title: Uptake of fluorescent gentamicin by peripheral vestibular cells after systemic administration.
abstract: OBJECTIVE
  In addition to cochleotoxicity, systemic aminoglycoside pharmacotherapy causes vestibulotoxicity resulting in imbalance and visual dysfunction. The underlying trafficking routes of systemically-administered aminoglycosides from the vasculature to the vestibular sensory hair cells are largely unknown. We investigated the trafficking of systemically-administered gentamicin into the peripheral vestibular system in C56Bl/6 mice using fluorescence-tagged gentamicin (gentamicin-Texas-Red, GTTR) imaged by scanning laser confocal microscopy to determine the cellular distribution and intensity of GTTR fluorescence in the three semicircular canal cristae, utricular, and saccular maculae at 5 time points over 4 hours.
  
  
  RESULTS
  Low intensity GTTR fluorescence was detected at 0.5 hours as both discrete puncta and diffuse cytoplasmic fluorescence. The intensity of cytoplasmic fluorescence peaked at 3 hours, while punctate fluorescence was plateaued after 3 hours. At 0.5 and 1 hour, higher levels of diffuse GTTR fluorescence were present in transitional cells compared to hair cells and supporting cells. Sensory hair cells typically exhibited only diffuse cytoplasmic fluorescence at all time-points up to 4 hours in this study. In contrast, non-sensory cells rapidly exhibited both intense fluorescent puncta and weaker, diffuse fluorescence throughout the cytosol. The numbers and size of fluorescent puncta in dark cells and transitional cells increased over time. There is no preferential GTTR uptake by the five peripheral vestibular organs' sensory cells. Control vestibular tissues exposed to Dulbecco's phosphate-buffered saline or hydrolyzed Texas Red had negligible fluorescence.
  
  
  CONCLUSIONS
  All peripheral vestibular cells rapidly take up systemically-administered GTTR, reaching peak intensity 3 hours after injection. Sensory hair cells exhibited only diffuse fluorescence, while non-sensory cells displayed both diffuse and punctate fluorescence. Transitional cells may act as a primary pathway for trafficking of systemic GTTR from the vasculature to endolymph prior to entering hair cells.
authors: Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon, United States of America; Department of Otology and Skull Base Surgery, Eye Ear Nose and Throat Hospital,Fudan University, Shanghai, China.
authors: Jianping
authors: J
authors: Liu
authors: Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon, United States of America.
authors: Allan
authors: A
authors: Kachelmeier
authors: Department of Otology and Skull Base Surgery, Eye Ear Nose and Throat Hospital,Fudan University, Shanghai, China.
authors: Chunfu
authors: C
authors: Dai
authors: Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon, United States of America.
authors: Hongzhe
authors: H
authors: Li
authors: Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon, United States of America.
authors: Peter S
authors: PS
authors: Steyger
mesh_terms: D000818:Animals; D005456:Fluorescent Dyes / Q000737:chemistry; D005839:Gentamicins / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism*; D054777:Hair Cells, Ampulla / Q000378:metabolism; D018069:Hair Cells, Vestibular / Q000378:metabolism; D051379:Mice; D054776:Semicircular Ducts / Q000166:cytology / Q000378:metabolism; D013997:Time Factors; D014722:Vestibule, Labyrinth / Q000166:cytology* / Q000378:metabolism*
chemical_list: D005456:Fluorescent Dyes; D005839:Gentamicins