[Effects of electroacupuncture at different time on brain methionine-enkephalin contents in rats]

The basic level of methionine-enkephalin (MEK) in rat medulla oblongata plus pons was the highest at 05:00 o'clock and the lowest at 23:00. In both the hypothalamus and the striatum at 05:00 MEK levels were respectively higher than those at 11:00, 17:00 amd 23:00. In both the hippocampus and the midbrain at 05:00 and 23:00 they were respectively higher than those at 11:00 and 17:00. In the cortex it was higher at 05:00 than those at 11:00 and 17:00. Electroacupuncture (EA) at 05:00 increased the MEK content in the medulla oblongata plus pons and decreased the MEK content in the hypothalamus. EA at 11:00 produced decreases of MEK concentrations in the medulla oblongata plus pons and the midbrain and increases of MEK content in the cortex. At 17:00 it increased the MEK level in the hypothalamus and at 23:00 it reduced the level of MEK in the hippocampus. The results suggest that there are very marked circadian rhythms in the MEK basic levels of the six discrete brain regions observed and EA at different hours produces different effects on brain MEK levels.