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Results for “Retinal Horizontal Cells”

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PubMed2003

Stimulation of sodium pump restores membrane potential to neurons excited by glutamate in zebrafish distal retina.

Glutamate either depolarizes or hyperpolarizes retinal neurons. Those are the initial and primary effects. Using a voltage probe (oxonol, DiBaC4 (5)) to study dissociated zebrafish retinal neurons, we find a secondary, longer-term effect: a post-excitatory restoration of membrane potential, termed after-hyperpolarization (AHP). AHP occurs only in neurons that are depolarized by glutamate and typically peaks about 5 min after glutamate application. AHP is seen in dissociated horizontal cells (HCs) and hyperpolarizing, or OFF type, bipolar cells (HBCs). These cells commonly respond with only an AHP component. AHP never occurs in depolarizing, or ON type, bipolar cells (DBCs), which are cell types hyperpolarized by glutamate. AHP is blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). It is evoked by kainate, AMPA and the AMPA-selective agonist (S)-5-fluorowillardiine, but not by NMDA, D-aspartate, the kainate-selective agonist SYM 2081 or by DL-2-amino-4-phosphonobutyric acid (DL-AP4). Cells with exclusively AHP responses are tonically depolarized. Resting potentials can be restored by nifedipine, suggesting a tonic, depolarizing action of L-type Ca2+ channels. However AHP is not blocked by nifedipine and is insensitive to [Cl-]o. AHP is blocked by Li+o substitution for Na+o and by ouabain. A mechanism is proposed in which Na+ entering through ionotropic AMPA channels stimulates Na+,K+-ATPase, which, by electrogenic action, restores membrane potential, generating the AHP response. Patterns of ATPase immunoreactivity support localization in the outer plexiform layer (OPL) as cone pedicles, HCs and BCs were positively labelled. Labelling was weaker in the inner plexiform layer (IPL) than in nuclear layers, though two IPL bands of immunoreactive BC terminals could be discerned, one in sublamina a and the other in sublamina b. Persistent stimulation of distal retina by photoreceptor glutamate may induce increased expression and activity of Na+,K+-ATPase, with a consequent impact on distal glutamate responses.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed2002

[Morphological changes in the parr masou salmon Oncorhynchus masou retina in experimental change of geomagnetic field].

Topography of photoreceptor cells in young salmon Oncorhynchus masou retina, their properties and morphology of cellular organelles in external and internal segments of photoceptors have been first described. Morphological changes of retina cells were analysed in day and night time, and also in the experiment for indemnification of geomagnetic field (GMF) in the body of the aquarium. A comparison of retina structure in fishes of night and day time controls with that in experimental fishes has shown that the external cone segments in the latter occupy, in relation to the external limiting membrane, an intermediate position, characteristic of retinae exposed to twilight lighting. It is supposed that GMF indemnification was equivalent to weak light pulse, which, however, could considerably change melatonin production by retina photoreceptor cells. Thus, at experimental indemnification of GMF, retina sensitive cells demonstrate typical retinomotor response. Some ultrastructural changes in retina cells were also detected, in particular, size changes in ribbon synapses in rod and cone terminations. In addition, nematosomes appeared in the internal nuclear layer, and in the spinules, i.e. digitiform invaginations of terminal dentrites of horizontal cells into cone nervous terminations, the quantity of an electron dense material was noticeably magnified in comparison with a night control. The noted changes testify, in our opinion, to essential modifications in metabolic processes of retina photoreceptors under effect of GMF variations, in particular, to changes in retinal melatonin synthesis.

Animals↗

PubMed1978

Development of the hamster retina: a morphologic study.

Hamster retinas were examined by light and electron microscopy during the first 15 postnatal days and at the adult stage. At birth, these retinas were more primitive than those of other rodents, but eventually they became very similar. Initial postnatal growth and development were more rapid than in other rodents of comparable ages. Mitotic figures were present throughout the first 9 days. The primitive inner plexiform layer formed during days 2 to 4; on day 7, several developmental changes became apparent: outer segment disks of the photoreceptor cells formed from flattened, smooth vesicles, horizontal cells became readily identifiable, the outer plexiform layer appeared, and ribbon synapses formed in the receptor cell axon terminals. By day 11, there were numerous conventional synapses in the inner plexiform layer, and ribbon synapses were beginning to appear in the terminal portions of the bipolar axons. The retinal tissue was progressively invaded by developing vasculature. The first photoreceptor outer segment disks formed from smooth membranous vesicles flattening radially around the ends of the connecting cilium. After the outer segment assumed a more mature appearance, with a stacked disk arrangement, further disk formation occurred by plasma membrane infoldings at the outer segment base. The adult hamster retinas were similar to those of other rodents.

Animals↗

PubMed1996

Absence of spectrally specific lateral inputs to midget ganglion cells in primate retina.

Visual information is conveyed to the brain by the retinal ganglion cells. Midget ganglion cells serve fine spatial vision by summing excitation from a receptive field 'centre', receiving input from a single cone in the central retina, with lateral inhibition from a receptive field 'surround', receiving input from many surrounding cones. Midget ganglion cells are also thought to serve colour opponent vision because the centre excitation is from a cone of one spectral type, while the surround inhibition is from cones of the other type. The two major cone types, middle(M)- and long-(L)wavelength sensitive, are equally numerous and randomly distributed in the primate central retina, so a spectrally homogeneous surround requires that the cells mediating lateral interactions (horizontal or amacrine cells) receive selective input from only one cone type. Horizontal cells cannot do this because they receive input indiscriminately from M and L cones. Here we report that the amacrine cells connected to midget ganglion cells are similarly indiscriminate. The absence of spectral specificity in the inhibitory wiring raises doubt about the involvement of midget ganglion cells in colour vision and suggest that colour opponency may instead be conveyed by a different type of ganglion cell.

Animals↗

PubMed1995

Pattern recognition of amino acid signatures in retinal neurons.

Pattern recognition of amino acid signals partitions the cells of the goldfish retina into nine statistically unique biochemical theme classes and permits a first-order chemical mapping of virtually all cellular space. Photoreceptors, bipolar cells, and ganglion cells display a set of unique, nominally glutamatergic type E1, E1+E2, and E4 signatures, respectively. All horizontal cells are assignable to a GABAergic gamma 2 class or a non-GABAergic class with a glutamate-rich E3 signature. The amacrine cell layer is largely a mixture of (1) a taurine-dominated T1 Müller's cell signature and (2) GABAergic gamma 1, glycinergic G1, and dual glycinergic/GABAergic G gamma 1 amacrine cell signatures. Several major conclusions emerge from this work. (1) Glutamatergic, GABAergic, and glycinergic neural signatures and glial signatures account for over 99% of the cellular space in the retina. (2) All known neurons in the goldfish retina are associated with a set of conventional nonpeptide neurotransmitters. (3) Multiple forms of metabolic profiles are associated with a single nominal neurotransmitter category. (4) Glutamate and aspartate contents exhibit overlapping distributions and are not adequate univariate probes for identifying cell classes. (5) Signatures can serve as quantitative measures of cell state.

Amino Acids↗

PubMed2000

Somatostatin and somatostatin subtype 2A expression in the mammalian retina.

This review discusses the expression and cellular localization of the neuropeptide somatostatin (SRIF) and one of the SRIF subtype (sst) receptors, sst(2A) in the mammalian retina. SRIF immunoreactivity is predominantly localized to a sparse population of amacrine and displaced amacrine cells in the ganglion cell layer in several mammalian retinas including the rat, rabbit, cat, and primate. These cells, characterized by multiple processes, form a sparse network in the inner plexiform layer (IPL) in all retinal regions. Very few processes are also in the outer plexiform layer. In contrast to the predominant distribution of SRIF processes to the IPL, there is a widespread distribution of sst(2A) immunoreactivity to both the inner and outer retina in all mammalian retinas studied to date. In rabbit retina, sst(2A) immunoreactivity is predominant in rod bipolar cells and in sparse wide-field amacrine cells. In the rat retina, sst(2A) immunoreactivity is localized to several neuronal cell types-cone photoreceptors, horizontal cells, rod and cone bipolar cells, and amacrine cells. Reverse-transcriptase-polymerase chain reaction analysis found that sst(2A) mRNA is expressed in the rat retina, while sst(2B) mRNA is not detected. Finally, in the primate retina sst(2) immunoreactivity is predominant in cone photoreceptors, with additional immunostained cell bodies and processes in the inner retina. These findings indicate that SRIF may modulate several neuronal cell types in the retina, and that it has a broad influence on both scotopic and photopic visual pathways.

Animals↗

PubMed1984

Color fundamentals deduced from carp ganglion cell responses.

Retinal ganglion cell responses were used to derive the action spectra (fundamentals) of the photopic color mechanisms in carp. Both silencing and chromatic adaptation techniques were used. The former proved to be more successful than the latter, because weak (even subthreshold) dynamic signals in one mechanism (mostly the red) caused strong effects on the other mechanisms. With chromatic adaptation these interacting signals were unavoidable, whereas with the silencing technique the modulation of the silenced mechanism was eliminated. The resultant pure action spectra agree well with the electrophysiological data of cone pedicles and horizontal cells. They differ, however, from the log-absorption specta found by microspectrophotometry. Apart from the differences in the slope of the long wavelength tails, the spectra also differ in the short wavelength region. The latter may indicate that in A-2 pigments, the beta-band absorption has a lower efficiency than the main-band absorption.

Action Potentials↗

PubMed1996

Spatiotemporal pattern of ontogenetic expression of calbindin-28/kD in the retinorecipient layers of rat superior colliculus.

Using an antibody against calbindin-28kD, we have studied the spatial pattern of expression of this protein in the superior colliculi (SC) of four strains of mature laboratory rats. In all four strains, calbindin-expressing cells (CECs) formed horizontally oriented tiers in the retinorecipient and intermediate gray layers but were diffusely distributed throughout the deep layers. Ontogenetically, calbindin-28kD was expressed for the first time in the retinorecipient layers at postconceptional day 20 (PCD 20), by cells located in the rostrolateral region where the first born retinal ganglion cells (RGCs) are represented. Although on the day of birth (PCD 22/23), the CECs were distributed more widely, they were still absent in the most medial part of the SC, that is, the region where the latest born RGCs are represented. The spatial distribution of CECs became adultlike only by PCD 29, that is, at the end of the period of the naturally occurring death of the RGCs. Monocular eye enucleations on PCD 23 prevented the expression of calbindin in the medial fifth of the retinorecipient layers of the contralateral SC, while the unilateral removal of the visual cortices had no discernable effect on the numbers and distribution of the CECs in either SC. Thus, the spatiotemporal pattern of ontogenetic expression of calbindin-28kD in the retinorecipient layers of SC reflects the spatiotemporal pattern of generation of the RGCs, and the retinal input appears to induce neuronal expression of calbindin-28kD in these layers.

Animals↗

PubMed2002

Axonal neurofilament-H immunolabeling in the rabbit retina.

A monoclonal antibody directed at the multiphosphorylated epitope of axonal neurofilament-H (NF-H) was used to label axon-like fibers in the rabbit retina. NF-H-immunopositive fibers were found in the outer plexiform layer (OPL), inner plexiform layer (IPL), and optic fiber layer (OFL). The morphological characteristics of the labeled processes identified those in the OPL as horizontal cell axons and axon terminals and fibers in the OFL as axons of ganglion cells. The NF-H-positive profiles in the OPL formed a subset of horizontal cell processes labeled for calbindin. In the IPL, NF-H-immunoreactive profiles lay at all levels but were detected most often in the middle strata, 2-4. Occasionally, we observed NF-H-immuoreactive processes emerging from the IPL and entering either the GCL or the inner nuclear layer (INL). The labeled fibers in the IPL were typically very thin, less than 1 microm in diameter, and could often be followed for over 1 mm as they ran laterally across the retina. Cell bodies were never labeled by the immunoserum. To identify the NF-H-immunopositive fibers in the IPL, standard immunocytochemical double-labeling techniques were applied, using antibodies directed against several neurotransmitters or modulators thought to be expressed by axon-bearing amacrine cells. The NF-H-positive processes in the IPL were found to correspond to those labeled for tyrosine hydroxylase, somatostatin, substance P, and NADPH diaphorase activity. However, the NF-H labels did not colocalize with those against the vasoactive intestinal peptide-associated protein PHM27. Our results indicate that putative axons in the retina possess the multiphosphorylated NF-H protein found within classic axons in the central nervous system. These results thus support the idea that certain subtypes of amacrine and horizontal cells maintain true axons in the mammalian retina.

Amacrine Cells↗

PubMedDate not supplied

Tetrachromatic input to turtle horizontal cells.

Recent physiological experiments support behavioral and morphological evidence for a fourth type of cone in the turtle retina, maximally sensitive in the ultraviolet (UV). This cone type has not yet been included in the models proposed for connectivity between cones and horizontal cells. In this study, we examined the inputs of UV, S, M, and L cones to horizontal cells. We used the high-resolution Dynamic Constant Response Method to measure the spectral sensitivity of horizontal cells without background light and after adaptation to UV, blue (B), green (G), and red (R) light. We concluded the following: (1) Tetrachromatic input to a Y/B horizontal cell was identified. The spectral-sensitivity curves of the cell in three of the adaptation conditions were well represented by L-, M-, and S-cone functions. Adaptation to blue light revealed a peak at 372 nm, the same wavelength location as that determined behaviorally in the turtle. A porphyropsin template could be closely fitted to the sensitivity band in that region, strong evidence for input from a UV cone. (2) The spectral-sensitivity functions of R/G horizontal cells were well represented by the L- and M-cone functions. There was no indication of UV- or S-cone inputs into these cells. (3) The spectral sensitivities of the monophasic horizontal cells were dominated by the L cone. However, the shape of the spectral-sensitivity function depended on the background wavelength, indicating secondary M-cone input. Connectivity models of the outer retina that predict input from all cone types are supported by the finding of tetrachromatic input into Y/B horizontal cells. In contrast, we did not find tetrachromatic input to R/G and monophasic horizontal cells. Chromatic adaptation revealed the spectral-sensitivity function of the turtle UV cone peaking at 372 nm.

Adaptation, Ocular↗

PubMed2001

Choroidal infarction, anterior ischemic optic neuropathy, and central retinal artery occlusion from polyarteritis nodosa.

PURPOSE: Ocular ischemia from polyarteritis nodosa (PAN) is rare. The authors present a case of multifocal ocular infarction from PAN. METHODS AND RESULTS: A 70-year-old woman developed hand and foot numbness followed by intermittent blurred vision and binocular horizontal diplopia. Two weeks later, she suddenly lost vision in the right eye from a central retinal artery occlusion and then developed a left anterior ischemic optic neuropathy and bilateral triangular choroidal abnormalities consistent with infarction. Her erythrocyte sedimentation rate and C-reactive protein were elevated. Although giant cell arteritis was suspected, a multiple mononeuropathy was demonstrated by electromyogram and nerve conduction velocity studies. Biopsy specimens from her sural nerve and biceps muscle showed a necrotizing vasculitis with fibrinoid necrosis, consistent with PAN. CONCLUSIONS: Polyarteritis nodosa can produce ischemia of a variety of ocular structures, including the retina, choroid, and optic nerve. In our patient, all three structures were affected. To our knowledge, this is the first reported case of the triangular sign of Amalric in PAN.

Aged↗

PubMed1971

Rod-dependent intracellular responses to light recorded from the pigment epithelium of the cat retina.

1. Intracellular recordings from pigment epithelial cells reveal rod-dependent hyperpolarizing responses to light which are identical with the c-wave of the electroretinogram. These responses were studied as a function of the duration, intensity and area of light flashes and also were compared with rod-dependent horizontal cell responses recorded under similar conditions.2. Because of the long time constant of the response (800 msec), pigment epithelial responses increased in amplitude as flash duration was increased over a wide range. The response reached a plateau at a flash duration of 2.4 sec so that longer flashes only increased the duration of the response. Responses to repetitive flashes, even at a slow rate of 2/sec were integrated to produce a sustained voltage.3. The growth of pigment epithelial response amplitude as a function of flash duration could be divided into two components. The increase in amplitude as flash duration was increased from 5-50 msec was also observed in horizontal cells and was assumed to have originated in the rods. The growth in amplitude with longer flashes was unique to the pigment epithelial response.4. The pigment epithelial response increased in amplitude as spot size was increased, reaching 90% of maximum with an 0.36 mm diameter spot. A precise measurement of the receptive field could not be obtained, because the responses were recorded in the tapetal area of dark-adapted retinas. The b-wave of the local electroretinogram which was ;picked-up' intracellularly exhibited a much greater area effect.5. Pigment epithelial responses increased in amplitude as flash intensity was increased but the amplitude-log intensity functions differed as a function of flash duration. With long flashes (> 2.4 sec) the growth in amplitude was a power function of intensity (exponent = 0.6-0.7) and the response reached an amplitude ceiling at about 3.0 log td scotopic. At higher intensities the responses increased in duration (the rod after-effect). With short flashes, e.g. 480 msec, the responses continued to increase in amplitude with flash intensity well above the intensity needed to produce amplitude-ceilings for rod-dependent responses. This additional increase in amplitude resulted from integration of the rod after-effect by the pigment epithelial response.6. Rod-dependent horizontal cell responses followed the amplitude-log intensity functions that were recorded in pigment epithelial cells with long flashes. The rod after-effect was also the same function of log intensity in both responses.7. It was concluded that the pigment epithelial response is not generated by a late photoproduct. Rather, it appears to depend upon the same mechanism of rod excitation as the horizontal cell response, and the essential characteristics of both rod-dependent responses originate in individual rods.

Animals↗

PubMed1982

Retinotopic organization of extra-retinal saccade-related input to the visual cortex in the cat.

Single unit activity of 842 cells has been recorded in cat visual cortex and analyzed with respect to vestibular induced, and spontaneous saccadic eye movements performed in the dark. This study has been done in awake, chronically implanted cats, subsequently placed in "acute" conditions to achieve the precise retinotopic mapping of the cortical areas previously investigated. In areas 17 and 18, respectively, 27% and 24% of the cells tested were influenced by horizontal saccadic eye movements in the dark (E.M. cells). In the Clare-Bishop area, the proportion of E.M. cells was 12%, while only 2% of such cells were found in areas 19 and 21. The distribution of E.M. cells in areas 17 and 18 with respect to retinotopy showed that E.M. cells were more numerous in the cortical zones devoted to the representation of the area centralis (38% in area 17, 27% in area 18) than in the zones subserving the periphery of the visual field (17% and 12%, respectively). Two of the characteristics of E.M. cell activations appear dependent on the retinotopic organization. First, larger number of E.M. cells presenting an asymmetry in their responses to horizontal saccadic eye movements in opposite directions (directional E.M. cells) were encountered in the cortical representation of the peripheral visual field. 53% of E.M. cells recorded in area 17 and 71% in area 18 were directional in the cortex corresponding to the peripheral visual field. This percentage was of 23% and 25% respectively in the cortex devoted to area centralis. Second, E.M. cells were found to have a latency from the onset of the saccade systematically larger than 100 ms (i.e., they discharged at, or after the end of the eye movement) if they were located in the cortical representation of the area centralis, while E.M. cells related to the peripheral visual field displayed a wider range of latencies (0-240 ms). Results obtained in Clare Bishop area, although limited to the representation of the peripheral visual field, were quantitatively and qualitatively similar to those observed in the homologous retinotopic zones of areas 17 and 18. It is concluded that an extra-retinal input related to oculomotor activity is sent to the cat visual cortex and is organized, at least in areas 17 and 18, with respect to the retinotopic representation of the visual field. These data support the hypothesis of a functional duality between central and peripheral vision and are discussed in the context of visual-oculomotor integration.

Animals↗

PubMed1994

Climbing fiber responses of Purkinje cells to retinal image movement in cat cerebellar flocculus.

1. The complex spike (CS) of the floccular Purkinje cell has been reported to be driven by retinal image movement in the rabbit, the rat, and the monkey, but not yet in the cat, in which the floccular neuronal network is well known. We recorded the CS activity together with concomitant simple spike (SS) activity of the floccular Purkinje cells that responded to large-field visual pattern movement in the anesthetized cat. 2. On the basis of the direction selectivity we divided the cells into two major types: the horizontal type that preferred horizontal stimuli and the vertical type that preferred vertical stimuli. The CS activity of the horizontal-type cell increased during stimuli directed contralaterally to the recording site and decreased during ipsilaterally directed stimuli, whereas that of the vertical-type cell increased during upward stimuli and decreased during downward stimuli. 3. In both types the CS response was larger at lower-velocity stimuli and the response was well maintained at higher-velocity stimuli < or = 180 degrees/s tested. The mean response decline was only 50% at stimulus velocities 90-150 degrees/s compared with the response amplitude at 2 degrees/s stimulus velocity. 4. The majority of the horizontal-type cells were modulated by the stimuli presented to either eye and the dominant eye was ipsilateral to the recording site. The majority of the vertical-type cells were also modulated by the stimuli presented to either eye without obvious differences between two eyes. 5. In both types the receptive field of the ipsilateral eye always included the area centralis and extended widely on both visual hemifields. The receptive field of the contralateral eye also included the area centralis and was usually restricted within the ipsilateral visual hemifield. The stimuli of small visual field (15 degrees x 15 degrees) projecting to the area centralis evoked especially large responses (70% of the full-screen response). 6. The CS and SS responses were reciprocal to each other, that is, when the CS firing increased the SS firing decreased and vice versa. 7. These CS responses are well suited for the direction detection of large-field retinal image motion at a wide velocity range. In light of the present unitary spike data together with the anatomic and eye movement data reported previously, we conclude that the cat flocculus is responsible for reduction of the large-field retinal image motion by producing eye movement in the same direction with the visual motion.

Acceleration↗

PubMed1983

Retinal GABA neuron labelling with [3H]isoguvacine in different species.

Retinas from goldfish, chicken, rate, guinea-pig, rabbit and humans were exposed to [3H]isoguvacine either by intravitreal injection in vivo or by incubation in a balanced salt solution. The distribution of radioactivity was then studied by autoradiography. The substance labelled a set of presumed amacrine cells in all types of animals. The inner plexiform layer was well demarcated and a variable number of ganglion cells was marked. In goldfish and chicken, radioactivity could also be seen in horizontal cells, particularly when the retina had detached from the pigment epithelium. Even 24 hr after an intraocular injection there was a significant amount of radioactivity left in nerve cells. Only a little glial labelling could be seen at any time. Since the distribution of labelled neurones was similar to that of GABA neurones and since isoguvacine is a potent GABA agonist, it seems reasonable to presume that [3H]isoguvacine labels GABA neurones. The uptake is predominantly neuronal with strong binding to presumed GABA storage sites.

Animals↗

PubMed1996

Histopathological and immunocytochemical demonstration of retinal degeneration in the squirrel monkey.

Here we describe the spontaneous appearance of a retinal degeneration in two squirrel monkeys (New World monkey). Since the retinal pathology sufficiently resembles that seen in human degenerative disorder, studies of degeneration in monkeys could contribute to the prevention and treatment of the human disorder. The histopathological examination of horizontal sections comprising the optic disc and the fovea revealed photoreceptor outer and inner segments only in the central fovea. The morphology of the photoreceptors and outer nuclear layer changed rapidly away from the central fovea. There was a loss of outer segments, a shortening of inner segments and disorganized and flattened cells were found in the outer nuclear layer. AO labelling not only detected opsin in the few areas where outer segments were present, but also in the inner segments and the outer nuclear layer. The OS-2 antibody failed to stain the outer segments of the blue sensitive cones. The COS-1 antibody stained many red/green sensitive cones in the fovea, but their density decreased quickly outside this region. Thus, we have detected retinal degeneration in two outbred squirrel monkeys who were being examined for other reasons unrelated to research in retinal degeneration. One was feral and the other was only two generations removed from the feral state. The identification of retinal degeneration in a non-human primate holds great promise for the development of a treatment for human retinitis pigmentosa because access to a primate model would be of invaluable importance for studying the biochemistry behind these disorders.

Animals↗

PubMed1971

Receptive fields of cones in the retina of the turtle.

1. Intracellular recordings have been made of the responses to light of single cones in the retina of the turtle. The shape of the hyperpolarizing response to a flash depends on the pattern of retinal illumination as well as the stimulus intensity.2. Although changes in the stimulus pattern can produce changes in the effective stimulus intensity, the responses to certain patterns cannot be matched by any adjustment of stimulus intensity.3. The initial portion of responses to large or small stimulating spots is proportional to light intensity; this allows comparison of responses when the amount of light on a cone is kept constant but the light on surrounding cones is changed. For equal light intensity on the cone, the response to a spot 2 or 4 mu in radius is smaller than that to a spot 70 mu in radius.4. Responses to spots 70 and 600 mu in radius coincide over their rising phases and peaks without any adjustment of stimulus intensity. The responses to the larger spot, however, contain a delayed depolarization not present with the smaller spot.5. During steady illumination of a cone with a small central spot, the response to transient illumination superimposed on the same area is greatly reduced. Illumination of cones in the near surround, however, produces a hyperpolarizing response, and illumination of cones in the more distant surround generates a delayed depolarization.6. The results described above suggested that synaptic signals might impinge on cones. This possibility was tested by electrically polarizing one retinal cell while recording from another.7. Currents passed through a cone within 40 mu of another cone can change the membrane potential of the latter. Not all cones within this distance show the interaction, however, and it has never been detected at distances greater than 50 mu.8. Hyperpolarization of a horizontal cell with applied current can produce a depolarization of a cone in the vicinity. During this depolarization, the response of the cone to a flash is reduced in size and altered in shape.9. It is concluded that the response of a cone to light may be modified by synaptic mechanisms which are activated by peripheral illumination.

Action Potentials↗

PubMed1996

Retinal slip neurons in the nucleus of the optic tract and dorsal terminal nucleus in cats with congenital strabismus.

1. Visual response properties of neurons in the nucleus of the optic tract (NOT) and dorsal terminal nucleus of the accessory optic tract (DTN) were electrophysiologically investigated in five congenitally strabismic cats and compared with normal adult cats and 3- to 4-wk-old kittens. 2. As in normal cats, NOT-DTN cells of strabismic cats preferred horizontal ipsiversive stimulus movement. However, NOT-DTN neurons in strabismic cats altered their activity to a lesser amount per degree change of stimulus direction than do normal adult cats. In addition, NOT-DTN cells in strabismic cats exhibited a broader directional tuning, i.e., they increase their activity to a broader range of directions than control NOT-DTN cells. 3. Spontaneous activity and activity difference between preferred and nonpreferred direction were significantly lower in NOT-DTN neurons of strabismic cats than in normal adult cats and resembled that found in 3-wk-old kittens. Maximal stimulus-related activity was lower than in normal adult cats but higher than in kittens. 4. Visual latencies to onset of movement in the preferred direction were indistinguishable in strabismic and in normal adult cats. Visual latencies to onset of movement in the nonpreferred direction, however, were shorter in strabismic cats than in normal adult cats. 5. The average velocity tuning curve of NOT-DTN cells in strabismic cats was very flat without a well-defined optimal stimulus velocity. Thus it closely resembled data from 3-wk-old kittens. 6. Binocular convergence was significantly altered to a stronger dominance of the contralateral eye in NOT-DTN of strabismic cats. This reduction of binocular neurons was less pronounced than in cats with artificially induced strabismus or in 3-wk-old kittens. 7. In conclusion, the data presented here for retinal slip neurons in the NOT-DTN of strabismic cats closely resemble those from 3-wk-old kittens where no functional cortical input to the NOT-DTN is present. However, the elevated stimulus-driven activity and the still relatively high degree of binocularity give a clear indication of a functional, albeit weak and abnormal, cortical input to the NOT-DTN in these naturally strabismic cats.

Animals↗