DOS, a novel pleckstrin homology domain-containing protein required for signal transduction between sevenless and Ras1 in Drosophila

The specification of the R7 photoreceptor cell in the developing eye of Drosophila is dependent upon activation of the Sevenless (SEV) receptor tyrosine kinase. By screening for mutations that suppress signaling via a constitutively activated SEV protein, we have identified a novel gene, daughter of sevenless (dos). DOS is required not only for signal transduction via SEV but also in other receptor tyrosine kinase signaling pathways throughout development. The presence of an amino-terminally located pleckstrin homology domain and many potential tyrosine phosphorylation sites suggests that DOS functions as an adaptor protein able to interact with multiple signaling molecules. Our genetic analysis demonstrates that DOS functions upstream of Ras1 and defines a signaling pathway that is independent of direct binding of the DRK SH2/SH3 adaptor protein to the SEV receptor tyrosine kinase.

Monitoring for clenbuterol abuse in N. Ireland 1989-1994

Laboratory testing in N. Ireland for the illegal growth promoting agent, clenbuterol (CBL), is centralized at the Veterinary Sciences Division, Belfast. During the past 6 years a variety of testing schemes have evolved to determine the level of abuse of this drug in the local meat industry. The types of samples from cattle tested during this period altered as pharmacokinetic data for the compound increased. Initially, fluids such as urine and bile were used, however testing switched to more appropriate tissues such as liver, eyes, and hair. The first positive samples were detected in 1990, with 43 out of 121 samples tested showing detectable residues. In the following year, this number increased to 139 out of 286 tests. Despite substantial increases in the number of samples analysed over the succeeding years, the numbers of positive results steadily declined, thus giving strong evidence that abuse was also on the decline. From the data collected over the 6-year period, it became clear that the EU National Surveillance Scheme designed to detect abuse of illegal substances was ineffective and locally designed programmes were required to effectively tackle the problem.

Localization of mRNAs for insulin-like growth factor-I (IGF-I), IGF-I receptor, and IGF binding proteins in rat eye

PURPOSE

To localize mRNAs for insulin-like growth factor (IGF)-I, IGF-I receptor (IGF-IR), and IGF binding protein (BP)-1 to IGFBP-6 in the rat eye.

METHODS

cDNA sequences for IGF-I, IGF-IR, and IGFBP-1 to IGFBP-6 were used to synthesize 35S-CTP labeled antisense and sense probes for in situ hybridization on 5-microns sections of the rat eye, including the retina, choroid, sclera, ciliary body, and cornea.

RESULTS

IGF-I mRNA was demonstrated over ganglion cells of the retina and endothelial cells of the choroid and ciliary processes. IGF-IR mRNA showed more extensive distribution, localizing to the retinal ganglion cell layer, inner nuclear layer, and outer limiting membrane and also the outer nonpigmented epithelium of the ciliary processes and cornea, conjunctiva, and lens. IGFBP-2 mRNA localized to outer nonpigmented epithelia of the ciliary processes and the germinal layer of corneal epithelium as well as iris, conjunctiva, and sclera. Messenger RNAs for IGFBP-3 to IGFBP-6 localized to choroidal endothelial cells and chromatophores and also to the inner pigmented epithelium of the ciliary processes. Messenger RNAs for IGFBP-5 and IGFBP-6 were seen in the inner and outer nuclear layers of the neural retina. IGFBP-1 mRNA was not detected within the rat eye.

CONCLUSIONS

Using in situ hybridization, we have demonstrated mRNAs for IGF-I, IGF-IR, and IGFBP-2 to IGFBP-6 in specific histologic layers of the retina, choroid, ciliary body, and cornea in the rat. The characterization of the IGF system in vivo suggests specific roles in the normal eye and provides a basis for studying the IGF system in eye pathology.

Detection of neuron-specific protein gene product (PGP) 9.5 in the rat and zebrafish using anti-human PGP9.5 antibodies

Protein gene product (PGP) 9.5 is a developmentally regulated neuron- and neuroendocrine cell-specific ubiquitin carboxy-terminal hydrolase (UCHL1) expressed throughout the mammalian central and peripheral nervous systems. We have compared the use of monoclonal and polyclonal antibodies raised against human PGP9.5 for immunodetection of the protein in tissues of the zebrafish and rat. We show that a monoclonal antibody 13C4, which recognises an N-terminal epitope, detects PGP9.5 on Western blots as a single 27 kDa band present at high levels in zebrafish and rat brain. By contrast, the polyclonal antisera recognises multiple tissue-specific proteins in the rat and fails to detect PGP9.5 in the zebrafish. Finally, we have developed a specific ELISA assay for detection of cellular PGP9.5 using MAb13C4 and have employed the assay to show that PGP9.5 is not upregulated during nerve growth factor (NGF)-induced differentiation of rat PC12 cells.

Localization of the prostaglandin F2 alpha receptor messenger RNA and protein in the cynomolgus monkey eye

PURPOSE

To determine the distribution of the prostaglandin F2 alpha (FP) receptor within the monkey eye.

METHODS

The expression and localization of the FP receptor was studied by in situ hybridization and immunohistochemistry. Cryosections of the eye were hybridized with a 35S-labeled FP receptor riboprobe, and paraffin sections were immunostained with polyclonal antibodies against an FP receptor peptide. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed on cultured cell populations from the eye.

RESULTS

Results of the three methods largely correlated with each other. The highest expression of FP receptor mRNA and protein was found in the corneal, conjunctival, and iridial epithelium, the ciliary muscle, and ciliary processes. Iridial and choroidal melanocytes, the retina, and the optic nerve expressed lower levels of both FP receptor message and protein. Using immunohistochemistry, the FP receptor protein was found in connective tissue fibroblasts, the corneal endothelium, and the vasculature; however, FP receptor expression was not detected using in situ hybridization. With RT-PCR, cultured retinal pigment epithelial and ciliary muscle cells from the cynomolgus monkey eye were found to express the FP receptor.

CONCLUSIONS

The FP receptor was found to be distributed widely in the ocular tissues, suggesting an array of autocrine and paracrine functions of PGF2 alpha in the eye.

Expression of TGF-beta type I and type II receptors in rat eyes

Transforming growth factor beta (TGF-beta) transduces signals through mediation of type I and type II serine/threonine kinase receptors. The expression of TGF-beta type I (T beta R-I) and II (T beta R-II) receptors in rat eyes was investigated immunohistochemically. T beta R-I and T beta R-II immunoreactivity was detected in corneal and conjunctival epithelial cells, corneal endothelial cells, ciliary epithelial cells, lens epithelial cells, retinal pigment epithelial cells, and choroidal vessels. This co-expression of T beta R-I and T beta R-II indicates that the above cells respond to TGF-beta and, because TGF-beta is reported to be produced in ocular tissues, that it may have important autocrine and/or paracrine roles in the growth and metabolism of ocular tissues in situ.

Eye ancestry: old genes for new eyes

The vast differences between vertebrate and arthropod eyes suggest that the recently discovered homologous master control genes for eye development had another function before eyes evolved in the early Cambrian.

Histological study of oxalosis in the eye and adnexa of AIDS patients

Review of a series of 98 eyes removed at autopsy from 86 AIDS patients identified 12 cases (14%) showing varying degrees of microscopic calcium oxalate deposition. The oxalate crystals were birefringent using polarisation microscopy and were stained histochemically by the silver nitrate-rubeanic acid method (Yasue), a stain considered to be specific for calcium oxalate. In two cases, the deposition was extensive and involved the surface of the ciliary processes, ciliary body and pars plana of the retina, the retinal and optic nerve blood vessel wall, a few retinal pigment cells, and the anterior inner sclera. A lesser degree of intraocular involvement was observed in the remaining 10 cases. In all but two eyes, where a peripheral active area of cytomegalovirus retinitis was present, no other significant microscopical abnormality was found. Clinically, these patients were asymptomatic. At autopsy, oxalate deposits were found in the kidney and/or thyroid in seven of the patients.

Differentiation of photoreceptors, glia, and neurons in the retina of the cichlid fish Aequidens pulcher; an immunocytochemical study

Light-microscopic immunocytochemistry was carried out to investigate the developmental dynamics of several neurochemical markers in the retina of blue acara (Aequidens pulcher). As a rule, double-label experiments were performed in order to determine the absolute and relative timing of the appearance of these markers. The diameter of eye-ball (from 0.6 to 1.2 mm) and the body length (from 4.6 to 9.4 mm) enlarged in parallel during the observation period of 2 to 9 days after spawning (day 2-9); hatching took place usually on day 2. Immunoreactive proliferating cell nuclear antigen (ir-PCNA) was present in all neuroblasts (the embryonic homogeneous cell stage; day 1.0-2.0), but was lost progressively in a center-to-periphery and apparent proximal-to-distal sequence as the cells and layers differentiated. In late larvae and juveniles, ir-PCNA was confined to a ring of dividing neuroblasts at the retinal margin and to a population of scattered rod precursors in the outer nuclear layer. Immunoreactive structures of representative antigens progressively appeared after ir-PCNA had decayed. Around hatching, at the synaptic separation stage (day 2.0-2.5), luteinizing hormone-releasing hormone-ir centrifugal fibers, visinin-ir cones, glial fibrillary acidic protein-ir structures and gamma-aminobutyric acid-ir cell bodies appeared, which were followed by the emergence of rhodopsin-ir rods and tyrosine hydroxylase-ir interplexiform cells (on day 2.5-3.0) and serotonin-, neuropeptide Y- and substance P-ir amacrine cells (on day 3.0-4.0). The results indicate that photoreceptor cells, and especially rods start to differentiate at an earlier stage of retinogenesis than has previously been proposed. In addition, an extraretinal tissue in the brain identified as the prospective pineal organ was found to be visinin- and rhodopsin-immunoreactive on day 1.5-2.0 before these photoreceptor-specific antigens became positive in the retina.

Immune corticotropin-releasing hormone is present in the eyes of and promotes experimental autoimmune uveoretinitis in rodents

We examined the presence and potential role of local corticotropin-releasing hormone (CRH) in experimental uveitis in rodents. This 41-amino acid peptide, originally isolated from the hypothalamus, is also secreted locally in experimentally induced and natural inflammatory sites, where it exerts autocrine or paracrine proinflammatory effects. Female Lewis rats were immunized with the major pathogenic epitope (R16 peptide) of the interphotoreceptor retinoid-binding protein in complete Freund's adjuvant, monitored daily, and killed 8, 9, 10, 12, 14, or 18 days later, after having developed uveoretinitis. Immunoreactive CRH (IrCRH) was detected by immunohistochemistry in the uveitic eyes in the cytoplasm of inflammatory cells (macrophages, lymphocytes, and polymorphonuclear cells) infiltrating the iris, ciliary body, vitreous, retina, and choroid depending on the stage of the disease. The intensity of the IrCRH staining was positively correlated with the severity of the disease based on morphological criteria. The amount of IrCRH measured by RIA varied between 0.18 +/- 0.03 (mean +/- SE) and 0.79 +/- 0.07 pmol/g wet tissue (8th and 14th day of the disease, respectively). Ophthalmic IrCRH in uveitic rat eyes had similar chromatographic mobility as rat/human CRH-(1-41) by HPLC. Furthermore, female B10.A mice were immunized with interphotoreceptor retinoid-binding protein and treated during the induction (0-7 days) or expression (8-16 days) stages of the disease with ip injections of the anti-CRH antibody TS-2 or placebo nonimmune rabbit serum. The early anti-CRH treatment significantly decreased the disease intensity compared to that in placebo- or late-treated animals (P < 0.05, by analysis of variance). We conclude that IrCRH is present at the site of inflammation in rodent experimental uveitis and that its expression correlates with the natural history and intensity of the disease. Immune CRH appears to play an early pathogenetic role in the induction of experimental uveitis.

Localization of a corneal basement membrane glycoconjugate in bovine eye

Lectin histochemistry was used to analyze the ocular surface basement membrane in order to identify novel, tissue-specific glycoconjugates. Soybean agglutinin (SBA), a lectin marker for N-acetylgalactosamine residues, recognized a 130 kDa glycoconjugate in corneal but not conjunctival basement membrane. Following corneal epithelial cell wounding in vitro, the glycoconjugate was not expressed at the epithelial cell-stromal interface until 72-96 h in culture, much later than the expression of other basement membrane molecules. In epithelial cells maintained on various extracellular matrix substrates (laminin, collagen type IV, or a mixture of laminin, collagen type IV and heparan sulfate proteoglycan), the glycoconjugate localization patterns changed with time in culture from a diffuse cellular or perinuclear ring to an extensive extracellular filament network. The presence of SBA in the culture medium did not affect migration or adhesion in either the wound healing model or in culture cells. However, the presence of SBA did delay the deposition of laminin at the zone of basement membrane reformation in the wound healing model. The 130 kDa glycoconjugate is a candidate for molecules which impart a tissue-specificity to the corneal basement membrane, and which may be involved in cell-matrix interaction.

Presence of beta-citryl-L-glutamic acid in the lens: its possible role in the differentiation of lens epithelial cells into fiber cells

The beta-CG concentration in the chicken brain was high during embryonic development and decreased rapidly to a lower level close to hatching, while the concentration in the eyeball which was also high during the embryonic life retained a fairly high level after hatching. The distribution of beta-CG in the bovine eye was determined. About 95% of total beta-CG content in the whole eye was localized in the lens. However, the distribution of beta-CG in the eye varied depending on species. beta-CG was exclusively localized in the lens in the eyes of fish and mammals, but distributed in both lens and retina in frogs. The molecule was localized in the retina rather than the lens in the chicken eye, although the concentrations was extremely low compared to those in the mammalian, amphibian and fish eyes. It was found that beta-CG is present ubiquitously in the lens or retina in various species. The distribution of beta-CG in the bovine lens was determined in the three cortex regions and nucleus. beta-CG was present at the highest concentration in the equatorial cortex, at a moderate concentration in the posterior and anterior cortex, and at the lowest concentration in the nucleus. Similar distribution patterns were also found in the rabbit and rat lens. When embryonic chick lens epithelial cells were cultured in the presence of fetal calf serum, the cells elongated, differentiated into fiber cells and formed lentoid bodies. The cells of lentoid bodies were stained strongly by the anti-beta-CG antibody, while cells around the structures were not. In addition, the beta-CG content in the lenses from the galactose cataractous rat decreased to about 20-30% of that in the normal lens. These findings suggest that beta-CG may play a role in the differentiation of epithelial cells into fiber cells.

Regulation of growth factor mRNA levels in the eyes of diabetic rats

The underlying etiology of diabetic microvascular disease remains unknown. To examine the potential contribution of basic fibroblast growth factor (bFGF), which is an angiogenic factor, and insulin-like growth factor-I (IGF-I) to the development of diabetic microvascular disease, bFGF and IGF-I mRNA levels were measured in tissues of control, diabetic, and insulin-treated diabetic rats. Diabetes was induced in rats by intravenous injection of streptozotocin (STZ) 65 mg/kg, and the rats were maintained for 21 days. bFGF mRNA levels increased threefold in the eyes of diabetic versus control rats, whereas a consistent change in bFGF mRNA levels was not observed in other tissues. In contrast, IGF-I mRNA levels decreased in the eyes and other tissues, including kidney, lung, and skeletal muscle, of diabetic as compared with control rats. Insulin treatment prevented the diabetes-induced increase in bFGF and decrease in IGF-I mRNA levels. Acidic FGF (aFGF) mRNA levels were unchanged in eyes from diabetic versus control rats. In partially purified retinas, diabetes increased bFGF mRNA levels twofold as compared with levels in control retinas, whereas IGF-I mRNA levels decreased to 58% of control levels in retinas from diabetic rats. Insulin treatment again prevented the diabetes-induced increase in IGF-I mRNA levels in the retina but had no effect on the diabetes-induced increase in bFGF mRNA levels. bFGF peptide levels were minimally increased in diabetic versus control retinas.(ABSTRACT TRUNCATED AT 250 WORDS)

Accumulation of the beta-agonist clenbuterol by pigmented tissues in rat eye and hair of veal calves

Two independent experiments were carried out to determine whether Clenbuterol is accumulated by pigmented tissues. In the first experiment, unpigmented and pigmented rats were injected two times with 5 micrograms of Clenbuterol subcutaneously and the eyes were analyzed after 63 h of withdrawal by enzyme immunoassay. Only pigmented rat eyes showed a clear accumulation of Clenbuterol (68.1 to 81.5 ng/g), whereas the eyes of unpigmented treated rats demonstrated levels similar to the negative controls (< .27 ng/g). In the second experiment, two Holstein-Friesian calves were fed with .8 microgram of Clenbuterol/kg BW two times a day (therapeutic dose) in milk replacer and black and white hair was collected separately before, during, and after the treatment. The hair was analyzed with an enzyme immunoassay that provided blanks less than 1.0 ng/g and a mean recovery of 67%. This experiment showed an accumulation of Clenbuterol in both sets of hair, but a definitely higher accumulation of Clenbuterol in black (pigmented) hair than in white hair. The black/white quotient amounted to approximately 50 at 1 wk after treatment. Results of these experiments favor the use of the eye as well as the hair for residue analysis but in case of hair, variation of pigmentation in different animals must be considered.

Effects of ground flaxseed in swine diets on pig performance and on physical and sensory characteristics and omega-3 fatty acid content of pork: I. Dietary level of flaxseed

Forty-eight barrows and gilts were fed diets containing 0 (CO), 5, 10, or 15% ground flaxseed (FS) for the final 25 d before slaughter. Flaxseed treatments did not affect any production or carcass traits (P > .10). No pork processing problems due to lack of firmness were encountered. Amounts (milligrams/gram of tissue) of alpha-linolenic acid (ALA [18:3n-3]) and eicosapentaenoic acid (EPA [20:5n-3]) increased (P < .01) in both backfat layers and ALA increased (P < .01) in kidney (leaf) fat after FS. Alpha-linolenic acid and EPA increased (P < .001) in the raw belly in response to FS; the effect was maintained throughout processing (P < .01) to microwaved bacon. Alpha-linolenic acid and EPA increased (P < .01, P < .05, respectively) with amount of FS in longissimus thoracis and liver. In the brain, DHA decreased (P < .05) with amount of FS. Trained panelists in triangle tests were able to identify bacon from pigs fed 10 and 15% flaxseed. Panelists could not identify various treatments in the loin tests.

Control of Drosophila photoreceptor cell fates by phyllopod, a novel nuclear protein acting downstream of the Raf kinase

The phyllopod (phyl) gene regulates the fates of a subset of cells in the developing Drosophila eye; in the absence of phyl function, the R1, R6, and R7 photoreceptors are transformed into additional cone cells, whereas ectopic phyl expression in the cone cell precursors transforms these cells into additional R7 cells. Within this group of cells, phyl expression thus mimics activation of the Raf pathway in its ability to induce photoreceptor rather than cone cell development. Furthermore, the transformation of cone cells into R7 cells in response to Raf activation is both accompanied by and dependent upon ectopic phyl expression. phyl thus represents a possible target gene of the Raf pathway during eye development, controlling the fates of a novel subset of photoreceptors.

Localisation of glycoproteins and glycosaminoglycans during early eye development in the macaque

The composition of the extracellular matrix (ECM) was examined in the developing lens and optic cup (stages 11-16) of the long-tailed monkey (Macaca fascicularis) using peroxidase immunocytochemistry. The glycoproteins, fibronectin, laminin, and collagen types I and IV, were consistently associated with basement membranes (BM) of ocular epithelia at all stages examined. Discontinuity of the optic cup BM was observed during the early stages of evagination (stages 11 and 12); the even distribution of all 4 components was reestablished by stage 13 when the optic vesicle is closely apposed to the thickened lens placode. While fibronectin was most predominant in the mesenchymal matrix, all 4 glycoproteins were observed to variable degrees in the periocular mesenchyme. Particularly strong glycoprotein reactivity was observed in the interspace between the invaginating lens vesicle and optic cup whereas no significant reactivity occurred within the lens, developing retina or future corneal epithelium. Two glycosaminoglycans, hyaluronic acid and chondroitin sulphate, had virtually identical widespread staining patterns in all ocular BM and throughout the periocular mesenchyme and adjacent epithelial tissues, including the lens and retina. The observed temporal and regional staining patterns suggest that these ECM components are morphogenetic factors in the macaque eye, facilitating the complex series of integrated tissue interactions, movements and shape changes during the earliest stages of lens and optic vesicle morphogenesis. The macaque offers a valuable model to study these interactions due to the prolonged period of ocular development which is morphologically identical to humans.

Immuno-localization of the calcitriol receptor, calbindin-D28k and the plasma membrane calcium pump in the human eye

Using immunohistochemical methods, we detected epitopes of the calcitriol receptor, the ATP-dependent plasma membrane calcium pump and the 28kD vitamin D-dependent calcium-binding protein in sections of the human eye. In retinal photoreceptors, vitamin D receptor, plasma membrane calcium pump and calcium-binding protein epitopes were detected in the outer nuclear layer. Epitopes for the vitamin D receptor and the calcium-binding protein were present in the inner and outer segments of the photoreceptors, where visual transduction occurs. All three proteins were detected in some cells of the ganglion cell layer, the inner nuclear layer, and the retinal pigment epithelium. Epitopes for these proteins also were noted in the ciliary body epithelium. VDR epitopes were seen in lens epithelium. Some immunostaining for VDR, PMCA and calbindin-D28k also was present in the endothelium and in the basal epithelium of the cornea. The presence of these proteins in several tissues of the human eye suggests that the proteins may play a role in the cellular physiology of the eye. Their exact functions in the eye remain undetermined.

Isolation and expression of an arrestin cDNA from the horseshoe crab lateral eye

Electrophysiological studies of photoreceptors from the horseshoe crab Limulus polyphemus continue to provide fundamental new knowledge of the photoresponse in invertebrates. Therefore, it is of particular interest to characterize the molecular components of the photoresponse in this system. Here we describe an arrestin cloned from a cDNA library constructed using poly(A)+ RNA isolated from Limulus lateral eyes. The protein, deduced from the arrestin cDNA, is most similar to arrestin from locust antennae (56% identity) and Drosophila phosrestin I (53% identity). Limulus arrestin was expressed in a heterologous system, and its properties were compared with those of a 46-kDa light-regulated phosphoprotein (pp46A) in Limulus photoreceptors described in previous studies from this laboratory. Arrestin and pp46A (a) have the same apparent molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, (b) have an isoelectric point in the basic pH range, (c) require calmodulin and elevated Ca2+ levels for phosphorylation, (d) are immunoreactive with monoclonal antibody C10C10 directed against a sequence in bovine arrestin (S-antigen) that is perfectly conserved in the deduced arrestin protein, and (e) are associated with photoreceptors. We conclude that the arrestin described here and pp46A are the same protein. The results of this and previous studies show that in Limulus photoreceptors, light regulates the phosphorylation of arrestin in complex ways.

Immunohistochemical localization of fibrillin in human ocular tissues. Relevance to the Marfan syndrome

OBJECTIVE

To better understand the ocular manifestations of the Marfan syndrome, we investigated the distribution of fibrillin in normal human ocular tissues. Fibrillin, a microfibrillar glycoprotein component of the extracellular matrix, has been found to be the defective gene product in the Marfan syndrome.

METHODS

Frozen sections from seven pairs of normal eyes were stained with mouse anti-human fibrillin antibodies using the avidin-biotin immunoperoxidase technique.

RESULTS

In the anterior segment, the following exhibited positive staining for fibrillin: the lens capsule and zonules; connective tissues of the iris, ciliary body, ciliary processes, and conjunctiva; and the basement membrane regions of the corneal epithelium and endothelium of Schlemm's canal. Posteriorly, fibrillin localized to the lamina cribrosa, sclera, choroid, and Bruch's membrane.

CONCLUSIONS

Fibrillin is widely distributed in ocular connective tissues. The implications of defects in these tissues and the resultant ocular abnormalities in the Marfan syndrome such as ectopia lentis and glaucoma are discussed.

Localisation of thromboxane A2 receptors and the corresponding mRNAs in human eye tissue

Thromboxane A2 (TxA2) receptors in human eye sections were identified and localised using a potent TxA2 specific agonist, 125-iodinated 5-heptenoic acid 7-[3-[3-hydroxy-4-[4-(iodo-125I) phenoxy]-1-butenyl]-7- oxabicyclo[2.2.1]hept-2-yl]-,[1S-[1a,2a,(Z),3B(1E,3S*),4a]]-C23 H29 IO5 (125I-BOP) in a binding assay. TxA2 receptors were concentrated in several specific loci within ocular tissues, including the corneal epithelium, the ciliary processes, retina, and posterior ciliary arteries. In addition, we have used the method of in situ hybridisation to observe the distribution of TxA2 receptor mRNA. The distributions of both receptor binding sites and receptor mRNAs showed a close correlation. These studies employed film autoradiography which does not permit cellular resolution. In order to obtain enhanced cellular resolution and more detailed information about the localisation of the receptors and their corresponding mRNAs, emulsion autoradiography was used after ligand binding and in situ hybridisation. This approach showed further that TxA2 receptors are mainly concentrated on non-pigmented epithelial cells of the ciliary processes, on photoreceptors within the retina, and on endothelial cells of the posterior ciliary arteries. These results may be helpful for understanding the pathophysiological effects of TxA2 in the human eye.