Chemogenetic Manipulations of Ventral Tegmental Area Dopamine Neurons Reveal Multifaceted Roles in Cocaine Abuse

Abstract

Ventral tegmental area (VTA) dopamine (DA) neurons perform diverse functions in motivation and cognition, but their precise roles in addiction-related behaviors are still debated. Here, we targeted VTA DA neurons for bidirectional chemogenetic modulation during specific tests of cocaine reinforcement, demand, and relapse-related behaviors in male rats, querying the roles of DA neuron inhibitory and excitatory G-protein signaling in these processes. Designer receptor stimulation of G q signaling, but not G s signaling, in DA neurons enhanced cocaine seeking via functionally distinct projections to forebrain limbic regions. In contrast, engaging inhibitory G i/o signaling in DA neurons blunted the reinforcing and priming effects of cocaine, reduced stress-potentiated reinstatement, and altered behavioral strategies for cocaine seeking and taking. Results demonstrate that DA neurons play several distinct roles in cocaine seeking, depending on behavioral context, G-protein-signaling cascades, and DA neuron efferent targets, highlighting their multifaceted roles in addiction. Significance Statement G-protein-coupled receptors are crucial modulators of ventral tegmental area (VTA) dopamine neuron activity, but how this metabotropic signaling impacts the complex roles of dopamine in reward and addiction is poorly understood.Here, we bidirectionally modulate dopamine neuron G-protein signaling with DREADDs (designer receptors exclusively activated by designer drugs) during a variety of cocaine-seeking behaviors, revealing nuanced, pathway-specific roles in cocaine reward, effortful seeking, and relapse-like behaviors. G q and G s stimulation activated dopamine neurons, but only G q stimulation robustly enhanced cocaine seeking. G i/o inhibitory signaling reduced some, but not all, types of cocaine seeking. Results show that VTA dopamine neurons modulate numerous distinct aspects of cocaine addiction-and relapse-related behaviors, and point to potential new approaches for intervening in these processes to treat addiction.

Mesolimbic dopamine projections mediate cue-motivated reward seeking but not reward retrieval

“…As previously reported (Mahler et al, 2019), hM4Di expression in VTA dopamine 380 neurons resulted in transport of DREADDs to axonal terminals in the NAc and mPFC 381 ( Figure 2). We took advantage of this to investigate the roles of these two pathways in 382 PIT performance, again distinguishing between the influence of reward-paired cues on 383 reward seeking and reward retrieval.…”

“…We took advantage of this to investigate the roles of these two pathways in 382 PIT performance, again distinguishing between the influence of reward-paired cues on 383 reward seeking and reward retrieval. Guide cannulae were aimed at the NAc or mPFC 384 in rats expressing hM4Di in VTA dopamine neurons (Experiment 3A; Figure 4A and 385 Figure 4B), 386 as described above, but were pretreated with intra-NAc or mPFC injections of CNO 387 (1mM) or vehicle to achieve local inhibition of neurotransmitter release (Mahler et al, 388 2014;Stachniak et al, 2014;Lichtenberg et al, 2017), an approach previously shown to 389 be effective in inhibiting dopamine release (Mahler et al, 2019). Figure 4C shows that, 390 in hM4Di-expressing rats, the CS+ specific increase in lever pressing (CS Period * CS 391…”

“…Animals: In total, 89 male and female Long-Evans Tyrosine hydroxylase 70 (Th):Cre+ rats (hemizygous Cre+) (Witten et al, 2011;Mahler et al, 2019) and wildtype 71 (WT) littermates were used for this study. Subjects were at least 3 months of age at the 72 start of the experiment and were single-or paired-housed in standard Plexiglas cages 73 on a 12h/12h light/dark cycle.…”

“…Chambers were illuminated by a houselight during all sessions. 87 Surgery: Th:Cre+ rats were anesthetized using isoflurane and placed in a 88 stereotaxic frame for microinjections of a Cre-dependent (DIO) serotype 2 adeno-89 associated virus (AAV) vectors to induce dopamine neuron-specific expression of the 90 inhibitory designer receptor exclusively activated by designer drug (DREADD) hM4Di 91 fused to mCherry (AAV-hSyn-DIO-hM4Di-mCherry), or mCherry alone (AAV-hSyn-DIO-mCherry) (University of North Carolina Chapel Hill vector Core, Chapel Hill, NC, USA / 93 Addgene, Cambridge, MA, USA; Experiment 2 was replicated with both sources) 94 (Witten et al, 2011;Mahler et al, 2019). The AAV was injected bilaterally into the VTA 95 (-5.5 mm AP, +/-0.8 mm ML, -8.15 mm DV; 1uL / side).…”

Amperometric measurements of cocaine cue and novel context-evoked glutamate and nitric oxide release in the nucleus accumbens core

“…Importantly, striato-nigral projections are not required for cocaine plus cue-induced reinstatement of cocaine seeking following the SA paradigm used herein ), suggesting that serial connectivity between the ventral and dorsal striatum is not required for cue-induced reinstatement under an FR1 schedule of reinforcement during SA. Additionally, chemogenetic inhibition of VTA dopamine neurons has no impact on cue-induced reinstatement (Mahler et al 2019). In contrast, exploration of a novel environment elevates dopamine in the NAcore, which is prevented by inactivation of the vSub (Legault & Wise 2001).…”