The meso-diencephalic region, a preliminary parcellation study

Abstract

The posterior diencephalon, the mesencephalon and the bordering region of the anterior rhombencephalon were parcellated according to their cholinesterase activity. For comparison, Niss1 and myelin stained sections were also studied. An effort was made to review the literature regarding the present available knowledge on the connections of the various regions here described. This applies, in particular, to those regions which have already reached general acceptance. Existing nomenclatures were respected as far as possible. Otherwise, new names were introduced, on a topographical basis, that is, by taking into account the position of the region in respect to adjacent and clearly defined landmarks. On the basis of their enzyme activity, some regions could be clearly determined even though they may appear diffuse when studied with other techniques. Among these are three subdivisions of the thalamus, called anterior, lateral and medial entogeniculate nuclei, a centrally located nucleus entothalamicus, two differently staining parts of the subthalamic nucleus (nucleus of Luys) as well as certain subdivisions of the subthalamic area. At the meso-diencephalic transition the pretegmental nuclei could be outlined as new entities. In the central grey substance of the mesencephalon certain symmetrical dorsal and lateral nuclei were identified in view of their outstanding enzyme activity. In the posterior mesencephalon a small nucleus (Gudden) exhibits two subdivisions. A resembling nucleus in the central grey is linked to a short, very dark staining ventrad coursing fiber tract. In the raphe several subdivisions of the nucleus centralis superior are evident. A strikingly extensive cholinesterase active region surrounding the brachium conjunctivum could be established.