The effect of diabetes and centrally administered insulin on anterior hypothalamic estrogen receptor alpha immunoreactivity

Diabetic rats have characteristic reproductive deficits. Peripheral and central (intra-cerebro-ventricular [ICV]) insulin restores the reproductive phenotype to control levels. In this experiment, we evaluated a possible defect in steroid feedback by evaluating hypothalamic estrogen receptor (ER) alpha availability using ERalpha immunocytochemistry. Animals were ovariectomised and given estradiol and progesterone. Diabetic and control animals were given ICV insulin or saline. Nuclear and/or cytoplasmic ERalpha immunoreactivity was evaluated in the paraventricular nucleus (PVN) and the organum vasculosum laminae terminalis (OVLT). In the PVN, nuclear immunoreactivity was increased among diabetic, ICV insulin-treated animals. Diabetic saline-treated and nondiabetic animals had similar ERalpha immunoreactivity. The OVLT had lower numbers of immunoreactive neurons compared to the PVN; no differences among the treatment groups were found in the OVLT. Central insulin treatment increased the number of PVN nuclear ERalpha immunoreactive neurons among diabetic animals. However, there was no reduction in ERalpha when comparing saline-treated diabetic animals to non-diabetic rats, suggesting that decreases in hypothalamic ERalpha in the regions studied do not account for diabetes-induced reproductive deficits.