TEMPORAL CHANGES OF C-FOS EXPRESSION IN OXYTOCINERGIC MAGNOCELLULAR NEUROENDOCRINE CELLS OF THE RAT HYPOTHALAMUS WITH RESTRAINT STRESS

The present experiments were undertaken to examine c-fos expression in magnocellular neuroendocrine cells (MNCs) of the rat hypothalamus wit h restraint stress using dual immunohistochemistry for c-fos and oxyto cin. Restraint stress induced c-fos expression in oxytocinergic MNCs i n the supraoptic nucleus (SON) and paraventricular nucleus (PVN). Quan titative immunohistochemical analysis revealed that percentages of c-f os-positive cells to oxytocin-immunoreactive MNCs in the SON and PVN m aximally increased at 2 h after restraint stress had started, and bega n to decline in spite of the fact that the restraint of animals were c ontinued. Similar results were obtained from time course of c-fos expr ession in parvocellular neurons of the PVN. When animals were released to move freely in their home cages following the 3-h restraint, the p lasma 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, T hese results demonstrate that restraint stress induces c-fos expressio n in oxytocinergic MNCs in the SON and PVN, and that time course of c- fos expression is transient even in the continuation of restraint stre ss.