In this study, a comparative analysis of metal-related neuronal vulnerability was performed in two brainstem nuclei, the locus coeruleus (LC) and substantia nigra (SN), known targets of the etiological noxae in Parkinson's disease and related disorders. LC and SN pars compacta neurons both degenerate in Parkinson's disease and other Parkinsonisms; however, LC neurons are comparatively less affected and with a variable degree of involvement. In this study, iron, copper, and their major molecular forms like ferritins, ceruloplasmin, neuromelanin (NM), manganese-superoxide dismutase (SOD), and copper͞zinc-SOD were measured in LC and SN of normal subjects at different ages. Iron content in LC was much lower than that in SN, and the ratio heavy-chain ferritin͞iron in LC was higher than in the SN. The NM concentration was similar in LC and SN, but the iron content in NM of LC was much lower than SN. In both regions, heavy-and light-chain ferritins were present only in glia and were not detectable in neurons. These data suggest that in LC neurons, the iron mobilization and toxicity is lower than that in SN and is efficiently buffered by NM. The bigger damage occurring in SN could be related to the higher content of iron. Ferritins accomplish the same function of buffering iron in glial cells. Ceruloplasmin levels were similar in LC and SN, but copper was higher in LC. However, the copper content in NM of LC was higher than that of SN, indicating a higher copper mobilization in LC neurons. Manganese-SOD and copper͞zinc-SOD had similar age trend in LC and SN. These results may explain at least one of the reasons underlying lower vulnerability of LC compared to SN in Parkinsonian syndromes. L ocus coeruleus (LC) is the main brain region containing norepinephrine neurons. The rostral projections from these neurons seem to be involved in the modulation of neuronal activity, metabolism, and memory (1, 2), whereas the spinal cord projections are known to modulate spinal motoneuron function (3, 4).Neuronal loss in LC occurs in conditions such as Parkinson's disease (PD) and Alzheimer's disease and Down's syndrome (5, 6) with different cellular loss in rostral and caudal parts of LC. In Alzheimer's disease and Down's syndrome, it is not clear whether neuronal loss in LC is a primary event or a consequence of retrograde degeneration of cortically projecting cells due to the loss of cortical synapses. In idiopathic PD, most studies have documented a higher degree of neuronal loss in substantia nigra (SN) compared to LC (5-8). However, a recent study reported extensive impairment of LC neurons in PD (9). SN and LC share anatomical and biochemical similarities, being both pigmented because of neuromelanin (NM), and both composed of catecholaminergic neurons. Yet, in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridineintoxicated subjects, LC neurons are spared, whereas a large neuronal depletion occurs in SN (10, 11). Also, in other types of Parkinsonian syndromes caused by exposure to toxins, the LC neurons seem less damaged than those of...