EFFECT OF FASTING AND IMMOBILIZATION STRESS ON ESTROGEN-RECEPTOR IMMUNOREACTIVITY IN THE BRAIN IN OVARIECTOMIZED FEMALE RATS

The present study examined the effect of 48-h fasting and 1-h immobili zation on estrogen receptor immunoreactivity in selected hypothalamic areas and the nucleus of the solitary tract (NTS) in ovariectomized ra ts. Fasting induced an increase in ER-immunoreactive cells in the para ventricular nucleus (PVN), periventricular nucleus (PeVN) and NTS comp ared with the unfasted control group. Similarly, immobilization caused an increase in ER-positive cells in the same areas, PVN, PeVN and NTS , versus the non-immobilized group. There was no significant increase in the number of ER-immunoreactive cells in the preoptic area (POA), a rcuate nucleus (ARC) or ventromedial hypothalamic nucleus (VMH) follow ing fasting and immobilization. Our previous work in ovariectomized ra ts with estrogen microimplants in the brain revealed that the PVN and A2 region of the NTS are the feedback sites of estrogen in activating the neural pathway to suppress pulsatile LH secretion during 48-h fast ing. The result in the food-deprived rats suggests that estrogen modul ation of the suppression of LH secretion during fasting is partly due to the increase in estrogen receptors in the PVN and A2 region. The ph ysiological significance of the increase in neural ER following immobi lization remains to be elucidated.