bluuebunny/crossref_metadata_2025 huggingface dataset:
Sodium channels in cultured cardiac cells.
Authors: Cachelin A B , De Peyer J E , Kokubun S , Reuter H
Published: December 2014

Primary cardiac cell cultures were prepared from the hearts of neonatal rats. The patch‐clamp method (Hamill, Marty, Neher, Sakmann & Sigworth, 1981) was applied for studying whole‐cell Na+ currents and single‐channel Na+ currents, respectively. Whole‐cell recordings yielded voltage‐ and time‐dependent Na+ currents which could be blocked by tetrodotoxin. Single‐channel Na+ currents were directly compared in cell‐attached patches and in inside‐out patches. In cell‐attached patches the elementary current was about ‐1 pA at ‐10 mV and the slope conductance over a 50 mV voltage range was 15.1 +/‐ 1.6 pS (mean +/‐ S.D.). Inactivation during depolarization and after conditioning clamp steps, in the steady state, resulted from a reduced opening probability of Na+ channels. In inside‐out patches, with identical solutions at both membrane surfaces, there was a large (40‐50 mV) shift of channel opening and inactivation kinetics towards more negative potentials. However, for levels of comparable opening probabilities, mean open times of Na+ channels were similar in cell‐attached and inside‐out patches. Tetrodotoxin (10‐20 microM) had no effect on Na+ channels when applied from the inside, but blocked them completely after application to the outside membrane surface.
The fatigue of voluntary contraction and the peripheral electrical propagation of single motor units in man
Authors: Borg Jörgen , Grimby Lennart , Hannerz Jan
Published: December 2014

1. Single human motor units from the short extensors of the toes were classified by their voluntary threshold and axonal conduction velocity. The voluntary discharge intervals, and the shortest discharge intervals at which action potentials were conducted to the muscle fibres, were studied during maximal voluntary effort maintained for 1 min, and were compared with the intervals calculated to be necessary for full fusion.

2. Electromyographic techniques were used. High selectivity of the recordings was obtained after blocking of the main motor nerve with lidocaine in subjects with an accessory innervation of just a few motor units or 6 months after lesions to intramuscular nerve twigs, when the muscle‐fibre density within the motor units was increased.

3. For a whole minute of maximal voluntary effort, motor units with low threshold and low conduction velocity fired tonically at a rate that should have been sufficient for maximal tension. These intervals were longer than the intervals at which blocking occurred.

4. In ordinarily motivated and untrained subjects, motor units with high threshold and high conduction velocity fired tonically at intervals sufficient for full tension for some seconds. Under these circumstances the voluntary intervals were longer than the critical ones.

5. Through extraordinary motivation and training, motor units with high threshold and high conduction velocity could also be driven tonically for 20‐60 s at the high rates required for full tension. The critical intervals then approached the voluntary ones. Blockings occurred and increased in frequency as the contraction continued.

6. When motor units with high threshold and high conduction velocity were tetanized electrically at 20 Hz, which was the lowest discharge rate of these units in tonic voluntary contraction, blockings occurred within 60 s.

7. The role of the peripheral block is discussed in relation to loss of tension in prolonged voluntary contraction.
Spatial properties of cells in the rabbit's striate cortex.
Authors: Glanzman D L
Published: December 2014

The rabbit's striate cortex contains a variety of receptive‐field types, including concentric, uniform, simple and complex types. The spatial summation of these receptive fields was studied. Two types of linearity tests were performed: null tests and drifting grating tests. For the null tests, stimuli were sine‐wave gratings, temporally modulated by either a 1 Hz sine‐wave or by a 1 Hz on‐off square wave. For the drifting grating tests, the stimuli were sine‐wave gratings moved across the cells' receptive fields at 1‐3 Hz. Fourier analyses were performed on the averaged data from both the null tests (sine‐wave modulation) and the drifting grating tests. Thirty‐one concentric cells were studied. Of these, nine were classified as X and fourteen as Y based upon their responses to ratings. The X cells exhibited linear spatial summation; their responses were mainly at the fundamental modulation frequency. The Y cells exhibited non‐linear spatial summation. Their responses contained, in addition to a fundamental component, a second harmonic component whose relative strength increased as the spatial frequency of the display was raised. Eight other concentric cells responded poorly to gratings and were classified as sluggish. Other properties of concentric cells were examined, particularly their responses to standing contrast. The X cells' responses were generally sustained, the Y cells' responses generally transient. Sluggish cells were either sustained or transient, but their responses to standing contrast could frequently be distinguished from those of X and Y cells. All five uniform cells studied exhibited non‐linear spatial summation. Their behaviour on the linearity tests was indistinguishable from that of Y cells. Of the seventeen simple cells studied, seven behaved like X cells (linear simple) and ten like Y cells (non‐linear simple). However, near their optimum spatial frequencies the responses of both linear and non‐linear simple cells were dominated by the fundamental component. Two complex cells behaved like complex cells in the cat's striate cortex (Movshon, Thompson & Tolhurst, 1978b). Their responses were qualitatively like those of non‐linear simple cells, but were quantitatively more non‐linear. Near their optimum spatial frequencies, harmonic components dominated their responses. The behaviour of nine other complex cells was difficult to describe. Generally, they were unresponsive to gratings. When they could be made to respond to gratings, they gave phase‐sensitive responses like those of simple cells.
Timing of corticofugal actions on the gracile and cuneate nuclei of the cat.
Authors: Cole J D , Gordon G
Published: December 2014

A comparison is presented of the latencies of corticofugal effects from the contralateral somatosensory cortex (SI) onto the cat's dorsal column nuclei (d.c.n.) under pentobarbitone anaesthesia. The latencies for transmission in the ascending pathway from d.c.n. to SI after stimulation within the gracile and cuneate nuclei were found to be 3.3 ms for the former and 2.8 ms for the latter. The time courses of inhibition of a medial lemniscal mass response following cortical conditioning and evoked by stimulation of peripheral nerves were measured. All latencies were corrected to exclude the different times taken for stimuli to reach the nuclei from the two limbs. The optimal condition‐test interval was 12 ms with a duration of 14.3 ms for the superficial radial nerve (s.r.n.) and 45 ms and 30 ms respectively for the medial plantar nerve (m.p.n.). In each case cortical conditioning inhibited the wave by about 50%. The effect of cortical conditioning upon spontaneously firing d.c.n. single units was investigated. For cuneate cells the mean latency was 6.8 ms and the mean duration 36.8 ms. For gracile cells the latency of onset of inhibition was 17.2 ms and its duration 129 ms. In 75% of cells mixed effects were seen with facilitation preceding inhibition. The latencies of ‘corticofugal reflex’ action on the gracile and cuneate nuclei after stimulation of the s.r.n. and m.p.n. were determined. The gracile response had a latency approximately 4 times that for the cuneate response. The temporal asymmetry of these corticofugal effects suggests that the pathway is not purely a simple feed‐back loop, but may be concerned in other physiological contexts, some of which are discussed.
The structural correlate of the receptive field centre of alpha ganglion cells in the cat retina.
Authors: Peichl L , Wässle H
Published: December 2014

The correlation between the receptive field centre and the dendritic tree of individual brisk transient, or alpha, ganglion cells in the cat retina was investigated by a combination of physiological and anatomical techniques. The sizes of receptive field centres of brisk transient (Y) cells were measured with a flickering spot of light. Contour maps and response (or sensitivity) profiles were measured at mesopic and scotopic backgrounds. Recording positions on the retina and nearby blood vessels were back‐projected onto the receptive field plots on the tangent screen. After recording, whole amount preparations of the retinae were stained by a reduced silver method to stain all alpha cells together with their dendritic trees. By comparing the landmarks on the screen plot with those of the whole mount it was possible to identify the recorded cells in the preparation and to study their morphology. The dendritic tree of an alpha cell determines the position, size and shape of its receptive field centre. The mesopic receptive field centres were found to be a factor of 1.4 +/‐ 0.13 larger than their respective dendritic fields. It is suggested that the dendritic fields of presynaptic neurones (bipolar and amacrine cell processes) add to the ganglion cell dendritic tree to produce the larger centre summating area.
Interaction of hypoxia and hypercapnia on ventilation, tidal volume and respiratory frequency in the anaesthetized rat
Authors: Cragg Patricia A. , Drysdale D. B.
Published: December 2014

1. Ventilation (V̇E), tidal volume (VT), respiratory frequency (f) and arterial and end‐tidal gas tensions were measured in seventy‐one tracheostomized New Zealand white rats (∼ 405 g) anaesthetized with an initial dose of pentobarbitone followed by repeated small doses to ensure that a weak limb‐withdrawal reflex remained.

2. O2 consumption (1.2 ml (s.t.p.d.) min−1 100 g−1), CO2 production (1.0 ml (s.t.p.d.) min−1 100 g−1), heart rate (357 min−1), V̇E (43 ml min−1 100 g−1), Pa,CO2 (34 mmHg) and Pa,O2 (84 mmHg) in the control periods did not change significantly during the course of the experiment.

3. Inspirates of 21% O2 with 2‐10% CO2, 15, 10 or 7.5% O2 with either no or sufficient CO2 to maintain normocapnia and 15 or 10% O2 with 4, 6 or 8% CO2 were tested. Steady‐state responses were measured after 2 min of exposure.

4. Hypoxic—hypercapnic interaction on V̇E, VT and f determined by a three‐inspirate test ((i) hypoxia alone, (ii) hypercapnia and (iii) these hypoxic and hypercapnic levels combined) yielded various conclusions depending on the level of asphyxia examined. Essentially, the milder the asphyxia the more the interaction appeared additive or even multiplicative and the stronger the asphyxia the more the interaction appeared occlusive. However, this test is unsuitable for accurately showing interactions because the Pa,O2 achieved in asphyxia was higher than in hypoxia and the asphyxial Pa,CO2 was lower than in hypercapnia.

5. For isoxic conditions (Pa,O2 = 97, 77 and 51 mmHg), V̇E and VT were related linearly to Pa,CO2 whilst f was related hyperbolically with convexity upwards (Pa,O2 97 mmHg) or downwards (Pa,O2 77 and 51 mmHg).

6. For isocapnic conditions (Pa,CO2 = 33, 40 and 48 mmHg), V̇E and VT were inversely related to Pa,O2 with a hyperbolic curve (convexity downwards) whilst f was inversely and linearly related (Pa,CO2 33 mmHg) or constant (Pa,CO2 40 and 48 mmHg).

7. Multivariate analyses showed that the hypoxic—hypercapnic interaction was additive for VT but occlusive for V̇E and f and the occlusion was more severe in the latter. This was illustrated graphically for the variable plotted against Pa,CO2 or Pa,O2 as parallel shifts in regression lines for VT, flatter regression lines for V̇E during asphyxia and a virtually constant f during asphyxia.

8. V̇E responses and sensitivities to hypoxia and hypercapnia, the shape of V̇E, VT and f regression lines against Pa,O2 and Pa,CO2 and the type of hypoxic—hypercapnic interaction on each variable in the rat were compared with other species.

9. Possible causes of the occlusive hypoxic—hypercapnic interaction in the rat were considered.
The effect of intravenous adrenaline and noradrenaline infusion of peripheral lymph flow in the sheep.
Authors: McHale N G , Roddie I C
Published: December 2014

Pressure fluctuations and lymph flow were measured in popliteal, prefemoral and mesenteric efferent lymphatic vessels in conscious sheep. Intravenous adrenaline infusion increased frequency of lymphatic contraction and lymph flow in all three vessels. In the case of the prefemoral vessels flow remained high after the infusion had stopped. Intravenous noradrenaline infusion also increased frequency of contraction and lymph flow in all three vessels but prefemoral flow was depressed after the infusion had stopped. Lymphatic frequency of contraction and lymph flow increased when the animals were started. Anaesthetizing the animals with pentobarbitone did not abolish lymphatic contractions, nor did it prevent the response to adrenaline and noradrenaline infusion. The most obvious interpretation of these results is that adrenaline and noradrenaline act by increasing frequency and force of pumping of lymphatic vessels.
Raised intracellular free calcium within the lens causes opacification and cellular uncoupling in the frog.
Authors: Jacob T J
Published: December 2014

Ion‐sensitive micro‐electrodes were used to measure the levels of intracellular free Ca2+ within the intact amphibian lens. The free [Ca2+] was found to constitute 0.4% of the total lens calcium. The pCa measured at the anterior lens surface was found to 6.59, while that at the posterior was 5.70. An 8‐fold anterior/posterior Ca2+ gradient thus exists along the optical axis. The intracellular free Ca2+ could be manipulated by incubating the lens in high‐Ca2+ or cA2+‐free EGTA Ringer solutions. Raising the intracellular free Ca2+ to 0.22 mM caused lens opacification and cellular uncoupling; the coupling ratio was reduced from 1 in control to 0.41 in high Ca2+.
Depression of calcium‐dependent potassium conductance of guinea‐pig myenteric neurones by muscarinic agonists.
Authors: North R A , Tokimasa T
Published: December 2014

Intracellular recordings were made from myenteric neurones of the guinea‐pig ileum. Muscarinic agonists acetylcholine (ACh) and oxotremorine reduced membrane potassium conductance (gK). Calcium carried into the neurone by one or more action potentials increased membrane potassium conductance (gK, Ca). The time course of the muscarinic changes in gK was compared to that of the change in gK, Ca following an action potential. The time course of conductance decrease was similar in both cases, and both time courses had the same temperature coefficient. Concentrations of ACh (100 nM) which were too low to cause a detectable reduction in resting gK shortened the duration of the gK, Ca increase which followed an action potential. Low concentrations of barium (10‐100 microM) had the same effect as ACh. This was not due to a reduction in calcium entry during the action potential. Higher concentrations of ACh and barium also reduced resting membrane conductance. The conductance changes during the muscarinic action and the action potential after‐hyperpolarization did not add linearly. It is proposed that muscarinic agonists and barium may act by reducing the availability of calcium ions at a site within the membrane which controls gK.
Cells responsive to free‐field auditory stimuli in guinea‐pig superior colliculus: distribution and response properties.
Authors: King A J , Palmer A R
Published: December 2014

We have investigated the responses of superior colliculus neurones in the anaesthetized guinea‐pig to free‐field auditory stimulation. The auditory cells were located throughout the deeper laminae and also in the lower part of the stratum opticum. Auditory cells were not found in the rostral pole of the superior colliculus. The auditory responses consisted of a few spikes at stimulus onset with a latency from stimulus arrival at the ear of 7‐27 ms. Frequency response areas were measured for forty‐five neurones; many of these areas were broad or multipeaked although some were well defined and ‘V’ shaped. White noise was a more effective stimulus than tones. The majority of cells in our sample responded best to sounds from a restricted horizontal location. Two major response types were found: (1) neurones responding to the same localized area of space despite changes in sound level and (2) neurones responding only to a localized area of space near threshold, but to an extensive area for louder sounds. As the site of the recording electrode was moved from the rostral to the caudal part of the superior colliculus, the location of the auditory receptive fields shifted from the anterior to the posterior field of the animal, thus indicating the presence of a map of auditory space. The visual projection to the guinea‐pig superior colliculus was determined and found to be similar to that in other vertebrates. Comparison of visual and auditory space maps in the guinea‐pig superior colliculus reveals that receptive fields are coincident over a wide range, but severe discrepancies were evident between the visual and auditory receptive field positions represented at single locations in rostral and caudal colliculus.
The ionic basis of action potentials in petrosal ganglion cells of the cat.
Authors: Gallego R
Published: December 2014

The ionic conductances underlying the action potential and after‐hyperpolarization of the cat petrosal ganglion neurones with myelinated axons in the carotid nerve were studied in vitro. Neurones were divided into two groups based on the presence or absence of an inflexion or hump on the spike falling phase. The application of tetrodotoxin (TTX, 3 X 10(‐7)‐3 X 10(‐6) M) revealed the presence of a TTX‐resistant component in spikes with a hump, which was abolished in Na+‐free solution. The action potential without a hump was blocked by TTX. The spike hump decreased or was abolished when Ca2+‐channel blockers (Mn2+, 3‐4 mM or Co2+, 5 mM) or low‐Ca2+ solutions (0.1‐0.2 mM) were applied to the preparation. In neurones with a hump on the spike, regenerative responses were obtained in Na+‐free, high‐Ca2+ (8.8 mM) solution; these responses were antagonized by Mn2+, and their amplitude was proportional to the external Ca2+ concentration. It is concluded that the action potential with a hump was produced by an Na+ current, a part of which was TTX‐resistant, and by a Ca2+ current which is responsible for the hump. Neurones without a hump had a TTX‐sensitive Na+ spike. The spike with a hump was followed by a long‐lasting after‐hyperpolarization which reversed polarity at about ‐82 mV. During the hyperpolarization an increase in membrane conductance was observed. The amplitude and duration of the long hyperpolarizing potential decreased when Ca2+‐channel blockers or low‐Ca2+ solutions were applied. In Na+‐free solution, regenerative responses were followed by a long hyperpolarization associated with an increase in membrane conductance. It is concluded that the long after‐hyperpolarization is produced by activation of the Ca2+‐dependent K+ conductance.
The number of synaptic boutons terminating on Xenopus cardiac ganglion cells is directly correlated with cell size.
Authors: Sargent P B
Published: December 2014

The relationship between the size of parasympathetic neurones and the number of synaptic boutons terminating upon them has been studied in the cardiac ganglion of Xenopus laevis. Synaptic boutons were visualized by impregnation with zinc iodide and osmium (ZIO), which by electron microscopy was shown to stain heavily all synaptic boutons in six preparations. Light microscopic examination of the unipolar ganglion cells in intact tissue reveals that larger neurones have more synaptic boutons. The number of boutons terminating on the cell body is significantly correlated with its surface area. By statistical means it was possible to demonstrate that the relation between bouton number and surface area is linear and that the regression line has a y‐intercept not significantly different from zero. Therefore the density of synaptic boutons, one per 127 micron2 of cell body surface, is independent of cell size. The size of synaptic boutons, measured as the area of apposition between bouton and cell body, is similar for small and for large ganglion cells; thus a constant fraction (2%) of the cell body on average is covered by synaptic boutons, regardless of cell size. The correlation between bouton number and cell body surface area is not the result of interaction between boutons. The frequency distribution of boutons per normalized cell was found to be similar to that expected from the Poisson distribution. Thus the probability that a bouton will be ‘assigned’ to a particular cell is independent of how many other boutons are present. The only factor that appears to influence the number of boutons on the cell body is its size.
Amplitude fluctuations in synaptic potentials evoked in cat spinal motoneurones at identified group Ia synapses.
Authors: Redman S , Walmsley B
Published: December 2014

Excitatory post‐synaptic potentials (e.p.s.p.s) were evoked in spinal motoneurones (of anaesthetized cats) by impulses in single group Ia axons. The morphological details of the Ia axon‐motoneurone connexion involved in generating each e.p.s.p. were subsequently reconstructed, as described by Redman & Walmsley (1983). The fluctuation pattern of the peak amplitude of each e.p.s.p. was determined using a deconvolution method, taking into account the recording noise. Four e.p.s.p.s were analysed. One did not fluctuate in amplitude; the others fluctuated between discrete amplitudes which were separated by quantal increments. The number of increments which must be added to produce the largest peak amplitude of each e.p.s.p. was always less than, or equal to, the number of synaptic boutons in the connexion at which the e.p.s.p. was generated. The results are consistent with the hypothesis that transmission occurs in an all‐or‐none manner at each synaptic bouton. Different boutons in the termination of a Ia axon with a motoneurone have different probabilities of releasing transmitter, and this probability is sometimes zero at low stimulation rates. The results support the idea that the discrete amplitudes of an evoked e.p.s.p. result from intermittent transmission, in an all‐or‐none manner, at some or all of the boutons in the termination.
Post‐natal development of the cerebello‐cerebral projection in kittens.
Authors: Kawaguchi S , Samejima A , Yamamoto T
Published: December 2014

Post‐natal development of the cerebello‐cerebral response was investigated in 126 kittens from birth to 142 days of age by analysis of laminar field potentials in the cerebral cortex; the thalamocortical projection mediating the cerebello‐cerebral response was examined on four new‐born and three one‐month‐old kittens by means of anterograde axonal transport of horseradish peroxidase. A marked response was evoked in the frontal motor cortex from birth and an appreciable response could be evoked in the parietal association cortex at 2 days after birth. The latency of response in the frontal cortex decreased sharply from birth till 3 weeks of age whereas that in the parietal cortex remained almost unchanged until 2 weeks of age. Maturation of the cerebello‐cerebral projection, in every respect, proceeds earlier in the frontal cortex than in the parietal cortex. The cerebello‐cerebral response in kittens at any age, like in adult cats, consisted of two types of elementary responses: one which is characterized by a surface positive‐depth negative (s.p.‐d.n.) wave and the other which is characterized by a surface negative‐depth positive (s.n.‐d.p.) wave. The response in the frontal cortex was a sequential occurrence of the two waves while the responses in the parietal cortex was a pure form of the s.n.‐d.p. wave. Two types of thalamocortical projections corresponding to the two types of elementary responses were revealed: one is the projection mainly onto layer I which appears to mediate the s.n.‐d.p. wave and the other is the projection mainly onto layer III which appears to mediate the s.p.‐d.n. wave. Development of the cerebello‐cerebral response and changes in the terminal distribution of the thalamocortical projection during maturation are consistent with the principle of ontogenesis of the mammalian neocortical organization, i.e. ascending sequential maturation.
Post‐synaptic potentials in a population of motoneurones following activity of single interneurones in the cat.
Authors: Brink E , Harrison P J , Jankowska E , McCrea D A , Skoog B
Published: December 2014

The technique of recording post‐synaptic potentials from a population of motoneurones, by recording from ventral roots perfused with isotonic sucrose, has been applied to investigate the action of single last‐order interneurones; the target motoneurones were in either caudal L7 or S1 segments. Using spike‐triggered averaging, the inhibitory action of 70% of previously identified last‐order interneurones (Renshaw cells and lamina VII Ia inhibitory interneurones) has been detected. Previous observations had suggested that interneurones mediating disynaptic non‐reciprocal inhibition from group I muscle afferents should be characterized by (i) location in laminae V‐VI, (ii) monosynaptic group I input and (iii) ascending collateral axonal projection to upper lumbar segments. 65% of interneurones with these characteristics were found to inhibit motoneurones. In addition, spike‐triggered averaging from this group of laminae V‐VI interneurones sometimes revealed a depolarizing potential which preceded the inhibitory potential evoked by the interneurone. The depolarizing potential is interpreted as being due to the action of some presynaptic fibres which branch to innervate both the investigated interneurones and motoneurones.
N‐methyl aspartate activates voltage‐dependent calcium conductance in rat hippocampal pyramidal cells.
Authors: Dingledine R
Published: December 2014

The depolarizing actions of N‐methyl‐DL‐aspartate (NMA) and L‐glutamate on pyramidal neurones were compared in a hippocampal slice preparation. Tetrodotoxin (1 microM) was added to the perfusion solution to suppress regenerative Na conductances. Depolarization evoked by ionophoretic application of NMA triggered slow, high‐threshold regenerative spikes. These are considered to be Ca spikes since the amplitude and rate of rise could be reduced by verapamil, D‐600, Co2+ and Mn2+, and increased by Ba2+. Multiple Ca‐spike thresholds could be demonstrated in the same cell. In contrast, depolarizations evoked by L‐glutamate only rarely triggered Ca‐spikes. The minimum latency to the onset of depolarization evoked by NMA was less than 20 ms. The latency and amplitude of NMA‐evoked responses were highly dependent on the position of the ionophoretic pipette; movements of the pipette by as little as 10‐50 micron could markedly change the size of the response. Spatially separate hot spots for NMA and glutamate were not found. Depolarizations evoked by small to moderate ionophoretic currents of NMA were usually associated with an apparent rise in input resistance, as tested by the response to transmembrane current pulses. Ionophoresis of L‐glutamate, or high NMA doses, however, usually caused a fall in input resistance. Both the depolarization and the conductance change evoked by NMA were highly voltage‐dependent within the approximate range ‐50 to ‐80 mV; they could be increased by modest depolarization and reduced by hyperpolarization of the membrane. No reversal potential could be demonstrated in the hyperpolarizing direction. Rather, the NMA response approached zero asymptotically at sufficiently hyperpolarized membrane potentials. Subthreshold depolarizations and conductance changes elicited by NMA could be blocked by Co2+, Mn2+ and Cd2+, and reduced by D‐600 and verapamil. These Ca2+ antagonists had little or no effect on resting membrane potential or input resistance, or on responses to L‐glutamate. Ba2+ increased the amplitude of subthreshold NMA responses. Intracellular injection of Cs+ plus tetraethylammonium caused cells to fire large, prolonged (up to 15 s) Ca spikes, presumably because most K+ conductances were blocked. Under these conditions the effect of NMA was unchanged or enhanced. Raising [K+]o to 10.5 mM (from the normal 3.5 mM) caused a depolarization and fall in input resistance, but did not change the amplitude or voltage dependence of the NMA response. Reducing [Na+]o caused an initial increase, then usually a delayed decrease in the amplitude of the NMA response.(ABSTRACT TRUNCATED AT 400 WORDS)
Neuroendocrine responses to stimulation of the vagus nerves in bursts in conscious calves.
Authors: Adrian T E , Bloom S R , Edwards A V
Published: December 2014

Effects of stimulation of the peripheral ends of the vagus nerves below the heart at 4 Hz continuously, and at 40 Hz for 1 s at 10 s intervals, have been compared in conscious calves below behavioural threshold. Neither pattern of stimulation caused any significant change in mean aortic blood pressure or heart rate but both invariably produced a substantial increase in the flow of intestinal lymph. Each form of stimulation provoked release of glucagon, insulin and pancreatic polypeptide from the pancreas and produced a small but significant rise in mean arterial plasma glucose concentration. The release of gastric inhibitory peptide‐ and bombesin‐like molecules from the gastrointestinal tract was not affected by vagal stimulation whereas release of vasoactive intestinal peptide was observed in response to both patterns of vagal stimulation. Evidence was obtained to suggest that gastrin‐like peptides are preferentially released into the bloodstream whereas cholecystokinin‐like peptides are not. Vagal stimulation releases somatostatin from the gastrointestinal tract but discontinuous stimulation seems to inhibit the release of somatostatin into the general circulation. The results that have been obtained, employing this particular protocol, suggest that the pattern of the stimulus that is applied to the vagal splanchnic innervation has relatively little effect on neuroendocrine response in this species.
Motor unit size and synaptic competition in rat lumbrical muscles reinnervated by active and inactive motor axons.
Authors: Ribchester R R , Taxt T
Published: December 2014

The size of motor units has been measured in adult rat muscles reinnervated by active and inactive motor axons. The results suggest that active nerve terminals have a competitive advantage over inactive terminals during neuromuscular synapse elimination. The experiments were done using the fourth deep lumbrical muscle in the rat hind foot, which receives its motor innervation from the lateral plantar nerve (l.p.n.) and the sural nerve (s.n.). The muscles were denervated by a nerve crush close to the muscle. Five to ten days later, nerve impulse conduction in the l.p.n. was blocked for 1‐2 weeks by chronic superfusion of the nerve with tetrodotoxin (Betz, Caldwell & Ribchester, 1980 b). After 2 weeks of l.p.n. block, the isometric tetanic tension of s.n. motor units increased about two‐fold, compared with contralateral control muscles. This was due to an increase in the number of muscle fibres innervated by s.n. motor axons. Intracellular recordings showed that more fibres were innervated by the s.n. than in normal muscles. In some animals, the blocked l.p.n. was cut 1‐2 weeks later. The l.p.n. terminals were allowed to degenerate for 1‐2 days. There were more s.n. terminals in zinc iodide‐osmium stained preparations of these muscles than in normal muscles. Calculation of tetanic tension overlap between l.p.n. and s.n. motor units, and the amount of mono‐neuronal innervation seen in intracellular recordings suggested that a larger fraction of the muscles was innervated only by s.n. motor nerve terminals than in controls. This fraction increased with time, ultimately reaching about 14% of the muscle per s.n. motor unit. The expansion of the s.n. motor units appeared to take place by terminal and preterminal sprouting of motor axons. The l.p.n.‐evoked tetanic tension decreased in parallel with the increase in the s.n. tetanic tension. The decrease in the l.p.n. twitch tension did not parallel the increase in the s.n. twitch tension. At least part of this discrepancy was due to repetitive firing of the regenerated, inactive l.p.n. terminals when the nerve was stimulated electrically. The results support the notion that modifications in connectivity between pre‐ and post‐synaptic cells can come about by growth or withdrawal of terminals, as a result of differences in the level of activity in the presynaptic cells (Hebb, 1949).
Effects of vasoactive intestinal polypeptide (VIP) on renal function and plasma renin activity in the conscious rabbit.
Authors: Dimaline R , Peart W S , Unwin R J
Published: December 2014

Conscious rabbits received either vasoactive intestinal polypeptide (VIP) at a dose of 1, 10 or 25 pmol kg‐1 min‐1 or vehicle alone (control) through an ear vein for 2 h. Experimental design followed a randomized Latin square arrangement. VIP led to a decrease in effective renal plasma flow and glomerular filtration rate (P less than 0.01) during infusion of the middle and high doses. Mean arterial blood pressure rose slightly (P less than 0.05) and filtration fraction increased (P less than 0.01) during infusion of the middle dose. The high dose produced a rise in heart rate, a fall in plasma sodium, potassium and phosphate concentrations and a rise in plasma solids (P less than 0.01). In spite of the renal haemodynamic effects and changes in plasma composition during infusion of the high dose, fractional excretion of sodium, potassium and chloride doubled (P less than 0.05), suggesting a direct action of VIP on renal tubular function. Plasma renin activity increased between 2‐ and 3‐fold (P less than 0.01). The mechanism of the renin response is uncertain. These results, together with the reported presence of VIP‐like material in the renal cortex, may indicate a role for VIP in the regulation of renal function, including renin release.
Effects of extracellular calcium and of light adaptation on the response to dim light in honey bee drone photoreceptors.
Authors: Raggenbass M
Published: December 2014

Light responses in honey bee drone photoreceptors were recorded with intracellular micro‐electrodes in superfused slices of retina. The effects of changes in extracellular calcium on the size and the shape of the response to dim light were studied and compared with the effects of light adaptation. Dim light stimuli were used so that the amplitude of the response was linearly related to the number of the photons absorbed, the effects of voltage‐dependent mechanisms were negligible and no detectable light adaptation was produced by the stimulus. Lowering the extracellular calcium concentration increased the amplitude and the duration of the response. Raising the extracellular calcium concentration produced the opposite effects. Changing the extracellular calcium concentration modified the response without altering either the linearity of the intensity‐‐response relation or the resting membrane potential in the dark. Light adaptation decreased the amplitude and the duration of the response in a manner that could be quantitatively simulated, in the same photoreceptors, by an increase in the extracellular calcium concentration. Changing the extracellular calcium concentration, or light‐adapting the preparation, modified the response without altering its early depolarizing phase. Lowering external calcium either did not affect, or slightly increased, the maximum rate of the light‐induced depolarization; raising external calcium, or light‐adapting the preparation, either did not affect, or slightly decreased, the maximum rate of the light‐induced depolarization. The experimental data can be quantitatively described by a mathematical model with the basic assumption that calcium acts in the process of light adaptation by decreasing the mean open time of the light‐activated channels.
Sarcoplasmic reticulum calcium release in frog skeletal muscle fibres estimated from Arsenazo III calcium transients.
Authors: Baylor S M , Chandler W K , Marshall M W
Published: December 2014

Single twitch fibres, dissected from frog muscle, were injected with the metallochromic dye Arsenazo III. Changes in dye‐related absorbance measured at 650 or 660 nm were used to estimate the time course of myoplasmic free [Ca2+] following either action potential stimulation or voltage‐clamp depolarization (temperature, 15‐17 degrees C). The amplitude of the Ca2+ transient decreased when fibres were stretched to sarcomere spacings approaching 4 microns. The effect appeared to be less marked in H2O Ringer than in D2O Ringer, where a reduction of about 40% was observed in going from 3.0 microns to 3.7‐3.9 microns. In fibres heavily injected with dye (1.5‐2.2 mM‐dye) at least 0.1 mM‐Ca2+ was complexed with Arsenazo III following a single action potential, implying that at least 0.1 mM‐Ca2+ was released from the sarcoplasmic reticulum (s.r.) into the myoplasm. Computer simulations were carried out to estimate the flux of Ca2+ between the s.r. and myoplasm (in fibres containing no more that 0.8 mM‐dye). The amounts and time courses of Ca2+ bound to the Ca2+‐regulatory sites on troponin and to the Ca2+, Mg2+ sites on parvalbumin were estimated from the free [Ca2+] wave form and the law of mass action. In the computations the total myoplasmic [Ca2+] was taken as the total amount of Ca2+ existing either as free ion or as ion complexed with dye, troponin or parvalbumin. The time derivative of total myoplasmic [Ca2+] was used as an estimate of net Ca2+ flux (release minus uptake) from the s.r. into myoplasm. Rate constants for formation of cation: receptor complex were taken from published values. For the Ca2+‐regulatory sites on troponin, three sets of rate constants, corresponding to two values of dissociation constant (0.2 and 2 microM) were used. Each set of three simulations was carried out both with and without parvalbumin. The simulations show that following action potential stimulation, 0.2‐0.3 mM‐Ca2+ enters the myoplasm from the s.r. The wave form of s.r. Ca2+ release is early and brief compared with the wave form of free [Ca2+]. Neither the selection of troponin rate constants nor the inclusion of parvalbumin has much effect on the shape of the release wave form; the main effect of varying these parameters is to change the magnitude. After the initial, rapid phase of Ca2+ release from the s.r. there is a longer, maintained period of Ca2+ uptake.(ABSTRACT TRUNCATED AT 400 WORDS)
Plasticity in the binocular correspondence of striate cortical receptive fields in kittens.
Authors: Dürsteler M R , von der Heydt R
Published: December 2014

The influence of visual experience on the correspondence in position and orientation of receptive fields in the two eyes of cortical neurones was studied. Kittens were reared viewing the environment through lenses that magnified the image by 9% in one direction (meridional size lenses) with axes of magnification oriented 45 degrees left and right of vertical for the two eyes. The unequal deformations in the two eyes produced gradients of position disparity and systematic variation of orientation disparity which could not be influenced by eye movements. Two types of arrangement of the lenses, producing opposite disparities, were used; each was worn by two kittens. The receptive fields of cortical neurones were studied in the four kittens aged 3‐4 months. In the binocular cells, the positions of the response fields were plotted, and the preferred orientations determined, using automatic stimulus variation, quantitative analysis, and eye‐drift correction. By means of regression analysis, the degree of ‘interocular deformation’ was assessed; a coefficient D was derived from the positions, an angle beta from the orientations. D specified the position incongruity as a fraction of retinal eccentricity, beta the difference between the orientation incongruities of cells with near‐vertical and near‐horizontal receptive fields. Both D and beta were found to be of opposite signs in the two groups of kittens, as predicted by the optical effects of the lenses. The difference in D between the groups was 0.197 (predicted: 0.172); the difference in beta was 17.0 degrees (predicted: 18.9 degrees). Thus, the difference in visual environment had been completely compensated by adjustments in the positions as well as the orientations of the receptive fields. Since D and beta are independent of the alignment of the eyes, the differences between the groups reflected different functional connexions at the cortical level. Possible advantages of plasticity for the development of binocular vision are discussed. It is argued that the plasticity demonstrated here reflects a more general property of cortical receptive fields.
Synaptic activation of phasic bursting in rat supraoptic nucleus neurones recorded in hypothalamic slices.
Authors: Hatton G I , Ho Y W , Mason W T
Published: December 2014

Using slices of rat hypothalamus (400‐500 micron thick), intracellular and extracellular recordings were made of activity from eight‐eight neurones in the supraoptic nucleus (s.o.n.). Electrical stimulation with single stimuli dorsolateral to s.o.n. was excitatory to fifty‐nine phasically firing cells (67% of total, 95% of phasic cells). In intracellularly recorded cells, such stimulation reliably evoked excitatory post‐synaptic potentials which often gave rise to action potentials. Trains of stimuli reliably triggered bursts of action potentials which continued after stimulation had ceased. Stimulation more dorsal or more lateral to the critical region or in the optic tract adjacent to the s.o.n. did not evoke responses. Stimulation dorsomedial to the nucleus produced only direct, probably antidromic, activation of s.o.n. neurones. Application of acetylcholine (ACh) by microperifusion in the s.o.n. region mimicked the effect of electrical stimulation by evoking prolonged discharge in eight of eight tested phasically firing s.o.n. neurones. Non‐phasic, continuously firing neurones were either inhibited or unaffected by electrical stimulation in the critical region. The discharge pattern of unaffected cells (six cells) was not modified by locally applied ACh, although they were excited by local application of sodium glutamate. The excitatory, synaptically mediated, responses to stimulation in the dorso‐lateral region were blocked reversibly by the nicotinic blockers, d‐tubocurarine chloride and hexamethonium bromide (in seven of seven cells tested), but were unaffected by the muscarinic blocker, atropine, even at high concentrations (two of two cells tested). Thus, this activation appears to be mediated by nicotinic receptors. In separate experiments with the position of stimulating and recording electrodes reversed, s.o.n. stimulation was effective in antidromically activating one cell of sixty‐eight recorded extracellularly in the dorsolateral region. Some slowly firing s.o.n. neurones (less than 4 Hz) were inhibited by electrical stimulation in the same area in which phasically active cells were excited. In these cases, stimulation produced large summating i.p.s.p.s. and/or inhibition of ongoing activity for the duration of the stimulus train. These results support evidence from earlier studies that the cholinergic input to s.o.n. neurones originates from cells in its close proximity, and suggests this input to be via a monosynaptic pathway.
Voltage‐clamp study of the conductance activated at fertilization in the starfish egg.
Authors: Lansman J B
Published: December 2014

Ionic currents underlying the fertilization potential of the egg of the starfish Mediaster aequalis were studied using a two‐micro‐electrode voltage clamp. Mature eggs were fertilized in vitro under voltage‐clamp conditions. The fertilization current, here termed IF, was induced by adding sperm to sea water bathing the egg. At a holding potential of ‐70 mV, IF was inward. It reached a peak within 2‐4 min and then decayed over the next approximately 20 min with a rate which depended on the holding membrane potential. Instantaneous current‐voltage relations measured at different times during IF were approximately linear and reversed at a potential of +6.0 +/‐ 5.8 mV (mean +/‐ S.D., n = 11). Membrane chord conductance was highest at the peak of inward current and the declining phase of IF was due to a decrease in conductance towards the pre‐fertilization level. When the membrane potential was rapidly stepped to levels more positive than about ‐45 mV, the conductance underlying IF decreased in a manner which depended on both membrane potential and time. The fertilization‐specific conductance showed a sigmoidal activation curve between ‐50 and +10 mV with a half‐activation level of ‐25 mV. Analysis of the steady‐state voltage dependence indicated that at the peak of the fertilization potential (+10 to +15 mV) only 4‐5% of the total available channels would be open. Current relaxations followed first‐order kinetics and the relaxation time constant depended upon the membrane potential during the voltage pulse. The relation between the time constant and voltage was bell‐shaped, decreasing at potentials more negative than ‐40 and more positive than 0 mV. Both the steady‐state conductance‐voltage relation and the kinetics of the current relaxations were consistent with a simple two‐state gating model in which the probability of a channel being open is determined by a single gating particle with an effective valency of ‐1.7 moving through the entire membrane field. The shifts in reversal potential with changes in external Na (at 10 mM‐external K) were analysed using the constant field expression, which gave a relative permeability of Na to K of approximately 0.6.(ABSTRACT TRUNCATED AT 400 WORDS)
Relationship between intestinal motility, tone, water absorption and lymph flow in the rat.
Authors: Lee J S
Published: December 2014

The relations between motility, tone, water absorption rate (Jv) and lymph flow (J1), were studied in an exteriorized upper jejunal preparation in vivo, with its serosal side bathed in Krebs‐Ringer or other solutions. Neither Jv nor J1 was correlated with motility. When the luminal fluid consisted of an isotonic solution of MgSO4, glucose or LiCl, motility was greatly increased with no increase in J1. When the serosal fluid consisted of an isotonic solution of mannitol, glucose or MgSO4, motility was depressed with a large decrease in tone, and Jv was increased by 51‐83% with a decrease in J1. When the serosal fluid consisted of an isotonic solution of NaCl, Na2SO4, LiCl or KCl, motility was decreased with either no change or an increase in tone, and both Jv and J1 were much decreased. When isotonic choline Cl solution was employed as the serosal fluid, motility increased with an increase in tone, Jv became negative (fluid secretion), and J1 decreased to 0. Acetylcholine depressed motility but increased tone with a decrease in Jv and J1. Eserine increased both tone and motility with a decrease in Jv and J1. Serotonin caused no change in motility but increased tone with a decrease in Jv and J1. Noradrenaline and adrenaline depressed motility and reduced tone with an increase in Jv and J1. Isoprenaline abolished motility and reduced tone with a large increase in Jv but no change in J1. Pentobarbitone depressed motility and reduced tone with an increase in Jv but a decrease in J1. It is concluded that the intestine responds to various stimuli with a change in motility, or tone, or both. Intestinal motility per se does not produce lymph. Since an increase or decrease in tone always results in a decrease or increase in Jv, respectively, regardless of the nature of the conditions, a relaxation of the intestinal musculature appears to be associated with an increase in water absorption.