bluuebunny/crossref_metadata_2025 huggingface dataset:
The uptake of [14C]glycine by slices of mammalian spinal cord
Authors: Neal M. J.
Published: December 2014

1. The accumulation of [14C]glycine by slices of mammalian spinal cord has been measured.

2. When slices of rat cord were incubated at 37° C in a medium containing [14C]glycine, tissue:medium ratios of about 30:1 were attained after a 40 min incubation.

3. After incubations at 37° C for 40 min, almost all (98%) the radioactivity in the tissue was present as unchanged [14C]glycine.

4. The process responsible for [14C]glycine uptake showed many of the properties of an active transport system: it was temperature sensitive, required the presence of sodium ions in the external medium, was inhibited by dinitrophenol and ouabain and showed saturation kinetics.

5. The estimated Km value of glycine was 3·1 × 10−5
M, and Vmax was 0·48 μ‐mole/min.g cord.

6. The uptake of [14C]glycine was not affected by the presence of large molar excesses of
L‐histidine,
L‐proline,
L‐aspartate,
L‐glutamate,
L‐valine or GABA, but was inhibited in the presence of
L‐alanine and
L‐leucine.

7. The uptake of [14C]glycine was not reduced by strychnine, but a significant reduction in uptake was produced by p‐hydroxymercuribenzoate.

8. The uptake of [14C]glycine by the grey matter of rabbit spinal cord was 2 to 6 times greater than the uptake by slices of white matter incubated under the same conditions.

9. Rat cerebral cortex, cerebellar cortex and medulla also accumulated [14C]glycine, and the uptake by the tissue slices in vitro appeared to parallel the concentration of glycine in these areas in vivo.

10. It is suggested that the glycine uptake system may represent a possible mechanism for the inactivation of glycine at inhibitory synapses in the spinal cord.
Rapid changes and hysteresis in spatial integration for human rod vision
Authors: Hallett P. E.
Published: December 2014

1. Two previous papers (Hallett, 1969a, b) were concerned with the visual threshold appropriate to a peripheral retinal point and in particular with the rapid changes in point threshold produced by illuminating the dark‐adapted eye with large brief duration backgrounds. This paper extends this approach to testing signals of larger subtense.

2. Spatial integration for the rods can rapidly diminish and recover within a few hundred milliseconds.

3. A brief duration background which raises the threshold at a retinal point as much as some steady background is more effective than the steady background in reducing the extent of spatial integration.

4. Hysteresis can be substantial; the extent of spatial integration varies, even for a given point threshold, according to whether the threshold is rising or falling, or temporarily or permanently steady.

5. A possible type of non‐linear model is discussed in the next paper (Hallett, 1971).
Release of endogenous noradrenaline from an isolated muscular artery
Authors: Bell C. , Vogt Marthe
Published: December 2014

1. The release of noradrenaline by field stimulation of vasoconstrictor nerves has been studied in isolated preparations of the main uterine artery of the guinea‐pig.

2. In preparations from virgin animals stimulation with trains of 3000 square pulses at 5 and 25 pulses/sec resulted in mean overflows of 0·56 ng/g.pulse and 1·53 ng/g.pulse respectively.

3. Inhibition of monoamine oxidase and catechol‐O‐methyltransferase had no consistent effect on overflow at either stimulation frequency.

4. Desmethylimipramine (10−5
M) caused, on the average, a 2·4‐fold increase in overflow following stimulation at 5 pulses/sec while phenoxybenzamine (10−5
M) caused a 3·8‐fold increase. Neither of these drugs caused a significant alteration of the overflow during stimulation at 25 pulses/sec.

5. Treatment of the tissues with desmethylimipramine plus normetanephrine (4·5 × 10−4
M) caused no more increase in overflow than treatment with desmethylimipramine alone.

6. It is concluded that enzymatic metabolism of noradrenaline at the synapse is of little functional importance in this tissue, and that the most important mechanism of transmitter inactivation is by nervous re‐uptake. Although phenoxybenzamine was more effective than desmethylimipramine in increasing transmitter overflow, no evidence was obtained to support the view that this effectiveness was due partly to blockade of ‘Uptake 2’.

7. There was sometimes very low overflow of noradrenaline from arteries taken from animals in the last week of pregnancy. In these instances overflow following stimulation at 5 pulses/sec was not increased by phenoxybenzamine treatment of the tissue.

8. Methylene blue and fluorescence microscopic techniques indicated that the terminal adrenergic axons in each artery possess approximately 8·74 × 105 varicosities. The mean tissue content of noradrenaline was found to be 9·6 μg/g or 29 ng/artery. These results have been correlated with known morphological and electrophysiological data to derive a peak post‐junctional concentration of noradrenaline during transmission of about 4 × 10−4
M.

9. The fraction of total noradrenaline content of the artery released per pulse (under the influence of phenoxybenzamine) had a mean value of 2·2 × 10−4.
Action potentials and release of neurohypophysial hormones in vitro
Authors: Dreifuss J. J. , Kalnins Ilva , Kelly J. S. , Ruf K. B.
Published: December 2014

1. Isolated rat neurohypophyses were studied in vitro and the hormones released on electrical stimulation of the pituitary stalk or on exposure to excess potassium were estimated by a milk‐ejection assay.

2. The stalk was stimulated with trains of 500 stimuli, or multiples thereof, applied at different frequencies. Below frequencies of ca. 35 c/s, hormone release was found to depend on the total number of stimuli applied as well as on the frequency of stimulation. Above ca. 35 c/s, identical numbers of stimuli were progressively less effective as the frequency of stimulation was increased, and the dependence of the hormone output on the total number of stimuli was less apparent.

3. The amplitude of the compound action potential recorded from the neurohypophysis following electrical stimulation of the stalk was found to decrease as a function of the frequency of stimulation. Stimulation at 50 c/s reduced its amplitude about sevenfold within 30 sec.

4. The addition of tetrodotoxin (TTX) to the incubation media abolished the compound action potential recorded from the neural lobe as well as the release of hormones evoked by electrical stimulation. Resting release, however, was unaffected by TTX.

5. In TTX‐treated neural lobes, excess potassium was still effective in eliciting graded secretory responses. This indicates the independence of the release process from the action potential generating mechanism and suggests that TTX‐paralysed preparations represent a useful model for the study of hormone release in the absence of conducted action potentials.

6. The release of hormones from the neurohypophysis and the release of neurotransmitters at chemical synapses both depend on the entry of calcium into the nerve terminals following their depolarization by invading action potentials. In both systems, experimental separation of the release mechanism can be achieved by the use of TTX. These and other parallels suggest that the release process is similar.
Effects of cold, eating, efferent nerve stimulation and angiotensin on heart rate in sheep before and after autonomic blockade
Authors: Hays F. L. , Webster A. J. F.
Published: December 2014

1. Effects of the natural stimuli of cold exposure and feeding on heart rate were tested in conscious sheep in which blockade of the cardiac efferent nerves was achieved by administration of propranolol and atropine. Effects of direct nerve stimulation, isoproterenol and angiotensin on heart rate before and after autonomic blockade were studied in acute preparations anaesthetized with pentobarbitone sodium.

2. Propranolol reduced the extent of cardioacceleration induced both by exposure to cold and by eating. Heart rate in propranolol treated animals exposed to cold did not exceed about 120 beats/min. During eating, heart rate in propranolol treated animals showed no upper limit and increased on occasions to over 170 beats/min.

3. Heart rate in conscious sheep following administration of atropine and propranolol was about 110 beats/min; in anaesthetized sheep following vagal section and propranolol it was usually about 120 beats/min. This was taken as intrinsic heart rate.

4. Angiotensin administered to normal anaesthetized sheep usually reduced heart rate. After vagal section and propranolol, angiotensin injection usually, and angiotensin infusion invariably, increased heart rate.

5. It was concluded that there exists in sheep a mechanism which during eating elevates heart rate by a means other than through the parasympathetic and sympatho‐adrenal systems. It is suggested that this mechanism involves a direct chronotropic effect of angiotensin secreted in association with eating.
The accumulation of [14C]5‐hydroxyindol‐3‐ylacetic acid by the rabbit choroid plexus in vitro
Authors: Pullar I. A.
Published: December 2014

1. The lateral and fourth ventricular choroid plexuses of the rabbit have been shown to be capable of the in vitro accumulation of 5‐hydroxyindol‐3‐ylacetic acid (5‐HIAA).

2. The accumulation of 5‐HIAA occurs against a concentration gradient and is dependent on metabolic energy.

3. It is possible to inhibit the accumulation of 5‐HIAA by the presence of the dopamine metabolite, 3‐methoxy‐4‐hydroxyphenylacetic acid (HVA) or of probenecid in the incubation medium.

4. It would appear that the characteristics of the accumulation of 5‐HIAA by the isolated choroid plexuses are consistent with the involvement of this tissue in the in vivo active transfer of 5‐HIAA from the c.s.f. to the blood.
A comparison of the spindles in two different muscles of the frog
Authors: Brown M. C.
Published: December 2014

1. The responses of spindles in the iliofibularis muscle of frogs to stretch during either small motor nerve fibre stimulation or the application of suxamethonium were compared.

2. All spindles which were excited by small motor nerve fibre stimulation were also excited by suxamethonium, and their responses to these two methods of excitation were very similar. The drug dose was usually 5‐10 μg/ml. but smaller and larger doses were effective. Large doses (> 100 μg/ml.) could sometimes lead to a reversible partial block of the spindle response to stretch.

3. Suxamethonium also caused a prolonged contraction in extrafusal slow muscle fibres. This contraction was not responsible for the effect on the spindle, because the time course of its action on the muscle tension and on the spindle afferent was different.

4. It was concluded that suxamethonium stimulated prolonged contraction in the small intrafusal muscle fibres, which are known to be innervated by the small motor nerve fibres.

5. Only about half of the spindles in the iliofibularis muscle were excited by suxamethonium.

6. In the sartorius muscle which has no slow extrafusal muscle fibres, no spindles were found to be excited by suxamethonium in the way characteristic of that due to small intrafusal muscle fibre contraction.

7. It is concluded that, in frog muscles which have no slow extrafusal fibres, the muscle spindles do not have small intrafusal muscle fibres of the kind found in the iliofibularis muscle.
The responses of chemoreceptors at reduced temperatures
Authors: Paintal A. S.
Published: December 2014

1. The responses of aortic chemoreceptors and pulmonary stretch receptors of cats were studied by recording impulses in individual fibres at normal body temperatures and thereafter at various temperatures down to 24–26° C while cooling the cat with ice.

2. Reduction of metabolism by lowering the temperature did not obviously slow the PO2 sensing mechanism of chemoreceptors but it greatly slowed the development of excitation after circulatory arrest. It also greatly reduced the excitatory effect of hypoxia.

3. The Q10 for the frequency of discharge of chemoreceptors (during maximal activity) was estimated by comparing the activity of the endings at normal body temperature after circulatory arrest (i.e. at a local PO2 of 0 mm Hg) with similar activity at reduced body temperatures. This averaged 2·5 in nine endings. The Q10 for the peak frequency of discharge also averaged 2·5 in seven endings. These values are similar to those of some mechano‐receptors.

4. Apart from the reduction in the frequency of discharge (Q10 = 2·6) lowering the temperature did not alter the stimulus—response relationship of pulmonary stretch receptors.

5. The poor responses to ACh at lower temperatures indicate that ACh is not likely to be a transmitter at chemoreceptors.
The volume of the T‐system and its association with the sarcoplasmic reticulum in slow muscle fibres of the frog
Authors: Flitney F. W.
Published: December 2014

1. A study has been made of the T‐system and sarcoplasmic reticulum (SR) in slow muscle fibres of the frog, Rana temporaria.

2. The size of the T‐system was measured by an autoradiographic method, using tritium‐labelled albumin as a marker. Its volume, expressed as a fraction of that of the fibre, was found to be 1·8 × 10−3, as compared with a figure of 3·9 × 10−3 for the T‐system in a twitch fibre.

3. The spatial distribution of the T‐tubules, and their association with the SR, was studied with the electron microscope, employing ferritin and the enzyme peroxidase as markers. The observations show (a) the tubules form a three dimensional, rather than transverse, network and (b) the area of triadic (and diadic) contact with the SR is 5‐10 × smaller than in a twitch fibre.

4. The possibility that the T‐system and SR of the slow fibre participate in linking membrane excitation with contraction is discussed in the light of these findings.
Membrane potential of smooth muscle cells in K‐free solution
Authors: Casteels R. , Droogmans G. , Hendrickx H.
Published: December 2014

1. The changes of the ion content, the membrane potential and of the membrane permeability of taenia coli cells have been studied during exposure to K‐free solutions. The relative value of the total membrane conductance was determined by measuring the electrotonic potential during constant current pulses with an intracellular electrode. The PK values were calculated from 42K‐efflux in K‐free solutions.

2. In solutions containing penetrating anions the cells initially depolarize. Thereafter they hyperpolarize to about − 85 mV and again depolarize after 90 min to − 5 mV. These potential changes are much smaller if large anions are used as chloride substitutes. Moreover, the final depolarization is only reached after 4‐5 hr. This hyperpolarization is not inhibited by 10−5
M ouabain.

3. These potential changes are accompanied by a progressive exchange of intracellular K by Na. In solutions containing chloride or nitrate the relative value of the total membrane conductance increases to a maximal value, corresponding to the peak value of the calculated PK. Such changes of the membrane conductance and of PK do not occur in K‐free solutions containing large anions.

4. It is proposed that the initial depolarization is probably caused by an inhibition of an electrogenic Na pump. In chloride or nitrate solution the hyperpolarization is due to an increase of the [K]i/[K]o ratio and to an increase of the K permeability. In the presence of large anions the hyperpolarization remains small because this increase of PK does not occur.
Variation in the permeability properties of the inhibitory post‐synaptic membrane of the crayfish neuromuscular junction when activated by different concentrations of GABA
Authors: Takeuchi A. , Takeuchi Noriko
Published: December 2014

1. The membrane conductance of the crayfish muscle was measured with intracellular micro‐electrodes. Increase in the membrane conductance induced by various concentrations of γ‐amino butyric acid (GABA) was measured in the Br−, NO3−, I− and CNS− solutions and compared with that in Cl− solution. When the membrane was activated by lower concentrations of GABA, the resulting membrane conductance in NO3− and I− solutions was larger than in Cl− solution, while the membrane conductance activated by higher concentrations in NO3− and I− solutions were smaller than in Cl− solution. The membrane conductance activated by GABA was larger in Br− solution and smaller in CNS− solution than the membrane conductance activated in Cl− solution, throughout the concentration range of GABA examined.

2. The reversal potential of inhibitory junctional potentials (i.j.p.s) was measured shortly after replacing Cl− by foreign anions: Br−, NO3−, I− and CNS−. In I− solution the i.j.p.s produced by lower stimulation frequencies showed a reversal potential at a more hyperpolarized level than those produced by higher stimulation rates.

3. Shortly after replacing Cl− by I−, the GABA potential induced by iontophoretic application showed a triphasic potential change at the ‘reversal’ potential. The reversal level of the GABA potential produced by smaller doses was at a more hyperpolarized level than that produced by larger doses.

4. Possibilities of a concentration effect of GABA are discussed. It is suggested that the relative permeability of the crayfish inhibitory membrane to anions changes depending on the concentration of GABA.
Changes in body temperature of the unanaesthetized monkey produced by sodium and calcium ions perfused through the cerebral ventricles
Authors: Myers R. D. , Veale W. L. , Yaksh T. L.
Published: December 2014

1. In the unanaesthetized Rhesus monkey, solutions containing sodium, calcium, potassium or magnesium in excess of the normal concentration of extracellular fluid were perfused from a lateral to the fourth ventricle through chronically implanted cannulae.

2. Sodium (11·0–88·0 m
M in excess of the physiological concentration) perfused through the ventricles, caused an immediate rise in body temperature which was accompanied by vasoconstriction, piloerection and shivering. The latency of the hyperthermia was related directly to the rate of perfusion and the concentration of sodium, whereas the magnitude of the response depended upon the concentration only. When the perfusion was terminated, shivering ceased and the temperature of the monkey returned to the base line level.

3. When calcium ions were perfused in concentrations 2·5–47·9 m
M in excess of that of extracellular fluid, a fall in the temperature of the animal occurred. The magnitude of the decreases depended upon the concentration of calcium in the perfusion fluid. Vasodilatation, sedation and a reduction in withdrawal reflexes accompanied the calcium‐induced hypothermia. After the perfusion ended, the temperature continued to fall until the monkey began to shiver and vasoconstriction was observed in many skin areas.

4. The perfusion through the cerebral ventricles with modified Krebs solution alone or with the Krebs solution which contained potassium or magnesium ions in concentrations five to ten times normal had virtually no effect on the temperature of the monkey.

5. Since the temperature of the monkey was unchanged as long as the physiological ratio of sodium to calcium in the perfusion fluid remained constant, we conclude that the balance between these two essential cations within the brain stem could determine the neural mechanism whereby the set‐point for body temperature of the primate is established.
Rectification in instantaneous potassium current—voltage relations in Myxicola giant axons
Authors: Binstock L. , Goldman L.
Published: December 2014

1. Measurements of the instantaneous K current, under voltage clamp, were obtained using paired de‐ and hyperpolarizing clamp pulse sequences. The instantaneous potassium current—voltage relations so obtained showed constant field type rectification.

2. The zero current potential of the instantaneous K current—voltage relation, when examined as a function of the K concentration, [K]o, behaved like a Nernst concentration cell potential for K. It was concluded that during the generation of the delayed current, the membrane shows substantial selectivity for K.

3. The equivalent of the ‘Frankenhaeuser—Hodgkin space’ in Myxicola was found to be more difficult to load with K ions than in squid. The thickness of the space may be taken as effectively about seven times larger than in squid.

4. Myxicola axons were found to show little or no long time constant delayed current inactivation as has been described for squid.

5. In high [K]o a negative steady‐state conductance was observed which was predictable from the independence principle with a suitable scaling factor.
Human thyroxine‐binding globulin and thyroxine‐binding pre‐albumin: dissociation rates
Authors: Hillier A. P. , Balfour W. E.
Published: December 2014

1. A simple method is described for estimating the rate of thyroxine dissociation from binding sites in plasma.

2. At tracer concentrations in human plasma thyroxine dissociates at two distinct exponential rates. These are due to the two thyroxine‐binding proteins present in human plasma.

3. The t½ for thyroxine dissociation from thyroxine‐binding globulin is 8·1 ± 0·7 (
S.E.) min at room temperature and 38·6 ± 2·1 sec at 37° C.

4. The t½ for thyroxine dissociation from thyroxine‐binding pre‐albumin is 53 ± 5·0 sec at room temperature and 7·9 ± 0·3 sec at 37° C.

5. Dissociation of thyroxine from both proteins is a single exponential process, suggesting that each protein has only one type of specific binding site.

6. These results indicate that the minute pool of free thyroxine in plasma is turning over about 100 times each second, with about two thirds of this flux being due to release and binding of the hormone by pre‐albumin.
Ionic permeability changes induced by some cholinergic agonists on normal and denervated frog muscles
Authors: Feltz Anne , Mallart Alberto
Published: December 2014

1. The reversal potential of responses to iontophoretic application of acetylcholine, carbamylcholine and decamethonium has been measured at junctional and extrajunctional sensitive areas of the normal sartorius muscle of the frog.

2. The values obtained with any one of the drugs at junctional spots were similar to those previously reported for the end‐plate potential (about — 16 mV).

3. On the other hand, at extrajunctional areas the reversal potential of responses to these agonists was found to have a mean value of — 42 mV. The muscle‐tendon responses to acetylcholine reversed at — 51 mV.

4. The response to decamethonium was used to determine the nature of the ionic permeability changes mediated by the extrajunctional receptors. The results obtained show that extrajunctional responses are due to an increase in conductance to Na+ and K+ but not to Cl−.

5. The reversal potential of acetylcholine responses in denervated frog sartorius was — 42 mV both at former junctional spots and at non‐neural sensitized regions.

6. These different values of the reversal potential can be due either to effects of receptor density on the ionic selectivity of the membrane or to regional variations in the extracellular ionic accumulation during the transmitter action.
Ionic effects on spindle adaptation
Authors: Husmark I. , Ottoson D.
Published: December 2014

1. Effects of changes in ionic environment on the receptor potential were studied in isolated frog spindle. Particular attention was focused on the action of potassium removal on the early adaptive decline of the response.

2. Removal of potassium caused a reduction and final disappearance of the dynamic overshoot of the receptor potential. The static phase of the response was also reduced although to less extent. The repolarization phase of the response following release of phasic or maintained stretch was greatly prolonged.

3. Increased potassium concentration caused a reduction of the response, but did not change its general time course. The amount of reduction was related to the potassium concentration.

4. Removal of sodium caused a marked diminution of the response, the static phase being in general more affected than the dynamic phase.

5. It is suggested that the effects of potassium removal are caused by a delay in sodium inactivation and a partial depolarization of the endings. It is concluded that the greater part of the early adaptation of the spindle proper may be attributed to ionic mechanisms in the transducer membrane.
Participation of the anterior hypothalamus in the baroreceptor reflex
Authors: Hilton S. M. , Spyer K. M.
Published: December 2014

1. On the basis of discrete electrical stimulation in the pre‐optic region and anterior hypothalamus of anaesthetized cats, a depressor area has been defined, stimulation of which elicits a fall of arterial blood pressure of 30–50 mm Hg and a bradycardia of some 25%, caused by inhibition of sympathetic vasomotor tone and by vagal activation respectively. These are accompanied by a reduction in rate and depth of respiration.

2. The depressor area, from which this pattern of response is elicited, lies ventral and caudal to the anterior commissure, and extends caudally in the dorsal hypothalamus, dorsal to the fornix.

3. The pattern of response elicited from identified points in the depressor area was shown to be indistinguishable from that to baroreceptor afferent stimulation.

4. A lesion destroying the hypothalamic depressor area bilaterally reduced the response to baroreceptor afferent stimulation. Lesions in the medullary depressor area which spared a large part of the nucleus of the tractus solitarius also reduced, but did not abolish, the baroreceptor reflex response. The two lesions combined abolished the reflex.

5. It is concluded that the whole brain‐stem depressor area, from the hypothalamus through the mid‐brain to the medulla, constitutes a functional unit which integrates the response to baroreceptor afferent stimulation.
Distribution of magnesium in the arterial wall
Authors: Palatý Vladimír
Published: December 2014

1. The Mg, Ca, Na and K content were determined in the rat tail artery in vitro under various experimental conditions.

2. The arterial Mg could be varied selectively at a constant [Mg]o by altering the content of intracellular compounds capable of forming complexes with Mg2+ such as nucleoside‐5′‐triphosphates or citrate.

3. The release of tissue Mg during incubation in Mg‐free solutions was found to consist of a fast and a slow component. The size of the fast component was dependent on the original [Mg]o. The size of the slow component was dependent on the content of intracellular compounds forming complexes with Mg2+. The rate of efflux of the slow component could be increased by increasing [Mg2+]i, by removing external Ca, or by making the artery metabolically inactive.

4. The results seem to indicate that [Mg2+]i in metabolically active vascular smooth muscle cells is maintained at a level of ca. 10−4
M.
Muscle spindle response at the onset of isometric voluntary contractions in man. Time difference between fusimotor and skeletomotor effects
Authors: Vallbo Å. B.
Published: December 2014

1. Impulses in single muscle afferents were recorded from the median nerves of waking human subjects with percutaneously inserted tungsten needle electrodes. During isometric voluntary contractions, unitary discharges were analysed from muscle spindle endings in the wrist and finger flexor muscles and the electromyographic activity from these muscles was recorded simultaneously.

2. When the subject activated the muscle portion in which a spindle was located, the afferent discharge increased in spite of the mechanical unloading effects of the skeletomotor contraction indicating a concomitant fusimotor activation. This was valid for slowly rising contractions as well as small fast rising twitches.

3. The time of onset of spindle acceleration was determined in relation to the time of onset of the electromyographic activity for thirty‐one units studied altogether in more than seven hundred contractions. It was found that spindle acceleration regularly occurred after the onset of the electromyographic activity.

4. There was a considerable variation from one test to the other, for the individual units, with regard to the exact time of onset of spindle acceleration, although spindle acceleration occurred mostly within 0·5 sec after the onset of the electromyographic activity in sustained contractions and within 0·1 sec in small fast rising twitches. It was not possible to assess to what extent this variation was accounted for by variations in the mechanical unloading effects of the skeletomotor contraction or variations in the timing of the fusimotor outflow.

5. For many units, spindle acceleration did not occur until 10–50 msec after the onset of the skeletomotor contraction. This time is of the same order of magnitude as the time difference in latency from the spinal cord to the recording points in the two systems, as estimated from reasonable assumptions.

6. It was concluded that the fusimotor system does not participate in the initiation of voluntary contractions in man, but that the skeletomotor activity is initiated by descending impulses from supraspinal structures and their effects on the neuronal organization within the spinal cord.

7. The fact that fusimotor activation occurs also in very small and short lasting twitches, when spindle acceleration must have a negligible influence on the skeletomotor outflow, suggests that the fusimotor and the skeletomotor systems are rigidly co‐activated in voluntary contractions.

8. The finding that spindle acceleration does not occur until 10–50 msec after the onset of the electromyographic activity suggests that there is an approximately simultaneous onset of the fusimotor and the skeletomotor outflows from the spinal cord.
Sodium and rubidium fluxes in rat red blood cells
Authors: Beaugé L. A. , Ortíz Olga
Published: December 2014

1. The Na content of rat red cells was found to be 4·40 m‐mole/l. cells. When incubated in K(Rb)‐free Na this value was doubled in 1 hr, whereas in K(Rb)‐free choline it was reduced to about 35% in the same period of time.

2. In cells with elevated Na (13·70 m‐mole/l.) the activation curve of Rb influx by external Rb reached the same Vmax in sodium as in choline. The shape of the curve was sigmoid in the first case (Km about 1·05 m
M) and hyperbolic in the second (Km about 0·20 m
M).

3. The activation curve of rubidium influx by internal sodium was linear at least up to 12 m‐mole/l. cells with a slope of 0·84. From this concentration it could increase more steeply, though the data is insufficient to assure it.

4. In normal cells the efflux of Na in K(Rb)‐free Na Ringer was 5·64 m‐mole/l. cells. hr, and it was reduced to 4·32 m‐mole by 10−4
M ouabain. This was accompanied by a reduction of Na influx by 4·14 m‐mole, representing then a Na‐Na ouabain‐sensitive exchange mechanism.

5. At a concentration of 5 m
M, external Rb increased Na efflux in 2·32 m‐mole/l. cells. hr above the K(Rb)‐free levels, and reduced Na influx by 2·13 m‐mole.

6. It is proposed that the Na pump is able to operate even in the absence of external K(Rb), though at reduced rate and on a Na‐Na exchange basis (Na is the only monovalent cation in the bathing solution). External K(Rb) would have two actions: to increase the rate of shuttling of the carrier (catalytic effect) and to switch the Na‐Na to a Na‐K(Rb) exchange.

7. These results raise a question of the real significance of the Na/K(Rb) ‘coupling’ ratio and the K‐free effect on the Na pump mechanism.
Changes in the physiology and fine structure of the taenia of the guinea‐pig caecum following transplantation into the anterior eye chamber
Authors: Burnstock G. , Gannon B. J. , Malmfors T. , Rogers D. C.
Published: December 2014

1. The taenia of the guinea‐pig caecum has been used as a model to study the re‐establishment of autonomic innervation following transplantation into the anterior eye chamber. The ultrastructure, the histochemical localization of noradrenaline and acetylcholinesterase and the pharmacology of transmission to the taenia have been examined 1 day to 16 weeks following transplantation. Both ganglion‐free strips of the taenia and caecal wall segments including the underlying Auerbach's plexus were used.

2. Caecal wall preparations: nerve fibres from intramural ganglion cells retracted during the first 2 days following transplantation, but reappeared in the muscle soon afterwards. Adrenergic nerves from the iris formed terminals about ganglion cells at about 2‐4 weeks. Both cholinergic excitatory and non‐adrenergic (‘purinergic’) inhibitory transmission to the muscle was re‐established by 2‐4 days following transplantation.

3. Taenia strip preparations: both adrenergic and cholinergic nerve fibres were demonstrated histochemically in muscle bundles by 2‐4 weeks. Non‐adrenergic inhibitory and cholinergic transmission was not re‐established until 2‐4 weeks following transplantation. There was an abnormally dense re‐innervation of the muscle by adrenergic nerve fibres by about 8 weeks which is compared with the innervation of aganglionic bowel in Hirschsprung's disease.

4. The origin of non‐adrenergic inhibitory responses in the transplanted taenia is discussed and the results considered in relation to the re‐innervation of transplants of the vas deferens and of intestine during early development.
Excitation—contraction coupling in frog ventricle: evidence from voltage clamp studies
Authors: Morad M. , Orkand R. K.
Published: December 2014

1. Membrane potential, tension and membrane current were simultaneously recorded from frog ventricular strips in a modified sucrose‐gap which enabled control of membrane potential by voltage clamp.

2. Shortening the frog ventricular action potential by repolarizing the membrane to the resting potential terminates contraction.

3. Depolarization to the level of the normal action potential plateau for longer than about 80–100 msec (up to 30 sec) produces and maintains tension for the duration of the depolarization.

4. Depolarizations less than about 80 msec in duration generate no tension but can facilitate the tension response to subsequent depolarizations. The facilitating effect of a short depolarizing pulse persists for no longer than 0·5 sec.

5. The mechanical threshold is about −50 mV; the relation between membrane potential and tension is fairly linear from about +5 to +80 mV.

6. Variation of holding potential, below the mechanical threshold, has no effect on the tension—voltage relation. The absolute membrane potential rather than pulse amplitude determines the developed tension.

7. Increasing external calcium increases the slope of the voltage—tension relation.

8. Contraction of the frog ventricle is directly controlled by the electrical activity of the surface membrane.
Excitatory input from the distal colon to the inferior mesenteric ganglion in the guinea‐pig
Authors: Crowcroft P. J. , Holman Mollie E. , Szurszewski J. H.
Published: December 2014

1. Intracellular recordings were obtained from ganglion cells in the guinea‐pig inferior mesenteric ganglion (IMG) with a segment of the distal colon attached to the lumbar colonic nerves.

2. Continuous electrical activity consisting of excitatory synaptic potentials and action potentials was recorded from ganglion cells in all regions of the IMG.

3. The ‘spontaneous’ synaptic potentials were indistinguishable from those elicited by submaximal stimulation of any of the nerve trunks connected to the IMG.

4. The excitatory activity was irreversibly abolished when the lumbar colonic nerves were cut and reversibly abolished when tetrodotoxin (5 × 10−7 g/ml.) was added to the colon side of a two‐compartment organ bath.

5. Addition of dihydro‐β‐erythroidine (5 × 10−6 g/ml.) to the ganglion side of the bath abolished the synaptic activity of colonic origin and the synaptic responses to stimulation of any of the nerve trunks connected to the IMG.

6. Addition of dihydro‐β‐erythroidine (1 × 10−5 g/ml.) to the colon side of the bath markedly depressed the synaptic input of colonic origin but had no effect on synaptic responses produced by preganglionic nerve stimulation.

7. Distension of the colonic segment and the application of 5‐HT (1 × 10−5 g/ml.) to the mucosal surface of the colon increased the frequency of synaptic input.

8. The synaptic input from the colon was transiently blocked following repetitive stimulation of any of the nerve trunks connected to the IMG. The discharge of miniature synaptic potentials was unaffected.

9. Addition of noradrenaline (1 × 10−7 to 1 × 10−6 g/ml.) to the colon side of the bath reduced, and in some cases completely abolished, the synaptic input to the IMG. Phentolamine (1 × 10−6 g/ml.), when added to the colon side of the bath, blocked the effect of noradrenaline and the transient inhibition following repetitive nerve stimulation.

10. Addition of noradrenaline (1 × 10−4 g/ml.) to the ganglion side of the bath reduced but never abolished the amplitude of the synaptic potentials of colonic origin.

11. It was concluded that in the guinea‐pig, the IMG is involved in a peripheral reflex whose afferent limit of this reflex consists of the axons of cholinergic neurones within the wall of the colon. Many of these neurones are driven either directly or indirectly by cholinergic synapses. The efferent noradrenergic neurones of the IMG function as a group of inhibitory neurones which depress the activity of the excitatory neurones of the colon which are driving them.
Splanchnic nerve inhibition of gastric acid secretion and mucosal blood flow in anaesthetized cats
Authors: Reed J. D. , Sanders D. J.
Published: December 2014

1. Efferent electrical splanchnic nerve stimulation will significantly inhibit gastric acid secretion and mucosal blood flow (MBF) stimulated by either large
I.V. doses of pentapeptide or histamine, if the rise in blood pressure is prevented.

2. Splanchnic stimulation will also reduce the increase in MBF in response to infusions of isopropylnoradrenaline, if the blood pressure rise is prevented.

3. Evidence is presented which suggests that the splanchnic nerve inhibitory effect is not due to reducing the amount of stimulant arriving at the gastric mucosa.

4. By analysing the responses to histamine, when acid secretion is accompanied by a large MBF relative to the pentapeptide responses, it is suggested that the inhibitory effect of splanchnic nerve stimulation is due to vasoconstriction.

5. It remains possible that there is a direct inhibitory effect on the parietal cells.
Peristalsis in the rabbit distal colon
Authors: Mackenna B. R. , McKirdy H. C.
Published: December 2014

1. The motility of the distal colon of the rabbit has been examined by the conventional Trendelenburg method and by an isometric, isovolumic modification of this method.

2. The colon shows a range of movements, and tetrodotoxin and cold‐storage have been used in an attempt to differentiate between myogenic and neurally integrated activities.

3. The observable myogenic movements are pendulum movements, ‘tone rings’ and ‘tone waves’; the last of these can be weakly propulsive. The rabbit colon also shows a neurally organized and powerfully propulsive movement which corresponds to the peristaltic wave.

4. The implication of a role for nervous structures in the propulsive activity of the rabbit distal colon is at variance with the view of Lee (1960).

5. The myenteric reflex arc in the colon has been examined pharmacologically. Cholinergic neural transmission has been implicated at the ganglionic‐synaptic and neuroeffector junctions, but additional noncholinergic mechanisms of chemical transmission have not been excluded.
Recurrent inhibition of antidromically identified rat supraoptic neurones
Authors: Dreifuss J. J. , Kelly J. S.
Published: December 2014

1. In anaesthetized male rats, the hypothalamus and pituitary stalk were exposed by a transpharyngeal approach. The compound field potential of the supraoptic nucleus evoked by stimulation of the pituitary stalk, was recorded with glass electrodes inserted near the origin of the anterior cerebral artery.

2. The mean latency of 169 antidromically evoked action potentials isolated from the field was 9·9 msec with an extreme range of 6–26 msec. Although the wave form of the antidromic action potential showed a variety of shapes and sizes and the initial wave could be of either polarity, the majority were strikingly similar in form. The initial wave was positive with an inflexion on the rising phase and was followed by a shallow rather longer lasting negative potential.

3. The antidromic nature of the action potential was confirmed when the action potential evoked at constant latency after the stimulus was observed to be cancelled by another occurring spontaneously. Although the antidromic action potentials followed stimulation frequencies greater than 100 Hz, the response to high frequency stimulation was seldom tested since the amplitude of the action potential was greatly reduced at frequencies above 30 Hz if the number of shocks exceeded a critical number, as few as 3‐6 at 100 Hz.

4. Stimulation of the pituitary stalk at intensities below and near threshold for antidromic invasion of the cell under study was shown by means of post‐stimulus time histograms to be associated with an inhibitory period lasting on average 80 msec (
S.D. = 13, N = 30).

5. An increase in the intensity and duration of the inhibitory period occurred as the intensity of the stimulation was increased as might be expected if the response was mediated synaptically. The inhibitory pathway is believed to involve the recurrent collateral axons already demonstrated anatomically since the stimulation intensities necessary to produce either a marked inhibitory response or antidromic invasion of the cell in question are in most instances nearly the same.
Adrenergic re‐innervation of smooth muscle of nictitating membrane by preganglionic sympathetic fibres
Authors: Ceccarelli B. , Clementi F. , Mantegazza P.
Published: December 2014

1. The preganglionic and post‐ganglionic trunks of the cervical sympathetic nerve were joined in an end‐to‐end anastomosis after excision of the superior cervical ganglion in the cat.

2. Seventy‐five days after the anastomosis the diameter of the pupil was nearly normal and there was almost complete recovery of the prolapsed palpebra and of the nictitating membrane. The contraction of the nictitating membrane, induced by electrical stimulation, caudally to the point of anastomosis, showed that the smooth muscle of the nictitating membrane had been re‐innervated.

3. Neither hexamethonium nor nicotine had any marked effect on the contraction of the nictitating membrane. Severing the regenerated nerve trunk produced a degeneration contraction. These results are strong evidence that the denervated membranes were re‐innervated by true cholinergic preganglionic fibres.

4. Our pharmacological studies indicated that in the re‐innervated preparations neuromuscular transmission was adrenergic in the sense that it was blocked by phentolamine and not by atropine. These results were confirmed by the histochemical‐fluorescence studies which showed that the endings of the regenerated axons contained high concentrations of catecholamines.

5. Electron microscopy showed that the regenerated terminals contained none of the small dense‐core vesicles, considered to be typical of adrenergic nerve endings, but contained clear synaptic vesicles and an unusually great number of large granular vesicles.

6. Our results suggest that the denervated nictitating membranes were re‐innervated by cholinergic presynaptic sympathetic fibres that had been modified so that they could release catecholamines in addition to, or instead of, acetylcholine.
The isoenzymes of carbonic anhydrase: kinetic properties with particular reference to the functions in the intestinal tract
Authors: Carter M. J. , Parsons D. S.
Published: December 2014

1. Details are given of an electrometric method for measuring the activity of isoenzymes of carbonic anhydrase (EC 4.2.1.1) in catalysing the hydration of carbon dioxide under different conditions at 0° C. In the method, a measured volume of water saturated with carbon dioxide at a known partial pressure and appropriate temperature is introduced into a buffered solution. Using a sensitive electrometer and recording instrument, the subsequent change in hydrogen ion concentration is recorded as a function of time. Under the conditions of assay, the pH change induced in the presence of substrate is very small (ΔpH < 0·05 units) and the period of observation need not exceed 10 sec.

2. For enzymes isolated from guinea‐pig tissues, it is found that the specific activity of the ‘high activity’ isoenzyme (carbonic anhydrase C, carbonic anhydrase II, HACA) is about eighteen times that of the ‘low activity’ counterpart (carbonic anhydrase B, carbonic anhydrase I, LACA) when measured at 0° C, pH 7·2, and ionic strength 0·19. Under the same conditions, the Km was found to be 10 m
M for the ‘high activity’ isoenzyme and 23 m
M for the ‘low activity’ isoenzyme. No differences were found between the equivalent kinetic parameters of the corresponding isoenzymes isolated from different tissues.

3. The isoenzymes isolated from guinea‐pig tissues are found to be inhibited by acetazolamide in a non‐competitive manner. It is also found that the ‘high activity’ isoenzyme is many times more sensitive to this inhibitor than is the ‘low activity’ isoenzyme. Evidence is presented which indicates that one acetazolamide binding site is present on each molecule of either isoenzyme.

4. While chloride ions specifically inhibit the ‘low activity’ component of guinea‐pig carbonic anhydrase (I0·5 = 40 m
M), acetate, butyrate and pyruvate inhibit both isoenzymes. Under the conditions employed, acetate and pyruvate are more strongly inhibitory to the ‘low activity’ isoenzyme than to the ‘high activity’ isoenzyme, while butyrate is more strongly inhibitory to the ‘high activity’ isoenzyme.

5. The findings are discussed with particular reference to the physiological significance of the presence of the isoenzymes in the gastro‐intestinal tract. Also considered are possible relationships between the distribution of the ‘low activity’ isoenzyme in these tissues and the transport and metabolism of products of fermentation occurring in the intestinal lumen.
A comparison of the behaviour to ions of the P III component of the pigeon cone and rat rod electroretinogram
Authors: Arden G. B. , Ernst W.
Published: December 2014

1. Isolated pigeon and rat retinas were incubated in various media and the effect of changing ions on the P III component of the electroretinogram was studied, with particular regard to the influence of calcium on other ions.

2. In pigeon, without calcium, reduction of sodium and chloride both reduce P III. This behaviour continues in the presence of calcium but only if the retina has been treated with ouabain. Under these conditions, the effect of calcium is to prevent the appearance of inverted responses.

3. Under other conditions, calcium renders the pigeon P III insensitive to change in chloride. Sensitivity is rapidly restored by the use of ouabain, 2,4‐DNP, or by cooling.

4. Calcium does not alter the linear relationship between sodium and response amplitude.

5. In pigeon, increasing potassium increases P III amplitude, though the exact relationship is altered by calcium.

6. In the rat retina treated with ouabain, increasing sodium increases P III, and increasing potassium decreases P III. This result is similar to that of Sillman, Ito & Tomita (1969b). If calcium is absent, inverted P IIIs can be obtained.

7. If calcium is present in the medium, reducing sodium also reduces rat P III.

8. If calcium is reduced below 10−7
M, then reducing sodium increases P III, and large responses are obtainable from solutions which contain almost no ions. These responses vanish very rapidly if the retina is cooled or treated with ouabain.