Firing Properties And Electrotonic Structure Of Xenopus Larval Spinal Neurons. Benoit Saint Mleux And L. E. Moore. Laboratoire De Neurobiologie Des Reseaux Sensorimoteurs, Cnrs-Upresa 7060, 45 Rue Des Saints- Pères, Paris, France.
APStracts 6:0546N, 1999.
Whole cell voltage and current clamp measurements were done on intact Xenopus laevis larval spinal neurons at developmental stages 42-47. Firing patterns and electrotonic properties of putative interneurons from the dorsal and ventral medial regions of the spinal cord at myotome levels 4-6 were measured in isolated spinal cord preparations. Passive electrotonic parameters were determined with internal cesium sulfate solutions as well as in the presence of active potassium conductances. Step clamp stimuli were combined with white noise frequency domain measurements in order to determine both linear and non-linear responses at different membrane potential levels. Comparison of analytical and compartmental dendritic models provided a way to determine the number of compartments needed to describe the dendritic structure. The electrotonic structure of putative interneurons was correlated with their firing behavior such that highly accommodating neurons (Type B) had relatively larger dendritic areas and lower electrotonic lengths compared to neurons that showed sustained action potential firing in response to a constant current (Type A). Type A neurons had a wide range of dendritic areas and potassium conductances that were activated at membrane potentials more negative than observed in Type B neurons. The differences in the potassium conductances were in part responsible for a much greater rectification in the steady state current voltage (I/V curve) of the strongly accommodating neurons compared to repetitively firing cells. The average values of the passive electrotonic parameters found for Rall Type A and B neurons were csoma = 3.3 & 2.6 pF, gsoma = 187 & 38 pS, L = 0.36 & 0.21 and A=3.3 & 6.5 for soma capacitance, soma conductance, electrotonic length and the ratio of the dendritic to somatic areas, respectively. Thus, these experiments suggest that there is a correlation between the electrotonic structure and the excitability properties elicited from the somatic region.
Received 7 July 1999; accepted in final form 28 October 1999.
APS Manuscript Number J554-9.
Article publication pending Journal of Neurophysiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 21 December 1999