Synaptic Reorganization Response in the Cochlear Nucleus Following Intense Noise Exposure.

The cochlear nucleus, located in the brainstem, receives its afferent auditory input exclusively from the auditory nerve fibers of the ipsilateral cochlea. Noise-induced neurodegenerative changes occurring in the auditory nerve stimulate a cascade of neuroplastic changes in the cochlear nucleus resulting in major changes in synaptic structure and function. To identify some of the key molecular mechanisms mediating this synaptic reorganization, we unilaterally exposed rats to a high-intensity noise that caused significant hearing loss and then measured the resulting changes in a synaptic plasticity gene array targeting neurogenesis and synaptic reorganization. We compared the gene expression patterns in the dorsal cochlear nucleus (DCN) and ventral cochlear nucleus (VCN) on the noise-exposed side versus the unexposed side using a PCR gene array at 2 d (early) and 28 d (late) post-exposure. We discovered a number of differentially expressed genes, particularly those related to synaptogenesis and regeneration. Significant gene expression changes occurred more frequently in the VCN than the DCN and more changes were seen at 28  d versus 2 d post-exposure. We confirmed the PCR findings by in situ hybridization for Brain-derived neurotrophic factor (Bdnf), Homer-1, as well as the glutamate NMDA receptor Grin1, all involved in neurogenesis and plasticity. These results suggest that Bdnf, Homer-1 and Grin1 play important roles in synaptic remodeling and homeostasis in the cochlear nucleus following severe noise-induced afferent degeneration.

Lack of association between SNP rs3914132 of the RELN gene and otosclerosis in India.

Otosclerosis (MIM 166800) is primarily a metabolic bone disorder of the otic capsule, which leads to bony fixation of the stapedial footplate in the oval window; it is among the most common causes of acquired hearing loss. The etiology of this disease is largely unknown, although epidemiological studies suggest the involvement of both genetic and environmental factors. Recently, a reelin gene, SNP rs3914132, located in intron 2, was shown to be associated with otosclerosis in a European population. When we sequenced blood DNA samples of 85 individuals with otosclerosis and 85 controls, four SNPs of this gene: rs3914131 (P = 0.6463), rs3914132 (P = 0.1822), rs9641319 (P = 0.7371), and rs10227303 (P = 0.5669) were not significantly associated with this disease. In one familial case, a novel variant (C/T) at contig position 2923488 was found to be inherited by the proband and affected family members.

GJB2 and GJB6 gene mutations found in Indian probands with congenital hearing impairment.

Genetically caused deafness is a common trait affecting one in 1000 children and is predominantly inherited in an autosomalrecessive fashion. Several mutations in the GJB2 gene and a deletion of 342 kb in GJB6 gene (delGJB6-D13S1830) have been identified worldwide in patients with hearing impairment. In the present study, 303 nonsyndromic hearing-impaired patients (140 familial; 163 sporadic) were examined clinically and screened for mutations in GJB2 and GJB6 genes. Mutations in GJB2 gene were found in 33 (10.9%) patients of whom six (18.2%) were carriers for the mutant allele. The most frequent mutation was p.W24X accounting for 87% of the mutant alleles. In addition, six other sequence variations were identified in the GJB2 gene viz., c.IVS1+1G>A, c.167delT, c.235delC, p.W77X, p.R127H (polymorphism), p.M163V. None of the samples showed del(GJB6-D13S1830) or any point mutations in GJB6 gene.

Comparison of a novel semi-nested polymerase chain reaction (PCR) with a uniplex PCR for the detection of Acanthamoeba genome in corneal scrapings.

A semi-nested polymerase chain reaction (snPCR) was developed to improve the sensitivity of detection of Acanthamoeba sp. genome from corneal scrapings of Acanthamoeba keratitis patients. The snPCR was developed using a laboratory designed inner forward primer targeting the 450-bp product of the 18s rRNA-gene-based PCR. The snPCR was optimized using 11 Acanthamoeba sp. culture isolates and further applied onto 35 corneal scrapings from keratitis patients. The sensitivity and specificity of the snPCR was compared against conventional methods (smear and/or culture-gold standard) and the uniplex PCR described by Schroeder et al. Eleven out of the 35 corneal scrapings were positive by the gold standard and snPCR, whereas only 3 of these 11 were positive by the uniplex PCR. The clinical sensitivity and specificity of the snPCR was 100% when compared with the gold standard. DNA sequencing was performed on first round amplicons of four culture isolates and one specimen, and all of them were identified as genus Acanthamoeba when compared with the GenBank database sequences. Application of snPCR on the 11 culture isolates yielded amplicons ranging 120-160 bp in size, indicating sequence variation among the different culture isolates. The clinical sensitivity of snPCR was higher than the conventional methods and the uniplex PCR reported earlier.