The missing link between Circadian Rhythm and Learning Memory

Suprachiasmatic nuclei (SCN) is a tiny structure in the hypothalamus responsible for the regulation of circadian rhythms in an organism. There are several cell types in the SCN and contain two main types of peptide hormones including Vasopressin (AVP) and Vasoactive Intestinal Peptide (VIP).

Chronic circadian dysfunction impairs memory function in human, as seen in patients with Neurodegenerative Diseases such as Alzheimer’s. By manipulating the circadian clocks of Siberian hamster, Fernandez et al. found that memory and learning functions in those animals are disrupted when the clock did not work properly (Science 2014 Nov 14: 854-7). This suggests that rodent SCN also has an important role in learning and memory. Interesting, as the researchers surgically removed SCN from the hamster, their memory abilities returned in full, even when the hamsters’ circadian rhythms were still out of sync.

The mechanism of how SCN affects learning and memory is still unclear. SCN does not innervate hippocampus directly, but through the medial septum (MS), which is the primary subcortical input to the hippocampus. The author proposed that the arrhythmic SCN might release GABA in a non-circadian manner, thereby provides continuous inhibition to the MS, leading to memory dysfunction. Another report showed that melatonin, a hormone induced by SCN, suppresses memory processes in zebrafish (Science 2007 Nov 16: 1144-46).

Although the mechanism remains to be elucidated, this finding suggested the possibility of new and provocative therapy for neurodegenerative diseases, which is to pharmacologically shut off SCN as a way of restoring memory abilities in these patients.

To further understand why SCN ablation restores memory completely, we provide Suprachiasmatic Nuclei (SCN) Marker Antibody Duo (ARG30154) consists of VIP and AVP antibodies for the identification of SCN structure in the brain. Melatonin (ARG80461) and GABA (ARG80452) ELISA kits detect changes in the level of these factors when circadian rhythm falls apart.  Alzheimer’s Disease Related Protein Antibody Panel (ARG30147) investigates the conditions of Alzheimer’s model upon SCN ablation.