Two modes of corticospinal reinnervation occur close to spinal targets following unilateral lesion of the motor cortex in neonatal hamsters

• Published in: Neuroscience Vol. 90; no. 1; pp. 53 - 67
• Main Authors: Aisaka, A, Aimi, Y, Yasuhara, O, Tooyama, I, Kimura, H, Shimada, M
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.01.1999; Elsevier
• Subjects: Animals; Animals, Newborn; Axons - physiology; Biological and medical sciences; Cerebral Cortex - injuries; Cholera Toxin; cortical ablation; corticospinal recrossing; corticospinal tract; Cricetinae; CTb; Development. Senescence. Regeneration. Transplantation; Dogs; Female; Fundamental and applied biological sciences. Psychology; Hindlimb - innervation; Image Processing, Computer-Assisted; Male; Mesocricetus; Mesocricetus auratus; Models, Neurological; Motor Cortex - injuries; Motor Cortex - pathology; Motor Neurons - physiology; Muscle, Skeletal - innervation; PHA-L; Phytohemagglutinins; Pyramidal Tracts - pathology; Pyramidal Tracts - physiology; quantitative analysis; Spinal Cord - pathology; Vertebrates: nervous system and sense organs; CTb; PBS-T, phosphate-buffered saline containing 0.3% Triton X-100; PHA-L; P, postnatal day; PB, phosphate buffer; PBS, phosphate-buffered saline; cortical ablation; PHA-L, Phaseolus vulgaris-leucoagglutinin; corticospinal tract; corticospinal recrossing; CTb, cholera toxin B subunit; quantitative analysis; Vertebrata; Mammalia; Newborn animal; Motor cortex; Rodentia; Corticospinal bundle; Reinnervation; Lesion; Hamster
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(98)00424-2

Although it has been shown that unilateral neonatal cortical ablation induces bilateral corticospinal projections, the explanation for the pathways responsible for this bilateral innervation remains controversial. We hypothesized that such reinnervation may be supplied from newly formed fibers sprouting at the level rostral to, or at, or caudal to the pyramidal decussation. In order to test our hypothesis, we examined the brain and spinal cord of young hamsters which had a unilateral ablation of the right motor cortex at six days postnatally, and then received an injection of an anterograde neuronal lectin tracer, Phaseolus vulgaris-leucoagglutinin, into the hindlimb area of the left motor cortex at 21 days postnatally. For the identification of motoneurons in the lumbar spinal cord, some of these animals also received an injection of cholera toxin subunit B, a retrograde tracer, into the gastrocnemius muscle. A quantitative analysis in the left gray matter of the lumbar spinal cord indicated that the lectin labeling was two to eight times higher in cortically ablated animals than in intact animals. Immunohistochemical detection of the lectin revealed that innervation of the left spinal cord occurred close to targets at lower levels in the spinal cord. Two modes of reinnervation (types I and II) by the intact corticospinal tract were recognized. The type I fibers consisted of recrossing axon collaterals sprouted from the intact dorsal funiculus near their targets, while the type II fibers were recrossing parent axons which entered the intact, right gray matter several levels rostral to their targets, and then changed direction toward the targets. The recrossing at lower spinal levels yielded a large number of ipsilaterally labeled axons and their terminals in the gray matter of the denervated lumbar cord, with a distribution pattern similar to that seen on the intact side. The present results indicate that such ipsilateral innervation may play an important role in the sparing and recovery of function following neonatal hemicortical injury.