bluuebunny/crossref_metadata_2025 huggingface dataset:
The strength‐duration relationship for excitation of myelinated nerve: computed dependence on membrane parameters.
Authors: Bostock H
Published: December 2014

Thresholds to applied current pulses have been determined for the myelinated nerve model of Goldman & Albus (1968). Strength‐duration curves have been plotted, and compared with three strength‐duration equations that have been proposed in the past. The simple, linear relation between stimulus charge and stimulus duration proposed by Weiss (1901) provided the best fit to the computed data. The effects on the strength‐duration relationship of changes in twelve parameters of the model were determined and expressed in terms of the strength‐duration time constant and rheobasic current. The rheobase depended primarily on conductances, whereas the strength‐duration time constant depended on the electrotonic time constant and also on the rate of sodium activation. The model predicts strength‐duration curves of the same form, for extracellular or intracellular stimulation where the external resistance is low and uniform. Tripolar stimulation, with anodes over adjacent rather than remote nodes, is predicted to result in much shorter strength‐duration time constants, but with a similar sensitivity to nodal membrane parameters. The limitations of strength‐duration measurements on myelinated nerves are discussed in the light of these simulations.
Permeability changes induced by L‐glutamate at the crayfish neuromuscular junction.
Authors: Dekin M S
Published: December 2014

Two different methods are described which allow the reversal potential (Er) for the channels opened by L‐glutamate at the voltage‐clamped, crayfish neuromuscular junction to be measured accurately. In both cases the value of Er was found to be about +6 mV. Reversal potentials were also measured in solutions where Na+ was replaced by K+, Ca2+, or Mg2+; or in which Cl‐ was replaced by isethionate. In solutions where Na+ was partially replaced by K+, the measured reversal potentials were compared to theoretical values predicted by both the constant‐field and equivalent‐circuit equations. The experimental values were more accurately described by the constant‐field equation. Permeability ratios (PX/PNa) for K+, Ca2+, Mg2+, and Cl‐ were calculated using the constant‐field equation. K+ and Na+ were equally permeant while Ca2+ and Mg2+ were about half as permeant as the monovalent cations. Cl‐ was impermeant. The results of these experiments indicate that the L‐glutamate activated channel is non‐selective for cations. Furthermore, the value of the permeability ratios for the physiological cations tested are very similar to those obtained for the acetylcholine activated channel in vertebrate skeletal muscle.
An intracellular characterization of neurones and neural connexions within the left coeliac ganglion of cats.
Authors: Decktor D L , Weems W A
Published: December 2014

Intracellular recordings were made in vitro from neurones located within the left coeliac ganglion of the cat solar plexus. Thirty percent of the neurones within left coeliac ganglia were identified as efferent neurones. Within this neuronal population, splenic‐efferent and renal‐efferent neurones were identified specifically. Neurones within left coeliac ganglia were characterized as either phasic (fast adapting) neurones or tonic (slowly adapting) neurones depending upon their prolonged firing behaviour. Electrophysiological properties of neurones varied considerably. The wide range of values obtained for both input resistance and input capacitance suggest that sizeable differences in either specific membrane resistance or cell geometry exist within the over‐all neurone population. Frequency distributions of input resistance, time constant, input capacitance and current threshold for tonic and phasic neurones were found to be significantly different. Compound excitatory post‐synaptic potentials were produced by stimulation of the ipsilateral splanchnic nerves in 69% of the neurones tested and in 3% of the neurones tested upon stimulation of the contralateral splanchnic nerves. Electrical stimulation of nerve fibres located in the coeliac plexus, the superior mesenteric plexus or the left renal nerves generated excitatory synaptic potentials in neurones located within left coeliac ganglia. It is concluded that neurones within the left coeliac ganglion are innervated by splanchnic nerve fibres primarily contained within the left splanchnic nerves, receive excitatory synaptic input from splenic, renal and other peripheral preganglionic fibres and have extremely varied electrophysiological properties.
The effects of some inhalation anaesthetics on the sodium current of the squid giant axon.
Authors: Haydon D A , Urban B W
Published: December 2014

The effects of diethyl ether, methoxyflurane, halothane, dichloromethane and chloroform on the ionic currents and electrical capacity of the squid giant axon have been examined. The peak inward current in voltage‐clamped axons was reduced reversibly by each substance. Sodium currents under voltage clamp were recorded in intracellularly perfused axons before, during, and sometimes after exposure to the test substances, and the records were fitted with equations similar to those proposed by Hodgkin & Huxley (1952). Shifts in the dependence of the steady‐state activation and inactivation parameters (m infinity and h infinity) on membrane potential, reductions in the peak heights of the activation and inactivation time constants (tau m and tau h) and decreases in the maximum Na conductance (gNa) have been tabulated. For each of the anaesthetics the steady‐state inactivation curve was shifted in the hyperpolarizing direction though less markedly than for the hydrocarbons. The steady‐state activation curve was in each instance shifted in the depolarizing direction, as for the alcohols and other surface active substances. In common with both the hydrocarbons and the surface active substances the peak time constants were invariably reduced. The membrane capacity at 100 kHz was affected significantly only by methoxyflurane, where decreases of ca. 9% were observed for 3 mM solutions. The extent to which the results can be accounted for in terms of the perturbation of membrane lipid has been discussed.
The effect of naloxone on vasopressin release from rat neurohypophysis incubated in vitro.
Authors: Knepel W , Meyer D K
Published: December 2014

Rat posterior pituitaries were superfused in vitro and stimulated electrically. The concentrations of vasopressin in the superfusion medium were determined by radioimmunoassay. When the pulses were applied in 10 sec trains with 10 sec intervals, vasopressin release per pulse increased progressively over the frequency range of 3‐12 pulses/sec applied within the trains. The release was blocked by addition of tetrodotoxin or by removal of calcium ions from the superfusion medium. The opiate antagonist naloxone 1 or 10 microM was introduced into the superfusion medium before a second period of stimulation and enhanced vasopressin release from neurointermediate lobes after phasic stimulation at 9 pulses/sec within the trains, when compared to controls. However, naloxone 10 microM had not effect on vasopressin release from isolated neural lobes (intermediate lobes removed), although the addition of camel beta‐endorphin 2 microM inhibited vasopressin release in a naloxone‐reversible manner. After continuous stimulation at a frequency of 13 Hz naloxone 10 microM did not influence the release of vasopressin from neurointermediate lobes. We conclude that the evoked release of vasopressin from the neurointermediate lobe is reduced by an endogenous opiate of intermediate lobe origin, possibly beta‐endorphin. Appropriate stimulation conditions are necessary for this mechanism to function.
The effect of hyperthyroidism on capillarity and oxidative capacity in rat soleus and gastrocnemius muscles.
Authors: Capó L A , Sillau A H
Published: December 2014

Muscle fibre composition and capillarity were evaluated in frozen sections stained for myosin ATPase of the soleus and the white area of the medial head of the gastrocnemius of rats made hyperthyroid by injections of triiodothyronine (300‐400 micrograms/kg body weight, every other day) for 2, 3 and 4 weeks. O2 consumption of homogenates of these muscles in the presence of excess inorganic phosphate (Pi) and ADP with pyruvate and malate as substrates was also measured. Increased oxidative capacity was observed in the soleus homogenates of hyperthyroid animals after 2 weeks of treatment while no changes were observed in the oxidative capacity of the homogenates of the white area of the medial head of the gastrocnemius, even after 4 weeks of treatment. Hyperthyroid animals showed a greater capillarity than controls in both muscles. In the soleus this was evident after 2 weeks of treatment while in the white area of the medial head of the gastrocnemius, it was evident only after 4 weeks of treatment. Fibre composition was affected in the soleus after 4 weeks of treatment. In control animals two fibre types were present in the soleus: slow‐twitch oxidative fibres (s.o. or type I fibres) with a high ATPase activity after acid pre‐incubation and fast‐twitch glycolytic oxidative fibres (f.o.g. or type IIa fibres) with a low ATPase activity after acid pre‐incubation. In the soleus of the hyperthyroid animals, a third fibre type with intermediate ATPase activity after acid pre‐incubation was also present. This most probably represents a change in the type of myosin being synthesized by some fibres. No changes in fibre composition were observed in the white area of medial head of the gastrocnemius which was made up of only fast‐twitch glycolytic fibres (f.g. or type IIb fibres). The changes in oxidative capacity and capillarity in the soleus preceded and did not seem to be related to the changes in the type of myosin being synthesized. The increased capillarity found in the white area of the medial head of the gastrocnemius of the hyperthyroid animals, in the absence of an increase in the oxidative capacity, indicates that the latter is not the only factor that determines capillarity in skeletal muscle.
Chemical modification of potassium channel gating in frog myelinated nerve by trinitrobenzene sulphonic acid.
Authors: Cahalan M D , Pappone P A
Published: December 2014

We investigated the actions of externally applied trinitrobenzene sulphonic acid (TNBS) on the K currents of voltage‐clamped frog myelinated nerve fibres. TNBS treatment irreversibly slowed the tail currents for K channel closing up to 10‐fold. Time constants for the tail currents appear shifted 60‐80 mV in the hyperpolarizing direction following TNBS treatment. The time course of K channel opening was unaffected for depolarizing pulses to potentials positive to ‐20 mV. For smaller pulses to potentials between ‐80 and ‐30 mV the activation time course was slower following TNBS treatment. TNBS had little or no effect on the steady‐state conductance‐voltage relation of K channels determined from tail current amplitude. The instantaneous current‐voltage relation for K channels and potency of block by external TEA were unaffected by TNBS. K tail currents showed fast and slow components both before and after TNBS treatment. Reaction with TNBS caused the fast component to decline in amplitude and the slow component to increase both in magnitude and time constant. The rate of reaction increased with increasing pH. Full expression of altered K channel kinetics depends upon the ionic composition of the external solution. Tail currents were up to 10‐fold slower when measured in 117.5 mM‐K than when measured with 80% of the external K replaced by Na. The differential effects of TNBS on K channel closing and opening were modelled in a three‐state kinetic scheme, with an increase in the energy barrier for closing an open channel following TNBS treatment.
The luteotrophic complex in hysterectomized and pregnant goats.
Authors: Buttle H L
Published: December 2014

The pituitary hormones responsible for the maintenance of progesterone secretion by the corpus luteum have been determined by replacement therapy in hysterectomized‐hypophysectomized goats and in goats hypophysectomized on day 40 of pregnancy. Progesterone concentrations were 7.2 +/‐ 0.81 ng/ml plasma (mean +/‐ S.E. of mean) in intact goats during the luteal phase of the cycle and were 5.9 +/‐ 0.56 ng/ml plasma after hysterectomy. After hypophysectomy of hysterectomized goats, treatment with 25 or 150 i.u. prolactin/day failed to maintain the corpora lutea, and progesterone concentrations fell to below 1.0 ng/ml plasma. Treatment with 1.0 mg luteinizing hormone (LH)/day after hypophysectomy maintained progesterone concentrations at 2.5 +/‐ 0.48 ng/ml and treatment with 1.0 mg LH and 150 i.u. prolactin/day resulted in increased peripheral concentrations of 12.9 +/‐ 1.66 ng progesterone/ml plasma. In goats hypophysectomized on day 40 of pregnancy treatment with 1.0 mg LH/day or 1.0 mg LH and 150 i.u. prolactin/day resulted in maintenance of the pregnancy and maintenance of high peripheral concentrations of 15.0 +/‐ 1.77 ng progesterone/ml plasma, with no difference between the two treatments. The results show that LH is the pituitary hormone primarily responsible for the maintenance of progesterone secretion by the corpora lutea in the goat and that prolactin is synergistic with LH in stimulating this function. The difference in the pituitary luteotrophic complex between non‐pregnant and pregnant animals may be explained if placental lactogen can substitute for prolactin in the luteotrophic complex of pregnant goats.
Dependence of the single photon response on longitudinal position of absorption in toad rod outer segments.
Authors: Schnapf J L
Published: December 2014

Light responses were recorded from toad rods in order to study the dependence of the kinetics and amplitude of the single photon response on the longitudinal position of excitation within the rod outer segment. Membrane current was recorded from the inner segment of an isolated rod with a suction electrode while stimulating the outer segment with a dim transverse slit of light. Flashes at the tip of the outer segment gave smaller average responses than flashes at the base. Comparison of amplitude histograms from the two positions revealed that the fraction of incident photons eliciting an electrical response was the same at tip and base. Characteristic differences in flash sensitivity are therefore attributed to differences in the amplitude of the single photon response. Flash responses from the tip were slower than those from the base. For most cells, the tip response could be fitted by the same multistage filter equation that fitted the base response when only one of the filter time constants was increased. For both tip and base responses, the ensemble variance as a function of time was proportional to the square of the ensemble average. This indicates that single photon responses had the same wave form as their respective averages, and that there was no significant contribution of fluctuations in response latency to the wave form of the average. Background light reduced flash sensitivity at the tip more than at the base. The calculated cable attenuation of rod outer segments is not sufficient to explain the observed differences between the responses of the tip and base. The differences might instead be associated with a longitudinal gradient of internal sodium concentration, or with ageing of the outer segment discs. Calculations suggest that in the intact eye, the amplitude and time course of the average electrical response to absorption of a photon should depend slightly on the wave‐length of the photon.
Mechanisms of hypoxia‐induced periodic breathing during sleep in humans.
Authors: Berssenbrugge A , Dempsey J , Iber C , Skatrud J , Wilson P
Published: December 2014

Ventilation was studied during wakefulness and sleep in six healthy humans in normoxia (mean barometric pressure (PB) = 740 torr), and in hypobaric hypoxia (PB = 455 torr). Hypoxia caused hyperventilation and hypocapnic alkalosis (delta Pa,CO2 = ‐7 torr) during wakefulness and in all sleep states. Periodic breathing was the predominant pattern of breathing in all stages of non‐rapid eye movement (non‐r.e.m.) sleep in hypoxia, but was rarely observed during wakefulness or r.e.m. sleep. Periodic breathing was composed of repetitive oscillations of reproducible cycle length characterized by clusters of breaths with augmented inspiratory effort (VT/TI) and highly variable distribution of breath‐to‐breath minute ventilation (VE) and tidal volume (VT), which alternated regularly with prolongations of the expiratory pause of the last breath of each cluster (apnea duration = 5‐18 sec). Hypoxia‐induced periodic breathing was eliminated by: (a) acute restoration of normoxia coincident with a 3‐6 torr increase in Pa,CO2; and (b) augmented FI,CO2 (at constant arterial oxygen saturation) which rapidly and reversibly eliminated apneas and stabilized breathing pattern with a less than 2 torr increase in Pa,CO2. If hypocapnia was prevented (by augmented FI,CO2) during acute induction of hypoxia in non‐r.e.m. sleep, periodic breathing was also prevented. We propose that the genesis of hypoxia‐induced periodic breathing requires the combination of hypoxia and hypocapnia. Periodicity results from oscillations in CO2 about a CO2‐apnea threshold whose functional expression is critically linked to sleep state.
Comparison of the focal electroretinogram and the pattern electroretinogram in the pigeon.
Authors: Holden A L , Vaegan
Published: December 2014

A comparison has been made, under focal conditions, of the electroretinogram (e.r.g.) and the pattern electroretinogram (p.e.r.g.) of the central yellow field of the pigeon retina, using vitreal and intraretinal recordings. The sum of the on and off e.r.g. is of shorter time‐to‐peak and of smaller amplitude than the p.e.r.g. elicited by a grating of 1 cycle/degree, as predicted by the spatial tuning of the p.e.r.g. Depth profiles were made to compare with p.e.r.g. and the sum of the on and off e.r.g. The two responses co‐vary in terms of amplitude, time‐to‐peak and form. This suggests that the p.e.r.g. has a conventional electroretinographic location.
Neural control of periodic secretion of the pancreas and the stomach in fasting dogs.
Authors: Magee D F , Naruse S
Published: December 2014

The role of nerves in periodic secretion of the pancreas and the stomach in relation to the motility of the upper gastrointestinal tract was studied in conscious fasting dogs which had previously been provided with chronic gastric and pancreatic fistulae and a Heidenhain pouch. Both atropine and pentolinium abolished the periodic increase in gastric and pancreatic secretion and motility of the gut. Bilateral cervical vagal blockade with lidocaine reduced the motility of the stomach, the duodenum and the pouch preceding their peaks, but the motility at the peaks remained unchanged except in the case of the stomach. Pancreatic secretion preceding its peak was also decreased by vagal blockade but that at the peak was not significantly different from the control peak. Periodic pepsin secretion, from both the fistula and pouch, was decreased by vagal blockade. It is concluded that the secretion and motility of the upper gut in fasting dogs is controlled by periodic activity of the vagus and intrinsic nerves.
Vasodilatation by acetylcholine is endothelium‐dependent: a study by sonomicrometry in canine femoral artery in vivo.
Authors: Angus J A , Campbell G R , Cocks T M , Manderson J A
Published: December 2014

External diameter of the femoral artery was measured by sonomicrometry in the anaesthetized dog. Intra‐arterial acetylcholine lowered arterial pressure and thereby passively lowered diameter. When blood flow and distal resistance were controlled by roller pump and Starling resistor respectively, acetylcholine (0.1‐10 microM) and substance P (0.1‐1 nM) both caused up to 10% increase in diameter. Removal of endothelium by mechanically rubbing the artery lumen abolished the dilator response to acetylcholine and substance P but did not affect the response to nitroprusside. Constrictor responses to noradrenaline were unaltered by endothelium removal. Topical application of acetylcholine and substance P onto the adventitial surface of the artery also caused an increase in diameter but both agents were 50‐100 times less potent by this route compared with intra‐arterial infusion. These dilator responses were abolished by endothelium removal. In these circumstances acetylcholine caused constriction. We conclude that acetylcholine and substance P require an intact endothelium to elicit vasodilatation in vivo, at least for the large femoral artery. The results from the topical application experiments suggest that local neural release of vasoactive substances such as acetylcholine and substance P depend on an intact endothelium to cause vasodilatation.
On the distinctness of simple and complex cells in the visual cortex of the cat.
Authors: Dean A F , Tolhurst D J
Published: December 2014

The behaviour of neurones in cat striate cortex was examined in response to moving sinusoidal gratings and flashed bright and dark lines. The responses were summarized by three indices: discreteness was a measure of the degree of separation of inhibitory and excitatory regions in the receptive field; spatial summation ratio showed the degree of spatial summation within each region; relative modulation was a measure of the degree of modulation in the response to a moving grating. Some neurones had receptive fields with completely discrete excitatory and inhibitory regions; others responded equally to stimulus onset and offset throughout their receptive fields; however, some had overlapping excitatory and inhibitory regions. The degree of overlap varied continuously from complete separation to complete overlap. For neurones with discrete receptive fields, the widths of the regions were compared with the width of the bars in a grating of optimum spatial frequency to assess the degree of spatial summation within the regions. Most neurones with discrete receptive fields showed roughly predictable spatial summation, in that the two width measures agreed; but about 10% of them had receptive field regions that were too large by a factor of over two. The neurones which showed incomplete spatial summation also had considerable overlap of their excitatory and inhibitory regions. The waveforms of the responses to moving gratings of optimal spatial frequency were examined. The degree of modulation in the response was continuously distributed between low values typical of complex cells and high values typical of simple cells; the distribution was not bimodal. The degree of response modulation was closely correlated with the degree to which the excitatory and inhibitory regions in the receptive field were discrete. Both the degree of spatial summation and the degree of response modulation have been previously proposed as means for distinguishing simple and complex cells. In the present study, the continuity of the distributions of both indices ensured that neither index alone could be used to class all neurones unequivocally. However, a criterion based on two indices did allow classification. Simple and complex cells showed distinctive behaviour. However, complex cells with distinguishable excitatory and inhibitory regions in their receptive fields were not distinctly different from other complex cells.
Effect of vasopressin on prostaglandin excretion in conscious dogs.
Authors: Fejes‐Tóth G , Filep J , Mann V
Published: December 2014

A controversy persists around the effect of vasopressin on urinary prostaglandin excretion. In an attempt to explain part of this controversy, in the present study we re‐investigated the effect of vasopressin on urinary prostaglandin excretion in conscious dogs after water loading and during hydropenia. In water diuresis, during the administration of arginine vasopressin or 1‐deamino‐8‐D‐arginine vasopressin, prostaglandin excretion and urine flow decreased in parallel. Prostaglandin E2 excretion fell from 1086 +/‐ 454 to 353 +/‐ 122 and from 754 +/‐ 216 to 226 +/‐ 74 pg min‐1 as urine flow decreased by 74 and 66% with arginine vasopressin and 1‐deamino‐8‐D‐arginine vasopressin, respectively. In hydropenia both arginine vasopressin and 1‐deamino‐8‐D‐arginine vasopressin increased prostaglandin E2 excretion (from 85 +/‐ 15 to 261 +/‐ 82 pg min‐1; and from 115 +/‐ 33 to 272 +/‐ 66 pg min‐1, respectively), while urine flow remained practically unchanged. The changes in prostaglandin F2 alpha excretion were similar to those observed with prostaglandin E2. Plasma renin activity was reduced during arginine vasopressin infusion but was unaltered during 1‐deamino‐8‐D‐arginine vasopressin infusion. These results indicate that, in the conscious dog, urine flow is a major determinant of prostaglandin excretion but they also show that when large changes in urine flow are avoided vasopressin may increase urinary prostaglandin excretion.
Response to the length of moving visual stimuli of the brisk classes of ganglion cells in the cat retina.
Authors: Cleland B G , Harding T H , Tulunay‐Keesey U
Published: December 2014

Response histograms were collected for brisk‐sustained and brisk‐transient ganglion cells in the cat retina as narrow bars were moved backwards and forwards across their receptive fields. When a bar of fixed length was moved across the centre of the receptive field with contrast proportional to velocity, a constant response was obtained as long as the centre of the receptive field was crossed within the summation time. However, if the length of the bar was such that it extended beyond the centre, then there was a small but steady increase in surround antagonism for an increase in velocity. The same response was produced by a brief whole‐field flash as by an extended bar moving across the receptive field at high velocity if both stimulus conditions delivered the same energy uniformly across the receptive field. With brisk‐sustained cells it was observed, for small bar lengths, that bar length and contrast could be exchanged to give a constant response, even when there was considerable non‐linearity in the over‐all stimulus‐response relationship. Thus conditions that resulted in constant stimulus flux produced a constant response. This property was seen at both high and low velocities for the majority of brisk‐sustained units. The stimulus‐response relationship had a greater range of linearity at high velocities than at low velocities. From similar experiments with brisk‐transient cells it was observed that bar length and contrast could only be exchanged to give a constant response at high velocities. At low velocities there was considerable non‐linearity: there appeared to be saturation of the response from local regions and it was necessary to extend the bar outside such a region to obtain an increase in response. At lower velocities, despite the changes seen in length‐response curves under different conditions of contrast and velocity, the degree of surround antagonism remained constant for a given cell. Further, both brisk‐sustained and brisk‐transient cells showed the same degree of surround antagonism.
Response to the velocity of moving visual stimuli of the brisk classes of ganglion cells in the cat retina.
Authors: Cleland B G , Harding T H
Published: December 2014

Extracellular recording of the responses of cat retinal ganglion cells to narrow moving bars revealed systematic response variations with changes in stimulus velocity. These response variations were studied by collecting peri‐stimulus histograms from brisk‐sustained (X) and brisk‐transient (Y) ganglion cells as narrow elongated bars were moved backwards and forwards across their receptive fields. Velocity‐response curves were produced from plots of the amplitude of the main peak of the histograms as a function of velocity. The shape of these curves was found to be reasonably constant for both classes of ganglion cells. For a given cell, the peak of the velocity‐response curve shifted to both a higher response level and a higher velocity as the stimulus contrast was increased. Within both classes of cells there was a systematic shift in the velocity‐response curve as a function of the size of the receptive field centre. For brisk‐sustained cells this was seen as an increase in both the response and velocity at the peak for larger centre sizes, while for brisk‐transient cells it was an increase in velocity at the peak with negligible change in response. When the velocity required to produce a small criterion response was determined, there were distinct differences between the two classes of cells. When plotted on a double‐logarithmic scale as a function of centre size the brisk‐sustained cells had a slope of 2.00 while brisk‐transient cells had a slope of 1.20. Within the area centralis brisk‐transient cells responded more readily at high velocities than brisk‐sustained cells. This was not the case in the peripheral retina, where both cell classes responded about equally at high velocities.
Reduced activity during development delays the normal rearrangement of synapses in the rabbit ciliary ganglion.
Authors: Jackson P C
Published: December 2014

The number of preganglionic axons that innervate individual ciliary ganglion cells has been investigated after cutting one or both optic nerves in new‐born rabbits. In agreement with previous work (Johnson & Purves, 1981), ciliary ganglion cells in normal rabbits lose, on average, about one‐half of their inputs from preganglionic axons during the first month of post‐natal life. Although severing one optic nerve at birth abolished the subsequent appearance of the direct pupillary light response on that side, ciliary ganglion cells of normal neonatal rabbits are driven synaptically in the absence of direct retinal illumination when tested in vivo. This tonic activity persisted for at least 3 months after interruption of the optic nerve at birth. Thus neonatal optic nerve section reduced, but did not eliminate, synaptic activation of ciliary ganglion cells. Optic nerve section at birth delayed the elimination of synaptic connexions in the ipsilateral but not the contralateral ciliary ganglion. Through the first 4 post‐natal weeks ciliary ganglion cells on the operated side had, on average, more than the normal number of inputs from preganglionic axons. By 8 weeks of age, however, the normal number of connexions was established in spite of the unilateral visual deprivation. The elimination of connexions in ganglia on the unoperated side followed a normal time course. The effect of bilateral optic nerve section on synaptic rearrangement was the same as the ipsilateral effect after cutting only one optic nerve. It is concluded that the rate of synaptic rearrangement in this ganglion is slowed by a chronic reduction of synaptic activity.
Oscillatory motion of intra‐axonal organelles of Xenopus laevis following inhibition of their rapid transport.
Authors: Kendal W S , Koles Z J , Smith R S
Published: December 2014

The motion of optically detected organelles in myelinated axons of Xenopus laevis was studied in axons bathed in a potassium glutamate based medium and in axons in a similar medium to which various inhibitors of axonal transport were added. Organelles in the potassium glutamate medium had a motion which was indistinguishable from that previously described for organelles in axons bathed in a conventional physiological saline. Colchicine, dimethylsulphoxide, 2,4‐dinitrophenol, hyperosmotic solutions, raised concentrations of intracellular calcium ions, and media made up in deuterium oxide caused either a complete or partial inhibition of both anterograde and retrograde organelle transport. When directioned transport had been inhibited by any of the agents used, organelles displayed a longitudinally oriented oscillatory motion. An analysis of the variable, or oscillatory, component of organelle motion in axons not treated with inhibitors and in axons in which transport was partially or completely inhibited produced evidence that the dominant frequency components were similar in each case. A maximal estimate of the dominant frequency of oscillatory motion was 0.18 +/‐ 0.02 Hz. The distribution of instantaneous velocities about the mean velocity was not substantially altered as the transport of organelles was inhibited. The evidence suggested that the variable component of motion of organelles which show directioned transport is related to the oscillatory motion of organelles whose transport is inhibited.
Calcium tail currents in voltage‐clamped intact nerve cell bodies of Aplysia californica.
Authors: Eckert R , Ewald D
Published: December 2014

Calcium tail currents were measured in axotomized Aplysia neurones L2‐L6 using a two‐electrode voltage clamp and micro‐electrodes of specially low resistance. Measurements were made at ‐40 mV following depolarizing pulses of 7 or 10 ms duration in the presence of 45 microM‐tetrodotoxin and 200 mM‐tetraethylammonium. Symmetrical currents were eliminated by addition of digitally stored current traces produced in response to equivalent hyperpolarizations. The remaining current, identified as a tail current, was blocked by replacement of extracellular calcium with cobalt or manganese. Computer fits showed that the tail current closely approximated the sum of two exponentially decaying components. The first had a time constant, tau 1, of 0.38 +/‐ 0.05 ms, which may have been frequency‐limited by the speed of the clamp; the second had a time constant, tau 2, of 2.0 +/‐ 0.8 ms. A more slowly decaying third tail current component (tau 3 = 30 ms), which developed more slowly, may be related to the non‐specific current rather than the calcium current. The tau 1 and tau 2 components of the tail current lost amplitude with increasing pulse duration along an approximately bi‐exponential time course that resembled the time course of relaxation of the calcium current during a prolonged depolarization. The slow third component of the tail current showed no such inactivation. The amplitudes of the first and second components of the calcium tail current both increased as sigmoidal functions of the test pulse voltage, reaching half maximum at +20 mV and plateauing above +60 mV. The voltage dependencies of the two components were similar. The rate of decay of the tau 1 component increased with increasing temperature and with increasing negative potential, whereas tau 2 showed little dependence on these parameters. The rates of decay of neither the tau 1 nor the tau 2 component were affected by large changes in the amplitude of the test depolarization or in the amplitude of the tail current or by injection of calcium ions or EGTA. Thus, the kinetics of the tail current as resolved under our conditions appear to be virtually independent of calcium‐mediated inactivation. Activation time constants (tau m) predicted from tau 1 are 3 to 5 times longer than the values of tau m determined from the half‐time to peak of activation. These kinetics are slower than those reported for Limnaea by factors of 2.5 to 3.5.(ABSTRACT TRUNCATED AT 400 WORDS)
Selective absence of calcium spikes in Purkinje cells of staggerer mutant mice in cerebellar slices maintained in vitro.
Authors: Crepel F , Dupont J L , Gardette R
Published: December 2014

The bioelectrical properties of Purkinje cells (intrasomatic recordings) were studied in sagittal cerebellar slices of both adult staggerer and control mice. Mean input resistances of Purkinje cells were 25 +/‐ 4 M omega and 48 +/‐ 7 M omega in normal and staggerer mice respectively. In both groups, time‐dependent inward rectifications were apparent in the hyperpolarizing voltage‐responses. In normal mice, tetrodotoxin (TTX)‐sensitive simple spikes and slower‐rising multiphasic spikes, abolished when Ca was replaced by Cd in the bath, spontaneously occurred in Purkinje cells. These Na‐ and Ca‐dependent spikes were also elicited by depolarizing current pulses. In the mutant, Ca spikes were never observed, even in strongly depolarized cells. On the contrary, TTX‐sensitive simple spikes occurred spontaneously or were elicited by depolarizing current pulses. When Ca was replaced by Ba in the bath, the Ca spikes evoked in normal Purkinje cells by direct stimulation were first enhanced and then replaced by prolonged action potentials (1‐6 s in duration) which were TTX‐resistant and Cd‐sensitive. These (Ba) action potentials were also triggered by climbing fibre activation of the cells. In staggerer mice, Ca spikes were never elicited by direct stimulation in Ba‐containing medium, although in a few cells prolonged action potentials were occasionally elicited by depolarizing current pulses. However, this latter type of response was never evoked by climbing fibre activation of Purkinje cells. In the mutant, extracellular application of tetraethylammonium (TEA) generated prolonged action potentials, the plateaux of depolarization of which were less positive than those elicited by Ba in control mice. These plateaux were abolished by TTX and left unaffected by the substitution of Ca by Cd in the bath, suggesting that they were due to a non‐inactivating Na conductance. On the whole, the present study strongly suggests that voltage‐dependent Ca channels are missing in most staggerer Purkinje cells or at least that their characteristics and/or distribution are such that they cannot be activated. Na channels appear unaffected.
Actions of substance P on rat spinal dorsal horn neurones.
Authors: Murase K , Randić M
Published: December 2014

The membrane actions of substance P (SP) and the effects on the Ca‐dependent action potential of dorsal horn neurones have been investigated by means of intracellular recording techniques in the immature rat in vitro spinal cord slice preparation. Bath application of SP (2 X 10(‐6) to 1 X 10(‐5) M) induced a biphasic membrane response consisting of an initial hyperpolarization followed by a depolarization in about one‐third of the cells examined. Initial hyperpolarization was not observed when synaptic activity was blocked by perfusing the slice with a tetrodotoxin‐containing or low Ca, high Mg Ringer solution. This result is consistent with a presynaptic action of SP mediated through excitation of inhibitory interneurones. This interpretation was supported by recording of repetitive spontaneous inhibitory post‐synaptic potential (i.p.s.p.)‐like hyperpolarizing potentials during the initial hyperpolarization. When Co ions were used to block voltage‐dependent Ca conductance and possible indirect presynaptic actions, SP induced only a small depolarization of membrane potential. It seems, therefore, that Ca conductance may have contributed to the depolarizing phase of the SP response, either through its mediation of synaptic transmission or through direct effects as a charge carrier for inward current. When tetrodotoxin was used, the SP‐induced increase in neuronal input resistance was not modified, although depolarization was slightly diminished. In contrast, in medium containing tetrodotoxin and tetraethylammonium, the SP‐depolarizing response was enhanced and accompanied by a small decrease in input resistance and firing of Ca spikes. These results suggest that SP‐induced depolarization might be a consequence of a reduction in a voltage‐dependent K conductance allowing Na and/or Ca conductances to dominate. SP modified the duration of Ca‐dependent action potentials of dorsal horn neurones, the most consistent change being an initial dose‐dependent and reversible decrease in the spike duration. The decrease in Ca spike duration was associated with a small reduction in the rate of rise and peak amplitude, and a significant parallel increase in dV/dt of the falling phase of the Ca spike. Our data indicate that the initial decrease in Ca spike duration was not due to the depolarizing action of SP, although shunting of the membrane resistance, either through presynaptic or post‐synaptic mechanisms, has not been ruled out. Alternatively, these data are consistent with the possibility that SP shortens the duration of the Ca spike by decreasing a voltage‐sensitive inward Ca current and/or augmenting an outward K current.(ABSTRACT TRUNCATED AT 400 WORDS)
Some effects of procaine at the toad end‐plate are not consistent with a simple channel‐blocking model.
Authors: Gage P W , Wachtel R E
Published: December 2014

Miniature end‐plate currents (m.e.p.c.s) were recorded extracellularly from toad sartorius muscle fibres exposed to solutions containing procaine at pH 5.4, 7.4 and 9.9. The decay phase of m.e.p.c.s was analysed to determine whether the effects of procaine were consistent with a sequential channel‐blocking model. Averaged m.e.p.c.s measured in the presence of procaine were biphasic, decaying as the sum of two exponential components. However, about 10‐15% of m.e.p.c.s decayed as single exponentials and were not biphasic. At pH 9.9 the relative amplitudes of the fast and slow phases were generally consistent with the decay time constants, according to the predictions of the blocking model. Such a correlation was not found at pH 5.4 or 7.4. In addition, the rate of decay of m.e.p.c.s at pH 5.4 did not increase as predicted with procaine concentration. These results demonstrate that the sequential blocking model is unable to account for all of the effects of procaine on m.e.p.c. decay. In addition, the finding that some m.e.p.c.s are single exponentials, while most are biphasic, suggests a heterogeneity of receptor‐channel complexes.
Bimodal miniature and evoked end‐plate potentials in adult mouse neuromuscular junctions.
Authors: Kelly S S , Robbins N
Published: December 2014

Intracellular recordings of spontaneous miniature end‐plate potentials (m.e.p.p.s) in muscles from adult CBF‐1 mice revealed a population of muscle fibres in which the amplitude distribution of m.e.p.p.s was bimodal. The large mode m.e.p.p.s were similar to those from fibres having unimodal amplitude distributions and the small mode m.e.p.p.s were about one‐half to one‐quarter the amplitude of the large mode. In five diverse muscle groups (extensor digitorum communis, gluteus maximus, diaphragm, extensor digitorum longus, and soleus) from mice 10‐12 or 31 months of age, bimodal m.e.p.p. amplitude distributions were present in about 20% of fibres sampled. In the common bimodal distribution (type 1), the rise times of small mode m.e.p.p.s were similar to those of large mode m.e.p.p.s. A rare class of small mode m.e.p.p.s (type 2) having long rise times was also observed. Amplitudes and half‐decay times of type 1 small mode m.e.p.p.s increased in the presence of an anticholinesterase (edrophonium). Increasing extracellular potassium concentration led to an increase in large mode m.e.p.p. frequency but had more variable effects on small mode frequency. In the few cases available for study, type 2 small mode m.e.p.p.s disappeared after addition of edrophonium or increased potassium. When the extracellular calcium/magnesium ratio was reduced, large mode but not small mode m.e.p.p. frequency decreased. In almost all muscle fibres in which end‐plate potentials (e.p.p.s) were evoked by nerve stimulation at 20 Hz in low calcium/high magnesium solution, small mode e.p.p.s similar to small mode m.e.p.p.s appeared during 'failures' of large mode m.e.p.p.s. Also, in twelve out of fifteen fibres which had unimodal m.e.p.p. amplitude distributions, small mode e.p.p.s appeared which were similar in amplitude to small mode m.e.p.p.s in fibres with type 1 bimodal m.e.p.p.s. Thus, if both spontaneous and evoked potentials are included, small mode m.e.p.p.s are present at most CBF‐1 mouse adult neuromuscular junctions independent of muscle type or animal age. Small and large mode m.e.p.p.s differ in certain responses but both are evoked by nerve stimulation at physiological frequencies and therefore participate in normal neuromuscular synaptic activity. The possible origin of small mode m.e.p.p.s is discussed.
The influence of mucus on the diffusion of chloride ions across the oesophagus of the minnow (Phoxinus phoxinus (L.].
Authors: Shephard K L
Published: December 2014

Micro‐electrodes sensitive to Cl‐ have been used to measure Cl‐ activities in the mucous layer on the mucosal surface of an isolated oesophageal preparation of the fresh‐water teleost, Phoxinus phoxinus (L.). The technique has also been used to estimate the diffusion coefficient of Cl‐ in mucus in situ on the mucosal surface of this preparation. The mucous layer supports a linear gradient of Cl‐ which represents approximately 20% of the gradient of Cl‐ between mucosal and serosal solutions. The estimate of the diffusion coefficient of Cl‐ in mucus was 0.30 X 10(‐5) +/‐ 0.029 X 10(‐5) cm2 s‐1 (mean +/‐ S.E. of mean, n = 13). This value is approximately 20% of published values of the diffusion coefficient in pure NaCl solutions or in teleost saline. It is suggested that the mucous layer acts to lower the permeability of the oesophagus in two ways. Its viscous and gel‐forming nature encourages the formation of an unstirred layer, through which diffusion is the only means whereby salts can move. Also, it provides a layer through which Cl‐ and possibly other ions diffuse much more slowly than they would through a similar layer of mucosal solution without mucus.
Sensory‐motor processing in substantia nigra pars reticulata in conscious cats.
Authors: Schwarz M , Sontag K H , Wand P
Published: December 2014

Extracellular recordings were made with chronically implanted micro‐electrodes from 109 substantia nigra neurones in conscious cats. Ninety‐six of 109 neurones met the criteria of presumed non‐dopaminergic pars reticulata (s.n.r.) neurones. Background discharge, in animals in a state of relaxed wakefulness and in the absence of overt movements, was in the range of 11‐37 impulses/s, mean 19.2 impulses/s. The discharges of fifty‐two of ninety‐six neurones tested were modified by innocuous mechanical skin stimulation. Neurones responded chiefly to stimuli delivered to the contralateral body side. Responses generally comprised net excitation and occurred with short latency (range 10‐34 ms; mean 17.3 ms). Convergence from both forelimbs or the contralateral fore‐ and hind limbs was evident in a few cases. One‐fourth (twenty‐four out of ninety‐six) of the s.n.r. neurones tested were sensitive to passive manipulation of limb joints in the quiet, conscious cat and responded exclusively to angular displacement of one contralateral joint. Responses were directional and phasic. None of the s.n.r. neurones tested responded to clicks and/or light flashes. However, stimuli moving across the contralateral visual field substantially modified the discharge rate of ten out of ninety‐six s.n.r. neurones. Responses were directional and invariably associated with eye movements. Animals were also trained to walk on a treadmill and to perform certain self‐generated limb movements. S.n.r. neurones with a receptive field on a limb regularly showed modulations in discharge during locomotion, phase‐related to the step cycle, and also short‐latency responses during disturbance of such movements. Ten out of ninety‐six s.n.r. neurones discharged almost exclusively prior to and during self‐generated movements of a single limb. Their most powerful modulations in firing rate occurred, whenever an animal tried to overcome an external impediment or to resist an imposed movement. These observations on s.n.r. neurones, taken together with previous findings on nigral influences on spinal motor circuitry, indicate that the s.n.r. represents an output station of the basal ganglia which is involved in the subconscious processing of convergent multimodal sensory information and which participates in setting appropriate gains and biasses of spinal motor neuronal systems to adequately deal with changing motor requirements.