Calbindin-D28K cells selectively contact intra-SCN neurons

Abstract

Calbindin-D 28K -immunoreactive cells are tightly packed within a discrete region of the caudal aspect of the suprachiasmatic nuclei of hamsters. These cells receive direct retinal input and are Fos-positive in response to a light pulse. Knowledge of their afferent and efferent connections is necessary to understand suprachiasmatic nucleus organization. The first aim of the present study is to identify interconnections between calbindin and other peptidergic cells of the suprachiasmatic nuclei, using epi-and confocal microscopy and intra-suprachiasmatic nucleus tract tracing. The results indicate that essentially all calbindin cells receive numerous appositions from vasoactive intestinal polypeptide (VIP), neuropeptide Y and serotonin fibers and that most receive appositions from gastrin releasing peptide (GRP) and cholecystokinin (CCK) fibers. Reciprocal connections are seen from VIP, GRP and CCK cells but surprisingly, not from dorsomedial vasopressin cells. Injection of biotinylated dextran amine into the suprachiasmatic nucleus indicates that the ventrolateral suprachiasmatic nucleus projects to the entire nucleus, while the dorsal and medial regions of the suprachiasmatic nucleus project densely to most of the nucleus, except to the calbindin region. Analysis of colocalization of the peptides in the calbindin cell region shows that 91% of the substance P cells, 42% of the GRP cells and 60% of the VIP cells in the calbindin subnucleus coexpress calbindin-D 28K .Our results reveal a highly specialized topographical organization of connections among suprachiasmatic nucleus cells. Keywords suprachiasmatic nucleus; calbindin; vasopressin; confocal microscopy; tract tracingThe suprachiasmatic nuclei (SCN) are the locus of the brain clock regulating circadian rhythms in mammals (reviewed in Silver and Moore, 1998). In rodents, these paired hypothalamic nuclei are each composed of about 8000 neurons that are heterogeneous in their content of neuronal antigens (van den Pol, 1980;van den Pol and Tsujimoto, 1985). Some of the neuropeptides that have been identified to date in the rodent SCN are vasopressin (AVP), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine, gastrin releasing peptide (GRP), sub-stance P (SP), cholecystokinin (CCK) and somatostatin. We have reported that a subregion in the caudal SCN is characterized by the (Silver et al., 1996). These cells are densely packed, receive direct retinal synaptic input (Bryant et al., 2000) and are responsive to photic stimuli, with about 80% of the cells showing Fos-like immunoreactivity (ir) following a light pulse given during subjective night (Silver et al., 1996). The foregoing evidence indicates these CalB cells are on the input pathway for photic stimuli reaching the SCN.The function of this subregion of the SCN has been examined in hamsters. Animals with lesions that destroyed the CalB subnucleus, but spared other compartments of the SCN, lost their locomotor activity rhythm. Animals with partial bilateral SCN lesions sparing part ...

Expression of 5-HT7 receptor mRNA in the hamster brain: Effect of aging and association with calbindin-D28K expression

“…Distinct but faint labeling was detected in a small circular region of the ventral mid-caudal SCN of young hamsters, but appeared to be absent from this region in most of the middle-aged and old animals. Previous studies have indicated that the ventral mid-caudal region of the hamster SCN is unique in its expression of the calcium-binding protein calbindin, and furthermore, this region is essential for generation of circadian rhythms (LeSauter et al, 2002;Hamada et al, 2003;Kriegsfeld et al, 2004a;Antle and Silver, 2005). This experiment investigated if the expression of 5-HT 7 receptor mRNA occurs in the same region of the SCN that expresses calbindin mRNA, and if aging effects the expression of 5-HT 7 receptor mRNA or calbindin mRNA within this region.…”

“…Finally, the dentate gyrus (DG) and fields CA1, CA2, and CA3 of the hippocampus were also studied. The results of Experiment 1 indicated that expression of 5-HT 7 receptor mRNA is localized to a small subregion of the SCN that resembled the calbindin subnucleus previously described in the hamster SCN (LeSauter et al, 2002;Hamada et al, 2003;Kriegsfeld et al, 2004a;Antle and Silver, 2005). Therefore, this experiment investigated if the expression of 5-HT 7 receptor mRNA occurs in the same region of the SCN that expresses calbindin mRNA, and if aging effects the expression of 5-HT 7 receptor mRNA or calbindin mRNA within this region.…”

“…The calbindin subnucleus is also innervated by serotonin-and neuropeptide Y-immunoreactive fibers (LeSauter et al, 2002;Antle and Silver, 2005). Because NPY projections from the IGL and serotonin projections from the median raphe are known to communicate nonphotic information to the suprachiasmatic nucleus (Meyer-Bernstein and Morin, 1998;Cutrera et al, 1994;Schuhler et al, 1999;Janik and Mrosovsky, 1994), it is possible that the calbindin subnucleus may be involved in mediating nonphotic resetting of the circadian pacemaker.…”

Signaling within the Master Clock of the Brain: Localized Activation of Mitogen-Activated Protein Kinase by Gastrin-Releasing Peptide

“…Gastrin-releasing peptide (GRP) is a promising candidate for such a signal. GRP is colocalized with CalB (LeSauter et al, 2002). c-fos expression is observed in GRP neurons after a light pulse in hamsters (Munch et al, 2002) and rats (Earnest et al, 1993;Romijn et al, 1996).…”

“…GRP applied to the SCN resets the circadian clock in a manner similar to that of light both in vivo (Piggins et al, 1995) and in vitro (McArthur et al, 2000). GRP fibers leave the CalB region and course toward the dorsal SCN (LeSauter et al, 2002). GRP receptor-deficient mice demonstrate impaired phase shifts and gene expression responses to light pulses (Aida et al, 2002).…”