Cytology of the Subthalamic Nucleus
In the discussion on the cytology of the STN two main themes are present: first, is the nucleus closed or open? This means, are the dendritic branches restricted to the nuclear area (closed) or do the dendrites reach out to other areas (open) (Mannen 1960
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Cytology of the Subthalamic Nucleus
2 Cytology of the Subthalamic Nucleus In the discussion on the cytology of the STN two main themes are present: first, is the nucleus closed or open? This means, are the dendritic branches restricted to the nuclear area (closed) or do the dendrites reach out to other areas (open) (Mannen 1960)? The second point of discussion is the presence of interneurons within the STN. The original studies on the cytology of the STN were carried out by Forel (1877; see Fig. 3). Ramon y Cajal (facsimile from 1955) demonstrated with the Golgi technique that the neurons in the STN are multipolar with pigment, spindle shaped or polygonal. The neurons bring forward long dendrites with spines that branch
Fig. 3 Cytology of the subthalamic nucleus taken from Forel (1877). Carmine colouration; N, neurons; G, blood vessels; F, fine nerve fibres without organization; K, small granula; K’, large granula. “The dendrites are difficult to stain, as is normal in this region,” noted Forel (1877) in the figure text
Cytology of the Subthalamic Nucleus
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regularly. The initial axonal segment bows regularly, by which the axons are difficult to follow, towards bundles of descending fibres. An analogous description can also be found in Dejerine’s Anatomie des centres nerveux (1901), in which he explicitly indicates that most of the neurons are of the Golgi type I as described by Kölliker (1891, 1896). In Winkler (1928) at least two types of human subthalamic neurons are discerned: parvo and magnocellular (Fig. 4). The magnocellular spindle-shaped neurons are on average two to three times larger in perikaryon diameter. Moreover, Winkler (1928) noticed that the magnocellular neurons in the medial part of the nucleus are smaller than those in its lateral part. The STN in its ventro-medial part connects to the substantia nigra, and since the subthalamic magnocellular neurons contain pigment, it is difficult to border both nuclei. The small neurons are placed in a “gelatine-like substance rich of myelinated fibres”. The pigment in the subthalamic neurons belongs to lipofuscin granula in Macaca mulatta and M. nemestrina (Rafols and Fox (1976) and seemingly not to neuromelanin as Winkler (1928) indicated (see also Usunoff et al. 2002). Lipofuscin granula show a dispersed presence in M. mulatta and an overall presence in M. nemestrina (for lipofuscin information, see Marani et al. 2006). The question of an open or closed nucleus has been studied in several articles. Going from rat to man, the nucleus evolves from an open to a closed nucleus (see below). In rat the nucleus is considered clearly an open nucleus, since
Fig. 4 A-c Large neuron of the STN, B-b small neuron of the STN (from Winkler 1928). For comparison, Winkler depicted a neuron of the rostral part of the nigra B-a
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Cytology of the Subthalamic Nucleus
dendrites penetrate even the zona incerta, lateral hypothalamus and cerebral peduncle (Afsharpour 1985a, b). The nucleus is closed in cat (see e.g. Ramon y Cajal 1955), monkey and man. The dendrites ar
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