Date of Award
Doctor of Philosophy (PhD)
Wheeler, Robert A.
The ability to adjust behavior appropriately following an aversive experience is essential for survival, yet variability in this process contributes to a wide range of disorders, including drug addiction. It is clear that proper approach and avoidance is regulated, in part, by the activity of the mesolimbic dopamine system. While the importance of this system as a critical modulator of reward learning has been extensively characterized, its involvement in directing aversion-related behaviors and learning is still poorly understood. Recent studies have revealed that aversive stimuli and their predictors cause rapid reductions in nucleus accumbens (NAc) dopamine concentrations. Furthermore, a normally appetitive stimulus that is made aversive through association with cocaine also decreases dopamine, and the magnitude of the expressed aversion predicts drug-taking. However, whether the presentation of a drug cue that reduces dopamine, and evokes a negative affective state, can motivate relapse is unknown. Here we demonstrate that the presentation of an aversive drug cue both reduces dopamine and causes cocaine-seeking. This finding is provocative because drug seeking in reinstatement designs is typically associated with increased dopamine signaling. Using a combination of fast scan cyclic voltammetry (FSCV) and in vivo electrophysiology we subsequently show that the presence of an aversive drug cue abolishes the dopaminergic encoding of other drug cues and alters NAc neuronal activity patterns. Importantly, a subpopulation of neurons that subsequently encode aspects of drug-seeking behavior increase their baseline firing rates during this aversive experience. We then examine the mechanistic regulation of dopamine signaling by aversive stimuli under more natural conditions. Using FSCV and site-specific behavioral pharmacology we demonstrate that blockade of ventral tegmental area kappa opioid receptors attenuates aversion-induced reductions in dopamine, and prevents proper avoidance learning caused by punishment. By maintaining D2 receptor occupancy within the NAc during punishment, we demonstrate the requirement of aversion-induced reductions in dopamine for aversive learning. Together, these studies inform an evolving model of striatal physiology. Our findings emphasize a role for both increases and decreases in dopamine signaling that modulate behavior by promoting the stimulus-specific activity of distinct striatal output pathways. The continued interrogation of this model may offer novel targets for therapeutic development aimed at treating neurodegenerative disease and drug addiction.
Available for download on Tuesday, March 30, 2021