RESUMEN
Following retrograde transport of horseradish peroxidase from the optic nerve to the retina in Xenopus laevis, biplexiform ganglion cell were revealed. Their synaptic association with the other elements of the outer plexiform layer (OPL) were studied in serial ultrathin sections. The dendrites in the OPL of two regrogradely labelled biplexiform ganglion cells (GC1 and GC2) were completely reconstructed from the sections. Both cells had similar dendritic field sizes (0.026 and 0.025 m2, respectively) in the OPL, and received a few dozens of synapses (GC1: 39, GC2: 56) synapses. None of the ganglion cell dendrites were found in presynaptic position. Of the synapses, 10 derived from rods, 22 from cones and 7 from horizontal cells to GC1 and 13 from rods, 32 from cones and 10 from horizontal cells to GC2. Synapses were seen neither between interplexiform cell axons and biplexiform ganglion cell dendrites nor bipolar and biplexiform ganglion cell dendrites in the OPL. These observations indicate that the dendrites of biplexiform ganglion cells preferentially but not exclusively receive synapses from photoreceptor cells in the OPL.
Asunto(s)
Retina/fisiología , Sinapsis/ultraestructura , Animales , Recuento de Células , Dendritas/ultraestructura , Femenino , Ganglios/ultraestructura , Masculino , Microscopía Electrónica , Xenopus laevisRESUMEN
The central termination and the transmitter content of the optic fibers and the neurochemical nature of their synaptic targets was investigated in the optic tectum of the toad Bufo marinus. Retinal ganglion cells were retrogradely filled from the tectum with the fluorescent dye DiI and the retinal wholemounts were immunostained for glutamate. Most of the dye-filled cells could be double labeled. In addition, double-labeling for gamma-aminobutyric acid an glutamate were also made, when colocalization of these markers was not observed in the neurons of the retinal ganglion cell layer. In order to identify retinal terminals in the optic tectum, optic axons were retrogradely filled with horseradish peroxidase. Postembedding immunocytochemistry showed that 88% of the optic axon terminals were glutamate-like immunoreactive, 6% gamma-aminobutyric acid-immunoreactive and 6% were negative for both GABA and glutamate. Optic fibre terminals synapsed on gamma-aminobutyric acid- or glutamate-containing postsynaptic profiles (58% and 7%, respectively), while the rest on immunonegative elements. Optic fibres containing glutamate rarely synapsed with glutamate-like immunoreactive postsynaptic elements. In contrast, 67% of the gamma-aminobutyric acid-immunoreactive optic terminals synapsed onto gamma-aminobutyric acid-positive dendrites. It has been observed after combination of anterograde tracer transport and double-label immunocytochemistry, that 57% of the optic terminals synapsed on gamma-aminobutyric acid-immunoreactive elements and 38% on dendrites containing neither gamma-aminobutyric acid- nor glutamate-immunoreactive materials. These results suggest that (1) a large number of ganglion cells use glutamate and some gamma-aminobutyric acid as a transmitter, (2) a substantial proportion of the optic axons terminate on gamma-aminobutyric acid-containing inhibitory interneurons in the tectum, (3) some intrinsic neurons in the tectum are glutamate-like immunoreactive. We also propose, that (4) gamma-aminobutyric acid-immunoreactive optic axons may form an effective disinhibitory circuit in the tectum by synapsing preferentially with local inhibitory interneurons.
Asunto(s)
Axones/ultraestructura , Ácido Glutámico/análisis , Células Ganglionares de la Retina/fisiología , Colículos Superiores/anatomía & histología , Colículos Superiores/fisiología , Sinapsis/ultraestructura , Ácido gamma-Aminobutírico/análisis , Animales , Transporte Axonal , Axones/fisiología , Bufo marinus , Dendritas/ultraestructura , Peroxidasa de Rábano Silvestre , Inmunohistoquímica , Microscopía Electrónica , Microscopía Inmunoelectrónica , Fibras Nerviosas/ultraestructura , Células Ganglionares de la Retina/citología , Colículos Superiores/citología , Sinapsis/fisiología , Vesículas Sinápticas/ultraestructuraRESUMEN
The synaptic connections of amacrine cells synthesizing or accumulating serotonin in the retina of the cane toad, Bufo marinus, were studied by using preembedding double-labeling electron-microscopic immunocytochemistry. The binding sites of an anti-serotonin antibody were revealed by the diaminobenzidine reaction, whilst a colloidal gold-conjugated secondary antibody was used to detect an antibody to phenylalanine hydroxylase. Since the latter antibody recognizes tryptophan 5-hydroxylase, one of the synthesizing enzymes for serotonin, as well as tyrosine hydroxylase, the rate-limiting enzyme for catecholamine synthesis, the double labeling of the present study enabled us to identify three groups of labeled profiles at the ultrastructural level. The profiles of serotonin-synthesizing amacrine cells contained both diaminobenzidine reaction product and colloidal gold particles, whilst those of serotonin-accumulating and dopaminergic amacrine cells contained only diaminobenzidine reaction product or colloidal gold particles, respectively. The synapses of serotonin-synthesizing or serotonin-accumulating amacrine cells were distributed all through the inner plexiform layer of the retina. The profiles of serotonin-synthesizing amacrine cells predominantly received synapses from, and made synapses onto, unlabeled amacrine cell dendrites. They also received synapses from, and made synapses onto, bipolar cell terminals. They also made synapses onto presumed ganglion cell dendrites. However, the profiles of serotonin-accumulating cells made synapses only with unlabeled amacrine cell processes. There were close contacts between the profiles of serotonin-synthesizing and serotonin-accumulating amacrine cells. No synaptic relationships were observed between dopaminergic and serotonin-synthesizing or serotonin-accumulating amacrine cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Retina/metabolismo , Serotonina/biosíntesis , Sinapsis/fisiología , Transmisión Sináptica/fisiología , Animales , Bufo marinus , Técnicas para Inmunoenzimas , Inmunohistoquímica , Microscopía Inmunoelectrónica , Neuronas/metabolismo , Neuronas/fisiología , Neuronas/ultraestructura , Retina/fisiología , Retina/ultraestructura , Sinapsis/ultraestructura , Vías VisualesRESUMEN
The morphology of projection neurons of the isthmic nucleus was studied in Rana esculenta, R. nigromaculata, Bufo marinus, B. bufo gargarizans, and Xenopus laevis from a comparative anatomical point of view. The main point of this work was to provide an anatomical basis for electrophysiological studies. Neurons projecting to the ipsilateral optic tectum were labeled by retrograde transport of horseradish peroxidase and cobaltous lysine complex injected into the optic tectum. Contralaterally projecting cells were filled by injecting the tracer substances into the crossed isthmotectal tract. Cells of the anterior nonrim cortex and the rostral part of the medulla project to the ipsilateral tectum. A band of cells in the middle of the medulla, a few cells in the caudal part of the medulla, and most of the neurons in the rim cortex project to the contralateral tectum. Five types of neurons were distinguished in the rim cortex of R. esculenta. Most of them have piriform perikarya and their dendrites arborize in the rim neuropil. In the medulla of the isthmic nucleus of R. esculenta, seven types of neurons were distinguished. Most of these neurons also exist in the other species. Medullary cells are piriform, fusiform, or multipolar, and are variable in size and in dendritic arborization. The isthmic neurons of the two Ranae and Bufo species are similar. The dominant cell types in Xenopus are multipolar with extensive dendritic arborization, which occupies more space in the nucleus than in the other species. Neurons with narrow dendritic trees may represent a system of fine resolution, and those neurons with extensive dendritic arborization may belong to a coarser system.
Asunto(s)
Anuros/fisiología , Encéfalo/fisiología , Vías Nerviosas/fisiología , Neuronas/fisiología , Animales , Encéfalo/citología , Bufonidae/fisiología , Cobalto , Peroxidasa de Rábano Silvestre , Neuronas/ultraestructura , Ranidae/fisiología , Xenopus laevis/fisiologíaRESUMEN
Wholemounts and sectioned retina from adults of two lizard species, Pogona vitticeps and Varanus gouldii, were studied by immunohistochemistry for neuropeptide Y (NPY)-like immunoreactivity. In both species the morphology of two classes of amacrine cells (types A and B) were described. Cell somata were located mostly in the inner nuclear layer (INL) but were occasionally displaced into the ganglion cell layer (GCL). In the Pogona retina, type A cells had large somata and dendritic arbor that branched in sublamina (S) 1 and 2/3 of the inner plexiform layer (IPL). Type B amacrine cells had smaller somata and dendritic arbor branching mostly in S5 of the IPL. In the Varanus retina, the levels of dendritic branching of types A and B amacrine cells in the IPL were similar to those in Pogona although branching in the middle of the IPL occurred at S3. NPY-immunoreactive cells with small somata and narrow to medium sized dendritic fields were predominant. Unclassified cells also displayed NPY-like immunoreactivity; however, their dendritic morphology could not be determined due to the faint and inconsistent staining. In transverse retinal sections three bands of NPY-like immunoreactivity were evident in the IPL of both species, to which the unclassified cells also contributed. In both species type A cells were most numerous. Total NPY-immunoreactive cells were estimated to be 8,600 in Pogona and 32,860 in Varanus. In both species types A and B cells were non-uniformly distributed across the retina. The most apparent non-uniformity in distribution was observed in type A cells in Varanus. Peak cell density was found across the horizontal meridian of the retina from where cell density decreased towards the dorsal and ventral retinal margins. The results of this study provide evidence for the presence of NPY-immunoreactive amacrine cells in the lizard retina of which two types were morphologically characterized. Cross-species comparisons were also made among NPY-immunoreactive amacrine cells, and their possible function/s discussed.
Asunto(s)
Lagartos/anatomía & histología , Neuronas/ultraestructura , Neuropéptido Y/análisis , Retina/ultraestructura , Animales , Australia , Dendritas/ultraestructura , Técnica del Anticuerpo Fluorescente , Técnicas para Inmunoenzimas , Lagartos/metabolismo , Neuronas/químicaRESUMEN
Horseradish peroxidase was applied to the proximal stump of the cut optic nerve, and the anterogradely transported tracer was visualised by the cobalt-intensified diaminobenzidine method. The optic fibre receiving laminae of the optic tectum were systematically searched for those synapses in which the tracer-filled profiles occupied postsynaptic positions. Optic terminals were rarely but regularly postsynaptic to unlabelled, small clear vesicle-containing profiles, mostly in lamina A. Quantitative analysis showed that only in 0.95% of the synapses formed by optic fibres could this arrangement be substantiated. These results suggest that presynaptic modulatory mechanisms may play a role in optic information processing.
Asunto(s)
Axones , Colículos Superiores/citología , Transmisión Sináptica , Animales , Bufo marinus , Microscopía Electrónica , Retina , Sinapsis , Membranas SinápticasRESUMEN
The synapses of serotonin-like immunoreactive retinal neurons were studied in Bufo marinus and Xenopus laevis and those of 5,7-dihydroxytryptamine-labelled cells in Xenopus. Immunoreactivity to serotonin was mostly confined to amacrine cells. Synapses formed by profiles of labelled cells were almost uniformly distributed in the inner plexiform layer in both species. Interamacrine synapses were the most frequent, and in some cases two labelled amacrine cell profiles made a gap junction. Some of the labelled amacrine cells synapsed on to presumed ganglion cell dendrites and onto bipolar cell terminals. Labelled bipolar cell terminals synapsed on to non-labelled amacrine cell dendrites and received inputs both from labelled and non-labelled amacrine cells. Labelled bipolar cell profiles were not observed in the outer plexiform layer. After preloading and photoconversion of 5,7-dihydroxytryptamine in the Xenopus retina, labelled bipolar cell dendrites in the outer plexiform layer were observed to be postsynaptic to cone pedicles and less frequently to rods and horizontal cells. In the inner plexiform layer, synapse types formed by labelled bipolar cells were similar to those with serotonin immunoreactivity. The frequency of synapses formed by 5,7-dihydroxytryptamine-labelled amacrine cells increased, compared with serotonin immunocytochemistry. Labelled amacrine cells synapsed mostly with non-labelled amacrine cells, although the ratio of contacts formed by two labelled profiles increased. Synapses from labelled amacrine cell dendrites to non-labelled bipolar cell terminals and from non-labelled bipolar cell terminals to labelled amacrine cell profiles increased in number, while those from labelled amacrine cells to presumed ganglion cell dendrites decreased. The quantitative data obtained by the two approaches enabled us to propose different neuronal circuits for serotonin-synthesizing and -accumulating neurons of the Xenopus retina.
Asunto(s)
5,7-Dihidroxitriptamina/metabolismo , Neuronas/metabolismo , Retina/ultraestructura , Serotonina/fisiología , Sinapsis/ultraestructura , Animales , Bufo marinus , Dendritas/inmunología , Dendritas/metabolismo , Inmunohistoquímica , Microscopía Electrónica , Neuronas/inmunología , Células Fotorreceptoras/inmunología , Células Fotorreceptoras/metabolismo , Retina/citología , Retina/fisiología , Serotonina/inmunología , Sinapsis/inmunología , Sinapsis/metabolismo , Xenopus laevisRESUMEN
Serotonin-synthesizing neurons in the retina of Xenopus laevis have been identified using anti-phenylalanine hydroxylase (PH) antibody which recognizes tryptophan 5-hydroxylase, the rate-limiting enzyme for serotonin synthesis. Double-labelling experiments, using anti-PH antibody and anti-serotonin antibody/5,7-dihydroxytryptamine (5,7-DHT) uptake, have shown that some serotonin-like immunoreactive/5,7-DHT-labelled neurons exhibit PH-like immunoreactivity (PH-LI) (serotonin-synthesizing neurons), but the others do not (serotonin-accumulating neurons). In the present study, triple-labelling experiments were performed using 5,7-DHT uptake and antibodies raised against GABA and PH, to determine the possible co-localization of y-aminobutyric acid (GABA) in serotonin-synthesizing and/or -accumulating neurons in the Xenopus retina. All 5,7-DHT-labelled bipolar cells lacked PH-LI; all of them were immunoreactive to GABA. In contrast, all 5,7-DHT-labelled large amacrine cells exhibited PH-LI, but none of them expressed GABA-LI. Small amacrine cells labelled with 5,7-DHT but not PH-LI exhibited GABA-LI, whilst the small amacrine cells with PH-LI lacked GABA-LI. These observations indicate that GABA is co-localized in serotonin-accumulating amacrine and bipolar cells, whereas serotonin-synthesizing large and small amacrine cells do not contain GABA-LI.
Asunto(s)
Neuronas/metabolismo , Retina/metabolismo , Serotonina/metabolismo , Xenopus laevis/metabolismo , Ácido gamma-Aminobutírico/metabolismo , 5,7-Dihidroxitriptamina , Animales , Anticuerpos/inmunología , Inmunohistoquímica , Microscopía Fluorescente , Fenilalanina Hidroxilasa/inmunología , Retina/citología , Distribución Tisular , Ácido gamma-Aminobutírico/inmunologíaRESUMEN
We have previously shown that an antibody against neuron-specific enolase (NSE) selectively labels Müller cells (MCs) in the anuran retina (Wilhelm et al. 1992). In the present study the light- and electron-microscopic morphology of MCs and their distribution were described in the retina of the toad, Bufo marinus, using the above antibody. The somata of MCs were located in the proximal part of the inner nuclear layer and were interconnected with each other by their processes. The MCs were uniformly distributed across the retina with an average density of 1500 cells/mm2. Processes of MCs encircled the somata of photoreceptor cells isolating them from each other by glial sheath, except for those of the double cones. Some of the photoreceptor pedicles remained free of glial sheath. Electron-microscopic observations confirmed that MC processes provide an extensive scaffolding across the neural retina. At the outer border of the ganglion cell layer these processes formed a non-continuous sheath. The MC processes traversed through the ganglion cell layer and spread beneath it between the neuronal somata and the underlying optic axons. These processes formed a continuous inner limiting membrane separating the optic fibre layer from the vitreous tissue. Neither astrocytic nor oligodendrocytic elements were found in the optic fibre layer. The significance of the uniform MC distribution and the functional implications of the observed pattern of MC scaffolding are discussed.
Asunto(s)
Bufo marinus/anatomía & histología , Retina/citología , Animales , Técnica del Anticuerpo Fluorescente , Inmunohistoquímica , Microscopía Electrónica , Neuroglía/ultraestructura , Neuronas/ultraestructura , Retina/ultraestructuraRESUMEN
Serotonin-synthesizing neurons in the retinas of goldfish, axolotl, turtle, chick, rabbit and cat were identified using double labelling with anti-serotonin and anti-phenylalanine hydroxylase antibodies. The latter antibody recognizes tryptophan 5-hydroxylase, one of the synthesizing enzymes for serotonin. Neurons labelled by both markers were considered to be serotonin-synthesizing neurons, while those only with serotonin-immunoreactivity were assumed to be serotonin-accumulating neurons. In the goldfish and chick retinas, all serotonin-immunoreactive amacrine cells (S1) were positive for phenylalanine hydroxylase. In the axolotl and turtle retinas, all the S1 amacrine cells, and only 52.8% and 40.5% of S2 amacrine cells were double-labelled. Although serotonin-immunoreactive bipolar cells were observed in the turtle and chick retinas, the synthesizing enzyme for serotonin could not be detected in these cells. In the rabbit and cat retinas, tryptophan hydroxylase could not be revealed in any cell type with immunocytochemistry. In control experiments SLI neurons in the raphe nuclei of the brain stem always exhibited PH-LI in all species examined, including mammals, indicating that our anti-PH antibody is able to recognize tryptophan hydroxylase across vertebrate classes. These results indicate that the majority of serotonin-immunoreactive amacrine cells are able to synthesize serotonin and are the source of endogenous serotonin in the non-mammalian retina, while some serotonin-immunoreactive amacrine and bipolar cells possibly only accumulate serotonin. We also suggest that serotonin may not be a primary neurotransmitter in the serotonin-accumulating bipolar and amacrine cells of the non-mammalian retina.
Asunto(s)
Neuronas/metabolismo , Retina/citología , Serotonina/biosíntesis , Ambystoma mexicanum , Animales , Gatos , Pollos , Carpa Dorada , Inmunohistoquímica , Conejos , Triptófano Hidroxilasa/metabolismo , TortugasRESUMEN
Previous studies have shown that a small proportion of the retinal fibres to the optic tectum terminates in the deep tectal cellular layers (layers 6 and 4) in Anura. Horseradish peroxidase was applied to the cut central end of the optic nerve of Bufo marinus to study the synaptic connections of these retinotectal afferents. Some of the retinotectal afferents arrive at the deep tectal layers and form synapses with dendrites (7% of all tectal inputs) and on the somata of the deep tectal cells (0.4% of all tectal inputs). These synapses may either serve as elements of the dimming detection system or could be the morphological substrates of a direct link between the visual and the descending motor system.
Asunto(s)
Axones/fisiología , Neuronas/fisiología , Terminales Presinápticos/fisiología , Colículos Superiores/fisiología , Animales , Axones/ultraestructura , Bufo marinus , Femenino , Histocitoquímica , Peroxidasa de Rábano Silvestre , Masculino , Microscopía Electrónica , Fibras Nerviosas/fisiología , Fibras Nerviosas/ultraestructura , Neuronas/ultraestructura , Terminales Presinápticos/ultraestructura , Colículos Superiores/citología , Colículos Superiores/ultraestructuraRESUMEN
We have recently reported that about 50% of amacrine cells and some of the bipolar and ganglion cells are GABA-immunoreactive in the retina of Bufo marinus. Synapses formed by these elements in the inner plexiform layer were studied. GABA-immunoreactive amacrine cell processes were found most frequently in synaptic contact with non-immunoreactive amacrine cells. Double-label experiments showed that some of these non-GABA-immunoreactive elements contain tyrosine hydroxylase immunoreactivity. Another source of input to the GABA-immunoreactive amacrine cells were the bipolar cells; some of which were GABA-immunoreactive. GABA-immunoreactive amacrine cells synapsed also onto bipolar cell terminals, and ganglion cell dendrites that were identified by the retrograde transport of horseradish peroxidase from the optic nerve. Synapses between GABA-immunoreactive amacrine cells and bipolar and ganglion cells were non-uniformly distributed in the inner plexiform layer. Synaptic contacts with bipolar cells were more frequent in the OFF-sublamina, and those with ganglion cell dendrites in the ON-sublamina. These results demonstrate that GABA-immunoreactive amacrine cells (1) preferentially synapse with OFF-responding bipolar and ON-centre ganglion cells in the through-pathway, (2) synapse with tyrosine hydroxylase-immunoreactive amacrine cells in both the OFF- and ON-sublaminae, and (3) synapse directly with GABA-immunoreactive ganglion cells. The synapses between GABA-immunoreactive amacrine and GABA-immunoreactive ganglion cells may inhibit the centrally projecting inhibitory ganglion cells, causing disinhibition in the visual centres.
Asunto(s)
Bufo marinus/metabolismo , Dopamina , Retina/química , Sinapsis/química , Ácido gamma-Aminobutírico/análisis , Animales , Bufo marinus/anatomía & histología , Proteínas del Ojo/análisis , Inmunohistoquímica , Proteínas del Tejido Nervioso/análisis , Retina/ultraestructura , Células Ganglionares de la Retina/química , Células Ganglionares de la Retina/ultraestructura , Especificidad de la Especie , Tirosina 3-Monooxigenasa/análisis , Vertebrados/anatomía & histología , Vertebrados/metabolismoRESUMEN
Using antibodies against parvalbumin and neurofilament triplet protein, colocalization of these two neuronal markers was revealed in all of type A horizontal cells and alpha ganglion cells and in a small number of AII amacrine cells of the cat retina. Besides the double-labeled neurons, parvalbumin alone was present in type B horizontal cells, in small numbers of starburst- and A13-like amacrine cells and in the somata of unidentified ganglion cells. The processes of the double- or single-labeled amacrine cells did not have a continuous retinal cover. Although the parvalbumin- and neurofilament-immunolabeled amacrine cells belonged to groups of neurons with well-defined cell morphologies, their neurochemical features differed from other AII, starburst and A13 amacrine cells. The presence of these cells may be due to an accidental expression of an unusual combination of neurochemical features during retinal development. It is also possible that these cells support the functioning of ganglion cells with rarely occurring complex receptive fields.
Asunto(s)
Proteínas de Neurofilamentos/metabolismo , Parvalbúminas/metabolismo , Retina/metabolismo , Animales , Gatos , Inmunohistoquímica , Proteínas de Neurofilamentos/inmunología , Parvalbúminas/inmunología , Retina/citología , Retina/inmunología , Células Ganglionares de la Retina/inmunología , Células Ganglionares de la Retina/metabolismoRESUMEN
Neuron-specific enolase (NSE) immunocytochemistry was carried out in retinae of goldfish, axolotl, clawed frog, cane toad, lizard, chick, guinea-pig, rabbit, rat, cat and human. With the exception of Anura, strong immunoreactivity was seen in the large ganglion, amacrine cells and horizontal cells of the retina in all of the other species. Photoreceptors were found to be labelled in the rat and human retina and only one cone type in rabbit. Photoreceptor pedicles and ellipsoids were stained in the goldfish and the somata and inner segments of some photoreceptors in axolotl. In the axolotl retina, besides neurons, Müller cells (MCs) were also immunolabelled. In the retina of the cane toad and the clawed frog MCs were the only stained elements. Similarly in other parts of the central nervous system of the cane toad, glial elements of the optic tectum and spinal cord were immunoreactive. In contrast, in the peripheral nervous system, neurons of the 1st sympathetic ganglion and the 2nd dorsal root ganglion were labelled. In double-labelling experiments, glial fibrillary acidic protein and NSE showed colocalisation both in the glial elements of the optic tectum and spinal cord and in MCs of the retina of the cane toad.
Asunto(s)
Anuros/anatomía & histología , Fosfopiruvato Hidratasa/análisis , Retina/metabolismo , Ambystoma/anatomía & histología , Animales , Pollos/anatomía & histología , Ganglios Simpáticos/metabolismo , Proteína Ácida Fibrilar de la Glía/metabolismo , Carpa Dorada/anatomía & histología , Cobayas , Humanos , Lagartos/anatomía & histología , Neuroglía/metabolismo , Conejos , Retina/ultraestructuraRESUMEN
The earliest appearance of serotonin-like immunoreactivity (SLI) in different cell types and the development of large SLI amacrine cells were studied in the retina of Xenopus laevis from stage 33/34 to adult. Intense SLI was first found in the somas of large amacrine cells at stage 39. The somas of small amacrine cells showed weak SLI at stage 41, followed by bipolar cells at stage 43. The number of large SLI amacrine cells in the inner nuclear layer of the retina increased from 57 at stage 40 to 774 in adult. Over the same period, retinal area increased from 0.19 mm2 to 24.57 mm2 with an accompanying decrease of cell density from 301/mm2 to 32/mm2. in adult animals large SLI amacrine cells were non-uniformly distributed. Peak cell density of 50-60/mm2 was located in the center of the ventrotemporal quadrant and a trough of 8-15/mm2 in the dorsal periphery of the retina. Peak cell density region of the adult retina corresponded to part of the retina formed at early developmental stages where the rate of cell generation of large SLI amacrine cells was higher. These observations indicate that (1) SLI is expressed first by large amacrine cells, followed by small amacrine and bipolar cells; (2) large SLI amacrine cells are generated continuously throughout life, (3) the non-uniform retinal distribution of large cells results from a spatio-temporally differential cell generation at the ciliary margin.
Asunto(s)
Retina/citología , Serotonina/fisiología , Animales , Dendritas/inmunología , Dendritas/fisiología , Inmunohistoquímica , Larva , Retina/crecimiento & desarrollo , Retina/fisiología , Serotonina/inmunología , Xenopus laevisRESUMEN
Serotonin-synthesizing and serotonin-accumulating neurons were studied in the retinas of Xenopus laevis and Bufo marinus. All previously identified cell types exhibiting serotonin-like immunoreactivity (SLI) were labeled by intravitreal injection of 5,7-dihydroxytryptamine (5,7-DHT). They included two amacrine cell types (large and small) in both species, and one bipolar cell type in Xenopus. Incubation of retinas in culture medium in the ambient light reduced SLI in amacrine cells and enhanced the labeling in bipolar cells. After incubation, some photoreceptor cell bodies and large numbers of outer segments also displayed SLI in both species. Incubation with the serotonin-uptake inhibitor, fluoxetine, reduced immunolabeling in bipolar cells and outer segments to the level in the untreated retinas. Both large SLI and 5,7-DHT-accumulating amacrine cells in Xenopus and Bufo were labeled with an antibody raised against phenylalanine hydroxylase (PH), which binds to tryptophan 5-hydroxylase, one of the synthesizing enzymes for serotonin. Small SLI and 5,7-DHT-accumulating amacrine cells in both species represented two populations, one with and the other without PH-like immunoreactivity (PH-LI). The anti-PH antibody failed to label any SLI or 5,7-DHT-accumulating bipolar cells in Xenopus. These observations indicate that all large and some small SLI amacrine cells in the retinas of Xenopus and Bufo synthesize serotonin, while other small SLI amacrine, bipolar and photoreceptor cell bodies, and outer segments only accumulate serotonin.
Asunto(s)
Neuronas/metabolismo , Retina/metabolismo , Serotonina/biosíntesis , 5,7-Dihidroxitriptamina/administración & dosificación , Animales , Bufo marinus , Recuento de Células , Técnica del Anticuerpo Fluorescente , Fluoxetina/farmacología , Luz , Neuronas/ultraestructura , Fenilalanina Hidroxilasa/metabolismo , Retina/ultraestructura , Serotonina/metabolismo , Xenopus laevisRESUMEN
The generation and retinal distribution of displaced amacrine cells (DAs) were studied from metamorphosis to adult in the cane toad Bufo marinus. Displaced amacrine cells were identified by inducing chromatolytic changes in ganglion cells (GCs) following optic nerve section. Cells that did not chromatolyse in the ganglion cell layer (GCL) of the retina were regarded as DAs. The number of DAs increased considerably from an estimated 10,000 at metamorphosis to 211,000 in the adult toad, and was accompanied by a substantial decrease of average cell density. In contrast to the reported 6:1 cell density gradient of all cells of the GCL in adult toad (Nguyen and Straznicky 1989) only a shallow 1.6:1 density gradient of DAs from the visual streak to the dorsal and ventral retinal margins was detected. Consequently, the incidence of DAs increased from 15% of all cells of the GCL in the visual streak to 30% in the dorsal and ventral peripheral retina. These results indicate that the ratio of the newly generated DAs and GCs at the ciliary margin must be changing during development. More GCs are generated before and around metamorphosis then DAs, in contrast to the relative increase of the percentage of DAs generated after metamorphosis. The possible control of the numbers of DAs in the GCL is discussed.
Asunto(s)
Bufo marinus/anatomía & histología , Bufo marinus/crecimiento & desarrollo , Neuronas/citología , Retina/citología , Retina/crecimiento & desarrollo , Animales , Recuento de Células , Metamorfosis Biológica , Células Ganglionares de la Retina/citologíaRESUMEN
The numbers of neurons of the ganglion cell layer (GCL) and their distribution in the retina of an Australian lizard Ctenophorus nuchalis were investigated. Retinal wholemounts and sections were prepared for light microscopic and optic nerves for electron microscopic study. Counts of cell numbers in the GCL from wholemounts varied from 200,000 to 380,000. Neurons in the GCL were non-uniformly distributed, forming a high cell density streak along the naso-temporal axis of the retina. Neurons of the GCL formed 2 to 9 layers in the visual streak and a single layer in the rest of the retina. The number of neurons of the GCL in this area was estimated at about 2,100,000. Although the visual streak represented only 16% of the total retinal surface area, it contained about 90% of all neurons of the GCL. Optic axon counts yielded 147,000 myelinated and 2,643,000 unmyelinated fibres. The estimated optic fibre number of 2,790,000 was 18.2% less than the total number of neurons counted from sections in the GCL of the same eye. The unexpected high number of neurons in the area of the visual streak indicates that cell numbers obtained only from wholemount preparations may vastly underestimate the total neuron numbers in the GCL of the lizard retina.
Asunto(s)
Lagartos/anatomía & histología , Nervio Óptico/citología , Retina/citología , Animales , Axones , Recuento de Células , Neuronas/citologíaRESUMEN
Neuron populations in the retina of the toad, Bufo marinus, were labelled with a monoclonal antibody raised against microtubule-associated protein 2 (MAP2). A subpopulation of cones, probably corresponding to the blue-sensitive small single cones, large diameter amacrine cells in the most proximal row of the inner nuclear layer and some large ganglion cells in the ganglion cell layer were labelled. Double labelling experiments were carried out to establish the colocalisation of MAP2 with known putative transmitter substances of the anuran amacrine cells. MAP2 was colocalised in a subpopulation of serotonin-immunoreactive and in all tyrosine hydroxylase-immunoreactive amacrine cells. The results indicate, that the MAP2 content in the neurons of the anuran retina can be correlated with other well-defined neurochemical and/or physiological properties.
Asunto(s)
Proteínas Asociadas a Microtúbulos/análisis , Neuronas/química , Retina/química , Serotonina/análisis , Tirosina 3-Monooxigenasa/análisis , Animales , Anticuerpos Monoclonales , Bufo marinus , Proteínas de Unión al Calcio/análisis , Ganglios/química , Inmunohistoquímica , Neuronas/ultraestructura , Retina/citologíaRESUMEN
An antibody (SMI-32) raised against the non-phosphorylated form of the neurofilament protein triplet (NFP) revealed immunoreactivity in the soma and dendritic arborization of a group of large ganglion cells in the human retina. In addition, a population of smaller somas was also faintly labeled with this antibody in the ganglion cell layer. The completely stained cells amounted to 44,000 and were non-uniformly distributed across the retina with a peak density of 100 cells/mm2 in the retinal periphery. The soma sizes increased about two-fold and dendritic field sizes about 3-fold with retinal eccentricity. The immunoreactive dendrites branched in the vitread sublamina of the inner plexiform layer. The dendritic branching pattern of these cells indicated that they correspond to the previously described shrub cells. Antibodies against NFP and neuropeptide Y showed colocalization of these markers in all of the completely stained cells.