Altered hormone levels and circadian rhythm of activity in the WKY rat, a putative animal model of depression

Leah C. Solberg*, Susan Losee Olson, Fred W. Turek, Eva Redei

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

119 Scopus citations


The Wistar Kyoto (WKY) rat is hyperreactive to stress and exhibits depressive-like behavior in several standard behavioral tests. Because patients with depressive disorders often exhibit disruptions in the circadian rhythm of activity, as well as altered secretory patterns of the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid hormones, we tested the hypothesis that these phenomena occur in the WKY rat. Plasma ACTH and corticosterone levels remained significantly higher after the diurnal peak for several hours in WKY rats relative to Wistar rats. Also, plasma levels of thyroid-stimulating hormone were significantly higher in WKY relative to Wistar rats across the 24-h period, despite normal or slightly higher levels of 3,5,3′-triiodothyronine. In addition, under constant darkness conditions, WKY rats exhibited a shorter free running period and a decreased response to a phase-delaying light pulse compared with Wistar rats. In several ways these results are similar to those seen in other animal models of depression as well as in depressed humans, suggesting that the WKY rat could be used to investigate the genetic basis for these abnormalities.

Original languageEnglish (US)
Pages (from-to)R786-R794
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number3 50-3
StatePublished - 2001


  • Forced swim test
  • Hypothalamic-pituitary-adrenal axis
  • Hypothalamic-pituitary-thyroid axis

ASJC Scopus subject areas

  • General Medicine


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