Toxicity of 6‐hydroxydopamine and dopamine for dopaminergic neurons in culture

Abstract

Toxicity of 6-hydroxydopamine (6-OHDA) and dopamine were studied in cultures of dissociated fetal rat mesencephalic cells. To assess survival and function of dopaminergic cells we quantified the number of tyrosine hydroxylase-positive cells and measured dopamine uptake. Non-dopaminergic cells were monitored by counting the number of cells visible with phase-contrast microscopy and measuring GABA uptake. 6-OHDA, in contrast to MPP+, which selectively destroyed dopaminergic neurons, was found to be a non-selective neurotoxin in this culture system. Between 10 and 100 microM, dopaminergic and non-dopaminergic cells were destroyed. At concentrations higher than 100 microM, i.e., concentrations frequently used to lesion catecholaminergic neurons in vivo, 6-OHDA resulted in structural fixation and loss of viability of dopaminergic and non-dopaminergic cells. Dopamine produced the same actions at slightly higher concentrations. One hundred to 300 microM was toxic for all cell types, and concentrations above 300 microM resulted in fixation. The findings suggest that 6-OHDA cannot be considered a selective toxin for catecholaminergic neurons in vitro. The demonstrated toxicity of dopamine tends to support speculations that processes related to dopamine metabolism may play a role in the pathogenesis of Parkinson's disease.

Glutathione Is Involved in the Granular Storage of Dopamine in Rat PC12 Pheochromocytoma Cells: Implications for the Pathogenesis of Parkinson’s Disease

“…This demonstrated that, in PC12 cells cultured under our conditions the major part of intracellularly synthesized, endogenous DA is sequestered in the storage granules and does not exert any toxic effect on the cells, as is observed in case of exogenous DA (Michel and Hefti, 1990). Interestingly, the reserpine-mediated emptying of the granular DA stores was accompanied by a substantial and sustained rise in the intracellular total GSH (i.e., reduced GSH ϩ GSSG) content.…”

Causes and consequences of methamphetamine and MDMA toxicity

“…41 It has been hypothesized that the excessive increases in intracellular dopamine that follow METH and MDMA administration could lead to the formation of dopamine quinones and reactive oxygen species (ROS). 6 Accordingly, there is considerable evidence that the increase in dopaminergic activity evoked by METH and MDMA plays an important role in mediating the toxicity to 5-HT and/or DA terminals. 42 , 43 For Figure 1.…”

“…The excessive extracellular dopamine (DA) concentrations resulting from the ability of the substituted amphetamines to reverse the carrier-mediated dopamine uptake system 5 can be oxidized enzymatically and nonenzymatically to form highly reactive dopamine quinones and reactive oxygen species, leading to increase in oxidative stress. 6 Glutamate has also been implicated in the toxicity produced by the substituted amphetamines. METH, but not MDMA, has been shown to increase the extracellular concentrations of glutamate in the striatum and the hippocampus.…”

Cytoprotective effects of growth factors: BDNF more potent than GDNF in an organotypic culture model of Parkinson's disease

“…The black appearance of these melanin-containing cells is the basis for the name substantia nigra, meaning black substance. In experimental conditions, DA is toxic in a variety of neuronal and non-neuronal cells both in vitro (159) and in vivo (160). However, DA metabolism is specific to dopaminergic neurons, but not exclusive to the A9 group.…”

“…Given the permeability of purines and pyrimidines through the bidirectional AQP9 (11), it is not unlikely that these toxic nucleosides or other endogenous toxic compounds may be imported into dopaminergic neurons from the microenvironment, thereby increasing the vulnerability of these cells (Figure 4). Moreover, ROS and highly reactive quiones generated from DA metabolism can further be converted to 6-OHDA, particularly due to the high levels of iron in the SN (156), thus forming a neurotoxin widely used to model PD (159,376,432). AQP9 may potentially allow diffusion of this neurotoxin.…”