Role of serotonergic neurons in L-DOPA-derived extracellular dopamine in the striatum of 6-OHDA-lesioned rats

THE effect of L-dihydroxyphenylalanine (L-DOPA) on extracellular dopamine ( DA) in the striatum was determined by microdialysis in 6-hydroxydopamine (6 -OHDA)-lesioned rats treated with and without the serotonergic neurotoxin 5 ,7-dihydroxytryptamine (5,7-DHT). At the same time the intensity of L-DOPA- induced rotational behavior was assessed. In 6-OHDA-lesioned rats treated w ith 5,7-DHT, L-DOPA (50mg/kg, i.p.) increased extracellular DA only to 20% of that measured in animals not treated with 5,7-DHT. Likewise, 6-OHDA-lesi oned rats treated with 5,7-DHT exhibited a significantly lower number of L- DOPA-induced rotations. These results suggest that serotonergic terminals i n the striatum can convert exogenously administered L-DOPA into DA that can be released into the extracellular space. (C) 1999 Lippincott Williams & W ilkins.