Determinants of neuron-sensory receptor cell interaction during development of the inner ear

Trophic interactions are best defined as interactions between nerves and other cells which initiate or control molecular modification in the other cells and/or neurons. Interactions between the neurons which compose the statoacoustic ganglion and the cells which become the hair cells of the inner ear sensory receptors occur during the development of these sensory receptors. The hypothesis that the program for sensory hair cell cytodifferentiation is intrinsic and does not require the extrinsic stimulus of neuronal interaction to trigger its expression is presented with supporting data from in vivo, in ovo and in vitro experiments. A second hypothesis pertaining to a mechanism for the ingrowth of statoacoustic ganglion dendrites to their appropriate target sites within the inner ear is presented with accompanying in vitro experiments as supporting evidence. This hypothesis proposes that the mechanism for guiding neuritic elements of the statoacoustic ganglion to their appropriate target tissues is that attractant fields are established by the differentiating sensory epithelia of the inner ear to which nerve growth cones of ingrowing afferent neurites are attracted

Age-dependent disruption of basal lamina and extracellular matrix formation in l-proline analog treated otic explants

l-azetidine-2-carboxylic acid, LACA, a naturally occurring vegetable imino acid, can be incorporated into mammal proteins instead of proline. This incorporation has an especially inhibitive effect on collagen secretion. Exposure of embryonic mouse inner ear explants to LACA causes dysmorphogenesis and retarded differentiation, reduces the number of collagen fibrils in the perilymphatic spaces and capsules, and gives rise to a dose-dependent derangement of the basal lamina. In control specimens, both in vivo and in vitro, the inner ear epithelia had a dense contiguous basal lamina overlying a well-developed network of collagen fibrils. When the inner ears were exposed to LACA at a concentration of 150 μg per ml of medium, there was a loss of the collagen network and gaps appeared in the basal lamina. At exposure to 300 μg LACA/ml, scarcely any collagen fibrils were present and the basal lamina was disrupted in many areas, especially beneath the sensory epithelia

In vitro ototoxicity of aminoglycosides and platin derivatives. A semi-automatic assay for sensory hair cell damage in explanted rat organ of corti.

The ototoxic damage that drugs such as neomycin, kanamycin, colistin, cisplatin, transplatin and carboplatin cause on outer and inner hair cells in postnatal day 3 rat cochlear explants was investigated. Phalloidin-fluorescein conjugate-stained stereocilia bundles of sensory hair cells were quantified by video image analysis as a measurement of ototoxic effect. The video image quantification system established dose-response curves for ototoxic drugs (e.g. calculation of an IC50) and allowed comparisons between several ototoxins from the same family. This methodology provided the means to assess the efficacy of otoprotectant agents in preventing ototoxicity. Poly-l-aspartate (10-5M) and poly-l-glutamate (10-5M) protected auditory hair cells from neomycin (10-3M) toxicity while reduced glutathione (10-3M) provided protection against cisplatin (10-4M)-induced hair cell damage

A peptide inhibitor of c-Jun N-terminal kinase protects against both aminoglycoside and acoustic trauma-induced auditory hair cell death and hearing loss.

Hearing loss can be caused by a variety of insults, including acoustic trauma and exposure to ototoxins, that principally effect the viability of sensory hair cells via the MAP kinase (MAPK) cell death signaling pathway that incorporates c-Jun N-terminal kinase (JNK). We evaluated the otoprotective efficacy of D-JNKI-1, a cell permeable peptide that blocks the MAPK-JNK signal pathway. The experimental studies included organ cultures of neonatal mouse cochlea exposed to an ototoxic drug and cochleae of adult guinea pigs that were exposed to either an ototoxic drug or acoustic trauma. Results obtained from the organ of Corti explants demonstrated that the MAPK-JNK signal pathway is associated with injury and that blocking of this signal pathway prevented apoptosis in areas of aminoglycoside damage. Treatment of the neomycin-exposed organ of Corti explants with D-JNKI-1 completely prevented hair cell death initiated by this ototoxin. Results from in vivo studies showed that direct application of D-JNKI-1 into the scala tympani of the guinea pig cochlea prevented nearly all hair cell death and permanent hearing loss induced by neomycin ototoxicity. Local delivery of D-JNKI-1 also prevented acoustic trauma-induced permanent hearing loss in a dose-dependent manner. These results indicate that the MAPK-JNK signal pathway is involved in both ototoxicity and acoustic trauma-induced hair cell loss and permanent hearing loss. Blocking this signal pathway with D-JNKI-1 is of potential therapeutic value for long-term protection of both the morphological integrity and physiological function of the organ of Corti during times of oxidative stress

Dexamethasone treatment of tumor necrosis factor-alpha challenged organ of Corti explants activates nuclear factor kappa B signaling that induces changes in gene expression that favor hair cell survival

The objective was to determine the role of nuclear factor kappa B (NFκB) in dexamethasone base (DXMb) protection of auditory hair cells from tumor necrosis factor-alpha (TNFα)-induced loss on gene expression and cell signaling levels. Organ of Corti (OC) explants from 3-day-old rats were cultured under one of the following conditions: (1) media only—no treatment; (2) media+TNFα; (3) media+TNFα+DXMb; (4) media+TNFα+DXMb+NFκB-Inhibitor (NFκB-I); or (5) media+TNFα+DXMb+NFκBI-Scrambled control (NFκBI-C). A total of 60 organ of Corti explants (OC) were stained with FITC-Phalloidin after 96 h in culture (conditions 1–5) for hair cell counts and imaging of surface characteristics. A total of 108 OC were used for gene expression studies (i.e. B-actin, Bax, Bcl-2, Bcl-xl, and TNFR1) after 0, 24, or 48 h in vitro (conditions 1–4). A total of 86 OC were cultured (conditions 1–3) for 48 h, 36 of which were used for phosphorylated NFκB (p-NFκB) ELISA studies and 50 for whole mount anti-p-NFκB immunostain experiments. TNFα+DXMb exposed cultures demonstrated significant upregulation in anti-apoptotic Bcl-2 and Bcl-xl genes and downregulation in pro-apoptotic Bax gene expression; DXMb treatment of TNFα explants also lowered the Bax/Bcl-2 ratio and inhibited TNFR1 upregulation. After inhibiting NFκB activity with NFκB-I, the gene expression profile following TNFα+DXMb treatment now mimics that of TNFα-challenged OC explants. The levels of p-NFκB and the degree of nuclear translocation are significantly greater in TNFα+DXMb exposed OC explants than observed in the TNFα and control groups in the middle+basal turns of OC explants. These findings were supported by the results of the hair cell counts and the imaging results obtained from the whole mount OC specimens. DXMb protects against TNFα-induced apoptosis of auditory hair cells in vitro via activation of NFκB signaling in hair cell nuclei, and regulation of the expression levels of anti- and pro-apoptotic genes and a pro-inflammatory gene. ▶TNFα can initiate programmed cell death in rat organ of Corti explants. ▶DXM protects against TNFα-induced apoptosis of rat auditory hair cells. ▶DXM treatment promotes activation and nuclear translocation of NFκB. ▶NFκB activation results in changes in gene expression that favor hair cell survival

Recht in Context: Naar een brede academische vorming van juristen

Dit artikel is een pleidooi voor een academische verbreding van de universitaire rechtenopleiding, waarbij het recht wordt bestudeerd in een bredere, sociale, morele en theoretische context. De rechtenopleiding dient meer ruimte te bieden aan reflectie en verbreding en meer gebruik te maken van alternatieve en activerende werkvormen, die studenten stimuleren zelf na te denken en het recht vanuit verschillende perspectieven te zien. Daarmee is ook de rechtspraktijk gediend. De jurist van morgen is geen juridisch specialist, maar een breed geschoolde academicus die het recht in een ruimere context kan plaatsen en kan meedenken over de wetenschappelijke en maatschappelijke uitdagingen van de toekomst

Blocking c-Jun-N-terminal kinase signaling can prevent hearing loss induced by both electrode insertion trauma and neomycin ototoxicity.

Neomycin ototoxicity and electrode insertion trauma both involve activation of the mitogen activated protein kinase (MAPK)/c-Jun-N-terminal kinase (JNK) cell death signal cascade. This article discusses mechanisms of cell death on a cell biology level (e.g. necrosis and apoptosis) and proposes the blocking of JNK signaling as a therapeutic approach for preventing the development of a permanent hearing loss that can be initiated by either neomycin ototoxicity or electrode insertion trauma. Blocking of JNK molecules incorporates the use of a peptide inhibitor (i.e. D-JNKI-1), which is specific for all three isoforms of JNK and has been demonstrated to prevent loss of hearing following either electrode insertion trauma or loss of both hearing and hair cells following exposure to an ototoxic level of neomycin. We present previously unpublished results that control for the effect of perfusate washout of aminoglycoside antibiotic by perfusion of the scala tympani with an inactive form of D-JNKI-1 peptide, i.e. JNKI-1(mut) peptide, which was not presented in the original J. Neurosci. article that tested locally delivered D-JNKI-1 peptide against both noise- and neomycin-induced hearing loss (i.e. Wang, J., Van De Water, T.R., Bonny, C., de Ribaupierre, F., Puel, J.L., Zine, A. 2003a. A peptide inhibitor of c-Jun N-terminal kinase protects against both aminoglycoside and acoustic trauma-induced auditory hair cell death and hearing loss. J. Neurosci. 23, 8596-8607). D-JNKI-1 is a cell permeable peptide that blocks JNK signaling at the level of the three JNK molecular isoforms, which when blocked prevents the increases in hearing thresholds and the loss of auditory hair cells. This unique therapeutic approach may have clinical application for preventing: (1) hearing loss caused by neomycin ototoxicity; and (2) the progressive component of electrode insertion trauma-induced hearing loss