bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium, magnesium and the electrical activity of guinea‐pig olfactory cortex in vitro
Authors: Richards C. D. , Sercombe R.
Published: December 2014

1. Evoked electrical activity was observed in slices from guinea‐pig olfactory cortex maintained in vitro. This evoked activity was studied in saline solutions containing various concentrations of Ca2+ and Mg2+.

2. The evoked potentials recorded from the surface of the prepiriform cortex comprised a negative wave (N‐wave) of about 10–15 msec duration upon which a variable number of short duration positive notches were superimposed. The N‐wave was identified as a population excitatory post‐synaptic potential (EPSP) of the olfactory cortex neurones and the positive notches were identified with synchronous discharge of cortical neurones.

3. The relation between the EPSP amplitude and saline Ca2+ concentration was sigmoid. The N‐wave amplitude (EPSP) was proportional to [Ca2+]on. When saline Ca2+ was between 0·4 and 1 m
M n averaged 2·5 (range 1·5–4·3).

4. The EPSP amplitude was reduced by increasing saline [Mg2+]. High Mg2+ salines (about 10 m
M) abolished the EPSP.

5. Both Ca2+ and Mg2+ in high concentrations depressed the positive notches.

6. Salines containing little or no Ca2+ and Mg2+ caused the preparation to show signs of hyperexcitability. Under these conditions the evoked potentials were very variable and unstable. ‘Ca2+‐free’ salines caused a reversible loss of excitability.

7. The results indicated that Ca2+ and Mg2+ had antagonistic effects on the release of the transmitter substance(s). Increased Ca2+ concentrations increased the output of transmitter, increased Mg2+ concentrations reduced the output of transmitter. Both Ca2+ and Mg2+ in increasing concentration increased the threshold for action potential generation.
Parallel spindle systems in the small muscles of the rat tail
Authors: Thompson J.
Published: December 2014

1. The examination consisted of a histological analysis using paraffin sections, gold chloride staining and osmic acid techniques.

2. The parallel spindle system found in the rat tail muscles is compared with that found in frog muscles. The rat spindle system occasionally included extrafusal fibres.

3. It was evident that there are basic Class differences between the frog and rat tail parallel spindles, but it is suggested that they may serve a similar proprioceptive role in muscles having almost isometric contractions.

4. Other short muscles of the rat that might have an analogous function to the tail muscles were examined, but only the capitus and deep masseter muscles showed parallel spindle systems, and none contained extrafusal fibres.

5. Of other mammals examined, the muscles of the tails of the cat, rabbit, mouse and guinea‐pig contained parallel spindles, while the dog and mole showed none in the small sample taken.

6. Nerve trunk fibre size histograms, including de‐efferented trunks, indicated a high proportion of sensory nerve fibres from the tail (55%), a low motor unit ratio (1:60) and a beta axon motor supply both to the spindles and to the small muscles of the tail.

7. A generalized schema of the rat tail anatomy is presented, and a tabulation of the large sensory endings expected to be found in any particular small tail muscle.

8. It was concluded that the rat tail has a spindle density enough to provide a proprioceptive sensitivity equivalent to that of a caudal digit.
Electrotonic characteristics of alpha motoneurones of varying size
Authors: Burke R. E. , ten Bruggencate G.
Published: December 2014

1. The neuronal membrane responses to long constant current pulses (essentially current steps) have been studied in cat triceps surae motoneurones identified as to the type of muscle fibres, fast twitch (type F) or slow twitch (type S), innervated by the cell being studied. For each motoneurone the membrane time constant, τM, and input resistance, RN, were determined from the response to a current step. In addition, shorter time constants (‘equalizing time constants’) resulting from current spread into the dendrites were estimated by graphical analysis.

2. The electrotonic length of the combined motoneurone soma and dendritic tree was estimated from the current step data using the neuronal equivalent cylinder model formulated by Rall (Rall, 1969). The mean electrotonic length of the motoneurone equivalent cylinder was approximately 1·5 in both type F and type S motoneurones. The mean membrane time constant of type F cells was 5·6 msec and that of type S motoneurones was 6·7 msec. This difference in mean τM values was of border line statistical significance.

3. The results indicate that the electrotonic length of the combined dendritic trees of both large type F and small type S motoneurones is essentially the same. The implication of this conclusion for interpretation of previous analyses of the monosynaptic EPSP is discussed.
Electrotonic coupling between neurones in the rat mesencephalic nucleus
Authors: Baker R. , Llinás R.
Published: December 2014

Electrical stimulation of the trigeminal nerve evokes a ‘short latency depolarization’ (SLD) in the first order sensory neurones of the mesencephalic nucleus (MSN) of the Vth nerve in the rat. A series of experiments suggesting ‘electrotonic coupling’ as the mechanism for this SLD is provided.

1. Electrical activity of MSN neurones was recorded intracellularly as action potentials were conducted from the periphery (somatopetally) to the masticatory nucleus. Typical sequential invasion of the initial segment and somatic region (IS—S) of the neurones was seen. The somatopetal activation of MSN neurones was characterized by the brevity, short refractoriness, high safety factor (IS—S), and short after‐hyperpolarization of the spike potential.

2. In twenty‐three (10·5%) of the penetrated neurones, stimulation at levels subthreshold for somatopetal activation uncovered a SLD with a mean latency of 180 μsec.

3. The SLDs were found to be all‐or‐none in nature, and to have constant amplitude and latency for a given cell, plus a short half decay time.

4. Hyperpolarization of a MSN neurone through the recording electrode produced a blockage of the IS—S spike and revealed M‐spikes and SLDs which could be clearly separated, in every instance, as distinct all‐or‐none components. The amplitude of the SLD was found to be insensitive to the level of membrane potential within the ranges tested.

5. In fifteen neurones the SLD generated action potentials which were conducted somatofugally as shown by their collision with somatopetally conducted action potentials in the same cell. The lack of collision between the SLD and somatopetal spikes demonstrated the independent origin of these two potentials.

6. The independence of the SLD from the somatopetal invasion of the cell was also demonstrated by collision of a somatofugal action potential following direct stimulation through the recording micro‐electrode and a somatopetal spike following trigeminal stimulation.

7. Two possible mechanisms are considered for the genesis of the SLD: chemical synaptic transmission and electrotonic coupling between neighbouring cells. The conclusion is drawn that SLDs must be generated by the latter mechanism.
Sensory cells in the spinal cord of the sea lamprey
Authors: Martin A. R. , Wickelgren Warren O.
Published: December 2014

1. Intracellular recordings were made from dorsal cells in the spinal cord of the sea lamprey.

2. Dorsal cells were excited by mechanical stimulation of the ipsilateral skin and were established as first‐order sensory cells using a variety of physiological criteria. Receptive fields were mapped.

3. Dorsal cells were subdivided into three functional types on the basis of their responses to mechanical stimulation of the skin. Touch (T) cells gave rapidly adapting responses to indentation of the skin. Pressure (P) cells gave slowly adapting responses to indentation of the skin. Nociceptive (N) cells gave slowly adapting responses to severe (often destructive) indentation of the skin. The three types also differed in their spontaneous activity and in their response to repeated stimulation.

4. Pressure and nociceptive cells were excited by heating the skin over the receptive field. The amount of heat necessary to excite nociceptive cells was greater than that necessary for pressure cells and often left a permanent burn mark on the skin.

5. The three types of dorsal cell also showed differences in resting potential, membrane time constant, spike threshold, and response to sustained depolarization.
Anion interaction at the inhibitory post‐synaptic membrane of the crayfish neuromuscular junction
Authors: Takeuchi A. , Takeuchi Noriko
Published: December 2014

1. The membrane potential and the membrane conductance of the crayfish muscle fibre in solutions containing various anions were measured with intracellular micro‐electrodes.

2. When Cl− in the solution was replaced by Br−, NO3−, I− or CNS−, the addition of γ‐amino butyric acid (GABA) produced a transient hyperpolarization of the membrane.

3. The reversal potential of the inhibitory junctional potentials (i.j.p.s) was at a slightly depolarized level relative to the resting potential in the normal Cl− solution. When Cl− in the bathing solution was replaced by foreign anions, the reversal potential shifted towards the hyperpolarized level. The hyperpolarization was in the order CNS− > I− > NO3− > Br−.

4. When a part of Cl− in the bathing solution was substituted by Br−, the inhibitory membrane conductance activated by GABA was increased as the concentration of Br− increased. The inhibitory membrane conductance decreased when one quarter or a half of Cl− was replaced by CNS−, NO3− or I−, but it increased again in higher concentrations of these anions.

5. Ca2+, Mg2+ and Ba2+ showed no appreciable effect on the inhibitory membrane conductance activated by GABA, while they decreased the conductance of the resting muscle membrane.

6. It was suggested that, at the activated inhibitory membrane, there is an interaction between anions and the permeability of Cl− is decreased by the presence of foreign anions, such as CNS−, I− and NO3−. The present results support the idea that the activated inhibitory membrane is charged positively and anions penetrate the membrane interacting with the charge sites.
Metabolic, respiratory and vasomotor responses to heating the scrotum of the ram
Authors: Hales J. R. S. , Hutchinson J. C. D.
Published: December 2014

1. Oxygen consumption, respiratory frequency, and temperatures of the rectum, common carotid artery, external auditory meatus, and skin on the ears, near the distal end of the metacarpus and metatarsus, upper thigh and mid‐side of the body, were measured in five rams before, during and after heating the scrotum. Effects on the woolly animal exposed to ambient temperatures of 17–19° C, and on the shorn animal exposed to ambient temperatures of 5·6–24·5° C, were determined.

2. In eight experiments on woolly animals scrotal heating resulted in vigorous panting and a lowering of deep body temperatures by 0·3–1·1° C within 50 min. There was no significant change in oxygen consumption or body skin and upper thigh temperature. Changes in skin temperature of the extremities indicated, on average, a vasodilator response to heating. However, individual responses were unpredictable, there sometimes being dilation and constriction in different extremities of the same animal.

3. In twelve experiments on shorn animals in environments below 20° C, oxygen consumption before scrotal heating was higher than when the animal was woolly. Scrotal heating resulted in a fall in oxygen consumption and a lowering of deep body temperatures by 0·2–0·9° C within 50 min. There was no change in respiratory frequency or body skin and upper thigh temperature. As in the woolly animal, vasomotor responses were disorganized, although there was a tendency towards vasodilation.

4. In three shorn animals in environments of 20·5 and 24·5° C, oxygen consumption before scrotal heating was only slightly higher than when the animal was woolly. In two of these animals (in 20·5 and 24·5° C) scrotal heating resulted in a slight lowering of oxygen consumption and mild panting, and deep body temperature fell by 0·9° C in 50 min. In the third animal (in 24·5° C) there was no change in oxygen consumption but vigorous panting and vasodilation, and deep body temperature fell by 1·3° C in 50 min.

5. In a number of experiments on shorn animals scrotal heating was continued for more than 100 min. Deep body temperature was controlled at a new low level after the initial fall, and the possibility of a resetting of the ‘set‐point’ temperature is discussed.

6. The previously unexplained fall in body temperature of the shorn ram in which panting did not follow scrotal heating may now be mainly ascribed to a reduction in metabolic rate. Also, the possible role of cutaneous evaporation should not be discounted. The inhibition of panting in the shorn sheep at environmental temperatures below 20° C remains unexplained.

7. Body heating alone, by covering the shorn animal with a sheep skin coat in an environment of 19° C, elicited well organized vasomotor changes in the ears and lower legs.

8. As a result of the present study and previous work by others, it is clear that all thermoregulatory mechanisms, with the exception of vasomotor changes, may be influenced in a predictable manner by temperature changes of the scrotum.
Intrarenal distribution of blood flow and cortico‐medullary sodium gradient after unilateral splanchnicotomy in the dog
Authors: Bencsáth P. , Takács L.
Published: December 2014

1. Intrarenal distribution of blood flow and cortico‐medullary sodium gradients have been studied in anaesthetized dogs, previously subjected to unilateral splanchnicotomy. Experiments were carried out on hydropoenic, normal, isotonic and hypotonic volume expanded animals.

2. Polyuria and natriuresis were present under all experimental conditions after denervation.

3. Denervation resulted in an increase in medullary blood flow, particularly in hydropoenic and normal dogs. In isotonic and hypotonic volume expansion, the increases in the medullary circulation were smaller despite a greater increase in urine flow and sodium excretion of the denervated side.

4. Under no experimental condition did the cortico‐medullary sodium gradient of denervated kidneys differ significantly from that of the intact kidneys.

5. It is concluded that denervation polyuria might be attributed in part to an increase in medullary blood flow; the natriuresis, however, could not be accounted for by these circulatory changes. Other possibilities are discussed.
Stimulus—response relationships in first‐order sensory fibres from cat vibrissae
Authors: Hahn J. F.
Published: December 2014

1. In the infraorbital nerve of anaesthetized cat, recordings were made from single units serving the vibrissae. The directional sensitivity of individual units was rather gross, but comparison of the outputs of several units from the same vibrissa could provide information that was more precise about the direction of vibrissa deflexion.

2. Many of the units showed ‘spontaneous’ activity. The majority of rates were less than 1 impulse/sec, so that this activity is not likely to be an important carrier of information.

3. When sinusoidal deflexions in the frequency range of 0·5–100 Hz were applied, the frequency responses of about half of the units were those to be expected if they were responding to the velocity of the stimulus; most of the remainder responded to both the velocity and the magnitude of the deflexion. This form of information presentation has been shown to be well suited for compensatory tracking tasks, and it is suggested that the vibrissae are important for such tasks in the animal's life, rather than merely serving as obstacle detectors.

4. Greatest deflexion sensitivity typically was at higher frequencies than could be attained in this experiment, but would be greater than the median threshold deflexion angle of 12 min found at 50 Hz. It is suggested that these low thresholds are more appropriate for a tracking system than for an obstacle detector.
The binding of tetrodotoxin to nerve membranes
Authors: Keynes R. D. , Ritchie J. M. , Rojas E.
Published: December 2014

1. The% reduction in size of the externally recorded action potential produced by concentrations of tetrodotoxin (TTX) in the range 6–300 n
M was determined for the small non‐myelinated fibres of the rabbit cervical vagus nerve and of the walking leg nerves of crab and lobster. The concentration of TTX for 50% reduction was around 80 n
M for rabbit vagus and 14 n
M for crab nerve.

2. Bio‐assay procedures were devised to measure the amount of TTX taken up by a nerve when it was exposed to a very small volume of a solution whose TTX content was just great enough to produce 100% block of conduction. The extracellular space of each nerve was determined with [14C]sugar so that an allowance could be made for extracellular dilution.

3. The TTX binding by rabbit, crab and lobster nerve was respectively 0·064, 0·053 and 0·036 p‐mole/mg wet weight of nerve.

4. The binding of saxitoxin was measured in rabbit vagus nerve, and found to be much the same as that of TTX.

5. Control experiments on rabbit sciatic nerve, where the area of excitable membrane was much smaller, showed that there was relatively little unspecific binding of TTX.

6. In view of the evidence presented here and elsewhere that the blocking of sodium conductance by TTX involves the attachment of only one TTX molecule at each sodium site, and that unspecific binding of TTX does not cause serious errors, these results suggest that in 1 μm2 of nerve membrane the number of sodium sites is 75 for rabbit, 49 for crab, and 36 for lobster nerve.
Pulmonary stretch receptor activity in man: a comparison with dog and cat
Authors: Guz A. , Trenchard Diana W.
Published: December 2014

1. The ‘collision’ technique has been shown to be suitable for recording orthodromic ‘A’ fibre activity in a whole, functioning cervical vagus nerve. This activity predominantly arises from pulmonary stretch receptors.

2. The amount and frequency of discharge from pulmonary stretch receptors in man, dog and cat, have been shown to increase with inspiration and decrease with expiration—the larger the tidal volume, the greater the discharge. At the end‐expiratory level in man and dog, a tonic stretch receptor discharge is present. The results in cat and dog are in broad agreement with older work using single fibre techniques.

3. The stretch receptor discharge in man may be greater for a given degree of lung ‘stretch’ than in cat or dog. There is certainly a discharge during eupnoea in man, and this must be contrasted with the absence of a Hering—Breuer inflation reflex in adult anaesthetized man with lung inflations of the order of a eupnoeic tidal volume. Furthermore, man does not develop slow, deep breathing with bilateral vagal block.

4. Since the characteristics of the activity from pulmonary stretch receptors with eupnoea in man are similar to those seen in other species, it must be concluded that this activity does not reach the central threshold to affect the respiratory centre.
The role of non‐myelinated vagal afferent fibres from the lungs in the genesis of tachypnoea in the rabbit
Authors: Guz A. , Trenchard Diana W.
Published: December 2014

1. The use of a direct current (d.c.) to produce a differential block of conduction in the cervical vagus nerves of rabbits is described; the myelinated fibres are blocked, while the non‐myelinated ‘C’ fibres conduct normally. The method produces reproducible and reversible results.

2. The block is equally effective for low and high frequencies of discharge (1–100 Hz). During recovery or development of the block, lower frequencies of discharge can pass but higher frequencies cannot.

3. Block of conduction in myelinated fibres is associated with slower, deeper breathing, confirming previous work with cooling.

4. A further slowing and deepening of breathing may occur when a differentially blocked (‘non‐myelinated’) nerve is sectioned, and this is mainly apparent when there are pathological conditions in the lungs.

5. The respiratory response to the right atrial injection of phenyl diguanide is mediated by non‐myelinated thoracic vagal afferent fibres.

6. The tachypnoeic response to lung deflation is not mediated by non‐myelinated fibres.

7. Head's Paradoxical reflex has been demonstrated during partial recovery of conduction in myelinated fibres when only lower frequencies of afferent discharge can pass the area of block.

8. A standard technique for providing a reproducible vagally mediated, tachypnoeic response to pulmonary micro‐embolism is described using inert carbon‐coated microspheres of 50 μm diameter. This tachypnoeic response was unchanged during a differential block indicating that the response was mediated by non‐myelinated ‘C’ fibres.

9. Pathological changes such as haemorrhage, oedema, infarction and collapse were absent after micro‐embolism, and there were no systematic changes in lung resistance and compliance. The walls of arterioles and adjacent alveoli are distorted by the emboli and these areas are the probable sites of afferent stimulation.
The membrane potential and permeabilities of the L cell membrane to Na, K and chloride
Authors: Lamb J. F. , MacKinnon M. G. A.
Published: December 2014

1. The chloride content and fluxes, and the membrane potential of L cells have been measured.

2. L cells contain chloride, 70 m‐mole/l. intracellular water and have a flux of 5·5 p‐mole/cm2 sec.

3. The membrane potential is −15 mV.K‐free Krebs causes an increase in Em and replacing chloride with sulphate causes a temporary reduction in Em.

4. These values for Em and chloride, and previously obtained values for Na and K fluxes and contents were used to calculate the permeabilities of the various ions using the Goldman constant field theory. This gave permeabilities of 6·3, 4·2 and 51 × 10−9 cm/sec for K, Na and chloride respectively, a ratio of 1:0·67:8·10.

5. It is concluded that these cells have a low membrane potential because the PK is some 100 times lower than in skeletal muscle, therefore leading to a PK of the same order as PNa.
Does curare affect transmitter release?
Authors: Auerbach A. , Betz W.
Published: December 2014

1. The effect of curare on the amount of transmitter released by a nerve stimulus was studied in frog and rat nerve—muscle preparations using electrophysiological techniques.

2. When the frog sartorius nerve—muscle preparation was exposed to low doses of curare, the amplitudes of spontaneous miniature end‐plate potentials and end‐plate currents (e.p.c.s, measured under ‘voltage clamp’ conditions) were reduced to the same extent, suggesting that the drug did not alter the number of transmitter quanta released by nerve stimulation.

3. With higher doses of curare in frog muscle treated with glycerol to abolish twitching, quantum content was estimated from the coefficient of variation (CV) of e.p.c.s. The measured CV increased slightly in curare; this increase probably resulted from a relatively greater contribution of random noise to the observed fluctuations when the e.p.c. was reduced by curare.

4. In the rat diaphragm, muscle fibres were cut to block twitching. This procedure produced, among other changes, a reduction in the muscle fibre space constant, so that junctional signals were distorted by the cable properties of the muscle fibre when, as often occurred, micro‐electrodes were more than 100–200 μ from the end‐plate focus. This produced errors in estimates of quantum content; when these errors were accounted for, it appeared that curare did not significantly alter quantum content.

5. It is concluded that if curare affects transmitter release at all, its effect must be much smaller than its well known post‐synaptic blocking action.
The effects of altering mean pressure, pulse pressure and pulse frequency on the impulse activity in baroreceptor fibres from the aortic arch and right subclavian artery in the rabbit
Authors: James Jennifer E. Angell
Published: December 2014

1. A method is described for perfusing an isolated preparation of the rabbit aortic arch with independently controlled mean pressure, pulse pressure and pulse frequency.

2. Recordings made from single or few‐fibre preparations from the aortic arch and right subclavian baroreceptor regions show that the number of impulses per second or per cycle in a single fibre is the same during pulsatile perfusion as during non‐pulsatile perfusion if the pressure is above the threshold pressure to non‐pulsatile perfusion during all phases of the pressure cycle.

3. In multi‐fibre recordings the total number of impulses is greater during pulsatile perfusion than during non‐pulsatile perfusion due largely to recruitment of fibres during systole.

4. The relationship between instantaneous impulse frequency and aortic arch pressure during one pressure cycle forms an elliptiform curve.

5. Increasing the pulse pressure increases the ellipse and causes additional recruitment of other fibres during systole, thus augmenting the total impulse activity.

6. Increasing the pulse frequency reduces the number of impulses per cycle for single fibres but produces a small increase in the total impulse frequency in one second period due to recruitment.

7. Increasing the rate of change of pressure by increasing the pulse pressure or pulse frequency produced a small reduction or no change of the threshold pressure. Similarly the ‘cut off’ pressure was elevated in some fibres.

8. At low initial mean pressures, an increment of pressure, at constant pulse pressure and pulse frequency, increases the total impulse activity by increasing the frequency of impulses in single fibres already active during systole and diastole and by additional recruitment of other fibres. At higher mean pressures there is little increase in impulse activity as the maximum frequency of fibres is attained or superseded and there is little recruitment.
The lymphatics of the kidney and the formation of renal lymph
Authors: McIntosh G. H. , Morris Bede
Published: December 2014

1. The anatomy of the renal lymphatics and the flow and composition of renal lymph have been investigated in sheep. Lymphatic capillaries were demonstrated in the cortex and cortico‐medullary areas of the sheep's kidney but not within the medulla. The lymph formed in the sheep's kidney drains from the hilum through several small lymphatics; there is no lymphatic drainage from the renal capsule.

2. Lymph flow from the sheep's kidney varied from 0·5 to 3·0 ml./hr. The concentrations of electrolytes and urea in renal lymph were found to be similar to lymph from other regions of the body, but the concentration of endogenous creatinine was lower. The average concentration of protein in renal lymph was 43% of the plasma levels; there was a significantly higher proportion of albumin in renal lymph than in plasma. When labelled albumin was injected intravenously, the specific activities of the plasma and renal lymph albumin equilibrated in about 2 hr.

3. When [14C]inulin, [125I]hippuran or [14C]creatinine were infused intravenously radioactivity appeared rapidly in the renal lymph. When steady‐state levels were reached in the circulating plasma, the renal lymph/jugular vein plasma ratios for [14C]inulin and [14C]creatinine were 0·82 while for [125I]hippuran the ratio was 0·34. It was considered that the concentration of these substances in renal lymph was similar to the concentration in renal vein plasma.

4. The concentration of renin enzyme was on the average about 8 times higher in renal lymph than in jugular vein or renal vein plasma or in lymph from the hind limbs.

5. Renal lymph appeared to be formed principally, if not entirely, in the renal cortex and appeared to be a modified filtrate derived from post‐glomerular blood capillaries. If any contribution to renal lymph does come from the medulla, it must be small in relation to the volume of lymph formed in the cortex.
The effect of variations in heart rate and regional distribution of blood flow on the normal pressor response to diving in ducks
Authors: Butler P. J. , Jones D. R.
Published: December 2014

1. During a 2 min period of submersion of normal ducks, sciatic artery blood flow fell to 10 ± 1·5% control and carotid artery blood flow was reduced to 71 ± 7% control. Mean arterial blood pressure (
M.A.P.), however, was maintained at 83 ± 3·5% of control. The whole animal showed a constrictor response during submersion, with the sciatic vascular bed showing average constriction. Both resistance to flow and yield pressure increased in the sciatic bed but changed little in the carotid bed. After 1 min submersion Pa,O2 was 52 ± 1 mm Hg.

2. Upon emersion, as soon as ventilation commenced, the whole animal showed a dilator response. The carotid bed exhibited marked vasodilatation whereas the sciatic bed returned to its control level.

3. After α‐receptor blockade, ducks were submerged for 1 min. During this time
M.A.P. fell to 64 ± 5·6% of control and heart rate was reduced to 49 ± 8·3% of control. Blood flow through the sciatic and carotid arteries also fell to values of 41 ± 6·9% of control and 91 ± 13% of control respectively. There was little change in either resistance to flow or yield pressure in the sciatic bed compared to normal ducks, and the carotid bed showed reductions in resistance to flow and yield pressure during submersion. Pa,O2 after 1 min under water was 41 ± 1·1 mm Hg.

4. β‐receptor blockade had no effect on any of the measured variables during submersion. Upon surfacing, however, although the whole animal response was one of dilatation, the carotid bed was less dilated than in normal ducks at this time and the sciatic bed was more constricted.

5. Injection of atropine not only abolished the bradycardia during submersion but also caused a rise in
M.A.P. and sciatic blood flow during the period under water. After 1 min submersion Pa,O2 was 30 ± 1·2 mm Hg.

6. It is concluded that stimulation of adrenergic α‐receptors is responsible for the increase in resistance to flow through the sciatic artery and the maintenance of blood pressure during submersion in the normal animals. This selective constrictor activity and the resulting ischaemia is important in the maintenance of Pa,O2 during submersion. Adrenergic β‐receptors (cardiac and/or peripheral) are involved, to a small extent, in the blood pressure and blood flow changes that occur when ventilation commences upon emersion.
An electrical description of the motoneurone, and its application to the analysis of synaptic potentials
Authors: Jack J. J. B. , Redman S. J.
Published: December 2014

1. The Rall model of the motoneurone, which consists of a lumped resistance and capacitance, representing the soma, in parallel with a distributed resistance—capacitance network of finite length, representing the equivalent dendritic cable, has been used to investigate the effects of varying electrical and geometrical parameters on the time course of transients generated at the model soma.

2. An analytical solution has been obtained for the voltage at the model soma, following a brief current injection at any point on the dendritic cable, in terms of the dendritic to soma conductance ratio, the electrotonic length of the cable, the membrane time constant, and the electrotonic distance between the point of current injection and the soma. This solution has been used to study the response at the soma to currents with a smooth time course, and to brief rectangular current pulses. Computations of these voltage transients are given to illustrate the effect of the above parameters on voltage time course.

3. A method for determining the membrane time constant, the dendritic to soma conductance ratio, and the electrotonic length of the dendritic cable, is described. The method involves measurements from the decay time course of the transient at the soma following a brief current pulse being applied at the soma.

4. A method is described whereby the time course of a synaptic potential, assumed to be generated by synaptic knobs located exclusively at the soma, may be used to determine the motoneurone parameters, and a parameter describing the time course of current injection.

5. A method for estimating the distance between soma and origin of a non‐somatic synaptic potential, once the parameters of the motoneurone are known, is described.
Cardiovascular changes associated with skeletal muscle spasm in tetraplegic man
Authors: Corbett J. L. , Frankel H. L. , Harris P. J.
Published: December 2014

1. A study has been made of the effect of spontaneous and induced muscle spasms on blood pressure, heart rate, hand blood flow, calf blood flow and occluded vein pressure in the hand and foot in non‐bedridden patients with chronic, closed, complete, localized transection of the cervical spinal cord.

2. Both types of spasm produced a similar response consisting of an increase in blood pressure and occluded vein pressure and a decrease in heart rate and hand and calf blood flow. The changes commenced within 2‐3 sec and usually reached maxima in 20–30 sec. On some occasions there was a temporary initial increase in heart rate and calf blood flow.

3. The changes occurred independently of changes in bladder pressure.

4. It is concluded that the changes in peripheral blood vessels result from a spinal sympathetic reflex to somatic afferents associated with muscular contraction.
Spinal integration of segmental, cortical and breathing inputs to thoracic respiratory motoneurones
Authors: Aminoff M. J. , Sears T. A.
Published: December 2014

1. The spinal integration of cortical, segmental and breathing inputs to thoracic motoneurones was studied in anaesthetized, paralysed cats: the breathing input was intensified by underventilation or abolished by hyperventilation.

2. In apnoeic animals, low intensity stimulation of an internal intercostal nerve evoked a brief latency polysynaptic reflex discharge of expiratory motoneurones (direct response) in several adjacent segments with no or little response of the inspiratory motoneurones.

3. A similar direct response of expiratory motoneurones occurred with brief tetanic stimulation of the trunk area in the contralateral sensorimotor cortex.

4. Conditioning of an intercostal‐intercostal test reflex by a prior stimulus to an intercostal nerve or to the cortex gave conditioning curves showing facilitation of transmission to expiratory motoneurones at short intervals (5–25 msec) and inhibition at long intervals (25–200 msec).

5. The direct response of expiratory motoneurones to the cortical or segmental inputs was depressed during the inspiratory phase when the animal was underventilated; conversely the spontaneous activity of the inspiratory motoneurones was inhibited for a period that corresponded with the direct response or to the phase of facilitated transmission to expiratory motoneurones. During the expiratory phase, the cortically or segmentally induced direct response was facilitated but the inhibition of inspiratory motoneurone activity was concealed by the absence of spontaneous activity.

6. It was possible with discrete lesions of the spinal cord to differentiate between the pathways subserving the responses to cortical stimulation and the spontaneous activity due to the breathing input.

7. To account for the results a working hypothesis is proposed utilizing a segmental interneuronal network which transmits mutual reciprocal inhibition between inspiratory and expiratory motoneurones.
The effect of tetanus toxin in the goldfish
Authors: Diamond J. , Mellanby Jane
Published: December 2014

1. The effects of tetanus toxin have been investigated both on central nervous and peripheral neuromuscular systems of goldfish.

2. Tetanus toxin kills goldfish when administered in minute doses. The lethal effect is temperature dependent. Unlike mammals, in which tetanus toxin produces spastic paralysis and convulsions, the tetanus‐intoxicated goldfish die with an apparently flaccid paralysis.

3. Inhibition and excitation were investigated on the Mauthner cells of goldfish which had been paralysed with tetanus toxin for at least 24 hr, and which were subsequently kept alive for up to 3 days by perfusing the gills with oxygenated water. In such fish, antidromically and orthodromically excited Mauthner cells were quite normal, and there was no apparent effect on either the collateral inhibition or the crossed VIIIth nerve inhibition.

4. Local injection of sublethal doses of tetanus toxin into the pectoral fin muscles produced local paralysis of the fin. Nerve—muscle preparations were isolated from such goldfish; in tetanus toxin‐paralysed fins, the muscle no longer responded to stimulation of its nerve. The nerve compound action potential was still present and the muscle still responded vigorously to direct electrical stimulation.

5. It is concluded that the major part of the lethal action of the toxin in the fish must be ascribed to a peripheral effect, the blocking of neuromuscular transmission. The inhibitory neuronal systems acting on the Mauthner cells of the goldfish, in apparent contrast to those acting on mammalian spinal neurones, are highly insensitive to tetanus toxin.
The mechanism of acetylcholine release from parasympathetic nerves
Authors: Paton W. D. M. , Vizi E. S. , Zar M. Aboo
Published: December 2014

1. The output of acetylcholine from the plexus of the guinea‐pig ileum longitudinal strip has been used to study the mechanism of acetylcholine release. From the effects of hexamethonium and tetrodotoxin, it was inferred that 60% of the normal resting output is due to propagated activity in the plexus, and 40% to spontaneous release. Tetrodotoxin virtually abolishes the increase in output in response to electrical stimulation.

2. Resting acetylcholine output is increased when the bathing medium is changed in the following ways:

(a) sodium replacement by sucrose, trometamol or lithium;

(b) addition of ouabain or p‐hydroxymercuribenzoate (PHMB), or withdrawal of potassium;

(c) the combination of PHMB and partial sodium replacement;

(d) addition of potassium; this increase in output becomes greater in the absence of sodium.

3. The resting output is virtually abolished by calcium withdrawal, and is restored by barium substitution for calcium. It is also reduced by raising the magnesium concentration.

4. The enhanced resting output in response to sodium withdrawal also occurs in the absence of calcium.

5. Cooling to 5° C greatly reduces both the resting output and the output in response to raised potassium concentration or to electrical stimulation.

6. The increase in resting output due to potassium excess is slight up to 25 m
M [K+]o, but increases thereafter with about the fourth power of the potassium concentration; it is resistant to tetrodotoxin.

7. Synthesis of acetylcholine by the longitudinal strip is increased when output is enhanced by electrical stimulation, by potassium excess or by addition of barium, so that the acetylcholine content of the strip is maintained approximately normal. Synthesis is reduced, in relation to output, by potassium lack or by treatment with ouabain, and is virtually abolished by sodium withdrawal.

8. The theory is discussed that acetylcholine release depends on inhibition of the activity of a (Na+ + K+ + Mg2+)‐activated ATPase at the axonal membrane.
Synaptic transmission in the superior cervical ganglion of the cat after reinnervation by vagus fibres
Authors: Ceccarelli B. , Clementi F. , Mantegazza P.
Published: December 2014

1. A vagus‐sympathetic anastomosis was performed in the cat by connecting end to end the cranial trunk of the vagus to the cranial end of the cervical sympathetic trunk, both severed under the ganglia.

2. Forty to sixty days after the anastomosis, the ocular signs of sympathetic paralysis (such as myosis and prolapse of the nictitating membrane) which had developed shortly after the operation, had completely disappeared, thus suggesting the recovery of synaptic transmission in the ganglion. In case of plain preganglionic denervation after the same period the ocular signs of cervical sympathetic paralysis were still present.

3. Contraction of the nictitating membrane could be induced by electrical stimulation of both the vagus preanastomotic and the sympathetic postanastomotic—preganglionic trunks. Ganglionic blocking agents induced the blockade of the ‘new’ ganglionic synaptic function, while nicotine and pilocarpine provoked a marked contraction of the nictitating membrane.

4. Electron microscopy showed that the preganglionic regeneration of vagus fibers resulted in the formation of new synapses, mainly of axodendritic type, identical to normal ganglionic synapses. Moreover, after cutting the preanastomotic trunk of the vagus, these new ganglionic presynaptic profiles degenerated, thus proving their vagal origin.

5. During restoration of the synaptic contacts readjustment of dendritic tips occurred.
The function of the paramedian reticular nucleus in the control of heart rate in the cat
Authors: Calaresu F. R. , Thomas M. R.
Published: December 2014

1. Selective electrical stimulation of the paramedian reticular nucleus (PRN) in anaesthetized and decerebrate‐anaesthetized cats elicited cardiac slowing which was shown to be due to inhibition of the sympathetic input to the heart.

2. In decerebrate preparations stimulation of the PRN elicited cardioacceleration which was abolished by bilateral vagotomy.

3. It is suggested that these changes in heart rate in opposite directions can be accounted for by an inhibitory influence of the PRN on both neural inputs to the heart. In the absence of vagal activity, demonstrated in anaesthetized and decerebrate‐anaesthetized preparations, the response to stimulation of the PRN resulted in cardiac slowing. In contrast, when both sympathetic and parasympathetic pathways were active (decerebrate preparation) stimulation of the PRN resulted in cardio‐acceleration, due to simultaneous inhibition of the two neural inputs to the heart.

4. It is concluded that the two inhibitory functions of the PRN are probably mediated by two different populations of neurones and that the PRN plays an integrative role in the medullary control of heart rate.
Age changes in cross striated muscle of the rat
Authors: Gutmann E. , Hanzlíková V. , Vyskočil F.
Published: December 2014

1. Senile muscle atrophy is characterized by a marked reduction in the frequency of spontaneous transmitter release with no electrophysiological evidence of denervation.

2. In spite of the reduced number of muscle fibres, there is no ultrastructural evidence for denervation at the end‐plates. There is agglutination of synaptic vesicles, neurotubules and filaments, thickening of the basement membrane, widening of the primary synaptic cleft, and irregular branching of the junctional infoldings, but no axonal degeneration.

3. The contractile process in senile muscles is slowed down as is indicated by a prolongation of contraction time, latency period, maximum rate of twitch tension and relaxation time.

4. The muscle fibres show proliferation of the T system and increased SR but no fragmentation as is observed in denervation atrophy.

5. Senile muscle atrophy thus presents some specific features affecting both pre‐ and post‐synaptic structures, related to a very slow process of deterioration of the neuromuscular contact.
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.