The objective of this study is to determine if prenatal exposure to ultrasound will result in behavioral and functional alterations in the neonatal and young adult Wistar rat and to correlate such alterations with neuropathologic changes, and to relate these results to diagnostic ultrasound applications. An ultrasound chamber will be constructed which will be capable of delivering highly controlled exposure dosages. Appropriate dosimetric procedures will be utilized. A preselected postnatal behavioral testing procedure will be used which includes physiologic markers, neonatal reflex tests, and adult behavioral analyses. Central nervous system light and electron microscopic as well as protein kinase-C analyses will be completed. The protocol consists of exposure of pregnant rats to 1 of 2 frequencies (3.5 or 5.0 MHz), at 1 of 3 instantaneous intensity levels (spatial peak-temporal peak); 500, 1,500 and 5,000 W/cm2. The basic deviation from the clinically encountered acoustic exposure conditions will be in the increase of instantaneous peak intensities. The total exposure time will be 15-60 minutes, representing a full range of typical clinical ultrasound exposures. The pulse repetition frequency (PRF) will be fixed at 1 MHz, the pulse duration itself being approximately 1-2 microseconds, again, typical of many ultrasound machines. An additional 2 groups will be sham-irradiated or serve as colony (home cage) controls. Each animal will be irradiated on days 15, 17 and 19 of gestation. Following birth, the offspring will be given 5 reflex tests (negative geotaxis, auditory startle, air righting, surface righting, visual placing) and 4 physiologic parameter tests (eye opening, pinna detachment, testes descent, vaginal opening) to be initiated on postnatal day 3. The 6 adult behavioral tests (forelimb hanging, swimming, water T-maze, activity wheel, open field, conditioned avoidance response) will begin on day 60. Postnatal growth will be monitored throughout the test period. Other animals in each group will be analyzed for morphologic or enzymatic changes at 3 time periods: immediately following irradiation; at birth; and at a postnatal age corresponding to completion of the adult behavioral test procedures. All data will be statistically analyzed. These studies will aid in determining if prenatal exposure to ultrasound at clinically relevant dosage levels will cause significant alterations in postnatal growth and neurophysiologic development.
