Heterogeneity in calbindin-D28k expression in oxytocin-containing magnocellular neurons of the rat hypothalamus.

We have used a double-labeling immunofluorescence method to examine whether oxytocin-containing magnocellular neurons possess a calcium-binding protein, calbindin-D28k, in the hypothalamus of the rat. In the supraoptic nucleus, most oxytocin-immunoreactive cells were also stained for calbindin-D28k. However, in the magnocellular part of the paraventricular nucleus nearly all oxytocin-labeled cells were devoid of calbindin-D28k. In the anterior commissural nucleus, approximately one-third of oxytocin-stained cells were also calbindin-D28k-immunoreactive, but the other cells were negative for calbindin-D28k. This study indicates that there may be distinct chemical features between oxytocin-containing magnocellular neurons of the supraoptic nucleus compared to those of the paraventricular nucleus.