Voltammetric measurements of 5-hydroxyindole compounds in the suprachiasmatic nuclei: Circadian fluctuations

Abstract

This study concerns the voltammetric signal appearing at a +300 mV potential (peak 3) recorded from the suprachiasmatic nuclei (SCN) of rats under acute and chronic conditions. In acute conditions, and in order to accurately localize the working electrode, a topographical study of the peak 3 height was first realized in the frontal plane containing the SCN by use of differential pulse voltammetry and monocarbon fiber electrodes. In the same conditions, the effects of clorgyline and reserpine were studied. Clorgyline decreased peak 3 while reserpine increased it. Contrary to 5-HT, 5-HIAA contents of the SCN, measured with high performance liquid chromatography, demonstrate analogous variations. All these data suggest that it is essentially 5-HIAA which is responsible for peak 3 from the SCN. In unanesthetized, freely moving rats, under a 1212h light-dark cycle, spontaneous and circadian variations of the SCN's peak 3 were studied, during the rest-activity cycle. Multifiber working electrodes were used for this purpose. During spontaneous and successive periods of rest and activity peak 3 height was always found to be higher during activity. Further, these spontaneous variations were superimposed with a circadian variation exhibiting its acrophasis during the dark period. Our data suggest that the release and catabolism of serotonin is greater in waking than in sleeping animals. They also suggest, that the rostral raphe system, phase locked with the SCN, plays an important role in the circadian variations measured.