title: Endogenous circadian rhythmicity of somatostatin like-immunoreactivity in the rat suprachiasmatic nucleus.
abstract: The suprachiasmatic nucleus (SCN) of the hypothalamus has been established as the locus of the circadian pacemaker in mammals. The SCN is histochemically divided into two subdivisions: dorsomedial and ventrolateral subfields. The dorsomedial SCN is characterized, in part, by dense somatostatin-like immunoreactivity (SS-LI), but its functional significance in circadian pacemaking remains unclear. Our previous study revealed that 24 h SS-LI contents of the SCN in rats kept under light-dark (LD) conditions or blinded by orbital enucleation showed a distinct circadian rhythm. In the present study, 24 h SS-LI contents of the SCN in sighted rats kept under constant darkness (DD) conditions for prolonged periods were measured by enzyme immunoassay. Cellular contents of SS-LI exhibited a clear circadian rhythm on the third day of constant darkness (DD) with a peak at circadian time (CT) 5, corresponding to the time of peak levels found in LD conditions and in enucleated animals. This endogenous free-running rhythm continued to oscillate without attenuation of the amplitude even at 14 days in constant darkness. Moreover, SS-LI rhythm was found to be similar to the vasopressin rhythm in the SCN. In summary, these findings further strengthen the idea that the cellular content of SS-LI in the SCN is under the control of the endogenous circadian pacemaker.
authors.affiliation: Laboratory of Integrative Brain Function, Mitsubishi Kasei Institute of Life Sciences, Tokyo, Japan.
authors.forename: C
authors.initials: C
authors.lastname: Fukuhara
authors.forename: K
authors.initials: K
authors.lastname: Shinohara
authors.forename: K
authors.initials: K
authors.lastname: Tominaga
authors.forename: Y
authors.initials: Y
authors.lastname: Otori
authors.forename: S T
authors.initials: ST
authors.lastname: Inouye
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism; D002940:Circadian Rhythm; D007032:Hypothalamus, Anterior / Q000378:metabolism; D007124:Immunoenzyme Techniques; D008297:Male; D010455:Peptides / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013004:Somatostatin / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: D010455:Peptides; C029993:somatostatin-like peptides; D013004:Somatostatin