Differential localization of alpha-, beta- and gamma-synucleins in the rat CNS

Alpha-synuclein is a presynaptic protein that normally participates in the homeostasis of synaptic vesicles. Missense mutations in its gene cause the protein to participate actively in the development of heritable forms of Parkinson's disease. Moreover, its metabolism is perturbed in all cases of Parkinson's disease where alpha-synuclein accumulates in a filamentous form in the Lewy body nerve cell lesion. Lewy bodies also develop in other common neurodegenerative disorders, like dementia with Lewy bodies and Lewy body variant of Alzheimer's disease. In the present study, we have studied the detailed distribution of alpha-, beta- and gamma-synuclein in the rat CNS. Alpha-synuclein was not observed in perikarya, but was distributed with high intensity in nerve terminals in the caudate and putamen and ventral pallidum, where beta-synuclein was much weaker and less densely distributed in the caudate and putamen. Gamma-synuclein was not found in the caudate and putamen. Alpha-synuclein was robustly distributed in the substantia nigra pars reticulata, but was very weak or virtually absent from the perikarya of the neurons in the pars compacta. In contrast, beta-synuclein was very weak or absent from the substantia nigra. gamma-Synuclein was absent from the terminals of substantia nigra pars reticulata, but sparsely distributed gamma-synuclein-containing neurons were detected in the substantia nigra pars compacta. In the brainstem, alpha-synuclein as well as gamma-synuclein were present in the locus coeruleus with high intensity, while beta-synuclein was very weak. In addition, alpha-synuclein was intense in the vagus nucleus, but weak in the oculomotor, facial, hypoglossal, accessory and ambiguous nuclei, where beta-synuclein was very intensely present. Furthermore, gamma-synuclein was localized in the terminals and in cell bodies of the Edinger-Westphal nucleus, the red nucleus, locus coeruleus, and most cranial nerve-related nuclei. In the spinal cord, alpha- and gamma-synucleins were intensely present in laminae I and II and in the preganglionic sympathetic nuclei, whereas beta-synuclein was very weak. These results indicate that alpha-synuclein is abundant in central catecholaminergic regions. Beta-synuclein is more localized in the somatic cholinergic components, while it is particularly weak or absent from catecholaminergic neurons. Gamma-synuclein appears to be present in both cholinergic and catecholaminergic regions, but very weak in the forebrain.