Novel Sites of Oxytocin Receptor Expression in the Mouse Periphery and Modulation of Pupillary Behavior by Oxytocin

Oxytocin (OXT) is a peptide with important regulatory roles in both physiological and behavioral contexts. OXT binds to the OXT receptor (OXTR) in the central and peripheral nervous systems, with diverse patterns of expression dependent on many variables including but not limited to species, sex, and stage of development. OXT is an important hormone during adulthood for the transition to parenthood in many species, from mating behaviors through parturition all the way to parental care. OXT signaling in the parent is crucial during these stages, and deficits in parental OXT can have persisting developmental consequences for the offspring. However, less research has investigated how the infant processes OXT-mediated parental care. The aims of this research were to assess peripheral sites of OXTR in the infant that may inform how the infant perceives OXT from the environment. This cross-species analysis sought to identify regions that were conserved among species and identify differences in OXTR expression that may correlate with developmental behaviors. A novel site of OXTR-binding, the eye, was further assessed in neonates and adults for the presence of mRNA that could potentially inform synthesis and function. Finally, a battery of behavioral tasks to assess differences in pupillary responsiveness were performed in adult transgenic mice strains of Oxt and Oxtr wild-type and knockout. Results from OXTR autoradiography indicated several sites of specific binding in the mouse, prairie vole, and rat. There were species and strain differences in regions of interest including the periodontium and the ciliary bodies of the eye. OXTR autoradiography in adult mice demonstrated that OXTR in the ciliary bodies persist into adulthood. Oxtr mRNA was detected by in situ hybridization (ISH) in the neonatal mouse eye and by reverse-transcriptase polymerase chain reaction (RT-PCR) in the adult mouse eye. Regions relevant to pupillary modulation and processing sensory information from the eye displayed robust Oxtr signal by ISH, including the conjunctiva, ciliary bodies, ciliary ganglion, oculomotor nerve, and superior cervical ganglion. Behavioral assessments in adult mice demonstrated a significantly constricted baseline pupil diameter in Oxt knockout mice, which is rescued by the topical application of OXT. These data support a potential role for OXT mediating autonomic development in the visual system.