Distribution of vesicular glutamate transporter 2 and glutamate receptor 1 mRNA in the central nervous system of the pigeon (Columba livia)

Abstract

Glutamate acts as the excitatory neurotransmitter in the central nervous system (CNS) and is mediated largely by the vesicular glutamate transporters (VGLUT1-3) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) types of glutamate receptors (GluR1-4) in mammals. In the present study, we determined the cDNA sequences of pigeon VGLUT2 and GluR1 and mapped the distribution of their mRNA in the pigeon CNS. The predicted amino acids of pigeon VGLUT2 and GluR1 showed a 93% identity to human VGLUT2 and GluR1 both. In situ hybridization autoradiograms showed VGLUT2 mRNA expression exclusively in the pallium of the telencephalon, and no expression in the subpallium. Within the diencephalon, VGLUT2 mRNA was more abundant in the thalamus than in the hypothalamus. Rich VGLUT2 mRNA expression was found in the optic tectum, nucleus mesencephalicus lateralis, pars dorsalis, nucleus isthmi, pars parvocellularis, isthmo-optic nucleus, pontine nuclei, and granular layer of the cerebellum. Moderate expression was noted in the cerebellar nuclei, vestibular nuclei, cochlear nuclei, inferior olivary nucleus, and gray matter of the spinal cord. GluR1 mRNA was expressed abundantly in the pallium and subpallium of the telencephalon, but it was poor in the diencephalon, midbrain, medulla, cerebellar cortex, and gray matter of the spinal cord. These results suggest that the cDNA sequences of VGLUT2 and GluR1 in the pigeon are comparable to those of VGLUT2 and GluR1 in mammals, respectively. The distribution of pigeon GluR1 mRNA resembles that of mammals, but the distribution of VGLUT2 mRNA resembles that of both VGLUT1 and VGLUT2 in mammals.

Immunohistochemical localization of vesicular glutamate transporter 2 (vGluT2) in the central nervous system of the pigeon (Columba livia)

“…However, vGluT2 immunoreactivity in the telencephalon of the pigeon differs from that of vGluT2 in the mammalian telencephalon and instead displays a similar pattern to that of mammalian vGluT1. Thus, except for the globus pallidus, the pigeon telencephalon shows intense vGluT2 immunoreactivity, a finding that agrees with in situ hybridization data showing intense expression of vGluT2 mRNA in the telencephalon (Islam and Atoji, 2008). In the cerebellar cortex, pigeon vGluT2 labels parallel fibers whose cell bodies express vGluT2 mRNA (Islam and Atoji, 2008).…”

“…vGluT2 immunoreactivity is distributed in neuropil and at the ultrastructural level it is localized in presynaptic terminals of asymmetric synapses that contact spines, dendrites, and perikarya. The results contribute to an exploration of glutamatergic projections or circuits, with the evidence of vGluT2 mRNA-expressing neurons obtained from an in situ hybridization study in birds (Islam and Atoji, 2008). …”

“…In birds, vGluT1 gene has not yet been identified. In contrast, vGluT2 gene is reported in the chicken (accession numbers: JF320001) and pigeon (Islam and Atoji, 2008; accession number: FJ428226), and that of vGluT3 is published in the chicken (accession number: XM 425451) and zebra finch (accession number: XM002190327).…”

“…A peptide, EEFVQEEVQDSYNYKEGDYS, which corresponds to C-terminal 20 amino acids (residues 562-581) of pigeon vGluT2 (Islam and Atoji, 2008), was synthesized.…”

“…Islam and Atoji (2008) reported the sequence of pigeon vGluT2 cDNA (accession number: FJ428226), whose amino acid shows 99% and 93% identity to the chicken and human vGluT2, respectively. The previous in situ hybridization study demonstrated that vGluT2 mRNA was distributed in neuronal cell bodies in the pallium of the telencephalon, in many nuclei in the ascending auditory and visual systems, and in granule cells of the cerebellar cortex (Islam and Atoji, 2008). However, in situ hybridization histochemistry does not reveal the projection targets of glutamatergic neurons.…”