Dissertation

Expression of genes encoding glutamate receptors and transporters in morphologically identified cells of the primate retina

Hanna, Michael C

2004

Overview

Photoreceptors in the retina respond to changes in light by modulating the tonic release of glutamate from their axon terminals. Visual information is encoded in the binding of released glutamate to receptors localized to diverse types of bipolar cells that parcel visual information into parallel pathways. Understanding this physiological diversity requires knowledge of the glutamate receptors expressed by bipolar cells. Since glutamate release at the photoreceptor synapse is graded, with the highest concentrations approaching normally toxic levels, bipolar cells might also express glutamate transporters to sharpen their physiological response. I examined the expression of genes encoding glutamate receptors and transporters for the two primary bipolar cell pathways in the retina of the primate Macaque fascicularis: the rod bipolar cell (RBC), which collects rod signals and mediates vision at night, and the diffuse bipolar cell #3 (DB3), which collects from cones and contributes to motion and color vision. RBCs depolarize to light and are known to express the metabotropic glutamate receptor mGluR6, while DB3 cells hyperpolarize to light and are likely to express one or more ionotropic glutamate receptors (GluR). I explored the genetic diversity between RBCs and DB3 cells by creating cDNA libraries from individual cells and probing these libraries using gene-specific PCR, subtractive library hybridization, and random cloning. These libraries were compared to expression in whole retina. I demonstrated for the first time in primate retina genes encoding the AMPA subunits GluR1–4, the kainate subunits GluR5–7 and KA1–2, and the metabotropic subunits mGluR1–8, including a newly described splice variant of mGluR8. I also demonstrated broad expression of the transporters EAAT1–5, including the first evidence of EAAT4 in retina. The RBC expresses the ionotropic subunits GluR1–2 and GluR4, as well as the metabotropic subunits mGluR3 and mGluR6. These cells also express the transporters EAAT2 and EAAT4. In contrast, the DB3 cell expresses only ionotropic subunits GluR1–4 and GluR6, as well the EAAT2 transporter. The results indicate that both pathways for rod and cone vision require not only multiple subunits of glutamate receptors, but also of glutamate transporters to shape their responses to light-induced changes in glutamate concentration.

• Publisher: ProQuest Dissertations & Theses
• Subject: Molecular biology / Neurology / Neurosciences
• ISBN: 0496734075, 9780496734078