Quantitative analysis of dopamine receptor messages in the mouse cochlea.

Dopamine receptor isoforms were examined in the cochlea of the CBA(J) mouse by RT-PCR analysis and nucleotide sequencing, utilizing primers specific for known dopamine receptor isoforms. Cochlear cDNA sequences corresponding to dopamine D2(long) and D3 receptors were amplified, whereas those representing D1A, D1B, D2(short), and D4 were not detected. Utilizing quantitative competitive PCR analysis, relative levels of dopamine receptor transcripts were found to be 0.002, 0.014, 0.016, and 1.000 for D2(long) cochlea, D3 cochlea, D3 brain, and D2(long) brain, respectively. In the context of previously published findings, the current work provides key quantitative evidence necessary to establish that dopamine is a neurotransmitter in the auditory inner ear.

Expression of adenylyl cyclase type I in cochlear inner hair cells.

Expression of calcium/calmodulin-activated adenylyl cyclase type I (ACI) mRNA has been determined in the cochlea and in an organ-of-Corti subdissected tissue fraction by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Amplification products of predicted size were obtained from the mouse cochlea and rat organ of Corti with nucleotide sequences corresponding to respective ACI brain transcripts. In addition, ACI template was detected in a rat inner hair cell cDNA library by PCR. Immunoreactivity to ACI has been localized within the organ of Corti to the inner hair cell, with diaminobenzidine staining found in both the cell body and in the stereocilia. Evidence, thus, has been obtained that both ACI transcript and protein are expressed in the inner hair cell, the primary mechanosensory receptor cell of the cochlea. We hypothesize that ACI is activated by calcium influx through a calcium/calmodulin interaction and that this adenytyl cyclase isoform may have a role in modulation of receptoneural afferent transmission and/or mechanosensory transduction in the cochlea.

Analysis of the human neurofibromatosis type 2 gene promoter and its expression.

OBJECTIVE: It is hypothesized that transcriptional regulation plays an important role for neurofibromatosis type 2 (NF2) expression in Schwann cells and other cell types. The objective of this study is the isolation and characterization of the transcriptional regulatory elements of the NF2 gene. STUDY DESIGN AND SETTING: A bacterial artificial chromosome library and a partial genomic DNA library were used to isolate the human NF2 gene; NF2 promoter-luciferase constructs were generated, and promoter activities were assayed. This study was carried out in a molecular biology laboratory. RESULTS: A bacterial artificial chromosome clone with an approximately 100-kilobase insert containing nearly the entire human NF2 gene has been isolated. An additional 5' NF2 sequence has also been cloned. Transient transfection experiments demonstrate strong promoter activity from the NF2 5' flanking DNA. CONCLUSIONS: The NF2 gene is approximately 100 kilobases long. Both positive and negative regulatory elements are present in NF2 5' flanking regions. SIGNIFICANCE: Better understanding of the NF2 gene and its regulation will improve molecular diagnostics and ultimately treatment of patients with NF2.

Autoimmune inner ear disease: steroid and cytotoxic drug therapy.

The goal of this study was to assess the effects of immunosuppressive therapy on hearing in patients with presumed autoimmune sensorineural hearing loss (AISNHL) and a Western blot assay positive for a 68 kD inner ear antigen. To achieve this objective, we conducted a retrospective review of 39 such patients who were treated with either a steroid alone or with a steroid followed by a cytotoxic agent. Pure-tone average (PTA) at 500 Hz, 1 kHz, 2 kHz, and 3 kHz, and speech discrimination scores (SDS) were used as objective measures of outcome. At the completion of treatment, 23 of the 39 patients (59.0%) exhibited a positive response to therapy. The steroid-only responders (n = 6) tended to demonstrate a greater improvement in PTA (14.8 vs 4.5 dB), while the cytotoxic-agent responders (n = 17) had a significantly greater improvement in SDS (26.2 vs 6.9%; p < 0.01). We conclude that most patients with AISNHL benefit from immunosuppressive therapy and that cytotoxic medications appear to improve SDS, even in some patients who have not responded to corticosteroid therapy.