PI: Markita Landry (Assistant Professor, UC Berkeley Chemical and Biomolecular Engineering) Project Abstract Imaging presynaptic correlates of cocaine locomotor sensitization with near infrared catecholamine nanosensors Cocaine locomotor sensitization is thought to be, in part, driven by changes in dopamine signaling within the nucleus accumbens (NAc). One potentially early contributing mechanism is internalization and degradation of D2 autoreceptors within dopamine neurons (Madhavan et al. 2013) and their long range processes. We recently developed a technique for imaging dopamine neurotransmission in the striatum using synthetic near infrared catecholamine nanosensors (nIRCats) (Beyene et al. 2019). nIRCats are compatible with a wide variety of dopamine receptor drugs, and can resolve individual dopamine release “hotspots” ~2 µm in size. We aim to determine how cocaine locomotor sensitization affects D2 autoreceptor regulation of dopamine release at individual nIRCat hotspots. Adult male & female C57/Bl6 mice will undergo a five day locomotor sensitization protocol (control: saline; cocaine: 15 mg/kg). Twenty-four hours after the final locomotor testing session, acute brain slices will be prepared from saline or cocaine-treated mice, and will be labeled with nIRCat. Dopamine release will be electrically evoked within the NAc or dorsal striatum to image dopamine release spatiotemporal kinetics. Via bath application of 1 µM quinpirole and repeating the stimulation protocol, we will assess the change in evoked nIRCat ∆F/F to assay presynaptic D2 autoreceptor function. By thus probing dopamine autoreceptor response to quinpirole, we will compare drug effects across treatment conditions and striatal subregions to answer if and how repeated cocaine administration influences the regulation of presynaptic dopamine release by D2 autoreceptors. We predict that quinpirole will show a reduced ability to suppress dopamine release in cocaine-sensitized animals relative to the saline control, and will explore differences in sensitization across individual dopamine release sites in striatum and NAc of sensitized animals. This work will establish near infrared imaging, nIRCat nanosensors, and pharmacology as valuable tools to measure dopamine transients at the level of individual synapses and to analyze the relationship between their modulation by D2 receptor drugs and locomotor sensitization. Landry ABSTRACT AB-1