Yoko Hashimoto

The network properties of bipolar-bipolar cell coupling in the retina of teleost fishes

Retinal bipolar cells exhibit a center-surround antagonistic receptive field to a light stimulus (Werblin & Dowling, 1969; Kaneko, 1970), and thus constitute an early stage of spatial information processing. We injected Lucifer Yellow and a small biotinylated tracer, biocytin, into bipolar cells of the teleost retina to examine electrical coupling in these cells. Lucifer-Yellow coupling was observed in one of 55 stained bipolar cells; the coupling pattern was one injected bipolar cell and three surrounding cells. Biocytin coupling was observed in 16 of 55 stained bipolar cells, six of which were ON center and ten OFF center. Although biocytin usually coupled to three to six bipolar cells, some OFF-center bipolar cells showed strong coupling to more than 20 cells. The biocytin-coupled bipolar cells were morphologically homologous. Membrane appositions resembling gap junctions were found between dendrites and between axon terminals of neighboring bipolar cells. In the strongest biocytin-coupled bipolar cells, the contacts between bipolar cells and cone photoreceptor cells were examined after reconstruction of the dendritic trees of five well-stained, serially sectioned OFF-center bipolar cells. Each of these bipolar cells was in contact with different numbers of cones: 11 to 20 for twin cones and two to four for single cones. This implies that, although these bipolar cells belong to the same category, the signal inputs differ among bipolar cells. Numerical simulation conducted on a hexagonal array network model demonstrated that the electrical coupling of bipolar cells can decrease the difference in input (approximately 80%) without causing significant loss of spatial resolution. Our results suggest that electrical coupling of bipolar cells has the advantage of decreasing the dispersion of input signals from cones, and permits bipolar cells of the same class to respond to light with similar properties.

Dopaminergic amacrine cells in the retina of Japanese dace.

The morphological and physiological identification of the cells in the inner retina of Japanese dace was made by means of intracellular single cell recording and dye injection techniques. Our flat mounts and physiological classification revealed that 97 out of 102 sample cells were amacrine cells except for 3 transient neurons possibly being ganglion cells. Only two cells were identified as interplexiform cells. The double-labeling histochemical technique showed that 17 cells including the two interplexiform cells are dopaminergic neurons. Therefore, 15 of 97 amacrine cells in dace retina were dopaminergic cells, a finding which is different from the previously published data.

Characteristics of second order neurons in the dace retina: Physiological and morphological studies

The different kinds of cones in the retina of the date, Tribolodon hukonensis. are distributed in a very regular row mosaic pattern. This pattern is the same as Engstriim in 1960 described in the retina of the roach, Lwciscus rutilus. He found at least three clearly distinct types of cones: (1) short single cones without myoid, (2) long single cones and (3) unequal double cones. Figure 1 illustrates the cone types of tc~~tcisc~rs which is reproduced from EngstrSm (1960). The upper diagram (a) shows a transverse section. The ellipsoids are found at three separate levels; those at the distal level are in the unequal doubie cone (C), more proximaily are shown those of the long single cones (B). and most proximally are shown those of the short single cones (A). The lower diagram (b) shows a tangential section in which the single and double cones can be seen organized in a regular pattern. The rows of double cones alternated with rows of single cones. Schoies and Morris (1973) and &holes (1975) described the morphology of receptors and some bipolars in the rudd retina, Stwrtlinius c,r!,thrclphthlrlrIllrs. According to their studies, the rudd retina contains rods and five morphologically distinct kinds of cones, that is, paired elements of unequal double cones and three unpaired cones (free principal cones, singfe cones and oblique cones). Scholes also measured the visual pigments in these cones by microdensitometry. Mean absorption spectra indicated that the principal cone of double cones contained pigment showing a mean absorption maximum at 625 nm, the accessory cone of the double cones had its maximum absorption at 530 nm, and the peak absorption for the singie cone pigment was at 427 nm. Wagner (1978) described the pattern of connectivity in the external plexiform layer of mosaic retinas of 18 different teleost species. but the mainly investigated the retina of cichlidae, ~unnu~ur~ anomalu, which has a square mosaic.

Identification of the interplexiform cell in the dace retina by dye-injection method.

The responses of interplexiform cells in the dace retina were recorded intracellularly and identified morphologically. The response pattern closely resembles the response of bipolar cells and amacrine cells (on- and off-types). Morphologically, the perikaryon of most of these cells lies in the amacrine cell layer, and is usually large in size. Distal and proximal processes arise from the soma directly. The distal process ramifies and extends widely in the outer plexiform layer, but does not make contact with receptor terminals. The proximal process branches and extends widely in the inner plexiform layer. The majority of these cells resembles the dopaminergic interplexiform cells, but a few resemble the glycinergic interplexiform cells in the goldfish retina.

Effects of ALCAR on the fast axoplasmic transport in cultured sensory neurons of streptozotocin-induced diabetic rats.

The effects of acetyl-L-carnitine (ALCAR) on fast axoplasmic transport were studied in cultured dorsal root ganglion (DRG) neurons of diabetic rats. Three-month-old male rats were used 7 days after streptozotocin injection. Neurons obtained from ganglia were cultured with a high concentration of glucose. The amount and the mean velocity of retrogradely transported particles, reduced in the diabetic animal, were transiently recovered by 1 mM ALCAR. The number of particles moving at 0.8-1.2 microm/s, considered to be lysosomes, increased in the velocity distribution. ALCAR did not modify the amount and mean velocity of anterograde particles which were unaffected by diabetes, or of bidirectional particles in neurons of control rats. This study suggests that diabetic neuropathy may be relieved by ALCAR via recovering retrograde axoplasmic transport.

Disruption of type 5 adenylyl cyclase negates the developmental increase in Gαolf expression in the striatum

The two stimulatory G protein α subunits, Gαs and Gαolf, activate adenylyl cyclase in a similar way. We examined whether type 5 adenylyl cyclase knockout, the major striatal isoform, can differentially and/or developmentally change the expression of these G proteins in the striatum. Gαs and Gαolf expressions at birth were unaffected in knockouts, which, however, demonstrated a blunted developmental increase in Gαolf, but not Gαs. Adenylyl cyclase activity was unaffected at birth, but subsequently became lower in knockouts. These findings suggest that type 5 adenylyl cyclase does not contribute to striatal cAMP signaling at birth. However, it may play an important role in developmental changes in the expression of Gαolf, but not Gαs.

Effects of acetylcholine and adrenaline on axoplasmic transport at different regions of mouse superior cervical ganglion cells in culture

Adrenaline and acetylcholine (ACh) were applied locally at three different positions in cultured superior cervical ganglion cells, i.e., cell body, neurite, and growth cone and the effects on the axoplasmic transport were measured with a video-enhanced microscope. Local ACh application to the cell body, neurite, and growth cone caused the same decreasing effect, but the effects of local adrenaline application were different from each other. Local adrenaline application to the cell body and growth cone caused an increase of axoplasmic transport, but local application at the neurite caused no effect. These data may indicate that there was a lack of beta 2 adrenergic receptors in the neurite. Desensitization of axoplasmic transport was also examined in the SCG neurons. Repetitive adrenaline application to the cell body caused desensitization to the stimulus of adrenaline application.

Preference of Peanut Agglutinin Labeling for Long-wavelength-sensitive Cone Photoreceptors in the Dace Retina

Peanut agglutinin (PNA) was known for its selective binding to cone cells. In the present study, we investigated whether there was any difference in PNA binding among various subtypes of cone photoreceptor cells in the dace retina. The outer segments of the long-double- and long-single-cone cells were preferentially labeled with PNA. Ultrastructural pre-embedding labeling revealed that the binding sites of PNA were confined to the calycal processes of these cells. By contrast, only slight labeling was discerned on the corresponding regions of other types of cone cells. The results indicate that PNA can distinguish the long-wavelength-sensitive cone from the short-to-middle-wavelength-sensitive cone cells.

Receptive-field properties of retinal amacrine cells in homotypic gap junction networks

Gap junctions were evaluated in four classes of physiologically identified retinal amacrine cells, after simultaneous injection of Lucifer yellow and biotinylated compounds. In addition, the morphology of these cells was correlated with their photoresponses. Two types of homotypic junctions (those between cells of the same class) were found: tip contacts and crossing-contacts, i.e. those at dendrite tips versus those between dendritic shanks. The receptive field of cells electrically coupled with tip contacts was monotonic, while that of cells with crossing-contacts also had sustained antagonistic surrounds.

Hyperpolarizing interplexiform cell of the dace retina identified physiologically and morphologically.

One type of interplexiform cell (IPC) in the dace retina was discriminated physiologically from other cell classes and identified morphologically with HRP staining. This type responded with slow hyperpolarizing potentials to white diffuse light, and in addition a slow hyperpolarization (after potential) was observed after the cessation of light with relatively high intensities. The latency of the ON phase of the response was always longer than that of the second-order neurons and the amacrine cells. Morphologically, this type of IPC was similar in appearance with the dopaminergic IPC. The conventional synaptic specialization between this type of IPC and horizontal cells was observed, and the IPC was presynaptic.