Neuropeptide Y-like immunoreactive amacrine cells in the retina of Bufo marinus

Neuropeptide Y-like immunoreactive (NPY-LI) amacrine cells of the Bufo marinus retina were morphologically characterized, and their retinal distribution was established using immunohistochemistry on retinal wholemount preparations and sectioned material. The somas of NPY-LI amacrine cells were situated in the innermost part of the inner nuclear layer and their dendrites branched primarily in the scleral sublamina of the inner plexiform layer. A subgroup of the NPY-LI cells had dendrites in both the scleral and vitreal sublamina. All immunoreactive cells had large dendritic fields (average 0.5 mm2) that resulted in a high dendritic overlap across the retina. NPY-LI amacrine cells were evenly distributed across the retina, with an average density of 30 cells/mm2, although higher densities were observed at regions adjacent to the ciliary margin. The dendritic field size of the NPY-LI cells, together with the previously characterized substance P-like immunoreactive (SP-LI) amacrine cells, indicates that they belong to the class of wide-field amacrine cells. However, unlike the SP-LI neurons whose dendrites branch in the vitreal sublamina of the inner plexiform layer, the dendrites of the majority of the NPY-LI neurons branch in the scleral sublamina.     

Choline acetyltransferase is expressed by non-starburst amacrine cells in the ground squirrel retina

We have used immunostaining techniques to reveal a new type of amacrine cell that is immunoreactive for choline acetyltransferase (ChAT), the acetylcholine synthesizing enzyme, in the Ground Squirrel (Spermophilus beecheyi) retina. Cryostat sections and double immunostained wholemount preparations were examined by confocal microscopy. This new ChAT type III cell is distinct in morphology and neurotransmitter content from the well know 'starburst' amacrine cells (types I and II) that are so well represented in the ground squirrel retina [J. Comp. Neurol. 365 (1996) 173-216]. The type III cell colocalizes glycine with the acetylcholine and does not appear to be GABAergic or exhibit calcium-binding proteins like the well-known starburst type. As well, type III cells do not occur as a mirror-symmetric pair with normally placed and displaced varieties. The type III cell is probably a small field amacrine type branching broadly in upper sublamina b of the inner plexiform layer, and is most likely A6 of the Ground Squirrel retina [J. Comp. Neurol. 365 (1996) 173-216]. Type III cells are ideally placed in the architecture of the Ground Squirrel retina to influence ON directionally selective ganglion cell types.     

GABA-like immunoreactivity in cholinergic amacrine cells of the rabbit retina

In the ganglion cell layer of the rabbit retina, the inhibitory transmitter γ-aminobutyric acid (GABA) and its analogues are accumulated by neurons that appear to match in size and number the population of displaced amacrine cells that synthesize the excitatory transmitter acetylcholine. In this double-label study, we have established directly that the cholinergic amacrine cells, selectively stained with diamidino-phenylindole, are strongly immunoreactive with GABA antisera. The coexistence of two classical transmitters, one excitatory and the other inhibitory, in this defined neuronal population, suggests that stimulation of the cholinergic amacrines may give rise to complex responses in their target neurons.     

Corticotropin releasing factor-like immunoreactive neurons in the rat retina

Corticotropin releasing factor (CRF)-like immunoreactive neurons have been identified in the rat retina by immunohistochemical methods using antisera directed against ovine and rat CRF. CRF-like immunoreactivity was observed in both amacrine and ganglion cells which projected fine varicose processes to the inner plexiform layer of the retina. It is suggested that CRF may play a role in retinal function.     

Glycine high-affinity uptake labels a subpopulation of somatostatin-like immunoreactive cells in theRana pipiens retina

Somatostatin-like immunoreactivity (Som-LI) and glycine high-affinity uptake have been characterized in the Rana pipiens retina. These labels are found in both the outer and inner plexiform layers (OPL and IPL), suggesting that interplexiform cells (IPCs) contain both Som and glycine in this retina. In double-label experiments these labels colocalize to an abundant population of cells in the mid-inner nuclear layer (INL), in the second or third cell layer distal from the IPL. These cells have medium sized spherical or oval somas, each with a single thin descending dendrite which ramifies in the distal IPL. Processes ascending from cells at this location were not visualized by immunocytochemistry, but could be seen by autoradiography of tissue processed for glycine high-affinity uptake. In autoradiographs apparent IPCs were the most intensely labeled cell type in this retina. Som-LI is also found in two types of probable amacrine cells in the proximal INL adjacent to the IPL, neither of which is labeled by glycine high-affinity uptake. One of these is rare (about 10 cells/mm ²), and has a large pyriform soma with a thick dendrite that branches in the proximal IPL. The other type is more common (324 ± 20cells/mm²), has medium-sized spherical or horizontally elongated elliptical somas, and has multiple thin dendrites projecting into the distal IPL. In addition to the above cell types, faint Som-LI was seen in cells of the ganglion cell layer, possibly indicating the presence of somatostaninergic ganglion cells or displaced amacrine cells.     

Two groups of TH-like immunoreactive neurons in the frog (Rana pipiens) retina

The morphology and distribution of TH-like immunoreactive (TH-IR) cells in the retina of Rana pipiens were studied in retinal whole mounts and in radial and horizontal sections. A large majority (96%) of the immunoreactive cells were found in the inner nuclear layer while a few cells were found in the ganglion cell layer. All TH-IR cells had round to oval somata with average diameter of 10 μm. The 2–4 primary processes of these cells distributed extensively to sublamina 1 of the inner plexiform layer (IPL) and sparsely to sublamina 5. Two groups of TH-IR cells were distinguished: one, designated thin cells, had only thin (<2 μm diameter) primary processes; the second, designated thick cells, had one or more primary processes with diameter(s) exceeding 2 μm for a distance of 5 μm or more from the soma. The thin cells did not significantly differ from the thick cells in soma diameter, number of primary processes, horizontal spread of processes or vertical lamination of processes. Nearest neighbor analyses of the two types revealed that the population of TH-IR cells (thick and thin together) have an orderly distribution while the thick cells alone are more randomly distributed, indicating that the thick cells do not comprise a functional population. The total number of TH-IR cells varied between retinas; the variability was due principally to variation of thin cell density. It is hypothesized that the thick cells are a subpopulation of the TH-IR cells which are in a particular physiological state at the time of fixation.     

Laminar asymmetry in the distribution of choline acetyltransferase-immunoreactive neurons in the retina of the tree shrew (Tupaia belangeri)

Cholinergic neurons in the retina of the tree shrew were identified immunocytochemically using a monoclonal antibody directed against choline acetyltransferase (ChAT). The chief result is that roughly 4 times as many ChAT-immunoreactive neurons are found in the inner nuclear layer (INL) as in the ganglion cell layer (GCL). In the INL, two classes of cholinergic neuron can be distinguished on the basis of soma size, one large and one small. The large neurons correspond closely in size and number to the displaced cholinergic neurons in the GCL, suggesting that these are the matching populations of cholinergic amacrine cells reported in other species. The small ChAT-immunoreactive neurons, on the other hand, which make up 60% of the total number of ChAT-positive neurons in the retina, appear to have no counterpart in the GCL. Whether these small neurons are a separate class of amacrine cell or some other cell type (e.g. bipolar, interplexiform, etc.) remains to be determined.     

Zn(2+) modulates light responses of color-opponent bipolar and amacrine cells in the carp retina

The effects of Zn(2+) on color-opponent bipolar cells (BCs) and amacrine cells (ACs) were studied in the isolated superfused carp retina using intracellular recording techniques. Bath-applied Zn(2+) (25 micro M) depolarized R(+)G(-)-type BCs and suppressed both depolarizing responses of these cells to red (680 nm) flashes and hyperpolarizing ones to green (500 nm) flashes. Following Zn(2+) application, G(+)R(-)-type BCs were hyperpolarized, which was accompanied by a potentiation of their depolarizing responses to green flashes and a suppression of hyperpolarizing ones to red flashes. Similar Zn(2+) effects were observed in R(+)G(-)- and G(+)R(-)-type ACs. The Zn(2+) effects persisted in the presence of picrotoxin and strychnine, suggesting that modulation by Zn(2+) of GABA and glycine receptors was unlikely involved. Using whole-cell recording techniques, it was found Ca(2+) currents in cone terminals were dose-dependently suppressed by Zn(2+), suggesting that Zn(2+) may reduce glutamate release from cone photoreceptors. Furthermore, lowering extracellular Ca(2+), a procedure that increases glutamate release from photoreceptors, exerted actions on R(+)G(-)- and G(+)R(-)-type BCs, almost opposite to the Zn(2+) effects on these two types of BCs. It is therefore postulated that the Zn(2+) effects reported in the present work may reflect a consequence of the changes in input resistances of color-opponent BCs and driving forces for their light responses resulted from the reduced glutamate release by Zn(2+).     

Substance P-like immunoreactive amacrine cells in the cat retina

Substance P-like immunoreactivity was localized by immunocytochemical techniques to two subpopulations of amacrine cells in the cat retina. One cell was a unistratified amacrine with processes ramifying within stratum 4 of the inner plexiform layer. The other cell type was a bistratified cell with processes in both stratum 1 (s1) and stratum 4 (s4). Both cell types were seen with their somas displaced to the ganglion cell layer as well as in the conventional amacrine location in the inner nuclear layer. Substance P cells were present in the greatest density within the area centralis and decreased in number toward the periphery. The ratio of amacrine to displaced amacrine cells also decreased peripherally. However, the coverage by immunoreactive fibers in s4 remained three times that seen in s1. Computer-assisted analysis confirmed the location of substance P-containing processes at 5-15% (s1) and 50-70% (s4) depth levels in the inner plexiform layer. A comparison of substance P-like immunoreactivity in light- and dark-adapted cat retinas showed no apparent differences in the distribution of immunoreactivity due to lighting conditions.     

Immunocytochemical staining of cholinergic amacrine cells in rabbit retina

Cholinergic neurons of rabbit retina were labelled with an antibody against choline acetyltransferase, the synthesizing enzyme for acetylcholine. Two populations of cells are immunoreactive. Type a cell bodies lie in the inner nuclear layer (INL), their dendrites branching narrowly in sublamina a of the inner plexiform layer (IPL), while type b cell bodies lie in the ganglion cell layer (GCL) with dendrites branching in sublamina b of the IPL. The irregular networks of clustered immunoreactive dendrites are similar, but not identical, in the two sublaminae. Type b cells are more numerous than type a cells in central retina. No axons were stained. It appears that the immunoreactive neurons are normally placed and displaced starburst/cholinergic amacrine cells.     

Neuropeptide Y- and substance P-like immunoreactive amacrine cells in the retina of the developing Xenopus laevis.

The development of neuropeptide Y-like (NPY-LI) and substance P-like (SP-LI) immunoreactive neurons was studied in retinas of Xenopus laevis from young tadpole through to adult animals. In adult retina these neuropeptides are present in wide-field amacrine cells located in the inner nuclear layer and the ganglion cell layer of the retina. Retinal wholemount preparations and sectioned material showed that immunoreactive cells appeared during early larval life and NPY-LI occurred earlier than SP-LI cells. The primary dendritic branching of NPY-LI neurons appeared from early larval life whilst SP-LI was evident in dendrites from mid-larval stages. In postmetamorphic animals the numbers of immunoreactive cells increased in proportion to retinal area growth with a relatively constant cell density of about 35 cells/mm2 for SP-LI and 45 cells/mm2 for NPY-LI. The maturation of dendritic morphology of both NPY- and SP-LI amacrine cells appeared later in larval development than the appearance of immunoreactivity in cell somas. However, the sequence of expression of NPY- or SP-LI and their dendritic maturation was different for the two classes of amacrine cells. It is suggested that the maturation of dendritic fields of amacrine cells is complete just prior to metamorphosis, consistent with the postmetamorphic onset of electrophysiological features of ganglion cells attributed to amacrine cells.     

Neuropeptide Y-like immunoreactivity in cat spinal cord with special reference to autonomic areas

The distribution of nerve terminal-like structures (herein called nerve terminals), fibers, and neurons containing neuropeptide Y-like immunoreactivity (NPY-ir) was studied immunohistochemically in cat spinal cord with and without colchicine treatment. Rexed laminae II and III of the dorsal horn contained large amounts of immunoreactive nerve terminals and few fibers at all levels of the cord whereas laminae I and IV-VI contained fewer terminals and numerous fibers. In segments C7-T3, fibers with NPY-ir in the superficial laminae collected into bundles which travelled ventromedially toward the dorsal gray commissure (DGC). In addition, another bundle of fibers was present in segments C8-T2 and T11-S2; these fibers also originated from the upper dorsal laminae and travelled along the dorsomedial border of the gray matter to cross the midline in the DGC. In the intermediate and central gray, most immunoreactivity was found in the autonomic areas: terminals and fibers containing NPY-ir were found in the intermediolateral cell column pars principalis (IMLp) in all segments between C8 and L4 with the densest accumulation in segments T6 and T7. All other autonomic areas contained immunoreactive structures in nearly all thoracolumbar segments except for the IML pars funicularis, which contained small numbers of immunoreactive fibers only between segments T2 and T8, inclusive. In the sacral cord, the autonomic areas in the intermediate and central gray also contained relatively large numbers of immunoreactive terminals and fibers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dopaminergic cell differentiation in the developing chick retina

The distribution and morphology of dopaminergic (DA) neurons in the chick retina was studied in the course of development. Fluorescent DA cells were first detected on the 13th day of incubation. They were always found in positions two or three cell rows externally from the junction between the inner plexiform layer (IPL) and inner nuclear layer (INL). On the 14th day, DA cells were found in the innermost row of the INL. Subsequently their processes extended not only bilaterally along the IPL-INL junction but also vertically into the IPL. As a result, three fiber layers were formed as laminae 1, 3 and 5 in the IPL. In the newly-hatched chick retina, a number of growth cone-like fluorescent structures with fine spikes were seen at the IPL-INL junction, indicating that DA fibers were still growing and elongating at least at hatching. On the 4th postnatal day, the ramification of dendritic processes was very prominent and they often showed a spiral configuration.     

Quantitative studies of enkephalin's coexistence with γ-aminobutyric acid, glycine and neurotensin in amacrine cells of the chicken retina

Previous double-label studies demonstrate that enkephalin coexists with γ-aminobutyric acid, glycine or neurotensin in amacrine cells of the chicken retina. The present study utilizes double- and triple-label paradigms to quantitatively analyze these coexisting relationships. Twenty-eight percent of enkephalin-like immunoreactive amacrine cells were found to exhibit high-affinity uptake of [³H]GABA, while 53% of enkephalin-amacrine cells specifically accumulate [³H]glycine. Moreover, the present study predicts that at least 26% of enkephalin-amacrine cells which accumulate [³H]glycine should also be immunoreactive for neurotensin.     

Connectivity of glycine immunoreactive amacrine cells in the cat retina

The synaptic relationships of glycine immunoreactive amacrine cells in the cat retina were studied through the use of postembedding immunogold techniques. Glycine immunoreactive amacrine cells were found to synapse extensively with other amacrines and ganglion cells, particularly in strata 1-3 of the inner plexiform layer. This contrasts with GABA immunoreactive amacrine cells which provide major input to bipolar cells in strata 3-5. Glycine containing amacrine terminals exhibited diversity with respect to the morphology of their synaptic vesicles. The three types of terminals which could be distinguished were characterized by small pleomorphic (32-35 nm), medium-sized flattened (38-45 nm), or larger rounded (48-55 nm) vesicles. Comparison of retinal sections processed for glycine immunoreactivity with adjacent sections stained for GABA reactivity revealed a colocalization of glycine and GABA in 3% of the cells in the amacrine layer and approximately 40% of the cells in the ganglion cell layer. The amacrine terminals in which glycine and GABA were colocalized typically contained the small pleomorphic type of vesicles.     

[Leu]enkephalin-like immunoreactive amacrine cells are under nicotinic excitatory control during darkness in chicken retina

Based on the principle that retinal levels of [Leu⁵]enkephalin-like immunoreactivity (LELI) are set by the rate of release and thus reflect neural activity, we partially defined the dark-associated increase in excitatory control of LELI amacrine cells in chicken. Retinal levels of LELI were measured by radioimmunoassay (RIA). Intravitreal injection of cholinergic antagonists decreased the rate of depletion of LELI during the dark phase, suggesting the presence of cholinergic excitatory control of the LELI neurons. This cholinergic control involves nicotinic rather than muscarinic receptors, as tubocurarine appeared over 100 times more effective than atropine in inhibiting the decrease in retinal levels of LELI in the dark. (The ED₅₀s were estimated at 3.2 and 450 nmol, respectively.) The lack of effect of the antagonists when applied during the light phase, suggest that there is little cholinergic input to the LELI amacrine cells in the light. Superfusing isolated retinas with buffer containing tubocurarine (10 μM) decreased the efflux of LELI by 35%, compared to the spontaneous release during the dark. Atropine (10 μM) had no effect on the release of LELI, and pilocarpine (100 μM) increased the release of LELI from retinas superfused in the light by 20%. We conclude that, in addition to previously reported glycinergic and dopaminergic inhibition, the LELI amacrine cells receive cholinergic excitatory input. A shift in balance between glycinergic and dopaminergic inhibitory, and cholinergic excitatory control may underly the light-driven variation in activity of the LELI neurons in chicken retina.     

Synaptic analysis of amacrine cells with neuropeptide Y-like immunoreactivity in turtle retina

Neuropeptide Y-like immunoreactivity has been localized previously within three classes of amacrine cells in the turtle retina. We have used the avidin-biotin with horseradish peroxidase technique to label these neurons for examination at the ultrastructural level to answer the following questions. Where are the synaptic contacts of these neurons made? What types of neurons are involved pre- and postsynaptically? What is the intracellular distribution of the immunoreactivity? Processes with neuropeptide Y-like immunoreactivity were located primarily within three regions of the inner plexiform layer: stratum 1, stratum 3, and at the border between strata 4 and 5. In all three regions the processes with neuropeptide Y-like immunoreactivity received synaptic contacts from both unlabeled amacrine and bipolar cells, but the majority of the synaptic input in all three regions was from unlabeled amacrine cells. Processes with neuropeptide Y-like immunoreactivity were presynaptic to unlabeled amacrine cells in all three regions, but also formed contacts onto unlabeled bipolar cells in the region between strata 4 and 5. The immunoreactivity within these cells gave rise to a diffuse reaction product that was distributed throughout the cytoplasm and within large vesicles. This localization of neuropeptide Y-like immunoreactivity within large vesicles suggests that this peptide may play a neuromodulatory role. Such a role would be consistent with previous studies of neuropeptides in the turtle retina.     

The expression and cellular localization of brain/kidney protein in the rat retina

Brain/kidney (B/K) protein is a new protein of 474 amino acids, which contains two C2 domains structurally homologous to those present in synaptotagmins. The expression of B/K protein was identified in the rat retina and B/K protein immunoreactivity was localized to a number of ganglion cells, a few amacrine cells and the radial processes of Müller cells. Thus, B/K protein appears to be important in the homeostasis in these cells of the rat retina.