Comparison of the Morphological and Electrotonic Properties of Renshaw Cells, Ia Inhibitory Interneurons, and Motoneurons in the Cat

Abstract

. The morphological and electrotonic properties of 4 motoneurons, 8 Ia inhibitory interneurons, and 4 Renshaw cells were compared. The morphological analysis, based on 3-D reconstructions of the cells, revealed that dendrites of motoneurons are longer and more extensively branched. Renshaw cells have dendrites that are shorter and simpler in structure. Dendrites of Ia inhibitory interneurons could be as long as those of motoneurons but the branching structure resembled that of Renshaw cells. Compartmental models were used to determine the electrotonic properties of the paths from each dendritic terminal to the soma. The attenuations of steady-state voltage changes in motoneurons were 3 and 7 times larger than in Ia inhibitory interneurons and Renshaw cells, respectively. The same relative order was observed for current attenuation and electrotonic length. The dendritic input resistances in Renshaw cells were 2 and 4 times larger than in Ia inhibitory interneurons and motoneurons, respectively. The difference in these electrotonic properties increased during higher synaptic activity as modeled by a decrease of R m . The peak amplitudes of voltage transients at sites of brief, synaptic-like changes in conductance were highly dependent on cell class and were largest in Renshaw cells and smallest in motoneurons. In combination with class-specific differences in the attenuation of transient voltage signals, this led to large differences in the peak amplitudes of somatic voltage transients. Differences in the rise times and half-widths of the voltage transients were observed as well. Thus, based on passive properties, each cell class has a unique set of input/output properties.

Primary Afferent Synapses on Developing and Adult Renshaw Cells

“…Other work indicated that adult Renshaw cells receive polysynaptic excitation from ipsilateral group II and III muscle and cutaneous afferents (for review, see Baldissera et al, 1981). Monosynaptic connections from these afferents would be unlikely because they do not project (Brown, 1981;Fyffe, 1984) to ventral spinal cord regions containing Renshaw cell dendrites (Jankowska and Lindstrom, 1971;Lagerback and Kellerth, 1985;Alvarez et al, 1997;Bui et al, 2003).…”

Simulation system of spinal cord motor nuclei and associated nerves and muscles, in a Web-based architecture

“…Interneuron electrotonic properties were adopted according to data published by Bui et al (2003), but adjusted to a one-compartment interneuron model and with the added assumption that Ib interneurons are similar to Ia interneurons. For Renshaw cells, these values were adapted so that the membrane time constant could make the cell fire a burst of action potentials in response to a supra-threshold input (Hultborn and Pierrot-Deseilligny 1979).…”

L-Measure: a web-accessible tool for the analysis, comparison and search of digital reconstructions of neuronal morphologies

“…Other typical examples include the relation between morphometric distributions that can be easily extracted from LM output and the electrotonic structure of the dendrites (e.g. comparing multiple classes of principal and inhibitory cells in the cat spinal cord 45 ). In some cases, the morphometric changes may be linked to the expression of growth factors activated during development.…”