bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmembrane ion balance in slowly and rapidly adapting lobster stretch receptor neurones.
Authors: Edman A , Gestrelius S , Grampp W
Published: December 2014

The transmembrane exchange of Na+, K+, and Cl‐ in slowly and rapidly adapting lobster stretch receptor neurones was studied using ion‐sensitive microelectrodes in combination with conventional electrophysiological techniques. The investigation was founded on the assumption that the transmembrane ion exchange is accomplished by active and passive transports which add up to zero in steady state for each ion involved. The active transports are assumed to include Na+ and K+ transports driven by an electrogenic Na‐K pump. To these transports are also added equimolar fluxes of K+ and Cl‐ leaking from the impaling micro‐electrode. The passive transports are assumed to pass through membrane channels in accordance with constant field kinetics. For a quantitative evaluation of the transmembrane ion exchange in resting conditions measurements were made of the resting concentrations of Na+, K+ and Cl‐; the voltage dependence of the ungated leak current; and ouabain‐induced changes in resting membrane current and intracellular ion concentrations. From the results it follows that both the resting pump current and the leak permeabilities for the ions investigated have values which do not seem to differ between slowly and rapidly adapting receptor neurones. For a quantitative evaluation of the relation between internal Na+ and pump current production, measurements were made of the outward membrane current as a function of internal Na+ and K+ following a shift of these ions by means of prolonged repetitive impulse activation. It was found that the investigated relation is compatible with Garay‐Garrahan kinetics (Garay & Garrahan, 1973) in both receptor neurones, but the results imply a larger maximum Na+‐extrusion capacity in slowly than in rapidly adapting cells. From recordings of the time course of post‐tetanic normalization of both the membrane current and intracellular Na+ concentration, cell volume values could be deduced which were closely similar in slowly and rapidly adapting receptors. A corresponding similarity was also found for the cell area which was derived from membrane capacitance measurements.
Periodic increase of cytoplasmic free calcium in fertilized hamster eggs measured with calcium‐sensitive electrodes.
Authors: Igusa Y , Miyazaki S
Published: December 2014

The hamster egg at fertilization shows transient, periodic hyperpolarizing responses due to a Ca2+‐activated K+ conductance. The suggested increase of the intracellular Ca2+ concentration ([Ca2+]i) was measured with Ca2+‐sensitive microelectrodes in combination with the voltage‐clamp technique. Calculated values of the basal [Ca2+]i before fertilization averaged in the range 0.2‐0.4 microM. Insemination of eggs induced periodic Ca2+ transients with exact one‐to‐one correspondence to periodic, Ca2+‐activated K+ currents. They were recorded anywhere in the cytoplasm, even far from the site of sperm‐egg fusion, indicating that [Ca2+]i increases in the whole egg upon each response. During a series of responses after insemination the increase in [Ca2+]i reached 1‐2 microM in the first three responses and the peak value decreased to 0.7‐0.8 microM in the later responses. The rise and decay times of each Ca2+ transient were 6.8 +/‐ 2.8 and 22 +/‐ 6 s (mean +/‐ S.D., n = 36), respectively. No significant difference in the amplitude and time course of the Ca2+ transient was detected in relation to the depth of the cytoplasm about 3‐30 micron from the surface. The basal [Ca2+]i increased gradually from 0.39 to 0.56 microM (average in fourteen eggs) during the series of Ca2+ transients. The biological significance and mechanism of the periodic increase in [Ca2+]i and the response time of the Ca2+ electrode are discussed.
Comparison of the effects of potassium and membrane potential on the calcium‐dependent sodium efflux in squid axons.
Authors: Allen T J , Baker P F
Published: December 2014

Experiments are described in which the [Ca]o‐dependent component of 22Na efflux is monitored under conditions of membrane potential control by voltage clamp. The apparent affinity of the efflux system for external Ca is very low in choline sea water (apparent KD approximately 50 mM); but increases dramatically when choline is replaced isosmotically by Li or K (apparent KD approximately 1‐2 mM). Ca influx changes in a parallel fashion. Tris behaves much like choline and guanidinium is about two‐thirds as effective as Li. Replacement of Li by K has little effect on the apparent affinity for external Ca but brings about a small (30‐40%) increase in the maximal flux. The increase in maximum flux can be removed by electrical hyperpolarization to the potential before application of K and, in the absence of K, can be mimicked by electrical depolarization. These experiments suggest that the stimulatory effect of K on the Ca‐dependent Na efflux into Li sea water is electrical in origin. Partial replacement of choline by K stimulates the Ca‐dependent Na efflux; but only part of this stimulation can be removed by electrical hyperpolarization and, in the absence of K, electrical depolarization only brings about a relatively small stimulation. This is because only part of the stimulation that follows addition of K to choline sea waters is electrical in origin: the rest reflects an increase in the apparent affinity for external Ca that is brought about by K acting chemically. The maximum efflux into K is about 40% higher than that into choline. That this may reflect an electrical effect is supported by the observation that electrical depolarization increases the flux into choline sea water containing 110 mM‐Ca where the Ca‐binding site is close to saturation. The voltage clamp was used to determine the voltage dependence of the Ca‐dependent Na efflux into Li sea water, choline sea water and choline sea water containing 100 mM‐Na. In all three cases the flux increased with depolarization and was still rising at +70 mV. The dependence on potential was not very steep, an e‐fold increase occurred over approximately 50 mV.
The role of anion transport in the passive movement of lead across the human red cell membrane.
Authors: Simons T J
Published: December 2014

Passive Pb transport across the red cell membrane has been studied by measuring Pb uptake from Pb‐buffered solutions into resealed ghosts containing EGTA. Over 90% of Pb uptake occurs by a pathway which is inhibited by drugs which block anion transport. The order of effectiveness is 4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid (DIDS) and 4‐acetamido‐4'‐isothiocyanostilbene‐2,2'‐disulphonic acid (SITS) greater than phloretin greater than furosemide and bumetanide. Ouabain and cytochalasin B are ineffective. This implicates the anion‐exchange mechanism in Pb uptake. The rate of Pb uptake by this route is directly proportional to external Pb2+ and HCO3‐ concentrations, and inversely proportional to the H+ concentration. These findings suggest that Pb transport depends on the formation of PbCO3 in solution. Pb transport depends upon the presence of a second anion. In the presence of HCO3‐, the rate is stimulated in the order ClO4‐ less than NO3‐ and CH3CO2‐ less than F‐ less than Cl‐ less than Br‐ less than I‐. The temperature dependence of Pb uptake is similar to that of HCO3‐(‐)Cl‐ exchange. Changes in membrane potential appear to influence Pb transport. The effects are small and somewhat variable, but in general a negative internal potential accelerates uptake and reduces exit. A positive internal potential reduces uptake and accelerates exit. These results suggest that Pb is transported on the anion exchanger. Exchange of PbCO3 for a monovalent anion best fits the experimental data, although transport of a ternary PbCO3(‐)anion‐ complex is a possibility.
Electromechanical effects of okadaic acid isolated from black sponge in guinea‐pig ventricular muscles.
Authors: Kodama I , Kondo N , Shibata S
Published: December 2014

Okadaic acid is a monocarboxylic acid with a unique molecular structure of C44H66O13. Okadaic acid, at concentrations above 10(‐5) M, caused a dose‐dependent increase of contractile force in guinea‐pig isolated ventricular muscles. The increase of contractile force by okadaic acid (1‐4 X 10(‐5) M) was accompanied by a prolongation of action potential duration (a.p.d.), while a.p.d. was shortened by okadaic acid at above 10(‐4) M. The okadaic‐acid‐induced changes in contractile force and a.p.d. were abolished by pre‐treatment with verapamil (2 X 10(‐6 M) or nifedipine (10(‐6) M). In a low‐Ca2+ medium (0.12 mM), the contractile response to okadaic acid (4 X 10(‐5) M) was inhibited, whereas the a.p.d. was more prolonged by the drug than in a control medium (containing 1.2 mM‐Ca2+). In a low‐Na+ (70 mM) medium or in a low‐Na+ (70 mM) and low‐Ca2+ (0.12 mM) medium both the contractile force and a.p.d. were unaffected by okadaic acid (4 X 10(‐5) M). The positive inotropic effect of okadaic acid (4 X 10(‐5) M) was not inhibited by treatment with tetrodotoxin (TTX, 2 X 10(‐6) M) or with ryanodine (2 X 10(‐6) M). In voltage‐clamp experiments using a single sucrose‐gap technique, okadaic acid (4 X 10(‐5) M), caused a significant increase of slow inward current, while it did not affect the net outward current. These findings suggest that okadaic acid has a positive inotropic effect on the heart, probably due to the enhancement of slow Ca2+ and/or Na+ inward current through the cell membrane.
Thalamic burst patterns in the naturally sleeping cat: a comparison between cortically projecting and reticularis neurones.
Authors: Domich L , Oakson G , Steriade M
Published: December 2014

Unit discharges were extracellularly recorded from antidromically identified thalamocortical neurones of ventralis lateralis (v.l.) and centralis lateralis (c.l.) nuclei as well as from reticularis thalami (re.) neurones during wakefulness and electroencephalogram‐synchronized sleep of the behaving cat. Various parameters of sleep‐related discharge bursts were analysed. Statistical analyses revealed striking similarities between motor relay (v.l.) and intralaminar (c.l.) neurones. More than 60% of bursts consist of three to five spikes at 250‐400 Hz. The defining feature of bursts in all cortically projecting neurones is a progressive increase in the duration of successive interspike intervals. As in thalamocortical cells, all re. neurones change their tonic discharges in waking to bursting firing in sleep, regardless of the increased or decreased firing rates from wake to sleep in individual neurones. The bursts of re. neurones are essentially different from those of thalamocortical cells. In re. neurones, burst structure consists of an initial progressive decrease in duration of interspike intervals, followed by an increase in duration of successive intervals, eventually leading to a long‐lasting tonic spike train at about 100 Hz. In contrast with bursts of thalamocortical neurones, only 6% of re. bursts are shorter than 50 ms; the total duration of the burst extends between 50 ms and 1.5 s. Population periburst histograms show the beginning of a decline in firing probability about 1.5 s prior to burst onset and an increased firing probability persisting for 300‐350 ms after burst onset. The different electrophysiological properties underlying the burst structure of cat's thalamocortical and re. neurones are discussed, with emphasis on dissimilar aspects of re. bursts in unanaesthetized and barbituratized preparations. Various factors that may account for the transition from tonic mode in waking to bursting mode in sleep are envisaged.
Immediate ventilatory response to sudden changes in venous return in humans.
Authors: Cummin A R , Iyawe V I , Jacobi M S , Mehta N , Patil C P , Saunders K B
Published: December 2014

We changed venous return transiently by postural manoeuvres, and by lower body positive pressure, to see what happened simultaneously to ventilation. Cardiac output was measured by a Doppler technique. In seven subjects, after inflation of a pressure suit to 80 and 40 mmHg at 30 deg head‐up tilt, both cardiac output and ventilation increased. Ventilation increased rapidly to a peak in the first 5 s, cardiac output more slowly to a steady state in about 20 s, at 80 mmHg inflation. After inflation to 80 mmHg in six subjects at 12.5 deg head‐up and 30 deg head‐down tilt, cardiac output did not change in the first, and fell in the second case. There were no significant changes in ventilation. On release of pressure there were transient increases in both cardiac output and ventilation, with ventilation lagging behind cardiac output, in contrast to (2) above. In five subjects, elevation of the legs at 30 deg head‐up tilt caused a rise in both cardiac output and ventilation, but in two subjects neither occurred. In all seven subjects there was a transient increase in cardiac output and ventilation when the legs were lowered. Ventilation and cardiac output changes were approximately in phase. We were therefore unable to dissociate entirely increasing cardiac output from increasing ventilation. The relation between them was certainly not a simple proportional one.
Stabilization of sodium channel states by deltamethrin in mouse neuroblastoma cells.
Authors: Chinn K , Narahashi T
Published: December 2014

The effect of the pyrethroid insecticide deltamethrin on sodium channels of mouse neuroblastoma cells was investigated using the patch‐clamp technique. The study was aimed at determining how the effects of deltamethrin at the whole cell level would be reflected in the modified properties of single sodium channel currents. Whole cell recording showed that deltamethrin prolonged sodium currents in neuroblastoma cells by several orders of magnitude. Single channel recordings showed that a variety of channel states were prolonged by deltamethrin. Not only was the open state prolonged by several orders of magnitude but a closed or inactivated state was also prolonged, leading to less frequent channel openings. A subconducting state and a flickering state were observed in the presence of deltamethrin as well as a state in which channels opened with some delay after the termination of a depolarizing pulse. The results are compatible with the hypothesis that deltamethrin stabilizes a variety of channel states by reducing the transition rates between them. This allows states that are normally very brief to be detected more easily.
Intrinsic reflexes underlying peristalsis in the small intestine of the domestic fowl.
Authors: Hodgkiss J P
Published: December 2014

Peristalsis in the chicken small intestine was studied using either a modified Trendelenburg method or a technique in which changes in circular muscle activity were recorded in response to application of a localized radial distension. A localized radial distension had no effect on either the resting tension or the spontaneous activity of the circular muscle on the oral side of distension. On the aboral side of the distension a transient contraction was recorded in the ileum and jejunum after a mean delay of 2.74 s at 37 degrees C. In about a third of the preparations a tonic contraction was also present which persisted for as long as distension was maintained. The transient contraction was blocked by hyoscine (0.6‐2.3 microM) and hexamethonium (275 microM); whereas the tonic contraction persisted in the presence of hyoscine. Both types of contraction were blocked by tetrodotoxin (0.31 microM). No such responses were recorded in the duodenum. The descending excitatory reflex responses were followed in all preparations by a fall in the amplitude and frequency of spontaneous contractions and in a few preparations by a concomitant fall in the tone of the circular muscle lasting for up to 3 min. This inhibitory component of the descending reflex was not blocked by guanethidine (3‐10 microM). The transient contraction, which originated most frequently at the site of distension, always propagated aborally at a mean speed of 14.2 mm s‐1. Surgical interruption of the longitudinal muscle and myenteric plexus effectively blocked the transmission of the excitatory and inhibitory components of the descending reflex past the site of the lesion. In the modified Trendelenburg apparatus raising the intraluminal pressure elicited peristalsis in the isolated ileum. Peristaltic contractions never started at the most oral end of the preparation but appeared instead at any other point on the ileum. This resulted in several contractions contributing to each emptying cycle. Peristalsis was blocked by tetrodotoxin (0.31 microM). These results are discussed in the terms of the organization of the descending reflex. It is suggested that within the enteric nervous system of the ileum and jejunum of the chicken, there are cholinergic and non‐cholinergic excitatory neurones and non‐adrenergic inhibitory neurones. The results of this study demonstrate that neurogenic peristalsis in the avian small intestine does not conform to the 'law of the intestine' as originally postulated by Bayliss & Starling (1899).
Continuity of orientation columns between superficial and deep laminae of the cat primary visual cortex.
Authors: Murphy P C , Sillito A M
Published: December 2014

1. Recent reports of a marked and consistent dislocation between orientation columns in the superficial and deep layers of cat striate cortex (Bauer, 1982, 1983) directly contradict the traditional view of the system (Hubel & Wiesel, 1962). This has considerable implications for our current understanding of cortical organization, and in order to clarify the issue we have carried out experiments to test the continuity of the columnar system with depth, in central regions of area 17. 2. In twenty‐four penetrations, eighteen of which were placed as perpendicular as possible to the surface of the cortex, orientation preference was assessed at regular intervals both qualitatively and using a randomly interleaved quantitative technique. The distribution of preferred orientations was analysed with reference to a detailed histological reconstruction of the electrode track, including the location of laminar boundaries and the course of radial tiers of cells and capillaries. 3. From a further series of eighteen near‐perpendicular penetrations, the change in average orientation between one superficial and one deep layer recording site was compared with the deviation of the track from perpendicular to the surface and hence parallel to the orientation columns. 4. In penetrations perpendicular to the surface of the cortex, orientation preference showed little variation between superficial and deep laminae. In oblique penetrations, preferred orientation generally changed according to a single, smooth trend. Those irregularities that were encountered were confined to oblique penetrations, and were distributed throughout the cortical laminae. 5. In conclusion, our evidence does not support the presence of a systematic discontinuity with depth within the orientation columnar system. It is therefore entirely consistent with earlier evidence on the subject.
Endothelium‐derived relaxing factor alters calcium fluxes in rabbit aorta: a cyclic guanosine monophosphate‐mediated effect.
Authors: Collins P , Griffith T M , Henderson A H , Lewis M J
Published: December 2014

1. Measurement of tension and 45Ca influx and efflux were used to study the effects of endothelium‐derived relaxing factor (EDRF), sodium nitroprusside and 8‐bromo‐cyclic guanosine monophosphate (GMP) on contractile responses and calcium movements in aortic ring preparations of the rabbit. 2. EDRF activity, induced by stimulating endothelium‐containing rings with acetylcholine, was associated with relaxation of noradrenaline‐constricted rings and with a marked reduction of noradrenaline‐stimulated increase in calcium influx. Sodium nitroprusside and 8‐bromo‐cyclic GMP had a similar effect in de‐endothelialized preparations. 3. EDRF also inhibited noradrenaline‐stimulated calcium efflux. Sodium nitroprusside and 8‐bromo‐cyclic GMP had a similar effect in de‐endothelialized preparations, both in the presence and absence of extracellular calcium. 4. The vascular smooth muscle relaxant effect of EDRF and of nitrovasodilators may be effected by a cyclic GMP‐mediated reduction of cytosolic calcium, through both inhibition of calcium influx and reduction of intracellular calcium release.
Brain intracellular pH and metabolism during hypercapnia and hypocapnia in the new‐born lamb.
Authors: Cady E B , Chu A , Costello A M , Delpy D T , Gardiner R M , Hope P L , Reynolds E O
Published: December 2014

1. The effects of hypercapnia and hypocapnia on brain intracellular pH (pHi) and metabolism were investigated in new‐born lambs under barbiturate anaesthesia. 2. 31P nuclear magnetic resonance (n.m.r.) spectroscopy was used to determine brain pHi and the relative concentrations of compounds containing mobile phosphorus nuclei including phosphocreatine (PCr), nucleoside triphosphates (NTP) and inorganic phosphate (Pi). Simultaneous measurements were made of the molar ratio of glucose to oxygen uptake by the brain. 3. During normocapnia (arterial partial pressure of CO2 Pa, CO2, 39 +/‐ 1 mmHg mean +/‐ S.E. of mean, n = 9) brain pHi was 7.13 +/‐ 0.02. Hypercapnia (Pa, CO2, 98 +/‐ 3 mmHg) was associated with a fall in brain pHi to 6.94 +/‐ 0.03 (n = 19, P less than 0.001), whereas no significant change in brain pHi occurred during hypocapnia (Pa, CO2, 16 +/‐ 1 mmHg; brain pHi 7.15 +/‐ 0.01). 4. During hypercapnia there was an increase in the ratio of Pi to NTP from 1.09 +/‐ 0.08 to 1.47 +/‐ 0.06 (P less than 0.001) and a decrease in the ratio PCr/Pi from 1.60 +/‐ 0.08 to 0.93 +/‐ 0.04 (P less than 0.001). There was a linear correlation between Pi/NTP and brain pHi. 5. Alterations in arterial PCO2 had no significant effect on the molar ratio of glucose to oxygen uptake by the brain, which remained close to unity. 6. The change in brain pHi observed during hypercapnia can be accounted for by the known physico‐chemical buffering capacity of brain tissue. Homoeostasis of brain pHi during hypocapnia provides further evidence that additional regulatory mechanisms operate in these circumstances. 7. The observed changes in PCr and Pi can be accounted for in part by the [H+] dependence of the creatine kinase reaction.
Inhibitory synaptic potentials recorded from mammalian neurones prolonged by blockade of noradrenaline uptake.
Authors: Surprenant A , Williams J T
Published: December 2014

1. Intracellular recordings of membrane potential and membrane current were made from neurones of the rat nucleus locus coeruleus and the guinea‐pig submucous plexus. These neurones exhibit inhibitory post‐synaptic potentials (i.p.s.p.s) which result from noradrenaline acting on alpha 2‐adrenoceptors to cause an increase in potassium conductance. 2. Cocaine (0.2‐30 microM) reversibly increased the duration of the i.p.s.p. or inhibitory post‐synaptic current (i.p.s.c.) in locus coeruleus neurones and submucous plexus neurones by approximately 750% and 350% respectively. The concentrations of cocaine causing half‐maximal prolongation of the synaptic current were 3 microM in locus coeruleus and 0.5 microM in submucous plexus. The prolongation was due entirely to a slower rate of decay of the synaptic response. 3. Cocaine (10 microM) produced a maintained hyperpolarization (2‐10 mV) or outward current (20‐120 pA) in locus coeruleus neurones; in submucous plexus neurones cocaine increased the amplitude and duration of spontaneous i.p.s.p.s. 4. Outward currents produced by superfusion with noradrenaline were increased by cocaine with maximum effects being observed at 10‐30 microM‐cocaine. The maximum leftward shift in the relation between outward current or membrane hyperpolarization and noradrenaline concentration was 18‐ to 100‐fold in locus coeruleus neurones and 4‐fold in submucous plexus neurones. The concentrations of cocaine which caused a half‐maximal increase in sensitivity to superfused noradrenaline were similar in both tissues, being 4 microM in locus coeruleus and 2 microM in submucous plexus. 5. These results show that neuronal uptake of noradrenaline released from adrenergic nerves plays a significant role in determining the time course of synaptic potentials mediated by noradrenaline.
On the action of ruthenium red and neuraminidase at the frog neuromuscular junction.
Authors: Robertson B , Wann K T
Published: December 2014

1. The actions of the polyvalent cationic dye Ruthenium Red and the enzyme neuraminidase were studied at the frog neuromuscular junction. 2. Both Ruthenium Red (0.5‐40 microM) and neuraminidase (1, 2 and 4 u.) reduced the miniature end‐plate potential (m.e.p.p.) amplitude irreversibly with little change in frequency. This effect could be attributed to the depressant action of these agents on the amplitude of extracellularly recorded miniature end‐plate currents (m.e.p.c.s) coupled with their shortening effect on the duration of these m.e.p.c.s. For example, 10 microM‐Ruthenium Red reduced the time constant of decay (tau D) of extracellular m.e.p.c.s to 35% of the control value. 3. Ruthenium Red (5, 10 and 15 microM) produced a pronounced reduction in the post‐synaptic end‐plate sensitivity to microiontophoretically applied acetylcholine. In some cases this effect was fully reversible on wash‐out of the dye. 4. Amplitude histograms of m.e.p.c.s recorded under voltage clamp showed a similar shift of the modal value to lower levels in the presence of Ruthenium Red. Over the voltage range ‐70 to ‐110 mV the action of Ruthenium Red on the tau D was not voltage dependent. 5. The actions of Ruthenium Red on tau D were not affected by anaesthetic agents, such as the short‐chain alcohols which increased tau D, or ketamine which decreased tau D. 6. Some possible modes of action of Ruthenium Red and neuraminidase are briefly discussed.
Photopic spectral sensitivity of the cat.
Authors: Loop M S , Millican C L , Thomas S R
Published: December 2014

1. The psychophysical spectral sensitivity of cats was assessed using a two‐choice visual discrimination task by determining increment thresholds and critical flicker frequency on white and chromatic backgrounds. 2. For large increments, on 0.0, 0.3 and 3.0 cd/m2 white backgrounds, the cats were most sensitive to 497 nm indicating that these backgrounds are scotopic. On 30 and 300 cd/m2 white backgrounds, the cats were most sensitive to about 454 and 561 nm indicating that these backgrounds are photopic. Sensitivity to intermediate wave‐lengths indicated independent action of 'blue' and 'green' cones. 3. For large increments, thresholds on photopic yellow and magenta backgrounds indicated the additive influence of 'blue' and 'green' cones. 4. Spectral sensitivity functions obtained with a critical flicker frequency criterion of 10 Hz on a 30 cd/m2 white background reflected only the activity of the 'green' cone while at 20 Hz the function reflected an additive contribution of both 'blue' and 'green' cones. 5. For small increments, on a 30 cd/m2 white or 96 cd/m2 orange background, sensitivity reflected only the activity of the 'green' cone. 6. The cat's photopic spectral sensitivity is influenced by the psychophysical test upon which it is based in a manner that is similar to what has been found for other vertebrates. No evidence was found for a 500 nm mechanism active at photopic levels.
The organization and post‐natal development of area 18 of the cat's visual cortex.
Authors: Blakemore C , Price D J
Published: December 2014

1. We made extracellular recordings from 1176 single units in area 18 of adult cats and kittens aged between 7 days and 10 weeks, and from 137 single units in area 17 in kittens aged between 12 days and 10 weeks. 2. All cells examined in area 18 of adult cats were visually responsive, 84% being orientation selective, 9% orientation biased and 7% non‐oriented. Orientation columns and ocular dominance columns were identified. There was an over‐all bias towards horizontal and vertical in the distribution of preferred orientations in the rostral part of area 18, where we were recording. 3. In area 18 of 7‐day‐old, visually inexperienced kittens the majority of cells (60%) were visually unresponsive; the remainder were either non‐oriented (25%) or orientation biased (15%), and no orientation‐selective units were found. Nevertheless there seemed to be a rudimentary columnar system, even in the youngest animals, in that orientation‐biased cells tended to occur in clusters with neighboring neurones having similar orientation preferences. In normal animals of 3 weeks and younger we found that the distribution of preferred orientations of a sample of neurones in area 18 with receptive fields scattered over much of the left lower quadrant of the visual hemifield was biased to oblique orientations. 4. As in adult cats, most cells in area 18 in young kittens were binocularly driven, and periodic alternation of dominance along oblique penetrations, characteristic of ocular dominance columns, was sometimes seen, even at the earliest ages. 5. Many of the developmental changes that we observed in area 18 occurred during the first 4 post‐natal weeks. Orientation selectivity, orientation tuning, directionality and responsiveness of neurones matured rapidly over this period. The proportions of simple and complex cells were similar in kittens aged 4 weeks or more to those in adult cats, whereas prior to this most neurones that displayed an orientation preference appeared to be immature simple cells. 6. A laminar analysis revealed that very few units in the superficial layers (I, II and III) in area 18 are visually responsive in kittens during their first and second weeks, but orientation selectivity rapidly develops during the third week. By contrast, even in very young, visually inexperienced kittens, the majority of neurones found in deeper laminae (IV, V and VI) are visually responsive and a few of them already show an orientation preference; however, the subsequent appearance of larger proportions of orientation‐selective cells in these lower layers is a more prolonged process than in upper laminae.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of dark‐rearing on the development of area 18 of the cat's visual cortex.
Authors: Blakemore C , Price D J
Published: December 2014

1. We recorded extracellularly from 420 single units in area 18 in visually inexperienced kittens aged 7 days and dark‐reared kittens aged between 3 and 12 weeks and from 60 single units in area 17 in dark‐reared kittens aged 5 and 11 weeks. 2. Visual deprivation generally depressed the maturation of area 18, although some features were affected more than others and certain developmental improvements still occurred. The percentage of visually responsive units in area 18 increased from 40% in 7‐day‐old kittens to about 75% in dark‐reared animals 10‐12 weeks. At each age a proportion of cells was orientation biased (between 15 and 45%) and these neurones appeared to be arranged in a crude columnar fashion. However, dark‐rearing, from birth, prevented the development of a significant proportion of orientation‐selective cells in area 18; no more than 5% of neurones were orientation‐selective at any age. We found no major bias in the over‐all distribution of preferred orientations of cells in area 18 in dark‐reared kittens. 3. Simple cells, which are found in area 18 even in very young, visually inexperienced kittens, persisted after dark‐rearing, although most retained immature properties. Relatively few complex cells were found in area 18 in visually deprived animals. 4. The majority of neurones in area 18 of dark‐reared kittens were binocularly driven, many equally well by either eye; evidence for regional variation in ocular dominance (indicative of a columnar pattern) was found in these deprived animals. 5. A laminar analysis in area 18 showed that percentages of non‐oriented and orientation‐biased cells changed little, if at all, in lower laminae (IV, V, and VI) but increased substantially in upper layers (above layer IV) in the absence of visual stimulation, over the first 12 post‐natal weeks. 6. A comparison of the effects of dark‐rearing on areas 17 and 18 indicates that the normal development of visual responsiveness and specific receptive field properties is suppressed in both areas during the first 12 post‐natal weeks. It is possible that area 17 has a greater degree of orientation selectivity than area 18 in young visually deprived kittens and this may reflect a difference in the type of afferent inputs.
Baclofen reduces post‐synaptic potentials of rat cortical neurones by an action other than its hyperpolarizing action.
Authors: Howe J R , Sutor B , Zieglgänsberger W
Published: December 2014

1. Intracellular recordings were obtained from neurones in layers 2 and 3 of the rat frontal neocortex in an in vitro slice preparation. Three distinct types of stimulation‐evoked post‐synaptic potentials were recorded in these neurones: excitatory post‐synaptic potentials (e.p.s.p.s); bicuculline‐sensitive, chloride‐dependent inhibitory post‐synaptic potentials (i.p.s.p.s) with times to peak of 20‐25 ms (fast(f)‐i.p.s.p.s); bicuculline‐insensitive, potassium‐dependent i.p.s.p.s with bicuculline‐insensitive, potassium‐dependent i.p.s.p.s with times to peak of 150‐250 ms (long(l)‐i.p.s.p.s). 2. The effects of baclofen were investigated on seventy‐one neurones. Baclofen was applied by ionophoresis or pressure ejection from micropipettes or was added to the superfusion medium. 3. Baclofen depressed stimulation‐evoked e.p.s.p.s in fifty‐seven of the sixty neurones tested. This effect was associated with an increase in the stimulation intensity required to produce a synaptically evoked action potential for thirty‐nine of forty‐four neurones. 4. Baclofen depressed f‐i.p.s.p.s in thirty‐seven of the thirty‐nine neurones tested and l‐i.p.s.p.s in each one of the seventeen neurones tested. Reversal potential values for each type of i.p.s.p. were not changed by baclofen and its depressions of each were independent of membrane potential (Em). Baclofen reduced the magnitude and the duration of the conductance increases that were associated with f‐ and l‐i.p.s.p.s. 5. Baclofen hyperpolarized forty of seventy‐one neurones and produced outward currents in three of four neurones recorded in voltage clamp at holding potentials between ‐55 and ‐65 mV. These actions were associated with 10‐58% reductions of neuronal input resistance (RN) and 10‐20% increases in neuronal input conductance (gN), respectively. Baclofen decreased the direct excitability of twenty‐three of twenty‐seven neurones tested. Determinations of the reversal potential for baclofen‐induced changes of Em indicate that baclofen increases the conductance of rat neocortical neurones to potassium ions. 6. The EC50 for each action of DL‐baclofen was approximately 1 microM. L‐Baclofen was greater than 100 times more potent than D‐baclofen. 7. Concentrations of bicuculline that blocked f‐i.p.s.p.s and responses to ionophoretically applied gamma‐aminobutyric acid (GABA) had no effect on the depressions of e.p.s.p.s or the hyperpolarizations and decreases in RN that baclofen produced. 8. Baclofen did not reduce the duration of action potentials that were prolonged with intracellular injections of caesium ions or by superfusions with medium that contained 10 mM‐tetraethylammonium (TEA).(ABSTRACT TRUNCATED AT 400 WORDS)
Analysis of gated membrane currents and mechanisms of firing control in the rapidly adapting lobster stretch receptor neurone.
Authors: Edman A , Gestrelius S , Grampp W
Published: December 2014

1. The gated membrane currents (a tetrodotoxin‐sensitive Na+ current and a tetraethylammonium‐ and 4‐aminopyridine‐sensitive K+ current) of the rapidly adapting stretch receptor neurone of lobster were investigated with respect to their kinetic properties using electrophysiological, pharmacological, and mathematical techniques. 2. The currents were found to be controlled by slow inactivations as well as by fast Hodgkin‐Huxley (1952) gating processes. They could be described by kinetic expressions which differed from those inferred for the slowly adapting receptor (Gestrelius & Grampp, 1983a; Gestrelius, Grampp & Sjölin, 1983) only with respect to some of the parameter values. 3. With these expressions, and additional equations for the cell's pump and leak current components (Edman, Gestrelius & Grampp, 1986), a mathematical receptor model was formulated which accurately predicts the impulse activity of the living preparation in different functional circumstances and which, therefore, was adopted as an appropriate theory of firing regulation. 4. From a model analysis it appeared (a) that the 'rapid' adaptation of the receptor's impulse activity is mainly an effect of slow Na+ current inactivation starting a regenerative process of accommodation which, basically, is due to a small ratio of subthreshold Na+ to K+ currents; (b) that, because of the transmembrane Na+ influx being limited by accommodation, impulse firing is only little affected by a Na+‐dependent pump current activation; and (c) that the phenomenon of increased firing frequency initially during prolonged stimulation ('negative adaptation') is an effect of the slow K+ current inactivation being faster than the slow Na+ current inactivation at comparable degrees of membrane polarization. 5. From further model studies it also appeared that, during depolarizations between successive action potentials evoked by constant stimulation, the membrane behaves like a high‐resistance constant‐current generator feeding into a short‐circuiting capacitor. In consequence, the cell's stimulus sensitivity (change in firing frequency with stimulation strength) is, at functionally relevant stimulation intensities, mainly determined by the membrane capacitance and by the amplitude of the interspike membrane depolarization while, at higher stimulation intensities and firing frequencies, it becomes more and more a function of the spike duration itself.
Electrical constants of arterially perfused rabbit papillary muscle.
Authors: Kléber A G , Riegger C B
Published: December 2014

1. Right ventricular rabbit papillary muscles were arterially perfused with a mixture of Tyrode solution, bovine erythrocytes, dextran and albumin. In the recording chamber, they were surrounded by a H2O‐saturated atmosphere of O2 and CO2 which served as an electrical insulator. 2. Conduction velocity and passive electrical properties were determined from intra‐ and extracellular potentials measured during excitation and during flow of subthreshold current. 3. The propagation of the action potential was linear along the muscle at a velocity of 55.6 cm/s. The extracellular wave‐front voltage was 51.5 mV. 4. The following values for passive cable properties were obtained: (i) a ratio of extra‐ to intracellular longitudinal resistance of 1.2; (ii) an extracellular specific resistance (Ro) of 63 omega cm; (iii) an intracellular specific resistance (Ri) of 166 omega cm; (iv) a space constant lambda of 0.357 mm; (v) a membrane time constant tau of 2.57 ms. The space constant lambda* recalculated for zero extracellular resistance was 0.528 mm. 5. Arresting perfusion with drop of perfusion pressure was associated with an immediate increase of the extracellular longitudinal resistance by 35% and a decrease of conduction velocity by 13%. 6. The present results demonstrate the important contribution of the extracellular resistance to electrotonic interaction and propagation in densely packed myocardial tissue. Moreover, changes in perfusion pressure are associated with changes in extracellular resistance, probably as a consequence of changes in intravascular volume.
Botulinum toxin inhibits quantal acetylcholine release and energy metabolism in the Torpedo electric organ.
Authors: Dunant Y , Esquerda J E , Loctin F , Marsal J , Muller D
Published: December 2014

1. Type A Botulinum toxin (BoTX) blocked nerve‐electroplaque transmission in small fragments of Torpedo marmorata electric organ incubated in vitro. The effect was observed either with the crystalline toxin complex (associated with haemagglutinin) or with the purified neurotoxin (molecular weight approximately 150,000). 2. The quantal content of the evoked post‐synaptic response was reduced by BoTX but the quantum size remained unchanged till complete blockade of the evoked response. 3. Spontaneous electroplaque potentials were composed of two populations: one with a bell‐shaped amplitude distribution (miniature potentials or quanta) and a population of small events with a skewed distribution (subminiatures). In BoTX‐poisoned tissue, the bell‐distributed miniatures progressively disappeared, but the subminiatures kept on occurring. Occasionally, larger spontaneous potentials with a slow time course were recorded; they were also BoTX resistant. 4. A biochemical assay showed that evoked acetylcholine (ACh) release was impaired by BoTX. During the period when evoked transmission was blocked, spontaneous ACh release transiently increased. 5. At the time of transmission blockade, there was no significant change of ACh content, of ACh turnover, of ACh repartition in the vesicle‐bound and free compartments, or of the number of synaptic vesicles. 6. The amount of ATP was reduced to 50% by BoTX, and that of creatine phosphate (CrP) to less than 20%. The ATP‐CrP‐converting enzyme, creatine kinase, was inhibited in BoTX‐poisoned tissue. 7. Thus, the electrophysiological effects of BoTX are very similar at the nerve‐electroplaque and the neuromuscular junctions. The present work suggests in addition that suppression of quantal release by BoTX is related to marked alterations of the energy metabolism in the tissue.
The role of joint receptors in human kinaesthesia when intramuscular receptors cannot contribute.
Authors: Ferrell W R , Gandevia S C , McCloskey D I
Published: December 2014

1. Kinaesthetic acuity was tested at the distal interphalangeal joint of the middle finger when the hand was postured so that the joint was effectively disengaged from its muscular attachments. Subjects were required to detect the direction of 5 deg movements applied at different angular velocities from a mid‐position under control conditions, after intra‐articular injection of a plasma expander and after intra‐articular injection of a local anaesthetic. 2. Kinaesthetic performance was enhanced after the injection of a plasma expander and deteriorated after injection of local anaesthetic. This deterioration could not be explained by spread of the local anaesthesic from the injection site on the dorsum of the joint. 3. The results suggest that the discharge of joint receptors can produce perceived signals of joint movement. Under normal conditions these receptors may duplicate the kinaesthetic input from muscle spindle endings.
Cell death of axotomized motoneurones in neonatal rats, and its prevention by peripheral reinnervation.
Authors: Kashihara Y , Kuno M , Miyata Y
Published: December 2014

1. Motoneurone death induced by axotomy in the rat was studied following section of the medial gastrocnemius nerve near the muscle 4 days after birth. 2. The maximum twitch tension of the medial gastrocnemius muscle achieved by motor reinnervation after section of its nerve was about 70% of that measured on the contralateral, intact side. 3. The number of motor units counted at 35‐45 days of age in the animals whose medial gastrocnemius nerves had been sectioned on day 4 was 62% of that observed in normal rats. 4. The number of medial gastrocnemius motoneurones retrogradely labelled with horseradish peroxidase (HRP) 30‐40 days after section of the medial gastrocnemius nerve was 77% of that labelled on the contralateral, intact side. 5. When the medial gastrocnemius nerve had been sectioned on day 4 and prevented from peripheral reinnervation, the number of medial gastrocnemius motoneurones labelled with HRP was, on the average, only 18% of that labelled on the control side. 6. Decreased number of medial gastrocnemius motoneurones labelled with HRP following prevention of peripheral reinnervation was associated with a decrease in the neurone density of the motor cell column, indicating the occurrence of motoneurone death. 7. The majority of medial gastrocnemius motoneurones axotomized 4 days after birth appear to maintain their survival for about 2 weeks without target contact. 8. The area of the compound action potential of medial gastrocnemius motor fibres once decreased after axotomy on day 4 began to recover from the 12th day after the operation if reinnervation by the cut peripheral nerve had been allowed, whereas the compound action potential continued to decrease in those axotomized motoneurones whose reinnervation had been prevented. 9. It is concluded that target dependence of motoneurone survival previously observed at embryonic stages is still present during the early post‐natal period.
Sodium currents in axon‐associated Schwann cells from adult rabbits.
Authors: Chiu S Y
Published: December 2014

1. Patch‐clamp and electron‐microscopic studies were carried out on individual axon‐Schwann‐cell complexes 2‐6 h after they were isolated from the sciatic nerves of rabbits 5, 10 and 20 weeks old. 2. Under Hoffman modulation contrast optics Schwann cells associated with both myelinated and non‐myelinated axons could be seen. Frequently, fine cable‐like structures about 1 micron in diameter, which are presumably axons, could be seen in isolation from a Schwann cell. 3. Cross‐sectional electron‐microscopic studies directly demonstrated the presence of axons engulfed by Schwann cells. For Schwann cells associated with non‐myelinated axons, multiple fine axons (approximately 1 micron) could be seen enclosed by one or few turns of spiralling tongues of Schwann cells. Schwann cells associated with a single large myelinated axon showed characteristic compact myelin wrappings. No membrane fusion between Schwann cells and the axons could be detected. 4. Giga‐seals could readily be formed when a patch pipette was pressed against the body region of a Schwann cell associated with either non‐myelinated or myelinated axons. In contrast, giga‐seals were only infrequently obtained on fine cable‐like structures (1 micron) visually identified to be separated from the Schwann cell body. 5. Whole‐cell recordings made from the body region of a Schwann cell revealed a TTX‐sensitive fast inward current. Intriguingly, the expression of this current appeared to be dependent on the type of associated axon; this current was detectable in virtually all recordings made at the body region of Schwann cells associated with small non‐myelinated axons, but not from those associated with large myelinated axons. 6. The inward current was like a neuronal sodium current; it had voltage‐gated kinetics similar to the Hodgkin‐Huxley sodium current, and exhibited a reversal potential close to the expected Nernstian potential for sodium ions. 7. From the observed size of the whole‐cell membrane capacity and the electron‐microscopic observations that the surface area of the Schwann cell at the body region was much larger than that of a 1 micron non‐myelinated axon, it was argued that the whole‐cell recordings were from Schwann cells rather than from single axons. Furthermore, the peak sodium current density was similar to that of Schwann cells cultured from new‐born rabbits in which axons were presumed to be absent. 8. The results suggested that Schwann cells normally associated with non‐myelinated axons in the rabbit sciatic nerves maintain an active synthesis of neuronal‐like sodium channels throughout normal development.