bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the effects of some thiamine analogues upon thiamine transport across the blood‐brain barrier of the rat.
Authors: Greenwood J , Pratt O E
Published: December 2014

The flux of thiamine from the blood into the brain has been measured by a specially devised procedure in which a steady raised level of the vitamin, with or without radioactive labelling, was achieved rapidly and maintained steadily in the circulating blood plasma. This was done by a single rapid I.V. injection followed by a continuous injection given at a rate adjusted according to a pre‐determined programme, so as to replace the injected material at the rate at which it had been found to leave the circulation in preliminary experiments. A series of four chemical analogues of thiamine were given to see how each affected the flux of thiamine into the brain and the findings are compared with those for a fifth analogue studied in previous work. Pyrithiamine, thiamine disulphide and acetylthiamine, like amprolium, inhibited thiamine transport across the blood‐brain barrier. Kinetic analysis shows that they compete mainly for the saturable component of thiamine flux across the blood‐brain barrier, with only a slight inhibition of the non‐saturable component, most clearly seen with pyrithiamine. Oxythiamine, despite its close chemical similarity to thiamine did not have any significant effect upon the flux of the vitamin into the brain. These findings help to explain the efficacy of pyrithiamine administration, especially in conjunction with a thiamine‐deficient diet, in rapidly producing central neurological signs of deficiency.
Morphological and electrophysiological determination of the projections of jaw‐elevator muscle spindle afferents in rats.
Authors: Appenteng K , Donga R , Williams R G
Published: December 2014

The fluorescent compound Lucifer Yellow was injected into the somata of nine identified jaw‐elevator muscle spindle afferents, located in the V mesencephalic nucleus. Reconstructions of the central course of their axons were subsequently made from serial, transverse, sections to identify sites of projection. Three sites of termination were identified on the basis of collaterals that ended in varicosities and/or boutons. All afferents projected to the V nucleus oralis and, all but one, also to the V motor nucleus. Two out of nine afferents had terminations in the supra‐trigeminal nucleus, though a further four appeared to send collaterals to this area. The relative density of projection, judged by the number of collaterals supplied to each area, decreased in the order: V nucleus oralis, V motor nucleus and supra‐trigeminal nucleus. The central course of the afferent axons was such that impulses from the periphery would arrive first at the V motor nucleus, then the V nucleus oralis, the supra‐trigeminal nucleus, and finally the afferent somata in the V mesencephalic nucleus. In animals in which the masseter nerve was exposed in‐continuity for electrical stimulation, electrophysiological recordings were made in the three areas described above to identify units that received a monosynaptic input from spindles in the masseter muscle. Criteria were formulated on the basis of the pattern of responses on stimulation of the masseter nerve, and the morphology of labelled neurones, for differentiating between afferents, interneurones, and motoneurones. In the V motor nucleus, monosynaptic excitatory post‐synaptic potentials (e.p.s.p.s) were obtained in both synergist and masseter motoneurones. These were assumed to arise from a masseter muscle spindle input as the thresholds for exciting such afferents and eliciting e.p.s.p.s were similar. Some interneurones, chiefly in the V nucleus oralis, were activated at thresholds close to that of muscle spindle afferents and could also fire in response to muscle stretch. As their latencies (measured extracellularly) were similar to that of e.p.s.p.s in motoneurones, they were assumed to receive a monosynaptic muscle spindle input. However, most interneurones were activated at longer latencies (up to 7 ms) and some also fired to muscle stretch. Arguments are advanced, based on the long rise time of e.p.s.p.s recorded in some, that the majority of these may also be candidates for monosynaptic activation.(ABSTRACT TRUNCATED AT 400 WORDS)
Development of the monosynaptic stretch reflex in the rat: an in vitro study.
Authors: Kudo N , Yamada T
Published: December 2014

The properties and development of the stretch reflex pathway were investigated in new‐born and fetal rats using the isolated spinal cord‐hind limb preparation. Muscle afferent discharge was elicited by small stretch of the triceps surae muscle in the new‐born rat and in the fetus. It appeared as early as embryonic day 18.5. Ramp‐and‐hold stretch elicited only phasic discharges in most afferent fibres. A phasic reflex response was evoked in the triceps surae muscle by brief or ramp‐and‐hold stretch of the muscle in the new‐born rat. The threshold stretch required for evoking the reflex response was close to that for eliciting the afferent discharge. A reflex response in the triceps surae muscle was also evoked by electrical stimulation of the triceps surae muscle nerve or the sciatic nerve in the new‐born rat. Excitatory post‐synaptic potentials (e.p.s.p.s) in the triceps surae motoneurones were evoked by stimulation of the muscle nerve in the new‐born rat. The amplitude of the e.p.s.p.s was large enough to generate spike potentials. Homonymous e.p.s.p.s were significantly larger than heteronymous e.p.s.p.s. The amplitudes of the e.p.s.p.s were very susceptible to the rate of stimulus repetition. At a stimulus frequency of 10 Hz they were depressed to less than 10% of the control value. Presynaptic impulses evoked by stimulation of afferents in the muscle nerve appear in the motor nucleus less than 1.0 ms before the onset of synaptically evoked field potentials. The interval between the arrival of impulses evoked by dorsal root stimulation and the onset of e.p.s.p.s in motoneurones was 0.56 +/‐ 0.16 ms, indicating monosynaptic transmission from the primary afferents to the motoneurones. In the fetus, a reflex response in the triceps surae muscle was observed following a small stretch of the muscle (or electrical stimulation of the sciatic nerve) in all preparations at embryonic day 20.5 and in about half of those examined at embryonic day 19.5. Neither stimulation evoked a reflex response at embryonic day 18.5. Latencies of the reflex responses evoked by muscle stretch or by nerve stimulation were similar to those in the new‐born rat. It is concluded that the monosynaptically evoked stretch reflex response in the triceps surae muscle first appear at embryonic day 19.5. Natural and electrical stimulation of the plantar skin evoked a reflex response with long latencies in flexor muscles. Such a cutaneous reflex was first present at embryonic day 17.5, two days earlier than the onset of the stretch reflex.
The absence of spread of adaptation between rod photoreceptors in turtle retina.
Authors: Copenhagen D R , Green D G
Published: December 2014

Adaptation by weak backgrounds and the spatial spread of desensitization between rods was studied in the snapping turtle retina, Chelydra serpentina. Intracellular membrane potentials were recorded from these photoreceptors in an eyecup preparation. The kinetics and sensitivity of rod responses were changed significantly by large, very dim backgrounds. For the twenty‐five most sensitive rods where the dark‐adapted flash sensitivity, SDF, was greater than 1.0 mV/Rh*, Rh* being the number of effective photo‐isomerizations per rod, the background intensity required to halve the amplitude of the linear range response averaged 0.21 Rh* s‐1. The time‐to‐peak of the test responses was reduced up to 50% by these dim backgrounds. The desensitizing effects of full field backgrounds of various intensities on the responses to large test spots were measured. The dependence of incremental flash sensitivity, SF, on background intensity, IB, followed the form (FORMULA: SEE TEXT) where I0 is the background intensity which halved SDF. The same intensity dependence held for slit‐shaped background fields that desensitized responses to small test spots. The desensitizing effects of large, very dim flashed and continuous backgrounds took several seconds to appear and decay to dark levels. This in conjunction with the sparsity of photons suggests, that the desensitization from a single photoisomerization can persist for several seconds. A comparison of the desensitizing effects of spot and annular backgrounds revealed that small spot backgrounds superimposed on the centered test spots desensitized rods more effectively than annular fields. This finding held true even when annular patterns produced a greater maintained hyperpolarization in the rods. Thus, there was no unique relationship between desensitization and the steady maintained hyperpolarization evoked by a background field. The dependence of adaptation on distance from the impaled rod was determined with slit‐shaped background fields placed at different positions across the rod's receptive field. The desensitizing effect of displaced slit stimuli was found to decline much more rapidly with distance than excitation. Displacing the slit by 20 micron from the centre reduced its desensitizing effect by more than 1 log unit. In contrast, excitation fell to about 80% at the same distance (lambda ranging from 50 to 70 micron). The fall off of desensitization with distance matched the calculated fall off with distance of light scatter from a slit. No difference was noted in the kinetics of test responses in the presence of equally desensitizing, superimposed and displaced slits.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium‐force relationships as detected with aequorin in two different vascular smooth muscles of the ferret.
Authors: DeFeo T T , Morgan K G
Published: December 2014

The bioluminescent calcium indicator aequorin was chemically loaded into isolated strips of ferret portal vein and ferret aorta. Aequorin light emission (a function of [Ca2+]i) was recorded simultaneously with tension. Assuming an [Mg2+]i of 0.5 mM, [Ca2+]i was 1.8 X 10(‐7) M in the unstimulated portal vein at 22 degrees C where there was negligible resting tone. In contrast, in the unstimulated aorta at 22 degrees C where there was significant basal tone, the [Ca2+]i was 2.7 X 10(‐7) M. In both portal vein and aorta, potassium depolarization caused a monophasic rise in intracellular Ca2+ in parallel with the rise in tension, whereas phenylephrine caused an initial spike of light during the period of the force development which then fell to a much lower plateau level during the period of force maintenance. Calcium‐force curves were generated by plotting calibrated aequorin light against force while intracellular [Ca2+] was made to change either by increasing degrees of potassium depolarization or decreasing extracellular [Ca2+]. The steady‐state calcium‐force curve in the presence of phenylephrine was shifted to the left of the curve in the presence of potassium depolarization in both the portal vein and aorta. In the aorta there was a counter‐clockwise hysteresis in the calcium‐force relationship. In contrast, in the portal vein there was no demonstrable hysteresis, indicating that the apparent change in calcium sensitivity of the contractile apparatus in the presence of phenylephrine must be caused by a second messenger other than calcium.
Activation of cat muscle spindles by static skeletofusimotor axons.
Authors: Jami L , Petit J , Scott J J
Published: December 2014

The discharges from primary and secondary spindle endings of the cat peroneus tertius muscle were recorded during stimulation of static skeletofusimotor (static beta) axons at frequencies comparable with the presumed range of motoneuronal firing rates. When stimulated at 20‐40/s, static beta‐axons exerted typical static actions on the spindles they innervated, including activation of primary endings with reduction of their dynamic sensitivity and activation of secondary endings. For these frequencies, the extrafusal portions of static beta‐motor units developed unfused contractions producing oscillations of tension within the muscle. After suppression of extrafusal contractions, the effects of the stimulation of static beta‐axons on spindle discharge could persist unaltered, showing that extrafusal events need not interfere with the specific intrafusal actions of static beta‐axons. Stimulation of a static beta‐axon at 20‐40/s often elicited a response of primary endings in which the discharge exactly followed the stimulation frequency, i.e. it was driven 1:1. Purely mechanical excitation of a spindle by unfused extrafusal contractions could also drive its discharge at the stimulation frequency. The persistence of static beta‐driving after suppression of extrafusal contraction provided evidence for its intrafusal origin. Driving elicited by static beta‐axons could persist during changes in muscle length, but small fluctuations in the delay between each impulse and the preceding stimulus were observed. These fluctuations were clearly related to the changes in muscle length, indicating that although the primary ending discharge remained driven 1:1 at the stimulation frequency, the receptor was not totally insensitive to length changes.
Adenosine agonists reduce voltage‐dependent calcium conductance of mouse sensory neurones in cell culture.
Authors: MacDonald R L , Skerritt J H , Werz M A
Published: December 2014

Adenosine and several of its analogues produced a concentration‐dependent shortening of calcium‐dependent action potential (c.a.p.) duration of mouse dorsal root ganglion (d.r.g.) neurones in dissociated cell culture. The following rank order of potency was obtained: N6‐(L‐phenylisopropyl)adenosine greater than N6‐(D‐phenylisopropyl)adenosine greater than N6‐cyclohexyladenosine greater than 2‐chloroadenosine much greater than 1‐methylisoguanosine greater than adenosine. Effects of adenosine agonists on c.a.p. duration were blocked by methylxanthine adenosine antagonists. Adenosine monophosphate (AMP) and cyclic AMP shortened c.a.p.s in d.r.g. neurones, while ATP also depolarized cells. Voltage‐clamp analysis revealed that the effect arose from reduction of a voltage‐dependent calcium conductance. Adenosine agonists reduced depolarization‐evoked inward currents but did not alter membrane conductance following blockade of calcium channels by cadmium. Additionally, adenosine reduced the instantaneous current‐voltage slope (chord conductance) during step commands that produced maximal activation of voltage‐dependent calcium conductance. If effects of adenosine on neuronal somata and synaptic terminals are similar, adenosine agonists may inhibit neurotransmitter release in the central nervous system by inhibiting a voltage‐dependent calcium conductance. Since effects of adenosine agonists did not correspond with their relative potencies as modulators of adenylate cyclase activity or inhibitors of neurotransmitter release in peripheral tissues, a novel adenosine receptor may be involved in regulation of this conductance.
Calcium‐activated potassium channels in single smooth muscle cells of rabbit jejunum and guinea‐pig mesenteric artery.
Authors: Benham C D , Bolton T B , Lang R J , Takewaki T
Published: December 2014

Single‐channel studies were made using the patch‐clamp technique of K channels in dispersed single smooth muscle cells from rabbit longitudinal jejunal muscle and guinea‐pig small (less than 0.2 mm o.d.) mesenteric arteries. In isolated inside‐out patches from these two types of smooth muscle cell there was a population of K channels which had single‐channel conductances of about 100 pS in near physiological K gradients and about 200 pS with symmetrical 126 mM‐K solutions. Their conductance and other properties distinguish them from a K channel of smaller conductance which we have previously described in these cells. The relative permeability of the channel with respect to K was 1.4 Tl:1.0 K:0.7 Rb: less than 0.05 Na: less than 0.05 Cs. Cs (1 mM applied to the outside of the membrane) interfered with inward K movement when the membrane was hyperpolarized. Rb conductance of the channel when both sides of the membrane were exposed to 126 mM‐Rb was 30 pS. When the Ca concentration on the inside of the membrane ([Ca]i) was about 10(‐9) M, K channel opening was rarely observed and then only at strongly positive potentials. At [Ca]i between 10(‐9) M and 10(‐7) M mean channel open time increased and the probability of channel opening increased steeply; both were further increased by increasing membrane positivity. At [Ca]i between 10(‐6) M and 2.5 mM the channel was mainly in the open state and the probability of channel conducting state often declined with increasing membrane positivity. The effects of varying [Ca]i from 10(‐7) M to 2.5 mM on the kinetic activity of a single channel was studied largely in mesenteric artery patches containing one active channel. The distribution of open times could be fitted by a single exponential at low (less than 10(‐6) M) [Ca]i but a component of fast openings (to less than 1.0 ms) was observed at all potentials at [Ca]i 2.5 mM. Closed time distribution required the sum of three exponentials to fit it all [Ca]i greater than 10(‐7) M; at [Ca]i 10(‐6) M or greater evidence of a fourth component, probably caused by Ca block of open channels, was obtained. Raising [Ca]i increased the mean duration of the (long) open state and decreased or had no effect on the duration of short, intermediate, and long mean closed states.
Carbonic anhydrase in the sarcoplasmic reticulum of rabbit skeletal muscle.
Authors: Bruns W , Dermietzel R , Gros G
Published: December 2014

Sarcoplasmic reticulum vesicles and mitochondria were prepared from red and white skeletal muscles of the rabbit. The preparations were characterized in terms of their specific activities of citrate synthase, basal (Mg2+‐dependent) and Ca2+‐dependent ATPase (the latter two in the presence of NaN3 and ouabain), and their specific carbonic anhydrase activities were determined. Skeletal muscle mitochondria had high specific activities of citrate synthase (700‐1200 mu. mg protein‐1) and low carbonic anhydrase activities (0.1‐0.4 u. ml mg protein‐1). The latter are likely to be due to a contamination of the preparations with sarcoplasmic reticulum (s.r.) Preparations of s.r. vesicles showed negligible activities of citrate synthase and the expected differing patterns of basal and Ca2+‐dependent ATPase in red and white muscles. Specific carbonic anhydrase activities in s.r. from both muscle types were high (2‐4 u. ml mg protein‐1). The highest carbonic anhydrase activity, 11 u. ml mg protein‐1, was found in s.r. from rabbit m. masseter. The inhibition constant of s.r. carbonic anhydrase towards acetazolamide was 4‐6 X 10(‐8) M and similar but not identical to that of cytosolic carbonic anhydrase II. It appears possible that the carbonic anhydrase II‐like enzyme previously found by us in muscle homogenates (Siffert & Gros, 1982) originates from the s.r. Histochemical studies using the dansylsuphonamide method described previously (Dermietzel, Leibstein, Siffert, Zamboglou & Gros, 1985) showed an intracellular pattern of carbonic anhydrase staining compatible with the presence of the enzyme in s.r.: spots homogeneously distributed across the fibre cross‐sections in transversely sectioned fibres and thin, longitudinally oriented, bands in longitudinally sectioned fibres. It is estimated that s.r. carbonic anhydrase accelerates CO2 hydration within the s.r. approximately 1000‐fold. Thus, CO2 and HCO3‐ react fast enough to provide a rapid source and sink for protons leaving and entering the s.r. in exchange for Ca2+.
Lesions in the cat prepositus complex: effects on the optokinetic system.
Authors: Cheron G , Gillis P , Godaux E
Published: December 2014

The effects of bilateral lesions within and around the prepositus hypoglossi (p.h.) nuclei on the optokinetic system were studied. The pure optokinetic nystagmus (o.k.n.) was evoked by a step of velocity (60 deg/s, 30 s duration) of the surrounding. The visual‐vestibular interaction was investigated by measuring the gain and phase of the vestibulo‐ocular reflex (v.o.r.) as a function of frequency before and after lesion under three different conditions of testing: basic v.o.r. tested in the dark, v.o.r. tested in the light and v.o.r. suppressed by vision. The tested amplitude was +/‐ 20 deg. A posterior vermectomy was performed for controls in two cats. A bilateral electrolytic p.h. lesion including the rostral pole of this nucleus was added to the posterior vermectomy in three cats. A lesion similar but sparing the rostral pole of the nucleus was carried out in three other cats. In one cat a bilateral electrolytic lesion of the medial vestibular nuclei (m.v.n.) was combined with a posterior vermectomy. In two cats the medulla was cut on the mid line after a posterior vermectomy. The posterior vermectomy affected neither the optokinetic response nor the visual‐vestibular interactions. In cats where p.h. lesion included its rostral pole and in the cat with m.v.n. lesion, all the tested optokinetic effects (step o.k.n., and visual‐vestibular interactions) were abolished. In the three cats where p.h. lesion spared its rostral pole, the optokinetic effects were quite normal in one cat, mildly reduced in the second one, and seriously affected but not completely abolished in the third one. The surgical cut of the medulla on the mid line did not dramatically disturb the various optokinetic effects. The most marked deficit was the loss of the optokinetic after‐nystagmus (o.k.a.n.). From the comparison of these results with the neuroanatomical data and with the Robinson's model concerning the optokinetic processing, it was suggested that: (a) the rostral p.h. could be the location of the o.k.n. integrator or could be an essential link on the o.k.n. pathway, (b) the posterior four‐fifths of the p.h. could not be an essential relay on the o.k.n. pathway, (c) the loss of o.k.a.n. after mid‐line lesion could be due to the interruption of the positive feed‐back loop formed by the reciprocal inhibitory connexions between the two m.v.n.
Extracellular activation and membrane conductances of neurones in the guinea‐pig deep cerebellar nuclei in vitro.
Authors: Jahnsen H
Published: December 2014

The responses of cerebellar nuclear cells to extracellular stimulation in a slice preparation were studied and the ionic basis of their electroresponsiveness was investigated with blockers of membrane conductances and with ion substitutions in the extracellular medium. The cells could be activated antidromically from the cerebellar cortex and the white matter surrounding the nuclei. The dominating response to orthodromic stimulation was an inhibitory synaptic potential presumably produced by activation of Purkinje cell fibres. The action potentials and the subthreshold spikelets were shown to be Na+ dependent and are presumably generated by a voltage‐dependent inactivating Na+ conductance. Plateau potentials with a low threshold were also Na+ dependent, but these long‐lasting potentials are probably produced by activation of a voltage‐dependent non‐inactivating Na+ conductance. Plateau potentials with a high threshold and high‐threshold spikelets were Ca2+ dependent and seem to be generated by non‐inactivating and possibly inactivating Ca2+ conductances. The spike after‐hyperpolarizations had an early voltage‐dependent K+ component and a late Ca2+‐dependent K+ component. They are therefore produced by voltage‐sensitive and Ca2+‐dependent K+ conductances. By analogy with the distribution of conductances in Purkinje cells it is proposed that the Na+ conductances are mainly located in the somatic and axonal membrane and that the Ca2+ conductances are located in the dendrites. The functional implications of the complex electroresponsive properties of cerebellar nuclear cells are discussed.
Voltage dependence of 5‐hydroxytryptamine release at a synapse between identified leech neurones in culture.
Authors: Dietzel I D , Drapeau P , Nicholls J G
Published: December 2014

The release of 5‐hydroxytryptamine (5‐HT) from presynaptic terminals has been studied by the voltage‐clamp technique at synapses made by isolated Retzius and pressure (P) sensory neurones dissected from the leech C.N.S. and maintained in tissue culture. At these synapses facilitation, depression and modulation of release occur with action potentials and with voltage‐clamp pulses. Depolarization of Retzius cells from a constant holding potential by steps of varying amplitude (5 ms in duration) caused graded release of 5‐HT. The steep transfer function for release using these short test pulses resembled that seen at the giant synapse of the squid: synaptic potentials increased markedly with presynaptic depolarizations beyond ‐25 mV and decreased with large depolarizing pulses beyond +40 mV. When the steady holding potential of voltage‐clamped Retzius cells was suddenly displaced to a new value within the range of ‐40 mV to ‐85 mV, there followed a slow but smaller change of the post‐synaptic P‐cell membrane potential in the same direction. After an initial delay of about 40 ms, the post‐synaptic potential reached its new level with an exponential time course and a time constant of 0.7 s. Since Retzius and P cells are not electrically coupled, these effects can be accounted for by alterations in tonic release of transmitter. Changes of presynaptic holding potential to a more depolarized level resulted in an increase in voltage noise recorded in the P cell. Conversely, hyperpolarization from a depolarized level reduced noise. Noise analysis showed that these changes could be accounted for by quantal events with a mean amplitude of about 0.15 mV. This value is similar to that for spontaneous miniature potentials and quantal fluctuations observed at synapses between Retzius and P cells. Changes in steady holding potential also had marked effects upon the transfer function observed with brief depolarizing pulses of the Retzius cell. The post‐synaptic responses evoked by depolarizations to 0 mV with pulses of 5 ms duration were reduced in amplitude as the holding potential of the Retzius cell was increased from the resting value of ‐45 to ‐75 mV. For example, depolarization to 0 mV starting from ‐45 mV evoked synaptic potentials as much as ten times larger than those evoked by depolarizations to 0 mV starting from ‐75 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
Actions of noradrenaline recorded intracellularly in rat hippocampal CA1 pyramidal neurones, in vitro.
Authors: Madison D V , Nicoll R A
Published: December 2014

CA1 pyramidal neurones were studied in rat in vitro hippocampal slices using standard intracellular and single‐electrode voltage‐clamp recording techniques to examine the actions of noradrenaline (NA). NA had two different effects on the resting membrane potential of pyramidal neurones; either a hyperpolarization accompanied by a decrease in membrane input resistance, or less commonly, a depolarization accompanied by an increase in input resistance. In many cells, both effects, a hyperpolarization followed by a depolarization were observed. The depolarization was mediated by a noradrenergic beta‐receptor. The hyperpolarization was more difficult to characterize, but may result from alpha‐receptor activation. NA reduced the amplitude and duration of the slow calcium‐activated potassium after‐hyperpolarization (a.h.p.) that follows depolarization‐induced action potentials. This action of NA was mediated by beta 1‐noradrenergic receptors. NA, in the presence of tetrodotoxin and tetraethylammonium, reduced the a.h.p. without reducing the size of the calcium action potential which preceded it. This was unlike the action of the calcium channel blocker, cadmium, which reduced the calcium action potential and the a.h.p. in parallel. Furthermore, NA did not reduce the amplitude of calcium or barium currents recorded under voltage clamp after blockade of potassium currents. A functional consequence of this blockade of the calcium‐activated a.h.p. was a reduction of the accommodation of action potential discharge such that the excitatory responses of the neurone to depolarizing stimuli, such as glutamate application or current passed through the recording electrode, were enhanced. We conclude that the effects of NA on calcium‐activated potassium conductance and on resting membrane potential can interact to increase the signal‐to‐noise ratio of hippocampal pyramidal neurone responsiveness.
Some characteristics of histamine secretion from rat peritoneal mast cells stimulated with nerve growth factor.
Authors: Pearce F L , Thompson H L
Published: December 2014

Nerve growth factor (NGF) isolated from mouse submandibular gland or from snake venom produced a dose‐dependent release of histamine from isolated rat peritoneal mast cells. The response was almost totally dependent on the presence of extracellular calcium ions and on added phosphatidylserine or its lyso‐derivative. At high concentrations, strontium ions could substitute for calcium. The process was non‐cytotoxic, relatively slow, pH dependent and blocked by polyclonal antibodies to NGF. Binding of NGF to the mast cell was not dependent on added calcium. The release was unaffected by low molecular weight glucose polymers or specific quaternary ammonium salts and thus differed from that evoked by clinical dextran or polyamines. The release was not inhibited by soluble rat IgE or IgG and was unimpaired in mast cells recovered from specific pathogen free rats. As such it did not appear to be mediated through interaction with cell‐fixed antibodies. The process further differed from anaphylactic histamine release in that there was no accompanying change in the intracellular level of adenosine 3',5'‐cyclic monophosphate (cyclic AMP), the activated state induced by NGF was much more persistent than that evoked by antigen, and there was no cross‐desensitization between the two latter stimuli. In total, these data suggest that NGF may induce secretion from rat mast cells by interaction with a specific receptor on the plasma membrane, possibly similar to that present on sensory and sympathetic neurones.
A patch‐clamp study of potassium currents in resting and acetylcholine‐stimulated mouse submandibular acinar cells.
Authors: Gallacher D V , Morris A P
Published: December 2014

Salivary acini were enzymatically isolated from submandibular glands of adult male mice. The patch‐clamp technique was employed to investigate the conductive properties and activities of a large‐conductance K+ channel in both cell‐attached and in excised patches of basolateral acinar cell membranes. In excised, inside out, patches with identical high‐K+ solutions (145 mM‐KCl) on either side of the membrane the current‐voltage (I‐V) plot was linear. The mean single‐channel conductance was 245 +/‐ 4.8 ps with a single‐channel permeability of 4.6 X 10(‐13) cm3 s‐1. At Ca2+ concentrations of 10(‐9)‐10(‐8) M bathing the intracellular membrane face the channel was exquisitely sensitive to changes in transmembrane potential, i.e. voltage sensitive. At 10(‐7) M‐Ca the channel was almost always open and displayed little sensitivity to voltage. Single‐channel currents were recorded in cell‐attached patches. When the recording pipettes contained the high‐K+ solution the I‐V plots were linear and the mean single‐channel conductance and permeability almost identical to that in the excised patches. The mean spontaneous resting potential of the acinar cells bathed in physiological saline (140 mM‐NaCl, 4.5 mM‐KCl) was ‐43 +/‐ 1.8 mV. The voltage sensitivity of the in situ K+ channel was very similar to that recorded in excised patches at 10(‐9)‐10(‐8) M‐Ca. In experiments designed to reproduce the physiological ionic gradients across the patch membrane pipettes were filled with the high‐Na+ solution. The I‐V plot was not linear but showed pronounced rectification at negative membrane potentials. The channel is K+ selective and the extrapolated reversal potential was close to ‐90 mV. The single‐channel conductance at the spontaneous resting membrane potential was about 35 pS. The single‐channel permeability was however only slightly reduced at 4.29 X 10(‐13) cm3 s‐1. It was demonstrated that current flow through the open K+ channel could be accurately modelled using constant field electrodiffusion theory. Continuous in situ recordings before and after application of the agonist acetylcholine to the solution bathing the acini revealed that acetylcholine stimulation is associated with a marked increase in the frequency and duration of K+ currents in the patch membrane. The increased current activity in the patch membrane during acetylcholine application must be mediated via an intracellular second messenger and was very similar to that observed in the excised patches on increasing ionized Ca2+ concentrations from 10(‐8) to 10(‐7) M.(ABSTRACT TRUNCATED AT 400 WORDS)
Observations on the automatic compensation of reflex gain on varying the pre‐existing level of motor discharge in man.
Authors: Matthews P B
Published: December 2014

The human stretch reflex is well known to show 'automatic gain compensation'; in other words, the electromyographic (e.m.g.) response evoked by a given disturbance increases progressively with the level of pre‐existing voluntary activity, and so remains an approximately constant proportion of the background. Such behaviour has now been observed using vibration as the stimulus to Ia action and recording the reflexly developed force, in addition to the e.m.g. Inhibition was studied as well as excitation by vibrating the antagonist as well as the agonist, and found to be similarly regulated. The experiments were performed on the elbow flexors while they were contracting isometrically under voluntary drive. The vibration was either square‐wave modulated at 5 Hz or delivered in bursts of one to five pulses. The latency of the e.m.g. responses produced by the latter was sufficiently short to show that gain compensation was a feature of spinal reflex action. In the Discussion, it is concluded that in principle 'automatic gain compensation' can be readily attributed to the known organization of the motoneurone pool. As the background force increases so does the number of active motoneurones available to be frequency‐modulated by a given input, and the larger and stronger will be those motor units which are on the verge of recruitment or de‐recruitment.
Labile heat and changes in rate of relaxation of frog muscles.
Authors: Peckham M , Woledge R C
Published: December 2014

Observations were made of the labile heat and the progressive slowing of relaxation as a function of tetanus duration (Abbott effect) during isometric tetani of frog extensor longus digiti IV (e.l.d. iv) and sartorius muscle. Both the labile heat and slowing of relaxation are less marked in e.l.d. iv than in sartorius muscle. Both effects are depressed to the same extent in the second of two closely spaced tetani in sartorius muscle. The repriming of both effects follows the same time course in sartorius muscle. The hypothesis is discussed that both effects result from binding of calcium to parvalbumin during a tetanus, and that their repriming is due to the removal of calcium from parvalbumin by the sarcoplasmic reticulum.
Innervation and function of hind‐limb muscles in the cat after cross‐union of the tibial and peroneal nerves.
Authors: Gordon T , Stein R B , Thomas C K
Published: December 2014

Peripheral nerves to flexor (common peroneal) and extensor (tibial) nerves in a hind limb of seven 2‐6 month old cats were cut and cross‐united to study the plasticity in the spinal cord. The extent to which motoneurones from extensor and flexor motor pools were misdirected to their antagonistic muscles was determined by measuring the potentials generated at the spinal roots from the crossed nerves. The axons contributing to the extensor nerves normally leave the cord in the L7 and S1 ventral and dorsal roots while the axons contributing to the flexor nerves normally leave the cord in the L6 and L7 ventral and dorsal roots. Following cross‐union, medial gastrocnemius (m.g.) and lateral gastrocnemius‐soleus (l.g.s.) nerves were primarily supplied by L6 and L7 ventral and dorsal roots, and common peroneal (c.p.) nerves were primarily supplied by L7 and S1 ventral and dorsal roots. A method for quantifying the completeness of cross‐reinnervation was developed. The pattern of e.m.g. activity in cross‐reinnervated muscles during locomotion was primarily determined by the innervating nerve with the reinnervated flexor muscles being activated during the extensor phase. However, the cross‐reinnervated extensor muscles showed evidence of extensor activity in addition to the double‐burst pattern typical of flexor nerves. This extensor activity was more prominent when the nerve cross was less complete. We conclude that during locomotion the activity of spinal motoneurones was not substantially modified by inappropriate peripheral connexions, even when the nerve cross was carried out in young animals. This conclusion is discussed in relation to previous studies which suggested some degree of functional modification.
Vasoactive intestinal polypeptide depolarizations in cat bladder parasympathetic ganglia.
Authors: Akasu T , Gallagher J P , Hirai K , Shinnick-Gallagher P
Published: December 2014

The effect of vasoactive intestinal polypeptide (VIP) on the neuronal membranes of isolated cat vesical pelvic ganglia and its underlying ionic mechanism were examined by means of intracellular recording and voltage‐clamp techniques. Application of VIP (0.05‐50 microM) to the neurones by pressure 'puff' ejection through a micropipette placed close to the neurones produced a depolarizing response (2‐15 mV) in 83% of neurones tested; this effect was concentration dependent. The VIP‐induced depolarization frequently evoked spontaneous action potentials in quiescent neurones and increased the frequency of action potentials in spontaneously firing neurones. The VIP depolarization was not blocked in a Ca2+‐free, high‐Mg2+ solution or in a solution containing hexamethonium (1 mM) and atropine (1 microM). Tetrodotoxin (TTX; 1 microM) also did not affect the VIP depolarization. The VIP depolarization was associated with an increase in membrane resistance and the slope of a current‐voltage relation (I‐V curve) was increased by VIP. Conditioning hyperpolarization and depolarization of the membrane increased and decreased the amplitude of the VIP depolarization, respectively. The VIP depolarization reversed polarity around‐‐100 mV. The reversal potential shifted about 20 mV to a more positive level in a high‐K+ (10 mM) solution in accord with the Nernst equation. Substituting Cl‐ with isethionate in the superfusate did not affect the reversal potential of the VIP depolarization. Closure of M‐channels does not underlie VIP action since the VIP depolarization was enhanced by muscarine (10 microM) and unchanged in the presence of Ba (5 mM), or intracellular or extracellular Cs+, conditions known to block the M‐channels (Adams, Brown & Constanti, 1982a, b). Tetraethylammonium (TEA; 20 mM) also did not affect the VIP depolarization. Voltage‐clamp analyses showed that VIP applied by pressure ejection produced an inward current of 80‐110 pA associated with a decrease in membrane conductance (from 2.8 to 3.5 nS) at a holding potential of‐‐60 mV. VIP inward current was diminished by either repetitive or continuous application of VIP (5 microM) suggesting desensitization of the VIP receptor. It is concluded that VIP produces a depolarization in neurones of bladder parasympathetic ganglia by decreasing a K+ conductance, the pharmacological characteristics of which are unlike previously described K+ conductance mechanisms.
Multilocular adipocytes from muscovy ducklings differentiated in response to cold acclimation.
Authors: Barré H , Cohen-Adad F , Duchamp C , Rouanet J L
Published: December 2014

Morphological and functional aspects of adipose tissue from 6‐week‐old cold‐acclimated muscovy ducklings reared at 4 degrees C ambient temperature (Ta) from the age of 1 week were examined for the occurrence of brown adipose tissue (b.a.t.) in order to explain non‐shivering thermogenesis (n.s.t.) observed at this age. Metabolic rate and integrated muscle electrical activity (e.m.g.) were measured at different Ta (from ‐10 to +28 degrees C) in cold‐acclimated and in control ducklings reared at thermoneutrality. The results confirm the existence of n.s.t. in 6‐week‐old cold‐acclimated muscovy ducklings. In cold‐acclimated ducklings, typical multilocular adipocytes were found in subcutaneous adipose deposits instead of the unilocular white adipocytes as in control ducklings. Mitochondria isolated from this differentiated tissue were less abundant than in b.a.t. of mammals. Their respiration rate was similar to the respiration rate of white adipose tissue mitochondria from control rats and much lower than the b.a.t. mitochondria rate from cold‐acclimated rats. It is therefore unlikely that this differentiated adipose tissue contributes to the n.s.t. observed, an n.s.t. whose capacity reached 5.26 W/kg (+73.5% above resting metabolic rate) in cold‐acclimated ducklings. The role of this differentiated adipose tissue in the metabolic adaptation to cold is discussed.
Selective block of inward but not outward rectification in rat sensory neurones infected with herpes simplex virus.
Authors: Mayer M L
Published: December 2014

Neurones from the dorsal root ganglia of neonatal rat pups were grown in tissue culture and voltage clamped using patch electrodes for whole cell recording. The electrodes were filled with a KMeSO4 solution containing 1.1 mM‐EGTA. 15‐24 h prior to recording cultures were infected with one of three strains of herpes simplex virus type 1 previously characterized on the basis of a cell fusion assay in cultures of the MRC‐5 and BHK‐21 cell lines. Infection of sensory neurones with either of the two non‐syncitial strains of virus caused a nearly complete loss of the hyperpolarization‐activated inward rectifying conductance normally present in these neurones, but did not appear to affect depolarization‐activated, calcium‐dependent outward currents or voltage‐dependent delayed outward rectification. The loss of inward rectification appeared to result from inactivation of the underlying conductance mechanism, rather than from a shift in the gating properties of the conductance mechanism to unphysiological values. In contrast to these results inward rectification was present in sensory neurones infected with another, syncitial, strain of herpes simplex virus. However, quantitative analysis suggested a reduced availability compared to that recorded in uninfected neurones.
Experimental human muscle damage: morphological changes in relation to other indices of damage.
Authors: Jones D A , Newham D J , Round J M , Tolfree S E
Published: December 2014

The effects of eccentric exercise have been examined in human calf and biceps muscles. Release of muscle creatine kinase and uptake of technetium pyrophosphate have been followed for up to 20 days after the exercise and the results are related to the morphological changes seen in needle biopsy samples. The response to exercise was variable, all subjects developing pain and tenderness in the exercised muscles after 1‐2 days and this was followed, in most subjects, by a large increase in plasma creatine kinase 4‐6 days after the exercise. This was paralleled by an increased uptake of technetium pyrophosphate into the exercised muscle. Biopsies of the affected muscles showed little or no change in the first 7 days after the exercise but later degenerating fibres were seen, as well as infiltration by mononuclear cells and eventually, by 20 days, signs of regeneration. Very extensive changes were seen in the calf muscle of one subject; changes in the biceps were qualitatively similar but not so severe. In the severely affected calf muscle type II fibres were preferentially damaged. Mononuclear cell infiltration both between and within degenerating fibres was maximal well after the time of peak plasma creatine kinase and it is likely that in eccentrically exercised muscle infiltrating mononuclear cells act to scavenge cellular debris rather than to cause damage to the muscle.
Calcium levels measured in a presynaptic neurone of Aplysia under conditions that modulate transmitter release.
Authors: Connor J A , Kretz R , Shapiro E
Published: December 2014

We have utilized the Ca2+ indicator dye, Arsenazo III, to examine the role of presynaptic Ca2+ concentration in two types of synaptic plasticity observed at the synapses of cell L10 in Aplysia californica; post‐tetanic potentiation (p.t.p. ‐ the increased transmitter release which follows high frequency stimulation), and resting membrane potential modulation of release. Intracellular Ca2+ was monitored in the cell body and main neurites of L10 injected with Arsenazo III. Tetanic stimulation caused an increase in intracellular Ca2+ concentration that decayed, after tetanus, with fast and slow time constants which paralleled the time course of decay of p.t.p. When the voltage‐sensitive Ca2+ current was reduced by removing external Ca2+ (0 mM‐Ca2+, 4 mM‐EGTA) or by blocking Ca2+ channels with divalent cation channel blocker (4 mM‐Cd2+), tetanic stimulation did not cause increases in Arsenazo absorbance even when Na+ currents were not blocked. This finding suggests that Ca2+ entering the cell through voltage‐dependent Ca2+ channels was the major source of Ca2+ which accumulated during the tetanus. Transmitter release is increased when L10 is maintained at a depolarized membrane potential, and is decreased when L10 is hyperpolarized. We found that the base‐line Arsenazo absorbance signal in L10 increased when L10 was depolarized from ‐60 to ‐40 mV and decreased when L10 was hyperpolarized. This finding supports the idea that the steady‐state Ca2+ concentration contributes to the membrane‐potential modulation of transmitter release. These results support the idea that transmitter release can be modulated by the residual or resting Ca2+ concentration of the presynaptic cell.
Circadian variation in sensitivity of suprachiasmatic and lateral geniculate neurones to 5‐hydroxytryptamine in the rat.
Authors: Mason R
Published: December 2014

Extracellular single‐unit recordings were obtained from neurones in the suprachiasmatic nuclei (s.c.n.) of the rat (a putative circadian pace‐maker), the ventral lateral geniculate nucleus (v.l.g.n.) and the hippocampus. These areas receive a 5‐hydroxytryptamine (5‐HT) innervation from the raphe nuclei. Recording of neuronal activity in the s.c.n., v.l.g.n. and the hippocampus revealed a diurnal variation in the response to the ionophoresis of 5‐HT. This variation was manifest as a 2‐3‐fold increase in post‐synaptic sensitivity to 5‐HT during the subjective dark (active) phase of the circadian cycle. In contrast there was no apparent circadian variation in the sensitivity of s.c.n., v.l.g.n. or hippocampal neurones to ionophoresed gamma‐aminobutyric acid (GABA). Neuronal activity recorded in the s.c.n., v.l.g.n. and hippocampus also exhibited a circadian variation in the recovery from 5‐HT‐induced suppression of firing. This may reflect reuptake processes as recovery can be prolonged by ionophoresis of uptake blockers (imipramine or fluoxetine). Rats (n = 15) expressing circadian arrhythmicity in their rest‐activity behaviour induced by long‐term continuous illumination (150‐200 lx) showed no apparent circadian variation in 5‐HT sensitivity. This loss was accompanied by either the development of a 5‐6‐fold subsensitivity to ionophoresed 5‐HT (eleven out of fifteen rats) or a 2‐3‐fold supersensitivity to ionophoresed 5‐HT (four out of fifteen rats). A similar loss of circadian variation and the development of a subsensitivity to ionophoresed 5‐HT was also found in three rats sustaining complete electrolytic lesions of the s.c.n. These changes were not found in rats (n = 4) with partial s.c.n. lesions. These results implicate the s.c.n., or fibres passing through it, in the circadian modulation of 5‐HT sensitivity in neurones both intrinsic to the s.c.n. circadian pace‐maker itself and in the hippocampus and lateral geniculate nucleus (regions remote from the s.c.n.).