bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of fasting on the potential difference across the brush‐border membrane of enterocytes in rat small intestine.
Authors: Debnam E S , Thompson C S
Published: December 2014

The effects of starvation on the magnitude of the potential difference across the brush‐border membrane of rat small intestine (Vm) have been studied in vitro. The mean values obtained for Vm in jejunal tissue after a fast of either 24 or 72 h duration (‐53.5 and ‐55.0 mV respectively) were significantly greater than the mean value of ‐45.3 mV recorded using intestine from fed rats. A similar hyperpolarization was observed after a 72 h fast using intestine from a more distal region. The response to fasting seen in the jejunum appears to be caused by a decrease in Na+ permeability of the mucosal membrane. The addition of D‐galactose (4 mM) or L‐valine (4 mM) to the mucosal fluid caused a depolarization of Vm. Using jejunum from fed animals, Vm in the presence of galactose and valine was found to be ‐40.3 and ‐39.2 mV respectively. Following a fast of 72 h duration, the values of Vm for the two substrates were ‐43.4 and ‐43.1 mV respectively. Phlorhizin (10(‐4) M) abolished the galactose‐induced depolarization in both fed and fasted conditions but was without effect on the response to valine. It is concluded that starvation increases the electrical driving force for Na+ during Na+ coupled non‐electrolyte transport into the enterocyte. The possible mechanisms involved in this adaptive response are discussed.
Outward currents in voltage‐clamped rat sympathetic neurones.
Authors: Galvan M , Sedlmeir C
Published: December 2014

Outward membrane currents were studied in neurones of the isolated rat superior cervical ganglion by using a two‐micro‐electrode or single‐micro‐electrode voltage‐clamp technique. Under current clamp, depolarization elicited electrotonic potentials that displayed marked outward rectification. From negative resting potentials (‐70 mV) a short latency, short duration outward rectification was observed. From more positive potentials (‐40 mV) a longer latency persistent outward rectification could be demonstrated. Under voltage clamp, four distinct outward currents were observed: a delayed rectifier (IK); a transient outward current (IA); a Ca2+‐activated current (IC) and the M‐current (IM). The maximum amplitude of IK, IA and IC was 1‐2 orders of magnitude greater than IM. Depolarizing from ‐40 mV to potentials more positive than ‐20 mV co‐activated IK and IC, producing a characteristic N‐shaped current voltage curve with a minimum at about +80 mV. Superfusion with Mn2+‐containing solutions reduced outward current at all voltages and abolished the N‐characteristic; the remaining current (IK) slowly inactivated (tau greater than 1 s). Raising [K+]o from 6 to 36 mmol/l reversed outward tail currents observed in normal solution. Addition of tetraethylammonium ions (1‐3 mmol/l) strongly reduced the amplitude of IK and IC. IA was characterized by very rapid activation at potentials more positive than ‐60 mV and by fast and complete inactivation at potentials in the activation range. The amplitude of IA was dependent on [K+]o and was reduced by external 4‐aminopyridine (1‐3 mmol/l). The activation appeared to depend on the nature and concentration of divalent cations present in the superfusate. It is concluded that the soma membrane of rat sympathetic neurones, like many other vertebrate and invertebrate neurones, contains multiple populations of K+ channels. The possible functions of these in the control of ganglion cell excitability are discussed.
Calcium and potassium currents in spermatogenic cells dissociated from rat seminiferous tubules.
Authors: Hagiwara S , Kawa K
Published: December 2014

The electrophysiological properties of the cell membrane of rat spermatogenic cells were studied using the whole‐cell variation of the patch‐electrode voltage‐clamp technique. In late primary spermatocytes and early spermatids isolated from adult testis, a transient inward current followed by a slowly developing outward current was produced when the membrane potential was made more positive than ‐60 mV. Early spermatogenic cells which consist of spermatogonia and early spermatocytes were isolated either from new‐born rats (12‐14 days old) of from adult cryptorchid rats 15‐21 days after the operation. In early spermatogenic cells, some showed a slowly developing outward current with negligible initial inward current, while others showed a recognizable inward current followed by the slowly developing outward current. The inward currents are identified as Ca2+‐carried current, since replacement of external Ca2+ with Mn2+ reversibly diminished the current whereas Ba2+ or Sr2+ substituted for Ca2+. The reversal potential of the outward current changed from ‐65 to ‐12 mV when [K+]o was raised from 5 to 100 mM. The outward current was independent of [Ca2+]o and was blocked by tetraethylammonium chloride. Thus the current was identified as membrane‐potential‐dependent K+ current. During spermatogenesis from spermatogonia to early spermatids, the density of Ca2+ current increased while the K+ current density decreased significantly.
Functional and topographical properties of field potentials evoked in rat dorsal horn by cutaneous C‐fibre stimulation.
Authors: Schouenborg J
Published: December 2014

Extracellular field potentials in the lumbosacral dorsal horn evoked by stimulation of cutaneous C fibres in the sural nerve were explored in the halothane‐anaesthetized rat. C‐fibre‐evoked field potentials were prominent in lamina II and lamina V of the dorsal horn. These potentials had a latency of 80‐130 ms and a duration of more than 200 ms. A peak in the C‐fibre‐evoked field potential, termed the CI potential, with a median latency of 120 ms, range 105‐150 ms, was distinguished in lamina II. The time from onset to peak of the CI potential was, on average, 13 ms when all C fibres were activated. The amplitude of the CI potential in lamina II was directly proportional to the amplitude of the C‐fibre‐evoked nerve volley, whereas the relation between the C‐fibre nerve volley and the C‐fibre‐evoked field potential in lamina V was non‐linear. A selective block of A fibres did not influence the amplitude of these field potentials. Following stimulation of C afferent fibres in the medial sural nerve, at frequencies higher than 0.1 Hz, the CI potential in lamina II, but not the C‐fibre‐evoked field potential in lamina V, was increased. There was no concomitant change of the A‐fibre‐evoked field potentials. The magnitude of the potentiation of the CI potential was dependent both on the frequency and the number of stimuli. Mean percentage potentiation was 200%, range 150‐300%, after seventy stimulations at a frequency of 1.0 Hz. During the stimulation the CI potential increased monotonically. The decay of the potentiation of the CI potential was well described by two exponentially declining phases. There was a positive correlation between the size of the time constants of the decay and the number of stimuli during conditioning. Following noxious radiant heat (temperature 50‐55 degrees C) applied to a restricted part of the skin (area 20‐30 mm2) within the receptive field of the medial sural nerve for 10‐20 s, the CI potential was potentiated by 50‐130%. The duration of this potentiation was 3‐15 min. This potentiation was somatotopically organized. By contrast, there was no effect on the amplitude of the CI potential following innocuous skin stimulation (slowly moving contact, brushing the skin, warmth 40 degrees C).(ABSTRACT TRUNCATED AT 400 WORDS)
Analysis of 'off' tails of intramembrane charge movements in skeletal muscle of Rana temporaria.
Authors: Huang C L
Published: December 2014

Components of non‐linear charge were isolated in transients obtained in response to hyperpolarizing ('off') voltage‐clamp steps in frog muscle fibres. 'Off' currents of the q gamma charge were isolated by comparing records obtained from long depolarizing steps with those resulting from short steps which intercepted the 'on' currents of the q gamma charge. The 'off' transients of the q gamma component so deduced were rapid decays lasting 10‐15 ms, in contrast with their prolonged time course in the preceding 'on' steps. 'Off' responses were rapid even at voltages when the 'on' current, obtained from imposed 10 mV steps made at a series of closely incremented conditioning voltages, was delayed and prolonged. Such slow transfers of charge could not be demonstrated in 'off' tails. Large depolarizing steps resulted in rapid q gamma transients in 'on' currents not distinguishable from the rest of the charge movement. Nevertheless, by separating the q gamma component through its inactivation by prolonged depolarization, it was possible to show that q gamma currents in the 'off' tails were still rapid decays. It is concluded that in contrast to the varied pattern shown by q gamma in 'on' transients, its 'off' responses are everywhere relatively fast decays. These features can be predicted by a simple two‐state model in which the forward and backward rate constants depend upon the amount of charge moved, as well as the membrane voltage.
The after‐effects of stretch and fusimotor stimulation on the responses of primary endings of cat muscle spindles.
Authors: Morgan D L , Prochazka A , Proske U
Published: December 2014

These experiments explore the after‐effects of repetitive movements and dynamic fusimotor stimulation on the responses of primary endings of soleus muscle spindles in the anaesthetized cat. If immediately following a series of conditioning stretch and shortening movements, the muscle was held at the stretched length for 3 s before being returned to its rest length, the subsequent response to a brief dynamic fusimotor tetanus given during a slow test stretch produced only a small increase in spindle firing. If, on the other hand, the muscle was returned to its rest length immediately after the movements, the fusimotor tetanus evoked a much larger afferent burst. This difference in the size of the burst could only be observed if the fusimotor tetanus was given soon after onset of the test stretch. If it was delayed and given at a time when the test stretch passed through the length at which the muscle had been held stretched after the movements, there was no difference in the size of the afferent burst. If following the movements the muscle was held stretched for less than 3 s, the response to the subsequent tetanus was not fully depressed. Once the depressed condition had been achieved, the muscle had to be left undisturbed for up to half an hour before the response had recovered its original fully undepressed size. Conditioning repetitive stimulation of the fusimotor fibre was just as effective as using alternating movements in producing the effects. If the test tetanus, which was normally ten shocks in 50 ms, was made longer, the change in size of the impulse burst became a change in latency of onset of the response to the tetanus. Holding the muscle stretched at the end of the conditioning movements/tetanus produced a delay in onset of the response to the test tetanus without significantly altering its size. These observations have been interpreted as arising from development of stable cross‐bridges between actin and myosin filaments in the intrafusal fibres. During repetitive movements or fusimotor stimulation, stable bridges become detached and during the subsequent 3 s they re‐attach, at the length at which the muscle is being held after conditioning.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic hyperpolarization and inhibition of turtle cochlear hair cells.
Authors: Art J J , Fettiplace R , Fuchs P A
Published: December 2014

Intracellular recordings were made from turtle cochlear hair cells in order to examine the properties of the post‐synaptic potentials evoked by electrical stimulation of the efferent axons. Single shocks to the efferents generated a hair cell membrane hyperpolarization with an average amplitude generally less than 1 mV and lasting for about 100 ms. With short trains of shocks, the size of the post‐synaptic potential grew markedly to a maximum of 20‐30 mV. The interaction between pairs of shocks separated by a varying interval was studied. For an interval of 4 ms, the response to the second shock was increased on average by a factor of 3 and the conditioning effect of the first shock decayed with a time constant of about 100 ms. We suggest the augmentation in response to trains of shocks may be partly due to facilitation of efferent transmitter release. The efferent post‐synaptic potentials could be reversibly abolished by perfusion with perilymphs containing 3 microM‐curare or atropine, and infusion of acetylcholine gave a transient membrane hyperpolarization. These observations are consistent with efferent action being mediated via a cholinergic synapse onto the hair cells. The post‐synaptic potentials could be reversed in polarity by injection of hyperpolarizing currents through the recording electrode. The reversal potential was estimated as about ‐80 mV, 30 mV negative to the resting potential. Near reversal, a small brief depolarization was evident and may constitute a minor component of the synaptic response. The value of the reversal potential was unaffected by substitution of the perilymphatic chloride, but was altered in a predictable manner by changes in extracellular potassium concentration indicating that the post‐synaptic potentials arise mainly by an increase in the permeability of the hair cell membrane to potassium ions. Throughout the post‐synaptic hyperpolarization there was a reduction in the sensitivity of the hair cell to tones at its characteristic frequency. The desensitization, maximal for low sound pressures, varied in different cells from a factor of 1.6 to 28. At the peak of the largest synaptic potentials, the receptor potential remained negative to the resting potential with all but the loudest characteristic frequency tone s. We suggest that there are two factors in efferent inhibition; one a r duction in the receptor potential at the hair cell's characteristic frequency and the other a hyperpolarization of its membrane potential which should reduce the release of excitatory transmitter onto the afferent terminals.
Factors influencing threshold of the fundamental electrical response to sinusoidal excitation of human photoreceptors.
Authors: Abraham F A , Alpern M
Published: December 2014

The amplitude and phase of the fundamental Fourier component of the electroretinogram (e.r.g.) in response to sinusoidally modulated light were studied in the range 7‐50 Hz. Sensitivity was best at the lowest frequency. The threshold‐frequency relationship divided into two parts. A weak steady background depressed sensitivity of the low, but increased sensitivity of the high, frequency component. At 8 Hz a small test spot was 0.7 log10 units more effective on the most sensitive part of the retina than on the optic disk. On the fovea, it was 0.1‐0.2 log10 units less effective than on the disk. The fovea was 0.7 log10 units more sensitive to 25 Hz than the blind spot. Psychophysical and e.r.g. dark‐adaptation curves were similar, but the former was 10(4) times more sensitive than the latter. Four sets of experiments examined the possibility that the Fourier component of the e.r.g. response at the modulation frequency of 8 Hz during the 'rod' phase of the e.r.g. dark‐adaptation curve arose from excitation of rods alone. The only hint of a possible cone contribution was a very small but systematic increase in phase delay with increase in background wave number found while measuring the field sensitivity action spectrum. No suggestion was found that the fundamental Fourier component of threshold e.r.g. responses at the modulation frequency of 25 Hz was influenced by photons absorbed in rods.
Pressure‐volume relationships and elastance in the knee joint of the dog.
Authors: Nade S , Newbold P J
Published: December 2014

This study has investigated changes in intra‐articular hydrostatic pressure in the knee joints of normal dogs in response to continuous and stepwise infusions of fluids. The relationship between pressure and volume in the joint was examined over the pressure range of ‐8 to +50 mmHg, and also at much higher pressures often associated with joint disease or injury. The effects of joint angle and dog weight on the pressure‐volume relationship and on elastance of the dogs' knees were also examined. With liquid paraffin B.P. the pressure was found to increase more with each unit volume infused at subatmospheric pressures than at pressures around atmospheric, and increased more again at higher pressures. The pressure‐volume curve with saline infusions was affected by egress of fluid from the joint at supra‐atmospheric pressure. Above +5 mmHg the rise in pressure per unit volume infused was less than that for paraffin at the same volume. Elastance and compliance of the normal joint capsule were calculated from the pressure‐volume data. Elastance was high at subatmospheric pressures, decreased rapidly as atmospheric pressure was approached and rose as a linear function of pressure above 12 mmHg. The biphasic shape of the elastance‐pressure curve is discussed, and explanations for the shape are suggested. After intra‐articular pressure in the knee was raised by infusion of paraffin oil the joint was moved through the range of positions from 125 deg extension to 50 deg flexion. Intra‐articular pressure did not change across the range 125‐110 deg. However, increasing the angle of flexion from 110 to 50 deg resulted in a rise in pressure which became steeper for each volume increment. Increasing intra‐articular fluid volume caused a decrease in the total range of movement of the joint. The pressure‐volume curves measured at extended angles of 110, 125 and 140 deg, where the starting pressures were subatmospheric, were the same. At flexed joint positions of 80 and 50 deg, where the starting pressures were supra‐atmospheric, the pressure‐volume curves became steeper with greater flexion. Elastance of the joint tissues increased with flexion. The elastance at each joint angle depended also on the volume or pressure. Significant differences were found to exist between pressure‐volume curves for three groups of animals of different weight.(ABSTRACT TRUNCATED AT 400 WORDS)
An investigation of threshold properties among cat spinal alpha‐motoneurones.
Authors: Gustafsson B , Pinter M J
Published: December 2014

In anaesthetized cats, thresholds for long (rheobase) and brief duration current pulses have been obtained from spinal motoneurones and compared with other cell parameters and membrane properties. Rheobase showed only weak over‐all relationships with conduction velocity and with cell size, estimated as the total capacitance of individual motoneuronal equivalent cylinders. Rheobase showed a clear tendency to vary inversely with after‐hyperpolarization (a.h.p.) duration and was strongly correlated with the input conductance and with the inverse of the membrane time constant. However, the range of rheobase current exceeded that of input conductance by almost a factor of 2. Part of this range discrepancy arose because threshold depolarization tended to increase with rheobase current. Thus, among motoneurones grouped according to rheobase magnitude (three groups), those within the lowest rheobase group had threshold depolarizations about 6 mV on average lower than those within the highest rheobase group. Even though this difference was not directly related to resting potential differences between the groups, further analysis suggested that it may have arisen secondarily to impalement‐induced depolarization. The finding that experimentally estimated threshold depolarizations in individual motoneurones were generally larger than those predicted by the product of input resistance and rheobase indicated that a subthreshold rectification process also contributed to the range of rheobase. The difference was largest in the low‐rheobase group and smallest in the high‐rheobase group. Because these differences were proportional to the differences in input resistance between the separate motoneurone groups, it is suggested that the magnitude of the current underlying the rectification process does not differ systematically among motoneurones. Within groups of motoneurones classified on the basis of rheobase or a.h.p. duration, significant correlations existed between rheobase current and input conductance. An analysis of variance indicated that even within such functional subgroups of motoneurones, rheobase was appreciably better correlated with membrane time constant than with estimated cell size. Although showing a range approximately half that of rheobase, the brief current threshold was similar to rheobase in its relations with total cell capacitance, a.h.p. duration and the inverse of membrane time constant.(ABSTRACT TRUNCATED AT 400 WORDS)
Influence of external calcium and glucose on internal total and ionized calcium in the rat lens.
Authors: Duncan G , Jacob T J
Published: December 2014

Free calcium in the rat lens, measured by ion‐sensitive electrodes, is 1.8 microM while the total, measured by atomic absorption, is of the order of 600 microM. The measured free calcium concentration (pCa) varies with the depth below the surface. It is lowest in the region 100‐400 micron below the capsule and again in the nucleus, while the intervening perinuclear cortex has a relatively high free calcium. In young rats (less than 16 weeks) the free calcium in the posterior and anterior cortical regions is the same, while in the older lenses the free calcium is lower in the anterior and the regional variation is greater. Rat lenses incubated in a medium of similar ionic composition to aqueous humour for 15‐24 h maintained a low level of free calcium. The maintenance of low internal calcium (both free and total) was dependent on external glucose and on removing glucose the intracellular free calcium increased from 5 to 15 microM while the total calcium increased from 600 to over 1000 microM. Following incubation in high calcium (10 mM), the free and total calcium increased to 40 and 3000 microM respectively. Omitting glucose from the high‐calcium solution led to a further increase in both free and total calcium to 400 and 10000 microM respectively. The incubated control lenses maintained their normal sodium and potassium levels and resting potential, while removing glucose gave rise to an increase in sodium, a decrease in potassium and a depolarization of the membrane potential. Increasing external calcium also depolarized the membrane potential, but there was no change in internal sodium and potassium.(ABSTRACT TRUNCATED AT 250 WORDS)
A fast transient outward current in the rat sympathetic neurone studied under voltage‐clamp conditions.
Authors: Belluzzi O , Sacchi O , Wanke E
Published: December 2014

Post‐ganglionic neurones of the isolated rat superior cervical ganglion were voltage clamped at 37 degrees C using separate intracellular voltage and current micro‐electrodes. Control experiments in current clamp suggested that the neurone is electrotonically compact, the soma and the proximal dendritic membranes being under good spatial voltage uniformity. Depolarizing voltage steps from membrane potentials near ‐50 mV evoked: (i) a voltage‐dependent inward Na+ current, (ii) an inward Ca2+ current, (iii) a voltage‐dependent outward K+ current, (iv) a Ca2+‐activated K+ outward current. Depolarizations from holding potentials more negative than ‐60 mV elicited, besides the currents mentioned above, a fast transient outward current IA which peaked in 1‐2.5 ms and then decayed to zero following an exponential time course. The IA current was shown to be primarily, if not exclusively, carried by K+. It was unaffected by removal of external Ca2+ or addition of Cd2+ and was weakly blocked by tetraethylammonium ions and partially by 4‐aminopyridine. The IA current showed a linear instantaneous current‐voltage relationship. Its activation ranged from ‐60 to 0 mV with a mid‐point at ‐30 mV. The A conductance could be described in terms of a simple Boltzmann distribution for a single gating particle with a valency of +3. Both the development and removal of inactivation followed a single exponential time course with a voltage‐dependent time constant which was large near the resting potential (42 ms at ‐70 mV) and small (11 ms) near ‐100 and ‐40 mV. Steady‐state inactivation h infinity ranged from ‐100 to ‐50 mV, with a mid‐point at ‐78 mV, suggesting that approximately 50% of the IA channels are available at the physiological resting potential. Action potentials elicited from various holding potentials showed maximal repolarization rates dependent on the holding potential itself. This voltage dependence was found to be in reasonably good agreement with that of h infinity curve. These data are consistent with the view that in the rat sympathetic neurone, under physiological conditions, it is the IA current rather than the delayed outward current that is responsible for the fast action potential repolarization.
Failure of glucose to affect 86rubidium efflux and 45calcium uptake of fetal rat pancreatic islets.
Authors: Ammon H P , Fahmy A , Mark M , Strölin W , Wahl M A
Published: December 2014

Ion movements and insulin secretion of pancreatic islets of adult and fetal rats have been studied at three glucose concentrations. In islets of adult rats, 86Rb efflux is maximally decreased by 5.6 mM‐glucose. 16.7 mM‐glucose caused a biphasic efflux pattern which may be due to glucose‐stimulated Ca uptake. In islets of fetal rats elevation of the glucose concentration from 3 to 5.6 or 16.7 mM does not cause a change of 86Rb efflux, and the fractional efflux from fetal islets in the presence of 3 mM‐glucose is similar to that from adult rat islets in the presence of 5.6 mM‐glucose. Elevation of the glucose concentration from 3 to 16.7 mM is not associated with an increase in 45Ca uptake into fetal islets, although this change in glucose concentration doubles 45Ca uptake into adult islets. When challenged with 16.7 mM‐glucose, fetal islets exhibit no insulin secretory response; however, they do respond to theophylline. It is concluded that the failure of fetal islets to exhibit an insulin‐secretory response when challenged with glucose might be related to the inability of glucose to affect 86Rb efflux and Ca uptake. The present data are discussed in light of differences between pancreatic islets of fetal and adult rats with respect to the redox state of pyridine nucleotides, thiols and glucose metabolism.
Alveolar liquid lining: Langmuir method used to measure surface tension in bovine and canine lung extracts.
Authors: Hills B A
Published: December 2014

The Langmuir trough has been used to study monolayers of surfactant from beef lung extracts, dog lavage and the principal component (dipalmitoyl lecithin; DPL) in which surface tension has been simultaneously monitored on each film by the Wilhelmy method and the original Langmuir method whose readings are independent of contact angle. Readings on the Wilhelmy balance at 80% film compression reached the near‐zero values recorded in previous studies, averaging 2.0 dyn cm‐1, but Langmuir readings on the same films averaged 13.5 dyn cm‐1 for DPL with no reading below 7.0 dyn cm‐1. Similar differences were found for bovine extracts and dog lung lavage and have been attributed to a serious contact‐angle artifact in the Wilhelmy method widely used in studying pulmonary surfactant. Higher minimum values of surface tension determined by the Langmuir method are shown to be incompatible with normal physiological function in the smaller mammals on the basis of the traditional bubble model of the alveolus. When Langmuir or Wilhelmy values are determined under more physiological conditions of area change, pH, temperature, humidity etc., values for surface tension are even higher and less compatible with the concept of a continuous liquid lining for the alveolar diameter of any mammal.
Efflux of 5‐hydroxytryptamine and noradrenaline into spinal cord superfusates during stimulation of the rat medulla.
Authors: Hammond D L , Tyce G M , Yaksh T L
Published: December 2014

High pressure liquid chromatography with electrochemical detection was used to quantify the efflux, in the same sample, of endogenous 5‐hydroxytryptamine (5‐HT), noradrenaline (NA), and 5‐hydroxyindoleacetic acid (5‐HIAA) into superfusates of the rat spinal cord in vivo. The efflux of these three agents was measured prior to, and during, electrical stimulation of the nucleus raphe magnus (n.r.m.) and nucleus reticularis paragigantocellularis (n.r.p.g.), two medullary nuclei implicated in antinociception. In untreated rats, basal efflux of 5‐HT and NA was 0.21 and 0.12 ng/ml of superfusate respectively; the basal efflux of 5‐HIAA was 18.17 ng/ml. Stimulation of the n.r.m. and n.r.p.g. in these animals increased the efflux of 5‐HT and 5‐HIAA, but did not alter the efflux of NA. 60 min after administration of fluoxetine (10 mg/kg, I.P.), a 5‐HT uptake inhibitor, basal efflux of 5‐HT and NA was unaltered, but the basal efflux of 5‐HIAA was decreased. In these rats, stimulation of the n.r.m. and n.r.p.g. increased the efflux of 5‐HT and of NA. The efflux of 5‐HIAA was not altered. In rats pre‐treated with both fluoxetine and desipramine (10 mg/kg, I.P.), the basal efflux of NA was increased while that of 5‐HIAA was decreased; the basal efflux of 5‐HT was not affected. The efflux of NA, but not of 5‐HT, was increased in these animals during stimulation of the n.r.m. and n.r.p.g. The efflux of 5‐HIAA was not changed by stimulation. Addition of fluoxetine alone or with desipramine to the superfusate in high concentrations greatly increased basal efflux of 5‐HT. Failure of stimulation of the ventromedial medulla to increase the efflux of 5‐HT in these animals may be related to feed‐back inhibition of release by the high concentration of 5‐HT initially present in the superfusate. These results indicate that electrical stimulation of the n.r.m. and n.r.p.g. increases the efflux of endogenous 5‐HT and NA from the spinal cord. These stimulation sites are coincident with brain‐stem sites at which stimulation produces antinociception by activation of spinal serotonergic and noradrenergic receptors. Thus, the ability of stimulation at these sites to evoke the spinal release of the probable neurotransmitters further supports the hypothesis that the antinociceptive effect is mediated by activation of serotonergic and noradrenergic neurones projecting to the spinal cord.
Spatial‐frequency characteristics of neurones of area 18 in the cat: dependence on the velocity of the visual stimulus.
Authors: Bisti S , Carmignoto G , Galli L , Maffei L
Published: December 2014

The spatial and temporal response properties of neurones of areas 17 and 18 were studied in single units (165) of anaesthetized and paralysed cats. The visual stimuli were drifting or alternating gratings. We confirmed and extended the observation by Tolhurst & Movshon (1975) showing that the spatial‐frequency characteristics of neurones of area 17 are largely independent of the temporal parameters of drifting or alternating gratings. The spatial‐frequency tuning curves of neurones of area 18 shift along the spatial‐frequency axis when the velocity or the temporal frequency of the drifting grating are changed. The effect of an increase either of velocity or temporal frequency is to shift the cell spatial‐frequency tuning curve down the spatial‐frequency scale, keeping relatively constant the strength and band width of the response. The spatial‐frequency tuning curves of neurones of area 18 do not show this temporal‐frequency‐dependent phenomenon when the stimuli are gratings alternated in phase. In this case neurones of areas 17 and 18 show a similar behaviour. The response properties of neurones of area 18 are compared with recent psychophysical results obtained in similar experimental conditions. The hypothesis is advanced that both areas 17 and 18 are devoted to the processing of spatial information. Area 17 would be responsible for the processing of patterns in stationary or quasi‐stationary situations while area 18 would be responsible for that of patterns moving at high velocities.
Electrogenic active proton pump in Rana esculenta skin and its role in sodium ion transport.
Authors: Ehrenfeld J , Garcia-Romeu F , Harvey B J
Published: December 2014

Kinetic and electrophysiological studies were carried out in the in vitro Rana esculenta skin, bathed in dilute sodium solution, to characterize the proton pump and coupling between sodium absorption (JNa+n) and proton excretion (JH+n). JNa+n and JH+n were both dependent on transepithelial potential (psi ms); hyperpolarizing the skin decreased JNa+n and increased JH+n; depolarization produced the opposite effects. Amiloride (5 X 10(‐5) M) at a clamped psi ms of +50 mV inhibited JNa+n without affecting JH+n. Variations of psi ms or pH had identical effects on JH+n. Ethoxzolamide inhibited JH+n and simultaneously increased psi ms by 15‐30 mV. These changes were accompanied by depolarization of the apical membrane potential psi mc from ‐47 to ‐25 mV and an increase in apical membrane resistance of 30%; no significant effects on basolateral membrane potential (psi cs) and resistance (Rb) nor on shunt resistance (Rj) were observed. The proton pump appears to be localized at the apical membrane. The proton pump was also inhibited by deoxygenation, oligomycin, dicyclohexylcarbodiimide and vanadate (100, 78, 83 and 100% inhibition respectively). The variations of JH+n and of the measured electrical currents were significantly correlated. These findings are supportive evidence of a primary active proton pump, electrogenic and strictly linked to aerobic metabolism. The current‐voltage (I‐V) relation of the proton pump was obtained as the difference in the I‐V curves of the apical membrane extracted before and after proton‐pump inhibition by ethoxzolamide during amiloride block of sodium transport. The proton‐pump current (IP) was best described by a saturable exponential function of psi mc. Maximal pump current (ImaxP) was calculated to be 200 nequiv h‐1 cm‐2 at a psi mc of +50 mV and the pump reversal potential ERP was ‐130 mV. The effect of ethoxzolamide to depolarize psi mc was dependent on the relation between psi mc and ERP. Maximal induced depolarization occurred at a psi mc of +50 mV whereas ethoxzolamide exerted minimal effect on psi mc when the ERP was approached either by voltage clamping the apical membrane or by the addition of amiloride. We show that electroneutral sodium‐proton countertransport is not the mechanism of active proton excretion in frog skin but that it is the proton excretion which provides a favourable electrical driving force for passive apical sodium entry.(ABSTRACT TRUNCATED AT 400 WORDS)
The transport of sugars across the perfused choroid plexus of the sheep.
Authors: Deane R , Segal M B
Published: December 2014

The blood‐perfused choroid plexuses from the lateral ventricles of the sheep were used to determine the nature of sugar exchanges between blood and cerebrospinal fluid (c.s.f.). There was a net entry of sugars from blood to c.s.f. at all concentrations of sugars which were used and this net entry was seen when the sugars were measured either directly by enzymic analysis or by the use of isotopically labelled sugars. From competition experiments the order of affinity of the transporting system from both blood to c.s.f. and c.s.f. to blood was the same, i.e. 2‐deoxy‐D‐glucose much greater than D‐glucose greater than 3‐O‐methyl‐D‐glucose much greater than D‐galactose. The transport of sugars from c.s.f. to blood and blood to c.s.f. consists in both cases of a non‐saturable and a saturable component. However, the affinity of the two systems is markedly different, the blood to c.s.f. being a system of low affinity and high capacity while that of the c.s.f. to blood has a high affinity and a low capacity. The concentration of glucose in the newly formed c.s.f. was estimated from the rate of c.s.f. secretion and the net flux of glucose across the choroid plexus. The concentration of glucose in this fluid was some 45‐60% of that in plasma and so the low glucose concentration observed in bulk c.s.f. would appear to be a result of the entry process and not that of cerebral metabolism.
The role of the sympathetic system in the control of insulin release in response to hyperglycaemia in conscious calves.
Authors: Bloom S R , Edwards A V
Published: December 2014

The effects of the adrenoceptor blocking agents, phentolamine and propranolol, on the release of pancreatic glucagon and insulin in response to exogenous glucose have been investigated in conscious 2‐‐6‐week‐old calves. There were no significant differences between the changes in mean plasma glucagon or insulin concentration, which occurred in response to hyperglycaemia, in calves pre‐treated with both propranolol and phentolamine, phentolamine alone and normal calves. However, the rise in mean plasma insulin concentration was effectively abolished by pre‐treatment with propranolol alone and there was a small but significant fall in mean plasma glucagon concentration which was not observed in any of the other groups. The results are discussed in relation to previous studies of the role of the autonomic innervation to the endocrine pancreas in the control of insulin release during hyperglycaemia in conscious calves and weaned lambs.
Action and localization of gamma‐aminobutyric acid in the cat retina.
Authors: Bolz J , Frumkes T , Voigt T , Wässle H
Published: December 2014

The effects of iontophoretically applied GABA (gamma‐aminobutyric acid) and bicuculline on retinal ganglion cells were studied in the optically intact eye of the anaesthetized cat. GABA suppressed both the spontaneous activity and light‐evoked discharge of all retinal ganglion cells, regardless of their type and regardless of the visual stimulus used. Bicuculline antagonized the action of iontophoretically applied GABA. Bicuculline enhanced the spontaneous activity of on‐centre cells, but suppressed the spontaneous activity of most off‐centre cells. The light‐evoked response of on‐centre cells was increased by bicuculline. A more complicated picture emerged for off‐centre cells. Weak light responses were suppressed by bicuculline, but during strong light responses the initial transient phase of the response was dramatically enhanced. Amacrine cells of the inner nuclear layer and displaced amacrine cells of the ganglion cell layer were labelled, using glutamic acid decarboxylase (GAD) immunohistochemistry and [3H]muscimol uptake. GAD‐positive dendrites were found throughout the inner plexiform layer and no sign of dendritic stratification was detected.
Influence of divalent cations on the phospholipase‐independent action of beta‐bungarotoxin at frog neuromuscular junctions.
Authors: Caratsch C G , Miledi R , Strong P N
Published: December 2014

The influence of different divalent cations on the phospholipase‐independent inhibition of transmitter release caused by beta‐bungarotoxin (beta‐BuTx), has been investigated by measuring the frequency of spontaneous miniature end‐plate potentials (m.e.p.p.s) at frog neuromuscular junctions. After adding the toxin to normal calcium Ringer solution the m.e.p.p. frequency fell quickly to very low values. This was followed by an increase in frequency characterized by bursts of m.e.p.p.s. The temperature had a negligible effect on the speed of the first inhibition. In Ringer solutions where calcium had been substituted by other divalent cations (5 mM) in the presence of ethyleneglycol‐bis‐(beta‐aminoethylether)N, N'‐tetraacetic acid (EGTA, 1 mM), this beta‐BuTx‐induced decrease in m.e.p.p. frequency was markedly slower. The potency of cations in promoting the initial phase of toxin action was in the sequence: calcium greater than magnesium greater than strontium congruent to cobalt greater than manganese. This phospholipase‐independent inhibition of transmitter release followed approximately first‐order kinetics, suggesting that it depends mainly on toxin concentration. In the absence of any divalent cations in the Ringer solution beta‐BuTx had practically no effect on m.e.p.p. frequency. It appears that beta‐BuTx requires divalent cations in order to bind to motor nerve terminals and exert its initial inhibitory action on spontaneous release of transmitter quanta.
Long‐term potentiation of synaptic acetylcholine release in the superior cervical ganglion of the rat.
Authors: Briggs C A , McAfee D A , McCaman R E
Published: December 2014

The release of endogenous acetylcholine (ACh) from the in vitro rat superior cervical ganglion was measured by assaying the bathing medium. Simultaneously, synaptic transmission in the ganglion was assessed by recording post‐ganglionic compound action potentials. A brief period of tetanic preganglionic stimulation (20 Hz for 20 s) induced a long‐term potentiation of the post‐ganglionic compound action potential. The same tetanic stimulation also consistently induced a long‐term potentiation of stimulated ACh release. Spontaneous (non‐stimulated) ACh release was not enhanced after tetanic stimulation. The content of ACh in the ganglion was not measurably increased after tetanic stimulation. These results suggest that the long‐term increase in synaptic efficacy is due, at least in part, to an increase in the amount of ACh released by the afferent impulse.
Heterosynaptic changes accompany long‐term but not short‐term potentiation of the perforant path in the anaesthetized rat.
Authors: Abraham W C , Bliss T V , Goddard G V
Published: December 2014

Brief high‐frequency trains of electrical stimulation delivered to the perforant path result in long‐term potentiation (l.t.p.) of field potentials recorded extracellularly from granule cells of the dentate gyrus. L.t.p. of the population spike is often disproportionately greater than l.t.p. of the population excitatory post‐synaptic potential (e.p.s.p.). We have investigated the basis of this effect in rats anaesthetized with sodium pentobarbitone. A series of graded stimuli were given before and after tetanization of the perforant path. From data obtained in this way, we plotted stimulus‐response curves, and the relation (E‐S curve) between the slope of the population e.p.s.p. (E) and the amplitude of the population spike (S). Curves relating spike onset latency to the slope of the e.p.s.p. were also constructed. Tetanization of the combined medial and lateral components of the perforant path led to long‐term changes in the relation between the e.p.s.p. and the population spike. For a given e.p.s.p., the corresponding population spike was of greater amplitude and earlier onset. This E‐S potentiation was marked by a shift to the left of the E‐S amplitude curve and a downward displacement of the E‐S latency curve. Tetanization of the lateral component of the perforant path had two long‐term effects on responses evoked by test stimuli to the untetanized medial component: (1) long‐term depression of the medial e.p.s.p. and (2) long‐term E‐S potentiation. The net result of these two heterosynaptically induced effects was to leave unaltered information transfer across medial perforant path‐granule cell synapses; for a given test volley the e.p.s.p. was smaller, but because of E‐S potentiation the population spike remained relatively unaffected. Short‐term potentiation, which has a time course of only a few minutes and is presumed to be mediated by presynaptic mechanisms, was not accompanied by E‐S potentiation or by corresponding changes in spike latency. Possible mechanisms of long‐term heterosynaptic depression of the e.p.s.p. and of homo‐ and heterosynaptic E‐S potentiation, are discussed. We conclude that although these effects probably reflect a generalized post‐synaptic change, this change is unlikely to be a prolonged reduction in the membrane potential of granule cells.
Mucosal responses evoked by stimulation of ganglion cell somas in the submucosal plexus of the guinea‐pig ileum.
Authors: Carey H V , Cooke H J , Zafirova M
Published: December 2014

The effects of electrical field stimulation and tetrodotoxin on the mucosal secretory response were compared in guinea‐pig ileal mucosa with and without the submucosal plexus. Short‐circuit currents and transmural electrical potential differences were similar in ganglionated and aganglionated tissues. Total tissue conductance was greater after removal of the submucosal ganglia. Electrical field stimulation evoked a tetrodotoxin‐sensitive increase in short‐circuit current in ganglionated tissues, and little or no response in aganglionated tissues. Both ganglionated and aganglionated tissues responded similarly to carbachol, vasoactive intestinal polypeptide, scorpion venom and alanine. These results suggest that electrical field stimulation of guinea‐pig ileum evokes an increase in short‐circuit current that reflects chloride secretion by exciting ganglion cell bodies whose axons project to the transporting cells and/or endocrine cells. Direct electrical activation of enteroendocrine cells is not a factor in the stimulus‐evoked secretory response.
Blood glucose levels modulate efferent activity in the vagal supply to the rat liver.
Authors: Niijima A
Published: December 2014

Efferent discharges were recorded from nerve filaments dissected from the hepatic branch of the vagus nerve in the rat. Intravenous administration of D‐glucose enhanced efferent activity in the hepatic branch of the vagus nerve, whereas 2‐deoxyglucose and insulin suppressed this activity. The rate at which these fibres fire was found to be related to the concentration of glucose in the blood. Vagal hepatic nerve activity was effectively blocked by section of the left cervical vagus indicating that this nerve is the main pathway of vagal efferent fibres innervating the liver. It is concluded that changes in the rate of hepatic glycogenesis, which occur in response to changes in blood glucose concentration, are mediated in part by the vagal efferent innervation of the liver.
Measurement of net transplacental transfer of fluid to the fetal sheep.
Authors: Lumbers E R , Smith F G , Stevens A D
Published: December 2014

If fetal drinking activity is prevented and it is assumed that in the latter third of gestation the fetus is capable of maintaining itself in fluid balance, then the net amount of fluid gained across the placenta by the fetus is equal to the amount of fluid lost from the fetus, by routes other than the placenta, plus fluid deposited in growing tissues minus the amount of water produced as a result of oxidative metabolism. Net transplacental transfer of fluid to the fetus over a 3 h period was measured in eight chronically catheterized fetal sheep in which drinking activity was prevented by ligating the oesophagus. Urine and lung liquid flow rates were measured. In the latter third of gestation, these are the only significant sources of fluid loss from these fetuses during the 3 h experimental period. Water produced as a result of oxidative metabolism was calculated, as was the amount of fluid deposited in growing tissues during the course of the experiment. The weight of the fetus at the beginning of the experiment and the change in weight that occurred during the experiment was calculated by measuring the weight of the fetus at death (within 30 h) and applying an equation which describes the body weight‐gestation age relationship for merino sheep. Net transplacental fluid transfer was 0.40 +/‐ 0.09 ml min‐1 kg‐1 (range 0.30‐0.54 ml min‐1 kg‐1). Fetal urine flow rate averaged 0.30 +/‐ 0.11 ml min‐1 kg‐1. It was 72.8 +/‐ 10.0% of the volumes used to calculate net transplacental fluid transfer to the fetus. Lung liquid flow rate was 0.079 +/‐ 0.039 ml min‐1 kg‐1. It was 20.2 +/‐ 9.2% of the volumes used to calculate net fluid intake. The amount of fluid deposited as a result of tissue growth was 0.023 +/‐ 0.001 ml min‐1 kg‐1; it was 5.94 +/‐ 1.1% of the volumes used in the equation, while the production of water as a result of metabolism was 3.9 X 10(‐3) ml min‐1 kg‐1 (Conrad & Faber, 1977) and constituted 1.01 +/‐ 0.22% of the volumes used in the equation. This method of measuring net transplacental fluid transfer to the fetus can be used to measure fetal fluid intake over relatively short periods of time. It also means that the effects of disturbances in maternal fluid and electrolyte balance on fluid transfer to the fetus can be studied and quantitated.