Development and regulation of response properties in spinal cord motoneurons

The intrinsic response properties of spinal motoneurons determine how conve rging premotor neuronal input is translated into the final motor command tr ansmitted to muscles. From the patchy data available it seems that these pr operties and their underlying currents are highly conserved in terrestrial vertebrates in terms of both phylogeny and ontogeny. Spinal motoneurons in adults are remarkably similar in many respects ranging from the resting mem brane potential to pacemaker properties. Apart from the axolotls, spinal mo toneurons from all species investigated have latent intrinsic response prop erties mediated by L-type Ca2+ channels. This mature phenotype is reached g radually during development through phases in which A-type potassium channe ls and T-type calcium channels are transiently expressed. The intrinsic res ponse properties of mature spinal motoneurons are subject to shortterm adju stments via metabotropic synaptic regulation of the properties of voltage-s ensitive ion channels. Recent findings also suggest that regulation of chan nel expression may contribute to long-term changes in intrinsic response pr operties of motoneurons, (C) 2001 Elsevier Science Inc.