The stress sensitization of adult rat Increased by stress in childhood and the neural mechanism

Abstract

Objective To observe the influence of stress in childhood on adult rat's stress sensitization and the neural mechanism. Methods Sixty male Sprague-Dawley rats were randomly divided into stress group (thirty) and non-stress group(thirty). The rats in stress group were given 14 repeated daily forced swimming. The emotional behaviors were tested at the beginning of the experiment and when stress of forced swimming ended 8 weeks later. When the appraisal of behavior ended,the pyramidal neuron in the left hippocampal CA3 regions were counted under the light microscope, the pictures of synapses in the left hippocampal CA3 regions were got under the electromicroscope,and the morphological changes of synapses were analyzed with the automatic image analyzing system. Results (1) The score (1.20±0.60) of emotional behavior of stress group increased more than non-stress group(-0.13±0.83) (P<0.05). (2) The number of pyramidal neuron in the left hippocampal CA3 re-gions of stress group rats was small than that of non-stress group rats. (3) The number density [(1.01±0.15) N/ μm3 ], prosop density (0.20±0.04 )μm2/μm3], the average area of synaptic linkage [(0.05±0.02) μm2], the length of active areas [(314.78±46.32) nm], the curvatures (1.02±0.04), the thickness of postsynaptic dense material [(46.35±6.81) nm] in the left hippocampal CA3 regions of the stress group were small than those of non-stress group (P<0.05). Conclusion The stress in childhood could increase the stress sensitization of adult rats,and the decrease of synaptic plasticity might be the mechanism. Key words: Forced swimming test; Stress sensitization; Synapse; Pyramidal neuron; Rats