DISTRIBUTION OF CALBINDIN-D-28K IN THE BRAIN OF THE FETAL SHEEP IN LATE-GESTATION

Immunocytochemical distribution of calbindin-D-28k was examined in the brains of fetal sheep at 100-105 and 120-125 days of gestation (dGA) and at term in labor (term similar to 150 dGA) and compared to adult sheep. Brains were perfused, cut frozen and immunostained as freely floating sections with a polyclonal anti-calbindin-D-28K antibody. Light microscopy revealed that calbindin-D-28K immunogenicity in fetal cerebellum, rhombencephalon, mesencephalon, diencephalon and telencephalon was overall very similar to that seen in the brains of adult sheep. In addition even though fetal sheep peripheral plasma cortisol concentrations increase 10-20 times over the last 3-4 weeks of gestation to peak during labor and delivery, no glucocorticoid dependent increases in calbindin-D-28K in the hippocampal formation could be seen in the sheep fetus as have been demonstrated for the adult rat given exogenous glucocorticoids. It is concluded that: (1) the basic pattern of calbindin-(D28K) distribution seen in adult sheep brains is established by at least 100 dGA in the sheep fetus; and (2) the pattern of calbindin-D-28K expression in fetal sheep hippocampal formation is not related to peripheral plasma glucocorticoid concentrations.