FICTIVE MOTOR ACTIVITIES IN ADULT CHRONIC SPINAL RATS TRANSPLANTED WITH EMBRYONIC BRAIN-STEM NEURONS

The present study was designed to examine the effects of an intraspina l transplantation of embryonic brainstem neurons on fictive motor patt erns which can develop in hindlimb nerves of adult chronic spinal rats . Seventeen adult rats were spinalized at T8-9 level and, 8 days later , a suspension of embryonic cells obtained either from the raphe regio n (RR, n=8) or from the locus coeruleus (LC, n=9) was injected caudall y (T12-13) to the cord transection. Eight control animals (control rat s) were spinalized and injected with vehicle under the same conditions . One to three months later, the animals were decorticated and fictive motor patterns were recorded in representative hindlimb nerves. The d ata revealed that both control and grafted spinal rats could exhibit t wo distinctly different fictive motor patterns, one which could be ass ociated with stepping and the other with hindlimb paw shaking. They fu rther showed that following transplantation of embryonic RR or LC neur ons the excitability of the spinal stepping generator was increased, w hereas that of the spinal neural circuits which generate hindlimb paw shaking was not significantly affected. A histological analysis perfor med on the spinal cord segments below the transection revealed complet e absence of serotonin and noradrenaline immunoreactivity in control s pinal animals and, in both types of grafted rats, an extensive monoami nergic reinnervation with synaptic contacts between monoaminergic tran splanted neurons and host interneurons and/or motoneurons. The possibl e mechanisms by which grafted monoaminergic neurons can influence the spinal motor networks are discussed.