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1. The effects of hypertonic solutions on excitation-contraction (e.-c.) coupling in frog skeletal muscle fibres were investigated using Arsenazo III to monitor intracellular calcium transients in voltage-clamped fibres. 2. In solutions made hypertonic with sucrose or sodium chloride, the size of the Arsenazo signal evoked by a 5 ms depolarization to 0 mV was little altered by increases in tonicity up to about twice normal, but declined in higher tonicities, and was almost completely suppressed at 4 times normal tonicity. 3. The latency to onset of the Arsenazo signal was increased in hypertonic solutions (2.3 and 3.1 times normal tonicity), but the decay time constant of the signal was little changed with tonicities up to 2.3 times normal. 4. The rheobase potential for a just-detectable Arsenazo signal was shifted about 4 mV more negative by increases in tonicity up to 2.3 times normal, but further increases reversed the direction of the shift, and in 3.95 times normal tonicity the rheobase was 10 mV more positive than in normal Ringer solution. 5. With short (less than 10 ms) pulse durations the depolarization needed to elicit a threshold Arsenazo signal increased steeply with increasing tonicity. Changes in the strength-duration curve could be accounted for by an increase in the time constant for build-up of a hypothetical coupler in the e.-c. coupling process. 6. Solutions of about twice normal tonicity are commonly used to suppress muscle contraction. Since the size of the Arsenazo signal was only slightly reduced by this tonicity, the main effect is presumably on the contractile proteins.

The importance of strength duration (SD) curves as a method to asses (1) the electrical characteristics of different electrodes for pacing, as well as (2) the patient safety margin for stimulation with modern multiprogrammable units, has been recently reported by Irnich [1]. Various electrode designs to optimally match electrodes to pulse generators have been developed by several manufacturers; i.e. solid, ring, porous and carbon tip electrodes. To study the characteristics of these electrodes, one hundred electrodes of different types: 50 porous, 7.5-9 mm2 surface (SA); 40 solid, 8-12 mm2 (SA); 10 carbon tip have been implanted and evaluated using acute, voltage SD curves at various pulse widths ranging from 0.05 to 2.0 ms. A linear regression computer program was used to calculate Chronaxie (C) and Rheobase (R) values. Acute and chronic thresholds (pulse width) were also obtained for most of the implanted electrodes. The correlation coefficient of linear regression for a majority of the SD curves was greater than 0.97. The smallest average chronaxie points from the SD curves were obtained with porous (0.30) and the smallest average Rheobase with the carbon tip electrode (0.16). Solid tip electrodes of smaller surface areas (8 mm2) exhibited lower chronaxie points as compared to solid electrodes with larger surface areas (12 mm2). Although porous electrodes acutely have lower thresholds as compared to solid electrodes, these differences were chronically statistically significant only for electrodes of different surface areas.

Discharge properties of cat cervical motoneurons innervating distal forelimb muscles were investigated by intracellular current injection. Values for rheobase current, afterhyperpolarization duration and several measures of repetitive discharge characteristics were in most respects similar to those obtained for hindlimb motoneurons.

1. 1. In artificial heart stimulation, the essential quantity is the density of current, j , in the intramyocardial wall. Dosage of the pulse amplitude in volts can have serious consequences for the patient. Curve indications in volts on pacemakers and in publications and records must, therefore, be rejected. 2. 2. Hence, the pacemaker should supply stabilized current pulses even while the load impedance is increasing. 3. 3. The distortion of the voltage curve at stabilized current is an electrode effect. 4. 4. Separate measurement and registration of the physical quantities involved in stimulation is advisable. The values obtained in every individual patient warrant conclusions as to the method of choice. It is recommended that one start with the Furman and Schwedel method, i.e., with one electrode in the right ventricle and the other placed subcutaneously in the thorax (a noncritical location). 5. 5. Measurements on the canine heart in situ with block, carried out with currents pulses of rectangular configuration, revealed that, when the Furman method is used, chronaxy and rheobase of the myocardium are dependent on the position of the electrodes. 6. 6. The phase which the heart is in when the current pulse is supplied is a factor of importance for the heart's following of the imposed frequency rate.

Rats were trained to self-stimulate for 100 Hz sine wave stimulation delivered through electrodes implanted in the lateral hypothalamus. The thresholds of the reinforcing stimulation were determined in eight rats by a new method over stimulus train durations of 0.01–1.0 sec. The resulting strength-duration curve showed that threshold current decreased rapidly as train duration was increased to 0.1 sec and approached a rheobase for longer wave trains. When expressed in terms of amount of electricity (charge) the reward thresholds increased linearly with train durations from 0.01 to 1.0 sec. At stimulus trains below 0.1-sec duration the energy required to maintain threshold was invariant at about 5 μJ. Beyond 0.1 sec threshold energy increased linearly with duration.

Strength-duration curves were constructed from threshold measurements obtained with unipolar anodal and cathodal stimuli at various temperatures. Stimuli ranging in duration from .1 to 50 msec. were delivered during diastole via an electrode sutured to the left ventricular surface. Thresholds were measured at 37°, 29°, 23° and 19°C. Plotting thresholds against reciprocal of stimulus duration it was possible to transform the strength-duration curves into straight lines. All lines demonstrated a progressive increase in slope with low temperatures, the increase being greater for the anodal strength-duration lines. The changes in chronaxie were secondary to the slight changes in rheobase and the more important increases in slope of the strength-duration lines. It is concluded that cold causes a decrease in excitability to stimuli of short duration, this effect being greater for anodal than for cathodal stimuli.

Effects of electric currents on the duration of single node action current were observed.1. An inward pulse applied to an active node shortened the duration of the action current. The effect was the more marked, the stronger the pulse (fig.1).2. Conducted action currents were abolished by inward pulses of high in-tensities. The intensity required was always smaller when the pulse was ap-plied in the falling phase than in the rising or at the peak of the action current. The relation remained unaltered in altered composition of the Ringer solution employed (fig.1).3. The current intensity requisite for abolition was more than ten times stronger than the peak value of the normal action current, when examined in the rising phase.4. On the contrary, outward pulses prolonged the duration (fig.4).5. The duration was shortened by anelectrotonus and prolonged by catelec-trotonus (figs.5-7).6. Anode break excitations were found readily elicitable in single node preparations if only a strong (more than10times the rheobase) pulse was used. Thereby, the duration of the response was found longer than a normal make-response (figs.2and3).

Summary Afferent and efferent unmyelinated fibres have been compared with respect to their tendency to react with repetitive impulse discharges to stimulation with constant currents. Stimulation with constant currents of the efferent C fibres in the lower part of the vagus nerve of the cat does not initiate a repetitive discharge with strengths up to more than 4 times the rheobase. On the other hand C fibres of dorsal root origin are extremely sensitive to stimulation with constant currents of just supra-rheobasic strength. Peripheral vasodilatation can be elicited by local heating of the peripheral stump of the dorsal roots. The difference between the afferent and efferent C fibres with respect to stimulation by constant currents agrees with their differential thermal sensitivity.

The excitability of a single motoneuron soma in a toad's spinal cord is compared with that of a single motor fibre from a experimental point of view.The following is the results of the experiments.(1) The strength-duration curve of the neuron soma is compared with that of the motor fibre; it is noticed that the rheobase of the neuron soma is lower and the chronaxie of it is longer than those of the motor fibre. The Weiss formula is acceptable in these two strength-duration curves.(2) The neuron soma produces more easily multiple responses than the motor fibre by direct current stimulation; but the results obtained from single nervepreparation are not same in every case, and the author has grouped four types according to the character of multiple responses and the accommodation curve.(3) The effect of the electrotonus on the neuron soma is different from that on the motor fibre.(4) No differences of the latency are detectable between the neuron soma and the motor fibre.(5) The relative refractory period of the neuron soma is shorter than that of the motor fibre; the refractoriness of the neuron soma is followed by the supernormal phase which is not recognized with the motor fibre under the same conditions.

Strength-duration curves for space-clamped squid axons, using square wave anode breaks as stimuli, established the existence of four distinct regions. For the average experimental axon the intersection of the first two regions, tau(1), occurs at about 7 msec. This agrees with computations based on the Hodgkin-Huxley (HH) equations and corresponds to the accommodation time constant found previously for a linearly rising ramp, as given by the HH equations and as found experimentally. The second break in the curve, tau(2), at about 200 msec, and the third break, tau(3), at 1 sec, are far beyond the range of the HH equations and may be the counterpart in the excitability of the long time constants, which have been apparent from a number of other types of experiments. The regions of the curve before 1 msec and beyond 2 or 3 sec are quite variable and may represent breakdown. Rheobase increases in both experimental and computed axons when temperature is raised. In both experimental and computed axons tau(1) descreases slightly when the temperature is raised from 10 to 15 degrees C. At 20 and 25 degrees C, tau(1) of the experimental axon increases markedly.

1) The skin plays an important role in interfering with the measurement of threshold value of electric stimulation of nerves and muscles in the human body.2) It is possible to measure the threshold of the nerve or muscle by balancing the polarization in the skin. This is called a Balancing Network Method3) Explanations were given on a simple arrangement used for measuring the threshold clinically.4) The true V-t curve was obtained by eliminating the influence of the skin by the B.N.M. The values of chronaxie and rheobase were calculated theoretically. The values of four kinds of nerves and muscles were compared with each other.5) Explanations were given on the measurement of the constant concerning the slope factor.6) Explanations were given on the measurement of threshold for AnOC.

1. The effects of strychnine upon the nerve fibres of toads were investigated.2. Strychnine had little effect on the myelinated portion, while it had markedeffects on the node of Ranvier.3. The rheobasic voltage of the node was decreased by the application ofstrychnine solutions of lower concentration (from about10-17M to10-5M), butwas increased by higher strychnine concentrations (more than10-4M).4. The rheobase of the node in Ringer solution rose by strychnization of theneighbouring node.5. Thesholds for repetitive response to constant current was decreased bystrychnization of the fibre. The decreased threshold for repetitive response pro-duced by strychnization of the fibre was hardly possible to be restored to theinitial value by washing the fibre with fresh Ringer solution.6. The relative refractory phase of nerve fibres became shorter than in thenormal, and the supernormality of the fibre was increased and prolonged by weakstrychnization, but the recovery process was depressed by strong strychnization.7. The strychnine concentration, which was necessary to decrease therheobase of the fibre, became high by raising the room temperature over20°C.8. Repetitive responses due to single shock stimulation were observed instrychnine-treated nerve fibres (from about10-7M to10-4M) at temperatureshigher than about20°C.

1. Pacinian corpuscles or non-myelinated nerve terminals in Pacinian corpuscles, from which lamellae had been removed, were stimulated with linearly increasing compression of varying rate, which decayed linearly after a maximum compression. 2. An impulse was initiated with a compression having a rate of increase greater than a critical slope. The critical slope was 1·1-1·2 rheobase/msec in both intact corpuscles and decapsulated terminals. 3. The receptor potential of the terminal increased in magnitude and rate of rise with an increase in the rate of compression. Its rate of rise was linearly related to the rate of compression. 4. Hyperpolarization was observed on removal of compression, and an impulse was initiated upon recovery of the hyperpolarized membrane potential. 5. In some corpuscles or decapsulated terminals hyperpolarization was produced on compression and a depolarizing response was produced upon removal of compression. After rotation by 90° along their long axis, they produced depolarization on compression. 6. Difference in the directional sensitivity of corpuscles and decapsulated terminals was confirmed and was explained on the basis of the shape of the terminal. 7. On- and off-responses of variable latency recorded from a central portion of the axon to Pacinian corpuscles were explained by the depolarizing and hyperpolarizing responses in the terminal.

1. Responses of receptors with fibres in the interosseous nerve of the duck's leg have been studied by recording unit discharges in filaments dissected from the sciatic nerve.2. Seventy-two of the ninety-four units examined served highly phasic, vibration-sensitive mechanoreceptors in the interosseous region interpreted as being Herbst corpuscles. Receptor types for most of the other units could not be determined, but some were slowly adapting mechanoreceptors.3. Rheobase threshold values for the most sensitive vibration-receptors were similar to those of mammalian Pacinian corpuscles.4. Threshold-frequency relationships for the vibration receptors showed a wider range of low frequency cut-off values, and a greater capacity to signal high frequencies, than is the case with Pacinian corpuscles.5. Fibres of the vibration-receptors had calculated diameters ranging from 5 to 10 mum and account for the bulk of the larger fibres in the interosseous nerve.6. It is suggested that Herbst corpuscles in the legs of birds might act as a warning device by detecting vibratory disturbances of the ground or other supporting surface.

1. The kinetics of mechanical activation were examined in muscle fibres of the frog's sartorius muscle, using a voltage clamp to control membrane potential, tetrodotoxin to eliminate electrical activity and microscopic observations to determine the mechanical threshold.2. The strength-duration curve was determined over a range of membrane potentials varying between -52 mV (rheobase) and +90 mV. At 4 degrees C the critical duration was about 11 msec at -30 mV, 4 msec at 0 mV and 2 msec at +40 mV.3. For pulses where V > -10 mV the threshold criterion at 4 degrees C was that the ;area above -30 mV' must exceed about 120 mV msec.4. The effect of a brief subthreshold pulse declines with a time constant of about 3 msec at -100 mV and about 8 msec at -85 mV at 4 degrees C.5. Although the strength-duration curve is well fitted by assuming a first-order mechanism in which the rate of release of activator increases with membrane potential, other experiments show that the over-all mechanism is probably second order in time.6. A short pulse must be at least 50% threshold if it is to give a visible contraction when added to a long pulse which is just below rheobase.7. Delayed rectification was conspicuous with medium or long pulses which were just below the mechanical threshold, but short pulses could give contraction without turning on any appreciable potassium conductance.8. The Appendix extends Falk's (1968) treatment of the charging of the tubular system under a voltage clamp.

Responses to current steps were recorded from pyramidal tract (PT) cells of the cat by means of intracellular microelectrodes. PT cells with resting potentials from -60 to -80 mV set up a well sustained repetitive discharge during stimulation. When comparing fast and slow PT cells, quantitative differences were found between them in the pattern of repetitive firing. Thus, (1) the rheobase is lower in slow PT cells (mean and S.D.; 0.53±0.63 nA) than in fast cells (1.57±1.11 nA). (2) Following stimulation with a current step twice rheobase the latency and the successive interspike intervals are shorter in fast PT cells than in slow cells. (3) The interspike interval distribution shows a greater irregularity in fast PT cells than in slow cells. At firing rates around 30 impulses/sec the coefficient of variation has a mean value of 0.243 for fast PT cells and 0.085 for slow cells. (4) Fast PT cells show a greater decrease of firing rate during the initial 300 msec of current stimulation (adaptation) than do slow cells. The mean value of this initial decrease is 1.85 times the later steady firing rate in fast PT cells and 0.56 times in slow cells. (5) The slope constant of the firing rate-current relationship is larger in fast PT cells, being five times or more than in slow cells. These characteristics of firing pattern are termed “kinetic” and “tonic” for fast and slow PT cells respectively, and their functional meanings are discussed in comparison with other neural organs.

1. Some of the data obtained by HAGIWARA (1954) on the interval fluctuations of the sensory nerve impulse have been reanalysed with a modified model.2. The modification consisted essentially of the introduction of a factor characterizing the rate of fluctuation of a random process that is thought to be super-imposed on the threshold of the impulse triggering mechanism.3. The mean rate of change in amplitude of the step-wise defined random process was found to be in the order of a few hundred per second.4. Some of the implications of the model: the time course of the random function immediately after an impulse, the large value of the noise intensity relative to the rheobase and, as a consequence, the predicted existence of spontaneous discharge, were discussed.

1) The effect of electrodes of a long polarization on the time-factor as well intensity-factor in electric excitation was examined. First the i-t-relation in normal condition was measured. Then three i-t-relations were measured in a certain order after onset of the polarization, and from transition of changes suffered by the relations the effect aimed at was deduced.2) The normal i-t-relation satisfies the Weiss' formula. The relation follows also the formula during the polarization with its constants for the time-factor and intensity-factor varying with time of the polarization.3) By the cathodal polarization the rheobase increases and the chronaxie decreases and by the anodal vice versa. The changes occur almost exponentially and their magnitude grows proportionately to the voltage of polarization.4) Under low temperature the effect of cathodal polarization on both the rheobase and chronaxie is weakened and that of anodal strengthened. All the findings under 3) and 4) agree well with Suzuki's classification of environmental conditions into two counteracting groups.

The lowering of external sodium raised both the constant quantity threshold, Q(o), and the rheobase, I(o), in both real space-clamped squid axons and the theoretical axon as computed on the basis of the standard Hodgkin-Huxley equations. In both real and theoretical axons the minimum intensity for excitability for short pulses, which occurs at about 15 degrees C, was still present when low sodium replaced seawater. Low sodium did not affect the temperature dependence of the strength-duration relationship in the range, 5 degrees to 25 degrees C. The excitability of tetrodotoxin-treated real axons was found to be more temperature-dependent than that of normal real axons. Also the data on dosage-response to TTX of real axons fit the dose-response relationship of a hypothetical system in which one TTX ion binds reversibly to its receptor to produce a fraction of the inhibitory effect, the curve being identical to a simple adsorption isotherm. The Hodgkin-Huxley equations describe the broad outline of events occurring during excitation quite well.

THE action potential evoked from an artificially produced excitable node of isolated crab axon membrane1 shows similar changes to those described for the isolated toad node2, when currents are applied during the action potential itself. The rising phase of the action potential can be modified only by very considerable anodal currents (some 40 times rheobase), but the repolarization phase shows changes when weak currents of either polarity are applied (Fig. 1). Repolarization is delayed by cathodal current and is hastened by anodal current, when these are applied during the falling phase of the action potential. The divergence of the voltage profile of repolarization, produced by a constant current pulse of either polarity, is greater the later it is applied, as would be expected from the form of the change in membrane resistance that accompanies the voltage change of the action potential. The changes in the rate of repolarization are proportional to the strength of the applied current and its duration, so that complete repolarization can be achieved with strong anodal current, that is, the later phase of the action potential can be abolished.

The effects of high hydrostatic pressure upon isolated single nerve fibers were investigated. Single nerve fibers were isolated from the nerve innervating the sartorius or semitendinosus muscle of the toad ( Bufo marinus). The responses of single nerve fibers were recorded using the ‘bridge-insulator,’ the ‘interface’ and the ‘three-compartment’ methods. Hydrostatic pressures up to 16,000 psi were developed with a hand operated hydraulic pump. The most striking effect of high pressures was the prolongation of the duration of the response. At 10,000 psi the duration was 4.5–5.0 times the duration at atmospheric pressures. The duration of prolonged responses (by previous tetanization) was not appreciably altered by high pressures. The amplitude, rheobase and shock-response interval were only slightly affected. At 5000 psi the shock-response interval increased by 5–15% and the rheobase by 10–15%.

SummaryMephenesin and P105 both consistently increase rheobase (r), the time constant of excitatiion (k), and stability (R/k) of frog sartorius muscle.

Serotonergic modulation of precerebellar nuclei may be crucial for the function of the entire cerebellar system. To study the effects of serotonin (5-HT) on neurons located within the pontine nuclei (PN), the main source of cerebellar mossy fibers, we performed standard intracellular recordings from PN neurons in a slice preparation of the rat pontine brain stem. Application of 5 μM 5-HT significantly altered several intrinsic membrane properties of PN neurons. First, it depolarized the somatic membrane potential by 6.5 ± 3.5 mV and increased the apparent input resistance from 49.5 ± 14.6 to 62.7 ± 21.1 MΩ. Second, 5-HT altered the I-V relationship of PN neurons: it decreased the inward rectification in hyperpolarizing direction, but increased it when depolarizing currents were applied. Third, it decreased the rheobase from 0.32 ± 0.14 to 0.24 ± 0.14 nA without affecting the firing threshold. Finally, the amplitude of medium-duration afterhyperpolarizations was reduced from −14.9 ± 2.0 to −12.3 ± 2.4 mV. Together, these 5-HT effects on the intrinsic membrane properties result in an increase in excitability and instantaneous firing rate. In addition, application of 5 μM 5-HT also modulated postsynaptic potentials (PSPs) evoked by electric stimulations within the cerebral peduncle. The amplitude, maximal slope, and integral of these PSPs were reduced to 46.2 ± 23.4%, 45.7 ± 23.7%, and 61.4 ± 28.4% of the control value, respectively. In contrast, we found no change in the decay and voltage dependence of PSPs. To test modulatory effects on short-term synaptic facilitation, we applied pairs of electrical stimuli at intervals between 10 and 1,000 ms. 5-HT selectively enhanced the paired-pulse facilitation for interstimulus-intervals >20 ms. The alteration of paired-pulse facilitation points to a presynaptic site of action for 5-HT effects on synaptic transmission. Pharmacological experiments suggested that pre- and postsynaptic effects of 5-HT were mediated by two different kinds of 5-HT receptors: changes in intrinsic membrane properties were blocked by the 5-HT2 receptor antagonist cinanserin while the reduction of PSPs was prevented by the 5-HT1 receptor antagonist cyanopindolol. In conclusion, 5-HT increases the excitability of PN neurons but decreases the synaptic transmission on them. The selective enhancement of synaptic facilitation may, however, allow high-frequency inputs to effectively drive PN neurons, thus the PN may act as a high-pass filter during periods of 5-HT release.

We studied the rapid changes in electrical properties of lumbar motoneurons between postnatal days 3 and 9 just before mice weight-bear and walk. The input conductance and rheobase significantly increased up to P8. A negative correlation exists between the input resistance (Rin) and rheobase. Both parameters are significantly correlated with the total dendritic surface area of motoneurons, the largest motoneurons having the lowest Rin and the highest rheobase. We classified the motoneurons into three groups according to their discharge firing patterns during current pulse injection (transient, delayed onset, sustained). The delayed onset firing type has the highest rheobase and the fastest action potential (AP) whereas the transient firing group has the lowest rheobase and the less mature AP. We found 32 and 10% of motoneurons with a transient firing at P3–P5 and P8, respectively. About 20% of motoneurons with delayed onset firing were detected at P8. At P9, all motoneurons exhibit a sustained firing. We defined five groups of motoneurons according to their discharge firing patterns in response to ascending and descending current ramps. In addition to the four classical types, we defined a fifth type called transient for the quasi-absence of discharge during the descending phase of the ramp. This transient type represents about 40% between P3–P5 and tends to disappear with age. Types 1 and 2 (linear and clockwise hysteresis) are the most preponderant at P6–P7. Types 3 and 4 (prolonged sustained and counter clockwise hysteresis) emerge at P8–P9. The emergence of types 3 and 4 probably depends on the maturation of L type calcium channels in the dendrites of motoneurons. No correlation was found between groups defined by step or triangular ramp of currents with the exception of transient firing patterns. Our data support the idea that a switch in the electrical properties of lumbar motoneurons might exist in the second postnatal week of life in mice.

Anna Binda,1 Alice Panariti,1 Andrea Barbuti,2 Carmen Murano,1 Roberta Dal Magro,1 Massimo Masserini,1,3,4 Francesca Re,1,3,4 Ilaria Rivolta,1,3,4 1School of Medicine and Surgery, University of Milano-Bicocca, Monza, Italy; 2Department of Biosciences, ThePaceLab and Interuniversity Center of Molecular Medicine and Applied Biophysics (CIMMBA), University of Milan, Milano, Italy; 3Milan Center for Neuroscience (NeuroMI), University of Milano-Bicocca, Monza, Italy; 4Nanomedicine Center NANOMIB, University of Milano-Bicocca, Milano, Italy Purpose: Nanotechnologies turned out to be promising in the development of diagnostic and therapeutic approaches toward neurodegenerative disorders. However, only a very scant number of nanodevices until now proved to be effective on preclinical animal models. Although specific tests in vivo are available to assess the potential toxicity of these nanodevices on cognitive functions, those to evaluate their biosafety in vitro on neurons are still to be improved. Materials and methods: We utilized the patch-clamp technique on primary cultures of cortical neural cells isolated from neonatal rats, aiming to evaluate their electrical properties after the incubation with liposomes (mApoE-PA-LIPs), previously proved able to cross the blood–brain barrier and to be effective on mouse models of Alzheimer’s disease (AD), both in the absence and in the presence of β-amyloid peptide oligomers. Results: Data show a high degree of biocompatibility, evaluated by lactate dehydrogenase (LDH) release and MTT assay, and the lack of cellular internalization. After the incubation with mApoE-PA-LIPs, neuronal membranes show an increase in the input resistance (from 724.14±76 MΩ in untreated population to 886.06±86MΩ in the treated one), a reduction in the rheobase current (from 29.6±3 to 24.2±3pA in untreated and treated, respectively), and an increase of the firing frequency, consistent with an ultimate increase in intrinsic excitability. Data obtained after co-incubation of mApoE-PA-LIPs with β-amyloid peptide oligomers suggest a retention of liposome efficacy. Conclusion: These data suggest the ability of liposomes to modulate neuronal electrical properties and are compatible with the previously demonstrated amelioration of cognitive functions induced by treatment of AD mice with liposomes. We conclude that this electrophysiological approach could represent a useful tool for nanomedicine to evaluate the effect of nanoparticles on intrinsic neuronal excitability. Keywords: neurodegenerative disorders, nanomedicine, action potential, electrophysiology, patch clamp, β-amyloid peptide

To examine mechanisms underlying the role of chronic stress in post-infectious irritable bowel syndrome (PI-IBS), we previously studied the effect of chronic stress and prior infectious colitis in the C. rodentium infected mouse (day 30 post infection), a model of human E. coli self-limiting colitis (NGM A:257,2010). Water avoidance stress (WAS; 1 hr on days 21-30 following infection) increased stress hormones (corticosterone and epinephrine), excitability of colonic nociceptive DRG neurons and colonic multi-unit afferent firing, compared to post-infected animals alone The current study examined pathways underlying this stress-post-infection effect using patch clamp recordings from Fast Blue labeled colonic DRG neurons to measure changes in excitability (rheobase (Rh) and/or increases in action potential discharge (APD)). At day 30, infection had resolved and histopathology was normal. However, tissue trypsin-like activity (>10 fold; p

The strength-duration function is a classic measure of neural excitability. When studied on peripheral motor axons it reflects the intrinsic nodal membrane properties, and its time-constant (tau(SD) or chronaxie) predominantly depends on non-voltage-gated, rest Na(+) inward conductances. We assessed the strength-duration curve of ulnar motor axons in 22 nerves of healthy controls, in 18 nerves of patients with multifocal motor neuropathy with conduction blocks (MMN), and in 19 nerves of patients with motor neurone disease (MND). The compound muscle action potential (CMAP) was smaller in nerves of both groups of patients than in controls (P0.05). The rheobasic current (rh(50%)) [mean +/- standard deviation (SD)] was higher in patients with MMN than in controls (13.3 +/- 16.3 mA; controls 4.7 +/- 1.7 mA, P0.05). The tau(SD) was differentially abnormal in the nerves of the two groups of patients: it was prolonged in the nerves of patients with MND foror=40 years (227.2 +/- 34.5 micro s; controls 190.9 +/- 51.0 micro s, P0.05), but it was shortened in the nerves of patients with MMN (146.5 +/- 55.4 micro s; controls 208.6 +/- 51.2 micro s, P0.05) who had not been treated recently with high-dose intravenous immunoglobulin (IVIg). Nerves of patients with recently treated MMN (6 weeks) who were under the therapeutic effect of IVIg had a normal tau(SD)(.) Our results suggest that, probably due to an immuno-mediated rest Na(+) channel dysfunction, Na(+) conductances are reduced in MMN. This abnormality is a function of the time after the last IVIg treatment and involves also the axonal membrane outside the conduction block. Conversely, in MND, possibly owing to the ionic leakage of degenerating membrane, rest Na(+) conductances are increased. Measuring the strength-duration curve of the ulnar motor axons might be useful in the differential diagnosis between de novo MMN and MND.

Nernst's law of stimulation (stimulus = current √ time) has been proven for currents from 0.0002 to 0.001 seconds duration, but Lapique showed that a minimum time was necessary and was different for different tissues. A minimal current flowing infinitely which just causes a contraction is called the rheobase, the rheobase is then doubled and the time for stimulation is measured, this time is called the chronaxie. Owing to the uncertainties of the form of many of the currents used in determining chronaxie or to the undesirability of the form of the current (asymptotic) we have adopted a different procedure.Our studies of the electric stimulation of muscle with alternating current have led us to believe that what is called the “summation of stimulus” is due to the direct current component of the alternating current. The induction coil gives a current having a unidirectional competent, as shown by Washburn, who inserted a silver coulometer in series with the secondary of an induction coil and obtained a depo...

Cerianthus responds to a single condenser shock by a rapid contraction of tentacles and column. The response is symmetrical no matter where the shock is applied, from aboral end to tentacle tips, is propagated with a velocity of 1–2 m.sec., and is independent of the strength of the stimulus above threshold. The response is followed by an absolute refractory period of 60–70 m.sec. at 22–23° C. and a relative refractory period up to 200 m.sec. after the stimulus. For stimulation of either tentacles or column a threshold at twice the rheobase was obtained by discharge of a 0.05 µF. condenser through a total electrode-plus-preparation resistance of 3,000 ohms, thus giving a capacitance-resistance value of 0.15 m.sec. and chronaxie of 0.05 m.sec. Non-polarizable zinc–sulphate–zinc–agar glass tube electrodes of 0.5 mm. orifice diameter were used. With the same apparatus the chronaxie of the column through-conducting system of Naples specimens of Calliactis was 1.0 m.sec. Hill's1 equation for the excitation of nerve fits the strength-duration curve for Calliactis but does not approximate closely to that for Cerianthus. Complete curves of the strength-duration relation and the relative refractory period will be published elsewhere.

In a preliminary study undertaken to ascertain the changes produced in excitability of the excised turtle ventricle by rest and activity, 11 hearts were used from Chelydra serpentina and Emys sp. The Lapicque potentiometer and chronaximeter were used. The stimuli were applied by way of non-polarizable electrodes.The results, confirming and extending those previously reported by Garrey and Ashman1 and by Ashman and Hafkesbring,2 were variable, but certain conclusions clearly emerge.1. Excitability, expressed either as rheobase, chronaxie or least time is greatly influenced by activity.2. In hearts in good physiological condition when excised (3 examples) there was a treppe in excitability, comparable to the treppe in contractility, and the treppe was demonstrable both in rheobase and “least time.” Our evidence shows, although less clearly, that there was a treppe in chronaxie. Expressed in terms of quantity of electrical energy required to excite the tissue, activity definitely increased the excitability.3...

Dantrolene sodium is thought to affect some step in the excitation-contraction coupling process. Using a point voltage clamp to determine mechanical thresholds of individual fibers of frog, rat and goat skeletal muscle preparations, we found that dantrolene both raises (moves to more positive potentials) the rheobasic potential and increases the steepness of the strength-duration curve for mechanical threshold. The effect of raising the rheobase reaches a maximum at 1.2 x 10-5M dantrolene whereas the steepness effect occurs only at a saturating concentration (3.8x10-5M),indicating that dantrolene has two sites of action. The rheobase effect is absent below 18 degrees C (suggesting a phase transition) and it is competitively antagnoized by the calcium ionophore A23187 which can release calcium from the sarcoplasmic reticulum. The data indicate that dantrolene raises the rheobase by directly decreasing the release of calcium from the sarcoplasmic reticulum. We propose that dantrolene inhibits the movement of a natural calcium ionophore. Measurements of the voltage-dependent charge movement associated with excitation-contraction coupling showed that dantrolene did not significantly change the amount of charge moved. The time to peak of the ON current was not significantly changed, but that of the OFF current was significantly shortened. This action of dantrolene on the kinetics of the OFF current may account for its effect on the steepness of the strength-duration curve.

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative motoneuron (MN) where in fast fatigable motor units (MUs) of vulnerable motor pools preferentially degenerate followed by fast fatigue resistant and slow MUs . Excitability is a key endogenous mechanism of MN neuroprotection [1] and therefore we hypothesize that pre-symptomatic excitability indicates impending disease development. Using a transgenic mouse model for ALS, we performed in vitro patchclamp electrophysiology in ALS-vulnerable trigeminal motoneurons (TMNs) retrogradely labeled from jaw closer muscles at P8-12. We proposed a novel k-means clustering approach to classify TMNs into putative fast fatigable (PFF), fast fatigue resistant (PFR) and slow (PS) MUs based on rheobase and input resistance. Interestingly, hyper-excitability was noted in PFF and PFR

Spinal muscular atrophy (SMA) - the most common genetic cause of death in infancy - is a motor neuron disease caused by reduced expression of the survival motor neuron (SMN) protein. It is currently unknown why reduction in SMN, leads to selective motor deficits and muscle weakness. Using the SMA-Δ7 mouse model, we have previously reported that the sensory-motor circuit is dysfunctional early in the disease and precedes any motor neuron loss. Motor neurons in the L1 segment, innervating proximal muscles, are abnormally hyperexcitable and more affected than L5 motor neurons, innervating distal hindlimbs early after birth. To test whether this hyperexcitability is either due to synaptic dysfunction or SMN deficiency per se in motor neurons, we recorded intracellularly from L5 motor neurons at a time (P4) when there was no significant functional synaptic impairment.We employed the in vitro intact spinal cord preparation. Whole-cell patch clamp recordings revealed that the intrinsic properties of SMA L5 motor neurons were not significantly different than wild type (WT) age-matched counterparts. The passive membrane property of input resistance was on average 72.7±18.1 MΩ in WT (n=10) and 53.9±21.7 MΩ in SMA (n=5) motor neurons. Similarly, the time constant was 1.9±0.5 ms in WT and 2.0 ± 0.7 ms in SMA. Furthermore, the active membrane properties of: Rheobase (WT: 0.7±0.2 nA; SMA:0.8±0.2 nA), Vthreshold (WT: −31.6±3.7 mV; SMA: −33.6±2.6 mV), action potential amplitude (WT: 72.8±5.2 mV; SMA: 73.2±3.6 mV) and rate of rise (WT: 48.8±6.2 mV/ms; SMA: 40.2±10.0 mV/ms) were not significantly different (t-test).These results indicate that the intrinsic hyperexcitability of SMA motor neurons stems from dysfunctional spinal circuits and raise the possibility that SMA may be a disease of motor circuits acting via non-cell autonomous mechanisms.