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Abstract
<p class="first" id="d8830687e117">Histopathologic examination of the testis from
juvenile rats is often necessary to
characterize the safety of new drugs for pediatric use and is a required end point
in male pubertal development and thyroid function assays. To aid in evaluation and
interpretation of the immature testis, the characteristic histologic features of the
developing rat testis throughout postnatal development are described and correlated
with published neuroendocrine parameter changes. During the neonatal period (postnatal
day [PND] 3-7), seminiferous tubules contained gonocytes and mitotically active immature
Sertoli cells. Profound proliferation of spermatogonia and continued Sertoli cell
proliferation occurred in the early infantile period (PND 8-14). The spermatogonia
reached maximum density forming double-layered rosettes with Sertoli cells in the
late infantile period (PND 15-20). Leptotene/zygotene spermatocytes appeared centrally
as tubular lumina developed, and individual tubules segregated into stages. The juvenile
period (PND 21-32) featured a dramatic increase in number and size of pachytene spermatocytes
with the formation of round spermatids and loss of "infantile" rosette architecture.
In the peri-pubertal period (PND 32-55), stage VII tubules containing step 19 spermatids
were visible by PND 46. The presented baseline morphologic and endocrinologic information
will help pathologists distinguish delayed development from xenobiotic effects, determine
pathogenesis when confronted with nonspecific findings, and identify sensitive time
points for targeted study design.
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