Date of Award

Spring 5-2021

Document Type

Honors Thesis

Degree Name

Bachelor of Science

Department

Biology

Advisor/Committee Chair

Annalisa Scimemi

Major

Biology

Committee Member

Robert Rosellini

Abstract

EAAC1 is a neuronal glutamate transporter expressed in the brain and the peripheral system, including kidney. Within the brain EAAC1 is mostly expressed in the cortex and striatum, two regions involved in the execution of stereotyped movements and reward-based behaviors. EAAC1 is expressed post-synaptically at excitatory synapses. By contrast, EAAC1 is expressed presynaptically at inhibitory synapses. Here, by transporting glutamate into the presynaptic terminal, EAAC1 supports GABA synthesis and release, as glutamate is a precursor for the biosynthesis of GABA. It is currently unknown whether EAAC1 is differentially expressed and whether it exerts a different modulatory effect at different types of GABAergic inhibitory synapses. The striatum contains two types of GABAergic long-range projection neurons, which receive dopaminergic inputs from the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA). These neurons, called medium spiny neurons (MSNs) based on their morphology, can be distinguished based on immunohistochemical and anatomical criteria. The first group of neurons expresses D1 dopamine receptors; the second group expresses D2 dopamine receptors. D1-MSNs project to the SNc, whereas D2-MSNs project indirectly to the SNc via an intermediate synapse in the globus pallidus. Here we ask how EAAC1 modulates synaptic inhibition among D1-D1, D1- D2, D2-D1and D2-D2 synapses. We first target the expression of the light-gated ion channel Channelrhodopsin-2 (ChR2) to D1- or D2-MSNs by taking advantage of the Cre-LoxP system using BAC transgenic mice. We then use a fluorescence in situ hybridization (FISH) approach to determine whether EAAC1 is differentially expressed in D1- and D2-MSNs. Our data show that there is a preferential effect of EAAC1 at D1-D1 synapses as opposed to D1-D2, D2-D1, and D2- D2 synapses, and that this preferential effect may be due to an increased concentration of EAAC1 in D1-MSNs. These findings shed light on the interplay of neuronal circuits in the striatum, and may better our understanding of neuropsychiatric disorders such as OCD.

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