bluuebunny/crossref_metadata_2025 huggingface dataset:
Resting tension and the form of the twitch of rat skeletal muscle at low temperature
Authors: Hill D. K.
Published: December 2014

1. A study has been made of the effect of temperature on the resting tension and on the form of the isometric twitch of isolated rat skeletal muscle. The soleus and the extensor digitorum longus (EDL) were used as representatives of slow and fast types of muscle. The main interest is in the behaviour at low temperature, when rat muscle shows characteristics which are not found with frog muscle.

2. At higher temperatures both soleus and EDL of the rat resemble frog muscle in showing a ‘rubber‐like’ form of resting tension, i.e. the tension increases with warming: this has not previously been demonstrated in mammalian muscle. But at low temperatures (below 15° C) the converse is observed; tension then increases as temperature falls. This ‘cold tension’ is much larger with soleus than with EDL. The ‘cold tension’ is the converse of the ‘rubber‐like’ tension also in its dependence on length; it becomes smaller when the muscle is stretched.

3. These muscles remain excitable and give consistent twitches with transverse stimulation at temperatures down to about 3° C provided the exposure to cold is not prolonged beyond a few minutes. The amplitude of the twitch is reduced by cooling, e.g. at 3° C it is about 30–50% of that at 25° C.

4. The twitch becomes very prolonged at low temperatures. With a soleus at 3‐4° C it may last 40 sec. The temperature coefficient of the rate constant of the relaxation phase is very high compared with that of frog's muscle.

5. The rate constant of relaxation in a twitch at low temperature increases when the muscle is stretched. This is the reverse of what happens at higher temperature.

6. The extreme prolongation of the twitch with cooling indicates a very large decrease in the rate of decay of the active state, and it is suggested that the increase of resting tension at low temperature is due to an accumulation of ‘activator’.
Visual acuity in the blue cone monochromat
Authors: Green Daniel G.
Published: December 2014

1. To isolate the blue cones of the normal eye, blue sine‐wave gratings were superimposed on a bright yellow background. Threshold contrasts for resolution of the gratings were then determined.

2. Under these conditions visual acuity for high contrast gratings on four normal subjects was on the average 0·31 min−1. This is about a factor of 6 lower than grating acuity under optimal conditions.

3. The contrast sensitivity of two subjects who lack the normal red and green receptor mechanisms was measured using blue sinusoidally modulated gratings. Visual acuity was found to be greatly reduced from normal. The low acuity of these individuals is due to both a reduction in contrast sensitivity and a reduction in resolution.

4. The spatial resolving characteristics of these subjects resembles the vision of the normal eye under conditions which isolate the blue sensitive mechanisms.

5. The vision of the cone monochromat differs significantly from that of the more typical rod monochromat. The rod monochromat has even lower acuity than the blue cone monochromat for high contrast gratings but has much greater contrast sensitivity for gratings of low spatial frequency.
Effects of denervation and reinnervation on the responses of kitten muscles to acetylcholine and suxamethonium
Authors: Jones Rosemary , Vrbová Gerta
Published: December 2014

1. The development of the high sensitivity of the adult neuromuscular junction to the blocking and depolarizing action of suxamethonium was studied in kittens of different ages.

2. It was found that the sensitivity to the depolarizing effects of suxamethonium increases simultaneously with that to the blocking effects of the drug during the 3rd–6th week of life. The increase of sensitivity to the blocking effects of suxamethonium during development can therefore be accounted for by the depolarizing effect of the drug.

3. When the nerve is crushed during the first week of the animal's life and then left to regenerate, the development of the high sensitivity of the neuromuscular junction to suxamethonium and acetylcholine is impaired. Thus during development the nerve is essential for the induction of the high sensitivity of the neuromuscular junction to acetylcholine as well as to other depolarizing drugs.

4. The blocking and depolarizing effects of suxamethonium on reinnervated muscles of cats at different ages were compared. The depolarizing action of suxamethonium on reinnervated end‐plates is always smaller, but its blocking effect is not. In young animals the blocking effect of suxamethonium on reinnervated muscles is smaller, whereas reinnervated muscles of adult animals are extremely sensitive to the blocking effects of the drug.

5. 24–36 hr after denervation cat muscles were more sensitive to the blocking effects of suxamethonium but the depolarizing effect of the drug on the end‐plate region was smaller. It thus appears that the nerve not only induces but also maintains the high sensitivity of the end‐plate region to depolarizing drugs.
Time course of changes in renal tissue and urinary composition after cessation of constant infusion of lysine vasopressin in the conscious, hydrated rat
Authors: Atherton J. C. , Green R. , Thomas S. , Wood Jeanne A.
Published: December 2014

1. The changes in urinary and renal tissue composition in conscious rats were determined for up to 2 hr following the cessation of intravenous infusion of lysine vasopressin, LVP (at 60 μu./min. 100 g body wt. for 4½ hr). A constant water load (4% body wt.) was maintained during and after lysine vasopressin infusion, by quantitative replacement of excreted water. In these circumstances, any changes in urinary and renal tissue composition are presumed to represent direct consequences of the rapid plasma and tissue clearance of lysine vasopressin.

2. Urinary flow increased and osmolality decreased, rapidly, reaching stable values characteristic of sustained water diuresis after about 60 min.

3. The steepness of the corticomedullary solute concentration gradients also decreased rapidly. Papillary Na and urea concentrations fell to values characteristic of sustained water diuresis in about 45 min.

4. The changes in medullary composition were compounded of a moderate significant increase in water content, a moderate, significant decrease in Na content, and a profound decrease in urea content.

5. In the eventual steady‐state water diuresis, urinary outputs of Na and K were significantly lower, and of NH4 significantly higher, than those observed in control experiments where LVP infusion was continued for the corresponding 2 hr.

6. It is concluded that the diuresis following the cessation of LVP infusion is due not merely to reduced nephron permeability to water but also to a rapid reduction in the osmotic force responsible for water reabsorption from the collecting duct.
The onset and development of transmission in the chick ciliary ganglion
Authors: Landmesser Lynn , Pilar G.
Published: December 2014

1. The onset and development of transmission has been studied electro‐physiologically in the isolated chick ciliary ganglion from Stage 25 (Hamburger & Hamilton, 1951) until 28 days after hatching. Ultrastructure of the synapses was concomitantly investigated.

2. Synaptic transmission began at Stage 26½ and was 100% in both cell groups, ciliary and choroid, by Stage 33. It was initially chemical until Stage 41 when effective electrical coupling first appeared in the ciliary population. The proportion of electrically transmitting synapses increased to 80% by 1‐2 days post‐hatching.

3. Few morphological synapses were present at Stage 33½ when all ganglion cells were transmitting. A scarcity of synaptic vesicles persisted until late in embryonic development when all ciliary cells possessed calyces. At hatching the calyces were filled with synaptic vesicles.

4. Initial synaptic contacts were by fine terminal branches often on the intricate processes of early ganglion cells. Calyces formed from Stage 36½ and there was a concomitant retraction of ganglion cell processes, so that by Stage 40 all ciliary cells had simple calyces. The calyx was a transitory structure, which from the first week post‐hatching began to break up into a cluster of boutons.

5. Chemical post‐synaptic potentials (PSPs) were at Stage 40 long (30 × the membrane time constant) and further prolonged by eserine. By Stage 43, PSPs had become markedly shortened and were unaffected by eserine. No simple explanation can be offered for the changes in PSP time course and sensitivity to anticholinesterases during development.

6. Intracellular records from Stage 40 ciliary cells, which all possess calyces, showed 1‐2 mV amplitude, diphasic, fast decaying electrical coupling potentials (CPs). Later in development the CPs became 20–40 mV amplitude, more slowly decaying and monophasic. This seemed to be correlated with faster presynaptic conduction velocities and myelination of the cell soma. Such changes in CPs may reflect a shift from capacitative to more resistive coupling and point to several factors contributing in varying degrees to the electrical transmission.

7. Presynaptic fibres innervating ciliary cells were from the start of lower threshold and faster conduction velocity than those innervating ciliary cells, as occurred in the adult. It is concluded that these preganglionic fibres were probably specified by the time transmission starts and that they selectively innervated the proper post‐synaptic cells.
Hypothalamic endogenous noradrenaline and thermoregulation in the cat and rabbit
Authors: Cranston W. I. , Hellon R. F. , Luff R. H. , Rawlins M. D.
Published: December 2014

1. The imino‐dibenzyl drugs, imipramine and desipramine, which inhibit the uptake by neurones of noradrenaline, were injected into the lateral cerebral ventricles of cats and rabbits: changes in body temperature resulted which were different for the two species, but nevertheless closely resembled those following intraventricular injection of relatively large quantities of exogenous noradrenaline.

2. The endogenous noradrenaline content of the hypothalamus in both species was reduced by repeated injections into the lateral ventricle of the methyl ester of
DL‐α‐methyl‐p‐tyrosine: in animals so treated the hypothalamic content of 5‐hydroxytryptamine was not significantly changed.

3. Noradrenaline‐depleted animals showed significantly reduced responses to intraventricular imipramine and desipramine. The diminished responses were primarily due to reduction in endogenous noradrenaline.

4. These observations indicate that endogenous noradrenaline, present in the hypothalamus, can influence body temperature in cats and rabbits.
The mechanical efficiency of treadmill running against a horizontal impeding force
Authors: Lloyd B. B. , Zacks R. M.
Published: December 2014

1. A method for determining the apparent mechanical efficiency of running against a horizontal impeding force is described. The results of studies on three well trained athletes have been summarized.

2. A linear relation was found between metabolic rate and external work rate. The apparent mechanical efficiency was calculated as the inverse of the slope of the linear regression line of metabolic rate on external work rate × 102 (percentage).

3. The over‐all mean for apparent load‐running efficiency (LRE) was 36·1%. The differences in LRE between subjects were not statistically significant. No measurable change in LRE occurred with habituation.

4. Values are given for Ek, the net energy cost of unloaded horizontal treadmill running per kilogram of bodyweight and per kilometre of distance covered. The over‐all mean for Ek was 0·83 kcal. kg−1. km−1.

5. The efficiency values obtained are discussed and compared with other values of running efficiency obtained by different methods, and with studies on isolated muscle.
Changes in the activity of sarcoplasmic reticulum fragments and actomyosin isolated from skeletal muscle of thyroxine‐treated cats
Authors: Ash A. S. F. , Besch H. R. , Harigaya S. , Zaimis Eleanor
Published: December 2014

1. Sarcoplasmic reticulum fragments (SRF) and actomyosin were isolated from skeletal muscle of cats treated either with thyroxine or with placebo tablets, for 5–16 months.

2. Ca2+ uptake and binding by SRF, measured in the presence and absence of oxalate respectively, were reduced by thyroxine treatment.

3. Actomyosin from the thyroxine‐treated animals underwent ATP‐induced syneresis at a faster rate than did that from the controls.

4. Syneresis of the actomyosin preparations from controls and treated animals was inhibited to the same extent by EGTA when rates of syneresis were made the same by adjustment of the KCl concentration in the assay media. In contrast, at any given KCl concentration, syneresis of actomyosin from thyroxine‐treated animals was inhibited to a lesser extent by EGTA.

5. At the end of the isolation procedure, the amount of Ca2+ remaining in the actomyosin suspension was similar for both treated and control animals.

6. It was concluded that the effect of thyroxine on skeletal muscle may be the result of an action on both the sarcoplasmic reticulum and the contractile protein complex.
Magnesium exchange in rat ventricle
Authors: Page Ernest , Polimeni Philip I.
Published: December 2014

1. The exchange of cellular Mg with external 28Mg in the rat left ventricle was measured in vivo and, under conditions approximating a steady state, in an isolated, working rat heart perfused and contracting at 36–38° C.

2. About 98% of cellular Mg exchanged at a single rate.

3. The rate of exchange in vivo was the same as that observed in independent in vitro measurements of the influx and efflux at the physiological external Mg2+ concentration of 0·56 m
M. The rate was 0·15 ± 0·02 m‐mole/(kg dry ventricle.min) or 0·21 ± 0·02 p‐mole/(cm2.sec).

4. In the perfused heart the dependence of the influx on the external Mg concentration was hyperbolic with an apparent Vmax of 0·31 ± 0·04 m‐moles/(kg dry weight.min) and an apparent Km of 0·57 ± 0·08 m
M.

5. The Mg efflux into a solution containing 2·8 m
M‐Mg was markedly faster than that into a Mg‐free solution.

6. These results are interpreted as consistent with a carrier‐mediated transport of Mg across the plasma membrane.
Physiological and structural changes in the cat's soleus muscle due to immobilization at different lengths by plaster casts*
Authors: Tabary J. C. , Tabary C. , Tardieu C. , Tardieu G. , Goldspink G.
Published: December 2014

1. Passive length—tension curves were established for cat soleus muscles that had been immobilized in different positions. Muscles that had been immobilized in the lengthened position showed no difference in their length—tension properties to those of normal muscles. However, those immobilized in the shortened position showed a considerable decrease in extensibility.

2. Muscle fibre length, sarcomere length and the total number of sarcomeres along single teased fibres were also determined for muscles immobilized in different positions. Soleus muscles immobilized in the lengthened position were found to have 20% more sarcomeres in series than normal muscles whilst those immobilized in the shortened position had 40% less than normal muscles.

3. When the plaster casts were removed from muscles that had been immobilized in the shortened position, the length—tension curves and sarcomere number returned to normal within 4 weeks. Muscles that were immobilized in a shortened position and then immobilized in a second position were found to rapidly adjust to the second position with respect to their passive length—tension properties and sarcomere number.

4. A change in the number of sarcomere in series seems to be the way in which the sarcomere length of the muscle is adjusted to its new functional length. The change in the length—tension properties which accompanies a decrease in sarcomere number appears to be the mechanism which prevents the muscle from being overstretched.
Species difference in the choleretic response to bile salts
Authors: Klaassen Curtis D.
Published: December 2014

1. Cholic, taurocholic and dehydrocholic acids were administered
I.V. to rats, rabbits and dogs (3·12–100 mg/kg). With the higher doses of cholic acid, the bile flow was increased sixfold in the dog and only 2 to 2½‐fold in the rat and rabbit. The choleretic response was also maintained for a longer time in the dog (90 min) than in the rat or rabbit (20–30 min).

2. Similar species differences in the choleretic response to taurocholic acid and dehydrocholic acid were observed. However, the bile flow returned to control rates more rapidly for cholic acid (10–15 min for rat and rabbit, 45 min for dog) and more slowly for dehydrocholic acid (25–40 min for rat and rabbit, 120 min for dog).

3. Cholic acid is conjugated more rapidly by the rabbit and rat than dog.

4. An increase in the biliary bile acid concentration was observed in all three species after the
I.V. administration of the bile acid excreted by each species.

5. Control bile flow was much higher in the rat (50 μl./min.kg) and the rabbit (70 μl./min.kg) than in the dog (5 μl./min.kg).

6. Part of the difference in the choleretic response of the three species to the bile acids appears to be due to this difference in basal bile production.

7. Administration of taurocholic acid to the rat increases the biliary bile acid concentration in the bile but the bile flow may either increase or decrease, questioning the mechanism by which bile acids increase bile flow.
The post‐natal changes in minimal metabolic rate in the pig
Authors: Studzinski T.
Published: December 2014

1. Minimal metabolic rate was measured as oxygen consumption in new‐born pigs when environmental temperature was rising and passing through thermal neutrality.

2. Three different periods were observed in 20 days after birth. The first period included the time from birth to 82 hr and was characterized by a continuous rise in minimal metabolic rate from 9·4 to 16·0 ml. O2/kg.min (70% increase). The second period extended from 82 hr to 9·5 days with values near to 16 ml. O2/kg.min. The third period beginning on the eleventh day lasted until observations ceased on the twentieth day and was characterized by a 25–30% fall in minimal metabolic rate when compared with the second period.

3. Minimal metabolic rates from the second and third period were proportional to body weight and not to the surface area. Exponential factors for body weight were 0·93 and 0·96 for the second and third periods respectively.

4. Rectal temperature rose from 38·6° C on the first day to 39·3° C on the second and 39·5° C on the fourth day after birth.

5. Environmental temperature associated with minimal metabolic rate showed a general tendency to fall from 36·5 in the first 4 days to between 33 and 34° C in the following days.

6. Age rather than body weight is the decisive factor influencing changes in minimal metabolic rate in the new‐born pig.
Axon‐schwann cell interaction in the squid nerve fibre
Authors: Villegas Jorge
Published: December 2014

The electrical properties of Schwann cells and the effects of neuronal impulses on their membrane potential have been studied in the giant nerve fibre of the squid.

1. The behaviour of the Schwann cell membrane to current injection into the cell was ohmic. No impulse‐like responses were observed with displacements of 35 mV in the membrane potential. The resistance of the Schwann cell membrane was found to be approximately 103 Ω cm2.

2. A long‐lasting hyperpolarization is observed in the Schwann cells following the conduction of impulse trains by the axon. Whereas the propagation of a single impulse had little effect, prolonged stimulation of the fibre at 250 impulses/sec was followed by a hyperpolarization of the Schwann cell that gradually declined over a period of several minutes.

3. The prolonged effects of nerve impulse trains on the Schwann cell were similar to those produced by depolarizing current pulses applied to the axon by the voltage‐clamp technique. Thus, a series of depolarizing pulses in the axon was followed by a long‐lasting hyperpolarization of the Schwann cells. In contrast, the application of a series of hyperpolarizing 100 mV pulses at a frequency of 1/sec had no apparent effects.

4. Changes in the external potassium concentration did not reproduce the long‐lasting effects of nerve excitation.

5. The hyperpolarizing effects of impulse trains were abolished by the incubation of the nerve fibre in a sea‐water solution containing trypsin.

6. These findings are discussed in relation to the possible mechanisms that might be responsible for the long‐lasting hyperpolarizations of the Schwann cells.
Chromatic sensitivity and spatial organization of LGN neurone receptive fields in cat: cone‐rod interaction
Authors: Hammond P.
Published: December 2014

1. The results described are for detailed analyses of fifty‐four isolated LGN units, in response to monochromatic stimuli presented against achromatic, mid‐mesopic backgrounds. Forty‐seven were positively identified cells from the A‐laminae; the remaining seven were fibres from the optic radiation.

2. Cells are classified according to firing pattern. Phasic cells respond almost exclusively with a discharge transient. Tonic cells, by contrast, give a maintained component in addition. In general, tonic cells possess higher spontaneous firing frequencies than phasic cells and the antagonistic surrounds of their receptive fields are more potent. In other respects the two classes appear to be functionally similar.

3. All cells within the A‐laminae receive input involving both rods and 556 nm cones.

4. The spatial organization of geniculate receptive fields, unlike retinal fields, is little different for cone and rod vision. In the infrequent instances where a change is apparent, it is small and can go in either direction: rod fields are then on balance slightly larger than cone fields.

5. The locus of maximum sensitivity for the receptive field surround is described by a circle, concentric with the field centre; it is invariant with respect to stimulus geometry, or changeover from cone to rod vision.

6. This result implies that the receptive field surround mechanism does not extend through the field centre. It supports the notion that the centre and surround of each geniculate cell receptive field are mediated by discrete retinal inputs.
Conductance change during the inhibitory potential in the guinea‐pig taenia coli
Authors: Tomita T.
Published: December 2014

1. Effects of membrane polarization and of reduction in external K and Cl concentration on the inhibitory potential were investigated in the guinea‐pig taenia coli.

2. Depolarization of the membrane increased the inhibitory potential while hyperpolarization decreased it. The relationship between the degree of membrane polarization and the amplitude of inhibitory potential was linear. The inhibitory potential was abolished or slightly reversed in polarity, when the membrane was hyperpolarized by 25–40 mV in different preparations.

3. Removal of external K ion depolarized the membrane for about 5 min and increased the inhibitory potential more than could be accounted for by the depolarization. Readmission of K transiently hyperpolarized the membrane, probably due to an activation of the Na‐K pump, and reduced the inhibitory potential, but no reversal of polarity in the inhibitory potential was observed during this hyperpolarizing phase.

4. The membrane was transiently depolarized when the external Cl concentration was reduced by substituting with isethionate. Hyperpolarization was produced by restoring the external Cl concentration to normal. Changes in the amplitude of inhibitory potentials during alterations in Cl concentration occurred as expected from the shift of the membrane potential.

5. From the results, it is concluded that the membrane conductance is increased during the inhibitory potential, and that an increase in the K permeability is the main factor for hyperpolarization of the membrane.
The receptors concerned in the actions of catecholamines on glucose release, membrane potential and ion movements in guinea‐pig liver
Authors: Haylett D. G. , Jenkinson D. H.
Published: December 2014

1. Experiments have been made to identify the kinds of receptors concerned in the actions of catecholamines in increasing potassium efflux, membrane potential and glucose release in tissue slices prepared from guinea‐pig liver.

2. Glucose release could be accelerated by activation of either of two distinct receptors, one of which resembles the α receptor of Ahlquist's classification, the other being β‐like. Thus both amidephrine and isoprenaline (sympathomimetic amines which selectively activate α and β receptors respectively) elicited the response.

3. The effect of isoprenaline on glucose release was inhibited by the β blocking agent propranolol (1 μ
M) but not by the α blocker phentolamine (10 μ
M), whereas the converse held for amidephrine. However, the degree of antagonism observed with phentolamine was less than found in smooth muscle, suggesting that the α‐like receptor in the liver may differ somewhat from that in other tissues, or be less accessible to the antagonist.

4. Amidephrine, like noradrenaline, increased the efflux of 42K from the slices and caused hyperpolarization, suggesting that the increase in potassium permeability underlying these responses is α‐mediated. This conclusion was supported by the finding that the effect of amidephrine on membrane potential was inhibited by phentolamine but not propranolol (1 μ
M).

5. In keeping with this interpretation, low concentrations (20–50 n
M) of isoprenaline, although sufficient to activate the β receptors (as judged by the effect on glucose release) had little effect on the ionic composition of the tissue, and caused only a small increase in 42K efflux. Thus the ‘ion movement’ and ‘glucose’ responses could be largely dissociated.

6. Larger concentrations (1–6 μ
M) of isoprenaline increased 42K efflux to a greater extent, although the effect was always less than with the same concentration of noradrenaline.

7. Activation of the β‐receptors caused a small and inconsistent hyperpolarization which became more pronounced and also more reproducible on replacing the chloride content of the bathing fluid by the larger anion isethionate.

8. Although these results show that activation of either of two distinct adrenergic receptors in guinea‐pig liver can cause the same end‐response (e.g. an increase in glucose release, or, under some circumstances, hyperpolarization of the cell membrane), the underlying mechanisms cannot be assumed to be identical. This is discussed.
Cholinergic and non‐cholinergic transmission in the medial geniculate nucleus of the cat
Authors: Tebēcis Andris K.
Published: December 2014

1. Studies involving the electrophoretic administration of antagonists of ACh (atropine, DHβE) and cholinesterase inhibitors (neostigmine, physostigmine) to MGN neurones indicate that ACh is an excitatory transmitter in the feline MGN, most probably released from fibres which originate in or traverse the mesencephalon.

2. Auditory afferents to the MGN, cortico‐geniculate fibres and the excitatory fibres which mediate ‘spontaneous’ firing of MGN neurones are unlikely to be cholinergic.

3. Almost all geniculo‐cortical relay cells are excited by ACh, this excitation being mediated by receptors which have both muscarinic and nicotinic properties. The excitation of relay cells by ACh is sometimes preceded or followed by a depression of firing which is resistant to atropine and DHβE, but the significance of this depression is unknown.

4. The firing of many unidentified MGN neurones is depressed by ACh in the absence of any excitation, and this depression is blocked by both atropine and DHβE, and potentiated by anticholinesterases. This type of depression by ACh may be related to cholinergic inhibition, but this possibility has yet to be investigated.
Prostaglandin action on pancreatic blood flow and on electrolyte and enzyme secretion by exocrine pancreas in vivo and in vitro
Authors: Case R. M. , Scratcherd T.
Published: December 2014

1. Intra‐arterial injection or infusion of prostaglandins E1 and E2 into anaesthetized cats caused a fall in arterial blood pressure, a reduction in pancreatic blood flow and an inhibition of secretin‐stimulated pancreatic electrolyte secretion. In some experiments these effects were preceded by a transient increase in blood flow and secretion.

2. The fall in blood pressure and reduction in blood flow, but not the inhibition of secretion, were much less marked following administration of the α‐adrenergic blocking agent phenoxybenzamine.

3. Prostaglandins F1α and F2α caused only a slight reduction in blood pressure and had very little effect on pancreatic blood flow or electrolyte secretion.

4. Addition of prostaglandins to the perfusate of the saline‐perfused cat pancreas stimulated electrolyte secretion, with E1 = E2 ≫ F1α = F2α. This stimulatory action was markedly potentiated by theophylline.

5. Enzyme secretion was not stimulated by any of the prostaglandins, even in the presence of theophylline.

6. It is concluded that prostaglandins can stimulate electrolyte transport by exocrine pancreas, perhaps through a mechanism involving adenylate cyclase, but that in vivo this action is masked by a secondary inhibition resulting either from vasoconstriction, or from the libration of an antisecretory agent, or both.
The kinetics of transmitter release at the frog neuromuscular junction
Authors: Barrett Ellen F. , Stevens C. F.
Published: December 2014

1. Fluctuations in the latency of focally recorded end‐plate currents were analysed to determine the time course of the probabilistic presynaptic process underlying quantal release evoked after single nerve stimuli at the frog neuromuscular junction.

2. The early falling phase of the presynaptic probability function can be fitted by a single exponential over two orders of magnitude of quantal release rate. The time constant of the early falling phase is about 0·5 msec at 11° C, and increases with decreasing temperature with a Q10 of at least 4 over the range 1–12° C.

3. After this early exponential fall, quantal release probability returns to control levels with a much slower time course.

4. Conditioning nerve stimuli increase the magnitude and slightly prolong the early time course of release evoked by a test stimulus. When facilitation is calculated for matched time intervals following the conditioning and testing stimuli, it is found that the magnitude of the small, late residual tail of release is facilitated by a greater percentage than the magnitude of larger, early portions of release.

5. These results are discussed in terms of the hypothesis (Katz & Miledi, 1968) that evoked release and facilitation are mediated by a common presynaptic factor which activates release in a non‐linear manner.
Synaptic frequency response: the influence of sinusoidal changes in stimulation frequency on the amplitude of the end‐plate potential
Authors: Landau E. M. , Lass Y.
Published: December 2014

1. The synaptic response to frequency modulated trains of stimuli was investigated at the neuromuscular junction of the frog. The frequency of stimulation was usually varied sinusoidally about a carrier frequency of ca. 25 impulses per sec (Hz).

2. The post‐synaptic response to sinusoidally modulated trains of nerve stimuli was found to grow almost linearly when the variations in input frequency were increased up to 60% of the carrier frequency.

3. The synaptic frequency response (gain and phase) was reminiscent of that of a low‐pass filter, best transmitting slow variations in input frequency.

4. The synaptic filter characteristics could not be explained by the post‐synaptic cable properties, but were attributed to presynaptic facilitation processes.
The rate equation and activation energies for the uptake of α‐aminoisobutyric acid by mouse brain slices
Authors: Cohen Stephen R.
Published: December 2014

1. The initial influx of the amino acid analogue AIB at medium concentrations of 0·05–20 mM into mouse cerebrum slices incubated at temperatures from 20 to 45° C follows the rate law v = Vmax/(1 + Kt/S)+kuS. The linear term kuS arises from an unsaturable process of concentrative uptake.

2. At 37° C the kinetic constants are Kt = 1·12 mM; Vmax = 0·39 μmole AIB/g final wet wt. of slices. min; and ku = 0·054 μmole AIB/g final wet wt. of slices. mM‐AIB. min.

3. At infinitesmal substrate concentrations 13% of influx is via the unsaturable process. This rises to 73% for 20 mM substrate.

4. Kt is independent of temperature. The other constants increase rapidly with temperature. Arrhenius activation energies are 14·1 kcal/mole for Vmax and 17·4 kcal/mole for ku.
Transmitter release by mammalian motor nerve terminals in response to focal polarization
Authors: Cooke J. D. , Quastel D. M. J.
Published: December 2014

1. A method is described by which mammalian motor nerve terminals may be uniformly polarized by focally applied current, and the extra‐cellular potential in the synaptic cleft, corresponding to any current, estimated.

2. The relationship between log m.e.p.p. frequency and local extra‐cellular field is flat for hyperpolarization and ascends linearly with depolarization. With depolarization, m.e.p.p. frequency is multiplied about tenfold for every — 18 mV. This characteristic becomes steeper the closer the polarizing electrode to the nerve terminal with a limiting value of ten‐fold per — 15 mV.

3. There exists a population of small m.e.p.p.s which are generated at the same end‐plate as normal m.e.p.p.s.

4. Following a prolonged depolarizing pulse there is an increase of m.e.p.p. frequency which continues for periods of up to several minutes.

5. With hyperpolarizing pulses m.e.p.p. frequency may increase in a characteristic ‘bursty’ manner. Similar bursts of m.e.p.p.s also occur spontaneously, but far less frequently, without polarization.

6. During a depolarizing pulse, m.e.p.p. frequency becomes maximal or near maximal within 2 sec. There is little subsequent alteration of m.e.p.p. frequency. Numbers of m.e.p.p.s occurring during depolarizing pulses follow the Poisson distribution.

7. Following a depolarizing pulse, numbers of m.e.p.p.s released by a subsequent pulse may be either increased or diminished.

8. Comparison of the response of m.e.p.p. frequency to raised [K] and to extrinsic presynaptic polarization leads to the conclusion that the presynaptic transmembrane potential change corresponding to any focal current pulse is about two thirds of the local extracellular potential field. Hence the slope of the linear portion of the presynaptic transfer function is about tenfold per 10 mV presynaptic depolarization.
The role of calcium in depolarization—secretion coupling at the motor nerve terminal
Authors: Cooke J. D. , Okamoto K. , Quastel D. M. J.
Published: December 2014

1. The relation between m.e.p.p. frequency (F) and [Ca] was studied at the mouse neuromuscular junction, at varied concentrations of K+ and at nerve terminals depolarized by focal depolarization.

2. Under all conditions the relation between log F and log [Ca] was sigmoid, with a maximum slope that increased with depolarization or raised [K+]. In addition, depolarization or raised K+ caused a progressive shift of the sigmoid curve upward and to the left (to reduced log [Ca]) and increased the range over which log F could be altered by [Ca].

3. Reduction of osmotic pressure changed the relation between log F and log [Ca] in the same way as increase of depolarization, while increase of osmotic pressure did the opposite.

4. Raised [Mg] acted in two ways: (a) to shift the curve of log F vs. log [Ca] to the right and (b) to reduce maximum Δ log F/Δ log [Ca] without altering the range of log F sensitive to [Ca].

5. The relation between log quantal content of e.p.p.s and log [Ca] was similar to that between log m.e.p.p. frequency and log [Ca].

6. Individual nerve terminals varied in both Ca‐dependent and Ca‐independent fractions of log F; a large Ca‐independent portion appears to be associated with a low Ca‐dependent portion and vice versa. With large prolonged depolarization the Ca‐independent portion was increased, apparently at the expense of the Ca‐dependent portion.

7. The results of all experiments were summarized in terms of parameters found by fitting the observed log release —log [Ca] curves to two theoretical equations, each derived on the basis of a model: (a) all‐or‐nothing activation of release probability by Ca‐complex(es) and (b) graded activation of release probability by Ca complex(es).

8. On the basis of the all‐or‐nothing model, from which follows alinear relation between F and amounts of Ca complex(es), the number of Ca2+ atoms that ‘cooperate’ to mediate release appeared to increase progressively with presynaptic depolarization, to a value of 4 or more with a presynaptic action potential.

9. On the basis of the graded activation model, which predicts an exponential relation between F and amount of Ca complex, the number of Ca2+ atoms that combine with Ca receptor appears to be independent of presynaptic depolarization.

10. Various models which could account for the data are discussed. It was concluded that all the data are consistent with a model in which:

(i) quantal release probability is continuously graded with the amount of a simple Ca complex (CaX) inside the nerve terminal.

(ii) Ca entry is governed by presynaptic membrane potential (increasing exponentially with depolarization) and by the amount of a Ca complex (Ca2Y) on or in the membrane.

(iii) Mg2+ competes with Ca2+ at both receptors, X and Y.

(iv) The internal Ca receptor X is also increased by presynaptic depolarization.
The effect of some molecules and ions on gastric function in the milk‐fed calf
Authors: Bell F. R. , Razig S. A. D.
Published: December 2014

1. The abomasum of the milk‐fed calf has been examined using an adaptation of the Serial Test Meal method devised by Hunt & Spurrell (1951). The emptying process, acid secretion and pepsin secretion were studied.

2. Using serial test meals of simple solutions instilled into the abomasum via a cannula, our investigation leaves no doubt that the osmolarity of the abomasal contents significantly modifies the rate of abomasal emptying.

3. Hypotonic and isotonic solutions of sodium chloride and sodium bicarbonate increase abomasal emptying but bicarbonate is most effective.

4. Increasing the concentration of solutes in the abomasal contents slows abomasal emptying. Sodium chloride, sodium bicarbonate, ammonium chloride and urea do not delay abomasal emptying until hypertonic concentrations are attained. Hypotonic solutions of potassium chloride, calcium chloride, glucose, lactose, hydrochloric acid and acetic acid delay abomasal emptying.

5. The results obtained in the calf show that the abomasum is under restraint probably from duodenal receptors as is the simple stomach (Hunt & Knox, 1968) and that an osmoreceptor as postulated by Hunt (1956) is an important factor in this mechanism.

6. Acid secretion is inhibited when hypertonic solutions are instilled into the abomasum.

7. Pepsin secretion is not affected by simple solutions in the abomasum.

8. Gastric function in the milk‐fed calf appears to be controlled by mechanisms essentially similar to those already demonstrated in the simple stomach.
Cortical and peripheral modification of cerebellar climbing fibre activity arising from cutaneous mechanoreceptors
Authors: Leicht Rolf , Rowe Mark J. , Schmidt Robert F.
Published: December 2014

1. In cats anaesthetized with Nembutal climbing fibre (CF) responses evoked in individual cerebellar Purkyně cells by mechanical stimulation of the skin were conditioned by preceding stimuli both to the periphery and to the precruciate area of the cerebral cortex.

2. Cortical stimulation, generally subthreshold for evoking a CF response itself, induced an inhibition of cutaneous evoked CF responses in 65% of all Purkyně cells tested. The maximum inhibition ranged from 40 to 100% of the control responses at conditioning‐testing intervals of 30–70 msec and the duration of the inhibition was usually 125 msec.

3. In most cases the corticofugal inhibition of cutaneously evoked CF responses was mediated by inhibitory mechanisms outside the cerebellar cortex, probably at relays within the spino‐olivocerebellar pathways. Purkyně cells undergoing corticofugal inhibition were distributed widely within both the vermis and the pars intermedia of the anterior lobe.

4. In 40% of all Purkyně cells tested, there was evidence for afferent inhibition of their peripherally evoked CF responses as revealed by conditioning stimuli applied to the skin outside the receptive field. Again it was found that the inhibition was exerted at levels prior to the cerebellum.

5. It is concluded that the afferent input transmitted to Purkyně cells via climbing fibres can be modified by corticofugal and peripheral influences exerted on the relays of the CF pathways outside the cerebellar cortex.
Types of afferent nervous activity which may be measured in the vagus nerve of the sheep foetus
Authors: Ponte J. , Purves M. J.
Published: December 2014

1. Afferent activity was measured in the vagus nerves in sixteen foetuses within 2–3 days of natural term and in two foetuses 130 and 135 days gestational age, exteriorized by hysterotomy from seventeen ewes given either a spinal anaesthetic (ten) or pentobarbitone sodium (seven).

2. Activity from aortic chemoreceptors was observed which increased in rate with foetal hypoxia, NaCN or nicotine and temporary occlusion of the umbilical cord or veins. Activity was abolished or reduced with saline equilibrated with air.

3. Activity from baroreceptors was observed which was synchronous with the arterial pulse and which followed changes in arterial pressure.

4. Activity designated as arising from stretch receptors in the lungs or lower airways was observed which consisted of a regular discharge at 15–45 impulses sec−1, which varied with intra‐tracheal pressure, which increased with negative intrathoracic pressure generated by spontaneous respiratory movements, which, when the umbilical cord was occluded, at first increased in rate and then fell to zero at or about the occasion of the first breath. After breathing had been established, activity assumed the rhythmical pattern and showed evidence of slow adaptation of receptors seen in the adult. This activity was frequently modulated by the heart beat and after breathing had started it was reduced when carbon dioxide was raised.

5. Respiratory movements with a frequency of 10–20/min occurred spontaneously in foetuses from ewes given a spinal anaesthetic and were associated with a modulation of the stretch receptor discharge. They could be induced by withdrawing fluid from the trachea and so lowering both intra‐tracheal pressure and receptor discharge and were abolished by raising intra‐tracheal pressure. These changes were abolished by sectioning the vagi just caudal to the nodose ganglion.

6. These results indicate that there are excitatory and inhibitory pathways in the vagus nerves which are active in the foetus and which may well be concerned with the limitation of respiratory movements of the foetus and the onset of maintained respiration at birth.
An analysis of light‐induced admittance changes in rod outer segments
Authors: Falk G. , Fatt P.
Published: December 2014

1. Measurements were made of the time course and amplitude of the change in real part of admittance, ΔG, of a suspension of frog rod outer segments, following a flash of light bleaching about 1% of the rhodopsin content of the rods. The measurements, based on the use of a specially designed marginal oscillator, covered the frequency range between 500 Hz and 17 MHz.

2. The components of response, previously described for rods prepared by a method involving exposure to strongly hypertonic sucrose solutions, are present in similar form when rods are isolated and maintained in isotonic solutions made up with equi‐osmotic concentrations of NaCl and sucrose or with Na2SO4.

3. Component I, identified as a slowly developing positive ΔG apparent at very low frequencies, is temperature‐independent up to the characteristic frequency of admittance for the suspension, fY (about 2 MHz for rods suspended in a solution having the conductivity of Ringer solution), but decreases at still higher frequencies.

4. Component II, identified as a rapidly developing positive ΔG which appears only above a critical frequency about 2·5 decades below fY, increases approximately logarithmically with frequency to reach a limiting amplitude in the region of fY.

5. The amplitude of component II, ΔGII, measured in the region of fY, varies linearly with the conductivity of the suspending medium, Go, under conditions in which the conductivity of the rod interior is also a linear function of the external conductivity. The relation for a flash bleaching 1% of the rhodopsin content of the dark‐adapted rod is [Formula: see text]

6. Measurements made on rods suspended in a low‐conductivity solution, which has the effect of reducing the conductivity of the rod interior to about one ninth its value for rods suspended in Ringer solution, reveal a decline in component II for frequencies above 8 MHz.

7. To explain the frequency dependence of component II and its dependence on conductivity, it is proposed that component II arises from a light‐induced increase in conductance of the disk membranes which obstruct the longitudinal flow of current through the rod interior except at very high frequencies.

8. The disk‐membrane conductance increase for rods suspended in a solution having the conductivity of Ringer solution is calculated to be 4·3 × 10−11 mho/rhodpsin molecule bleached, a value which is similar to what has been found for ionic channels operated by membrane potential change in the nerve membrane and by synaptic transmitter in the postjunctional membrane.

9. No component of response has been observed which could be reliably attributed to a surface membrane conductance decrease of the type observed in receptor cells in the retina.
Polyneuronal innervation of kitten skeletal muscle
Authors: Bagust J. , Lewis D. M. , Westerman R. A.
Published: December 2014

1. Isometric contractions of kitten soleus and flexor hallucis longus (FHL) muscles have been examined for evidence of polyneuronal innervation. The sum of tetanic tensions of two almost equal divisions of the ventral roots was greater than the tetanic tension elicited by stimulating both the divisions simultaneously. The difference was large in kittens aged about 3 days, was less at 2 weeks and was small or absent at 6 weeks.

2. A tetanus elicited from one division of the ventral root potentiated a twitch elicited from the other root division. The time course of this potentiation was similar to that of post‐tetanic potentiation induced from the same root from which the twitch was elicited.

3. It is concluded that polyneuronal innervation exists in the kitten limb muscles.

4. The observed degree of tension excess was less if the divisions of the root were not equal. The observations were compatible with a model which assumed a random distribution of nerve axons to the muscle fibres.