Tracking gonadotropin-releasing hormone-mediated movement in-vivo using quantum dot nanoparticles: insights into pathways leading to sperm release

Abstract As the number of conservation breeding programs for at-risk amphibians increase, application of assisted reproductive technologies (ARTs) has likewise grown, with hormone therapy being the most widely utilized technique. Significant interest has been raised for viable alternatives to traditional intracelomic injection for hormone treatment that may be simpler, require less hormone, induce a faster response and be more suitable for animals of different sizes or for minimal contact. We utilized quantum dot (QD) nanoparticles conjugated to GnRHa (GnRHa-QDs) as a means of monitoring exogenous GnRHa dispersal through living Fowler’s toads to investigate how delivery route may affect hormone pathway and efficacy after intracelomic, nasal, and oral administration. Real-time GnRHa-QD movement was tracked using in vivo imaging while hormone binding and QD aggregation were validated using fluorescence microscopy and measurements of spermiation responses following the administration of unconjugated GnRHa, unconjugated QDs, and GnRHa-QDs GnRHa alone was found to induce spermiation in 58.3%, 76.9% and 92.3% of males when administered by intracelomic, oral and nasal routes, respectively. When given through intracelomic injection GnRHa-QD caused spermiation and dispersed throughout the abdominal cavity to then aggregate within the brain, heart, liver, gastrointestinal (GI) tract, kidneys, and testes while unconjugated QDs did not. By contrast, GnRHa-QDs administered by oral or nasal routes were observed moving to the tympanic membrane and down the throat to the GI tract of the toads, but only nasal-administered GnRHa-QDs showed organ aggregation and were only found in the kidneys. Unconjugated QDs exhibited similar in vivo signal dispersal as their conjugated counterparts initially but did not aggregate in any organs over time nor induce spermiation. Through the use of novel QD hormone conjugates, in vivo imaging, and histology we were able to gain insight into how hormone pathways and efficacy might be impacted by delivery route which result in variations in physiological response to hormone treatment.