Monitoring of circadian fluctuations of N-acetylserotonin in the rat pineal body by differential pulse voltammetry.

Circadian fluctuations of the electrochemical signal appearing at +270 mV (peak 3) recorded from the pineal body of freely moving rats were first monitored for 24 hours using the in vivo voltammetry technique. The peak 3 height increased after injection of pargyline and S-adenosyl-L-homocysteine but decreased after injection of NSD-1015, while probenecid did not cause any change. Under a 12/12 hours light-dark cycle, the peak 3 height represented circadian fluctuations, similar to those of N-acetyltransferase activity, which were higher in the dark than in the light period. These data suggest that the compound responsible for peak 3 in the pineal body is essentially due to extracellular N-acetylserotonin.