Neurogenesis of ascending supraspinal projection neurons: ipsi- versus contralateral projections.
The present study tests the hypothesis that contralaterally projecting supraspinal projection neurons (SPNs) are generated prior to ipsilaterally projecting SPNs. Neuronal time of origin was determined by injecting pregnant rats with tritiated thymidine on one of embryonic (E) days E12 through E15. In mature offspring of thymidine-treated dams, SPNs in the lumbar cord were retrogradely labelled with True Blue delivered at the site of a hemisection in spinal segment C3. Ipsi and contralaterally projecting SPNs in laminae I, VII and VIII and the lateral spinal nucleus, which are known to give rise to long sensory pathways, were generated simultaneously throughout their neurogenic period (E12-E14), while ipsilaterally projecting SPNs in lamina IV and the nucleus dorsalis, which give rise to short sensory pathways, completed neurogenesis one day later (E15). Results suggest that the projection target and its distance from the nerve cell body of origin are more consistent correlates of the duration of the neurogenic period than the course of the axon.
Nandi
K N
KN
Department of Cellular Biology and Anatomy, Louisiana State University Medical Center, Shreveport 71130-3932.
Knight
D S
DS
Beal
J A
JA
D000818:Animals; D001572:Benzofurans; D005314:Embryonic and Fetal Development; D005456:Fluorescent Dyes; D007839:Functional Laterality; D005865:Gestational Age; D009474:Neurons / Q000166:cytology*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000166:cytology / Q000196:embryology*
D001572:Benzofurans; D005456:Fluorescent Dyes; C038675:true blue