As rod photoreceptors are responsible for night vision, we administered isotretinoin to rats to learn whether night blindness resulted from rod cell death or from rod functional impairment. High-dose isotretinoin was given daily for 2 months and produced systemic toxicity, but this caused no histological loss of rod photoreceptors, and rod-driven electroretinogram amplitudes were normal after prolonged dark adaptation. Additional studies showed, however, that even a single dose of isotretinoin slowed the recovery of rod signaling after exposure to an intense bleaching light, and that rhodopsin regeneration was markedly slowed. When only a single dose was given, rod function recovered to normal within several days. Rods and cones both showed slow recovery from bleach after isotretinoin in rats and in mice. HPLC analysis of ocular retinoids after isotretinoin and an intense bleach showed decreased levels of rhodopsin chromophore, 11-cis retinal, and the accumulation of the biosynthetic intermediates, 11-cis and all-trans retinyl esters. Isotretinoin was also found to protect rat photoreceptors from light-induced damage, suggesting that strategies of altering retinoid cycling may have therapeutic implications for some forms of retinal and macular degeneration.vitamin A ͉ rhodopsin ͉ rat ͉ electroretinogram ͉ rod photoreceptor V isual response in vertebrate rod photoreceptors begins when light isomerizes the rhodopsin chromophore 11-cis retinal to all-trans retinal. The bleached photopigment activates the signal transduction cascade within the rod, leading to membrane hyperpolarization and thereby to retinal visual signaling. Part of the recovery mechanism from bleach requires reconversion of the chromophore to 11-cis retinal by enzymatic reactions (the vitamin A cycle) that occur within the adjacent retinal pigment epithelium (RPE) (1). Disruption of the vitamin A cycle retards restoration of night vision sensitivity. Human dietary vitamin A deficiency can cause night blindness (2), as does dietary substitution of retinoic acid in rats (3). Alternatively, night blindness can result from death and loss of rod photoreceptors in retinal degeneration (4), including some forms involving mutations in genes necessary for retinoid processing in the RPE (5). Some isotretinoin patients report impaired visual sensitivity at night and daytime glare sensitivity, suggesting photoreceptor compromise or loss (6). We have investigated the mechanism of isotretinoin-induced night blindness by evaluating ERGs, rates of rhodopsin regeneration, and retinoid processing in rats. We also evaluated the possible therapeutic benefit of isotretinoin in the rat light-damage model of retinal degeneration. Materials and MethodsAnimals. Protocols were approved by the University of Michigan's Committee on the Use and Care of Animals. SpragueDawley male 7-wk-old albino rats (Charles River Breeding Laboratories) were housed in 12:12 h light͞dark cycle of 5 lux fluorescent white light. Rats were fed high-fat breeding chow (Formulab; PMI Feeds, St. Lou...

Spiral ganglion Schwann cells (SGSCs) myelinate spiral ganglion neurons (SGNs) and represent a potential source of neurotrophic support for SGNs. Deafening due to loss of hair cells results in gradual degeneration and death of SGNs. Successful efforts to maintain or regenerate a functional auditory nerve may depend on a healthy population of SGSCs, yet the responses of SGSCs to neural injury remain largely unknown. Here we investigate the role of p75NTR in SGSC responses to gradual denervation. Following deafening, SGSCs in the osseous spiral lamina (OSL) and, subsequently, in Rosenthal's canal (RC) expressed elevated p75NTR compared to hearing controls. p75NTR-positive cells co-labeled with S100 and RIP antibodies (Schwann cell markers), but not with anti-neurofilament. The pattern of p75NTR expression mirrored the pattern of neural degeneration, beginning in the OSL of the cochlea base and later extending into the apex. SGSCs expressed sortilin, a p75NTR co-receptor for pro-neurotrophins. Both pro-nerve growth factor (pro-NGF) and pro-brain derived neurotrophic factor (proBDNF) induced apoptosis in cultured SGSCs. Deafened animals exhibited significantly higher levels of SGSC proliferation (as measured by BrdU uptake) compared to hearing animals while total Schwann cell density remained stable, suggesting a tight regulation of SGSC proliferation and cell death. SGSCs undergoing cell division lose p75NTR expression from the cell surface and demonstrate nuclear localization of the intracellular domain (ICD), raising the possibility that p75NTR cleavage and ICD nuclear localization regulate SGSC proliferation. These results suggest that p75NTR contributes to SGSC responses to deafening and neural degeneration.

Objectives/Hypothesis: To confirm and extend reported successful treatment of posterior glottic stenosis in pediatric patients using endoscopic laser division of the posterior cricoid plate with augmentation using costal cartilage.Study Design: A retrospective chart review and case series. Methods: Medical records were examined to determine the surgical indications, outcomes, and postoperative complications of this procedure.Results: Twelve patients underwent the procedure, six females and six males, with an average age of 7 years (range, 2-26 years). There were 8/12 (67%) patients successfully decannulated after being tracheostomy dependent. There were no consistent anatomic abnormalities or surgical findings predictive of failure to decannulate. Average hospital stay was 3.6 days (range, 2-9 days). There were no deaths or other major complications; one patient had extrusion.Conclusions: Endoscopic posterior cricoid grafting is a valuable surgical option for patients with posterior glottic stenosis. The procedure is associated with low morbidity and permits decannulation in the majority of patients.

Objective-To determine the ability of ErbB inhibitors to reduce the growth of vestibular schwannoma (VS) xenografts.Methods-VS xenografts were established in the interscapular fat pad in nude mice for 4 weeks. Initially, a small cohort of animals was treated with the ErbB2 inhibitor, trastuzumab, or saline for 2 weeks. Animals also received BrdU injections to label proliferating cells. In a longer-term experiment, animals were randomized to receive trastuzumab, erlotinib (an ErbB kinase inhibitor), or placebo for 12 weeks. Tumor growth was monitored by magnetic resonance imaging (MRI) over the treatment period. Cell death was analyzed by terminal dUTP nick end labeling (TUNEL).Results-Tumors could be distinguished with T2 weighted MRI sequences. Trastuzumab significantly reduced the proliferation of VS cells compared to control (p<0.01) as determined by BrdU uptake. Control tumors demonstrated slight growth over the 12 week treatment period. Both trastuzumab and erlotinib significantly reduced the growth of VS xenografts (p<0.05). Erlotinib, but not trastuzumab, resulted in a significant increase in the percent of TUNEL-positive VS cells (p<0.01).Conclusions-In this preliminary study, the ErbB inhibitors trastuzumab and erlotinib decreased growth of VS xenografts in nude mice raising the possibility of using ErbB inhibitors in the management of patients with schwannomas, particularly those with neurofibromatosis type 2.