Distribution of a metabotropic glutamate receptor, mGluR2, in the central nervous system of the rat and mouse: an immunohistochemical study with a monoclonal antibody
Introduction
The metabotropic glutamate receptors (mGluRs) are involved in many brain functions and pathology, and functional diversity of mGluRs is reflected in the presence of multiple receptor subtypes (for review, see Nakanishi and Masu, 1994, Pin and Duvoisin, 1995). Eight subtypes of mGluRs have so far been cloned, several of which exist in alternative splicing variants. They are classified into three groups according to their amino acid sequence similarities, transduction mechanism, and agonist selectivity: mGluR1 and mGluR5 (group I); mGluR2 and mGluR3 (group II); mGluR4, mGluR6, mGluR7 and mGluR8 (group III) (for review, Nakanishi and Masu, 1994, Pin and Duvoisin, 1995; also see Flor et al., 1997).
Group II mGluRs, mGluR2 and mGluR3, are about 70% identical to each other in amino acid sequence, negatively linked to adenylate cyclase activity via G protein, and selectively activated with (2S,1′R,2′R,3′R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV) (Tanabe et al., 1993, Hayashi et al., 1993). On the other hand, the in situ hybridization histochemistry in the rat has indicated the distinct patterns of distribution of mGluR2 and mGluR3 (Ohishi et al., 1993a, Ohishi et al., 1993b), and revealed the most prominent expression of mGluR2 mRNA in the accessory olfactory bulb and the hippocampal dentate gyrus. In the rat accessory olfactory bulb, it has been indicated that activation of mGluR2 on granule cell dendrites at the presynaptic sites of the dendrodendritic synapses between the granule cells and the mitral cells inhibits the GABAergic transmission from the granule cells to the mitral cells (Hayashi et al., 1993). In the mouse hippocampus, activation of mGluR2 on mossy fiber terminals from the granule cells of the dentate gyrus has been suggested to suppress glutamatergic synaptic transmission from the mossy fiber terminals to the hippocampal pyramidal neurons in CA3 (Yokoi et al., 1996).
The previous studies also reported the distribution of immunoreactivity for group II mGluRs in the rat brain by using polyclonal antibodies (Ohishi et al., 1994, Petralia et al., 1996). The antibodies used in these studies, however, recognize both mGluR2 and mGluR3. Thus, we raised a monoclonal antibody against an N-terminal sequence of rat mGluR2 (MAb mG2Na-5; Neki et al., 1996a) and obtained immunohistochemical evidence indicating that mGluR2 is located not only presynaptically but also postsynaptically (Neki et al., 1996a, Neki et al., 1996b). In the present study, the distribution of immunoreactivity for mGluR2 was examined systematically throughout the brain and spinal cord in the adult rat and mouse. The brains of the mGluR2 gene-lacking mouse (Yokoi et al., 1996) were also immunostained with the monoclonal antibody to confirm the specificity of mGluR2-like immunoreactivity. The distribution pattern of mGluR2-like immunoreactivity (mGluR2-LI) as revealed with the monoclonal antibody for mGluR2 was different from that as revealed with the polyclonal antibody for mGluR2/3.
Section snippets
Materials and methods
A total of eight adult male rats weighing between 200 and 300 g (Sprague–Dawley; Oriental Bioservice, Kyoto, Japan) were used to examine the distribution of mGluR2-like immunoreactivity (mGluR2-LI) in the brain and spinal cord by using the mouse monoclonal antibody, which was produced by using a glutathione S-transferase fusion protein containing an N-terminal sequence of rat mGluR2, putative extracellular amino acid residues 87–134 (MAb mG2Na-5; Neki et al., 1996a). Six male adult wild-type
Results
The both groups of the sections, the sections fixed by PA fixation and those fixed by non-PA fixation, were immunostained in each of the CNS regions in the rat and mouse. In the sections fixed by PA fixation, mGluR2-LI was observed as diffuse immunostaining of neuropil. In most of mGluR2-like immunoreactive neuropil, no profiles of immunostained neurons were detectable. On the other hand, in the sections fixed by non-PA fixation, neuronal cell bodies and proximal dendrites were immunostained,
Discussion
In the previous immunohistochemical studies so far reported, two kinds of polyclonal antibodies were used to examine the distribution of group II mGluRs. Ohishi et al. (1994)made a polyclonal antibody from a bacterial fusion protein, of which immunoreactivity was blocked with a synthetic 25-amino acid peptide corresponding to a C-terminus of rat mGluR2 (residues 848–872). This 25-amino acid sequence differed by five amino acids from that of rat mGluR3 C-terminus (residues 855–879), and the
Acknowledgements
The authors are grateful for photographic help of Mr Akira Uesugi. The authors also express their gratitudes for the support of Drs Satoru Fukuchi, Ritsu Hayashi, Sohzaburo Hayashi, Mizuho Katsurada, Hitoshi Kawai, Yutaka Kitani, Toshihiko Kuroda, Keiko Kumagai, Hiroshi Matsubara, Hiroshi Matsushima, Chisato Minakuchi, Gonpei Niwa, Hajime Oda, Masahiko Ohbayashi, Sei-ichi Ohbayashi, Hiroyasu Ohtsuka, Shigeo Tamaki, Eizo Watanabe, Kazuo Yoshino, and Toshiaki Yoshino. This work was supported in
References (40)
- et al.
Characterization of cholinergic neurons in the rat neostriatum. A combination of choline acetyltransferase immunocytochemistry, Golgi-impregnation and electron microscopy
Neuroscience
(1984) - et al.
The corticostriatal projection: from synaptic plasticity to dysfunctions of the basal ganglia
Trends Neurosci.
(1996) - et al.
A novel splice variant of a metabotropic glutamate receptor, human mGluR7b
Neuropharmacology
(1997) - et al.
Pre- and postsynaptic localization of a metabotropic glutamate receptor, mGluR2, in the rat brain: an immunohistochemical study with a monoclonal antibody
Neurosci. Lett.
(1996) - et al.
Metabotropic glutamate receptors mGluR2 and mGluR5 are expressed in two non-overlapping populations of Golgi cells in the rat cerebellum
Neuroscience
(1996) - et al.
Thalamostriatal neurons with collateral projection onto the rostral reticular thalamic nucleus: anatomical study in the rat by retrograde axonal transport of iron-dextran and horseradish peroxidase
Brain Res.
(1982) - et al.
Immunohistochemical localization of metabotropic glutamate receptors, mGluR2 and mGluR3, in rat cerebellar cortex
Neuron
(1994) - et al.
Distribution of the messenger RNA for a metabotropic glutamate receptor, mGluR2, in the central nervous system of the rat
Neuroscience
(1993) - et al.
Retrograde transport of d-[3H]aspartate in thalamocortical neurones
Neurosci. Lett.
(1983) - et al.
The metabotropic glutamate receptors, mGluR2 and mGluR3, show unique postsynaptic, presynaptic and glial localizations
Neuroscience
(1996)