Calbindin-D(28K) cells selectively contact intra-SCN neurons

Area of Science:

• Neuroscience
• Chronobiology
• Cell Biology

Background:

• Calbindin-D(28K)-immunoreactive cells are located in the suprachiasmatic nucleus (SCN) of hamsters.
• These cells receive direct retinal input and are activated by light pulses, indicated by Fos expression.
• Understanding the afferent and efferent connections of these cells is vital for comprehending SCN organization.

Purpose of the Study:

• To investigate the interconnections between calbindin-D(28K) cells and other peptidergic cells within the SCN.
• To map the afferent and efferent connections of calbindin-D(28K) cells in the hamster SCN.

Main Methods:

• Epi- and confocal microscopy were employed to visualize cellular interactions.
• Intra-suprachiasmatic nucleus tract tracing techniques were utilized to identify neuronal projections.
• Biotinylated dextran amine injections into the SCN were used to trace efferent pathways.

Main Results:

• Calbindin-D(28K) cells receive significant input from vasoactive intestinal polypeptide (VIP), neuropeptide Y, and serotonin fibers.
• Most calbindin-D(28K) cells also receive input from gastrin-releasing peptide (GRP) and cholecystokinin (CCK) fibers.
• Reciprocal connections were observed with VIP, GRP, and CCK cells, but not with dorsomedial vasopressin cells.

Conclusions:

• The study reveals a highly specialized topographical organization of connections within the SCN.
• A significant percentage of substance P, GRP, and VIP cells within the calbindin subnucleus coexpress calbindin-D(28K).
• These findings enhance our understanding of neuronal circuitry and information processing in the SCN, the master circadian clock.