bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dialysable and non‐dialysable hydroxyproline in the rat's urine: age related and diurnal variations
Authors: Gaggi Renato , Gianni Anna Maria , Montanaro Nicola 
Published: December 2014

1. Urinary dialysable and non‐dialysable hydroxyproline, which are considered good indices of bone resorption and neoformation respectively, were determined in rats under conditions that modify skeleton metabolism, such as body growth and parathyroid or calcitonin administration. It was also investigated whether dialysable and non‐dialysable hydroxyproline excretions showed significant circadian fluctuations in rats of different ages.2. Dialysable hydroxyproline excretion sharply decreased from the first to the fifth months of age and underwent further gradual reduction up to the fourteenth month of life. Non‐dialysable hydroxyproline excretion followed a smoother decrease up to the fifth month, then remained constant. Urinary excretion of non‐dialysable hydroxyproline expressed as a percentage of the total hydroxyprolinuria (n.d.%) slowly increased with advancing rat age.3. In 2‐, 4‐ and 6‐month old rats, dialysable hydroxyproline excretion showed significant circadian fluctuations with minima and maxima at the end of the dark and light fraction of the cycle respectively. Daily fluctuations were greater in young and adult rats (50‐65% of the respective average levels) than in 4‐month old rats (25%). Non‐dialysable hydroxyproline excretion followed similar but less pronounced patterns. Significant circadian fluctuations of n.d.% were detectable only in 2‐ and 4‐month old rats, with peaks at 04.00‐05.00 hr, thus indicating that the bone formation/resorption ratio increased in the nocturnal fraction of the cycle.4. Young rats administered with calcitonin exhibited reduced levels of urinary dialysable but not of non‐dialysable hydroxyproline when the hormone was given at 13.30 hr. No changes were observed when calcitonin was injected at 19.30 hr. On the contrary, both diurnal and nocturnal parathyroid hormone administration to young rats caused increased levels of dialysable and non‐dialysable hydroxyproline of the same magnitude.
Sustained synaptic input to ganglion cells of mudpuppy retina
Authors: Belgum Jack H. , Dvorak David R. , McReynolds John S. 
Published: December 2014

1. Intracellular responses were recorded from on‐centre and off‐centre ganglion cells in isolated eyecups of the mudpuppy, Necturus maculosus.2. Current—voltage relations were measured in darkness, during illumination of the receptive field centre, and after chemically mediated synaptic inputs were blocked by 4 mM‐cobalt chloride.3. In on‐centre cells the membrane potential in darkness was ‐56±6 mV (mean±S.D.). Addition of Co2+ resulted in an average depolarization of 10 mV and an average decrease in conductance of 2·1 nS. These results suggest that in darkness on‐centre cells are tonically inhibited by synaptic input which increases conductance and has a reversal potential more negative than the dark membrane potential.In off‐centre cells the membrane potential in darkness was ‐46±5 mV. Addition of Co2+ caused an average hyperpolarization of 6 mV and an average decrease in conductance of 1·5 nS. These results suggest that in darkness off‐centre cells receive a tonic excitatory input which increases conductance and has a reversal potential more positive than the dark membrane potential.4. In on‐centre cells light causes a sustained depolarization. This response involves an increase in a tonic excitatory input which increases conductance and has a reversal potential more positive than the dark membrane potential.5. In off‐centre cells, light causes a sustained hyperpolarization. This response involves an increase in a sustained inhibitory input which increases conductance and has a reversal potential more negative than the dark membrane potential.6. The depolarizing off‐response of off‐centre cells is associated with an increase in an excitatory input which increases conductance and has a reversal potential more positive than the dark membrane potential. This response may be due to a temporary increase in the excitatory input which is tonically active in darkness or may reflect an additional excitatory input.7. It is suggested that in both on‐ and off‐centre ganglion cells the balance of sustained excitatory and inhibitory synaptic inputs determines the resting potential in darkness. Centre illumination alters the balance of these inputs, by increasing one and decreasing the other, to produce the characteristic sustained light responses.8. The possible presynaptic sources of the sustained excitatory and inhibitory inputs are discussed.
Measurement of intracellular chloride in guinea‐pig vas deferens by ion analysis, 36chloride and micro‐electrodes
Authors: Aickin C. Claire , Brading Alison F. 
Published: December 2014

1. Cl‐sensitive micro‐electrodes were used to measure the intracellular Cl activity (aCli) in smooth muscle cells of the guinea‐pig vas deferens. The values obtained were compared with those of intracellular Cl (Cli) found by both ion analysis and 36Cl efflux.2. Various combinations of filling solution for recording membrane potential (Em), and type of micro‐electrode were tested. The most successful, which allowed continuous recording of aCli for several hours, was a double‐barrelled electrode using the reference liquid ion exchanger (RLIE; Thomas & Cohen, 1981). However, aCli measured both by simultaneous impalements of separate cells with Cl‐sensitive and conventional micro‐electrodes, and by double‐barrelled micro‐electrodes, was about 42 mM in normal Krebs solution. This is five times higher than the value from a passive distribution. ECl was about ‐24 mV, more than 40 mV positive to Em.3. On complete removal of extracellular Cl (Clo), aCli fell to an apparent level of about 3 mM. If this represents interference from other anions, the maximum error in ECl measured in normal Krebs solution is 2·5 mV. Replacement of Clo caused a rapid increase in aCli. This must be caused by an active transport of Cl− ions into the cell against their electrochemical gradient.4. The stabilized values of aCli measured at different levels of Clo agree surprisingly well with aCli estimated from ion analysis and 36Cl efflux, assuming that the intracellular activity coefficient was the same as measured in the normal Krebs solution. The relationship of aCli to Clo was hyperbolic.5. It is concluded that Cl‐sensitive micro‐electrodes accurately measure aCli in smooth muscle cells. The remarkable agreement between the direct and indirect methods of measuring Cli suggests that Cl− ions are not bound to a significant extent and that the compartment seen by the micro‐electrodes is probably representative of the whole cell.
Membrane potential responses of the mouse anococcygeus muscle to ionophoretically applied noradrenaline
Authors: Large W. A. 
Published: December 2014

1. Membrane potential responses to ionophoretically applied noradrenaline and to field stimulation were studied in the mouse anococcygeus muscle using intracellular recording techniques.2. The ionophoretic application of noradrenaline produced charge‐dependent depolarizations whose total duration was 1‐2 s at room temperature and which were characterized by a delay between the start of the ionophoretic pulse and the onset of depolarization (termed the latency of the responses). On occasion ionophoresis of noradrenaline did not depolarize the muscle even though it seemed that successful ejection of noradrenaline had occurred as small localized contractions could be seen.3. The characteristics of these depolarizations were unaffected by tetrodotoxin (10−7 M) and could not be reproduced when the ionophoretic pipette contained 2 M‐NaCl rather than noradrenaline. Moreover noradrenaline still produced depolarizations in denervated muscle and thus it is concluded that the responses were caused by noradrenaline released from the ionophoretic micropipette and not from the intrinsic noradrenergic nerves.4. Field stimulation of innervated muscle usually evoked excitatory junction potentials (e.j.p.s), but sometimes inhibitory junction potentials (i.j.p.s) or a mixture of e.j.p.s and i.j.p.s were observed. The time course of the e.j.p.s was slightly longer than that of the ionophoretic depolarizations which was accounted for by a smaller latency of the ionophoretically induced responses.5. The pharmacology of the nerve‐evoked e.j.p.s and the ionophoretically induced depolarizations was similar as both types of responses were antagonized by α1‐adrenoceptor blocking agents (phentolamine and prazosin) but were unaffected by the β‐adrenoceptor antagonist, propranolol. It is probable that noradrenaline released from the intrinsic nerves and that from the ionophoretic micropipette were acting on the same adrenoceptors.6. The latency and to a lesser extent the rise‐time of the depolarizations produced by the ionophoretic application of noradrenaline was highly sensitive to changes in temperature of the bathing fluid (Q10s > 2) whereas the half‐decay time was relatively insensitive to temperature changes (Q10 ∼ 1·5). In addition the latency of the depolarizations was not altered by inhibiting the noradrenaline‐uptake mechanism with cocaine (2 × 10−6 M) or by α‐adrenoceptor blocking agents. Thus it seems likely that the latency of the responses is a property of the noradrenaline—receptor interaction rather than being caused by other phenomena such as diffusion of noradrenaline.
Effects of hypercapnia on tracheal pressure, diaphragm and intercostal electromyograms in unanaesthetized fetal lambs
Authors: Dawes G. S. , Gardner W. N. , Johnston Barbara M. , Walker D. W. 
Published: December 2014

1. The electromyographic (e.m.g.) activity of the diaphragm and intercostal muscles has been recorded during breathing movements of unanaesthetized lambs in utero (109‐135 days), and compared with the changes of tracheal pressure.2. The diaphragm e.m.g. was irregular in size, shape and timing, with a variable rate of rise during inspiration, often with a flattening of integrated activity before the end of a breath and with little or no post‐inspiratory activity.3. The diaphragm e.m.g. gave the most reliable measurements of breath interval and incidence: in eucapnia mean TI was 0.45±0.02 (S.E. of mean) and TE was 0.74±0.05 sec, and 58‐100% of the diaphragm bursts were associated with identifiable and appropriate changes of tracheal pressure.4. During fetal hypercapnia, produced by increasing the maternal inspired CO2 in a single change or series of step changes, tracheal pressure amplitude and its rate of change during inspiration increased progressively over the Pa, CO2 range of 37‐87 mmHg.5. In eucapnia the area, amplitude and inspiratory slope of the integrated diaphragm e.m.g. were not always correlated with tracheal pressure amplitude, and in hypercapnia they increased only in the lower part of the Pa, CO2 range. Inspiratory intercostal activity increased progressively as the Pa, CO2 was raised.6. The frequency histograms of variables derived from the tracheal pressure, diaphragm and intercostal e.m.g.s were skewed to the left in eucapnia but became normalized during hypercapnia. The rate and depth of breathing became regular.7. The response to mild asphyxia was a combination of the responses to hypercapnia and hypoxia.8. The interpretation of the tracheal pressure and diaphragm e.m.g. as measures of the ‘depth’ of breathing and respiratory ‘drive’ in the fetal lamb is discussed.
Phasic bursting activity of rat paraventricular neurones in the absence of synaptic transmission
Authors: Hatton Glenn I. 
Published: December 2014

1. The purpose of this study was to determine whether the phasic bursting activity, characteristic of certain magnocellular neuropeptidergic neurones in rat hypothalamus, is dependent upon chemical synaptic input.2. Slices of hypothalamus were placed in an in vitro chamber with hippocampal slices. The synaptic response in the CA1 cell layer from Schaffer collateral stimulation was monitored before, during and after synaptic transmission was blocked by superfusion of medium containing high Mg2+ (either 18·7 or 9·3 mM) and low Ca2+ (0·05 mM). This well studied pathway was chosen as an assay of synaptic blockade because hypothalamic circuitry is relatively unknown.3. The electrical activity of twenty‐two phasic bursting neurones in the lateral portion of the paraventricular nucleus (p.v.n.) was recorded. Nineteen of twenty‐two phasic p.v.n. neurones were recorded only after synaptic transmission was blocked. The remaining three cells were firing phasically in standard medium when first encountered and continued to display phasic bursting activity for up to 1·25 hr after synaptic blockade. Active cells in nearby hypothalamic areas did not show phasic bursting patterns either before or after synaptic transmission was blocked.4. The phasic bursting activity of the p.v.n. neurones in this study and that of previously reported p.v.n. cells in vivo were similar in (a) firing rate within bursts (b) burst length and (c) silent period duration.5. It is concluded that phasic bursting in p.v.n. magnocellular neuropeptidergic cells is not dependent upon synaptically mediated excitation or recurrent inhibition as has been hypothesized earlier.6. Alternative hypotheses, based upon acute changes in [K+]o, endogenous membrane currents and electrotonic coupling are discussed as possible explanations of phasic bursting in these magnocellular neuropeptidergic cells.
Forestomach motility in the chronically vagotomized sheep
Authors: Gregory P. C. 
Published: December 2014

1. The motility of the reticulo‐rumen and omasum in conscious sheep was studied by electromyography from chronically implanted nichrome wire electrodes. The sheep were subjected to vagotomy and were maintained totally by intragastric infusion of liquid nutrients before and after vagotomy. Before vagotomy the motility of the forestomach was essentially similar to that seen in roughage‐fed sheep.2. Bilateral thoracic vagotomy transiently abolished all electrical activity of the reticulo‐rumen and omasum, but within 1 day some activity returned. Frequent periods of rhythmic local small group discharges were seen over the reticulo‐rumen, while the omasum showed prolonged (1‐5 min) bursts of mainly slow wave activity.3. Within 1‐2 weeks of vagotomy strong contractions of the reticulo‐rumen were visible by radiography. Electromyographically, they comprised a rhythmic series of some two to five large group discharges recurring approximately once a minute. Each series of activity was separated from the next by a short period of quiescence. The discharges occurred almost simultaneously over the whole reticulo‐rumen and so contrasted with the progressive forward or backward spread of activity seen in the intact animal. The bursts of activity in the omasum, lasting 0·5‐2 min, were not co‐ordinated with the activity of the reticulo‐rumen as they are in the intact animal.4. The activity in the reticulo‐rumen and omasum was not affected by bilateral section of the splanchnic nerves and removal of the coeliaco‐mesenteric ganglia. Reticulo‐rumen but not omasal activity was abolished by atropine (0·1 mg/kg) or hexamethonium (2 mg/kg), while both were stimulated by pentagastrin (3 μg/kg).5. Following vagotomy reticulo‐rumen motility was no longer influenced by feeding, or by tactile stimulation of the buccal cavity or oesophagus. Severe distension of the abomasum caused a slight acceleration of the motility rhythm compared to the inhibition seen before vagotomy.6. It is concluded that the reticulo‐rumen motility observed after vagotomy is an intrinsic cholinergic motility which is dependent upon the activity of the myenteric plexus. The motility of the omasum after vagotomy is similar to that seen in the intact animal and differs from that of the rumen in that it appears not to depend wholly upon cholinergic control.
Temperature‐dependence of shortening velocity and rate of isometric tension development in rat skeletal muscle
Authors: Ranatunga K. W. 
Published: December 2014

1. The temperature‐dependence of the maximum velocity of shortening and of the maximum rate of isometric tension development were examined in a rat fast twitch muscle, extensor digitorum longus (e.d.l.), and a slow twitch muscle, soleus, in vitro and with direct stimulation. The temperature range was 35‐20 °C.2. The maximum velocity of shortening and the maximum rate of tension development decreased with cooling in both muscles. The decrease was such that their logarithms were linearly related to the reciprocal of the absolute temperature over the temperature range of 35‐20 °C in e.d.l. and 35‐25 °C in soleus.3. The calculated Arrhenius activation energy for maximum velocity of shortening was around 40‐45 kJ in both muscles. The activation energies for maximum rate of tension development were 48 kJ in e.d.l. and 56 kJ in soleus. Similar analyses made on the time to peak and time to half‐relaxation of the isometric twitch showed that their activation energies were higher, between 60‐80 kJ, in both muscles.4. The results are examined in relation to biochemical findings and discussed in relation to A. F. Huxley's (1957) cross‐bridge theory.
Long‐term potentiation of excitatory synaptic transmission in the rat hippocampus: the role of inhibitory processes
Authors: Haas H. L. , Rose G. 
Published: December 2014

1. The possibility that changes in inhibitory processes are responsible for long‐term potentiation (l.t.p.) was examined using the rat hippocampal slice preparation.2. Inhibitory pathways were characterized using both extra‐ and intracellular recordings from the CA1 pyramidal cell layer. Stimulating electrodes were placed in either stratum radiatum or the alveus to allow orthodromic or antidromic activation of the pyramidal cells.3. Using extracellular recordings, inhibition was studied by applying paired pulses at interstimulus intervals of 20‐500 msec through either the same or different stimulating electrodes, and quantifying the reduction in the population spike. An antidromic conditioning pulse was least effective in influencing the test response, while paired stimuli delivered through separate stimulators in stratum radiatum revealed the longest duration effects. Inhibition was either reduced or enhanced, depending upon the stimulation paradigm, with increasing stimulus intensity.4. With l.t.p., alterations in paired‐pulse inhibition were observed corresponding to the changes in conditioning pulse amplitude. Reducing stimulus intensity to restore the initial conditioning pulse amplitude eliminated these effects.5. Using intracellular recordings, the effects of l.t.p. on inhibition were studied by examining changes in e.p.s.p.—i.p.s.p. sequences, i.p.s.p.s evoked by antidromic stimulation, and spontaneous depolarizing i.p.s.p.s observed with KCl‐filled electrodes.6. Following l.t.p. enhanced e.p.s.p.s and slightly reduced, but prolonged, i.p.s.p.s were observed in response to orthodromic stimulation. Antidromically evoked, as well as spontaneous, i.p.s.p.s were unaffected.7 It is concluded that alterations in inhibitory processes are not responsible for l.t.p. in hippocampal subfield CA1. However, changes in the strength of inhibitory synapses as a consequence of long‐term potentiation may modify the functional character of the hippocampal connexions.
Modulation of stretch reflexes during locomotion in the mesencephalic cat
Authors: Akazawa K. , Aldridge J. W. , Steeves J. D. , Stein R. B. 
Published: December 2014

1. A cat preparation was used to study the modulation of stretch reflexes during locomotion. The brain stem was transected and locomotion was induced by electrical stimulation of the mesencephalic locomotor region below the level of transection. Three legs walked normally on a treadmill, while the fourth leg, which was denervated except for the soleus muscle, was held fixed. Brief length perturbations were applied to the soleus muscle at various phases of the stepping cycle.2. The stretch reflex in this muscle was deeply modulated during the step cycle, and reached its peak at or before the peak in soleus e.m.g. activity associated with the locomotion. A similar variation was observed when the sciatic nerve was stimulated electrically at a strength which elicited reflex activity (H wave), but did not directly elicit motor nerve activity (M wave). Variation in the reflex during electrical stimulation could not be accounted for by cyclic variation in fusimotor activity or in the afferent volley, but must be due to post‐synaptic changes in α‐motoneurones or in the presynaptic inputs to them.3. Large changes were also observed in intrinsic muscle stiffness during the step cycle. The maximum stiffness occurred near the time the limb would normally strike the ground during locomotion. A high stiffness would be useful in reducing the amount that the limb would yield under the weight of the body during the extension phase of the step cycle. The variation of the stretch reflex in parallel with stiffness suggests that reflexes could assist in this load compensation. The variation is not consistent with the idea that the stretch reflex is used to compensate for changes in intrinsic muscle properties, so that the total system behaves more like a spring of constant stiffness than does muscle alone.
The effects of low calcium and background light on the sensitivity of toad rods
Authors: Bastian Bruce L. , Fain Gordon L. 
Published: December 2014

1. We have examined the effects of decreases in extracellular Ca2+ concentration on the intracellularly recorded light responses of rods from the toad, Bufo marinus. In agreement with previous results (Brown & Pinto, 1974; Lipton, Ostroy & Dowling, 1977), Ca2+ concentrations below 10−6 M produced a depolarization of rod resting membrane potential of approximately 30‐40 mV and a corresponding increase in the maximum amplitude of the rod's light responses, so that saturating flashes in normal and low Ca2+ Ringer produced hyperpolarizations to approximately the same membrane potential.2. The rod's sensitivity was reduced in low Ca2+ Ringer by an amount dependent upon the extracellular Ca2+ concentration. At 10−6 M‐Ca2+, sensitivity was approximately 0·6 log units below normal. Thereafter, it dropped nearly linearly with [Ca2+]o to a value approximately 4·0 log units below normal at 10−9 M‐Ca2+. Most of the decline occurred within 1‐2 min after the solution change as the membrane potential depolarized, but sensitivity continued to fall slowly with time at the lowest Ca2+ concentrations. Exposure to low Ca2+ solutions altered the kinetics of the receptor response to brief flashes, delaying response onset and time‐to‐peak but affecting the time course of decay very little.3. The sensitivity of the rod to maintained steps of light was also reduced in low Ca2+. Furthermore, the changes in sensitivity produced by background illumination were very much smaller in low Ca2+ than in normal Ringer. In some cases backgrounds actually increased sensitivity.4. In 10−8 M‐Ca2+, backgrounds which themselves produced no response in the rod and no changes in rod sensitivity produced large decreases in response latency for responses of all amplitudes, and pronounced changes in time‐to‐peak and time‐to‐decay for moderate and large amplitude responses.5. Since the effects of background light and low Ca2+ on the wave form of the rod are distinct and in some cases antagonistic, and since the changes in receptor sensitivity produced by backgrounds and low Ca2+ are not additive, the decreases in sensitivity produced by exposure to low Ca2+ appear to be caused by a mechanism distinct from normal light adaptation. We suggest that they are caused by an increase in the buffering capacity of the receptor cytosol for Ca2+ and that Ca2+ is the excitatory messenger or ‘internal transmitter’, as originally suggested by Yoshikami & Hagins (1971).