AIMTo elucidate the mechanism of depression induced by chronic unpredictable mild stress (CUMS), the effects of CUMS on serotonin (5-HT), tryptophan, stress hormones and behaviour were investigated in rats.

METHODSDepression was induced by for 8 weeks CUMS and confirmed by behavioral tests, the brain and plasma levels of monoamine neurotransmitters were analyzed by HPLC-ECD techniques, the content of plasma corticosterone was evaluated by I125 cortisol radioactivity immunoassay and the serum tryptophan content was measured by HTTACHI L-8800 amino acid analyzer.

RESULTS(1) Rats exposed to a series of mild, unpredictable stressors for 8 weeks displayed the decreased body weight, reduced scores of open-field test and preference of sucrose solution (P < 0.05). (2) Plasma and brain 5-HT contents in rats after exposure to CUMS 8 weeks decreased significantly (P < 0.05). While serum tryptophan content increased at the same time (P < 0.05). (3) Plasma norepinephrine and epinephrine in rats were increased after CUMS 8 weeks, but there was no difference between control and CUMS group in plasma corticosterone.

CONCLUSIONThe behavioral changes induced by CUMS for 8 weeks are similar to the features of human depression, which may be related to the disturbances of tryptophan metabolism induced by increased norepinephrine and epinephrine in CUMS rat.