Chronaxie Measurements in Patterned Neuronal Cultures from Rat Hippocampus.

Excitation of neurons by an externally induced electric field is a long standing question that has recently attracted attention due to its relevance in novel clinical intervention systems for the brain. Here we use patterned quasi one-dimensional neuronal cultures from rat hippocampus, exploiting the alignment of axons along the linear patterned culture to separate the contribution of dendrites to the excitation of the neuron from that of axons. Network disconnection by channel blockers, along with rotation of the electric field direction, allows the derivation of strength-duration (SD) curves that characterize the statistical ensemble of a population of cells. SD curves with the electric field aligned either parallel or perpendicular to the axons yield the chronaxie and rheobase of axons and dendrites respectively, and these differ considerably. Dendritic chronaxie is measured to be about 1 ms, while that of axons is on the order of 0.1 ms. Axons are thus more excitable at short time scales, but at longer time scales dendrites are more easily excited. We complement these studies with experiments on fully connected cultures. An explanation for the chronaxie of dendrites is found in the numerical simulations of passive, realistically structured dendritic trees under external stimulation. The much shorter chronaxie of axons is not captured in the passive model and may be related to active processes. The lower rheobase of dendrites at longer durations can improve brain stimulation protocols, since in the brain dendrites are less specifically oriented than axonal bundles, and the requirement for precise directional stimulation may be circumvented by using longer duration fields.

Essential oil of Croton zehntneri and its main constituent anethole block excitability of rat peripheral nerve.

Croton zehntneri is an aromatic plant native to Northeast Brazil and employed by local people to treat various diseases. The leaves of this plant have a rich content of essential oil. The essential oil of C. zehntneri samples, with anethole as the major constituent and anethole itself, have been reported to have several pharmacological activities such as antispasmodic, cardiovascular, and gastroprotective effects and inducing the blockade of neuromuscular transmission and antinociception. Since several works have demonstrated that essential oils and their constituents block cell excitability and in view of the multiple effects of C. zehntneri essential oil and anethole on biological tissues, we undertook this investigation aiming to characterize and compare the effects of this essential oil and its major constituent on nerve excitability. Sciatic nerves of Wistar rats were used. They were mounted in a moist chamber, and evoked compound action potentials were recorded. Nerves were exposed in vitro to the essential oil of C. zehntneri and anethole (0.1-1 mg/mL) up to 180 min, and alterations in excitability (rheobase and chronaxie) and conductibility (peak-to-peak amplitude and conduction velocity) parameters of the compound action potentials were evaluated. The essential oil of C. zehntneri and anethole blocked, in a concentration-dependent manner with similar pharmacological potencies (IC50: 0.32 ± 0.07 and 0.22 ± 0.11 mg/mL, respectively), rat sciatic nerve compound action potentials. Strength-duration curves for both agents were shifted upward and to the right compared to the control curve, and the rheobase and chronaxie were increased following essential oil and anethole exposure. The time courses of the essential oil of C. zehntneri and anethole effects on peak-to-peak amplitude of compound action potentials followed an exponential decay and reached a steady state. The essential oil of C. zehntneri and anethole caused a similar reduction in conduction velocities of the compound action potential waves investigated. In conclusion, we demonstrated here that the essential oil of C. zehntneri blocks neuronal excitability and that this effect, which can be predominantly attributable to its major constituent, anethole, is important since these agents have several pharmacological effects likely related to the alteration of excitability. This finding is relevant due to the use of essential oils in aromatherapy and the low acute toxicity of this agent, which exhibits other effects of potential therapeutic usefulness.

Effects of chronic hypoxia during maturation on the negative chronotropic effect of [H+] on the rabbit sino-atrial node.

Previous studies in our laboratory have shown an effect of 12 weeks of hypoxia on the electrophysiology of the heart. This study was designed to determine the effects of hypoxia for shorter periods (1, 2, 3 and 6 weeks) on the neonatal heart as well as the chronotropic effects of [H+] on sino-atrial automaticity. Rabbits (2 days of age) were raised for 1, 2, 3 or 6 weeks in either a normal or hypoxic environment. At the end of 1, 2, 3 or 6 weeks, they were killed and studied using an isolated sino-atrial tissue preparation and standard microelectrode techniques. Measurements of hematocrit, ventricular weight and ventricular total protein were made. Right ventricular hypertrophy appeared at 2 and 3 weeks in the hypoxic hearts. There was no difference in left ventricular weight or total protein between normal and hypoxic groups over the time studied. Both the basal and maximal (isoproterenol stimulated) spontaneous rates decreased with age. The baseline and maximal rates from hypoxic rabbits were significantly less than those from normal rabbits at 3 and 6 weeks (p less than 0.05). The net negative chronotropic effect of elevated [H+] was more pronounced in the hypoxic than the normal preparations at 3 and 6 weeks. In summary, neonates raised in hypoxia for as short a period as 3 weeks show right ventricular hypertrophy and a decrease in sino-atrial automaticity. The net negative chronotropic effect of [H+] is enhanced with development and chronic hypoxia.

Dietary-induced changes in lipid and fatty acid composition can modify chronaxie values in the rat sciatic nerve.

The present investigation aimed at clarifying the possible correlations among dietary lipids, peripheral fatty acid composition of nerve lipids and an index of the nervous tissue excitability, the chronaxie. The experiments were performed on female albino rats fed diets containing olive oil (OO) and fish oil (FO) along two generations. Total lipids fatty acid composition of the sciatic nerves from the two groups differed in the proportions of 18:1(n-9), 20:1(n-9), 22-1, 20:5(n-3) and 22:6(n-3). Also the lipid class composition showed significant differences among FO and OO specimens (free cholesterol more concentrated in the OO lipids; triacylglycerols more concentrated in the FO ones). The sciatic nerve isolated from FO rats showed a significant decrease in the chronaxie values if compared to the OO specimens. These results could follow from dietary-induced changes in the perineural permeability and/or possible modifications in the cable properties of the peripheral nerve fibers related to the myelin sheath composition.

[Use of beta-aminoethylmethacrylate in traumatic paralysis of the sciatic nerve]. / Primenenie beta-aminoétilmetakrilata pri travmaticheskom paraliche sedalishchnogo nerva.

It has been discovered in experiments on rats with traumatic paralysis of the sciatic nerve that a methacrylic acid derivative, beta-aminoethylmethacrylate (AEM), displays marked neurotropic, particularly strychnine-like activity. Using visual, electrophysiological and biochemical research methods it has been demonstrated that the substance has a normalizing action on the function of the neuromuscular apparatus in paralysis and that this action is more powerful than that produced by strychnine, securinine, proserine, dibasol, thiamine, and cyanocobalamin. AEM has a beneficial effect on metabolism of the muscles of an injured limb, raising in them the content of glycogen and decreasing the activity of succinate dehydrogenase and acid phosphatase since the first day after trauma. The drug does not only accelerates the progress of the recovery but also reduced a direct effect of nervous trunk injury on the muscle.

Effects of various osmotic solutions on membrane properties of smooth muscle cells of the guinea pig ureter.

Effects of various osmotic solutions on membrane properties of smooth muscle cells of the guinea pig ureter were investigated using the microelectrode and double sucrose gap methods. In Krebs solution, the mean membrane potential was -53 mV, chronaxie was 104 msec, length constant of the tissue was 1.03 mm, time constant of the membrane was 65.8 msec, and conduction velocity of excitation was 19.2 mm per sec. Hyperosmotic solution (1.5, 2.0, or 2.5 times the normal osmolarity) depolarized the membrane, generated the spike activity, reduced the length constant of the tissue, increased the time constant of the membrane, prolonged the chronaxie, and reduced the conduction velocity. Hyposmotic solutions (0.85 and 0.67 times the normal osmolarity) produced opposite changes on the passive and active characteristics of the membrane compared to findings in hyperosmotic solution except that the time constant of the membrane was increased in both hyper- and hyposmolar solutions. Increase in the time constant of the membrane and reduced length constant of the tissue in hyperosmotic solution can be explained by an increase in the internal resistance, including the cell to cell junctional resistance and shrinkage of the cell diameter (from 6.2 to 3.0 micrometer).

Nerve accommodation in chronic alcoholic subjects.

Chronaxie, rheobase, conduction velocity and nerve accommodation of 50 alcoholic subjects were studied by applying rectangular and exponentially rising currents to the median nerve. A statistically significant decrease in nerve accommodation indexes and a change in the slope of the accommodation curve were found. The results show that nerve accommodation is more sensitive than other excitability parameters and should be used in the diagnosis and prognosis of alcoholic neuropathies.

Relationship of antiarrhythmic to inotropic activity and antiarrhythmic qualities of the optical isomers of verapamil.

1. The relationship of antiarrhythmic to inotropic activity of the optical isomers of verapamil was studied by comparing their effects on functional refractory period and force of contraction in the isolated left atrium of the guinea pig and on maximum follow frequency and contractility in the dog heart. To evaluate the antiarrhythmic profile of the optical isomers of verapamil the relationship between threshold voltage and impulse duration in the left atrium of the guinea pig and the antagonistic action against ventricular arrhythmias in the rat were studied. 2. (-)Verapamil is nearly 10 times more effective than (+)verapamil in prolonging the functional refractory period in the isolated left atrium of the guinea pig. 3. In the dog heart (-)verapamil is about 8 times more active in reducing a maximum follow frequency at atrial pacing, as well as spontaneous heart rate and in prolonging PQ-duration. 4. In the guinea pig atrium (+)verapamil shows less negative inotropic activity than its enantiomorph. With (+)verapamil the concentration producing a 25% decrease in contractility is 3.7 times higher than that causing a 25% increase in refractory period. With (-)verapamil these concentrations are identical. 5. In the dog i.v. infusion of the isomers, at a dosage inducing identical reduction of maximum follow frequency, is accompanied by a decrease in left ventricular dp/dtmax with (-)verapamil, whereas with the (+)isomer a significant increase of dp/dtmax is observed at a certain dose level. 6. Because of the higher antiarrhythmic activity of (-)verapamil, the antiarrhythmic profile and the inotropic pattern of the racemic compound are mainly due to this isomer. 7. (+)Verapamil shifts the voltage duration curve of the isolated left atrium of the guinea pig to the right and leads to a significant increase in the chronaxie value. (-)Verapamil has no comparable effects on the excitability of the atrial myocardium. 8. In the intact animal (+)verapamil shows additional antiarrhythmic qualities. Like procainamide, but with higher activity, it antagonizes ventricular arrhythmias (ectopic beats, automaticity and flutter or fibrillation) which can be provoked in the rat by i.v. infusion of aconitine. (-)Verapamil and the racemic compound are ineffective against these ventricular rhythm disorders.

Differences in the cardiac actions of the calcium antagonists verapamil and nifedipine.

1. It was investigated whether the calcium antagonistic coronary drugs verapamil and nifedipine have similar antiarrhythmic properties. Their effects on functional refractory period and contractile force in the isolated left guinea pig atrium were compared. To assess their influence on myocardial excitability the relation between threshold voltage and pulse duration was studied in the left guinea pig atrium. Furthermore, the influence on AV conduction was investigated in the conscous dog in haemodynamically equieffective dose ranges. 2. Verapamil as well as nifedipine cause a dose-dependent prolongation of the functional refractory period in the isolated left guinea pig atrium. The slope of the dose-response curve of nifedipine is, however, significantly less steep than that of verapamil. Maximum prolongation of refractory period which can be induced by nifedipine is significantly inferior to that occurring after verapamil; under nifedipine this prolongation is, however, accompanied by a significantly greater reduction in contractility. 3. In the isolated left guinea pig atrium the voltage-duration curve is shifted to the right and the chronaxia value is significantly increased by verapamil. Even in the highest dose possible nifedipine has no effect on atrial excitability. 4. In the conscious dog verapamil considerably prolongs AV conduction time whereas a moderate yet dose-dependent shortening of PQ duration is observed with equieffective nifedipine doses regarding the decrease in blood pressure and increase in heart rate. 5. The results indicate that nifedipine does not exert antiarrhythmic effects comparable to those of verapamil.

Effects of ethanol on compound action potential and refractory periods of toad sciatic nerve.

The action of ethanol on compound action potential, refractory periods and chronaxia are analyzed in 28 isolated sciatic nerves of toads. 85 mM ethanol increases the compound action potential and decreases the refractory periods. 342 and 513 mM ehtanol decrease the compound action potential and increase the absolute and relative refractory periods. These biphasic effects are discussed in relation with changes in Na+ and K+ permeabilities and to the greater sensitivity of thin fibers to the chemicals.

[Toxicological evaluation of ethyl acetate in conditions of sealed cabin atmospheres]. / Toksikologicheskaia otsenka étilatsetata v usloviiakh atmosfery germeticheskikh kabin

Ethyl acetate was studied as an atmosphere contaminant in an enclosed environment. A 90-day continuous experiment on 160 white rats and 120 white mice with three concentrations of the compound (43, 10 and 2 mg/m3) was carried out. Ethyl acetate used in the first two concentrations caused functional disturbances in the state of animals and morphological changes in their viscera. Ethyl acetate at a concentration of 2 mg/m3 was ineffective. The data obtained allow recommendations of permissible concentrations of ethyl acetate vapours in an enclosed atmosphere in relation to a different time of man's exposure.