A circulating ghrelin mimetic attenuates light-induced phase delay of mice and light-induced Fos expression in the suprachiasmatic nucleus of rats.
Anatomical evidence suggests that the ventromedial arcuate nucleus (vmARC) is a route for circulating hormonal communications to the suprachiasmatic nucleus (SCN). Whether this vmARC-SCN connection is involved in the modulation of circadian activity of the SCN is not yet known. We recently demonstrated, in rats, that intravenous (i.v.) injection of a ghrelin mimetic, GHRP-6, during the daytime activated neurons in the vmARC and reduced the normal endogenous daytime Fos expression in the SCN. In the present study we show that i.v. administration of GHRP-6 decreases light-induced Fos expression at ZT13 in the rat SCN by 50%, indicating that light-induced changes in the SCN Fos expression can also be reduced by GHRP-6. Because it is difficult to study light-induced phase changes in rats, we examined the functional effects of GHRP-6 on light-induced phase shifts in mice and demonstrated that peripherally injected GHRP-6 attenuates light-induced phase delays at ZT13 by 45%. However, light-induced Fos expression in the mice SCN was not blocked by GHRP-6. These results illustrate that acute stimulation of the ghrelinergic system may modulate SCN activity, but that its effect on light-induced phase shifts and Fos expression in the SCN might be species related.
Yi
Chun-Xia
CX
Netherlands Institute for Neuroscience, Amsterdam, The Netherlands. c.yi@nin.knaw.nl
Challet
Etienne
E
Pévet
Paul
P
Kalsbeek
Andries
A
Escobar
Carolina
C
Buijs
Ruud M
RM
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000187:drug effects; D016762:Genes, fos / Q000187:drug effects*; D054439:Ghrelin / Q000031:analogs & derivatives*; D008027:Light; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013045:Species Specificity; D013493:Suprachiasmatic Nucleus / Q000187:drug effects* / Q000378:metabolism
D054439:Ghrelin; D009842:Oligopeptides; C041048:growth hormone releasing hexapeptide