title: A transient component of the developing corticospinal tract arises in visual cortex.
abstract: Following injections of tritiated leucine restricted to occipital (visual) regions of cerebral cortex during the first postnatal week (days 3--6), labeled corticofugal axons were followed caudally through the pons, medullary pyramid, pyramidal decussation and into the cervical spinal cord. However, when similar injections were made into visual cortex during the second postnatal week, labeled corticofugal axons could not be traced beyond mid-pontine levels where abundant axon terminal labeling was evident in the basilar pontine nuclei. Since axonal labeling did not subsequently appear at levels caudal to the pons during later stages of development or in the adult, it is suggested that the contribution to the corticospinal system made by visual cortical axons in the first postnatal week is a transient connection which is eventually lost either by a process of selective axon collateral elimination or cell death.
mesh_terms: D000818:Animals; D001345:Autoradiography; D001369:Axons / Q000648:ultrastructure; D002454:Cell Differentiation; D002540:Cerebral Cortex / Q000166:cytology*; D009044:Motor Cortex / Q000166:cytology; D009115:Muridae; D009410:Nerve Degeneration; D009434:Neural Pathways / Q000166:cytology; D009778:Occipital Lobe / Q000166:cytology; D011149:Pons / Q000166:cytology; D013003:Somatosensory Cortex / Q000166:cytology; D013116:Spinal Cord / Q000166:cytology*; D014793:Visual Cortex / Q000166:cytology*