Developmental expression of protein kinase C subspecies in rat brain-pituitary axis

We have examined the neonatal developmental expression of protein kinase C subspecies (PKCs) in rat brain, pituitary glands and cells by enzymatic activity assays, immunohistochemistry and Western blot analysis with type-specific antibodies. A very large increase (455%) was noticed in brain PKC activity during the first week of life with the particulate fraction (22% of total enzyme activity on day 1) increasing dramatically (900%) during the first week to 50% of enzyme activity. In contrast, the pituitary gland showed high activity on day 1 that decreased progressively to reach the lowest levels at 1 year of age. Paradoxically, the number of pituitary cells immunolabeled for PKC increases as a function of age. Western blot analysis showed only small changes in PKCα, PKCβ and PKCε when brains from 6-day-old and 3-month-old female rats were compared, whereas PKCτ and PKCδ increased markedly during this period. On the other hand, brain PKCζ decreased between 6 days and 3 months of age. Western blot analysis showed no major changes in pituitary PKCα, PKCβ and PKCζ when 6-day-old and 3-month-old female rats were compared, while PKCτ was not detected. The major band of pituitary PKGδ (76 kDa) decreased markedly between 6 days and 3 months of age whereas the minor band (68 kDa) did not change. On the other hand PKCε which appeared as one band (92 kDa) in the 6-day-old pituitaries, increased markedly in the 3-month-old rat and was followed by a second major band (68 kDa) which was not observed in the juvenile rat. The increase in the PKC-positive cells and the decrease in histone phosphorylation in the developing pituitary is probably due to the marked dominance of PKCε in the adult rat pituitary.