bluuebunny/crossref_metadata_2025 huggingface dataset:
The antagonism of amino acid‐induced excitations of rat hippocampal CA1 neurones in vitro.
Authors: Collingridge G L , Kehl S J , McLennan H
Published: December 2014

1. The effects of the ionophoretic application of a number of excitatory amino acids and antagonists to the dendrites of CA1 neurones of rat hippocampal slices maintained in vitro were examined. Cells were excited by N‐methyl‐DL‐aspartate (NMA), kainate, quisqualate, L‐aspartate and L‐glutamate; NMA was unique in causing cells to fire in bursts of repetitive discharges in contrast to the sustained firing seen with the other compounds. 2. D‐(‐)‐alpha‐aminoadipate (DAA) and (+/‐)‐2‐amino‐5‐phosphonovalerate (APV) were selective NMA antagonists, the latter appearing to be the more potent; in addition both compounds potentiated the responses to kainate and quisqualate. L‐glutamate excitations were affected less by APV than were those of L‐aspartate. The antagonist properties of APV appeared to reside with the D‐(‐)‐isomer. 3. gamma‐D‐glutamylglycine (DGG) in low ionophoretic doses inhibited NMA‐, kainate‐ and aspartate‐induced cell firing but at higher doses the quisqualate and glutamate responses were also decreased. 4. Kainate and NMA responses were blocked by D‐(‐)‐2‐amino‐4‐phosphonobutyrate (D‐APB) which also had some action against the excitatory effects of L‐aspartate. L‐APB had no antagonistic effects, but often produced potentiation of amino acid excitations or was itself an excitant. 5. The effects of NMA and those of kainate and quisqualate were blocked by (+/‐)‐cis‐2,3‐piperidine dicarboxylate (PDA), but this compound itself had a direct excitatory effect. L‐glutamate diethylester (GDEE) did not show specific antagonism of any amino acid excitations. 6. DGG and APV did not affect ACh excitations and these selective antagonists should be of value in studying the involvement of the excitatory amino acids in synaptic transmission in the hippocampus. Because they are less potent and/or have complicating direct effects PDA, GDEE, D‐ and L‐APB may be less useful in this regard.
Presynaptic effect of Erythrosin B at the frog neuromuscular junction: ion and photon sensitivity.
Authors: Augustine G J , Levitan H
Published: December 2014

1. The anionic dye Erythrosin B increases quantal transmitter release from frog neuromuscular synapses. Experiments were performed to determine the role of ions and light in this presynaptic effect. 2. In calcium‐free saline containing 1 mM‐EGTA, Erythrosin B increased miniature end‐plate potential (m.e.p.p.) frequency at a more rapid rate than in normal saline. 3. The dye's effect was influenced by extracellular calcium ions in a complex manner. Dye‐induced release was minimal in Ringer solution containing 0.1 mM‐calcium, and higher in calcium concentrations above or below 0.1 mM. 4. Erythrosin B‐induced spontaneous release also occurred in saline which contained 1 mM‐EDTA and was free of both calcium and magnesium ions. 5. Temporary removal of external sodium ions did not alter the progressive increase in m.e.p.p. frequency produced by the dye. 6. Elevation of the potassium concentration of the external medium (from 2 to 20 mM), which presumably depolarized nerve terminals and increased their calcium permeability, did not change the rate of increase of dye‐induced release when preparations were in a reversed (outward) electrochemical gradient for calcium ions. 7. A reduction in light intensity of at least six orders of magnitude reduced the effect of Erythrosin B by 50%, suggesting that photoactivation is not the primary basis for the dye's action. 8. These results indicate that Erythrosin B is not acting solely by altering the ionic permeability of the presynaptic nerve terminal to calcium, magnesium, or sodium ions, or by altering the calcium metabolism of the terminal. The enhanced effect of the dye in calcium‐free saline suggests that it may be competing with calcium at a common site, while the enhancement of its effect in elevated external calcium suggests that the dye may also increase the permeability of the nerve terminal to calcium ions.
Innervation of individual guinea‐pig superior cervical ganglion cells by axons with similar conduction velocities.
Authors: Wigston D J
Published: December 2014

1. Individual neurones in the guinea‐pig superior cervical ganglion were studied to determine whether they are innervated by preganglionic axons with similar conduction velocities. 2. Latencies of synaptic responses recorded intracellularly in ganglion cells after stimulation of individual ventral roots varied from 28 to 430 msec. Most of this variability arose from differences in preganglionic conduction velocity. 3. The twelve different axons that on average innervate each ganglion cell tended to have broadly similar conduction velocities; a neurone receiving a rapidly conducting input was usually contacted by other rapidly conducting axons, and vice versa. 4. Preferential innervation of individual neurones by axons with similar conduction velocities was evident even when only axons arising from the same spinal segment were compared. Thus preferential innervation by axons of similar conduction velocity cannot be simply a manifestation of segmental preferences. 5. These results suggest that the mature pattern of innervation in mammalian sympathetic ganglia reflects the functional as well as the positional qualities of the synaptic partners.
Effects of stimulation of aortic chemoreceptors on abdominal vascular resistance and capacitance in anaesthetized dogs.
Authors: Hainsworth R , Karim F , McGregor K H , Rankin A J
Published: December 2014

1. Dogs were anaesthetized with chloralose, ventilated artificially, and the regions of the aortic arch and carotid sinuses were isolated vascularly and perfused with blood. The abdominal circulation was isolated vascularly, perfused at constant flow and drained from the inferior vena cava at constant venous pressure. Changes in vascular resistance were determined by calculating changes in abdominal aortic perfusion pressure, and changes in capacitance by integrating the changes in venous outflow. 2. Stimulation of aortic body chemoreceptors, either by changing the aortic arch perfusate from arterial to venous blood at constant perfusion pressure or by injection of sodium cyanide into the aortic arch, resulted in an increase in abdominal vascular resistance and a decrease in abdominal vascular capacitance. 3. After both cervical vagosympathetic trunks had been cut, stimulation of aortic chemoreceptors no longer resulted in resistance or capacitance responses. 4. These results indicate that stimulation of aortic chemoreceptors, like carotid chemoreceptors, results in reflex constriction of both resistance and capacitance vessels in the abdominal circulation.
Reduction of long‐term potentiation in the dentate gyrus of the rat following selective depletion of monoamines.
Authors: Bliss T V , Goddard G V , Riives M
Published: December 2014

1. Brief, high‐frequency stimulation of the perforant path results in a long‐term potentiation (l.t.p.) of the field response evoked in the dentate gyrus by single shocks to the perforant path. We have compared the magnitude and duration of l.t.p. in normal, anaesthetized rats with animals depleted of noradrenaline (NA), 5‐hydroxytryptamine (5‐HT), or both. 2. All animals were exposed to an identical sequence of eight high‐frequency trains of increasing intensity given over a period of 140 min to the perforant path of one hemisphere. The potential evoked by test shocks to the perforant path was monitored in both hemispheres throughout this period and for a further 96 min after the last train. 3. Plots of the mean potentiation of the population e.p.s.p. as a function of time were computed for all animals in each group. L.t.p. in the NA‐depleted group was about 50% of that in the non‐depleted control group throughout the course of the experiment. L.t.p. in the 5‐HT‐depleted group was more severely affected; mean potentiation did not exceed 30% of that in the control group at any time. 4. The duration of l.t.p. was unaffected by NA depletion and reduced by 5‐HT depletion. 5. The threshold for the intensity of high‐frequency current pulses necessary to elicit l.t.p. was unaffected by NA depletion and raised by 5‐HT depletion. 6. Short‐term potentiation of the population e.p.s.p. was unaffected by either NA depletion or 5‐HT depletion. 7. The effect of monoamine depletion on granule cell excitability was investigated. 5‐HT depletion, but not NA depletion, induced an increase in the excitability of the granule cell population, in the sense that a population e.p.s.p. of a given size was associated with a larger population spike. 8. Long‐term potentiation of granule cell excitability was not affected by NA depletion, but was reduced by 5‐HT depletion. 9. These results show that monoamines can modulate long‐term changes in synaptic function in the dentate gyrus, and suggest that 5‐HT is more potent in this respect than NA.
The function of the antagonist muscle during fast limb movements in man.
Authors: Marsden C D , Obeso J A , Rothwell J C
Published: December 2014

We have examined fast flexion movements of the human thumb and fast extension movements of the elbow over three different distances at a variety of speeds in order to elucidate the function of the antagonist muscle in these circumstances. All movements were of such a velocity that they showed the typical bi‐ or triphasic pattern of muscle activation in agonist and antagonist. Slower movements, with continuous agonist activity, were not analysed. For movements made through the same angle at different velocities, there was a linear relationship between the amount of antagonist activity needed to halt the movement and the peak velocity. However, the slope of this relationship was a function of the distance moved. Movements made through large angles showed less antagonist activity than those made through small angles at the same speed. The timing of the antagonist activity also changed as a function of both distance and speed. Fast, small movements showed earlier onset of antagonist activity than slow, large ones. Movements which were halted mechanically with the subject's prior knowledge had little or no antagonist activity, since it was no longer necessary in these conditions. The complexity of these relations indicates that the triphasic pattern of muscle activity underlying these movements can no longer be regarded as a simple immutable ‘programme'. The size and timing of the bursts of muscle activity are subtly adjusted to the precise nature of the task.
Studies on rat intestinal epithelial cell receptors for serotonin and opiates.
Authors: Gaginella T S , Rimele T J , Wietecha M
Published: December 2014

We have employed the receptor‐ligand binding technique in an attempt to determine if specific binding sites (receptors) for serotonin and opiates are present on rat intestinal epithelial cell membranes. A wide variety of ligands for serotonin and opiate receptors bound to specific receptor sites in rat brain. However, the same ligands failed to bind in a specific (receptor‐related) manner to isolated membranes of rat ileal and colonic cells. Additional washing of the tissue pellet (to remove soluble peptidases), pretreatment with p‐chlorophenylalanine (to deplete endogenous serotonin), alteration of sodium concentration (to antagonize the effects of putative endogenous inhibitors of opiate ligand binding), changes in incubation time, temperature, tissue protein and tritiated ligand concentration failed to yield meaningful results with the enterocyte membranes. We conclude that, as assessed under the present conditions, serotonergic and opiate receptors are not present or are not accessible on rat intestinal epithelial cell membranes.
Time‐dependence of the pressure‐volume relationship in the synovial cavity of the rabbit knee.
Authors: Knight A D , Levick J R
Published: December 2014

The pressure‐volume curve of the synovial cavity of the rabbit knee has been determined by the infusion of a non‐absorbable oil into the joint space. Pressure (greater than 3 cm H2O) at a given volume decayed as a curvilinear function of time. In consequence, a plot of volume against pressure immediately after a volume increment (the immediate compliance curve) was steeper than a plot of volume against pressure after 5‐20 min (the delayed compliance curve) above atmospheric pressure. Similarly, the compliance curve for a rapidly expanded joint was steeper than the compliance curve for the opposite, slowly expanded joint. Observations 2 and 3 indicated that the joint investment was visco‐elastic. Pressure at a given volume during aspiration of the expanded joint was always less than pressure at the same volume during infusion. This hysteresis was substantial, the mean energy dissipation being about 37%. Pressure at a given volume increased as a function of time during aspiration, but the pressure recovery was less pronounced than pressure decay during infusion. When the cycle of infusion and aspiration was repeated, the pressure‐volume hysteresis loop was displaced progressively towards the volume axis. Observations 5 and 6 were attributed to plasticity of the joint investment. It is concluded that intra‐articular pressure at a given volume depends on the rate of change of volume, the direction of change, and the previous history of the joint. The relevance of these properties to fluid dynamics in other interstitial compartments, in arthritic human joints, and to the neurophysiology of mechanoreceptors in the joint investment is discussed.
Effect of tetanus toxin on the excitatory and the inhibitory post‐synaptic potentials in the cat motoneurone.
Authors: Kanda K , Takano K
Published: December 2014

Tetanus toxin (100 mouse minimal lethal doses per kilogram) was injected into the medial gastrocnemius muscle of the cat. At various times thereafter, homonymous and heteronymous group Ia excitatory post‐synaptic potentials (e.p.s.p.s), disynaptic reciprocal Ia inhibitory post‐synaptic potentials (i.p.s.p.s) and post‐synaptic potentials (p.s.p.s) produced by sural nerve stimulation were recorded in the medial gastrocnemius motoneurones. The duration of the after‐hyperpolarization, the input resistance and the axonal conduction velocity of motoneurones were also measured. Homonymous Ia e.p.s.p.s remained normal until 72 h after toxin injection. However, 5 days after toxin injection, the amplitudes of Ia e.p.s.p.s. were significantly smaller than those in control animals (1.5 +/‐ 1.0 mV versus 5.6 +/‐ 2.7 mV; t test, P less than 0.001). Heteronymous Ia e.p.s.p.s produced by stimulation of the lateral gastrocnemius‐soleus nerve 5 days after toxin injection were also significantly smaller than those in control animals (0.6 +/‐ 0.6 mV versus 2.5 +/‐ 1.5 mV; P less than 0.001). However, these heteronymous Ia e.p.s.p.s remained normal when the lateral gastrocnemius‐soleus nerve was ligated and sectioned at the entry to those muscles just before the toxin injection. The ascending volleys, which are supposed to represent mainly the action potentials of the dorsal spinocerebellar tract and to be elicited monosynaptically by collaterals of group I afferents, were essentially the same in the left tetanic and right control sides up to 5 days after toxin injection. Ia i.p.s.p.s and the hyperpolarizing component of sural p.s.p.s could not be produced or were very small in motoneurones sampled later than 30 h after toxin injection. The duration of the after‐hyperpolarization and the input resistance of motoneurones remained normal. Axonal conduction velocity of motoneurones measured 5 days after toxin injection was 89.4 +/‐ 12.7 m/s, and was significantly slower than that of control motoneurones (94.1 +/‐ 15.4 m/s) (P less than 0.005). Differences in the amplitude of group I incoming volleys between tetanic leg and contralateral control leg were not observed. These results suggest that tetanus toxin blocks excitatory synapses in the central nervous system as well as inhibitory synapses.
Purine receptors in the rat anococcygeus muscle.
Authors: Stone T W
Published: December 2014

Adenosine triphosphate (ATP) caused contraction of the resting isolated rat anococcygeus muscle. Non‐phosphorylated purines did not cause contraction of the resting muscle but did so in muscles in which the tone was raised by carbachol or guanethidine. Adenosine, (‐)N6‐phenylisopropyladenosine (PIA) and 5'‐N‐ethyl‐carboxamide adenosine (NECA) were approximately equipotent, and these responses were not prevented by theophylline, quinidine, 2,2'‐pyridylisatogen tosylate, phentolamine, methysergide, dipyridamole, hexobendine or indomethacin. The contractions became smaller as muscle tone progressively declined, and it is suggested that this effect may explain the apparent blockade of ATP responses by indomethacin reported previously. Adenosine, 2‐chloroadenosine, ATP, PIA and NECA inhibited contractile responses of the anococcygeus to field stimulation of the excitatory adrenergic innervation. This inhibitory action was blocked by theophylline, and as PIA was easily the most potent purine tested, it may involve activation of an A1/Ri receptor. It is also argued, however, that the A/R scheme of classification may be inappropriate for the description of responses of intact tissues. As response to noradrenaline were not changed by the purines, the inhibitory effect on stimulation‐evoked contractions is probably mediated at a presynaptic site. None of the purines tested had any effect on the neurally mediated inhibition of the anococcygeus which is seen when intrinsic tone is raised and the excitatory adrenergic nerves are blocked.
Comparison of aspirin and indomethacin pre‐treatments on the responses to reduced renal artery pressure in conscious dogs.
Authors: Anderson W P , Bartley P J , Casley D J , Selig S E
Published: December 2014

To examine the role of prostaglandins in physiologically induced renin release, we reduced renal artery pressure within the autoregulatory range in chronically instrumented conscious dogs with aspirin, indomethacin or no pre‐treatment. In untreated dogs, reduction of renal artery pressure to 60 mmHg for 90 min produced rises in plasma renin activity (+ 5.4 +/‐ 1.0 ng ml.‐1 hr‐1) and mean arterial pressure (+ 17 +/‐ 2 mmHg) without significant effect on renal blood flow (n = 13). Aspirin pre‐treatment (2 X 25‐40 mg kg‐1 orally) had no effect on the renin, arterial pressure or renal blood flow responses to renal artery pressure reduction (n = 7). In contrast, indomethacin pre‐treatment (2 X 2‐3 mg kg‐1 orally) significantly lessened the increase in plasma renin activity during reduced renal artery pressure (+ 2.0 +/‐ 0.3 ng ml.‐1 hr‐1, n = 11). The relative effectiveness of aspirin and indomethacin in inhibiting prostaglandin production in the kidney was then tested in separate experiments by measuring the renal blood flow responses to renal artery injections of arachidonate (5‐200 micrograms kg‐1). In the doses used above, aspirin markedly attenuated the blood flow response to arachidonate but indomethacin had almost no effect. Both aspirin and indomethacin abolished the hypotensive effect of intravenous arachidonate (0.5 mg kg‐1). These results tentatively suggest that indomethacin may not effectively inhibit renal prostaglandin production in conscious dogs at the doses used in these experiments. Thus the reduced renin release in response to lowered renal artery pressure in indomethacin pre‐treated dogs may have been due to another, non‐prostaglandin action of indomethacin. The results from the aspirin pre‐treated dogs suggest that prostaglandins are not involved in the release of renin in response to reduced renal artery pressure in conscious dogs.
Denervation increases the degradation rate of acetylcholine receptors at end‐plates in vivo and in vitro.
Authors: Bevan S , Steinbach J H
Published: December 2014

We have studied the effect of denervation on the degradation of the existing junctional acetylcholine (ACh) receptors at end‐plates in rat muscles. ACh receptors were labelled by injecting animals with iodinated alpha‐bungarotoxin (I‐alpha BT); 1 day later the left hemidiaphragm was denervated. The degradation of bound I‐alpha BT in normal and denervated muscles was examined in organ culture, beginning at various times after denervation in vivo. The original, pre‐labelled end‐plate ACh receptors are degraded more rapidly after denervation. The rate of degradation begins to increase shortly after the nerve is cut and reaches a maximum value at about 9 days of denervation. Muscles denervated only on transfer to organ culture also show an increase in the degradation rate of bound I‐alpha BT with increasing time of denervation (time in culture). In normal diaphragm muscles, the initial rate of degradation of functional ACh receptors, after correcting for non‐degradative loss of I‐alpha BT, is 0.0018 h‐1 (t1/2 = 383 h). The maximal rate at denervated end‐plates is 0.0073 h‐1 (t1/2 = 94 h). For soleus, sternomastoid, plantaris and intercostal innervated muscles the apparent rate of ACh receptor degradation either in vitro or in vivo ranged from 0.0005 h‐1 to 0.002 h‐1. The rate of loss of bound I‐alpha BT in vivo is more rapid at denervated end‐plates than at innervated end‐plates. For diaphragm muscles, the rates of I‐alpha BT degradation measured in organ culture are able to describe the relative rates of loss of I‐alpha BT from innervated and denervated muscles in vivo. At short times after labelling, a fraction (10‐20%) of the I‐alpha BT bound to innervated muscles is degraded more rapidly than the remaining toxin. The possibility that these I‐alpha BT binding sites are degraded at the rate characteristic of extrajunctional receptors on denervated muscle fibres is discussed.
Neither a purine nor VIP is the mediator of inhibitory nerves of opossum oesophageal smooth muscle.
Authors: Daniel E E , Helmy‐Elkholy A , Jager L P , Kannan M S
Published: December 2014

Effects of stimulation of intramural nerves in the circular smooth muscle layer of the body of the oesophagus of the opossum (Didelphis marsupialis) were studied, simultaneously measuring the membrane potential of muscle cells using the sucrose‐gap technique and contractions of the muscle. Electrical field stimulation of the preparation, superfused with Krebs solution at 27 degrees C, induced a transient hyperpolarization of the smooth muscle cell membrane (i.j.p.) followed by a transient depolarization on which muscle action potentials were often superimposed. The muscle did not develop active tension spontaneously; it therefore did not relax during the i.j.p., but often contracted during the ‘off’ depolarization. The i.j.p. and the responses following it were characterized as mediated by intramural, non‐adrenergic, non‐cholinergic (n.a.n.c.) nerves. The i.j.p. amplitude was reduced by raising the external K concentration. When Cl was replaced by isethionate, a small hyperpolarization of the smooth muscle cell membrane ensued along with a comparable small reduction of the i.j.p. amplitude. The ‘off’ activity following the i.j.p. disappeared completely in Cl‐free medium. Apamin (10(‐7)‐10(‐5) M) did not influence this preparation nor the i.j.p. Adenosine and its related adenine nucleotides in concentrations up to 10(‐3) M hardly affected the preparation. Prolonged superfusion with adenosine and 6‐chloroadenosine revealed a gradually increasing attenuation of the i.j.p. Exogenously applied vasoactive intestinal polypeptide (VIP) induced rhythmic depolarizations of the smooth muscle cell membrane and spontaneous contractions, which were insensitive to neurotoxins but absent in Cl‐free media. Field stimulation in the presence of VIP caused an i.j.p. which transiently interrupted the VIP‐induced contractile responses. It is concluded that the inhibitory mediator of the intramural n.a.n.c. nerves present in the circular smooth muscle layer of the opossum oesophagus is neither a purine nor VIP. The i.j.p. may result from a selective increase in K permeability of the smooth muscle cell membrane, the ‘off’ depolarization may involve an increase in the Cl ion conductance. The suggestion is made that the release of neurotransmitter from intramural n.a.n.c. nerves is modulated presynaptically via P1‐purinoceptors and that VIP is a likely candidate for an excitatory transmitter, released simultaneously with the inhibitory transmitter.
Sugar transport in giant barnacle muscle fibres.
Authors: Carruthers A
Published: December 2014

The kinetics of 3‐O‐methylglucose transport in the giant muscle cells of Balanus nubilus have been studied both in intact fibres and in fibres subjected to intracellular solute control using internal dialysis. 3‐O‐methylglucose is not metabolized by barnacle muscle and at equilibrium the 3‐O‐methylglucose space of the tissue does not differ significantly from the water content of the muscle. These results indicate that 3‐O‐methylglucose transfer in barnacle muscle is mediated by a passive process. 3‐O‐methylglucose transport is facilitated by a saturable, symmetric transfer mechanism inhibited by cis but not trans sugars and by low concentrations of phloretin and cytochalasin B. The kinetic constants for uptake and exit are identical. These features indicate that sugar transport in barnacle muscle is mediated by a limited number of membrane transport sites. The number of sugar‐displaceable cytochalasin B binding sites in barnacle muscle is 3 X 10(13) cm‐2. Indirect kinetic estimates indicate that the number of sugar transport sites is in the order of 1.6 X 10(12) cm‐2. This passive, facilitated, selective, saturable transport system is consistent with both symmetric mobile carrier (one‐site) and symmetric simultaneous carrier (two‐site) models for transport.
Vagal mechanoreceptors located in the lower oesophageal sphincter of the cat.
Authors: Clerc N , Mei N
Published: December 2014

In anaesthetized cats, sixty‐two vagal sensory units with afferent endings in the lower oesophageal sphincter were recorded by means of extracellular glass micro‐electrodes implanted in the nodose ganglion. All the receptors had non‐medullated fibres, with conduction velocities ranging from 0.8 to 1.2 m/s. From the direct stimulation of the lower oesophageal sphincter, three types of mechanoreceptors were identified. Thirty‐one were activated by natural stimuli:tonic contraction of the sphincter and distension elicited by the passage of a bolus. Artificial stimulation effected by digital compression was also effective. These receptors were similar to muscular endings already described in the digestive tract. Their main characteristic, i.e. their slow adaptation, suggests that they act as sensors of sphincter opening and closure. This was corroborated by observations obtained during distension of the cervical or thoracic oesophagus; a maximum decrease occurred in the lower oesophageal sphincter mechanoreceptor discharge when the distension was produced between 9 and 12 cm from the lower oesophageal sphincter. Twenty‐nine endings were found in the superficial layers (mucosae). Contrary to the muscular receptors, the mucosal receptors were not affected by normal contractions or distensions of the lower oesophageal sphincter. They were activated only by strong stimuli like digital compression or distension achieved with a balloon. In addition, mucosal stroking was a potent stimulus. Whatever the stimulus used, the mucosal receptors showed rather rapidly adapting discharges. These receptors should be considered to be sensors of bolus consistency. Two mechanoreceptors, located in the serous membrane of the lower oesophageal sphincter, were identified by touching or by stretching. Their discharges showed that they belonged to the rapidly adapting type. A comparison of the three types of receptors found in the lower oesophageal sphincter is made with known digestive endings and their possible role is discussed.
Acetylcholine‐induced current fluctuations and fast excitatory post‐synaptic currents in rabbit sympathetic neurones.
Authors: Derkach V A , Selyanko A A , Skok V I
Published: December 2014

Post‐synaptic currents and responses to ionophoretically applied acetylcholine (ACh) were recorded at 34‐37 degrees C from rabbit superior cervical ganglion neurones clamped at ‐80 mV membrane potential. Atropine (1 microM) was used to block muscarinic receptors. The fast excitatory post‐synaptic current (e.p.s.c.) reversed at ‐9.6 +/‐ 1.7 mV and decayed with a single exponential time course. The e.p.s.c. decay time constant, tau d, was 4.5 +/‐ 0.3 msec and increased as the membrane was hyperpolarized (e‐fold increase in tau d corresponded to 140 mV hyperpolarization). Miniature e.p.s.c.s. (m.e.p.s.c.s) decayed with time constants similar to those of the e.p.s.c. The decay of the e.p.s.c. was slowed by lowering temperature but remained a single exponential; the changes of tau d with temperature followed the Arrhenius equation (Q10 = 3.7). In most of the neurones studied the analysis of ACh noise spectra revealed two kinetic components with mean time constants tau N1 = 1.1 +/‐ 0.1 msec and tau N2 = 5.0 +/‐ 0.5 msec. In a few neurones only the tau N1 component was found. Similar two‐component ACh noise spectra were observed in the neurones not treated with atropine. tau N1 and tau N2 components revealed temperature dependences similar to each other and close to that of tau d. The values of tau N1 and tau N2 and the ratio between the contributions of the tau N1 and tau N2 components to the ACh noise spectrum did not depend on the dose of ACh. The single channel conductance is 36 +/‐ 3 pS. A single ACh quantum opens about 150 ionic channels and the e.p.s.c. consists of 4‐243 quanta. It is suggested that in mammalian sympathetic ganglion neurones there are two types of nicotinic ACh receptor channels, with short and long lifetimes, and that the kinetics of e.p.s.c. and m.e.p.s.c. are determined by the activity of the longer lifetime channel type.
Experimental analysis of alternative models of charge movement in frog skeletal muscle.
Authors: Huang C L
Published: December 2014

A series of pulse procedures was used to distinguish experimentally between a ‘capacitative’ (Schneider & Chandler, 1973) and a ‘resistive’ (Matthias, Levis & Eisenberg, 1980) model of ‘charge movements’ in skeletal muscle. A general condition describing the conservation of charge in a non‐linear capacitor that was used as the basis for the experiments is derived in the Appendix. It was shown that earlier criteria concerning equality of ‘on’ and ‘off’ charge in response to large steps are insufficient to exclude resistive models. However, the capacitative, but not the resistive model successfully explained results bearing on charge conservation assessed through pulse procedures involving: (i) small, 10 mV voltage steps from a series of prepulse voltages, (ii) voltage steps to a fixed potential from a series of hyperpolarized voltages, (iii) pulse sequences incorporating a ‘staircase’ of voltage steps. It is concluded that the earlier use of ‘on’ and ‘off’ equality in response to large voltage steps is insufficient to exclude a resistive basis for the non‐linear transient. However pulse procedures explicitly designed to distinguish the two models give results consistent with a capacitative model for the non‐linear charge and at variance with a resistive one.
Kinetic properties of calcium channels of twitch muscle fibres of the frog.
Authors: Sánchez J A , Stefani E
Published: December 2014

Calcium currents (ICa) were recorded in frog skeletal muscle fibres using the three‐micro‐electrode voltage‐clamp technique. The sartorius muscle was bathed in TEA methanesulphonate saline with 350 mM‐sucrose. 5 mM‐3,4‐diaminopyridine was added to the saline to minimize K+ currents. The I‐V relationship for peak Ca2+ currents showed that ICa was detected at ‐40 mV and reached a maximum value at ca. ‐10 mV. No net inward current was recorded at potentials positive to ca. +40 mV. Remaining K+ currents (IK) were recorded by replacing 10 mM‐Ca2+ with 5.5 mM‐Co2+. They were not noticeably time‐dependent up to +20 mV and would tend to diminish the amplitude of ICa without greatly affecting its time course. ICa tail currents could be separated from non‐linear capacity currents. Tail currents were measured 5 msec after repolarization and extrapolated to the end of the pulse. ICa tail‐current amplitudes at EK were measured with pulses of different durations. The envelope of tail‐current amplitudes declined with a time course similar or identical to that of inward current during a maintained depolarization. Consequently, the decline of inward current cannot be explained by an increase of outward IK with time. ICa inactivated with 9 sec prepulses which did not elicit detectable ICa. The fitted h infinity curve had a mid point of ‐33.0 mV and a steepness of 6.3 mV. ICa between ‐30 mV and +20 mV could be described adequately using the Hodgkin‐Huxley m3h relationship. The fitted m infinity curve had a mid point of ‐35.2 mV and a steepness of 9.9 mV. The limiting Ca2+ permeability PCa was 1.4 +/‐ 0.4 X 10(‐4) cm/sec.
Involvement of melatonin and thyroid hormones in the control of sleep, food intake and energy metabolism in the domestic fowl.
Authors: Bermudez F F , Forbes J M , Injidi M H
Published: December 2014

Growing male domestic fowl of an egg‐laying strain were fed ad libitum and injected intraperitoneally with melatonin or intramuscularly with triiodothyronine (T3) to study the effects on sleep, food intake, blood glucose, e.e.g., oxygen consumption and carbon dioxide production. Melatonin caused a dose‐related depression of food intake with sleep and aphagia lasting for 2 1/2 hr following 8 mg, drowsiness and greatly reduced intake following 4 and 2 mg and a slight reduction in food intake after 1 mg. T3 injection was followed by increased feeding within the range 50‐200 micrograms. The higher dose (200 micrograms) completely prevented the effects of 10 mg melatonin injected simultaneously. Melatonin (10 mg) depressed plasma glucose levels whereas T3 (200 micrograms) elevated blood glucose. Either darkness or melatonin (10 mg) caused an increase in amplitude and a decrease in frequency of the e.e.g. Birds fasted for 3 hr before injection showed significantly lower oxygen consumption and carbon dioxide production when given melatonin (10 mg); T3 had no effect within the 4 hr period after injection and did not modify the effects of melatonin. It is postulated that the rapid effects of melatonin and T3 which were observed result from direct effects of these hormones on the central nervous system.
The sweetness‐inducing effect of miraculin; behavioural and neurophysiological experiments in the rhesus monkey Macaca mulatta
Authors: Brouwer J. N. , Glaser D. , af Segerstad C. Hard , Hellekant G. , Ninomiya Y. , van der Wel H.
Published: December 2014

1. The gustatory effects of miraculin, the sweetness‐inducing protein from the miracle fruit Synsepalum dulcificum, was studied in the rhesus monkey, Macaca mulatta.

2. The intake of five acids was recorded in two‐bottle preference tests, one bottle containing acid and the other tap water, before and after miraculin treatment. All the acids tasted more pleasant after miraculin.

3. The electrical activity of the chorda tympani nerve to stimulation of the tongue with a variety of sweeteners, acids, sodium chloride and quinine hydrochloride was recorded in anaesthetized animals.

4. Pre‐treatment of the tongue with 0·3‐5 mg miraculin doubled the summated nerve response to the acids and diminished the response to sucrose by about 10%. The enhancement lasted for at least an hour and the diminution up to 20 min.

5. After miraculin treatment the Spearman's rank correlation coefficient between the order of increased intake of acids and the order of enhancement of the summated nerve response was 0·99.

6. A solution of 0·1 mg miraculin per ml. elicited a weak nerve response. No preference over water for this concentration of miraculin was recorded in the two‐bottle tests.

7. The activity of twenty‐nine single taste fibres, selected for their responsiveness to sweetness or acids or both, was recorded after miraculin treatment. Effects were obtained in nine fibres which were similar but more pronounced than those observed in the summated recordings. Before miraculin, these fibres responded better and to a larger variety of sweeteners (81%) than the other fibres (40%). After miraculin, acids elicited on the average 2·3 times more activity than before, while the response to sweeteners was depressed. In twenty fibres no effect of miraculin was observed. These fibres responded to fewer of the sweeteners and were more stimulated by the non‐sweet stimuli than the first group.

8. The results suggest that miraculin acts on those structures in the taste cell membrane that are involved in perception of the sweet taste, making them sensitive to acids. The new quality of sweetness after miraculin treatment is signalled by taste fibres which normally respond to sweet substances but which, under the influence of miraculin, are responding to acids. It is likely that the quality of a taste stimulus is conveyed by the identity of the taste fibres.
Calcium‐activated outward current in voltage‐clamped hippocampal neurones of the guinea‐pig.
Authors: Brown D A , Griffith W H
Published: December 2014

Slow clamp currents were recorded from CA1 and CA3 pyramidal neurones in slices of guinea‐pig hippocampus maintained in vitro, using a single micro‐electrode sample‐and‐hold technique. Depolarizing voltage commands evoked a time‐ and voltage‐dependent outward current which was suppressed by removing external Ca or by adding Cd (0.5 mM) or Mn (5 mM). This Ca‐dependent current (Ic) was not reduced by muscarinic agonists (unlike IM) but was greatly reduced by 5‐20 mM‐tetraethylammonium (TEA). Repolarizing IC tail currents reversed at ‐73 +/‐ 5 mV in 3 mM‐K solution. The reversal potential became about 30 mV more positive on raising [K]o to 15 mM. No clear change in current amplitude or tail‐current reversal potential occurred on adding Cs (2 mM), reducing [Cl]o from 128 to 10 mM, or replacing external Na with Tris. The underlying conductance GC was activated at membrane potentials positive to ‐45 mV. At ‐32 mV GC showed an approximately exponential increase with time, with a time constant of approximately 0.6 sec at 26 degrees C. Repolarizing tail currents declined exponentially with time, the time constant becoming shorter with increasing negative post‐pulse potentials. When the clamp was switched off at the end of a depolarizing command of sufficient amplitude and duration to activate IC, a membrane hyperpolarization to ‐73 mV ensued, of similar amplitude and decay time to that following spontaneous action potentials. It is concluded that the clamp current observed in these experiments is probably the Ca‐activated K current thought to contribute to the post‐activation after‐hyperpolarization in hippocampal neurones.
Pattern‐evoked responses and luminance‐evoked responses in the human electroretinogram.
Authors: Korth M
Published: December 2014

Electrical potentials were recorded from the cornea of the human eye in response to the onset and offset of square‐wave stripe patterns varying in spatial frequency, luminance and contrast. Under high retinal illumination (50119 photopic td) the response to pattern onset was a positive wave (pattern‐onset wave) followed by a negative after‐potential. As long as the pattern was presented, a steady potential of positive polarity (plateau potential) was observed. The response to pattern offset was a biphasic negative‐positive wave followed by a negative after‐potential. A comparison between wave forms obtained with pattern onset‐offset stimuli and luminance increase‐decrease stimuli suggests: (a) the pattern‐onset wave is the result of an interaction between a luminance‐increase and a luminance‐decrease response; (b) the plateau potential is mainly an additive superposition of two receptor processes originating from retinal areas that receive increases and decreases in local luminance; (c) the negative‐positive potential is an a‐wave and a b‐wave originating from retinal areas that receive increases in local luminance. The amplitude of the pattern‐onset wave was greatest at a spatial frequency around 3‐4 c/deg. This behaviour was closely correlated with contrast sensitivity determined psychophysically by previous investigators. Therefore, the pattern‐onset wave seems to be a pattern‐evoked response. The amplitude of the b‐wave following pattern offset showed a monotonic decrease with increasing spatial frequency. It is mainly a luminance‐evoked response. Under low retinal illumination (457 photopic td) the pattern‐onset wave and the b‐wave at pattern offset were smaller. However, the pattern‐onset wave had its maximum amplitude at a lower spatial frequency. When increases or decreases in space‐average luminance were combined with pattern onset or offset, transitions between pattern‐ and luminance‐evoked responses could be observed. The results suggest that a decrease in local luminance is the essential stimulus for evoking a pattern‐related response while increases in local light intensity generate luminance‐evoked responses.
Effects of acute changes in blood volume on the carotid sinus baroreceptor reflex in conscious rabbits.
Authors: Faris I B , Jamieson G G , Ludbrook J
Published: December 2014

The control of blood pressure, heart rate, cardiac output and systemic vascular resistance by the carotid sinus baroreceptor reflex was studied in six conscious rabbits during states of acute hypervolaemia and acute hypovolaemia. These states were produced by infusing blood equal to 20% and 40%, and withdrawing blood equal to 20% and 35%, of the initial blood volume. The properties of the reflex were characterized by creating sinusoidal pressure changes across the wall of the carotid sinus at a frequency of 0.01 Hz and amplitudes of 54 and 83 mmHg. From the effects of the lower‐amplitude stimulus the dynamic gain of the reflex was calculated for blood pressure, heart rate, cardiac output and systemic vascular resistance. The higher‐amplitude stimulus was used to determine the near maximal responses of the circulatory variables to changes in carotid sinus transmural pressure. The gain for systemic vascular resistance was reduced by hypervolaemia, and increased by 20% hypovolaemia. The gains for heart rate and blood pressure were not affected by hypervolaemia or by 20% hypovolaemia. 35% hypovolaemia reduced the gain for heart rate, but the resting value was close to the upper limit of the reflex response. It also reduced the gain for cardiac output and blood pressure, and the increase in gain for systemic vascular resistance that had been caused by 20% hypovolaemia was not sustained.
Ion currents in Drosophila flight muscles
Authors: Salkoff Lawrence B. , Wyman Robert J.
Published: December 2014

1. The dorsal longitudinal flight muscles of Drosophila melanogaster contain three voltage‐activated ion currents, two distinct potassium currents and a calcium current. The currents can be isolated from each other by exploiting the developmental properties of the system and genetic tools, as well as conventional pharmacology.

2. The fast transient potassium current (IA) is the first channel to appear in the developing muscle membrane. It can be studied in isolation between 60 and 70 hr of pupal development. The channels can be observed to carry both outward and inward currents depending on the external potassium concentration. IA is blocked by both tetraethylammonium ion (TEA) and 3‐ or 4‐aminopyridine. The inactivation and recovery properties of IA are responsible for a facilitating effect on membrane excitability.

3. The delayed outward current (IK) develops after maturation of the IA system. IK can be isolated from IA by use of a mutation that removes IA from the membrane current response and can be studied before the development of Ca2+ channels. IK shows no inactivation. The channels are more sensitive to blockage by TEA than IA channels, but are not substantially blocked by 3‐ or 4‐aminopyridine.

4. The calcium current (ICa) is the last of the major currents to develop and must be isolated pharmacologically with potassium‐blocking agents. ICa shows inactivation when Ca2+ is present but not when Ba2+ is the sole current carrier. When Ca2+ is the current carrier, the addition of Na+ or Li+ retards the inactivation of the net inward current. When the membrane voltage is not clamped, Ba2+ alone, or Ca2+ with Na+ (or Li+), produces a plateau response of extended duration.

5. The synaptic current (IJ) evoked by motoneurone stimulation is the fastest and largest of the current systems. It has a reversal potential of approximately ‐5 mV, indicating roughly equal permeabilities of Na+ and K+. During a nerve‐driven muscle spike, IJ is the major inward current, causing a very rapid depolarization away from resting potential. An exceptionally large synaptic current is necessary to rapidly discharge the high membrane capacitance (0·03 μF/cell) in these large (0·05 × 0·1 × 0·8 mm) isopotential cells.
Contractile response of the rabbit aorta to maitotoxin, the most potent marine toxin.
Authors: Ohizumi Y , Yasumoto T
Published: December 2014

Maitotoxin (MTX), the most potent marine toxin, caused a dose‐dependent contraction of the rabbit isolated aorta at concentrations of 10(‐10)‐3 X 10(‐8) g/ml. The dose‐contractile response curve for MTX was shifted to the right in a parallel manner by verapamil (10(‐6) M), was slightly shifted to the right by phentolamine (10(‐6) M) and was not or little affected by tetrodotoxin, methysergide, chlorpheniramine or indomethacin. The MTX‐induced contraction was abolished by incubation in Ca2+‐free medium and was increased in a linear fashion with Ca2+ concentrations between 0.03 and 1.2 mM. In Ca2+‐free solution, the contractile responses produced by re‐introduction of Ca2+, Sr2+ or Ba2+ were potentiated after treatment with MTX (10(‐8) g/ml.) and a high concentration of KCl (4 X 10(‐2) M). After treatment with verapamil (10(‐7)‐10(‐6) M), the dose‐contractile response curve for Ca2+, Sr2+ or Ba2+ in the presence of MTX or KCl was shifted to the right in a parallel manner, indicating competitive antagonism. But the dose‐response curve for Ca2+ in the presence of A23187 (3 X 10(‐5) M), a Ca ionophore, was not affected at all by verapamil (10(‐6) M). The tissue Ca content of the aorta was increased 31% by treatment with MTX (10(‐8) g/ml.). This effect of MTX was markedly inhibited in the presence of verapamil. On the basis of these results, it is suggested that the MTX‐induced contraction of the aorta is caused mainly by a direct action on smooth muscle, possibly due to an increase in Ca2+ permeability which occurred through voltage‐sensitive Ca2+ channels in the smooth muscle cell membrane.
Effects of drugs on acetylcholine‐activated ionic channels of internally perfused chick myoballs.
Authors: Farley J M , Narahashi T
Published: December 2014

The effects of intracellular application of three compounds ‐ QX314, N‐ethylguanidine and N‐octylguanidine ‐ on the acetylcholine‐activated ionic channels in chick myoballs were examined. Voltage‐clamped myoballs were internally perfused using the suction‐pipette technique. Changes in the internal ionic environment of myoballs were demonstrated by: (1) alteration of the reversal potential for both acetylcholine‐activated ionic currents and voltage‐gated sodium currents in a manner predicted by the Goldman‐Hodgkin‐Katz equation, and (2) elimination of potassium currents after removal of intracellular and extracellular potassium. Ethylguanidine (5 mM) and octylguanidine (5 microM) blocked acetylcholine‐induced currents by 83% when applied externally. QX314 (0.5 mM) and octylguanidine (100 microM) had no effect on acetylcholine‐induced currents when perfused internally, although in the same cells these compounds caused marked inhibition of voltage‐gated sodium currents. Ethylguanidine (10 mM) reduced acetylcholine‐induced currents by approximately 20‐30% after internal application. It was much less potent from inside than from outside, and the inhibition was not voltage‐dependent. We conclude that the internal mouth of the acetylcholine‐activated channel must be much more selective with respect to drug binding than is the external channel mouth. Internally applied ethylguanidine may penetrate into the channel beyond the selectivity filter to a drug binding site to cause block.