Objective:To investigate the changes of the CNPase+ oligodendrocytes in the subregion of hippocampus in the depression rats induced by chronic unpredictable stress(CUS). Methods:Male Sprague-Dawley(SD) rats(n =40) were randomly divided into control group(n=10)and CUS group(n=30). A depression model(n=10)containing separation and CUS was built for four weeks. The sucrose preference was used to screen the depressed rats at the end of 4th week. Meanwhile

the effects of chronic unpredictable stress on the behaviors were investigated by means of open field test and forced swimming test. Immunohistochemistry methods combined with modern stereological methods were used to precisely quantify the total number of CNPase+oligodendrocytes in the subregion of hippocampus. Results:The results indicated that CUS group induced a decrease in body weight [(228.7 ±13.5) g

(276.2±18.6)g

P=0.000]

the sucrose preference[(75.9±9.7)%

(94.5±3.2)%

P =0.000]

the total score in open field test[(150.4±29.9)

(76.4±45.4)

P=0.000] when compared with those values under control condition. Also

the immobility time in CUS group was longer than that in control condition[(151.8±33.0)s

(108.7±32.9)s

P=0.009]. The results showed that there was no significant difference in the CNPase positive cells in the CA1 field of the hippocampus between CUS group and control group[(33 318.0±10 332.3)EA

(42 037.3±8 879.2)EA

P=0.149]. In contrast

the CNPase positive cells in CUS group were significantly decreased in CA3[(29 487.8±4 483.0)EA

(37 942.3±5 909.9)EA

P=0.02] and DG[(30 843.8±6 048.2)EA

(48 463.7±9 901.2)EA

P=0.004] areas when compared with those of control group. Conclusion:CNPase+ oligodendrocytes are reduced in CA3 and DG fields not in CA1 field may provide important theoretical evidences in the depression rats induced by CUS.