Raloxifene and estradiol benzoate both fully restore hippocampal choline acetyltransferase activity in ovariectomized rats

Abstract

Selective estrogen receptor modulators (SERMs) demonstrate tissue-specific estrogen receptor (ER) agonist or antagonist properties. Raloxifene, a prototypical SERM, has ER agonist properties in bone and on cholesterol metabolism but full antagonist properties in the uterus and breast. To characterize the ER agonist/antagonist profile of raloxifene in the brain, we have examined its effect on the activity of a known estrogen-responsive gene product, choline acetyltransferase (ChAT), in the hippocampus and other brain regions of 6-month-old ovariectomized (OVX) Sprague–Dawley rats. Three weeks post-ovariectomy, animals received estradiol benzoate (EB, 0.03 mg or 0.3 mg kg -1 day -1 for 3 or 10 days); raloxifene HCl (3.0 mg kg -1 day -1 for 3 or 10 days), tamoxifen (3.0 mg kg -1 day -1 for 10 days) or vehicle (20% CDX). As previously reported, ChAT activity decreased by approximately 20%–50% in the hippocampus of OVX compared with SHAM-operated control rats with no change in ChAT activity observed in the hypothalamus. Raloxifene or EB reversed the OVX-induced decrease in ChAT activity in the hippocampus but did not change ChAT activity in the hypothalamus. Animals that received combined EB (0.03 mg/kg) plus raloxifene (1 mg/kg) or tamoxifen alone (3.0 or 10 mg/kg) also showed increased hippocampal ChAT activity. Raloxifene failed to increase uterine weight and blocked the estrogen-induced increase in uterine weight, while another SERM, tamoxifen, increased uterine weight. These data demonstrate that raloxifene has estrogen-like properties on hippocampal ChAT activity in vivo, and suggest that benzothiophene SERMs may exert estrogen-like beneficial effects on cholinergic neurotransmission in brain without producing peripheral stimulation of breast or uterine tissue.