bluuebunny/crossref_metadata_2025_split huggingface dataset:
Somatic motor axons can innervate autonomic neurones in the frog heart
Authors: Proctor William , Roper Stephen , Taylor Barbara 
Published: December 2014

1. The effects of sympathetic and parasympathetic stimulation on the heart rate in frogs were tested after hearts were reinnervated with a somatic motor nerve. When frogs were vagotomized and hypoglossal axons were redirected to the heart for 8 or more weeks, stimulating the redirected hypoglossus nerve produced a parasympathetic‐like inhibition of the heart. Stimulating sympathetic rami of the anastomosed hypoglossus nerve produced cardiac acceleration.2. Individual parasympathetic neurones received synaptic input from hypoglossal terminals. The excitatory post‐synaptic potentials evoked by hypoglossal stimulation were much smaller than those evoked by vagal stimulation in control or vagal‐reinnervated ganglia. However, hypoglossal axons innervated most (71%) of the ganglion cells and this level of innervation persisted for at least 60 weeks.3. Hypoglossal axons formed networks of varicose terminals within cardiac ganglia and established axo‐axonic synapses with parasympathetic neurones. Hypoglossal terminals did not reinnervate the neuronal perikarya, in contrast to vagal axons in control or vagal‐reinnervated ganglia.4. Axo‐axonic synapses from redirected hypoglossal axons were identified in cardiac ganglia by bathing isolated hearts in horseradish peroxidase (HRP) and stimulating the redirected nerve. Electron micrographs showed that axo‐axonic synapses contained HRP‐labelled presynaptic vesicles.5. The source of foreign innervation in experimental cardiac ganglia was confirmed to be hypoglossal motoneurones (a), by comparing the conduction velocity of the redirected presynaptic axons (1·32 m/sec) with regenerating vagal preganglionic fibres (< 0·3 m/sec), and (b), by retrograde HRP‐labelling of large motoneurones in the hypoglossal nucleus after applying peroxidase to the axons which had grown into the heart.
The role of vagal and intramural inhibitory reflexes in the regulation of intragastric pressure in the ferret
Authors: Andrews P. L. R. , Lawes I. N. C. 
Published: December 2014

1. The step inflation technique combined with nerve section and pharmacological receptor blockade was used to determine the gastric distribution of the vagal inhibitory fibres and their role in the regulation of intragastric pressure in the anaesthetized ferret.2. Under the conditions described the predominant effect of the vagus was inhibitory. The dorsal abdominal vagus mediated more inhibition than the ventral vagal trunk. There was partial overlap in the inhibitory effects of the two trunks but, in contrast to excitatory effects, this overlap was less than complete.3. No evidence was found to indicate that the intramural inhibitory neurones (demonstrated pharmacologically) could be activated by a local distensive stimulus or that local inhibitory reflexes played an independent role in the regulation of intragastric pressure. The vago—vagal inhibitory reflexes play the major (possibly the only) part in the over‐all regulation of intragastric pressure.4. After a step gastric inflation (50 ml. in < 3 sec) the time taken for the intragastric pressure to fall to 1/e of the peak pressure was a function of the number of inflations; the time decreased with increased number of inflations. It was apparently unaffected by nerve lesions.5. The intragastric pressure in response to an inflation, besides being a function of the neural reflexes evoked, was also related to the gastric weight and hence the size of the animal.6. The sum of the prevailing intragastric pressure and the response to vagal stimulation (10 Hz, 10 sec) was similar, irrespective of the intragastric fluid volume (10‐80 ml.).7. The volume of fluid in the corpus was shown to be a major determinant of the contraction produced in response to vagal stimulation: as the corpus volume increased the corpus contraction decreased but the relaxation that follows the contraction increased. A similar effect was observed with intra‐arterial ACh which implies that the response to stimulation was modified directly by the degree of stretch of the smooth muscle cells. Inhibitory effects were not apparent unless the stomach was moderately inflated.8. The relative roles of the vagal reflexes, intramural reflexes and the smooth muscle in the regulation of intragastric pressure are discussed in the light of the above observations.
Mammary development in mice: effects of hemihysterectomy in pregnancy and of litter size post partum
Authors: Knight C. H. , Peaker M. 
Published: December 2014

1. Mice were hemihysterectomized on day 8 of pregnancy to reduce the number of feto‐placental units.2. Fetal mortality was not affected by hemihysterectomy; mean single‐pup weight at birth was increased when compared with sham‐operated controls.3. Pregnant sham‐operated and hemihysterectomized animals were killed on days 13 and 18 of gestation, and their mammary glands were analysed for total DNA (DNAt) and RNA (RNAt). Both were significantly lower in the hemihysterectomized group on day 18, but not on day 13.4 Milk yield was assessed, by daily weighing of the litter, in groups of sham‐operated and hemihysterectomized lactating animals suckling nine pups each. There was no difference in yield between the two groups.5. One group of sham‐operated mice suckling nine pups, one of hemihysterectomized mice suckling nine pups and one of hemihysterectomized mice suckling four pups were killed on day 5 of lactation for mammary gland analysis. There was no significant difference in mammary weight or DNAt between the sham‐operated and hemihysterectomized animals suckling nine pups, although RNAt was still reduced in the latter. Mammary weight, DNAt and RNAt were all significantly lower in the hemihysterectomized group suckling four pups than in either of the other two groups.6. It is concluded that the less well developed mammary glands of mice which give birth to small litters are capable of compensatory growth during the first few days of lactation if a sufficiently strong suckling stimulus is given.7. It is suggested that control of mammary development by the fetus during gestation and by the suckling young during early lactation are both mechanisms designed to ensure that milk yield is appropriate to the needs of the young.
Variations in the time course of the synchronization of intercostal motoneurones in the cat
Authors: Kirkwood P. A. , Sears T. A. , Tuck D. L. , Westgaard R. H. 
Published: December 2014

1. Synchronization of intercostal motoneurones was studied by the construction of cross‐correlation histograms which related the firing times of paired groups of efferent inspiratory or expiratory discharges recorded from filaments of the external or internal nerves of anaesthetized or decerebrate cats.2. The principal feature of the histograms was always a central peak but the time course of the central peak showed considerable variation. Three forms of synchronization were defined on the basis of the time course of the central peak: (i) short‐term synchronization (Sears & Stagg, 1976), where the peak was narrow, extending over about ±3 ms but sometimes with weak shoulders to about ±5 ms; (ii) broad‐peak synchronization where the peak was wider than this (often ±20 ms or more) but where there were no strong periodicities; (iii) high‐frequency oscillation (h.f.o) synchronization, which was named from the related phenomena in medullary and phrenic recordings (Cohen, 1979), where there were periodic peaks on either side of the central peak with a frequency in the range 60‐120 Hz. Combinations of these forms of synchronization were seen in some histograms.3. When different animals were compared, broad peak synchronization was seen in association with light anaesthesia and with polysynaptic excitation of the motoneurones from muscle spindle afferents.4. In individual animals, additional anaesthesia depressed both broad peak and h.f.o. synchronization.5. Raising PA, CO2, which increased the respiratory drive to the motoneurones, favoured short‐term or h.f.o. synchronization at the expense of broad‐peak synchronization.6. In three decerebrate animals only short‐term or h.f.o. synchronization was seen.7. Spinal cord lesions above or below the segments of interest promoted broad‐peak synchronization, even with high PA, CO2 or deep anaesthesia.8. We conclude: (i) that short‐term synchronization, due mainly to the branching of presynaptic axons, is generated mainly by those axons which transmit the respiratory drive, that drive providing most of the excitation of the motoneurones in moderately deep anaesthesia; (ii) that h.f.o. synchronization arises from the periodic synchronization of the discharges in these same presynaptic axons; (iii) that broad‐peak synchronization is generated by the activity of other presynaptic neurones whose discharges are also synchronized, but aperiodically, these neurones most likely including spinal cord interneurones which are active in light anaesthesia or when released by spinal cord lesions.9. These conclusions are supported by comparisons between intracellular recordings from inspiratory motoneurones in animals showing different forms of motoneurone synchronization, the comparison including the measurements of ‘average common excitation’ (a.c.e.) potentials (Kirkwood & Sears, 1978).
The properties of single cones isolated from the tiger salamander retina
Authors: Attwell David , Werblin Frank S. , Wilson Martin 
Published: December 2014

1. The properties of isolated single cones were studied using the voltage‐clamp technique, with two micro‐electrodes inserted under visual control.2. Single cones had input resistances, when impaled with two electrodes, of up to 270 MΩ. This is probably lower than the true membrane resistance, because of damage by the impaling electrodes. The cone capacitance was about 85 pF.3. The cone membrane contains a time‐dependent current, IB, controlled by voltage, and a separate photosensitive current.4. The gated current, IB, is an inward current with a reversal potential around ‐25 mV. It is activated by hyperpolarization over the range ‐30 to ‐80 mV, and at constant voltage obeys first order (exponential) kinetics. The gating time constant is typically 50 ms at the resting potential of ‐45 mV, rises to 170 ms at ‐70 mV, and decreases for further hyperpolarization.5. The spectral sensitivity curve of the cone light response peaks at 620 nm wave‐length, and is narrower than the nomogram for vitamin A2‐based pigments. The light responses of isolated cones are spectrally univariant.6. Voltage‐clamped photocurrents were recorded at various membrane potentials, for light steps of various intensities. The photocurrent reversed at around ‐8 mV. The time course of the photocurrent, for a given intensity, was approximately independent of voltage (although its magnitude was voltage‐dependent). The shape of the peak current—voltage relation of the light‐sensitive current was independent of light intensity (although its magnitude was intensity‐dependent).7. These results can be explained if: (a) light simply changes the number of photosensitive channels open, without altering the properties of an open channel; (b) the reactions controlling the production of internal transmitter, the binding of internal transmitter to the photosensitive channels, and the closing and opening of the channels are unaffected by the electric field in the cone membrane, even though at least some of these reactions take place in the membrane.8. IB plays only a small role in shaping the cone voltage response to light.
The role of spinal cord transmission in the ventilatory response to electrically induced exercise in the anaesthetized dog
Authors: Cross Brenda A. , Davey A. , Guz A. , Katona P. G. , Maclean M. , Murphy K. , Semple S. J. G. , Stidwill R. 
Published: December 2014

1. The ventilatory response to electrically induced ‘exercise’ was studied in six chloralose‐anaesthetized dogs. The on‐transient and steady‐state responses to ‘exercise’ were compared in the same dogs before and after spinal cord transection at T8/9 (dermatome level T6/7) on fifteen occasions.2. Phasic hind limb ‘exercise’ was induced for periods of 4 min by passing current (2 Hz modulated 50 Hz sine wave) between two needles inserted through the hamstring muscles. The maximum current used was 30 mA. This was below the level previously found to produce an artifactual stimulation of breathing with the cord intact.3. Cord transection produced no significant change in either the resting values of ventilation (V̇I) and CO2 production (V̇CO2) or the ventilatory equivalent for CO2 during ‘exercise’ (△ V̇I/ △ V̇CO2).4. During the steady state of exercise Pa, CO2 was on average significantly lower than at rest with the cord intact (mean △Pa, CO2, ‐ 2·1 mmHg; range ‐ 5·7 to + 1), and higher, though not significantly, with the cord cut (mean Pa, CO2, + 1·2 mmHg; range ‐ 1·5 to + 4·3). However, even in the absence of spinal cord transmission, the ventilatory response to exercise could not be accounted for on the basis of CO2 sensitivity; the △ V̇I/ △Pa,CO2 obtained with exercise (apparent sensitivity) was significantly greater than that obtained with CO2 inhalation (true sensitivity) both before and after cord section.5. V̇I and V̇CO2 increased more slowly with the cord cut than with the cord intact. This was thought to be due to a slower increase in venous return in the absence of sympathetic innervation of the lower half of the body following cord transection.6. Similar experiments were performed during muscle paralysis (following gallamine triethiodide). Ventilation was maintained with a respirator controlled by phrenic nerve activity. These experiments showed an increase in ventilation, independent of muscle contraction, which was only present when the cord was intact and which was confined to the on‐transient. Only in the absence of spinal cord transmission could there be certainty that the dynamics of the ventilatory response to electrically induced ‘exercise’ was free of artifact.7. It was concluded that spinal cord transmission is not necessary for the steady‐state ventilatory response to electrically induced exercise of the hind limbs.8. The dog with spinal cord transection provides a suitable model for the study of the chemical control of breathing during electrically induced exercise.
Micropuncture study of changes in glomerular filtration and ion and water handling by the rat kidney during pregnancy
Authors: Garland H. O. , Green R. 
Published: December 2014

1. In rats receiving 200 μl. min−1 sodium chloride, glomerular filtration rate, single nephron glomerular filtration rate, and fractional reabsorption were measured at various points along the nephron, and ionic concentrations measured in early distal tubular fluid in virgin and 6, 12 and 19 day pregnant rats.2. Glomerular filtration increased progressively until the twelfth day of pregnancy. At 19 days of pregnancy the glomerular filtration rate, while still above virgin levels, was reduced below 12 day pregnant levels.3. Single nephron glomerular filtration rates measured in proximal and distal tubules were different at both 12 and 19 days of pregnancy, indicating an alteration of tubuloglomerular feed‐back.4. A change in the ratio of glomerular filtration rate: distal single nephron filtration rate indicated a redistribution of glomerular filtrate to juxtamedullary nephrons by the sixth day of pregnancy.5. Fluid reabsorption is similar up to the early distal tubule but it is not possible to say whether reabsorption is the same in proximal tubules. More fluid is reabsorbed by late distal tubules and collecting ducts in 12 and 19 day pregnant animals than in the virgin and 6 day pregnant animals.6. Changes in ion reabsorption by the loop of Henle occurred during pregnancy; sodium reabsorption was increased by the sixth day of pregnancy and potassium reabsorption by the twelfth day.
Calcium‐ and length‐dependent force production in rat ventricular muscle
Authors: Hibberd M. G. , Jewell B. R. 
Published: December 2014

1. Trabeculae from the right ventricles of rat hearts were ‘skinned’ by immersion for 30 min in a solution containing the non‐ionic detergent Brij‐58 at a concentration of 1%.2. The average sarcomere length in the central region of the relaxed preparation was estimated by laser diffraction and set at pre‐determined values within the range of 1·9‐2·4 μm by adjustment of muscle length. Isometric contractions were then induced by raising the Ca2+ concentration under carefully controlled chemical conditions.3. The dependence of Ca2+‐activated force production on sarcomere length over the ascending limb of the length—force relation was examined at Ca2+ concentrations giving partial and full activation of the contractile system of the muscle.4. The dependence of Ca2+‐activated force on Ca2+ concentration was compared at sarcomere lengths on the ascending limb and plateau of the length—force relation.5. The results obtained from both kinds of experiment showed that the sensitivity of the contractile system to Ca2+ increases with sarcomere length over the ascending limb of the length—force relation.6. Possible explanations for this observation have been discussed.
The electrogenic sodium—potassium pump of mouse pancreatic B‐cells
Authors: Henquin J. C. , Meissner H. P. 
Published: December 2014

1. The contribution of the sodium pump to the membrane potential of mouse pancreatic B‐cells was studied with micro‐electrodes.2. In 0 or 3 mM‐glucose, ouabain rapidly (within 2 min) depolarized the B‐cell membrane by an average of 7 mV, whereas K omission hyperpolarized it markedly.3. In 6 or 7 mM‐glucose, ouabain still produced depolarization, but K omission had no consistent effect. Both induced electrical activity in certain cells.4. In 10 mM‐glucose, withdrawal of ouabain or K re‐introduction caused a transient hyperpolarization with suppression of electrical activity. Duration and amplitude of the hyperpolarization increased with the time of pump blockade and with the concentration of ouabain.5. The hyperpolarization following K re‐admission was abolished by ouabain and that following ouabain withdrawal was prevented by K omission. Re‐admission of various K concentrations showed that the hyperpolarization was not due to depletion of K just outside of the membrane.6. In 10 mM‐glucose, the membrane potential of B‐cells exhibited repetitive slow waves with bursts of spikes on the plateau. These electrical events were modified by ouabain in a dose‐dependent manner. The frequency of the slow waves augmented markedly because of an increase in the slope of the pre‐potential and a shortening of the intervals; the slope of their repolarization phase decreased, but their duration was not changed.7. Omission of K increased the slope of the pre‐potential and the frequency of the slow waves. It also accelerated their repolarization phase and reduced their duration, likely because of the increase in driving force for K efflux. Increasing K concentration to 8 mM slowed the repolarization phase and lengthened the slow waves without changing their frequency.8. Even when K permeability of the B‐cell membrane was increased by high extracellular Ca, ouabain and K omission augmented the frequency of the slow waves.9. In 0 or 10 mM‐glucose, ouabain increased 86Rb+ efflux from perifused islets, whereas K omission decreased it. In 10 mM‐glucose, a marked decrease in 86Rb+ efflux accompanied ouabain withdrawal and K re‐introduction. The hyperpolarization is thus not due to an increase in K permeability.10. It is concluded that, in pancreatic B‐cells, the sodium pump is truly electrogenic, contributes to the resting potential and modulates the slow waves of membrane potential induced by glucose. Rapid changes in insulin release occurring upon inhibition or activation of the sodium pump may thus be due to the changes in B‐cell membrane potential.
Visualization of the spread of electrical activity in rat hippocampal slices by voltage‐sensitive optical probes
Authors: Grinvald A. , Manker A. , Segal M. 
Published: December 2014

1. Voltage‐sensitive membrane‐bound dyes and a matrix of 100 photodetectors were used to detect the spread of evoked electrical activity at the CA1 region of rat hippocampus slices. A display processor was designed in order to visualize the spread of electrical activity in slow motion.2. The stimulation of the Schaffer collateral‐commissural path in the stratum radiatum evoked short latency (2‐4 msec) fast optical signals, followed by longer latency (4‐15 msec) slow signals which decayed within 20‐50 msec. Multiple fast signals were frequently detected at the stratum pyramidale; they propagated toward the stratum oriens with an approximate conduction velocity of 0.1 m/sec.3. The fast signals were unaltered in a low Ca2+ high Mg2+ medium but were blocked by tetrodotoxin. These signals probably represent action potentials in the Schaffer collateral axons. Their conduction velocity was about 0.2 m/sec and their refractory period about 3‐4 msec.4. The slow signals were absent in a low Ca2+ medium and probably represent excitatory post‐synaptic potentials (e.p.s.p.s) generated in the apical dendrites of the pyramidal cells. They were generated in the stratum radiatum, where the presynaptic signals were seen, and spread into somata and basal dendrites (the stratum pyramidale and oriens, respectively).5. The timing of the signals with fast rise‐time, which were detected at the statum pyramidale, approximately coincided with the timing of the extracellularly recorded field potentials. These multiple discharges probably represent action potentials of the pyramidal cells. They spread back into the apical dendrites but with significant attenuation of the amplitudes of the high frequency components of the pyramidal action potentials.6. Hyperpolarizing potentials could be detected when strong stimuli were applied to the stratum radiatum or alveus. The net hyperpolarizations were detected only in the stratum pyramidale and the border region between the stratum pyramidale and radiatum. Frequently the inhibition was masked by the large e.p.s.p.s. However, its existence could be demonstrated by treatment of the slice with picrotoxin or a low Cl− medium. Under these conditions a long‐lasting depolarization of the apical dedrites was evoked by the stimulation. This was associated with an increase of the multiple discharges in the stratum pyramidale and oriens.7. These studies illustrate the usefulness of voltage‐sensitive dyes in the analysis of passive and active electrical properties, pharmacological properties and synaptic connexions in mammalian brain slices, at the level both of small neuronal elements (dendrites, axons) and of synchronously active neuronal populations.