MORPHOLOGICAL AND IMMUNOCYTOCHEMICAL FEATURES OF THE PINEAL ORGAN OF C3H AND C57BL MICE AT DIFFERENT STAGES OF POSTNATAL-DEVELOPMENT

Considerable progress is currently being made in elucidating the molec ular basis of the circadian (photoneuroendocrine) system by use of tra nsgenic mice generated from the inbred strains C57BL and C3H. As in al l other vertebrate species, the pineal organ is an important component of the photoneuroendocrine system in these mouse strains, but very li ttle is known about its morphological and immunocytochemical features. We therefore investigated the pineal organ and the adjacent epithalam ic region of adult, 10-, and 5-day-old C57BL and C3H mice for S-antige n, serotonin, and dopamine-beta-hydroxylase (DBH) immunoreactions. In adult animals, the pineal organ was more than 2 times bigger in C3H th an in C57BL mice. In younger animals, this difference was already evid ent, but less pronounced. The S-antigen immunoreactivity was more inte nse in adult C3H than in C57BL mice. This difference developed with in creasing age; it was not yet detectable in 5-day-old animals. The inte nsity of the serotonin immunoreaction was similar in both strains at a ll stages investigated. However, the serotonin immunoreaction was more pronounced in adult than in young animals. The relative DBH-immunorea ctive area (used as a marker for the sympathetic innervation of the pi neal organ) was much bigger in C3H than in C57BL mice; within each str ain it remained relatively constant during postnatal development. Adul t individuals of both strains contained S-antigen-and serotonin-immuno reactive cells in the habenular complex. Their number increased with a ge, but they were always more numerous in C3H. In conclusion, the stud y has shown considerable differences in pineal morphology between C3H and C57BL, which may be related to the well-known differences in melat onin formation between these two strains.