LAUSR

INTRODUCTION This study describes the prenatal development of the principal inferior olivary nucleus (PO) in humans. MATERIAL/METHODS Ten brains were obtained from preterm infants aged 21-43 postmenstrual weeks (PW). After fixation, the brains were processed into 30-μm serial sections, which were stained using the Klüver-Barrera method. RESULTS At mid-gestation, the dorsal and ventral lamellae were distinguishable. The dorsal lamella (DL) was composed of ballooned and folded portions, with many neurons peripherally gathered in the ballooned portion, and neurons densely packed in the folded portion. Clusters of pyknotic neurons were observed in the lateral portion of the PO at 21PW. The PO acquired thin complicated folds by 28-29 PW. Then, it regained the width of a nuclear band, and further elaborated the folds. The 3D-reconstruction models showed that the basic pattern of folding like in adults was attained at 28-29PW, and that the rostro-medial region of DL was microgyric. The nuclear volume increased exponentially with age. The total surface area increased progressively, while the surface density varied in a biphasic manner, wherein it increased initially and then decreased. The neuronal profile area increased uniformly. The total neuronal number increased uniformly, while the numerical density decreased rapidly during 21-29 PW. CONCLUSION After mid-gestation, the period of 21-29 PW may be critical, because the PO undergoes extensive folding after massive neuronal death.