Developmental exposure of mice to pulsed ultrasound.

Exposure of pregnant mice on gestation day (gd) 8 to 1 MHz continuous-wave ultrasound (0, 0.05, 0.50, or 1.00 W/cm2) was reported previously to result in a slight (nonsignificant) increase in malformations. The present study was conducted in a similar fashion using pulsed ultrasound but was designed to maximize the likelihood of finding effects of gd 8 ultrasound exposure on prenatal development. Pregnant ICR mice (approximately 60 animals/group) were exposed on gd 8 to pulsed ultrasound with a center frequency of 1 MHz at levels of 0 (sham control), 0.05, 0.50, or 1.00 W/cm2 (spatial average, temporal average intensities; ISATA) with a spatial peak, pulse average intensity (ISPPA) of 90 W/cm2 and pulse duration of 6.5 microseconds. Anesthetized animals were placed in a degassed water bath (30 degrees C) and exposed for two 10 min intervals during which the beam was centered 1 cm on either side of the abdominal midline. On gd 17, dams were killed; the uterus and its contents were weighed and examined; and live fetuses were weighed and examined for external, visceral, and skeletal malformations. Although one female in the 0.50 W/cm2 group and seven animals in the 1.00 W/cm2 group died following exposure, no other significant change from controls was seen in any maternal or fetal parameter evaluated. Thus the results of this study indicate that there was no detectable effect on prenatal development of mice following exposure to ultrasound on gd 8 (a time of maximal sensitivity), even at exposure intensities that were lethal to some maternal animals.

Toxicology of medical device material.

The 1976 amendments to the Food, Drug, and Cosmetic Act established requirements for obtaining approval to market new medical devices, including the necessity for demonstrating safety and effectiveness. Evaluation of the potential toxicity of medical devices presents toxicologists with unique problems related to route of exposure, estimation of exposure dose, exposure to by-products generated during manufacture, and matrix effects. A symposium was organized to address the need for toxicologists to examine the potential toxicities of medical device materials, to appreciate the unique problems associated with medical device safety evaluation, to present novel testing methodologies, and to discuss future research needs.

Behavioral effects of erythrosine following light exposure.

Three studies were conducted to examine the effects of erythrosine on the activity level of mice in a figure 8 maze. Results of the first study show that activity in a dark maze is not influenced by intraperitoneal doses as high as 1.25 mg/kg. In two additional studies, subjects were subjected to combinations of dye and pre-exposure to blue (Experiment II) or blue and green (Experiment III) light. Light exposure consistently produced increased activity levels. However, there was little evidence of a dye-light interaction effect.

The embryotoxic effects of ultrasound exposure in pregnant ICR mice.

The embryotoxicity of ultrasound exposure during pregnancy was investigated in DUB:(ICR) mice. On day 0 of gestation (day of plug), pregnant mice were assigned to one of five groups: cage control, sham exposed (0 W/cm2), 0.05 W/cm2, 0.50 W/cm2. or 1.00 W/cm2. Females were anesthetized on day 8 of gestation and their abdomens were shaved to assure good acoustic coupling. The animals were strapped on a lucite board and placed vertically into a distilled degassed water bath (30 degrees C) so that the abdomen was fully submerged and centered in the axis of the ultrasonic beam. Insonation was carried out using a PZT transducer with a radius of 1.27 cm and a frequency of 1 MHz under continuous wave conditions. Each animal was placed at a distance of 25 cm from the transducer and exposed to the appropriate intensity for 120 seconds. On day 17 of gestation, the maternal animals were killed, the uterine contents were examined, and live fetuses were weighed and then shipped in cold lactated Ringer's solution from Maryland to Arkansas. Fetuses were examined on the day following maternal sacrifice for external and visceral defects and skeletons were prepared and examined subsequently. Slight but significant differences were detected between the cage control and sham-exposed groups. No statistically significant changes were seen that could be attributed to ultrasound exposure, although there was a slight increase in the incidence of malformed fetuses and the occurrence of multiple malformations in individual fetuses as intensity of the ultrasonic exposure increased.

Effects of noinionizing radiation on the central nervous system, behavior, and blood: a progress report.

This paper presents a progress report on the U. S. research which has been designated as collaborative research with the Soviet Union to study the biological effects of nonionizing radiation on the central nervous system, behavior, and blood. Results of investigations to study the effects of microwaves on isolated nerves, synaptic function, transmission of neural impulses, electroencephalographic recordings, behavior, and on chemical, cytochemical and immunological properties of the blood are presented. Specifically, the effects of microwave exposure on chick brain and cat spinal cords, on EEG patterns of rats, on behavioral of neonatal rats exposed during development, on behavior of adult rats, on behavior of rhesus monkeys and on the pathology, hematology, and immunology of rabbits will be reported in a summary format. Much of the information is new and has not been published previously.

Stimulus control in a two-choice discrimination procedure.

The relation between performance during discriminative training and subsequently obtained measures of stimulus control was investigated. Pigeons served as experimental subjects. In the discriminative training phase, a single peck on the center key, transilluminated by a bright or dim white light, resulted in the onset of the side keys, one red and one green. If the center key was brightly lighted, a response on the red side key was correct. A response on the green side key was correct if the center key was dimly lighted. Correct responses were reinforced on independently arranged variable-interval schedules. Following discriminative training, tests of stimulus control were administered during which white light of 11 intensities was projected on the center key and responses on the red and green side keys recorded. The proportion of correct responses in the presence of a bright or dim center-key stimulus decreased with decreases in the frequency of reinforcement of correct red or correct green responses, respectively. The slopes of the stimulus control gradients were related to the extent of response bias during training. The greater the bias to respond on the green key, the flatter the gradient showing the proportion of green-key responses to each stimulus and the steeper the corresponding gradient of red-key responses.

Conditioned reinforcement and discrimination performance.

Pigeons were trained in a three-key chamber to peck one side key in the presence of a vertical line on the center key and to peck the other side key in the presence of a horizontal line. Correct choice responses were reinforced with food according to fixed- and variable-ratio, fixed-interval, and differential-reinforcement-of-long-latency schedules of reinforcement. For each schedule, the birds performed under each of two conditions: (1) each correct choice response produced a brief presentation of stimuli intermittently paired with food, then the next trial; (2) each correct choice response produced an intertrial interval only. For all schedules except one long latency schedule, response rates were higher under the condition of brief stimulus presentation than under the comparable control condition. Presentation of brief magazine stimuli increased choice accuracy. The amount of change in accuracy was correlated with the rate of food presentation. Performance under the schedules with highest food reinforcement rates showed no enhancement; performance under the schedules with the lowest reinforcement rates showed the greatest enhancement.

Visual acuity in a stumptail macaque.

Visual acuity in a normal stumptail macaque is 1.4 minutes of arc-similar to man's. Destruction of the fovea by photocoagulation decreased acuity to 9 minutes of arc. These facts suggest that the fovea in the macaque has the same physiological role in visual acuity as in man.