Evidence for dopamine-derived hydroxyl radical formation in the nigrostriatal system in response to axotomy.
We have evaluated the ability of the injured nigrostriatal dopaminergic system to produce highly reactive hydroxyl radicals ((*)OH) by the electrochemical detection of salicylate hydroxylation. Unilateral transection of the medial forebrain bundle transiently increased the formation of (*)OH in substantia nigra (SN) but not in striatum during the first 48 h postlesion, when most relevant changes in terms of oxidatively modified proteins take place. Short-term adaptive axotomy-induced changes in substantia nigra included downregulation of nigral tyrosine hydroxylase (TH) and dopamine transporter (DAT) mRNA expression and more intense TH immunoreactivity. Maintained inhibition of monoamine oxidase activity with deprenyl totally prevented the axotomy-induced formation of (*)OH, thus demonstrating the dopaminergic nature of these radicals. In contrast, deprenyl treatment, which is associated with a diminution in free radical production, failed to delay the onset of dopaminergic degeneration. This observation highlights the importance of being extremely cautious when analyzing parameters of oxidative stress and extrapolating them as a primary cause of cell death in the context of neurodegeneration. Long-term adaptive changes included a dramatic downregulation of DAT mRNA expression along with a moderate decrease in TH mRNA levels in SN. We anticipate a key regulatory role of the DAT to maximally optimize dopaminergic transmission in the synaptic cleft under conditions of degeneration.
Venero
Jos L
JL
Department of Biochemistry, Faculty of Pharmacy, University of Seville, Seville, Spain.
Revuelta
Mati
M
Atiki
Leila
L
Santiago
Marti
M
Toms-Camardiel
Mayka C
MC
Cano
Josefina
J
Machado
Alberto
A
D000818:Animals; D019771:Axotomy; D003342:Corpus Striatum / Q000201:enzymology / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins; D017665:Hydroxyl Radical / Q000737:chemistry*; D007150:Immunohistochemistry; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins / Q000235:genetics; D017551:Microdialysis; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012642:Selegiline / Q000494:pharmacology; D013378:Substantia Nigra / Q000201:enzymology / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics
D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; C493216:Slc6a3 protein, rat; D012642:Selegiline; D017665:Hydroxyl Radical; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine