Effect of 2450-MHz microwave energy on the blood-brain barrier to hydrophilic molecules

Microwave energy at 2450 MHz 120 Hz AM was found ineffective in increasing the permeability of the blood-brain barrier to the hydrophilic tracers HRP and [14C] sucrose. Furthermore, a diminished permeability to HRP and sodium fluorescein was apparent after 180 minutes of exposure to microwaves at an incident power density of 20 mW/cm2. Colonic temperature, as well as temperature within the cerebral cortex, hypothalamus, cerebellum and medulla, were elevated by less than 10C over those of sham-exposed rats. A significant decrease in the permeability to HRP and [14C] sucrose occurred after exposure to an incident power density of 65 mW/cm2 for 30 minutes. The reduction in permeability to HRP correlated with a suppressed incorporation of the tracer by pinocytosis in cerebral microvessels. Suppression of blood-brain barrier permeability to hydrophilic tracers was most pronounced at brain temperatures exceeding approx. 400C and is demonstrated to be temperature dependent