Mycorrhizal feedbacks influence global forest structure and diversity.

One mechanism proposed to explain high species diversity in tropical systems is strong negative conspecific density dependence (CDD), which reduces recruitment of juveniles in proximity to conspecific adult plants. Although evidence shows that plant-specific soil pathogens can drive negative CDD, trees also form key mutualisms with mycorrhizal fungi, which may counteract these effects. Across 43 large-scale forest plots worldwide, we tested whether ectomycorrhizal tree species exhibit weaker negative CDD than arbuscular mycorrhizal tree species. We further tested for conmycorrhizal density dependence (CMDD) to test for benefit from shared mutualists. We found that the strength of CDD varies systematically with mycorrhizal type, with ectomycorrhizal tree species exhibiting higher sapling densities with increasing adult densities than arbuscular mycorrhizal tree species. Moreover, we found evidence of positive CMDD for tree species of both mycorrhizal types. Collectively, these findings indicate that mycorrhizal interactions likely play a foundational role in global forest diversity patterns and structure.

Impacts of insect frass and cadavers on soil surface litter decomposition along a tropical forest temperature gradient.

Insect herbivores play important roles in shaping many ecosystem processes, but how climate change will alter the effects of insect herbivory are poorly understood. To address this knowledge gap, we quantified for the first time how insect frass and cadavers affected leaf litter decomposition rates and nutrient release along a highly constrained 4.3°C mean annual temperature (MAT) gradient in a Hawaiian montane tropical wet forest. We constructed litterbags of standardized locally sourced leaf litter, with some amended with insect frass + cadavers to produce treatments designed to simulate ambient (Control = no amendment), moderate (Amended-Low = 2 × Control level), or severe (Amended-High = 11 × Control level) insect outbreak events. Multiple sets of these litterbags were deployed across the MAT gradient, with individual litterbags collected periodically over one year to assess how rising MAT altered the effects of insect deposits on litter decomposition rates and nitrogen (N) release. Increased MAT and insect inputs additively increased litter decomposition rates and N immobilization rates, with effects being stronger for Amended-High litterbags. However, the apparent temperature sensitivity (Q 10) of litter decomposition was not clearly affected by amendments. The effects of adding insect deposits in this study operated differently than the slower litter decomposition and greater N mobilization rates often observed in experiments which use chemical fertilizers (e.g., urea, ammonium nitrate). Further research is required to understand mechanistic differences between amendment types. Potential increases in outbreak-related herbivore deposits coupled with climate warming will accelerate litter decomposition and nutrient cycling rates with short-term consequences for nutrient cycling and carbon storage in tropical montane wet forests.

Interannual variation in rainfall modulates temperature sensitivity of carbon allocation and flux in a tropical montane wet forest.

Tropical forests exert a disproportionately large influence on terrestrial carbon (C) balance but projecting the effects of climate change on C cycling in tropical forests remains uncertain. Reducing this uncertainty requires improved quantification of the independent and interactive effects of variable and changing temperature and precipitation regimes on C inputs to, cycling within and loss from tropical forests. Here, we quantified aboveground litterfall and soil-surface CO2 efflux ("soil respiration"; FS ) in nine plots organized across a highly constrained 5.2°C mean annual temperature (MAT) gradient in tropical montane wet forest. We used five consecutive years of these measurements, during which annual rainfall (AR) steadily increased, in order to: (a) estimate total belowground C flux (TBCF); (b) examine how interannual variation in AR alters the apparent temperature dependency (Q10 ) of above- and belowground C fluxes; and (c) quantify stand-level C allocation responses to MAT and AR. Averaged across all years, FS , litterfall, and TBCF increased positively and linearly with MAT, which accounted for 49, 47, and 46% of flux rate variation, respectively. Rising AR lowered TBCF and FS , but increased litterfall, with patterns representing interacting responses to declining light. The Q10 of FS , litterfall, and TBCF all decreased with increasing AR, with peak sensitivity to MAT in the driest year and lowest sensitivity in the wettest. These findings support the conclusion that for this tropical montane wet forest, variations in light, water, and nutrient availability interact to strongly influence productivity (litterfall+TBCF), the sensitivity of above- and belowground C fluxes to rising MAT (Q10 of FS , litterfall, and TBCF), and C allocation patterns (TBCF:[litterfall+TBCF]).

Mean annual temperature influences local fine root proliferation and arbuscular mycorrhizal colonization in a tropical wet forest.

Mean annual temperature (MAT) is an influential climate factor affecting the bioavailability of growth-limiting nutrients nitrogen (N) and phosphorus (P). In tropical montane wet forests, warmer MAT drives higher N bioavailability, while patterns of P availability are inconsistent across MAT. Two important nutrient acquisition strategies, fine root proliferation into bulk soil and root association with arbuscular mycorrhizal fungi, are dependent on C availability to the plant via primary production. The case study presented here tests whether variation in bulk soil N bioavailability across a tropical montane wet forest elevation gradient (5.2°C MAT range) influences (a) morphology fine root proliferation into soil patches with elevated N, P, and N+P relative to background soil and (b) arbuscular mycorrhizal fungal (AMF) colonization of fine roots in patches. We created a fully factorial fertilized root ingrowth core design (N, P, N+P, unfertilized control) representing soil patches with elevated N and P bioavailability relative to background bulk soil. Our results show that percent AMF colonization of roots increased with MAT (r 2 = .19, p = .004), but did not respond to fertilization treatments. Fine root length (FRL), a proxy for root foraging, increased with MAT in N+P-fertilized patches only (p = .02), while other fine root morphological parameters did not respond to the gradient or fertilized patches. We conclude that in N-rich, fine root elongation into areas with elevated N and P declines while AMF abundance increases with MAT. These results indicate a tradeoff between P acquisition strategies occurring with changing N bioavailability, which may be influenced by higher C availability with warmer MAT.

Impact of Mean Annual Temperature on Nutrient Availability in a Tropical Montane Wet Forest.

Despite growing understanding of how rising temperatures affect carbon cycling, the impact of long-term and whole forest warming on the suite of essential and potentially limiting nutrients remains understudied, particularly for elements other than N and P. Whole ecosystem warming experiments are limited, environmental gradients are often confounded by variation in factors other than temperature, and few studies have been conducted in the tropics. We examined litterfall, live foliar nutrient content, foliar nutrient resorption efficiency (NRE), nutrient return, and foliar nutrient use efficiency (NUE) of total litterfall and live foliage of two dominant trees to test hypotheses about how increasing mean annual temperature (MAT) impacts the availability and ecological stoichiometry of C, N, P, K, Ca, Mg, Mn, Fe, Zn, and Cu in tropical montane wet forests located along a 5.2°C gradient in Hawaii. Live foliage responded to increasing MAT with increased N and K concentrations, decreased C and Mn concentrations, and no detectable change in P concentration or in foliar NRE. Increases in MAT increased nutrient return via litterfall for N, K, Mg, and Zn and foliar NUE for Mn and Cu, while decreasing nutrient return for Cu and foliar NUE for K. The N:P of litterfall and live foliage increased with MAT, while there was no detectable effect of MAT on C:P. The ratio of live foliar N or P to base cations and micronutrients was variable across elements and species. Increased MAT resulted in declining N:K and P:K for one species, while only P:K declined for the other. N:Ca and N:Mn increased with MAT for both species, while N:Mg increased for one and P:Mn increased for the other species. Overall, results from this study suggest that rising MAT in tropical montane wet forest: (i) increases plant productivity and the cycling and availability of N, K, Mg, and Zn; (ii) decreases the cycling and availability of Mn and Cu; (iii) has little direct effect on P, Ca or Fe; and (iv) affects ecological stoichiometry in ways that may exacerbate P-as well as other base cation and micronutrient - limitations to tropical montane forest productivity.

The impacts of degradation, deforestation and restoration on mangrove ecosystem carbon stocks across Cambodia.

Mangrove forest conservation can help reduce global C emissions. Despite this benefit to climate change mitigation and adaptation, mangrove forests are being deforested or degraded at an alarming rate, though restoration efforts may offset these losses. The impacts of deforestation to C stocks are relatively intuitive and result in significant decreases in C stocks. It remains unclear how degradation from selective harvesting of trees affects C stocks or how effective restoration efforts are at restoring C stocks. Furthermore, total ecosystem C (TEC) stocks of pristine mangroves can significantly vary spatially. To address these issues, we conducted an intensive, national assessment of mangrove forests across Cambodia using a grid approach to: 1) examine how land use land cover (i.e., pristine, deforested, degraded, and restored forests) impacts TEC stocks, and 2) how TEC stocks vary spatially across the country. TEC stocks from deforested mangroves were always lower than pristine forests, resulting in an overall loss of 60% C (480 Mg C ha-1). However, TEC stocks from degraded and 25-year-old restored mangroves forests did not differ from pristine forests. Mean TEC in mangroves was 784.7 ± 30.1 Mg C ha-1, decreasing from 957.2 ± 32.8 Mg C ha-1 in the northern region to 628.9 ± 33.1 Mg C ha-1 in the central region to 386.2 ± 19.1 Mg C ha-1 in the southern region of Cambodia. Intensive sampling in mangroves across Cambodia verified impacts of deforestation reported elsewhere, revealed the lack of degradation impacts on TEC stocks, and demonstrated the effectiveness of restoration on TEC stocks after only 25 years. Our gridded sampling approach was able to capture spatial variability across Cambodia and provide a more realistic TEC stock information that can be used for national reporting or participation in C markets.

Changes in soil bacterial community diversity following the removal of invasive feral pigs from a Hawaiian tropical montane wet forest.

Nonnative, invasive feral pigs (Sus scrofa) modify habitats by disturbing soils and vegetation, which can alter biogeochemical processes. Soil microbial communities drive nutrient cycling and therefore also play important roles in shaping ecosystem structure and function, but the responses of soil microbes to nonnative ungulate removal remains poorly studied. We examined changes in the soil bacterial community over a ~25 year chronosequence of feral pig removal in tropical montane wet forests on the Island of Hawai'i. We extracted bacterial eDNA from soil samples collected inside and outside of ungulate exclosures along this chronosequence and sequenced the eDNA using the Illumina platform. We found that ungulate removal increased diversity of soil bacteria, with diversity scores positively correlated with time since removal. While functional and phylogenetic diversity were not significantly different between pig present and pig removed soils, soil bulk density, which decreases following the removal of feral pigs, was a useful predictor of dissimilarity among sites and correlated to changes in functional diversity. Additionally, increases in soil porosity, potassium, and calcium were correlated to increases in functional diversity. Finally, sites with greater mean annual temperatures were shown to have higher scores of both functional and phylogenetic diversity. As such, we conclude that feral pigs influence overall bacterial community diversity directly while influencing functional diversity indirectly through alterations to soil structure and nutrients. Comparatively, phylogenetic differences between communities are better explained by mean annual temperature as a climatic predictor of community dissimilarity.

Non-native mangroves support carbon storage, sediment carbon burial, and accretion of coastal ecosystems.

Mangrove forests play an important role in climate change adaptation and mitigation by maintaining coastline elevations relative to sea level rise, protecting coastal infrastructure from storm damage, and storing substantial quantities of carbon (C) in live and detrital pools. Determining the efficacy of mangroves in achieving climate goals can be complicated by difficulty in quantifying C inputs (i.e., differentiating newer inputs from younger trees from older residual C pools), and mitigation assessments rarely consider potential offsets to CO2 storage by methane (CH4 ) production in mangrove sediments. The establishment of non-native Rhizophora mangle along Hawaiian coastlines over the last century offers an opportunity to examine the role mangroves play in climate mitigation and adaptation both globally and locally as novel ecosystems. We quantified total ecosystem C storage, sedimentation, accretion, sediment organic C burial and CH4 emissions from ~70 year old R. mangle stands and adjacent uninvaded mudflats. Ecosystem C stocks of mangrove stands exceeded mudflats by 434 ± 33 Mg C/ha, and mangrove establishment increased average coastal accretion by 460%. Sediment organic C burial increased 10-fold (to 4.5 Mg C ha-1  year-1 ), double the global mean for old growth mangrove forests, suggesting that C accumulation from younger trees may occur faster than previously thought, with implications for mangrove restoration. Simulations indicate that increased CH4 emissions from sediments offset ecosystem CO2 storage by only 2%-4%, equivalent to 30-60 Mg CO2 -eq/ha over mangrove lifetime (100 year sustained global warming potential). Results highlight the importance of mangroves as novel systems that can rapidly accumulate C, have a net positive atmospheric greenhouse gas removal effect, and support shoreline accretion rates that outpace current sea level rise. Sequestration potential of novel mangrove forests should be taken into account when considering their removal or management, especially in the context of climate mitigation goals.

Climate sensitive size-dependent survival in tropical trees.

Survival rates of large trees determine forest biomass dynamics. Survival rates of small trees have been linked to mechanisms that maintain biodiversity across tropical forests. How species survival rates change with size offers insight into the links between biodiversity and ecosystem function across tropical forests. We tested patterns of size-dependent tree survival across the tropics using data from 1,781 species and over 2 million individuals to assess whether tropical forests can be characterized by size-dependent life-history survival strategies. We found that species were classifiable into four 'survival modes' that explain life-history variation that shapes carbon cycling and the relative abundance within forests. Frequently collected functional traits, such as wood density, leaf mass per area and seed mass, were not generally predictive of the survival modes of species. Mean annual temperature and cumulative water deficit predicted the proportion of biomass of survival modes, indicating important links between evolutionary strategies, climate and carbon cycling. The application of survival modes in demographic simulations predicted biomass change across forest sites. Our results reveal globally identifiable size-dependent survival strategies that differ across diverse systems in a consistent way. The abundance of survival modes and interaction with climate ultimately determine forest structure, carbon storage in biomass and future forest trajectories.

Home range use and movement patterns of non-native feral goats in a tropical island montane dry landscape.

Advances in wildlife telemetry and remote sensing technology facilitate studies of broad-scale movements of ungulates in relation to phenological shifts in vegetation. In tropical island dry landscapes, home range use and movements of non-native feral goats (Capra hircus) are largely unknown, yet this information is important to help guide the conservation and restoration of some of the world's most critically endangered ecosystems. We hypothesized that feral goats would respond to resource pulses in vegetation by traveling to areas of recent green-up. To address this hypothesis, we fitted six male and seven female feral goats with Global Positioning System (GPS) collars equipped with an Argos satellite upload link to examine goat movements in relation to the plant phenology using the Normalized Difference Vegetation Index (NDVI). Movement patterns of 50% of males and 40% of females suggested conditional movement between non-overlapping home ranges throughout the year. A shift in NDVI values corresponded with movement between primary and secondary ranges of goats that exhibited long-distance movement, suggesting that vegetation phenology as captured by NDVI is a good indicator of the habitat and movement patterns of feral goats in tropical island dry landscapes. In the context of conservation and restoration of tropical island landscapes, the results of our study identify how non-native feral goats use resources across a broad landscape to sustain their populations and facilitate invasion of native plant communities.

Leaf litter decomposition rates increase with rising mean annual temperature in Hawaiian tropical montane wet forests.

Decomposing litter in forest ecosystems supplies nutrients to plants, carbon to heterotrophic soil microorganisms and is a large source of CO2 to the atmosphere. Despite its essential role in carbon and nutrient cycling, the temperature sensitivity of leaf litter decay in tropical forest ecosystems remains poorly resolved, especially in tropical montane wet forests where the warming trend may be amplified compared to tropical wet forests at lower elevations. We quantified leaf litter decomposition rates along a highly constrained 5.2 °C mean annual temperature (MAT) gradient in tropical montane wet forests on the Island of Hawaii. Dominant vegetation, substrate type and age, soil moisture, and disturbance history are all nearly constant across this gradient, allowing us to isolate the effect of rising MAT on leaf litter decomposition and nutrient release. Leaf litter decomposition rates were a positive linear function of MAT, causing the residence time of leaf litter on the forest floor to decline by ∼31 days for each 1 °C increase in MAT. Our estimate of the Q 10 temperature coefficient for leaf litter decomposition was 2.17, within the commonly reported range for heterotrophic organic matter decomposition (1.5-2.5) across a broad range of ecosystems. The percentage of leaf litter nitrogen (N) remaining after six months declined linearly with increasing MAT from ∼88% of initial N at the coolest site to ∼74% at the warmest site. The lack of net N immobilization during all three litter collection periods at all MAT plots indicates that N was not limiting to leaf litter decomposition, regardless of temperature. These results suggest that leaf litter decay in tropical montane wet forests may be more sensitive to rising MAT than in tropical lowland wet forests, and that increased rates of N release from decomposing litter could delay or prevent progressive N limitation to net primary productivity with climate warming.

Ecosystem carbon storage does not vary with mean annual temperature in Hawaiian tropical montane wet forests.

Theory and experiment agree that climate warming will increase carbon fluxes between terrestrial ecosystems and the atmosphere. The effect of this increased exchange on terrestrial carbon storage is less predictable, with important implications for potential feedbacks to the climate system. We quantified how increased mean annual temperature (MAT) affects ecosystem carbon storage in above- and belowground live biomass and detritus across a well-constrained 5.2 °C MAT gradient in tropical montane wet forests on the Island of Hawaii. This gradient does not systematically vary in biotic or abiotic factors other than MAT (i.e. dominant vegetation, substrate type and age, soil water balance, and disturbance history), allowing us to isolate the impact of MAT on ecosystem carbon storage. Live biomass carbon did not vary predictably as a function of MAT, while detrital carbon declined by ~14 Mg of carbon ha(-1) for each 1 °C rise in temperature - a trend driven entirely by coarse woody debris and litter. The largest detrital pool, soil organic carbon, was the most stable with MAT and averaged 48% of total ecosystem carbon across the MAT gradient. Total ecosystem carbon did not vary significantly with MAT, and the distribution of ecosystem carbon between live biomass and detritus remained relatively constant across the MAT gradient at ~44% and ~56%, respectively. These findings suggest that in the absence of alterations to precipitation or disturbance regimes, the size and distribution of carbon pools in tropical montane wet forests will be less sensitive to rising MAT than predicted by ecosystem models. This article also provides needed detail on how individual carbon pools and ecosystem-level carbon storage will respond to future warming.

Species and gender differences in the formation of an active metabolite of a substituted 2,4-thiazolidinedione insulin sensitizer.

1. The metabolism of a substituted 2,4-thiazolidinedione (P1) with dual PPARalpha/gamma activity was evaluated in male and female rats, dogs and monkeys. A para-hydroxylated metabolite (M1) with potent PPARgamma-selective agonist, was a major circulating drug-related component in female rats, dogs and monkeys, but not in male rats (M1-to-P1 exposure ratio of <1, 3-5, 5 and 5-11 in male rat, monkey, female rat, and dog, respectively). 2. M1 (%) formed in vitro (5, 53, 57-65, 67 and 67% in male rat, monkey, female rat, dog, and human liver microsomes, respectively), rank ordered with M1 (%) formed in vivo (24-45, 53-57, 78, 75-85%, for male rat, monkey, female rat and dog, respectively, after oral administration of P1). 3. The plasma clearance of M1 was higher in male rats (32 ml min(-1) kg(-1) compared with 6, 7 and 2 ml min(-1) kg(-1) in female rat, male monkey and male dogs, respectively). 4. The low amounts of M1 observed in male rats, with the appearance of products of the cleavage of the propyl group between the phenyl groups was probably due to the presence of the sex-specific CYP2C11, which cleaves P1 at the propyl bridge. None of the CYPs present in female rats cleaved P1 at this site and M1 was only produced by CYP2C6. In humans, only CYP2C8 and the polymorphic CYP2C19 produced M1.

Identification of novel metabolites of pioglitazone in rat and dog.

1. Four new metabolites of pioglitazone were identified by liquid chromatography-mass spectrometry (LC-MS/MS) as being formed by hydroxylation (M-VII and M-VIII), opening of the thiazolidinedione ring (M-X) and by desaturation of the terminal ethyl side chain or tether ethoxy moiety (M-IX), respectively. The structure of one of the hydroxylated metabolites (M-VII) was confirmed by chemical modification using the Jones reaction. 2. Oxidative cleavage of the thiazolidinedione ring is a novel pathway not previously reported for pioglitazone. 3. The hydroxylated M-VII was detected in incubations with rat, dog and human liver and kidney microsomes, and in plasma from rats and dogs dosed orally with [(3)H]pioglitazone. 4. The carboxylic acid derivative of M-VII (M-V) and its taurine conjugate were the major radioactive components in dog bile.

Total hip arthroplasty with cement in patients who have rheumatoid arthritis. A minimum ten-year follow-up study.

One hundred and six consecutive total hip arthroplasties with cement were performed by one surgeon, at least ten years before the time of the present clinical and radiographic review, in seventy-five patients who had adult-onset rheumatoid arthritis. Two patients (three hips) were lost to follow-up. Seven (7 per cent) of the remaining 103 hips were revised. The revisions were performed because of infection (three hips), dislocation (two hips), or aseptic loosening (two hips). Of the ninety-eight hips that were not lost to follow-up or revised because of infection or dislocation, eight (8 per cent) had radiographic loosening of the acetabular component and two (2 per cent) had radiographic loosening of the femoral component. Although the prevalence of radiographic loosening of the acetabular component was four times greater than the prevalence of radiographic loosening of the femoral component, the prevalence of revision because of aseptic loosening of the acetabular component was identical to that for the femoral component (one component each). These results compared favorably with those of total hip arthroplasty with cement, performed by the same surgeon, for the treatment of other diagnoses. Loosening of the acetabular component was significantly associated with a younger age at the time of the index operation (p = 0.03) and with acetabular osteolysis (p = 0.0006). Of forty-eight hips in thirty-two patients who survived for at least ten years, 96 per cent (forty-six hips) were considered by the patients to have a satisfactory result. At the time of the latest follow-up, twenty-four (75 per cent) of the patients had no pain in the hip. Although eighteen patients (56 per cent) could walk without support at a minimum of ten years after the operation, we found that the functional results for patients who had rheumatoid arthritis were inferior to those observed for patients who had had a total hip arthroplasty with cement, performed by the same surgeon, for the treatment of other diagnoses.

Changes in human mucosal gamma delta T cell repertoire and function associated with the disease process in inflammatory bowel disease.

BACKGROUND: Although gamma delta T cells are a major component of the human intestinal mucosa, it is not clear what role they play in mucosal immunity or if they are involved in the disease process of inflammatory bowel disease (IBD). MATERIALS AND METHODS: Flow cytometry and reverse transcriptase-polymerase chain reaction (RT-PCR) assays were used to identify quantitative and qualitative changes in the repertoire of gamma delta T cells present in surgical and/or biopsy samples or normal and inflamed colon from individual patients with ulcerative colitis (UC) or Crohn's disease (CD). Cytokine production and the ability to adhere to and interact with colonic fibroblasts were used to compare the functional properties of gamma delta T cells isolated from the normal and diseased colonic mucosa. RESULTS: Increased numbers of gamma delta T cells localized in areas of inflammation and tissue injury were found in the majority of patients, irrespective of the type of IBD present. This expansion was attributable to an increase in V delta 1+ cells expressing a V delta 1-(D delta 3)-J delta 1-encoded T cell receptor and was seen in patients with severe disease as well as those with newly diagnosed or less severe forms of IBD. Among T cells present in the inflamed mucosa of patients with CD, gamma delta T cells, particularly V delta 1+ cells, were a major source of the proinflammatory cytokine interferon-gamma and could interact with colonic fibroblasts. CONCLUSIONS: Our results demonstrate that the chronic inflammatory immune response characteristic of IBD is associated with distinct changes in the number, distribution, composition, and function of mucosal gamma delta T cells. Through the production of cytokines and physical interaction with other cells, gamma delta T cells can perform an immunoregulatory function and contribute to the pathophysiology of IBDs.

Mental disabilities under the ADA: a management rights approach.

While numerous sources have focused on employee rights and employer obligations under the Americans with Disabilities Act, this article will emphasize employer rights with respect to mental disabilities under the ADA. Specifically, it addresses the ADA's definition of "mental disability," the right of employers to screen job applicants in spite of the ADA, the conditions under which an employer may require an employee to undergo a "fitness for duty" examination, and the limits of the duty to "reasonably accommodate" an employee with a mental disability.

Radiation cataractogenesis induced by neutron or gamma irradiation in the rat lens is reduced by vitamin E.

Although cataract of the eye lens is a known late effect of ionizing radiation exposure, most of the experimental work to date has concentrated on single, acute high doses or multiple, fractionated, chronic exposures. Many papers have dealt with biochemical alterations in metabolism and cellular components, with microscopic and electron microscopic lesions to the epithelial and cortical layers, and with clinical cataract formation. However, the minimum cataractogenic dose for rats has for many years been considered to be about 2 Gy for a single, acute dose of low LET radiation. Our purpose in designing this pilot study was three fold: firstly, to determine whether any physical damage could be detected after low, acute exposure to neutron radiation (10 and 100 cGy); secondly, to compare the relative effectiveness of fast (14 MeV) neutrons with gamma-rays; and thirdly, to investigate the possibility that vitamin E could protect the lenses from radiation damage. The results revealed that morphological damage was already discernible within minutes after exposure to neutrons or gamma-rays, that it became greater after 24 hours, that neutrons were more damaging than gamma-rays, and that vitamin E could effectively reduce the cataractogenic damage induced by ionizing radiation. Control, non-irradiated lenses with or without vitamin E, either in vivo or in vitro, showed no damage. Also, it appeared that in vitro irradiation was more damaging to lenses than in vivo irradiation, so this culture technique may prove to be a sensitive tool for assessing early damage caused by ionizing radiation.(ABSTRACT TRUNCATED AT 250 WORDS)

51Cr release and oxidative stress in the lens.

Examination of the opaque areas of human cortical cataracts has shown that a large portion of the opacity could be attributed to the globules found there. We tested models involving globule formation as a result of oxidative damage to rat lens cells in culture and whole chick embryo lenses. When cell monolayers from a lens cell line were exposed to oxidizing conditions they developed globules on the cell surface. The cells were protected from damage by the addition of glutathione and vitamin C. Thirteen-day chick embryo lenses were also incubated in oxidizing conditions and the amount of cellular damage was assessed using a chromium-51 release assay we have developed. After 24 hr the percent 51Cr in the medium increased by an average of 20% as a result of 10 mM hydrogen peroxide treatment. The addition of the 10 mM vitamin C to the hydrogen peroxide significantly reduced the 51Cr leakage to the control level. Light microscopy of sections of the lens showed a breakdown of the equatorial fibre arrangement in the presence of H2O2, while addition of vitamin C restored the fibre organization to almost normal. The findings suggest that oxidative stress is an important step in cataractogenesis and point towards the use of water soluble antioxidants as protective agents.