Calbindin-D28K and calretinin are homologous calcium-binding proteins localized in many neurons of the central nervous system. We have compared polyclonal antibodies against calbindin and calretinin and have shown by western blots using purified calbindin and calretinin from rat that (1) anti-calretinin does not recognize calbindin and (2) anti-calbindin presents some cross-reactivity with calretinin.

In this report, we have compared by immunohistochemistry the localization of both calcium-binding proteins in the retina of monkey, pig, sheep, rat, cat, pigeon, and salamander. These results are compared with previous data for chick. There are many differences between species and not within species, but some aspects of the distribution are conserved. All species, except rat and monkey, have some cones which contain calbindin only. Most species also have some bipolar cells containing calbindin only. Calretinin is rarely seen in photoreċeptors or bipolar cells. All species have horizontal cells which contain calretinin or calbindin or both. All species have amacrine cells and ganglion cells containing one or other protein.

In the cat ganglion cell layer, the calretinin antisera define a new, asymmetric, type of cell.

The distribution patterns of GABA immunoreactive (+) and immunonegative (−) amacrine cell synapses and profiles in the inner plexiform layer (IPL) were analyzed in three macaque monkey retinas using postembedding electron-microscopic (EM) immunogold cytochemistry. Synapses and profiles were counted at 5% intervals throughout the IPL depth in three EM montages (total area = 6509 μm2), with 0% depth at the inner nuclear layer/IPL border. Nearly 70% of all amacrine synapses were GABA+, and they contacted all major classes of neurons that arborize in the IPL: bipolars (45%), ganglion cells (25%), and GABA+ (20%) and GABA− (10%) amacrines. A major relationship was seen between GABA+ amacrine processes and bipolar terminals: 76% of all amacrine-to-bipolar synapses were GABA+, and 82% of bipolar output dyads contained at least one GABA+ amacrine.

GABA+ amacrine profiles (N = 2455) were concentrated in three wide bands at IPL depths of 0–25%, 40–60%, and 75–100%, corresponding to the dense bands seen with light-microscopic immunocytochemistry. In contrast, GABA+ amacrine synapses (N = 1081) were distributed evenly throughout the IPL depth, rather than being confined to the three dense bands. GABA− amacrine synapses (N = 516) were concentrated at 40% and 60% depths.

Each category of amacrine output synapses had a characteristic pattern of stratification in the IPL. GABA+amacrine-to-bipolar synapses occurred throughout the IPL but were most frequent at 20% and 80% IPL depths, where the dendrites of midget cone bipolars arborize (Polyak, 1941). In contrast, GABA+amacrine-to-ganglion cell synapses were concentrated at 30% and 70% IPL depths, near the dendritic arborizations of parasol ganglion cells (Watanabe & Rodieck, 1989). GABA+ synapses onto bipolars and amacrines were also concentrated at the level of rod bipolar terminals. GABA+ amacrines must play significant but different roles in ON and OFF midget and parasol pathways as well as the rod pathway.

In order to evaluate the normal eye movements of the turtle, Pseudemys scripta elegans, the positions of each eye were recorded simultaneously using two search-coil contact lenses. Optokinetic nystagmus (OKN) was strikingly unyoked in this animal such that one eye's slow-phase velocity was substantially independent of that of the other eye. On the other hand, the fast-phase motions of both eyes occurred more or less in synchrony.

An eye's slow-phase gain is primarily dependent on the direction and velocity of the stimulus to that eye. Using monocular stimuli, the highest mean gain (0.54 ± 0.047; mean ± standard error of mean) occurred using temporal-to-nasal movement at 2.5 deg/s. The mean OKN gain for nasal-to-temporal movement was only 0.13 ± 0.015 at that velocity. Additionally, using the optimal monocular stimulus (temporal-to-nasal stimulation at 2.5 deg/s) only drove the occluded eye to move nasal-to-temporally at 0.085 deg/s, equivalent to a “gain” of only 0.034 ± 0.011.

The binocular OKN gain during rotational stimuli was higher than monocular gain, especially during nasal-to-temporal movement at high velocities. Also the difference in slow-phase eye velocity between the two eyes was smaller during binocular rotational stimuli. In contrast, when each eye simultaneously viewed its temporal-to-nasal stimulus at an equal velocity, two behaviors were observed. Often, OKN alternated between an animal's left eye and right eye. Occasionally, both eyes moved at equal but opposite velocities.

These behavioral data provide a quantitative baseline to interpret the properties of the retinal slip information in the turtle's accessory optic system. Those properties are similar to the behavior of the turtle in that both are tuned to direction and velocity independently for each eye (Rosenberg & Ariel, 1990).

Many studies on human retinal development have cited the third gestational month as a period when the posterior retina undergoes rapid differentiation and maturation, including a lining up of cone precursors. Ultrastructural data on the posterior retina during the third month are very limited, and totally lacking for the cone monolayer. We have examined two human fetal retinas between ten and 11 gestational weeks. Before the appearance of the cone monolayer, the outer neural retina consists of a homogeneous population of undifferentiated neuroblasts. Mitotic figures are still evident, even posteriorally. There is no outer plexiform layer (OPL). The interface of neural retina to retinal pigment epithelium (RPE) is largely featureless. By 11 weeks, the posterior retina has a thin OPL that separates the many rows of cells in the developing inner nuclear layer from the single tier of macular cone precursors. The RPE monolayer consists of cuboidal cells whose apical surface elaborates ridges of cytoplasm and branched processes that project into the subretinal space. The large, cuboidal cones are linked to each other and Müller cells at the outer limiting membrane. They show definitive signs of the structural polarity typical of vertebrate photoreceptors. Their apical cytoplasm contains many organelles common to the inner segment, while the basal cytoplasm has synaptic ribbons and vesicles, and receives invaginating contacts from processes in the OPL neuropil arising from differentiating second-order neurons. Lateral cone surfaces are mutually underlain by large subsurface cisterns.

This study has shown that the retinae of Prototherian (egg-laying) mammals possess two neuronal types that are present in non-mammalian retinae, but absent or morphologically different in the retinae of Eutherian (placental) mammals. First, endogenous serotonin-like immunoreactivity has been localized in a population of presumptive amacrine cells in the platypus retina, the first such report in a mammalian retina. Second, the protein kinase C-immunoreactive (PKC-IR) bipolar cells in the echidna retina appear similar to the PKC-IR bipolars in the chicken retina, in that their dendrites give rise to a Landolt's club and their axons are multistratified. By contrast, the PKC-IR rod bipolar cells in the rabbit and in the brushtail possum, a Metatherian (marsupial) mammal, have no Landolt's clubs and their axons form terminal lobes in the innermost stratum of the inner plexiform layer.

We have examined the distribution of immunoreactivity for the monoclonal antibody Cat-301 in visual cortex of the macaque monkey. Remarkably, those portions of striate cortex (V1) and extrastriate cortex that are most immunoreactive for Cat-301 are anatomically interconnected and are dominated by inputs arising from the magnocellular layers of the LGN (which are themselves highly immunoreactive). In particular, we found that a band of Cat-301 labeled neurons known to exist in layer 4 of V1 is centered on the boundary between layers 4Cα and 4B and thus includes portions of both the primary target of the magnocellular LGN and its subsequent relay through layer 4B. We also demonstrated consistently strong Cat-301 immunoreactivity in all three extrastriate targets of layer 4B: areas V3, MT, and the cytochrome-oxidase (CO) enriched thick stripes of V2. In V2, there was a close correlation between Cat-301 labeling and clusters of cells projecting to MT but not to V4. This was true even in regions where the CO pattern was equivocal or irregular, indicating that Cat-301 is a more reliable marker than CO for the thick-stripe subregions of V2. Finally, we found strong Cat-301 immunoreactivity in at least parts of areas V3A, the MST complex, and the posterior parietal complex, but not in area V4 or inferotemporal cortex. The molecular specificity revealed by this single marker thus correlates with functionally specific subdivisions at each hierarchical level over nearly the entire known extent of the visual pathway in macaques. This supports the notion that these subdivisions form an anatomically, physiologically, and now molecularly distinct pathway known as the M-stream.

In a series of physiological experiments, a total of 203 neurons at the Area 17/18 border were recorded with a callosal link either demonstrated by antidromic or transsynaptic activation from stimulating electrodes located in the homotopic contralateral hemisphere (CH), or in the splenial segment of the corpus callosum (CC). Forty-four percent of the transcallosal cells could also be driven from stimulating electrodes in or just above the lateral geniculate nucleus (OR1). The majority (69%) of transcallosal neurons were classifiable as belonging to the complex family (B and C cells) and most of these were found in the supragranular laminae and in lamina 4A. The ocular dominance distribution of transcallosal cells was trimodal, consisting of roughly equal numbers of monocularly dominated and binocularly balanced neurons. Estimates of conduction time and synaptic delay were obtained for neurons driven from CH, CC, and from OR1, and in most instances the response latency was short enough to suggest a monosynaptic input from either the ipsi- or contra-lateral hemisphere. The distribution of transcallosal conduction times showed that S cells, as a class, had significantly faster conduction than cells of the complex family but otherwise there was no obvious signs of multimodality in the distribution curve. An analysis of the synaptic delays in transcallosal activation produced a mean of 0.6 to 0.7 ms but some were too short to be consistent with a transsynaptic drive, suggesting that some cells with an antidromic drive may have been included in the transsynaptic category. Results are interpreted in terms of the contribution made by the corpus callosum to stereoscopic vision.

The course of optic axons that take different routes at the chiasm have been traced through horizontally sectioned optic nerves in the cat, after unilateral injections of horseradish peroxide into the optic tract. Behind the eye and for most of the course of the nerve, nearly all of the axons that remain uncrossed at the chiasm are located in a retinotopically appropriate position, in the lateral aspect of the nerve. However, in the most caudal segment of the nerve an increasing proportion of these axons are located in regions that are retinotopically inappropriate. Just before the nerve joins the chiasm, uncrossed axons can be found across the full medio-lateral extent of the nerve, although there is still a relative increase in their density laterally.

Labeled axons that cross at the chiasm course in a relatively parallel manner along the greater proportion of the nerve. However, in the caudal segment of the nerve their relative positions change and they appear to course in an irregular manner. This occurs where the uncrossed projection becomes increasingly more widespread.

Axons in the optic nerve are grouped into fascicules. This pattern of organization also changes in the caudal region of the nerve. Although clear fascicular patterns are present along the greater part of the nerve, they become progressively less distinct caudally. The change in the pattern of fasciculation occurs over the same region of the nerve as the relative changes in axon trajectory and distribution.

These results demonstrate that irrespective of chiasmatic route, optic axons in the cat are reorganized in the caudal segment of the nerve. This reorganization is not confined to changes in relative axon position, but is reflected in the structure of the nerve by the change of axon grouping from a fascicular to a non-fascicular arrangement.