bluuebunny/crossref_metadata_2025_split huggingface dataset:
The carotid body in the duck and the consequences of its denervation upon the cardiac responses to immersion
Authors: Jones D. R. , Purves M. J. 
Published: December 2014

1. The anatomy of the carotid body and its afferent nerve supply was studied in the duck and a method of denervating the carotid body which ensures a satisfactory post‐operative course is described.2. The effect of denervating the carotid body upon the cardiac response to immersion of the head in water was studied in ten ducks which at the time of the test were unanaesthetized.3. When the nerves were intact, immersion of the head caused a fall in heart rate after a latent period of between 1 and 9 sec to an average of 24% of the resting rate after 30 sec. Simultaneous measurement of arterial oxygen tension (Pa, O2) in the brachiocephalic artery showed a rapid initial fall during the initial 10 sec from control levels, 93–103 mm Hg, to between 42 and 47 mm Hg, followed by a gradual fall of 3‐5 mm Hg for each subsequent 30 sec period of submergence.4. Following carotid body denervation, the latent period before heart rate started to fall was no different from control but the average fall in heart rate was now to 90% of the resting rate and brachiocephalic Pa. O2 continued to fall steadily during submergence reaching levels of between 10 and 21 mm Hg by the end of the second minute.5. Stimulation of the central end of branches of the IXth (glossopharyngeal) nerve supplying the glottis caused apnoea and bradycardia.6. It is concluded that apnoea and bradycardia during submergence in the duck is initiated reflexly from receptors in the nares, pharynx and glottis but that the profound degree of bradycardia and mechanisms which maintain a relatively high Pa, O2 are regulated by peripheral chemoreceptor activity.
Inotropic changes in the left ventricle: the effect of changes in heart rate, aortic pressure and end‐diastolic pressure
Authors: Furnival C. M. , Linden R. J. , Snow H. M. 
Published: December 2014

1. Under conditions where heart rate, mean aortic pressure and enddiastolic pressure in the left ventricle are held constant, the intravenous infusion of isoprenaline is accompanied by large changes in dP/dt max in the left ventricle.2. Under similar conditions, during stepwise increments in the rate of infusion of isoprenaline the changes in dP/dt max (measured at a constant paced heart rate) were proportional to changes in the free (intrinsic) heart rate. It is concluded that dP/dt max is a quantitative index of inotropic changes in the left ventricle.3. In comparison to dP/dt max, three other variables which have been used to indicate inotropic changes in the heart (peak pressure in the left ventricle, duration of systole and stroke work at constant end‐diastolic pressure), were shown to be unreliable indices of inotropic changes.4. Using dP/dt max to indicate inotropic changes, alteration in the heart rate while mean aortic pressure and end‐diastolic pressure in the left ventricle were held constant, and in mean aortic pressure while heart rate ane end‐diastolic pressure in the left ventricle were held constant, were each shown to be accompanied by small inotropic changes in the heart.5. Under similar conditions, changes in end‐diastolic pressure in the left ventricle alone were not accompanied by inotropic changes as indicated by dP/dt max.
Interaction between heart rate and calcium concentration in the control of contractile strength of the frog heart
Authors: Chapman R. A. , Niedergerke R. 
Published: December 2014

1. The changes in twitch tension during the ascending and descending staircase of the frog heart have been examined under various experimental conditions including the hypodynamic and prehypodynamic state.2. The descending staircase resembles the tension change after reduction of external calcium concentration in showing two consecutive phases, an initial rapid and later slow phase of tension decline.3. The time course of the ascending staircase depends on the condition of the heart; it is slow after, and rapid before, development of the hypodynamic state. It is also rapid when elicited after conditioning periods of increased heart rate.4. The tension transients in response to brief concentration steps of external calcium concentration were examined at various levels of heart rate. The results indicate that at high heart rates the sensitivity of heart cells to external calcium is increased.5. The results are interpreted along the lines of a previous hypothesis relating tension development to the cooperative action of two intracellular calcium compounds. The additional assumption is made that an intermediary exists which facilitates calcium movements in heart cells to an extent depending on the level of heart rate.
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.