Biomedical subjects

Oliver Biehlmaier

Publications and source records attributed to Oliver Biehlmaier.

9 recordsLinked to original sources

PubMed2006

A rat model of Parkinsonism shows depletion of dopamine in the retina.

The retinal dopamine (DA) deficiency is an important feature of the pathogenesis in Parkinson's disease (PD) visual dysfunction. Systemic inhibition of complex I (rotenone) in rats has been proposed as a model of PD. In this study, we investigated whether systemic inhibition of complex I can induce impairment of DA-ergic cells in the retina, similar to the destruction of retinal cells found in PD patients. Rotenone (2.5mg/kg i.p., daily) was administered over 60 days. Neurochemically, rotenone treated rats showed a depletion of DA in the striatum and substantia nigra (SN). In addition, the number of retinal DA-ergic amacrine cells was significantly reduced in the rotenone treated animals. This study is the first one giving highlight towards a deeper understanding of systemic complex I inhibition (rotenone as an environmental toxin) and the connection between both, DA-ergic degeneration in the nigrostriatal pathway, and in the DA-ergic amacrine cells of the retina.

Animals↗

PubMed2006

Time course and development of light adaptation processes in the outer zebrafish retina.

Retinomotor movements are morphological changes in the outer retina in response to changing light conditions. They can be separated into two components: Migration of pigment granules within the microvilli of the retinal pigment epithelium (RPE) and positional changes in photoreceptor cells. These positional changes optimize exposure of the cone and rod photoreceptors to light. The aim of this study was to analyze both the time course of retinomotor movements in the adult zebrafish and the maturation of these processes in the developing fish. We show that retinomotor movements are used as a dark/light adaptation mechanism in zebrafish. In adult zebrafish, melanin granules of the RPE migrate with constant speed and reach the fully light adapted (LA) state approximately after 1 h. In contrast, about two thirds of double cone outer segment movements are finished in 5 min, and are fully completed in 10 to 20 min. During development there are three crucial stages leading to mature retinomotor movements in response to light: at 5 dpf (days post fertilization) the migration of pigment granules begins, at 20 dpf the pigment granules condense in the apical part of the RPE microvilli, and at 28 dpf, concomitant with the functional maturation of rods, the double cones contract as in adult retinas.

Adaptation, Ocular↗

PubMed2006

Nyctalopin is essential for synaptic transmission in the cone dominated zebrafish retina.

The first synapse in the vertebrate visual system is the photoreceptor synapse between rod and cone photoreceptors and the second-order bipolar cells. Although mutations in the nyctalopin gene (NYX) in humans lead to congenital stationary night blindness (CSNB1), affecting synaptic transmission between both types of photoreceptors and ON-bipolar cells, the function of nyctalopin in cone-dominant animal models has not been studied. Because the larval zebrafish retina is cone-dominant, we isolated the zebrafish nyx ortholog and raised a polyclonal antibody against the protein. Nyctalopin is expressed postsynaptically in both synaptic layers of the retina. Functional disruption via morpholino antisense injection leads to characteristic defects in the electroretinogram and defects in visual contrast sensitivity. We therefore demonstrated that nyctalopin plays a similar role in retinal synapse function in the cone pathway as in the rod pathway, thereby creating a genetic model for CSNB1 and its effects on cone vision.

Animals↗

PubMed2006

The Zebrafish fade out mutant: a novel genetic model for Hermansky-Pudlak syndrome.

PURPOSE: To characterize retinal morphology and visual system function in the zebrafish mutant fade out (fad) and to establish the mutant as a lower vertebrate model for Hermansky-Pudlak syndrome (HPS). METHODS: Retinal morphology of fad larvae was examined between 3 and 9 days postfertilization (dpf) by standard histology, transmission electron microscopy, and immunohistochemistry examination. Apoptotic cells were visualized by TdT-mediated dUTP nick-end labeling (TUNEL) staining. Visual system function was probed by electroretinography and behavioral assessment by optokinetic response measurements. Blood clotting was evaluated by time to occlusion testing of blood vessels as an arterial thrombosis assay. The chromosomal location of fad was determined by simple sequence-length polymorphism mapping. Genomic fragments of candidate genes were cloned by standard molecular techniques and mapped to the zebrafish genome by radiation hybrid mapping. RESULTS: Mutant fad larvae are hypopigmented and show structural defects in the outer retina. Melanosomes of these larvae in the retinal pigment epithelium are hypopigmented, generally smaller, and progressively reduced in number compared to nonmutant larvae. Progressive microvilli protrusions into the photoreceptor cell layer are not detectable, and photoreceptor outer segments get shorter and are misaligned. Photoreceptors subsequently undergo apoptosis, with a peak of cell death at 6 dpf. Electrical responses of the retina and visual performance are severely reduced. Blood clotting is prolonged in mutant fad larvae. Genomic mapping of fad reveals distinct genomic positions of the mutant gene from known human HPS genes. CONCLUSIONS: The fad mutant shows syndromic defects in pigmentation, outer retinal structure and function, and blood clotting. This syndrome is characteristic of Hermansky-Pudlak syndrome (HPS), making fad a novel genetic model of HPS. The gene does not cosegregate with the known human HPS genes, suggesting a novel molecular cause of HPS.

Animals↗

PubMed2005

Knockdown of cone-specific kinase GRK7 in larval zebrafish leads to impaired cone response recovery and delayed dark adaptation.

Phosphorylation of rhodopsin by rhodopsin kinase GRK1 is an important desensitization mechanism in scotopic vision. For cone vision GRK1 is not essential. However, cone opsin is phosphorylated following light stimulation. In cone-dominant animals as well as in humans, but not in rodents, GRK7, a cone-specific homolog of GRK1, has been identified in cone outer segments. To investigate the function of GRK7 in vivo, we cloned two orthologs of grk7 in zebrafish and knocked down gene expression of grk7a in zebrafish larvae by morpholino antisense nucleotides. Photoresponse recovery in Grk7a-deficient larvae was delayed in electroretinographic measurements, and temporal contrast sensitivity was reduced, particularly under bright-light conditions. These results show that function of a cone-specific kinase is essential for cone vision in the zebrafish retina and argue that pigment bleaching and spontaneous decay alone are not sufficient for light adaptation and rapid cone response inactivation.

Animals↗

PubMed2005

Photoreceptor morphology is severely affected in the beta,beta-carotene-15,15'-oxygenase (bcox) zebrafish morphant.

The retinoic acid molecule, a vitamin A derivative, is of key importance for eye and photoreceptor development in vertebrates. Several studies have provided evidence that the ventral part of the retina is particularly susceptible to impairment in retinoid signalling during the period of its development. In zebrafish, targeted gene knockdown of beta,beta-carotene-15,15'-oxygenase (bcox), the key enzyme for vitamin A formation, provokes a loss of retinoid signalling during early eye development that results in microphthalmia at larval stages. Using this model, we analysed the consequences of this for the retinal morphology of the fish larvae in structural details. Our analyses revealed that rods and cones do not express photoreceptor specific proteins (rhodopsin, peanut agglutinin, zpr1) in the peripheral retina. The photoreceptors in the central retina showed shortened outer segments, and electron dense debris in their intermembranal space. The number of phagosomes was increased, and cell death was frequently observed in the outer nuclear layer. Furthermore, the number of Muller cells was significantly reduced in the inner nuclear layer. Thus, we found that the lack of retinoid signalling strongly effects photoreceptor development in the ventral and dorsal retina. In addition, shortened outer segments and cell death of the remaining photoreceptors in the central retina indicate that there is an ongoing need for retinoid signalling for photoreceptor integrity and survival at later developmental stages.

Animals↗

PubMed2003

Synaptic plasticity and functionality at the cone terminal of the developing zebrafish retina.

Previous studies have analyzed photoreceptor development, some inner retina cell types, and specific neurotransmitters in the zebrafish retina. However, only minor attention has been paid to the morphology of the synaptic connection between photoreceptors and second order neurons even though it represents the transition from the light sensitive receptor to the neuronal network of the visual system. Here, we describe the appearance and differentiation of pre- and postsynaptic elements at cone synapses in the developing zebrafish retina together with the maturation of the directly connecting second order neurons and a dopaminergic third order feedback-neuron from the inner retina. Zebrafish larvae were examined at developmental stages from 2 to 7dpf (days postfertilization) and in the adult. Synaptic maturation at the photoreceptor terminals was examined with antibodies against synapse associated proteins. The appearance of synaptic plasticity at the so-called spinule-type synapses between cones and horizontal cells was assessed by electron microscopy, and the maturation of photoreceptor downstream connection was identified by immunocytochemistry for GluR4 (AMPA-type glutamate receptor subunit), protein kinase beta(1) (mixed rod-cone bipolar cells), and tyrosine hydroxylase (dopaminergic interplexiform cells). We found that developing zebrafish retinas possess first synaptic structures at the cone terminal as early as 3.5dpf. Morphological maturation of these synapses at 3.5-4dpf, together with the presence of synapse associated proteins at 2.5dpf and the maturation of second order neurons by 5dpf, indicate functional synaptic connectivity and plasticity between the cones and their second order neurons already at 5dpf. However, the mere number of spinules and ribbons at 7dpf still remains below the adult values, indicating that synaptic functionality of the zebrafish retina is not entirely completed at this stage of development.

Animals↗

PubMed2003

Retinal defects in the zebrafish bleached mutant.

The recessive zebrafish mutant bleached has, apart from its defects in pigmentation, a heritable defect leading to larval blindness. Here, we analyze the retina of homozygous bleached larvae, employing morphological and electrophysiological methods. Electroretinography revealed a complete lack of electrical signals in response to light. Histological analysis of mutant retinae showed a severely affected outer retina with a hypopigmented pigment epithelium and a disorganized outer nuclear layer containing few or no intact photoreceptors. Using the TUNEL assay for cell death detection, we noticed a strong increase of apoptotic cells in all retinal cell layers, starting in young larvae even before retinal support of visual function. At later stages cell death is most pronounced at the marginal zone, where new cells are constantly added to the retina. At early stages increased apoptosis is mainly confined to the retina, while at later stages elevated cell death is al so apparent in extra-retinal tissues, particularly in the brain. Hence, the lack of visual responses in homozygous bleached larvae can be attributed to a severe defect of the outer retina, preceded by increased levels of apoptotic cell death in all retinal cell layers.

Animals↗

PubMed2003

Double cone dystrophy and RPE degeneration in the retina of the zebrafish gnn mutant.

PURPOSE: To characterize morphologic alterations in the retina of the visual mutant zebrafish gantenbein (gnn) and to examine whether these alterations correlate with those present in human hereditary eye diseases. METHODS: The gnn mutant was isolated by behavioral and macroscopic screening. Retinas of gnn zebrafish larvae were examined at different developmental stages from 2 to 9 days postfertilization (dpf) by standard histologic staining techniques and by immunocytochemistry. Ultrastructural alterations were examined by electron microscopy. The genetic map position of the induced mutation was identified by mapping with two candidate primer pairs on single larvae. RESULTS: The gnn mutant exhibited shortened outer photoreceptor segments and altered RPE morphology. In the photoreceptor layer of the mutant, the total number of lectin-labeled cones was reduced in all developmental stages from 2 to 7 dpf, whereas the amount of rhodopsin-positive cells remained at the wild-type (WT) level. Labeling with zebrafish opsin antibodies revealed dystrophic red cones at 5 dpf, whereas the morphology of all other cone types was largely unaffected. Electron microscopy unveiled electron-dense deposits between the discs of the double cone outer segments. In addition, the onset of progressive RPE degeneration was observed at this stage of development. At later stages, all cone types and the RPE became degenerative. The morphology of distinct second-order neurons remained largely unaffected by the mutation. The gnn mutation was located approximately 4.3 cM from the simple sequence length polymorphism (SSLP) marker Z15453 on linkage group 16. CONCLUSIONS: In gnn mutant zebrafish, cones, and especially red cones, are dystrophic in early retinal development. Subsequent to this cone dystrophy, the RPE becomes dysfunctional and starts to degenerate in later stages of development. Thus, the early developmental morphology of gnn exhibits similarities to cone dystrophies most commonly seen in age-related macular degeneration (AMD) among humans, whereas the later stages of degeneration in gnn resemble RPE alterations in retinitis pigmentosa (RP) in humans. The gnn zebrafish mutant may therefore be a useful model for examining the possible interplay and connection between cone dystrophy and RPE degeneration.

Animals↗