Deterioration in brain and heart functions following a single sub-lethal (0.8 LCt50) inhalation exposure of rats to sarin vapor: a putative mechanism of the long term toxicity.

The main injuries among victims of the terrorist act in the Tokyo subway resulted from sub-lethal inhalation and whole body exposure to sarin vapor. In order to study the long term effects of such exposure and to simulate these conditions, freely moving rats were exposed to sarin vapor (27.2±1.7 µg/l) for 10 min. About 50% of the rats showed no overt symptoms and the rest had mild to moderate clinical symptoms that subsided within 4h following exposure. A reduction of weight was noted during the first 3 days with full recovery on the 4th day. Rat's heart was challenged with epinephrine 1 and 6 months post exposure. A significant reduction in the threshold for epinephrine-induced arrhythmia (EPIA) was noted in rats exposed to sarin. A time dependent increase in the kD and Bmax values of muscarinic auto receptors (M2) was recorded in the rat's cortex and striatum. No changes were recorded in the rats' brain trans locator protein (TSPO) levels, concomitant with no observed changes in the animals' performance in A Morris water maze test. A significant increase in open field activity was noted 6 months following exposure to sarin vapor as well as a significant decrease in prostaglandin E2 (PGE2) production in the brain. It is speculated that down regulation of the M2 auto receptor function, caused hyper reactivity of the cholinergic system which leads to the changes described above. The continuous reduction in M2 auto-receptor system through an unknown mechanism may be the cause for long lasting decline in sarin-exposed casualties' health.

Acute and long-lasting cardiac changes following a single whole-body exposure to sarin vapor in rats.

Epinephrine-induced arrhythmias (EPIA) are known to be associated with local cardiac cholinergic activation. The present study examined the development of QT prolongation and the effect on EPIA of whole-body exposure of animals to a potent acetylcholine esterase inhibitor. Freely moving rats were exposed to sarin vapor (34.2 +/- 0.8 microg/liter) for 10 min. The electrocardiograms (ECG) of exposed and control animals were monitored every 2 weeks for 6 months. One and six months post exposure, rats were challenged with epinephrine under anesthesia, and the threshold for arrhythmias was determined. Approximately 35% of the intoxicated rats died within 24 h of sarin exposure. Additional occasional deaths were recorded for up to 6 months (final mortality rate of 48%). Surviving rats showed, agitation, aggression, and weight loss compared to non-exposed rats, and about 20% of them experienced sporadic convulsions. Sarin-challenged rats with severe symptoms demonstrated QT segment prolongation during the first 2-3 weeks after exposure. The EPIA that appeared at a significantly lower blood pressure in the treated group in the first month after intoxication lasted for up to 6 months. This decrease in EPIA threshold was blocked by atropine and methyl-atropine. Three months post exposure no significant changes were detected in either k(D) or B(max) values of (3)H-N-methyl scopolamine binding to heart homogenates, or in the affinity of carbamylcholine to cardiac muscarinic receptors. The increase in the vulnerability to develop arrhythmias long after accidental or terror-related organophosphate (OP) intoxication, especially under challenging conditions such as stress or intensive physical exercise, may explain the delayed mortality observed following OP exposure.

Measurement of NO and NO synthase.

Nitric oxide (NO) is a key biosignaling molecule produced in both peripheral tissues and the central nervous system by a family of enzymes known as nitric oxide synthases (NOSs). NOSs convert L-arginine to stoichiometric quantities of NO and L-citrulline using molecular oxygen and NADPH as cofactors. Techniques for measurement of NO and NOS activity are essential to demonstrate the role of NO and NO-derived species in biological systems. This unit describes two methods for detection of NO: a direct method employing chemiluminescent detection and one based on quantification of the stable oxidation products with detection using the Griess reagent. Additionally, NOS activity can be quantified by measuring the conversion of radiolabeled L-arginine to radiolabeled L-citrulline.

Factors associated with corneal scarring in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study.

PURPOSE: The multicenter Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a prospective, observational study of 1,209 keratoconus patients. We report on the factors associated with corneal scarring at baseline. METHODS: We defined corneal scarring as scars that had been detected both by the clinician examining the patient with the slit-lamp biomicroscope and by masked readers of corneal photographs at the CLEK Photography Reading Center. We investigated associations between corneal scarring and patient variables including gender, ethnicity, a family history of keratoconus, a history of ocular trauma, eye rubbing, contact lens wear, rigid contact lens fitting relationships, and corneal findings (such as curvature, Vogt's striae, Fleischer's ring, and central/apical staining). Multiple logistic regression analysis using generalized estimating equations to adjust for the correlation between eyes was used for analysis. RESULTS: The following factors were found to increase the odds of corneal scarring at baseline in the CLEK Study: corneal staining (odds ratios (OR) = 3.40, 95% confidence interval 2.53-4.59), contact lens wear (OR = 3.51, 95% confidence interval 2.27-5.45), Fleischer's ring (OR = 1.63, 95% confidence interval 1.11-2.40), steeper first definite apical clearance lens base curve radius (per diopter, OR = 1.29, 95% confidence interval 1.25-1.33), and age (per decade, OR = 1.54, 95% confidence interval 1.35-1.75). CONCLUSIONS: These baseline data suggest that corneal scarring in keratoconus is associated with corneal staining, contact lens wear, Fleischer's ring, a steeper cornea, and increasing age. The factors that imply added risk for corneal scarring that may be affected by practitioner intervention are staining of the cornea, contact lens wear, and the contact lens fitting relationship.

The involvement of the NMDA receptor complex in the protective effect of anticholinergic drugs against soman poisoning.

Organophosphate poisoning is associated with adverse effects on the central nervous system such as seizure/convulsive activity and long term changes in neuronal networks. This study reports on investigations designed to assess the consequences of soman exposure on excitatory amino acids receptors in the rat brain. In addition, the protective effects of caramiphen which acts at these receptors, and scopolamine, which does not, was determined on soman-induced alteration in rat brain functions. Administration of soman (1xLD50) to pyridostigmine pretreated rats produced seizure activity (measured by EEG monitoring) in all animals tested. Estimation of [3H]MK-801 binding to brain membranes from intoxicated rats revealed a marked decrease in Bmax value 24 but not 2 hrs following soman administration. The specific nature of these effects of soman was demonstrated by the findings that [3H]flunitrazepam binding to central benzodiazepine receptors remained unchanged in soman-poisoned rat brain membranes. Both scopolamine and caramiphen, when used prophylactically prevented the lethal effect of soman and completely blocked the development of electrographic seizure activity (EGSA). In contrast, only caramiphen abolished soman-induced modifications in NMDA/ion channel characteristics. Caramiphen displaced [3H]MK-801 bound to the NMDA/ion channel complex, possibly by interacting with the Zn2+ site whereas scopolamine did not. Moreover, caramiphen, but not scopolamine, partially protected mice from NMDA-induced lethality. Thus, it is suggested that an important component of the protective efficacy of caramiphen against organophosphate poisoning might be attributed to its ability to modulate NMDA receptors in addition to its anticholinergic properties.

Keratoconus with good unaided visual acuities: two case reports.

BACKGROUND: Ophthalmic evaluation of patients with keratoconus (KC) often reveals highly myopic and irregular astigmatic refractive corrections. Irregular corneal astigmatism and central corneal scarring in patients with KC often result in a loss of best-corrected spectacle acuity. Rigid gaspermeable contact lenses generally optimize visual acuities for patients with KC. CASE REPORTS: Two cases are discussed of patients who manifested clinically diagnosed KC but unusually good unaided Snellen visual acuities (20/25+ or better) in both eyes. CONCLUSION: Good unaided visual acuities are not necessarily inconsistent with the diagnosis of KC.

Complexity of contact lens fitting following penetrating keratoplasty.

The aim of this study was to quantify the complexity of contact lens (CL) fitting following penetrating keratoplasty (PKP).The CL care of 40 eyes following PKP was analyzed retrospectively and compared to that of 40 age-matched and gender-matched controls. We evaluated the numbers of diagnostic and ordered rigid gas permeable (RGP) CLs, office visits for 6-month follow-up, best spectacle and RGP CL-corrected logMar visual acuities (VAs), and RGP CL success and complication rates. Post-PKP corneas required more diagnostic CLs (p = 0.009), ordered CLs (p = 0.0003), and office visits (p = 0.001) than did controls. Corrected logMAR VAs post-PKP improved from 0.31 +/- 0.31 (mean +/- SD) with spectacles (20/41) to 0.076 +/- 0.19 (20/24) with RGP CLs (p < 0.0001). Controls logMAR spectacle and CL-corrected VAs were 0.0043 +/- 0.12 (20/20) and -0.023 +/- 0.058 (20/19), respectively (no significant difference, p = 0.096). Ninety percent of PKP eyes and 100% of controls were successful, and 30% of PKP and 12.5% controls had CL-related complications; these differences did not reach statistical significance.Post-PKP eyes require more diagnostic CLs, ordered CLs, and professional office visits. They also have greater improvement of VAs with RGPs than normals compared to spectacles. CL wear post-PKP does not statistically increase the rate of CL complications or alter the success rate of CL wear.

An autoinhibitory control element defines calcium-regulated isoforms of nitric oxide synthase.

Nitric oxide synthases (NOSs) are classified functionally, based on whether calmodulin binding is Ca2+-dependent (cNOS) or Ca2+-independent (iNOS). This key dichotomy has not been defined at the molecular level. Here we show that cNOS isoforms contain a unique polypeptide insert in their FMN binding domains which is not shared with iNOS or other related flavoproteins. Previously identified autoinhibitory domains in calmodulin-regulated enzymes raise the possibility that the polypeptide insert is the autoinhibitory domain of cNOSs. Consistent with this possibility, three-dimensional molecular modeling suggested that the insert originates from a site immediately adjacent to the calmodulin binding sequence. Synthetic peptides derived from the 45-amino acid insert of endothelial NOS were found to potently inhibit binding of calmodulin and activation of cNOS isoforms. This inhibition was associated with peptide binding to NOS, rather than free calmodulin, and inhibition could be reversed by increasing calmodulin concentration. In contrast, insert-derived peptides did not interfere with the arginine site of cNOS, as assessed from [3H]NG-nitro-L-arginine binding, nor did they potently effect iNOS activity. Limited proteolysis studies showed that calmodulin's ability to gate electron flow through cNOSs is associated with displacement of the insert polypeptide; this is the first specific calmodulin-induced change in NOS conformation to be identified. Together, our findings strongly suggest that the insert is an autoinhibitory control element, docking with a site on cNOSs which impedes calmodulin binding and enzymatic activation. The autoinhibitory control element molecularly defines cNOSs and offers a unique target for developing novel NOS activators and inhibitors.

Contact lens correction of patients with Marfan syndrome.

BACKGROUND: Marfan syndrome, a genetic connective tissue disorder, manifests many problems: high myopia, astigmatism, crystalline lens subluxation, and cataracts. No published studies have described the contact lens corrections that can be used with Marfan syndrome patients. This report describes the variety of contact lens modalities used for a subpopulation of patients with Marfan syndrome. METHODS: The clinical records of eight patients with Marfan syndrome (16 eyes) from two hospital-based contact lens practices were retrospectively reviewed. Seven different contact lens modalities were used for this subpopulation. RESULTS: Mean unaided visual acuities were 20/296, while mean best-corrected optimal spectacle refraction visual acuities were 20/33. Contact lenses improved the mean visual acuity to 20/27. Patients wore the contact lenses for an average of 12 hours per day. Complications of contact lens wear occurred in approximately 70% of eyes and included neovascularization, giant papillary conjunctivitis, 3 and 9 o'clock staining, and central superficial punctate staining. Additionally, ocular non-contact lens-related complications occurred in 50% of patients. CONCLUSIONS: A variety of contact lens designs may be used during the care of patients with Marfan syndrome. However, patients may experience an increased rate of complications associated with contact lens wear or unrelated to lens wear, and thus they deserve more intensive follow-up care than non-Marfan syndrome patients.

Corneal pannus associated with contact lens wear.

PURPOSE: To determine whether contact lens, related corneal pannus regressed when eyes were refitted with rigid gas-permeable contact lenses and to investigate the role of hypoxia as the putative origin of this complication. METHODS: Twenty-three eyes of 14 patients with corneal pannus were identified retrospectively from a referral practice population and were separated into two subgroups. One subgroup accepted refitting with rigid gas-permeable contact lenses or discontinued contact lens wear, and the other elected to continue wearing hydrogel or polymethylmethacrylate contact lenses. The response of pannus was observed by slit-lamp biomicroscopy and photographs and was compared between the two subgroups. One eye of each of six patients identified with bilateral corneal pannus secondary to daily wear of hydrogel contact lenses was selected at random. Duplicates of the hydrogel contact lenses worn by these eyes were obtained, and their peripheral oxygen transmissibility (Dk/Lp) values were compared with those of a control group of hydrogel contact lenses identical to those worn by another group of patients, matched by age, gender, and laterality to the study group, but who did not have corneal vascularization. RESULTS: Vascularization regressed in 14 eyes of nine patients refitted with rigid gas-permeable contact lenses and also in both eyes of one patient who discontinued contact lens wear. All seven eyes of five patients who declined refitting showed persistence or increase of pannus. The mean Dk/Lp of the hydrogel contact lenses for six eyes with pannus was 3.8 X 10(-9) cm ml O2/s ml mm Hg; mean Dk/Lp was 8.6 X 10(-9) cm ml O2/s ml mm Hg for the lens of the control eyes. This difference was found to be statistically significant (P = .028). CONCLUSION: Peripheral, contact lens-induced hypoxia is a risk factor for corneal pannus, and conversion from hydrogel or polymethylmethacrylate contact lenses to daily wear rigid gas-permeable contact lenses in these eyes successfully reversed this complication.

Oxygen transmissibility at various locations in hydrogel toric prism-ballasted contact lenses.

PURPOSE: Corneal metabolism is known to be adversely affected by anterior surface hypoxia. It has been demonstrated that contact lens (CL) oxygen transmissibility (Dk/L in cmmL O2/s mL mm Hg) is a direct function of the oxygen permeability (Dk in cm2 ml O2/mm Hg mL mm Hg) of the plastic divided by the thickness of the lens (L in cm). It has also been shown recently that the cornea should be sensitive to the Dk/L of that portion of a CL immediately overlying the tissue, in the absence of tear exchange and mixing; such is the case for all hydrogel CLs. Because hydrogel toric CLs are known to have anisomorphically variable thickness profiles, we have measured lens thickness along the vertical meridian and calculated local oxygen transmissibilities (Dk/L) for a series of hydrogel CLs. METHODS: Thickness was measured at 5 locations along the vertical meridian of 16 different prescription toric hydrogel CLs of each of 6 brands (5 prism-ballasted design and 1 double-slab off design) and 12 different prescription spherical CLs of 2 brands (controls). Dk (at 38 degrees C) was calculated for each material from the nominal water content by a known relation. RESULTS: We found that the average Dk/L for all lenses was greatest from the center (mean +/- SD of 8 +/- 4 x 10(-9)) to the superior portion (12 +/- 2 x 10(-9) at 6 mm from the CL center and 13 +/- 4 x 10(-9) at 3 mm from the CL center) of prism-ballast design toric CLs, and least in the lower portions (4 +/- 2 x 10(-9) at 6 mm from the lens center and 6 +/- 1 x 10(-9) at 3 mm from the CL center) of these CLs. Analysis of covariance showed that the effect of location for the prism-ballasted CLs is statistically significant (F = 203.11, p < 0.00005). One nonprism ballast toric CL design and the spherical designs showed minimal differences across the vertical meridian. We therefore conclude that clinicians should carefully monitor the physiological hypoxic response of the cornea, in particular the inferior area, during wear of prism-ballasted hydrogel lenses.

Clinical experience with piggyback contact lens systems on keratoconic eyes.

BACKGROUND: A piggyback contact lens system (PBCLS) is used when traditional lenses do not provide optimal vision or tolerance. This study assessed the use of PBCLS in keratoconic patients. METHODS: The charts of 205 keratoconic patients were retrospectively reviewed and 16 patients wearing PBCLS were identified. Visual acuity, average wearing time, and ocular complication data with PBCLS were analyzed. RESULTS: Vision and average lens wearing time were stable, if not improved, for the 16 patients when the data was compared to the patients' wear of rigid gas permeable contact lenses. Although two patients developed neovascularization and one patient developed giant papillary conjunctivitis, all pre-existing corneal complications resolved with PBCLS wear. Average Dk/L through the center and mid-periphery of the PBCLS were 8.4 +/- 1.2 x 10(-9) (mean +/- standard deviation) and 4.5 +/- 1.8 x 10(-9) cm2ml O2/sec ml mmHg (mean +/- standard deviation) respectively. No gross corneal edema was noted upon slit lamp observation. CONCLUSIONS: PBCLS can be beneficial in the management of keratoconus.

Dose-dependent effect of nitric oxide synthase inhibition following transient forebrain ischemia in gerbils.

The extensive research concerning the interaction between nitric oxide (NO) and ischemic brain tissue has yielded contradictory results. The present study was designed to explore the effect of gradual inhibition of NO production on brain ischemia. Gerbils were administered (i.p.) either saline (control-ischemia), or 5, 10, 25 or 50 mg/kg of NG-nitro-L-arginine (NARG), a specific inhibitor of NO synthase (NOS), and 4 h later were subjected to 5 min of forebrain ischemia. A group receiving 50 mg/kg NARG with sham operation served as a second control (control-NARG) group. Body weights and spontaneous activity were monitored daily until day 6, when the gerbils were sacrificed and their brains processed for histologic-morphometric evaluation. All ischemia groups displayed significant decreases in body weights starting on day 1, as compared to control-NARG (non-ischemic) gerbils. At 24 h post-ischemia spontaneous activity was increased in all ischemia groups in a dose-dependent manner, reaching a peak at 25 mg/kg. Typical ischemia-induced neuronal cell degeneration was observed at the hippocampal CA1 layer in control-ischemia and in each of the dose-groups of 10 mg/kg NARG and above. The 5 mg/kg group displayed damage which was not different from control-NARG, and was milder (P < 0.01) than control-ischemia gerbils and each of the other dose-groups. It is suggested that during ischemia, NO activates a series of processes which are beneficial to brain tissue, whereas an excess amount of NO causes neurotoxic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Ring corneal clouding in keratoconus.

Rings of corneal edema were noted in one eye of each of three keratoconic patients, all wearing McGuire design rigid contact lenses of limited oxygen transmissibility (Dk/La). This finding appears to be analogous to the previously reported "central circular clouding" (CCC) with this specific appearance associated with the particulars of the keratoconic cornea-contact lens relation. Estimation of local oxygen transmissibilities suggests that a Dk/L < 3 x 10(-9) may produce this gross clinical sign underneath the lens midperiphery, whereas central Dk/L > or = 6 x 10(-9) may be sufficient to prevent its appearance.

An introduction to ocular immunology.

The interdigitated mechanisms by which an organism protects itself from microbiological infection have been collectively termed the immune system. We have been given the impression that the eye is "immunologically privileged" because the cornea accepts allografts. Despite the common success of corneal grafts, however, the ocular surface must perpetually combat infection with an array of immunological machinery. This includes mechanical protection as well as elements of humoral, cellular, adaptive, and innate immunity in the tears, conjunctiva, and even the cornea. Optometrists who fit contact lenses strive to help patients achieve safe contact lens wear by minimizing the risk of corneal infection and overaction (hypersensitivity) of the immune system in response to contact lenses and related care products. An understanding of immunology in general and the ocular response(s) in particular enables the clinician to provide a broader scope of care.

The role of pili in the attachment of Pseudomonas aeruginosa to unworn hydrogel contact lenses.

Contamination of contact lenses is thought to increase the risk of infectious keratitis, yet factors promoting attachment of bacteria to contact lenses are not fully understood. It has been suggested that strains of Pseudomonas aeruginosa attach to mucosal surfaces via pili which are appendages found on some strains. This study investigated the role of pili and the effect of incubation time on the attachment of P. aeruginosa to 20 unworn hydrogel lenses representative of each of the four FDA categories. Ten lenses were incubated for 15 minutes and another ten for 180 minutes. Lenses were incubated with either PAK + P. aeruginosa which possessed pili or its isogenic mutant pair, PAK-, which was genetically similar except for the absence of pili. Bacteria were quantified, following homogenization of the contact lens, by viable counts. Non-piliated bacteria were significantly more likely to adhere to the lenses (p < 0.001). A significant interaction between lens type and incubation time was observed (p < 0.05); thus it is difficult to generalize about either of these effects in isolation. These results show that surface characteristics may confer an attachment advantage to bacteria.

Areal differences in oxygen supply to a cornea wearing an optically powered hydrogel contact lens.

If there is little lateral diffusion of oxygen in an optically powered hydrogel contact lens, then point-to-point differences in the thickness of the lens can result in different areas of the cornea receiving different amounts of oxygen. Specifically, areas under the thicker portions of the lens will receive less oxygen. Cells in these oxygen-deprived areas may produce metabolic products that spread laterally in the cornea resulting in cornea-wide edema. The fact that most of a contact lens transmits adequate oxygen to the cornea does not lead to satisfactory lens performance, if some part of the lens is too thick. We address the problem of lateral diffusion of oxygen in a contact lens and describe the methods for quantifying the point-to-point thickness of optically powered hydrogel lenses. Areal differences in oxygen supply to the cornea are found to be almost totally dependent on optical power; water content and lens design have far less effect.

The effectiveness of daily wear contact lenses for the correction of infantile aphakia.

OBJECTIVE: To evaluate the effectiveness and safety of daily wear contact lenses in the treatment of infantile aphakia. DESIGN: A study of prognosis using a cohort followed up for a mean of 58 months. SETTING: All operations, contact lens care, and follow-up were conducted at a university referral center. PATIENTS: Of 111 children undergoing surgery for cataract between 1980 and 1990, 51 (68 eyes) met the criteria of age younger than 2 years at the time of surgery and of cataract of nontraumatic origin. Patients were evaluated for visual acuity, complications, number of contact lenses worn per year, and changes in contact lens refractive power per month. A subgroup of 28 eyes of patients undergoing surgery before age 7 months and followed up for at least 24 months was studied. INTERVENTION: Following cataract surgery, all patients were fitted with daily wear contact lenses. MAIN OUTCOME MEASURE: Final visual acuity and complications were studied. The distribution of mean contact lens power for each month of age was determined. RESULTS: During the follow-up period, no serious complications were encountered. The visual acuity outcome was better following bilateral cataract surgery than unilateral surgery (P < .001 using chi 2 analysis) and was comparable with that achieved with extended wear contact lenses. CONCLUSION: Daily wear contact lenses were found to be safe and effective in the treatment of infantile surgical aphakia. The daily care was easily learned by the parents.