Abstract: Objective: The purpose of this study was to observe the changes of c-Fos protein expression in supraoptic nucleus（SO） and paraventricular nuclei（PVN） to investigate the dysfunction mechanism in blood，osmotic pressure and thermoregulation of climacteric period following different ambient temperature stimulation to ovariectomized rats. Methods: Rats of ovariectomy group（OVX group） and Sham operation group（Sham group） were placed in incubators at 4 ℃，10 ℃，25 ℃，33 ℃ and 38 ℃ for 2 hours respectively， and then remove their brains after anesthesia. c-Fos expression was detected by immunohistochemical method. Results: Comparison of c-Fos protein expression- positive cell densities in OVX and Sham groups under the same temperature: SO has markedly low strong positive cell densities under 4 ℃，10 ℃ and 38 ℃；PVN has low strong positive cell densities under 4 ℃，10 ℃，33 ℃ and 38 ℃. The c-Fos protein expression-positive cell densities in SO and in PVN of Sham group and OVX group under different temperatures share the same change rule，i.e. below 25 ℃ the cell densities decrease as the temperature rises，while above 25 ℃ they increase as the temperature rises. Under different temperatures，the strong positive cell densities of Sham group in SO and PVN are significantly different between adjacent temperatures；the strong positive cell densities of OVX group in SO share the same rules，except between 4 ℃ and 10 ℃ and between 33 ℃ and 38 ℃；while OVX group in PVN have difference only between 25 ℃and 33 ℃. Conclusions: Under the same temperature stimuli，the expression of c-Fos protein of different groups in SO and in PVN differs. Under different temperature stimuli，the range of excitatory neurons in SO and in PVN narrows and the densities decrease，which may possibly resulting in abnormalities of blood and osmotic pressure and thermoregulation and further leading to a series of climacteric symptoms such as dizziness，fluctuation of blood pressure and hot flashes.

Key words: Supraoptic nucleus, Paraventricular hypothalamic nucleus, Temperature, Ovariectomy, Proto-oncogene proteins c-Fos