Axonal Mechanisms Regulating Dopamine Release

About This Grant

Project Summary Dopamine (DA) release from terminal axons in the striatum is crucial for regulating movement and associative learning. Dysregulation of DA release contributes to substance use disorders like nicotine use disorder (NUD), leading to significant health impacts in the United States. DA release in the striatum is controlled by the regulation of action potential (AP) firing in dopaminergic (DAergic) cell bodies as well as inputs onto DAergic axons in the terminal region of the striatum. Decades of research have brought insight into the somatic mechanisms regulating AP initiation, but the mechanisms controlling axonal excitability are not well understood due to difficulties in recording axonal voltage. There is therefore a gap in the understanding of how DA release is modulated by axonal inputs. To fill this gap, we will use direct recording of axonal voltage to record excitability of DAergic axons during physiological striatal transmission that modulates DA release. Striatal cholinergic interneurons (CINs) are large neurons that densely innervate the striatum with terminals that release acetylcholine (ACh). They are involved in reward-related behaviors and the development of substance use disorders and are also central to the axonal regulation of DA release through a novel axo-axonic excitatory synaptic transmission. CINs release ACh directly onto DAergic axons, activating nicotinic receptors (nAChRs) to produce depolarizing potentials that can initiate APs and evoke DA release. Despite clear evidence from brain slice preparation that CINs cause DA release, new evidence suggests they may also inhibit DA release. Thus, the complexities of CIN-mediated control of DAergic axons remain poorly understood. The research in this proposal will clarify how CINs regulate DA release to better understand NUD etiology. Our central hypothesis is that the spontaneous activity of CINs controls DA axon excitability over prolonged durations. We will employ our new technique for direct voltage recordings from DAergic axons in the striatum to address three specific aims: (1) Establish how tonic CIN firing affects AP kinetics and propagation in DAergic axons, focusing on resting membrane potential (RMP) regulation, AP-mediated calcium entry, and nAChR modulation of AP propagation. (2) Determine the mechanisms regulating cholinergic axo-axonic synaptic transmission by tonic CIN activity, identifying synaptic properties and nAChR desensitization dynamics through voltage recordings and optical measurements. (3) Reveal how nicotine modulates DAergic axonal excitability, examining nicotine's effects on axonal nAChRs and axo-axonic ACh signaling. The research here is innovative, in our opinion, because we will directly measure the voltage of DAergic axons during physiological patterns of CIN activity. The research is significant, because it provides new insight into the mechanisms regulating terminal DA release by clarifying how CINs modulate axonal excitability. The findings will reveal how endogenous ACh and nicotine modulate presynaptic terminals, offering insights into potential therapeutic targets for NUD.