Pigeon Retina Research Articles

Seeing the Forest for the Trees, and the Ground Below My Beak: Global and Local Processing in the Pigeon's Visual System.

Non-human animals tend to solve behavioral tasks using local information. Pigeons are particularly biased toward using the local features of stimuli to guide behavior in small-scale environments. When behavioral tasks are performed in large-scale environments, pigeons are much better global processors of information. The local and global strategies are mediated by two different fovea in the pigeon retina that are associated with the tectofugal and thalamofugal pathways. We discuss the neural mechanisms of pigeons’ bias for local information within the tectofugal pathway, which terminates at an intermediate stage of extracting shape complexity. We also review the evidence suggesting that the thalamofugal pathway participates in global processing in pigeons and is primarily engaged in constructing a spatial representation of the environment in conjunction with the hippocampus.

The expression, localisation and interactome of pigeon CRY2

Cryptochromes (CRY) are highly conserved signalling molecules that regulate circadian rhythms and are candidate radical pair based magnetoreceptors. Birds have at least four cryptochromes (CRY1a, CRY1b, CRY2, and CRY4), but few studies have interrogated their function. Here we investigate the expression, localisation and interactome of clCRY2 in the pigeon retina. We report that clCRY2 has two distinct transcript variants, clCRY2a, and a previously unreported splice isoform, clCRY2b which is larger in size. We show that clCRY2a mRNA is expressed in all retinal layers and clCRY2b is enriched in the inner and outer nuclear layer. To define the localisation and interaction network of clCRY2 we generated and validated a monoclonal antibody that detects both clCRY2 isoforms. Immunohistochemical studies revealed that clCRY2a/b is present in all retinal layers and is enriched in the outer limiting membrane and outer plexiform layer. Proteomic analysis showed clCRY2a/b interacts with typical circadian molecules (PER2, CLOCK, ARTNL), cell junction proteins (CTNNA1, CTNNA2) and components associated with the microtubule motor dynein (DYNC1LI2, DCTN1, DCTN2, DCTN3) within the retina. Collectively these data show that clCRY2 is a component of the avian circadian clock and unexpectedly associates with the microtubule cytoskeleton.

Immunohistological Localization of Mel1a Melatonin Receptor in Pigeon Retina.

BackgroundMelatonin (N-acetyl-5-methoxytryptamine), a significant indoleamine neuromodulator implicated in circadian rhythms and sleep patterns, regulates diverse rhythmic functions via activating its high-affinity G-protein-coupled receptors. However, the detailed cellular expression of the Mel1a receptor in the retina is still a research gap.MethodsThe expression of the Mel1a receptor in pigeon retina was assessed using Western blot analysis and immunofluorescent staining. The cellular localization of the Mel1a receptor was studied using double immunofluorescent staining and laser-scanning confocal microscopy.ResultsOur data suggested that the Mel1a receptor was extensively expressed in the outer segment of Rho4D2-labeled rod and L/M-opsin-labeled red/green cone and in the somata of the CB-labeled horizontal cell, TH-labeled dopaminergic amacrine cell, ChAT-labeled cholinergic amacrine cell, PV-labeled AII amacrine cell, Brn3a-labeled conventional ganglion cell, melanopsin-containing ganglion cell and CRALBP-labeled Müller glial cell. In addition, the Mel1a receptor was diffusely distributed throughout the full thickness of the inner plexiform layer. However, the outer segment of S-opsin-labeled blue cone, the somata of ChX-10-labeled bipolar cell and outer plexiform layer seemed to lack immunoreactivity of the Mel1a receptor.ConclusionThe finding that multiple types of retinal cells express the Mel1a receptor provides a new neurobiological basis for the participation of melatonin in the regulation of retinal functions through activating the Mel1a receptor.

Assessment of the pigeon (Columba livia) retina with spectral domain optical coherence tomography.

BackgroundTo assess the normal retina of the pigeon eye using spectral domain optical coherence tomography (SD-OCT) and establish a normative reference.MethodsTwelve eyes of six ophthalmologically normal pigeons (Columba livia) were included. SD-OCT images were taken with dilated pupils under sedation. Four meridians, including the fovea, optic disc, red field, and yellow field, were obtained in each eye. The layers, including full thickness (FT), ganglion cell complex (GCC), thickness from the retinal pigmented epithelium to the outer nuclear layer (RPE-ONL), and from the retinal pigmented epithelium to the inner nuclear layer (RPE-INL), were manually measured.ResultsThe average FT values were significantly different among the four meridians (p < 0.05), with the optic disc meridian being the thickest (294.0 ± 13.9 µm). The average GCC was thickest in the optic disc (105.3 ± 27.1 µm) and thinnest in the fovea meridian (42.8 ± 15.3 µm). The average RPE-INL of the fovea meridian (165.5 ± 18.3 µm) was significantly thicker than that of the other meridians (p < 0.05). The average RPE-ONL of the fovea, optic disc, yellow field, and red field were 91.2 ± 5.2 µm, 87.7 ± 5.3 µm, 87.6 ± 6.5 µm, and 91.4 ± 3.9 µm, respectively. RPE-INL and RPE-ONL thickness of the red field meridian did not change significantly with measurement location (p > 0.05).ConclusionsMeasured data could be used as normative references for diagnosing pigeon retinopathies and further research on avian fundus structure.

Searching for magnetic compass mechanism in pigeon retinal photoreceptors.

Migratory birds can detect the direction of the Earth’s magnetic field using the magnetic compass sense. However, the sensory basis of the magnetic compass still remains a puzzle. A large body of indirect evidence suggests that magnetic compass in birds is localized in the retina. To confirm this point, an evidence of visual signals modulation by magnetic field (MF) should be obtained. In a previous study we showed that MF inclination impacts the amplitude of ex vivo electroretinogram (ERG) recorded from isolated pigeon retina. Here we present the results of an analysis of putative MF effect on one component of ERG, the photoreceptor’s response, isolated from the total ERG by adding sodium aspartate and barium chloride to the perfusion solution. Photoresponses were recorded from isolated retinae of domestic pigeons Columba livia. The retinal samples were placed in MF that was modulated by three pairs of orthogonal Helmholtz coils. Light stimuli (blue and red) were applied under two inclinations of MF, 0° and 90°. In all the experiments, preparations from two parts of retina were used, red field (with dominant red-sensitive cones) and yellow field (with relatively uniform distribution of cone color types). In contrast to the whole retinal ERG, we did not observe any effect of MF inclination on either amplitude or kinetics of pharmacologically isolated photoreceptor responses to blue or red half-saturating flashes. A possible explanations of these results could be that magnetic compass sense is localized in retinal cells other than photoreceptors, or that photoreceptors do participate in magnetoreception, but require some processing of compass information in other retinal layers, so that only whole retina signal can reflect the response to changing MF.

Investigating Neurogenesis in Birds.

The macula and fovea make human vision unique among mammals. An understanding of the genetic network underlying the development and maintenance of this highly specialized region is instrumental to address issues about human macula-related retinopathies. The pigeon retina, unlike currently available animal models, shares numerous key characteristics of the primate macula and represents a promising new model for the study of retinal development. We provide key elements to take advantage of this new model for the study of retina and brain development. This includes precise embryo staging, transfection of genetic material (reporter plasmid, expression vectors, siRNAs) using in ovo and ex vivo electroporation, live imaging, high-resolution confocal imaging, and data layout and instructions for data analysis.

Cellular localization of melatonin receptor Mel1b in pigeon retina

Melatonin, an important neuromodulator involved in circadian rhythms, modulates a series of physiological processes via activating its specific receptors, namely Mel1a (MT1), Mel1b (MT2) and Mel1c receptors. In this work, the localization of Mel1b receptor was studied in pigeon retina using double immunohistochemistry staining and confocal scanning microscopy. Our results showed that Mel1b receptor widely existed in the outer segment of photoreceptors and in the somata of dopaminergic amacrine cells, cholinergic amacrine cells, glycinergic AII amacrine cells, conventional ganglion cells and intrinsically photosensitive retinal ganglion cells, while horizontal cells, bipolar cells and Müller glial cells seemed to lack immunoreactivity of Mel1b receptor. That multiple types of retinal cells expressing Mel1b receptor suggests melatonin may directly modulate the activities of retina via activating Mel1b receptor.

Delayed neurogenesis with respect to eye growth shapes the pigeon retina for high visual acuity.

The macula and fovea located at the optical centre of the retina make primate visual perception unique among mammals. Our current understanding of retina ontogenesis is primarily based on animal models having no macula and no fovea. However, the pigeon retina and the human macula share a number of structural and functional properties that justify introducing the former as a new model system for retina development. Comparative transcriptome analysis of pigeon and chicken retinas at different embryonic stages reveals that the genetic programmes underlying cell differentiation are postponed in the pigeon until the end of the period of cell proliferation. We show that the late onset of neurogenesis has a profound effect on the developmental patterning of the pigeon retina, which is at odds with the current models of retina development. The uncoupling of tissue growth and neurogenesis is shown to result from the fact that the pigeon retinal epithelium is inhibitory to cell differentiation. The sum of these developmental features allows the pigeon to build a retina that displays the structural and functional traits typical of primate macula and fovea.

Expression of ionotropic glutamate receptors, AMPA, kainite and NMDA, in the pigeon retina

Glutamate is an excitatory neurotransmitter in the vertebrate retina. A previous study found vesicular glutamate transporter 2 (vGluT2) mRNA in the pigeon retina, suggesting that bipolar and ganglion cells are glutamatergic. The present study examined the localization of ionotropic glutamate receptors to identify receptor cells in the pigeon retina using in situ hybridization histochemistry. Nine subunits of AMPA receptor (GluA1, GluA2, GluA3, and GluA4), kainate receptor (GluK1, GluK2, and GluK4), and NMDA receptor (GluN1 and GluN2A) were found to be expressed in the inner nuclear layer (INL) and ganglion cell layers. GluA1, GluA2, GluA3, and GluA4 were primarily expressed in the inner half of INL, and the signal intensity was strong for GluA2, GluA3, and GluA4. GluK1 was intensely expressed in the outer half of INL, whereas GluK2 and GluK4 were mainly localized in the inner half of INL. GluN1 and GluN2A were moderately expressed in the inner half of INL. Horizontal cells expressed GluA3 and GluA4, and ganglion cells expressed all subunits examined. These results suggest that the glutamatergic neurotransmission in the pigeon retina is similar to that in mammals.

Photoreceptor and ganglion cell topographies correlate with information convergence and high acuity regions in the adult pigeon (Columba livia) retina

The fovea and area dorsalis are high acuity vision regions in the pigeon retina. However, the degree of neural convergence (an important determinant of acuity) has not been quantified consistently in this bird. The purpose of the study was to determine the topographic density changes and degree of photoreceptor to ganglion cell convergence in the fovea and the area dorsalis. Total photoreceptor and ganglion cell densities were calculated on the horizontal and vertical meridia. In four eyes, retinal topography was mapped for photoreceptors and ganglion cells. Rod density was quantified by counting anti-rod opsin-stained outer segments across the retina. The ratio of cone photoreceptors to ganglion cells, a rough measure of information convergence, was calculated. The fovea and the red field contained significantly higher mean cone and ganglion cell densities compared with the yellow field. Rods were missing from the fovea. Outside the fovea, rods comprised 20% of the photoreceptor population, with no significant density changes across the retina. The ratio of photoreceptors to ganglion cells was highest in the yellow field, suggesting a high degree of information convergence and low acuity. Our data indicate that convergence of cones onto ganglion cells in the red field is similar to that observed in the fovea. Convergence ratios in both the fovea and red field suggest greater visual acuity compared to that of the surrounding yellow field, which is consistent with the higher visual acuities that have been reported in these regions.

Distribution of vesicular glutamate transporter 2 and glutamate receptor 1 and 2 mRNA in the pigeon retina

Glutamate is an excitatory neurotransmitter in the central and peripheral nervous systems of the vertebrate. The previous studies show the presence of mRNAs of AMPA-type glutamate receptors, GluR1 and GluR2, in the optic tectum of the pigeon, suggesting glutamatergic input from the retina. The present study examined localization of vesicular glutamate transporter 2 (VGLUT2) and GluR1 and GluR2 to confirm source of glutamatergic neurons in the pigeon retina by in situ hybridization histochemistry. VGLUT2 mRNA expressed in the inner nuclear layer and ganglion cells, while GluR1 and GluR2 mRNAs were observed in the inner nuclear layer, ganglion cells, and superficial layers of the optic tectum. The results suggest that photoreceptor cells, bipolar cells and ganglion cells are glutamatergic in the avian retina as in mammals.

The area centralis in the chicken retina contains efferent target amacrine cells

The retinas of birds receive a substantial efferent, or centrifugal, input from a midbrain nucleus. The function of this input is presently unclear, but previous work in the pigeon has shown that efferent input is excluded from the area centralis, suggesting that the functions of the area centralis and the efferent system are incompatible. Using an antibody specific to rods, we have identified the area centralis in another species, the chicken, and mapped the distribution of the unique amacrine cells that are the postsynaptic partners of efferent fibers. Efferent target amacrine cells are found within the chicken area centralis and their density is continuous across the border of the area centralis. In contrast to the pigeon retina then, we conclude that the chicken area centralis receives efferent input. We suggest that the difference between the two species is attributable to the presence of a fovea within the area centralis of the pigeon and its absence from that of the chicken.

A Complex Expression Pattern ofPax6in the Pigeon Retina

The retina of some avian species contains two macular regions, making it an excellent model for retinal, and especially macular, development. Previous studies have provided evidence of the involvement of Pax6 in macular development. The purpose was to perform a comprehensive expression analysis of Pax6 isoforms in different regions of the pigeon retina. The different mRNA transcripts were amplified by RT-PCR and characterized by sequencing analysis. Semiquantitative PCR and quantitative real-time PCR analyses were used to study the level of expression of each transcript. Western blot analysis was performed on both the cytosolic and nuclear cell fractions. An evolutionary analysis of all human-chicken retinal homologues revealed that Pax6 is one of the most conserved retinal genes. By alternative splicing and alternative initiation of transcription, Pax6 produces 41 different mRNA transcripts, encoding 17 protein isoforms in the pigeon retina, five of which are paired-less cytosolic proteins. Semiquantitative expression analysis revealed that the short, paired-less, transcripts have a relatively high level of expression. Quantitative real-time PCR analysis of the central macula, red area, and peripheral retina revealed a spatial and temporal expression profile indicating that many Pax6 transcripts take a part in macular development. These data suggest that Pax6, a highly conserved gene, can maintain evolutionarily conserved variability at the protein level by alternative splicing and initiation mechanisms, allowing it to perform multiple functions. The variability in the length of the paired domain suggests that the different Pax6 isoforms activate different sets of genes.

Sustained upregulation of glial fibrillary acidic protein in Müller cells in pigeon retina following disruption of the parasympathetic control of choroidal blood flow

Choroidal blood flow in pigeon eyes is light driven and controlled by a parasympathetic input from ciliary ganglion (CG) neurons that receive input from the medial subdivision of the ipsilateral nucleus of Edinger–Westphal (EWM). EWM lesions diminish basal ChBF and irreversibly prevent ipsilateral light-evoked increases in ChBF, presumably rendering the retina mildly ischemic. To characterize the location, severity, and time course of the retinal abnormality caused by an EWM lesion, we quantitatively analyzed the cellular and regional extent of Müller cell glial fibrillary acidic protein (GFAP) immunolabeling up to nearly a year after an EWM lesion. We found that unilateral EWM lesions greatly increased Müller cell GFAP throughout the entire retinal depth and topographic extent of the affected eye, up to nearly a year post lesion. By contrast, destruction of the pupilloconstrictive pretectum or of the pupilloconstrictive part of lateral EW (EWL) did not appreciably increase Müller cell GFAP. Thus, the large increase in Müller cell GFAP following an EW lesion is attributable to an ongoing defect in choroidal vasodilatory function rather than to chronic pupil dilation. The Müller cell GFAP increase was greater ipsilateral than contralateral to the EWM destruction for the retinal territory deep to the heavily CG-innervated superior and temporal choroid, but not for the retinal territory deep to the poorly CG-innervated inferior and nasal choroid. The GFAP increase was light-dependent, since it did not occur in EW-lesioned birds housed in dim illumination. Our results show that the chronic vascular insufficiency caused by the loss of the EWM-mediated parasympathetic control of choroidal blood flow leads to a significant and sustained increase in retinal Müller cell GFAP. This increase could be a sign of a disturbance in retinal homeostasis that eventually leads to retinal injury and impaired visual function.

Distribution of ganglion cells in the pigeon retina labeled via retrograde transneuronal transport of the fluorescent dye rhodamine β-isothiocyanate from the telencephalic visual Wulst

The distribution of retinal ganglion cells (RGCs) providing input to the thalamofugal visual system in the pigeon was studied with an anatomical transneuronal transport technique using the fluorescent dye rhodamine β-isothiocyanate (RITC). Unilateral injections of RITC made into the telencephalic visual Wulst resulted in the retrograde (1) first-order labeling (FOL) of dorsal thalamic (n. dorsolateralis anterior and n. superficialis parvocellularis: SPC) and brainstem somata as well as (2) second-order labeling of other cell populations within the brain and of retinal ganglion cells in both eyes obtained after transneuronal transfer of the tracer from neurons labeled directly via FOL. The mapping and counting of labeled RGCs in retinal flat-mounts showed that they were mainly distributed within the nasal portion of the retinal yellow field (YF) and that their total numbers were consistently higher (averaging 57%) in the eye contralateral to the tracer injection. Labeled RGCs in the retinal red field (RF) represented 13.4% and 12.0% of total labeled cells in the ipsilateral and contralateral eye, respectively. Moreover, the average densities of labeled cells/mm 2 in the RF and YF were respectively 8.4 and 42.8 (ipsilateral) and 17.9 and 54.0 (contralateral). The preferential distribution of labeled RGCs within the nasal YF supports the notion that the thalamofugal visual system in the lateral-eyed pigeon is mainly concerned with viewing in the lateral visual field. Conversely, the relatively low numbers of labeled RGCs observed within the specialized RF indicate that, unlike the case in frontal-eyed bird species and mammals, this system does not appear to be involved in binocular visual processing.

Regional Variation in Receptive Field Properties of Tectal Neurons in Pigeons

The present study provides the first electrophysiological evidence for dorsoventral variation in the receptive field properties of tectal cells in pigeons. According to their receptive field organization, visual response properties and laminar locations, 95 tectal neurons recorded in the present study could be categorized into two groups: (1) Fifty-five DL-neurons were recorded in the dorsal, dorso-lateral, lateral and ventro-lateral tectum and characterized by an excitatory receptive field surrounded by an inhibitory receptive field. Most of them almost equally responded to white and black objects, but did not respond to switch-on and -off of a light spot. (2) Forty VC-neurons were recorded in the ventral tectum and characterized by an excitatory receptive field alone. Their responses to switch-on of a light spot and to a white object were significantly stronger than those to light-off and to a black object, respectively. DL-neurons preferred higher velocity, whereas VC-neurons preferred lower velocity. The recording sites of 53 of 95 cells (56%) examined were marked with pontamine sky blue, showing that DL-neurons were located in tectal layers I–IV, predominantly in layer II, whereas VC-neurons were mainly concentrated in sublayer IIc. The receptive fields of VC-neurons were located within the rostroventral visual field possibly corresponding to the red field of the pigeon retina, suggesting that they might be associated with visual food-foraging behaviors.

Immunocytochemical demonstration of taurine in the retina and pineal organ of the pigeon.

Taurine-like immunoreactivity (TLI) is found in the pigeon retina at high levels within cones, in select cells of the inner nuclear layer and in sublaminae of the inner plexiform layer. At the ultrastructural level a high density of immuno-gold particles in visualized in the ellipsoid, but not in the paraboloid area of the inner segment. It is present in perikarya and the presynaptic endings of cones, but not in postsynaptic cell processes. The immuno-gold particles are not associated directly with the synaptic vesicles. In the pineal organ TLI was confined to the so-called dark pinealocytes which are surrounded by only family stained light pinealocytes. Clusters of protein A-gold particles are located in the ergastoplasm between polyribosomes adjacent to fibrous proteins and in chains along filamentous structures. Granules, vesicles and membrane whorls, which originate from modified cilia remain unlabeled. The results are discussed on the basis of previous findings; a direct or indirect functional relationship of taurine to ATP-dependent processes is suggested.

Immunocytochemical demonstration of taurine in the retina and pineal organof the pigeon

Taurine-like immunoreactivity (TLI) is found in the pigeon retina at high levels within cones, in select cells of the inner nuclear layer and in sublaminae of the inner plexiform layer. At the ultrastructural level a high density of immuno-gold particles is visualized in the ellipsoid, but not in the paraboloid area of the inner segment. It is present in perikarya and the presynaptic endings of cones, but not in postsynaptic cell processes. The immuno-gold particles are not associated directly with the synaptic vesicles. In the pineal organ TLI was confined to the so-called dark pinealocytes which are surrounded by only faintly stained light pinealocytes. Clusters of protein A-gold particles are located in the ergastoplasm between polyribosomes adjacent to fibrous proteins and in chains along filamentous structures. Granules, vesicles and membrane whorls, which originate from modified cilia remain unlabeled. The results are discussed on the basis of previous findings; a direct or indirect functional relationship of taurine to ATP-dependent processes is suggested.

Neurotensin-Immunoreactive Ganglion Cells in the Pigeon Retina.

Neurotensin immunocytochemistry was carried out in the pigeon retina after colchicine had been injected into a ventricle of the brain. Immunoreactivity was observed in the ganglion cells and amacrine cells. The ganglion cells were stained in small and large types. This result indicates the presence of neurotensin in the ganglion cells of the pigeon retina.

The photopic sensitivity of the yellow field of the pigeon's retina to ultraviolet light

The photopic spectral sensitivity of the yellow field of the pigeon's retina to UV light was determined electrophysiologically. The sensitivity curve could be approximated with a model in which the activity of only two cone types were incorporated. In this model, the first type of cone had a maximum sensitivity at 366 nm and was combined with an oil droplet that is completely transparent in the UV wavelength range. The second type had a sensitivity maximum at 415 nm and was associated with an oil droplet cutting off light below 390 nm.