Search

The exceptional navigational capabilities of migrating birds are based on the perception and integration of a variety of natural orientation cues. The “Wulst” in the forebrain of night-migratory songbirds contains a brain area named “Cluster N”, which is involved in processing directional navigational information derived from the Earth´s magnetic field. Cluster N is medially joined by the hippocampal formation, known to retrieve and utilise navigational information. To investigate the connectivity and neurochemical characteristics of Cluster N and the hippocampal formation of migratory birds, we performed morphological and histochemical analyses based on the expression of calbindin, calretinin, parvalbumin, glutamate receptor type 1 and early growth response protein-1 in the night-migratory Garden warbler (Sylvia borin) and mapped their mutual connections using neuronal tract tracing. The resulting expression patterns revealed regionally restricted neurochemical features, which mapped well onto the hippocampal and hyperpallial substructures known from other avian species. Magnetic field-induced neuronal activation covered caudal parts of the hyperpallium and the medially adjacent hippocampal dorsomedial/dorsolateral subdivisions. Neuronal tract tracings revealed connections between Cluster N and the hippocampal formation with the vast majority originating from the densocellular hyperpallium, either directly or indirectly via the area corticoidea dorsolateralis. Our data indicate that the densocellular hyperpallium could represent a central relay for the transmission of magnetic compass information to the hippocampal formation where it might be integrated with other navigational cues in night-migratory songbirds.

Cryptochromes are photolyase-related blue-light receptors acting as core components of the mammalian circadian clock in the cell nuclei. One or more members of the cryptochrome protein family are also assumed to play a role in avian magnetoreception, but the primary sensory molecule in the retina of migratory birds that mediates light-dependent magnetic compass orientation has still not been identified. The mRNA of cryptochrome 2 (Cry2) has been reported to be located in the cell nuclei of the retina, but Cry2 localisation has not yet been demonstrated at the protein level. Here, we provide evidence that Cry2 protein is located in the photoreceptor inner segments, the outer nuclear layer, the inner nuclear layer and the ganglion cell layer in the retina of night-migratory European robins, homing pigeons and domestic chickens. At the subcellular level, we find Cry2 both in the cytoplasm and the nucleus of cells residing in these layers. This broad nucleic expression rather points to a role for avian Cry2 in the circadian clock and is consistent with a function as a transcription factor, analogous to mammalian Cry2, and speaks against an involvement in magnetoreception.

Horizontal cells in the mouse retina are of the axon-bearing B-type and contribute to the gain control of photoreceptors and to the center-surround organization of bipolar cells by providing feedback and feedforward signals to photoreceptors and bipolar cells, respectively. Horizontal cells form two independent networks, coupled by dendro-dendritic and axo-axonal gap junctions composed of connexin57 (Cx57). In Cx57-deficient mice, occasionally the residual tracer coupling of horizontal cell somata was observed. Also, negative feedback from horizontal cells to photoreceptors, potentially mediated by connexin hemichannels, appeared unaffected. These results point to the expression of a second connexin in mouse horizontal cells. We investigated the expression of Cx50, which was recently identified in axonless A-type horizontal cells of the rabbit retina. In the mouse retina, Cx50-immunoreactive puncta were predominantly localized on large axon terminals of horizontal cells. Electron microscopy did not reveal any Cx50-immunolabeling at the membrane of horizontal cell tips invaginating photoreceptor terminals, ruling out the involvement of Cx50 in negative feedback. Moreover, Cx50 colocalized only rarely with Cx57 on horizontal cell processes, indicating that both connexins form homotypic rather than heterotypic or heteromeric gap junctions. To check whether the expression of Cx50 is changed when Cx57 is lacking, we compared the Cx50 expression in wildtype and Cx57-deficient mice. However, Cx50 expression was unaffected in Cx57-deficient mice. In summary, our results indicate that horizontal cell axon terminals form two independent sets of homotypic gap junctions, a feature which might be important for light adaptation in the retina.

Pannexin1 (Panx1) belongs to a class of vertebrate proteins that exhibits sequence homology to innexins, the invertebrate gap junction proteins, and which also shares topological similarities with vertebrate gap junction proteins, the connexins. Unlike gap junctional channels, Panx1 forms single-membrane channels, whose functional role in neuronal circuits is still unsettled. We therefore investigated the subcellular distribution of Panx1 in the mouse retina of wildtype and Panx1-null mice by reverse-transcription polymerase chain reaction (RT-PCR), immunohistochemistry, and electron microscopy. Use of Panx1-deficient mice served as a model to assess the physiological role of Panx1 by electroretinographic recordings and also to ensure the specificity of the anti-Panx1 antibody labeling. Expression of Panx1 was found in type 3a OFF bipolar cells and in dendrites and axonal processes of horizontal cells. Panx1 was also found in horizontal cell dendrites representing the lateral elements of the triad synapse at cone and rod terminals. In vivo electroretinography of Panx1 knockout mice indicated an increased a- and b-wave compared to Panx1 wildtype mice under scotopic conditions. The effect on the b-wave was confirmed by in vitro electroretinograms from the inner retina. These results suggest that Panx1 channels serve as sinks for extracellular current flow making them possible candidates for the mediation of feedback from horizontal cells to photoreceptors.

Seit einigen Jahren ist eine spürbare Entgrenzung und Neuverhandlung der traditionellen Konzeption von Kunsttheater zu beobachten: vom Authentizitätsdiskurs, über die Debatten um »Experten des Alltags« und Partizipation bis hin zur jüngsten Diskussion um Theater mit und von behinderten Darstellern. Immer geht es darum, die Grenzen dessen, was wir als Kunsttheater kennen und anerkennen, produktiv zu verhandeln, sodass uns die historische Dimension unseres Denkens des Theaters vor Augen geführt wird. Unsere Beiträge gehen von der These aus, dass sich Kunsttheater seit der Moderne stets im Aushandlungsprozess zwischen einem ›professionellen‹ und einem ›dilettantischen Dispositiv‹ konstituiert und beleuchtet das Spannungsfeld zwischen dem Kunsttheater und seinem ›Anderen‹ auf gesellschaftlicher, institutioneller und ästhetischer Ebene, und zwar sowohl aus historischer Perspektive als auch am Beispiel der aktuellen Theaterpraxis mit und von Behinderten., + ID: 549457 + Reihentitel: Theater + PeerReviewed

Cryptochromes are ubiquitously expressed in various animal tissues including the retina. Some cryptochromes are involved in regulating circadian activity. Cryptochrome proteins have also been suggested to mediate the primary mechanism in light-dependent magnetic compass orientation in birds. Cryptochrome 1b (Cry1b) exhibits a unique carboxy terminus exclusively found in birds so far, which might be indicative for a specialised function. Cryptochrome 1a (Cry1a) is so far the only cryptochrome protein that has been localised to specific cell types within the retina of migratory birds. Here we show that Cry1b, an alternative splice variant of Cry1a, is also expressed in the retina of migratory birds, but it is primarily located in other cell types than Cry1a. This could suggest different functions for the two splice products. Using diagnostic bird-specific antibodies (that allow for a precise discrimination between both proteins), we show that Cry1b protein is found in the retinae of migratory European robins (Erithacus rubecula), migratory Northern Wheatears (Oenanthe oenanthe) and pigeons (Columba livia). In all three species, retinal Cry1b is localised in cell types which have been discussed as potentially well suited locations for magnetoreception: Cry1b is observed in the cytosol of ganglion cells, displaced ganglion cells, and in photoreceptor inner segments. The cytosolic rather than nucleic location of Cry1b in the retina reported here speaks against a circadian clock regulatory function of Cry1b and it allows for the possible involvement of Cry1b in a radical-pair-based magnetoreception mechanism.

The identification of the proteins that make up the gap junction channels between rods and cones is of crucial importance to understand the functional role of photoreceptor coupling within the retinal network. In vertebrates, connexin proteins constitute the structural components of gap junction channels. Connexin36 is known to be expressed in cones whereas extensive investigations have failed to identify the corresponding connexin expressed in rods. Using immunoelectron microscopy, we demonstrate that connexin36 (Cx36) is present in gap junctions of cone but not rod photoreceptors in the mouse retina. To identify the rod connexin, we used nested reverse transcriptase polymerase chain reaction and tested retina and photoreceptor samples for messenger RNA (mRNA) expression of all known connexin genes. In addition to connexin36, we detected transcripts for connexin32, connexin43, connexin45, connexin50, and connexin57 in photoreceptor samples. Immunohistochemistry showed that connexin43, connexin45, connexin50, and connexin57 proteins are expressed in the outer plexiform layer. However, none of these connexins was detected at gap junctions between rods and cones as a counterpart of connexin36. Therefore, the sought-after rod protein must be either an unknown connexin sequence, a connexin36 splice product not detected by our antibodies, or a protein from a further gap junction protein family.

Birds seem to use a light-dependent, radical-pair-based magnetic compass. In vertebrates, cryptochromes are the only class of proteins that form radical pairs upon photo-excitation. Therefore, they are currently the only candidate proteins for light-dependent magnetoreception. Cryptochrome 4 (Cry4) is particularly interesting because it has only been found in vertebrates that use a magnetic compass. However, its structure and localization within the retina has remained unknown. Here, we sequenced night-migratory European robin (Erithacus rubecula) Cry4 from the retina and predicted the currently unresolved structure of the erCry4 protein, which suggests that erCry4 should bind Flavin. We also found that Cry1a, Cry1b, and Cry2 mRNA display robust circadian oscillation patterns, whereas Cry4 shows only a weak circadian oscillation. When we compared the relative mRNA expression levels of the cryptochromes during the spring and autumn migratory seasons relative to the non-migratory seasons in European robins and domestic chickens (Gallus gallus), the Cry4 mRNA expression level in European robin retinae, but not in chicken retinae, is significantly higher during the migratory season compared to the non-migratory seasons. Cry4 protein is specifically expressed in the outer segments of the double cones and long-wavelength single cones in European robins and chickens. A localization of Cry4 in double cones seems to be ideal for light-dependent magnetoreception. Considering all of the data presented here, especially including its localization within the European robin retina, its likely binding of Flavin, and its increased expression during the migratory season in the migratory bird but not in chicken, Cry4 could be the magnetoreceptive protein. Günther et al. suggest that Cry4 could be the magnetoreceptive protein in night-migratory songbirds. Cry4 seems to bind Flavin, shows only weak circadian oscillations, is specifically located in double cones and long-wavelength single cones, and is upregulated during the migratory season in night-migratory European robins but not in chicken.

Horizontal cells in the mouse retina are of the axon-bearing B-type and contribute to the gain control of photoreceptors and to the center-surround organization of bipolar cells by providing feedback and feedforward signals to photoreceptors and bipolar cells, respectively. Horizontal cells form two independent networks, coupled by dendro-dendritic and axo-axonal gap junctions composed of connexin57 (Cx57). In Cx57-deficient mice, occasionally the residual tracer coupling of horizontal cell somata was observed. Also, negative feedback from horizontal cells to photoreceptors, potentially mediated by connexin hemichannels, appeared unaffected. These results point to the expression of a second connexin in mouse horizontal cells. We investigated the expression of Cx50, which was recently identified in axonless A-type horizontal cells of the rabbit retina. In the mouse retina, Cx50-immunoreactive puncta were predominantly localized on large axon terminals of horizontal cells. Electron microscopy did not reveal any Cx50-immunolabeling at the membrane of horizontal cell tips invaginating photoreceptor terminals, ruling out the involvement of Cx50 in negative feedback. Moreover, Cx50 colocalized only rarely with Cx57 on horizontal cell processes, indicating that both connexins form homotypic rather than heterotypic or heteromeric gap junctions. To check whether the expression of Cx50 is changed when Cx57 is lacking, we compared the Cx50 expression in wildtype and Cx57-deficient mice. However, Cx50 expression was unaffected in Cx57-deficient mice. In summary, our results indicate that horizontal cell axon terminals form two independent sets of homotypic gap junctions, a feature which might be important for light adaptation in the retina.

Wc compared the central motor conduction time (CMCT) obtained by magnetic stimulation of the central nervous system (CNS) of 181 patients who fulfilled the criteria (see Fukuda 1994) for CFS with those of 27 healthy control subjects. A cortical and a cervical stimulation was performed on each person under standardised conditions, and the motor evoked potentials (MEP) either from Musculus Abductor Pollicis Brevis (M. APB) or from Musculus Abductor Digiti Minimi (M. ADM) was recorded.For the CFS patients a significant prolongation of the central motor conduction time (M. APB right: p < 0.0001; M. A DP left: p < 0.00005; M. ADM right: p < 0.00005; M. ADM left: p < 0.005) was observed compared to controls. The results presented in this study suggest a central nervous system dysfunction in CFS.