bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of stimulus parameters on contractions of isolated frog muscle fibres
Authors: Rüdel R. , Taylor S. R.
Published: December 2014

1. Reversible changes in twitch and tetanus contractions of isolated frog muscle fibres were produced by varying the duration and strength of a transversely applied d.c. stimulus.

2. When the stimulus strength was at least 1·1 times threshold the peak force of the contraction elicited was reduced by stimulus durations longer than 1 msec at 20 °C, and by durations longer than 3 msec at 2‐5 °C.

3. As the strength of a prolonged stimulus was progressively increased to 3 times rheobase or more, peak twitch and tetanus force declined to 40–70% of the amplitude with short (0·2–0·5 msec) stimuli. The time to peak of the twitch was slightly decreased and the first phase of relaxation was accelerated.

4. Cine‐micrography of fibres which were permitted to shorten under a light load revealed that the side of the fibre adjacent to the anode was unactivated under conditions which also reduced peak force output.

5. With stimulus durations longer than 20 msec, peak force, time to peak, and relaxation time increased as the stimulus strength increased from 2·5 to 3 times rheobase. This might have been produced by a cathodal contracture following the action potential.

6. The results are discussed in relation to previous studies of activation in striated muscle.
An electrophysiological study of the innervation of the smooth muscle of the colon
Authors: Furness J. B.
Published: December 2014

1. Micro‐electrodes were used to examine transmission from intrinsic and extrinsic nerves to single cells of the longitudinal and circular muscle coats of colons from guinea‐pigs and rabbits.

2. When intrinsic nerves were stimulated, inhibitory junction potentials (IJPs) were observed in over 90% of the cells of the longitudinal coat and nearly all of the cells of the circular coat. The characteristics of IJPs in the guinea‐pig and rabbit were similar. Facilitation of two or three successive IJP's was sometimes observed. The IJPs were unaffected by guanethedine but were blocked by procaine. IJPs could not be elicited by stimulation of either the pelvic parasympathetic or periarterial sympathetic nerves. In some cells, the IJP was preceded by a brief depolarization, which probably results from the stimulation of excitatory nerves to the same cell.

3. Excitatory junction potentials (EJPs) were observed in about 5% of cells of the longitudinal coat in response to stimulation of the intramural nerves. When the pelvic nerves were stimulated, EJPs were observed in most cells of both the longitudinal and circular muscle coats. The EJP in the guinea‐pig colon was blocked by hyoscine.

4. The interaction of the IJP evoked by intrinsic nerve stimulation and the EJP evoked by pelvic nerve stimulation was examined. When both nerve supplies were stimulated together, only an IJP was observed.

5. The nature of the innervation of the colon and the origin of intrinsic non‐adrenergic inhibitory neurones is discussed.
Ionic, histological and vascular factors in the reaction of the sheep's parotid to high and low mineralocorticoid status
Authors: Blair-West J. R. , Coghlan J. P. , Denton D. A. , Nelson J. , Wright R. D. , Yamauchi A.
Published: December 2014

1. The blood capillaries from the alveolar areas of the sheep's parotid gland drain into a sinusoidal portal venous system which is in close relation to the striated intralobular ducts.

2. The alveoli of the gland are surrounded by a mesh of muscular processes of myoepithelial cells: there are no myoepithelial structures in relation to the ducts.

3. In close relation to the alveoli are nerve fibres, some containing noradrenaline and some with cholinesterase at their cellular contact area. Stimulation of the cervical sympathetic trunk for 1–2 min (or intra‐arterial injection of noradrenaline) causes expulsion from each gland of a regular amount of saliva without changing the long term appearance rate of saliva. Stimulation of the secretomotor nerve (or acetylcholine
I.A.) causes an increase in saliva production.

4. It is proposed that the saliva which appears due to sympathetic stimulation is expelled from the alveoli by contraction of the myoepithelial network and is little changed during its rapid transit through the duct system.

5. The results indicate that the alveolar cells react to increasing aldosterone status by increasing concentration of K+ in alveolar fluid with inverse change of Na+ in alveolar secretion over a wide range of flow rates.

6. No histological evidence of innervation of the intralobular striated ducts by sympathetic or secretomotor nerves was obtained.

7. The secretory ducts appear to be the site of exchange of HCO3− and phosphate, Na+ and K+, and for enrichment of SCN− and I− in the alveolar fluid.

8. During stimulation of the secretomotor nerve supply, the gland, whether in adrenally insufficient or in hyperaldosterone status, shows the initial transient of discharge of K+ into saliva and blood and then maintains K+ intake from plasma as near to output in saliva as does the gland in the replete animal with basal aldosterone status.
Influence of prehydration on the changes in renal tissue composition induced by water diuresis in the rat
Authors: Hai M. A. , Thomas S.
Published: December 2014

1. The composition of renal tissue was determined in rats before and immediately after intravenous infusion of dextrose (2·5 g/100 ml.) in amounts sufficient to administer a positive fluid load of 4% body weight over 2 hr. The rats were classified into three groups, according to the preinfusion urine osmolality: hydropaenia, normal and moderately diuretic (over 2400, 800‐1500 and below 800 μ‐osmoles/g H2O, respectively).

2. In non‐infused rats, the steepness of the corticomedullary osmolal gradient varied, due to differences in both water and solute (sodium and urea) contents, and was related to urinary osmolality. Whereas differences in medullary and papillary solute contents occurred between all three groups, papillary water content was significantly higher only in the moderately diuretic animals.

3. Dextrose infusion caused the induction of water diuresis, the lowest urinary osmolalities being produced in the previously moderately diuretic animals.

4. Dextrose infusion caused a considerable reduction in the steepness of the corticomedullary osmolal gradient in all rats, particularly in the previously hydropaenic animals, due to changes in both solute (sodium and urea) and water contents. Whereas reductions in medullary and papillary solute contents occurred in all three groups, there was no further increase in papillary water content from the already high values seen in the noninfused diuretic animals.

5. Thus, dextrose infusion largely abolished any previous differences in tissue water content, whereas significant, though small, differences in osmolal (particularly urea) content persisted.

6. These data are discussed in terms of changes and differences in endogenous antidiuretic hormone (A.D.H.) release.

7. Changes in the magnitude and direction of the urinary‐papillary urea concentration difference are discussed in terms of passive transport, with probable A.D.H.‐induced changes in nephron urea permeability.
Use of a miniature GM counter and a whole body counter in the study of potassium transport by the colon of normal, sodium‐depleted and adrenalectomized rats in vivo
Authors: Barnaby C. F. , Edmonds C. J.
Published: December 2014

1. A method is described employing a whole‐body counter and a miniature GM counter placed within the lumen of the gut which can be used to study the absorption rates and kinetics of labelled substances in the mucosal epithelium in vivo. The method was applied to the study of K transport by the mucosa of the descending colon of normal, Na‐depleted and adrenalectomized rats.

2. The K influx rate was linearly related to luminal [K] over the range 5–80 m
M. NaCN in the lumen produced a fall of electrical potential difference (p.d.) and of K secretion rate but did not reduce K influx rate. The findings were consistent with passive K influx.

3. The mucosal 42K content reached a steady value after 60–90 min of exposure to 42K in the lumen. The value was similar in normal and adrenalectomized rats but was greater in Na‐depleted rats.

4. After replacement of luminal solution by a non‐radioactive solution the fall of mucosal 42K content could be described, in the majority, by a curve having two exponential components with half‐times of 8–10 and 65–106 min. Approximately half of the 42K outflow passed to the lumen. The rate constants were similar in all groups of rats.

5. The results analysed on the basis of representing the mucosal K as in two compartments, indicated that the observed absorption rate could not be accounted for by transport through these compartments alone and that most of the 42K crossed the mucosa by a fast pathway not detectable by the miniature GM counter. Most of the mucosal K was relatively inaccessible from the lumen.

6. Na depletion raised the transmucosal p.d., increased the K secretion rate and appeared to increase K permeability of the mucosa but the kinetics were unaltered. Accumulation of 42K in the mucosa was greater, suggesting that the permeability of the luminal face had increased. Adrenalectomy produced only one change, namely a reduction of K secretion rate.
The effects of hypophysial portal plasma on the content of immunoreactive growth hormone in the anterior pituitary
Authors: Buse M. G. , Fulmer J. D. , Kansal P. C. , Worthington W. C.
Published: December 2014

1. Blood plasma obtained from the hypophysial portal vessels of rats has been tested in assay animals for effects on the content of growth hormone in the anterior pituitary.

2. Growth hormone was estimated by radioimmuno‐assay at 15 min, 30 min, 1 hr and 2 hr after intracarotid or intravenous infusion of portal plasma. There was a significant increase in growth hormone content at 15 min after infusion, but not at 30 min, 1 hr and 2 hr.

3. Insulin, cold stress, haemorrhage and treatment with growth hormone had no effect on growth hormone content of the pituitary under the conditions of application of these stimuli.

4. Growth hormone was measured in plasma obtained from the pituitary of control and insulin‐treated animals. In control animals the amount of growth hormone in this plasma was higher than in base line samples and in the insulin‐treated animals it was lower than in base line samples. A calculation based on the growth hormone content of blood obtained directly from the pituitary indicates a daily rate of synthesis and release of about 10 μg.

5. The hypothesis that portal plasma stimulated the synthesis of immuno‐assayable growth hormone by the anterior pituitary is considered.

6. Discrepancies between our results using immuno‐assay and those of others using bio‐assay are discussed.
Release of acetylcholine by chick embryo heart before innervation
Authors: Coraboeuf E. , Le Douarin G. , Obrecht‐Coutris G.
Published: December 2014

1. In chick embryo hearts, 3‐day‐old and not yet innervated, repetitive direct stimulation causes a transitory inhibition of the spontaneous rhythm.

2. The degree of post‐stimulation inhibition depends on the frequency and duration of the artificial stimulation and on the concentration of K and Ca ions in the extracellular solution.

3. After treatment with atropine (10−5 g/ml.) post‐stimulation inhibition is no longer observed. The spontaneous rhythm is accelerated by atropine. The findings therefore suggest that an ACh‐like substance is released from the non‐innervated embryonic heart during activity.

4. By use of the dorsal muscle of the leech for biological assay the liberation of an ACh‐like substance from the non‐innervated embryonic heart was confirmed.
Hypothalamic control of adrenaline secretion in response to insufficient glucose
Authors: Himsworth R. L.
Published: December 2014

1. The rise of plasma glucose consequent upon the release of adrenaline following the systemic administration of 3‐O‐methylglucose is prevented by previous infiltration with lignocaine of the lateral hypothalamic area on both sides.

2. The similarity between this effect and that of the same procedure in preventing the hypersecretion of gastric acid in response to the same stimulus, together with the known fact that hypoglycaemia or the systemic administration of some glucose analogues produce both gastric and adrenal medullary hypersecretion, provides strong presumptive evidence that there exists in the lateral hypothalamic area a chemoreceptor which controls the release of adrenaline. The cells of this receptor like those of the chemoreceptor controlling gastric acid secretion, are activated by an insufficiency of metabolizable glucose.
The involvement of the complement system in the pressor response to the injection of Forssman antibody in the guinea‐pig
Authors: Darlow G. , Gough G. F. , Tanalp R.
Published: December 2014

1. When the hind limbs of the guinea‐pig were perfused at constant volume inflow with undiluted pooled blood, an intra‐arterial injection of the Forssman antibody caused a rapid and long‐lasting pressor response.

2. In the whole animal the pressor response was accompanied by a fall in the number of circulating platelets, but perfusion experiments suggest that serotonin was not responsible for the pressor response.

3. When decomplemented serum was perfused through the hind‐limb preparation the Forssman antibody failed to produce a rise in pressure, but a pressor response developed when unheated serum was subsequently introduced. This suggests that the actual combination of antibody with its tissue antigen is not the immediate cause of the pressor reaction.

4. The cause of the pressor response is still unknown but apparently depends on the activation of the complement system. The effectiveness of serum shows that polypeptides split off from fibrinogen are not involved.
Sympathetic denervation of the smooth muscle of the vas deferens
Authors: Birmingham A. T.
Published: December 2014

1. The post‐ganglionic nerve fibres to the vas deferens of the guinea‐pig and rat were interrupted in vivo by stripping one vas deferens of its serous coat; the other vas deferens was left intact as a control.

2. Four to eight days later the stripped vas deferens did not contract in response to electrical transmural stimulation in vitro at 0·1 msec pulse duration. Pulses of 1·0 msec duration produced small contractions which were not abolished by local anaesthetic or adrenergic neurone‐blocking drugs.

3. Log dose—response curves to noradrenaline were, for stripped vasa deferentia, to the left of those for control vasa. The increase in sensitivity to noradrenaline at 8 days was about sixteenfold for rat vasa and about tenfold for guinea‐pig vasa. Tyramine did not contract stripped vasa from guinea‐pigs or rats.

4. The noradrenaline and adrenaline content of guinea‐pig and rat vasa was greatly reduced or abolished 8 days after the stripping operation.

5. Fluorescent nerve terminals were usually absent when transverse sections of stripped vasa were examined by fluorescence microscopy after treatment by the formaldehyde condensation method for demonstrating catecholamines.

6. It is concluded that post‐ganglionic sympathetic denervation is achieved by stripping the vas deferens in vivo of its serous coat and mesenteric attachments.
The effect of diet and acute starvation on the deiodination of thyroxine and triiodothyronine in the thyroidectomized rat
Authors: Nathanielsz P. W.
Published: December 2014

1. General agreement exists that the level of thyroid function is depressed by starvation. The virtually complete cessation of biliary‐faecal thyroxine loss in the starved animal makes the significance of this reduction difficult to assess in physiological terms.

2. Deiodination of [131I]thyroxine was investigated in thyroidectomized rats. Thus central feed‐back effects were eliminated and the changes in peripheral utilization of thyroxine could be observed. The simultaneous use of [125I] sodium iodide permitted changes in renal handling of iodide to be taken into consideration.

3. Rats fed oxoid (Oxo Ltd. diet 41 B) deiodinated a significantly greater proportion of thyroxine in the 24 hr after injection of a tracer dose of [131I]thyroxine than did the starved or glucose‐fed rat. [131I]triiodothyronine was also probably deiodinated at a faster rate in oxoid‐fed rats than in starved or glucose‐fed rats.

4. Thyroxine was deiodinated at a faster rate by starved rats than by rats fed glucose.

5. Thyroxine disappeared significantly faster from the blood in oxoid‐fed than in the starved or glucose‐fed rat. Thyroxine also disappeared faster from the blood in the starved rat than in the glucose‐fed rat over 24 hr.

6. These results are discussed in relation to previous findings of depressed pituitary—thyroid function in starvation.
The effects of distension of the pulmonary vein—atrial junctions upon peripheral vascular resistance
Authors: Carswell F. , Hainsworth R. , Ledsome J. R.
Published: December 2014

1. Small balloons were inserted through the left pulmonary veins so as to lie at the pulmonary vein—left atrial junctions.

2. Distension of the balloons caused a reflex increase in heart rate. The afferent path was in the vagus nerves and the efferent path was in the cardiac sympathetic nerves.

3. Only small and variable changes in vascular resistance in a perfused hind limb accompanied the increase in heart rate when a steady state had been reached.

4. In about half of the experiments a transient vasodilatation was observed in the perfused hind limb, occurring immediately after distension of the pulmonary vein—atrial junctions and lasting about 22 sec.

5. The transient dilatation was due to a decrease in sympathetic vasoconstrictor nervous activity.

6. Stimulation of left atrial receptors causes an increase of sympathetic nervous activity to the heart but does not cause a corresponding increase in sympathetic nervous activity to the hind limbs.
The relation between membrane potential, membrane currents and activation of contraction in ventricular myocardial fibres
Authors: Beeler G. W. , Reuter H.
Published: December 2014

1. Membrane currents and contractile responses have been measured in ventricular myocardial preparations under voltage clamp conditions.

2. In Tyrode solution, steady‐state contraction was obtained only after 5‐8 depolarizations to a given potential level. The threshold of steady‐state tension was identical to the potential where the calcium inward current, ICa, was activated (about −35 mV). Both thresholds were shifted in the same direction along the voltage axis and by the same amount by changing [Ca]o or [Na]o. Maximum tension was obtained at inside positive potentials.

3. The time courses of steady‐state tension and of activation of ICa were different by more than one order of magnitude in Tyrode solution. But in order to achieve any appreciable steady‐state tension, ICa had to flow during several identical depolarizations. Tension decreased again at potentials above ECa. This suggests that calcium inward current must flow in order to fill intracellular calcium stores from which calcium can be released by an unknown mechanism.

4. The ability of a fibre bundle to contract again after a preceding twitch is greatly dependent on the membrane potential between two equal depolarizations. In Tyrode solutions with 1·8 and 7·2 m
M‐CaCl2 half restoration of this ability occurred at −45 ± 3 mV (±
S.E. of mean) and −23 ± 4 mV, respectively.

5. In sodium‐free bathing solutions, steady‐state tension was attained upon the first depolarization provided ICa was activated. Furthermore, at different potentials, the time courses of activation of tension and of activation of ICa were identical, i.e. tension reached its maximum when ICa was fully activated. This suggests that in sodium‐free solutions the flow of calcium ions into the fibre directly activates contraction.
Signals from cones
Authors: Alpern M. , Rushton W. A. H. , Torii S.
Published: December 2014

1. We have studied red and green cones by contrast flash inhibition and found them both to be very similar to rods in their response to flash energy, except that all light quantities must be some 100‐fold greater in cones for the same effect.

2. Using the methods of a previous paper (A.R.T. a) where no backgrounds were employed, we plotted log test flash λ against log surround flash ϕ with criterion that λ should just be detected. The experiment was repeated with a ‘windmill stop’ interposed in the ϕ flash which reduced its area symmetrically to ⅛. From these two curves it is possible to extract the relation between N, the inhibitory signal, and ϕ, the test flash. It isN = ϕ/(ϕ+σ),where σ, the semi‐saturation constant, is about 4·5 log td sec.

3. Using the methods of (A.R.T. b) where backgrounds were studied, we measured the increment threshold for the surround flash ϕ against its background θ using as criterion not that ϕ should just be seen but that it should generate a fixed inhibitory signal N so that the fixed test flash λ could just be seen.

4. This increment threshold curve resembled the Aguilar & Stiles (1954) curve for rods, showed saturation and a complete symmetry about the 45° line through the point with co‐ordinates (log θD, log σ).

5. These results imply that the cone signal N is related to flash ϕ and steady background θ by [Formula: see text], where θD is receptor noise (= eigengrau), and ϕ and θ are expressed in units of quantum catch.

6. The ordinary increment threshold for cones does not show saturation because a steady saturating background bleaches all the pigment away. When the background is presented for only 100 msec with dark pauses between, no great bleaching occurs and saturation is seen.
On the degeneration of rat neuromuscular junctions after nerve section
Authors: Miledi R. , Slater C. R.
Published: December 2014

1. A study was made of functional and structural changes during degeneration of end‐plates in the rat diaphragm after phrenic nerve section at two levels.

2. For 8–10 hr after cutting the nerve in the neck, all end‐plates retain the ability to transmit impulses. During the following 8–10 hr, an increasing number of end‐plates lose this ability so that after a total of about 20 hr, no end‐plates can transmit.

3. Transmission failure occurs abruptly at most end‐plates. This failure is usually accompanied by cessation of spontaneous miniature end‐plate potentials (min.e.p.p.s), though in a few cases min.e.p.p.s persist after junctional transmission has failed. Several degenerating junctions were observed where the frequency of min.e.p.p.s was very low, suggesting an intermediate stage in min.e.p.p. failure.

4. The time of junctional failure depends on the length of the degenerating nerve stump. For each additional centimetre of nerve, failure is delayed about 45 min.

5. Changes in ultrastructure of nerve endings closely parallel those of function. For about 8–12 hr after cutting the nerve, nearly all end‐plates appear normal. During the period when transmission is failing, some end‐plates are clearly undergoing structural break‐down. By the time functional failure is complete, all end‐plates appear grossly abnormal.

6. During degeneration, the contents of the axoplasm undergo disruption and the nerve terminal breaks up into small fragments. In contrast, the Schwann cell appears to become very active and its processes extend into the synaptic cleft to surround fragments of the nerve terminal. Ultimately, the Schwann cell completely replaces the axon at the end‐plate.

7. Increasing the length of the peripheral nerve stump delays the onset of structural break‐down. Disruption of end‐plates near the site of nerve entry into the muscle occurs before those farther away.

8. It is suggested that end‐plate degeneration is triggered by a signal which passes from the site of injury to the nerve terminal. The duration of the period after transection when end‐plates appear to be normal would then reflect the time required for this signal to travel the length of the isolated nerve stump.
Action of kinins on salivary myoepithelial cells
Authors: Emmelin N. , Garrett J. R. , Ohlin P.
Published: December 2014

1. Bradykinin and kallidin were injected close‐arterially into the submaxillary glands of dogs and the effects on the pressure in the salivary ducts were recorded.

2. Both kinins in very low dosage (threshold about 0·001 μg/kg) caused a pressure rise in the salivary duct without eliciting any salivary secretion, indicating that they produced contraction of the salivary myoepithelial cells.

3. This effect was obtained even after administration of atropine, dihydroergotamine and propranolol.
Secretory behaviour and histamine formation in the rat Heidenhain pouch following antrectomy
Authors: Svensson S. E.
Published: December 2014

1. In conscious rats provided with a Heidenhain pouch, the changes in the secretion of acid and pepsin following antrectomy were investigated in the interdigestive state and in response to graded doses of intravenous hog gastrin II and methacholine. The change in mucosal histamine formation (histamine‐forming capacity, HFC, i.e. histidine decarboxylase activity) was determined in the fasting state in the Heidenhain pouch following antrectomy.

2. Antrectomy was followed by a substantial reduction in the interdigestive secretion of acid.

3. Methacholine infusion when the antrum was intact evoked a maximal acid secretory response that exceeded twice the response obtained with gastrin.

4. After resection of the antrum the acid response to graded doses of methacholine and to gastrin at maximal but not at submaximal dose levels was significantly reduced.

5. After antrectomy, threshold or submaximal infusion of gastrin accentuated the acid secretory responses to methacholine, but did not restore the maximal secretory response to methacholine obtained before antrectomy.

6. The changes in pepsin secretion following antrectomy were similar to those in acid secretion but smaller.

7. Mucosal HFC of the pouch was significantly lowered following antrectomy.

8. After antrectomy gastrin failed to accelerate histamine formation in the mucosa in the usual way.
Early facilitation at corticomotoneuronal synapses
Authors: Porter R.
Published: December 2014

1. Corticomotoneuronal EPSPs have been generated in lumbar motoneurones of the monkey by single and paired corticospinal volleys. The facilitation of the second of a pair of EPSPs with respect to the size of the first has been measured.

2. The relationship between the degree of facilitation of the second response and the interval between the two volleys has been studied. Average facilitation of minimal EPSPs was found to be maximal about 2 msec after the arrival of the corticospinal volley and to decay roughly exponentially thereafter with a time constant of about 10 msec.

3. The degree of facilitation varied from one minimal corticomotoneuronal EPSP to another but this facilitation was not statistically correlated with the time course of the individual EPSPs.

4. Significant facilitation (0·4) was still present 10 msec after a corticospinal volley so that this phenomenon could play a part in the initiation of motoneuronal discharge by corticospinal activity at natural frequencies of the order of 100 impulses/sec.
Electron microscopic and electrophysiological studies on the carotid body following intracranial section of the glossopharyngeal nerve
Authors: Biscoe T. J. , Lall A. , Sampson S. R.
Published: December 2014

1. The innervation of carotid body Type I cells has been investigated in seventeen cats. At a sterile operation the glossopharyngeal and vagus nerve roots were cut intracranially on one side.

2. From 1½ to 378 days after the operation the carotid bodies were fixed in situ and prepared for electron microscopy. Nerve endings on Type I cells were found to degenerate with a prolonged time course. In each cat there was a decrease in the number of nerve endings on the operated side as compared with the non‐operated side.

3. Before the carotid bodies were fixed, recordings were made from chemoreceptor, and baroreceptor, afferent fibres in the sinus nerve on the operated side. The chemoreceptors responded in the usual way to changes in arterial O2, CO2 and pH; the injection of cyanide evoked a brisk response.

4. It is concluded that the nerve endings on Type I cells are efferent rather than afferent and the cell bodies of their axons are probably in the brain stem.
Activity patterns in respiratory muscles and in respiratory neurones of the rostral medulla of the cat
Authors: Waldron Ingrid
Published: December 2014

1. In the rostral medulla the activity patterns of respiratory neurones are of two main types: inspiratory and expiratory (Fig. 1). Some expiratory neurones begin activity early enough to fit Cohen & Wang's (1959) category of ‘inspiratory—expiratory’. However, in the rostral medulla, ‘inspiratory—expiratory’ neurones do not constitute a distinct category within the expiratory group, since all intermediate activity patterns are observed. Similarly, no distinct categories of activity patterns can be distinguished within the inspiratory group.

2. Expiratory neurones are rare in the extreme medial and lateral portions of the respiratory regions on each side of the rostral medulla (Fig. 3). Respiratory neurones are not bunched in anatomical clusters within each region, though a medio‐dorsal group of neurones on each side is somewhat anatomically separated from the rest.

3. At any one time there are at the very least 1000 respiratory neurones on each side of the rostral medulla.

4. Many of the patterns of single unit activity recorded in respiratory muscles of the nose, throat and pharynx are different from the patterns of activity typical of respiratory neurones in the medulla near the cranial motor nuclei (Figs. 1 and 4). This suggests that many of the medullary recordings are from cells other than the motor neurones innervating these muscles.
Some factors influencing stimulation‐induced release of potassium from the cat submandibular gland to fluid perfused through the gland
Authors: Petersen O. H.
Published: December 2014

1. The release of K from the cat submandibular gland to the extracellular fluid (ECF) after stimulation with acetylcholine (ACh) and the subsequent uptake of K from the ECF was studied in glands perfused artificially with Locke solutions.

2. The first injection of ACh after shift of the perfusion fluid from control to K‐free Locke solution evoked a normal loss of K and a normal secretion of saliva. The second injection only evoked a small release of K and a reduced secretion.

3. Perfusion with dinitrophenol (DNP) (10−4
M) containing solutions, Na‐free Li Locke solutions and chloride‐free nitrate Locke solutions inhibited salivary secretion and the uptake of K. The first injection of ACh after shift of the perfusion fluid from control to test solution gave a normal K loss, but thereafter the ACh‐induced K‐loss declined.

4. Perfusion with g‐strophanthin (10−5‐10−4
M) always inhibited K uptake whereas K release was not affected primarily. The sensitivity of the secretory mechanism of different glands to strophanthin varied considerably.

5. Perfusion with tetraethylammonium Locke solution inhibited secretion, K uptake and release of K.

6. It is suggested that the release of K from salivary glands to the ECF after stimulation with ACh can be explained by diffusion as a consequence of an enhanced permeability of the cell membranes to K. Concomitantly with the release of K, Na is taken up. It is suggested that the subsequent uptake of K and extrusion of Na is due to active transport processes probably involving a Na—K activated ATP‐ase.
The metabolism of [3H]noradrenaline released by electrical stimulation from the isolated nictitating membrane of the cat and from the vas deferens of the rat
Authors: Langer S. Z.
Published: December 2014

1. The noradrenaline (NA) stores of the isolated medial muscle of the cat's nictitating membrane were labelled with [3H]NA and the tissue was set up in an isolated organ bath for field stimulation. The tritiated NA and its metabolites released spontaneously and by field stimulation were determined by scintillation counting following chromatographic separation.

2. NA represented 11·8 ± 1·0% of the total radioactivity of the spontaneously released tritiated compounds. The rest was accounted for by NA metabolites: (a) normetanephrine (NMN), 35%; (b) 4‐hydroxy‐3‐methoxymandelic acid (VMA), 20%; (c) 3,4‐dihydroxyphenylglycol (DOPEG), 10%; (d) 3,4‐dihydroxymandelic acid (DOMA), 10%; (e) 4‐hydroxy‐3‐methoxyphenylglycol (MOPEG), 14%.

3. Field stimulation at 25 shocks/sec with supramaximal stimuli of 1 msec duration increased the outflow of NA six to eightfold and that of NMN, DOPEG and VMA two to threefold. The increase in outflow of DOMA and MOPEG was small. NA represented 35·8 ± 4·1% of the total increase in radioactivity.

4. After pargyline pretreatment field stimulation increased the outflow of NA and NMN. Stimulation in the presence of pyrogallol raised the release of NA, DOMA and DOPEG. Neither pargyline nor pyrogallol affected the total release induced by stimulation.

5. Cocaine 0·3 μg/ml. increased the release due to stimulation at 4 shocks/sec but not at 25 shocks/sec. Cocaine did not affect the metabolism of the released transmitter.

6. Phenoxybenzamine (10 μg/ml.) increased release by stimulation at 4 and 25 shocks/sec. Metabolism of the released transmitter was prevented in the presence of phenoxybenzamine.

7. Phentolamine (3 μg/ml.), like phenoxybenzamine, blocked responses to field stimulation, but failed to modify release and subsequent metabolism of NA liberated by field stimulation.

8. The main NA metabolites in the rat vas deferens were DOPEG, DOMA and MOPEG. Stimulation at 4 shocks/sec resulted in an increased outflow of NA and of DOPEG. Fifty per cent of the total increase of radioactive compounds was accounted for by NA metabolites.

9. These experiments show that for the calculation of the actual output of transmitter it is important to include the metabolites and not to rely on the determination of [3H]NA alone.
Rigor contraction and the effect of various phosphate compounds on glycerinated insect flight and vertebrate muscle
Authors: White D. C. S.
Published: December 2014

1. Glycerol‐extracted flight muscle from the giant water‐bug, Lethocerus cordofanus, undergoes contraction when deprived of ATP. This rigor contraction occurs in the presence of the calcium chelating agent EGTA, under conditions in which the predicted free calcium ion concentration is less than 5 × 10−9
M. A mechanically similar contraction has been observed by depriving the muscle of Mg2+, in the presence of 5 m
M‐ATP.

2. In the rigor contraction tensions of up to 120 mN/mm2 under isometric conditions, and shortenings of between 2½ and 6% under isotonic conditions, have been observed at 20° C.

3. Muscles in rigor can be relaxed by the addition of ATP. The minimum concentration of ATP required to give full relaxation depends upon other ionic constituents of the solutions, and upon temperature, but is between 0·3 and 1 m
M at 20° C. Lower concentrations result in partial reduction of tension and stiffness.

4. Pyrophosphate (PP) causes a reduction in the tension of muscle which has developed rigor under isometric conditions, but the stiffness, when measured at frequencies between 1 and 100 Hz, remains indistinguishable from that of rigor muscle. The stiffness when measured by applying slow length changes is comparable to that of ATP‐relaxed muscle. It is suggested that in PP‐relaxed muscle the cross‐bridges remain in close proximity to, but are not rigidly attached to, the I filaments, resulting in a high viscous interaction between the two sets of filaments.

5. The addition of low concentrations of ADP (less than about 0·7 m
M) to rigor muscle in the absence of ATP causes an increase in tension. The effect is sigmoid, and is probably due to the formation of low concentrations of ATP throughout the body of the fibre by myokinase activity. Larger concentrations of ADP (about 5 m
M) added to rigor muscle cause relaxation, probably due to the formation of higher ATP concentrations.

6. AMP and inorganic orthophosphate have little effect upon the mechanical properties of rigor muscle.

7. There is a delay of about 1 min before the onset of rigor contraction when fibres are transferred from an ATP‐solution to one containing no ATP, due to the transfer of ATP in the body of the fibres. Both ATP hydrolysis by the fibres and diffusion of ATP into the bathing solution contribute significantly to the rate of depletion of ATP.

8. Rabbit psoas muscle shows a similar rigor contraction in the presence of EGTA, and has mechanical properties similar to those described for Lethocerus flight muscle in the presence of pyrophosphate.
Voltage clamp experiments in striated muscle fibres
Authors: Adrian R. H. , Chandler W. K. , Hodgkin A. L.
Published: December 2014

1. Membrane currents during step depolarizations were determined by a method in which three electrodes were inserted near the end of a fibre in the frog's sartorius muscle. The theoretical basis and limitations of the method are discussed.

2. Measurements of the membrane capacity (CM) and resting resistance (RM) derived from the current during a step change in membrane potential are consistent with values found by other methods.

3. In fibres made mechanically inactive with hypertonic solutions (Ringer solution plus 350 m
M sucrose) step depolarizations produced ionic currents which resembled those of nerve in showing (a) an early transient inward current, abolished by tetrodotoxin, which reversed when the depolarization was carried beyond an internal potential of about +20 mV, (b) a delayed outward current, with a linear instantaneous current—voltage relation, and a mean equilibrium potential with a normal potassium concentration (2·5 m
M) of −85 mV.

4. The reversal potential for the early current appears to be consistent with the sodium equilibrium potential expected in hypertonic solutions.

5. The variation of the equilibrium potential for the delayed current (V′K) with external potassium concentration suggests that the channel for delayed current has a ratio of potassium to sodium permeability of 30:1; this is less than the resting membrane where the ratio appears to be 100:1. V′K corresponds well with the membrane potential at the beginning of the negative after‐potential observed under similar conditions.

6. The variation of V′K with the amount of current which has passed through the delayed channel suggests that potassium ions accumulate in a space of between ⅓ and ⅙ of the fibre volume. If potassium accumulates in the transverse tubular system (T system) much greater variation in V′K would be expected.

7. The delayed current is not maintained but is inactivated like the early current. The inactivation is approximately exponential with a time constant of 0·5 to 1 sec at 20° C. The steady‐state inactivation of the potassium current is similar to that for the sodium current, but its voltage dependence is less steep and the potential for half inactivation is 20 mV rate more positive.

8. Reconstructions of ionic currents were made in terms of the parameters (m, n, h) of the Hodgkin—Huxley model for the squid axon, using constants which showed a similar dependence on voltage.

9. Propagated action potentials and conduction velocities were computed for various conditions on the assumption that the T system behaves as if it were a series resistance and capacity in parallel with surface capacity and the channels for sodium, potassium and leak current. There was reasonable agreement with observed values, the main difference being that the calculated velocities and rates of rise were somewhat less than those observed experimentally.
The afferent innervation of two infrahyoid muscles of the cat
Authors: Fernand V. S. V.
Published: December 2014

1. The afferent innervation of the straplike muscles of the infrahyoid region were investigated in two ways. The morphology of spindles and counts of tendon organs were investigated by the gold chloride technique in ten muscles. Spindle counts were made in forty pairs of thyrohyoid and infrahyoid muscles. De‐efferenting of the nerves to these muscles was done in three cats and the calibre spectra of the afferent innervation investigated. These were compared with the total counts of fibres in intact nerves.

2. In the thyrohyoid, spindles are frequently absent. No tendon organs were seen. In the large infrahyoid (combined sternohyoid and sternothyroid), spindle counts varied from 0 to 20 and the mean spindle count per gram of muscle was 3·5. A maximum of five tendon organs were seen in the muscle. Both spindle and tendon organ counts are low when compared with a limb muscle of similar weight and size.

3. In the infrahyoid muscle complex spindles were about equal in number to simple spindles.

4. Counts of spindles in the infrahyoid muscle in families of three or more siblings suggest that some families of kittens tend to have higher spindle counts than other families.

5. The afferent innervation of the two muscles varied between 21 and 42% of the total fibre population and the fibre diameter spectrum is in keeping with the low counts of encapsulated endings.
The effect of the internal sodium concentration on calcium fluxes in isolated guinea‐pig auricles
Authors: Glitsch H. G. , Reuter H. , Scholz H.
Published: December 2014

1. Calcium efflux from guinea‐pig auricles followed saturation kinetics when [Ca]o and [Na]o were changed while the ratio [Ca]o/[Na]o2 was kept constant. The Michaelis constant, KmCa+Na = 40 m
M, suggests that a hypothetical carrier system, responsible for sodium—calcium exchange, is far from saturation with the inside concentrations of these ions.

2. [Na]i was altered in the auricles between 12·5 and 60 m
M/kg fibre water while total cellular calcium concentration ([Ca]t) at the beginning of the influx period was not significantly different in the various groups of preparations.

3. 45Ca influx increased appreciably with increasing [Na]i. 45Ca influx from sodium‐poor solution corresponded to an almost equal increase in [Ca]t, while [Ca]t did not change much in preparations loaded with 45Ca in Tyrode solution. When the sodium‐activated fraction of calcium influx was plotted against [Na]i2 the resulting curve indicated saturation with KmNa = 3500 (m
M [Na]i)2 and maximal influx rate, Ji, maxCa' = 1·35 m
M/kg wet weight × 10 min.

4. When the preparations were re‐equilibrated for various times in normal Tyrode solution after [Na]i had been increased, both the sodium‐activated component of calcium influx and [Na]i2 decreased with approximately the same rate constants.

5. Calcium efflux from auricles with high [Na]i was increased when it was measured in Tyrode solution while the efflux in sodium‐poor solution was inhibited.

6. Auricles with increased [Na]i showed a positive inotropic contractile response.

7. The main conclusion reached by these experiments is that calcium influx is affected by [Na]i in a way which is compatible with a carrier‐mediated sodium—calcium exchange system.
Suprathreshold spectral properties of single optic tract fibres in cat, under mesopic adaptation; cone—rod interaction
Authors: Andrews D. P. , Hammond P.
Published: December 2014

1. Responses of 122 on‐centre or off‐centre ganglion cells in cat to suprathreshold monochromatic stimulation have been analysed under mesopic adaptation with white light, recording from their single fibres in the optic tract at a level posterior to the chiasma. Fields described are monocularly driven, located in the right half‐fields of either eye, and are all within 30° of the area centralis.

2. Retinal receptors are of two types, viz. 556 nm cones and 502 nm rods. At high mesopic adaptation (1 log cd/m2) all units receive mixed cone—rod input. Under low mesopic adaptation (0 log cd/m2) the great majority receive mixed input; a few receive pure rod input. These results are in agreement with the threshold data (Andrews & Hammond, 1970).

3. Peaks of spectral response curves of units, to suprathreshold monochromatic stimuli of different wave‐length but equal quantum flux, fall primarily between 550 and 560 nm for high mesopic adaptation, and between 500 and 520 nm for low mesopic adaptation. Peak position depends on the degree of rod or cone contamination, in units treated under high or low mesopic levels respectively.

4. Units with cone—rod input to the field centre receive similar but antagonistic cone—rod input to the surround. In units with pure rod input to the field centre, only rods input to the surround.

5. Cone and rod components of on‐centre discharges are identifiable in terms of colour sensitivity and latency. The cone component is primarily a short‐latency, high‐frequency, excitatory transient; the rod component is a longer latency, lower frequency, maintained phase of excitation.

6. Less direct evidence indicates that cone and rod input to the field surround give rise to inhibitory components of comparable latency, magnitude and time course.

7. The identified cone and rod components of responses are used in further experiments to show that cone and rod input have different spatial organization both in the receptive field centre and in the surround.

8. The boundary between the field centre and surround for rods has a diameter on average about twice as large as that for cones. This organization is such that the field centre for rods substantially overlies the cone surround.

9. Changes in receptive field organization occur within the mesopic range, associated with the changeover from cone to rod vision.

10. It is suggested that the difference between cone and rod input in the mesopic range may form the basis of the cat's ability behaviourally to discriminate between colours.