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PubMed1986

GABA neurones in retinas of different species and their postnatal development in situ and in culture in the rabbit retina.

The localisation of GABA immunoreactive neurones in retinas of a variety of animals was examined. Immunoreactivity was associated with specific populations of amacrine neurones in all species examined, viz. rat, rabbit, goldfish, frog, pigeon and guinea-pig. All species, with the exception of the frog, possessed immunoreactive perikarya in their retinal ganglion cell layers. These perikarya are probably displaced amacrine cells because GABA immunoreactivity was absent from the optic nerves and destruction of the rat optic nerve did not result in degeneration of these cells. GABA immunoreactivity was also associated with the outer plexiform layers of all the retinas studied; these processes are derived from GABA-positive horizontal cells in rat, rabbit, frog, pigeon and goldfish retinas, from bipolar-like cells in the frog, and probably from interplexiform cells in the guinea-pig retina. The development of GABA-positive neurones in the rabbit retina was also analysed. Immunoreactivity was clearly associated with subpopulations of amacrine and horizontal cells on the second postnatal day. The immunoreactivity at this stage is strong, and fairly well developed processes are apparent. The intensity of the immunoreactivity increases with development in the case of the amacrine cells. The immunoreactive neurones appear fully developed at about the 8th postnatal day, although the immunoreactivity in the inner plexiform layer becomes more dispersed as development proceeds. The immunoreactive horizontal cells become less apparent as development proceeds, but they can still be seen in the adult retina. The GABA immunoreactive cells in rabbit retinas can be maintained in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1999

Dopamine receptor localization in the mammalian retina.

After a short history of dopamine receptor discovery in the retina and a survey on dopamine receptor types and subtypes, the distribution of dopamine receptors in the retinal cells is described and correlated with their possible role in cell and retinal physiology. All the retinal cells probably bear dopamine receptors. For example, the recently discovered D1B receptor has a possible role in modulating phagocytosis by the pigment epithelium and a D4 receptor is likely to be involved in the inhibition of melatonin synthesis in photoreceptors. Dopamine uncouples horizontal and amacrine cell-gap junctions through D1-like receptors. Dopamine modulates the release of other transmitters by subpopulations of amacrine cells, including that of dopamine through a D2 autoreceptor. Ganglion cells express dopamine receptors, the role of which is still uncertain. Müller cells also are affected by dopamine. A puzzling action of dopamine is observed in the ciliary retina, in which D1- and D2-like receptors are likely to be involved in the cyclic regulation of intraocular pressure. Most of the dopaminergic actions appear to be extrasynaptic and the signaling pathways remain uncertain. Further studies are needed to better understand the multiple actions of dopamine in the retina, especially those that implicate rhythmic regulations.

Animals↗

PubMed1989

Responses of retinal ganglion cells to eyeball deformation: a neurophysiological basis for "pressure phosphenes".

By means of microelectrodes, the activity of single neurons (on-center, off-center ganglion cells, latency class I and class II neurons) was recorded from the optic tract of anesthetized cats. Eyeball deformation in total darkness led fairly consistently to an activation of the on-center ganglion cells, while off-center ganglion cells were inhibited. The latency and strength of this activation or inhibition seemed to be mainly dependent on the strength of eyeball indentation and the location of the neurons relative to the point of eyeball indentation. Some on-center neurons (mostly latency class I) also exhibited a short activation at "deformation off". For comparison, the responses of retinal ganglion cells to eyeball deformation in a hydrostatically open system and to a sudden increase in the intraocular pressure (closed system) are described. The neurophysiological data are explained by the assumption that eyeball indentation leads to a nonuniform tangential stretch of the retina, which exerts a locally variable depolarization of horizontal cells. This horizontal cell depolarization leads either directly or via a feedback loop through cone pedicles to a depolarization of on-bipolars and a hyperpolarization of off-bipolars. These effects determine in turn the responses seen at the ganglion cell level. It is emphasized that eyeball deformation can be used as an independent tool in transmitter studies of the retina.

Action Potentials↗

PubMed1987

Double-label analysis of GAD- and GABA-like immunoreactivity in the rabbit retina.

Rabbits were injected intravitreally with colchicine and the retinas were subsequently processed for simultaneous visualization of GAD-like and GABA-like immunoreactivity (LIR) at the light microscopical level. The use of specific antisera from unrelated species minimized the possibility of crossreactivity between the two markers. Colocalization of GABA-LIR and GAD-LIR was observed in approximately 32% of somata on the inner border of the inner nuclear layer (INL) and roughly 15% of the somata in the ganglion cell layer (GCL). All GAD-positive cells were double labeled whereas 15% of the GABA-LIR cells in the INL and 52% of those in the GCL were negative for GAD-LIR. Both markers were seen throughout the inner plexiform layer. In addition, processes coursing through the OPL, perhaps from interplexiform cells, and horizontal cell bodies were double-labeled with these GABAergic probes.

Animals↗

PubMed1996

Modulation of horizontal cell receptive fields in the light adapted goldfish retina.

In the isolated goldfish retina, 700 nm background illumination increases the horizontal cell receptive field size, as measured with 565 nm slits of light, but decreases the receptive field size, when measured with 660 nm slits. These background-induced changes in receptive field size are absent when the depolarizing responses in bi- and triphasic horizontal cells are blocked by lowering the [Ca2+] in the Ringer's solution from 1.0 to 0.1 mM. These results cannot be explained by the linear properties of the horizontal cell layers, nor by slow adaptational processes, but are consistent with the concept that feedback from horizontal cells to cones modifies the horizontal cell receptive field properties.

Adaptation, Ocular↗

PubMed2004

[The structual and temporal characteristics of four intermediate filament proteins during retinal development of rat].

OBJECTIVE: To investigate the markers of retinal progenitor cells and their spatio-temporal characteristics during retinal development of rat. METHODS: The time sequence, location and intensity of the expression of four intermediate filament proteins in retina were studied in rats (from postnatal day 0 to 12 months) by means of immunohistochemistry staining. RESULTS: Retinal differentiation of rat was not accomplished until 2 weeks after birth. Nestin positive cells were seen in neurocytes, glial cells and capillary endothelial cells of rat retina 2 weeks after birth. The number of Nestin positive cells and intensity of Nestin staining in rat retina decreased obviously after 2 weeks of birth then turned to negative at 4 weeks after birth. However, the expression of Nestin was persisted in cells from a few ciliary processes during the development and the intensively positive staining cells were observed in ciliary process, mostly in pigment epithelium cells in adult. In addition, Nestin positive cells were also found in the optic nerve of adult rat. The expression pattern of Vimentin is similar to that of Nestin within 2 weeks after birth. But the expression of Vimentin was persisted with high level lifetime in all glial cells and nonpigment epithelium cells of ciliary. Besides the horizontal cells, positive staining of Vimentin was also found in Muller cells and amacrine cells at 4 weeks after birth. The positive expression of GFAP and neurofilament were only found in mature glial cells and in the axons of ganglion cells, respectively. CONCLUSION: Nestin could be considered as the marker of retinal progenitor cells. Retinal progenitor cells of adult rat are also present in optic nerve and in a few ciliary processes.

Animals↗

PubMedDate not supplied

Changes in human short-wavelength-sensitive and achromatic resolution acuity with retinal eccentricity and meridian.

Psychophysical measurements using achromatic grating resolution acuity in peripheral vision show a prominent retinal asymmetry in acuity which is consistent with predicted values based on available estimates of midget ganglion cell density. Recent studies have shown that peripheral grating resolution acuity values for short-wavelength-sensitive (SWS) isolating gratings in normal observers are closely related to predicted values based on the underlying small bistratified ganglion cell density. By measuring SWS resolution acuity at different locations across the visual field, we wished to see if any significant acuity asymmetry exists for the short-wavelength system. In addition to this, we wanted to compare SWS and achromatic resolution acuity at different retinal locations of equal eccentricity. SWS and achromatic grating resolution acuity was measured in two observers at a number of different retinal meridians of 10- and 25-deg eccentricity from the fovea, and out to 35-deg eccentricity along the horizontal meridian. Achromatic resolution acuity was higher than SWS resolution acuity at all locations. At 10-deg eccentricity there was slight radial asymmetry in SWS and achromatic acuity, both displaying highest acuity along the horizontal meridian. At 25-deg eccentricity, SWS and achromatic acuity showed significant asymmetry with acuity being higher in the nasal retina compared to the temporal retina and with higher acuity in the superior retina compared to the inferior retina. At 35-deg eccentricity, the acuity asymmetry along the horizontal meridian was maintained with acuity for both significantly higher in the nasal retina. The SWS acuity changes with eccentricity and meridian were qualitatively similar to that found for achromatic acuity at the majority of retinal locations. Like achromatic acuity, SWS acuity shows significant asymmetry at different retinal locations of equal eccentricity. This suggests that both the midget and small bistratified ganglion cell population density changes significantly with retinal location and eccentricity. SWS acuity appears to change in parallel with achromatic acuity for the majority of retinal locations measured, although the amount of nasotemporal asymmetry appears to be slightly less for the SWS system at 25- and 35-deg eccentricity.

Adult↗

PubMed1984

Respirator retina.

Retinas from 14 comatose patients, who had been sustained with a respirator for one or more days before death, had selective characteristic alterations (ie, autophagy, cell swelling, and coagulation necrosis) of inner nuclear layer in a patchy pattern in posterior fundus. Bipolar cells were most often affected, but amacrine and horizontal cells also were substantially damaged. Cells of Müller and vascular cells were largely spared. These lesions are ascribed to oligemia (ischemia) since the inner nuclear layer is a microscopic vascular watershed (boundary zone) between the choroidal and retinal circulations.

Adolescent↗

PubMed1991

Ultracytochemistry of enzymes in cell biology of the retina.

In matured chick retina, alkaline phosphatase activity is specifically localized in the outer plexiform layer and in the horizontal and Müller cells. In developing chick retina, the activity is recognized in growing neurites from horizontal cells, when synaptogenesis begins in the outer plexiform layer. Using levamisole, a potent inhibitor of alkaline phosphatase, on chick retina in vivo and in vitro, the enzyme was shown to play a significant role in retinal cell differentiation. 5'-Nucleotidase is used as a marker for the rod photoreceptors. It became apparent that the 'displaced' rod cells are localized in the inner nuclear layer of postnatal retina. High activity of glucose-6-phosphatase is confirmed in the cisternae of the smooth and rough endoplasmic reticulum, together with the space of the perinuclear envelope in the pigment epithelium of rat. The process of disc membrane recycling in the rod outer segment was investigated cytochemically to reveal sequential changes in lysosomal digestion both by conventional enzyme cytochemistry and by high voltage electron microscopy. With conventional enzyme histochemistry as well as with rapid freeze substitution enzyme cytochemistry, all enzyme for cGMP metabolism were observed to be on the cytoplasmic side of the disc membranes.

5'-Nucleotidase↗

PubMed1997

Metabotropic glutamate receptor-mediated suppression of an inward rectifier current is linked via a cGMP cascade.

Glutamate, the neurotransmitter released by photoreceptors, excites horizontal cells and OFF-type bipolar cells by activating ionotropic receptors. This study investigated an additional action of glutamate in which it modulates a voltage-gated ion channel in horizontal cells. We find that glutamate and APB (2-amino-4-phosphonobutyrate) produce a delayed and moderately prolonged suppression of an inward rectifier current (IRK+). This effect is proposed to occur via an APB-sensitive metabotropic glutamate receptor (mGluR) because common agonists for the ionotropic or APB-insensitive mGluRs are ineffective and the APB-insensitive receptor antagonist alpha-methyl-4-carboxyphenylglycine (MCPG) does not block the actions of glutamate or APB. 8-Br-cGMP, 1-methyl-3-isobutylxanthine (IBMX), and atrial natriuretic peptide (ANP) but not 8-Br-cAMP mimic the suppression of IRK+. The effects of glutamate and APB are blocked by protein kinase inhibitors including Rp-8-pCPT-cGMPS, H-8, and H-7 as well as by ATPgammaS. We hypothesize that the APB receptor suppresses IRK+ via upregulation of cGMP and subsequent activation of a cGMP-dependent protein kinase. This pathway is likely regulated by an ATP-dependent phosphorylation. This is a novel signaling pathway for mGluRs and indicates that at least two distinct APB-activated pathways exist in the retina. Functionally, this APB receptor-mediated action found in horizontal cells would provide a means by which spatially restricted changes of glutamate, produced by local illumination of photoreceptors, could regulate IRK+ and consequently the response properties of these neurons. This would serve to adapt selectively retinal regions stimulated by small regions of the visual world.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1989

Transient calcium current of retinal bipolar cells of the mouse.

1. Isolated bipolar cells were obtained by enzymic (papain) dissociation of the adult mouse retina. The membrane voltage was clamped and the membrane currents were measured by the whole-cell version of the patch-clamp technique. Isolated bipolar cells and horizontal cells of the goldfish retina were also studied for comparison. 2. Hyperpolarization from the holding voltage, Vh, of -46 mV evoked a slowly activating, Cs+-sensitive, inward current (probably an h-current), and depolarization evoked a TEA- and Cs+-sensitive outward current (probably a combination of K+ currents). 3. Depolarization from a more negative Vh (e.g. -96 mV) evoked a transient inward current that had maximal amplitude between -40 and -20 mV. This current was identified as a Ca2+ current (ICa): its amplitude was increased with elevated [Ca2+]o and was decreased with reduced [Ca2+]o, and it was blocked by 4 mM-Co2+, but not by 5 microM-TTX. 4. Both the perikaryon and the axon terminal generated ICa with similar properties. 5. The plot of Ca2+ conductance (gCa) against membrane voltage (activation curve) was sigmoidal: in 10 mM [Ca2+]o, gCa increased for membrane voltages more positive than -65 mV, was half-maximal at about -25 mV, and reached saturation at about +30 mV. The plot of inactivation of gCa against membrane voltage was also sigmoidal: with 1 s conditioning depolarization in 10 mM [Ca2+]o, gCa decreased for membrane voltages more positive than -80 mV, was half-maximal at about -50 mV, and was fully suppressed for voltages greater than -30 mV. 6. ICa in the mouse bipolar cells was insensitive to 50 microM-Cd2+, 10 microM-nifedipine and 10 microM-Bay K 8644. In contrast, the calcium currents of bipolar and horizontal cells of the goldfish retina were markedly suppressed by 50 microM-Cd2+ and 10 microM-nifedipine, and were augmented several fold by 10 microM-Bay K 8644. The calcium currents of goldfish bipolar and horizontal cells were sustained, and were activated in a more positive range of potentials than the ICa of mouse bipolar cells. 7. The voltage range at which the ICa of mouse bipolar cells is activated includes the presumed range of membrane potentials spanned during light-evoked responses; thus, this current may participate in synaptic transmission. The transient character of ICa may also help to shape transient responses of ganglion cells.

Animals↗

PubMed1984

Relations between the human retinal cone and ganglion cell distribution.

The distribution of human cone cells is well known and is frequently cited. The distribution of human ganglion cells is less well known and was published in a booklet which is less frequently cited in the eye literature. Selected published curves provided by these authors and Snellen acuity data were digitally encoded, transformed to linear vertical axes where necessary, scaled and compared. Comparisons were possible along the temporal hemi-meridian and provided correlations (r = 0.99 for ganglion cells versus cone cells; r = 0.99 for ganglion cells versus acuity, and r = 0.98 for cone cells versus acuity). Integration of densities along the horizontal hemi-meridian out to 50 degrees showed that approximately 50% of the cone cells are within 18 degrees of the foveola and that approximately 50% of the ganglion cells are within 13 degrees of the foveola. Appreciation of the strong interrelations between the cone-ganglion cell distributions may provide for a better understanding of the visual of inner-retinal disease. Presently it accounts for aspects of the production of pattern-elicited retinal signals which are under intense investigation in many centers.

Humans↗

PubMedDate not supplied

Diversity of neuronal phenotypes expressed in monolayer cultures from immature rabbit retina.

We have used monolayer cultures prepared from early postnatal rabbit retinae (days 2-5) by the sandwich technique to study the capacity of immature neurons to express specific neuronal phenotypes in a homogeneous in vitro environment. Applying morphological, immunocytochemical, and autoradiographic criteria, we demonstrate that a variety of phenotypes could be distinguished after 7-14 days in vitro, and correlated with known retinal cell types. Bipolar cell-like neurons (approximately 4% of total cell number) were identified by cell type-specific monoclonal antibodies (115A10) and their characteristic bipolar morphology. Small subpopulations (about 1%) of GABA-immunoreactive neurons acquired elaborate morphologies strikingly similar to those of A- and B-type horizontal cells. Amongst putative amacrine cells several different subpopulations could be classified. GABA-immunoreactive amacrine-like neurons (6.5%), which also showed high affinity [3H]-GABA uptake, comprised cells of varying size and shape and could be subdivided into subpopulations with respect to their response to different glutamate receptor agonists (NMDA, kainic acid, quisqualic acid). In addition, a small percentage of [3H]-GABA accumulating cells with large dendritic fields showed tyrosine-hydroxylase immunoreactivity. Presumptive glycinergic amacrine cells (18.5%) were rather uniform in shape and had small dendritic fields. Release of [3H]-glycine from these neurons was evoked by kainic and quisqualic acid but not by NMDA. Small [3H]-glutamate accumulating neurons with few short processes were the most frequent cell type (73%). This cell type also exhibited opsin immunoreactivity and probably represented incompletely differentiated photoreceptor cells. Summing the numbers of characterized cells indicated that we were able to attribute a defined retinal phenotype to most, if not all of the cultured neurons. Thus, we have demonstrated that immature neuronal cells growing in monolayer cultures, in the absence of a structured environment, are capable of maintaining or producing specific morphological and functional properties corresponding to those expressed in vivo. These results stress the importance of intrinsic factors for the regulation of neuronal differentiation. On the other hand, morphological differentiation was far from perfect indicating the requirement for regulatory factors.

Animals↗

PubMed1995

Lesion topography and new histological features in feline taurine deficiency retinopathy.

Previous studies of feline taurine deficiency retinopathy have established that the retinopathy begins as a focal lesion at the area centralis (feline central retinal degeneration) and progresses to form a horizontal band of retinal degeneration which, in some cases, eventually involves the whole retina. Several theories have been proposed to account for the strikingly unusual geographic distribution of lesions in this disease, including a preferential cone photoreceptor effect, and damage by exposure to light. In this paper evidence is provided that the regional lesions in advanced cases of taurine deficiency retinopathy extend circumferentially to form a peripheral annular band-like arrangement around the retinal extremity. The circumferential annulus is confluent with both temporal and nasal extremes of the horizontal band-shaped lesion. The topographic arrangement of the advanced lesion thus approximates the shape of the Greek letter theta, theta. A previously unreported sclerad displacement of photoreceptor cells into the subretinal space was commonly observed histologically. Radially sectioned material also revealed pathological changes in photoreceptors over a much more widespread region than the focal lesions observable ophthalmoscopically and in whole-mounts of the retina. The issue is therefore to account for the advanced photoreceptor cell loss in the focal lesions. A preferential effect on cone photoreceptors is insufficient to explain the lesion distribution, and unilateral tarsorrhaphy experiments exclude light damage as a major factor. Some other factor, or combination of factors, is most likely involved in determining the unique geographic distribution of lesions in feline taurine deficiency retinopathy.

Animals↗

PubMed2003

Engraftment of adult neural progenitor cells transplanted to rat retina injured by transient ischemia.

PURPOSE: To optimize delivery parameters for achieving engraftment, migration, and differentiation of adult neural progenitor cells transplanted to the retinas of rats after transient retinal ischemia. METHODS: Retinal ischemia was induced by transiently raising the intraocular pressure. Some animals then received transplantation of green fluorescent protein (GFP)-expressing cells derived from the adult rat hippocampus and were allowed to recover for 6 hours to 9 weeks. Retinal cryosections were prepared for TUNEL analysis to determine the time course of ischemia-induced cell death, and some sections were prepared for immunohistochemistry for retinal neuronal antigens. RESULTS: TUNEL analysis revealed that ischemia-induced cell death peaked at 24 hours. By 96 hours, the inner nuclear (INL) and ganglion cell (GCL) layers were largely obliterated in the central retina, sparing peripheral regions. By 2 weeks after transplantation, numerous GFP-expressing cells had engrafted into the host retina, migrated to the inner retina, and extended processes. At 4 weeks, many GFP-labeled cells were present throughout the INL and displayed horizontal-, bipolar-, and amacrine cell-like morphologies. GFP-expressing cells were also present in the GCL with fibers extending into the nerve fiber layer. At 5 weeks, many GFP-expressing cells were present at the optic nerve head, and some GFP-labeled fibers were present in the optic nerve, occasionally passing through the full extent of the lamina cribrosa. Only rarely were GFP-expressing cells found that coexpressed retinal phenotypic markers at any time point examined. CONCLUSIONS: Adult hippocampus-derived neural progenitor cells transplanted to the subretinal space readily engraft into a host retina that has undergone ischemic injury. Many cells migrate to specific retinal cellular layers and undergo limited morphologic differentiation reminiscent of retinal neurons, including extension of processes into the optic nerve. Concurrent control studies demonstrate that optimal engraftment is achieved by subretinal delivery within a specific temporal window. These results imply that certain inductive cues may be regulated after injury, and they demonstrate the potential for adult neural progenitor cell transplantation for the treatment of retinal neurodegenerative diseases.

Animals↗

PubMed2005

Endothelin-1 and endothelin receptors in light-induced retinal degeneration.

We have studied the distribution of endothelinergic molecules: prepro-endothelin-1 (PPET-1), endothelin-1 (ET-1), and receptors A and B (ET-A) and (ET-B) in the retina of mice. The localization of these molecules in normal mice was compared to their localization in retinas from animals submitted to continuous illumination during 1, 6, 9 or 18 days. We also evaluated the distribution of smooth muscle actin (SMA) and glial markers, glial fibrillary acidic protein (GFAP) and glutamine synthase (GS). PPET-1 immunoreactivity mainly appeared in retinal pigment epithelium (RPE) and cells of the ganglion cell layer (GCL), whereas ET-1 immunoreactivity was present in the RPE, outer plexiform layer (OPL) and astrocytes. Astrocytes exhibited the strongest immunostaining in the retina. ET-A immunoreactivity was observed in endothelium, RPE, OPL and cells of the GCL. By contrast, ET-B immunoreactivity could be detected in endothelial cells, horizontal cells and astrocytes. Astrocytes of the optic nerve also exhibited ET-1, ET-A, and ET-B immunoreactivities. After light-induced degeneration, there was an increase of RPE immunostaining. Degeneration of photoreceptors was accompanied by disappearance of immunoreactivity in the OPL. However, ET-A immunoreactivity appeared in the amacrine sublayer of the INL. There was an enormous increase in astrocytes and its cell processes. The increase of astrocytic immunoreactivities for ET-1 and ET-B was confirmed by quantitative image analysis. Growth of astrocytic cell processes was most marked around retinal blood vessels. Our findings indicate that there are at least three endothelinergic pathways in the normal retina: (1) between the RPE and choriocapillaris, (2) at the OPL, and (3) between blood vessels, astrocytes and cells of the GCL. After light-induced degeneration of photoreceptors, endothelinergic molecules were overexpressed at the RPE and astrocytes, but mostly disappeared from the OPL.

Animals↗

PubMed1980

Fluorescence and electron microscopical observations on the amine-accumulating neurons of the cebus monkey retina.

The organization of the Cebus monkey regina was analysed after the intraocular injection of 5,6-dihydroxytryptamine. This amine was taken up not only by the previously known dopaminergic neurons, but also by a set of indoleamine-accumulating neurons, whose processes are confined to the inner plexiform layer. The synaptic contacts of the dopaminergic neurons were analysed in the electron microscope after the processes of the indoleamine-accumulating neurons were destroyed by the intravitreal injection of the neurotoxic indoleamine, 5,7-dihydroxytryptamine. The subsequent injection of 5,6-dihydroxytryptamine induces certain changes in the dopaminergic neurons which accumulate the substance: electron-dense cores appear in the synaptic vesicles, and increased electron-density of mitochodrial and cellular membranes is often observed. The dopaminergic neurons were found to be presynaptic to amacrine cell perikarya and processes in the inner plexiform layer. In the outer plexiform layer they were presynaptic to both bipolar and horizontal cells, but they did not contact photoreceptors. The dopaminergic neurons received synapses only in the inner plexiform layer, from amacrine cell processes. It is inferred that in Cebus most dopaminergic neurons belong to a special class of retinal neuron, the interplexiform cells, which appear to transmit information centrifugally within the retina, from the inner to the outer plexiform layers. There are considerable similarities between the synaptology of the dopaminergic interplexiform neurons in the Cebus monkey and the goldfish retina, and the function of interplexiform neurons may therefore be similar in these two species.

5,6-Dihydroxytryptamine↗

PubMed1975

A golgi study of the optic tectum of the tegu lizard, Tupinambis nigropunctatus.

The dendritic patterns of cells in the optic tectum of the tegu lizard, Tupinambis nigropunctatus, were analyzed with the Ramon-Moliner modification of the Golgi-Cox technique. Cell types were compared with those described by other authors in the tectum of other reptiles; particular comparisons of our results were made with the description of cell types in the chameleon (Ramń, 1896), as the latter is the most complete analysis in the literature. The periventricular gray layers 3 and 5 consist primarily of two cell types--piriform or pyramidal shaped cells and horizontal cells. Cells in the medial portion of the tectum, in an area coextensive with the bilateral spinal projection zone, possess dendrites that extend across the midline. The latter cells have either fusiform or pyramidal shaped somas. The central white zone, layer 6, contains fibers, large fusiform or pyramidal shaped cells, fusiform cells, and small horizontal cells. The central gray zone, layer 7, is composed predominately of fusiform cells which have dendrites extending to the superficial optic layers, large polygonal cells, and horizontal cells. The superficial gray and white layers, layers 8-13, contain polygonal, fusiform, stellate, and horizontal elements. Layer 14 is composed solely of afferent optic tract fibers. Several differences in the occurrence and distribution of cell types between the tegu and the other reptiles studied are noted. Additionally, the laminar distribution of retinal, tectotectal, telencephalic, and spinal projections in the tegutectum can be related to the distribution of cell types, and those cells which may be postsynaptic to specific inputs can be identified. The highly differentiated laminar structure of the reptilian optic tectum, both in regard to cell type and to afferent and efferent connections, may serve as a model for studying some functional properties of lamination common to cortical structures.

Animals↗