Fifteen adult Soay rams were employed in this study to investigate the effect of melatonin on the
scrotal skin using histological, histochemical, and morphometrical analysis. The results revealed
that the melatonin treated group showed a significant increase in the thickness of the epidermis, the
cross-sectional area of blood capillaries and nerve fibers compared with the control one. In addition,
obvious hypertrophy and hyperplasia were detected in the sebaceous glands in association with a
significant increase in the number and diameter of apocrine sweat glands with well-developed secretory
activity. S100 protein and cytokeratin-19 strongly stained the basal cells of sebaceous glands in the
melatonin treated group incomparable to the control group. Moreover, the nerve fibers were intensively
immunoreacted for S100 and cytokeratin proteins in the melatonin treated group in contrast to the
control one. A high number of telocytes (TCs) could be identified in the treated group around the
nerve fibers and blood vessels in the dermis. The number of Langerhans cells showed a significant
increase in the melatonin groups that were identified by MHC II and PGP 9.5 within the epidermal layer.
Furthermore, a significant increase in the number of dendritic cells was identified in the melatonin
group, which were distributed within the dermis, around hair follicles, sebaceous glands, and sweat
glands and were strongly expressed PGP-9.5, MHC-II, VAMP, SNAP, keratin-5, and cytokeratin-19
immunoreactivity. Notably, Merkel cells showed a significant increase in the number in the melatonin
group that could be stained against nestin, SNAP, and VAMP. On the other hand, the secretory
granules in sweat glands were exhibited a strong positive reactivity for synaptophysin in melatonin
group. The current study showed that the administration of melatonin induced a stimulatory effect on
keratinocytes, non-keratinocytes, sebaceous and sweat glands, hair follicles, as well as the vascular,
neuronal, and cellular constituents of the dermis.