Substance use disorders involve profound, long-lasting adaptations in neural circuitry that drive persistent drug-seeking and relapse. A critical pathway implicated in this behavior is the projection from the prefrontal cortex (PFC) to the nucleus accumbens core (NAcore). Although discrete neuronal ensembles linked to drug-related experiences have been identified within both regions, significant gaps remain regarding how these specific ensembles structurally connect and how polysubstance use alters this connectivity.
To address these questions, this research combines sophisticated behavioral models with advanced molecular and anatomical techniques, including activity-dependent neural ensemble labeling and enhanced green fluorescent protein reconstitution across synaptic partners (eGRASP). This approach enables the precise quantification and examination of PFC inputs specifically converging onto NAc core neurons associated with cocaine-related experiences. By comparing synaptic connectivity between ensemble and non-ensemble populations, the project aims to uncover how targeted neural connections contribute to the persistence of drug-seeking behavior and identify potential mechanisms underlying relapse.
Project Significance & Core Objectives
Mapping Circuit-Specific Connectivity: Utilizing eGRASP and activity-dependent labeling to visualize and quantify physical synaptic connections between prefrontal cortex ensembles and the nucleus accumbens core following cocaine exposure.
Elucidating Relapse Mechanisms: Comparing ensemble versus non-ensemble connectivity to understand how specific neural circuits drive maladaptive behavior and how these pathways are impacted by polysubstance use.
Previous research has established that neural ensembles, or sparse populations of neurons activated synchronously, can be specifically linked to drug-related behaviors (Cruz et al., 2013). After characterizing cocaine-seeking ensembles in the nucleus accumbens core (Bobadilla et al., 2020), a key region of the brain reward pathway, we aim to causally link the ensembles to seeking behaviors (Figure 1), and compare ensemble-specific structural (Figure 2, Figure 3) and functional plasticity between drug and natural rewards.
We use the targeted recombination in active populations (TRAP) strategy (Guenthner et al., 2013; DeNardo et al., 2018; Ye et al., 2016) and the FosCreERxAi14 mouse line (cFos-TRAP), which allows Cre-dependent expression of tdTomato (Tom+) in neurons expressing the immediate early gene Fos only in the presence of 4-hydroxytamoxifen (4-OHT), resulting in durable labeling of the neurons specifically activated during cocaine seeking.
FIGURE 1
In this figure, we see expression of the designer receptors exclusively activated by a designer drug (DREADD) virus, tagged in yellow, or mCitrine, allowing us to activate (Gq-DREADD) or silence (Gi-DREADD) the cocaine-seeking ensemble (tagged in red, or Tomato) to show the role of the ensemble on seeking behavior. *=Tom+ mCitrine+ cell, bar= 20 μm.
FIGURE 2
Ensemble-specific structural spine plasticity measurements. cFos-TRAP2 neuron tagged during cocaine seeking reveals adequate morphology to measure spine plasticity. White arrows within the insert feature dendritic spines.
FIGURE 3
Detail of a dendritic spine and spine analysis on the imaging software IMARIS. Acquired by undergraduate student Skylar Hodgins.
