title: Correlation between electrophysiological properties, morphological maturation, and olig gene changes during postnatal motor tract development.
abstract: This study investigated electrophysiological and histological changes as well as alterations of myelin relevant proteins of descending motor tracts in rat pups. Motor-evoked potentials (MEPs) represent descending conducting responses following stimulation of the motor cortex to responses being elicited from the lower extremities. MEP responses were recorded biweekly from postnatal (PN) week 1 to week 9 (adult). MEP latencies in PN week 1 rats averaged 23.7 ms and became shorter during early maturation, stabilizing at 6.6 ms at PN week 4. During maturation, the conduction velocity (CV) increased from 2.8 ± 0.2 at PN week 1 to 35.2 ± 3.1 mm/ms at PN week 8. Histology of the spinal cord and sciatic nerves revealed progressive axonal myelination. Expression of the oligodendrocyte precursor markers PDGFRα and NG2 were downregulated in spinal cords, and myelin-relevant proteins such as GalC, CNP, and MBP increased during maturation. Oligodendrocyte-lineage markers Olig2 and MOG, expressed in myelinated oligodendrocytes, peaked at PN week 3 and were downregulated thereafter. A similar expression pattern was observed in neurofilament M/H subunits that were extensively phosphorylated in adult spinal cords but not in neonatal spinal cords, suggesting an increase in axon diameter and myelin formation. Ultrastructural morphology in the ventrolateral funiculus (VLF) showed axon myelination of the VLF axons (99.3%) at PN week 2, while 44.6% were sheathed at PN week 1. Increased axon diameter and myelin thickness in the VLF and sciatic nerves were highly correlated to the CV (rs > 0.95). This suggests that MEPs could be a predicator of morphological maturity of myelinated axons in descending motor tracts.
authors.affiliation: Departments of Pediatrics and Anatomical Sciences and Neurobiology, University of Louisville School of Medicine, Louisville, Kentucky 40202, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Cai
authors.forename: Yi Ping
authors.initials: YP
authors.lastname: Zhang
authors.forename: Lisa B E
authors.initials: LB
authors.lastname: Shields
authors.forename: Zoe Z
authors.initials: ZZ
authors.lastname: Zhang
authors.forename: Naikui
authors.initials: N
authors.lastname: Liu
authors.forename: Xiao-Ming
authors.initials: XM
authors.lastname: Xu
authors.forename: Shi-Qing
authors.initials: SQ
authors.lastname: Feng
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Shields
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure*; D004525:Efferent Pathways / Q000254:growth & development* / Q000502:physiology / Q000648:ultrastructure; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D009185:Myelin Proteins / Q000378:metabolism; D009186:Myelin Sheath / Q000648:ultrastructure*; D009836:Oligodendroglia / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology / Q000254:growth & development* / Q000502:physiology; D050781:Transcranial Magnetic Stimulation
chemical_list: D009185:Myelin Proteins
keywords: conduction velocity; maturation; motor-evoked potentials; sciatic nerve; spinal cord; ventrolateral funiculus