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PubMed1981

In vitro frog sural nerve test: a monitor for detecting neurotoxin solutes.

In order to evaluate the in vitro neurotoxicity of MM fractions obtained by chromatographic analytical methods from plasma of uremic polyneuropathic patients and urine of healthy subjects, we performed an in vitro test on isolated frog sural nerve. The nerve is incubated in various media and stimulated by a rectangular shock (0.05ms, 1Hz, intensity supramaximal). Action potential are recorded. Results were expressed by the inhibition index Ii = 1 divided by t 1/2 x 100 where t 1/2 is the time (in min) necessary to reduce the 1/2 the spike amplitude. When the nerve is immerged in Ringer solution or plasma of healthy subjects Ii congruent to 0. Among MM fractions obtained by gel chromatography Sephadex G-15 from uremic polyneuropathic subjects' plasma and healthy subjects' urine, only fraction b gives a positive response (Ii congruent to 0.86 +/- 0.02, n = 4). From the 6 sub-fractions obtained by anion exchange chromatography DEAE Sephadex A-25 of fraction b, only sub-fraction b4-2 exhibits a reduction of the spike amplitude, Ii = 0.54 when concentration b4-2 is 6 mg/L, Ii = 1.30 when b4-2 plasma concentration is 14 mg/L. These values increase with the severity of neurologic symptoms. A positive correlation was found between Ii and various b4-2 concentrations of standard solutions and plasma ultrafiltrate (y = 0.089x + 0.046, r = 0.890, n = 13). In vitro sural nerve test demonstrated its sensitivity as a tool for monitoring analytical and preparative procedures developed for isolation of neurotoxic solutes.

Animals↗
PubMed2006

Electrosynthetically patterned conducting polymer films for investigation of neural signaling.

The ion-mediated conduction and versatility of device fabrication of conducting polymers provide a route to the study of neural signaling. Patterned junctions of conducting polypyrrole have been electropolymerized on commercially available microelectrode arrays, with typical dimensions 200 mum between electrodes, each electrode being 30 mum in diameter. Tetrabutylammonium perchlorate or sodium p-toluenesulfonate were used as electrolyte/counterion in the organic solvent. Individual polypyrrole junctions, when synthesized and connected in a three-electrode configuration, exhibit current-switching behavior analogous to neural weighting. Junctions copolymerized with thiophene exhibit current rectification and the nonlinear current-voltage behavior requisite for complex neural systems (i.e., the activation function).

Journal Article↗
PubMed1988

Theoretical evaluation of the Rosenblueth hypothesis.

Rosenblueth's hypothesis states that atrioventricular (AV) nodal conduction delay and Wenckebach periodicity of AV transmission are not due to overall decremental conduction within the AV node but are due to a single step delay which is caused by a special element or layer of the AV nodal tissue. This paper discusses some theoretical considerations which allow detailed evaluation of the original hypothesis. Two artificial conduction structures which incorporate the Rosenblueth phenomenon are presented and tested by theoretical experiments that consider the potential of these structures to produce (a) basic pattern of Wenckebach periods, (b) decremental shortening of RR intervals during Wenckebach periods. These experiments are also employed to test whether or not the Rosenblueth concept can be used to explain (c) appropriate dependence of AV conduction changes on the prematurity of atrial depolarizations, and of (d) alternating cycle lengths such as may be seen with atrioventricular reentrant tachycardia. The results of the theoretical considerations show that the original concept of the Rosenblueth hypothesis is sufficient to explain (a) but it cannot be used for realization of (b), (c) and (d). A modification of the original concept complying with both (a) and (b) is proposed. This modified structure can also reproduce (c), but not simultaneously with (b). The experiments show that anisotropy of intra AV nodal conduction may create an electrophysiological mechanism of single-step delay. Different anisotropic conduction structures have to be considered to reproduce phenomenon (d).

Atrial Function↗