VGLUT1 mRNA and protein expression in the visual system of prosimian galagos (Otolemur garnetti)

Abstract

The presynaptic storage and release of glutamate, an excitatory neurotransmitter, is modulated by a family of transport proteins known as vesicular glutamate transporters. Vesicular glutamate transporter 1 (VGLUT1) is widely distributed in the central nervous system of most mammalian and nonmammalian species, and regulates the uptake of glutamate into synaptic vesicles as well as the transport of filled glutamatergic vesicles to the terminal membrane during excitatory transmission. In rodents, VGLUT1 mRNA is primarily found in the neocortex, cerebellum, and hippocampus, and the VGLUT1 transport protein is involved in intercortical and corticothalamic projections that remain distinct from projections involving other VGLUT isoforms. With the exception of a few thalamic sensory nuclei, VGLUT1 mRNA is absent from subcortical areas and does not colocalize with other VGLUT mRNAs. VGLUT1 is similarly restricted to a few thalamic association nuclei and does not colocalize with other VGLUT proteins. However, recent work in primates has shown that VGLUT1 mRNA is also found in several subcortical nuclei as well as cortical areas, and that VGLUT1 may overlap with other VGLUT isoforms in glutamatergic projections. In order to expand current knowledge of VGLUT1 distributions in primates and gain insight on glutamatergic transmission in the visual system of primate species, we examined VGLUT1 mRNA and protein distributions in the lateral geniculate nucleus, pulvinar complex, superior colliculus, V1, V2, and the middle temporal area (MT) of prosimian galagos. We found that, similar to other studies in primates, VGLUT1 mRNA and protein are widely distributed in both subcortical and cortical areas. However, glutamatergic projections involving VGLUT1 are largely limited to intrinsic connections within subcortical and cortical areas, as well as the expected intercortical and corticothalamic projections. Additionally, VGLUT1 expression in galagos allowed us to identify laminar subdivisions of the superior colliculus, V1, V2, and MT.

Keywords:

• excitatory neurotransmitter
• vesicular glutamate transporters
• glutamatergic projections
• lateral geniculate nucleus
• pulvinar complex
• superior colliculus

Acknowledgments

We thank Laura Trice for assistance with tissue processing and histology, Dr Toru Takahata and the Yamamori laboratory (National Institute for Basic Biology, Japan) for supplying the VGLUT1 probe, Brett Begley and the Conti Core for assistance with Western blots, Dr Lisa de la Mothe for assistance with image processing, and Mary Fuertado for assistance in animal care.

Disclosure

This research was funded by National Eye Institute grants T32 EY 007135 and P30 EY 08126 to the Vanderbilt Vision Research Center and EY 02686 to JHK, and a National Institutes of Health/National Institute on Deafness and other Communication Disorders grant R01 DC 04318 to TAH. The authors report no other conflicts of interest in this work.