EFFECTS OF PRENATAL ULTRASOUND ON POSTNATAL DEVELOPMENT
This is a continuation of a grant already in progress whose objective is to determine if prenatal exposure to ultrasound will result in behavioral and functional alterations in the neonatal and young adult Wistar rat. During the present study an ultrasound chamber was constructed and appropriate dosimetric computer programs and hardware for controlling exposure were developed. Thus the system is capable of delivering highly controlled exposure dosages. A preselected postnatal behavioral testing procedure is used which includes physiologic markers, neonatal reflex tests, and adult behavioral analyses. The protocol consisted of exposure of pregnant rats to 1 of 2 frequencies (3.5 or 5.0 MHz), at 1 of 3 spatial peak-temporal peak (SPTP) intensity levels (500, 1500, or 5000 W/cm(2)). Mimicking the diagnostic condition, the exposure time was 35 minutes. The pulse repetition frequency (PRF) was fixed at 1 kHz, the pulse duration itself being approximately 1-2 microseconds, again, typical of many ultrasound machines. Thus the experiment carried out represents a full range of typical clinical ultrasound exposure. Reference models and sham groups were also used. Each pregnant animal was insonified on days 15, 17, and 19 of gestation. Following birth, the offspring were given 5 reflex tests (negative geotaxis, surface righting, air righting, auditory startle, visual placing) and 4 physiologic parameter tests (vaginal opening, testes descent, eye opening, pinna detachment). The adult behavioral tests were conditioned avoidance response, water T-maze, activity wheel, and open field, and were given at 60 days of age. Postnatal growth was also monitored. Complete statistical analyses are being completed.
The present proposal uses the same paradigm so that all data can be compared. During the period of the continuation: a.Studies will continue on the pulse-echo bioeffects: 5 MHz, 5000 W/cm2 (SPTP); 3.5 MHz, 1500(SPTP) and 5000 W/cm2 (SPTP) (36 animals, 288 offspring); b. The exposure equipment will be modified for CW and pulsed Doppler studies; c.Biologic testing will commence with CW Doppler insonification at 2 MHz,30 mW/cm2 (SPITA) for 30 minutes or 2 hours and with pulsed Doppler insonification at 3 MHz, 900 mW/cm2 (SPTA), 30, 60, or 90 minutes, again, closely mimicking the diagnostic examination procedure by combining pulse-echo and pulsed Doppler exposure (see Methods for details), on days 15, 17, and 19 of gestation; d. Postnatal testing will proceed following exposure. There will be 12 pregnant rats in each of 7 groups (5 insonification and 2 sham), each rat producing 8 offspring/litter. These exposure levels represent clinically relevant levels. The exposure times used in this study represent typical obstetrical pulse-echo and Doppler examinations, ranging between 8 and 55 minutes, mean examination time equalling 15 minutes.
These studies will aid in determining if prenatal exposure to ultrasound at clinically relevant dosage levels and conditions will cause significant alterations in postnatal growth and neurophysiologic development.