Arginine‐vasopressin and vasointestinal polypeptide rhythms in the suprachiasmatic nucleus of the mouse lemur reveal aging‐related alterations of circadian pacemaker neurons in a non‐human primate

Aug 24, 2005The European journal of neuroscience

Daily patterns of two brain chemicals in the internal clock of mouse lemurs show age-related changes in time-keeping neurons

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Abstract

Aging in mouse lemurs is associated with significant shifts in the circadian peaks of neuropeptides in the suprachiasmatic nucleus.

In adult mouse lemurs, AVP levels peaked during the second part of the day, while VIP levels peaked at night.
In aged mouse lemurs, the peak timing of AVP shifted to the beginning of the night, and VIP peaked at the start of daytime.
The observed changes indicate that aging modifies the daily rhythms of neuropeptide expression in the SCN.
Differential regulation of AVP and VIP in aged lemurs may impact the SCN's ability to convey rhythmic signals to other brain areas.

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The suprachiasmatic nucleus (SCN) of the hypothalamus, the mammalian circadian pacemaker, is entrained by external cues and especially by photic information. Light is transmitted primarily via the retinohypothalamic tract, which terminates in the ventral part (or core) of the SCN, where vasoactive intestinal polypeptide (VIP)-containing neurons are located. VIP cells are mainly intrinsic and project to the dorsal part (or shell) of the SCN, where neurons containing arginine-vasopressin (AVP) reside. As aging leads to marked changes in the expression of circadian rhythms, we examined in primates whether age-related decay in biological rhythmicity is associated with changes in the oscillation of peptide expression in SCN neurons. We used double immunohistochemistry and quantitative analysis in the SCN of mouse lemurs, which provide a unique model of aging in non-human primates. In adult animals, VIP-positive and AVP-positive SCN neurons exhibited daily rhythms of their number and immunostaining intensity: AVP immunoreactivity peaked during the second part of the day, and VIP peaked during the night. In aged mouse lemurs, the peaks of AVP and VIP immunopositivity were significantly shifted, so that AVP was most intense at the beginning of the night, whereas VIP peaked at the beginning of daytime. The results show that the circadian rhythm of neuropeptides in the SCN is modified by aging in primates, with a differential regulation of the two main peptidergic cell populations. These changes may affect the ability of the SCN to transmit rhythmic information to other neural target sites, and thereby to modify the expression of some biological rhythms.

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Arginine‐vasopressin and vasointestinal polypeptide rhythms in the suprachiasmatic nucleus of the mouse lemur reveal aging‐related alterations of circadian pacemaker neurons in a non‐human primate

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