bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma oxytocin and oxytocin neurone activity during delivery in rabbits.
Authors: O'Byrne K T , Ring J P , Summerlee A J
Published: December 2014

The extracellular electrical activity of magnocellular neurones was recorded from unanaesthetized, unrestrained rabbits in birth and the post partum suckling period. The activity of oxytocin neurones was differentiated from that of vasopressin cells on the basis of their stereotyped activity in suckling. Oxytocin neurones showed five to fourteen discrete bursts of accelerated discharge in parturition. Each burst lasted 2‐22 s and represented a 3‐100‐fold increase in the rate of firing, compared with pre‐partum values, and was followed 10‐34 s later by delivery. After parturition, the spontaneous activity of these neurones returned to pre‐partum rates of firing. Vasopressin neurones did not show any bursts of discharge in delivery. There was a significant fall in the discharge frequency compared with pre‐partum levels (P less than 0.05: Student's t test) and a significant (P less than 0.01) lengthening of the modal interspike interval. Serial blood samples were obtained during parturition in ten rabbits. Simultaneous recordings of magnocellular neurones activity and plasma oxytocin measurements were made in four of these experiments. Plasma oxytocin profiles were related to the observed events of parturition. Frequent blood samples (0.2‐0.3 ml every 10‐15 s) were taken throughout delivery and plasma oxytocin measured by sensitive radioimmunoassay in unextracted plasma (lower limit sensitivity of assay 5 pg ml‐1). Before birth, plasma oxytocin was 53 +/‐ 12 pg ml‐1 (mean +/‐ S.E. of mean) and rose to 2846 +/‐ 326 pg ml‐1 within 40‐120 s of the onset of the expulsive phase of delivery. Peak concentrations of oxytocin were coincident with delivery of the first or second fetus. No sign of pulsatile release of oxytocin was demonstrated in the profiles but significantly (P less than 0.001) greater variance in oxytocin titres was found during birth compared with pre‐partum values which is suggestive of pulsatile release. There was a straight line relationship between peak oxytocin concentrations in the plasma and the speed of delivery, implying that oxytocin facilitates as well as maintains labour in the rabbit.
Transport of calcium by the placenta of the rat.
Authors: Stulc J , Stulcová B
Published: December 2014

Transport of 45Ca and of radioactively labelled inert saccharides across the intact or perfused placenta was measured in the rat on day 21 of pregnancy, the day after mating being day 1. The values of permeability‐‐surface area product (PS) of the intact placenta to radioactive mannitol, sucrose, raffinose, and methoxyinulin were approximately proportional to their diffusion coefficients in water. This suggests that diffusion of inert hydrophilic molecules across the rat placenta takes place through wide aqueous channels. Net flux of Ca from mother to fetus, estimated from the increase of the fetal Ca content between day 20 and day 21 is 100 +/‐ 4 nmol min‐1 (the limits here and below are S.E. of means). The unidirectional maternal‐fetal flux of Ca (Jmf) in non‐anaesthetized animals, estimated from the flux of 45Ca, is 100 +/‐ 7 nmol min‐1. The similarity of the two values suggests that the fetal‐maternal flux (Jfm) is small The umbilical vascular bed of the rat placenta was perfused in situ with Krebs‐dextran fluid. Jmf estimated from the transfer of 45Ca from maternal plasma to perfusate was 81 +/‐ 4 nmol min‐1. PS of the perfused placenta to radioactive sucrose was 2.6 +/‐ 0.3 microliter min‐1. Jmf decreased reversibly when the placenta was perfused with 0.5 mM‐dinitrophenol or 1 mM‐CN‐, which is consistent with the presumed active nature of the maternal‐fetal transport of Ca. Jmf did not decrease when the placenta was perfused with Na‐free fluids (substitution with Tris, Li or sucrose), indicating that Na‐Ca exchange across the fetal border of the placental trophoblast is not involved in maternal‐fetal transport of Ca. Transport of 45Ca to the perfusate was reduced to about 60% when maternal plasma concentration of Ca was doubled. This suggests that the affinity of the maternal‐fetal transport system to Ca is high. Jmf did not change when the umbilical concentration of Ca was varied between 0.1 and 3 mM. There thus seems to be no rapid feed‐back between umbilical concentration of Ca and transport of Ca from mother to fetus. Fetal‐maternal transfer of Ca, estimated from the steady‐state extraction of 45Ca from the umbilical perfusate, is only about 20% of the maternal‐fetal transfer. Umbilical extraction of 45Ca changed only little when umbilical concentration of Ca was varied between 0.1 and 3 mM. This suggests that either most of the fetal‐maternal transport of Ca is diffusional or the fetal‐maternal transport system has a very low affinity to Ca.(ABSTRACT TRUNCATED AT 400 WORDS)
Increase in polyneuronal innervation in frog muscle after muscle injury.
Authors: Pécot-Dechavassine M
Published: December 2014

The proportion of polyneuronal innervation was evaluated electrophysiologically in curare‐blocked frog cutaneous pectoris muscles after local injury to the muscle fibres on one side. Focal polyneuronal innervation was revealed by recording end‐plate potentials evoked by a gradual increase in the stimulus intensity applied to the motor nerve. An increase in the proportion of focally polyneuronally innervated muscle fibres appeared in the injured muscle 3‐5 days after injury. The difference between the values obtained 3‐5 days and 7‐9 days (31 and 38%, respectively) and the control value (18%) was highly significant. A similar increase in the proportion of pluri‐innervated muscle fibres was observed in the contralateral muscle, but after a longer period. The different components of complex end‐plate potentials (e.p.p.s) usually had similar latencies and rise times in control and experimental muscles. This may indicate that the axons had similar conduction velocities and that synapses were located close to each other. A repeated muscle fibre section 24 h after the initial injury resulted in an enhanced polyneuronal innervation (52%) 7‐9 days after the first section. The experiments were repeated on partially blocked muscles in order to detect small e.p.p.s with an amplitude similar to that of spontaneous miniature end‐plate potentials (m.e.p.p.s). The proportion of polyneuronally innervated fibres estimated by this technique in control muscles approximated 40%. Polyneuronal innervation was also found to be significantly increased in cut muscles 7‐9 days after muscle injury and a week later in contralateral muscles. Combined silver and cholinesterase staining was used to detect morphologically polyneuronal innervation. The comparison of morphological and electrophysiological data indicated that the increase in polyneuronal innervation after muscle injury is likely due to nerve sprouting and formation of new synapses. The results suggest that the signal for nerve sprouting originates from the damaged muscle cell and that it is transferred transneuronally to the contralateral side.
Desensitization of the acetylcholine‐induced increase of potassium conductance in rabbit cardiac Purkinje fibres.
Authors: Carmeliet E , Mubagwa K
Published: December 2014

In rabbit cardiac Purkinje fibres, acetylcholine (ACh) changes membrane electrophysiological properties in a biphasic time course. On wash‐out of ACh a rebound phenomenon is observed (Mubagwa & Carmeliet, 1983). The underlying mechanisms have been studied by the voltage‐clamp technique. The ACh‐induced increase in K+ current follows a biphasic time course during exposure to ACh. This time course is not due to intercellular accumulation or depletion of K+, but results from a desensitization process. On wash‐out a rebound is obtained, i.e. the membrane K+ conductance transiently decreases below the control value. In contrast, the inhibition of ACh of the catecholamine‐induced increase of slow inward current follows a monophasic time course. The desensitization process or secondary decrease of ACh‐induced change in K+ current follows a mono‐ or a biexponential time course. The extent and rate of desensitization depend on ACh concentration. The rate of desensitization is not influenced by membrane potential but its extent seems to be increased by depolarization. Recovery from desensitization is relatively rapid and has a half‐time of about 2 min. Different existing models for desensitization are discussed, no one of which accounts for all results in rabbit Purkinje fibres. Therefore, a three‐state receptor model is proposed to explain the results. The model assumes that the K+ channel is directly associated with the muscarinic receptor and that the channel‐receptor complex may be in closed, open or desensitized state, in the presence as well as in the absence of agonist.
Red nucleus inputs to retractor bulbi motoneurones in the cat.
Authors: Grant K , Horcholle-Bossavit G
Published: December 2014

Rubral projections to retractor bulbi motoneurones were investigated by intracellular recording in the accessory abducens nucleus in the cat. Their post‐synaptic effects were compared with those of trigeminal afferent pathways. Post‐synaptic potentials evoked by stimulation of the contralateral red nucleus were predominantly excitatory, with latencies in the monosynaptic range. Post‐synaptic potentials evoked by stimulation of the ipsilateral red nucleus, at threshold, were predominantly inhibitory with latencies indicating a di‐ or trisynaptic pathway. At above threshold intensity, an earlier excitatory post‐synaptic potential (e.p.s.p.) preceded the inhibitory post‐synaptic potential (i.p.s.p.) in about half the recorded neurones. Convergence of rubral and trigeminal inputs was also observed in other neurones, not identified as retractor bulbi motoneurones, but situated within the accessory abducens nucleus.
Responsiveness and ultrastructure of slowly adapting type I cutaneous mechanoreceptors in vitamin A deficient rats.
Authors: Baumann K I , Cheng-Chew S B , Hamann W , Leung M S
Published: December 2014

Single‐unit recordings were made from afferent nerve fibres supplying slowly adapting type I (s.a. I) cutaneous mechanoreceptors in anaesthetized vitamin A deficient and control rats. Trains of thirty repetitive mechanical stimuli with 0.1 s rise time, 1.9 s plateau phase, and 0.7 s interstimulus interval were applied. A feed‐back mechanism maintained the force of stimulation at 20 mN during the plateau phases and the contact force between stimuli at 0.5 mN. All displacement values in the group of vitamin A deficient rats were significantly larger than the corresponding control values. Residual indentations were increased by 70‐100% while maximal indentations were only about 40% higher. These results indicate a non‐linear increase in compliance of the skin and underlying tissues. S.a. I receptors were found to be significantly less responsive in vitamin A deficient animals. Mean numbers of impulses were about 25% lower in the vitamin A deficient group than in controls throughout the entire train of thirty stimuli. In vitamin A deficient rats, Merkel cells and adjoining nerve terminals showed signs of degeneration of a variety of cell organelles, particularly the mitochondria. Degenerative changes induced by vitamin A deficiency especially in the Merkel cells appeared to be a major cause of the reduction of responsiveness in s.a. I receptors.
The effect of pregnancy on the changes in hind‐limb vascular resistance following haemorrhage in the rabbit.
Authors: Humphreys P W , Joels N
Published: December 2014

The change in vascular resistance of the skinned hind limb perfused at constant flow has been measured following rapid removal of 10% of the blood volume in anaesthetized pregnant rabbits (27‐29 days gestation) and compared with that of non‐pregnant rabbits. 5 s after haemorrhage was completed vascular resistance had risen in all rabbits, but in the pregnant ones this increase was only one‐fifth of that in the non‐pregnant ones. After section of either the carotid sinus and aortic nerves or the sympathetic innervation to the hind limb the increases of vascular resistance at this time were abolished. It is concluded that the previously described diminution during pregnancy of the protective function of the baroreflexes during haemorrhage results, to some extent, from their diminished role in a vascular bed not associated with the reproductive process. The blood withdrawn was not re‐infused for 10 min, throughout which, in all rabbits with sinus, aortic and sympathetic nerves intact, the increase in vascular resistance was sustained. After section of the carotid sinus and aortic nerves and the sympathetic innervation there was, during this 10 min, a slow increase in vascular resistance comparable in final size to that which occurred immediately in the respective innervated preparations, i.e. it was smaller in the pregnant than in the non‐pregnant rabbits. A possible difference in action during pregnancy of a vasoconstrictor substance released during haemorrhage is discussed briefly.
Presence of a noradrenaline uptake system on a ligated cat sympathetic nerve.
Authors: Ceña V , García A G , Pi F , Sánchez-García P
Published: December 2014

[3H]noradrenaline [( 3H]NA) uptake studies were carried out in cat hypogastric nerves ligated in vivo, 2 cm distal to the inferior mesenteric ganglion, for different time periods. Atria from the same animals served as controls to determine the uptake of the amine by the U1 uptake system present in noradrenergic nerve terminals. The net uptake of [3H]NA by hypogastric nerves increased with time of ligation, reaching a maximum 24 h after ligation in the segment of nerve immediately proximal to the ligature (P1 segment, neurosome). No further increase in uptake was observed at 48 or 72 h. Segments distal (D1) to the ligature also retained significant amounts of [3H]NA. In both cases the uptake was blocked by cocaine (3 microM). Reserpine pre‐treatment (2 mg/kg I.M.) markedly decreased the endogenous NA content to 1‐2% of untreated cats and the net uptake of [3H]NA was lowered to 25% both in cat hypogastric nerve and atria. The uptake was further decreased in the presence of cocaine (3 microM). 6‐Hydroxydopamine (100 microM) did not modify the [3H]NA uptake by ligated cat hypogastric nerves but almost abolished the [3H]NA net uptake by right atria from the same animals. After collagenase pre‐treatment (0.05% for 15 min) the net uptake of [3H]NA was not altered in the atrium. However, collagenase‐pre‐treated ligated nerves, took up almost twice as much [3H]NA; under these conditions, 6‐hydroxydopamine produced a marked decrease in [3H]NA net uptake. These data suggest the presence in the perineurium of a diffusion barrier for very polar substances, including 6‐hydroxydopamine. In conclusion, our data demonstrate that the cat hypogastric nerve ligated in vivo has a cocaine‐sensitive system for NA uptake which resembles the NA uptake mechanism (U1) present in noradrenergic nerve terminals. Our data further support the view that the ligated cat hypogastric nerve (neurosome) could be considered as a model of noradrenergic nerve terminal free of effector cell.
Botulinum toxin prevents stimulus‐induced backfiring produced by neostigmine in the mouse phrenic nerve‐diaphragm.
Authors: Aizenman E , Bierkamper G G , Stanley E F
Published: December 2014

The origin of motor nerve antidromic activity (backfiring) induced by anticholinesterase treatment was examined in the mouse phrenic nerve‐hemidiaphragm preparation. Botulinum toxin was used to determine whether backfiring is due to (a) a direct effect of the cholinesterase inhibitor on the nerve terminal, or (b) an indirect effect via the prolongation of the action of acetylcholine. In previously untreated control preparations, neostigmine produced spontaneous and stimulus‐induced antidromic activity in the phrenic nerve when rapidly introduced into the diaphragm via its vasculature. This activity could be reversibly blocked by d‐tubocurarine and decamethonium, but not by atropine. Neostigmine‐induced backfiring did not occur in preparations in which transmitter release was blocked with botulinum toxin. Infusion of a small bolus of a high concentration of acetylcholine following neostigmine treatment resulted in a short‐term increase in the incidence of antidromic activity, followed by block, in both controls and botulinum toxin‐treated preparations. It is concluded that transmitter release is necessary for the production of backfiring following cholinesterase inhibition since neostigmine alone does not elicit antidromic activity in botulinum toxin‐treated preparations at concentrations which are effective in controls. Our results support the hypothesis that the effects of neostigmine on the motoneurone terminal are mediated by the prolonged action of acetylcholine that occurs with inhibition of acetylcholinesterase.
Effects of vagal deafferentation on oesophageal motility and transit in the sheep.
Authors: Falempin M , Madhloum A , Rousseau J P
Published: December 2014

Effects of vagal deafferentation on oesophageal motility and transit were studied in conscious sheep by recording the electromyographic activity of different parts of oesophagus during swallowing of saliva, or balloons inflated with 20 ml of air. Surgical isolation and subsequent sectioning of the nodose ganglion, leaving the bundles of motor fibres intact, can be performed in sheep. Division of both ganglia led to immediate death of sheep. However, vagal deafferentation of the thoracic oesophagus could be achieved by sectioning the thoracic vagus nerve in association with sectioning the contralateral nodose ganglion. The sectioning of one vagus nerve did not affect primary oesophageal peristalsis during swallowing of saliva or of a bolus. Balloons inflated in the pharyngeal cavity and left free to move caudally, failed to pass into the stomach within the normal time of 2‐2.3 s in only 4‐16% of the tests. In these cases, they were always stopped in the thoracic oesophagus. Following total deafferentation of the thoracic oesophagus, balloons were prevented from being propelled into the stomach in each test. They were stopped for several minutes at the beginning of the deafferented part of the oesophagus. Electromyographic activity recorded from the deafferented part was reduced during swallowing of balloons or saliva. Deafferentation was confirmed by the failure of the presumed deafferented segment of oesophagus to respond to distension. These experiments provide direct evidence that the vagus carries information from the oesophagus which influences the central pattern generator during swallowing of a bolus or saliva. In sheep, this feed‐back is essential for the effective swallowing of a bolus although not for saliva.
Blood pressure effects of leptazol applied to the ventral surface of the brain stem of cats.
Authors: Feldberg W , Guertzenstein P G
Published: December 2014

In anaesthetized cats leptazol (200 mg/ml) and sodium pentobarbitone (30 mg/ml) were applied topically to an area of the exposed ventral surface of the medulla oblongata, which lies between the rootlets of the twelfth cranial and first cervical nerve. The drugs were applied either bilaterally by means of paired Perspex rings or unilaterally by means of a single Perspex ring. Their effects on arterial blood pressure, heart rate and respiration were examined during two stages of anaesthesia, during 'surgical anaesthesia' produced by an intravenous injection of chloralose at 60 mg/kg, and during deeper anaesthesia attained by two additional intravenous injections of chloralose at 30 mg/kg. Both the bilateral and unilateral application of leptazol produced a fall in arterial blood pressure during surgical anaesthesia, but a rise during deepened anaesthesia. After a preceding topical application of sodium pentobarbitone the fall became attenuated or abolished, whereas the rise became potentiated. Sodium pentobarbitone itself affected blood pressure as well as respiration when applied bilaterally. It then produced pronounced tachypnoea independent of the depth of anaesthesia and a fall in arterial blood pressure during deepened anaesthesia. Its unilateral application did not affect respiration, nor did it affect usually arterial blood pressure, although during deepened anaesthesia it occasionally produced a fall in blood pressure. The area from which the pressor response to leptazol was obtained lay 7‐11 mm caudal to the lower border of the trapezoid bodies, i.e. about 2 mm more caudally than the 'nicotine‐sensitive area' from which a depressor response to leptazol is evoked. Thus the two areas, though not identical, overlap. The result obtained with sodium pentobarbitone suggest that the area for the pressor response to leptazol plays a role in maintaining vasomotor tone during deepened anaesthesia and exerts a strong inhibitory effect on the respiratory rate during both surgical and deepened anaesthesia.
Some properties of the contractile system and sarcoplasmic reticulum of skinned slow fibres from Xenopus muscle.
Authors: Horiuti K
Published: December 2014

Properties of both the contractile system and the sarcoplasmic reticulum (s.r.) of slow fibres from the iliofibularis muscle of Xenopus laevis were examined by using 'skinned' preparations mainly at 4 degrees C and pH 7.0. The results were compared with those of skinned fast fibres. The contractile system was activated with various concentrations of alkaline earth metal ions and it was found that the sensitivity of the contractile system of slow fibres to Sr2+ and Ba2+ was much higher than that of fast fibres while their Ca2+ sensitivity was similar. Caffeine (20‐50 mM) reversibly induced appreciable active steady contraction of the slow fibre with one‐third to one‐half maximal isometric tension in the practical absence of Ca2+ (in the presence of 40 mM‐EGTA) at relatively high temperatures (10‐20 degrees C). The speed of unloaded shortening of caffeine‐activated skinned slow fibres in the absence of Ca2+ was not slow but even faster than fibres activated to the same isometric tension level with Ca2+. When the s.r. of a skinned slow fibre was loaded with Ca2+ or Sr2+, 25 mM‐caffeine caused transient contraction of the fibre due to a release of Ca2+ or Sr2+ from the s.r. The magnitude of such caffeine contracture was used as a quantitative indicator of the amount of Ca2+ or Sr2+ in the s.r. The dependence on [Ca2+] or [Sr2+] of the initial rate of Ca2+ or Sr2+ uptake by the empty s.r. of slow fibres was almost the same as that of fast fibres. In both types of fibres, a much higher concentration of Sr2+ than Ca2+ was required to activate the pump. When [Ca2+] outside the s.r. was sufficiently high (e.g. 10(‐5) M), the maximum level to which the slow fibre s.r. could take up Ca2+ decreased, suggesting that the Ca2+‐induced Ca2+ release mechanism also exists in slow fibre s.r. The rate of the Ca2+ leakage from slow fibre s.r. into the media without Ca2+ was higher than that from fast fibre s.r. In the absence of ATP, the enhancing effect of caffeine on the Ca2+‐induced Ca2+ release mechanism was much weaker in slow fibres than in fast fibres, although adenosine‐5'‐monophosphate (AMP) enhanced it to a similar extent in both slow and fast fibres.(ABSTRACT TRUNCATED AT 400 WORDS)
Catechol: a potent and specific inhibitor of the fast potassium channel in frog primary afferent neurones.
Authors: Ito I , Maeno T
Published: December 2014

The effects of catechol on various ionic channels of isolated primary afferent neurones of the bull‐frog were examined by a single‐suction‐electrode clamp system, which combined internal perfusion and current or voltage clamp using an electronic switching circuit. Catechol was found to inhibit rather specifically the fast K+ current as does 4‐aminopyridine (4‐AP). Ca2+, Na+ and slow K+ currents were not affected. Although both 4‐AP and catechol were inhibitors of the fast K+ channels, their sites of action were quite different. Catechol was effective when applied on the external surface of the cell membrane whereas 4‐AP acted preferably internally. We assumed that a single fast K+ channel has two distinct sites for blockers: the catechol site is exposed to the external medium or situated at the outer orifice of the pore, and the 4‐AP site is located within the same channel but is more easily accessible from inside the nerve cell than outside. The 4‐AP and catechol sites were not, however, completely separate and independent of each other since a synergistic interaction was observed between catechol and 4‐AP.
The determinants of the step frequency in walking in humans.
Authors: Cavagna G A , Franzetti P
Published: December 2014

The mechanical power spent during walking in lifting and accelerating the centre of mass, Wext, has been measured at three given speeds maintained at different step frequencies: at any given speed, Wext is smaller the greater the step frequency used. The mechanical power spent in accelerating the limbs relative to the centre of mass during walking at a given speed, but with different step frequencies, Wint, was calculated from previous data obtained during free walking (Cavagna & Kaneko, 1977). At a given walking speed, Wint increases with the step frequency. The total power, Wtot = Wext + Wint, reaches a minimum at a step frequency which is 20‐30% less than the step frequency freely chosen at the same period. The step frequency at which Wtot is minimum increases with speed in a similar way to the natural step frequency during free walking.
Lanthanum as a surrogate for calcium in transmitter release at mouse motor nerve terminals.
Authors: Curtis M J , Quastel D M , Saint D A
Published: December 2014

The mechanism by which lanthanum (La3+) causes an increased frequency of miniature end‐plate potentials (m.e.p.p.s) was studied at the mouse neuromuscular junction. At concentrations as low as 0.25 microM, La3+ caused a progressive rise in m.e.p.p. frequency, to a maximum of several hundred per second. 'Washing' with solution containing EDTA arrested the rise, but did not substantially reduce the raised m.e.p.p. frequency. At partially 'lanthanized' junctions high frequencies of m.e.p.p.s were maintained indefinitely, even in 0 Ca2+/EDTA solutions. The rate of development of high m.e.p.p. frequency was increased by repetitive nerve stimulation or by depolarization of the nerve terminal (high K+ or focally applied current), and appeared to be proportional to the concentration of La3+ over the range of 0.25‐5 microM. At low concentrations of La3+ the rise of m.e.p.p. frequency depended upon the co‐presence of a small amount of Ca2+ (greater than 10 microM) and was slowed and partially blocked by Cd2+, or by Ca2+ at about 10 microM. The quantal content of end‐plate potentials was usually reduced in the presence of La3+, but was increased over control values after removal of La3+ by 'washing' with solution containing EDTA, once a raised m.e.p.p. frequency had developed. At partially lanthanized junctions the absolute increases in m.e.p.p. frequency produced by Ca2+ (in raised K+), ethanol, or by nerve stimulation in the presence of Ba2+, were greater than at control junctions, but in each case the increases in the logarithm of m.e.p.p. frequency were less than at control junctions. It is concluded that La3+ causes transmitter release only after entry into the nerve terminal via voltage‐sensitive channels, probably those that normally admit Ca2+, that La3+ and Ca2+ may co‐operate at internal sites to induce transmitter release, and that these ions both co‐operate and compete at external sites that regulate their entry into the nerve terminal.
Quantitative studies of enhancement and suppression zones in the receptive field of simple cells in cat striate cortex.
Authors: Heggelund P
Published: December 2014

The configuration and extension of enhancement and suppression zones were compared with the configuration and extension of on‐ and off‐response zones across the receptive field of simple cells in cat striate cortex. The enhancement and suppression zones were determined by a dual‐stimulus technique where a stationary flashing light slit produced activity against which activation profiles across the receptive field were plotted with a parallel stationary test slit. The activation profiles showed less variation in receptive field configuration than plots of on‐ and off‐discharge zones. Whereas the number of on‐ and off‐zones varied between one and five, the activation profiles showed at least three distinct subregions in the receptive field, i.e. a central zone with an adjacent oppositely responding zone on each side. The responsivity was clearly stronger in one of these proximal flank zones. An additional zone occurred distal to the strong proximal flank zone in 53% of the cells, and in 10% such a distal zone occurred distal to both proximal flank zones. There was good correspondence between the location of on‐ and off‐discharge zones and the location of the enhancement and suppression regions, although some subregions seen in the activation profiles did not appear in plots made with a single slit. The maximum discharge and the maximum enhancement and suppression effects in a subregion were found at the same receptive field location. The width of a subregion was measured as the width of the eventual on‐ or off‐discharge zone determined with a single slit, as the width of the enhancement zone, and as the width of the suppression zone determined with the dual‐slit technique. The enhancement zone was narrower, and the suppression zone wider than the discharge zone. The strong proximal flank zone had the same width as the central zone, but was wider than the weak proximal flank zone. For most cells the distances between successive extreme points across the activation profiles were constant, and this may explain the selectivity of the cells for spatial frequency of periodic stimuli. The strongest flank suppression occurred for most cells in that of the two proximal flank zones which had the strongest discharge to the single slit. Nevertheless, there was no correlation between the degree of discharge and the degree of suppression produced by opposite light cycles.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of the renin‐angiotensin system on the reflex response of the adrenal medulla to hypotension in the dog.
Authors: MacLean M R , Ungar A
Published: December 2014

We have studied the influence of the renin‐angiotensin system on the control of catecholamine release from innervated and denervated adrenal glands of anaesthetized dogs. Captopril reduced the resting release of catecholamines and inhibited release evoked either by lowering carotid sinus pressure or by stimulating the peripheral end of the cut splanchnic nerve. Both responses were restored by exogenous angiotensin II, and the reflex response could also be restored by corticotrophin. Cycloheximide, in the presence of captopril, further reduced the resting release of catecholamines and prevented the restoration of the reflex response by angiotension II. Plasma renin activity did not rise during baroreceptor tests lasting 10 min, but catecholamine release was evoked from the first minute. We conclude that the response of the adrenal medulla to sympathetic activity requires a minimum circulating concentration of angiotensin II. It is severely impaired by inhibition of the renin‐angiotensin system but function can be restored either by exogenous angiotensin II or by corticotrophin.
A physiological basis for subclassifying beta‐adrenoceptors examined by chemical sympathectomy of guinea‐pigs.
Authors: Broadley K J , Chess-Williams R G , Grassby P F
Published: December 2014

Chemical sympathectomy of guinea‐pigs was induced by chronic pretreatment with 6‐hydroxydopamine over a 20 day period. Control animals were sham injected with vehicle at the same times. Isolated tissues were removed from the animals and beta‐adrenoceptor sensitivity assessed from cumulative concentration‐response curves for isoprenaline, followed after wash‐out by a partial agonist (salbutamol, ritodrine or prenalterol). The following responses were measured: increases in force and rate of contraction of left and right atria respectively, inhibition of carbachol‐induced ileal contractions, relaxation of intrinsic tone of lung strips and tracheal spirals, inhibition of contractions of vas deferens and soleus muscle induced by field stimulation. Left and right atria and ileum from 6‐hydroxydopamine‐pretreated guinea‐pigs exhibited supersensitivity to beta‐adrenoceptor stimulation. This was measured as a leftwards shift of the concentration‐response curve for isoprenaline and as an elevation of the partial agonist maximum response (relative to isoprenaline), when compared with tissues from sham‐injected controls. The supersensitivity was assumed to be due to the loss of endogenous neurotransmitter release by chemical sympathectomy and specific for the beta‐adrenoceptor. In contrast, lung strips, vas deferens and soleus muscle were not supersensitive. The responses of these tissues are thought to be mediated via beta 2‐adrenoceptors whereas cardiac and ileal responses are beta 1‐adrenoceptor mediated. The latter receptor subtype would therefore appear to be under the influence of sympathetic innervation, but since no supersensitivity occurred at beta 2‐adrenoceptors these were presumed to be non‐innervated but stimulated by circulating adrenaline. These results obtained by use of chemical sympathectomy with 6‐hydroxydopamine support the contention that the physiological basis of beta‐adrenoceptor subclassification is that the beta 1‐subtype are innervated whereas the beta 2‐subtype are non‐innervated.
Binding of [51Cr]ethylenediaminetetraacetate to proteins of human plasma.
Authors: Babiker M M
Published: December 2014

Binding of [51Cr]EDTA to human plasma proteins was investigated using chemical and chromatographic techniques of separation of the proteins and protein fractions. Total plasma proteins isolated with ethanol retained 12.95 +/‐ 0.46% of the initial plasma activity. Proteins separated by other precipitants retained about 16% of the initial radioactivity. Globulins exhibited the highest binding capacity for [51Cr]EDTA and retained about 11.7% of the initial plasma activity following chromatographic separation. This value represents about 70% of the radioactivity bound by the total proteins of the plasma. gamma‐Globulins contributed most of the binding attributed to the globulins and retained about 8.7% of the initial [51Cr]EDTA activity. The repeatedly reported underestimation of the renal glomerular filtration rate when estimated as the clearance of [51Cr]EDTA could be adequately accounted for by the extent of binding of this marker to the plasma proteins.
Lateral nasal gland secretion in the anaesthetized dog.
Authors: Wells U , Widdicombe J G
Published: December 2014

The effects of pharmacological and nervous stimuli on the flow of secretion from the dog lateral nasal gland following catheterization are described. Drugs were injected close‐arterially into the arterial supply to the nose, or intravenously. Cholinergic agonists (pilocarpine, methacholine), given intravenously (I.V.) or intra‐arterially (I.A.), and stimulation of the vidian nerve produced a copious flow of secretion which was blocked by atropine. The adrenoceptor agonists phenylephrine (alpha) and salbutamol (beta 2), given I.V. or I.A., and stimulation of the vagosympathetic nerve produced a small but consistent flow of secretion. Histamine (50 micrograms), substance P (0.1 micrograms) and prostaglandin E1 (1‐5 micrograms), injected I.A., produced small flows of secretion. Bradykinin (25 ng‐50 micrograms), 5‐hydroxytryptamine (100 ng‐50 micrograms) and vasoactive intestinal peptide (VIP) (10 ng‐50 micrograms) did not cause secretion. The total protein content, the composition of secretions as revealed by sodium dodecyl sulphate‐polyacrylamide agarose gel electrophoresis, and changes in [Na] and [K] in relation to flow of secretion are described. Differences in ion and protein concentrations, and in protein composition, are described for vidian nerve‐induced and vagosympathetically induced secretions. Electron microscopy revealed that the gland contains serous cells in the secretory region, and ducts morphologically similar to the intercalated, striated and excretory ducts of salivary glands.
Organization of motor units following cross‐reinnervation of antagonistic muscles in the cat hind limb.
Authors: Gordon T , Stein R B , Thomas C K
Published: December 2014

Peripheral reorganization of nerve and muscle properties was studied following misdirection of regenerating axons to foreign muscles. The tibial nerve, which innervates all of the distal extensor muscles, was cross‐united with the common peroneal nerve, which innervates all of the distal flexor muscles, in one hind limb of seven 2‐6 month old cats. After 18‐24 months the properties of the motor units in the reinnervated triceps surae muscles were studied by dissection and stimulation of the ventral root filaments. The normal size relationships were re‐established in reinnervated medial gastrocnemius (m.g.) and lateral gastrocnemius‐soleus (l.g.s.) muscles in so far as motor unit force was directly correlated with the extracellularly recorded amplitude of the axon potential and with contractile speed. The range of sizes of motor units in reinnervated m.g. and l.g.s. muscles was similar to normal, both in terms of the muscle unit size (determined by measuring tetanic tension) and axon size (determined from the amplitude of the extracellularly recorded action potential). The amplitude of the axon potentials in the crossed nerves was weakly correlated with calculated conduction velocities because of the variation in the conduction delays across the suture line. As axon potential amplitude is a direct function of axon size at the recording site, it provided a reliable measure of regenerating axon size. Motor units were classified as slow (s.), fast fatigue resistant (f.r.), fast intermediate (f.i.) or fast fatigable (f.f.) by their contractile speed and fatigue properties. Tetanic tensions generally increased from slow to fast units with s. less than f.r. less than f.i. less than f.f. in reinnervated and normally innervated muscles, but the overlap between different unit types was considerably greater in reinnervated muscles. Thus, peripheral reorganization of nerve and muscle properties according to size can occur in reinnervated muscles, irrespective of the source of the regenerating nerves.
Arsenazo III transients and calcium current in a normally non‐spiking neuronal soma of crayfish.
Authors: Bruner J , Czternasty G , Shimahara T , Stinnakre J
Published: December 2014

Arsenazo III was used to investigate Ca2+ transients in the normally non‐excitable soma of the motor giant neurones of the crayfish Procambarus clarkii. Two kinds of regenerative potentials could be obtained depending on membrane potential conditioning: a fast spike after a pre‐hyperpolarization to ‐90 mV and a slow action potential after a pre‐depolarization to ‐50 mV. Only the second of these was accompanied by an Arsenazo III transient. In voltage‐clamped, somata injected, with tetraethylammonium chloride, an absorbance change could be obtained by pulsing the membrane potential above ‐44 mV. The relationship between absorbance change and potential peaked between 0 and +10 mV then fell off to zero at ca. +150 mV. Changes in light absorbance studied using double‐pulse protocols suggested that the inactivation of Ca2+ entry was predominantly mediated by the intracellular free Ca2+ concentration. External application of 1 mM‐CdCl2 abolished both the absorbance changes and the (Ca2+) inward current. The voltage dependence of this current was similar to that of the absorbance change. For positive membrane potential the current‐voltage relationship showed a voltage‐dependent conductance property, the origin of which is discussed.
Apparent acetylcholine receptor channel conversion at individual rat soleus end‐plates in vitro.
Authors: Schuetze S M , Vicini S
Published: December 2014

Miniature end‐plate currents (m.e.p.c.s.) were recorded extracellularly from individual fibres in neonatal rat soleus muscles for 2‐24 h. In agreement with previous studies, the decay phases of m.e.p.c.s at many end‐plates were doubly exponential with time constants of approximately 6 ms and approximately 1.5 ms at 21 degrees C. Earlier studies have shown that doubly exponential decays are due to the combined action of embryonic‐type acetylcholine (ACh) receptors (AChRs) with long channel open times and adult‐type AChRs with brief open times. When individual end‐plates with doubly exponential m.e.p.c.s were studied for several hours or more, the relative size of the slow decay component frequently decreased with time. There was no evidence for a corresponding decrease in total m.e.p.c. amplitude. The time constants of the fast and slow components did not change. M.e.p.c. decays were stable at end‐plates that were either very mature (small slow decay component) or very immature (small fast decay component). In these cases, the decay phases were virtually singly exponential and the time constant did not change. These data indicate that at end‐plates with a mixture of adult‐type and embryonic‐type channels, the fraction of adult‐type AChRs increases with time. This is similar to what occurs at end‐plates developing in vivo. The results of ACh noise analysis experiments support this interpretation.
Topographical projections of segmental nerves to the frog glutaeus muscle during loss of polyneuronal innervation.
Authors: Bennett M , Lavidis N
Published: December 2014

The development of synaptic connexions to the frog (Limnodynastes tasmaniansis) glutaeus muscle from segmental nerves 8 and 9 was determined using glycogen depletion, contraction and electrophysiological methods between stages 54 and 60 (Nieuwkoop & Faber, 1975). There was no change in the number of muscle cells in the glutaeus from stage 55 onwards; the maturation of muscle cells was most advanced at the point of nerve entry on the ventral surface of the glutaeus and least advanced at the dorsal surface. Electrophysiological determination of the segmental innervation of the dorsal surface of the muscle in low calcium (0.5 mM) indicated that the muscle was almost uniquely innervated by nerve 8 at stage 54. Weak nerve 9 terminals were detected at stage 54 only if the calcium concentration was raised to 6.0 mM. Innervation by nerve 9 was first detected in low calcium at stage 55. There was then a progressive decrease in the innervation of the glutaeus muscle by nerve 8 in regions apposed to the iliofibularis muscle, until stage 59 when this part of the glutaeus was almost completely innervated by nerve 9. Glycogen depletion of muscle fibres following tetanic stimulation of either segmental nerve confirmed that the region of the glutaeus muscle apposed by the iliofibularis becomes progressively innervated by nerve 9 during development. Contraction studies of the segmental innervation of the glutaeus muscle in normal calcium (2 mM) indicated that the muscle was predominantly innervated by nerve 8 at stage 54. There was then a progressive increase in the number of nerve 9 motor units up to stage 56. The size of individual motor units declined for both nerves 8 and 9 until stage 59, when the average motor unit size was about 9% of the muscle. It is suggested that the decline in the innervation by nerve 8 of the side of the glutaeus muscle apposing the iliofibularis muscle is due to this region of the muscle selectively favouring synapse formation by nerve 9 over nerve 8.
Forskolin and calcium: interactions in the control of renin secretion and perfusate flow in the isolated rat kidney.
Authors: Fray J C , Park C S
Published: December 2014

Forskolin (activator of adenyl cyclase), high concentrations of K+ and high renal perfusion pressure (manoeuvres known to increase Ca2+ permeability), and calmidazolium (the specific blocker of calmodulin) were used to investigate the mechanisms whereby adenosine 3',5'‐phosphate (cyclic AMP) and Ca2+ interact to control renin secretion and perfusate flow in the isolated perfused rat kidney. Forskolin stimulated renin secretion and caused vasodilation in a dose‐dependent manner in medium containing 5 mM‐Ca2+. Reducing the Ca2+ concentration to 1.25 mM did not affect the renin stimulatory response but blunted the vasodilation. High K+ concentration reversed the forskolin‐induced renin secretion and vasodilation. Conversely, forskolin reversed the high K+‐induced renin inhibition of renin secretion and vasoconstriction. These effects of forskolin and high K+ were absent when Ca2+ was withheld from the perfusion medium. High renal perfusion pressure also reversed the forskolin‐induced renin secretion. Calmidazolium prevented the inhibition mediated by high K+ and high perfusion pressure and thereby restored the forskolin‐induced stimulation. Calmidazolium also caused a prompt and marked vasoconstriction. The calmidazolium‐induced stimulation of renin secretion was Ca2+‐dependent since the drug was ineffective in the absence of Ca2+. On the other hand, the prompt and potent vasoconstriction was present even in the Ca2+‐free medium. These results support the hypothesis that cyclic AMP stimulates renin secretion by a mechanism which involves a lowering of membrane permeability to Ca2+ in addition to lowering cytosolic Ca2+ concentration. High K+ and high renal perfusion pressure inhibit renin secretion by raising the membrane permeability to Ca2+, thereby raising the intracellular Ca2+ concentration which then inhibits renin secretion by a calmodulin‐dependent process. A further general conclusion from these studies is that membrane permeability to Ca2+ and cellular Ca2+ concentration are of central importance in the control of renin secretion and renal blood flow.
The cardiovascular effects of vasopressin after haemorrhage in anaesthetized rats.
Authors: Chapman J T , Hreash F , Laycock J F , Walter S J
Published: December 2014

The cardiovascular effects of an acute haemorrhage (2% of the body weight) were studied over a 60 min period in three groups of rats: (a) Brattleboro rats with hereditary hypothalamic diabetes insipidus (b.d.i.) lacking circulating vasopressin, (b) control rats of the parent Long Evans (l.e.) strain, and (c) l.e. rats treated with an antagonist of the vascular action of vasopressin. Prior to the haemorrhage there were no significant differences between the three groups of rats with respect to mean arterial blood pressure, cardiac output, stroke volume or total peripheral resistance. Following the haemorrhage cardiac output and stroke volume were severely reduced in all three groups of rats. Total peripheral resistance was relatively unaffected in antagonist‐treated l.e. rats and b.d.i. rats, but rose substantially in response to the loss of blood in the control l.e. group. Both total peripheral resistance and mean arterial blood pressure were markedly greater in the untreated l.e. control rats than in the other two groups of animals during the first 20 min after haemorrhage. The mean heart rate measured in Brattleboro rats was elevated compared with that of control l.e. rats throughout the experiment and, in addition, significantly greater than that of antagonist‐treated l.e. rats during the first 40 min after the haemorrhage. Survival rate for the b.d.i. rats following the 2% haemorrhage was lower than that for l.e. control rats and antagonist‐treated l.e. rats. The results indicate that the recovery of the blood pressure following an acute arterial haemorrhage is significantly influenced by vasopressin, particularly during the first 20 min, and that the predominant effect of the hormone is to increase the total peripheral resistance. The higher mortality associated with volume depletion in the b.d.i. rats is unlikely to be directly related to the absence of the vascular action of vasopressin, since administration of the vasopressin antagonist to normal l.e. rats does not reduce their survival rate.