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The effects of argon laser trabeculoplasty (LTP) on outflow facility, Schlemm's canal morphology, trabecular cellularity, and trabecular glycosaminoglycan composition were determined in 33 pairs of eye-bank human eyes. At two levels of intraocular pressure, measured outflow facility did not immediately drop in response to LTP. Schlemm's canal distention was observed only at 40 mmHg intraocular pressure, where the canal normally tends to collapse. Trabecular cell density was reduced by about 40% in the eyes receiving laser treatment. The organ cultured trabecular meshworks in response to LTP altered their incorporation of 35S-sulfate, compared to controls, suggesting a change in the synthesis or turnover of the extracellular matrix of the trabeculum after trabeculoplasty. At least three potential mechanisms were identified in response to laser trabeculoplasty, including some mechanical distortion of the trabeculum at high intraocular pressures. We also hypothesize that laser trabeculoplasty dislodges some trabecular cells and may stimulate the remaining cells to renew more active synthesis and/or turnover of the trabecular extracellular matrix.

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The Amazon molly, Poecilia formosa, a small, live-bearing fish native to Texas, has an unusual mode of reproduction that makes it highly suitable for carcinogenicity studies. The species is easy to rear and breed, and withstands handling well. Large broods of young are born, numbering up to 90 when the parent fish are fully grown. The Amazon molly reproduces gynogenetically; eggs are activated after mating with males of closely related species. The male makes no genetic contribution; sperm provides only the stimulus for egg development. The offspring of a female comprise a clone with genotypes identical to that of the mother's so that cell and tissue transplants made between members of the clone are not rejected. We used the Amazon molly as an animal model to show that damage to DNA caused by UV and ionizing radiation and by certain chemicals results in tumor development. Thyroid cells were taken from donor mollies, treated precisely in vitro with the agents, and then injected into homologous recipients. Eight months later, recipient fish had developed large thyroid tumors. The genetic homogeneity of the clone also makes the Amazon molly invaluable in acute or chronic bioassays because variability in the responses of the individual fishes is minimal. Therefore, a limited number will suffice to give statistically significant results. The findings from a study of chronic exposure to asbestos are also described.

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Histological surveys of the brains of guppies throughout their lifespan showed no overall loss of tissue with advancing age. Brain and body increased in size at a similar rate throughout adult life in male fish. In old females after the age of two years, brain growth apparently ceased, although body growth continued at a low rate. In both sexes there was a loss of neurones from the stratum griseum periventriculare in the midbrain roof in old age; the decrease in size was significant. The midbrain is a major correlative center concerned with spatial orientation. How far neuronal loss may contribute to functional behavioral disorder in old age is unknown, but a loss of orientation could render the older fish more susceptible to predation.

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Histological surveys of the kidneys of two poeciliid fishes, the Amazon molly Poecilia formosa and the guppy P. reticulatus, throughout their lifespans showed no regular aging trends. Few kidney lesions were found in the Amazon molly until very late in life, 60 months or more, when obsolescent glomeruli and dilated renal tubules occurred. Guppies showed involutional changes of the renal system earlier, and the lesions became more severe with age, particularly in male fish. Hemopoietic tissue was reduced in amount in older fish of both species. Guppies of a year and older had marked accumulation of melanin in the melanomacrophage centers of the kidney, and the amount present increased with age. By contrast, there was little melanin deposition in mollies until almost the end of the lifespan. Hyaline droplets were consistently seen in the renal tubules of the mollies, but were rare in guppies. The degenerative changes in the kidneys of these two teleosts are similar to those seen in the kidneys of aging mammals. Despite the loss of normal structure in older fish, it seemed unlikely that degeneration of the kidney was directly involved in aging and death.

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Various cytological factors, including interphase chromosome volume (ICV), nuclear volume (NV), cell volume, DNA content per nucleus and per chromosome, have been reviewed to determine their usefulness as indices to predict radiosensitivity. Fourteen topics are discussed. They are: a historical development of the concept of using karyotypic features to estimate radiosensitivity; interrelationships between cellular parameters; relationship of the karyotype to the duration of mitosis and meiosis; relationships between chronic and acute irradiation and ICV using several radiobiological end points for woody and herbaceous species; correlations between dose and cellular parameters ftween chromosome aberrations and cellular characteristics after chronic irradiation; polyploidy and plant radiosensitivity; radiation-induced petal mutations in plants and their relationship to cellular parameters; correlations between mean survival time facter irradiation and cellular parameters in amphibians and higher plants; correlations between radiobiological end points and cellular parameters after whole-body irradiation in amphibians. insects and mammals; correlations between radiosensitivity and cellular parameters in diverse single-cell organisms; correlations between radiobiological end points and cellular parameters in higher plants irradiated with neutrons and the value of cell parameters to estimate relative biological effectiveness (RBE); and energy absorption and trends in radiosensitivity among species and radiobiological end points. It is concluded that ICV is usually the most useful parameter for predicting radiosensitivity.

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