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

Abstract

Glutamatergic neurons are distributed widely in the telencephalic pallium of birds, but their targets are unknown. In the present study, a polyclonal antibody was produced against pigeon vesicular glutamate transporter 2 (vGluT2) and was used for Western blot and immunohistochemistry to detect projection targets of glutamatergic neurons in the pigeon central nervous system. The molecular weight of vGluT2 was measured at 65 kDa. vGluT2 immunoreactivity was observed in neuropil, but not in neuronal cell bodies or glia. Immunoreactive neuropil generally appeared homogeneous, but fine granules or puncta were found in many areas or nuclei. The telencephalon showed strong immunoreactivity, except for the globus pallidus. In particular, the mesopallium and hippocampal formation revealed the most intense immunostaining. In the diencephalon, vGluT2 immunoreactivity was intense in the dorsal thalamus and hypothalamus. In the midbrain, strong immunostaining was seen in the periaqueductal gray, the dorsal part of the lateral mesencephalic nucleus, and the isthmo-optic nucleus. The optic tectum showed moderate immunoreactivity. In the cerebellar cortex, glomeruli in the granular layer were intensely immunoreactive, and the molecular layer showed intensely homogeneous immunostaining. In the caudal brainstem, the cochlear magnocellular and angular nuclei showed strongly immunoreactive puncta around neuronal cell bodies. In the spinal cord, the dorsal horn revealed moderate immunoreactivity and the marginal nucleus was strongly immunoreactive. Ultrastructural observations revealed that vGluT2 immunoreactivity is localized in asymmetric, presynaptic terminals. The present results indicate an extensive distribution of glutamatergic projections and circuits in the avian central nervous system.