Neuropeptide oxytocin is central to maternal and reproductive behaviors, anxiolysis, and social interaction, and is thus critical to our social well-being. Oxytocin has also been implicated in the pathogenesis of various social impairment disorders, including Autism Spectrum Disorder (ASD). Our understanding of oxytocin’s function in the brain is incomplete, however, as both normal and aberrant oxytocin signaling pathways remain uncharacterized. There is a demonstrable need for an imaging probe with the specificity and spatiotemporal resolution requisite for endogenous oxytocin signaling (seconds, microns). Leveraging the optical properties of single-walled carbon nanotubes (SWNT) and the molecular recognition capacity of biopolymers, our lab has previously developed sensors for imaging dopamine in the brain. Herein, we present a peptide fragment of the endogenous oxytocin receptor protein (OXTp) as the molecular recognition element when conjugated to near-infrared fluorescent SWNT, to produce a peptide-SWNT oxytocin imaging probe. To synthesize the OXTp-SWNT probe, SWNT are first functionalized with triazine handles and carboxylated. The receptor peptide is then conjugated to the carboxyl groups through EDC/NHS chemistry, and the OXTp-SWNT is subsequently wrapped with C12 DNA to impart colloidal stability. In solution, the OXTp(C12)-SWNT oxytocin probe binds to oxytocin reversibly and demonstrates a dF/F0 of &gt;150% in response to 100 µM oxytocin. In the paraventricular nucleus (PVN) of mouse brain slices, where oxytocin is centrally released, the OXTp(C12)-SWNT probe enables imaging of oxytocin upon 0.5 mA electrical stimulation and maintains this response after incubation with 1 µM quinporole, a dopamine receptor agonist. Furthermore, OXTp(C12)-SWNT both respond to and can be used to image oxytocin in acute brain slice in the presence of atisoban, an oxytocin receptor antagonist. Our results herein demonstrate that the OXTp(C12)-SWNT probe can be employed to image neuropeptide oxytocin both in solution and in acute slices, towards a more complete understanding of oxytocin signaling in the brain and its role in neurological disorders such as ASD.

Reversible near-infrared fluorescent nanosensor reports oxytocin release in the brain

ACS Fall 2021

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