Elsevier

Brain Research

Volume 1043, Issues 1–2, 10 May 2005, Pages 95-106
Brain Research

Research report
Expression of groups I and II metabotropic glutamate receptors in the rat brain during aging

https://doi.org/10.1016/j.brainres.2005.02.046Get rights and content

Abstract

Age-dependent changes in the expression of group I and II metabotropic glutamate (mGlu) receptors were studied by in situ hybridization, Western blot analysis and immunohistochemistry. Male Fisher 344 rats of three ages (3, 12 and 25 months) were tested. Age-related increases in mGlu1 receptor mRNA levels were found in several areas (thalamic nuclei, hippocampal CA3) with parallel increases in mGlu1a receptor protein expression. However, a slight decrease in mGlu1a receptor mRNA expression in individual Purkinje neurons and a decline in cerebellar mGlu1a receptor protein levels were detected in aged animals. In contrast, mGlu1b receptor mRNA levels increased in the cerebellar granule cell layer. Although mGlu5 receptor mRNA expression decreased in many regions, its protein expression remained unchanged during aging. Compared to the small changes in mGlu2 receptor mRNA levels, mGlu3 receptor mRNA levels showed substantial age differences. An increased mGlu2/3 receptor protein expression was found in the frontal cortex, thalamus, hippocampus and corpus callosum in aged animals. These results demonstrate region- and subtype-specific, including splice variant specific changes in the expression of mGlu receptors in the brain with increasing age.

Introduction

Normal aging is accompanied by alterations of many neurotransmitter and second messenger systems in the brain. Recently, the glutamatergic neurotransmitter system has received a great deal of attention in particular, in research examining impairments in normal and pathological aging. Several studies have recognized age-related changes in the density and function of the different ionotropic glutamate receptors [22], [26], [29], [57]. Although metabotropic glutamate (mGlu) receptors are involved in synaptic plasticity [2], there are only few studies that have investigated age-related changes in the characteristics of mGlu receptor neurotransmission due to lack of subtype-specific agonists and/or antagonists. Metabotropic glutamate receptors form a family of at least eight subtypes [11], which are subdivided into three groups on the basis of sequence homology, pharmacological profile of activation, transduction pathways and several of these have multiple splice variants. While group I mGlu receptors (mGlu1a, b, c, d, g and mGlu5a, b) are coupled to the polyphosphoinositide signaling pathway, group II mGlu receptors (mGlu2 and mGlu3) and group III mGlu receptors (mGlu4a, b; mGlu6; mGlu7a, b; and mGlu8a, b) are linked to the inhibition of cAMP cascade [11], [36].

An early study by Parent et al. [33] investigated the group I/II mGlu receptor agonist trans-1-amino-cyclopentyl-1,3-dicarboxylate (ACPD) stimulated inositol phosphate (IP) turnover in aged Long–Evans rats based on their performance in the Morris water maze. They found an increase in IP turnover in the frontal cortex and the hippocampus of cognitive impaired animals as compared to the aged unimpaired and the young rats. In addition, a significant decrease in IP turnover was shown in the parietal cortex which was independent of the cognitive performance. In contrast, Nicolle et al. [30] showed a decreased IP turnover in the hippocampus of aged rats, which was correlated with the impairment in the water maze learning. Receptor binding studies with C57B1 mice did not find correlation with performance in the Morris water maze and the results revealed no changes in receptor binding during aging, but the metabotropic type 1 (high quisqualate affinity) binding sites showed a declining trend, especially in the hippocampus [21]. McGahon and Lynch [25] showed an age-related deficit in the glutamate release by adding ACPD and arachidonic acid to hippocampal synaptosomes. Another pertinent finding is that ACPD increased dopamine efflux in the prefrontal cortex of aged rats but had no effect in young rats [38].

These studies suggested further investigations to determine the effect of aging on specific subtypes of mGlu receptors. Our earlier study showed a significant decrease in the level of mGlu1a receptor protein in the cerebellum of 24-month-old C57BL/6NNIA mice as compared to the 5- and 15-month-old groups. However, a progressive increase in the mRNA level of mGlu1 receptor was found in the granule cell layer during aging [49]. In the present study, we systematically analyzed region- and subtype-specific, including splice variant-specific changes in the expression of group I and group II mGlu receptors in Fisher 344 rat brain during aging by quantitative in situ hybridization, Western blot analysis and immunohistochemistry.

Section snippets

Animals and tissue preparations

Male Fisher 344 rats of three age groups were used, 3-month-old (young adult), 12-month-old (middle-aged) and 25-month-old (aged). All animals were obtained from the National Institute on Aging colonies (Harlan, Indianapolis, IN). Animals were acclimatized for a week before use. On the day of the experiment, animals were anesthetized with isoflurane and decapitated. The brains were removed and frozen in powdered dry ice.

In situ hybridization

Twelve μm coronal or sagittal sections were used for in situ hybridization.

Changes in mGlu1a receptor protein

Western blot analysis of mGlu1a receptors revealed a major band at 145 kDa corresponding to receptor monomers. Consistent with previous findings [49], mGlu1a receptor expression was reduced in the cerebellum of 25-month-old rats. Interestingly, we observed a substantial increase in mGlu1a receptor expression in the caudate–putamen of aged rats, while a smaller increase was observed in the cerebral cortex of 12-month old rats (Fig. 2). Immunohistochemical analysis of mGlu1a receptors confirmed

Age-associated changes in group I mGlu receptors

There are only few reports on the effect of aging on the expression and function of group I mGlu receptors. A recent study showed a decrease in the stimulation of PI hydrolysis by mGlu receptor agonists in the hippocampus of aged animals, which was significantly correlated with the impairment of spatial learning [30]. This effect, however, reflected a reduction in phospholipase-Cβ1 levels, rather than changes in the expression of mGlu1 or -5 receptors [30]. The mGlu1/5 receptor agonist,

Acknowledgments

This study was partially supported by NIH NIA 1P01 AG18357 and the Missouri's Alzheimer's Association.

References (58)

  • S. Mary et al.

    The rat mGlu1d receptor splice variant shares functional properties with the other short isoforms of mGlu1 receptor

    Eur. J. Pharmacol.

    (1997)
  • B. McGahon et al.

    The synergism between ACPD and arachidonic acid on glutamate release in hippocampus is age-dependent

    Eur. J. Pharmacol.

    (1996)
  • J.J. Mitchell et al.

    Age-related changes in [3H]MK-801 binding in the Fisher 344 rat brain

    Neurobiol. Aging

    (1998)
  • F.L. Neto et al.

    Differential distribution of metabotropic glutamate receptor subtype mRNAs in the thalamus of the rat

    Brain Res.

    (2000)
  • N.R. Nichols et al.

    GFAP mRNA increases with age in rat and human brain

    Neurobiol. Aging

    (1993)
  • Y. Nomura et al.

    Activation of adenylate cyclase by dopamine, GTP, NaF and forskolin in striatal membranes of neonatal, adult and senescent rats

    Eur. J. Pharmacol.

    (1984)
  • H. Ohishi et al.

    Distribution of a metabotropic glutamate receptor, mGluR2, in the central nervous system of the rat and mouse—An immunohistochemical study with a monoclonal antibody

    Neurosci. Res.

    (1998)
  • R.S. Petralia et al.

    The metabotropic glutamate receptors, mGluR2 and mGluR3, show unique postsynaptic, presynaptic and glial localizations

    Neuroscience

    (1996)
  • J.-P. Pin et al.

    The metabotropic glutamate receptors: structure and functions

    Neuropharmacology

    (1995)
  • A. Pintor et al.

    Metabotropic glutamate receptor agonist (1S,3R-ACPD) increased frontal cortex dopamine release in aged but not in young rats

    Eur. J. Pharmacol.

    (1998)
  • M.T. Price et al.

    Age-related changes in the glutamate concentration and synaptosomal glutamate uptake in adult rat striatum

    Life Sci.

    (1981)
  • A. Simonyi et al.

    Age differences in the expression of metabotropic glutamate receptor 1 and inositol 1,4,5-trisphosphate receptor in mouse cerebellum

    Neurosci. Lett.

    (1998)
  • A. Simonyi et al.

    Changes in mRNA levels for group I metabotropic glutamate receptors following in utero hypoxia–ischemia

    Dev. Brain Res.

    (1999)
  • A. Simonyi et al.

    Region-specific decline in the expression of metabotropic glutamate receptor 7 mRNA in rat brain during aging

    Mol. Brain Res.

    (2000)
  • M.M. Soloviev et al.

    Identification, cloning and analysis of expression of a new alternatively spliced form of the metabotropic glutamate receptor mGluR1 mRNA

    Biochem. Biophys. Acta

    (1999)
  • Y. Tamaru et al.

    Distribution of metabotropic glutamate receptor mGluR3 in the mouse CNS: differential location relative to pre- and postsynaptic sites

    Neuroscience

    (2001)
  • Y. Tanabe et al.

    A family of metabotropic glutamate receptors

    Neuron

    (1992)
  • J.C. Tu et al.

    Coupling of mGluR/Homer and PSD-95 complexes by the shank family of postsynaptic density proteins

    Neuron

    (1999)
  • J.P. Turner et al.

    Synaptic activation of the group I metabotropic glutamate receptor mGlu1 on the thalamocortical neurons of the rat dorsal lateral geniculate nucleus in vitro

    Neuroscience

    (2000)
  • Cited by (40)

    • Metabotropic Glutamate Receptors at the Aged Mossy Fiber – CA3 Synapse of the Hippocampus

      2021, Neuroscience
      Citation Excerpt :

      The authors postulated that the increased phosphoinositol hydrolysis was a compensatory mechanism in response to aging (Parent et al., 1995; see also Le Jeune et al., 1996). Simonyi et al. (2005) reported increased expression levels of mGluR1 mRNA and receptor protein in the DG and CA3 PCs of aged animals. Consistent with these data, hippocampal G proteins Gαq and Gα11, that couple to group I mGluRs exhibit altered functionality in the aged area CA3 (McQuail et al., 2013).

    • Age and gender effects of <sup>11</sup>C-ITMM binding to metabotropic glutamate receptor type 1 in healthy human participants

      2017, Neurobiology of Aging
      Citation Excerpt :

      In male Fisher 344 rats, age-related increases in mGluR1 mRNA levels were found in the thalamic nucleus (25%–32%), parietal cortex (19%), and hippocampus CA3 area (14%), with parallel increases in mGluR1a protein expression (Simonyi et al., 2005). Immunohistochemical analysis also confirmed the age-dependent increase in mGluR1a in the striatum and cerebral cortex, whereas a slight decrease in mGlu1a mRNA levels in Purkinje neurons and a decline in cerebellar mGluR1a protein levels were detected in 25-month-old rats (Simonyi et al., 2005). In the cerebellum, an age-dependent increase in mGluR1 mRNA levels in the granular cell layer (with no change in the Purkinje cell layer) was observed despite a reduction in mGluR1a protein levels.

    • Metabotropic glutamate receptor, mGlu5, mediates enhancements of hippocampal long-term potentiation after environmental enrichment in young and old mice

      2017, Neuropharmacology
      Citation Excerpt :

      In rats, late LTP (>24 h) also requires mGlu5-activation (Manahan-Vaughan and Braunewell, 2005; Naie and Manahan-Vaughan, 2004; Neyman and Manahan-Vaughan, 2008). It was surprising to find that LTP in old mice was unaffected by mGlu5 antagonism, despite reports by others that mGlu5 expression remains relatively constant in adulthood through to relatively advanced ages (ca. 24 months) in rodents (Simonyi et al., 2005; Canas et al., 2009). The involvement of mGlu receptors in hippocampal LTP is influenced by the intensity of the HFS protocol used (Wilsch et al., 1998), and thus, it is possible that a change in the frequency-dependency of mGlu5-dependent LTP occurs during aging.

    View all citing articles on Scopus
    View full text