Abstract
Background:
The testicles are located in a muscular, skin-covered, highly pigmented sac called the scrotum. The testicles produce both sperm and androgens, such as testosterone.

Aim:
The current study aimed to evaluate the immunohistochemical characteristics of the testis in three age groups (kitten, adult, and senior) of Scottish cat breeds (Felis catus) during the postnatal period, focusing on changes in Sertoli cells and Leydig cells. These two cell types play essential roles in male reproductive function, as Sertoli cells provide structural and metabolic support for spermatogenesis, while Leydig cells are responsible for testosterone production.

Methods:
Testicular samples were collected from clinically healthy cats and categorized into three age groups. The tissues were processed using routine histological techniques, followed by immunohistochemical staining to detect specific cellular markers for Sertoli and Leydig cells. The immunoreactivity and cellular distribution were evaluated and compared among the different age groups.

Results:
The findings demonstrated clear age-dependent variations in both cell populations. In kittens, weak immunoreactivity and incomplete development of seminiferous tubules were observed, indicating functional immaturity of the testis. Adult cats showed the highest immunoreactivity and well-organized seminiferous tubules, reflecting active spermatogenesis and optimal endocrine function. In contrast, senior cats exhibited a marked reduction in immunostaining intensity and structural degeneration of the seminiferous tubules, accompanied by a decrease in Leydig cell density.

Conclusion:
The study concludes that testicular structure and function in Scottish cats undergo significant age-related changes. Peak reproductive activity occurs in adulthood, while aging is associated with a decline in both cellular activity and structural integrity of the testis, affecting overall reproductive efficiency.

Key words: Cat; Immunohistochemistry; Leydig cell; Sertoli cell; Testis.