bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation of GABA‐gated chloride currents by intracellular Ca2+ in cultured porcine melanotrophs.
Authors: Mouginot D , Feltz P , Schlichter R
Published: December 2014

1. The modulatory role of intracellular Ca2+ concentration ([Ca2+]i) on gamma‐aminobutyric acid type A (GABAA) receptor‐gated Cl‐ currents was investigated in dialysed and intact cells of cultured porcine pituitary intermediate lobe (IL) cells using the patch‐clamp technique. In order to isolate Ca2+ and Cl‐ currents all other membrane currents were blocked pharmacologically. Isoguvacine, a specific GABAA receptor agonist, was used to activate selectively GABAA receptor‐mediated whole‐cell and single‐channel Cl‐ currents. 2. In the whole‐cell recording (WCR) configuration inward Ca2+ currents triggered before and/or during the application of isoguvacine (100 microM), did not inhibit the GABAA receptor‐mediated response. This lack of effect of calcium currents was obtained in all situations tested, i.e. when the intracellular Ca2+ concentration was only weakly buffered (0.5 mM‐EGTA in the pipette solution), not buffered at all (no EGTA added to the pipette solution) or when the resting [Ca2+]i was buffered at 10(‐7) M (pCa 7) with internal EGTA. 3. At pCa 7, simultaneous application of isoguvacine (100 microM) and caffeine (10 mM) resulted in a 47 +/‐ 15% reduction of the whole‐cell GABAA response. In the same conditions, a ten times lower concentration of caffeine (1 mM), induced a transient increase of the GABAA response which turned into a steady‐state inhibition during the subsequent applications. 4. At pCa 7, when isoguvacine (100 microM) was applied together with 3Me‐His2‐TRH (50 nM), a potent analogue of the calcium‐recruiting thyrotrophin‐releasing hormone, the GABAA receptor‐gated Cl‐ current was increased by 40 +/‐ 8%. In the absence of the Ca2+ chelator EGTA in the pipette solution, either potentiating or inhibitory effects of 3Me‐His2‐TRH on the GABAA response were observed. 5. If a high concentration (18 mM) of the calcium chelator EGTA was included in the pipette solution, caffeine and 3Me‐His2‐TRH had markedly lower effects on the GABAA response than those observed at pCa 7, suggesting that the effect of both substances was mediated by an increase in [Ca2+]i. 6. In the absence of extracellular Ca2+, the effects of caffeine and 3Me‐His2‐TRH were not significantly different from those obtained in the presence of Ca2+ (5 mM), suggesting that Ca2+ influx was not the major route for increasing [Ca2+]i. 7. In the cell‐attached (CA) configuration, the presence of isoguvacine (3‐5 microM) in the pipette solution triggered the opening of channels displaying multiple current levels.(ABSTRACT TRUNCATED AT 400 WORDS)
Respiratory‐associated rhythmic firing of midbrain neurones in cats: relation to level of respiratory drive.
Authors: Chen Z , Eldridge F L , Wagner P G
Published: December 2014

1. We recorded phrenic nerve activities and single unit firing of mesencephalic neurones in unanaesthetized supracollicularly decerebrated, paralysed and ventilated cats, in which vagi and carotid sinus nerves had been ablated. We made these measurements first at low levels of respiratory drive associated with normal PCO2 levels, then with increased respiratory drive and levels of phrenic activity produced by hypercapnia or by carotid sinus nerve stimulation. 2. We found that at least a quarter of the neurones in the central tegmental field of the mesencephalon, which were irregularly tonic or silent at low respiratory drives, developed a rhythmic increase of firing associated with each respiration. There appeared to be a threshold at about 50% of maximum respiratory activity, below which the respiratory‐associated rhythm did not occur. Above this level, neuronal firing increased in graded fashion with increasing magnitude of respiratory activity. The latency from onset of phrenic activity to onset of increased neuronal firing was quite long (1.0 s) at drives just above the threshold but shortened to as little as 0.3 s as drive increased towards its maximum. 3. Cutting the spinal cord at C1‐C2 had no effect on the ability of increased respiratory activity to generate a respiratory‐associated rhythm in mesencephalic neurones. 4. Short‐lasting anaesthesia with the agent Saffan caused mesencephalic neurones to lose the respiratory‐associated rhythm with little change in phrenic activity and no change in respiratory cycle timing. 5. We also found a mesencephalic response to ventilator‐induced chest expansion. The latency of the response from onset of expansion, indexed by fall of airway PCO2, to onset of neurone firing was shorter (0.2 s) than that found with the respiratory‐associated rhythm. In seventeen neurones we found both the respiratory‐associated rhythm and the independent ventilator‐associated rhythm. 6. We interpret our findings to show that the respiratory‐associated rhythmic firing of midbrain neurones is not primarily involved in generation or modulation of the motor function of the respiratory oscillator. We believe, instead, that these neurones are part of a sensory pathway conveying information about the magnitude of central neural respiratory drive, as well as spinally transmitted information from receptors in the chest wall, to thalamus and cortex. We suggest that the sensation ultimately generated may be that of ‘air hunger’ or dyspnoea.
Tonic interocular suppression and binocular summation in human vision.
Authors: Denny N , Frumkes T E , Barris M C , Eysteinsson T
Published: December 2014

1. Spatial sensitivity of human foveal vision was examined using sinusoidally modulated gratings. Our primary concern was the influence of interocular light adaptation upon monocular visibility. 2. Interocular adapting influences depend upon spatial frequency and adapting luminance. Interocular adaptation has a negligible influence upon the sensitivity to 1 cycle/deg gratings. Any visible interocular adapting field improves the sensitivity to intermediate spatial frequencies (2‐5 cycles/deg). 3. Brighter interocular backgrounds (greater than 0.1 cd/m2) improve sensitivity to higher spatial frequencies (10‐20 cycles/deg). 4. The interocular adapting influences summarized in (2) and (3) above cannot be duplicated by monocular or binocular adaptation. Similarly, monocular or binocular adaptation have negligible influences upon binocular visibility. 5. The interocular adapting effect summarized in (3) above can be duplicated by pressure blinding the contralateral eye. We conclude that monocular spatial sensitivity is subject to a tonic interocular suppression (TIS) from the dark‐adapted eye. 6. The spatial sensitivity resulting from binocular viewing is nearly identical to that observed by combining monocular viewing with interocular light adaptation. We suggest that the improvement in sensitivity resulting from two‐eyed viewing may be attributable to the removal of TIS instead of to binocular physiological summation.
Ontogenic development of lamb intestinal sodium‐glucose co‐transporter is regulated by diet.
Authors: Shirazi‐Beechey S P , Hirayama B A , Wang Y , Scott D , Smith M W , Wright E M
Published: December 2014

1. The ontogenic development of the intestinal Na(+)‐glucose co‐transporter was measured in lambs as a function of diet. Transport activity was assayed in brush‐border membrane vesicles and the expression of transport protein in the brush‐border membrane determined by Western analysis. 2. Na(+)‐dependent D‐glucose transport increased to a maximum (300‐700 pmol mg‐1 s‐1) within the first 2 weeks of birth and then declined to negligible amounts (less than 10 pmol mg‐1 s‐1) over the next 8 weeks. There was no further change over the next 2‐3 years. Early changes were associated with modifications in both the maximum velocity Vmax for transport and expression of carrier protein in the brush‐border plasma membrane. 3. Maintaining lambs on a milk replacer diet beyond the normal weaning period prevented the normal decline in the expression of Na(+)‐glucose co‐transport. At 5 weeks the transport rate was 433 +/‐ 150 pmol mg‐1 s‐1 in lambs maintained on milk replacer, but only 79 +/‐ 40 pmol mg‐1 s‐1 in normally reared control lambs. 4. Infusing the proximal intestine of 2‐ to 3‐year‐old sheep with 30 mM‐D‐glucose for four days increased the rate of transport 40‐ to 80‐fold above that found in control animals perfused with mannitol. A similar but smaller increase was observed in one animal perfused with the non‐metabolizable sugar alpha‐methyl‐D‐glucopyranoside. The induced increase in glucose transport was correlated with the expression of the co‐transporter protein in the brush‐border plasma membrane. 5. It is concluded that the age‐related decline in Na(+)‐glucose co‐transport in the sheep intestine is directly due to the decrease in D‐glucose (and D‐galactose) reaching the small intestine after development of the rumen. These results further suggest that luminal sugar substrates for the co‐transporter promote both the maintenance and the up‐regulation of the brush‐border transport protein and it is the intact sugar itself which controls gene expression during enterocyte maturation.
Endoneurial blood flow in rat sciatic nerve during development.
Authors: Kihara M , Weerasuriya A , Low P A
Published: December 2014

1. Endoneurial blood flow (EBF) in the sciatic nerve of rats aged 2‐12 weeks was studied using microelectrode H2 polarography. 2. EBF is highest in 2‐week‐old rats and progressively declines during development. Mean arterial pressure (MAP) is low at 2 weeks of age, gradually increases through the next 4 weeks, and is relatively constant thereafter. The decrease in EBF, in spite of an increase in MAP, occurs because the endoneurial vascular resistance is increasing faster than the MAP. 3. The higher EBF in younger rats is not due to the smaller diameter of their nerves. Sural and tibial nerves of 12‐week‐old rats, with diameters comparable to that of the sciatic nerve of a 3‐week‐old rat, have EBFs similar to that of the sciatic nerve of a 12‐week‐old rat. 4. There was no compelling evidence of autoregulation of EBF in 3‐week‐old rats over a MAP range from ‐40 to +30 mmHg of the normal value. 5. The increase of nerve vascular resistance with maturation is probably due to a decrease in capillary density and, to a lesser extent, to an increase in plasma viscosity and haematocrit. 6. The higher EBF in immature rats is likely to be a developmentally adaptive mechanism which permits greater blood‐nerve exchange of material to accommodate the greater metabolic needs of rapidly elongating and myelinating axons and proliferating Schwann cells.
The mechanism of prediction in human smooth pursuit eye movements.
Authors: Barnes G R , Asselman P T
Published: December 2014

1. Experiments have been conducted on human subjects to determine the role of prediction in smooth eye movement control. Subjects were required to actively pursue a small target or stare passively at a larger display as it moved in the horizontal plane. 2. Target motion was basically periodic, but, after a random number of cycles an unexpected change was made in the amplitude, direction or frequency of target motion. Initially, the periodic stimulus took the form of a square waveform. In subsequent experiments, a triangular or sawtooth waveform was used, but in order to examine the timing of the response in relation to stimulus appearance, the target was tachistoscopically illuminated for 40‐320 ms at the time that it passed through the mid‐line position. 3. When subjects either actively pursued the target or stared passively at the larger display a characteristic pattern of steady‐state eye movement was evoked composed of two phases, an initial build‐up of eye velocity that reached a peak after 200 ms, followed by a decay phase with a time constant of 0.5‐2 s. The build‐up phase was initiated prior to target displacement for square‐wave motion and before onset of target illumination for other waveforms. 4. The peak eye velocity evoked gradually increased over the first two to four cycles of repeated stimulation. Simultaneously, the response became more phase advanced, the reaction time between stimulus onset and the time at which peak velocity occurred decreasing from an average of 300 to 200 ms for triangular waveform stimuli. 5. When there was a sudden and unexpected change in amplitude and direction of the stimulus waveform, the eye movement induced had a peak velocity and direction that was inappropriate for the current visual stimulus, but which was highly correlated with the features of the preceding sequence in the stimulus. 6. When there was a sudden change in the frequency of the stimulus waveform the predictive eye movement was induced with a timing appropriate to the periodicity of the previous sequence but inappropriate to the new sequence. 7. The results indicate that prediction is carried out through the storage of information about both the magnitude and timing of eye velocity. The trajectory of the averaged eye velocity response was similar in form irrespective of the duration of target exposure or basic stimulus frequency, suggesting that the predictive estimate is released as a stereotyped volley of constant duration but varying magnitude under the control of a periodicity estimator.(ABSTRACT TRUNCATED AT 400 WORDS)
Metabolic capacity and myosin expression in single muscle fibres of the garter snake.
Authors: Wilkinson R S , Nemeth P M , Rosser B W , Sweeney H L
Published: December 2014

1. The transversus abdominis muscle of the garter snake contains fibres of three types: tonic (T), slower twitch (S) and faster twitch (F). Fibre types can be determined by anatomical criteria in living preparations. Individual fibres identified as T, S or F were excised from the muscle and subdivided for two types of biochemical examination. Enzymes of energy metabolism were assayed using quantitative microfluorometric methods. Myosin heavy chain composition was determined by gel electrophoresis. In separate experiments, twitch time‐to‐peaks of F and S fibres were measured to assess the range of contraction times present within the muscle's twitch fibre population. 2. Metabolic subgroups of fibres were delineated by the relative activities of adenylokinase (AK), lactate dehydrogenase (LDH) and beta‐hydroxyacyl‐CoA‐dehydrogenase (beta OAC). The metabolic subgroups corresponded to the anatomical fibre types. Type F fibres had high levels of enzymes associated with glycolytic (LDH) and high‐energy phosphate (AK) metabolism. Type T fibres had high levels of the oxidative enzyme beta OAC. Type S fibres had both types of enzyme activity in intermediate and variable amounts. 3. Three myosin heavy chain isoforms were present in the muscle. Type F and type T fibres each expressed a single isoform, denoted F and T respectively. Type S fibres expressed significant quantities of two isoforms: an isoform unique to this fibre type (denoted S) and the F isoform. 4. Electrophoretic mobility and antibody reactivity of the F myosin heavy chain isoform resembled that of mammalian fast‐twitch myosin. By the same criteria, the T isoform resembled mammalian slow‐twitch myosin. The S isoform exhibited intermediate characteristics: its antibody reactivity was similar to mammalian fast‐twitch myosin, but its electrophoretic mobility was that of mammalian slow‐twitch myosin. 5. Based on whole‐muscle analysis, two myosin alkali light chains, denoted ALC1 and ALC2, and one myosin regulatory light chain were present. Gel patterns suggested that ALC1 and ALC2 exist as both homodimers and heterodimers. 6. The population of type S fibres within a given muscle exhibited a much wider range of twitch contraction times than did the population of type F fibres. Diversity of contractile properties among type S fibres may result, in part, from differential co‐expression of two myosin heavy chain isoforms, together with highly variable ratios of enzymes from two major metabolic pathways. 7. The clear biochemical distinction among fibre types indicates that each type possesses a unique and limited range of physiological properties.(ABSTRACT TRUNCATED AT 400 WORDS)
Intracellular analysis of inherent and synaptic activity in hypothalamic thermosensitive neurones in the rat.
Authors: Curras M C , Kelso S R , Boulant J A
Published: December 2014

1. Intracellular neuronal activity was recorded in rat preoptic‐anterior hypothalamic tissue slices. Thirty neurones were classified as warm sensitive, cold sensitive or temperature insensitive, based on their firing rate response to temperature changes. Seventy‐seven per cent of the neurones were temperature insensitive, which included both spontaneously firing and silent neurones. Of all neurones, 10% were warm sensitive and 13% were cold sensitive. 2. Silent temperature‐insensitive neurones had lower input resistances (126 +/‐ 21 M omega) than thermosensitive neurones (179 +/‐ 24 M omega). Regardless of neuronal type, however, resistance was inversely related to temperature. 3. Warm‐sensitive neurones were characterized by a slow, depolarizing pre‐potential, whose rate of rise was temperature dependent. This depolarizing potential disappeared during current‐induced hyperpolarization, suggesting that intrinsic mechanisms are responsible for neuronal warm sensitivity. 4. Spike activity in cold‐sensitive neurones correlated with putative excitatory and inhibitory postsynaptic potentials, whose frequency was thermosensitive. This suggests that cold sensitivity in these neurones depends on synaptic input from nearby neurones. 5. Like cold‐sensitive neurones, action potentials of temperature‐insensitive neurones often were preceded by short duration (less than 20 ms), rapidly rising pre‐potentials, whose rates of rise were not affected by temperature. In some temperature‐insensitive neurones, depolarizing current injection increased both firing rate (by 5‐8 impulses s‐1) and warm sensitivity, with pre‐potentials having temperature‐dependent rates of rise. We suggest that temperature‐insensitive neurones employ two opposing, thermally dependent mechanisms: a voltage‐dependent depolarizing conductance and a hyperpolarizing sodium‐potassium pump.
Voltage‐activated potassium channels in blowfly photoreceptors and their role in light adaptation.
Authors: Weckström M , Hardie R C , Laughlin S B
Published: December 2014

1. The membrane properties of the photoreceptors of the blowfly (Calliphora vicina) were investigated in situ by making intracellular recordings in the intact retina, using discontinuous single‐electrode current and voltage clamp techniques. Single channels were investigated using inside‐out patches from dissociated photoreceptors. 2. Photoreceptors have a resting potential in darkness of ‐60.4 +/‐ 6.6 mV (mean +/‐ S.D.; n = 43), a resting input resistance of 32 +/‐ 3 M omega (n = 11) and membrane time constant of 4.1 +/‐ 1 ms (n = 9). These values give a total cell capacitance of 0.13 nF and an effective membrane area of 1.3 x 10(‐4) cm2. 3. Single‐electrode voltage clamp reveals a voltage‐sensitive outward current with an activation threshold at approximately ‐75 mV. This conductance has two kinetic components, the slower component activating at more depolarized levels. On the basis of its kinetics, a reversal potential of ‐85 +/‐ 6 mV (n = 6), sensitivity to intracellularly injected tetraethylammonium chloride (TEA), and its slow and partial inactivation (approximately 25%) this mechanism is classified as a delayed rectifier potassium conductance. 4. Voltage‐sensitive potassium channels showing similar properties were found in excised inside‐out patches from dissociated photoreceptors. Single‐channel conductances are ca 20 pS for both fast and slow kinetic components, indicating a channel density in the intact cell of ca 2 microns ‐2. The reversal potential follows the Nernst slope for potassium ions. 5. The voltage dependence of the conductance was determined in patches containing channels of predominantly one or the other kinetic component. The midpoint of the activation curve is ‐65 mV for the fast and ‐50 mV for the slow component. Activation time constants (measured from a holding potential of ‐100 mV) are voltage dependent, and in the range 1‐10 ms for the fast and 5‐40 ms for the slow component. Both kinetic components are blocked by TEA (greater than 2.5 mM). The slow component is more sensitive to quinidine (greater than 200 microM), and the fast component to 4‐aminopyridine (4‐AP; greater than 200 microM). 6. In the intact preparation the outward current shows no dependence on light stimulation in the studied ranges of voltage (up to ‐25 mV) and intensity (up to 5.5 x 10(4) effective photons). Ensemble averages of channel openings in perfused inside‐out patches show no dependence on calcium concentration in the range 10 nM‐1.8 mM.(ABSTRACT TRUNCATED AT 400 WORDS)
Voltage‐dependent calcium and potassium channels in Schwann cells cultured from dorsal root ganglia of the mouse.
Authors: Amédée T , Ellie E , Dupouy B , Vincent J D
Published: December 2014

1. Whole‐cell patch clamp studies were carried out on Schwann cells in organotypic cultures of dorsal root ganglia (DRG) from OF1 mice embryos (18‐19 days). 2. In standard external solution, from a holding potential of ‐70 mV, two types of voltage‐dependent K+ currents were recorded: a fast transient current and a delayed sustained current. With a holding potential of ‐30 mV, only the delayed sustained current could be evoked. 3. Both K+ currents were inhibited by tetraethylammonium chloride (TEA) and 4‐aminopyridine (4‐AP) in a dose‐dependent manner. For the transient current the half‐maximal effective dose was 100 mM for TEA and 1.3 mM for 4‐AP. For the delayed sustained current the half‐maximal effective dose was 11 mM for TEA and 4 mM for 4‐AP. Both currents were insensitive to external Ca2+. 4. The delayed sustained current, isolated by use of a holding potential of ‐30 mV displayed a ‘cumulative inactivation’ which was removed by hyperpolarizing the membrane to ‐70 mV between each test pulse. 5. In K(+)‐free external and pipette solutions, with 10 mM‐external Ca2+, from a holding potential of ‐70 mV voltage‐dependent Ca2+ channel currents were recorded. The threshold for activation was ‐45.3 +/‐ 5.4 mV (mean +/‐ S.D., n = 5) and the current inactivated fully at the end of the test potential. The current was unaffected by 2 microM‐tetrodotoxin (TTX) and totally blocked by 5 mM‐Co2+. 6. Equimolar replacement of external Ca2+ by Ba2+ did not significantly modify the voltage dependence (threshold for activation ‐42.8 +/‐ 6.4 mV, n = 7) or the magnitude of the inward current. Ca2+ and Ba2+ were equally permeant. The fully inactivating current was insensitive to both nifedipine and Bay K 8644 (1 microM each). Increasing the external Ba2+ concentration from 10 to 89 mM enhanced the Ba2+ current and shifted the voltage dependence of the current (threshold for activation, ‐30.5 +/‐ 7.3 mV, n = 9) along the voltage axis as expected for altered external surface potential. 7. In 89 mM‐external Ba2+ solution, some cells displayed an additional slowly decaying current which was totally blocked by nifedipine (1 microM). 8. Ca2+ channel currents were recorded only when DRG neurons were present in the culture, as excision of explants and subsequent axonal degeneration led to loss of detectable Ca2+ channel currents. This phenomenon was never observed for K+ currents. 9. We conclude that mouse Schwann cells in organotypic culture possess voltage‐dependent K+ and Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Differential response of renin secretion to vasoconstrictors in the isolated perfused rat kidney.
Authors: Scholz H , Kaissling B , Inagami T , Kurtz A
Published: December 2014

1. We have examined whether an increase of renal vascular resistance is generally accompanied by an inhibition of renin secretion. The effects of vasoconstriction produced by angiotensin II (Ang II), arginine‐vasopressin (AVP), and potassium (KCl) depolarization on vascular resistance and on renin release from isolated rat kidneys perfused at constant pressure of 100 mmHg were investigated. 2. Histological examination performed on some representative kidneys revealed that the tubular lumina of all segments within the cortex were patent and the brush borders of the proximal tubules were well preserved. The renal vasculature and the juxtaglomerular region appeared to be morphologically intact. By immunocytochemistry, renin‐positive cells were found exclusively in the wall of the afferent arterioles. 3. Basal flow rate through isolated kidneys was 14.5 +/‐ 2.0 ml min‐1 (g kidney weight (gkw))‐1 (mean +/‐ S.E.M., n = 10). Under control conditions renin secretory rates were in the range of 30‐40 (ng Ang I h‐1) min‐1 gkw‐1. 4. Ang II (100 pM) caused a decrease of renal flow rate to 42 +/‐ 2% of control which was accompanied by a reduction of renin secretion rates by a factor of 4. 5. AVP (10 pM to 1 nM) reduced renal perfusate flow in a dose‐dependent fashion to a minimum of 25 +/‐ 3% of control. The vasoconstrictor effect of AVP was paralleled by a concentration‐dependent increase of renin secretory rates reaching a factor of maximally 5 when AVP was used at a concentration of 1 nM. The stimulatory effect of AVP on renin release could be mimicked by [deamino‐Cys1, D‐Arg8]‐vasopressin (dDAVP), a vasopressin analogue with prevalent V2 receptor agonistic properties. In the presence of dDAVP (100 nM, 1 microM) renal flow rate reversibly increased by 8 and 12% of control values, respectively. 6. Depolarizing concentrations of KCl (30 mM) decreased perfusate flow to 20 +/‐ 4% of control. The vasoconstrictor effect of KCl was paralleled by an increase of the arterio‐venous difference of perfusate renin activity to such an extent that the rate of renin release remained unaltered. 7. Our findings suggest that there exists no general inverse relationship between renal arteriolar resistance and renin secretion. Our study, moreover, does not support a functional role of potential operated calcium channels in the control of renin secretion. Finally, we conclude that V2 receptors are present on juxtaglomerular epithelioid cell membranes and mediate the stimulatory effect of AVP on renin release from isolated rat kidneys.
Effect of conduction block at axon bifurcations on synaptic transmission to different postsynaptic neurones in the leech.
Authors: Gu X N
Published: December 2014

1. The cutaneous receptive field of the medial pressure (mP) sensory neurone in the leech has been examined. The cell has one major receptive field and an anterior and a posterior minor receptive field, principally on lateral and dorsal skin. The two minor receptive fields are contiguous with the major receptive field and are innervated by fine anterior and posterior axons, but there is no overlap between major and minor receptive fields. 2. At low frequencies of stimulation of the minor receptive fields, conduction block takes place in the mP cell at the central branch point within the leech ganglion. 3. The mP cell synapses directly with many other cells in the leech ganglion, including the anterior pagoda (AP) cell, longitudinal (L) motoneurone and the annulus erector (AE) motoneurone, which were studied as a group of postsynaptic neurones. Conduction block in the mP cell affects its synaptic transmission to all three postsynaptic neurones, but the effect can be different in different postsynaptic neurones. Block at the central branch point for an impulse travelling along the anterior axon reduces transmission to the AE cell much more than to the AP or L cells, while block at the central branch for an impulse travelling along the posterior axon has the reverse effect. 4. The distribution of functional connections of the branches of the mP cell with each postsynaptic cell was studied. For this analysis, branches of the mP cell were selectively silenced either during conduction block or by laser microsurgery. Generally, nearly all of the functional connections with the L and AP cell are made by anterior branches of the mP cell while the connection with the AE cell was primarily made by posterior branches of the mP cell. 5. The possible sites of contact between the mP cell and postsynaptic cells were determined by injecting separate markers into the mP cell and a postsynaptic cell. In confirmation of physiology, the mP cell's posterior branches had few, if any, contacts with the AP cell, while anterior branches had few, if any, contacts upon the AE cell. 6. Conduction block can thus act as a switch in the central nervous system (CNS), altering the mP cell's pattern of synaptic transmission to different postsynaptic neurons depending upon the region of a single sensory neurone's receptive field that is stimulated. This effect, dependent upon inputs to a single neurone, may be expected to influence the performance of the system and its outputs.
Rapid resetting of human baroreflex working range: insights from sympathetic recordings during acute hypoglycaemia.
Authors: Fagius J , Berne C
Published: December 2014

1. Human muscle nerve sympathetic activity (MSA), which is governed by baroreflexes and involved in blood pressure homeostasis, is increased during acute insulin‐induced hypoglycaemia. 2. To elucidate the detailed relationship between MSA and blood pressure during hypoglycaemia, 0.15 i.u. (kg body weight)‐1 regular human insulin was given intravenously to eight fasting, healthy volunteers. Microneurographic recording of MSA in the peroneal nerve was made with simultaneous monitoring of arterial blood pressure by a finger cuff (Finapres). The course of MSA and blood pressure was monitored for 30 min before and 60 min after insulin injection. In three subjects control recording without insulin injection was made for the same duration. 3. Stimulus‐response regression lines were constructed by plotting diastolic blood pressure against the occurrence frequency of MSA for the period of initial rest, the period of maximal MSA outflow during hypoglycaemia and the period of glucose counter‐regulation. The control experiments were analysed for the corresponding periods. 4. The stimulus‐response line was stable throughout the control experiments, whereas it was shifted either to the left or to the right during hypoglycaemia, and regularly shifted to the left (i.e. towards a lower blood pressure) during glucose counter‐regulation, without change of slope. 5. It is concluded that the changes in MSA during acute hypoglycaemia are not secondary to baroreflex regulation but instead are characterized by acute resetting of the baroreflex working range without change of sensitivity.
The effect of naloxone on spinal reflexes to electrical and mechanical stimuli in the anaesthetized, spinalized rat.
Authors: Hartell N A , Headley P M
Published: December 2014

1. Previous studies of the effects of naloxone on spinal neural responses have yielded disparate results. The reasons for this remain unclear but may relate to the diversity of animal preparations used, the route of administration of naloxone, the site and modality of the stimuli and the intensity of afferent input used. 2. A model requiring little preparative surgery compared to most other electrophysiological preparations has now been used to investigate the effects of naloxone (1, 10, 20 and 50 micrograms kg‐1 I.V.) on single‐motor‐unit flexion reflex responses to alternating mechanical and electrical stimuli in spinalized rats, anaesthetized with alpha‐chloralose. 3. Naloxone caused a dose‐dependent facilitation of reflex responses to electrical stimuli delivered at intensities sufficient to activate either A fibres alone or A and C fibre afferents together. The component of the responses presumed to be due primarily to activation of C fibres was enhanced relatively more than the A fibre component. 4. Responses evoked during high‐intensity mechanical pinch stimuli were not facilitated by equivalent doses of naloxone. The post‐stimulus after‐discharge was, however, enhanced by a similar percentage to the response to high‐intensity electrical stimuli. 5. Lowering the intensity of the mechanical stimulus led to a diminished firing rate of the units during the stimulus itself. The stimulus was, nevertheless, still noxious. Naloxone was found to have a facilitatory effect on this smaller evoked response both during the pinch stimulus and during the period of after‐discharge. The apparent lack of effect of naloxone during the higher intensity mechanical stimulus may be due to neurones in the polysynaptic pathway being activated at near‐maximal firing rates. 6. We conclude that the ability of naloxone to facilitate spinal reflexes is not dependent on the nature of the stimulus, at least between electrical and mechanical stimuli, but is more a function of the intensity of the applied stimulus.
The effect of strophanthidin on action potential, calcium current and contraction in isolated guinea‐pig ventricular myocytes.
Authors: Levi A J
Published: December 2014

1. A method is described for producing high yields of calcium‐tolerant ventricular myocytes from guinea‐pig hearts (73.4% rod‐shaped cells, n = 19). Their action potential (AP) and membrane currents were recorded using conventional microelectrodes and cell shortening was measured optically using a linear photodiode array. 2. The sensitivity of the guinea‐pig Na(+)‐K+ pump to strophanthidin (a rapidly acting digitalis analogue) was determined by measuring the inhibition of outward pump current by different doses. The pump was found to have a dissociation constant (KD) for strophanthidin of 1.11 x 10(‐5) M, and 5 x 10(‐4) M‐strophanthidin inhibited the pump maximally. 3. Exposure to strophanthidin resulted in an initial lengthening followed by a shortening of the AP, and an increased contraction. Initial AP lengthening was associated with a more positive AP plateau which became more negative as the AP shortened. 4. There was a reversible reduction of Ca2+ current (ICa) during exposure to strophanthidin. ICa changed reciprocally with contraction and with a similar time course. 5. Strophanthidin exposure caused a reduction of ICa at all activating voltages, suggesting that it resulted in a reduction of Ca2+ conductance with little change of its voltage dependence. 6. The role of an increase of intracellular calcium (Cai2+) was investigated by impaling myocytes with microelectrodes containing BAPTA 1,2‐bis (2‐amino‐phenoxy)ethane‐N,N,N',N'‐tetraacetic acid, a calcium chelator) to increase Cai2+ buffering. Strophanthidin still shortened the AP when BAPTA was present, suggesting that a rise of Cai2+ is not a major cause of AP shortening. 7. Although AP shortening was little affected, the decline of ICa with strophanthidin was markedly reduced when BAPTA was present, suggesting that a rise of Cai2+ was the cause of the ICa decline with strophanthidin. 8. When barium ions carried the current through Ca2+ channels, strophanthidin did not reduce Ca2+ channel current, suggesting that this compound does not have a direct inhibitory effect on the channel. 9. The results suggest that strophanthidin causes a reduction of ICa by increasing Cai2+, via the mechanism of Cai(2+)‐dependent inactivation of ICa. The reduction of ICa at least partially explains the AP shortening and more negative plateau with strophanthidin. 10. The shortening of the AP, more negative plateau and reduced ICa have negative inotropic effects which oppose the direct positive inotropic effect of strophanthidin.
The role of adenosine in dilator responses induced in arterioles and venules of rat skeletal muscle by systemic hypoxia.
Authors: Mian R , Marshall J M
Published: December 2014

1. In experiments on anaesthetized rats, we have studied the role of adenosine in mediating responses induced in individual arterioles and venules of the spinotrapezius muscle by systemic hypoxia. 2. During systemic hypoxia induced by breathing 6% O2 for 3 min, some arterioles and venules dilated while others constricted. Topical application of the adenosine receptor antagonist, 8 phenyl‐theophylline (8‐PT), to the spinotrapezius had no effect on the constrictor responses but greatly reduced the dilator responses. The vessels nearest to the capillary bed‐terminal arterioles and collecting venules‐‐were most affected; their mean changes in diameter were reduced from 39 and 8% to 11 and ‐1.6% respectively. 3. In accord with these results, topical application of adenosine (2 x 10(‐7)‐2 x 10(‐3) M) produced graded dilation of all sections of the arterial and venous trees; the terminal arterioles and collecting venules were most responsive, being dilated at maximum by 31 and 15% respectively. The dilator responses induced in those vessels that constricted during hypoxia were fully comparable with those that dilated during hypoxia. 4. Histochemical analysis of the spinotrapezius revealed that oxidative fibres that most readily release adenosine, glycolytic and mixed fibres were all evenly distributed throughout the muscle. There is no reason to suppose that some vessels are preferentially influenced by oxidative fibres. 5. These results indicate that adenosine plays a major role in dilating both arterioles and venules of muscle during systemic hypoxia. But, they are consistent with the idea that the adenosine that is important is not released from muscle fibres, but synthesized by 5'‐nucleotidase localized to the blood vessels; its activity may decrease proximally along the vascular tree and may vary from one vessel to another depending on the local O2 tension.
The length‐response properties of cells in the feline dorsal lateral geniculate nucleus.
Authors: Jones H E , Sillito A M
Published: December 2014

1. In this report we have systematically examined the length‐response properties of a large population of cells recorded in the cat dorsal lateral geniculate nucleus (dLGN). The responses of A laminae dLGN cells were assessed by the use of conventional single‐unit extracellular recording techniques. The length preference of these cells was examined by plotting multihistogram length tuning curves to moving bars of light. Bar length was randomized in an interleaved fashion under computer control. The other stimulus parameters were standardized within the limits of those routinely used to assess the length preference of cortical cells. 2. The majority of cells (186/198), whose length‐response properties are considered in detail in this report, exhibited strong centre‐surround antagonism and a mean degree of length tuning equivalent to, or exceeding, that seen in most cortical hypercomplex cells (71 +/‐ 1.18%, S.E.M., n = 186). 3. The values for X cells (74 +/‐ 1.41%, S.E.M., n = 100) and Y cells (67 +/‐ 2.13%, S.E.M., n = 74) were very similar, as were those of the on‐centre (71 +/‐ 1.51%, S.E.M., n = 123) and off‐centre (71 +/‐ 1.85%, S.E.M., n = 63) subgroups. 4. A distinct subgroup of the Y cell population was identified. These comprised the remaining twelve out of the 198 cells examined and their response properties were sufficiently distinct to merit classification as a discrete subpopulation of cells which we have termed nlY cells. They were characterized by very poor levels of both centre‐surround antagonism and length tuning, and were most frequently encountered close to laminar borders. Their response properties have been described in detail elsewhere. 5. We quantitatively compared the degree of length tuning seen with moving bars to the strength of centre‐surround antagonism assessed with flashing spots. The degree of length tuning did not necessarily follow the level of centre‐surround antagonism. 6. Examination of the effects of unilaterally extending bar length to one or other side of the receptive field did not reveal the type of asymmetry frequently seen in cortical hypercomplex cells. 7. The high degree of length tuning seen in this study underlines the potential importance of geniculate response properties to the generation of the length‐response properties of cortical hypercomplex cells. The findings are discussed in relation to the synaptic mechanisms contributing to the generation of length tuning at subcortical and cortical levels.
Both ATP and the peptide VIP are inhibitory neurotransmitters in guinea‐pig ileum circular muscle.
Authors: Crist J R , He X D , Goyal R K
Published: December 2014

1. Intracellular membrane potential recordings were made from circular smooth muscle cells of the guinea‐pig ileum in the presence of atropine (1 microM) and nifedipine (0.1 microM) at 30 degrees C. 2. Perfusion with adenosine triphospate (ATP, 100 microM) and vasoactive intestinal peptide (VIP, 2 microM) resulted in membrane hyperpolarizations of 6.4 +/‐ 0.3 and 6.8 +/‐ 0.3 mV, respectively. Picospritzes of ATP (10 mM in pipette) and VIP (100 microM in pipette) resulted in membrane hyperpolarizations of 6.9 +/‐ 0.4 and 6.3 +/‐ 0.4 mV, respectively. 3. The ATP‐induced hyperpolarizations were antagonized by alpha, beta‐methylene ATP desensitization (100 microM for 30 min) and the ATP antagonist Reactive Blue 2 (200 microM), but were unaffected by the VIP antagonist VIP 10‐28 (1 microM). 4. The VIP‐induced hyperpolarizations were antagonized by VIP 10‐28, but unaffected by alpha, beta‐methylene ATP desensitization and Reactive Blue 2. 5. A single pulse of transmural nerve stimulation (2 ms, 15 mA) resulted in an inhibitory junction potential (IJP) that reached a maximal amplitude of 12.9 +/‐ 0.5 mV at 378 +/‐ 20 ms from the stimulus. This fast IJP was abolished by apamin (2 microM) or tetrodotoxin (1 microM), antagonized by alpha, beta‐methylene ATP desensitization or Reactive Blue 2, but unaffected by VIP 10‐28. 6. In the presence of apamin (1 microM), four pulses of transmural stimulation (2 ms, 20 Hz, 15 mA) resulted in an IJP that reached a maximal amplitude of 4.8 +/‐ 0.2 mV at 1.4 +/‐ 0.1 s from the stimulus. This slow IJP was antagonized by tetrodotoxin (1 microM) or VIP 10‐28 (1 microM), augmented by Reactive Blue 2 (200 microM), and unaffected by alpha, beta‐methylene ATP desensitization. 7. These findings provide evidence that both ATP and VIP are inhibitory neurotransmitters in the circular muscle layer of the ileum and that ATP may be the neurotransmitter responsible for the fast IJP and VIP the neurotransmitter responsible for the slow IJP.
Haemodynamic effects of distension of the descending colon in anaesthetized dogs.
Authors: Cevese A , Mary D A , Poltronieri R , Schena F , Vacca G
Published: December 2014

1. This study was undertaken to determine whether distension of the descending colon in anaesthetized dogs reflexly affects the heart rate, arterial blood pressure or the left ventricular inotropic state. 2. Experiments were performed on twenty‐six dogs, which were anaesthetized with sodium pentobarbitone and artificially ventilated. A segment of the distal descending colon was isolated and was distended with warm Ringer solution at a steady intraluminal pressure. 3. In each animal, distension of the colon caused an increase in heart rate and aortic blood pressure. The response of an increase in heart rate was augmented by preventing changes in aortic blood pressure, and was graded in seven dogs by step increments in the distending pressure. In the same animals, distension of the colon always caused a small increase in left ventricular (dP/dt)max at constant heart rate and aortic blood pressure. 4. In four of the twenty‐six dogs, cutting the pelvic nerves did not abolish the observed responses to the distension. In seven of the twenty‐six dogs, which included the four animals with sectioned pelvic nerves, cutting the hypogastric nerves completely abolished all the observed responses. 5. In thirteen of the twenty‐six dogs, propranolol or bretylium tosylate completely abolished the reflex increases in heart rate and left ventricular (dP/dt)max, and phentolamine or bretylium tosylate abolished the reflex increase in aortic blood pressure. 6. These results showed that distension of the colon reflexly increased the heart rate, arterial blood pressure and left ventricular inotropic state. These reflex responses were mediated by sympathetic effects and their afferent limb involved the hypogastric nerves.
Central command influences cardiorespiratory response to dynamic exercise in humans with unilateral weakness.
Authors: Innes J A , De Cort S C , Evans P J , Guz A
Published: December 2014

1. Changes in ventilation and cardiovascular variables which occur during exercise may be partly due to ‘radiation’ of activity in central neurones innervating exercising muscles to the respiratory and cardiovascular control areas. To test this hypothesis, we compared ventilatory and cardiovascular responses to two levels of steady‐state exercise with each leg separately, in subjects with painless unilateral leg weakness. We assumed that exercise with a weak leg would require more central neural drive than the same level of exercise with the normal leg. 2. Ventilation during exercise with the weak leg was greater than with the normal leg (P less than 0.02). This was a result of greater tidal volume (Vt; P less than 0.005). There was a greater increase in heart rate (P less than 0.005), and systolic (P = 0.001) and diastolic (P less than 0.02) blood pressures during exercise with the weak leg compared to exercise with the normal leg. The increases in stroke volume and cardiac output during exercise were not different with the two legs. 3. These results support the hypothesis that ventilation, blood pressure and heart rate are influenced by the central neural drive to exercise.
Respiratory modulation of the activity in sympathetic neurones supplying muscle, skin and pelvic organs in the cat.
Authors: Boczek‐Funcke A , Häbler H J , Jänig W , Michaelis M
Published: December 2014

1. The respiratory‐related modulation of activity in neurones of the lumbar sympathetic outflow to skeletal muscle, skin and pelvic organs was investigated in anaesthetized, paralysed and artificially ventilated cats, using single‐ and multi‐unit recordings. The activity of the neurones was analysed with respect to the phrenic nerve discharge under various experimental conditions. 2. Neurones tentatively classified as muscle vasoconstrictor and visceral vasoconstrictor neurones exhibited two activity peaks, one caused by baroreceptor unloading during the declining phase of the second order blood pressure waves and a respiratory drive‐dependent peak in parallel with inspiration. The two peaks were separated by depressions of activity in early inspiration and post‐inspiration. After cutting vagus and buffer nerves the activity peak during inspiration remained and was followed and sometimes preceded by a depression of activity. 3. The majority of the neurones tentatively classified as cutaneous vasoconstrictor neurones exhibited no respiratory modulation in their activity. Others exhibited an activity peak in expiration, an activity peak in inspiration, or a respiratory profile similar to that in muscle vasoconstrictor neurones. During increased respiratory drive (induced by hypercapnia) some neurones with unmodulated activity changed to an inspiratory or an expiratory pattern. Neurones discharging predominantly in inspiration projected preferentially to hairless skin. 4. Neurones which were tentatively classified as sudomotor neurones discharged predominantly in early expiration. 5. Some preganglionic neurones which were tentatively classified as motility‐regulating neurones discharged during expiration. The majority of these neurones disclosed no respiratory modulation of their activity. 6. The study shows that different types of neurone of the lumbar sympathetic system exhibit distinct patterns of respiratory modulation in their activity. We conclude that the type and degree of central coupling between respiratory system and sympathetic nervous system may vary according to the destination of the sympathetic neurones.