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Am J Physiol Regul Integr Comp Physiol 292: R586-R597, 2007. First published August 17, 2006; doi:10.1152/ajpregu.00043.2006
0363-6119/07 $8.00
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SLEEP AND TEMPERATURE REGULATION

Gonadal hormone effects on entrained and free-running circadian activity rhythms in the developing diurnal rodent Octodon degus

Daniel L. Hummer,1,2 Tammy J. Jechura,1,2 Megan M. Mahoney,1,2 and Theresa M. Lee1,2,3

1Department of Psychology, 2Reproductive Sciences Program, and 3Neuroscience Program, University of Michigan, Ann Arbor, Michigan

Submitted 18 January 2006 ; accepted in final form 7 August 2006

The slowly maturing, long-lived rodent Octodon degus (degu) provides a unique opportunity to examine the development of the circadian system during adolescence. These studies characterize entrained and free-running activity rhythms in gonadally intact and prepubertally gonadectomized male and female degus across the first year of life to clarify the impact of sex and gonadal hormones on the circadian system during adolescence. Gonadally intact degus exhibited a delay in the phase angle of activity onset ({Psi}on) during puberty, which reversed as animals became reproductively competent. Gonadectomy before puberty prevented this phase delay. However, the effect of gonadal hormones during puberty on {Psi}on does not result from changes in the period of the underlying circadian pacemaker. A sex difference in {Psi}on and free-running period ({tau}) emerged several months after puberty; these developmental changes are not likely to be related, since the sex difference in {Psi}on emerged before the sex difference in {tau}. Changes in the levels of circulating hormones cannot explain the emergence of these sex differences, since there is a rather lengthy delay between the age at which degus reach sexual maturity and the age at which {Psi}on and {tau} become sexually dimorphic. However, postnatal exposure to gonadal hormones is required for sexual differentiation of {Psi}on and {tau}, since these sex differences were absent in prepubertally gonadectomized degus. These data suggest that gonadal hormones modulate the circadian system during adolescent development and provide a new model for postpubertal sexual differentiation of a central nervous system structure.

adolescent development; puberty; phase angle; tau; sexual differentiation


Address for reprint requests and other correspondence: T. M. Lee, Psychology Dept., Univ. of Michigan, 530 Church St., Ann Arbor, MI 48109-1043 (e-mail: terrilee{at}umich.edu)






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