bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recurrent inhibition of fusimotor neurones exhibiting background discharges in the decerebrate and the spinal cat
Authors: Ellaway P. H. 
Published: December 2014

1. Discharges of functionally single fusimotor neurones have been recorded from the nerves to hamstring and triceps surae muscles in the cat. Background discharges were examined for both muscle groups in decerebrate animals but only for hamstrings in spinal preparations.2. Background discharges in forty‐six out of sixty‐seven triceps and twenty‐one out of twenty‐five flexor hamstring fusimotor neurones were inhibited by an antidromic volley in other efferent axons. One semimembranosus neurone was similarly inhibited.3. The inhibition was due to impulses in α motoneurone axons. It had a mean central delay of 2·3 ± 0·2 msec and 2·7 ± 0·2 msec for triceps and hamstring muscles respectively and was detectable for up to 100 msec, although shorter durations of the order of 10 msec were common.4. It was possible for a fusimotor neurone in one ventral root to be inhibited by an antidromic volley in an adjacent ventral root. The origin of the inhibition was not confined to a unit's own muscle nerve.5. The actions of eserine and strychnine on the inhibition were similar to their effects on recurrent inhibition of α motoneurones. Eserine potentiated and strychnine reduced the inhibition following an antidromic volley.6. The inhibition was found in spinal and in decerebrate cats but it was depressed following spinal section.
L‐Dopa in the spinal animal depressed the background discharge of some neurones and potentiated that of others. Both sets of neurones could be inhibited by antidromic volleys.7. It is concluded that antidromic inhibition of some fusimotor neurones does occur and that it is highly likely to be mediated via recurrent collaterals and Renshaw interneurones. The evidence from the use of
L‐Dopa indicates that the inhibition is present to both dynamic and static fusimotor neurones.
The plantar cushion reflex circuit: an oligosynaptic cutaneous reflex
Authors: Egger M. David , Wall Patrick D. 
Published: December 2014

1. Reflex toe extension elicited by pressure on the plantar cushion (PC) was studied in cats anaesthetized with Dial. Receptive fields and adequate stimuli for the reflex were evaluated. It was concluded that the receptors for the reflex were chiefly cutaneous pressure receptors in PC.2. The fastest impulses from the PC receptors for this reflex are conducted to the spinal cord at about 64 m/sec via fibres about 10–11 μm in diameter, i.e. the largest afferent fibres from PC. The motoneurones active in the reflex mainly supplied the intrinsic plantar muscles. Most active axons ran in the S1 ventral root.3. Extracellular recordings of interneurones in the dorsal horn of L7 spinal segment revealed that many units at the medial edge of the dorsal horn, chiefly in Rexed's laminae IV and V, were activated by stimuli similar to those eliciting the PC—toe extension reflex. These were termed intermediate threshold PC units. Some of these medially located units were activated monosynaptically by PC stimulation. Intermediate threshold PC units activated disynaptically or polysynaptically were also found in this medial region of the dorsal horn, as well as ventrolaterally and caudally in lamina V.4. No intermediate threshold PC units sent axons into dorsolateral ipsilateral thoracic white matter, in contrast to lower threshold PC units, 42% of which were driven by lateral column stimulation.5. Extracellular and intracellular recordings were made from motoneurones activated by adequate stimuli for the reflex. Minimum latencies of EPSPs revealed that, for the fastest component of the reflex, at most two interneurones could be interposed between a primary sensory neurone and a motoneurone.6. Although convergence of low threshold PC units on to intermediate threshold PC units or on to motoneurones may play a part in the PC—toe extension reflex, it appears probable that the two populations of intermediate threshold PC interneurones described above, that is, the monosynaptic and the disynaptic (with higher order interneurones), mediate the reflex.
Rod‐dependent intracellular response to light recorded from the pigment epithelium of the cat retina
Authors: Schmidt Rainer , Steinberg Roy H. 
Published: December 2014

1. Intracellular recordings from pigment epithelial cells reveal rod‐dependent hyperpolarizing responses to light which are identical with the c‐wave of the electroretinogram. These responses were studied as a function of the duration, intensity and area of light flashes and also were compared with rod‐dependent horizontal cell responses recorded under similar conditions.2. Because of the long time constant of the response (800 msec), pigment epithelial responses increased in amplitude as flash duration was increased over a wide range. The response reached a plateau at a flash duration of 2·4 sec so that longer flashes only increased the duration of the response. Responses to repetitive flashes, even at a slow rate of 2/sec were integrated to produce a sustained voltage.3. The growth of pigment epithelial response amplitude as a function of flash duration could be divided into two components. The increase in amplitude as flash duration was increased from 5‐50 msec was also observed in horizontal cells and was assumed to have originated in the rods. The growth in amplitude with longer flashes was unique to the pigment epithelial response.4. The pigment epithelial response increased in amplitude as spot size was increased, reaching 90% of maximum with an 0·36 mm diameter spot. A precise measurement of the receptive field could not be obtained, because the responses were recorded in the tapetal area of dark‐adapted retinas. The b‐wave of the local electroretinogram which was ‘picked‐up’ intracellularly exhibited a much greater area effect.5. Pigment epithelial responses increased in amplitude as flash intensity was increased but the amplitude‐log intensity functions differed as a function of flash duration. With long flashes (> 2·4 sec) the growth in amplitude was a power function of intensity (exponent = 0·6–0·7) and the response reached an amplitude ceiling at about 3·0 log td scotopic. At higher intensities the responses increased in duration (the rod after‐effect). With short flashes, e.g. 480 msec, the responses continued to increase in amplitude with flash intensity well above the intensity needed to produce amplitude‐ceilings for rod‐dependent responses. This additional increase in amplitude resulted from integration of the rod after‐effect by the pigment epithelial response.6. Rod‐dependent horizontal cell responses followed the amplitude—log intensity functions that were recorded in pigment epithelial cells with long flashes. The rod after‐effect was also the same function of log intensity in both responses.7. It was concluded that the pigment epithelial response is not generated by a late photoproduct. Rather, it appears to depend upon the same mechanism of rod excitation as the horizontal cell response, and the essential characteristics of both rod‐dependent responses originate in individual rods.
Incremental responses to light recorded from pigment epithelial cells and horizontal cells of the cat retina
Authors: Steinberg Roy H. 
Published: December 2014

1. Rod‐dependent incremental responses were recorded intracellularly in both pigment epithelial cells and horizontal cells of the cat retina. They were elicited by test flashes which were superimposed on background flashes after a delay.2. In pigment epithelial cells smaller test responses were produced as background intensity was raised. The incremental sensitivity function was linear for about 1·4 log units, with a slope of 0·86, and the approach of saturation occurred at about 2·5 log td scotopic.3. The amplitude of pigment epithelial test responses could be estimated from the dark‐adapted amplitude—log intensity function obtained with single flashes. Test flashes produced the voltage increment predicted by the slope of this function just above the point on the curve equal to the background intensity. The pigment epithelial response to a test flash, therefore, is the response expected if the background were presented alone and made more intense by the amount of the test flash.4. Rod‐dependent incremental sensitivity functions of horizontal cells closely resembled the ones obtained from pigment epithelial cells.5. It was concluded that the adaptive effects observed in pigment epithelial cells originated in individual rods. These effects arose from the compressive nature of the dark‐adapted amplitude—intensity function. In horizontal cell responses these effects may be modified by the failure of the background response to maintain its initial voltage.
Switching of the respiratory phases and evoked phrenic responses produced by rostral pontine electrical stimulation
Authors: Cohen Morton I. 
Published: December 2014

1. In midcollicular‐decerebrate, gallamine‐paralysed, vagotomized cats, efferent phrenic discharge was recorded as an indicator of the central respiratory cycle. Electrical stimulation (50–250/sec) delivered in the rostral lateral pontine ‘pneumotaxic centre’ region (in and near nucleus parabrachialis), and set to occur at specified times in the cycle, produced powerful respiratory effects: (a) at dorsolateral points, inspiratory‐facilitatory effects (increase of phrenic discharge, shortening of the expiratory phase); (b) at ventrolateral points, expiratory‐facilitatory effects (decrease of phrenic discharge, shortening of the inspiratory phase, lengthening of the expiratory phase).2. At both inspiratory‐facilitatory and expiratory‐facilitatory points, a single stimulus delivered during the inspiratory phase produced a short‐latency (4–7 msec) reduction of phrenic discharge, followed by a wave of increased activity. The short latency of the response indicates the existence of paucisynaptic descending inhibitory pathways. Succeeding stimuli in a high‐frequency train produced alternating waves of evoked activity and depression; the form of the responses depended on stimulus frequency and on locus of stimulation.3. At inspiratory‐facilitatory points, short stimulus trains (10–30 stimuli) of adequate strength delivered in the middle and late expiratory phase caused early termination of the phase (latency 100–300 msec) and switching to a complete inspiratory phase, in which the phrenic discharge pattern resembled that in a normal inspiratory phase. Similarly, adequate stimulus trains applied at expiratory‐facilitatory points during the middle and late inspiratory phase caused early termination of the phase and switching to a complete expiratory phase.4. The threshold for occurrence of each type of phase‐switching response depended on stimulus current, frequency, number of stimuli, and time of stimulus delivery. As stimulus trains were delivered later in the phase, the threshold for switching to the succeeding phase was progressively reduced. Moreover, the nature of the evoked effects was a non‐linear function of stimulus characteristics: a small increase of stimulus efficacy changed the system's response from (a) moderate shortening of the phase or transient change in phrenic discharge, to (b) complete termination of the phase.5. These results indicate that, as each respiratory phase progresses, there is a steady increase of excitability in systems which promote the onset of the succeeding phase. Further, the existence of a relatively sharp threshold for switching of the respiratory phases suggests that the phase transitions occur when critical levels of excitation and inhibition are reached synchronously in populations of respiratory neurones.
Responses of inferior collicular neurones of bats to tone bursts with different rise times
Authors: Suga N. 
Published: December 2014

1. A study was made of the responses of single neurones in the inferior colliculus of bats to tone bursts with different rise times (or with different rates of amplitude increase) in order to determine whether the neurones were specialized for analysis of amplitude‐modulated sound, especially the rising phase in amplitude.2. The response patterns of neurones which showed phasic on‐responses usually did not change with rise time, although the response patterns of some neurones changed from phasic on‐responses to inhibitory responses.3. The thresholds of responses to tone bursts increased when the rise time was lengthened. The amount of increase greatly differed from neurone to neurone. For the excitation of neurones which showed a large increase in threshold, the stimulus amplitude should quickly increase in amplitude. For tone bursts with a short rise time, some neurones showed an upper‐threshold above which the sounds failed to excite them. The upper‐threshold usually disappeared when the rise time was lengthened. For the excitation of neurones which showed an upper‐threshold, the rate of amplitude increase and its extent were very important parameters.4. Lengthening the rise time of a tone burst from 0·5 to 98 msec caused various types of change in the excitatory area. In some cases, there was a diminution of the area and, in others, there was an expansion of the area. Neurones showing these changes may be considered to be specialized for responding to tone bursts with either a rapid or slow increase in amplitude.5. Changes with rise time occurred not only in the excitatory area, but also in the inhibitory area. The change in the inhibitory area of a given neurone, however, was not necessarily the same as that in the excitatory area.6. The latency of response usually changed as a function of stimulus amplitude and rise time. In 26% of the neurones studied, however, the latency was relatively constant regardless of stimulus amplitude and rise time. Some of the latency‐constant neurones appeared to have properties suited for echo‐ranging.7. The changes in excitatory area with rise time appear to involve neural inhibition and/or accommodation. Possible neural mechanisms for the changes in threshold, upper‐threshold and response pattern and the properties of latency‐constant neurones are discussed.
Vagal non‐adrenergic inhibition of guinea‐pig stomach
Authors: Beani L. , Bianchi Clementina , Crema A. 
Published: December 2014

1. The effect of vagal and sympathetic stimulation on the mechanical and electrical activity (intracellular recording) of the body of the guinea‐pig stomach was investigated in vitro.2. Following atropine, 1 × 10−6‐1 × 10−7 g/ml., vagal responses were reversed from excitatory to inhibitory.3. Sympathetic blockade, produced by α‐ and β‐receptor antagonists and adrenergic neurone‐blocking agents, reduced or abolished sympathetic, but not vagal inhibition.4. Hexamethonium (5 × 10−5 g/ml.) reduced vagal relaxation to 11–30% according to the stimulation rate. The residual response was maintained in the presence of 5‐hydroxytryptamine tachyphylaxis.5. Many muscle cells were observed to be under the influence of both vagus and sympathetic nerves: the effect of sympathetic stimulation was always inhibitory in nature, but high stimulation rates were required. The effect of vagal stimulation was both excitatory and inhibitory even in the absence of atropine: low stimulation rates gave rise either to E.J.P.s (excitatory junctional potentials), often followed by spikes, or to I.J.P.s (inhibitory junctional potentials).6. In some spontaneously firing cells the interruption of electrical activity produced by vagal stimulation at 2/sec and sympathetic stimulation at 20/sec was recorded for a long enough time to check the effect of guanethedine (5 × 10−6 g/ml.): the drug selectively blocked sympathetic inhibition.7. The significance of the inhibitory non‐adrenergic transmitter, released by the intramural neurones activated by preganglionic vagal fibres, is discussed.
Projection from low‐threshold muscle afferents of hand and forearm to area 3a of baboon's cortex
Authors: Phillips C. G. , Powell T. P. S. , Wiesendanger M. 
Published: December 2014

1. The precentral and postcentral banks of the Rolandic fissure of the arm area of the baboon's cortex have been probed to their depths with extracellular micro‐electrodes under nitrous oxide and oxygen anaesthesia, supplemented by minimal intravenous pentobarbitone or chloralose.2. Afferent volleys were sent in from the deep (motor) radial nerve and the deep palmar (motor) branch of the ulnar nerve. Their entry into the central nervous system was timed at the dorsal root entry zone. The nerves were stimulated in continuity and the effects of stimuli below threshold for the motor axons were investigated.3. Area 3a, in the depths of the postcentral bank, which is cytoarchitectonically transitional between areas 3 and 4, is the receiving area for afferent impulses from muscle.4. Evoked potential waves and unitary discharges began 4 msec, and the majority of units discharged between 5 and 10 msec, after the afferent volley reached the dorsal root entry zone.5. Similar responses were elicited by a brief pull (70 μ in 1 msec) or brief vibration (50 μ at 250–400 Hz) applied to the tendons of m. extensor digitorum communis.6. No potential waves were evoked in area 4, even in the depths adjacent to area 3a, by muscle afferent volleys.
Rhodopsin kinetics in the human eye
Authors: Alpern M. 
Published: December 2014

1. Rhodopsin has been measured by Rushton's method of reflexion densitometry in a retinal region 18° temporal to the fovea, using a wavelength of measuring light (555 nm) so far into the long wave part of the spectrum that possible blue absorbing intermediates (e.g. transient orange) do not interfere.2. Rhodopsin was bleached by a strong light for 10 sec and then held steady by a weaker light. During a 10 sec bleach, no regeneration occurs and the rate of bleaching is proportional to the quantum catch. The proportionality constant is about 10−7 (td sec)−1.3. From 2, the rate of photolysis at equilibrium produced by the steady light was calculated. Since conditions were at equilibrium, photolysis matched regeneration. It was found that the rate of generation was proportional to the amount of pigment still bleached. The proportionality constant was about 0·0025 sec−1.4. It was found by several different methods that the constant in 3 is the same in the light or dark and hence regeneration occurs independently of bleaching.5. Therefore, the results from bleaching and regeneration experiments can be combined to give the general equation [Formula: see text], where p is the fraction of rhodopsin, t is time in sec and I is the retinal illuminance.6. This equation describes the results of partial bleaching and regeneration experiments under a variety of different exposure intensities of moderately long (at least 10 min) exposure durations.7. The dark adaptation curve in a peripheral region of the rod monochromat's retina where there are few cones follows a simple exponential course over nearly 7 log10 units. Rhodopsin regeneration and log threshold for this region are described by the same curve with a time constant of about 400 sec. Each log unit fal in threshold is accompanied by 0·835% increase in rhodopsin. This time constant is in agreement with Rushton's (1961) finding, but appreciably longer than that reported by Ripps & Weale (1969a).8. The Ripps & Weale result was, however, obtained by bleaching with a very short bright xenon flash (as they did). Under these conditions, blue absorbing intermediate(s) is (are) formed, the time constant of regeneration of rhodopsin is much faster than after long tungsten bleaches, and the kinetic equation is not valid.9. The general equation, together with the relation found in 7, successfully accounts for results previously published by others of the effect of duration and intensity of bleaching on the recovery of rod threshold in the dark, provided only that more than 5% of the rhodopsin was bleached at the beginning of dark adaptation.
Catecholamine synthesis and excretion in rats exposed intermittently to cold
Authors: Bibbiani Cecilia , Viola-Magni Maria Pia 
Published: December 2014

Previous findings have shown a turnover of nuclear DNA, a condition related to the functional activity of these cells, in the adrenal medullae of rats intermittently exposed to cold. Striking differences have been observed between various strains of rats, particularly Italico and Wistar rats.In order to evaluate the function of the adrenal medullary cells, the content of catecholamines in the organ and their urinary excretion have been evaluated, with the fluorimetric method, in rats of Italico and Wistar strains kept at room temperature and exposed intermittently to cold. The results show that (i) at room temperature the levels of excretion are lower in Italico than in Wistar rats in spite of the equal amine contents of the adrenal medullae, (ii) the first exposure to cold causes a large increase in the urinary excretion and a decrease of adrenaline and noradrenaline content of the adrenal glands in both strains, (iii) after 3 days the catecholamine content in the organ was higher than normal in Wistar rats, whereas in the Italico strain it continued to decrease, and (iv) a new steady state at higher levels is reached after 20 days of exposure, when not only the catecholamine content but also the urinary excretion is equal in both strains.These differences between the two strains of rats during intermittent cold exposure are discussed in relation to the behaviour of DNA.
Depression of the reflex tachycardia from the left atrial receptors by acidaemia
Authors: Harry J. D. , Kappagoda C. T. , Linden R. J. , Snow H. M. 
Published: December 2014

1. The effects are described of an acidaemia, produced either by the inhalation of carbon dioxide or by an intravenous infusion of hydrochloric acid, on the reflex increase in heart rate which results from stimulation of the left atrial receptors in the anaesthetized dog.2. The results show that during acidaemia the reflex increase in heart rate from stimulation of the left atrial receptors is reduced. The extent of the reduction is related to the degree of the acidaemia.3. It is suggested that it is necessary to monitor and correct changes in the pH of arterial blood in experiments which involve reflex changes in heart rate, especially if the efferent pathway involves the sympathetic nerves.4. It is also suggested that the occurrence of such an acidaemia in anaesthetized surgically traumatized animals may be a factor contributing to the variability in results from investigations involving reflex changes in heart rate in response to stimulation of the left side of the heart.
A new approach for determining the volume of cerebral extracellular fluid and demonstration of its communication with c.s.f
Authors: Friede Reinhard L. , Hu Kuo Hao 
Published: December 2014

1. A new technique is presented for determining the volume of extracellular space in bowfin (Amia calva) brain during in vitro incubation. It consists of solving simultaneous equations which are applied to determine the volume of extracellular space as well as intracellular marker concentration. This technique allows for a better insight into the redistribution of marker between incubation medium and extracellular space as well as between extracellular and intracellular space.2. Na+, K+ and Cl− equilibrated within 10–15 min between incubation medium and extracellular space. There was no evidence of a homoeostatic mechanism controlling the concentration of these ions in the extracellular fluid, which appeared to be in equilibrium with cerebrospinal fluid. The extracellular spaces of these ions were identical: Na+, 23·4; K+, 23·3 and Cl−, 23·2%.3. Sorbitol equilibrated with the extracellular fluid within 45 min and indicated an extracellular space of 22·6%, nearly identical with that for electrolytes.4. Vastly different ‘spaces’ were obtained for [3H]methoxy inulin, which equilibrated within 45 min with a 13% space and [14C]carboxyl inulin, which showed a 46% space value for only 30 min. The difference may be explained by marker decomposition. The 9% difference between the [3H]methoxy inulin and sorbitol spaces may be explained by a ‘packing’ factor attributable to molecular size.