Integration of free pulses in electrical self-stimulation of the rat brain.

Frequency thresholds for electrical self-stimulation of the medial forebrain bundle were estimated in rats while low frequencies of pulses were applied continuously. When continuous pulses were delivered to the same electrode that received the 0.5-sec trains of response-initiated stimulation, thresholds decreased by the free-pulse frequency (Experiment 1), consistently across current (Experiment 2). Estimates of the reward added by concurrent, response-contingent stimulation of the opposite electrode of a bilateral pair predicted the drop in threshold caused by the noncontingent pulses applied to the opposite hemisphere (Experiment 3), again, robustly across test current (Experiment 4). Continuous pulses restricted to times between self-initiated trains lost their effect (Experiment 5). The perception of reward was invariant despite changes in the overall activity of the self-stimulation substrate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Temporal summation decay" in hypothalamic self-stimulation: Threshold changes at long intrapair intervals due to axonal subnormal periods.

Rats were trained to bar press for trains of conditioning (C) and test (T) pulses delivered via lateral hypothalamic electrodes. As intrapair (C–T) intervals increased from 10 msec to 100 msec, the frequency of pulses required for self-stimulation increased, similar to results of N. S. Smith and E. E. Coons (1970). This effect was observed only for electrode placements where self-stimulation was obtained at frequencies below 16 Hz and currents of 600 μA and higher. The effect was larger when the train duration was increased from 0.5 sec to 2.0 sec. The threshold increase was abolished when the T pulses were greater in current than the C pulses but not when C pulses were larger than T pulses. The larger T pulses also removed relative refractory period effects at a C–T interval of 1.0 msec. Therefore, the increase in required current or frequency at long C–T intervals appears to be due to a decline in axonal excitability (i.e., the subnormal period) rather than a decay in synaptic temporal summation. Possible flaws in other reports of paired-pulse "temporal summation decay" at long C–T intervals using 2 electrodes are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Subjective reward magnitude of medial forebrain stimulation as a function of train duration and pulse frequency.

The growth of the subjective reward magnitude of medial forebrain bundle stimulation in the rat (Sprague-Dawley) as a function of train duration and pulse frequency was measured in 2 ways: (1) a titration method, which used differences in rate of reward on 2 levers to compensate for differences in the magnitude of the rewards; and (2) a direct method, in which the ratio of the reward magnitudes at the 2 levers was assumed to be given by the ratio of times spent on each lever. The results of the 2 methods agree. Reward magnitude grows as approximately a power function of train duration up to train durations of about 1 sec, then declines somewhat over the interval from 2–20 sec. The exponent of growth varies from 0.4 to 2.3. With stronger stimulation (higher pulse frequency), peak reward magnitude is bigger, but the saturating train duration is approximately the same. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of gonadotropin-releasing hormone pulse frequency modulation on the reproductive axis of photoinhibited male Siberian hamsters

In Siberian hamsters, photostimulation evokes differential release of the gonadotropins, with FSH rising rapidly and LH levels rising much later. We have tested the hypothesis that differential release of gonadotropins in this species can be mediated by changes in the frequency of pulsatile GnRH stimulation. Photoinhibited Siberian hamsters received GnRH pulses at frequencies of 1 pulse every 45 (fast), 90 (medium), or 180 min (slow). Animals were killed at 0, 3, 5, 10, 20, and 30 days after treatment. There was a clear GnRH pulse frequency effect on LH release, with fast pulses > medium pulses > slow pulses > short-day (SD) controls. In addition, 10 days of fast-frequency GnRH pulses produced LH levels significantly greater than LH levels in animals exposed to 10 days of medium or slow GnRH pulse frequencies. Pulsatile GnRH produced the following serum FSH relationships: medium pulses > fast pulses > SD. The FSH response to slow GnRH frequency fell between the two faster frequencies. The effect of GnRH pulse frequency on paired testes weight was as follows: fast pulses = medium pulses > slow pulses > SD controls. The differing GnRH pulse frequencies produced the following testosterone relationships; fast pulses > medium pulses = slow pulses = SD controls. These results agree with studies showing that slower GnRH pulse frequencies facilitate FSH release, while faster GnRH pulse frequencies favor LH release. Our observations are also consistent with the idea that the singular release of FSH after transfer of hamsters to a long-day photoperiod is mediated by alterations in the frequency of endogenous pulsatile GnRH release.     

Relapse after video-assisted thoracoscopic surgery for spontaneous pneumothorax

Many cochlear prostheses employ charge-balanced biphasic current pulses. These pulses have little energy at low frequencies resulting in limited stimulation of low frequency hearing by mechanical responses to the electrical stimulus. However, if electro-mechanical transduction within the cochlea is nonlinear, electrical stimulation with asymmetric, charge-balanced current pulses may result in a mechanical response with significantly more low frequency energy. We estimated the mechanical response at low frequencies to pulsatile electrical stimulation of the cochlea. The auditory nerve compound action potential evoked by low frequency tones was forward-masked by a train of symmetric or asymmetric current pulses. Masking by asymmetric current pulses was not significantly different from masking by symmetric pulses matched for pulse duration and charge. In conclusion, there appears to be no advantage to using asymmetric current pulses for the mechanical stimulation of residual low frequency hearing by electrical stimulation of the cochlea.     

Action potentials and underlying voltage-dependent currents studied in cultured spiral ganglion neurons of the postnatal gerbil

The excitability of cultured spiral ganglion (SG) neurons from early postnatal gerbil (P0-P1) was examined with the whole-cell patch-clamp technique. The role of voltage-gated currents in shaping the kinetics of action potentials (APs) was analyzed. Cultured SG neurons displayed spontaneous APs with a low rate (< 0.1 Hz). The kinetics of APs were studied by injecting neurons with current pulses of various frequencies and duration. A single depolarizing pulse of long duration elicited only one AP in most SG neurons. When excited by a train of short current pulses given at rates greater than 50 Hz, the firing pattern displayed an adaptive mechanism with the result that successive APs fired with lower amplitude, broader duration and delayed peak time. Pulse trains of higher frequencies had higher failure rates in initiating APs. Current pulses given at 20 Hz or lower elicited APs that had very similar amplitudes. However, the width of the APs gradually broadened. Duration of APs was also found to be affected by the membrane potential of neurons. Between -75 mV and -55 mV, AP duration was broadened at a rate of about 33% per 10 mV depolarization. Voltage-gated currents that underlie the generation of APs were examined under voltage-clamp conditions. Tetrodotoxin-sensitive sodium currents and dihydropyridine-sensitive L-type calcium currents were found. More importantly, inactivation properties of the potassium current provided a direct explanation for the cumulative broadening of APs. This work demonstrated that SG neurons were able to fire APs long before hearing commences in gerbil. Possible roles of spontaneous APs in the development of the cochlea and the role of voltage-gated currents in the function of SG neurons under normal and pathological conditions are discussed.     

Electrostimulated machining of metals

New mechanical equipment requires structural materials whose high performance cannot be ensured by traditional methods. A promising approach to the shaping of steel is the use of powerful unipolar current pulses with the following characteristics: amplitude 10–15 kA; pulse frequency up to 400 Hz; pulse length up to 100 μs. The widespread industrial use of this technique is hindered by the low efficiency of the corresponding pulse generators, which also draw considerable power from the ac grid and are not sufficiently controllable. In the present work, a generator of powerful unipolar current pulses that is free of those defects is described. It includes a charging system connected to power capacitors; and a thyristor switch that discharges the capacitors to a low-resistance load. To reduce the power drawn from the grid, the generator includes a recharging device based on a thyristor, which is connected to a reverse-parallel thyristor switch. To permit regulation of the pulse amplitude and increase its power, the uncontrollable dc source in the charging system is replaced by two irreversible thyristor converters in series. That permits control of the voltage at the power capacitors. To optimize capacitor charging, a two-loop subordinate control system regulates the parameters of the pulse generator: the external control loop governs the voltage charging the capacitors, while the internal control loop governs the charging current. MATLAB Simulink software is used to create a model of the proposed generator. The model corresponds to the actual pulse generator used at Siberian State Industrial University to investigate the electrostimulated plastic deformation of metals and alloys. The model permits improvement in the characteristics of the pulse generator and its operating conditions. A benefit of the proposed generator over its counterparts is that the power drawn from the grid is considerably reduced, while the voltage charging the capacitor may be regulated in the range up to 600 V, with pulse frequencies up to 400 Hz. The generator may be used industrially—in particular, in rolling mills when drawing steel wire that is hard to deform.     

Self-stimulation in the rat: Quantitative characteristics of the reward pathway.

Quantitative characteristics of the neural pathway that carries the reinforcing signal in electrical self-stimulation of the male Sprague-Dawley rat's brain were established by finding which combinations of stimulation parameters give the same performance in a runway. The reward for each run was a train of evenly spaced monophasic cathodal pulses from a monopolar electrode. With train duration and pulse frequency held constant, the required current was a hyperbolic function of pulse duration, with chronaxie c?=?1.5 msec. With pulse duration held constant, the required strength of the train (the charge delivered per second) was a hyperbolic function of train duration, with chronaxie C?=?500 msec. To a first approximation, the values of c and C were independent of the choice either of train duration and pulse frequency or of pulse duration, respectively. Hence, the current intensity required by any choice of train duration, pulse frequency, and pulse duration depended on only 2 basic parameters, c and C, and 1 quantity, Qi, the required impulse charge. These may reflect, respectively, current integration by directly excited neurons; temporal integration of neural activity by synaptic processes in a neural network; and the peak of the impulse response of the network, assuming that the network has linear dynamics and that the reward depends on the peak of the output of the network. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Voltage- and frequency-dependent modulation of L-type Ca2+ channel by MPC-1304, a novel calcium antagonist in guinea-pig hearts

The electrophysiological effects of MPC-1304, a novel calcium antagonist, were examined using the conventional microelectrode and whole-cell patch-clamp techniques in guinea-pig hearts. MPC-1304, at 100 nM or higher concentrations, produced a dose-dependent reduction in the action potential duration of guinea-pig papillary muscles, without changes in resting membrane potentials and maximum rate of rise of action potentials. In guinea-pig ventricular myocytes, MPC-1304 (1-100 nM) dose-dependently depressed the initial inward currents induced by depolarizing pulses from a holding potential of -30 mV in the external Tyrode solution, as did nifedipine, whereas the late outward current was not changed by MPC-1304. In the presence of 100 nM of MPC-1304 or 100 nM of nifedipine, the first depolarizing pulse from a holding potential of -80 mV caused a depression of the isolated L-type Ca2+ current (I(Ca)) by 29.5 % and 29.4 % of the control, respectively (tonic block), and successive pulses further suppressed I(Ca) in a use-dependent manner (use-dependent block). The degree of steady state use-dependent block of I(Ca) by 100 nM of MPC-1304 was 25.5 % at the stimulus frequency of 1 Hz and further increased to 34.0 % at 2 Hz (frequency-dependent block), which were significantly larger than those by 100 nM of nifedipine at both frequencies. The onset rate of use-dependent block by 100 nM MPC-1304 was significantly smaller than that by 100 nM nifedipine. MPC-1304 (100 nM) and nifedipine (100 nM) shifted the steady state inactivation curve of I(Ca) toward the negative potential by 3.3 mV and 9.1 mV in the mid-potential of the curve, respectively. The estimated dissociation constants of MPC-1304 were 137.7 and 49.9 nM for the resting and inactivated states of the L-type Ca2+ channel, respectively, and those of nifedipine were 113.9 and 18.1 nM, respectively. We conclude that MPC-1304 suppress the L-type Ca2+ channel with slow kinetics in a voltage- and frequency-dependent manner, which might be caused by its high affinity to the activated as well as to the inactivated state of the channel.     

Electrically evoked saccades from the dorsomedial frontal cortex and frontal eye fields: a parametric evaluation reveals differences between areas

Using electrical stimulation to evoke saccades from the dorsomedial frontal cortex (DMFC) and frontal eye fields (FEF) of rhesus monkeys, parametric tests were conducted to compare the excitability properties of these regions. Pulse frequency and pulse current, pulse frequency and train duration, and pulse current and pulse duration were varied to determine threshold functions for a 50% probability of evoking a saccade. Also a wide range of frequencies were tested to evoke saccades, while holding all other parameters constant. For frequencies beyond 150 Hz, the probability of evoking saccades decreased for the DMFC, whereas for the FEF this probability remained at 100%. To evoke saccades readily from the DMFC, train durations of greater than 200 ms were needed; for the FEF, durations of less than 100 ms were sufficient. Even though the chronaxies of neurons residing in the DMFC and FEF were similar (ranging from 0.1 to 0.24 ms) significantly higher currents were required to evoke saccades from the DMFC than FEF. Thus the stimulation parameters that are optimal for evoking saccades from the DMFC differ from those that are optimal for evoking saccades from the FEF. Although the excitability of neurons in the DMFC and FEF are similar (due to similar chronaxies), we suggest that the density of saccade-relevant neurons is higher in the FEF than in the DMFC.     

Dorsal diencephalic self-stimulation: A movable electrode mapping study.

The function relating electrical self-stimulation (ESS) barpressing rate to the frequency of cathodal pulses (0.2 mA and 0.1 msec) was obtained for several positions of a movable electrode in the dorsal diencephalon of the rat. The rate–frequency functions were fitted to a sigmoid model to obtain the asymptotic rate and threshold frequency. ESS was found along the epithalamic route (stria medullaris, habenula, and fasciculus retroflexus) and in the following thalamic nuclei: mediodorsal, paratenial, interanteromedial, centromedial, reuniens, and rhomboid. The lowest threshold (～5 pulses/train), which was found in the stria medullaris and the junction of the paratenial and centromedial nuclei, was comparable to that usually obtained for the brain areas where the ESS is most effectively rewarding (medial forebrain bundle, dorsal raphe, and amygdala). However, most threshold estimates were 4 to 8 times higher. In most brain sites, ESS was accompanied by epileptiform, motor, or aversive reactions (or a combination of these). These reactions may explain the fact that the maximum rates were generally very low. Nevertheless, no correlation was found between maximum rates and threshold frequencies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrical filtering in gerbil isolated type I semicircular canal hair cells

1. Membrane potential responses of dissociated gerbil type I semicircular canal hair cells to current injections in whole cell current-clamp have been measured. The input resistance of type I cells was 21.4 +/- 14.3 (SD) M omega, (n = 25). Around the zero-current potential (Vz = -66.6 +/- 9.3 mV, n = 25), pulsed current injections (from approximately -200 to 750 pA) produced only small-amplitude, pulse-like changes in membrane potential. 2. Injecting constant current to hyperpolarize the membrane to around -100 mV resulted in a approximately 10-fold increase in membrane resistance. Current pulses superimposed on this constant hyperpolarization produced larger and more complex membrane potential changes. Depolarizing currents > or = 200 pA caused a rapid transient peak voltage before a plateau. 3. Membrane voltage was able to faithfully follow sine-wave current injections around Vz over the range 1-1,000 Hz with < 25% attenuation at 1 kHz. A previously described K conductance, IKI, which is active at Vz, produces the low input resistance and frequency response. This was confirmed by pharmacologically blocking IKI. This conductance, present in type I cells but not type II hair cells, would appear to confer on type I cells a lower gain, but a much broader bandwidth at Vz, than seen in type II cells.     

Bursting and tonic discharges in two classes of reticular thalamic neurons

1. Two types of cat reticular (RE) thalamic cells were disclosed by means of intracellular recordings under urethan anesthesia. The RE neurons were identified by their typical depolarizing spindle oscillations in response to synchronous stimulation of the internal capsule. 2. In type I neurons (n = 41), depolarizing current pulses induced tonic firing at the resting or slightly depolarized membrane potential (Vm) and triggered high-frequency spike bursts at a Vm more negative than -75 mV. As well, these cells discharged rebound bursts at the break of a hyperpolarizing current pulse. Internal capsule stimulation elicited spindle sequences made off by depolarizing waves giving rise to spike bursts. 3. Type II cells (n = 9) did not discharge spike bursts to large depolarizing current pulses even when the Vm reached -100 mV, nor did they fire rebound bursts after long-lasting hyperpolarizing current pulses or spike bursts riding on the rhythmic depolarizing components of spindle sequences. 4. Compared with type I cells, type II cells showed less frequency accommodation during tonic firing. The latter neuronal class discharged at high frequencies (40 Hz) with slight DC depolarization, approximately 8-10 Hz at the resting Vm, and no underlying synaptic or subthreshold oscillatory events could be detected when the firing was blocked by DC hyperpolarization. 5. The presence of two cell classes in the RE nucleus challenges the common view that this nucleus consists of a single neuronal class. We suggest that a different set of conductances is present in type II RE neurons, thus preventing the low-threshold Ca2+ current from dominating the behavior of these cells.     

Lorentz force infiltration of fibrous preforms

A new process for the production of metal matrix composites, whereby molten metal is forced into the interstices of a fibrous preform using electromagnetic body forces, is presented. These forces are created by subjecting the molten matrix to a concentrated transient magnetic field which, in turn, induces intense eddy currents in the melt. This gives rise to Lorentz forces which propel the metal into the preform. Equations governing the mechanics of Lorentz force infiltration of an axisymmetric preform surrounded by molten metal are solved numerically. A finite difference algorithm is applied to solve Maxwell's equation of electromagnetic field propagation and to determine the flux density as a function of radial position. The resulting Lorentz force is then calculated and balanced with the inertial, fluid friction and capillary forces, taking preform compression into account, to predict infiltration velocity and cumulative infiltration distance. Apparatuses were designed and constructed to infiltrate cylindrical preforms of 24 vol pct 3-μm-diameter chopped alumina fiber preforms with commercial purity aluminum. Two capacitor banks were charged from 1 to 4 kV and rapidly discharged to produce magnetic pulses of up to 4 tesla peak, at frequencies of 2 to 3 kHz in the infiltrating furnace. A commercial MAGNEFORM unit was also used to produce fields of up to 5 tesla at 5.6 kHz.-Sound composite samples were produced, to a depth of 1.8 mm into the preforms, with little or no breakage of fibers. Good agreement between theoretical model predictions and experimentally measured infiltration depths was demonstrated. Primary process variables for a given matrix-preform system, were the number of discharges, the magnetic pulse intensity and frequency, and the melt ring thickness. The model predicts a pulse frequency below which infiltration does not occur and an optimum frequency for maximum infiltration depth. Successive pulses are predicted to produce only slightly decreasing increments in infiltration depth with the parameters explored, indicating that the process allows greater infiltration depths than were attained with preforms and apparatuses used in this work.     

Control of the delayed outward potassium currents in bursting pace-maker neurones of the snail, Helix pomatia

The net outward current in bursting pace-maker neurones of the snail (Helix pomatia) during sustained and repeated voltage clamp pulses was studied. The properties of currents remaining in cobalt-Ringer or after TEA injection were compared with those in untreated cells. 2. With sustained voltage clamp depolarizations the net outward current first increases to a maximum at 150 msec and then declines to 60% or less of its peak intensity. This depression, which is greater during repetition of short pulses (e.g. 100 msec pulses at 0-5 sec intervals), represents a true decrease in the outward flow of K (designated IK) and is not due to a decreased driving force resulting from extracellular K accumulation. The steady-state current-voltage (I-V) relationship for IK is N-shaped (Heyer & Lux, 1976). 3. A component of IK persists when Ca and Mg in the medium are replaced by Co (ICo-res). With voltage clamp depolarizations ICo-res increases rapidly to a maximum and then partially inactivates with voltage dependent time constants of hundredths or tenths of seconds. Repolarization removes the inactivation. Thus, repeated stimulation with short pulses does not increase the depression of ICo-res-ICo-res (e.g. measured during voltage steps from holding potentials of -50 to near 0 mV) is smaller in test pulses preceded by depolarization and larger in pulses preceded by hyperpolarization. The steady state I-V relationship is not N-shaped. ICo-res is blocked by intracellular injection of tetraethylammonium (TEA). 4. Repeated voltage clamp depolarization to near 0 mV with 100 msec pulses for neurones with large Ca currents in normal Ringer produces a long-term depression which is maximal with 300-400 msec repolarizations (to -50 mV) between pulses. This corresponds with stimulus parameters for the maximum Ca current (Heyer & Lux, 1976). Intracellular injection of Ca2+ (also Ba2+ and Co2+) likewise reduces the total net outward current and especially the delayed outward current under voltage clamp. 5. The component of IK which is removed by Co is identified as Ca dependent and designated IK(Ca). With single voltage clamp pulses IK(Ca) follows the approximate time course and voltage dependence of the slow inward Ca current (Iin slow; Heyer & Lux, 1976). Several lines of evidence suggest that Ca ions moving through the membrane activate IK(Ca). 6. Part of IK cannot be blocked by intracellular TEA injection. In different neurones the magnitude of the IK component resistant to TEA (ITEA-res) is approximately proportional to the relative magnitudes of Iin slow.ITEA-res does not inactivate with sustained depolarization and shows pronounced long-term depression with repetitive stimulation at intermediate intervals and an increased outward current at the onset of the second and subsequent pulses following short repolarizations. The steady-state I-V relationship is N-shaped. ITEA-res is abolished by extracellular Co. 7. A net inward current with low depolarizations can be measured after TEA injection...     

Rhesus monkey behavior during exposure to high-peak-power 5.62-GHz microwave pulses

Limits on the exposure to high-peak-power, short-duration microwave pulses have only recently been adopted. Additional data, however, are needed to understand the effects that may be produced by exposure to high-peak-power pulsed microwaves. Four male rhesus monkeys (Macaca mulatta) were trained on an operant task for food pellet reward to investigate the behavioral effects of very high-peak-power 5.62 GHz microwaves. The operant task required monkeys to pull one plastic lever on a variable interval schedule (VI-25 s) and then respond to color signals and pull a second lever to obtain food. The monkeys were conditioned to perform a color discrimination task using one of three colors displayed by a fiber-optic cable. A red signal was the discriminative stimulus for responding on the first lever. A response on the second lever when a green signal was presented (1 s duration) delivered a food pellet. If a response on the second lever was made in the presence of a white signal, a 30-s timeout occurred. While performing the behavioral task, the monkeys were exposed to microwave pulses produced by either a military radar (FPS-26A) operating at 5.62 GHz or the same radar coupled to a Stanford linear energy doubler (SLED) pulse-forming device (ITT-2972) that enhanced peak power by a factor of nine by adding a high power pulse to the radar pulse. The effects of both types of pulses were compared to sham exposure. Peak field power densities tested were 518, 1270, and 2520 W/cm2 for SLED pulses and 56, 128, and 277 W/cm2 for the radar pulses. The microwave pulses (radar or SLED) were delivered at 100 pps (2.8 microseconds radar pulse duration; approximately 50 ns SLED pulse duration) for 20 min and produced averaged whole-body SARs of 2, 4, or 6 W/kg. Compared to sham exposures, significant alterations of lever responding, reaction time, and earned food pellets occurred during microwave exposure at 4 and 6 W/kg but not at 2 W/kg. There were no differences between radar or SLED pulses in producing behavioral effects.     

Uses of double-pulse stimulation behaviorally to infer refractoriness, summation, convergence, and transmitter characteristics of hypothalamic reward systems.

Conducted 5 experiments with 13 male Sprague-Dawley rats. To self-administer strains of pulse pairs, Ss with electrodes in the hypothalamic reward system would press a lever at lower current thresholds or faster latencies, the shorter the intrapair interval--unless the interval was so short that each 2nd pulse fell within the refractory period following the first. By delivering all 2nd pulses to the contralateral reward system, not only was this refractory period limitation on temporal summation circumvented but spatial summation of the 2 reward systems was demonstrated. Evidently, they converge somewhere upon common neurons. Nearby nonreward structures did not share in this convergence. Assuming that the temporal-summation decline at longer intrapair intervals reflected the course of transmitter disposal at the synapse, imipramine and diisopropylfluorophosphate were peripherally administered. These drugs, which retard disposal in adrenergic and cholinergic synapses, respectively, indeed prolonged temporal summation, thus supporting the assumption and implying that adrenergic and cholinergic mechanisms both mediate self-stimulation. (11/2 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of sarcoplasmic reticulum (SR) calcium content on SR calcium release elicited by small voltage-clamp depolarizations in frog cut skeletal muscle fibers equilibrated with 20 mM EGTA

Cut muscle fibers from Rana temporaria (sarcomere length, 3.5-3.9 micro(m); 14-16 degreesC) were mounted in a double Vaseline-gap chamber and equilibrated with an external solution that contained tetraethyl ammonium- gluconate and an internal solution that contained Cs as the principal cation, 20 mM EGTA, and 0 Ca. Fibers were stimulated with a voltage-clamp pulse protocol that consisted of pulses to -70, -65, -60, -45, and -20 mV, each separated by 400-ms periods at -90 mV. The change in total Ca that entered into the myoplasm (Delta[CaT]) and the Ca content of the SR ([CaSR]) were estimated with the EGTA/phenol red method (Pape, P.C., D.-S. Jong, and W.K. Chandler. 1995. J. Gen. Physiol. 106:259-336). Fibers were stimulated with the pulse protocol, usually every 5 min, so that the resting value of [CaSR] decreased from its initial value of 1,700-2, 300 microM to values near or below 100 microM after 18-30 stimulations. Three main findings for the voltage pulses to -70, -65, and -60 mV are: (a) the depletion-corrected rate of Ca release (release permeability) showed little change when [CaSR] decreased from its highest level (>1,700 microM) to approximately 1,000 microM; (b) as [CaSR] decreased below 1,000 microM, the release permeability increased to a maximum level when [CaSR] was near 300 microM that was on average about sevenfold larger than the values observed for [CaSR] > 1,000 microM; and (c) as [CaSR] decreased from approximately 300 microM to <100 microM, the release permeability decreased, reaching half its maximum value when [CaSR] was approximately 110 microM on average. It was concluded that finding b was likely due to a decrease in Ca inactivation, while finding c was likely due to a decrease in Ca-induced Ca release.     

Self-stimulating rats combine subjective reward magnitude and subjective reward rate multiplicatively.

For rats that bar pressed for intracranial electrical stimulation in a 2-lever matching paradigm with concurrent variable interval schedules of reward, the authors found that the time allocation ratio is based on a multiplicative combination of the ratio of subjective reward magnitudes and the ratio of the rates of reward. Multiplicative combining was observed in a range covering approximately 2 orders of magnitude in the ratio of the rates of reward (from about 1:10 to 10:1) and an order of magnitude change in the size of rewards. After determining the relation between the pulse frequency of stimulation and subjective reward magnitude, the authors were able to predict from knowledge of the subjective magnitudes of the rewards and the obtained relative rates of reward the subject's time allocation ratio over a range in which it varied by more than 3 orders of magnitude. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phase and particle size composition of carbides formed during electric spark erosion machining of tungsten

Pulse repetition rates and pulse shapes have been studied in phase and particulate compositions obtained as electric spark erosion products. The experimental work was carried out at pulse frequencies (f) = 1 to 440 kHz with rectangular and ridge shaped pulses, and the number of current bridges (n) = 3 to 20. Maximum yields for tungsten monocarbide and the black form were noted when the pulse was ridged in shape and the number of current bridges was up to 10 and the pulse repetition rate was in excess of 100 kHz. The powder consists chiefly of spherical particles with a narrow size distribution range (0 to 7 m).Translated from Poroshkovaya Metallurgiya, No. 10, pp. 61–64, October, 1992.