Abstract
In order to examine the underlying brain mechanism of depression, we designed to investingate the changes in brain monoamines of the "depression model animal". For this purpose, we used female rats which had a regular cycle of spontaneous running activity corresponding to the estrus cycle.Having confirmed the regular cyclic activity, animals were repeatedly exposed to stress in terms of forced running. We thus succeeded in producing chronically inactive animals in which the estrus cycle had been abolished even after the animals recovered from physical exhaustion. This stress-induced, long lasting, inactive state, accompanied by the abolition of hormone dependent cyclic behavior, was suppused to be a "depression analogue". Rat's brains were examined by the fluorescence histochemical method. The most significant findings common to the "depression model rats" were as follows : 1.Fluorescence intensity in nerve cells of the ascending NA systems(A1.A2.A5.A6.A7.)was markedly increased. 2.Fluorescence intensity in cell bodies and nerve terminals of the tubero-infundibular DA systems was decreased. Since these findings were also found in the rats immediately after the stress and were restored to control levels in the "recovery rat", it is conceivable that the changes in brain monoamines induced by stress remain unrestored due to a certain mechanism for long time in "depression model animals".
