Effect of ultrasound on the neonatal rat brain.

Six-day-old rat neonates were exposed to 2.25 MHz continuous wave (CW) ultrasound for 5 min at an intensity of 2.5 W/cm2 (SATA). The temperatures on the head surface and in the mouth were measured. There was a higher average temperature elevation in the mouth (9 degrees C) than on the head surface (7 degrees C). Survival differs between control and exposed groups at 30 days after exposure. Ninety percent of the control group lived to 30 days, versus 59.7% for the exposed group. At differing times following exposure, the brains of the pups were removed and tested for enzymatic activities. Changes in acetylcholine esterase and in 2',3'-cyclic nucleotide phosphohydrolase activities were not statistically significantly different from controls. There were no significant differences in brain weight and total protein between control and exposed pups.