Study of SCN Neurochemistry Using In vivo Microdialysis in the Conscious Brain:Correlation with Overt Circadian Rhythms

摘要

We have completed the assessment of the diurnal variation in serotonergicactivity in the SCN and its temporal relationship to wheel-running behavior under light-entrained (LD 14:10) and free-running (DD) conditions. First, under LD there was a marked diurnal rhythm in serotonergic activity with peak levels occurring at lightoff during the animals' initial bout of wheel-running activity. Thereafter, serotonergic activity decreased to daytime levels by the next morning, despite robusts bouts of nocturnal wheel running behavior. Also, daytime periods of activity exhibited by some individuals was not associated with increased serotonergic activity. From these results, it is hypothesized that serotonin in the SCN does not acutely trigger motor activity. Instead it appears that serotonin is involved in coordinating light-entrained activity rhythms with the LD cycle, which is consistent with the findings of other researches using lesions or pharmacological approaches. Our second original finding is that the diurnal rhythm is serotonergic activity is lost, or greatly diminished, in free-running hamsters held under DD for 3 wks. Thus, the rhythm in serotonergic activity seen under LD probably is not circadian in nature, but is passively driven by an external influence, i.e. the light-dark cycle.