Loss of human photoreceptor sensitivity associated with chronic exposure to ultraviolet radiation

The crystalline lens of the human eye absorbs most of the incident ultraviolet radiation (UVR), but when the lens is removed, this radiation can reach the photoreceptors. The consequences of UVR exposure on cone receptor sensitivity were determined from psychophysical measurements in patients who had undergone bilateral cataract extraction and implantation of intraocular lenses (IOLs). The IOL implanted in one eye contained chromophores that absorb incident UVR, whereas that implanted in the other eye transmitted UVR. Five years of exposure to ambient UVR was associated with a selective loss in sensitivity of the short-wave cone photoreceptors. These results are consistent with the hypothesis that chronic exposure to UVR may damage the human retina.

[The central regulation of pain sensitivity in rats after irradiation with high doses of ionizing radiation]

It was shown that during 24 h following whole-body exposure of male rats to gamma-quanta (150 Gy) the latent period of their response to the thermal effect increased a "tail-flick" test) and the threshold of the nociceptive response to an electric stimulus (the vocalization threshold) decreased. A correlation was found between the initial response to the nociceptive effects and variation of these values in irradiated animals.

Effect of semiconductor GaAs laser irradiation on pain perception in mice

The influence of subacute exposure (11 exposures within 16 days) of mice to the low power (GaAs) semiconductive laser-stimulated irradiation on pain perception was investigated. The pain perception was determined by the latency of foot-licking or jumping from the surface of a 53 degrees C hot plate. Repeated hot-plate testing resulted in shortening of latencies in both sham- and laser-irradiated mice. Laser treatment (wavelength, 905 nm; frequency, 256 Hz; irradiation time, 50 sec; pulse duration, 100 nsec; distance, 3 cm; peak irradiance, 50 W/cm2 in irradiated area; and total exposure, 0.41 mJ/cm2) induced further shortening of latencies, suggesting its stimulatory influence on pain perception. Administration of morphine (20 mg/kg) prolonged the latency of response to the hot plate in both sham- and laser-irradiated mice. This prolongation tended to be lesser in laser-irradiated animals. Further investigations are required to elucidate the mechanism of the observed effect of laser.

Intermittent exposure of rats to 2450 MHz microwaves at 2.5 mW cm2: behavioral and physiological effects

Long-Evans male adult rats were intermittently exposed for 14 weeks to continuous wave (CW) 2450-MHz microwaves at an average power density of 2.5 mW/cm2. The mean specific absorption rate was 0.70 W/kg (+/- 0.02 SEM). The rats were exposed 7 h/day, 7 days/week in a radiation chamber with a monopole above ground, while housed in Plexiglas cages. Weekly measures of body mass and food intake did not indicate statistically significant effects of microwave irradiation. Assessments of threshold for electric-footshock detection revealed a significant difference between microwave and sham-exposed animals. Assessments of cholinesterase and sulfhydryl groups in blood and 17-ketosteroids in urine did not distinguish the two groups of rats. Behavioral measures made at the end of the 14-week exposure included an open-field test, shuttlebox avoidance performance, and schedule-controlled lever-pressing for food pellets. Statistically significant differences between microwave- and sham-exposed rats were observed for these measures. Examination of adrenal tissue, plasma electrolytes, and organ masses after 14 weeks of exposure revealed no difference between the two groups of rats.

Recovery of absolute threshold with UVA-induced retinal damage

A within-trial psychophysical procedure tracked the initial loss and subsequent recovery of visual thresholds in albino rats exposed to ultraviolet light at 350 nanometers and 0.4 milliwatts per square centimeter. Absolute thresholds increased up to 5 log units immediately following the 15 hour ultraviolet exposure, with a daily recovery of 1-2 log to asymptotic thresholds over a 7-day post-exposure period. The corresponding retinal damage on Day 1 included extensive vesiculation of the photoreceptor outer segments, vacuolation of the inner segments, and pyknosis of cell nuclei. The total number of photoreceptor nuclei and outer segments was unchanged relative to control eyes through post-exposure Day 3. Both nuclei and outer segment counts then consistently decreased 15-20 percent between Days 3-7. The two-stage loss of photoreceptors but daily recovery of absolute thresholds again suggests a significant dissociation of retinal structure and psychophysical function in light-induced ocular pathology.