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 PKC alpha, PKC beta and PKC epsilon when brains from 6-day-old and 3-month-old female rats were compared, whereas PKC tau and PKC delta increased markedly during this period. On the other hand, brain PKC zeta decreased between 6 days and 3 months of age. Western blot analysis showed no major changes in pituitary PKC alpha, PKC beta and PKC zeta when 6-day-old and 3-month-old female rats were compared, while PKC tau was not detected. The major band of pituitary PKC delta (76 kDa) decreased markedly between 6 days and 3 months of age whereas the minor band (68 kDa) did not change.(ABSTRACT TRUNCATED AT 250 WORDS)