Mitochondrial function after associating liver partition and portal vein ligation for staged hepatectomy in an experimental model

BACKGROUND

Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) is a two-stage strategy to induce rapid regeneration of the remnant liver. The technique has been associated with high mortality and morbidity rates. This study aimed to evaluate mitochondrial function, biogenesis and morphology during ALPPS-induced liver regeneration.

METHODS

Male Wistar rats (n = 100) underwent portal vein ligation (PVL) or ALPPS. The animals were killed at 0 h (without operation), and 24, 48, 72 or 168 h after intervention. Regeneration rate and proliferation index were assessed. Mitochondrial oxygen consumption and adenosine 5'-triphosphate (ATP) production were measured. Mitochondrial biogenesis was evaluated by protein level measurements of peroxisome proliferator-activated receptor γ co-activator (PGC) 1-α, nuclear respiratory factor (NRF) 1 and 2, and mitochondrial transcription factor α. Mitochondrial morphology was evaluated by electron microscopy.

RESULTS

Regeneration rate and Ki-67 index were significantly raised in the ALPPS group compared with the PVL group (regeneration rate at 168 h: mean(s.d.) 291·2(21·4) versus 245·1(13·8) per cent, P < 0·001; Ki-67 index at 24 h: 86·9(4·6) versus 66·2(4·9) per cent, P < 0·001). In the ALPPS group, mitochondrial function was impaired 48 h after the intervention compared with that in the PVL group (induced ATP production); (complex I: 361·9(72·3) versus 629·7(165·8) nmol per min per mg, P = 0·038; complex II: 517·5(48·8) versus 794·8(170·4) nmol per min per mg, P = 0·044). Markers of mitochondrial biogenesis were significantly lower 48 and 72 h after ALPPS compared with PVL (PGC1-α at 48 h: 0·61-fold decrease, P = 0·045; NRF1 at 48 h: 0·48-fold decrease, P = 0·028). Mitochondrial size decreased significantly after ALPPS (0·26(0·05) versus 0·40(0·07) μm² ; P = 0·034).

CONCLUSION

Impaired mitochondrial function and biogenesis, along with the rapid energy-demanding cell proliferation, may cause hepatocyte dysfunction after ALPPS. Surgical relevance Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) is a well known surgical strategy that combines liver partition and portal vein ligation. This method induces immense regeneration in the future liver remnant. The rapid volume increase is of benefit for resectability, but the mortality and morbidity rates of ALPPS are strikingly high. Moreover, lagging functional recovery of the remnant liver has been reported recently. In this translational study, ALPPS caused an overwhelming inflammatory response that interfered with the peroxisome proliferator-activated receptor γ co-activator 1-α-coordinated, stress-induced, mitochondrial biogenesis pathway. This resulted in the accumulation of immature and malfunctioning mitochondria in hepatocytes during the early phase of liver regeneration (bioenergetic destabilization). These findings might explain some of the high morbidity if confirmed in patients.

Photopigment coexpression in mammals: comparative and developmental aspects

In mammals, each cone had been thought to contain only one single type of photopigment. It was not until the early 1990s that photopigment coexpression was reported. In the house mouse, the distribution of color cones shows a characteristic division. Whereas in the upper retinal field the ratio of short wave to middle-to-long wave cones falls in the usual range (1:10), in the ventral retinal field M/L-pigment expression is completely missing. In the transitional zone, numerous dual cones are detectable (spatial coexpression). In other species without retinal division, dual cones appear during development, suggesting that M/L-cones develop from S-cones. Dual elements represent a transitory stage in M/L-cone differentiation that disappear with maturation (transitory coexpression). These two phenomena seem to be mutually exclusive in the species studied so far. In the comparative part of this report the retinal cone distribution of eight rodent species is reported. In two species dual cones appear in adult specimens without retinal division, and dual elements either occupy the dorsal peripheral retina, or make up the entire cone population. This is the first observation proving that all cones of a retina are of dual nature. These species are good models for the study of molecular control of opsin expression and renders them suitable sources of dual cones for investigations on the role and neural connections of this peculiar cone type. In the developmental part, the retinal maturation of other species is examined to test the hypothesis of transitory coexpression. In these species S-pigment expression precedes that of the M/L-pigment, but dual cones are either identified in a small number or they are completely missing from the developing retina. These results exclude a common mechanism for M/L-cone maturation: they either transdifferentiate from S-cones or develop independently.

Nonvisual photoreceptors of the deep brain, pineal organs and retina

The role of the nonvisual photoreception is to synchronise periodic functions of living organisms to the environmental light periods in order to help survival of various species in different biotopes. In vertebrates, the so-called deep brain (septal and hypothalamic) photoreceptors, the pineal organs (pineal- and parapineal organs, frontal- and parietal eye) and the retina (of the "lateral" eye) are involved in the light-based entrain of endogenous circadian clocks present in various organs. In humans, photoperiodicity was studied in connection with sleep disturbances in shift work, seasonal depression, and in jet-lag of transmeridional travellers. In the present review, experimental and molecular aspects are discussed, focusing on the histological and histochemical basis of the function of nonvisual photoreceptors. We also offer a view about functional changes of these photoreceptors during pre- and postnatal development as well as about its possible evolution. Our scope in some points is different from the generally accepted views on the nonvisual photoreceptive systems. The deep brain photoreceptors are hypothalamic and septal nuclei of the periventricular cerebrospinal fluid (CSF)-contacting neuronal system. Already present in the lancelet and representing the most ancient type of vertebrate nerve cells ("protoneurons"), CSF-contacting neurons are sensory-type cells sitting in the wall of the brain ventricles that send a ciliated dendritic process into the CSF. Various opsins and other members of the phototransduction cascade have been demonstrated in telencephalic and hypothalamic groups of these neurons. In all species examined so far, deep brain photoreceptors play a role in the circadian and circannual regulation of periodic functions. Mainly called pineal "glands" in the last decades, the pineal organs actually represent a differentiated form of encephalic photoreceptors. Supposed to be intra- and extracranially outgrown groups of deep brain photoreceptors, pineal organs also contain neurons and glial elements. Extracranial pineal organs of submammalians are cone-dominated photoreceptors sensitive to different wavelengths of light, while intracranial pineal organs predominantly contain rod-like photoreceptor cells and thus scotopic light receptors. Vitamin B-based light-sensitive cryptochromes localized immunocytochemically in some pineal cells may take part in both the photoreception and the pacemaker function of the pineal organ. In spite of expressing phototransduction cascade molecules and forming outer segment-like cilia in some species, the mammalian pineal is considered by most of the authors as a light-insensitive organ. Expression of phototransduction cascade molecules, predominantly in young animals, is a photoreceptor-like characteristic of pinealocytes in higher vertebrates that may contribute to a light-percepting task in the perinatal entrainment of rhythmic functions. In adult mammals, adrenergic nerves--mediating daily fluctuation of sympathetic activity rather than retinal light information as generally supposed--may sustain circadian periodicity already entrained by light perinatally. Altogether three phases were supposed to exist in pineal entrainment of internal pacemakers: an embryological synchronization by light and in viviparous vertebrates by maternal effects (1); a light-based, postnatal entrainment (2); and in adults, a maintenance of periodicity by daily sympathetic rhythm of the hypothalamus. In addition to its visual function, the lateral eye retina performs a nonvisual task. Nonvisual retinal light perception primarily entrains genetically-determined periodicity, such as rod-cone dominance, EEG rhythms or retinomotor movements. It also influences the suprachiasmatic nucleus, the primary pacemaker of the brain. As neither rods nor cones seem to represent the nonvisual retinal photoreceptors, the presence of additional photoreceptors has been supposed. Cryptochrome 1, a photosensitive molecule identified in retinal nerve cells and in a subpopulation of retinal photoreceptors, is a good candidate for the nonvisual photoreceptor molecule as well as for a member of pacemaker molecules in the retina. When comparing various visual and nonvisual photoreceptors, transitory, "semi visual" (directional) light-perceptive cells can be detected among them, such as those in the parietal eye of reptiles. Measuring diffuse light intensity of the environment, semivisual photoreceptors also possess some directional light perceptive capacity aided by complementary lens-like structures, and screening pigment cells. Semivisual photoreception in aquatic animals may serve for identifying environmental areas of suitable illumination, or in poikilotermic terrestrial species for measuring direct solar irradiation for thermoregulation. As directional photoreceptors were identified among nonvisual light perceptive cells in the lancelet, but eyes are lacking, an early appearance of semivisual function, prior to a visual one (nonvisual --> semivisual --> visual?) in the vertebrate evolution was supposed.

Comparative ultrastructure and cytochemistry of the avian pineal organ

The breeding of birds is expected to solve problems of nourishment for the growing human population. The function of the pineal organ synchronizing sexual activity and environmental light periods is important for successful reproduction. Comparative morphology of the avian pineal completes data furnished by experiments on some frequently used laboratory animals about the functional organization of the organ. According to comparative histological data, the pineal of vertebrates is originally a double organ (the "third" and the "fourth eye"). One of them often lies extracranially, perceiving direct solar radiation, and the other, located intracranially, is supposed to measure diffuse brightness of the environment. Birds have only a single pineal, presumably originating from the intracranial pineal of lower vertebrates. Developing from the epithalamus, the avian pineal organ histologically seems not to be a simple gland ("pineal gland") but a complex part of the brain composed of various pinealocytes and neurons that are embedded in an ependymal/glial network. In contrast to organs of "directional view" that develop large photoreceptor outer segments (retina, parietal pineal eye of reptiles) in order to decode two-dimensional images of the environment, the "densitometer"-like pineal organ seems to increase their photoreceptor membrane content by multiplying the number of photoreceptor perikarya and developing follicle-like foldings of its wall during evolution ("folded retina"). Photoreceptor membranes of avian pinealocytes can be stained by antibodies against various photoreceptor-specific compounds, among others, opsins, including pineal opsins. Photoreceptors immunoreacting with antibodies to chicken pinopsin were also found in the reptilian pineal organ. Similar to cones and rods representing the first neurons of the retina in the lateral eye, pinealocytes of birds possess an axonal effector process which terminates on the vascular surface of the organ as a neurohormonal ending, or forms ribbon-containing synapses on pineal neurons. Serotonin is detectable immunocytochemically on the granular vesicles accumulated in neurohormonal terminals. Pinealocytic perikarya and axon terminals also bind immunocytochemically recognizable excitatory amino acids. Peripheral autonomic fibers entering the pineal organ through its meningeal cover terminate near blood vessels. Being vasomotor fibers, they presumably regulate the blood supply of the pineal tissue according to the different levels of light-dependent pineal cell activity.

Immunocytochemical demonstration of visual pigments in the degenerate retinal and pineal photoreceptors of the blind cave salamander (Proteus anguinus)

Visual pigments in the regressed eye and pineal of the depigmented neotenic urodele, the blind cave salamander (Proteus anguinus anguinus), were studied by immunocytochemistry with anti-opsin antibodies. The study included light- and electron-microscopic investigations of both the eye and the pineal organ. A comparison was made with the black pigmented subspecies Proteus anguinus parkelj (black proteus), which has a normal eye structure. In the retina of the black proteus, we found principal rods, red-sensitive cones and a third photoreceptor type, which might represent a blue- or UV-sensitive cone. Photoreceptors in the regressed eye of the blind cave salamanders from the Planina cave contained degenerate outer segments, consisting of a few whorled discs and irregular clumps of membranes. The great majority of these outer segments showed immunolabelling for the red-sensitive cone opsin and only a few of them were found to be positive for rhodopsin. An even more pronounced degeneration was observed in the photoreceptors of the animals derived from the Otovec doline, which are completely devoid of an outer segment, most of them not even possessing an inner segment. Even in some of these highly degenerate cells, the presence of rhodopsin could be detected in the plasma membrane; however, immunoreactions with antibodies recognizing cone visual pigment were negative. In the pineals of all studied animals, the degenerate photoreceptor outer segments were recognized exclusively by the antibody against the red-sensitive cone opsin. The presence of immunopositive visual pigments indicates the possibility of a retained light sensitivity in the blind cave salamander photoreceptors.

Cone differentiation with no photopigment coexpression

PURPOSE

To decide whether the transitory coexpression of cone visual pigments described in the developing rat and gerbil retina is a universal feature of dichromatic mammalian species.

METHODS

The rabbit, a species widely used in eye research, was selected for the study and a search made for the presence of cones that bound more than one cone antibody during the first postnatal week. To plot the densities of individual cone types and to colocalize the two visual pigments, immunocytochemistry on retinal wholemounts and consecutive tangential sections, respectively, were used.

RESULTS

The sequence in which the visual pigments began to be expressed was the same as that observed in other mammals: first, rhodopsin; second, blue pigment; and last, green pigment. The striking increase in blue cone density numbers observed in the rat, however, did not occur in the rabbit. Instead, some days after the first blue cones appeared, the green cones also started to express their visual pigment, and this cone type soon outnumbered the blue cones. Within the limits of the immunocytochemical method, it was established that unlike the developing rat, the presence of double-labeled cones was not a character of the rabbit retina.

CONCLUSIONS

Visual pigment coexpression is an interesting phenomenon of retinal development, however, it is not the exclusive scenario of photoreceptor differentiation. Each species must be carefully studied before deciding whether its retinal cones synthesize both pigments during retinal development.

Photoreceptor cells in the Xenopus retina

This review summarizes our present state of knowledge about spectrally different photoreceptor cell types in the Xenopus retina. The classification of the photoreceptors was based on morphology, combined with immunolabelling with various anti-visual pigment antibodies and other molecular probes on semithin sections and retinal wholemounts. The majority of photoreceptors is represented by rods. Altogether 97-98% of the total rod population consists of the principal ("red") rods that are selectively labeled by N-terminal specific anti-bovine rhodopsin monoclonal antibodies (mAbs) and are maximally sensitive to green light. The other, rare, blue-sensitive rod type ("green rod") is thinner, not stained by these antibodies but binds C-terminal specific anti-rhodopsin mAbs. The major representatives of the cones are red-sensitive and consist of a morphologically heterogeneous group comprising both (principal and accessory) members of double cones, as well as large single cones. Outer segments in this group are selectively labeled by mAb COS-1, specific to the L/M group of cone visual pigments. Another, relatively rare cone type is similar in size, but slightly smaller than the large single cone and is not labeled by mAb COS-1. This cone type is assumed to have a blue-sensitive cone visual pigment. The third, least abundant, and immunocytochemically distinct cone type is a small single (miniature) cone, which binds mAb OS-2 relatively strongly, and anti-rhodopsin mAbs 4B4 and 1D4 weakly. By exclusion, this small single cone may be identical with the UV-sensitive cone. Further studies are needed, however, to identify the color sensitivity of the latter two cone types.

Degeneration of cone photoreceptors induced by expression of the Mas1 protooncogene

Although transgenic expression of oncogenes typically leads to tumorigenesis, oncogene expression directed to the rod photoreceptors leads to cell death without tumor formation. To evaluate the cellular and functional changes induced in cone photoreceptors by an oncogene, the Mas1 protooncogene was targeted to the cones of transgenic mice by the human red/green opsin promoter. Mas1 was chosen because of its exclusive expression in the nervous system and its homology to opsin. The overall histologic appearance of the transgenic retina was normal and retinal tumors were never observed. While rod-mediated electroretinograms were normal in all respects, cone-mediated responses were diminished in direct relationship to the level of transgene expression as determined by Northern blot analysis. Responses of UV- and green-sensitive cones were reduced equivalently, and Northern analysis and immunocytochemistry indicated that cone photoreceptor densities were markedly diminished throughout transgenic retinas. These results indicate that oncogene expression in cones induces cell death without tumor formation and support the possibility that aberrant oncogene expression may underlie some forms of hereditary retinal diseases. The Mas1 transgenic mice may be useful in understanding the cone photoreceptor degeneration that occurs in cone dystrophies and age-related macular degeneration and in evaluating potential therapies for these disorders.

Photoreceptor distribution in the retinas of subprimate mammals

Relevant data on the distribution of color cones are summarized, with special emphasis on the marked dorsoventral asymmetries observed in a number of mammalian species. In addition, an overview is given of studies that demonstrate the coexistence of two visual pigments within the same cone cell. The biological significance of these phenomena is discussed in conjunction with comparative immunocytochemical analyses of subprimate retinas. Based on various cone distribution patterns and temporal and spatial visual pigment coexpression, two models of cone photoreceptor differentiation are suggested.

Immunoreactive pinopsin in pineal and retinal photoreceptors of various vertebrates

Pinopsin is a pineal specific opsin newly identified in the pineal of birds which has an absorption maximum at 470 nm. As the opsin content of photoreceptors in the pineal complex of several species is not yet known, in the present work, we studied their pinopsin immunoreactivity in various vertebrates from cyclostomes to mammals. We also compared the immunoreactivity of pineal photoreceptors to that of retinal cones and rods of each animal. For the immunocytochemistry, we raised antibodies in rabbits against a 14 amino acids containing part of the chicken pinopsin molecule. The immunoreaction was performed at the electron microscopic level. The pineal organs show a great diversity in vertebrates: there is a pineal organ present from cyclostomes to mammals, in addition, there is a parapineal organ in cyclostomes and fishes, a frontal organ in frogs and a parietal eye in several reptiles. We detected a strong pinopsin immunoreaction on most of the pinealocytes of birds and on the large photoreceptor-type of the pineal of reptiles. Rod-type photoreceptors of the avian retina and a cone of the reptile retina was immunoreactive as well. According to the known absorption maximum of pinopsin, the immunoreactivity may indicate a green-blue light-sensitivity for these photoreceptors. The immunoreactivity was less pronounced or absent in mammals as well as in less differentiated species. The pineal organ of snakes and the parietal eye of reptiles equally failed to exhibit pinopsin immunoreactive photoreceptors, presumably, due to the absence of green-blue light-sensitive photoreceptors of pinopsin-type in these species.

The pineal organ as a folded retina: immunocytochemical localization of opsins

The most simple pineal complex (the pineal and parapineal organs of lampreys), consists of saccular evaginations of the diencephalic roof, and has a retina-like structure containing photoreceptor cells and secondary neurons. In more differentiated vertebrates, the successive folding of the pineal wall multiplies the cells and reduces the lumen of the organ, but the pattern of the histological organization remains similar to that of lampreys; therefore, we consider the histological structure of the pineal organ of higher vertebrates as a 'folded retina'. The cell membrane of several pineal photoreceptor outer-segments of vertebrates immunoreact with anti-retinal opsin antibodies supporting the view of retina-like organization of the pineal. Some other pineal outer segments do not react with retinal anti-opsin antibodies, a result suggesting the presence of special pineal photopigments in different types of pinealocytes that obviously developed during evolution. The chicken pinopsin, detected in the last years, may represent one of these unknown photopigments. Using antibodies against chicken pinopsin, we compared the immunoreactivity of different photoreceptors of the pineal organs from cyclostomes to birds at the light and electron microscopic levels. We found pinopsin immunoreaction on all pinealocytes of birds and on the rhodopsin-negative large reptilian pinealocytes. As the pinopsin has an absorption maximum at 470 nm, these avian and reptilian immunoreactive pinealocytes can be regarded as green-blue light-sensitive photoreceptors. Only a weak immunoreaction was observed on the frog and fish pinealocytes and no reaction was seen in cyclostomes and in the frontal organ of reptiles. Some photoreceptors of the retina of various species also reacted the pinopsin antibodies, therefore, pinopsin must have certain sequential similarity to individual retinal opsins of some vertebrates.

The photoreceptors and visual pigments of the garter snake (Thamnophis sirtalis): a microspectrophotometric, scanning electron microscopic and immunocytochemical study

Scanning electron microscopy, immunocytochemistry, and single cell microspectrophotometry were employed to characterize the photoreceptors and visual pigments in the retina of the garter snake, Thamnophis sirtalis. The photoreceptor population was found to be comprised entirely of cones, of which four distinct types were identified. About 45.5% of the photoreceptors are double cones consisting of a large principal member joined near the outer segment with a much smaller accessory member. About 40% of the photoreceptors are large single cones, and about 14.5% are small single cones forming two subtypes. The outer segments of the large single cones and both the principal and accessory members of the doubles contain the same visual pigment, one with peak absorbance near 554 nm. The small single cones contain either a visual pigment with peak absorbance near 482 nm or one with peak absorbance near 360 nm. Two classes of small single cones could be distinguished also by immunocytochemistry and scanning electron microscopy. The small single cones with the 360-nm pigment provide the garter snake with selective sensitivity to light in the near ultraviolet region of the spectrum. This ultraviolet sensitivity might be important in localization of pheromone trails.

A 221-bp fragment of the mouse opsin promoter directs expression specifically to the rod photoreceptors of transgenic mice

Mutations in the human rod opsin gene have been shown to segregate with autosomal dominant retinitis pigmentosa (ADRP) and photoreceptor degeneration in transgenic mice. While these degenerations are characterized by the primary degeneration of rods, cones eventually die as well. To determine whether this subsequent cone degeneration is the result of expression of mutant rod opsin in the cones, the retinal cell-type specificity of a 221-bp fragment of the mouse rod opsin promoter was evaluated. Two transgenic mouse lines generated by injecting a fusion gene comprised of a 221-bp fragment of the mouse rod opsin promoter and the simian virus 40 large tumor antigen gene (Tag) were examined. The expression of Tag causes photoreceptor cell degeneration in members of both transgenic lines. However, the two lines differed with respect to the level of Tag expression and the rate and extent of photoreceptor cell degeneration. Immunocytochemical localization of opsin and Tag in surviving photoreceptor cells was determined and the results were confirmed by reverse transcriptase polymerase chain reaction (RT-PCR). Rod- and cone-mediated function was evaluated by electroretinography (ERG). In the higher Tag-expressing transgenic line only one row of nuclei remained in the outer nuclear layer at postnatal day (P) 150. While these nuclei showed no antigenicity for rod opsin or Tag, they did stain with an antibody that reacts with both rod and cone S-antigens (arrestins), indicating that these cells were surviving photoreceptor nuclei. Positive staining with peanut agglutinin, which uniquely decorates matrix domains surrounding cones in the normal retina, confirmed that the surviving photoreceptor nuclei were of cone origin. RT-PCR substantiated the results from immunostaining; amplification product was obtained using blue cone opsin transcripts but not from either Tag or rod opsin transcripts. The second transgenic mouse line exhibited a much slower photoreceptor cell death that was associated with low levels of Tag transgene transcript. At P120, approximately 50% of photoreceptors remained and an approximately 45% reduction in the rod ERG a-wave was observed. Cone-mediated ERGs, however, were normal. The results demonstrate the rod-specific expression of Tag as directed by the 221-bp fragment of the mouse rod opsin promoter and suggest that the cone degeneration in ADRP or transgenic mice associated with mutations in the rod opsin gene is a secondary effect of rod degeneration.

Distribution of cone photoreceptors in the mammalian retina

The retina of mammals contains various amounts of cone photoreceptors that are relatively evenly distributed and display a radially or horizontally oriented area of peak density. In most mammalian species two spectrally different classes of cone can be distinguished with various histochemical and physiological methods. These cone classes occur in a relatively constant ratio, middle-to-longwave sensitive cones being predominant over short-wave cones. Recent observations do not support the idea that each cone subpopulation is uniformly distributed across the retina. With appropriate type-specific markers, unexpected patterns of colour cone topography have been revealed in certain species. In the mouse and the rabbit, the "standard" uniform pattern was found to be confined exclusively to the dorsal retina. In a ventral zone of variable width all cones express short-wave pigment, a phenomenon whose biological significance is not known yet. Dorso-ventral asymmetries have been described in lower vertebrates, matching the spectral distribution of light reaching the retina from various sectors of the visual field. It is not clear, however, whether the retinal cone fields in mammals carry out a function similar to that of their counterparts in fish and amphibians. Since in a number of mammalian species short-wave cones are the first to differentiate, and the expression of the short-wave pigment seems to be the default pathway of cone differentiation, we suggest that the short-wave sensitive cone fields are rudimentary areas conserving an ancestral stage of the photopigment evolution.

The opossum photoreceptors--a model for evolutionary trends in early mammalian retina

The topography and spectral characteristics of mammalian photoreceptors correlate with both, the present ecological demands and the evolutionary history. The South American Opossum is a marsupial mammal with unspecialized habitus and crepuscular lifestyle. A sparse population of cones (max. = 3000/mm2) can be differentiated into four subtypes by morphological, topographical and immunocytochemical criteria. In spite of this unusual diversity the cone types can be split into two functional groups: The population of single cones labeled by antibody OS-2 for short wavelength sensitive pigments was ubiquitous but at very low densities (200/mm2). The single cones labeled by antibody (COS-1) against long wavelength sensitive pigments constitute the dominant population in the area centralis (2300/mm2). These two single cone types correlate with the pair typically present in placental mammals. Discrimination of spatial and color contrast may be provided by this "modern" set. The COS-1 labeled double and single cones bearing an oil droplet, display a different pattern by being restricted to the inferior (non-tapetal) half of the retina (max = 800/mm2). This additional set of cones with oil droplets and long wavelength pigments is a conservative feature of the opossum retina and other marsupials. As an accessory cone system it is possibly providing enhanced sensitivity at mesopic conditions. During the early evolution of nocturnal mammals with its prominent expansion of rod vision these cone types were conserved but then were lost in placental mammals. Thus the unique features of mammalian retinas are the result of two evolutionary steps: first a reduction of cone based vision, followed by a secondary differentiation of photopic vision and behaviour relying on the remaining set of cones.

Microspectrophotometric and immunocytochemical identification of ultraviolet photoreceptors in geckos

Retinas of the nocturnal geckos, Hemidactylus turcicus, Hemidactylus garnotii, and Teratoscincus scincus, were studied with microspectrophotometry and immunocytochemistry against various visual pigment epitopes to reveal UV-sensitive photoreceptors. From 6-20% of the thinner members of type C double photoreceptors, earlier believed to be blue-sensitive, were found to contain a UV-absorbing visual pigment with lambda max at 363-366 nm. The pigment had bleaching and dichroic properties typical of other photoreceptor cell types of the retina. Presumptive UV-sensitive cells in retinal sections were "negatively" labeled as they did not react with either the cone-specific monoclonal antibody COS-1 or with the anti-rhodopsin polyclonal serum AO, which together labeled all of the remaining photoreceptor types (green-sensitive A singles, B doubles, and thicker members of C doubles, as well as the blue-sensitive majority of thinner members of C doubles). UV cells were moderately stained with the mAb K42-41 produced against the 5-6 loop of bovine rhodopsin, which also moderately labeled blue-sensitive cells. mAb OS-2 strongly stained all outer segments, including the UV-sensitive ones. Similarities between gecko UV visual pigments, and UV visual pigments of other vertebrates, as well as possible functional significance of these cells are discussed.

Photoreceptors in a primitive mammal, the South American opossum, Didelphis marsupialis aurita: characterization with anti-opsin immunolabeling

The retinas of placental mammals appear to lack the large number and morphological diversity of cone subtypes found in diurnal reptiles. We have now studied the photoreceptor layer of a South American marsupial (Didelphis marsupialis aurita) by peanut agglutinin labeling of the cone sheath and by labeling of cone outer segments with monoclonal anti-visual pigment antibodies that have been proven to consistently label middle-to-long wavelength (COS-1) and short-wavelength (OS-2) cone subpopulations in placental mammals. Besides a dominant rod population (max. = 400,000/mm2) four subtypes of cones (max. = 3000/mm2) were identified. The outer segments of three cone subtypes were labeled by COS-1: a double cone with a principal cone containing a colorless oil droplet, a single cone with oil droplet, and another single cone. A second group of single cones lacking oil droplets was labeled by OS-2 antibody. The topography of these cone subtypes showed striking anisotropies. The COS-1 labeled single cones without oil droplets were found all over the retina and constituted the dominant population in the area centralis located in the temporal quadrant of the upper, tapetal hemisphere. The population of OS-2 labeled cones was also ubiquitous although slightly higher in the upper hemisphere (200/mm2). The COS-1 labeled cones bearing an oil droplet, including the principal member of double cones, were concentrated (800/mm2) in the inferior, non-tapetal half of the retina. The two spectral types of single cones resemble those of dichromatic photopic systems in most placental mammals. The additional set of COS-1 labeled cones is a distinct marsupial feature. The presence of oil droplets in this cone subpopulation, its absence in the area centralis, and the correlation with the non-tapetal inferior hemisphere suggest a functional specialization, possibly for mesopic conditions. Thus, sauropsid features have been retained but probably with a modified function.

Two different visual pigments in one retinal cone cell

The retina of the mouse, rabbit, and guinea pig is divided into a superior area dominated by green-sensitive (M) cones and an inferior area in which cones possess practically only short wavelength-sensitive (S) photopigments. The present study shows that the transitional zone between these retinal areas is populated by cones labeled by both the M and S cone photopigment-specific antibodies COS-1 and OS-2. It is concluded that the overwhelming majority of the transitional cones express both visual pigments. A small population of the transitional cones was strongly labeled exclusively by OS-2 (genuine S cones). The results indicate that, in contrast to the generally accepted idea of one visual pigment per one cone cell, cones of certain mammalian species can express different opsins simultaneously under natural conditions. We speculate that the coexpression may be due to the overlapping of regulatory factors determining the M and S fields.

Different patterns of retinal cone topography in two genera of rodents, Mus and Apodemus

Recently, we have reported the peculiar topographic separation of shortwave- and middlewave-sensitive (S and M) cones in the retina of the common house mouse (Mus musculus) and in a number of inbred laboratory mouse strains derived from the same species. In an attempt to follow the phylogeny of the complementary cone fields, we have investigated the retina of other mouse-like rodents. Two monoclonal anti-visual pigment antibodies, OS-2 and COS-1, specific to the S and M cones, respectively, have been used to identify the two cone types. Immunocytochemistry on retinal sections and on whole-mount preparations have shown that, as in the house mouse, the two cone types in the mound builder mouse (Mus spicilegus) occupy opposite halves of the retina. In contrast, in the wood mouse (Apodemus sylvaticus), both cone types are scattered uniformly across the whole retinal surface. Another distinguishing feature between the two genera is the frequency of the S cones. Whereas their density in the Mus species is above 7,000/mm2 in the S-field, the maximum density of the S cones in A. sylvaticus is one order of magnitude smaller. In another species of this genus (the herb field mouse, A. microps), the S cones are completely missing.

Complementary cone fields of the rabbit retina

PURPOSE

Complementary cone fields have been considered a unique feature of the mouse retina. In an attempt to map the arrangement of the color-specific cones in other mammals, the authors investigated the rabbit, a commonly used experimental animal for vision research.

METHODS

For the identification of the different cone types immunocytochemistry was used with two monoclonal antibodies, each specific to the middle- to long-wave (red-green) and short-wave (blue) sensitive visual pigments, respectively.

RESULTS

The major part of the retinal surface, including the visual streak, exhibited a dominance of M (middle-wave sensitive) cones (6 to 13,000/mm2) versus S (short-wave sensitive) cones (1 to 2,500/mm2). In contrast, the lower 5% to 6% of the total retinal area showed a complete lack of green cones and a high density of blue cones (11,000/mm2). The authors designate this crescent-like area the blue streak of the rabbit retina.

CONCLUSION

In addition to the visual streak primarily abundant in green cones, there is a specialized area of the rabbit retina that is densely and exclusively populated with blue cones. Although the relative extension of this peculiar cone field is considerably smaller than the S-field of the mouse retina, its position is similar in that it occupies the lowermost part of the retina. The functional implication of this area is unknown.

Difference in PNA label intensity between short- and middle-wavelength sensitive cones in the ground squirrel retina

PURPOSE

Peanut agglutinin lectin (PNA) is known for its selective binding to cone cells and to the cone domains of the interphotoreceptor matrix. In the current study, the authors investigated whether there is any difference in PNA binding between color-specific cones of the cone-dominant ground squirrel.

METHODS

Consecutive serial sections of the retina of Spermophilus tridecemlineatus were reacted alternately with PNA and antivisual pigment antibodies. The PNA labels associated with short- and middle-wavelength-sensitive cones (S-cones and M-cones, respectively) were compared with fluorescent lectin cytochemistry.

RESULTS

Although all rod-like cells were left unstained, the cones exhibited a specific lectin label. There was, however, a significant difference between the two cone types; the intensity of the ring-like PNA label in the matrix sheath around S-cones significantly exceeded that of the M-cones.

CONCLUSIONS

The difference in PNA label intensity indicates a difference in the composition of the matrix sheaths surrounding the two respective cone types. To the authors' knowledge, this is the first report on lectin-cytochemical discrimination of cone matrix sheaths and the first lectin study in the ground squirrel retina leading to the observation that PNA can distinguish the three characteristic photoreceptor types in this animal. In this respect, the rod-like cells of the ground squirrel retina were shown to be no different from rod cells of other species.

Binding sites of photoreceptor-specific antibodies COS-1, OS-2 and AO

The chicken red-sensitive cone visual pigment (iodopsin) and several synthetic peptides of cone and rod visual pigments were used to find the binding sites of our photoreceptor-specific antibodies with immunocytochemistry. The ability of iodopsin to block immunolabeling with monoclonal antibodies COS-1 and OS-2 furnished direct evidence that both antibodies are specific to visual pigments. Immunocytochemistry on whole-mount retinas with and without detergent, as well as electron microscopic labeling of cone photoreceptor membranes revealed the binding sites of COS-1 and OS-2 to be on the cytoplasmic side of the membrane. By testing several synthetic peptides, mainly from the C-terminal region of the cone visual pigments, we found that the domain consisting of the last 6 amino acids of the human red/green-, and the chicken red-sensitive cone pigments completely blocked immunolabeling with COS-1, while the sequence consisting of the last 12 amino acids of the human blue cone pigment was effective to block the binding of OS-2. Both monoclonals can be regarded therefore C-terminal specific antibodies. OS-2 was found to bind to the dark-adapted photopigment more strongly than to the light-adapted one. The binding of the polyclonal rhodopsin antibody AO was almost entirely inhibited by the N-terminal synthetic peptide of bovine rhodopsin indicating that this antibody binds primarily to the N-terminal domain of rhodopsin in a tissue environment.

Spatial and temporal differences between the expression of short- and middle-wave sensitive cone pigments in the mouse retina: a developmental study

In an earlier study we found a topographic separation of middlewave-sensitive (M) and shortwave-sensitive (S) cones in the adult mouse retina. In the present study we investigated the development of the two colour-specific cone types to see whether there is also a temporal difference between the expression of the specific cone visual pigments. Using two anti-cone visual pigment antibodies, COS-1 and OS-2, we compared the densities of immunopositive cone outer segments on retinal whole mounts derived from mice of various ages. The first detectable cone outer segments were the S-cones which appeared in the inferior half of the retina on postnatal day 4. At this stage, the density of the S-cones was very low (30-40 cones/retina) but increased steadily on the following days to reach a value comparable to that of adults by P30 (18,000/mm2). This cone type always remained much more abundant in the lower part of the retina throughout the whole retinal development. In the superior half of the retina, a few S-cones appeared from postnatal day 7; however, their number always remained about one order of magnitude lower than in the inferior part. In contrast, M-cone outer segments were not identifiable earlier than postnatal day 11 and were confined exclusively to the superior part of the retina during the whole developmental process. On postnatal day 12, their density was 1,900/mm2 and increased to a value of 11,000/mm2 by postnatal day 30, which represented the adult stage. As shown by comparison of isodensity lines derived from immunocytochemical reactions of whole mount retinas, the two cone types occupied complementary halves of the mouse retina with maximum density centres located in opposite retinal quadrants. We conclude that 1) in contrast to the primate retina, mouse S-cones precede the M-cones in their development, and 2) the spatial arrangements of the two cone types is maintained throughout the whole differentiation process.

Unique topographic separation of two spectral classes of cones in the mouse retina

We have found two immunologically distinguishable cone types in the retina of the mouse, each localized to two opposite halves of the eye. One cone type was labelled by the monoclonal antibody COS-1 specific to the middle-to-long wave sensitive visual pigment of the mammals, while the other type was stained by the shortwave-specific monoclonal antibody (OS-2). These results were confirmed with other antibodies directed against specific sequences of the visual pigments. As a result of the uneven distribution of the two cone types the mouse retina is divided into two fields separated by an oblique meridional line. The middlewave sensitive cones were present exclusively in the dorsal half of the mouse retina (M-field). The overwhelming majority of the shortwave sensitive cones occupied the ventral half (S-field), and only a small number was scattered among the middlewave sensitive cones in the dorsal retina. The ratio of the two cone types in the M-field corresponds to what has been found in the retina of other mammals, including rodents such as the gerbil and the rat. The S-field represents an entirely unique area with the unusually great number of shortwave sensitive cones and with the complete lack of the middlewave sensitive ones. The present study provides the structural basis for dichromacy in a rodent species considered for a long time to be monochromat. In addition, it shows that the ventral retina, containing exclusively S-cones in a relatively high density, is a unique retinal field not present in other mammalian species studied so far.

Two cone types of rat retina detected by anti-visual pigment antibodies

The presence of two distinct cone types was demonstrated in the retina of the rat using two cone-specific monoclonal anti-visual pigment antibodies. Cones labelled by antibody COS-1 constituted the large majority (about 93%) of cones, and are most probably responsible for the green photopic sensitivity of the rat. About 7% of the cones were recognized by antibody OS-2, and are thought to be blue-sensitive elements. While OS-2 positive cones were evenly distributed throughout the retina, there were slight differences in the distribution of COS-1 positive cones. The cones made up about 0.85% of all photoreceptor cells. Although the OS-2 positive cones occur in a very low number (0.05% of all photoreceptors) and probably do not appreciably contribute to the photopic system of the rat, their presence in the rat strengthens the presumption that most mammalian species exhibit a dual cone system with a shortwave and a middle-to-longwave sensitivity.

Immunocytochemical reactivity of rod and cone visual pigments in the sturgeon retina

Microspectrophotometry and immunocytochemistry with several antivisual pigment antibodies were used to study visual cells of the Siberian sturgeon, Acipenser baeri Brandt. The retina contained rods and three morphological types of cones: large cones with oil drops, small cones with oil drops, and cone-like cells without oil drops. Rods and cone-like drop-free cells were found to possess porphyropsin-549, while the large oil drop-bearing cones contained red-sensitive (P613), green-sensitive (P542), and blue-sensitive (P462) visual pigments. The immunocytochemical staining pattern with three antibodies to visual pigment proteins also revealed one visual pigment in rods and three visual pigments in cones. Rods were labeled with all three antibodies, while the majority of large cones (type I), presumably the red-sensitive ones, were negative with the polyclonal serum AO against bovine opsin. A less-frequently occurring large cone type (type II) was stained by all three antibodies including mAb COS-1 specific to middle-to-long-wave visual pigments in birds and mammals, and is thought to be green-sensitive. An even less-frequent large cone type (type III, probably the blue-sensitive one) did not bind COS-1. The small cones with oil droplets showed immunoreactivities similar to either type II or type III cones. The oil drop-free small photoreceptor exhibited a staining pattern identical with that of rods. These results indicate that the immunocytochemical approach can be used to reveal photoreceptor-specific neural connections in the sturgeon retina.

Cones in the retina of the Mongolian gerbil, Meriones unguiculatus: an immunocytochemical and electrophysiological study

Immunocytochemistry revealed in the retina of the Mongolian gerbil three immunologically distinct photoreceptor cell types. Rods comprising about 87% of the total receptor population were selectively recognized by an antirhodopsin serum (AO). The most abundant cone type (11-13% of photoreceptors) was labeled by the monoclonal antibody COS-1, specific in mammals to the middle-to-long-wave sensitive cone visual pigments. A minor cone population (2.5-5% of the cones) reacted with the monoclonal antibody OS-2, shown earlier to bind to the blue cones in mammalian species. Color substitution experiments revealed on the ERG level a color discrimination capability which must be attributed to the cooperative activity of green-sensitive (COS-1 positive) and blue-sensitive (OS-2 positive) cones. We conclude that the Mongolian gerbil has a well developed cone system, and that it may possess dichromatic green-blue color vision.

Immunocytochemical identification of outer segment proteins in the rd chicken

Immunoreactivities of two monoclonal antibodies (MAbs) that recognize cone photopigments were tested in the retinas of congenitally blind retinal degenerate (rd) chicks and compared to normally sighted carrier chicks, heterozygous for the mutation. MAb OS-2 had been previously determined to label rod and most cone outer segment membranes in normal chick retinas and is believed to bind to an epitope that is common to several photopigments in chickens. MAb COS-1 labels specifically middle-to-long-wavelength-sensitive cone photopigments in a number of vertebrate species. In rd chicks MAb OS-2 labeled the same number of rod outer segments at the same densities as carrier chicks. However, cone outer segments were less frequently and significantly less heavily labeled with this MAb at all ages tested (1 day, 1 week and 2 weeks post hatching). MAb COS-1 labeled the same number of cone outer segments in both rd and carrier retinas at 1 day of age, however, those outer segments that were labeled in rd specimens had significantly fewer gold particles on them. At both 1 week and 2 weeks of age, rd chick retinas had a significant reduction in numbers of cone outer segments labeled by COS-1. These findings support the hypothesis that the cone photopigment protein is abnormal in the rd chick model of hereditary blindness and retinal degeneration.

Binding pattern of anti-rhodopsin monoclonal antibodies to photoreceptor cells: an immunocytochemical study

A panel of anti-rhodopsin monoclonal antibodies (MAbs) of defined epitope specificity has been evaluated by immunocytochemistry. Most of the IgG class MAbs (23/27) gave positive results, but only a few of the IgM class MAbs (2/21) were useful for this application. MAbs specific to the N-terminal region stained rod outer segments most strongly, with progressively less staining in the Golgi, perikarya, plasma membrane of the inner segment, and synaptic region. Phagosomes located basally in the pigment epithelium were stained; cone cells were consistently negative. Antibodies to the C-terminus of rhodopsin labeled the same cell structures (except for phagosomes) but showed diversity in their binding pattern. Many of these MAbs bound to cone outer segments in addition to rods, and showed different patterns of binding to red/green and blue cones. Antibodies specific for rhodopsin sequence 340-348 labeled different types of cone cells, indicating differences in their binding sites. Two MAbs were found to label hydrophilic loop sequences which connect rhodopsin's transmembrane segment: MAb K42-41 which binds loop 5-6, and MAb A1-55 which binds loop 2-3. At least these two regions of the rhodopsin sequence in addition to the C- and N-termini, are available for antibody reaction in fixed retina.

Immunocytochemical reactivity of Xenopus laevis retinal rods and cones with several monoclonal antibodies to visual pigments

Immunocytochemical reactions with several antibodies to visual pigments were used to study visual cells of the Xenopus laevis retina. Monoclonal antibodies to bovine opsin "E," 1D4, and 4B4 (reactive with the N- and C-terminus and with the loop connecting transmembrane segments 5-6, respectively) and to chicken visual pigments COS-1 and OS-2 (binding to mammalian red/green and blue cones, respectively), as well as a rabbit antifrog opsin serum 11-7, were applied to semithin and thin sections of the retina. The bound antibodies were detected with the peroxidase technique at the light microscopic level; a three-stage immunogold procedure was used for electron microscopic immunocytochemistry. The overwhelming majority of rods were labeled by monoclonal antibodies "E," 4B4, 1D4, OS-2, and serum 11-7. A small fraction (2-3%) of rods did not bind monoclonal antibodies "E" and 4B4, but this minor population of rods was strongly reactive with 1D4 and to a lesser extent with OS-2, indicating the presence of different visual pigment. These rods differ in shape from the major rod type; they are thinner, shorter, and may be comparable to the blue-sensitive ("green") rods of other amphibia. Cones were morphologically heterogeneous: double cones, large single cones, and small single cones were found, and the large single and the double cones were occasionally duplicated. Double cones and large single cones (as well as their duplicated varieties) strongly bound monoclonal antibodies COS-1 and were unlabeled by all other monoclonal antibodies, except OS-2. The small single cone was remarkably unreactive with COS-1 and "E," weakly labeled by 1D4 and 4B4, and most reactive with OS-2 and 11-7. This unique pattern of immunocytochemical reactions in the small cone type indicates the uniqueness of its visual pigment from other cone types in the Xenopus retina. The present study shows the existence of two different opsins in morphologically distinct (thick and thin) rod types and at least two cone pigments in the heterogeneous cone population.

Carbohydrate components recognized by the cone-specific monoclonal antibody CSA-1 and by peanut agglutinin are associated with red and green-sensitive cone photoreceptors

Previous investigations have demonstrated that the monoclonal antibody CSA-1 and peanut agglutinin label specifically cone photoreceptor cells. In the present study, we compared the binding of CSA-1 and peanut agglutinin to that of the monoclonal antibodies COS-1 and OS-2, which have been shown to recognize the red/green- and blue-sensitive cone visual pigments, respectively. Using lectin and immunocytochemistry on serial semithin sections of the pig retina, we have demonstrated in the present study that both CSA-1 and peanut agglutinin label specifically the red-, and green-sensitive, but not the blue-sensitive cone cell outer segments. Peanut agglutinin does bind, however, to the cone matrix sheaths associated with all three types of cones. These observations support the idea that red-, and green-sensitive cone cells share some common molecular epitopes and may represent a differentiation line of cones, considerably different from that of blue-sensitive cones.

Four cone types characterized by anti-visual pigment antibodies in the pigeon retina

Using three antibodies to visual pigments (monoclonal antibodies COS-1 and OS-2, and a polyclonal anti-opsin serum), four different types of cone cells could be distinguished in the red area (dorsoposterior part with the highest density of cones) of the pigeon retina. Both members of the double cone and the single cone with the red oil droplet were labelled with our monoclonal antibody COS-1 (type I cone). The single cone with the orange oil droplet was positive both with anti-opsin and monoclonal antibody OS-2 (type II cone). The single cone exhibiting a yellowish-green oil droplet, fluorescent in ultraviolet light, also reacted with anti-opsin but lacked the antigenic determinant recognized by OS-2 (type III cone). The thin cone with the small colorless oil droplet was negative with both COS-1 and anti-rhodopsin (type IV cone). We propose that the four immunologically distinguishable cone types correspond to cones expressing visual pigments with different (long-, middle-, short-wavelength and ultraviolet) color sensitivities.

Identification of the blue-sensitive cones in the mammalian retina by anti-visual pigment antibody

Monoclonal antibodies to visual pigments produced in our laboratory were applied to analyze the distribution of color-specific photoreceptor cells in the retina (photoreceptor mosaic). We demonstrated in two ways that the monoclonal antibody OS-2 specifically recognized the blue-sensitive cone cells in the mammalian retina. First, rabbit photoreceptors damaged selectively by intense blue light were recognized by OS-2 antibody. Second, OS-2-positive cones in the ground squirrel were those with thick inner segments, which is known to be characteristic of the blue-sensitive cones. In addition, the OS-2-positive cones in monkeys have a distribution and pattern characteristic of blue-sensitive cones in that species. In several other species (human, rabbit, cow, and pig), the OS-2-positive cones represent an appropriate minority of the population of photoreceptor cells. The visual pigment recognized by the OS-2 antibody had a relative molecular weight of 36,000, as shown by immunoblotting of 3 mammalian species. All other cones were recognized by another monoclonal antibody, COS-1, which is regarded as specific to middle-to-long-wavelength-sensitive photoreceptors.

Immunocytochemical localization of vitamin A in the retina and pineal organ of the frog, Rana esculenta

Vitamin A immunoreactive sites were studied in the retina and pineal organ of the frog, Rana esculenta, by the peroxidase antiperoxidase, avidin-biotinperoxidase and immunogold methods. In dark-adapted material, strong immunoreaction was found in the outer and inner segments of the photoreceptor cells of both retina and pineal organ, as well as in the pigment epithelium, retinal Müller cells and pineal ependymal cells. In light-adapted retina, cones and green (blue-sensitive) rods were immunopositive. At the electron microscopic level, immunogold particles were found on the membranes of the photoreceptor outer segments as well as on the membranes of the endoplasmic reticulum and mitochondria. Individual retinal photorecptor cells exhibited strong immunoreaction in the distal portion of the inner segment, the ciliary connecting piece and the electron-dense material covering the outer segment. In the pigment epithelium, the immunolabeling varied in intensity in the basal and apical cytoplasm and phagocytosed outer segments. The immunocytochemical results indicate that retinoids (retinal, retinol and possibly retinoic acid) are present not only in the photoreceptor cells of the retina but also in those of the pineal organ. The light-dependent differences in the immunoreactivity of vitamin A underlines its essential role in the visual cycle of the photopigments. Our results suggest that the pineal ependyma plays a role comparable to that of the Müller cells and pigment epithelium of the retina with regard to the transport and storage of vitamin A. The presence of a retinoid in nuclei, mitochondria and cytoplasmic membranes suggests an additional role of vitamin A in other metabolic processes.

Slow regeneration of immune complex binding sites on the macrophage surface after previous digestion with pronase

Peroxidase-antiperoxidase (PAP) binding sites on the rat peritoneal macrophage surface were damaged by pronase digestion and the reappearance of functionally intact receptors was investigated morphologically and spectrophotometrically. Pronase digestion decreased the PAP binding ability of macrophages to about 40% of the original value. Removing the pronase the regeneration of ligand binding was very protracted with only about 60% intact receptors even after 30 min. From these findings we conclude that the recycling of internalized Fc receptors greatly contribute to the replenishment of receptors on the cell surface.

Four photoreceptor types in the ground squirrel retina as evidenced by immunocytochemistry

Previous morphological and electrophysiological data show that the ground squirrel retina consists of one rod and two different cone systems. In the present study, immunological evidence is presented that four different photoreceptor cell types are located in the retina of the European ground squirrel (Citellus citellus). In addition to the green and blue cones two rod-like photoreceptor cell types (types 1 and 2) can be distinguished using color specific anti-visual pigment antibodies.

Reappearance of immune complex binding sites on macrophages after internalization and its inhibition by monensin

Receptor-mediated endocytosis of IgG and immune complexes in macrophages is terminated with digestion of the ligand in lysosomes. However, there are controversial data on whether Fc receptors are degraded together with the ligand or recycled to the cell surface. In the present study, rat peritoneal macrophages were incubated at 4 degrees C with rat peroxidase-antiperoxidase (PAP) complex for 1 h, washed and warmed up to 37 degrees C for different time periods and reincubated with new PAP at 4 degrees C. In another series of experiments, the cells were preincubated with 50 nM monensin, then cooled to 4 degrees C and reincubated with PAP in the presence of monensin. The cells were fixed and processed for electron microscopy at different stages of the experiments. Quantitative data were obtained by measuring PAP-binding membrane lengths on electron micrographs (morphometry) and by determining surface-bound PAP with spectrophotometry. In macrophages which had bound PAP at 4 degrees C and were warmed up for 5 min, the PAP was cleared from the cell surface and was found in endosome-like structures. When reincubated with PAP at 4 degrees C, such cells again bound the ligand on the cell surface, mainly in labyrinthic invaginations of the plasma membrane (synonyms: lacunae, caveolar indentations). Macrophages which had been warmed up for longer periods (30 and 60 min) showed the bound ligand all along the plasma membrane. Treatment of cells with monensin did not affect internalization of PAP, however, it decreased the ligand binding ability of macrophages considerably. These findings led us to assume an Fc receptor replenishment from a cytoplasmic pool.

Monoclonal antibody-recognizing cone visual pigment

Monoclonal antibodies were raised to a crude photoreceptor-membrane suspension from chicken retinas. Clones producing antibodies against cone outer segments were selected by screening with immunocytochemistry on semithin sections of the retina. One monoclonal antibody, called COS-1, specifically labelled outer segments of double cones and one type of single cones; outer segments of rods and several single cones were not stained. On immunoblots of retinal photoreceptor membranes, this antibody recognized a protein with an apparent molecular mass of 33,000. The visual pigment character of the 33,000 protein was indirectly established by another monoclonal antibody, OS-2, which labelled all outer segments on semithin sections and four bands (33,000-, 36,000-, 38,000-40,000- and a composite band between 66,000-72,000 MW) on immunoblots. Of these, the 36,000- and the 72,000 MW protein bands were identified with an anti-rhodopsin polyclonal antibody as rhodopsin monomer and dimer. Monoclonal antibody OS-2 is assumed therefore to represent an antibody against a common epitope of all visual pigments of the chicken. The monoclonal antibody COS-1 was found to bind to certain cone outer segments of many other vertebrate species as well.

Immunocytochemical discrimination of visual pigments in the retinal photoreceptors of the nocturnal gecko Teratoscincus scincus

Using a monoclonal antibody (COS-1) against a chicken cone visual pigment and an anti-rhodopsin serum, two visual pigments were distinguished in the gecko retina. One pigment, recognized by the monoclonal antibody COS-1, was found in the outer segments of all photoreceptor cells except the thinner members of type C double cells and the middle members of the triplet cells. These COS-1-negative photoreceptors contained another pigment which could be demonstrated by the anti-rhodopsin serum. Based on an earlier microspectrophotometric study, the visual pigment recognized by COS-1 is a green-sensitive pigment, while the one demonstrated by anti-rhodopsin is a blue-sensitive photopigment.

Heterogeneity of chicken photoreceptors as defined by hybridoma supernatants. An immunocytochemical study

Immune cells producing antibodies to chicken photoreceptor membranes were fused with myeloma cells and supernatants of the resulting hybridoma cells were used to test various types of photoreceptor cells in the chicken retina by means of immunocytochemistry. A polyclonal antibody raised against the protein component of bovine rhodopsin was also used. Outer segments of various photoreceptor cells were labelled by the following antibodies: rods were positive with the anti-rhodopsin antibody, both members of the double cones were stained by supernatant A1, while one type of single cones (designated as type A) was specifically labelled by supernatants A5, B3 and D6. The other type of single cones (type B) reacted with anti-rhodopsin and supernatant A1. The results indicate that there are distinct differences in the molecular structure of various photoreceptor outer segments.

pH-dependent binding of peroxidase-antiperoxidase /PAP/ immune complex to Fc receptors of macrophages

Rat peritoneal macrophages were incubated at 4 degrees C in media of varying pH-s containing rat peroxidase-antiperoxidase /PAP/ immune complex. Two binding maxima were found at pH 5.5 and 7.0, resp. There was a sharp decrease in binding between 5.5 and 5.0. The peak at pH 7.0 was found to be trypsin-sensitive.

Receptor-mediated pinocytosis of IgG and immune complex in rat peritoneal macrophages: an electron microscopic study

The uptake mechanism of homologous IgG and immune complex, and the participation of coated vesicles in this process were studied in rat peritoneal macrophages. Peroxidase-antiperoxidase (PAP) immune complex produced in rat, and purified rat IgG adsorbed to gold particles (IgG-Au) were used as ligands. Freshly collected peritoneal macrophages were preincubated with the ligands at 4 degrees C, washed, warmed up to 37 degrees C, maintained in a serum-free culture medium for 5 sec to 30 min and subsequently fixed for electron microscopy. In the IgG-Au experiments, acid phosphatase reaction was also applied to identify lysosomes, and ruthenium red to trace membranes exposed to the extracellular space. At the end of the preincubation period PAP and IgG were found randomly distributed on the external surface of the plasma membrane. After warming up the cells to 37 degrees C, the ligands bound to the plasma membrane showed a tendency to move towards deep labyrinthic invaginations of the cell surface from where they were internalized via coated pits and coated vesicles. In the initial period, these structures seemed to be the primary carriers of the ligands. In the period between 5 and 10 min, ligands were concentrated in vacuoles (endosomes) located in the deeper cytoplasm, while after 30 min, they were present in large lysosome-like or multivesicular bodies, which were found to be acid phosphatase positive.

Cerebrospinal fluid-contacting neurons, sensory pinealocytes and Landolt's clubs of the retina as revealed by means of an electron-microscopic immunoreaction against opsin

Opsin-immunoreactive sites of hypothalamic cerebrospinal fluid (CSF)-contacting neurons, pinealocytes and retinal cells were studied in various vertebrates (Carassius auratus, Phoxinus phoxinus, Triturus cristatus, Bombina bombina, Rana esculenta) by means of postembedding immuno-electron microscopy with the use of the protein A-gold labeling method. The retina of the rat served as a general reference tissue for the quality of the immunocytochemical reaction. A strong opsin immunoreaction (rat-antibovine opsin serum) was obtained in the rod-type outer segments of photoreceptors in the retina of all species studied. Cone-type outer segments exhibited only very few antigenic binding sites. In the pineal organ of the goldfish and the frog, outer segments of the photoreceptor cells displayed strong immunoreactivity. No immunoreaction was found in hypothalamic CSF-contacting neurons and Landolt's clubs of nerve cells of the bipolar layer of the retina. The morphological similarity between the ciliated dendritic terminal of the Landolt's club and the intraventricular dendritic ending of the CSF-contacting neurons is emphasized.

Early membrane retrieval following exocytosis in rat mast cells

The fate of the surplus membrane following exocytosis of mast cell granules was studied by the extracellular tracer Ruthenium red (Ru red). Isolated rat peritoneal mast cells were stimulated with 4 micrograms/ml polylysine, washed and maintained in a culture medium for 80 min. Mast cells were observed both with the light microscope after adding Ru red in physiological solution and with the electron microscope after fixation in Ru red-containing fixatives. Whereas all exocytotic cavities were found to be stained with Ru red immediately after stimulation, a gradual lack of staining was observed in the subsequent period. The exits of the cavities were sealed by membrane fusions which resulted in closed vacuoles containing exocytosed granule remnants. These vacuoles often fused with each other to form a few giant vacuoles. The overwhelming majority of the vacuoles were observed to be closed 30 to 80 min after stimulation. In one experiment a quantitative analysis was performed to assess the degree of membrane recapture by sealing of the exocytotic cavities. A considerable portion of the plasma membrane area was retrieved in this way as early as between 15 and 30 min after stimulation. We conclude that the dominant mechanism of membrane retrieval in the early period following exocytosis is the recapture of large membrane areas by sealing of exocytotic cavities.