Nonresonant Raman imaging of protein distribution in single human cells

A confocal Raman microscope is used to study the protein distribution inside biological cells. It is shown that high quality Raman imaging of the protein distribution can be obtained using confocal nonresonant Raman imaging (lambda(exc) = 647.1 nm). The results are shown for two different human cell types. Perpheral blood lymphocytes are used as an example of the fully maturated cells with a low level of nuclear transcription. Human eye lens epithelial cells are used as an example of cells with a high level of nuclear activity. The protein distribution in both cell types is completely different. The nuclear distribution of the protein largely varies in the peripheral blood lymphocyte cells, while proteins are more homogenously distributed over the nuclear space in the eye lens epithelial cells. The imaging time is approximately 20 min for a field of view of 10 x 10 microm(2). The size of the sampling volume is 1.4 fL using a full width at half-maximum criterion along the z axis and a 1/e(2) criterion in the xy plane. The results presented here indicate that Raman imaging is particularly of interest in the study of cellular processes, like phagocytosis, apoptosis, chromatin compaction, and cellular differentiation, which are accompanied by relatively large-scale redistributions of the materials.

Nonresonant confocal Raman imaging of DNA and protein distribution in apoptotic cells

Nonresonant confocal Raman imaging has been used to map the DNA and the protein distributions in individual single human cells. The images are obtained on an improved homebuilt confocal Raman microscope. After statistical analysis, using singular value decomposition, the Raman images are reconstructed from the spectra covering the fingerprint region. The data are obtained at a step interval of approximately 250 nm and cover a field from 8- to 15- micro m square in size. Dwell times at each pixel are between 0.5 and 2 s, depending on the nature and the state of the cell under investigation. High quality nonresonant Raman images can only be obtained under these conditions using continuous wave high laser powers between 60 and 120 mW. We will present evidence that these laser powers can still safely be used to recover the chemical distributions in fixed cells. The developed Raman imaging method is used to image directly, i.e., without prior labeling, the nucleotide condensation and the protein distribution in the so-called nuclear fragments of apoptotic HeLa cells. In the control (nonapoptotic) HeLa cells, we show, for the first time by Raman microspectroscopy, the presence of the RNA in a cell nucleus.

Transient activation of cyclin B/Cdc2 during terminal differentiation of lens fiber cells

Previous work has shown that postmitotic, differentiating fiber cells of the embryonic chicken lens express cyclin B and Cdc2. The present study explores the possible physiological role of these proteins in lens differentiation by examining the developmental regulation of cyclin B/Cdc2 expression and activity in lens fiber cells of embryonic and newborn rats. Cyclin B mRNA and protein were detected not only in the lens epithelium, which contains proliferating cells, but also in postmitotic, differentiating fiber cells. In contrast, cyclin A mRNA and protein were detected only in epithelial cells. Immunoprecipitation with cyclin B antibody coprecipitated Cdc2 from both epithelial and fiber cell extracts. Immunoprecipitates of cyclin B from both epithelial cells and fiber cells showed H1 kinase activity when assayed in vitro, but the developmental pattern of cyclin B-associated kinase activity in these two lens fractions was markedly different. In the epithelium, H1 kinase activity decreased gradually with developmental age in parallel with the decrease in epithelial cell proliferation, whereas, in the fiber cells, kinase activity peaked sharply at embryonic day 18 (E18) and E19. Microscopic examination of rat lenses indicated that peak cyclin B/Cdc2 activity was correlated with changes in chromatin structure and nuclear envelope breakdown in the terminally differentiating primary lens fiber cells. These findings suggest that cyclin B/Cdc2 activity may play an active role in nuclear changes leading to primary fiber cell denucleation.

A correlated study of metabolic cell communication and gap junction distribution in the adult frog lens

By using low molecular weight dye injection and laser scanning confocal microscopy it has been possible to assess the degree of dye communication in several regions (intraepithelial, epithelium-fibre cell, fibre-epithelium and fibre-fibre) of the adult frog lens. These same areas of the lens have also been examined by freeze fracture electron microscopy for the presence and organisation of gap junctions. Epithelial cell lateral membranes have numerous gap junctions which efficiently transmitted dye to their neighbours though none was detectable in the underlying fibre cells. This was correlated with an apparent absence of gap junctions at the epithelium/fibre cell interface. Dye spread between cortical fibre cells was only observed in a subset of fibres in the bow region of the lens. Neither mature cortical fibres nor immature bow fibres appeared to be dye-coupled and we detected no dye passed from fibre cells to adjacent epithelial cells at their anterior ends. This pattern of dye communication was also correlated with the apparent absence of recognisable gap junctions on the lateral membranes of either the recently differentiated bow fibres or the mature cortical fibres. Classical gap junctions were only found on the membranes of fibres between five and ten cells in from the lens bow, i.e. the subset of fibres which were dye-coupled. No gap junctions were found between deeper cortical fibres or nuclear fibres, although they were characterised by a number of square arrays. Though electrically well coupled the adult frog lens may be relatively poorly dye coupled and this could depend on the age and differentiation stage of the cells concerned. The model of a freely communicating lens clearly requires re-examination by correlated physiological and morphological studies.

Sympathetic innervation of the rat's eye and peripheral ganglia: an electron microscopic autoradiographic tracing study

The sympathetic innervation of the rat anterior eye segment and related peripheral ganglia was studied using light and electron microscopic autoradiography after anterograde tracing with 3H-leucine from the superior cervical ganglion. In the trigeminal and pterygopalatine ganglia, unmyelinated nerve fibers were labeled. Some fibers contained accumulations of small vesicles. Close apposition of these labeled sympathetic fibers with other unmyelinated fibers was common, and was also observed at sites where accumulations of vesicles were found. In the iris, ciliary body and trabeculum, numerous fibers and vesicle-containing varicosities were labeled, which all had a similar morphology. No labeling was found in the cornea. Sympathetic fibers traversing the trigeminal and pterygopalatine ganglion closely appose other unmyelinated fibers and contain clusters of vesicles without forming classical synaptic contacts. However, non-synaptic information transfer needs further investigation. The anterior eye segment, except for the cornea, is densely innervated by sympathetic nerve terminals.

Dysfunction of the blood-retina barrier following white light exposure. A tracer study with horseradish peroxidase and ferrous gluconate

The aim of this investigation was to study the ultrastructural effects of white light on the retinas of pigmented rabbits. The retinas were exposed to white light (400-740 nm) at intensities between 65 and 140 mW/cm2 for 1 h. Two days after exposure, the increased leakage of fluorescein measured with vitreous fluorophotometry could be mimicked on electron microscopy by the tracers ferrous gluconate and horseradish peroxidase (HRP). In cases of minimal fluorescein leakage, traces of HRP were found in the basal folds of the retina pigment epithelium (RPE). No HRP was observed apical to the tight junctions of the RPE cells. When there was a great amount of fluorescein leakage, HRP completely filled the RPE cytoplasm, the extracellular spaces, and several cells in the neuroretina. It is concluded that after exposure to low intensities of white light, blood-retina barrier dysfunction may be due to disruption of the RPE basal fold membrane, leading to increased transcellular passage. The intact tight junctions suggest the under these circumstances intercellular leakage is not a component of BRB dysfunction.

Membrane architecture as a function of lens fibre maturation: a freeze fracture and scanning electron microscopic study in the human lens

The ultrastructure of fibre membranes in human lenses, varying in age from premature to 40 years, was investigated using a strict protocol regarding their localization within the lens. The ultrastructural approaches used were scanning electron microscopy (SEM), and transmission electron microscopy (TEM) of ultrathin sections and freeze-fracture replicas. Irrespective of the age of the lens, superficial fibre membranes are characterized by a high density of intramembrane particles (IMPs) and numerous gap junctions (GJs). In contrast deep cortical fibres, at the SEM-level characterized by grooves and ridges, are largely free of IMPs but still contain numerous GJs. In between these regions a transitional zone was observed. At the SEM-level the transitional fibres are characterized by wrinkled membranes and formation of grooves and ridges. In freeze-fracture replicas the presence of numerous square arrays (SAs) associated with GJs is most remarkable. It is concluded that at all ages studied, the maturation and compaction of lens fibres results in a transformation of membrane architecture leading to clear-cut ultrastructural differences between superficial and deep cortical membranes. It is argued that this ultrastructural heterogeneity parallels the gradients observed biochemically for intrinsic membrane proteins and cholesterol:phospholipid ratios. The observations confirm the electrophysiological view that superficial membranes have an 'average' permeability and that deep cortical membranes are 'degenerate' or 'non-leaky'.

Square arrays in early cortical lens opacities

A combined freeze-fracture and scanning electron microscopic study of early opaque spots in the aging human lens showed the absence of gap junctions and the presence of square arrays in the membranes of disturbed fibers and neighboring unaffected fibers. Square arrays, with membrane particles of 6-7 nm, are considered as rearranged gap junctions and/or intramembranous particles, with particle sizes between 8.5-9.5 nm; they are a sign of electric and metabolic uncoupling. These ultrastructural observations lend support to the idea of an uncoupling mechanism in the aging human lens, conserving the transparency of unaffected parts of the lens, as postulated previously.

The Hermansky-Pudlak syndrome. Variable reaction to 1-desamino-8D-arginine vasopressin for correction of the bleeding time

The effect of the synthetic vasopressin derivative 1-desamino-8D-arginine vasopressin (DDAVP = Minrin) on bleeding time was studied in nine patients with Hermansky-Pudlak syndrome; four of them were Dutch, five were Belgian. Shortening of bleeding time was observed in four of the patients with this type of storage pool disease; in one patient the response was equivocal, in two patients the response was not dramatic and in two there was no response at all. DDAVP may be useful in managing the bleeding disorder in some patients with Hermansky-Pudlak syndrome. Therefore, every patient with this syndrome should be tested with DDAVP as a preventive measure.

Biomicroscopy and scanning electron microscopy of early opacities in the aging human lens

A large sample of lenses obtained from donor eyes spended for cornea transplantation were biomicroscopically screened and a representative subsample of lenses (about 30) exhibiting early opacities were studied at the scanning electron microscopic (SEM) level. Two types of early cortical opacities (Lens Opacities Classification System cortical grade 1a, 1b) could be distinguished biomicroscopically: (1) radial shades, and (2) circular shades. The prevalence of both types is age related, with an earlier occurrence of radial shades than of circular shades. In addition, radial shades proved to occur as single entities in isolation in lenses from people younger than the age of 40, whereas circular shades are only occasionally found in isolation in older lenses. SEM analysis substantiated the existence of the two early forms of opacity. Radial shades were found to consist of restricted parts of a small group of fibers in the deep cortex. These affected parts had membranes with a fine globular aspect and in cross-section proved to be filled with medium to large globular elements. Neighboring fibers and the nonaffected parts of the fibers involved in the radial shades had a normal SEM ultrastructure. Circular shades proved to originate as fractures of a large cohort of fibers in the deep equatorial cortex perpendicular to the course of the fibers. The fractured faces were slightly swollen, but the membranes on both sides of the fracture had a normal ultrastructure. In cross-sections of more advanced circular shades it proved that the broken fibers are filled with globular elements and are opaque. This opacification proved to extend only in one direction: either anteriorly or posteriorly. The results strongly suggest that two distinct early cataractogenic cellular processes are operating in the aging human lens. The possible induction of circular shades by radial shades, as can tentatively be concluded on account of the difference in appearance during aging of circular and radial shades, needs further verification by SEM analysis of more severely affected lenses. The observations corroborate the suggestion by Bron and Brown of the existence of mechanisms within the lens that separate damaged from undamaged fibers (segregation) or separate affected parts from unaffected parts of individual fibers (sealing).

Lamellar separation in the human lens: the case for fibre folds. A combined in vivo and electron microscopy study

Lamellar separation is seen as parallel lines in the lens cortex. It has been the subject of a joint study between Oxford and Amsterdam. The condition was studied in vivo by macro photography and in vitro by scanning electron microscopy. The lines are seen to run concentric with the lens equator, crossing the lens fibres at right angles. The lines are commonly limited by a spoke cataract, a water cleft, or a lens suture. The line may continue beyond these features with a change in direction. The lines may branch and rejoin. The lines extend in depth into the lens, polarised light showing that the lines are due to reflection. The name 'lamellar separation' implied that the appearance is due to separation between the lens lamellae. Lamellar separation is now shown by electron microscopy to be due to folds crossing the lens fibres. The clinical study showed the lines occurring with spoke cataract and the electron microscopy showed the association with the novel finding of peripheral breaks in the fibres. A new name 'Fibre Folds' is proposed.

Lens fiber organization in four avian species: a scanning electron microscopic study

The three-dimensional organization of the eye lenses of the chicken, the canary, the song-thrush and the kestrel was studied using light and scanning electron microscopy. The lenses of birds are characterized by the presence of two distinct compartments: the annular pad and the main lens body, separated by a cavum lenticuli. The annular pad fibers had a hexagonal circumference all contained a round nucleus and except for the canary were smooth-surfaced and lacking anchoring devices. In the canary, however, the annular pad fibers were studded with edge protrusions and ball-and-socket junctions. The semicircular main lens body fibers of all four species were studded with ball-and-socket junctions and edge protrusions. In contrast with mammals these anchoring devices were present throughout the lens up to the embryonal nucleus. Superficially the main lens body fibers were extremely flat. Additionally membrane elevations and depressions and globular elements were found on these central fibers in three species, the kestrel being the exception. At the transition between annular pad and main lens body the fibers turned their course and the nuclei became oval and disappeared in the deeper aspect of the main lens body. The cavum lenticuli was filled with globules tied off from the annular pad fibers. It seems attractive to assume that the presence of a separated annular pad, a cavum lenticuli filled with globular elements, the extreme flatness of the superficial central fibers and the studding of these central fibers with anchoring devices up to the embryonal nucleus are morphological expressions of the mouldability of the bird's eye lenses and consequently would explain their efficient accommodative mechanism including formation of a lenticonus. The presence of nuclei in the annular pad fibers and their typical change at the transitional zone between annular pad and main lens body are suggestive for a two-phased differentiation in bird's lens fibers: differentiation of the germinative epithelial cells to annular pad fibers which migrate to the main lens body after which they differentiate further to main lens body fibers.

Neodymium YAG laser effects on rabbit lenses

The immediate and long-term effects of Q-switched and mode-locked neodymium (Nd) yttrium-aluminum-garnet (YAG) lasers on the fine structure of lens fibers were studied with stereomicroscopic and scanning electron microscopic methods. This study shows that both laser systems produced very restricted lesions that, at a 1-h survival time, were characterized by an empty central hole surrounded by a thin amorphous wall. Fibers adjacent to the hole looked normal, apart from some compression in the immediate vicinity of the hole. At medium and long-term survival times the empty bubbles now appeared to be filled with a crystal-clear amorphous mass. The wall surrounding the empty lesions had disappeared, and at medium survival times adjacent fibers incidentally showed fiber alterations like local swellings and microplicae. At 180 days the fibers surrounding the central mass showed numerous swellings, microplicae and confluence of fibers. These fiber alterations are also seen in different types of cataracts. Thus, short-pulsed laser lesions may act as cataractogenic centers.

Development of synapses on pyramidal and multipolar non-pyramidal neurons in the visual cortex of rabbits. A combined Golgi-electron microscope study

A combined Golgi-electron microscope method was used to study the ultrastructural maturation of synapses on identified pyramidal and multipolar non-pyramidal neurons in the visual cortex of young and adult rabbits. In samples of 10 (time of eye opening), 14, 20 day old and 7 month old animals, fully impregnated pyramidal neurons within the layers II-V and multipolar non-pyramidal neurons mainly located in lower layer III and layer IV was studied. We found that synapses in 10 and 14 day old animals were occasionally immature in appearance. They were characterized by either a poorly defined postsynaptic band or equal rims of pre- and postsynaptic electron-dense material and could therefore not be classified as Gray type I or II. The distinction between both types of synapses was easier at day 20 and in the adults when the postsynaptic band of the asymmetrical (type I) synapses had become remarkably thicker. In pyramidal neurons the cytoplasmic organelles increased in number during development. Although a few symmetrical synapses were present on dendritic spines of pyramidal neurons in 14 and 20 day old animals, all pyramidal neurons exhibited the same types of synapses on specific sites of their neuronal surface. They received exclusively type II synapses on their somata, type I synapses on their dendritic spines and both types of synapses on their dendritic shafts. However, in the adult animals the frequency of occurrence of type II synapses, especially on basal dendritic shafts, had increased. In some cases only type II and no type I synapses were present. A striking finding in all young and adult animals was that synapses at the borderline between somata and apical dendritic shafts as well as on dendritic spines were frequently complex or interrupted. The characteristic ultrastructural features of adult spine-free and sparsely spiny multipolar non-pyramidal neurons e.g. the many cytoplasmic organelles and type I and II synapses on somata and on dendrites were already present at day 10. After day 10 the number of organelles and synapses increased prominently and in adult animals the different types of synapses on dendrites were located at relatively short intervals of about 4 microns. In contrast with the dendritic shafts of pyramidal neurons many asymmetrical synapses were observed on dendritic shafts of the non-pyramidal neurons analysed in the adult animals. Furthermore, it appeared that the number of synapses on these non-pyramidal neurons is about twice that on pyramidal neurons in day 20 old animals and about four times in adult animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptic characteristics of identified pyramidal and multipolar non-pyramidal neurons in the visual cortex of young and adult rabbits. A quantitative Golgi-electron microscope study

The visual cortex of 20 day old rats and rabbits has been considered as mature on the basis of the observations that the dendritic arborization and the overall synaptic population have almost reached their adult stage in these animals. In the present study we have investigated the visual cortex of 20 day and 7 month old (adult) rabbits in order to determine whether this apparent adult appearance also holds for the synaptic organization of individual neurons. Neurons mainly located in layers III and IV of the primary visual cortex (area 17) were Golgi-impregnated, gold toned and deimpregnated and were then, after embedding in plastic, sectioned serially. The number and length of synaptic profiles, and the length of the neuronal boundaries were analysed in every tenth section. From these counts and measurements the size distribution of the synaptic discs, the number of synapses per 100 micron2 neuronal surface and the receptive surface expressed as the percentage of the total neuronal surface covered with synaptic contacts were estimated using stereological methods. At both ages studied, the density of synapses was significantly higher for the non-pyramidal neurons than for the pyramidal neurons. Differences in the amount of receptive surface were parallel to the differences observed for the number of synapses per 100 micron2. At day 20 the receptive surface of the non-pyramidal neurons was significantly larger than that of the pyramidal neurons. The receptive surface of the non-pyramidal neurons in the adult stage was not only larger than that of the pyramidal neurons in the adults, but also larger than that of the day 20 non-pyramidal neurons. From our results the following conclusions can be drawn: (1) The synaptic input received by the pyramidal neurons is mainly established at day 20 of postnatal life, i.e. prior to the establishment of adult visual behaviour. (2) The non-pyramidal neurons complete their maturation in a later stage than the pyramidal neurons. (3) Medium to large sized synaptic contacts are newly formed after day 20 and are mainly added to the synaptic population on dendrites of non-pyramidal neurons. (4) The specific increase in the number of synapses on non-pyramidal neurons is discussed in relation to intracortical inhibition which is thought to be important for the fine regulation of visual function during development.

Variations in presynaptic grid size in the granular and molecular layer of the cerebellar cortex of the cat. I. A quantitative ultrastructural study on semithin E-PTA sections

The size distribution of synapses in the cerebellar cortex of the cat was defined on 0.5-micron semithin sections stained with ethanolic phosphotungstic acid (E-PTA). The surface area (SA) of synaptic grids was measured and the number of dense projections per grid (NDP) was counted. The results show large differences in mean values between molecular and granular layer. Within the molecular layer the differences in mean values at different levels below the pial surface were small; however, the frequency distributions differed significantly. In the granular layer a confined unimodal frequency distribution of SA and NDP was observed (mean NDP, 7.02 +/- 0.10), in the molecular layer a considerable variation in the size of the synaptic discs was observed (mean NDP, 20.40 +/- 0.43). Only a small percentage of the synaptic discs have less than 5 or more than 47 DPs. The sharply defined differences in synaptic size between the granular and molecular layer and the smaller differences within the granular and molecular layer are discussed in the context of the congruity hypothesis of Chan-Palay.

The ultrastructure of the lens of the cephalopod Sepiola: a scanning electron microscopic study

The ultrastructure of the eye lens of Sepiola atlantica was investigated using scanning electron microscopy. The main lens elements in both the anterior and posterior half of the Sepiola lens are plate-like configurations with fiber-like extensions at their margins. Anteriorly the plates are plano-convex, posteriorly subspherical. The central, primordial, posterior plates are spherical with no marginal extensions. The plates are mutually anchored by protrusions and invaginations and by push-button attachments. The posterior and anterior halves are separated by a septum which consists of concentric zones of radially orientated elongated cells. The marginal extensions of the plates and the septal elements are closely associated. The unique structure of the septum makes it a good candidate for the high resistance barrier between the posterior and anterior halves of the Sepiola lens (Jacob and Duncan, 1981).

Retinopretectal projections in albino and pigmented rabbits: an autoradiographic study

The ipsilateral and contralateral retinal projection was studied in pigmented rabbits and in 3 strains of albino rabbits by anterograde transport of [3H]proline and [3H]fucose combined with autoradiographic techniques. Special attention was paid to the terminals in the pretectal area of both the pigmented and albino strains. On the contralateral side terminal labeling was found in both pigmented and albino rabbits in the nucleus of the optic tract (NOT), the anterior pretectal nucleus (PA), the posterior pretectal nucleus (PP) and the pretectal olivary nucleus (PO). Ipsilaterally labeling was found only in the pigmented strain in small patches in the PP. Ipsilateral projection was not found in the albinos in the pretectal area. The results are in agreement with the findings of Scalia in pigmented rabbits. The absence of ipsilateral labeling in the pretectal region in albinos is in contrast with earlier findings of Giolli and Takahashi et al., in pigmented rabbits but is in agreement with the observations of Takahashi and Oyster. Since no radioactively labeled fibers were found to project to the NOT in either pigmented or albino rabbits, these results do not support the hypothesis of Collewijn that the inverted optokinetic nystagmus in albinos is due to misrouting of the ipsilateral retinal fibers to the NOT.

The three-dimensional organization of lens fibers in the rhesus monkey

The three-dimensional organization of lens fibers in the Rhesus monkey was studied by means of scanning electron microscopy. The mutual anchoring of lens fibers is brought about by three types of interlocking devices: (1) interlocking protrusions on the apical and lateral edges, (2) ball-and-socket junctions on the apical and lateral surfaces, and (3) microplicae or tongues and grooves on the apical and lateral surfaces. Interlocking protrusions are present all over the lens, whereas ball-and-socket junctions and microplicae are restricted to cortical and nuclear regions, respectively. The distinction between interlocking protrusions and ball-and-socket junctions is discussed in detail.

Argon laser lesions of the rabbit iris: quantitative aspects

The destructive effect of nonperforating argon laser coagulations in the brown irides of rabbits was studied with quantitative histological methods. Power, spot size, and exposure time were systematically varied. The lateral and axial extensions of the crater and the denaturation of the adjacent tissue were studied. The main conclusions are: (1) the extent of tissue damage is significantly correlated with power and spot size, though the correlation is not proportional; (2) the lateral extension of the tissue reaction is far more pronounced than the axial extension; (3) increase in exposure time is effective up to 0.2 s, though a further increase up to 0.5 s does not enhance the tissue reaction. It is discussed that for conventionally switched lasers the main determinant for the final extension of the lesion is the density and distribution of the pigment granules within the iris. The radial distribution of the protrusions of the melanocytes in brown irides of the rabbits used in this study favors the lateralization of the tissue reaction. The nonlinearity of the tissue reaction and exposure time might be due to the fact that after initial damage in early phases of irradiation (e.g., up to 50 or 100 ms, the absorbed laser energy is dissipated in already destroyed tissue. Some practical aspects for iridectomy are discussed.

[Argon laser treatment of the iris: an experimental study (author's transl)]

Description of various affections of the iris which may be treated with argon-laser. The problem of the laser iridectomy in the treatment of glaucoma is illustrated by a histologic study of the evolution of the lesions up to four months after coagulation of rabbit's iris.

The three-dimensional organization of lens fibers in the rabbit. A scanning electron microscopic reinvestigation

The importance of the present reinvestigation of the three-dimensional structure of lens fibers in the rabbit is that it has shown the presence of all types of membrane specializations described before in one single lens of one species, the restricted distribution of some specializations, and the conformational changes within one fiber. Interlocking protrusions are present throughout the whole lens and must be considered as the main anchoring processes in the rabbit. Ball-and-socket junctions are present in restricted regions and can be considered an additional anchoring processes. Undulations of the apical and lateral edges of the hexagonal fibers and folds and bends of the lateral surface have a limited distribution. It is postulated that they may play a role in lens changes during accommodation.

Rejected human corneal grafts. II. Light and electron microscopic study

Six rejected human corneal grafts out of a group of 40 'bad-risk corneas' were systematically studied by light and electron microscopy. Remarkable fine structural similarities in this sample of corneas were observed. Granulocytes, lymphocytes and plasma cells are common in all rejected grafts. Furthermore, the epithelial and endothelial linings and the stroma reveal the characteristic alterations. The observations indicate an immunological reaction of the recipient to the donor corneas.

Rejected human corneal grafts. I. Clinical study

As introduction to a light- and electron-microscopial examination of rejected human corneal grafts a summary is given of the clinical signs of rejection. It is extremely important to recognize these signs in time and to initiate the correct therapy. Most failures in corneal transplantation are due to rejection. Rejection reactions are often not recognized early enough. The differential diagnosis is difficult because so many factors can trigger off a rejection. As the diagnosis is so often missed it is a good thing to consider the clinical picture of graft rejection once more. Maumenee: 'most ophthalmologists do not recognize the signs of early graft failure and usually do not refer the patient back for therapy until considerable oedema has developed from endothelial destruction' (1962). In the cases with a good prognosis the rejection percentage is plus or minus 12%; in vascularized corneas and complicated corneal transplantations as high as 75% (Polack, 1977).

The presynaptic grid: a new approach

A new electron microscopic facility is described which enables systematic visualization of E-PTA-stained presynaptic grids in full en face position. This EM-facility is used to analyze the size and the number of dense projections of synaptic grids in different brain areas of the rabbit. The observations support the view that dense projections form an intrinsic part of all central synapses and are organized in a hexagonal or triangular pattern. The observation of annulate and horseshoe-shaped synaptic grids is in agreement with previous observations on synaptic connections with subsynaptic plate perforations. A non-normal frequency distribution of dense projections per synaptic grid with distinct peaks is suggestive for the existence of distinct size classes of synaptic contacts. Analyses of the frequency distribution of dense projections in different areas and at different levels below the pial surface in adult animals point to a specificity of the distinct size classes related to the afferent origin or the target cell they are projecting on. Investigation of grid size and number of dense projections during a period of rapid synaptogenesis reveals that newly formed synapses also have a specific size. The complementarity of dense projections and vesicle attachment sites implicit in the model of Akert et al. has been used to calculate the number of vesicle attachment sites per sq. micrometer on account of the density of projections per grid. The agreement between our values and those of Akert and Peper, based on the analyses of vesicle attachment sites in freeze-etch specimen, is striking. The possible implications of these observations in relation to synaptic efficacy and neuronal microcicuitry are discussed.

Quantitative aspects of the synaptic organization of the superior colliculus in control and dark-reared rabbits

Fine structural and quantitative aspects of the synaptic organization of the superior colliculus of the rabbit were studied. The synaptic density, the frequency of the distinct types of terminals, the length of the contact zones, the percentage of serial contacts and the number of synaptic vesicles per terminal were estimated in control, dark-reared and dark-reared-recovered animals. The ultrastructure of the synaptic terminals and the complex interconnectivity correspond to that described for other species. The depth distribution of terminals with round synaptic vesicles agrees quite well with the distribution of cortical and retinal afferents found in lesion experiments. Dark-rearing has little effect on the quantitative organization of the synaptic terminals. In contrast with previous observations in the visual cortex of the same animals37 no changes in the density of synaptic vesicles is observed in the superior colliculus after long term dark-rearing.

Visual performance and synapses in the visual cortex of rabbits

The density of synaptic connections, the length of the contact zones and the number of synaptic vesicles are quantitatively studied in the left and right hemisphere of a group of rabbits a number of which showed marked ocular dominance. No systematic differences in the parameters studied could be observed in the visual cortex between symmetric animals, indicating that the ocular dominance cannot be explained by hemispheric differences in density of synapses.

The effects of monocular deprivation on synaptic terminals in the visual cortex of rabbits. A quantitative electron microscopic study

The effect of prolonged (7 month) monocular deprivation (right eye sutured) on the density of synapses (NA) and the number of synaptic vesicles (Nves) in the visual cortex of rabbits is studied. The results can be summarized as follows: (1) No changes (NA and Nves) are observed in the non-deprived hemisphere (visual areas I and II, motor cortex) as compared to control animals. (2) NA has not changed, as compared to control animals, in the binocular field of the deprived visual cortex. (3) A significant rise in NA, as compared to control animals, is observed in the monocular field of area I and in the motor cortex of the deprived cortex. This rise is similar to that found after recovery from prolonged dark rearing. (4) The increase in NA is mainly restricted to the laminae I-II, indicating that, most likely, we are not dealing with an increase in specific visual afferents. (5) The deprived visual cortex shows a significant decrease (16%) in NVes. This decrease is less pronounced than after dark rearing (40%). This probably points to the fact that eye suturing does not fully prevent light penetration. The results are discussed in the light of recent discussions on the plasticity of synapses and the effect of retinal input on the development of the visual system.