Mitochondrial Complex Inhibitors Preferentially Damage Substantia Nigra Dopamine Neurons in Rat Brain Slices

Abstract

Using a rat brain slice preparation, we investigated the role of energy impairment on the selective loss of dopamine neurons in the substantia nigra (SN). Brain slices (400 μm) were incubated at 35°C for 2 h in the presence or absence of mitochondrial complex inhibitors, rotenone, MPP +, 3-nitropropionic acid, and antimycin A. Slices were also incubated in rotenone with excitatory amino acid (EAA) receptor antagonists, MK-801 and CNQX, to determine whether rotenone-induced damage was mediated by EAAs. The slices were then fixed, recut into 30-μm sections, and immunolabeled for tyrosine hydroxylase (TH) to identify catecholamine neurons and to quantify loss of TH-labeled dendrites after treatment. Quantitative comparison was made between SN dopamine neurons, in which rotenone-induced dendrite loss was severe, and hypothalamic A11 dopamine neurons, which were spared. Adjacent sections that were immunolabeled for calbindin or stained with cresyl violet also revealed a striking dendritic degeneration of SN neurons in rotenone-exposed slices, whereas noncatecholamine neurons, such as those in the perifornical nucleus (PeF), were more resistant. Preferential damage to SN dopamine neurons was also evident with other mitochondrial complex inhibitors, MPP + and antimycin A. EAA receptor antagonists provided partial protection to SN neurons in slices incubated with rotenone (3 μM). The particular vulnerability of SN dopamine neurons in the slice is consistent with the vulnerability of SN in Parkinson's disease. The selective effect of mitochondrial complex inhibition in SN dopamine neurons implies a fundamental deficit in the capacity of these neurons to defend against toxic insult.