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    Evaluation of dopamine signaling in the rat ventromedial striatum for varying reward proximity
    (İstanbul Medipol Üniversitesi Fen Bilimleri Enstitüsü, 2020) Haziq, Muhammad; Kocatürk, Mehmet
    Dopaminergic neurons play an important role in reward-mediated learning and motor control. In this work, we studied the transient changes in dopamine concentration in the ventromedial striatum (VMS) or nucleus accumbens (NAcc) during movement of a robotic actuator which is visible and brings reward to the rat through different trajectories. The goal of our work was to identify the relationship between the spatial proximity of the reward and the dopamine concentration in the VMS. In order to monitor the changes in dopamine concentration with subsecond temporal resolution, we chronically implanted two Wistar rats with carbonfiber microelectrodes in the ventromedial striatum (VMS) unilaterally and performed recordings using the fast-scan cyclic voltammetry (FSCV) system we developed. Presentation of unexpected reward and instrumental conditioning was used for engaging the rats with the behavioral tasks. Offline analysis was performed on the acquired data using principle component regression (PCR). During presentation of unexpected reward, a phasic increase in dopamine concentration was measured as 20.96 ± 7.0 nM for Rat-1 and 29.46 ±8.1 nM for Rat-2 (n = 15 trials). During instrumental conditioning in which rats performed a nose poke through a hole for delivery of reward, the phasic increase in dopamine concentration was 29.1 ± 9.1 nM for Rat-1 and 58.43 ± 11.9 nM for Rat-2 (n= 15 trials). In experiments with reward carrying robotic actuator movements, an increase in dopamine concentration was observed as robotic actuator approaches toward the reward area. Fluctuations in dopamine concentration were observed during varying trajectories of the robotic actuator. Based on our voltammetric recordings with two rats, the phasic increase in dopamine concentration was significantly larger in instrumental conditioning in a comparison with presentation of unexpected reward (p<0.0005). With different trajectories of the robotic actuator, increase in dopamine concentration occurred only when the actuator, in other words reward cue, reaches the reward area (121.01 ± 13.9 nM for Rat-1 and 61.98 ± 20.01 nM for Rat-2; n= 15 trials). Our results based on the recordings from two rats indicate that the spatial proximity of the reward cue can be identified by monitoring the fluctuations of dopamine concentration in the ventromedial striatum.