Journal of Neurophysiology, Vol 51, Issue 5 968-977, Copyright © 1984 by APS

ARTICLES

Relations among threshold, spike height, electrode distance, and conduction velocity in electrical stimulation of certain medullospinal neurons

I. D. Hentall, G. Zorman, S. Kansky and H. L. Fields

This report describes how the threshold for extracellular, electrical stimulation of cell bodies in the rat's rostromedial medulla depends on the distance to the stimulating electrode. A monopolar microelectrode both delivered current pulses near medullospinal neurons and, after decay of the stimulus artifact, detected whether an orthodromic spike had occurred by collision of that spike with a suitably timed antidromic spike initiated at the thoracic spinal cord. The liminal current and the height of antidromic spikes were noted at a series of vertical electrode positions. Regression analysis was performed to determine whether threshold and the inverse of peak-to-peak spike height varied more as the radial distance or its square. The square relationship provided a much better fit for threshold and a marginally better fit for the inverse of spike height. The spatial decline in excitability (K2) averaged 859 microA/mm2, falling within the range of values found for fibers and cell bodies in other studies. The constant of spatial decline in spike height (C2) in millivolts per square millimeter was positively correlated with K2. Both C2 and K2 were negatively correlated with conduction velocity. From threshold distance curves fitted by regression analysis, the mean separation of sites of spike maxima and threshold minima along each electrode path was 16 micron; the estimated distance from these sites to, respectively, the loci of spike generation and spike excitation were positively correlated and similar. The variation of C2 and K2 with conduction velocity may be due either to an influence of the size and shape of the dendritic tree on the spatial decrement of excitability and spike height or to a confounding in the studied equations of the space-independent effect of the size of a cell body on spike height and excitability.

This article has been cited by other articles:

				E. J. Tehovnik, A. S. Tolias, F. Sultan, W. M. Slocum, and N. K. Logothetis Direct and Indirect Activation of Cortical Neurons by Electrical Microstimulation J Neurophysiol, August 1, 2006; 96(2): 512 - 521. [Abstract] [Full Text] [PDF]

				M. G. Sirota, H. A. Swadlow, and I. N. Beloozerova Three Channels of Corticothalamic Communication during Locomotion J. Neurosci., June 22, 2005; 25(25): 5915 - 5925. [Abstract] [Full Text] [PDF]

				E. J. Tehovnik, W. M. Slocum, C. E. Carvey, and P. H. Schiller Phosphene Induction and the Generation of Saccadic Eye Movements by Striate Cortex J Neurophysiol, January 1, 2005; 93(1): 1 - 19. [Abstract] [Full Text] [PDF]

				J. Kohyama, Y.-Y. Lai, and J. M. Siegel Reticulospinal Systems Mediate Atonia With Short and Long Latencies J Neurophysiol, October 1, 1998; 80(4): 1839 - 1851. [Abstract] [Full Text] [PDF]

				B. Kably and T. Drew Corticoreticular Pathways in the Cat. I. Projection Patterns and Collaterization J Neurophysiol, July 1, 1998; 80(1): 389 - 405. [Abstract] [Full Text] [PDF]

				B. Kably and T. Drew Corticoreticular Pathways in the Cat. II. Discharge Activity of Neurons in Area 4 During Voluntary Gait Modifications J Neurophysiol, July 1, 1998; 80(1): 406 - 424. [Abstract] [Full Text] [PDF]

				H. A. Swadlow, I. N. Beloozerova, and M. G. Sirota Sharp, Local Synchrony Among Putative Feed-Forward Inhibitory Interneurons of Rabbit Somatosensory Cortex J Neurophysiol, February 1, 1998; 79(2): 567 - 582. [Abstract] [Full Text] [PDF]