title: Ultradian corticosterone secretion is maintained in the absence of circadian cues.
abstract: Plasma levels of corticosterone exhibit both circadian and ultradian rhythms. The circadian component of these rhythms is regulated by the suprachiasmatic nucleus (SCN). Our studies investigate the importance of the SCN in regulating ultradian rhythmicity. Two approaches were used to dissociate the hypothalamic-pituitary-adrenal (HPA) axis from normal circadian input in rats: (i) exposure to a constant light (LL) environment and (ii) electrolytic lesioning of the SCN. Blood was sampled using an automated sampling system. As expected, both treatments resulted in a loss of the circadian pattern of corticosterone secretion. Ultradian pulsatile secretion of corticosterone however, was maintained across the 24 h in all animals. Furthermore, the loss of SCN input revealed an underlying relationship between locomotor and HPA activity. In control (LD) rats there was no clear correlation between ultradian locomotor activity and hormone secretion, whereas, in LL rats, episodes of ultradian activity were consistently followed by periods of increased pulsatile hormone secretion. These data clearly demonstrate that the ultradian rhythm of corticosterone secretion is generated through a mechanism independent of the SCN input, supporting recent evidence for a sub-hypothalamic pulse generator.
authors: Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK. eleanor.waite@bristol.ac.uk
authors: Eleanor J
authors: EJ
authors: Waite
authors: Mervyn
authors: M
authors: McKenna
authors: Yvonne
authors: Y
authors: Kershaw
authors: Jamie J
authors: JJ
authors: Walker
authors: Kwangwook
authors: K
authors: Cho
authors: Hugh D
authors: HD
authors: Piggins
authors: Stafford L
authors: SL
authors: Lightman
mesh_terms: D000204:Activity Cycles / Q000502:physiology*; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology; D003345:Corticosterone / Q000097:blood* / Q000378:metabolism; D003463:Cues; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism; D008297:Male; D009043:Motor Activity; D010913:Pituitary-Adrenal System / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D003345:Corticosterone