Effect of photoperiod reversal on twenty-four hour patterns for dopamine levels in the corpus striatum and upper and lower brainstem of the rat.

Dopamine levels were measured in the corpus striatum, upper and lower brainstem at 6 hour intervals for a period of 24 hours in rats adapted for 3 weeks to either of two concomitantly-conducted lighting programs. On the normal cycle the animals were illuminated from 08(00)--20(00); on the reverse cycle, from 20(00)--08(00). In the corpus striatum dopamine levels peaked during the dark phase of both illumination cycles indicating that 24 hour rhythm is exogenous. On the other hand, in the upper and lower brainstem, dopamine peaks occurred in both light cycles at 00(00) or 06(00) indicating that these 24 hour rhythms are endogenous in nature. Photoperiod reversal resulted in significantly elevated dopamine levels in the corpus striatum and lower brainstem. The existence of a stress as well as a seasonal factor which affects striatal dopamine is suggested.