Temporal changes of c- fos expression in oxytocinergic magnocellular neuroendocrine cells of the rat hypothalamus with restraint stress

Abstract

The present experiments were undertaken to examine c- fos expression in magnocellular neuroendocrine cells (MNCs) of the rat hypothalamus with restraint stress using dual immunohistochemistry for c- fos and oxytocin. Restraint stress induced c- fos expression in oxytocinergic MNCs in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). Quantitative immunohistochemical analysis revealed that percentages of c- fos—positive cells to oxytocin-immunoreactive MNCs in the SON and PVN maximally increased at 2 h after restraint stress had started, and began to decline in spite of the fact that the restraint of animals were continued. Similar results were obtained from time course of c- fos expression in parvocellular neurons of the PVN. When animals were released to move freely in their home cages following the 3-h restraint, the plasma levels of oxytocin declined to reach basal levels within 30 min and c- fos immunoreactivity in the hypothalamic MNCs and parvocellular neurons disappeared faster than those of the continually restrained. These results demonstrate that restraint stress induces c- fos expression in oxytocinergic MNCs in the SON and PVN, and that time course of c- fos expression is transient even in the continuation of restraint stress.