Effects of Chronic Restraint Stress and Estradiol Replacement on Glutamate Release and Uptake in the Spinal Cord from Ovariectomized Female Rats

Glutamate is an excitatory neurotransmitter involved in neuronal plasticity and neurotoxicity. Chronic stress produces several physiological changes on the spinal cord, many of them presenting sex-specific differences, which probably involve glutamatergic system alterations. The aim of the present study was to verify possible effects of exposure to chronic restraint stress and 17β-estradiol replacement on [³H]-glutamate release and uptake in spinal cord synaptosomes of ovariectomized (OVX) rats. Female rats were subjected to OVX, and half of the animals received estradiol replacement. Animals were subdivided in controls and chronically stressed. Restraint stress or estradiol had no effect on [³H]-glutamate release. The chronic restraint stress promoted a decrease and 17β-estradiol induced an increase on [³H]-glutamate uptake, but the uptake observed in the restraint stress +17β-estradiol group was similar to control. Furthermore, 17β-estradiol treatment caused a significant increase in the immunocontent of the three glutamate transporters present in spinal cord. Restraint stress had no effect on the expression of these transporters, but prevented the 17β-estradiol effect. We suggest that changes in the glutamatergic system are likely to take part in the mechanisms involved in spinal cord plasticity following repeated stress exposure, and that 17β-estradiol levels may affect chronic stress effects in this structure.