Selective gentamicin uptake by cytochemical subpopulations of guinea-pig geniculate ganglion cells

Kanamycin Damages Early Postnatal, but Not Adult Spiral Ganglion Neurons

Although aminoglycoside antibiotics such as kanamycin are widely used clinically to treat life-threatening bacterial infections, ototoxicity remains a significant dose-limiting side effect. The prevailing view is that the hair cells are the primary ototoxic target of aminoglycosides and that spiral ganglion neurons begin to degenerate weeks or months after the hair cells have died due to lack of neurotrophic support. To test the early developmental aspects of this issue, we compared kanamycin-induced hair cell and spiral ganglion pathology in rat postnatal day 3 cochlear organotypic cultures with adult whole cochlear explants. In both adult and postnatal day 3 cultures, hair cell damage began at the base of the cochleae and progressed toward the apex in a dose-dependent manner. In postnatal day 3 cultures, spiral ganglion neurons were rapidly destroyed by kanamycin prior to hair cell loss. In contrast, adult spiral ganglion neurons were resistant to kanamycin damage even at the highest concentration, consistent with in vivo models of delayed SGN degeneration. In postnatal day 3 cultures, kanamycin preferentially damaged type I spiral ganglion neurons, whereas type II neurons were resistant. Spiral ganglion degeneration of postnatal day 3 neurons was associated with upregulation of the superoxide radical and caspase-3-mediated cell death. These results show for the first time that kanamycin is toxic to postnatal day 3 spiral ganglion neurons, but not adult neurons.

Decreased Striatal Levels of PEP-19 Following MPTP Lesion in the Mouse

PEP-19 is a neuronal calmodulin-binding protein, and as such, a putative modulator of calcium regulated processes. In the present study, we used proteomics technology approaches such as peptidomics and imaging MALDI mass spectrometry, as well as traditional techniques (immunoblotting and in situ hybridization) to identify PEP-19 and, specifically, to measure PEP-19 mRNA and protein levels in an animal model of Parkinson's disease. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in mice resulted in a significant decrease in striatal PEP-19 mRNA. Capillary nano-flow liquid chromatography electrospray mass spectrometry analysis of striatal tissue revealed a significant decrease of the PEP-19 protein level. Moreover, imaging MALDI mass spectrometry also showed that PEP-19 protein was predominantly localized to the striatum of the brain tissue cross sections. After MPTP administration, PEP-19 levels were significantly reduced by 30%. We conclude that PEP-19 mRNA and protein expression are decreased in the striatum of a common animal model of Parkinson's disease. Further studies are needed to show the specific involvement of PEP-19 in the neurodegeneration seen in MPTP lesioned animals. Finally, this study has shown that the combination of traditional molecular biology techniques with novel, highly specific and sensitive mass spectrometry methods is advantageous in characterizing molecular events of many diseases, including Parkinson's disease.