bluuebunny/crossref_metadata_2025 huggingface dataset:
Autonomic control of penile erection in the dog.
Authors: Carati C J , Creed K E , Keogh E J
Published: December 2014

1. In anaesthetized dogs, resting mean penile artery pressure (p.a.p.) and corpus cavernosum pressure (c.c.p.) were 70‐100% and 10‐15% of mean systemic blood pressure, respectively. 2. Stimulation of the pelvic nerve at 10 Hz produced an immediate drop in p.a.p. and c.c.p., followed 10‐30 s later by a rise in c.c.p. to the level of p.a.p. This level was 60‐90% of systemic pressure, and was maintained throughout stimulation. 3. The threshold for a rise in c.c.p. was 3‐5 Hz. Atropine (1 mg/kg), phentolamine (200 micrograms kg‐1) and propranolol (200 micrograms kg‐1) had no effect on the response to pelvic nerve stimulation. 4. C.c.p., p.a.p. and their changes in response to pelvic nerve stimulation were not significantly altered by either stimulation or section of the hypogastric nerves. 5. Cutting the sympathetic chain on both sides at L5, or administration of phentolamine, had no effect on resting c.c.p. or p.a.p. However, subsequent responses to pelvic nerve stimulation were enhanced. 6. When the pelvic nerve was stimulated during excitation of the sympathetic chain, there was still an initial drop in p.a.p. and c.c.p. but the subsequent increase in c.c.p. was delayed or abolished. These effects were mimicked by close arterial injection of phenylephrine and blocked by alpha‐adrenergic antagonists. 7. This study suggests that erections in response to pelvic nerve stimulation result from an initial increase in volume of the corpus spongiosum, followed 20 s later by a stiffening of the corpus cavernosum as its pressure increases. Only the latter process is inhibited by activity of the sympathetic fibres.
Transient outward currents and changes of their gating properties after cell activation in thrombocytes of the newt.
Authors: Kawa K
Published: December 2014

1. The electrical properties of the cell membrane of thrombocytes in the newt, Triturus pyrrhogaster, were studied using the whole‐cell variation of the patch‐electrode voltage‐clamp technique. 2. In medium containing Ca2+ (1.8 mM), activated thrombocytes became round and then spread on the glass. Activation of thrombocytes was inhibited by the removal of external Ca2+ and addition of 1 w/v% albumin to the external media. 3. For thrombocytes kept in the resting state, depolarizations more positive than ‐30 mV evoked transient outward currents which decayed completely during the duration of the depolarization (150 ms). The half‐decay time of the currents became smaller as the depolarizing pulse strengthened, reaching about 20 ms at +30 mV (20 degrees C). 4. The outward currents are identified as K+ currents, since (1) their reversal potential depended on extracellular K+ concentration and (2) the outward currents were suppressed either by external application of 4‐aminopyridine (1 mM) or by internal application of Cs+ (120 mM). The monovalent cation selectivities of the K+ channels were evaluated from the reversal potential as Tl (1.68) greater than K(1.0) greater than Rb (0.89) greater than NH4 (0.13) greater than Na(less than 0.03). 5. When the thrombocytes had been activated, depolarization again evoked K+ currents. The currents, however, showed negligible or small decay during the duration of the depolarization (150 ms). The rate of recovery from preceding depolarization was also reduced to about one‐sixth. 6. The sensitivity to 4‐aminopyridine and the selectivity of the K+ channels were not changed by cell activation. 7. We conclude that during activation of thrombocytes the inactivation of the K+ channels is almost eliminated. Removal of inactivation of the K+ channels was also induced in resting thrombocytes by intracellular application of 4‐bromoacetamide (50 microM).
The kinetics of heat production in response to active shortening in frog skeletal muscle.
Authors: Ford L E , Gilbert S H
Published: December 2014

1. Tension and heat production were measured at 0 degree C in sartorius muscles from Rana temporaria in response to two extents of shortening at five velocities. Shortening was from approximately 2.4 to 2.2 microns, 2.4 to 2.3 microns and 2.3 to 2.2 micron at velocities per half‐sarcomere from 0.2 to 1.56 micron s‐1. 2. Tension became approximately constant at all velocities. Records of heat rate obtained by differentiating traces from which thermoelastic heat had been subtracted became negative early in shortening and then rose. Heat rate became constant during shortening only at the lowest velocity and was still rising at the end of shortening at higher velocities. The highest heat rate occurred at the end of shortening at the two highest velocities. At the end of shortening at all velocities heat rate gradually approached the isometric level measured at the short length, the half‐time for decline being largest following the slowest larger shortening. 3. Heat produced as a consequence of shortening but not associated with tension recovery was determined by subtracting shortening heat measured in response to two extents of shortening to the same muscle length. The differences in shortening heat continued to increase after shortening ended, and more of the extra heat produced in response to shortening appeared after the end of rapid shortening than during shortening itself. 4. Shortening heat coefficients calculated in different ways were similar to coefficients determined in previous studies. Coefficients calculated from measurements that excluded heat produced by tension recovery and allowed for continued production of heat by processes initiated by shortening were found to increase linearly with the force maintained during shortening. 5. The results show that the kinetics of heat production during and after shortening are very sensitive to the speed of shortening and that steady rates of energy liberation are not attained during shortening of less than or equal to 10% of muscle length at velocities greater than or equal to 12% of maximum velocity.
The influence of gastrointestinal infusion of fats on regulation of food intake in pigs.
Authors: Gregory P C , Rayner D V
Published: December 2014

1. The influence of gastrointestinal infusions of fat on short‐term and 24 h control of food intake were studied in twenty‐four pigs fed twice per day and seventeen fed three times per day. The pigs were fitted with up to four catheters placed in the stomach, the duodenum, and at 2, 4 and 8 m from the ligament of Treitz. 2. Various infusions were given into the catheters beginning 30 min before the first meal (two feeds) or second meal (three feeds) of the day and continuing until the end of the feeding period or until the pigs stopped eating. 3. Infusions of a fat emulsion (Intralipid) into the stomach, of oleic acid or glycerol into the duodenum, or of glycerol into the ileum (8 m from the ligament of Treitz) inhibited food intake during the infusion according to the amount of energy infused. 4. Food intake was inhibited by more than the amount of energy infused with duodenal infusion of Intralipid or monoglyceride, or with infusion of Intralipid mixed with bile salts and lipase (but not with Intralipid alone) into 2 or 4 m from the ligament of Treitz. 5. Duodenal infusion of glycerol, and ileal (8 m from the ligament of Treitz) infusion of monoglyceride or glycerol inhibited food intake at the following meal according to the amount of energy infused. 6. It is concluded that fats can exert both pre‐ and post‐absorptive control of food intake and that since Intralipid infusion to the stomach but not to the duodenum inhibits food intake according to the amount of energy infused, it is likely that control of food intake is related to control of stomach emptying. 7. The inhibition of food intake by more than the amount of energy infused during upper intestinal infusion of fat is likely to be a result of digestion of the fat to monoglycerides, and interaction of monoglycerides with receptors in the proximal 4 m of intestine.
Investigation of factors affecting the intracellular sodium activity in the smooth muscle of guinea‐pig ureter.
Authors: Aickin C C
Published: December 2014

1. The intracellular Na+ activity (aNai) of the smooth muscle cells from guinea‐pig ureter has been measured using double‐barrelled Na+‐sensitive micro‐electrodes. aiNa in modified Krebs solution at 35 degrees C was of a mean 7.4 +/‐ 2.9 mM (n = 32, S.D. of an observation), equivalent to a Na+ equilibrium potential (ENa) of +66.7 mV. Membrane potential (Em) was of a mean ‐50.8 +/‐ 4.6 mV. 2. Inhibition of the Na+ pump by application of ouabain or removal of external K+ (K+o) resulted in a restricted rise of aNai. The rate of rise was faster in the presence of ouabain (10(‐4) M) but the stabilized aNai was not significantly different from that observed after the prolonged absence of K+o. The mean aiNa recorded after prolonged Na+ pump inhibition was 20.6 +/‐ 5.5 mM (n = 28), equivalent to an ENa of +39.6 mV. Neither removal of K+o after aNai had stabilized in the presence of ouabain nor application of ouabain after aNai had stabilized in K+‐free solution caused a rise in aiNa, suggesting that the Na+ pump was fully inhibited by either procedure. 3. Reduction of Na+o resulted in a rapid fall in aiNa against the electrochemical gradient, both before and after Na+ pump inhibition. At each level of Na+o, aNai stabilized such that ENa remained approximately constant in either condition. Readdition of Na+o resulted in a rapid recovery of aNai. 4. Elevation of Ca2+o (at constant Na+o) caused a fall in aNai of much the same time course as that observed on reduction of Na+o, both before and after Na+ pump inhibition. The extent of the fall was dependent upon the initial aNai. Reduction of Ca2+o resulted in a rise in aNai. 5. Elevation of the external divalent cation concentration with Mn2+ or, to a lesser extent, Mg2+ reduced aiNa in the presence of a functional Na+ pump. But after prolonged exposure to ouabain or K+‐free solution, elevation of Mg2+o had no effect on aiNa while application of Mn2+o caused a slow rise. These results suggest that Ca2+o affects aiNa in two ways. One is mimicked by Mg2+ and Mn2+ and is probably due to alteration of the Na+ leak. The other is a specific effect, revealed by Na+ pump inhibition. 6. It is concluded that aiNa can be maintained far from equilibrium in the absence of a functional Na+ pump. Several lines of evidence are discussed which indicate the participation of Na+‐Ca2+ exchange in Na+ extrusion in this condition.
Action potential repolarization and a fast after‐hyperpolarization in rat hippocampal pyramidal cells.
Authors: Storm J F
Published: December 2014

1. The repolarization of the action potential, and a fast after‐hyperpolarization (a.h.p.) were studied in CA1 pyramidal cells (n = 76) in rat hippocampal slices (28‐37 degrees C). Single spikes were elicited by brief (1‐3 ms) current pulses, at membrane potentials close to rest (‐60 to ‐70 mV). 2. Each action potential was followed by four after‐potentials: (a) the fast a.h.p., lasting 2‐5 ms; (b) an after‐depolarization; (c) a medium a.h.p., (50‐100 ms); and (d) a slow a.h.p. (1‐2 s). Both the fast a.h.p. and the slow a.h.p. (but not the medium a.h.p.) were inhibited by Ca2+‐free medium or Ca2+‐channel blockers (Co2+, Mn2+ or Cd2+); but tetraethylammonium (TEA; 0.5‐2 nM) blocked only the fast a.h.p., and noradrenaline (2‐5 microM) only the slow a.h.p. This suggests that two Ca2+‐activated K+ currents were involved: a fast, TEA‐sensitive one (IC) underlying the fast a.h.p., and a slow noradrenaline‐sensitive one (IAHP) underlying the slow a.h.p. 3. Like the fast a.h.p., spike repolarization seems to depend on a Ca2+‐dependent K+ current of the fast, TEA‐sensitive kind (IC). The repolarization was slowed by Ca2+‐free medium, Co2+, Mn2+, Cd2+, or TEA, but not by noradrenaline. Charybdotoxin (CTX; 30 nM), a scorpion toxin which blocks the large‐conductance Ca2+‐activated K+ channel in muscle, had a similar effect to TEA. The effects of TEA and Cd2+ (or Mn2+) showed mutual occlusion. Raising the external K+ concentration reduced the fast a.h.p. and slowed the spike repolarization, whereas Cl‐ loading of the cell was ineffective. 4. The transient K+ current, IA, seems also to contribute to spike repolarization, because: (a) 4‐aminopyridine (4‐AP; 0.1 mM), which blocks IA, slowed the spike repolarization; (b) depolarizing pre‐pulses, which inactivate IA, had a similar effect; (c) hyperpolarizing pre‐pulses speeded up the spike repolarization; (d) the effects of 4‐AP and pre‐pulses persisted during Ca2+ blockade (like IA); and (e) depolarizing pre‐pulses reduced the effect of 4‐AP. 5. Pre‐pulses or 4‐AP broadened the spike less, and in a different manner, than Ca2+‐free medium, Cd2+, Co2+, Mn2+, TEA or CTX. The former broadening was uniform, with little effect on the fast a.h.p., whereas the latter affected mostly the last two‐thirds of the spike repolarization and abolished the fast a.h.p.(ABSTRACT TRUNCATED AT 400 WORDS)
An electrophysiological and morphological study of the innervation and reinnervation of cat dentine.
Authors: Holland G R , Matthews B , Robinson P P
Published: December 2014

1. Experiments were carried out to determine which, if any, of the cellular processes in cat dentine are nerves. This was done by examining in the electron microscope the contents of the dentinal tubules in control teeth and in teeth that had been denervated 56 h previously. The extent of any reinnervation, and associated return of neural responses to dentine stimulation were investigated 12 weeks after denervation. 2. In five cats, the inferior alveolar nerve was sectioned on one side and the cut ends reapposed. 3. Each of the tubules in the predentine of control teeth contained one process with a cross‐sectional area of 0.21‐1.14 micron2 and up to eight other, secondary processes which were generally smaller. The proportion which contained secondary processes was highest (83%) near the tip of the pulp and decreased further down the side of the crown of the tooth. 4. 56 h after denervation, almost all the secondary processes had disappeared, leaving just one of the larger processes in each tubule. It is concluded that these larger processes are odontoblast processes and that all the secondary processes are nerve terminals. 5. 12 weeks after denervation, small processes were again present in some tubules. Recordings in three cats showed that inferior alveolar nerve fibres had regenerated into the canine pulp and that some of these had re‐established receptor properties similar to those in normal teeth.
Stumbling reactions in man: significance of proprioceptive and pre‐programmed mechanisms.
Authors: Dietz V , Quintern J , Sillem M
Published: December 2014

1. Electromyogram (e.m.g.) responses of the leg musculature and the corresponding joint movements were studied following a perturbation of the limb during walking on a treadmill, produced by a randomly timed treadmill acceleration impulse, either predictable, or unpredictable in its amplitude and rate of acceleration. 2. The rate of rise of ipsilateral gastrocnemius e.m.g. response following a perturbation was dependent on the rate of treadmill acceleration. For a given acceleration rate the amplitude of the e.m.g. response and the timing of its peak was dependent on the amplitude of the impulse and the rate of rise of the gastrocnemius response was the same for impulses of both small and large amplitude. The onset latency was shorter (65 ms) for high accelerations and longer (85 ms) for lower ones. 3. The amplitude of the ipsilateral biceps femoris response was much smaller than the gastrocnemius response but was larger following unpredictable than predictable impulses. 4. The initial gastrocnemius response was followed by a tibialis anterior activation associated with a gastrocnemius depression and sometimes with a second, weak gastrocnemius activation. The gastrocnemius depression ended within a fixed time range relative to the onset of the response. The tibialis anterior activation was most pronounced when unpredictable impulses with high acceleration but a small amplitude were induced. 5. It is concluded that generation of the first gastrocnemius response is obviously under continuous control by muscle proprioceptive information and can be best described in terms of a stretch reflex response. It is suggested that, on the evidence of the diphasic or triphasic e.m.g. pattern, a close interaction occurs between a central programme and muscle proprioceptive input in order to generate the appropriate e.m.g. pattern. 6. On the basis of earlier work (Berger, Dietz & Quintern, 1984a) and on the present results it is suggested that the e.m.g. responses may be mediated mainly by muscle proprioceptive input from group II afferents. This input is modulated and processed by spinal interneuronal circuits, closely connected with spinal locomotor centres. The mode of processing depends on various factors, such as the predictability of the nature of the impulse.
The dynamics of the cat retinal X cell centre.
Authors: Victor J D
Published: December 2014

1. The dynamics of the centre mechanism of individual cat X retinal ganglion cells is investigated. The visual stimuli consist of temporal contrast modulation of stationary patterns. In order to study the response of the centre mechanism, patterns were either sine gratings of high spatial frequency or small circular spots positioned over the receptive‐field centre. 2. Responses to contrast reversal are approximately linear. However, as the modulation depth of the stimulus increases, responses become more transient. Ganglion cell responses show this phenomenon at moderate contrasts (e.g. 0.1), which do not elicit discharges that approach the maximum firing rate of the ganglion cell. 3. A sequence of dynamical models are constructed from responses elicited by sum‐of‐sinusoids modulation of the spatial pattern. The first model is strictly linear. It consists of a series of low‐pass filters and a single high‐pass filter. The linear model predicts the approximate shape of the step response, but does not account for the change in shape of the response as a function of modulation depth. 4. The second model, a quasi‐linear model, allows the 'linear' dynamics to vary slowly with a neural measure of contrast. The main effect of high contrast is a shorter time constant in the high‐pass filter. This model accounts qualitatively for the increased transience of the response, but fails to predict the magnitude of the effect at higher modulation depths. 5. In the third model, the transfer characteristics of the centre response adjust rapidly as contrast changes. This intrinsically non‐linear model provides excellent agreement with observed response to steps and more complex modulation patterns. 6. The non‐linearity necessitated by a voltage‐to‐spikes transduction is analysed quantitatively. In most ganglion cells, a simple truncation at 0 impulses/s (and no saturation) explains the changes in apparent gain and mean firing rate that occur as modulation depth is increased. A non‐linear voltage‐to‐spike transduction per se cannot account for the observed effect of contrast on dynamics. 7. The parameters of the dynamical model are measured for a population of twenty‐seven X ganglion cells (nineteen on‐centre and eight off‐centre). The low‐pass stage and the strength of the high‐pass stage are relatively uniform across the population. The over‐all gain and the dynamics of the high‐pass stage vary substantially across the population, but show no consistent dependence on the on‐off distinction or on retinal location. Some implications of this variability for retinal function are discussed.
Phase coherence in vibration‐induced responses of tactile fibres associated with Pacinian corpuscle receptors in the cat.
Authors: Greenstein J , Kavanagh P , Rowe M J
Published: December 2014

1. In pentobarbitone‐anaesthetized cats, responses were recorded in peripheral nerves or cervical dorsal columns from sensory fibres associated with Pacinian corpuscle (P.c.) receptors in the forelimb footpads. Factors affecting the phase of response to cutaneous vibration in individual P.c. fibres, and the extent of phase coherence in the responses of different P.c. fibres were examined when sinusoidal vibratory stimuli at 100‐400 Hz were delivered using a 1 mm diameter probe. 2. Increases in vibration amplitude from the absolute to the 1:1 threshold for the P.c. fibre led to phase advances in the response, often of about 60 deg, in over 85% of fibres tested at 200 and 300 Hz, but further increases had little effect. 3. Variations in stimulus position within the receptive field led to unpredictable changes in the response phase that ranged from minimal change to shifts of 180 deg. As the response phase was unrelated to the distance from the point of peak sensitivity it is likely that at high vibration frequencies (greater than or equal to 100 Hz) the recruited population of P.c. fibres will respond over the whole range of phase angles. 4. The calculated phase of spike initiation in different pairs of P.c. fibres that shared coincident points of best sensitivity on the skin ranged from near synchrony to maximum asynchrony indicating that there is little phase coherence even in the subpopulation of somatotopically related P.c. fibres recruited by high‐frequency cutaneous vibration. 5. Paired recordings from P.c. fibres within the cervical dorsal columns revealed a broad range of phase discrepancies in the responses of P.c. fibres to vibration at 200 and 300 Hz. 6. Several hypotheses are considered to explain the known presence of phase‐locked responses to high‐frequency (greater than or equal to 100 Hz) vibration in the central neurones of dorsal column nuclei.
Actions of single sensory fibres on cat dorsal column nuclei neurones: vibratory signalling in a one‐to‐one linkage.
Authors: Ferrington D G , Rowe M J , Tarvin R P
Published: December 2014

1. The synaptic linkage between single, identified sensory fibres associated with Pacinian corpuscle (P.c.) receptors and central neurones of the dorsal column nuclei was examined in decerebrate or anaesthetized cats. Paired recordings were made from individual neurones in the gracile division of the dorsal column nuclei and from the hind‐limb interosseous nerve in which it is possible to identify and monitor the activity of each P.c. fibre activated when recording from the intact nerve with a platinum hook electrode. Individual P.c. fibres were activated by vibration delivered with an 0.2 mm diameter probe to the interosseous P.c. receptors. 2. Thirty‐five P.c. fibre‐gracile neurone pairs were isolated in which activity in the single, identified P.c. fibre evoked suprathreshold responses (mean latency +/‐ S.D., 10.3 +/‐ 1.5 ms) in the gracile neurone. A single impulse arriving over one P.c. fibre could generate pairs or triplets of output spikes from several target neurones thus revealing a potent synaptic organization within the dorsal column nuclei for the transmission and amplification of weak sensory signals. 3. The potency of the linkage for some pairs resulted in post‐synaptic response levels of up to 400 impulses s‐1 when a single input fibre was discharging one impulse on each vibration cycle at 200‐400 Hz. 4. Gracile neurones driven by single P.c. fibres had phase‐locked responses to vibration at frequencies of up to 400‐500 Hz. However, the responses displayed much greater phase dispersion than those of P.c. fibres, indicating that a major component of phase dispersion in the vibration‐induced responses of dorsal column nuclei neurones is attributable to the properties of the synaptic linkage between an individual fibre and the target neurone. 5. The potent actions of single, identified P.c. fibres on their target neurones are consistent with the hypothesis that phase‐locked responses in dorsal column nuclei neurones to vibration at 100‐400 Hz may reflect the functional domination of the target neurone's output by one or a few of its converging fibres.
Kinetics and selectivity of a low‐voltage‐activated calcium current in chick and rat sensory neurones.
Authors: Carbone E , Lux H D
Published: December 2014

1. Using the whole‐cell recording mode of the patch‐clamp technique, we have investigated kinetic and selectivity properties of a low‐voltage‐activated (l.v.a.) Ca2+ current in chick and rat dorsal root ganglion (d.r.g.) neurones. 2. L.v.a currents were activated at about ‐50 mV and reached maximum amplitudes between ‐30 and ‐20 mV with averages of ‐0.16 nA in chick and ‐0.3 nA in rat d.r.g. cells with 5 mM‐extracellular Ca2+. Between ‐60 and ‐20 mV, the time to peak, tp, of this current decreased with increasing membrane depolarizations. An e‐fold change of tp required a 14 mV potential change in chick and a 17 mV change in rat d.r.g. cells at 22 degrees C. 3. Between ‐50 and +20 mV inactivation of this current was fast, single exponential and voltage dependent. In rat, the time constant of inactivation, tau h, was smaller and less voltage dependent than in chick. 4. The amplitude of these currents increased by a factor of 5‐10, when the extracellular Ca2+ concentration was changed from 1 to 95 mM. Amplitudes and kinetic parameters of the currents showed typical shifts along the voltage axis. No correlation between Ca2+ current amplitudes and activation‐inactivation kinetics was found, suggesting that the reaction rates which control these processes are not dependent on Ca2+ entry. 5. Recovery from inactivation was voltage dependent and developed with a time constant, tau r, in the order of 1 s. tau r was nearly halved by changing the potential from ‐80 to ‐120 mV. 6. Tail currents associated with membrane repolarization were also voltage dependent and developed exponentially. Their time constant decreased by a factor of 3 when the potential was changed from ‐60 to ‐100 mV. 7. A second and more prominent Ca2+ current was activated at potentials positive to ‐20 mV (high‐voltage‐activated Ca2+ currents, h.v.a.), masking the time course of l.v.a. currents. Between ‐20 and 0 mV, time to peak of the entire current increased by a factor of 2 but decreased again at higher membrane potentials. Inactivation also became significantly slower in this potential range. 8. The contribution of the h.v.a. component to the total membrane current was markedly reduced using a high intracellular Ca2+ concentration, [Ca2+]i, or internal fluoride salts. This made it possible to study the kinetic parameters and the I‐V characteristics of the l.v.a. current more precisely over a wider potential range (‐50 to +30 mV).(ABSTRACT TRUNCATED AT 400 WORDS)
The velocity dependence of direction selectivity of visual cortical neurones in the cat.
Authors: Duysens J , Maes H , Orban G A
Published: December 2014

1. The range of velocities, yielding direction‐selective responses, was investigated in a total of 167 direction‐selective cells from areas 17 and 18 of the cat, using a high‐contrast light bar moving at velocities ranging from 0.6 to 900 deg s‐1. 2. 11% of the cells were direction selective over the full range of velocities tested. Most cells (66%) gave only responses at low velocities and thus were not direction selective at high velocities. The remaining cells gave responses over a broad range of velocities but the direction selectivity was limited to either high or intermediate velocities (18 and 5% of the cells, respectively). Cells with direction selectivity at high but not at low velocities had large receptive fields with non‐overlapping 'on' and 'off' subregions and they responded quickly and phasically to stationary flashes. This suggests that the latter cells relied on fast and brief interactions over large distances. 3. In thirty cells the spatial and temporal limits of direction selectivity were investigated using a stroboscopically illuminated moving light bar. In all cells direction selectivity depended both on the interflash distance and the interflash time interval. Area 17 cells with large receptive field at high eccentricity tolerated much larger interflash spacings than area 17 cells with small receptive fields near the area centralis. For eleven of the thirty cells the effective interflash distance could be larger than the width of the receptive field. The largest effective interflash time interval varied between 35 and 250 ms. 4. Eight of the thirty cells were direction selective at high but not at low velocities. These eight cells all remained direction selective over large interflash distances and they required brief interflash intervals (less than or equal to 65 ms). 5. Responses to single stroboscopic flashes within the sequence were observed in ten cells, which all responded well at high apparent velocities. While most cells (eight out of ten) showed both response increments in the preferred direction and response decrements in the non‐preferred, the decrements constituted the dominant element in the direction selectivity of six out of ten cells while the remaining four cells relied mainly on response increments. 6. It is concluded that the range of direction‐selective velocities of some cat visual cortical cells can be predicted from a knowledge of the spatial extent and the time course of the direction‐selective interactions.(ABSTRACT TRUNCATED AT 400 WORDS)
Synaptic activation of slow depolarization in rat supraoptic nucleus neurones in vitro.
Authors: Dudek F E , Gribkoff V K
Published: December 2014

1. The effects of synaptic activation on rat supraoptic nucleus (s.o.n.) neurones were studied in the hypothalamic slice preparation. Intracellular recordings were obtained from forty‐one probable magnocellular neuroendocrine cells using microelectrodes filled with 3 M‐potassium acetate. Responses to single and repetitive stimulation of the area dorsolateral to the s.o.n., which would be expected to activate a cholinergic pathway (Hatton, Ho & Mason, 1983), were analysed. 2. In forty of forty‐one cells, responses to single stimuli consisted of a short‐latency excitatory post‐synaptic potential (e.p.s.p.), which was often followed by a brief burst of fast depolarizing events which resembled spontaneous e.p.s.p.s. When the membrane was depolarized, single stimuli could consistently produce a burst of action potentials. 3. Brief trains of orthodromic stimuli produced three effects in most cells. Spontaneous fast depolarizing events, which appeared to be primarily e.p.s.p.s. significantly increased in frequency after the train. A slow membrane depolarization, which lasted up to 1‐2 min, was observed in twenty‐eight of forty‐one cells. In several cells the slow depolarization was accompanied by an increase in input resistance (Ri). In some cells an after‐discharge occurred during the slow depolarization. Slow depolarizations were observed in each of eleven phasic neurones, and in a smaller percentage of non‐phasic and silent cells. 4. All components of the response to dorsolateral stimulation could be reduced or blocked in low‐Ca2+, high‐Mg2+ bathing medium. 5. Slow depolarizations were observed when action potentials were not elicited by the stimulus train. The slow depolarization was still present after manipulations that blocked discharge during the stimulus train, including injection of hyperpolarizing current and diffusion of the quaternary ammonium compound QX314. These data argue that the slow depolarization can occur independent of spike depolarizing after‐potentials (d.a.p.s). 6. In some cells antidromic stimulation at an intensity just suprathreshold for the recorded cell did not produce comparable bursts of fast depolarizing events or slow depolarizations; similar periods of depolarizing current injection, which produced repetitive discharge, also did not mimic the effects of orthodromic stimulation. 7. The fast depolarizing events appear to reflect spontaneous e.p.s.p.s; increases in the frequency of these events may reflect the after‐discharge of nearby neurones that are presynaptic to the recorded neurone.(ABSTRACT TRUNCATED AT 400 WORDS)
Co‐operative action of calcium ions in dopamine release from rat brain synaptosomes.
Authors: Nachshen D A , Sanchez‐Armass S
Published: December 2014

1. The release of [3H]dopamine from isolated presynaptic nerve terminals (synaptosomes) prepared from rat striata was measured as a function of the external Ca2+ concentration ([Ca2+]o). 2. In synaptosomes depolarized by the addition of 50 mM‐K+, release of [3H]dopamine increased in a highly non‐linear manner with [Ca2+]o. The release could be described as a third power function of [Ca2+]o. 3. Both 45Ca2+ influx and the change in the free cytosolic Ca2+ concentration ([Ca2+]i, measured with the fluorescent Ca2+ indicator fura‐2) that were evoked by depolarization increased in a linear manner with [Ca2+]o. 4. These results suggest that non‐linearity in the [Ca2+]o dependence of transmitter release originates in a co‐operative relation between [Ca2+]i and exocytosis.
Action of externally applied adenosine triphosphate on single smooth muscle cells dispersed from rabbit ear artery.
Authors: Benham C D , Bolton T B , Byrne N G , Large W A
Published: December 2014

1. Adenosine triphosphate (ATP), applied in the bathing solution or ionophoretically, depolarized freshly dispersed single arterial smooth muscle cells obtained by collagenase and elastase treatment of the rabbit ear artery. 2. Ionophoretic application of ATP evoked an inward current with a latency of about 70 ms and a time to peak of about 230 ms in cells held under voltage clamp using whole‐cell patch‐pipette techniques. 3. Bath application of 10 microM‐ATP evoked a transient inward current at negative holding potentials. The amplitude of the ATP‐induced current was linearly related to the clamp potential with a reversal potential near 0 mV. Removal of extracellular calcium, buffering intracellular calcium with high EGTA concentration, or depleting calcium stores with caffeine or noradrenaline treatment did not affect the ATP‐evoked current. 4. Changing the chloride concentration gradient by decreasing extracellular or intracellular chloride concentration, or using the chloride channel blocker, frusemide, had no effect on the currents. 5. Replacing sodium with Tris shifted the reversal potential to more negative potentials. The reversal potential was not affected by exchanging intracellular potassium for caesium or sodium. Replacing extracellular sodium with 89 mM‐barium also had little effect on the reversal potential. 6. These results are consistent with ATP activating a conductance that is cation selective but allows both monovalent and divalent cations to pass across the membrane.
Electrogenic sodium‐calcium exchange in cultured embryonic chick heart cells.
Authors: Jacob R , Lieberman M , Liu S
Published: December 2014

1. The membrane potential (Em) of cultured chick embryonic heart cells depolarized to ‐36 mV after inhibition of the Na+‐K+ pump by 0.1 mM‐ouabain in a [K+]o of 24 mM: this was accompanied by a rise in Na+ content of approximately 65% in 3 min. Lowering [Na+]o to 27 mM then caused a fall in Na+ content, a rise in Ca2+ content and a small hyperpolarization of approximately 5 mV. The fall in Na+ content indicated a movement of Na+ which was in the opposite direction to the Na+ electrochemical gradient (a countergradient movement). 2. In the presence of 10 mM‐Cs+ or 1 mM‐Ba2+ the hyperpolarization was approximately 10 or approximately 30 mV, respectively. A 30 mV hyperpolarization took Em negative to the reversal potentials for K+, and Cl‐ as measured by ion‐selective micro‐electrodes. 3. The decay of the intracellular Na+ activity alpha iNa, in an [Na+]o of 27 mM followed a simple exponential time course (time constant, 36 s). The initial rate depended on the value to which [Na+]o was lowered in a manner suggesting a simple competitive inhibition of the exchange by external Na+. 4. The low‐[Na+]o hyperpolarization was unaffected by amiloride (0.1 or 1 mM) or verapamil (20 microM). Both La3+ (1 mM) and Mn2+ (20 mM) blocked the hyperpolarization sufficiently to prevent Em hyperpolarizing negative to the reversal potentials for K+, Na+ and Cl‐. 5. Re‐establishing [Na+]o caused a rise in Na+ content and a countergradient drop in Ca2+ content. The effects of verapamil (20 microM), amiloride (0.1 and 1 mM), dichlorobenzamil (0.1 mM), quinidine (1 mM), Mn2+ (20 mM) and La3+ (1 mM) were tested on the movements of Na+ and Ca2+ both during exposure to an [Na+]o of 27 mM and on re‐establishing [Na+]o. The only consistent and substantial effects were the attenuation by La3+ and Mn2+ and Ca2+ movements during exposure to an [Na+]o of 27 mM. However, neither La3+ nor Mn2+ affected the movements of Na+ and Ca2+ on re‐establishing [Na+]o. 6. We conclude that cultured embryonic chick heart cells contain a Na+‐Ca2+ exchange evidenced by the ability to cause movements of Na+ and Ca2+ which are counter to their respective electrochemical gradient and which are accompanied by downhill movements of the counter ion.(ABSTRACT TRUNCATED AT 400 WORDS)
Conduction block silences parts of a chemical synapse in the leech central nervous system.
Authors: Macagno E R , Muller K J , Pitman R M
Published: December 2014

1. The pressure (P) sensory neurones innervating the ventral skin of the medicinal leech have receptive fields comprising a central region of skin innervated by two thicker axons and two neighbouring regions innervated by two thinner axons. Impulses originating in the thinner axons may fail to propagate through the central ganglion, apparently blocked at the branch point of large and small axons. 2. The P neurone excites the longitudinal (L) motoneurone, and blocked impulses originating in the anterior fine axon produce e.p.s.p.s that are less than one‐half normal amplitude. Blocked impulses in the posterior fine axon are typically ineffective. 3. The branches of P and L neurones, marked with intracellularly injected horseradish peroxidase or with Lucifer Yellow, make synaptic contact at up to sixty‐six sites within the neuropile. Of P neurone branches emerging from two fine axons, those from the posterior axon make fewer contacts, usually one or two at most, while branches from the anterior axon represent no more than half the total contacts. From cell to cell there is some variation in the total number of contacts, the distribution of branches, and the strength of transmission. 4. The locations of contacts measured morphologically correlate well with their distributions as predicted from reductions in e.p.s.p. amplitude during conduction block.
Two distinct kinetic phases of desensitization of acetylcholine receptors of clonal rat PC12 cells.
Authors: Boyd N D
Published: December 2014

1. The desensitization of nicotinic acetylcholine receptors on the PC12 sympathetic cell line was investigated by using a 22Na+ influx assay to measure receptor activation. 2. The rate of desensitization was dependent on temperature and at 4 degrees C two distinct kinetic phases were readily discernible: a rapid phase that was characterized by rate constants that were dependent on the chemical nature and concentration of the agonist, and a slower phase that was characterized by rate constants that were less dependent on these. 3. For acetylcholine, carbamylcholine and l‐nicotine, the equilibrium desensitization parameter, Kdes, the concentration that produces half‐maximal desensitization, was determined and compared with the corresponding value for Kact, the concentration that results in a half‐maximal increase in the permeability response. For each agonist, the value of Kdes was found to be lower than Kact, a result to be expected if desensitization is associated with a higher‐affinity state of the receptor than that associated with ion channel activation. Thus, extensive receptor desensitization can occur even at agonist concentrations that do not produce appreciable channel activation. Both activation and desensitization functions exhibited positive cooperativity so that each function occurs over a narrow range of agonist concentrations. 4. Following removal of the agonist, recovery from desensitization was reversible and occurred by two distinct kinetic phases characterized by rate constants that were independent of the chemical nature and concentration of the agonist that produced the desensitization. The relative contribution of each kinetic phase of recovery was, however, dependent on the duration of prior exposure to agonist. Following short incubation periods with agonist, most of the receptors were in a rapidly recovering state. With increasing duration of exposure, progressively more of the receptors were converted to a desensitized state that recovered more slowly. 5. The rate constants associated with the two kinetic phases of recovery were dependent on the recovery temperature. Following the initial rapid phase of desensitization, recovery at 4 degrees C was characterized by a time constant, t1/2, of 1.9 min, a value that was about 3‐fold greater than that observed at 22 degrees C. The rate of recovery of the desensitized state achieved following equilibrium exposures to agonists was considerably more temperature dependent: recovery of this desensitized state was characterized at 4 degrees C by a t1/2 of 62 min that was about 37‐fold greater than that at 22 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)
The role of myogenic relaxation, adenosine and prostaglandins in human forearm reactive hyperaemia.
Authors: Carlsson I , Sollevi A , Wennmalm A
Published: December 2014

1. Forearm blood flow was measured bilaterally in healthy young male and female volunteers, in the basal state and after upper‐arm occlusion of arterial or venous blood flow for 1‐20 min. The investigations were repeated after pre‐treatment with drugs affecting vascular prostaglandins and/or adenosine. 2. Simultaneous arterial occlusion in one arm and venous occlusion in the contralateral arm for up to 20 min elicited a considerable reactive hyperaemia in the arm subjected to arterial occlusion, but completely failed to elevate the post‐occlusive flow in the arm subjected to venous occlusion above the pre‐occlusive level. 3. When the arterial occlusion was increased from 1 to 20 min there was a progressive increase in the subsequent reactive hyperaemia, up to 30 ml 100 ml tissue‐1. The time dependence following 1‐3 min of arterial occlusion was based on a facilitation of the peak post‐occlusive flow, while prolongation of the arterial occlusion from 3 to 20 min augmented the reactive hyperaemia mainly by increasing its duration. 4. Inhibition of prostaglandin synthesis with ibuprofen reduced the total reactive hyperaemia following 3‐5 min of arterial occlusion by up to 70%. This attenuation was due both to a reduction of peak post‐occlusive flow and to a shortening of the duration of the post‐occlusive hyperaemia. 5. The adenosine receptor antagonist theophylline reduced the reactive hyperaemia following 5 min of arterial occlusion by about 35%. Combined treatment with ibuprofen and theophylline did not reduce the reactive hyperaemia more than either drug alone. 6. Infusion of dipyridamole, a drug which inhibits the elimination of adenosine, reinforced the reactive hyperaemia by about 45%. This effect of dipyridamole was completely inhibited by administration of theophylline, and also by ibuprofen. 7. Plasma levels of adenosine, hypoxanthine and uric acid were maintained during the reactive hyperaemia, indicating increased production of purines during or immediately after the ischaemia. 8. It is concluded that the adequate stimulus for vascular relaxation in response to interruption of blood flow is omission of vessel wall distension. Local metabolic factors like endogenously formed prostaglandins and adenosine may act synergistically to this myogenic response but seem to be inactive alone. The lack of additive effects of ibuprofen and theophylline suggests a link between vascular relaxation induced by prostaglandins and by adenosine.
Independent control of channel closure and block of open channels by methylxanthines at acetylcholine receptors in frog.
Authors: Silinsky E M , Vogel S M
Published: December 2014

1. A series of related methylxanthines were studied for their effects on the kinetics of decay of end‐plate currents (e.p.c.s) and miniature end‐plate currents (m.e.p.c.s) at motor end‐plates of the frog. 2. Isobutyl methylxanthine (IBMX, 50 microM‐3 mM) produced a concentration‐dependent depression of the peak e.p.c. and m.e.p.c. amplitude and a change in the kinetics of e.p.c. and m.e.p.c. decay from the normal single‐exponential to a double‐exponential function. Drug effects of this nature are generally attributed to open‐channel blockade. 3. After wash‐out of IBMX, the decay of the e.p.c. or m.e.p.c. was restored to a single‐exponential function but with a significantly prolonged time constant. 4. Caffeine or theophylline derivatives (0.1‐4 mM), during exposure to drug, produced effects similar to those observed after the application of IBMX; namely a prolongation of the time course of e.p.c.s and m.e.p.c.s without changing the single‐exponential nature of the function. 5. Computer simulations were made of the m.e.p.c.s in IBMX. The effects of IBMX could be fitted to the sequential model of channel block only if the prolonged time constant observed upon wash‐out was used for the rate constant of channel closure. Independent calculations of the rate constant of channel closure during IBMX application were in agreement with those measured during wash‐out. 6. The theophylline derivative 8‐phenyltheophylline, a selective adenosine receptor blocker with minimal effects on phosphodiesterase (PDE), increased the time constant of e.p.c. decay in a manner similar to theophylline and caffeine. Non‐xanthine PDE inhibitors, either had no effect on m.e.p.c. decay (papaverine) or decreased the time constant of decay (RO 20‐1724). It is thus unlikely that PDE inhibition is responsible for the post‐junctional effects of IBMX. 7. IBMX (50 microM‐2 mM) increased quantal ACh release in the virtual absence of extracellular calcium and also increased the efficacy of adenosine derivatives in inhibiting ACh release. Adenosine (10‐100 microM) or 2‐chloroadenosine (1‐10 microM) had no effect on the time constant of e.p.c. decay nor did these adenosine receptor agonists alter the post‐junctional actions of IBMX. The effects of IBMX on end‐plate channel kinetics are thus not due to the blockade of adenosine receptors.(ABSTRACT TRUNCATED AT 400 WORDS)