bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of mechanical and chemical stimulation of fine muscle afferents upon primate spinothalamic tract cells.
Authors: Foreman R D , Schmidt R F , Willis W D
Published: December 2014

1. Injections of algesic chemicals were made into the arterial circulation of the triceps surae muscles in anaesthetized monkeys. 2. The responses of a sample of primary muscle afferents suggest that what is known about the activation of muscle afferents in the cat by algesic agents applies also to the monkey. One exception to this is the activation of many group I afferents by KCl in the monkey, but not in the cat. 3. Many spinothalamic tract cells were powerfully excited by the intra‐arterial injection of algesic chemicals (bradykinin, 5‐hydroxytryptamine (5‐HT), KCl) in preparations in which the hind limb was denervated except for the nerves to the triceps surae muscles. The excitatory action of bradykinin had a slower time course than did that of 5‐HT or KCl. 4. A number of the spinothalamic tract cells which failed to respond to chemical activation of muscle afferents were located in lamina I of the spinal cord. 5. Repeated injections of bradykinin produced similar responses, whereas the effects of 5‐HT injections showed marked tachyphylaxis. 6. No evidence was obtained that activation of muscle spindle afferents by succinylcholine injections resulted in the excitation of spinothalamic tract neurones in the population sampled. 7. Injections of hypertonic NaCl into muscle or tendon produced a prolonged excitation of many spinothalamic tract cells. 8. It is concluded that a substantial proportion of primate spinothalamic tract cells receive a convergent input from cutaneous and muscle receptors. The muscle receptors involved appear to include primary afferents of group III and IV calibre. The possibility is suggested that such cells could play a role in the production of poorly localized pain.
Sodium and calcium fluxes in a clonal nerve cell line.
Authors: Stallcup W B
Published: December 2014

1. 22Na+ and 45Ca2+ fluxes were studied in the clonal nerve cell line PC12. Three distinct types of ion channels were found: (a) voltage‐dependent Na+ channels, (b) voltage‐dependent Ca2+ channels, and (c) acetylcholine‐activated channels permeable to both ions. 2. 22Na+ uptake through voltage‐dependent Na+ channels is induced by veratridine and scorpion venom, and is inhibited 50% by 5 X 10(‐7) M‐tetrodotoxin and greater than 98% by 5 X 10(‐6) M‐tetrodotoxin. 3. 45Ca2+ uptake through voltage‐dependent Ca2+ channels is induced by depolarizing the cells in 50 mM‐KCl. This flux is not dependent on the presence of Na+ in the medium and is insensitive to 5 X 10(‐6) M‐tetrodotoxin. However, 1 mM‐Mn2+ causes a 95% inhibition of K+‐induced 45Ca2+ uptake. 4. Veratridine and scorpion venom also induce voltage‐dependent 45Ca2+ uptake which can be blocked by 1mM‐Mn2+. In contrast to KCl‐induced 45Ca2+ uptake, this flux is completely blocked by 5 X 10(‐6) M‐tetrodotoxin and is abolished by removal of Na+ from the medium. Thus the depolarizing stimulus for Ca2+ uptake in this case is Na+ from the medium. Thus the depolarizing stimulus for Ca2+ uptake in this case is Na+ influx through voltage‐dependent Na+ channels. 5. Carbamylcholine induces both 22Na+ and 45Ca2+ fluxes which are blocked by nicotinic cholinergic antagonists with the exception of alpha‐bungarotoxin. The 22Na+ flux occurs exclusively via acetylcholine receptor channels, as evidenced by the lack of effect of 5 X 10(‐6) M‐tetrodotoxin. In the presence of Na+, almost all of the 45Ca2+ uptake can be blocked by 1 mM‐Mn2+ and thus occurs via voltage‐dependent Ca2+ channels which are activated by the depolarizing Na+ influx. 6‐‐8% of the total 45Ca2+ flux, however, is insensitive to 1 mM‐Mn2+, suggesting that this portion of the uptake occurs via the acetylcholine receptor channels. In Na+‐free medium, the Mn2+‐resistant 45Ca2+ component increases to 40% of the total uptake, apparently due to lack of competition from Na+ for the acetylcholine receptor channels. This receptor‐linked flux still causes sufficient depolarization to induce the additional 60% of the Ca2+ flux through voltage‐dependent, Mn2+ sensitive Ca2+ channels. 6. Mn2+ inhibits Ca2+ flux through voltage‐dependent Ca2+ channels by competing for entry through these channels. 50 mM‐KCl induces 54Mn2+ fluxes in PC12 cells that are comparable in magnitude to 45Ca2+ fluxes. 7. In normal saline 45Ca2+ efflux from PC12 cells is several times more rapid than in Na+‐free medium, indicating the presence of a Ca2+‐Na+ exchange mechanism.
Electrolyte secretion by the isolated cat pancreas during replacement of extracellular bicarbonate by organic anions and chloride by inorganic anions.
Authors: Case R M , Hotz J , Hutson D , Scratcherd T , Wynne R D
Published: December 2014

1. The effect of replacing extracellular bicarbonate and chloride by other anions on the volume and composition of secretin‐stimulated pancreatic juice has been analysed in the isolated, perfused cat pancreas. 2. The anions of some aliphatic carboxylic acids were able partially to substitute for bicarbonate in sustaining pancreatic secretion. The order of effectiveness was: acetate greater than proprionate greater than butyrate greater than formate. 3. The rate of secretion in the presence of 25 mM‐acetate was 42% of that achieved with 25 mM‐bicarbonate. The concentration of acetate in the secretion varied with flow rate, reaching a maximum of 120 mM at high flow rates and declining at lower flow rates, with reciprocal changes in chloride concentration. Bicarbonate was always present in the secretion at a concentration of 5‐‐7 mM. 4. Inorganic anions were able totally or partially to substitute for chloride in sustaining secretion. In relation to chloride, their degree of effectiveness was: chloride = bromide = or greater than nitrate greater than iodide greater than sulphate greater than methyl sulphate greater than isethionate. Those anions which had no effect on secretion rate (i.e. bromide and nitrate) also had no effect on the bicarbonate concentration of the secretion and themselves appeared in the secretion in place of chloride. Those anions which inhibited secretion increased the bicarbonate concentration in the secretion in proportion to the degree of inhibition they caused (i.e. the increase was greatest with isethionate). 5. When perfusate chloride was only partially replaced by bromide or iodide the ratios of chloride: bromide and chloride: iodide in the secretion were approximately equal to those in the perfusate. 6. The carbonic anhydrase inhibitor acetazolamide reduced secretory rate and bicarbonate concentration when added to normal perfusion fluid or chloride‐substituted fluids, but had no effect following replacement of perfusate bicarbonate by acetate. 7. These observations illustrate that an extracellular source of permeant anions is required for optimal pancreatic bicarbonate secretion to occur. This may indicate the participation of an anion exchange carrier in the transport events responsible for this secretory process.
Cation transport across the guinea‐pig placenta perfused in situ.
Authors: Bailey D J , Bradbury M W , France V M , Hedley R , Naik S , Parry H
Published: December 2014

1. The guinea‐pig placenta perfused in situ via the umbilical circulation has been used to measure unidirectional fluxes of Na from mother to fetus, and in the reverse direction, with 24Na and 22Na. There was no significant difference between the two fluxes, each being 22 mumole.min‐1. 2. Ouabain 10(‐5) M in the perfusion fluid had no detectable effect on radioisotopic movements of Na in either direction. 3. Unidirectional fluxes of 42K in both directions were approximately equal at 1.7 mumole.min‐1 mother fetus and 1.8 mumole.min‐1 in the reverse direction, despite a K concentration of 3.4 mM on the maternal side and 5.0 mM on the fetal side of the placenta. 4. Extraction of 42K and 86Rb from the perfusion fluid was inhibited by 43% by 10(‐5) M‐ouabain in the fluid. This effect was largely due to a reduction of isotope uptake by the placental tissue. 5. The relative permeabilities of the placenta, mother to fetus, were Rb approximately K (3.2) greater than Na (1.0) greater than Li (0.55). 6. Under the experimental conditions, the electrical potential difference between perfusion fluid and maternal blood was 6 mV (fetus negative). It was shifted towards the positive by a low Na fluid. 7. The results suggest the presence of a dominant Na‐K pump (active component towards mother) sited at the maternal‐facing membrane of the syncytiotrophoblast together with a subsidiary pump oriented in the opposite direction and probably sited together with a subsidiary pump oriented in the opposite direction and probably sited at the fetal‐facing membrane of the syncytiotrophoblast. 8. A high proportion of Na movement particularly towards the fetus is probably passive, occurring through water‐filled spaces, whilst K movement is more dependent on active transport.
On the effect of ionophoretically applied dopamine on salivary gland cells of Nauphoeta cinerea.
Authors: Blackman J G , Ginsborg B L , House C R
Published: December 2014

1. Responses to ionophoretically applied dopamine ('ionophoretic responses') have been recorded with an intracellular micro‐electrode from acini of isolated salivary glands of the cockroach, Nauphoeta cinerea. They resembled responses to nerve stimulation ('neural responses') but they usually decayed more slowly and were sometimes more rapid in onset. 2. As already described for neural resonses, ionophoretic responses (i) included a secondary phase of depolarization (although more rarely than neural responses), (ii) increased in duration with increased amplitude and (iii) when small, added superlinearly. These features therefore reflect post‐synaptic processes. By contrast, tachyphylaxis was much more marked for neural responses and is therefore mainly of presynaptic origin. 3. Ionophoretic and neural responses were affected similarly by increase in temperature. The times‐to‐peak of both decreased with values for Q10 of about 3. 4. The differences between the onset and decay of ionophoretic and neural responses can probably be explained by the inherently different conditions of application of the agonist. The similarities therfore provide further support for dopamine as the neurotransmitter.
Movements of monosaccharides between blood and tissues of vascularly perfused small intestine.
Authors: Boyd C A , Parsons D S
Published: December 2014

1. A method involving the analysis of pulse transients of the vascular concentrations of test sugar and extracellular marker has been used to study the movements of non‐metabolized sugars between the cells and vascular fluid of the vascularly perfused small intestine of R. ridibunda. Reasons are given for supposing that the method does properly measure the net entry of sugars into a cellular compartment that includes at least the epithelium. 2. It is found that while the glucose analogues, 3‐O‐methyl‐D‐glucose (3MG) and 2‐deoxy‐D‐glucose (2)DG) are able to enter a cellular compartment when they are added to the vascular bed, alpha‐methyl‐D‐glucoside (alpha MG) is able to enter the compartment only at a very slow rate from the vascular bed. In contrast, 3MG and alaph MG are well absorbed from the lumen whereas the inward permeability of 2DG across the lumen face of the epithelium is very low and, unlike 3MG and alpha MG, is not influenced by the presence in the lumen of other transported sugars. 3. The presence of phlorizin in the intestinal lumen increases the flux of alpha MG and of 3MG in the direction vascular bed‐‐bulk phase of lumen. Reasons are given for supposing that the movement of sugars from the vascular bed into the lumen may involve a cellular route but occurs, at least in part, through a paracellular, extracellular route. 4. The exit of monosaccharides that have been loaded previously into the epithelium either from the lumen or from the vascular bed has been investigated. 3MG washes out rapidly into the vascular bed and the exit is stimulated by the addition of D‐glucose to the intestinal lumen and by the addition of 2DG, but not alpha MG, to the arterial infusate. In contrast, alpha MG, loaded into the epithelium from the lumen, washes out of the cells only slowly into the vascular bed, so that even with high rates of vascular perfusion alpha MG accumulates within the tissue. The sustained accumulation of alpha MG implies that not only is the permeability for exit into the blood restricted for this sugar, but also the permeability is low across the brush border in an outward direction, cell to lumen ('lobster pot effect'). The wash‐out of 3MG into the vascular effluent is sufficently rapid that only in the absence of vascular perfusion is 3MG accumulated within the tissue. 5. The contrasting properties of the monosaccharide transport systems accessible from the intestinal lumen and the vascular bed respectively are discussed in relation to the problems of epithelial transport of monosaccharide.
The nature of the receptor mediating stimulant effects of histamine on rapidly adapting vagal afferents in the lungs.
Authors: Sampson S R , Vidruk E H
Published: December 2014

1. The effects of histamine H1‐ and H2‐agonists on these airway sensory receptors were also examined. 2. Neither I.V. infusion of metiamide (5 mg/kg, min for 35 min) in seven experiments, nor I.V. bolus injection of burimamide (15 mg/kg) in six other experiments, both substances being H2‐antagonists, altered the response of rapidly adapting receptors to aerosols of histamine (from 0.1 or 1.0% solutions). 3. Chlorpheniramine (H1‐antagonist), 2‐‐5 mg/kg, I.V., completely abolished responses of rapidly adapting receptors to histamine in seven experiments in which metiamide had been given previously and in seven other preparations in which it had not, but had no effect on responses to prostaglandin F2 alpha. Chlorpheniramine itself caused a brief stimulation of rapidly adapting receptors. 4. The H2‐agonist S‐[3‐(N,N‐dimethylamino) propyl] isothiourea (Dimaprit), given as aerosol (1% solution for 2 min) or I.V. (2 mg/kg), was without effect on activity of four airway rapidly adapting receptors. These receptors were stimulated, however, by the H1‐agonist 2,(2 pyridylethylamine) dihydrochloride (PEA), administered both as aerosol (from a 10% solution) and I.V. (0.4‐‐2 mg/kg). These stimulant effects were abolished by chlorpheniramine. 5. The results indicate that stimulation of airway rapidly adapting receptors by histamine is mediated by histamine H1‐receptors.
The origin of the hind limb vasodilatation evoked by stimulation of the motor cortex in the cat.
Authors: Hilton S M , Spyer K M , Timms R J
Published: December 2014

In cats under Althesin anaesthesia, the hind limb area of the motor cortex has been stimulated by means of monopolar, semi‐micro‐electrodes with careful experimental control so as to avoid reflex effects evoked through stimulation of meningeal afferent fibres or stimulus spread to non‐cortical structures. 2. Localized cortical stimulation which elicited muscle contractions in the contralateral hind limb also elicited vasodilation in the same limb: the stimulus threshold was the same for both effects, and the magnitude of the dilatation was related to the strength of contraction. 3. Reduction of the somatic motor response, caused by lesions in the medullary pyramidal tract, was accompanied by a parallel reduction of the vascular response. 4. Prevention of the motor response by gallamine or by spinal cord section at L4‐‐L5 (which leaves the sympathetic outflow to the hind limbs intact) led to abolition of the vascular response. During recovery from gallamine, contraction and vasodilatation returned in parallel. 5. The muscle vasodilatation was insensitive to atropine or guanethidine. 6. It is concluded that the hind limb vasodilatation observed on stimulation of the motor cortex is simply a post‐contraction hyperaemia, and that it is independent of the sympathic nervous system. Previous conclusions of a sympathetically mediated vasodilatation probably resulted from inadequate control of the stimulus or a failure to recognize weak muscle contractions.
Inhibitory mechanisms influencing complex cell orientation selectivity and their modification at high resting discharge levels.
Authors: Sillito A M
Published: December 2014

1. These experiments have investigated the contribution made by GABA‐mediated inhibitory processes to the orientation tuning of complex cells in the cat's striate cortex. The GABA antagonist bicuculline has been ionophoretically applied to individual complex cells and the modifications produced in their orientation tuning documented. 2. In terms of the type of change produced in orientation tuning by the application of bicuculline, it seems that there are two categories of complex cells. 3. In one of these categories the orientation selectivity was eliminated during bicuculline application. The excitatory input to these cells would therefore appear to be non‐orientation specific. Their orientation selectivity is presumably generated by a GABA‐mediated inhibitory input. 4. In the other category of complex cells, although the orientation selectivity was decreased during bicuculline application, the cells retained a preference for a range of orientations that was generally centred around the original optimal orientation. It is suggested that for these cells the inhibitory input enhances the orientation tuning of an excitatory input that is already broadly orientation tuned. 5. Comparison of normal orientation tuning curves with those observed during the application of bicuculline provides a basis for estimating the orientation tuning of the GABA‐mediated inhibitory input. In all cases, it is clear that at normal resting discharge levels, orientations either side of the optimal, and not those centred on the optimal, generate the most powerful inhibitory input. 6. These results would seem to be best explained by inhibitory interconnexions between cortical columns sensitive to different orientations. This type of lateral interaction between columns may serve to enhance the contrast in the orientation domain for the cortical representation of a specific stimulus orientation. 7. Increasing the resting discharge level of a complex cell, without blocking the action of GABA appeared to increase the gain of the inhibitory mechanisms acting on the cell. The normal excitatory responses to optimal or near optimal orientations were greatly reduced, or replaced by inhibitory responses, and non‐optimal orientations produced only inhibitory responses. These inhibitory effects were blocked on the context of other observations in the literature. It is tentatively suggested that the interneurones providing the inhibitory drive to complex cells receive an input from recurrent collaterals of the recipient complex cells. Their other inputs would derive from neighbouring colums and from the afferent input to the parent column. The inputs from neighbouring columns would mediate the lateral inhibitory interactions in the orientation domain, and the recurrent collateral feed‐back the decreased responsiveness at high resting discharge levels.
An investigation into the validity of subatmospheric pressure recordings from synovial fluid and their dependence on joint angle.
Authors: Levick J R
Published: December 2014

1. Synovial fluid hydrostatic pressures were measured in normal knee (stifle) joints of anaesthetized rabbits using perforated cannulae. Pressures were subatmospheric in seventy out of seventy‐two joints, with a mean value of ‐4.6 cm H2O (range 0 to ‐12 cm H2O) at joint angles of 120‐‐150 degrees. 2. Similar values were obtained by a wick‐in‐needle technique (mean ‐4.0 cm H2O), which along with several other tests indicated that the subatmospheric values were not artifactual. 3. A slow rise in pressure of 1‐‐2 cm H2O per hour in the motionless joint was attributed to a net filtration of fluid into the joint space. 4. Pressure increased as a curvilinear function of joint angle when the joint was flexed passively, the slope of the relationship depending on synovial fluid volume. Pressure also increased on active flexion of the joint, or on passively increasing the tension of soft peri‐articular tissues. 5. Positive (above atmospheric) pressures in acutely flexed joints declined with time. Pressures declined less rapidly when synovial fluid was replaced by nonabsorbable paraffin oil. It was concluded that joint fluid can be absorbed by the synovium during acute flexion. 6. Processes which might generate subatmospheric pressures are discussed. The hypothesis is advanced that the flexion‐dependent 'trans‐synovial pump', possibly in series with a lymphatic pump, may account for the maintenance of a small synovial fluid volume and subatmospheric pressure in the face of a net filtration of fluid from synovial capillaries into the joint space.
The influence of hydrostatic pressure on trans‐synovial fluid movement and on capsular expansion in the rabbit knee.
Authors: Levick J R
Published: December 2014

1. The flow of Ringer solution or paraffin oil from an infusion reservoir into the cavity of the knee (stifle) joint was measured in anesthetized rabbits, as intraarticular pressure was progressively elevated from its intrinsic slightly subatmospheric value to +25 cm H2O. 2. Paraffin oil did not penetrate the tissues lining the joint cavity, yet a continuous flow of oil occurred into the joint at pressures over +2 cm H2O. It was concluded that the joint investment behaved as a visco‐elastic tissue. 3. Trans‐synovial flow of Ringer solution was calculated by correcting the observed inflow for visco‐elastic expansion of the joint capsule. At intra‐articular pressures +2 to +9 cm H2O, trans‐synovial flow increased at an average rate of 0.49 microliter min‐1.cm H2O‐1. The hydraulic conductivity of the synovium was therefore similar to that of subcutaneous connective tissue. At around +9 cm H2O, the 'breaking pressure', the slope of the pressure‐flow relationship increased by almost sixfold to 2.81 microliter min‐1.cm H2O‐1. 4. Changes in joint visco‐elasticity, synovial surface area, blood pressure, colloid osmotic pressure of plasma and of joint fluid, and inflammation were excluded as explanations of the marked increase in rate of fluid absorption, which is tentatively attributed to increases in synovial hydraulic conductivity. Some physiological and clinical implications of the data are discussed.
Characteristics of sodium and calcium conductance changes produced by membrane depolarization in an Aplysia neurone.
Authors: Adams D J , Gage P W
Published: December 2014

1. The time course and voltage dependence of Na and Ca conductance changes produced by depolarization of the soma of the neurone R15 in the abdominal ganglion of Aplysia juliana were examined at temperatures of 10‐‐14 degrees C. 2. During a maintained depolarization, Na currents turned on then decayed (inactivated). Inactivation was exponential with time constant tauh. Activation (after correction for inactivation) was reasonably well described by the expression G'Na(t) = G'Na (infinity) (1 ‐ exp [‐t/taum])3 over a wide range of potentials. 3. taum and tauh were both voltage dependent. In the range ‐20 to +40 mV, taum varied from 5 to 0.5 msec and tauh from 25 to 8 msec (13.5 degrees C). Steady‐state Na conductance (corrected for inactivation) was voltage dependent also, increasing sigmoidally with depolarization to a maximum of 25‐‐30 muS at +10 to +20 mV. Half‐maximal Na conductance occurred at a membrane potential of ‐8 mV and from ‐15 to ‐5 mV, a 5 mV change in membrane potential produced an e‐fold change in steady‐state Na conductance. 4. Steady‐state inactivation of Na conductance (hNa(infinity)) was voltage dependent with half‐inactivation occurring at a membrane potential of ‐32 mV. Recovery from Na inactivation followed an exponential time course with a voltage‐dependent time constant. 5. During a maintained depolarization Ca currents activated then decayed (inactivated) more slowly than Na currents. The decay was exponential with time constant tauH. The decay of Ca current was not an artifact porduced by an outward current. The amplitude of calcium tail currents, produced by voltage steps back to epsilonK at different times during the decay of ICa, decayed also with a time constant close to tauH. 6. Ca conductance (after correction for inactivation) could be described approximately by the expression G'Ca(t) = G'Ca(infinity) (1 ‐ exp [‐t/tauM])p but it was necessary to vary p from 1 to 2 at different potentials. No value of p gave as good a fit to this model as that obtained for Na currents. 7. taum and tauH were voltage dependent. In the range of potentials from 0 to +60 mV, tauM varied from 9 to 5 msec and tauH from 300 to 50 msec (13.5 degrees C). Steady‐state Ca conductance (corrected for inactivation) was voltage dependent also, increasing sigmoidally with depolarization to a maximum of 10‐‐15 muS at +30 to +40 mV. Half‐maximal Ca conductance occurred at a membrane potential of +12 mV, and from +10 to +20 mV a 6 mV change in membrane potential produced an e‐fold change in Ca conductance. 8. Steady‐state inactivation of Ca conductance (hCa(infinity)) varied with holding potential (VH). Half‐inactivation occurred with depolarization to ‐20 mV. At potentials more negative than ‐40 mV, hCa(infinity) was less than at ‐40 mV, i.e. hyperpolarization produced Ca 'inactivation'. 9...
Dual innervation of end‐plate sites and its consequences for neuromuscular transmission in muscles of adult Xenopus laevis.
Authors: Angaut-Petit D , Mallart A
Published: December 2014

1. Electrophysiological study of dually innervated end‐plate sites was carried out in Xenopus laevis pectoral muscle fibres. End‐plate potentials (e.p.p.s) and miniature end‐plate potentials (m.e.p.p.s) have been recorded in Mg‐blocked preparations. 2. The mean quantal content (m) of each e.p.p. at dually innervated end‐plates was significantly smaller than the corresponding values obtained at singly innervated ones. At a given doubly innervated end‐plate site the values of m tended to be inversely related, so that the compound value of m (obtained by adding them) was in the same range as that found in singly innervated junctions. These findings were taken to suggest the existence of an upper limit in the average amount of transmitter released at a synaptic site. 3. It was found that neither intermittent presynaptic conduction block, nor particular muscle fibre properties could account for the low values of m in dual end plates. The small size of the nerve terminals appears to be the most likely explanation. 4. The sensitivity to acetylcholine and muscle fibre electrical properties were investigated; no differences were found between fibres with sub‐ or suprathreshold e.p.p.s. 5. The nature of the factors responsible for this presumed small size of the nerve endings (competition between nerve endings for a limited synaptic space on the muscle membrane or reciprocal interaction between closely located terminals) as well as the possible origins of polyinnervation are discussed.
Responses of neurones in nucleus interpositus of the cerebellum to cutaneous nerve volleys in the awake cat.
Authors: Armstrong D M , Rawson J A
Published: December 2014

1. A method is described which permitted stable extracellular recordings to be made from 115 neurones in nucleus interpositus of the cerebellum in unanaesthetized free‐to‐move cats. At least 95% of the neurones were cerebellar efferent cells since they were antidromically invaded following electrical stimulation of the brachium conjunctivum in the region of the contralateral red nucleus. 2. In cats in a state of quiet wakefulness the majority of interpositus neurones were tonically active at rates ranging from 12 to 77 impulses/sec (over‐all mean 34/sec). The remaining neurones were silent or discharged only a few impulses throughout observation periods of a few minutes. 3. Cutaneous afferent volleys elicited by single shocks to the superficial radial nerves in the forearm at intensities too weak to evoke a flexion reflex or behavioural arousal produced changes in firing frequency in 62% of eighty‐one cells tested. Response patterns varied widely but in 86% of the responding cells the earliest change was a short latency (6‐‐20 ms) increase in discharge probability which from post‐stimulus time histograms was found usually to average around one impulse per stimulus. In only four cells (8%) the earliest response was a depression of the tonic firing. However, in many cells the initial acceleration was followed by a reduction in firing frequency which lasted between 10 and 85 ms. 4. In 56% of the responding cells a longer latency (25‐‐80 ms) acceleration was present. Such accelerations varied widely in duration (from 55 to 550 ms) but most commonly lasted 100‐‐200 ms. These responses were usually the most prominent feature in the response pattern: in the majority of neurones between two and five impulses were added per stimulus. 5. Considering the whole time course of the responses, the net effect of nerve volleys was to produce an increase in nuclear cell output. 6. These neurones which were influenced by nerve stimulation also discharged in response to taps to the forepaws. 7. The responses to nerve stimulation are compared with those encountered in previous studies using cats anaesthetized with chloralose or barbiturates and with the responses of Purkinje (P) cells and it is suggested that the longer latency excitatory responses result in large part from a reduction in the tonic inhibitory action exerted on the interpositus neurones by Purkinje cells. 8. The possibility is discussed that interpositus responses to cutaneous input from the limbs might contribute (via the rubrospinal system) to the regulation of spinal flexor mechanisms during locomotion and/or contact placing reactions.
Some effects of hypertonic solution on the properties of spontaneous transmitter release in the hypogastric ganglia of guinea‐pigs.
Authors: Bornstein J C
Published: December 2014

1. The effects of hypertonic solutions on spontaneous transmitter release at synapses in the hypogastric ganglia of guinea‐pigs were studied using intracellular recording techniques. 2. Hypertonic solutions were found to cause a marked hyperpolarization of the ganglion cells and this was accompanied by an increase in both the threshold and input resistance of these cells. 3. The frequency of spontaneous quantal release was found to depend exponentially on the tonicity of the bathing solution with a 50% increase in tonicity producing a 7‐9 fold increase in the frequency of release. 4. Hypertonic solutions were also found to increase the degree of bursting within the spontaneous process so that the proportion of multiquantal spontaneous potentials was found to be increased in such solutions. 5. Two different models, the 'charge‐screening' model (Van der Kloot & Kita, 1973) and the 'Ca‐increase' model (Shimoni, Alnaes & Rahamimoff, 1977), for the mechanism underlying the effects of hypertonic solution were considered.
Nonlinear spatial summation and the contrast gain control of cat retinal ganglion cells.
Authors: Shapley R M , Victor J D
Published: December 2014

1. We studied how responses to visual stimuli at spatially separated locations were combined by cat retinal ganglion cells. 2. The temporal signal which modulated the stimuli was a sum of sinusoids. Fourier analysis of the ganglion cell impulse train yielded first order responses at the modulation frequencies, and second order responses at sums and differences of the input frequencies. 3. Spatial stimuli were spots in the centre and periphery of the cell's receptive field. Four conditions of stimulation were used: centre alone, periphery alone, centre and periphery in phase, centre and periphery out of phase. 4. The effective first order response of the centre was defined as the response due to centre stimulation in the presence of periphery stimulation, but independent of the relative phases of the two regions. Likewise, the effective first order response of the periphery was defined as the response due to periphery in the presence of centre stimulation, but independent of the relative phases of the two regions. These effective responses may be calculated by addition and subtraction of the measured responses to the combined stimuli. 5. There was a consistent difference between the first order frequency kernal of the effective centre and the first order kernel of the centre alone. The amplitudes of the effective centre responses were diminished at low frequencies of modulation compared to the isolated centre responses. Also, the phase of the effective centre's response to high frequencies was advanced. Such non‐linear interaction occurred in all ganglion cells, X or Y, but the effects were larger in Y cells. 6. In addition to spatially uniform stimuli in the periphery, spatial grating patterns were also used. These peripheral gratings affected the first order kernal of the centre even though the peripheral gratings produced no first order responses by themselves. 7. The temporal properties of the non‐linear interaction of centre and periphery were probed by modulation in the periphery with single sinusoids. The most effective temporal frequencies for producing non‐linear summation were: (a) 4‐15 Hz when all the visual stimuli were spatially uniform, (b) 2‐8 Hz when spatial grating patterns were used in the periphery. 8. The characteristics of non‐linear spatial summation observed in these experiments are explained by the properties of the contrast gain control mechanism which we have previously postulated.
Segmental and supraspinal input to cells of origin of non‐primary fibres in the feline dorsal columns.
Authors: Jankowska E , Rastad J , Zarzecki P
Published: December 2014

1. The synaptic input to ascending tract cells with axons in the dorsal columns was investigated using intracellular recording. 2. E.p.s.p.s evoked by stimulation of the lateral funiculus were analysed to test for the possibility of collateral connexions between spino‐cervical tract cells and dorsal column cells. Three groups of fibres were found to contribute to such e.p.s.p.s: fibres which terminated or originated between spinal segments C3‐4 and C1, or Th9 and C3‐4 and cortico‐spinal tract fibres. The latencies and thresholds of e.p.s.p.s evoked by stimulation of the first group of fibres were compatible with their origin via axon collaterals of spino‐cervical tract cells. The occurrence of these e.p.s.p.s in dorsal column cells which were disynaptically excited from cutaneous afferents further corroborated this possibility. 3. E.P.S.P.S of specifically cervical origin were also found in some other neurones in the dorsal horn, probably segmental interneurones, but were absent in spinocervical tract cells. 4. Convergence of group I muscle afferents (possibly both group Ia and group Ib) and cutaneous afferents was found in about 50% of the dorsal column cells. The shortest latency e.p.s.p.s from cutaneous and group I afferents were evoked with segmental delays indicating monosynaptic and disynaptic coupling. 5. I.p.s.p.s were evoked from cutaneous and group I muscle afferents in either the same or different nerves as those from which the e.p.s.p.s were elicited. Excitatory potentials were, however, dominating.
Desensitization of glutamate receptors on innervated and denervated locust muscle fibres.
Authors: Clark R B , Gration K A , Usherwood P N
Published: December 2014

Depolarizations to L‐glutamate, applied locally by microinophoresis to the extrajunctional membrane of locust extensor tibiae muscle fibres and measured either in current clamp or voltage clamp, increased in amplitude for equivalent doses of glutamate following chronic denervation of the muscle. 2. A two‐pulse method was used to examine recovery from desentization of junctional and extrajunctional receptors. A 'response ratio', i.e. the amplitude of response to the second (test) of a pair of glutamate pulses over to the pulses. The 'response ratio' for extrajunctional depolarizations of innervated fibres increased exponentially with pulse interval, with a time constant of 15.6 +/‐ 4.7 sec (n = 11). Recovery of extrajunctional receptor populations from desensitization was accelerated after denervation. The recovery kinetics for responses from fibres 6‐22 days after denervation were generally described by two exponential terms, with time constants in the range 0.5‐10 sec which were inversely related to the glutamate sensitivity of the extrajunctional membrane. For junctional receptors on both innervated and denervated fibres the recovery kinetics were described by a single exponential with a time constant of 0.2‐1 sec. 3. The results suggest that the increased extrajunctional glutamate sensitivity which occurs after denervation results from the 'appearance' of glutamate receptors with properties similar to those found at the post‐junctional membrane on locust muscle fibres.
Evidence of a neurotransmitter role for aspartate and γ‐aminobutyric acid in the rat olfactory cortex
Authors: Collins G. G. S.
Published: December 2014

1. Using a cortical cup technique, the release of seven endogenous amino acids from the isolated rat olfactory cortex slice has been monitored.

2. Electrical stimulation of the lateral olfactory tract at a frequency of 4 min−1 was accompanied by a significant increase in the release of aspartate, GABA and taurine; the release of GABA and aspartate but not that of taurine was Ca2+‐dependent.

3. Chronic unilateral bulbectomy was accompanied by a specific, significant fall in the aspartate content of the olfactory cortex which reached a maximum 5 days after surgery and persisted for at least a further 5 days. Electrical stimulation of the lateral olfactory tract of such preparations did not release any of the amino acids under investigation.

4. When slices from the unoperated side were exposed to solutions containing 25 m
M‐K+ or stimulated with electrodes placed directly on the cortex enclosed by the cup there was a Ca2+‐dependent release of aspartate and GABA accompanied by a Ca2+‐independent release of taurine. Following chronic bulbectomy, these procedures failed to evoke significant release of aspartate whereas the characteristics of GABA and taurine release were unaltered.

5. It is concluded that aspartate may be the excitatory transmitter of some of the terminals of the lateral olfactory tract fibres and that GABA may be a transmitter at some inhibitory synapses of the rat olfactory cortex.
The neuronal organization of the rat subfornical organ in vitro and a test of the osmo‐ and morphine‐receptor hypotheses.
Authors: Buranarugsa P , Hubbard J I
Published: December 2014

1. Extracellular action potentials (units) were recorded from rat subfornical organ explants in vitro in response to addition of angiotensin II (AII) or carbamyl‐choline (carbachol) or serotonin (5‐HT) to the superfusion solution. The frequency recorded was dose dependent over a wide range (AII, 0.05‐‐5 nM; carbachol, 2.7‐‐2700 nM; 5‐HT, 1‐‐100 nM). Appropriate antagonists, sarc1‐ala2 angiotensin (saralasin) for AII, atropine sulphate for carbachol and methysergide maleate for 5‐HT, blocked these excitations. The effects were reversible except for that of atropine. 2. Two populations of AII‐excited units were found. A superficial population lying between 15 and 45 microns from the ependymal surface was blocked only by saralasin and another population lying more than 55 microns below the ependymal surface could be blocked by atropine as well as saralasin. Carbachol‐evoked units generally lay below 45 microns, and 5‐HT‐evoked units were scattered evenly over the subfornical organ. It is suggested that superficial AII‐excited neurones have a cholinergic excitatory synapse with the deeper carbachol‐excited neurones. 3. No evidence was found for the hypothesis that neurones of the subfornical organ are excited by morphine or by changes in extracellular osmotic pressure. 4. All types of drug‐excited unit, both superficial (15‐‐55 microns) and deep (below 55 microns), could be driven polysynaptically from the body or columns of the fornix. Units driven antidromically or antidromically and synaptically were almost all more than 55 microns from the surface. 5‐HT‐evoked units were driven antidromically only by stimulation of the columns of the fornix. AII‐ and carbachol‐evoked units could be driven antidromically or antidromically and synaptically by stimulation of the body or the columns of the fornix. It is suggested that AII units driven antidromically are actually carbachol‐sensitive neurones driven by the more superficial AII‐sensitive cells. 5. A model of the neuronal organization of the subfornical organ is suggested in which AII‐sensitive neurones lying superficially are excited by substances borne by blood or cerebrospinal fluid and synapse with deeper carbachol‐sensitive neurones. The axons of these deep neurones pass out of the subfornical organ in the columns and body of the fornix. Afferent fibres from the body and columns of the fornix polysynaptically excite both superficial and deep neurones. A recurrent inhibitory circuit is suggested on the output path.
Contribution of calcium and potassium permeability changes to the off response of scallop hyperpolarizing photoreceptors.
Authors: Cornwall M C , Gorman A L
Published: December 2014

1. The membrane response of the distal photoreceptors in the retina of the scallop Pectin irradians to the termination of a bright white light (off response) is shown to be composed of the decay of the hyperpolarizing receptor potential and an action potential with slow kinetics. 2. The action potential can be produced in darkness in the absence of external Na+ ions by membrane depolarization. 3. The action potential is maintained by replacement of external Ca2+ with Sr2+ or Ba2+, but not by Mg2+. In normal external Ca2+ (9mM), the action potential is abolished by the addition of the Ca2+ inhibitors, La3+, Co2+, and Mn2+ or the organic Ca2+ antagonist D‐600. 4. Elevated external Ca2+ concentrations increase the rate of rise and peak amplitude of the action potential as well as the rate of repolarization and after hyperpolarization, but decrease the duration. 5. The rate of rise and peak amplitude of the action potential are increased by the K+ antagonists tetraethylammonium (TEA) 4‐amino‐phyridine (4‐AP), Ba2+ and procaine. The antagonists have different effects on subsequent phases of the response, however. External TEA and Ba2+ increase the duration, but decrease the rate of repolarization and abolish the after hyperpolarization, whereas external 4‐AP and procaine increase the rate of repolarization, decrease the duration and increase the after hyperpolarization. 6. The ratio of the Ca2+ to K+ permeability (P Ca/P K) estimated from the constant field equation at the peak of the action potential in different external Ca2+ concentrations is close to 1. 7. The maximum rate of rise and the peak amplitude of the action potential are increased by membrane hyperpolarization and decreased by membrane depolarization. They are decreased by background light intensity relative to their value in the dark. 8. In normal ASW the action potential can be identified during the off response as a small overshoot of membrane potential relative to its value in the dark. 9. The rate of repolarization of the off response in normal ASW is reduced by agents or conditions which inhibit or reduce Ca2+ permeability changes, e.g. external Co2+ and La2+ or zero external Ca2+. 10. Our results suggest that a voltage‐dependent increase in membrane permeability to Ca2+ and to K+ ions modifies the repolarizing phase of the receptor potential.
Effects of temperature on tension, tension‐dependent heat, and activation heat in twitches of frog skeletal muscle.
Authors: Rall J A
Published: December 2014

1. The effects of temperature on muscle energy liberation (heat plus work production) and isometric twitch force production were measured at rest length (l o) and at long muscle lengths (approx. 1.35 l o) where twitch force was greatly depressed. 2. Force production and energy liberation at l o declined progressively as muscle temperature was elevated from 0 to 20 degrees C. Force production decreased to a greater extent than did energy liberation. A plot of energy liberation vs. twitch force suggested that a fraction of the l o energy liberation was produced independent of temperature. 3. The energy liberated at long muscle lengths, the activation heat, was independent of muscle temperature. The activation heat is interpreted as reflecting the energy dissipated during Ca2+ cycling and thus suggests that, under the conditions of these experiments, the amount of Ca2+ released with stimulation is independent of muscle temperature and subsequent muscle force production. 4. Analysis of the results also supports the conclusions that skeletal muscle energy liberation is dependent on muscle force production and that the energy liberation associated with Ca2+ cycling is essentially independent of muscle length in the range of l o‐‐1.35 l o.
Lysine transport across rat jejunum: distribution between the transcellular and the paracellular routes.
Authors: Munck B G , Rasmussen S N
Published: December 2014

Transport of lysine across the rat jejunum has been studied measuring transmural fluxes, Jms and Jsm, under short‐circuit conditions, influx across the brush‐border membrane, Jmc, under open‐circuit and voltage‐clamp conditions, and steady‐state uptake by the isolated mucosa. 1. Jlysmc can be described as the sum of a saturable process with a Kt of 3 mM and a Jmax of 2.25 micromole/cm2.hr and a diffusional component corresponding to a lysine permeability of 0.014 cm/hr. Also Jlysms is well described as the sum of a saturable process and a diffusional contribution described by the same permeability as for Jlysmc. 2. The effects of the transmural p.d. on Jlysmc indicate that at 60 mM this flux includes a diffusional contribution, which corresponds to a lysine permeability of 0.014 cm/hr. 3. The passage of an electrical current across the gut wall changes the electrical conductance as expected for a cation‐selective epithelium. The effect of a mucosa to serosa current on the Jms value of mannitol provides confirmation of the expected current effect on transepithelial volume flow. These effects on conductance and solute flux, together with the electrostatic effect on lysine movements, suffice to account for the p.d. effects on Jmc, Jms, and Jsm of lysine. 4. Jlyssm is in a saturable manner stimulated by increasing concentrations of D‐glucose. At higher (10 mM) concentrations of lysine this effect leads to a net secretion of lysine. Qualitatively and quantitatively these effects are consistent with the model of a glucose‐induced fluid circuit between the mucosal solution and the lateral intercellular spaces. 5. All observations are consistent with a paracellular, transepithelial pathway for lysine, which includes the lateral intercellular spaces. 6. The transport of lysine across the basolateral membrane is analysed. Togethet the data on transcellular passage of lysine are very similar to those reported for rabbit ileum, except that more than one transport process could not be demonstrated.