Neurotrophic Effects of l‐DOPA in Postnatal Midbrain Dopamine Neuron/Cortical Astrocyte Cocultures

Abstract

L-DOPA IS toxic to catecholamine neurons in culture, but the toxicity is reduced by exposure to astrocytes. We tested the effect of L-DOPA on dopamine neurons using postnatal ventral midbrain neuron/cortical astrocyte cocultures in serum-free, glia-conditioned medium. L-DOPA (50 tiM) protected against dopamine neuronal cell death and increased the number and branching of dopamine processes. In contrast to embryonically derived glia-free cultures, where L-DOPA is toxic, postnatal midbrain cultures did not show toxicity at 200 1iM L-DOPA. The stereoisomer D-DOPA (50-400 btM) was not neurotrophic. The aromatic amino acid decarboxylase inhibitor carbidopa (25~zM) did not block the neurotrophic effect. These data suggest that the neurotrophic effect of L-DOPA is stereospecific but independent of the production of dopamine. However, L-DOPA increased the level of glutathione. Inhibition of glutathione peroxidase by Lbuthionine sulfoximine (3 1iM for 24 h) blocked the neurotrophic action of L-DOPA. N-Acetyl-L-cysteine (250 1iM for 48 h), which promotes glutathione synthesis, had a neurotrophic effect similar to that of L-DOPA. These data suggest that the neurotrophic effect of L-DOPA may be mediated, at least in part, by elevation of glutathione content. Key Words: L-DOPA-Glia-Glutathione-Parkinson's disease-Dopamine neurons.

Oxidative Stress ActivatesFUS1andRLM1Transcription in the YeastSaccharomyces cerevisiaein an Oxidant-dependent Manner

“…The effect of catecholamines on survival has been studied so far only in mammalian cells (Han et al, 1996;Mena et al, 1997;Varella et al, 1999) However, it has been shown that apomorphine, a dopamine agonist, and its oxidation product 8-oxo-seimiquinone are toxic for the cells, but sublethal concentrations enhance survival when cells are pretreated with other oxidants (Picada et al, 2003). It also has been suggested that l-dopa as well as dopamine stimulate the MAPK activity of the classical extracellular signal-regulated kinase (ERK) pathway in neuronally derived cultured PC12 cells (Yan et al, 1999;Koshimura et al, 2000).…”

“…The catecholamines have been shown to be toxic because of their ability to oxidize and produce reactive oxygen species and quinones in contrast to the other tested structural analogues of l-dopa that do not undergo autooxidation (Basma et al, 1995;Han et al, 1996;Mena et al, 1997). We hypothesized that l-dopa and the other catecholamines activated the yeast mating MAPK via autooxidation by forming reactive oxygen species.…”

Driving GDNF expression: The green and the red traffic lights

“…Many in vitro studies showed toxic effects of L-DOPA on midbrain dopaminergic neurons but its toxicity has not been proven in vivo (reviewed by Olanow et al, 2004). In fact, trophic effects of L-DOPA were observed on dopaminergic neurons cocultured with astrocytes (Mena et al, 1997) but, to our knowledge, our group is the only describing the effect of L-DOPA on GDNF levels in the nigrostriatal system. We have shown that L-DOPA induces GDNF up-regulation at the mRNA and protein levels in substantia nigra neuron-glia cell cultures, in a process involving soluble mediators that signal astrocytes to increase GDNF expression (Saavedra et al, 2006).…”

Presynaptic Recording of Quanta from Midbrain Dopamine Neurons and Modulation of the Quantal Size

“…Postnatally derived cultures of midbrain neurons were prepared as described earlier (Rayport et al, 1992) except that serumfree medium was used (Mena et al, 1997). Recordings were performed 3-6 weeks postplating.…”