Course Of Degeneration Research Articles

Changes in stiffness of the extracellular and pericellular matrix in the anulus fibrosus of lumbar intervertebral discs over the course of degeneration.

Analogous to articular cartilage, changes in spatial chondrocyte organisation have been proposed to be a strong indicator for local tissue degeneration in the intervertebral disc (IVD). While a progressive structural and functional degradation of the extracellular (ECM) and pericellular (PCM) matrix occurs in osteoarthritic cartilage, these processes have not yet been biomechanically elucidated in the IVD. We aimed to evaluate the local stiffness of the ECM and PCM in the anulus fibrosus of the IVD on the basis of local chondrocyte spatial organisation. Using atomic force microscopy, we measured the Young's modulus of the local ECM and PCM in human and bovine disc samples using the spatial chondrocyte patterns as an image-based biomarker. By measuring tissue from 31 patients and six bovine samples, we found a significant difference in the elastic moduli (E) of the PCM in clusters when compared to the healthy patterns single cells (p = 0.029), pairs (p = 0.016), and string-formations (p = 0.010). The ECM/PCM ratio ranged from 0.62-0.89. Interestingly, in the bovine IVD, the ECM/PCM ratio of the E significantly varied (p = 0.002) depending on the tissue origin. Overall the reduced E in clusters demonstrates that cluster formation is not only a morphological phenomenon describing disc degeneration, but it marks a compromised biomechanical functioning. Immunohistochemical analyses indicate that collagen type III degradation might be involved. This study is the first to describe and quantify the differences in the E of the ECM in relation to the PCM in the anulus fibrosus of the IVD by means of atomic force microscopy on the basis of spatial chondrocyte organisation.

Role of Müller cells in cone mosaic rearrangement and retinal remodelling in photoreceptor degenerations

AbstractPhotoreceptor degenerative diseases (e.g., retinitis pigmentosa or age‐related macular degeneration) are currently one of the leading causes of irreversible blindness in the world. Although their pathophysiological mechanisms may vary, they all share some features such as initial photoreceptor loss associated with glial activation and subsequent retinal remodelling. It is well known that glial activation is an early feature of photoreceptor degenerations that is involved in retinal remodelling, which, in turn, is thought to be the cause of the secondary death of the retinal ganglion cells. The mammalian retina contains three types of glial cells. Two types of macroglial cells: astrocytes and Müller cells, and microglial cells. Of them, Müller cells appear to be involved in the reorganization of the photoreceptor mosaic in empty rings of photoreceptor degeneration in the early stages of photoreceptor loss. Müller cells are the principal glial cells in the retina with a wide range of physiological and retinal structural support functions. The basic morphological scheme of Müller cells consists of a soma located in the inner nuclear layer from which an inner and an outer trunk emerge. The inner trunk contributes to the formation of the inner limiting membrane, and the outer trunk divides into complex rootlets spanning photoreceptor nuclei and finally forming the outer limiting membrane of the retina. In the early stages of photoreceptor degeneration, macroglial cell reactivity, namely increased expression of glial fibrillary acidic protein (GFAP) and Müller cells hypertrophy, leads to the formation of a glial scar or glial seal by hypertrophic Müller cell processes in the outer retina that may be related to the formation of empty rings of photoreceptor degeneration. Interestingly, Müller cells extend their external processes horizontally and radially within the rings of photoreceptor degeneration, filling the empty space left by dead photoreceptors. These rings become larger as photoreceptor loss increases, which suggests that they are the result of photoreceptor loss. As rings increase in size and, eventually, merge, the increased expression in the processes of Müller cells continues in the periphery of the rings. Perhaps in an attempt to complete the glial seal to isolate the remnant of the neural retina from the retinal pigment epithelium and choroid which, in turn, may represent a physical barrier to axonal regrowth and migration and therefore may impede the success of therapies aimed at replacing or substituting photoreceptors. Indeed, as photoreceptor loss progresses, the glial sea is more evident, covering large areas of the retina. Although the exact function of the glial seal is not known at this stage, it is thought that it may have a mechanical function in conferring some stability to the retina during the course of degeneration, but also a protective function, since in the later stages of retinal remodelling, focal gaps in the glial seal may allow the migration of retinal pigment epithelium cells to the inner retina, triggering a series of progressive events that eventually cause retinal ganglion cell death.

Regulation of perineuronal net components in the synaptic bouton vicinity on lumbar α-motoneurons in the rat after spinalization and locomotor training: New insights from spatio-temporal changes in gene, protein expression and WFA labeling

Chondroitin sulfate proteoglycans (CSPGs) consist of core proteins and glycosaminoglycan side chains. Tenascins, and hyaluronan and proteoglycan link protein 1 (HAPLN), link CSPGs with a hyaluronan backbone to constitute perineuronal nets (PNNs), which ensheath preferentially highly active neurons to maintain architecture and stabilize synapses, but restrict repair plasticity. Spinal cord injury increases CSPG core protein levels in the lesion proximity, limiting permissiveness of the extracellular milieu for fiber regrowth, however regulation of PNNs structure in the vicinity of distant α-motoneurons (MNs) in the course of degeneration and reorganization of their inputs requires research. Here, we examined early and late changes in CSPGs, HAPLN1, tenascin-R, and glial activation along the spinal cord in male rats with complete spinal cord transection (Th10), and their impact on PNNs ensheathing lumbar MNs innervating ankle extensor and flexor muscles, which are in different loading states in paraplegic rats. We show that (1) distance from the lesion site and time after injury (2–5 weeks) differentiate degree of changes in transcription rates (measured with RT-qPCR) of PNNs proteins with increased CSPGs and decreased HAPLN1 transcripts, suggesting long-term PNN destabilization in majority of spinal segments, (2) in lumbar segments PNN composition is not MN-class (extensor vs flexor) specific, both showing early decrease and late upregulation of Wisteria floribunda agglutinin (WFA) labeling in vicinity of synaptic boutons on MNs, (3) long-term locomotor training tends to reduce WFA(+) PNNs, but not their protein components (immunofluorescence measurements) around MNs. Our results suggest that training-induced regulation may target glycan structures of CSPGs.

ON-bipolar cell gene expression during retinal degeneration: Implications for optogenetic visual restoration

PurposeRetinal bipolar cells survive even in the later stages of inherited retinal degenerations (IRDs) and so are attractive targets for optogenetic approaches to vision restoration. However, it is not known to what extent the remodelling that these cells undergo during degeneration affects their function. Specifically, it is unclear if they are free from metabolic stress, receptive to adeno-associated viral vectors, suitable for opsin-based optogenetic tools and able to propagate signals by releasing neurotransmitter. MethodsFluorescence activated cell sorting (FACS) was performed to isolate labelled bipolar cells from dissociated retinae of litter-mates with or without the IRD mutation Pde6brd1/rd1 selectively expressing an enhanced yellow fluorescent protein (EYFP) as a marker in ON-bipolar cells. Subsequent mRNA extraction allowed Illumina® microarray comparison of gene expression in bipolar cells from degenerate to those of wild type retinae. Changes in four candidate genes were further investigated at the protein level using retinal immunohistochemistry over the course of degeneration. ResultsA total of sixty differentially expressed transcripts reached statistical significance: these did not include any genes directly associated with native primary bipolar cell signalling, nor changes consistent with metabolic stress. Four significantly altered genes (Srm2, Slf2, Anxa7 & Cntn1), implicated in synaptic remodelling, neurotransmitter release and viral vector entry had immunohistochemical staining colocalising with ON-bipolar cell markers and varying over the course of degeneration. ConclusionOur findings suggest relatively few gene expression changes in the context of degeneration: that despite remodelling, bipolar cells are likely to remain viable targets for optogenetic vision restoration. In addition, several genes where changes were seen could provide a basis for investigations to enhance the efficacy of optogenetic therapies.

Simultaneous rather than retrograde spiral ganglion cell degeneration following ototoxically induced hair cell loss in the guinea pig cochlea

Severe damage to the organ of Corti leads to degeneration of the spiral ganglion cells (SGCs) which form the auditory nerve. This degeneration starts at the level of synaptic connection of the peripheral processes (PPs) of SGCs with the cochlear hair cells. It is generally thought that from this point SGC degeneration progresses in a retrograde fashion: PPs degenerate first, followed by the SGC soma with a delay of several weeks to many months. Evidence for this course of events, both in animals and in humans, is not unambiguous, while this knowledge is important since the presence or absence of the different neural elements may greatly influence the response to electrical stimulation with a cochlear implant (CI). We therefore aimed to provide a comprehensive account of the course of SGC degeneration in the guinea pig cochlea after ototoxic treatment. Histological analysis of eighteen healthy and thirty-three deafened cochleas showed that the degeneration of SGCs and their peripheral processes was simultaneous rather than sequential. As the site of excitation for electrical stimulation with a CI may depend on the course of degeneration of the various neural elements, this finding is relevant both for understanding the electrophysiological mechanisms behind cochlear implantation and for recent efforts to induce PP resprouting for improved electrode-neural interface. Since excitation of the PPs is often thought to result in (secondary) longer-latency activity, we tested the hypothesis that having relatively many PPs produces a larger N2 peak in the electrically evoked compound action potential (eCAP); the present findings however do not support this theory. The course of the degeneration process may vary among species, and may depend on the cause of deafness, but the present findings at least indicate that gradual retrograde degeneration of the auditory nerve is not an elemental process following severe damage to the organ of Corti.

Failure of Autophagy-Lysosomal Pathways in Rod Photoreceptors Causes the Early Retinal Degeneration Phenotype Observed in Cln6nclf Mice.

Vision loss caused by photoreceptor death represents one of the first symptoms in neuronal ceroid lipofuscinosis, a condition characterized by accumulation of intracellular waste. Cln6nclf mice have a naturally occurring mutation in ceroid-lipofuscinosis neuronal (CLN) protein 6 and are a model of this disorder. In order to identify the effect intracellular waste (lipofuscin) accumulation plays in driving retinal degeneration, the time course of degeneration was carefully characterized functionally using the electroretinogram and structurally using histology. Cln6nclf and C57BL/6J, wild-type, mice were studied at postnatal day 18 (P18), P30, P60, P120, and P240, and retinal degeneration was correlated with changes in the retinal pigment epithelial (RPE) and neuronal autophagy-lysosomal pathways using super-resolution microscopy. In Cln6nclf mice there was significant loss of rod photoreceptor function at P18, prior to photoreceptor nuclei loss at P60. In contrast, cone pathway function was not affected until P240. The loss of rod photoreceptor function correlated with significant disruption of the autophagy-lysosomal degradation pathways within photoreceptors, but not in the RPE or other retinal neurons. Additionally, there was cytosolic accumulation of P62 and undigested mitochondrial-derived, ATP synthase subunit C in the photoreceptor layers of Cln6nclf mice at P30. These results suggest that rod photoreceptors have an increased sensitivity to disturbances in the autophagy-lysosomal pathway and the subsequent failure of mitochondrial turnover, relative to other retinal cells. It is likely that primary failure of the rod photoreceptors rather than the RPE or other retinal neurons underlies the early visual dysfunction that occurs in the Cln6nclf mouse model.

Optic coherence tomography shows inflammation and degeneration in major depressive disorder patients correlated with disease severity

BackgroundPrevious research has consistently detected inflammation in the etiology of depression and neuroimaging studies have demonstrated gray matter abnormalities implying a neurodegenerative process in depression. The aim of this study was to compare ganglion cell layer (GCL), and inner plexiform layer (IPL) volumes and retinal nerve fiber layer (RNFL) thickness between first episode and recurrent major depressive disorder (MDD) patients and controls using optic coherence tomography (OCT) in order to detect findings supporting a degenerative process. Also choroid thicknesses of the same groups were compared to examine effects of inflammation on MDD. MethodsThis study included 50 recurrent MDD patients, 50 first episode MDD patients and 50 controls. OCT measurements were performed by a spectral OCT device. GCL and IPL volumes and RNFL and choroid thicknesses were measured automatically by the device. ResultsGCL and IPL volumes were significantly smaller in recurrent depression patients than first episode patients and in all MDD patients than controls. Also there were significant negative correlations between their volumes and disease severity parameters such as Ham-D and CGI scores, and disease duration. RNFL thicknesses were also lower in recurrent MDD patients than first episode patients and all MDD patients than controls but statistical significance was achieved only for global RNFL and temporal superior RNFL. Mean choroid thickness was higher in MDD patients than controls and in first episode MDD patients than recurrent MDD patients. LimitationsCross-sectional design of our study limits conclusions about progressive degeneration during the course of MDD. Lack of a control neuroimaging method like magnetic resonance imaging makes it hard to draw firm conclusions from our results. ConclusionsOCT finding of decreased GCL and IPL volumes supports previous research suggesting degeneration in MDD. OCT may be an important tool to track neurodegeneration in patients with major depression. Considering RNFL to be the latest layer that will be affected during course of degeneration, GCL and IPL volumes appear to be better parameters to follow. In addition, choroid may be an important structure to detect acute attack period and to follow inflammatory process in MDD like in systemic inflammatory diseases.

Degeneration Process of Fungiform Taste Buds After Severing the Human Chorda Tympani Nerve—Observation by Confocal Laser Scanning Microscopy

To elucidate the degeneration process of fungiform taste buds after severing the chorda tympani nerve (CTN) by confocal laser scanning microscopy in vivo. Prospective study. University hospital. Seven consecutive patients whose CTN was severed during tympanoplasty for middle ear cholesteatoma. Diagnostic. Preoperative and postoperative gustatory functions were assessed by electrogustometry (EGM). An average of 10 fungiform papillae (FP) in the midlateral region of the tongue were periodically observed, and the number of taste buds was counted using a confocal laser microscope. Among them, 2 to 3 reference FPs were selected based on the typical form of the FP or characteristic arrangements of taste pores. Observation was performed before surgery, 1 or 2 days after surgery, 2 or 3 times a week until 2 weeks after surgery, once a week between 2 and 4 weeks, and every 2 to 4 weeks thereafter until all taste buds had disappeared. EGM thresholds showed no response within 1 month after surgery in all patients. The initial change in the degeneration process was the disappearance of taste pores. The surface of taste buds became covered with epithelium. Finally, taste buds themselves atrofied and disappeared. The time course of degeneration differed depending upon individuals, each FP, and each taste bud. By employing the generalized linear mixed model under the Poisson distribution, it was calculated that all taste buds would disappear at around 50 days after surgery. Confocal laser scanning microscopy was useful for clarifying the degeneration process of fungiform taste buds.

Neurotrauma and inflammation: CNS and PNS responses.

Traumatic injury to the central nervous system (CNS) or the peripheral nervous system (PNS) triggers a cascade of events which culminate in a robust inflammatory reaction. The role played by inflammation in the course of degeneration and regeneration is not completely elucidated. While, in peripheral nerves, the inflammatory response is assumed to be essential for normal progression of Wallerian degeneration and regeneration, CNS trauma inflammation is often associated with poor recovery. In this review, we discuss key mechanisms that trigger the inflammatory reaction after nervous system trauma, emphasizing how inflammations in both CNS and PNS differ from each other, in terms of magnitude, cell types involved, and effector molecules. Knowledge of the precise mechanisms that elicit and maintain inflammation after CNS and PNS tissue trauma and their effect on axon degeneration and regeneration is crucial for the identification of possible pharmacological drugs that can positively affect the tissue regenerative capacity.

Morphometric and hemodynamic features of the age-related macular degeneration course in combined pathology: age-related macular degeneration in association with glaucoma

Purpose. To determine the characteristics of anatomical retinal changes and of the choroidal blood flow in patients with combined pathology: age-related macular degeneration (AMD) and primary open-angle glaucoma (POAG). Materials and methods. We investigated two study groups (SG): SG1 - AMD in association with POAG, 113 patients; SG2 - AMD without glaucomatous nerve damage , 92 patients; mean age - 71.9 ± 9.3 years. Measurements of the neuro-sensory retina (NSR) thickness and of the ganglion cells complex (GCC) thickness by optical coherence tomography (OCT) in manual regimen (42 eyes in SG1, 38 eyes in SG2) and the estimation of choroidal blood flow (HBF) by ultrasonography (18 eyes in SG1, 38 eyes in SG2) were performed in two areas: area I - 4 mm laterally to the optic nerve head; area II - 4 mm medially to the optic nerve head. Results. The GCC thickness in patients with combined pathology (SG1) was significantly lower than in patients with AMD (IG2) in the areas I and II; the thickness index of the GCC was significantly reduced in SG1 in areas I and II, whereas in SG2 this index was increased. Significant differences of HBF in areas I and II in SG1 were found, as well as reduced peak systolic flow velocity, the time-averaged maximum velocity of blood flow, maximum end-diastolic flow velocity, as compared with SG2. The index of peripheral resistance was reduced in SG1 in area I and increased in area II, whereas in SG2 it was increased in area I and reduced in area II. Conclusion. In patients with combined pathology - AMD and POAG - NSR thickness was reduced due to the thinning of the ganglion cell layer and the formation of an ischemic pattern of choroidal blood flow in the macula and medially to the optic nerve head.

Time course of degeneration of dopaminergic neurons and respective compensatory processes in the nigrostriatal system in mice.

160 Neurons are known to die continuously during the whole life of a human or animals [1]. However, until advanced age or even death, this neuronal loss does not influence negatively the functioning of the brain, including its involvement in neural or neuroendocrine regulation of the most important body functions. Even an increase in the rate of demise of specific neurons induced by unknown reasons in neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease (PD), and others, does not impair brain func� tions, such as cognitive functions in Alzheimer’s dis� ease or motor functions in PD, for several decades [1]. This may be explained by compensation of functional insufficiency caused by neuronal loss related to the mechanisms of brain plasticity. However, at a certain threshold level of neuronal degeneration, compensa� tory capabilities of the brain become insufficient or exhausted, which results in impairments of specific body functions [2]. From the viewpoint of basic neu� rophysiology, it is important to understand the tempo� ral and functional relationships between two linked processes, neurodegeneration and compensation of functions of dead neurons, which continuously occur in the brain. This basic knowledge is very important for medicine too, because it may allow us to understand the mechanisms of regulation of both processes and to cope with them using prospective drugs. The aim of the present study was to examine the development of the linked processes of degeneration

Transplantation of Activated Nucleus Pulposus Cells after Cryopreservation: Efficacy Study in Canine Disc Degeneration Model

IntroductionTissue disruption and altered function of the intervertebral disc (IVD) leads to progression of degenerative disc disease. Transplantation of viable cells that can function to maintain ...

Early alteration of retinal neurons in Aipl1-/- animals.

Mutations in the photoreceptor cell-specific gene encoding aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) lead to Leber congenital amaurosis (LCA4), retinitis pigmentosa, and cone-rod dystrophy. Gene therapy appears to be promising in the treatment for AIPL1-mediated vision loss in humans. Prior to initiating these treatments, however, it is crucial to understand how the retinal neurons remodel themselves in response to photoreceptor cell degeneration. In this study, using an animal model for AIPL1-LCA, Aipl1(-/-) mice, we investigate the changes in postreceptoral retinal neurons during the course of photoreceptor cell loss. Morphology of the Aipl1(-/-) retina from postnatal day 8 to 150 was compared to that of age-matched, wild-type C57Bl6/J retina (WT) by immunocytochemistry using cell-specific markers. Expression of postsynaptic proteins in bipolar cells is reduced prior to photoreceptor cell degeneration at postnatal day 8. Bipolar and horizontal cells retract their dendrites. Cell bodies and axons of bipolar and horizontal cells are disorganized during the course of degeneration. Müller cell processes become hypertrophic and form a dense fibrotic layer outside the inner nuclear layer. An early defect in photoreceptor cells in the AIPL1-LCA mouse model affects the expression of postsynaptic markers, suggesting abnormal development of bipolar synapses. Once degeneration of photoreceptor cells is initiated, remodeling of retinal neurons in the Aipl1(-/-) animal is rapid.

Cytoskeleton dynamics in the retina.

Cytoskeleton is one of the essential forms of protein, important in the existence of both eukaryotic as well as prokaryotic cells. Its transformation plays a vital role in cell division and intracellular transportation by facilitating intracellular vesicular traffic. Among the various tissue types in the body, the neural tissue exhibits the maximum heterogeneity, and hence the role of cytoskeleton at both developmental and functional levels becomes paramount. Cytoskeleton dynamics have been established in the neural physiology, but only at the level of axonal development and growth. Retina has not been adequately studied in the context of cytoskeletal proteins. We reviewed the last 10 years of literature with reference to the development, growth, degeneration, and regeneration of the retina and the role of cytoskeleton in each aspect. We have focused on various changes that the retina undergoes at the cytosolic and cytoskeletal levels in the course of degeneration as well as regeneration. For this review, we compiled research articles pertaining to the role of cytoskeletal and other associated proteins involved in development of retina, which used various animal models. The effect of SNPs in the cytoskeletal proteins and their impact in retinal degeneration is also discussed. Studies describing the role of cytoskeleton in the anatomy and physiology of retina and its layers, although they are few, collectively provide an opportunity to understand retinal development in the context of cytoskeleton dynamics.

The influence of vitreomacular adhesion on the pathogenesis and course of age-related macular degeneration

This article describes the age-related changes in vitreous and different types of posterior vitreous detachment. Possible effect of normal and pathological posterior vitreous detachment (in particular vitreomacular adhesion and traction syndrome) on the age-related macular degeneration course are considered. Vitrectomy and pharmacological vitreolysis potentials in the treatment of vitreomacular adhesion are discussed.

The time course of retrograde trans-synaptic degeneration following occipital lobe damage in humans

Following damage to the human post-geniculate visual pathway retrograde trans-synaptic degeneration of the optic nerve fibres occurs. It has been known for some time from investigations carried out in primates that a decline in the number of retinal ganglion cells follows occipital lobectomy. However, this is not detectable in all species studied and whether this occurs in humans was controversial until recent studies that have shown that following lesions of the occipital lobe, the retinal nerve fibre layer thickness measured by optical coherence tomography is reduced and corresponding shrinkage of the optic tract can be demonstrated by magnetic resonance imaging. The time course of the degeneration in humans is, however, unknown. In the present study, we have used optical coherence tomography to demonstrate for the first time progressive thinning of the retinal nerve fibre layer following occipital lobe/optic radiation damage due to stroke. First, in a group of 38 patients the measurement was taken on a single occasion at a known time interval since the stroke, ranging from 6 days to 67 years. Here, a negative straight line relationship (linear regression r = 0.54, P < 0.001) was found between nerve fibre layer thickness and elapsed time since injury in log years, giving a rate of decline of 9.08 µm per log year after adjusting for age. This indicates a decelerating rate of loss that differs from the rate of decline found with chronological age in this same group, which shows a steady rate of thinning by 0.4 µm per year (P = 0.006) after adjusting for duration of the disease. In a second study serial measurements were taken following the acute event in a group of seven patients with homonymous hemianopia; here a negative straight line relationship was found between time and nerve fibre layer thickness in micrometres over a period of data collection beginning at a mean of 36.9 days post-stroke (range 5-112) and ending at a mean of 426.6 days post-stroke (range 170-917). Evidence from clinical observation (funduscopy) suggested that retrograde trans-synaptic degeneration occurred in humans only where the damage to the post-geniculate pathway occurred prenatally. The results reported herein add weight to the previous demonstration that this type of degeneration does indeed occur in the human visual system by showing that it can be monitored over time and hence may provide a model for trans-synaptic degeneration in the human central nervous system.

Emerging imaging tools for use with traumatic brain injury research.

This article identifies emerging neuroimaging measures considered by the inter-agency Pediatric Traumatic Brain Injury (TBI) Neuroimaging Workgroup. This article attempts to address some of the potential uses of more advanced forms of imaging in TBI as well as highlight some of the current considerations and unresolved challenges of using them. We summarize emerging elements likely to gain more widespread use in the coming years, because of 1) their utility in diagnosis, prognosis, and understanding the natural course of degeneration or recovery following TBI, and potential for evaluating treatment strategies; 2) the ability of many centers to acquire these data with scanners and equipment that are readily available in existing clinical and research settings; and 3) advances in software that provide more automated, readily available, and cost-effective analysis methods for large scale data image analysis. These include multi-slice CT, volumetric MRI analysis, susceptibility-weighted imaging (SWI), diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), arterial spin tag labeling (ASL), functional MRI (fMRI), including resting state and connectivity MRI, MR spectroscopy (MRS), and hyperpolarization scanning. However, we also include brief introductions to other specialized forms of advanced imaging that currently do require specialized equipment, for example, single photon emission computed tomography (SPECT), positron emission tomography (PET), encephalography (EEG), and magnetoencephalography (MEG)/magnetic source imaging (MSI). Finally, we identify some of the challenges that users of the emerging imaging CDEs may wish to consider, including quality control, performing multi-site and longitudinal imaging studies, and MR scanning in infants and children.

Preservation of the Y Transcriptome in a 10-Million-Year-Old Plant Sex Chromosome System

Classical genetic studies discovered loss of genes from the ancient sex chromosome systems of several animals (genetic degeneration), and complete genome sequencing confirms that the heterogametic sex is hemizygous for most sex-linked genes. Genetic degeneration is thought to result from the absence of recombination between the sex chromosome pair (reviewed by [1]) and is very rapid after sex chromosome-autosome fusions in Drosophila [2-4]. Plant sex chromosome systems allow study of the time course of degeneration, because they evolved from a state wholly without sex chromosomes (rather than after a large genome region fused to a preexisting sex chromosome), and, in several taxa, recombination stopped very recently. However, despite increasing genetic and physical mapping of plant nonrecombining sex-determining regions [5-8], it remains very difficult to discover sex-linked genes, and it is unclear whether Y-linked genes are losing full function. We therefore developed a high-throughput method using RNA-Seq to identify sex linkage in Silene latifolia. Recombination suppression between this plant's XY sex chromosome pair started only about 10 million years ago [9]. Our approach identifies several hundred new sex-linked genes, and we show that this young Y chromosome retains many genes, yet these already have slightly reduced gene expression and are accumulating changes likely to reduce protein functions.

Mechanically‐induced hair cell death using the zebrafish lateral line as a model system.

Noise‐induced hearing loss is a major type of hearing impairment that affects the quality of life for millions of Americans. The cause of noise‐induced hearing loss is the death of sensory hair cells in the ear. The primary goal of the present study is to have a better understanding of mechanisms underlying noise‐induced hearing and balance deficits. Mechanically‐induced hair cell degeneration was investigated using the zebrafish (Danio rerio), which has become a model system for biomedical research because of a combination of powerful genetics, excellent embryology, and exceptional in vivo visualization in one organism. Zebrafish have the lateral line system containing superficial neuromasts in the head and trunk, and each neuromast has a cluster of hair cells that structurally and functionally resemble the hair cells in the ear. In this study, hair cells in single neuromasts of zebrafish larvae of 5 to 10 days post fertilization were stimulated by a piezoelectric actuator and the time course of degeneration of hair cells exposed to overstimulation was obtained using light microscopy. Microphonic potentials of neuromast hair cells were also recorded to show effects of intense mechanical stimulation on the function of hair cells. [Work supported by NIH/NIDCD R21DC009879 and Gabelli Fellowship.]

Relative Time Course of Degeneration of Different Cochlear Structures in the CD/1 Mouse Model of Accelerated Aging

Presbycusis (age-related hearing loss) can result from various cochlear pathologies. We have studied the time course of degeneration in a mouse that shows accelerated presbycusis, the CD/1 mouse, as a possible model to investigate stem-cell strategies to prevent or ameliorate presbycusic changes. CD/1 mice from 0 to 72 weeks old were examined by light and electron microscopy. Early pathological changes were detected in basal turn spiral ligament fibrocytes and spiral ganglion, but the latter was variable as both satellite cells and neurons were normal in some cochleae. Light microscopic counts in the spiral ligament of 20-week-old mice revealed that of the five main types (types I-V), only type V fibrocytes showed no reduction in numbers compared with 3-week-old animals, and type IV showed the greatest losses. However, all types of fibrocyte showed subtle damage when examined using electron microscopy, in the form of swollen mitochondria, as early as 2 weeks. The extent of mitochondrial damage showed a degree of correspondence with the light microscopic pattern of fibrocyte loss in that types III and IV fibrocytes had the most abnormal mitochondria and type V the least, especially at early stages. By 10-15 weeks, ultrastructural features of fibrocyte damage were similar to longer term changes reported in gerbils. Stria vascularis, spiral ganglion and hair cells showed few consistent early signs of damage but became increasingly affected, lagging behind the fibrocyte damage. Our data suggest that fibrocyte pathology may precede other presbycusic changes; breakdown of homeostatic mechanisms to which they contribute may cause the subsequent degeneration of the hair cells. Overall, there were many similarities to presbycusic changes in other rodents and humans. Therefore, the features of accelerated aging in this mouse make it a suitable model for rapidly assessing possible strategies to prevent or ameliorate presbycusic changes.