Prenatal exposure to diagnostic ultrasound impacts blood-brain barrier permeability in rats

The central nervous system vasculature consists of a tightly sealed endothelium that forms the blood-brain barrier (BBB); these blood vessels are impermeable to large-molecular-size agents. The aim of this study was to determine the influence of prenatal ultrasound exposure on blood-brain barrier (BBB) integrity as measured by the permeation of Evans blue (EB) through the BBB during the postnatal development of the rat. Diagnostic levels of ultrasound (2.89 MHz, mechanical index = 1.1, acoustic output power = 70.5 mW) for 1 h and 2 h per day, for 9 consecutive days were used on Sprague-Dawley rats. Offspring were assessed postnatally on days 10, 17, 24 and 38. Our analysis of over 139 animals reveals that, when exposed to diagnostic levels of ultrasound during embryonic development, a statistically significant amount of EB extravasation into the cerebrum and cerebellum could be detected on postnatal day 10 but not later. In addition, small changes in pup body weight, cerebrum weight and cerebellum weight were observed after relatively prolonged ultrasound exposure on all postnatal days. Taken together, these results emphasize the need for further investigation of the effects of ultrasound exposure during the potentially vulnerable period of intense BBB development in the human fetus.