bluuebunny/crossref_metadata_2025 huggingface dataset:
A unique amino acid of the Drosophila GABA receptor with influence on drug sensitivity by two mechanisms.
Authors: Zhang H G , ffrench-Constant R H , Jackson M B
Published: December 2014

1. The Drosophila gene Rdl (resistance to dieldrin) encodes a GABA receptor. An alanine‐to‐serine mutation in this gene at residue 302 confers resistance to cyclodiene insecticides and picrotoxin. Patch clamp analysis of GABA receptors in cultured neurons from wild type and mutant Drosophila was undertaken to investigate the biophysical basis of resistance. 2. In cultured neurons from both wild type and mutant strains, GABA activated a channel that reversed near 0 mV in symmetrical chloride. GABA dose‐response characteristics of wild type and mutant receptors were very similar. 3. GABA responses in neurons from the mutant strains showed reduced sensitivity to the GABA antagonists picrotoxin, lindane and t‐butyl‐bicyclophosphorothionate. Resistance ratios were 116, 970 and 9 for the three blockers, respectively. Inhibition increased with blocker concentration in a manner consistent with saturation of a single binding site. 4. The mutation reduced the single channel conductance by 5% for inward current and 17% for outward current. The single channel current was approximately 60% lower for outward current than for inward current in both wild type and mutant. 5. Open and closed times were both well fitted by the sum of two exponentials. Resistance was associated with longer open times and shorter closed times, reflecting a net stabilization of the channel open state by a factor of approximately five. 6. The mutation was associated with a marked reduction in the rate of GABA‐induced desensitization, and a net destabilization of the desensitized conformation by a factor of 29. 7. The Rdl mutation manifests resistance through two different mechanisms. (a) The mutation weakens drug binding to the antagonist‐favoured (desensitized) conformation by a structural change at the drug binding site. (b) The mutation destabilizes the antagonist‐favoured conformation in an allosteric sense. The global association of a single amino acid replacement with cyclodiene resistance suggests that the resistance phenotype depends on changes in both of these properties, and that insecticides have selected residue 302 of Rdl for replacement because of its unique ability to influence both of these functions. 8. The location of alanine 302 in the sequence of the Rdl gene product supports a mechanism of action in which convulsants such as picrotoxin bind within the channel lumen, where they induce a rapid conformational change to the desensitized state.
Lemniscal and non‐lemniscal synaptic transmission in rat auditory thalamus.
Authors: Hu B , Senatorov V , Mooney D
Published: December 2014

1. The central auditory pathway linking the inferior colliculus (IC) and the medial geniculate body (MGB) of the thalamus consists of a segregated ventral lemniscal and dorsal non‐lemniscal projection whose synaptic transmission mechanisms remain unknown. Extracellular and intracellular recordings combined with axonal tract tracing and cell staining were made from lemniscal and non‐lemniscal divisions of adult rat MGB maintained acutely in in vitro explants containing parallel tectothalamic projections. 2. Biocytin deposition within the brachium of the IC revealed dense axonal fibres projecting to the MGB. Thin axonal terminals were found throughout the ventral (MGv) and dorsal (MGd) divisions of the MGB. Bushy cells with tufted or bitufted dendritic branches were primarily found in the MGv. In the MGd, cells were mainly seen as stellate neurones having a radiate dendritic arbor. 3. Electrical stimulation of the brachium of IC invariably elicits fast, excitatory synaptic potentials in both MGv and MGd cells. The evoked responses occurred monosynaptically and were exclusively mediated by glutamate acting on both N‐methyl‐D‐aspartate (NMDA) and non‐NMDA receptors. Non‐lemniscal MGd neurones recorded extracellularly exhibited a strong tendency to discharge in bursts in response to brachium stimulation. In contrast, a large proportion of ventral lemniscal cells tended to discharge in single or dual spikes. Intracellularly, MGd cells, but not MGv cells, showed a predominant, slow synaptic potential mediated by NMDA receptors. 4. It is concluded that the central auditory circuitry linking the tectum and the thalamus is connected monosynaptically via glutamatergic synapses. Lemniscal and non‐lemniscal thalamic neurones possess distinct response properties which cannot be accounted for by a differential transmitter system or polysynaptic delays as postulated previously.
Counter‐transport of potassium by the glutamate uptake carrier in glial cells isolated from the tiger salamander retina.
Authors: Amato A , Barbour B , Szatkowski M , Attwell D
Published: December 2014

1. To investigate the transport of potassium on the glutamate uptake carrier, the glutamate uptake current in isolated retinal Müller cells was monitored by whole‐cell clamping, while measuring changes of potassium concentration outside the cells ([K+]o) with an ion‐sensitive microelectrode. 2. Activating glutamate uptake led to an accumulation of potassium outside the cells, consistent with the hypothesis, based on less direct evidence, that the glutamate uptake carrier transports potassium out of the cell. 3. The glutamate‐evoked rise of [K+]o showed the pharmacology and sodium dependence of glutamate uptake. 4. The rise in [K+]o was proportional to the uptake current flowing between 0 and ‐80 mV, implying that the ratio of K+ transported to charge transported by the uptake carrier is constant over this voltage range. The K+ to charge transport ratio was the same for uptake of D‐aspartate and L‐glutamate. 5. By clamping cells with pipettes containing solutions of different [K+], the dependence of the glutamate and aspartate uptake currents on intracellular [K+] was determined. L‐ and D‐aspartate transport showed a smaller maximum uptake current (Imax), and a smaller apparent Michaelis constant (Km) for activation by intracellular K+, than did L‐glutamate transport. The ratio of Imax to Km was the same for these three analogues, a result which can be predicted from simple models of the carrier's operation. 6. Fully activating glutamate uptake in Müller cells in the intact retina would produce a K+ load into the extracellular space of about 0.6 mM s‐1. Suppression of glutamate release from photoreceptors by light will reduce K+ efflux from Müller cells in the outer retina; this may contribute to the light‐evoked fall of [K+]o observed in the outer retina, and thus contribute to shaping the electroretinogram.
Mutation of the proto‐oncogene c‐kit blocks development of interstitial cells and electrical rhythmicity in murine intestine.
Authors: Ward S M , Burns A J , Torihashi S , Sanders K M
Published: December 2014

1. Interstitial cells of Cajal (ICs) have been proposed as pacemakers in the gastrointestinal tract. We studied the characteristics and distribution of ICs and electrical activity of small intestinal muscles from mice with mutations at the dominant‐white spotting/c‐kit (W) locus because the tyrosine kinase function of c‐kit may be important in the development of the IC network. 2. W/WV mutants (days 3‐30 postpartum) had few ICs in the myenteric plexus region compared with wild type (+/+) siblings. The few ICs present were associated with neural elements and lay between myenteric ganglia and the longitudinal muscle layer. 3. Electrical recordings from intestinal muscle strips showed that electrical slow waves were always present in muscles of +/+ siblings, but were absent in W/WV mice. 4. Muscles from W/WV mice responded to stimulation of intrinsic nerves. Neural responses, attributed to the release of acetylcholine, nitric oxide and other unidentified transmitters, were recorded. 5. These findings are consistent with the hypothesis that ICs are a critical element in the generation of electrical rhythmicity in intestinal muscles. The data also show that neural regulation of gastrointestinal muscles can develop independently of the IC network. 6. W locus mutants provide a powerful new model for studies of the physiological role of ICs and the significance of electrical rhythmicity to normal gastrointestinal motility.
Oxytocin receptors on oxytocin neurones: histoautoradiographic detection in the lactating rat.
Authors: Freund‐Mercier M J , Stoeckel M E , Klein M J
Published: December 2014

1. The purpose of the present study was the detection at the cellular scale of the oxytocin (OT) receptors involved in the facilitatory effect of this neuropeptide on its own release during the milk ejection reflex. 2. OT binding sites were demonstrated in brain sections by using a highly selective 125I‐labelled OT antagonist detected by film‐ and histoautoradiography. 3. Film autoradiographs revealed the presence of OT binding sites in the hypothalamic magnocellular (supraoptic, paraventricular and anterior commissural) nuclei in lactating rats, suckled or not. This detection was only possible after acute i.c.v. injection of OT antagonist which probably induced an upregulation of the OT binding sites to autoradiographically detectable levels. 4. Combined application of histoautoradiographic and immunohistochemical techniques showed that the OT binding sites were concentrated on OT magnocellular neurones. Labelling concerned cell bodies and dendrites but not the axons and endings in the pituitary neural lobe. 5. The presently detected somatodendritic autoreceptors on OT neurones probably mediate the facilitatory effect of OT on its own release during the milk ejection reflex.
Dependence of ATP consumption on cross‐bridge phosphorylation in swine carotid smooth muscle.
Authors: Wingard C J , Paul R J , Murphy R A
Published: December 2014

1. Ca(2+)‐dependent phosphorylation of the myosin regulatory light chain (MRLC) initiates cross‐bridge cycling and contraction in smooth muscle. A four‐state cross‐bridge model, in which Ca(2+)‐dependent phosphorylation is the only proposed regulatory mechanism, can predict the mechanical output of the swine carotid media. Our aims were to determine whether ATP consumption rates and the economy of force maintenance are regulated functions of MRLC phosphorylation as predicted by the model. 2. Steady‐state force and oxygen consumption were measured in medial rings of swine carotid arteries activated with depolarizing solutions and agents capable of maintaining a wide range of steady‐state myoplasmic Ca2+ and MRLC phosphorylation levels. 3. Suprabasal ATP consumption increased almost linearly with MRLC phosphorylation and exhibited a hyperbolic increase with active stress, as predicted. 4. The economy of stress maintenance fell with increases in suprabasal phosphorylation. 5. In absolute terms the energetic cost of covalent regulation by cross‐bridge phosphorylation was small, although it may be a significant fraction of the ATP consumption associated with contraction.
Effects of increased and decreased tissue pressure on haemodynamic and capillary events in cat skeletal muscle.
Authors: Mellander S , Albert U
Published: December 2014

1. The controversial problem concerning the unusual haemodynamics of the deranged circulation during increased hydrostatic tissue pressure (PT) was elucidated by detailed studies of arterial, capillary and venous functions in cat skeletal muscle exposed to graded experimental changes of PT over a wide range. 2. The results indicated that the impaired circulatory state in skeletal muscle during raised tissue pressure is characterized by the following train of events: (a) a primary partial passive compression of the most distal part of the venous system due to negative vascular transmural pressure selectively at this site, in turn leading to the prompt development of a distinct ‘venous outflow orifice resistance’ graded in relation to the PT rise; (b) a consequent reduction of blood flow graded in relation to this resistance increase; (c) a rise in intramuscular venous pressure proximal of the ‘venous outflow orifice’ by the same extent as the PT increase; (d) transmission of the raised venous pressure to more proximal vessels in relation to the prevailing segmental resistance ratios; (e) a consequent maintenance of clearly positive transmural pressures in all vascular sections proximal to the ‘venous outflow orifice’, preventing collapse of these vessels; (f) maintenance of a largely normal capillary filtration coefficient and functional capillary surface area; and (g) an increase in capillary pressure by approximately 85% of the PT rise which reduces the rate of net transcapillary fluid absorption to about one‐seventh of that expected from the PT rise per se. 3. Previous concepts of a ‘vascular waterfall phenomenon’, a capillary collapse, or an arteriolar ‘critical closure phenomenon’ did not seem to be valid for the skeletal muscle circulation during increased PT. 4. The rate of net transcapillary fluid flux per unit PT change was much smaller during positive than negative PT, since capillary pressure rose considerably when PT was increased above control, but was largely unchanged when PT was decreased below control. 5. Possible ways to improve the circulatory state in conditions with an oedema‐induced tissue pressure rise are discussed.
Mechanosensitive ion channels in skeletal muscle from normal and dystrophic mice.
Authors: Franco-Obregón A , Lansman J B
Published: December 2014

1. We examined the activity of single mechanosensitive ion channels in recordings from cell‐attached patches on myoblasts, differentiated myotubes and acutely isolated skeletal muscle fibres from wild‐type and mdx and dy mutant mice. The experiments were concerned with the role of these channels in the pathophysiology of muscular dystrophy. 2. The predominant form of channel activity recorded with physiological saline in the patch electrode arose from an approximately 25 pS mechanosensitive ion channel. Channel activity was similar in undifferentiated myoblasts isolated from all three strains of mice. By contrast, channel activity in mdx myotubes was approximately 3‐4 times greater than in either wild‐type or dy myotubes and arose from a novel mode of mechanosensitive gating. 3. Single mechanosensitive channels in acutely isolated flexor digitorum brevis fibres had properties indistinguishable from those of muscle cells grown in tissue culture. The channel open probability in mdx fibres was approximately 2 times greater than the activity recorded from wild‐type fibres. The overall level of activity in fibres, however, was roughly an order of magnitude smaller than in myoblasts or myotubes. 4. Histological examination of the flexor digitorum brevis fibres from mdx mice showed no evidence of myonecrosis or regenerating fibres, suggesting that the elevated channel activity in dystrophin‐deficient muscle precedes the onset of fibre degeneration. 5. An early step in the dystrophic process of the mdx mouse, which leads to pathophysiological Ca2+ entry, may be an alteration in the mechanisms that regulate mechanosensitive ion channel activity.
Ion selectivity and gating of small conductance Ca(2+)‐activated K+ channels in cultured rat adrenal chromaffin cells.
Authors: Park Y B
Published: December 2014

1. The ion selectivity and gating of apamin‐sensitive, small conductance Ca(2+)‐activated K+ (SK) channels were studied in cultured rat adrenal chromaffin cells using patch clamp techniques. 2. The amplitude of slow tail currents showed a bell‐shaped dependence on depolarization potentials. Slow tail currents were abolished in a Ca(2+)‐free external solution or by adding 100 microM Cd2+ to the external solution. Reversal potentials followed the predictions of the Nernst equation for a K+ electrode. 3. Slow tail currents were largely blocked by external application of apamin (dissociation constant, Kd, 4.4 nM), (+)‐tubocurarine (Kd, 20 microM), and tetraethylammonium (Kd, 5.4 mM). 4. The relative permeability (PX/PK, where X may be any one of the ions listed) of SK channels was: Tl+ (1.87) > K+ (1.0) > Rb+ (0.81) > Cs+ (0.16) > NH4+ (0.11). Na+, Li+ and methylamine were not measurably permeant (PX/PK < 0.005). Open SK channels seem to have an effective pore diameter of 0.34‐0.38 nm. The relative conductance (gX/gK) was: Tl+ (1.29) > K+ (1.0) > Rb+ (0.85) > Cs+ (0.45) approximately NH4+ (0.44). 5. With mixtures of Tl+ and K+, SK channels showed anomalous mole‐fraction behaviour. 6. Ca2+ dependence of SK channel gating was studied using inside‐out macropatches. The [Ca2+] required for half‐maximal activation and the Hill coefficient were 0.69 microM and 1.7, respectively, and independent of membrane potentials. 7. Single‐channel conductance was 13‐14 pS (160 mM K+).
Effects of preoptic warming on subretrofacial and cutaneous vasoconstrictor neurons in anaesthetized cats.
Authors: McAllen R M , May C N
Published: December 2014

1. Sympathetic and subretrofacial neuron responses to preoptic warming were studied in chloralose‐ or Saffan‐anaesthetized, paralysed cats. 2. Warming a thermode in the preoptic region inhibited the activity of cutaneous vasoconstrictor fibres supplying hairy skin. Muscle vasoconstrictor fibre activity recorded at the same time was either unaffected or raised. 3. Small injections of sodium glutamate (5 nl, 0.1 M) were made into the region of the subretrofacial nucleus in the ventrolateral medulla. The part of that region where glutamate injections evoked brisk increases in cutaneous vasoconstrictor fibre activity was chosen for further study. 4. Extracellular single unit recordings were made in that area from seventy‐seven subretrofacial neurons, which were identified by their barosensitivity (inhibition by carotid blind sac inflation). Forty‐seven of them were antidromically activated by stimulation in the spinal cord. 5. The activity of twenty subretrofacial neurons (twelve proven bulbospinal) was significantly reduced by periods of preoptic warming. Cutaneous vasoconstrictor activity recorded at the same time also fell. Forty‐nine subretrofacial neurons (thirty‐five proven bulbospinal) were unaffected or excited by periods of preoptic warming that inhibited cutaneous vasoconstrictor fibres. The response of eight neurons was unclear. 6. No difference in either mean firing rate or axonal conduction velocity was found between neurons inhibited by preoptic warming and other subretrofacial neurons. 7. The subretrofacial neurons inhibited by warming were found intermingled with those unaffected or excited. Marked recording sites of warm‐inhibited neurons were clustered around the ventromedial border of the subretrofacial nucleus. 8. In two cats, bilateral inhibition of subretrofacial neurons by surface application of 1 M glycine reduced cutaneous vasoconstrictor fibre activity to 32 and 44% of control levels. 9. The results suggest that specific cutaneous vasoconstrictor premotor neurons exist in the subretrofacial nucleus. These apparently provide most of the background excitatory drive to cutaneous vasomotor neurons. Central warming stimuli may act, at least in part, by withdrawing that drive.
Time‐varying enhancement of human cortical excitability mediated by cutaneous inputs during precision grip.
Authors: Johansson R S , Lemon R N , Westling G
Published: December 2014

1. We have investigated the afferent neurogram, muscular activity and mechanical responses while subjects restrained, with a precision grip, an object subjected to pulling loads directed away from the hand. At unpredictable times ‘ramp‐and‐hold’ loads of 1 N were delivered at a rate of ca 80 N s‐1. The load ramp produced a sharp increase in multiunit activity recorded from cutaneous afferents of the median nerve. The first response in the EMG of distal hand muscles commenced at 51 +/‐ 2.4 ms (mean +/‐ S.D.); a further steep increase in activity began about 20 ms later, and this was associated with a marked augmentation of the grip force increase. 2. In four subjects, transcranial magnetic stimulation (TMS) was delivered to the contralateral motor cortex in 1000 out of a total of 1500 loading trials. The time of the stimulus was randomly selected to occur either at one of nine defined points (separated by 20 ms) before and after the computer command triggering the load force increase, or during steady periods of grip. 3. In most hand and arm muscles, there was a powerful facilitation of the short‐latency EMG responses evoked by TMS delivered 40‐140 ms after the load force command. The amplitudes of the largest responses (TMS delivered at 80‐100 ms) were 850% higher on average than those observed when subjects gripped the unloaded object or when they restrained the statically loaded object. This large modulation was only obtained with stimulus intensities that were subthreshold in the relaxed subject. 4. The modulation was not simply a reflection of the time‐varying level of motoneuronal activity during the loading trial. In most muscles, changes in the amplitude of the TMS‐evoked responses were disproportionately larger than the corresponding modulation of the background EMG activity. At its maximum, the modulation in the TMS‐evoked response was nearly 300% larger. Furthermore, the strength of the TMS‐evoked responses did not strictly co‐vary with amplitude of background EMG, i.e. inverse relationships were seen. 5. Since motor responses to the loading of the object depend on cutaneous afferent input from the gripping digits, the results demonstrate an interaction between the effects of these inputs and those of TMS. A possible site of this interaction is the primary motor cortex; the strong modulation of the responses to TMS could reflect variation in the excitability of cortical neurons mediated by the cutaneous afferent input. However, such excitability changes lagged the predicted onset of cortical excitation in a manner suggesting that the earliest 20 ms of the subjects’ EMG responses to the load increase are subcortical in origin. In contrast, the results are consistent with a cortical mediation of the subsequent powerful boosting of the EMG responses associated with the robust grip force response.
The effects of mechanical loading and changes of length on single guinea‐pig ventricular myocytes.
Authors: White E , Boyett M R , Orchard C H
Published: December 2014

1. The effects of mechanical loading and changes of length on the contraction of single guinea‐pig ventricular myocytes has been investigated. 2. Cell shortening was monitored during isotonic contractions (in which the cell shortened freely) and after attaching carbon fibres of known compliance to the ends of the cell, so that the cell contracted auxotonically (the cell both shortened and developed force). 3. Mechanically loading the cells decreased the amount of shortening during a contraction and abbreviated the contraction. There were, however, no consistent changes in the action potential or the [Ca2+]i transient (measured with the fluorescent dye fura‐2). 4. Increasing stimulation rate increased the size of the contraction and the [Ca2+]i transient in both isotonic and auxotonic conditions. The increase in the size of the contraction induced by an increase in stimulation rate was greater in auxotonic conditions but the increase in the size of the [Ca2+]i transient was not. 5. When cells were stretched, there was a step increase in the size of the contraction and a prolongation of its time course. However, neither the size nor the time course of the accompanying [Ca2+]i transient was significantly altered by this intervention. 6. When a stretch was maintained, a further, slow increase in the size of the contraction occurred during the following 3‐11 min, in about half the cells studied. The probability of this slow response occurring was increased if the initial degree of activation of the cell was decreased. 7. These data suggest that the mechanisms underlying the responses to mechanical loading and changes of length are the same in both multicellular and single cell preparations of cardiac muscle.
The effects of thyroid hormones on oxygen and glucose metabolism in the sheep fetus during late gestation.
Authors: Fowden A L , Silver M
Published: December 2014

1. The effects of thyroid hormones on fetal metabolism during late gestation were examined by measuring the rates of glucose and oxygen utilization rates in chronically catheterized sheep fetuses made hypothyroid by either fetal thyroidectomy (TX) or hypophysectomy (HX). The values were compared with those in intact fetuses and in thyroxine (T4)‐treated TX and HX fetuses. 2. Umbilical O2 uptake expressed on a weight‐specific basis was reduced by 20‐30% in the hypothyroid fetuses and was restored to normal values when plasma T4 levels were maintained in the TX and HX fetuses by exogenous T4 administration. 3. The low O2 consumption rates of the untreated hypothyroid fetuses were accompanied by fetal growth retardation, an abnormal blood gas status, and in the TX fetuses, by significant reductions in the rates of glucose oxidation, CO2 production from glucose carbon and O2 utilization for glucose oxidation. 4. When T4 levels were maintained in the TX fetuses, these metabolic rates and fetal blood gas status were restored to their normal values. Replacement of T4 also sustained growth in TX but not in HX fetuses. 5. When the data from all fetuses were combined irrespective of treatment, there were significant positive correlations between plasma levels of T4 (but not triiodothyronine (T3)) and the rates of umbilical O2 uptake, glucose oxidation, CO2 production from glucose carbon and O2 utilization for glucose oxidation in the individual fetuses. 6. These findings demonstrate that T4 is a physiological regulator of O2 utilization by the sheep fetus close to term.
Inhibition of acetylcholine release from mouse motor nerve by a P‐type calcium channel blocker, omega‐agatoxin IVA.
Authors: Hong S J , Chang C C
Published: December 2014

1. The effects were studied of the central neurone P‐type Ca2+ channel blockers, omega‐agatoxin IVA, omega‐conotoxin MVIIC (polypeptide toxins) and synthetic funnel‐web spider polyamine toxin on acetylcholine release from mouse motor nerve. 2. omega‐Agatoxin IVA decreased the quantal content of endplate potentials and blocked synaptic transmission in the nanomolar range in a reversible manner, whereas the other toxins depressed transmission in the hundred micromolar range. 3. The polyamine toxin, but not the polypeptide toxins, decreased the amplitude of the miniature endplate potential. The increase in the frequency of miniature endplate potentials evoked by high [K+], but not that evoked by alpha‐latrotoxin, was effectively antagonized by omega‐agatoxin IVA. 4. In the presence of omega‐agatoxin IVA, high frequency nerve stimulation produced facilitation of endplate currents and tetanic contractions. 5. The results suggest that, under physiological conditions, the Ca2+ necessary for nerve action potential‐evoked acetylcholine release is translocated via a subtype of the P‐type Ca2+ channel sensitive to omega‐agatoxin IVA.
The genetic advantage hypothesis in cystic fibrosis heterozygotes: a murine study.
Authors: Cuthbert A W , Halstead J , Ratcliff R , Colledge W H , Evans M J
Published: December 2014

1. The delta F508 mutation of the cystic fibrosis (CF) gene is of high frequency in man (1 in 25) and in homozygotes causes cystic fibrosis. It is suggested that cystic fibrosis heterozygotes withstand secretory diarrhoea better than normal individuals and so are genetically advantaged. This hypothesis has been examined by measuring electrogenic chloride secretion in gut epithelia of normal and heterozygous CF mice. 2. Chloride secretory responses of normal and heterozygous colonic epithelia to forskolin, vasoactive intestinal polypeptide (VIP), isoprenaline, cholera toxin, heat‐stable enterotoxin (STa), guanylin, carbachol and lysylbradykinin were examined. No significant differences in responses of tissues of the two genotypes were found. 3. Responses of normal and heterozygous ileal epithelia to forskolin and glucose were investigated. Heterozygous tissues responded as well as normal tissues. 4. Frusemide (furosemide) caused virtually identical inhibition of the chloride secretory responses to forskolin in colonic epithelia of both genotypes. 5. No evidence to support the genetic advantage hypothesis in ileal or colonic epithelia of the null CF mouse has been found, at least for acute responses. If the hypothesis is true then either (a) other non‐cystic fibrosis transmembrane conductance regulator (non‐CFTR) transport processes are involved, (b) prolonged exposure to secretagogues is required, or (c) delta F508 CFTR is responsible for the protective effect.
Number of junctional acetylcholine receptors: control by neural and muscular influences in the rat.
Authors: Andreose J S , Fumagalli G , Lømo T
Published: December 2014

1. The number of acetylcholine receptors (AChRs) per neuromuscular junction in soleus muscles of adult rats was estimated from counts of 125I‐alpha‐bungarotoxin binding sites. The muscles were either denervated, denervated and electrically stimulated, paralysed by botulinum toxin (BoTX), or paralysed by tetrodotoxin (TTX). 2. After denervation, the number of junctional AChRs was normal after 18 days and then fell to 54 and 35% of normal after 33 and 57 days, respectively. 3. Direct high frequency muscle stimulation (100 Hz) maintained a normal number of junctional AChRs for at least 2 months when the stimulation started on the day of denervation. When the stimulation was started progressively later, the effect of the stimulation on AChR number disappeared within about a week. The disappearance was gradual and appeared to affect all the muscle fibres equally. 4. Stimulation at 100 Hz, starting on the day of denervation and stopping after 18 days, did not prevent the endplates from losing AChRs during the subsequent 15 days without stimulation. Thus 100 Hz stimulation and innervation are not equivalent in their effects on junctional AChR number. 5. Direct low frequency muscle stimulation from the day of denervation did not maintain a normal number of junctional AChRs, as the number of AChRs fell to 70 and 62% of normal after 33 days of stimulation at 20 and 10 Hz, respectively. 6. Endplates paralysed by BoTX or TTX for 33 days lost about as many junctional AChRs (54 and 55%) as endplates denervated for 33 days (46%). Direct stimulation at 100 Hz during the last 15 days of BoTX treatment reduced but did not prevent this AChR loss (36% loss at 33 days). 7. The results show that when motor nerve terminals in rat soleus muscles are removed by axotomy, they leave a ‘trace’ which, in conjunction with appropriate muscle stimulation, can maintain a normal number of AChRs in the postsynaptic region. In non‐stimulated muscles the trace responsible for this maintenance disappears within about a week. In stimulated muscles it persists for at least 2 months. From indirect evidence it appears that the trace is a factor, or the postsynaptic effect of a factor, released by impulse activity in the nerve, and that its degradation after denervation is accelerated by the acute effects of nerve degeneration.
Adenosinergic modulation of respiratory neurones and hypoxic responses in the anaesthetized cat.
Authors: Schmidt C , Bellingham M C , Richter D W
Published: December 2014

1. The modulatory effects of intracellularly injected adenosine on membrane potential, input resistance and spontaneous or evoked synaptic activity were determined in respiratory neurones of the ventral respiratory group. 2. The membrane potential hyperpolarized and sometimes reached values which were beyond the equilibrium potential of Cl(‐)‐dependent IPSPs. At the same time, neuronal input resistance decreased. 3. Spontaneous and stimulus‐evoked postsynaptic activities were decreased, as were mean respiratory drive potentials. 4. Systemic injection of the A1 adenosine receptor antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX; 0.01‐0.05 mg kg‐1) resulted in an increase in mean peak phrenic nerve activity when arterial chemoreceptors were denervated. In contrast, phrenic nerve activity decreased when arterial chemoreceptors were left intact. 5. The depressant effect of adenosine on synaptic activity was abolished after systemic DPCPX administration. DPCPX caused an increase in respiratory drive potentials, increased the amplitude of stimulus‐evoked IPSPs, and hyperpolarized membrane potential. 6. Administration of DPCPX blocked the early hypoxic depression of stimulus‐evoked IPSPs, doubled the delay of onset of hypoxic apnoea and shortened the time necessary for recovery of the respiratory rhythm. 7. The data indicate that adenosine acts on pre‐ and postsynaptic A1 receptors resulting in postsynaptic membrane hyperpolarization and depression of synaptic transmission. Blockade of A1 receptors increases respiratory activity, indicating that adenosine A1 receptors are tonically activated under control conditions. Further activation contributes to the hypoxic depression of synaptic transmission in the respiratory network.
Human perceptual learning in identifying the oblique orientation: retinotopy, orientation specificity and monocularity.
Authors: Schoups A A , Vogels R , Orban G A
Published: December 2014

1. Human perceptual learning in discrimination of the oblique orientation was studied using psychophysical methods. Subjects were trained daily to improve their ability to identify the orientation of a circular 2.5 deg diameter unidimensional noise field. Dramatic improvements in sensitivity to contour orientation occurred over a period of 15‐20 days. The improved performance persisted for several months. Improvement was more evident between daily sessions than within sessions. This was partly due to fatigue interfering with the learning effect. Moreover, a consolidation period seemed to be required. 2. Improvement was restricted to the position of the stimulus being trained. This position dependency of the learning effect proved very precise. After training at a specific stimulus position, merely displacing the stimulus to an adjacent position caused a marked increase in thresholds. 3. No transfer of the training effect was observed between orientations. Following a shift of 90 deg away from the trained orientation, performance fell, even below the initial level. 4. We observed complete to almost complete transfer between the two eyes. 5. Our results suggest plastic changes at a level of the visual processing stream where input from both eyes has come together, but where generalization for spatial localization and orientation has not yet occurred.
Ca2+ modulation of the cGMP‐gated channel of bullfrog retinal rod photoreceptors.
Authors: Nakatani K , Koutalos Y , Yau K W
Published: December 2014

1. The outer segment of an isolated rod photoreceptor from the bullfrog retina was drawn into a pipette containing choline solution for recording membrane current. The rest of the cell was sheared off with a glass probe to allow internal dialysis of the outer segment with a bath potassium solution (‘truncated rod outer segment’ preparation). The potential between the inside and the outside of the pipette was held at 0 mV. 2. Application of bath cGMP, in the presence of 3‐isobutyl‐1‐methylxanthine (IBMX), gave rise to an outward membrane current. At saturating cGMP concentrations, this current was insensitive to intracellular Ca2+ at concentrations between 0 and 10 microM. At subsaturating cGMP concentrations, however, this current was inhibited by intracellular Ca2+. This sensitivity to Ca2+ declined after dialysis with a low‐Ca2+ solution, suggesting the involvement of a soluble factor. 3. At low (nominally 0) Ca2+, the half‐maximal activation constant and Hill coefficient for the activation of the cGMP‐gated current by cGMP were 27 microM and 2.0, respectively. At high (ca 10 microM) Ca2+, the corresponding values were 40 microM cGMP and 2.4. 4. The inhibition of the current by Ca2+ was characterized at 20 microM cGMP. Ca2+ inhibited the current by up to 60%, with half‐maximal inhibition at 48 nM Ca2+ and a Hill coefficient of 1.6.
Nerve‐dependent regulation of succinate dehydrogenase in junctional and extrajunctional compartments of rat muscle fibres.
Authors: Jasmin B J , Campbell R J , Michel R N
Published: December 2014

1. We studied the distribution of the mitochondrial enzyme succinate dehydrogenase (SDH) within junctional and extrajunctional compartments of rat soleus muscle fibres. Using quantitative microphotometric imaging techniques, we showed that the motor endplate region of soleus fibres displays SDH activity that is two‐ and threefold higher than in subsarcolemmal (SS) and intermyofibrillar (IM) compartments, respectively, and that essentially all endplate SDH activity is of postsynaptic origin. 2. In addition, we examined the influence of the motor nerve on the regulation of this enzyme within these compartments using denervation and tetrodotoxin (TTX)‐induced blockade of nerve impulse conduction. Both models of short‐term muscle paralysis reduced SDH activity to a comparable extent (approximately 30%) in both the SS and IM compartments, suggesting that expression of this enzyme is co‐ordinately regulated in these two regions. Alternatively, denervation and TTX inactivation led to distinct alterations at the level of the motor endplate. SDH activity at denervated endplates was dramatically reduced (by 60%) in comparison to controls, whereas at endplates of TTX‐inactivated counterparts, this reduction was significantly less (35%). 3. These findings suggest that motor activity per se is the key factor regulating expression of SDH in non‐innervated regions of muscle fibres and that accumulation of SDH activity within the postsynaptic sarcoplasm is equally subject to local mechanisms involving nerve‐derived trophic factors.
Loss of power during fatigue of human leg muscles.
Authors: James C , Sacco P , Jones D A
Published: December 2014

1. We have investigated the loss of power seen during high‐intensity exercise of human leg muscles such as might occur during sprinting. Subjects exercised the quadriceps and hamstring muscle groups using a Cybex dynamometer at an angular velocity of 90 deg s‐1 once a second for 6 min. At 1 min intervals the quadriceps were electrically stimulated via the femoral nerve to produce an isometric contraction which was then released into an isokinetic shortening contraction at 90 deg s‐1. 2. The extent of central fatigue was assessed by comparing the force of a voluntary isokinetic contraction with that elicited by electrical stimulation during isokinetic releases. Two subjects were repeatedly tested. In the first series of experiments, exercising the quadriceps of one leg, the instantaneous power fell to about 50% over the course of 2 min and remained constant for the rest of the exercise. For one subject the voluntary and electrically stimulated forces declined in parallel while for the second subject the voluntary force was 10% less than the stimulated force at the end of the exercise. These results show that central fatigue represented a minor factor contributing no more than one‐fifth of the total loss of power in these circumstances. 3. In a second series of experiments the subjects alternately contracted the quadriceps and the hamstrings of both legs in an exercise which had a high rating of perceived exertion and entailed considerable respiratory and cardiovascular effort. The time course and proportionate loss of power were very similar to those seen with the one‐leg exercise and neither subject showed evidence of significant central fatigue. The pattern of force loss was very similar for the hamstrings. We conclude that, for determined subjects, afferent feedback from muscles, tendons and joints or from the respiratory and cardiovascular systems does not have a major role in inhibiting voluntary activation of the quadriceps during heavy exercise. 4. In both series of experiments the power output during electrically stimulated isokinetic contractions was reduced to 50% of the initial value after 2 min of exercise while the isometric force, measured immediately before the release, fell to only 75%. This suggests that fatigue affects isometric and shortening contractions to different extents and the loss of power may be due to a combination of factors, only one of which is evident in the loss of isometric force.
Enhancement by muscarinic agonists of a high voltage‐activated Ca2+ current via phosphorylation in a snail neuron.
Authors: Golowasch J , Paupardin-Tritsch D , Gerschenfeld H M
Published: December 2014

1. In previous work we have shown that in the snail Helix aspersa neuron F1 carbamylcholine (CCh) and other muscarinic agonists enhance the inward current carried through high voltage‐activated Ca2+ channels by Ba2+ (HVA‐ICa). It was also found that cyclic nucleotides, inositol trisphosphate or arachidonic acid are not involved in this modulation. Moreover, despite the effect of CCh being blocked by intracellular injection of EGTA, neither protein kinase C nor Ca(2+)‐calmodulin‐dependent protein kinase II appeared to play a role. 2. In the present paper, the intracellular mechanism of this muscarinic modulation was investigated further by studying the effects of inhibitors of Ser‐Thr protein phosphatases (PP) on both the HVA‐ICa of neuron F1 and its enhancement by CCh. 3. Intracellular injections in the F1 neuron of either microcystin LR or okadaic acid, both inhibitors of PP1 and PP2A, mimic the action of CCh on the HVA‐ICa and occlude the effects of CCh on this current. In contrast, cyclosporin A, an inhibitor of PP2B (calcineurin), affects neither the HVA Ca2+ current itself nor its modulation by CCh. 4. The efficacy of PP inhibitors was tested in F1 neurons in which serotonin (5‐HT) induces an inward current involving intracellular increases in cAMP and a protein kinase A‐dependent closing of K+ channels. We found that intracellular injection of either microcystin LR or okadaic acid mimicked the 5‐HT‐induced inward current and occluded the effect of further application of 5‐HT.(ABSTRACT TRUNCATED AT 250 WORDS)
Dual modulation of synaptic inhibition by distinct metabotropic glutamate receptors in the rat hippocampus.
Authors: Poncer J C , Shinozaki H , Miles R
Published: December 2014

1. The effects of metabotropic glutamate receptor (mGluR) activation on synaptic inhibition were examined using whole‐cell recordings of spontaneous and miniature inhibitory synaptic currents from CA3 pyramidal cells in rat hippocampal slices. 2. The mGluR agonist (1S,3R)trans‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (tACPD) increased spontaneous IPSC (spIPSC) frequency by up to 5‐fold. At doses above 5 microM the increase was transient (15‐45 s) and was followed by a decline to control frequency. In these conditions, elevating external K+ from 2 to 8 mM could still increase spIPSC frequency. 3. Miniature IPSCs (mIPSCs) were recorded in the presence of 1 microM TTX, 5 mM Mg2+ and nominally zero Ca2+. At concentrations above 50 microM, tACPD induced a sustained, reversible reduction in mIPSC frequency by up to 43%. 4. Quisqualate, at doses as low as 50 nM, increased spIPSC frequency, but did not affect mIPSC frequency at concentrations up to 10 microM. 5. The specific mGluR2 and 3 agonist (2S,1'R,2'R,3'R)‐2‐(2,3‐dicarboxycyclopropyl)glycine (DCG‐IV, 3 microM) reduced mIPSC frequency by 40 +/‐ 4% but did not increase spIPSC frequency. 6. The putative mGluR antagonist L‐2‐amino‐3‐phosphonopropionate (L‐AP3, 1 mM) blocked the effect of tACPD on mIPSC but not spIPSC frequency. The broad‐spectrum antagonist (RS)‐alpha‐methyl‐4‐carboxyphenylglycine (MCPG, 500 microM) blocked both responses. 7. mGluR activation also had dual effects on IPSCs evoked by focal extracellular stimulation. Application of 5 microM tACPD increased the mean amplitude of evoked IPSCs by 112 +/‐ 9%, largely by reducing the proportion of response failures. In contrast, IPSC amplitude was reduced to 44 +/‐ 1% of control values by 3 microM DCG‐IV. 8. These results suggest hippocampal inhibitory cells express two distinct mGluR subtypes. One receptor (possibly mGluR1 or 5) is located on somato‐dendritic membrane and enhances cell excitability. Another (mGluR2 or 3) is present at inhibitory terminals and reduces the probability of GABA release.
Inhibition of N‐ and P‐type calcium currents and the after‐hyperpolarization in rat motoneurones by serotonin.
Authors: Bayliss D A , Umemiya M , Berger A J
Published: December 2014

1. We investigated the effects of serotonin (5‐hydroxytryptamine, 5‐HT) on whole‐cell barium currents through calcium channels in visualized neonatal rat hypoglossal motoneurones (HMs) in a thin brainstem slice preparation. 2. High voltage‐activated (HVA) currents were elicited by depolarizing voltage steps from ‐70 to 0 mV; low voltage‐activated (LVA) currents were evoked using steps to between ‐30 and ‐40 mV from hyperpolarized potentials (< ‐80 mV). 5‐HT (1.0 microM) inhibited HVA currents by at least 10% in 70% of HMs tested (n = 99); in those responsive neurones, 5‐HT decreased HVA current by 22 +/‐ 1.3% (mean +/‐ S.E.M.). In contrast, 5‐HT had no effect on LVA current amplitude in HMs (n = 7). 3. Calcium current inhibition was mimicked by 5‐carboxamidotryptamine maleate (5‐CT), a 5‐HT1 receptor agonist, and by R(+)‐8‐hydroxydipropylaminotetralin hydrobromide (8‐OH‐DPAT), a specific 5‐HT1A agonist; N‐(3‐trifluoromethylphenyl) piperazine hydrochloride (TFMPP), a 5‐HT1B agonist, was without effect. The effect of 5‐HT was blocked by the 5‐HT1A antagonist 1‐(2‐methoxyphenyl)‐4‐[4‐(2‐phthalimido)butyl]piperazine hydrobromide (NAN‐190) but not by ketanserin, a 5‐HT2A/2C antagonist. Although R(‐)‐1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane hydrochloride (DOI), a 5‐HT2A/2C agonist, mimicked the current inhibition by 5‐HT, it was ineffective in the presence of NAN‐190. These data indicate that 5‐HT1A receptors mediate calcium current inhibition by 5‐HT. 4. Following application of either omega‐conotoxin‐GVIA (omega‐CgTX) or omega‐agatoxin‐IVA (omega‐Aga‐IVA), to block N‐ and P‐type components of calcium current, the 5‐HT‐sensitive current was reduced; 5‐HT had no effect on the current remaining after application of both toxins. Thus, 5‐HT inhibits both N‐ and P‐type calcium currents in neonatal HMs. 5. Inhibition of HVA current by 5‐HT was irreversible, and subsequent applications of 5‐HT were occluded, when GTP gamma S was substituted for GTP in the pipette. In addition, inhibition of HVA current by 5‐HT was relieved following depolarizing prepulses. These data indicate that inhibition of calcium channels by 5‐HT is mediated by G proteins. 6. Under current clamp, both 5‐HT and 8‐OH‐DPAT decreased the amplitude of the after‐hyperpolarization (AHP) that followed action potentials, indicating involvement of a 5‐HT1A receptor.(ABSTRACT TRUNCATED AT 400 WORDS)
Extracellular volume and blood volume in chronically catheterized fetal sheep.
Authors: Gibson K J , Lumbers E R
Published: December 2014

1. To determine the extracellular volume (ECV) in fetal sheep and its distribution between the plasma and interstitial spaces, ECV, blood volume (BV) and haematocrit were measured in ten chronically catheterized fetal sheep aged 121‐133 days. Relationships with age, weight and other fetal variables, including glomerular filtration rate (GFR), were studied. 2. ECV was measured as the mean of the volumes of distribution of [3H]inulin and [14C]mannitol extrapolated to time zero. The time zero volume of distribution was 1506 +/‐ 79 ml (means +/‐ S.E.M.) for inulin and 1590 +/‐ 80 ml for mannitol. The ECV was 1548 +/‐ 79 ml (632 +/‐ 18 ml (kg fetal wt)‐1). BV, measured using 51Cr‐labelled red cells, was 351 +/‐ 27 ml (141 +/‐ 6 ml kg‐1). Haematocrit, plasma volume and interstitial volume were 34 +/‐ 1%, 229 +/‐ 17 ml (92 +/‐ 3 ml kg‐1) and 1319 +/‐ 63 ml (540 +/‐ 17 ml kg‐1), respectively. 3. Interstitial volume per kilogram fell with increasing fetal weight (P = 0.026). BV per kilogram did not change with weight or age. 4. The plasma: interstitial volume ratio was 0.17 +/‐ 0.01. This ratio increased as fetal weight and age increased (P = 0.026 and P = 0.044), that is, the proportion of ECV that was contained outside the vascular compartment was lower in heavier or older fetuses. 5. Since GFR was 3.4 +/‐ 0.4 ml min‐1, the entire fetal ECV was filtered by the fetal kidney only 3.1 +/‐ 0.3 times per day.