise in follicular cells. 7. The responses of PGE, oxytocin and ANF thus resembled currents elicited by catecholamines, adenosine, gonadotrophins and vasoactive intestinal peptide (VIP). However, PGE, oxytocin and ANF responses were not blocked by catecholaminergic or purinergic antagonists. Moreover, when comparing follicles isolated from different frogs, the sensitivity to PGE and oxytocin varied independently of that to gonadotrophin or VIP. These experiments suggest that Xenopus ovarian follicles contain specific and distinct receptors for PGE, oxytocin and ANF. 8. Acetylcholine attenuated the cyclic nucleotide‐mediated K+ responses, including currents elicited by PGE, oxytocin and ANF. Attenuation was not dependent on, or mimicked by, activation of the inositol phosphate‐diacylglycerol messenger pathways located in the oocyte itself, nor was it appreciably blocked by loading follicle‐enclosed oocytes with 0.1‐1.5 mM‐EGTA.
5‐Hydroxytryptamine acts at 5‐HT2 receptors to decrease potassium conductance in rat nucleus accumbens neurones.
Authors: North R A , Uchimura N
Published: December 2014

1. Intracellular recordings were made from neurones in the nucleus accumbens in slices from the rat brain maintained in vitro. 2. 5‐Hydroxytryptamine (5‐HT.1‐100 microM) depolarized 170 of 203 (84%) neurones and caused them to discharge action potentials. The depolarization was associated with an increase in the input resistance, and was reversed in polarity by conditioning hyperpolarization; this reversal potential was linearly related to the logarithm of the extracellular potassium concentration. 3. Application of 5‐HT to neurones voltage‐clamped near their resting potential (typically about ‐80 mV) caused an inward current and a decrease in the slope conductance. The current caused by 5‐HT reversed polarity at the potassium equilibrium potential. Analysis with an equivalent circuit model of the neurone at steady state indicated that 5‐HT selectively reduced the inward rectifier potassium conductance. 4. The depolarization caused by 5‐HT persisted in tetrodotoxin (1 microM). It was reduced but not abolished by a solution that contained lower levels of calcium (0.24 instead of 2.4 mM), higher levels of magnesium (5 instead of 1.2 mM), and cobalt (2 mM). 5. The depolarization caused by 5‐HT was competitively antagonized by the 5‐HT2 antagonists ketanserin and mianserin with dissociation equilibrium constants of 3 and 45 nM respectively: spiperone (300 nM) also blocked the action of 5‐HT. The depolarization was not mimicked or blocked by a number of other agonists and antagonists selective for the 5‐HT1 and 5‐HT3 receptor types.
Voltage‐dependent properties of electrical synapses formed between identified leech neurones in vitro.
Authors: Davis R L
Published: December 2014

1. The voltage‐dependent properties of rectifying and non‐rectifying electrical synapses formed between identified leech neurones were quantified during their regeneration in vitro. 2. Junctional conductance increased with time in culture. This was evaluated by making comparisons between cell pairs maintained in vitro for differing amounts of time, as well as by taking repeated measurements from a single cell pair at different time intervals. 3. Non‐rectifying electrical synapses were formed between certain identified neurones of the same type. Thus, Leydig cells cultured with Leydig cells established non‐rectifying electrical connections, as did Retzius cells, longitudinal motoneurones (L cells) and anterior pagoda (AP) cells, each paired with its own cell type. 4. Rectifying synapses developed when sensory neurones (P cells or N cells) were paired with the other neurones mentioned above that form non‐rectifying connections between themselves. The cell combinations examined were L cell‐P cell. Leydig cell‐N cell, and AP cell‐P cell. The direction of current flow across these rectifying synapses was consistently from the sensory neurone to the other cell in the pair. 5. Non‐rectifying connections early in the process of synapse regeneration (1‐3 days) showed non‐linearities greater than those observed in established non‐rectifying synapses. There was a subtle, but clear, voltage dependence even at the later stages of synapse formation (4‐18 days). 6. In contrast to non‐rectifying connections, rectifying synapses formed between cells at early times in culture showed less voltage dependence than those observed at later times. 7. The marked non‐linearities of the non‐rectifying connections at early stages in synapse formation along with the reduced voltage dependence of the rectifying connections within the same time period revealed unexpected similarities between the two. At the early stages of synapse formation, the two types of electrical synapse were essentially indistinguishable for one direction of junctional current.
Sympathetic nerves in the mediation of renal response to localized stimulation of atrial receptors in anaesthetized dogs.
Authors: Karim F , Majid D S , Summerill R A
Published: December 2014

1. Dogs were anaesthetized with chloralose and artificially ventilated. Localized stimulation of left atrial receptors for 23‐25 min was achieved by distension of three small balloons at the pulmonary vein‐atrial junctions and one in atrial appendage. Renal blood flows were measured by electromagnetic flow probes, glomerular filtration rate by creatinine clearance, urinary sodium excretion by flame photometry and solute excretion by osmometry. The mean aortic pressure was held constant at 92.2 +/‐ 2.4 mmHg (mean +/‐ S.E.M., n = 27) by means of a pressure bottle connected to the aorta and beta‐adrenergic receptor activity was blocked by continuous infusion of propranolol (17 micrograms kg‐1 min‐1, I.V.). 2. In twelve dogs stimulation of left atrial receptors resulted in significant increases of 11.8 +/‐ 2.4% (P less than 0.001) in renal blood flow; 32.5 +/‐ 7.2% (P less than 0.001) in glomerular filtration rate; 19.5 +/‐ 5.0% (P less than 0.005) in filtration fraction: 36.3 +/‐ 9.0% (P less than 0.001) in urine flow: 32.7 +/‐ 9.2% (P less than 0.005) in sodium excretion: 36.6 +/‐ 9.9% (P less than 0.005) in osmolar excretion and a decrease of 31.3 +/‐ 11.2% (P less than 0.025) in free water clearance. Left atrial pressure and heart rate did not change significantly. In eight of the dogs ligation of the renal nerves resulted in similar changes in all of the renal variables; subsequent stimulation of atrial receptors did not cause significant changes in the renal variables. 3. In five additional dogs, in which heart rate and aortic pressure were allowed to change, stimulation of left atrial receptors for the same period resulted in significant increases in heart rate (4.3 +/‐ 0.7%. P less than 0.001) and mean aortic pressure (2.0 +/‐ 0.6%, P less than 0.025). Under this condition both the intact right kidneys and the denervated left kidneys showed significant responses in urine flow, sodium excretion, osmolar excretion and free water clearance. 4. The results show that the renal sympathetic nerves mediate the primary renal responses to atrial receptor stimulation, at least in the short term. The influence of any humoral factor in this reflex seems to be secondary to changes in heart rate and systemic blood pressure, possibly via arterial baroreceptors.
Neuroendocrine responses to stimulation of the splanchnic nerves in bursts in conscious, adrenalectomized, weaned lambs.
Authors: Bloom S R , Edwards A V , Jones C T
Published: December 2014

1. Effects of stimulation of the peripheral ends of the splanchnic nerves below behavioural threshold at either 4 or 7 Hz continuously for 10 min, or at 40 or 70 Hz for 1 s at 10 s intervals for 10 min. have been compared in conscious adrenalectomized lambs. 2. Both patterns of stimulation resulted in an abrupt rise in mean aortic blood pressure of closely similar extent which was associated with reflex bradycardia. 3. At the lower frequencies both patterns of stimulation elicited a closely similar rise in mean plasma glucose, glucagon and pancreatic polypeptide concentration, but the fall in mean plasma insulin concentration was significantly greater during continuous stimulation. 4. Unlike other species in which the release of NPY and bombesin‐like immunoreactivity (BLI) is potentiated by intermittent high‐frequency stimulation, no significant differences were produced by changing the pattern of stimulation. The release of BLI was found to be frequency related over the ranges tested (4‐7 Hz continuously and 40‐70 Hz in bursts) whereas the release of NPY was not. 5. Splanchnic nerve stimulation also produced detectable rises in the mean plasma concentrations of noradrenaline and adrenaline. The mean average concentration of noradrenaline during stimulation in bursts was significantly higher than that during continuous stimulation (P less than 0.02). There was also a steady rise in mean plasma 3,4‐dihydroxyphenylacetic acid (DOPAC) during stimulation followed by a further rise to significantly higher values (P less than 0.02) following stimulation in bursts at 40 Hz. 6. It is concluded that the pattern of stimulation is a less important determinant of autonomic responses to splanchnic nerve stimulation in sheep than in certain other species.
The photoreceptors in atypical achromatopsia.
Authors: Hess R F , Mullen K T , Sharpe L T , Zrenner E
Published: December 2014

1. The receptoral mechanisms underlying the vision of two atypical achromats of the complete variety were studied with standard psychophysical procedures. 2. Under scotopic conditions the spectral sensitivity of each achromat was well described by the CIE (Commission Internationale de l'Eclairage) scotopic sensitivity function and the recovery of sensitivity after a retinal bleach showed characteristic duplex behaviour with the time constant of recovery of the slower phase matching that of normal rod vision for both foveal and peripheral stimulation. 3. Their spectral sensitivity was measured under conditions of chromatic adaptation in order to reveal any residual middle or long wavelength cone activity. Only one photopic spectral responses was found and this was adequately described by the spectral sensitivity function of Stiles pi 3 mechanism of normal vision. 4. Increment threshold measurements as a function of background intensity revealed a double‐branched function in the fovea. The lower branch was found to have the spectral sensitivity of the rods; the upper branch that of Stiles' pi 3 mechanism. Stiles‐Crawford measurements of directional sensitivity confirmed that the branch with the rhodopsin action spectrum had the directional sensitivity of rods and that the branch with the action spectrum of pi 3 had the directional sensitivity of cones. 5. These was no evidence for hue discrimination under photopic conditions. Regions of apparently normal performance on hue discrimination tests on more careful examination could be explained by luminosity judgements mediated by short wavelength‐absorbing receptors. 6. We reject the notion of there being rhodopsin‐filled cones in the fovea of these subjects. The foveal and peripheral vision of each of these achromats can be adequately described in terms of the participation of only two types of receptor, namely normally functional rods under scotopic conditions and normally functioning short wavelength‐absorbing cones under photopic conditions. They are therefore functional blue mono‐cone monochromats, an explanation which was originally proposed by Blackwell & Blackwell (1957) over thirty years ago.
Rectification of synaptic and acetylcholine currents in the mouse submandibular ganglion cells.
Authors: Yawo H
Published: December 2014

1. Synaptic currents and responses to acetylcholine (ACh) were recorded from mouse submandibular ganglion (SMG) cells under whole‐cell voltage clamp. 2. The peak amplitude of excitatory synaptic currents (ESCs) as well as the currents evoked by the ionophoretic application of ACh followed a unique non‐linear current‐voltage (I‐V) relation. The chord conductance of the whole‐cell currents decreased with depolarization of the membrane potential and became virtually 0 at 50 mV. 3. The decay of ESCs was described by two exponential functions. Both the fast (tau f) and slow (tau s) time constants were sharply decreased at depolarizing potentials beyond ‐40 mV, being insensitive to hyperpolarizing potentials more than ‐50 mV. 4. Single ACh receptor channels were characterized by the whole‐cell current noise analysis. The single‐channel currents followed Ohm's law at negative membrane potentials but tended to reach a plateau at positive membrane potentials. The mean slope conductance measured between ‐40 and ‐20 mV was 28.5 pS. 5. The product of the number of functional channels (N) and the probability of a channel being open (p) showed a steep voltage dependence. The value of Np at 20 mV was only 31% of that at ‐20 mV. 6. The noise power spectrum was best fitted by a double‐Lorentzian function. Both the fast (tau f) and slow (tau s) time constants were sharply decreased by depolarizations beyond ‐20 mV. being less sensitive to membrane potentials more negative than ‐30 mV. 7. The non‐linear I‐V relation of ESCs was attributed in part to the voltage dependence of p and in part to the voltage dependence of the single‐channel conductance (gamma) of ACh receptor channels.
Activation of cells in the anterior pretectal nucleus by dorsal column stimulation in the rat.
Authors: Rees H , Roberts M H
Published: December 2014

1. The responses of neurones in the anterior pretectal nucleus (APTN) to electrical stimulation of the dorsal columns at twice the threshold for A fibres were studied in the rat anaesthetized with urethane. 2. APTN cells were excited by dorsal column stimulation. Forty‐six discharged phasically in response to a single stimulus. Sixteen cells did not respond phasically but slowly increased the discharge rate with repeated stimulation. 3. Electrical stimulation of the contralateral gracile fasciculus caused neurones in the APTN to discharge with a variable latency of 2‐22 ms. Stimulations of the ipsilateral gracile and contralateral cuneate fasciculi had weaker effects. 4. Microinjection of DL‐homocysteic acid into the contralateral gracile nucleus increased the discharge rate of APTN neurones. Microinjection of gamma‐aminobutyric acid into the contralateral gracile nucleus blocked the gracile fasciculus evoked excitation of APTN neurones. 5. On thirteen occasions cells in the gracile nucleus were driven antidromically by electrical stimulation of the APTN. 6. It is concluded that electrical stimulation of the gracile fasciculus activates a monosynaptic excitatory input to the APTN.
Antinociceptive effects of dorsal column stimulation in the rat: involvement of the anterior pretectal nucleus.
Authors: Rees H , Roberts M H
Published: December 2014

1. The effects of stimulating A fibres in the dorsal columns on the responses of dorsal horn neurones to intense cutaneous stimuli were studied in the rat anaesthetized with urethane. 2. Multireceptive cells deep in the lumbar dorsal horn were excited for 5‐10 ms by dorsal column stimulation and subsequently responses to noxiously hot water placed on the cutaneous receptive field were reduced for the following 4‐5 min. Seven of the cells studied projected to the brain via the contralateral anterolateral funiculus. 3. If the discharge of the multireceptive neurones was raised by ionophoretic application of DL‐homocysteic acid, a brief period of inhibition lasting for 100‐150 ms was seen following a single stimulus to the dorsal columns. Studies were conducted to determine if this brief inhibition could account for the long‐lasting inhibition of responses to high‐threshold stimuli. 4. Dorsal columns were transected at cervical levels. Stimulation caudal to the transection evoked only the brief excitation and subsequent inhibition for 100‐150 ms. No long‐lasting inhibition of high‐threshold cutaneous afferent input was seen. 5. Stimulation of the dorsal columns rostral to transection did not evoke the brief excitation or inhibition of multireceptive dorsal horn neurones. However, the 4‐5 min inhibition of responses to high‐threshold cutaneous stimuli was present. 6. The long‐lasting inhibition of responses to high‐threshold stimuli by dorsal column stimulation was blocked by microinjection of gamma‐aminobutyric acid into the anterior pretectal nucleus (APTN) but not by microinjections into adjacent areas of the brain. 7. Ipsilateral lesions of the dorsolateral funiculus at the cervical level also blocked the long‐lasting inhibitory effects of dorsal column stimulation. 8. It is concluded that the brief excitation and inhibition of multireceptive dorsal horn neurones is due to antidromic action potentials passing caudally in the dorsal columns to activate spinal segmental mechanisms. The longer‐lasting inhibition of responses to high‐threshold cutaneous stimuli is due to action potentials ascending in the dorsal columns to activate cells in the APTN which in turn activate a descending inhibition mediated by the dorsolateral funiculus.
Slow inward tail currents in rabbit cardiac cells.
Authors: Giles W , Shimoni Y
Published: December 2014

1. A whole‐cell gigaseal suction microelectrode voltage‐clamp technique has been used to study slow inward tail currents in single myocytes obtained by enzymatic dispersion of rabbit ventricle and atrium. A variety of stimulation protocols, Tyrode solutions and pharmacological agents have been used to test three hypotheses: (a) that the slow inward tail current is generated by an electrogenic Na(+)‐Ca2+ exchanger; (b) that a rise in [Ca2+]i, due to release from the sarcoplasmic reticulum can modulate the activity of this exchanger; and (c) that the uptake of calcium by the sarcoplasmic reticulum is a major determinant of the time course of the tail current. 2. As shown previously in amphibian atrium and guinea‐pig ventricle, slow inward tail currents can be observed consistently under conditions in which action potentials and ionic currents are recorded using microelectrode constituents which only minimally disturb the intracellular milieu. 3. In ventricular cells, the envelope of these tail currents obtained by varying the duration of the preceding depolarizations shows that (a) the tail currents are activated by pulses as short as 10 ms, and reach a maximum for pulse durations of 100‐200 ms, (b) the rate of decay of the tail current gradually increases as the activating depolarizations are prolonged, and (c) the tails cannot be due to deactivation of calcium currents, in agreement with other studies in frog heart. 4. When the mean level of [Ca2+]i is raised following inhibition of the Na(+)‐K+ pump by strophanthidin (10(‐5) M) or reductions in [K+]o (0.5 mM), the slow inward tail grows in size prior to the onset of a contracture or other signs of calcium‐induced toxicity. 5. In a number of different preparations, replacement of [Ca2+]o with BaCl2 markedly or completely inhibits the Na(+)‐Ca2+ exchanger, whereas Sr2+ replacement does not have this effect. In myocytes from rabbit ventricle the slow inward tails are reduced significantly and decay more slowly in 0.5‐2.2 mM‐BaCl2 Tyrode solution, while in 2.2 mM SrCl2 these tails are not altered. 6. The slow inward tail also shows a dependence on [K+]o, corresponding to previous data on Na(+)‐Ca2+ exchange in other tissues. Increasing [K+]o in the Tyrode solution to a final concentration of 10‐15 mM results in a marked inhibition of the slow tails. This effect cannot be accounted for by changes in the inwardly rectifying potassium current, IK1. 7. The slow tail currents were changed significantly by increasing the temperature of the superfusing Tyrode solution.(ABSTRACT TRUNCATED AT 400 WORDS)
Barbiturate regulation of kinetic properties of the GABAA receptor channel of mouse spinal neurones in culture.
Authors: MacDonald R L , Rogers C J , Twyman R E
Published: December 2014

1. Barbiturate regulation of the kinetic properties of gamma‐aminobutyric acidA (GABA) receptor channel chloride currents from somata of mouse spinal cord neurones were investigated using whole‐cell and excised outside‐out patch‐clamp recording techniques. 2. GABA (2 microM), GABA (2 microM) plus phenobarbitone (PhB) (500 microM) and GABA (2 microM) plus pentobarbitone (PB) (50 microM), applied by pressure ejection from blunt perfusion micropipettes, evoked inward chloride currents when neurones or patches were voltage clamped at ‐75 mV and the chloride equilibrium potential was 0 mV. GABA receptor channel currents were increased by PhB and PB. 3. Single GABA receptor channel currents were recorded with a main conductance state of 27 pS and a less frequent subconductance state of 16.5 pS. The conductances of the two states were unchanged by the barbiturates. 4. The main conductance state kinetics were analysed. GABA alone or with the barbiturates gated the channel open singly and in groups of openings. 5. The barbiturates increased GABA receptor channel mean open time and shifted frequency histograms of channel open times to longer times. 6. Three exponential functions were required to fit the frequency histograms of GABA receptor channel open times, suggesting that the channel has at least three open states (O1, O2, O3). The time constants for the exponential functions (0.9, 2.7 and 7.8 ms, respectively) were unchanged by the barbiturates. The increases in mean open times and the shifts of the open‐time frequency histograms by the barbiturates were due to a reduction in relative frequency of occurrence of the two short open states (O1 and O2) and to an increase in the relative frequency of occurrence of the longest open state (O3). 7. Frequency histograms of GABA receptor channel closed times were fitted with five exponential functions, suggesting that the channel has multiple closed states. None of the time constants nor areas of the exponential functions were significantly changed by the barbiturates. 8. For analysis, a burst was defined as openings surrounded by closures greater than a critical closed time, tc, of 5 ms. For GABA (2 microM), frequency histograms of GABA receptor channel bursts were fitted with three exponential functions, suggesting that the channel has three burst states (B1, B2, B3). The B1 burst state was probably a single opening to the O1 open state while the B2 and B3 burst states were probably composed of multiple openings to the O2 and O3 open states.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic behaviour of myenteric neurones in the gastric corpus of the guinea‐pig.
Authors: Schemann M , Wood J D
Published: December 2014

1. Synaptic behaviour of ganglion cells in the myenteric plexus of the corpus of the guinea‐pig stomach was investigated using intracellular recording methods. Synaptic potentials were evoked by focal electrical stimulation of interganglionic fibre tracts or the surface of the ganglion containing the cell body from which the recording was obtained. 2. Fast excitatory postsynaptic potentials (EPSPs) mediated by nicotinic cholinergic receptors were the most common stimulus‐evoked or spontaneously occurring synaptic events. 3. Fast EPSPs were evoked in every neurone and most neurones received multiple inputs from axons arriving in several different interganglionic fibre tracts. Several neurones received input from multiple axons in individual fibre tracts. 4. Fast EPSPs were evoked at stimulus frequencies up to 80 Hz without evidence of the ‘run‐down’ phenomenon that characterizes fast EPSPs in the intestine. 5. Trains of EPSPs in the ganglion cell soma occurred with relatively long latencies following spike discharge evoked by intracellular current injection in the same neurone. This appeared to reflect return of excitatory synaptic input to the soma along recurrent connections within the synaptic network. 6. The safety factor for fast EPSPs to evoke spike discharge was highest for gastric I neurones. Probability of fast EPSPs triggering spikes was intermediate in neurones classified electrophysiologically as gastric II and was lowest in gastric III neurones, which never discharged spikes during a fast EPSP. 7. No slow excitatory or inhibitory synaptic potentials, like those found in intestinal ganglion cells, were evoked in gastric neurones by focal stimulation of the fibre tracts. 8. The results suggest that myenteric neurones in the gastric corpus of the guinea‐pig have distinctive synaptic behaviour different from intestinal neurones in the same animal. This may be a reflection of adaptation for neural control of the specialized function of the effector systems in this region of the stomach.
Task‐dependent changes in the size of response to magnetic brain stimulation in human first dorsal interosseous muscle.
Authors: Datta A K , Harrison L M , Stephens J A
Published: December 2014

1. Electromyographic responses have been recorded from human first dorsal interosseous muscle (FDI) in response to magnetic and transcutaneous electrical stimulation of the brain. 2. Following magnetic but not electrical stimulation of the brain, the recorded EMG response was larger when FDI was active during voluntary isometric index finger abduction than during a power grip. 3. In the same experiment, cutaneous reflex responses have been recorded from FDI following electrical stimulation of the digital nerves. The long‐latency excitatory component at about 60 ms (E2) was larger when recorded during voluntary finger abduction than during a power grip. This difference in size of E2 with task bore no simple relationship to the difference in size with task of the motor response to magnetic brain stimulation. 4. The results are discussed in relation to the presumed site of action of magnetic and electrical brain stimulation. It is concluded that the results may best be interpreted by assuming a higher level of cortical activity during a voluntary index finger abduction than during a grip and that this could in part explain the task‐dependent changes in the long‐latency response to cutaneous stimulation.
The effect of loading on position sense at the proximal interphalangeal joint of the human index finger.
Authors: Ferrell W R , Smith A
Published: December 2014

1. Proprioceptive acuity was tested at the proximal interphalangeal joint of the index finger of normal subjects. 2. Examination of the ability of the subjects to match finger positions (position matching procedure) revealed that digital nerve block (DNB) of the finger resulted in characteristic alignment errors at the extremes in all subjects. 3. When one finger (target finger) is positioned close to full extension, all subjects hyperextended the anaesthetized matching finger, whilst target finger positioning towards full flexion resulted in hyperflexion of the matching finger. At intermediate positions the pattern of matching errors was more variable but tended to be consistent for a given subject. 4. When the matching finger was isotonically loaded into flexion, there was little change in matching performance for most subjects. However, when the matching finger was anaesthetized, such loading now produced clear alteration in performance in all subjects. This indicates that muscle receptors contribute to proprioceptive sensations at this joint, but require other afferent sources to optimally resolve position when the finger is loaded. 5. Two other test procedures (angle reproduction and assigned positions) were assessed and compared with the results obtained by the position matching technique. Although alterations in proprioceptive performance during DNB could be detected with these procedures, they tended to be less sensitive than the position matching procedure.
Differing control of neural activities during various portions of expiration in the cat.
Authors: St John W M , Zhou D
Published: December 2014

1. Activities of the phrenic nerve, intercostal nerve and nerves innervating the thyroarytenoid (TA) muscle of the larynx and triangularis sterni (TS) muscle of the chest wall were recorded in decerebrate, vagotomized, paralysed and ventilated cats. 2. Neural inspiration was defined by the phase of phrenic activity. Neural expiration was divided into two phases with phase I corresponding to the duration of TA activity and phase II to TS activity: intercostal nerves discharged across both phases. 3. Phrenic activity was terminated prematurely by electrical stimulation of the superior laryngeal nerve or of the dorsolateral region of the rostral pons. Following stimulation, neural activities during phase I of expiration rose and those during phase II fell in most animals. 4. Stimulation of the superior laryngeal nerve during phase I caused augmentations of both TA and TS activity. At the termination of stimulation, a phase of TA discharge was recorded followed by a phase of TS activity. The durations of these post‐stimulation phases of TA and TS activities approximated those of cycles without stimulation. 5. Stimulation of the superior laryngeal nerve during phase II caused a resetting of neural expiration. Following stimulation, phases of TA and TS activity were recorded which had durations approximating those of cycles without stimulation. 6. The current required to induce a premature onset of phrenic activity by stimulation of the dorsolateral region of the rostral pons fell dramatically with the change from phase I to phase II of expiration. 7. We conclude that the control of neural activities differs markedly between phase I and phase II of expiration. The data support the hypothesis that post‐inspiratory medullary respiratory neurones play a fundamental role in the definition of the ventilatory cycle.
The probability of quantal secretion at release sites in different calcium concentrations in toad (Bufo marinus) muscle.
Authors: Bennett M R , Lavidis N A
Published: December 2014

1. The number of quanta secreted from visualized release sites along terminal branches at toad (Bufo marinus) neuromuscular junctions in different extracellular concentrations of calcium ions. [Ca2+]o, and during facilitation was determined. Terminal branches were visualized by prior staining with the fluorescent dye, 3‐3 diethyloxardicarbocyanine iodide (DiOC2(5)). 2. Increasing [Ca2+]o between 0.25 and 0.4 mM gave a similar proportional increase in the mean quantal content of the end‐plate potential recorded with an extracellular electrode (me) at all sites along terminal branches. Thus the length constant for the experimental decline in me along terminal branches (the quantal length constant) remained constant with an increase in [Ca2+]o. The increase in m with [Ca2+]o followed a fourth power relation at both proximal and distal release sites. 3. The increase in me with [Ca2+]o was almost entirely due to an increase in the binomial probability for secretion, pe, which increased as the third to fourth power of [Ca2+]o. However, at higher [Ca2+]o there was an increasing tendency for the binomial parameter ne to increase. It is shown that when ne increases by about 1 there is very little change in pe, suggesting that the new release site recruited at high [Ca2+]o has a relatively low probability for secretion. 4. Test impulses gave a similar proportional increase in me following a conditioning impulse at all sites along terminal branches. The quantal length constant remained constant for both conditioning and test values of me. The increase in me for the test impulse increased linearly with an increase in me for the conditioning impulse at all release sites. 5. Facilitation of me declined exponentially with an increase in the test‐conditioning interval. The time constant for this decline (30‐40 ms) was similar at both proximal and distal release sites. Changes in facilitation of me were almost entirely due to changes in pe except at very short test‐conditioning intervals of about 10 ms. At these intervals ne frequently increased by about 1 and there was very little change in pe. Again, this suggests that additional release sites recruited at short intervals have relatively low probability for secretion. 6. The results indicate that relatively low probability release sites exist in close juxtaposition to relatively high probability release sites which themselves decline in probability along the length of terminal branches.
Sodium depletion decreases hepatic metabolism of vasoactive intestinal peptide in the rabbit.
Authors: Duggan K A , Hawley C M , Macdonald G J , Shelley S
Published: December 2014

1. Reports that a greater natriuresis occurs after gastric rather than intravenous sodium loads suggest that a gastric sodium monitor exists which releases a humoral natriuretic factor. As vasoactive intestinal peptide (VIP) is natriuretic, it might act as this mediator. To determine whether it released from the gut in response to sodium we measured VIP levels in portal and systemic plasma of anaesthetized rabbits after a gastric sodium load. Levels of VIP in systemic plasma were also measured in conscious rabbits after gastric and portal sodium loads to determine the contributions of anaesthesia or increased sodium concentration in the portal tract to any observed rise in systemic VIP levels. 2. In the anaesthetized rabbit study portal and systemic VIP levels had both increased significantly from control values by 5 min after the sodium load in the low salt diet group (P less than 0.025, portal: P less than 0.05, systemic). By 10 min the levels in systemic and portal plasma were equal. 3. In the conscious rabbits an increase in systemic VIP levels was observed in the group on a low salt diet after a gastric but not a portal sodium load. 4. We conclude that VIP is released in response to gastric sodium loads in rabbits on low salt diets and that hepatic metabolism of VIP is reduced in this group.
Cerebral regulation of renal sodium excretion in sheep infused intravenously with hypertonic NaCl.
Authors: Chodobski A , McKinley M J
Published: December 2014

1. The natriuretic response to intravenous infusion of 2 M‐NaCl was investigated in six conscious sheep. This hypertonic NaCl load resulted in relatively small, physiological (2‐3 mmol l‐1) increases in plasma Na+ concentration and was followed by a natriuresis with a maximum mean urinary sodium excretion 5 times higher than pre‐infusion values. 2. Intravenous infusion of isotonic NaCl, delivering the same Na+ load as hypertonic NaCl infusion, did not induce natriuresis. This suggested, therefore, that with the hypertonic sodium load administered in the present study, the rise in plasma Na+ and/or tonicity rather than increase in blood volume is important in evoking the natriuretic response. 3. Intracerebroventricular infusion of low‐Na+ artificial cerebrospinal fluid (CSF) reduced CSF Na+ concentration, decreased plasma vasopressin (AVP) levels and caused a copious water diuresis. This was associated with excessive loss of water and large increases in plasma Na+ concentration and osmolality. 4. The natriuresis induced by intravenous hypertonic NaCl load could be blocked by lowering CSF Na+ concentration in situations where water diuresis was either prevented or reduced by intravenous infusion of AVP or by delayed intracerebroventricular infusion of low‐Na+ CSF, respectively. 5. The results of the present study provide further evidence that renal sodium excretion can be controlled by the central nervous system.
Bicuculline‐ and phaclofen‐sensitive components of N‐methyl‐D‐aspartate‐induced hyperpolarizations in rat dorsolateral septal nucleus neurones.
Authors: Gallagher J P , Hasuo H
Published: December 2014

1. Intracellular recordings were made from rat dorsolateral septal nucleus (DLSN) neurones in vitro. Pressure application (puff) of N‐methyl‐D‐aspartate (NMDA) usually produced a hyperpolarization followed by a depolarization in normal Mg2+ solution. 2. A hyperpolarizing response and a depolarizing response could be evoked separately by appropriate positioning of the puff pipette. The NMDA‐induced hyperpolarization was blocked by a low‐Ca2+ solution or a tetrodotoxin (TTX)‐containing solution, but under these conditions the NMDA‐induced depolarization was spared. The amplitude of NMDA‐induced hyperpolarizations was 7.7 +/‐ 2.7 mV (n = 13) at the resting membrane potential level. 3. An NMDA‐induced hyperpolarization had two components. A fast component reversed at about ‐76 mV and a slow component reversed at ‐90 mV. The reversal potential of the slow component shifted in the depolarizing direction of hyperpolarizing direction when the slice was bathed in a high or low‐K+ solution, respectively. 4. The reversal potentials of NMDA‐induced hyperpolarizations were similar to the synaptic potentials evoked by fimbrial stimulation. The reversal potentials of the fast and slow components were close to the IPSP reversal potential (‐70 mV) and the late hyperpolarizing potential (LHP) reversal potential (‐95 mV), respectively. 5. NMDA‐induced hyperpolarizations were blocked by the specific NMDA receptor antagonist 2‐amino‐5‐phosphonopontanoate (APV). The fast component of an NMDA‐induced hyperpolarization was blocked by the specific GABAA receptor antagonist, bicuculline, and the slow component was depressed by the specific GABAB receptor antagonist, phaclofen. 6. Glutamate receptor subtype‐specific agonists, such as kainate or quisqualate, could induce similar hyperpolarizations which had bicuculline‐sensitive and insensitive components. These non‐NMDA‐type agonist‐induced hyperpolarizations were not affected by APV (50 microM) but were blocked by kynurenic acid (1 mM). 7. We conclude that these excitatory amino acid‐induced hyperpolarizations observed in the rat DLSN are mediated by GABAergic interneurones which have both non‐NMDA‐type and NMDA‐type receptors.
Calcium channels in solitary retinal ganglion cells from post‐natal rat.
Authors: Karschin A , Lipton S A
Published: December 2014

1. Calcium currents from identified, post‐natal retinal ganglion cell neurones from rat were studied with whole‐cell and single‐channel patch‐clamp techniques. Na+ and K+ currents were suppressed with pharmacological agents, allowing isolation of current carried by either 10 mM‐Ca2+ or Ba2‐ during whole‐cell recordings. For cell‐attached patch recordings, the recording pipette contained 96‐110 mM‐BaCl2 while the bath solution consisted of isotonic potassium aspartate in order to zero the neuronal membrane potential. 2. A transient component, present in approximately one‐third of the whole‐cell recordings resembles closely the T‐type calcium current observed previously in other tissues. This component activates at low voltages (‐40 to ‐50 mV from holding potentials negative to ‐80 mV), inactivates with a time constant of 10‐30 ms at 35 degrees C, and is carried equally well by Ba2+ or Ca2+. In single‐channel recordings small (8 pS) channels are observed whose aggregate microscopic kinetics correspond well to the macroscopic current obtained during whole‐cell measurements. 3. During whole‐cell recordings, a more prolonged component activates in all retinal ganglion cells at ‐40 to ‐20 mV from a holding potential of ‐90 mV. This component is substantially larger when equimolar Ba2+ replaces Ca2+ as the charge carrier, and is sensitive to the dihydropyridine agonist Bay K8644 (5 microM) and antagonists nifedipine (1‐10 microM) and nimodipine (1‐10 microM). Thus, the dihydropyridine pharmacology of this prolonged component resembles that of the L‐type calcium current found in dorsal root ganglion neurones and in heart cells. Also reminiscent of the L‐current, the prolonged component in this preparation is less inactivated at depolarized holding potentials (‐60 to ‐40 mV) than the transient component. In cell‐attached recordings, large (20 pS) channels are observed with activation properties similar to those of the prolonged portion of the whole‐cell current. 4. omega‐Conotoxin fraction GVIA (omega‐CgTX VIA), a peptide from the venom of the snail Conus geographus, produces a readily reversible blockade of all components of the calcium current in these central mammalian neurones. This finding is in contrast to that of other preparations in which this toxin is responsible for an ephemeral block of T‐current but a long‐lasting block of other components of calcium current. 5. In summary, at least two components of calcium current with discrete underlying unitary events are present in post‐natal retinal ganglion cells from rat. One component closely resembles the T or transient current observed in other cell types.(ABSTRACT TRUNCATED AT 400 WORDS)