Influence of the corticosterone rhythm on photic entrainment of locomotor activity in rats.
The question of involvement of glucocorticoid hormones as temporal signals for the synchronization of the timekeeping system was addressed in rats with different corticosterone status. The authors showed that adrenalectomy had no effects on the synchronization of wheel-running activity rhythms to a steady-state LD 12:12 cycle, regardless of whether it was compensated for by a corticosterone replacement therapy that either reinstated constant plasma concentrations of the hormone or mimicked its natural rhythm. However, after a 12-h phase shift (daylight reversal), the lack of circulating corticosterone induced a significant shortening of the resynchronization rate (less than 3 days vs. 7 days). Normalization required restoration of a rhythmic corticosterone secretion that was synchronized to the new photoperiod. Under constant darkness, the corticosterone rhythm did not show any synchronizing effect, providing evidence that it participates in entrainment of the locomotor activity rhythm through modulation of light effects. It is proposed that, under stable lighting conditions, circulating glucocorticoids contribute to stabilizing activity rhythms by reinforcing resistance of the circadian timing system to variations of the photoperiod. Experimental evidence that serotonergic neurons are involved in relaying their modulatory effects to the clock is also presented.
Sage
Dominique
D
Interactions Fonctionnelles en Neuroendocrinologie, Institut Fédératif de Recherche Jean-Roche, Faculté de Médecine, Université de la Méditerranée, Marseille, France.
Ganem
Julien
J
Guillaumond
Fabienne
F
Laforge-Anglade
Geneviève
G
François-Bellan
Anne-Marie
AM
Bosler
Olivier
O
Becquet
Denis
D
D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000311:Adrenal Glands / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001522:Behavior, Animal; D002940:Circadian Rhythm; D003345:Corticosterone / Q000378:metabolism*; D003624:Darkness; D005938:Glucocorticoids / Q000378:metabolism; D007150:Immunohistochemistry; D008027:Light; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009474:Neurons / Q000378:metabolism; D017440:Photoperiod; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000378:metabolism; D013997:Time Factors
D005938:Glucocorticoids; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D003345:Corticosterone