Photic regulation of peptides located in the ventrolateral subdivision of the suprachiasmatic nucleus of the rat: daily variations of vasoactive intestinal polypeptide, gastrin-releasing peptide, and neuropeptide Y

Abstract

We have determined, by enzyme immunoassay, daily and circadian patterns of the concentrations of three peptides, which are located in the ventrolateral subdivision of the suprachiasmatic nucleus (SCN): vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), and neuropeptide Y (NPY). The contents of VIP and GRP, which are synthesized in the SCN, did not show circadian rhythms in constant darkness (DD). Under light-dark (LD) conditions, GRP content increased and VIP content decreased over the course of the light period and then gradually recovered during the dark period. Responsiveness of these peptides to light suggests that VIP and GRP may transmit visual information on duration of illumination. NPY, which is transported from the intergeniculate leaflet of the lateral geniculate body, showed a circadian rhythm with a peak at circadian time 12 hr in DD. This endogenous rhythm was remarkably modulated by photic stimulation. Under LD conditions, the NPY content in the SCN exhibited a bimodal rhythm with peaks at both the light-dark and dark-light transition points. Thus, NPY may convey visual information on the transitions. All these results indicate that the levels of VIP, GRP, and NPY are mainly regulated by light stimulation and suggest that peptides in the ventrolateral SCN are involved in the mediation of photic information to the pacemaker.

Phenotype Matters: Identification of Light-Responsive Cells in the Mouse Suprachiasmatic Nucleus

“…Retinal terminals on VIP cells have been observed in the rat but not in the hamster (Tanaka et al, 1993;Aioun et al, 1998). VIP, like gastrin-releasing peptide, is rhythmic in LD but not in DD, although the former peaks at night and the latter in the day (Shinohara et al, 1993). The precise distinct roles of these peptides remain to be determined.…”

Circadian dynamics of vasopressin in mouse selection lines: Translation and release in the SCN

“…Low amino transmitter content due to a higher level of release has been suggested for a variety of SCN neuropeptides [40,17]. As a possible consequence of release, AVP levels dropped below immunocytochemical detection levels, and therefore the counts of AVP-ir neurons decreased.…”

“…When high levels of SCN-AVP immunoreactivity indicate low levels of AVP release [17,40], high AVP immunoreactivity reflects a less dynamic SCN-AVP system. Our results support this statement, because we found high levels of AVP immunoreactivity and low levels of AVP release in the SCN of S-mice compared to B-mice.…”

Both Neuropeptide Y and Serotonin Are Necessary for Entrainment of Circadian Rhythms in Mice by Daily Treadmill Running Schedules

“…Recent studies further indicate that photic entrainment is likely mediated by glutamatergic retinal afferents to the SCN (Ebling, 1996) and that both 5-HT and NPY provide inhibitory modulation of this input (Biello, 1995;Weber et al, 1995;Miller et al, 1996; but see Shibata et al, 1994) (glutamate may in turn inhibit N PY, Biello et al, 1997). Both 5-HT and N PY activity within the SCN are increased during periods of behavioral arousal and activity (Jhanwar-Uniyal et al, 1991;Glass et al, 1992;Shinohara et al, 1993;Dudley and Glass, 1996) and may mediate inhibition of photic shifting by concurrent behavioral activity (Ralph and Mrosovsky, 1992). Behavioral activity also can phase shift and entrain circadian rhythms, independent of retinal input to the pacemaker.…”