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Postnatal development and differentiation of contractile cells within the rabbit testis.

This study has been determined the postnatal development and differentiation of smooth muscle cells within the rabbit testicular capsule and within the peritubular tissue surrounding seminiferous tubules. Smooth muscle cells within the tunica albuginea are not identifiable at birth by light microscopy but by electron microscopy myocytes in early stages of development may be shown to be present. It is not until 42 to 49 days postnatum that smooth muscle cells can be identified by light microscopy. Differentiation of smooth muscle cells within the capsule is completed by 128 days postnatum. At this time, the muscle is arranged in two organized layers, a superficial layer of longitudinally oriented cells and a deeper layer of circularly arranged cells. At birth, the peritubular tissue consists of two to four layers of undifferentiated cells and, during the first postnatal week, the tissue becomes more condensed and generally is arranged in two cellular layers. Cells of the inner layer contain small bundles of microfibrils whereas cells of the outer layer are fibroblast in nature. Differentiation of the peritubular tissue is completed by 112 days postnatum. At this stage, it consists of four layers, two acellular and two cellular. The inner cellular layer, composed of attentuated myoid cells, possesses a basal lamina on both surfaces and is surrounded by two delicate connective tissue lamellae. The myoid cells of the peritubular tissue thus achieve structural maturity at approximately the same time postnatally as do those within the testicular capsule, which corresponds to the time when spermatogenesis becomes established. The relative contributions of the myoid cells in the peritubular tissue and within the testicular capsule to the movement of non-motile spermatozoa out of the testis and the possible significance of the peritubular tissue as a component of the permeability barrier are discussed in relation to the present findings.