The pineal body of the mink and horse with special reference to the reproductive cycle. An ultrastructural and immunocytochemical study.

An ultrastructural and immunohistochemical analysis was performed on the epiphysis of two species of mammals: mink and horse. These animals present a reproductive cycle that varies along the year according to the light exposition. The aim of the study was to define possible structural changes connected with the gonadal activity. Structural aspects in common emerged such as those in concern with the epiphysis cells, their immunocytochemical characteristics (NSE and Synaptophysin positivity of pinealocytes, as well as CFAP positivity of further cells), and those in concern with the general ultrastructure. This latter has in particular revealed significant differences in relation to the biological cycles considered. In the presence of gonadal activity the mink pinealocyte displays a modest cytological organization which, on the contrary, after the mating and in arrest of the gonadal activity, appears as fully restored. In the horse, in both natural and artificially induced photoperiods, significant variations were noted these in connection with the various phases of development of the electron-dense granules, typical of the horse pinealocyte, interpreted as melanosomes. These aspects confirm the role of the epiphysis in the regulation of the reproductive cycle, albeit in the presence of species-specific peculiarities.