Elsevier

Molecular Brain Research

Volume 87, Issue 2, 5 March 2001, Pages 196-203
Molecular Brain Research

Research report
Aging selectively suppresses vasoactive intestinal peptide messenger RNA expression in the suprachiasmatic nucleus of the Syrian hamster

https://doi.org/10.1016/S0169-328X(01)00015-8Get rights and content

Abstract

Aging leads to many changes in the expression of circadian rhythms, including reduced amplitude, altered relationship to the environmental illumination cycle, and reduced sensitivity to phase resetting signals. Neuropeptide synthesizing neurons in the suprachiasmatic nucleus (SCN), the principal circadian pacemaker in mammals, play a role in regulating pacemaker function and in coupling the pacemaker to overt circadian rhythms. Aging may alter the activity of neuropeptide neurons in the SCN, which could be reflected in changes in mRNA expression. Therefore, this study investigated whether aging alters the level or rhythm of expression of neuropeptide mRNAs in the SCN of male Syrian hamsters, a well established model for the study of age-related changes in circadian rhythms. Three age groups of hamsters (young [3–5 months old], middle-aged [12–15 months old] and old [19–22 months old] were sacrificed at five times of day. Their brains were dissected and sections through the suprachiasmatic nucleus were prepared and used for in situ hybridization for mRNAs for vasoactive intestinal peptide (VIP), arginine vasopressin (AVP) and somatostatin (SS). Aging selectively decreased the SCN expression of VIP mRNA without affecting AVP mRNA or SS mRNA. Also, only AVP mRNA expression exhibited a robust 24-h rhythm, in contrast to previous findings in other species that VIP mRNA and SS mRNA, as well as AVP mRNA, exhibit 24-h rhythms in the SCN. The present findings suggest that age-related reductions in VIP mRNA expression may contribute to the alterations in entrainment and attenuated sensitivity to phase resetting signals that are characteristic of aging. Furthermore, the results demonstrate that neuropeptide gene expression in the SCN is differentially regulated by aging and varies among species.

Introduction

Circadian rhythms govern the behavior and physiological processes of virtually all organisms. By facilitating adjustments to the daily changes in illumination, temperature and other conditions, circadian rhythms enhance survival. In fact, robust and coordinated circadian rhythms favor good health, longevity and optimal cognitive ability in a variety of species, including humans [10], [20], [38], [39], [58].

Aging brings about many changes in circadian rhythms. One age-related change is a reduction in amplitude, a common feature of melatonin rhythms in old rodents [43], [44]. During aging, circadian rhythms also become disrupted or fragmented, and their phase relationship to environmental time signals is altered [11], [31], [40], [48], [61]. For example, locomotor activity rhythms in old hamsters exhibit fragmentation and an earlier onset of the active phase in relationship to the onset of darkness [11], [40], [48], [61]. Also, circulating cortisol rhythms in old men are dampened and phase-advanced compared to the rhythms in young men [51]. During aging, the circadian pacemaker becomes more resistant to phase resetting signals, such as injections of triazolam or 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) [41], [55]. Finally, aging may induce a dissociation of circadian rhythms within an individual [47]. Studies of circadian rhythms in drinking behavior, body temperature, and neuronal activity in old rats showed that some individuals exhibited a loss of all three rhythms, while other experienced a loss of only one or two of these rhythms [47]. Thus, aging disrupts the coordinated expression of circadian rhythms.

The neural basis for these age-related alterations in circadian rhythms may involve functional changes in the circadian pacemaker in the hypothalamic suprachiasmatic nucleus (SCN). The SCN responds to timing signals received from afferent pathways and drives overt circadian rhythms through its efferent connections [25], [37], [57]. The SCN consists of neurons that synthesize a variety of neuropeptides, including vasoactive intestinal peptide (VIP), arginine vasopressin (AVP), and somatostatin (SS), and appear to play multiple roles in circadian timekeeping [7], [23], [52]. VIP and AVP have been identified in several efferent pathways from the SCN and thus may be involved in the regulation of overt circadian rhythms [25], [57]. AVP and SS have been shown to modulate the function of the SCN. AVP neurons provide endogenous excitatory tone to the SCN [34]. Somatostatin administration inhibits SCN neuronal firing in vitro [22]. Somatostatin neurons are also involved in regulating the phase of circadian rhythms. Depletion of somatostatin induces phase advances in locomotor activity rhythms and SCN electrical activity rhythms, and permits rhythmic release of VIP from the SCN in vitro [15], [16]. The demonstration that VIP neurons receive synaptic inputs from the retinohypothalamic tract, the geniculohypothalamic tract and the serotonergic projection from the median raphe nucleus suggests that the VIP neurons are involved in entrainment of the circadian pacemaker [18], [19], [21], [29]. This concept is supported by findings that VIP microinjections in the SCN region induce phase-dependent phase shifts in locomotor activity rhythms [1], [2], [42].

Because neuropeptide neurons play important roles in regulating circadian timekeeping, alterations in their function may contribute to age-related changes in circadian rhythms. For example, aging modulates the VIP mRNA rhythm in the rat SCN [28], [30]. However, it remains to be determined if aging changes the rhythmic expression of VIP mRNA or other neuropeptide mRNA in the SCN of the Syrian hamster, a well-characterized model of age-related changes in behavioral circadian rhythms [45], [54], [62]. Therefore, the current study tested the hypothesis that aging alters the SCN rhythmic expression of messenger RNA for VIP, AVP or SS in Syrian hamsters. In order to assess each mRNA species at the site of greatest expression within the SCN, a preliminary study was conducted to delineate the regional distribution of VIP mRNA, AVP mRNA and SS mRNA.

Section snippets

Animals and tissue preparation

Male Syrian hamsters obtained from Harlan Labs (Harlan, HsdHan:AURA) were maintained in the Department of Laboratory Animal Research at the University of Kentucky under a 14-h light, 10-h dark photoperiod (lights on from 06:00 to 20:00 h) for at least 1–2 weeks. Food (Teklad, Amway) and water were available continuously. Three age groups were studied: young (3–5 months old), middle-aged (12–15 months old) and old (19–22 months old). The hamsters were sacrificed at five different times of day,

Regional distribution of neuropeptide mRNA expression in the SCN

The Syrian hamster SCN expressed all three mRNA species investigated: VIP, AVP and SS (Fig. 1). VIP mRNA expression, which was localized to the ventral SCN, exhibited a statistically significant variation throughout the rostral to caudal axis of the SCN, characterized by greatest expression in the middle and no detectable expression at either pole (Fig. 2). The expression of AVP mRNA and SS mRNA expression in the dorsal region of the SCN were homogeneous along the rostral to caudal axis of the

Discussion

In order to elucidate the neural basis for age-related changes in circadian rhythms, this study investigated the effect of aging on expression of neuropeptide mRNAs in the SCN, the major mammalian circadian pacemaker. The results showed that aging decreased VIP mRNA expression without affecting AVP mRNA or SS mRNA expression. These findings support the hypothesis that aging modulates SCN expression of neuropeptide messenger RNA.

The selectivity of this effect for VIP suggests that it may be

Acknowledgements

We thank Anthony Deveraux for assistance with these experiments and Dr Kathryn Scarbrough for helpful consultation concerning in situ hybridization for VIP mRNA expression. NIH Grant AG-13418 supported these studies.

References (63)

  • F. Kawakami et al.

    Serotonin depletion by p-chlorophenylalanine decreases VIP mRNA in the suprachiasmatic nucleus

    Neurosci. Lett.

    (1994)
  • F. Kawakami et al.

    Loss of day–night differences in VIP mRNA levels in the suprachiasmatic nucleus of aged rats

    Neurosci. Lett.

    (1997)
  • J. Kiss et al.

    Serotoninergic endings on VIP-neurons in the suprachiasmatic nucleus and on ACTH-neurons in the arcuate nucleus of the rat hypothalamus. A combination of high resolution autoradiography and electron microscopic immunocytochemistry

    Neurosci. Lett.

    (1984)
  • C. Manrique et al.

    Impairment of serotoninergic transmission is followed by adaptive changes in 5HT1B binding sites in the rat suprachiasmatic nucleus

    Brain Res.

    (1994)
  • R. Mihai et al.

    Suppression of suprachiasmatic nucleus neurone activity with a vasopressin receptor antagonist: possible role for endogenous vasopressin in circadian activity cycles in vitro

    Neurosci. Lett.

    (1994)
  • L.P. Morin et al.

    Projections of the suprachiasmatic nuclei, subparaventricular zone and retrochiasmatic area in the golden hamster

    Neuroscience

    (1994)
  • K. Scarbrough et al.

    Quantitative differences in the circadian rhythm of locomotor activity and vasopressin and vasoactive intestinal peptide gene expression in the suprachiasmatic nucleus of tau mutant compared to wildtype hamsters

    Brain Res.

    (1996)
  • R. Teclemariam-Mesbah et al.

    Direct vasoactive intestinal polypeptide-containing projection from the suprachiasmatic nucleus to spinal projecting hypothalamic paraventricular neurons

    Brain Res.

    (1997)
  • A.N. van den Pol et al.

    Neurotransmitters of the hypothalamic suprachiasmatic nucleus: Immunocytochemical analysis of 25 neuronal antigens

    Neuroscience

    (1985)
  • O. Van Reeth et al.

    Aging alters the entraining effects of an activity-inducing stimulus on the circadian clock

    Brain Res.

    (1993)
  • J. Vanecek et al.

    Melatonin inhibits the increase of cyclic AMP in rat suprachiasmatic neurons induced by vasoactive intestinal peptide

    Neurosci. Lett.

    (1998)
  • W.S. Young et al.

    Vasopressin and oxytocin mRNAs in adrenalectomized and Brattleboro rats: analysis by quantitative in situ hybridization histochemistry

    Mol. Brain Res.

    (1986)
  • Y. Zhang et al.

    Effects of aging on light-induced phase-shifting of circadian behavioral rhythms, Fos expression and CREB phosphorylation in the hamster suprachiasmatic nucleus

    Neuroscience

    (1996)
  • H.E. Albers et al.

    Avian pancreatic polypeptide phase shifts hamster circadian rhythms when microinjected into the suprachiasmatic region

    Science

    (1984)
  • H.E. Albers et al.

    Interaction of colocalized neuropeptides: Functional significance in the circadian timing system

    J. Neurosci.

    (1991)
  • S.F. Altschul et al.

    Gapped BLAST and PSI-BLAST: a new generation of protein database search programs

    Nucleic Acids Res.

    (1997)
  • E.C. Azmitia et al.

    An autoradiographic analysis of the differential ascending projections of the dorsal and median raphe nuclei in the rat

    J. Comp. Neurol.

    (1978)
  • R.M. Buijs, J. Wortel, J.J. Van Heerikhuize, M.G. Feenstra, Ter, Horst, H.J. Romijn, A. Kalsbeek, Anatomical and...
  • J.P. Card et al.

    Immunocytochemical localization of vasoactive intestinal polypeptide-containing cells and processes in the suprachiasmatic nucleus of the rat: Light and electron microscopic analysis

    J. Neurosci.

    (1981)
  • I.R. Cohen et al.

    Age-related changes in the diurnal rhythm of serotonin turnover in microdissected brain areas of estradiol-treated ovariectomized rats

    Endocrinology

    (1988)
  • R.A. Cohen et al.

    Disruption of human circadian and cognitive regulation following a discrete hypothalamic lesion: A case study

    Neurology

    (1991)
  • Cited by (61)

    • Age-related changes in circadian rhythms and non-visual responses to light during adulthood

      2023, Encyclopedia of Sleep and Circadian Rhythms: Volume 1-6, Second Edition
    • Alterations in glutamatergic signaling contribute to the decline of circadian photoentrainment in aged mice

      2018, Neurobiology of Aging
      Citation Excerpt :

      Changes in the SCN with age have already been reported in laboratory animals such as mice, rats, and hamsters. These include altered expression of primary neuropeptides typically responsible for SCN cell orchestration, decreases in glucose uptake, and declines in oscillatory activity of SCN neurons (Biello, 2009; Duncan et al., 2001; Kawakami et al., 1997; Krajnak et al., 1998; Madeira et al., 1995; Satinoff et al., 1993; Wise et al., 1988). SCN output function appears to be compromised with age, given that multiple studies report dampened amplitude of the circadian rhythm in neuronal spontaneous cell firing (Farajnia et al., 2012; Leise et al., 2013; Nakamura et al., 2011).

    • Aging and circadian rhythms

      2015, Sleep Medicine Clinics
    • Neurophysiological analysis of the suprachiasmatic nucleus: A challenge at multiple levels

      2015, Methods in Enzymology
      Citation Excerpt :

      Note that this antiphase/phase relationship is typical of a decrease in interneuronal coupling. This decrease in coupling among neurons within an aged network is consistent with a decrease in neurotransmitter function within the SCN, including GABA (Farajnia et al., 2012; Palomba et al., 2008) and VIP (Duncan, Herron, & Hill, 2001; Zhou, Hofman, & Swaab, 1995), both of which are believed to play a major role in coupling within the SCN (Albus et al., 2005; Colwell et al., 2003; Liu & Reppert, 2000; Maywood et al., 2006). The presence of networks gives rise to robustness in the system.

    View all citing articles on Scopus
    View full text