Abstract by Chao Wu

Cocaine use disorder (CUD) is a chronic and relapsing disorder characterized by compulsive drug seeking and a high vulnerability to relapse. Despite extensive efforts to characterize the neural substrates of cocaine addiction, effective pharmacological treatments remain lacking. Selective targeting of M1 receptor (M1R) by using allosteric and bitopic modulators presents a promising therapeutic approach for managing CUD. The bitopic M1R modulator VU0364572 reduces cocaine-enhanced glutamatergic transmission in the nucleus accumbens (NAc), a central hub in addiction circuitry, as demonstrated by microdialysis experiments, and decreases cocaine-seeking behaviour in a cocaine-food choice paradigm. However, the circuit- and cell-specific mechanisms underlying these actions remain poorly understood.

In this thesis, we used electrophysiology, viral tracing, optogenetics, and behavioural assays to determine how different concentrations of VU0364572 modulate excitatory transmission within the NAc in male and female mice. We further sought to identify the circuit- and cellular-level mechanisms through which M1R activation regulates synaptic transmission and to evaluate its potential impact on cocaine-related behaviours.

Manuscript I demonstrates that VU0364572 produces concentration- and sex-dependent modulation of excitatory synaptic transmission in NAc medium spiny neurons (MSNs). Moderate doses enhance excitatory drive, whereas higher concentrations suppress it and reduce neuronal excitability. Female mice required higher concentrations to achieve effects observed in males, indicating sex-specific pharmacodynamics.

Manuscript II reveals that VU0364572 decreases excitatory inputs onto NAc MSNs by attenuating excitatory transmission from the direct prefrontal cortex (PFC-NAc) pathway, PFC- paraventricular thalamus (PFC-PVT) pathway, and the polysynaptic PFC-PVT-NAc circuit. Behavioural experiments further revealed that VU0364572 facilitated the extinction of cocaine-conditioned place preference.

Manuscript III employs bulk and single-photon calcium imaging to show that VU0364572 elevates basal intracellular calcium in NAc MSNs while attenuating cocaine-induced calcium influx in males.

This work expands our understanding of how the bitopic M1R modulator VU0364572 modulates excitatory transmission in the NAc across varying concentrations, sexes, and neural circuits. We demonstrate that VU0364572 exerts concentration- and sex-dependent effects on excitatory synaptic transmission within the NAc. Moreover, it regulates excitatory inputs via both direct corticostriatal projections and a thalamostriatal polysynaptic pathway. The finding that VU0364572 facilitates the extinction of cocaine-associated contextual learning underscores the behavioural relevance of these synaptic modulations. This work highlights M1R activation as a promising therapeutic strategy for modulating maladaptive corticostriatal and thalamostriatal circuits implicated in CUD.