bluuebunny/crossref_metadata_2025_split huggingface dataset:
The pattern of breathing following step changes of alveolar partial pressures of carbon dioxide and oxygen in man
Authors: Gardner W. N. 
Published: December 2014

1. The pattern of breathing during the approach to the steady state following step changes of end‐tidal PCO2 and PO2 has been determined in normal conscious human subjects. Three types of step were studied: (a) steps of PA, CO2 against a constant background of hyperoxia (PA, O2 ∼ 200), an almost pure intracranial chemoreceptor stimulus, (b) steps of PA, O2 between ∼ 50 and 80 torr against a background of constant mild hypercapnia, an arterial chemoreceptor stimulus, and (c) steps of PA, CO2 against a background of constant hypoxia (PA, O2 ∼ 50), a mixed stimulus. Steps were small and the responses barely detectable by the subjects.2. Steps of CO2 in hyperoxia produced the slowest approach to the steady state. A single exponential fitted the ventilation response up to about 4 min (mean half time 83 sec for the ‘up’ and 69 sec for the ‘down’ transients). During the transient the pattern of change of tidal volume (VT) and expiratory time (TE) was the same as in the steady state. Inspiratory time (TI), however, in the early part of the transient, changed in the opposite direction to TE, returning to its steady value only after 1½‐3 min. This effect occurred in both ‘up’ and ‘down’ transients and resulted in a smaller change of respiratory frequency than would have been predicted from the steady‐state response.3. Hypoxic steps produced the fastest approach to the steady state with mean half‐times for ventilation of 10·9 sec for the ‘up’ transients and 6·6 sec for the ‘down’. TI followed the same pattern during the transient as in the steady state, whereas TE, following the step out of hypoxia, lengthened to far beyond its final steady value within five breaths of the step, only returning to its steady‐state value 3‐4 min after the step. This resulted in an exaggerated change of frequency during the early part of the transient.4. Steps of CO2 in hypoxia, a mixed peripheral and central chemoreceptor stimulus, showed a ventilation response which was best fitted by two exponentials, the half‐times of which were consistent with those obtained for the separate responses. The patterning was also consistent with a mixed response, more so for TI than for TE.5. The steady‐state pattern derived from the pre‐switch means was consistent with the pattern previously described.6. Possible mechanisms are discussed. It is suggested that these results could explain the different patterns seen in the past by those using re‐breathing and steady‐state techniques.7. The validity of using one or two breath oxygen or nitrogen tests (or other similar tests) as a quantitative measure of the hypoxic response in man is questioned.
Intensity of sensation related to activity of slowly adapting mechanoreceptive units in the human hand
Authors: Knibestöl M. , Vallbo Å. B. 
Published: December 2014

1. Impulses were recorded from single afferent fibres in the median and ulnar nerves of human subjects. The response of slowly adapting mechanosensitive units with receptive fields in the glabrous skin of the hand were studied when rectangular indentations of varying amplitudes and invariant time duration were delivered. Simultaneously the subject was asked to estimate the magnitude of his sensation associated with the stimuli.2. Stimulus—response plots of the afferent units were constructed and compared with the psychophysical magnitude estimation plots.3. The stimulus—response data of the afferent units fell along monotonous curves which were largely decelerating when stimuli above the static threshold were taken into account. When responses below the static threshold were taken into account many plots were S‐shaped.4. The psychophysical plots were monotonous and either decelerating, linear or accelerating.5. Power functions were fitted to the two sets of data. The group average differed considerably with regard to the exponent of the fitted functions which was 0·7 for the neural and 1·0 for the psychophysical function.6. There was considerable variation between shapes of curves derived from individual test points. The range of exponents for the neural function was 0·26‐1·92 and for the psychophysical function 0·36‐2·09. The variation in psychophysical functions was partly accounted for by relatively stable inter‐subject differences, whereas no such inter‐subject difference was evident for the neural functions, which seemed to vary randomly.7. There was no indication of a correlation between the shapes of the neural functions and the shapes of the psychophysical functions when data from individual subjects or individual test points were compared. Moreover, when two groups of data were considered, one with accelerating and one with decelerating psychophysical functions, the associated neural functions did not differ between the two groups.8. It was concluded that the hypothesis of a close agreement between the stimulus—response functions of slowly adapting mechanoreceptors in the human hand and the psychophysical magnitude estimation functions is not tenable. This was evident when average group data were compared as well as when data from individual subjects and individual target points were compared. The findings suggest that the shapes of the psychophysical magnitude estimation functions are highly dependent on central mechanisms and are not a direct function of the properties of the afferent units as has been claimed in previous investigations.
The intracellular sodium activity of sheep heart Purkinje fibres: effects of local anaesthetics and tetrodotoxin
Authors: Deitmer Joachim W. , Ellis David 
Published: December 2014

1. The intracellular Na activity (aNai) of quiescent sheep heart Purkinje fibres has been measured using Na+‐sensitive glass micro‐electrodes. The effects of local anaesthetics (procaine and lidocaine) and tetrodotoxin (TTX) have been investigated.2. Local anaesthetics reduced the steady‐state level of the intracellular Na activity in a dose‐dependent manner. The highest concentrations used (10−2
M) reduced the intracellular Na activity by about 25%.3. TTX decreased the steady‐state level of the intracellular Na activity. At a concentration of 10−6 g/ml. (3·13 × 10−6
M), TTX produced a decrease in intracellular Na activity of approximately 10%.4. The initial rate of rise of the intracellular Na activity upon addition of the cardioactive steroid strophanthidin (10−5
M) was used to estimate the net passive Na influx.5. Procaine (5 × 10−4
M) caused a 50% reduction of this rate of rise of the intracellular Na activity. The highest concentration of procaine used (10−2
M) decreased the rate of rise by approximately 80%.6. Procaine (5 × 10−3
M) also reduced the rate of rise of intracellular Na produced by the removal of external K (Ko), and prevented the large depolarization associated with the absence of Ko.7. TTX also produced a decrease in the rate of rise of the intracellular Na activity that occurs upon addition of strophanthidin. A maximum effect was produced in our experiments at a TTX concentration of 10−6 g/ml. At this concentration the rate of rise of intracellular Na activity was reduced by approximately 40% at a membrane potential of ‐70 mV.8. We conclude from our experiments that the effects of local anaesthetics and TTX on the intracellular Na activity are brought about by a reduction of the Na permeability of the cell membrane, and that at the normal resting potential, Na entry through TTX‐sensitive channels contributes greatly to the total net Na influx.
The superior colliculus and movements of the head and eyes in cats
Authors: Harris Laurence R. 
Published: December 2014

1. The superior colliculus has been studied in alert cats which were restrained and whose head and eye movements were monitored.2. Microstimulation within the rostral part of the colliculus, which represents the central 25 deg of the visual field, evokes saccadic eye movements that carry the area centralis to that region of visual space previously occupied by the receptive fields of the cells that were stimulated (‘foveation’). These saccades are not generally accompanied by a movement of the head.3. At more caudal locations the visual receptive fields of collicular neurones lie at a greater eccentricity relative to the area centralis than the maximum possible deviation of the eyes from the central position in normal circumstances. At these sites electrical stimulation produces a combined movement of the head and eyes whose co‐ordination is identical to that of natural gaze changes in response to novel stimuli. Prolonged stimulation results in the addition of further co‐ordinated eye‐head movements.4. The addition of a movement of the head does not increase the area of visual space that may be foveated in a single gaze change. Movements of the head are compensated by the vestibulo‐ocular reflex. The visual receptive fields of cells at more caudal locations cannot be foveated by a single gaze change.5. A third class of response to electrical stimulation is also occasionally found in the caudal part of the colliculus. The head movement often begins before an accompanying eye movement and continues smoothly for the entire stimulation duration or until limited by the range of mobility.6. Electrical microstimulation was never found to produce so‐called ‘goal‐directed eye movement, in which the eyes move, in a single saccade, to a fixed orbital position regardless of their starting position.7. Ninety‐nine cells were recorded from the superior colliculus and classified into four types based on their responses, or lack of responses, during or preceding eye and head movements. Type 1 cells did not show changes in activity prior to gaze changes Type 2 cells were inhibited prior to and during eye movements. Cells discharging before normal saccadic eye movements (type 3) were found only in the rostral part of the colliculus. Cells discharging before head movements (type 4) were found only in the caudal part.8. These results are discussed with respect to the production of gaze changes in the cat.
Metabolic mapping of neural pathways involved in gastrosecretory response to insulin hypoglycaemia in the rat
Authors: Kadekaro Massako , Savaki Helen , Sokoloff Louis 
Published: December 2014

1. The central nervous structures involved in the gastrosecretory effect of insulin hypoglycaemia were investigated in twenty urethane‐anaesthetized rats, previously provided with a chronic gastric fistula, by means of the 2‐deoxy‐
D‐[14C]glucose autoradiographic technique.2. Gastric secretion increased in animals in which plasma glucose concentration was reduced to a range of 84‐133 mg/100 ml. (mean ±
S.E. of mean, 94 ± 3) as compared to a range of 125‐215 mg/100 ml. (mean ±
S.E. of mean, 162 ± 8) in animals with normal gastric secretion.3. In fourteen of nineteen structures examined the rate of glucose utilization remained constant over the range of plasma glucose concentrations of 84‐215 mg/100 ml. These structures included the ventromedial nucleus of the hypothalamus, the mamillary nuclei, the medial geniculate nuclei, globus pallidus, zona incerta, nucleus ambiguus, supraoptic nucleus, paraventricular nucleus, medial nucleus of the solitary tract, dorsal tegmental nucleus, red nucleus, inferior olivary nucleus, hippocampus and amygdaloid complex.4. A significant inverse correlation between plasma glucose concentration and the rate of glucose consumption was found in the lateral nucleus of the solitary tract, dorsal nucleus of the vagus, perifornical area where fibres of the medial forebrain bundle course, the superior olivary nucleus and the interstitial nucleus of the stria terminalis.5. Except for the superior olivary nucleus and the interstitial nucleus of the stria terminalis, all the structures affected by low plasma glucose concentration have previously been shown to participate in the gastrosecretory response to blockade of glucose utilization by pharmacological doses of 2‐deoxy‐
D‐glucose, indicating that these same nuclei are also activated by hypoglycaemia.
Proteins in cerebrospinal fluid and plasma of fetal sheep during development
Authors: Dziegielewska K. M. , Evans C. A. N. , Fossan G. , Lorscheider F. L. , Malinowska D. H. , Møllgård K. , Reynolds M. L. , Saunders N. R. , Wilkinson S. 
Published: December 2014

1. The concentration of total protein in c.s.f. and plasma has been measured in fetal sheep of different gestational ages and in the adult. In c.s.f. it was highest (approximately 840 mg/100 ml.) in the youngest fetuses (35 days) and declined steeply by 60 days (260 mg/100 ml.). It decreased less markedly in the last half of gestation to reach about 50 mg/100 ml. at 125 days which is twice the adult value. Protein concentration in plasma was lowest in the youngest fetuses and did not rise much until the second half of gestation during which time it doubled. There was a further rather larger increase between the late fetal (125 days) stage and the adult.2. Albumin, fetuin, α‐fetoprotein (AFP), transferrin and lipoprotein were identified in c.s.f. and plasma.3. The concentrations of albumin, AFP and fetuin in c.s.f. and plasma at different gestational ages were measured using immunodiffusion and radioimmuno‐assays.4. Albumin was the major protein in plasma at all ages studied (35‐128 days gestation and adult). Its concentration increased throughout gestation whereas that of fetuin was similar at all fetal ages and that of AFP declined markedly during the second half of gestation. In the adult, fetuin was only about 0·1% of the total protein in plasma and AFP was not detectable.5. In 35‐40 day fetuses albumin, AFP and fetuin accounted for 90% of the total protein concentration in plasma and for about 70‐80% of the total protein concentration of c.s.f. As gestation progressed the concentration of all three proteins in c.s.f. declined. But the concentration of AFP and fetuin fell more rapidly and to a greater extent than that of albumin; neither AFP nor fetuin could be detected in adult c.s.f.6. The c.s.f.: Plasma ratio was above 50% for AFP and above 60% for fetuin at 35 days compared with about 25% for albumin at the same fetal age. The c.s.f.: plasma ratios for all three proteins declined with increasing fetal age and were not significantly different from each other by about mid gestation.
Blood—cerebrospinal fluid transfer of plasma proteins during fetal development in the sheep
Authors: Dziegielewska K. M. , Evans C. A. N. , Malinowska D. H. , Møllgård K. , Reynolds M. L. , Saunders N. R. 
Published: December 2014

1. The penetration of human and sheep plasma proteins from blood into c.s.f. of sheep fetuses (57‐86 days gestation) has been studied. The proteins were injected intravenously via cotyledonary vessels. After different time periods the c.s.f. concentrations of marker proteins were estimated by radioactive counting of iodinated human or sheep proteins or by immunoassay of human proteins.2. Several proteins of similar molecular size penetrated into c.s.f. to a different extent in 60 day fetuses. The steady‐state c.s.f.: plasma ratios were about 15% for human AFP, 10% for human transferrin and sheep albumin, 7% for human α1‐antitrypsin, and 5% for human albumin. In older fetuses the penetration of protein from blood into c.s.f. was much reduced and no evidence for differential penetration of different proteins was found.3. The penetration of human AFP, transferrin and sheep albumin from blood into c.s.f. was greater than can be accounted for by passive diffusion.4. The results of this paper are discussed in relation to those of the preceding paper on the identification and quantification of proteins in fetal c.s.f. and plasma. The hypothesis is put forward that the choroid plexus of the immature (60 days and less) sheep fetus contains a mechanism for the transcellular transfer of plasma proteins which may be selective in nature and of importance for some aspects of brain development.
Discharges of Purkinje cells and mossy fibres in the cerebellar vermis of the monkey during saccadic eye movements and fixation
Authors: Kase Manabu , Miller David C. , Noda Hiroharu 
Published: December 2014

1. Discharges of Purkinje cells and of presumed mossy fibres were extracellularly recorded from vermal lobules VI and VII of two monkeys during saccadic eye movements and fixation. Among the units showing changes in activity in relation to either saccades or eye position, eighty‐four units were identified as mossy fibres and ninety‐one units were Purkinje cells.2. Based on the discharge patterns associated with saccades, mossy fibre units were classified into long‐lead burst, burst, and burst‐tonic units. The long‐lead burst units (twenty‐eight units) started firing long before the saccades, the discharge consisting of a prelude (average lead time: 160 msec) and a burst (average lead time: 16 msec). In twenty‐two units the saccade‐related bursts showed a directional preference. The burst units (thirty‐seven units) started firing slightly before the saccade onset (average lead time: 7·4 msec) and thirteen units showed directional preference. The bursts in burst‐tonic units (thirteen units) had an average lead time of 0·2 msec.3. Among the ninety‐one Purkinje cells, eighty‐eight cells showed bursts associated with saccades. Three units paused for all directions of saccades.4. Seventy‐one units out of the eighty‐eight burst Purkinje cells showed bursts beginning approximately at the saccade onset (average lead time: 0·6 msec) and lasting throughout the saccade. The durations of bursts and saccades were highly correlated (correlation coefficients ranging from 0·70 to 0·88).5. In the remaining seventeen burst Purkinje cells, the bursts followed the saccade onset (average delay: 32 msec). The bursts started approximately 40 msec before the end of a saccade and persisted on the average 70 msec after its completion. Peak firing rate occurred with a close temporal relation to the end of the saccade.6. The tonic activity in nineteen mossy fibres and five Purkinje cells changed with eye positions. In the nineteen mossy fibres, there were thirteen burst‐tonic and six tonic units. The activity in the five Purkinje cells was a linear function of horizontal eye position.
The respiratory frequency response to carbon dioxide inhalation in conscious rabbits
Authors: Maskrey M. , Nicol S. C. 
Published: December 2014

1. The respiratory responses to CO2 inhalation were measured in New Zealand White rabbits. Prior to testing, the rabbits either received drinking water ad libitum (C), or were subjected to 72 hr water deprivation (WD). The rabbits were tested in a climatic chamber at either 20 °C, (C20, WD20) or 30 °C (C30, WD30).2. CO2 exposure caused increases in both tidal volume (VT) and minute volume (VE). The direction and magnitude of changes in respiratory frequency (f), however, were dependent upon treatment.3. Linear regressions were drawn for f vs.% CO2 in inhaled gas. Treatment C20 showed zero slope, treatment C30 a large negative slope, and treatments WD20 and WD30 a significant positive slope.4. The slopes of the regression lines obtained from plotting f vs.% CO2 were plotted against their intercepts for each rabbit under each treatment condition. This yielded a highly significant linear regression from which it could be concluded that the frequency response to CO2 exposure is dependent upon the initial frequency when the rabbits are breathing air.5. It is suggested that frequency is shifted during hypercapnia towards an optimal value which is dependent upon the existing% CO2 in the inspired gas.6. Comparison of the results obtained for the rabbit with results reported for the conscious dog and sheep suggest that a similar relationship may hold for these species.
Morphological aspects of the safety factor for action potential propagation at axon branch points in the crayfish
Authors: Smith Dean O. 
Published: December 2014

1. In the crayfish, regions of axonal bifurcation where action potential propagation failed during repetitive activity were visualized using modulation‐contrast optics. To determine if a reduced safety factor for conduction at the branch sites has a morphological basis, the geometrical ratio (GR) of axon diameters, where GR = (d13/2+d23/2)/dp3/2, was calculated; d1, d2, and dp are the diameters of the two daughter branches and the parent axon, respectively.2. Values of GR at sites of conduction block were usually slightly higher than 1, indicating a small drop in safety factor; however the values were well below the level at which failure might occur due to an impedance mismatch.3. Calculated values of GR were generally higher in the most peripheral axon regions where propagation was observed to block most readily.4. Short collaterals containing numerous synaptic vesicles and apparent release sites were observed to have relatively low values of GR (about 0.8); collaterals containing densely populated mitochondria were characterized by relatively high values of GR (about 1.3).5. It is concluded that the morphological characteristics of the axon in the branching region are conducive to an inherent low safety factor for conduction, but that they cannot play a major role in block development.
The effect of feeding on cerebral blood flow and oxygen consumption in the new‐born calf
Authors: Gardiner R. M. 
Published: December 2014

1. The effect of feeding on cerebral blood flow and oxygen consumption has been investigated in unrestrained calves between 7 and 28 days after birth.2. Cerebral blood flow was determined using an inert gas clearance technique, and oxygen consumption by the simultaneous measurement of the arterio—cerebral venous oxygen content difference.3. Cerebral blood flow increased during feeding from 74 ± 4 to 116 ± 9 ml. 100 g−1 min−1 and reverted afterwards to the pre‐feed level. No alteration in cerebral oxygen consumption occurred.4. Feeding was associated with an increase in mean arterial blood pressure and heart rate, and mild asphyxia.5. The sensitivity of the cerebral circulation to alterations in arterial PCO2 was investigated in seven calves under sodium pentobarbitone anaesthesia. In the range of arterial PCO2 15‐75 mm Hg the relationship was linear (r = 0.71; P < 0.001) with an average slope of 0.68 ml. 100 g−1 min−1 mmHg Pa,CO2−1.6. Increases in mean arterial blood pressure comparable to those occurring during feeding (96 ± 6 to 159 ± 8 mmHg) were produced by compression of the thoracic aorta in three calves under sodium pentobarbitone anaesthesia and were associated with an increase in cerebral blood flow from 48 ± 4 to 76 ± 8 ml. 100 g−1 min−1. No significant change in calculated cerebral vascular resistance occurred during either feeding or aortic compression.7. These results suggest that the rise in blood pressure which occurs during feeding in the calf exceeds the autoregulatory capacity of the cerebral circulation.