Abstract

Studies with targeted disruption in the Period2 ( Per2 ) gene suggest that the PER2 protein participates in the regulation of circadian behavioral rhythms. Moreover, it has been shown that direct suppression of PER2 expression in the suprachiasmatic nucleus (SCN) with antisense oligonucleotides disrupts photic resetting of the SCN clock. The effect of such suppression on behavioral rhythms is unknown. Here double-stranded RNA (dsRNA) to Per2 was used to transiently suppress PER2 expression in the SCN of adult rats. Bilateral infusions of dsRNA into the SCN (6 g/side) disrupted circadian wheel running activity rhythms for up to 10 days in experimental rats housed in constant darkness; whereas, control infusions into the SCN or dorsal infusions of dsRNA to Per2 had no effect. Relative to controls PER2 suppression in the SCN was evident 12 days post-dsRNA infusion; however, maximal suppression was observed at day 3. In addition to the suppression of PER2 expression in the SCN, a blunted PER2 rhythm was observed in the oval nucleus of the bed nucleus of the stria terminalis, central nucleus of the amygdala and dentate gyrus. These results provide direct evidence that the expression of PER2 in the SCN is essential for the maintenance of circadian locomotor activity rhythms and for the expression of PER2 rhythms in the limbic forebrain in rats. The specificity of this effect was validated by demonstrating no difference between cFos expression in any of the above areas in control rats and rats treated with dsRNA to Per2.