Effect of spinal cord hemisection on rubrospinal neurons in the albino rat.

After injection of horseradish peroxidase (HRP) into the lumbar cord segments of adult albino rats, the rubrospinal (RS-LS) neurons projecting to lumbar cord segments are located predominantly in the ventral and ventrolateral region of the contralateral red nucleus, with a small contingent located ipsilaterally, as reported previously (Shieh et al. 1983). The same pattern of labelling occurs in animals subjected to right cervical and thoracic cord hemisections in rats aged 3-10 days, 20 days and 2-3 months. Nor are there statistically significant differences in the numbers of contralateral (P less than 0.3) and ipsilateral (P less than 0.3) RS-LS neurons between the control and experimental animals. In the experimental group, there are also no significant differences between the numbers of contralaterally (P less than 0.2) versus ipsilaterally (P less than 0.5) labelled RS-LS neurons in animals hemisected 3-5 days and 20-90 days postnatally. The lack of sprouting to the lumbar cord from the RS-LS neurons on either side might be correlated with the existence of the rubrospinal projection at birth. In at least two 3 days, two 10 days, two weanling and two adult experimental animals, an increase in the total area of contralaterally labelled RS-LS neurons could be demonstrated. An increase also occurs in the proportion of medium sized neurons in the lateral horn region of the contralaterally labelled RS-LS neurons in at least three neonatal and three adult experimental animals.