bluuebunny/crossref_metadata_2025 huggingface dataset:
The contribution of membrane hyperpolarization to adaptation and conduction block in sensory neurones of the leech
Authors: Van Essen David C.
Published: December 2014

The factors underlying sensory adaptation and conduction block have been studied in cutaneous mechanoreceptor neurones of the leech. A touch‐sensitive cell was activated by applying mechanical or electrical stimuli to its receptive field on the skin. Impulses were recorded extracellularly from its axons and intracellularly from its cell body, which is situated within the
C.N.S.

1. Activation of the touch cell by mechanical stimuli revealed two distinct types of adaptation with characteristically different time courses. Sustained pressure on the skin caused a brief burst of impulses at the onset of the stimulus. This rapid adaptation to pressure was restricted to the part of the receptive field that had been stimulated mechanically. A second type of adaptation developed more slowly during the course of repetitive mechanical stimulation. It persisted for many seconds after the end of a train of impulses and appeared as an increase in the threshold to mechanical stimuli not only in the region of skin that had been rubbed but throughout the receptive field of the cell.

2. Impulses initiated in the cell body propagated antidromically towards the skin and also raised the threshold to touch, indicating that after‐effects of impulse activity were responsible for the long‐lasting threshold increase.

3. Repetitive mechanical stimulation could also produce a reversible conduction block in branches of the touch cell. The block occurred in discrete regions of low safety factor such as axonal branch points both within the ganglion and in the periphery. In some experiments impulses intermittently failed to reach one axonal branch yet continued to invade a separate branch of the same cell.

4. Several lines of evidence indicate that both conduction block and the slow component of adaptation are linked to a prolonged hyperpolarization that follows repetitive stimulation of the touch cell. Strophanthidin, which blocks the after‐hyperpolarization in touch cells, reduced the adaptation following trains of impulses and also relieved a conduction block previously established by repetitive stimulation. Furthermore, a comparison of the effects of hyperpolarizations produced by current injection and by repetitive firing showed that most of the threshold increase in the cell body after a train of impulses could be attributed directly to the membrane hyperpolarization.

5. These experiments suggest several ways in which repetitive activity can have pronounced and long‐lasting effects on the performance of a highly branched sensory cell. Thus a relatively small number of impulses in a touch cell can markedly decrease its sensitivity to touch. The functional role of the conduction block observed during vigorous stimulation is not as clear because activity for many seconds or minutes is usually needed to establish a block in the larger branches of the cell.
The transport of L‐tryptophan from cerebrospinal fluid in the dog
Authors: Geddes Claire , Martin M. J. , Moir A. T. B.
Published: December 2014

1. Endogenous tryptophan is uniformly distributed in dog cerebrospinal fluid (c.s.f.) and is about one tenth of the normal fasting plasma level.

2. Using a recirculatory ventriculo‐cisternal perfusion technique in conscious dogs it was found that
L‐tryptophan was removed from c.s.f. by a non‐saturable mechanism in addition to bulk absorption of c.s.f. The clearance of
L‐tryptophan from c.s.f. was unaffected by thiopentone anaesthesia.

3. Dialysis of dog plasma against an artificial c.s.f. solution containing
L‐tryptophan demonstrated that a large proportion of the tryptophan in dog plasma was protein‐bound and that the unbound diffusible proportion would equilibrate with tryptophan concentrations equivalent to those normally found in dog c.s.f.

4. Use of an open‐circuit ventriculo‐cisternal perfusion system in unanaesthetized dogs revealed the presence of a saturable component in the transport of tryptophan from c.s.f.

5. As [14C]
L‐tryptophan infused into a recirculatory perfusion system produced no radioactively labelled metabolites, it was concluded that removal of tryptophan from c.s.f. by cerebral metabolism does not contribute substantially to maintaining the low levels of tryptophan in c.s.f. but that brain uptake associated with protein‐binding may give rise to a small saturable component. The results indicate that the actual concentration gradient of tryptophan between plasma and c.s.f. is much less than it appears from the total concentration of tryptophan in the two fluids, and that the mechanism by which the c.s.f. — plasma distribution of tryptophan is maintained is mainly attributable to simple diffusion.
Spontaneous quantal transmitter release: a statistical analysis and some implications
Authors: Hubbard J. I. , Jones S. F.
Published: December 2014

1. Miniature end‐plate potentials (m.e.p.p.s) were intra‐ and extracellularly recorded from neuromuscular junctions in rat phrenic nerve—diaphragm preparations in vitro.

2. Statistical analysis of the intervals between m.e.p.p.s showed that when the mean number of events in time t was plotted as a function of the variance of the events in time t there was a significant deviation from the straight line relationship expected for a Poisson process. Computer simulation showed that this deviation is explicable if release was generated by the random phasing of the activity of a number of releasing sites.

3. There was no indication that release of one quantum influences the probability of release of remaining quanta (drag, clustering). It is suggested that m.e.p.p.s whose amplitude is larger than the mode result from the release of the contents of vesicles whose volume is also supramodal.

4. The effects of depolarization of nerve terminals upon the variance‐mean curve suggest an increase in the activity of sites rather than an increase in their number.

5. Statistical analysis indicated at least 200 ± 100 (mean ± 1
S.E.) releasing sites. This number is of the same order as the number of sites of vesicle aggregation and presynaptic membrane density seen in electron micrographs of nerve terminals of this preparation.
Body fluids and temperature responses of heat‐exposed women before and after ovulation with and without rehydration
Authors: Senay L. C.
Published: December 2014

1. Four females (21–25 yr) were exposed to 43·3° C dry bulb, 28–29° C wet bulb, for 10 hr both early and late in two menstrual cycles. During the experiments in one cycle, the subjects were rehydrated while during the experiments in another cycle, the subjects were allowed to progressively dehydrate.

2. Rates of weight loss and oral temperatures were determined hourly while venous blood samples were obtained before and then after 1, 2, 3, 4, 6, 8, and 10 hr of heat exposure.

3. Pre‐ovulatory results were compared with post‐ovulatory results and dehydration experiments with rehydration experiments. In addition, the data on these female subjects were compared with those presented elsewhere for similarly treated male subjects.

4. When compared to males, these resting females did not significantly haemodilute when heat exposed. In addition, the female subjects apparently suffered a decrease in plasma volume and body water at a rate some 1·5 times that of similarly exposed males.

5. In general,% change in total protein/unit volume of plasma for these female subjects was similar to previously published results for males. However, there were significant differences in the manner in which albumin and globulin fractions changed before and after ovulation.

6. The rates of body weight loss for these subjects were similar to those determined for males. No difference was noted between pre‐ and post‐ovulatory rates of weight loss. Dehydration significantly depressed the rates of weight loss during heat exposure.

7. Stimulation of sweating (assessed as weight loss) appeared to require similar amounts of heat storage before and after ovulation though initial post‐ovulatory temperatures were generally higher.

8. Progressive dehydration of females before ovulation was accompanied by rates of increase in oral temperatures that were similar to those seen for similarly exposed males.

9. When females progressively dehydrated after ovulation, there was no statistically significant correlation between temperature rise and weight loss as had been noted in pre‐ovulatory experiments. In addition, for all subjects, the rise in body temperature with dehydration was less after than before ovulation. Two subjects showed an ability to decrease their body temperature in the face of continued dehydration.

10. Based on these results, the differences in the responses of males and females to heat exposure were ascribed mainly to two causes: a, inherent differences such as skin surface: blood volume ratios, and b, the inability of females to maintain their vascular volume during heat exposure.
Long‐lasting potentiation of synaptic transmission in the dentate area of the anaesthetized rabbit following stimulation of the perforant path
Authors: Bliss T. V. P. , Lømo T.
Published: December 2014

1. The after‐effects of repetitive stimulation of the perforant path fibres to the dentate area of the hippocampal formation have been examined with extracellular micro‐electrodes in rabbits anaesthetized with urethane.

2. In fifteen out of eighteen rabbits the population response recorded from granule cells in the dentate area to single perforant path volleys was potentiated for periods ranging from 30 min to 10 hr after one or more conditioning trains at 10–20/sec for 10–15 sec, or 100/sec for 3–4 sec.

3. The population response was analysed in terms of three parameters: the amplitude of the population excitatory post‐synaptic potential (e.p.s.p.), signalling the depolarization of the granule cells, and the amplitude and latency of the population spike, signalling the discharge of the granule cells.

4. All three parameters were potentiated in 29% of the experiments; in other experiments in which long term changes occurred, potentiation was confined to one or two of the three parameters. A reduction in the latency of the population spike was the commonest sign of potentiation, occurring in 57% of all experiments. The amplitude of the population e.p.s.p. was increased in 43%, and of the population spike in 40%, of all experiments.

5. During conditioning at 10–20/sec there was massive potentiation of the population spike (‘frequency potentiation’). The spike was suppressed during stimulation at 100/sec. Both frequencies produced long‐term potentiation.

6. The results suggest that two independent mechanisms are responsible for long‐lasting potentiation: (a) an increase in the efficiency of synaptic transmission at the perforant path synapses; (b) an increase in the excitability of the granule cell population.
Innervation of extrafusal and intrafusal fibres in snake muscle
Authors: Cliff G. S. , Ridge R. M. A. P.
Published: December 2014

1. Intrafusal fibres of snake receive motor supply from branches of axons innervating extrafusal motor units. By intramuscular stimulation of motor units by single shocks, and critical curarization of the muscle, we have identified at least some of the motor units contributing motor supply to individual intrafusal fibres. Intrafusal fibre activation was observed by visual examination of the contracting intrafusal fibre, and by recording the resulting spindle afferent discharge.

2. The main finding is that in some cases the motor supply to one intrafusal fibre comes from more than one motor unit. The contributing motor units may be either dissimilar twitch units, or twitch and tonic units. Thus some of the intrafusal fibres studied showed polyneuronal motor innervation of heterogeneous origin.

3. In critically curarized muscle, the time course of a spindle afferent discharge, following single‐shock stimulation of a motor unit contributing motor supply to the intrafusal fibre, showed little variation with the type of motor unit being stimulated.

4. The response of each spindle to a standard stretch was recorded. There was no correlation between dynamic index and type of motor unit or units contributing motor supply. However, the method limits the value of negative findings, and this is discussed.

5. The contraction times and tensions of a sample of motor unit isometric twitches are described.
Effect of lateral cervical cord lesions on the respiratory rhythm of anaesthetized, decerebrate cats after vagotomy
Authors: Remmers John E. , Tsiaras W. G.
Published: December 2014

1. The lateral cervical cord of vagotomized, anaesthetized cats was superficially lesioned at the C3 or the C7 level before or after midcollicular decerebration.

2. These cord lesions eliminated the inhibition of diaphragmatic discharge caused by chest compression. Previous work (Remmers, 1973) indicates that this change can be attributed to loss of reflex inhibition of inspiratory activity by intercostal afferents, probably as a result of interruption of tracts ascending in the lateral columns.

3. Decerebrate cats with bilateral cervical cord lesions displayed abnormal respiratory patterns, ranging from apnoea to apneusis.

4. The results are consistent with the hypothesis that the lateral columns carry proprioceptive feed‐back from intercostal mechanoreceptors which promotes rhythmic breathing in the anaesthetized decerebrate cat.
Splanchnic slowly adapting mechanoreceptors with punctate receptive fields in the mesentery and gastrointestinal tract of the cat
Authors: Morrison J. F. B.
Published: December 2014

1. A class of slowly adapting mechanoreceptors with A‐delta and C fibres running in the splanchnic nerves of cats is described.

2. The mechanoreceptors have punctate regions of mechanical sensitivity at macroscopic vascular branching points and have been found in the lesser omentum, the mesentery of the gall‐bladder, porta hepatis, portal vein, pancreas, spleen and the duodenum, jejunum, ileum, colon and their mesenteries.

3. The receptive fields of these mechanoreceptors vary considerably in size in the different regions. The largest receptive fields were found in the small intestinal mesentery and consisted of up to seven points of mechanical sensitivity at vascular divisions, each separated by distances of a few up to about 40 mm. The smallest receptive fields were single or double points of mechanical sensitivity which were most commonly found in relation to the portal vein in the root of the mesentery.

4. Maintained stretch of the receptive field elicited a train of impulses which had phasic and tonic components. The tonic discharge was sometimes maintained for more than 1 min.

5. Distension of a neighbouring viscus often caused a discharge which had a phasic component and a variable tonic component. The occurrence of the latter appeared to depend on the relative positions of the bowel and mesentery, and was probably associated with a change in tension on the mesentery.

6. Occlusion of the portal vein resulted in some units in a discharge which began soon after the start of the occlusion.

7. The receptors do not appear to be affected by acid, hypoxia or hypercapnia.
Gastric emptying in young pigs
Authors: Ochia B. A.
Published: December 2014

1. Gastric emptying in young pigs has been studied by using a serial test meal procedure.

2. Phenol red was used as a reference substance. In acute experiments the recovery of phenol red from the stomach with the pylorus occluded was 94·8 ± 2·2 (
S.E.)% of that introduced.

3. Gastric emptying was examined in seven fasted conscious pigs provided with a chronic gastric cannula. After emptying the stomach 500 ml. of a liquid meal containing 20 g citrus pectin, 35·0 g sucrose and 100 mg phenol red made up to 1 l. was introduced. After 5–60 min the meal was withdrawn, the volume of meal that had left the stomach was assessed from the recovery of phenol red and the secretion of gastric juice was calculated from the dilution of phenol red and the rate of emptying. After an initial very rapid outflow, the rate of emptying fell with time, as did the rate of secretion.

4. In three pigs 200, 400, 600 or 800 ml. meal was introduced into the stomach and the stomach was emptied 20 min later. The rate of gastric emptying varied directly with the volume of meal introduced.

5. Atropine sulphate, 0·5 mg/kg body weight, injected
I.M. 30 min before the test, greatly inhibited gastric emptying and secretion.
The formation of synapses in reinnervated mammalian striated muscle
Authors: Bennett M. R. , McLachlan Elspeth M. , Taylor R. S.
Published: December 2014

1. The hemidiaphragm of the adult rabbit has a single band of end‐plates running around the middle of the muscle. A study has been made of the formation of synapses during spontaneous reinnervation of this muscle, using histological, ultrastructural and electrophysiological techniques.

2. Following spontaneous reinnervation, 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 regenerated nerve terminals were observed with the electronmicroscope in positions overlying or adjacent to the old synaptic folds.

4. Spontaneous miniature end‐plate potentials and evoked synaptic potentials were recorded only in the middle of the muscle fibres after reinnervation.

5. The growth of the regenerating axons was not oriented towards the end‐plate zone but followed muscle fibres and blood vessels in random directions.

6. It is concluded that, in adult mammalian striated muscle, the old end‐plate region is preferentially reinnervated as a consequence of some special property of the muscle fibre at this site.
Effects of cold exposure on tissue blood flow in the new‐born lamb
Authors: Alexander G. , Bell A. W. , Hales J. R. S.
Published: December 2014

1. Conscious lambs less than 2 days old were exposed to thermoneutral and to cold environments, and the radioactive microsphere technique was used to obtain measurements of blood flow to most tissues of the body.

2. Cold stress was such as to evoke a summit metabolic response. Deep body temperature was within the normal range for thermoneutral conditions, while metabolic rate increased by about 300%, cardiac output by about 30%, and blood pressure by about 25%.

3. Blood flow to the thermogenic tissues increased: perirenal, inguinal, pericardial, prescapular and cervical brown fat depots showed a five‐ to sixfold increase, while the longissimus dorsi, trapezius, gastrocnemius and biceps femoris muscles showed a five‐ to ninefold increase.

4. There was an increase in blood flow in the diaphragm, intercostal, panniculus and cardiac muscles, but a decrease in flow in the skin of the leg, ear and midside, the maxillo turbinals, thyroids, spleen, kidneys, liver and gut. There were no significant changes in total or regional blood flow in the brain or spinal cord, or in the adrenals, nasal mucosa or tongue.

5. Results support other evidence that thermogenesis in both brown fat and skeletal muscle is very important in the new‐born lamb exposed to cold. Changes in flow in other tissues correlated with known functions in the cold animal. The redistribution of cardiac output during cold stress is a further example of circulatory adjustments which enable animals to cope with stress states.

6. Many differences between blood flow values obtained by the radio‐active microsphere and other techniques for measuring blood flow are noted and discussed.
The role of a reactive disulphide bond in the function of the acetylcholine receptor at the frog neuromuscular junction
Authors: Ben-Haim D. , Landau E. M. , Silman I.
Published: December 2014

1. The effects of disulphide bond reduction and reoxidation on synaptic transmission in the frog neuromuscular preparation have been studied.

2. The amplitudes of end‐plate potentials (e.p.p.s) and miniature e.p.p.s (m.e.p.p.s) were decreased irreversibly by the reducing agent dithiothreitol (DTT). Recovery of e.p.p.s and m.e.p.p.s could be achieved, however, by subsequent reoxidation employing 5,5'‐dithio‐bis‐(2‐nitrobenzoic acid) (DTNB).

3. No change in e.p.p. quantal content was produced by treatment with DTT and DTNB. The reduction of m.e.p.p. frequency found in DTT was attributed mainly to our inability to distinguish small m.e.p.p.s from the background noise. However, a genuine reduction in m.e.p.p.s frequency could not be ruled out.

4. The ‘reactive’ disulphide bond which is acted upon by DTT and DTNB could be located within a few Ångstrom from the anionic site of the receptor for acetylcholine (ACh), by employing the active‐site directed reagent bromoacetylcholamine (BACA).

5. Reduction of the ‘reactive’ disulphide bond did not cause changes in the post‐synaptic membrane input impedance nor was the e.p.p. reversal potential affected. Treatment with DTT and DTNB was found to modify only the conductance of the synaptic membrane.

6. No synaptic effects were produced by DTT in a non‐cholinergic synapse, the crab neuromuscular preparation.

7. It is concluded that the receptor for ACh, besides including the well‐known anionic site for binding quaternary ammonium groups, also contains a unique ‘reactive’ disulphide bond. This bond controls synaptic conductance but not the relative permeability of the synaptic membrane to Na+ and K+. It is not yet clear whether the ‘reactive’ bond controls the interaction of ACh with the receptor or the translation of this interaction into ionic permeability changes.
Presbyopia and the water content of the human crystalline lens
Authors: Fisher R. F. , Pettet Barbara E.
Published: December 2014

1. The water content of the human crystallaline lens nucleus is 63·4%
S.D. ± 2·9%, and cortex 68·6%
S.D. ± 4·3%.

2. Neither the total water content of the cortex, nor that of the nucleus show any significant changes with age, so ‘sclerosis’ of the lens due to loss of water is not a cause of presbyopia.

3. The initial loss of water from the nucleus of the lens substance obtained by drying in vacuo at 20° C for 2 hr is related to age (P = 0·05) and deformability (0·02 > P > 0·01).

4. The lens fibres of the ageing nucleus have an increased resistance to deformation associated with a decrease in initial water loss. These characteristics can be explained by a common physical property of the fibres, namely increased adhesion to each other as the lens nucleus ages. The newly formed cortical fibres do not appear to show these changes.
The attenuation of passively propagating dendritic potentials in a motoneurone cable model
Authors: Redman S. J.
Published: December 2014

1. The Rall model of the motoneurone, which consists of a lumped resistance and capacitance, representing the soma, in parallel with a number of distributed resistance‐capacitance networks of finite and equal electrical length, representing equivalent dendritic cables, has been used to study the effects of varying electrical and geometrical parameters on the time course and amplitude of transients generated at different locations on the dendritic cables.

2. An analytical solution has been obtained for the time course of the voltage transient generated at the point of current injection on the parallel combination of all dendritic cables, in terms of the distance from the soma to the current injection point, the electrotonic length of the equivalent dendritic cable, the dendritic to soma conductance ratio and the membrane time constant. The current applied is a current impulse, and the response to any synaptic current time course may be obtained from the analytical expression for the current impulse response. A smooth current time course of the form Te—αT has been used in computations.

3. An analytical expression has been obtained for the early part of the voltage response at the point of current injection, when the current is applied to a fraction of the total dendritic cable. This response is in terms of all the cable parameters, and the assumed fraction of the dendritic cable which receives the synaptic current. Computations of this response have been carried out assuming a smooth time course of synaptic current.

4. The computations of the peak amplitude of the voltage transient obtained from these expressions, together with similar computations for the peak amplitude of the voltage transient after propagation to the soma (Jack & Redman, 1971b), have been used to derive a set of attenuation curves for dendritic propagation. These curves give the ratio of the peak amplitude of the voltage transient at the synaptic location on the dendritic cable, and the peak amplitude after propagation to the soma, in terms of the electrotonic distance to the synaptic location, the time course of current injection, and the cable parameters for the motoneurone model.
Blood flow and fatty acid release by cervical adipose tissue of rabbits
Authors: Hardman M. J. , Hull D.
Published: December 2014

1. A direct technique was used to measure blood flow and exchange of metabolites by cervical adipose tissue in 3‐month‐old and adult rabbits.

2. The initial blood flow from adipose tissue of fed 3‐month‐old rabbits was 0·45 ml./g tissue.min and the tissue released fatty acids and glycerol. In similar rabbits unfed for 24 hr, fatty acid release increased fourfold. Both the rate of blood flow and the arterio‐venous difference of fatty acid increased. In fed adult rabbits blood flow was 0·16 ml./g tissue.min.

3. Noradrenaline infusion in both young and adult rabbits stimulated a rapid and large increase in cervical adipose tissue blood flow together with an increase in fatty acid and glycerol release. Glucose uptake remained small. No increase in local heat production in cervical adipose tissue was detected during noradrenaline infusion.

4. It is concluded that cervical adipose tissue in adult rabbits is actively concerned in energy storage and supply.
Some effects of preganglionic nerve stimulation on synaptic vesicle populations in the rat superior cervical ganglion
Authors: Quilliam J. P. , Tamarind D. L.
Published: December 2014

1. The ‘local vesicle population’, namely the population of synaptic vesicles lying within a zone 0·25 μm wide adjacent to the presynaptic membrane and expressed as ‘vesicles μm−2’ has been estimated in rat superior cervical ganglia maintained in vitro for 1 h. Ganglia were either unstimulated or stimulated tetanically during the last few minutes of the in vitro period.

2. Individual local vesicle populations at synapses in groups of ganglia which had received the same treatment showed an approximately normal frequency distribution.

3. The technique of stimulation did not permit fixation during tetanus, but the mean local vesicle population in ganglia fixed a few seconds after 10 Hz tetani of up to 10 min duration were significantly (P < 0·001) higher than the unstimulated control value of 124·0 ±
S.E. 3·2. Ganglia fixed a few seconds after 3 min tetani at 10 Hz had a mean local vesicle population of 155·7 ±
S.E. 5·7, rising slightly but not significantly to 165·0 ±
S.E. 4·3 at 1 min and 163·1 ±
S.E. 5·2 at 2 min after tetanus. Thereafter the mean local vesicle population fell slowly, reaching control level between 10 and 20 min after tetanus.

4. In terms of the vesicle hypothesis, the observations suggest that post‐tetanic potentiation might arise from a closer clustering of vesicles about release areas resulting in an increase in fractional release. It is suggested that stimulation increased the local vesicle population by promoting vesicle mobilization rather than by altering the size or shape of the presynaptic terminals. The ‘mobilizing agent’ might be intracellular Ca2+.

5. The results appear to be consistent with those of other workers where experimental conditions and the region in which vesicles were counted were comparable.

6. Alternative interpretations for the findings, not involving the vesicle hypothesis, are considered.
The post‐synaptic action of efferent fibres in the lateral line organ of the burbot Lota lota
Authors: Flock Åke , Russell Ian J.
Published: December 2014

1. The post‐synaptic action of efferent fibres on lateral line organs in the burbot was investigated with extracellular electrodes.

2. Selective excitation of efferent fibres or stimulation of the lateral line nerve causes a negative efferent potential in the epithelium, an increase in the microphonic potential, and inhibition of afferent nerve impulses.

3. Stimulation of the lateral line nerve causes antidromic impulses in the afferent fibres in addition to exciting the efferent fibres. However, stimulation of the lateral line nerve has no post‐synaptic influence on lateral line organs when the efferent synapses are selectively blocked by gallamine.

4. The influence of efferent stimulation on the microphonic potential is greater at large amplitudes of mechanical stimulation than at low.

5. The similarities between the effects of efferent stimulation in the lateral line organ and in the cochlea suggest similar synaptic mechanisms.
Kinetics of rhodopsin bleaching in the isolated human retina
Authors: Baumann Ch. , Bender Silvia
Published: December 2014

1. Pieces of human retina were dissected from eyes enucleated because of malignant tumours. The isolated retinas were perfused by an ionic medium (36° C) and investigated spectrophotometrically.

2. Rhodopsin was identified on the basis of its difference spectrum. The maximum absorbance change on bleaching was about 0·1 (λ = 500 nm).

3. The process of bleaching was quantitatively analysed in terms of four slow reactions, viz. (a) conversion of metarhodopsin II into metarhodopsin III, (b) hydrolysis of metarhodopsin II into retinal and opsin, (c) decay of metarhodopsin III to retinal, and (d) reduction of retinal to retinol.

4. First‐order rate constants for the reactions in 3 were 9 × 10−3 sec−1 (a), 3 × 10−3 sec−1 (b), 4 × 10−3 sec−1 (c), and 3 × 10−2 sec−1 (d).

5. With two simplified versions of the model summarized in 3 and 4, the description of experimental data was less accurate.
Localization of pulmonary stretch receptors in the airways of the dog
Authors: Miserocchi G. , Mortola J. , Sant'Ambrogio G.
Published: December 2014

1. During respiratory efforts against a closed airway, the afferent activity of vagal fibres from pulmonary stretch receptors does not appreciably increase during the inspiratory phase because the lung is prevented from expanding.

2. Occlusion at different levels of the airways allows the localization of pulmonary stretch receptors in the tracheo‐bronchial tree.

3. 144 fibres from pulmonary stretch receptors on the left side of the tracheo‐bronchial tree have been studied in eleven dogs and their localization was as follows: 17·4% in the upper half of the intrathoracic trachea, 27·1% in the lower half of the intrathoracic trachea and the carina, 11·1% in the main bronchus, 13·9% in the upper lobe and 30·5% in the lower lobe.

4. From the surface area of the tracheo‐bronchial tree at different levels on the assumption of a total of 2000 stretch receptors on each side, their average concentration was as follows: 34·8% receptors/cm2 in the upper half of the intrathoracic trachea, 54·2/cm2 in the lower half of the intrathoracic trachea, 56·8/cm2 in the main bronchus, 0·37/cm2 in the intrapulmonary airways.

5. Occlusion of the main bronchus caused an increase of the eupnoeic oesophageal pressure swing by about 75% whereas occlusion of the inferior lobar bronchus led to an increase of only 20%. Therefore the reflex effects induced on the respiratory activity by occluding the airways at various levels show the greatest importance of the hilar portions of the airways where the concentration of pulmonary stretch receptors has been found to be greater.
Plasma aldosterone, cortisol and corticosterone concentrations in the new‐born guinea‐pig
Authors: Malinowska K. W. , Nathanielsz P. W.
Published: December 2014

1. Plasma aldosterone concentrations have been measured by radio‐immunoassay in the new‐born and adult guinea‐pig and related to plasma cortisol and corticosterone concentrations.

2. Plasma aldosterone concentrations were high in the hours immediately after birth with peak values of 552 pg/ml. at between 6 and 24 hr of age. Adult male plasma concentrations were 72 pg/ml. in plasma taken by cardiac puncture and 126 pg/ml. when measured in blood taken from an indwelling arterial catheter.

3. The major plasma glucocorticoid was cortisol and earlier reports of values above 1 μg/ml. were confirmed by more exacting column chromatography with Sephadex LH 20.

4. There was no constant relation between aldosterone and glucocorticoid concentrations in the animals studied, either new‐born or adult.

5. Plasma cortisol: corticosterone ratios were not constant but varied considerably. In the adult a sevenfold rise in plasma cortisol concentration occurred under certain conditions without any change in plasma corticosterone concentrations.
Electrophysiological investigation of GABA‐mediated inhibition at the hermit crab neuromuscular junction
Authors: Earl Janet , Large W. A.
Published: December 2014

1. The inhibitory neuromuscular junction of the abductor muscle of the large claw of the hermit crab (Eupagurus bernhardus) was investigated using electrophysiological intracellular techniques in order to elucidate further the relative contributions of the pre‐ and post‐synaptic mechanisms of action of GABA and of neural inhibition.

2. The electrical constants of the post‐synaptic membrane, calculated using the equations for a ‘short cable’ model, were characteristic of a poorly developed electrical excitability; the specific membrane resistance was usually < 1000 Ω cm2 and the specific membrane capacitance was > 40 μF/cm2.

3. Stimulation of the excitatory axon to the abductor muscle of the large claw at a frequency of 20 Hz evoked highly facilitating excitatory junction potentials (e.j.p.s); stimulation of the inhibitory axon (60‐220 Hz) during the excitatory train elicited inhibition which was manifest as an attenuation of the e.j.p.s.

4. The addition of γ‐aminobutyric acid (GABA) to the bathing solution produced a dose‐dependent reduction of e.j.p. amplitude and membrane resistance. The inhibitory effect of concentrations (5 × 10−5 and 1 × 10−4
M) which caused a 40–75% e.j.p. attenuation could largely be accounted for by a post‐synaptic action on membrane conductance.

5. Experiments with picrotoxin suggest that presynaptic inhibitory mechanisms have an important role in neurally evoked inhibition.

6. Picrotoxin (1–5 × 10−5
M) effectively blocked neural inhibition and the actions of GABA in this preparation, whereas bicuculline proved to be considerably less potent and therefore less useful as a physiological tool for studying GABA‐mediated inhibition in crustacea.
Does the vestibular apparatus play a role in the development of the visual system?
Authors: Blakemore C. , Papaioannou J.
Published: December 2014

1. The receptive field properties of visual cortical neurones were investigated in kittens that had been subjected to either unilateral or bilateral labyrinthectomy shortly after birth.

2. Two kittens were reared in a normal visual environment. Another two were reared in the dark with recurrent exposures to vertically oriented black and white stripes, which in normal kittens is known to bias the distribution of receptive field orientations.

3. For both normally reared and stripe‐reared labyrinthectomized kittens, no differences were detected in cell types, preferred orientations, binocularity, columnar organization, or any other neuronal properties, compared with similarly reared intact kittens.

4. The failure to detect deficits in visual development after labyrinthectomy is discussed in relation to other reports of vestibular influences on the visual system of the adult cat.
Analysis of the role of cyclic adenosine 3′,5′‐monophosphate in catecholamine release
Authors: Jaanus Siret D. , Rubin R. P.
Published: December 2014

1. Cyclic adenosine 3′,5′‐monophosphate (cyclic AMP) levels and catecholamine release were measured in cat adrenal glands perfused in situ with Locke solution.

2. Cyclic AMP was present in the medulla in an amount which represented approximately one fifth of that present in the cortex.

3. Perfusion with acetylcholine (ACh) or nicotine increased cyclic AMP both in the intact adrenal and in the perfusate. The time course of the changes in tissue cyclic AMP during stimulation was out of phase with the time course of catecholamine release. Maximal increases in cyclic AMP were not manifest until after 8 min of exposure to the secretogogue, whereas maximal rates of secretion occurred during the first minute.

4. Theophylline (0·5 m
M) increased basal and stimulated adrenal cyclic AMP levels, but did not potentiate the secretory response to ACh or nicotine.

5. Perfusion with cyclic AMP or its dibutyryl derivative (0·2–4 m
M) failed to effect a consistent or significant increase in the rate of catecholamine release and was unable to potentiate the secretory response to a submaximal concentration of ACh or calcium.

6. The results suggest that, unlike calcium, cyclic AMP is not a direct mediator of medullary secretion.
The development of a blood‐brain barrier mechanism in foetal sheep
Authors: Evans C. A. N. , Reynolds J. M. , Reynolds M. L. , Saunders N. R. , Segal M. B.
Published: December 2014

1. The penetration of a metabolically inert, small molecular radius lipid insoluble substance ([13C] and [4H]sucrose), from blood into brain and c.s.f., has been studied in developing sheep from 50 days gestation (term, 150 days) through to the new‐born stage. Around 50 days gestation sucrose accumulated rapidly into brain and c.s.f., and reached a steady‐state level in brain of about 12% of the plasma level by 3 hr. By 60 days sucrose penetrated less freely into brain and c.s.f.; the brain steady‐state level was 10% by 4½ hr. A large decrease in sucrose penetration occurred by 70 days gestation, and by 123 days (just before the time when a foetal lamb becomes viable) both the rate of penetration and the brain steady‐state level of sucrose were similar to those of the adult of other species.

2. The rate of c.s.f. secretion at different ages has been estimated by dye dilution during ventriculo‐cisternal perfusion. The turnover of c.s.f. in 60 day foetuses was high (1·36%/min.g wet weight brain). From 123 days gestation to the adult stage the turnover was much lower, 0·02%/min.g at 123 and 137 days gestation and 0·01%/min.g in the adult ewe.

3. A simple new method for measuring c.s.f. volume is described. The volume at 51 days was estimated to be 0·14 ml.,
S.E. ± 0·03, n = 4 (brain weight = 0·87 g ± 0·11), at 59 days it was 0·45 ml.,
S.E. ± 0·04, n = 6 (brain weight = 2·0 g ± 0·1) and near term it was 7·28 ml
S.E. ± 1·29, n = 4 (brain weight 42·0 g ± 0·5).

4. The results are discussed in relation to possible changes in permeability of the cerebral capillary endothelium, the sink effect of c.s.f., and changes in extracellular space of the brain during its development. It is concluded that the high rate of penetration and raised brain steady‐state level of sucrose in immature sheep foetuses is probably due to immaturity of a permeability barrier at the level of the cerebral capillary endothelium or its associated glial processes. Some clinical implications of these findings are considered briefly.
Cell structure and function in the visual cortex of the cat
Authors: Kelly J. P. , Van Essen D. C.
Published: December 2014

1. The organization of the visual cortex was studied with a technique that allows one to determine the physiology and morphology of individual cells. Micro‐electrodes filled with the fluorescent dye Procion yellow were used to record intracellularly from cells in area 17 of the cat. The visual receptive field of each neurone was classified as simple, complex, or hypercomplex, and the cell was then stained by the iontophoretic injection of dye.

2. Fifty neurones were successfully examined in this way, and their structural features were compared to the varieties of cell types seen in Golgi preparations of area 17. The majority of simple units were stellate cells, whereas the majority of complex and hypercomplex units were pyramidal cells. Several neurones belonged to less common morphological types, such as double bouquet cells. Simple cells were concentrated in layer IV, hypercomplex cells in layer II + III, and complex cells in layers II + III, V and VI.

3. Electrically inexcitable cells that had high resting potentials but no impulse activity were stained and identified as glial cells. Glial cells responded to visual stimuli with slow graded depolarizations, and many of them showed a preference for a stimulus orientation similar to the optimal orientation for adjacent neurones.

4. The results show that there is a clear, but not absolute correlation between the major structural and functional classes of cells in the visual cortex. This approach, linking the physiological properties of a single cell to a given morphological type, will help in furthering our understanding of the cerebral cortex.
Influence of dendritic location and membrane properties on the effectiveness of synapses on cat motoneurones
Authors: Barrett J. N. , Crill W. E.
Published: December 2014

1. Measurements of the specific membrane properties and neuronal geometry of cat motoneurones were used to calculate the excitatory postsynaptic potentials (e.p.s.p.s) produced by unit (quantal) conductance changes occurring at various locations on the dendritic tree.

2. Calculations demonstrate that conductance changes of 80–190 × 10−10 mho are required to produce e.p.s.p.s having the same rise time and peak amplitude as the quantal e.p.s.p.s recorded in motoneurones by Kuno & Miyahara (1969b). Because quantal conductance changes are so large, synaptic activity can significantly reduce the effective specific resistance of the motoneuronal membrane.

3. A quantal conductance change occurring at a high‐impedance distal dendritic site is calculated to produce an e.p.s.p. of 15–20 mV peak amplitude at that site. Significant non‐linear summation will occur between the e.p.s.p.s produced by conductance changes occurring simultaneously on the same dendritic branch.

4. Calculations which take into account both non‐linear summation and the loss of synaptic charge through dendritic membranes predict that for these motoneurones the time integral of soma‐recorded quantal e.p.s.p.s originating on distal dendrites should be at least 20% as great as the time integral of a quantal e.p.s.p. originating directly on the soma. Quantal conductance changes occurring on 76% of the dendritic tree should produce soma e.p.s.p. time integrals at least 50% as great as those produced by somatic synapses.
Blood flow in resting (contralateral) arm and leg during isometric contraction
Authors: Eklund Brita , Kaijser L. , Knutsson E.
Published: December 2014

1. Blood flow in resting forearm and calf were measured plethysmographically in healthy young men during isometric contraction performed both as a handgrip and as a dorsiflexion of the foot. The isometric contraction was maintained for 2 min at one third maximal voluntary contraction for the handgrip and half maximal voluntary contraction for the dorsiflexion of the foot. In some experiments the possible influence on blood flow of inadvertent muscle activation in the resting limb was checked by recording the e.m.g.

2. Both handgrip and dorsiflexion of the foot produced substantial increases in heart rate and mean arterial pressure, the pressure rise being almost linear with time throughout the contraction.

3. Isometric contraction produced a rapid increase in forearm blood flow which reached a maximum on average two and a half times the resting value after 1 min and then declined slightly. Similar increases in forearm blood flow were produced by handgrip and dorsiflexion of the foot.

4. Unlike in the resting forearm, the blood flow in the resting calf increased only slightly during the first minute of contraction and then decreased again to the resting level.

5. The flow increase in the resting limbs could not be ascribed to inadvertent muscle activation as judged from the e.m.g. recordings.

6. It is concluded that isometric muscle contraction produces a rapid increase in blood flow in the resting forearm, but only a very slight flow increase in the calf. Since the flow increased faster than the arterial pressure it must to a certain extent be induced by active neurogenic vasodilatation. Similarly, the relative flow decrease during the latter half of the contraction concomitantly with a progressively rising arterial pressure suggests that the neurogenic effect on the resistance vessels changes character, becoming more vasoconstrictive, and this might be related to increased effort in sustaining the contraction.
Properties of rarely encountered types of ganglion cells in the cat's retina and on overall classification
Authors: Cleland B. G. , Levick W. R.
Published: December 2014

1. In a reference sample of 960 cat retinal ganglion cells, seventy‐three had receptive fields departing from the concentric centre—surround pattern.

2. Five classes were distinguished among the subset: local edge detectors, direction‐selective cells, colour‐coded cells, uniformity detectors, edge inhibitory off‐centre cells.

3. Local edge detectors (forty‐five) possessed a radially symmetrical pattern of responses to both centrifugal and centripetal movements of both black and white small targets, an on—off receptive field with a silent inhibitory surround and a low or zero maintained discharge. Their operation could be interpreted as the detection of a contrasting border confined to a small region of the visual field.

4. With direction‐selective units (eleven) it was possible to find an axis through the receptive field along which sharply different responses could be obtained for opposite directions of movement of small black or white targets.

5. Colour units (six) were mostly of the single opponent type having excitatory input from blue‐sensitive cones and inhibitory input from long wave‐length cones. Both inputs coexisted at the centre of the field and either could be spatially more extensive than the other. One example changed over to rod input under scotopic conditions, another did not.

6. Uniformity detectors (five) had a brisk maintained discharge which was reduced or abolished temporarily by all forms of visual stimulation.

7. Edge inhibitory off‐centre units (three) behaved like uniformity detectors for small targets and fine gratings but like off‐centre on‐surround units for large targets. Their receptive fields consisted of three concentric regions: a small sized, central edge inhibitory region; a larger zone of off‐responsiveness; and an outlying annulus of on‐responsiveness.

8. It is argued that the above physiological types belong to the morphologically heterogeneous class of cells called γ cells. The argument is based on similarity in the sizes of receptive fields and dendritic trees and on evidence that the axons are thinner than those of the brisk‐sustained and brisk‐transient ganglion cells.

9. The physiological classification of cat retinal ganglion cells developed in this paper and the preceding one is summarized in a Table.

10. It now appears that cat and rabbit possess a qualitatively similar complement of receptive field types among their ganglion cells; the differences reside in the quantitative expression of the various classes.