title: Light-induced c-Fos expression in suprachiasmatic nuclei neurons targeting the paraventricular nucleus of the hamster hypothalamus: phase dependence and immunochemical identification.
abstract: The suprachiasmatic nuclei (SCN) contain a master clock driving the majority of circadian rhythms in mammals. It is believed that the SCN confers circadian rhythmicity as well as light responsiveness to pineal melatonin secretion via a direct projection to the paraventricular nucleus of the hypothalamus (PVN). Neurons in the SCN respond to light during subjective night with an expression of the immediate early gene c-fos. The number and distribution of c-Fos protein-containing neurons depend on the zeitgeber time (ZT) at which the light stimulus is presented. To investigate whether this phase-dependent activity is present in the SCN output neurons targeting the PVN, we combined retrograde cholera toxin subunit B (ChB) tracing from the PVN with c-Fos immunohistochemistry. Male golden hamsters were injected iontophoretically with ChB into the PVN area and 7 days later given a 1.5-hr light stimulus at either ZT 14 or ZT 19 followed by vascular fixation. Light stimulation at ZT 19 gave rise to more c-Fos containing neurons in the SCN than light presented at ZT 14. Double immunostaining for ChB and c-Fos revealed that light stimulation at ZT 14 induced c-Fos expression in 26.6% +/- 2.8% of the retrogradely filled perikarya, whereas light-stimulation at ZT 19 increased this fraction to 40.7% +/- 1.9%. This demonstrates the presence of a phase-dependent c-Fos induction in the suprachiasmatic-paraventricular projection system. Triple immunohistochemistry showed that light-activated output neurons contained both gastrin-releasing peptide and vasoactive intestinal polypeptide and to a lesser extent vasopressin. The present findings provide functional evidence of light activation of central pathways involved in the regulation of circadian output rhythms.
authors.affiliation: Department of Medical Anatomy, University of Copenhagen, 2200 Copenhagen, Denmark.
authors.forename: Inger Christine
authors.initials: IC
authors.lastname: Munch
authors.forename: Morten
authors.initials: M
authors.lastname: Møller
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Larsen
authors.forename: Niels
authors.initials: N
authors.lastname: Vrang
mesh_terms: D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D002772:Cholera Toxin; D002940:Circadian Rhythm / Q000502:physiology*; D006224:Cricetinae; D005455:Fluorescent Antibody Technique; D019886:Gastrin-Releasing Peptide / Q000378:metabolism; D008297:Male; D008647:Mesocricetus; D008845:Microinjections / Q000379:methods; D018613:Microscopy, Confocal; D009434:Neural Pathways / Q000166:cytology / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology / Q000378:metabolism*; D010775:Photic Stimulation; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000378:metabolism*; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism; D014667:Vasopressins / Q000378:metabolism
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D014667:Vasopressins; D014660:Vasoactive Intestinal Peptide; D019886:Gastrin-Releasing Peptide; D002772:Cholera Toxin