Objective      To investigate the changes of dentate gyrus volume

and density and number of spinal synapses from the depressed rats induced by chronic unpredictable stress (CUS) by unbiased stereology.       Methods      Male Sprague-Dawley (SD) rats (4- to 5-week-old) were randomly divided into control group (n=15) and CUS group (n=23). The rats from the CUS group were housed in single and given CUS including cold/warm water

food/water deprivation i

n order to build a depressed model. The animals of the control group were housed in 5 and given ad libitum access to food and water. During the 4 weeks of modeling

the rats of the both groups were evaluated using the sucrose preference test

open field test and elevated plus maze test for the behavior assessment. Then the total volume of DG

and numerical density and total number of spinal synapses in DG were studied with immunohistochemical assay and stereology.       Results      The body mass and percentage of sucrose preference were significantly decreased in the CUS group than the control group (both P0.05). In the open field test

the total time spent in the inner area and total traveled distance of 5 min in the inner area were significantly lower in the CUS group than control group (P0.05). According to the stereological results

the numerical density and total number of spinal synapses in DG were significantly decreased in the CUS group when compared to the control group (0.48±0.13/μm

3

vs 0.15±0.03/μm

3

2.103 3×10

9

vs 6.713 5×10

8

P0.05).       Conclusion      The synapse loss in the hippocampal DG area in the CUS-induced depressed rats might be one of the important neurological structure bases for pathogenesis of depression.