Reto Weiler

Light-dependent change of cone-horizontal cell interactions in carp retina

Carp H2 horizontal cells were investigated at various stages of dark and light adaptation. Their state of adaptation was verified by evaluating in computer reconstructed serial sections the number of small, fingerlike protrusions originating from H1 processes. These so-called spinules are absent in the dark-adapted state and are reformed during light adaptation. Intracellular recordings showed that long-wave-induced depolarization thought to be mediated by sign-inverted feedback from H1 horizontal cells onto green-sensitive cones could not be demonstrated in completely dark-adapted specimens. This type of response only developed with increasing light adaptation. Following electrophysiological characterization, the cells were injected with horseradish peroxidase and identified light and electronmicroscopically. Our results show a good correlation between the number of spinules and the degree of electrophysiological feedback suggesting that the spinules may be the sites of the feedback synapses in teleost retinas. Several models of synaptic transmission from H1 terminals to cone pedicles are discussed.

Neural principles in vision

Opening Remarks.- 1 Vertebrates.- 1.1 Patterns of Golgi-Impregnated Neurons in a Predator-Type Fish Retina.- 1.2 A Comparative Study of the Horizontal Cells in the Vertebrate Retina: I. Mammals and Birds.- 1.3 Neuronal Connections and Cellular Arrangement in the Fish Retina.- 1.4 Golgi, Procion, Kernels and Current Injection.- 1.5 Electrophysiological and Histological Studies of the Carp Retina.- 1.6 Interactions and Feedbacks in the Turtle Retina.- 1.7 Interactions between Cones and Second-Order Neurons in the Turtle Retina.- 1.8 Synaptic Transmission from Photoreceptors to the Second-Order Neurons in the Carp Retina.- 1.9 Retinal Physiology in the Perfused Eye of the Cat.- 2 Arthropods.- 2.1 Adaptations of the Dragonfly Retina for Contrast Detection and the Elucidation of Neural Principles in the Peripheral Visual System.- 2.2 Voltage Noise in Insect Visual Cells.- 2.3 Spectral and Polarization Sensitivity of Identified Retinal Cells of the Fly.- 2.4 Neuronal Processing in the First Optic Neuropile of the Compound Eye of the Fly.- 2.5 Beyond the Wiring Diagram of the Lamina Ganglionaris of the Fly.- 2.6 Mosaic Organizations, Layers, and Visual Pathways in the Insect Brain.- 2.7 Structure and Function of the Peripheral Pathway in Hymenopterans.- 2.8 Neuronal Architecture and Function in the Ocellar System of the Locust.- 2.9 The Resolution of Lens and Compound Eyes.- 3 Molluscs.- 3.1 Ultrastructural Observations on the Cortex of the Optic Lobe of the Brain of Octopus and Eledone.- 3.2 The Question of Lateral Interactions in the Retina of Cephalopods.- 3.3 Hyperpolarizing Photoreceptors in Invertebrates.- 3.4 The Economy of Photoreceptor Function in a Primitive Nervous System.

Morphological and pharmacological analysis of putative serotonergic bipolar and amacrine cells in the retina of a turtle, Pseudemys scripta elegans

SummaryUsing immunocytochemical methods, we have been able to demonstrate serotonin-like immunoreactivity (SLI) in amacrine and bipolar cells of the turtle retina. Inhibition of monoamine oxidase with pargyline drastically increases the amount of 5-hydroxytryptamine within both cell types. The indoleamine 6-hydroxytryptamine is taken up by both cell types and both types are destroyed within 10 days following intraocular injection of 5,7-dihydroxyryptamine. Increasing the external potassium concentration induces release of serotonin in both cell types. Our data support the idea that these neurons use serotonin during neuronal processing. Morphologically, amacrine and bipolar cells with SLI can be subdivided into two and three subclasses, respectively, based on their ramification pattern within the inner plexiform layer. A comparison of the morphological data with those of intracellularly stained amacrine and bipolar cells suggests that all bipolar cells with SLI are center-hyperpolarizing cells and all amacrine cells center-depolarizing cells.

Immunocytochemical demonstration ofγ-amino butyric acid and glutamic acid decarboxylase in R7 photoreceptors and C2 centrifugal fibres in the blowfly visual system

SummaryNeurons within the compound eye of the flyCalliphora erythrocephala, suspected of containing gamma-aminobutyric acid were revealed immunocytochemically, using antibodies directed against gamma-aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD). The GABA content within putative GABAergic neurons was increased by high affinity uptake of GABA and selective blocking of GABA metabolism with Gabaculine. Only neuronal populations which were labelled with the GABA as well as the GAD antibodies were presumed to be GABAergic. The first optic neuropil (lamina) exhibited two distinct GA-BAergic fibre populations amongst a larger population comprised of fourteen cell classes. One fibre population was formed by the axons of the photopic photoreceptors R7 which pass through the lamina and terminate in the second optic neuropil (the medulla). The identity of R7 was established from longitudinal and transverse sections of the retina where R7 can be unequivocally distinguished from the six scotopic photoreceptors R1-6 and the other photopic receptor, R8.The other fibre population matched the profiles in the lamina of terminals of efferent C2 neurons. These neurons project distally from beneath the medulla out to the lamina ganglionaris where each retinotopic unit (cartridge) contains a characteristic hook-like terminal arbor distally. We propose from these data that the photoreceptors R7 and the efferent C2 neurons use GABA as a neurotransmitter.

Horizontal Cells of the Carp Retina: Golgi Impregnation and Procion-Yellow Injection*

SummaryApplication of two methods for the selective staining of neurons, Golgi impregnation and intracellular marking with Procion Yellow, has revealed the anatomical arrangements of the horizontal cells in the carp retina. There are two basic horizontal-cell types, those with axons and these without. The former can be subdivided into three groups on the basis of the pattern of branching of the dendrites. These three structural groups are also functionally distinct, as shown by the electrical recordings made during Procion-Yellow injection. The axons of these three types of cell project into the proximal part of the inner nuclear layer, where they expand to form morphologically indistinguishable terminals. Fine horizontal processes leave the surfaces of these axon terminals. The functional behavior of a terminal resembles that of the associated soma. The horizontal cells lacking axons vary in morphological appearance, but they are similar functionally.

Immunocytochemical localization of serotonin in intracellularly analyzed and dye-injected ganglion cells of the turtle retina

Combining intracellular recording techniques with immunocytochemistry revealed the existence of serotonin within a few ganglion cells of the turtle retina. Lucifer yellow was intracellularly injected into physiologically classified ganglion cells. Sections containing labeled somata were subsequently incubated with an antibody directed against serotonin and immunoreactivity was revealed using horseradish peroxidase as a marker. In 3 ganglion cells the two markers were co-localized. These cells ramified in layers 2 and 3 of the inner plexiform layer and produced color opponent ON-OFF photoresponses.

Mesencephalic pathway to the retina exhibits enkephalin-like immunoreactivity

Using immunocytochemical methods it was possible to demonstrate a small number of fibers within the optic nerve of the turtle Pseudemys scripta elegans exhibiting Met-enkephalin-like immunoreactivity. The fibers project to the retina where they ramify within the inner plexiform layer in the region of the visual streak. Retrograde labelling with Nuclear Yellow in combination with immunocytochemical staining revealed the origin of these fibers within visceral nuclei of the caudal mesencephalon. The existence of a mesencephalic, enkephalinergic pathway to the retina will facilitate further studies of opiate action in the retina by offering the possibility of selectively stimulating the endogenous release.

The distribution of center-depolarizing and center-hyperpolarizing bipolar cell ramifications within the inner plexiform layer of turtle retina

SummaryCenter-depolarizing and center-hyperpo-larizing photoresponses were recorded intracellularly from different bipolar cells in the turtle retina and subsequently injected with Procion Yellow for morphological analysis. The results indicate that the type of photoresponse is neither related to large or small soma sized cells nor to the number of axonal ramifications within the inner plexiform layer (IPL). It was found that axonal arborizations of center-depolarizing cells are restricted to the inner 60% of IPL, whereas arborizations of the center-hyperpolarizing cells are present at all levels of IPL.

Kainic acid-induced release of serotonin from OFF-bipolar cells in the turtles retina

The immunofluorescence of antibody-labelled serotonin was used as an indicator for the amount of intracellular serotonin. Incubation in Ringer solution containing serotonin and pargyline increased the immunofluorescence which was subsequently decreased in a calcium-dependent manner by incubation in high-potassium Ringer. If preloaded retinas were exposed to 10 microM kainic acid, the immunofluorescence decreased in a time-dependent way. This kainic acid-induced release was blocked by piperidine dicarboxylic acid. These results support the idea that serotonin is a transmitter in OFF-bipolar cells.

S-neurons and not L-neurons are the source of GABAergic action in the ocellar retina

SummaryElectrophysiological evidence obtained with current- and voltage clamp experiments from single L-neurons of the ocellar nerve of locust (Locusta migratoria) questions a direct synaptic feedback from these neurons onto the photoreceptors. The synaptic currents recorded under voltage clamp reflected the photoresponse of the L-neuron, despite the fact it developed no synaptic activity under these conditions. This result is contrary to GABAergic feedback models proposed in the literature. Electrophysiological recordings, as well as immunocytochemistry revealing GABA and glutamate decarboxylase, indicated a possible contribution of S-neurons in such a feedback system. A population of probable S-neurons whose somas were in the pars intercerebralis adjacent to the ocellar nerve tracts was heavely labelled. About 10 fibres entered each tract and formed a dense network of fine arborizations within the ocellar plexiform layer. L-neurons showed no GABA-immunoreactivity. Based on these data a new model for GABAergic feedback is proposed and discussed.