The structure of the interstitial tissue of the active and resting avian testis.

The interstitial tissue of the testis was studied in gonadally active and gonadally inactive domestic fowl (Gallus gallus domesticus), guinea-fowl (Numida meleagris), duck (Anas platyrhynchos) and Japanese quail (Coturnix coturnix japonica). Gonadal inactivity in the fowl was induced by a single subcutaneous injection of 50 mg oestradiol benzoate. The structure of this tissue was similar in all the birds studied. Lymphatic vessels were mostly thin and meandered between the peritubular tissue peripherally and the centrally located blood vessels, Leydig cells and macrophages. The basal lamina rested on a closely associated homogeneous microfibrillar layer free of collagen fibres. The myofibroblast layer was several cells thick, and quite compact. The basal lamina of gonadally resting birds was highly irregular, relatively electron-dense, contained electron-lucent globules, and sent numerous finger-like processes or plicae into the seminiferous epithelium, particularly into the Sertoli cells. The Leydig cells were few but typical in structure. In gonadally inactive birds they accumulated lipid droplets, dense heterogeneous bodies, probably lysosomes, and appeared to degenerate. The avian testicular interstitium is similar to that of the human and cat in possessing a multi-layered myofibroblast component, and to that of the rodent in possessing a small number of Leydig cells, as well as in the location of the lymphatic vessels. Thus the bird combines characteristics of the interstitium found variably in mammals.