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A subpopulation of retinal ganglion cells projecting to the pigeon ventral lateral geniculate nucleus was shown to contain cholecystokinin-like immunoreactivity. These ganglion cells were mainly distributed in the peripheral retina, and their somata sizes were medium to large (14–23 μm). Taken together with previous findings, these results indicate that th retinal input to the ventral geniculate is chemically heterogeneous.

The morphology, dendritic stratification and laminal position of the soma of retinal ganglion cells were analyzed in Golgi preparations and in other rabbit retinas containing cells backfilled from the superior colliculus. Only one type, among 40 Golgi-impregnated types identified, always had its cell body displaced to the amacrine ell sublayer of the inner nuclear layer. The displaced ganglion cell of rabbit retina has a small cell body, very wide dendritic field with sometimes unbranched dendrites extending up to a millimeter from the cell body. The dendritic tree is narrowly stratified just under the amacrine cell bodies in stratum 1, and therefore does not co-stratify with starburst (cholinergic) amacrine cells, but rather with dopaminergic amacrine cells. Its correlate among ganglion cells backfilled from tectum is apparently a very sparse population of small-bodied cells mixed with a variable population of misplaced ganglion cells of varying size and type. The authentic displaced ganglion cell of rabbit retina, unlike the large displaced ganglion cell of birds, is apparently not a directionally selective ganglion cell, and its functional role in vision is presently unknown.

γ-Aminobutyric acid (GABA)-like immunoreactive (IR) neurons in the retina of the cane toad Bufo marinus were revealed using immunohistochemistry on retinal wholemount preparation and sectioned material. GABA-IR neurons included horizontal, bipolar and amacrine cells in the inner nuclear layer and small to medium sized cells in the ganglion cell layer. A few IR axons were seen in the optic fiber layer of the retina. Following the injection of the carbocyanine dye, DiI into the optic tectum ganglion cells were retrogradely filled. A small population of DiI-filled ganglion cells (2.8%) was found to be GABA-IR. GABA-IR neurons in the ganglion cell layer without DiI label were considered to be displaced amacrine cells of which 45.3% were GABA positive. It is proposed that GABA-containing ganglion cells may form an inhibitory projection to visual centers of the anuran brain.

After introduction of small amounts of horseradish peroxidase (HRP) into known visual centers of the brain, retinal ganglion cells projecting to these regions were detected by the accumulation of HRP-positive granules in their somata. Control experiments indicated that the HRP-positive granules had reached the ganglion cell somata by retrograde axonal transport, and did not represent blood-borne or endogenous peroxidase. Using this technique, it has been determined that axons of both large and medium-sized neurons in the ganglion cell layer of adult and immature rat retinae terminate in the superior colliculus and lateral geniculate body, and that characteristic displaced ganglion cells with axonal connections to these visual centers occur regularly in these retinae. In addition, certain small cells in the retinal ganglion cell layer are described which may represent glia or interneurons, or ganglion cells which lack the ability to transport peroxidase or which lack central connections to these visual centers of the brain.

The pattern of retinal projection to the hypothalamus and the morphological properties of the retinal ganglion cells that comprise the retinohypothalamic tract have been examined in the cat. Intraocular injections of horseradish peroxidase revealed a dense retinal projection to the ventral suprachiasmatic nucleus; however, lighter projections were seen in the dorsal suprachiasmatic nucleus, and in hypothalamic regions both dorsal and lateral to the suprachiasmatic nucleus. Intrasuprachiasmatic nucleus injections of horseradish peroxidase retrogradely labelled retinal ganglion cells that were small to medium in soma size. The labelled ganglion cells exhibited long thin dendrites that were sparsely branched. The labelled retinal ganglion cells exhibited a significant change in soma size associated with retinal eccentricity. The morphological characteristics of the ganglion cells that project to the suprachiasmatic nucleus are similar to those of gamma cells.

The influence of horizontal cells on ganglion cells in the rabbit retina was examined by injecting current intracellularly into horizontal cells while simultaneously monitoring the extracellular spike activity of nearby single-unit ganglion cells. Hyperpolarizing current injected into horizontal cells decreased the firing rate of on-center brisk ganglion cells and increased the firing rate of off-center brisk ganglion cells. Depolarizing current produced opposite effects on on-center and off-center brisk ganglion cells. These findings are consistent with the view that horizontal cells in the rabbit contribute to the antagonistic surround excitation of brisk ganglion cells.

Macaque retinal ganglion cells whose receptive-field center recieves input from blue-sensitive cones show an overt asymmetry of the frequency of ON-center and OFF-center varieties, an asymmetry not present in ganglion cells whose center receives input from the other two cone types. A similar asymmetry of ON/OFF responses is found in the local electrotetinogram (d-wave) mediated by signals from blue-sensitive cones. ‘Blue-ON-center’ ganglion cells have larger receptive-field centers and shorter conduction latencies than other opponent-color varieties, suggesting an appreciable degree of receptor convergence and presumably large cell bodies. Intracellular stainings of these neurons with Procion Yellow show that they correspond to diffuse stratified (Parasol) ganglion cells whose flat-topped dendritic arborization stratifies in the sclerad half of the inner plexiform layer. In view of the known characteristics of macaque bipolar cells and of the ON/OFF asymmetry, it is proposed that these ganglion cells are postsynaptic to cone-specific flat bipolars possibly mediating sign-inverting synaptic contacts. The results also indicate a reversal, for the blue-cone pathway, of the ON/OFF lamination of the inner plexiform layer that has recently been described in other species.

Ganglion cell morphology has been analyzed in the retina of the adult, albino rat by the Golgi technique and evidence has been obtained that the ganglion cells of this species show a far greater variety and complexity of organization than described previously. Both diffuse ganglion cells, whose dendrites ramify throughout the inner plexiform layer, and stratified ganglion cells, whose dendritic branching is restricted to one or two planes, have been identified. Evidence is also presented for distinct stratification of the inner plexiform layer in this species, based on radioautographic analysis following intravitreal injection of tritiated amino acids.

Single unit recording techniques were used in decerebrate, immobilized domestic chicks to investigate the effects of electrical stimulation of the peripheral end of the severed isthmo-optic tract on the receptive field properties of ganglion cells in the contralateral retina. Tract stimulation always worked to enhance ganglion cell visual responses and was never observed to depress them. However, activation of the tract did not itself generate ganglion cell firing and centrifugal effects were only apparent when the retinal cells were receiving visual stimulation. Visual stimuli such as large, centred spots which were normally ineffective in driving ganglion cells because they enroached on the inhibitory surround, often produced activity when combined with tract stimuli. Experiments with spots and annuli suggest that this centrifugal enhancement probably results from suppression of the inhibitory surround mechanisms (disinhibition) since in such cases tract stimuli were only effective when paired with both spot and annulus, and not with either target alone. Occasionally, the centrifugal input seemed to increase ganglion cell excitability through a direct effect on central excitatory mechanisms (facilitation), since in these cases tract stimulation produced considerably increased firing to small, centred spots whilst failing to exert any appreciable effect on responses to either the annulus alone, or the annulus in combination with the spot. The possible functional significance of these findings is discussed.

The patterns of cell death and division are described in the normal postnatal rat retina and following transection of the optic nerve on the day of birth. Optic nerve transection on the day of birth results in the rapid degeneration of the ganglion cells. Mitosis at the outer retinal surface ceases first in the temporal retina, then in the nasal retina and becomes progressively more restricted to peripheral regions. Mitotic activity was not affected by the loss of ganglion cells. Cell death takes place in a wave passing from the ganglion cell to the inner nuclear to the outer nuclear layer. The time course of cell death is not affected by the loss of ganglion cells following optic nerve transection, and there is no significant increase in the number of cells which degenerate in the inner nuclear layer. The effects of removing a major postsynaptic target of local circuit neurones appears to be less pronounced than has been reported for relay neurones.

A ganglion cell density map was produced from the Nissl-stained retinal whole mount of the Japanese quail. Ganglion cell density diminished nearly concentrically from the central area toward the retinal periphery. The mean soma area of ganglion cells in isodensity zones increased as the cell density decreased. The histograms of soma areas in each zone indicated that a population of small-sized ganglion cells persists into the peripheral retina. The total number of ganglion cells was estimated at about 2.0 million. Electron microscopic examination of the optic nerve revealed thin unmyelinated axons to comprise 69% of the total fiber count (about 2.0 million). Since there was no discrepancy between both the total numbers of neurons in the ganglion cell layer and optic nerve fibers, it is inferred that displaced amacrine cells are few, if any. The spectrum in optic nerve fiber diameter showed a unimodal skewed distribution quite similar to the histogram of soma areas of ganglion cells in the whole retina. This suggests a close correlation between soma areas and axon diameters. Retinal ganglion cells filled from the optic nerve with horseradish peroxidase were classified into 7 types according to such morphological characteristics as size, shape and location of the soma, as well as dendritic arborization pattern. Taking into account areal ranges of somata of each cell type, it can be assumed that most of the ganglion cells in the whole retinal ganglion cell layer are composed of type I, II and III cells, and that the population of uniformly small-sized ganglion cells corresponds to type I cells and is an origin of unmyelinated axons in the optic nerve.

Teleosts exist under conditions where the intensity and spectral composition of available light is a function of media transmissivity, season, and geographic location. Moreover, the composition of a stimulus is dependent upon the object's direction and distance from the subject. Even should the same stimulus be presented repeatedly, the animal's ability to perceive it will be a function of temperature and season. Such diverse visual conditions have been dealt with (evolutionarily) by the development of specialized features such as a reflective tapetum, area and temperature dependent distribution of visual pigments, and an area-specific distribution of photoreceptor types. The cyprinid retina has a least 7 distinct photoreceptor types. Each of the photoreceptor types make synaptic contacts with bipolar and horizontal cells of one or more classes. There are at least 4 horizontal cell classes, 3 of which are thought to make color-specific feedback connections on photoreceptors. The receptors are not only the first neural retinal element, but also act as interneurons and display the first indication of antagonistic spectral and spatial response properties. Indeed, the complexity of the spectral response patterns observed within horizontal and receptor cells makes one wonder how information is sorted out in order to produce the high spectral and spatial resolution at the ganglion cell level. Two points must be kept in mind: (1) a photoreceptor's response is due primarily to quantum capture in that receptor's outer segment and is not due to horizontal cell feedback or inter-receptor connections; (2) bipolar cells form direct contacts with receptors and ganglion cells. The bipolar cells therefore provide a direct — straight-through — information transfer pathway. The importance of primary, direct neural pathways should not be underestimated. In general, the direct pathways, RECEPTOR→BIPOLAR→GANGLION CELL, provide the primary and most direct means of chromatic information transfer (Fig. 19). The secondary, internal, pathways, which include the horizontal and amacrine cells, are important only to the extent that they modify and contribute to both spectral and spatial contrast. The horizontal cells do contribute to the bipolar cell's surround properties, but the bipolar cell's greatest sensitivity and most dominant responses are within its central receptive field. The same can be said of the ganglion cells, their dominant response properties are to central field stimulation. The surround responses of both bipolars and ganglions are weak and temporally slow. The direct neural pathways can be subdivided into two systems which shall be termed the ON and OFF channels. Each of these channels consist of receptor, bipolar and ganglion cell combinations. These direct pathways are functionally defined by the response polarity of the bipolar and ganglion cell pair to a step increase in illumination. The ON pathways or channels consist of bipolar/ganglion cell combinations, each of which depolarizes to an increase in stimulus energy (+ΔI stimulus). Each component of the OFF pathways hyperpolarizes to the same stimulus. The ON and OFF pathways can also be identified anatomically. The ON pathways obviously make sign-inverting synapses between photoreceptors and bipolar cells, in order to transform the receptor's hyperpolarization into a depolarization: an ON response. The ON bipolar also terminates in only one lamina of the inner plexiform layer (layer b). The OFF pathways conserve the photoreceptors' hyperpolarizing response and the OFF bipolar cells terminate in sublamina ‘a’ of the IPL where they contact OFF ganglion cells. The ON and OFF pathways are believed to have different spectral sensitivities, with the ON channels representing the shorter wavelengths and the OFF channels favoring the longer wavelengths. The transfer of chromatic information is obviously more complex than simply ON and OFF responses. In addition to the independent ON and OFF pathways, some amacrine and ganglion cells receive input from both ON and OFF bipolars, forming the ON-OFF (transient) amacrine and ganglion cell classes. The ON-OFF cells terminate in both sublaminae of the IPL (Fig. 19). This combined input produces transient depolarizations to stimulus onset and cessation, due to the dominate depolarizing phase of the individual bipolar cell's response. The 3 identified ganglion cell types, ON, OFF, and ON-OFF may represent 3 distinct cell classes, or simply be components of a continuum with different ganglion cells contacting ON and OFF bipolar cells with different ratios. The continuum theory is supported by the observation that individual ganglion cells may produce ON, OFF, or ON-OFF responses depending on stimulus conditions, i.e., a ganglion cell's response may be altered by selecting stimulus conditions which favor ON or OFF bipolar cell types. The chromatic response properties of individual retinal neurons can best be described be defining which photoreceptor systems supply which interneurons. However, of all the bipolar cell types, only one or two have been adequately described in terms of receptor inputs. Moreover, no attempts have been made to define which bipolar cell types contact which ganglion cell classes. Therefore, it remains impossible to describe discrete (cell class to cell class) retinal chromatic pathways. It is impossible to determine the general response properties of such pathways by recording from ganglion cells. A spectrally/spatially defined ganglion cell permits one to deduce the spectral properties of the participating bipolar cells and whether they are ON or OFF units. With this information, the participating horizontal and receptor cell types can be described. The optic nerve may also affect chromatic information transfer. It is suggested that different size ganglion cells convey different chromatic information. Since there is a direct correlation between cell size and axon diameter and between axon diameter and conduction velocity, short versus long wavelength information may be transmitted to the CNS at different rates. Retinal ganglion cells project to and innervate numerous CNS structures. The optic tectum receives the majority of the projections. Even though numerous histological and functional studies on optic tectum have been reported, information on the response properties of individual cell types is non-existent. For example, the cytoarchitecture of the optic tectum is known, but no information is available on neural pathways or cellular interactions. We also do not know which CNS structures are involved in particular behavioral patterns. It is clear that different behavioral patterns are associated with different spectral sensitivities, i.e., spectral sensitivity is task dependent. Reflex type behaviors are apparently mediated by long wavelength stimuli, whereas more complex behaviors require differential integration across CNS structures and tend to be associated with medium and short wavelength stimuli. Data have been presented which suggest that spectral sensitivity is also a function of previous experience and may be altered during critical developmental periods. The major voids in our knowledge of chromatic information processing exist in CNS pathways, degree of task dependency and neural plasticity.

Summary The responses of Necturus retinal ganglion cells were recorded extracellularly. Each cell was characterized by its response type and the distance between its receptive field center and the center of the optic disc. There was a statistically reliable difference between the locations of sustained-ON cells and the locations of sustained-OFF and ON-OFF cells. Thus, the different classes of Necturus retinal ganglion cells are differentially distributed across the surface of the retina.

We wished to determine whether retinal ganglion cells that have axons terminating in the dorsal lateral geniculate and/or the superior colliculus have specific sizes of somata, comprising only part of the entire size range of ganglion cell somata. If so, then perhaps the specific functional types described by Michael might be associated with morphological types based on soma size. HRP was injected into either the superior colliculus (SC) or dorsal lateral geniculate nucleus (LGd) of thirteen-lined ground squirrels. Soma diameter of labeled ganglion cells was measured and the relation between cell size and frequency determined. After SC injections HRP-filled cells were mostly small and medium-sized. They ranged in diameter from 3 to 14 microns and the mean diameter of labeled neurons was 7.35 microns. Cells labeled after SC injections were often distributed as doublets or triplets in the retina. After LGD injections the majority of labeled cells were medium and large-sized. They ranged from 4 to 18 microns in diameter with a mean of 9.1 microns and were more regularly spaced within the retinal region of labeled cells. Thus, the present results provide reason to believe that functional classes of ganglion cells in ground squirrels may be correlated with particular morphological types.

N-Acetylaspartyglutamate-like immunoreactivity (NAAG-L) was identified in retinal ganglion cell bodies and their axons. The presence of the dipeptide in ganglion cell projection areas, the lateral geniculate nucleus (LGN) and superior colliculus (SC), was confirmed following NAAG purification from these tissues by a high-performance liquid chromatographic method. NAAG-L was identified in the optic tract as well as within fibers and puncta in the LGN and SC. The hypothesis that NAAG is present within ganglion cell axons in the brain was tested by unilateral enucleation which resulted in loss of NAAG and NAAG-L within the contralateral LGN and SC.