bluuebunny/crossref_metadata_2025 huggingface dataset:
Interrelationships of the volume and time components of individual breaths in resting man.
Authors: Davis J N , Stagg D
Published: December 2014

1. The volume and time components of individual breaths have been investigated under ‘steady‐state’ conditions during air‐breathing in fifteen subjects and, in a further six subjects, also during the addition of 1–5 and 3% CO2 to the inspired gas. 2. A computer‐assisted method has been used to derive from the air flow record the individual breath values of tidal volume (VT), inspiratory duration (TI), expiratory duration (TE) and cycle duration (TC = TI + TE) for a sequence of breaths in the various steady‐state conditions. 3. When the subjects were breathing room air, for breath sequences of over 200 breaths (n = 228–365), mean values of TI (TI) mostly lay between 1 and 2–5 sec, TE between 2‐0 and 3–5 sec and VT between 0–4 and 0–91. The distributions of VT, TI and TE were in general unimodal. 4. Significant negative correlations between VT and F, and positive correlations between VT and TC, have been confirmed. 5. In all fifteen subjects, a highly significant positive correlation existed between VT and TI (mean r = +0–704), which was stronger than that between VT and TC (mean r = +0–533). Weaker positive correlations were demonstrated between VT and TE, and between TI and TE (mean r = +0–359 and +0–381 respectively). 6. The intercept of the regression of VT on TI passed close to the origin, typically slightly positive on the VT axis (mean = +0–0991.). This, coupled with the strong positive correlation between VT and TI, indicates that the mean inspiratory flow rate (VI = VT/TI) for each breath is held relatively constant from breath to breath. 7. In the six subjects studied during CO2 inhalation, the mean % contributions of VT and F to the increase in ventilation associated with breathing 3% CO2 were 75 and 25% respectively. 8. At the three different levels of ventilation, neither VT, TI nor TE showed a wholly consistent trend, although VT tended to increase, TE to decrease and TI to be unchanged. In contrast, the average values of VI (VI) consistently increased as the chemical stimulus was raised. 9. It is concluded that the previously observed tendency for ventilation to be held constant from breath to breath during steady‐state breathing depends predominantly on the tendency for VI to be held constant. Close restraints are evidently not imposed on the individual values of VT and TI under these conditions. The neural mechanism generating breathing appears to control ventilation principally by regulating the rate of inspiratory air flow and secondarily TE.
Contribution of an electrogenic sodium pump to membrane potential in mammalian skeletal muscle fibres.
Authors: Akaike N
Published: December 2014

1. Relationship between the resting membrane potential and the changes in the intraceullar Na and K concentrations ([Na]i and [K]i) was studied in ‘Na‐loaded’ and K‐depleted' soleus (SOL) muscles of rats which had fed a K‐free diet for 40 and more days. 2. The extracellular space of the muscles was not significantly different between normal and K‐deficient rats. The inulin space in both the ‘fresh’ and Na‐rich' muscles can be determined by the same function relating the space to the muscle weight. 3. Presence of 2‐5–15 mM‐K in the recovery solution hyperpolarized the ‘Na‐rich’ muscul fibres at the beginning of recovery. The hyperpolarized membrane potential exceeded, beyond the measured potential of ‘fresh’ muscle fibres, the theoretical potential derived from the ionic theory, or even beyond Ek. Then, the measured membrane potential declined progressively during the immersion in a recovery solution and returned to the steady‐state value When a considerable Na extrusion and K uptake took place, the measured membrane potential became equal to Ek. 4.he maximal hyperpolarization occurring immediately after immersion in the recovery solution became smaller and had a shorter duration when increasing the external K concentration ([K]o) from 2‐5 to 15mM. 5. The K‐sensitive hyperpolarization was completely abolished on exposure to 0mM [K]o, on cooling to ca. 4 degrees C, and in the presence of oubain (10(−4) M). The inhibitory effects were reversed on returning to the control conditions. The membrane potential obtained after inhibition of the electrogenic Na‐pump with cooling or ouabain agrees well with that predicted by the ‘constant‐field’ equation. 7. The external Cl ions had a short‐circuiting effect on the electrogenic Na‐pumping activated on adding K ions. 8. The replacement of Na ions in a recovery solution with Li ions resulted in a faster rate of depolarization from the maximal hyperpolarizationp. It is concluded that the resting membrane potential of ‘Na‐loaded’ and ‘K‐depleted’ SOL muscle fibres is the sum of an ionic diffusion potential predicted by either the Nernst equation or the constant‐field equation and of the potential produced by an electrogenic Na‐pump.
Alterations in secretory patterns following antrectomy in rats with Pavlov pouches.
Authors: Lundell L
Published: December 2014

1. In conscious rats provided with Pavlov pouches, with the antrum retained or resected,the gastric secretory response to various stimuli has been studied. Each acid secretory response was related to that obtained with maximal doses of methacholine and histamine in combination, presumed to reflect the maximal secretory capacity of the mucosa. 2. Three weeks after the operation, the maximal acid secretory capacity was 60 percent lower in the antrectomized than in the intact Pavlov pouch rats; the difference was still larger at 6 weeks and 3‐5 months, owing to a gradual increase in the rats with the antrum retained. 3. Antrectomy reduced interdigestive secretion of acid to the same degree as the concomitant reduction in maximal secretory capacity. 4. Acid secretion in response to a maximal infusion of pentagastrin was reduced by about 50 percent at 3 and about 65 percent at 6 weeks after antrectomy. No significant difference was, however, noted between the antrectomized and intact rats when the responses were related to the maximal secretory capacity. The dose response curve to pentagastrin revealed a redcued responsiveness to submaximal doses of this agent following antrectomy. 5. The maximal acid secretory response to histamine was reduced after antrectomy, although the sensitivity to submaximal infusions of histamine appeared to be increased. 6. The mean secretroy output to 2‐deoxy‐D‐glucose was reduced by about 65 percent and that to food by about 85 percent following antrectomy. 7. After antrectomy a background infusion of pentagastrin enhanced the secretory responses to 2‐deoxy‐D‐glucose and to food but did not restore the responses to the levels in the intact rats. The feeding responses as related to the maximal secretory capacity were, however, similar in the two groups on infusing pentagastrin in the antrectomized rats. 8. Interdigestive secretion of pepsin was reduced by about 60 percent after antrectomy, while the peak response to 2‐deoxy‐Dglucose was about twice the interdigestive level in both groups. Pepsin secretion in response to food showed an increased secretion above the interdigestive level of longer duration in the antrectomized than in the intact Pavlov pouch rats. 9. The irreversibily reduced responsiveness of the gastric mucosa after antrectomy is discussed in relation to known morphological and biochemical changes.
Chemical stimulatory mechanism in gastric secretion.
Authors: Cieszkowski M , Konturek S J , Obtulowicz W , Tasler J
Published: December 2014

1. The serum gastrin level, gastric mucosal blood flow and acid secretion from the canine Heidenhain pouch have been measured in response to the introduction of bovine serum albumin, pepsin‐digested albumin, an amino acid mixture, liver extract and mannitol used as control. 2. Distention of the Heidenhain pouch with mannitol or albumnin at pH 5‐0 produced a similar pressure‐related increase of acid secretion reaching a peak of only 10 percent of the maximal response to histamine. Pepsin‐digested albumin was capable of producing larger acid outputs than undigested albumin.The highest acid output, attaining about 80 percent of the maximal response to histamine, was obtained with liver extract both before and after exhaustive dialysis to remove all the amino acids and short peptide fragments. An amino acid mixture containing all essential amino acids was also found to stimulate acid secretion but a lesser degree than liver extract. 3. This concluded that it is not the intact protein but the products of its digestion, the polypeptides and free amino acids, which are potent chemical stimulants of acid secretion from the oxyntic gland area. Since the serum gastrin level was not changed during acid secretion induced by peptic digests bathing the oxyntic gland area, the mechanism of chemical stimulation appears to be gastrin‐independent. 4. The response to chemical stimulation by peptic digests can be greatly potentiated by combining this with distention of the oxyntic gland area. Topical application of xylocaine or atropine causes a marked decrease of Heidenhain pouch response to peptic digests, suggesting a possible neural reflex component in the mechanism of chemical stimulation of the oxyntic gland area. 5. When the pH of the liver extract in the Heidenhain pouch was gradually decreased in sequential order from 5–0 to 1–0, this resulted in a pH‐related decrease in acid secretion and in the mucosal blood flow falling to the basal level at pH 1–0. Exogenous secretion given in graded doses from 0–5 to 8–0 u./kg. hr caused a small but dose‐related inhibition of acid response to liver extract accompanied by a decrease of mucosal blood flow but without any significant change in the serum gastrin level. 6. The results indicate that the chemical stimulation of the oxyntic gland area by peptic digests is capable of inducing acid secretion by a local, gastrin‐independent, partially neural reflex mechanism; sensitive to pH, pressure and secretin.
An experimental method of identifying and quantifying the active transfer electrogenic component from the diffusive component during sugar absorption measured in vivo.
Authors: Debnam E S , Levin R J
Published: December 2014

1. The kinetics of absorption of glucose, galactose and alpha‐methyl glucoside have been measured in rat jejunum in vivo using a chemical method and a new electrical technique. 2. Sugar absorption estimated by chemical methods exhibited two components. One component was phlorrhizin‐sensitive, saturable and generated electrical potential differences (electrogenic active component) while the other was phlorrhizin‐insensitive, non‐saturable and did not generate electrical potentials (diffusive component). 3. The diffusive component of the actively transported sugars was indentical to the absorption behaviour of sorbose, a hexose that is not actively transferred. 4. A method for correcting the data obtained from chemical absorption studies for the diffusive component was developed. The corrected, operational kinetic constants for ‘apparent Km’ obtained by this method were not significantly different to values obtained electrically. The identity between the values obtained by both methods supports the concept that they represent a measure of the same rate‐limiting step in the absorption process. 5. The application and significance of the techniques is discussed in relation to the clinical assessment of intestinal sugar absorption.
Pancreatic islet cells: effects of monosaccharides, glycolytic intermediates and metabolic inhibitors on membrane potential and electrical activity.
Authors: Dean P M , Matthews E K , Sakamoto Y
Published: December 2014

1. The effects of monosaccharides, glycolytic intermediates, metabolic inhibitors and anxia, have been studied on the membrane electrical activity of mouse pancreatic islet cells in vitro using a single intracellular micro‐electrode for both voltage recording and current injection. 2. In addition to D‐glucose (28mM), D‐mannose (16–6mM), and L‐leucin (10mM), the substances D‐glyceraldehyde (11mM), and acetoacetate (20 mM), induced action potentials in islet cells but other glucos analogues and metabolic intermediates including L‐glucose dod not. 3. Mannoheptulose 20 mM), but not D‐galactose or 2‐deoxy‐D‐glucose, antagonized the electrical activity induced in islet cells by D‐glucose, 28mM. Prior treatment of the cells with mannoheptulose caused them to hyperpolarize and completely prevented the appearance of electrical activity on subsequent exposure to D‐glucose. 4. Electrical activity induced by D0glucose 28mM, was progressively inhibited by phloridzin, 10mM, if the cells were exposed to D‐glucose and inhibitor simultaneously, and abolished on pretreatment with inhibitor for 30–60 min. Phloridzin also caused depolarization of the islet cells which was independent of extracellular glucose. 5. Anoxia completely blocked the electrical activity induced by glucose but not that evoked by D‐glyceraldehyde, L‐leucine, tolbutamide or glibenclamide. 6. Iodoacetic acid, 5 mM, rapidly blocked glucose‐induced electrical activity whilst that elicited by tolbutamide was relatively resistant to inhibition. 7. The nature and possible location of the glucoreceptor in pancreatic islet cells is discussed in relation to the origin and functional significance of glucose‐induced electrical activity and insulin secretion.
The possible role of cyclic AMP in the neurotrophic control of skeletal muscle.
Authors: Carlsen R C
Published: December 2014

1. Motoneurones provide trophic control of some of the functional characteristics of skeletal muscle fibres. This study has been designed to test whether the adenylate cyclase: cyclic AMP system may offer one potential mechanism for the mediation of neurotrophic regulation. 2. The concentration of cyclic AMP was measured at various intervals after muscle denervation. Muscle cyclic AMP concentration increases for the first 2 days after nerve section. It reaches a maximum value at 48 h and subsequently returns to the control value at 7 days. 3. Cyclic AMP concentration is unchanged by muscle disuse for the first 3 days following limb immobilization. Four days after immobilization, however, cyclic AMP increases in both the disused and contralateral control muscles. This phenomenon has been tentatively ascribed to some aspect of the inflammatory response. 4. Changing the level of nerve section, and therefore the length of the residual nerve stump, changes the temporal pattern of the increase in muscle cyclic AMP concentration. 5. Reinnervation of a denervated muscle produces a decrease in muscle cyclic AMP concentration. 6. It is concluded from the results that some aspect of nerve function provides trophic regulation of the muscle adenylate cyclase: cyclic AMP system. The mechanisms by which this regulation may be applied are considered in the Discussion.
Responses of inner and outer muscle of the sheep carotid artery to injury.
Authors: Graham J M , Keatinge W R
Published: December 2014

1. Direct injury to the smooth muscle of the sheep carotid artery in vivo caused large, persistent and sharply limited annular contraction, even with tetrodotoxin 10(−5)M present to block nerves. 2. Surcose gap records from artery strips showed that mechanical injury caused slow, prolonged depolarization of the smooth muscle that spread for a few millimetres in a circular direction in relation to the intact artery wall with an apparent space constant of 1‐26‐‐3.49 mm. In the longitudinal direction, no depolarization was recorded 1 mm from the site of injury. No spikes were recorded more than 1 mm in either direction from the site of injury except when procaine, which facilitates electrical activity in the smooth muscle, was present. 3. When responses of inner and outer muscle were recorded separately, injury caused comparable contraction of both parts. 4. Clotted blood caused large contractions of intact artery strips; it contracted inner much more than outer muscle. 5. The main factors in the intact vessel's response to injury therefore seem to be inner and outer muscles' direct response to injury, reinforced by spread of depolarization round the vessel wall, and inner muscle's response to vasoconstrictor agents released by clotting blood.
Salt‐induced changes in sodium transport across the skin of the euryhaline toad, Bufo viridis.
Authors: Katz U
Published: December 2014

1. Euryhaline toads (Bufo viridis) were adapted to either distilled water, 115 or 200 mM‐NaCl solutions. Na transport across the skin of these animals was studied in in vitro preparations. 2. Salinity adaptation caused a reduction in transepithelial potential and short‐circuit current across the skin, and increased its electrical resistance. 3. Na influx across the skin was decreased. The reduction accounted fairly well for the measured reduction in short‐circuit current. 4. Short‐term Na uptake at the outer barrier of the skin was greatly reduced in preparations from salt adapted animals. Amiloride, which usually inhibits Na uptake, did not affect it in skins from salt adapted toads. 5. Sodium conductance decreased by a factor of three in skins from 115 mM‐NaCl adapted toads, and to zero in skins from 200 mM‐NaCl adapted animals. Shunt conductance was only little affected by the salinity of adaptation. 6. ‘Amiloride‐sensitive component’ of transepithelial Na transport was 55, 21‐5, and 4‐5 muA/cm‐2 in skins from toads which were adapted to distilled water, 115, and 200 mM‐NaCl solutions, respectively. 7. It is concluded that the effect of salinity adaptation on the skin of the toad is to reduce the number of Na selective sites at the outer barrier. This change is reflected in a decrease in the ‘amiloride‐sensitive component’ of Na transport across the skin, and could not be increased by aldosterone. Other changes may occur as secondary to that.
Surround contribution to light adaptation in cat retinal ganglion cells.
Authors: Enroth‐Cugell C , Lennie P , Shapley R M
Published: December 2014

1. The sensitivity of a cat's retinal ganglion cell to a small, dim, spot flashed upon the middle of the receptive field depends upon the size of a concentric steady background: sensitivity is reduced monotonically with background area. All backgrounds which equal or exceed in size the central summing area of the ganglion cell produce an equivalent reduction of sensitivity, even though only backgrounds which extend outside the central summing area depress the maintained discharge. 2. If a small background lies upon the middle of the receptive field, and the test spot is made intense enough to evoke a strong response, steady illumination of the periphery may make the response larger. 3. This change in response is not due to an enhancement of centre sensitivity by the surround, but is readily understood if steady illumination of the periphery adapts out the surround's antagonism of the centre's response to the test flash. 4. The failure of steady stimulation of the surround to alter centre sensitivity implies that signals from the surround subtract from, or add to, those from the centre.
Dynamic properties of fast and slow skeletal muscles in the cat and rat following cross‐reinnervation.
Authors: Luff A R
Published: December 2014

1. Cross‐reinnervation was performed between the slow‐twitch soleus (SOL) and fast‐twitch extensor digitorum longus (EDL) muscles in the cat and the SOL and fast‐twitch flexor hallucis longus (FHL) muscles in the rat. The isometric and force‐velocity properties of the muscles were subsequently determined. 2. As a result of cross‐reinnervation the dynamic properties of both slow‐ and fast‐twitch muscles in the cat were considerably altered. The isometric twitch time to peak was 33–9 msec in the X‐SOL compared with 84–7 msec in the N‐SOL. The intrinsic speed of shortening and a/P0 values were 25–4 mum. sec‐1 and 0–34 respectively in the X‐SOL and 14–4 mum. sec‐1 and 0–20 in the N‐SOL. In the X‐EDL the twitch time to peak was 52–6 msec compared with 23–4 msec in the N‐EDL; the intrinsic speed of shortening and a/P0 values were 14–1 mum. sec‐1 and 0–29 respectively, whereas they were 31–9 mum. sec‐1 and 0–44 in the N‐EDL. 3. In the rat X‐SOL there was shortening of the isometric twitch time to peak from 39–5 msec in the N‐SOL to 19–7 msec and an increase in the intrinsic speed of shortening from 17–7 mum. sec‐1 to 32–3 mum. sec‐1, although over most of the force‐velocity curve the X‐SOL values were only slightly greater than those for N‐SOL. The force‐velocity data for the X‐SOL muscles could not be fitted by Hill's equation. 4. The isometric and force‐velocity results of the X‐SOL of the rat suggested that the muscle contained a significant proportion of slow fibres. An examination of the motor unit characteristics of the N‐FHL showed the presence of approximately 14% small, slow units. 5. It is concluded that there are no fundamental differences between the rat and the cat with regard to the effect of cross‐reinnervation on hind‐limb muscles. However, these, and previously published results, suggest that there may be important differences between heterologous muscles in the degree of influence that their respective motor nerves can exert on an alien muscle.
Properties of surface and junctional membranes of embryonic cells isolated from blastula stages of Xenopus laevis.
Authors: Slack C , Warner A E
Published: December 2014

1. Some membrane properties of endoderm and mesoderm cells isolated from late blastula stages of Xenopus laevis have been examined using electrophysiological techniques. 2. Cells were isolated by treatment of whole embryos with Ca‐free EDTA containing media, or mechanically by micro‐dissection, and cultured in Ca‐containing Holtfreter solution (60 mM‐NaCl) or Ringer solution (120 mM‐NaCl). 3. Membrane potentials lay between −6 and −84 mV; specific membrane resistances ranged from 500 to 29,000 omega cm2; there was no difference between EDTA isolated and mechanically isolated cells. 4. Relative and absolute cation and anion conductances varied from cell to cell. Some cells were anion impermeable; the cation conductance ranged from 35 to 300 mumho/cm2. 5. The resting potential of some cells was largely determined by the concentration gradient and membrane permeability of K ions. In other cells the potential was maintained either by some other ion or by an electrogenic pump. [K]i came to approximately 130 mM in Ringer solution (the value pertaining in the intact embryo) and similar to 60 mM in Holtfreter solution. 6. In most pairs and small clumps of cells ionic current spread from one cell to the next; some single cells and groups of cells were uncoupled from their neighbours. 7. The junctional resistance lay between 10(5) and 10(8) omega; it behaved as a linear resistor in most cell pairs studied. In three pairs the intercellular junction showed rectifying properites. 8. By the late blastula stage of development presumptive endoderm and mesoderm cells form a heterogeneous population with widely varying passive membrane properties. The significance of these findings is discussed in relation to current hypotheses for the formation of spatial patterns during differentiation.
Intracellular potentials in cells of the seminiferous tubules of rats.
Authors: Cuthbert A W , Wong P Y
Published: December 2014

1. Membrane potentials have been recorded from cells of seminiferous tubules of rats in vitro using micro‐electrodes. The value in 808 impalements was −28–2 +/− 0–3 mV (mean +/− S.E.) at 33 degrees C. 2. Increasing the potassium concentration depolarized the cells, a tenfold increase in concentration causing a depolarization of 16 mV. Removal of sodium from the bathing solution caused a hyperpolarization of 3 mV at a potassium concentration of 5‐9 m‐equiv/l. Removal of chloride and replacement with impermeant anions had no effect on potential. Removal of calcium from the bathing solution caused a minor but significant depolarization. 3. Ouabain (10–3 M), dinitrophenol (2–5 times 10–4 M) or removal of glucose from the bathing fluid all caused depolarization. The membrane potentials of the cells were sensitive to temperature over the range 10–33 degrees C, the apparent activation energy for the reactions maintaining the potential being approximately 6 kcal/mole. 4. Membrane potentials in seminiferous tubules were independent of age of the animal, were insensitive to previous hypophysectomy and were insensitive to a number of hormones (FSH, LH, HCG, oxytocin). In high concentration prostaglandin E1 caused depolarization. 5. Acetazoleamide (4 times 10–5 M) caused a rapid, but reversible, depolarization of the tubular cells. This was also true in conditions when the HCO'3/CO2 buffer system was replaced with Tris‐buffer. Another carbonic anhydrase inhibitor (p‐sulphonamido‐benzoic acid) had similar effects on cell potentials as acetazoleamide. These results are discussed in relation to the nature of the ionic secretion produced in the tubules. 6. Occasional cells showed phasic variations in membrane potential. A possible connexion between these variations and the contractile activity of the tubules is discussed.
Structural, mechanical and myothermic properties of rabbit rectococcygeus muscle.
Authors: Davey D F , Gibbs C L , McKirdy H C
Published: December 2014

1. The fine structure of rabbit rectococcygeus muscle has been studied with the electron microscope. 2. The mechanical performance and the heat production of this muscle has been investigated during tetanic contractions at 27 degrees C. 3. In isometric contractions a force of 164 +/− 27 mN/mm2 (mean +/− S.D., n = 17) is developed and the heat production is linearly related to the force. 4. There is a relationship between the duration of stimulation (t) and the total heat production (H) of the type H = A plus bt, where A and b are constants. 5. After‐loaded isotonic experiments show that the relationship between force and velocity can be fitted by the ‘characteristic equation’ of Hill (1938). 6. The value of a/P0 (0–302 +/− 0–093, mean +/− S.D.) is slightly higher than in frog skeletal muscle but the constant b is about 50 times smaller. 7. The ratio of work/total energy production, for the stimulus conditions employed, was maximally 0–185. 8. The ratio of total enthalpy to initial enthalpy is difficult to measure accurately but is probably about 2.
Sugar absorption by foetal and neonatal rat intestine in vitro.
Authors: Bamford D R , Ingham P A
Published: December 2014

1. Sugar absorption by foetal and neonatal rat intestine has been examined using an in vitro accumulation technique. 2. The capacity for active sugar absorption is present in the rat intestine by the 17th day of gestation. Considerable variation in uptake occurs during the first month post partum; the greatest uptake place during the first week. 3. The absorption of sugars by the developing gut resembles in several respects that by the mature intestine. However, the adult pattern of functional localization along the intestine is not fully established until after the 3rd week post partum. 4. Kinetic studies indicate that variations with age in the distribution of sugar ‘carriers’ along the intestine, rather than changes in the ‘carriers’ themselves, account for the observed variations in absorption.
Temperature dependence of the circulation pattern in the upper extremities.
Authors: Raman E R , Vanhuyse V J
Published: December 2014

1. The rate of blood flow D through the hand and the rate of heat H transferred by that blood flow into the hand were measured on eleven subjects between 18 and 22 years old. The hand was immersed in water, at temperatures ranging from 10 to 40 degrees C. 2. The rate of blood flow was measured with a water‐air displacement plethysmograph, which was adapted also to give heat loss measurements. 3. Comparison of the relative values of D and H at different temperatures gives information about the change in distribution of blood flow with temperature. On decreasing water temperature, the change in distribution starts at about 25 degrees C and continues gradually to about 15 degrees C, suggesting that more and more blood is shunted to deep veins. For one of the subjects, no change in distrubiton pattern was found.
The development of functional innervation in the hind limb of the chick embryo.
Authors: Landmesser L , Morris D G
Published: December 2014

1. The development of functional motor innervation was studied in the hind limb of chick embryos from Stages 25 to 43 by observing contraction of individual muscles and by recording the resultant tension when individual spinal nerves were electrically stimulated. 2. At later developmental stages (35–43) a given muscle always received functional innervation from specific spinal nerves. This pattern, with respect to the craniocaudal position of motoneurones, was similar to those described for amphibians and mammals. 3. The observed pattern was similar throughout development from the time that movement could first be elicited at Stages 27–28. There was no indication that motoneurones form initial synapses with inappropriate muscles. 4. Recordings from muscle nerves during excitation of individual spinal nerves gave results similar to the tension recordings, showing that even at early developmental stages muscle nerves did not contain substantial numbers of inappropriate axons. 5. Most limb muscles or primitive muscle masses became functionally innervated at the same time with no clearly defined proximo‐distal sequence of limb innervation. 6. It appears that chick motoneurones are initially specified with respect to their peripheral destination and grow out selectively to synapse with appropriate muscles from the outset.
Pattern and flicker detection analysed by subthreshold summation.
Authors: King‐Smith P E , Kulikowski J J
Published: December 2014

1. We confirm Keesey's (1972) observation that, when a flickering line is viewed, there are distinct thresholds for detecting flicker (or movement) and for detecting a well localized line (pattern detection). Our measurements of the temporal sensitivity of these two mechanisms are similar to Keesey's. 2. The flicker and pattern detection mechanism have been analysed using subthreshold summation, i.e. by observing the effect of subthreshold flickering stimuli (lines and gratings) on the contrast threshold for a flickering test line. 3. The pattern detector shows linear spatial summation of contrast while the flicker detector is non‐linear in this respect. 4. The receptive field of the (most sensitive) flicker detector is about two to four times broader than that of the pattern detector. 5. The flicker detector has relatively weak surround inhibition and so, unlike the pattern detector, it is sensitive to a uniform flickering field. 6. The spatial arrangement of the pattern detector is the same at all temporal frequencies (including steady presentation); for flicker detection, the width of the receptive field increases with temporal frequency and the strength of lateral inhibition decreases at high frequencies. 7. Flicker detectors of various widths were demonstrated by using different test stimuli (for 12 Hz modulation); surround ingibition was relatively weak for the broadest detector. 8. There is a delay of surround inhibition of about 3 ms for both flicker and pattern detection. 9. By using a broad test stimulus modulated at a high frequency, a detector can be found with no significant surround inhibition. At threshold, this stimulus produces a sensation of flicker without the appearance of lateral motion observed for finer test lines at lower frequencies. 10. The characteristics of pattern and flicker (movement) detection are compared to electrophysiological studies on X (sustained) and Y (transient) neurones respectively, and correlations are described for studies of temporal frequency response, non‐linearity, width of receptive field, strength of the inhibitory surround and motion sensitivity.
Adrenergic influences on the electrical potential across the colonic mucosa of the rabbit.
Authors: Lennane R J , Peart W S , Shaw J
Published: December 2014

1. An investigation was undertaken of the role of adrenergic influences on the transient change in colonic potential difference (p.d.) induced by handling in the rabbit. 2. P.d. was increased from 9–5 +/− 0–5 to 27–05 +/− 1‐94 mV during a 2 hr period of handling and wrapping. Atropine and alpha‐adrenergic block during this 2 hr period did not alter the magnitude of the response and the response in adrenalectomized animals was not significantly different from that of normal animals. 3. ‘Total’ adrenergic block and selective beta‐adrenergic block abolished the change in p.d. with handling and infusion of an alpha‐receptor agonist during the 2 hr period significantly reduced the response. 4. The changes in colonic p.d. with handling were greatly increased by the infusion of a beta‐receptor agonist during the 2 hr test period. 5. The results indicate that the change in colonic p.d. with handling is a direct effect of the autonomic nervous system mediated via beta‐receptors and that the changes were not related to the effects of circulating catecholamines or to changes in aldosterone production.
Selective and non‐selective reinnervation of fast‐twitch and slow‐twitch rat skeletal muscle.
Authors: Hoh J F
Published: December 2014

1. The problem of selectivity during reinnervation of skeletal muscle fibres was investigated in the rat using the fast‐twitch extensor digitorum longus (EDL) and the slow‐twitch soleus muscles and their nerves. 2. After an operation on these nerves permitting them to compete for reinnervation of one or the other muscle (hereafter called Y‐union), virtually the total isometric tetanic tension of EDL muscle could be elicited by stimulating the EDL nerve, while stimulating the soleus nerve yielded little or no tension. In the case of the soleus muscle, stimulation of either nerve elicited about half of the total isometric tetanic tension. 3. During the course of reinnervation of these muscles in non‐competitive situations, the time course of increase in the ratio of tension elicited by nerve stimulation to that by direct stimulation was slower in the case of soleus nerve reinnervating EDL muscle, compared with cross‐reinnervation in the reverse direction or reinnervation of each muscle by its own nerve. 4. Crushing the common peroneal nerve 12 days after a Y‐union in an attempt to retard the EDL nerve did not favour reinnervation of the EDL by soleus nerve, but crushing the nerve again or just once at 1 month after the original operation produced substantial partial reinnervation of the EDL by the soleus nerve. 5. It is concluded that soleus nerve fibres form functioning neuromuscular synapses on EDL muscle fibres only with difficulty. The pattern of reinnervation reveals characteristic differences between fast‐twitch and slow‐twitch muscles on the one hand and between their respective nerves on the other.
The formation of synapses in amphibian striated muscle during development.
Authors: Bennett M R , Pettigrew A G
Published: December 2014

1. A study has been made of the formation of synapses in developing reinnervated and cross‐reinnervated amphibian twitch muscles which receive either a focal (iliofibularis) or a distributed (sartorius) innervation from 'en plaque' nerve terminals using histological, ultrastructural and electrophysiological techniques. 2. During the development of the tadpole through metamorphosis to the adult frog, the sartorius myofibres increased in length at about twice the rate of the iliofibularis myofibres, due to a fast rate of growth at their insertions on to the pelvic tendon. 3. The short iliofibularis and sartorius myofibres of young tadpoles (800 mum long) possessed only a single synapse and the iliofibularis myofibres did not receive any further innervation during development. However the sartorius myofibres received further transient innervation on the new muscle laid down during development at the fast growing pelvic insertion, until the distance between the original synapse formed on the myofibres and the synapse at the pelvic end of the muscle was about 12 mm. 4. During development synapses possessed either skewed, multimodal, or unimodal m.e.p.p. amplitude‐frequency distributions; the intervals between m.e.p.p.s. were not distributed randomly according to a Poisson process, as m.e.p.p.s. of similar amplitudes tended to be separated by very short intervals; the unit‐size e.p.p. had a similar amplitude‐frequency distribution as the m.e.p.p.s. if these had a unimodal distribution. 5. Reinnervation or cross‐reinnervation of the sartorius and the iliofibularis muscles in adults or at a late stage of development simply reconstituted the normal focal and distributed innervation patterns of the muscles, as found in the control muscles of the contralateral and unoperated legs. 6. These observations on synapse formation in amphibia are consistent with the hypothesis that during development the axon making the initial synaptic contact on the muscle cells induces a property over a length of muscle membrane adjacent to this site which makes it refractory to synapse formation; thus during reinnervation or cross‐reinnervation of adult muscles this refractory property constrains synapse formation to these sites.
Impulse activity and receptor potential of primary and secondary endings of isolated mammalian muscle spindles.
Authors: Hunt C C , Ottoson D
Published: December 2014

1. An isolated muscle spindle preparation from a tail muscle of cat is described. The afferent response to a ramp‐and‐hold stretch was recorded in individual axons from identified primary and secondary endings. 2. Primary endings exhibit a prominent dynamic response, including an initial burst. They also show a well‐maintained static discharge. Secondary endings also show a well‐sustained static discharge but generally have a much lower dynamic sensitivity. The response of primary and secondary endings of the isolated spindle are similar to the typical responses seen in vivo in groups Ia or group II afferent fibres respectively. 3. Following impulse blockade by tetrodotoxin, the receptor potential was recorded from primary and from secondary endings in response to ramp‐and‐hold stretch. 4. During the dynamic phase the receptor potential of primary endings consists of a depolarization which has two components. (a) An initial component occurs early during ramp stretch, depends in rate of rise and amplitude on velocity of stretch and is reduced on repetitive stretch; it appears to be responsible for the initial burst. (b) A late dynamic component, which follows, is also dependent on stretch velocity and produces the late dynamic discharge. At the end of ramp stretch the receptor potential falls, and may undershoot, the static level. There is a subsequent adaptive fall during hold stretch, then a maintained static level of receptor potential. On release from stretch the membrane is hyperpolarized. 5. Secondary endings usually show a smaller dynamic response, lacking the initial component seen in primary endings. They also generally lack an undershoot following the ramp and have less of a post‐release hyperpolarization. 6. Static levels of receptor potential in both primary and secondary endings are related to amplitude of stretch. 7. The receptor potentials of primary and secondary endings account for the major features of the impulse responses of these endings to ramp‐and‐hold stretch. In primary endings the dynamic frequencies may also depend upon a sensitivity of the impulse initiating site to rate of change of receptor current.
Neurotrophic regulation of dynamic properties of skeletal muscle: effects of botulinum toxin and denervation.
Authors: Drachman D B , Johnston D M
Published: December 2014

In order to determine the role of acetylcholine (ACh) transmission in neurotrophic regulation of dynamic properties of muscle, the effects of botulinum toxin treatment were compared with those of denervation. The extensor digitorum longus (EDL) and soleus muscles of rats were either denervated or injected with botulinum toxin. At times up to 25 days the isometric properties of these muscles were determined. 2. Both botulinum treatment and denervation produced progressive slowing of the time to peak of the twitch (TPT) and half‐relaxation time of the twitch (1/2 RT), which was more pronounced in the EDL than in the soleus. 3. Both treatments produced slowing of the relaxation curve following tetanic contraction, more marked in the EDL than in the soleus muscle. This indicates a slowing of relaxation, and suggests a prolongation of the active state of the muscle. 4. The maximum rate of rise of the tetanus did not change significantly in the EDL and soleus muscles after botulinum treatment or denervation. This suggests that there is no major change in the speed of contraction under conditions of botulinum treatment or denervation. 5. The changes produced by botulinum treatment and denervation were virtually identical in all parameters tested. This is interpreted meaning that cholinergic transmission (including muscle usage), or some other factor closely related to cholinergic transmission, accounts for the motor nerve's trophic influence in maintaining these dynamic properties of skeletal muscles.
Micro‐electrode measurement of the internal pH of crab muscle fibres.
Authors: Aickin C C , Thomas R C
Published: December 2014

The internal pH of crab muscle fibres was measured using recessed‐tip pH‐sensitive micro‐electrodes. Immediately following electrode penetration the mean internal pH was 7‐21 +/‐ 0‐02 (S.E. of mean) and the mean membrane potential was ‐64‐9 +/‐ 0‐6 mV (S.E. of mean). If H+ ions were passively distributed across the fibre membrane the internal pH would have been 6‐39. 2. The internal pH tended to rise before stabilizing at a mean value of 7‐27 +/‐ 0‐02 (S.E. of mean). The difference between immediate and stabilized values is highly significant and suggests acid injury on electrode penetration. 3. Changing the membrane potential or external pH had only small, slow effects on internal pH. 4. External CO2 caused a large and rapid decrease in internal pH. With low concentrations of CO2, the effect was dependent on the initial pH as predicted by the Law of Mass Action. During a long exposure to 2‐65% CO2 at pH 7‐5, the internal pH returned slowly to its previous value, suggesting active transport of H+ (or OH‐ or HCO3‐) ions across the fibre membrane. 5. The internal buffering power calculated from the response to 2‐65% CO2 was 47‐3 +/‐ 2‐8 slykes (m‐equiv H+/pH unit per l.) (S.E. of mean).
Influence of the insulin sensitive central nervous system glucoregulator receptor on hepatic glucose metabolism.
Authors: Szabo A J , Szabo O
Published: December 2014

Excitation of the insulin sensitive glucoregulator receptor in the central nervous system (C.N.S.) causes an immediate decrease in the systemic blood sugar level in rats. 2. A study was made in animals that were subjected either to evisceration or to evisceration and functional‐hepatectomy, in order to assess the role of the liver and pancreatic hormones in the blood sugar decrease following insulin injection into the carotid artery. 3. The results indicate that the change in the systemic blood sugar level, induced by exposing the C.N.S. to insulin, was effected through a direct influence of the receptor centre on glucose metabolism of the liver. 4. Excitation of the insulin‐sensitive receptor in the C.N.S. regulates carbohydrate metabolism of the liver, both by inhibiting hepatic glucose output and by facilitating hepatic glucose uptake. 5. The data derived from these animal models reveal that the mode of transmission of the impulse from the C.N.S. region is through efferent neural pathways that directly influence the hepatic carbocydrate metabolism, and not through a modification of pancreatic hormone secretion.
Cardiovascular and endocrine responses to feeding in the young calf.
Authors: Bloom S R , Edwards A V , Hardy R N , Malinowska K , Silver M
Published: December 2014

A number of cardiovascular and endocrine responses which occur during and after feeding in the unweaned calf are described. 2. There was a substantial increase in both heart rate and mean aortic blood pressure during feeding in these animals. This occurred within the first few seconds and persisted throughout the period of ingestion. 3. The concentrations of glucose, insulin and gastrin in arterial plasma rose abruptly during, or immediately after, feeding and elevated values persisted for at least 2 hr. A transient increase in glucagon concentration was also observed. In contrast, feeding appeared to produce no immediate rise in enteroglucagon concentration. 4. The adrenal output of glucocorticoids rose transiently in response to feeding but that of catecholamines was unaffected. 5. Cardiovascular responses to feeding were also examined in other species. In unweaned kids the changes were essentially similar to those observed in the calf but were less pronounced. In lambs a persistent hypertension occurred which was associated with a brief initial tachycardia. In adult dogs ingestion of solid food also caused tachycardia but although the aortic blood pressure rose for a short period at the beginning of feeding, hypotension developed thereafter. 6. The possibility that both the cardiovascular and endocrine responses, which occur during or immediately after feeding, are mediated by the autonomic nervous system is discussed.
Effects of external potassium on potassium efflux and accumulation by rat adipocytes.
Authors: Horn L W , Zierler K
Published: December 2014

Effects of external K+ concentration, [K+]o, on K+ transport rate and on relative K+, an index of intracellular K+ concentration, were studied in adipocytes isolated from rat epididymal fat pads. 2. Relative K+ changed upon a step change of [K+]o from normal, but with continued exposure to the second [K+]o the relative K+ returned to or approached the initial level. 3. Reversal of the initial change in relative K+ was accelerated by restoration of a normal [K+]o. 4. 42K efflux from cells exposed to a single [K+]o was described by a single rate constant for a wash‐out period of up to four half‐times. 5. The rate constant was bi‐stable with respect to [K+]o, with the critical [K+]o between 3‐6 and 4‐8 mM. 6. Rate constants were independent of relative K+ and uncorrelated with net fluxes. 7. It is suggested that [K+]o exerts its effects only at the outer surface of the adipocyte membrane.
The effects of prolactin and oxytocin on milk secretion and on the permeability of the mammary epithelium in the rabbit.
Authors: Linzell J L , Peaker M , Taylor J C
Published: December 2014

The effects of prolactin or oxytocin on milk secretion and the permeability of the mammary epithelium have been investigated in rabbits. 2. Milk yield was increased by prolactin treatment in late (25‐28 days) but not in established (11‐14 days) lactation. 3. Prolactin treatment increased milk [lactose] and [K] and decreased [Na] and [Cl] in late lactation, and thus reversed the normal changes in late lactation, but had no significant effect in established lactation. 4. [14C]sucrose movements from blood to milk were significantly decreased to levels characteristic of established lactation, following prolactin treatment in late lactation. No significant effect was evident with treatment in established lactation. Na and Cl movements showed similar trends. 5. It is suggested that prolactin in some way affects paracellular movements of ions and small molecules like lactose across the mammary epithelium, and that this mechanism is responsible for the changes in the composition of the aqueous phase of milk. 6. Immediately following a single dose of 100 m‐u. oxytocin no significant effects on milk composition were evident but after 1 u. milk [Na] and [cl] were significantly increased. 7. Twenty‐four hr after 1 u. oxytocin, milk [Na] and [cl] were decreased while [K], [lactose], [fat] and [protein] were increased. 8. During an I.V. infusion of oxytocin milk [Na] and [Cl] increased while [K] and [lactose] decreased. The passage of [(14)C]sucrose, 24Na and (36)Cl from blood to milk also increased. 9. These effects of oxytocin are discussed in relation to the permeability of the mammary epithelium and the pathways for ion movements, and to other studies on milk composition in the rabbit involving the administration of oxytocin to aid in the evacuation of milk.