Abstract: Objective：To investigate regional changes in 5-hydroxytryptamine（5-HT）1A receptors（5-HT1AR） and 5-hydroxytryptamine（5-HT） 2A receptors（5-HT2AR） in the OVX rat preoptic area of hypothalamus after 1-4 weeks treatment with isopropanolic black cohosh extract—remifemin（ICR）， and explore its potential mechanism of alleviating hot flushes during the peri-menopausal period. Methods：The rats were divided into four groups, ovariectomy （OVX） group，sham group，ovariectomy with estradiol valerate（E2） treatment（OVX+E2）group， and ovariectomy with ICR treatment（OVX+ICR） group. The sham group underwent a sham operation without
ovariectomies，while the other three groups underwent bilateral ovariectomies under sterile conditions. All rats were given 2 weeks to recover after the operation，then each group was given a different treatment lasting 1 week，2 weeks，3 weeks and 4 weeks. The expression of 5-HT1AR and 5-HT2AR in the rat preoptic area of hypothalamus（POAH）were detected by immunohistochemistry. Results：①After 1-4 weeks′ treatment，the number of 5-HT1AR positive cells and the optical density（OD） in POAH of OVX group significantly increased compared with that in the same period of sham group；while the number of 5-HT1AR positive cells and the optical density in periventricular zone of OVX+ICR group and OVX+E2 group significantly decreased compared with that in the same period of OVX group. ②After 1-4 weeks′ treatment， the number of 5-HT2AR positive cells and the optical density （OD） in intermediate zone and lateral zone of OVX group significantly increased compared with that in the same period of sham group. The number of 5-HT2AR positive cells and the optical density（OD） in intermediate zone and lateral zone of OVX+ICR group and OVX+E2 group significantly increased compared with that in the same period of OVX group after 1-2 weeks′ treatment. While the result is reverse after 3-4 weeks′ treatment. Conclusions：Ovariectomized rats had increased expression of 5-HT1AR and 5-HT2AR.After treatment with remifemin or estradiol valerate，the expression of 5-HT1AR in POAH significantly decreased. While the expression of 5-HT2AR in POAH decreased following an increased period. Regulating the expression of 5-HT1AR and 5-HT2AR in POAH may be one of the mechanisms of remifemin alleviating menopausal hot flush .

Key words: Cimicifuga, Estrogens, Receptor, serotonin, 5-HT1A, Receptor, 5-HT2A, Immuno- histochemistry, Rats, Sprague-Dawley