The distribution of 3-dehydroretinal (Ral2) in dorsal, middle, and ventral slices of eyes of the crayfish Procambarus clarkii was examined by HPLC. No pronounced differences were found. Similar results were obtained when the eyes were cut into anterior, intermediate, and posterior portions.

Dichroic difference spectra were measured in single halves of microvillar layers of isolated rhabdoms and the proportions of rhodopsin (P1) and porphyropsin (P2) estimated by comparison with computer-generated mixtures of these pigments, whose spectra are known from previous work. The fraction of visual pigment that is porphyropsin appears to be uniform throughout individual retinular cells and among the retinular cells of individual rhabdoms, but various substantially among different rhabdoms from the same eye.

The interommatidial variation in the amount of P2 greatly exceeds the gross regional variation in Ral2. This means there is an intermingling of ommatidia with different levels of P2. The variability in P2 among ommatidia is not likely to have important implications for the vision of the crayfish but suggests that in the metabolism of retinoids, individual ommatidia are quasi-independent metabolic units. The results are compatible with a single opsin for both crayfish rhodopsin and porphyropsin.

Vertical slices of 6-day postnatal (P6) rat retina were cut at a thickness of 100 μm and cultured using the roller-tube technique. After 14–21 days in vitro there was significant distortion of normal retinal architecture, but localized areas of the slices showed the typical pattern of layering of mature retina. The following immunocytochemical markers were used to characterize the different retinal cell types: antibodies against protein kinase C (PKC), calcium binding protein (CabP 28kD), neurofilaments (NF), glia-specific antibodies (GFAP, vimentin), and transmitter-specific antibodies (GABA, TH). The expression of these markers was compared in P6 retina, adult retina, and slice culture. To further characterize the cultured cells, patch-clamp recordings were performed in combination with intracellular injection of Lucifer Yellow (LY). Transmitter-and voltage-gated membrane currents were recorded from morphologically identified neurons. The experiments show that a mammalian slice culture can be used to study differentiation and function of retinal cell types.

The goldfish retina grows throughout the animal’s life, primarily by a balloon-like expansion. With this expansion, dendritic arbors of ganglion cells show scaled growth; arbors increase in size from small to large with no change in their architecture (Hitchcock & Easter, 1986; Bloomfield & Hitchcock, 1991). The study reported here showed that ganglion cell arbors acquire new synapses with this growth. Arbors from a single type of ganglion cell in retinas of small, young and large, old fish were intracellularly filled with horseradish peroxidase, examined electron microscopically, and the synapses contacting them counted and compared (small arbors vs. large arbors). The small and large arbors had similar numbers and orders of dendritic branches (i.e. similar architectures), but the large arbors were significantly larger than the small ones. The increase in arbor size was correlated with a 2.7x and 1.9x increase in the number of ribbon and conventional synaptic contacts, respectively. The addition of new synapses is proposed as a mechanism by which the signaling properties of the enlarging ganglion cells can remain constant.

The histaminergic innervation of the thalamic dorsal and ventral lateral geniculate nuclei and the perigeniculate nucleus of the cat was examined immunohistochemically by means of an antibody to histamine.

We find histamine-immunoreactive neurons in the cat brain are concentrated in the ventrolateral portion of the posterior hypothalamus, confirming a previous report. However, this cell group also spreads into medial, dorsal, and extreme lateral regions of the posterior hypothalamus and extends as far rostral as the optic chiasm.

Histamine-labeled fibers cover all regions of the lateral geniculate complex, but the density of labeling varies. The ventral lateral geniculate nucleus (vLGN) is most densely labeled, the A laminae of the dorsal lateral geniculate are sparsely labeled, and the geniculate C laminae and the perigeniculate nucleus show intermediate amounts of label. Thus, histaminergic fibers demonstrate a predilection for zones innervated by the W-cell system. Labeled fibers exhibit few branchings and numerous en passant swellings, lending a beaded appearance. The vLGN showed more instances of fibers with larger-sized swellings (up to 2 μm).

Following injections of biotinylated tracers into the hypothalamus, we find labeled fibers throughout the lateral geniculate complex. The anterogradely labeled fibers resemblethe histaminergic fibers in morphology, distribution, and relative bouton size. Thus, the hypothalamus appears to be the source of the histaminergic fibers in the lateral geniculate complex.

Histamine-labeled fibers in the dorsal lateral geniculate nucleus (dLGN) exhibit uncommon ultrastructural morphology. Many extremely large, round, or elliptical vesicles fill the fiber swellings. Swellings are directly apposed to a variety of other dendritic and axonal profiles, but thus far no convincing synaptic contacts have been seen. The distribution and appearance of these histaminergic fibers resembles those reported for serotonergic fibers.

Our results support the idea that histamine works nonsynaptically as a neuromodulator in the lateral geniculate complex, affecting the level of visual arousal.

The results of previous studies suggest that class-specific interactions contribute to the development of the different classes of retinal ganglion cells. We tested this hypothesis by examining the morphologies and distributions of alpha (α) cells in regions of mature cat retina selectively depleted of beta (β) cells as a result of visual cortex lesions at birth. We find that α cells in regions of central retina depleted of β cells are abnormally large while α cells in regions of peripheral retina depleted of β cells are abnormally small. The normal central-to-peripheral α cell soma-size gradient is absent in hemiretinae depleted of β cells. The dendritic fields of α cells in the border of β-cell-depleted hemiretina extend preferentially into the β-cell-poor hemiretina. In spite of this, α cell bodies retain their normal retinal distribution and remain distributed in a nonrandom mosaic-like pattern. Thus, it appears that the development of α retinal ganglion cells is influenced by interactions both with other α cells (class-specific interactions) and with surrounding β cells (nonclass-specific interactions).

We evaluated the subcortical pathways’ contribution to human adults’ horizontal OKN by using a method similar to that used previously with cats (Harris & Smith, 1990; Smith & Harris, 1991). Five normal adults viewed plaids composed of two drifting sinusoidal gratings arranged such that their individual directions of drift were 60 deg or more from the direction of coherent motion of the overall pattern. Physiological evidence indicates that under monocular viewing, nasalward coherent motion gives advantage to any crossed subcortical contribution while temporalward coherent motion minimizes it. We recorded horizontal eye movement by infrared reflection and asked subjects to report the perceived direction of motion.

During both binocular and monocular viewing, the direction of the slow phase of OKN fell closer to the direction of coherent movement than to that of the oriented components. Monocular viewing produced no nasal-temporal asymmetries in the influence of coherent motion on the direction of OKN. This suggests that in humans the influence of coherent motion is mediated primarily by cortical mechanisms and, unlike in cats, with little or no involvement of subcortical mechanisms in the generation of horizontal OKN.

We have described the currents flowing across the presynaptic membranes of the four median photoreceptors of the giant barnacle, Balanus nubilus, using a quasi-voltage clamp arrangement. Membrane potential, measured in the terminal region of one photoreceptor, was controlled in all four terminals by feedback current supplied through the nerve containing the photoreceptors’ axons. The [Ca2+] ∘ in the saline was reduced to decrease the Ca2+ current, enabling better voltage control, and tetraethylammonium ion (TEA, 20 mM) was added to block a fast voltage-dependent K+ conductance.

Depolarizing voltage steps from the resting potential in the dark (−60 mV) evoked slow, inward Ca2+-dependent currents which could be blocked by Co2+, Mg2+, or Cd2+. The Ca2+ currents were followed by large outward currents that persisted for many seconds after the offset of moderate or large pulses. These tail currents increased in magnitude and duration with pulse duration and reversed at about −80 mV, consistent with previous evidence for a Ca2+-activated K+ conductance in this membrane. When the Ca2+-activated outward current was reduced to zero by increasing the [K+]∘ so as to set EK at −20 mV, and then stepping the voltage to this value, the step evoked a steady inward Ca2+ current. Thus, the Ca2+ current did not show voltage- or Ca2+-dependent inactivation. When Ba2+ was substituted for Ca2+, 500-ms depolarizing steps evoked steady inward currents but no outward currents. In any given experiment, the activation voltage of the Ca2+ or Ba2+ current did not depend on holding potential.

At the barnacle photoreceptor’s synapse, the postsynaptic cell adapts to maintained presynaptic voltage by a mechanism that is not understood. We conclude that neither Ca2+ current inactivation nor a shift in activation voltage with holding potential can account for this adaptation.

The distribution of somatostatin (SS)-containing neurons was investigated by immunocytochemical methods in the central visual system of adult, developing, and retina-ablated pigeons. In normal adult brains, SS-positive cells and processes were present in the optic tectum, the nucleus of the basal optic root, the visual Wulst, and the ectostriatum. During development, progressive increase or decrease in the numerical density and the total number of SS-containing neurons occurred as determined by quantitative analysis. Changes in SS immunoreactivity also occurred as a consequence of unilateral and bilateral retina removal immediately after hatching, i.e. before retinofugal connections have been established. In spite of the segregation of visual inputs due to the almost completely crossed retinal projections, unilateral and bilateral deafferentation differentially affected SS-containing visual regions. In addition, different effects were observed on the relative packing density of labeled cells as compared to their total number. A possible role of retinal axons in regulating the distribution of SS immunoreactivity was suggested by its altered expression induced by retinal deafferentation. In addition, parallels with the distribution of SS immunoreactivity in the pigeon’s visual system were used to suggest possible equivalence between cell populations in the avian and the mammalian brains.

Whole-cell voltage-clamp recordings were used to examine the unusual pharmacological properties of the electrical coupling between rod-driven horizontal cells in skate retina as revealed previously by receptive-field measurements (Qian & Ripps, 1992). The junctional resistance was measured in electrically coupled cell pairs that had been enzymatically isolated and maintained in culture; the typical value was about 19.92 MΩ(n = 45), more than an order of magnitude lower than the nonjunctional membrane resistance. These data and the intercellular spread of the fluorescent dye Lucifer Yellow provide a good indication that skate horizontal cells are well coupled. The junctional conductance between cells was not modulated by the neurotransmitters dopamine (200 μM) or GABA (1 mM), nor was it affected by the membrane-permeable analogues of cAMP or cGMP, or the adenylate cyclase activator, forskolin. Although resistant to agents that have been reported to alter horizontal-cell coupling in cone-driven horizontal cells, the junctional conductance between paired horizontal cells of skate was greatly reduced by the application of 20 mM acetate, which is known to effectively reduce intracellular pH. Together with the results obtained in situ on the receptive-field properties of skate horizontal cells, these findings indicate that the gap-junctional properties of rod-driven horizontal cells of the skate are fundamentally different from those of cone-driven horizontal cells in other species. This raises the possibility that there is more than one class of electrical synapse on vertebrate horizontal cells.

We have previously reported that during optic nerve regeneration in the frog, 30–40% of retinal ganglion cells die, the loss being complete within 10 weeks. In the present study, we crushed the optic nerve, waited 10 weeks, and then recrushed the nerve at the same site. Retinae were examined 10 weeks later. We estimated ganglion cell numbers from cresyl-violet-stained wholemounts and found a fall of 53% compared to normals. The loss was significantly greater than the losses of 36% and 35%, respectively, in frogs which received a single optic nerve crush and were examined 10 or 20–24 weeks later. The results indicate that a second episode of ganglion cell death took place when the optic nerve regenerated a second time. We conclude that ganglion cells in the frog are not comprised of two subpopulations, only one of which intrinsically possesses the ability to regenerate.

We have investigated the distribution of ON- and OFF-center responses in the lateral geniculate nucleus of ferrets with normal and abnormal retinal projections. Electrophysiological recordings in normal pigmented animals confirm previous studies on mustelids showing that ON-center responses are found in the anterior, inner parts of laminae A and AI and OFF-center responses in posterior, outer leaflets. In albino animals, lamina A displays normal patterns of ON/OFF segregation but in lamina AI, which receives an abnormal crossed retinal projection, no consistent patterns of segregation are found. Following monocular enucleation on the day of birth, the uncrossed projection in pigmented ferrets remains expanded across the LGN. Anatomically and physiologically, this projection is segregated into two leaflets: an anterior, inner ON-center leaflet and a posterior outer OFF-center leaflet. We conclude that the persistence of ON/OFF segregation, independent of geniculate location, suggests that self-sorting of retinal input is an important factor in generating the segregation.

Dendrites of retinal ganglion cells (RGCs) tend to be distributed preferentially toward areas of reduced RGC density. This, however, does not occur in the retina of normal pigmented rats, in which it has been suggested that the centro-peripheral gradient of RGC density is too shallow to provide directional guidance to growing dendrites. In this study, laterally displaced dendrites of RGCs retrogradely labeled with horseradish peroxidase were related to cell density gradients induced experimentally in the rat retina. Neonatal unilateral lesions of the optic tract produced retrograde degeneration of contralaterally projecting RGCs, but spared ipsilaterally projecting neurons in the same retina. These lesions created an anomalous temporal to nasal gradient of cell density across the decussation line, opposite to the nasal to temporal gradient found along the same axis in either normal rats or rats that had the contralateral eye removed at birth. RGCs in rats that received optic tract lesions had their dendrites displaced laterally toward the depleted nasal retina, while in either normal or enucleated rats there was no naso-temporal asymmetry. The lateral displacement affected both primary dendrites and higher-order branches. However, the gradient of cell density after optic tract lesions was less steep than the gradient in either normal or enucleated rats. To test for the presence of steeper gradients at early stages of development, RGC density gradients were also examined at postnatal day 5 (P5). In normal rats, the RGCs were homogeneously distributed throughout the retina, while rats given optic tract lesions at birth already showed a temporo-nasal density gradient at P5. Still, this anomalous gradient was less steep than that found in normal adults. It is concluded that the time course, rather than the steepness of the RGC density gradient, is the major determinant of the lateral displacement of dendritic arbors with respect to the soma in developing RGCs. The data are consistent with the idea that the overall shape of dendritic arbors depends in part on dendritic competition during retinal development.

This study examined the influence of the pontomesencephalic peribrachial region (PBR) on the visual response properties of cells in the dorsal lateral geniculate nucleus (LGN). The response of single cells to a stationary flashing light spot was recorded with accompanying electrical stimulation of the PBR. The major objectives were to compare the effects of PBR stimulation on lagged and nonlagged cells, to examine how the visual response pattern of lagged cells could be modified by PBR stimulation and to examine whether the physiological criteria used to classify lagged and nonlagged cells are applicable during increased PBR input to the LGN. During PBR stimulation, the visual response was enhanced to a similar degree for lagged and nonlagged cells and the latency to half-rise of the visual response was reduced, particularly for the lagged X cells. The latency to half-fall of the visual response of lagged cells was not changed by PBR stimulation. Accordingly, the division of LGN cells into lagged and nonlagged cells based on visual response latencies was maintained during PBR stimulation. The initial suppression that a visual stimulus evokes in lagged cells was resistant to the effects of PBR stimulation. For the lagged cells, the largest response increase occurred for the initial part of the visual response. For the nonlagged cells, the largest increase occurred for the tonic part of the response. The results support the hypothesis that the differences in temporal response properties between lagged and nonlagged cells belong to the basic distinctions between these cell classes.

Monoclonal antibodies to the three isozymes of protein kinase C (PKC) (α, β, and γ) 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-α antibody stained rod bipolar cells throughout the retina. EM analysis confirmed they were PKC-α-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-α-IR, and EM showed them to engage in narrow-cleft ribbon junctions in blue cone pedicles.

The PKC-β 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-β-IR bipolar axons in stratum 2 of the IPL suggests that OFF-center as well as ON-center types were included.

The PKC-γ 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.

We have recorded whole-cell membrane currents in response to exogenously applied acetylcholine (ACh), nicotine, and 1,1 dimethyl-4-phenyl piperazinium iodide on retinal ganglion cells enzymatically dissociated from goldfish retina. Agonist applications induced nicotinic-type responses in a majority of cells when cells were isolated under optimal conditions. Currents were reminiscent of nicotinic-type ganglionic responses. Dose-response measurements of ACh-induced currents indicated an EC50 of 52 μM and a Hill coefficient of 0.6. Currents were selective for Na+ over Cl− and were highly inwardly rectifying. Responses were blocked reversibly by d-tubocurarine, hexamethonium chloride, and N-methyl-D-glucamine. In 50% of the cases, α-bungarotoxin reversibly blocked the current induced by ACh application. The blocking action of mecamylamine was irreversible and independent of the presence of agonist but was more effective in the presence of ACh. We conclude that functional nicotinic ACh receptors exist on most goldfish retinal ganglion cells.

As in other primates, the lateral geniculate nucleus (LGN) of the prosimian primate, bush baby (Galago crassicaudatus), contains three morphologically and physiologically distinct cell classes [magnocellular (M), parvocellular (P), and koniocellular (K)] (Norton & Casagrande, 1982; Casagrande & Norton, 1991). The present study examined quantitatively the center/surround relationships of cells in all three classes. Estimates of receptive-field center size (Rc) and sensitivity (Kc) and of surround size (Rs) and sensitivity (Ks) were obtained from 47 LGN relay cells by fitting a difference of Gaussians function to contrast-sensitivity data. For M and P cells, center size (Rc) increases with eccentricity but is about two times larger for M than for P cells at a given eccentricity. Surround size (Rs) increases with eccentricity for P but not for M or K cells. The center sensitivity (Kc) is inversely related to center size (Rc) and surround sensitivity (Ks) is inversely related to surround size (Rs) for cells in all classes, a result consistent with the sensitivity regulation that is produced by light adaptation. High spatial-frequency cutoff (acuity) is inversely related to center size (Rc). However, the peak contrast sensitivity is relatively independent of Rc. The ratio of the integrated strength (volume) of the surround to the volume of the center remains relatively constant (median, 0.87) across all three cell classes. This ratio is an excellent predictor of a cell’s rolloff in contrast sensitivity at low spatial frequencies: cells with a low surround/center ratio have less low-frequency rolloff. Although M, P, and K cells generally display similar center/surround relationships, differences in center size and the other parameters between the classes distinguish most M, P, and K cells. These findings demonstrate that both similarities and differences in the visual-response properties of primate LGN cells in these three parallel afferent pathways can be explained by basic center/surround relationships.

Recent empirical and theoretical evidence has implicated the geometrical birefringence of the double cones of the green sunfish (Lepomis cyanellus) as the biophysical basis of this vertebrate’s sensitivity to polarized light. Because of the intimate link between the organization of the cone-photoreceptor mosaic and the psychophysical details of polarization sensitivity, we have examined the structural features of the green sunfish cone-photoreceptor mosaic, in particular the orientation of the elliptical cross sections of the double cones. Our primary observations are that (1) the arrangement of the cone-photoreceptor mosaic is constant across the retina (with two regional exceptions), with double cones arranged in a rhombic mosaic and aligned roughly ±45 deg to the nearest retinal margin; (2) the double-cone/single-cone ratio is everywhere the same; (3) cone density is inhomogeneous across the retina, with the highest densities in the temporal hemiretina. These results are discussed as they relate to the animal’s retinal growth and visual mechanisms, particularly the sensitivity to polarized light.

Two discrete areas in frontal cortex are involved in generating saccadic eye movements—the frontal eye field (FEF) and the supplementary eye field (SEF). Whereas FEF represents saccades in a topographic retinotopic map, recent evidence indicates that saccades may be represented craniotopically in SEF. To further investigate the relationship between these areas, the topographic organization of afferents to FEF from SEF in Macaco mulatto was examined by placing injections of distinct retrograde tracers into different parts of FEF that represented saccades of different amplitudes. Central FEF (lateral area 8A), which represents saccades of intermediate amplitudes, received afferents from a larger portion of SEF than did lateral FEF (area 45), which represents shorter saccades, or medial FEF (medial area 8A), which represents the longest saccades in addition to pinna movements. Moreover, in every case the zone in SEF that innervated lateral FEF (area 45) also projected to medial FEF (area 8A). In one case, a zone in rostral SEF projected to both lateral area 8A from which eye movements were evoked by microstimulation as well as medial area 8A from which pinna movements were elicited by microstimulation. This pattern of afferent convergence and divergence from SEF onto the retinotopic saccade map in FEF is indicative of some sort of map transformation between SEF and FEF. Such a transformation would be necessary to interconnect a topographic craniotopic saccade representation in SEF with a topographic retinotopic saccade representation in FEF.