Nuclear Volume Changes in Cells of the Nucleus arcuatus (NA) During Prenatal Development in Man

Abstract

It is known that the adenohypophyseal function begins during embryonic life. It is not known whether a functional relationship between the hypothalamus and hypophysis exists in fetuses, or at what time this relationship is established. The present study was undertaken in order to elucidate this problem. The extent of development and cell differentiation of the nucleus arcuatus (NA) was detected by karyometric methods. A total of 60 fetuses, from 11 to 31 weeks old (males and females) were studied. The hypothalami of full-term infants were investigated to obtain data for comparison. Adjacent sagittal paraffin sections were stained with cresyl violet and Gomori’s CHP. Nuclear volumes were measured on 100 nuclei from each NA, projected onto paper, and the average volume was calculated for each fetus. The mean nuclear volume of NA neurons in both males and females increases steadily from 11 to 19 weeks. However, the mean nuclear volume decreases at 20–21 weeks. Thus, the average nuclear volume in 18–19 week-old fetuses amounts to 138 and 142 μm³ , but that of 20–21 week-old fetuses is 81 and 192 μm³, in females and males respectively. After this time the nuclei of cells of the NA show a marked growth; by 24–25 weeks the average nuclear volume (192 μm³) reaches that of full-term infants (189 μm³). Consequently, by 20 weeks of embryogenesis the NA is formed as a separate hypothalamic structure. After this, the process of cell differentiation continues to increase and the average nuclear volume reaches a maximum at 24–25 weeks. It is suggested that the specific function of NA of human fetuses begins by 24–25 weeks.