Quantitative differences in collateralization of the descending spinal pathways from red nucleus and other brain stem cell groups in rat as demonstrated with the multiple fluorescent retrograde tracer technique.

In 8 rats 'True Blue' was injected into dorsal half of C5-C8 spinal grey, 5 days later 'Nuclear Yellow' was injected in midthoracic, upper lumbar, lumbosacral and sacral cord respectively. The animals were sacrificed about 43 hours after NY injections. The distribution of retrogradely labeled neurons was studied in Red Nucleus, in Ventrolateral Pontine Tegmentum and in Nucleus Raphe Magnus, all of which project to spinal dorsal grey. In Red Nucleus large populations of single TB-labeled neurons and single NY-labeled ones occurred in the dorsomedial and ventrolateral part, respectively. In addition, about 8% of the neurons labeled with TB from C5-C8 were double labeled with NY from L5-S1, and 35% from T7-8, which percentages resemble those of electrophysiological studies. However, in ipsilateral Nucleus Raphe Magnus about 40% of the TB-labeled neurons were double labeled from L5-S1. This percentage resembles the 66% obtained in electrophysiological studies of reticulospinal collaterals. These findings in rat support electrophysiological findings in cat and show, that rubrospinal neurons distribute their fibers primarily to the grey matter of specific groups of spinal segments, while many of the raphe spinal neurons distribute fibers throughout the spinal cord.