Light-induced c-Fos expression in suprachiasmatic nuclei neurons targeting the paraventricular nucleus of the hamster hypothalamus: phase dependence and immunochemical identification.
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.
Munch
Inger Christine
IC
Department of Medical Anatomy, University of Copenhagen, 2200 Copenhagen, Denmark.
Møller
Morten
M
Larsen
Philip J
PJ
Vrang
Niels
N
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
D016760:Proto-Oncogene Proteins c-fos; D014667:Vasopressins; D014660:Vasoactive Intestinal Peptide; D019886:Gastrin-Releasing Peptide; D002772:Cholera Toxin