A mathematical model of a myelinated nerve fiber for analysis of impulse conduction mechanisms during the relative refractory period

It was shown by means of a mathematical model of a myelinated nerve fiber (Frankenhaeuser — Huxley) that an increase in threshold and decrease in the amplitude of the action potential (AP) during the relative refractory period are due mainly to sodium inactivation. The contribution of increased potassium permeability to these changes is small, for the chief component of the outgoing ionic current in the node of Ranvier is not the potassium current, but the leak current. Given the ratio between these currents the increase in threshold and graduation of the action potential in the node membrane are less marked than in the membrane of the squid giant axon. At the beginning of the relative refractory period the AP evoked by strong stimulation is conducted only to the next node. Later in the refractory period impulses are conducted incrementally, and the threshold for the spreading impulse is higher than the threshold for spike excitation in the stimulated node. Delay in impulse conduction between refractory nodes leads to the formation of a retrograde depolarization wave. The reasons for differences in the mechanisms of impulse conduction along unmyelinated and myelinated refractory fibers are discussed.Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 201–207, March–April, 1972.     

Effect of colchicine and lumicolchicine on the ultrastructure of non-myelinated axons in autonomic nerves in cat in vitro]

The effects of colchicine and lumicolchicine on the ultrastructure of non-myelinated axons in cat autonomic nerves were studied using in vitro preparations of inferior mesenteric ganglion/hypogastric nerves. After 24 hrs of in vitro incubation with colchicine added to the medium (10 microng/ml) a significant decrease in number of neurotubules per 1 axon was observed. In the presence of a solution of alpha-beta and gamma-lumicolchicine (10 microng/ml) severe degenerative changes occured in axons and Schwann cells. At a lower dose of lumicolchicine (3 microng/ml) these changes were less frequent and the number of neurotubules per 1 axon did not differ from that in control nerves.     

Cardiac contractility modulation by electric currents applied during the refractory period

Inotropic effects of electric currents applied during the refractory period have been reported in cardiac muscle in vitro using voltage-clamp techniques. We investigated how electric currents modulate cardiac contractility in normal canine hearts in vivo. Six dogs were instrumented to measure regional segment length, ventricular volume (sonomicrometry), and ventricular pressure. Cardiac contractility modulating (CCM) electric currents (biphasic square pulses, amplitude +/-20 mA, total duration 30 ms) were delivered during the refractory period between pairs of electrodes placed on anterior and posterior walls. CCM significantly increased index of global contractility (E(es)) from 5.9 +/- 2.9 to 8.3 +/- 4.6 mmHg/ml with anterior CCM, from 5.3 +/- 1.8 to 8.9 +/- 4.0 mmHg/ml with posterior CCM, and from 6.1 +/- 2.6 to 11.0 +/- 7.0 mmHg/ml with combined CCM (P < 0.01, no significant change in volume axis intercept). End-systolic pressure-segment length relations showed contractility enhancement near CCM delivery sites, but not remotely. Relaxation was not influenced. CCM increased mean aortic pressure, but did not change peripheral resistance. Locally applied electrical currents enhanced global cardiac contractility via regional changes in myocardial contractility without impairing relaxation in situ.     

Electric currents applied during refractory period enhance contractility and systolic calcium in the ferret heart

We investigated the mechanism of positive inotropism of electric currents applied during the absolute refractory period. Ten Langendorff-perfused ferret hearts were instrumented to measure isovolumic left ventricular pressure (LVP) and the aequorin luminescence. Biphasic square-wave electric currents (+/-20 mA, total duration 30 ms) were delivered between pairs of electrodes. Six hearts were perfused at different extracellular Ca(2+) concentrations ([Ca(2+)](o); 1, 2, 4, and 8 mM). These signals increased LVP from 50.0 +/- 9.4 to 70.1 +/- 14.7, from 67.5 +/- 11.0 to 79.0 +/- 15.6, from 79.3 +/- 21.0 to 87.1 +/- 22.8, and from 84.6 +/- 24.0 to 91.8 +/- 28.5 mmHg at the respective [Ca(2+)](o) (P < 0.05). Peak free intracellular [Ca(2+)] ([Ca(2+)](i)) increased from 0.52 +/- 0.13 to 1.37 +/- 0.23, from 0.76 +/- 0.23 to 1.73 +/- 0.14, from 1.10 +/- 0.24 to 2.05 +/- 0.33, and from 1.41 +/- 0.36 to 2.24 +/- 0.36 microM/ml, respectively (P < 0.001). With the use of 1 mg/l propranolol with 1 mM [Ca(2+)](o), LVP and [Ca(2+)](i) were increased significantly from 48.7 +/- 8.18 to 56.3 +/- 6.11 mmHg and from 0.61 +/- 0.11 to 1.17 +/- 0.20 microM, respectively (P < 0.05). In conclusion, positive inotropism of such electrical currents was due to increased peak [Ca(2+)](i) and Ca(2+) responsiveness of the myofilaments did not change significantly.     

Prevalence of malaria in Ouagadougou and the surrounding rural environment during the period of maximal transmission

The prevalence of malaria infections was estimated in six different areas of the town of Ouagadougou, Burkina Faso, and in three neighbouring villages. Thick and thin blood films from a total of 2,117 children less than 5 years old were examined at the peak of the transmission season (August-September). Plasmodium falciparum was found in more than 98% of the positive slides. The overall parasite index at Ouagadougou was 16%, while indices from 51 to 88% were recorded in the three villages. Significant differences were observed between the six urban areas within the town as well as between the three villages. The highest parasite rates in the town were clearly associated with major breeding places of An. gambiae s.l. indicating a remarkable focality of transmission. Significant differences were observed between groups of children from houses only 300 m apart. Chemoprophylaxis appears to play an important role in determining parasite rates lower than expected in one of the three villages.     

Significance of refractory period in the method of counter flows

The results of model tests accomplished for precision and evaluation of present restrictions in the collision method are demonstrated in this work. The reduction of induced antidromic potential due to its "collision" takes place in the interelectrode area. This fact is of a great importance for the use of the collision method as it increases probable encounters of anti- and orthodromic impulses and possible intervals between stimulation and exploring electrodes.     

Intramembrane events during the nerve impulse

In current literature the cell adhesion to solid surfaces has been treated in the context of basic physicochemical forces. However, in all these reports the concept of solid surface force has not been properly analyzed. The surface forces acting across an interface formed when two phases meet has been shown to consist of dispersion (attraction) forces and polar forces (arising from different interactions). Current theories have repeatedly neglected the role of polar forces in the cell adhesion. In order to clarify this concept, the particular case, i.e. adhesion of cells on polystyrene surfaces with varying degree of polar groups is described. In this case, the adhesion of cells was reported to increase with polarity of polystyrene, and this agrees with the present study that the solid polar force component increased in the same manner.