| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 323447 | Hormones and Behavior | 2011 | 12 Pages |
During puberty, humans develop a later chronotype, exhibiting a phase-delayed daily rest/activity rhythm. The purpose of this study was to determine: 1) whether similar changes in chronotype occur during puberty in a laboratory rodent species, 2) whether these changes are due to pubertal hormones affecting the circadian timekeeping system. We tracked the phasing and distribution of wheel-running activity rhythms during post-weaning development in rats that were gonadectomized before puberty or left intact. We found that intact peripubertal rats had activity rhythms that were phase-delayed relative to adults. Young rats also exhibited a bimodal nocturnal activity distribution. As puberty progressed, bimodality diminished and late-night activity phase-advanced until it consolidated with early-night activity. By late puberty, intact rats showed a strong, unimodal rhythm that peaked at the beginning of the night. These pubertal changes in circadian phase were more pronounced in males than females. Increases in gonadal hormones during puberty partially accounted for these changes, as rats that were gonadectomized before puberty demonstrated smaller phase changes than intact rats and maintained ultradian rhythms into adulthood. We investigated the role of photic entrainment by comparing circadian development under constant and entrained conditions. We found that the period (τ) of free-running rhythms developed sex differences during puberty. These changes in τ did not account for pubertal changes in entrained circadian phase, as the consolidation of activity at the beginning of the subjective night persisted under constant conditions in both sexes. We conclude that the circadian system continues to develop in a hormone-sensitive manner during puberty.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (198 K)Download as PowerPoint slideResearch Highlights► The circadian system is still developing and hormone-sensitive during puberty. ► Rhythms of peripubertal rats were more phase-delayed and bimodal than those of adults. ► Males showed larger changes in entrained circadian phase during puberty than females. ► Gonadal hormones partially accounted for pubertal circadian changes. ► These changes persisted under constant conditions independent of free-running period.
