Abstract Introduction The CA1 region of the
hippocampus has an important
role in
learning and
memory. It has been shown that
estrogen deficiency may reduce the synaptic density in the region and that
hormone replacement therapy may attenuate the reduction. Objectives This study aimed to evaluate the effects of
estrogen and
raloxifene on the synaptic density profile in the CA1 region of the
hippocampus in ovariectomized
rats.
Methods Sixty ovariectomized three-month-old virgin
rats were randomized into six groups (n = 10).
Treatments started either three days (early
treatment) or sixty days (late
treatment) after
ovariectomy. The groups received
propylene glycol vehicle (0.5 mL/
animal/day), equine
conjugated estrogens (50 μg/
animal/day), or
raloxifene (3 mg/kg/day) either early or late after
ovariectomy. The
drugs were administered orally by gavage for 30 days. At the end of the
treatments, the
animals were anesthetized and transcardially perfused with
ether and
saline solution. The brains were removed and prepared for
analysis under
transmission electron microscopy and later fixed. Results Results showed a significant increase in the synaptic density profile of the
hippocampal CA1 region in both the early
estrogen (0.534 ± 0.026 µ/m2) and the early
raloxifene (0.437 ± 0.012 µ/m2)
treatment groups compared to the early or late vehicle-treated
control groups (0.338 ± 0.038 µ/m2 and 0.277 ± 0.015 µ/m2 respectively). Conclusions The present data suggest that the
raloxifene effect may be lower than that of
estrogen, even early or late
treatment, on synaptic density in the
hippocampus.