bluuebunny/crossref_metadata_2025 huggingface dataset:
Immunoreactive luteinizing hormone releasing factor (LRF) in pituitary stalk plasma from female rats: effects of stimulating diencephalon, hippocampus and amygdala.
Authors: Chiappa S A , Fink G , Sherwood N M
Published: December 2014

1. Previous studies on the effect of preoptic and median eminence stimulation on the immunoreactive LRF content of pituitary stalk blood from pro‐oestrous rats have been extended. Stimulation of the suprachiasmatic nuclei and anterior hypothalamic area produced increments in LRF which were 66 and 18% respectively, of that produced by preoptic stimulation, and 38 and 9%, respectively, of that produced by stimulation of the median emience. Stimulation of the amygdala and hippocampus had no effect. 2. The LRF response was not affected significantly when preoptic stimulation was accompanied by stimulation of the hippocampus. 3. In animals subjected to section of the dorsal afferents of the diencephalon, the LRF response to preoptic stimulation was similar to that in intact rats. However, the facilitatory effect of oestrogen on the LRF response to preoptic stimulation was significantly reduced in the roof sectioned compared with intact animals. The post‐operative resumption of oestrous cycles was delayed but not abolished by dorsal deafferentation.
Interacting effects of temperature and extracellular calcium on the spontaneous release of transmitter at the frog neuromuscular junction
Authors: Duncan C. J. , Statham Helen E.
Published: December 2014

1. Temperature has a characteristic effect on the frequency of m.e.p.p.s at the frog neuromuscular junction; the spontaneous release of transmitter is not affected by temperature changes below 10° C whereas the system is highly temperature‐sensitive above 20° C.

2. A very similar result is obtained when the experiment is repeated in saline containing Ca2+ buffered at 5 × 10−7
M, suggesting that it is unlikely that the major action of temperature is to cause an increase in Ca2+ influx.

3. It is suggested that the main effect of temperature at the presynaptic terminals is a modification of [Ca2+]i by an action on intracellular Ca2+ stores.

4. The interacting effects of theophylline and the divalent cation ionophore A23187 on m.e.p.p. frequency suggest that intracellular Ca2+ stores, in addition to the mitochondria, may well be of importance in controlling [Ca2+]i.

5. Changes in [Ca2+]o produce a modification of m.e.p.p. frequency, but the details of the response are dependent on temperature. The spontaneous release of transmitter is most sensitive to an increase in [Ca2+]o at 23° C, whereas the greater effect is found at 13° C when [Ca2+]o is lowered.

6. It is suggested (i) that m.e.p.p. frequency is primarily determined by [Ca2+]i at the presynaptic terminals, (ii) that the presynaptic terminals are normally able to maintain [Ca2+]i almost constant in spite of increases in Ca influx associated with ionophore treatment or with a rise in [Ca2+]o. However, if the steady‐state position of [Ca2+]i is previously raised by an increased efflux from intracellular stores (produced by elevated temperature or theophylline pre‐treatment), increased influx causes a rise in both [Ca2+]i and in m.e.p.p. frequency.
Self‐facilitation of ganglion cells in the retina of the turtle
Authors: Marchiafava P. L. , Torre V.
Published: December 2014

1. Ganglion cells responses to illumination and to optic nerve stimulation were recorded intracellularly from the retina of the turtle. All ganglion cells were identified by their antidromic responses to optic nerve stimulation.

2. When solitary spikes are produced following antidromic, orthodromic or intracellular stimulation, about 20% of the recorded ganglion cells show an additional depolarization along the falling phase of the action potential (post‐spike depolarization, PSD).

3. The PSD following the antidromic action potential disappears upon collision with a direct spike or when the antidromic spike is prevented from invading the cell soma.

4. By pairing two optic nerve stimuli the PSD is depressed with brief interstimulus intervals, but gradually recovers to the control amplitude 600‐800 msec after the conditioning shock.

5. The PSD is tentatively interpreted as an e.p.s.p. transmitted by ganglion cell collaterals originating at the level of the soma dendritic complex of the recorded cell.

6. The interspike interval histogram of ganglion cells showing PSD is characterized by a peak at about 10 msec, as opposed to a peak between 12 and 100 msec observed in cells without PSD. It is suggested that the occurrence of PSD facilitate the onset of additional action potentials at brief interspikes intervals, thus potentiating ganglion cell discharges.
Release of adenosine triphosphate from isolated adult heart cells in response to hypoxia
Authors: Forrester T. , Williams Carole A.
Published: December 2014

1. Adult rat heart cells were isolated enzymically and ATP was identified in the cell suspension using the firefly luminescence technique. Adenosine 5′‐triphosphate (ATP) was not detected from cell suspensions obtained from hearts which had been left asystolic for 10 min.

2. It was found that ATP 0·34 ± 0·22 μ
M/mg protein was released by cells kept in an oxygenated condition, while ATP 1·28 ± 0·41 μ
M/mg protein was initially released by cells made hypoxic.

3. Addition of Ca2+ in a concentration of 2 m
M caused cells to initially extrude ATP 0·40 ± 0·14 μ
M/mg protein. This was attributed to an inotropic effect.

4. Extracellular ATPase activity in the fluid suspension was partially characterized, giving a Km of 13 μ
M and a V/2 of hydrolysed ATP 18·3 μ
M/min at 37° C. Q10 was found to be 4 between 25 and 37° C. Enzyme activity remained unaffected by either hypoxic conditions or ouabain.

5. If these amounts of ATP are released from myocardial cells rendered hypoxic in vivo, then it must be concluded that ATP plays a principal role in the local control of myocardial blood flow.

6. It is proposed that release of ATP occurs through the sarcolemma from an intracellular pool, and that alteration of the configuration of structural membrane protein controls the amounts of ATP extruded.
The effects of breathing of alternate breaths of air and a carbon dioxide rich gas mixture in anaesthetized cats
Authors: Wolff C. B.
Published: December 2014

1. An in vivo pH electrode was used to assess the effect in anaesthetized cats of the administration of 5% CO2 (21% O2, balance N2) and air as alternate inspirates upon the time course of the carotid arterial pH, and by inference, the PCO2.

2. This method of administration of CO2 and air resulted in a lowering of the recorded pH with the production of oscillations of twice the duration seen on air alone. These larger oscillations had a period of two respiratory cycles and their amplitude was approximately twice that of normal oscillations.

3. The respiratory response consisted in all cases of an increase in mean tidal volume and ventilation, and in 50‐60% of recorded runs, of a highly specific sequence of tidal volume changes. The specific sequence was composed of alternately larger and smaller breaths which persisted while the larger oscillations continued.

4. The use of the in vivo pH electrode made it possible to determine whether or not the tidal volume alternation was a result of sensitivity to carotid arterial PCO2 oscillations. By diverting the carotid arterial blood through a mixing chamber the amplitude of the double (respiratory) period oscillations was, in some cases, reduced but not eliminated. In these cases the specific pattern of tidal volume changes was still present in 60% of trials. In the cases where the pH fluctuations were completely eliminated the specific respiratory pattern was never present.

5. Average breath to breath differences in tidal volume seen during control runs with large oscillations present ranged in size from 3·6 to 8·6% of the mean tidal volume. When the oscillations were completely eliminated by means of the mixing chamber the breath by breath differences only ranged from 0·2 to 2·7% of mean tidal volume. The change was highly significant.

6. Mean tidal volume and ventilation were not altered by eliminating the large (double period) oscillations.

7. It has been shown that the tidal volume is made to change from breath to breath in a persistent manner when there are recurrent changes in carotid arterial blood chemistry. The effects on respiration involve vascular receptors above the mid carotid arterial region. It is argued that the effects involve the sensitivity of the carotid bodies to rapid (within breath) changes in Pa, CO2. There appears to be no significant effect on mean ventilation of the dynamic component of the arterial PCO2 changes produced in these experiments.
Measurement of transmembrane potential and current in cardiac muscle: a new voltage clamp method.
Authors: Goldman Y , Morad M
Published: December 2014

1. A single sucrose gap voltage clamp technique was developed to correct for artifacts of 'leakage' corrent and extracellular resistance making possible improved measurement of membrane current and membrane potential in cardiac muscle. 2. A fourth compartment termed 'guard gap' was added to the sucrose gap. The guard gap is maintained at the same potential as the Reinger pool, so that no extracellular leakage current can flow into the Ringer pool. Comparison of experimental results with the predictions of an idealized cable model indicates that the guard gap is effective in trapping leakage current. 3. The slow charging of membrane capacitance due to extracellular series resistance was accelerated by applying a 'pre‐pulse' of the command potential past the final voltage clamp value. 4. A second technique, termed 'chopped current pulse clamp', was used to compensate for the extracellular resistance throughout the voltage clamp step. The applied current was turned on and off at a frequency of 0‐5‐2 kHz. The membrane potential sampled during the zero current phase was fed back through the clamp loop. 5. With either of these compensation techniques, the voltage and current traces settle to effectively constant values within 2‐4 msec after initiation of a hyperpolarizing voltage clamp step from rest. 6. The membrane conductance measured by the prepulse and chopped current‐pulse technique are equal and confirm a higher conductance at rest than during the plateau of the action potential. 7. The 'instantaneous' current‐voltage relation of the membrane is linear during the plateau of the frog ventricular action potential.
The termination of transmitter action at the crustacean excitatory neuromuscular junction.
Authors: Crawford A C , McBurney R N
Published: December 2014

1. Excitatory junctional currents (e.j.c.s) and miniature excitatory junctional currents (mine.e.j.c.s) have been followed by recording the focal extracellular potential at excitatory neuromuscular junctions of Maia squinado, the Spider Crab. 2. If L‐aspartate (concentrations less than or equal to 1 mM) is present in the saline, the average e.j.c. is prolonged by an increase in the duration of its falling phase. 3. No change occurs in the time course of the probablility of release of quanta in the e.j.c. as determined from the histogram of first quantal latencies. 4. The min.e.j.c. is also prolonged by L‐aspartate (concentrations less than or equal to 0‐5 mM). The rise time increases slightly, the pre‐exponential period of the decay phase almost doubles, and the time constant of the final exponential decay increases to a value larger than the average lifetime of the elementary conductance event produced by L‐glutamate. 5. Changes in e.j.c.s and min.e.j.c.s produced by aspartate show a striking similarity to the action of neostigmine on the time course of the vertebrate end‐plate current. It is proposed that aspartate exerts its action by blocking a process normally reponsible for clearing the synaptic cleft of transmitter.
In vitro measurement of rate of fluid secretion in rat isolated seminiferous tubules: effects of metabolic inhibitors and ions.
Authors: Cheung Y M , Hwang J C , Wong P Y
Published: December 2014

1. An in vitro technique for measuring secretory rate in rat isolated seminiferous tubules is described. 2. The basal rate of fluid secretion was 0‐44+/‐0‐06 nl. cm‐1 min‐1 (S.E.) (n=21). The rate was found to be inhibited by cooling, addition of metabolic inhibitor 2,4‐dinitrophenol (2‐5 x 10(‐4) M) and removal of glucose from the incubating solution. This indicates that fluid secretion in isolated rat seminiferous tubules is an energy dependent process. 3. Removal of K+ from the incubating medium inhibited the secretory rate in the isolated seminiferous tubules, whereas a fivefold increase in [K+]0 to 23‐5 mM had no effect. The secretory rate was also unaffected by the absence of Cl‐ in the peritubular fluid. 4. Removal of Ca2+ from the peritubular medium caused a rise in the secretory rate. 5. Ouabain (10(‐3) M) and acetazolamide (4 x 10(‐5) M) caused a fall in the rate of fluid secretion in isolated seminiferous tubules. 6. These results are discussed in relation to the nature of the ionic secretion produced in the tubules.
Discrimination between nicotinic receptors in vertebrate ganglia and skeletal muscle by alpha‐bungarotoxin and cobra venoms.
Authors: Bursztajn S , Gershon M D
Published: December 2014

1. We have used snake neurotoxins, alpha‐bungarotoxin and venoms from Naja naja siamensis and Naja nivea, to distinguish the nicotinic receptors of ganglia from those of skeletal neuromuscular junctions. 2. These neurotoxins failed to block responses of isolated guinea‐pig longitudinal muscle with adherent myenteric plexus to the nicotinic agonists, nicotine or dimethylphenylpiperazinium, to acetylcholine (ACh), or to electrical field stimulation. 3. The toxins failed to affect responses of the isolated guinea‐pig stomach to pregnaglionic stimulation by way of the vagus nerves or of the vas deferens to preganglionic stimulation via the hypogastric nerves. 4. Snake neurotoxins did not block non‐adrenergic inhibitory responses of the rabbit small intestine to nicotine or electrical field stimulation. 5. Neurotoxins were ineffective blockers against nicotinic agonists in new‐born rabbit or embryonic chick intestine. 6. Attempts to increase the penetration of the toxins into tissues with dimethylsulphoxide, exposure to hypertonic solutions, or to ethylene‐diaminetetracetic acid did not enable the toxins to act as nicotinic antagonists. 7. In contrast to diaphragmatic or oesophageal skeletal neuromuscular junctions no binding of rhodamine or tritium labelled toxins to structures in ganglia could be detected. 8. No potential permeability barriers were found by electron microscopy of the ganglia of the guinea‐pig myenteric plexus. 9. The tracers, lanthanum ion and ruthenium red, readily penetrated into all regions of the myenteric plexus including synaptic gaps. 10. It is concluded that the failure of snake neurotoxins to act as nicotinic antagonists or to bind to ganglia is not due to their inability to reach ganglionic nicotinic receptors. Therefore, it is likely that ganglionic nicotinic receptors are different from those of the skeletal neuromuscular junction.
The role of calcium in renin secretion from the isolated perfused cat kidney.
Authors: Lester G E , Rubin R P
Published: December 2014

1. Isolated cat kidneys were perfused in situ with Locke solution and renin release in response to isoprenaline was studied. 2. Perfusion with isoprenaline produced a concentration‐dependent enhancement of renin secretion. Increasing the concentration of stimulant also prolonged the duration of the secretory response. 3. After a 10 min exposure to isoprenaline (0‐3 micrometer), there was a rapid facilitation of renin release which diminished after 10‐30 min, followed by a second transient increase which declined over the next 40‐60 min. Cycloheximide did not prevent augmented release when added together with the isoprenaline but did produce a reversible inhibition of the late phase when added 10 min after the isoprenaline. 4. Omission of calcium from the perfusion medium failed to depress the renin release induced by isoprenaline, glucagon, or furosemide. However, during prolonged calcium deprivation, the cycloheximide‐sensitive phase of isoprenaline‐evoked release was depressed. 5. The calcium antagonist D‐600 failed to block the early phase of isoprenaline‐induced renin secretion but inhibited the late phase of secretion. 6. Calcium alone elicited an explosive discharge of renin when added after a prolonged period of calcium‐free perfusion. 7. These results support the view that extracellular calcium does not play an essential role in the mechanism of renin secretion from the renal juxtaglomerular cells, but that an increased influx of this cation is needed for synthesis and/or mobilization of the enzyme. It is tentatively proposed that the release of calcium from intracellular storage sites may be the signal which triggers renin secretion.
Development of neuromuscular transmission in a larval tunicate
Authors: Ohmori Harunori , Sasaki Shigeto
Published: December 2014

1. The time sequence of the development of acetylcholinesterase (AChE), acetylcholine (ACh) receptors and functional synapses on the embryonic muscle membrane in a tunicate larva (Halocynthia roretzi) was investigated in vivo.

2. The fertilized tunicate egg was incubated in natural sea water at 9° C. Sixty‐eight hr after fertilization the free‐swimming larva was hatched, which had six striated muscle fibres in the tail. The developmental stage of the embryo was indicated by the developmental hours after fertilization.

3. The transmitter at the neuromuscular junction in the hatched larva is ACh. (i) Neuromuscular transmission was completely blocked by
D‐tubocurarine (1‐5 × 10−5
M). (ii) Eserine (5‐10 × 10−7
M) approximately doubled the time constant of the falling phase of miniature excitatory junctional currents (e.j.c.s). (iii) The reversal potential of the membrane response to iontophoretically applied ACh was ‐10 mV and similar to that of e.j.c.s. (iv) AChE was present on the muscle membrane surface.

4. AChE activity became visible histochemically on the embryonic cell membrane in the presumptive muscle region as early as the late gastrula stage (27 hr after fertilization, 12 hr before the ACh response appeared).

5. The response to iontophoretically applied ACh was present at 39 hr after fertilization but could not be evoked at 38 hr.

6. Between 39 and 41 hr after fertilization, the ACh responses increased rapidly, then remained relatively unchanged until larval hatching.

7. The stage of the initial appearance of the ACh response corresponded to the stage when the Ca current abruptly increased in the muscle membrane.

8. The first sign of neuromuscular transmission was appearance of a giant excitatory junctional potential (e.j.p.) with uniform amplitude (about 15‐20 mV) and slow time course (time constant of the falling phase of a giant e.j.c. was 23·4 ± 6·9 msec, mean and
S.D., at ‐60 mV and 11° C).

9. Within a few hours, these giant e.j.p.s disappeared and were successively replaced by medium‐sized e.j.p.s and then e.j.p.s similar to those seen in hatched larvae (time constant of the falling phase of a miniature e.j.c. was 8·5 ± 1·8 msec at ‐60 mV and 11° C).
Cone signals in the cat's retina
Authors: Enroth-Cugell Christina , Hertz B. Gevene , Lennie P.
Published: December 2014

1. The discharges of ganglion cells in the cat's retina were recorded under conditions intended to isolate the cone system.

2. Stiles' two‐colour threshold technique permitted the photopic system to be studied when at its highest sensitivity. The absolute sensitivity of a ganglion cell, expressed in equivalent photons of λmax at the cornea per impulse discharged, was about 2500 times less when driven by cones than when driven by rods. This ratio improves to around 200 when allowance is made for the much smaller fraction absorbed by cones of photons incident on the cornea.

3. The number of extra impulses discharged in response to a brief flash was approximately proportional to the number of photons in the flash, up to a limit.

4. There was a region in the middle of the receptive field within which the area of a test spot and its illumination for threshold varied inversely. A flash extending over the peripheral part of the receptive field raised threshold above its minimum, presumably as a result of surround antagonism. Assessed from area—threshold curves, the balance of centre‐surround antagonism in the photopic receptive field did not seem to depend upon background illumination.

5. The threshold for a small (0·2°) flash confined to the middle of the receptive field was independent of background illumination until the background exceeded a particular level, the ‘dark light’ (Io). In different units this ranged about a mean of 7·89 log photons (560 nm equivalent) deg−2 sec−1. For backgrounds that exceeded Io, threshold followed approximately Weber's law up to the highest illuminations that could be produced.

6. With test flashes that filled the centre of the receptive field, the Weber fraction (test flash illumination/background illumination) in some units fell below 1%.

7. Changes in the time course and latency of response accompanied the changes in sensitivity caused by alterations in background illumination. Responses of both X‐ and Y‐cells became more transient and faster.

8. The loss of sensitivity to a test flash brought about by a steady background light depended upon the size of that light. Sensitivity varied inversely with background area within a central region that matched closely the summing area for test flashes.
Calcium movements during the release of catecholamines from the adrenal medulla: effects of methoxyverapamil and external cations
Authors: Aguirre J. , Pinto J. E. B. , Trifaró J. M.
Published: December 2014

1. Cortex‐free adrenal glands previously labelled with the isotope 45Ca have been perfused with Locke or modified Locke solution to assess Ca2+ movements under different conditions.

2. Substitution of Na+ by either sucrose or choline during perfusion with Ca2+‐free Locke solution induced a significant and sustained decrease in the 45Ca efflux. Concomitant with this effect there was an increase in the output of catecholamines from the perfused gland.

3. In the presence of Ca2+ (2·2 m
M) in the perfusion fluid, Na+ omission induced an increase in the 45Ca efflux. This increase was significantly reduced if 3 × 10−4
M methoxyverapamil (D‐600) was present in the perfusion fluid. However, the increased catecholamine output in response to Na+ deprivation remained unchanged.

4. Excess of Mg2+ (20 m
M) in the extracellular medium blocked the increase in catecholamine output in response to Na+ omission. However, the decrease in the 45Ca efflux produced by Na+ deprivation in the presence of this high concentration of Mg2+ was similar to that observed in the presence of 1·2 m
M‐Mg2+.

5. In the absence of Mg2+ in the extracellular medium, substitution of Na+ by either sucrose or choline induced a sharp and transient increase in the 45Ca efflux rate coefficient. This increased 45Ca efflux, which has similar time course as the enhanced catecholamine output, was not affected by the presence of 3 × 10−4
M methoxyverapamil.

6. In the absence of Mg2+, the graded substitution of Na+ in the perfusion medium by sucrose enhanced the efflux of 45Ca. This increase in the 45Ca outward movement was linearly related to the logarithm of the extracellular Na+ concentration.

7. After perfusion of glands with Ca2+‐free Locke solution, the reintroduction of Ca2+ (2·2 m
M) into the perfusion fluid produced an increase in the 45Ca efflux. This was accompanied by a discharge of catecholamines.

8. Although Mg2+ (20 m
M) was effective in blocking catecholamine release, this divalent cation did not modify the increase in the 45Ca efflux produced by Ca2+ reintroduction.

9. In contrast to these later observations, methoxyverapamil (3 × 10−4
M) was effective in inhibiting both increases in catecholamine output and 45Ca efflux in response to Ca2+ reintroduction.

10. It is concluded from these experiments that (a) Ca2+ movements in the adrenal medulla may involve both Na+‐Ca2+ and Ca2+‐Ca2+ exchange mechanisms; (b) the omission of Na+ from the extracellular environment produces not only an increase in the output of catecholamines but it may increase the intracellular levels of Ca2+ and that this may result in an increased Ca2+ efflux when Mg2+ is omitted from the perfusion fluids, and that (c) the competition between Ca2+ and Mg2+ during the secretory process may involve an intracellular site.
Absorption of amino penicillins from everted rat intestine.
Authors: Dixon C , Mizen L W
Published: December 2014

1. Using an in vitro everted gut sac method based on that of Wilson & Wiseman (1954), a number of amino penicillins were tested in order to identify the involvement of any specialized transport mechanisms in their absorption across rat intestine. 2. Only one of the amino penicillins, cyclacillin (1‐amino‐cyclohexyl penicillin) was shown to be actively transported. The other penicillins appeared to diffuse passively across the intestine. 3. Cyclacillin was found to concentrate against a gradient at 37 degrees C but not at 19 degrees C. 4. Transport of cyclacillin across the mucosal membrane was saturated at mucosal concentrations greater than 1000 microgram/ml. 5. The rate of the forward flux of cyclacillin was many times that of its back flux. 6. No relationship between the active transport of cyclacillin and that of amino acids could be demonstrated.
Regulation of compensatory kidney hypertrophy by its own products
Authors: Dicker S. E. , Morris Christine A. , Shipolini R.
Published: December 2014

1. The ligation of blood vessels of one kidney of adult rats resulted in the compensatory hypertrophy of the other kidney. In most animals the rate of hypertrophy was indistinguishable from that observed after unilateral nephrectomy, but in a few cases the onset was retarded when the renal artery alone had been ligated and the collateral circulation increased.

2. When the blood vessels of one kidney of adult rats were ligated and the cortex was excised, the rate of compensatory renal hypertrophy was similar to that observed after unilateral nephrectomy.

3. In animals operated for simultaneous partial hepatectomy and unilateral nephrectomy, there was no sign of compensatory renal hypertrophy while the liver was undergoing regeneration. Renal hypertrophy started after 7 days, when about 98% of the amount of liver removed had been regenerated.

4. Neither aseptic autolysis of one kidney following suppression of its blood supply, nor unilateral nephrectomy affected the rate of liver regeneration after simultaneous partial hepatectomy.

5. Total splenectomy did not affect the rate of compensatory renal hypertrophy following unilateral nephrectomy.

6. The heterotopic graft of renal cortical, but not of medullary, cells inhibited compensatory renal hypertrophy in adult rats. The removal of the graft after 14 days was followed by the resumption of compensatory hypertrophy.

7. The inhibiting action of fractions of renal cortical extracts fractionated on Sephadex G100 resin and DEAE‐52 cellulose were assayed on the ‘growth’ of renal explants reared in vitro. The final material, though only partially purified, proved to have an inhibiting activity between 250 and 500 times greater than that of the initial extract.

8. When injected into unilaterally nephrectomized rats, the partially purified extract from the renal cortex had an inhibiting effect on compensatory renal hypertrophy.

9. Immunofluorescence technique showed that the partially purified cortical extract affected the proximal convoluted tubes specifically, irrespective of animal species.
Diffusion of oxygen at the endothelial surface of the rabbit cornea.
Authors: Barr R E , Hennessey M , Murphy V G
Published: December 2014

1. An in vitro investigation was made to determine the oxygen tension level required at the endothelial surface of rabbit cornea to produce a net oxygen flux into the cornea across this surface when the epithelial surface was exposed to air. 2. The experimental design was based on a mathematical model which showed that the direction of oxygen flux measured in an agar layer adjacent to the endothelium was the same as the direction of oxygen flux across the endothelial surface. 3. From micro‐electrode measurements of oxygen tension in the agar layer, it was found that an oxygen tension greater than 102 mmHg at the endothelial surface was required tocause a net flux of oxygen into the cornea. 4. Comparing this result to the in vivo situation,it was concluded that all layers of the rabbit cornea receive oxygen from the atmosphere under open eye conditions.
The secretion of pepsin.
Authors: Kondo T , Magee D F
Published: December 2014

1. Ligation and division of the vessels supplying the stomach, except those from the spleen, result in greatly increased pepsin secretion in response to pentagastrin, pilocarpine or 2‐deoxy‐D‐glucose. 2. This effect was still present 6 months after initial ligation. 3. Analysis of dose‐response curves shows that for pepsin secretion the Vmax values were raised by this procedure. 4. Right‐sided vessel ligation and division does not alter acid secretion in response to the stimuli used. 5. It is suspected that the procedure of right‐sided vessel ligation removes a non‐competitive inhibitor mechanism to gastric pepsin secretion.
Ganglion cell discharge and proximal negativity in the pigeon retina.
Authors: Holden A L
Published: December 2014

1. Proximal negativity has been compared with the spike responses and membrane responses of pigeon ganglion cells. 2. Spike discharge peaks develop during the rising phase of proximal negativity. 3. Proximal negativity is never directional, even when recorded concurrently with directional ganglion cells. 4. To moving stimuli, on‐centre cells respond in association with the leading edge of the stimulus, off‐centre cells with the trailing edge, and on‐off cells with the leading and trailing edges. Proximal negativity is produced in association with the leading and trailing edges. 5. Quasi‐intracellular records show that discharge peaks occur in association with depolarizing potentials. The synaptic responses of on‐off cells bear a closer resemblance to the proximal negative response than do the responses of on‐centre cells, off‐centre cells, or directional cells.
Responses of directional ganglion cells in the pigeon retina.
Authors: Holden A L
Published: December 2014

1. Extracellular single‐unit records were taken from ganglion cells in the pigeon retina, and average response histograms were recorded, with base line spike counts. 2. Movements in the preferred direction in directional cells produce discharge peaks. Movements in the null direction produce spike deletion suggesting there is an inhibitory patch offset from the field centre, towards the start of the null sweep. 3. Bi‐directional responses can be obtained from the preferred side of the field centre; bi‐directional inhibition can be obtained at the null side. Scans orthogonal to the null‐preferred direction passing through the inhibitory patch can produce deletions. 4. The latency of deletions from the inhibitory patch is slightly greater than of excitation from the field centre, judged by flashed or moving stimuli.
An X‐ray diffraction study of the cross‐circulated canine heart.
Authors: Matsubara I , Suga H , Yagi N
Published: December 2014

1. The equatorial X‐ray diffraction pattern was recorded from a papillary muscle of a cross‐circulated canine heart at different phases of the cardiac cycle. The intensity ratio of the 1, 0 and the 1, 1 reflexions (I1, o/I1,1) was 0‐79 in the systolic phase and 1‐19 in the diastolic phase. 2. Using the intensity ratio obtained, the approximate proportion of the myosin projections present in the vicinity of the thin filaments was calculated. This was 70‐71% in the systolic phase and 51‐52% in the diastolic phase of the total myosin projections. 3. The peak systolic tension was roughly proportional to the proportion of the projections present in the vicinity of the thin filaments during systole. 4. The projections which stayed in the vicinity of the thin filaments during diastole did not produce significant contractile force.
The influence of food intake and ambient temperature on the rate of thyroxine utilization.
Authors: Ingram D L , Kaciuba-Uscilko H
Published: December 2014

Young growing pigs of both sexes were subjected to changes in (1) energy intake, (2) ambient temperature, and (3) bulk of food. The rate of disappearance of injected 125I‐labelled thyroxine from the plasma (K) was measured. An analysis of variance revealed that the effect attributable to changes in the energy content of the food intake was statistically significant (P less 0‐01). A change in ambient temperature had no statistically significant effect on K, nor did a change in the bulk of food when energy intake was constant (P less than 0‐05).
The effect of prolonged inactivity upon the contraction characteristics of fast and slow mammalian twitch muscle (cat)
Authors: Davis C. J. F. , Montgomery A.
Published: December 2014

1. Prolonged inactivity of soleus (slow twitch) and medial head of flexor digitorum longus (fast twitch: previously commonly known as flexor hallucis longus and hereafter referred to as FDL) muscles of the cat was produced by sodium pentobarbitone anaesthesia or spinal isolation. Isometric contraction characteristics were examined after 4‐22 days and 8‐49 days respectively.

2. Sleep of up to 3 weeks' duration was associated with progressive changes in the weight, maximum tetanic tension, speed of contraction and absolute refractory period of fast twitch muscle. The slow muscle showed corresponding changes which were not so pronounced. Cord isolation resulted in similar changes which tended to be reversed after longer periods of disuse.

3. Fast muscle frequently exhibited an after‐contraction with corresponding electromyographic activity following two weeks or more of disuse.

4. The time to peak of FDL was prolonged, becoming approximately one and a half times normal. In contrast to other reports of disuse, that of soleus was normal or slightly prolonged.

5. The ratio of twitch to tetanic tension of FDL increased to twice the normal value or greater and remained high. The soleus muscle showed a smaller increase with evidence of a return towards normal after longer periods of inactivity.

6. Absolute refractory period of FDL was considerably prolonged (more than 50%) following barbiturate sleep and this also occurred, but to a lesser degree, with soleus after 4‐7 weeks of cord isolation.

7. The observation that inactivity produced slowing rather than an increased speed of switch contraction indicates that aggregate activity is not the controlling factor. Changes seen in the contraction characteristics of FDL are noted to show a general similarity to those occurring following denervation.
The effect of lung inflation on the control of respiratory frequency in the neonate
Authors: Boychuk Rodney B. , Rigatto Henrique , Seshia Mary M. K.
Published: December 2014

1. We have measured the relationship between tidal volume (VT) and the duration of inspiration (Ti) and expiration (Te) for individual breaths (30 in each steady state).

2. Ten pre‐term and ten term infants were studied during steady state while breathing 21% O2, then 21% O2 plus 2 and 4% CO2.

3. In all infants, the average Ti at the various chemical drives was remarkably constant, and did not decrease as the tidal volume increased. However, at any given level of respiratory drive, there was a slightly positive correlation of VT with Ti and Te in 95% of the cases.

4. In four pre‐term and two term infants, Te increased with increasing respiratory drive. In these infants, therefore, instantaneous respiratory frequency (1/(Ti + Te)) actually decreased as lung volume increased.

5. We suggest that Ti is independent of VT within the range of volumes studied (up to 2 times the resting VT) and that changes in instantaneous respiratory frequency (1/(Ti + Te)) result from changes in Te.
Metabolism of the frog outer segments: a kinetic study
Authors: Bignetti E. , Cavaggioni A.
Published: December 2014

1. The reaction of the high‐energy phosphate esters of the frog isolated rods, with the firefly lantern extract, has been studied by recording the luminescence in a stopped‐flow apparatus. The onset of the reaction was determined by the rapid mixing of the firefly lantern extract with the high‐energy phosphates released from the rods fragmented during the mixing.

2. The time course of the reaction, i.e. of the luminescence, was not typical of adenosine‐5′‐triphosphate (ATP), indicating that the major part of the rod nucleotides is not ATP.

3. The isolated rods were fragmented 1 sec‐2 min after a flash of light. As soon as 1 sec after illumination, a substantial decrease of the luminescent yield has been detected in a range of light bleaching from 0·007 to 20% of the rhodopsin, indicating an early reduction of the high‐energy phosphate esters.

4. At longer times, flashes that bleached 7 or 20% of the rhodopsin induced a progressive decrease of the luminescent yield that was half completed in 6‐9 sec, and was nearly complete in 20 sec, whereas a more or less complete recovery was observed after flashes bleaching from 0·7 to 0·007% of the rhodopsin, indicating the presence of buffering mechanisms.

5. Also, the time course of the reaction was modified in a complex way after stimulation of the rods, suggesting that other nucleotides beside ATP are hydrolysed.

6. The light‐induced reduction of the high‐energy phosphates has been observed also in broken rods, in the presence of the calcium chelating agent EGTA, suggesting that calcium is not needed for this effect.

7. Cyclic guanosine monophosphate (10−4
M) interfered with the photic effect.

8. The rapid effect of light on the content of high‐energy phosphate esters suggests a physiological role in the mechanism of excitation.
Location of U.V.‐absorbing substance in isolated skeletal muscle fibres: the effect of stimulation (frog, snake)
Authors: Lännergren J.
Published: December 2014

1. In an attempt to study the intracellular location of ATP in skeletal muscle the distribution of substances which absorb light at 260 nm wave‐length has been studied in isolated muscle fibres with the aid of a modified U.V.‐microscope.

2. U.V.‐absorption in resting frog fibres was found to be higher in the I band than in the A band which confirms earlier findings. In stretched fibres (sarcomere length 2·9‐3·6 μm) an absorbing substance could be seen to be concentrated in a pair of narrow lines, centred at the Z‐line. The separation of the lines increased with increasing sarcomere length.

3. Snake fibres, with sparse triads located at the A‐I junction, displayed an absorption pattern very similar to that of frog fibres. It is concluded that it is unlikely that the absorbing substance is associated with the sarcotubular system.

4. The absorption pattern of frog fibres remained unchanged during a tetanus. No clear changes could be detected after a period of stimulation, neither after single twitches nor after repeated tetani.

5. In further attempts to cause exhaustion, metabolically poisoned fibres were stimulated repetitively until they went into rigor. The absorption pattern was essentially unchanged also when rigor tension started to develop.

6. The characteristic absorption pattern was observed also in glycerol‐extracted fibres. It was confirmed by spectrophotometry that glycerol‐extraction led to the disappearance of a large amount of a substance with the spectral characteristics of ATP.

7. The higher U.V.‐absorption in the I band does not prove that the major part of the ATP in the fibre is concentrated here; the absorption could either be due to a minor fraction of the ATP or to RNA.
The membrane properties of the smooth muscle cells of the rabbit main pulmonary artery
Authors: Casteels R. , Kitamura K. , Kuriyama H. , Suzuki H.
Published: December 2014

1. The membrane potential of the smooth muscle cells of the rabbit main pulmonary artery amounts to ‐57 mV, the length constant of the tissue is 1·48 mm and the time constant of the membrane 182 msec. On the basis of the electrical properties of its membrane, this smooth muscle tissue is classified as a single‐unit type. During outward current pulses, the membrane shows marked rectification and action potentials can never be generated.

2. Tetraethylammonium (10 m
M) and procaine (5 m
M) depolarize the membrane and increase the membrane resistance. By studying the effect of both substances on the 42K efflux, it could be concluded that they reduce the K‐permeability of the membrane. They also suppress the rectification of the membrane and increase the length constant of the membrane. In the presence of TEA and procaine, a graded response of the membrane can be induced by outward current pulses, but overshoot potentials never occur.

3. Noradrenaline, in concentrations between 2 × 10−8 and 10−7
M, evokes contraction without depolarizing the membrane. When the concentration is increased above 2 × 10−7
M, noradrenaline depolarizes the membrane and reduces the membrane resistance. A study of the effect of noradrenaline on the K, Cl and Na fluxes has revealed that it increases the permeability of the membrane for these three ions.

4. The tissue concentrations of Na and K are 80 and 38 m‐mole/kg wet wt., respectively. The amount of Cl in the cellular compartment was measured by an extrapolation procedure and found to be 13 m‐mole/kg wet wt. The extracellular space measured with [14C]sorbitol is 550 ml./kg wet wt. and the dry wt./wet wt. ratio 19%. The calculated equilibrium potentials for K, Na and Cl (EK, ENa and ECl) are ‐83, +59 and ‐26 mV, respectively. In efflux experiments under steady‐state conditions, the following rate constants have been calculated: 0·092 min−1 for Na, 0·029 min−1 for Cl and 0·0054 min−1 for K. The calculated value for the ratio PNa/PK was 0·22 and for PCl/PK 0·63.

5. K‐free solution and 2 × 10−6
M ouabain depolarize the cells by about 8 mV. After exposure of the cells to K‐free solution, they hyperpolarize on readmission of K, suggesting that part of the membrane potential could be due to electrogenic transport of ions.

6. A decrease of external Ca depolarizes the cells and increases the membrane resistance. Na‐deficiency hyperpolarizes these smooth muscle cells but this procedure does not prevent the depolarization induced by Ca deficiency.
Characterization of the responses of oxytocin‐ and vasopressin‐secreting neurones in the supraoptic nucleus to osmotic stimulation
Authors: Brimble M. J. , Dyball R. E. J.
Published: December 2014

1. Extracellular action potentials were recorded from forty antidromically identified single units in the supraoptic nucleus of lactating, urethane‐anaesthetized female rats. The activity was monitored both during reflex milk ejection and during an increase of 10‐15 m‐osmole/kg in plasma osmotic pressure induced by intraperitoneal injection of 1 ml. of 1.5
M‐NaCl solution.

2. About half (eighteen) the cells showed a burst of activity before reflex milk ejection and were dubbed oxytocin cells. Oxytocin cells responded to a hypertonic injection with a smooth sustained threefold increase in firing rate.

3. The remainder (twenty‐two) showed no burst of activity before reflex milk ejection and were dubbed vasopressin cells. Vasopressin cells doubled their firing rate as plasma osmotic pressure increased. Neither cell type increased its firing rate after injections of isotonic NaCl.

4. A phasic firing pattern was rarely seen in slow firing vasopressin cells (< 2 spikes/sec) but was seen in almost all vasopressin cells (twelve out of fourteen) firing between 3 and 8 spikes/sec. Above 8 spikes/sec, some vasopressin cells fired continuously. Phasic firing was only once encountered in an oxytocin cell.

5. The firing rate of both oxytocin and vasopressin cells decreased when plasma osmotic pressure was reduced 10‐15 m‐osmole/kg by an intragastric water load of 10 ml.

6. Hypothalamic cells lying just outside the supraoptic nucleus did not show a consistent response to injection of hypertonic NaCl.

7. Clearly, both oxytocin and vasopressin cells are osmoresponsive, but phasic firing is characteristic of stimulated vasopressin cells. Thus, osmotic activation allows discrimination between oxytocin‐ and vasopressin‐secreting neurones.
An in vitro system for studying insulin release: effects of glucose and glucose‐6‐phosphate
Authors: Davis Brian , Lazarus Norman R.
Published: December 2014

1. Investigation of the ionic requirements of the in vitro insulin release system, which consists of cod islet plasma membrane and rabbit islet granules incubated at pH 6.5, showed that the presence of Ca2+ was obligatory for the system to operate.

2. Glucose‐initiated insulin release was as effective in the presence of β‐γ‐methylene ATP, as it was in the presence of ATP. This analogue of ATP is a substrate neither for adenylate cyclase nor for any known animal membrane proteases. The effect of ATP on glucose mediated release is allosteric.

3. Glucose (16 m
M)‐initiated insulin release was slower than that induced by glucose‐6‐phosphate (4 m
M); 150 and 120 sec, respectively.

4. The lag found with glucose‐mediated insulin release was dependent upon glucose concentration. The lower the glucose concentration, the longer the lag. With 1 m
M glucose the lag extended to 30 min.

5. Once insulin release was initiated, the rate and amount of insulin release was independent of the glucose concentration.

6. Pre‐incubation of membranes with Ca2+, glucose and ATP prior to the addition of granules, abolished the extended lag that had been obtained with 1 m
M glucose. Events in the plasma membrane are the major contributor to the generation of the extended lag.

7. The glucose analogue 5′thio‐
D‐glucose, although not able to release insulin, was shown to compete with glucose for the glucoreceptor. By increasing the ratio of analogue to glucose the lag time increased. Thus, the lag time is dependent upon the ‘effective’ external glucose concentration.

8. The max. amount of insulin released by 4 ng of membrane in the presence of glucose (16 m
M) was 300 ng. The fact that membranes became refractory to glucose after this max. amount of insulin was released showed that recycling of release sites was not taking place in vitro and that granule: granule interactions were not occurring.

9. The 120 sec lag before glucose‐6‐phosphate‐initiated release was independent of glucose‐6‐phosphate concentration. The rate of insulin release with glucose‐6‐phosphate was concentration dependent.

10. Glucose‐6‐phosphate did not cause further insulin release from a membrane that had released the max. amount of insulin it was capable of in the presence of glucose. The addition of tolbutamide (10 m
M) to such a membrane did cause insulin release. This suggests that glucose and glucose‐6‐phosphate share a final common pathway.

11. Adrenaline and somatostatin did not inhibit glucose‐mediated insulin release.