Blood biomarkers for assessment of mitochondrial dysfunction: An expert review.

Although mitochondrial dysfunction is the known cause of primary mitochondrial disease, mitochondrial dysfunction is often difficult to measure and prove, especially when biopsies of affected tissue are not available. In order to identify blood biomarkers of mitochondrial dysfunction, we reviewed studies that measured blood biomarkers in genetically, clinically or biochemically confirmed primary mitochondrial disease patients. In this way, we were certain that there was an underlying mitochondrial dysfunction which could validate the biomarker. We found biomarkers of three classes: 1) functional markers measured in blood cells, 2) biochemical markers of serum/plasma and 3) DNA markers. While none of the reviewed single biomarkers may perfectly reveal all underlying mitochondrial dysfunction, combining biomarkers that cover different aspects of mitochondrial impairment probably is a good strategy. This biomarker panel may assist in the diagnosis of primary mitochondrial disease patients. As mitochondrial dysfunction may also play a significant role in the pathophysiology of multifactorial disorders such as Alzheimer's disease and glaucoma, the panel may serve to assess mitochondrial dysfunction in complex multifactorial diseases as well and enable selection of patients who could benefit from therapies targeting mitochondria.

Increased ratios of complement factors C3a to C3 in aqueous humor and serum mark glaucoma progression.

INTRODUCTION: We recently performed a combined analysis of publicly available proteomic studies of aqueous humor (AH) of patients with primary open angle glaucoma (POAG). This analysis revealed changes in complement protein concentrations in the AH of progressive POAG patients, which suggested that the complement system may play a role in POAG progression. As the proteomic studies could not provide information on the activity of the complement system, we addressed this question in the current study. METHODS: Blood serum and AH were obtained from 30 patients: 10 progressive POAG, 10 stable POAG and, as controls, 10 cataract patients. Glaucoma patients with a visual field Mean Deviation (MD) change of at least 1.0 dB/year were considered progressive; a MD change of less than 0.5 dB/year was considered stable. The ratio between the levels of complement factors C3a and C3 was used as indicator for activation of the complement cascade. The factors were measured with commercially available ELISA kits. RESULTS: AH levels of complement factors C3 and C3a did not significantly differ between groups. In serum, complement factor C3 did not differ between groups whereas C3a was significantly elevated in progressive POAG patients compared to controls (p < 0.05). The resulting complement C3a/C3 ratio was significantly higher in progressive POAG patients in both AH (p < 0.05) and serum (p < 0.01), and this ratio significantly correlated between the two body fluids (p < 0.001). Furthermore, there was a strong correlation between disease progression and C3a/C3 activation ratio both in AH (p < 0.01) and in serum (p < 0.001). The higher the complement C3a/C3 ratio, the faster the disease progression. CONCLUSION: Significant increases in AH and serum complement C3a/C3 ratios were observed in progressive POAG patients but not in stable POAG patients. Furthermore, the complement C3a/C3 ratio correlated strongly with the rate of disease progression in both AH and serum. These findings suggest that activation of the complement system plays a role in glaucoma progression and that progressive glaucoma patients may have systemic changes in complement activation.

Aqueous humor proteome of primary open angle glaucoma: A combined dataset of mass spectrometry studies.

Analysis of the proteins of the aqueous humor can help to elucidate the complex pathogenesis of primary open angle glaucoma. Thanks to advances in liquid chromatography tandem mass spectrometry (LC-MS/MS) it is now possible to identify hundreds of proteins in individual aqueous humor samples without the need to pool samples. We performed a systematic literature search to find publications that performed LC-MS/MS on aqueous humor samples of glaucoma patients and of non-glaucomatous controls. Of the seven publications that we found, we obtained the raw data of three publications. These three studies used glaucoma patients that were clinically similar (i.e. undergoing glaucoma filtration surgery) which prompted us to reanalyse and combine their data. Raw data of each study were analysed separately with the latest version of MaxQuant (version v1.6.11.0). Outcome files were exported to Microsoft Excel. Samples belonging to the same patient were averaged to obtain peptide expression values per individual. We compared the overlap of identified proteins using the VLOOKUP function of Excel and a publicly available Venn diagram software. For the peptide sequences that can belong to multiple proteins (usually of the same protein family), we initially included all possibly identified proteins. This ensured that we would not miss a potential overlap between the studies due to differences in identified peptide counts. Next, of those peptides of which we compared multiple proteins, only one unique protein was included in our analysis i.e. either the protein overlapping between studies or in case of no overlap, the protein that had the highest identified peptide count. This yielded 639 unique proteins detected in aqueous humor of either glaucoma patients or non-glaucomatous controls. In our manuscript entitled "The aqueous humor proteome of primary open angle glaucoma: An extensive review" [1], we further analysed this dataset. The dataset was exported to Perseus (version 1.6.5.0). We removed contaminants and filtered for proteins detected with high confidence, i.e. in more than 70% of the samples of at least one study. This yielded 248 proteins of which we compared the expression in glaucoma patients against control patients. Gene ontology enrichment analysis and pathway analysis was used to interpret the results. The unfiltered dataset reported in this data article and the approach reported here to reanalyse and combine raw data of different studies can be applied by other glaucoma researchers to gain more insight in the pathogenesis of glaucoma.

The aqueous humor proteome of primary open angle glaucoma: An extensive review.

BACKGROUND: We reviewed the literature on the aqueous humor (AH) proteome of primary open angle glaucoma (POAG) patients in order to obtain deeper insight into the pathophysiology of POAG. METHODS: We searched Pubmed and Embase up to May 2019 for studies that compared AH protein composition between POAG (cases) and cataract (controls). Untargeted studies (measuring the whole proteome, by LC-MS/MS) were divided into two subgroups depending on the type of surgery during which POAG AH was collected: glaucoma filtration surgery (subgroup 1) or cataract surgery (subgroup 2). We reanalyzed the raw data (subgroup 1) or combined the reported data (subgroup 2) to perform GO enrichment (GOrilla) and pathway analysis (Pathvisio). RESULTS: Out of 93 eligible proteomic studies, seven were untargeted studies that identified 863 AH proteins. We observed 73 differentially expressed proteins in subgroup 1 and 87 differentially expressed proteins in subgroup 2. Both subgroups were characterized by activation of the acute immune response, dysregulation of folate metabolism and dysregulation of the selenium micronutrient network. For subgroup 1 but not for subgroup 2, proteins of the complement system were significantly enriched. CONCLUSION: AH proteome of POAG patients shows strong activation of the immune system. In addition, analysis suggests dysregulation of folate metabolism and dysregulation of selenium as underlying contributors. In view of their glaucoma surgery, POAG patients of subgroup 1 most likely are progressive whereas POAG patients in subgroup 2 most likely have stable POAG. The proteome difference between these subgroups suggests that the complement system plays a role in POAG progression.

Stem Cell Derived Retinal Pigment Epithelium: The Role of Pigmentation as Maturation Marker and Gene Expression Profile Comparison with Human Endogenous Retinal Pigment Epithelium.

In age-related macular degeneration (AMD) the retinal pigment epithelium (RPE) deteriorates, leading to photoreceptor decay and severe vision loss. New therapeutic strategies aim at RPE replacement by transplantation of pluripotent stem cell (PSC)-derived RPE. Several protocols to generate RPE have been developed where appearance of pigmentation is commonly used as indicator of RPE differentiation and maturation. It is, however, unclear how different pigmentation stages reflect developmental stages and functionality of PSC-derived RPE cells. We generated human embryonic stem cell-derived RPE (hESC-RPE) cells and investigated their gene expression profiles at early pigmentation (EP) and late pigmentation (LP) stages. In addition, we compared the hESC-RPE samples with human endogenous RPE. We used a common reference design microarray (44 K). Our analysis showed that maturing hESC-RPE, upon acquiring pigmentation, expresses markers specific for human RPE. Interestingly, our analysis revealed that EP and LP hESC-RPE do not differ much in gene expression. Our data further showed that pigmented hESC-RPE has a significant lower expression than human endogenous RPE in the visual cycle and oxidative stress pathways. In contrast, we observed a significantly higher expression of pathways related to the process adhesion-to-polarity model that is typical of developing epithelial cells. We conclude that, in vitro, the first appearance of pigmentation hallmarks differentiated RPE. However, further increase in pigmentation does not result in much significant gene expression changes and does not add important RPE functionalities. Consequently, our results suggest that the time span for obtaining differentiated hESC-RPE cells, that are suitable for transplantation, may be greatly reduced.

Dealing with a life changing event: The influence of spirituality and coping style on quality of life after survival of a cardiac arrest or myocardial infarction.

BACKGROUND: Survivors of a cardiac arrest often have cognitive and emotional problems. As a cardiac arrest is also an obvious life-threatening event, other psychological sequelae associated with surviving such as spirituality may also affect quality of life. OBJECTIVES: To determine the relationship between spirituality, coping and quality of life in cardiac patients both with and without a cardiac arrest. METHODS: In this retrospective cohort study, participants received a questionnaire by post. The primary outcome measure was quality of life (LiSat-9). Secondary outcome measures were spiritual well-being (FACIT-Sp12), coping style (UPCC), emotional well-being (HADS, IES), fatigue (FSS) and daily activities (FAI). Statistical analyses included multiple regression analyses. RESULTS: Data were available from 72 (60% response rate) cardiac arrest survivors and 98 (47%) patients with a myocardial infarction. Against our hypothesis, there were no differences in spirituality or other variables between the groups, with the exception of more depressive symptoms in patients with myocardial infarction without arrest. Analysis of the total data set (170 participants) found that a better quality of life was associated with higher levels of meaning and peace in life, higher levels of social and leisure activities, and lower levels of fatigue. CONCLUSIONS: Quality of life after a cardiac arrest and after a myocardial infarction without arrest are not different; fatigue, a sense of meaning and peace, and level of extended daily activities are factors related to higher life satisfaction.

Disseminated arterial calcification and enhanced myogenic response are associated with abcc6 deficiency in a mouse model of pseudoxanthoma elasticum.

OBJECTIVE: Pseudoxanthoma elasticum is an inherited metabolic disorder resulting from ABCC6 gene mutations. It is characterized by progressive calcification and fragmentation of elastic fibers in the skin, retina, and the arterial wall. Despite calcium accumulation in the arteries of patients with pseudoxanthoma elasticum, functional consequences remain unknown. In the present study, we investigated arterial structure and function in Abcc6(-/-) mice, a model of the human disease. APPROACH AND RESULTS: Arterial calcium accumulation was evaluated using alizarin red stain and atomic absorption spectrometry. Expression of genes involved in osteochondrogenic differentiation was measured by polymerase chain reaction. Elastic arterial properties were evaluated by carotid echotracking. Vascular reactivity was evaluated using wire and pressure myography and remodeling using histomorphometry. Arterial calcium accumulation was 1.5- to 2-fold higher in Abcc6(-/-) than in wild-type mice. Calcium accumulated locally leading to punctuate pattern. Old Abcc6(-/-) arteries expressed markers of both osteogenic (Runx2, osteopontin) and chondrogenic lineage (Sox9, type II collagen). Abcc6(-/-) arteries displayed slight increase in arterial stiffness and vasoconstrictor tone in vitro tended to be higher in response to phenylephrine and thromboxane A2. Pressure-induced (myogenic) tone was significantly higher in Abcc6(-/-) arteries than in wild type. Arterial blood pressure was not significantly changed in Abcc6(-/-), despite higher variability. CONCLUSIONS: Scattered arterial calcium depositions are probably a result of osteochondrogenic transdifferentiation of vascular cells. Lower elasticity and increased myogenic tone without major changes in agonist-dependent contraction evidenced in aged Abcc6(-/-) mice suggest a reduced control of local blood flow, which in turn may alter vascular homeostasis in the long term.

The dynamic nature of Bruch's membrane.

Bruch's membrane (BM) is a unique pentalaminar structure, which is strategically located between the retinal pigment epithelium (RPE) and the fenestrated choroidal capillaries of the eye. BM is an elastin- and collagen-rich extracellular matrix that acts as a molecular sieve. BM partly regulates the reciprocal exchange of biomolecules, nutrients, oxygen, fluids and metabolic waste products between the retina and the general circulation. Accumulating evidence suggests that the molecular, structural and functional properties of BM are dependent on age, genetic constitution, environmental factors, retinal location and disease state. As a result, part of the properties of BM are unique to each human individual at a given age, and therefore uniquely affect the development of normal vision and ocular disease. The changes occurring in BM with age include increased calcification of elastic fibres, increased cross-linkage of collagen fibres and increased turnover of glycosaminoglycans. In addition, advanced glycation end products (AGEs) and fat accumulate in BM. These age-related changes may not only influence the normal age-related health of photoreceptor cells, but also the onset and progression of diseases like retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Undoubtedly, BM is the site of drusen development. Confluent drusen and uncontrolled activation of the complement cascade are most likely the first signs of AMD. Furthermore, the nature of adhesive interactions between the RPE and BM are instrumental in the development of retinal detachments and proliferative retinal disease. Finally, BM is passively or actively involved in a range of other retinal disorders such as Pseudoxanthoma elasticum (PXE), Sorsby's Fundus Dystrophy and Malattia Leventinese. Here, we review the dynamic nature of Bruch's membrane, from molecule to man, during development, aging and disease. We propose a simple and straightforward nomenclature for BM deposits. Finally, we attempt to correlate recently published mRNA expression profiles of the RPE and choroid with molecular, structural and functional properties of BM. Our review may shed light on the complex involvement of BM in retinal pathology, notably age-related macular degeneration.

[From gene to disease; pseudoxanthoma elasticum and the ABCC6 gene]. / Van gen naar ziekte; pseudoxanthoma elasticum en het ABCC6-gen.

Pseudoxanthoma elasticum (PXE) is a hereditary disease of the connective tissue characterized by progressive dystrophic mineralization of elastic fibres. PXE patients have skin lesions, may experience loss of visual acuity and cardiovascular complications. The inheritance pattern of PXE is almost always autosomal recessive. In less than 2% of the families, PXE may be inherited in an autosomal dominant fashion. PXE is caused by mutations in the ABCC6 (MRP6) gene. The R1141X mutation is by far the most common mutation; it has been identified in 19 patients, or 30% of all PXE-patients in the Netherlands. The molecular pathology of PXE is complicated by yet unknown factors causing a variable clinical expression of the disease. In 80% of the 110 PXE patients the authors studied, at least one ABCC6 mutation was found. Molecular diagnostics of PXE is especially useful to confirm the clinical diagnosis.

The effects of two stereoisomers of N-acetylcysteine on photochemical damage by UVA and blue light in rat retina.

High doses of light can cause damage to the retina, e.g. during intraocular surgery. Previously, thiols have been demonstrated to protect against retinal damage in various damage models. Such protection is very promising for clinical practice. Retinal light damage can be caused by a relatively short exposure to high irradiance levels. These conditions occur during intraocular surgery. In the current study we therefore investigated whether the thiol N-acetylcysteine protects against retinal light damage under high irradiance conditions in the rat retina. Two stereoisomers of this thiol were tested for protection against two spectrally defined types of retinal light damage. Shortly after administration N-acetyl-L-cysteine in doses of 270-1000 mg/kg intraperitoneally protected against 380 nm (UVA) light but not against 470 nm (blue) light. Two hours after injection the protection had diminished. We observed no protection by the stereoisomer N-acetyl-D-cysteine. From this study we conclude that N-acetyl-L-cysteine protects stereospecifically against retinal damage in the UV but not in the visible part of the spectrum. This limits the possible applications.

Temporal sequence of changes in rat retina after UV-A and blue light exposure.

Two spectral types of retinal light damage were induced in pigmented rats by irradiating small retinal patches at either 380 or 470 nm. The temporal sequence of changes in the retina was followed for up to 2 months by funduscopy and histology. For both damage types, fundus changes were best visible after 3 days. Histology showed that 380 nm specifically damaged photoreceptor cells, particularly the rods. All cell compartments of the rods, including the nucleus were affected already after 3 h. In the next days, damaged rods degenerated. At high doses (2.5 x the funduscopic threshold dose) all rods in the irradiated area were lost, resulting in a local photoreceptor lesion, which was still present at 2 months after the irradiation. At 470 nm, damage occurred both in the photoreceptor layer and in the pigment epithelium. Acute changes, at 1 h after irradiation, consisted mainly of damaged mitochondria in these layers. Next, the pigment epithelium showed swelling, an altered melanin distribution and, at high doses (2.5 x threshold), interruptions of the monolayer. Degeneration of photoreceptor cells was initially limited to a few scattered cells, but 3 days after high doses focal areas of massive degeneration were seen. At late stages, the cells of the pigment epithelium recovered and the photoreceptor layer showed a loss of cells. The results show that the spectral damage types are distinct in the early phases, indicating that different mechanisms are involved. Yet, the end effect of both damage types after exposure at doses up to 2.5 x the funduscopic threshold is remarkably similar and consists of local photoreceptor lesions.

Filling-in after focal loss of photoreceptors in rat retina.

We investigated the fate of isolated photoreceptor lesions in rat retina over a time span of 6 months. With a carefully selected dose of UV-A (380 nm) a complete loss of photoreceptors was caused in sharply demarcated areas of 200, 400 or 800 microm wide, without visible damage to other retinal layers. One day after irradiation, all rods were pyknotic. Three weeks later practically all damaged photoreceptors were removed. The size of the lesion had decreased as the surrounding photoreceptors had migrated into the lesion. The outer segment tips had moved inwards up to 200 microm, but the innermost nuclei in the outer nuclear layer had moved inwards substantially less. The distance over which the photoreceptors migrated increased with lesion size, but only 200 microm defects were filled-in completely on the level of the outer segments. Between three weeks and six months after irradiation, no further decrease in lesion size occurred. We conclude that after local loss of photoreceptor cells the bordering photoreceptors rapidly shift into the lesion area, but complete filling-in is limited to very small lesions.

Effects of education and support on self-care and resource utilization in patients with heart failure.

AIMS: To test the effect of education and support by a nurse on self-care and resource utilization in patients with heart failure. METHODS: A total of 179 patients (mean age 73, 58% male, NYHA III-IV) hospitalized with heart failure were evaluated prospectively. Patients were randomized to the study intervention or to 'care as usual'. The supportive educative intervention consisted of intensive, systematic and planned education by a study nurse about the consequences of heart failure in daily life, using a standard nursing care plan developed by the researchers for older patients with heart failure. Education and support took place during the hospital stay and at a home visit within a week of discharge. Data were collected on self-care abilities, self-care behaviour, readmissions, visits to the emergency heart centre and use of other health care resources. RESULTS: Education and support from a nurse in a hospital setting and at home significantly increases self-care behaviour in patients with heart failure. Patients from both the intervention and the control group increased their self-care behaviour within 1 month of discharge, but the increase in the intervention group was significantly more after 1 month. Although self-care behaviour in both groups decreased during the following 8 months, the increase from baseline remained statistically significant in the intervention group, but not in the control group. No significant effects on resource utilization were found. CONCLUSIONS: Intensive, systematic, tailored and planned education and support by a nurse results in an increase in patients' self-care behaviour. No significant effects were found on use of health care resources. Additional organisational changes, such as longer follow-up and the availability of a heart failure specialist would probably enhance the effects of education and support.

Ultraviolet-B induced hyperplasia and squamous cell carcinomas in the cornea of XPA-deficient mice.

In Xeroderma Pigmentosum (XP) patients, due to a defective repair of UV-induced DNA damage, neoplastic changes occur in sunlight-exposed areas of the skin and eyes. There are seven complementation groups in XP (XP-A to XP-G). Recently, we have generated XPA-deficient mice (group-A XP) by gene targeting in embryonic stem cells. In order to evaluate UV-B sensitivity, XPA-deficient mice (n = 20), wild type (n = 7) and heterozygous mice (n = 13) were exposed to low daily doses of UV-B for 14 weeks at a cumulative dose of 22 kj m-2 (250-400 nm). For a period of 32 weeks, the mice were checked twice a week for the development of pathology. The UV-B treatment induced eye abnormalities in the XPA-deficient mice. Initially, photophobia was noticed, followed by a loss of transparency of the cornea, eventually affecting nearly all XPA-deficient mice (19 out of 20). In 12 out of 19 mice, the pathology progressed to give eye protrusion. Histology of these eyes showed hyperplasia and squamous cell carcinomas of the corneal epithelium. No eye-lesions were found in control (wild-type and heterozygous) mice that were exposed to the same UV-B dose. The corneal abnormalities found in the XPA-deficient mice appear to be similar to those found in human XP patients. These results confirm the role of the functional XPA gene in protecting the cornea from pathology by UV-B irradiation. In addition, they suggest that the XPA-deficient mouse is a suitable animal model for the study of XPA ocular disorders.

Two spectral types of retinal light damage occur in albino as well as in pigmented rat: no essential role for melanin.

Earlier we showed that two spectral types of retinal damage occur in the pigmented rat. In the present study we investigated whether the same is true for albino rats. When investigating this issue we implicitly investigated the role of melanin in both damage types. An albinotic (Wistar) and a pigmented (Long Evans) strain of rats were used. Under anesthesia, a small part of the retina was irradiated at either 380 nm or at 470 nm. Three days later, the retina was analysed by funduscopy and prepared for light microscopy. Funduscopy showed no signs of damage in the albinotic retina. In the pigmented retina a decoloration of the fundus was noticed after irradiations starting from retinal doses of 0.6+/-0.1 J cm-2 at 380 nm, and from 489+/-71 J cm-2 at 470 nm. By light microscopy, retinal damage was found in the albino retina. The histologic manifestations at 380 nm differed from those at 470 nm. Irradiation at 380 nm at a dose of 0. 5-0.9 J cm-2 damaged a few scattered photoreceptor cells. At doses of 1.2-1.6 J cm-2 all rods were damaged, while the other retinal layers showed no changes. These findings were similar to those found at 380 nm in the pigmented rat. At 470 nm, damage was found most prominently in the retinal pigment epithelium. These cells showed swelling and an increased number of dark inclusions. Threshold damage occurred at doses of 250-500 J cm-2. Again, the pathology in the pigmented rat was highly similar to that in the albino rat. The results show that both spectral damage types occur in albino as well as in pigmented retina. Therefore, melanin plays no crucial role in these light damage types.

Effect of body temperature on retinal damage by 488 nm light in rat.

Retinal light damage is influenced by the body temperature during exposure, but previous studies do not agree on the magnitude of the effect. A study in rats with broadband green light reported a much larger effect than a study with 380 nm light. The present study set out to clarify whether the spectral composition of the damaging light is responsible for this discrepancy by using 488 nm instead of 380 nm light. Wavelengths in the range of 470-550 nm are known to produce a different damage type than 380 nm. Small patches of retina of anesthetized rats were exposed to 488 nm radiation of an argon ion laser. Body temperature was varied between 30 and 40.5 degrees C. Three days after irradiation, the retina was inspected by funduscopy and prepared for light microscopy. The dose of radiation needed for a just visible change in fundo decreased by 6% per degree increase in body temperature. Damage was mainly found in the retinal pigment epithelium. Temperature had no effect on damage morphology. The temperature effect at 488 nm is much smaller than reported for broadband green light. We conclude that the spectral composition of the damaging light is not responsible for the discrepancy on the magnitude of the temperature effect. Other differences between the studies must be responsible, such as difference in retinal irradiance levels.

Occurrence of arrhythmias in general practice.

OBJECTIVE: To study the occurrence and distribution of arrhythmias in patients with symptoms possibly caused by arrhythmias, in order to support the diagnostic process in general practice. DESIGN: From 1989-1991 all patients who consulted their general practitioner with symptoms or signs possibly indicating an arrhythmia had a transtelephonic electrocardiogram, which was sent to the Department of Cardiology for interpretation. SETTING: 20 Dutch general practices, serving a population of nearly 50,000 inhabitants. SUBJECTS: A total of 868 patients were included in the study. RESULTS: An arrhythmia was documented by ECG in 32% of the patients. Of these, 31% clinically more relevant arrhythmias needed medical attention. An incidence of 2.6 arrhythmias per 1000 listed patients was calculated. There was a highly positive correlation between the occurrence of arrhythmias and age. Relatively more arrhythmias were seen in men, in patients with occasional findings, and when there were symptoms that possibly indicated haemodynamic imbalance. CONCLUSION: Clinically relevant arrhythmias can be detected in general practice with 12-lead ECG recording in a significant proportion of patients with symptoms and physical findings suggesting an arrhythmia. The distribution of arrhythmias described in this study can help general practitioners in their diagnostic management.

Ultraviolet and green light cause different types of damage in rat retina.

PURPOSE: To assess the influence of wavelength on retinal light damage in rat with funduscopy and histology and to determine a detailed action spectrum. METHODS: Adult Long Evans rats were anesthetized, and small patches of retina were exposed to narrow-band irradiations in the range of 320 to 600 nm using a Xenon arc and Maxwellian view conditions. After 3 days, the retina was examined with funduscopy and prepared for light microscopy. RESULTS: The dose that produced a change just visible in fundo was determined for each wavelength. This threshold dose for funduscopic damage increased monotonically from 0.35 J/cm2 at 320 nm to 1600 J/cm2 at 550 nm. At 600 nm, exposure of more than 3000 J/cm2 did not cause funduscopic damage. Morphologic changes in retinas exposed to threshold doses at wavelengths from 320 to 440 nm were similar and consisted of pyknosis of photoreceptors. Retinas exposed to threshold doses of 470 to 550 nm had different morphologic appearances. Retinal pigment epithelial cells were swollen, and their melanin had lost the characteristic apical distribution. Some pyknosis was found in photoreceptors. CONCLUSIONS: Damage sensitivity in rat increases enormously from visible to ultraviolet wavelengths. Compelling evidence is presented that two morphologically distinct types of damage occur in the rat retina, depending on the wavelength. Because two types also have been described in monkey, a remarkable similarity seems to exist across species.

Spectral transmittance of the rat lens.

The spectral transmittance of the isolated rat lens for radiation of wavelengths from 300 to 700 nm was measured using a spectrophotometer. Transmittance decreased from 93-95% at 700 nm, to 70-80% at 400 nm, 50-60% at 360 nm, 4-18% at 320 nm, and to < 2% at 310-300 nm. These results indicate that the rat lens is remarkably transparent for UVA radiation, which has consequences for rat vision, and for interpretation of earlier studies on retinal light damage.

Junctional specializations between growth cones and glia in the developing rat pyramidal tract: synapse-like contacts and invaginations.

The ultrastructure of contacts between axonal growth cones and glial cells in the developing pyramidal tract was examined by serial sectioning at the third cervical spinal cord segment in 0-, 2-, and 4-day-old rats. Junctional specializations, composed of synapse-like contacts and invaginations, were frequently observed at the contact zone between growth cones and glial elements. The synapse-like contacts consist of clear, round vesicles of 43 +/- 6 nm in the presynaptic growth cone, a pre- and a postsynaptic density, separated by a cleft of 12.1 +/- 0.9 nm. The invaginations consist of small protrusions of the growth cone into the glial element. The invaginated glial membrane is coated. Within the glial element, close to the invagination, frequently organelles were observed that closely resemble endosomes and prelysosomes. Therefore, it is suggested that the invagination represents a stage in endocytosis or possibly phagocytosis of the protruding part of the growth cone by the glial cell. The junctional specializations are formed by growth cones and, less frequently, by axon shafts. The targets of these specialized contacts are, in general, immature glial cells located within the tract area. Occasionally, however, invaginations were also observed into myelinating oligodendrocytes, suggesting that the population of immature target cells includes oligodendrocyte precursors. With regard to the functional significance of these temporary growth cone-glial contacts, several possibilities are discussed, including the suggestion that outgrowing pyramidal tract axons provide immature glial cells with chemical messages, which may influence the timing of glial cell maturation in the tract.