Biomedical subjects

J Ammermüller

Publications and source records attributed to J Ammermüller.

27 records · Page 2Linked to original sources

PubMed1989

Immunohistochemical and electrophysiological evidence that locust ocellar photoreceptors contain and release histamine.

Immunohistochemistry with an antiserum directed against histamine revealed histamine-like immunoreactivity in ocellar photoreceptors of Locusta migratoria. Prefixative incubation of the tissue in Ringer solution containing 10 microM histamine increased number and intensity of labeled photoreceptors. Additionally, glial cells became immunoreactive. High extracellular potassium concentration abolished labeling in retinula cells but not in glial cells. These results suggest that locust ocellar photoreceptors contain histamine and release it upon depolarization. Histamine itself or/and a metabolite is taken up by photoreceptors and glial cells. In high-potassium/calcium-free Ringer solution labeling in photoreceptors persisted, indicating that release is calcium-dependent. Electrophysiological recordings confirm the hyperpolarizing and localized action of histamine onto dendrites of second-order neurons in the ocellar cup. These results support the hypothesis that histamine is a neurotransmitter in insect photoreceptor cells.

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PubMed1988

Physiological and morphological characterization of OFF-center amacrine cells in the turtle retina.

OFF-center amacrine cells were intracellularly recorded and stained with Lucifer yellow to investigate the cell correlations between photoresponses and morphological features. All OFF-amacrine cells were monostratified and branched within the outer half of the inner plexiform layer. In the flat-mounted retina, however, three distinct morphological classes were distinguishable, which correlated with observed physiological differences. Class 1 consisted of wide-field, stellate amacrine cells with long, thin processes, which branched only close to the soma. The diameter of the circular dendritic field ranged from 0.8 mm to 2.0 mm. Their photoresponse to spot stimulation was a hyperpolarization during light-ON and a small depolarization after light-OFF. They showed strong antagonistic center-surround organization of the receptive field. Its size was approximately equal to the dendritic field size. Class 2 consisted of wide-field, giant amacrine cells with a "central" dendritic field formed by thick dendrites, and a "peripheral" dendritic field formed by a few long and thin, "axonlike" processes. The shape of the dendritic field was elongated, with the long axis parallel to the visual streak. Their receptive field size was considerably smaller than their dendritic field size, which was several millimeters of diameter along the long axis. Their photoresponse to spot stimulation was a fast depolarization after light-OFF, and about 50% of these cells showed strong antagonistic center-surround receptive field organization. Class 3 consisted of small- or medium-field, "starburstlike" amacrine cells with circular dendritic fields of 0.1 mm to 0.6 mm diameter. Their fine, beaded dendrites branched predominantly in the distal parts of the dendritic field. their photoresponses to light were similar to those of the giant amacrine cells; however, their receptive field size exceeded the dendritic field size. Radial sections of the retinas with labeled cells were incubated in antisera to reveal the putative transmitters GABA, serotonin, neurotensin, met-enkephalin and glucagon. No immunoreactivity with these antisera was detected within the stained OFF-center amacrine cells.

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PubMed1986

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.

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PubMed1985

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

Electrophysiological 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.

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PubMed1981

The ramification pattern of amacrine cells within the inner plexiform layer of the carp retina.

The morphology of amacrine cells in the retina of the carp is described using the Golgi technique. The ramification pattern of these cells was analyzed in flat-mounts of retinas, Based on these observations classification into five groups was made. Cells possessing one principal process leaving the soma were subdivided into starburst A-neurons and radiate neurons. Cells having two or more principal processes were subdivided into starburst B-neutrons and spindle-shaped soma neurons. Small, diffuse amacrine cells form the fifth group. With respect to the shape of the field of arborization, the following cell types could be distinguished: (i) uniform cells, (ii) cells with a preferential direction, and (iii) cells with a marked edge, i.e., cells that lack processes in one direction. The latter form rarely occurs among starburst neurons; most of the spindle-shaped soma cells possess processes with a preferred direction, and cells with a marked edge are mainly found among the radiate neurons. All five cell types are found throughout the retina. The size of the cells varies within each group, and there is no correlation between size and distance from the optic nerve. The radial arborization pattern of each cell was examined in serial transverse sections. Starburst A-neurons ramify in the middle of the inner plexiform layer (IPL), radiate neurons in the inner half, and spindle-shaped soma neurons without overlapping processes (type B) as well as starburst B-neurons in the outer half. The ramification can be monostratified (narrow or broad), bistratified or multistratified. Small, diffuse amacrine cells and spindle-shaped soma neurons with overlapping process (type A) ramify throughout the entire IPL.

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PubMedDate not supplied

Short-term effects of dopamine on photoreceptors, luminosity- and chromaticity-horizontal cells in the turtle retina.

The effects of dopamine on luminosity-type horizontal cells have been documented in different vertebrate retinas, both in vivo and in vitro. Some of these effects may reflect direct action of dopamine onto these cells, but indirect effects mediated by presynaptic neurons cannot be ruled out. Furthermore, direct effects of dopamine on horizontal cells may affect other, postsynaptic neurons in the outer plexiform layer. To test these possibilities, we studied the effects of dopamine on photoreceptors and all types of horizontal cells in the turtle (Pseudemys scripta elegans) retina. Receptive-field properties, responsiveness to light, and time course of light responses were monitored with intracellular recordings. Dopamine at a concentration of 40 microM exerted effects with two different time courses. "Short-term" effects were fully developed after 3 min of dopamine application and reversed within 30 min of washout of the drug. "Long-term" effects were fully developed after about 7-10 min and could not be washed out during the course of our experiments. Only the "short-term" effects were studied in detail in this paper. These were expressed in a reduction of the receptive-field size of all types of horizontal cells studied; L1 and L2 luminosity types as well as Red/Green and Yellow/Blue chromaticity types. The L1 horizontal cells did not exhibit signs of reduced responsiveness to light under dopamine, while in the L2 cells and the two types of chromaticity cells responsiveness decreased. None of the rods, long-wavelength-sensitive, or medium-wavelength-sensitive cones exhibited any apparent reduction in their receptive-field sizes or responsiveness to light. The present results suggest that the "short-term" effects of dopamine are not mediated by photoreceptors and are probably due to direct action of dopamine on horizontal cells.

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PubMedDate not supplied

Asymmetrical dynamics of voltage spread in retinal horizontal cell networks.

Lateral voltage spread in electrically coupled retinal horizontal cell networks is the substrate of center-surround antagonism in bipolar and ganglion cells. We studied its spatial and temporal properties in more detail in turtle L1 horizontal cells by using a contrast border as light stimulus. Experimental data were contrasted with expectations from a linear continuum model to specify the impact of nonlinearities. The assumptions for the diffusion term of the continuum model were justified by neurobiotin labeling. Measured voltage spread revealed two different length constants lambda+ and lambda0, under illuminated and nonilluminated regions of the retina, respectively, as predicted by the linear model. Length constants in the illuminated region showed strong temporal dynamics. For the initial phase of the horizontal cell responses lambda+ was larger than lambda0. This was also in accordance with the model. Right at the peak of the response, however, lambda+ dropped below lambda0 and did not change any more. It is this temporal reversal of asymmetry in voltage spread and not the decrease of lambda+ itself that is lacked by the linear model. The observed independence of the mean ratio lambda+/lambda0 from light intensity in both the peak and the plateau phases of horizontal cell responses contradicts the linear assumption, too. These two effects have to be addressed to local nonlinearities in the horizontal cell network like a negative feedback loop from photoreceptors and/or voltage-dependent conductances. Due to the failure of the linear model, firm conclusions about the membrane resistance and the coupling resistance of the horizontal cell network cannot be drawn from length constant measurements.

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PubMedDate not supplied

Identification and localization of connexin26 within the photoreceptor-horizontal cell synaptic complex.

Connexin26 (Cx26) is a member of the family of integral membrane proteins that normally form intercellular gap junctional channels. We have used Western blotting, immunofluorescence, immunoelectron microscopy, and single-cell reverse-transcriptase polymerase chain reaction amplification (RT-PCR) to analyze the expression and cellular localization of Cx26 in the carp retina. In the outer plexiform layer, strong clustered Cx26 immunolabeling was concentrated at and restricted to the terminal dendrites of horizontal cells. Single-cell RT-PCR confirmed the expression of Cx26 in carp retinal horizontal cells. 248-bp fragments amplified from cDNAs of four different horizontal cells were cloned and each nucleotide sequence encodes a protein fragment (AA 104-185) with highly significant homology to rat and mouse Cx26. Immunoelectron microscopy revealed that only the invaginating dendrites of horizontal cells in intimate lateral association with the presynaptic ribbon complex were labeled. No labeling was found at the photoreceptor membrane and there was no septalaminar structure, indicative of gap junctions, between photoreceptors and horizontal cells. The focal location of Cx26 at the membrane of the dendritic tips of horizontal cells and the lack of gap junctional morphology suggests that Cx26 might form hemichannels.

Amino Acid Sequence↗

PubMedDate not supplied

Different types of synapses with different spectral types of cones underlie color opponency in a bipolar cell of the turtle retina.

Electrophysiologically, color-opponent retinal bipolar cells respond with opposite polarities to stimulation with different wavelengths of light. The origin of these different polarities in the same bipolar cell has always been a mystery. Here we show that an intracellularly recorded and HRP-injected, red-ON, blue/green-OFF bipolar cell of the turtle retina made invaginating (ribbon associated) synapses exclusively with L-cones. Non-invaginating synapses resembling wide-cleft basal junctions were made exclusively with M-cones. Input from S-cones was not seen. From these results we suggest sign-inverting transmission from L-cones at invaginating synapses via metabotropic glutamate receptors, and sign-conserving transmission from M-cones at wide-cleft basal junctions via ionotropic receptors. To explain the pronounced blue sensitivity of the bipolar cell, computer simulations were performed using a sign-conserving input from a yellow/blue chromaticity-type (H3) horizontal cell. The response properties of the red-ON, blue/green-OFF bipolar cell could be quantitatively reproduced by this means. The simulation also explained the asymmetry in L- and M-cone inputs to the bipolar cell as found in the ultrastructural analysis and assigned a putative role to H3 horizontal cells in color processing in the turtle retina.

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