bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of changes of extramural, ‘intrathoracic’, pressure on aortic arch baroreceptors
Authors: James Jennifer E. Angell
Published: December 2014

1. The isolated aortic arch was perfused by a method enabling the mean pressure, pulse pressure and pulse frequency to be varied independently. The preparation was also subjected to phasic and non‐phasic changes of extramural pressure.

2. The aortic arch baroreceptor impulse activity in single or few‐fibre preparations was increased by raising the intra‐aortic pressure and by applying a negative extramural pressure at constant intra‐aortic pressure.

3. Curves relating impulse frequency and negative extramural pressure were similar to those relating impulse frequency to intra‐aortic pressure. The effective stimulus to the aortic arch baroreceptors is the transmural pressure resulting from the algebraic difference of the intra‐aortic and extramural pressures.

4. Rhythmical alterations in extramural pressure caused phasic changes in baroreceptor impulse activity. As the pressure became more negative, the impulse frequency increased and other baroreceptors were recruited.

5. During pulsatile perfusion of the aortic arch the maximum impulse activity occurred when the negative phase of extramural pressure coincided with the systolic phase of the perfusion pressure.

6. These findings are discussed in relation to the effects of changes of intrathoracic pressure on aortic baroreceptor activity in vivo
Transfer of alanine isomers by rat small intestine
Authors: de la Noüe J. , Newey H. , Smyth D. H.
Published: December 2014

1. A study was made of the transfer of
L‐alanine,
D‐alanine and β‐alanine by sacs of everted small intestine of the rat.

2.
D‐Alanine and β‐alanine are transported against a concentration gradient and in this respect resemble
L‐alanine.

3. Transfer of all three isomers was stimulated in presence of glucose, but stimulation was much greater with
D‐alanine and β‐alanine.

4. Transfer of all three isomers was inhibited by galactose.

5. The effect of hexoses on amino acid transfer was relatively independent of the effect on fluid transfer.

6.
L‐Methionine inhibited transfer of the three isomers in descending order,
L‐alanine,
D‐alanine and β‐alanine, while the magnitude of sarcosine inhibition was in the reverse order.

7. At the concentration used (1 m
M),
L‐alanine was transferred mostly by the methionine carrier, and β‐alanine mostly by the sarcosine carrier.
D‐Alanine occupied an intermediate position.
Receptive fields of cones in the retina of the turtle
Authors: Baylor D. A. , Fuortes M. G. F. , O'Bryan P. M.
Published: December 2014

1. Intracellular recordings have been made of the responses to light of single cones in the retina of the turtle. The shape of the hyperpolarizing response to a flash depends on the pattern of retinal illumination as well as the stimulus intensity.

2. Although changes in the stimulus pattern can produce changes in the effective stimulus intensity, the responses to certain patterns cannot be matched by any adjustment of stimulus intensity.

3. The initial portion of responses to large or small stimulating spots is proportional to light intensity; this allows comparison of responses when the amount of light on a cone is kept constant but the light on surrounding cones is changed. For equal light intensity on the cone, the response to a spot 2 or 4 μ in radius is smaller than that to a spot 70 μ in radius.

4. Responses to spots 70 and 600 μ in radius coincide over their rising phases and peaks without any adjustment of stimulus intensity. The responses to the larger spot, however, contain a delayed depolarization not present with the smaller spot.

5. During steady illumination of a cone with a small central spot, the response to transient illumination superimposed on the same area is greatly reduced. Illumination of cones in the near surround, however, produces a hyperpolarizing response, and illumination of cones in the more distant surround generates a delayed depolarization.

6. The results described above suggested that synaptic signals might impinge on cones. This possibility was tested by electrically polarizing one retinal cell while recording from another.

7. Currents passed through a cone within 40 μ of another cone can change the membrane potential of the latter. Not all cones within this distance show the interaction, however, and it has never been detected at distances greater than 50 μ.

8. Hyperpolarization of a horizontal cell with applied current can produce a depolarization of a cone in the vicinity. During this depolarization, the response of the cone to a flash is reduced in size and altered in shape.

9. It is concluded that the response of a cone to light may be modified by synaptic mechanisms which are activated by peripheral illumination.
Cardiovascular reflex responses to cutaneous and visceral stimuli in spinal man
Authors: Corbett J. L. , Frankel H. L. , Harris P. J.
Published: December 2014

1. A study has been made of the effects of pinprick and a cold pack applied to the skin above and below the level of denervation, deep inspiration, squeezing the chest, and bladder percussion in non‐bedridden patients with chronic, closed, complete, localized transection of the cervical spinal cord. Variables studied were blood pressure, heart rate, calf blood flow, hand blood flow and occluded vein pressure in the hand and foot.

2. Cutaneous stimuli above the lesion, mental arithmetic and noise from gunshot produced no response.

3. Pinprick and cold applied below the lesion usually produced an increase in mean arterial pressure, little change in pulse pressure or heart rate, clear decreases in calf and hand blood flow, and occasional venoconstriction.

4. Deep inspiration produced an initial rise in blood pressure and heart rate which was sometimes followed by a decrease in one or both. Squeezing the chest usually produced an increase in blood pressure and a decrease in heart rate. Both stimuli caused decreases in calf and hand blood flow and venoconstriction, the latter being more common after squeezing the chest.

5. Bladder percussion produced contraction of the wall of the bladder and this was regularly associated with increased arterial mean and pulse pressures, a decreased heart rate and calf and hand blood flow, and venoconstriction. The responses occurred whether or not the bladder was full and whether or not a rise of intravesical pressure occurred.
The reflex nature of the pressor response to muscular exercise
Authors: Coote J. H. , Hilton S. M. , Perez‐Gonzalez J. F.
Published: December 2014

1. In anaesthetized cats tetanic contraction of the hind‐limb muscles, elicited by stimulating the ventral roots L6—S1, caused a rise of arterial blood pressure, usually accompanied by small increases in heart rate and pulmonary ventilation: in decerebrate cats, all components of the response were much increased.

2. With tetani of different strengths, obtained by stimulating with different intensities at the same frequency, the pressor response increased with increasing tension.

3. When muscle contraction had been abolished by gallamine, or when dorsal roots L6—S1 had been sectioned, ventral root stimulation no longer caused a pressor response. The response is therefore a reflex, initiated in the exercising limb.

4. The pressor response was not affected by section of all articular nerves to knee and ankle joints, or by section of the vagi. The stimulus therefore originates in the contracting muscles alone.

5. The pressor response is potentiated by occluding the circulation through the working muscles. Reasons are discussed for concluding that the stimulus is chemical rather than mechanical, and that the ‘metabolic receptors’ for this exercise reflex are the free endings of group III and IV sensory nerve fibres located around the blood vessels.
The flow of juice from the pancreatic gland of the cat in response to vagal stimulation
Authors: Lenninger Sven , Ohlin P.
Published: December 2014

1. Stimulation of the vagus nerve of the cat causes a pancreatic secretion in most animals. The volume of the secretion is about 20% of the maximal response of the gland to exogenous secretin.

2. Maximal secretory effect of vagal stimulation is obtained with frequencies between 8 and 15 c/s.

3. The effect of the nerve stimulation is direct on the pancreas and not mediated by gastro‐intestinal hormones.

4. The secretion of water in response to vagal stimulation is not depressed by anticholinergic agents in doses which profoundly depress the secretion of enzymes.

5. The secretion of water in response to submaximal vagal stimulation is not increased by eserinization of the gland, whereas the output of proteins is strongly augmented by this procedure.

6. The significance of the finding that the watery and enzymic secretion can be dissociated pharmacologically is discussed.
Reflex effects on the heart of stimulating left atrial receptors
Authors: Furnival C. M. , Linden R. J. , Snow H. M.
Published: December 2014

1. Stimulation of left atrial receptors, by distension of the pulmonary vein/left atrial junctions, is known to cause a reflex increase in heart rate; the efferent pathway is known to be solely in the sympathetic nerves.

2. In expectation of a concomitant positive inotropic response the effect of stimulating the left atrial receptors on the inotropic state of the left ventricle was studied, using as a known sensitive index of inotropic changes the maximal rate of rise of pressure in the left ventricle (dP/dt max).

3. Stimulation of left atrial receptors resulted in an increase in heart rate but there were no significant concomitant changes in dP/dt max.

4. It is concluded that activity in this discrete efferent pathway does not include an inotropic effect on the left ventricle and therefore the reflex involves only those sympathetic nerves which innervate the sinu‐atrial node.

5. The possible function of atrial receptors in the regulation of heart volumes is discussed.
Responses to visual contours: spatio‐temporal aspects of excitation in the receptive fields of simple striate neurones
Authors: Bishop P. O. , Coombs J. S. , Henry G. H.
Published: December 2014

1. The properties of the receptive fields of simple cells in the cat striate cortex have been studied by preparing average response histograms both to moving slits of light of different width and to single light‐dark edges or contours.

2. The movement of a narrow (< 0·3°) slit across the receptive field gives rise to average response histograms that are either unimodal, bimodal or multimodal. A slit of light has leading (light) and trailing (dark) edges. By increasing the width of the slit it was shown that a discharge peak in the histogram coincides with the passage of one or other of the two edges over a particular region (discharge centre) in the receptive field. Each edge has its own discharge centre which is fired when the edge has the correct orientation and direction of movement.

3. The discharge centres in forty‐three simple cell receptive fields were located by using one or more of the following stimuli for each cell:

(i) slits of different width;

(ii) single light and dark edges;

(iii) a wide (3°) slit moved over a range of different velocities.

The same locations were obtained when all three procedures were used on the same cell.

4. Most cells (79%) discharged to both edges though not necessarily in the same direction of movement. The majority (72%) fired in only one direction and most commonly (51%) the cells responded to both edges in this one direction. In only 16% of cells did both types of edge excite in both directions of movement. When the one type of edge, light or dark, was considered, 84% of the cells were direction selective and, for these cells, the other edge fired only in the same direction (51%), in both directions (7%), only in the opposite direction (5%) or not at all (21%).

5. Cells responding in one direction with a unimodal average response histogram may be responding to both edges, the two responses being concealed in the one discharge peak. The two discharge centres are then either nearly coincident or, more usually, slightly offset with respect to one another. Most commonly the dark edge centre is slightly in advance of the light edge centre.

6. The discharge peaks in the bimodal and multimodal types come from discharge centres that are spatially separate, each centre firing to only one type of edge. In the case of the bimodal type the light edge centre always lies ahead of the dark edge centre.

7. When a cell responds to a single edge in both directions of movement, the type of contrast effective in one direction is always the reverse of that in the other. When the cell responded in both directions, whether to one or both edges, most commonly a light edge discharge centre in one direction occupied approximately the same location in space as the dark edge centre in the reverse direction and vice versa for the other edge.

8. Temporal aspects of the discharge of simple cells have been examined by recording the responses to moving slits and single edges over a wide range of velocities.
Effect of temperature on muscle energy metabolism and endurance during successive isometric contractions, sustained to fatigue, of the quadriceps muscle in man
Authors: Edwards R. H. T. , Harris R. C. , Hultman E. , Kaijser L. , Koh D. , Nordesjö L-O.
Published: December 2014

1. The effects of altered tissue temperature on muscle metabolism during successive isometric contractions, sustained to fatigue, have been studied in the quadriceps muscle of man by combining biochemical analyses of metabolites in needle biopsy samples with measurements of endurance time with a force of 2/3 maximum voluntary contraction. Fatigue and recovery were observed repeatedly in a series of seven contractions at intervals of 20 sec, following immersion of the test leg in water at 12, 26 or 44° C for 45 min. Muscle temperatures corresponding to these water temperatures were 22·5, 32·6 and 38·6° C respectively.

2. Increased levels of several glycolytic intermediates at rest in the heated muscle suggested an increased rate of glycolysis. ATP and phosphoryl creatine were lower at the end of the first contraction and the calculated rate of ATP utilization (including the contribution from anaerobic glycolysis) was highest in the heated nuscle.

3. Significantly shorter endurance times were found for the heated muscle. These could not be attributed to depletion of local energy resources in muscle. Fatigue may be due to a reduction in the rate of regeneration of ATP from anaerobic glycolysis below that needed to maintain the contraction force. Lower values for the ratio of fructose 1,6‐diphosphate: fructose 6‐phosphate at the end of contractions, particularly at the highest temperature, are compatible with the hypothesis that there is partial inhibition of the rate controlling enzyme phosphofructokinase, possibly due to the accumulation of hydrogen ions in muscle.
On the regulation of depth and rate of breathing
Authors: Clark F. J. , von Euler C.
Published: December 2014

1. The relationships between the depth of a breath and the durations of the inspiratory and expiratory phases have been studied in cat and in man during rebreathing, and in cat using artificial inflations of different magnitudes and timings.

2. In the cat, the apparent volume threshold for termination of inspiration (Hering—Breuer threshold) decreased with time from the onset of the inspiratory phase.

3. Both in rebreathing experiments and with artificially imposed inflations in the cat, the inspiratory duration TI was dependent upon tidal volume VT, and this dependence could be expressed by a hyperbolic relationship of the form (VT‐V0) TI = C where V0 and C are constants.

4. The time course of this ‘Hering—Breuer’ threshold was dependent on intact vagus nerves. After vagotomy the inspiratory duration remained essentially constant with changes in tidal volume produced either by artificial inflation or by the increased respiratory drive due to accumulation of CO2 during rebreathing.

5. In man during rebreathing, the relation between volume and inspiratory duration typically showed two different characteristics. 1, at tidal volumes up to 1·5–2 times eupnoeic values, inspiratory duration did not change as tidal volume increased in response to increased PCO2. This range of operation has been designated range 1. 2, as tidal volume increased above this range 1 a second range designated range 2 was observed where inspiratory duration was volume dependent in the same manner as in the cat.

6. In cat under pentobarbitone anaesthesia, a range 1 operation was not seen except after vagotomy. However, under urethane anaesthesia a range 1 plus a range 2 operation could be seen.

7. The differences between cat and man appeared to be largely quantitative rather than qualitative.

8. In both cat and man, expiratory duration was dependent on inspiratory duration, usually with a linear relationship.

9. The experimental results were assembled in the form of an inspiratory characteristic and a timing relationship that serve as a model of the respiratory mechanisms controlling the depth and rate of breathing. The model predicts that the depth and duration of a breath are related in a definite manner fixed by the system characteristics and that ventilation is adjusted by setting the appropriate operating point on these characteristics. The operating point is determined primarily by how quickly lung volume increases, i.e. the rate of increase of inspiratory motor activity.
Voltage—clamp analysis of the early current in frog skeletal muscle fibre using the double sucrose‐gap method
Authors: Ildefonse Michèle , Rougier Oger
Published: December 2014

1. The early membrane currents in skeletal muscle fibres have been studied with the double sucrose‐gap method, according to the experimental procedure used for the study of the giant axon of the squid.

2. The earliest observable current is a capacitative transient. An equivalent circuit with two capacity‐resistance systems can account for such a current. The components of the electrical circuit are estimated from the records.

3. The capacitative transient current is followed by an initial current, the time and voltage dependence of which are analogous to those of nerve fibres. During this phase of current, the membrane behaves like a sodium electrode for modifications of the external sodium concentration.

4. Using tetrodotoxin, a specific inhibitor of the sodium permeability, it is possible to separate two current components, (i) a transient component, suppressed by tetrodotoxin, which reflects the modifications, with time and voltage, of the membrane permeability towards sodium ions; the larger the depolarization, the shorter the time to reach peak current. This current is inward for depolarizations (V) of about +30 mV to about +130 mV (VNa). There was some variation in these values between individual fibres. Beyond VNa, the current is outward. This current shows a small rectification — inward going — for high depolarizations which is comparable to the behaviour of the Ranvier node membrane. (ii) A quasi‐instantaneous outward component, only voltage dependent. The current—voltage relation of this current shows an outward going rectification for high depolarizations. This current can be considered as a ‘leak’ current, in which chloride ions could play an important role.

5. A sodium tail current is observed when the imposed potential fall occurs during the time course of the initial current. It corresponds to the deactivation of the sodium current previously activated. Because of the large contemporary capacitative currents, it is difficult to measure accurately its maximum amplitude and its time course: yet, the instantaneous current—voltage relation seems to show a slight rectification for the largest depolarizations, as observed on the Ranvier node membrane.

6. The inactivation properties of the sodium current are studied in experiments similar to those described by Hodgkin & Huxley. As in nerve fibres the ability of the membrane to undergo an increase of the sodium permeability depends on the membrane potential. In our experimental conditions, the availability of the sodium carrying system is 90 per cent at the resting potential; the half‐inactivation occurs for V = +11 mV. This potential value corresponds to the smallest value of τh−1, in agreement with the equations proposed by Hodgkin & Huxley (1952d) for the inactivation process.

7. The activation parameters (m∞, τm) are determined by a fitting method, taking account of the values of τh previously established. The potential of half‐activation is near V = +40 mV.
An estimate of adenosine triphosphate release into the venous effluent from exercising human forearm muscle
Authors: Forrester T.
Published: December 2014

1. Human subjects performed a sustained contraction of the forearm muscles for 4 min in the presence of arterial and venous occlusion.

2. The contraction was maintained at 5% of the maximum voluntary contraction, a tension during which the muscle blood flow might be expected to increase by about three times (Lind & McNicol, 1967).

3. Adenosine triphosphate (ATP) was identified in the venous effluent from occluded exercising forearm, but not in the venous effluent from occluded forearm without exercise.

4. The rate of degradation of ATP was assessed in plasma at 37° C, with an estimate of the percentage loss occurring between sampling and testing. This enabled the rate of appearance of ATP in the blood at the time of exercise to be calculated as approximately 7·5–10·5 μg/min (14–20 n‐mole/min). These amounts are compared with 16 μg/min that was infused intra‐arterially into human forearm to cause a threefold increase in blood flow (Duff, Patterson & Shepherd, 1954).

5. It is likely that the ATP detected in the venous effluent has active muscle as the source; if so, then the amounts calculated to be released could satisfy the vasodilator requirements of active skeletal muscle.

6. The effects of circulating ATP on respiration and coronary blood flow during exercise is discussed, including the role it may play locally in the production of ischaemic pain.
Changes in light scattering that accompany the action potential in squid giant axons: potential‐dependent components
Authors: Cohen L. B. , Keynes R. D. , Landowne D.
Published: December 2014

1. To obtain information about structural events that occur in axons, changes in light scattering from squid giant axons were measured during action potentials and voltage‐clamp steps.

2. The scattering changes were measured at several scattering angles. Because the changes in scattering divided by the resting scattering were between 10−6 and 10−5, signal‐averaging techniques were used to increase the signal‐to‐noise ratio.

3. The scattering changes during the action potential were different at different angles. Two types were found, one at 10–30° (forward angles) and the other at 60–120° (right angles).

4. At forward angles, there was a transient scattering decrease during the action potential. The time course of the change was similar to that of the action potential; this change was thought to be potential‐dependent.

5. At right angles, there was a transient scattering increase during the action potential followed later by a second, longer‐lasting increase. Indirect evidence indicated that neither component could be totally potential‐dependent.

6. To further analyse these effects, scattering was measured during voltage‐clamp steps. The changes seen during hyperpolarizing steps were presumed to be potential‐dependent; again two different changes were found, one at forward angles and one at right angles.

7. The potential‐dependent change at right angles occurred with a time course that could be approximated by a single exponential with a time constant τ = 24 μsec. The change at forward angles required two exponentials, τ1 = 23 μsec, τ2 = 900 μsec, to represent its time course.

8. The size of both potential‐dependent changes was proportional to the square of potential. The change at right angles, but not that at forward angles, was increased in size by the addition of butanol or octanol to the bathing solution.
Effects of heating and cooling the spinal cord and medulla oblongata on thermoregulation in monkeys
Authors: Chai C. Y. , Lin M. T.
Published: December 2014

1. In the unanaesthetized monkey (Macaca cyclopis), heating the spinal cord or the medulla oblongata from 38 to 42–43° C produced subcutaneous vasodilatation, respiratory acceleration (frequently interrupted with a period of apnoea in the medullary experiment), bradycardia and hypotension. The animal became drowsy and had a slight decrease of body temperature. Heating the medulla oblongata often induced retching and/or emesis.

2. Cooling the spinal cord or medulla oblongata from 38 to 32–33° C produced subcutaneous vasoconstriction, slower respiration, tachycardia and hypertension. The animal became restless and had a slight increase of body temperature. Cooling the spinal cord induced shivering of the four limbs, while cooling the medulla oblongata induced only shivering of the jaws.

3. The effects of heating or cooling of the spinal cord or the medulla oblongata were antagonized by simultaneous application of temperature displacement of the opposite nature in the same areas or vice versa.

4. The data suggest that some thermosensitive elements possibly responsible for thermoregulation reside in the spinal cord and the medulla oblongata.
Changes in statistical parameters during facilitation at the crayfish neuromuscular junction
Authors: Wernig A.
Published: December 2014

1. Transmitter release at excitatory neuromuscular junctions of the crayfish was studied at different frequencies of stimulation ranging from 1/sec to 20/sec.

2. Over this frequency range the average number of quanta released per stimulus (m) increased with frequency by a factor of 6–7.

3. Analysis of the fluctuations in quantal release using binomial statistics indicated that the increase in m was associated with increase in the average quantal release probability (p) at stimulation frequencies between 5/sec and 20/sec. Between 1/sec and 5/sec there was an apparent increase in the number of quanta available for release (n).
Vasopressin clearance and secretion during haemorrhage in normal dogs and in dogs with experimental diabetes insipidus
Authors: Errington M. L. , E Silva M. Rocha
Published: December 2014

1. The secretion of vasopressin in response to haemorrhagic shock has been investigated in anaesthetized dogs.

2. The changes in the plasma concentrations of vasopressin were followed over a period of 5 hr, during which the arterial blood pressure was kept constant at 40 mm Hg. It was found that vasopressin concentration in plasma rose to a high peak shortly after the onset of shock and gradually declined thereafter. Five hours later, it was still 3·5 times higher than control. Re‐transfusion of blood was followed by a return to control levels.

3. The clearance of vasopressin was calculated before and during shock in normal dogs and in dogs with experimental diabetes insipidus. Soon after the onset of shock, the clearance rate dropped to one quarter of its normal level but slowly recovered, returning to near control values at the fifth hour of shock. Clearance rates did not vary as a function of infusion rates, suggesting that there is no maximal transport rate for the removal of the hormone over the entire secretory range found in normal and hypotensive dogs.

4. From the clearance rates and from the plasma concentrations of endogenously secreted vasopressin it has been possible to calculate the approximate secretory rates of the hormone in response to shock. Secretion rose to a very high level, some 40 times greater than control, at the onset of shock. This was followed by a fairly constant secretory plateau. At the fifth hour of shock secretion was 3·5 times higher than control.

5. The half‐life of vasopressin was measured in normal and hypotensive dogs. Control measurements confirm the generally accepted value of approximately 5 min. The half‐life was significantly higher in the early stage of shock, but returned to control values in the later stage.

6. Haemorrhage experiments performed in normal and diabetic dogs suggest that vasopressin may play a part in the development of irreversible haemorrhagic shock: all normal animals died within a few hours of retransfusion, whereas four out of eight diabetic dogs similarly treated survived a 24 hr observation period. In a separate set of experiments, eight diabetic dogs were subjected to the haemorrhage procedure while receiving a constant infusion of vasopressin: only two of these survived. Surviving dogs showed none of the characteristic lesions of irreversible haemorrhagic shock.
Daily changes in foetal urine and relationships with amniotic and allantoic fluid and maternal plasma during the last two months of pregnancy in conscious, unstressed ewes with chronically implanted catheters
Authors: Mellor D. J. , Slater J. S.
Published: December 2014

1. The fluid sacs and bladders of ten foetuses and the allantoic sacs of five foetuses were catheterized between 79 and 96 days gestational age and daily samples were withdrawn until lambs were born naturally at ∼147 days. Maternal jugular plasma obtained daily allowed the nutritional status of each ewe to be regulated and monitored. All lambs were observed for 7 weeks, and at post‐mortem no abnormalities were seen in those operated upon in utero.

2. The osmolality, [Na+], [K+], [Cl−], [glucose], [fructose], [urea], [amino acid] and pH of all samples were measured.

3. Foetal surgery seemed to affect the actual concentrations of some solutes, but gestational trends in foetal fluid composition were unaltered.

4. Until about 7 days before birth the foetal urine osmolality, [Na+], [Cl−] and [fructose] decreased, its [urea], [amino acid] and pH remained relatively constant, and from about 120 days gestational age the [K+] increased. During the last 7 days there was a marked increase in the osmolality and the concentrations of all these solutes, and a decrease in pH.

5. Entry of foetal urine into the fluid sacs tended to decrease the osmolality, [Na+], [K+], [Cl−] and [glucose] of both foetal fluids and the [amino acid] of allantoic fluid, and tended to increase the [fructose] and [urea] of both fluids and the [amino acid] of amniotic fluid.

6. Changes in urine composition suggested large daily variations in the secretion of foetal antidiuretic hormone and also a rapid increase in its secretion during the last 7 days, and particularly the last 2–4 days before birth.

7. Changes in the [Na+]/[K+] ratios of foetal urine and allantoic fluid were parallel during post‐operative recovery, during the course of pregnancy and immediately before birth, and this was consistent with a simultaneous action of foetal plasma corticosteroids on the foetal kidneys and chorioallantois.

8. Variations in the [fructose] of foetal urine and allantoic fluid were parallel to changes in their [Na+]/[K+] ratios and suggested an involvement of foetal corticosteroids in the regulation of the [fructose] of foetal plasma.

9. Further evidence has been presented supporting the hypothesis that maternal induced foetal hypoglycaemia effects a relative increase in the secretion of foetal corticosteroids having an action on the chorioallantois. Also, high concentrations of maternal plasma corticosteroids may decrease the permeability of the placenta to glucose.
The pharmacology and ionic dependency of amino acid responses in the frog spinal cord
Authors: Barker J. L. , Nicoll R. A.
Published: December 2014

1. The isolated frog spinal cord was used to study the action of amino acids and their antagonists on primary afferent terminals and motoneurones. The direct effects of these substances were observed by bathing the cord in 20 m
M magnesium sulphate (thus blocking synaptic transmission) and recording the polarization level of the dorsal and ventral roots.

2. γ‐Aminobutyric acid (GABA) and glutamic acid depolarized the dorsal root and reduced dorsal‐root potentials, while glycine produced only weak and variable effects. Glutamic acid also depolarized the ventral root; GABA usually produced either a hyperpolarization or had little effect, while glycine caused variable effects.

3. Bicuculline and picrotoxin antagonized all the synaptic potentials recorded on the dorsal root, as well as the GABA responses on both dorsal and ventral roots.

4. All the synaptic potentials examined remained and were markedly prolonged in the absence of external chloride except the ventral root‐dorsal root potential. Replacement of the physiologic complement of chloride during chloride‐free perfusion restored the potentials to their original time courses.

5. Depolarizing amino acid responses remained in the absence of external chloride, while hyperpolarizing responses were reversed into depolarizations. Return to normal Ringer solution re‐established the hyperpolarizations.

6. Removal of external sodium reversibly abolished the amino acid depolarizations but had little effect on the depolarizations in response to applications of high external potassium concentrations.

7. The results support the hypotheses (a) that GABA mediates presynaptic inhibition by depolarizing primary afferent terminals and (b) that the GABA‐mediated depolarization is sodium dependent.

8. The results also indicate that GABA utilizes different ionic mechanisms to mediate presynaptic inhibition (sodium) and post‐synaptic inhibition (chloride) in the amphibian (and presumably in the mammal).
Nervous activity of afferent cardiac sympathetic fibres with atrial and ventricular endings
Authors: Malliani A. , Recordati G. , Schwartz P. J.
Published: December 2014

1. We recorded the electrical activity of single afferent cardiac fibres isolated from the third and fourth left thoracic sympathetic rami communicantes of anaesthetized cats. Their conduction velocities ranged from 12 to 32 m/sec.

2. The endings of each fibre were localized to one cardiac chamber by mechanical probing of the opened heart performed at the end of the experiment.

3. The impulse activity was spontaneous and, in fibres with atrial or ventricular endings, it was in phase with a particular atrial or ventricular event.

4. This nervous activity increased during increases in pressure occurring in the chamber where the endings were located. Conversely, decreases in pressure were accompanied by decreased nervous discharge.

5. In some experiments the left coronary artery was perfused at different flows and pressures. Brief decreases or increases in coronary flow and pressure decreased or increased, respectively, the discharge of fibres with atrial or ventricular endings. Fibres were excited by intracoronary injections of veratridine.

6. Cessation of coronary pump flow increased the discharge of fibres with atrial or ventricular endings only when myocardial ischaemia was accompanied by signs of heart failure.

7. These afferent cardiac sympathetic fibres which provide the spinal cord with continuous specific information on cardiac events are likely to contribute to the neural control of circulation.
Chronotropic and inotropic effects on the dog heart of stimulating the efferent cardiac sympathetic nerves
Authors: Furnival C. M. , Linden R. J. , Snow H. M.
Published: December 2014

1. The chronotropic and inotropic responses of the dog heart to stimulation of the ansae subclaviae were studied.

2. The maximum rate of rise of pressure in the left ventricle (dP/dt max) was used as an index of the inotropic changes.

3. In experiments in which the secondary inotropic effects of changes in heart rate and blood pressure were prevented it was shown that, using stimuli which produced the same chronotropic response, stimulation of the left ansa subclavia resulted in an inotropic change which was about eight times greater than that which resulted from stimulation of the right ansa subclavia.

4. In experiments in which heart rate and blood pressure were allowed to change freely it was shown that the secondary inotropic effects of changes in blood pressure and heart rate amounted to about 70% of the total inotropic change when the right ansa subclavia was stimulated and about 20% of the total change when the left ansa subclavia was stimulated.
The visual areas in the splenial sulcus of the cat
Authors: Kalia Madhu , Whitteridge D.
Published: December 2014

1. The extreme periphery of the visual field is represented in the upper wall of the splenial sulcus where the sulcus is horizontal, and in its anterior wall more posteriorly where the sulcus runs downwards and laterally. About half the cells whose fields lie between 50 and 90° from the area centralis have a sharply horizontal preferred orientation.

2. Beyond the lateral edge of visual I there is a narrow band of visual cortex in which the receptive fields return towards the area centralis as one moves 1–1·5 mm laterally. Their receptive fields are usually about 20–30° degrees across, but all orientations are found. The more central fields may be binocular and those at the area centralis may be as small as 1° in diameter.

3. This band has been called the splenial visual area. It does not seem to have properties corresponding to those of visual II nor of visual III.
The formation of synapses in mammalian striated muscle reinnervated with autonomic preganglionic nerves
Authors: Bennett M. R. , McLachlan Elspeth M. , Taylor R. S.
Published: December 2014

1. A study has been made of the formation of synapses during reinnervation of the hemidiaphragm of adult rabbits with preganglionic fibres of the thoracic vagus, using histological, ultrastructural and electrophysiological techniques.

2. Following reinnervation with preganglionic axons, silver‐stained nerve terminals were found in association with cholinesterase‐stained end‐plates only in the region of the muscle corresponding to the original innervation band.

3. The fine preganglionic axons retained their normal structure in striated muscle, but were found to synapse over discrete areas of dimensions not larger than those of the original end‐plates.

4. The regenerated varicose preganglionic nerve terminals were observed with the electronmicroscope in positions either overlying or in the vicinity of the old synaptic folds.

5. Spontaneous potentials and evoked synaptic potentials were recorded only in the middle of the muscle fibres after vagus reinnervation.

6. In a few cases, multiple synaptic potentials with similar time courses were recorded, suggesting that several axons had formed synapses at a single site on a muscle fibre.

7. It has been shown that, during reinnervation of adult mammalian striated muscle fibres with nerves other than those of the somatic system, synapses are formed preferentially in the region of the old end‐plates.
Ionic mechanism for the photoreceptor potential of the retina of Bufo marinus
Authors: Brown J. E. , Pinto L. H.
Published: December 2014

1. Membrane potentials were recorded from single rods in the isolated retina of Bufo marinus while the ionic composition of the extracellular medium was rapidly changed. Substitution of 2 m
M aspartate− for Cl− produced a prompt depolarization of horizontal cells, but no modification of either resting potential or response to light in receptor cells. This implies that feed‐back from horizontal cells to receptor cells was not active.

2. During substitution of choline+ or Li+ for Na+, and during isosmotic substitution of sucrose for NaCl, the resting potential of receptor cells became more negative and responses to light were abolished. During exposure to K+‐free medium, the resting potential became slightly more negative and the responses to light became larger and developed small after‐depolarizations. Exposure to [K+]out of four times normal resulted in permanent diminution of response magnitude and permanent change of response waveshape. Removal of Mg2+, four times normal [Mg2+]out or substitution of methylsulphate− for Cl− had no effect on resting potential or responses to light. With the exception of the small effects seen with altered [K+]out these results are consistent with the receptor potential being generated by a light‐induced decrease of membrane conductance to Na+.

3. Exposure to decreased [Ca2+]out caused both a depolarization of the receptor membrane in the dark and an increase in the magnitude of the maximal response that could be evoked by a test stimulus. The magnitude of the increase in response equalled the magnitude of the depolarization. Exposure to increased [Ca2+]out or steady background light caused both a steady hyperpolarization and a decrease in the magnitude of the maximal response that could be evoked by a test stimulus. For steady hyperpolarizations greater than 3·5 mV, whether caused by elevated [Ca2+]out or steady background light, the decrease in response magnitude exceeded the magnitude of the hyperpolarization. These results imply that externally applied Ca2+ ions mimic the effects of steady background lights, but the applied Ca2+ ions must do more than merely decrease membrane conductance to Na+.
The afferent discharge pattern of atrial mechanoreceptors in the cat during sinusoidal stretch of atrial strips in situ
Authors: Arndt J. O. , Brambring P. , Hindorf K. , Röhnelt M.
Published: December 2014

1. The differences in spike discharge from atrial mechanoreceptors in vivo suggest the existence of different receptor types. To test this possibility, and to see how atrial receptors compare with other mechanoreceptors, their response was studied under comparable stimulus conditions.

2. Sinusoidal length changes, with frequencies from 1 to 10 Hz and amplitudes of 1·5–5·0 mm at a given static extension, were imposed in situ on strips of atrial receptor areas of cats.

3. The receptor response was evaluated from functional single fibres in terms of number of spikes per stimulus period, average discharge rate, instantaneous spike frequency, and phase angle between forcing function and instantaneous frequency.

4. Irrespective of the fibre type, atrial fibres appear to originate from identical mechanoreceptors which sense length at low stimulus frequency and low stimulus amplitudes, but also sense velocity in the high frequency range and with large stimulus amplitudes.

5. The difference in the discharge pattern and in the functional behaviour of the atrial fibres in vivo can be explained on the basis of identical receptors.

6. The difference in the temporal occurrence of the atrial burst is still open to debate, but probably is related to the site of the receptor.
Raising rabbits in a moving visual environment: an attempt to modify directional sensitivity in the retina
Authors: Daw N. W. , Wyatt H. J.
Published: December 2014

1. Rabbits were raised inside drums with vertical stripes painted on the inside. The rabbits were held stationary while the drum rotated continually around them: rotation was always in the same direction for any one animal. Rabbits in one litter were put in the drum for 15 min/day from 10–15 days after birth to about 60 days after birth, with the drum rotating to the right. Rabbits in another litter were put in for 15 min/day with the drum moving left. Rabbits in three other litters were put in for 2‐3 hr/day with the drum moving right. All rabbits were kept in the dark when not in the drum.

2. Optokinetic nystagmus was measured by photographing eye movements during drum rotation at various stages of development. The response to rotation in both directions was measured in a few adult animals. Only small differences were found in the adult animals between optokinetic nystagmus in response to a drum moving right compared to a drum moving left.

3. Recordings were made from ganglion cells in the retina and their receptive fields were mapped. A total of 607 cells from deprived rabbits were analysed. The percentages of on‐centre and off‐centre centre‐surround types, on‐off directionally sensitive types, and on‐directionally sensitive types were not significantly different from normal.

4. The percentages of directionally sensitive cells responding in the anterior, posterior, superior and inferior directions were normal. The fall‐off in sensitivity for these cells with change in direction from the preferred direction was normal.

5. A few orientation sensitive cells were found responding to horizontally oriented bars.

6. We conclude that this selective deprivation of rabbits had little effect on the optokinetic response and no effect on the organization of the retina.
On the repetitive discharge in myotonic muscle fibres
Authors: Adrian R. H. , Bryant S. H.
Published: December 2014

1. Muscle fibres from myotonic goats respond to injected constant currents with a train of action potentials. If the number of action potentials in an evoked train exceeds 10–15, stopping the current does not stop the repetitive firing of action potentials.

2. Normal muscle fibres (goat) in a chloride‐free Ringer respond in the same way to constant current.

3. In the absence of self‐maintained activity both myotonic fibres and normal fibres in chloride‐free Ringer show an after‐depolarization which is proportional to the number of driven impulses. The half‐time for the decay of this after‐potential is about 0·5 sec.

4. Tubular potassium accumulation resulting from the initially driven activity and the known low chloride conductance of myotonic muscle fibres appear to account for the initiation of the myotonic discharge.
The formation of synapses in reinnervated and cross‐reinnervated striated muscle during development
Authors: Bennett M. R. , Pettigrew A. G.
Published: December 2014

1. A study has been made of the formation of synapses in reinnervated and cross‐reinnervated developing striated muscles which normally receive either a focal or distributed innervation, using histological, ultrastructural and electrophysiological techniques.

2. The focally innervated mammalian tibialis anterior muscle, denervated soon after birth, was reinnervated at both the original end‐plates as well as on the new muscle added during the period of denervation; but not on the muscle present at the time of denervation. Nearly all the synapses which had formed, other than at the original end‐plates, disappeared by 6 weeks post‐natal.

3. The avian anterior latissimus dorsi muscle (ALD), which receives a distributed innervation, was denervated during the first week post‐hatched, and became reinnervated both at the original synaptic sites as well as on the new muscle added during the period of denervation; all these synapses were spaced approximately 200 μm apart along the length of individual muscle cells.

4. The myofibres of the ALD muscle cross‐reinnervated at hatching with the superior brachialis nerve, which contains fast motor axons that normally form a focal innervation, were each focally innervated by a single ‘en plaque’ terminal; these synapses had the same electrical properties as normal synapses formed by fast motor axons.

5. Many of the myofibres of the avian posterior latissimus dorsi (PLD), which normally receive a focal innervation, received a distributed innervation from ‘en grappe’ terminals when cross‐reinnervated with the ALD nerve at hatching.

6. It is suggested that during development the nerve type determines the pattern of synapses over an effector; this is achieved by the nerve, after forming the initial synaptic contact, making the rest of the muscle cell membrane refractory to further synapse formation for some distance, this distance being determined by the nerve type.