[Comparison of visual and auditory pathway]. / Vergleich von Sehbahn und Hörbahn.

Humans receive information from their environment via the visual and auditory systems. This information protects us from dangers and guarantees vital actions, such as social interaction, locomotion, work processes and nutrition. The most important anatomical and functional features of these two sensory systems are compared and elucidated with respect to their interaction/functional complementarity. For this purpose, a selective literature search was carried out in the databases PubMed (also in the Europe PubMed Central), Psychline, Google Scholar, Cochrane Library and Web of Science. Additional information was obtained from relevant books and websites in the fields of (neuro)anatomy, (neuro)physiology, (neuro)ophthalmology and (neuro)otology. Search terms were Hörbahn, Sehbahn, visual system, auditory system, visual pathway, auditory pathway, receptors, spatial hearing, spatial cognition, auditory cognition and visual cognition.

[Structure and function of the visual pathway]. / Aufbau und Funktion der Sehbahn.

Humans receive information from their environment mainly via the visual system. Signals from the photoreceptors of the retina via bipolar and ganglion cells are projected onto specific neuronal subpopulations in the lateral geniculate body and from there are forwarded to appropriate layers of the primary visual cortex. The most important anatomical and functional features of the visual system are explained. For this purpose, a selective literature search was carried out in the databases PubMed (also in Europe PubMed Central), Psychline, Google Scholar, Cochrane Library and Web of Science as well as additional information in relevant books or websites in the fields of (neuro)anatomy, (neuro)physiology, (neuro)ophthalmology and (neuro)otology, among others with the search terms Sehbahn, visual system, visual pathway, receptors, spatial cognition and visual cognition.

Chromatic coding from cone-type unselective circuits in the mouse retina.

Retinal specializations such as cone-photoreceptor opsin-expression gradients, as found in several vertebrate species, are intuitively considered detrimental to color vision. In mice, the majority of cones coexpress both "blue" and "green" opsin. The coexpression ratio changes along the dorsoventral axis, resulting in a "green"-dominant dorsal and a "blue"-dominant ventral retina. Here, we asked how these specializations affect chromatic processing, especially with respect to the opsin transitional zone, the band where opsin coexpression shifts from "green" to "blue." Using electrophysiology, modeling, and calcium imaging, we found that "alpha-like" retinal ganglion cells, which previously have not been implicated in chromatic processing, display color-opponent responses when located in the vicinity of the opsin transitional zone. Moreover, direction-selective ganglion cells within this zone respond differentially to color sequences. Our data suggest that the dorsoventral opsin distribution, in combination with conventional spatiotemporal processing, renders mouse ganglion cell responses color-opponent without requiring cone-type selective connectivity.

Chromatic bipolar cell pathways in the mouse retina.

Like most mammals, mice feature dichromatic color vision based on short (S) and middle (M) wavelength-sensitive cone types. It is thought that mammals share a retinal circuit that in dichromats compares S- and M-cone output to generate blue/green opponent signals, with bipolar cells (BCs) providing separate chromatic channels. Although S-cone-selective ON-BCs (type 9 in mouse) have been anatomically identified, little is known about their counterparts, the M-cone-selective OFF-BCs. Here, we characterized cone connectivity and light responses of selected mouse BC types using immunohistochemistry and electrophysiology. Our anatomical data indicate that four (types 2, 3a/b, and 4) of the five mouse OFF-BCs indiscriminately contact both cone types, whereas type 1 BCs avoid S-cones. Light responses showed that the chromatic tuning of the BCs strongly depended on their position along the dorsoventral axis because of the coexpression gradient of M- and S-opsin found in mice. In dorsal retina, where coexpression is low, most type 2 cells were green biased, with a fraction of cells (≈ 14%) displaying strongly blue-biased responses, likely reflecting S-cone input. Type 1 cells were also green biased but did not comprise blue-biased "outliers," consistent with type 1 BCs avoiding S-cones. We therefore suggest that type 1 represents the green OFF pathway in mouse. In addition, we confirmed that type 9 BCs display blue-ON responses. In ventral retina, all BC types studied here displayed similar blue-biased responses, suggesting that color vision is hampered in ventral retina. In conclusion, our data support an antagonistically organized blue/green circuit as the common basis for mammalian dichromatic color vision.

A novel type of interplexiform amacrine cell in the mouse retina.

Mammalian retinas comprise an enormous variety of amacrine cells with distinct properties and functions. The present paper describes a new interplexiform amacrine cell type in the mouse retina. A transgenic mouse mutant was used that expressed the gene for the enhanced green fluorescent protein (EGFP) instead of the coding DNA of connexin45 in several retinal cell classes, among which a single amacrine cell population was most prominently labelled. Staining for EGFP and different marker proteins showed that these amacrine cells are interplexiform: they stratify in stratum S4/5 of the inner plexiform layer and send processes to the outer plexiform layer. These cells were termed IPA-S4/5 cells. They belong to the group of medium-field amacrine cells and are coupled homologously and heterologously to other amacrine cells by connexin45. Immunostaining revealed that IPA-S4/5 cells are GABAergic and express GAT-1, a plasma-membrane-bound GABA transporter possibly involved in non-vesicular GABA release. To characterize the light responses of IPA-S4/5 cells, patch-clamp recordings in retinal slices were made. Consistent with their stratification in the ON sublamina of the inner plexiform layer, cells depolarized in response to light ON stimuli and transiently hyperpolarized in response to light OFF. Responses of cells to green (578 nm) and blue (400 nm) light suggest that they receive input from cone bipolar cells contacting both M- and S-cones, possibly with reduced S-cone input. A new type of interplexiform ON amacrine cell is described, which is strongly coupled and uses GABA but not dopamine as its neurotransmitter.

Eyecup scope--optical recordings of light stimulus-evoked fluorescence signals in the retina.

Dendritic signals play an essential role in processing visual information in the retina. To study them in neurites too small for electrical recording, we developed an instrument that combines a multi-photon (MP) microscope with a through-the-objective high-resolution visual stimulator. An upright microscope was designed that uses the objective lens for both MP imaging and delivery of visual stimuli to functionally intact retinal explants or eyecup preparations. The stimulator consists of a miniature liquid-crystal-on-silicon display coupled into the optical path of an infrared-excitation laser-scanning microscope. A pair of custom-made dichroic filters allows light from the excitation laser and three spectral bands ('colors') from the stimulator to reach the retina, leaving two intermediate bands for fluorescence imaging. Special optics allow displacement of the stimulator focus relative to the imaging focus. Spatially resolved changes in calcium-indicator fluorescence in response to visual stimuli were recorded in dendrites of different types of mammalian retinal neurons.

Lateral modulation boosts image quality in single plane illumination fluorescence microscopy.

A new microscope combines optical sectioning by fluorophore excitation using a single light sheet with structured illumination. Several images with laterally intensity-modulated light sheets are recorded from scattering fluorescent specimens. By applying a simple data processing scheme, the nonmodulated volumes are identified. The blurred features become dark, and the resultant images are improved in terms of contrast and resolution. Hence, the instrument is capable of discriminating against contributions to the image that are induced by the optical properties of the specimen. The new microscope's capabilities are demonstrated by imaging the internals of the head of an adult Drosophila melanogaster (fruit fly) expressing green fluorescent protein-labeled polycomb proteins.