HyFlex EDM: superficial features, metallurgical analysis and fatigue resistance of innovative electro discharge machined NiTi rotary instruments.

AIM: To evaluate the surface and microstructural alterations of new and used HyFlex EDM prototypes and to test their fatigue resistance. METHODOLOGY: Fifteen HyFlex EDM prototypes were used for in vitro instrumentation of severely curved root canals. Surface and microstructural characteristics of new and used files were compared by ESEM analysis equipped with energy dispersive X-ray spectrophotometry (EDS) and optical metallographic imaging. Usage-induced degradation was assessed. Thirty additional HyFlex EDM prototypes and 20 standard manufactured HyFlex CM files were subjected to cyclic fatigue tests. Time to fracture was recorded, and results were validated using the Kruskal-Wallis test (α-level 0.05). Fatigued files were analysed by ESEM for fractographic evaluation. RESULTS: Surface and microstructural characterization of EDM prototypes revealed the typical spark-machined surface of a NiTi EDM alloy. No fractures were registered during root canal instrumentation. No evident surface alterations and minor degradation were observed between new and used instruments. The metallographic analysis of new and used files disclosed a homogeneous structure, mostly composed of lenticular martensite grains, and some residual austenite. The cyclic fatigue test showed an increase of fatigue resistance up to 700% on the EDM compared to CM files. CONCLUSIONS: Spark-machined peculiar surface is the main feature of HyFlex EDM. Low degradation was observed after multiple canal instrumentations. Prototypes exhibited surprising high values of cyclic fatigue resistance and a safe in vitro use in severely curved canals.

Evaluation of fixation stability using different targets with the MP1 microperimeter.

The aim of this study was to evaluate fixation stability using two different fixation targets with the Nidek MP1 microperimeter. Twenty-nine healthy subjects with a mean age of 26.53 ± 7.35 years and visual acuity ≥0.0 logMAR were enrolled in this study. Fifty-eight eyes of 29 patients without ophthalmic and/or systemic disease underwent a fixation test with the MP1 microperimeter. Fixation stability related to a red cross (central) and/or a red circle (pericentral) target was quantified using either Fujii classification or by calculating the bivariate contour ellipse area (BCEA). For statistical analysis, BCEA values were converted into their logarithms (logBCEA) and all data obtained were analyzed using paired Student's t test. The inclination values of the axis of BCEA were analyzed with Chi squared test. The mean values of logBCEA and the mean values of the major and minor axis of the ellipses related to the cross and the circle fixation target were significantly different (68.2 %, p = 0.00; 95.4 %, p = 0.00; 99.6 %, p = 0.00, respectively) for each BCEA standard deviation. Fixation was significantly less stable for the pericentral fixation target in normal subjects, indicating an advantage for central fixation targets. These results are of particular interest when evaluation of changes in fixation is needed.

Bioelectrical impedance analysis in patients with posterior vitreous detachment.

OBJECTIVE: The purpose of the study is to assess body hydration in patients with posterior vitreous detachment (PVD) by bioelectrical impedance analysis (BIA). PVD, one of the most common eye diseases, is associated in both research and the collective image with reduced daily water intake, but this finding is not supported by strong evidence in the literature. PATIENTS AND METHODS: Based on Spectral Domain Optical Coherence Tomography (SD-OCT) evaluation, different PVD stages are identified: absent posterior vitreous detachment, partial posterior vitreous detachment (P-PVD), or complete posterior vitreous detachment (C-PVD). BIA is a simple, non-invasive bedside method used to assess body composition. Patients underwent BIA and completed a floaters symptoms. 30 patients were enrolled and divided into two groups according to the degree of vitreous detachment, in P-PVD (n=12) and C-PVD (n=18). Patients underwent BIA and completed a floaters symptoms questionnaire. BIA measured the Resistance (R), Reactance (Xc), Phase Angle (PhA), Total Body Water (TBW), Extracellular Water (ECW), Fat Mass (FM), Fat-Free Mass (FFM), and Body Cell Mass Index (BCMI). Finally, patients received a test to assess adherence to the Mediterranean diet (Mediterranean Diet Test Score, MDTS) with the addition of daily water intake. RESULTS: Relevant data were obtained from the BIA evaluation: the values of R and Xc were lower in the P-PVD group than C-PVD group (respectively 417.08±58.12 Ω vs. 476.94±51.29 Ω p=0.006 and 41.33±8.23 Ω vs. 50.61±7.98 Ω p=0.004). Instead, patients in the P-PVD group reported higher values of TBW and ECW than C-PVD group (respectively 44.13±7.57 L vs. 37.96±6.27 L p=0.021 and 21.03±4.06 L vs. 17.24±2.63 L p=0.004). CONCLUSIONS: In the present study, we reported a significant correlation between vitreous pathology and anthropometric and BIA measurements.

Subclinical microvascular changes in ANCA-vasculitides: the role of optical coherence tomography angiography and nailfold capillaroscopy in the detection of disease-related damage.

BACKGROUND: Both cardiovascular and complement-mediated disorders might lead to microvascular damages in anti-neutrophil cytoplasm autoantibodies (ANCA)-associated vasculitides (AAV). We aimed at investigating, for the first time, subclinical microvascular abnormalities with non-invasive techniques in AAV patients by analyzing both retinal and nailfold capillary changes. Retinal plexi were investigated using optical coherence tomography angiography (OCT-A), while nailfold capillary changes by video-capillaroscopy (NVC). Potential correlations between microvessels' abnormalities and disease damage were also explored. METHODS: An observational study was conducted on consecutive patients who met the inclusion criteria of defined diagnosis of eosinophilic granulomatosis with polyangiitis (EGPA), granulomatosis with polyangiitis (GPA), and microscopic polyangiitis (MPA), age ≥ 18 ≤ 75 yrs, and no ophthalmological disorders. Disease activity was assessed by Birmingham Vasculitis Activity Score (BVAS), damage by Vasculitis Damage Index (VDI), and poorer prognosis by the Five Factor Score (FFS). Quantitative analysis of vessel density (VD) was performed by OCT-A in both superficial and deep capillary plexi. Figures and detailed analysis from NVC were performed for all subjects in the study. RESULTS: Included AAV patients (n = 23) were compared with 20 age/sex-matched healthy controls (HC). Retinal VD in superficial whole and parafoveal plexi resulted significantly decreased in AAV compared to HC (P = 0.02 and P = 0.01, respectively). Furthermore, deep whole and parafoveal vessel density was strongly reduced in AAV than HC (P ≤ 0.0001 for both). In AAV patients, significant inverse correlations occurred between VDI and OCTA-VD in both superficial (parafoveal, P = 0.03) and deep plexi (whole, P = 0.003, and parafoveal P = 0.02). Non-specific NVC pattern abnormalities occurred in 82% of AAV patients with a similar prevalence (75%) in HC. In AAV, common abnormalities were edema and tortuosity in a comparable distribution with HC. Correlations between NVC changes and OCT-A abnormalities have not been described. CONCLUSION: Subclinical microvascular retinal changes occur in patients with AAV and correlate with the disease-related damage. In this context, the OCT-A can represent a useful tool in the early detection of vascular damage. AAV patients present microvascular abnormalities at NVC, whose clinical relevance requires further studies.

A literature review of hypertensive retinopathy: systemic correlations and new technologies.

OBJECTIVE: Hypertensive retinopathy (HR) is the most common ocular manifestation of systemic arterial hypertension. This paper aims to summarize the current knowledge of HR, reviewing its classical features, such as epidemiology, pathophysiology, clinical manifestations, classifications, management and the most significant systemic correlations. We also provide an update on the latest advances in new technologies focusing on novel instrumental classifications. MATERIALS AND METHODS: A literature search was performed to identify articles regarding HR listed in Embase, PubMed, Medline (Ovid) and Scopus database up to 1 December 2021. The reference lists of the analyzed articles were also considered a source of literature information. The following keywords were used in various combinations: hypertensive retinopathy, hypertension and eye, hypertensive retinopathy and systemic correlations, optical coherence tomography (OCT) and hypertensive retinopathy, optical coherence tomography angiography (OCTA) and hypertensive retinopathy, adaptive optics (AO) and hypertensive retinopathy. The authors analyzed all English articles found using the aforementioned keywords. All the publications were thoroughly reviewed to create a detailed overview of this issue. RESULTS: HR signs have a significative association with cardiovascular, cerebrovascular and other systemic diseases. Patients with arteriosclerotic changes and, at the same time, severe HR, are at increased risk for coronary disease, peripheral vascular disease, stroke and dementia. HR is even now diagnosed and classified by its clinical appearance on a fundoscopic exam that is limited by interobserver variability. New technologies, like OCT, OCTA, AO and artificial intelligence may be used to develop a new instrumental classification that could become an objective and quantitative method for the evaluation of this disease. They could be useful to evaluate the subclinical retinal microvascular changes due to hypertension that may reflect the involvement of other vital organs. CONCLUSIONS: The eye is the only organ in the human body where changes in the blood vessels due to systemic hypertension can be studied in vivo. All doctors should be familiar with this disease because it has been largely demonstrated that signs of HR are correlated to patient's health and mortality. Researchers should develop a new common, standardized, and objective method to assess hypertensive retinal changes; new technologies may have a significant role in this field. This review takes most of the literature published so far, including the OCTA studies in order to stimulate new points of reference to standardize parameters and new diagnostic markers of this disease.

Is there a rational basis for cannabinoids research and development in ocular pain therapy? A systematic review of preclinical evidence.

BACKGROUND: Purpose of the present systematic review is to investigate preclinical evidence in favor of the working hypothesis of efficacy of cannabinoids in ocular pain treatment. METHODS: Literature search includes the most relevant repositories for medical scientific literature from inception until November, 24 2021. Data collection and selection of retrieved records adhere to PRISMA criteria. RESULTS: In agreement with a priori established protocol the search retrieved 2471 records leaving 479 results after duplicates removal. Eleven records result from title and abstract screening to meet the inclusion criteria; only 4 results are eligible for inclusion in the qualitative synthesis impeding meta-analysis. The qualitative analysis highlights the antinociceptive and anti-inflammatory efficacy of Δ8-tetrahydrocannabinol, cannabidiol and its derivative HU-308 and of new racemic CB1 allosteric ligand GAT211 and its enantiomers GAT228 and GAT229. Moreover, CB2R agonists RO6871304 and RO6871085 and CB2R ligand HU910 provide evidence of anti-inflammatory efficacy. CB2 agonist HU308 reduces of 241% uveitis-induced leukocyte adhesion and changes lipidome profile. Methodological and design issues raise concern of risk of bias and the amount of studies is too small for generalization. Furthermore, the ocular pain model used can resemble only inflammatory but not neuropathic pain. CONCLUSIONS: The role of the endocannabinoid system in ocular pain is underinvestigated, since only two studies assessing the effects of cannabinoid receptors modulators on pain behavior and other two on pain-related inflammatory processes are found. Preclinical studies investigating the efficacy of cannabinoids in ocular inflammatory and neuropathic pain models are needed to pave the way for clinical translation.

Potential role of IL-13 in neuroprotection and cortical excitability regulation in multiple sclerosis.

BACKGROUND: Inflammation triggers secondary neurodegeneration in multiple sclerosis (MS). OBJECTIVES: It is unclear whether classical anti-inflammatory cytokines have the potential to interfere with synaptic transmission and neuronal survival in MS. METHODS: Correlation analyses between cerebrospinal fluid (CSF) contents of anti-inflammatory cytokines and molecular, imaging, clinical, and neurophysiological measures of neuronal alterations were performed. RESULTS: Our data suggest that interleukin-13 (IL-13) plays a neuroprotective role in MS brains. We found, in fact, that the levels of IL-13 in the CSF of MS patients were correlated with the contents of amyloid-ß(1-42). Correlations were also found between IL-13 and imaging indexes of axonal and neuronal integrity, such as the retinal nerve fibre layer thickness and the macular volume evaluated by optical coherence tomography. Furthermore, the levels of IL-13 were related to better performance in the low-contrast acuity test and Multiple Sclerosis Functional Composite scoring. Finally, by means of transcranial magnetic stimulation, we have shown that GABAA-mediated cortical inhibition was more pronounced in patients with high IL-13 levels in the CSF, as expected for a neuroprotective, anti-excitotoxic effect. CONCLUSIONS: The present correlation study provides some evidence for the involvement of IL-13 in the modulation of neuronal integrity and synaptic function in patients with MS.

Major surface protein complex of Treponema denticola induces the production of tumor necrosis factor alpha, interleukin-1 beta, interleukin-6 and matrix metalloproteinase 9 by primary human peripheral blood monocytes.

BACKGROUND AND OBJECTIVE: Treponema denticola is a micro-organism that is involved in the pathogenesis of periodontitis. Major surface protein complex (MSPc), which is expressed on the envelope of this treponeme, plays a key role in the interaction between T. denticola and gingival cells. The peptidoglycan extracted from T. denticola induces the production of a large variety of inflammatory mediators by macrophage-like cells, suggesting that individual components of T. denticola cells induce the inflammatory response during periodontal disease. This study was designed to demonstrate that MSPc of T. denticola stimulates release of proinflammatory mediators in primary human monocytes. MATERIAL AND METHODS: Primary human monocytes were separated from the blood of healthy donors and incubated for up to 24 h with varying concentrations of MSPc. The production of tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6) and matrix metalloproteinase 9 (MMP-9) was measured at different time points with commercially available enzyme-linked immunosorbent assays. RESULTS: T. denticola MSPc induced the synthesis of TNF-alpha, IL-1 beta, IL-6 and MMP-9 in a dose- and time-dependent manner. Similar patterns of TNF-alpha, IL-1 beta and IL-6 release were observed when cells were stimulated with 100 and 1000 ng/mL of MSPc. The production of MMP-9 was significant only when cells were treated with 1000 ng/mL of MSPc. CONCLUSION: These results indicate that T. denticola MSPc, at concentrations ranging from 100 ng/mL to 1.0 microg/mL, activates a proinflammatory response in primary human monocytes.

Comparative evaluation of genome-wide gene expression profiles in ruptured and unruptured human intracranial aneurysms.

Few studies have evaluated the over or the underexpression of genes directly in samples of aneurysmal wall and extracranial pericranial vascular tissue to investigate the genetic influence in formation and rupture of intracranial aneurysms. We present the results obtained using the DNA microarray technique analysis on sample tissues collected during surgery. We collected and analyzed 12 aneurismal and 9 peripheral arteries (superficial temporal (STA) and middle meningeal artery (MMA) specimens from ruptured aneurysm group patients (13 cases), 10 aneurismal and 12 STA and MMA samples from unruptured aneurysm group patients (14 cases) and 5 STA and MMA artery specimens from control group patients (4 cases). Total RNA was isolated from samples and subjected to cDNA microarray analysis with the use of the human genome U133A GeneChip oligonucleotide microarray (Affymetrix, Santa Clara, CA), which allows to analyze a total number of 14,500 genes in the same time. For genes of interest, real-time RT-PCR was performed to confirm their expression level. Total RNA was isolated from samples and subjected to DNA microarray analysis with the use of the human genome U133A GeneChip oligonucleotide microarray, which allows to analyze a total number of 14,500 genes at the same time. For genes of interest, real-time RT-PCR was performed to confirm their expression level. Regarding ruptured aneurysms, genes were identified showing differential expressions (overexpressed or downregulated) pertaining to specific pathways, particularly those for the structural proteins of the extracellular matrix, members of matrix metalloproteinase (MMP) family (which resulted as being overexpressed) and genes involved in apoptotic phenomena. Particularly, real-time RT-PCR analysis confirmed the upregulation of MMP-2, MMP-9 and pro-apoptotic genes, such as Fas, Bax and Bid, and the downregulation of anti-apoptotic genes, such as Bcl-X(L) and Bcl-2. In a compared analyses of ruptured vs unruptured aneurysms, a different expression was also detected regarding gene coding the tissue inhibitor of matrix metalloproteinases 3 (TIMP-3), which appeared markedly downregulated in unruptured aneurysms, where its expression in unruptured aneurysms was similar to that observed in controls. Another gene differently expressed is nitric oxide synthase (iNOS), which appeared overexpressed in ruptured aneurysms when compared to unruptured aneurysms. Our study is the first, to our knowledge, that compares gene expression profiles (genoma-wide) in intracranial aneurysms. The results of our study suggest that the inhibitor of the metalloproteinase, the pathway of nitric oxide and the apoptotic process play a key-role in reducing the resistance of the arterial wall, that can result in formation and rupture of the intracranial aneurysms.

Disruption of structural brain networks in Primary Open Angle Glaucoma.

Primary open angle glaucoma (POAG) is one of the most common causes of permanent blindness in the world. Recent studies have originated the hypothesis that POAG could be considered as a central nervous system pathology which results in secondary visual involvement. The aim of this study is to assess possible structural whole brain connectivity alterations in POAG by combining multi-shell diffusion weighted imaging, multi-shell multi-tissue probabilistic tractography, graph theoretical measures and a newly designed disruption index, which evaluates the global reorganization of brain networks in group-wise comparisons. We found global differences in structural connectivity between Glaucoma patients and controls, as well as in local graph theoretical measures. These changes extended well beyond the primary visual pathway. Furthermore, group-wise and subject-wise disruption indices were found to be statistically different between glaucoma patients and controls, with a positive slope. Overall, our results support the hypothesis of a whole-brain structural reorganization in glaucoma which is specific to structural connectivity, possibly placing this disease within the recently defined groups of brain disconnection syndrome.

Modulation of pro-survival and death-associated pathways under retinal ischemia/reperfusion: effects of NMDA receptor blockade.

Loss of retinal ganglion cells occurs in a variety of pathological conditions, including central retinal artery occlusion, diabetes and glaucoma. Using an experimental model of retinal ischemia induced by transiently raise the intraocular pressure (IOP), In this study, we report the original observation that ischemic retinal ganglion cells death is associated with the transient deactivation of the pro-survival kinase Akt and activation of GSK-3beta followed, during reperfusion, by a longer lasting, PI3K-dependent, activation of Akt and phosphorylation of GSK-3beta. Under these experimental conditions, retinal ischemia induced the expression of Bad, a pro-apoptotic protein, member of the Bcl-2 family. The detrimental effects yielded by the ischemic stimulus were minimized by intravitreal administration of the NMDA receptor antagonist, MK801, that reduced the expression of Bad and significantly increased Akt phosphorylation. In conclusion, our present results contribute to unravel the mechanisms underlying retinal damage by high IOP-induced transient ischemia in rat. In addition, these data implicate the pro-survival PI3K/Akt pathway and the observed reduced expression of Bad in the neuroprotection afforded by MK801.

Neuroprotective agents in the management of glaucoma.

Glaucoma is an optic neuropathy, specifically a neurodegenerative disease characterized by loss of retinal ganglion cells (RGCs) and their axons. The pathogenesis of RGC loss in glaucoma remains incompletely understood and a broad range of possible mechanisms have been implicated. Clinical evidence indicates that lowering intraocular pressure (IOP) does not prevent progression in all patients; therefore, risk factors other than those related to IOP are involved in the disease. The need for alternative, non-IOP-lowering treatments focused at preventing progression, that is, neuroprotectants, has become of interest to both the patient and the physician. Experimental evidence accumulated during the past two decades lend a great deal of support to molecules endowed with neuroprotective features. However, translation to the clinic of the latter drugs results unsuccessful mostly because of the lack of reliable in vivo measure of retinal damage, thus hampering the good therapeutic potential of neuroprotective agents given alone or as adjuvant therapy to IOP-lowering agents. Further research effort is needed to better understand the mechanisms involved in glaucoma and the means to translate into clinic neuroprotective drugs.

Anterior Segment Optical Coherence Tomography Analysis of Iris Morphometric Changes Induced by Prostaglandin Analogues Treatment in Patients with Primary Open Angle Glaucoma or Ocular Hypertension.

BACKGROUND: The study aimed to evaluate iris thickness changes in patients with Primary Open Angle Glaucoma (POAG) or Ocular Hypertension (OHT) under treatment with Prostaglandin Analogues (PG). OBJECTIVES: Primary outcome measures were iris thickness at the region of Dilator Muscle Region (DMR) and Sphincter Muscle Region (SMR). DMR/SMR ratio was also evaluated. The secondary outcome was the correlation between PG treatment length and iris parameters. METHODS: The charts of patients with POAG or OHT who underwent Visante OCT were retrospectively selected. The patients were divided in a group using PG for at least 6 months and a group using hypotensive drops not including PG or alpha-adrenergic agonists. A third group included healthy subjects. RESULT: 98 subjects were selected. Patients with POAG or OHT using PG eyedrops showed a significant iris thickness reduction at DMR compared to healthy subjects and to patients using hypotensive eyedrops not containing PG. Significantly higher SMR thickness values were found in PG group compared to both control groups. DMR/SMR ratio significantly reduced in PG group. No correlation was found between PG treatment length and iris parameters. CONCLUSION: The present data indicate that PG treatment induced DMR thickness reduction and an increase in SMR thickness. These changes were not related to the duration of PG exposure.

Cataract Surgery in Patients with Keratoconus: Pearls and Pitfalls.

BACKGROUND: Keratoconus (KC) is a common ectatic disorder resulting in progressive corneal thinning and irregular astigmatism. It has been observed that patients affected by KC are more likely to develop lens opacities earlier compared to non-keratoconic patients. OBJECTIVE: Intraocular lens (IOL) selection and refractive outcome prediction are among a number of factors that can make cataract surgery in keratoconic patients challenging. Accurate biometry is often difficult to obtain due to unreliable K measurements and lack of dedicated biometric formulae. The use of toric IOLs has also been investigated. CONCLUSIONS: Determining the stage of KC, pre-operative patient counselling and the preferred method of refractive correction are all crucial to obtain successful postoperative outcomes and good patient satisfaction. The use of toric IOLs can achieve good results only in selected low-grade keratoconic eyes.

Direct costs of glaucoma and severity of the disease: a multinational long term study of resource utilisation in Europe.

BACKGROUND: Resource utilisation and direct costs associated with glaucoma progression in Europe are unknown. As population progressively ages, the economic impact of the disease will increase. METHODS: From a total of 1655 consecutive cases, the records of 194 patients were selected and stratified by disease severity. Record selection was based on diagnoses of primary open angle glaucoma, glaucoma suspect, ocular hypertension, or normal tension glaucoma; 5 years minimum follow up were required. Glaucoma severity was assessed using a six stage glaucoma staging system based on static threshold visual field parameters. Resource utilisation data were abstracted from the charts and unit costs were applied to estimate direct costs to the payer. Resource utilisation and estimated direct cost of treatment, per person year, were calculated. RESULTS: A statistically significant increasing linear trend (p = 0.018) in direct cost as disease severity worsened was demonstrated. The direct cost of treatment increased by an estimated 86 for each incremental step ranging from 455 euro per person year for stage 0 to 969 euro per person year for stage 4 disease. Medication costs ranged from 42% to 56% of total direct cost for all stages of disease. CONCLUSIONS: These results demonstrate for the first time in Europe that resource utilisation and direct medical costs of glaucoma management increase with worsening disease severity. Based on these findings, managing glaucoma and effectively delaying disease progression would be expected to significantly reduce the economic burden of this disease. These data are relevant to general practitioners and healthcare administrators who have a direct influence on the distribution of resources.

The gene encoding DRAP (BACE2), a glycosylated transmembrane protein of the aspartic protease family, maps to the down critical region.

We applied cDNA selection methods to a genomic clone (YAC 761B5) from chromosome 21 located in the so-called 'Down critical region' in 21q22.3. Starting from human fetal heart and brain mRNAs we obtained and sequenced several cDNA clones. One of these clones (Down region aspartic protease (DRAP), named also BACE2 according to the gene nomenclature) revealed a striking nucleotide and amino acid sequence identity with several motifs present in members of the aspartic protease family. In particular the amino acid sequences comprising the two catalytic sites found in all mammalian aspartic proteases are perfectly conserved. Interestingly, the predicted protein shows a typical membrane spanning region; this is at variance with most other known aspartic proteases, which are soluble molecules. We present preliminary evidence, on the basis of in vitro translation studies and cell transfection, that this gene encodes a glycosylated protein which localizes mainly intracellularly but to some extent also to the plasma membrane. Furthermore DRAP/BACE2 shares a high homology with a newly described beta-secretase enzyme (BACE-1) which is a transmembrane aspartic protease. The implications of this finding for Down syndrome are discussed.

N omega-nitro-L-arginine methyl ester prevents apoptosis induced in the lateral geniculate nucleus by light deprivation in adult rabbit.

Exposure of adult rabbits to darkness for 48 h produces bilateral DNA fragmentation in the lateral geniculate nucleus as revealed in brain sections by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labelling (TUNEL) technique, suggesting an apoptotic type of cell death. In agreement with the latter deduction, light microscopy assessment of the morphological characteristics showed marginalization and condensation of nuclear chromatin, typical features of apoptosis. These effects were abolished by systemic administration of N omega-nitro-L-arginine methyl ester, an inhibitor of nitric oxide (NO) synthesis, whereas the D isomer was ineffective. In conclusion, the present data demonstrate that light deprivation for 48 h produces apoptosis in the lateral geniculate nucleus of rabbit and suggest that NO might be involved.

N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptor antagonists protect from apoptosis induced in the lateral geniculate nucleus of rabbits exposed to the dark.

Mono or binocular deprivation, during early postnatal development, produces dramatic effects on the anatomy and physiology of the visual system. Here we report that dark exposure induces apoptotic cell death in the lateral geniculate nucleus (LGN) of adult rabbit and this may be related to activation of N-methyl-D-aspartate (NMDA) and non-NMDA subtypes of glutamate receptors. In situ DNA fragmentation (TUNEL) was observed in the LGN of rabbits exposed to dark for 48 h. Morphological changes were confirmed on hematoxylin-eosin stained brain tissue coronal sections. Systemic treatment with CGP 040116 or MK 801, two NMDA receptor antagonists, and with GYKI 52466, a non-NMDA receptor antagonist, prevented in situ DNA fragmentation and nuclear chromatin marginalization and condensation. In no instance was apoptosis seen in rabbits kept under a normal light-dark cycle. Our findings indicate that glutamate, acting on NMDA and non-NMDA receptors, may be involved in the mechanisms of apoptotic cell death induced in the LGN of adult rabbits exposed to darkness.

Nitric oxide enhances amino acid release from immature chick embryo retina.

Nitric oxide (NO) was investigated for its ability to induce amino acid release from immature chick retina. The production of endogenous NO by activation of NO synthase after stimulation of N-methyl-D-aspartate (NMDA) subtype of glutamate receptor caused a significant increase in basal release of gamma-aminobutyric acid (GABA) and glutamine, whereas a more modest increase in the glutamate release was also observed. The exposure of chick retina from 9-day-old embryos to NO-generating compounds, S-nitroso-N-acetylpe-nicillamine (SNAP) and sodium nitroprusside (SNP) produced a dose dependent increase in GABA, glutamine, and glutamate release. This effect was reduced by about 80% by haemoglobin. These results indicate that NO has a stimulatory effect on amino acid release from chick embryo immature retina. However, this effect does not appear to involve a cGMP-related mechanism because 8-bromo-cGMP, a stable analogue of cGMP, failed to affect spontaneous amino acid release and because zaprinast did not enhance NMDA-stimulated release. In conclusion, our present observations may account for a role of NMDA-mediated events in the biochemical maturation under depolarizing conditions.