A new look at calretinin-immunoreactive amacrine cell types in the monkey retina

We have examined amacrine cells that are calretinin-immunoreactive (-IR) in the macaque monkey retina with the aim of classifying them into morphological and functional subtypes. There are calretinin-IR cells in the fovea and throughout the retina. Their highest density is reached at 1.0 mm from the foveal pit (10500 cells/mm(2)) and falls to 2600/mm(2) by 10 mm of eccentricity. Nearest-neighbor statistics for the calretinin-IR cell body distribution indicate a nonregular pattern, with a regularity index of 1.4-1.6. There is an increase or "bump" of cell density 3.5-4.0 mm from the foveal pit, corresponding to the rod photoreceptor density peak. Based on morphological differences, there appear to be three types of amacrine cell that are calretinin-IR. To determine the types, we doubly immunolabeled retinas, from fovea to periphery, for calretinin-IR in combination with other calcium binding proteins and inhibitory amino acid neurotransmitters. Labeling with parvalbumin and calretinin antibodies indicated that 70% of the amacrine cells were solely calretinin-IR, and 30% contained parvalbumin-IR as well. In the same way, 70% of the calretinin-IR amacrine cells colocalized calbindin, but 30% were only calretinin-IR. Among the calretinin/calbindin-colocalized cells, there were small-field and wide-field types. Double labeling with antibodies to calretinin and gamma-aminobutyric acid (GABA) and to calretinin and glycine revealed the majority to be glycine-IR, but some were GABA-IR. The glycine-IR population consists mainly of AII amacrine cell types, but clearly another non-AII type is involved. The non-AII glycine-IR population resembles a small- to medium-field diffuse type. The calretinin-IR wide-field type is GABAergic and corresponds to an A19 type. The central, rod-free, fovea contains the calretinin-IR, non-AII glycine-IR type and the calretinin-IR, GABAergic type only. To learn more concerning the circuitry of the calretinin/glycine-IR, non-AII amacrine cell type in isolation from AII amacrine cells, we concentrated on the rod-free fovea, where AII amacrine cells are absent. We performed a serial section electron microscopy (EM) study on four calretinin-IR cells. They were involved with cone pathway circuitry. They got input from ON and OFF midget bipolar cells, reciprocated synapses to these bipolar cells, and provided synapses to ON-center ganglion cells. Thus we have obtained new information on a cone pathway amacrine cell of the central monkey fovea that is involved in the midget system.

Differential staining of neurons in the human retina with antibodies to protein kinase C isozymes

Monoclonal antibodies to the three isozymes of protein kinase C (PKC) (alpha, beta, and gamma) were applied to postmortem human retina. Immunostaining was done on wholemount, or cryostat-sectioned retina, and visualized after ABC/DAB procedures by light (LM) and electron (EM) microscopy. The PCK-alpha antibody stained rod bipolar cells throughout the retina. EM analysis confirmed they were PKC-alpha-immunoreactive (IR) on their characteristic dendritic and axonal synaptology. Putative blue cone bipolar cells with wide-field axon terminals, stratifying in s5 of the inner plexiform layer (IPL), were also PKC-alpha-IR, and EM showed them to engage in narrow-cleft ribbon junctions in blue cone pedicles. The PKC-beta antibody stained cone bipolar cells, many amacrine cells, and most ganglion cells. Cone bipolar cells were stained all the way into the foveal center: both midget and diffuse varieties were included. The IPL was densely PKC-IR and individual neurons could not be identified on stratification patterns. EM of the outer plexiform layer (OPL) revealed that both flat and invaginating cone bipolar types were IR and that IR axon terminals were presynaptic in all strata of the IPL. The occurrence of PKC-beta-IR bipolar axons in stratum 2 of the IPL suggests that OFF-center as well as ON-center types were included. The PKC-gamma antibody gave inferior staining compared with results from the other two antibodies; however, two varieties of wide-field monostratified amacrine cell and a large-bodied ganglion cell type were discernible. PKC in one form or another appears to be a second messenger used in neurotransmission by both rod and cone systems and ON- and OFF-center systems in the human retina.

Immunocytochemical staining with antibodies against protein kinase C and its isozymes in the turtle retina

An LM immunocytochemical study has investigated the patterns of staining in turtle retina with monoclonal antibodies to the alpha, beta and gamma isozymes of protein kinase C. The protein kinase C-gamma antibody reveals cells in the ganglion cell layer, occasional amacrine cells and faint banding in strata 2 and 4 of the inner plexiform layer. The protein kinase C-beta antibody stains primarily amacrine cells that have dendrites running in strata 2, in 4 close to the 3/4 border and on the 4/5 border of the inner plexiform layer. Protein kinase C-alpha immunoreactivity is seen in a population of bipolar cells. The latter are characterized by stained axon terminals in strata 3 and 4 of the inner plexiform layer. A type of amacrine cell, different from those seen with the other antibodies, is also immunoreactive to protein kinase C-alpha. EM immunocytochemistry (using a polyclonal antibody) reveals protein kinase C immunoreactivity in photoreceptor cells, bipolar cells, amacrine cells and ganglion cells. In photoreceptors protein kinase C immunoreactivity occurs as patchy staining associated with vesicles and the plasmalemma in pedicles and telodendria. Some varieties of bipolar cell display protein kinase C reaction product throughout the entire cell. Their dendrites contact photoreceptor pedicles at wide-cleft basal junctions and ribbon and non-ribbon related narrow cleft junctions. A few lateral elements per cone or rod pedicle are always protein kinase C-immunoreactive. Amacrine and ganglion cells typically show small clumps of protein kinase C immunoreactivity around vesicles and close to the postsynaptic membranes. Synaptic boutons of some varieties of amacrine cell stain more uniformly. Protein kinase C-immunoreactive bipolar cells are most commonly presynaptic in stratum 4 of the inner plexiform layer, while protein kinase C-immunoreactive amacrine cells are both pre- and postsynaptic throughout strata 1, 2, 3 and 4. Stratum 5 appears to be almost devoid of protein kinase C-immunoreactive neural profiles.

Postembedding immunocytochemistry for GABA and glycine reveals the synaptic relationships of the dopaminergic amacrine cell of the cat retina

Postembedding electron microscope immunocytochemistry of glycine and GABA conjugated to colloidal gold has been applied to pre-embedded cat retina stained with the antibody against tyrosine hydroxylase (Toh+). Toh+ stained cells are the equivalent of A18 amacrine cells of Golgi descriptions (Kolb et al., '81). The dendrites of Toh+ cells synapse upon several different types of glycine-positive amacrine cell bodies. We suggest that these are the A8, A3/A4, and AII amacrine cell varieties by analogous immunocytochemical staining intensity, to glycine autoradiographic labeling intensity (Pourcho and Goebel, '85). The greatest number of synapses from Toh+ dendrites are directed at the least glycine-positive amacrine, which is the AII cell by all morphological criteria. A few glycine-positive profiles are also presynapatic to the Toh+ stained cell body itself. Toh+ profiles are also presynaptic to GABA-positive amacrine cell bodies. The commonest amacrine synapsed upon is very heavily labeled with GABA immunocytochemistry. We consider it to be the A17 amacrine cell, which is known to label strongly by [3H] muscimol autoradiography (Pourcho and Goebel, '83). The cell body of the Toh+ amacrine cell also receives many synapses, which appear to be GABA-positive, and Toh+ profiles running in stratum 1 of the inner plexiform layer (IPL) are both pre- and postsynaptic to GABA-positive amacrine cell profiles. In addition, the cell body and primary dendrites of the Toh+ cell receive input from a bipolar type and GABA- or glycine-negative profiles. GABA-positive profiles, belonging to the interplexiform cell (IPC), are synapsed upon by Toh+ profiles that run in the outer plexiform layer (OPL).(ABSTRACT TRUNCATED AT 250 WORDS)

Midget ganglion cells of the parafovea of the human retina: a study by electron microscopy and serial section reconstructions

In this study we used serial section electron microscopy and three-dimensional reconstructions to examine four midget ganglion cells of the human retina. The four cells were located in the parafoveal retina 2.5 mm or 8 degrees from the foveal center. Both type a (with dendritic trees in distal inner plexiform layer) and type b (with dendritic trees in proximal inner plexiform layer) midget ganglion cells have been studied. These cells have dendritic trees of 7-9 microns diameter, and their complete dendritic trees in the neuropil of the inner plexiform layer can be analyzed, as well as the bipolar cell axon terminals having synaptic input, by a study of 100-150 serial ultrathin sections. Type a midget ganglion cells appear to be in a one-to-one relationship with flat midget bipolar cell axon terminals ending in distal inner plexiform layer. Type b midget ganglion cells are in a one-to-one synaptic relationship with invaginating midget bipolar cell axon terminals in proximal inner plexiform layer. The midget bipolar cells primarily involved with the midget ganglion cells do not contact other ganglion cell dendrites. In other words, midget bipolar cells appear to be in exclusive contact with single midget ganglion cells in the human retina. The midget ganglion cells receive most of their input from their associated midget bipolar cells in the form of ribbon synapses at dyads or monads (55-81 ribbons total), although ribbonless synapses are seen occasionally. In all four midget ganglion cells reconstructed, one or two other bipolar cell axon terminals, presumed to be from wide-field bipolar types, provide 1-3 ribbon synapses each. The number of amacrine synapses upon a midget ganglion cell's dendritic tree is approximately equal to the number of bipolar ribbon inputs (43%-56% bipolar ribbons: 44%-57% amacrine synapses). We assume from our knowledge of response characteristics of ganglion cells in other mammalian retinas (Nelson et al., '78: J. Neurophysiol. 41:427-483), that the type a midget ganglion cell and its exclusive connectivity with a flat midget bipolar cell forms a single cone connected OFF-center pathway, whereas the type b midget ganglion cell with its exclusive connectivity to an invaginating midget bipolar cell forms a single cone connected ON-center pathway, through the retina to the brain.

The synaptic organization of the dopaminergic amacrine cell in the cat retina

The dopaminergic amacrine cells of the cat retina have been stained by immunocytochemistry using an antibody to tyrosine hydroxylase (Toh). The complete population of Toh+ cells has been studied by light microscopy of retinal wholemounts to evaluate morphological details of dendritic structure and branching patterns. Selected Toh+ amacrine cells have been studied by serial-section electron microscopy to analyse synaptic input and output relationships. The majority of Toh+ amacrine cells occur in the amacrine cell layer of the retina and have their dendrites ramifying and forming the characteristic rings in stratum 1 of the inner plexiform layer. A minority of Toh+ cells have cell bodies displaced to the ganglion cell layer but their dendrites also stratify in stratum 1. All Toh+ cells have some dendritic branches running in stratum 2 as well as in stratum 1, and frequently they have long 'axon-like' processes (500-1000 microns long) dipping down to run in stratum 5 before passing up to rejoin the major dendritic arbors in stratum 1. In addition Toh+ stained processes follow blood vessels in the inner plexiform layer and in the ganglion cell layer. A population of Toh+ cells found in the inferior retina appears to give rise to stained processes that pass to the outer plexiform layer and therein to run for as far as one millimeter. Electron microscopy reveals that Toh+ amacrine cells are postsynaptic to amacrine cells and a few bipolar cell terminals in stratum 1 of the inner plexiform layer and are primarily presynaptic to AII amacrine cell bodies and lobular appendages, and to another type of amacrine cell body and amacrine dendrites hypothesized to be the A17 amacrine cell. The Toh+ dendrites in stratum 2 are presynaptic to AII lobular appendages primarily. Stained 'axon-like' processes running in stratum 5 prove to be presynaptic to AII amacrine dendrites as they approach the rod bipolar axon terminals and they may also be presynaptic to the rod bipolar terminal itself. The Toh+ stained dendrites that have been followed in the outer plexiform layer run along the top of the B-type horizontal cell somata and may have small synapses upon them. The only clear synapses seen in the outer plexiform layer are from the Toh+ profiles upon vesicle filled amacrine-like profiles that are in turn presynaptic to bipolar cell dendrites in the outer plexiform layer. We presume the cells postsynaptic to the Toh+ dendrites in the outer plexiform layer are interplexiform cells.(ABSTRACT TRUNCATED AT 400 WORDS)