bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of ionophoresed noradrenaline on the spontaneous activity of neurones in rat primary somatosensory cortex.
Authors: Armstrong‐James M , Fox K
Published: December 2014

Changes in spontaneous activity of rat S1 cortical neurones with identified receptive fields were investigated in reply to ionophoresed noradrenaline (NA). Extracellular levels of NA were maintained constant by continuous electrochemical analysis at the carbon fibre recording tip of the multibarrel micro‐electrode. In the absence of NA there were clear differences in spike amplitude, firing rate and pattern of firing of deep (800‐1400 micron) and superficial (0‐800 micron) cells. Superficial cells responded to low (5 X 10(‐8) to 5 X 10(‐7) M) NA concentrations with simple inhibition. Recovery occurred within a minute or so of extracellular NA concentrations falling below detectable (10(‐8) M) levels. Increases in local concentration merely stopped cells firing. In contrast, cells located in the deep zone could often be excited by very low NA concentrations (less than 10(‐8) M), with inhibition occurring at levels 10‐100 times greater. Most cells, however, were inhibited, with threshold doses for a 50% change in firing rate much higher than for superficial cells. Some cells in the deep zone showed sustained increases in firing rate following an ionophoretic trial. This could occur for periods of up to 1 h after ceasing a trial. Such effects could be produced by levels as low as 10(‐7) M‐NA. Interspike interval analysis for deep cells suggested that their spontaneous activity resembled that established for slow‐wave sleep. During and after excitation by NA the pattern of firing of small groups of these cells changed to that established for the waking state. The effect could persist for up to 1 h following a short (2‐5 min) ionophoretic trial.
Proprioceptive sensation at the terminal joint of the middle finger.
Authors: Gandevia S C , Hall L A , McCloskey D I , Potter E K
Published: December 2014

This paper extends previous work (Gandevia & McCloskey, 1976) on proprioception in the terminal joint of the middle finger. By positioning the finger in appropriate ways proprioceptive acuity at the joint can be assessed when no muscular afferents could contribute, or when afferents in the flexor but not the extensor could contribute, or when afferents from both muscles could contribute. Digital nerve block anaesthetizes joint and cutaneous receptors and so was used to study the contributions from muscle afferents in isolation. Displacements (10 degrees) at various angular velocities were better detected when muscle afferents from both flexor and extensor muscles could contribute. This was so whether joint and cutaneous receptors were also available, or after digital anaesthesia. Performance when only muscle afferents are available is, however, inferior to that when all sensory mechanisms are intact. It is concluded that muscle afferents contribute to kinaesthesia, and that a full complement of such receptors from agonist and antagonist muscles gives superior acuity to that achieved when only the receptors of one of the muscle groups is available. The angular displacements necessary for 70% correct detection were determined at angular velocities between 0.25 degrees and 160 degrees/s. Proprioceptive performance was optimal with all proprioceptive mechanisms intact over the range of angular velocities 10 degrees ‐80 degrees/s: 70% correct detection of displacements of 0.8 degrees‐1.2 degrees occurred in this range. Performance deteriorated slightly at higher velocities of displacement. Performance was significantly poorer when only joint and cutaneous receptors could contribute (in the absence of intramuscular receptors), and when only intramuscular receptors could contribute (in the absence of joint and cutaneous receptors). Full proprioceptive acuity depends upon the availability of receptors in muscles and in skin and/or joints.
Persistence of extra‐junctional sensitivity to acetylcholine after reinnervation by a foreign nerve in frog skeletal muscle.
Authors: Sayers H , Tonge D A
Published: December 2014

Extra‐junctional sensitivity to acetylcholine (ACh) was determined in fibres of the cutaneous pectoris (c.p.) muscle of adult Rana pipiens after denervation and subsequent reinnervation by either the original nerve or an implanted hypoglossal nerve. The mean sensitivity of denervated fibres was 89.1 (S.E. +/‐ 36) mV/nC which fell to 0.36 (S.E. +/‐ 0.21) mV/nC after reinnervation by the original nerve. In contrast the mean sensitivity of fibres after innervation by the implanted hypoglossal nerve was 21.4 (S.E. +/‐ 2.5) mV/nC. Stimulation of the implanted hypoglossal nerve in vitro evoked action potentials in many of the fibres in c.p. There was no apparent difference in extra‐junctional sensitivity to ACh between those fibres in which hypoglossal stimulation evoked action potentials and those in which it did not. Recordings of electromyogram activity indicated that the implanted hypoglossal nerve evoked activity in the c.p. muscle in the intact animal. The significance of these results in relation to current theories of the ways in which nerves control muscle sensitivity to ACh is discussed.
Contribution of polycythaemia to pulmonary hypertension in simulated high altitude in rats.
Authors: Barer G R , Bee D , Wach R A
Published: December 2014

A rat model was used to assess the viscosity factor in pulmonary hypertension of high altitude. Rats exposed to 10% O2 for three weeks developed increased pulmonary vascular resistance (p.v.r.) and polycythaemia; the haematocrit (Hct) was 50‐60%, values similar to those in normal men at high altitudes. The contribution of high Hct to the increased p.v.r. was assessed in isolated perfused lungs of chronically hypoxic rats perfused with their own high Hct blood, or normal Hct blood from control rats. Pressure/flow relationships were measured over a wide range and the slope (P/Q) of this relationship and its extrapolated intercept on the pressure axis were increased by high Hct blood. A return to low Hct blood did not restore initial conditions although a second perfusion with high Hct blood again increased p.v.r. and intercept. Lack of reversibility was attributed to changes with time in blood or lung. In a second experiment designed to eliminate time changes, chronically hypoxic or litter‐mate control rats were each perfused with only one blood, their own or each other's and P/Q relations were rapidly measured. The P/Q slope and pressure intercept increased progressively in the following groups: control rats perfused with their own blood (Hct 34%), control rats perfused with chronically hypoxic blood (Hct 56%), chronically hypoxic rats perfused with control blood (Hct 35%) and chronically hypoxic rats perfused with chronically hypoxic blood (Hct 53%). To exclude factors in chronically hypoxic blood other than high Hct which might increase p.v.r., control rats were perfused with blood of different Hct obtained by centrifugation. High Hct again increased p.v.r. There was a significant relationship in all rats between pulmonary artery pressure (Ppa), which takes into account both P/Q slope, intercept and Hct. There was substantial batch variation which may reflect sensitivity to hypoxia. In chronically hypoxic rats with high Hct blood, Ppa varied from 29‐47 mmHg; with low Hct blood the range was 26‐38 mmHg. Comparable values for control rats were 21‐29 and 17‐20 mmHg. We conclude that the polycythaemic blood of chronic hypoxia contributes substantially to pulmonary hypertension. Where it is excessive, it may prejudice tissue blood flow.
Open‐loop comparison of carotid sinus reflex respiratory and circulatory effects in cats.
Authors: Borison H L , Borison R , Sadig T
Published: December 2014

Isolated control of pressure in the carotid sinus was exercised bilaterally by means of pump‐driven autoperfusion in anaesthetized heparinized cats breathing 100% O2. In cats with vagus nerves intact, a rise of intrasinus pressure resulted in a non‐adapting fall in arterial blood pressure and a short‐lasting depression in tidal volume and frequency of breathing that adapted fully in the steady state. Vagotomy increased the steady‐state gain of the intrasinus pressure‐vasodepressor relationship and resulted sometimes in a measurable sustained inhibition of breathing, following its initial adaptation, at the upper levels of intrasinus pressure tested. Pharmacological stabilization of the blood pressure with the use of guanethidine plus phenylephrine did not detectably affect the adapting character of the sinus reflex respiratory response. Denervation of the carotid sinuses abolished all responses previously evoked by shifts of intrasinus pressure. It is concluded that the reflex effects of carotid sinus autoperfusion are produced by selective activation of the baroreceptors and that the respiratory adaptation results from signal processing in the central nervous system different from the processing involved in the non‐adapting vasodepressor effect.
Glucose handling by distal portions of the nephron during pregnancy in the rat.
Authors: Bishop J H , Green R
Published: December 2014

Reabsorption of glucose, salt and water was measured in 7‐8 day pregnant and virgin rats by micropuncturing distal nephrons during saline and glucose infusions. Unidirectional fluxes of glucose were measured in loops of Henle and collecting ducts. There were no significant differences in single nephron glomerular filtration rate (S.N.G.F.R.) between virgin and pregnant animals during saline infusion. During glucose infusion S.N.G.F.R. was higher in pregnant animals than in virgins. There is no evidence of a failure of reabsorption of glucose by the proximal tubule in pregnant animals. More glucose is reabsorbed from the loop of Henle in virgin animals than in pregnant animals during saline infusion but during glucose infusion the converse is true. During both saline and glucose infusion there is less reabsorption of glucose from the collecting duct in pregnant animals than in virgin animals. It is concluded that the increased excretion of glucose during pregnancy can be attributed to alteration of glucose handling by distal segments of the nephron.
Movements of the luminal contents in two different regions of the caput epididymidis of the rat in vitro.
Authors: Jaakkola U M , Talo A
Published: December 2014

Transport of the epididymal contents was studied in vitro by filming, for 1‐2.5 h, the movements of tiny, stained oil droplets injected through a micropipette into two regions of the lumen of the caput epididymidis: the most proximal part, with the widest outer diameter (region I), and the neighbouring, narrowest portion (region II). The movements of the oil droplets were pendular. Displacement, caused by a contraction of the wall spreading in either direction, was followed by a shorter, usually passive reflux leading to a small net displacement, delta l. The distance of transport during 5 min periods varied between 0.09 and 16.79 mm (median 1.0 mm) in region I and 0.05 and 3.62 mm (median 0.42 mm) in region II. Transport divided into periods when little or no net transport took place (slow transport) and periods when the transport was effective (fast transport). Although the periods of fast transport were infrequent, their significance in transport towards the ductus deferens was high. During 5 min sampling periods of fast transport, the pendular movements were longer in both regions: delta l was longer in region I and the probability of delta l being in the direction of transport was higher than during slow transport in both regions. The mean probability of delta l being in the direction of the ductus deferens was 0.63 in region I and 0.57 in region II. Higher frequency of pendular movements, longer delta l values and higher probability of delta l being towards the ductus deferens in region I than II suggest that the transport speed is higher in region I than II. Transport consisting of short steps occurring with variable probabilities in both directions is a stochastic process.
Adapting lights and lowered extracellular free calcium desensitize toad photoreceptors by differing mechanisms.
Authors: Greenblatt R E
Published: December 2014

Extracellular recordings were made across the outer segment layer of isolated, superfused toad retinas. Under these recording conditions, the photovoltage reflects primarily the current flowing through the outer‐segment membrane of red rods. In normal toad Ringer solution, a dim conditioning flash desensitized a test flash response. The desensitization reached a peak 1.8‐2.0 s after the conditioning flash and then declined approximately as an exponential with time constant 6 s. Lowered extracellular calcium, [Ca2+]o, desensitized the photoresponse. It required approximately ten times more light to reach a half‐maximal response for each ten‐fold change in [Ca2+]o from 10(‐6) to 10(‐9) M. When [Ca2+]o was less than 10(‐7) M, substitution of Li+ for Na+ as the predominant monovalent cation in the superfusate permitted responses to continue and a resensitization of up to approximately 1 log unit was observed. The effects of lowered [Ca2+]o on response kinetics were markedly different from the effects of background lights producing a comparable desensitization. Low [Ca2+]o increased absolute latency and time‐to‐peak of the flash response. Background lights decreased time‐to‐peak, leaving latency unchanged. The effects of background lights and lowered [Ca2+]o are not additive. Moderate backgrounds had little effect on the intensity/response function in low [Ca2+]o. Conditioning flashes facilitated the test flash response in 10(‐7) M‐[Ca2+]o superfusate. These results can be understood in terms of the Ca2+ hypothesis of transduction (Hagins & Yoshikami, 1974) if it is assumed that lowered [Ca2+]o exposes an endogenous Ca2+ buffer. The data also provide evidence for a role of Na+/Ca2+ exchange in regulating intracellular Ca2+ concentration in the toad photoreceptor. A quantitative model based on these assumptions is derived and compared with the experimental data.
Studies of single calcium channel currents in rat clonal pituitary cells.
Authors: Hagiwara S , Ohmori H
Published: December 2014

Single Ca channel currents in tissue cultured clonal cells (GH3) isolated from a rat anterior pituitary tumour were studied with a patch voltage‐clamp electrode filled with 100 mM‐BaCl2 solution. The open time histogram was reasonably well expressed by a single exponential function with a time constant, which was about 1 msec and almost voltage‐independent in the range of membrane potential studied (‐20 to +40 mV). The closed time histogram was expressed by a sum of two exponential functions, one with a relatively voltage‐independent time constant of about 1 msec and the other with a substantially larger voltage‐dependent time constant. The latency (the time from the onset of the voltage‐clamp pulse to the first channel opening) histogram could be expressed as the difference of two exponential functions with time constants which appeared to be voltage‐dependent. The tentative conclusion is that the channel enters the activated state with voltage‐dependent and relatively slow kinetics, and then flickers between open and closed states with substantially faster and relatively voltage‐independent kinetics. The amplitude of the single channel current was similar to that estimated from noise analysis of the whole cell current (about ‐0.7 pA at 0 mV in 100 mM‐BaCl2 solution); the apparent slope conductance was about 7‐8 pS.
The signal‐to‐noise characteristics of rod—cone interaction
Authors: Bauer G. M. , Frumkes T. E. , Nygaard R. W.
Published: December 2014

1. The influence of rods on cone‐mediated vision was assessed in eight human observers. To this end, increment threshold functions were obtained by determining thresholds of a cone‐detected test flash (25 ms duration, 655 nm wave‐length, 13′ diameter) as a function of the illuminance of larger, 500 ms duration, rod‐detected masking flashes. The type of photoreceptor influenced by each stimulus was carefully checked by means of a series of control procedures involving action spectra and selective rod adaptation.

2. When the rod mask was 512 nm in wave‐length, 40′ in diameter, and less than one scotopic td in illuminance, increment threshold functions show that [Formula: see text], where ICth is cone test threshold, IR is rod mask illuminance, and D is a dark noise term similar to that used by Barlow (1956). Further increases in IR have no additional influences on cone test threshold until threshold is influenced by the combined action of the mask on both rods and cones. If IR is expressed in terms of scotopic flux rather than illuminance, the functional relationship obtained with all rod masks ≤ 40′ diameter and ≤ 580 nm wave‐length is identical.

3. Over the range of illuminance where a square‐root relationship is obtained, probability of seeing functions show that a signal‐to‐noise mechanism limits the detectability of the cone test flash. These findings suggests a quantitative model in which cones produce a signal in a detector which is proportional to the illuminance of the cone test flash. Within a neural locus designated E (excitatory spatial summator), a response is produced which over at least a 40′ diameter area, is proportional to the scotopic flux of the rod mask. E, however, feeds into a gain box, S, which saturates at illuminance levels at least 3 log10 units less than usual estimates of rod saturation. Other than saturation, S behaves in a linear fashion.

4. As diameter increases beyond 60′, rod masks of equal scotopic illuminance have progressively less influence on cone test threshold; rod masks > 2° have negligible influence on cone test threshold. We propose that I (inhibitory spatial summator), a neural locus which responds to scotopic flux provided over a very large area, attenuates the activity of E. The combined action of E and I is designated a rod channel. The response of cones and the rod channel summate at a detector. Within the detector, cone signals are distinguished from rod‐related activity and intrinsic dark noise on the basis of signal‐to‐noise discriminations.

5. The neural substrate for this rod channel most probably involves the combined action of several neurones which synapse within the inner plexiform layer of the retina. The relationship of this rod channel to other perceptual phenomena is discussed.
Neurotrophic control of channel properties at neuromuscular synapses of rat muscle
Authors: Brenner H. R. , Sakmann B.
Published: December 2014

1. Ectopic neuromuscular synapses formed when the fibular nerve was implanted into the proximal part of rat soleus muscle and the soleus nerve was cut. The gating properties of acetylcholine (ACh) receptor channels in the newly formed ectopic and in the denervated original end‐plates were examined at various stages of ectopic synapse formation.

2. At ectopic end‐plates the apparent mean open time of ACh receptor channels changes during synaptic development. Channels in immature ectopic end‐plates, examined 1 week after cutting the soleus nerve, have apparent mean open times of ∼4 ms (at ‐70 mV, 22 °C), similar to those of the extrasynaptic ACh receptor channels of completely denervated fibres. The channel gating of mature ectopic end‐plates, examined 3‐7 weeks after nerve section, is characterized by a mean open time of ∼1 ms and resembles that found in normal end‐plates of adult fibres.

3. The conversion of end‐plate channel gating occurs during the second and third week of synapse formation. During this period two discrete classes of channels with different gating behaviour are present in the ectopic end‐plate.

4. Examination of ectopic end‐plates in the electron microscope reveals that junctional folds begin to appear in the subsynaptic membrane during the period of channel conversion.

5. At the denervated original end‐plates of ectopically innervated fibres the apparent mean open time of ACh receptor channels remains similar to that of normally innervated end‐plates. Original end‐plates retain the normal synaptic class of channel for at least 42 days after denervation. At this time, most of the ACh receptors present originally in the membrane have been replaced by newly inserted receptors.

6. At former end‐plates of completely denervated fibres ACh activates two classes of channels, even when most of the ACh receptors originally present in the end‐plate have been replaced by new receptors.

7. The results show that during synapse formation a neurally controlled conversion of ACh receptor channels occurs about 2‐3 weeks after establishment of the nerve muscle contact. Thereafter end‐plate channel properties are independent of neural influences. These observations are consistent with a mechanism of channel conversion whereby the nerve modifies not the ACh receptor channel itself, but another constituent of the end‐plate membrane which determines the gating properties of end‐plate channels.
Origin and sagittal termination areas of cerebro‐cerebellar climbing fibre paths in the cat.
Authors: Andersson G , Nyquist J
Published: December 2014

Climbing fibre responses were recorded in the cerebellar anterior lobe on stimulation of the cerebral cortex. A zonal pattern was demonstrated in the cortical projection, which was related to the cerebellar sagittal zones, as identified from peripheral climbing fibre input. In all zones, except c2, a co‐variation of the responses evoked on peripheral nerve stimulation and on stimulation of the corresponding part of the sensorimotor cortex was found. There was a bilateral projection to the a, b, c2 and d1 zones which also, to a varying extent, receive a bilateral peripheral input. The x, c1 and c3 zones, receiving an ipsilateral peripheral input, were activated exclusively from the contralateral cortex. Stimulation of the posterior sigmoid gyrus (p.s.g.) evoked responses in all the zones. These responses had, in all zones except d1, lower thresholds and shorter latencies than the responses from other cortical areas. Two separate p.s.g. areas were shown to project to the pars intermedia zones (c1, c2, c3 and d1), the lateral area to the caudal parts and the medial area to the rostral parts of the zones. In contrast, the b zone received a projection from only one p.s.g. area, centred between, but overlapping, the two areas projecting to the pars intermedia zones. Stimulation of the anterior sigmoid gyrus evoked short‐latency responses in the d1 zone and long‐latency responses in all other zones. Stimulation of the first and second somatosensory areas (SI and SII) was generally less effective in evoking climbing fibre responses than was stimulation of the p.s.g. The only exception was the c2 zone, in which responses were evoked from the SII with nearly as low thresholds and short latencies as on p.s.g. stimulation. From the parietal cortex, long‐latency responses were regularly evoked in the d1 zone and less frequently in the a, b and c2 zones.
Spinal inhibition in man: depression of the soleus H reflex by stimulation of the nerve to the antagonist muscle.
Authors: El-Tohamy A , Sedgwick E M
Published: December 2014

A period of inhibition of the soleus H reflex, called D1 inhibition, follows stimulation of the nerve to the antagonist muscles, the peroneal nerve, in normal man. The results confirm earlier descriptions of D1 and show an intracord latency of approximately 4‐5 msec and a reduction of the H reflex by about 60%. D1 reaches its maximum 15‐20 msec after stimulation and its duration is more than 30 msec. Effective stimuli were volleys of two to five pulses given as 10 msec duration bursts at a strength of 1.2 motor thresholds. Cutaneous afferents were ineffective and the possibility that D1 is mediated by low threshold muscle afferents is discussed. D1 produces the same proportions of inhibition of the H reflex when the H reflex is facilitated by plantarflexion or depressed by dorsiflexion.
Apportionment of the terminals from single preganglionic axons to target neurones in the rabbit ciliary ganglion.
Authors: Hume R I , Purves D
Published: December 2014

We have studied the apportionment of terminals from single preganglionic axons to target neurones in the ciliary ganglion of adult rabbits. Both electrical recording and intra‐axonal injection of horseradish peroxidase (HRP) showed that each preganglionic axon innervates only a small fraction of the ganglion cell population (about 10‐20 of the approximately 400 ganglion cells). Examination of ganglia in whole mounts showed that neurones whose cell bodies were enveloped by HRP‐labelled boutons from a single axon were often surrounded by other neurones which received no contacts from the labelled fibre. Electron microscopical examination of labelled presynaptic terminals on individual ganglion cells confirmed that the boutons of single axons were sharply confined to particular target cells. This suggests that individual target neurones (or portions of them) are the unit of innervation during the development of these synaptic connexions. Comparison of the amplitudes of synaptic responses in singly and multiply innervated ganglion cells indicated that, on average, an individual axon made a weaker synaptic connexion with a multiply innervated neurone than with neurone that received only one input. Moreover, neurones innervated by several different axons tended to have fewer synapses on their somata than neurones innervated by only one or two preganglionic axons. Individual post‐synaptic profiles were often contacted exclusively by labelled terminals when examined in the electron microscope. Since many of these neurones are multiply innervated, this observation suggests some regional separation of the several inputs contacting the same cell. For several reasons, however, this inference must be regarded as tentative. Taken together, these findings provide a possible explanation of the correlation between the dendritic geometry of ganglion cells and the number of different axons that innervate them (Purves & Hume, 1981). The several axons that initially innervate ganglion cells without dendrites evidently compete during early life until only a single input remains. On ganglion cells with dendrites, however, the number of inputs that persists is proportional to dendritic complexity. The present results suggest that the diminished competition between axons innervating neurones with dendrites may result from some degree of terminal segregation on dendritic arborizations.
Distribution of monosynaptic Ia excitatory post‐synaptic potentials in the motor nucleus of the cat semitendinosus muscle.
Authors: Botterman B R , Hamm T M , Reinking R M , Stuart D G
Published: December 2014

Evidence is presented for a lack of localization of monosynaptic Ia excitatory post‐synaptic potentials (e.p.s.p.s) in the motor nucleus supplying the atypical cat hind limb muscle semitendinosus, which has anatomically distinct in‐series compartments. Recordings were made from dorsal root filaments containing functionally isolated Ia, spindle group II and Ib axons from the proximal and distal compartments of semitendinosus. Twitch of either of these in‐series compartments resulted in accelerated discharge of Ia and spindle group II fibres in the other compartment. Ib fibres of either compartment showed an in‐series response to twitch of a single compartment which was weaker than twitch of the whole muscle, a finding which was consistent with the diminished force produced by twitch of either compartment alone. In addition, intracellular recordings were made from semitendinosus motoneurones in anaesthetized low‐spinal cats during electrical stimulation of the nerve branches to proximal semitendinosus and distal semitendinosus. Comparison of proximal semitendinosus and distal semitendinosus motoneurones failed to reveal any difference between the two cell groups with respect to the average Ia e.p.s.p. amplitude produced by either the proximal or distal semitendinosus nerve branch. However, e.p.s.p.s due to stimulation of distal semitendinosus were approximately 65% larger, on average, than those due to stimulation of proximal semitendinosus in either motoneurone group. Analysis of cell location along the rostro‐caudal axis of the spinal cord indicated that the proximal and distal semitendinosus cell groups are largely co‐extensive. Recordings of volleys in the proximal and distal semitendinosus nerve branches in response to stimulation of the L6, L7 and S1 dorsal roots showed that group I afferents from the proximal semitendinosus compartment tend to have a more rostral entry point to the spinal cord than do distal semitendinosus afferents. E.p.s.p. amplitude in either cell group due to stimulation of either nerve branch showed little dependence on cell location in the spinal cord. The results are discussed with respect to the relation between muscle function and the distribution of monosynaptic Ia connexions.
Acute responses during blood substitution in the conscious rat.
Authors: Hardy R N , Lowe K C , McNaughton D C
Published: December 2014

Changes in the cellular components of blood in response to exchange transfusion with the fluorocarbon emulsion blood substitute Fluosol‐DA 20% have been examined in conscious chronically catheterized rats. Continuous isovolemic exchange transfusion at 1 ml X min‐1 for 40 min reduced the mean haematocrit from 36% to less than 2%. The animals behaved normally during blood replacement and no significant changes in mean arterial blood pressure, heart rate or respiration rate were observed. An exponential decline in circulating red and total white cell count was observed during exchange transfusion. However, the rates of decline were significantly different for red and white cells as was reflected in the half‐times (t1/2) for the decrease in cell numbers (red blood cells: 7.5 min; white blood cells: 27.5 min) and the fractional turnover rates (k). An exponential decline in total plasma protein and plasma albumin concentrations occurred in response to blood substitution with highly significant inverse log‐linear relationships with time and with closely similar half‐times (t1/2) for the decrease in concentration (total protein: 10.5 min; albumin: 11.3 min) and the fractional turnover rates (k). If a single well‐mixed compartment is assumed for each type of blood cell and plasma proteins, the differences in turnover rates can be attributed to the volumes of these compartments (red blood cells: 10.9 ml.; white blood cells: 40.0 ml.; total protein: 15.2 ml.; albumin: 16.4 ml.). Possible anatomical boundaries for these compartments are considered. Plasma sodium concentration showed a significant decrease in response to blood substitution; no corresponding changes in either plasma potassium or total plasma calcium concentrations were observed. A progressive rise in plasma glucose concentration occurred during blood substitution, with levels at the end of the experiment approximately 2‐fold higher than the mean initial value. There was also a small but not statistically significant decrease in plasma urea concentration during the procedure.
The role of calcium in the regulation of sugar transport in the pigeon red blood cell.
Authors: Simons T J
Published: December 2014

The saturable, ‘carrier‐mediated’ pathway for sugar transport in pigeon red blood cells may be stimulated by metabolic depletion or by loading the cells with Ca by means of a high‐voltage discharge or the ionophore A 23187. All of these methods for stimulating the saturable pathway of sugar transport also cause a drop in cellular ATP levels. The relationship between the stimulation of transport and the fall in ATP is very similar in metabolically depleted or Ca‐loaded cells, but cells treated with Ca and A23187 show a greater stimulation of transport than would be expected from the decline in ATP. Altering free Ca2+ levels during metabolic depletion has little or no effect on stimulation of the saturable pathway. Conversely, metabolic depletion of fresh cells in Ca‐free solutions has no detectable effect on intracellular free Ca2+ levels. These results suggest that Ca2+ ions are not involved in regulation of this pathway. The non‐saturable pathway for sugar transport is stimulated by a rise in cell Ca. This process is probably stimulated half‐maximally by about 10 microM‐free Ca2+.
Tactile discrimination of textured surfaces: peripheral neural coding in the monkey.
Authors: Lamb G D
Published: December 2014

Recordings were made from single mechanoreceptive afferents in the median or ulnar nerve of the anaesthetized monkey while the appropriate digital pad was stimulated by a textured surface moving at a constant velocity tangentially across the skin. The surface was swept across the afferent's receptive field many times, each time having been displaced sideways (laterally) by a small amount. The neural responses showed a temporal rhythm directly related to the period of the raised dots on the surface in the dimension parallel to the direction of movement. The responses also displayed direct dependence on the position of the dots and the period size in the lateral surface dimension. It was clear that only information from a large number of afferents could enable the discrimination of the textured surfaces examined. For large‐dot (2.0 mm period) surfaces, increases of up to 8% in the period of the dots, in either surface dimension, produced a roughly linear increase in the mean response rate of every rapidly adapting (r.a.) afferent. There was virtually no change in the response rate of any slowly adapting (s.a.) afferent when the period of the dots was increased by similar small amounts, and the pacinian afferents (p.c.) displayed a wide range of behaviour to such period changes. In contrast, the mean response rate of p.c. afferents seemed most able of the three populations to transmit information about changes in the period in the case of small‐dot (1.0 mm period) surfaces. The adequacy of a number of neural codes in accounting for all the psychophysical discrimination reported in the preceding paper (Lamb, 1983) was examined. A strong case could be made for a code involving the total or mean number of impulses evoked (a rate code), based on the r.a. afferent responses for the large‐dot surfaces and, less certainly, on the p.c. afferent responses for the small‐dot surfaces.
Naloxone enhancement of spinal reflexes in the rabbit.
Authors: Catley D M , Clarke R W , Pascoe J E
Published: December 2014

The effects of intravenous morphine, (‐)‐naloxone and (+)‐naloxone have been studied on three ipsilateral cutaneo‐muscular reflexes in spinal rabbits. Morphine, 3 mg/kg caused a slow‐onset depression of all three reflexes. This effect was naloxone reversible. The ipsilateral extensor reflexes, sural to gastrocnemius medialis and saphenous to vastus lateralis were both enhanced to more than double control size following a 5 micrograms/kg dose of naloxone given in the absence of morphine. For the sural‐gastrocnemius reflex, naloxone potentiated the reflex drive from all groups of myelinated afferent fibres. The ipsilateral flexion reflex, sural to semitendinosus, was only weakly enhanced by naloxone, the 5 micrograms dose leading to an increase in the size of the reflex to 130% of control. All observed actions of naloxone were stereospecific as the enantiomer (+)‐naloxone failed to affect any of the reflexes even in a dose of 50 micrograms/kg. We conclude from these findings that opioid peptides are tonically released in rabbit spinal cord, and that they have differential effects in control of flexion and extension reflexes. It is suggested that the ipsilateral extension reflexes are held under a more powerful opioid‐mediated depression than that operating upon the flexion reflexes, and that this difference may be related to the greater inhibitory inflow to extensor motoneurones from ipsilateral skin areas.
The role of 5‐hydroxytryptamine as a transmitter between identified leech neurones in culture.
Authors: Henderson L P
Published: December 2014

The synthesis, storage, release and synaptic actions of 5‐hydroxytryptamine (5‐HT or serotonin) were studied in order to characterize the synaptic connexion that develops between pairs of identified neurones dissected from the central nervous system of the leech and maintained in culture. Experiments were made with Retzius cells (which are known to contain 5‐HT in vivo) and pressure sensory neurones on which they form chemical synapses in culture. Individual, isolated Retzius cells in culture synthesized [3H]5‐HT from either [3H]tryptophan or [3H]5‐hydroxytryptophan [( 3H]5‐HTP). These cells did not synthesize other putative neurotransmitters, such as acetylcholine, dopamine, octopamine, noradrenaline or gamma‐aminobutyric acid from their respective precursors. The monoaminergic character of Retzius cells was also demonstrated by staining with Neutral Red and by histofluorescence. Individual, isolated Retzius cells that had synthesized and accumulated [3H]5‐HT released this compound when depolarized. Transmitter release was calcium‐dependent and was blocked by magnesium. When incubated with [3H]5‐HT and washed, Retzius cells in culture accumulated approximately 100 times more labelled 5‐HT than did non‐serotonergic cells, and 10 times more than Retzius cell somata acutely isolated from the animal and incubated in vitro. Chlorimipramine, a blocker of 5‐HT uptake, decreased the amount of [3H]5‐HT accumulated by Retzius cells and also caused a reversible increase in the amplitude of the synaptic response in the pressure sensory cell elicited by stimulation of the Retzius cell. Pressure sensory neurones in culture and in vivo responded to 5‐HT focally applied by pressure ejection from a micropipette. Small pulses elicited a small, slow hyperpolarization. This response was due, at least in part, to an increase in chloride conductance and desensitized rapidly. With larger pulses, a larger, faster non‐desensitizing depolarization was elicited. Together, these results provide evidence that 5‐HT released from Retzius cells could be responsible for the chemical synaptic potentials seen in pressure sensory neurones in culture.
Simple and complex spike activity of cerebellar Purkinje cells during active and passive movements in the awake monkey.
Authors: Bauswein E , Kolb F P , Leimbeck B , Rubia F J
Published: December 2014

Two Rhesus monkeys (Macaca mulatta) were trained to pursue a target light signal by moving the hand at the wrist joint. Additionally, a d.c. motor could be attached to the lever in order to perform similar passive movements. During performance of the task, single Purkinje cells were recorded from the intermediate part of the cerebellar anterior lobe. Electromyographic activity of the flexor and extensor muscles of the forearm was recorded simultaneously. Passive hand movements evoked changes in the complex spike and simple spike discharge of Purkinje cell. The complex spike responded most sensitively to the beginning of the movement; the activity pattern had phasic character and could be related specifically to the movement direction. The simple spike response was usually weak and hence revealed‐less specific relations. During active movements the simple spike frequency change was generally stronger than during passive movements and reached a maximum (or minimum) at the beginning of hand deflexion. The complex spike activity during active movements was characterized by a contrast between the time phases before and after the movement onset. In most of the cases, where a phase of increased activity stopped at the movement onset, the sensory feed‐back signal seen during passive movements was cancelled. The possible consequences of the convergence of the complex and simple spike signal for the motor control function of the cerebellum are discussed.
Different types of blockade of crustacean acetylcholine‐induced currents.
Authors: Lingle C
Published: December 2014

The voltage dependence, concentration dependence, and agonist dependence of blocking and unblocking produced by anticholinergic agents on the ionophoretically activated cholinergic currents of the lobster gastric mill 1 (g.m.1) muscle were examined. Although the ionophoretic technique provides only qualitative information as to blocking mechanisms it is useful in revealing slow components of the blocking action of some drugs. At least two qualitatively different types of voltage‐dependent block of the crustacean cholinergic currents were observed. For pempidine, mecamylamine and decamethonium (also chlorisondamine: Lingle, 1983), a slowly developing voltage‐dependent block was produced that led to the formation of a stable‐blocked state. Recovery from this stable‐blocked state is largely dependent on subsequent application of agonist. In contrast, recovery from the voltage‐dependent block produced by QX‐222, atropine, procaine and curare either proceeds independently of agonist application or occurs too rapidly to be observed by the present methods. Blockade by hexamethonium reveals anomalous voltage dependence, being enhanced over some voltages and relieved with additional hyperpolarization. Blockade by trimetaphan is largely independent of membrane potential except at higher concentrations.
A voltage‐clamp analysis of inward (anomalous) rectification in mouse spinal sensory ganglion neurones.
Authors: Mayer M L , Westbrook G L
Published: December 2014

Mouse embryo dorsal root ganglion neurones were grown in tissue culture and voltage‐clamped with two micro‐electrodes. Hyperpolarizing voltage commands from holding potentials of ‐50 to ‐60 mV evoked slow inward current relaxations which were followed by inward tail currents on repolarization to the holding potential. These relaxations are due to the presence of a time‐ and voltage‐dependent conductance provisionally termed Gh. Gh activates over the membrane potential range ‐60 to ‐120 mV. The presence of Gh causes time‐dependent rectification in the current‐voltage relationship measured between ‐60 and ‐120 mV. Gh does not inactivate within this range and thus generates a steady inward current at hyperpolarized membrane potentials. The current carried by Gh increases when the extracellular K+ concentration is raised, and is greatly reduced in Na+‐free solutions. Current‐voltage plots show considerably less inward rectification in Na+‐free solution; conversely inward rectification is markedly enhanced when the extracellular K+ concentration is raised. The reversal potential of Ih is close to ‐30 mV in media of physiological composition. Tail‐current measurement suggests that Ih is a mixed Na+‐K+ current. Low concentrations of Cs+ reversibly block Ih and produce outward rectification in the steady‐state current‐voltage relationship recorded between membrane potentials of ‐60 and ‐120 mV. Cs+ also reversibly abolishes the sag and depolarizing overshoot that distort hyperpolarizing electrotonic potentials recorded in current‐clamp experiments. Impermeant anion substitutes reversibly block Ih; this block is different from that produced by Cs+ or Na+‐free solutions: Cs+ produces outward rectification in the steady‐state current‐voltage relationship recorded over the Ih activation range; in Na+‐free solutions inward rectification, of reduced amplitude, can still be recorded since Ih is a mixed Na+‐K+ current; in anion‐substituted solutions the current‐voltage relationship becomes approximately linear. It is concluded that in dorsal root ganglion neurones anomalous rectification is generated by the time‐and voltage‐dependent current Ih. The possible function of Ih in sensory neurones is discussed.
Capsaicin causes release of a substance P‐like peptide in guinea‐pig inferior mesenteric ganglia.
Authors: Dun N J , Kiraly M
Published: December 2014

The effects of capsaicin (0.5‐100 microM) on neurones of the isolated inferior mesenteric ganglia (i.m.g.) of the guinea‐pig were investigated by means of intracellular recording techniques. When applied to neurones of the i.m.g. that exhibited a slow non‐cholinergic excitatory potential (Dun & Jiang, 1982), capsaicin caused in the large majority of these cells a long lasting depolarization accompanied by intense neuronal discharges. During and immediately following the depolarization, repetitive presynaptic stimulation consistently failed to elicit the non‐cholinergic depolarization; a partial recovery was observed in relatively few neurones. The fast (nicotinic) excitatory post‐synaptic potentials (e.p.s.p.s) were not suppressed by capsaicin in any of these cells. The membrane potential, input resistance and the amplitude of fast e.p.s.p.s in neurones of the i.m.g. that generated no detectable non‐cholinergic depolarizations were not affected by capsaicin. Post‐synaptic membrane sensitivity to exogenous application of substance P was not altered following capsaicin superfusion even though the latter effectively abolished the non‐cholinergic depolarization in the same neurones. Superfusing the i.m.g. with a Ca‐free Krebs solution markedly attenuated or abolished the depolarizing effect of capsaicin whereas tetrodotoxin (1 microM) was without effect. Capsaicin was without effect in a few neurones that generated a non‐cholinergic depolarization; the latter was not desensitized by bath application of substance P. Capsaicin caused no appreciable effects in neurones of the bullfrog sympathetic ganglia; thus, the fast and slow post‐synaptic potentials including the late slow e.p.s.p. the transmitter of which is the peptide luteinizing hormone‐releasing hormone (Jan & Jan, 1982) were not affected. The results suggest that the depolarizing effect of capsaicin in neurones of the guinea‐pig i.m.g. is due to a selective release of ganglionic substance P or a substance P‐like peptide in a Ca‐dependent manner, and that the non‐cholinergic potentials elicited in capsaicin‐insensitive neurones may be generated by a transmitter(s) other than substance P.
After‐effects of repetitive stimulation at low frequency on fast‐contracting motor units of cat muscle.
Authors: Jami L , Murthy K S , Petit J , Zytnicki D
Published: December 2014

Twitch and tetanic contractions of single motor units of the cat peroneus tertius muscle were examined after application of a test allowing their identification as either fast fatigable (f.f.) or fast fatigue‐resistant (f.r.) or fast intermediate (f.i.) or slow units as established by Burke, Levine, Tsairis & Zajac (1973). The test was found to leave two kinds of after‐effects in f.f., f.r. and f.i. units whereas it did not affect slow units. The first after‐effect was an early and brief potentiation of twitch tension occurring in all f.r. and f.i. units and in most f.f. units. The second after‐effect, termed ‘delayed fatigue', was a prolonged depression of tension output, that developed slowly following the early potentiation in all f.f. and f.i. units and more than half of the f.r. units. One hour after the test, unfused tetanic contractions elicited by 20‐40/sec stimulation were deeply depressed in motor units that had been left without stimulation since the end of the test. Recovery took place in 3‐5 hr. Motor units affected by delayed fatigue could nevertheless be made to develop nearly normal tension by gradual build‐up upon prolonged stimulation at 30‐40/sec. Maximal tetanic contractions elicited by 200/sec stimulation were much less depressed during delayed fatigue than unfused tetanic contractions. These observations suggest that contractile mechanism were not impaired by delayed fatigue. Since absence of change in muscle action potential indicated that excitation of muscle fibres was not affected either, delayed fatigue might be due to a temporary failure of excitation‐contraction coupling.