bluuebunny/crossref_metadata_2025 huggingface dataset:
Extravascular albumin in bone tissue.
Authors: Owen M , Triffitt J T
Published: December 2014

1. The amount of albumin in extravascular tissue fluid in bone, kidney, intestine, skin and muscle and in plasma of young rabbits has been measured by radial immunodiffusion. 2. The majority of extravascular albumin in kidney, intestine, skin and muscle is exchangeable with plasma albumin, whereas in bone, only the proportion which is in tissue fluid is readily exchangeable; the remaining fraction in calcified matrix is more permanently fixed. 3. About 27% of the albumin in young bone is in tissue fluid, about 57% in calcified matrix and about 16% is intravascular. The total amount of extravascular albumin per unit mass of bone is similar to that found in soft tissues. 4. The volume of intravascular plasma in tissues was determined in two ways: from 51Cr‐erythrocyte radioactivity and the venous haematocrit and from the '5 min 125I‐fibrinogen space'. 5. The rate of egress of albumin from blood vessels has been estimated from the initial slope of the ratio of extravascular radioactivity in the tissue to plasma radioactivity plotted against time after injection of 125I‐albumin. 6. The rate of clearance of the albumin in extravascular tissue fluid in bone is approximately once every hour. This is more rapid than in skin and muscle, comparable with intestine and less rapid than in kidney. 7. The amount of albumin incorporated into calcified matrix of bone per day is calculated to be less than 0‐5% of the total albumin passing through the tissue fluid of bone per day.
Correlation analysis of muscle spindle responses to single motor unit contractions.
Authors: Binder M D , Kroin J S , Moore G P , Stauffer E K , Stuart D G
Published: December 2014

1. Cross‐correlation techniques have been used to study the responses of muscle spindle afferents from the soleus muscle of the cat to twitch contractions of single motor units. 2. Cross‐correlograms (post‐stimulus time histograms) were used to give the frequency of occurrence of a receptor spike at various times following the initiation of a motor unit contraction together with a display of the average twitch tension wave form. 3. The cross‐correlograms revealed that the contraction of a single motor unit can be an effective stimulus to a spindle receptor and may induce afferent firing pattern alterations similar to those observed with whole muscle contraction. 4. The cross‐correlograms also revealed quantitative differences in the response of a receptor to contraction of different motor units and to contraction of the same motor unit at different lengths. These differences reflect subtle changes in receptor deformation developed by the twitch of a motor unit under different conditions and by the twitches of different motor units. The results are consistent with anatomical data on the number and distribution of motor units and receptor organs in cat soleus. 5. These findings emphasize that rather than simply acting as generalized force or length sensors for the muscle as a whole, each receptor's spike train carries information about the state of a particular set of motor units.
Dual role for potassium in Balanus photoreceptor: antagonist of calcium and suppression of light‐induced current.
Authors: Brown H M , Ottoson D
Published: December 2014

1. The mechanism of reduction and final abolition of the depolarizing receptor potential of Balanus eburneus photoreceptors in K+‐free saline was examined with electro‐physiological techniques including voltage‐clamp and ion specific electrodes. 2. An extended exposure to K+‐free saline reduces the transient peak and the steady phases of the depolarizing receptor potential by approximately equal amounts. The process can be reversed in normal saline although the wave form of the response is often more rectangular upon recovery. Restoration of K+ induces a transient hyperpolarization of the resting membrane for several minutes. 3. The depolarizing receptor potential can also be restored in K+‐free solution by reducing the Ca2+ concentration. This saline depolarizes the resting membrane, and the wave form of the depolarizing receptor potential assumes a rectangular configuration. 4. Voltage‐clamp experiments revealed that an extended exposure to K+‐free saline produced an extreme reduction of the inward light‐induced current (LIC), but no detectable change in the membrane potential at which the current reverses sign. Membrane conductance in darkness showed little change. Reduction of the Ca2+ concentration from 20 to 0‐2 mM in K+‐free restored the current and produced a negative 8‐10 mV shift in the zero current potential. There was also a significant decrease in membrane conductance in darkness. 5. Current‐voltage relations of the membrane in K+‐free, low Ca2+, or K+‐free low Ca2+ salines were somewhat dependent upon the order the salines were presented. 6. Low Ca2+ saline (0‐2 mM) by itself produced a ‐5 mV shift in the zero‐current potential. Removing K+ in low Ca2+ produced an additional shift (‐5 mV) in the zero‐current potential.
Histamine metabolism of the guinea‐pig gastric mucosa.
Authors: Bergmark J , Granerus G , Henningsson S , Lundell L , Rosengren E
Published: December 2014

1. The mobilization of gastric mucosal histamine as reflected by changes in formation and content has been studied in guinea‐pigs on feeding and after injections of pentagastrin or 2‐deoxy‐D‐glucose. 2. Re‐feeding fasting guinea‐pigs as well as injections of pentagastrin or 2‐deoxy‐D‐glucose raised the rate of mucosal histamine formation; pentagastrin induced a fourfold rise. 3. Some properties of the enzyme catalysing the formation of histamine were examined. The results indicated that this enzyme is histidine decarboxylase, L‐histidine carboxy‐lyase, E.C. 4.1.1. 22. 4. The enzyme imidazole‐N‐methyl transferase, E.C. 2.1.1.8, which carries out methylation of the imidazole ring to yield 1‐methyl‐4‐(beta‐aminoethyl)imidazole (methylhistamine), was found in high amounts in the mucosa. The enzyme did not change upon stimulation of the mucosa. 5. The metabolism of histamine within the gastric mucosa is discussed in relationship to a suggested role of the amine in exciting acid secretion.
Localization of calcium‐accumulating structures in the anterior byssal retractor muscle of Mytilus edulis and their role in the regulation of active and catch contractions.
Authors: Atsumi S , Sugi H
Published: December 2014

1. The localization of Ca‐accumulating structures in the anterior byssal retractor muscle (ABRM) of Mytilus edulis and their role in the contraction‐relaxation cycle were studied by fixing the ABRM at rest or during various phases of mechanical activity with a 1% osmium tetroxide solution containing 2% potassium pyroantimonate. 2. In the resting ABRM, electron‐opaque pyroantimonate precipitate was observed at the inner surface of the plasma membrane, the vesicles and the mitochondria. 3. Electron X‐ray microanalysis showed the presence of Ca in the precipitate, indicating that the precipitate provides a valid measure for Ca localization. 4. In the ABRM fixed at the peak of mechanical response to the Ca‐removal or to acetylcholine, the precipitate was found to be diffusely distributed in the myoplasm in the form of a number of particles. At the completion of spontaneous relaxation, the precipitate was again seen at the inner surface of the plasma membrane. 5. During the catch state, the precipitate was found to be re‐accumulated in the peripheral structures with a corresponding decrease of the precipitate in the myoplasm. 6. These results not only provide evidence for the involvement of the Ca‐accumulating structures in the contraction‐relaxation cycle in the ABRM, but also suggest that the transition from active to catch contractions is related to a decrease in myoplasmic free Ca ion concentration.
The effect of calcium ions on the binomial statistic parameters that control acetylcholine release at preganglionic nerve terminals.
Authors: Bennett M R , Florin T , Pettigrew A G
Published: December 2014

1. A study has been made of the effects of changing [Ca]O and [Mg]O on the binomial statistic parameters p and n that control the average quantal content (m) of the excitatory post‐synaptic potential (e.p.s.p.) due to acetylcholine release at preganglionic nerve terminals. 2. When [Ca]O was increased in the range from 0‐2 to 0‐5 mM, p increased as the first power of [Ca]O whereas n increased as the 0‐5 power of [Ca]O; when [Mg]O was increased in the range from 5 to 200 mM, p decreased as the first power of [Mg]O whereas n decreased as the 0‐5 power of [Mg]O. 3. The increase in quantal release of a test impulse following a conditioning impulse was primarily due to an increase in n; the increase in quantal content of successive e.p.s.p.s in a short train was due to an increase in n and p, and the increase in n was quantitatively described in terms of the accumulation of a Ca‐receptor complex in the nerve terminal. 4. The decrease in quantal content of successive e.p.s.p.s during long trains of impulses over several minutes was primarily due to a decrease in n. These results are discussed in terms of an hypothesis concerning the physical basis of n and p in the release process.
Effects of various ambient temperatures and of heating and cooling the hypothalamus and cervical spinal cord on antidiuretic hormone secretion and urinary osmolality in pigs.
Authors: Forsling M L , Ingram D L , Stanier M W
Published: December 2014

1. Plasma ADH concentration, urinary and plasma osmolality and haematocrit were measured in young pigs placed in cold, thermoneutral, warm and hot ambient temperatures. In some experiments a thermode placed in the hypothalamus or over the cervical spinal cord was heated or cooled at various ambient temperatures. 2. Plasma ADH concentration remained at a low level (0‐5‐‐5 muu. ml.‐1) over 2 hr or 3 hr periods when the pigs were in cold, thermoneutral or warm ambient temperatures. A hot environment, which caused a marked rise in the pigs' rectal temperature, was associated with a large rise in plasma ADH level. 3. The rise in plasma ADH level which occurred during an increase in body temperature was consistently and completely suppressed by simultaneous cooling of the thermode in the pre‐optic region to 5 to 10 degrees C. When the thermode was in the region of the supraoptic nucleus the rise in ADH was only partly suppressed, and when it was over the cervical cord it was only sometimes suppressed. 4. Cooling the thermodes in any position at a cold or thermoneutral ambient temperature, or heating them at a thermoneutral or warm ambient temperature, caused no consistent change in ADH. 5. A diuresis, with a urinary flow‐rate of at most 1 ml. min‐1 and minimal urinary osmolality of 53 m‐osmole kg‐1, was observed on only three occasions, twice during cooling of a thermode in the hypothalamus and once after the end of a period when the thermode was heated. In each case, the plasma ADH was less than 2 muu. ml.‐1. 6. A slight rise of haematocrit in cold ambient conditions and a slight fall in the warm were observed. Otherwise changes in haematocrit were trivial, and a shift of water between vascular system and interstitium could not be invoked to account for changes in ADH levels. Observed variation of plasma osmolality was also slight.
Input‐output relation of transmission through cuneate nucleus.
Authors: Krnjević K , Morris M E
Published: December 2014

1. In decerebrate cats, micro‐electrodes were inserted into the cuneate nucleus to stimulate afferent terminals with single shocks of varying intensities. Estimates of the input and output of the nucleus were obtained by integrating antidromic responses in forelimb cutaneous nerves and orthodromic responses in the medial lemniscus. 2. Input‐output curves were normally very non‐linear, reflecting the high synaptic potency of small inputs. They were fitted readily by power functions, with exponents averaging 0‐50. 3. The normal input‐output relation rapidly disappeared after interruption of the blood supply. A loss of synaptic efficiency of small inputs was indicated by curves with exponents of greater than or equal to 1; this was associated with a sharp increase in terminal excitability. 4. Within the range of surface temperature 30‐40 degrees C, warming made the input‐output curves steeper but reduced terminal excitability, whereas cooling had the opposite effect. The efficiency of transmission was thus inversely correlated with terminal excitability. 5. The non‐linear shape of cuneate input‐output curves is probably not determined by inhibitory control, since picrotoxin depressed rather than enhanced outputs. 6. On the other hand, pentobarbitone made the input‐output curves markedly steeper and tended to lower terminal excitability.
The interaction of secretin and stimulants of gastric acid secretion in anaesthetized cats.
Authors: Braganza J M , Gibbs A C , Howat H T
Published: December 2014

1. In fasting anaesthetized cats in which the pylorus and common bile duct were occluded, acid secretion in response to caerulein, desulphated caerulein, histamine and N methyl histamine given singly and combined with Boots secretin 4 C.H.R. u./kg hr has been studied. 2. Eight separate estimates of the calculated maximal response of acid (four acid stimulants given with and without secretin) did not differ significantly from one another. In the presence of secretin the E.D.50 of each acid stimulant was lowered. 3. Outputs of acid in response to the smallest doses of desulphated caerulein, histamine and N methyl histamine increased significantly when secretin was infused (P less than 0‐05). 4. On a weight basis caerulein was 23, 474 and 95 times more potent than desulphated caerulein, histamine and N methyl histamine respectively. 5. When secretin was infused simultaneously caerulein was 8, 171 and 165 times more potent than desulphated caerulein, histamine and N methyl histamine respectively. 6. N methyl histamine was 5‐6 times more potent than histamine on a weight basis when infused on its own; and 1‐16 times more potent than histamine when given in the presence of secretin.
The location of cardiac vagal preganglionic motoneurones in the medulla of the cat.
Authors: McAllen R M , Spyer K M
Published: December 2014

1. Electrophysiological techniques have been used to locate the origin of preganglionic vagal motoneurones supplying the heart of the cat. 2. The right cardiac vagal branches were identified anatomically and their ability to slow the heart was assessed by electrical stimulation. Control experiments revealed that contamination of cardiac branches by bronchomotor and oesophageal efferent fibres was likely to be small. 3. Fifty‐seven neurones in the medulla were activated antidromically on stimulating the cardiac branches at up to 5 times the threshold for cardiac slowing. They had axons with conduction velocities between 3 and 15 m/sec, corresponding to B fibres. 4. None of these were located in the region of the dorsal motor nucleus of the vagus, in spite of repeated sampling there, but all were located in the region of the nucleus ambigus. Histological examination of marked neurones (forty‐six of the fifty‐seven neurones) revealed that they were associated with its principal column, rostral to the obex. 5. Sampling motoneurones of the dorsal motor nucleus revealed that most sent axons down the thoracic vagus below the cardiac branches. Only three of thirty‐three could be activated antidromically by high intensity stimulation of the cardiac branches, but on the basis of their thresholds and conduction velocities, it is argued that they were unlikely to be cardio‐inhibitory neurones. 6. It is concluded that preganglionic cardio‐inhibitory neurones arise not in the dorsal motor nucleus, but in the principal column of the nucleus ambiguus.
A comparison of the presynaptic and post‐synaptic actions of pentobarbitone and phenobarbitone in the neuromuscular junction of the frog.
Authors: Proctor W R , Weakly J N
Published: December 2014

1. Pentobarbitone or phenobarbitone, in increasing concentrations up to 0‐5 mM, progressively reduced the amplitude of miniature end‐plate potentials (min.e.p.p.s). Pentobarbitone was the more potent of the two barbiturates in this regard. 2. Both barbiturates produced a monotonic increase in mean quantum content of the end‐plate potential (e.p.p.) with increasing concentrations up to 0‐5 mM. Pentobarbitone and phenobarbitone were equally potent in their action on evoked transmitter release. 3. The effect, if any, of increasing concentrations of barbiturates on the e.p.p. amplitude was depression. Therefore, over the range of concentrations examined the enhancement of transmitter release was quantitatively less than the reduction in responsiveness of the post‐synaptic membrane. 4. Because of the greater ratio of post‐synaptic to presynaptic actions, pentobarbitone was more potent than phenobarbitone in reducing synaptic efficacy (e.p.p. amplitude). 5. It is concluded that the presynaptic actions of pentobarbitone and phenobarbitone contribute significantly to barbiturate‐induced changes in synaptic efficacy at low levels of transmitter release in the frog neuromuscular junction.
A voltage‐clamp study of the effect of two lidocaine derivatives on the time course of end‐plate currents.
Authors: Beam K G
Published: December 2014

1. Voltage‐clamped end‐plate currents (e.p.c.s) have been studied in the glycerol‐treated Rana pipiens sartorius nerve‐muscle preparations in normal Ringer solution and in the presence of QX‐222 and QX‐314. 2. Both QX‐222 and QX‐314, the trimethyl and triethyl analogues, respectively, of lidocaine, greatly modify end‐plate current kinetics. The altered e.p.c.s still show a true reversal potential, which is essentially the same as the reversal potential before drug treatment. The time course of the altered end‐plate currents varies with both membrane potential and drug concentration. 3. In the presence of 0‐1‐1‐0 mM QX‐222, end‐plate currents decay as the sum of three exponentials: I(t) =I1(0)e‐k1t+I2(0)e‐k2t+I3(0)e‐k3t, where the subscipts 1, 2 and 3 refer to the rapidly, intermediately, and slowly decaying components, respectively. Both the amplitudes, Ij(0), and the decay rates, kj, depend upon membrane potential. 4. Hyperpolarization increases the relative size of the first and third components, i.e. I1(0) and I3(0) increase relative to I2(0). Depolarization increases the relative size of the second component. 5. Hyperpolarization causes a decrease in the decay rates k2 and k3 and causes a slight increase in the decay rate k1. Dependence of the three decay rates on membrane potential is well described by: kj=bjeajv. 6. The Q10 of each of the kj is about 3. 7. Raising QX‐222 concentration, at any given membrane potential, augments I1(0) and I3(0) at the expense of I2(0). Raising concentration increases k1 and decreases k3; their voltage‐dependence is little affected. 8. At all QX‐222 concentrations tested the decay rate k2 is nearly the same as the decay rate of a normal e.p.c. recorded at an equivalent holding potential from the same fibre before drug exposure. 9. End‐plate currents in the presence of 0‐1 mM‐QX‐314 show a "major" or rapidly decaying phase and a very small, slowly decaying phase or "tail", but no intermediate component. Only the major component is discernible for end‐plate currents in 0‐5 mM‐QX‐314. 10. Voltage‐ and concentration‐dependence of the decay rate of the major component in QX‐314 is similar to k1 and QX‐222. Voltage‐dependence of the tails decay rate appears to be similar to k3. It is hypothesized that the second component in QX‐222 represents currents of unaltered or normal conductance kinetics, and that the first and third components in QX‐222, as well as the major component and tail in QX‐314, represent current of "QX‐altered conductance kinetics".
Vasodepressor effects obtained by drugs acting on the ventral surface of the brain stem.
Authors: Feldberg W , Guertzenstein P G
Published: December 2014

1. In cats anaesthetized with I.P. pentobarbitone sodium and atropinized with intravenous atropine methyl nitrate, the effects on arterial blood pressure were examined of nicotine, physostigmine, carbachol, glycine and pentobarbitone sodium applied to the exposed ventral surface of the brain stem by means of paired Perspex rings placed across the medulla. The drugs were placed inside each ring in a volume of 10mul. 2. Nicotine (0‐5‐6mg/ml.) produced a fall in blood pressure when the upper limit of the areas covered by the rings was about 5‐6 mm caudal, but not when it was just caudal to the trapezoid bodies. The depressor effect was obtained both on bilateral and unilateral application. After application the nicotine sensitive area became for several minutes insensitive to its renewed application. 3. The depressor effect of nicotine was sensitive to hexamethonium (50 mg/ml.) but resistant to atropine (50 mg/ml.) similarly applied. 4. When the nicotine sensitive areas had become insensitive to nicotine, bilateral carotid occulusion produced its normal sustained pressor response. 5. By applying the nicotine through a single Perspex ring which could be moved stepwise along and across the medulla, the nicotine sensitive area was localized and the highest sensitivity was found in a region around and a little caudal to the rootlets of the XIIth cranial nerve. 6. Physostigmine (25 and 50 mg/ml.) and carbachol (6 mg/ml.) produced a fall in blood pressure when the uppermost limits of the areas covered by the paired rings were 5‐6 mm caudal to and also when they were just caudal to the trapezoid bodies. From both regions the effects were obtained on bilateral and unilateral application. Their depressor effects were sensitive to atropine but resistant to hexamethonium similarly applied. 7. Glycine (200 mg/ml.) and pentobarbitone sodium (100 mg/ml.) produced scarcely any blood pressure effects when applied bilaterally to the nicotine sensitive areas but produced strong depressor effects on more rostral application, i.e. when the uppermost limit of the areas covered by the rings were just caudal to the trapezoid bodies. 8. It is concluded that the ventral surface of the medulla contains at least two bilateral areas from which vasodepressor effects are obtained on topical application of drugs: a more caudally situated one which is sensitive to nicotine, but insensitive to glycine and pentobarbitone sodium; a more rostrally situated one which is insensitive to nicotine but sensitive to glycine and pentobarbitone sodium; and both areas are sensitive to carbachol and physostigmine.
Transduction properties of tracheal stretch receptors.
Authors: Bartlett D , Sant'ambrogio G , Wise J C
Published: December 2014

1. Using single fibre vagal afferent recording, we have studied the behavior of slowly adapting stretch receptors located in an isolated, in situ, segment of the trachea in dogs. Responses to positive and negative steady and oscillating transmural pressures were investigated. 2. Seventy‐eight per cent of the receptors studied were tonically active at resting tracheal volume. Ninety per cent showed a more pronounced response to positive than to negative transmural pressures. 3. During pressure oscillations the majority of the receptors had a higher discharge frequency at any given pressure during the ascending phase of the pressure wave than at the same pressure under static conditions. During most of the ensuing descent of pressure toward zero the discharge frequency led transmural pressure. 4. With increasing frequency of oscillation the differences from the static responses increased (dP/dt sensitivity), especially during the ascending limb of the pressure oscillation (rectifying behavior). 5. In a small number of receptors, discharge frequency lagged behind transmural pressure or was in phase with it ("no loop" pattern). 6. In three cases the same receptor exhibited dP/dt sensitivity during positive pressure oscillations, whereas discharge frequency lagged behind pressure during negative pressure oscillations. This indicates that the lack of dP/dt sensitivity exhibited under negative pressure conditions does not represent an intrinsic property of these receptors, but reflects some aspect of their mechanical arrangement within the airway wall. 7. THESE PATTERNS OF RESPONSE ARE DISCUSSed in terms of intrinsic and extrinsic characteristics of the receptors. 8. The physiological implications of stretch receptor behaviour are also considered.
Co‐transport of glycine and sodium across the mucosal border of the midgut epithelium in the marine shrimp, Penaeus marginatus.
Authors: Ahearn G A
Published: December 2014

1. Influxes of glycine and Na across the mucosal border of the epithelial cells lining the midgut lumen of a marine shrimp have been examined. 2. Both mucosal JG and JNa displayed Michaelis‐Menten kinetics and the influx of each solute was markedly dependent upon the presence of the other solute in the bathing solution. A portion of JG occurred in the absence of Na, but JNa appeared to be completely dependent upon glycine. 3. Glycine influx Kt and Jmax were dependent upon [Na] while Na influx Kt and Jmax depended upon [glycine]. 4. K acted as a competitive inhibitor of Na binding to the co‐transport carrier by altering the Kt of glycine influx, but was without significant effect on the amino acid Jmax. 5. The coupling coefficient of mucosal co‐transport (JNa/JG) varied with the [Na] being 1‐1 at low [Na] (471 mM). 6. A model is proposed in which Na and glycine share ternary (NaXG) and quaternary (Na2XG) carrier complexes during their coupled influxes, but in which glycine may also traverse the mucosal membrane alone by way of an unshared binary (XG) carrier complex.
Growth of rats' kidneys after unilateral uretero‐caval anastomosis.
Authors: Morris G C
Published: December 2014

1. The relative significance of reduced excretion of urinary constituents and reduced renal mass, as stimuli to growth of one kidney after the other has been removed, has been investigated. 2. To abolish the excretory function of one kidney without removing it, the right ureter was drained into the vena cava through a compound cannula for 6 weeks. Uretero‐caval anastomoses were performed in twenty‐four male rats at 10 weeks of age: six survived without evidence of ureteric obstruction (and a further five with minimal obstruction). 3. The rats with anastomoses grew less than six other rats from which the right kidney had been removed or six which had been submitted to a sham operation, and their plasma urea and creatinine concentrations were higher. 4. Relative to body weight, the dry weight of each kidney after uretero‐caval anastomosis without obstruction was 18% greater than after sham operation; taking both kidneys together, the total increase was almost as much as in the left kidney alone after right nephrectomy (46%). 5. Histologically and in terms of DNA concentration, the growth of both kidneys after uretero‐caval anastomosis was of the same kind as in the left kidney after right nephrectomy. 6. The return of urine from one kidney into the blood provided a powerful stimulus to renal growth in spite of the restraining effect of increased renal mass.
Sites of autoregulatory escape of blood flow in the mesenteric vascular bed.
Authors: Greenway C V , Scott G D , Zink J
Published: December 2014

1. Stimulation of the sympathetic nerves to the intestinal vascular bed results in an initial decrease in blood flow followed by a recovery towards the control level. This recovery was termed autoregulatory escape by Folkow and his co‐workers and they suggested it was associated with a redistribution of blood flow within the intestinal wall. This theory has been examined in cats anaesthetized with pentobarbitone sodium. 2. The sympathetic nerves to the intestinal vascular bed were stimulated for 4 min periods at a submaximal frequency (4 Hz). The blood flows to individual parts of the superior mesenteric arterial bed (whole intestine, mucosal and submucosal layer, muscle layer of intestine, mesentery and lymph nodes, appendix and colon) were measured using radioactive microspheres before, at the peak of the vasoconstriction (30 sec), after autoregulatory escape had occurred (3‐5 min) and during the hyperaemia after cessation of nerve stimulation. 3. All parts of the mesenteric vascular bed showed a significant initial vasoconstriction followed by a recovery in the flow to a level not significantly different from the pre‐stimulation control flow. All parts showed a significant hyperaemia after cessation of stimulation. The distribution of the superior mesenteric flow at the peak of the vasoconstriction, after autoregulatory escape had occurred and during the hyperaemia after cessation of nerve stimulation was not significantly different from that during the control period. 4. It is concluded that all parts of the mesenteric vascular bed show autoregulatory escape and that this phenomenon is not associated with a redistribution of blood flow within the intestinal wall. Autoregulatory escape must involve relaxation of the same vessels which were originally constricted and various theories on the mechanism of the escape are discussed.
Stimulation of the sodium pump by azide and high internal sodium: changes in the number of pumping sites and turnover rate.
Authors: Erlij D , Grinstein S
Published: December 2014

1. The effects of 5 mM azide on [3H]ouabain uptake and 22Na efflux were determined. Both glycoside uptake and 22Na efflux were enhanced by azide. 2. Azide stimulated the Na pump in muscles whose pumping sites had been inhibited by ouabain and then transferred to a glycoside‐free solution. This stimulation was observed before detecting any recovery of the initial pumping activity. 3. When both the resting and the azide‐stimulated 22Na efflux had been blocked by ouabain, an additional exposure to azide, in a ouabain‐free solution, had no further effects on 22Na efflux. 4. It is concluded that the increase in Na pumping caused by azide is due in part to an increase in the number of pumping sites. 5. [3H]ouabain binding was measured in muscles with different intracellular alkali cation concentrations. Variations in [Na]i from 15 up to 50 mM did not significantly affect the amount of glycoside bound. A substantial increase in binding occurred when [Na]i reached 70 mM. 6. It is proposed that the increase in Na extrusion that occurs during the recovery of Na loaded muscles mostly results from an increased turnover rate of the pump rather than from an increase in number of pumping sites.
Kinetics and energetics of calcium efflux from intact squid giant axons.
Authors: Baker P F , McNaughton P A
Published: December 2014

The Ca efflux from intact squid axons consists of three major components: one that is activated by Cao, one that is activated by Nao and a residual flux that persists in the nominal absence of both Cao and Nao. The properties of these components have been investigated in unpoisoned axons and in axons poisoned with cyanide. 2. Under all conditions the shape of the curve relating Cao to Cao‐activated Ca efflux approximates to a section of a rectangular hyperbola, consistent with simple Michaelis activation. 3. The external Ca concentration giving half‐maximal activation of Cao‐activated Ca efflux is about 2 muM in unpoisoned axons immersed in Na‐ASW, but on poisoning changes progressively to values in the range 1‐10 mM. The residual efflux from unpoisoned axons may reflect activation by traces of Ca present immediately external to the axolemma. 4. The apparent affinity for Cao of Cao‐activated Ca efflux is very similar in unpoisoned axons immersed in sea waters containing Na, Li, Tris or K as major cation, whereas in poisoned axons the affinity in Na and Li is about the same but higher than that in choline and Tris. 5. In unpoisoned axons Ca influx increases linearly as Cao is increased from 2 muM to 110 mM. The absolute value of the Ca influx from 10 muM‐Cao is less than 1% of the Cao‐activated Ca efflux at this external Ca concentration. In poisoned axons the sizes of Cao‐activated Ca efflux and Ca influx were similar at all Ca concentrations examined. 6. The shape of the curve relating Nao to Nao‐activated Ca efflux approximates to a section of rectangular hyperbola in unpoisoned axons but is clearly sigmoidal in axons that have been fully poisoned with cyanide. The sigmoidal shape develops progressively during poisoning. ...
Threshold setting by the surround of cat retinal ganglion cells.
Authors: Barlow H B , Levick W R
Published: December 2014

1. The slope of curves relating the log increment threshold to log background luminance in cat retinal ganglion cells is affected by the area and duration of the test stimulus, as it is in human pyschophysical experiments. 2. Using large area, long duration stimuli the slopes average 0‐82 and approach close to 1 (Weber's Law) in the steepest cases. Small stimuli gave an average of 0‐53 for on‐centre units using brief stimuli, and 0‐56 for off‐centre units, using long stimuli. Slopes under 0‐5 (square root law) were not found over an extended range of luminances. 3. On individual units the slope was generally greater for larger and longer test stimulus, but no unit showed the full extent of change from slope of 0‐5 to slope of 1. 4. The above differences hold for objective measures of quantum/spike ratio, as well as for thresholds either judged by ear or assessed by calculation. 5. The steeper slope of the curves for large area, long duration test stimuli compared with small, long duration stimuli, is associated with the increased effectiveness of antagonism from the surround at high backgrounds. This change may be less pronounced in off‐centre units, one of which (probably transient Y‐type) showed no difference of slope, and gave parallel area‐threshold curves at widely separated background luminances, confirming the importance of differential surround effectiveness in changing the slope of the curves. 6. In on‐centre units, the increased relative effectiveness of the surround is associated with the part of the raised background light that falls on the receptive field centre. 7. It is suggested that the variable surround functions as a zero‐offset control that sets the threshold excitation required for generating impulses, and that this is separate from gain‐setting adaptive mechanisms. This may be how ganglion cells maintain high incremental sensitivity in spite of a strong maintained excitatory drive that would otherwise cause compressive response non‐linearities.
The effect of temperature on the reaction of carbon monoxide with oxygenated haemoglobin.
Authors: Sirs J A
Published: December 2014

1. The rate at which carbon monoxide displaces oxygen from its combination with haemoglobin in solution, has been measured spectrophotometrically, using a rapid‐mixing stopped‐flow technique. 2. In the presence of carbon dioxide, the reaction proceeds by a unimolecular dissociation, with a rate constant r. 3. The relationship of the reciprocal of r to the ratio PO2/PCO is non‐linear, and a different curve is obtained at each carbon monoxide concentration. 4. From measurements of the rate constant at temperatures between 5 and 35 degrees C, it is concluded that the non‐linearity is due to the formation at a finite rate of an intermediate complex, CO2Hb4O6, by the reaction of carbon dioxide with Hb4O6.
Stimulation of 45Ca2+ efflux from rat pituitary by luteinizing hormone‐releasing hormone and other pituitary stimulants.
Authors: Williams J A
Published: December 2014

1. Rat anterior pituitaries were incubated in medium containing 45Ca2+, superfused with non‐radioactive medium and the efflux of 45Ca2+ studied. 2. When pituitaries from overiectomized rats were used the addition of LH‐RH to the medium at a time when slow exponential efflux of Ca2+ was occurring produced a transient increase in 45Ca2+ efflux simultaneous with or before an increased release of LH. The stimulation of both 45Ca2+ efflux and LH release showed a similar concentration dependence on LH‐RH. 3. Increasing the K+ concentration of the medium tenfold also stimulated 45Ca2+ efflux and LH release. The response to LH‐RH of both parameters was reduced by superfusion with calcium‐free medium. 4. LH‐RH induced only a small increase in pituitary 45Ca2+ efflux when intact or thyroidectomized male rats were used. TRH increased 45Ca2+ efflux from thyroidectomized rat pituitaries but had only a small effect when pituitaries from intact or ovariectomized rats were studied. 5. Pretreatment of ovariectomized rats with oestradiol inhibited the subsequent increase in 45Ca2+ efflux induced by LH‐RH. 6. It is concluded that the secretagogue induced increase in 45Ca2+ efflux results from an increase in cellular Ca2+ activity which is presumably active in stimulus‐secretion coupling.
Influence of amygdala stimulation on the activity of identified tuberoinfundibular neurones in the rat hypothalamus.
Authors: Renaud L P
Published: December 2014

1. Extracellular action potentials were recorded from 1246 neurones in the mediobasal hypothalamus of pentobarbitone or urethane anaesthetized male rats. Antidromic invasion from the surface of the median eminence identified 165 cells, located in the arcuate and ventromedial nuclei and the periventricular area, as tuberoinfundibular neurones. The majority (65%) of these cells displayed no spontaneous activity. 2. Latencies for antidromic invasion from median eminence ranged from 0‐5 to 14‐0 msec (mean 4‐3 +/‐ 2‐9 msec, S.D.). Conduction velocities for axons of tuberoinfundibular neurones were under 1‐0 m/sec, and were slowest (under 0‐2 m/sec) for those tuberoinfundibular neurones located in the arcuate nucleus. 3. Single 1 HZ stimulation of amygdala evoked short latency (mean 18‐8 +/‐ 7‐0 msec; n = 30) excitation of tuberoinfundibular neurones in the ventromedial nucleus. Stria terminalis stimulation evoked similar responses at a shorter latency (mean 10‐2 +/‐ 3‐5 msec; n = 12) from other ventromedial tuberoinfundibular neurones. Three of these neurones were also excited by amygdala stimulation at comparably longer latencies. In spontaneously active tuberoinfundibular cells, the initial excitation was followed by a decrease in excitability lasting 70‐150 msec. Tuberoinfundibular neurones soldom followed orthodromic activation at frequencies beyond 30 HZ. 4. An initial decrease in activity at latencies of 18‐40 msec (mean 29‐2 +/‐ 10‐2 msec) characterized the amygdala evoked responses from nine tuberoinfundibular neurones. A similar response from one other tuberoinfundibular neurone followed stria terminalis stimulation at a latency of 11 msec. Most of these tuberoinfundibular neurones were located in the dorsal part of the ventromedial nucleus. 5. Two ventromedial tuberoinfundibular neurones also displayed antidromic invasion from the amygdala; interaction studies suggested an axon collateral pathway that originated close to the origin of the axon. 6. Tuberoinfundibular neurones unresponsive to amygdala stimulation were usually located in the arcuate nucleus or periventricular area. 7. These results provide electrophysiological evidence for a direct influence of the amygdala on the activity of tuberoinfundibular neurones in the ventromedial hypothalamic nucleus. There are also data to indicate that some ventromedial tuberoinfundibular neurones have axon collaterals that return to the amygdala. These reciprocal connexions between the amygdala and ventromedial tuberoinfundibular neurones may indicate neural circuits important for extrahypothalamic modulation of adenohypophyseal secretion.
Regeneration of afferent and efferent fibres to muscle spindles after nerve injury in adults cats.
Authors: Brown M C , Butler R G
Published: December 2014

1. The nerves to cat peroneus longus and tenuissimus muscles were either cut or crushed close to the muscle and the afferent and efferent nerve supply to the muscle spindles was studied electrophysiologically between 2 and 32 weeks later. 2. Recovery was more rapid and complete after crush than section for both afferent and efferent fibres. After recovery from either procedure normal primary and secondary afferents and static and dynamic gamma efferent fibres were found. 3. Some abnormally occurring neurones were found. One group consisted of beta fibres which had a static action on muscle spindles. Static beta fibres are very rarely found in normal muscles. 4. The results indicate that some guidance mechanism exists which after crush injuries of nerves may restore muscle receptor function almost to normal. Even after nerve section some muscle spindles may become correctly reinnervated.
Integrated electromyogram and oxygen uptake during positive and negative work.
Authors: Bigland-Ritchie B , Woods J J
Published: December 2014

1. Integrated electromyogram (e.m.g.) from the vastus lateralis muscles, and steady‐state rates of oxygen uptake, were measured simultaneously during the performance of set rates of positive (concentric) and negative (eccentric) work at 50 rev/min on a motorized bicycle ergometer. 2. Similar experiments were also carried out at other pedalling rates and using other leg muscles. 3. The relationships between each of the variables (integrated e.m.g., oxygen consumption) and mean torque on pedals were found to be linear (r greater than 0‐98) with a remarkable degree of reproducibility in surface e.m.g. for each subject over several months. 4. The ratio of the e.m.g. slopes at 50 rev/min (positive/negative) was 1‐96 +/‐ 0‐12 while the same ratio for the oxygen uptake slopes was 6‐34 +/‐ 0‐82. The discrepancy between the ratios suggests that not only is less muscle fibre activity required to maintain the same exerted force during negative work exercise, but there is also a substantial reduction in the oxygen uptake when the fibres are stretched. This was observed for all speeds of pedalling.
Spike initiation by transmembrane current: a white‐noise analysis.
Authors: Bryant H L , Segundo J P
Published: December 2014

1. Those features of a transmembrane current correlated with spike initiation were examined in Aplysia neurones using a Gaussian white‐noise stimulus. This stimulus has the advantages that it presents numerous wave forms in random order without prejudgement as to their efficacies, and that it allows straightforward statistical calculations. 2. Stimulation with a repeating segment of Gaussian white‐noise current revealed remarkable invariance in the firing times of the tested neurones and indicated a high degree of reliability of their response. 3. Frequencies (less than 5 Hz) involved in spike triggering propagated faithfully for up to several millimetres, justifying intrasomatic current injection to examine spike initiation at the trigger locus. 4. Examination of current wave forms preceding spikes indicated that a wide variety could be effective. Hence, a statistical analysis was performed, including computation of probability densities, averages, standard deviations and correlation coefficients of pairs of current values. Each statistic was displayed as a function of time before the spike. 5. The average current trajectory preceding a spike was multiphasic and depended on the presence and polarity of a d.c. bias. An early relatively small inward‐ or outward‐going phase was followed by a large outward phase before the spike. The early phase tended to oppose the polarity of the d.c. bias. 6. The late outward phase of the average current trajectory reached a maximum 40‐‐75 msec before triggering the action potential (AP) and returned to near zero values at the moment of triggering. The fact that the current peak occurs in advance of the AP may be partially explained by a phase delay between the transmembrane current and potential. The failure of the average current trajectory to return to control values immediately following the peak argues for a positive role of the declining phase in spike triggering. 7. Probability densities preceding spikes were Gaussian, indicating that the average was also the most probable value. Although the densities were broad, confirming that spikes were preceded by a wide variety of current wave forms, their standard deviations were reduced significantly with respect to controls, suggesting preferred status of the average current trajectory in spike triggering. 8. The matrix of correlation coefficients between current pairs suggested that spikes tended to be preceded by wave forms that in part kept close to the average current trajectory and in part preserved its shape. 9. The average first and second derivatives of spike‐evoking epochs revealed that current slope and acceleration, respectively, were most crucial in the last 200 msec before spike triggering, and that these dynamic stimulus components were more important for a cell maintained under a depolarizing, rather than a hyperpolarizing bias. 10...
Lung inflation and alveolar permeability to non‐electrolytes in the adult sheep in vivo.
Authors: Egan E A , Nelson R M , Olver R E
Published: December 2014

1. Experiments were performed on adult sheep to determine the effect of lung distension on the passive permeability of alveoli to water soluble non‐electrolytes. With the animal breathing oxygen spontaneously, a segment of one lung was isolated by passing a balloon‐tipped catheter through a tracheostomy into a distal bronchus. This isolated atelectatic segment was filled with an isosomotic saline solution containing radio‐labelled solutes of known molecular size: [125I]albumin, [14C]inulin, [14C]‐sucrose, [3H]mannitol, and [14C]urea. The segment was inflated with oxygen either to a preselected pressure, or to a predetermined fraction of its capacity. Inflation was then maintained for several 10‐15 min periods between which the oxygen supply was disconnected and the saline sampled, allowing the tracer concentrations to be measured. 2. At low inflating pressures (20‐32 cmH2O) and at low volumes (24‐54% of capacity), alveolar permeability to water soluble solutes was slight and could be characterized in terms of a membrane penetrated by cylindrical water filled pores of 0‐5‐1‐6 nm radius. In all experiments showing restricted diffusion, absorption of saline occurred. 3. There was a positive correlation between the degree of lung inflation and pore radius in both the pressure controlled and volume controlled experiments. At high inflating pressures and at inflation volumes which were close to the total capacity of the isolated segment, restriction of solute diffusion was lost; in five out of six such experiments there was a net movement of liquid into the alveoli. 4. These results can be explained by postulating that as the lung epithelium is progressively stretched there is an opening up of water filled channels between alveolar cells. At peak inflation, restriction of diffusion of water soluble solutes is lost, and the alveolar epithelium ceases to function as a barrier between the circulation and air spaces.