Morphology and mosaic of on- and off-beta cells in the cat retina and some functional considerations

The beta type of ganglion cell can be subdivided in Golgi-stained whole mounts of the cat retina according to the branching level of the dendritic tree in the inner plexiform layer. The dendritic branching level of on-beta cells is nearer to the cell body; that of off-beta cells is about 10 micrometers further outwards. After horseradish peroxidase (HRP) injection into the lateral geniculate nucleus all beta cells were labelled. In this way it is shown that about 55% of all ganglion cells, irrespective of retinal topography, are beta cells. The spatial distribution of on- and off-beta cells was studied from the HRP-labelled material. On-beta cells form a lattice with regular inter-cell spacings; off-beta cells are also regularly arrayed. The two lattices are superimposed independently of each other. Beta cells are commonly assumed to be associated with the resolution of fine detail in the cat vision system. The mosaic of beta cells imposes some constraints and permits some predictions to be made with respect to the cat's visual discrimination.     

Morphological identification of on- and off-centre brisk transient (Y) cells in the cat retina

Brisk transient (Y) cells were recorded extracellularly in the cat retina. The position and shape of their receptive field centres were plotted on a tangent screen, together with retinal landmarks, such as blood vessels adjacent to the recording area. After recording the retina was processed as a whole mount and stained with a reduced-silver method (see appendix). This technique stains the entire alpha cell population including the dendritic trees. Alpha cells are the morphological correlate of the brisk transient cells (Boycott & W?ssle 1974; Cleland et al. 1975). Maps of the screen plot and the histological preparation could be accurately superimposed by means of the retinal landmarks and each recorded brisk transient unit could unequivocally be attributed to a particular alpha cell. Alpha cell dendritic trees are unistratified in either of two laminae within the inner plexiform layer: (1) close to the inner nuclear layer border, 'outer alpha cells', or (2) about 10 micrometers further towards the ganglion cell layer, 'inner alpha cells'. This stratification difference can be observed in whole mounts for large populations of cells (W?ssle et al. 1981). Of the recorded brisk transient cells, all on-centre units were inner alphas and all off-centre units outer alphas.     

猫视网膜多巴胺能神经元的形态和发育

Morphology and development of dopaminergic neurons has been studied in the kitten retina, using tyrosine hydroxylase (TH) immunocytochemistry. TH immunoreactive (TH+) cells are already presented in whole amount and sectioned retina at first postnatal day (P1). According to soma size, shape, dendritic process pattern and immunoreactivity, two classes, type I or large dark staining TH+ cells and type II or small light staining TH+ cells are recognized. The TH I cells which consisting of normal placed DA amacrine cells, displaced DA amacrine cells and DA interplex-form-like cells, gradually mature during postnatal development, while TH II cells decrease quickly and through disappear at P30. After eye opening TH I amacrine cells, especially their dendrites develop quickly. The soma diameters increase from 11.8 microns (P1) to 14.2 microns (P30). The dendritic fields increase in size and complexity. At P1 the thick radiating dendrites emerge from the cell body with small or large "spines" and many growth cones. At P13 the dendritic field is markedly enlarged and only a few growth cones can be seen on some stained dendrites. In addition, the dendritic spines are no longer apparent and they are a part of rudimentary rings. By P30 the dendritic plexus of TH+ dendrites and rings in the out most part of IPL, typical of the adult cells, are complete. The influence of light on the development of DA cells after eye opening and the possibility of neurotransmitter changing are discussed.     

Receptive field mechanisms of ganglion cells in the cat retina

On the basis of anatomical and physiological results of the vertebrate retina, a method is proposed for analysing the respective fields of ganglion cells in the cat retina. In the model, we assume the following: (a) Ganglion cells receive their input from bipolar and/or amacrine cells. (b) The nonlinearity of ganglion cell responses is due to the activities of transient type amacrine cells. The method has been proved to be effective. According to the results of this investigation, the receptive field properties of X type and Y type ganglion cells are heterogeneous. Thus, it may be considered that their receptive fields consist of center and surround mechanisms. The receptive field properties of X-cells are almost linear and the X-cells seem to receive most of their input from bipolar cells. On the other hand, the ones of Y-cells are highly nonlinear. Consequently, it is conceivable that the Y-cells receive their input mainly from transient type amacrine cells.     

The nonlinear pathway of Y ganglion cells in the cat retina

Retinal ganglion cells of the Y type in the cat retina produce two different types of response: linear and nonlinear. The nonlinear responses are generated by a separate and independent nonlinear pathway. The functional connectivity in this pathway is analyzed here by comparing the observed second-order frequency responses of Y cells with predictions of a "sandwich model" in which a static nonlinear stage is sandwiched between two linear filters. The model agrees well with the qualitative and quantitative features of the second-order responses. The prefilter in the model may well be the bipolar cells and the nonlinearity and postfilter in the model are probably associated with amacrine cells.     

Topography of horizontal cells in the retina of the domestic cat.

Neurofibrillar methods stain a class of horizontal cells in the cat retina which are shown to be identical with the A-type horizontal cell of Golgi-staining. Thus all of the A-type cells of a single retina can be observed. On this basis the changes in density and dendritic field size of A-type horizontal cells with respect to retinal eccentricity were measured. The decrease in density from centre to periphery is balanced by a corresponding increase in size of the dendritic field. Consequently each retinal point--independent of retinal position--is covered by the dendritic fields of three of four A-type horizontal cells. The nuclei and nucleoli of B-type horizontal cells could also be recognized in neurofibrillar-stained material and thus their distribution was determined. The density ratio B-type: A-type is 2.8 +/- 0.4 and does not vary much from the centre to the periphery of the retina. Each retinal point is also covered by four B-type horizontal cells. Thus a single cone can contact a maximum of eight horizontal cells. The rate of density decrease from centre to periphery is closely similar in cones and horizontal cells but greater in ganglion cells.     

The morphology and topographic distribution of AII amacrine cells in the cat retina

When cat retina is incubated in vitro with the fluorescent dye, 4',6-diamidino-2-phenyl-indole (DAPI), a uniform population of neurons is brightly labelled at the inner border of the inner nuclear layer. The dendritic morphology of the DAPI-labelled cells was defined by iontophoretic injection of Lucifer yellow under direct microscopic control: all the filled cells had the narrow-field bistratified morphology that is distinctive of the AII amacrine cells previously described from Golgi-stained retinae. Although the AII amacrines are principal interneurons in the rod-signal pathway, their density distribution does not follow the topography of the rod receptors, but peaks in the central area like the cone receptors and the ganglion cells. There are some 512 000 AII amacrines in the cat retina and their density ranges from 500 cells per square millimetre at the superior margin to 5300 cells per square millimetre in the centre (retinal area is 450 mm2). The isodensity contours are kite-shaped, particularly at intermediate densities, with a horizontal elongation towards nasal retina. The cell body size and the dendritic dimensions of AII amacrines increase with decreasing cell density. The lobular dendrites in sublamina a of the inner plexiform layer span a restricted field of 16-45 microns diameter, while the arboreal dendrites in sublamina b form a varicose tree of 18-95 microns diameter. The dendritic field coverage of the lobular appendages is close to 1.0 (+/- 0.2) at all eccentricities whereas the coverage of the arboreal dendrites doubles within the first 1.5 mm and then remains constant at 3.8 (+/- 0.7) throughout the periphery.     

Receptor contacts of horizontal cells in the retina of the domestic cat.

The terminal aggregations of A- and B-type horizontal cells, stained by the Golgi-Colonnier method, have been analysed. The pattern of the aggregations is regular and is shown to be in register with the cone mosaic. Both tyes of horizontal cell are in contact with at least 80% of the cones above their dendritic fields. Therefore, the different horizontal cell classes cannot be selective for a special kind of cone but must have at least 60% of the cone input in common. Each A-type horizontal cell makes contacts with between 120 and 170 cones, and each B-type horizontal cell with 60-90 cones. An individual A-type horizontal cell occupies an average of 20% of the lateral elements of the triads in a cone pedicle, but an individual B-type cell fills only some 13%. Each and every cone is connected with several of both types of horizontal cell. An estimation of the number of rods converging onto a single axon terminal system showed that it could be as many as 3000.     

Rhodopsin kinetics in the cat retina

The bleaching and regeneration of rhodopsin in the living cat retina was studied by means of fundus reflectometry. Bleaching was effected by continuous light exposures of 1 min or 20 min, and the changes in retinal absorbance were measured at 29 wavelengths. For all of the conditions studied (fractional bleaches of from 65 to 100%), the regeneration of rhodopsin to its prebleach levels required greater than 60 min in darkness. After the 1-min exposures, the difference spectra recorded during the first 10 min of dark adaptation were dominated by photoproduct absorption, and rhodopsin regeneration kinetics were obscured by these intermediate processes. Extending the bleaching duration to 20 min gave the products of photolysis an opportunity to dissipate, and it was possible to follow the regenerative process over its full time-course. It was not possible, however, to fit these data with the simple exponential function predicted by first-order reaction kinetics. Other possible mechanisms were considered and are presented in the text. Nevertheless, the kinetics of regeneration compared favorably with the temporal changes in log sensitivity determined electrophysiologically by other investigators. Based on the bleaching curve for cat rhodopsin, the photosensitivity was determined and found to approximate closely the value obtained for human rhodopsin; i.e., the energy Ec required to bleach 1-e-1 of the available rhodopsin was 7.09 log scotopic troland-seconds (corrected for the optics of the cat eye), as compared with approximately 7.0 in man.     

The morphology and topographic distribution of substance-P-like immunoreactive amacrine cells in the cat retina

In cat retinal wholemounts, substance-P-like immunoreactivity (SP-IR) was localized in a distinct population of amacrines whose cell bodies were normally placed in the ganglion cell layer. Although displaced amacrines accounted for 80-95% of the SP-IR amacrines in peripheral retina, this proportion decreased considerably within the area centralis, accounting for 50-80% of the labelled cells at maximum density. The SP-IR cells in both the inner nuclear and ganglion cell layers gave rise to well-defined varicose dendrites of uniform appearance that stratified around 60% depth (S3/S4) of the inner plexiform layer. In addition, sparse fine dendrites in stratum 1 (S1) could sometimes be traced to inner nuclear cells and occasionally to displaced amacrines. The combined SP-IR cell density ranged from less than 50 cells mm-2 in the far periphery to more than 500 cells mm-2 in the area centralis; the maximum density showed little individual variation despite wide differences in the proportion of displaced cells. The 39,000 SP-IR amacrines in a mapped retina had a triangular topographic distribution, with intermediate isodensity lines extending vertically in superior retina and horizontally along both arms of the visual streak. Colocalization experiments established that all SP-IR cells in cat retina showed GABA-like immunoreactivity, and that the SP-IR amacrines were quite distinct from the cholinergic amacrines identified by choline acetyltransferase immunohistochemistry.     

Effects of hypoxia on potassium homeostasis and pigment epithelial cells in the cat retina

Intracellular recordings show that light-evoked hyperpolarizations of the apical and basal membranes of the cat retinal pigment epithelium (RPE) are altered by mild hypoxia. RPE cells, like glia, have a high K+ conductance, and measurements with K+-sensitive microelectrodes show that the hypoxic changes in the RPE cell are largely the result of changes in extracellular [K+] in the subretinal space [( K+]o) rather than direct effects on RPE cells. During hypoxia, light-evoked [K+]o responses and membrane responses have longer times to peak, slower and less complete recovery during illumination, and larger amplitudes. In addition to the effects on light-evoked responses, hypoxia causes a depolarization of first the apical and then the basal membranes of RPE cells under dark-adapted conditions. The basal depolarization is accompanied by a decrease in basal membrane resistance. These depolarizations appear to be caused by a rapid increase in [K+]o at the onset of hypoxia, which is maximal in dark adaptation, and smaller if the retina is subjected to maintained illumination. All of the effects are graded with the severity of hypoxia and can be observed at arterial oxygen tensions as high as 65 mmHg, although the threshold may be even higher. We argue that the origin of hypoxic [K+]o changes is probably an inhibition of the photoreceptors' Na+/K+ pump. This work then suggests that photoreceptors are more sensitive to hypoxia than previously believed, and that the high oxygen tension normally provided by the choroidal circulation is necessary for normal photoreceptor function.     

Convergence and divergence of cones onto bipolar cells in the central area of cat retina

In the central area of cat retina the cone bipolar cells that innervate sublamina b of the inner plexiform layer comprise five types, four with narrow dendritic fields and one with a wide dendritic field. This was shown in the preceding paper (Cohen & Sterling 1990 a) by reconstruction from electron micrographs of serial sections. Here we show by further analysis of the same material that the coverage factor (dendritic spread x cell density) is about one for each of the narrow-field types (b1, b2, and b4). The same is probably true for the other narrow-field type (b3), but this could not be proved because its dendrites were too fine to trace. The dendrites of types b1, b2, and b4 collect from all the cone pedicles within their reach and do not bypass local pedicles in favour of more distant ones. The dendrites of type b5, the wide-field cell, bypass many pedicles. On average 5.1 +/- 1.0 pedicles coverage on a b1 bipolar cell; 6.0 +/- 1.2 converge on a b2 cell and 5.7 +/- 1.5 converge on a b4 cell. Divergence within a type is minimal: one pedicle contacts only 1.2 b1 cells, 1.0 b2 cells, and 1.0 b4 cells. Divergence across types is broad: each pedicle apparently contacts all four types of the narrow-field bipolar cells that innervate sublamina b. Each pedicle probably also contacts an additional 4-5 types of narrow-field bipolar cell that innervate sublamina a. There are several possible advantages to encoding the cone signal into multiple, parallel, narrow-field pathways.(ABSTRACT TRUNCATED AT 250 WORDS)     

Flash photolysis of rhodopsin in the cat retina

The bleaching of rhodopsin by short-duration flashes of a xenon discharge lamp was studied in vivo in the cat retina with the aid of a rapid, spectral-scan fundus reflectometer. Difference spectra recorded over a broad range of intensities showed that the bleaching efficacy of high-intensity flashes was less than that of longer duration, steady lights delivering the same amount of energy. Both the empirical results and those derived from a theoretical analysis of flash photolysis indicate that, under the conditions of these experiments, the upper limit of the flash bleaching of rhodopsin in cat is approximately 90%. Although the fact that a full bleach could not be attained is attributable to photoreversal, i.e., the photic regeneration of rhodopsin from its light-sensitive intermediates, the 90% limit is considerably higher than the 50% (or lower) value obtained under other experimental circumstances. Thus, it appears that the duration (approximately 1 ms) and spectral composition of the flash, coupled with the kinetic parameters of the thermal and photic reactions in the cat retina, reduce the light-induced regeneration of rhodopsin to approximately 10%.     

Morphology of the cat auditory cortex

The ultrastructural features of the primary auditory cortex of the cats and the character of the endings of geniculo-cortical afferent fibers in the early stages of experimental degeneration evoked by destruction of the medial geniculate body were studied. In all layers of the cortex asymmetrical synapses with round synaptic vesicles on dendritic spines and on thin dendritic branches of pyramidal and nonpyramidal neurons are predominant. Symmetrical synapses with flattened or polymorphic vesicles are distributed chiefly on the bodies of the neurons and their large dendrites. Because there are few symmetrical synapses which could be regarded as inhibitory it is postulated that inhibitory influences may also be transmitted through asymmetrical synapses with round vesicles. Other types of contacts between the bodies of neurons, dendrites, and glial processes also were found in the auditory cortex. Degenerating terminals of geniculo-cortical fibers were shown to terminate chiefly in layer IV of the cortex on pyramidal and nonpyramidal neurons. Degeneration was of the dark type in asymmetrical synapses with round vesicles. The results are dicussed in connection with electrophysiological investigations of the auditory cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 519–524, September–October, 1973.     

A distinct centro-peripheral gradient of development in dopaminergic amacrine cells of cat retina

The centro-peripheral gradient of development in dopaminergic (DA) amacrine cells of cat retina has been studied by TH immunocytochemical method. Type I of TH immunoreactive neurons is typical DA cell. They reveal a clear centro-peripheral gradient of differentiation and maturation in space and time course during postnatal development. (1) At P1 stage, the TH I cells vary in TH immunoreactivity, soma sizes and dendritic maturation. Responding to degree of development, they can be divided into I1, I2 and I3. The more differentiated I1 cells, larger and darkly immuno-stained stellate cells mostly concentrates at central retina, while the less differentiated I3 cells, smaller and lightly immunostained irregular cells concentrate at peripheral retina. I2 cells of moderate differentiation distribute over all the retina. (2) During the postnatal development, from P1 to P13, the dense area of the TH I1 cells spreads peripherally in company with the increase of the total number of TH I1 cells, comprising the central 30% of the retina at P1, 65% at P6 and almost the whole of the retina by P13. After eye opening, as the TH I cells have spread at far peripheral region, the differences in soma diameters and dendritic maturation of TH I cells between central and peripheral retina decrease gradually and the centro-peripheral gradient of maturity of TH I cells becomes less distinct. At P23, no significant difference is visible in either soma diameter or dendritic maturation in these two areas: thus, the centro-peripheral gradient is no longer apparent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Photopic action of thyrotropin-releasing hormone in the cat retina

The effects of iontophoretically applied thyrotropin-releasing hormone (TRH) on cat retinal brisk-sustained(X) and brisk-transient(Y) ganglion cells were studied in the intact eye in vivo. Under photopic illumination we found a differential action of TRH on ON- and OFF-centre cells: the maintained activity and light response were suppressed in ON-centre cells and enhanced in OFF-centre cells. This was true for both brisk-sustained(X) and brisk-transient(Y) cells. In contrast, TRH did not influence the ganglion cell discharge under scotopic stimulus conditions. These results indicate that TRH acts on neurons presynaptic to ganglion cells and these neurons are only active under photopic conditions. We suggest that a possible functional role of this specific action of TRH is in light adaptation.     

Morphology of the giant nerve cells in the bovine retina. Study of silver-impregnated total specimen

Application of several silver impregnation methods on whole mounts of the bovine retina selectively elicits the giant ganglion cells of the peripheral retina. As determined by the branching pattern of their dendrites they coudl be classified in three types: 1. predominant branching in one directions; 2. branching in two opposite direction; 2. branching in two opposite directions; 3. branches radiate in all directions. Cells of the first type were mainly found in the temporal and dorsal (superior) segment; those of the second type in the nasal part; those of the third type were present in the ventral (inferior) part of the peripheral retina. The sizes of their dendritic fields differ. Another ganglion cell with a large perikaryon was found infrequently in each retina; its dendrites are located in the inner plexiform layer, ending with occasionally large knob- or clubshaped tips. An axon was never found. Evidently, they show a special topographical relationship to the blood vessels. Their function is as yet unknown.