Probing neuropeptide volume transmission in vivo by a novel all-optical approach

Abstract

Neuropeptides are essential signaling molecules in the nervous system involved in modulating neural circuits and behavior. Although hypothesized to signal via volume transmission through G-protein coupled receptors (GPCR), remarkably little is known about their extrasynaptic diffusion. Here, we developed an all-optical approach to probe neuropeptide volume transmission in mouse neocortex. To control neuropeptide release, we engineered photosensitive nanovesicles with somatostatin-14 (SST) that is released with near-infrared light stimulation. To detect SST, we created a new cell-based neurotransmitter fluorescent engineered reporter (CNiFER) using the SST2 GPCR. Under two-photon imaging, we determined the time to activate SST2R at defined distances as well as the maximal distance and loss rate for SST volume transmission in neocortex. Importantly, we determined that SST transmission is significantly faster in neocortex with a chemically degraded extracellular matrix, a diseased condition indicated in neuroinflammation and Parkinson′s disease. These new neurotechnologies can reveal important biological signaling processes previously not possible, and provide new opportunities to investigate volume transmission in the brain.

Adolescent binge drinking leads to long-lasting changes in cortical microcircuits in mice

“…Although limited work has assessed changes in SST peptide release or expression in substance use disorders, SST represents a potential therapeutic target for a variety of neuropsychiatric illnesses (Brockway and Crowley, 2020). Future experiments should investigate changes in SST peptide release throughout development and following alcohol exposure using both optogenetic techniques (Dao et al, 2019), in vivo recording (Brockway et al, 2022, preprint), and novel biosensors (Wang et al, 2022, preprint; Xiong et al, 2021, preprint).…”

A toolkit of highly selective and sensitive genetically encoded neuropeptide sensors

“…Peptides tagged with large fluorescent proteins or reporters such as EGFP, pHluorin, and GCaMP provide a relatively fast readout of peptide release and describe knockout phenotypes related to peptide release in vitro, but this approach is limited to modified peptides, not the endogenous peptides, and is hardly possible to apply in vivo (Burke et al, 1997;de Wit et al, 2009;Ding et al, 2019;Lang et al, 1997;van den Pol, 2012;Xia et al, 2009). Finally cellbased neurotransmitter fluorescent engineered reporters (CNiFERs) have been used to detect neuropeptides; however, the need to implant exogenous cells in specific brain regions limits the utility of this approach (Jones et al, 2018;Lacin et al, 2016;Xiong et al, 2021). Thus, the precise spatiotemporal dynamics and release patterns of endogenous peptides remain poorly understood.…”

Somatostatin peptide signaling dampens cortical circuits and promotes exploratory behavior

“…Such changes in SST modulation may contribute to dysregulation of PL cortical neurons and outputs and, ultimately be causal to some disease-relevant behaviors. Importantly, the rapid emergence of new optical biosensors for peptides including SST (Xiong et al ., 2021; Wang et al ., 2022) will allow for new in vivo investigation of neurotransmitter versus peptide dynamics. These emerging technologies will allow for the decoupling of SST peptide signaling versus co-released GABA (and potentially other peptides as well).…”