Interrogating Dynamic Regulation of Pre-Synaptic Release Probability In Vivo - Project Summary: This proposal will interrogate pre-synaptic release properties in vivo in order to extend observations made in reduced system to the awake brain. Release probability (P(r)) varies greatly between synapses. Understanding this fundamental feature of neurotransmission has implications for several basic and translational aspects of neuroscience: P(r) serves as gating node for information transfer between neurons and an understanding of P(r) is required to understand information flow; P(r) is implicated in maintaining healthy network activity; understanding dynamic regulation of P(r) will enhance understanding of plasticity within the healthy brain. This aligns with the mission of NINDS by contributing to an understanding of healthy physiology which may become perturbed in neurological and neuropsychiatric disorders. I will use novel imaging methods to investigate spatiotemporal P(r) regulation and how it is altered by arousal and neuromodulatory systems. P(r) is a core determinant of how information flow from pre-synaptic to post-synaptic cells (Fernandez- Chacon et al. 2001, Kaeser et al. 2013, Korber et al. 2016). In vitro and ex vivo experiments have revealed a wealth of information on how P(r) is dynamically regulated by various neuromodulatory and circuit functions (Higley et al. 2009, Munoz et al. 2014) and how it differs for synapses formed by the same axon (Reyes et al. 1998, Markram et al. 1998, Koester et al. 2005, Martinetti et al. 2022). The overall goals addressed in aims 1 of this proposal are to extend these observations to the awake, behaving brain by leveraging novel tools. In addition to functions localized at the synapse, global behavioral state as measured by pupil diameter, whisking, and locomotion has been extensively studied in relation to cortical dynamics and neuromodulation via acetylcholine (ACh) (Vinck et al. 2015; Lohani et. al. 2021; Benisty et al. 2021; Tang and Higley 2020; McCormick et al. 2020). Further, ACh interacts directly with muscarinic receptors on pre-synaptic terminals to influence glutamate release in part via Gi/o coupled signaling (Maeda et al. 2020; Higley et al. 2009; Guo et al. 2012). Leveraging the ability to quantify P(r) in vivo, I will probe interactions between state, ACh, and P(r) at cortical synapses during behavior. Aim 2 will interrogate behavioral state and ACh mediated neuromodulation. The laboratory of Dr. Higley is an excellent environment in which to conduct this investigation. Dr. Higley has extensive experience with synaptic release and plasticity as well as in vivo imaging methods. In addition, the Neuroscience Department at Yale boasts a highly-collaborative set of leading experts on synaptic physiology and biochemistry who will serve as advisors and mentors concurrent with the goals of the Training Plan herein.
