bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucose transport by brush‐border membrane vesicles after proximal resection or ileo‐jejunal transposition in the rat.
Authors: Menge H , Murer H , Robinson J W
Published: December 2014

1. The functional properties of the ileal mucosa following jejunal resection or interposition in the jejunum were studied with the help of membrane vesicles. 2. Despite the development of functional and morphological features in the mucosa which are more generally associated with the jejunum than with the ileum, examination of brush‐border vesicles derived from ileal and jejunal enterocytes from resected or transposed intestines reveals that the functional characteristics of apical membranes isolated from the different regions of the intestine are maintained after these surgical manoeuvres. Vesicles from control ileum develop an 'overshoot' uptake of glucose that is 3‐4 times smaller than that of jejunal vesicles, a difference that is still observed in membranes prepared from mucosa of ileal loops following proximal resection or interposition in the jejunum.
The generation of nerve impulses in mammalian axons by changing the concentrations of the normal constituents of extracellular fluid.
Authors: Orchardson R
Published: December 2014

1. Experiments have been performed to determine what changes in normal constituents of extracellular fluid are necessary to generate action potentials in mammalian axons. 2. Single and multifibre preparations of rat spinal roots were tested with Krebs solutions in which Na+, K+, Ca2+, Mg2+, pH, PCO2 or osmotic pressure were varied. 3. [Ca2+] below 1.0 mM produced impulses in all preparations. Lowering [Mg2+] did not generate any impulses but did enhance the response to low [Ca2+]. 4. Increasing [Na+] or [K+] caused excitation in some of the multifibres; increased [Na+] evoked 'off' responses in two single fibre preparations. The response to low [Ca2+] was enhanced by increasing [Na+] and depressed by increasing [K+]. 5. Increasing the osmotic pressure (with glucose) did not generate impulses and depressed the response to low [Ca2+]. 6. Changing the pH of Krebs solution did not generate impulses, but modified the response to other stimuli. The response to low [Ca2+] was increased as pH increased from pH 7.4 to 8.2, and decreased with pH in the range pH 7.4‐‐6.2. 7. Altering pCO2 did not have any effect on the responses to low [Ca2+] unless pH also changed.
Effect of repetitive activation on the afterhyperpolarization in dorsal spinocerebellar tract neurones.
Authors: Gustafsson B , Zangger P
Published: December 2014

1. The changes in the afterhyperpolarization (a.h.p.) with repetitive activation have been studied in dorsal spinocerebellar tract cells of the cat using intracellular recording techniques. 2. The a.h.p. following a single spike was conditioned at different interspike intervals by a single preceding spike. In the majority of neurones the a.h.p. following a spike added approximately linearly with that generated by a preceding spike. 3. In other cells the a.h.p. following a spike was instead depressed by a preceding spike. THis depression was approximately constant at interspike intervals less than the a.h.p. duration (50‐100 msec). Thereafter the a.h.p. slowly recovered during the next 100‐300 msec. There was no associated decrease in the initial brief hyperpolarizing undershoot. 4. With shortlasting repetitive activation at high frequency (greater than 100 impulses/sec) the a.h.p, peak amplitude increased progressively with successive spikes (5‐15 spikes). No change in the time constant of decay was observed. A good correspondence was found between the observed increase in peak amplitude of the a.h.p.s and that given by a theoretical linear superposition of the successive a.h.p.s. 5. Changes in the brief hyperpolarizing undershoot with repetitive activation is also described.
Actions of EGTA and high calcium on the cones in the turtle retina.
Authors: Bertrand D , Fuortes M G , Pochobradsky J
Published: December 2014

1. The effects of Ca2+ on the activity of retinal cones were investigated by recording intracellular responses from turtle retinae perfused with solutions containing different Ca2+ concentrations. 2. Lowering extracellular Ca2+ concentration with EGTA increased membrane conductance and evoked depolarization in darkness. 3. Responses to bright lights were increased by EGTA by an amount equal to the depolarization in darkness; responses to dim lights instead were usually reduced. In addition EGTA modified the time course of responses to flashes. These changes were especially evident during the later phases of the response. 4. A steady light applied during EGTA perfusion can restore the original membrane potential. The kinetics of responses in these conditions, however, differ profoundly from those prevailing Ca2+ concentrations evoked hyperpolarization of the cones and decreased the amplitude of their responses to bright lights. The time course of responses to flashes was not appreciably modified by high Ca2+. 6. A steady light which hyperpolarizes the cone membrane by the same amount as high Ca2+ has an equal effect on the amplitude of responses to bright flashes but has an entirely different action on response kinetics and on the amplitude of responses to dimmer flashes. 7. The effects of EGTA on resting potential, conductance and response amplitudecan be interpreted assuming that the drug opens channels which are normally closed by Ca2+ in darkness. Conversely, the changes caused by high Ca2+ suggest that raising the concentration of outside Ca2+ reduces the number of light‐sensitive channels open in darkness. 8. The observation that Ca2+ and light have different effects on kinetics and sensitivities is difficult to reconcile with the hypothesis that Ca2+ is the substance liberated by light to cause photoresponses.
A comparison of the action of glutamate, ibotenate and other related amino acids on feline spinal interneurones.
Authors: MacDonald J F , Nistri A
Published: December 2014

1. The effects of microiontophoretically applied glutamate, ibotenate and other related amino acids on the spike activity of feline spinal interneurones were investigated. 2. Unlike the other amino acids, which evoked excitatory responses only, ibotenate evoked slow biphasic responses (excitation‐depression) from the majority of these neurones. The depressant action was associated with an increase in spike height and was reversible. 3. The ibotenate depression could be observed as a temporary reduction in background firing rate, a loss of sensitivity to other amino acids, a progressive decrease in the excitatory responses to repetitive ibotenate applications or a fading of excitation following a prolonged administration of ibotenate. 4. The onset of the excitatory effects of glutamate, quisqualate and ibotenate was relatively well fitted by diffusion equations for a continuous point source. However, radial distances for diffusion in the case of ibotenate responses were comparatively greater than those for glutamate and quisqualate. 5. The depressant action of ibotenate was not antagonized by strychnine, picrotoxin or bicuculline. 6. Some methods of quantifying the responses to excitatory amino acids are described. The excitatory potency of quisqualate and N‐methyl‐D‐aspartate was several times greater than that of glutamate. Aspartate and ibotenate were equipotent, while alpha‐aminopimelate and alpha‐methyl‐DL‐aspartate were much weaker. 7. It is suggested that the biphasic action of ibotenate on spinal interneurones might be the result of activation of excitatory and inhibitory sites fairly remote from the cell somata where extracellular recordings were probably made.
Effects of picrotoxin and strychnine on rabbit retinal ganglion cells: lateral interactions for cells with more complex receptive fields.
Authors: Caldwell J H , Daw N W , Wyatt H J
Published: December 2014

1. The effects of picrotoxin and strychnine were tested on the receptive fields of direction sensitive cells, orientation sensitive cells, local edge detectors, uniformity detectors and large field units in the rabbit retina. 2. Picrotoxin eliminated the direction specificity and size specificity of 'on‐off' and 'on' directionally sensitive cells for both black and white objects. Picrotoxin also made 'on' directionally sensitive cells responsive to faster velocities. 3. Picrotoxin eliminated the orientation specificity of orientation sensitive cells, and changed the bar‐flank arrangement of the receptive field into a centre surround arrangement. Thus, the orientation specificity is due to inhibitory rather than excitatory mechanisms. 4. Picrotoxin altered the speed sensitivity of large field units so that they responded to slow speeds as well as fast ones, like centre surround Y cells. 5. Strychnine abolished the size specificity of local edge detectors and changed their speed specificity so that they responded to faster speeds. 6. Picrotoxin changed a uniformity detector into a sustained on centre cell. 7. Strychnine did not effect the direction specificity of directionally sensitive cells, the orientation specificity of orientation sensitive cells, or the speed specificity of large field units. Picrotoxin did not affect the size specificity of local edge detectors. 8. Picrotoxin and strychnine usually had opposing effects on the transient responses of these units to spots and annuli. In general picrotoxin prolonged and enhanced these responses at both on and off, and strychnine shortened them. 9. The effect of these drugs for every type of ganglion cell with complex receptive field properties was to make the receptive field more simple. The orientation selective cells, large field cells, 'on' direction selective cells and uniformity detectors seem to be centre surround cells with special properties that are abolished by these drugs. The 'on‐off' direction selective cells and local edge detectors still on‐off receptive fields, but in each case one of the drugs abolished the feature that was the basis for the cell's name.
Renal handling of phenol red. III. Bidirectional transport.
Authors: Gerdes U , Kristensen J , Møller J V , Sheikh M I
Published: December 2014

1. The renal excretion of phenol red and other phenolsulphophthalein dyes (bromophenol blue and bromothymol blue) was studied in clearance experiments on anaesthetized rabbits. 2. Net tubular excretion of phenol red reached a maximal value of 8 mumole/min at a plasma concentration of ultrafiltrable dye of about 0.1 mM and was decreased at higher plasma concentrations. Decreases in net tubular excretion at high plasma concentrations were also obtained for bromophenol blue and bromothymol blue suggesting tubular reabsorption in addition to tubular secretion of the dye. Conclusive evidence for reabsorption was provided by administration of probenecid which caused a fall in the excretion of the dyes below that filtered by the glomeruli. 3. Tubular reabsorption of phenol red during probenecid administration appeared to be proportional to the glomerular load and was increased under experimental conditions leading to a decrease of urinary pH. Experiments involving efflux of phenol red from liposomes gave no evidence of a significant role of transmembrane passage by non‐ionic diffusion. It is suggested that the pH dependence of the reabsorptive process is the result of preferential reabsorption of the acid as compared to the basic form of the indicator dye across a hydrophilic pathway in the transporting membranes. 4. Clearance ratio of phenol red to that of p‐aminohippurate at low plasma concentrations was about 0.3. They low degree of extraction of phenol red from renal plasma is attributed both to tubular reabsorption and binding of the dye by plasma proteins.
The third visual complex of rhesus monkey prestriate cortex.
Authors: Zeki S M
Published: December 2014

1. Two independent but neighbouring visual areas, V3 and V3A, sharing a common cytoarchitectural plan, but in each one of which the visual fields are separately represented, have been studied anatomically, functionally, and in combined anatomico‐physiological experiments. 2. The properties of single cells in the two areas are so similar, judged by the techniques used in this study, that it is often impossible to tell whether any one penetration was sampling from cells in V3 or V3A. This is especially so if the cells have receptive fields in the lower hemi‐quadrants, since the vertical meridian of the lower visual fields is represented along the V3‐V3A boundary and since a transition from V3 to V3A along this border is not accompanied by a shift in receptive field positions of cells. 3. Since the visual fields, including the vertical meridian, are separately represented in these two areas, and since regions of vertical meridian representation are callosally connected, a simple and certain method of specifying the boundary between V3 and V3A is to examine the degeneration following section of the callosal splenium. A heavy patch of degeneration then marks the V3‐V3A boundary. Within this patch, however, is a sub‐patch containing fewer callosal fibres, or none at all. The boundary between V3 and V3A was taken to be at this subpatch. 4. Since the horizontal meridian is represented at the V2‐V3 boundary, and since V1 projects to both these areas, sending coarse fibres to V3 and fine fibres to V2, it was found that the boundary between V2 and V3 could be precisely drawn by making a lesion in the horizontal meridian representation in V1 and noting where, in the prestriate cortex, fine fibres give way to coarse ones, without an intervening gap. 5. Double tracer anatomical experiments, in which tritiated proline was injected into V1 of animals whose callosal splenium had been sectioned, showed that whereas V3 receives a direct input from V1, V3A does not. V3A, instead, was found to receive an input from V3. Double tracer anatomical experiments were undertaken to study a possible input from V2 to V3A. Although such experiments did not reveal a direct input from V2 to V3A, they were not entirely conclusive. 6. The vast majority of cells in V3 and V3A were binocularly driven, without obvious monocular preferences. Some cells, however, though responding to stimulation of the individual eyes, summated their responses to binocular stimulation. Others responded only when both eyes were simulataneously stimulated. In any oblique penetration, cells preferring binocular stimulation only occurred either singly or in groups. 7. In an oblique penetration, the shift from a cell responding to binocular stimulation only to one responding equally well to stimulation of either eye was not necessarily accompanied by a shift in orientational preferences, shifts in the former...
Blood flow in the resting forearm during prolonged contralateral isometric handgrip at maximal effort
Authors: Eklund Brita , Kaijser Lennart
Published: December 2014

1. In earlier studies we have shown that muscle contraction performed as handgrip at constant force, one third of maximal voluntary contraction (MVC), induces a rapid vasodilation in the resting contralateral forearm which in all probability is neurogenically mediated, followed by a relative increase in resistance.

2. The maintenance of contraction at one third MVC for 2 min requires continuously increasing effort because of fatigue, as also evidence by the e.m.g. The biphasic response of the vascular bed may then be related to the increasing intensity of somatomotor activation which is needed to maintain contraction force, or, alternatively, to differences in vasomotor activity on initiation of and continued muscle activity.

3. To elucidate these two possibilities blood flow in the resting forearm was measured during contralateral handgrips at constant maximal effort for 6 min (in which case force will drop) and compared to handgrip at constant force, one third MVC, for 2 min.

4. The flow reaction during prolonged contraction at maximal effort was similar to that induced by contraction at constant force with a marked transient lowering of vascular resistance, although maximal vasodilation tended to be more pronounced and occur earlier.

5. The results indicate that the rapid decrease in vascular resistance is related primarily to the initiation of somatomotor activity, whereas continued muscle contraction produces a relative increase in vasoconstrictor activity irrespective of changes in contraction effort.
Unitary recordings of near threshold responses of receptor cells in the olfactory mucosa of the frog.
Authors: Drongelen W
Published: December 2014

1. Receptor cell activity in the frog's eminentia olfactoria was recorded using metal‐filled micro‐electrodes. 2. Several units discharged spontaneously with a mean frequency lower than 0.2 spikes per sec, or were silent in periods of up to 5 min. The other units displayed spontaneous activities between 0.2 and 1.05 spikes per sec; their activity could be modelled with a Poisson process. 3. Near‐threshold responses to odour stimulation were investigated, considering several stimulations within a small concentration range. Low concentration stimulations were sometimes followed by a response, sometimes not. The concept of response probability is introduced to describe this incertitude. 4. The distribution of the number of spikes in several odour trials at low concentrations showed a reasonable agreement with two types of Poisson distribution. 5. The findings are discussed in connexion with receptor cell sensitivity and the excitation of second order neurones in the bulb.
Glycine fluxes in squid giant axons.
Authors: Caldwell P C , Lea T J
Published: December 2014

1. The influx of a number of amino acids into squid giant axons has been studied. Particular emphasis has been placed on glycine and to a lesser extent glutamate. 2. To facilitate the study of the uptake of 14C‐labelled amino acids a technique was devised in which the 14C taken up was measured directly in the intact axon with a glass scintillator fibre. This technique gave results similar to the usual technique in which the axoplasm was extruded for the assay of radioactivity. 3. The changes in glycine influx with extracellular glycine concentration suggests that two saturating components are present, one with high affinity and one with low affinity. 4. The glycine influx does not seem normally to be sensitive to the removal of extracellular sodium by replacement with choline. A Na‐sensitive component appeared, however, after a period of immersion in artificial sea water. There was also some depression of glycine influx if Na were replaced by Li. 5. Glutamate uptake was greatly reduced by removal of extracellular Na in confirmation of work by Baker & Potashner (1973). Orthophosphate uptake was also greatly reduced by removal of extracellular Na. 6. CN reversibly inhibited glycine uptake after a delay, indicating that part of the uptake mechanism may require ATP. 7. 14C‐labelled glycine injected into squid axons was found not to exchange to any serious extent with other compounds over periods of a few hours. The glycine efflux could therefore be studied. This was found to be markedly increased by extracellular glycine and by certain other neutral amino acids applied extracellularly in the artificial sea water. 8. The enhanced glycine efflux in extracellular glycine was not affected by ouabain and CN. 9. It is suggested that glycine uptake in squid axons involves two components. One is sensitive to CN and ouabain and probably derives energy from ATP break‐down. The other is probably an ATP independent exchange diffusion system in which other amino acids as well as glycine can exchange for glycine. Both these systems are independent of extracellular Na concentration. A third Na‐dependent system may appear under certain conditions.
Early development of visual cortical cells in normal and dark‐reared kittens: relationship between orientation selectivity and ocular dominance.
Authors: Frégnac Y , Imbert M
Published: December 2014

1. 535 units were recorded in the primary visual cortex in twelve normally reared and fifteen dark‐reared kittens aged between 8 and 50 days. These results were pooled with a previous study of 582 units recorded from thirty‐five kittens reared in similar conditions. 2. These 1117 cells were classified into four functional classes of neurones: (a) visually unresponsive cells, (b) non‐specific cells which were sensitive to spots or slits of light moving in any direction, (c) immature cells which were preferentially activated by a rectilinear stimulus but unselective regarding its precise orientation and (d) specific cells that appeared to be as selective for orientation as the simple or complex cells in the adult cat. 3. The results confirm that cells having the same orientation‐specific response properties as adult cortical visual neurones are present in the earliest stages of post‐natal development, independently of visual experience. However, to maintain and develop these specific cells after the third week of post‐natal life, visual experience is necessary. 4. The ocular dominance of visual cells is not constant from the earliest stages of development. A significant increase in binocularly driven neurones occurs with age. 5. Before 3 weeks of age, whatever the rearing conditions, there are more specific cells coding horizontal and vertical orientations than those coding oblique orientations. These 'horizontal and vertical detectors' are preferentially driven by the contralateral eye. 5. After 4 weeks of age, specific neurones are found at all orientations in normally reared kittens. At this stage of development the ocular dominance is independent of orientation preference, of the functional class of neurones considered and of the rearing conditions. The proportion of binocularly driven cells is slightly below adult standard. 7. A hypothesis of differential plasticity is proposed: contralateral, monocular 'horizontal and vertical detectors' are supposed to be stable; they would remain so until they become binocular. Binocular cells, for which competition between two inputs occurs, are the labile units which can be despecified or specified under the control of visual experience.
Sprouting and regression of neuromuscular synapses in partially denervated mammalian muscles.
Authors: Brown M C , Ironton R
Published: December 2014

1. The capacity of motor units to sprout after partial denervation and the ability of regenerating axons to suppress newly formed sprouts was examined in mouse skeletal muscle. Most experiments were performed on the peroneus tertius muscle which has 300 muscle fibres and eleven motor units ranging in strength from 1 to 35% of the total muscle tension. 2. Individual units, regardless of starting size, were able to sprout by up to 5 times their normal size following interruption of one of the two spinal roots innervating the muscle. In practive this resulted in muscles which had three or more units left intact becoming completely innervated again within 12 days. The majority of the sprouts probably innervated the old denervated end‐plate sites. In the absence of re‐innervation by the severed motor axons the sprouts persisted. In peroneus tertius about 60% of the sprouts giving rise to end‐plates arose terminally and 40% collaterally. In soleus almost all the sprouts were terminal. 3. Re‐innervation of the muscle by the severed motor axons occurred, starting from 14 days onwards after a crush injury, 19 days onwards after a cut. Re‐innervation occurred even in muscles which presumably had no remaining denervated muscle fibres at the time regenerating axons reached the muscle. The re‐innervating fibres grew to the original end‐plate sites. 4. Following re‐innervation the size of sprouted motor units apparently decreased. Thus, after re‐innervation of muscles with three or more sprouted motor units, the sprouted units no longer caused contraction of all the muscle. However, the normal state of the muscle was not restored and the sprouted units continued to innervate more muscle fibres than normal, returning axons less than normal, and a small percentage of muscle fibres (ca. 10%) remained functionally innervated by axons of both sorts. 5. It is concluded that (i) in the mouse, axonal sprouting is a rapid and efficient process for restoring innervation; (ii) re‐innervation of already innervated fibres can occur if the regenerating axons can return to existing end‐plate sites; (iii) some of the redundant innervation is removed or repressed. 6. Possible mechanisms of competition between axon terminals are considered.
Clumping and oscillations in evoked transmitter release at the frog neuromuscular junction.
Authors: Meiri H , Rahamimoff R
Published: December 2014

1. Time series analysis of evoked transmitter release was performed at the frog neuromuscular synapse. 2. Clumping of end‐plate potentials with similar amplitude was found in the time domain. 3. At low quantal contents periodic oscillations were observed with a period of 14 sec. 4. Clumping and oscillations are phenomena of presynaptic origin. 5. The results are explained on the hypothesis that periodic fluctuations occur in Ca concentration inside the presynaptic nerve terminal.
Synaptic transmission to the horizontal cells in the retina of the larval tiger salamander.
Authors: Marshall L M , Werblin F S
Published: December 2014

1. The receptive field diameter for most horizontal cells far exceeds the lateral spread of processes for any cell. Therefore horizontal cells probably receive synaptic input from neighbours as well as from the photoreceptors. The electrical effects of these two synaptic inputs were studied. 2. We have characterized the electrical properties of the horizontal cell inputs by determining the current‐voltage curves in dark and light. These curves were compared with those obtained in the presence of Co2+ or Mg2 was nearly identical to the curve in the light. 4. The putative transmitter substances glutamate, aspartate and GABA depolarized the cells by increasing conductance. Current‐voltage curves measured in the presence of these substances intersected the dark and light curves at +50 mV, the same level at which the dark and light curves intersect. 5. The light response of cells uith broad receptive fields, between 1.0 and 2.0 mm, showed little or no change in conductance associated with the light response. The input resistance was near 20 Momega, and the current‐voltage curves intersected at an extrapolated potential level near 200 mV. 6. In the presence of ACh, electrical properties of the broad field cells reverted to those of the narrow field cells: the receptive field was reduced to 0.5 mm, the imput resistance increased, and the current‐voltage curves intersected near +50 mV. Thus ACh appeared to interrupt synaptic input from neighbouring horizontal cells. 7. The results confirm the suggestion that horizontal cells receive a tonic excitatory input from the photoreceptors which is decreased by light. They show that horizontal cells receive an additional input from their neighbours, not associated with a measurable conductance change. The input from neighbours is selectively interrupted by ACh, but the nature of this synapse and of the cholinergic action is not known.
Effects of ouabain and potassium‐free media on cellular volume regulation in rat renal cortical slices.
Authors: Cooke K R
Published: December 2014

1. Changes in water and ion contents of rat renal cortical slices were followed over 4 hr incubation at 25 degrees C in potassium‐free media and media with ouabain. Slices that lost potassium more rapidly swelled earlier. 2. Greater swelling with lower tissue potassium contents was also observed in slices preincubated and leached in potassium‐depleting media and in slices incubated in lithium medium with 10 mM‐ouabain and in potassium‐free lithium medium with 10 mM‐ouabain. 3. This swelling associated with potassium depletion was also observed when slices were incuabted in media where the substrate was malate in place of glucose. 4. No distinct fall in the oxygen consumption of potassium‐depleted slices was detected during the period in which slices commenced swelling. 5. These results suggest that the swelling observed in potassium‐depleted rat renal cortical slices is unlikely to be secondary to inhibition of cellular energy production.
Evidence of active sodium transport in the visceral yolk sac of the rat in vitro.
Authors: Chan S T , Wong P Y
Published: December 2014

1. Na transport has been studied in the isolated rat visceral yolk sac from day 17.5 of gestation to term. 2. The transepithelial potential difference (p.d.) and the short circuit current (s.c.c.) in the isolated yolk sac were found to vary with gestational age, with peak values at day 19.5. The maximal p.d. and s.c.c. were 3.85 +/‐ 0.32 mV (the fetal side positive) and 19.5 +/‐ 5.3 microamperemeter cm‐2 respectively. 3. Simultaneous determination of the two‐way Na+ flux and the s.c.c. revealed a preferential active movement of Na in the maternal to fetal direction. The net flux was found to be 50% higher than the s.c.c. 4. Both the p.d. and the s.c.c. were found to be reduced by cooling and by the uncoupling agent 2,4‐dinitrophenol. 5. The s.c.c. altered in a curvilinear fashion with the Na+ concentration in the bathing solution, with an apparent Km of about 20 mM‐Na+. Removing Cl ions from the bathing solutions had no effect on the p.d. and s.c.c. 6. Addition of amiloride (10(‐4) M) to either side of the visceral yolk sac had no effect on the s.c.c. but application of ouabain (10(‐5) M) to the fetal side caused a profound fall in the s.c.c. 7. The possible physiological role of this active Na transport by the visceral yolk sac in the formation of amniotic fluid is discussed.
Mechanisms of post‐synaptic excitation in amphibian motoneurones.
Authors: Shapovalov A I , Shiriaev B I , Velumian A A
Published: December 2014

1. Post‐synaptic excitation produced in motoneurones of the isolated perfused frog spinal cord by different monosynaptic inputs and by ionophoretically applied glutamate was analysed with intracellular recording technique. 2. Ca2+‐deficient, high Mg2+ (5‐‐20 mM) media or addition of Mn2+ (2mM) or Co2+ (5 mM) reversibly abolished chemically mediated e.p.s.p.s derived from medullary reticular formation, ventral and lateral columns, but not the short‐latency, rapidly rising e.p.s.p.s derived from dorsal roots or muscle nerves, suggesting electric coupling between some primary afferents and spinal motoneurones. This conclusion is consistent with the dynamic properties of dorsal root e.p.s.p.s, their small sensitivity to cooling, and with results of correction of intracellular records made for contribution of extracellular field potential. E.p.s.p.s evoked by ventral root stimulation were also insensitive to Ca2+‐lack and presence of 5‐‐10 mM‐Mg2+. 3. As the post‐synaptic membrane was made more negative the amplitude of electrotonic dorsal root e.p.s.p.s was increased, and it was decreased by depolarizing currents. No reversal of the early part of the electrotonic e.p.s.p. was observed, although the presence of the local response would account for the occasional reversal of its later phase seen with depolarization. 4. When hyperpolarizing and depolarizing currents were applied to motoneurones in which chemically mediated e.p.s.p.s of the reticular cells, the ventral and lateral columns, were evoked, the actual reversal of the early part of e.p.s.p. was not observed, and there was no correlation between the sensitivity of the e.p.s.p.s to injected currents and their time course. The positive values of the extrapolated reversal potentials and the effects of changes in ionic content of perfusing media suggest that synaptically released transmitter triggers off the Na permeability of the subsynaptic membrane. 5. The amplitude of depolarization produced by ionophoretically applied glutamate depends non‐linearly on membrane potential and the curvature of this dependence differs from that seen with chemically mediated s.p.s.p.s. The asymptotic nature of this relationship is explicable by a dependence of the membrane conductance change upon the membrane voltage. 6. The results of conductance measurements during the glutamate induced depolarization, the values of apparent reversal potentials and their dependence on external Na+ and K+ and internal Cl‐ is explicable by the opening post‐synaptic channel gates for Na+ and closing post‐synaptic channel gates for K+. 7. Chemical and electrical transmission in the amphibian cord is discussed in relation to recent anatomical findings.
An intracellular study of dendrodendritic inhibitory synapses on mitral cells in the rabbit olfactory bulb.
Authors: Mori K , Takagi S F
Published: December 2014

1. In the rabbit olfactory bulb, intracellular potentials were recorded from mitral cells and from neurones in the granule cell layer (g.c.l.) following lateral olfactory tract (l.o.t.) stimulation. 2. Most recordings from mitral cells showed large (5‐21 mV) and prolonged (60‐650 msec) i.p.s.p.s subseuqent to the antidromic spikes. These i.p.s.p.s decreased in amplitude and then reversed in polarity by progressive increase in hyperpolarizing current applied intracellularly. They were accompanied by a prominent and long lasting (up to 100 msec) conductance increase of the mitral cell membrane. 3. Reversed i.p.s.p.s of mitral cells having quite different time courses from the original hyperpolarizing i.p.s.p.s suggest that the inhibitory synapses are widely distributed on the soma and dendrites. 4. E.p.s.p.s could be recorded from g.c.l. cells whose onset latency was approximately 0.6 msec shorter than that of mitral cell i.p.s.p.s. Comparison of the behaviour of e.p.s.p.s in g.c.l. cells and that of mitral cell i.p.s.p. under various conditions of l.o.t. stimulation suggests that these g.c.l. cells are the inhibitory interneurones mediating mitral cell inhibition. 5. The results support the hypothesis of dendrodentritic pathways for activation of granule cells and subsequent inhibition of mitral cells.
Reversible depletion of synaptic vesicles induced by application of high external potassium to the frog neuromuscular junction
Authors: Gennaro Joseph F. , Nastuk William L. , Rutherford Dorothy T.
Published: December 2014

1. Reversible depletion of synaptic vesicles from frog cutaneous pectoris neuromuscular junctions was studied by application of a Ringer solution containing 115 m
M‐K propionate.

2. During the release of transmitter, the synaptic vesicle membrane is added to the axolemmal membrane. Under the conditions of high K+‐induced release, the synaptic vesicle membrane accumulates as folds formed in the region of the axolemmal membrane between the active zones. In depleted terminals, large vesicular structures appear and the evidence shows that some of them (possibly all) are formed as axolemmal infoldings. During formation of such infoldings the active zones remain fixed in position with respect to the post‐junctional membrane.

3. During recovery in normal Ringer solution, which followed 30 min depolarization in high K+ Ringer solution, spontaneous m.e.p.p.s were detected as early as 9 min after the start of the recovery period and the average time for their reappearance was 17 min.

4. At the end of a 20 min recovery period which followed K+ depolarization, small accumulations of synaptic vesicles were again found within the terminal close to the active zones. At this time coated vesicles and coated pits were seen associated with the prejunctional axolemma and its infoldings. It appears that synaptic vesicles are re‐formed directly from these coated vesicles.

5. After 60 min recovery from K+ depolarization, at which time stimulation of the motor nerve induced a muscle twitch, the structure of the terminals closely resembled that of control preparations.

6. The entire synaptic vesicle recycling process can take place in the absence of the neurone soma.
Possible mediators of functional hyperaemia in skeletal muscle.
Authors: Hilton S M , Hudlická O , Marshall J M
Published: December 2014

1. (a) In experiments on gastrocnemius muscles of the cat performing external work, the work was graded, either by altering the intensity of motor nerve stimulation or by changing the load. Only under the former conditions was the steady‐state increase in blood flow conductance at all consistently related to the work performed. (b) In such experiments, efflux of inorganic phosphate and of potassium were closely correlated with the increase in vascular conductance, in the form of a typical dose‐response curve. There was no significant relationship between changes in plasma osmolarity and conductance. 2. (a) Whereas most soleus muscles in the cat exhibit virtually no functional vasodilation, those with a relatively low resting flow tend to do so. (b) There was a relationship between the vasodilation, if any, and release of phosphate in fifteen out of seventeen experiments on soleus muscles. No relationship was found between any release of potassium or change of plasma osmolarity, and absence or extent of functional vasodilation. 3. (a) Terminal arterioles and collecting venules in the rat's spinotrapezius muscle were observed in vivo under low power magnification while the muscle was bathed in various test solutions, so that the vasodilator properties of hyperosmolar solutions, potassium and phosphate could be studied. (b) The dilator effect of hyperosmolar solutions was much the weakest: solutions of 340 m‐osmole/kg elicited the largest responses, but these seldom exceeded 50% mM‐K+ and 3.2‐‐6.4 mM‐Pi (as NaH2PO4) elicited 25‐‐50% of maximum dilation, while 9‐‐10 mM‐K+ and 16‐‐20 mM‐Pi dilated arterial vessels fully. The latency to onset of dilation was shortest (5 sec) with Pi and longest (15 sec) with K+. 4. These findings, together with those already in the literature, lead to the conclusions that (a) hypersomolarity is unlikely to be in an important factor initiating or maintaining functional hyperaemia in skeletal muscle, (b) while K+ release may contribute in fast muscle it can hardly be the factor initiating the response, and (c) inorganic phosphate is the only substance tested so far whose efflux is consistently related to the vascular response in all muscles under a variety of experimental conditions, and whose efficacy as a vasodilator seems adequate.
Measurement of flow and sampling of digesta in the preruminant calf.
Authors: Sissons J W , Smith R H
Published: December 2014

1. Methods of measuring and sampling the flow of digesta passing through intestinal cannulas in preruminant calves were studied and compared. 2. The effect of collecting digesta from a duodenal cannula on abomasal emptying in a calf given whole milk was determined. When digesta were collected and returned to the duodenum manually in large amounts (about 200 g) the outflow of abomasal contents was intermittent. When digesta were returned to the animal either manually or automatically in amounts of less than about 50 g abomasal emptying was smooth. 3. An automatic apparatus for measuring and sampling the flow of digesta continuously was developed. The device allowed effluent to be returned smoothly to an ingoing cannula at the same rate that digesta left the outgoing cannula. After a feed of whole milk abomasal contents were observed to enter the duodenum in an orderly series of gushes. Each gush consisted of about 5‐‐30 g of digesta. 4. The apparatus was rearranged to measure the effects of composition of duodenal digesta on abomasal emptying. Replacement of duodenal digesta with a suspension containing heated soyabean flour slowed the abomasal outflow of a feed containing casein. 5. Automatic apparatus was used to collect digesta arriving at the distal ileum. Withholding effluent from the large intestine did not affect the movement of digesta from the ileum.
Effect of actively transported hexoses on afferent nerve discharge from rat small intestine.
Authors: Hardcastle J , Hardcastle P T , Sanford P A
Published: December 2014

1. The afferent discharge of mesenteric nerves has been recorded while perfusing salines of different composition through the lumen of rat ileum. The p.d. across the ileum and hexose absorption have also been measured. 2. The ileal mesenteric nerves were sensitive to actively transported hexoses. The discharge recorded increased dramatically on perfusion with 10 or 50 mM‐glucose, quietening within 3 min of returning to glucose‐free saline. A similar response was obtained with galactose. 3. No change in afferent discharge could be detected on perfusion of mannitol or the slowly transferred hexose, mannose. It is concluded that the response to glucose and galactose is not dependent on the stimulation of non‐specific luminal osmoreceptors. 4. Phlorhizin prevented glucose from increasing the afferent nerve discharge. Subsequent perfusion with saline removed the phlorhizin and an afferent nerve response to glucose was restored. It is concluded that this response requires glucose transfer beyond the phlorhizin‐sensitive glucose entry mechanism at the luminal side of the mucosal epithelial cell. 5. Very small amounts of glucose or galactose were absorbed under the conditions employed. The time course for the change in p.d. correlated well with that described for the alteration in afferent nerve discharge. 6. Electron micrographs show that ileal nerves consist of bundles of small non‐myelinated fibres of approximately 1 micron diameter. 7. The significance of the findings is discussed remembering that carbohydrate absorption is considered to be completed normally in the jejunum.
Saccadic, smooth pursuit, and optokinetic eye movements of the trained cat.
Authors: Evinger C , Fuchs A F
Published: December 2014

1. Cats were trained to track a small target by rewarding them for keeping their eyes on target. Eye movements were measured by the electromagnetic search coil technique. 2. Cat saccades are qualitatively similar to primate saccades, but exhibit more variability in their parameters. However, they have longer durations and lower maximum velocities than primate saccades. As in the monkey, the duration of the horizontal or vertical component of an oblique saccade is lengthened when the orthogonal component has a larger amplitude. Cat saccades can be modified in midflight like human saccades. Opening the visual feed‐back loop by controlling target position with eye position causes the cat to execute a staircase of equal amplitude saccades if a retinal error is present. Increasing the amount of visual feed‐back induces saccadic oscillations. 3. Horizontal smooth pursuit of a 0 . 5 deg visual target is limited to velocities of less than 1 deg/sec. However, moving an optokinetic background with the 0 . 5 deg target enables the cat to achieve higher horizontal smooth eye velocities of up to 8 . 5 deg/sec. Prolonged (10‐20 sec) constant velocity rotation of an optokinetic drum evokes horizontal slow‐phase velocities of up to 28 deg/sec. In response to vertical movements of the target and optokinetic background, smooth eye movements reached 6 deg/sec maximum upward velocities but only 2 . 5 deg/sec maximum downward velocities. Opening the feed back loop with no retinal error present causes the eye to exhibit a growing smooth trajectory. The response to a Rashbass step‐ramp target suggests that the feline smooth response is a function of target movement rather than displacement. 4. These data suggest that cat saccadic eye movements resemble those of primates while the cat smooth pursuit and optokinetically induced eye movements are more similar to those of the rabbit.
The cardiovascular effects of circulating catecholamines in fetal sheep.
Authors: Jones C T , Ritchie J W
Published: December 2014

1. Adrenaline and noradrenaline have been infused into the fetal sheep to produce plasma concentrations comparable to those seen during hypoxia and the cardiovascular changes compared with those seen in response to hypoxia. The effect of isoprenaline, methoxamine, and beta‐ and alpha‐adrenergic antagonists were also investigated. 2. There were no significant changes in the blood gas values during any of the infusions except for a mean fall in pH of 0.04 during adrenaline infusion. 3. Adrenaline caused a fall in the fetal heart rate followed by a rise above the control value after 15‐20 min. The fall in heart rate was abolished when the rise in blood pressure was blocked with phentolamine. The rise in heart rate was blocked by propranolol. The exact cause of the biphasic changes in heart rate during adrenaline infusion is not clear. 4. A fall in heart rate was not seen with noradrenaline; a small rise was. Propranolol changed this into a fall in heart rate while phentolamine increased the size of the heart rate rise. 5. Phentolamine alone increased the fetal heart rate by 25% and reduced blood pressure by 12%; propranolol alone reduced heart rate by 14% and had no effect on blood pressure. Isoprenaline increased fetal heart rate and reduced blood pressure. 6. The incidence of fetal breathing movements was highly variable. Despite this a significant increase was observed during adrenaline infusion. None of the other infusions had consistent effects. 7. The role of the circulating catecholamines in mediating or modifying the cardiovascular responses to hypoxia in the fetal sheep is discussed.
Photoresponses of a sensitive extraretinal photoreceptor in Aplysia.
Authors: Andresen M C , Brown A M
Published: December 2014

1. The light‐evoked membrane current, photo‐current, of an extraretinal photo‐receptor, the ventral photoresponsive neurone (v.p.n.), in the abdominal ganglion of Aplysia californica, was studied using the voltage clamp method. Flashes and steps of monochromatic light were used as stimuli. 2. Flashes of light 100 msec in duration elicit slowly developing outward currents which peak at 5‐‐10 sec and then return to dark levels within 30‐‐60 sec. 3. The peak of the action spectrum of v.p.n. is at 470 nm and is similar to the peak for R2, another photoresponsive extraretinal Aplysia neurone, and to the peak of absorption spectra of molluscan rhodopsins. V.p.n. also contains membrane‐bound cytoplasmic pigmented granules similar to those found in R2, and these are thought to mediate the light response. 4. Photo‐current is associated with an increase in membrane conductance. In normal sea water photo‐current has a reversal potential at the K equilibrium potential, EK and the reversal potential has a Nernstian relationship with external K concentration. The current‐‐voltage relationships for peak and steady‐state photo‐current are fitted by the same constant field equation; currents measured when voltage was changed in steps at peak photo‐current also have a similar relationship with voltage. The results are similar when saturating or non‐saturating light intensities were used. Thus it appears that the light‐activated K+ conductance is neither time nor voltage dependent. 5. Minimally detectable responses occurred at flash photon densities of 10(12) photons cm‐2 which is 10(‐3) that for R2. This value is comparable to those reported for retinal photoreceptors of Pecten irradians, a scallop, and Salpa democratica, a pelagic tunicate, and is lower than values reported for extraretinal photoreceptors such as the pineal photoreceptors of Salmo gairdnerii irideus, the rainbow trout, and the caudal photoreceptor in the sixth abdominal ganglion of Procambarus clarkii, a crayfish. 6. V.p.n. has a linear amplitude response range for low intensities of light and a non‐linear range that saturates at high intensities. In the accompanying paper the response wave form and its temperature dependence are interpreted according to a diffusion‐based model.