DIRECT EVIDENCE FOR THE LINK BETWEEN MONOAMINERGIC DESCENDING PATHWAYS AND MOTOR-ACTIVITY .1. A STUDY WITH MICRODIALYSIS PROBES IMPLANTED IN THE VENTRAL FUNICULUS OF THE SPINAL-CORD

Monoaminergic projections to the spinal cord are involved in the modul ation of motor, autonomic, and sensory functions. More specifically, t he increase of electrical activity of serotonergic neurons in raphe ob scurus has been correlated with locomotion in treadmill-trained cats [ Jacobs, B.L. and Formal, C., Trends Neurosci., 9 (1993) 346-352]. In o rder to test the direct correlation between locomotion and the release of monoamines, microdialysis probes were permanently implanted for 45 days into the ventral funiculus of the spinal cord (white matter) of adult rats. Eight days after implantation, these rats were subjected t o an endurant exercise on a treadmill, and dialysis sessions were orga nized in such a way that microdialysate samples of 15 min duration wer e collected during pre-, per- and post-exercise periods. Measurements of serotonin, 5-hydroxyindoleacetic acid, dopamine and 3-methoxy-4-hyd roxyphenylethylglycol concentration in the extracellular space showed significant increases during locomotion when compared with both pre- a nd post-exercise values. Histological analysis shows that serotonergic axons were present close to the dialysis probe. These results demonst rate that the implantation of a microdialysis probe in the ventral fun iculus, close to a potential target of monoaminergic projections, is a suitable technique for the collection of neuromediators released duri ng spontaneous running.