Dexamethasone's effect in the retrocochlear auditory centers of a noise-induced hearing loss mouse model.

OBJECTIVE: Examine prophylactic effects of dexamethasone (Dex) in retrocochlear auditory centers in a noise-induced hearing loss (NIHL) mouse model. STUDY DESIGN: Prospective animal study. SETTING: Academic research center. SUBJECTS AND METHODS: Thirty-two mice were divided into control, untreated, saline (2 and 10 µL), and Dex (2 and 10 µL) groups. Dex was applied intratympanically (IT) prior to 110 to 120 dB noise over 6 hours. Auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) were performed at 1 day, 1 week, 1 month, and 2 months. Retrocochlear neuronal cells were labeled with FluoroGold and counted. Hair cells of the organ of Corti were labeled with fluorescein isothiocyanate-conjugated phalloidin and counted. RESULTS: Auditory brainstem response thresholds of untreated NIHL, 2 and 10 µL IT saline, and 2 and 10 µL IT Dex were 21.7 ± 2.9 dB, 20 ± 0 dB, 20 ± 5 dB, 18.3 ± 2.9 dB, and 18.3 ± 2.9 dB, respectively. At 1-day post NIHL, all groups demonstrated profound hearing loss. At 2 weeks, 2 and 10 µL Dex thresholds improved to 47.5 ± 3.5 dB and 48.8 ± 18.9 dB, respectively, whereas the untreated and saline groups remained unchanged. Mean cell counts in the cochlear nucleus (CN), superior olivary complex (SOC), and lateral lemniscus (LL) of control mice were 1483 ± 190, 2807 ± 67, and 112 ± 20, respectively. After acoustic trauma, the untreated, saline, and 2 µL Dex groups yielded decreased neuronal counts in the SOC. In contrast, the 10 µL Dex group had 1883 ± 186 (CN), 2774 ± 182 (SOC), and 166 ± 18 (LL). There was sporadic hair cell loss for all traumatized groups. CONCLUSION: Our NIHL mouse model demonstrated dose-dependent Dex pretreatment otoprotection against NIHL with preservation of retrocochlear auditory neurons.

Analysis of speech perception outcomes among patients receiving cochlear implants with auditory neuropathy spectrum disorder.

OBJECTIVE: Cochlear implantation (CI) is currently the main device option for children with auditory neuropathy spectrum disorder (ANSD) who receive minimal benefit from conventional amplification. This study examines potential prognostic factors associated with post-CI speech performance in this population. STUDY DESIGN: Retrospective chart review. SETTING: Academic center. PATIENTS: ANSD patients without inner ear abnormalities implanted with unilateral or bilateral CI between 1998 and 2010. INTERVENTION: CI and speech perception testing. MAIN OUTCOME MEASURE: Post-CI speech perception testing at 50 dBHL. "Good" performers were defined as patients with greater than 70% speech perception and "poor" performers less than 70%. Medical comorbidity, educational information, and social history were gathered. RESULTS: Twenty-seven patients met inclusion criteria. Mean age at diagnosis, first CI, and second CI in good performers were 2.5 ± 3.4, 3.4 ± 3.6, and 3.8 ± 1.6 years, respectively, compared with 9.7 ± 7.8, 14.8 ± 12.9, and 8.9 ± 3.5 in poor performers. Mean speech perception after first and second implantation for good performers trended at 85% and 90%, respectively, compared with 36% and 73% in poor performers. Better pre-CI PTA correlated with better post-CI speech perception. Patients with bilateral CI demonstrated better speech perception outcomes compared with unilateral CI use. Poor performers had later age of implantation, lower socioeconomic status, and lack of family support compared with good performers. CONCLUSION: ANSD patients who do not benefit from conventional amplification do well when implanted at a young age with proper access to education and habilitation training. Medical, social, and economic information may be helpful in predicting positive outcomes.

Specific targeting of retrocochlear auditory pathway for optimal pharmacotherapy delivery using a mouse model.

HYPOTHESIS: Optimal pharmacotherapy entails a safe delivery method that specifically targets auditory structure(s) of interest. A retrocochlear neuronal tracer may enable comparison of various pharmacotherapy delivery methods and localization of the drug along the auditory pathway. BACKGROUND: Sensorineural hearing loss (SNHL) can involve cochlear hair cell or neural cell death, which often is accompanied by secondary degeneration of central auditory neurons. Targeting the precise location of nerve degeneration is important for treatment success. To be clinically relevant, the method of drug delivery must be safe and reliable while being maximally absorbed by the relevant inner ear structures of interest. METHODS: We compared 3 methods of FluoroGold (FG) delivery, a retrograde neuronal tracer, in delineating the retrocochlear auditory pathway using a normal-hearing strain of CBA mice. FG was delivered either intratympanic (IT), intracochlear (IC), or through the round window (RW). Five days after FG injection, mice were sacrificed for cell counts in the cochlear nucleus (CN), superior olivary complex (SOC), and the lateral lemniscus (LL). RESULTS: Although neurons in the CN and SOC were abundantly labeled by FG in all 3 injection methods, the IT method was the most reproducible and specific. The average cells for the CN, SOC, and LL were 851 ± 121, 2629 ± 367, and 112 ± 30, respectively. Accurate cell counts could not be established for the IC and RW injection methods because of nonspecific cell staining. Only 1 of the 5 IC-injected mice had specific labeling along the retrocochlear auditory pathway. Cell counts for the single mouse with specific IC staining in the CN, SOC, and LL were 177, 1839, and 56, respectively. Similarly, 2 of the 5 RW-injected mice had specific labeling, whereas the rest were nonspecific. The average cell counts for the 2 mice with specific labeling in the CN, SOC, and LL was 723.5 ± 580.0, 2173.5 ± 998.0, and 131.5 ± 8.0, respectively. CONCLUSION: The IT injection method resulted in reproducible, specific staining of neuronal cells along the retrocochlear auditory pathway compared with the RW or IC route of delivery.

Hypoxia-inducible factor-1 (HIF-1) is involved in the regulation of hypoxia-stimulated expression of monocyte chemoattractant protein-1 (MCP-1/CCL2) and MCP-5 (Ccl12) in astrocytes.

BACKGROUND: Neuroinflammation has been implicated in various brain pathologies characterized by hypoxia and ischemia. Astroglia play an important role in the initiation and propagation of hypoxia/ischemia-induced inflammation by secreting inflammatory chemokines that attract neutrophils and monocytes into the brain. However, triggers of chemokine up-regulation by hypoxia/ischemia in these cells are poorly understood. Hypoxia-inducible factor-1 (HIF-1) is a dimeric transcriptional factor consisting of HIF-1alpha and HIF-1beta subunits. HIF-1 binds to HIF-1-binding sites in the target genes and activates their transcription. We have recently shown that hypoxia-induced expression of IL-1beta in astrocytes is mediated by HIF-1alpha. In this study, we demonstrate the role of HIF-1alpha in hypoxia-induced up-regulation of inflammatory chemokines, human monocyte chemoattractant protein-1 (MCP-1/CCL2) and mouse MCP-5 (Ccl12), in human and mouse astrocytes, respectively. METHODS: Primary fetal human astrocytes or mouse astrocytes generated from HIF-1alpha+/+ and HIF-1alpha+/- mice were subjected to hypoxia (<2% oxygen) or 125 muM CoCl2 for 4 h and 6 h, respectively. The expression of HIF-1alpha, MCP-1 and MCP-5 was determined by semi-quantitative RT-PCR, western blot or ELISA. The interaction of HIF-1alpha with a HIF-1-binding DNA sequence was examined by EMSA and supershift assay. HIF-1-binding sequence in the promoter of MCP-1 gene was cloned and transcriptional activation of MCP-1 by HIF-1alpha was analyzed by reporter gene assay. RESULTS: Sequence analyses identified HIF-1-binding sites in the promoters of MCP-1 and MCP-5 genes. Both hypoxia and HIF-1alpha inducer, CoCl2, strongly up-regulated HIF-1alpha expression in astrocytes. Mouse HIF-1alpha+/- astrocytes had lower basal levels of HIF-1alpha and MCP-5 expression. The up-regulation of MCP-5 by hypoxia or CoCl2 in HIF-1alpha+/+ and HIF-1alpha+/- astrocytes was correlated with the levels of HIF-1alpha in cells. Both hypoxia and CoCl2 also up-regulated HIF-1alpha and MCP-1 expression in human astrocytes. EMSA assay demonstrated that HIF-1 activated by either hypoxia or CoCl2 binds to wild-type HIF-1-binding DNA sequence, but not the mutant sequence. Furthermore, reporter gene assay demonstrated that hypoxia markedly activated MCP-1 transcription but not the mutated MCP-1 promoter in transfected astrocytes. CONCLUSION: These findings suggest that both MCP-1 and MCP-5 are HIF-1 target genes and that HIF-1alpha is involved in transcriptional induction of these two chemokines in astrocytes by hypoxia.