Connexions between retinal neurons with identified neurotransmitters

Selective Colour Vision Deficits in Multiple Sclerosis at Different Temporal Stages

Multiple sclerosis (MS) without optic neuritis causes color-vision deficit but the evidence for selective color deficits in parvocellular-Red/Green (PC-RG) and koniocellular-Blue/Yellow (KC-BY) pathways is inconclusive. We investigated selective color-vision deficits at different MS stages. Thirty-one MS and twenty normal participants were tested for achromatic, red-green and blue-yellow sinewave-gratings (0.5 and 2 cycles-per-degree (cpd)) contrast orientation discrimination threshold. Red-green mean threshold at 0.5cpd in established-MS and blue-yellow mean threshold in all MS participants were abnormal. These findings show blue-yellow versus red-green color test is useful in differentiating MS chronicity, which helps to better understand the mechanism of colour-vision involvement in MS.

DARPP-32 involvement in the photic pathway of the circadian system

The multifunctional regulator of protein kinases and phosphatases dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) is an important molecular target of the dopamine signaling pathway. In the present study, we investigated the possible involvement of DARPP-32 regulation in the circadian system using DARPP-32 knock-out (KO) mice. These mice showed normal entrainment to a 12 h light/dark cycle and free run in constant darkness with a period similar to that of wild-type controls. After light exposure, however, the behavioral phase-delay response and the expression of light-induced clock gene mPer2 were attenuated in the DARPP-32 KO mice. Attenuated phase delays were also seen in animals bearing a point mutation in DARPP-32 at the PKA (Thr34) but not at the casein kinase I (Ser130) phosphorylation site. We next examined DARPP-32 expression in the retina and intergeniculate leaflet (IGL), both of which convey light information to the suprachiasmatic nucleus (SCN), the locus of a master circadian clock, and in the SCN itself. DARPP-32 was expressed in the retina but not in the IGL or the SCN. The results indicate that DARPP-32 is involved in the retinal pathway transmitting photic information that resets the circadian clock.

Motor impairment influences Farnsworth-Munsell 100 Hue test error scores in Parkinson's disease patients

Farnsworth-Munsell 100 Hue test (FMT) error scores and peg insertion abilities significantly differ between Parkinson's disease (PD) patients and controls. Both tasks ask for performance of voluntary movements. The objective of this study was to demonstrate a relation between FMT error scores and peg insertion outcomes. We successively performed both tasks in 28 previously untreated PD patients. The FMT error score was significantly (p=0.016) lower in patients with better peg insertion outcome. A significant (Spearman R=0.47, p=0.012) correlation between peg insertion results and the FMT error scores appeared. Motor impairment influences FMT error scores in PD patients.

Colour vision abnormalities and movement time in Parkinson's disease

Visual system dysfunction has been reported in Parkinson's disease (PD). The objective of the present study was to evaluate a putative association of distorted colour vision and delayed initiation and execution of movement in PD. We performed the Farnsworth-Munsell 100-hue test and estimated the total error score in 30 previously untreated parkinsonian patients and 30 age- and sex-matched controls. We then determined slowness in motor readiness and motor programming in the parkinsonian subjects on the same day. Subjects were asked to press a start button and release it after the randomized appearance of a visual stimulus and to move their right index finger to a reaction button as quickly as possible. Reaction time was considered as elapsed time between onset of the stimulus light and release of the start button, movement time was the time period between release of the start button and the pressing of the reaction button. Significant differences appeared between parkinsonian patients' and controls' reaction times (P = 0.007), movement time (P = 0.001) and total error score (P = 2.23E-08). A significant relation (Spearman R = 0.473, P = 0.008) was found between movement time and total error score, but not between reaction time and total error score (Spearman R = 0.259, P = 0.166). We conclude, that visual dysfunction and execution of movement are more influenced by altered dopaminergic neurotransmission in PD in comparison to the initiation of movement.

Colour discrimination thresholds in Parkinson's disease: results obtained with a rapid computer-controlled colour vision test

A dysfunction of dopaminergic retinal neurons is thought to occur in Parkinson's disease, manifesting itself in impaired performance on various visual discrimination tasks. We have investigated whether differences in colour discrimination could readily be detected between a normal group and a Parkinsonian group, using a computer-controlled test of colour vision. Although some individual Parkinsonian patients showed an abnormal elevation of colour discrimination thresholds, there was no significant difference between the normal group and the Parkinsonian group.

Visual thresholds to low-contrast pattern displacement, color contrast, and luminance contrast stimuli in Parkinson's disease

We used the computerized Moorfield Vision System to demonstrate specific increases in various perceptual visual thresholds in idiopathic Parkinson's syndrome. Fifteen patients were compared to 13 age-matched normals. Motion detection was impaired maximally (2 p < 0.01 and better in two-tailed t test) at luminance contrasts of 3-7%. Stimulus was an achromatic vertical 4 cycles/degrees sine wave grating subtending 3 degrees x 2 degrees, centered 5 degrees in the nasal field and oscillating at 5 Hz. In addition, stationary color and luminance contrast thresholds were tested with flashed display of 5 degrees x 6 degrees random letters, which were presented for 200 ms (color) and 50 ms (achromatic). Color discrimination was impaired in the tritan axis only (2 p < 0.05 in two-tailed t test). All achromatic stimuli--luminance increments, decrements, and phase reversing stimuli--were equally well seen by patients and controls. We conclude that the dopaminergic deficit of retinal amacrine cells in Parkinson patients can be monitored by combined low-contrast and motion (displacement) stimuli. Future studies will determine if moving colored targets are more effective in discriminating patients from controls than are the achromatic gratings used in this work.

The development of GABA immunoreactivity in the retina of the zebrafish (Brachydanio rerio)

The goal of this study was to determine the pattern of gamma-aminobutyric acid (GABA) expression in the retina and optic nerve of the zebrafish (Brachydanio rerio) during embryonic development. Zebrafish embryos were fixed at intervals between 1 and 4 days postfertilization, and semithin plastic sections were prepared for postembedding immunocytochemistry with antisera against GABA. Sections were also prepared from several adult zebrafish eyes for comparison. GABA immunoreactivity first appeared in the optic nerve at 2 days postfertilization, and by 2.5 days the inner nuclear layer (INL), inner plexiform layer (IPL), retinal ganglion cell layer, and optic nerve were all positive for GABA. The GABA expression in the retinal ganglion cell layer and optic nerve was transient, however, and these structures were largely unlabeled by 4 days postfertilization. The pattern of GABA immunoreactivity at 4 days resembled that seen in the adult zebrafish: A large population of presumptive amacrine cells was labeled at the base of the INL, and the IPL was positive for GABA, as were occasional cells in the ganglion cell layer. Horizontal cells, particularly at the retinal margins, were also GABA positive beginning at about 3 days postfertilization. The transient expression of GABA in retinal ganglion cells and their axons during the period when synaptic contacts are being established both within the retina and between the retina and central targets suggests that GABA may have a role in the development of this system, in addition to serving as a classical neurotransmitter.

The expression of GAP-43 and synaptophysin in the developing rat retina

We have undertaken a detailed study of the expression of GAP-43 and synaptophysin immunoreactivity in the developing postnatal rat retina. We found that these two 'presynaptic' proteins have quite different expression patterns. GAP-43 was first expressed in the optic nerve and the optic fiber layer of the retina, where it disappeared between the 8th and 16th postnatal day. From the 5th postnatal day on, GAP-43 also appeared in the inner plexiform layer, where it was present in three distinct bands. This expression changed little in postnatal development and persisted in the adult retina. GAP-43 was not detected in the outer plexiform layer of the retina. Synaptophysin was absent from the optic nerve and optic fibers at all postnatal stages. It was first expressed in the developing outer plexiform and, with reduced intensity, in the outer nuclear layer between postnatal days 2 and 5. In the inner plexiform layer, synaptophysin could be first detected between postnatal days 8 and 12. The intensity of staining increased during postnatal development in both plexiform layers. The developmental sequence of synaptophysin expression can be correlated with the maturation of presynaptic terminals of photoreceptors and bipolar cells. The rather complex pattern of GAP-43 expression is not easily compatible with a single model of GAP-43 function, and suggests diverse functions of this molecule in the retina.

Effect of dopamine and acetylcholine on the visual evoked potential

Visual evoked potentials were measured on patients with Parkinson's disease and Alzheimer's disease and normal controls to assess the function of dopamine and acetylcholine in the visual system. Dopamine is a neurotransmitter known to be present in the retina of primates and is found to be severely depleted in the substantia nigra of patients with Parkinson's disease. Acetylcholine is also known to be present in the retina, visual cortex, and superior colliculus and is found to be grossly reduced in patients with Alzheimer's disease. Stimuli were designed to preferentially activate functionally separate pathways in the visual system described as magnocellular and parvocellular. The four stimuli were a diffuse flash; an achromatic, 73' check counterphasing at 6 Hz at a contrast of 30%; an achromatic 10' check counterphasing at 2 Hz at a contrast of 85%; and an isoluminant red/green grating of 4 cpd presented using an on and off cosine ramp of 200 ms. The results indicate that an acetylcholine deficit produces a delay to the flash P2 component of the visual evoked potential. No change was detected when other stimuli were used.

A removable ocular microdialysis system for measuring vitreous biogenic amines

A microdialysis system with a removable probe and a fixed scleral entry port is presented. The probe can be inserted several times with minimal trauma, permitting repeated sampling in one animal. The functioning of the setup is illustrated by the measurement of dopamine, dihydroxyphenyl acetic acid, and noradrenaline in the vitreous of healthy rabbits under physiological conditions.

Large serotonin-like immunoreactive amacrine cells in the retina of developing Xenopus laevis

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.

Serotonin synthesis and accumulation by neurons of the anuran retina

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.

Development of catecholaminergic, indoleamine-accumulating and NADPH-diaphorase amacrine cells in rabbit retinae

We have investigated the ontogeny of four classes of amacrine cells in the rabbit retina. In particular, the distribution, number, soma diameter, dendritic field diameter, and pattern of dendritic stratification were studied in catecholaminergic (CA) and indoleamine-accumulating (IA) amacrines and in two classes of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase amacrine cells. The first CA and IA cells are observed on the 27th postconceptional day (27PCD) and the first NADPH-diaphorase cells on 28PCD. These first cells are concentrated in the central part of the visual streak, and at subsequent ages, cells in this part of the streak have larger somata and more mature dendritic fields than those elsewhere, supporting the notion that the peak density region is a developmentally advanced part of the retina. Throughout development, amacrine cells of all classes are concentrated in the visual streak, with their density reaching minima at the superior and inferior retinal margins. As their total number increases, the difference in cell density between the streak and the periphery decreases, presumably because proportionately more cells are added at the periphery. Their total number peaks around 42PCD, followed by a decline of 12-31% to adult values. Once the peak number of cells has been reached, the difference in cell density between the streak and periphery begins to increase. The rate of this increase is closely correlated with the increase in retinal area. This redistribution of amacrine cells, as well as a greater expansion of their dendritic fields in peripheral retina, is almost certainly the product of nonuniform retinal expansion.

Serotonin-like immunoreactivity in the retina of the clawed frog Xenopus laevis

Using an antiserum directed against serotonin, we have studied the morphology and distribution of serotonin-containing and serotonin-accumulating neurons in the retina of Xenopus laevis. Endogenous serotonin-like immunoreactivity was found in two classes of amacrine cell, one class of bipolar cell and a few centrifugal fibres. Kainic acid-induced depletion of serotonin, under various conditions, enabled us to determine the distribution of stained bipolars, amacrine cells and centrifugal fibres within the meshwork of serotonin-like immunoreactivity-labelled processes. Kainic acid-induced release of serotonin by bipolar cells is calcium dependent. Stimulation of release by kainic acid as well as the fact that all serotonin-like immunoreactive bipolar cells ramify in sublayer 1 of the inner plexiform layer suggest that serotonergic bipolars are OFF centre cells. Release of serotonin from amacrine cells is largely calcium independent. Serotonin-containing amacrines send primary dendrites into layer 1 of the inner plexiform layer; short off-shoots from the primary dendrites descend into sublayers 3-5 in which they ramify into a fine network. Serotonergic amacrines have an uneven distribution in the Xenopus retina. Their highest density occurs in the posterolateral quadrant, whereas large portions of the anteromedial quadrant lack serotonin-like immunoreactivity altogether. The uneven distribution of serotonin-containing elements in the Xenopus retina with its peak falling onto the retinal area which generates binocular vision, suggests its involvement in binocular perception.

gamma-Aminobutyric acid system in developing and degenerating mouse retina

Freeze-dried sections (14 microns thick) of retinal layers were prepared from mice with retinal degeneration (C3H strain) and control mice (C57BL strain). The weighed sections (2-30 ng dry weight) were analyzed using our microassay methods. In the control retina, gamma-aminobutyric acid (GABA) concentration and glutamate decarboxylase (GAD) activity, on a dry weight basis, increased from birth to 9 weeks of age and decreased slightly at 20 weeks. In the degenerated retina, the levels of GABA and GAD activity were higher at birth than in the control retina, and continued to increase until 20 weeks of age, at which time the GAD activity reached a markedly high level. This increase was found when the total GABA and GAD levels per retina were determined. In the normal retinal layers, GABA and GAD were confined primarily to the inner plexiform layer. In the degenerated retina, GAD activity gradually increased in the inner layers during postnatal development, but by 20 weeks the increase was most prominent in the inner part of inner nuclear layer and in the outer part of inner plexiform layer. GABA transaminase activity and its distribution were not much different in both normal and degenerated retinas during development.

Tyrosine hydroxylase immunohistochemistry in the normal and 1-methyl-4-phenyl-tetrahydropyridine (MPP+)-treated retina of goldfish

Dopaminergic interplexiform neurons have been identified in the inner nuclear layer of goldfish retina, with tyrosine hydroxylase (TH) immunocytochemistry in whole-mounted retinae and in cryosections. The neurotoxin 1-methyl-4-phenylpyridinium ion (MPP+), which selectively damages dopaminergic neurons in mammals, caused a marked depletion of TH immunoreactivity in goldfish retina. Three days after intravitreal injection, retinae showed no significant decrease in the number of TH-positive neurons. However most of the TH-immunoreactive cell bodies showed an evident depletion of TH immunoreactivity and their processes, ramified in the inner and outer plexiform layers, disappeared almost completely.

Ontogeny of catecholaminergic and cholinergic cell distributions in the cat's retina

The development of catecholaminergic and cholinergic neurones in the cat's retina has been examined with antibodies against their respective rate-limiting enzymes, tyrosine hydroxylase (TH) and choline acetyl transferase (ChAT). ChAT-immunoreactive (IR) cells were first detected at E (embryonic day) 56 with somata in the ganglion cell layer (GCL) or in the inner cytoblast layer (CBL). At P (postnatal day) 1, two faint bands of ChAT-IR fibres were evident in an inner and outer strata of the inner plexiform layer (IPL) and by P26, the bands were similar to those in the adult. TH immunoreactivity was first detected at E59 in either darkly labelled somata in the inner CBL with processes extending toward the IPL or in lightly labelled somata also located in CBL but with no processes. At P1, most TH-IR cells had prominently labelled dendrites and, by P8, most of the features of the adult cells were evident. Soma size gradients among TH-IR cells were first detected at P8, with cells in temporal retina being larger than those in nasal retina or at the area centralis. The smaller sizes of cells at the area centralis emerged after P26. The smaller sizes of ChAT-IR somata at the area centralis, by contrast, emerged between P8 and P26. The number of both TH-IR and ChAT-IR cells declined from the time they first appeared till adulthood. The decline was smaller among ChAT-IR cells (24%) than among TH-IR cells (68%). In distribution, the differential expansion of the retina appeared to be largely responsible for generating the final adult distribution of ChAT-IR cells. However, during late postnatal development (P26 to adulthood), the density of ChAT-IR cells in the periphery declined more than that of the ganglion cells, suggesting that some ChAT-IR cells may die in the periphery during this time. Prior to P26, the changes in the distribution of TH-IR cells were inconsistent with the pattern of retinal expansion. It is suggested that during this period, regional cell loss and cell addition may account for the changes in distribution of TH-IR cells. Later in development (P26 to adulthood), the changes in the density of TH-IR cells closely conformed to the differential expansion of the retina.

Cyclic adenosine monophosphate as a second messenger in horizontal cell uncoupling in the teleost retina

The reduction in the receptive field of horizontal cells of the teleost Eugerres plumieri observed upon dopamine (DA) superfusion is thought to be due to cell uncoupling. The possible mechanisms by which activation of DA receptors modify the electric coupling between horizontal cells were studied in the present work. It was found that the effect of DA in different preparations is mediated by a modification of intracellular concentration of cAMP and H+. The effects of intracellular injection of cAMP and H+ were studied in retinal horizontal cells of the teleost E. plumieri. A triple microelectrode was used to inject the ion iontophoretically, to pass current pulses, and to record voltages from the same cell, while a fourth microelectrode was used to record voltages from a neighboring cell in the same retinal layer. Responses evoked by light spots and annuli were evaluated simultaneously. Coupling ratios between neighboring horizontal cells ranged from 0.22 to 0.45. The intercellular resistance (Rc), 0.5-3.5 x 10(6) ohms, and that of the remaining cell membrane resistance (Rm), 2.5-18 x 10(6) ohms, were calculated by means of a passive electrical model that has a hexagonal array. The microinjection of H+ with injection current from +5 to +30 nA for 40 to 100 sec led to temporary and reversible light response reduction. The coupling ratio between two impaled cells was reduced by about 30%, and intercellular resistance (Rc) increment was 320% while cell membrane resistance (Rm) did not change consistently. There was also a temporary and reversible Rm reduction (70-85%) and an Rc increment of 170-330% when cyclic adenosine monophosphate was iontophoretically injected with current from -30 to -40 nA for 50 to 170 sec. The coupling ratio between two impaled cells was reduced by about 40%, and light responses recorded from the injected cell showed a reduction in amplitude with the same time course as that of the resistive changes. The injection of Lucifer yellow into a horizontal cell under normal conditions always results in pronounced fluorescence for more distant cells; however, under constant injection of H+ or cAMP only the injected cell is fluorescent, which provides direct evidence of the reduction in the effectiveness of coupling between horizontal cells. The observed effects of intracellular H+ or cAMP injection correspond to the resistive changes in Rc and coupling ratio that occur in the horizontal cell network upon superfusion with a dopamine (DA) solution.

Distribution and morphology of tyrosine hydroxylase-immunoreactive neurons in the developing mouse retina

An antibody to tyrosine hydroxylase (TH), the rate-limiting enzyme in the production of catecholamines, was used to examine the morphology and distribution of catecholaminergic neurons in whole-mounted retinae of the developing and adult mouse. At adulthood TH-labeled cell bodies were located in the inner nuclear layer, stratifying mainly at the border to the inner plexiform layer (IPL). Few processes were found in the middle of the IPL. The majority of all TH-labeled cells also extended processes towards the outer plexiform layer and thus are interplexiform cells; the rest were considered to be amacrine cells. The TH-positive neurons were regularly distributed throughout the adult mouse retina. During development, the first TH-immunoreactive cells were observed by postnatal day 6 (P6) and most of them were present after the third postnatal week. The dendrites in the IPL only acquired varicosities after the eyes opened at P15. Biochemical measurements of the endogenous catecholamine content showed that at all developmental stages only dopamine was detectable, suggesting that the TH-labeled cells represent dopaminergic neurons. The content of dopamine was low before P6 and continuously increased during the following days. A strong increase in dopamine was observed during the time when varicosities formed.

Serotoninergic neurons in the retina of Xenopus laevis: selective staining, identification, development, and content

Uptake of 3H-serotonin followed by autoradiography, and uptake of the serotonin analog 5,7-dihydroxytryptamine (5,7-DHT), with subsequent staining, were each used to define a unique set of neurons in the retina of the African clawed frog, Xenopus laevis. Both techniques demonstrated the same population of neurons, on the basis of perikaryal size, shape, and position within the retina. Two classes of amacrine cells accumulated 5,7-DHT at the proximal (vitread) margin of the inner nuclear layer; the two classes were distinguished by the size of their perikarya. Two similar populations of cells, observed in the ganglion cell layer with lower frequency, may represent "displaced" counterparts of these two amacrine cell types. A class of bipolar cells whose perikarya were located in middle-to-distal regions of the inner nuclear layer also accumulated 5,7-DHT and 3H-serotonin. Processes of these cells contributed to a dense plexus of fine fibers that appeared evenly distributed throughout the inner plexiform layer. 3H-Serotonin-accumulating cells first appeared in the developing retina at stage 35/36, a time immediately after retinal stratification but before elaboration of either plexiform layer. Electron microscopic analysis permitted an identification of 3H-serotonin-accumulating terminals in the inner plexiform layer. Serotonin-labeled terminals containing conventional contacts, suggestive of amacrine cells, were presynaptic to unidentified processes and postsynaptic to bipolar cells. Labeled terminals containing ribbon contacts, indicative of bipolar cells, were postsynaptic to amacrine cells. The amount of serotonin contained in isolated retinas was 15 pmol/mg protein as measured by HPLC with electrochemical detection. We attempted to stimulate the release of accumulated 3H-serotonin from mature retinas by increasing the K+-concentration in the bathing medium. Although preloaded glycine is readily released from 14C-glycine-accumulating neurons, from the same retinas there was no calcium-dependent, K+-stimulated release of 3H-serotonin. This finding suggests that serotonin and glycine are processed differently by retinal neurons, the consequence of which results in differing responses to 40 mM K+.

Catecholaminergic and cholinergic neurons in the developing retina of the rat

We have examined the development of catecholaminergic and cholinergic neurons in the retina of the rat by using antibodies against the enzymes tyrosine hydroxylase (TH) and choline acetyl transferase (ChAT), respectively. TH-immunoreactivity was first detected at P (postnatal day) 3 in somata located in the inner part of the cytoblast layer (CBL) and in fine dendrites extending toward the middle of the inner plexiform layer (IPL). These cells were similar in shape and soma size to the class 2 TH-immunoreactive (TH-IR) cells of the adult rat. At P6, TH-immunoreactivity was expressed by a second population of cells. Their somata were in the inner part of the inner nuclear layer (INL), but were distinctly larger, with short thick dendrites extending into the outer and/or middle parts of the IPL. Over subsequent days, the dendrites of these larger cells spread profusely in the outer part of the IPL, making it likely that they are the class 1 TH-IR cells of the adult. ChAT-immunoreactive (ChAT-IR) cells were not detected until P15, when ChAT-IR somata were observed in the ganglion cell layer (GCL) and INL, and their dendrites were observed already segregated into the distinct strata of the IPL in which they are found in the adult. The subsequent growth of TH-IR somata of both classes was uneven, persisting longer in temporal than in nasal retina. This extended growth of temporal cells establishes the marked nasotemporal differences in soma diameter apparent among TH-IR cells in the adult (Mitrofanis and Stone, '86; Mitrofanis et al., '88b). The growth and adult size of ChAT-IR somata, on the other hand, did not vary with retinal position; their diameters were similar to those of the adult cells from the time they first appeared. The distribution of ChAT-IR cells at P15 shared several features of the distribution of ganglion cells. The density of ChAT-IR cells was greatest at the area of peak ganglion cell density and declined toward the periphery. In contrast, TH-IR cells concentrated from the time they first appeared at the superior temporal margin, peripheral to the area of peak density of ganglion and ChAT-IR cells.

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

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

Neurotoxic effect of 1-methyl-4-phenylpyridinium ion on dopaminergic neurons of the retina of goldfish

Dopaminergic neurons of the goldfish retina were selectively destroyed after a single intravitreal injection of 1-methyl-4-phenylpyridinium ion (MPP+). The ultrastructural analysis of the retina 3 days after toxin administration shows darkening of some retinal neurons present in the inner nuclear layer including their cytoplasmic processes. Both uptake and release of dopamine were reduced in the toxin-injected retina, whereas choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities, as well as the uptake of D-[3H]aspartate were not affected.

Distribution of catecholaminergic cells in the retina of the rat, guinea pig, cat, and rabbit: independence from ganglion cell distribution

By using an antibody against tyrosine hydroxylase (TH), the rate-limiting enzyme in the production of catecholamines, we have examined the morphology and distribution of catecholaminergic cells in the retinas of the rat, guinea pig, cat, and rabbit. In the albino rat, as reported by others, most TH-immunoreactive (TH-IR) cells were amacrine cells, and formed two morphological classes. Cells of one class (class 1) are stellate amacrine cells, the somata of most being in the inner part of the inner nuclear layer (INL). Cells of the second class (class 2) were seen only as small somata, also in the inner part of the INL. Cells of both classes were found in all areas of the retina, with a distinct but broad concentration around the superior-temporal margin of the retina. A small number of TH-IR interplexiform cells was seen. In the pigmented rat, only class 1 cells were recognized, also concentrating at the superior-temporal margin. In the guinea pig, cat, and rabbit, TH-IR cells also seemed to form one morphological class of amacrine cells, which resembled the class 1 cells of the albino rat. In the guinea pig and cat, their distribution resembled that seen in the rat, with the cells concentrating at the superior-temporal margin of the retina. In the rabbit, TH-IR cells concentrated weakly in the visual streak, but at both ends of the streak the concentration of TH-IR cells extended farther peripherally than the concentration of ganglion cells. Overall, the distribution of TH-IR cells seems largely or (in the rabbit) partially independent of the distribution of ganglion cells. This independence raises questions of the development and function of this group of amacrine cells.

Effects of retinal dopamine depletion on the rabbit electroretinogram

This study evaluated the effects of intravitreal injections of 300 micrograms of 6-hydroxydopamine (6-OHDA) on electroretinogram (ERG) amplitudes and implicit response times of adult pigmented rabbits. One eye was injected intravitreally with 300 micrograms 6-OHDA and 600 micrograms ascorbic acid in a 0.3 ml 0.9% NaCl solution; the fellow eye received a similar solution containing only 600 micrograms ascorbic acid. Following this treatment ERG recordings were performed at 1, 4, and 7 days. After the last recordings, animals were sacrificed and retinas were isolated for biochemical analyses. Significant and progressive reductions in retinal concentrations of dopamine (DA) and its main metabolites homovanillic acid (HVA), and dihydroxyphenylacetic acid (DOPAC) were found in treated retinas. Concentrations of norepinephrine (NE), serotonin (5HT), and 5 hydroxyindoleacetic acid (5-HIAA) were not affected, thus demonstrating the specific neurotoxic action of 6-OHDA on retinal dopaminergic neurons. Concurrently, significant increases in ERG a- and b-wave amplitudes as well as in implicit response times were observed. These electrophysiological changes were progressive reaching a maximum 7 days after intravitreal injections. Changes in b-wave amplitudes and response times were more pronounced at low intensities of stimulation. These results clearly show that, in rabbits, selective decreases in retinal DA concentrations result in pronounced ERG changes, which offer additional evidence supporting a role for this transmitter in lateral inhibition in the retina.

GABA concentration and GAD activity levels in normal and degenerated retinas from mice

Freeze-dried sections (14 microns thick) were prepared from mice with normal (C57BL strain) and degenerated (C3H strain) retinas. GABA concentration and GAD activity were determined in the microsamples (1.8-20 ng dry weight) of retinal layers and sublayers, using an enzymatic amplication reaction, NADP cycling. GABA was distributed over all layers of normal retina with a broad concentration peak covering both inner nuclear and plexiform layers. In contrast, GAD activity was mostly localized in the inner plexiform layer. GABA concentration was similar in one-fourth of the sublayers of each inner nuclear or plexiform layer. GAD activity was highest in the innermost sublayer of the inner nuclear layer. An increasing gradient of GAD activity was present in the inward direction in the inner plexiform layer. In the degenerated retina, lacking in photoreceptors, the inner nuclear and plexiform layers remained, and GABA and GAD levels in these layers were similar to those in normal retina.

Demonstration of histaminergic neurons in horizontal cells of guinea pig retina

The existence of L-histidine decarboxylase (HDC, EC 4.1.1.22)-like immunoreactive (HDC-I) cells in guinea pig retina was demonstrated using antiserum raised against HDC purified from fetal rat liver. The anti-HDC antiserum partially cross-reacted guinea pig L-DOPA decarboxylase (DDC, EC 4.1.1.28), so the histaminergic neurons were carefully identified. Comparison of HDC-I and DDC-like immunoreactive (DDC-I) cell types in adjacent sections revealed that HDC-I structures were found in some horizontal cells and amacrine cells, and double-staining procedures with anti-HDC antiserum and monoclonal anti-DDC antibody showed that HDC-I horizontal cells had no DDC-I structures, but all the HDC-I amacrine cells had DDC-I structures. From the results, some horizontal cells (with HDC-like immunoreactivities but without DDC-like immunoreactivities) were concluded to be histaminergic.

Serotonin containing neurons in the retina of the teleost Eugerres plumieri

The concentration and localization of serotonin was determined in the retina of the teleost Eugerres plumieri by using high performance liquid chromatography (HPLC) and immunohistochemical techniques. Serotonin and dopamine were measured simultaneously, their concentrations in the retina being 77 +/- 8 and 516 +/- 23 ng/mg tissue respectively. Treatment of the animals with pargyline significantly increased the levels of dopamine and serotonin. When retinas were treated with the neurotoxin 5,6-dihydroxytryptamine, the level of serotonin was reduced by more than 90% while the dopamine content only diminished by 20% when compared to controls. By using immunohistochemistry with a monoclonal anti-serotonin antibody it was possible to localize this amine in cell bodies of a population of amacrine cells with processes extending mainly into a thin layer of the most external lamina of the inner plexiform layer. Very few ramifications were seen projecting to the internal lamina of this layer. When visualized in flat mount preparations, dense arborization of fluorescent processes was observed. This is the first direct evidence that serotonin is apparently present in amacrine cells of the retina of E. plumieri with a distribution of the serotonergic terminals similar to goldfish but somewhat different when compared to other species.

Morphological identification of serotonin-accumulating neurons in the living retina

Neurons that accumulate the transmitter serotonin have been identified in the living retina by being labeled with 5,7-dihydroxytryptamine (5,7-HT), an autofluorescent serotonin analog. Iontophoretic injection of Lucifer yellow into the labeled cells under microscopic control revealed that the serotonin-accumulating neurons in rabbit retina constitute two morphological types of amacrine cells, termed S1 and S2, whose distal dendrites are stratified at the inner margin of the inner plexiform layer. The dendritic overlap of the S1 type is extraordinarily large: each point on the retina is covered by the fields of 550 to 900 S1 amacrines, and 6 to 8 meters of their dendrites are packed into each square millimeter of retina. Such a pervasive neuropil may provide an effective substrate for diffuse transmitter release, as proposed for serotonergic fibers elsewhere in the central nervous system.

Retinal GABA neurons: localization in vertebrate species using an antiserum to rabbit brain glutamate decarboxylase

Retinal gamma-aminobutyric acid (GABA) neurons have been localized immunocytochemically using a new antiserum against rabbit brain glutamate decarboxylase (GAD). The animals examined were: dogfish, ratfish, goldfish, catfish, turtle, chick, mouse, rat, pig, rabbit, cat and New World monkey. GAD-containing processes, observed as punctate deposits of immunochemical reaction product, formed discrete bands within the inner plexiform layers of all retinas examined. Immunoreactive, and therefore presumably GABAergic, amacrine cells were observed in all species. Displaced GABAergic amacrine cells were observed in the retinas of goldfish, catfish, turtle and chick, and sparsely in the rabbit as well. GABAergic horizontal cells were detected in catfish, goldfish, chick and turtle. Interplexiform cells in the cat and the rat were clearly immunoreactive for glutamate decarboxylase; this is the first report of GABAergic interplexiform cells in the rat.

Neurotransmitter release by certain neuropeptides in the chicken retina

The ability of certain neuropeptides (glucagon, somatostatin, leu-enkephalin and neurotensin) to release known neurotransmitters (glycine, GABA, dopamine and 5-hydroxytryptamine) was tested in the chicken retina. Tritiated neurotransmitters were injected intravitreally in chicken eyes. After excision, the retina was stimulated in vitro with the neuropeptide in micromolar concentrations while monitoring the efflux of radioactivity from the retina. A rise of the efflux represents a stimulus dependent release. Neurotensin release [3H] glycine, [3H]dopamine and [3H]5-hydroxytryptamine. Leu-enkephalin released [3H]dopamine and somatostatin released [3H]5-hydroxytryptamine. Glucagon was without effect. [3H]GABA was not released by any of the neuropeptides.

NADPH diaphorase cells in the mammalian inner retina

The distribution of the enzyme NADPH diaphorase was examined histochemically in the retina of the rat, rabbit, cat, owl monkey, squirrel monkey, rhesus macaque, and human being. In all species tested the enzyme was concentrated in cells 10-12 microns in diameter at the vitread margin of the inner nuclear layer. The population was sparse (less than 2,000 cells/rat retina). In several species additional minor populations were observed. While a clear function for NADPH diaphorase has yet to be described, an abundance of the enzyme characterizes a similar subpopulation of retinal cells in a wide variety of mammals.

Uptake of 3H-glycine in the outer plexiform layer of the retina of the toad, Bufo marinus

The uptake of 3H-glycine in the retina of the toad, Bufo marinus, was investigated by light and electron microscopical autoradiography. Uptake of 3H-glycine was very prominent in large cell bodies in the inner nuclear layer as well as in discrete clusters in both the outer plexiform layer (OPL) and the inner plexiform layer. This pattern in similar to that described for 3H-glycine-accumulating putative interplexiform cells in goldfish, frog, and Xenopus retinas. Electron microscopical autoradiography of the OPL revealed large, grain-containing varicosities which had electron-lucent cytoplasm and contained both small, agranular and large, dense-core vesicles. The varicosities made extensive en passant and spine synapses in the OPL. Definitive identification of their postsynaptic targets was not achieved. However, autoradiographic analysis with 3H-GABA uptake as well as electrophysiological evidence suggests that axons but not cell bodies or dendrites of 3H-GABA-accumulating horizontal cells (H1 cells) are postsynaptic targets of the varicosities. The presence of dense-core vesicles in the varicosities suggested co-occurrence of glycine and a biogenic amine or neuropeptide. The indirect immunofluorescence technique was used to determine whether any such substances were present in the OPL of the toad retina. However, no specific labeling was found in the OPL for any of 19 substances tested. The extensive synaptic output provided by glycine-accumulating varicosities in the toad OPL may indicate an important role of glycine in the synaptic function of the distal toad retina. We suggest that these varicosities derive from a presumably glycinergic interplexiform cell.

Interactions between enkephalin and GABA in avian retina

In addition to conventional neurotransmitters such as acetylcholine, dopamine, glycine and gamma-aminobutyric acid (GABA), a number of peptide-immunoreactive substances have recently been localized in the vertebrate retina. The functional roles of these retinal peptides and their interactions with conventional neurotransmitters are largely unknown. We have previously shown that exogenous opiates affect both the release of GABA and the firing patterns of ganglion cells in the goldfish retina, and we have now begun a systematic characterization of the opioid pathways in the chicken retina, because, among vertebrate retinas, avian retinas contain the highest concentration of enkephalins. Monoclonal antibodies specific for enkephalin have been used to demonstrate that a subpopulation of enkephalin-containing amacrine cells exists in the chicken retina. This retina also synthesizes Met-enkephalin and releases it on cell depolarization. The enkephalin-induced inhibition of GABA release in goldfish retina led us to examine whether similar interactions occur in chicken, and if so, whether enkephalins and GABA coexist in the same amacrine cells. Our results, presented here, indicate that exogenous enkephalins do indeed inhibit GABA release in the chicken retina. Surprisingly, we found that although some amacrine cells contain both enkephalin and GABA, others contain only one or the other.

Mechanisms of synaptic transmission in the retina

This paper reviews the mechanisms of transmitter release, the kinetics of synaptic transfer, the mechanisms for the production of conductance changes by transmitters, and the nature of the conductance changes at synapses in vertebrate retina. A method for the culturing of adult retinal cells is described, together with preliminary experiments on the identification of cells in culture.