Subcellular and subsynaptic localization of group I metabotropic glutamate receptors in the monkey subthalamic nucleus

Abstract

Both subtypes of group I metabotropic glutamate receptor, mGluR1 and mGluR5, are expressed postsynaptically in neurons of the subthalamic nucleus (STN), and their activation induces different physiological responses. To test whether these effects could be explained by a differential localization of the two group I mGluRs, we analyzed the subcellular and subsynaptic distribution of mGluR1a and mGluR5 in the monkey STN. Double-immunofluorescence and light microscopic analyses revealed that both group I mGluR subtypes were strongly coexpressed in the neuropil and neuronal perikarya. Astrocytic perikarya exhibited intense mGluR1a, but no detectable mGluR5, immunoreactivity. At the electron microscopic level, immunoperoxidase labeling for both mGluR1a and mGluR5 was localized mainly in dendrites. A significant proportion of the total pool of mGluR1a-immunoreactive elements was accounted for by glial cell processes, whereas glial cell labeling was much less frequently encountered in sections immunostained for mGluR5. Preembedding immunogold labeling in STN dendrites revealed that 60-70% of the gold labeling for both mGluR subtypes was intracellular, whereas 30-40% was apposed to the plasma membrane. Of the plasma membrane-apposed particles, more than 90% were extrasynaptic; fewer than 10% were associated with symmetric or asymmetric synapses. Most of the synapse-associated labeling was found at the edges of both asymmetric and symmetric postsynaptic specializations. Some extrasynaptic gold particles were aggregated on parts of the plasma membrane tightly apposed by glial processes. These findings demonstrate that mGluR1a and mGluR5 exhibit a similar pattern of subsynaptic localization in monkey STN neurons, with both receptor subtypes exhibiting substantial extrasynaptic and perisynaptic localization.

Subcellular and subsynaptic localization of group I metabotropic glutamate receptors in the nucleus accumbens of cocaine-treated rats

“…These studies showed that brain tissue from mGluR1a knockout mice did not display any specific mGluR1a labeling compared to wild-type. In addition, immunoblotting of cells transfected with mGluR1a, but not mGluR5, labeled a band of 140kD (Kuwajima et al, 2004). Preadsorption studies in rat retina cells abolished mGluR1a labeling (Koulen et al, 1997).…”

“…Specificity of the mGluR5 antibody has been shown in previous studies from our laboratory using knockout mice, transfected cells and homogenates of rat brain. These studies showed that brain tissue from mGluR5 knockout mice do not stain for mGluR5 and HEK-293 cells transfected with mGluR5 label a band of the correct molecular weight (Kuwajima et al, 2004). Furthermore, immunoblot analysis on proteins isolated from various brain regions labels a band that corresponds to the size of mGluR5 in regions known to express mGluR5 protein and mRNA (Mannaioni et al, 2001).…”

Localization and Expression of Group I Metabotropic Glutamate Receptors in the Mouse Striatum, Globus Pallidus, and Subthalamic Nucleus: Regulatory Effects of MPTP Treatment and Constitutive Homer Deletion

“…To localize group I mGluRs, we used rabbit antimGluR1a (Millipore, Billerica, MA) and rabbit anti-mGluR5 (Millipore) polyclonal antibodies. The mGluR1a and mGluR5 antibodies have previously been tested for specificity with Western immunoblot using samples from transfected cells (Marino et al, 2001;Kuwajima et al, 2004) and knock-out mice brain tissue (Ferraguti et al, 1998), as well as immunohistochemistry performed with antibody preabsorption (Testa et al, 1998) or on knock-out brain tissues (Kuwajima et al, 2004). For the immunoperoxidase localization of Homer proteins, rabbit polyclonal antibodies against H1b/c (1:5000), H2 (1:5000), and H3 (1:5000) were used (Shiraishi et al, 2003(Shiraishi et al, , 2004.…”

“…Group I metabotropic glutamate receptors (mGluRs) are G qcoupled heptahelical receptors that are widely expressed postsynaptically in basal ganglia nuclei, including the GP (Hanson and Smith, 1999) and STN (Kuwajima et al, 2004). Although coupled to the same second messenger cascade, mGluR1 and mGluR5 can serve different physiologic functions even when they are coexpressed in the same basal ganglia neurons (Valenti et al, 2002).…”

Parkinson's Disease Therapeutics: New Developments and Challenges Since the Introduction of Levodopa

“…Although group II mGluRs are also widely distributed throughout the basal ganglia circuitry, the modulation of these receptors does not offer significant benefit in animal models of PD Conn et al, 2005;Niswender and Conn, 2010). The mGluR5 is heavily distributed postsynaptically in key basal ganglia nuclei, including the striatum, the globus pallidus, and the STN (Hanson and Smith, 1999;Smith et al, 2000Smith et al, , 2001Hubert et al, 2001;Paquet and Smith, 2003;Kuwajima et al, 2004;Conn et al, 2005;Kuwajima et al, 2007;Poisik et al, 2007;Niswender and Conn, 2010). In each of these structures, the localization and physiological properties of this receptor have been carefully studied in rodents and nonhuman primates Awad et al, 2000;Marino et al, 2001;Poisik et al, 2003;Conn et al, 2005;Galvan et al, 2006).…”