Postnatal maturation of the parenchymal cell types in the rabbit pineal gland

Abstract

An ultrastructural study on the maturation of the parenchymal rabbit pineal cell types from the first postnatal day up to 120 days is presented. Two main cell types are distinguished from the first 24h of postnatal life. Pinealocytes of the types 1 and 11 display different developmental degrees. Both immature cell types are arranged in groups. In addition, type 11 pinealocytes form rosette-like structures. Both cell types progressively become isolated and display cell processes. The nucleus and the cytoplasm of type 1 pinealocytes are barely electrondense. During the postnatal period, the number of cytoplasmic organelles, cell processes and terminal clubs increase progressively. Terminal clubs are frequently seen near blood vessels. After 30 days, type 1 pinealocytes show characteristics of adult pinealocytes. However, the maturation of rnost type 1 pinealocytes does not complete until the 90th postnatal day. Type 11 pinealocytes present a fairly electrondense nucleus and cytoplasm. Mature forms can be seen after the 5th postnatal day. During the postnatal period, a close relationship is determined arnong type 11 pinealocytes and cell processes and terminal clubs of type 1 pinealocytes.