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Edwin W Rubel

Publications and source records attributed to Edwin W Rubel.

32 records · Page 2Linked to original sources
PubMed2003

Timing and topography of nucleus magnocellularis innervation by the cochlear ganglion.

This series of experiments examined the arrival and organization of cochlear nerve axons in the primary auditory brainstem nucleus, nucleus magnocellularis (NM), of the chick. DiI and DiD were injected into the cochlear nerve, cochlear ganglion, and basilar papilla (i.e., avian cochlea) in fixed tissue and labeled axons were studied in NM and its vicinity. Cochlear nerve axons first penetrate NM between stages 29 (E6) and 36 (E10). Axons penetrate NM in a middle-to-posterior-to-anterior developmental sequence; the anterior, high-frequency region of NM receives axons last. When cochlear nerve axons arrive in the NM, they are already organized in a topographic map related to the position of their cell bodies along the basilar papilla, foreshadowing the tonotopic mapping observed between NM and the basilar papilla later in development. Evidence of a topographic map was also observed in the other primary auditory brainstem nucleus, nucleus angularis. These results indicate that topographic mapping of position (and ultimately characteristic frequency) between the basilar papilla and NM is established as cochlear nerve axons arrive in the NM prior to the onset of synaptic activity. .

Animals↗
PubMed2003

Ultrastructural analysis of [3H]thymidine-labeled cells in the rat utricular macula.

Ototoxic drugs stimulate cell proliferation in adult rat vestibular sensory epithelia, as does the infusion of transforming growth factor alpha (TGFalpha) plus insulin. We sought to determine whether new hair cells can be regenerated by means of a mitotic pathway. Previously, studies have shown that the nuclei of some newly generated cells are located in the lumenal half of the sensory epithelium, suggesting that some may be newly generated sensory hair cells. The aim of this study was to examine the ultrastructural characteristics of newly proliferated cells after TGFalpha stimulation and/or aminoglycoside damage in the utricular sensory epithelium of the adult rat. The cell proliferation marker tritiated-thymidine was infused, with or without TGFalpha plus insulin, into the inner ears of normal or aminoglycoside-damaged rats for 3 or 7 days by means of osmotic pumps. Autoradiographic techniques and light microscopy were used to identify cells synthesizing DNA. Sections with labeled cells were re-embedded, processed for transmission electron microscopy, and the ultrastructural characteristics of the labeled cells were examined. The following five classes of tritiated-thymidine labeled cells were identified in the sensory epithelium: (1) labeled cells with synaptic specializations that appeared to be newly generated hair cells, (2) labeled supporting cells, (3) labeled leukocytes, (4) labeled cells that we have classified as "active cells" in that they are relatively nondescript but contain massive numbers of polyribosomes, and (5) labeled degenerating hair cells. These findings suggest that new hair cells can be generated in situ by means of a mitotic mechanism in the vestibular sensory epithelium of adult mammals.

Acoustic Maculae↗
PubMed2003

Neomycin-induced hair cell death and rapid regeneration in the lateral line of zebrafish (Danio rerio).

Mechanoreceptive hair cells are extremely sensitive to aminoglycoside antibiotics, including neomycin. Hair cell survival was assessed in larval wild-type zebrafish lateral line neuromasts 4 h after initial exposure to a range of neomycin concentrations for 1 h. Each of the lateral line neuromasts was scored in live fish for the presence or absence of hair cells using the fluorescent vital dye DASPEI to selectively label hair cells. All neuromasts were devoid of DASPEI-labeled hair cells 4 h after 500 microM neomycin exposure. Vital DASPEI staining was proportional to the number of hair cells per neuromast identified in fixed larvae using immunocytochemistry for acetylated tubulin and phalloidin labeling. The time course of hair cell regeneration in the lateral line neuromasts was also analyzed following neomycin-induced damage. Regenerated hair cells were first observed using live DASPEI staining 12 and 24 h following neomycin treatment. The potential role of proliferation in regenerating hair cells was analyzed. A 1 h pulse-fix protocol using bromodeoxyuridine (BrdU) incorporation was used to identify S-phase cells in neuromasts. BrdU incorporation in neomycin-damaged neuromasts did not differ from control neuromasts 4 h after drug exposure but was dramatically upregulated after 12 h. The proliferative cells identified during a 1 h period at 12 h after neomycin treatment were able to give rise to new hair cells by 24-48 h after drug treatment. The results presented here provide a standardized preparation for studying and identifying genes that influence vertebrate hair cell death, survival, and regeneration following ototoxic insults.

Acetylation↗
PubMed2003

Developmental differences in susceptibility to neomycin-induced hair cell death in the lateral line neuromasts of zebrafish (Danio rerio).

Mechanosensory hair cells of the inner ear are susceptible to death when exposed to a variety of drugs including aminoglycoside antibiotics. During avian and mammalian development, there is a period of relative insensitivity to aminoglycoside-induced hair cell death. This study was designed to test the hypothesis that zebrafish (Danio rerio) have developmental differences in sensitivity to aminoglycoside-induced hair cell death in the lateral line neuromasts. Larval zebrafish of various ages were exposed to several concentrations of neomycin, and their hair cells were examined using the potentiometric vital dye, DASPEI. Results indicate that zebrafish larvae aged 4 days post-fertilization are relatively insensitive to aminoglycoside-induced hair cell death compared to older fish. Thus zebrafish hair cells show developmental differences in sensitivity to aminoglycoside-induced death similar to those reported for inner ear hair cells of birds and mammals.

Analysis of Variance↗
PubMed2003

Hair cell regeneration: winging our way towards a sound future.

The discovery of hair cell regeneration in the inner ear of birds provides new optimism that there may be a treatment for hearing and balance disorders. In this review we describe the process of hair cell regeneration in birds; including restoration of function, recovery of perception and what is currently known about molecular events, such as growth factors and signalling systems. We examine some of the key recent findings in both birds and mammals.

Animals↗
PubMed2002

Hair cell death in the avian basilar papilla: characterization of the in vitro model and caspase activation.

Caspases are a family of proteases that have been implicated as key mediators of cell death. Although nonspecific inhibition of caspase activation has been reported to prevent mammalian sensory hair cell death, the exact roles of individual caspases during hair cell death are unclear. In other systems, the activation of initiator caspases, such as caspase-8 and caspase-9, can lead to the activation of the effector caspase-3. We have begun to systematically characterize hair cell death in an in vitro system by examining the activation of these specific caspases in degenerating hair cells after acutely damaging the whole avian basilar papilla with gentamicin. Basilar papillae (BP) displayed a dose-dependent hair cell loss after a 24-h treatment with gentamicin at concentrations of 0.1, 0.5, and 2.0 mM. When treated with 0.5 mM gentamicin for 6, 12, or 24 h, hair cells first began to degenerate in the basal third of the BP and damage progressed apically. Supplementation of z-VAD-fmk, a general caspase inhibitor, provided short-term protection against gentamicin-induced hair cell death. Treatment with gentamicin for 6 or 12 h promoted the expression of active caspase-3 and active caspase-9 in many hair cells along the BP as shown by immunohistochemistry. At these time-points, specific fluorescent-labeled peptide substrates detected more active caspase-3, caspase-8, and caspase-9 in gentamicin-treated hair cells relative to controls. Our data indicate that auditory hair cells degenerate as a result of gentamicin exposure in a caspase-dependent manner. Specifically, the upstream caspases, caspase-8 and caspase-9, and the downstream caspase-3 are activated in aminoglycoside-damaged hair cells.

Animals↗
PubMed2002

Expression of EphB receptors and EphrinB ligands in the developing chick auditory brainstem.

Nucleus magnocellularis (NM) in the avian auditory brainstem receives auditory input from nerve the VIIIth and projects bilaterally to nucleus laminaris (NL). This projection preserves binaural segregation in that ipsilateral NM projects to dorsal dendrites of NL and contralateral NM projects to ventral dendrites of NL. We have begun to examine the molecular signals that influence segregation of inputs onto discrete regions of NL cells. We previously showed that the Eph receptor, EphA4, is expressed selectively in the dorsal NL neuropil from embryonic day (E) 9 to E11, when NM axons grow into the NL neuropil. This asymmetric distribution suggests that EphA4 acts as a guidance molecule during binaural segregation. We report here on the developmental changes in the expression of two other Eph receptors, EphB2 and EphB5, and two ligands, ephrin-B1 and ephrin-B2, in the chick auditory brainstem. These proteins are expressed in the auditory nuclei during the maturation of the NM-NL projection. EphB2, EphB5, and ephrin-B1 are expressed in dorsal and ventral NL neuropil and at the midline of the brainstem at E10-E12. At this age, ephrin-B2, a ligand for EphB receptors and for EphA4, is expressed in NL cell bodies and NM-NL axons. The expression of these proteins diminishs in the posthatch ages examined. These results suggest that several members of the Eph family are involved in maturation of the nuclei and their projections. Moreover, ephrin-B2 in growing axons may interact with the asymmetrically expressed EphA4 during the establishment of binaural segregation.

Animals↗
PubMed2002

Caspase activation in hair cells of the mouse utricle exposed to neomycin.

Aminoglycoside exposure results in the apoptotic destruction of auditory and vestibular hair cells. This ototoxic hair cell death is prevented by broad-spectrum caspase inhibition. We have used in situ substrate detection, immunohistochemistry, and specific caspase inhibitors to determine which caspases are activated in the hair cells of the adult mouse utricle in response to neomycin exposure in vitro. In addition, we have examined the hierarchy of caspase activation. Our data indicate that both upstream caspase-8 and upstream caspase-9, as well as downstream caspase-3 are activated in hair cells exposed to neomycin. The inhibition of caspase-9-like activity provided significant protection of hair cells exposed to neomycin, whereas the inhibition of caspase-8-like activity was not effective in preventing neomycin-induced hair cell death. In addition, caspase-9 inhibition prevented the activation of downstream caspase-3, whereas the inhibition of caspase-8 did not. These data indicate that caspase-9 is the primary upstream caspase mediating neomycin-induced hair cell death in this preparation.

Amino Acid Chloromethyl Ketones↗
PubMed2002

Vocal memory and learning in adult Bengalese Finches with regenerated hair cells.

Critical learning periods are common in vertebrate development. In many birds, song learning is limited by a critical period; juveniles copy songs from adult birds by forming memories of those songs during a restricted developmental period and then using auditory feedback to practice their own vocalizations. Adult songs are stable over time regardless of exposure to other birds, but auditory feedback is required for the maintenance of stable adult song. A technique was developed to reversibly deafen Bengalese Finches by destruction and regeneration of inner ear auditory hair cells. With this approach, we asked two questions about the plasticity of song information stored in the adult brain. First, do adult birds store memories or "templates" of their songs that exist independent of auditory reinforcement? Such memories could be used to control vocal output by acting as fixed models of song to which ongoing vocalizations are matched. Second, can adult song learning, which does not normally occur in this species, be induced by removing and then restoring hearing? Studying changes in adult song behavior during hair cell loss and regeneration revealed two findings: (1) adult birds store memories or templates of their songs that exist independent of auditory input and can be used to restore normal vocal behavior when hearing is restored; (2) under experimental circumstances, adult birds can be induced to acquire song material from other birds. Results suggest that, in Bengalese Finches, the degree of behavioral and neural plasticity in juvenile and adult birds may be less distinct that previously thought.

Animals↗
PubMed2002

bcl-2 Overexpression eliminates deprivation-induced cell death of brainstem auditory neurons.

Deprivation of afferent input in young animals results in transneuronal degeneration of postsynaptic sensory neurons in a variety of species and sensory pathways. Transneuronal degeneration is generally not seen in adult animals. The cellular and molecular basis for this dramatic developmental change in susceptibility is not understood. One possibility is that genes involved in the apoptotic process are involved in determining cell death or survival after afferent deprivation. To further investigate this possibility, we performed unilateral cochlear ablation on wild-type and bcl-2-overexpressing mice at a variety of ages. In postnatal day 5 (P5) or P8 wild-type mice, cochlea removal resulted in a 54% or 31% neuronal loss in the anteroventral cochlear nucleus (AVCN), respectively. When the same manipulation is performed on a P30 mouse, no loss of AVCN neurons occurs. This confirmed a rather abrupt change in the sensitivity to disruption of afferent input, a critical period. However, in littermates expressing bcl-2 under a neuron-specific enolase promoter, no significant loss of AVCN neurons was observed at any age after unilateral cochlear ablation. Furthermore, wild-type mice demonstrate rapid expression of activated caspase-3 in AVCN neurons within hours of deafferentation, whereas bcl-2-overexpressing mice do not. This suggests that bcl-2 can influence cell survival after removal of afferent input during the critical period and is consistent with the hypothesis that caspase-3 is one effector of cell death under these circumstances. These data are the first to indicate that known apoptotic mediators can play a role in central neuronal plasticity in models of afferent deprivation.

Age Factors↗
PubMed2002

Auditory system development: primary auditory neurons and their targets.

The neurons of the cochlear ganglion transmit acoustic information between the inner ear and the brain. These placodally derived neurons must produce a topographically precise pattern of connections in both the inner ear and the brain. In this review, we consider the current state of knowledge concerning the development of these neurons, their peripheral and central connections, and their influences on peripheral and central target cells. Relatively little is known about the cellular and molecular regulation of migration or the establishment of precise topographic connection to the hair cells or cochlear nucleus (CN) neurons. Studies of mice with neurotrophin deletions are beginning to yield increasing understanding of variations in ganglion cell survival and resulting innervation patterns, however. Finally, existing evidence suggests that while ganglion cells have little influence on the differentiation of their hair cell targets, quite the opposite is true in the brain. Ganglion cell innervation and synaptic activity are essential for normal development of neurons in the cochlear nucleus.

Animals↗
PubMed2002

Effects of age on the distortion product otoacoustic emission growth functions.

Age-related hearing loss (presbycusis) is thought to result from age-related degeneration (aging) of the cochlea plus the cumulative effects of extrinsic damage (noise and other ototoxic agents) and intrinsic disorders (e.g. systemic diseases). Previous studies have implicated dysfunction of the hair cells (sensory presbycusis) as the principal mechanism of age-related hearing loss. However, recent evidence from quiet-reared gerbils suggests that cochlear aging results primarily from atrophy of the stria vascularis, which is associated with diminished endocochlear potential (EP), spiral ganglion atrophy, and a relatively flat audiometric loss, termed metabolic presbycusis. Because it is not currently possible to measure EP directly in the clinical setting, we wondered if cochlear metabolic dysfunction might be evidenced indirectly from existing clinical tests, specifically, the input-output (IO) growth function of the distortion product (DP) otoacoustic emissions in relation to behavioral hearing threshold levels (HTL). We anticipated finding discordance between the IO functions and HTL with either a greater decline with age in HTL than in IO functions if an age-related metabolic dysfunction of the cochlea was operant, or a greater loss of IO function than HTL if outer hair cell dysfunction was the dominant pathology. To address this supposition we analyzed existing auditory data from a large cohort of adults to determine the change with age in three aspects of the DP IO function: area under the curve, threshold, and slope. The analyses demonstrated a greater effect of age on HTL than on the DP IO measures. This effect supports the hypothesis that strial dysfunction is a substantive factor in cochlear aging. The etiology and mechanisms for this dysfunction are conjectural at present.

Adult↗
PubMedDate not supplied

Afferent regulation of neuron number in the cochlear nucleus: cellular and molecular analyses of a critical period.

The neurons of the cochlear nucleus are dependent on input from the auditory nerve for survival during a critical period of development in a variety of vertebrate species. The molecules that underlie this age-dependent vulnerability to deafferentation are for the most part unknown, although recent studies have begun to yield interesting candidate genes. Here, we review the studies that originally described the presence of afferent dependent neuron survival in the cochlear nucleus and the age-dependency of this effect, as well as more recent work that seeks to understand the mechanisms underlying the neuron loss that occurs and the basis of this critical period. While much of the past work on cochlear nucleus neuronal susceptibility has been conducted looking at one or two genes at a time, recent advances in genomics make it possible to screen tens of thousands of genes while looking for candidate genes that are determinants of the critical period response to afferent deprivation.

Afferent Pathways↗