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PubMedDate not supplied

Center-surround organization in bipolar cells: symmetry for opposing contrasts.

Intracellular recordings were obtained from 73 cone-driven bipolar cells in the light-adapted retina of the tiger salamander (Ambystoma tigrinum). Responses to flashes of negative and positive contrast for centered spots and concentric annuli of optimum spatial dimensions were analyzed as a function of contrast magnitude. For both depolarizing and hyperpolarizing bipolar cells, it was found that remarkably similar responses were observed for the center and surround when comparisons were made between responses of the same response polarity and thus, responses to opposite contrast polarity. Thus, spatial information and contrast polarity appear to be rather strongly confounded in many bipolar cells. As a rule, the form of the contrast/response curves for center and surround approximated mirror images of each other. Contrast gain and C50 (the contrast required for half-maximal response) were quantitatively similar for center and surround when comparisons were made for responses of the same response polarity. The average contrast gain of the bipolar cell surround was 3-5 times higher than that measured for horizontal cells. Contrast/latency measurements and interactions between flashed spots and annuli showed that the surround response is delayed by 20-80 ms with respect to that of the receptive-field center. Cones showed no evidence for center-surround antagonism while for bipolar cells, the average strength of the surround ranged from about 50% to 155% of the center, depending on the test and response polarity. The results of experiments on the effects of APB (100 microM) on depolarizing bipolar cells suggest that the relative contribution of the feedback pathway (horizontal cell to cones) and the feedforward pathway (horizontal cell to bipolar cell) to the bipolar surround varies in a distributed manner across the bipolar cell population.

Adaptation, Ocular↗

PubMed1999

Horizontal cells of the rabbit retina are non-selectively connected to the cones.

Mammalian horizontal cells have generally been assumed to be spectrally non-selective in their cone contacts until recently, when specific contacts have been found for some species. The rabbit retina is frequently studied as a representative of dichromatic mammalian retinae. These are the reasons for elucidating the connections of the two types of horizontal cells (A-HCs and B-HCs) with the green-sensitive and blue-sensitive cones of the rabbit retina. Individual A-HCs and B-HCs were revealed by Lucifer Yellow injections, the total cone population overlying them was stained using peanut agglutinin, and the blue cones among these were identified by the antiserum JH 455 against blue cone opsin. Both A-HCs and B-HCs indiscriminately contact the two cone types available. This holds for the green cone-dominated dorsal retina and the blue cone-dominated ventral retina. No evidence was found for a third, potentially blue cone-selective, horizontal cell type [postulated by Famiglietti, E. V. (1990) Brain Res., 535, 174-179].

Animals↗

PubMed1993

The visual system of the Florida garfish, Lepisosteus platyrhincus (Ginglymodi). III. Retinal ganglion cells.

The vitreal vascularization, optic nerve fiber layer and the retinal ganglion cells are examined in the Florida garfish, one of the two surviving genera of the ginglymode group of actinopterygian fishes. In the absence of a choroidal gland, a well developed system of hyaloid blood vessels overlie the inner retina. The optic nerve fiber and ganglion cell layers are integrated to form a series of alternating columns or fascicles emanating from an elongated optic nerve head. Horseradish peroxidase or cobaltous lysine infusion from the optic nerve reveals seven ganglion cell classes based on soma size and position, dendritic field size, retinal coverage and terminal stratification. Two discrete populations of giant ganglion cells with large somata and large dendritic fields stratify either within the sclerad region (type I cells) and/or within the middle region (type 2 cells) of the inner plexiform layer. Both giant ganglion cell populations (1% of total) form evenly distributed arrays with the dendritic arbor of each type covering the retina completely. Between seven and nine type 2 cells overlap the dendritic field of a single type 1 cell. Type 3 cells are small and located in the inner nuclear layer with a multistratified dendritic field terminating throughout the inner plexiform layer. Topographic analysis of the population of type 3 cells (4% of total) reveals a temporal area centralis (6.25 x 10(2) cells per mm2) and a ventral horizontal streak (6.25 x 10(2) cells per mm2). The large population of cells within the ganglion cell layer are classified as types 4, 5 and 6 based on soma size, dendritic field size and dendritic stratification and collectively these cells match the distribution of ganglion cells within the inner nuclear layer with 5.3 x 10(3) cells per mm2 in the temporal area centralis and 8.6 x 10(3) cells per mm2 in the horizontal streak. Type 7 cells possess small somata and send branches into both the inner and outer plexiform layers and have been termed biplexiform ganglion cells. Phylogenetic comparisons of several morphological features of the garfish retina reveals the polarity, conservation and the evolution of a number of visual characters.

Animals↗

PubMed2000

Induction of visual orientation modules in auditory cortex.

Modules of neurons sharing a common property are a basic organizational feature of mammalian sensory cortex. Primary visual cortex (V1) is characterized by orientation modules--groups of cells that share a preferred stimulus orientation--which are organized into a highly ordered orientation map. Here we show that in ferrets in which retinal projections are routed into the auditory pathway, visually responsive neurons in 'rewired' primary auditory cortex are also organized into orientation modules. The orientation tuning of neurons within these modules is comparable to the tuning of cells in V1 but the orientation map is less orderly. Horizontal connections in rewired cortex are more patchy and periodic than connections in normal auditory cortex, but less so than connections in V1. These data show that afferent activity has a profound influence on diverse components of cortical circuitry, including thalamocortical and local intracortical connections, which are involved in the generation of orientation tuning, and long-range horizontal connections, which are important in creating an orientation map.

Animals↗

PubMed1990

Relationships between physiological and morphological properties of retinocollicular axons in the hamster.

Intracellular recording and HRP injection were used to characterize retinocollicular axons in the hamster. Eighteen retinotectal axons were filled with HRP. The type of axon recovered most often (N = 10) had a receptive field with center-surround organization, gave sustained responses to flashed spots, had linear spatial summation, and responded only to more slowly moving stimuli. These fibers had a mean axonal diameter of 0.58 microns (SD = 0.21) and an average conduction latency of 3.4 msec (SD = 1.2) to optic chiasm (OX) stimulation. They gave rise to circular or vertically elongated arbors with an average cross-sectional area of 33,238 microns2 (SD = 12,763) and were almost completely restricted to the stratum griseum superficiale (SGS). We recovered 6 fibers with very different structural and functional properties. The receptive fields of these axons also had center-surround organization, but gave phasic responses to flashed stimuli, had nonlinear spatial summation, and responded to rapidly moving stimuli. These axons had an average diameter of 0.84 micron (SD = 0.09) and an average latency of 2.1 msec (SD = 0.40) to OX stimulation. They had elongated arbors with an average cross-sectional area of 78,045 microns2 (SD = 14,252) and innervated the SGS, the stratum opticum (SO), and upper stratum griseum intermediale (SGI). We also recovered 2 fibers that had thin (0.3 and 0.6 micron) axons and latencies of 4.2 and 3.6 msec to OX stimulation. They both gave rise to horizontally oriented arbors in the stratum zonale (SZ) and upper SGS.

Animals↗

PubMed1996

Circuitry for color coding in the primate retina.

Human color vision starts with the signals from three cone photoreceptor types, maximally sensitive to long (L-cone), middle (M-cone), and short (S-cone) wavelengths. Within the retina these signals combine in an antagonistic way to form red-green and blue-yellow spectral opponent pathways. In the classical model this antagonism is thought to arise from the convergence of cone type-specific excitatory and inhibitory inputs to retinal ganglion cells. The circuitry for spectral opponency is now being investigated using an in vitro preparation of the macaque monkey retina. Intracellular recording and staining has shown that blue-ON/yellow-OFF opponent responses arise from a distinctive bistratified ganglion cell type. Surprisingly, this cone opponency appears to arise by dual excitatory cone bipolar cell inputs: an ON bipolar cell that contacts only S-cones and an OFF bipolar cell that contacts L- and M-cones. Red-green spectral opponency has long been linked to the midget ganglion cells, but an underlying mechanism remains unclear. For example, receptive field mapping argues for segregation of L-and M-cone signals to the midget cell center and surround, but horizontal cell interneurons, believed to generate the inhibitory surround, lack opponency and cannot contribute selective L- or M-cone input to the midget cell surround. The solution to this color puzzle no doubt lies in the great diversity of cell types in the primate retina that still await discovery and analysis.

Animals↗

PubMed2001

Localization of kainate receptors at the cone pedicles of the primate retina.

In the macaque monkey retina cone pedicles, the output synapses of cone photoreceptors, contain between 20 and 45 ribbon synapses (triads), which are the release sites for glutamate, the cone transmitter. Several hundred postsynaptic dendrites contact individual cone pedicles, and we studied the glutamate receptors expressed and clustered at these contacts, particularly the kainate receptor subunits GluR5, GluR6/7, and KA2. Pre- and postembedding immunocytochemistry and electron microscopy were used to localize GluR5 and GluR6/7 to specific synaptic contacts at the cone pedicle base. The GluR5 subunit was aggregated at bipolar cell flat contacts. The GluR6/7 subunit was aggregated at bipolar cell flat contacts and at the desmosome-like junctions formed by horizontal cell processes underneath the cone pedicles. KA2 immunoreactivity was observed at the invaginating dendritic tips of ON-cone and rod bipolar cells, which we interpret as a cross-reactivity of the KA2 antiserum with some other, unknown protein of the monkey retina. Kainate receptors are preferentially expressed by OFF-cone bipolar cells and to a lesser extent by horizontal cells. We also performed double-labeling experiments with the ribbon-specific marker bassoon and with antibodies against GluR5 and GluR6/7 in order to define the position of the flat bipolar cell contacts with respect to the triads. There was a tendency of GluR6/7 clusters to represent triad-associated contacts, whereas GluR5 clusters represented non-triad-associated contacts. The GluR5 and GluR6/7 subunits were clustered at different bipolar cell contacts. We studied a possible cone-selective expression of the kainate receptor subunits by double labeling cone pedicles for the S-cone opsin and for the different receptor subunits. We observed a reduced expression of both GluR5 and GluR6/7 at the S-cone pedicles. The reduced expression of GluR6/7 was analyzed in more detail and it appears to be a consequence of a horizontal cell-specific expression: H1 horizontal cells express GluR6/7, whereas H2 horizontal cells, which preferentially innervate S-cones, show no expression of GluR6/7.

Animals↗

PubMedDate not supplied

Localization of NMDA receptor subunits and mapping NMDA drive within the mammalian retina.

Glutamate is a major neurotransmitter in the retina and other parts of the central nervous system, exerting its influence through ionotropic and metabotropic receptors. One ionotropic receptor, the N-methyl-D-aspartate(NMDA) receptor, is central to neural shaping, but also plays a major role during neuronal development and in disease processes. We studied the distribution pattern of different subunits of the NMDA receptor within the rat retina including quantifying the pattern of labelling for all the NRI splice variants, the NR2A and NR2B subunits. The labelling pattern for the subunits was confined predominantly in the outer two-thirds of the inner plexiform layer. We also wanted to probe NMDA receptor function using an organic cation, agmatine (AGB); a marker for cation channel activity. Although there was an NMDA concentration-dependent increase in AGB labelling of amacrine cells and ganglion cells, we found no evidence of functional NMDA receptors on horizontal cells in the peripheral rabbit retina, nor in the visual streak where the type A horizontal cell was identified by GABA labelling. Basal AGB labelling within depolarizing bipolar cells was also noted. This basal bipolar cell AGB labelling was not modulated by NMDA and was completely abolished by the use of L-2-amino-4-phosphono-butyric acid,which is known to hyperpolarize retinal depolarizing bipolar cells. AGB is therefore not only useful as a probe of ligand-gated drive, but can also identify neurons that have constitutively open cationic channels. In combination,the NMDA receptor subunit distribution pattern and the AGB gating experiments strongly suggests that this ionotropic glutamate receptor is functional in the cone-driven pathway of the inner retina.

Agmatine↗

PubMed1998

Presynaptic and postsynaptic localization of GABA(B) receptors in neurons of the rat retina.

The recently cloned GABA(B) receptors were localized in rat retina using specific antisera. Immunolabelling was detected in the inner and outer plexiform layers (IPL, OPL), and in a number of cells in the inner nuclear layer and the ganglion cell layer. Double-labelling experiments for GABA (gamma-aminobutyric acid) and GABA(B) receptors, respectively, demonstrated a co-localization in horizontal cells and amacrine cells. Electron microscopy showed that GABA(B) receptors of the OPL were localized presynaptically in horizontal cell processes invaginating into photoreceptor terminals. In the IPL, GABA(B) receptors were present presynaptically in amacrine cells, as well as postsynaptically in amacrine and ganglion cells. The postnatal development of GABA(B) receptors was also studied, and immunoreactivity was observed well before morphological and synaptic differentiation of retinal neurons. The present results suggest a presynaptic (autoreceptor) as well as postsynaptic role for GABA(B) receptors. In addition, the extrasynaptic localization of GABA(B) receptors could indicate a paracrine function of GABA in the retina.

Amino Acid Sequence↗

PubMed2004

Carbenoxolone inhibition of voltage-gated Ca channels and synaptic transmission in the retina.

We show that carbenoxolone, a drug used to block hemichannels in the retina to test the ephaptic model of horizontal cell inhibitory feedback, has strong inhibitory effects on voltage-gated Ca channels. Carbenoxolone (100 microM) reduced photoreceptor-to-horizontal cell synaptic transmission by 92%. Applied to patch-clamped, isolated cone photoreceptors, carbenoxolone inhibited Ca channels with an EC(50) of 48 microM. At 100 microM, it reduced cone Ca channel current by 37%, reduced depolarization-evoked [Ca(2+)] signals in fluo-4 loaded retinal slices by 57% and inhibited Ca channels in Müller cells by 52%. A synaptic transfer model suggests that the degree of block of Ca channels accounts for the reduction in synaptic transmission. These results suggest broad inhibitory actions for carbenoxolone in the retina that must be considered when interpreting its effects on inhibitory feedback.

Ambystoma↗

PubMed2001

Early onset of glutamatergic and GABAergic synaptic activity in the visual layers of the rodent superior colliculus.

During postnatal development, the retinocollicular pathway undergoes activity-dependent refinement, resulting in the precise retinotopic map seen in adults. Previous studies established that retinal efferents reach the mouse superior colliculus (SC) by embryonic day 16. Morphologically, synapses were found in the rat SC before birth. As part of an extended project aimed at understanding the development of synaptic transmission in the visual layers of the SC, we report here the presence of functionally active synapses immediately after birth. Circuit activity in mouse SC neurons was detected in horizontal slices of the visual layers using cell-attached voltage clamp. The spontaneous discharge of action potentials was abolished by glutamatergic blockers and facilitated by bicuculline, showing that circuit activity is based on synaptic transmission and that the action of gamma-aminobutyric acid is inhibitory. Using whole-cell voltage clamp, spontaneous glutamatergic postsynaptic currents as well as miniature GABAergic postsynaptic currents were recorded on postnatal day 1. Excitatory and inhibitory postsynaptic currents could also be evoked by electrical stimulation. Glutamatergic postsynaptic currents comprised both (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate receptor-mediated components. The early function of glutamatergic and GABAergic synaptic transmission in the visual layers of SC suggests that SC neurons are able to process information originating from retinal axons immediately after birth.

2-Amino-5-phosphonovalerate↗

PubMed1971

Incremental responses to light recorded from pigment epithelial cells and horizontal cells of the cat retina.

1. Rod-dependent incremental responses were recorded intracellularly in both pigment epithelial cells and horizontal cells of the cat retina. They were elicited by test flashes which were superimposed on background flashes after a delay.2. In pigment epithelial cells smaller test responses were produced as background intensity was raised. The incremental sensitivity function was linear for about 1.4 log units, with a slope of 0.86, and the approach of saturation occurred at about 2.5 log td scotopic.3. The amplitude of pigment epithelial test responses could be estimated from the dark-adapted amplitude-log intensity function obtained with single flashes. Test flashes produced the voltage increment predicted by the slope of this function just above the point on the curve equal to the background intensity. The pigment epithelial response to a test flash, therefore, is the response expected if the background were presented alone and made more intense by the amount of the test flash.4. Rod-dependent incremental sensitivity functions of horizontal cells closely resembled the ones obtained from pigment epithelial cells.5. It was concluded that the adaptive effects observed in pigment epithelial cells originated in individual rods. These effects arose from the compressive nature of the dark-adapted amplitude-intensity function. In horizontal cell responses these effects may be modified by the failure of the background response to maintain its initial voltage.

Animals↗

PubMedDate not supplied

3H-adenosine uptake selectively labels rod horizontal cells in goldfish retina.

There are four types of horizontal cell in the goldfish retina, three cone- and one rod-type. The neurotransmitter of only one type, the H1 (cone) horizontal cell, has been identified as GABA. 3H-adenosine uptake was examined as a possible marker for the other classes of horizontal cell. Isolated goldfish retinae were incubated in 3H-adenosine (10-40 microCi) in HEPES-buffered saline for 30 min, then fixed, embedded in plastic, and processed for light-microscopic autoradiography (ARG). For double-label immuno/ARG studies, 1-micron-thick sections were processed for GABA postembed immunocytochemistry, then for ARG. 3H-adenosine uptake was localized to cone photoreceptors, presumed precursor cells in the proximal outer nuclear layer, and to a single, continuous row of horizontal cell bodies in the inner nuclear layer. No uptake was localized to the region of horizontal cell axon terminals. 3H-adenosine uptake did not colocalize with GABA-IR in H1 horizontal cells, but it did colocalize with adenosine deaminase immunoreactivity. It is concluded that 3H-adenosine uptake selectively labels rod horizontal cells in the goldfish retina based on position and staining pattern, which are similar to rod horizontal cells stained by Golgi or HRP injection methods. The use of 3H-adenosine uptake may provide a useful tool to study other properties of rod horizontal cells (i.e. development) as well as provide clues as to the transmitter used by these interneurons.

Adenosine↗

PubMed1997

Neurobiology of the regenerating retina and its functional reconnection with the brain by means of peripheral nerve transplants in adult rats.

Axotomy-induced degradation of retinal ganglion cells (RGC) can be delayed if the destructive features of activated microglial cells are pharmacologically neutralized, and prevented if the axons are permitted to regrow into transplanted autologous peripheral nerve (PN) pieces. Axotomized central nervous system neurons, whose regenerating axons are guided to their natural target areas in the brain with the aid of PN grafts, are capable of establishing synaptic contacts with normal morphological and electrophysiological properties. This study was undertaken to 1) morphometrically characterize and classify the regenerating rat RGC, 2) examine target-dependent effects on survival of subsets of neurons, and 3) investigate whether reconnected neurons are capable of restoring visual functions. In analogy to the normal rat retina, as a first step, the retrogradely labeled, regenerating RGC were categorized into five classes which are morphologically distinct and reminiscent of normal RGC correlates (called types RI, RII, RIII, Rdelta-cells, and displaced RGC). It appeared that all types of ganglion cells contributed proportionally to regeneration of axons. Transplantation of a PN graft which was not reconnected with a central target (blind-ending group) and monitoring of the extant neurons showed a progressive disappearance of the regenerating RGC, such that 6 months after surgery predominantly few, large cells survived. When the retinas were treated with macrophage/microglia inhibiting factor (MIF), and the regenerating axons were guided into the pretectum, predominantly large RGC of type RI survived. Guidance of the axons into their major natural target, the superior colliculus (SC), resulted in selective survival of many small, RII-like RGC. Calculation of the dendritic coverage factors for the major types of RGC revealed that dendrites of the most abundant, small cells of type RII overlapped uniformly and covered the retinal surface completely, whereas cells of types RI and RIII did not suffice for surface coverage. The results of this first part of the work suggest that combined suppression of axotomy-induced microglial activation and guidance of regenerating axons with a PN graft into central targets is a suitable technique to produce sufficient numbers of regenerating axons which may retrieve some functional properties. Target-specific neuronal contacts are likely involved in morphological stabilization and better survival of regenerating neurons. The second goal of this study was to analyze the functional significance of the reestablished synaptic contacts made by regenerated retinocollicular neurons. Adult rats were trained in a T- or Y-maze to obtain a food reward with the aid of visual cues. One of their optic nerves was transected and the regenerating axons were guided into the optic tract with a PN graft, to enable them to reinnervate the SC and thalamus. Postoperative testing of the animals showed a drastic improvement of visual perception. The protocol of denervation of the SC (prior to, simultaneous with, or with a delay with respect to fiber arrival) determined the performance of the animals. Rats belonging to the first two groups performed almost as well as they had before the transplantation. The functional integrity of the retina was assessed by electroretinography, which revealed typical rod spectral sensitivity at 380 and 500 nm but reduced responsiveness to illumination. In accordance, neuroanatomical assessment of the functionally relevant RGC revealed intact morphologies and multiple synaptic contacts both within the retina and within the SC. Neuroanatomical tracing of small contingents of axons throughout the regenerative pathway revealed a rough retinotopic arrangement within the graft and the area of termination. Thus, animals could discriminate between simplified vertical versus horizontal stripes, and visual evoked potentials were positive after grafting. (ABSTRACT TRUNCATED)

Animals↗

PubMed1989

Anterograde labelling from the optic nerve reveals multiple central targets in teleost, Lethrinus chrysostomus (Perciformes).

Cobaltous-lysine is transported anterogradely from the optic nerve of the teleost, Lethrinus chrysostomus (Lethrinidae, Perciformes). The marginal optic tract is labelled in longitudinal bands of light and dark staining fibres which persists caudally within the ventral division but not in the dorsal division. This species possesses multiple central targets in the contralateral preoptic, diencephalic, pretectal, periventricular and tectal regions of the brain. In addition, a greater subdivision of the marginal optic tract is found to project to various nuclei. Ipsilateral projections are found in the suprachiasmatic nucleus and in the region of the horizontal commissure. Projections are also found in the telencephalic region of the nucleus olfactoretinalis and the thalamic region of the nucleus thalamoretinalis. The retinotopicity of some of these nuclei, found in previous studies, is discussed in relation to the possibility of specific sub-populations of retinal ganglion cells having different central targets.

Animals↗

PubMed1984

Effects of neonatally induced strabismus on binocular responses in cat area 18.

Responses to binocular visual stimulation were compared in cortical area 18 of normal cats and in cats in which one eye was exodeviated by surgery early in postnatal life. In contrast to normal cats where most units (58%) were binocularly activated, relatively few units (10%) in strabismic cats were activated well by stimulation of either eye. Rather individual units were driven mainly via one eye or the other but not both. In addition, there was a tendency for more units to be driven well via the unoperated eye than via the exodeviated eye. Fewer cells preferring vertically oriented than horizontally oriented stimuli were found in area 18 of strabismic cats. This trend was observed for cells driven by either the normal or deviated eye and was especially marked among the small number of binocularly activated cells. Generally binocular responses and binocular interactions were found with stimulation at corresponding retinal points. In a few striking instances, however, the receptive fields of binocular neurons were located on noncorresponding retinal points at loci which would enable the cat to correlate the two images of an external object despite the large divergent strabismus. Quantitative responses to binocular stimuli presented at varied disparities and to stimuli with varied directions of motion in depth were compared in normal and strabismic cats. Despite the large strabismus, a reduced fraction of cortical neurons displayed substantial binocular interactions. In fact, binocular facilitation was as marked in the population of cells studied in strabismic cats as it was in normal animals. The major effect of strabismus was a reduction in the strength of binocular inhibition when units were tested with sideways motion. Disparity-specific responses to motion toward or away from the organism were little affected by strabismus. The degree of binocular facilitation and binocular inhibition among the cell population was similar in normal and strabismic cats. A subpopulation of units encountered in strabismic cats showed strong disparity-specific interactions for motion toward or away from the animal without equivalent modulation for sideways moving stimuli. Units with these properties were not found in normal animals and may, therefore, represent a special adaptation of the strabismic animals.

Animals↗

PubMed1990

A distinctive soma size gradient among catecholaminergic neurones of human retinae.

We have examined the soma diameters and distribution of catecholaminergic (CA) cells in human retinae, by using an antibody to tyrosine hydroxylase (TH), the rate limiting enzyme in the production of catecholamines. TH-immunoreactivity was detected in two classes of cells (CA1 and CA2 cells). CA1 cells had relatively large somata (mean diameter 14 microns) located in either the inner nuclear layer (INL) or in the ganglion cell layer and extensive dendrites spreading into the other strata of the inner plexiform layer (IPL). CA2 cells had smaller, weakly labelled somata (mean diameter 9.6 microns) located principally in the inner regions of the INL and weakly labelled dendrites extending into the IPL. The mean density of CA2 cells in the far retinal periphery was approximately 38/mm2. The number of CA1 cells averaged approximately 15,600 per retina, with a mean density of 16/mm2. The density distribution of CA1 cells closely paralleled the distribution of ganglion cells, their density peaking at the foveal rim, with an area of relatively high density extending horizontally from the macula region toward the nasal margin (along the visual streak). A distinctive gradient was detected among the soma diameters of CA1 cells: they were largest in the mid-periphery, in a visual streak-like configuration around the optic disk. This gradient of soma size among CA cells closely corresponds to the density distribution of the rod photoreceptors in human retinae.

Animals↗

PubMed1990

Somatostatin and prosomatostatin in the retina of the rat: an immunohistochemical, in-situ hybridization, and chromatographic study.

Specific antisera, raised in rabbits, against somatostatin 1-14, somatostatin 1-28, the fragment 1-12 of somatostatin 1-28, and prosomatostatin 20-36 were used for immunohistochemistry and gel filtration of the rat retina. With all antisera, immunoreactive perikarya could be located in the inner nuclear and ganglion cell layers. In the inner nuclear layer, amacrine cells with processes extending predominantly into the first sublayer of the inner plexiform layer were observed. Some processes extended also to the ganglion cell layer. In addition, somatostatin-immunoreactive interplexiform cells were present in the inner nuclear layer. In the ganglion cell layer, perikarya were found located in the midperiphery and in the far periphery of the retina. The neurons located in the midperiphery of the retina possessed a round perikaryon from which processes could be followed going into the inner plexiform layer, where they dichotomized in the third and first sublayers. The perikarya in the far periphery of the retina near the ora serrata exhibited an ovoid-shaped cell body from which processes extended horizontally in a bipolar manner in the layer itself. By use of an [35S]-labeled antisense oligonucleotide probe, in situ hybridization of the rat retina showed the presence of perikarya in the inner nuclear layer and ganglion cell layer containing mRNA encoding for prosomatostatin. Gel filtration of the retinal extracts followed by radioimmunoassay showed the presence of somatostatin 1-14, the fragment 1-12 of somatostatin 1-28, and prosomatostatin 1-64. However, somatostatin 1-28 was not detected. The results obtained in this study verify the presence of somatostatin 1-14 in the rat retina located in perikarya and processes in the inner nuclear and ganglion cell layers. The positive in-situ hybridization signals show that the intraneuronal somatostatin immunoreactivity is due to synthesis of the peptide and not uptake in the neurons. The presence of the somatostatin propeptide and fragments of this propeptide, in both intraretinal perikarya and fibers, indicate a posttranslational modification of this neuropeptide in the perikarya and the processes as well.

Animals↗