Tyrosine hydroxylase activity in discrete brain regions of depression model rats

Tyrosine hydroxylase (TH) activity was measured in discrete brain regions of rats during short-term forced running stress (FRS). TH activity was also determined in a depression-like state and in a recovered state after a long-term FRS. Under the short-term FRS, the TH activity showed a significant increase in the locus ceruleus, certain limbic regions and tuberoinfundibular system. In the depression-like state, however, there was a significant decrease in the locus ceruleus and certain limbic regions, but a significant increase was seen in the median eminence. The TH activity in recovered rats showed no difference from the level in the controls. These findings demonstrate an adaptive increase in the TH activity in relation to stress, and may also indicate a failure of adaptation in the depression-like state.