bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of factors influencing synapse formation by a foreign nerve in skeletal muscle of Rana pipiens.
Authors: Sayers H , Tonge D A
Published: December 2014

The possible influence of the pathway taken by regenerating axons on the characteristics of the synapses they form was investigated by tying the proximal stump of the hypoglossal nerve (h.n.) to the distal stump of the cutaneus pectoris (c.p.) nerve. This technique allowed the axons from the h.n. to innervate the c.p. muscle via the neural tubes of the degenerated original nerve. The synapses formed by the inappropriate hypoglossal axons in the c.p. muscle after tying the two nerves together were more efficient than synapses formed by the h.n. in the c.p. muscle in a previous study, when the hypoglossal axons had grown across the muscle fibres in an apparently disorganized fashion, rather than within the neural tubes. However, the synapses formed by hypoglossal axons after tying the h.n. and c.p. nerves together were still abnormal compared to unoperated or self‐reinnervated muscles. In a further experiment, the brachial nerve (b.n.), which originates from the same spinal segments as the nerve to the c.p. muscle was tied to the distal stump of the c.p. nerve. Synapses formed in the c.p. muscle by the regenerated brachial axons were more efficient than those formed by the h.n. in the c.p. muscle. These results suggest that both the pathway taken by regenerating axons and the segmental origin of the nerves may influence the characteristics of synapses formed by a foreign nerve in frog skeletal muscle.
Prolongation of calcium action potentials by gamma‐aminobutyric acid in primary sensory neurones of lamprey.
Authors: Leonard J P , Wickelgren W O
Published: December 2014

Intracellular recordings from primary mechanosensory neurones (dorsal cells) in the lamprey spinal cord were used to test the membrane effects of a variety of putative neuromodulatory agents. gamma‐Aminobutyric acid (GABA) produced a dose‐dependent increase in the duration of mixed Na‐Ca or pure Ca action potentials in these cells. L‐Glutamate and glycine produced minimal broadening of Ca action potentials. Acetylcholine, noradrenaline, serotonin, met‐enkephalin, D‐glutamate and dopamine had no effect. The pharmacology of GABA's action appeared to be complex. While the GABAA receptor antagonists, bicuculline, picrotoxin and curare, did not block GABA's effect, both the GABAA receptor agonist, muscimol, and the GABAB‐receptor agonist, baclofen, occasionally broadened Ca action potentials in these cells. GABA had no effect on the resting potential, passive current‐voltage (I‐V) characteristics and pure Na action potential of dorsal cells, ruling out an action on passive membrane channels, transmitter‐activated channels, or on those voltage‐dependent channels activated during the Na action potential. Thus, GABA affected dorsal cells only when a significant Ca current was evident. GABA appeared not to increase the conductance of the Ca channels since its action was accompanied by an increase in input resistance, suggesting an inhibition of Ca‐dependent conductance that normally acts to repolarize the membrane during a Ca action potential. An inhibitory effect of GABA on a Ca‐dependent Cl conductance was ruled out in experiments where the Cl gradient was altered by removal of extracellular Cl without affecting GABA‐induced Ca action potential prolongation. Dorsal cells have a prominent Ca‐dependent K conductance (gK(Ca], and it is this conductance that GABA may inhibit. Consistent with this was the observation that the hyperpolarizing after‐potential that follows Ca action potentials in dorsal cells, which reflects gK(Ca) in these cells and whose duration is normally increased when the Ca action potential duration increases, was not prolonged when the Ca action potential was broadened by GABA. Further, the failure of GABA to prolong Ba action potentials was consistent with this proposed mechanism of action, since Ba apparently does not activate gK(Ca) in these cells. Forskolin, a specific adenylate cyclase activator, caused broadening of Ca action potentials in lamprey dorsal cells comparable in magnitude to that of GABA. Thus, an increase in intracellular cyclic AMP is a candidate for the intracellular mediator of GABA's effect on these cells.
Caffeine potentiation of calcium release in frog skeletal muscle fibres.
Authors: Delay M , Ribalet B , Vergara J
Published: December 2014

The effects of caffeine at concentrations up to 3 mM were studied on Ca signals obtained using the metallochromic Ca indicator dyes Arsenazo III and Antipyrylazo III in cut frog skeletal muscle fibres mounted in a triple Vaseline‐gap chamber and stimulated by voltage clamp or action potential. The peak amplitude of the transient absorbance change due to Ca2+ release following action potential stimulation is potentiated by an amount dependent on caffeine concentration up to 0.5 mM, and by a concentration‐independent amount between 0.5 and 2 mM. At 3 mM‐caffeine, the potentiation is reduced, and the Ca signal can have a smaller amplitude than under the control condition. The time course of the rising phase of the Ca signal is preserved by the potentiating effect of caffeine; however, the decay rate of the Ca signal is increasingly slowed at caffeine concentrations greater than 0.5 mM. No substantial change was found in the resting myoplasmic Ca2+ level at caffeine concentrations near 0.5 mM. Even if the free Ca2+ concentration in the presence of this level of caffeine were to increase by 0.04 microM (the threshold of detectability), the calculated potentiation of the Ca signal due to increased partial saturation of intracellular Ca2+ buffers would amount to only about 7%. This value is significantly less than the amount of potentiation observed (up to 40%) following action potentials at caffeine levels of 0.5 mM and above. Experiments made with the impermeant potentiometric dye NK2367 show no alteration by caffeine of the electrical properties of the tubular system. Caffeine at up to moderate concentrations causes a substantial increase in the maximal Ca2+ release obtained following large depolarizations. The voltage dependence of the Ca2+ release is characterized by a caffeine concentration‐dependent shift towards more negative membrane potentials. The potentiation of Ca2+ release by caffeine was found to be independent of the external free Ca2+ level. The potentiation of the Ca2+ release process by caffeine is likely to occur at a step subsequent to the depolarization of the transverse tubule membrane, and suggests the presence of an intermediate step, or second messenger, in the excitation‐contraction coupling process.
The distribution of on‐ and off‐centre X‐ and Y‐like cells in the A layers of the cat's lateral geniculate nucleus.
Authors: Bowling D B , Wieniawa-Narkiewicz E
Published: December 2014

Responses to light were recorded extracellularly from single cells in the A laminae of the dorsal lateral geniculate nucleus (d.l.g.n.) in the cat. Micro‐electrodes were passed through the nucleus parallel to the laminar borders allowing the depths of the cells to be measured accurately and the depth distributions of the different cell types to be determined. 1200 cells were recorded in thirty cats along ninety‐nine tracks through layers A and A1. The cells were identified physiologically as on‐ or off‐centre cells (hereafter called on or off cells) and most (n = 960) were classified as X‐ or Y‐like cells (hereafter called X or Y cells). Both on and off cells were found throughout layers A and A1 but their proportions changed in a graded fashion with depth. On cells were the predominant type at the tops of the layers, the on and off cells were in balance in the centres, and off cells were the predominant type at the bottoms. The steepest gradient and the maximum differences in proportions occurred in layer A while in A1 the same pattern appeared to be present but was weak and not statistically significant in the present sample. X and Y cells were also distributed differently through the depths of the layers but in patterns that differed from those of the on and off cells. The Y cells were concentrated at the borders and there was a complementary increase of X cells toward the centres of the layers. Again, the pattern was strong in A but weak and not statistically significant in A1. The distribution of X‐on cells peaked near the top of layer A while the distribution of X‐off cells peaked near the bottom. This was not so in A1 where the distributions of X‐on and X‐off cells were nearly uniform and similar to one another except for a slight predominance (56%) of X‐on over X‐off cells that was not related to depth. The Y‐on and Y‐off cells showed similar patterns of distribution in both layers A and A1 with Y‐on cells predominant at the tops of the layers and Y‐off cells predominant at the bottoms. The differences in the distributions of the four cell types (X‐on, X‐off, Y‐on, Y‐off) through the depths of the layers result in unique combinations of cells at different depths. It is suggested in the Discussion that the changing balance between the cells may have functional consequences.
Catecholamine secretion and adrenal nerve activity in response to movements of normal and inflamed knee joints in cats.
Authors: Sato A , Sato Y , Schmidt R F
Published: December 2014

The effects of articular stimulation on adrenal catecholamine secretion and adrenal sympathetic nerve activity were studied using halothane anaesthetized cats. Various natural passive movements were applied to the normal and inflamed knee joints. Rhythmic flexions and extensions as well as rhythmic inward and outward rotation of normal knee joints within their physiological range of motion did not change nerve activity or the secretion of adrenal catecholamines. Static outward rotation in the normal working range was also ineffective. However, as soon as this static rotation was extended into the noxious range, significant increases in both of these variables were elicited. In the acutely inflamed knee joint, various passive movements produced increases in both adrenal sympathetic and catecholamine secretion. Especially noteworthy was the finding that movements of the inflamed knee joint that were within the normal range of motion produced increases in all variables. Articularly induced increases in adrenal sympathetic nerve activity were diminished by severing various hind‐limb somatic afferent nerves and abolished by complete denervation of the knee joint. Additionally, section of the adrenal sympathetic nerves eliminated the catecholamine secretion response. From these data it was concluded that the responses observed in these experiments were reflexes having an afferent limb in hind‐limb nerves and an efferent limb in the adrenal sympathetic nerves. A contribution of supraspinal structures was suggested for the reflex responses of sympatho‐adrenal medullary function evoked by knee joint stimulations, since spinal transection at the C2 level completely abolished the responses.
Asymmetric charge movement in contracting muscle fibres in the rabbit.
Authors: Lamb G D
Published: December 2014

The Vaseline‐gap technique was used to record asymmetric charge movement in small segments of muscle fibres from the white sternomastoid or the soleus muscle of the rabbit. At 22 degrees C, non‐linear ionic currents (Na+, K+, Cl‐, Ca2+) were virtually eliminated for potential steps to 0 mV or below by specific blocking agents or ion substitution. A Boltzmann fit of charge movement (Q) vs. potential (V) produced the mean values Qmax = 15.2 nC/microF, V = ‐26.8 mV and k = 15.3 mV for twenty‐three sternomastoid fibres, and 4.8 nC/microF, ‐32 mV and 13.7 mV for seven soleus fibres. Qmax for the sternomastoid fibres was similar to that for other fast‐twitch fibres when normalized by surface area rather than capacitance. Using a 55 ms step, the mean threshold potential (Vth) for contraction in twenty‐eight fibres was ‐25.9 (+/‐ 2.9) mV (+/‐ S.E. of mean), and the mean amount of charge moved (qth) at the threshold potential was 8.5 (+/‐ 0.4) nC/microF. In some contracting fibres, a component of charge movement was observed which was analogous to q gamma in amphibian muscle in its time course and potential dependence. Addition of 80 mM‐sucrose to the external solution increased the speed of both the asymmetric charge movement and the charging of the linear capacitance of each fibre. The effect was reversible. A clear relation between the time course of these two parameters was established, and this strongly indicated that the majority of the asymmetric charge was located in the transverse tubular system or beyond. Moreover, it was shown that at 22 degrees C nearly all asymmetric charge moved in less than 0.5 ms after depolarization of the T‐system. Sucrose in the external solution affected the Q vs. V relation, steepening the curve and shifting it to more negative potentials, as well as slightly increasing Qmax. The actions of sucrose strongly suggest that it effectively dilates and/or shortens the transverse tubular system, probably by osmotic effects.
Inactivation of the low‐threshold transient calcium current in rat sensory neurones: evidence for a dual process.
Authors: Bossu J L , Feltz A
Published: December 2014

In rat cranial sensory neurones a transient Ca current (iCa,t) is elicited by depolarizing the membrane potential from ‐80 mV to beyond ‐50 mV. In this paper the characteristics of the slow and fast inactivation processes of this current are described. Recordings were obtained in whole‐cell clamp conditions from Cs‐loaded cells. For most experiments, cells were dialysed at an internal pCa of 8, and Na and K currents were eliminated using a choline chloride‐ and K‐free external medium containing 5 mM‐Ca and 2 mM‐Mg. The decay of iCa,t could be approximately fitted by a single exponential with a voltage‐dependent time constant which decreased from about 150 ms at ‐50 mV to about 25 ms at ‐20 mV. This suggests a single process of inactivation but a detailed kinetic analysis of the onset and the offset of the inactivation revealed biphasic processes. The onset of inactivation displays two exponential phases. The fast phase lasts for 100‐500 ms, and the slow phase lasts for a few seconds. The relative amplitude and the time constants of each phase vary with the inactivating potential. The recovery from inactivation is also biphasic, with either a fast or a slow component predominating, depending on whether a short‐ (some hundreds of milli‐seconds) or a long‐ (in the order of tens of seconds) inactivating pulse has been used. At ‐80 mV, after a 300 ms inactivating pulse, responses recover to at least 40% of maximum within 200 ms and recovery is complete within 1 s; after a long predepolarization (10‐20 s), recovery takes 4‐5 s. Fast recovery was observed best after large but brief depolarizations and slow recovery was observed best following long inactivating pre‐pulses of small amplitude. The voltage‐dependence of slow and fast inactivation was determined by realizing inactivation curves. Fast inactivation developed between ‐60 and ‐20 mV while the slow process occurred at more hyperpolarized potentials, e.g. at ‐75 to ‐50 mV. Fast inactivation was not altered by the entry of Ca during the previous activation of the channel. Further, decay of iCa,t was not modified when Ba was substituted for Ca or the internal pCa was decreased. These are indications of a uniquely voltage‐dependent process. A possible role of Ca entry in slow inactivation is discussed.(ABSTRACT TRUNCATED AT 400 WORDS)
Selective degeneration of optic nerve fibres in the cat produced by a pressure block.
Authors: Burke W , Cottee L J , Garvey J , Kumarasinghe R , Kyriacou C
Published: December 2014

Using a technique described previously, we have applied pressure to the optic nerve of a cat sufficient to cause conduction block of the t1 response (the response of the Y optic nerve fibres). A greater pressure, usually sufficient to cause a transient block of the t2 response (the response of the X fibres), leads to degeneration of the Y axons caudal to the block. This is demonstrated by the disappearance of the t1 response in this region after 4‐5 days and by the presence in electron micrographs of degenerating large (Y) fibres. Some small fibres also show degeneration, but the medium (X) fibres are largely spared. The time course of loss of response in the Y fibres is similar whether the loss is due to a pressure block or to enucleation, suggesting that the pressure block as used by us causes a disruption of the axon. If the pressure is great enough to block part of the t2 response (X fibres) there is also a similarity in time course of loss of response to that following enucleation. Both for the enucleated and the pressure‐blocked cat the t2 response fails about 1 day before the t1 response. This is in apparent disagreement with the morphological findings in the literature, confirmed here, indicating an earlier degeneration of the larger fibres. The post‐synaptic response in the lateral geniculate nucleus to the t1 input (the r1 response) also fails about 1 day before the t1 response. In the visual cortex the loss of the r1 response reveals more clearly than is normally possible an r2 response, the response of the X optic radiation fibres. The response in the optic nerve or tract to a bright flash of light is dominated by the response of the Y fibres. When these are blocked the response is greatly reduced.
Blood flow to the respiratory and limb muscles and to abdominal organs during maximal exertion in ponies.
Authors: Manohar M
Published: December 2014

Using radionuclide‐labelled microspheres, 15 micron in diameter, we studied blood flow in the respiratory muscles (diaphragm and intercostal muscles), abdominal organs (adrenal glands, kidneys, pancreas, spleen and the small and large intestines), muscles of propulsion (gluteus medius and biceps femoris), and other working (triceps brachii and longissimus dorsi lumborum) and non‐working (temporal and masseter) muscles of ponies at rest and during maximal exercise performed on a treadmill. During maximal exercise heart rate, whole body O2 consumption, cardiac output and mean aortic pressure increased 4.4‐fold, 38‐fold, 8‐fold and 1.5‐fold of their resting values, respectively. During maximal exertion arterial CO2 tension and arterial pH decreased while arterial O2 content increased by 58% due to a 59.6% rise in haemoglobin concentration. Arterial O2 tension decreased somewhat and the calculated alveolar to arterial O2 tension gradient widened during exertion. During maximal exertion blood flow in the adrenal glands increased while that in the kidneys, spleen, pancreas, small intestine and colon decreased precipitously. Thus ponies exhibited intense vasoconstriction in the renal and splanchnic vascular beds, similar to that reported in man but not in exercising dogs. During maximal exertion stride (and hence respiratory) frequency of galloping ponies was 138 +/‐ 3 min‐1, and the blood flow and O2 delivery in the diaphragm were not different from those in other strenuously working muscles, namely gluteus medius, biceps femoris (muscles of propulsion) and triceps brachii. Blood flow in the intercostal muscles was only 54% of that in the diaphragm at rest, but with maximal exercise it registered a marked increment and the perfusion became similar to that in the longissimus dorsi lumborum, a powerful extensor of the back and loins.
Paired recordings from supraoptic and paraventricular oxytocin cells in suckled rats: recruitment and synchronization.
Authors: Belin V , Moos F
Published: December 2014

Oxytocin cells in the paraventricular (p.v.) and contralateral supraoptic (s.o.) nuclei were pair‐recorded (with two micro‐electrodes) in suckled rats after being anaesthetized with urethane (1.2 g/kg), to study the synchronization of their neurosecretory bursts, the importance of cell recruitment and their firing characteristics. The synchronization of paired bursts was determined by measuring the onset time‐lag (time in milliseconds between the onset of two corresponding bursts) and the maximum firing time‐lag (time in milliseconds between the two shortest interspike intervals for the corresponding bursts). For each cell, the characteristics studied were: the background activity and the frequency and amplitude (total number of spikes) of the neurosecretory bursts. All paired p.v.‐s.o. cells recorded were activated simultaneously 12‐18 s before each milk ejection. The onset of a burst could vary either way, up to 680 ms, in relation to the other (mean onset time‐lag was 206 +/‐ 18 ms; n = 85) but the maximum activation periods fitted more closely, the mean maximum firing time‐lag being 122 +/‐ 14 ms (n = 64). Both parameters varied randomly, in duration and order from one pair of cells to another, from one pair of bursts to another for successive bursts of a given pair of cells and independently, whether the cells were in the p.v. or the s.o. nucleus. However, in most cases, the neurosecretory burst with the highest amplitude began and reached its peak firing rate before the corresponding burst from the other cell. Cell recruitment was observed when the milk ejection reflex began, for both the p.v. and the s.o. cells. The bursts of the non‐responsive cells developed progressively with the reflex, but, as soon as a cell was recruited, all its successive bursts were simultaneous with those of the first‐recruited oxytocin cells. During a regular pattern of milk ejections, the mean background activity of sixty p.v. cells (3.1 +/‐ 0.2 spikes/s) was significantly higher than that of their s.o. counterparts (1.9 +/‐ 0.2 spikes/s). Nevertheless, the mean amplitude of the neurosecretory bursts of the sixty p.v. cells (49 +/‐ 3 spikes) did not differ significantly from that of their s.o. counterparts (55 +/‐ 4 spikes).(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of 16,16‐dimethyl prostaglandin E2 on the myoelectric activity of the gastrointestinal tract of the opossum.
Authors: Coelho J C , Gouma D J , Li Y F , Moody F G , Schlegel J F
Published: December 2014

Myoelectric recordings of the opossum gastrointestinal tract were performed during continuous infusion of 16,16‐dimethyl prostaglandin E2 at 0.1, 1, 2 and 5 micrograms/kg X h. Continuous administration of prostaglandin caused a dose‐dependent reduction of the duration of the migrating myoelectric complex cycle and an increase in the velocity of phase III migration from the duodenum to the terminal ileum. The reduction of the migrating myoelectric complex cycle was due to a shortening of the duration of both phase I and II. Bolus administration of 16,16‐dimethyl prostaglandin E2 caused intense spike activity for 2‐4 min in all recording sites simultaneously. Administration of indomethacin did not change the myoelectric activity of the gastrointestinal tract. Infusion of prostaglandin E2 caused diarrhoea in eight of forty experiments. These changes in gastrointestinal motility may be important contributory factors in the pathogenesis of prostaglandin‐induced diarrhoea.
The diving response in man: effects on sympathetic activity in muscle and skin nerve fascicles.
Authors: Fagius J , Sundlöf G
Published: December 2014

Multi‐unit recordings of muscle‐nerve sympathetic activity (m.s.a) or skin‐nerve sympathetic activity (s.s.a) were made in the left peroneal nerve of sixteen healthy volunteers during simulated diving by immersion of the face in a tub of water. The procedure was varied by the use of different water temperatures, by diving with snorkel breathing, by apnoea without diving, and by apnoea with a stream of air against the face instead of immersion in water. Diving for 12 s elicited a pronounced activation of m.s.a., the mean increase from control periods being 360%. The response was stronger with lower water temperatures. Immersion of the whole face evoked a stronger increase in m.s.a. than immersion of mouth and nose only. Diving without apnoea elicited a significant but weaker increase in m.s.a., whereas apnoea only for 12 s did not influence the sympathetic outflow. Cool air against the face during apnoea for 12 s was associated with a significant increase in m.s.a. The increase in m.s.a. usually occurred before the bradycardia. On emersion, m.s.a. ceased abruptly, whereas the bradycardia persisted for a few seconds. Mental arithmetic during diving did not change the m.s.a. response but reduced the bradycardia. M.s.a. increased despite increasing blood pressure levels. On emersion, m.s.a. did not reappear until the pre‐diving blood pressure level was attained. S.s.a was inhibited on diving, with concomitant vasodilatation in the skin as recorded in the big toe. It is concluded that the response of m.s.a. to diving is initiated by a central 'pattern recognition' of an input from facial receptors, that this input and the effects of apnoea, acting by mutual reinforcement, maintain the strong sympathetic outflow, and that the mechanism releasing m.s.a. on diving overrides the normal blood pressure regulatory function of m.s.a. Diving exerts differentiated influence on different parts of the sympathetic nervous system, as illustrated by the inhibition of s.s.a.
Influence of membrane potential on calcium efflux from giant axons of Loligo.
Authors: Allen T J , Baker P F
Published: December 2014

Experiments are described in which Ca efflux is monitored in axons under voltage clamp. As Ca efflux consists of more than one component, conditions were sought where one component predominates. Thus external Na‐dependent Ca efflux can be studied in relative isolation either at pH 9.0 or in fully poisoned axons immersed in Ca‐free media; external Ca‐dependent Ca efflux can be studied in fully poisoned axons immersed in Na‐free media and the Na‐independent, energy requiring, pump is best examined in Na and Ca‐free sea waters. Both in unpoisoned axons at pH 9.0 and fully poisoned axons at pH 7.8, the external Na‐dependent Ca efflux is activated by hyperpolarization and inhibited by depolarization. Depolarizations achieved either electrically or by exposure to high K are roughly comparable and the inhibition brought about by high K can largely be removed by electrical hyperpolarization to the initial resting potential. In both Na sea waters and choline sea waters containing 100 mM‐Na, Ca efflux is increased e‐fold over approximately 50 mV. In choline sea water, external Ca‐dependent Ca efflux from fully poisoned axons is unaffected by voltage over the range ‐80 to ‐30 mV. But addition of K or Li activates the flux and this activation is increased by hyperpolarization and decreased by depolarization, suggesting that the activating cation may also be transported into the axon. The Na‐independent, energy‐requiring, flux is inhibited by electrical hyperpolarization and stimulated by electrical depolarization. External K also stimulates the flux and part of this stimulation can be removed by electrical hyperpolarization. These data show that the energy‐dependent pump is sensitive to membrane potential in the physiological range and suggest that it may be an electrogenic process. The finding that voltage affects the energy‐dependent (uncoupled) pump and external Na‐dependent fluxes in opposite directions may help explain why the total Ca efflux from intact axons responds to potential in a very variable manner.
A search for brain stem cell groups integrating the defence reaction in the rat.
Authors: Hilton S M , Redfern W S
Published: December 2014

The defence areas of the rat brain stem have been extensively explored using electrical and chemical stimulation in an attempt to locate the regions containing the perikarya of neurones which may initiate or integrate the visceral and behavioural components of the defence reaction. In rats anaesthetized with alphaxalone‐alphadolone, a cannula electrode was used to compare the responses to electrical stimuli with those evoked by microinjection of the excitatory amino acid D,L‐homocysteic acid (DLH), at the same site. A total of 128 sites throughout the brain stem was studied in 75 rats. The pattern of visceral and somatic changes characteristic of the defence reaction, viz. increases in arterial blood pressure and heart rate, vasodilatation in hind‐limb muscles and vasoconstriction in the kidney, hyperpnoea and tachypnoea, exophthalmos, mydriasis, twitching of the vibrissae and retroflexion of the tail, was evoked by electrical stimulation within well‐defined regions of the brain stem, from the anterior hypothalamus to the pons. Microinjection of DLH into the same regions could evoke the full defence reaction, as defined above, but only from the dorsomedial periaqueductal grey matter. Three other regions were defined from which almost all the autonomic components of the defence reaction were evoked, except that blood pressure fell. These were located: immediately dorsal to the optic chiasma, in the medial tuberal region of the hypothalamus and in the lateral pontine tegmentum. In conscious rats with implanted guide cannulae, darting and flight responses were evoked by microinjections of DLH into the periaqueductal grey matter but not from the hypothalamus or tegmentum. Brisk locomotion followed injections of DLH into the region overlying the optic chiasma. It is concluded that the brain stem neurones involved in integrating the somatic and visceral components of the defence reaction are concentrated within the four regions defined above. Whereas neurones in the periaqueductal grey matter can initiate the fully integrated defence reaction, those concentrated in the three other areas cannot be shown to do so. Of these three cell groups, the suprachiasmatic neurones seem to be closer in function to the periaqueductal group than are the neurones in the tuberal hypothalamus and pontine tegmentum.
The transport of uric acid across mouse small intestine in vitro.
Authors: Bronk J R , Shaw M I
Published: December 2014

The in vitro recirculation technique was used to study the uptake and transport of uric acid by the jejunum of mouse small intestine. Three components of the serosal secretions appeared to be endogenously derived nucleic acid derivatives; two of these were identified as uric acid and uracil. There was no detectable metabolism of uric acid by the intestine. Uric acid transported from the lumen appeared in the serosal fluid at a concentration higher than that in the lumen. The final serosal/luminal concentration ratio of about 1.18 for exogenous uric acid was found to be constant over the concentration range studied (0.01‐0.1 mM). The presence of exogenous uric acid in the lumen did not affect the production of endogenous uric acid by the intestine and its release into the serosal secretions. Mucosal concentration of exogenous uric acid was below, but the total mucosal concentration (exogenous+endogenous) was above, that in the lumen. There was no evidence for the secretion of endogenous uric acid into the lumen. Oxypurinol significantly decreased the rate of serosal appearance of exogenous uric acid. Allopurinol did not affect the transport of exogenous uric acid from the lumen and there was negligible metabolism of allopurinol to oxypurinol by the tissue. Uracil did not affect the transport of exogenous uric acid from the lumen, or the serosal appearance of endogenous uric acid. Likewise uracil transport was unaffected by luminal uric acid.
The influence of intestinal infusion of fats on small intestinal motility and digesta transit in pigs.
Authors: Gregory P C , Rayner V , Wenham G
Published: December 2014

The influence of duodenal and ileal infusion of nutrients on small intestinal transit of digesta, measured by the passage of phenol red marker, was studied in twelve pigs fitted with duodenal and ileal catheters, and a terminal ileal cannula. Changes in gastrointestinal motility were observed by electromyography and by use of an X‐ray image intensifier in four of the pigs fitted additionally with nichrome wire electrodes in the gut wall and in seven pigs fitted only with a gastric catheter. Small intestinal transit time was unaffected by intestinal catheterization per se, or by duodenal or ileal infusion of glucose or peptone. It was reduced by duodenal infusion of fat or of some of the products of fat digestion including oleic acid and a monoglyceride containing unsaturated fatty acids (monoglyceride LS) but was not affected by infusion of glycerol, stearic acid or a monoglyceride containing saturated fatty acids (monoglyceride P). Ileal transit time was greatly reduced by ileal infusion of soya bean oil mixed with bile salts and lipase and by monoglyceride LS but not by soya bean oil alone. Total small intestinal transit time was reduced to a lesser degree by ileal infusion of soya bean oil mixed with bile salts and lipase and by monoglyceride LS and was unaffected by soya bean oil alone. The level of irregular spiking activity of the small intestine was greatly reduced by both duodenal and ileal infusion of fat, but rapidly propagated spike bursts were initiated from the point of infusion (identified radiologically as peristaltic rushes) many of which travelled right through to the ileo‐caecal junction. It is concluded that intestinal infusion of fat accelerates small intestinal transit in pigs by induction of peristaltic rushes; that since the ileal transit times were more severely reduced than total small intestinal transit times by ileal infusion of fat the response is probably only seen over those areas of intestine in direct contract with the fat; and that the effect depends upon the presence of fat digestion products, i.e. the fatty acid and the monoglyceride, although probably only those containing unsaturated fatty acids.
The reaction of ouabain with the sodium pump of guinea‐pig myocardium in relation to its inotropic effect.
Authors: Ebner F , Korth M , Kühlkamp V
Published: December 2014

[3H]ouabain binding (1.85‐500 nmol/l) was evaluated in resting guinea‐pig papillary muscles at 1.2‐12 mmol K/l. The time course of binding was biphasic. This finding excluded a homogeneous population of non‐interacting binding sites of ouabain, even though the identical susceptibility of both phases to K suggested the occupation of similarly operative receptors. Concomitant with ouabain binding, intracellular Na ion activity (aiNa) increased in the presence of 2.4 or 12 mmol K/l. Occupation of the receptor molecule by ouabain, therefore, conformed to Na‐pump inhibition. Although K antagonized both ouabain binding and its effect on aiNa, the antagonistic effect on aiNa was more pronounced. The reduction of passive Na influx with depolarization as well as the stimulation of the Na pump by K presumably contributed to the antagonistic effect of K. The decrease in aiNa from 8 to 5 mmol/l, when in the absence of ouabain K was raised from 2.4 to 12.0 mmol/l, confirmed the relevance of Na fluxes. Simultaneous changes in aiNa and in the force of rested‐state contractions were apparent upon addition of ouabain. At 2.4 mmol K/l, increase in aiNa raised the force of contraction by constant proportions. At 12 mmol K/l, the inotropic effect produced at comparable values of aiNa was approximately tenfold higher and was susceptible to a change in extracellular Ca concentration. Increase in aiNa, however, was differently effective on force of contraction of low as compared with high values of aiNa. The influence of resting membrane potential on electrogenic Na‐Ca exchange is supposed to interfere with the inotropic effectiveness of aiNa after the cell membrane depolarized from ‐102 mV to ‐65 mV with the increase of K from 2.4 to 12 mmol/l. In view of the role of both membrane potential and aiNa not just a single mechanism appeared to be involved in the control of force of contraction.
Differences in synaptic efficacy at neuromuscular junctions in frog twitch muscles.
Authors: Banner L R , Herrera A A
Published: December 2014

A comparison was made of neuromuscular junctions in cutaneous pectoris and cutaneous dorsi muscles of Rana pipiens in order to study mechanisms controlling synaptic efficacy. Other than a small difference in junctional size, the two muscles were structurally and functionally very similar. Despite these similarities, cutaneous pectoris junctions had substantially higher synaptic safety margins. With intracellular recording, it was apparent that the difference in safety margin was due to a large difference in transmitter release. In low‐Ca2+ solutions, levels of evoked and spontaneous release were 4 times higher in the cutaneous pectoris. When corrected for differences in nerve terminal size at identified junctions, there remained a 3‐fold difference in evoked release and a 6‐fold difference in spontaneous release per unit terminal length. Differences in normal Ringer solution were 1.8‐ and 2.5‐fold for evoked and spontaneous release, respectively. There was no simple relationship between synaptic efficacy and the total amount of nerve terminal supported by each motoneurone in different frog muscles. We concluded that there can be large differences in synaptic efficacy without correlated structural differences visible with the light microscope.
The probability of quantal secretion along visualized terminal branches at amphibian (Bufo marinus) neuromuscular synapses.
Authors: Bennett M R , Jones P , Lavidis N A
Published: December 2014

The number of quanta secreted from selected sites along terminal branches at toad (Bufo marinus) neuromuscular junctions was determined. Terminal branches were visualized by prior staining with the fluorescent dye, 3‐3 Diethyloxadicarbocyanine iodide (DiOC2(5)); neither impulse conduction nor quantal release were affected by DiOC2(5) at concentrations less than 10 microM. The evoked quantal release recorded with an extracellular micro‐electrode (me) at different sites along the length of terminal branches was determined in an external calcium concentration, [Ca]o, of 0.35‐0.45 mM. For short branches (40‐80 microns), me remained approximately constant for over 60% of the branches; for the rest, me declined approximately exponentially with an average length constant of 17 +/‐ 2 microns (mean +/‐ S.E. of mean). For both medium (81‐120 microns) and long branches (121‐160 microns), me declined in nearly all cases approximately exponentially with length constants of 39 +/‐ 5 and 54 +/‐ 8 microns respectively. These changes in me were observed at synapses having a wide range of terminal branching patterns. Some DiOC2(5)‐stained branches possessed discontinuous cholinesterase staining. In general, me declined along these branches in the same way as along DiOC2(5)‐stained branches with continuous cholinesterase staining. It is suggested that because of the decline in me along most medium and long terminal branches, many release sites have a very low probability for secretion in low [Ca]o. Release sites near the point of nerve entry, which have a relatively high probability, therefore make the main contribution to secretion recorded with an intracellular micro‐electrode. As a consequence, transmitter secretion from the whole terminal does not fluctuate from impulse to impulse as much as expected if there were a large number of release sites, each with a low probability of secretion. Transmitter secretion then follows binomial rather than Poisson statistics.
The involvement of basolateral potassium channels in the intestinal response to secretagogues in the rat.
Authors: Hardcastle J , Hardcastle P T
Published: December 2014

The possible involvement of basolateral K+ channels in the intestinal response to secretagogues was investigated using stripped sheets of rat mid‐intestine. Increasing the serosal K+ concentration reduced the rise in short‐circuit current induced by acetylcholine, 5‐hydroxytryptamine, theophylline and prostaglandin E2 (PGE2) without affecting the change caused by glucose. The secretagogue‐induced rise in short‐circuit current was inhibited by quinine, but not by tetraethylammonium chloride, apamin or 3,4‐diaminopyridine. Acetylcholine stimulated 86Rb efflux into the serosal fluid from pre‐loaded intestinal sheets and a smaller response was observed with PGE2. The acetylcholine‐induced stimulation of 86Rb efflux was inhibited by serosal quinine and lack of serosal Ca2+. Furosemide in the serosal fluid reduced the electrical response to acetylcholine without affecting the increase in 86Rb efflux. It is concluded that as well as increasing luminal Cl‐ permeability, intestinal secretagogues also enhance the basolateral K+ conductance by activating Ca2+‐dependent K+ channels.
Sulphate transport into vesicles prepared from human placental brush border membranes: inhibition by trace element oxides.
Authors: Boyd C A , Shennan D B
Published: December 2014

Inhibitors of SO4(2‐) entry into and efflux from vesicles prepared from the brush border membrane of term human placenta have been studied, using 35SO4(2‐) and an anion‐exchange column assay. Divalent anions were found to be either potent or relatively feeble inhibitors of SO4(2‐) uptake. Those which, like SO4(2‐) itself, have a tetrahedral configuration, were strongly inhibitory and all of these anions were the metal oxides of elements of group VI (A and B) of the Periodic Table (chromate, molybdate, tungstate, selenate and thiosulphate). Divalent anions which were only weak inhibitors of SO4(2‐) uptake were arsenate, phosphate and tetraborate. Chromate and to a lesser extent molybdate were effective inhibitors of SO4(2‐) efflux from vesicles pre‐loaded with SO4(2‐). SO4(2‐) efflux was insensitive to the electrical potential across the vesicle membrane. These results are discussed with respect to the mechanism for SO4(2‐) transport across this membrane from mother to fetus and in the context of the transport to the feto‐placental unit of the essential trace elements, selenium, chromium and molybdenum.
5‐Hydroxytryptamine decreases the sensitivity of nicotinic acetylcholine receptor in bull‐frog sympathetic ganglion cells.
Authors: Akasu T , Koketsu K
Published: December 2014

The post‐synaptic effects of 5‐hydroxytryptamine (5‐HT) were examined in neurones of bull‐frog sympathetic ganglia with intracellular micro‐electrode and voltage‐clamp recording techniques. Atropine (1 microM) was used to block the muscarinic cholinoceptors. 5‐HT reduced the amplitude of the fast excitatory post‐synaptic potential (fast e.p.s.p.). 5‐HT also reduced the mean amplitude of the miniature excitatory post‐synaptic potentials (m.e.p.s.p.s) without affecting their frequency. Voltage‐clamp studies showed that 5‐HT decreased in a dose‐dependent manner the amplitude of the acetylcholine (ACh) current produced by ionophoretic application of ACh to sympathetic neurones. The relationship between the log of the ACh dose, applied ionophoretically, and the peak ACh current (the dose‐response curve) was examined in voltage‐clamped neurones. 5‐HT caused a parallel shift to the right of the dose‐response curve for ACh. Analysis using a double reciprocal plot (Lineweaver‐Burk plot) revealed that 5‐HT increased the apparent dissociation constant (Km) of ACh for the receptor without changing the maximum ACh current (Vmax), suggesting a competitive antagonism. The relationship between the 5‐HT dose and the magnitude of inhibition of the ACh current was obtained using two different amplitudes for the ACh response. The dose‐response curve of 5‐HT‐induced inhibition using a relatively high amplitude ACh current, S1, was parallel with that for a relatively low amplitude ACh current, S2. The Dixon plot of these two curves yielded an apparent inhibition constant (Ki) of 42 microM. Both fast excitatory post‐synaptic currents (fast e.p.s.c.s) and miniature excitatory post‐synaptic currents (m.e.p.s.c.s) had single‐exponential decay time courses. The time constants of fast e.p.s.c. decay (tau e) and m.e.p.s.c. decay (tau m) were not altered by 5‐HT, suggesting that 5‐HT does not change the kinetics of opening and closing of the ionic channel associated with the nicotinic receptor. 5‐HT did not alter the reversal potential of the fast e.p.s.c. These results suggest that 5‐HT decreases the sensitivity of the nicotinic receptor of sympathetic neurones, by interfering with ACh binding at the active site on the receptor‐ionic‐channel complex. 5‐HT may physiologically inhibit cholinergic transmission as it is an endogenous substance which antagonizes the nicotinic receptor in post‐ganglionic neurones of bull‐frog sympathetic ganglia.
Inactivation of calcium channel current in rat uterine smooth muscle: evidence for calcium‐ and voltage‐mediated mechanisms.
Authors: Jmari K , Mironneau C , Mironneau J
Published: December 2014

Ca channel currents were recorded in Cs‐loaded myometrial strips from pregnant rats after addition of tetraethylammonium chloride and 4‐aminopyridine (10 mM each) by means of a double sucrose‐gap technique. During a depolarizing pulse, the decay of Ca channel current was slowed down when external Ca was replaced by Ba or Sr. This decay represented an inactivation phenomenon, as assessed by the decreased amplitude of inward tail currents following progressively longer depolarizations, the absence of shift in peak conductance curves against membrane potential, and the stable value of the reversal potential when Ba current was increased during conditioning pulses. Inactivation of Ca and Ba currents through Ca channels was studied using the double‐pulse method. Conditioning pulses that produced maximal Ca current induced maximal inactivation; with stronger depolarizations, inactivation decreased but was not completely prevented at the expected Ca reversal potential. Increasing the amount of Ca entering the cell during the pre‐pulse reduced both amplitude and kinetics of test Ca currents. These results were not observed with Ba as charge carrier suggesting the participation of different mechanisms in inactivation. With Ca as charge carrier, increasing the external Ca speeded the rate of inactivation. This was not observed with Ba outside. Addition of Co (2.5 mM) reduced the amplitude of both Ca and Ba currents but slowed the inactivation of only the Ca current. Recovery from inactivation was described as a two‐exponential process only when the conditioning pulse elicited a Ca inward current. In all other cases, recovery from inactivation was represented as a single exponential curve. It is suggested that inactivation of Ca channels in rat uterine smooth muscle is mediated by both internal Ca‐dependent and potential‐dependent mechanisms.