Thesis Defense Announcement
To:  The George Mason University Community

Candidate: Valerie Lewitus

Program: M.S. in Biology

Date:   Monday April 16, 2018

Time:   1:00 P.M.

Place:  Krasnow Bldg, Room 222
             George Mason University
             Fairfax Campus

Title: "Differences in LTP Between Dorsomedial and Dorsolateral Striatum: Induction Frequency and D1 Receptors"

Committee Chair: Dr. Kim Blackwell
Committee Members: Dr. Ancha Baranova, Dr. Karl Fryxell

This is a public defense and all are invited to attend.

Abstract: 
The striatum of the basal ganglia is associated with learning, such as the acquisition of precise motor control and habits. The dorsomedial (DM) striatum receives input from the association cortex and is involved in spatial learning and goal-oriented behavior, while the dorsolateral (DL) striatum receives input from the primary sensorimotor cortex and is involved in procedural learning and habit formation. Previous studies have found that neuron spiking is entrained to a higher theta frequency in the DM than the DL striatum. In addition, previous studies have considered whether D1 receptors are required for the induction of long-term potentiation (LTP), a form of learning at the cellular level, with some showing that D1 receptors are required in the DM striatum and others showing that these receptors are not required in the DL striatum. This apparent regional difference may be due to different stimulation protocols, which could recruit different molecular mechanisms. To investigate regional differences in learning between these two areas, we tested whether the induction of LTP in the DM and DL striatum differed across different theta burst stimulation (TBS) frequencies and in the presence or absence of D1 receptors. To test TBS frequency, we obtained extracellular field recordings in adult male C57Bl6 mouse brain slices in response to a theta burst stimulation of either 10.5 Hz or 5 Hz. We found that 10.5 Hz – but not 5 Hz – produces LTP dorsomedially; in contrast, 5 Hz – but not 10.5 Hz – produces similar LTP amplitudes dorsolaterally. To test for the requirement of D1 receptors, we blocked the receptors using SCH23390 in the DL striatum and found that this blocks LTP, which is similar to what has been found in the DM striatum. Additionally, in order to determine whether female mice are appropriate subjects to use in this study, we observed whether mouse sex or estrus status influences the ability to induce LTP using 10.5 Hz in the DM striatum. We found that female mice who are not in the estrus stage exhibit LTP of a similar amplitude to male mice, but female mice who are in the estrus stage do not exhibit LTP under the same induction protocol.

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