We examined the grating acuity and contrast sensitivity of cats whose eye position was monitored with a scleral search-coil technique. During each trial, the cat was required to maintain fixation on a laser spot and respond to the presence or the absence of a grating by pressing a right or left pedal. With this procedure, acuity was measured along the horizontal and vertical meridian over a range of eccentricities in the nasal, temporal, superior, and inferior retina. In addition, contrast sensitivity for stationary and drifting gratings was measured for the temporal retina along the horizontal meridian. Acuity in area centralis reached about 3.5 cycle\deg and declined by 0.5 octaves at 4 deg and by about 1.3 octaves at 16-deg eccentricity in the nasal retina. The acuity was higher in the nasal than temporal retina. At all eccentricities, spatial resolution exceeded the resolution limit derived from Y (alpha)-cell properties. Contrast sensitivity also decreased as the eccentricity increased when the target size was held constant. The slope of sensitivity-eccentricity function was relatively shallow for a low spatial frequency (0.30 cycle\deg) with sensitivity decreasing by a factor of 1.5–2 at 8-deg eccentricity. The slope of the sensitivity falloff for high spatial-frequency gratings (1.2 cycle\deg) was steeper, with a 5–10-fold difference in sensitivity between 0 and 8 deg. By varying the target size, we determined that the summation area in the cat is about a factor of 3 smaller in area centralis than a 16-deg eccentricity. When the size of the centrally and peripherally viewed targets was scaled relative to visual acuity, the sensitivity was constant across the visual field.

Eyes of stomatopod crustaceans, or mantis shrimps, contain the greatest diversity of visual pigments yet described in any species, with as many as ten or more spectral classes present in a single retina. In this study, the eyes of seven species of mantis shrimp from three superfamilies of stomatopods were examined for their content of retinoids. Only retinal and retinol were found; neither hydroxyretinoids nor dehydroretinoids were detected. The principal isomers were 11 -cis and all-trans. The eyes of most of these species contain stores of 11 -cis retinol, principally as retinyl esters, and in amounts in excess of retinal. Squilla empusa is particularly noteworthy, with over 5000 pmoles of retinol per eye.

In order to elucidate the role of putative indoleaminergic amacrine cells in visual processing, we have employed pharmacological agents specific for the two classes of serotonin receptor, 5-HT2 and 5-HT1, which have been identified in both the retina and brain. Perfusion of the rabbit retina with 5-HT2 selective antagonists decreases the ON-excitation of all classes of ganglion cell as well as the spontaneous activity of these cells. The effect on OFF-responses depends on the cell type: OFF-excitation of center-surround brisk and sluggish cells is increased or not affected by these drugs, but OFF excitation of ON/OFF direction selective cells is reduced. No disruption of the trigger features of direction selective or orientation selective cells was discovered, suggesting that indoleaminergic amacrine cells do not play a role in the generation of the complex properties of these cells.

5-HT1 receptors are heterogeneous and classified as a, b, or c subtypes. Since no selective antagonists are available for these sites, we have employed specific agonists. The most specific of these are for the 5-HT1A receptor. Perfusion with these agonists had physiological effects similar to those with perfusion of 5-HT2 antagonists. Thus, we have suggested that these two classes of serotonin receptors mediate opponent processes in the neural pathway. Since indoleaminergic cells make reciprocal synaptic connections with rod bipolar cell terminals, which are depolarizing in the rabbit retina, we hypothesize that 5-HT2 receptors facilitate the synaptic transmission from the depolarizing rod bipolar cell thus facilitating ON-excitation in the retinal network while 5-HT1A receptors mediate an inhibitory process. Similar self-opponent processing appears to take place in the hypothalamic and hippocampal serotonergic systems as well as in the dopaminergic retinal system. Thus, it is likely that this organization is a general feature of monoamine signal transmission in the central nervous system.

Rod bipolar cells constitute the second-order neuron in the rod pathway. Previous investigations of the rabbit retina have evaluated the development of other components of the rod pathway, namely the dopaminergic and All amacrine cell populations. To gain further insights into the maturation of this retinal circuitry, we studied the development of rod bipolar cells, identified with antibodies directed to the α isoform of protein kinase C (PKC), in the rabbit retina. Lightly immunostained PKC-immunoreactive (IR) somata are first observed at postnatal day (PND) 6 in the distal inner nuclear layer (INL). Immunostaining is also observed in the outer plexiform layer (OPL), indicating the presence of PKC-IR dendrites. PKC-IR axons are present in the INL oriented toward the inner plexiform layer (IPL). Several of them terminate with enlarged structures resembling growth cones. At PND 8, some immunostained terminal bulbs, characteristic of rod bipolar cells, are detected in the proximal IPL. PKC-IR cells at PND 11 (eye opening) display stronger immunostaining and more mature characteristics than at earlier ages. The dendritic arborizations of these cells in the OPL and their axon terminals in the IPL attain mature morphology at later ages (PND 30 or older). The density of PKC-IR cells shows a peak at PND 11 followed by a drastic decrease up to adulthood. The total number of PKC-IR cells increases from PND 6 to PND 11 and then it remains almost unchanged until adulthood. The mosaic of PKC-IR cells is nonrandom in some retinal locations at PND 6, but the overall regularity index at PND 6 is lower than at older ages. The present data provide a comprehensive evaluation of the development of rod bipolar cells in the postnatal rabbit retina and are consistent with those previously reported for dopaminergic and All amacrine cell populations, indicating that different components of the rod pathway follow a similar pattern of maturation, presumably allowing the rod pathway to be functional at eye opening.

Single neurons were recorded in cat primary visual cortex, and the effect of iontophoresis of the metabotropic glutamate agonist 1S,3R-aminocyclopentane-1.3-dicarboxylic acid (ACPD) was observed. In nearly all cases (41/43), ACPD reduced the visual response. In some cases ACPD also reduced spontaneous activity (24/43), and in other cases ACPD increased spontaneous activity (18/43). Increases were generally seen in infragranular layers (V and VI), and decreases in supragranular layers (II and III). The reduction in the visual response was also largest in supragranular layers. We conclude that activation of metabotropic glutamate receptors has both facilitatory and depressive effects in visual cortex, and the effect depends on the layer of the cell recorded.

To characterize the postnatal development of geniculocortical axon arbor morphology in owl monkeys at a series of ages from birth to adulthood, individual arbors were bulk-filled with HRP in brain slice preparations and were reconstructed from serial sections. At all ages, cortical layers and sublayers were obvious. Presumed M or magnocellular arbors were largely confined to layer IVα, but they also extended into layer IIIc (IVB of Brodmann, 1909); presumed P or parvocellular arbors were almost exclusively confined to layer IVβ. Other axons that may reflect feedback projections from MT terminated in layer IIIc. Overall, M axon arbors increased in size and complexity from birth to adulthood with mean surface-view arbor areas ranging from 0.08 ± 0.01 mm2 in newborns to 0.24 ± 0.02 mm2 in adults. The developing P arbor areas were, on average, as large or larger than adult (newborn = 0.07 ± 0.01 mm2, adult = 0.047 ± 0.01 mm2; n.s.) but the arbors were somewhat less complex. Since the brain and area 17 increase in size postnatally, the proportion of area 17 subserved by each P arbor would decrease in postnatal development. Terminal boutons with immature features were evident in both M and P populations at all developmental ages. The results indicate that, while both LGN axon types in monkeys undergo morphological changes postnatally, M arbors appear to mature by increasing arbor size and terminal branching complexity, whereas P arbors increase in complexity but not in size. These distinct programs of axon arbor development suggest that the periods of susceptibility of geniculocortical axon arbors to postnatal influences of the environment, and the types of plastic responses they potentially exhibit, are class-specific.

The existence in cat cortex of linearly operating simple cells with relative spatial-frequency bandwidths of between 0.5 and 1 octave is confirmed.

Acetylcholine (ACh) affects the response properties of many retinal ganglion cells (GCs) through the activation of nicotinic acetylcholine receptors (nAChRs). To date there have been few studies directly correlating the expression of specific nAChR subtypes with the physiological and morphological characteristics of specific retinal GCs. This study was designed to correlate responses to nicotine application with immunohistochemical evidence of nAChR expression in physiologically and morphologically identified ganglion cells. Extracellular recordings were used to physiologically identify rabbit retinal GCs, based on responses to light stimulation. Cells were then tested for responses to nicotine application and/or for expression of nAChRs, as judged by immunoreactivity to mAb210, an nAChR antibody. The morphologies of many physiologically identified cells were also determined by dye injection. More than three-fourths of ganglion cells tested responded to nicotine application under cobalt-induced synaptic blockade. The nicotine sensitivity was consistent with nAChR immunoreactivity and was also correlated with specific morphological subgroups of GCs. Overall, approximately two-thirds of all physiologically identified GCs that were processed for immunohistochemistry displayed immunoreactivity. In total, 18 of 22 physiologically identified cells demonstrated both sensitivity to nicotine application under synaptic blockade and mAb210 immunoreactivity (mAb210-IR). Thus, mAb210-IR is likely to represent functional nAChRs that can modulate retinal information processing and visual functioning via direct excitation of a number of GC classes.

Transient uniformity detectors (UDs) are a unique type of retinal ganglion cell (RGC) whose maintained firing is transiently suppressed by all types of visual stimuli. In this study, we have characterized the dendritic morphology and tracer-coupling pattern of UDs that were labeled by loose-seal electroporation of Neurobiotin following functional identification in the isolated rabbit retina. The UDs have a bistratified dendritic tree, branching near the margins of the inner plexiform layer in stratum 1 (part of the OFF sublamina) and stratum 4/5 (part of the ON sublamina). Characteristically, many of the distal dendrites in the OFF arbor do not terminate there but dive recurrently back to the ON arbor. As a consequence, the ON dendritic arbor is usually twice as large as the OFF dendritic arbor in area. The UDs sometimes show homologous tracer coupling to neighboring RGCs with the same morphology, and from this material, we estimate that the UDs have a threefold dendritic field overlap and a maximum density of ~100 cells/mm2 on the peak visual streak, accounting for ~2% of RGCs in rabbit retina. The UDs also show strong heterologous tracer coupling to a novel type of amacrine cell that costratifies with the ON arbor of the UD. Consistent with their unistratified medium-field morphology, these St4/5 amacrine cells appear to be GABAergic: their somata are immunopositive for GABA but immunonegative for glycine and glycine transporter 1. We compare the dendritic morphology of the UDs to that of other types of bistratified RGCs described in rabbit retina and note that the stratification levels and distinctive recurrent dendrites closely resemble those of the “ON bistratified diving” RGCs. This raises the possibility that there are two types of RGCs with distinctive physiological properties that have almost identical bistratified dendritic morphologies.

Electrical synapses, or gap junctions, are widely distributed in the vertebrate retina and are thought to play critical roles in the transmission and coding of visual signals. To investigate the molecular basis of this form of neural communication in the retina, we have isolated, characterized, and functionally expressed a cDNA for a gap junction channel derived from the retina of the teleost fish Danio aquipinnatus (giant danio). The cDNA contained an open reading frame of 1146 nucleotides encoding a connexin with a predicted molecular mass of 43.3 kDa which shared extensive identity with Rattus norvegicus Cx43 (78%). This protein (DACX43) contained several consensus phosphorylation sequences in the c-terminal region, some of which are conserved among Cx43 orthologs. RNA blot hybridization revealed that DACX43 was expressed in the brain as well as in the retina. In addition, Southern analysis suggested that there are multiple copies of DACX43, or other closely related sequences, in the Danio aquipinnatus genome. When DACX43 was expressed by stable transfection in gap-junction-deficient mouse N2A neuroblastoma cells, functional gap junctions were formed as indicated by dual whole-cell recordings of electrical coupling. We conclude that DACX43 is a connexin43 ortholog, which is expressed in the retina of Danio aquipinnatus, and when translated is able to form functional gap junction channels.

The discontinuities of phase-shifted abutting line gratings give rise to perception of an “illusory contour” (IC) along the line terminations. Neuronal responses to such ICs have been interpreted as evidence for a specialized visual mechanism, since such responses cannot be predicted from conventional linear receptive fields. However, when the spatial scale of the component gratings (carriers) is large compared to the neuron's luminance passband, these IC responses might be evoked simply by the luminance edges at the line terminations. Thus by presenting abutting gratings at a series of carrier spatial scales to cat A18 neurons, we were able to distinguish genuine nonlinear responses from those due to luminance edges. Around half of the neurons (both simple and complex types) showed a bimodal response pattern to abutting gratings: one peak at a low carrier spatial frequency range that overlapped with the luminance passband, and a second distinct peak at much higher frequencies beyond the neuron's grating resolution. For those bimodally responding neurons, the low-frequency responses were sensitive to carrier phase, but the high-frequency responses were phase-invariant. Thus the responses at low carrier spatial frequencies could be understood via a linear model, while the higher frequency responses represented genuine nonlinear IC processing. IC responsive neurons also demonstrated somewhat lower spatial preference to the periodic contours (envelopes) compared to gratings, but the optimal orientation and motion direction for both were quite similar. The nonlinear responses to ICs could be explained by the same energy mechanism underlying responses to second-order stimuli such as contrast-modulated gratings. Similar neuronal preferences for ICs and for gratings may contribute to the form-cue invariant perception of moving contours.

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).

Previous authors have hypothesized that retinotopic projections may be influenced by ‘preordering’ of the axons as they grow towards their targets. In some nonmammalian species, axons are reorganized at or near the optic nerve head to establish a retinotopic order. Data are ambiguous concerning the retinotopy of the mammalian retinal nerve fiber layer and whether fibers become reorganized at the optic nerve head. We have examined this question in fetal and newborn ferrets (Mustela putorius furo) by comparing the arrangement of axons in the retinal nerve fiber layer with that in the optic nerve. Dil or DiA crystals were implanted into fixed tissue in the innermost layers of the retinal periphery, or at a location midway between the periphery and the optic nerve head. Fluorescence labelling was examined in 100–200 μm Vibratome sections, or the eyecup and nerve were photooxidized and 1–2 μm longitudinal or transverse sections were examined. Regardless of fetal age, eccentricity or quadrant of the implant site, a segregation of labelled peripheral axons from unlabelled central ones was not detected within the nerve fiber layer. Axons coursed into the nerve head along the margin of their retinal quadrant of origin, often entering the optic nerve as a radial wedge, thus preserving a rough map of retinal circumference. However, peripheral axons were in no way restricted to the peripheral (nor central) portions of the nerve head or nerve, indicating that the optic axons do not establish a map of retinal eccentricity. Our results demonstrate that (1) the nerve fiber layer is retinotopic only with respect to circumferential position and (2) optic axons are not actively reorganized to establish a retinotopic ordering at the nerve head. The present results suggest that any degree of order present within the optic nerve is a passive consequence of combining the fascicles of the retinal nerve fiber layer; optic axons are not instructed to establish, nor constrained to maintain, a retinotopic order within the optic nerve.

Two physiologically distinct, HRP-marked turtle retinal ganglion cells were examined for their morphology, GABAergic, glycinergic, and bipolar cell synaptic inputs, using electron-microscopic autoradiography and postembedding immunocytochemistry. One cell was a color-opponent, transient ON/OFF ganglion cell. Its center response to red was a sustained hyperpolarization, and its center response to green was a depolarization with increased spiking at onset. The HRP-injected cell most resembled G6, from previous Golgi-impregnation studies (Kolb, 1982; Kolb et al., 1988). It was a narrow-field bistratified cell, whose two broad dendritic strata peaked at approximately levels L20–25 (sublamina a) and L60 (sublamina b) of the inner plexiform layer. Bipolar cell synapses onto G6 were found evenly distributed between its distal and proximal dendritic strata, spanning L20–75. These inputs probably originated from several different bipolar cells, reflecting the complexity of the center response. GABAergic inputs were found onto both the distal and proximal strata, from near L20–L85. Only a few glycinergic inputs, confined to dendrites at L50–70, were observed.

A second ganglion cell type that we physiologically characterized and HRP-injected had sustained ON-center, sustained OFF-surround responses. Two examples were studied; both were bistratified in sublamina b, near L60–70 and L85–100, with branches up to near L40. They resembled G10, from previous Golgi-impregnation studies (Kolb, 1982; Kolb et al., 1988). One cell was partially reconstructed to look at the distributions of GABAergic and glycinergic amacrine cell, and bipolar cell inputs. Although synapses from bipolar cells were equally divided between the two major dendritic strata of G10, the inputs to the distal stratum were close to the soma, and the inputs to the more proximal stratum were on the peripheral dendrites. This arrangement may reflect input from two distinct types of ON-bipolar cell. GABAergic and glycinergic inputs to G10 costratified to both strata and to the distal branches; but where glycinergic inputs were found distributed throughout the arbor, GABAergic inputs appeared to be confined to peripheral dendrites. We hypothesize on the neural elements involved and the circuitry that may underlie the physiologically recorded receptive fields of these two very different ganglion cell types in the turtle retina.

We studied the development of multibank rod retinae by monitoring the size-related addition of new layers of rod inner and outer segments in four species of deep-sea fishes and found two different growth paradigms. In the mesopelagic Chauliodus sloani, new banks of rod inner and outer segments are added as long as the fish increases in size, as observed earlier by Locket (1980). By contrast, in three bathybenthic species (Antimora rostrata, Coryphaenoides (Coryphaenoides) guentheri, and Coryphaenoides (Nematonurus) armatus), the final complement of banks is reached when the specimens have grown to between 20 and 47% of their maximal size, suggesting that the visual system is mature only after this stage. Increase in retinal area, density of rod nuclei, and densities of rod inner and outer segments were also studied in these and additional species. Taken together with previous data on rod proliferation patterns and outer segment membrane synthesis, our findings indicate that at least in species with no continual addition of new banks, there is no major functional difference between the innermost and outermost banks of rod inner and outer segments. While Chauliodus spends all its life in the mesopelagic environment, the three bathybenthic species live in this environment during early development and descend towards greater depths only upon maturation. We speculate that this coincides with the stage when the full complement of rod banks is formed in the retina, as a possible prerequisite for a life outside the reach of sunlight.

Putative GABAergic mechanisms were studied in the cat retina by exogenous application of the GABAA antagonists picrotoxin (PTX), native bicuculline (BCC), and bicuculline methyl bromide (BCC MeBr). When recording intracellular responses from horizontal cells (HCs) and amacrine cells as well as electroretinograms (ERGs), drugs were added to the perfusate used to maintain the isolated eyecup; when recording extracellular spikes from ganglion cells of anesthetized cats, drugs were introduced by iontophoretic injection. Both PTX and BCC MeBr had relatively little influence upon the response properties of HCs. In contrast, native BCC tended to decrease the amplitude of and to slow the photic response to light onset and both to quicken and to increase the amplitude of response to light offset; in the presence of native BCC, HC responses were dominated by a prominent spike-like “Off-overshoot.” The influence of GABAA agonists upon HC responses was not blocked by GABAA antagonists. ERG b−wave amplitude was reduced both by PTX and by native BCC, but was not influenced by BCC MeBr. Latency (time to half-peak) was increased by low doses of native BCC, and to a lesser extent PTX but not BCC MeBr. Rod-amacrine On-transient responses were increased in amplitude by PTX. Extracellular recordings from On- and Off- X and Y ganglion cell types became considerably more transient with application of either PTX, native BCC, or BCC MeBr; this tendency was greater in Off-type ganglion cells. Collectively, these results strengthen conclusions from the previous paper suggesting that GABA serves to slow onset and offset kinetics of retinal neurons, making them more sustained and less phasic. They also suggest that in mammalian retina heterogeneous types of GABAA receptors exist, segregated into different zones: a distal zone, sensitive only to native BCC, a central zone sensitive to both native BCC and PTX, and a proximal zone sensitive to native BCC, BCC methyl halides (BCC MeH), and PTX. Only the proximal zone obeys conventional GABAA pharmacology.

In the δAsn20 Drosophila stock, the N-linked glycosylation site of opsin in Rl-6 receptors (Rhl) is absent. We used electroretinography (ERG), microspectrophotometry (MSP), and electron microscopy (EM) to quantify visual cell defects. Positive controls, w9, had wild type Rhl. MSP revealed minimal photopigment in δAsn20 for 6 days posteclosion; w9 had near normal visual pigment. ERG sensitivity and prolonged depolarizing afterpotential (PDA) were compared for δAsn20 and w9. δAsn20's Rl-6 function is decreased 100–fold at eclosion and diminishes until only R7/8 functions at 11 days. What little rhodopsin is routed to the rhabdomere functions. Morphometry showed smaller Rl-6 rhabdomeres in δAsn20 for 8 days posteclosion. Rhabdomeres in w9 were normal. A negative control, ninaE0117, a deletion of the Rhl gene, also has small rhabdomeres. δAsn20 and ninaE0117 lack the extreme rhabdomere elimination of ora (outer rhabdomeres absent), a nonsense mutant interrupting Rhl's coding sequence. δAsn20 and ora have surplus membrane while ninaE0117 does not. Freeze fracture reveals that δAsn20's rhabdomeric P-face particle count is as low as for vitamin A deprivation, consistent with an opsin defect. High particle density, organized into rows, is present in adjacent plasmalemma where surplus membrane accumulates. In summary, δAsn20 interferes with either synthesis, deployment, or maintenance of opsin.

Light dependence of the effects of taurine depletion on retinal function and biochemistry was examined in albino rats housed either in cyclic lighting or in continuous darkness. Measurements of retinal taurine, DNA, and rhodopsin contents, and electroretinogram amplitudes were made at weekly intervals. Naka-Rushton parameters were estimated for the b wave amplitude-intensity function. No significant effects of lighting regime were observed on retinal taurine levels in untreated rats, or on the time course or extent of taurine depletion in animals treated with guanidinoethyl sulfonate, an antagonist of taurine transport. In both lighting schemes, treatment led to a linear reduction of retinal taurine content which plateaued after 5–6 weeks at 50% of control despite continued treatment. DNA values did not differ among groups, whereas rhodopsin levels doubled in both groups of dark-maintained rats. For treated rats housed in cyclic lighting, the onset of electroretinogram deficits paralleled the loss of retinal taurine in the absence of changes in rhodopsin levels or cell death. Vmax was significantly reduced after 4 weeks of treatment. In contrast, for rats housed in continuous darkness, there were no significant differences in electroretinogram parameters between control and taurine-depleted rats until after 10–14 weeks of treatment. This implies that light exposure accelerates the appearance of functional changes associated with retinal taurine deficiency. The basis of the light dependence and the interpretation of related studies is discussed.

The Golgi-stained dendrites of a two-cone bipolar cell of a vervet monkey were serially sectioned for electron microscopy and shown to make basal synapses with two neighboring cones. The synapses were all on the cone pedicle membrane adjacent to the bipolar processes invaginating to form the triads. This is the characteristic position for flat midget bipolar cells. The numbers of triads in nine adjacent cone pedicles were not significantly different from those in the cones contacted by the bipolar. Based on this measure the two-cone bipolar does not contact a special population of cones.

The advantages and disadvantages of using vertical or horizontal sections for the determination by electron microscopy of the connectivity of the dendrites of Golgi-stained flat bipolar cells are discussed.

Retinitis pigmentosa (RP) is an inherited disease that causes primary degeneration of rod photoreceptors in the retina. Although the causal gene (e.g. rhodopsin) is thought to be expressed in all rods across the retina, the degeneration is typically nonuniform, with rods in the far periphery surviving significantly longer than those in the midperiphery and macula. Basic fibroblast growth factor (bFGF) is a putative survival factor for photoreceptors, and the characteristic regional pattern of rod cell survival in RP suggested that bFGF might be distributed nonuniformly in the human retina. We performed double-label immunocytochemistry on 15 normal human retinas, using anti-bFGF and other antibody markers for retinal neurons and glia. Immunoreactivity for bFGF was consistently absent from cones but was present in rods, populations of cone bipolar and amacrine cells, Müller glial cells, and astrocytes. In the macula, the percentage of bFGF-reactive rods was very low (~0.5%) but it increased in a central to peripheral gradient, accounting for up to ~88% of the rods in the far periphery. These findings suggest that a central to peripheral gradient of rod bFGF is present in normal human retina and may influence the pattern of photoreceptor degeneration in RP. The absence of bFGF in cones and the low number of bFGF-positive rods in the macula may correlate with the vulnerability of these cells in RP, age-related macular degeneration, and other retinal diseases.