IS INFANCY A QUIESCENT PERIOD OF TESTICULAR DEVELOPMENT - HISTOLOGICAL, MORPHOMETRIC, AND FUNCTIONAL-STUDY OF THE SEMINIFEROUS TUBULES OF THE CEBUS MONKEY FROM BIRTH TO THE END OF PUBERTY

The objective of this study was to describe the maturational changes o bserved in the seminiferous tubules of the monkey Cebus apella, a New World primate species, from birth to the end of puberty. Nineteen anim als were subdivided into four groups: neonatal (1-40 days), infantile (4 months to 1 yr), early pubertal (i yr, 8 months to 2 yr, 9 months), and late pubertal (4-8 yr). Volumetric determinations of different te sticular components were made, tubule diameter and length were calcula ted, and spermatogenic cells, Sertoli cells, and androgen-binding prot ein secretion were quantified. Testicular and seminiferous tubule volu mes increased significantly in the first 5 months of life and during p uberty due to the combined increment in seminiferous tubule diameter a nd length. The total number of spermatogonia increased until late pube rty to stabilize subsequently. Spermatocytes and spermatids appeared d uring puberty and increased dramatically until the end of this period. The germ cell ratios, indicative of spermatogenic efficiency, improve d continuously in late puberty coincidentally with a reduction of sper matocyte degeneration. Sertoli cells proliferated in the neonatal and infantile periods, determining a longitudinal growth of the seminifero us tubules, but remained stable during puberty, when androgen-binding protein secretion increased significantly. The multiplication of germ cells is the main factor responsible for the increment in tubule diame ter during puberty and determines the most noticeable postnatal modifi cation of testicular volume. During late puberty, the reduction of spe rmatocyte degeneration leads to an increment in germ cell ratios and a progressive, but slow, improvement of spermatogenic efficiency, expla ining why pubertal development of the testis occurs over such a prolon ged period in this primate. This is in contrast to what happens in mos t laboratory animals and suggests that the Cebus is a useful model for studies of human male puberty.