Ultrastructure of noise-induced cochlear synaptopathy.

Acoustic overexposure can eliminate synapses between inner hair cells (IHCs) and auditory nerve fibers (ANFs), even if hair-cell function recovers. This synaptopathy has been extensively studied by confocal microscopy, however, understanding the nature and sequence of damage requires ultrastructural analysis. Here, we used focused ion-beam scanning electron microscopy to mill, image, segment and reconstruct ANF terminals in mice, 1 day and 1 week after synaptopathic exposure (8-16 kHz, 98 dB SPL). At both survivals, ANF terminals were normal in number, but 62% and 53%, respectively, lacked normal synaptic specializations. Most non-synapsing fibers (57% and 48% at 1 day and 1 week) remained in contact with an IHC and contained healthy-looking organelles. ANFs showed a transient increase in mitochondrial content (51%) and efferent innervation (34%) at 1 day. Fibers maintaining synaptic connections showed hypertrophy of pre-synaptic ribbons at both 1 day and 1 week. Non-synaptic fibers were lower in mitochondrial content and typically on the modiolar side of the IHC, where ANFs with high-thresholds and low spontaneous rates are normally found. Even 1 week post-exposure, many ANF terminals remained in IHC contact despite loss of synaptic specializations, thus, regeneration efforts at early post-exposure times should concentrate on synaptogenesis rather than neurite extension.

Functional considerations between flap and non-flap reconstruction in oral tongue cancer: A systematic review.

This systematic review aims to provide insight into the ideal reconstructive approach of the oral tongue in oral tongue cancer (OTC) by investigating the relationship between functional outcomes and the extent of tongue resection. A structured search was performed in Ovid MEDLINE, EMBASE, and Web of Science. Studies comparing patient-reported and objective measurements of the oral tongue function between flap vs. non-flap reconstruction were included. Functional outcomes of interest were speech production, deglutition efficiency, tongue mobility, overall quality of life, and postoperative complications. A total of nine studies were retrieved and critically appraised. Patients with 20 % or less of oral tongue resected had superior swallowing efficiency and speech intelligibility with a non-flap reconstruction while patients with a tongue defect of 40-50 % self-reported or demonstrated better swallowing function with a flap repair. The data in intermediate tongue defects (20-40 % tongue resected) was inconclusive, with several studies reporting comparable functional outcomes between approaches. A longitudinal multi-institutional prospective study that rigidly controls the extent of tongue resected and subsites involved is needed to determine the percentage of tongue resected at which a flap reconstruction yields a superior functional result in OTC.