Role of oxidation in the neurotoxic effects of intrastriatal dopamine injections.

We have examined the biochemical and histological effects of high concentrations of dopamine (0.05-1.0 micromol) injected into the rat striatum. Twenty-four hours after such injections, the oxidation products of dopamine and dihydroxyphenylacetic acid were detected as both free and protein-bound cysteinyl dopamine and cysteinyl dihydroxyphenylacetic acid. Protein-bound cysteinyl catechols were increased 7- to 20-fold above control tissue levels. By 7 days postinjection, the protein-bound cysteinyl catechols were still detectable, although reduced in concentration, whereas the free forms could no longer be measured. Histological examination of striatum at 7 days revealed a central core of nonspecific damage including neuronal loss and gliosis. This core was surrounded by a region containing a marked reduction in tyrosine hydroxylase immunoreactivity but no apparent loss of serotonin or synaptophysin immunoreactivity. When dopamine was injected with an equimolar concentration of either ascorbic acid or glutathione, the formation of protein-bound cysteinyl catechols was greatly reduced. Moreover, the specific loss of tyrosine hydroxylase immunoreactivity associated with dopamine injections was no longer detectable, although the nonspecific changes in cytoarchitecture were still apparent. Thus, following its oxidation, dopamine in high concentrations binds to protein in the striatum, an event that is correlated with the specific loss of dopaminergic terminals. We suggest that the selective degeneration of dopamine neurons in Parkinson's disease may be caused by an imbalance between the oxidation of dopamine and the availability of antioxidant defenses.

Antibodies against the T61 antigen inhibit neuronal migration in the chick optic tectum.

Cell migration in the central nervous system depends, in part, on receptors and extracellular matrix molecules that likewise support axonal outgrowth. We have investigated the influence of T61, a monoclonal antibody that has been shown to inhibit growth cone motility in vitro, on neuronal migration in the developing optic tectum. Intraventricular injections of antibody-producing hybridoma cells or ascites fluid were used to determine the action of this antibody in an in vivo environment. To document alterations in tectal layer formation, a combination of cell-nuclei staining and axonal immunolabeling methods was employed. In the presence of T61 antibody, cells normally destined for superficial layers accumulated in the ventricular zone instead, leading to a reduction of the cell-dense layer in the tectal plate. Experiments with 5-bromo-2'-deoxyuridine labeling followed by antibody staining confirmed that the nonmigrating cells remaining in the ventricular zone were postmitotic and had differentiated. The structure of radial glial cells, as judged by staining with a glia-specific antibody and the fluorescent tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), remained intact in these embryos. Our findings suggest that the T61 epitope is involved in a mechanism underlying axonal extension and neuronal migration, possibly by influencing the motility of the leading process.