bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of chronic hypoxia from birth on the ventilatory response to acute hypoxia in the newborn rat.
Authors: Eden G J , Hanson M A
Published: December 2014

1. Newborn rats and their mothers were exposed from birth in a normobaric environmental chamber to an inspired O2 fraction (FI,O2) of 0.13‐0.15 for 5‐10 weeks. 2. The respiratory response to reducing FI,O2 to 0.12 or 0.08 for 6 min was measured in the conscious chronically hypoxic rat pups on post‐natal days 5 and 14 and again at 5‐10 weeks of age. On days 5 and 14 the responses were compared to those of normoxic control pups also exposed acutely to an FI,O2 of 0.12 or 0.08. 3. No significant respiratory response to the acute reduction in FI,O2 was found in the chronically hypoxic pups on post‐natal days 5 and 14, whereas the normoxic pups showed a "biphasic" respiratory response on day 5 and a sustained ('adult') response on day 14. A "biphasic" respiratory response to an FI,O2 of 0.08, but not to an FI,O2 of 0.12, was seen in the chronically hypoxic pups at 5‐10 weeks of age. 4. At 5‐10 weeks recordings from the carotid sinus nerve were made in anaesthetized, paralysed and artificially ventilated rats. The isocapnic hypoxic response curves of chronically hypoxic rats were not significantly different from those of age‐matched normoxic rats. 5. Our results suggest that limiting the rise in arterial O2 pressure which usually occurs at birth alters the ventilatory response to acute hypoxia by post‐natal day 5 and this alteration is still evident at 5‐10 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)
Depletion of calcium from the sarcoplasmic reticulum during calcium release in frog skeletal muscle.
Authors: Schneider M F , Simon B J , Szucs G
Published: December 2014

1. Free intracellular calcium transients (delta[Ca2+] were monitored in cut segments of frog skeletal muscle fibres voltage clamped in a double Vaseline‐gap chamber and stretched to sarcomere lengths that eliminated fibre movement. The measured calcium transients were used to calculate the rate of calcium release from the sarcoplasmic reticulum (s.r.) as previously described (Melzer, Rios & Schneider, 1984, 1987). 2. Conditioning pulses were found to suppress the rate of calcium release in test pulses applied after the conditioning pulse. Various combinations of conditioning and test pulses were used to investigate the basis of the suppression of calcium release by the conditioning pulse. 3. Using a constant test pulse applied at varying intervals after a constant conditioning pulse, recovery from suppression of release was found to occur in two phases. During the fast phase of recovery, which was completed within about 1 s, the rate of calcium release was smaller and had a different wave form than the unconditioned control release. The early peak in release that is characteristic of the control release wave form was absent or depressed. During the slow phase of recovery, which required about 1 min for completion, the release wave form was the same as control but was simply scaled down compared to the control. 4. Conditioning pulses also slowed the rate of decay of delta[Ca2+] after a constant test pulse, probably due to an increased occupancy by calcium of slowly equilibrating myoplasmic sites that bind some of the calcium released by the conditioning pulse. Since calcium binding to these sites contributes to the decay of delta[Ca2+], their increased occupancy would slow the decay of delta[Ca2+] following the test pulse. This effect was used to estimate the calcium occupancy of the slowly equilibrating sites. 5. Comparison of the time course of the slow recovery from suppression of release following a constant conditioning pulse with the time course of the loss of calcium from the slowly equilibrating myoplasmic calcium binding sites indicated that the two processes occurred in parallel. 6. Using a set 1 s recovery period and a constant test pulse but varying the amplitude and/or duration of the conditioning pulse, the degree of slowly recovering suppression of release was found to be directly related to the amount of calcium remaining outside of the s.r. at the start of the test pulse. 7. Points 3, 5 and 6 above indicate that the slow recovery from suppression of release may be due to slow recovery from depletion of calcium from the s.r.(ABSTRACT TRUNCATED AT 400 WORDS)
The calcium channel current of pregnant rat single myometrial cells in short‐term primary culture.
Authors: Amédée T , Mironneau C , Mironneau J
Published: December 2014

1. The passive and active electrical properties of pregnant rat single myometrial cells in short‐term primary culture were analysed using a single‐electrode voltage or current clamp. 2. Action potentials and membrane currents were recorded in the presence of tetraethylammonium chloride and 4‐aminopyridine (10 mM each) and with Cs+ solution (4 M) in the microelectrode. 3. The voltage dependence, the action of Ca2+ antagonists and the effects of Sr2+ or Ba2+ substitution were studied. The peak Ca2+ current density was in the range 15‐20 microA/cm2 in 10 mM‐Ca2+ solution. 4. According to both measurement of the reversal potential of Ca2+ channel currents and comparison of the inward currents after correction for changing surface charge, the relative selectivity sequence of the Ca2+ channel for divalent cations was Ca2+ greater than Sr2+ = Ba2+. 5. The decay of Ca2+ channel current during a maintained depolarization was slowed when external Ca2+ was replaced by Sr2+ or Ba2+. The decay reflected an inactivation of Ca2+ channel conductance, as assessed by the decreased amplitude of inward tail currents following progressively longer depolarizations and the stable value of the reversal potential when Ca2+ channel current was increased during conditioning pulses. 6. Voltage‐dependent inactivation was illustrated by inactivation of outward Ca2+ channel current due to K+ and/or Cs+ efflux with external Ba2+ or in the absence of any permeant divalent cation. 7. The relationship between inactivation and the intracellular Ca2+ concentration was assessed by a double‐pulse method. Conditioning pulses that produced maximal Ca2+ current induced maximal inactivation; with stronger depolarizations, inactivation decreased but was not completely prevented at the expected Ca2+ reversal potential. Increasing the amount of Ca2+ entering the cell during the pre‐pulse reduced both amplitude and kinetics of test Ca2+ currents. These results were not observed with Ba2+ as the charge carrier. 8. Ca2+ channel current inactivation was best fitted by a two‐exponential function. The fast time constant of inactivation was larger in Ba2+ solution than in Ca2+ solution but both time constants showed little variation with membrane potential. The slow time constants of inactivation were steeply voltage dependent.(ABSTRACT TRUNCATED AT 400 WORDS)
Role of sodium and potassium permeabilities in the depolarization of denervated rat muscle fibres.
Authors: Kotsias B A , Venosa R A
Published: December 2014

1. Na+ and K+ flux measurements and membrane potential (Vm) determinations were performed on normal and denervated rat extensor digitorum longus (e.d.l.) muscles. 2. The mean Vm in normal muscle fibres was ‐74.6 mV. During the first week after denervation Vm fell about 20 mV following an S‐shaped time course. 3. In that period the Na+ permeability (PNa) increased and the K+ permeability (PK) decreased, so that by the sixth day post‐denervation, the PNa/PK ratio was increased by a factor of 2.7. 4. The decrease in PK preceded the increase in PNa. 5. No major contribution to the fall of Vm by a reduced activity of an electrogenic Na+ pump could be detected. 6. A good agreement was found between the experimental values of the depolarization and those calculated using the constant‐field equation assuming Cl‐ is at equilibrium and no significant change of the intracellular K+ concentration ([K+]i) during the first week after denervation. 7. It is concluded that the depolarization promoted by denervation in e.d.l. rat muscle fibres can be fully explained in terms of changes in PNa and PK.
Sodium‐dependent suppression of gamma‐aminobutyric‐acid‐gated chloride currents in internally perfused frog sensory neurones.
Authors: Akaike N , Maruyama T , Sikdar S K , Yasui S
Published: December 2014

1. The effects of the Na+ electrochemical potential gradient on gamma‐aminobutyric acid (GABA)‐induced Cl‐ currents (ICl) in frog sensory neurones were studied, using a suction pipette technique with which internal perfusion can be accomplished under current‐ and voltage‐clamp conditions. 2. Under current clamp, the depolarizing response to GABA decreased in the presence of external Na+. A similar external Na+‐dependent reduction in the GABA‐induced inward ICl was observed under voltage clamp. The reversal potential of GABA‐induced ICl (EGABA) was nearly equal to the Cl‐ equilibrium potential (ECl), irrespective of the presence or absence of external Na+. 3. Varying the Na+ influx by changing the holding membrane potential (VH) altered the GABA response: the GABA‐induced ICl decreased progressively as VH became more negative. 4. The effects of changing the external and internal Na+ concentrations ([Na+]o and [Na+]i) on the GABA‐induced ICl were also studied. Increasing [Na+]o at a constant [Na+]i reduced this current while increasing [Na+]i at a fixed [Na+]o facilitated it. 5. A high temperature coefficient of about 3 was estimated with respect to the percentage reduction in GABA‐induced ICl due to [Na+]o. 6. These results indicate that the [Na+]o‐dependent suppression of GABA‐induced ICl was mediated chiefly by the uptake of GABA subserved by a Na‐GABA co‐transport mechanism. 7. GABA dose‐response measurements were made with and without external Na+. The [Na+]o‐induced suppression was more pronounced in relative amount at lower concentrations and in absolute amount at intermediate concentrations. Analysis of these data indicates, however, that the Na+‐coupled GABA influx kept increasing at GABA concentrations high enough to nearly saturate GABA‐induced ICl, and the same saturating level was observed as in the Na+‐free case. This indicates that the electrogenic co‐transport current was much smaller so that our measurements of GABA‐induced ICl' were contaminated very little. Thus, the present method based on recording of GABA‐induced ICl was legitimate for the analysis of the Na‐GABA co‐transport. 8. By analysing the [Na+]o‐dependent suppression of GABA‐induced ICl, the stoichiometric ratio of the underlying co‐transport was estimated to be one: one Na+ ion per GABA molecule. 9. The ICl induced by GABA agonists such as beta‐alanine, taurine, l‐GABOB (l‐gamma‐amino‐beta‐hydroxybutyric acid) and muscimol was not affected by the amount of external Na+ present, suggesting difference in the affinity between receptor and transport carrier.
The distribution of sodium and potassium channels in single demyelinated axons of the frog.
Authors: Shrager P
Published: December 2014

1. Frog sciatic nerves were focally demyelinated by intraneural injection of lysolecithin. Fibres were examined 1‐8 days later. At early times axons contained zones just a few micrometers long that were covered by myelin debris. These zones lengthened and the debris was cleared over the next several days. 2. The loose patch clamp technique was used to measure ionic currents in the demyelinated axolemma in both internodal and paranodal regions. 3. Transient inward currents that have been identified as Na+ currents on the basis of voltage dependence and sensitivity to tetrodotoxin were recorded at all stages tested. There was no significant increase in internodal peak Na+ current with time over the first 8 days after injection. 4. Peak inward currents varied relatively little with distance along the internode at 1 day post‐injection. However, sharp gradients were detected at demyelinated paranodal and nodal membranes. 5. By combining the patch clamp with external stimulation proximal to the patch site it has been possible to record membrane current responses to propagating signals invading the demyelinated zone. With demyelination only in the distal heminode the extent of Na+ channel activation is similar to that predicted for normal nodes of Ranvier by Frankenhaeuser & Huxley (1964). 6. The ratio of K+ conductance to Na+ conductance is much higher in demyelinated internodes than in normal nodes of Ranvier. 7. It is concluded that Na+ channels are likely to be present in normal internodes. The total number of these internodal channels may be about 40 times the total number at nodes. Steep gradients of Na+ channel density remain at nodal regions at least up to 6 days following demyelination.
Effects of cell volume changes on membrane ionic permeabilities and sodium transport in frog skin (Rana ridibunda).
Authors: Costa P M , Fernandes P L , Ferreira H G , Ferreira K T , Giraldez F
Published: December 2014

1. Membrane potential and conductances and short‐circuit current were continuously measured with microelectrodes and conventional electrophysiological techniques in a stripped preparation of frog skin epithelium. The effects of the removal of chloride or sodium ions and the concentration or dilution of the serosal (inner) bathing solution were studied. 2. Chloride‐ or sodium‐free solutions produced a cell depolarization of about 30 mV in parallel with a fall in the short‐circuit current. Mucosal and serosal membrane conductances both decreased and the sodium permeability of the mucosal barrier was calculated to fall to about one‐half its value in standard Ringer solution. The observed decrease in the short‐circuit current is probably related to the combined effect of the decrease in sodium permeability and the decrease in the driving force across the mucosal membrane. 3. The removal of chloride or sodium ions reduced the depolarization caused by serosal perfusion with high‐potassium solutions (50 mM‐KCl). The ratio of the change in cell membrane potential under short‐circuit conditions to the change in the potassium equilibrium potential (delta Ec(s.c.)/delta EK), was 0.59 in standard Ringer solution and 0.26 and 0.24 after the removal of chloride or sodium respectively. The depolarizing effect of barium‐containing solutions (2 mM‐BaCl2) was also markedly reduced in chloride‐ or sodium‐free solutions, suggesting a decrease of the potassium selectivity of the serosal membrane in these conditions. 4. Increasing the osmolality of the serosal bathing solution produced similar effects, i.e. cell depolarization, fall in the short‐circuit current and membrane conductances and reduction of the depolarizing effect of high‐potassium and barium solutions. On the contrary, dilution of the serosal bath produced the opposite effects, consistent with an increase in the serosal permeability to potassium. 5. The effects of chloride‐ or sodium‐free solutions were reversed by the dilution of the serosal bath. Cells repolarized when exposed to low‐osmolality solutions after being in the absence of serosal chloride or sodium. The repolarization ran in parallel with the restoration of the short‐circuit current and the potassium selectivity of the serosal membrane. 6. The results show that the effects produced by the removal of sodium or chloride ions from the serosal bathing solution are most probably mediated by a reduction in cell volume. Cell volume changes would lead to changes in the serosal membrane selectivity to potassium and thus to changes in cell membrane potential and sodium transport.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of stimulating the sympathetic innervation in bursts on submandibular vascular and secretory function in cats.
Authors: Bloom S R , Edwards A V , Garrett J R
Published: December 2014

1. The effects of continuous stimulation of the peripheral end of the ascending cervical sympathetic nerve were compared with those of intermittent stimulation, so arranged as to deliver the same total number of impulses, in cats under chloralose anaesthesia. 2. Continuous stimulation caused a flow of saliva at 5‐10 Hz, but not at 2 Hz. In contrast, the same total number of impulses delivered intermittently in bursts elicited a prompt secretion at a frequency as low as 20 Hz for 1 s at 10 s intervals (corresponding to 2 Hz continuously) and a significantly higher rate of secretion at 50 Hz in bursts than that obtained in response to 5 Hz continuously. 3. Continuous stimulation also caused a rise in submandibular vascular resistance (s.v.r.), which persisted throughout the period of stimulation, and was followed immediately thereafter by an intense but transient fall in s.v.r. During stimulation in 1 s bursts, each burst was followed first by a brief rise in s.v.r. and shortly after by a fall. The balance between these two components varied widely between individual animals but often led to an overall fall in s.v.r. during stimulation i.e. complete reversal of the mean vascular effect. A further fall in s.v.r. was then recorded when the stimulus was discontinued. 4. Propranolol (1.0 mg/kg) reduced but failed to abolish the secretory response. It also altered the balance between the two phases of the vascular response slightly in favour of a rise in s.v.r. during stimulation, without apparently affecting the size of the after‐dilatation. 5. Pre‐treatment with dihydroergotamine (1.0 mg/kg) invariably blocked secretion and revealed a small vasodilator response during sympathetic stimulation with either pattern of stimulation; it also blocked the after‐dilatation. 6. Following combined pre‐treatment with propranolol and dihydroergotamine, to produce total adrenergic blockade, there was a small residual vasoconstrictor component which amounted to an increase in mean s.v.r. of about 20% during stimulation at 10 Hz continuously. This may have been due to release of neuropeptide Y (NPY). 7. Small but significantly greater amounts of NPY were released into the effluent blood during stimulation of the ascending cervical sympathetic nerve at 70 Hz in bursts than during continuous stimulation. No significant release of vasoactive intestinal peptide (VIP), somatostatin, bombesin, substance P or calcitonin gene‐related peptide (CGRP) was observed during stimulation at any frequency.(ABSTRACT TRUNCATED AT 400 WORDS)
Stimulated calcium efflux from fura‐2‐loaded human platelets.
Authors: Rink T J , Sage S O
Published: December 2014

1. The reduction of cytoplasmic free calcium, [Ca2+]i following stimulation, has been investigated in fura‐2‐loaded human platelets in the presence of low extracellular calcium concentration. Thrombin produced a rapid rise in [Ca2+]i which then fell back to the basal level within 2 min. 2. Ionomycin produced a rapid elevation in [Ca2+]i which then declined to a plateau well above the basal calcium level. The addition of thrombin after ionomycin accelerated the decline in [Ca2+]i back towards basal levels, an action mimicked by phorbol myristate acetate (PMA). 3. Thrombin promoted the efflux of 45Ca2+ from cells co‐loaded with fura‐2 and the isotope. Ionomycin also promoted an efflux of 45Ca2+ which was increased by the subsequent addition of thrombin or PMA. These results confirm the ability of thrombin and PMA to stimulate Ca2+ removal from the cells. 4. The complete substitution of extracellular Na+ with N‐methyl‐D‐glucamine (NMDG) did not alter the time course of the return of [Ca2+]i to basal following stimulation by thrombin, nor the ability of thrombin or PMA to promote Ca2+ efflux after elevation of [Ca2+]i by ionomycin. 5. The insensitivity to external Na+ suggests that the stimulated Ca2+ efflux is mediated by a Ca2+‐ATPase rather than Na+‐Ca2+ exchange. This pump does not appear to be activated by Ca2+‐calmodulin since [Ca2+]i remains high when elevated by ionomycin. The ability of PMA to stimulate removal suggests that its known target, protein kinase C, can stimulate the Ca2+ pump. Forskolin, which stimulates adenylate cyclase, did not stimulate a fall in [Ca2+]i in the presence of ionomycin, indicating that cyclic AMP‐dependent protein kinase does not stimulate Ca2+ extrusion.
Changes in sodium, calcium and potassium currents during early embryonic development of the ascidian Boltenia villosa.
Authors: Block M L , Moody W J
Published: December 2014

1. The whole‐cell variation of the patch clamp was used to study ion channel properties in the unfertilized oocyte, and in surgically isolated blastomeres from 2‐, 4‐, and 8‐cell embryos of the ascidian, Boltenia villosa. 2. The unfertilized oocyte has three major voltage‐dependent currents: a transient, inward Na+ current; a transient, inward Ca2+ current; and an inwardly rectifying K+ current. 3. The total surface area of the embryo, either measured by capacitance or calculated from cell diameters, increased about 2.5‐fold between fertilization and the 8‐cell stage. 4. The Na+ current almost completely disappeared from the embryo by the time of first cleavage and was undetectable in any of the blastomeres at the 8‐cell stage. This loss was too large to be explained by the dilution of channels in the oocyte due to newly added membrane. 5. Both the Ca2+ current and the inwardly rectifying K+ current were maintained at constant or slightly increased density through the first three cleavage cycles. This suggests that these channels are added along with new membrane during these stages. 6. No differences in mean current densities of blastomeres of different developmental fates were detected through the 8‐cell stage. 7. Continuous recordings in single egg cells between fertilization and first cleavage, using two‐microelectrode voltage clamp, revealed the increase in capacitance, Ca2+ current amplitude, and K+ current amplitude, and the loss of Na+ current predicted from the blastomere studies.
Altered renal function in chronically hyperprolactinaemic rats.
Authors: Garland H O , Lewis A G , Milne C M
Published: December 2014

1. Standard renal clearance techniques were used to investigate the effects of chronic hyperprolactinaemia on kidney function in male, female and ovariectomized female rats. 2. All hyperprolactinaemic rats showed a significantly increased glomerular filtration rate (G.F.R.) compared to controls. Values were (microliter min‐1) 2738 +/‐ 146 vs. 2299 +/‐ 99 for males (P less than 0.05), 2236 +/‐ 79 vs. 1865 +/‐ 74 for females (P less than 0.01) and 2200 +/‐ 76 vs. 1941 +/‐ 62 for ovariectomized females (P less than 0.05). 3. Hyperprolactinaemic rats in all groups also showed a significant increase in absolute tubular reabsorption of water, sodium and chloride compared to their respective controls. Increases here averaged 19%. 4. There was a significantly greater fractional tubular reabsorption of fluid and solutes in hyperprolactinaemic male rats compared to controls. Values were (%) 92.9 +/‐ 0.6 vs. 90.3 +/‐ 0.7 for water, 93.0 +/‐ 0.4 vs. 91.0 +/‐ 0.6 for sodium and 89.9 +/‐ 0.7 vs. 86.5 +/‐ 0.9 for chloride. In each case P less than 0.05. 5. These results imply an osmoregulatory role for prolactin which is not specific to pregnancy or related female reproductive states.
Diurnal‐ and behaviour‐related activity of ventromedial hypothalamic neurones in freely behaving rats.
Authors: Ono T , Sasaki K , Shibata R
Published: December 2014

1. Long‐term (25‐93 h) single‐neurone activity of seventy‐eight ventromedial hypothalamic (v.m.h.) neurones was analysed in freely behaving rats. 2. The activity of fifty‐seven (73%) of the seventy‐eight neurones tested depended on arousal and sleep, determined by electroencephalogram (e.e.g.), and varied diurnally. The activity of 39.8% (31/78) increased during e.e.g. arousal, and decreased during slow‐wave sleep. Activity of 33.3% (26/78) varied inversely. 3. The activity of 21.8% (17/78) was independent of e.e.g. arousal and sleep. The activity of all except one of the seventeen increased in the dark period and varied diurnally. Activity of one increased during light stimulation. 4. The activity of the remaining 5.1% (4/78) was less than 0.5 spikes/s, and was not related to e.e.g. arousal or sleep or the diurnal cycle. 5. The effects of bilateral lesions of the suprachiasmatic nuclei (s.c.n.) were investigated on six v.m.h. neurones. All of these lost their diurnal variation; five retained their dependence on e.e.g. arousal and sleep, and one retained its independence of e.e.g. arousal and sleep. 6. There was no discernible relation between v.m.h. recording site and any of the tested characteristics of these neurones. 7. Of seventy‐eight v.m.h. neurones tested, seventy‐four were classified as either: (1) diurnal, sleep‐arousal related, or (2) diurnal, sleep‐arousal independent. Because s.c.n. lesions abolished the circadian rhythm of v.m.h. activity in every neurone tested, it was concluded that at least some v.m.h. diurnal variation is driven from the s.c.n. as a biological clock. It is clear also that responses related to e.e.g. are driven from some source other than the s.c.n.
Behaviour of canine pulmonary vagal afferent receptors during sustained acute pulmonary venous pressure elevation.
Authors: Kappagoda C T , Man G C , Teo K K
Published: December 2014

1. The effects of an acute sustained increase in pulmonary venous pressure induced by partial obstruction of the mitral valve on the activity of the four types of pulmonary receptors, namely, slowly adapting, rapidly adapting, pulmonary C‐fibre and bronchial C‐fibre receptors, were studied in the dog. 2. Fifteen slowly adapting receptors, eleven rapidly adapting receptors and nine bronchial C‐fibre receptors showed significant sustained increases in activity when stimulated by the elevated left atrial pressure by 9.4 +/‐ 0.2 mmHg for 15 min. Nine pulmonary C‐fibre receptors did not show a significant increase (six of these nine receptors increased their activity in response to the stimulus). 3. When the left atrial pressure was increased in graded steps of 5 mmHg for 5 min each up to 15 mmHg, a significant graded response was found in all of seven slowly adapting receptors, five rapidly adapting receptors and five bronchial C‐fibre receptors. The five pulmonary C‐fibre receptors examined also showed increases, but the changes were not statistically significant. 4. In response to stimulation by the elevated left atrial pressure, increases in activity occurred within 1 min of application of the stimulus in all the receptors and returned to control levels within 1 min of removal of this stimulus. 5. It is concluded that in the dog, pulmonary vagal receptors are influenced by small increases in pulmonary venous pressure induced by partial obstruction of the mitral valve. The changes appeared to be greatest in the case of rapidly adapting receptors. The physiological significance of these responses remains to be investigated.
Inhibition of calcium‐dependent spike after‐hyperpolarization increases excitability of rabbit visceral sensory neurones.
Authors: Weinreich D , Wonderlin W F
Published: December 2014

1. Conventional intracellular recordings were made from rabbit nodose neurones in vitro. Prostaglandins D2 and E2, but not F2 alpha, produced a selective, concentration‐dependent (1‐100 nM) inhibition of a slow, Ca2+‐dependent spike after‐hyperpolarization (a.h.p.). Block of the slow a.h.p. was accompanied by an increased membrane resistance and a small (less than 10 mV) depolarization of the membrane potential. Inhibition of the slow a.h.p. produced no change in the voltage‐current relationship other than the increased membrane resistance. 2. In C neurones with slow a.h.p.s, trains of brief depolarizing current pulses (2 ms duration, 0.1‐10 Hz) could not elicit repetitive action potentials without failure at rates above 0.1 Hz. By contrast, C neurones without slow a.h.p.s could respond at stimulus frequencies up to 10 Hz. The frequency‐dependent spike firing ability of slow a.h.p. neurones was eliminated by inhibition of the slow a.h.p. 3. Action potentials were also evoked by intrasomatic injection of paired, depolarizing current ramps (1 nA/10 ms, 0.1‐5 s inter‐ramp interval). For neurones without a slow a.h.p., the current threshold and number of evoked spikes were the same for both ramps, and the ramps were nearly superimposable. In neurones with a slow a.h.p., the current threshold for the first spike in the second ramp was greatly increased (300‐500%) and the number of evoked spikes was reduced. Following inhibition of the slow a.h.p., the current threshold and number of evoked spikes was the same for both ramps. 4. Forskolin, a direct activator of the catalytic subunit of adenylate cyclase, also produced a concentration‐dependent inhibition of the slow a.h.p., with 50% block at 30 nM. Prostaglandin D2 and forskolin produced identical enhancement of excitability in C neurones and neither substance produced any effect on C neurones that could not be attributed to inhibition of the Ca2+‐dependent K+ conductance associated with the slow a.h.p. We propose that, in some visceral sensory neurones, the level of excitability is regulated by cyclic AMP‐mediated control of the slow a.h.p.
Differential control of sympathetic fibres supplying hindlimb skin and muscle by subretrofacial neurones in the cat.
Authors: Dampney R A , McAllen R M
Published: December 2014

1. Simultaneous recordings were made from postganglionic sympathetic fibres supplying hindlimb skin and skeletal muscle in chloralose‐anaesthetized, artificially ventilated cats. Single‐fibre activity was either isolated by dissection or discriminated from few‐fibre preparations of fascicles in the left superficial peroneal or sural nerve (innervating hairy skin) and common peroneal nerve (innervating muscle). Vasoconstrictor fibres were identified by their spontaneous activity as well as their responses to stimulation of the lumbar sympathetic chain and to changes in baroreceptor activity. The baroreceptors were then denervated by bilateral section of the vagi, carotid sinus and aortic nerves. 2. In five cats, neurones in the region of the subretrofacial nucleus were activated chemically by microinjections of 2‐10 nl 0.5 M‐sodium glutamate from a micropipette inserted into the ventral surface of the medulla. Both skin and muscle vasoconstrictor fibres were activated by glutamate injections into this region on either side of the medulla. Arterial pressure also rose. 3. Glutamate injections at forty‐two sites evoked a positive response, defined as an increase in cutaneous and/or muscle vasoconstrictor fibre activity of at least 25%. This response was evoked only in the cutaneous fibre at sixteen of these sites ('skin points'), only in the muscle fibre at seven sites ('muscle points'), and in both fibres in the remainder ('mixed points'). The largest percentage increases in activity of either type of fibre were obtained from mixed points. 4. The blood pressure rises following glutamate stimulation of muscle points were significantly greater than those produced by stimulation of skin points. Analysis of all positive responses showed that the evoked rise in blood pressure was significantly correlated with muscle sympathetic activity but not with cutaneous sympathetic activity. 5. Glutamate stimulation at different sites could evoke differential responses in skin and muscle vasoconstrictor fibres without any detectable change in the pattern of phrenic nerve discharge. 6. Skin points were grouped in the medial part of the subretrofacial region, and muscle points in the lateral part. In addition, for all positive responses there was a highly significant correlation between the ratio of muscle to cutaneous sympathetic activity evoked, and the distance from the mid‐line of the corresponding injection site. 7. These results demonstrate a functional differentiation among subretrofacial neurones in their relative control of the sympathetic vasoconstrictor supply to skin and skeletal muscle.(ABSTRACT TRUNCATED AT 400 WORDS)
Waveform and amplitude characteristics of evoked responses to dendritic stimulation of CA1 guinea‐pig pyramidal cells.
Authors: Turner D A
Published: December 2014

1. Dendritic synaptic responses were evoked in CA1 hippocampal pyramidal cells using a microstimulation protocol which included focal excitation of proximal and distal apical afferents. Ensembles of excitatory postsynaptic potentials (EPSPs) were analysed for magnitude, waveform parameters and fluctuation characteristics between responses. 2. The peak amplitude of the minimal detectable responses to dendritic stimulation ranged from 0.12 to 0.89 mV. Control experiments showed separation of the minimal EPSPs from extracellular field potentials and somatic inhibition. The EPSPs demonstrated no significant amplitude trends over ensembles of 150‐300 responses, at a 2 Hz stimulation rate. 3. Both minimal (less than 1 mV) and large (1‐5 mV) proximal and distal evoked EPSPs were clearly different in terms of all waveform parameters analysed. However, the large EPSPs exhibited substantially less proximal‐distal separation than the minimal responses. 4. The separation of minimal proximal and distal responses was similar to that predicted by earlier dendritic model simulations, after revision of the model parameter determining shape of the synaptic input. The proximal and distal synapses are separated by approximately 0.6 dendritic length constants (lambda), within an average apical dendritic tree of 0.9 lambda. 5. The decrease in proximal‐distal separation with increasing EPSP size may stem from recruitment of non‐laminar dendritic afferents and the addition of feed‐forward inhibitory potentials. These circuitry features of the CA1 region lead to an effective electrical shortening of the apical dendritic tree for large EPSPs and in particular to an enhanced efficacy of distal synapses.
Do oxygen tension variations contribute to the respiratory oscillations of chemoreceptor discharge in the cat?
Authors: Kumar P , Nye P C , Torrance R W
Published: December 2014

1. A high‐frequency high‐flow ventilator has been developed which will produce abrupt changes in alveolar gas tensions. We have used it to study the individual contributions of PCO2 and PO2 in producing the oscillations which occur in the discharge of carotid chemoreceptors in the cat with respiration, by producing repeated end‐tidal alternations (i) of PCO2 in constant hypoxia, (ii) of PO2 in constant normocapnia and (iii) of both PO2 and PCO2, i.e. of asphyxia. 2. The chemoreceptor response to alternations of PCO2 was always brisker than that to alternations of PO2 at 2, 4 or 8 s cycle durations. 3. An increase in the frequency of the alveolar alternation shortened the difference between the response times to PCO2 and PO2 but it increased the phase difference between the stimulus and the response waveforms. 4. With 4 s cycles, in normocapnic hypoxia, PCO2 was 2.9 times more effective (impulses s‐1 Torr‐1) than PO2 in producing oscillations in discharge. 5. The oscillations in discharge to simultaneous alternations of PO2 and PCO2 were not significantly different from the sum of individual oscillations to alternations of PCO2 and of PO2 alone. This was true with respect to timing and to amplitude of the oscillation. 6. Usually the amplitude of the chemoreceptor discharge oscillation in response to an asphyxial alternation was greater than the amplitude of the oscillation to either its PCO2 or its PO2 component alone. However, at the highest frequencies used, the phase relation between the PCO2 and PO2 components of the response could lead to the summed asphyxial response being less than its individual components. 7. The amplitudes and shapes of the oscillations in response to 4 s PCO2 alternations were not affected by changing either the steady‐background PO2 or PCO2, but the amplitudes of the oscillations to pure PO2 alternations were enhanced by hypoxia and by hypercapnia. The importance of PO2 and PCO2 in giving rise to the natural respiratory oscillations in chemoreceptor discharge depends on the mean levels of the two gases. In normocapnic hypoxia (PO2 ca. 50 Torr) they are equally important but when PO2 is raised it becomes less important.
The extent of visual recovery from early monocular or binocular visual deprivation in kittens.
Authors: Mitchell D E
Published: December 2014

1. The rate and extent of recovery of vision was studied in the deprived eye of kittens that had been monocularly deprived from near birth for periods that lasted from 6 weeks to 18 months. Recovery was measured in the two situations, where either both eyes were open following the initial deprivation (binocular recovery), or else the non‐deprived eye was occluded so as to force the animal to employ its deprived eye (reverse occlusion). 2. Measurements were made of the visual acuity of the deprived eye for gratings at frequent intervals during recovery by means of a simple behavioural technique. 3. The acuity that the deprived eye eventually attained declined with increasing length of deprivation in a manner that could be approximated by a simple exponential decay. Only minimal visual recovery was observed in animals deprived beyond 1 year of age; only two of six animals recovered sufficient vision to enable measurement of visual acuity. In general, animals that were reverse occluded recovered better vision than did those that had both eyes open during recovery. 4. The recovery of vision in the deprived eye of monocularly deprived kittens was compared to that observed following equivalent periods of two forms of binocular deprivation, namely dark‐rearing and binocular eyelid suture. 5. The recovery from the two forms of binocular deprivation was quite different. Whereas the extent of recovery from dark‐rearing was considerably greater than that observed after equivalent periods of monocular deprivation, the recovery of a limited sample of cats that were binocularly deprived by eyelid suture was worse. 6. These findings suggest that some plasticity remains in the visual pathways for a longer time than indicated by experiments that examine the physiological effects of monocular deprivation on various visual cortical structures.
Effects of the vagus nerves on gastric motility and release of vasoactive intestinal polypeptide in the anaesthetized lamb.
Authors: Reid A M , Shulkes A , Titchen D A
Published: December 2014

1. Effects of the vagus nerves on the activity of the reticulo‐omasal orifice (ROO) and the abomasum and the concentration of vasoactive intestinal polypeptide (VIP) in gastric and intestinal venous effluent were studied in anaesthetized lambs. 2. Both excitatory and inhibitory effects of the vagus on the ROO and abomasum were demonstrated. Excitation of activity of the ROO was dominant with stimulation at lower frequencies (less than or equal to 20 Hz) whereas higher frequencies (50‐70 Hz) caused inhibition. 3. Inhibition but not stimulation of the ROO and abomasum were obtained with vagal stimulation after administration of atropine (200‐500 micrograms kg‐1 I.V.). 4. The concentration of VIP in gastric venous effluent blood rose by 41 +/‐ 10 pmol l‐1 (n = 13) within 90 s of the start of stimulation (10 Hz, 5 ms pulse duration, 10 V for 180 s) of a vagus nerve and fell within 60 s of its cessation to or near basal levels. The effects of vagal stimulation in changing the concentration of VIP were not altered by administration of atropine. 5. The concentration of VIP in the intestinal venous effluent increased during stimulation (10 Hz, 5 ms pulse duration, 10 V, for 180 s) of a vagus nerve by 15 +/‐ 5 pmol l‐1 (n = 11) and remained elevated for more than 10 min after the stimulus had ceased. 6. The changes in gastric motility and in concentration of VIP in gastric and intestinal venous blood with stimulation of the vagus nerves have been discussed in relation to similar alterations which occur in lambs during sucking of milk.
The effects of vasoactive intestinal polypeptide on gastric motility in the lamb.
Authors: Reid A M , Shulkes A , Titchen D A
Published: December 2014

1. Intra‐arterial infusions of vasoactive intestinal polypeptide (VIP) were made in anaesthetized lambs in which activity of the reticulo‐omasal orifice (ROO) was recorded manometrically and in conscious lambs in which activity of the reticulum, ROO and abomasum were recorded by electromyographic (EMG) techniques. 2. Spontaneous rhythmic opening and closing movements of the ROO occurred in anaesthetized lambs at 3‐5 min‐1. Infusions of VIP into the left gastric artery at rates of 0.5‐3.0 nmol min‐1 produced changes in activity of the ROO. Within 120 s of commencement of the infusions there was an increase in frequency and magnitude of the movements of the ROO for up to 120 s. This was followed with infusion of VIP at the lower levels (0.5‐1.0 nmol min‐1), by a marked reduction and sometimes complete loss of the rhythmic movements. There was always complete cessation of activity of the ROO with infusion of VIP at 1.5‐3.0 nmol min‐1. 3. In conscious lambs the frequency of the diphasic reticular EMG bursts which recur at intervals of ca. 1 min was not affected by infusions of VIP at 3.0 nmol min‐1 for 10 min. 4. Between each diphasic reticular EMG burst in the conscious lamb there was normally phasic activity of the ROO consisting of EMG bursts of long (ca. 4 s) and short (ca. 1 s) duration. Within 90 s of commencement of infusion of VIP at 3.0 nmol min‐1 short‐burst EMG activity disappeared with the remaining long bursts being of greater duration (5.4 +/‐ 1.2 s) than before infusion. After a series of four to fifteen such more prolonged long bursts there was quiescence of the EMG of the ROO. After infusion of VIP EMG activity recommenced first as a series of eight to fourteen long bursts which was followed by the reappearance also of short‐burst activity. Infusions of VIP at 8‐10 nmol min‐1 produced a more prompt cessation of EMG activity of the ROO. Of other peptides which were infused only PHI (a peptide with N‐terminal histidine and C‐terminal isoleucine amide) produced cessation of the EMG activity of the ROO. However, on a molar basis VIP was 2‐3 times more potent than PHI in causing cessation of activity of the ROO. 5. Infusion of VIP at 3.0 nmol min‐1 produced a cessation or diminution of EMG activity of the body, antrum and pylorus of the abomasum.(ABSTRACT TRUNCATED AT 400 WORDS)
Multi‐ and single‐fibre mesenteric and renal sympathetic responses to chemical stimulation of intestinal receptors in cats.
Authors: Stein R D , Weaver L C
Published: December 2014

1. In cats anaesthetized with alpha‐chloralose and artificially respired, stimulation of intestinal receptors with bradykinin caused greater reflex excitation of mesenteric than of renal efferent multifibre nerve activity and significant pressor responses. 2. Activity of all nerve bundles used in this study was inhibited by stimulation of pressoreceptors. Increases in systemic arterial pressure caused inhibition of activity of renal nerves which was significantly greater than that of mesenteric nerves. 3. Spinal transection caused significant decreases in tonic renal nerve activity without altering the ongoing discharge rate of mesenteric nerves. Stimulation of intestinal receptors in spinal cats still caused significant increases is discharge of mesenteric and renal nerves, indicating that this reflex contains a spinal component. 4. Recordings of activity of individual fibres within mesenteric (21) and renal (23) nerves provided information regarding the basis for the multifibre responses to stimulation of intestinal receptors. The same proportion of fibres from both nerves was excited, but the increase in activity of mesenteric fibres was significantly greater than that of renal fibres. 5. Mesenteric fibres could be classified into two groups, based on their sensitivity to pressoreceptor influences. Fibres that exhibited pressoreceptor‐independent discharge had the greatest responses to stimulation of intestinal receptors. 6. Following spinal transection the majority of mesenteric fibres continued to fire, whereas most renal fibres became quiescent. 7. The non‐uniform pattern of neuronal excitation to chemical stimulation of intestinal receptors was manifest after spinal transection, demonstrating that exclusively spinal pathways can mediate this differential response pattern. 8. These results support the hypothesis that viscero‐sympathetic reflexes may be organized to cause preferential excitation of neural activity directed to the organ from which the reflex originates.
Changes in excitable membrane properties in Schwann cells of adult rabbit sciatic nerves following nerve transection.
Authors: Chiu S Y
Published: December 2014

1. Whole‐cell patch clamp studies were carried out on Schwann cells associated with myelinated and non‐myelinated axons in the distal nerve stump of transected adult rabbit sciatic nerves which had undergone in vivo degeneration for 0‐13 days. 2. Voltage‐gated sodium current of Schwann cells associated with non‐myelinated axons decreased in amplitude following nerve transection; the peak current density decreased to about 51% by day 3, and to 27% by day 6. The number of non‐myelinated axons, determined from cross‐sectional electron microscopy of the whole nerve bundle, also exhibited a similar decline to 48% (day 3) and 17% (day 6) of the control values. 3. In contrast, both voltage‐gated sodium and potassium currents of Schwann cells associated with myelinated axons showed an increase following nerve transection. These two currents, normally not detectable in these Schwann cells, first appeared at around day 4 after nerve transection and increased progressively with time thereafter as Wallerian degeneration persisted. 4. The whole‐cell membrane capacity of Schwann cells also exhibited different pattern of changes, depending on whether the cell normally lacked or produced myelin. In the former, the cell capacity remained relatively constant following nerve transection. In the latter, the whole cell capacity was reduced to 11% of control values by day 13. This capacity decline is consistent with the observed detachment of myelin membranes from these latter Schwann cells. 5. There was an apparent inverse relation between the whole‐cell capacity and the density of sodium and potassium currents in Schwann cells undergoing progressive myelin loss. It is suggested that the appearance of sodium and potassium currents in these cells might be related to myelin degeneration. 6. A hypothesis is proposed that the expression of excitable ion channels (sodium and potassium) on a Schwann cell is under opposing regulation by degenerating myelin and by axons. Axonal degeneration leads to a decline of Schwann cell sodium currents. Myelin degeneration, in contrast, leads to an increase of both Schwann cell sodium and potassium currents. 7. The above hypothesis that axons normally exert a positive trophic influence on Schwann cells to express sodium channels is discussed in relation to a recent speculation of a Schwann‐to‐axon transfer of excitable ion channels.