The effect of glia-conditioned medium on dopamine neurons in culture. Modulation of apoptosis, tyrosine hydroxylase expression and 1-methyl-4-phenylpyridinium toxicity

Recent experiments have shown that glia-conditioned medium (GCM) protects a gainst L-3,4-Dihydroxyphenylalanine (L-DOPA) toxicity for dopamine neurons in culture. In this study we have investigated the effect of GCM on the num ber of tyrosine hydroxylase (TH) immunoreactive neurons, levels of dopamine , number of high affinity dopamine uptake sites, and percentage of apoptoti c cells in midbrain neuronal cultures, before and after exposure to 1-methy l-4-phenylpyridinium (MPP+). Fetal midbrain neuronal cultures were treated with vehicle, MPP+, 10(-5) M, mesencephalic GCM, or MPP+ plus GCM. GCM was administered a) simultaneousl y, b) 24 hours before MPP+, and c) 24 and d) 72 hours after MPP+, respectiv ely. In the absence of GCM, MPP+ reduced the number of TH immunoreactive ne urons and increased apoptosis. GCM increased the number of TH+ neurons and the levels of dopamine and decreased apoptosis. In the cultures treated wit h GCM and MPP+, GCM counteracted the effects of MPP+ and increased the leng th and arborization of TH+ neurites. The protective effect of GCM was maxim al in cultures co-treated with GCM and MPP+ simultaneously, but it also res tored dopamine parameters in cultures receiving GCM 1 or 3 days after MPP+. The protective effect of GCM was negligible in cultures pretreated with GC M and receiving MPP+ 24 hours later. In neuronal cultures, grown for 8 days in vitro untreated with MPP+, short term exposure to GCM reversed the effe ct of aging and restored the number of TH+ neurons to levels higher than th ose observed at the time of seeding. Therefore, GCM does not only protect a gainst MPP+ but does also induce de novo expression of dopamine phenotype i n midbrain cultures.