Psychophysical measurement of temporal modulation sensitivity in the tree shrew (Tupaia belangeri).

Temporal modulation sensitivity functions (MSFs) were measured behaviorally in three adult tree shrews (Tupaia belangeri). Shrews were trained to detect temporal sinusoidally-modulated full-field luminance variations in one of three stimuli, the two alternatives being static stimuli of equal size and time-averaged luminance (34 cd/m2). Modulation depth was varied trial-by-trial using a modified staircase technique under ambient illumination of 16 lux. Threshold modulation depths were determined for five temporal frequencies ranging from 3.7 to 47 Hz. Results revealed temporal MSFs that peaked at 15 Hz with a low-frequency roll-off and an extrapolated high-frequency cut-off beyond 50 Hz. These findings confirm the comparatively good temporal vision of Tupaia predicted by behavioral observations.

How low birthweight and gestational age contribute to increased inpatient costs for multiple births.

The dramatic rise in the number of multiple gestation births has led to concerns about heavy resource use by these newborns and the design of cost-effective interventions. This study uses medical records data to compare single and multiple births in terms of hospital charges by cost center, length of stay, neonatal intensive care unit (NICU) days, and discharge status. Potential mediators examined were gestational age and birthweight. These factors, respectively, accounted for 50% and 40% of the increase in total charges due to multiple gestation. The remaining "direct effect" was due primarily to longer hospital stays among twins and higher daily charges among higher-order multiples. Room and board charges were higher for multiples, while charges in other categories were actually lower, after controlling for birthweight and gestational age. Birthweight and gestational age accounted fully for the increased use of NICU services among multiples. These results show that while prevention of multiple gestation, where possible, is of paramount importance, strategies that decrease preterm delivery and/or increase birthweight should attenuate the adverse economic impact of multiple gestation pregnancies.

Selective photoreceptor damage in albino rats using continuous blue light. A protocol useful for retinal degeneration and transplantation research.

PURPOSE: To develop a retinal degeneration model with selective photoreceptor loss and RPE sparing, to be used as recipient for evaluating retinal transplants. METHODS: Albino rats were exposed to blue light, continuously, for 1-7 days (24-168 h) in a specially designed cage. Eyes were histologically analyzed at periods between 2 h and 8 months after the light exposure. Electroretinograms (ERGs) were recorded from some rats at 12-216 days after exposure. Using behavioral methods, visual thresholds of some rats were determined before exposure and re-measured between 18 and 52 days following exposure. RESULTS: Apoptotic nuclei appeared exclusively in the photoreceptor layer after 1-5 days exposure to blue light. Light microscopy revealed that 2-4 days of light exposure reduced the outer nuclear layer (normally eight to ten rows) to 1 row of cells in the central retina and to two to three rows in the periphery, both in the superior and the inferior retina. Average ERG a- and b-wave amplitudes of light-damaged rats were both reduced by about 98%. Visual performance in the behavioral test was substantially impaired. CONCLUSIONS: Continuous exposure of albino rats to moderate blue light for 2-5 days selectively eliminates most of the photoreceptors while leaving the RPE initially intact.

The economic impact of multiple-gestation pregnancies and the contribution of assisted-reproduction techniques to their incidence.

BACKGROUND: Although the medical complications associated with multiple-gestation pregnancies have been well documented, little is known about the effects of such pregnancies on the use of health care resources and the associated costs. This is an important issue because of the increasing use of assisted-reproduction techniques, which commonly result in multiple-gestation pregnancies. METHODS: We determined hospital charges and the use of assisted-reproduction techniques (such as induction of ovulation, in vitro fertilization, and gamete intrafallopian transfer) for 13,206 pregnant women (11,986 with singleton pregnancies, 1135 with twin pregnancies, and 85 with more than two fetuses) who were admitted for delivery to Brigham and Women's Hospital, Boston, in 1986 through 1991 and their 14,033 neonates (11,671 singletons, 2144 twins, and 218 resulting from higher-order multiple gestations). RESULTS: After we controlled for variables known to affect hospital charges, the predicted total charges to the family in 1991 for a singleton delivery were $9,845, as compared with $37,947 for twins ($18,974 per baby) and $109,765 for triplets ($36,588 per baby). Assisted-reproduction techniques were used in 2 percent of singleton, 35 percent of twin, and 77 percent of higher-order multiple-gestation pregnancies; such procedures were approximately equally divided between induction of ovulation alone and in vitro fertilization or gamete intrafallopian transfer. CONCLUSIONS: Multiple-gestation pregnancies, a high proportion of which result from the use of assisted-reproduction techniques, dramatically increase hospital charges. If all the multiple gestations resulting from assisted-reproduction techniques, dramatically increase hospital charges. If all the multiple gestations resulting from assisted-reproduction techniques had been singleton pregnancies, the predicted savings to the health care delivery system in the study hospital alone would have been over $3 million per year. Although assisted reproduction provides tremendous benefits to families with infertility, the increased medical risks entailed by multiple-gestation pregnancies and the associated costs cannot be ignored. We suggest that more attention be paid to approaches to infertility that reduce the likelihood of multiple gestation.