Cell and tissue researchSep 21, 2002

Characteristics of Two Types of Daily Rhythm Neurons in the Brain’s Timekeeping Center of a Day-Active Rodent Compared to a Night-Active Rat

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 27, 2026

Abstract

Expression of clock genes Per1 and Per2 is mostly restricted to the dorsomedial part of the suprachiasmatic nuclei in both diurnal and nocturnal rodents.

The study identifies the phenotype of neurons expressing Per1 and Per2 during the day in both a diurnal species, Arvicanthis ansorgei, and a nocturnal species, the rat.
Per1 and Per2 are often coexpressed with arginine vasopressin (AVP) in the dorsomedial part of the suprachiasmatic nuclei.
A few vasoactive intestinal polypeptide (VIP) neurons also express Per1 and Per2.
The expression patterns of Per1 and Per2 are more distinct in the diurnal species compared to the nocturnal species.
These findings suggest a significant role for the dorsomedial part of the suprachiasmatic nuclei in maintaining circadian rhythms.

Simplified

In mammals, the suprachiasmatic nuclei (SCN) are the site of the master circadian pacemaker whose molecular core mechanism is based on interlocking transcriptional/translational feedback loops involving clock genes. Among clock genes, Per1 and Per2 are important for both the maintenance of circadian rhythmicity and entrainment to light cues. Several circadian rhythms (e.g., locomotor activity) present opposite patterns in diurnal and nocturnal species. To test whether a differential cellular expression of clock genes in the SCN could constitute the neural substrate leading to diurnal or nocturnal behavior, we identified, by single or double non-radioactive hybridizations, the phenotype of neurons expressing Per1 and Per2 during the day in a diurnal species, Arvicanthis ansorgei, and in a nocturnal species, the rat (Rattus norvegicus). We show that in both species, expression of Per1 and Per2 is mostly restricted to the dorsomedial part of the SCN, often coexpressed with arginine vasopressin (AVP). A few vasoactive intestinal polypeptide (VIP) neurons were also shown to express Per1 and Per2. This differential expression of Per1 and Per2 in AVP and VIP neurons is more distinct in A. ansorgei than in the rat. Thus, our data suggest a major role for the dorsomedial part of the SCN in the maintenance of circadian rhythmicity. Furthermore, the similar diurnal pattern of Per1 and Per2 expression in diurnal and nocturnal rodents suggests that the circadian organization of locomotor activity rhythms probably relies on differential cellular integration mechanisms downstream of the clock.

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Characteristics of Two Types of Daily Rhythm Neurons in the Brain’s Timekeeping Center of a Day-Active Rodent Compared to a Night-Active Rat

Abstract

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