bluuebunny/crossref_metadata_2025 huggingface dataset:
Neural differentiation in cleavage‐arrested ascidian blastomeres induced by a proteolytic enzyme.
Authors: Okado H , Takahashi K
Published: December 2014

1. As previously reported, ectodermal a4‐2 blastomeres isolated from 8‐cell embryos of the ascidian, Halocynthia roretzi or aurantium, and cultured under conditions of cleavage arrest always differentiated into an epidermal phenotype, showing long‐lasting Ca(2+)‐dependent action potentials and/or tunic on the cell surface. a4‐2 blastomeres contacted by a chordamesodermal blastomere, A4‐1, differentiated into a neural phenotype, characterized by fast Na(+)‐dependent spikes. Differentiation to a similar neural phenotype occurred when isolated a4‐2 blastomeres from H. aurantium embryos were treated with > 0.003% subtilisin for 60 min at the 32‐cell stage of the control embryo. Comparisons between induction by cell contact and induction by proteolytic enzymes were made and showed them to be similar in several respects. 2. When the serine protease, subtilisin, was used as the neural inducer, neural competence of a4‐2 blastomeres, measured as the percentage frequency of the induction of Na+ spikes, increased after the 32‐cell stage and decreased during the gastrula stage. The time course of the neural competence was the same as that for contact with the A4‐1 blastomere. 3. The neural competence of four different ectodermal blastomeres isolated from the 16‐cell embryo was also examined using subtilisin as a neural inducer, and by contact with the A4‐1 blastomere from the 8‐cell embryo. The competence was higher in anterior blastomeres than in posterior blastomeres for both types of induction. This regional difference in neural competence along the antero‐posterior axis paralleled that expected from neural cell lineage during normal development, i.e. blastomeres with more cells of neural lineage among their derivatives showed higher competence. 4. Streptomyces subtilisin inhibitor, SSI (0.1%), a specific protease inhibitor for subtilisin‐type serine proteases, significantly suppressed (50%) neural induction of the ectodermal blastomere, a4‐2, by contact with the chordamesodermal blastomere, A4‐1. 5. Monensin, brefeldin A and bafilomycin A1, all of which affect secretory processes, suppressed the neural inducing ability of the chordamesodermal blastomere, A4‐1. 6. These results permit the hypothesis that a protease secreted from the chordamesoderm‐generating blastomere induces the ectodermal blastomere to differentiate into neural cell type.
Alterations in intracellular calcium and tension of activated ferret papillary muscle in response to step length changes.
Authors: Saeki Y , Kurihara S , Hongo K , Tanaka E
Published: December 2014

1. To study the effects of mechanical constraints on the calcium (Ca2+) affinity of cardiac troponin C, we analysed the tension and aequorin light (AL, intracellular Ca2+) transients in response to a step length change in aequorin‐injected ferret right ventricular papillary muscles. The muscle preparations were continuously activated with ouabain (10(‐4) M) (ouabain contracture) or with high frequency stimuli in the presence of ryanodine (5 microM) (tetanic contraction). 2. The tension transient in response to either the release or stretch was oscillatory: tension decreased rapidly during the release and then increased, after which it lapsed into a new steady level in a series of damped oscillations. The opposite was true for the stretch. The oscillatory responses were conspicuous and less damped in ouabain‐activated preparations (oscillation frequency of 2.2‐2.3 Hz at 22 degrees and 4.5‐4.6 Hz at 30 degrees C) and much more damped in ryanodine‐treated preparations. 3. The transient AL response was also oscillatory, the time course of which corresponded to that of the transient tension response. Regardless of the difference in the time course of the transients in two different preparations and at two different temperatures, the increase in AL corresponded to the decrease in tension, likewise the decrease in AL to the increase in tension. 4. The mean level of AL after release was lower than the control level present just prior to the release in ouabain‐activated preparations, but the AL after release finally returned to the nearly control level in ryanodine‐treated preparations. 5. When the ryanodine‐treated muscle was further treated with 2,3‐butanedione monoxime (BDM) (20 mM), the tetanic tension decreased remarkably without affecting the AL signal. The tension transient of this preparation was quite similar to that of the resting muscle, which changed in a nearly stepwise fashion; AL was hardly affected by step length changes, as in the resting muscle, in spite of the higher AL level. 6. These results suggest that the Ca2+ affinity of cardiac troponin C is increased with an increase in tension (i.e. the cross‐bridge attachment) and decreased with a decrease in tension i.e. the cross‐bridge detachment), and that the mean [Ca2+]i is lowered by release, at least in a Ca(2+)‐overloaded condition, mainly through the sarcoplasmic reticulum.
Respiratory responses to electrical and chemical stimulation of the area postrema in the rabbit.
Authors: Srinivasan M , Bongianni F , Fontana G A , Pantaleo T
Published: December 2014

1. The respiratory role of the area postrema (AP) has been investigated in pentobarbitone‐ or alpha‐chloralose‐anaesthetized, vagotomized, paralysed and artificially ventilated rabbits, by means of electrical stimulation and microinjections of DL‐homocysteic acid (DLH). Phrenic nerve activity was used as an index of central respiratory drive. 2. Bipolar electrical or chemical stimulation (microinjections of DLH, 5‐30 nl; 160 mM) of the caudal compact portion of the AP provoked excitatory effects on the inspiratory motor output, without apparent changes in the arterial blood pressure. 3. Depressant effects on inspiratory activity, accompanied on some occasions by changes in arterial blood pressure (as a rule, increases > or = 30 mmHg) were induced by DLH microinjections in close neighbouring areas (including the medial part of the nucleus tractus solitarii) or in the IV ventricle. 4. These results support a role for the AP in the neural control of respiration. The findings are discussed in connection with other autonomic functions to which the AP has been reported to contribute, in different animal species.
Pyramidal and corticospinal synaptic effects over reticulospinal neurones in the cat.
Authors: Canedo A , Lamas J A
Published: December 2014

1. The spontaneous activity of 103 precruciate neurones (fifty‐eight activated antidromically from the pyramidal tract but not from the corticospinal tract, PTNs; forty‐five activated from both sites, CSNs) was used to trigger the average of the intracellularly recorded synaptic noise in 294 reticulospinal neurones (RSNs). These RSNs were recorded in the nucleus reticularis gigantocellularis of the contralateral medial bulbar reticular formation (NRGc) in chloralose‐anaesthetized cats. 2. Twelve pyramidal tract neurones (six CSNs) were tested with a single RSN, twenty‐six (10 CSNs) with two RSNs each, thirty (13 CSNs) with three RSNs each, and thirty‐five (16 CSNs) with four RSNs each. Postsynaptic potentials were observed in the averages generated by twenty PTNs and fifteen CSNs. 3. The only synaptic effect produced by both PTNs and CSNs upon RSNs in our sample was excitatory, and in none of the tested cases (n = 15) were any changes found in the amplitude, shape, or duration of the excitatory postsynaptic potentials (EPSPs) after injection of depolarizing or hyperpolarizing currents. This suggests that the synapses are probably located at the distal dendrites. 4. Recording of the presynaptic spike allowed separation of the conduction time and synaptic delay from the total latency. According to our data there appear to be two different types of excitation of corticofugal neurones over RSNs: a monosynaptic effect produced by both PTNs and CSNs, and a disynaptic effect produced by PTNs but not by CSNs. The disynaptic EPSPs had statistically significant slower rise times and longer widths than the monosynaptic EPSPs.
Capsaicin did not evoke pain from human hand vein segments but did so after injections into the paravascular tissue.
Authors: Arndt J O , Kindgen‐Milles D , Klement W
Published: December 2014

1. To see if pain from veins is mediated by C fibre endings, the C fibre stimulant capsaicin was applied intravenously, and, for comparison, paravenously and intracutaneously. 2. Capsaicin, dissolved in the fat emulsion Intralipid, was applied intravenously by continuous perfusion of vascularly isolated hand vein segments as well as by injections into occluded finger veins. Using the latter approach chemicals reach the paravascular space. 3. Pain intensities were recorded continuously with an electronically controlled visual analogue scale for deriving capsaicin concentration‐pain intensity relations and the time course of pain (latencies, pain durations). 4. Capsaicin always evoked pain upon injection into skin and paravenous tissue (0.3‐6.5 microM) and into occluded finger veins (3.3‐33 microM), whereas it had no effect whatsoever when perfused through hand vein segments even at a concentration of 650 microM. 5. Pain intensity increased with concentration and usually reached the tolerance maximum at the fivefold threshold concentration, so that the concentration‐pain intensity relations were congruent for the various routes of drug application. 6. The latencies and pain durations were independent of the capsaicin concentration, but were substantially longer with injections into occluded finger veins (latency 10‐30 s, pain duration 60‐120 s) than with intradermal or paravenous injections (2‐9 s, 10‐28 s). 7. These observations show for the first time a functional similarity between the nociceptive C fibre system of the skin and the paravascular tissues, and by inference, they dismiss the possibility that C fibre endings mediate pain in cutaneous veins.
Activation of nicotinic acetylcholine receptors on cultured Drosophila and other insect neurones.
Authors: Albert J L , Lingle C J
Published: December 2014

1. Using whole‐cell and single channel recordings, we have examined the properties of acetylcholine (ACh)‐activated currents in neurones from larval and pupal Drosophila melanogaster (fruit fly), larval and embryonic Musca domestica (house fly), and nymphal Schistocerca gregaria (locust). 2. In all preparations, single channel recordings revealed two major classes of ACh‐activated channels, with average conductances of approximately 32 and 59 pS. 3. At ACh concentrations from 1 to 10 microM, channel activity in Drosophila larval neurones occurs in bursts with an average of 1‐2 openings. Open times and burst durations are described by one or two exponentials. Burst durations for the 32 pS channel (approximately 3 ms, slow component) were longer than those for the 59 pS channel (approximately 1.0 ms). The mean open interval duration for the 32 pS channel (slow component) was also longer than that of the 59 pS channel. 4. At high ACh (20‐200 microM) concentrations, bursts of the smaller conductance channel occur in clusters separated by long‐lived periods without channel activity. Considerable kinetic heterogeneity was observed among clusters. 5. The whole‐cell dose‐response curve suggests that activation of current by ACh increases up to at least 100 microM and that multiple ligand binding steps are involved. 6. Drosophila and Musca larval neuronal ACh‐activated channels show some unique features in their cholinergic pharmacological properties: (a) they are only weakly activated by the potent neuromuscular nicotinic agonist suberyldicholine, (b) hexamethonium and decamethonium are weak, but approximately equi‐effective blockers, and (c) alpha‐ and kappa‐bungarotoxin (BTX) both blocked reversibly, though alpha‐BTX appears to be the more potent inhibitor.
Feed artery role in blood flow control to rat hindlimb skeletal muscles.
Authors: Williams D A , Segal S S
Published: December 2014

1. Vasomotor tone and reactivity were investigated in feed arteries of the extensor digitorum longus and soleus muscles. Feed arteries are located external to the muscle and give rise to the microcirculation within each muscle. Resting diameter was smaller in feed arteries of the soleus muscle. 2. Feed arteries of both muscles dilated to similar peak values with sodium nitroprusside. 3. Micropressure measurements demonstrated resistance to blood flow in the feed arteries supplying both muscles. Feed arteries supplying soleus muscle demonstrated greater resistance to blood flow compared to feed arteries of extensor digitorum longus muscle. 4. Greater resting tone and larger pressure drop for feed arteries of soleus muscle suggest greater range of flow control compared to feed arteries of extensor digitorum longus muscle. 5. In both muscles, feed artery diameter increased with muscle contraction (functional dilatation) and in response to transient ischaemia (reactive dilatation). The magnitude of these responses varied between muscles. 6. Feed arteries are active sites of blood flow control in extensor digitorum longus and soleus muscles of the rat. These muscles differ in fibre type and recruitment properties. Differences in feed artery reactivity may contribute to differences in blood flow between these muscles observed at rest and during exercise.
Ionic dependence of a slow inward tail current in rat dorsal raphe neurones.
Authors: Penington N J , Kelly J S
Published: December 2014

1. The mechanism underlying a large slow inward tail current was studied in serotonergic dorsal raphe (DR) neurones. The tail current is most easily observed under conditions of suppressed K+ channel outward currents and follows the activation of a calcium current. This current may underlie a slow after‐depolarizing potential (ADP) which follows action potentials observed in acutely isolated DR neurones. 2. The after‐hyperpolarizing potential (AHP) following action potentials which should reverse at EK (the reversal potential for potassium) becomes an ADP at less negative potentials than expected due to contamination by the slow inward tail current. 3. DR neurones were acutely isolated enzymatically; the ADP in current clamp and the tail current underlying it in voltage clamp were studied using the patch clamp method. When the external Na+ was replaced with TEA or choline the slow inward tail current was completely abolished. Blocking K+ channels from the inside of the cell membrane with 40 mM TEACl or large concentrations of internal Cs+ also blocked the slow inward tail current. 4. The tail current proved to be independent of calcium influx or intracellular calcium release as it was not affected by inorganic calcium channel blockers or caffeine. 5. The tail grew exponentially upon lengthening the depolarizing test pulse and appeared to reverse close to 0 mV indicating that the current was carried by a nonselective cation conductance. Removal of external Na+ and replacement with Li+ ions reversibly blocked the tail current by 77%. 6. The data rule out several mechanisms for the generation of the current, namely: a calcium‐activated chloride conductance, a calcium‐activated non‐selective cation conductance, a Na(+)‐Ca2+ exchange pump current or a sodium‐activated K+ conductance. 7. The slow tail current may be explained by postulating an inward movement of Na+ through a channel which is blocked by high concentrations of external TEA and Li+ or internal Cs+ or 40 mM TEA.
Coupling of dual acid extrusion in the guinea‐pig isolated ventricular myocyte to alpha 1‐ and beta‐adrenoceptors.
Authors: Lagadic‐Gossmann D , Vaughan‐Jones R D
Published: December 2014

1. Intracellular pH (pHi) was recorded in single, isolated guinea‐pig ventricular myocytes using the pH‐sensitive fluorophore, carboxy‐SNARF‐1 (AM‐loaded). 2. The dual acid extrusion system in this cell (Na(+)‐H+ antiport and Na(+)‐HCO3‐ symport) was activated by inducing an intracellular acid load, produced by addition and subsequent removal of extracellular 10 mM NH4Cl. Under these conditions, it is known that both acid‐equivalent extruders are activated about equally. 3. Application of phenylephrine (100 microM; alpha‐adrenergic agonist) resulted in an inhibition of pHi recovery from an acid load, recorded in HCO3‐buffered medium containing 1.5 mM amiloride (amiloride inhibits Na(+)‐H+ antiport; under these conditions pHi recovery is mediated through only the Na(+)‐HCO3‐ symport carrier). This inhibitory effect of phenylephrine was prevented by the alpha 1‐antagonist, prazosin (0.1 microM) and was unaffected by propranolol (1 microM). 4. Application of phenylephrine in Hepes‐buffered medium (only Na(+)‐H+ antiport is active under these conditions) elicited a stimulation of pHi recovery, again prevented by prazosin (0.1 microM). 5. These results point to an alpha 1 inhibition of Na(+)‐HCO3‐ symport and an alpha 1 stimulation of Na+‐H+ antiport. 6. Both adrenaline (1‐5 microM) and noradrenaline (5 microM) slowed pHi recovery recorded in HCO3(‐)‐buffered solution containing amiloride (1.5 mM). The similarity of this result with that obtained previously using phenylephrine (paragraph 3) suggests that all three agonists inhibit the Na(+)‐HCO3‐ symport through alpha 1 activation. 7. Isoprenaline (1 microM; beta‐adrenergic agonist) slowed pHi recovery in Hepes‐buffered solution but stimulated recovery in a HCO3(‐)‐buffered solution containing amiloride (1.5 mM). These results suggest that beta activation slows Na(+)‐H+ antiport but stimulates Na(+)‐HCO3‐ symport. 8. When both acid‐equivalent extrusion carriers were inhibited in Na(+)‐free, HCO3(‐)‐buffered medium, phenylephrine or isoprenaline had no effect on pHi, ruling out any effect of the adrenergic agonists on background acid‐loading mechanisms. 9. Under physiological conditions (CO2/HCO3(‐)‐buffered solution, no amiloride), when both acid extruders would be activated by an intracellular acid load, application of phenylephrine, adrenaline or noradrenaline were found to slow pHi recovery. In contrast, isoprenaline stimulated pHi recovery under the same conditions.(ABSTRACT TRUNCATED AT 400 WORDS)
Decreased energy requirement of toad retina during light adaptation as demonstrated by 31P nuclear magnetic resonance.
Authors: Apte D V , Ebrey T G , Dawson M J
Published: December 2014

1. The effect of light and dark adaptation on the levels of phosphorus metabolites (nucleotide di‐ and triphosphates, phosphocreatine, pyridine nucleotide, inorganic phosphate, phosphodiesters, phosphomonoesters, and uridine diphosphate‐glucose) in the toad (Bufo marinus) retina and retinal extracts was studied by 31P nuclear magnetic resonance (NMR) spectroscopy. 2. Spectra were acquired using an NMR probe specifically designed for superfusion and illumination of a single retina. Retinae were maintained at a steady state for up to 10 h in an electrolyte solution containing 10 mM Hepes buffer and bubbled with 98% O2‐2% CO2, pH 7.8 at 20 degrees C. 3. The intracellular concentrations of the phosphorus metabolites were measured in total darkness or during prolonged exposure to light. The concentration of nucleoside triphosphates (NTP) in the dark‐adapted retina was about 1.5 mM and that of phosphocreatine (PCr) was about 0.7 mM. 4. In saturating levels of light, 6.0 x 10(11) or 1.5 x 10(13) quanta s‐1 cm‐2 at 520 nm, the levels of PCr and phosphomonoesters rose, the levels of NTP and protons (pH) were maintained, and the levels of pyridine nucleotides and nucleotide diphosphates (NDP) fell. 5. A rise in the level of PCr in the presence of an unchanged level of NTP in the light‐adapted retina indicates that the energy consumption of the retina is greater in the dark. 6. These results are in agreement with the results of oxygen consumption, glucose dependence, and electrophysiological studies which also indicate that the metabolic energy requirement of the retina decreases in light.
Intracellular ATP modifies the voltage dependence of the fast transient outward K+ current in Lymnaea stagnalis neurones.
Authors: Lozovaya N A , Vulfius C A , Ilyin V I , Krasts I V
Published: December 2014

1. The action of intracellular ATP on the fast transient outward K+ current (A‐current) was studied in dialysed voltage‐clamped Lymnaea stagnalis neurones. 2. When introduced intracellularly in millimolar concentrations ATP caused a shift of the steady‐state inactivation curve along the voltage axis in the direction of positive potentials and decreased A‐current at all test voltages. 3. Intracellular treatment with an inhibitor of ATP synthesis, sodium arsenate, led to the opposite changes. The action of arsenate was not reversed upon its removal. After wash‐out of arsenate ATP restored the initial voltage dependence. 4. Addition of Mg2+ to the solution weakened the action of ATP in proportion to the Mg2+: ATP concentration ratio. On the other hand, in neurones pretreated with arsenate, Mg2+ did not affect the ATP action. 5. When a mixture of glycolytic substrates was applied after arsenate wash‐out the activation and inactivation curves shifted towards positive voltages. A substrate of oxidative phosphorylation was ineffective in the same conditions. 6. Non‐hydrolysable analogues of ATP, adenosine‐5'‐O‐gamma‐thiotriphosphate and adenylyl imidodiphosphate, did not mimic the ATP action. This means that the ATP effect is mediated by some enzymatic process(es). 7. Elevation of total cytosolic Ca2+ concentration as well as intracellular application of agents increasing intracellular free Ca2+ reduced A‐current amplitude but failed to alter its voltage dependence. Therefore, ATP action cannot be related to activation of Ca2+ transport. 8. Treatment of the neurones with alkaline phosphatase evoked a shift of the inactivation voltage dependence towards hyperpolarizing potentials and increased the A‐current amplitudes at all test voltages. 9. The data indicate that a change in intracellular ATP concentration modulates the A‐current voltage dependence. The effect of ATP is probably the result of phosphorylation of a channel protein or some associated proteins, but lowering of free Mg2+ concentration cannot be excluded. The possible physiological significance of the phenomenon is discussed.
Differences in adaptation between on‐ and off‐centre ganglion cells and rod‐mediated cone sensitization in cat retina.
Authors: Guenther E , Zrenner E
Published: December 2014

1. Response properties of on‐ and off‐centre retinal ganglion cells were investigated in cats. The stimulus parameters were selected so as to demonstrate interactions between the rod and the cone systems. 2. Response versus log stimulus intensity (R‐log I) functions were determined for the receptive field centres while both test stimulus irradiance and the background illumination were varied over a range up to 7 log units. In order to determine the course of adaptation to chromatic stimuli, threshold versus intensity (t.v.i.) functions were measured over a wide range of adaptation levels. 3. An increase in background illuminance produced a shift of the R‐log I functions to higher irradiances of test stimuli in most ganglion cells, indicating a desensitization of the centre response in the presence of background lights. Using test stimuli which most efficiently stimulate the rods (501 nm), clear differences could be seen in the adaptation behaviour of on‐ and off‐centre ganglion cells. Chromatic backgrounds (blue‐green and orange) reduced the responses of off‐centre cells more than those of on‐centre cells (the difference between them amounting to as much as 2 log units). Simultaneously, equivalent t.v.i. functions had significantly steeper slopes (0.94 and 1.1) in the linear proportions of off‐centre cells compared to on‐centre cells (0.76 and 0.75) under light levels mediated by rods. Such differences were not observed when a test stimulus of 575 nm was used which resulted primarily in stimulating the long‐wavelength cone (L‐cone) system. 4. In a subpopulation of off‐centre cells (20% of the total number of off‐centre cells recorded), a strikingly different adaptation behaviour was observed. Here, the presentation of a dim short‐wavelength background produced a shift of R‐log I functions to lower test stimulus irradiances. The receptive field centre became even more sensitive, by up to 1.5 log units, in the presence of dim adapting backgrounds rather than in the dark‐adapted state. Accordingly, the t.v.i. function did not increase monotonically but showed a ‘dip’ in the presence of dim backgrounds. Only at photoic levels, the t.v.i. functions revealed a response behaviour similar to the other ganglion cells. The sensitization with dim backgrounds was only observed in the case of test stimuli designed to stimulate the cone system (575 nm) and in the presence of a rod‐adapting blue‐green background.(ABSTRACT TRUNCATED AT 400 WORDS)
Mechanoreceptors around the tooth evoke inhibitory and excitatory reflexes in the human masseter muscle.
Authors: Brodin P , Türker K S , Miles T S
Published: December 2014

1. The reflex responses evoked in the human masseter muscle by controlled mechanical stimulation of an incisor tooth were examined electromyographically. The stimuli were (slow) pushes and (brisk) taps of about 0.5‐3 N peak force, applied orthogonally to the labial surface. 2. The brisk taps elicited a short‐latency inhibitory reflex that was often followed by an excitatory peak, as has been described earlier. The inhibition increased as the taps became stronger. 3. Slow pushes evoked a long‐latency, primarily excitatory response. The excitation increased with stronger, faster rise‐time pushes; however, with the stronger stimuli, the short‐latency inhibitory response often became evident before the onset of the excitation. 4. The reflex responses to 3 N pushes and 2 N taps were abolished when the receptors around the tooth were blocked with local anaesthetic, indicating that the response was elicited from receptors located within the periodontal area. 5. Prolonged, rapid‐onset displacements evoked a complex reflex response that combined the characteristics of the taps and the pushes. 6. The most likely explanation for the different responses evoked by the pushes and taps is that the patterns of afferent activity elicited by the slow and fast tooth displacements activated different interneuronal pathways to motoneurones. 7. The inhibitory response to taps is essentially a protective reflex which probably serves to reduce the activity of the jaw‐closing muscles when one bites unexpectedly on hard objects. It is suggested that the excitatory response may contribute to the muscle activity required to hold food between the teeth during chewing, or may act as a load compensation reflex to control chewing force.
Visual transduction in human rod photoreceptors.
Authors: Kraft T W , Schneeweis D M , Schnapf J L
Published: December 2014

1. Photocurrents were recorded with suction electrodes from rod photoreceptors of seven humans. 2. Brief flashes of light evoked transient outward currents of up to 20 pA. With increasing light intensity the peak response amplitude increased along an exponential saturation function. A half‐saturating peak response was evoked by approximately sixty‐five photoisomerizations. 3. Responses to brief dim flashes rose to a peak in about 200 ms. The waveform was roughly like the impulse response of a series of four to five low‐pass filters. 4. The rising phases of the responses to flashes of increasing strength were found to fit with a biochemical model of phototransduction with an ‘effective delay time’ and ‘characteristic time’ of about 2 and 800 ms, respectively. 5. Spectral sensitivities were obtained over a wavelength range from 380 to 760 nm. The action spectrum, which peaked at 495 nm, followed the template described for photoreceptors in the macaque retina. Variation between rods in the position of the spectrum on the wavelength axis was small. 6. The scotopic luminosity function derived from human psychophysical experiments was found to agree well with the measured rod action spectrum after adjustments were made for lens absorption and photopigment self‐screening in the intact eye. 7. Responses to steps of light rose monotonically to a maintained level, showing little or no relaxation. Nevertheless, the relationship between light intensity and steady‐state response amplitude was shallower than that expected from simple response saturation. This is consistent with an adaptation mechanism acting on a rapid time scale. 8. Flash sensitivity fell with increasing intensities of background light according to Weber's law. Sensitivity was reduced twofold by lights evoking about 120 photoisomerizations per second. Background lights decreased the time to peak and the integration time of the flash response by up to 20%.
Quantification of exponential Na+ current activation in N‐bromoacetamide‐treated cardiac myocytes of guinea‐pig.
Authors: Mitsuiye T , Noma A
Published: December 2014

1. The activation kinetics of the Na+ current was investigated in single ventricular cells of the guinea‐pig heart using an improved oil‐gap voltage clamp method. The inactivation of the current was removed by an intracellular application of N‐bromoacetamide (NBA) for less than 1 min. Although the NBA treatment slightly decreased the peak amplitudes (81.7 +/‐ 13.4% of control, n = 15), the Na+ current remained stable after the removal of inactivation. 2. On depolarization, the activation of Na+ current took an exponential time course after the capacitive current decreased to 5% of its peak amplitude (40‐100 microseconds after the pulse onset). The time course of deactivation, recorded on repolarization from 1.2 ms depolarization, was also a single exponential. 3. The time constants of activation and deactivation were almost identical when compared at a given test potential within a range of ‐50 to ‐30 mV. These findings indicate that the cardiac Na+ current activation is determined by m1 kinetics, or one rate‐limiting step. 4. At potentials negative to ‐60 mV, the deactivation was complete, and its time constant decreased e‐fold per 20.3 +/‐ 1.8 mV hyperpolarization (n = 7). 5. The degree of steady‐state activation (m(infinity)) was fitted to a Boltzmann equation with a slope factor of 7.4 +/‐ 0.3 mV and a half‐maximum potential of ‐33.3 +/‐ 0.8 mV (n = 8). 6. Rate constants for the rate‐limiting activation step between a closed state and an open state (alpha m, beta m), were determined from m(infinity) and tau m over a potential range between ‐100 and +50 mV. On a logarithmic scale, beta m‐1 was a linear function of the membrane potential over the range ‐100 and ‐30 mV. 7. Fitting the newly determined activation kinetics to the rising phase of the action potential indicated that the activation kinetics in the present study is relevant to the physiological action potential. The density of the Na+ channels thus obtained was 1075 +/‐ 186 pF‐1 (n = 6). 8. The measurements in the NBA‐treated Na+ current were compared with those obtained without treatment.
Projection of cat jaw muscle spindle afferents related to intrafusal fibre influence.
Authors: Taylor A , Durbaba R , Rodgers J F
Published: December 2014

1. A method of classification of muscle spindle afferents using succinylcholine (SCh) and ramp stretches has recently been described, which appears to estimate separately the strength of influence of bag1 (b1) and of bag2 (b2) intrafusal fibres. Increase in dynamic difference (delta DD) indicates b1 influence whilst increase in initial frequency (delta IF) indicates b2 influence. The significance of this classification has now been examined by correlation with the strength of synaptic projection of jaw muscle spindle afferents to the fifth motor nucleus (MotV) and the supratrigeminal region (STR) in anaesthetized cats. 2. Projection strength was estimated by computing the extracellular focal synaptic potential (FSP) from spike‐triggered averages of 1024 sweeps at 100 microns intervals along tracks through STR and MotV. Trigger pulses were derived from spindle afferent cell bodies of the jaw‐closer muscles recorded in the mesencephalic trigeminal nucleus, and characterized by the effect of SCh on their responses to ramp‐and‐hold stretches. 3. The maximum size of FSPs in tracks traversing STR and MotV ranged from 2.08 to 36.99 microV with a mean of 7.55 microV. The amplitudes were bimodally distributed into roughly equal‐sized groups with high and low amplitude FSPs. 4. Mean values of delta IF were significantly greater for the group with large FSPs than for those with small FSPs. There were no significant differences in delta DD. FSP amplitude was significantly positively correlated with delta IF, but not with delta DD. 5. Spindle afferents with high values of FSP amplitude in MotV had a wide range of values of delta DD (b1b2c and b2c groups), while units with large FSPs in STR were all in the b2c category. Some evidence is presented to indicate that this reflects a preferential projection of secondary afferents to the STR. 6. For those units with projection to both STR and to MotV, there was a significant positive correlation between FSP amplitude in the two nuclei. 7. These results indicate that the extent of the b2 influence on spindle afferents predicts the central projection strength better than does the b1 influence. This finding is discussed from the viewpoint of possible developmental and functional issues.
Na+ pump current‐voltage relationships of rabbit cardiac Purkinje cells in Na(+)‐free solution.
Authors: Bielen F V , Glitsch H G , Verdonck F
Published: December 2014

1. The Na+ pump current (Ip) of isolated, single rabbit cardiac Purkinje cells in Na(+)‐free solution was measured at 32‐34 degrees C by means of whole‐cell recording. 2. The Ip amplitude was studied as a function of clamp potential (Vc) and external concentration of various monovalent cations known to activate the Na(+)‐K+ pump. 3. Under conditions which strongly activated Ip the Ip‐Vc curve of the cells displayed a positive slope at membrane potentials negative to ‐20 mV and little variation at more positive potentials. 4. The Ip‐Vc relationship showed an extended region of negative slope at positive and negative potentials in solutions containing low concentrations of activator cations which caused little Ip activation. A positive slope of the Ip‐Vc curve was occasionally observed at clamp potentials negative to ‐60 mV under these conditions. 5. The shape of the Ip‐Vc relation was independent of the cation species used as external Ip activator. 6. At zero membrane potential half‐maximum Ip activation (K0.5(Vc = 0 mV) occurred at 0.05 mM Tl+, 0.08 mM K+, 0.4 mM NH4+ and 1.5 mM Cs+. The Hill coefficient derived amounted to 0.9 for Tl+, 1.2 for K+, 1.04 for NH4+ and 1.5 for Cs+. 7. The concentrations of external activator cations required for half‐maximum Ip activation increased with depolarization. The voltage dependence of the K0.5 values could be described by a single exponential function for clamp potentials positive to ‐40 mV. 8. The steepness of the function is determined by a factor alpha, indicating the apparent fraction of an elementary charge which moves in the electrical field across the sarcolemma when external monovalent cations bind to the Na(+)‐K+ pump. 9. The alpha values were calculated to be 0.32 for Tl+, 0.24 for K+, 0.29 for NH4+ and 0.18 for Cs+. Possible interpretations of the alpha values are considered. 10. It is suggested that binding of external monovalent activator cations to the Na(+)‐K+ pump (or a process related to the binding) is voltage dependent. This potential‐dependent process determines mainly the shape of the Ip‐Vc curve in cardiac Purkinje cells superfused with Na(+)‐free media containing low concentrations (< K0.5(Vc = 0 mV)) of K+ or its congeners.
Activation of a common potassium channel in molluscan neurones by glutamate, dopamine and muscarinic agonist.
Authors: Bolshakov VYu  , Gapon S A , Katchman A N , Magazanik L G
Published: December 2014

1. The potassium currents evoked in isolated and identified neurones of molluscan pedal ganglia by either glutamate, dopamine or the muscarinic agonist F‐2268 were investigated using voltage and patch clamp techniques. 2. Potassium currents induced by either dopamine or F‐2268 could be blocked by pertussis toxin, as well as by a prolonged intracellular injection of the G protein inhibitor, GDP‐beta‐S. Loading the neurones with the G protein activator, GppNHp, on the other hand, induced a potassium current. This current was not additive to the currents evoked by agonist application. 3. Intracellular injection of the calcium buffer BAPTA failed to affect any of the agonist‐induced currents, although it effectively blocked the after‐hyperpolarization following directly evoked action potentials. 4. The activity of the potassium channels seen in cell‐attached patches was greatly enhanced by application to the bath of either glutamate, dopamine, or F‐2268. 5. The only effect of an addition of agonists to the bath was to increase the open probability (Po) of the K+ channel already active in the control conditions. The identity of the spontaneously active and agonist‐activated channels was concluded from the identity of their channel conductances, rectification properties and current amplitudes. 6. Phorbol‐12,13‐dibutyrate, when applied to the bath, induced an increase in open time and caused an increase in Po, as did the agonists. Staurosporine completely prevented changes of Po induced by the phorbol ester but not those induced by the agonists. 7. The same inwardly rectifying potassium channel may be opened by both the receptor‐linked G protein (with glutamate, dopamine, F‐2268) and by protein kinase C (with phorbol ester) activation. 8. Strong evidence was obtained against the involvement of any known secondary messenger systems (formation of nucleotides, phosphoinositide turnover and subsequent activation of protein kinase C, formation of nitric oxide, metabolism of arachidonic acid) in the transduction mechanism of F‐2268‐, dopamine‐ and glutamate‐induced responses. 9. Since none of the known secondary messenger systems seems to affect the activation by agonists applied to receptors outside the patch of channels located under the patch electrode, it appears that some as yet undescribed linking system must exist that could connect the spatially separated receptor‐G protein complex and the potassium channel.
The nature of the decrease in blood‐cerebrospinal fluid barrier exchange during postnatal brain development in the rat.
Authors: Habgood M D , Knott G W , Dziegielewska K M , Saunders N R
Published: December 2014

1. The blood‐cerebrospinal fluid (CSF) exchange of a wide range of passively transported lipid insoluble compounds (0.43‐5.4 nm molecular radius) has been investigated in rats at different stages of postnatal development (2 days old to adult). A novel ‘litter‐based’ model for investigating blood‐CSF barrier exchange in immature animals is described. 2. At each age investigated there was a clear inverse correlation between molecular radius and blood‐CSF barrier exchange, in addition to an overall decrease in blood‐CSF barrier exchange with increasing age. 3. The decrease in blood‐CSF barrier exchange with age was not consistent with a reduction in pore diameters, nor does it appear to be due to an increase in the CSF sink effect with age. It seems likely to be due to a relative decrease in the number of a population of large diameter pores.
Purine nucleoside transport and metabolism in isolated rat jejunum.
Authors: Stow R A , Bronk J R
Published: December 2014

1. The absorption and metabolism of purine nucleosides and their constituent bases has been investigated by perfusion through the lumen of isolated loops of rat jejunum. In control perfusions and those with luminal purines or purine nucleosides, high‐performance liquid chromatography (HPLC) revealed uric acid as the only detectable purine in the mucosal epithelial layer and the serosal secretions unless the xanthine oxidase inhibitor allopurinol was present. 2. Adenosine (0.5 mM) was quantitatively deaminated to inosine in the lumen after perfusion for 30 min. 3. Luminal inosine and hypoxanthine (0.15‐1.0 mM) increased the serosal uric acid concentration significantly (P < 0.001); at 0.5 and 1.0 mM the nucleoside gave a significantly greater (P < 0.01) rate of serosal uric acid appearance than the base. 4. Luminal guanosine (0.05‐0.50 mM) and guanine (0.05‐0.15 mM) increased the serosal uric acid concentration significantly (P < 0.001); with 0.15 mM nucleoside the serosal uric acid appeared significantly faster (P < 0.01) than it did from the base. 5. Luminal allopurinol (0.3 mM) inhibited xanthine oxidase by 80% and reduced serosal purine appearance significantly (P < 0.01) from luminal guanine, hypoxanthine and inosine. With allopurinol, guanosine (0.1 and 0.15 mM) and inosine (0.1‐1.0 mM) gave significantly higher (P < 0.01) total serosal purine concentrations than their respective bases. 6. Inosine and guanosine were cleaved to their respective bases plus ribose phosphate by the action of a cytoplasmic nucleoside phosphorylase, which was found to have widely different Michaelis constants (Km; 318 +/‐ 45 and 41.4 +/‐ 3.6 microM for inosine and guanosine, respectively) and maximum velocities (Vmax; 79.3 +/‐ 4.0 and 20.5 +/‐ 0.05 mumol min‐1 (mg protein)‐1 for inosine and guanosine, respectively). 7. We conclude that hypoxanthine and guanine absorbed by rat small intestine are oxidized to uric acid which is released in the serosa. The corresponding nucleosides are split by phosphorolysis after absorption and the resulting purine bases are converted to uric acid which appears on the serosal side with similar quantities of ribose phosphate.
Splenic control of intravascular volume in the rat.
Authors: Kaufman S , Deng Y
Published: December 2014

1. We tested the hypothesis that hypervolaemia causes an increase in intrasplenic filtration of cell‐free fluid out of the vasculature. To this end we developed a preparation in the anaesthetized rat whereby the splenic vein could be non‐occlusively cannulated. 2. Haematocrit and plasma protein concentrations were measured in the splenic afferent and efferent blood supplies. 3. In response to volume loading with saline (1% body weight), there was a sustained increase in the arterial‐venous differential of haematocrit, i.e. there was a relative increase in the haematocrit of the blood draining from the spleen. There was no such change in plasma protein concentration. By contrast, this degree of volume loading had no effect on the haematocrit of blood passing through the hindquarters of the animal. 4. Following volume expansion, there was no significant difference in the protein concentration of the plasma and the lymph fluid collected from the splenic lymphatic duct. 5. Distension of the superior vena caval‐right atrial junction by means of a small inflatable balloon, caused a similar increase in the splenic venous haematocrit, and again, no change in plasma protein concentration. 6. We interpret these results to mean that, in response to expansion of the intravascular space, there is increased intrasplenic filtration of plasma out of the blood and into the lymphatic system.
Indomethacin reduces acute baroreceptor resetting in the dog.
Authors: Wang W , Brändle M , Zucker I H
Published: December 2014

1. The influence of local perfusion of the carotid sinus with the cyclo‐oxygenase blocker indomethacin on acute baroreceptor resetting was investigated in anaesthetized dogs. 2. The carotid sinus was isolated and perfused with oxygenated Krebs‐Henseleit solution. Single units from the carotid sinus nerve were recorded. The carotid sinus was conditioned with static pressures of 50, 100 and 150 mmHg for 15 min. Following the conditioning period a carotid sinus pressure (CSP)‐discharge curve was constructed using static stepwise increases in CSP. 3. Perfusion of the carotid sinus with indomethacin (20 microM) caused an elevation in the threshold at every conditioning pressure (96.8 +/‐ 4.8 vs. 83.8 +/‐ 4.1 mmHg for 100 mmHg, P < 0.01; 91.9 +/‐ 4.7 vs. 70.3 +/‐ 4.4 mmHg for 50 mmHg, P < 0.01; and 103.5 +/‐ 4.4 vs. 96.4 +/‐ 4.1 mmHg for 150 mmHg, P = 0.06, respectively) and a significant reduction in the peak discharge rate at each conditioning pressure (32.0 +/‐ 4.4 vs. 48.2 +/‐ 5.5 spikes/s for 100 mmHg, P < 0.01; 32.2 +/‐ 5.8 vs. 45.8 +/‐ 5.1 spikes/s for 50 mmHg, P < 0.01; 32.0 +/‐ 3.7 vs. 51.1 +/‐ 8.1 spikes/s for 150 mmHg, P < 0.01). The resetting ratio (change in threshold/change in conditioning CSP) for both downward resetting (conditioning CSP from 100 to 50 mmHg) and upward resetting (conditioning CSP from 100 to 150 mmHg) was significantly decreased after indomethacin (0.10 +/‐ 0.02 vs. 0.27 +/‐ 0.02 for downward resetting, P < 0.01 and 0.14 +/‐ 0.03 vs. 0.25 +/‐ 0.01 for upward resetting, P < 0.01, respectively). 4. Conversely, perfusion of the carotid sinus with arachidonic acid (20 microM) significantly decreased the threshold at each conditioning CSP and increased the peak discharge rate at each conditioning CSP. The resetting ratio was significantly increased after arachidonic acid. 5. There was no change in resting carotid diameter or in the carotid sinus pressure‐carotid diameter relationship after indomethacin or arachidonic acid. 6. Removal of the endothelial cells in the carotid area with saponin did not prevent the effects of indomethacin on baroreceptor resetting. 7. These results suggest that prostaglandins have a tonic effect on the activity of the carotid sinus baroreceptor and may play a role in acute baroreceptor resetting.
Experimental myopia in a diurnal mammal (Sciurus carolinensis) with no accommodative ability.
Authors: McBrien N A , Moghaddam H O , New R , Williams L R
Published: December 2014

1. We examined the functional morphology of the intra‐ocular muscles of the grey squirrel using pharmacological and histological methods. Using sympathomimetic (phenylephrine) and parasympathomimetic (carbachol) agents, administered by transcorneal iontophoresis, the response of the iris sphincter and dilator muscles and the ciliary muscle were recorded. Measurement techniques included both streak retinoscopy and coincidence optometry for measurement of ocular refraction and high resolution ultrasonography to monitor changes in the intra‐ocular component dimensions. 2. The grey squirrel was found not to possess a functional accommodative system. No change in ocular refraction or intra‐ocular dimensions could be induced with 40% carbachol. Marked changes in pupil diameter occurred with topical application of both phenylephrine (dilation) and carbachol (constriction). Histological findings were in agreement with pharmacological findings in showing well developed iris sphincter and dilator muscles but only a poorly developed ciliary muscle. 3. Calculation of the depth of focus of the grey squirrel eye reveals that this could be sufficient to account for the behavioural observations of near viewing habits. 4. We then determined whether we could induce axial elongation of the vitreous chamber and a consequent myopia by monocular deprivation (MD) of pattern vision. 5. Monocular deprivation of pattern vision produced a significant experimental myopia due to axial elongation of the vitreous chamber in the deprived eye. 6. The results demonstrate that a functional accommodative system is not necessary to induce experimental myopia in the grey squirrel eye.