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PubMed2005

Functional GABA(B) receptors are expressed at the cone photoreceptor terminals in bullfrog retina.

GABA(B) receptors at the cone terminals in bullfrog retina were characterized by immunocytochemical and whole-cell patch clamp techniques in retinal slice preparations. Somata, axons and synaptic terminals (pedicles) of cones were both GABA(B) receptor (GABA(B)R) 1 and GABA(B)R2 immunoreactive. Physiologically, barium/calcium currents of cones to voltage steps were significantly reduced in size when GABA was puffed to cone terminals in the presence of picrotoxin that is supposed to block both GABA(A) and GABA(C) receptors. Similar reduction in barium currents was obtained with puff application of baclofen to cone terminals. These results suggest the presence of functional GABA(B) receptors at the bullfrog cone terminals. Suppression of barium currents of cones by baclofen was dose-dependent. Moreover, barium currents of cones were potentiated by background illumination, as compared with those recorded in the dark. 6,7-Dinitroquinoxaline-2,3-dione, an antagonist of non-NMDA receptors that hyperpolarizes horizontal cells and reduces GABA release from these cells, and saclofen, a GABA(B) receptor antagonist, both potentiated barium currents of cones in the dark, thereby mimicking the effects of background illumination. It is suggested that changes in calcium influx into the cone synaptic terminals due to activation of GABA(B) receptors may provide a negative feedback mechanism for regulating signal transmission between cones and second-order neurons in the retina by modifying the amount of glutamate released from the cones.

Animals↗

PubMedDate not supplied

Horizontal cell connections with short-wavelength-sensitive cones in macaque monkey retina.

This study describes the connectivity between horizontal cells and short-wavelength-sensitive (SWS) cones in macaque monkey retina. H1 and H2 horizontal cells were either labelled with the carbocyanine dye, DiI, or injected intracellular with Neurobiotin. The retinas were then processed with an antiserum against human SWS cone pigment, which usually stained the entire SWS cone. In these double-labelled retinas, the pattern of connectivity of H1 (n = 91) and H2 (n = 7) cells with SWS cones has been determined. About 85% of the H1 cells examined do not contact SWS cones. The dendritic terminal knobs of five H1 cells that do contact SWS cones were counted. They have, at most, 3% of their dendritic terminal knobs at SWS cones. All H2 cells examined make contact with SWS cones. The dendritic terminal knobs of one H2 cell were counted; about 11% of the dendritic terminal knobs are at the SWS cone. We conclude that horizontal cells in macaque monkey retina show specific patterns of connectivity to SWS cones.

Animals↗

PubMed2000

Astrocytes and blood vessels define the foveal rim during primate retinal development.

PURPOSE: To investigate the relationship between development of the perifoveal blood vessels and formation of the foveal depression. METHODS: Retinal sections and flatmounts from monkeys aged between fetal day (Fd)80 and 2 years of age were double labeled using antisera to CD31 or von Willebrand factor to detect vascular endothelial cells and antiserum to glial fibrillary acidic protein to detect astrocytes. Sections were studied by fluorescence or confocal microscopy. RESULTS: From Fd88 to 115, vessels on the horizontal meridian were found only at the level of the ganglion cell layer (GCL)-inner plexiform layer (IPL) border where they form the ganglion cell layer plexus (GCP). Stellate astrocytes accompany GCP vessels and extend closer to the fovea than vessels. The foveal avascular zone was present within the GCP at Fd101, and at Fd105 a shallow foveal depression encircled by the GCP was present. The GCP foveal margin had the same dimensions as the adult foveal pit. Both blood vessels and astrocytes were excluded from the emerging fovea throughout development. After Fd140, capillary plexuses in the outer retina anastomosed with the GCP on the foveal slope to form a perifoveal plexus, but this plexus did not mature until a month or more after birth. After Fd142, astrocytes rapidly disappeared from the GCP and most of central retina. CONCLUSIONS: An avascular area is outlined by the GCP before the foveal pit begins to form, suggesting that molecular factors in this region exclude both vessels and astrocytes. These factors may also guide neuronal migration to form the pit. Because the perifoveal plexus is formed during late gestation, both capillary growth and foveal development may be affected adversely by prematurity.

Animals↗

PubMed1978

The eel retina. Receptor classes and spectral mechanisms.

Light and electron microscopy revealed that there are both rods and cones in the retina of the eel Anguilla rostrata. The rods predominate with a rod to cone ratio of 150:1. The spectral sensitivity of the dark-adapted eyecup ERG had a peak at about 520 nm and was well fit by a vitamin A2 nomogram pigment with a lambdamax = 520 nm. This agrees with the eel photopigment measurements of other investigators. This result implies that a single spectral mechanism--the rods--provides the input for the dark-adapted ERG. The spectral sensitivity of the ERG to flicker in the light-adapted eyecup preparation was shifted to longer wavelengths; it peaked at around 550 nm. However, there was evidence that this technique might not have completely eliminated rod intrusion. Rod responses were abolished in a bleached isolated retina preparation, in which it was shown that there were two classes of cone-like mechanisms, one with lambdamax of 550 nm and the other with lambdamax of less than 450 nm. Ganglion cell recording provided preliminary evidence for opponent-color processing. Horizontal cells were only of the L type with both rod and cone inputs.

Animals↗

PubMed2004

Localization of Mel1b melatonin receptor-like immunoreactivity in ocular tissues of Xenopus laevis.

The circadian signaling molecule, melatonin, is produced by pinealocytes and retinal photoreceptors. In the retina, melatonin is thought to diffuse into the inner retina to act as a paracrine signal of darkness by binding to specific receptors in retinal neurons. The retinal cell locations of the Mel1a and Mel1c melatonin receptor types have been reported, but the localization of the Mel1b receptor, which is the most highly expressed melatonin receptor type in the retina, is unknown. To determine the cellular distribution of Mel1b melatonin receptor protein in the Xenopus laevis retina and other ocular tissues, polyclonal antibodies were raised against a peptide fragment of the X. laevis Mel1b receptor. Western blot analysis of several ocular tissues revealed the presence of one or more immunoreactive bands in the sclera, cornea, lens, retinal pigment epithelium (RPE)/choroid, and neural retina. In the neural retina, the major immunoreactive bands displayed electrophoretic mobilities corresponding to approximately 35, 42, 45, and 80 Kd. Sections of X. laevis eyes were analyzed by immunocytochemistry and confocal microscopy, in combination with antibodies against the Mel1a melatonin receptor, a rod photoreceptor-specific protein, opsin, and two amacrine cell-specific markers, tyrosine hydroxylase (TOH; dopaminergic cells) and glutamic acid decarboxylase (GAD; GABA-ergic cells). Mel1b immunoreactivity was localized to the apical membranes of RPE cells, and punctate Mel1b immunoreactivity was observed in both rod and cone photoreceptor inner segments. Presumptive horizontal cells that ramify in the outer plexiform layer (OPL) were immunoreactive for Mel1b, and were exclusive of the Mel1a immunoreactivity present in the OPL. Neither TOH nor GAD co-localized with the Mel1b immunoreactivity that was present in the inner plexiform layer (IPL), suggesting that Mel1b is not expressed in dopaminergic or GABA-ergic amacrine cells. Mel1b immunoreactivity was observed in ganglion cells of the retina, a population of cells covering the outer surface of the outer fibrous layer of the sclera, and in lens fibers located in the outer regions of the lens. These results suggest that melatonin may influence retinal function by binding to receptors on RPE and photoreceptor cells, and by acting on neurons of the inner retina that do not use dopamine or GABA as a neurotransmitter. Furthermore, melatonin may bind to receptors on cells located in the sclera and lens, perhaps to modify the growth or function of these ocular tissues.

Animals↗

PubMed1975

The function of the retina in the perfused eye.

The data show that the enucleated eye of the cat can be maintained in apparently physiologically functioning condition by appropriate arterial perfusion. Under appropriate conditions, photically evoked electrical mass responses can be recorded from various parts of the isolated, perfused eye for 8 to 10 hours. ERGs as well as responses from axonal bundles of the optic nerve exhibit shapes, amplitudes and time courses comparable to their counterparts in vivo. Homeostasis of the perfusion ensures the stability of these light-evoked electrical responses. Transient changes in biophysical parameters of the perfusate rapidly induce marked, although reversible, changes in the amplitudes of b-waves of the ERGs. Increases or decreases in the flow rate of the perfusate induce parallel increases or decreases in the amplitudes of the b-waves as well as of the optic nerve responses. Similar alterations in the oxygen concentration of the perfusate induce similar and proportional changes in the amplitudes of the b-waves. It is concluded, that low flow rates of hemoglobin-free perfusate induce hypoxia; consequently, acceleration of the flow can compensate for hypoxia in a certain range. Previous studies on the effects of and recovery after transient hypoxia in mammalian retina are in concordance with the present data. Progressive decrease of temperature induces gradual and reversible reductions in the amplitudes of the b-waves and increases their latencies and peak-times. It is suggested, that initial hypothermia, which occurs during the period of cannulation, reduces the deliterious effects of the coincident unavoidable hypoxia on retinal neuronal elements. Since light-evoked electrical responses can be maintained for many hours in these preparations and since movements of cardiovascular and respiratory origin, invariably present to varying extent in the in vivo experiments, are eliminated, this preparation is suitable for intracellular recordings from neuronal elements of the retina. Potentials were recorded from cells in various layers of the retina of the cat; intracellular recordings from horizontal cells (S-potentials) are described in detail. Spectral analysis of S-potentials allowed to distinguish between three types according to their inputs: a mixed, rod-cone type, which was most frequently encountered, a pure cone- and a pure rod-type. Light- and electronmicroscopic investigation of the retina after perfusion revealed that (1) the extent of cellular damage depends on the flow rate of the perfusate; (2) little cellular damage is observed if medium flow rates, which maintain physiologic responsiveness of the isolated eye to light, were applied for two hours; (3) high flow rates applied for two hours, or medium flow rates applied for 7 hours appear to induce cystic changes in the pigment epithelium, but only minor changes in the cells of the inner nuclear layer.

Animals↗

PubMed1978

Horizontal cells of the turtle retina. I. Light microscopy of Golgi preparations.

In Golgi preparations of turtle retina, four types of horizontal cells were observed and their morphological characteristics determined in vertical thick sections, whole mount preparations, and reconstructions from serial 1-micrometer sections. H1 consists of a nucleated, stellate cell body (H1CB) and an irregular, tuberous axon terminal (H1AT) connected by a slender axon. Both parts of these cells make contact with receptor cells. H1CB's appear to correspond to "L2-type cells" while H1AT's correspond to "L1-type cells" described in the physiological literature. H2 and H3 are axonless stellate cells which are similar to one another in vertical profile and may occasionally appear similar in horizontal view. In general, the dendritic tree is more densely branched and the density of receptor cell contacts is higher for H2 than for H3. H2-type cells may correspond to "R/G C-type cells." H4 is also an axonless stellate cell type which is smaller than H2 or H3 at equivalent retinal locations. The dendritic fields of H1CB's vary widely, but systematically, in size and shape over the retina. Their size is inversely related to receptor cell density, and the shape of the dendritic tree varies from roughly circular in the central area to elliptical in the periphery of the retina.

Animals↗

PubMed1990

Synapsin I expression in the rat retina during postnatal development.

The expression of the synapsin I gene was studied during postnatal development of the rat retina at the mRNA and protein levels. In situ hybridization histochemistry showed that synapsin I mRNA was expressed already in nerve cells in the ganglion cell layer of the neonatal retina, while it appeared in neurons of the inner nuclear layer from postnatal day 4 onward. Maximal expression of synapsin I mRNA was observed at P12 in ganglion cells and in neurons of the inner nuclear layer followed by moderate expression in the adult. At the protein level a shift of synapsin I appearance was observed from cytoplasmic to terminal localization during retinal development by immunohistochemistry. In early stages (P4 and P8), synapsin I was seen in neurons of the ganglion cell layer and in neurons of the developing inner nuclear layer as well as in the developing inner plexiform layer. In the developing outer plexiform layer synapsin I was localized only in horizontal cells and in their processes. Its early appearance at P4 indicated the early maturation of this cell type. A shift and strong increase of labelling to the plexiform layers at P12 indicated the localization of synapsin I in synaptic terminals. The inner plexiform layer exhibited a characteristic stratified pattern. Photoreceptor cells never exhibited synapsin I mRNA or synapsin I protein throughout development.

Animals↗

PubMed2005

Calbindin and calretinin immunoreactivity in the retina of adult and larval sea lamprey.

The presence of calretinin and calbindin immunoreactivity is studied in the retina of larval and adult lamprey and their respective distributions are compared. Calretinin distribution is also studied in the retina of transforming stages. Western blot analysis in brain extracts showed a 29-kDa band with both polyclonal anti-calbindin and anti-calretinin antibodies. Calbindin and calretinin immunoreactivity has shown a partially different distribution. In the adult retina large and small bipolar cells, with respectively stratified or diffuse axons, the inner row of horizontal cells and ganglion cells and/or some amacrine cells were labeled with anti-calretinin antibody. The anti-calbindin antibody labels the same cell types except most of ganglion cells, but the label was less conspicuous. Therefore, the possible existence of these two calcium-binding proteins in the central nervous system of the sea lamprey could be discussed. In the differentiated central retina of larval lampreys, numerous calretinin immunoreactive bipolar and ganglion cells were observed, while, in the lateral retina, only ganglion cells were labeled, accordingly with the lack of differentiation of other neural cell types. CR-ir bipolar cells appeared in the retina by the stage 5 of transformation, i.e. about the time when differentiation of photoreceptors occurs. The comparison of the distribution of calretinin and calbindin between adult and larval central retina of lampreys shows striking differences that could be related to the different functionality of eyes in these two stages of the life cycle of lampreys. In addition, this is the first report on the presence of calcium-binding proteins in the larval and transforming lamprey retina, on the presence of calretinin- and calbindin-immunoreactive horizontal cells in adult lamprey retinas and on the differential stratification of bipolar cell terminals.

Animals↗

PubMed1994

AE3 anion exchanger isoforms in the vertebrate retina: developmental regulation and differential expression in neurons and glia.

Plasma membrane anion exchangers constitute a multigene family that contributes to the regulation of intracellular pH and chloride concentration in many cell types. We have characterized two polypeptide isoforms of the AE3 gene that are expressed in the rat retina. Using antipeptide antibodies specific for defined NH2-terminal and COOH-terminal epitopes, we have identified a 165 kDa polypeptide whose expression is restricted to the primary glial cell type of the retina, the Müller cell, and a 125 kDa polypeptide that is expressed in horizontal neurons. Expression of the Müller cell isoform exhibits a polarized distribution and is highest in basal endfoot processes. These AE3 isoforms exhibit a distinct developmental expression pattern in postnatal rat retina. The neuronal isoform is undetectable in neonatal retina until postnatal day 10-15, correlating strongly with the onset of retinal function.

Aging↗

PubMed1999

Expression, distribution and ultrastructural localization of the synapse-organizing molecule agrin in the mature avian retina.

At the vertebrate neuromuscular junction the extracellular matrix molecule agrin is responsible for the formation, maintenance and regeneration of most if not all postsynaptic specializations. Several agrin isoforms are generated by alternative splicing which differ in their function and which are all expressed in the CNS. To analyse the role of agrin in the CNS, we investigated the expression and ultrastructural localization of agrin in the posthatched chick retina. In situ hybridization revealed the presence of agrin mRNA in all cellular layers of the mature retina, indicating that most if not all major retinal cell types synthesize agrin. Pan-specific as well as isoform-specific antiagrin antisera stained the optic fibre layer and the outer plexiform layer. However, only the pan-specific antiserum additionally stained the inner limiting membrane. Immunoelectron microscopy showed that in the optic fibre layer agrin was associated with ganglion cell axons and that at least part of this agrin corresponds to a neuronal isoform of agrin. In the outer plexiform layer, agrin was localized in the cleft between the photoreceptor terminals and the invaginating horizontal and bipolar cell dendrites. In the synapse-containing inner plexiform layer both antisera revealed punctate immunoreactivity. This staining corresponded to agrin concentrated in the synaptic cleft of conventional synapses as determined by preembedding immunoelectron microscopy. Agrin is thus concentrated at mature interneuronal synapses as it is at the neuromuscular junction, consistent with a role of agrin during formation and/or maintenance of synapses in the CNS.

Agrin↗

PubMed2005

Early changes in synaptic connectivity following progressive photoreceptor degeneration in RCS rats.

The Royal College of Surgeons (RCS) rat has a retinal pigment epithelial cell defect that causes progressive loss of photoreceptors. Although it is extensively used in retinal degeneration and repair studies, how photoreceptor degeneration affects retinal circuitry has not been fully explored. This study examined the changes in synaptic connectivity between photoreceptors and their target cells using immunocytochemistry and correlated these changes with retinal function using the electroretinogram (ERG). Immunostaining with bassoon and synaptophysin (as presynaptic markers) and metabotropic glutamate receptor (mGluR6, a postsynaptic marker for ON-bipolar dendrites) was already impaired at postnatal day (P) 21 and progressively lost with infrequent pairing of presynaptic and postsynaptic elements at P60. By P90 to P120, staining became increasingly patchy and was eventually restricted to sparsely and irregularly distributed foci in which the normal pairing of presynaptic and postsynaptic markers was lost. ERG results showed that mixed scotopic a-waves and b-waves were already reduced by P21 but not oscillatory potentials. While cone-driven responses (photopic b-wave) reached normal levels at P30, they were impaired by P60 but could still be recorded at P120, although with reduced amplitude; rod responses never reached normal amplitudes. Thus, only cone-driven activity attained normal levels, but declined rapidly thereafter. In conclusion, the synaptic markers associated with photoreceptors and processes of bipolar and horizontal cells show abnormalities prior to significant photoreceptor loss. These changes are paralleled with the deterioration of specific aspects of ERG responsiveness with age. Besides providing information on the effects of photoreceptor dysfunction and loss on connection patterns in the retina, the work addresses the more general issue of how disorder of input neurons affects downstream circuitry.

Age Factors↗

PubMed2005

Topography of pig retinal ganglion cells.

In the present work we analyzed the distribution of retinal ganglion cells (RGCs) in the pig retina. RGCs were retrogradely labeled in vivo by injecting Fluoro-Gold into the optic nerve. RGC density and the distribution of RGCs in terms of soma size were analyzed. Different regions of the porcine retina were identified following analysis of the distribution of RGCs in terms of cell density and soma size: in the central retina, we found a high-density horizontal RGC band lying dorsal to the optic disc. Moreover, in this region, a high proportion of RCGs with small soma size was observed. From the central to the more peripheral retina, we observed a decrease in RGC density, together with a greater presence of RGCs with larger somas. The results of this study should prove to be useful as a foundation for future studies with the porcine retina as a model in ophthalmic research. The study also highlights the necessity to label the RGC population specifically with retrograde tracers in order to quantify precisely alterations in the cell population associated with experimental treatments.

Animals↗

PubMed1994

Distribution of phosphate-activated glutaminase-like immunoreactivity in the retina of rodents.

The distribution of phosphate-activated glutaminase-like immunoreactivity was examined in the retinas of rodents. Intense glutaminase immunoreactivity was observed in many neuronal perikarya in the ganglion cell layer and inner nuclear layer including those of ganglion, bipolar and amacrine cells and possibly horizontal cells. Almost all bipolar cells containing protein kinase C were immunoreactive for glutaminase, suggesting that the majority of glutaminase immunoreactive bipolar cells were of the ON type. Intense glutaminase immunoreactivity was also found in the neuropil of the inner and outer plexiform layers and around the outer limiting membrane. Weak to moderate immunoreactivity was seen in the outer nuclear layer and photoreceptor inner and outer segments. Under electron microscopy, glutaminase immunoreactivity was seen in bipolar cell axons and amacrine cell processes in the inner plexiform layer. In the outer plexiform layer, immunoreactivity was found in the Müller cell processes, but not in the photoreceptor cell terminals. These results indicate that ganglion cells and ON type bipolar cells use glutaminase to produce transmitter glutamate and suggest glutaminase has additional roles in Müller cells. A population of amacrine cells and horizontal cells showed immunoreactivity to glutaminase.

Animals↗

PubMed1999

Distribution of retinogeniculate cells in the tammar wallaby in relation to decussation at the optic chiasm.

Partial decussation of the optic nerve in mammals is related to the laterofrontal placement of the eyes. To investigate this relationship in the wallaby (Macropus eugenii), injections of wheat germ agglutinin-conjugated to horseradish peroxidase were made into one dorsal lateral geniculate nucleus to label retinal ganglion cell bodies in both retinas. Contralaterally, labelled ganglion cells were present across the nasotemporal axis, except for the far temporal retina where they were absent or very sparsely scattered compared with the density of labelled cells at similar nasal eccentricities in the same retinas. Ipsilaterally, labelling was confined to the temporal retina. Cell counts confirmed a visual streak and an area centralis in the contralateral projection. Diameters of labelled cells ranged from 9 microm to 30 microm with a hint of three categories of cells based on size. Only the large alpha-type cells were easily separated. Measurement of the acceptance angles of the eye in the anaesthetised animal showed about 15% of the horizontal visual field of each eye projects into a region of binocular overlap giving a binocular field of 50 degrees . The uniocular visual field extends from -25 degrees (nasally) to + 162 degrees (temporally) in azimuth, giving the wallaby a monocular visual field width of 187 degrees and a total visual field width of 324 degrees . In elevation, field ranges from 70 degrees inferior to +120 degrees superior, encompassing 190 degrees in the vertical plane. The wallaby shows partial decussation of optic nerve fibres projecting to the lateral geniculate nucleus that could allow stereopsis, plus an extensive panoramic field.

Animals↗

PubMed1984

Single cell activity in area 18 of the cat's visual cortex during optokinetic nystagmus.

Single cell activity was recorded in area 18 during optokinetic nystagmus (OKN) in awake cats. The search coil technique was used to record the horizontal and vertical eye movements. Cells showing direction specific responses to a moving large area random dot pattern (70%) were tested with different velocities in the preferred and in the null-direction. Their response characteristics can be classified according to the two phases of the OKN. 41% responded specifically to the retinal slip velocity, having their response optimum at different values between 2 and 100 degrees/s. Additionally, in 60% of all tested cells the resetting saccades of the OKN were correlated with brief activity bursts of 39 ms latency on the average. These results are discussed in terms of two concepts: the classic concept of a corollary discharge from the oculomotor system and the concept of a gating function of the reticular system on thalamic and cortical transmission.

Animals↗

PubMed1983

The distribution of centrifugal terminals in the pigeon retina.

The terminals of the centrifugal fibres of the pigeon retina have been labelled by anterograde axonal transport or diffusion of horseradish peroxidase, and their distribution studied in whole amounts of the retina. Centrifugal terminal arborisations are concentrated in a band near the projection of the horizontal meridian on the retina. Within this band there are high density areas next to the area centralis and in the mid-temporal retina. The arborisations are largely absent from the red field and are nearly randomly arrayed. Their distribution resembles that of the displaced ganglion cells but not of other retinal neurons. We estimate that approximately 7,000 centrifugal terminal arborisations are present in each retina. Approximately two-thirds of these are convergent, with branches ending in large terminals clustered around a single cell in the amacrine sublayer; often penetrating up to 10 microns into the inner nuclear layer. The remainder are divergent endings which innervate a larger area of retina with widely spaced small terminals about 1 micron in diameter. Possible synaptic contacts between centrifugal terminals and displaced ganglion cells are occasionally seen; these contacts and the similarity in distribution suggest a link between the centrifugal and accessory optic systems.

Animals↗

PubMed1998

Neural mechanisms underlying stereoscopic vision.

The progressive frontalization of both eyes in mammals causes overlap of the left and right visual fields, having as a consequence a region of binocular field with single vision and stereopsis. The horizontal separation of the eyes makes the retinal images of the objects lying in this binocular field have slight horizontal and vertical differences, termed disparities. Horizontal disparities are the main cue for stereopsis. In the past decades numerous physiological studies made on monkeys, which have in many aspects a similar visual system to humans, showed that a population of visual cells are capable of encoding the amplitude and sign of horizontal disparity. Such disparity detectors were found in cortical visual areas V1, V2, V3, V3A, VP, MT (V5) and MST of monkeys and in the superior colliculus of the cat and opossum. According to their disparity tuning function, these cells were first grouped into tuned excitatory, tuned inhibitory, near and far sub-groups. Subsequent studies added two more categories, tuned near and tuned far cells. Asymmetries between left and right receptive field position, on and off regions, and intra-receptive field wiring are believed to be the neural mechanisms of disparity detection. Because horizontal disparity alone is insufficient to compute reliable stereopsis, additional information about fixation distance and angle of gaze is required. Thus, while there is unequivocal evidence of cells capable of detecting horizontal disparities, it is not known how horizontal disparity is calibrated. Sensitivity to vertical disparity and information about the vergence angle or eye position may be the source of this additional information.

Depth Perception↗