Diurnal Variation in 5-Hydroxyindole-Acetic Acid Output in the Suprachiasmatic Region of the Siberian Hamster Assessed by in vivo Microdialysis: Evidence for Nocturnal Activation of Serotonin Release

Abstract

In vivo brain microdialysis was used to characterize the daily pattern of 5-hydroxyindole-acetic acid (5-HIAA) release in the region of the suprachiasmatic nuclei (SCN) in freely behaving male Siberian hamsters housed under 16L:8D. A marked diurnal variation in the concentration of extracellular 5-HIAA was apparent, with peak levels (147 ± 5% of the daily mean; p M). Localized applications of KC1 (150 mil) or veratridine (100 µM) decreased 5-HIAA by 62 ± 5 or 49 ± 11%, respectively. The effect of KC1 was not significantly affected by specific calcium channel blockers. Perfusion with TTX markedly decreased SCN 5-HIAA during the dark phase, but had little effect during the light phase (42 ± 8 vs. 12 ± 5% suppression, respectively; p M) to the perfusate significantly stimulated 5-HIAA output. This treatment increased the release of 5-HIAA more during the dark than during the light phase (61 ± 8 vs. 25 ± 5%, respectively; p