Morphometric study of the prepubertal rabbit testis: Germ cell numbers and seminiferous tubule dimensions

Abstract

Testes from rabbits aged 1-9 weeks were examined by light microscopy. Changes in seminiferous tubule dimensions, testicular volume, and volume fraction of tubules were assessed. Germ cells and Sertoli cells were counted in round tubular cross sections and total germ cell number in each testis was estimated. Mitotic, meiotic, and degenerative activities of germ cells as well as their basal or central positions within tubules were quantified. A marked, steady increase in testis volume and in tubular length and volume occurred over the prepubertal period; but diameter underwent no significant increase and in fact decreased until week 4. Overall, tubules lengthened 40-fold and testis volume increased 25-fold; the percentage volume of the testis occupied by tubules rose from one-third neonatally to three-fifths at the onset of spermatogenesis. The ratio of germ cells to total tubular (germ and Sertoli) cells was lowest at 3 weeks. However, the total number of germ cells increased little until 3 weeks, after which it rose at a sharp rate commensurate with testis volume. Percentage of germ cells in mitosis peaked sharply at 3 weeks, dropped in subsequent weeks, and then rose at 7 weeks at the initiation of spermatogenesis. Importantly, the surge in mitosis at 3 weeks was followed by a redistribution of germ cells to a predominantly basal location from 3 to 7 weeks. Meiotic activity was sparse at 7 weeks and became abundant by 9 weeks. Germ cell degeneration remained relatively constant during weeks 1 through 6, with an increase at 7 weeks.

Gonad Differentiation in the Rabbit: Evidence of Species-Specific Features

“…Considering that RA induces meiosis in both sexes, this probably indicates that in the testis, an RA-dependent stimulus could induce meiosis in the same way as in ovaries around birth. This concurs with previously reported observations of XY germ cells at the preleptoten stage in rabbit testes at around birth and for two weeks after [5], [7], [8]. In the present study as well, the presence of preleptoten like figures at 7 and 18 dpp indicates that meiosis was initiated in the testes but aborted thereafter since no more advanced stages of meiosis were further detected.…”

“…Finally, ovocytes are blocked at the diploten stage [5]. In XY rabbit, several authors have reported figures of germ cells in the preleptoten stage before birth, at the same stage as in the female, without any signs of further true meiosis; however, the first signs of true meiosis were only observed in the male 2–3 months after birth [5], [7], [8].…”

“…Follicle differentiation initiates after meiosis, as it has been described extensively [9]. In XY gonads, meiotic activity appears by 50 days post partum (d pp ) and becomes abundant by 63 d pp [8]. Interestingly, XY germ cells at preleptoten stages have been detected around birth and for two weeks thereafter in the testis, at the same time as meiosis occurs in the ovary, but without any further signs of more advanced meiotic stages [5], [7].…”

“…At 16 d pc , most germ cells have already entered the genital crests. In XY and XX gonads, germ cells undergo a series of mitoses, starting from the early stages and lasting until their final differentiation at meiosis [6]–[8]. In XX gonads, the first signs of meiosis have been reported around birth; meiosis spans a period of two weeks after birth.…”

Prespermatogenesis and spermatogoniogenesis in the bovine testis

“…In search for a better parameter than postnatal age we found that the tubular diameter, which increases postnatally from about 50 µm to about 200 µm, reflects more reliably the developmental state of its germ cell population. Thus, the situation in the postnatal prepubertal bovine differs from that in the rabbit for which a marked steady increase in tubular length, but no increase in tubular diameter over the prepubertal period is reported (Iczkowski et al 1991). For the study of germ cell behavior in the prenatal and perinatal bovine testis, the developmental age can be used as a suitable scale of reference.…”