Effects of long-term oral estrogen on cholinergic neurons in hippocampal formation of ovariectomized rats

Objective To quantify the effects of long-term estrogen deficiency and estrogen replacement therapy (ERT) of compound nylestriol tablet (NL) and low-dose 17β-estradiol on cholinergic neurons in hippocampal formation of ovariectomized (OVX) rat. Methods Female Sprague-Dawley rats aged 7 months were randomly divided into 5 groups: normal control, sham, OVX, OVX plus 17β-estradiol (OVX/ERT), and OVX plus compound nylestriol tablet (OVX/NL). The determination of the changes of cholinergic neuron number and choline acetyltransferase (ChAT) expression in hippocampal formation were quantitatively analyzed using immunohistochemistry of ChAT. Results Cholinergic neuron number and optical density of hippocampal formation in OVX rats markedly derceased but there was no difference among normal control, sham, OVX/NL, and OVX/ERT rats. Conclusion Estrogen deficiency may result in a decrease of cholinergic neuron number and the expression of ChAT, which may be the factor related to memory deficit in OVX rats while replacement therapy of low-dose 17β-estradiol or compound nylestriol tablet can equally maintain the integrity and plasticity of cholinergic neurons in OVX rat hippocampal formation.