Author ORCID Identifier
Date Available
7-31-2025
Year of Publication
2023
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Medicine
Department/School/Program
Pharmacology and Nutritional Sciences
Advisor
Dr. Pavel I. Ortinski
Abstract
Nucleus accumbens is involved in processing of motivational and affective behaviors and plays a significant role in development and maintenance of substance use. Released from the ventral tegmental area into the nucleus accumbens, the mesolimbic dopamine controls incentive salience and facilitates learning of reinforcement and reward-related motor functions. Recent studies reveal that, in the context of cocaine exposure, dopamine transmission in the ventromedial striatum is pivotal to the regulation of initial drug use. Astrocytes, a major subpopulation of the brain glial cells, are an active component of the so-called tripartite synapse and communicate with neurons through the release of transmitters via a calcium ion dependent mechanism. Astrocyte morphology has been shown to be affected by dopamine and cocaine, but functional role of astrocytic signaling in cocaine use remains unclear. The goal of this dissertation was to address astrocytic adaptations within nucleus accumbens under short and extended access cocaine exposure regimes.
Using acute slice whole-cell patch-clamp recordings, we discovered that dopamine upregulated expression of 4AP-insensitive K+ channels in NAc shell astrocytes in a dose-dependent manner. Pharmacological treatment with XE991 inhibited K+ channel currents to the similar level of naïve ones, suggesting a specific up-regulation of KCNQ type channels. To characterize astrocyte response to cocaine-induced dopamine elevation, we used a rat self-administration model. Animals went through cocaine self-administration under two regimes, short- (1h/day) and extended- (6h/day) access for 14 days. Extended-access, but not short-access, to cocaine led to escalation of drug taking behavior as previously described. To identify functional effects of cocaine exposure on astrocytes, we imaged astrocytes expressing calcium indicator, GCamp6f. Calcium signaling within NAc astrocytes was differentially affected by short- or extended- access cocaine self-administration. For example, extended exposure significantly decreased the amplitude of spontaneous Ca2+ transients. Notably, XE991 showed opposite effects on calcium signaling in short- and extended cocaine experienced rats. To examine whether the astrocytic KCNQ channels may also be responsible for different behavioral outcomes under short- and extended-access to self-administered cocaine, we implanted stereotaxically-guided cannulas into the nucleus accumbens shell for local application of Fluorocitrate (FC), an astrocyte selective metabolic toxin, or Saline plus XE991, a KCNQ channel antagonist. Fluorocitrate by itself depressed lever presses in both short and extended access groups, with larger effect after extended access. In vivo microinjection of XE991 on the last day of cocaine self-administration suppressed cocaine-seeking behavior in extended-access rats, supporting the results from in vitro electrophysiological recordings. Pre-treatment with FC attenuated the XE991 effect, suggesting a cell-type specific regulatory role of astrocytic KCNQ channels.
These results indicated a potential regulatory role of astrocytic signaling in the NAc shell on neural mechanisms underlying substance use, via cell-specific upregulation of the KCNQ potassium channels.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2023.319
Funding Information
This study was supported by the grants:
National Institutes of Health, R01DA041513 (PIO) in 2017;
National Institutes of Health, R01DA053070 (PIO, JRT) in 2021.
Recommended Citation
Xia, Mengfan, "EFFECTS OF ELEVATED EXTRACELLULAR DOPAMINE ON ASTROCYTES IN THE NUCLEUS ACCUMBENS" (2023). Theses and Dissertations--Pharmacology and Nutritional Sciences. 51.
https://uknowledge.uky.edu/pharmacol_etds/51
