Three-dimensional structure of the human cerebellar dentate nucleus: a computerized reconstruction study

To explore the regional differences in neuronal cytoarchitecture of human dentate nucleus, we examined first the three-dimensional structure of this nucleus with a computerized reconstruction technique, after making serial sections of the brain in seven fetuses aged from 20 to 39 weeks of gestation (WG), an infant (1-month-old) and two adults (22- and 85-year-old). The surface was broadly smooth at 20-22 weeks, but primary gyri or fissures were noticed in the rostral half of the lateral surface, earliest in its dorsal region. A small cavity (the hilus nuclei dentati) was situated in the middle of the medial surface, with four distinct margins. A great progress in gyration was noted after 22 weeks: gyri were observed over the entire surface by 28-29 weeks. Gyri were thicker in the caudal half than the rostral half both in the lateral and the medial surfaces. At this stage, the rostral margin of the hilus was partially cut off and the hilus was elongated toward the rostral tip, but its relative size appeared to be grossly equal to that at 22 weeks. The hilus began to open wider and wider after 30 weeks. Subdivision of the human dentate nucleus into two different parts (the smaller microgyric rostral part and the larger macrogyric caudal part) was accomplished by 35 weeks. We have previously, using morphometric approaches, reported that a vulnerable (or critical) period may exist during 20-30 weeks in the fetal development of the dentate nucleus. It is possible that this special ten weeks of mid-gestation may be coincident with the time of extensive growth in gyration for this nucleus. It will be necessary to sample the neurons independently from at least two different parts, as described above, to design further microscopic studies on the regional differences or on other cytological investigations.